Sample records for electron donor-acceptor complexes

  1. Charge transfer in the electron donor-acceptor complex BH3NH3. (United States)

    Mo, Yirong; Song, Lingchun; Wu, Wei; Zhang, Qianer


    As a simple yet strongly binding electron donor-acceptor (EDA) complex, BH(3)NH(3) serves as a good example to study the electron pair donor-acceptor complexes. We employed both the ab initio valence bond (VB) and block-localized wave function (BLW) methods to explore the electron transfer from NH(3) to BH(3). Conventionally, EDA complexes have been described by two diabatic states: one neutral state and one ionic charge-transferred state. Ab initio VB self-consistent field (VBSCF) computations generate the energy profiles of the two diabatic states together with the adiabatic (ground) state. Our calculations evidently demonstrated that the electron transfer between NH(3) and BH(3) falls in the abnormal regime where the reorganization energy is less than the exoergicity of the reaction. The nature of the NH(3)-BH(3) interaction is probed by an energy decomposition scheme based on the BLW method. We found that the variation of the charge-transfer energy with the donor-acceptor distance is insensitive to the computation levels and basis sets, but the estimation of the amount of electron transferred heavily depends on the population analysis procedures. The recent resurgence of interest in the nature of the rotation barrier in ethane prompted us to analyze the conformational change of BH(3)NH(3), which is an isoelectronic system with ethane. We found that the preference of the staggered structure over the eclipsed structure of BH(3)NH(3) is dominated by the Pauli exchange repulsion.

  2. Donor acceptor complexes of noble gases. (United States)

    Mück, Leonie Anna; Timoshkin, Alexey Y; von Hopffgarten, Moritz; Frenking, Gernot


    Donor-acceptor (DA) complexes of noble gases (Ng) of the general type A noble gas, a lone pair of the donor molecule and a vacant orbital of the acceptor molecule. Detailed bonding analysis of the model compounds F(3)Al-Ng-NH(3) reveals that Ng-ammonia interaction is repulsive due to Pauli repulsion. Bonding interaction between Ng and N is mostly electrostatic. In contrast, strong orbital interactions are responsible for the attractive interactions between Ng and AlF(3). Due to the repulsive interactions with the donor molecule and a sizable reorganization energy of the acceptor molecule, optimization attempts of the A noble gases. These are the first examples of the thermodynamically stable Ar and Kr compounds. Application of the push-pull cryptand ligands featuring multiple (two and three) donor-acceptor induced chemical bonds is expected to yield stable complexes with virtually any electron-rich element in the periodic table.

  3. Spectroscopic Studies of the Electron Donor-Acceptor Interaction of ...

    African Journals Online (AJOL)


    base-acid reaction between two or more different chemical constituents, preferably aromatic nucleus–based compounds with electron–rich centers and electron-deficient compounds. The formation of electron-donor- acceptor (EDA) complexes can be rapidly assessed for its validity as a simple quantitative analytical method ...

  4. Charge transfer in the electron donor-acceptor complexes of a meso-phenol BODIPY dye with chloranils and fullerenes. (United States)

    Karmakar, Animesh; Chaudhuri, Tandrima; Mula, Soumyaditya; Chattopadhyay, Subrata


    UV-Vis spectral investigations of electron donor-acceptor complexes of laser dye 2,6-Diethyl-4,4-difluoro-1,3,5,7-tetramethyl-8-(4'-hydroxyphenyl)-4-bora-3a,4a-diaza-s-indecene (1c) with chloranils and fullerenes are reported in toluene medium. Well defined charge transfer (CT) absorption bands have been located in the visible region. Oscillator strengths, transition dipole and resonance energies of the CT complexes have been estimated. Vertical ionization potential of 1c has been determined utilizing Mulliken's equation. A possible mechanism for the interaction between electronic subsystems of chloranils, [60]- and [70]fullerenes with three different BODIPY dyes (1a, 1b and 1c shown in Fig. 1) have been discussed in comparing the parameters like degree of charge transfer and binding constant in nonpolar toluene. Comparison of 1c complexes is done with DFT/B3LYP/6-31G optimized gas phase geometries. Copyright © 2014 Elsevier B.V. All rights reserved.

  5. Time-resolved electron paramagnetic resonance spectra of photoexcited triplet states of electron-donor-acceptor complexes in frozen solution: Methylated benzenes and chlorinated phthalic anhydrides (United States)

    Murai, Hisao; Minami, Masashi; I'Haya, Yasumasa J.


    Phthalic anhydride (PA) and chlorinated PAs in frozen methyl substituted benzenes provided the time-resolved electron paramagnetic resonance (TREPR) spectra of the electron-donor-acceptor (EDA) complexes. The chlorine substitution of PA reduced the zero-field splitting parameters, D, due to the contribution of the spin-orbit interaction caused by heavy atoms such as chlorine. The increase of the number of methyl group on benzene, which apparently reduced the ionization potential, worked to decrease the D value of the EDA complex. The charge-transfer (CT) ratios were measured more exactly by the absolute value of (Delta m(sub s)) = 1 transition of the triplet states. The major axes of these systems were also safely presumed. The sign of the 100% charge transferred EDA complex was found negative because of the CT ratio plots and the spin-polarization pattern of the TREPR spectra.

  6. 2012 Gordon Research Conference, Electron donor-acceptor interactions, August 5-10 2012

    Energy Technology Data Exchange (ETDEWEB)

    McCusker, James [Michigan State Univ., East Lansing, MI (United States)


    The upcoming incarnation of the Gordon Research Conference on Electron Donor Acceptor Interactions will feature sessions on classic topics including proton-coupled electron transfer, dye-sensitized solar cells, and biological electron transfer, as well as emerging areas such as quantum coherence effects in donor-acceptor interactions, spintronics, and the application of donor-acceptor interactions in chemical synthesis.

  7. Ultrafast Photoinduced Electron Transfer in Bimolecular Donor-Acceptor Systems

    KAUST Repository

    Alsulami, Qana A.


    The efficiency of photoconversion systems, such as organic photovoltaic (OPV) cells, is largely controlled by a series of fundamental photophysical processes occurring at the interface before carrier collection. A profound understanding of ultrafast interfacial charge transfer (CT), charge separation (CS), and charge recombination (CR) is the key determinant to improving the overall performances of photovoltaic devices. The discussion in this dissertation primarily focuses on the relevant parameters that are involved in photon absorption, exciton separation, carrier transport, carrier recombination and carrier collection in organic photovoltaic devices. A combination of steady-state and femtosecond broadband transient spectroscopies was used to investigate the photoinduced charge carrier dynamics in various donor-acceptor systems. Furthermore, this study was extended to investigate some important factors that influence charge transfer in donor-acceptor systems, such as the morphology, energy band alignment, electronic properties and chemical structure. Interestingly, clear correlations among the steady-state measurements, time-resolved spectroscopy results, grain alignment of the electron transporting layer (ETL), carrier mobility, and device performance are found. In this thesis, we explored the significant impacts of ultrafast charge separation and charge recombination at donor/acceptor (D/A) interfaces on the performance of a conjugated polymer PTB7-Th device with three fullerene acceptors: PC71BM, PC61BM and IC60BA. Time-resolved laser spectroscopy and high-resolution electron microscopy can illustrate the basis for fabricating solar cell devices with improved performances. In addition, we studied the effects of the incorporation of heavy metals into π-conjugated chromophores on electron transfer by monitoring the triplet state lifetime of the oligomer using transient absorption spectroscopy, as understanding the mechanisms controlling intersystem crossing and

  8. Organic Donor-Acceptor Complexes as Novel Organic Semiconductors. (United States)

    Zhang, Jing; Xu, Wei; Sheng, Peng; Zhao, Guangyao; Zhu, Daoben


    Organic donor-acceptor (DA) complexes have attracted wide attention in recent decades, resulting in the rapid development of organic binary system electronics. The design and synthesis of organic DA complexes with a variety of component structures have mainly focused on metallicity (or even superconductivity), emission, or ferroelectricity studies. Further efforts have been made in high-performance electronic investigations. The chemical versatility of organic semiconductors provides DA complexes with a great number of possibilities for semiconducting applications. Organic DA complexes extend the semiconductor family and promote charge separation and transport in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In OFETs, the organic complex serves as an active layer across extraordinary charge pathways, ensuring the efficient transport of induced charges. Although an increasing number of organic semiconductors have been reported to exhibit good p- or n-type properties (mobilities higher than 1 or even 10 cm2 V-1 s-1), critical scientific challenges remain in utilizing the advantages of existing semiconductor materials for more and wider applications while maintaining less complicated synthetic or device fabrication processes. DA complex materials have revealed new insight: their unique molecular packing and structure-property relationships. The combination of donors and acceptors could offer practical advantages compared with their unimolecular materials. First, growing crystals of DA complexes with densely packed structures will reduce impurities and traps from the self-assembly process. Second, complexes based on the original structural components could form superior mixture stacking, which can facilitate charge transport depending on the driving force in the coassembly process. Third, the effective use of organic semiconductors can lead to tunable band structures, allowing the operation mode (p- or n-type) of the transistor to be

  9. Donor-Acceptor Properties of a Single-Molecule Altered by On-Surface Complex Formation. (United States)

    Meier, Tobias; Pawlak, Rémy; Kawai, Shigeki; Geng, Yan; Liu, Xunshan; Decurtins, Silvio; Hapala, Prokop; Baratoff, Alexis; Liu, Shi-Xia; Jelínek, Pavel; Meyer, Ernst; Glatzel, Thilo


    Electron donor-acceptor molecules are of outstanding interest in molecular electronics and organic solar cells for their intramolecular charge transfer controlled via electrical or optical excitation. The preservation of their electronic character in the ground state upon adsorption on a surface is cardinal for their implementation in such single-molecule devices. Here, we investigate by atomic force microscopy and scanning tunneling microscopy a prototypical system consisting of a π-conjugated tetrathiafulvalene-fused dipyridophenazine molecule adsorbed on thin NaCl films on Cu(111). Depending on the adsorption site, the molecule is found either in a nearly undisturbed free state or in a bound state. In the latter case, the molecule adopts a specific adsorption site, leading to the formation of a chelate complex with a single Na(+) alkali cation pulled out from the insulating film. Although expected to be electronically decoupled, the charge distribution of the complex is drastically modified, leading to the loss of the intrinsic donor-acceptor character. The chelate complex formation is reversible with respect to lateral manipulations, enabling tunable donor-acceptor molecular switches activated by on-surface coordination.

  10. Spectroscopic Studies of the Electron Donor-Acceptor Interaction of ...

    African Journals Online (AJOL)

    Conformity with Beer\\'s law was evident over the concentration range 0.8 – 8.0 mg/100 ml of chloroquine phosphate; thus making it possible for an accurate quantitative determination of the drug. Conclusion: The studied complexation phenomenon formed a basis for the quantitative determination of both pure samples and ...

  11. Interplay of alternative conjugated pathways and steric interactions on the electronic and optical properties of donor-acceptor conjugated polymers

    KAUST Repository

    Lima, Igo T.


    Donor-acceptor π-conjugated copolymers are of interest for a wide range of electronic applications, including field-effect transistors and solar cells. Here, we present a density functional theory (DFT) study of the impact of varying the conjugation pathway on the geometric, electronic, and optical properties of donor-acceptor systems. We consider both linear ("in series"), traditional conjugation among the donor-acceptor moieties versus structures where the acceptor units are appended orthogonally to the linear, donor-only conjugated backbone. Long-range-corrected hybrid functionals are used in the investigation with the values of the tuned long-range separation parameters providing an estimate of the extent of conjugation as a function of the oligomer architecture. Considerable differences in the electronic and optical properties are determined as a function of the nature of the conjugation pathway, features that should be taken into account in the design of donor-acceptor copolymers.

  12. Donor-acceptor conjugated polymers used as electron acceptors in bulk heterojunction photovoltaics (United States)

    Bailey, Christopher; Taylor, Barney; Mei, Jianguo; Reynolds, John; Henderson, John; Leever, Benjamin; Durstock, Michael


    Synthetic control over the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) has been of significant importance in organic photovoltaics due to the nature of charge separation in donor/acceptor blends. One technique for obtaining tunability of the HOMO and LUMO levels with polymer synthesis is to combine electron donating and electron accepting moieties separated by a conjugated linkage unit. This technique has been utilized to produce highly efficient devices reaching power conversion efficiencies above 8% in polymer/fullerene blends. In this work, we report the characterization of poly(2,7-divinylene fluorene-co-benzothiadiazole) (F10DVBT), and performs best as an electron acceptor when mixed with poly(3-hexylthiophene) (P3HT) with an open circuit voltage of 1.2V. A combination of morphological and photo-physical studies highlights interesting properties of this material and its interactions with P3HT. The donor-acceptor conjugated structure of F10DVBT appears to strongly affect the photocurrent of these devices, and may result from the interactions between intramolecular and intermolecular charge transfer processes.

  13. Electron transfer in proteins: nonorthogonal projections onto donor-acceptor subspace of the Hilbert space. (United States)

    de Andrade, Paulo C P; Freire, José A


    We develop nonorthogonal projectors, called Löwdin projectors, to construct an effective donor-acceptor system composed of localized donor (D) and acceptor (A) states of a long-distance electron transfer problem. When these states have a nonvanishing overlap with the bridge states these projectors are non-Hermitian and there are various possible effective two-level systems that can be built. We show how these can be constructed directly from the Schrödinger or Dyson equation projected onto the D-A subspace of the Hilbert space and explore these equations to determine the connection between Hamiltonian and Green function partitioning. We illustrate the use of these effective two-level systems in estimating the electron transfer rate in the context of a simple electron transfer model. (c) 2004 American Institute of Physics

  14. 2004 Electron Donor Acceptor Interactions Gordon Conference - August 8-13, 2004

    Energy Technology Data Exchange (ETDEWEB)



    The 2004 Gordon Conference on Donor/Acceptor Interactions will take place at Salve Regina University in Newport, Rhode Island on August 8-13, 2004. The conference will be devoted to the consequences of charge interaction and charge motion in molecular and materials systems.

  15. Selective and non-extractive spectrophotometric determination of cefdinir in formulations based on donor-acceptor complex formation

    Directory of Open Access Journals (Sweden)

    Babita K. Singh


    Full Text Available Cefdinir has broad spectrum of activity and high prescription rates, hence its counterfeiting seems imminent. We have proposed a simple, fast, selective and non-extractive spectrophotometric method for the content assay of cefdinir in formulations. The method is based on complexation of cefdinir and Fe under reducing condition in a buffered medium (pH 11 to form a magenta colored donor-acceptor complex (λ max = 550 nm; apparent molar absorptivity = 3720 L mol-1 cm-1. No other cephalosporins, penicillins and common excipients interfere under the test conditions. The Beer's law is followed in the concentration range 8-160 µg mL-1.

  16. The electronic structure and second-order nonlinear optical properties of donor-acceptor acetylenes - A detailed investigation of structure-property relationships (United States)

    Stiegman, A. E.; Graham, Eva; Khundkar, Lutfur R.; Perry, Joseph W.; Cheng, L.-T.; Perry, Kelly J.


    A series of donor-acceptor acetylene compounds was synthesized in which systematic changes in both the conjugation length and the donor-acceptor strength were made. The effect of these structural changes on the spectroscopic and electronic properties of the molecules and, ultimately, on the measured second-order molecular hyperpolarizabilities (beta) was investigated. It was found that increases in the donor-acceptor strength resulted in increases in the magnitude of beta. For this class of molecules, the increase is dominated by the energy of the intramolecular charge-transfer transition, while factors such as the ground to excited-state dipole moment change and the transition-moment integral are much less important. Increasing the conjugation length from one to two acetylene linkers did not result in an increase in the value of beta; however, beta increased sharply in going from two acetylenes to three. This increase is attributed to the superposition of several nearly isoenergetic excited states.

  17. Electron Donor-Acceptor Interaction of 8-Hydroxyquinoline with Citric Acid in Different Solvents: Spectroscopic Studies

    Directory of Open Access Journals (Sweden)

    Demelash Jado


    Full Text Available Charge transfer complex formation between 8-hydroxyquinoline as the electron donor and citric acid as the electron acceptor has been studied spectrophotometrically in ethanol and methanol solvents at room temperature. Absorption band due to charge transfer complex formation was observed near 320 and 325 nm in ethanol and methanol, respectively. The stoichiometric ratio of the complex has been found 3 : 1 by using Job’s and conductometric titration methods. Benesi-Hildebrand equation has been applied to estimate the formation constant and molecular extinction coefficient. It was found that the value of formation constant was larger in ethanol than in methanol. The physical parameters, ionization potential, and standard free energy change of the formed complex were determined and evaluated in the ethanol and methanol solvents.

  18. Donor-acceptor complex formation in evaporated small molecular organic photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Susarova, Diana K.; Troshin, Pavel A.; Lyubovskaya, Rimma N.; Razumov, Vladimir F. [Institute of Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1, Chernogolovka, Moscow 142432 (Russian Federation); Hoeglinger, Doris; Koeppe, Robert; Serdar Sariciftci, N. [Linz Institute for Organic Solar Cells (LIOS), Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz (Austria); Babenko, Sergey D. [Institute for Energy Problems of Chemical Physics, Russian Academy of Sciences (Branch), Semenov Prospect 1/10, Chernogolovka, Moscow 142432 (Russian Federation)


    Novel perylene diimide Py-PDI and naphthalene diimide Py-NDI possessing chelating pyridyl groups have been synthesized. The materials are comparatively investigated as electron acceptors in small molecular photovoltaic cells comprising zinc phthalocyanine ZnPc as an electron donor component. It was shown that these compounds form self-assembled coordination complexes with ZnPc in solution and co-evaporated solid blends. Py-PDI and Py-NDI used as electron acceptor materials in photovoltaic cells with donor ZnPc significantly outperform the reference materials, i.e. perylene and naphthalene diimides that possess no chelating pyridyl groups. Superior photovoltaic performance of Py-PDI and Py-NDI is explained by a complex formation between these compounds and ZnPc. Such interactions of donor and acceptor materials strongly improve photoinduced charge carrier generation. This gives great advantages not just for the construction of organic solar cells but also for organic photodetectors. The devices fabricated in this study are also useful as fast and highly sensitive photodetectors with response times of less than 10 microseconds as well as a strong photoconductive behavior under forward bias. (author)

  19. 2008 Electron Donor Acceptor Interactions Gordon Research Conference-August 3-8, 2009

    Energy Technology Data Exchange (ETDEWEB)

    Forbes, Malcolm [Univ. of North Carolina, Chapel Hill, NC (United States); Gray, Nancy Ryan [Gordon Research Conferences, West Kingston, RI (United States)


    The conference presents and advances the current frontiers in experimental and theoretical studies of Electron Transfer and Transport in Molecular and Nano-scale Systems. The program includes sessions on coupled electron transfers, molecular solar energy conversion, biological and biomimetic systems, spin effects, ultrafast reactions and technical frontiers as well as electron transport in single molecules and devices.

  20. The impact of driving force on electron transfer rates in photovoltaic donor-acceptor blends. (United States)

    Ward, Alexander J; Ruseckas, Arvydas; Kareem, Mohanad Mousa; Ebenhoch, Bernd; Serrano, Luis A; Al-Eid, Manal; Fitzpatrick, Brian; Rotello, Vincent M; Cooke, Graeme; Samuel, Ifor D W


    The effect of acceptor energy level on electron transfer rate in blends of the polymer solar-cell material poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl

  1. Ultrafast electron transfer in all-carbon-based SWCNT-C60 donor-acceptor nanoensembles connected by poly(phenylene-ethynylene) spacers (United States)

    Barrejón, Myriam; Gobeze, Habtom B.; Gómez-Escalonilla, María J.; Fierro, José Luis G.; Zhang, Minfang; Yudasaka, Masako; Iijima, Sumio; D'Souza, Francis; Langa, Fernando


    Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an electron donating or accepting photosensitizer while the second part should fulfil the role of an electron acceptor or donor. In the present work, we have successfully addressed this issue by synthesizing covalently linked all-carbon-based donor-acceptor nanoensembles using single-walled carbon nanotubes (SWCNTs) as the donor and C60 as the acceptor. The donor-acceptor entities in the nanoensembles were connected by phenylene-ethynylene spacer units to achieve better electronic communication and to vary the distance between the components. These novel SWCNT-C60 nanoensembles have been characterized by a number of techniques, including TGA, FT-IR, Raman, AFM, absorbance and electrochemical methods. The moderate number of fullerene addends present on the side-walls of the nanotubes largely preserved the electronic structure of the nanotubes. The thermodynamic feasibility of charge separation in these nanoensembles was established using spectral and electrochemical data. Finally, occurrence of ultrafast electron transfer from the excited nanotubes in these donor-acceptor nanohybrids has been established by femtosecond transient absorption studies, signifying their utility in building light energy harvesting devices.Building all-carbon based functional materials for light energy harvesting applications could be a solution to tackle and reduce environmental carbon output. However, development of such all-carbon based donor-acceptor hybrids and demonstration of photoinduced charge separation in such nanohybrids is a challenge since in these hybrids part of the carbon material should act as an

  2. Electron transfer in multiply bridged donor-acceptor molecules: Dephasing and quantum coherence. (United States)

    Goldsmith, Randall H; Wasielewski, Michael R; Ratner, Mark A


    We present a simple theoretical treatment of nonadiabatic electron transfer in multiply bridged donor-bridge-acceptor molecules using the density matrix formalism. Destructive interference can result from different signed couplings between bridge sites, with the simplest system being a four-site Joachim-type molecular interferometer. Previous work has shown that deposition of energy on the bridge sites erases the interference and recovers transport. We show that pure local dephasing, a completely elastic process, is also capable of eliminating destructive interference and regaining transport. Destructive interference as a result of system connectivity can explain the familiar ortho-meta-para reactivity of benzene bridges. We also show that pure dephasing can yield a coalescence of ortho, meta, and para effective coupling strengths and suggest a system to observe this effect experimentally.

  3. First principles study for the key electronic, optical and nonlinear optical properties of novel donor-acceptor chalcones. (United States)

    Muhammad, Shabbir; Al-Sehemi, Abdullah G; Su, Zhongmin; Xu, Hongliang; Irfan, Ahmad; Chaudhry, Aijaz Rasool


    Using first-principle methods, several key electronic, optical and nonlinear optical properties are calculated for two recently synthesized chalcone derivatives i.e. (2E)-3-(4-methylphenyl)-1-(3-nitrophenyl)prop-2-en-1-one (comp.1) and (2E)-3-[4-(dimethylamino)phenyl]-1-(3-nitrophenyl)prop-2-en-1-one (comp.2). The calculation of dipole moment, polarizability , anisotropy of polarizability as well as second hyperpolarizability (usually considered as a signature for two photon absorption phenomenon) are performed using density functional theory methods at PBE0/6-311G** level of theory. The linear average polarizability for comp.1 and comp.2 are found to be 32.15×10-24 and 38.76×10-24esu, respectively. Similarly, the second hyperpolarizability amplitudes of comp.1 and comp.2 are found to be reasonably larger mounting to 79.31×10-36 and 181.36×10-36esu, respectively. The importance of donor end is determined by comparing p-methylphenyl group of comp.1 with that of N,N-dimethylaniline group of comp.2 that results a remarkable increase in its amplitude, which is ∼2 times larger as compared with that of comp.1 owing to the stronger donor-acceptor configuration of comp.2. Interestingly, a comparison of average static third-order nonlinear polarizabilities shows that amplitudes of comp.1 and comp.2 are ∼13 times and ∼29 times larger than that of para-nitroaniline (a typical standard push-pull NLO-phore) at the same PBE0/6-311G** level of theory, which indicates a real time NLO application of our titled compounds. Time dependent density functional theory (TD-DFT) calculations along with frontier molecular orbitals, density of states (DOS), second hyperpolarizability density analysis and molecular electrostatic potential (MEP) diagrams are used to trace the origin of electro-optical as well as structure property relationships. Copyright © 2016 Elsevier Inc. All rights reserved.

  4. Theoretical investigation of self-assembled donor-acceptor phthalocyanine complexes and their application in dye-sensitized solar cells. (United States)

    Yu, Lijuan; Lin, Li; Liu, Yuwen; Li, Renjie


    A theoretical investigation of self-assembled donor-acceptor dyads (ZnPca, ZnPcb and ZnPcc) formed by axial coordination of zinc phthalocyanines appended with 4-carboxyl pyridine has been conducted with the density functional theory (DFT) method and time-dependent DFT (TD-DFT) calculations. A comparison between the molecular structures, atomic charges, molecular orbitals, UV-vis spectra and infrared (IR) spectra has been studied. Further, as sensitizers for the TiO2-based dye-sensitized solar cells, the photovoltaic performances have been investigated. The ZnPcc-sensitized solar cell exhibits a higher conversion efficiency than the ZnPcb and ZnPca-sensitized ones under AM 1.5G solar irradiation, while the ZnPca-sensitized cell performs the poorest due to the lack of peripheral substituents (n-butyoxyl groups) which can be confirmed by the result of the theoretical research. It shows that the directionality of charge transfer in the self-assembled donor-acceptor dyads is important and benefit for the efficiency of the DSSC. Copyright © 2015 Elsevier Inc. All rights reserved.

  5. Frenkel and Charge-Transfer Excitations in Donor-acceptor Complexes from Many-Body Green's Functions Theory. (United States)

    Baumeier, Björn; Andrienko, Denis; Rohlfing, Michael


    Excited states of donor-acceptor dimers are studied using many-body Green's functions theory within the GW approximation and the Bethe-Salpeter equation. For a series of prototypical small-molecule based pairs, this method predicts energies of local Frenkel and intermolecular charge-transfer excitations with the accuracy of tens of meV. Application to larger systems is possible and allowed us to analyze energy levels and binding energies of excitons in representative dimers of dicyanovinyl-substituted quarterthiophene and fullerene, a donor-acceptor pair used in state of the art organic solar cells. In these dimers, the transition from Frenkel to charge transfer excitons is endothermic and the binding energy of charge transfer excitons is still of the order of 1.5-2 eV. Hence, even such an accurate dimer-based description does not yield internal energetics favorable for the generation of free charges either by thermal energy or an external electric field. These results confirm that, for qualitative predictions of solar cell functionality, accounting for the explicit molecular environment is as important as the accurate knowledge of internal dimer energies.

  6. Photoinduced electron transfer in hydrogen bonded donor--acceptor systems. Free energy and distance dependence studies and an analysis of the role of diffusion. (United States)

    Smitha, M A; Prasad, E; Gopidas, K R


    The free energy dependence of electron transfer in a few small-molecule donor--acceptor systems having hydrogen-bonding appendages was studied to evaluate the role of diffusion in masking the inverted region in bimolecular PET reactions. A small fraction of the probe molecules associate and this led to the simultaneous observation of unimolecular and diffusion-mediated quenching of the probe fluorescence. Free energy dependence studies showed that the unimolecular electron transfer obeys Marcus behavior and the diffusion-mediated electron transfer obeys Rehm--Weller behavior. The absence of an inverted region in bimolecular PET reactions is thus attributed to diffusion. The results of the free energy dependence studies suggest that distance dependence of electron transfer plays a role in masking the inverted region. To ascertain this aspect we have carried out a study of the distance dependence of electron transfer in the hydrogen-bonded donor--acceptor systems. For a system in the normal region an exponential rate decrease was observed. For a system in the inverted region it was observed that the rate depends very feebly on distance. Thus distance dependence studies did not confirm the prediction of enhanced rates at larger distances in the inverted region.

  7. Shape similarity of charge-transfer (CT) excitation energy curves in a series of donor-acceptor complexes and its description with a transferable energy of CT orbital (United States)

    Gritsenko, O. V.


    A simple nature of charge-transfer (CT) in the prototype complexes Dp -F2 (Dp =NH3 , H2O) manifests itself in a very close shape of their CT excitation energy curves ωCT (R) along the donor-acceptor separation R. It affords a simple orbital description in terms of the CT orbitals (CTOs) obtained with a transformation of the virtual orbitals of the standard local density approximation (LDA). The transferable energy of the relevant CTO as a function of R closely approximates the common shape of ωCT (R) , while the height of the individual curve is determined with the ionization potential of Dp .

  8. Monofunctional platinum(II) complexes with potent tumor cell growth inhibitory activity: the effect of a hydrogen-bond donor/acceptor N-heterocyclic ligand. (United States)

    Margiotta, Nicola; Savino, Salvatore; Gandin, Valentina; Marzano, Christine; Natile, Giovanni


    In this paper we investigate the possibility of further increase the role of the N-donor aromatic base in antitumor Hollis-type compounds by conferring the possibility to act as a hydrogen-bond donor/acceptor. Therefore, we synthesized the Pt(II) complex cis-[PtCl(NH3 )2 (naph)]NO3 (1) containing the 1,8-naphthyridine (naph) ligand. The naphthyridine ligand is generally monodentate, and the second nitrogen atom can act as H-bond donor/acceptor depending upon its protonation state. The possibility of forming such an H-bond could be crucial in the interaction of the drug with DNA or proteins. Apart from the synthesis of the compound, in this study we evaluated its in vitro antitumor activity in a wide panel of tumor cell lines, also including cells selected for their sensitivity/resistance to oxaliplatin, which was compared with that of previously reported complex 2 ([PtI(2,9-dimethyl-1,10-phenanthroline)(1-methyl-cytosine)]I) and oxaliplatin and cisplatin as reference compounds. The cytotoxicity data were correlated with the cellular uptake and the DNA platination levels. Finally, the reactivity of 1 towards guanosine 5'-monophosphate (5'-GMP) and glutathione was investigated to provide insights into its mechanism of action. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Controlling electron transfer through the manipulation of structure and ligand-based torsional motions: a computational exploration of ruthenium donor-acceptor systems using density functional theory. (United States)

    Meylemans, Heather A; Damrauer, Niels H


    Computational studies using density functional theory (DFT) are reported for a series of donor-acceptor (DA) transition metal complexes and related excited-state and electron transfer (ET) photoproduct models. Three hybrid Hartree-Fock/DFT (HF/DFT) functionals, B3LYP, B3PW91, and PBE1PBE, are employed to characterize structural features implicated in the dynamical control of productive forward and energy wasting back ET events. Energies and optimized geometries are reported for the lowest energy singlet state in [Ru(dmb)(2)(bpy-phi-MV)](4+) (DA1), [Ru(dmb)(2)(bpy-o-tolyl-MV)](4+) (DA2), [Ru(dmb)(2)(bpy-2,6-Me(2)-phi-MV)](4+) (DA3), and [Ru(tmb)(2)(bpy-2,6-Me(2)-phi-MV)](4+) (DA3'), where dmb is 4,4'-dimethyl-2,2'-bipyridine, tmb is 4,4',5,5'-tetramethyl-2,2'-bipyridine, MV is methyl viologen, and phi is a phenylene spacer. These indicate that the dihedral angle theta(1) between the aryl substituent and the bipyridine fragment to which it is bound, systematically increases with the addition of steric bulk. Energies, optimized geometries, and unpaired electron spin densities are also reported for the lowest energy triplet state of [Ru(dmb)(2)(4-p-tolyl-2,2'-bipyridine)](2+) (D1*), [Ru(dmb)(2)(4-(2,6-dimethylphenyl)-2,2'-bipyridine)](2+) (D2*), [Ru(dmb)(2)(4-mesityl-2,2'-bipyridine)](2+) (D3*), and [Ru(tmb)(2)(4-mesityl-2,2'-bipyridine)](2+) (D3'*). Each of these serves as a model of a reactant excited state in the forward electron-transfer photochemistry allowing us to qualify and quantify the role of excited-state intraligand electron delocalization in driving substantial geometry changes (especially with respect to theta(1)) relative to its respective DA counterpart. Next, energies, optimized geometries, and spin densities are reported for the lowest energy triplet of each DA species: (3)DA1, (3)DA2, (3)DA3, and (3)DA3'. These are used to model the ET photoproduct and they indicate that theta(1) increases following ET, thus, verifying switch-like properties

  10. Evaluating the Performance of DFT Functionals in Assessing the Interaction Energy and Ground-State Charge Transfer of Donor/Acceptor Complexes: Tetrathiafulvalene−Tetracyanoquinodimethane (TTF−TCNQ) as a Model Case

    KAUST Repository

    Sini, Gjergji


    We have evaluated the performance of several density functional theory (DFT) functionals for the description of the ground-state electronic structure and charge transfer in donor/acceptor complexes. The tetrathiafulvalene- tetracyanoquinodimethane (TTF-TCNQ) complex has been considered as a model test case. Hybrid functionals have been chosen together with recently proposed long-range corrected functionals (ωB97X, ωB97X-D, LRC-ωPBEh, and LC-ωPBE) in order to assess the sensitivity of the results to the treatment and magnitude of exact exchange. The results show an approximately linear dependence of the ground-state charge transfer with the HOMO TTF-LUMOTCNQ energy gap, which in turn depends linearly on the percentage of exact exchange in the functional. The reliability of ground-state charge transfer values calculated in the framework of a monodeterminantal DFT approach was also examined. © 2011 American Chemical Society.

  11. Electron and excitation energy transfers in covalently linked donor-acceptor dyads: mechanisms and dynamics revealed using quantum chemistry. (United States)

    Cupellini, Lorenzo; Giannini, Samuele; Mennucci, Benedetta


    Photoinduced electron transfer (ET), hole transfer (HT), charge recombination (CR) and energy transfer (EET) are fundamental mechanisms, which occur in both natural and artificial light harvesting systems. Here, we present a computational strategy which determines ET, HT, CR and EET rates in a consistent way and merges them in a kinetic model to reproduce the net excited state dynamics. The effects of the solvent are included in all steps of the calculations making the present strategy a useful tool for a rational design of charge and energy transfer processes in complex systems. An application to covalently linked zinc and free-base porphyrin-naphthalenediimide dyads is presented. For each of the two systems, ultrafast optical spectroscopy experiments have shown a specific photophysics with different processes taking place simultaneously. The model reveals that such a diversity is mainly due to the different relative stability of the charge-separated state, while the electronic couplings for charge and energy transfer processes are quite similar in the two dyads.

  12. Analyses of Levofloxacin Adsorption on Pretreated Barley Straw with Respect to Temperature: Kinetics, π-π Electron-Donor-Acceptor Interaction and Site Energy Distribution. (United States)

    Yan, Bei; Niu, Catherine Hui; Wang, Jian


    Levofloxacin, representative of an important class of fluoroquinolone antibiotics, has been considered to be one of the emerging pollutants in various water sources. In this paper, adsorption of levofloxacin from artificial contaminated water was done by pretreated barley straw adsorbent obtained from raw barley straw after modification by H3PO4 impregnation and microwave heating. The adsorption kinetics was investigated at various temperatures and levofloxacin concentrations, and the activation energy was determined. In addition, site energy distribution of the pretreated barley straw for levofloxacin adsorption was estimated based on the equilibrium adsorption data. The average site energy and standard deviation of the distribution were determined and applied to analyze the interaction strength between the adsorbent and adsorbate, and adsorption site heterogeneity. The π-π electron-donor-acceptor interactions between the π* aromatic C═C of pretreated barley straw adsorbent and π* carbon atom in benzene ring attached to fluorine of levofloxacin was investigated by C K-edge X-ray absorption near-edge structure spectroscopy. The results and methodologies in this work could be transferrable to investigate extended systems of water treatment.

  13. Bimolecular electron transfer reactions in coumarin amine systems: Donor acceptor orientational effect on diffusion-controlled reaction rates (United States)

    Satpati, A. K.; Nath, S.; Kumbhakar, M.; Maity, D. K.; Senthilkumar, S.; Pal, H.


    Electron transfer (ET) reactions between excited coumarin dyes and different aliphatic amine (AlA) and aromatic amine (ArA) donors have been investigated in acetonitrile solution using steady-state (SS) and time-resolved (TR) fluorescence quenching measurements. No ground state complex or emissive exciplex formation has been indicated in these systems. SS and TR measurements give similar quenching constants ( kq) for each of the coumarin-amine pairs, suggesting dynamic nature of interaction in these systems. On correlating kq values with the free energy changes (Δ G0) of the ET reactions show the typical Rehm-Weller type of behavior as expected for bimolecular ET reactions under diffusive condition, where kq increases with -Δ G0 at the lower exergonicity (-Δ G0) region but ultimately saturate to a diffusion-limited value (kqDC) at the higher exergonicity region. It is, however, interestingly observed that the kqDC values vary largely depending on the type of the amines used. Thus, kqDC is much higher with ArAs than AlAs. Similarly, the kqDC for cyclic monoamine 1-azabicyclo-[2,2,2]-octane (ABCO) is distinctly lower and that for cyclic diamine 1,4-diazabicyclo-[2,2,2]-octane (DABCO) is distinctly higher than the kqDC value obtained for other noncyclic AlAs. These differences in the kqDC values have been rationalized on the basis of the differences in the orientational restrictions involved in the ET reactions with different types of amines. As understood, n-type donors (AlAs) introduce large orientational restriction and thus significantly reduces the ET efficiency in comparison to the π-type donors (ArAs). Structural constrains are inferred to be the reason for the differences in the kqDC values involving ABCO, DABCO donors in comparison to other noncyclic AlAs. Supportive evidence for the orientational restrictions involving different types of amines donors has also been obtained from DFT based quantum chemical calculations on the molecular orbitals of

  14. Long-range coupling of electron-hole pairs in spatially separated organic donor-acceptor layers (United States)

    Nakanotani, Hajime; Furukawa, Taro; Morimoto, Kei; Adachi, Chihaya


    Understanding exciton behavior in organic semiconductor molecules is crucial for the development of organic semiconductor-based excitonic devices such as organic light-emitting diodes and organic solar cells, and the tightly bound electron-hole pair forming an exciton is normally assumed to be localized on an organic semiconducting molecule. We report the observation of long-range coupling of electron-hole pairs in spatially separated electron-donating and electron-accepting molecules across a 10-nanometers-thick spacer layer. We found that the exciton energy can be tuned over 100 megaelectron volts and the fraction of delayed fluorescence can be increased by adjusting the spacer-layer thickness. Furthermore, increasing the spacer-layer thickness produced an organic light-emitting diode with an electroluminescence efficiency nearly eight times higher than that of a device without a spacer layer. Our results demonstrate the first example of a long-range coupled charge-transfer state between electron-donating and electron-accepting molecules in a working device. PMID:26933691

  15. Photoinduced electron donor/acceptor processes in colloidal II-VI semiconductor quantum dots and nitroxide free radicals (United States)

    Dutta, Poulami

    Electron transfer (ET) processes are one of the most researched topics for applications ranging from energy conversion to catalysis. An exciting variation is utilizing colloidal semiconductor nanostructures to explore such processes. Semiconductor quantum dots (QDs) are emerging as a novel class of light harvesting, emitting and charge-separation materials for applications such as solar energy conversion. Detailed knowledge of the quantitative dissociation of the photogenerated excitons and the interfacial charge- (electron/hole) transfer is essential for optimization of the overall efficiency of many such applications. Organic free radicals are the attractive counterparts for studying ET to/from QDs because these undergo single-electron transfer steps in reversible fashion. Nitroxides are an exciting class of stable organic free radicals, which have recently been demonstrated to be efficient as redox mediators in dye-sensitized solar cells, making them even more interesting for the aforementioned studies. This dissertation investigates the interaction between nitroxide free radicals TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), 4-amino-TEMPO (4-amino- 2,2,6,6-tetramethylpiperidine-1-oxyl) and II-VI semiconductor (CdSe and CdTe) QDs. The nature of interaction in these hybrids has been examined through ground-state UV-Vis absorbance, steady state and time-resolved photoluminescence (PL) spectroscopy, transient absorbance, upconversion photoluminescence spectroscopy and electron paramagnetic resonance (EPR). The detailed analysis of the PL quenching indicates that the intrinsic charge transfer is ultrafast however, the overall quenching is still limited by the lower binding capacities and slower diffusion related kinetics. Careful analysis of the time resolved PL decay kinetics reveal that the decay rate constants are distributed and that the trap states are involved in the overall quenching process. The ultrafast hole transfer from CdSe QDs to 4-Amino TEMPO observed

  16. Magnetic field enhanced electroluminescence in organic light emitting diodes based on electron donor-acceptor exciplex blends (United States)

    Baniya, Sangita; Basel, Tek; Sun, Dali; McLaughlin, Ryan; Vardeny, Zeev Valy


    A useful process for light harvesting from injected electron-hole pairs in organic light emitting diodes (OLED) is the transfer from triplet excitons (T) to singlet excitons (S) via reverse intersystem crossing (RISC). This process adds a delayed electro-luminescence (EL) emission component that is known as thermally activated delayed fluorescence (TADF). We have studied electron donor (D)/acceptor(A) blends that form an exciplex manifold in which the energy difference, ΔEST between the lowest singlet (S1) and triplet (T1) levels is relatively small (field of 50 mT at ambient. Moreover the MEL response is activated with activation energy similar that of the EL emission. This suggests that the large magneto-EL originates from an additional spin-mixing channel between singlet and triplet states of the generated exciplexes, which is due to TADF. We will report on the MEL dependencies on the temperature, bias voltage, and D-A materials for optimum OLED performance. Supported by SAMSUNG Global Research Outreach (GRO) program, and also by the NSF-Material Science & Engineering Center (MRSEC) program at the University of Utah (DMR-1121252).

  17. donor-acceptor reactions: good bye to the laboratory jargon

    African Journals Online (AJOL)


    Fig. 5: Mental model of proton transfer between electron clouds [9]. ALTERNATIVE MENTAL MODELS OF DONOR-ACCEPTOR REACTIONS. The figures 1-4 suggest independently co-existing protons and electrons that move from one particle to another. This mental model should be preliminary for the learners in Piaget's.

  18. Real-Space Bonding Indicator Analysis of the Donor-Acceptor Complexes X3BNY3, X3AlNY3, X3BPY3, and X3AlPY3 (X, Y = H, Me, Cl). (United States)

    Mebs, Stefan; Beckmann, Jens


    Calculations of real-space bonding indicators (RSBI) derived from Atoms-In-Molecules (AIM), Electron Localizability Indicator (ELI-D), Non-Covalent Interactions index (NCI), and Density Overlap Regions Indicator (DORI) toolkits for a set of 36 donor-acceptor complexes X3BNY3 (1, 1a-1h), X3AlNY3 (2, 2a-2h), X3BPY3 (3, 3a-3h), and X3AlPY3 (4, 4a-4h) reveal that the donor-acceptor bonds comprise covalent and ionic interactions in varying extents (X = Y = H for 1-4; X = H, Y = Me for 1a-4a; X = H, Y = Cl for 1b-4b; X = Me, Y = H for 1c-4c; X, Y = Me for 1d-4d; X = Me, Y = Cl for 1e-4e; X = Cl, Y = H for 1f-4f; X = Cl, Y = Me for 1g-4g; X, Y = Cl for 1h-4h). The phosphinoboranes X3BPY3 (3, 3a-3h) in general and Cl3BPMe3 (3f) in particular show the largest covalent contributions and the least ionic contributions. The aminoalanes X3AlNY3 (2, 2a-2h) in general and Me3AlNCl3 (2e) in particular show the least covalent contributions and the largest ionic contributions. The aminoboranes X3BNY3 (1, 1a-1h) and the phosphinoalanes X3AlPY3 (4, 4a-4h) are midway between phosphinoboranes and aminoalanes. The degree of covalency and ionicity correlates with the electronegativity difference BP (ΔEN = 0.15) < AlP (ΔEN = 0.58) < BN (ΔEN = 1.00) < AlN (ΔEN = 1.43) and a previously published energy decomposition analysis (EDA). To illustrate the importance of both contributions in Lewis formula representations, two resonance formulas should be given for all compounds, namely, the canonical form with formal charges denoting covalency and the arrow notation pointing from the donor to the acceptor atom to emphasis ionicity. If the Lewis formula mainly serves to show the atomic connectivity, the most significant should be shown. Thus, it is legitimate to present aminoalanes using arrows; however, for phosphinoboranes the canonical form with formal charges is more appropriate.

  19. Hydrogen bond, electron donor-acceptor dimer, and residence dynamics in supercritical CO(2)-ethanol mixtures and the effect of hydrogen bonding on single reorientational and translational dynamics: A molecular dynamics simulation study. (United States)

    Skarmoutsos, Ioannis; Guardia, Elvira; Samios, Jannis


    The hydrogen bonding and dynamics in a supercritical mixture of carbon dioxide with ethanol as a cosolvent (X(ethanol) approximately 0.1) were investigated using molecular dynamics simulation techniques. The results obtained reveal that the hydrogen bonds formed between ethanol molecules are significantly more in comparison with those between ethanol-CO(2) molecules and also exhibit much larger lifetimes. Furthermore, the residence dynamics in the solvation shells of ethanol and CO(2) have been calculated, revealing much larger residence times for ethanol molecules in the ethanol solvation shell. These results support strongly the ethanol aggregation effects and the slow local environment reorganization inside the ethanol solvation shell, reported in a previous publication of the authors [Skarmoutsos et al., J. Chem. Phys. 126, 224503 (2007)]. The formation of electron donor-acceptor dimers between the ethanol and CO(2) molecules has been also investigated and the calculated lifetimes of these complexes have been found to be similar to those corresponding to ethanol-CO(2) hydrogen bonds, exhibiting a slightly higher intermittent lifetime. However, the average number of these dimers is larger than the number of ethanol-CO(2) hydrogen bonds in the system. Finally, the effect of the hydrogen bonds formed between the individual ethanol molecules on their reorientational and translational dynamics has been carefully explored showing that the characteristic hydrogen bonding microstructure obtained exhibits sufficiently strong influence upon the behavior of them.

  20. An electronic spectroscopic study of micellisation of surfactants and solvation of homomicelles formed by cationic or anionic surfactants using a solvatochromic electron donor acceptor dye. (United States)

    Kedia, Niraja; Sarkar, Amrita; Purkayastha, Pradipta; Bagchi, Sanjib


    Solvatochromic absorption and fluorescence bands of a donor-acceptor dye have been utilised for following the micellisation and for probing the polarity of the aqueous homomicellar phase provided separately by cationic (cetyltrimethylammonimum bromide, CTAB and dodecyltrimethylammonimum bromide, DTAB) and anionic (sodium dodecyl sulphate, SDS) surfactant. Results indicate that for a low concentration of surfactant (below cmc) the dye forms a dimer in aqueous solution. In a micellar media, however, the dye exists as monomers. A strong dye-micelle interaction, as indicated by the shift of the solvatochromic intramolecular charge transfer band of the dye, has also been indicated. The absorption and fluorescence parameters of the dye have been utilised for studying the onset of aggregation of the surfactants. An iterative procedure has been developed for the estimation of cmc and the distribution coefficient (KD) of the dye between the aqueous and the micellar phase. All the parameters provide convergent values of cmc. A high value of KD indicates that the dye exists predominantly in the micellar phase. The solvatochromic parameters characterising the dipolarity-polarisability (π(*)) and H-bond donation ability (α) of modes of solvation interaction in different micellar media have been estimated. The dye is found to distribute itself between two regions in a catanionic vesicle formed by surfactants SDS and DTAB, one being relatively polar than other. The distribution coefficients have been found out using the fluorescence data. Copyright © 2014 Elsevier B.V. All rights reserved.

  1. Supramolecular donor-acceptor hybrids of porphyrins/phthalocyanines with fullerenes/carbon nanotubes: electron transfer, sensing, switching, and catalytic applications. (United States)

    D'Souza, Francis; Ito, Osamu


    Since the three-dimensional electron-accepting fullerene has been found to be an excellent building block for self-assembled supramolecular systems, we have investigated photoinduced electron transfer processes in supramolecular fullerene systems with porphyrins and phthalocyanines as electron donors to mimic natural photosynthesis. We have successfully formed self-assembled supramolecular dyads and triads via metal-ligand coordination, crown-ether inclusion, ion pairing, hydrogen-bonding, or pi-pi stacking interactions. Although the single mode of binding gives usually flexible supramolecular structures, the newly developed strategy of multiple modes of binding results in conjugates of defined distance and orientation between the donor and acceptor entities, which influences the overall electron transfer reactions. In these conjugates, we observe the anticipated acceleration of the charge separation process and deceleration of the charge recombination process. Applications of these supramolecular systems for reversible photoswitching of inter- and intramolecular electron transfer events open up new opportunities in the area of photosensors. Extension of the self-assembly approaches to single wall carbon nanotubes (SWNT) results in SWNT-porphyrin/phthalocyanine nanohybrids capable of undergoing photoinduced electron transfer. These photochemical processes lead to photocatalytic reactions accumulating redox active substances of electron acceptor/mediator entities with the help of a sacrificial electron donor. Studies on these self-assembled supramolecular dyads, triads, tetrads, etc., are only in the beginning stages and future studies anticipate involvement of more complex systems targeted for better performances in light-driven devices.

  2. Dynamics of transfer of electron excitation in a donor-acceptor system with a carbon chain and ways of its relaxation

    Directory of Open Access Journals (Sweden)

    M.M. Sevryukova


    Full Text Available The optical properties and dynamics of transport of electron excitation and the ways of its relaxation in the supramolecular D–π–A complex on the basis of merocyanines have been investigated. There have been found two components in the transfer of charge: fast and slow, which correspond to different conformational states of the carbon chain in merocyanines. It was found that the main photoluminescence of the studied molecular solutions of merocyanines by its nature is similar to the exciplex luminescence, as a manifestation of resonant and charge transfer interaction in an excited state. The lifetime in this state is about 2000 ps.

  3. Effects of donor-acceptor groups on the structural and electronic properties of 4-(methoxymethyl)-6-methyl-5-nitro-2-oxo-1,2-dihydropyridine-3-carbonitrile. (United States)

    Gümüş, Hacer Pir; Tamer, Ömer; Avcı, Davut; Atalay, Yusuf


    Quantum chemical calculations on the geometric parameters, harmonic vibrational wavenumbers and 1H and 13C nuclear magnetic resonance (NMR) chemical shifts values of 4-(methoxymethyl)-6-methyl-5-nitro-2-oxo-1,2-dihydropyridine-3-carbonitrile [C9H9N3O4] molecule in ground state were performed using the ab initio HF and density functional theory (DFT/B3LYP) methods with 6-311++G(d,p) basis set. The results of optimized molecular structure were presented and compared with X-ray diffraction results. The theoretical vibrational frequencies and 1H and 13C NMR chemical shifts values were compared with experimental values of the investigated molecule. The observed and calculated values were found to be in good agreement. Since the title compound contains different electron-donor and -acceptor groups as well as lone pair electrons, and multiple bonds, the effects of these groups on the structural and electronic properties are found out. In addition, conformational, natural bond orbital (NBO), nonlinear optical (NLO) analysis, frontier molecular orbital energies, molecular surfaces, Mulliken charges and atomic polar tensor based charges were investigated using HF and DFT methods. Copyright © 2014 Elsevier B.V. All rights reserved.

  4. Exploring the formation pathways of donor-acceptor catenanes in aqueous dynamic combinatorial libraries. (United States)

    Cougnon, Fabien B L; Au-Yeung, Ho Yu; Pantoş, G Dan; Sanders, Jeremy K M


    The discovery through dynamic combinatorial chemistry (DCC) of a new generation of donor-acceptor [2]catenanes highlights the power of DCC to access unprecedented structures. While conventional thinking has limited the scope of donor-acceptor catenanes to strictly alternating stacks of donor (D) and acceptor (A) aromatic units, DCC is demonstrated in this paper to give access to unusual DAAD, DADD, and ADAA stacks. Each of these catenanes has specific structural requirements, allowing control of their formation. On the basis of these results, and on the observation that the catenanes represent kinetic bottlenecks in the reaction pathway, we propose a mechanism that explains and predicts the structures formed. Furthermore, the spontaneous assembly of catenanes in aqueous dynamic systems gives a fundamental insight into the role played by hydrophobic effect and donor-acceptor interactions when building such complex architectures.

  5. Design, synthesis and study of supramolecular donor-acceptor systems mimicking natural photosynthesis processes (United States)

    Bikram, Chandra

    This dissertation investigates the chemical ingenuity into the development of various photoactive supramolecular donor -- acceptor systems to produce clean and carbon free energy for the next generation. The process is inspired by the principles learned from nature's approach where the solar energy is converted into the chemical energy through the natural photosynthesis process. Owing to the importance and complexity of natural photosynthesis process, we have designed ideal donor-acceptor systems to investigate their light energy harvesting properties. This process involves two major steps: the first step is the absorption of light energy by antenna or donor systems to promote them to an excited electronic state. The second step involves, the transfer of excitation energy to the reaction center, which triggers an electron transfer process within the system. Based on this principle, the research is focused into the development of artificial photosynthesis systems to investigate dynamics of photo induced energy and electron transfer events. The derivatives of Porphyrins, Phthalocyanines, BODIPY, and SubPhthalocyanines etc have been widely used as the primary building blocks for designing photoactive and electroactive ensembles in this area because of their excellent and unique photophysical and photochemical properties. Meanwhile, the fullerene, mainly its readily available version C60 is typically used as an electron acceptor component because of its unique redox potential, symmetrical shape and low reorganization energy appropriate for improved charge separation behavior. The primary research motivation of the study is to achieve fast charge separation and slow charge recombination of the system by stabilizing the radical ion pairs which are formed from photo excitation, for maximum utility of solar energy. Besides Fullerene C60, this dissertation has also investigated the potential application of carbon nanomaterials (Carbon nanotubes and graphene) as primary

  6. How intermolecular geometrical disorder affects the molecular doping of donor-acceptor copolymers

    NARCIS (Netherlands)

    Di Nuzzo, D.; Fontanesi, C.; Jones, R.; Allard, S; Dumsch, I.; Scherf, U.; von Hauff, E.L.; Schumacher, S.; Da Como, E.


    Molecular doping of conjugated polymers represents an important strategy for improving organic electronic devices. However, the widely reported low efficiency of doping remains a crucial limitation to obtain high performance. Here we investigate how charge transfer between dopant and donor-acceptor

  7. Organic Materials in the Undergraduate Laboratory: Microscale Synthesis and Investigation of a Donor-Acceptor Molecule (United States)

    Pappenfus, Ted M.; Schliep, Karl B.; Dissanayake, Anudaththa; Ludden, Trevor; Nieto-Ortega, Belen; Lopez Navarrete, Juan T.; Ruiz Delgado, M. Carmen; Casado, Juan


    A series of experiments for undergraduate courses (e.g., organic, physical) have been developed in the area of small molecule organic materials. These experiments focus on understanding the electronic and redox properties of a donor-acceptor molecule that is prepared in a convenient one-step microscale reaction. The resulting intensely colored…

  8. Donor-Acceptor Block Copolymers: Synthesis and Solar Cell Applications

    Directory of Open Access Journals (Sweden)

    Kazuhiro Nakabayashi


    Full Text Available Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with donor polymeric materials and high cost for synthesis and purification. Therefore, the investigation of non-fullerene acceptor materials that can potentially replace fullerene derivatives in OPVs is increasingly necessary, which gives rise to the possibility of fabricating all-polymer (polymer/polymer solar cells that can deliver higher performance and that are potentially cheaper than fullerene-based OPVs. Recently, considerable attention has been paid to donor-acceptor (D-A block copolymers, because of their promising applications as fullerene alternative materials in all-polymer solar cells. However, the synthesis of D-A block copolymers is still a challenge, and therefore, the establishment of an efficient synthetic method is now essential. This review highlights the recent advances in D-A block copolymers synthesis and their applications in all-polymer solar cells.

  9. Electroluminescence from charge transfer states in Donor/Acceptor solar cells

    DEFF Research Database (Denmark)

    Sherafatipour, Golenaz; Madsen, Morten

    Charge photocurrent generation is a key process in solar energy conversion systems. Effective dissociation of the photo-generated electron-hole pairs (excitons) has a strong influence on the efficiency of the organic solar cells. Charge dissociation takes place at the donor/acceptor interface via...... charge transfer (CT) excitons, which is Coulombically bound interfacial electron- hole pairs residing at the donor/acceptor heterojunctions. The CT state represents an intermediate state between the exciton dissociation and recombination back to the ground state. Since the recombination of photo-generated...... charges is a major limitation for the efficiency of the organic solar cells, a thorough understanding of this loss mechanism is crucial to improve the performance of the devices. Furthermore, examining this interfacial state is of great importance in order to maximize open-circuit voltage and photocurrent...

  10. Kinetically-constrained ring-polymer molecular dynamics for non-adiabatic chemistries involving solvent and donor-acceptor dynamical effects. (United States)

    Kretchmer, Joshua S; Miller Iii, Thomas F


    We investigate the performance of the recently developed kinetically-constrained ring polymer molecular dynamics (KC-RPMD) method for the description of model condensed-phase electron transfer (ET) reactions in which solvent and donor-acceptor dynamics play an important role. Comparison of KC-RPMD with results from Golden-Rule rate theories and numerically exact quantum dynamics calculations demonstrates that KC-RPMD accurately captures the combination of electronic- and nuclear-dynamical effects throughout the Marcus (intermediate solvent friction) and Zusman (large solvent friction) regimes of ET. It is also demonstrated that KC-RPMD accurately describes systems in which the magnitude of the diabatic coupling depends on the position of a dynamical donor-acceptor mode. In addition to these successes, however, we present an unsurprising failure of KC-RPMD to capture the enhancement of the ET rate in the low solvent friction regime associated with nuclear coherence effects. In this analysis, we re-visit several aspects of the original KC-RPMD formulation, including the form of the kinetic constraint and the choice of the mass of the auxiliary electronic variable. In particular, we introduce a Langevin bath for the auxiliary electronic variable to correct for its unphysically low coupling with the nuclear degrees of freedom. This work demonstrates that the KC-RPMD method is well suited for the direct simulation of non-adiabatic donor-acceptor chemistries associated with many complex systems, including those for which solvent dynamics plays an important role in the reaction mechanism.

  11. Cation-reinforced donor-acceptor pseudorotaxanes

    NARCIS (Netherlands)

    Pascu, Sofia I.; Jarrosson, Thibaut; Naumann, Christoph; Otto, Sijbren; Kaiser, Guido; Sanders, Jeremy K.M.


    Formation of a series of pseudorotaxanes from an electron-rich crown ether (host 1), pyromellitic diimide (guest 2) and alkali salt templates MX, where M = Li+ and Na+, and X- = Br-, I-, CF3SO3-, [B(C6F5)4]- and [B{3,5-(CF3)2(C6H3)}4]-, is reported. Mixing of 1 and 2 in CH2Cl2 or a mixture of CHCl3

  12. Control of electric field strength and orientation at the donor-acceptor interface in organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Liu, A.; Zhao, S.; Wu, J. [Materials Science and Engineering Department, Stanford University, Stanford, CA (United States); Rim, S.B. [Electrical Engineering Department, Stanford University, Stanford, CA (United States); Koenemann, M.; Erk, P. [BASF GmbH, Ludwigshafen (Germany); Peumans, P.


    Electrical doping is essential to achieve efficient photocurrent extraction in small-molecular-weight organic solar cells. It is shown that such doping creates strong electric fields at the donor-acceptor interface that prevent geminate electron-hole recombination. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

  13. Phthalimide containing donor-acceptor polymers for effective dispersion of single-walled carbon nanotubes

    Directory of Open Access Journals (Sweden)

    Baris Yilmaz


    Full Text Available Single-walled carbon nanotubes have been dispersed by novel phthalimide containing donor-acceptor type copolymers in organic media. Brominated phthalimide comonomer has been copolymerized with several electron rich structures using Suzuki and Stille coupling reactions. Carbon nanotube dispersion capability of the resultant polymers has been assessed by exploiting the non-covalent interaction of nanotube surface with the pi-system of conjugated backbone of polymers. Four polymers have been found to be good candidates for individually dispersing nanotubes in solution. In order to identify the dispersed nanotube species, 2D excitation-emission map and Raman spectroscopy have been performed. Molecular dynamics modelling has been utilized to reveal the binding energies of dispersants with the nanotube surface and the simulation results have been compared with the experimental findings. Both experimental and theoretical results imply the presence of a complex mechanism that governs the extent of dispersion capacity and selectivity of each conjugated polymeric dispersant in solubilizing carbon nanotubes.

  14. Syntheses of donor-acceptor-functionalized dihydroazulenes

    DEFF Research Database (Denmark)

    Broman, Søren Lindbæk; Jevric, Martyn; Bond, Andrew


    The dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch has been of interest for use in molecular electronics and advanced materials. The switching between the two isomers has previously been found to depend strongly on the presence of donor and acceptor groups. The fine-tuning of opt......The dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch has been of interest for use in molecular electronics and advanced materials. The switching between the two isomers has previously been found to depend strongly on the presence of donor and acceptor groups. The fine......-tuning of optical and switching properties relies on ready access to new derivatives via efficient synthetic protocols. The central DHA core is conveniently prepared in a four-step synthesis starting from acetophenone and tropylium substrates. Here, the outcome of this reaction as a function of the nature...... of the substituent group on the phenyl unit of acetophenone is investigated in detail. A wide variety of functional groups (nitro, cyano, halo, alkyl, amido, and thioether) was tolerated, and the route provided access to a large selection of substituted DHA derivatives (position 2 of DHA). These compounds were...

  15. Donor-Acceptor Chromophores based on Acetylenic Scaffolds and Indenofluorenes

    DEFF Research Database (Denmark)

    Christensen, Mikkel Andreas

    The work described in this thesis has been focused on synthesizing donor-acceptor chromophores with conjugated π-bridges. It has also led to the development of an alternative synthetic tool for acetylenic scaffolding. The first chapter focuses on the nitrophenol D-π-A system – A phenol in conjuga...... to palladium ratio, and using an excess of terminal alkyne. Vinyl iodide ≥ vinyl triflate > vinyl bromide ≥ chloroalkyne ≥ aryl iodide > aryl triflate ≥ aryl bromide >> aryl chloride...

  16. Donor-acceptor interactions between resonance-excited silver nanoparticles and halide ions in water solutions (United States)

    Konstantinova, E. I.; Tikhomirova, N. S.; Samusev, I. G.; Slezhkin, V. A.; Bryukhanov, V. V.


    Donor-acceptor interactions between silver nanoparticles (NPs), resonance-excited by optical quanta of light, and halide ions are studied in aqueous solutions. It is shown that deactivation of the plasmon excitation of Ag NP proceeds according to the exchange mechanism of electron transfer. Plasmon excitation quenching constants are determined and a correlation between quenching and the donor properties of halide ions is found. The efficiency of electrostatic interaction between resonantly-excited Ag NPs and halide ions is studied, and their dipole moment is determined.

  17. A Selenophene-Based Low-Bandgap Donor-Acceptor Polymer Leading to Fast Ambipolar Logic

    KAUST Repository

    Kronemeijer, Auke J.


    Fast ambipolar CMOS-like logic is demonstrated using a new selenophene-based donor-acceptor polymer semiconductor. The polymer exhibits saturation hole and electron mobilities of 0.46 cm 2/Vs and 0.84 cm 2/Vs. Inverters are fabricated with high gains while three-stage ring oscillators show stable oscillation with an unprecedented maximum frequency of 182 kHz at a relatively low supply voltage of 50 V. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Bipyridinium Polymers That Dock Tetrathiafulvalene Guests in Water Driven by Donor-Acceptor and Ion Pair Interactions. (United States)

    Zhang, Yun-Chang; Qin, Ying; Wang, Hui; Zhang, Dan-Wei; Yang, Guanyu; Li, Zhan-Ting


    Two water-soluble para-xylylene-connected 4,4'-bipyridinium (BIPY(2+) ) polymers have been prepared. UV-Vis absorption, (1) H NMR spectroscopy, and cyclic voltammetry experiments support that in water the BIPY(2+) units in the polymers form stable 1:1 charge-transfer complexes with tetrathiafulvalene (TTF) guests that bear two or four carboxylate groups. These charge-transfer complexes are stabilized by the donor-acceptor interaction between electron-rich TTF and electron-deficient BIPY(2+) units and electrostatic attraction between the dicationic BIPY(2+) units and the anionic carboxylate groups attached to the TTF core. On the basis of UV-Vis experiments, a lower limit to the apparent association constant of the TTF⋅BIPY(2+) complexes of the mixtures, 1.8×10(6)  m(-1) , has been estimated in water. Control experiments reveal substantially reduced binding ability of the neutral TTF di- and tetracarboxylic acids to the BIPY(2+) molecules and polymers. Moreover, the stability of the charge-transfer complexes formed by the BIPY(2+) units of the polymers are considerably higher than that of the complexes formed between two monomeric BIPY(2+) controls and the dicarboxylate-TTF donor; this has been attributed to the mutually strengthened electron-deficient nature of the BIPY(2+) units of the polymers due to the electron-withdrawing effect of the BIPY(2+) units. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Unraveling the Photoswitching Mechanism in Donor-Acceptor Stenhouse Adducts. (United States)

    Lerch, Michael M; Wezenberg, Sander J; Szymanski, Wiktor; Feringa, Ben L


    Molecular photoswitches have opened up a myriad of opportunities in applications ranging from responsive materials and control of biological function to molecular logics. Here, we show that the photoswitching mechanism of donor-acceptor Stenhouse adducts (DASA), a recently reported class of photoswitches, proceeds by photoinduced Z-E isomerization, followed by a thermal, conrotatory 4π-electrocyclization. The photogenerated intermediate is manifested by a bathochromically shifted band in the visible absorption spectrum of the DASA. The identification of the role of this intermediate reveals a key step in the photoswitching mechanism that is essential to the rational design of switching properties via structural modification.

  20. Conjugated block copolymers as model materials to examine charge transfer in donor-acceptor systems (United States)

    Gomez, Enrique; Aplan, Melissa; Lee, Youngmin

    Weak intermolecular interactions and disorder at junctions of different organic materials limit the performance and stability of organic interfaces and hence the applicability of organic semiconductors to electronic devices. The lack of control of interfacial structure has also prevented studies of how driving forces promote charge photogeneration, leading to conflicting hypotheses in the organic photovoltaic literature. Our approach has focused on utilizing block copolymer architectures -where critical interfaces are controlled and stabilized by covalent bonds- to provide the hierarchical structure needed for high-performance organic electronics from self-assembled soft materials. For example, we have demonstrated control of donor-acceptor heterojunctions through microphase-separated conjugated block copolymers to achieve 3% power conversion efficiencies in non-fullerene photovoltaics. Furthermore, incorporating the donor-acceptor interface within the molecular structure facilitates studies of charge transfer processes. Conjugated block copolymers enable studies of the driving force needed for exciton dissociation to charge transfer states, which must be large to maximize charge photogeneration but must be minimized to prevent losses in photovoltage in solar cell devices. Our work has systematically varied the chemical structure, energetics, and dielectric constant to perturb charge transfer. As a consequence, we predict a minimum dielectric constant needed to minimize the driving force and therefore simultaneously maximize photocurrent and photovoltage in organic photovoltaic devices.

  1. Graphene oxide-Li(+)@C60 donor-acceptor composites for photoenergy conversion. (United States)

    Supur, Mustafa; Kawashima, Yuki; Ohkubo, Kei; Sakai, Hayato; Hasobe, Taku; Fukuzumi, Shunichi


    An ionic endohedral metallofullerene (Li(+)@C60) with mild hydrophilic nature was combined with graphene oxide (GO) to construct a donor-acceptor composite in neat water. The resulting composite was characterised by UV-Vis and Raman spectroscopy, powder X-ray diffraction, dynamic light scattering measurements and transmission electron microscopy. Theoretical calculations (DFT at the B3LYP/6-31(d) level) were also utilized to gain further insight into the composite formation. As detected by electron paramagnetic resonance spectroscopy, photoexcitation of the GO-Li(+)@C60 composite results in electron transfer from GO to the triplet excited state of Li(+)@C60, leading to photocurrent generation at the OTE/SnO2 electrode.

  2. Microwave assisted synthesis of bithiophene based donor-acceptor-donor oligomers and their optoelectronic performances (United States)

    Bathula, Chinna; Buruga, Kezia; Lee, Sang Kyu; Khazi, Imtiyaz Ahmed M.; Kang, Youngjong


    In this article we present the synthesis of two novel bithiophene based symmetrical π conjugated oligomers with donor-acceptor-donor (D-A-D) structures by microwave assisted PdCl2(dppf) catalyzed Suzuki coupling reaction. These molecules contain electron rich bithiophene as a donor, dithienothiadiazole[3,4-c]pyridine and phthalic anhydride units as acceptors. The shorter reaction time, excellent yields and easy product isolation are the advantages of this method. The photophysical prerequisites for electronic application such as strong and broad optical absorption, thermal stability, and compatible energy levels were determined for synthesized oligomers. Optical band gap for the oligomers is found to be 1.72-1.90 eV. The results demonstrated the novel oligomers to be promising candidates in organic optoelectronic applications.

  3. The role of amino acid electron-donor/acceptor atoms in host-cell binding peptides is associated with their 3D structure and HLA-binding capacity in sterile malarial immunity induction

    Energy Technology Data Exchange (ETDEWEB)

    Patarroyo, Manuel E., E-mail: [Fundacion Instituto de Inmunologia de Colombia (FIDIC), Bogota (Colombia); Universidad Nacional de Colombia, Bogota (Colombia); Almonacid, Hannia; Moreno-Vranich, Armando [Fundacion Instituto de Inmunologia de Colombia (FIDIC), Bogota (Colombia)


    Highlights: Black-Right-Pointing-Pointer Fundamental residues located in some HABPs are associated with their 3D structure. Black-Right-Pointing-Pointer Electron-donor atoms present in {beta}-turn, random, distorted {alpha}-helix structures. Black-Right-Pointing-Pointer Electron-donor atoms bound to HLA-DR53. Black-Right-Pointing-Pointer Electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. -- Abstract: Plasmodium falciparum malaria continues being one of the parasitic diseases causing the highest worldwide mortality due to the parasite's multiple evasion mechanisms, such as immunological silence. Membrane and organelle proteins are used during invasion for interactions mediated by high binding ability peptides (HABPs); these have amino acids which establish hydrogen bonds between them in some of their critical binding residues. Immunisation assays in the Aotus model using HABPs whose critical residues had been modified have revealed a conformational change thereby enabling a protection-inducing response. This has improved fitting within HLA-DR{beta}1{sup Asterisk-Operator} molecules where amino acid electron-donor atoms present in {beta}-turn, random or distorted {alpha}-helix structures preferentially bound to HLA-DR53 molecules, whilst HABPs having amino acid electron-acceptor atoms present in regular {alpha}-helix structure bound to HLA-DR52. This data has great implications for vaccine development.

  4. Donor-acceptor conjugated polymers based on multifused ladder-type arenes for organic solar cells. (United States)

    Wu, Jhong-Sian; Cheng, Sheng-Wen; Cheng, Yen-Ju; Hsu, Chain-Shu


    Harvesting solar energy from sunlight to generate electricity is considered as one of the most important technologies to address the future sustainability of humans. Polymer solar cells (PSCs) have attracted tremendous interest and attention over the past two decades due to their potential advantage to be fabricated onto large area and light-weight flexible substrates by solution processing at a lower cost. PSCs based on the concept of bulk heterojunction (BHJ) configuration where an active layer comprises a composite of a p-type (donor) and an n-type (acceptor) material represents the most useful strategy to maximize the internal donor-acceptor interfacial area allowing for efficient charge separation. Fullerene derivatives such as [6,6]-phenyl-C61 or 71-butyric acid methyl ester (PCBM) are the ideal n-type materials ubiquitously used for BHJ solar cells. The major effort to develop photoactive materials is numerously focused on the p-type conjugated polymers which are generally synthesized by polymerization of electron-rich donor and electron-deficient acceptor monomers. Compared to the development of electron-deficient comonomers (acceptor segments), the development of electron-rich donor materials is considerably flourishing. Forced planarization by covalently fastening adjacent aromatic and heteroaromatic subunits leads to the formation of ladder-type conjugated structures which are capable of elongating effective conjugation, reducing the optical bandgap, promoting intermolecular π-π interactions and enhancing intrinsic charge mobility. In this review, we will summarize the recent progress on the development of various well-defined new ladder-type conjugated materials. These materials serve as the superb donor monomers to prepare a range of donor-acceptor semi-ladder copolymers with sufficient solution-processability for solar cell applications.

  5. Chemical composition of donor-acceptor complexes of hydroxyoxo(5,10,15,20-tetraphenylporphinato)molybdenum(V) with 3,5-dimethylpyrazole and equilibrium constants for their formation (United States)

    Motorina, E. V.; Lomova, T. N.


    The results from a quantitative study of reactions between hydroxyoxo(5,10,15,20-tetraphenylporphinato)molybdenum(V) (O=Mo(OH)TPP) and 3,5-dimethylpyrazole, a biologically active base, in toluene are presented. The chemical structure and key parameters of intermediates and reaction products are determined by spectral means. The equilibrium constant ( K = 51.3 L/mol) is calculated and a full kinetic description of simple reactions that occur in this system during complex transformation is obtained. The prospect of using a mixed porphyrin-containing complex as a receptor for 3,5-dimethylpyrazole, a building block for alkaloids and pharmaceutical preparations, is substantiated.

  6. Tuning Optoelectronic Properties of Organic Semiconductors Via Donor-Acceptor Cocrystals and Interfacial Composites (United States)

    Wang, Chen

    Organic donor-acceptor (D-A) interaction has attracted intensive research interest because of the promising applications in electronic devices and renewable energy. Depending on the interaction process, the optoelectronic properties of organic semiconductors may change dramatically. To improve their performance and expand the applications, we have investigated the structure-property relationship in D-A cocrystals and nanofibril composites. These materials provide unique D-A interface structures, thus allowing tunable charge transfer across the interface, which can be modified and controlled by exquisite molecule design and supramolecular assembly. In Chapter 2, we studied the fabrication, conductivity, and chemiresistive sensor performance of tetrathiafulvalene (TTF) - 7,7,8,8-tetracyanoquinodimethane (TCNQ) charge transfer cocrystal microfibers. Compared to TCNQ and TTF, TTF-TCNQ cocrystal has much higher conductivity under ambient conditions, due to the high yield of charge separation, which also induces high polarization at the interface, resulting in different binding intensity towards alkyl and aromatic amines. Based on this investment, we developed a TTF-TCNQ chemiresistive sensor to efficiently discriminate alkyl and aromatic amine vapors. In Chapter 3, we further designed a new series of D-A cocrystals, and studied the coassembly and optical properties. The cocrystal is composed of coronene and perylene diimide at 1:1 molar ratio and belongs to the triclinic system, as confirmed by X-ray analysis. The donor and acceptor molecules perform an alternate pi-pi stacking along the (100) direction, leading to the strong one-dimensional growth tendency of macroscopic cocrystal. Additionally, due to the charge transfer interaction, the cocrystal shows a new and largely red-shifted photoluminescence band, compared to the crystals of the components. In Chapter 4, we alternatively developed a series of donor-acceptor nanofibril composites, in which the donor and

  7. α,β-Unsubstituted meso-Positioning Thienyl BODIPY: A Promising Electron Deficient Building Block for the Development of Near Infrared (NIR) p-type Donor-Acceptor (D-A) Conjugated Polymers

    KAUST Repository

    Squeo, Benedetta


    It is demonstrated that α,β-unsubstituted meso-positioning thienyl BODIPY is an electron deficient unit that leads to the development of ultra low optical band gap (Egopt < 1 eV) π-conjugated D-A quarterthiophene polymers. Furthermore, it is revealed that the optoelectronic, electrochemical and charge transporting properties of the resulting α,β-unsubstituted meso-positioning thienyl BODIPY quaterthiophene-based polymers are alkyl side chain positioning dependent. Tail-to-tail (TT) positioning of the alkyl side chains at the two central thiophenes of the quaterthiophene segment results to lower Egopt, higher energy levels and increased hole mobility as compared to head-to-head (HH) positioning. Finally, even though the synthesized polymers exhibit high electron affinity, higher even to that of the fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), they present only p-type behaviour in field effect transistors (FETs) independent to the alkyl side chain positioning.

  8. Impact of the Crystallite Orientation Distribution on Exciton Transport in Donor-Acceptor Conjugated Polymers. (United States)

    Ayzner, Alexander L; Mei, Jianguo; Appleton, Anthony; DeLongchamp, Dean; Nardes, Alexandre; Benight, Stephanie; Kopidakis, Nikos; Toney, Michael F; Bao, Zhenan


    Conjugated polymers are widely used materials in organic photovoltaic devices. Owing to their extended electronic wave functions, they often form semicrystalline thin films. In this work, we aim to understand whether distribution of crystallographic orientations affects exciton diffusion using a low-band-gap polymer backbone motif that is representative of the donor/acceptor copolymer class. Using the fact that the polymer side chain can tune the dominant crystallographic orientation in the thin film, we have measured the quenching of polymer photoluminescence, and thus the extent of exciton dissociation, as a function of crystal orientation with respect to a quenching substrate. We find that the crystallite orientation distribution has little effect on the average exciton diffusion length. We suggest several possibilities for the lack of correlation between crystallographic texture and exciton transport in semicrystalline conjugated polymer films.

  9. Rigid and flexible azopolymers modified with donor/acceptor groups. Synthesis and photochromic behavior

    Directory of Open Access Journals (Sweden)


    Full Text Available The aim of this work is to investigate the photochromic behavior and nano-structuration capacity of azo-polymers with different architectures and main chain flexibilities, modified with donor/acceptor groups. As a function of the chemical structure and the substitution degree, the azo-polymers can generate physical interactions and lead to different polymer chain conformational re-organization under optical excitation. Nano-structuration experiments were performed on samples with different chemical structures. Surface relief gratings have been realized both in poly(chloromethyl styrene and polysiloxanes polymers. The complexity of the phenomena that take place under optical excitation of the azo-benzene molecules are reflected by the samples behavior during the nano-structuration process. Preliminary tests to determine the ability of the azo-polysiloxanic films to support cell growth were performed. The films showed remarkable properties to sustain both cell adhesion and proliferation.

  10. Analysis of nonlinear optical properties in donor-acceptor materials. (United States)

    Day, Paul N; Pachter, Ruth; Nguyen, Kiet A


    Time-dependent density functional theory has been used to calculate nonlinear optical (NLO) properties, including the first and second hyperpolarizabilities as well as the two-photon absorption cross-section, for the donor-acceptor molecules p-nitroaniline and dimethylamino nitrostilbene, and for respective materials attached to a gold dimer. The CAMB3LYP, B3LYP, PBE0, and PBE exchange-correlation functionals all had fair but variable performance when compared to higher-level theory and to experiment. The CAMB3LYP functional had the best performance on these compounds of the functionals tested. However, our comprehensive analysis has shown that quantitative prediction of hyperpolarizabilities is still a challenge, hampered by inadequate functionals, basis sets, and solvation models, requiring further experimental characterization. Attachment of the Au2S group to molecules already known for their relatively large NLO properties was found to further enhance the response. While our calculations show a modest enhancement for the first hyperpolarizability, the enhancement of the second hyperpolarizability is predicted to be more than an order of magnitude.

  11. Merocyanines: polyene-polymethine transition in donor-acceptor-substituted stilbenes and polyenes

    Energy Technology Data Exchange (ETDEWEB)

    Rettig, Wolfgang; Dekhtyar, Marina


    Three series of donor-acceptor-substituted conjugated compounds, namely, stilbenes, the open-chain polyenes of equivalent length, and the species of intermediate structure (polyenes terminated with only one phenyl ring) have been studied by the AM1 and HMO methods to elucidate and compare the structural prerequisites of the ideal polymethinic state ('cyanine limit'). The transition from polyenic to polymethinic properties has been traced in terms of bond-length (bond-order) alternation using the variation of terminal donor and acceptor substituents. Stilbenes manifest themselves as notably 'retarded' polyenes since a larger electronic asymmetry is necessary for them to reach the same degree of polymethinic character. The ground and the excited state have been shown to differ much more strongly for stilbenes than for polyenes with respect to the position of the bond equalization point on the scale of donor-acceptor difference. For the compounds containing one phenyl ring, the features revealed are intermediate between stilbenes and polyenes. The large S{sub 0}-S{sub 1} discrepancy in terms of bond alternation is a general property of aromatic ring-terminated chains (stilbenes) and is related to the influence of the aromatic character which can be quantified in this way. In this context, the most relevant definition for the cyanine limit (based on the bond invariance upon excitation) was selected from the existing definitions. The major trends revealed in the polyenic/polymethinic behaviour of the molecules can be interpreted on a topological basis within HMO or even simpler models with some additional influence due to the interelectronic repulsion which is taken into account in the AM1 treatment.

  12. Donor-acceptor type blends composed of black phosphorus and C60 for solid-state optical limiters. (United States)

    Shi, Makai; Huang, Shutong; Dong, Ningning; Liu, Zhiwei; Gan, Fan; Wang, Jun; Chen, Yu


    Novel donor-acceptor blends composed of black phosphorus (BP) as an electron donor and C60 as an electron acceptor have been prepared and successfully embedded into a non-optically active poly(methylmethacrylate) (PMMA) matrix producing a BP:C60/PMMA film. In contrast to C60, BP and non-annealed BP:C60 blends, annealed BP:C60 blends show a significantly enhanced optical limiting response due to the thermal-induced intermolecular charge transfer effect between BP and C60.

  13. Impact of donor-acceptor morphology on the charge carrier generation in organic photovoltaic devices (United States)

    Inche Ibrahim, M. L.


    We investigate the impact of donor-acceptor morphology on the generation of charge carriers in organic photovoltaic cells and photodiodes based on a recently proposed model. It is found that for devices with typical values of permittivity and actual charge carrier mobilities, the donor-acceptor morphology plays an important role in the charge carrier generation, practically at all operating electric fields. Higher permittivity and actual mobilities increase the charge carrier generation, and also decrease the effect of donor-acceptor morphology on the charge carrier generation. Although the donor-acceptor morphology is important for charge carrier generation in general, but having permittivity and/or actual mobilities that are significantly higher than the typical values are more desirable in order to maximize the charge carrier generation.

  14. Direct measurement of photoinduced charge separation distances in donor-acceptor systems for artificial photosynthesis using OOP-ESEEM. (United States)

    Carmieli, Raanan; Mi, Qixi; Ricks, Annie Butler; Giacobbe, Emilie M; Mickley, Sarah M; Wasielewski, Michael R


    The distance over which two photogenerated charges are separated in electron donor-acceptor systems for artificial photosynthesis depends on the structure of the system, while the lifetime of the charge separation and, ultimately, its ability to carry out useful redox chemistry depend on the electronic coupling between the oxidized donor and reduced acceptor. The radical ions produced by charge separation are frequently delocalized over the pi systems of the final oxidized donor and reduced acceptor, so that there is often significant uncertainty as to the average distance between the separated charges, especially in low dielectric constant media, where the Coulomb attraction of the ions may be significant and the charge distribution of the ions may be distorted, so that the average distance between them may be shorter than that implied by their chemical structures. The charge separation distances between photogenerated radical ions in three donor-acceptor molecules having different donor-acceptor distances were measured directly from their dipolar spin-spin interactions using out-of-phase electron spin echo envelope modulation (OOP-ESEEM). The measured distances in toluene at 85 K compare favorably to the calculated distances between the centroids of the spin distributions of the radical ions within the radical ion pairs. These results show that despite the intrinsically nonpolar nature of medium, the spin (and charge) distributions of the RPs are not significantly distorted by Coulomb attraction over these long distances. This study shows that OOP-ESEEM is well-suited for probing the detailed structural features of charge-separated intermediates that are essential to understanding how to design molecular structures that prolong and control charge separation for artificial photosynthesis.

  15. Designing novel copolymers of donor-acceptor polymers using an artificial intelligence method (United States)

    Kapoor, Vinita; Bakhshi, A. K.


    Using the ab initio Hartree-Fock crystal orbital results of three donor-acceptor polymers, PFUCO ([A]x), PSIFCO ([B]x) and PSIFCH ([C]x), the electronic properties of their novel quasi-one-dimensional copolymers (AmBn)x and (AmCn)x were investigated using an artificial intelligence technique, the genetic algorithm, in combination with negative factor counting and inverse iteration method. The repeat units in PFUCO consist of bifuran bridged by electron accepting groups Y (>Cdbnd O); while in PSIFCO and PSIFCH, the repeat units consist of bicyclopentadifluorosilole bridged by electron accepting groups Y (Y is >Cdbnd O in PSIFCO, and >Cdbnd CH2 in PSIFCH). The trends in the electronic properties of the copolymers (AmBn)x and (AmCn)x as a function of block sizes m and n, and arrangement of units (periodic and random) in the copolymer chain are also discussed. The results obtained are important guidelines for molecular designing of copolymers with tailor-made conduction properties.

  16. Impact of Thermal Annealing on Organic Photovoltaic Cells Using Regioisomeric Donor-Acceptor-Acceptor Molecules. (United States)

    Zhang, Tao; Han, Han; Zou, Yunlong; Lee, Ying-Chi; Oshima, Hiroya; Wong, Ken-Tsung; Holmes, Russell J


    We report a promising set of donor-acceptor-acceptor (D-A-A) electron-donor materials based on coplanar thieno[3,2-b]/[2,3-b]indole, benzo[c][1,2,5]thiadiazole, and dicyanovinylene, which are found to show broadband absorption with high extinction coefficients. The role of the regioisomeric electron-donating thienoindole moiety on the physical and structural properties is examined. Bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on the thieno[2,3-b]indole-based electron donor NTU-2, using C70 as an electron acceptor, show a champion power conversion efficiency of 5.2% under AM 1.5G solar simulated illumination. This efficiency is limited by a low fill factor (FF), as has previously been the case in D-A-A systems. In order to identify the origin of the limited FF, further insight into donor layer charge-transport behavior is realized by examining planar heterojunction OPVs, with emphasis on the evolution of film morphology with thermal annealing. Compared to as-deposited OPVs that exhibit insufficient donor crystallinity, crystalline OPVs based on annealed thin films show an increase in the short-circuit current density, FF, and power conversion efficiency. These results suggest that that the crystallization of D-A-A molecules might not be realized spontaneously at room temperature and that further processing is needed to realize efficient charge transport in these materials.

  17. Charge separation and carrier dynamics in donor-acceptor heterojunction photovoltaic systems

    Directory of Open Access Journals (Sweden)

    Joël Teuscher


    Full Text Available Electron transfer and subsequent charge separation across donor-acceptor heterojunctions remain the most important areas of study in the field of third-generation photovoltaics. In this context, it is particularly important to unravel the dynamics of individual ultrafast processes (such as photoinduced electron transfer, carrier trapping and association, and energy transfer and relaxation, which prevail in materials and at their interfaces. In the frame of the National Center of Competence in Research “Molecular Ultrafast Science and Technology,” a research instrument of the Swiss National Science Foundation, several groups active in the field of ultrafast science in Switzerland have applied a number of complementary experimental techniques and computational simulation tools to scrutinize these critical photophysical phenomena. Structural, electronic, and transport properties of the materials and the detailed mechanisms of photoinduced charge separation in dye-sensitized solar cells, conjugated polymer- and small molecule-based organic photovoltaics, and high-efficiency lead halide perovskite solar energy converters have been scrutinized. Results yielded more than thirty research articles, an overview of which is provided here.

  18. A Strong Donor-Acceptor System Based on a Metal Chalcogenide Cluster and Porphyrin. (United States)

    Xu, Jing; Xue, Li-Jun; Hou, Jin-Le; Yin, Zhong-Nan; Zhang, Xuan; Zhu, Qin-Yu; Dai, Jie


    Although great progress has been made for charge transfer (CT) compounds of various organic donor-acceptor systems, no CT compounds containing both inorganic chalcogenide cluster anions and organic porphyrin cations have been reported. Herein, a germanium chalcogenide cluster (Ge4S10(4-)) is chosen as an electron donor and a methylated tetrakis(4-pyridyl)porphyrin (5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin, TMPyP) is selected as an electron acceptor to create chalcogenide cluster-porphyrin CT compounds (TMPyP-Ge4S10)·5H2O (1) and (MnTMPyP-Ge4S10)·13H2O (2). Their crystal structures have been characterized by single-crystal X-ray diffraction. Compound 1 is an ionic CT salt assembled through interion interactions, and compound 2 is a neutral CT dyad formed by metal-ligand axial coordination of the chalcogenide cluster with manganese porphyrin. The strong charge transfer properties are revealed by electronic spectra, theoretical calculations, (1)H NMR, and ESR. The CT intensity of the chalcogenide cluster-porphyrin system can be modulated by metalation. The fluorescence and photocurrent response properties of 1 and 2 are related to the CT intensity.

  19. Role of the charge transfer state in organic donor-acceptor solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Deibel, Carsten; Strobel, Thomas [Experimental Physics VI, Julius-Maximilians-University of Wuerzburg (Germany); Dyakonov, Vladimir [Experimental Physics VI, Julius-Maximilians-University of Wuerzburg (Germany); Bavarian Centre for Applied, Energy Research (ZAE Bayern), Wuerzburg (Germany)


    Charge transfer complexes are interfacial charge pairs residing at the donor-acceptor heterointerface in organic solar cell. Experimental evidence shows that it is crucial for the photovoltaic performance, as both photocurrent and open circuit voltage directly depend on it. For charge photogeneration, charge transfer complexes represent the intermediate but essential step between exciton dissociation and charge extraction. Recombination of free charges to the ground state is via the bound charge transfer state before being lost to the ground state. In terms of the open circuit voltage, its maximum achievable value is determined by the energy of the charge transfer state. An important question is whether or not maximum photocurrent and maximum open circuit voltage can be achieved simultaneously. The impact of increasing the CT energy - in order to raise the open circuit voltage, but lowering the kinetic excess energy of the CT complexes at the same time - on the charge photogeneration will accordingly be discussed. Clearly, the fundamental understanding of the processes involving the charge transfer state is essential for an optimisation of the performance of organic solar cells. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  20. Dissociation of charge-transfer states at donor-acceptor interfaces of organic heterojunctions (United States)

    Inche Ibrahim, M. L.


    The dissociation of charge-transfer (CT) states into free charge carriers at donor-acceptor (DA) interfaces is an important step in the operation of organic solar cells and related devices. In this paper, we show that the effect of DA morphology and architecture means that the directions of CT states (where a CT state’s direction is defined as the direction from the electron to the hole of the CT state) may deviate from the direction of the applied electric field. The deviation means that the electric field is not fully utilized to assist, and could even hinder the dissociation process. Furthermore, we show that the correct charge carrier mobilities that should be used to describe CT state dissociation are the actual mobilites at DA interfaces. The actual mobilities are defined in this paper, and in general are not the same as the mobilities that are used to calculate electric currents which are the mobilites along the direction of the electric field. Then, to correctly describe CT state dissociation, we modify the widely used Onsager-Braun (OB) model by including the effect of DA morphology and architecture, and by employing the correct mobilities. We verify that when the modified OB model is used to describe CT state dissociation, the fundamental issues that concern the original OB model are resolved. This study demonstrates that DA morphology and architecture play an important role by strongly influencing the CT state dissociation as well as the mobilites along the direction of the electric field.

  1. Organic donor/acceptor photovoltaics : The role of C-60/metal interfaces

    NARCIS (Netherlands)

    Melzer, C; Krasnikov, VV; Hadziioannou, G


    The photovoltaic properties of thin films based on donor/acceptor heterojunctions, prepared by means of either consecutive evaporation or co-evaporation, and sandwiched between asymmetric contacts are investigated. (E,E,E,E)-1,4-bis[(4-styryl)styryl]-2-methoxy-5-(2'-ethylhexoxy)benzene (MEH-OPV5)

  2. Tailored Band Gaps in Sulfur- and Nitrogen-Containing Porous Donor-Acceptor Polymers

    Czech Academy of Sciences Publication Activity Database

    Schwarz, D.; Kochergin, Y. S.; Acharjya, A.; Ichangi, Arun; Opanasenko, Maksym; Čejka, Jiří; Lappan, U.; Arki, P.; He, J.; Schmidt, J.; Nachtigall, P.; Thomas, A.; Tarábek, Ján; Bojdys, Michael J.


    Roč. 23, č. 53 (2017), s. 13023-13027 ISSN 0947-6539 Institutional support: RVO:61388963 ; RVO:61388955 Keywords : conjugated microporous polymers * donor-acceptor dyads * photocatalysis * sulfur * triazine Subject RIV: CC - Organic Chemistry Impact factor: 5.317, year: 2016

  3. Thrilling strain! Donor-acceptor-substituted cyclobutanes for the synthesis of (hetero)cyclic compounds. (United States)

    Reissig, Hans-Ulrich; Zimmer, Reinhold


    The analogy goes further: Following the often-studied donor-acceptor-substituted cyclopropanes, the corresponding cyclobutane derivatives were employed for the ring-strain-driven stereoselective syntheses of carbo- and heterocycles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Organic donor-acceptor thin film systems. Towards optimized growth conditions

    Energy Technology Data Exchange (ETDEWEB)

    Keller, Kerstin Andrea


    In this work the preparation of organic donor-acceptor thin films was studied. A chamber for organic molecular beam deposition was designed and integrated into an existing deposition system for metallic thin films. Furthermore, the deposition system was extended by a load-lock with integrated bake-out function, a chamber for the deposition of metallic contacts via stencil mask technique and a sputtering chamber. For the sublimation of the organic compounds several effusion cells were designed. The evaporation characteristic and the temperature profile within the cells was studied. Additionally, a simulation program was developed, which calculates the evaporation characteristics of different cell types. The following processes were integrated: evaporation of particles, migration on the cell walls and collisions in the gas phase. It is also possible to consider a temperature gradient within the cell. All processes can be studied separately and their relative strength can be varied. To verify the simulation results several evaporation experiments with different cell types were employed. The thickness profile of the prepared thin films was measured position-dependently. The results are in good agreement with the simulation. Furthermore, the simulation program was extended to the field of electron beam induced deposition (EBID). The second part of this work deals with the preparation and characterization of organic thin films. The focus hereby lies on the charge transfer salt (BEDT-TTF)(TCNQ), which has three known structure variants. Thin films were prepared by different methods of co-evaporation and were studied with optical microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy (EDX).The formation of the monoclinic phase of (BEDT-TTF)(TCNQ) could be shown. As a last part tunnel structures were prepared as first thin film devices and measured in a He{sub 4} cryostat. (orig.)

  5. Direct correlation of charge transfer absorption with molecular donor:acceptor interfacial area via photothermal deflection spectroscopy

    KAUST Repository

    Domingo, Ester


    We show that the Charge Transfer (CT) absorption signal in bulk-heterojunction (BHJ) solar cell blends, measured by photothermal deflection spectroscopy (PDS), is directly proportional to the density of molecular donor/acceptor interfaces. Since the optical transitions from ground state to the interfacial CT state are weakly allowed at photon energies below the optical gap of both donor and acceptor, we can exploit the use of this sensitive linear absorption spectroscopy for such quantification. Moreover, we determine the absolute molar extinction coefficient of the CT transition for an archetypical polymer-fullerene interface. The latter is ~100 times lower than the extinction coefficient of the donor chromophore involved, allowing us to experimentally estimate the transition dipole moment (0.3 D) and the electronic coupling between ground state and CT state to be on the order of 30 meV.

  6. Alteration of the Donor/Acceptor Spectrum of the (S-Amine Transaminase from Vibrio fluvialis

    Directory of Open Access Journals (Sweden)

    Maika Genz


    Full Text Available To alter the amine donor/acceptor spectrum of an (S-selective amine transaminase (ATA, a library based on the Vibrio fluvialis ATA targeting four residues close to the active site (L56, W57, R415 and L417 was created. A 3DM-derived alignment comprising fold class I pyridoxal-5′-phosphate (PLP-dependent enzymes allowed identification of positions, which were assumed to determine substrate specificity. These positions were targeted for mutagenesis with a focused alphabet of hydrophobic amino acids to convert an amine:α-keto acid transferase into an amine:aldehyde transferase. Screening of 1200 variants revealed three hits, which showed a shifted amine donor/acceptor spectrum towards aliphatic aldehydes (mainly pentanal, as well as an altered pH profile. Interestingly, all three hits, although found independently, contained the same mutation R415L and additional W57F and L417V substitutions.

  7. Quantum efficiency enhancement in nanocrystals using nonradiative energy transfer with optimized donor-acceptor ratio for hybrid LEDs (United States)

    Nizamoglu, Sedat; Akin, Onur; Demir, Hilmi Volkan


    The quantum efficiency enhancement in nanocrystal solids is critically important for their efficient use as luminophors on color-conversion light emitting diodes (LEDs). For this purpose, we investigate energy gradient mixture of nanocrystal solids for recycling their trapped excitons by varying their donor-acceptor nanocrystal ratios and study the resulting quantum efficiency enhancement as a function of the donor-acceptor ratio in the solid film for hybrid LEDs. We achieve a maximum quantum efficiency enhancement of 17% in these nanocrystal solids when the donor-acceptor ratio is 1:1, demonstrating their highly modified time-resolved photoluminescence decays to reveal the kinetics of strong energy transfer between them.

  8. Characterization of donor-acceptor-pair emission in fluorescent 6H-SiC

    DEFF Research Database (Denmark)

    Ou, Yiyu; Jokubavicius, Valdas; Linnarsson, Margareta


    We investigated donor-acceptor-pair emission in N-B-doped 6H-SiC samples by using photoluminescence (PL) and angle-resolved PL. It is shown that n-type doping with concentrations larger than 10(18) cm(-3) is favorable for observing luminescence, and increasing nitrogen results in stronger lumines....... The results indicate that N-B-doped fluorescent SiC is a good wavelength converter in white LED applications....

  9. Field emission analysis of band bending in donor/acceptor heterojunction

    Energy Technology Data Exchange (ETDEWEB)

    Xing, Yingjie, E-mail:; Li, Shuai; Wang, Guiwei; Zhao, Tianjiao; Zhang, Gengmin [Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China)


    The donor/acceptor heterojunction plays an important role in organic solar cells. An investigation of band bending in the donor/acceptor heterojunction is helpful in analysis of the charge transport behavior and for the improvement of the device performance. In this work, we report an approach for detection of band bending in a donor/acceptor heterojunction that has been prepared on a small and sharp tungsten tip. In situ field emission measurements are performed after the deposition process, and a linear Fowler-Nordheim plot is obtained from the fresh organic film surface. The thickness-dependent work function is then measured in the layer-by-layer deposited heterojunction. Several different types of heterojunction (zinc phthalocyanine (ZnPc)/C60, copper phthalocyanine (CuPc)/3,4,9,10-perylenetetracarboxylic bisbenzimidazole, and CuPc/C60) are fabricated and analyzed. The different charge transfer directions in the heterojunctions are distinguished by field emission measurements. The calculation method used to determine the band bending is then discussed in detail. A triple layer heterojunction (C60/ZnPc/CuPc) is also analyzed using this method. A small amount of band bending is measured in the outer CuPc layer. This method provides an independent reference method for determination of the band bending in an organic heterojunction that will complement photoemission spectroscopy and current-voltage measurement methods.

  10. Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing

    National Research Council Canada - National Science Library

    Ning Li; José Darío Perea; Thaer Kassar; Moses Richter; Thomas Heumueller; Gebhard J Matt; Yi Hou; Nusret S Güldal; Haiwei Chen; Shi Chen; Stefan Langner; Marvin Berlinghof; Tobias Unruh; Christoph J Brabec


      The performance of organic solar cells is determined by the delicate, meticulously optimized bulk-heterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions...

  11. Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study

    KAUST Repository

    Fonari, A.


    We establish a reliable quantum-mechanical approach to evaluate the vibrational properties of donor-acceptor molecular crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as the electron donor and PMDA as the electron acceptor, is taken as a representative system for which experimental non-resonance Raman spectra are also reported. We first investigate the impact that the amount of nonlocal Hartree-Fock exchange (HFE) included in a hybrid density functional has on the geometry, normal vibrational modes, electronic coupling, and electron-vibrational (phonon) couplings. The comparison between experimental and theoreticalRaman spectra indicates that the results based on the αPBE functional with 25%-35% HFE are in better agreement with the experimental results compared to those obtained with the pure PBE functional. Then, taking αPBE with 25% HFE, we assign the vibrational modes and examine their contributions to the relaxation energy related to the nonlocal electron-vibration interactions. The results show that the largest contribution (about 90%) is due to electron interactions with low-frequency vibrational modes. The relaxation energy in anthracene-PMDA is found to be about five times smaller than the electronic coupling.

  12. Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study

    Energy Technology Data Exchange (ETDEWEB)

    Fonari, A.; Corbin, N. S.; Coropceanu, V., E-mail:, E-mail: [School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States); Vermeulen, D.; McNeil, L. E. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3255 (United States); Goetz, K. P.; Jurchescu, O. D. [Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27109-7507 (United States); Bredas, J. L., E-mail:, E-mail: [School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States); Solar and Photovoltaics Engineering Research Center, Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900 (Saudi Arabia)


    We establish a reliable quantum-mechanical approach to evaluate the vibrational properties of donor-acceptor molecular crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as the electron donor and PMDA as the electron acceptor, is taken as a representative system for which experimental non-resonance Raman spectra are also reported. We first investigate the impact that the amount of nonlocal Hartree-Fock exchange (HFE) included in a hybrid density functional has on the geometry, normal vibrational modes, electronic coupling, and electron-vibrational (phonon) couplings. The comparison between experimental and theoretical Raman spectra indicates that the results based on the αPBE functional with 25%-35% HFE are in better agreement with the experimental results compared to those obtained with the pure PBE functional. Then, taking αPBE with 25% HFE, we assign the vibrational modes and examine their contributions to the relaxation energy related to the nonlocal electron-vibration interactions. The results show that the largest contribution (about 90%) is due to electron interactions with low-frequency vibrational modes. The relaxation energy in anthracene-PMDA is found to be about five times smaller than the electronic coupling.

  13. Tailoring Photoisomerization Pathways in Donor-Acceptor Stenhouse Adducts: The Role of the Hydroxy Group. (United States)

    Lerch, Michael M; Medved, Miroslav; Lapini, Andrea; Laurent, Adèle D; Iagatti, Alessandro; Bussotti, Laura; Szymański, Wiktor; Buma, Wybren Jan; Foggi, Paolo; Di Donato, Mariangela; Feringa, Ben L


    Donor-acceptor Stenhouse adducts (DASAs) are a rapidly emerging class of visible light-activatable negative photochromes. They are closely related to (mero)cyanine dyes with the sole difference being a hydroxy group in the polyene chain. The presence or absence of the hydroxy group has far-reaching consequences for the photochemistry of the compound: cyanine dyes are widely used as fluorescent probes, whereas DASAs hold great promise for visible light-triggered photoswitching. Here we analyze the photophysical properties of a DASA lacking the hydroxy group. Ultrafast time-resolved pump-probe spectroscopy in both the visible and IR region show the occurrence of E-Z photoisomerization on a 20 ps time scale, similar to the photochemical behavior of DASAs, but on a slower time scale. In contrast to the parent DASA compounds, where the initial photoisomerization is constrained to a single position (next to the hydroxy group), 1 H NMR in situ-irradiation studies at 213 K reveal that for nonhydroxy DASAs E-Z photoisomerization can take place at two different bonds, yielding two distinct isomers. These observations are supported by TD-DFT calculations, showing that in the excited state the hydroxy group (pre)selects the neighboring C 2 -C 3 bond for isomerization. The TD-DFT analysis also explains the larger solvatochromic shift observed for the parent DASAs as compared to the nonhydroxy analogue, in terms of the dipole moment changes evoked upon excitation. Furthermore, computations provide helpful insights into the photoswitching energetics, indicating that without the hydroxy group the 4π-electrocyclization step is energetically forbidden. Our results establish the central role of the hydroxy group for DASA photoswitching and suggest that its introduction allows for tailoring photoisomerization pathways, presumably both through (steric) fixation via a hydrogen bond with the adjacent carbonyl group of the acceptor moiety, as well as through electronic effects on the

  14. Rational Design for Complementary Donor-Acceptor Recognition Pairs Using Self-Complementary Hydrogen Bonds. (United States)

    Sikder, Amrita; Ghosh, Boyli; Chakraborty, Saptarshi; Paul, Ankan; Ghosh, Suhrit


    An adaptable and efficient molecular recognition pair has been established by taking advantage of the complementary nature of donor-acceptor interactions together with the strength of hydrogen bonds. Such distinct molecular recognition propagates in orthogonal directions to effect extended alternating co-assembly of two different appended molecular entities. The dimensions of the assembled structures can be tuned by stoichiometric imbalance between the donor and acceptor building blocks. The morphology of the self-assembled material can be correlated with the ratio of the two building blocks. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC

    DEFF Research Database (Denmark)

    Ou, Yiyu; Jokubavicius, Valdas; Kamiyama, Satoshi


    In the present work, we investigated donor-acceptor-pair emission in N-B doped fluorescent 6H-SiC, by means of photoluminescence, Raman spectroscopy, and angle-resolved photoluminescence. The photoluminescence results were interpreted by using a band diagram with Fermi-Dirac statistics. It is shown...... intensity in a large emission angle range was achieved from angle-resolved photoluminescence. The results indicate N-B doped fluorescent SiC as a good wavelength converter in white LEDs applications....

  16. Interfacial Donor-Acceptor Engineering of Nanofiber Materials To Achieve Photoconductivity and Applications. (United States)

    Zang, Ling


    Self-assembly of π-conjugate molecules often leads to formation of well-defined nanofibril structures dominated by the columnar π-π stacking between the molecular planes. These nanofibril materials have drawn increasing interest in the research frontiers of nanomaterials and nanotechnology, as the nanofibers demonstrate one-dimensionally enhanced exciton and charge diffusion along the long axis, and present great potential for varying optoelectronic applications, such as sensors, optics, photovoltaics, and photocatalysis. However, poor electrical conductivity remains a technical drawback for these nanomaterials. To address this problem, we have developed a series of nanofiber structures modified with different donor-acceptor (D-A) interfaces that are tunable for maximizing the photoinduced charge separation, thus leading to increase in the electrical conductivity. The D-A interface can be constructed with covalent linker or noncovalent interaction (e.g., hydrophobic interdigitation between alkyl chains). The noncovalent method is generally more flexible for molecular design and solution processing, making it more adaptable to be applied to other fibril nanomaterials such as carbon nanotubes. In this Account, we will discuss our recent discoveries in these research fields, aiming to provide deep insight into the enabling photoconductivity of nanofibril materials, and the dependence on interface structure. The photoconductivity generated with the nanofibril material is proportional to the charge carriers density, which in turn is determined by the kinetics balance of the three competitive charge transfer processes: (1) the photoinduced electron transfer from D to A (also referred to as exciton dissociation), generating majority charge carrier located in the nanofiber; (2) the back electron transfer; and (3) the charge delocalization along the nanofiber mediated by the π-π stacking interaction. The relative rates of these charge transfer processes can be tuned by

  17. CVD graphene as interfacial layer to engineer the organic donor-acceptor heterojunction interface properties. (United States)

    Zhong, Shu; Zhong, Jian Qiang; Mao, Hong Ying; Wang, Rui; Wang, Yu; Qi, Dong Chen; Loh, Kian Ping; Wee, Andrew Thye Shen; Chen, Zhi Kuan; Chen, Wei


    We demonstrate the use of chemical-vapor-deposited (CVD) graphene as an effective indium-tin-oxide (ITO) electrode surface modifier to engineer the organic donor-acceptor heterojunction interface properties in an inverted organic solar cell device configuration. As revealed by in situ near-edge X-ray adsorption fine structure measurement, the organic donor-acceptor heterojunction, comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) and copper phthalocyanine (CuPc), undergoes an obvious orientation transition from a standing configuration (molecular π-plane nearly perpendicular to the substrate surface) on the bare ITO electrode to a less standing configuration with the molecular π-plane stacking adopting a large projection along the direction perpendicular to the electrode surface on the CVD graphene-modified ITO electrode. Such templated less-standing configuration of the organic heterojunction could significantly enhance the efficiency of charge transport along the direction perpendicular to the electrode surface in the planar heterojunction-based devices. Compared with the typical standing organic-organic heterojunction on the bare ITO electrode, our in situ ultraviolet photoelectron spectroscopy experiments reveal that the heterojunction on the CVD graphene modified ITO electrode possesses better aligned energy levels with respective electrodes, hence facilitating effective charge collection.

  18. Study of the potential energy conversion efficiency of organic solar cells based on donor/acceptor heterojunctions (United States)

    Geens, Wim


    Organic solar cells can offer an appealing alternative for bulk silicon solar cells due to their attractive properties such as flexibility and possibility to apply low-cost manufacturing techniques. The different types of existing organic solar cells reported in the literature have been critically assessed in terms of performance and processability, based on which it was concluded that the concept of the donor/acceptor bulk heterojunction sandwiched between a transparent and a metal electrode has the most potential. In order to gain more insight into the charge transport properties of spin-cast photovoltaic conjugated polymer/fullerene blends, these films were incorporated into field-effect transistors to derive values for the electron and hole mobilities. Model calculations showed that increasing these mobility values in combination with the use of thicker active layers could significantly enhance the short-circuit current density of the bulk heterojunction solar cells. Optimisation of the charge transport is required and was realised in this study by choosing PPV-oligomers and C60 as well-defined building blocks to construct the donor/acceptor networks. First, these materials were spin-cast in single-layer diodes to allow full electrical characterisation, which was then compared with simulation of the devices in dark as well as under illumination. The photovoltaic performance of blended PPV-oligomer/C60 devices remained rather low due to C60-induced shunting paths and high molecular disorder. In a second part, more morphological order was obtained by using vacuum evaporation to deposit the organic materials. Besides structural characterisation of the evaporated films, the electrical behaviour of single-layer devices was investigated and the influence of interfacial layers was addressed. Photovoltaic devices based on evaporated planar heterojunctions reaching a conversion efficiency of 1.9% and exhibiting an open-circuit voltage of over 1 V were realised

  19. Kinetic and Thermodynamic Studies of Charge-Transfer Complex ...

    African Journals Online (AJOL)

    The stoichiometry of the resulting complex was found to be 1:1 by the method of Job's continuous variation. The formation constants and thermodynamic parameters of the resulting electron-donor-acceptor (DA) complexes were determined by Benesi-Hildebrand and van't Hoff equations, respectively. The time-dependent ...

  20. Pyrimidine-based twisted donor-acceptor delayed fluorescence molecules: a new universal platform for highly efficient blue electroluminescence. (United States)

    Park, In Seob; Komiyama, Hideaki; Yasuda, Takuma


    Deep-blue emitters that can harvest both singlet and triplet excited states to give high electron-to-photon conversion efficiencies are highly desired for applications in full-color displays and white lighting devices based on organic light-emitting diodes (OLEDs). Thermally activated delayed fluorescence (TADF) molecules based on highly twisted donor-acceptor (D-A) configurations are promising emitting dopants for the construction of efficient deep-blue OLEDs. In this study, a simple and versatile D-A system combining acridan-based donors and pyrimidine-based acceptors has been developed as a new platform for high-efficiency deep-blue TADF emitters. The designed pre-twisted acridan-pyrimidine D-A molecules exhibit small singlet-triplet energy splitting and high photoluminescence quantum yields, functioning as efficient deep-blue TADF emitters. The OLEDs utilizing these TADF emitters display bright blue electroluminescence with external quantum efficiencies of up to 20.4%, maximum current efficiencies of 41.7 cd A(-1), maximum power efficiencies of 37.2 lm W(-1), and color coordinates of (0.16, 0.23). The design strategy featuring such acridan-pyrimidine D-A motifs can offer great prospects for further developing high-performance deep-blue TADF emitters and TADF-OLEDs.

  1. Photophysical study of a self-assembled donor-acceptor two-layer film on TiO2. (United States)

    Stranius, Kati; George, Lijo; Efimov, Alexander; Ruoko, Tero-Petri; Pohjola, Juuso; Tkachenko, Nikolai V


    The self-assembled monolayer (SAM) technique was employed to fabricate a two-layer donor-acceptor film on the surface of TiO2. The approach is based on using donor and acceptor compounds with anchoring groups of different lengths. The acceptor, a fullerene derivative, has a carboxyl anchor attached to the fullerene moiety via a short linker that places the fullerene close to the surface. The donor, a porphyrin derivative, is equipped with a long linker that can penetrate between the fullerenes and keep porphyrin on top of the fullerene layer. The two-layer fullerene-porphyrin structures were deposited on a mesoporous film of TiO2 nanoparticles by immersing the TiO2 film sequentially into fullerene and porphyrin solutions. Transient absorption spectroscopy studies of the samples revealed that after the selective photoexcitation of porphyrin a fast (TiO2 nanoparticles. The latter reaction is relatively slow with an average time constant of 230 ps. It involves roughly half of the primary generated charges, and the second half relaxes by the interlayer charge recombination. The resulting state with a porphyrin cation and electron in TiO2 has an extremely long lifetime and recombines with an average time constant of 23 ms.

  2. Fluorinated arene, imide and unsaturated pyrrolidinone based donor acceptor conjugated polymers: Synthesis, structure-property and device studies (United States)

    Liyanage, Arawwawala Don Thilanga

    After the discovery of doped polyacetylene, organic semiconductor materials are widely studied as high impending active components in consumer electronics. They have received substantial consideration due to their potential for structural tailoring, low cost, large area and mechanically flexible alternatives to common inorganic semiconductors. To acquire maximum use of these materials, it is essential to get a strong idea about their chemical and physical nature. Material chemist has an enormous role to play in this novel area, including development of efficient synthetic methodologies and control the molecular self-assembly and (opto)-electronic properties. The body of this thesis mainly focuses on the substituent effects: how different substituents affect the (opto)-electronic properties of the donor-acceptor (D-A) conjugated polymers. The main priority goes to understand, how different alkyl substituent effect to the polymer solubility, crystallinity, thermal properties (e.g.: glass transition temperature) and morphological order. Three classes of D-A systems were extensively studied in this work. The second chapter mainly focuses on the synthesis and structure-property study of fluorinated arene (TFB) base polymers. Here we used commercially available 1,4-dibromo-2,3,5,6-tetrafluorobenzene (TFB) as the acceptor material and prepare several polymers using 3,3'-dialkyl(3,3'-R2T2) or 3,3'-dialkoxy bithiophene (3,3'-RO2T2) units as electron donors. A detail study was done using 3,3'-bithiophene donor units incorporating branched alkoxy-functionalities by systematic variation of branching position and chain length. The study allowed disentangling the branching effects on (i) aggregation tendency, intermolecular arrangement, (iii) solid state optical energy gaps, and (iv) electronic properties in an overall consistent picture, which might guide future polymer synthesis towards optimized materials for opto-electronic applications. The third chapter mainly focused on

  3. Thermally stable and efficient polymer solar cells based on a novel donor-acceptor copolymer (United States)

    Synooka, O.; Eberhardt, K.-R.; Balko, J.; Thurn-Albrecht, T.; Gobsch, G.; Mitchell, W.; Berny, S.; Carrasco-Orozco, M.; Hoppe, H.


    We report high photovoltaic performance of a novel donor-acceptor (D-A) conjugated polymer poly[2,6[4,8-bis(2-ethyl-hexyl)benzo[1,2-b4,5-b‧]dithiophene-co-2,5-thiophene-co-4,7[5,6-bis-octyloxy-benzo[1,2,5]thiadiazole]-co-2,5-thiophene] (PBDTTBTZT) in bulk heterojunctions with [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM). A power conversion efficiency (PCE) of more than 7% is obtained for optimized charge-extracting electrodes. Upon application of thermal stress via annealing, a superior thermal stability is demonstrated as compared to poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4‧,7‧-di-2-thienyl-2‧,1‧,3‧-benzothiadiazole)] (PCDTBT).

  4. Donor-acceptor alternating copolymer nanowires for highly efficient organic solar cells. (United States)

    Lee, Jaewon; Jo, Sae Byeok; Kim, Min; Kim, Heung Gyu; Shin, Jisoo; Kim, Haena; Cho, Kilwon


    A donor-acceptor conjugated copolymer enables the formation of nanowire systems that can be successfully introduced into bulk-heterojunction organic solar cells. A simple binary solvent mixture that makes polarity control possible allows kinetic control over the self-assembly of the crystalline polymer into a nanowire structure during the film-forming process. The enhanced photoconductivity of the nanowire-embedded photoactive layer efficiently facilitates photon harvesting in the solar cells. The resultant maximum power conversion efficiency is 8.2% in a conventional single-cell structure, revealing a 60% higher performance than in devices without nanowires. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. AIEE Active Donor-Acceptor-Donor-Based Hexaphenylbenzene Probe for Recognition of Aliphatic and Aromatic Amines. (United States)

    Pramanik, Subhamay; Deol, Harnimarta; Bhalla, Vandana; Kumar, Manoj


    In the present investigation, an intramolecular charge transfer (ICT) and aggregation induced emission enhancement (AIEE) active donor-acceptor-donor (D-A-D) system 5 having fumaronitrile as the acceptor and hexaphenylbenzene (HPB) as the donor moieties joined through rotatable phenyl rings has been designed and synthesized that is highly emissive in the solid state and exhibits stimuli-responsive reversible piezochromic behavior upon grinding and heating. Because of its AIEE characteristics, HPB derivative 5 undergoes aggregation to form fluorescent aggregates in mixed aqueous media that exhibit ratiometric fluorescence response toward aliphatic amines (primary/secondary/tertiary) and turn-off response toward aromatic amines and hence differentiates between them. Further, the solution-coated portable paper strips of derivative 5 showed pronounced and sensitive response toward aromatic and aliphatic amines with a detection limit in the range of picogram and nanogram level, respectively.

  6. Dynamic combinatorial donor-acceptor catenanes in water: access to unconventional and unexpected structures. (United States)

    Au-Yeung, Ho Yu; Pantoş, G Dan; Sanders, Jeremy K M


    We describe here the assembly of new types of donor-acceptor [2]catenanes from dynamic combinatorial libraries (DCL) in water. These new catenanes contain both the donor and acceptor components in at least one of the interlocked rings, thereby possessing unusual and unexpected DAAD or DADD stacking sequences of the π units in their structures. The efficiency of the catenane assembly process can be enhanced by manipulating the DCL equilibrium in a variety of ways: adding a guest, changing the building block stoichiometries, or increasing the library concentration or the ionic strength of the solvent. The formation of catenanes and their constitutions are found to be dependent on subtle differences in the geometry, dimension, and flexibility of the donor building blocks.

  7. Magneto-ionic phase control in a quasi-layered donor/acceptor metal-organic framework by means of a Li-ion battery system (United States)

    Taniguchi, Kouji; Narushima, Keisuke; Yamagishi, Kayo; Shito, Nanami; Kosaka, Wataru; Miyasaka, Hitoshi


    Electrical magnetism control is realized in a Li-ion battery system through a redox reaction involving ion migrations; “magneto-ionic control”. A quasi-layered metal-organic framework compound with a cross-linked π-conjugated/unconjugated one-dimensional chain motifs composed of electron-donor/acceptor units is developed as the cathode material. A change in magnetic phase from paramagnetic to ferrimagnetic is demonstrated by means of electron-filling control for the acceptor units via insertion of Li+-ions into pores in the material. The transition temperature is as high as that expected for highly π-conjugated layered systems, indicating an extension of π-conjugated exchange paths by rearranging coordination bonds in the first discharge process.

  8. Amplitude-Mode Spectroscopy of Charge Excitations in PTB7 π -Conjugated Donor-Acceptor Copolymer for Photovoltaic Applications (United States)

    Baniya, Sangita; Vardeny, Shai R.; Lafalce, Evan; Peygambarian, Nasser; Vardeny, Z. Valy


    We measure the spectra of resonant Raman scattering and doping-induced absorption of pristine films of the π -conjugated donor-acceptor (D -A ) copolymer, namely, thieno[3,4 b]thiophene-alt-benzodithiophene (PTB7), as well as photoinduced absorption spectrum in a blend of PTB7 with fullerene phenyl-C61-butyric acid methyl ester molecules used for organic photovoltaic (OPV) applications. We find that the D -A copolymer contains six strongly coupled vibrational modes having relatively strong Raman-scattering intensity, which are renormalized upon adding charge polarons onto the copolymer chains either by doping or photogeneration. Since the lower-energy charge-polaron absorption band overlaps with the renormalized vibrational modes, they appear as antiresonance lines superposed onto the induced polaron absorption band in the photoinduced absorption spectrum but less so in the doping-induced absorption spectrum. We show that the Raman-scattering, doping-, and photoinduced absorption spectra of PTB7 are well explained by the amplitude mode model, where a single vibrational propagator describes the renormalized modes and their related intensities in detail. From the relative strengths of the induced infrared activity of the polaron-related vibrations and electronic transitions, we obtain the polaron effective kinetic mass in PTB7 using the amplitude mode model to be approximately 3.8 m* , where m* is the electron effective mass. The enhanced polaronic mass in PTB7 may limit the charge mobility, which, in turn, reduces the OPV solar-cell efficiency based on the PTB7-fullerene blend.

  9. Perylene-Diimide Based Donor-Acceptor-Donor Type Small-Molecule Acceptors for Solution-Processable Organic Solar Cells (United States)

    Ganesamoorthy, Ramasamy; Vijayaraghavan, Rajagopalan; Sakthivel, Pachagounder


    Development of nonfullerene acceptors plays an important role in the commercial availability of plastic solar cells. We report herein synthesis of bay-substituted donor-acceptor-donor (D-A-D)-type perylene diimide (PDI)-based small molecules (SM-1 to SM-4) by Suzuki coupling method and their use as acceptors in bulk heterojunction organic solar cells (BHJ-OSCs) with poly(3-hexylthiophene) (P3HT) polymer donor. We varied the number of electron-rich thiophene units and the solubilizing side chains and also evaluated the optical and electrochemical properties of the small molecules. The synthesized small molecules were confirmed by Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and high-resolution mass spectroscopy (HR-MS). The small molecules showed extensive and strong absorption in the ultraviolet-visible (UV-Vis) region up to 750 nm, with bandgap (E_{{g}}^{{opt}} ) reduced below energy levels of small molecules SM-1 to SM-4 were suitable for use as electron-accepting materials. The small molecules showed good thermal stability up to 300°C. BHJ-OSCs with SM-1 and P3HT polymer donor showed maximum power conversion efficiency (PCE) of 0.19% with V oc of 0.30 V, J sc of 1.72 mA cm-2, and fill factor (FF) of 37%. The PCE decreased with the number of thiophene units. The PCE of SM-2 was lower than that of SM-1. This difference in PCE can be explained by the higher aggregation tendency of the bithiophene compared with the thiophene unit. Introduction of the solubilizing group in the bay position increased the aggregation property, leading to much lower PCE than for the small molecules without solubilizing group.

  10. Beyond Donor-Acceptor (D-A) Approach: Structure-Optoelectronic Properties-Organic Photovoltaic Performance Correlation in New D-A1-D-A2Low-Bandgap Conjugated Polymers. (United States)

    Chochos, Christos L; Drakopoulou, Sofia; Katsouras, Athanasios; Squeo, Benedetta M; Sprau, Christian; Colsmann, Alexander; Gregoriou, Vasilis G; Cando, Alex-Palma; Allard, Sybille; Scherf, Ullrich; Gasparini, Nicola; Kazerouni, Negar; Ameri, Tayebeh; Brabec, Christoph J; Avgeropoulos, Apostolos


    Low-bandgap near-infrared polymers are usually synthesized using the common donor-acceptor (D-A) approach. However, recently polymer chemists are introducing more complex chemical concepts for better fine tuning of their optoelectronic properties. Usually these studies are limited to one or two polymer examples in each case study so far, though. In this study, the dependence of optoelectronic and macroscopic (device performance) properties in a series of six new D-A 1 -D-A 2 low bandgap semiconducting polymers is reported for the first time. Correlation between the chemical structure of single-component polymer films and their optoelectronic properties has been achieved in terms of absorption maxima, optical bandgap, ionization potential, and electron affinity. Preliminary organic photovoltaic results based on blends of the D-A 1 -D-A 2 polymers as the electron donor mixed with the fullerene derivative [6,6]-phenyl-C 71 -butyric acid methyl ester demonstrate power conversion efficiencies close to 4% with short-circuit current densities (J sc ) of around 11 mA cm -2 , high fill factors up to 0.70, and high open-circuit voltages (V oc s) of 0.70 V. All the devices are fabricated in an inverted architecture with the photoactive layer processed in air with doctor blade technique, showing the compatibility with roll-to-roll large-scale manufacturing processes. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Perylene-Diimide Based Donor-Acceptor-Donor Type Small-Molecule Acceptors for Solution-Processable Organic Solar Cells (United States)

    Ganesamoorthy, Ramasamy; Vijayaraghavan, Rajagopalan; Sakthivel, Pachagounder


    Development of nonfullerene acceptors plays an important role in the commercial availability of plastic solar cells. We report herein synthesis of bay-substituted donor-acceptor-donor (D-A-D)-type perylene diimide (PDI)-based small molecules (SM-1 to SM-4) by Suzuki coupling method and their use as acceptors in bulk heterojunction organic solar cells (BHJ-OSCs) with poly(3-hexylthiophene) (P3HT) polymer donor. We varied the number of electron-rich thiophene units and the solubilizing side chains and also evaluated the optical and electrochemical properties of the small molecules. The synthesized small molecules were confirmed by Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and high-resolution mass spectroscopy (HR-MS). The small molecules showed extensive and strong absorption in the ultraviolet-visible (UV-Vis) region up to 750 nm, with bandgap (E_{{g}}^{{opt}} ) reduced below polymer donor showed maximum power conversion efficiency (PCE) of 0.19% with V oc of 0.30 V, J sc of 1.72 mA cm-2, and fill factor (FF) of 37%. The PCE decreased with the number of thiophene units. The PCE of SM-2 was lower than that of SM-1. This difference in PCE can be explained by the higher aggregation tendency of the bithiophene compared with the thiophene unit. Introduction of the solubilizing group in the bay position increased the aggregation property, leading to much lower PCE than for the small molecules without solubilizing group.

  12. Comparison of fluctuating potentials and donor-acceptor pair transitions in a Cu-poor Cu2ZnSnS4 based solar cell (United States)

    Teixeira, J. P.; Sousa, R. A.; Sousa, M. G.; da Cunha, A. F.; Fernandes, P. A.; Salomé, P. M. P.; González, J. C.; Leitão, J. P.


    The structure of the electronic energy levels of a single phase Cu2ZnSnS4 film, as confirmed by Raman Scattering and x-ray diffraction, is investigated through a dependence on the excitation power of the photoluminescence (PL). The behavior of the observed asymmetric band, with a peak energy at ˜1.22 eV, is compared with two theoretical models: (i) fluctuating potentials and (ii) donor-acceptor pair transitions. It is shown that the radiative recombination channels in the Cu-poor film are strongly influenced by tail states in the bandgap as a consequence of a heavy doping and compensation levels. The contribution of the PL for the evaluation of secondary phases is also highlighted.

  13. Oligomeric Dithienopyrrole-Thienopyrrolodione (DTP-TPD) Donor-Acceptor Copolymer for Organic Photovoltaics: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Hammond, S. R.; Braunecker, W.; Garcia, A.; Larsen, R.; Owczarczyk, Z.; Olson, D.; Ginley, D.


    A new donor-acceptor copolymer system based upon a dithienopyrrole (DTP) donor moiety and a thienopyrrolodione (TPD) accepting moiety has been designed and synthesized for organic photovoltaic (OPV) applications. The TPD accepting moiety has recently gained significant attention in the OPV community and is being incorporated into a number of different polymer systems. In contrast, the DTP donor moiety has received only limited attention, likely due in part to synthetic difficulties relating to the monomer. In our hands, the bis(trimethyltin)-DTP monomer was indelibly contaminated with ~5% of the mono-destannylated DTP, which limited the Stille polymerization with the dibromo-TPD monomer (>99% pure) to produce material with Mn ~ 4130 g/mol (PDI = 1.10), corresponding to around eight repeat units. Despite this limitation, UV-visible absorption spectroscopy demonstrates strong absorption for this material with a band gap of ~1.6 eV. Cyclic voltammetry indicates a highest occupied molecular orbital (HOMO) energy level of -5.3 eV, which is much lower than calculations predicted. Initial bulk heterojunction OPV devices fabricated with the fullerene acceptor phenyl C61 butyric acid methyl ester (PCBM) exhibit Voc ~ 700 mV, which supports the deep HOMO value obtained from CV. These results suggest the promise of this copolymer system.

  14. Shedding Light on the Photoisomerization Pathway of Donor-Acceptor Stenhouse Adducts. (United States)

    Di Donato, Mariangela; Lerch, Michael M; Lapini, Andrea; Laurent, Adèle D; Iagatti, Alessandro; Bussotti, Laura; Ihrig, Svante P; Medved', Miroslav; Jacquemin, Denis; Szymański, Wiktor; Buma, Wybren Jan; Foggi, Paolo; Feringa, Ben L


    Donor-acceptor Stenhouse adducts (DASAs) are negative photochromes that hold great promise for a variety of applications. Key to optimizing their switching properties is a detailed understanding of the photoswitching mechanism, which, as yet, is absent. Here we characterize the actinic step of DASA-photoswitching and its key intermediate, which was studied using a combination of ultrafast visible and IR pump-probe spectroscopies and TD-DFT calculations. Comparison of the time-resolved IR spectra with DFT computations allowed to unambiguously identify the structure of the intermediate, confirming that light absorption induces a sequential reaction path in which a Z-E photoisomerization of C 2 -C 3 is followed by a rotation around C 3 -C 4 and a subsequent thermal cyclization step. First and second-generation DASAs share a common photoisomerization mechanism in chlorinated solvents with notable differences in kinetics and lifetimes of the excited states. The photogenerated intermediate of the second-generation DASA was photo-accumulated at low temperature and probed with time-resolved spectroscopy, demonstrating the photoreversibility of the isomerization process. Taken together, these results provide a detailed picture of the DASA isomerization pathway on a molecular level.

  15. Solution-processable functionalized graphene in donor/acceptor-type organic photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Zhiyong; He, Dawei; Wang, Yongsheng; Wu, Hongpeng; Wang, Jigang [Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China)


    An organic photovoltaic device based on an acceptor of solution-processable functionalized graphene (SPFGraphene) was designed. The devices were based on heterostructure polymer-graphene composite layers. The structural configuration of devices is ITO/PEDOT:PSS/P3HT:SPFGraphene/LiF/Al. Due to the functional groups of the graphene, a homogeneous blend of graphene-polymer composite could be obtained. In the graphene-polymer composite, the graphene acted as exciton dissociation sites and provided the transport pathway of LUMO-graphene-Al. Doping of graphene into P3HT resulted in appropriate energetic distance between HOMO and LUMO of the donor/acceptor for a high open circuit voltage and provided higher exciton dissociation volume mobility of carrier transport for a large short-circuit current density. The device containing only 10 wt% of graphene shows the best performance with a power conversion efficiency of 0.88%, an open-circuit voltage of 0.77 V, and a short-circuit current density of 3.72 mA/cm{sup 2}. (author)

  16. Coumarin-indole conjugate donor-acceptor system: Synthesis, photophysical properties, anion sensing ability, theoretical and biological activity studies of two coumarin-indole based push-pull dyes (United States)

    Aksungur, Tuğçe; Aydıner, Burcu; Seferoğlu, Nurgül; Özkütük, Müjgan; Arslan, Leyla; Reis, Yasemin; Açık, Leyla; Seferoğlu, Zeynel


    Two coumarin-indole conjugate fluorescent dyes having donor-acceptor-donor (D-A-D) (CI-1 and CI-2) were synthesized, and characterized using IR, 1H/13C NMR and HRMS. The absorption and emission properties of the dyes were determined in different solvents. The anion sensitivity and selectivity of the dyes were studied with some anions (CN-, F-, AcO-, Cl-, Br-, I-, HSO4- and H2PO4-) in DMSO, and their interaction mechanisms were evaluated by spectrophotometric and 1H NMR titration techniques. In addition, the molecular and electronic structures of CI-1, as well as the molecular complexes of CI-1, formed with the anions (F- and AcO-), were obtained theoretically and confirmed by DFT and TD-DFT calculations. CI-1 behaves as a colorimetric chemosensor for selective and sensitive detection of CN- in DMSO/H2O (9:1) over other competing anions such as F- and AcO-. However, only CN- interacts with chromophore CI-2 via Michael addition and the main absorption maxima shifts hypsochromically with an observed distinctive color change from orange to yellow. For using as a optic dye, the thermal stability properties of the dyes was determined by TGA (Thermal Gravimetric Analysis). Antimicrobial, antifungal and DNA-ligand interaction studies of the dyes were also examined. The dyes cause conformational changes on DNA and selectively bind to nucleotides of A/A and G/G.

  17. Contrasting performance of donor-acceptor copolymer pairs in ternary blend solar cells and two-acceptor copolymers in binary blend solar cells. (United States)

    Khlyabich, Petr P; Rudenko, Andrey E; Burkhart, Beate; Thompson, Barry C


    Here two contrasting approaches to polymer-fullerene solar cells are compared. In the first approach, two distinct semi-random donor-acceptor copolymers are blended with phenyl-C61-butyric acid methyl ester (PC61BM) to form ternary blend solar cells. The two poly(3-hexylthiophene)-based polymers contain either the acceptor thienopyrroledione (TPD) or diketopyrrolopyrrole (DPP). In the second approach, semi-random donor-acceptor copolymers containing both TPD and DPP acceptors in the same polymer backbone, termed two-acceptor polymers, are blended with PC61BM to give binary blend solar cells. The two approaches result in bulk heterojunction solar cells that have the same molecular active-layer components but differ in the manner in which these molecular components are mixed, either by physical mixing (ternary blend) or chemical "mixing" in the two-acceptor (binary blend) case. Optical properties and photon-to-electron conversion efficiencies of the binary and ternary blends were found to have similar features and were described as a linear combination of the individual components. At the same time, significant differences were observed in the open-circuit voltage (Voc) behaviors of binary and ternary blend solar cells. While in case of two-acceptor polymers, the Voc was found to be in the range of 0.495-0.552 V, ternary blend solar cells showed behavior inherent to organic alloy formation, displaying an intermediate, composition-dependent and tunable Voc in the range from 0.582 to 0.684 V, significantly exceeding the values achieved in the two-acceptor containing binary blend solar cells. Despite the differences between the physical and chemical mixing approaches, both pathways provided solar cells with similar power conversion efficiencies, highlighting the advantages of both pathways toward highly efficient organic solar cells.

  18. π-Conjugated Donor-Acceptor Systems as Metal-Free Sensitizers for Dye-Sensitized Solar Cell Applications

    Directory of Open Access Journals (Sweden)

    Zakeeruddin S. M.


    Full Text Available High extinction coefficients and easily tunable spectral properties of π- conjugated donor-acceptor dyes are of superior advantage for the design of new metalfree organic sensitizers for applications in dye-sensitized solar cells. Ultrafast transient absorption spectroscopy on the femtosecond and nanosecond time scales provided deep insights into the dependence of charge carrier dynamics in fully organic dye/TiO2 systems on i the donor-acceptor distance, ii the π-conjugation length, and iii the coupling to TiO2 by different anchoring groups. Importantly, the observed differences in charge transfer dynamics justify the variations of photovoltaic performances of the dyes as applied in solar cell devices. This leads to the conclusion that the photoconversion efficiencies strongly depend on a delicate interplay between the dyes’ building blocks, i.e. the donor, the π-conjugated spacer and the anchor/acceptor moieties, and may easily be tuned by molecular design.

  19. Triggering Gel Formation and Luminescence through Donor-Acceptor Interactions in a C3 -Symmetric Tris(pyrene) System. (United States)

    Lai, Thanh-Loan; Pop, Flavia; Melan, Caroline; Canevet, David; Sallé, Marc; Avarvari, Narcis


    Straightforward modulation of the gelation, absorption and luminescent properties of a tris(pyrene) organogelator containing a C3 -symmetric benzene-1,3,5-tricarboxamide central unit functionalized by three 3,3'-diamino-2,2'-bipyridine fragments is achieved through donor-acceptor interactions in the presence of tetracyanoquinodimethane. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. π-conjugated donor-acceptor porphyrin copolymers for organic photovoltaics (United States)

    Peng, Xiaobin; Huang, Yuying; Li, Lisheng; Cao, Yong


    Conjugated donor-acceptor (D-A) molecular structures play a very important role in the significant progress of organic photovotaics. However, the reports on conjugated D-A porphyrin polymers for organic solar cells are very limited. In this work, five conjugated D-A porphyrin copolymers PEZPEBTA(C12), PEZPEBT, PEZPEBTff, PEZPETPD(O), and PEZPETDPPT(O) were synthesized by Sonagashira coupling of a porphyrin donor unit with five typical acceptor units 2-dodecyl-2H-benzotriazole, benzo[1,2,5]thiadiazole, 5,6-difluoro-benzo[1,2,5]thiadiazole, 5-octyl-thieno[3,4-c]pyrrole-4,6-dione, and 3,6-bis-(thiophen-2-yl)-2,5-dioctyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione linked by ethynylene linkages, respectively. They possess excellent thermal stability with a decomposition temperature of around 400°C. All absorption spectra of the copolymers were significantly red shifted with enhanced Q bands at the near-infrared region both in solutions and in films due to the simultaneous introduction of ethynylene linkages and acceptor units, which make the polymer main chains coplanar and π-conjugated and enhance the intramolecular charge transfer. PEZPEBT and PEZPEBTff are electrochemically active in both the oxidation and reduction regions, while PEZPEBTA(C12), PEZPETPD(O), and PEZPETDPPT(O) show only oxidation peaks. Power conversion efficiencies of 0.12%, 0.41%, 0.26%, 0.19%, and 0.41% were achieved for the polymer solar cells based on PEZPEBTA(C12), PEZPEBT, PEZPEBTff, PEZPETPD(O), and PEZPETDPPT(O), respectively, under AM 1.5, 100 mW/cm2 with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) (1:2, w/w) as the active layer in the presence of 3% pyridine.

  1. Donor/Acceptor Molecular Orientation-Dependent Photovoltaic Performance in All-Polymer Solar Cells. (United States)

    Zhou, Ke; Zhang, Rui; Liu, Jiangang; Li, Mingguang; Yu, Xinhong; Xing, Rubo; Han, Yanchun


    The correlated donor/acceptor (D/A) molecular orientation plays a crucial role in solution-processed all-polymer solar cells in term of photovoltaic performance. For the conjugated polymers PTB7-th and P(NDI2OD-T2), the preferential molecular orientation of neat PTB7-th films kept face-on regardless of the properties of processing solvents. However, an increasing content of face-on molecular orientation in the neat P(NDI2OD-T2) films could be found by changing processing solvents from chloronaphthalene (CN) and o-dichlorobenzene (oDCB) to chlorobenzene (CB). Besides, the neat P(NDI2OD-T2) films also exhibited a transformation of preferential molecular orientation from face-on to edge-on when extending film drying time by casting in the same solution. Consequently, a distribution diagram of molecular orientation for P(NDI2OD-T2) films was depicted and the same trend could be observed for the PTB7-th/P(NDI2OD-T2) blend films. By manufacture of photovoltaic devices with blend films, the relationship between the correlated D/A molecular orientation and device performance was established. The short-circuit current (Jsc) of devices processed by CN, oDCB, and CB enhanced gradually from 1.24 to 8.86 mA/cm(2) with the correlated D/A molecular orientation changing from face-on/edge-on to face-on/face-on, which could be attributed to facile exciton dissociation at D/A interface with the same molecular orientation. Therefore, the power conversion efficiency (PCE) of devices processed by CN, oDCB, and CB improved from 0.53% to 3.52% ultimately.

  2. Blinking fluorescence of single donor-acceptor pairs: important role of "dark'' states in resonance energy transfer via singlet levels. (United States)

    Osad'ko, I S; Shchukina, A L


    The influence of triplet levels on Förster resonance energy transfer via singlet levels in donor-acceptor (D-A) pairs is studied. Four types of D-A pair are considered: (i) two-level donor and two-level acceptor, (ii) three-level donor and two-level acceptor, (iii) two-level donor and three-level acceptor, and (iv) three-level donor and three-level acceptor. If singlet-triplet transitions in a three-level acceptor molecule are ineffective, the energy transfer efficiency E=I_{A}/(I_{A}+I_{D}), where I_{D} and I_{A} are the average intensities of donor and acceptor fluorescence, can be described by the simple theoretical equation E(F)=FT_{D}/(1+FT_{D}). Here F is the rate of energy transfer, and T_{D} is the donor fluorescence lifetime. In accordance with the last equation, 100% of the donor electronic energy can be transferred to an acceptor molecule at FT_{D}≫1. However, if singlet-triplet transitions in a three-level acceptor molecule are effective, the energy transfer efficiency is described by another theoretical equation, E(F)=F[over ¯](F)T_{D}/[1+F[over ¯](F)T_{D}]. Here F[over ¯](F) is a function of F depending on singlet-triplet transitions in both donor and acceptor molecules. Expressions for the functions F[over ¯](F) are derived. In this case the energy transfer efficiency will be far from 100% even at FT_{D}≫1. The character of the intensity fluctuations of donor and acceptor fluorescence indicates which of the two equations for E(F) should be used to find the value of the rate F. Therefore, random time instants of photon emission in both donor and acceptor fluorescence are calculated by the Monte Carlo method for all four types of D-A pair. Theoretical expressions for start-stop correlators (waiting time distributions) in donor and acceptor fluorescence are derived. The probabilities w_{N}^{D}(t) and w_{N}^{A}(t) of finding N photons of donor and acceptor fluorescence in the time interval t are calculated for various values of the energy

  3. Graphene and Donor-Acceptor Molecules/Nanoparticle Composites for Advanced Electronics Technologies (United States)


    for the formation of methyl , methoxy and methane moieties from carbon dioxide on the nickel catalyst and also show that the methane formation via...MD) have been done to investigate the structure and energetics of single-stranded(ss) DNA assisted solubilisation of single-layer graphene in...walled carbon nanotubes (SWCNTs) and single-stranded DNA (ssDNA) of four different nucleobase sequences (i.e., ssdA14, ssdT14, ssdG14, and ssdC14

  4. Creation of Superheterojunction Polymers via Direct Polycondensation: Segregated and Bicontinuous Donor-Acceptor π-Columnar Arrays in Covalent Organic Frameworks for Long-Lived Charge Separation. (United States)

    Jin, Shangbin; Supur, Mustafa; Addicoat, Matthew; Furukawa, Ko; Chen, Long; Nakamura, Toshikazu; Fukuzumi, Shunichi; Irle, Stephan; Jiang, Donglin


    By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor-acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor π-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic π-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctions-a new type of heterojunction machinery, for photoinduced electron transfer and charge separation. We show that this polycondensation method is widely applicable to various metallophthalocyanines and diimides as demonstrated by the combination of copper, nickel, and zinc phthalocyanine donors with pyrommellitic diimide, naphthalene diimide, and perylene diimide acceptors. By using time-resolved transient absorption spectroscopy and electron spin resonance, we demonstrated that the COFs enable long-lived charge separation, whereas the metal species, the class of acceptors, and the local geometry between donor and acceptor units play roles in determining the photochemical dynamics. The results provide insights into photoelectric COFs and demonstrate their enormous potential for charge separation and photoenergy conversions.

  5. Photo-switchable Donor-Acceptor (D-A) Dyad Interfacial Self-Assembled Monolayers for Organic Photovoltaic Cells (United States)


    S) AND ADDRESS(ES) UNIVERSITY OF TEXAS AT EL PASO 500 UNIV ST ADMIN BLDG 209 EL PASO, TX 79968-0001 US 8.  PERFORMING ORGANIZATION      REPORT NUMBER...Number Contact phone number if there is a problem with the report 915-747-7573 Organization / Institution name Univ . of Texas - El Paso Grant/Contract...AFRL-AFOSR-VA-TR-2015-0396 (HBCU) Photo-switchable Donor-Acceptor for Organic Photovoltaic Cells Luis Echegoyen UNIVERSITY OF TEXAS AT EL PASO Final

  6. Ultrafast broadband laser spectroscopy reveals energy and charge transfer in novel donor-acceptor triads for photovoltaic applications

    Energy Technology Data Exchange (ETDEWEB)

    Roland, T; Ramirez, G Hernandez; Leonard, J; Mery, S; Haacke, S, E-mail: [Institut de Physique et Chimie des Materiaux de Strasbourg, Strasbourg University - CNRS UMR 7504, F-67034 Strasbourg (France)


    Triggered by the quest for new organic materials and micro-structures for photovoltaic applications, a novel class of donor-acceptor-donor (DAD) triads extended with siloxane chains has been synthesized in our labs. Because of the siloxane chains, the molecules self-organize into a smectic liquid crystal phase, resulting in a stacking of the DAD cores.We report here a preliminary study of the ultrafast dynamics of energy and charge transfer studied by femtosecond broadband transient absorption experiments on isolated triads in chloroform.

  7. Donor-acceptor conjugates-functionalized zinc phthalocyanine: Towards broad absorption and application in organic solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Fushun; Shi, Fan; Wang, Lifen; Su, Zhongmin [Department of Chemistry, Northeast Normal University, Changchun 130024 (China); Fu, Yingying; Xie, Zhiyuan [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Zhang, Xintong [Key Laboratory for UV-Emitting Materials and Technology of Ministry of Education, Northeast Normal University, Changchun 130024 (China)


    New zinc phthalocyanine (ZnPc-TDA), peripherally functionalized with donor-acceptor conjugates was synthesized, and its optical, thermal, electrochemical, and photovoltaic properties were studied. The black ZnPc-TDA exhibited both excellent solubility in common organic solvents, and broad absorption covering the range 300-900 nm. The photovoltaic devices with the configuration of ITO/PEDOT-PSS/ZnPc-TDA:PCBM/LiF/Al produced short circuit current densities of 2.26 mA/cm{sup 2}, the open circuit voltage of 0.68 V and power conversion efficiency of 0.4% under AM1.5G illumination. (author)

  8. Full-dimensional multilayer multiconfigurational time-dependent Hartree study of electron transfer dynamics in the anthracene/C60 complex

    Energy Technology Data Exchange (ETDEWEB)

    Xie, Yu; Zheng, Jie; Lan, Zhenggang, E-mail: [CAS Key Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101 (China); University of Chinese Academy of Sciences, Beijing 100049 (China)


    Electron transfer at the donor-acceptor heterojunctions plays a critical role in the photoinduced process during the solar energy conversion in organic photovoltaic materials. We theoretically investigate the electron transfer process in the anthracene/C60 donor-acceptor complex by using quantum dynamics calculations. The electron-transfer model Hamiltonian with full dimensionality was built by quantum-chemical calculations. The quantum dynamics calculations were performed using the multiconfigurational time-dependent Hartree (MCTDH) theory and multilayer (ML) MCTDH methods. The latter approach (ML-MCTDH) allows us to conduct the comprehensive study on the quantum evolution of the full-dimensional electron-transfer model including 4 electronic states and 246 vibrational degrees of freedom. Our quantum dynamics calculations exhibit the ultrafast anthracene → C60 charge transfer process because of the strong coupling between excitonic and charge transfer states. This work demonstrates that the ML-MCTDH is a very powerful method to treat the quantum evolution of complex systems.

  9. The impact of donor-acceptor phase separation on the charge carrier dynamics in pBTTT:PCBM photovoltaic blends. (United States)

    Gehrig, Dominik W; Howard, Ian A; Sweetnam, Sean; Burke, Timothy M; McGehee, Michael D; Laquai, Frédéric


    The effect of donor-acceptor phase separation, controlled by the donor-acceptor mixing ratio, on the charge generation and recombination dynamics in pBTTT-C14:PC70 BM bulk heterojunction photovoltaic blends is presented. Transient absorption (TA) spectroscopy spanning the dynamic range from pico- to microseconds in the visible and near-infrared spectral regions reveals that in a 1:1 blend exciton dissociation is ultrafast; however, charges cannot entirely escape their mutual Coulomb attraction and thus predominantly recombine geminately on a sub-ns timescale. In contrast, a polymer:fullerene mixing ratio of 1:4 facilitates the formation of spatially separated, that is free, charges and reduces substantially the fraction of geminate charge recombination, in turn leading to much more efficient photovoltaic devices. This illustrates that spatially extended donor or acceptor domains are required for the separation of charges on an ultrafast timescale (<100 fs), indicating that they are not only important for efficient charge transport and extraction, but also critically influence the initial stages of free charge carrier formation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Charge transport studies in donor-acceptor block copolymer PDPP-TNT and PC71BM based inverted organic photovoltaic devices processed in room conditions

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Shashi B.; Singh, Samarendra P., E-mail: [Department of Physics, Shiv Nadar University, Gautam Buddha Nagar, Uttar Pradesh, India-201307 (India); Sonar, Prashant [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Australia-4001 (Australia)


    Diketopyrrolopyrole-naphthalene polymer (PDPP-TNT), a donor-acceptor co-polymer, has shown versatile behavior demonstrating high performances in organic field-effect transistors (OFETs) and organic photovoltaic (OPV) devices. In this paper we report investigation of charge carrier dynamics in PDPP-TNT, and [6,6]-phenyl C{sub 71} butyric acid methyl ester (PC71BM) bulk-heterojunction based inverted OPV devices using current density-voltage (J-V) characteristics, space charge limited current (SCLC) measurements, capacitance-voltage (C-V) characteristics, and impedance spectroscopy (IS). OPV devices in inverted architecture, ITO/ZnO/PDPP-TNT:PC71BM/MoO{sub 3}/Ag, are processed and characterized at room conditions. The power conversion efficiency (PCE) of these devices are measured ∼3.8%, with reasonably good fill-factor 54.6%. The analysis of impedance spectra exhibits electron’s mobility ∼2 × 10{sup −3} cm{sup 2}V{sup −1}s{sup −1}, and lifetime in the range of 0.03-0.23 ms. SCLC measurements give hole mobility of 1.12 × 10{sup −5} cm{sup 2}V{sup −1}s{sup −1}, and electron mobility of 8.7 × 10{sup −4} cm{sup 2}V{sup −1}s{sup −1}.

  11. Studies on TMPD:TCNB; a Donor-Acceptor with Room Temperature Paramagnetism and n-π Interactionâ€

    Directory of Open Access Journals (Sweden)

    J. L. Yarger


    Full Text Available A donor-acceptor compound based on N,N,N′,N′-tetramethyl-p-phenylene-diamine and 1,2,4,5-tetracyanobenzene (TMPD:TCNB has been synthesized. The crystalstructure of the black 1:1 complex formed between TMPD and TCNB has beendetermined by single crystal X-ray diffraction at room temperature. The compoundcrystallizes in the triclinic space group P-1 with cell dimensions: a = 7.4986(15 å, b =7.6772(11 å, c = 8.0764(15 å, α = 78.822(12°, β = 83.3779(19°, γ = 86.289(17°.TMPD and TCNB molecules are stacked alternately in infinite columns along the a-axis.The structure does not seem to show the usual π-π interaction between the two aromaticrings, but indicates an n-π interaction localized between the nitrogen atoms of the donorand the cyano groups of the acceptor.

  12. Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor-acceptor demixing. (United States)

    Li, Ning; Perea, José Darío; Kassar, Thaer; Richter, Moses; Heumueller, Thomas; Matt, Gebhard J; Hou, Yi; Güldal, Nusret S; Chen, Haiwei; Chen, Shi; Langner, Stefan; Berlinghof, Marvin; Unruh, Tobias; Brabec, Christoph J


    The performance of organic solar cells is determined by the delicate, meticulously optimized bulk-heterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions. Here we demonstrate an abnormal strong burn-in degradation in highly efficient polymer solar cells caused by spinodal demixing of the donor and acceptor phases, which dramatically reduces charge generation and can be attributed to the inherently low miscibility of both materials. Even though the microstructure can be kinetically tuned for achieving high-performance, the inherently low miscibility of donor and acceptor leads to spontaneous phase separation in the solid state, even at room temperature and in the dark. A theoretical calculation of the molecular parameters and construction of the spinodal phase diagrams highlight molecular incompatibilities between the donor and acceptor as a dominant mechanism for burn-in degradation, which is to date the major short-time loss reducing the performance and stability of organic solar cells.

  13. Tailored donor-acceptor polymers with an A-D1-A-D2 structure: controlling intermolecular interactions to enable enhanced polymer photovoltaic devices. (United States)

    Qin, Tianshi; Zajaczkowski, Wojciech; Pisula, Wojciech; Baumgarten, Martin; Chen, Ming; Gao, Mei; Wilson, Gerry; Easton, Christopher D; Müllen, Klaus; Watkins, Scott E


    Extensive efforts have been made to develop novel conjugated polymers that give improved performance in organic photovoltaic devices. The use of polymers based on alternating electron-donating and electron-accepting units not only allows the frontier molecular orbitals to be tuned to maximize the open-circuit voltage of the devices but also controls the optical band gap to increase the number of photons absorbed and thus modifies the other critical device parameter-the short circuit current. In fact, varying the nonchromophoric components of a polymer is often secondary to the efforts to adjust the intermolecular aggregates and improve the charge-carrier mobility. Here, we introduce an approach to polymer synthesis that facilitates simultaneous control over both the structural and electronic properties of the polymers. Through the use of a tailored multicomponent acceptor-donor-acceptor (A-D-A) intermediate, polymers with the unique structure A-D1-A-D2 can be prepared. This approach enables variations in the donor fragment substituents such that control over both the polymer regiochemistry and solubility is possible. This control results in improved intermolecular π-stacking interactions and therefore enhanced charge-carrier mobility. Solar cells using the A-D1-A-D2 structural polymer show short-circuit current densities that are twice that of the simple, random analogue while still maintaining an identical open-circuit voltage. The key finding of this work is that polymers with an A-D1-A-D2 structure offer significant performance benefits over both regioregular and random A-D polymers. The chemical synthesis approach that enables the preparation of A-D1-A-D2 polymers therefore represents a promising new route to materials for high-efficiency organic photovoltaic devices.

  14. Functionalized isothianaphthene monomers that promote quinoidal character in donor-acceptor copolymers for organic photovoltaics

    KAUST Repository

    Douglas, Jessica D.


    A series of low band gap isothianaphthene-based (ITN) polymers with various electron-withdrawing substituents and intrinsic quinoidal character were synthesized, characterized, and tested in organic photovoltaic (OPV) devices. The three investigated ITN cores contained either ester, imide, or nitrile functionalities and were each synthesized in only four linear steps. The relative electron-withdrawing strength of the three substituents on the ITN moiety was evaluated and correlated to the optical and electronic properties of ITN-based copolymers. The ester- and imide-containing p-type polymers reached device efficiencies as high as 3% in bulk heterojunction blends with phenyl C 61-butyric acid methyl ester (PC 61BM), while the significantly electron-deficient nitrile-functionalized polymer behaved as an n-type material with an efficiency of 0.3% in bilayer devices with poly(3-(4-n-octyl)phenylthiophene) (POPT). © 2012 American Chemical Society.

  15. Self-Assembled Core-Shell CdTe/Poly(3-hexylthiophene) Nanoensembles as Novel Donor-Acceptor Light-Harvesting Systems. (United States)

    Istif, Emin; Kagkoura, Antonia; Hernandez-Ferrer, Javier; Stergiou, Anastasios; Skaltsas, Theodosis; Arenal, Raul; Benito, Ana M; Maser, Wolfgang K; Tagmatarchis, Nikos


    The self-assembly of novel core-shell nanoensembles consisting of regioregular poly(3-hexylthiophene) nanoparticles (P3HT NPs ) of 100 nm as core and semiconducting CdTe quantum dots (CdTe QDs ) as shell with a thickness of a few tens of nanometers was accomplished by employing a reprecipitation approach. The structure, morphology, and composition of CdTe QDs /P3HT NPs nanoensembles were confirmed by high-resolution scanning transmission microscopy and dynamic light-scattering studies. Intimate interface contact between the CdTe QDs shell and the P3HT NPs core leads to the stabilization of the CdTe QDs /P3HT NPs nanoensemble as probed by the steady-state absorption spectroscopy. Effective quenching of the characteristic photoluminescence of CdTe QDs at 555 nm, accompanied by simultaneous increase in emission of P3HT NPs at 660 and 720 nm, reveals photoinduced charge-transfer processes. Probing the redox properties of films of CdTe QDs /P3HT NPs further proves the formation of a stabilized core-shell system in the solid state. Photoelectrochemical assays on CdTe QDs /P3HT NPs films show a reversible on-off photoresponse at a bias voltage of +0.8 V with a 3 times increased photocurrent compared to CdTe QDs . The improved charge separation is directly related to the unique core-shell configuration, in which the outer CdTe QDs shell forces the P3HT NPs core to effectively act as electron acceptor. The creation of novel donor-acceptor core-shell hybrid materials via self-assembly is transferable to other types of conjugated polymers and semiconducting nanoparticles. This work, therefore, opens new pathways for the design of improved optoelectronic devices.

  16. Substituent effect on the electron acceptor property of 1,4-benzoquinone towards the formation of molecular complex with sulfamethoxazole (United States)

    Ganesh, K.; Satheshkumar, A.; Balraj, C.; Elango, K. P.


    UV-Vis, 1H NMR, FT-IR, LC-MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of sulfamethoxazole with varying number of methoxy/chloro substituted 1,4-benzoquinones (MQ1-4) and to characterize the reaction products. The interactions of MQ1-4 with sulfamethoxazole (SULF) were found to proceed through the formation of a donor-acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies showed that the interaction between the donor and the acceptors are spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The results of the correlation of experimentally measured binding constants with electrochemical data and ab initio DFT calculations supported these observations.

  17. Synthesis of Donor-Acceptor Conjugated Polymers by "CLICK" Polymerization for OPV applications

    DEFF Research Database (Denmark)

    Brandt, Rasmus Guldbæk; Yu, Donghong

    The intent of this study was to utilize the Copper(I)-catalyzed Azide Alkyne Cycloaddition (CuAAC) as a polymerization technique (“Click” Polymerization) for synthesizing novel π-conjugated low band gap polymers for organic photovoltaic applications (OPV). The chosen approach was to synthesize...... an alternating electron donating (donor, D) and electron withdrawing (acceptor, A) co-polymer. The chosen monomers were well known units, and the novelty lies in using the monomer units with the click methodology. An insoluble alternating copolymer consisting of 2,7-diazido-9,9-dioctyl-9Hflourene and 1...

  18. Photoinduced charge-transfer dynamics of sequentially aligned donor-acceptor systems in an ionic liquid. (United States)

    Muramatsu, Masayasu; Katayama, Tetsuro; Ito, Syoji; Nagasawa, Yutaka; Matsuo, Daisuke; Suzuma, Yoshinori; Peng, Lifen; Orita, Akihiro; Otera, Junzo; Miyasaka, Hiroshi


    Photoinduced charge separation processes of linear phenyleneethynylene derivatives (PEN) with different sequences of electron-withdrawing perfluorophenyl groups (A) and electron-donating phenyl groups (D) were investigated in an ionic liquid (IL), BmimTFSI, by picosecond time-resolved fluorescence (TRF) and transient absorption (TA) spectroscopies. Very rapid photoinduced charge separation within 10 ps in AADD was followed by the stabilization of the charge-transfer (CT) state by the solvation, while the excited states in ADAD and ADDA were ascribable to the locally excited (LE) state. Equilibrium between the LE and CT states was established for DAAD with time constants of forward and backward processes much faster than the solvation time. The relative population of the CT state increases with time owing to the dynamic stabilization of the CT state by the solvation. The elementary charge separation process, the increase in the CT population, and their relation to the solvation time were discussed.

  19. Large Hyperpolarizabilities at Telecommunication-Relevant Wavelengths in Donor-Acceptor-Donor Nonlinear Optical Chromophores. (United States)

    Nayak, Animesh; Park, Jaehong; De Mey, Kurt; Hu, Xiangqian; Duncan, Timothy V; Beratan, David N; Clays, Koen; Therien, Michael J


    Octopolar D2-symmetric chromophores, based on the MPZnM supermolecular motif in which (porphinato)zinc(II) (PZn) and ruthenium(II) polypyridyl (M) structural units are connected via ethyne linkages, were synthesized. These structures take advantage of electron-rich meso-arylporphyrin or electron-poor meso-(perfluoroalkyl)porphyrin macrocycles, unsubstituted terpyridyl and 4'-pyrrolidinyl-2,2';6',2″-terpyridyl ligands, and modulation of metal(II) polypyridyl-to-(porphinato)zinc connectivity, to probe how electronic and geometric factors impact the measured hyperpolarizability. Transient absorption spectra obtained at early time delays (tdelay strategy to realize octopolar NLO chromophores exhibiting large βHRS values at telecom-relevant wavelengths. Generalized Thomas-Kuhn sum (TKS) rules were utilized to compute the effective excited-state-to-excited-state transition dipole moments from experimental linear-absorption spectra; these data were then utilized to compute hyperpolarizabilities as a function of frequency, that include two- and three-state contributions for both β zzz and β xzx tensor components to the RuPZnRu hyperpolarizability spectrum. This analysis predicts that the β zzz and β xzx tensor contributions to the RuPZnRu hyperpolarizability spectrum maximize near 1550 nm, in agreement with experimental data. The TKS analysis suggests that relative to analogous dipolar chromophores, octopolar supermolecules will be likely characterized by more intricate dependences of the measured hyperpolarizability upon irradiation wavelength due to the interactions among multiple different β tensor components.

  20. Materials for Fluorescence Resonance Energy Transfer Analysis: Beyond Traditional Donor-Acceptor Combinations (United States)


    coli DEAD- Box RNA helicase DbpAwith fluorescent nucleotide analogues as acceptor.[112] A Trp located within the core of a reductase protein...relative expression level.[14,20,21] The green fluorescent protein (GFP; Figure 9) derived from the jellyfish Aequorea victoria is the prototypical...derived from jellyfish , is a Ca2+-sensitive bioluminescent photoprotein consisting of the luciferase apoaequorin complexed to its coelenterazine

  1. Ultrasmall magnetic field-effect and sign reversal in transistors based on donor/acceptor systems

    Directory of Open Access Journals (Sweden)

    Thomas Reichert


    Full Text Available We present magnetoresistive organic field-effect transistors featuring ultrasmall magnetic field-effects as well as a sign reversal. The employed material systems are coevaporated thin films with different compositions consisting of the electron donor 2,2',7,7'-tetrakis-(N,N-di-p-methylphenylamino-9,9'-spirobifluorene (Spiro-TTB and the electron acceptor 1,4,5,8,9,12-hexaazatriphenylene hexacarbonitrile (HAT-CN. Intermolecular charge transfer between Spiro-TTB and HAT-CN results in a high intrinsic charge carrier density in the coevaporated films. This enhances the probability of bipolaron formation, which is the process responsible for magnetoresistance effects in our system. Thereby even ultrasmall magnetic fields as low as 0.7 mT can influence the resistance of the charge transport channel. Moreover, the magnetoresistance is drastically influenced by the drain voltage, resulting in a sign reversal. An average B0 value of ≈2.1 mT is obtained for all mixing compositions, indicating that only one specific quasiparticle is responsible for the magnetoresistance effects. All magnetoresistance effects can be thoroughly clarified within the framework of the bipolaron model.

  2. Single molecule-level study of donor-acceptor interactions and nanoscale environment in blends (United States)

    Quist, Nicole; Grollman, Rebecca; Rath, Jeremy; Robertson, Alex; Haley, Michael; Anthony, John; Ostroverkhova, Oksana


    Organic semiconductors have attracted considerable attention due to their applications in low-cost (opto)electronic devices. The most successful organic materials for applications that rely on charge carrier generation, such as solar cells, utilize blends of several types of molecules. In blends, the local environment strongly influences exciton and charge carrier dynamics. However, relationship between nanoscale features and photophysics is difficult to establish due to the lack of necessary spatial resolution. We use functionalized fluorinated pentacene (Pn) molecule as single molecule probes of intermolecular interactions and of the nanoscale environment in blends containing donor and acceptor molecules. Single Pn donor (D) molecules were imaged in PMMA in the presence of acceptor (A) molecules using wide-field fluorescence microscopy. Two sample configurations were realized: (i) a fixed concentration of Pn donor molecules, with increasing concentration of acceptor molecules (functionalized indenflouorene or PCBM) and (ii) a fixed concentration of acceptor molecules with an increased concentration of the Pn donor. The D-A energy transfer and changes in the donor emission due to those in the acceptor- modified polymer morphology were quantified. The increase in the acceptor concentration was accompanied by enhanced photobleaching and blinking of the Pn donor molecules. To better understand the underlying physics of these processes, we modeled photoexcited electron dynamics using Monte Carlo simulations. The simulated blinking dynamics were then compared to our experimental data, and the changes in the transition rates were related to the changes in the nanoscale environment. Our study provides insight into evolution of nanoscale environment during the formation of bulk heterojunctions.

  3. Steric ploy for alternating donor-acceptor co-assembly and cooperative supramolecular polymerization. (United States)

    Chakraborty, Saptarshi; Kar, Haridas; Sikder, Amrita; Ghosh, Suhrit


    The presence of a bulky peripheral wedge destabilizes the homo-assembly of an amide functionalized acceptor (A) monomer and thereby enables the formation of an alternating supramolecular copolymer with an amide appended donor (D) monomer via the synergistic effect of H-bonding and the charge-transfer (CT) interaction with a remarkably high Ka of 31 000 M(-1). In sharp contrast, H-bonding driven homo-polymers of A and D are formed by just replacing the bulky chains of the A monomer with linear hydrocarbons. By taking advantage of the clear difference in the critical temperature for the onset of the AA or DD homo-assemblies and DA co-assembly (TDA ≫ TAA or TDD), the supramolecular polymerization pathway of the NDI-monomer could be fully diverted from isodesmic to cooperative in the presence of a small amount of DAN which helped the in situ production of nucleating sites involving the D-A CT-complex at a relatively higher temperature and the subsequent chain growth at TAA following the nucleation-elongation model.

  4. Synthesis and properties of a decacyclene monoimide and a naphthalimide derivative as a three-dimensional acceptor-donor-acceptor system. (United States)

    Kawase, Takeshi; Yamamoto, Yuma; Yoshida, Miu; Morii, Takuya; Nishida, Jun-Ichi; Kitamura, Chitoshi


    A method, which employs Diels-Alder (DA) cycloadditions of diacenaphtheno[1,2-b;1',2'-d]thiophenes (DAT) with N-alkylacenaphthylene-5,6-dicarboximides (AI), was developed to synthesize decacyclene monoimides (DCMI). The reactions generate the corresponding 1:2 adducts (BAIAs) as major products together with 1:1 adducts (DCMIs). The molecular structure of BAIAb (N-octyl derivative) was unambiguously assigned as the bis-adduct having an endo,endo spatial disposition of the two acenaphthylene-5,6-dicarboximide moieties by using X-ray crystallographic analysis. Relative to that of decacyclene triimide (DCTIa, N-2-ethylhexyl derivative), the analogous N-2-ethylhexyl-substituted mono-adduct DCMIa exhibits a bathochromic shift in its absorption spectrum despite possessing a less delocalized π-electron system. DCMIa does not fluoresce in various organic solvents, while DCTIa emits yellow fluorescence in CH2Cl2 with a low quantum yield (SN). Moreover, DCMIa in CDCl3 displays concentration-dependent 1H-NMR behavior, suggesting that it self-aggregates with an (association constant (Ka) of 193 ± 50 M-1 at 20 °C. Despite the presence of four bulky t-butyl groups in DCMIa, its Ka value for aggregate formation is comparable to that of DCTIa (495 ± 42 M-1), which does not contain t-butyl substituents. Spectroscopic studies with the bis-adduct BAIAa (N-2-ethylhexyl derivative) show that it displays remarkable solvatofluorochromism corresponding to an emission maximum shift (ΔλEM) of 100 nm. The results of density functional theory (DFT) calculations on BAIAc (N-methyl derivative) demonstrate that a considerable spatial separation exists between the HOMO and LUMO coefficient distributions, indicating that the ground-to-excited state transition of the novel three-dimensional acceptor-donor-acceptor system BAIAa should have intramolecular charge transfer (ICT) character. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Ultrafast Photoinduced Charge Separation Leading to High-Energy Radical Ion-Pairs in Directly Linked Corrole-C60 and Triphenylamine-Corrole-C60 Donor-Acceptor Conjugates. (United States)

    Sudhakar, Kolanu; Gokulnath, Sabapathi; Giribabu, Lingamallu; Lim, Gary N; Trâm, Tạ; D'Souza, Francis


    Closely positioned donor-acceptor pairs facilitate electron- and energy-transfer events, relevant to light energy conversion. Here, a triad system TPACor-C60 , possessing a free-base corrole as central unit that linked the energy donor triphenylamine (TPA) at the meso position and an electron acceptor fullerene (C60) at the β-pyrrole position was newly synthesized, as were the component dyads TPA-Cor and Cor-C60. Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady-state fluorescence studies showed efficient energy transfer from (1) TPA* to the corrole and subsequent electron transfer from (1) corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron-transfer products, the corrole radical cation (Cor(⋅+) in Cor-C60 and TPA-Cor(⋅+) in TPACor-C60) and fullerene radical anion (C60(⋅-)), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, kCS , was found to be about 10(11)  s(-1), suggesting the occurrence of an ultrafast charge-separation process. Interestingly, although an order of magnitude slower than kCS , the rate of charge recombination, kCR , was also found to be rapid (kCR ≈10(10)  s(-1)), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge-separated species relaxed directly to the ground state in polar solvents while in toluene, formation of (3) corrole* was observed, thus implying that the energy of the charge-separated state in a nonpolar solvent is higher than the energy of (3) corrole* being about 1.52 eV. That is, ultrafast formation of a high-energy charge-separated state in toluene has been achieved in these closely spaced corrole

  6. Impact of electron delocalization on the nature of the charge-transfer states in model pentacene/C60 Interfaces: A density functional theory study

    KAUST Repository

    Yang, Bing


    Electronic delocalization effects have been proposed to play a key role in photocurrent generation in organic photovoltaic devices. Here, we study the role of charge delocalization on the nature of the charge-transfer (CT) states in the case of model complexes consisting of several pentacene molecules and one fullerene (C60) molecule, which are representative of donor/acceptor heterojunctions. The energies of the CT states are examined by means of time-dependent density functional theory (TD-DFT) using the long-range-corrected functional, ωB97X, with an optimized range-separation parameter, ω. We provide a general description of how the nature of the CT states is impacted by molecular packing (i.e., interfacial donor/acceptor orientations), system size, and intermolecular interactions, features of importance in the understanding of the charge-separation mechanism.

  7. A High-Energy Charge-Separated State of 1.70 eV from a High-Potential Donor-Acceptor Dyad: A Catalyst for Energy-Demanding Photochemical Reactions. (United States)

    Lim, Gary N; Obondi, Christopher O; D'Souza, Francis


    A high potential donor-acceptor dyad composed of zinc porphyrin bearing three meso-pentafluorophenyl substituents covalently linked to C60 , as a novel dyad capable of generating charge-separated states of high energy (potential) has been developed. The calculated energy of the charge-separated state was found to be 1.70 eV, the highest reported for a covalently linked porphyrin-fullerene dyad. Intramolecular photoinduced electron transfer leading to charge-separated states of appreciable lifetimes in polar and nonpolar solvents has been established from studies involving femto- to nanosecond transient absorption techniques. The high energy stored in the form of charge-separated states along with its persistence of about 50-60 ns makes this dyad a potential electron-transporting catalyst to carry out energy-demanding photochemical reactions. This type of high-energy harvesting dyad is expected to open new research in the areas of artificial photosynthesis especially producing energy (potential) demanding light-to-fuel products. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex (United States)

    Haverkate, Lucas A.; Zbiri, Mohamed; Johnson, Mark R.; Carter, Elizabeth; Kotlewski, Arek; Picken, S.; Mulder, Fokko M.; Kearley, Gordon J.


    Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10-2 electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

  9. Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

    Energy Technology Data Exchange (ETDEWEB)

    Haverkate, Lucas A.; Mulder, Fokko M. [Reactor Institute Delft, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Zbiri, Mohamed, E-mail:; Johnson, Mark R. [Institut Laue Langevin, 38042 Grenoble Cedex 9 (France); Carter, Elizabeth [Vibrational Spectroscopy Facility, School of Chemistry, The University of Sydney, NSW 2008 (Australia); Kotlewski, Arek; Picken, S. [ChemE-NSM, Faculty of Chemistry, Delft University of Technology, 2628BL/136 Delft (Netherlands); Kearley, Gordon J. [Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 (Australia)


    Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10{sup −2} electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

  10. Organocatalytically Generated Donor-Acceptor Cyclopropanes in Domino Reactions. One-Step Enantioselective Synthesis of Pyrrolo[1,2-a]quinolines. (United States)

    Sanchez-Diez, Eduardo; Vesga, Diana L; Reyes, Efraim; Uria, Uxue; Carrillo, Luisa; Vicario, Jose L


    An easy and straightforward procedure has been developed for the synthesis of highly enantioenriched pyrrolo[1,2-a]quinolines through a one-pot process that comprises a domino cyclopropane ring opening/aza-Michael/aldol reaction followed by acid-promoted lactamization. The key feature of the synthetic approach relies on the ability of conveniently functionalized cyclopropaneacetaldehydes to undergo organocatalytic activation by a chiral secondary amine that enables the catalytic generation of a donor-acceptor cyclopropane. This intermediate has the potential to undergo a ring opening that generates an electrophilic α,β-unsaturated iminium ion that subsequently reacts through the already mentioned domino sequence and in which stereochemical information is very efficiently transferred from the amine catalyst to the final products. Moreover, one of the alkoxycarbonyl moieties can be easily removed by standard hydrolysis/decarboxylation, providing access to the target adducts as single stereoisomers.

  11. G-Tetraplex-Induced FRET within Telomeric Repeat Sequences Using (Py) A-(Per) A as Energy Donor-Acceptor Pair. (United States)

    Kundu, Rajen


    G-tetraplex induced fluorescence resonance energy transfer (FRET) within telomeric repeat sequences has been studied using a nucleoside-tethered FRET pair embedded in the human telomeric G-quadruplex forming sequence (5'-A GGG TT(Py) A GGG TT(Per) A GGG TTA GGG-3', Py=pyrene, Per=perylene). Conformational change from a single strand to an anti-parallel G-quadruplex leads to FRET from energy donor ((Py) A) to acceptor ((Per) A). The distance between the FRET donor/acceptor partners was controlled by changing the number of G-quartet spacer units. The FRET efficiency decreases with increase in G-quartet units. Overall findings indicate that this could be further used for the development of FRET-based sensing and measurement techniques. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Electrochemical proton-coupled electron transfer of an osmium aquo complex: theoretical analysis of asymmetric tafel plots and transfer coefficients. (United States)

    Ludlow, Michelle K; Soudackov, Alexander V; Hammes-Schiffer, Sharon


    Electrochemical proton-coupled electron transfer of an osmium aquo complex attached to a self-assembled monolayer on a gold electrode is studied with a recently developed theoretical formulation. The calculated hydrogen/deuterium kinetic isotope effect for the standard rate constant, the cathodic transfer coefficient at zero overpotential, and the Tafel plot are in excellent agreement with experimental data. The input quantities to the heterogeneous rate constant expressions were calculated with density functional theory in conjunction with dielectric continuum models, and no parameters were fit to experimental data. The theoretical calculations indicate that the asymmetry of the Tafel plot and the deviation of the transfer coefficient at zero overpotential from the standard value of one-half arise from the change in the equilibrium proton donor-acceptor distance upon electron transfer. The direction of the asymmetry and deviation from one-half is determined by the sign of this distance change, and the magnitude of these effects is determined by the magnitude of this distance change, as well as the reorganization energy and the distance dependence of the overlap between the initial and final proton vibrational wave functions. This theory provides experimentally testable predictions for the impact of specific system properties on the qualitative behavior of the Tafel plots.

  13. Self-assembly of individually addressable complexes of C60 and phthalocyanines on a metal surface: Structural and electronic investigations

    Energy Technology Data Exchange (ETDEWEB)

    Samuely, Tomas [University of Basel (Switzerland); Liu, Shi-Xia; Haas, Marco; Decurtins, Silvio [University of Bern (Switzerland); Jung, Thomas [Paul-Scherrer-Institute (Switzerland); Stoehr, Meike [University of Groningen (Netherlands)


    A complex phase behavior was found for a specific phthalocyanine (Pc) derivative adsorbed on either Au(111) or Ag(111). The Pc molecule is symmetrically substituted with eight peripheral di-(tert-butyl)phenoxy (DTPO) groups. The pronounced ability of the DTPO groups to rotate, allows the molecule to adopt different conformations and hence to arrange itself in different ordered patterns. In particular, when all DTPO substituents are arranged above the plane of the Pc core (a bowl-like structure is formed), the interaction of the Pc core with the metal substrate is enabled. Moreover, for such an assembly the hosting properties for the adsorption of C{sub 60} were investigated. The C{sub 60} molecules adsorb at two clearly distinguishable positions on the predeposited Pc layer: they are in contact either with the metal substrate in between two adjacent Pc molecules or with the Pc core. For the latter case, the C{sub 60} is located directly above the pi-conjugated Pc core. Hence, the presented system combines the three following features: (i) the direct electronic interaction between donor and acceptor moieties, (ii) the formation by self-assembly, and (iii) thermal stability. Thereby, the direct investigation of a single donor-acceptor complex is enabled.

  14. Unusual low-energy near-infrared bands for ferrocenyl-naphthalimide donor-acceptor dyads with aromatic spacer groups

    DEFF Research Database (Denmark)

    Tagg, Tei; Kjærgaard, Henrik Grum; Lane, Joseph R.


    , very low energy near-IR (NIR) transitions in the electronic spectra of the oxidized species Fc+-S-A. Subsequent optically transparent thin layer electrolysis (OTTLE) spectroscopy experiments in the spectral range 1500-3200 nm reveal that, in each case, very low energy NIR bands are indeed...

  15. Donor/Acceptor-Stabilized 1-Silaketene: Reversible [2+2] Cycloaddition with Pyridine and Evolution by an Olefin Metathesis Reaction. (United States)

    Reyes, Morelia Lopez; Troadec, Thibault; Rodriguez, Ricardo; Baceiredo, Antoine; Saffon-Merceron, Nathalie; Branchadell, Vicenç; Kato, Tsuyoshi


    The reaction of silacyclopropylidene 1 with benzaldehyde generates a 1-silaketene complex 2 by a formal atomic silicon insertion into the C=O bond of the aldehyde. The highly reactive 1-silaketene 2 undergoes a reversible [2+2] cycloaddition with pyridine to give sila-β-lactam 3. Of particular interest, in the presence of 4-dimethylaminopyridine (DMAP), 1-silaketene complex 2 evolves through an intramolecular olefin metathesis reaction, generating a new 1-silaketene complex 8 and cis-stilbene. Theoretical studies suggest that the reaction proceeds through the formation of a transient silacyclobutanone, a four-membered-ring intermediate, similar to that proposed by Chauvin and co-workers for the transition-metal-based olefin metathesis. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Multidimensional treatment of stochastic solvent dynamics in photoinduced proton-coupled electron transfer processes: sequential, concerted, and complex branching mechanisms. (United States)

    Soudackov, Alexander V; Hazra, Anirban; Hammes-Schiffer, Sharon


    A theoretical approach for the multidimensional treatment of photoinduced proton-coupled electron transfer (PCET) processes in solution is presented. This methodology is based on the multistate continuum theory with an arbitrary number of diabatic electronic states representing the relevant charge distributions in a general PCET system. The active electrons and transferring proton(s) are treated quantum mechanically, and the electron-proton vibronic free energy surfaces are represented as functions of multiple scalar solvent coordinates corresponding to the single electron and proton transfer reactions involved in the PCET process. A dynamical formulation of the dielectric continuum theory is used to derive a set of coupled generalized Langevin equations of motion describing the time evolution of these collective solvent coordinates. The parameters in the Langevin equations depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties. The dynamics of selected intramolecular nuclear coordinates, such as the proton donor-acceptor distance or a torsional angle within the PCET complex, may also be included in this formulation. A surface hopping method in conjunction with the Langevin equations of motion is used to simulate the nonadiabatic dynamics on the multidimensional electron-proton vibronic free energy surfaces following photoexcitation. This theoretical treatment enables the description of both sequential and concerted mechanisms, as well as more complex processes involving a combination of these mechanisms. The application of this methodology to a series of model systems corresponding to collinear and orthogonal PCET illustrates fundamental aspects of these different mechanisms and elucidates the significance of proton vibrational relaxation and nonequilibrium solvent dynamics. © 2011 American Institute of Physics

  17. A comparison of donor-acceptor pairs for genetically encoded FRET sensors: application to the Epac cAMP sensor as an example.

    Directory of Open Access Journals (Sweden)

    Gerard N M van der Krogt

    Full Text Available We recently reported on CFP-Epac-YFP, an Epac-based single polypeptide FRET reporter to resolve cAMP levels in living cells. In this study, we compared and optimized the fluorescent protein donor/acceptor pairs for use in biosensors such as CFP-Epac-YFP. Our strategy was to prepare a wide range of constructs consisting of different donor and acceptor fluorescent proteins separated by a short linker. Constructs were expressed in HEK293 cells and tested for FRET and other relevant properties. The most promising pairs were subsequently used in an attempt to improve the FRET span of the Epac-based cAMP sensor. The results show significant albeit not perfect correlation between performance in the spacer construct and in the Epac sensor. Finally, this strategy enabled us to identify improved sensors both for detection by sensitized emission and by fluorescent lifetime imaging. The present overview should be helpful in guiding development of future FRET sensors.

  18. Intercalated vs Non-Intercalated Morphologies in Donor-Acceptor Bulk Heterojunction Solar Cells: PBTTT:Fullerene Charge Generation and Recombination Revisited

    KAUST Repository

    Collado Fregoso, Elisa


    In this contribution, we study the role of the donor:acceptor interface nanostructure upon charge separation and recombination in organic photovoltaic devices and blend films, using mixtures of PBTTT and two different fullerene derivatives (PC70BM and ICTA) as models for intercalated and non-intercalated morphologies, respectively. Thermodynamic simulations show that while the completely intercalated system exhibits a large free-energy barrier for charge separation, this barrier is significantly lower in the non-intercalated system, and almost vanishes when energetic disorder is included in the model. Despite these differences, both fs-resolved transient absorption spectroscopy (TAS) and TDCF exhibit extensive first-order losses in that system, suggesting that geminate pairs are the primary product of photoexcitation. In contrast, the system that comprises a combination of fully intercalated polymer:fullerene areas and fullerene aggregated domains (1:4 PBTTT:PC70BM), is the only one that shows slow, second-order recombination of free charges, resulting in devices with an overall higher short circuit current and fill factor. This study therefore provides a novel consideration of the role of the interfacial nanostructure and the nature of bound charges, and their impact upon charge generation and recombination.

  19. Measuring the micro-polarity and hydrogen-bond donor/acceptor ability of thermoresponsive N-isopropylacrylamide/N-tert-butylacrylamide copolymer films using solvatochromic indicators. (United States)

    Szczupak, Boguslaw; Ryder, Alan G; Togashi, Denisio M; Rochev, Yuri A; Gorelov, Alexander V; Glynn, Thomas J


    Thin polymer films are important in many areas of biomaterials research, biomedical devices, and biological sensors. The accurate in situ measurement of multiple physicochemical properties of thin polymer films is critical in understanding biocompatibility, polymer function, and performance. In this work we demonstrate a facile spectroscopic methodology for accurately measuring the micro-polarity and hydrogen-bond donor/acceptor ability for a series of relatively hydrophilic thermoresponsive copolymers. The micro-polarity of the N-isopropylacrylamide (NIPAM) and N-tert-butylacrylamide (NtBA) co-polymers was evaluated by means of the E(T)(30), alpha, beta, and pi empirical solvatochromic polarity parameters. The data shows that increasing the NtBA fraction in the dry copolymer film reduces polarity and hydrogen-bonding ability. Within the Kamlet-Taft polarity framework, the NIPAM/NtBA copolymer films are strong hydrogen-bond acceptors, strongly dipolar/polarizable, and rather moderate hydrogen-bond donors. This characterization provides a more comprehensive physicochemical description of polymers, which aids the interpretation of film performance. Comparison of the measured E(T)(30) values with literature data for other water-soluble polymers show that dry NIPAM/NtBA copolymers are slightly more polar than poly(ethylene oxide), less polar than polyvinylalcohol, and approximately the same polarity as poly(N-vinyl-2-pyrrolidone). These findings indicate that this spectroscopic method is a facile, rapid, and nondestructive methodology for measuring polymer properties in situ, suitable for most biomaterials research laboratories.

  20. Donors, Acceptors, and Traps in AlGaN and AlGaN/GaN Epitaxial Layers (United States)


    satellite (TES) region. By assuming that the DBE and TES lines represented, respectively, n=l and n=2 final states of the same donor, it was concluded that...present sample is 1.25 x 1016 cm-3. Using the screening formula, ED = EDO - CLND1/3 , with a = 2.1 x 10-5 meV-cm,15 we get an unscreened energy EDO = 75 6...two-electron satellite (TES) line of the new DBE line at 3.4732. (Note that TES lines result from bound-exciton transitions in which the donor is left

  1. An isoindigo containing donor-acceptor polymer: synthesis and photovoltaic properties of all-solution-processed ITO- and vacuum-free large area roll-coated single junction and tandem solar cells

    DEFF Research Database (Denmark)

    Brandt, Rasmus Guldbæk; Yue, Wei; Andersen, Thomas Rieks


    In this work, the design, synthesis, and characterization of a donor-acceptor polymer from dithieno[3,2-b:2',3'-d]pyrrole and isoindigo (i-ID) are presented. The synthesized polymer has been applied in large area ITO-free organic photovoltaics, both as spin coated and roll coated devices; the lat......In this work, the design, synthesis, and characterization of a donor-acceptor polymer from dithieno[3,2-b:2',3'-d]pyrrole and isoindigo (i-ID) are presented. The synthesized polymer has been applied in large area ITO-free organic photovoltaics, both as spin coated and roll coated devices......; the latter as both single junction and multi junction organic photovoltaic (OPV) architectures....

  2. Thermodynamic efficiency limit of molecular donor-acceptor solar cells and its application to diindenoperylene/C{sub 60}-based planar heterojunction devices

    Energy Technology Data Exchange (ETDEWEB)

    Gruber, Mark; Wagner, Julia; Hoermann, Ulrich; Opitz, Andreas; Bruetting, Wolfgang [Institut fuer Physik, Universitaet Augsburg, Universitaetsstr.1, 86135 Augsburg (Germany); Klein, Konrad; Stutzmann, Martin [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 4, 85748 Garching (Germany)


    In organic photovoltaic (PV) cells, the well-established donor-acceptor (D/A) concept enabling photo-induced charge transfer between two partners with suitable energy level alignment has proven extremely successful. Nevertheless, the introduction of such a heterojunction is accompanied with additional energy losses as compared to an inorganic homojunction cell, owing to the presence of a charge-transfer (CT) state at the D/A interface. Based on the principle of detailed balance, a modified Shockley-Queisser theory is developed including the essential effects of interfacial CT states, that allows for a quantitative assessment of the thermodynamic efficiency limits of molecular D/A solar cells. Key parameters, apart from the optical gap of the absorber material, entering the model are the energy (E{sub CT}) and relative absorption strength ({alpha}{sub CT}) of the CT state. It is demonstrated how the open-circuit voltage (V{sub OC}) and thus the power conversion efficiency are affected by different parameter values. Furthermore, it is shown that temperature dependent device characteristics can serve to determine the CT energy, and thus the upper limit of V{sub OC} for a given D/A combination, as well as to quantify non-radiative recombination losses. The model is applied to diindenoperylene (DIP)-based photovoltaic devices, with open-circuit voltages between 0.9 and 1.4 V, depending on the partner, that have recently been reported. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Electron Transfer in Biological Systems (United States)

    Evenson, Jeffrey Wayne


    A review of electron transfer in biology is provided. Chemiosmotic theory, a phenomenological discussion of electron transfer in the bacterial reaction center, and a general formalism for treating electron transfer in condensed systems (including biological systems) are presented. The effective electronic donor/acceptor coupling (H_{DA}) for a bridged electron transfer system is defined. An expression for H_{DA} in terms of the bridge Green's function is developed for systems represented by a tight-binding Hamiltonian. H_{DA } is computed exactly for two systems, and the existence of a dimensionless parameter which determines whether the effective coupling oscillates or decays with increasing donor/acceptor distance is shown. A numerical technique for computing H_{DA} is developed and shown to be significantly more powerful than the conventional Larsson technique. The inverse matrix technique and pathway methods for computing the effective coupling in bridged electron transfer systems are defined and compared. The inverse matrix technique is found to be more powerful on general theoretical grounds and more accurate for numerical calculations of the effective coupling for the butane-1-4-diyl diradical and dimethylene cyclohexane. Parameters for electron transfer Hamiltonians and multi-pathway effects are discussed. Calculations for a simple model electron transfer system and tuna cytochrome c demonstrate a dichotomy in the behavior of the effective coupling distance dependence. In one regime the effective coupling varies exponentially with distance and depends only on the average properties of the bridging material; in the other regime the effective coupling has a complex distance dependence and is sensitive to the details of the bridging material. Experiments and theory indicate that both regimes occur in biological systems, providing a new perspective on a recent controversy over the nature of the distance dependence. We review the status of effective coupling

  4. Host-guest complexation of [60]fullerenes and porphyrins enabled by "click chemistry". (United States)

    Ho, Khanh-Hy Le; Hijazi, Ismail; Rivier, Lucie; Gautier, Christelle; Jousselme, Bruno; de Miguel, Gustavo; Romero-Nieto, Carlos; Guldi, Dirk M; Heinrich, Benoit; Donnio, Bertrand; Campidelli, Stéphane


    Herein the synthesis, characterization, and organization of a first-generation dendritic fulleropyrrolidine bearing two pending porphyrins are reported. Both the dendron and the fullerene derivatives were synthesized by Cu(I) -catalyzed alkyne-azide cycloaddition (CuAAC). The electron-donor-acceptor conjugate possesses a shape that allows the formation of supramolecular complexes by encapsulation of C60 within the jaws of the two porphyrins of another molecule. The interactions between the two photoactive units (i.e., C60 and Zn-porphyrin) were confirmed by cyclic voltammetry as well as by steady-state and time-resolved spectroscopy. For example, a shift of about 85 mV was found for the first reduction of C60 in the electron-donor-acceptor conjugate compared with the parent molecules, which indicates that C60 is included in the jaws of the porphyrin. The fulleropyrrolidine compound exhibits a rich polymorphism, which was corroborated by AFM and SEM. In particular, it was found to form supramolecular fibrils when deposited on substrates. The morphology of the fibrils suggests that they are formed by several rows of fullerene-porphyrin complexes. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. synthesis and characterisation of some metal complexes of hybrid ...

    African Journals Online (AJOL)


    KEY WORDS: Aminophosphines, Metal complexes, Cobalt(II) complex, Crystal structure. INTRODUCTION. Transition metal complexes of tertiary phosphines have been extensively studied owing to the donor-acceptor properties of the phosphorus atom which provides enhanced coordination abilities of the ligands thus ...

  6. Electronic Excitations in Push-Pull Oligomers and Their Complexes with Fullerene from Many-Body Green's Functions Theory with Polarizable Embedding. (United States)

    Baumeier, Björn; Rohlfing, Michael; Andrienko, Denis


    We present a comparative study of excited states in push-pull oligomers of PCPDTBT and PSBTBT and prototypical complexes with a C60 acceptor using many-body Green's functions theory within the GW approximation and the Bethe-Salpeter equation. We analyze excitations in oligomers up to a length of 5 nm and find that for both materials the absorption energy practically saturates for structures larger than two repeat units due to the localized nature of the excitation. In the bimolecular complexes with C60, the transition from Frenkel to charge transfer excitons is generally exothermic and strongly influenced by the acceptor's position and orientation. The high CT binding energy of the order of 2 eV results from the lack of an explicit molecular environment. External polarization effects are then modeled in a GW-BSE based QM/MM approach by embedding the donor-acceptor complex into a polarizable lattice. The lowest charge transfer exciton is energetically stabilized by about 0.5 eV, while its binding energy is reduced to about 0.3 eV. We also identify a globally unbound charge transfer state with a more delocalized hole at higher energy while still within the absorption spectrum, which opens another potential pathway for charge separation. For both PCPDTBT and PSBTBT, the energetics are largely similar with respect to absorption and the driving force to form intermediate charge transfer excitations for free charge generation. These results support that the higher power conversion efficiency observed for solar cells using PSBTBT as donor material is a result of molecular packing rather than of the electronic structure of the polymer.

  7. Efficiency-limiting processes in cyclopentadithiophene-bridged donor-acceptor-type dyes for solid-state dye-sensitized solar cells

    KAUST Repository

    Hinkel, Felix


    The charge generation and recombination processes in three novel push-pull photosensitizers for dye-sensitized solar cells (DSSCs) are studied by ps–μs transient absorption (TA) and quasi-steady-state photoinduced absorption (PIA) spectroscopy. The three cyclopentadithiophene-based photosensitizer dye molecules exhibit comparably low power conversion efficiencies ranging from 0.8% to 1.7% in solid-state DSSCs. We find that the photocurrents increase in the presence of Li-salt additives. Both TA and PIA measurements observe long-lived dye cations created by electron injection from the dyes’ excited state for two dyes from the series. However, the third dye shows significantly lower performance as a consequence of the less efficient electron injection even after the addition of Li-salts and faster electron-hole recombination on the ns-μs time scale. In essence, the prerequisites for this class of donor-π bridge-acceptor photosensitizers to reach higher charge generation efficiencies are a combination of strong dipole moments and fine tuning of the electronic landscape at the titania-dye interface by Li-salt addition.

  8. To what extent can charge localization influence electron injection efficiency at graphene-porphyrin interfaces?

    KAUST Repository

    Parida, Manas R.


    Controlling the electron transfer process at donor- acceptor interfaces is a research direction that has not yet seen much progress. Here, with careful control of the charge localization on the porphyrin macrocycle using β -Cyclodextrin as an external cage, we are able to improve the electron injection efficiency from cationic porphyrin to graphene carboxylate by 120% . The detailed reaction mechanism is also discussed.

  9. Electron beam welding complex diagnostics automated system

    Directory of Open Access Journals (Sweden)

    Є. В. Нікітенко


    Full Text Available The structure of the system of technical diagnostics is investigated. The algorithm of technical diagnostic of electron beam welding complex, which serves as the basis for creation of automated system for technical diagnostics, is proposed

  10. Electronic properties of complex nanostructures (United States)

    Zhu, Zhen

    Nanostructured materials have brought an unprecedented opportunity for advancement in many fields of human endeavor and in applications. Nanostructures are a new research field which may revolutionize people's everyday life. In the Thesis, I have used theoretical methods including density functional theory (DFT), molecular dynamic simulations (MD) and tight-binding methods to explore the structural, mechanical and electronic properties of various nanomaterials. In all this, I also paid attention to potential applications of these findings. First, I will briefly introduce the scientific background of this Thesis, including the motivation for the study of a boron enriched aluminum surface, novel carbon foam structures and my research interest in 2D electronics. Then I will review the computational techniques I used in the study, mostly DFT methods. In Chapter 3, I introduce an effective way to enhance surface hardness of aluminum by boron nanoparticle implantation. Using boron dimers to represent the nanoparticles, the process of boron implantation is modeled in a molecular dynamics simulation of bombarding the aluminum surface by energetic B 2 molecules. Possible metastable structures of boron-coated aluminum surface are identified. Within these structures, I find that boron atoms prefer to stay in the subsurface region of aluminum. By modeling the Rockwell indentation process, boron enriched aluminum surface is found to be harder than the pristine aluminum surface by at least 15%. In Chapter 4, I discuss novel carbon structures, including 3D carbon foam and related 2D slab structures. Carbon foam contains both sp 2 and sp3 hybridized carbon atoms. It forms a 3D honeycomb lattice with a comparable stability to fullerenes, suggesting possible existence of such carbon foam structures. Although the bulk 3D foam structure is semiconducting, an sp2 terminated carbon surface could maintain a conducting channel even when passivated by hydrogen. To promote the experimental

  11. Modeling Electronic Properties of Complex Oxides (United States)

    Krishnaswamy, Karthik

    Complex oxides are a class of materials that have recently emerged as potential candidates for electronic applications owing to their interesting electronic properties. The goal of this dissertation is to develop a fundamental understanding of these electronic properties using a combination of first-principles approaches based on density functional theory (DFT), and Schr odinger-Poisson (SP) simulation (Abstract shortened by ProQuest.

  12. Novel donor-acceptor polymer containing 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole for polymer solar cells with power conversion efficiency of 6.21%. (United States)

    Han, Liangliang; Bao, Xichang; Hu, Tong; Du, Zhengkun; Chen, Weichao; Zhu, Dangqiang; Liu, Qian; Sun, Mingliang; Yang, Renqiang


    In order to improve the solution processability of 4,7-bis(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT)-based polymers, novel donor-acceptor polymer PTOBDTDTBT containing DTBT and benzo[1,2-b:4,5-b']dithiophene (BDT) with conjugated side chain is designed and synthesized with narrow band gap 1.67 eV and low lying HOMO energy level -5.4 eV. The blend film of PTOBDTDTBT and PC71 BM exhibits uniform and smooth film with root-mean-square (RMS) surface roughness 1.15 nm because of the excellent solubility of PTOBDTDTBT when six octyloxy side chains are introduced. The hole mobility of the blend film is measured to be 4.4 × 10(-5) cm(2) V(-1) s(-1) by the space-charge-limited current (SCLC) model. The optimized polymer solar cells (PSCs) based on PTOBDTDTBT/PC71 BM exhibits an improved PCE of 6.21% with Voc = 0.80 V, Jsc = 11.94 mA cm(-2) and FF = 65.10%, one of the highest PCE in DTBT containing polymers. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Ultrafast Photoinduced Electron Transfer in a π-Conjugated Oligomer/Porphyrin Complex

    KAUST Repository

    Aly, Shawkat Mohammede


    Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor-acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR are desirable for optimal device performance. In this Letter, the ultrafast excited-state CT between platinum oligomer (DPP-Pt(acac)) as a new electron donor and porphyrin as an electron acceptor is monitored for the first time using femtosecond (fs) transient absorption (TA) spectroscopy with broad-band capability and 120 fs temporal resolution. Turning the CT on/off has been shown to be possible either by switching from an organometallic oligomer to a metal-free oligomer or by controlling the charge density on the nitrogen atom of the porphyrin meso unit. Our time-resolved data show that the CT and CS between DPP-Pt(acac) and cationic porphyrin are ultrafast (approximately 1.5 ps), and the CR is slow (ns time scale), as inferred from the formation and the decay of the cationic and anionic species. We also found that the metallic center in the DPP-Pt(acac) oligomer and the positive charge on the porphyrin are the keys to switching on/off the ultrafast CT process.

  14. Influence of doped-charge transport layers on the photovoltaic performance of donor-acceptor blend p-i-n type organic solar cells

    Directory of Open Access Journals (Sweden)

    D. Gebeyehu


    Full Text Available This report demonstrates external power conversion efficiencies of 2% under 100 mW/cm2 simulated AM1.5 illumination for organic thin-film photovoltaic cells using a phthalocyanine-fullerene (ZnPc/C60 bulk heterojunction as an active layer, embedded into a p-i-n type architecture with doped wide-gap charge transport layers. For an optically optimized device, we found internal quantum efficiency (IQE of above 80% under short circuit conditions. Such optically thin cells with high internal quantum efficiency are an important step towards high efficiency tandem cells. The p-i-n architecture allows for the design of solar cells with high internal quantum efficiency where only the photoactive region absorbs visible light and recombination losses at contacts are avoided. The I-V characteristics, power conversion efficiencies, the dependence of short circuit current on incident white light intensity, incident photon to collected electron efficiency (IPCE and absorption spectra of the active layer system are discussed.

  15. Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies (United States)

    Pannipara, Mehboobali; Asiri, Abdullah M.; Alamry, Khalid A.; Arshad, Muhammad N.; El-Daly, Samy A.


    The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by 1H NMR, 13C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardt's correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

  16. Ruthenium ammine/crown ether interactions in solution: Effects of modification of both guest and host on the strength of second-sphere complexation

    Energy Technology Data Exchange (ETDEWEB)

    Todd, M.D.; Yuhua Dong; Horney, J.; Yoon, D.I.; Hupp, J.T. (Northwestern Univ., Evanston, IL (United States))


    Charge-transfer absorption, electrochemical, and NMR-NOE studies of monomeric and dimeric (ligand-bridged) ruthenium ammine guest interactions with several crown ether hosts show that second-sphere complexation is prevalent in nitromethane as solvent and that complexation or binding constants can be varied by ca. 10[sup 8]-fold by modifying both guest and host properties. For hosts, larger binding constants are obtained with larger macrocycles and with more flexible macrocycles (i.e. dicyclohexano vs dibenzo crowns). For guests, larger binding constants are observed in higher oxidation states and in the presence of strongly electron-withdrawing ancillary ligands. In all cases, binding appears to be driven primarily by ammine hydrogen/ether oxygen (Lewis acid/base) interactions. Evidence is also found, however, for contributions from favorable benzene(crown)/pyridine(complex) interactions and (apparently) benzene(crown) [yields] Ru(III) charge-transfer (donor/acceptor) interactions. 17 refs., 3 figs., 2 tabs.

  17. Electronic Structure of Metallacyclophosphazene and Metallacyclothiazene Complexes. (United States)

    Sundermann, Andreas; Schoeller, Wolfgang W.


    The electronic structure of metallacyclotriphosphazene complexes with several substituents at the phosphorus atoms and metallacyclothiazene complexes is explored for a variety of transition metal elements using density functional theory methods. Accordingly the metallacyclophosphazenes possess a large HOMO-LUMO energy separation while the metallacyclothiazenes bear stronger open-shell character. In addition our calculations predict the existence of experimentally so far unknown dimetallacyclophosphazenes. All structures show to be highly dynamical. The double bond character of the transition metal nitrogen bond is much less pronounced than in nitrido or imido complexes. For the ring compounds vibrational spectra are reported and compared with experimental data.

  18. A comparative theoretical study of exciton-dissociation and charge-recombination processes in oligothiophene/fullerene and oligothiophene/perylenediimide complexes for organic solar cells

    KAUST Repository

    Yi, Yuanping


    The exciton-dissociation and charge-recombination processes in donor-acceptor complexes found in α-sexithienyl/C60 and α-sexithienyl/perylenetetracarboxydiimide (PDI) solar cells are investigated by means of quantum-chemical methods. The electronic couplings and exciton-dissociation and charge-recombination rates have been evaluated for various configurations of the complexes. The results suggest that the decay of the lowest charge-transfer state to the ground state in the PDI-based devices: (i) is faster than that in the fullerene-based devices and (ii) in most cases, can compete with the dissociation of the charge-transfer state into mobile charge carriers. This faster charge-recombination process is consistent with the lower performance observed experimentally for the devices using PDI derivatives as the acceptor. © 2011 The Royal Society of Chemistry.

  19. Complexity in electronic negotiation support systems. (United States)

    Griessmair, Michele; Strunk, Guido; Vetschera, Rudolf; Koeszegi, Sabine T


    It is generally acknowledged that the medium influences the way we communicate and negotiation research directs considerable attention to the impact of different electronic communication modes on the negotiation process and outcomes. Complexity theories offer models and methods that allow the investigation of how pattern and temporal sequences unfold over time in negotiation interactions. By focusing on the dynamic and interactive quality of negotiations as well as the information, choice, and uncertainty contained in the negotiation process, the complexity perspective addresses several issues of central interest in classical negotiation research. In the present study we compare the complexity of the negotiation communication process among synchronous and asynchronous negotiations (IM vs. e-mail) as well as an electronic negotiation support system including a decision support system (DSS). For this purpose, transcripts of 145 negotiations have been coded and analyzed with the Shannon entropy and the grammar complexity. Our results show that negotiating asynchronically via e-mail as well as including a DSS significantly reduces the complexity of the negotiation process. Furthermore, a reduction of the complexity increases the probability of reaching an agreement.

  20. Microscopic models for proton transfer in water and strongly hydrogen-bonded complexes with a single-well proton potential

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens


    A new mechanism and formalism for proton transfer in donor-acceptor complexes with long hydrogen bonds introduced recently [1], is applied to a proton transfer in liquid water. "Structural diffusion" of hydroxonium ions is regarded as totally adiabatic process, with synchronous hindered translation...

  1. Advances in electron transfer chemistry

    CERN Document Server

    Mariano, Patrick S


    Advances in Electron Transfer Chemistry, Volume 3 presents studies that discuss findings in the various aspects of electron chemistry. The book is comprised of four chapters; each chapter reviews a work that tackles an issue in electron transfer chemistry. Chapter 1 discusses the photoinduced electron transfer in flexible biaryl donor-acceptor molecules. Chapter 2 tackles light-induced electron transfer in inorganic systems in homogeneous and heterogeneous phases. The book also covers internal geometry relaxation effects on electron transfer rates of amino-centered systems. The sequential elec

  2. Redox and photoinduced electron-transfer properties in short distance organoboryl ferrocene-subphthalocyanine dyads. (United States)

    Maligaspe, Eranda; Hauwiller, Matthew R; Zatsikha, Yuriy V; Hinke, Jonathan A; Solntsev, Pavlo V; Blank, David A; Nemykin, Victor N


    Reaction between ferrocene lithium or ethynylferrocene magnesium bromide and (chloro)boronsubphthalocyanine leads to formation of ferrocene- (2) and ethynylferrocene- (3) containing subphthalocyanine dyads with a direct organometallic B-C bond. New donor-acceptor dyads were characterized using UV-vis and magnetic circular dichroism (MCD) spectroscopies, NMR method, and X-ray crystallography. Redox potentials of the rigid donor-acceptor dyads 2 and 3 were studied using the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches and compared to the parent subphthalocyanine 1 and conformationally flexible subphthalocyanine ferrocenenylmethoxide (4) and ferrocenyl carboxylate (5) dyads reported earlier. It was found that the first oxidation process in dyads 2 and 3 is ferrocene-centered, while the first reduction as well as the second oxidation are centered at the subphthalocyanine ligand. Density functional theory-polarized continuum model (DFT-PCM) and time-dependent (TD) DFT-PCM methods were used to probe the electronic structures and explain the UV-vis and MCD spectra of complexes 1-5. DFT-PCM calculations suggest that the LUMO, LUMO+1, and HOMO-3 in new dyads 2 and 3 are centered at the subphthalocyanine ligand, while the HOMO to HOMO-2 in both dyads are predominantly ferrocene-centered. TDDFT-PCM calculations on compounds 1-5 are indicative of the π → π* transitions dominance in their UV-vis spectra, which is consistent with the experimental data. The excited state dynamics of the parent subphthalocyanine 1 and dyads 2-5 were investigated using time-resolved transient spectroscopy. In the dyads 2-5, the initially excited state is rapidly (ferrocene ligand. The lifetime of the charge transfer state demonstrates a systematic dependence on the structure of the bridge between the subphthalocyanine and ferrocene.

  3. Efficient two-step photogeneration of long-lived charges in ground-state charge-transfer complexes of conjugated polymer doped with fullerene

    NARCIS (Netherlands)

    Bakulin, Artem A.; Zapunidy, Sergey A.; Pshenichnikov, Maxim S.; van Loosdrecht, Paul H. M.; Paraschuk, Dmitry Yu.


    Polarization-sensitive time-resolved visible-infrared pump-probe experiments demonstrate that one can efficiently generate long-lived charges in donor-acceptor charge transfer complex (CTC) of conjugated polymer doped with fullerene, MEH-PPV/dinitroanthraquinone/C(60). In particular, a strong

  4. Electronic structure and magnetism of complex materials

    CERN Document Server

    Papaconstantopoulos, D A


    Recent developments in electronic structure theory have led to a new understanding of magnetic materials at the microscopic level. This enables a truly first-principles approach to investigations of technologically important magnetic materials. Among these advances have been practical schemes for handling non-collinear magnetic systems, including relativity, understanding of the origins and role of orbital magnetism within band structure formalisms, density functional approaches for magnons and low-lying spin excitations, understanding of the interplay of orbital, spin and lattice orderings in complex oxides, transport theories for layered systems, and the theory of magnetic interactions in doped semiconductors. The book covers these recent developments with review articles by some of the main originators of these advances.

  5. Molecular Orbital and Density Functional Study of the Formation, Charge Transfer, Bonding and the Conformational Isomerism of the Boron Trifluoride (BF3 and Ammonia (NH3 Donor-Acceptor Complex

    Directory of Open Access Journals (Sweden)

    Dulal C. Ghosh


    Full Text Available The formation of the F3B–NH3 supermolecule by chemical interaction of its fragment parts, BF3 and NH3, and the dynamics of internal rotation about the ‘B–N’ bond have been studied in terms of parameters provided by the molecular orbital and density functional theories. It is found that the pairs of frontier orbitals of the interacting fragments have matching symmetry and are involved in the charge transfer interaction. The donation process stems from the HOMO of the donor into the LUMO of the acceptor and simultaneously, back donation stems from the HOMO of acceptor into the LUMO of the donor. The density functional computation of chemical activation in the donor and acceptor fragments, associated with the physical process of structural reorganization just prior to the event of chemical reaction, indicates that BF3 becomes more acidic and NH3 becomes more basic, compared to their separate equilibrium states. Theoretically it is observed that the chemical reaction event of the formation of the supermolecule from its fragment parts is in accordance with the chemical potential equalization principle of the density functional theory and the electronegativity equalization principle of Sanderson. The energetics of the chemical reaction, the magnitude of the net charge transfer and the energy of the newly formed bond are quite consistent, both internally and with the principle of maximum hardness, PMH. The dynamics of the internal rotation of one part with respect to the other part of the supermolecule about the ‘B–N’ bond mimics the pattern of the conformational isomerism of the isostructural ethane molecule. It is also observed that the dynamics and evolution of molecular conformations as a function of dihedral angles is also in accordance with the principle of maximum hardness, PMH. Quite consistent with spectroscopic predictions, the height of the molecule’s barrier to internal rotation is very small. A rationale for the low height of the barrier has been put forward in terms of the energy partitioning analysis. On the question of origin of the barrier to internal rotation, we conclude that the conformational barrier to internal rotation does not originate from a particular region of the molecule, but rather it is a result of the subtle conjoint interplay of a number of opposing effects of one- and two-center bonded and nonbonded energy terms involving the entire skeleton of the molecule.

  6. Molecular Electronics

    DEFF Research Database (Denmark)

    Jennum, Karsten Stein

    This thesis includes the synthesis and characterisation of organic compounds designed for molecular electronics. The synthesised organic molecules are mainly based on two motifs, the obigo(phenyleneethynylenes) (OPE)s and tetrathiafulvalene (TTF) as shown below. These two scaffolds (OPE and TTF...... transistors (Part 2). The synthetic protocols rely on stepwise Sonogashira coupling reactions. Conductivity studies on various OPE-based molecular wires reveal that mere OPE compounds have a higher electrical resistance compared to the cruciform based wires (up to 9 times higher). The most spectacular result...... be potential candidates for future molecular electronics Synthesis of a new donor-acceptor chromophore based on a benzoquinone- TTF motif (QuinoneDTF) is also described herein (Part 2). Reaction of this molecule with acid induces a colour change from purple to orange. The purple colour can be restored...

  7. The Influence of Small Monovalent Cations on Neighbouring Hydrogen Bonds of Aquo-Protein Complexes (United States)

    Sagarik, Kritsana P.; Rode, Bernd M.


    The influence of small monovalent metal ions on hydrogen bonds of aquo-protein complexes is studied on Li+/HCONH2-OH2 as an example. Using results obtained from ab initio calculations with minimal GLO basis sets, the remarkable changes in the hydrogen bond energy and charge distribution, due to metal ion complex formation, are discussed. The metal ion seems to enhance strongly the donor-acceptor interaction of the O ... H-N-C=0 hydrogen-bonded system.

  8. Donor–Acceptor Copolymers of Relevance for Organic Photovoltaics: A Theoretical Investigation of the Impact of Chemical Structure Modifications on the Electronic and Optical Properties

    KAUST Repository

    Pandey, Laxman


    We systematically investigate at the density functional theory level how changes to the chemical structure of donor-acceptor copolymers used in a number of organic electronics applications influences the intrinsic geometric, electronic, and optical properties. We consider the combination of two distinct donors, where a central five-membered ring is fused on both sides by either a thiophene or a benzene ring, with 12 different acceptors linked to the donor either directly or through thienyl linkages. The interplay between the electron richness/deficiency of the subunits as well as the evolution of the frontier electronic levels of the isolated donors/acceptors plays a significant role in determining the electronic and optical properties of the copolymers. © 2012 American Chemical Society.

  9. Coupled motions direct electrons along human microsomal P450 Chains.

    Directory of Open Access Journals (Sweden)

    Christopher R Pudney


    Full Text Available Protein domain motion is often implicated in biological electron transfer, but the general significance of motion is not clear. Motion has been implicated in the transfer of electrons from human cytochrome P450 reductase (CPR to all microsomal cytochrome P450s (CYPs. Our hypothesis is that tight coupling of motion with enzyme chemistry can signal "ready and waiting" states for electron transfer from CPR to downstream CYPs and support vectorial electron transfer across complex redox chains. We developed a novel approach to study the time-dependence of dynamical change during catalysis that reports on the changing conformational states of CPR. FRET was linked to stopped-flow studies of electron transfer in CPR that contains donor-acceptor fluorophores on the enzyme surface. Open and closed states of CPR were correlated with key steps in the catalytic cycle which demonstrated how redox chemistry and NADPH binding drive successive opening and closing of the enzyme. Specifically, we provide evidence that reduction of the flavin moieties in CPR induces CPR opening, whereas ligand binding induces CPR closing. A dynamic reaction cycle was created in which CPR optimizes internal electron transfer between flavin cofactors by adopting closed states and signals "ready and waiting" conformations to partner CYP enzymes by adopting more open states. This complex, temporal control of enzyme motion is used to catalyze directional electron transfer from NADPH→FAD→FMN→heme, thereby facilitating all microsomal P450-catalysed reactions. Motions critical to the broader biological functions of CPR are tightly coupled to enzyme chemistry in the human NADPH-CPR-CYP redox chain. That redox chemistry alone is sufficient to drive functionally necessary, large-scale conformational change is remarkable. Rather than relying on stochastic conformational sampling, our study highlights a need for tight coupling of motion to enzyme chemistry to give vectorial electron

  10. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens


    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive ...

  11. Spectrophotometric studies of complexation of [60]fullerene with series of aromatic hydrocarbon molecules containing flexible phenyl substituents (United States)

    Ghosh, Kalyan; Chattopadhyay, Subrata; Banerjee, Manas; Bhattacharya, Sumanta


    The absorption spectra of the electron donor-acceptor complexes of [60]fullerene with five different aromatic hydrocarbon (AH) molecules containing flexible phenyl substituents have been investigated in toluene medium. An absorption band due to charge transfer (CT) transition is observed in each case in the visible region. The experimental CT transition energies are well correlated with the vertical ionization potentials of the AHs studied (through Mulliken's equation) from which we extract degrees of charge transfer, oscillator and transition dipole strengths of the CT complexes. The degrees of CT in the ground state of the complexes have been found to be very low (0.49-0.55%). The formation constants ( K) for the complexes of [60]fullerene with the aromatic hydrocarbons have been determined by UV-vis spectroscopy. Both K values and PM3 calculations on [60]fullerene/AH complexes reveal that nature of substitution in the donor moiety as well as steric compatibility with the acceptor molecule govern the process of EDA complex formation.

  12. Electron cloud in the CERN accelerator complex

    CERN Document Server

    AUTHOR|(CDS)2069325; Bartosik, Hannes; Belli, Eleonora; Iadarola, Giovanni; Li, Kevin Shing Bruce; Mether, Lotta Maria; Romano, Annalisa; Schenk, Michael


    Operation with closely spaced bunched beams causes the build-up of an Electron Cloud (EC) in both the LHC and the two last synchrotrons of its injector chain (PS and SPS). Pressure rise and beam instabilities are observed at the PS during the last stage of preparation of the LHC beams. The SPS was affected by coherent and incoherent emittance growth along the LHC bunch train over many years, before scrubbing has finally suppressed the EC in a large fraction of the machine. When the LHC started regular operation with 50 ns beams in 2011, EC phenomena appeared in the arcs during the early phases, and in the interaction regions with two beams all along the run. Operation with 25 ns beams (late 2012 and 2015), which is nominal for LHC, has been hampered by EC induced high heat load in the cold arcs, bunch dependent emittance growth and degraded beam lifetime. Dedicated and parasitic machine scrubbing is presently the weapon used at the LHC to combat EC in this mode of operation. This talk summarises the EC experi...

  13. Bay-annulated indigo (BAI) as an excellent electron accepting building block for high performance organic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yi; He, Bo; Pun, Andrew


    A novel electron acceptor based on bay-annulated indigo (BAI) was synthesized and used for the preparation of a series of high performance donor-acceptor small molecules and polymers. The resulting materials possess low-lying LUMO energy level and small HOMO-LUMO gaps, while their films exhibited high crystallinity upon thermal treatment, commensurate with high field effect mobilities and ambipolar transfer characteristics.

  14. Bay-annulated indigo (BAI) as an excellent electron accepting building block for high performance organic semiconductors (United States)

    Liu, Yi; He, Bo; Pun, Andrew


    A novel electron acceptor based on bay-annulated indigo (BAI) was synthesized and used for the preparation of a series of high performance donor-acceptor small molecules and polymers. The resulting materials possess low-lying LUMO energy level and small HOMO-LUMO gaps, while their films exhibited high crystallinity upon thermal treatment, commensurate with high field effect mobilities and ambipolar transfer characteristics.

  15. Donor-acceptor interactions in tri(phosphonio)methanide dications [(Ph3P)2CP(X)Ph2]2+ (X = H, Me, CN, NCS, OH, Cl, OTf, F). (United States)

    Yogendra, S; Hennersdorf, F; Bauzá, A; Frontera, A; Fischer, R; Weigand, J J


    The impact of the strongly electron donating carbodiphosphorane moiety in the series of tri(phosphonio)methanide dications as triflate salts [(Ph3P)2CP(X)Ph2][OTf]2 (X = H, Me, CN, NCS, OH, Cl, OTf, F) deriving from [(Ph3P)2CPPh2][OTf] (19[OTf]) is presented. The influence of the introduced substituents X on the electronic structures of these dications is investigated by means of detailed NBO analysis, NMR spectroscopy and X-ray analysis.

  16. Accelerator complex of ion and electron storage rings

    CERN Document Server

    Noda, A


    An accelerator complex consisting of storage rings of ions and electrons with their booster synchrotron of combined-function type is proposed as one of the candidates of the facility for the new campus of Kyoto University. Maximum energies for ions and electrons are 290 and 1500 MeV, respectively. Aimed beam intensities are 10 sup 1 sup 0 and 4x10 sup 1 sup 1 per pulse for ions and electrons, respectively. With use of this accelerator complex, merging of highly ionized ions and trial of laser beam cooling to ultimate low temperature might be possible. The possibility of laser cooling with use of free electron laser is also to be studied.

  17. Molecular complexes of L-phenylalanine with substituted 1,4-benzoquinones in aqueous medium: Spectral and theoretical investigations (United States)

    Ganesh, K.; El-Mossalamy, E. H.; Satheshkumar, A.; Balraj, C.; Elango, K. P.


    Various spectral techniques such as UV-Vis, FT-IR, and fluorescence have been employed to investigate the charge transfer interaction of L-phenylalanine (LPA) with substituted 1,4-benzoquinones (MQ1-4). Kinetic and thermodynamic properties of the complexes were determined in aqueous medium at physiological condition (pH = 7). The interaction of MQ1-4 with L-phenylalanine (LPA) was found to proceed through the formation of donor-acceptor complex, yielding a radical anion. The stoichiometry of the complexes was determined by Jobs continuous variation method and was found to be 1:1 in all the cases. Fluorescence quenching studies showed that the interaction between the donor and the acceptors is spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The order of the experimentally measured association constant of these complexes was well supported by DFT/B3LYP calculations.

  18. Electronic, adsorption, and transport properties of diamondoid-based complexes


    Adhikari, Bibek


    Quantum simulation is an invaluable tool to researchers from various fields of scientific research. It allows the investigation of various complex condensed matter in the regimes of physics, chemistry, and biology. In this work, we focused our attention in unraveling the physical, chemical, electronic, transport, and optical properties of diamondoids and their complexes through quantum simulations. We have implemented a bottom-up approach where we move from the doping and functionalization of...

  19. Structural complexities in the active layers of organic electronics. (United States)

    Lee, Stephanie S; Loo, Yueh-Lin


    The field of organic electronics has progressed rapidly in recent years. However, understanding the direct structure-function relationships between the morphology in electrically active layers and the performance of devices composed of these materials has proven difficult. The morphology of active layers in organic electronics is inherently complex, with heterogeneities existing across multiple length scales, from subnanometer to micron and millimeter range. A major challenge still facing the organic electronics community is understanding how the morphology across all of the length scales in active layers collectively determines the device performance of organic electronics. In this review we highlight experiments that have contributed to the elucidation of structure-function relationships in organic electronics and also point to areas in which knowledge of such relationships is still lacking. Such knowledge will lead to the ability to select active materials on the basis of their inherent properties for the fabrication of devices with prespecified characteristics.

  20. Mixed-Stack Architecture and Solvatomorphism of Trimeric Perfluoro-ortho-Phenylene Mercury complexes with Dithieno[3,2-b:2',3'-d]thiophene

    KAUST Repository

    Castañeda, Raúl


    The formation of the mixed-stack donor-acceptor complex of dithieno[3,2-b:2\\',3\\'-d]thiophene (1) and trimeric perfluoro-ortho-phenylene mercury (I) has been investigated under different conditions. Two solvatomorphs – mixed-stack complexes with a 1:1 donor-acceptor ratio and different solvent molecules in the solid state (dichloromethane (2) and dichloroethane (3)) have been obtained and characterized by experimental methods (FT-IR spectroscopy, differential thermogravimetric analysis, and X-ray crystallography) and quantum-chemical calculations at the density functional theory level. The differences in the solid state packing, thermal stability and potential charge-transfer properties of 2 and 3 are discussed.

  1. Spectral investigations, DFT based global reactivity descriptors, Inhibition efficiency and analysis of 5-chloro-2-nitroanisole as π-spacer with donor-acceptor variations effect for DSSCs performance (United States)

    Meenakshi, R.


    FTIR, FT-Raman, UV, NMR and quantum chemical calculation studies are performed on 5-chloro-2-nitroanisole, in order to gain the insights of its structural, spectroscopic and electronic properties (Fukui indices, HOMO and LUMO energy gap, MESP and Global reactivity descriptors). A complete vibrational analysis of 5-chloro-2-nitroanisole is performed by HF/B3LYP methods using 6-31G(d,p) basis set. To estimate the electronic transitions, the UV spectra of title compound are predicted in gas phase and ethanol. The obtained absorption maxima at 389.94 nm (in ethanol) is predicted possibly due to HOMO→LUMO transition with 85% contribution and assigned as π-π*. The MESP map shows that the negative potential sites are localized on oxygen atom (O10) as well as the positive potential sites are identified around the hydrogen and ring carbon atoms. The analysis of Fukui indices is also carried out to distinguish the nucleophilic and electrophiic centers. The prediction of reactive sites by MESP is well supported by this Fukui indices analysis. The correlations between the statistical thermodynamics and temperature are also obtained. It is seen that the heat capacities, entropies and enthalpies increase with increasing the intensities of the molecular vibrations. Furthermore, the first hyperpolarizability of 5-chloro-2-nitroanisole is calculated and the results are discussed. This result indicates that 5-chloro-2-nitroanisole is a good candidate of nonlinear optical materials.

  2. Patterning of high mobility electron gases at complex oxide interfaces

    DEFF Research Database (Denmark)

    Trier, Felix; Prawiroatmodjo, G. E. D. K.; von Soosten, Merlin


    Oxide interfaces provide an opportunity for electronics. However, patterning of electron gases at complex oxide interfaces is challenging. In particular, patterning of complex oxides while preserving a high electron mobility remains underexplored and inhibits the study of quantum mechanical effects...... where extended electron mean free paths are paramount. This letter presents an effective patterning strategy of both the amorphous-LaAlO3/SrTiO3 (a-LAO/STO) and modulation-doped amorphous-LaAlO3/La7/8Sr1/8MnO3/SrTiO3 (a-LAO/LSM/STO) oxide interfaces. Our patterning is based on selective wet etching...... of amorphous-LSM (a-LSM) thin films, which acts as a hard mask during subsequent depositions. Strikingly, the patterned modulation-doped interface shows electron mobilities up to ∼8 700 cm2/V s at 2 K, which is among the highest reported values for patterned conducting complex oxide interfaces that usually...

  3. Complex Moving Parts: Assessment Systems and Electronic Portfolios (United States)

    Larkin, Martha J.; Robertson, Royce L.


    The largest college within an online university of over 50,000 students invested significant resources in translating a complex assessment system focused on continuous improvement and national accreditation into an effective and efficient electronic portfolio (ePortfolio). The team building the system needed a model to address problems met…

  4. The impact of long-range electron-hole interaction on the charge separation yield of molecular photocells (United States)

    Nemati Aram, Tahereh; Ernzerhof, Matthias; Asgari, Asghar; Mayou, Didier


    We discuss the effects of charge carrier interaction and recombination on the operation of molecular photocells. Molecular photocells are devices where the energy conversion process takes place in a single molecular donor-acceptor complex attached to electrodes. Our investigation is based on the quantum scattering theory, in particular on the Lippmann-Schwinger equation; this minimizes the complexity of the problem while providing useful and non-trivial insight into the mechanism governing photocell operation. In this study, both exciton pair creation and dissociation are treated in the energy domain, and therefore there is access to detailed spectral information, which can be used as a framework to interpret the charge separation yield. We demonstrate that the charge carrier separation is a complex process that is affected by different parameters, such as the strength of the electron-hole interaction and the non-radiative recombination rate. Our analysis helps to optimize the charge separation process and the energy transfer in organic solar cells and in molecular photocells.

  5. Annealing effect on donor-acceptor interface and its impact on the performance of organic photovoltaic devices based on PSiF-DBT copolymer and C{sub 60}

    Energy Technology Data Exchange (ETDEWEB)

    Marchiori, Cleber F. N.; Yamamoto, Natasha A. D.; Koehler, Marlus; Roman, Lucimara S. [Department of Physics, Federal University of Paraná, P.O. Box 19044, 81531-990 Curitiba, Paraná (Brazil); Matos, Carolina F.; Zarbin, Aldo J. G. [Department of Chemistry, Federal University of Paraná, P.O. Box 19081, 81531-990 Curitiba, Paraná (Brazil); Kujala, Jiri; Tuomisto, Filip [Department of Applied Physics, Aalto University School of Science, P.O. Box 14100, FI-00076 Aalto (Finland); Macedo, Andréia G. [Department of Physics, Technological Federal University of Paraná, Curitiba 80230-901 (Brazil)


    In this work, poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl) benzo-2,1,3-thiadiazole] (PSiF-DBT) was used as active layer in bilayer solar cell with C{sub 60} as electron acceptor. As cast devices already show reasonable power conversion efficiency (PCE) that increases to 4% upon annealing at 100 °C. Space charge limited measurements of the hole mobility (μ) in PSiF-DBT give μ ∼ 1.0 × 10{sup −4} cm{sup 2}/(V s) which does not depend on the temperature of the annealing treatment. Moreover, positron annihilation spectroscopy experiments revealed that PSiF-DBT films are well stacked even without the thermal treatment. The variations in the transport of holes upon annealing are then small. As a consequence, the PCE rise was mainly induced by the increase of the polymer surface roughness that leads to a more effective interface for exciton dissociation at the PSiF-DBT/fullerene heterojunction.

  6. Organic structures design applications in optical and electronic devices

    CERN Document Server

    Chow, Tahsin J


    ""Presenting an overview of the syntheses and properties of organic molecules and their applications in optical and electronic devices, this book covers aspects concerning theoretical modeling for electron transfer, solution-processed micro- and nanomaterials, donor-acceptor cyclophanes, molecular motors, organogels, polyazaacenes, fluorogenic sensors based on calix[4]arenes, and organic light-emitting diodes. The publication of this book is timely because these topics have become very popular nowadays. The book is definitely an excellent reference for scientists working in these a

  7. Optical and electrochemical characteristics of Ir(III) complexes with metalated 4-(4-bromophenyl)-2-methyl-1,3-thiazole and isocyanide, ethylenediamine, and diethyldithiocarbamate ligands (United States)

    Katlenok, E. A.; Kinzhalov, M. A.; Eremina, A. A.; Balashev, K. P.


    The influence of donor-acceptor properties of tert-butyl-, 2.6-dimethylphenyl-, and 4-bromophenyl-isocyanides (BuNC, XylNC, BpNC), ethylenediamine (En), and diethyldithiocarbamate ions (Dtc-) on the 1H and 13C NMR, IR, optical, and electrochemical characteristics of Ir(III) complexes with metalated 4-(4-bromophenyl)-2-methyl-1,3-thiazole is studied. Enhancement of the donor properties of BpNC, XylNC, BuNC, En, and Dtc- ligands leads to a bathochromic shift of metal-to-ligand charge transfer (MLCT) bands and to a decrease in the difference between the one-electron oxidation and reduction potentials of complexes. The bathochromic shift of the low-temperature phosphorescence of complexes in frozen (77 K) solutions with increasing donor properties of BpNC, XylNC, BuNC, En, and Dtc-ligands is caused by a decrease in the admixture of MLCT to the intraligand excited state of {Ir(bptz)2}. Quenching of the phosphorescence of complexes in liquid solutions is attributed to the thermally-induced population of excited d- d* states with subsequent nonradiative deactivation.

  8. Perspective: Explicitly correlated electronic structure theory for complex systems. (United States)

    Grüneis, Andreas; Hirata, So; Ohnishi, Yu-Ya; Ten-No, Seiichiro


    The explicitly correlated approach is one of the most important breakthroughs in ab initio electronic structure theory, providing arguably the most compact, accurate, and efficient ansatz for describing the correlated motion of electrons. Since Hylleraas first used an explicitly correlated wave function for the He atom in 1929, numerous attempts have been made to tackle the significant challenges involved in constructing practical explicitly correlated methods that are applicable to larger systems. These include identifying suitable mathematical forms of a correlated wave function and an efficient evaluation of many-electron integrals. R12 theory, which employs the resolution of the identity approximation, emerged in 1985, followed by the introduction of novel correlation factors and wave function ansätze, leading to the establishment of F12 theory in the 2000s. Rapid progress in recent years has significantly extended the application range of explicitly correlated theory, offering the potential of an accurate wave-function treatment of complex systems such as photosystems and semiconductors. This perspective surveys explicitly correlated electronic structure theory, with an emphasis on recent stochastic and deterministic approaches that hold significant promise for applications to large and complex systems including solids.

  9. Cryo-electron Microscopy Analysis of Structurally Heterogeneous Macromolecular Complexes. (United States)

    Jonić, Slavica


    Cryo-electron microscopy (cryo-EM) has for a long time been a technique of choice for determining structure of large and flexible macromolecular complexes that were difficult to study by other experimental techniques such as X-ray crystallography or nuclear magnetic resonance. However, a fast development of instruments and software for cryo-EM in the last decade has allowed that a large range of complexes can be studied by cryo-EM, and that their structures can be obtained at near-atomic resolution, including the structures of small complexes (e.g., membrane proteins) whose size was earlier an obstacle to cryo-EM. Image analysis to identify multiple coexisting structures in the same specimen (multiconformation reconstruction) is now routinely done both to solve structures at near-atomic resolution and to study conformational dynamics. Methods for multiconformation reconstruction and latest examples of their applications are the focus of this review.

  10. Thiophene-based donor-acceptor conjugated polymer as potential ...

    Indian Academy of Sciences (India)

    Polymer light-emitting diodes are fabricated using PTh-CN as the emissive layer with a device configuration of ITO/PEDOT:PSS/PTh-CN/Al. The device showed stable saturated red electroluminescence with CIE coordinate values (0.65, 0.32) at 12 V, which are very close to the values for standard red demanded by the ...

  11. Self-Assembly Characteristics of a Multipolar Donor-Acceptor ...

    Indian Academy of Sciences (India)


    1. Synthesis and characterization of 1. S1. 2. FT-IR and MALDI-TOF Mass Spectrum. S2. 3. 500 MHz 1H NMR Spectra in DMSO-d6. S3. 4. Temperature dependant 1H NMR Spectra in DMSO-d6. S4. 5. 125 MHz 13C NMR, DEPT-135 and ATP Spectra in DMSO-d6. S5. 6. Unit cell diagram and Single Crystal X-ray Data. S6 ...

  12. Resonance energy transfer for the donor-acceptor pair curcumine ...

    African Journals Online (AJOL)

    If you would like more information about how to print, save, and work with PDFs, Highwire Press provides a helpful Frequently Asked Questions about PDFs. Alternatively, you can download the PDF file directly to your computer, from where it can be opened using a PDF reader. To download the PDF, click the Download link ...

  13. Device physics of donor/acceptor-blend solar cells

    NARCIS (Netherlands)

    Koster, Lambert Jan Anton


    Harvesting energy directly from the Sun is a very attractive, but not an easy way of providing mankind with energy. Efficient, cheap, lightweight, flexible, and environmentally friendly solar panels are very desirable. Conjugated polymers bear the potential of fulfilling these requisites. Due to

  14. Complex formation dynamics in a single-molecule electronic device. (United States)

    Wen, Huimin; Li, Wengang; Chen, Jiewei; He, Gen; Li, Longhua; Olson, Mark A; Sue, Andrew C-H; Stoddart, J Fraser; Guo, Xuefeng


    Single-molecule electronic devices offer unique opportunities to investigate the properties of individual molecules that are not accessible in conventional ensemble experiments. However, these investigations remain challenging because they require (i) highly precise device fabrication to incorporate single molecules and (ii) sufficient time resolution to be able to make fast molecular dynamic measurements. We demonstrate a graphene-molecule single-molecule junction that is capable of probing the thermodynamic and kinetic parameters of a host-guest complex. By covalently integrating a conjugated molecular wire with a pendent crown ether into graphene point contacts, we can transduce the physical [2]pseudorotaxane (de)formation processes between the electron-rich crown ether and a dicationic guest into real-time electrical signals. The conductance of the single-molecule junction reveals two-level fluctuations that are highly dependent on temperature and solvent environments, affording a nondestructive means of quantitatively determining the binding and rate constants, as well as the activation energies, for host-guest complexes. The thermodynamic processes reveal the host-guest binding to be enthalpy-driven and are consistent with conventional 1 H nuclear magnetic resonance titration experiments. This electronic device opens up a new route to developing single-molecule dynamics investigations with microsecond resolution for a broad range of chemical and biochemical applications.

  15. Stability of sulfate complexes of electronically excited uranyl

    Energy Technology Data Exchange (ETDEWEB)

    Ostakhov, S.S.; Kazakov, V.P.; Afonichev, D.D. [Inst. of Organic Chemistry, Ufa (Russian Federation)


    The complex formation of electronically excited uranyl ions with SO{sub 4}{sup 2-}anions in 0.1 M aqueous HClO{sub 4} has been studied by time-resolved luminescence spectroscopy. The stability constants of uranyl sulfate complexes (UO{sub 2}SO{sub 4}) (K=870 1 mol{sup -1}) and [UO{sub 2}(SO{sub 4}){sub 2}{sup 2-}](K=47000 1 mol{sup -1}) in excited state have been determined; they are more than an order of magnitude greater than those reported for complex formation of uranyl ions in the ground state. The complex formation of uranyl with sulfate ions is accompanied by the increase of the quantum yield of the uranyl lumenescence. The maxima of luminescence and absorption bands of uranyl ions are shifted with increasing the total concentration of SO{sub 4}{sup 2-} in solution, which supports the data obtained. The shift of the maxima of luminescence bands is observed at a sulfate concentration that is considerably lower than that causing the same shift of the maxima of the absorption bands. Such effect is consistent with the calculated stability constants of sulfate complexes of excited uranyl ions.

  16. Photo-induced electron transfer from a conducting polymer to buckminsterfullerene: A molecular approach to high efficiency photovoltaic cells. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Heeger, A.J.


    For photovoltaic cells made with pure conjugated polymers, energy conversion efficiencies were typically 10{sup {minus}3}--10{sup {minus}2}%, too low to be used in practical applications. The recent discovery of photoinduced electron transfer in composites of conducting polymers (as donors) and buckminsterfullerene, C{sub 60}, and its derivatives (as acceptors) provided a molecular approach to high efficiency photovoltaic conversion. Since the time scale for photoinduced charge transfer is subpicosecond, more than 10{sup 3} times faster than the radiative or nonradiative decay of photo-excitations, the quantum efficiency for charge transfer and charge separation from donor to acceptor is close to unity. Thus, photoinduced charge transfer across a donor/acceptor (D/A) interface provides an effective method of overcome early time carrier recombination in organic systems and thus to enhance the optoelectronic response of these materials. Progress toward creating bulk D/A heterojunction materials is described by summarizing two publications which resulted from this research, namely: Plastic photovoltaic cells made with donor-acceptor composites -- Enhanced carrier collection efficiency via a network of internal heterojunctions; and Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions.

  17. Cryo electron microscopy to determine the structure of macromolecular complexes. (United States)

    Carroni, Marta; Saibil, Helen R


    Cryo-electron microscopy (cryo-EM) is a structural molecular and cellular biology technique that has experienced major advances in recent years. Technological developments in image recording as well as in processing software make it possible to obtain three-dimensional reconstructions of macromolecular assemblies at near-atomic resolution that were formerly obtained only by X-ray crystallography or NMR spectroscopy. In parallel, cryo-electron tomography has also benefitted from these technological advances, so that visualization of irregular complexes, organelles or whole cells with their molecular machines in situ has reached subnanometre resolution. Cryo-EM can therefore address a broad range of biological questions. The aim of this review is to provide a brief overview of the principles and current state of the cryo-EM field. Copyright © 2016. Published by Elsevier Inc.

  18. Structural and Electronic Investigations of Complex Intermetallic Compounds

    Energy Technology Data Exchange (ETDEWEB)

    Ko, Hyunjin [Iowa State Univ., Ames, IA (United States)


    In solid state chemistry, numerous investigations have been attempted to address the relationships between chemical structure and physical properties. Such questions include: (1) How can we understand the driving forces of the atomic arrangements in complex solids that exhibit interesting chemical and physical properties? (2) How do different elements distribute themselves in a solid-state structure? (3) Can we develop a chemical understanding to predict the effects of valence electron concentration on the structures and magnetic ordering of systems by both experimental and theoretical means? Although these issues are relevant to various compound classes, intermetallic compounds are especially interesting and well suited for a joint experimental and theoretical effort. For intermetallic compounds, the questions listed above are difficult to answer since many of the constituent atoms simply do not crystallize in the same manner as in their separate, elemental structures. Also, theoretical studies suggest that the energy differences between various structural alternatives are small. For example, Al and Ga both belong in the same group on the Periodic Table of Elements and share many similar chemical properties. Al crystallizes in the fcc lattice with 4 atoms per unit cell and Ga crystallizes in an orthorhombic unit cell lattice with 8 atoms per unit cell, which are both fairly simple structures (Figure 1). However, when combined with Mn, which itself has a very complex cubic crystal structure with 58 atoms per unit cell, the resulting intermetallic compounds crystallize in a completely different fashion. At the 1:1 stoichiometry, MnAl forms a very simple tetragonal lattice with two atoms per primitive unit cell, while MnGa crystallizes in a complicated rhombohedral unit cell with 26 atoms within the primitive unit cell. The mechanisms influencing the arrangements of atoms in numerous crystal structures have been studied theoretically by calculating electronic

  19. Electron delocalization in diruthenium complexes of polycyclic arenes

    Energy Technology Data Exchange (ETDEWEB)

    Plitzko, K.D.; Boekelheide, V.


    A very rapid intramolecular two-electron transfer between Ru/sup 0/ and Ru/sup II/ or a species with two Ru/sup I/ centers is the explanation given for the unusual properties of the cation of the bis (eta/sup 6/-hexamethylbenzene)diruthenium complex of phenanthrene. /sup 1/H- and /sup 13/C-NMR spectra are highly symmetric, and further reduction to the Ru/sub 2//sup 0/ neutral complex first takes place at -1.177 +- 0.010 V (vs. SCE). The phenanthrene analogue - one double bond more - behaves completely differently: it obviously contains an Ru/sup II/ center and an Ru/sup 0/ center.

  20. The Tolman electronic parameter (TEP) and the metal-metal electronic communication in ditopic NHC complexes. (United States)

    Gusev, Dmitry G; Peris, Eduardo


    Whereas the electronic communication between metals in dimetallic organometallic compounds is often assessed through cyclic voltammetric measurements, we have found that the variations in the Tolman electronic parameter (TEP) can also be an alternative and effective way of determining this type of interaction. The TEP values of several (CO)3Ni-NHC-X systems with five different ditopic NHC ligand systems [triazolyldiylidene (A), bis(imidazolylidene) (B), benzobis(imidazolylidene) (C), cyclopenta[f,g]acenaphthylenebis(imidazolylidene) (D) and bis(imidazolidinylidene) (F)] were determined by means of DFT calculations. Based on these values, the electron-withdrawing character of the X metal fragments employed in this study was found to increase in the order IrCp(CO) → RhCl(COD) → Ni(CO)3 → Cr(CO)5 → RhCl(CO)2. We found that the degree of electronic interaction through the ditopic NHC ligands is the strongest in A, followed by B and F, while being weak in B and C. The TEP values and the quantitative analysis of the upper molecular orbitals of A and F and their (CO)3Ni-NHC-Ni(CO)3 complexes strongly suggest that the principal electronic interaction between the metal centres of the M-NHC-M' complexes is of σ-type, via the delocalized HOMO and HOMO - 1 orbitals of the NHC ligands.

  1. UV-Vis spectroscopy and density functional study of solvent effect on the charge transfer band of the n → σ* complexes of 2-Methylpyridine and 2-Chloropyridine with molecular iodine (United States)

    Gogoi, Pallavi; Mohan, Uttam; Borpuzari, Manash Protim; Boruah, Abhijit; Baruah, Surjya Kumar


    UV-Vis spectroscopy has established that Pyridine substitutes form n→σ* charge transfer (CT) complexes with molecular Iodine. This study is a combined approach of purely experimental UV-Vis spectroscopy, Multiple linear regression theory and Computational chemistry to analyze the effect of solvent upon the charge transfer band of 2-Methylpyridine-I2 and 2-Chloropyridine-I2 complexes. Regression analysis verifies the dependence of the CT band upon different solvent parameters. Dielectric constant and refractive index are considered among the bulk solvent parameters and Hansen, Kamlet and Catalan parameters are taken into consideration at the molecular level. Density Functional Theory results explain well the blue shift of the CT bands in polar medium as an outcome of stronger donor acceptor interaction. A logarithmic relation between the bond length of the bridging atoms of the donor and the acceptor with the dielectric constant of the medium is established. Tauc plot and TDDFT study indicates a non-vertical electronic transition in the complexes. Buckingham and Lippert Mataga equations are applied to check the Polarizability effect on the CT band.

  2. Focused Research Group in Correlated Electron and Complex Materials

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Ziqiang [Boston College, Chestnut Hill, MA (United States)


    While the remarkable physical properties of correlated and complex electronic materials hold great promise for technological applications, one of the key values of the research in this field is its profound impact on fundamental physics. The transition metal oxides, pnictides, and chalcogenides play a key role and occupy an especially important place in this field. The basic reason is that the outer shell of transition metals contains the atomic d-orbitals that have small spatial extent, but not too small to behave as localized orbtials. These d-electrons therefore have a small wave function overlap in a solid, e.g. in an octahedral environment, and form energy bands that are relatively narrow and on the scale of the short-range intra-atomic Coulomb repulsion (Hubbard U). In this intermediate correlation regime lies the challenge of the many-body physics responsible for new and unconventional physical properties. The study of correlated electron and complex materials represents both the challenge and the vitality of condensed matter and materials physics and often demands close collaborations among theoretical and experimental groups with complementary techniques. Our team has a track record and a long-term research goal of studying the unusual complexities and emergent behaviors in the charge, spin, and orbital sectors of the transition metal compounds in order to gain basic knowledge of the quantum electronic states of matter. During the funding period of this grant, the team continued their close collaborations between theory, angle-resolved photoemission spectroscopy, and scanning tunneling microscopy and made significant progress and contributions to the field of iron-based superconductors, copper-oxide high-temperature superconductors, triangular lattice transition metal oxide cobaltates, strontium ruthenates, spin orbital coupled iridates, as well as topological insulators and other topological quantum states of matter. These results include both new

  3. Role of 4 f electrons in crystallographic and magnetic complexity (United States)

    Pathak, Arjun K.; Paudyal, Durga; Mudryk, Yaroslav; Pecharsky, Vitalij K.


    The functionality of many magnetic materials critically depends on first manipulating and then taking advantage of highly nonlinear changes of properties that occur during phase transformations. Unique to lanthanides, property-defining 4 f electrons are highly localized and, as commonly accepted, play little to no role in chemical bonding. Yet here we demonstrate that the competition between 4 f -electron energy landscapes of Dy (4 f9 ) and Er (4 f11 ) is the key element of the puzzle required to explain complex interplay of magnetic and structural features observed in E r1 -xD yxC o2 , and likely many other mixed lanthanide systems. Unlike the parent binaries—DyC o2 and ErC o2 —E r1 -xD yxC o2 exhibits two successive magnetostructural transitions: a first order at TC, followed by a second order in the ferrimagnetically ordered state. Supported by first-principles calculations, our results offer new opportunities for targeted design of magnetic materials with multiple functionalities, and also provide a critical insight into the role of 4 f electrons in controlling the magnetism and structure of lanthanide intermetallics.

  4. Conjugated polymer-porphyrin complexes for organic electronics. (United States)

    Andernach, Rolf E; Rossbauer, Stephan; Ashraf, Raja S; Faber, Hendrik; Anthopoulos, Thomas D; McCulloch, Iain; Heeney, Martin; Bronstein, Hugo A


    We present the synthesis of novel conjugated polymer-porphyrin complexes for use in organic electronics. Linear and star-shaped platinated porphyrins were attached to regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) arms to investigate whether porphyrin stacking and increased dimensionality can be used to control polymer morphology. The novel materials display similar optical properties to P3HT, but give higher mobilities when used in organic field-effect transistors. Atomic force microscopy measurements show that incorporation of only a small amount of porphyrin into the conjugated polymer backbone leads to increased aggregation. These materials demonstrate that polymer morphology and performance can be tuned and enhanced effectively through the use of conjugatively linked porphyrins. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Single-particle cryo-electron microscopy of macromolecular complexes. (United States)

    Skiniotis, Georgios; Southworth, Daniel R


    Recent technological breakthroughs in image acquisition have enabled single-particle cryo-electron microscopy (cryo-EM) to achieve near-atomic resolution structural information for biological complexes. The improvements in image quality coupled with powerful computational methods for sorting distinct particle populations now also allow the determination of compositional and conformational ensembles, thereby providing key insights into macromolecular function. However, the inherent instability and dynamic nature of biological assemblies remain a tremendous challenge that often requires tailored approaches for successful implementation of the methodology. Here, we briefly describe the fundamentals of single-particle cryo-EM with an emphasis on covering the breadth of techniques and approaches, including low- and high-resolution methods, aiming to illustrate specific steps that are crucial for obtaining structural information by this method. © The Author 2015. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail:

  6. Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization. (United States)

    Lin, Qisheng; Miller, Gordon J


    complexity can be realized by small amounts of Li replacing Zn atoms in the parent binary compounds CaZn 2 , CaZn 3 , and CaZn 5 ; their phase formation and bonding schemes can be rationalized by Fermi surface-Brillouin zone interactions between nearly free-electron states. "Cation-rich", electron-poor polar intermetallics have emerged using rare earth metals as the electropositive ("cationic") component together metal/metalloid clusters that mimic the backbones of aromatic hydrocarbon molecules, which give evidence of extensive electronic delocalization and multicenter bonding. Thus, we can identify three distinct, valence electron-poor, polar intermetallic systems that have yielded unprecedented phases adopting novel structures containing complex clusters and intriguing bonding characteristics. In this Account, we summarize our recent specific progress in the developments of novel Au-rich BaAl 4 -type related structures, shown in the "gold-rich grid", lithiation-modulated Ca-Li-Zn phases stabilized by different bonding characteristics, and rare earth-rich polar intermetallics containing unprecedented hydrocarbon-like planar Co-Ge metal clusters and pronounced delocalized multicenter bonding. We will focus mainly on novel structural motifs, bonding analyses, and the role of valence electrons for phase stability.

  7. Structural Analysis of Protein Complexes by Cryo Electron Microscopy. (United States)

    Costa, Tiago R D; Ignatiou, Athanasios; Orlova, Elena V


    Structural studies of biocomplexes using single-particle cryo-electron microscopy (cryo-EM) is now a well-established technique in structural biology and has become competitive with X-ray crystallography. The latest advances in EM enable us to determine structures of protein complexes at 3-5 Å resolution for an extremely broad range of sizes from ~200 kDa up to hundreds of megadaltons (Bartesaghi et al., Science 348(6239):1147-1151, 2051; Bai et al., Nature 525(7568):212-217, 2015; Vinothkumar et al., Nature 515(7525):80-84, 2014; Grigorieff and Harrison, Curr Opin Struct Biol 21(2):265-273, 2011). The majority of biocomplexes comprise a number of different components and are not amenable to crystallisation. Secretion systems are typical examples of such multi-protein complexes, and structural studies of them are extremely challenging. The only feasible approach to revealing their spatial organisation and functional modification is cryo-EM. The development of systems for digital registration of images and algorithms for the fast and efficient processing of recorded images and subsequent analysis facilitated the determination of structures at near-atomic resolution. In this review we will describe sample preparation for cryo-EM, how data are collected by new detectors, and the logistics of image analysis through the basic steps required for reconstructions of both small and large biological complexes and their refinement to nearly atomic resolution. The processing workflow is illustrated using examples of EM analysis of a Type IV Secretion System.

  8. Defining the Electronic and Geometric Structure of One-Electron Oxidized Copper–Bis-phenoxide Complexes


    Storr, Tim; Verma, Pratik; Pratt, Russell C.; Wasinger, Erik C.; Shimazaki, Yuichi; Stack, T. Daniel P.


    The geometric and electronic structure of an oxidized Cu complex ([CuSal]+; Sal = N, N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) with a non-innocent salen ligand has been investigated both in the solid state and in solution. Integration of information from UV–vis–NIR spectroscopy, magnetic susceptibility, electrochemistry, resonance Raman spectroscopy, X-ray crystallography, X-ray absorption spectroscopy, and density functional theory calculations provides critical ...

  9. Host-guest complex of N-(2-chloroethyl), N-nitroso, N‧, N‧ -dicyclohexylsulfamid with β-cyclodextrin: Fluorescence, QTAIM analysis and structure-chemical reactivity (United States)

    Bensouilah, Nadjia; Fisli, Hassina; Bensouilah, Hamza; Zaater, Sihem; Abdaoui, Mohamed; Boutemeur-Kheddis, Baya


    In this work, the inclusion complex of DCY/CENS: N-(2-chloroethyl), N-nitroso, N‧, N‧-dicyclohexylsulfamid and β-cyclodextrin (β-CD) is investigated using the fluorescence spectroscopy, PM3, ONIOM2 and DFT methods. The experimental part reveals that DCY/CENS forms a 1:1 stoichiometric ratio inclusion complex with β-CD. The constant of stability is evaluated using the Benesi-Hildebrand equation. The results of the theoretical optimization showed that the lipophilic fraction of molecule (cyclohexyl group) is inside of β-CD. Accordingly, the Nitroso-Chloroethyl moiety is situated outside the cavity of the macromolecule host. The favorable structure of the optimized complex indicates the existence of weak intermolecular hydrogen bonds and the most important van der Waals (vdW) interactions which are studied on the basis of Natural Bonding Orbital (NBO) analysis. The NBO is employed to compute the electronic donor-acceptor exchanges between drug and β-CD. Furthermore, a detailed topological charge density analysis based on the quantum theory of atoms in molecules (QTAIM), has been accomplished on the most favorable complex using B3LYP/6-31G(d) method. The presence of stabilizing intermolecular hydrogen bonds and van der Waals interactions in the most favorable complex is predicted. Also, the energies of these interactions are estimated with Espinosa's formula. The findings of this investigation reveal that the correlation between the structural parameters and the electronic density is good. Finally, and based on DFT calculations, the reactivity of the interesting molecule in free state was studied and compared with that in the complexed state using chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors.

  10. Complex dynamics in planar two-electron quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Schroeter, Sebastian Josef Arthur


    Quantum dots play an important role in a wide range of recent experimental and technological developments. In particular they are promising candidates for realisations of quantum bits and further applications in quantum information theory. The harmonically confined Hooke's atom model is experimentally verified and separates in centre-of-mass and relative coordinates. Findings that are contradictory to this separability call for an extension of the model, in particular changing the confinement potential. In order to study effects of an anharmonic confinement potential on spectral properties of planar two-electron quantum dots a sophisticated numerical approach is developed. Comparison between the Helium atom, Hooke's atom and an anharmonic potential model are undertaken in order to improve the description of quantum dots. Classical and quantum features of complexity and chaos are investigated and used to characterise the dynamics of the system to be mixed regular-chaotic. Influence of decoherence can be described by quantum fidelity, which measures the effect of a perturbation on the time evolution. The quantum fidelity of eigenstates of the system depends strongly on the properties of the perturbation. Several methods for solving the time-dependent Schrödinger equation are implemented and a high level of accuracy for long time evolutions is achieved. The concept of offset entanglement, the entanglement of harmonic models in the noninteracting limit, is introduced. This concept explains different questions raised in the literature for harmonic quantum dot models, recently. It shows that only in the groundstate the electrons are not entangled in the fermionic sense. The applicability, validity, and origin of Hund's first rule in general quantum dot models is further addressed. In fact Hund's first rule is only applicable, and in this case also valid, for one pair of singlet and triplet states in Hooke's atom. For more realistic models of two-electron

  11. Cryo-Electron Tomography for Structural Characterization of Macromolecular Complexes (United States)

    Cope, Julia; Heumann, John; Hoenger, Andreas


    Cryo-electron tomography (cryo-ET) is an emerging 3-D reconstruction technology that combines the principles of tomographic 3-D reconstruction with the unmatched structural preservation of biological material embedded in vitreous ice. Cryo-ET is particularly suited to investigating cell-biological samples and large macromolecular structures that are too polymorphic to be reconstructed by classical averaging-based 3-D reconstruction procedures. This unit aims to make cryo-ET accessible to newcomers and discusses the specialized equipment required, as well as the relevant advantages and hurdles associated with sample preparation by vitrification and cryo-ET. Protocols describe specimen preparation, data recording and 3-D data reconstruction for cryo-ET, with a special focus on macromolecular complexes. A step-by-step procedure for specimen vitrification by plunge freezing is provided, followed by the general practicalities of tilt-series acquisition for cryo-ET, including advice on how to select an area appropriate for acquiring a tilt series. A brief introduction to the underlying computational reconstruction principles applied in tomography is described, along with instructions for reconstructing a tomogram from cryo-tilt series data. Finally, a method is detailed for extracting small subvolumes containing identical macromolecular structures from tomograms for alignment and averaging as a means to increase the signal-to-noise ratio and eliminate missing wedge effects inherent in tomographic reconstructions. PMID:21842467

  12. The 1:1 charge-transfer complex dibenzotetrathiafulvalene–pyromellitic dianhydride (DBTTF–PMDA

    Directory of Open Access Journals (Sweden)

    Margaret E. Payne


    Full Text Available The title charge-transfer (CT complex, C10H2O6·C14H8S4, composed of donor dibenzotetrathiafulvalene (DBTTF and acceptor pyromellitic dianhydride (PMDA, forms a mixed stacking pattern along the [-110] direction. The constituent molecules occupy crystallographic inversion centers. They are nearly parallel and lie ca.3.41 Å from each other. The crystals exhibit a high degree of donor/acceptor overlap [88.20 (4%] in the long direction of the DBTTF and PMDA molecules as compared with 51.27 (5% in the shortest direction of the molecules.

  13. Modelling of electron beam absorption in complex geometries (United States)

    Klassen, Alexander; Bauereiß, Andreas; Körner, Carolin


    Computational modelling of processes that involve highly energetic electrons like electron beam melting, welding, drilling or electron beam lithography, to name but a few, requires information about the attenuation of the electron beam as it passes through the sample. Depth-dose curves as a function of electron energy, target material as well as local surface obliquity have to be provided in situ during the calculation. The most efficient way to address this issue is by employing mathematical expressions. Therefore, we propose an electron beam model based on a set of semi-empirical equations available from different published literature and on theoretical considerations. Particular stress is thereby put on accuracy and the range of validity of the theoretical approach by comparison with experimental data. Finally, we apply our model to powder-bed based additive manufacturing. The numerical results demonstrate that electron beam absorption and depth of penetration have a strong influence on the quality of the fabricated product.


    Directory of Open Access Journals (Sweden)

    Vladimir A. Alekhin


    Full Text Available The educational complex on the electrical engineering and electronics has been developed. It contains a course of lectures and lecture notes in the electronic form, a new computer laboratory practical work and practical training. All electronic manuals are based on modeling of electric and electronic circuits in the new effective program TINA. The educational complex is being successfully used in educational process on internal and distant learning. 

  15. Improved Visualization of Vertebrate Nuclear Pore Complexes by Field Emission Scanning Electron Microscopy

    National Research Council Canada - National Science Library

    Shaulov, Lihi; Harel, Amnon


    Field emission scanning electron microscopy (FESEM) can provide high-resolution three-dimensional surface imaging of many biological structures, including nuclear envelopes and nuclear pore complexes (NPCs...

  16. Pure electronic metal-insulator transition at the interface of complex oxides

    National Research Council Canada - National Science Library

    Meyers, D; Liu, Jian; Freeland, J W; Middey, S; Kareev, M; Kwon, Jihwan; Zuo, J M; Chuang, Yi-De; Kim, J W; Ryan, P J; Chakhalian, J


    In complex materials observed electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism...

  17. Defining the Electronic and Geometric Structure of One-Electron Oxidized Copper–Bis-phenoxide Complexes (United States)

    Storr, Tim; Verma, Pratik; Pratt, Russell C.; Wasinger, Erik C.; Shimazaki, Yuichi; Stack, T. Daniel P.


    The geometric and electronic structure of an oxidized Cu complex ([CuSal]+; Sal = N, N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) with a non-innocent salen ligand has been investigated both in the solid state and in solution. Integration of information from UV–vis–NIR spectroscopy, magnetic susceptibility, electrochemistry, resonance Raman spectroscopy, X-ray crystallography, X-ray absorption spectroscopy, and density functional theory calculations provides critical insights into the nature of the localization/delocalization of the oxidation locus. In contrast to the analogous Ni derivative [NiSal]+ (Storr, T.; et al. Angew. Chem., Int. Ed. 2007, 46, 5198), which exists solely in the Ni(II) ligand-radical form, the locus of oxidation is metal-based for [CuSal]+, affording exclusively a Cu(III) species in the solid state (4–300 K). Variable-temperature solution studies suggest that [CuSal]+ exists in a reversible spin-equilibrium between a ligand-radical species [Cu(II)Sal•]+ (S = 1) and the high-valent metal form [Cu(III)Sal]+ (S = 0), indicative of nearly isoenergetic species. It is surprising that a bis-imine–bis-phenolate ligation stabilizes the Cu(III) oxidation state, and even more surprising that in solution a spin equilibrium occurs without a change in coordination number. The oxidized tetrahydrosalen analogue [CuSalred]+ (Salred = N, N′-bis(3,5-di-tert-butylhydroxybenzyl)-1,2-cyclohexane-(1R,2R)-diamine) exists as a temperature-invariant Cu(II)–ligand-radical complex in solution, demonstrating that ostensibly simple variations of the ligand structure affect the locus of oxidation in Cu–bis-phenoxide complexes. PMID:18939830

  18. Defining the Electronic And Geometric Structure of One-Electron Oxidized Copper-Bis-Phenoxide Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Storr, T.; Verma, P.; Pratt, R.C.; Wasinger, E.C.; Shimazaki, Y.; Stack, T.D.P.


    The geometric and electronic structure of an oxidized Cu complex ([CuSal](+); Sal = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) with a non-innocent salen ligand has been investigated both in the solid state and in solution. Integration of information from UV-vis-NIR spectroscopy, magnetic susceptibility, electrochemistry, resonance Raman spectroscopy, X-ray crystallography, X-ray absorption spectroscopy, and density functional theory calculations provides critical insights into the nature of the localization/delocalization of the oxidation locus. In contrast to the analogous Ni derivative [NiSal](+) (Storr, T.; et al. Angew. Chem., Int. Ed. 2007, 46, 5198), which exists solely in the Ni(II) ligand-radical form, the locus of oxidation is metal-based for [CuSal](+), affording exclusively a Cu(III) species in the solid state (4-300 K). Variable-temperature solution studies suggest that [CuSal](+) exists in a reversible spin-equilibrium between a ligand-radical species [Cu(II)Sal(*)](+) (S = 1) and the high-valent metal form [Cu(III)Sal](+) (S = 0), indicative of nearly isoenergetic species. It is surprising that a bis-imine-bis-phenolate ligation stabilizes the Cu(III) oxidation state, and even more surprising that in solution a spin equilibrium occurs without a change in coordination number. The oxidized tetrahydrosalen analogue [CuSal(red)](+) (Sal(red) = N,N'-bis(3,5-di- tert-butylhydroxybenzyl)-1,2-cyclohexane-(1R,2R)-diamine) exists as a temperature-invariant Cu(II)-ligand-radical complex in solution, demonstrating that ostensibly simple variations of the ligand structure affect the locus of oxidation in Cu-bis-phenoxide complexes.

  19. Defining the electronic and geometric structure of one-electron oxidized copper-bis-phenoxide complexes. (United States)

    Storr, Tim; Verma, Pratik; Pratt, Russell C; Wasinger, Erik C; Shimazaki, Yuichi; Stack, T Daniel P


    The geometric and electronic structure of an oxidized Cu complex ([CuSal](+); Sal = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) with a non-innocent salen ligand has been investigated both in the solid state and in solution. Integration of information from UV-vis-NIR spectroscopy, magnetic susceptibility, electrochemistry, resonance Raman spectroscopy, X-ray crystallography, X-ray absorption spectroscopy, and density functional theory calculations provides critical insights into the nature of the localization/delocalization of the oxidation locus. In contrast to the analogous Ni derivative [NiSal](+) (Storr, T.; et al. Angew. Chem., Int. Ed. 2007, 46, 5198), which exists solely in the Ni(II) ligand-radical form, the locus of oxidation is metal-based for [CuSal](+), affording exclusively a Cu(III) species in the solid state (4-300 K). Variable-temperature solution studies suggest that [CuSal](+) exists in a reversible spin-equilibrium between a ligand-radical species [Cu(II)Sal(*)](+) (S = 1) and the high-valent metal form [Cu(III)Sal](+) (S = 0), indicative of nearly isoenergetic species. It is surprising that a bis-imine-bis-phenolate ligation stabilizes the Cu(III) oxidation state, and even more surprising that in solution a spin equilibrium occurs without a change in coordination number. The oxidized tetrahydrosalen analogue [CuSal(red)](+) (Sal(red) = N,N'-bis(3,5-di- tert-butylhydroxybenzyl)-1,2-cyclohexane-(1R,2R)-diamine) exists as a temperature-invariant Cu(II)-ligand-radical complex in solution, demonstrating that ostensibly simple variations of the ligand structure affect the locus of oxidation in Cu-bis-phenoxide complexes.

  20. 77 FR 50726 - Software Requirement Specifications for Digital Computer Software and Complex Electronics Used in... (United States)


    ... COMMISSION Software Requirement Specifications for Digital Computer Software and Complex Electronics Used in... issuing for public comment draft regulatory guide (DG), DG-1209, ``Software Requirement Specifications for Digital Computer Software and Complex Electronics used in Safety Systems of Nuclear Power Plants.'' The DG...

  1. A facile, sensitive, and highly specific trinitrophenol assay based on target-induced synergetic effects of acid induction and electron transfer towards DNA-templated copper nanoclusters. (United States)

    Li, Haiyin; Chang, Jiafu; Hou, Ting; Ge, Lei; Li, Feng


    Reliable, selective and sensitive approaches for trinitrophenol (TNP) detection are highly desirable with respect to national security and environmental protection. Herein, a simple and novel fluorescent strategy for highly sensitive and specific TNP assay has been successfully developed, which is based on the quenching of the fluorescent poly(thymine)-templated copper nanoclusters (DNA-CuNCs), through the synergetic effects of acid induction and electron transfer. Upon the addition of TNP, donor-acceptor complexes between the electron-deficient nitro-groups in TNP and the electron-donating DNA templates are formed, resulting in the close proximity between TNP and CuNCs. Moreover, the acidity of TNP contributes to the pH decrease of the system. These factors combine to dramatically quench the fluorescence of DNA-CuNCs, providing a "signal-off" strategy for TNP sensing. The as-proposed strategy demonstrates high sensitivity for TNP assay, and a detection limit of 0.03μM is obtained, which is lower than those reported by using organic fluorescent materials. More significantly, this approach shows outstanding selectivity over a number of TNP analogues, such as 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4-dinitrophenol (DNP), 3-nitrophenol (NP), nitrobenzene (NB), phenol (BP), and toluene (BT). Compared with previous studies, this method does not need complex DNA sequence design, fluorescent dye labeling, or sophisticated organic reactions, rendering the strategy with additional advantages of simplicity and cost-effectiveness. In addition, the as-proposed strategy has been adopted for the detection of TNP in natural water samples, indicating its great potential to be applied in the fields of public safety and environmental monitoring. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Positronium Inhibition and Quenching by Organic Electron Acceptors and Charge Transfer Complexes

    DEFF Research Database (Denmark)

    Jansen, P.; Eldrup, Morten Mostgaard; Jensen, Bror Skytte


    Positron lifetime measurements were performed on a series of organic electron acceptors and charge-transfer complexes in solution. The acceptors cause both positronium (Ps) inhibition (with maybe one exception) and quenching, but when an acceptor takes part in a charge-transfer complex...... in terms of the spur reaction model of Ps formation. Correlation was also made to gas phase reaction between electron acceptors and free electron, as well as to pulse radiolysis data....

  3. High-resolution electron spectroscopy of lanthanide (Ce, Pr, and Nd) complexes of cyclooctatetraene: the role of 4f electrons. (United States)

    Kumari, Sudesh; Roudjane, Mourad; Hewage, Dilrukshi; Liu, Yang; Yang, Dong-Sheng


    Cerium, praseodymium, and neodymium complexes of 1,3,5,7-cyclooctatetraene (COT) complexes were produced in a laser-vaporization metal cluster source and studied by pulsed-field ionization zero electron kinetic energy spectroscopy and quantum chemical calculations. The computations included the second-order Møller-Plesset perturbation theory, the coupled cluster method with single, double, and perturbative triple excitations, and the state-average complete active space self-consistent field method. The spectrum of each complex exhibits multiple band systems and is assigned to ionization of several low-energy electronic states of the neutral complex. This observation is different from previous studies of M(COT) (M = Sc, Y, La, and Gd), for which a single band system was observed. The presence of the multiple low-energy electronic states is caused by the splitting of the partially filled lanthanide 4f orbitals in the ligand field, and the number of the low-energy states increases rapidly with increasing number of the metal 4f electrons. On the other hand, the 4f electrons have a small effect on the geometries and vibrational frequencies of these lanthanide complexes.

  4. Electronic Structure of Complex Materials: from First-principles study ...

    Indian Academy of Sciences (India)

    MOTIVATION. • Novel materials are key to new technologies. • Modeling is playing an ever increasing role in the search for new materials. • The chemistry controls the physical properties (e.g. electrical, magnetic, and optical properties) of materials. At the root of all are the Electrons! . – p.3/25 ...

  5. Electron Temperatures in W51 Complex from High Resolution, Low ...

    Indian Academy of Sciences (India)


    Mar 9, 2001 ... All the RRL results quoted above have been derived under the LTE approximation. The electron temperature is one of the most important parameters in understanding the physical properties of thermal HII regions. Low frequency continuum observations in the optically thick regime offer a direct estimate of ...

  6. Electron Capture Dissociation of Weakly Bound Polypeptide Polycationic Complexes

    DEFF Research Database (Denmark)

    Haselmann, Kim F; Jørgensen, Thomas J D; Budnik, Bogdan A


    We have previously reported that, in electron capture dissociation (ECD), rupture of strong intramolecular bonds in weakly bound supramolecular aggregates can proceed without dissociation of weak intermolecular bonds. This is now illustrated on a series of non-specific peptide-peptide dimers...

  7. Electronic Conductivity of Polypyrrole−Dodecyl Benzene Sulfonate Complexes

    DEFF Research Database (Denmark)

    West, Keld; Bay, Lasse; Nielsen, Martin Meedom


    The electronic conductivity of the electroactive polymer polypyrrole-dodecyl benzene sulfonate (PPy-DBS) has been characterized as function of the redox level. The polymer was synthesized with different isomers of the dopant anions: the common mixed DBS tenside and three well-defined synthetic...

  8. Electronically excited states of tryptamine and its microhydrated complex

    NARCIS (Netherlands)

    Schmitt, M.; Brause, R.; Marian, C.M.; Salzmann, S.; Meerts, W.L.


    The lowest electronically excited singlet states of tryptamine and the tryptamine (H2O)(1) cluster have been studied, using time dependent density functional theory for determination of the geometries and multireference configuration interaction for the vertical and adiabatic excitation energies,

  9. The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways. (United States)

    Tikhonov, Alexander N


    Regulation of photosynthetic electron transport at the level of the cytochrome b6f complex provides efficient performance of the chloroplast electron transport chain (ETC). In this review, after brief overview of the structural organization of the chloroplast ETC, the consideration of the problem of electron transport control is focused on the plastoquinone (PQ) turnover and its interaction with the b6f complex. The data available show that the rates of plastoquinol (PQH2) formation in PSII and its diffusion to the b6f complex do not limit the overall rate of electron transfer between photosystem II (PSII) and photosystem I (PSI). Analysis of experimental and theoretical data demonstrates that the rate-limiting step in the intersystem chain of electron transport is determined by PQH2 oxidation at the Qo-site of the b6f complex, which is accompanied by the proton release into the thylakoid lumen. The acidification of the lumen causes deceleration of PQH2 oxidation, thus impeding the intersystem electron transport. Two other mechanisms of regulation of the intersystem electron transport have been considered: (i) "state transitions" associated with the light-induced redistribution of solar energy between PSI and PSII, and (ii) redistribution of electron fluxes between alternative pathways (noncyclic electron transport and cyclic electron flow around PSI). Copyright © 2013 Elsevier Masson SAS. All rights reserved.

  10. Electron Temperatures in W51 Complex from High Resolution, Low ...

    Indian Academy of Sciences (India)

    We have made continuum radio observations of these HII regions of the W51 complex at 240, 610, 1060 and 1400 MHz using GMRT with lower resolution (20'' × 15'') at the lowest frequency. The observed spectra of the prominent thermal subcomponents of W51 have been fitted to a free-free emission spectrum and their ...

  11. Ab initio nonadiabatic molecular dynamics of the ultrafast electron injection from a PbSe quantum dot into the TiO2 surface. (United States)

    Long, Run; Prezhdo, Oleg V


    Following recent experiments [Science 2010, 328, 1543; PNAS 2011, 108, 965], we report an ab initio nonadiabatic molecular dynamics (NAMD) simulation of the ultrafast photoinduced electron transfer (ET) from a PbSe quantum dot (QD) into the rutile TiO(2) (110) surface. The system forms the basis for QD-sensitized semiconductor solar cells and demonstrates that ultrafast interfacial ET is instrumental for achieving high efficiencies in solar-to-electrical energy conversion. The simulation supports the observation that the ET successfully competes with energy losses due to electron-phonon relaxation. The ET proceeds by the adiabatic mechanism because of strong donor-acceptor coupling. High frequency polar vibrations of both QD and TiO(2) promote the ET, since these modes can rapidly influence the donor-acceptor state energies and coupling. Low frequency vibrations generate a distribution of initial conditions for ET, which shows a broad variety of scenarios at the single-molecule level. Compared to the molecule-TiO(2) interfaces, the QD-TiO(2) system exhibits pronounced differences that arise due to the larger size and higher rigidity of QDs relative to molecules. Both donor and acceptor states are more delocalized in the QD system, and the ET is promoted by optical phonons, which have relatively low frequencies in the QD materials composed of heavy elements. In contrast, in molecular systems, optical phonons are not thermally accessible under ambient conditions. Meanwhile, TiO(2) acceptor states resemble surface impurities due to the local influence of molecular chromophores. At the same time, the photoinduced ET at both QD-TiO(2) and molecule-TiO(2) interfaces is ultrafast and occurs by the adiabatic mechanism, as a result of strong donor-acceptor coupling. The reported state-of-the-art simulation generates a detailed time-domain atomistic description of the interfacial ET process that is fundamental to a wide variety of applications.

  12. Photoinduced intermolecular electron transfer in complex liquids: Experiment and theory (United States)

    Tavernier, H. L.; Kalashnikov, M. M.; Fayer, M. D.


    Photoinduced intermolecular electron transfer between Rhodamine 3B and N,N-dimethylaniline has been studied in a series of seven liquids: acetonitrile, ethanol, propylene glycol, and mixtures of ethanol, 2-butanol, ethylene glycol, propylene glycol, and glycerol. In each liquid, the donor and acceptors have different diffusion constants and experience distinct dielectric properties. Ps time-dependent fluorescence measurements and steady-state fluorescence yield measurements were made and analyzed using a detailed statistical mechanical theory that includes a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solvent structure. All solvent-dependent parameters necessary for calculations were measured, including dielectric constants, diffusion constants, and redox potentials, leaving the electronic coupling unknown. Taking the distance-dependence of the coupling to be β=1 Å-1, data were fit to a single parameter, the coupling matrix element at contact, J0. The theory is able to reproduce both the functional form of the time-dependence and the concentration-dependence of the data in all seven liquids by fitting only J0. Despite the substantial differences in the properties of the experimental systems studied, fits to the data are very good and the values for J0 are very similar for all solvents.

  13. Efficient charge separation in Li(+) @C60 supramolecular complexes with electron donors. (United States)

    Kawashima, Yuki; Ohkubo, Kei; Fukuzumi, Shunichi


    Lithium-ion-encapsulated fullerene (Li(+) @C60 ) exhibits greatly enhanced reactivity in photoinduced electron-transfer reduction with electron donors compared with pristine C60 . The enhanced reactivity of Li(+) @C60 results from the more positive one-electron reduction potential of Li(+) @C60 (+0.14 V versus a standard calomel electrode (SCE)) than that of C60 (-0.43 V versus SCE), whereas the reorganization energy of electron transfer of Li(+) @C60 (1.01 eV) becomes larger than that of C60 (0.73 eV) because of the change in electrostatic interactions of encapsulated Li(+) upon electron transfer. Li(+) @C60 can form strong supramolecular complexes with various anionic electron donors through electrostatic interactions. Li(+) @C60 can also form strong supramolecular π complexes with various electron donors, such as cyclic porphyrin dimers, corannulene, and crown ether fused monopyrrolotetrathiafulvalenes. Photoinduced electron transfer from electron donors to Li(+) @C60 afforded long-lived charge-separated states of supramolecular complexes between electron donors and Li(+) @C60 . A photoelectrochemical solar cell composed of supramolecular nanoclusters of Li(+) @C60 and zinc sulfonated meso-tetraphenylporphyrin exhibits significant enhancement in the photoelectrochemical performance than that of the reference system containing only a single component. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Virtual enterprise model for the electronic components business in the Nuclear Weapons Complex

    Energy Technology Data Exchange (ETDEWEB)

    Ferguson, T.J.; Long, K.S.; Sayre, J.A. [Sandia National Labs., Albuquerque, NM (United States); Hull, A.L. [Sandia National Labs., Livermore, CA (United States); Carey, D.A.; Sim, J.R.; Smith, M.G. [Allied-Signal Aerospace Co., Kansas City, MO (United States). Kansas City Div.


    The electronic components business within the Nuclear Weapons Complex spans organizational and Department of Energy contractor boundaries. An assessment of the current processes indicates a need for fundamentally changing the way electronic components are developed, procured, and manufactured. A model is provided based on a virtual enterprise that recognizes distinctive competencies within the Nuclear Weapons Complex and at the vendors. The model incorporates changes that reduce component delivery cycle time and improve cost effectiveness while delivering components of the appropriate quality.

  15. Ruthenium(II) Complex Based Photodiode for Organic Electronic Applications (United States)

    Tataroglu, A.; Ocaya, R.; Dere, A.; Dayan, O.; Serbetci, Z.; Al-Sehemi, Abdullah G.; Soylu, M.; Al-Ghamdi, Ahmed A.; Yakuphanoglu, F.


    In this study, the electrical and photoresponse properties of a photovoltaic device with Ruthenium(II) complex interfacial thin film were investigated. Heteroleptic Ru(II) complex including bidentate and tridentate ligands thin film was coated on n-Si substrate by the spin coating technique. From current-voltage ( I- V) measurements of an Au/Ru(II)/n-Si photodiode, it is observed that the reverse bias current under light is higher than that of the current in the dark. This indicates that the photodiode exhibits a photoconducting characteristic. The transient measurements such as photocurrent, photocapacitance and photoconductance were performed under various illumination conditions. These measurements indicate that the photodiode has a high photoresponsivity. The electrical parameters such as barrier height (Φb), ideality factor ( n) and series resistance ( R s) of the photodiode were determined from the analysis of I- V characteristics. Moreover, the capacitance/conductance-voltage characteristics of the photodiode highly depend on both voltage and frequency. Results show that the heterojunction can be used for various optoelectronic applications.

  16. Ruthenium(II) Complex Based Photodiode for Organic Electronic Applications (United States)

    Tataroglu, A.; Ocaya, R.; Dere, A.; Dayan, O.; Serbetci, Z.; Al-Sehemi, Abdullah G.; Soylu, M.; Al-Ghamdi, Ahmed A.; Yakuphanoglu, F.


    In this study, the electrical and photoresponse properties of a photovoltaic device with Ruthenium(II) complex interfacial thin film were investigated. Heteroleptic Ru(II) complex including bidentate and tridentate ligands thin film was coated on n-Si substrate by the spin coating technique. From current-voltage (I-V) measurements of an Au/Ru(II)/n-Si photodiode, it is observed that the reverse bias current under light is higher than that of the current in the dark. This indicates that the photodiode exhibits a photoconducting characteristic. The transient measurements such as photocurrent, photocapacitance and photoconductance were performed under various illumination conditions. These measurements indicate that the photodiode has a high photoresponsivity. The electrical parameters such as barrier height (Φb), ideality factor (n) and series resistance (R s) of the photodiode were determined from the analysis of I-V characteristics. Moreover, the capacitance/conductance-voltage characteristics of the photodiode highly depend on both voltage and frequency. Results show that the heterojunction can be used for various optoelectronic applications.

  17. Observation of Electronic Excitation Transfer Through Light Harvesting Complex II Using Two-Dimensional Electronic-Vibrational Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, NHC; Gruenke, NL; Oliver, TAA; Ballottari, M; Bassi, R; Fleming, GR


    Light-harvesting complex II (LHCII) serves a central role in light harvesting for oxygenic photosynthesis and is arguably the most important photosynthetic antenna complex. In this article, we present two-dimensional electronic–vibrational (2DEV) spectra of LHCII isolated from spinach, demonstrating the possibility of using this technique to track the transfer of electronic excitation energy between specific pigments within the complex. We assign the spectral bands via comparison with the 2DEV spectra of the isolated chromophores, chlorophyll a and b, and present evidence that excitation energy between the pigments of the complex are observed in these spectra. Lastly, we analyze the essential components of the 2DEV spectra using singular value decomposition, which makes it possible to reveal the relaxation pathways within this complex.

  18. Application of models for exchange of electronic documents in complex administrative services (United States)

    Glavev, Victor


    The report presents application of models for exchange of electronic documents between different administrations in government and business sectors. It shows the benefits of implementing electronic exchange of documents between different local offices of one administration in government sector such as a municipality and the way it is useful for implementing complex administrative services.

  19. Exploring the Interaction Natures in Plutonyl (VI) Complexes with Topological Analyses of Electron Density


    Jiguang Du; Xiyuan Sun; Gang Jiang


    The interaction natures between Pu and different ligands in several plutonyl (VI) complexes are investigated by performing topological analyses of electron density. The geometrical structures in both gaseous and aqueous phases are obtained with B3LYP functional, and are generally in agreement with available theoretical and experimental results when combined with all-electron segmented all-electron relativistic contracted (SARC) basis set. The Pu– O y l bond orders show significant line...

  20. Data Mining Approaches for Modeling Complex Electronic Circuit Design Activities

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Yongjin [Ajou University, Suwon, South Korea; Omitaomu, Olufemi A [ORNL; Wang, Gi-Nam [Ajou University, Suwon, South Korea


    A printed circuit board (PCB) is an essential part of modern electronic circuits. It is made of a flat panel of insulating materials with patterned copper foils that act as electric pathways for various components such as ICs, diodes, capacitors, resistors, and coils. The size of PCBs has been shrinking over the years, while the number of components mounted on these boards has increased considerably. This trend makes the design and fabrication of PCBs ever more difficult. At the beginning of design cycles, it is important to estimate the time to complete the steps required accurately, based on many factors such as the required parts, approximate board size and shape, and a rough sketch of schematics. Current approach uses multiple linear regression (MLR) technique for time and cost estimations. However, the need for accurate predictive models continues to grow as the technology becomes more advanced. In this paper, we analyze a large volume of historical PCB design data, extract some important variables, and develop predictive models based on the extracted variables using a data mining approach. The data mining approach uses an adaptive support vector regression (ASVR) technique; the benchmark model used is the MLR technique currently being used in the industry. The strengths of SVR for this data include its ability to represent data in high-dimensional space through kernel functions. The computational results show that a data mining approach is a better prediction technique for this data. Our approach reduces computation time and enhances the practical applications of the SVR technique.

  1. Tuning electronic structure and optical properties of SrTiO{sub 3} by site-specific doping by Nb with N/B from hybrid functional calculations

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yanyu; Zhou, Wei; Wu, Ping, E-mail:


    In this study, the extensive density functional theory calculations are performed to modify the electronic structure of perovskite SrTiO{sub 3} by doping with Nb and N/B. The unoccupied states induced by the Nb monodoping at the Sr or Ti site, which were passivated in the codoped systems (the substitution of Nb at Ti site with the replacement of N at O site: Nb@Ti/N@O and the substitution of Nb at Sr site with the replacement of B at O site: Nb@Sr/B@O). The charge-compensated donor-acceptor pair codoping creates the new occupied states within the band gap, which yields the absorption edge extend to visible light. And the calculated defect formation energy implies that the codoped systems are energetically favorable under the O-rich condition. Moreover, the band-edge alignment confirmed that the Nb@Ti/N@O system is desirable for the spontaneous water splitting under visible light and the Nb@Sr/B@O system can split water into hydrogen in presence of sacrificial agent. - Highlights: • A systematical study has been employed on SrTiO{sub 3} with the donor-acceptor codoping. • The donor-acceptor pair codoping yields the absorption edge extend to visible light. • The formation energy implies that the codoped systems are favorable under the O-rich condition. • The Nb@Ti/N@O system is desirable for the spontaneous water splitting under visible light. • The Nb@Sr/B@O system can split water into hydrogen in presence of sacrificial agent.

  2. Reactivity of seventeen- and nineteen-valence electron complexes in organometallic chemistry (United States)

    Stiegman, Albert E.; Tyler, David R.


    A guideline to the reactivity of 17- and 19-valence electron species in organometallic chemistry is proposed which the authors believe will supersede all others. The thesis holds that the reactions of 17-electron metal radicals are associatively activated with reactions proceeding through a 19-valence electron species. The disparate reaction chemistry of the 17-electron metal radicals are unified in terms of this associative reaction pathway, and the intermediacy of 19-valence electron complexes in producing the observed products is discussed. It is suggested that related associatively activated pathways need to be considered in some reactions that are thought to occur by more conventional routes involving 16- and 18-electron intermediates. The basic reaction chemistry and electronic structures of these species are briefly discussed.

  3. Metal complex-based electron-transfer mediators in dye-sensitized solar cells (United States)

    Elliott, C. Michael; Sapp, Shawn A.; Bignozzi, Carlo Alberto; Contado, Cristiano; Caramori, Stefano


    This present invention provides a metal-ligand complex and methods for using and preparing the same. In particular, the metal-ligand complex of the present invention is of the formula: L.sub.a-M-X.sub.b where L, M, X, a, and b are those define herein. The metal-ligand complexes of the present invention are useful in a variety of applications including as electron-transfer mediators in dye-sensitized solar cells and related photoelectrochromic devices.

  4. Photoelectron spectroscopy of hexachloroplatinate-nucleobase complexes: Nucleobase excited state decay observed via delayed electron emission (United States)

    Sen, Ananya; Matthews, Edward M.; Hou, Gao-Lei; Wang, Xue-Bin; Dessent, Caroline E. H.


    We report low-temperature photoelectron spectra of isolated gas-phase complexes of the hexachloroplatinate dianion bound to the nucleobases uracil, thymine, cytosine, and adenine. The spectra display well-resolved, distinct peaks that are consistent with complexes where the hexachloroplatinate dianion is largely intact. Adiabatic electron detachment energies for the hexachloroplatinate-nucleobase complexes are measured as 2.26-2.36 eV. The magnitudes of the repulsive Coulomb barriers (RCBs) of the complexes are all ˜1.7 eV, values that are lower than the RCB of the uncomplexed PtCl62- dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four clusters. The 266 nm spectra of the PtCl62- ṡ thymine and PtCl62- ṡ adenine complexes also display very prominent delayed electron emission bands. These results mirror recent results on the related Pt(CN)42- ṡ nucleobase complexes [A. Sen et al., J. Phys. Chem. B 119, 11626 (2015)]. The observation of delayed electron emission bands in the PtCl62- ṡ nucleobase spectra obtained in this work, as for the previously studied Pt(CN)42- ṡ nucleobase complexes, is attributed to one-photon excitation of nucleobase-centred excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment. Moreover, the selective, strong excitation of the delayed emission bands in the 266 nm spectra is linked to fundamental differences in the individual nucleobase photophysics at this excitation energy. This strongly supports our previous suggestion that the dianion within these clusters can be viewed as a "dynamic tag" which has the propensity to emit electrons when the attached nucleobase decays over a time scale long enough to allow autodetachment.

  5. Features of transformation of impurity-defect complexes in СdTe:Сl under the influence of microwave radiation

    Directory of Open Access Journals (Sweden)

    Budzulyak S. I.


    Full Text Available High-resistance cadmium telluride single crystals are promising material for production of ionizing radiation detectors. To increase crystal resistance, they are doped with chlorine. The detector quality depends on uniformity of chlorine impurity distribution over crystal. It is known that low-dose microwave irradiation can homogenize impurity distribution in a specimen. In the present work, we made an attempt to improve the detector material quality by using such post-technological treatment, as well as to study state variation for impurity-defect complexes. To this end, the effect of microwave irradiation on transformation of impurity-defect complexes in CdTe:Cl single crystals was investigated using low-temperature photoluminescence. It is shown that activation of ClTe donor centers by microwave irradiation for 10 s and presence of VCd acceptor centers in the specimens under investigation effectively facilitate formation of (VNd–ClTe defect centers at which excitons are bound. Detailed investigations of the band form for donor-acceptor pairs (DAPs in CdTe:Cl single crystals made it possible to determine the Huang—Rhys factor (that characterizes electron-phonon interaction in CdTe:Cl DAPs as a function of microwave treatment duration. It is shown for single crystals with NCl = 5·1017 cm–3 and 5·1019 cm–3 that the Huang—Rhys factor grows with microwave irradiation dose. This is related to both homogenization of donor and acceptor centers distribution and increase of donor—acceptor spacing. It is shown that microwave irradiation of CdTe:Cl single crystals results in concentration reduction for separate cadmium vacancies VCd because of formation of (VNd—ClTe defect centers at which excitons are bound.

  6. Pyran-Squaraine as Photosensitizers for Dye-Sensitized Solar Cells: DFT/TDDFT Study of the Electronic Structures and Absorption Properties

    Directory of Open Access Journals (Sweden)

    Reda M. El-Shishtawy


    Full Text Available In an effort to provide, assess, and evaluate a theoretical approach which enables designing efficient donor-acceptor dye systems, the electronic structure and optical properties of pyran-squaraine as donor-acceptor dyes used in dye-sensitized solar cells were investigated. Ground state properties have been computed at the B3LYP/6-31+G** level of theory. The long-range corrected density functionals CAM-B3LYP, PBEPBE, PBE1PBE (PBE0, and TPSSH with 6-311++G** were employed to examine absorption properties of the studied dyes. In an extensive comparison between experimental results and ab initio benchmark calculations, the TPSSH functional with 6-311++G** basis set was found to be the most appropriate in describing the electronic properties for the studied pyran and squaraine dyes. Natural transition orbitals (NTO, frontier molecular orbitals (FMO, LUMO, HOMO, and energy gaps, of these dyes, have been analyzed to show their effect on the process of electron injection and dye regeneration. Interaction between HOMO and LUMO of pyran and squaraine dyes was investigated to understand the recombination process and charge-transfer process involving these dyes. Additionally, we performed natural bond orbital (NBO analysis to investigate the role of charge delocalization and hyperconjugative interactions in the stability of the molecule.

  7. Molecular Understanding of Fullerene - Electron Donor Interactions in Organic Solar Cells

    KAUST Repository

    Ryno, Sean


    Organic solar cells hold promise of providing low-cost, renewable power generation, with current devices providing up to 13% power conversion efficiency. The rational design of more performant systems requires an in-depth understanding of the interactions between the electron donating and electron accepting materials within the active layers of these devices. Here, we explore works that give insight into the intermolecular interactions between electron donors and electron acceptors, and the impact of molecular orientations and environment on these interactions. We highlight, from a theoretical standpoint, the effects of intermolecular interactions on the stability of charge carriers at the donor/acceptor interface and in the bulk and how these interactions influence the nature of the charge transfer states as wells as the charge separation and charge transport processes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Bound Exciton Complexes (United States)

    Meyer, B. K.

    In the preceding chapter, we concentrated on the properties of free excitons. These free excitons may move through the sample and hit a trap, a nonradiative or a radiative recombination center. At low temperatures, the latter case gives rise to either deep center luminescence, mentioned in Sect. 7.1 and discussed in detail in Chap. 9, or to the luminescence of bound exciton complexes (BE or BEC). The chapter continues with the most prominent of these BECs, namely A-excitons bound to neutral donors. The next aspects are the more weakly BEs at ionized donors. The Sect. 7.4 treats the binding or localization energies of BEC from a theoretical point of view, while Sect. 7.5 is dedicated to excited states of BECs, which contain either holes from deeper valence bands or an envelope function with higher quantum numbers. The last section is devoted to donor-acceptor pair transitions. There is no section devoted specifically to excitons bound to neutral acceptors, because this topic is still partly controversially discussed. Instead, information on these A0X complexes is scattered over the whole chapter, however, with some special emphasis seen in Sects. 7.1, 7.4, and 7.5.

  9. Role of protein fluctuation correlations in electron transfer in photosynthetic complexes (United States)

    Nesterov, Alexander I.; Berman, Gennady P.


    We consider the dependence of the electron transfer in photosynthetic complexes on correlation properties of random fluctuations of the protein environment. The electron subsystem is modeled by a finite network of connected electron (exciton) sites. The fluctuations of the protein environment are modeled by random telegraph processes, which act either collectively (correlated) or independently (uncorrelated) on the electron sites. We derived an exact closed system of first-order linear differential equations with constant coefficients, for the average density matrix elements and for their first moments. Under some conditions, we obtained analytic expressions for the electron transfer rates and found the range of parameters for their applicability by comparing with the exact numerical simulations. We also compared the correlated and uncorrelated regimes and demonstrated numerically that the uncorrelated fluctuations of the protein environment can, under some conditions, either increase or decrease the electron transfer rates.

  10. Electronic coherence and the kinetics of inter-complex energy transfer in light-harvesting systems. (United States)

    Huo, Pengfei; Miller, Thomas F


    We apply real-time path-integral dynamics simulations to characterize the role of electronic coherence in inter-complex excitation energy transfer (EET) processes. The analysis is performed using a system-bath model that exhibits the essential features of light-harvesting networks, including strong intra-complex electronic coupling and weak inter-complex coupling. Strong intra-complex coupling is known to generate both static and dynamic electron coherences, which delocalize the exciton over multiple chromophores and potentially influence the inter-complex EET dynamics. With numerical results from partial linearized density matrix (PLDM) real-time path-integral calculations, it is found that both static and dynamic coherence are correlated with the rate of inter-complex EET. To distinguish the impact of these two types of intra-complex coherence on the rate of inter-complex EET, we use Multi-Chromophore Förster Resonance Energy Transfer (MC-FRET) theory to map the original parameterization of the system-bath model to an alternative parameterization for which the effects of static coherence are preserved while the effects of dynamic coherence are largely eliminated. It is then shown that both parameterizations of the model (i.e., the original that supports dynamic coherence and the alternative that eliminates it), exhibit nearly identical EET kinetics and population dynamics over a wide range of parameters. These observations are found to hold for cases in which either the EET donor or acceptor is a dimeric complex and for cases in which the dimeric complex is either symmetric or asymmetric. The results from this study suggest that dynamic coherence plays only a minor role in the actual kinetics of inter-complex EET, whereas static coherence largely governs the kinetics of incoherent inter-complex EET in light-harvesting networks.

  11. Influence of Humic Acid Complexation with Metal Ions on Extracellular Electron Transfer Activity (United States)

    Zhou, Shungui; Chen, Shanshan; Yuan, Yong; Lu, Qin


    Humic acids (HAs) can act as electron shuttles and mediate biogeochemical cycles, thereby influencing the transformation of nutrients and environmental pollutants. HAs commonly complex with metals in the environment, but few studies have focused on how these metals affect the roles of HAs in extracellular electron transfer (EET). In this study, HA-metal (HA-M) complexes (HA-Fe, HA-Cu, and HA-Al) were prepared and characterized. The electron shuttle capacities of HA-M complexes were experimentally evaluated through microbial Fe(III) reduction, biocurrent generation, and microbial azoreduction. The results show that the electron shuttle capacities of HAs were enhanced after complexation with Fe but were weakened when using Cu or Al. Density functional theory calculations were performed to explore the structural geometry of the HA-M complexes and revealed the best binding sites of the HAs to metals and the varied charge transfer rate constants (k). The EET activity of the HA-M complexes were in the order HA-Fe > HA-Cu > HA-Al. These findings have important implications for biogeochemical redox processes given the ubiquitous nature of both HAs and various metals in the environment. PMID:26593782

  12. Disentangling electronic and vibrational coherence in the Phycocyanin-645 light-harvesting complex

    CERN Document Server

    Richards, Gethin H; Curmi, Paul M G; Davis, Jeffrey A


    Energy transfer between chromophores in photosynthesis proceeds with near unity quantum efficiency. Understanding the precise mechanisms of these processes is made difficult by the complexity of the electronic structure and interactions with different vibrational modes. Two-dimensional spectroscopy has helped resolve some of the ambiguities and identified quantum effects that may be important for highly efficient energy transfer. Many questions remain, however, including whether the coherences observed are electronic and/or vibrational in nature and what role they play. We utilise a two-colour four-wave mixing experiment with control of the wavelength and polarization to selectively excite specific coherence pathways. For the light-harvesting complex PC645, from cryptophyte algae, we reveal and identify specific contributions from both electronic and vibrational coherences and determine an excited state structure based on two strongly-coupled electronic states and two vibrational modes. Separation of the cohe...

  13. Geometric and electronic structure of a peroxomanganese(III) complex supported by a scorpionate ligand. (United States)

    Colmer, Hannah E; Geiger, Robert A; Leto, Domenick F; Wijeratne, Gayan B; Day, Victor W; Jackson, Timothy A


    A monomeric Mn(II) complex has been prepared with the facially-coordinating Tp(Ph2) ligand, (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate). The X-ray crystal structure shows three coordinating solvent molecules resulting in a six-coordinate complex with Mn-ligand bond lengths that are consistent with a high-spin Mn(II) ion. Treatment of this Mn(II) complex with excess KO2 at room temperature resulted in the formation of a Mn(III)-O2 complex that is stable for several days at ambient conditions, allowing for the determination of the X-ray crystal structure of this intermediate. The electronic structure of this peroxomanganese(III) adduct was examined by using electronic absorption, electron paramagnetic resonance (EPR), low-temperature magnetic circular dichroism (MCD), and variable-temperature variable-field (VTVH) MCD spectroscopies. Density functional theory (DFT), time-dependent (TD)-DFT, and multireference ab initio CASSCF/NEVPT2 calculations were used to assign the electronic transitions and further investigate the electronic structure of the peroxomanganese(III) species. The lowest ligand-field transition in the electronic absorption spectrum of the Mn(III)-O2 complex exhibits a blue shift in energy compared to other previously characterized peroxomanganese(III) complexes that results from a large axial bond elongation, reducing the metal-ligand covalency and stabilizing the σ-antibonding Mn dz(2) MO that is the donor MO for this transition.

  14. A managerial framework for an electronic government procurement project: complex software projects management fundamentals


    Uzal, Roberto; Montejano, Germán Antonio; Riesco, Daniel Eduardo; Uzal, Javier


    An Electronic Government Procurement (e-GP) project, as most of complex software systems development and implantation, requires sophisticated and strong managerial concepts and skills. So, an effective and consistent managerial framework is needed. Traditional project management models, that propose a series of good practices and tools, must be extended, modified and improved to face, as an example, Electronic Government (e-Government) applications. These additional capabilities are very i...

  15. Electron Paramagnetic Resonance Spectroscopy of Photosynthetic Systems and Inorganic Model Complexes. (United States)

    Dexheimer, Susan Lynne


    This thesis discusses the application of parallel polarization electron paramagnetic resonance (EPR) spectroscopy, a technique sensitive to formally forbidden transitions in high spin states, to the study of the electronic structure of photosynthetic electron transfer centers and related inorganic model complexes. The theoretical basis for the origin of the parallel polarization transitions and the interpretation of the resulting spectra is presented, and experimental aspects of the detection of parallel polarization transitions are discussed. Parallel polarization EPR was used to study inorganic complexes of trivalent manganese that serve as models for the spectroscopic properties of biological electron transfer centers. X-band EPR spectra were detected from non-Kramers spin states of these complexes. EPR spectra of the S = 2 ground states of the mononuclear complexes Mn(III) tris -acetylacetonate and Mn(III) tris-picolinate and a low-lying excited state of the weakly antiferromagnetically coupled binuclear complex Mn_2(III,III) O(O_2CCH_3) _2 (HB(pz)_3) _2 (HB(pz)_3 = hydrotris(1-pyrazolyl)borate) are discussed. The spectra are interpreted using numerical simulations. Application of parallel polarization EPR to photosyntheic systems led to the detection of a new paramagnetic intermediate associated with photosynthetic water oxidation. The parallel polarization EPR signal is assigned to an S = 1 spin state of an exchange-coupled manganese center in the resting (S_1) state of the photosynthetic oxygen-evolving complex. The properties of the S _1 state parallel polarization EPR signal indicate that it corresponds to the reduced form of the species that gives rise to the previously established multiline conventional EPR signal in the light-induced S _2 state, and the behavior of the signal upon advancement to the S_2 state demonstrates the presence of two separate redox-active centers in the oxygen-evolving complex. The implications for the electronic structure of

  16. Classification of the Electronic Properties of Chelating Ligands in cis-[LL'Rh(CO)2] Complexes. (United States)

    Canac, Yves; Lepetit, Christine


    By analogy to the Tolman electronic parameter, a ligand electronic parameter, referred to as L2EP, is introduced here for estimating the donating ability of chelating ligands, featuring two coordinating extremities. It is based on the average of the computed infrared stretching frequencies of CO in a series of isostructural rhodium(I)-dicarbonyl complexes, that is linearly correlated to the number x of N-heterocyclic carbene coordinating ends (x = 0, 1, or 2). The L2EP values allow the design of an unified scale for the classification of the electron donation of chelating ligands, based on an ortho-phenylene bridge substituted by two coordinating extremities, which may have a different donating character. Strengths and limitations of the L2EP scale are illustrated for a large diversity of bidentate chelating ligands with coordinating ends ranging from extremely electron-rich phosphonium yldiides to extremely electron-poor amidiniophosphonites.

  17. Novel multi-chromophor light absorber concepts for DSSCs for efficient electron injection

    Energy Technology Data Exchange (ETDEWEB)

    Schuetz, Robert; Strothkaemper, Christian; Bartelt, Andreas; Hannappel, Thomas; Eichberger, Rainer [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Fasting, Carlo [Institut fuer Organische Chemie, Freie Universitaet Berlin, Takustrasse 3, 14195 Berlin (Germany); Thomas, Inara [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Institut fuer Organische Chemie, Freie Universitaet Berlin, Takustrasse 3, 14195 Berlin (Germany)


    Dye sensitized solar cells (DSSCs) operate by injecting electrons from the excited state of a light-harvesting dye into the continuum of conduction band states of a wide bandgap semiconductor. The light harvesting efficiency of pure organic dyes is limited by a narrow spectral electronic transition. A beneficial broad ground state absorption in the VIS region can be achieved by applying a single molecular dye system with multiple chromophors involving a Foerster resonance energy transfer (FRET) mechanism for an efficient electron injection. A model donor acceptor dye system capable for FRET chemically linked to colloidal TiO{sub 2} and ZnO nanorod surfaces was investigated in UHV environment. We used VIS/NIR femtosecond transient absorption spectroscopy and optical pump terahertz probe spectroscopy to study the charge injection dynamics of the antenna system. Different chromophors attached to a novel scaffold/anchor system connecting the organic absorber unit to the metal oxide semiconductor were probed.


    Directory of Open Access Journals (Sweden)

    R. E. Khoma


    Full Text Available The literature data on the synthesis, stoichiometry, structure and relative stability of molecular  complexes of sulphur dioxide with N,O-containing organic bases have been systematized and  generalized. It was shown that the yield of the reaction product of sulfur dioxide with organic  bases (such as amines are strongly influenced by the conditions of synthesis: the nature of  the solvent (basicity, polarity, the temperature and SO2:L ratio in the reaction medium. The stoichiometry of SO2*nL molecular complexes depends on ligand denticity, as well as its  ability to H-bonding. The reaction of the sulfur oxide (IV with organic bases can give S←N and S←O complexes. With the increase of the value of base proton affinity the decrease ΔrSN values has been marked. Characteristic parameter Δr SN = r SN – a1(rS+ rN (where rSNis the S←N donor-acceptor bond length has been determined by microwave spectroscopy and X-ray analysis, rSand rNwere the tabulated values of the homopolar covalent radii of sulphur and nitrogen heteroatoms. The dependence of formation enthalpy of molecular complexes of basic amines and spectral characteristics has been noted; enthalpy-entropy compensation for S←N and S←O complex-es has been stated. Despite the limited experimental data on the thermodynamics of complex formation and the lengths of donor-acceptor bonds for the same compounds it has been found bond S←N strength in SO2 molecular complexes to depend on the intrinsic value of ΔrSN. The contribution of van der Waals forces and charge transfer forces to the formation of molecular complexes of sulphur dioxide has been stated.

  19. Electronic structure of the [MNH2]+ (M = Sc-Cu) complexes. (United States)

    Hendrickx, Marc F A; Clima, Sergiu


    B3LYP geometry optimizations for the [MNH2]+ complexes of the first-row transition metal cations (Sc+-Cu+) were performed. Without any exception the ground states of these unsaturated amide complexes were calculated to possess planar geometries. CASPT2 binding energies that were corrected for zero-point energies and including relativistic effects show a qualitative trend across the series that closely resembles the experimental observations. The electronic structures for the complexes of the early and middle transition metal cations (Sc+-Co+) differ from the electronic structures derived for the complexes of the late transition metal cations (Ni+ and Cu+). For the former complexes the relative higher position of the 3d orbitals above the singly occupied 2p(pi) HOMO of the uncoordinated NH2 induces an electron transfer from the 3d shell to 2p(pi). The stabilization of the 3d orbitals from the left to the right along the first-row transition metal series causes these orbitals to become situated below the HOMO of the NH2 ligand for Ni+ and Cu+, preventing a transfer from occurring in the [MNH2]+ complexes of these metal cations. Analysis of the low-lying states of the amide complexes revealed a rather unique characteristic of their electronic structures that was found across the entire series. Rather exceptionally for the whole of chemistry, pi-type interactions were calculated to be stronger than the corresponding sigma-type interactions. The origin of this extraordinary behavior can be ascribed to the low-lying sp2 lone pair orbital of the NH2 ligand with respect to the 3d level.

  20. Metadislocations in complex metallic alloys: A high-resolution scanning transmission electron microscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Heggen, Marc; Houben, Lothar; Feuerbacher, Michael [Ernst Ruska Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Juelich GmbH, D-52425 Juelich (Germany)


    Metadislocations are highly complex defects which involve several hundreds of atoms in their core. We present a microstructural investigation on Metadislocations using aberration-corrected high-resolution scanning transmission electron microscopy. A novel and highly complex deformation mechanism is found which is based on the movement of a metadislocation core mediating strain and separate escort defects. Upon deformation, the escort defects move along with the metadislocation core and locally transform the material structure. This mechanism implies the coordinated movement of hundreds of atoms per elementary step. Although the mechanism is very complex, it can be described by a simple jigsaw-puzzle-like rearrangement of basic structural subunits.

  1. Integrative Modeling of Biomolecular Complexes : HADDOCKing with Cryo-Electron Microscopy Data

    NARCIS (Netherlands)

    van Zundert, Gydo C P; Melquiond, Adrien S J; Bonvin, Alexandre M J J


    Protein-protein interactions play a central role in all cellular processes. Insight into their atomic architecture is therefore of paramount importance. Cryo-electron microscopy (cryo-EM) is capable of directly imaging large macromolecular complexes. Unfortunately, the resolution is usually not

  2. Direct observation of surface reconstruction and termination on a complex metal oxide catalyst by electron microscopy

    KAUST Repository

    Zhu, Yihan


    On the surface: The surface reconstruction of an MoVTeO complex metal oxide catalyst was observed directly by various electron microscopic techniques and the results explain the puzzling catalytic behavior. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Localising versus standardising electronic human resource management: complexities and tensions between HRM and IT departments

    NARCIS (Netherlands)

    Tate, Mary; Furtmueller-Ettinger, Elfriede; Wilderom, Celeste P.M.


    In this paper, we provide an analysis of the complexities involved during global e-HRM (Electronic Human Resource Management) implementation. We present findings from a case study on the challenge of global integration versus local responsiveness of e-HRM systems. We take a local site lens,

  4. Renormalization of Optical Excitations in Molecules near a Metal Surface

    DEFF Research Database (Denmark)

    García Lastra, Juan Maria; Thygesen, Kristian Sommer


    The lowest electronic excitations of benzene and a set of donor-acceptor molecular complexes are calculated for the gas phase and on the Al(111) surface using the many-body Bethe-Salpeter equation. The energy of the charge-transfer excitations obtained for the gas phase complexes are found to be ...

  5. Non-electronic communication aids for people with complex communication needs. (United States)

    Iacono, Teresa; Lyon, Katie; West, Denise


    Non-electronic communication aids provide one form of augmentative and alternative communication (AAC) for people with complex communication needs. The aim here was to explore non-electronic communication aids as one AAC option and research challenges. This aim was addressed by reviewing funding for the provision of AAC systems, data from an Australian pilot project providing non-electronic communication aids, an audit of aided AAC published studies (2000-2009), and discussion of the review literature. Combined, these sources indicate that although there is great demand for non-electronic communication aids, funding schemes, both in Australia and internationally, have focused on electronic communication aids. Such funding has usually failed to meet the total device costs and has not provided for adequate speech-language pathology support. Data from the pilot indicated the demand for non-electronic communication aids, and patterns suggest potential factors that govern the types selected. Despite the high demand for non-electronic aids, the research literature has tended to focus on electronic communication aids, including within intervention studies and addressing design features and long-term outcomes. Concerns about ensuring that AAC systems are chosen according to the assessed needs of individuals are discussed within the context of limitations in outcomes research and appropriate outcome measures.

  6. Managing complex research datasets using electronic tools: A meta-analysis exemplar (United States)

    Brown, Sharon A.; Martin, Ellen E.; Garcia, Theresa J.; Winter, Mary A.; García, Alexandra A.; Brown, Adama; Cuevas, Heather E.; Sumlin, Lisa L.


    Meta-analyses of broad scope and complexity require investigators to organize many study documents and manage communication among several research staff. Commercially available electronic tools, e.g., EndNote, Adobe Acrobat Pro, Blackboard, Excel, and IBM SPSS Statistics (SPSS), are useful for organizing and tracking the meta-analytic process, as well as enhancing communication among research team members. The purpose of this paper is to describe the electronic processes we designed, using commercially available software, for an extensive quantitative model-testing meta-analysis we are conducting. Specific electronic tools improved the efficiency of (a) locating and screening studies, (b) screening and organizing studies and other project documents, (c) extracting data from primary studies, (d) checking data accuracy and analyses, and (e) communication among team members. The major limitation in designing and implementing a fully electronic system for meta-analysis was the requisite upfront time to: decide on which electronic tools to use, determine how these tools would be employed, develop clear guidelines for their use, and train members of the research team. The electronic process described here has been useful in streamlining the process of conducting this complex meta-analysis and enhancing communication and sharing documents among research team members. PMID:23681256

  7. Electron- and hydride-transfer reactivity of an isolable manganese(V)-oxo complex. (United States)

    Fukuzumi, Shunichi; Kotani, Hiroaki; Prokop, Katharine A; Goldberg, David P


    The electron-transfer and hydride-transfer properties of an isolated manganese(V)−oxo complex, (TBP8Cz)Mn(V)(O) (1) (TBP8Cz = octa-tert-butylphenylcorrolazinato) were determined by spectroscopic and kinetic methods. The manganese(V)−oxo complex 1 reacts rapidly with a series of ferrocene derivatives ([Fe(C5H4Me)2], [Fe(C5HMe4)2], and ([Fe(C5Me5)2] = Fc*) to give the direct formation of [(TBP8Cz)Mn(III)(OH)]− ([2-OH]−), a two-electron-reduced product. The stoichiometry of these electron-transfer reactions was found to be (Fc derivative)/1 = 2:1 by spectral titration. The rate constants of electron transfer from ferrocene derivatives to 1 at room temperature in benzonitrile were obtained, and the successful application of Marcus theory allowed for the determination of the reorganization energies (λ) of electron transfer. The λ values of electron transfer from the ferrocene derivatives to 1 are lower than those reported for a manganese(IV)−oxo porphyrin. The presumed one-electron-reduced intermediate, a Mn(IV) complex, was not observed during the reduction of 1. However, a Mn(IV) complex was successfully generated via one-electron oxidation of the Mn(III) precursor complex 2 to give [(TBP8Cz)Mn(IV)]+ (3). Complex 3 exhibits a characteristic absorption band at λ(max) = 722 nm and an EPR spectrum at 15 K with g(max)′ = 4.68, g(mid)′ = 3.28, and g(min)′ = 1.94, with well-resolved 55Mn hyperfine coupling, indicative of a d3 Mn(IV)S = 3/2 ground state. Although electron transfer from [Fe(C5H4Me)2] to 1 is endergonic (uphill), two-electron reduction of 1 is made possible in the presence of proton donors (e.g., CH3CO2H, CF3CH2OH, and CH3OH). In the case of CH3CO2H, saturation behavior for the rate constants of electron transfer (k(et)) versus acid concentration was observed, providing insight into the critical involvement of H+ in the mechanism of electron transfer. Complex 1 was also shown to be competent to oxidize a series of dihydronicotinamide adenine

  8. Electronic structures and magnetic/optical properties of metal phthalocyanine complexes

    Energy Technology Data Exchange (ETDEWEB)

    Baba, Shintaro; Suzuki, Atsushi, E-mail:; Oku, Takeo [Department of Materials Science, The University of Shiga Prefecture. 2500 Hassaka, Hikone, Shiga 522-8533 (Japan)


    Electronic structures and magnetic / optical properties of metal phthalocyanine complexes were studied by quantum calculations using density functional theory. Effects of central metal and expansion of π orbital on aromatic ring as conjugation system on the electronic structures, magnetic, optical properties and vibration modes of infrared and Raman spectra of metal phthalocyanines were investigated. Electron and charge density distribution and energy levels near frontier orbital and excited states were influenced by the deformed structures varied with central metal and charge. The magnetic parameters of chemical shifts in {sup 13}C-nuclear magnetic resonance ({sup 13}C-NMR), principle g-tensor, A-tensor, V-tensor of electric field gradient and asymmetry parameters derived from the deformed structures with magnetic interaction of nuclear quadruple interaction based on electron and charge density distribution with a bias of charge near ligand under crystal field.

  9. Complex of codes for computer-aided design of electron guns with grid control (United States)

    Petrosyan, A. I.; Juravleva, V. D.; Penzyakov, V. V.; Rogovin, V. I.


    The computer-aided design of gridded electron guns on a basis of two, two and half and 3D mathematical models is carried out. The parameters of cathode-grid assembly (CGA) are calculated, synthesis and the trajectories analysis of ungridded gun, in which a control grid is supposed to be established, are realized. The trajectories analysis of a beam in CGA cells is fulfilled, the coordinates, velocites and charges of large particles on an exit from CGA cells are used for definition of the initial data for solving beam motion equations in the gridded electron gun and further in magnetic focusing system. Electron-optical systems with gridded electron gun, designed with the help of this complex of codes, do not require experimental correction and provide good current permeability in microwave tubes.

  10. Electron tomography of negatively stained complex viruses: application in their diagnosis

    Directory of Open Access Journals (Sweden)

    Demeestere Lien


    Full Text Available Abstract Background Electron tomographic analysis can be combined with the simple and rapid negative staining technique used in electron microscopy based virus diagnosis. Methods Standard negative staining of representative examples of parapoxviruses and paramyxoviruses was combined with electron tomographic analysis. Results Digital sectioning of reconstructions of these viruses at a selected height demonstrated the viral ultrastructure in detail, including the characteristic diagnostic features like the surface threads on C-particles of a parapoxvirus and individual glycoproteins and the internal nucleoprotein strand of Newcastle disease virus. For both viruses, deformation and flattening were observed. Conclusion The combination of negative staining of complex viruses with electron tomographic analysis, allows visualizing and measuring artifacts typical for negative staining. This approach allows sharp visualisation of structures in a subnanometer-thick plane, avoiding blurring due to superposition which is inherent to TEM. In selected examples, such analyses can improve diagnosis of viral agents.

  11. Suitability of an electronic reminder device for measuring drug adherence in elderly patients with complex medication. (United States)

    Harbig, Philipp; Barat, Ishay; Damsgaard, Else M


    We evaluated an electronic reminder device for detecting non-adherence in elderly patients with complex medication regimens. Randomly selected, home-living elderly patients were studied. The patients were aged over 65 years and were taking more than four drugs. Patients received an electronic reminder device which contained a GSM communications module. They were visited three times over a one-year period by a nurse who counted their medicine supply. We compared the adherence measured by the electronic device with the actual adherence measured by the pill count. Almost half of the 315 patients dropped out of the study for various reasons, so the calculations were performed on 168 patients. The adherence measured by the electronic reminder system was 79% and was 92% measured by pill count (Padherence at morning/evening intake times with pill count adherence in the morning/evening only. For the pill count, there was almost no difference between morning and evening adherence rates (93%). For electronic measurement, adherence rates were lower in the evening (75%) than in the morning (81%). Electronic reminders were less reliable than the pill count in measuring adherence. However, the electronic system may be a useful supplement to other, more time consuming methods for measuring adherence.

  12. Proton transfer in phenol-amine complexes: phenol electronic effects on free energy profile in solution. (United States)

    Aono, Shinji; Kato, Shigeki


    Free energy profiles for the proton transfer reactions in hydrogen-bonded complex of phenol with trimethylamine in methyl chloride solvent are studied with the reference interaction site model self-consistent field method. The reactions in both the electronic ground and excited states are considered. The second-order Møller-Plesset perturbation (MP) theory or the second-order multireference MP theory is used to evaluate the effect of the dynamical electron correlation on the free energy profiles. The free energy surface in the ground state shows a discrepancy with the experimental results for the related hydrogen-bonded complexes. To resolve this discrepancy, the effects of chloro-substitutions in phenol are examined, and its importance in stabilizing the ionic form is discussed. The temperature effect is also studied. In contrast to the ground state, the ππ* excited state of phenol-trimethylamine complex exhibits the proton transfer reaction with a low barrier. The reaction is almost thermoneutral. This is attributed to the reduction of proton affinity of phenol by the ππ* electronic excitation. We further examine the possibility of the electron-proton-coupled transfer in the ππ* state through the surface crossing with the charge transfer type πσ* state. © 2010 Wiley Periodicals, Inc.

  13. Electronic structure of four-coordinate C3v nickel(II) scorpionate complexes: investigation by high-frequency and -field electron paramagnetic resonance and electronic absorption spectroscopies. (United States)

    Desrochers, Patrick J; Telser, Joshua; Zvyagin, S A; Ozarowski, Andrew; Krzystek, J; Vicic, David A


    A series of complexes of formula TpNiX, where Tp*- = hydrotris(3,5-dimethylpyrazole)borate and X = Cl, Br, I, has been characterized by electronic absorption spectroscopy in the visible and near-infrared (NIR) region and by high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy. The crystal structure of TpNiCl has been previously reported; that for TpNiBr is given here: space group = Pmc2(1), a = 13.209(2) A, b = 8.082(2) A, c = 17.639(4) A, alpha = beta = gamma = 90 degrees , Z = 4. TpNiX contains a four-coordinate nickel(II) ion (3d8) with approximate C3v point group symmetry about the metal and a resulting S = 1 high-spin ground state. As a consequence of sizable zero-field splitting (zfs), TpNiX complexes are "EPR silent" with use of conventional EPR; however, HFEPR allows observation of multiple transitions. Analysis of the resonance field versus the frequency dependence of these transitions allows extraction of the full set of spin Hamiltonian parameters. The axial zfs parameter for TpNiX displays pronounced halogen contributions down the series: D = +3.93(2), -11.43(3), -22.81(1) cm(-1), for X = Cl, Br, I, respectively. The magnitude and change in sign of D observed for TpNiX reflects the increasing bromine and iodine spin-orbit contributions facilitated by strong covalent interactions with nickel(II). These spin Hamiltonian parameters are combined with estimates of 3d energy levels based on the visible-NIR spectra to yield ligand-field parameters for these complexes following the angular overlap model (AOM). This description of electronic structure and bonding in a pseudotetrahedral nickel(II) complex can enhance the understanding of similar sites in metalloproteins, both native nickel enzymes and nickel-substituted zinc enzymes.

  14. Ultrafast Electron Transfer at Organic Semiconductor Interfaces: Importance of Molecular Orientation

    KAUST Repository

    Ayzner, Alexander L.


    © 2014 American Chemical Society. Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximately 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation.

  15. Electron transfer across a thermal gradient. (United States)

    Craven, Galen T; Nitzan, Abraham


    Charge transfer is a fundamental process that underlies a multitude of phenomena in chemistry and biology. Recent advances in observing and manipulating charge and heat transport at the nanoscale, and recently developed techniques for monitoring temperature at high temporal and spatial resolution, imply the need for considering electron transfer across thermal gradients. Here, a theory is developed for the rate of electron transfer and the associated heat transport between donor-acceptor pairs located at sites of different temperatures. To this end, through application of a generalized multidimensional transition state theory, the traditional Arrhenius picture of activation energy as a single point on a free energy surface is replaced with a bithermal property that is derived from statistical weighting over all configurations where the reactant and product states are equienergetic. The flow of energy associated with the electron transfer process is also examined, leading to relations between the rate of heat exchange among the donor and acceptor sites as functions of the temperature difference and the electronic driving bias. In particular, we find that an open electron transfer channel contributes to enhanced heat transport between sites even when they are in electronic equilibrium. The presented results provide a unified theory for charge transport and the associated heat conduction between sites at different temperatures.

  16. Distorted tetrahedral nickel-nitrosyl complexes: spectroscopic characterization and electronic structure. (United States)

    Soma, Shoko; Van Stappen, Casey; Kiss, Mercedesz; Szilagyi, Robert K; Lehnert, Nicolai; Fujisawa, Kiyoshi


    The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitrogen-based ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3), was prepared by the reaction of the potassium salt of the ligand with the nickel-nitrosyl precursor [Ni(NO)(Br)(PPh 3 ) 2 ]. The obtained nitrosyl complexes as well as the corresponding chlorido complexes [Ni(NO)(Cl)(PPh 3 ) 2 ] and [Ni(Cl)(L3)] were characterized by X-ray crystallography and different spectroscopic methods including IR/far-IR, UV-Vis, NMR, and multi-edge X-ray absorption spectroscopy at the Ni K-, Ni L-, Cl K-, and P K-edges. For comparative electronic structure analysis we also performed DFT calculations to further elucidate the electronic structure of [Ni(NO)(L3)]. These results provide the nickel oxidation state and the character of the Ni-NO bond. The complex [Ni(NO)(L3)] is best described as [Ni (II) (NO (-) )(L3)], and the spectroscopic results indicate that the phosphane complexes have a similar [Ni (II) (NO (-) )(X)(PPh 3 ) 2 ] ground state.

  17. Mixing of electronic states in molybdenum complexes involved in nitrogen activation

    Energy Technology Data Exchange (ETDEWEB)

    Stranger, Robert [Department of Chemistry, Australian National University, Canberra ACT 0200 (Australia); School of Chemistry, University of Tasmania, Private Bag 75, Hobart TAS 7001 (Australia); Yates, Brian F. [Department of Chemistry, Australian National University, Canberra ACT 0200 (Australia); School of Chemistry, University of Tasmania, Private Bag 75, Hobart TAS 7001 (Australia)], E-mail:


    The mechanism for nitrogen activation by molybdenum complexes is a complicated one, involving as it does the coupling of a quartet molybdenum reactant with a singlet nitrogen molecule, passing via a series of quartet and doublet encounter complexes to a triplet intermediate, with the subsequent spin crossing to the singlet surface which then leads via a singlet transition state to the final pair of singlet products. We have investigated in detail a variety of levels of theory to describe the crossing of these electronic surfaces and have calculated both lower-bound and actual minimum energy crossing points for the key spin inversion processes.

  18. Understanding the Influence of the Electronic Structure on the Crystal Structure of a TTF-PTM Radical Dyad. (United States)

    Vela, Sergi; Souto, Manuel; Ratera, Imma; Rovira, Concepció; Veciana, Jaume


    The understanding of the crystal structure of organic compounds, and its relationship to their physical properties, have become essential to design new advanced molecular materials. In this context, we present a computational study devoted to rationalize the different crystal packing displayed by two closely related organic systems based on the TTF-PTM dyad (TTF = tetrathiafulvalene, PTM = polychlorotriphenylmethane) with almost the same molecular structure but a different electronic one. The radical species (1), with an enhanced electronic donor-acceptor character, exhibits a herringbone packing, whereas the nonradical protonated analogue (2) is organized forming dimers. The stability of the possible polymorphs is analyzed in terms of the cohesion energy of the unit cell, intermolecular interactions between pairs, and molecular flexibility of the dyad molecules. It is observed that the higher electron delocalization in radical compound 1 has a direct influence on the geometry of the molecule, which seems to dictate its preferential crystal structure.

  19. The role of anions, solvent molecules and solvated electrons in layer formation processes on anode materials for rechargeable lithium batteries

    Energy Technology Data Exchange (ETDEWEB)

    Rahner, D. [Technische Univ. Dresden (Germany). Inst. fuer Physikalische Chemie und Elektrochemie


    The reactivity of anions, solvent molecules and solvated electrons against anode materials are coupled in a given electrolyte solution. The ratio between anion and solvent decomposition depends on the potential and the electrolyte composition. The life time of trapped solvated electrons within the growing SEI layer depends on the donor-acceptor properties of the incorporated solvent molecules and is in the range among 3-10 s. The places of the trapped electrons are the origin of 'metallic' lithium clusters within the forming layer. Their growth will lead to the well-known lithium dendrites on lithium-metal or the progressive irreversible capacity loss on lithium-carbons and therefore causes a lot of problems. Suggestions will be made how to solve these problems in order to achieve a homogeneous SEI with a reduced dendrite growth or decreased irreversible capacity loss. (orig.)

  20. Photoinduced charge-transfer electronic excitation of tetracyanoethylene/tetramethylethylene complex in dichloromethane (United States)

    Xu, Long-Kun; Bi, Ting-Jun; Ming, Mei-Jun; Wang, Jing-Bo; Li, Xiang-Yuan


    Based on the previous work on nonequilibrium solvation model by the authors, Intermolecular charge-transfer electronic excitation of tetracyanoethylene (TCE)/tetramethylethylene (TME) π -stacked complex in dichloromethane (DCM) has been investigated. For weak interaction correction, dispersion corrected functional DFT-D3 is adopted for geometry optimization. In order to identify the excitation metric, dipole moment components of each Cartesian direction, atomic charge, charge separation and Δr index are analyzed for TCE/TME complex. Calculation shows that the calculated excitation energy is dependent on the functional choice, when conjuncted with suitable time-dependent density functional, the modified nonequilibrium expression gives satisfied results for intermolecular charge-transfer electronic excitation.

  1. Pure electronic metal-insulator transition at the interface of complex oxides (United States)

    Meyers, D.; Liu, Jian; Freeland, J. W.; Middey, S.; Kareev, M.; Kwon, Jihwan; Zuo, J. M.; Chuang, Yi-De; Kim, J. W.; Ryan, P. J.; Chakhalian, J.


    In complex materials observed electronic phases and transitions between them often involve coupling between many degrees of freedom whose entanglement convolutes understanding of the instigating mechanism. Metal-insulator transitions are one such problem where coupling to the structural, orbital, charge, and magnetic order parameters frequently obscures the underlying physics. Here, we demonstrate a way to unravel this conundrum by heterostructuring a prototypical multi-ordered complex oxide NdNiO3 in ultra thin geometry, which preserves the metal-to-insulator transition and bulk-like magnetic order parameter, but entirely suppresses the symmetry lowering and long-range charge order parameter. These findings illustrate the utility of heterointerfaces as a powerful method for removing competing order parameters to gain greater insight into the nature of the transition, here revealing that the magnetic order generates the transition independently, leading to an exceptionally rare purely electronic metal-insulator transition with no symmetry change.

  2. Contrast of Backscattered Electron SEM Images of Nanoparticles on Substrates with Complex Structure (United States)

    Müller, Erich; Fritsch-Decker, Susanne; Hettler, Simon; Störmer, Heike; Weiss, Carsten; Gerthsen, Dagmar


    This study is concerned with backscattered electron scanning electron microscopy (BSE SEM) contrast of complex nanoscaled samples which consist of SiO2 nanoparticles (NPs) deposited on indium-tin-oxide covered bulk SiO2 and glassy carbon substrates. BSE SEM contrast of NPs is studied as function of the primary electron energy and working distance. Contrast inversions are observed which prevent intuitive interpretation of NP contrast in terms of material contrast. Experimental data is quantitatively compared with Monte-Carlo- (MC-) simulations. Quantitative agreement between experimental data and MC-simulations is obtained if the transmission characteristics of the annular semiconductor detector are taken into account. MC-simulations facilitate the understanding of NP contrast inversions and are helpful to derive conditions for optimum material and topography contrast. PMID:29109816

  3. Contrast of Backscattered Electron SEM Images of Nanoparticles on Substrates with Complex Structure. (United States)

    Kowoll, Thomas; Müller, Erich; Fritsch-Decker, Susanne; Hettler, Simon; Störmer, Heike; Weiss, Carsten; Gerthsen, Dagmar


    This study is concerned with backscattered electron scanning electron microscopy (BSE SEM) contrast of complex nanoscaled samples which consist of SiO2 nanoparticles (NPs) deposited on indium-tin-oxide covered bulk SiO2 and glassy carbon substrates. BSE SEM contrast of NPs is studied as function of the primary electron energy and working distance. Contrast inversions are observed which prevent intuitive interpretation of NP contrast in terms of material contrast. Experimental data is quantitatively compared with Monte-Carlo- (MC-) simulations. Quantitative agreement between experimental data and MC-simulations is obtained if the transmission characteristics of the annular semiconductor detector are taken into account. MC-simulations facilitate the understanding of NP contrast inversions and are helpful to derive conditions for optimum material and topography contrast.

  4. Contrast of Backscattered Electron SEM Images of Nanoparticles on Substrates with Complex Structure

    Directory of Open Access Journals (Sweden)

    Thomas Kowoll


    Full Text Available This study is concerned with backscattered electron scanning electron microscopy (BSE SEM contrast of complex nanoscaled samples which consist of SiO2 nanoparticles (NPs deposited on indium-tin-oxide covered bulk SiO2 and glassy carbon substrates. BSE SEM contrast of NPs is studied as function of the primary electron energy and working distance. Contrast inversions are observed which prevent intuitive interpretation of NP contrast in terms of material contrast. Experimental data is quantitatively compared with Monte-Carlo- (MC- simulations. Quantitative agreement between experimental data and MC-simulations is obtained if the transmission characteristics of the annular semiconductor detector are taken into account. MC-simulations facilitate the understanding of NP contrast inversions and are helpful to derive conditions for optimum material and topography contrast.

  5. Modeling Electronic-Nuclear Interactions for Excitation Energy Transfer Processes in Light-Harvesting Complexes. (United States)

    Lee, Mi Kyung; Coker, David F


    An accurate approach for computing intermolecular and intrachromophore contributions to spectral densities to describe the electronic-nuclear interactions relevant for modeling excitation energy transfer processes in light harvesting systems is presented. The approach is based on molecular dynamics (MD) calculations of classical correlation functions of long-range contributions to excitation energy fluctuations and a separate harmonic analysis and single-point gradient quantum calculations for electron-intrachromophore vibrational couplings. A simple model is also presented that enables detailed analysis of the shortcomings of standard MD-based excitation energy fluctuation correlation function approaches. The method introduced here avoids these problems, and its reliability is demonstrated in accurate predictions for bacteriochlorophyll molecules in the Fenna-Matthews-Olson pigment-protein complex, where excellent agreement with experimental spectral densities is found. This efficient approach can provide instantaneous spectral densities for treating the influence of fluctuations in environmental dissipation on fast electronic relaxation.

  6. Exploring the Interaction Natures in Plutonyl (VI) Complexes with Topological Analyses of Electron Density. (United States)

    Du, Jiguang; Sun, Xiyuan; Jiang, Gang


    The interaction natures between Pu and different ligands in several plutonyl (VI) complexes are investigated by performing topological analyses of electron density. The geometrical structures in both gaseous and aqueous phases are obtained with B3LYP functional, and are generally in agreement with available theoretical and experimental results when combined with all-electron segmented all-electron relativistic contracted (SARC) basis set. The Pu- O y l bond orders show significant linear dependence on bond length and the charge of oxygen atoms in plutonyl moiety. The closed-shell interactions were identified for Pu-Ligand bonds in most complexes with quantum theory of atoms in molecules (QTAIM) analyses. Meanwhile, we found that some Pu-Ligand bonds, like Pu-OH(-), show weak covalent. The interactive nature of Pu-ligand bonds were revealed based on the interaction quantum atom (IQA) energy decomposition approach, and our results indicate that all Pu-Ligand interactions is dominated by the electrostatic attraction interaction as expected. Meanwhile it is also important to note that the quantum mechanical exchange-correlation contributions can not be ignored. By means of the non-covalent interaction (NCI) approach it has been found that some weak and repulsion interactions existed in plutonyl(VI) complexes, which can not be distinguished by QTAIM, can be successfully identified.

  7. Exploring the Interaction Natures in Plutonyl (VI Complexes with Topological Analyses of Electron Density

    Directory of Open Access Journals (Sweden)

    Jiguang Du


    Full Text Available The interaction natures between Pu and different ligands in several plutonyl (VI complexes are investigated by performing topological analyses of electron density. The geometrical structures in both gaseous and aqueous phases are obtained with B3LYP functional, and are generally in agreement with available theoretical and experimental results when combined with all-electron segmented all-electron relativistic contracted (SARC basis set. The Pu– O y l bond orders show significant linear dependence on bond length and the charge of oxygen atoms in plutonyl moiety. The closed-shell interactions were identified for Pu-Ligand bonds in most complexes with quantum theory of atoms in molecules (QTAIM analyses. Meanwhile, we found that some Pu–Ligand bonds, like Pu–OH−, show weak covalent. The interactive nature of Pu–ligand bonds were revealed based on the interaction quantum atom (IQA energy decomposition approach, and our results indicate that all Pu–Ligand interactions is dominated by the electrostatic attraction interaction as expected. Meanwhile it is also important to note that the quantum mechanical exchange-correlation contributions can not be ignored. By means of the non-covalent interaction (NCI approach it has been found that some weak and repulsion interactions existed in plutonyl(VI complexes, which can not be distinguished by QTAIM, can be successfully identified.

  8. Influence of Copper Oxidation State on the Bonding and Electronic Structure of Cobalt-Copper Complexes

    Energy Technology Data Exchange (ETDEWEB)

    Eisenhart, Reed J.; Carlson, Rebecca K.; Clouston, Laura J.; Young, Jr., Victor G.; Chen, Yu-Sheng; Bill, Eckhard; Gagliardi, Laura; Lu, Connie C. (UC); (UMM); (MXPL)


    Heterobimetallic complexes that pair cobalt and copper were synthesized and characterized by a suite of physical methods, including X-ray diffraction, X-ray anomalous scattering, cyclic voltammetry, magnetometry, electronic absorption spectroscopy, electron paramagnetic resonance, and quantum chemical methods. Both Cu(II) and Cu(I) reagents were independently added to a Co(II) metalloligand to provide (py3tren)CoCuCl (1-Cl) and (py3tren)CoCu(CH3CN) (2-CH3CN), respectively, where py3tren is the triply deprotonated form of N,N,N-tris(2-(2-pyridylamino)ethyl)amine. Complex 2-CH3CN can lose the acetonitrile ligand to generate a coordination polymer consistent with the formula “(py3tren)CoCu” (2). One-electron chemical oxidation of 2-CH3CN with AgOTf generated (py3tren)CoCuOTf (1-OTf). The Cu(II)/Cu(I) redox couple for 1-OTf and 2-CH3CN is reversible at -0.56 and -0.33 V vs Fc+/Fc, respectively. The copper oxidation state impacts the electronic structure of the heterobimetallic core, as well as the nature of the Co–Cu interaction. Quantum chemical calculations showed modest electron delocalization in the (CoCu)+4 state via a Co–Cu σ bond that is weakened by partial population of the Co–Cu σ antibonding orbital. By contrast, no covalent Co–Cu bonding is predicted for the (CoCu)+3 analogue, and the d-electrons are fully localized at individual metals.

  9. Structural analysis of alternative complex III in the photosynthetic electron transfer chain of Chloroflexus aurantiacus. (United States)

    Gao, Xinliu; Xin, Yueyong; Bell, Patrick D; Wen, Jianzhong; Blankenship, Robert E


    The green photosynthetic bacterium Chloroflexus aurantiacus, which belongs to the phylum of filamentous anoxygenic phototrophs, does not contain a cytochrome bc or bf type complex which is found in all other known groups of phototrophs. This suggests that a functional replacement exists to link the reaction center photochemistry to cyclic electron transfer as well as respiration. Earlier work identified a potential substitute of the cytochrome bc complex, now named alternative complex III (ACIII), which has been purified from C. aurantiacus, identified, and characterized. ACIII functions as a menaquinol:auracyanin oxidoreductase in the photosynthetic electron transfer chain, and a related but distinct complex functions in respiratory electron flow to a terminal oxidase. In this work, we focus on elucidating the structure of photosynthetic ACIII. We found that ACIII is an integral membrane protein complex of approximately 300 kDa that consists of eight subunits of seven different types. Among them, there are four metalloprotein subunits, including a 113 kDa iron-sulfur cluster-containing polypeptide, a 25 kDa penta-heme c-containing subunit, and two 20 kDa monoheme c-containing subunits in the form of a homodimer. A variety of analytical techniques were employed in determining the ACIII substructure, including HPLC combined with ESI-MS, metal analysis, potentiometric titration, and intensity analysis of heme staining SDS-PAGE. A preliminary structural model of ACIII is proposed on the basis of the analytical data and chemical cross-linking in tandem with mass analysis using MALDI-TOF, as well as transmembrane and transit peptide analysis.

  10. Ferrocene-o-benzosemiquinonato tin(IV) electron-transfer complexes. (United States)

    Ilyakina, Ekaterina V; Poddel'sky, Andrey I; Fukin, Georgy K; Bogomyakov, Artem S; Cherkasov, Vladimir K; Abakumov, Gleb A


    The interaction of ferrocene with tin(IV) o-benzosemiquinonato complexes in acetonitrile results in a reversible electron transfer (ET) from ferrocene to the redox-active ligand with the formation of electron-transfer complexes [(3,6-Cat)SnBr3](-)[Cp2Fe](+) (1) and [(3,6-Cat)(3,6-SQ)SnCl2](-)[Cp2Fe](+) (2), where 3,6-Cat is the 3,6-di-tert-butyl-catecholate dianion and 3,6-SQ is the 3,6-di-tert-butyl-o-benzosemiquinonato radical anion. The ET process and the solvent effect in the system "ferrocene-o-benzosemiquinonato tin(IV) complexes" were investigated on the basis of a combination of spectroscopic and X-ray diffraction methods. The molecular structures of 1 and 2 were confirmed by X-ray analysis. Complex 2 demonstrates the ferromagnetic coupling in the linear chain alternating ···D(+•)A(-•)D(+•)A(-•)··· motif.

  11. High-resolution electron spectroscopy and structures of lithium-nucleobase (adenine, uracil, and thymine) complexes. (United States)

    Krasnokutski, Serge A; Lee, Jung Sup; Yang, Dong-Sheng


    Li complexes of adenine, uracil, and thymine were produced by laser vaporization of rods made of Li and nucleobase powders in a metal-cluster beam source and studied by pulsed-field-ionization zero-electron-kinetic-energy (ZEKE) spectroscopy and density functional theory calculations. The ZEKE measurements determined the adiabatic ionization energies of the three neutral complexes and frequencies of several vibrational modes for the metal-adenine and -uracil ions. The measured spectra were compared with spectral simulations to determine the preferred metal binding sites. For adenine, the most stable structure is formed by Li/Li(+) bidentately binding to both the N7 atom of the imidazole ring and the NH(2) group of the pyrimidine ring. For uracil and thymine, the ideal site for Li/Li(+) coordination is the O4 atom. Although it has only a small effect on the geometries of uracil and thymine, lithium coordination forces the rotation of the NH(2) group out of the adenine plane. The adiabatic ionization energies of the three complexes follow the trend of uracil (33910+/-5 cm(-1))>thymine (33386+/-5 cm(-1))>adenine (32240+/-5 cm(-1)), whereas their metal-ligand bond dissociation energies are about the same, (92-97) +/-6 kJ mol(-1). For all three complexes, the neutral bond energies are smaller than those of the corresponding ions due to a weaker electrostatic interaction and stronger electron repulsion.

  12. Localized reconstruction of subunits from electron cryomicroscopy images of macromolecular complexes. (United States)

    Ilca, Serban L; Kotecha, Abhay; Sun, Xiaoyu; Poranen, Minna M; Stuart, David I; Huiskonen, Juha T


    Electron cryomicroscopy can yield near-atomic resolution structures of highly ordered macromolecular complexes. Often however some subunits bind in a flexible manner, have different symmetry from the rest of the complex, or are present in sub-stoichiometric amounts, limiting the attainable resolution. Here we report a general method for the localized three-dimensional reconstruction of such subunits. After determining the particle orientations, local areas corresponding to the subunits can be extracted and treated as single particles. We demonstrate the method using three examples including a flexible assembly and complexes harbouring subunits with either partial occupancy or mismatched symmetry. Most notably, the method allows accurate fitting of the monomeric RNA-dependent RNA polymerase bound at the threefold axis of symmetry inside a viral capsid, revealing for the first time its exact orientation and interactions with the capsid proteins. Localized reconstruction is expected to provide novel biological insights in a range of challenging biological systems.

  13. Structural effects on the electronic characteristics of intramolecularly intercalated alkali-rubrene complexes

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tsung-Lung, E-mail: [Department of Electrophysics, National Chia-Yi University, 300 Hsueh-Fu Road, Chiayi, 60004, Taiwan, ROC (China); Lu, Wen-Cai, E-mail: [Laboratory of Fiber Materials and Modern Textile, Growing Base for State Key Laboratory, College of Physics, Qingdao University, Qingdao, Shandong 266071 (China); State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun, Jilin 130021 (China)


    The geometric and electronic structures of neutral monolithium- and monosodium-rubrene (Li{sub 1} Rub and Na{sub 1} Rub) isomers are investigated and compared with monopotassium-rubrene (K{sub 1} Rub). Based on the alkali binding site, all isomers of these alkali-rubrene complexes can be subdivided into two types: intramolecularly intercalated and extramolecularly adsorbed. The minimum-energy Li{sub 1} Rub and Na{sub 1} Rub are intercalated structures, whereas the minimum-energy K{sub 1} Rub is adsorbed. The fact that the intercalated Li{sub 1} Rub and Na{sub 1} Rub structures are energetically favorable over the adsorbed ones can be explained by two energy rules. First, “double” proximity of the intercalating alkali element to a pair of phenyl side groups enormously reduces the total energy. Second, accommodation of a minuscule intercalant does not significantly deform the carbon frame and, thus, increases the energy only by a small amount. Additionally, the peculiar effects of intramolecular intercalation on the electronic structures of molecules are also studied in this simulation of monoalkali intercalation. In the monoalkali-intercalated rubrene complex, only one of the two pairs of phenyl groups of rubrene is intercalated, intentionally leaving another pair pristine, which facilitates the comparison of electronic structures between the intercalated and pristine pairs of phenyl side groups in a single molecule. The uniformity of chemical environments of the phenyl groups of the intercalated Li{sub 1} Rub/Na{sub 1} Rub is deteriorated by the incorporation of the intercalant, and leads to their spectral characteristics in contrast to K{sub 1} Rub. In particular, the introduction of the intercalant promotes the carbon 2p orbitals of the intercalated phenyl pair to take part in the electronic structures of the HOMO and LUMO peaks of Li{sub 1} Rub/Na{sub 1} Rub. The unpaired electron in the HOMO is delocalized over the backbone with higher probability of

  14. Electronic states and metal-ligand bonding of gadolinium complexes of benzene and cyclooctatetraene. (United States)

    Roudjane, Mourad; Kumari, Sudesh; Yang, Dong-Sheng


    Gadolinium (Gd) complexes of benzene (C(6)H(6)) and (1,3,5,7-cyclooctatetraene) (C(8)H(8)) were produced in a laser-vaporization supersonic molecular beam source and studied by single-photon pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy. Adiabatic ionization energies and metal-ligand stretching frequencies were measured for the first time from the ZEKE spectra. Metal-ligand bonding and electronic states of the neutral and cationic complexes were analyzed by combining the spectroscopic measurements with ab initio calculations. The ground states of Gd(C(6)H(6)) and [Gd(C(6)H(6))](+) were determined as (11)A(2) and (10)A(2), respectively, with C(6v) molecular symmetry. The ground states of Gd(C(8)H(8)) and [Gd(C(8)H(8))](+) were identified as (9)A(2) and (8)A(2), respectively, with C(8v) molecular symmetry. Although the metal-ligand bonding in Gd(C(6)H(6)) is dominated by the covalent interaction, the bonding in Gd(C(8)H(8)) is largely electrostatic. The bonding in the benzene complex is much weaker than that in the cyclooctatetraene species. The strong bonding in Gd(C(8)H(8)) arises from two-electron transfer from Gd to C(8)H(8), which creates a strong charge-charge interaction and converts the tub-shaped ligand into a planar form. In both systems, Gd 4f orbitals are localized and play little role in the bonding, but they contribute to the high electron spin multiplicities.

  15. Photoinduced Electron Transfer from Various Aniline Derivatives to Graphene Quantum Dots. (United States)

    Ghosh, Tufan; Chatterjee, Swarupa; Prasad, Edamana


    The present study utilizes the luminescence nature of the graphene quantum dots (GQDs) to analyze the mechanistic aspects of the photoinduced electron transfer (PET) processes between GQDs and aniline derivatives. A systematic investigation of PET from various aniline derivatives to GQDs has been presented. Solution-processable GQDs have been synthesized from graphene oxide (GO) at 200 °C. The as-synthesized GQDs exhibit a strong green luminescence at 510 nm, upon photoexcitation at 440 nm. Various aniline derivatives (aniline, N-methylaniline, N,N'-dimethylaniline, N-ethylaniline, N,N'-diethylaniline, and N,N'-diphenylaniline) have been utilized as electron donors to probe the PET process. Results from UV-visible absorption and steady-state and time-resolve luminescence spectroscopy suggest that the GQDs interact with the aniline derivatives in the excited state, which results in a significant luminescence quenching of the GQDs. The bimolecular rate constants of the dynamic quenching have been deduced for various donor-acceptor systems, and the values are in the range of (1.06-2.68) × 10(9) M(-1) s(-1). The negative values of the free energy change of the electron transfer process suggest that PET from aniline derivatives to GQDs is feasible and could be responsible for the luminescence quenching. The PET has been confirmed by detecting radical cations for certain aniline derivatives, using a nanosecond laser flash photolysis setup. The present study shows that among the various types of graphene systems, GQDs are better candidates for understanding the mechanism of PET in graphene-based donor-acceptor systems.

  16. Probing the chemistry, electronic structure and redox energetics in pentavalent organometallic actinide complexes

    Energy Technology Data Exchange (ETDEWEB)

    Graves, Christopher R [Los Alamos National Laboratory; Vaughn, Anthony E [Los Alamos National Laboratory; Morris, David E [Los Alamos National Laboratory; Kiplinger, Jaqueline L [Los Alamos National Laboratory


    Complexes of the early actinides (Th-Pu) have gained considerable prominence in organometallic chemistry as they have been shown to undergo chemistries not observed with their transition- or lanthanide metal counterparts. Further, while bonding in f-element complexes has historically been considered to be ionic, the issue of covalence remains a subject of debate in the area of actinide science, and studies aimed at elucidating key bonding interactions with 5f-orbitals continue to garner attention. Towards this end, our interests have focused on the role that metal oxidation state plays in the structure, reactivity and spectral properties of organouranium complexes. We report our progress in the synthesis of substituted U{sup V}-imido complexes using various routes: (1) Direct oxidation of U{sup IV}-imido complexes with copper(I) salts; (2) Salt metathesis with U{sup V}-imido halides; (3) Protonolysis and insertion of an U{sup V}-imido alkyl or aryl complex with H-N{double_bond}CPh{sub 2} or N{triple_bond}C-Ph, respectively, to form a U{sup V}-imido ketimide complex. Further, we report and compare the crystallographic, electrochemical, spectroscopic and magnetic characterization of the pentavalent uranium (C{sub 5}Me{sub 5}){sub 2}U({double_bond}N-Ar)(Y) series (Y = OTf, SPh, C{triple_bond}C-Ph, NPh{sub 2}, OPh, N{double_bond}CPh{sub 2}) to further interrogate the molecular, electronic, and magnetic structures of this new class of uranium complexes.

  17. Synthesis and binding properties of arylethyne-linked porphyrin-zinc complexes for organic electronics applications. (United States)

    Reainthippayasakul, W; Paosawatyanyong, B; Bhanthumnavin, W


    Conjugated meso-alkynyl 5,15-dimesitylporphyrin metal complexes have been synthesized by Sonogashira coupling reaction in good yields. Alkynyl groups were chosen as a link at the meso positions in order to extend the pi-conjugated length of porphyrin rings. These synthesized porphyrin derivatives were characterized by 1H NMR spectroscopy and MALDI-TOF mass spectrometry. Moreover, UV-visible spectroscopy and fluorescence spectroscopy were also used to investigate their photophysical properties. It has been demonstrated that central metal ions as well as meso substituents on porphyrin rings affected the electronic absorption and emission spectra of the compounds. Spectroscopic results revealed that alkyne-linked porphyrin metal complexes showed higher pi-conjugation compared with porphyrin building blocks resulting in red shifts in both absorption and emission spectra. Coordination properties of synthesized porphyrins were preliminarily investigated by UV-visible absorption and fluorescence emission spectroscopic titration with pyridine as axial ligand. The formation of porphyrin-pyridine complexes resulted in significant red shifts in absorption spectra and decrease of fluorescence intensity in emission spectra. Moreover, the 1H NMR titration experiments suggested that central metal ions play an important role to coordinate with pyridine and the coordination of porphyrin zinc(II) complex with pyridine occur in a 1:1 ratio. From these spectroscopic results, alkyne-linked porphyrin metal complexes offer potential applications as materials for optical organic nanosensors.

  18. Changes in the surface electronic states of semiconductor fine particles induced by high energy ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Yamaki, Tetsuya; Asai, Keisuke; Ishigure, Kenkichi [Tokyo Univ. (Japan); Shibata, Hiromi


    The changes in the surface electronic states of Q-sized semiconductor particles in Langmuir-Blodgett (LB) films, induced by high energy ion irradiation, were examined by observation of ion induced emission and photoluminescence (PL). Various emission bands attributed to different defect sites in the band gap were observed at the initial irradiation stage. As the dose increased, the emissions via the trapping sites decreased in intensity while the band-edge emission developed. This suggests that the ion irradiation would remove almost all the trapping sites in the band gap. The low energy emissions, which show a multiexponential decay, were due to a donor-acceptor recombination between the deeply trapped carriers. It was found that the processes of formation, reaction, and stabilization of the trapping sites would predominantly occur under the photooxidizing conditions. (author)

  19. Theoretical Studies on the Electronic Structures and Properties of Complex Ceramic Crystals and Novel Materials

    Energy Technology Data Exchange (ETDEWEB)

    Ching, Wai-Yim


    This project is a continuation of a long program supported by the Office of Basic Energy Science in the Office of Science of DOE for many years. The final three-year continuation started on November 1, 2005 with additional 1 year extension to October 30, 2009. The project was then granted a two-year No Cost Extension which officially ended on October 30, 2011. This report covers the activities within this six year period with emphasis on the work completed within the last 3 years. A total of 44 papers with acknowledgement to this grant were published or submitted. The overall objectives of this project are as follows. These objectives have been evolved over the six year period: (1) To use the state-of-the-art computational methods to investigate the electronic structures of complex ceramics and other novel crystals. (2) To further investigate the defects, surfaces/interfaces and microstructures in complex materials using large scale modeling. (3) To extend the study on ceramic materials to more complex bioceramic crystals. (4) To initiate the study on soft condensed matters including water and biomolecules. (5) To focus on the spectroscopic studies of different materials especially on the ELNES and XANES spectral calculations and their applications related to experimental techniques. (6) To develop and refine computational methods to be effectively executed on DOE supercomputers. (7) To evaluate mechanical properties of different crystals and those containing defects and relate them to the fundamental electronic structures. (8) To promote and publicize the first-principles OLCAO method developed by the PI (under DOE support for many years) for applications to large complex material systems. (9) To train a new generation of graduate students and postdoctoral fellows in modern computational materials science and condensed matter physics. (10) To establish effective international and domestic collaborations with both experimentalists and theorists in materials

  20. Vibrational and electronic circular dichroism study of bile pigments: complexes of bilirubin and biliverdin with metals. (United States)

    Goncharova, Iryna; Urbanová, Marie


    Complexation of bilirubin (BR) and biliverdin (BV) with biogenic and toxic metals (Mn, Cu, Cd, Co, Fe, Ni, Zn, and Ag) has been studied by means of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD). Poly-L-lysine and beta-cyclodextrin in water were chosen as matrices capable of recognizing the single stereoconformer of the pigments with defined M-helicity. Such systems allow structural changes caused by complexation of pigments with metals in aqueous solution at pH 10-11 to be followed using chiroptical methods, which are intrinsically sensitive to spatial structure. These and other spectroscopic techniques have revealed that BV and BR form monomeric complexes with Cd, Cu, and Zn and dimeric complexes with Mn. The stabilities of the complexes with Fe, Ni, Co, and Ag are remarkably lower. The sign of the ECD and VCD patterns of the complexed BV does not change for the chelates of any of the studied metals other than Zn, this exception being interpreted in terms of manifestation of the opposite helicity of BV in its chelate with Zn. In the case of BR, the observed inversion of ECD signal after complexation, together with the analysis of VCD spectra, reveals that a flattening of the molecule takes place, i.e., an increase in the angle between the pyrrinone chromophores without an inversion of helicity. This chiral stereoselectivity, which is very specific in the case of the Zn chelates, is discussed in connection with the specific inhibition of Zn-required enzymes by bile pigments.

  1. The impact of alkali metal halide electron donor complexes in the photocatalytic degradation of pentachlorophenol

    Energy Technology Data Exchange (ETDEWEB)

    Khuzwayo, Z., E-mail:; Chirwa, E.M.N


    Highlights: • Facilitation of photocatalysis using simple metal-halides as VB hole scavengers. • Recombination prevention by coupled valence and conduction band approaches. • Determination of anions critical levels beyond which process retardation occurs. • Determination of the photocatalytic process rate of reaction kinetics. - Abstract: The performance of photocatalytic oxidation of chemical pollutants is subjected to the presence of anion complexes in natural waters. This study investigated the influence of alkali metal (Na{sup +} (sodium), K{sup +} (potassium)) halides (Cl{sup −} (chloride), Br{sup −} (bromide), F{sup −} (fluoride)) as inorganic ion sources in the photocatalytic degradation of pentachlorophenol (PCP) in batch systems. It was found that the exclusive presence of halides in the absence of an electron acceptor adequately facilitated the photocatalyst process below critical levels of anion populations, where beyond the critical point the process was significantly hindered. Below the determined critical point, the performance in some cases near matches that of the facilitation of the photocatalytic process by exclusive oxygen, acting as an electron scavenger. The coupling of halide ions and oxygenation presented significantly improved photo-oxidation of PCP, this was confirmed by the inclusion of formic acid as a comparative electron donor. The Langmuir-Hinshelwood kinetic expression was used to calculate the performance rate kinetics. The probable impact of the halide anions was discussed with regards to the process of electron hole pair recombination prevention.

  2. Characterization of complex phase steel using backscattered electron images with controlled collection angles. (United States)

    Sato, Kaoru; Sueyoshi, Hitoshi; Yamada, Katsumi


    For optimizing the microstructure of complex phase (CP) steels, characterization using scanning electron microscopy (SEM) is powerful because it allows observations from very low to high magnification. SEM specimens of steels are often etched in order to distinguish between the different phases by producing topographic information. This is however an 'indirect' method of characterization, which does not give precise structural information. We have developed a new technique for the selective imaging of the martensite (M) phase in a ferritic (F)-M complex phase steel. Backscattered electron (BSE) images at 15-20 kV were recorded by systematically changing the collection angle θ, where θ is measured from the specimen surface. When θ was 30-45°, strong channeling contrast was observed. For lower values of θ, it is the low energy loss electrons that mainly contribute to the contrast. As θ increases, the M phase exhibits brighter contrast. When θ exceeds 60°, a selective imaging of the M phase is achieved. This is not because martensite has a larger mean atomic number than ferrite, but is due to the fact that martensite has a high crystallographic defect density. Anomalously bright M contrast is due to multiple scattering of BSE due to the high density of planar defects and dislocations. Low angle BSE allows high resolution characterization of complex microstructures, while high angle BSE gives quantitative assessment of the distribution and the volume fraction of the martensite phase. © The Author 2015. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail:

  3. Imaging metazoan nuclear pore complexes by field emission scanning electron microscopy. (United States)

    Fichtman, Boris; Shaulov, Lihi; Harel, Amnon


    High resolution three-dimensional surface images of nuclear pore complexes (NPCs) can be obtained by field emission scanning electron microscopy. We present a short retrospective view starting from the early roots of microscopy, through the discovery of the cell nucleus and the development of some modern techniques for sample preparation and imaging. Detailed protocols are presented for assembling anchored nuclei in a Xenopus cell-free reconstitution system and for the exposure of the nuclear surface in mammalian cell nuclei. Immunogold labeling of metazoan NPCs and a promising new technique for delicate coating with iridium are also discussed. Copyright © 2014 Elsevier Inc. All rights reserved.

  4. Electron Transfer Mediators for Photoelectrochemical Cells Based on Cu(I Metal Complexes

    Directory of Open Access Journals (Sweden)

    Michele Brugnati


    Full Text Available The preparation and the photoelectrochemical characterization of a series of bipyridine and pyridyl-quinoline Cu(I complexes, used as electron transfer mediators in regenerative photoelectrochemical cells, are reported. The best performing mediators produced maximum IPCEs of the order of 35–40%. The J-V curves recorded under monochromatic light showed that the selected Cu(I/(II couples generated higher Vocs and fill factors compared to an equivalent I-/I3- cell, due to a decreased dark current.

  5. Distinct conformations of the protein complex p97-Ufd1-Npl4 revealed by electron cryomicroscopy. (United States)

    Bebeacua, Cecilia; Förster, Andreas; McKeown, Ciarán; Meyer, Hemmo H; Zhang, Xiaodong; Freemont, Paul S


    p97 is a key regulator of numerous cellular pathways and associates with ubiquitin-binding adaptors to remodel ubiquitin-modified substrate proteins. How adaptor binding to p97 is coordinated and how adaptors contribute to substrate remodeling is unclear. Here we present the 3D electron cryomicroscopy reconstructions of the major Ufd1-Npl4 adaptor in complex with p97. Our reconstructions show that p97-Ufd1-Npl4 is highly dynamic and that Ufd1-Npl4 assumes distinct positions relative to the p97 ring upon addition of nucleotide. Our results suggest a model for substrate remodeling by p97 and also explains how p97-Ufd1-Npl4 could form other complexes in a hierarchical model of p97-cofactor assembly.

  6. Cryo-electron microscopy reconstruction of a poliovirus-receptor-membrane complex (United States)

    Bubeck, Doryen; Filman, David J; Hogle, James M


    To study non-enveloped virus cell entry, a versatile in vitro model system was developed in which liposomes containing nickel- chelating lipids were decorated with His-tagged poliovirus receptors and bound to virus. This system provides an exciting opportunity for structural characterization of the early steps in cell entry in the context of a membrane. Here we report the three-dimensional structure of a poliovirus-receptor-membrane complex solved by cryo-electron microscopy (cryo-EM) at a resolution of 32Å. Methods were developed to establish the symmetry of the complex objectively. This reconstruction demonstrates that receptor binding brings a viral five-fold axis close to the membrane. Density is clearly defined for the icosahedral virus, for receptors (including known glycosylation sites) and for the membrane bilayer. Apparent perturbations of the bilayer close to the viral five-fold axis may function in subsequent steps of cell entry. PMID:15965485

  7. Tracking the charge and spin dynamics of electronic excited states in inorganic complexes (United States)

    Gaffney, Kelly


    Inorganic complexes have many advantageous properties for solar energy applications, including strong visible absorption and photocatalytic activity. Whether used as a photocatalyst or a photosensitizer, the lifetime of electronic excited states and the earth abundance of the molecular components represent a key property for solar energy applications. These dual needs have undermined the usefulness of many coordination compounds. Isoelectronic iron and ruthenium based complexes represent a clear example. Ru-polypyridal based molecules have been the workhorse of solar energy related research and dye sensitized solar cells for decades, but the replacement of low abundance Ru with Fe leads to million-fold reductions in metal to ligand charge transfer (MLCT) excited state lifetimes. Understanding the origin of this million-fold reduction in lifetime and how to control excited state relaxation in 3d-metal complexes motivates the work I will discuss. We have used the spin sensitivity of hard x-ray fluorescence spectroscopy and the intense femtosecond duration pulses generated by the LCLS x-ray laser to probe the spin dynamics in a series of electronically excited [Fe(CN)6-2N(2,2'-bipyridine)N]2 N - 4 complexes, with N = 1-3. These femtosecond resolution measurements demonstrate that modification of the solvent and ligand environment can lengthen the MLCT excited state lifetime by more than two orders of magnitude. They also verify the role of triplet ligand field excited states in the spin crossover dynamics from singlet to quintet spin configurations. Work supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  8. The electronic and transport properties of monolayer transition metal dichalcogenides: a complex band structure analysis (United States)

    Szczesniak, Dominik

    Recently, monolayer transition metal dichalcogenides have attracted much attention due to their potential use in both nano- and opto-electronics. In such applications, the electronic and transport properties of group-VIB transition metal dichalcogenides (MX2 , where M=Mo, W; X=S, Se, Te) are particularly important. Herein, new insight into these properties is presented by studying the complex band structures (CBS's) of MX2 monolayers while accounting for spin-orbit coupling effects. By using the symmetry-based tight-binding model a nonlinear generalized eigenvalue problem for CBS's is obtained. An efficient method for solving such class of problems is presented and gives a complete set of physically relevant solutions. Next, these solutions are characterized and classified into propagating and evanescent states, where the latter states present not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gaps, which describe the tunneling currents in the MX2 materials. The importance of CBS's and tunneling currents is demonstrated by the analysis of the quantum transport across MX2 monolayers within phase field matching theory. Present work has been prepared within the Qatar Energy and Environment Research Institute (QEERI) grand challenge ATHLOC project (Project No. QEERI- GC-3008).

  9. Insights on the Structural Details of Endonuclease EcoRI-DNA Complexes by Electron Spin Resonance (United States)

    Sarver, Jessica


    Pulsed electron spin resonance (ESR) was used to probe the binding specificity of EcoRI, a restriction endonuclease. Using site-directed spin labeling, a nitroxide side chain was incorporated into the protein, enabling the use of ESR to study structural details of EcoRI. Distance measurements were performed on EcoRI mutants when bound to varying sequences of DNA using the Double Electron-Electron Resonance experiment. These distances demonstrated that the average structure in the arm regions of EcoRI, thought to play a major role in binding specificity, is the same when the protein binds to different sequences of DNA. Also, it was determined that the arms exhibit higher flexibility when bound to sequences other than the specific sequence due to the larger distance distributions acquired from these spin labeled complexes. Molecular dynamics (MD) simulations were performed on the spin-label-modified specific EcoRI-DNA crystal structure to model the average nitroxide orientation. The distance distributions from MD were found to be narrower than experiment, indicating the need for a more rigorous sampling of the nitroxide conformers in silico.

  10. Bis(pentamethylcyclopentadienyl) ytterbium: Electron-transfer reactions with organotransition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Matsunaga, Phillip Thomas [Univ. of California, Berkeley, CA (United States)


    The divalent lanthanide complex, (Me5C5)2Yb, reacts with methylcopper to produce the base-free, ytterbium-methyl complex, (Me5C5)2YbMe. This product forms a asymmetric, methyl-bridged dimer in the solid state. The bulky alkyl complex, (Me5C5)2YbCH(SiMe3)2, displays similar chemistry to (Me5C5)2YbMe, but at a reduced reaction rate due to the limited accessibility of the metal in (Me5C5)3YbCH(SiMe5)2. Copper and silver halide salts react with (Me5C5)2V to produce the trivalent halide derivatives, (Me5C5)2VX (X + F, Cl, Br, I). The chloride complex, (Me5C5)2VCl, reacts with lithium reagents to form the phenyl and borohydride species. Nitrous oxide transfers an oxygen atom to (Me5C5)2V producing the vanadium-oxo complex, (Me5Ce5)2VO. The trivalent titanium species, (Me5C5)2TiX (X = Cl, Br, Me, BH4), form bimetallic coordination complexes with (Me5C5)2Yb. The magnetic behavior of the products indicates that electron transfer has not occurred. The solid state structures of the chloride and bromide complexes show unusual bend angles for the halide bridges between ytterbium and titanium. A model based on frontier orbital theory has been proposed to account for the bending behavior in these species. The bimetallic methyl complex contains a linear methyl bridge between ytterbium and titanium.

  11. Bis(pentamethylcyclopentadienyl) ytterbium: Electron-transfer reactions with organotransition metal complexes

    Energy Technology Data Exchange (ETDEWEB)

    Matsunaga, P.T.


    The divalent lanthanide complex, (Me{sub 5}C{sub 5}){sub 2}Yb, reacts with methylcopper to produce the base-free, ytterbium-methyl complex, (Me{sub 5}C{sub 5}){sub 2}YbMe. This product forms a asymmetric, methyl-bridged dimer in the solid state. The bulky alkyl complex, (Me{sub 5}C{sub 5}){sub 2}YbCH(SiMe{sub 3}){sub 2}, displays similar chemistry to (Me{sub 5}C{sub 5}){sub 2}YbMe, but at a reduced reaction rate due to the limited accessibility of the metal in (Me{sub 5}C{sub 5}){sub 2}YbCH(SiMe{sub 3}){sub 2}. Copper and silver halide salts react with (Me{sub 5}C{sub 5}){sub 2}V to produce the trivalent halide derivatives, (Me{sub 5}C{sub 5}){sub 2}VX (X + F, Cl, Br, I). The chloride complex, (Me{sub 5}C{sub 5}){sub 2}VCl, reacts with lithium reagents to form the phenyl and borohydride species. Nitrous oxide transfers an oxygen atom to (Me{sub 5}C{sub 5}){sub 2}V producing the vanadium-oxo complex, (Me{sub 5}Ce{sub 5}){sub 2}VO. The trivalent titanium species, (Me{sub 5}C{sub 5}){sub 2}TiX (X = Cl, Br, Me, BH{sub 4}), form bimetallic coordination complexes with (Me{sub 5}C{sub 5}){sub 2}Yb. The magnetic behavior of the products indicates that electron transfer has not occurred. The solid state structures of the chloride and bromide complexes show unusual bend angles for the halide bridges between ytterbium and titanium. A model based on frontier orbital theory has been proposed to account for the bending behavior in these species. The bimetallic methyl complex contains a linear methyl bridge between ytterbium and titanium.

  12. Dissociative electron attachment to hexafluoroacetylacetone and its bidentate metal complexes M(hfac)2; M = Cu, Pd (United States)

    Engmann, Sarah; Ómarsson, Benedikt; Lacko, Michal; Stano, Michal; Matejčík, Štefan; Ingólfsson, Oddur


    Beta-diketones are a versatile class of compounds that can complex almost any metal in the periodic table of elements. Their metal complexes are found to be fairly stable and generally have sufficient vapor pressure for deposition techniques requiring volatile metal sources. Motivated by the potential role of low energy electrons in focused electron beam induced deposition, we have carried out a crossed electron/molecular beam study on the dissociative electron attachment and non-dissociative electron attachment (NDEA) to hexafluoroacetylacetone (HFAc) and its bidentate metal complexes: bis-hexafluoroacetylacetonate copper(II), Cu(hfac)2 and bis-hexafluoroacetylacetonate palladium(II), Pd(hfac)2. The relative ion yield curves for the native precursor to the ligand as well as its stable, 16 valence electron Pd(II) complex and open shell, 17 valence electron Cu(II) complex, are presented and compared. For HFAc, the loss of HF leads to the dominant anion observed, and while NDEA is only weakly pronounced for Pd(hfac)2 and loss of hfac- is the main dissociation channel, [Cu(hfac)2]- formation from Cu(hfac)2 dominates. A comparison of the ion yield curves and the associated resonances gives insight into the role of the ligand in the attachment process and highlights the influence of the central metal atom.

  13. Highly Manufacturable Deep (Sub-Millimeter) Etching Enabled High Aspect Ratio Complex Geometry Lego-Like Silicon Electronics

    KAUST Repository

    Ghoneim, Mohamed T.


    A highly manufacturable deep reactive ion etching based process involving a hybrid soft/hard mask process technology shows high aspect ratio complex geometry Lego-like silicon electronics formation enabling free-form (physically flexible, stretchable, and reconfigurable) electronic systems.

  14. Reversible binding of molecular oxygen to catecholate and amidophenolate complexes of SbV: electronic and steric factors. (United States)

    Fukin, Georgy K; Baranov, Evgenii V; Poddel'sky, Andrey I; Cherkasov, Vladimir K; Abakumov, Gleb A


    Edge of reactivity: The reactions of reversible binding of molecular oxygen to catecholate and amidophenolate complexes of Sb(V) are investigated by analyzing the position of electronic (E(HOMO)) and steric (G-parameter) factors. The optimal electronic and steric parameters for such type reactions are found. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Towards building artificial light harvesting complexes: enhanced singlet-singlet energy transfer between donor and acceptor pairs bound to albumins. (United States)

    Kumar, Challa V; Duff, Michael R


    Specific donor and acceptor pairs have been assembled in bovine serum albumin (BSA), at neutral pH and room temperature, and these dye-protein complexes indicated efficient donor to acceptor singlet-singlet energy transfer. For example, pyrene-1-butyric acid served as the donor and Coumarin 540A served as the acceptor. Both the donor and the acceptor bind to BSA with affinity constants in excess of 2x10(5) M(-1), as measured in absorption and circular dichroism (CD) spectral titrations. Simultaneous binding of both the donor and the acceptor chromophores was supported by CD spectra and one chromophore did not displace the other from the protein host, even when limited concentrations of the host were used. For example, a 1:1:1 complex between the donor, acceptor and the host can be readily formed, and spectral data clearly show that the binding sites are mutually exclusive. The ternary complexes (two different ligands bound to the same protein molecule) provided opportunities to examine singlet-singlet energy transfer between the protein-bound chromophores. Donor emission was quenched by the addition of the acceptor, in the presence of limited amounts of BSA, while no energy transfer was observed in the absence of the protein host, under the same conditions. The excitation spectra of the donor-acceptor-host complexes clearly show the sensitization of acceptor emission by the donor. Protein denaturation, as induced by the addition of urea or increasing the temperature to 360 K, inhibited energy transfer, which indicate that protein structure plays an important role. Sensitization also proceeded at low temperature (77 K) and diffusion of the donor or the acceptor is not required for energy transfer. Stern-Volmer quenching plots show that the quenching constant is (3.1+/-0.2)x10(4) M(-1), at low acceptor concentrations (light harvesting, conversion and storage.

  16. A Protein Data Bank survey reveals shortening of intermolecular hydrogen bonds in ligand-protein complexes when a halogenated ligand is an H-bond donor.

    Directory of Open Access Journals (Sweden)

    Jarosław Poznański

    Full Text Available Halogen bonding in ligand-protein complexes is currently widely exploited, e.g. in drug design or supramolecular chemistry. But little attention has been directed to other effects that may result from replacement of a hydrogen by a strongly electronegative halogen. Analysis of almost 30000 hydrogen bonds between protein and ligand demonstrates that the length of a hydrogen bond depends on the type of donor-acceptor pair. Interestingly, lengths of hydrogen bonds between a protein and a halogenated ligand are visibly shorter than those estimated for the same family of proteins in complexes with non-halogenated ligands. Taking into account the effect of halogenation on hydrogen bonding is thus important when evaluating structural and/or energetic parameters of ligand-protein complexes. All these observations are consistent with the concept that halogenation increases the acidity of the proximal amino/imino/hydroxyl groups and thus makes them better, i.e. stronger, H-bond donors.

  17. A Protein Data Bank Survey Reveals Shortening of Intermolecular Hydrogen Bonds in Ligand-Protein Complexes When a Halogenated Ligand Is an H-Bond Donor (United States)

    Poznański, Jarosław; Poznańska, Anna; Shugar, David


    Halogen bonding in ligand-protein complexes is currently widely exploited, e.g. in drug design or supramolecular chemistry. But little attention has been directed to other effects that may result from replacement of a hydrogen by a strongly electronegative halogen. Analysis of almost 30000 hydrogen bonds between protein and ligand demonstrates that the length of a hydrogen bond depends on the type of donor-acceptor pair. Interestingly, lengths of hydrogen bonds between a protein and a halogenated ligand are visibly shorter than those estimated for the same family of proteins in complexes with non-halogenated ligands. Taking into account the effect of halogenation on hydrogen bonding is thus important when evaluating structural and/or energetic parameters of ligand-protein complexes. All these observations are consistent with the concept that halogenation increases the acidity of the proximal amino/imino/hydroxyl groups and thus makes them better, i.e. stronger, H-bond donors. PMID:24933273

  18. Intermolecular electron transfer between coumarin dyes and aromatic amines in Triton-X-100 micellar solutions: Evidence for Marcus inverted region (United States)

    Kumbhakar, Manoj; Nath, Sukhendu; Mukherjee, Tulsi; Pal, Haridas


    Photoinduced electron transfer (ET) between coumarin dyes and aromatic amines has been investigated in Triton-X-100 micellar solutions and the results have been compared with those observed earlier in homogeneous medium. Significant static quenching of the coumarin fluorescence due to the presence of high concentration of amines around the coumarin fluorophore in the micelles has been observed in steady-state fluorescence studies. Time-resolved studies with nanosecond resolutions mostly show the dynamic part of the quenching for the excited coumarin dyes by the amine quenchers. A correlation of the quenching rate constants, estimated from the time-resolved measurements, with the free energy changes (ΔG0) of the ET reactions shows the typical bell shaped curve as predicted by Marcus outer-sphere ET theory. The inversion in the ET rates for the present systems occurs at an exergonicity (-ΔG0) of ~0.7-0.8 eV, which is unusually low considering the polarity of the Palisade layer of the micelles where the reactants reside. Present results have been rationalized on the basis of the two dimensional ET model assuming that the solvent relaxation in micellar media is much slower than the rate of the ET process. Detailed analysis of the experimental data shows that the diffusional model of the bimolecular quenching kinetics is not applicable for the ET reactions in the micellar solutions. In the present systems, the reactions can be better visualized as equivalent to intramolecular electron transfer processes, with statistical distribution of the donors and acceptors in the micelles. A low electron coupling (Vel) parameter is estimated from the correlation of the experimentally observed and the theoretically calculated ET rates, which indicates that the average donor-acceptor separation in the micellar ET reactions is substantially larger than for the donor-acceptor contact distance. Comparison of the Vel values in the micellar solution and in the donor-acceptor close

  19. Random laser emission at dual wavelengths in a donor-acceptor dye mixture solution

    Directory of Open Access Journals (Sweden)

    Sunita Kedia

    Full Text Available The work was aimed to generate random laser emissions simultaneously at two wavelengths in a weakly scattering system containing mixture of binary dyes, rhodamine-B (Rh-B and oxazine-170 (O-170 dispersed with ZnO nano-particles serving as scattering centres. Random lasing performances for individual Rh-B dye were extensively studied for varying small signal gain/scatterer density and we found lasing threshold to significantly depend upon number density of dispersed nano-particles. In spite of inefficient pumping, we demonstrated possibility of random lasing in O-170 dye solution on account of resonance energy transfer from Rh-B dye which served as donor. At optimum concentrations of fluorophores and scatterer in dye mixture solution, incoherent random lasing was effectively attained simultaneously at two wavelengths centered 90 nm apart. Dual-emission intensities, lasing thresholds and rate of amplifications could be controlled and made equivalent for both donor and acceptor in dye mixture solution by appropriate choice of concentrations of dyes and scatterers. Keywords: Random lasing, Energy transfer, Rhodamine-B, Oxazine-170, Zinc oxide

  20. Silicon-Bridged donor-acceptor compounds : Synthesis and nonlinear optical properties

    NARCIS (Netherlands)

    Hissink, Catharina Everdina


    This thesis describes the synthesis and the spectroscopic and nonlinear optical characterization of a large series of donor- and acceptor-substituted diphenylsilanes with the structure DPh-(SiMez).-PhA and fragments thereof.Nonlinear optics (NLO) deals with the interaction of electromagnetic fields

  1. New Type of Donor-Acceptor Through-Space Conjugated Polymer

    Directory of Open Access Journals (Sweden)

    Lin Lin


    Full Text Available We report the synthesis and properties of a novel through-space conjugated polymer with a [2.2]paracyclophane skeleton. The obtained polymer possessed donor (fluorene and acceptor (2,1,3-benzothiadiazole segments that were alternately π-stacked in proximity via the [2.2]paracyclophane moieties. The good overlap between the emission peak of the donor unit (fluorene and the CT band of the acceptor unit (2,1,3-benzothiadiazole caused fluorescence resonance energy transfer, and the visible green light emission from the acceptor unit was observed.

  2. Water Based Inkjet Material Deposition Of Donor-Acceptor Nanoparticles For Usage In Organic Photovoltaics (United States)

    Penmetcha, Anirudh Raju

    Significant efficiency increases are being made for bulk heterojunction organic photovoltaic prototype devices with world records at 11%. However the chlorinated solvents most frequently used in prototype manufacture would cause local health and safety concerns or large scale environmental pollution upon expansion of these techniques for commercialization. Moreover, research to bridge prototype and large-scale production of these solar cells is still in its infancy. Most prototype devices are made in inert glove box environments using spin-coating. There is a need to develop a non-toxic ink and incorporate it into a material deposition system that can be used in mass production. In this thesis, P3HT:PCBM organic photovoltaic devices were fabricated with the help of inkjet printing. P3HT:PCBM blends were dissolved in organic solvent systems, and this solution was used as the ink for the printer. The "coffee-ring effect" as well as the effect of inkjet printing parameters on film formation were highlighted - thus the inkjet printing method was validated as a stepping stone between lab-scale production of OPVs and large-scale roll-to-roll manufacturing. To address the need of a non-toxic ink, P3HT:PCBM blends were then dispersed in water, using the miniemulsion method. The nanoparticles were characterized for their size, as well as the blending between the P3HT and PCBM within the nanoparticle. These dispersions were then converted into inks. Finally, these nanoparticle inks were inkjet-printed to fabricate OPV devices. Based on the results obtained here, tentative "next steps" have been outlined in order to improve upon this research work, in the future.

  3. Donor-acceptor reactions: Good bye to the laboratory jargon | Barke ...

    African Journals Online (AJOL)

    Thus, Broensted acids and bases are no more substances, but individual types of particles. Due to the autoprotolysis of H2O molecules (not "autoionization of water"), the following equilibrium exists: H2O + H2O H3O+(aq) + OH-(aq) Through this protolysis it is more advantageous to argue rather with H3O+(aq) ions than ...

  4. Donor-acceptor diblock copolymers based on PPV and C-60 : Synthesis, thermal properties, and morphology

    NARCIS (Netherlands)

    van der Veen, MH; de Boer, B; Stalmach, U; van de wetering, KI; Hadziioannou, G; Veen, Marleen H. van der; Wetering, Karin I. van de


    An improved synthetic method to nitroxide end-capped poly(p-phenylenevinylene)s is presented. The nitroxide-functionalized PPVs are extended with a second coillike block by employing them as macroinitiators in a nitroxide-mediated radical polymerization (NMRP) of monomers like styrene,

  5. Characterization of donor-acceptor-pair emission in fluorescent 6H-SiC

    DEFF Research Database (Denmark)

    Ou, Yiyu; Jokubavicius, Valdas; Linnarsson, Margareta

    and varies N concentrations were grown by the fast sublimation growth process (FSGP) and analyzed by the photoluminescence (PL) and angle-resolved PL measurements. Secondary ion mass spectrometry (SIMS) and Raman spectroscopy confirm the increasing N concentration from sample #a to #e [2]. The PL spectra...... are shown in Fig. 1. It is seen that high-level p-type sample (#a) exhibits extremely low DAP emission efficiency, while low-level p-type samples (#b, #c) have relatively stronger DAP emission but still at a low level. Intense DAP emission was observed in n-type samples (#d, #e) and the strongest DAP...... emission occurred in sample d with B and N concentration difference of 4.6 x 1018 cm-3. Despite the intensity difference, all the DAP emission spectra show the same peak wavelength at 584 nm and with a full width at half maximum (FWHM) of 120 nm. From Fig. 2, it is shown that the peak wavelength blue...

  6. Three-dimensional orientational colocalization of individual donor--acceptor pairs. (United States)

    Hubner, Christian G; Ksenofontov, Vsevolod; Nolde, Fabian; Mullen, Klaus; Basche, Thomas


    We report on the determination of the three-dimensional orientation of the donor and acceptor transition dipoles in individual fluorescence resonance energy transfer (FRET) pairs by means of scanning optical microscopy with annular illumination. Knowledge of the mutual orientation of the donor and acceptor dipole is mandatory for reliable distance determination based on FRET efficiency measurements. In our model system perylenediimide as the donor and terryelenediimide as the acceptor are coupled via a stiff p-terphenyl linker. The absorption dipoles of the donor and acceptor are selectively addressed by the 488 nm and 647 line of an Ar/Kr mixed gas laser, respectively. A clear deviation from collinearity is observed with a distribution of misalignment angles peaked around 22 degrees.

  7. Time resolved resonant photoemission study of energy level alignment at donor/acceptor interfaces (United States)

    Costantini, R.; Pincelli, T.; Cossaro, A.; Verdini, A.; Goldoni, A.; Cichoň, S.; Caputo, M.; Pedio, M.; Panaccione, G.; Silly, M. G.; Sirotti, F.; Morgante, A.; Dell'Angela, M.


    The knowledge of the picosecond dynamics of the energy level alignment between donor and acceptor materials in organic photovoltaic devices under working conditions is a challenge for fundamental material research. We measured by means of time-resolved Resonant X-ray Photoemission Spectroscopy (RPES) the energy level alignment in ZnPc/C60 films. We employed 800 nm femtosecond laser pulses to pump the system simulating sunlight excitation and X-rays from the synchrotron as a probe. We measured changes in the valence bands due to pump induced modifications of the interface dipole. Our measurements prove the feasibility of time-resolved RPES with high repetition rate sources.

  8. Design and synthesis of new processible donor-acceptor dyad and triads

    NARCIS (Netherlands)

    Dhanabalan, A.; Knol, J.; Hummelen, J.C.; Janssen, R.A.J.


    We report the design, synthesis and characterizarion ofnew processible well-defined donor (D)-acceptor (A) dyads and A-D-A triads for use in photovoltaic devices. The donor oligomers, which consist either of oligoaniline, thiophene-pyrrole-thiophene, phenyl-pyrrole-phenyl, or

  9. Steric control of the donor/acceptor interface: Implications in organic photovoltaic charge generation

    KAUST Repository

    Holcombe, Thomas W.


    The performance of organic photovoltaic (OPV) devices is currently limited by modest short-circuit current densities. Approaches toward improving this output parameter may provide new avenues to advance OPV technologies and the basic science of charge transfer in organic semiconductors. This work highlights how steric control of the charge separation interface can be effectively tuned in OPV devices. By introducing an octylphenyl substituent onto the investigated polymer backbones, the thermally relaxed charge-transfer state, and potentially excited charge-transfer states, can be raised in energy. This decreases the barrier to charge separation and results in increased photocurrent generation. This finding is of particular significance for nonfullerene OPVs, which have many potential advantages such as tunable energy levels and spectral breadth, but are prone to poor exciton separation efficiencies. Computational, spectroscopic, and synthetic methods were combined to develop a structure-property relationship that correlates polymer substituents with charge-transfer state energies and, ultimately, device efficiencies. © 2011 American Chemical Society.

  10. Structure of the dimeric RC-LH1-PufX complex from Rhodobaca bogoriensis investigated by electron microscopy

    NARCIS (Netherlands)

    Semchonok, Dmitry A.; Chauvin, Jean-Paul; Frese, Raoul N.; Jungas, Colette; Boekema, Egbert J.


    Electron microscopy and single-particle averaging were performed on isolated reaction centre (RC)antenna complexes (RC-LH1-PufX complexes) of Rhodobaca bogoriensis strain LBB1, with the aim of establishing the LH1 antenna conformation, and, in particular, the structural role of the PufX protein.

  11. Attaching naphthalene derivatives onto BODIPY for generating excited triplet state and singlet oxygen: Tuning PET-based photosensitizer by electron donors (United States)

    Zhang, Xian-Fu; Feng, Nan


    meso-Naphthalene substituted BODIPY compounds were prepared in a facile one pot reaction. The naphthalene functionalization of BODIPY leads up to a 5-fold increase in the formation efficiency of excited triplet state and singlet oxygen in polar solvents. Steady state and time resolved fluorescence, laser flash photolysis, and quantum chemistry methods were used to reveal the mechanism. All measured data and quantum chemical results suggest that these systems can be viewed as electron donor-acceptor (D-A) pair (BODIPY acts as the acceptor), photoinduced charge transfer (PCT) or photoinduced electron transfer (PET) occurs upon photo excitation (D-A + hν → Dδ +-Aδ -, 0 PET-based photosensitizers (PSs) show different features from traditional PSs, such as the strong tunability by facile structural modification and good selectivity upon medium polarity. The new character for this type of PSs can lead to important applications in organic oxygenation reactions and photodynamic therapy of tumors.

  12. Radical-Molecule Reaction Mechanisms: Role of Electron Delocalization, Complex Formation, and Intramolecular Energy Transfer. (United States)

    Dubey, Manvendra Krishna

    This thesis presents: (1) measurements of the kinetics of the reactions of the OH radical with several molecules by the discharge flow technique, (2) reactivity trend analysis, electronic structure, and transition state calculations, (3) molecular beam electric deflection experiments of hot polyatomics. A synthesis of these studies demonstrates that radical-molecule reactions frequently involve an indirect mechanism and are not necessarily direct, activated, bimolecular processes. Indirect mechanisms arise when the reactant frontier orbitals do not transform to the product configuration. Compact reactivity trends among homologous reaction sets are defined by the difference between the ionization potential of the electron donor and the electron affinity of the electron acceptor and show that charge-transfer stabilizations (rather than thermodynamics) govern radical-molecule reactivity. A multiple transition state model is developed to predict the mixed bimolecular/termolecular kinetics implicit in the indirect mechanism. The fundamental assumption of rapid intramolecular energy redistribution in the energized complex in the model is validated by our electric deflection studies. Model calculations for the rm OH + HNO_3to H_2O + NO_3 reaction reproduce the small A factor, negative activation energy, and pressure dependence of the rate. They elucidate the reaction mechanism in molecular detail. The OH first bonds to either the O or N atom of HNO_3 to form an energized complex, which subsequently suffers one of three fates: dissociation to reactants via a loose transition state, dissociation to products via a tight transition state with a negative threshold, or collisional stabilization. These processes compete to determine the overall kinetics. Isotopic scrambling rates are predicted. Our model predicts faster rates than the NASA recommendation at low temperatures with potential consequences for stratospheric photochemistry. The rate constants of the reactions of OH

  13. Geometric and electronic structures of five-coordinate manganese(ii) "picket fence" porphyrin complexes. (United States)

    Yu, Qiang; Liu, Yanhong; Liu, Diansheng; Li, Jianfeng


    Three five-coordinate, high spin manganese(ii) "picket fence" porphyrin complexes, [Mn(TpivPP)(L)] (TpivPP = α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrinato; L = 1-MeIm (1-methylimidazole), 1-EtIm (1-ethylimidazole) and 2-MeHIm (2-methylimidazole)), are synthesized and studied by single-crystal X-ray, UV-vis and electronic paramagnetic resonance (EPR) spectroscopy. Structural parameters are investigated and compared with analogues. Low temperature (90 K), high field EPR studies of [Mn(TpivPP)(1-MeIm)] and [Mn(TpivPP)(2-MeHIm)] showed five resonances including characteristic signals at ∼5.9 and ∼2.0. The simulations of the EPR spectra give the zero field splitting (zfs) parameters (D, E and λ) and the hyperfine coupling constant (A).

  14. Improved visualization of vertebrate nuclear pore complexes by field emission scanning electron microscopy. (United States)

    Shaulov, Lihi; Harel, Amnon


    Field emission scanning electron microscopy (FESEM) can provide high-resolution three-dimensional surface imaging of many biological structures, including nuclear envelopes and nuclear pore complexes (NPCs). For this purpose, it is important to preserve NPCs as close as possible to their native morphology, embedded in undamaged nuclear membranes. We present optimized methodologies for FESEM imaging in a cell-free reconstitution system and for the direct visualization of mammalian cell nuclei. The use of anchored chromatin templates in the cell-free system is particularly advantageous for imaging fragile intermediates inhibited at early stages of assembly. Our new method for exposing the surface of mammalian nuclei results in an unprecedented quality of NPC images, avoiding detergent-induced and physical damage. These new methodologies pave the way for the combined use of FESEM imaging with biochemical and genetic manipulation, in cell-free systems and in mammalian cells. Copyright © 2012 Elsevier Ltd. All rights reserved.

  15. Synthesis, electron paramagnetic resonance studies and molecular calculations of N-aminopyrimidine salicylaldiminato copper (II) complex (United States)

    Yalçın, Şerife Pınar; Ceylan, Ümit; Sönmez, Mehmet; Hacıyusufoğlu, Mehmet Emin; Karavelioğlu, Hatice


    In this study, Cu(II) complex, C52H40CuN6O10, was synthesized and the molecular structure was characterized by experimental Electron Paramagnetic Resonance (EPR), vibrational frequencies, absorption wavelengths and compared with theoretical methods. The molecular geometry was calculated and optimized by using Gaussian 09 software and DFT-B3LYP and B3PW91 methods with the LanL2DZ basis sets in ground state. The theoretical vibrational frequencies, was optimized geometric parameters such as bond lengths, bond angles and torsion angles and absorption wavelengths, NBO, FMO analysis, HOMO-LUMO energy and nonlinear optical properties, molecular electrostatic potential, spin density have been calculated via quantum chemical methods. Theoretically calculated data were compared with experimentally measured data. Also, the results obtained by using the two basis sets were compared with each other.

  16. Dose effects in electron beam irradiation of DNA-complex thin films (United States)

    Li, W.; Jones, R.; Spaeth, H.; Steckl, A. J.


    Electron beam irradiation of double-stranded DNA (dsDNA)-surfactant thin films was investigated. Irradiation caused dissociation, leading to increasing thin film solubility in water and degradation of dsDNA. These two effects produced a maximum concentration of dsDNA in aqueous solution at 400 μC/cm2 dose. These properties resulted in dual-mode resist characteristics of the DNA-surfactant films. At low dose, the DNA films functioned as positive resist while at high dose they worked as negative resist. The transition between the two regimes also occurred at 400 μC/cm2. This implies that the cross-linking process (typical for negative resists) first requires the dissociation of the DNA-surfactant complex.

  17. A heterogeneous electronics architecture for dealing with complexity in modular robots

    DEFF Research Database (Denmark)

    Garcia, Ricardo Franco Mendoza


    Modular robots are robots built from many similar modules that can be arranged in different configurations to suit tasks in hand. Although promising, current incarnations of this technology suffer of an important drawback: modules are usually extremely expensive. This thesis proposes a heterogene......Modular robots are robots built from many similar modules that can be arranged in different configurations to suit tasks in hand. Although promising, current incarnations of this technology suffer of an important drawback: modules are usually extremely expensive. This thesis proposes...... a heterogeneous electronics architecture that addresses the price and complexity of modular robots by focusing on the good aspects of homogeneous and heterogeneous designs, such as sequential implementation and reusable components. The architecture was implemented in four robots: Odin V1, Odin V2, Thor...

  18. Electronic Structure of Transition Metal Clusters, Actinide Complexes and Their Reactivities

    Energy Technology Data Exchange (ETDEWEB)

    Krishnan Balasubramanian


    This is a continuing DOE-BES funded project on transition metal and actinide containing species, aimed at the electronic structure and spectroscopy of transition metal and actinide containing species. While a long term connection of these species is to catalysis and environmental management of high-level nuclear wastes, the immediate relevance is directly to other DOE-BES funded experimental projects at DOE-National labs and universities. There are a number of ongoing gas-phase spectroscopic studies of these species at various places, and our computational work has been inspired by these experimental studies and we have also inspired other experimental and theoretical studies. Thus our studies have varied from spectroscopy of diatomic transition metal carbides to large complexes containing transition metals, and actinide complexes that are critical to the environment. In addition, we are continuing to make code enhancements and modernization of ALCHEMY II set of codes and its interface with relativistic configuration interaction (RCI). At present these codes can carry out multi-reference computations that included up to 60 million configurations and multiple states from each such CI expansion. ALCHEMY II codes have been modernized and converted to a variety of platforms such as Windows XP, and Linux. We have revamped the symbolic CI code to automate the MRSDCI technique so that the references are automatically chosen with a given cutoff from the CASSCF and thus we are doing accurate MRSDCI computations with 10,000 or larger reference space of configurations. The RCI code can also handle a large number of reference configurations, which include up to 10,000 reference configurations. Another major progress is in routinely including larger basis sets up to 5g functions in thee computations. Of course higher angular momenta functions can also be handled using Gaussian and other codes with other methods such as DFT, MP2, CCSD(T), etc. We have also calibrated our RECP

  19. Traceability and Risk Analysis Strategies for Addressing Counterfeit Electronics in Supply Chains for Complex Systems. (United States)

    DiMase, Daniel; Collier, Zachary A; Carlson, Jinae; Gray, Robin B; Linkov, Igor


    Within the microelectronics industry, there is a growing concern regarding the introduction of counterfeit electronic parts into the supply chain. Even though this problem is widespread, there have been limited attempts to implement risk-based approaches for testing and supply chain management. Supply chain risk management tends to focus on the highly visible disruptions of the supply chain instead of the covert entrance of counterfeits; thus counterfeit risk is difficult to mitigate. This article provides an overview of the complexities of the electronics supply chain, and highlights some gaps in risk assessment practices. In particular, this article calls for enhanced traceability capabilities to track and trace parts at risk through various stages of the supply chain. Placing the focus on risk-informed decision making through the following strategies is needed, including prioritization of high-risk parts, moving beyond certificates of conformance, incentivizing best supply chain management practices, adoption of industry standards, and design and management for supply chain resilience. © 2016 Society for Risk Analysis.

  20. Aberration-corrected scanning transmission electron microscopy for complex transition metal oxides (United States)

    Qing-Hua, Zhang; Dong-Dong, Xiao; Lin, Gu


    Lattice, charge, orbital, and spin are the four fundamental degrees of freedom in condensed matter, of which the interactive coupling derives tremendous novel physical phenomena, such as high-temperature superconductivity (high-T c SC) and colossal magnetoresistance (CMR) in strongly correlated electronic system. Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it, and also indispensable for designing new materials and devices. Scanning transmission electron microscopy (STEM) integrating multiple techniques of structure imaging and spectrum analysis, is a comprehensive platform for providing structural, chemical and electronic information of materials with a high spatial resolution. Benefiting from the development of aberration correctors, STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization; many improvements have been achieved in recent years, thereby giving an in-depth insight into material research. Here, we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides; atomic-scale mapping of ferroelectric polarization, octahedral distortions and rotations, valence state, coordination and spin ordering are presented. We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides. Project supported by the National Key Basic Research Project, China (Grant No. 2014CB921002), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB07030200), and the National Natural Science Foundation of China (Grant Nos. 51522212 and 51421002).

  1. Electron Solvation in Liquid Ammonia: Lithium, Sodium, Magnesium, and Calcium as Electron Sources. (United States)

    Chaban, Vitaly V; Prezhdo, Oleg V


    A free electron in solution, known as a solvated electron, is the smallest possible anion. Alkali and alkaline earth atoms serve as electron donors in solvents that mediate outer-sphere electron transfer. We report herein ab initio molecular dynamics simulations of lithium, sodium, magnesium, and calcium in liquid ammonia at 250 K. By analyzing the electronic properties and the ionic and solvation structures and dynamics, we systematically characterize these metals as electron donors and ammonia molecules as electron acceptors. We show that the solvated metal strongly modifies the properties of its solvation shells and that the observed effect is metal-specific. Specifically, the radius and charge exhibit major impacts. The single solvated electron present in the alkali metal systems is distributed more uniformly among the solvent molecules of each metal's two solvation shells. In contrast, alkaline earth metals favor a less uniform distribution of the electron density. Alkali and alkaline earth atoms are coordinated by four and six NH3 molecules, respectively. The smaller atoms, Li and Mg, are stronger electron donors than Na and Ca. This result is surprising, as smaller atoms in a column of the periodic table have higher ionization potentials. However, it can be explained by stronger electron donor-acceptor interactions between the smaller atoms and the solvent molecules. The structure of the first solvation shell is sharpest for Mg, which has a large charge and a small radius. Solvation is weakest for Na, which has a small charge and a large radius. Weak solvation leads to rapid dynamics, as reflected in the diffusion coefficients of NH3 molecules of the first two solvation shells and the Na atom. The properties of the solvated electrons established in the present study are important for radiation chemistry, synthetic chemistry, condensed-matter charge transfer, and energy sources.

  2. Integrative Modeling of Biomolecular Complexes: HADDOCKing with Cryo-Electron Microscopy Data. (United States)

    van Zundert, Gydo C P; Melquiond, Adrien S J; Bonvin, Alexandre M J J


    Protein-protein interactions play a central role in all cellular processes. Insight into their atomic architecture is therefore of paramount importance. Cryo-electron microscopy (cryo-EM) is capable of directly imaging large macromolecular complexes. Unfortunately, the resolution is usually not sufficient for a direct atomic interpretation. To overcome this, cryo-EM data are often combined with high-resolution atomic structures. However, current computational approaches typically do not include information from other experimental sources nor a proper physico-chemical description of the interfaces. Here we describe the integration of cryo-EM data into our data-driven docking program HADDOCK and its performance on a benchmark of 17 complexes. The approach is demonstrated on five systems using experimental cryo-EM data in the range of 8.5-21 Å resolution. For several cases, cryo-EM data are integrated with additional interface information, e.g. mutagenesis and hydroxyl radical footprinting data. The resulting models have high-quality interfaces, revealing novel details of the interactions. Copyright © 2015 Elsevier Ltd. All rights reserved.

  3. High-potential perfluorinated phthalocyanine-fullerene dyads for generation of high-energy charge-separated states: formation and photoinduced electron-transfer studies. (United States)

    Das, Sushanta K; Mahler, Andrew; Wilson, Angela K; D'Souza, Francis


    High oxidation potential perfluorinated zinc phthalocyanines (ZnF(n)Pcs) are synthesised and their spectroscopic, redox, and light-induced electron-transfer properties investigated systematically by forming donor-acceptor dyads through metal-ligand axial coordination of fullerene (C60) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine- (Py) and phenylimidazole-functionalised fullerene (C60Im) derivatives to the zinc centre of the F(n)Pcs. The determined binding constants, K, in o-dichlorobenzene for the 1:1 complexes are in the order of 10(4) to 10(5) M(-1); nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6-31G* method. The HOMO and LUMO levels are located on the Pc and C60 entities, respectively; this suggests the formation of ZnF(n)Pc(.+)-C60Im(.-) and ZnF(n)Pc(.+)-C60Py(.-) (n=0, 8 or 16) intra-supramolecular charge-separated states during electron transfer. Electrochemical studies on the ZnPc-C60 dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge-separated states. The energy of the charge-separated state for dyads composed of ZnF(n)Pc is higher than that of normal ZnPc-C60 dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar-energy harvesting and optoelectronic device building applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. High-resolution cryo-electron microscopy on macromolecular complexes and cell organelles. (United States)

    Hoenger, Andreas


    Cryo-electron microscopy techniques and computational 3-D reconstruction of macromolecular assemblies are tightly linked tools in modern structural biology. This symbiosis has produced vast amounts of detailed information on the structure and function of biological macromolecules. Typically, one of two fundamentally different strategies is used depending on the specimens and their environment. A: 3-D reconstruction based on repetitive and structurally identical unit cells that allow for averaging, and B: tomographic 3-D reconstructions where tilt-series between approximately ± 60 and ± 70° at small angular increments are collected from highly complex and flexible structures that are beyond averaging procedures, at least during the first round of 3-D reconstruction. Strategies of group A are averaging-based procedures and collect large number of 2-D projections at different angles that are computationally aligned, averaged together, and back-projected in 3-D space to reach a most complete 3-D dataset with high resolution, today often down to atomic detail. Evidently, success relies on structurally repetitive particles and an aligning procedure that unambiguously determines the angular relationship of all 2-D projections with respect to each other. The alignment procedure of small particles may rely on their packing into a regular array such as a 2-D crystal, an icosahedral (viral) particle, or a helical assembly. Critically important for cryo-methods, each particle will only be exposed once to the electron beam, making these procedures optimal for highest-resolution studies where beam-induced damage is a significant concern. In contrast, tomographic 3-D reconstruction procedures (group B) do not rely on averaging, but collect an entire dataset from the very same structure of interest. Data acquisition requires collecting a large series of tilted projections at angular increments of 1-2° or less and a tilt range of ± 60° or more. Accordingly, tomographic data

  5. Single particle electron microscopy reconstruction of the exosome complex using the random conical tilt method. (United States)

    Liu, Xueqi; Wang, Hong-Wei


    Single particle electron microscopy (EM) reconstruction has recently become a popular tool to get the three-dimensional (3D) structure of large macromolecular complexes. Compared to X-ray crystallography, it has some unique advantages. First, single particle EM reconstruction does not need to crystallize the protein sample, which is the bottleneck in X-ray crystallography, especially for large macromolecular complexes. Secondly, it does not need large amounts of protein samples. Compared with milligrams of proteins necessary for crystallization, single particle EM reconstruction only needs several micro-liters of protein solution at nano-molar concentrations, using the negative staining EM method. However, despite a few macromolecular assemblies with high symmetry, single particle EM is limited at relatively low resolution (lower than 1 nm resolution) for many specimens especially those without symmetry. This technique is also limited by the size of the molecules under study, i.e. 100 kDa for negatively stained specimens and 300 kDa for frozen-hydrated specimens in general. For a new sample of unknown structure, we generally use a heavy metal solution to embed the molecules by negative staining. The specimen is then examined in a transmission electron microscope to take two-dimensional (2D) micrographs of the molecules. Ideally, the protein molecules have a homogeneous 3D structure but exhibit different orientations in the micrographs. These micrographs are digitized and processed in computers as "single particles". Using two-dimensional alignment and classification techniques, homogenous molecules in the same views are clustered into classes. Their averages enhance the signal of the molecule's 2D shapes. After we assign the particles with the proper relative orientation (Euler angles), we will be able to reconstruct the 2D particle images into a 3D virtual volume. In single particle 3D reconstruction, an essential step is to correctly assign the proper orientation

  6. Spectrophotometric and spectroscopic studies of charge transfer complex of 1-Naphthylamine as an electron donor with picric acid as an electron acceptor in different polar solvents (United States)

    Singh, Neeti; Ahmad, Afaq


    The charge transfer complex of 1-Naphthylamine as a donor with π-acceptor picric acid has been studied spectrophotometrically in different solvents at room temperature. The results indicate that the formation of charge transfer complex is high in less polar solvent. The stoichiometry of the complex was found to be 1:1 by straight line method. The data are analysed in terms of formation constant ( KCT), molar extinction coefficient ( ɛCT), standard free energy (Δ G o), oscillator strength ( ƒ), transition dipole moment ( μ EN), resonance energy ( R N) and ionization potential ( I D). It is concluded that the formation constant ( KCT) of the complex is found to be depends upon the nature of both electron acceptor and donor and also on the polarity of solvents. Further the charge transfer molecular complex between picric acid and 1-Naphthylamine is stabilized by hydrogen bonding.

  7. Cooperative catalysis: electron-rich Fe-H complexes and DMAP, a successful "joint venture" for ultrafast hydrogen production. (United States)

    Rommel, Susanne; Hettmanczyk, Lara; Klein, Johannes E M N; Plietker, Bernd


    A series of defined iron-hydrogen complexes was prepared in a straightforward one-pot approach. The structure and electronic properties of such complexes were investigated by means of quantum-chemical analysis. These new complexes were then applied in the dehydrogenative silylation of methanol. The complex (dppp)(CO)(NO)FeH showed a remarkable activity with a TOF of more than 600 000 h(-1) of pure hydrogen gas within seconds. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Making oxidation potentials predictable: Coordination of additives applied to the electronic fine tuning of an iron(II) complex

    KAUST Repository

    Haslinger, Stefan


    This work examines the impact of axially coordinating additives on the electronic structure of a bioinspired octahedral low-spin iron(II) N-heterocyclic carbene (Fe-NHC) complex. Bearing two labile trans-acetonitrile ligands, the Fe-NHC complex, which is also an excellent oxidation catalyst, is prone to axial ligand exchange. Phosphine- and pyridine-based additives are used for substitution of the acetonitrile ligands. On the basis of the resulting defined complexes, predictability of the oxidation potentials is demonstrated, based on a correlation between cyclic voltammetry experiments and density functional theory calculated molecular orbital energies. Fundamental insights into changes of the electronic properties upon axial ligand exchange and the impact on related attributes will finally lead to target-oriented manipulation of the electronic properties and consequently to the effective tuning of the reactivity of bioinspired systems.

  9. Aligning complex processes and electronic health record templates: a quality improvement intervention on inpatient interdisciplinary rounds. (United States)

    Mosher, Hilary J; Lose, Daniel T; Leslie, Russell; Pennathur, Priyadarshini; Kaboli, Peter J


    Interdisciplinary rounds (IDR) with documentation have become a standard of care, but the process has been incompletely described in academic general medical settings. Checklists are promoted, yet standardized formats may not reflect the variability and work flow of rounds or support the cognitive development of medical trainees. We describe IDR processes in an academic general medicine inpatient setting and present a rapid cycle quality improvement (QI) project that improved IDR documentation rates in the electronic health record. The project team observed existing daily IDR rounds on two medical inpatient units at the Iowa City VA Medical Center, with three resident teams and maximum census of 42 patients. The major intervention was a redesigned note template, with accompanying resident educational materials. The primary outcome was note completion rates by charge nurses; IDR team member satisfaction and participation, discussion time and balancing metrics (i.e., excess bed days of care, length of stay, and 30-day readmissions) were also assessed. An electronic template and accompanying educational materials designed to parallel the heuristic problem-solving activities of the IDR team led to improvements in IDR note completion rates from 27 to 69 %. Team member satisfaction was high and participation was stable. Discussion time per patient increased modestly, but varied widely between resident teams and by patient. Balancing metrics were unchanged. Unstructured evaluation indicated that documentation times were reduced, and IDR documentation became more timely and useful. IDR notes designed to support the problem-solving processes of an interdisciplinary group improved the timeliness and perceived value of IDR documentation and met regulatory standards. Aligning complex processes and educational and documentation needs during IDR may create an efficient opportunity for sustainable interdisciplinary work and learning in an academic setting.

  10. Neuronal nitric oxide synthase immunopositive neurons in cat vestibular complex: a light and electron microscopic study. (United States)

    Papantchev, V; Paloff, A; Hinova-Palova, D; Hristov, S; Todorova, D; Ovtscharoff, W


    Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. Nevertheless, there are little data about the neuronal nitric oxide synthase immunoreactivity (nNOS-ir) in the vestibular complex of a cat. In this respect, the aims of this study were to: (1) demonstrate nNOS-ir in the neurons and fibers, from all major and accessory vestibular nuclei; (2) describe their light microscopic morphology and distribution; (3) investigate and analyze the ultrastructure of the NOS I-immunopositive neurons, fibers, and synaptic boutons. For demonstration of the nNOS-ir, the peroxidase-antiperoxidase-diaminobenzidin method was applied. Immunopositive for nNOS neurons and fibers were present in all major and accessory vestibular nuclei. On the light microscope level, the immunopositive neurons were different in shape and size. According to the latter, they were divided into four groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), large type I (with diameter from 30 to 40 microm), and large type II (with diameter greater than 40 microm). On the electron microscope level, the immunoproduct was observed in neurons, dendrites, and terminal boutons. According to the ultrastructural features, the neurons were divided into three groups--small (with diameter less than 15 microm), medium-sized (with diameter from 15 to 30 microm), and large (with diameter greater than 30 microm). At least two types of nNOS-ir synaptic boutons were easily distinguished. As a conclusion, we hope that this study will contribute to a better understanding of the functioning of the vestibular complex in cat and that some of the data presented could be extrapolated to other mammals, including human.

  11. The Electronic Structure of Mn in Oxides, Coordination Complexes, and the Oxygen-Evolving Complex of Photosystem II Studied by Resonant Inelastic X-ray Scattering (United States)

    Yano, Junko; Visser, Hendrik; Robblee, John H.; Gu, Weiwei; de Groot, Frank M. F.; Christou, George; Pecoraro, Vincent L.


    Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and to study the electronic structure in oxides, molecular coordination complexes, as well as the S1 and S2 states of the oxygen-evolving complex (OEC) of photosystem II (PS II). The RIXS data yield two-dimensional plots that can be interpreted along the incident (absorption) energy or the energy transfer axis. The second energy dimension separates the pre-edge (predominantly 1s to 3d transitions) from the main K-edge, and a detailed analysis is thus possible. The 1s2p RIXS final-state electron configuration along the energy transfer axis is identical to conventional L-edge absorption spectroscopy, and the RIXS spectra are therefore sensitive to the Mn spin state. This new technique thus yields information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, i.e., (3d,3d) and (2p,3d) two-electron interactions are crucial to describe the spectral shapes in all systems. We propose to explain the shift of the K pre-edge absorption energy upon Mn oxidation in terms of the effective number of 3d electrons (fractional 3d orbital population). The spectral changes in the Mn 1s2p3/2 RIXS spectra between the PS II S1 and S2 states are small compared to that of the oxides and two of the coordination complexes (MnIII(acac)3 and MnIV(sal)2(bipy)). We conclude that the electron in the step from S1 to S2 is transferred from a strongly delocalized orbital. PMID:15303869

  12. Hydrotris(triazolyl)borate complexes as functional models for Cu nitrite reductase: the electronic influence of distal nitrogens. (United States)

    Kumar, Mukesh; Dixon, Natalie A; Merkle, Anna C; Zeller, Matthias; Lehnert, Nicolai; Papish, Elizabeth T


    Hydrotris(triazolyl)borate (Ttz) ligands form CuNO(x) (x = 2, 3) complexes for structural and functional models of copper nitrite reductase. These complexes have distinct properties relative to complexes of hydrotris(pyrazolyl)borate (Tp) and neutral tridentate N-donor ligands. The electron paramagnetic resonance spectra of five-coordinate copper complexes show rare nitrogen superhyperfine couplings with the Ttz ligand, indicating strong σ donation. The copper(I) nitrite complex [PPN](+)[(Ttz(tBu,Me))Cu(I)NO(2)](-) has been synthesized and characterized and allows for the stoichiometric reduction of NO(2)(-) to NO with H(+) addition. Anionic Cu(I) nitrite complexes are unusual and are stabilized here for the first time because Ttz is a good π acceptor.

  13. Bis(. eta. sup 6 -hexamethylbenzene)(. eta. sup 6 ,. eta. sup 6 -polycyclic aromatic)diruthenium(II,II) complexes and their two-electron reduction to cyclohexadienyl anion complexes

    Energy Technology Data Exchange (ETDEWEB)

    Plitzko, K.; Wehrle, G.; Gollas, B.; Rapko, B.; Dannheim, J.; Boekelheide, V. (Univ. of Oregon, Eugene (USA))


    The bis({eta}{sup 6}-hexamethylbenzene)({eta}{sup 6},{eta}{sup 6}-polycyclic aromatic)diruthenium(II,II) complexes where the polycyclic aromatic ligands are phenanthrene, 9,10-dihydrophenanthrene, biphenyl, 3,3{prime},5,5{prime}-tetramethylbiphenyl, 4,5,9,10-tetrahydropyrene, and triphenylene, respectively, have been synthesized and their electrochemical properties measured. A two-electron chemical reduction of each of these 4+ diruthenium complexes has led to the isolation and characterization of each of their corresponding 2+ diruthenium complexes. On the basis of analyses of their {sup 1}H and {sup 13}C NMR spectra, structural assignments have been made for all of these 2+ diruthenium complexes.

  14. Electron spin resonance and optical resonance studies on copper(II) complexes with vanadate, molybdate and tungstate anions (United States)

    Singh, Raghuvir


    A series of complexes of the form Cu(An) nL x · yH 2O, where An = vanadate, molybdate or tungstate anion, L = pyridine, α-, β- or γ-picoline, n = 1 or 2; x = 1-4 and y = 0-3, have been synthesized and characterized by electron spin resonance, photoacoustic and electronic spectral studies as well as infrared spectroscopy in the solid and solution state. The different coordination sites of the ligands and anions have been interpreted from infrared and electronic spectral data. Electron spin resonance spectral data show the square planar or distorted octahedral (in a few cases five-coordinate geometry) stereochemistry around copper(II) in these complexes. Parameters such as g∥, g⊥, A∥, A⊥, , , α 2 and β 21 calculated from electron spin resonance data indicate the presence of unpaired electrons in dx2- y2 or dz2 orbitals. The results of electronic and photoacoustic spectral studies are in good accord with ESR data.

  15. Molecular dynamics simulations give insight into the conformational change, complex formation, and electron transfer pathway for cytochrome P450 reductase (United States)

    Sündermann, Axel; Oostenbrink, Chris


    Cytochrome P450 reductase (CYPOR) undergoes a large conformational change to allow for an electron transfer to a redox partner to take place. After an internal electron transfer over its cofactors, it opens up to facilitate the interaction and electron transfer with a cytochrome P450. The open conformation appears difficult to crystallize. Therefore, a model of a human CYPOR in the open conformation was constructed to be able to investigate the stability and conformational change of this protein by means of molecular dynamics simulations. Since the role of the protein is to provide electrons to a redox partner, the interactions with cytochrome P450 2D6 (2D6) were investigated and a possible complex structure is suggested. Additionally, electron pathway calculations with a newly written program were performed to investigate which amino acids relay the electrons from the FMN cofactor of CYPOR to the HEME of 2D6. Several possible interacting amino acids in the complex, as well as a possible electron transfer pathway were identified and open the way for further investigation by site directed mutagenesis studies. PMID:23832577

  16. Electron microscopy of complexes of isolated acetylcholine receptor, biotinyl-toxin, and avidin

    Energy Technology Data Exchange (ETDEWEB)

    Holtzman, E. (Columbia Univ., New York); Wise, D.; Wall, J.; Karlin, A.


    The principal curarimimetic toxin of Naja naja siamensis derivatized with biothinyl groups binds specifically both to acetylcholine receptor, isolated from Torpedo californica electric tissue, and to avidin. Isolated complexes of receptor monomer or dimer, biotinyl-toxin, and avidin were negatively stained and examined in the scanning transmission electron microscope. We measured the angle made by the radius to each avidin bound at the periphery of a monomeric unit in dimer to the axis connecting the centers of the monomers, starting at the crosslink between the monomers. We infer from the distribution of these angles that one toxin binding site is located in the range of 45/sup 0/ to 85/sup 0/ and another at about 100/sup 0/ further from the crosslink between the monomers. Because it is known that there are two toxin binding sites per monomer, associated with the two ..cap alpha.. chains, the bound avidins presumably point to portions of the ..cap alpha.. chains, indicating their positions relative to that portion of the delta chain located at the crosslink between monomers in dimer.

  17. Complexation and Electronic Communication between Corannulene-Based Buckybowls and a Curved Truxene-TTF Donor. (United States)

    Gallego, María; Calbo, Joaquín; Krick Calderon, Rafael M; Pla, Paula; Hsieh, Ya-Chu; Pérez, Emilio M; Wu, Yao-Ting; Ortí, Enrique; Guldi, Dirk M; Martín, Nazario


    The association behavior of an electron-donating, bowl-shaped, truxene-based tetrathiafulvalene (truxTTF) with two corannulene-based fullerene fragments, C32 H12 and C38 H14 , is investigated in several solvents. Formation of 1:1 complexes is followed by absorption titrations and complemented by density functional theory (DFT) calculations. The binding constants are in the range log Ka =2.9-3.5. DFT calculations reveal that the most stable arrangement is the conformation in which the 1,3-dithiole ring of truxTTF is placed inside the concave cavity of the corannulene derivative. This arrangement is confirmed experimentally by NMR measurements, and implies that a combination of π-π and CH-π interactions is the driving force for association. Time-dependent DFT calculations reproduce the experimental UV/Vis titrations and provide a detailed understanding of the spectral changes observed. Femtosecond transient absorption studies reveal the processes occurring after photoexcitation of either C32 H12 or C38 H14 and their supramolecular associates with truxTTF. In the case of truxTTF⋅C38 H14 , photoexcitation yields the charge-separated state truxTTF(.+) ⋅C38 H14(.-) with a lifetime of approximately 160 ps. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Electronic transient spectroscopy from the deep UV to the NIR: unambiguous disentanglement of complex processes. (United States)

    Riedle, Eberhard; Bradler, Maximilian; Wenninger, Matthias; Sailer, Christian F; Pugliesi, Igor


    Complex multi-stage relaxation and reaction pathways after the optical excitation of molecules makes the disentanglement of the underlying mechanisms challenging. We present four examples that a new transient spectrometer with excitation fully tunable from the deep UV to the IR and 225 to 1700 nm probing allows for an analysis with greatly reduced ambiguity. The temporal resolution of about 50 fs allows us to resolve all relevant processes. For each example there is a new twist in the sequence of relaxation steps that had previously been overlooked. In malachite green it appears that the importance of the phenyl twisting has been overemphasized and rather a charge transfer state should be considered. In TINUVIN-P the predicted twisting as the driving motion for the ultrafast IC is confirmed and leads to a resolution of the earlier puzzle that the sub-5 ps regime shows kinetics deviating from a pure cooling process despite the sub-ps proton transfer cycle. For the bond cleavage of Ph2CH-Cl and Ph2CH-Br the degree of electron transfer within the radical pair can now be determined quantitatively and leads to a profound understanding of the long-term cation yield. For the first time coherent wavepacket motion in the photoproducts is reported. Last but not least the measurement of the GSB recovery in the deep UV allows for the surprising result, that even after S2 excitation of cyclopentenones the triplet states are reached with near unity probability within a few picoseconds.

  19. Identification of Copper(II) Complexes in Aqueous Solution by Electron Spin Resonance: An Undergraduate Coordination Chemistry Experiment. (United States)

    Micera, G.; And Others


    Background, procedures, and results are provided for an experiment which examines, through electron spin resonance spectroscopy, complex species formed by cupric and 2,6-dihydroxybenzoate ions in aqueous solutions. The experiment is illustrative of several aspects of inorganic and coordination chemistry, including the identification of species…

  20. Formation of W(3)A(1) electron-transferring flavoprotein (ETF) hydroquinone in the trimethylamine dehydrogenase x ETF protein complex. (United States)

    Jang, M H; Scrutton, N S; Hille, R


    The electron-transferring flavoprotein (ETF) from Methylophilus methylotrophus (sp. W(3)A(1)) exhibits unusual oxidation-reduction properties and can only be reduced to the level of the semiquinone under most circumstances (including turnover with its physiological reductant, trimethylamine dehydrogenase (TMADH), or reaction with strong reducing reagents such as sodium dithionite). In the present study, we demonstrate that ETF can be reduced fully to its hydroquinone form both enzymatically and chemically when it is in complex with TMADH. Quantitative titration of the TMADH x ETF protein complex with sodium dithionite shows that a total of five electrons are taken up by the system, indicating that full reduction of ETF occurs within the complex. The results indicate that the oxidation-reduction properties of ETF are perturbed upon binding to TMADH, a conclusion further supported by the observation of a spectral change upon formation of the TMADH x ETF complex that is due to a change in the environment of the FAD of ETF. The results are discussed in the context of ETF undergoing a conformational change during formation of the TMADH x ETF electron transfer complex, which modulates the spectral and oxidation-reduction properties of ETF such that full reduction of the protein can take place.

  1. High-Frequency and -Field Electron Paramagnetic Resonance of High-Spin Manganese(III) in Porphyrinic Complexes. (United States)

    Krzystek, J.; Telser, Joshua; Pardi, Luca A.; Goldberg, David P.; Hoffman, Brian M.; Brunel, Louis-Claude


    High-field and -frequency electron paramagnetic resonance (HFEPR) spectroscopy has been used to study two complexes of high-spin manganese(III), d(4), S = 2. The complexes studied were (tetraphenylporphyrinato)manganese(III) chloride and (phthalocyanato)manganese(III) chloride. Our previous HFEPR study (Goldberg, D. P.; Telser, J.; Krzystek, J.; Montalban, A. G.; Brunel, L.-C.; Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1997, 119, 8722-8723) included results on the porphyrin complex; however, we were unable to obtain true powder pattern HFEPR spectra, as the crystallites oriented in the intense external magnetic field. In this work we are now able to immobilize the powder, either in an n-eicosane mull or KBr pellet and obtain true powder pattern spectra. These spectra have been fully analyzed using spectral simulation software, and a complete set of spin Hamiltonian parameters has been determined for each complex. Both complexes are rigorously axial systems, with relatively low magnitude zero-field splitting: D approximately -2.3 cm(-)(1) and g values quite close to 2.00. Prior to this work, no experimental nor theoretical data exist for the metal-based electronic energy levels in Mn(III) complexes of porphyrinic ligands. This lack of information is in contrast to other transition metal complexes and is likely due to the dominance of ligand-based transitions in the absorption spectra of Mn(III) complexes of this type. We have therefore made use of theoretical values for the electronic energy levels of (phthalocyanato)copper(II), which electronically resembles these Mn(III) complexes. This analogy works surprisingly well in terms of the agreement between the calculated and experimentally determined EPR parameters. These results show a significant mixing of the triplet (S = 1) excited state with the quintet (S = 2) ground state in Mn(III) complexes with porphyrinic ligands. This is in agreement with the experimental observation of lower spin ground states in

  2. A Mononuclear Mn(II) Pseudoclathrochelate Complex Studied by Multi-Frequency Electron-Paramagnetic-Resonance Spectroscopy. (United States)

    Azarkh, Mykhailo; Penkova, Larysa V; Kats, Svitlana V; Varzatskii, Oleg A; Voloshin, Yan Z; Groenen, Edgar J J


    Knowledge of the correlation between structural and spectroscopic properties of transition-metal complexes is essential to deepen the understanding of their role in catalysis, molecular magnetism, and biological inorganic chemistry. It provides topological and, sometimes, functional insight with respect to the active site properties of metalloproteins. The electronic structure of a high-spin mononuclear Mn(II) pseudoclathrochelate complex has been investigated by electron-paramagnetic-resonance (EPR) spectroscopy at 9.5 and 275.7 GHz. A substantial, virtually axial zero-field splitting with D = -9.7 GHz (-0.32 cm(-1)) is found, which is the largest one reported to date for a Mn(II) complex with six nitrogen atoms in the first coordination sphere.

  3. Impact of electric-field-dependent dielectric constants on two-dimensional electron gases in complex oxides (United States)

    van de Walle, Chris; Peelaers, Hartwin; Krishnaswamy, Karthik; Gordon, Luke; Steiauf, Daniel; Sarwe, Anna; Janotti, Anderson

    A high-density two-dimensional electron gas (2DEG) can be formed at interfaces of complex oxides. The electric field in the vicinity of the interface depends on the dielectric properties of the material as well as on the electron distribution. However, electric fields can strongly modify the dielectric constant of SrTiO3 (STO) as well as other complex oxides. Solving the electrostatic problem thus requires a self-consistent approach in which the dielectric constant varies according to the local magnitude of the field. We have implemented the field dependence of the dielectric constant in a Schrodinger-Poisson solver and use the SrTiO3/GdTiO3 interface as an example to discuss the importance of taking this field dependence into account when modeling interfaces of complex oxides. This work was supported by ONR and LEAST.

  4. Electron spin-lattice relaxation of the S0 state of the oxygen-evolving complex in photosystem II and of dinuclear manganese model complexes. (United States)

    Kulik, L V; Lubitz, W; Messinger, J


    The temperature dependence of the electron spin-lattice relaxation time T1 was measured for the S0 state of the oxygen-evolving complex (OEC) in photosystem II and for two dinuclear manganese model complexes by pulse EPR using the inversion-recovery method. For [Mn(III)Mn(IV)(mu-O)2 bipy4]ClO4, the Raman relaxation process dominates at temperatures below 50 K. In contrast, Orbach type relaxation was found for [Mn(II)Mn(III)(mu-OH)(mu-piv)2(Me3 tacn)2](ClO4)2 between 4.3 and 9 K. For the latter complex, an energy separation of 24.7-28.0 cm(-1) between the ground and the first excited electronic state was determined. In the S0 state of photosystem II, the T1 relaxation times were measured in the range of 4.3-6.5 K. A comparison with the relaxation data (rate and pre-exponential factor) of the two model complexes and of the S2 state of photosystem II indicates that the Orbach relaxation process is dominant for the S0 state and that its first excited state lies 21.7 +/- 0.4 cm(-1) above its ground state. The results are discussed with respect to the structure of the OEC in photosystem II.

  5. Fluorescent copper(II complexes: The electron transfer mechanism, interaction with bovine serum albumin (BSA and antibacterial activity

    Directory of Open Access Journals (Sweden)

    Madhumita Hazra


    Full Text Available Dinuclear copper(II complexes with formula [Cu2(L2(N32] (1 and [Cu2(L2(NCS2] (2 HL = (1-[(3-methyl-pyridine-2-ylimino-methyl]-naphthalen-2-ol were synthesized by controlling the molar ratio of Cu(OAC2·6H2O, HL, sodium azide (1 and ammonium thiocyanate (2. The end on bridges appear exclusively in azide and thiocyanate to copper complexes. The electron transfer mechanism of copper(II complexes is examined by cyclic voltammetry indicating copper(II complexes are Cu(II/Cu(I couple. The interactions of copper(II complexes towards bovine serum albumin (BSA were examined with the help of absorption and fluorescence spectroscopic tools. We report a superficial solution-based route for the synthesis of micro crystals of copper complexes with BSA. The antibacterial activity of the Schiff base and its copper complexes were investigated by the agar disc diffusion method against some species of pathogenic bacteria (Escherichia coli, Vibrio cholerae, Streptococcus pneumonia and Bacillus cereus. It has been observed that the antibacterial activity of all complexes is higher than the ligand.

  6. Mass, IR, electronic and EPR spectral studies on transition metal complexes with a new tetradentate 12-membered new macrocyclic ligand (United States)

    Chandra, Sulekh; Gupta, Lokesh Kumar


    Complexes of Cr(III), Co(II), Ni(II) and Cu(II) containing a novel macrocyclic tetradentate nitrogen donor (N 4) ligand prepared via reaction of 2,3-hexanedione and ethylenediamine has been prepared and characterized. The newly synthesized ligand (L) and its complexes have been characterized on the basis of elemental analysis, molar conductance, magnetic moment susceptibility, EI-Mass, IR, Electronic and EPR spectral studies. The complexes are of high-spin type and four coordinated tetrahedral, five coordinated square pyramidal and six coordinated octahedral/tetragonal geometries. The ligand (L) and its soluble transition metal complexes have also been screened against different bacteria and plant pathogenic fungi in vitro.

  7. Cobalt(II) "scorpionate" complexes as models for cobalt-substituted zinc enzymes: electronic structure investigation by high-frequency and -field electron paramagnetic resonance spectroscopy. (United States)

    Krzystek, J; Swenson, Dale C; Zvyagin, S A; Smirnov, Dmitry; Ozarowski, Andrew; Telser, Joshua


    A series of complexes of formula Tp(R,R')CoL, where Tp(R,R'-) = hydrotris(3-R,5-R'-pyrazol-1-yl)borate ("scorpionate") anion (R = tert-butyl, R' = H, Me, 2'-thienyl (Tn), L = Cl(-), NCS(-), NCO(-), N(3)(-)), has been characterized by electronic absorption spectroscopy in the visible and near-infrared (near-IR) region and by high-frequency and -field electron paramagnetic resonance (HFEPR). Reported here are also crystal structures of seven members of the series that have not been reported previously: R' = H, L = NCO(-), N(3)(-); R' = Me, L = Cl(-), NCS(-), NCO(-), N(3)(-); R' = Tn, L = Cl(-), NCS(-). These include a structure for Tp(t-Bu,Me)CoCl different from that previously reported. All of the investigated complexes contain a four-coordinate cobalt(II) ion (3d(7)) with approximate C(3v) point group symmetry about the metal ion and exhibit an S = (3)/(2) high-spin ground state. The use of HFEPR allows extraction of the full set of intrinsic S = (3)/(2) spin Hamiltonian parameters (D, E, and g values). The axial zero-field splitting parameter, D, for all investigated Tp(R,R')CoL complexes is always positive, a fact not easily determined by other methods. However, the magnitude of this parameter varies widely: 2.4 cm(-1) zinc enzymes.

  8. Synthesis, electronic and ESR spectral studies on copper(II) nitrate complexes with some acylhydrazines and hydrazones (United States)

    Singh, Vinod P.


    This paper describes the preparation of [Cu(bh) 2(H 2O) 2](NO 3) 2], [Cu(ibh) 2(NO 3) 2], [Cu(ibh) 2(H 2O) 2](NO 3) 2 and [Cu(iinh) 2(NO 3) 2] (bh = benzoyl hydrazine (C 6H 5CONHNH 2); ibh = isonicotinoyl hydrazine (NC 5H 4CONHNH 2); ibh = isopropanone benzoyl hydrazone (C 6H 5CONHN=C(CH 3) 2; iinh = isopropanone isonicotinoyl hydrazone (NC 5H 4CONHN=C(CH 3) 2). These copper(II) complexes are characterized by elemental analyses, molar conductances, dehydration studies, ESR, IR and electronic spectral studies. The electronic and ESR spectra indicate that each complex exhibits a six-coordinate tetragonally distorted octahedral geometry in the solid state and in DMSO solution. The ESR spectra of most of the complexes are typically isotropic type at room temperature (300 K) in solid state as well as in DMSO solution. However, all the complexes exhibit invariably axial signals at 77 K in DMSO solution. The trend g|| > g⊥ > ge, observed in all the complexes suggests the presence of an unpaired electron in the d-y orbital of the Cu(II). The bh and inh ligands bond to Cu(II) through the >C dbnd O and sbnd NH 2 groups whereas, ibh and iinh bond through >C dbnd O and >C dbnd N sbnd groups. The IR spectra of bh and ibh complexes also show H sbnd O sbnd H stretching and bending modes of coordinated water.

  9. Quantum Computational Studies of Electron Transfer in Respiratory Complex III and its Application for Designing New Mitocan Drugs (United States)

    Hagras, Muhammad Ahmed

    Electron transfer occurs in many biological systems which are imperative to sustain life; oxidative phosphorylation in prokaryotes and eukaryotes, and photophosphorylation in photosynthetic and plant cells are well-balanced and complementary processes. Investigating electron transfer in those natural systems provides detailed knowledge of the atomistic events that lead eventually to production of ATP, or harvesting light energy. Ubiquinol:cytochrome c oxidoreductase complex (also known as bc 1 complex, or respiratory complex III) is a middle player in the electron transport proton pumping orchestra, located in the inner-mitochondrial membrane in eukaryotes or plasma membrane in prokaryotes, which converts the free energy of redox reactions to electrochemical proton gradient across the membrane, following the fundamental chemiosmotic principle discovered by Peter Mitchell 1. In humans, the malfunctioned bc1 complex plays a major role in many neurodegenerative diseases, stress-induced aging, and cancer development, because it produces most of the reactive oxygen species, which are also involved in cellular signaling 2. The mitochondrial bc1 complex has an intertwined dimeric structure comprised of 11 subunits in each monomer, but only three of them have catalytic function, and those are the only domains found in bacterial bc1 complex. The core subunits include: Rieske domain, which incorporates iron-sulfur cluster [2Fe-2S]; trans-membrane cytochrome b domain, incorporating low-potential heme group (heme b L) and high-potential heme group (heme b H); and cytochrome c1 domain, containing heme c1 group and two separate binding sites, Qo (or QP) site where the hydrophobic electron carrier ubihydroquinol QH2 is oxidized, and Qi (or QN) site where ubiquinone molecule Q is reduced 3. Electrons and protons in the bc1 complex flow according to the proton-motive Q-cycle proposed by Mitchell, which includes a unique electron flow bifurcation at the Qo site. At this site, one

  10. Amyloid-beta leads to impaired cellular respiration, energy production and mitochondrial electron chain complex activities in human neuroblastoma cells. (United States)

    Rhein, V; Baysang, G; Rao, S; Meier, F; Bonert, A; Müller-Spahn, F; Eckert, A


    Evidence suggests that amyloid-beta (Abeta) protein is a key factor in the pathogenesis of Alzheimer's disease (AD) and it has been recently proposed that mitochondria are involved in the biochemical pathway by which Abeta can lead to neuronal dysfunction. Here we investigated the specific effects of Abeta on mitochondrial function under physiological conditions. Mitochondrial respiratory functions and energy metabolism were analyzed in control and in human wild-type amyloid precursor protein (APP) stably transfected human neuroblastoma cells (SH-SY5Y). Mitochondrial respiratory capacity of mitochondrial electron transport chain (ETC) in vital cells was measured with a high-resolution respirometry system (Oxygraph-2k). In addition, we determined the individual activities of mitochondrial complexes I-IV that compose ETC and ATP cellular levels. While the activities of complexes I and II did not change between cell types, complex IV activity was significantly reduced in APP cells. In contrast, activity of complex III was significantly enhanced in APP cells, as compensatory response in order to balance the defect of complex IV. However, this compensatory mechanism could not prevent the strong impairment of total respiration in vital APP cells. As a result, the respiratory control ratio (state3/state4) together with ATP production decreased in the APP cells in comparison with the control cells. Chronic exposure to soluble Abeta protein may result in an impairment of energy homeostasis due to a decreased respiratory capacity of mitochondrial electron transport chain which, in turn, may accelerate neurons demise.

  11. ESR, spectroscopic, and quantum-chemical studies on the electronic structures of complexes formed by Cu(I) with radicals

    Energy Technology Data Exchange (ETDEWEB)

    Gritsan, N.P.; Usov, O.M.; Shokhirev, N.V.; Khmelinskii, I.V.; Plyusnin, V.F.; Bazhin, N.M.


    The optical and ESR spectra have been examined for complexes of Cu(I) with various radicals, which contain various numbers of Cl/sup -/ ions in the central-atom coordination sphere. The spin-Hamiltonian parameters have been determined for all these radical complexes, and the observed ESR spectra have been compared with those calculated with allowance for second-order effects. The observed values for the isotropic and anisotropic components of the HFI constant from the central ion have been used to estimate the contributions from the 4s and 3d/sup 2//sub z/ orbitals of the copper ion to the unpaired-electron MO. Quantum-chemical calculations have been performed by the INDO method on the electronic structures and geometries of complexes formed by CH/sub 2/OH with Cu(I) for various Cl/sup -/ contents in the coordination sphere. The radical is coordinated by the ..pi.. orbital on the carbon atom, and the stabilities of the radical complexes decrease as the number of Cl/sup -/ ions in the coordination sphere increases. A geometry close to planar for the CuCl/sub 4//sup 3 -/ fragment in a complex containing four Cl/sup -/ ions.

  12. Naphthobischalcogenadiazole Conjugated Polymers: Emerging Materials for Organic Electronics. (United States)

    Osaka, Itaru; Takimiya, Kazuo


    π-Conjugated polymers are an important class of materials for organic electronics. In the past decade, numerous polymers with donor-acceptor molecular structures have been developed and used as the active materials for organic devices, such as organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). The choice of the building unit is the primary step for designing the polymers. Benzochalcogenadiazoles (BXzs) are one of the most familiar acceptor building units studied in this area. As their doubly fused system, naphthobischalcogenadiazoles (NXzs), i.e., naphthobisthiadiazole (NTz), naphthobisoxadiazole (NOz), and naphthobisselenadiazole (NSz) are emerging building units that provide interesting electronic properties and highly self-assembling nature for π-conjugated polymers. With these fruitful features, π-conjugated polymers based on these building units demonstrate great performances in OFETs and OPVs. In particular, in OPVs, NTz-based polymers have exhibited more than 10% efficiency, which is among the highest values reported so far. In this Progress Report, the synthesis, properties, and structures of NXzs and their polymers is summarized. The device performance is also highlighted and the structure-property relationships of the polymers are discussed. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. `Exotic' Electron Spectroscopy of Molecules in Electric Fields (United States)

    Pathak, Rajeev; Gurav, Nalini; Gejji, Shridhar

    Single molecules, whether polar or non-polar (in their free state), when subjected to an externally applied uniform electric field, are observed to exhibit remarkably different UV spectra from those of their zero-field counterparts. Significant spectral line-shifts, line-splitting, line-merging as well as disappearance, and emergence of `exotic' spectral lines are observed as a function of the applied electric field strength. In particular, we simulate the molecular electronic-transition spectra of methanol, hydrogen-peroxide, water and carbon-dioxide in an electric field, employing time dependent density functional theory (TD-DFT) under the versatile M06-2X dispersion-corrected DFT prescription. It is further demonstrated that the Natural Localized Molecular Orbitals (NLMOs), playing a dual donor-acceptor role, can best describe the electron density redistribution and the interplay of various bands in the UV spectrum which is traced back to mutations and crossings of the frontier molecular orbitals. We would like to thank the Center for Advanced Computing, Pune University Campus, for computer time.

  14. The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures

    Energy Technology Data Exchange (ETDEWEB)

    Radaelli, P. G.; Dhesi, S. S.


    We review some of the significant contributions to the field of strongly correlated materials and complex magnets, arising from experiments performed at the Diamond Light Source (Harwell Science and Innovation Campus, Didcot, UK) during the first few years of operation (2007–2014). We provide a comprehensive overview of Diamond research on topological insulators, multiferroics, complex oxides and magnetic nanostructures. Several experiments on ultrafast dynamics, magnetic imaging, photoemission electron microscopy, soft X-ray holography and resonant magnetic hard and soft X-ray scattering are described.

  15. The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures. (United States)

    Radaelli, P G; Dhesi, S S


    We review some of the significant contributions to the field of strongly correlated materials and complex magnets, arising from experiments performed at the Diamond Light Source (Harwell Science and Innovation Campus, Didcot, UK) during the first few years of operation (2007-2014). We provide a comprehensive overview of Diamond research on topological insulators, multiferroics, complex oxides and magnetic nanostructures. Several experiments on ultrafast dynamics, magnetic imaging, photoemission electron microscopy, soft X-ray holography and resonant magnetic hard and soft X-ray scattering are described. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  16. Spectroscopic studies on copper(II) halide complexes with isomeric benzoylpyridines: Electronic and electron spin resonance spectral evidence for five-coordinate copper(II) species in solution (United States)

    Ahuja, I. S.; Tripathi, Shailendra


    Coordination compounds formed by copper(II) chloride and bromide with 2-, 3- and 4-benzoylpyridines (BOP)Cu(2-BOP)Cl 2, Cu(3-BOP) 2Cl 2, Cu(4-BOP)Cl 2, Cu(2-BOP) 2Br 2, Cu(3-BOP) 2Br 2 and Cu(4-BOP) 2Br 2—have been characterized by elemental analyses, molar conductance, magnetic moments, electronic, IR and ESR spectral studies. It is suggested that Cu(2-BOP)Cl 2 is monomeric tetrahedral, Cu(3-BOP) 2Cl 2 and Cu(4-BOP)Cl 2 are dimeric octahedral and tetrahedral structures, respectively, bridging through chlorines while all the bromo complexes are polymeric octahedral structures with bridging bromine atoms in the solid state. Powder ESR data reveal rhombic symmetry for all the chloro complexes. Cu(2-BOP) 2Br 2 is suggested to have an axial symmetry while the other bromo complexes are isotropic in nature. Electronic and ESR spectral studies in DMSO solution suggest the interaction of solvent molecules with copper(II) ions in the axial plane. The solution spectral data are almost comparable suggesting same local symmetry for all the compounds consistent with five-coordinate square pyramidal geometry in each case. ESR spectra also suggest considerable CuCu interactions in Cu(3-BOP) 2Cl 2. Various Spin—Hamiltonian parameters calculated from ESR data indicate the presence of an unpaired electron in the d x2- y2 orbital of the copper(II) ion in an axial symmetry.

  17. Associative Electron Attachment to 2-Aminopyridine-(CO{sub 2}){sub 1} Complex: Photoelectron Spectroscopic and Theoretical Approach

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Namdoo [Seoul National Univ., Seoul (Korea, Republic of)


    We investigated the associative electron attachment to the [2AP-(CO{sub 2}){sub 1}] van der Waal complex using anion photoelectron spectroscopy and theoretical calculations. We found a covalent bond formation between 2AP and CO{sub 2} opposite to that seen in [Pd-(CO{sub 2}){sub 2}]{sup -} which could not form an additional covalent bond due to the steric hindrance. Excess negative charge is totally delocalized to the entire complex to give extended π-conjugation. Carbon dioxide is a very inert molecule whose reactivity is low at room temperature. It does not make a stable anion in the gas phase since it has a negative adiabatic electron affinity (AEA). Instead, it becomes a metastable anion with quite a long lifetime (< 100 μs) when it adopts a bent geometry which differs greatly from the geometry of the neutral species.

  18. Complex nano-patterning of structural, optical, electrical and electron emission properties of amorphous silicon thin films by scanning probe (United States)

    Fait, Jan; Čermák, Jan; Stuchlík, Jiří; Rezek, Bohuslav


    Preparation of nanoscale templates represents an important step for synthesis and assembly of diverse nanostructures and nanoscale devices. We show that complex nano-structural templates in a thin (40 nm) layer of hydrogenated amorphous silicon (a-Si:H) can be prepared by using locally applied electric field in an atomic force microscope (AFM). Depth of the resulting structures (1-40 nm) can be controlled by the process parameters (magnitude of electric field, exposure time, or nano-sweeping of the tip). We demonstrate that complex patterns can be scribed into the a-Si:H layer in that way. The prepared patterns exhibit different structural, optical, electrical, and electron emission properties, compared to the surroundings as detected by Raman micro-spectroscopy, scanning electron microscopy (SEM), and conductive AFM. The silicon thin films with locally modified properties can be useful in themselves or can serve as templates for further nanoscale growth or assembly.

  19. Geometric and Electronic Structure and Reactivity of a Mononuclear “Side-On” Nickel(III)-Peroxo Complex (United States)

    Cho, Jaeheung; Sarangi, Ritimukta; Annaraj, Jamespandi; Kim, Sung Yeon; Kubo, Minoru; Ogura, Takashi; Solomon, Edward I.; Nam, Wonwoo


    Metal-O2 adducts, such as metal-superoxo and -peroxo species, are key intermediates often detected in the catalytic cycles of dioxygen activation by metalloenzymes and biomimetic compounds. The synthesis and spectroscopic characterization of an end-on nickel(II)-superoxo complex with a 14-membered macrocyclic ligand was reported previously. Here we report the isolation, spectroscopic characterization, and high-resolution crystal structure of a mononuclear side-on nickel(III)-peroxo complex with a 12-membered macrocyclic ligand, [Ni(12-TMC)(O2)]+ (1) (12-TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). Different from the end-on Ni(II)-superoxo complex, the Ni(III)-peroxo complex is not reactive in electrophilic reactions, but is capable of conducting nucleophilic reactions. The Ni(III)-peroxo complex transfers the bound dioxygen to manganese(II) complexes, thus affording the corresponding nickel(II) and manganese(III)-peroxo complexes. The present results demonstrate the significance of supporting ligands in tuning the geometric and electronic structures and reactivities of metal-O2 intermediates that have been shown to have biological as well as synthetic usefulness in biomimetic reactions. PMID:20711413

  20. Interconversion of η3-H2SiRR' σ-complexes and 16-electron silylene complexes via reversible H-H or C-H elimination. (United States)

    Lipke, Mark C; Neumeyer, Felix; Tilley, T Don


    Solid samples of η(3)-silane complexes [PhBP(Ph)3]RuH(η(3)-H2SiRR') (R,R' = Et2, 1a; PhMe, 1b; Ph2, 1c, MeMes, 1d) decompose when exposed to dynamic vacuum. Gas-phase H2/D2 exchange between isolated, solid samples of 1c-d3 and 1c indicate that a reversible elimination of H2 is the first step in the irreversible decomposition. An efficient solution-phase trap for hydrogen, the 16-electron ruthenium benzyl complex [PhBP(Ph)3]Ru[η(3)-CH2(3,5-Me2C6H3)] (3) reacts quantitatively with H2 in benzene via elimination of mesitylene to form the η(5)-cyclohexadienyl complex [PhBP(Ph)3]Ru(η(5)-C6H7) (4). This H2 trapping reaction was utilized to drive forward and quantify the elimination of H2 from 1b,d in solution, which resulted in the decomposition of 1b,d to form 4 and several organosilicon products that could not be identified. Reaction of {[PhBP(Ph)3]Ru(μ-Cl)}2 (2) with (THF)2Li(SiHMes2) forms a new η(3)-H2Si species [PhBP(Ph)3]Ru[CH2(2-(η(3)-H2SiMes)-3,5-Me2C6H2)] (5) which reacts with H2 to form the η(3)-H2SiMes2 complex [PhBP(Ph)3]RuH(η(3)-H2SiMes2) (1e). Complex 1e was identified by NMR spectroscopy prior to its decomposition by elimination of Mes2SiH2 to form 4. DFT calculations indicate that an isomer of 5, the 16-electron silylene complex [PhBP(Ph)3]Ru(μ-H)(═SiMes2), is only 2 kcal/mol higher in energy than 5. Treatment of 5 with XylNC (Xyl = 2,6-dimethylphenyl) resulted in trapping of [PhBP(Ph)3]Ru(μ-H)(═SiMes2) to form the 18-electron silylene complex [PhBP(Ph)3]Ru(CNXyl)(μ-H)(═SiMes2) (6). A closely related germylene complex [PhBP(Ph)3]Ru[CN(2,6-diphenyl-4-MeC6H2)](H)(═GeH(t)Bu) (8) was prepared from reaction of (t)BuGeH3 with the benzyl complex [PhBP(Ph)3]Ru[CN(2,6-diphenyl-4-MeC6H2)][η(1)-CH2(3,5-Me2C6H3)] (7). Single crystal XRD analysis indicated that unlike for 6, the hydride ligand in 8 is a terminal hydride that does not engage in 3c-2e Ru-H → Ge bonding. Complex 1b is an effective precatalyst for the catalytic Ge-H dehydrocoupling

  1. Enhanced emission efficiency in organic light-emitting diodes using deoxyribonucleic acid complex as an electron blocking layer (United States)

    Hagen, J. A.; Li, W.; Steckl, A. J.; Grote, J. G.


    Enhanced electroluminescent efficiency using a deoxyribonucleic acid (DNA) complex as an electron blocking (EB) material has been demonstrated in both green- and blue-emitting organic light-emitting diodes (OLEDs). The resulting so-called BioLEDs showed a maximum luminous efficiency of 8.2 and 0.8cd/A, respectively. The DNA-based BioLEDs were as much as 10× more efficient and 30× brighter than their OLED counterparts.

  2. Acrosome formation and the centriolar complex in the spermatozoa of Sabella penicillum (Polychaeta): an electron microscopical study. (United States)

    Kryvi, H; Graebner, I


    The acrosomal vesicle of Sabella penicillum spermatids consists of an electrondense core and a more transparent surrounding zone. During subsequent differentiation the vesicle membrane forms several invaginations in the juxtanuclear area. These invaginations later establish contact with the core. In the mature spermatozoon the spaces between the invaginations appear as electron-dense "tubules"; this is probably due to a shift of material from core to periphery. The ultrastructure of the centriolar complex is described in detail.

  3. Optimization of electronic enclosure design for thermal and moisture management using calibrated models of progressive complexity

    DEFF Research Database (Denmark)

    Mohanty, Sankhya; Staliulionis, Zygimantas; Shojaee Nasirabadi, Parizad


    The thermal and moisture management of electronic enclosures are fields of high interest in recent years. It is now generally accepted that the protection of electronic devices is dependent on avoiding critical levels of relative humidity (typically 60–90%) during operations. Leveraging...... the development of rigorous calibrated CFD models as well as simple predictive numerical tools, the current paper tackles the optimization of critical features of a typical two-chamber electronic enclosure. The progressive optimization strategy begins the design parameter selection by initially using simpler...... equivalent RC-circuit models for concentration of water vapor and temperature in the electronic enclosure. After reducing the potential parameter-value space for the critical features using the RC-approach, the optimization strategy uses simpler 2D CFD models of temperature and moisture transport to further...

  4. Dense-shell glycodendrimers: UV/Vis and electron paramagnetic resonance study of metal ion complexation

    National Research Council Canada - National Science Library

    Dietmar Appelhans; Ulrich Oertel; Roberto Mazzeo; Hartmut Komber; Jan Hoffmann; Steffen Weidner; Bernhard Brutschy; Brigitte Voit; Maria Francesca Ottaviani


    ...(propyleneimine) glycodendrimers ranging up to the fifth generation that have either a dense maltose or maltotriose shell was investigated by UV/Vis spectroscopy and electron paramagnetic resonance (EPR...

  5. NDUFA4 is a subunit of complex IV of the mammalian electron transport chain

    NARCIS (Netherlands)

    Balsa, E.; Marco, R.; Perales-Clemente, E.; Szklarczyk, R.J.; Calvo, E.; Landazuri, M.O.; Enriquez, J.A.


    The oxidative phosphorylation system is one of the best-characterized metabolic pathways. In mammals, the protein components and X-ray structures are defined for all complexes except complex I. Here, we show that NDUFA4, formerly considered a constituent of NADH Dehydrogenase (CI), is instead a

  6. Spectroscopic mapping and selective electronic tuning of molecular orbitals in phosphorescent organometallic complexes – a new strategy for OLED materials

    Directory of Open Access Journals (Sweden)

    Pascal R. Ewen


    Full Text Available The improvement of molecular electronic devices such as organic light-emitting diodes requires fundamental knowledge about the structural and electronic properties of the employed molecules as well as their interactions with neighboring molecules or interfaces. We show that highly resolved scanning tunneling microscopy (STM and spectroscopy (STS are powerful tools to correlate the electronic properties of phosphorescent complexes (i.e., triplet emitters with their molecular structure as well as the local environment around a single molecule. We used spectroscopic mapping to visualize several occupied and unoccupied molecular frontier orbitals of Pt(II complexes adsorbed on Au(111. The analysis showed that the molecules exhibit a peculiar localized strong hybridization that leads to partial depopulation of a dz² orbital, while the ligand orbitals are almost unchanged. We further found that substitution of functional groups at well-defined positions can alter specific molecular orbitals without influencing the others. The results open a path toward the tailored design of electronic and optical properties of triplet emitters by smart ligand substitution, which may improve the performance of future OLED devices.

  7. Synthesis, characterization, electronic structure and catalytic activity of new ruthenium carbonyl complexes of N-[(2-pyridyl)methylidene]-2-aminothiazole (United States)

    Kundu, Subhankar; Sarkar, Deblina; Jana, Mahendra Sekhar; Pramanik, Ajoy Kumar; Jana, Subrata; Mondal, Tapan Kumar


    Reaction of ruthenium carbonyls, [Ru(CO)2Cl2]n/[Ru(CO)4I2] with bidentate Schiffs base ligands derived by the condensation of pyridine-2-carboxaldehyde with 2-aminothiazole in a 1:1 mole ratio in acetonitrile led to the formation of complexes having general formula [Ru(CO)2(L)X2] (X = Cl (1) and I (2)) (L = N-[(2-pyridyl)methylidene]-2-aminothiazole). The compounds have been characterized by various analytical and spectroscopic (IR, electronic and 1H NMR) studies. In acetonitrile solution the complexes exhibit a weak broad metal-ligand to ligand charge transfer (MLLCT) band along with ILCT transitions. The compounds are emissive in room temperature upon excitation in the ILCT band. The complexes exhibit a quasi-reversible one electron Ru(II)/Ru(III) oxidation couple at 1.44 V for 1 and 0.94 V for 2. Catalytic activity of these compounds is investigated to the oxidation of PhCH2OH to PhCHO, 2-butanol (C4H9OH) to 2-butanone, 1-phenylethanol (PhC2H4OH) to acetophenone, cyclopentanol (C5H9OH) to cyclopentanone, cyclohexanol to cyclohexanone, cycloheptanol to cycloheptanone and cycloctanol to cycloctanone using N-methylmorpholine-N-oxide (NMO) as oxidant. The catalytic efficiency of 2 is greater than complex 1 and well correlate with the metal oxidation potential of the complexes. DFT, NBO and TDDFT calculations are employed to explain the structural and electronic features and to support the spectroscopic assignments.

  8. Trinuclear copper complexes with triplesalen ligands: geometric and electronic effects on ferromagnetic coupling via the spin-polarization mechanism. (United States)

    Glaser, Thorsten; Heidemeier, Maik; Strautmann, Julia B H; Bögge, Hartmut; Stammler, Anja; Krickemeyer, Erich; Huenerbein, Robert; Grimme, Stefan; Bothe, Eberhard; Bill, Eckhard


    A series of trinuclear Cu(II) complexes with the tris(tetradentate) triplesalen ligands H(6)talen, H(6)talen(tBu(2) ), and H(6)talen(NO(2) ), namely [(talen)Cu(II) (3)] (1), [(talen(tBu(2) ))Cu(II) (3)] (2), and [(talen(NO(2) ))Cu(II) (3)] (3), were synthesized and their molecular and electronic structures determined. These triplesalen ligands provide three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The structure of [(talen)Cu(II) (3)] (1) was communicated recently. The structure of the tert-butyl derivative [(talen(tBu(2) ))Cu(II) (3)] (2) was established in three different solvates. The molecular structures of these trinuclear complexes show notable differences, the most important of which is the degree of ligand folding around the central Cu(II)-phenolate bonds. This folding is symmetric with regard to the central phloroglucinol backbone in two structures, where it gives rise to bowl-shaped overall geometries. For one solvate two trinuclear triplesalen complexes form a supramolecular disk-like arrangement, hosting two dichloromethane molecules like two pearls in an oyster. The FTIR spectra of these complexes indicate the higher effective nuclear charge of Cu(II) in comparison to the trinuclear Ni(II) complexes by the lower C--O and higher C=N stretching frequencies. The UV/Vis/NIR spectra of 1-3 reflect the stronger ligand folding in the tert-butyl complex 2 by an intense phenolate-to-Cu(II) LMCT. This absorption is absent in 1 and is obscured by the nitro chromophore in 3. The more planar molecular structures cause orthogonality of the Cu(II) d(x(2)-y(2) ) orbital and the phenolate O p(z) orbital, which leads to small LMCT dipole strengths. Whereas 1 and 3 exhibit only irreversible oxidations, 2 exhibits a reversible one-electron oxidation at +0.26 V, a reversible two-electron oxidation at +0.59 V, and a reversible one-electron oxidation at +0.81 V versus Fc(+)/Fc. The one-electron oxidized form 2

  9. Role of the bridge in photoinduced electron transfer in porphyrin-fullerene dyads. (United States)

    Pelado, Beatriz; Abou-Chahine, Fawzi; Calbo, Joaquín; Caballero, Rubén; de la Cruz, Pilar; Junquera-Hernández, José M; Ortí, Enrique; Tkachenko, Nikolai V; Langa, Fernando


    The role of π-conjugated molecular bridges in through-space and through-bond electron transfer is studied by comparing two porphyrin-fullerene donor-acceptor (D-A) dyads. One dyad, ZnP-Ph-C60 (ZnP = zinc porphyrin), incorporates a phenyl bridge between D and A and behaves very similarly to analogous dyads studied previously. The second dyad, ZnP-EDOTV-C60, introduces an additional 3,4-ethylenedioxythienylvinylene (EDOTV) unit into the conjugated bridge, which increases the distance between D and A, but, at the same time, provides increased electronic communication between them. Two essential outcomes that result from the introduction of the EDOTV unit in the bridge are as follows: 1) faster charge recombination, which indicates enhanced electronic coupling between the charge-separated and ground electronic states; and 2) the disappearance of the intramolecular exciplex, which mediates photoinduced charge separation in the ZnP-Ph-C60 dyad. The latter can be interpreted as a gradual decrease in electronic coupling between locally excited singlet states of D and A when introducing the EDOTV unit into the D-A bridge. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Molecular and electronic structure of osmium complexes confined to Au(111) surfaces using a self-assembled molecular bridge

    Energy Technology Data Exchange (ETDEWEB)

    Llave, Ezequiel de la; Herrera, Santiago E.; Adam, Catherine; Méndez De Leo, Lucila P.; Calvo, Ernesto J.; Williams, Federico J., E-mail: [INQUIMAE-CONICET, Departamento de Química Inorgánica, Analítica y Química-Física, Facultad Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, Buenos Aires C1428EHA (Argentina)


    The molecular and electronic structure of Os(II) complexes covalently bonded to self-assembled monolayers (SAMs) on Au(111) surfaces was studied by means of polarization modulation infrared reflection absorption spectroscopy, photoelectron spectroscopies, scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations. Attachment of the Os complex to the SAM proceeds via an amide covalent bond with the SAM alkyl chain 40° tilted with respect to the surface normal and a total thickness of 26 Å. The highest occupied molecular orbital of the Os complex is mainly based on the Os(II) center located 2.2 eV below the Fermi edge and the LUMO molecular orbital is mainly based on the bipyridine ligands located 1.5 eV above the Fermi edge.

  11. Effects of aging on activities of mitochondrial electron transport chain complexes and oxidative damage in rat heart. (United States)

    Tatarková, Z; Kuka, S; Račay, P; Lehotský, J; Dobrota, D; Mištuna, D; Kaplán, P


    Mitochondrial dysfunction and accumulation of oxidative damage have been implicated to be the major factors of aging. However, data on age-related changes in activities of mitochondrial electron transport chain (ETC) complexes remain controversial and molecular mechanisms responsible for ETC dysfunction are still largely unknown. In this study, we examined the effect of aging on activities of ETC complexes and oxidative damage to proteins and lipids in cardiac mitochondria from adult (6-month-old), old (15-month-old) and senescent (26-month-old) rats. ETC complexes I-IV displayed different extent of inhibition with age. The most significant decline occurred in complex IV activity, whereas complex II activity was unchanged in old rats and was only slightly reduced in senescent rats. Compared to adult, old and senescent rat hearts had significantly higher levels of malondialdehyde, 4-hydroxynonenal (HNE) and dityrosine, while thiol group content was reduced. Despite marked increase in HNE content with age (25 and 76 % for 15- and 26-month-old rats, respectively) Western blot analysis revealed only few HNE-protein adducts. The present study suggests that non-uniform decline in activities of ETC complexes is due, at least in part, to mitochondrial oxidative damage; however, lipid peroxidation products appear to have a limited impact on enzyme functions.

  12. Electron Tunneling in Lithium Ammonia Solutions Probed by Frequency-Dependent Electron-Spin Relaxation Studies (United States)

    Maeda, Kiminori; Lodge, Matthew T.J.; Harmer, Jeffrey; Freed, Jack H.; Edwards, Peter P.


    Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10−12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10−13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential

  13. Electron tunneling in lithium-ammonia solutions probed by frequency-dependent electron spin relaxation studies. (United States)

    Maeda, Kiminori; Lodge, Matthew T J; Harmer, Jeffrey; Freed, Jack H; Edwards, Peter P


    Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T(1)) and spin-spin (T(2)) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multiexponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1-10) × 10(-12) s over a temperature range 230-290 K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a time scale of ∼10(-13) s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great

  14. The full electron structure of the FKBP12/FK506 complex. (United States)

    Rossetto, Allison M; Zhou, Wenjin; Pang, Xiaodong; Zhou, Linxiang


    We present a study of FKBP12/FK506 using an electron structure calculation. These calculations employ a novel technique called eCADD on the protein's full electron structure along with its hydrophobic pocket and the frontier-orbital-perturbation theory. We first obtain the energy bands and orbital coefficients of protein FKBP12. On this basis, we found that the activity atoms and activity residues of FKBP12 were in good agreement with X-ray crystallography experiments. The results indicate that the interactions occur only between the LUMOs of FKBP12 and the HOMO of FK506, not between the HOMOs of FKBP12 and the LUMO of FK506. In other words, the activity sites of protein FKBP12 are located on its LUMOs, not HOMOs. The electron structures of FKBP12/FK506 give us a clearer understanding of their interaction mechanism and will help us design new ligands of FKBP12.

  15. A Cleaner Process for Selective Recovery of Valuable Metals from Electronic Waste of Complex Mixtures of End-of-Life Electronic Products. (United States)

    Sun, Zhi; Xiao, Y; Sietsma, J; Agterhuis, H; Yang, Y


    In recent years, recovery of metals from electronic waste within the European Union has become increasingly important due to potential supply risk of strategic raw material and environmental concerns. Electronic waste, especially a mixture of end-of-life electronic products from a variety of sources, is of inherently high complexity in composition, phase, and physiochemical properties. In this research, a closed-loop hydrometallurgical process was developed to recover valuable metals, i.e., copper and precious metals, from an industrially processed information and communication technology waste. A two-stage leaching design of this process was adopted in order to selectively extract copper and enrich precious metals. It was found that the recovery efficiency and extraction selectivity of copper both reached more than 95% by using ammonia-based leaching solutions. A new electrodeposition process has been proven feasible with 90% current efficiency during copper recovery, and the copper purity can reach 99.8 wt %. The residue from the first-stage leaching was screened into coarse and fine fractions. The coarse fraction was returned to be releached for further copper recovery. The fine fraction was treated in the second-stage leaching using sulfuric acid to further concentrate precious metals, which could achieve a 100% increase in their concentrations in the residue with negligible loss into the leaching solution. By a combination of different leaching steps and proper physical separation of light materials, this process can achieve closed-loop recycling of the waste with significant efficiency.

  16. Complexity

    Indian Academy of Sciences (India)

    Rahul Pandit


    Oct 31, 2008 ... ”The more complex a thing is, the more you can talk about it.” - attributed to Giorgio Parisi. ▻ ”C'est magnifique, mais ce n'est pas de la science.” (It is magnificent, but not all of it is science.) - attributed ... Earliest examples: theoretical computer science, algorithmic complexity, etc. ▻ Rapid progress after the ...

  17. The effect of electronic health records on the use of clinical care guidelines for patients with medically complex conditions. (United States)

    Fricton, James; Rindal, D Brad; Rush, William; Flottemesch, Thomas; Vazquez, Gabriela; Thoele, Merry Jo; Durand, Emily; Enstad, Chris; Rhodus, Nelson


    The emergence of health information technology provides an opportunity for health care providers to improve the quality and safety of dental care, particularly for patients with medically complex conditions. The authors randomized each of 15 dental clinics (HealthPartners, Bloomington, Minn.) to one of three groups to evaluate the impact of two clinical decision support (CDS) approaches during an 18-month study period. In the first approach--provider activation through electronic dental records (EDRs)--a flashing alert was generated at the dental visit to identify patients with medically complex conditions and to direct the dental care provider to Web-based personalized care guidelines. In the second approach--patient activation through personal health records--a secure e-mail was generated or a letter was mailed to patients before dental visits encouraging them to ask their dental care provider to review the care guidelines specific to their medical conditions. The authors evaluated the rate of reviewing care guidelines among 102 providers. Participants in the provider and patient activation groups increased their use of the system during the first six months, which had a generalized effect of increasing use of the guidelines for all patients, even if they were not part of the study (P electronic alerts. The study results demonstrated that review of clinical care guidelines for patients with medically complex conditions can be improved with CDS systems that involve the use of electronic health records. As the U.S. population ages, dentists must be vigilant in adapting care for patients with medically complex conditions to ensure therapeutic safety and effectiveness. Expanded use of CDS via EDRs can help dental care providers achieve this objective.

  18. Asymmetric Cycloaddition and Cyclization Reactions Catalyzed by Chiral N,N'-Dioxide-Metal Complexes. (United States)

    Liu, Xiaohua; Zheng, Haifeng; Xia, Yong; Lin, Lili; Feng, Xiaoming


    Catalytic asymmetric cycloadditions and cascade cyclizations are a major focus for the enantioselective construction of chiral carbo- and heterocycles. A number of chiral Lewis acids and organocatalysts have been designed for such reactions. The development of broadly applicable catalysts bearing novel chiral backbones to meet the demands of various applications is an ongoing challenge. Approximately 10 years ago, we introduced a group of conformationally flexible C2-symmetric N,N'-dioxide amide compounds, which represent a new class of privileged ligands. The coordination of the four oxygens of a chiral N,N'-dioxide around a central metal generates an octahedral tricyclometalated Lewis acid catalyst that can carry out various enantioselective reactions. In this Account, we summarize our recent studies on asymmetric cycloadditions between various dienophiles and dienes, dipoles and dipolarophiles, and cascade cyclizations catalyzed by chiral N,N'-dioxide-metal complexes. In principle, these unique chiral catalysts lower the LUMO energy of electron-deficient 2π components or heterodienes by coordination with the functional groups via various binding modes. With N-Boc-3-alkenyloxindole and alkylidene malonate as the electron-deficient 2π components, N,N'-dioxide-metal complexes provided excellent catalytic activities and asymmetric inductions for a variety of transformations, including [2 + 1], [3 + 2], [4 + 2], and [8 + 2] cycloadditions. Mechanistically, these substrates could be efficiently activated through bidentate coordination. The strategy was also useful for asymmetric cascade cyclizations to form polycyclic adducts. Monodentate or bidentate coordination of other α,β-unsubstituted carbonyl compounds to metal centers enabled both normal Diels-Alder reactions and inverse-electron-demand hetero-Diels-Alder reactions as well as [2 + 2] additions. Furthermore, hetero-Diels-Alder reactions of aldehydes, ketones, and imines are well-tolerated and afford various

  19. The Size and Morphological Study of Spherical Polyelectrolyte Complex Beads Using Environmental Scanning Electron Microscopy

    Czech Academy of Sciences Publication Activity Database

    Neděla, Vilém; Bučko, M.; Tihlaříková, Eva; Krajčovič, T.; Gemeiner, P.


    Roč. 21, S3 (2015), s. 1697-1698 ISSN 1431-9276 R&D Projects: GA ČR(CZ) GA14-22777S Institutional support: RVO:68081731 Keywords : PEC * ESEM * polymers * morphology Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.730, year: 2015

  20. Infrared and electron spin resonance spectral studies of some copper purine and pyrimidine complexes (United States)

    Masoud, Mamdouh S.; Abd El-Kaway, Marwa Y.


    Copper guanine and barbital complexes were prepared and characterized by elemental analyses and spectral measurements. The data typified the formation of stoichiometries 1:1 (M:L) with possible Cu-Cu interaction "association". The complexes are with different geometries: square planar, square pyramidal and tetrahedral. The mode of bonding was identified by IR spectra. EPR spectra of the powdered complexes were recorded at X band at the room temperature. Different ESR parameters were calculated and discussed: g//, g⊥, A//, , G, F, K, α2. Molecular modeling techniques and quantum chemical methods have been performed for copper complexes to correlate the chemical structures of the complexes with their physical molecular properties. Bond lengths, bond orders, bond angles, dihedral angles, close contact, dipole moment (μ), sum of the total negative charge (STNC), electronegativity (χ), chemical potential (Pi), global hardness (η), softness (σ), the highest occupied molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO) and the energy gap (ΔE) were calculated using PM3 semi-empirical and Molecular Mechanics (MM+) methods. The study displays a good correlation between the theoretical and experimental data which confirms the reliability of the quantum chemical methods.

  1. Computational studies of the electronic, conductivities, and spectroscopic properties of hydrolysed Ru(II) anticancer complexes. (United States)

    Adeniyi, Adebayo A; Ajibade, Peter A


    The mechanism of activation of metal-based anticancer agents was reported to be through hydrolysis. In this study, computational method was used to gain insight to the correlation between the chemistry of the hydrolysis and the anticancer activities of selected Ru(II)-based complexes. Interestingly, we observed that the mechanism of activation by hydrolysis and their consequential anticancer activities is associated with favourable thermodynamic changes, higher hyperpolarizability (β), lower band-gap and higher first-order net current. The Fermi contact (FC) and spin dipole (SD) are found to be the two most significant Ramsey terms that determine the spin-spin couplings (J(HZ)) of most of the existing bonds in the complexes. Many of the computed properties give insights into the change in the chemistry of the complexes due to hydrolysis. Besides strong correlations of the computed properties to the anticancer activities of the complexes, using the quantum theory of atoms in a molecule (QTAIM) to analyse the spectroscopic properties shows a stronger correlation between the spectroscopic properties of Ru atom to the reported anticancer activities than the sum over of the spectroscopic properties of all atoms in the complexes. Copyright © 2013 Elsevier B.V. All rights reserved.

  2. Infrared spectra and electronic structure calculations for NN complexes with U, UN, and NUN in solid argon, neon, and nitrogen. (United States)

    Andrews, Lester; Wang, Xuefeng; Gong, Yu; Kushto, Gary P; Vlaisavljevich, Bess; Gagliardi, Laura


    Reactions of laser-ablated U atoms with N2 molecules upon codeposition in excess argon or neon at 4 K gave intense NUN and weak UN absorptions. Annealing produced progressions of new absorptions for the UN2(N2)1,2,3,4,5 and UN(N2)1,2,3,4,5,6 complexes. The neon-to-argon matrix shift decreases with increasing NN ligation and therefore the number of noble gas atoms left in the primary coordination sphere around the NUN molecule. Small matrix shifts are observed when the secondary coordination layers around the primary UN2(N2)1,2,3,4,5 and UN(N2)1,2,3,4,5,6 complexes are changed from neon-to-argon to nitrogen. Electronic structure, energy, and frequency calculations provide support for the identification of these complexes and the characterization of the N≡U≡N and U≡N core molecules as terminal uranium nitrides. Codeposition of U with pure nitrogen produced the saturated U(NN)7 complex, which UV irradiation converted to the NUN(NN)5 complex with slightly lower frequencies than found in solid argon.

  3. Structure of the dimeric RC-LH1-PufX complex from Rhodobaca bogoriensis investigated by electron microscopy. (United States)

    Semchonok, Dmitry A; Chauvin, Jean-Paul; Frese, Raoul N; Jungas, Colette; Boekema, Egbert J


    Electron microscopy and single-particle averaging were performed on isolated reaction centre (RC)-antenna complexes (RC-LH1-PufX complexes) of Rhodobaca bogoriensis strain LBB1, with the aim of establishing the LH1 antenna conformation, and, in particular, the structural role of the PufX protein. Projection maps of dimeric complexes were obtained at 13 Å resolution and show the positions of the 2 × 14 LH1 α- and β-subunits. This new dimeric complex displays two open, C-shaped LH1 aggregates of 13 αβ polypeptides partially surrounding the RCs plus two LH1 units forming the dimer interface in the centre. Between the interface and the two half rings are two openings on each side. Next to the openings, there are four additional densities present per dimer, considered to be occupied by four copies of PufX. The position of the RC in our model was verified by comparison with RC-LH1-PufX complexes in membranes. Our model differs from previously proposed configurations for Rhodobacter species in which the LH1 ribbon is continuous in the shape of an S, and the stoichiometry is of one PufX per RC.

  4. On the calculation of electron atom collision processes using exterior complex dilated S-matrix expansions

    Energy Technology Data Exchange (ETDEWEB)

    Carlsund, C. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden) Dept. of Theoretical Physics, Royal Inst. of Tech., Stockholm (Sweden)); Krylstedt, P. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden) Dept. of Theoretical Physics, Royal Inst. of Tech., Stockholm (Sweden) Swedish National Defence Establishment, Stockholm (Sweden)); Elander, N. (Manne Siegbahn Inst. of Physics, Stockholm (Sweden)); Cowan, R.D. (Los Alamos National Lab., NM (USA))


    Our work on analytically continued scattering theory based on the Schroedinger equation is reviewed. We give a brief description of how resonances, here defined as partial wave S-matrix poles, can be calculated as complex eigenvalues to the complex scaled Schroedinger equation. A Mittag-Leffler type expansion is then introduced and it is shown how one can partition a scattering cross section into contributions from isolated S-matrix poles and a background. Computationally this method has proven to be considerably faster than conventional methods. A new, faster and more accurate integration method is used. Examples of detailed previous work as well as current research are given. (orig.).

  5. Infinite dwell time and group delay in resonant electron tunneling through double complex potential barrier (United States)

    Opacak, Nikola; Milanović, Vitomir; Radovanović, Jelena


    Tunneling times in complex potentials are investigated. Analytical expressions for dwell time, self-interference time and group delay are obtained for the case of complex double delta potentials. It is shown that we can always find a set of parameters of the potential so that the tunneling times achieve very large values and even approach infinity for the case of resonance. The phenomenon of infinite tunneling times occurs for only one particular positive value of the imaginary part of the potential, if all other parameters are given.

  6. Enzymatic activity of the alternative complex III as a menaquinol:auracyanin oxidoreductase in the electron transfer chain of Chloroflexus aurantiacus. (United States)

    Gao, Xinliu; Xin, Yueyong; Blankenship, Robert E


    The surprising lack of the cytochrome bc1 complex in the filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus suggests that a functional replacement exists to link the cyclic electron transfer chain. Earlier work identified the alternative complex III (ACIII) as a substitute of cytochrome bc1 complex. Herein, the enzymatic activity of ACIII is studied. The results strongly support the view that the ACIII functions as menaquinol:auracyanin oxidoreductase in the C. aurantiacus electron transfer chain. Among all the substrates tested, auracyanin is the most efficient electron acceptor of ACIII, suggesting that ACIII directly transfers the electron to auracyanin instead of cytochrome c-554. The lack of sensitivity to common inhibitors of the cytochrome bc1 complex indicates a different catalytic mechanism for the ACIII complex.

  7. Properties of electronically excited states of four squaraine dyes and their complexes with fullerene C70: A theoretical investigation (United States)

    Zhang, Jian; Li, Tingyu


    Solar cells sensitized by polypyridyl Ru(II) complexes exhibit relatively high efficiency, however those photo-sensitizers did not absorb the photons in the far-red and near-infrared region. At present, squaraine dyes have received considerable attention as their attractively intrinsic red light absorption and unusual high molar extinction coefficient. Here we applied density functional theory and time dependent density functional theory to investigate the properties of electronically excited states of four squaraine dyes and their complexes with fullerene C70. The influences of different functionals, basis sets and solvent effects are evaluated. To understand the photophysical properties, the investigations are basing on a classification method which splits the squaraine dyes and their complexes with fullerene C70 into two units to characterize the intramolecular density distribution. We present the signatures of their electronically excited states which are characterized as local excitation or charge-transfer excitation. The relationship between open-circuit voltage and the number of intramolecular hydrogen bonds in squaraine dyes are discussed.

  8. Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex. (United States)

    Lennox, J Christian; Dempsey, Jillian L


    A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru 3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pK a units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.

  9. Ruthenium and iron complexes with benzotriazole and benzimidazole derivatives as simple models for proton-coupled electron transfer systems

    Directory of Open Access Journals (Sweden)

    Rocha Reginaldo C.


    Full Text Available Iron and ruthenium complexes of the type [M-LH]n (where M = RuII,III(NH35(2+,3+, RuII,III(edta2-,- [edta = ethylenedinitrilotetraacetate], or FeII,III(CN5(3-,2- and LH = benzotriazole or benzimidazole were prepared and characterized in aqueous solutions by means of electrochemical and spectroelectrochemical methods. Special emphasis was given to the pH-dependent redox processes, exhibited by all the investigated complexes. From their related Pourbaix diagrams, which displayed a typically Nernstian behavior, the pKa and formal reduction potential values were extracted. In addition, these E1/2 versus pH curves were also used to illustrate the partitioning relationship concerning the redox and acid-base species, and their interconversion equilibria. The active area in which the dependence of the M III/M II couple on the pH takes place, as delimited by pKaIII and pKaII, was taken into account in order to evaluate the usefulness of such simple complexes as models for proton-coupled electron transfer (PCET. The results were interpreted in terms of the acceptor/donor electronic character of the ligands and sigma,pi-metal-ligand interactions in both redox states of the metal ion.

  10. Tuning Up an Electronic Structure of the Subphthalocyanine Derivatives toward Electron-Transfer Process in Noncovalent Complexes with C60 and C70 Fullerenes: Experimental and Theoretical Studies. (United States)

    Rhoda, Hannah M; Kayser, Mathew P; Wang, Yefeng; Nazarenko, Alexander Y; Belosludov, Rodion V; Kiprof, Paul; Blank, David A; Nemykin, Victor N


    Noncovalent π-π interactions between chloroboron subphthalocyanine (1), 2,3-subnaphthalocyanine (3), 1,4,8,11,15,18-(hexathiophenyl)subphthalocyanine (4), or 4-tert-butylphenoxyboron subphthalocyanine (2) with C60 and C70 fullerenes were studied by UV-vis and steady-state fluorescence spectroscopy, as well as mass (APCI, ESI, and CSI) spectrometry. Mass spectrometry experiments were suggestive of relatively weak interaction energies between compounds 1-4 and fullerenes. The formation of a new weak charge-transfer band in the NIR region was observed in solution only for subphthalocyanine 4 when titrated with C60 and C70 fullerenes. Molecular structures of the subphthalocyanines 2 and 4 as well as cocrystallite of 4 with C60 fullerene (4···C60) were studied using X-ray crystallography. One of the C60 fullerenes in the crystal structure of 4···C60 was found in the concave region between two subphthalocyanine cores, while the other three fullerenes are aligned above individual isoindole fragments of the aromatic subphthalocyanine. The excited-state dynamics in noncovalent assemblies were studied by transient absorption spectroscopy. The time-resolved photophysics data suggest that only electron-rich subphthalocyanine 4 can facilitate an electron-transfer to C60 or C70 fullerenes, while no electron-transfer from the photoexcited receptors 1-3 to fullerenes was observed in UV-vis and transient spectroscopy experiments. DFT calculations using the CAM-B3LYP exchange-correlation functional and the 6-31+G(d) basis set allowed an estimation of interaction energies for the noncovalent 1:1 and 1:2 (fullerene:subphthalocyanine) complexes. Theoretical data suggest that the weak (∼3.5-10.5 kcal/mol) van der Waals-type interaction energies tend to increase with an increase of the electron density at the subphthalocyanine core with compound 4 being the best platform for noncovalent interactions with fullerenes. DFT calculations also indicate that 1:2 (fullerene

  11. Dietary avocado oil supplementation attenuates the alterations induced by type I diabetes and oxidative stress in electron transfer at the complex II-complex III segment of the electron transport chain in rat kidney mitochondria. (United States)

    Ortiz-Avila, Omar; Sámano-García, Carlos Alberto; Calderón-Cortés, Elizabeth; Pérez-Hernández, Ismael H; Mejía-Zepeda, Ricardo; Rodríguez-Orozco, Alain R; Saavedra-Molina, Alfredo; Cortés-Rojo, Christian


    Impaired complex III activity and reactive oxygen species (ROS) generation in mitochondria have been identified as key events leading to renal damage during diabetes. Due to its high content of oleic acid and antioxidants, we aimed to test whether avocado oil may attenuate the alterations in electron transfer at complex III induced by diabetes by a mechanism related with increased resistance to lipid peroxidation. 90 days of avocado oil administration prevented the impairment in succinate-cytochrome c oxidoreductase activity caused by streptozotocin-induced diabetes in kidney mitochondria. This was associated with a protection against decreased electron transfer through high potential chain in complex III related to cytochromes c + c1 loss. During Fe(2+)-induced oxidative stress, avocado oil improved the activities of complexes II and III and enhanced the protection conferred by a lipophilic antioxidant against damage by Fe(2+). Avocado oil also decreased ROS generation in Fe(2+)-damaged mitochondria. Alterations in the ratio of C20:4/C18:2 fatty acids were observed in mitochondria from diabetic animals that not were corrected by avocado oil treatment, which yielded lower peroxidizability indexes only in diabetic mitochondria although avocado oil caused an augment in the total content of monounsaturated fatty acids. Moreover, a protective effect of avocado oil against lipid peroxidation was observed consistently only in control mitochondria. Since the beneficial effects of avocado oil in diabetic mitochondria were not related to increased resistance to lipid peroxidation, these effects were discussed in terms of the antioxidant activity of both C18:1 and the carotenoids reported to be contained in avocado oil.

  12. Structurally Complex Frank–Kasper Phases and Quasicrystal Approximants: Electronic Origin of Stability

    Directory of Open Access Journals (Sweden)

    Valentina F. Degtyareva


    Full Text Available Metal crystals with tetrahedral packing are known as Frank–Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number of valence electrons per atom. The significance of the electronic energy contribution is analyzed within the Fermi sphere–Brillouin zone interaction model for several typical examples: Cu4Cd3, Mg2Al3 with over a thousand atoms per cell, and for icosahedral quasicrystal approximants with 146–168 atoms per cell. Our analysis shows that to minimize the crystal energy, it is important that the Fermi sphere (FS is in contact with the Brillouin zones that are related to the strong diffraction peaks: the zones either inscribe the FS or are circumscribed by the FS creating contact at edges or vertices.

  13. Electron microprobe Th-U-Pb monazite dating and metamorphic evolution of the Acaiaca Granulite Complex, Minas Gerais, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Medeiros Junior, Edgar Batista; Marques, Rodson Abreu, E-mail:, E-mail: [Universidade Federal do Espirito Santo (UFES), Alegre, ES (Brazil). Departamento de Geologia; Jordt-Evangelista, Hanna; Queiroga, Glaucia Nascimento, E-mail:, E-mail: [Universidade Federal de Ouro Preto (UFOP), Ouro Preto, MG (Brazil). Escola de Minas. Departamento de Geologia; Schulz, Bernhard, E-mail: [TU Bergakademie - Institute of Mineralogy, Freiberg - Saxony (Germany)


    The Acaiaca Complex (AC) is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulite as well as lower grade gneisses and mylonite. The complex is distributed over an area of ca. 36 km by 6 km, surrounded by amphibolite facies gneisses of the Mantiqueira Complex (MC). The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometry calculations and electron microprobe Th-U-Pb monazite dating. Estimates of the metamorphic conditions of the granulite based on conventional geothermobarometry and THERMOCALC resulted in temperatures around 800 deg C and pressures between of 5.0 and 9.9 kbar and a retro metamorphic path characterized by near-isobaric cooling. Part of the granulite was affected by anatexis. The melting of felsic granulite resulted in the generation of pegmatites and two aluminous lithotypes. These are: 1) garnet-sillimanite granulite with euhedral plagioclase and cordierite that show straight faces against quartz, and is the crystallization product of an anatectic melt, and 2) garnet-kyanite-cordierite granulite, which is probably the restite of anatexis, as indicated by textures and high magnesium contents. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around 2060 Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronological related to the lower grade Mantiqueira Complex. (author)

  14. Electrolyte Gating of Correlated Electron Materials and Nanostructures in Complex Oxides (United States)


    UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Leland Stanford Junior University , The Stanford University 450 Serra Mall Stanford...interactions and spin physics play a role (notably spin liquids) and materials in which local conduction has recently been achieved or discovered...electrons, Mott transition, spin liquids 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON


    NARCIS (Netherlands)



    The crystal structure of the complex between the quinoprotein methylamine dehydrogenase (MADH) and the type I blue copper protein amicyanin, both from Paracoccus denitrificans, has been determined at 2.5-angstrom resolution using molecular replacement. The search model was MADH from Thiobacillus

  16. The Effectiveness of an Electronic Security Management System in a Privately Owned Apartment Complex (United States)

    Greenberg, David F.; Roush, Jeffrey B.


    Poisson and negative binomial regression methods are used to analyze the monthly time series data to determine the effects of introducing an integrated security management system including closed-circuit television (CCTV), door alarm monitoring, proximity card access, and emergency call boxes to a large privately-owned complex of apartment…

  17. Light and electron microscopic study on complex carbohydrates in the testis of Salamandra salamandra L. (Amphibia, Urodela). (United States)

    Schindelmeiser, J


    The distribution of complex carbohydrates was studied in the testis of the European fire salamander, Salamandra salamandra, by light- and electron-microscopic methods. The basal laminae and fibrous structures in the connective tissue between the lobules are PAS-positive. After alcianblue staining (at pH = 2.8), acid mucopolysaccharides could be demonstrated in steroid hormone-producing cells in the interstitial tissue between lobules containing spermatids, spermatozoa, and lobules after spermiation, as well as in most of the Sertoli cells in lobules after spermiation. In all spermatogenic stages from secondary spermatocytes to mature sperms, dictyosome-like structures and flat vesicles showed a distinct contrast enhancement, as did parts of the acrosome after treatment with the phosphotungstic acid-chromic acid method for electron microscopy.

  18. Syntheses, kinetics, and mechanism of ligand substitution reactions of 17-electron cyclopentadienyl and pentadienyl vanadium carbonyl complexes

    Energy Technology Data Exchange (ETDEWEB)

    Kowaleski, R.M.; Basolo, F.; Trogler, W.C.; Gedridge, R.W.; Newbound, T.D.; Ernst, R.D.


    Reported are the syntheses of bis(eta/sup 5/-pentadienyl)vanadium carbonyls and corresponding triethylphosphine compounds. The CO substitution lability in the complexes (eta/sup 5/-L)/sub 2/ VCO (L = C/sub 5/H/sub 5/, C/sub 5/Me/sub 5/, C/sub 5/H/sub 7/, 2,4-C/sub 7/H/sub 11/) was investigated. The exchange reaction of (eta/sup 5/-C/sub 5/H/sub 5/)/sub 2/V/sup 13/CO or of (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/V/sup 13/CO with CO is first-order in both CO and metal complex: for L = C/sub 5/Me/sub 5/, kinetic parameters in toluene are 2//sup double dagger/ = 8.9 +/- 0.7 kcal/mol, 2//sup double dagger/ = -21 +/- 3 cal/(mol K), and k/sub 2/ (0.0/sup 0/C) = 12.7 (+/- 0.1) M/sup -1/s/sup -1/. The rate of CO addition to the 15-electron complex CP*/sub 2/V is slower than the CO exchange rate for Cp*/sub 2/VCO: double dagger/ = 6.3 +/- 0.1 kcal/mol, double dagger/ = -37 +/- 4 cal/(mol K), and k (0.0/sup 0/C, toluene) = 0.424 +/- 0.005 M/sup -1/ s/sup -1/. The vanadium carbonyl complexes containing one or two pentadienyl ligands react 10/sup 3/-10/sup 4/ times slower than the bis(cyclopentadienyl) complexes, and the CO exchange rates depend only slightly on CO concentration. The electronic and steric features in these complexes, which allow for associative reactions for (eta/sup 5/-C/sub 5/H/sub 5/)/sub 2/ VCO and (eta/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ VCO but prohibit this pathway for the pentadienyl complexes, are discussed.

  19. Correlation of Electronic and Geometric Structure in Mononuclear Copper(II) Superoxide Complexes (United States)

    Ginsbach, Jake W.; Peterson, Ryan L.; Cowley, Ryan E.; Karlin, Kenneth D.; Solomon, Edward I.


    The geometry of mononuclear copper(II) superoxide complexes has been shown to determine their ground state where side-on bonding leads to a singlet ground state and end-on complexes have triplet ground states. In apparent contrast to this trend, the recently synthesized (HIPT3tren)CuII–O2•− (1) was proposed to have an end-on geometry and a singlet ground state. However, re-examination of 1 with resonance Raman (rR), magnetic circular dichroism (MCD), and 2H NMR spectroscopy indicates that 1 is in fact an end-on superoxide species with a triplet ground state that results from the single CuII–O2•− bonding interaction being weaker than the spin pairing energy. PMID:24164429

  20. Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens


    radicals containing two aromatic end groups connected by a flexible polymethylene chain or a rigid cyclohexane frame is thus trapped on either aromatic end group, and ET between these groups can be detected by ESR techniques. Intramolecular ET also occurs in binuclear transition metal complexes in which......, and for intramolecular and inner sphere ET for transition metal complexes. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....... the coupling between the metal centers [(Ru(II)/Ru(III) and Ru(II)/Co(III) couples] is sufficiently weak (class I or II mixed valence compounds). The ET mechanism can involve either direct transfer between the donor and acceptor groups or a higher order mechanism in which ET proceeds through intermediate...

  1. Influence of weak vibrational-electronic couplings on 2D electronic spectra and inter-site coherence in weakly coupled photosynthetic complexes

    Energy Technology Data Exchange (ETDEWEB)

    Monahan, Daniele M.; Whaley-Mayda, Lukas; Fleming, Graham R., E-mail: [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720 (United States); Ishizaki, Akihito [Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki 444-8585 (Japan)


    Coherence oscillations measured in two-dimensional (2D) electronic spectra of pigment-protein complexes may have electronic, vibrational, or mixed-character vibronic origins, which depend on the degree of electronic-vibrational mixing. Oscillations from intrapigment vibrations can obscure the inter-site coherence lifetime of interest in elucidating the mechanisms of energy transfer in photosynthetic light-harvesting. Huang-Rhys factors (S) for low-frequency vibrations in Chlorophyll and Bacteriochlorophyll are quite small (S ≤ 0.05), so it is often assumed that these vibrations influence neither 2D spectra nor inter-site coherence dynamics. In this work, we explore the influence of S within this range on the oscillatory signatures in simulated 2D spectra of a pigment heterodimer. To visualize the inter-site coherence dynamics underlying the 2D spectra, we introduce a formalism which we call the “site-probe response.” By comparing the calculated 2D spectra with the site-probe response, we show that an on-resonance vibration with Huang-Rhys factor as small as S = 0.005 and the most strongly coupled off-resonance vibrations (S = 0.05) give rise to long-lived, purely vibrational coherences at 77 K. We moreover calculate the correlation between optical pump interactions and subsequent entanglement between sites, as measured by the concurrence. At 77 K, greater long-lived inter-site coherence and entanglement appear with increasing S. This dependence all but vanishes at physiological temperature, as environmentally induced fluctuations destroy the vibronic mixing.

  2. Electrical properties and electronic states of molecular conductors based on unsymmetrical organometallic-dithiolene gold(III) complexes. (United States)

    Kubo, Kazuya; Nakao, Akiko; Ishii, Yasuyuki; Yamamoto, Takashi; Tamura, Masafumi; Kato, Reizo; Yakushi, Kyuya; Matsubayashi, Gen-etsu


    The electronic properties of cation radical salts derived from organometallic mixed-ligand complexes [(ppy)Au(S-S)](ppy- = C-dehydro-2-phenylpyridine(-); S-S(2-) = dithiolene ligand) with Au(III)-C sigma-bond were investigated. A 2:1 salt complex [(ppy)Au(C8H4S8)]2[PF6] (C8H4S8(2-) = 2-((4,5-ethylenedithio)-1,3-dithiole-2-ylidene)-1,3-dithiole-4,5-dithiolate(2-)) exhibited semiconductive behavior under ambient pressure (rho rt = 2.6 Omega cm, Ea = 0.03 eV). Magnetic measurements show that it is a Mott insulator close to the metal-insulator boundary. Raman and infrared spectra have revealed that the complex has a quasi-one-dimensional dimeric structure consisting of uniformly charged donor molecules. The complex exhibits metallic behavior at pressures above 0.8 GPa. In contrast, a similar compound [(ppy)Au(C8H4S6O2)]2[BF4] (C8H4S6O2(2-) = 2-((4,5-ethylenedioxy)-1,3-dithiole-2-ylidene)-1,3-dithiole-4,5-dithiolate(2-)) is a band insulator.

  3. Ionic Association and Electron Spin Relaxation Rates in Aquo Gadolinium(III) Complexes (United States)

    Sur, Sandip K.; Bryant, Robert G.


    The electron paramagnetic resonance linewidth of aquo gadolinium(III) ion changes with the counter-ion identity and concentration in aqueous solutions. The EPR linewidth of 2 mMgadolinium(III) chloride increases from 49.2 to 89.0 mT when carbonate ion is added and decreases to 17.3 mT when nitrite ion is added. These observations suggest association reactions between aquo gadolinium(III) ion and anions that change the electron spin relaxation rates of the aquo ion. The concentration dependence of the gadolinium(III) EPR linewidth is consistent with binding constants for nitrite and nitrate ion with the aquo gadolinium(III) ion of 37 ± 6 and 2.3 ± 0.3 L mol-1respectively. The decreases in the EPR linewidth factors with these association reactions are difficult to understand unless the anion reactions increase the symmetry of the metal center. Although first-coordination reactions may not be ruled out, the decrease in EPR linewidth is more consistent with an outer-sphere association reaction that also reduces the coordination number of the metal center from 9 to 8.

  4. Dinuclear manganese complexes for water oxidation: evaluation of electronic effects and catalytic activity. (United States)

    Arafa, Wael A A; Kärkäs, Markus D; Lee, Bao-Lin; Åkermark, Torbjörn; Liao, Rong-Zhen; Berends, Hans-Martin; Messinger, Johannes; Siegbahn, Per E M; Åkermark, Björn


    During recent years significant progress has been made towards the realization of a sustainable and carbon-neutral energy economy. One promising approach is photochemical splitting of H2O into O2 and solar fuels, such as H2. However, the bottleneck in such artificial photosynthetic schemes is the H2O oxidation half reaction where more efficient catalysts are required that lower the kinetic barrier for this process. In particular catalysts based on earth-abundant metals are highly attractive compared to catalysts comprised of noble metals. We have now synthesized a library of dinuclear Mn2(II,III) catalysts for H2O oxidation and studied how the incorporation of different substituents affected the electronics and catalytic efficiency. It was found that the incorporation of a distal carboxyl group into the ligand scaffold resulted in a catalyst with increased catalytic activity, most likely because of the fact that the distal group is able to promote proton-coupled electron transfer (PCET) from the high-valent Mn species, thus facilitating O-O bond formation.

  5. Simulation study on the effects of chemical structure and molecular size on the acceptor strength in poly(3-hexylthiophene)-based copolymer with alternating donor and acceptor for photovoltaic applications (United States)

    Rassamesard, Areefen; Pengpan, Teparksorn


    This research assessed the effects of various chemical structures and molecular sizes on the simulated geometric parameters, electron structures, and spectroscopic properties of single-chain complex alternating donor-acceptor (D-A) monomers and copolymers that are intended for use as photoactive layer in a polymer solar cell by using Kohn-Sham density functional theory with B3LYP exchange-correlation functional. The 3-hexylthiophene (3HT) was selected for electron donor, while eight chemicals, namely thiazole (Z), thiadiazole (D), thienopyrazine (TP), thienothiadiazole (TD), benzothiadiazole (BT), thiadiazolothieno-pyrazine (TPD), oxadiazole (OXD) and 5-diphenyl-1,2,4-triazole (TAZ), were employed as electron acceptor functional groups. The torsional angle, bridge bond length, intramolecular charge transfer, energy levels, and molecular orbitals were analyzed. The simulation results reveal that the geometry and electron structure of donor-acceptor monomer and copolymer are significantly impacted by heterocyclic rings, heteroatoms, fused rings, degree of steric hindrance and coplanarity of the acceptor molecular structure. Planar conformation was obtained from the D copolymer, and a pseudo-planar structure with the TD copolymer. The TAZ acceptor exhibited strong steric hindrance due to its bulky structure and non-planarity of its structure. An analysis of the electron structures indicated that the degree of intramolecular electron-withdrawing capability had the rank order TAZ  group provides a compromise in the characteristics of a donor-acceptor copolymer, useful in a polymeric candidate material for the photoactive layer in a polymer solar cell.

  6. Enzymatic activity of the alternative complex III as a menaquinol:auracyanin oxidoreductase in the electron transfer chain of Chloroflexus aurantiacus

    National Research Council Canada - National Science Library

    Gao, Xinliu; Xin, Yueyong; Blankenship, Robert E


    The surprising lack of the cytochrome bc 1 complex in the filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus suggests that a functional replacement exists to link the cyclic electron transfer chain...

  7. Acceleration of Long-Range Photoinduced Electron Transfer through DNA by Hydroxyquinolines as Artificial Base Pairs. (United States)

    Bätzner, Effi; Liang, Yu; Schweigert, Caroline; Unterreiner, Andreas-Neil; Wagenknecht, Hans-Achim


    The C-nucleoside based on the hydroxyquinoline ligand (Hq) is complementary to itself and forms stable Hq-Hq pairs in double-stranded DNA. These artificial Hq-Hq pairs may serve as artificial electron carriers for long-range photoinduced electron transfer in DNA, as elucidated by a combination of gel electrophoretic analysis of irradiated samples and time-resolved transient absorption spectroscopy. For this study, the Hq-Hq pair was combined with a DNA-based donor-acceptor system consisting of 6-N,N-dimethylaminopyrene conjugated to 2'-deoxyuridine as photoinducible electron donor, and methyl viologen attached to the 2'-position of uridine as electron acceptor. The Hq radical anion was identified in the time-resolved measurements and strand cleavage products support its role as an intermediate charge carrier. Hence, the Hq-Hq pair significantly enhances the electron hopping capability of DNA compared to natural DNA bases over long distances while keeping the self-assembly properties as the most attractive feature of DNA as a supramolecular architecture. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Carotenoids as electron or excited-state energy donors in artificial photosynthesis: an ultrafast investigation of a carotenoporphyrin and a carotenofullerene dyad

    NARCIS (Netherlands)

    Pillai, S.; Ravensbergen, J.; Antoniuk-Pablant, A.; Sherman, B.D.; van Grondelle, R.; Frese, R.N.; Moore, T.A.; Gust, D.; Moore, A.L.; Kennis, J.T.M.


    Photophysical investigations of molecular donor-acceptor systems have helped elucidate many details of natural photosynthesis and revealed design principles for artificial photosynthetic systems. To obtain insights into the factors that govern the partition between excited-state energy transfer

  9. Statistics and kinetics of single-molecule electron transfer dynamics in complex environments: a simulation model study. (United States)

    Paula, Luciana C; Wang, Jin; Leite, Vitor B P


    Dynamics of the environments of complex systems such as biomolecules, polar solvents, and glass plays an important role in controlling electron transfer reactions. The kinetics is determined by the nature of a complex multidimensional landscape. By quantifying the mean and high-order statistics of the first-passage time and the associated ratios, the dynamics in electron transfer reactions controlled by the environments can be revealed. We consider real experimental conditions with finite observation time windows. At high temperatures, exponential kinetics is observed and there are multiple kinetic paths leading to the product state. At and below an intermediate temperature, nonexponential kinetics starts to appear, revealing the nature of the distribution of local traps on the landscape. Discrete kinetic paths emerge. At very low temperatures, nonexponential kinetics continues to be observed. We point out that the size of the observational time window is crucial in revealing the intrinsic nature of the real kinetics. The mean first-passage time is defined as a characteristic time. Only when the observational time window is significantly larger than this characteristic time does one have the opportunity to collect enough statistics to capture rare statistical fluctuations and characterize the kinetics accurately.

  10. Solventless migratory-insertion reactions of substituted cyclopentadienyl iron complexes induced by electron donor ligands

    Directory of Open Access Journals (Sweden)

    Apollinaire Munyaneza


    Full Text Available Reaction between solid (C5H5Fe(CO 2CH3 and a range of solid phosphine ligands, L (L = PPh3, P(m-CH3C6H43, P(p-CH3C6H43, P(p-FC6H43, P(p-ClC6H43, PCy3 occurred in the absence of solvent in the melt phase to give the migratory-insertion products, (C5H5Fe(CO(COCH3(L. The reaction was more rapid with small electron withdrawing ligands. Insertion reaction between (RC5H4Fe(CO 2 R’ (R = H, CH3; R’ = CH3, CH2Ph and gaseous ligands such as SO2 and CO were also studied. The insertion of SO2 occurred readily for all the substrates investigated, but CO insertion did not occur (< 1 % using the solventless reaction condition.

  11. The influence of the electronic structure of adsorbate-substrate complexes on photoisomerization ability (United States)

    Bronner, Christopher; Schulze, Michael; Hagen, Sebastian; Tegeder, Petra


    We use time-resolved two-photon photoemission to study two molecular photoswitches at the Au(111) surface, namely azobenzene and its derivative tetra-tert-butyl-azobenzene (TBA). Electronic states located at the substrate-adsorbate interface are found to be a sensitive probe for the photoisomerization of TBA. In contrast to TBA, azobenzene loses its switching ability at the Au(111) surface. Besides the different adsorption geometries of both molecules, we partly attribute the quenching in the case of azobenzene to a shift of the highest occupied molecular orbital (HOMO) with respect to the gold d-bands, which renders the hole transfer involved in the photoisomerization mechanism of TBA inefficient.

  12. Electron-phonon scattering rates in complex polar crystals from ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Prange, Micah P.; Campbell, Luke W.; Kerisit, Sebastien N.


    The thermalization of fast electrons by phonons is studied in CsI, NaI, SrI2, and YAP. This numerical study uses an improvement to a recently developed ab initio method based on a density functional perturbation theoretical description of the phonon modes that provides a way to go beyond widely used phonon models based on binary crystals. Improvements to this method are described, and scattering rates are presented and discussed. The results here treat polar and nonpolar scattering on equal footing and allow an assessment of the relative importance of the two types of scattering. The relative activity of the numerous phonon modes in materials with complicated structures is discussed, and a simple criterion for finding the modes that scatter strongly is presented.

  13. Effect of gold nanoparticles on the structure and electron-transfer characteristics of glucose oxidase redox polyelectrolyte-surfactant complexes. (United States)

    Cortez, M Lorena; Marmisollé, Waldemar; Pallarola, Diego; Pietrasanta, Lía I; Murgida, Daniel H; Ceolín, Marcelo; Azzaroni, Omar; Battaglini, Fernando


    Efficient electrical communication between redox proteins and electrodes is a critical issue in the operation and development of amperometric biosensors. The present study explores the advantages of a nanostructured redox-active polyelectrolyte-surfactant complex containing [Os(bpy)2Clpy](2+) (bpy=2,2'-bipyridine, py= pyridine) as the redox centers and gold nanoparticles (AuNPs) as nanodomains for boosting the electron-transfer propagation throughout the assembled film in the presence of glucose oxidase (GOx). Film structure was characterized by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM), GOx incorporation was followed by surface plasmon resonance (SPR) and quartz-crystal microbalance with dissipation (QCM-D), whereas Raman spectroelectrochemistry and electrochemical studies confirmed the ability of the entrapped gold nanoparticles to enhance the electron-transfer processes between the enzyme and the electrode surface. Our results show that nanocomposite films exhibit five-fold increase in current response to glucose compared with analogous supramolecular AuNP-free films. The introduction of colloidal gold promotes drastic mesostructural changes in the film, which in turn leads to a rigid, amorphous interfacial architecture where nanoparticles, redox centers, and GOx remain in close proximity, thus improving the electron-transfer process. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Electronic and structural effects on the nonlinear optical behavior in push-pull TTF/tricarbonyl chromiun arene complexes. (United States)

    Insuasty, Braulio; Atienza, Carmen; Seoane, Carlos; Martín, Nazario; Garín, Javier; Orduna, Jesús; Alcalá, Rafael; Villacampa, Belén


    A novel D-pi-A system in which tetrathiafulvalene (TTF) and pi-extended TTFs as strong electron donors are covalently connected to a tricarbonyl (eta(6)-arene)chromium complex as the acceptor moiety through a systematically increased conjugated bridge of vinylene units (12a-c, 16a-c) have been synthesized by Wittig-Horner olefination reaction. The electronic spectra as well as the electrochemical data reveal a different behavior of TTF derivatives (12a-c) and of exTTF derivatives (16a-c). Cyclic voltammetry shows the influence of the tricarbonylchromium arene on the oxidation potentials in compounds 12a-c, and no remarkable effect is observed for exTTFs (16a-c). The nonlinear optical properties of 12a-c and 16a-c have been calculated by using the ab initio CPHF/6-31G//B3P86/6-31G model, and the time-dependent density functional theory (TD-DFT) method has been used for the calculation of the electronic transitions. The calculations reveal that an intraligand charge-transfer transition (ILCT) and the metal to ligand charge-transfer transition (MLCT) are responsible for the nonlinear response. In addition, the large angles formed by the ground-state dipole moment and the vectorial hyperpolarizability are responsible for the mubeta values determined experimentally by the EFISH technique.

  15. Direct Probing of Photoinduced Electron Transfer in a Self-Assembled Biomimetic [2Fe2S]-Hydrogenase Complex Using Ultrafast Vibrational Spectroscopy

    NARCIS (Netherlands)

    Li, P.; Amirjalayer, S.; Hartl, F.; Lutz, M.; de Bruin, B.; Becker, R.; Woutersen, S.; Reek, J.N.H.


    Photoinduced electron transfer in a supramolecular ZnTPP·Fe2S2 complex is investigated using femtosecond infrared spectroscopy, infrared spectro-electrochemistry, and DFT calculations. We find that the electron density is delocalized over the diiron core and the naphthalimide ligand, which explains

  16. Electronic coupling in a highly preorganized bimetallic complex comprising pyrazolate-bridged CpMn(CO)2 moieties. (United States)

    Röder, Jens C; Meyer, Franc; Hyla-Kryspin, Isabella; Winter, Rainer F; Kaifer, Elisabeth


    By means of a multistep synthetic procedure a dimanganese complex has been prepared, in which a N,N'-bridging pyrazolate ligand spans two CpMn(CO)(2) subunits in a highly preorganized chelate arrangement. The Xray crystallographic analyses of the Mn(I)Mn(I) complex K(+)1(-) and of its non-chelate precursor complex elucidate details of the molecular structure, in particular an unusual pyrazolate binding mode in the solid state and intertwining of the CO ligands in the crowded bimetallic array 1(-). The Mn(I)Mn(I) compound (1(-)), the mixed-valent Mn(I)Mn(II) (1), and the oxidized Mn(II)Mn(II) form (1(+)) have been characterized by various analytical and spectrosopic methods, such as electrochemistry, variable-temperature EPR spectroscopy, IR spectroelectrochemistry, and UV/Vis/NIR spectroelectrochemistry as well as by DFT and TD-DFT calculations. Strong electronic coupling in the mixed-valent complex is observed, but time- (and temperature-) dependent valence detrapping occurs, thus placing 1 in class II according to the Robin and Day assignment, close to the class II/III transition. From variable-temperature EPR spectroscopy a rough estimate of the activation energy and rate for thermal electron transfer can be deduced, with E(th) ( not equal )=13.6 kJ mol(-1) and k(th)=2.6 x 10(10) s(-1) at 298 K. Unexpectedly, no intervalence CT transition for 1 is detected in solution, but one appears in the optical spectrum of solid 1. The conclusions drawn from experiments are fully supported by DFT calculations that were carried out for all three forms of the dimanganese complex. A broken symmetry treatment for mixed-valent 1 reveals almost perfect localization of both spin and charge on one Mn center. According to TD-DFT the first excited states of 1 give rise to the IT processes in the NIR-energy region, as observed in the solid-state spectrum. The HOMOs are located at the Mn ions and are favorably arranged for pi interactions with the bridging pyrazolate.

  17. Mass mapping of a protein complex with the scanning transmission electron microscope. (United States)

    Engel, A; Baumeister, W; Saxton, W O


    A mass map of the hexagonally packed intermediate layer (HPI-layer), a regular protein monolayer from the cell envelope of Micrococcus radiodurans, has been obtained by scanning transmission electron microscopy. Samples were freeze-dried within the microscope, and low-dose images were recorded in the dark-field mode directly in digital form and processed by correlation averaging. The averaged projection of the unstained structure--i.e., the mass map--thus calculated shows a resolution to 3-nm period and reveals morphological features consistent with those obtained by negative staining. The mass of individual morphological domains was extracted by using variously the mass map itself or an average from a negatively stained HPI layer to define the domain boundaries. Protrusions as small as 1,300 daltons could be measured reproducibly within the unit cell of 655,000 daltons. The method developed opens an avenue to identify molecular species in situ and to correlate topographic information with biochemical data. Images PMID:6955791

  18. Transvenous lead extraction at the time of cardiac implantable electronic device upgrade: Complexity, safety, and outcomes. (United States)

    Barakat, Amr F; Wazni, Oussama M; Tarakji, Khaldoun; Saliba, Walid I; Nimri, Nayef; Rickard, John; Brunner, Michael; Bhargava, Mandeep; Kanj, Mohamed; Baranowski, Bryan; Martin, David O; Cantillon, Daniel; Callahan, Thomas; Dresing, Thomas; Niebauer, Mark; Chung, Mina; Lindsay, Bruce D; Wilkoff, Bruce; Hussein, Ayman A


    The practice of lead abandonment at the time of cardiac implantable electronic device upgrade remains a controversial topic but is affecting an increasing number of patients. Inherent risks include high-risk extractions of redundant leads when extraction is required at a later date. We aimed to report our experience with transvenous lead extraction (TLE) at the time of device upgrade. All consecutive TLE procedures at the time of device upgrade at the Cleveland Clinic between January 1, 1996 and December 31, 2012 were included (n = 503). Success and complications were defined according to the Heart Rhythm Society consensus document on TLE. There were a total of 984 leads in place, and 719 were targeted with extraction (589 pacer and 130 defibrillator leads, 63 of them being dual-coil leads). In all patients, TLEs aimed to avoid abandoning leads. Concomitant lead management issues included lead malfunction (15%), previously abandoned leads (9%), vascular access occlusion (6%), or leads on advisory (3%). In most procedures (75.4%), special extraction tools were needed. The complete procedural and clinical success rates were 96.6% and 97.2%, respectively. During planned extractions, damage of coexisting leads occurred in 19 patients (3.8%), eventually requiring extraction. The major and minor complication rates were 1% and 1.4%, respectively. In a high-volume center, TLEs at the time of device upgrade were successful in the vast majority of patients with a low complication rate. Copyright © 2017. Published by Elsevier Inc.

  19. A method to achieve homogeneous dispersion of large transmembrane complexes within the holes of carbon films for electron cryomicroscopy. (United States)

    Cheung, Martin; Kajimura, Naoko; Makino, Fumiaki; Ashihara, Masamichi; Miyata, Tomoko; Kato, Takayuki; Namba, Keiichi; Blocker, Ariel J


    Difficulties associated with using X-ray crystallography for structural studies of large macromolecular complexes have made single particle cryo-electron microscopy (cryoEM) a key technique in structural biology. The efficient application of the single particle cryoEM approach requires the sample to be vitrified within the holes of carbon films, with particles well dispersed throughout the ice and adopting multiple orientations. To achieve this, the carbon support film is first hydrophilised by glow discharge, which allows the sample to spread over the film. Unfortunately, for transmembrane complexes especially, this procedure can result in severe sample adsorption to the carbon support film, reducing the number of particles dispersed in the ice. This problem is rate-limiting in the single particle cryoEM approach and has hindered its widespread application to hydrophobic complexes. We describe a novel grid preparation technique that allows for good particle dispersion in the ice and minimal hydrophobic particle adhesion to the support film. This is achieved by hydrophilisation of the carbon support film by the use of selected detergents that interact with the support so as to achieve a hydrophilic and neutral or selectively charged surface. Crown Copyright © 2013. Published by Elsevier Inc. All rights reserved.

  20. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    Directory of Open Access Journals (Sweden)

    Maike Bublitz


    Full Text Available Membrane proteins are key players in biological systems, mediating signalling events and the specific transport of e.g. ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data reveal the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins.

  1. Complex reduction coefficient for a cylindrical electron beam with variable amplitude of the variable current component in the TWT

    Directory of Open Access Journals (Sweden)

    Chasnyk V. I.


    Full Text Available The conventional approach to calculating the space charge for the traveling-wave tube (TWT with phase velocity jumps is to use the same values of the depression coefficient as the ones for homogeneous helical TWTs. However, if the variable component of the exciting current in the expressions for determining the reduction coefficient is changed in amplitude, then the reduction factor is a complex value. Perhaps the neglect of this fact can significantly affect the volume discharge calculated value, and hence the non-synchronization parameter, for those of its values, which are characteristic of the TWT with a phase velocity jump. In this paper, formulas has been obtained for computation of real and imaginary parts of the complex reduction coefficient for a cylindrical electrons beam with exponential variable amplitude of variable current component in the TWT. Influence of complex reduction coefficient on the parameters of the TWT operating in the linear mode is estimated. It is shown that taking into account the imaginary part of the reduction coefficient for linear operation of the TWT makes it possible to change the estimated amount of space charge 1.5 to 2 times, which in its turn has quite a strong effect on the formation of the initial conditions of the nonlinear mode and, subsequently, on the output characteristics of the TWT.

  2. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    Energy Technology Data Exchange (ETDEWEB)

    Bublitz, Maike; Nass, Karol; Drachmann, Nikolaj D.; Markvardsen, Anders J.; Gutmann, Matthias J.; Barends, Thomas R. M.; Mattle, Daniel; Shoeman, Robert L.; Doak, R. Bruce; Boutet, Sébastien; Messerschmidt, Marc; Seibert, Marvin M.; Williams, Garth J.; Foucar, Lutz; Reinhard, Linda; Sitsel, Oleg; Gregersen, Jonas L.; Clausen, Johannes D.; Boesen, Thomas; Gotfryd, Kamil; Wang, Kai-Tuo; Olesen, Claus; Møller, Jesper V.; Nissen, Poul; Schlichting, Ilme


    Membrane proteins are key players in biological systems, mediating signalling events and the specific transport ofe.g.ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX) for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data reveal the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins.

  3. A study of the structure-property relationship of azole-azine based homoleptic platinum(II) complexes and tunability of the photo-physical properties (United States)

    Ranga Prabhath, Malaviarachchige Rabel

    Owing to superior energy efficiency, Light Emitting Diode (OLED) technology has become considerably commercialised over the last decade. Innovations in this field have been spurred along by the discovery of new molecules with good stability and high emission intensity, followed through by intense engineering efforts. Emissive transition metal complexes are potent molecular emitters as a result of their high quantum efficiencies related to facile intersystem crossing (ISC) between excited-state manifolds (efficient spin orbit coupling (SOC)) and resultant efficient emission from the triplet state (phosphorescence). These also allow rational tuning of the emission wavelengths. Tuning of the ground and excited state energies, and thus emission wavelength of these complexes can be achieved by subtle structural changes in the organic ligands. Pyridyl-triazole ligands have started receiving increasing attention in recent years as strong field ligands that are relatively straightforward to synthesise. In this study we explore the emission tunability of a newly synthesised series of 5-subsituted-Pyridyl-1,2,3-triazole-based ligands and their Pt(II) complexes. Studies have shown, substitution at the triazole moiety is less effective in achieving emission tunability. Alternatively we carried out the substitution at the 5th position of the pyridine ring with a wide range of electronically diverse, donor-acceptor groups (-N(CH3)2, -H, -CHO, -CHC(CN)2). The target ligands were approached through the serial application of the Sonogashira carbon–carbon coupling and the Sharpless copper-catalyzed Huisgen’s 1,3-dipolarcycloaddition procedures. As a result, coarse tunability of excimer emission was observed in thin-films, generating blue-(486 nm), green-(541 nm), orange-(601 nm) and red-(625 nm) luminescence respectively. This “turned-on” substituent effect was accounted for metallophilic Pt—Pt interaction-induced aggregates in the solid state. Excited state calculations

  4. P(CH)P pincer rhodium(I) complexes: the key role of electron-poor imidazoliophosphine extremities. (United States)

    Barthes, Cécile; Lepetit, Christine; Canac, Yves; Duhayon, Carine; Zargarian, Davit; Chauvin, Remi


    The coordination chemistry of a potentially pincer-type dicationic meta-phenylene-bis(imidazoliophosphine) ligand 3 to neutral and cationic carbonylrhodium(I) centers has been investigated. Similarly to what was observed previously for its ortho-phenylene counterpart, 3 was found to bind to the RhCl(CO) fragment in a trans-chelating manner that makes possible a weak Rh-C(H) interaction, inferred from the nonbonding but relatively short Rh-C and Rh-H contacts observed in the solid state structure of the dicationic adduct (3)RhCl(CO) (5). Formation of the target PCP-type pincer complex could not be triggered despite multiple attempts to deprotonate the central C-H moiety in the initial dicationic adduct 5, or in the tricationic species [(3)Rh(CO)](+) (8) generated by abstraction of the chloride ion from 5. Complex 8 was identified on the basis of NMR and IR analyses as a Rh(I)-stabilized P(CH)P-intermediate en route to the anticipated classical PCP-type pincer complex. Analysis of the electronic structure of this intermediate computed at the density functional level of theory (DFT level) revealed a bonding overlap between a Rh d-orbital and π-orbitals of the m-phenylene ring. NBO analyses and calculated Wiberg indices confirm that this interaction comprises an η(1)-C-Rh bonding mode, with only secondary contributions from the geminal C and H atoms. Although the target PCP-type pincer complex could not be generated, treatment of the tricationic intermediate with methanol induced a P-CN(2) bond cleavage at both imidazoliophosphine moieties, resulting in the formation of a dicationic "open pincer" species, that is, a nonchelated bis((MeO)PPh(2))-stabilized aryl-Rhodium complex that is the κC-only analogue of the putative κP,κC,κP-PCP complex sought initially. Theoretical studies at the DFT level of experimental or putative species relevant to the final C-H activation process ruled out the oxidative addition pathway. Two alternative pathways are proposed to explain

  5. Effect of principal and secondary ligands on the electronic structures and spectra of a series of ruthenium(II complexes

    Directory of Open Access Journals (Sweden)

    Zhang Yanli


    Full Text Available A DFT(density functional theory/TDDFT(time-dependent density functional theory investigation is performed to study the ground-state geometries, electronic structures, and absorption spectra of twelve ruthenium(II thiosemicarbazone complexes [Ru(CO(C(Ln], where Ln=derivatives of dibasic tetradentate Schiff-base ligand and X=AsPh3/PPh3/Py. The ground-state geometries are optimized at the B3LYP/6-31G(d-LANL2DZ level, and the spectra are simulated by means of TD-B3LYP/6-31G(d-LANL2DZ method on the basis of the optimized geometries. The influence of principal and secondary ligands (Ln and X on transition characters and absorption peak positions is evaluated.

  6. Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band. (United States)

    Chen, Jie; Zhang, Hua; Tomov, Ivan V; Ding, Xunliang; Rentzepis, Peter M


    The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co-O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal-oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism.

  7. Photosensitized electron transfer within a self-assembled norharmane-2'-deoxyadenosine 5'-monophosphate (dAMP) complex. (United States)

    Gonzalez, M Micaela; Rasse-Suriani, Federico A O; Franca, Carlos A; Diez, Reinaldo Pis; Gholipour, Yousef; Nonami, Hiroshi; Erra-Balsells, Rosa; Cabrerizo, Franco M


    Norharmane is a compound that belongs to a family of alkaloids called β-carbolines (βCs). These alkaloids are present in a wide range of biological systems, playing a variety of significant photo-dependent roles. Upon UV-A irradiation, βCs are able to act as efficient photosensitizers. In this work, we have investigated the photosensitized oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) by norharmane in an aqueous phase, upon UV-A (350 nm) irradiation. The effect of the pH was evaluated on both the interactions between norharmane and dAMP in the ground and electronic excited states, and on the dAMP photosensitized oxidation. A quite strong static interaction between norharmane and dAMP was observed, especially under those pH conditions where the protonated form of the alkaloid is present (pH dAMP complex is the operative mechanism in the dAMP photosensitization.

  8. Effect of electron count and chemical complexity in the Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor. (United States)

    von Rohr, Fabian; Winiarski, Michał J; Tao, Jing; Klimczuk, Tomasz; Cava, Robert Joseph


    High-entropy alloys are made from random mixtures of principal elements on simple lattices, stabilized by a high mixing entropy. The recently discovered body-centered cubic (BCC) Ta-Nb-Hf-Zr-Ti high-entropy alloy superconductor appears to display properties of both simple crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. Here we show that the valence electron count dependence of the superconducting transition temperature in the high-entropy alloy falls between those of analogous simple solid solutions and amorphous materials and test the effect of alloy complexity on the superconductivity. We propose high-entropy alloys as excellent intermediate systems for studying superconductivity as it evolves between crystalline and amorphous materials.

  9. PENTrack-a simulation tool for ultracold neutrons, protons, and electrons in complex electromagnetic fields and geometries (United States)

    Schreyer, W.; Kikawa, T.; Losekamm, M. J.; Paul, S.; Picker, R.


    Modern precision experiments trapping low-energy particles require detailed simulations of particle trajectories and spin precession to determine systematic measurement limitations and apparatus deficiencies. We developed PENTrack, a tool that allows to simulate trajectories of ultracold neutrons and their decay products-protons and electrons-and the precession of their spins in complex geometries and electromagnetic fields. The interaction of ultracold neutrons with matter is implemented with the Fermi-potential formalism and diffuse scattering using Lambert and microroughness models. The results of several benchmark simulations agree with STARucn v1.2, uncovered several flaws in Geant4 v10.2.2, and agree with experimental data. Experiment geometry and electromagnetic fields can be imported from commercial computer-aided-design and finite-element software. All simulation parameters are defined in simple text files allowing quick changes. The simulation code is written in C++ and is freely available at

  10. Collisions of electrons with hydrogen atoms II. Low-energy program using the method of the exterior complex scaling (United States)

    Benda, Jakub; Houfek, Karel


    While collisions of electrons with hydrogen atoms pose a well studied and in some sense closed problem, there is still no free computer code ready for ;production use;, that would enable applied researchers to generate necessary data for arbitrary impact energies and scattering transitions directly if absent in on-line scattering databases. This is the second article on the Hex program package, which describes a new computer code that is, with a little setup, capable of solving the scattering equations for energies ranging from a fraction of the ionization threshold to approximately 100 eV or more, depending on the available computational resources. The program implements the exterior complex scaling method in the B-spline basis.

  11. Hydrogen atom vs electron transfer in catecholase-mimetic oxidations by superoxometal complexes. Deuterium kinetic isotope effects. (United States)

    Simándi, Tatiana M; May, Zoltán; Szigyártó, Imola Cs; Simándi, László I


    Dioximato-cobalt(II), -iron(II) and -manganese(II) complexes (1)-(6), acting as functional catecholase and phenoxazinone synthase models, exhibit a deuterium kinetic isotope effect predicted by theory (k4H/k4D < or = 3) in the catalytic oxidative dehydrogenation of 3,5-di-tert-butylcatechol and 2-aminophenol by O2. KIEs in the range of (k4H/k4D approximately 1.79-3.51) are observed with (1) and (2) as catalysts, pointing to hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo ligand. Less significant KIEs (1.06-1.20) are exhibited by catalysts systems (3)-(6), indicating that proton-coupled electron transfer is the preferred route in those cases.

  12. Structure and Bonding Investigation of Plutonium Peroxocarbonate Complexes Using Cerium Surrogates and Electronic Structure Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Sweet, Lucas E.; Corbey, Jordan F.; Gendron, Frédéric; Autschbach, Jochen; McNamara, Bruce K.; Ziegelgruber, Kate L.; Arrigo, Leah M.; Peper, Shane M.; Schwantes, Jon M.


    Herein, we report the synthesis and structural characterization of K8[(CO3)3Pu]2(µ-η2-η2-O2)2•12H2O. This is the second plutonium-containing addition to the previously studied alkali metal peroxo-carbonate series M8[(CO3)3A]2(µ-η2-η2-O2)2•xH2O (M = alkali metal; A = Ce or Pu; x = 8, 10, 12 or 18), for which only the M = Na analog has been previously reported when A = Pu. The previously reported crystal structure for Na8[(CO3)3Pu]2(µ-η2-η2-O2)2•12H2O is not isomorphous with its known Ce analogue. However, a new synthetic route to these M8[(CO3)3A]2(µ-η2-η2-O2)2•12H2O complexes, described below, has produced crystals of Na8[(CO3)3Ce]2(µ-η2-η2-O2)2•12H2O that are isomorphous with the previously reported Pu analogue. Via this synthetic method, the M = Na, K, Rb, and Cs salts of M8[(CO3)3Ce]2(µ-η2-η2-O2)2•xH2O have also been synthesized for systematic structural comparison with each other and the available Pu analogues using single-crystal X-ray diffraction, Raman spectroscopy and density functional theory (DFT) calculations. The cerium salts in particular demonstrate subtle differences in the peroxide bond lengths which correlate to Raman shifts for the peroxide Op–Op stretch (Op = the oxygen atoms of the peroxide bridges) with each of the cations studied: Na+ (1.492(3) Å /847 cm-1), Rb+ (1.471(1) Å /854 cm-1), Cs+ (1.474(1) Å /859 cm-1), and K+ (1.468(6) Å, 870 cm-1). The trends observed in the M–Op and Op–Op bond distances appear to relate to supermolecular interactions between the neighboring cations.

  13. Development and implementation of an electronic interface for complex clinical laboratory instruments without a vendor-provided data transfer interface. (United States)

    Blank, Gary E; Virji, Mohamed A


    Clinical pathology laboratories increasingly use complex instruments that incorporate chromatographic separation, e.g. liquid chromatography, with mass detection for rapid identification and quantification of biochemicals, biomolecules, or pharmaceuticals. Electronic data management for these instruments through interfaces with laboratory information systems (LIS) is not generally available from the instrument manufacturers or LIS vendors. Unavailability of a data management interface is a limiting factor in the use of these instruments in clinical laboratories where there is a demand for high-throughput assays with turn-around times that meet patient care needs. Professional society guidelines for design and transfer of data between instruments and LIS were used in the development and implementation of the interface. File transfer protocols and support utilities were written to facilitate transfer of information between the instruments and the LIS. An interface was created for liquid chromatography-tandem mass spectroscopy and inductively coupled plasma-mass spectroscopy instruments to manage data in the Sunquest(®) LIS. Interface validation, implementation and data transfer fidelity as well as training of technologists for use of the interface was performed by the LIS group. The technologists were familiarized with the data verification process as a part of the data management protocol. The total time for the technologists for patient/control sample data entry, assay results data transfer, and results verification was reduced from approximately 20 s per sample to <1 s per sample. Sample identification, results data entry errors, and omissions were eliminated. There was electronic record of the technologist performing the assay runs and data management. Development of a data management interface for complex, chromatography instruments in clinical laboratories has resulted in rapid, accurate, verifiable information transfers between instruments and LIS. This has

  14. Probing the Role of the Eighth Bacteriochlorophyll in holo-FMO Complex by Simulated Two-Dimensional Electronic Spectroscopy

    CERN Document Server

    Yeh, Shu-Hao


    The Fenna-Matthews-Olson (FMO) protein-pigment complex acts as a molecular wire between the outer antenna system and the reaction center (RC); it is an important model system to study the excitonic energy transfer. Recent crystallographic studies report the existence of an additional (eighth) bacteriochlorophyll a (BChl a). To understand the functionality of this eighth BChl, we simulated the two-dimensional electronic spectra of both the 7-site (apo form) and the 8-site (holo form) variant of the FMO complex from green sulfur bacteria, Prosthecochloris aestuarii. By comparing the difference between the spectrum, it was found that the eighth BChl can affect two different excitonic energy transfer pathways, these being: (1) directly involve in the first pathway 6 $\\rightarrow$ 3 $\\rightarrow$ 1 of the apo form model by passing the excitonic energy to exciton 6; and (2) increase the excitonic wave function overlap between excitons 4 and 5 in the second pathway (7 $\\rightarrow$ 4,5 $\\rightarrow$ 2 $\\rightarrow$ ...


    Directory of Open Access Journals (Sweden)

    E. A. Yushkov


    Full Text Available Purpose. Designing of diagrams to optimize mathematic model of the ship power plant (SPP combined propulsion complexes (CPC for decreasing operational loss and increasing fuel efficiency with simultaneous load limiting on medium revolutions diesel generator (MRDG by criterion reducing of wear and increasing operation time between repairs. Methodology. After analyzing of ship power plant modes of CPC proposed diagrams to optimize mathematic model of the above mentioned complex. The model based on using of electronic controllers in automatic regulation and control systems for diesel and thruster which allow to actualize more complicated control algorithm with viewpoint of increasing working efficiency of ship power plant at normal and emergency modes. Results. Determined suitability of comparative computer modeling in MatLab Simulink for building of imitation model objects based on it block diagrams and mathematic descriptions. Actualized diagrams to optimize mathematic model of the ship’s power plant (SPP combined propulsion complexes (CPC with Azipod system in MatLab Simulink software package Ships_CPC for decreasing operational loss and increasing fuel efficiency with simultaneous load limiting on medium revolutions diesel generator (MRDG by criterion reducing of wear and increasing operation time between repairs. The function blocks of proposed complex are the main structural units which allow to investigate it normal and emergency modes. Originality. This model represents a set of functional blocks of the components SPP CPC, built on the principle of «input-output». For example, the function boxes outputs of PID-regulators of MRDG depends from set excitation voltage and rotating frequency that in turn depends from power-station load and respond that is a ship moving or dynamically positioning, and come on input (inputs of thruster rotating frequency PID-regulator models. Practical value. The results of researches planned to use in

  16. Catching the role of anisotropic electronic distribution and charge transfer in halogen bonded complexes of noble gases. (United States)

    Bartocci, Alessio; Belpassi, Leonardo; Cappelletti, David; Falcinelli, Stefano; Grandinetti, Felice; Tarantelli, Francesco; Pirani, Fernando


    The systems studied in this work are gas-phase weakly bound adducts of the noble-gas (Ng) atoms with CCl4 and CF4. Their investigation was motivated by the widespread current interest for the intermolecular halogen bonding (XB), a structural motif recognized to play a role in fields ranging from elementary processes to biochemistry. The simulation of the static and dynamic behaviors of complex systems featuring XB requires the formulation of reliable and accurate model potentials, whose development relies on the detailed characterization of strength and nature of the interactions occurring in simple exemplary halogenated systems. We thus selected the prototypical Ng-CCl4 and Ng-CF4 and performed high-resolution molecular beam scattering experiments to measure the absolute scale of their intermolecular potentials, with high sensitivity. In general, we expected to probe typical van der Waals interactions, consisting of a combination of size (exchange) repulsion with dispersion/induction attraction. For the He/Ne-CF4, the analysis of the glory quantum interference pattern, observable in the velocity dependence of the integral cross section, confirmed indeed this expectation. On the other hand, for the He/Ne/Ar-CCl4, the scattering data unravelled much deeper potential wells, particularly for certain configurations of the interacting partners. The experimental data can be properly reproduced only including a shifting of the repulsive wall at shorter distances, accompanied by an increased role of the dispersion attraction, and an additional short-range stabilization component. To put these findings on a firmer ground, we performed, for selected geometries of the interacting complexes, accurate theoretical calculations aimed to evaluate the intermolecular interaction and the effects of the complex formation on the electron charge density of the constituting moieties. It was thus ascertained that the adjustments of the potential suggested by the analysis of the

  17. Catching the role of anisotropic electronic distribution and charge transfer in halogen bonded complexes of noble gases

    Energy Technology Data Exchange (ETDEWEB)

    Bartocci, Alessio; Cappelletti, David; Pirani, Fernando [Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Perugia 06123 (Italy); Belpassi, Leonardo [Istituto di Scienze e Tecnologie Molecolari del CNR, Perugia 06123 (Italy); Falcinelli, Stefano [Dipartimento di Ingegneria Civile ed Ambientale, Università degli Studi di Perugia, 06125 Perugia (Italy); Grandinetti, Felice [Dipartimento per la Innovazione nei sistemi Biologici, Agroalimentari e Forestali (DIBAF), Università della Tuscia, 01100 Viterbo (Italy); Tarantelli, Francesco [Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Perugia 06123 (Italy); Istituto di Scienze e Tecnologie Molecolari del CNR, Perugia 06123 (Italy)


    The systems studied in this work are gas-phase weakly bound adducts of the noble-gas (Ng) atoms with CCl{sub 4} and CF{sub 4}. Their investigation was motivated by the widespread current interest for the intermolecular halogen bonding (XB), a structural motif recognized to play a role in fields ranging from elementary processes to biochemistry. The simulation of the static and dynamic behaviors of complex systems featuring XB requires the formulation of reliable and accurate model potentials, whose development relies on the detailed characterization of strength and nature of the interactions occurring in simple exemplary halogenated systems. We thus selected the prototypical Ng-CCl{sub 4} and Ng-CF{sub 4} and performed high-resolution molecular beam scattering experiments to measure the absolute scale of their intermolecular potentials, with high sensitivity. In general, we expected to probe typical van der Waals interactions, consisting of a combination of size (exchange) repulsion with dispersion/induction attraction. For the He/Ne-CF{sub 4}, the analysis of the glory quantum interference pattern, observable in the velocity dependence of the integral cross section, confirmed indeed this expectation. On the other hand, for the He/Ne/Ar-CCl{sub 4}, the scattering data unravelled much deeper potential wells, particularly for certain configurations of the interacting partners. The experimental data can be properly reproduced only including a shifting of the repulsive wall at shorter distances, accompanied by an increased role of the dispersion attraction, and an additional short-range stabilization component. To put these findings on a firmer ground, we performed, for selected geometries of the interacting complexes, accurate theoretical calculations aimed to evaluate the intermolecular interaction and the effects of the complex formation on the electron charge density of the constituting moieties. It was thus ascertained that the adjustments of the potential

  18. Molecular complexes of MoO/sub 2/Cl/sub 2/ with aromatic and heterocyclic azomethines

    Energy Technology Data Exchange (ETDEWEB)

    Abramenko, V.L.; Garnovskij, A.D.; Surpina, L.V. (Voroshilovgradskij Mashinostroitel' nyj Inst. (Ukrainian SSR); Rostovskij-na-Donu Inst. Sel' skokhozyajstvennogo Mashinostroeniya (USSR))


    Earlier unknown MoO/sub 2/Cl/sub 2/xnL(2) molecular complexes (n=0.5, 1, 2; L=Schitt bases (SB) from banzoic (L/sup 1/), Si cylic, ..beta..-oxynaphthoic aldehydes and aromatic, aliphatic, heterocyclic mono- and diamines) are prepared by MoO/sub 2/Cl/sub 2/ (1) interaction with SB in organic solvents. Complex composition is determined by ligand nature. The prepared compounds are finely crystalline substances easily hydrolized in water, unsoluble in most solvents. Increase of frequency of C=N-bond valent oscillations by 10-40 cm/sup -1/ as compared with its position in L spectrum is observed in IR spectra 2 that points out molybdenum coordination by azomethine atom of nitrogen. Bands of Ph-O valent oscillations (1280-1300 cm/sup -1/) and OH/sup -/ (2800-3200 cm/sup -1/) under complexing are not practically shifted that testifies to conservation of intramolecular hydrogen bond in coordinated molecules of the ligands. The mentioned peculiarities in IR spectra permitted to attribute 2 to molecular type complexes with donor-acceptor bond N ..-->.. Mo(6). According to conductometric measurements 2 are 1:2 electrolytes in MeOH and dimethylformamide solutions and they are subjected to the reaction of the main solvolysis.

  19. Development and Characterization of New Donor-Acceptor Conjugated Polymers and Fullerene Nanoparticles for High Performance Bulk Heterojunction Solar Cells (United States)


    with a Nanoscope III controller under tapping mode. Top contact organic FETs were fabricated on heavily n- doped silicon substrates with a 300 nm...hexafluorophosphate (0.1 M) in acetonitrile (electrochemical grade , Fisher Scientific) as electrolyte and indium tin oxide (ITO) and Ag/Ag+ as the working and...Mo boat. FETs characterization was carried out in air using the Agilent 4155B semiconductor parameter analyzer. The field-effect mobility was

  20. Organic charge transfer phase formation in thin films of the BEDT-TTF/TCNQ donor-acceptor system

    DEFF Research Database (Denmark)

    Solovyeva, Vita; Keller, K.; Huth, M.


    -evaporation experiments of (BEDT-TTF)-TCNQ and TCNQ. In the course of these experiments we found that (0ℓℓ)-oriented BEDT-TTF layers can be prepared on α-Al O (112̄0) substrates at about 100 °C using (BEDT-TTF)-TCNQ as source material. We speculate that due to its high vapor pressure the TCNQ component serves...

  1. Correlation between LUMO offset of donor/acceptor molecules to an open circuit voltage in bulk heterojunction solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Mola, Genene Tessema, E-mail: [School of. Chemistry and Physics, University of Kwazulu-Natal, Pietermaritzburg Campus, Private Bag X01, Scottsville 3209 (South Africa); Abera, Newayemedhin [Addis Ababa University, Department of Physics, P.O. BOX 1176, Addis Ababa (Ethiopia)


    The correlation between the open circuit voltage and the LUMO offset of the donor and acceptor polymers in the bulkheterojunction solar cell was studied for three different thiophene derivatives. The HOMO levels of all the polymers in this investigation were chosen to be similar which results in close values of ΔE{sub DA}=E{sub HOMO}{sup D}−E{sub LUMO}{sup A}. However, the measured V{sub oc} was found to be increasing with decreasing value of the LUMO offset that exists between the donor polymer and fullerene.

  2. The Impact of Donor-Acceptor Phase Separation on the Charge Carrier Dynamics in pBTTT:PCBM Photovoltaic Blends

    KAUST Repository

    Gehrig, Dominik W.


    The effect of donor–acceptor phase separation, controlled by the donor–acceptor mixing ratio, on the charge generation and recombination dynamics in pBTTT-C14:PC70BM bulk heterojunction photovoltaic blends is presented. Transient absorption (TA) spectroscopy spanning the dynamic range from pico- to microseconds in the visible and near-infrared spectral regions reveals that in a 1:1 blend exciton dissociation is ultrafast; however, charges cannot entirely escape their mutual Coulomb attraction and thus predominantly recombine geminately on a sub-ns timescale. In contrast, a polymer:fullerene mixing ratio of 1:4 facilitates the formation of spatially separated, that is free, charges and reduces substantially the fraction of geminate charge recombination, in turn leading to much more efficient photovoltaic devices. This illustrates that spatially extended donor or acceptor domains are required for the separation of charges on an ultrafast timescale (<100 fs), indicating that they are not only important for efficient charge transport and extraction, but also critically influence the initial stages of free charge carrier formation.

  3. A convenient tandem one-pot synthesis of donor-acceptor-type triphenylene 2,3-dicarboxylic esters from diarylacetylene. (United States)

    Feng, Chun; Tian, Xian-Li; Zhou, Jing; Xiang, Shi-Kai; Yu, Wen-Hao; Wang, Bi-Qin; Hu, Ping; Redshaw, Carl; Zhao, Ke-Qing


    A tandem one-pot method for the direct synthesis of polysubstituted triphenylene 2,3-dicarboxylic esters with different substitution patterns was developed by enyne metathesis of diarylacetylene, followed by Diels-Alder, aromatization and a cyclization cascade.

  4. Controlling molecular weight of a high efficiency donor-acceptor conjugated polymer and understanding its significant impact on photovoltaic properties. (United States)

    Li, Wentao; Yang, Liqiang; Tumbleston, John R; Yan, Liang; Ade, Harald; You, Wei


    The molecular weight (MW) of PBnDT-FTAZ can be precisely controlled by adjusting the stoichiometric ratio of the two monomers, following the Carothers equation. The study of a set of PBnDT-FTAZ polymers with different MWs reveals that the MW significantly influences the morphology and structural order of PBnDTFTAZ in its bulk heterojunction solar cells, with the highest efficiency (over 7%) achieved with the use of a MW of 40 000 g mol(-1) . © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Effect of heterocycles on field-effect transistor performances of donor-acceptor-donor type small molecules (United States)

    Chini, Mrinmoy Kumar; Mahale, Rajashree Y.; Chatterjee, Shyambo


    Two D-A-D small molecules comprising triphenylamine and diketopyrrolopyrrole were synthesized having either furan or thiophene connected to the fused lactam ring. In this design, furan/thiophene diketopyrrolopyrrole acts as an acceptor and triphenylamine acts as a donor. Propeller shaped triphenylamine has its effect on packing, processability and plays a vital role in determining the π-π molecular orbital stacking in such compounds and thus the mobility of charge carriers. With TDPPT and FDPPT, maximum hole carrier mobility obtained is 2.88 × 10-3 cm2 V-1 s-1 and 1.60 × 10-3 cm2 V-1 s-1, respectively using bottom gate bottom contact field-effect transistor.

  6. Description of the Charge Transfer States at the Pentacene/C60 Interface: Combining Range-Separated Hybrid Functionals with the Polarizable Continuum Model

    KAUST Repository

    Zheng, Zilong


    Density functional theory (DFT) approaches based on range-separated hybrid functionals are currently methods of choice for the description of the charge-transfer (CT) states in organic donor/acceptor solar cells. However, these calculations are usually performed on small-size donor/acceptor complexes and as result do not account for electronic polarization effects. Here, using a pentacene/C60 complex as a model system, we discuss the ability of long-range corrected (LCR) hybrid functionals in combination with the polarizable continuum model (PCM) to determine the impact of the solid-state environment on the CT states. The CT energies are found to be insensitive to the interactions with the dielectric medium when a conventional time-dependent DFT/PCM (TDDFT/PCM) approach is used. However, a decrease in the energy of the CT state in the framework of LRC functionals can be obtained by using a smaller range-separated parameter when going from an isolated donor/acceptor complex to the solid-state case.

  7. Structural characterization and electronic properties determination by high-field and high-frequency EPR of a series of five-coordinated Mn(II) complexes. (United States)

    Mantel, Claire; Baffert, Carole; Romero, Isabel; Deronzier, Alain; Pécaut, Jacques; Collomb, Marie-Noëlle; Duboc, Carole


    The isolation, structural characterization, and electronic properties of a series of high-spin mononuclear five-coordinated Mn(II) complexes, [Mn(terpy)(X)(2)] (terpy = 2, 2':6',2' '-terpyridine; X = I(-) (1), Br(-) (2), Cl(-) (3), or SCN(-) (4)), are reported. The X-ray structures of the complexes reveal that the manganese ion lies in the center of a distorted trigonal bipyramid for complexes 1, 2, and 4, while complex 3 is better described as a distorted square pyramid. The electronic properties of 1-4 were investigated by high-field and high-frequency EPR spectroscopy (HF-EPR) performed between 5 and 30 K. The powder HF-EPR spectra have been recorded in high-field-limit conditions (95-285 GHz) (D EPR experiments, the sign of D was unambiguously determined. D is positive for the iodo and bromo complexes and negative for the chloro and thiocyano ones. A structural correlation is proposed. Each complex is characterized by a significant rhombicity with E/D values between 0.17 and 0.29, reflecting the distorted geometry observed around the manganese. Finally, we compared the spin Hamiltonian parameters of our five-coordinated complexes and those previously reported for other analogous series of dihalo four- and six-coordinated complexes. The effect of the coordination number and of the geometry of the Mn(II) complexes on the spin Hamiltonian parameters is discussed.

  8. Electronic and atomic structure of complex defects in Al- and Ga-highly doped ZnO films

    Energy Technology Data Exchange (ETDEWEB)

    Menéndez-Proupin, Eduardo [Instituto de Energía Solar, Universidad Politécnica de Madrid (UPM), Ciudad Universitaria, 28040 Madrid (Spain); Departamento de Física, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, 780-0003 Ñuñoa, Santiago (Chile); Palacios, Pablo, E-mail: [Instituto de Energía Solar, Universidad Politécnica de Madrid (UPM), Ciudad Universitaria, 28040 Madrid (Spain); Dpt. FAIAN, E.T.S.I. Aeronáutica y del Espacio, UPM, Pz. Cardenal Cisneros 3, 28040 Madrid (Spain); Wahnón, Perla [Instituto de Energía Solar, Universidad Politécnica de Madrid (UPM), Ciudad Universitaria, 28040 Madrid (Spain); Dpt. TFO, E.T.S.I. Telecomunicación, UPM, Ciudad Universitaria, 28040 Madrid (Spain)


    Point defects in Ga- and Al-doped ZnO thin films are studied by means of first principles electronic structure calculations. Candidate defects are identified to explain recently observed differences in electrical and spectroscopic behavior of both systems. Substitutional doping in Ga–ZnO explain the metallic behavior of the electrical properties. Complexes of interstitial oxygen with substitutional Ga can behave as acceptor and cause partial compensation, as well as gap states below the conduction band minimum as observed in photoemission experiments. Zn vacancies can also act as compensating acceptors. On the other hand, the semiconducting behavior of Al–ZnO and the small variation in the optical gap compared with pure ZnO, can be explained by almost complete compensation between acceptor Zn vacancies and substitutional Al donors. Interstitial Al can also be donor levels and can be the origin of the small band observed in photoemission experiments below the Fermi level. Combinations of substitutional Al with interstitial oxygen can act simultaneously as compensating acceptor and generator of the mentioned photoemission band. The theoretical calculations have been done using density functional theory (DFT) within the generalized gradient approximation with on-site Coulomb interaction. In selected cases, DFT calculations with semilocal-exact exchange hybrid functionals have been performed. Results explain photoelectron spectra of Ga–ZnO and Al–ZnO at the corresponding doping levels. - Highlights: • Defects in Ga- and Al-heavy-doped ZnO films are studied by quantum calculations. • Defects compatible with electrical, optical, and HAXPES spectra are proposed. • Doping efficiency is reduced by Zn vacancies and O interstitials. • HAXPES bands near the Fermi level are induced by Al{sub i}, and complexes Ga{sub Zn}-O{sub i}, and Al{sub Zn}-O{sub i}.

  9. Application of an electronic bulletin board, as a mechanism of coordination of actions in complex systems - reference model

    Directory of Open Access Journals (Sweden)

    Katarzyna Grzybowska


    Full Text Available Background: In her previous research, the author of this publication indicates that coordination is a dependent variable which has a great driving force and is a very unstable factor. This results in the fact that all of the actions connected with coordination have an impact on other factors of cooperation as well as the integration of the enterprises in the structures of a supply chain type structure. Material and methods:  The article has been divided into two basic parts. The first part regards the reference models in complex systems (supply chain systems. They can constitute a starting point for the modelling of target processes in the built supply chain structure. The second part presents template process models (Reference Models for selected action coordination mechanisms during enterprise cooperation. The aim of the article is the presentation the model an Electronic Bulletin Board (EBB, as a mechanism of coordination of actions in complex systems. Results: The article was prepared on the basis of literature from the researched area. The material was also prepared on the basis of interviews with practitioners. They have allowed for the preparation of template process models (Reference Models for selected action coordination methods in the supply chain. Conclusions: The result of the work is a prepared model as well as its description in the use of IDEF0. The presented model is a demonstrative model. The proposed reference model makes it possible to define the parameters of a selected mechanism of coordination of actions, and forms a basis for affecting the progression of the process through an analysis of values of identified parameters. The parameterization of elements constitutes the foundation for the monitoring of the process via 1 unambiguous identification of the object of monitoring and 2 analysis of different variants of the progression of the process.

  10. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Enriquez, Miriam M.; Zhang, Cheng; Tan, Howe-Siang, E-mail: [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371 (Singapore); Akhtar, Parveen; Garab, Győző; Lambrev, Petar H., E-mail: [Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged (Hungary)


    The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Q{sub y} band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240–270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet–singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state.

  11. Some Perspectives on Solution-Phase Electron-Transfer Processes (United States)


    constants for corresponding self-exchange (k*) and electochemical exchange (k•) reactions:" kj/A" (k /Akr (3) where A" and Ab are the relevant...development was the design and synthesis (largely by the Meyer17,18 and Taube19,20 groups) of molecular donor-acceptor (D-A) systems featuring well

  12. Theoretical study on optical and electronic properties of bipolar molecules with 1,8-naphthalimide and triphenylamine moieties as organic light-emitting materials. (United States)

    Jin, Ruifa; Tang, Shanshan


    A series of D-π-A bipolar molecules with triphenylamine (TPA) fragments as donors, 1,8-naphthalimide (NI) fragments as acceptors, and different π-conjugated bridges (CB) as π-conjugated bridges have been designed to explore their optical, electronic, and charge transport properties as charge transport and luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbitals (FMOs), natural population analysis (NPA), and local density of states analysis have turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer (ICT). The calculated results show that their optical and electronic properties are affected by the π-conjugated bridges in bipolar molecules. The electron-donating (-withdrawing) π-conjugated bridges serve as donors (acceptors) for the compounds under investigation. Our results suggest that these bipolar molecules are expected to be promising candidates for holes transport and luminescent materials for OLEDs. The results presented show that varying the π-conjugated bridges of bipolar molecules is a highly promising approach to develop this series of materials for OLEDs applications. Copyright © 2013 Elsevier Inc. All rights reserved.

  13. Conservation of spin polarization during triplet-triplet energy transfer in reconstituted peridinin-chlorophyll-protein complexes. (United States)

    Di Valentin, Marilena; Tait, Claudia; Salvadori, Enrico; Ceola, Stefano; Scheer, Hugo; Hiller, Roger G; Carbonera, Donatella


    Peridinin-chlorophyll-protein (PCP) complexes, where the N-terminal domain of native PCP from Amphidinium carterae has been reconstituted with different chlorophyll (Chl) species, have been investigated by time-resolved EPR in order to elucidate the details of the triplet-triplet energy transfer (TTET) mechanism. This spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognizable spin-polarization effects in the observed time-resolved EPR spectra. The spin polarization produced at the acceptor site (peridinin) depends on the initial polarization of the donor (chlorophyll) and on the relative geometric arrangement of the donor-acceptor spin axes. A variation of the donor triplet state properties in terms of population probabilities or triplet spin axis directions, as produced by replacement of chlorophyll a (Chl a) with non-native chlorophyll species (ZnChl a and BacterioChl a) in the reconstituted complexes, is unambiguously reflected in the polarization pattern of the carotenoid triplet state. For the first time, in the present investigation spin-polarization conservation has been shown to occur among natural cofactors in protein complexes during the TTET process. Proving the validity of the assumption of spin conservation adopted in the EPR spectral analysis, the results reinforce the hypothesis that in PCP proteins peridinin 614, according to X-ray nomenclature (Hofmann, E.; et al. Science 1996, 272, 1788-1791), is the carotenoid of election in the photoprotection mechanism based on TTET.

  14. Electron-rich iron/ruthenium arylalkynyl complexes for third-order nonlinear optics: redox-switching between three states. (United States)

    Gauthier, Nicolas; Argouarch, Gilles; Paul, Frédéric; Toupet, Loic; Ladjarafi, Abdelkader; Costuas, Karine; Halet, Jean-François; Samoc, Marek; Cifuentes, Marie P; Corkery, T Christopher; Humphrey, Mark G


    The new [(η(2)-dppe)(η(5)-C(5)Me(5))Fe(C≡C-1,4-C(6)H(4)C≡C)Ru(η(2) -dppe)(2) C≡C(C(6)H(5))] complex (3-H) and its hexanuclear relative [{(η(2)-dppe)(η(5)-C(5) Me(5))Fe(C≡C-1,4-C(6)H(4)-C≡C)Ru(η(2)-dppe)(2)(C≡C-1,4-C(6)H(4)C≡C)(3)(1,3,5-C(6)H(3))] (4) have been synthesized and characterized. The linear and cubic nonlinear optical properties of these compounds in their various redox states have been studied along with those of the analogous complexes [(η(2)-dppe)(η(5)-C(5)Me(5))Fe(C≡C-1,4-C(6)H(4)C≡C)Ru(η(2)-dppe)(2)R][PF(6)](n) (n=0-2; R=Cl, 2-Cl; R=C≡C(4-C(6)H(4)NO(2)),3-NO(2)). We show that molecules exhibiting large third-order nonlinearities can be obtained by assembling such dinuclear Fe/Ru units around a central 1,3,5-substituted C(6)H(3) core. These data are discussed with a particular emphasis on the large changes in their nonlinear (third-order) optical properties brought about by oxidation. Experimental and computational (DFT) evidence for the electronic structures of these compounds in their various redox states is presented using 3-H(n+) as a prototypical model. Single crystals of this complex in its mono-oxidized state (3-H[PF(6)]) provide the first structural data for such carbon-rich Fe(III) /Ru(II) heteronuclear mixed-valent (MV) systems. Although experimental evidence for the structure of the dioxidized states was more difficult to obtain, the theoretical study reveals that 3-H(2+) can be considered to have a biradical structure with two independent spins. The low-lying absorptions that appear in the near-infrared (NIR) range for all these compounds following oxidation correspond to intervalence charge-transfer (IVCT) bands for the mono-oxidized states and to ligand-to-metal charge-transfer (LMCT) transitions for the dioxidized states. These play a crucial role in the strong optical modulation achieved. The possibility of accessing additional states with distinct linear or nonlinear optical properties is also briefly

  15. Complex evolution of the electronic structure from polycrystalline to monocrystalline graphene: generation of a new Dirac point (United States)

    Nunes, Ricardo; Araújo, Joice


    First calculations, employed to address the properties of polycrystalline graphene, indicate that the electronic structure of tilt grain boundaries in this system [1-4] displays a rather complex evolution towards graphene bulk, as the tilt angle decreases, with the generation of a new Dirac point at the Fermi level, and an anisotropic Dirac cone of low energy excitations. Moreover, the usual Dirac point at the K point falls below the Fermi level, and rises towards it as the tilt angle decreases. Further, our calculations indicate that the grain-boundary formation energy behaves non-monotonically with the tilt angle, due to a change in the the spatial distribution and relative contributions of the bond-stretching and bond-bending deformations associated with the formation of the defect.[4pt] [1] L. B. Biedermann et al., Phys. Rev. B 79, 125411 (2009). [0pt] [2] S. S. Datta et al., Nanoletters 9, 7 (2009). [0pt] [3] P. Simonis et al., Surf. Sci. 511, 319 (2002). [0pt] [4] G. Gu et al., Appl. Phys. Lett. 90, 253507 (2007).

  16. Characterization of Monomeric MnII/III/IV–Hydroxo Complexes from X- and Q-Band Dual Mode Electron Paramagnetic Resonance (EPR) Spectroscopy (United States)

    Gupta, Rupal; Taguchi, Taketo; Borovik, A. S.; Hendrich, Michael P.


    Manganese–hydroxo species have been implicated in C–H bond activation performed by metalloenzymes, but the electronic properties of many of these intermediates are not well characterized. The present work presents a detailed characterization of three Mnn–OH complexes (where n = II, III, and IV) of the tris[(N′-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3−) ligand using X- and Q-band dual mode electron paramagnetic resonance (EPR). Quantitative simulations for the [MnIIH3buea(OH)]2− complex demonstrated the ability to characterize similar MnII species commonly present in the resting states of manganese-containing enzymes. The spin states of the MnIII and MnIV complexes determined from EPR spectroscopy are S = 2 and 3/2, respectively, as expected for the C3 symmetry imposed by the [H3buea]3− ligand. Simulations of the spectra indicated the constant presence of two MnIV species in solutions of [MnIVH3buea(OH)] complex. The simulations of perpendicular- and parallel-mode EPR spectra allow determination of zero-field splitting and hyperfine parameters for all complexes. For the MnIII and MnIV complexes, density functional theory calculations are used to determine the isotropic Mn hyperfine values, to compare the excited electronic state energies, and to give theoretical estimates of the zero-field energy. PMID:24156406

  17. Characterization of monomeric Mn(II/III/IV)-hydroxo complexes from X- and Q-band dual mode electron paramagnetic resonance (EPR) spectroscopy. (United States)

    Gupta, Rupal; Taguchi, Taketo; Borovik, A S; Hendrich, Michael P


    Manganese-hydroxo species have been implicated in C-H bond activation performed by metalloenzymes, but the electronic properties of many of these intermediates are not well characterized. The present work presents a detailed characterization of three Mn(n)-OH complexes (where n = II, III, and IV) of the tris[(N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea](3-)) ligand using X- and Q-band dual mode electron paramagnetic resonance (EPR). Quantitative simulations for the [Mn(II)H3buea(OH)](2-) complex demonstrated the ability to characterize similar Mn(II) species commonly present in the resting states of manganese-containing enzymes. The spin states of the Mn(III) and Mn(IV) complexes determined from EPR spectroscopy are S = 2 and 3/2, respectively, as expected for the C3 symmetry imposed by the [H3buea](3-) ligand. Simulations of the spectra indicated the constant presence of two Mn(IV) species in solutions of [Mn(IV)H3buea(OH)] complex. The simulations of perpendicular- and parallel-mode EPR spectra allow determination of zero-field splitting and hyperfine parameters for all complexes. For the Mn(III) and Mn(IV) complexes, density functional theory calculations are used to determine the isotropic Mn hyperfine values, to compare the excited electronic state energies, and to give theoretical estimates of the zero-field energy.

  18. Impact of Temperature and Non-Gaussian Statistics on Electron Transfer in Donor-Bridge-Acceptor Molecules. (United States)

    Waskasi, Morteza M; Newton, Marshall D; Matyushov, Dmitry V


    A combination of experimental data and theoretical analysis provides evidence of a bell-shaped kinetics of electron transfer in the Arrhenius coordinates ln k vs 1/T. This kinetic law is a temperature analogue of the familiar Marcus bell-shaped dependence based on ln k vs the reaction free energy. These results were obtained for reactions of intramolecular charge shift between the donor and acceptor separated by a rigid spacer studied experimentally by Miller and co-workers. The non-Arrhenius kinetic law is a direct consequence of the solvent reorganization energy and reaction driving force changing approximately as hyperbolic functions with temperature. The reorganization energy decreases and the driving force increases when temperature is increased. The point of equality between them marks the maximum of the activationless reaction rate. Reaching the consistency between the kinetic and thermodynamic experimental data requires the non-Gaussian statistics of the donor-acceptor energy gap described by the Q-model of electron transfer. The theoretical formalism combines the vibrational envelope of quantum vibronic transitions with the Q-model describing the classical component of the Franck-Condon factor and a microscopic solvation model of the solvent reorganization energy and the reaction free energy.

  19. Excited singlet (S1) state interactions of calixarenes with chloroalkanes: A combination of concerted and stepwise dissociative electron transfer mechanism (United States)

    Mohanty, J.; Pal, H.; Nayak, S. K.; Chattopadhyay, S.; Sapre, A. V.


    Both steady-state and time-resolved studies in acetonitrile (ACN) solutions show that the excited singlet (S1) states of calixarenes (CX) undergo quenching by chloroalkanes (CA). It has been revealed by characterizing the Cl ions in the photolyzed CX-CA systems in ACN solutions that the quenching occurs due to dissociative electron transfer (DET) mechanism, whereby a C-Cl bond of the CAs undergoes dissociation on acceptance of an electron from excited CX. The bimolecular quenching constants (kq) in the present systems were correlated with the free energy changes for the concerted DET reactions based on a suitable DET theory. Such a correlation results in the recovery of an intramolecular reorganization energy, which is substantially lower to account for the C-Cl bond dissociation energy of the CAs. Comparing present results with those of an another donor-acceptor system (e.g., biphenyldiol-CA systems) where a concerted DET mechanism is applicable, it is inferred that in CX-CA systems both concerted and stepwise DET mechanisms operate simultaneously. It is proposed that the interaction of excited CXs with encaged CAs follows the stepwise mechanism whereas that with the out of cage CAs follows the concerted mechanism.

  20. Electron transfer reactions in condensed phase: effect of reversibility. (United States)

    Dhole, Kajal; Jena, Naresh K; Samanta, Alok; Ghosh, Swapan K


    We propose a generalized one-dimensional kinetic equation for multidimensional reversible electron transfer (ET) reaction with a nonequilibrium situation as the initial condition. The rate constant for the forward reversible ET reaction obtained here consists of the rate for the corresponding irreversible ET reaction, and an extra term due to reversibility of the ET process which includes the rates of diffusion dynamics in the reactant and product wells. In order to understand the effect of reversibility, we consider back ET reaction in a system consisting of an electron donor-acceptor pair in a solvent modeled through low frequency solvent collective coordinates (multidimensional) characterized by the orientational polarization and slowly relaxing one-dimensional vibrational mode. We propose here a new generalized polarization energy functional corresponding to the extension of the continuum version for the same, which has opened up the possibility of inclusion of molecular nature of the solvent into the solvent reorganization energy. We then derive an exact expression for the ET rate for this model system. The numerical results calculated by using the proposed one-dimensional approach are shown to be in good agreement with the available experimental results. Non-Marcus free energy gap dependence of the rates observed here for the reversible and irreversible ET reactions are very close to each other in the barrierless region, while for other situations, the rate for the former process is found to be less than the latter. The extra term, which makes the difference between the rate constants for irreversible and reversible ET reactions, is found to be contributed by the diffusion dynamics from both reactant and product wells but the dominating contribution is provided mainly by the product well.