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Sample records for charge transfer molecular

  1. Charge and Energy Transfer Dynamics in Molecular Systems

    CERN Document Server

    May, Volkhard

    2004-01-01

    This second edition is based on the successful concept of the first edition in presenting a unified perspective on molecular charge and energy transfer processes. The authors bridge the regimes of coherent and dissipative dynamics, thus establishing the connection between classic rate theories and modern treatments of ultrafast phenomena. The book serves as an introduction for graduate students and researchers. Among the new topics of this second edition are. - semiclassical and quantum-classical hybrid formulations of molecular dynamics. - the basics of femtosecond nonlinear spectroscopy. - e

  2. Positron annihilation studies of some charge transfer molecular complexes

    CERN Document Server

    El-Sayed, A; Boraei, A A A

    2000-01-01

    Positron annihilation lifetimes were measured for some solid charge transfer (CT) molecular complexes of quinoline compounds (2,6-dimethylquinoline, 6-methoxyquinoline, quinoline, 6-methylquinoline, 3-bromoquinoline and 2-chloro-4-methylquinoline) as electron donor and picric acid as an electron acceptor. The infrared spectra (IR) of the solid complexes clearly indicated the formation of the hydrogen-bonding CT-complexes. The annihilation spectra were analyzed into two lifetime components using PATFIT program. The values of the average and bulk lifetimes divide the complexes into two groups according to the non-bonding ionization potential of the donor (electron donating power) and the molecular weight of the complexes. Also, it is found that the ionization potential of the donors and molecular weight of the complexes have a conspicuous effect on the average and bulk lifetime values. The bulk lifetime values of the complexes are consistent with the formation of stable hydrogen-bonding CT-complexes as inferred...

  3. Molecular Dynamics Simulation on Charge Transfer Relaxation between Myoglobin and Water

    Institute of Scientific and Technical Information of China (English)

    CHENG Wei; ZHANG Feng-Shou; ZHANG Bo-Yang; ZHOU Hong-Yu

    2007-01-01

    Dynamical processes of myoglobin after photon-excited charge transfer between Fe ion and surrounding water anion ale simulated by a molecular dynamics model.The roles of Coulomb interaction effect and water effect in the relaxation process are discussed.It is found that the relaxations before and after charge transfer are similar.Strong Coulomb interactions and less water mobility decrease Coulomb energy fluctuations.An extra transferred charge of Fe ion has impact on water packing with a distance up to 0.86nm.

  4. Excited-state proton coupled charge transfer modulated by molecular structure and media polarization.

    Science.gov (United States)

    Demchenko, Alexander P; Tang, Kuo-Chun; Chou, Pi-Tai

    2013-02-01

    Charge and proton transfer reactions in the excited states of organic dyes can be coupled in many different ways. Despite the complementarity of charges, they can occur on different time scales and in different directions of the molecular framework. In certain cases, excited-state equilibrium can be established between the charge-transfer and proton-transfer species. The interplay of these reactions can be modulated and even reversed by variations in dye molecular structures and changes of the surrounding media. With knowledge of the mechanisms of these processes, desired rates and directions can be achieved, and thus the multiple emission spectral features can be harnessed. These features have found versatile applications in a number of cutting-edge technological areas, particularly in fluorescence sensing and imaging.

  5. Combining intra- and intermolecular charge-transfer: a new strategy towards molecular ferromagnets and multiferroics.

    Science.gov (United States)

    Di Maiolo, Francesco; Sissa, Cristina; Painelli, Anna

    2016-01-21

    Organic ferroelectric materials are currently a hot research topic, with mixed stack charge transfer crystals playing a prominent role with their large, electronic-in-origin polarization and the possibility to tune the transition temperature down to the quantum limit and/or to drive the ferroelectric transition via an optical stimulus. By contrast, and in spite of an impressive research effort, organic ferromagnets are rare and characterized by very low transition temperatures. Coexisting magnetic and electric orders in multiferroics offer the possibility to control magnetic (electric) properties by an applied electric (magnetic) field with impressive technological potential. Only few examples of multiferroics are known today, based on inorganics materials. Here we demonstrate that, by decorating mixed stack charge transfer crystals with organic radicals, a new family of robust molecular ferromagnets can be designed, stable up to ambient temperature, and with a clear tendency towards multiferroic behaviour.

  6. An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

    Science.gov (United States)

    Hendrickson, Heidi Phillips

    A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their

  7. Modeling molecular conduction in DNA wires: Charge transfer theories and dissipative quantum transport

    OpenAIRE

    Bulla, R; Gutierrez, R.; Cuniberti, G.

    2006-01-01

    Measurements of electron transfer rates as well as of charge transport characteristics in DNA produced a number of seemingly contradictory results, ranging from insulating behaviour to the suggestion that DNA is an efficient medium for charge transport. Among other factors, environmental effects appear to play a crucial role in determining the effectivity of charge propagation along the double helix. This chapter gives an overview over charge transfer theories and their implication for addres...

  8. Supercell convergence of charge-transfer energies in pentacene molecular crystals from constrained DFT

    CERN Document Server

    Turban, David H P; O'Regan, David D; Hine, Nicholas D M

    2016-01-01

    Singlet fission (SF) is a multi-exciton generation process that could be harnessed to improve the efficiency of photovoltaic devices. Experimentally, systems derived from the pentacene molecule have been shown to exhibit ultrafast SF with high yields. Charge-transfer (CT) configurations are likely to play an important role as intermediates in the SF process in these systems. In molecular crystals, electrostatic screening effects and band formation can be significant in lowering the energy of CT states, enhancing their potential to effectively participate in SF. In order to simulate these, it desirable to adopt a computational approach which is acceptably accurate, relatively inexpensive, which and scales well to larger systems, thus enabling the study of screening effects. We propose a novel, electrostatically-corrected constrained Density Functional Theory (cDFT) approach as a low-cost solution to the calculation of CT energies in molecular crystals such as pentacene. Here we consider an implementation in th...

  9. Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions

    CERN Document Server

    Oberhofer, H

    2009-01-01

    We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following earlier work of Wu et al. Phys. Rev. A 72, 024502 (2005), the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the charge constrained state. We investigate the dependence of the constrained energy and of the energy gap on the definition of the charge, and present expressions for the constraint forces. The method is applied to the Ru2+-Ru3+ electron self-exchange reaction in aqueous solution. Sampling the vertical energy gap along CDFT-MD trajectories, and correcting for finite size effects, a reorganization free energy of 1.6 eV is obtained. This is 0.1-0.2 eV lower than a previous estimate based on a continuum model for solvation. smaller value for re...

  10. Charge transfer complexes of fullerene[60] with porphyrins as molecular rectifiers. A theoretical study.

    Science.gov (United States)

    Montiel, Filiberto; Fomina, Lioudmila; Fomine, Serguei

    2015-01-01

    Molecular diodes based on charge transfer complexes of fullerene[60] with different metalloporphyrins have been modeled. Their current-voltage characteristics and the rectification ratios (RR) were calculated using direct ab initio method at PBE/def2-SVP level of theory with D3 dispersion correction, for voltages ranging from -2 to +2 V. The highest RR of 32.5 was determined for the complex of fullerene[60] with zinc tetraphenylporphyrin at 0.8 V. Other molecular diodes possessed lower RR, however, all complexes showed RR higher than 1 at all bias voltages. The asymmetric evolutions and alignment of the molecular orbitals with the applied bias were found to be essential for generating the molecular diode rectification behavior. Metal nature of metalloporphyrins and the interaction porphyrin-electrode significantly affect RR of molecular diode. Large metal ions like Cd(2+) and Ag(2+) in metalloporphyrins disfavor rectification creating conducting channels in two directions, while smaller ions Zn(2+) and Cu(2+) favor rectification increasing the interaction between gold electrode and porphyrin macrocycle.

  11. Fermi level alignment in molecular nanojunctions and its relation to charge transfer

    DEFF Research Database (Denmark)

    Stadler, Robert; Jacobsen, Karsten Wedel

    2006-01-01

    by orders of magnitude. We present a quantitative analysis of the relation between this level alignment (which can be estimated from charging free molecules) and charge transfer for bipyridine and biphenyl dithiolate (BPDT) molecules attached to gold leads based on density functional theory calculations...

  12. Supercell convergence of charge-transfer energies in pentacene molecular crystals from constrained DFT

    Science.gov (United States)

    Turban, David H. P.; Teobaldi, Gilberto; O'Regan, David D.; Hine, Nicholas D. M.

    2016-04-01

    Singlet fission (SF) is a multiexciton generation process that could be harnessed to improve the efficiency of photovoltaic devices. Experimentally, systems derived from the pentacene molecule have been shown to exhibit ultrafast SF with high yields. Charge-transfer (CT) configurations are likely to play an important role as intermediates in the SF process in these systems. In molecular crystals, electrostatic screening effects and band formation can be significant in lowering the energy of CT states, enhancing their potential to effectively participate in SF. In order to simulate these, it desirable to adopt a computational approach which is acceptably accurate, relatively inexpensive, and which scales well to larger systems, thus enabling the study of screening effects. We propose an electrostatically corrected constrained density functional theory (cDFT) approach as a low-cost solution to the calculation of CT energies in molecular crystals such as pentacene. Here we consider an implementation in the context of the onetep linear-scaling DFT code, but our electrostatic correction method is in principle applicable in combination with any constrained DFT implementation, also outside the linear-scaling framework. Our newly developed method allows us to estimate CT energies in the infinite crystal limit, and with these to validate the accuracy of the cluster approximation.

  13. Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals

    Science.gov (United States)

    Sherman, David M.

    1987-01-01

    A number of mixed valence iron oxides and silicates (e.g., magnetite, ilvaite) exhibit thermally induced electron delocalization between adjacent Fe2+ and Fe3+ ions and optically induced electronic transitions which are assigned to Fe2+→Fe3+ intervalence charge transfer.

  14. Molecular adsorption on ZnO(1010) single-crystal surfaces: morphology and charge transfer.

    Science.gov (United States)

    Chen, Jixin; Ruther, Rose E; Tan, Yizheng; Bishop, Lee M; Hamers, Robert J

    2012-07-17

    While ZnO has excellent electrical properties, it has not been widely used for dye-sensitized solar cells, in part because ZnO is chemically less stable than widely used TiO(2). The functional groups typically used for surface passivation and for attaching dye molecules either bind weakly or etch the ZnO surface. We have compared the formation of molecular layers from alkane molecules with terminal carboxylic acid, alcohol, amine, phosphonic acid, or thiol functional groups on single-crystal zinc oxide (1010) surfaces. Atomic force microscopy (AFM) images show that alkyl carboxylic acids etch the surface whereas alkyl amine and alkyl alcohols bind only weakly on the ZnO(1010) surface. Phosphonic acid-terminated molecules were found to bind to the surface in a heterogeneous manner, forming clusters of molecules. Alkanethiols were found to bind to the surface, forming highly uniform monolayers with some etching detected after long immersion times in an alkanethiol solution. Monolayers of hexadecylphosphonic acid and octadecanethiol were further analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements. AFM scratching shows that thiols were bound strongly to the ZnO surface, suggesting the formation of strong Zn-S covalent bonds. Surprisingly, the tridentate phosphonic acids adhered much more weakly than the monodentate thiol. The influence of organic grafting on the charge transfer to ZnO was studied by time-resolved surface photovoltage measurements and electrochemical impedance measurements. Our results show that the grafting of thiols to ZnO leads to robust surfaces and reduces the surface band bending due to midgap surface states.

  15. Lock-arm supramolecular ordering: a molecular construction set for cocrystallizing organic charge transfer complexes.

    Science.gov (United States)

    Blackburn, Anthea K; Sue, Andrew C-H; Shveyd, Alexander K; Cao, Dennis; Tayi, Alok; Narayanan, Ashwin; Rolczynski, Brian S; Szarko, Jodi M; Bozdemir, Ozgur A; Wakabayashi, Rie; Lehrman, Jessica A; Kahr, Bart; Chen, Lin X; Nassar, Majed S; Stupp, Samuel I; Stoddart, J Fraser

    2014-12-10

    Organic charge transfer cocrystals are inexpensive, modular, and solution-processable materials that are able, in some instances, to exhibit properties such as optical nonlinearity, (semi)conductivity, ferroelectricity, and magnetism. Although the properties of these cocrystals have been investigated for decades, the principal challenge that researchers face currently is to devise an efficient approach which allows for the growth of high-quality crystalline materials, in anticipation of a host of different technological applications. The research reported here introduces an innovative design, termed LASO-lock-arm supramolecular ordering-in the form of a modular approach for the development of responsive organic cocrystals. The strategy relies on the use of aromatic electronic donor and acceptor building blocks, carrying complementary rigid and flexible arms, capable of forming hydrogen bonds to amplify the cocrystallization processes. The cooperativity of charge transfer and hydrogen-bonding interactions between the building blocks leads to binary cocrystals that have alternating donors and acceptors extending in one and two dimensions sustained by an intricate network of hydrogen bonds. A variety of air-stable, mechanically robust, centimeter-long, organic charge transfer cocrystals have been grown by liquid-liquid diffusion under ambient conditions inside 72 h. These cocrystals are of considerable interest because of their remarkable size and stability and the promise they hold when it comes to fabricating the next generation of innovative electronic and photonic devices.

  16. Charge transfer and weak bonding between molecular oxygen and graphene zigzag edges at low temperatures

    CERN Document Server

    Boukhvalov, D W; Shames, A I; Takai, K; Hayashi, T; Enoki, T

    2016-01-01

    Electron paramagnetic resonance (EPR) study of air-physisorbed defective carbon nano-onions evidences in favor of microwave assisted formation of weakly-bound paramagnetic complexes comprising negatively-charged O2- ions and edge carbon atoms carrying pi-electronic spins. These complexes being located on the graphene edges are stable at low temperatures but irreversibly dissociate at temperatures above 50-60 K. These EPR findings are justified by density functional theory (DFT) calculations demonstrating transfer of an electron from the zigzag edge of graphene-like material to oxygen molecule physisorbed on the graphene sheet edge. This charge transfer causes changing the spin state of the adsorbed oxygen molecule from S = 1 to S = 1/2 one. DFT calculations show significant changes of adsorption energy of oxygen molecule and robustness of the charge transfer to variations of the graphene-like substrate morphology (flat and corrugated mono- and bi-layered graphene) as well as edges passivation. The presence of...

  17. Charge Transfer-Induced Molecular Hole Doping into Thin Film of Metal-Organic Frameworks.

    Science.gov (United States)

    Lee, Deok Yeon; Kim, Eun-Kyung; Shrestha, Nabeen K; Boukhvalov, Danil W; Lee, Joong Kee; Han, Sung-Hwan

    2015-08-26

    Despite the highly porous nature with significantly large surface area, metal-organic frameworks (MOFs) can be hardly used in electronic and optoelectronic devices due to their extremely poor electrical conductivity. Therefore, the study of MOF thin films that require electron transport or conductivity in combination with the everlasting porosity is highly desirable. In the present work, thin films of Co3(NDC)3DMF4 MOFs with improved electronic conductivity are synthesized using layer-by-layer and doctor blade coating techniques followed by iodine doping. The as-prepared and doped films are characterized using FE-SEM, EDX, UV/visible spectroscopy, XPS, current-voltage measurement, photoluminescence spectroscopy, cyclic voltammetry, and incident photon to current efficiency measurements. In addition, the electronic and semiconductor properties of the MOF films are characterized using Hall Effect measurement, which reveals that, in contrast to the insulator behavior of the as-prepared MOFs, the iodine doped MOFs behave as a p-type semiconductor. This is caused by charge transfer-induced hole doping into the frameworks. The observed charge transfer-induced hole doping phenomenon is also confirmed by calculating the densities of states of the as-prepared and iodine doped MOFs based on density functional theory. Photoluminescence spectroscopy demonstrates an efficient interfacial charge transfer between TiO2 and iodine doped MOFs, which can be applied to harvest solar radiations. PMID:26226050

  18. Synthesis and energy band characterization of hybrid molecular materials based on organic–polyoxometalate charge-transfer salts

    International Nuclear Information System (INIS)

    A cationic amphiphilic molecule was synthesized and employed to encapsulate Lindqvist ([M6O19]2−) and Keggin polyoxometalates ([SiM12O40]4−, M=Mo, W) to form hybrid molecules through electrostatic interaction. The X-ray diffraction results illustrate that the former hybrids possess lamellar nanostructures in their solid states, while the latter hybrids show a cubic Im3m packing model with low intensities and poor long-range order. These hybrids have clear charge-transfer characters as shown in their deeper colors and UV–vis diffuse reflectance spectra. According to the reported reduction potentials of the POM acceptors and the band gaps deduced from their diffuse reflectance spectra, we have calculated the theoretical values of the lowest unoccupied molecular orbital (LUMO) position similar to the electron affinity (EA) of solid materials. Such energy level parameters are comparable to those of electroluminescence and electron-transport materials commonly used in organic electroluminescence devices. These organic–polyoxometalate charge-transfer salts have more advantages, such as higher decomposition temperatures, easier film fabrication and better electron affinities, which presumably would be used for electron-transport materials in the area of the electroluminescence. - Graphical abstract: Hybrid molecular materials with charge-transfer characters formed by a positively charged donor L and acceptors of the Lindqvist-type and Keggin-type POMs have lamellar and cubic structures in their solid state. - Highlights: • Charge-transfer salts are obtained by self-assembling POMs with an anthracene cation. • Their energy parameters are comparable to those of optoelectronic materials in OLEDs. • These POM-based hybrids could be applied in the area of optoelectronic devices

  19. Synthesis and energy band characterization of hybrid molecular materials based on organic–polyoxometalate charge-transfer salts

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Chunxia [Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou City, Gansu Province (China); Traditional Chinese Medicine College of Gansu, Gansu (China); Bu, Weifeng, E-mail: buwf@lzu.edu.cn [Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou City, Gansu Province (China)

    2014-11-15

    A cationic amphiphilic molecule was synthesized and employed to encapsulate Lindqvist ([M{sub 6}O{sub 19}]{sup 2−}) and Keggin polyoxometalates ([SiM{sub 12}O{sub 40}]{sup 4−}, M=Mo, W) to form hybrid molecules through electrostatic interaction. The X-ray diffraction results illustrate that the former hybrids possess lamellar nanostructures in their solid states, while the latter hybrids show a cubic Im3m packing model with low intensities and poor long-range order. These hybrids have clear charge-transfer characters as shown in their deeper colors and UV–vis diffuse reflectance spectra. According to the reported reduction potentials of the POM acceptors and the band gaps deduced from their diffuse reflectance spectra, we have calculated the theoretical values of the lowest unoccupied molecular orbital (LUMO) position similar to the electron affinity (E{sub A}) of solid materials. Such energy level parameters are comparable to those of electroluminescence and electron-transport materials commonly used in organic electroluminescence devices. These organic–polyoxometalate charge-transfer salts have more advantages, such as higher decomposition temperatures, easier film fabrication and better electron affinities, which presumably would be used for electron-transport materials in the area of the electroluminescence. - Graphical abstract: Hybrid molecular materials with charge-transfer characters formed by a positively charged donor L and acceptors of the Lindqvist-type and Keggin-type POMs have lamellar and cubic structures in their solid state. - Highlights: • Charge-transfer salts are obtained by self-assembling POMs with an anthracene cation. • Their energy parameters are comparable to those of optoelectronic materials in OLEDs. • These POM-based hybrids could be applied in the area of optoelectronic devices.

  20. Molecular distortion and charge transfer effects in ZnPc/Cu(111)

    KAUST Repository

    Amin, B.

    2013-04-23

    The adsorption geometry and electronic properties of a zinc-phthalocyanine molecule on a Cu(111) substrate are studied by density functional theory. In agreement with experiment, we find remarkable distortions of the molecule, mainly as the central Zn atom tends towards the substrate to minimize the Zn-Cu distance. As a consequence, the Zn-N chemical bonding and energy levels of the molecule are significantly modified. However, charge transfer induces metallic states on the molecule and therefore is more important for the ZnPc/Cu(111) system than the structural distortions.

  1. Photoinduced interfacial electron transfer and lateral charge transport in molecular donor-acceptor photovoltaic systems.

    Science.gov (United States)

    Punzi, Angela; Brauer, Jan C; Marchioro, Arianna; Ghadiri, Elham; de Jonghe, Jelissa; Moser, Jacques E

    2011-01-01

    Nanostructured liquid/solid and solid/solid bulk heterojunctions designed for the conversion of solar energy offer ideal models for the investigation of light-induced ET dynamics at surfaces. Despite significant study of processes leading to charge generation in third-generation solar cells, a conclusive picture of the photophysics of these photovoltaic converters is still missing. More specifically searched is the link between the molecular structure of the interface and the kinetics of surface photoredox reactions. Fundamental scientific issues in this field are addressed by the research project undertaken in the frame of the NCCR MUST endeavor, an outline of which is given here.

  2. Investigation of positronium formation by molecular hydrogen ion impact with multiple scattering formulation in charge transfer channel

    Directory of Open Access Journals (Sweden)

    S Amiri

    2016-02-01

    Full Text Available In the present work the first and second order scattering amplitudes and the related phase were calculated in the charge transfer channel. The positronium formation, with the impact of molecular hydrogen ion, has been carried out using multiple channel scattering formulation and transition matrix. The calculation of differential cross section has been done by varying the scattering angle from 0 to 180 in the fixed orientation of the molecule. In the next calculation the scattering angles were fixed while the spatial molecular orientation was varied. At last the calculated differential cross section was compared with available results in the literature. The scattering angle spanned from 0 to 180 degrees in the second order nuclear and electronic terms were calculated while the molecular orientation was assumed to be fixed. Otherwise, the scattering angles were fixed in the calculation of the corresponding amplitudes while the orientation was varied. At last our calculations were compared with available results

  3. Packing effects in charge transfer dynamics in organic molecular heterojunctions consisting of TFB and F8BT

    Science.gov (United States)

    Fujii, Mikiya; Yamashita, Koichi

    2013-03-01

    Organic semiconductors have been widely investigated for photovoltaic and light emitting devices. Especially, further improvements for more efficient organic solar cells (OSCs) are desired. Thus, we explored computationally possibilities to make OSCs more efficient by adjusting the packing of molecular heterojunctions. We analyzed a molecular heterojunction that consists of poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylenediamine) (TFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Geometrical optimization of TFB(monomer)/F8BT(monomer) complex was carried out with DFT-D/B3LYP/6-31G*. Excited states were also calculated with CIS/6-31G*. To analyze packing effects, we rotated TFB around a principal axis. Then, charge transfer dynamics is analyzed with a quantum master equation (QME) approach in each packing From the excited states calculations, it is clarified that the packing strongly affects the energy level of the charge transfer state only. This packing dependency arises from a packing dependency of the exciton binding energy that is Coulomb interaction between an electron localized to F8BT and a hole localized to TFB. From the QME approach, it is confirmed that qualitative different electronic relaxation dynamics occurs in each different packing.

  4. Charge-transfer with graphene and nanotubes

    Directory of Open Access Journals (Sweden)

    C.N.R. Rao

    2010-09-01

    Full Text Available Charge-transfer between electron–donor and –acceptor molecules is a widely studied subject of great chemical interest. Some of the charge-transfer compounds in solid state exhibit novel electronic properties. In the last two to three years, occurrence of molecular charge-transfer involving single-walled carbon nanotubes (SWNTs and graphene has been demonstrated. This interaction gives rise to significant changes in the electronic properties of these nanocarbons. We examine charge-transfer phenomenon in graphene and SWNTs in this article in view of its potential utility in device applications.

  5. Probing photoinduced phase transition in a charge-transfer molecular crystal by 100 picosecond X-ray diffraction

    Science.gov (United States)

    Guérin, Laurent; Collet, Eric; Lemée-Cailleau, Marie-Hélène; Buron-Le Cointe, Marylise; Cailleau, Hervé; Plech, Anton; Wulff, Michael; Koshihara, Shin-Ya; Luty, Tadeusz

    2004-04-01

    Watching with an atomic resolution at structural changes as fast or ultra-fast photoinduced physical processes take place benefits from recent progresses in time-resolved X-ray diffraction. Molecular materials where electronic and structural changes are strongly coupled are model systems to perform such time-resolved crystallography studies. We report the structural investigation of photoinduced phase transformations between ionic and neutral states in an organic charge-transfer molecular material, using 100 picosecond (ps) synchrotron pulses. This light-induced phenomenon, triggered by an ultra-short optical pulse from a femtosecond laser, occurs by virtue of intrinsic cooperativity. Since electronic and structural changes are strongly coupled, it is of fundamental interest to perform time-resolved X-ray diffraction to obtain information at the atomic scale. We also discuss the problem of coexistence of phases and the interest of future investigations in faster timescale.

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

    KAUST Repository

    Domingo, Ester

    2015-04-09

    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.

  7. Engineering of an ultra-thin molecular superconductor by charge transfer

    Science.gov (United States)

    Hla, Saw Wai; Hassanien, Abdelrahim; Kendal, Clark

    2016-06-07

    A method of forming a superconductive device of a single layer of (BETS).sub.2GaCl.sub.4 molecules on a substrate surface which displays a superconducting gap that increases exponentially with the length of the molecular chain is provided.

  8. Quantum chemical study of the 1:1 complex between ferrocene and zinc porphyrin, a building-block of charge-transfer molecular materials

    International Nuclear Information System (INIS)

    The molecular and electronic structure of the 1:1 charge-transfer complex between ferrocene (Fc) and zinc porphyrin (ZnP) are investigated with the aid of dispersion-corrected density functional theory (DFT) calculations. Four stable configurations were obtained, two with the Fc molecule laying on the ZnP plane and the other two where Fc interacts with the porphyrin's perimeter. The dipole moment vectors of these Fc:ZnP complexes indicate that they are stabilized by the transfer of electronic charge density from Fc to ZnP or vice versa. (author)

  9. Model of mixed Frenkel and charge-transfer excitons in donor-acceptor molecular crystals: investigation of vibronic spectra

    Energy Technology Data Exchange (ETDEWEB)

    Lalov, I J [Faculty of Physics, Sofia University, Sofia 1164 (Bulgaria); Warns, C; Reineker, P [Institute of Theoretical Physics, Ulm University, Albert-Einstein-Allee 11, 89069 Ulm (Germany)], E-mail: peter.reineker@uni-ulm.de

    2008-08-15

    The mixing of Frenkel excitons (FEs) and charge-transfer excitons (CTEs) in a molecular stack of regularly arranged donor (D) and acceptor (A) molecules is considered a model case and its vibronic line shapes have been calculated for several parameter sets. The two types of excitons (FE and CTE) are coupled linearly and quadratically with one vibrational mode of the D molecule (or of the A molecule). Using the methods of canonical transformation and of Green's functions (at T=0), as well as the vibronic approach which is applicable in the case of a narrow exciton band, the linear optical susceptibility is calculated for the three spectral regions: (a) excitonic, (b) one-phonon vibronics, and (c) two-phonon vibronics. As the study is directed to centrosymmetrical stacks, the cases of mixing of gerade excitons and of ungerade excitons have been treated separately in the calculation of the linear absorption coefficients. Because until now experimental observations of FE-CTE mixing in DA charge-transfer systems are absent, the numerical calculations have been performed for hypothetical sets of parameters which include: the parameters of CTEs in DA stacks (like anthracene-PMDA) and the parameters of FE-CTE mixing in a one-component stack (like that of PTCDA). The simulations establish the main features of the excitonic and vibronic spectra in the case of FE-CTE mixing, namely (i) the mutual influence on the positions and on the absorption intensities of all terms of the vibronic progressions stemming from FE and CTE levels; (ii) in the case of vibration of an A molecule (if the FE is assumed to be an excited electronic state of the D molecule), only one vibronic progression is manifest and the vibronic levels closer to the FE will be most enhanced; (iii) the redistribution of the absorption intensities depends on the sign of the mixing constant and may be so strong that the terms of the two vibronic progressions could have comparable absorption; (iv) spectral lines

  10. Impact of exact exchange in the description of the electronic structure of organic charge-transfer molecular crystals

    KAUST Repository

    Fonari, Alexandr

    2014-10-21

    We evaluate the impact that the amount of nonlocal Hartree-Fock (%HF) exchange included in a hybrid density functional has on the microscopic parameters (transfer integrals, band gaps, bandwidths, and effective masses) describing charge transport in high-mobility organic crystals. We consider both crystals based on a single molecule, such as pentacene, and crystals based on mixed-stack charge-transfer systems, such as dibenzo-TTF–TCNQ. In the pentacene crystal, the band gap decreases and the effective masses increase linearly with an increase in the amount of %HF exchange. In contrast, in the charge-transfer crystals, while the band gap increases linearly, the effective masses vary only slightly with an increase in %HF exchange. We show that the superexchange nature of the electronic couplings in charge-transfer systems is responsible for this peculiar evolution of the effective masses. We compare the density functional theory results with results obtained within the G0W0 approximation as a way of benchmarking the optimal amount of %HF exchange needed in a given functional.

  11. Effect of Molecular Coupling on Ultrafast Electron-Transfer and Charge-Recombination Dynamics in a Wide-Gap ZnS Nanoaggregate Sensitized by Triphenyl Methane Dyes.

    Science.gov (United States)

    Debnath, Tushar; Maity, Partha; Dana, Jayanta; Ghosh, Hirendra N

    2016-03-01

    Wide-band-gap ZnS nanocrystals (NCs) were synthesized, and after sensitizing the NCs with series of triphenyl methane (TPM) dyes, ultrafast charge-transfer dynamics was demonstrated. HRTEM images of ZnS NCs show the formation of aggregate crystals with a flower-like structure. Exciton absorption and lumimescence, due to quantum confinement of the ZnS NCs, appear at approximately 310 and 340 nm, respectively. Interestingly, all the TPM dyes (pyrogallol red, bromopyrogallol red, and aurin tricarboxylic acid) form charge-transfer complexes with the ZnS NCs, with the appearance of a red-shifted band. Electron injection from the photoexcited TPM dyes into the conduction band of the ZnS NCs is shown to be a thermodynamically viable process, as confirmed by steady-state and time-resolved emission studies. To unravel charge-transfer (both electron injection and charge recombination) dynamics and the effect of molecular coupling, femtosecond transient absorption studies were carried out in TPM-sensitized ZnS NCs. The electron-injection dynamics is pulse-width-limited in all the ZnS/TPM dye systems, however, the back electron transfer differs, depending on the molecular coupling of the sensitizers (TPM dyes). The detailed mechanisms for the above-mentioned processes are discussed. PMID:26548569

  12. Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester: A fluorescence study in condensedphase and jet-cooled molecular beams

    Indian Academy of Sciences (India)

    Amrita Chakraborty; Samiran Kar; D N Nath; Nikhil Guchhait

    2007-03-01

    Photoinduced intramolecular charge-transfer reactions in 4-amino-3-methyl benzoic acid methyl ester (AMBME) have been investigated spectroscopically. AMBME, with its weak charge donor primary amino group, shows dual emission in polar solvents. Absorption and emission measurements in the condensed phase support the premise that the short wavelength emission band corresponds to local emission and the long wavelength emission band to the charge transfer emission. Laser-induced fluorescence excitation spectra show the presence of two low-energy conformers in jet-cooled molecular beams. Theoretical calculations using density functional theory help to determine structure, vibrational modes, potential energy surface, transition energy and oscillator strength for correlating experimental findings with theoretical results.

  13. Catalysis: Quantifying charge transfer

    Science.gov (United States)

    James, Trevor E.; Campbell, Charles T.

    2016-02-01

    Improving the design of catalytic materials for clean energy production requires a better understanding of their electronic properties, which remains experimentally challenging. Researchers now quantify the number of electrons transferred from metal nanoparticles to an oxide support as a function of particle size.

  14. Charge transfer in multicomponent oxides

    Science.gov (United States)

    Kohan, A. F.; Ceder, G.

    1998-02-01

    The transfer of charge between different ions in an oxide plays an essential role in the stability of these compounds. Since small variations in charge can introduce large changes in the total energy, a correct description of this phenomenon is critical. In this work, we show that the ionic charge in oxides can strongly depend on its atomic environment. A model to assign point charges to atoms as a function of their atomic environment has recently been proposed for binary alloys [C. Wolverton, A. Zunger, S. Froyen, and S.-H. Wei, Phys. Rev. B 54, 7843 (1996)] and proven to be very successful in screened solids such as semiconductors and metals. Here, we extend this formalism to multicomponent oxides and we assess its applicability. The simple point-charge model predicts a linear relation between the charge on an atom and the number of unlike neighbors, and between the net value of the charge and the Coulomb field at a given site. The applicability of this approach is tested in a large-supercell self-consistent tight-binding calculation for a random Zr-Ca-O alloy. The observed fluctuations of the ionic charge about the average linear behavior (as a function of the number of unlike neighbors) was larger than 0.25 electrons even when many shells of atomic neighbors were considered in the fit. This variation is significant since it can introduce large errors in the electrostatic energy. On the other hand, for small absolute values of the charge, the ionic charge varied linearly with the Coulomb field, in agreement with previous findings. However, for large Coulomb fields, this function saturates at the formal chemical charge.

  15. Two-photon absorption effect and the intra-molecular charge transfer of p-substituted stilbene-type pyridinium salts

    Institute of Scientific and Technical Information of China (English)

    王筱梅; 周玉芳; 王春; 赵显; 刘志强; 蒋民华; 孙真荣; 丁良恩

    2001-01-01

    The relationships between two-photon absorption (TPA) effect and excited state intra-molecular charge transfer (ICT) of p-substituted stilbene-type pyridinium salts have been investigated. Two-photon absorption cross section (δTPA) for all the compounds has been determined by open aperture Z-scanning technique, while two-photon pumped (TPP) up-converted lasing efficiencies (η) and optical limiting behavior have been measured by two-channel energy-meter, pumped by a mode locked Nd: YAG ps laser. Streak camera was used to record two-photon induced fluorescence and the fluorescence lifetimes. The experimental and calculated results have shown that the excited state larger intra-molecular charge transfer, in the excited state characterized by the charge density difference between the ground state (S0) and the first excited state (S1), has contributed to enhancing TPA cross section and may result in better optical limiting effect. And high TPP up-converted lasing efficiency is related to not only the δTPA value, but also the lifetime of two-photon induced fluorescence, etc.

  16. Charge fluctuation of the superconducting molecular crystals

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, T., E-mail: yamataka@chem.sci.osaka-u.ac.j [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Nakazawa, Y. [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Kato, R. [RIKEN, Wako, Saitama 351-0198 (Japan); Yakushi, K. [Institute for Molecular Science, Okazaki, Aichi 444-8581 (Japan); Akutsu, H.; Akustu, A.S. [School of Science and Graduate School of Material Sciences, University of Hyogo, Kamigouri, Hyogo 678-1297 (Japan); Yamamoto, H. [RIKEN, Wako, Saitama 351-0198 (Japan); Kawamoto, A. [Graduate School and Faculty of Sciences, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Turner, S.S. [Department of Chemistry, Warwick University, Gibbet Hill Road, Coventry CV4 7AL (United Kingdom); Day, P. [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)

    2010-06-01

    In recent years, concern has been raised about the charge fluctuation of the superconducting transition in the loosely dimerized molecular conductors. Not only the observation of the charge fluctuation is of considerably important but also the understanding of the mechanism of the fluctuation. We have observed degree of charge fluctuation of several {beta}''-type ET salts. The {beta}''-type ET salt is one of the best model compounds because the direction of the largest inter-site Coulomb interaction is perpendicular to that of the largest transfer integral. This structural property allows us to examine the role of inter-site Coulomb interaction from the viewpoint of the inter-molecular distance. The difference in the molecular charges between the charge rich site and the charge poor sites, {Delta}{rho}, is correlated with the conducting behavior; the superconducting materials have the small but finite {Delta}{rho}, whereas {Delta}{rho} of the insulating (metallic) materials is large (almost zero). After the analysis of the configuration in the inter-molecular distances, we have found that the degree of fluctuation, {Delta}{rho}, is attributed to the number of the most stable charge distribution(s), N{sub S}, and the number of the energy levels of the allowed charge distribution, N{sub A}. The superconducting materials belong to the condition of N{sub S{>=}}2 and N{sub A{>=}}2. Indeed, this condition contributes to the fluctuation of the molecular charges.

  17. The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C{sub 60} molecular triad

    Energy Technology Data Exchange (ETDEWEB)

    Olguin, Marco [Computational Science Program, University of Texas at El Paso, El Paso, Texas 79968 (United States); Basurto, Luis; Zope, Rajendra R. [Department of Physics, The University of Texas at El Paso, El Paso, Texas 79968 (United States); Baruah, Tunna, E-mail: tbaruah@utep.edu [Computational Science Program, University of Texas at El Paso, El Paso, Texas 79968 (United States); Department of Physics, The University of Texas at El Paso, El Paso, Texas 79968 (United States)

    2014-05-28

    We present a detailed study of charge transfer (CT) excited states for a large number of configurations in a light-harvesting Carotenoid-diaryl-Porphyrin-C{sub 60} (CPC{sub 60}) molecular triad. The chain-like molecular triad undergoes photoinduced charge transfer process exhibiting a large excited state dipole moment, making it suitable for application to molecular-scale opto-electronic devices. An important consideration is that the structural flexibility of the CPC{sub 60} triad impacts its dynamics in solvents. Since experimentally measured dipole moments for the triad of ∼110 D and ∼160 D strongly indicate a range in structural variability in the excited state, studying the effect of structural changes on the CT excited state energetics furthers the understanding of its charge transfer states. We have calculated the variation in the lowest CT excited state energies by performing a scan of possible variation in the structure of the triad. Some of these configurations were generated by incrementally scanning a 360° torsional (dihedral) twist at the C{sub 60}-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five different CPC{sub 60} conformations were studied to determine the effect of pi-conjugation and particle-hole Coulombic attraction on the CT excitation energies. Our calculations show that configurational changes in the triad induces a variation of ∼0.6 eV in CT excited state energies in the gas-phase. The corresponding calculated excited state dipoles show a range of 47 D–188 D. The absorption spectra and density of states of these structures show little variation except for the structures where the porphyrin and aryl conjugation is changed.

  18. Optimal Control of charge transfer

    OpenAIRE

    Werschnik, J.; Gross, E.K.U.

    2007-01-01

    In this work, we investigate how and to which extent a quantum system can be driven along a prescribed path in space by a suitably tailored laser pulse. The laser field is calculated with the help of quantum optimal control theory employing a time-dependent formulation for the control target. Within a two-dimensional (2D) model system we have successfully optimized laser fields for two distinct charge transfer processes. The resulting laser fields can be understood as a complicated interplay ...

  19. Electronic structure, molecular orientation, charge transfer dynamics and solar cells performance in donor/acceptor copolymers and fullerene: Experimental and theoretical approaches

    International Nuclear Information System (INIS)

    By combining experimental and theoretical approaches, the electronic structure, molecular orientation, charge transfer dynamics and solar cell performance in donor/acceptor copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl) benzo-2,1,3-thiadiazole] (PSiF-DBT) films and blended with 6,6.-phenyl-C 61-butyric acid methyl ester (PSiF-DBT:PCBM) were investigated. Good agreement between experimental and theoretical PSiF-DBT UV-Vis absorption spectrum is observed and the main molecular orbitals contributing to the spectrum were determined using DFT single point calculations. Non-coplanar configuration was determined by geometric optimization calculation in isolated PSiF-DBT pentamer and corroborated by angular variation of the sulphur 1s near-edge X-ray absorption fine structure (NEXAFS) spectra. Edge-on and plane-on molecular orientations were obtained for thiophene and benzothiadiazole units, respectively. A power conversion efficiency up to 1.58%, open circuit voltage of 0.51 V, short circuit current of 8.71 mA/cm2 and a fill factor of 35% was obtained using blended PSiF-DBT:PCBM as active layer in a bulk heterojunction solar cell. Ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core-hole clock methodology around sulphur 1s absorption edge. Electron delocalization times for PSiF-DBT and PSiF-DBT:PCBM polymeric films were derived for selected excitation energies corresponding to the main transitions in the sulphur 1s NEXAFS spectra. The mixture of PSiF-DBT with PCBM improves the charge transfer process involving the π* molecular orbital of the thiophene units

  20. Electronic structure, molecular orientation, charge transfer dynamics and solar cells performance in donor/acceptor copolymers and fullerene: Experimental and theoretical approaches

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Basabe, Y.; Borges, B. G. A. L.; Rocco, M. L. M., E-mail: lsroman@fisica.ufpr.br, E-mail: luiza@iq.ufrj.br [Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro 21941-909 (Brazil); Marchiori, C. F. N.; Yamamoto, N. A. D.; Koehler, M.; Roman, L. S., E-mail: lsroman@fisica.ufpr.br, E-mail: luiza@iq.ufrj.br [Departament of Physics, Federal University of Paraná, Curitiba 81531-990 (Brazil); Macedo, A. G. [Departament of Physics, Technological Federal University of Paraná, Curitiba 80230-901 (Brazil)

    2014-04-07

    By combining experimental and theoretical approaches, the electronic structure, molecular orientation, charge transfer dynamics and solar cell performance in donor/acceptor copolymer poly[2,7-(9,9-bis(2-ethylhexyl)-dibenzosilole)-alt-4,7-bis(thiophen-2-yl) benzo-2,1,3-thiadiazole] (PSiF-DBT) films and blended with 6,6.-phenyl-C 61-butyric acid methyl ester (PSiF-DBT:PCBM) were investigated. Good agreement between experimental and theoretical PSiF-DBT UV-Vis absorption spectrum is observed and the main molecular orbitals contributing to the spectrum were determined using DFT single point calculations. Non-coplanar configuration was determined by geometric optimization calculation in isolated PSiF-DBT pentamer and corroborated by angular variation of the sulphur 1s near-edge X-ray absorption fine structure (NEXAFS) spectra. Edge-on and plane-on molecular orientations were obtained for thiophene and benzothiadiazole units, respectively. A power conversion efficiency up to 1.58%, open circuit voltage of 0.51 V, short circuit current of 8.71 mA/cm{sup 2} and a fill factor of 35% was obtained using blended PSiF-DBT:PCBM as active layer in a bulk heterojunction solar cell. Ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core-hole clock methodology around sulphur 1s absorption edge. Electron delocalization times for PSiF-DBT and PSiF-DBT:PCBM polymeric films were derived for selected excitation energies corresponding to the main transitions in the sulphur 1s NEXAFS spectra. The mixture of PSiF-DBT with PCBM improves the charge transfer process involving the π* molecular orbital of the thiophene units.

  1. Biological charge transfer via flickering resonance.

    Science.gov (United States)

    Zhang, Yuqi; Liu, Chaoren; Balaeff, Alexander; Skourtis, Spiros S; Beratan, David N

    2014-07-15

    Biological electron-transfer (ET) reactions are typically described in the framework of coherent two-state electron tunneling or multistep hopping. However, these ET reactions may involve multiple redox cofactors in van der Waals contact with each other and with vibronic broadenings on the same scale as the energy gaps among the species. In this regime, fluctuations of the molecular structures and of the medium can produce transient energy level matching among multiple electronic states. This transient degeneracy, or flickering electronic resonance among states, is found to support coherent (ballistic) charge transfer. Importantly, ET rates arising from a flickering resonance (FR) mechanism will decay exponentially with distance because the probability of energy matching multiple states is multiplicative. The distance dependence of FR transport thus mimics the exponential decay that is usually associated with electron tunneling, although FR transport involves real carrier population on the bridge and is not a tunneling phenomenon. Likely candidates for FR transport are macromolecules with ET groups in van der Waals contact: DNA, bacterial nanowires, multiheme proteins, strongly coupled porphyrin arrays, and proteins with closely packed redox-active residues. The theory developed here is used to analyze DNA charge-transfer kinetics, and we find that charge-transfer distances up to three to four bases may be accounted for with this mechanism. Thus, the observed rapid (exponential) distance dependence of DNA ET rates over distances of ≲ 15 Å does not necessarily prove a tunneling mechanism. PMID:24965367

  2. Charge-transfer mechanism for electrophilic aromatic nitration and nitrosation via the convergence of (ab initio) molecular-orbital and Marcus-Hush theories with experiments.

    Science.gov (United States)

    Gwaltney, Steven R; Rosokha, Sergiy V; Head-Gordon, Martin; Kochi, Jay K

    2003-03-19

    The highly disparate rates of aromatic nitrosation and nitration, despite the very similar (electrophilic) properties of the active species: NO(+) and NO(2)(+) in Chart 1, are quantitatively reconciled. First, the thorough mappings of the potential-energy surfaces by high level (ab initio) molecular-orbital methodologies involving extensive coupled-cluster CCSD(T)/6-31G optimizations establish the intervention of two reactive intermediates in nitration (Figure 8) but only one in nitrosation (Figure 7). Second, the same distinctive topologies involving double and single potential-energy minima (Figures 6 and 5) also emerge from the semiquantitative application of the Marcus-Hush theory to the transient spectral data. Such a striking convergence from quite different theoretical approaches indicates that the molecular-orbital and Marcus-Hush (potential-energy) surfaces are conceptually interchangeable. In the resultant charge-transfer mechanism, the bimolecular interactions of arene donors with both NO(+) and NO(2)(+) spontaneously lead (barrierless) to pi-complexes in which electron transfer is concurrent with complexation. Such a pi-complex in nitration is rapidly converted to the sigma-complex, whereas this Wheland adduct in nitrosation merely represents a high energy (transition-state) structure. Marcus-Hush analysis thus demonstrates how the strongly differentiated (arene) reactivities toward NO(+) and NO(2)(+) can actually be exploited in the quantitative development of a single coherent (electron-transfer) mechanism for both aromatic nitrosation and nitration.

  3. Tuning the electronic and optical properties of graphene and boron-nitride quantum dots by molecular charge-transfer interactions: a theoretical study.

    Science.gov (United States)

    Bandyopadhyay, Arkamita; Yamijala, Sharma S R K C; Pati, Swapan K

    2013-09-01

    Spin-polarized first-principles calculations have been performed to tune the electronic and optical properties of graphene (G) and boron-nitride (BN) quantum dots (QDs) through molecular charge-transfer using tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) as dopants. From our results, based on the formation energy and the distance between QDs and dopants, we infer that both the dopants are physisorbed on the QDs. Also, we find that GQDs interact strongly with the dopants compared to the BNQDs. Interestingly, although the dopants are physisorbed on QDs, their interactions lead to a decrement in the HOMO-LUMO gap of QDs by more than half of their original value. We have found a spin-polarized HOMO-LUMO gap in certain QD-dopant complexes. Mülliken population analysis, generation of density of states (DOS) and projected DOS (pDOS) plots, and optical conductivity calculations have been performed to support and understand the reasons behind our findings.

  4. Long-range charge transfer in biopolymers

    Science.gov (United States)

    Astakhova, T. Yu; Likhachev, V. N.; Vinogradov, G. A.

    2012-11-01

    The results of theoretical and experimental studies on the charge transfer in biopolymers, namely, DNA and peptides, are presented. Conditions that ensure the efficient long-range charge transport (by several tens of nanometres) are considered. The known theoretical models of charge transfer mechanisms are discussed and the scopes of their application are analyzed. Attention is focused on the charge transport by the polaron mechanism. The bibliography includes 262 references.

  5. Backward Charge Transfer in Conjugated Polymers

    Institute of Scientific and Technical Information of China (English)

    CHENG Meng-Xing; LI Guang-Qi; Thomas F. George; SUN Xin

    2005-01-01

    It has been known that the static polarizability of a polymer chain with a biexciton is negative. In order to understand this peculiar fact, this paper studies the dynamical process of the charge transfer in the polymer chain induced by an external electric field E during forming the biexciton. The time dependence of the charge distribution in the chain reveals that the charge transfer is backward: the positive charge shifts in the opposite direction of the external electric field. Such a backward charge transfer (BCT) produces an opposite dipole, which makes the polarization negative. The effect of electron interaction on the BCT is illustrated.

  6. Charge Transfer and Charge Transport on the Double Helix

    OpenAIRE

    N. P. Armitage; Briman, M.; Gruner, G.

    2003-01-01

    We present a short review of various experiments that measure charge transfer and charge transport in DNA. Some general comments are made on the possible connection between 'chemistry-style' charge transfer experiments that probe fluorescence quenching and remote oxidative damage and 'physics-style' measurements that measure transport properties as defined typically in the solid-state. We then describe measurements performed by our group on the millimeter wave response of DNA. By measuring ov...

  7. Synthesis of molecular complexes based on porphyrins for the investigation of the energy transfer and primary charge separation in photosynthesis

    Science.gov (United States)

    Gribkova, S. E.; Evstigneeva, Rima P.; Luzgina, Valentina N.

    1993-10-01

    Data on the synthesis, steric structures, and photochemical properties of molecular diad systems based on porphyrins as synthetic models of the reaction centre in photosynthesis are considered and treated systematically. The bibliography includes 102 references.

  8. Charge transfer and transport in DNA

    OpenAIRE

    Jortner, Joshua; Bixon, Mordechai; Langenbacher, Thomas; Michel-Beyerle, Maria E.

    1998-01-01

    We explore charge migration in DNA, advancing two distinct mechanisms of charge separation in a donor (d)–bridge ({Bj})–acceptor (a) system, where {Bj} = B1,B2, … , BN are the N-specific adjacent bases of B-DNA: (i) two-center unistep superexchange induced charge transfer, d*{Bj}a → d∓{Bj}a±, and (ii) multistep charge transport involves charge injection from d* (or d+) to {Bj}, charge hopping within {Bj}, and charge trapping by a. For off-resonance coupling, mechanism i prevails with the char...

  9. Simulation for signal charge transfer of charge coupled devices

    Institute of Scientific and Technical Information of China (English)

    Wang Zujun; Liu Yinong; Chen Wei; Tang Benqi; Xiao Zhigang; Huang Shaoyan; Liu Minbo; Zhang Yong

    2009-01-01

    Physical device models and numerical processing methods are presented to simulate a linear buried channel charge coupled devices (CCDs). The dynamic transfer process of CCD is carried out by a three-phase clock pulse driver. By using the semiconductor device simulation software MEDICI, dynamic transfer pictures of signal charges cells, electron concentration and electrostatic potential are presented. The key parameters of CCD such as charge transfer efficiency (CTE) and dark electrons are numerically simulated. The simulation results agree with the theoretic and experimental results.

  10. Impact of Molecular Organization on Exciton Diffusion in Photosensitive Single-Crystal Halogenated Perylenediimides Charge Transfer Interfaces.

    Science.gov (United States)

    Pinto, Rui M; Gouveia, Wilson; Maçôas, Ermelinda M S; Santos, Isabel C; Raja, Sebastian; Baleizão, Carlos; Alves, Helena

    2015-12-23

    The efficiency of organic photodetectors and optoelectronic devices is strongly limited by exciton diffusion, in particular for acceptor materials. Although mechanisms for exciton diffusion are well established, their correlation to molecular organization in real systems has received far less attention. In this report, organic single-crystals interfaces were probed with wavelength-dependent photocurrent spectroscopy and their crystal structure resolved using X-ray diffraction. All systems present a dynamic photoresponse, faster than 500 ms, up to 650 nm. A relationship between molecular organization and favorable exciton diffusion in substituted butyl-perylenediimides (PDIB) is established. This is demonstrated by a set of PDIBs with different intra- and interstack distances and short contacts and their impact on photoresponse. Given the short packing distances between PDIs cores along the same stacking direction (3.4-3.7 Å), and across parallel stacks (2.5 Å), singlet exciton in these PDIBs can follow both Förster and Dexter exciton diffusion, with the Dexter-type mechanism assuming special relevance for interstack exciton diffusion. Yet, the response is maximized in substituted PDIBs, where a 2D percolation network is formed through strong interstack contacts, allowing for PDIBs primary excitons to reach with great efficiency the splitting interface with crystalline rubrene. The importance of short contacts and molecular distances, which is often overlooked as a parameter to consider and optimize when choosing materials for excitonic devices, is emphasized. PMID:26599347

  11. Charge-transfer collisions of multicharged ions with atomic and molecular hydrogen: measurements with low-energy accelerators

    International Nuclear Information System (INIS)

    Electron-capture cross sections for O/sup +q/ + H → O/sup +q-1/ + H+ and O/sup +q/ + H2 → O/sup +q-1/ + H2+ are shown for projectile energies from 10 to 1300 keV. At low energies the cross sections are determined by details of the quasi-molecule potential; at higher energies momentum transfer becomes the dominant mechanism, and the cross sections fall off similarly. Results with other projectiles are described briefly. 1 figure

  12. Multicomponent Molecular Puzzles for Photofunction Design: Emission Color Variation in Lewis Acid-Base Pair Crystals Coupled with Guest-to-Host Charge Transfer Excitation.

    Science.gov (United States)

    Ono, Toshikazu; Sugimoto, Manabu; Hisaeda, Yoshio

    2015-08-01

    Simple yet ubiquitous multimolecular assembly systems with color-tunable emissions are realized by cooperative electron donor-acceptor interactions, such as the boron-nitrogen (B-N) dative bond as a Lewis acid-base pair and charge transfer (CT) interactions. These are ternary-component systems consisting of a naphthalenediimide derivative (NDI), tris(pentafluorophenyl)borane (TPFB), and aromatic molecules (guest) with an NDI:TPFB:guest ratio of 1:2:2. The crystal shows guest-dependent color-tunable emissions such as deep blue to orange when a guest molecule of benzene is replaced with other π-conjugated systems. A good correlation between the emission wavelength and ionization potential of the guest and electronic structure calculations indicated that the emission is due to the CT transition from the guest to the NDI. The present study suggests that a rational solution of multcomponent molecular puzzles would be useful for obtaining novel photofunctional solid-state systems. PMID:26211567

  13. Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy

    Directory of Open Access Journals (Sweden)

    Mančal T.

    2013-03-01

    Full Text Available Two-dimensional electronic spectroscopy (2D-ES is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an energetic perturbation which promotes charge transfer across the complex.

  14. Symmetric charge transfer cross section of uranium

    International Nuclear Information System (INIS)

    Symmetric charge transfer cross section of uranium was calculated under consideration of reaction paths. In the charge transfer reaction a d3/2 electron in the U atom transfers into the d-electron site of U+(4I9/2) ion. The J value of the U atom produced after the reaction is 6, 5, 4 or 3, at impact energy below several tens eV, only resonant charge transfer in which the product atom is ground state (J=6) takes place. Therefore, the cross section is very small (4-5 x 10-15 cm2) compared with that considered so far. In the energy range of 100-1000eV the cross section increases with the impact energy because near resonant charge transfer in which an s-electron in the U atom transfers into the d-electron site of U+ ion. Charge transfer cross section between U+ in the first excited state (289 cm-1) and U in the ground state was also obtained. (author)

  15. Imidazole-Chloranil Charge Transfer Complex

    Institute of Scientific and Technical Information of China (English)

    Hai-long Wang; Tong-tong Lu; Tian-jing He; Dong-ming Chen

    2008-01-01

    UV-Vis absorption spectra of the molecular complex formed by imidazole (Im) and chloranil (CA) were measured in chloroform. The stoichiometry of the imidazole-chloranil (Im-CA) complex was determined as 1:1 by applying Benesi-Hildebrand's equation and Job's continuous variation method. Density function theory (DFT) and MP2 calculations were performed to study the structures and the binding energies of the Im-CA complex. The calculations located four conformations (denoted as S1-S4) for the Im-CA complex, two edge(lm)-to-face(CA) linked and two edgc(Im)-to-edge(CA) linked. It was found that the edgc-to-face conformers are more stable than the edge-to-edge ones. The bonding characteristics of these conformers were investigated with natural population analysis (NPA), topological analysis of electron density, and natural bond orbital (NBO) analysis. It was revealed that the edge-to-face conformers are charge-transfer (CT) complexes whereas the edge-to-edge conformers are the hydrogen bond complexes. For the most stable conformation of the Im-CA comp]ex (S1), the charge transfer interaction of the imidazole n(N15) lone pair orbital with the chloranil π*(C1=O7) orbital plays a crucial role in the Im-CA binding, and the binding is further strengthened by the 07… H20 hydrogen bond. The electronic excitation energies of the complex (S1) were calculated with time-dependent DFT (TDDFT), and the observed UV-Visiblc spectrum of the complex was analyzed based on the computed results.

  16. Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy

    OpenAIRE

    Mančal T.; Milota F.; Hauer J; Christensson N.; Bixner O.; Lukeš V.; Kauffmann H. F.

    2013-01-01

    Two-dimensional electronic spectroscopy (2D-ES) is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an en...

  17. What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends.

    Science.gov (United States)

    Jakowetz, Andreas C; Böhm, Marcus L; Zhang, Jiangbin; Sadhanala, Aditya; Huettner, Sven; Bakulin, Artem A; Rao, Akshay; Friend, Richard H

    2016-09-14

    In solar energy harvesting devices based on molecular semiconductors, such as organic photovoltaics (OPVs) and artificial photosynthetic systems, Frenkel excitons must be dissociated via charge transfer at heterojunctions to yield free charges. What controls the rate and efficiency of charge transfer and charge separation is an important question, as it determines the overall power conversion efficiency (PCE) of these systems. In bulk heterojunctions between polymer donor and fullerene acceptors, which provide a model system to understand the fundamental dynamics of electron transfer in molecular systems, it has been established that the first step of photoinduced electron transfer can be fast, of order 100 fs. But here we report the first study which correlates differences in the electron transfer rate with electronic structure and morphology, achieved with sub-20 fs time resolution pump-probe spectroscopy. We vary both the fullerene substitution and donor/fullerene ratio which allow us to control both aggregate size and the energetic driving force for charge transfer. We observe a range of electron transfer times from polymer to fullerene, from 240 fs to as short as 37 fs. Using ultrafast electro-optical pump-push-photocurrent spectroscopy, we find the yield of free versus bound charges to be weakly dependent on the energetic driving force, but to be very strongly dependent on fullerene aggregate size and packing. Our results point toward the importance of state accessibility and charge delocalization and suggest that energetic offsets between donor and acceptor levels are not an important criterion for efficient charge generation. This provides design rules for next-generation materials to minimize losses related to driving energy and boost PCE.

  18. What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends.

    Science.gov (United States)

    Jakowetz, Andreas C; Böhm, Marcus L; Zhang, Jiangbin; Sadhanala, Aditya; Huettner, Sven; Bakulin, Artem A; Rao, Akshay; Friend, Richard H

    2016-09-14

    In solar energy harvesting devices based on molecular semiconductors, such as organic photovoltaics (OPVs) and artificial photosynthetic systems, Frenkel excitons must be dissociated via charge transfer at heterojunctions to yield free charges. What controls the rate and efficiency of charge transfer and charge separation is an important question, as it determines the overall power conversion efficiency (PCE) of these systems. In bulk heterojunctions between polymer donor and fullerene acceptors, which provide a model system to understand the fundamental dynamics of electron transfer in molecular systems, it has been established that the first step of photoinduced electron transfer can be fast, of order 100 fs. But here we report the first study which correlates differences in the electron transfer rate with electronic structure and morphology, achieved with sub-20 fs time resolution pump-probe spectroscopy. We vary both the fullerene substitution and donor/fullerene ratio which allow us to control both aggregate size and the energetic driving force for charge transfer. We observe a range of electron transfer times from polymer to fullerene, from 240 fs to as short as 37 fs. Using ultrafast electro-optical pump-push-photocurrent spectroscopy, we find the yield of free versus bound charges to be weakly dependent on the energetic driving force, but to be very strongly dependent on fullerene aggregate size and packing. Our results point toward the importance of state accessibility and charge delocalization and suggest that energetic offsets between donor and acceptor levels are not an important criterion for efficient charge generation. This provides design rules for next-generation materials to minimize losses related to driving energy and boost PCE. PMID:27538341

  19. Charged Frenkel biexcitons in organic molecular crystals

    CERN Document Server

    Agranovich, V M; Kamchatnov, A M

    2001-01-01

    It is known that the energy of the lowest electronic transition in neutral molecules of anthracene, tetracene and other polyacenes is blue shifted in comparison with the corresponding transition energy in mono-valent molecular ions. This effect in molecular crystal may be responsible for the attraction between molecular (Frenkel) exciton and charge carrier. Due to this attraction the bound state of Frenkel exciton and free charge (charged Frenkel exciton) may be formed. The same mechanism can be responsible for formation of charged biexcitons (bound state of two Frenkel excitons and a charge carrier). Calculations are performed for molecular crystals like tetracene by means of one-dimensional lattice model

  20. Valence Topological Charge-Transfer Indices for Dipole Moments

    Directory of Open Access Journals (Sweden)

    Francisco Torrens

    2003-01-01

    Full Text Available New valence topological charge-transfer indices are applied to the calculation of dipole moments. The algebraic and vector semisum charge-transfer indices are defined. The combination of the charge-transfer indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moments of a homologous series of phenyl alcohols. Linear and non-linear correlation models are obtained. The new charge-transfer indices improve the multivariable non-linear regression equations for the dipole moment. When comparing with previous results, the variance decreases 92%. No superposition of the corresponding Gk–Jk and GkV – JkV pairs is observed. This diminishes the risk of co-linearity. Inclusion of the oxygen atom in the p-electron system is beneficial for the description of the dipole moment, owing to either the role of the additional p orbitals provided by the heteroatom or the role of steric factors in the p-electron conjugation. Linear and non-linear correlations between the fractal dimension and various descriptors point not only to a homogeneous molecular structure but also to the ability to predict and tailor drug properties.

  1. Charge Transfer in Nanocrystalline Semiconductor Electrodes

    Directory of Open Access Journals (Sweden)

    M. Bouroushian

    2013-01-01

    Full Text Available Nanocrystalline electrodes in liquid junction devices possess a number of unique properties arising from their convoluted structure and the dimensions of their building units. The light-induced charge separation and transport in photoelectrochemical systems using nanocrystalline/nanoporous semiconductor electrodes is discussed here in connection with the basic principles of the (Schottky barrier theory. Recent models for charge transfer kinetics in normal and unipolar (dye-sensitized cells are reviewed, and novel concepts and materials are considered.

  2. Radiative charge transfer in collisions of C with He+

    CERN Document Server

    Babb, James F

    2016-01-01

    Radiative charge exchange collisions between a carbon atom C(${}^3$P) and a helium ion He+, both in their ground state, are investigated theoretically. Detailed quantum chemistry calculations are carried out to obtain potential energy curves and transition dipole matrix elements for doublet and quartet molecular states of the HeC+ cation. Radiative charge transfer cross sections and rate coefficients are calculated and are found at thermal and lower energies to be large compared to those for direct charge transfer. The present results might be applicable to modelling the complex interplay of [C II] (or C+), C, and CO at the boundaries of photon dominated regions (PDRs) and in xray dominated regions (XDRs), where the abundance of He+ affects the abundance of CO.

  3. Charge Transfer Excitons at van der Waals Interfaces.

    Science.gov (United States)

    Zhu, Xiaoyang; Monahan, Nicholas R; Gong, Zizhou; Zhu, Haiming; Williams, Kristopher W; Nelson, Cory A

    2015-07-01

    The van der Waals interfaces of molecular donor/acceptor or graphene-like two-dimensional (2D) semiconductors are central to concepts and emerging technologies of light-electricity interconversion. Examples include, among others, solar cells, photodetectors, and light emitting diodes. A salient feature in both types of van der Waals interfaces is the poorly screened Coulomb potential that can give rise to bound electron-hole pairs across the interface, i.e., charge transfer (CT) or interlayer excitons. Here we address common features of CT excitons at both types of interfaces. We emphasize the competition between localization and delocalization in ensuring efficient charge separation. At the molecular donor/acceptor interface, electronic delocalization in real space can dictate charge carrier separation. In contrast, at the 2D semiconductor heterojunction, delocalization in momentum space due to strong exciton binding may assist in parallel momentum conservation in CT exciton formation. PMID:26001297

  4. Tight-binding parameters for charge transfer along DNA

    OpenAIRE

    Hawke, L. G.D.; Kalosakas, G.; Simserides, C.

    2009-01-01

    We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The $\\pi$ molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are discussed and then used for calculating the corresponding wavefunctions of the two B-DNA base-pairs (adenine-thymine and gua...

  5. Femtosecond direct observation of charge transfer between bases in DNA

    OpenAIRE

    Wan, Chaozhi; Fiebig, Torsten; Schiemann, Olav; Barton, Jacqueline K.; Zewail, Ahmed H.

    2000-01-01

    Charge transfer in supramolecular assemblies of DNA is unique because of the notion that the π-stacked bases within the duplex may mediate the transport, possibly leading to damage and/or repair. The phenomenon of transport through π-stacked arrays over a long distance has an analogy to conduction in molecular electronics, but the mechanism still needs to be determined. To decipher the elementary steps and the mechanism, one has to directly measure the dynamics in ...

  6. Ultrafast photoinduced intra- und intermolecular charge transfer and solvation

    OpenAIRE

    Bizjak, Tanja

    2004-01-01

    Intra- and intermolecular charge transfer as well as internal conversion processes are studied in various molecular systems. The dynamics of these fundamental photoinduced processes are investigated by pump-probe femtosecond spectroscopy and steady-state fluorescence. Transient spectra are obtained using white light continuum as probe, while time resolved measurements are performed by probing at specific wavelengths with non dispersive detec-tion. Noncollinearly phase matched optical parametr...

  7. Tight-binding parameters for charge transfer along DNA

    CERN Document Server

    Hawke, L G D; Simserides, C

    2009-01-01

    We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The $\\pi$ molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are discussed and then used for calculating the corresponding wavefunctions of the two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO and LUMO energies of the bases are in good agreement with available experimental values. Our results are then used for estimating the complete set of charge transfer parameters between neighboring bases and also between successive base-pairs, considering all possible combinations between them, for both electrons and holes. The calculated microscopic quantities can be used in mesoscopic theoretical models of electron or hole transfer along the DNA double helix, as they provide the necessar...

  8. Charge-Transfer Interactions in Organic Functional Materials

    Directory of Open Access Journals (Sweden)

    Bih-Yaw Jin

    2010-08-01

    Full Text Available Our goal in this review is three-fold. First, we provide an overview of a number of quantum-chemical methods that can abstract charge-transfer (CT information on the excited-state species of organic conjugated materials, which can then be exploited for the understanding and design of organic photodiodes and solar cells at the molecular level. We stress that the Composite-Molecule (CM model is useful for evaluating the electronic excited states and excitonic couplings of the organic molecules in the solid state. We start from a simple polyene dimer as an example to illustrate how interchain separation and chain size affect the intercahin interaction and the role of the charge transfer interaction in the excited state of the polyene dimers. With the basic knowledge from analysis of the polyene system, we then study more practical organic materials such as oligophenylenevinylenes (OPVn, oligothiophenes (OTn, and oligophenylenes (OPn. Finally, we apply this method to address the delocalization pathway (through-bond and/or through-space in the lowest excited state for cyclophanes by combining the charge-transfer contributions calculated on the cyclophanes and the corresponding hypothetical molecules with tethers removed. This review represents a step forward in the understanding of the nature of the charge-transfer interactions in the excited state of organic functional materials.

  9. Charge transfer processes of low charge state heavy ions

    International Nuclear Information System (INIS)

    In this paper, some aspects of the collision processes of accelerated heavy ions in very low charge state is reviewed, and the beam loss due to such collisions is estimated. The processes included in ion-atom collisions are electron capture, the electron stripping of ions, and target ionization. The stripping cross sections decrease slowly at high energy, and are much larger than the electron capture cross sections. At low energy, the electron capture is dominant, and this process plays a principal role near ion sources and preacceleration regions. This has not been taken into account properly. In order to keep the beam loss less than 0.1 percent, it is estimated that the average vacuum of about 10-7 to 10-8 Torr is required. An empirical formula to calculate the stripping cross sections of heavy ions in low charge state in collisions is derived. The beam loss due to ion-atom collisions can be estimated. The charge transfer and stripping processes in ion-ion collisions are also discussed. The typical processes in ion-ion collisions are almost same as those in ion-atom collisions. In order to minimize the ion beam loss due to charge-changing processes, it is important to choose the heavy ions with closed shell configurations, which correspond to the slightly more ionized states than the singly ionized state. (Kato, T.)

  10. Charge transfer reactions in nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Wiederrecht, G.P. [Argonne National Lab., IL (United States). Chemistry Div.; Wasielewski, M.R. [Argonne National Lab., IL (United States). Chemistry Div.]|[Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Galili, T.; Levanon, H. [Hebrew Univ. of Jerusalem (Israel). Dept. of Physical Chemistry

    1998-07-01

    Ultrafast transient absorption studies of intramolecular photoinduced charge separation and thermal charge recombination were carried out on a molecule consisting of a 4-(N-pyrrolidino)naphthalene-1,8-imide donor (PNI) covalently attached to a pyromellitimide acceptor (PI) dissolved in the liquid crystal 4{prime}-(n-pentyl)-4-cyanobiphenyl (5CB). The temperature dependencies of the charge separation and recombination rates were obtained at temperatures above the nematic-isotropic phase transition of 5CB, where ordered microdomains exist and scattering of visible light by these domains is absent. The authors show that excited state charge separation is dominated by molecular reorientation of 5CB perpendicular to the director within the liquid crystal microdomains. They also show that charge recombination is adiabatic and is controlled by the comparatively slow collective reorientation of the liquid crystal microdomains relative to the orientation of PNI{sup +}-PI{sup {minus}}. They also report the results of time resolved electron paramagnetic resonance (TREPR) studies of photoinduced charge separation in a series of supramolecular compounds dissolved in oriented liquid crystal solvents. These studies permit the determination of the radical pair energy levels as the solvent reorganization energy increases from the low temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal.

  11. Charge transport in columnar stacked triphenylenes: Effects of conformational fluctuations on charge transfer integrals and site energies

    OpenAIRE

    K. Senthilkumar; Grozema, F.C.; Bickelhaupt, F.M.; Siebbeles, L.D.A.

    2003-01-01

    Values of charge transfer integrals, spatial overlap integrals and site energies involved in transport of positive charges along columnar stacked triphenylene derivatives are provided. These parameters were calculated directly as the matrix elements of the Kohn–Sham Hamiltonian, defined in terms of the molecular orbitals on individual triphenylene molecules. This was realized by exploiting the unique feature of the Amsterdam density functional theory program that allows one to use molecular o...

  12. Extended-Charge-Transfer Excitons in Crystalline Supramolecular Photocatalytic Scaffolds.

    Science.gov (United States)

    Hestand, Nicholas J; Kazantsev, Roman V; Weingarten, Adam S; Palmer, Liam C; Stupp, Samuel I; Spano, Frank C

    2016-09-14

    Coupling among chromophores in molecular assemblies is responsible for phenomena such as resonant energy transfer and intermolecular charge transfer. These processes are central to the fields of organic photovoltaics and photocatalysis, where it is necessary to funnel energy or charge to specific regions within the system. As such, a fundamental understanding of these transport processes is essential for developing new materials for photovoltaic and photocatalytic applications. Recently, photocatalytic systems based on photosensitizing perylene monomimide (PMI) chromophore amphiphiles were found to show variation in hydrogen gas (H2) production as a function of nanostructure crystallinity. The 2D crystalline systems form in aqueous electrolyte solution, which provides a high dielectric environment where the Coulomb potential between charges is mitigated. This results in relatively weakly bound excitons that are ideal for reducing protons. In order to understand how variations in crystalline structure affect H2 generation, two representative PMI systems are investigated theoretically using a modified Holstein Hamiltonian. The Hamiltonian includes both molecular Frenkel excitations (FE) and charge-transfer excitations (CTE) coupled nonadiabatically to local intramolecular vibrations. Signatures of FE/CTE mixing and the extent of electron/hole separation are identified in the optical absorption spectrum and are found to correlate strongly to the observed H2 production rates. The absorption spectral signatures are found to sensitively depend on the relative phase between the electron and hole transfer integrals, as well as the diabatic energy difference between the Frenkel and CT exciton bands. Our analysis provides design rules for artificial photosynthetic systems based on organic chromophore arrays. PMID:27589150

  13. Coronene-based charge-transfer complexes.

    Science.gov (United States)

    Yoshida, Yukihiro; Isomura, Kazuhide; Kumagai, Yoshihide; Maesato, Mitsuhiko; Kishida, Hideo; Mizuno, Motohiro; Saito, Gunzi

    2016-08-01

    Recent developments in the arena of charge-transfer complexes composed of the D 6h-symmetric polycyclic aromatic hydrocarbon, coronene, are highlighted with emphasis on the structural and physical properties of these complexes. Because of the dual electron-donating and -accepting abilities of coronene, this group involves structurally-defined four cation salts and three anion salts. The Jahn-Teller distortions and in-plane motion of coronene molecules in the solids, both of which are closely associated with the high symmetry of coronene molecules, and syntheses of clathrate-type complexes are also presented. PMID:27294380

  14. Charge Redistribution and Transport in Molecular Contacts

    Science.gov (United States)

    Corso, Martina; Ondráček, Martin; Lotze, Christian; Hapala, Prokop; Franke, Katharina J.; Jelínek, Pavel; Pascual, J. Ignacio

    2015-09-01

    The forces between two single molecules brought into contact, and their connection with charge transport through the molecular junction, are studied here using non contact AFM, STM, and density functional theory simulations. A carbon monoxide molecule approaching an acetylene molecule (C2 H2 ) initially feels weak attractive electrostatic forces, partly arising from charge reorganization in the presence of molecular . We find that the molecular contact is chemically passive, and protects the electron tunneling barrier from collapsing, even in the limit of repulsive forces. However, we find subtle conductance and force variations at different contacting sites along the C2 H2 molecule attributed to a weak overlap of their respective frontier orbitals.

  15. Photoinduced charge-transfer materials for nonlinear optical applications

    Science.gov (United States)

    McBranch, Duncan W.

    2006-10-24

    A method using polyelectrolyte self-assembly for preparing multi-layered organic molecular materials having individual layers which exhibit ultrafast electron and/or energy transfer in a controlled direction occurring over the entire structure. Using a high molecular weight, water-soluble, anionic form of poly-phenylene vinylene, self-assembled films can be formed which show high photoluminescence quantum efficiency (QE). The highest emission QE is achieved using poly(propylene-imine) (PPI) dendrimers as cationic binders. Self-quenching of the luminescence is observed as the solid polymer film thickness is increased and can be reversed by inserting additional spacer layers of transparent polyelectrolytes between each active conjugated layer, such that the QE grows with thickness. A red shift of the luminescence is also observed as additional PPV layers are added. This effect persists as self-quenching is eliminated. Charge transfer superlattices can be formed by additionally incorporating C.sub.60 acceptor layers.

  16. Fluctuation spectroscopy in organic charge transfer salts

    International Nuclear Information System (INIS)

    Quasi-twodimensional organic charge-transfer salts show certain analogies to the High-Temperature Cuprate Superconductors (HTSC), e.g., the layered structure where conducting and insulating sheets do alternate as well as the direct proximity of the antiferromagnetic insulating ground state to the superconducting phase. At higher temperatures the formation of a pseudo-gap in the density of states is discussed also. In contrast to the HTSC the electronic properties of the organic charge-transfer salts can be easily influenced by external parameters such as hydrostatic or chemical pressure - in a generalized phase diagram the usage of different anions X can be mapped on the axis W/U as well, see Sec. 4.2 - or moderate temperatures. In the quasi-twodimensional K-(BEDT-TTF)2X salts, e.g., a moderate pressure of p ∝ 250 bar is sufficient to shift the antiferromagnetic-insulating system (X=Cu[N(CN)2]Cl) to the metallic side of the phase diagram showing even superconductivity below a critical temperature of Tc ∝ 12.8 K. Doping as in the HTSC and the undesirable disorder accompanied with it is not necessary to induce a metal-to-insulator transition. Therefore the experimental requirements are more easily met in this class of materials compared to other strongly correlated electron systems. All this makes the organic charge-transfer salts ideal model systems to study fundamental concepts of theoretical solid state physics some of which have been of academical interest only so far. In this work fluctuation spectroscopy has been used for the first time to investigate the low-frequency dynamics of the TT-electron system in the quasi-twodimensional organic charge-transfer salts K-(BEDT-TTF)2X with the aim to gain information about the temperature, pressure and magnetic field dependence of the power spectral density of the resistance noise and therefore about the dynamics of the charge carrier fluctuations. Especially in the vicinity of correlation driven ordering phenomena

  17. A charge-driven molecular water pump.

    Science.gov (United States)

    Gong, Xiaojing; Li, Jingyuan; Lu, Hangjun; Wan, Rongzheng; Li, Jichen; Hu, Jun; Fang, Haiping

    2007-11-01

    Understanding and controlling the transport of water across nanochannels is of great importance for designing novel molecular devices, machines and sensors and has wide applications, including the desalination of seawater. Nanopumps driven by electric or magnetic fields can transport ions and magnetic quanta, but water is charge-neutral and has no magnetic moment. On the basis of molecular dynamics simulations, we propose a design for a molecular water pump. The design uses a combination of charges positioned adjacent to a nanopore and is inspired by the structure of channels in the cellular membrane that conduct water in and out of the cell (aquaporins). The remarkable pumping ability is attributed to the charge dipole-induced ordering of water confined in the nanochannels, where water can be easily driven by external fields in a concerted fashion. These findings may provide possibilities for developing water transport devices that function without osmotic pressure or a hydrostatic pressure gradient. PMID:18654410

  18. Charge transfer reaction laser with preionization means

    Science.gov (United States)

    Lauderslager, J. B.; Pacala, T. J. (Inventor)

    1978-01-01

    A helium-nitrogen laser is described in which energy in the visible range is emitted as a result of charge transfer reaction between helium ions and nitrogen molecules. The helium and nitrogen are present in a gas mixture at several atmospheres pressure, with a nitrogen partial pressure on the order of a pair of main discharge electrodes, the gas mixture is preionized to prevent arcing when the discharge pulse is applied. The preionization is achieved by the application of a high voltage across a pair of secondary electrodes which are spaced apart in a direction perpendicular to the spacing direction of the main discharge electrodes and the longitudinal axis of the space in which the gas mixture is contained. Feedback, by means of a pair of appropriately spaced mirrors, is provided, to produce coherent energy pulses at a selected wavelength.

  19. Coulomb Traps and Charge Transport in Molecular Solids

    Science.gov (United States)

    Scher, Harvey

    2000-03-01

    A major result of experimental studies of a diverse assortment of disordered molecular solids is the observation of a common pattern in the charge transport properties. The transport ranges from charge transfer between molecules doped in an inert polymer to motion along the silicon backbone of polysilylenes. The pattern is the unusual combination of Poole Frenkel-like electric field dependence and non-Arrhenius temperature dependence of the mobility. The latter feature has been especially puzzling. We study the drift mobility of a molecular polaron in the presence of an applied field and Coulomb traps. The model is based on one previously developed for geminate recombination of photogenerated charge carriers. The key electric field and temperature dependencies of the mobility measurements are well reproduced by this model. Our conclusion is that this nearly universal transport behavior arises from competition between rates of polaron trapping and release from a very low density of Coulomb traps.

  20. Nucleic Acid Charge Transfer: Black, White and Gray

    OpenAIRE

    Venkatramani, Ravindra; Keinan, Shahar; Balaeff, Alexander; Beratan, David N.

    2011-01-01

    Theoretical studies of charge transport in deoxyribonucleic acid (DNA) and peptide nucleic acid (PNA) indicate that structure and dynamics modulate the charge transfer rates, and that different members of a structural ensemble support different charge transport mechanisms. Here, we review the influences of nucleobase geometry, electronic structure, solvent environment, and thermal conformational fluctuations on the charge transfer mechanism. We describe an emerging framework for understanding...

  1. Path integral approach to non-relativistic electron charge transfer

    International Nuclear Information System (INIS)

    A path integral approach has been generalized for the non-relativistic electron charge transfer processes. The charge transfer - the capture of an electron by an ion passing another atom, or more generally the problem of rearrangement collisions - is formulated in terms of influence functionals. It has been shown that the electron charge transfer process can be treated either as an electron transition problem or as ion and atom elastic scattering in the effective potential field. The first-order Born approximation for the electron charge transfer reaction cross section has been reproduced to prove the adequacy of the path integral approach for this problem. (author)

  2. Ultrafast Charge Photogeneration in MEH-PPV Charge-Transfer Complexes

    Science.gov (United States)

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

    Visible-pump-IR-probe spectroscopy is used to study the ultrafast charge dynamics in MEH-PPV based charge-transfer complexes and donor-acceptor blends. Transient anisotropy of the polymer polaron band provides invaluable insights into excitation localisation and charge-transfer pathways.

  3. Radiative transfer and molecular data for astrochemistry

    NARCIS (Netherlands)

    Tak, Floris van der

    2011-01-01

    The estimation of molecular abundances in interstellar clouds from spectroscopic observations requires radiative transfer calculations, which depend on basic molecular input data. This paper reviews recent developments in the fields of molecular data and radiative transfer. The first part is an over

  4. Charge-transfer excitons in DNA.

    Science.gov (United States)

    Conwell, E M; McLaughlin, P M; Bloch, S M

    2008-02-21

    There have been a number of theoretical treatments of excitons in DNA, most neglecting both the intrachain and interchain wavefunction overlaps of the electron and hole, treating them as Frenkel excitons. Recently, the importance of the intrachain and interchain coupling has been highlighted. Experiments have shown that in (dA)n oligomers and in duplex (dA)n.(dT)n, to be abbreviated (A/T), where A is adenine and T is thymine, the exciton wavefunction is delocalized over several bases. In duplexes it is possible to have charge-transfer (CT) excitons. Theoretical calculations have suggested that CT excitons in DNA may have lower energy than single chain excitons. In all the calculations of excitons in DNA, the polarization of the surrounding water has been neglected. Calculations have shown, however, that polarization of the water by an excess electron or a hole in DNA lowers its energy by approximately 1/2 eV, causing it to become a polaron. It is therefore to be expected that polarization charge induced in the surrounding water has a significant effect on the properties of the exciton. In what follows, we present calculations of some properties CT excitons would have in an A/T duplex taking into account the wavefunction overlaps, the effect of the surrounding water, which results in the electron and hole becoming polarons, and the ions in the water. As expected, the CT exciton has lowest energy when the electron and hole polarons are directly opposite each other. By appropriate choice of the dielectric constant, we can obtain a CT exciton delocalized over the number of sites found in photoinduced absorption experiments. The absorption threshold that we then calculate for CT exciton creation in A/T is in reasonable agreement with the lowest singlet absorption deduced from available data. PMID:18232682

  5. Metal-Organic Coordination Number Determined Charge Transfer Magnitude

    Science.gov (United States)

    Yang, Hung-Hsiang; Chu, Yu-Hsun; Lu, Chun-I.; Yang, Tsung-Han; Yang, Kai-Jheng; Kaun, Chao-Cheng; Hoffmann, Germar; Lin, Minn-Tsong

    2014-03-01

    By the appropriate choice of head groups and molecular ligands, various metal-organic coordination geometries can be engineered. Such metal-organic structures provide different chemical environments for molecules and give us templates to study the charge redistribution within the metal-organic interface. We created various metal-organic bonding environment by growing self-assembly nanostructures of Fe-PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) chains and networks on a Au(111) surface. Bonding environment dependent frontier molecular orbital energies are acquired by low temperature scanning tunneling microscopy and scanning tunneling spectroscopy. By comparing the frontier energies with the molecular coordination environments, we conclude that the specific coordination affects the magnitude of charge transfer onto each PTCDA in the Fe-PTCDA hybridization system. H.-H. Yang, Y.-H. Chu, C.-I Lu, T.-H. Yang, K.-J. Yang, C.-C. Kaun, G. Hoffmann, and M.-T. Lin, ACS Nano 7, 2814 (2013).

  6. Second order Born calculation for charge transfer

    International Nuclear Information System (INIS)

    Charge transfer cross sections, from the ground state of the target to the ground state of the projectile, have been computed in a second order Born approximation for protons incident upon hydrogen at energies of 1, 10, and 50 MeV. The exact second order matrix element is evaluated numerically, and the results are compared to a standard peaking approximation (SP), as well as to a new peaking approximation (LP) developed herein. At 50 MeV two distinct second order effects are evident in the differential cross section. For very small (center of mass) scattering angles (THETA approx. = .0320) the second order cross section is smaller than the first order cross section, while at larger angles (THETA approx. = .0540) a second Born peak occurs. This peak can be kinematically associated with a classical two step process which gives rise to the well known dominating v-11 asymptotic velocity dependence of the total cross section. The reduction of the differential cross section at smaller angles serves to decrease the total cross section, as is predicted by the asymptotic expression. At 10 MeV second order effects become less important, and at 1 MeV the kinematic peak has all but disappeared, while the second order cross section has here become larger than the first order cross section. At intermediate energies experimental results indicate that the first order cross section used here is itself too large

  7. Charge-transfer spectra of tetravalent lanthanide ions in oxides

    NARCIS (Netherlands)

    Hoefdraad, H.E.

    1975-01-01

    The charge-transfer spectra of Ce4+, Pr4+ and Tb4+ in a number of oxides are reported. It is noted that the position of the first charge-transfer band is fixed for the metal ion in an oxygen coordination of VI, but varies in VIII coordination as a function of the host lattice. It is argued that this

  8. Preparation and characterization of three charge-transfer complexes

    Energy Technology Data Exchange (ETDEWEB)

    Li Yuliang [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Gao Yuanming [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Wu Zi [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Bai Fenglian [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Li Yongfang [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Mo Yiming [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Zhang Bin [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Han Hongxian [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China); Zhu Daoben [Inst. of Chemistry, Chinese Academy of Sciences, Beijing, BJ (China)

    1995-03-15

    We wish to report the preparation and characterization of three new charge transfer complexes of derivatizations of tetrathiafulvalene with buckminsterfullerene. The charge transfer complexes had been characterized by electronic absorption, Fourier transform infrared spectroscopy (FTIR), and elemental analysis and the crystal structure had been analyzed. (orig.)

  9. On the HSAB based estimate of charge transfer between adsorbates and metal surfaces

    International Nuclear Information System (INIS)

    Graphical abstract: Left: molecule-to-metal electron charge transfer (ΔN) is proportional to the difference between the metal’s work function and molecular electronegativity. Right: correlation between the work function and explicitly DFT calculated ΔN. Highlights: ► HSAB based electron transfer parameter, ΔN, is analyzed for adsorbates on metal surfaces. ► ΔN gives reasonably estimated trends of charge transfer for atomic and molecular adsorbates. ► Adatom-metal bond strength is linearly proportional to metal-to-adatom charge transfer. ► DFT calculated adsorption energies of the N, O, and Cl adatoms on 11 different metals. ► DFT calculated work functions of low Miller index surfaces for 11 different metals. - Abstract: The applicability of the HSAB based electron charge transfer parameter, ΔN, is analyzed for molecular and atomic adsorbates on metal surfaces by means of explicit DFT calculations. For molecular adsorbates ΔN gives reasonable trends of charge transfer if work function is used for electronegativity of metal surface. For this reason, calculated work functions of low Miller index surfaces for 11 different metals are reported. As for reactive atomic adsorbates, e.g., N, O, and Cl, the charge transfer is proportional to the adatom valence times the electronegativity difference between the metal surface and the adatom, where the electronegativity of metal is represented by a linear combination of atomic Mulliken electronegativity and the work function of metal surface. It is further shown that the adatom-metal bond strength is linearly proportional to the metal-to-adatom charge transfer thus making the ΔN parameter a useful indicator to anticipate the corresponding adsorption energy trends.

  10. Symmetric laser-assisted charge transfer: A nonperturbative treatment

    International Nuclear Information System (INIS)

    We present a nonperturbative treatment of laser-assisted charge transfer under conditions of high laser intensity and low collision energy in a specific symmetric charge transfer system: H(1s) + H+ + mhw → H+ + H(n = 1, 2). Previous work in laser-assisted charge transfer has demonstrated that although perturbative treatments are generally valid for lower laser intensities and higher collision energies, nonperturbative treatments are necessary in the present regime where the influence of the laser on the cross sections is more pronounced. The present work is based on the semiclassical impact parameter method, choosing initial conditions appropriate to charge transfer and treating the projectile-target system within a quasimolecular framework. The interaction with the laser is treated semiclassically, in the velocity gauge. We investigate the effect of the laser on both resonant and nonresonant charge transfer processes and provide comparisons with perturbative results. Finally, we shall discuss possibilities for future research

  11. Excited State Structural Dynamics of Carotenoids and Charge Transfer Systems

    International Nuclear Information System (INIS)

    This dissertation describes the development and implementation of a visible/near infrared pump/mid-infrared probe apparatus. Chapter 1 describes the background and motivation of investigating optically induced structural dynamics, paying specific attention to solvation and the excitation selection rules of highly symmetric molecules such as carotenoids. Chapter 2 describes the development and construction of the experimental apparatus used throughout the remainder of this dissertation. Chapter 3 will discuss the investigation of DCM, a laser dye with a fluorescence signal resulting from a charge transfer state. By studying the dynamics of DCM and of its methyl deuterated isotopomer (an otherwise identical molecule), we are able to investigate the origins of the charge transfer state and provide evidence that it is of the controversial twisted intramolecular (TICT) type. Chapter 4 introduces the use of two-photon excitation to the S1 state, combined with one-photon excitation to the S2 state of the carotenoid beta-apo-8'-carotenal. These 2 investigations show evidence for the formation of solitons, previously unobserved in molecular systems and found only in conducting polymers Chapter 5 presents an investigation of the excited state dynamics of peridinin, the carotenoid responsible for the light harvesting of dinoflagellates. This investigation allows for a more detailed understanding of the importance of structural dynamics of carotenoids in light harvesting

  12. Transfer ionization cross-sections measured in collisions of highly charged argon ions with neon target

    Institute of Scientific and Technical Information of China (English)

    MA; Xinwen(马新文); LIU; Huiping; (刘惠萍); CHEN; Ximeng; (陈熙萌); YANG; Zhihu; (杨治虎); SHEN; Ziyong; (申自勇); WANG; Youde; (王友德); YU; Deyang; (于得洋); CAI; Xiaohong; (蔡晓红); LIU; Zhaoyuan; (刘兆远)

    2003-01-01

    Multiple electron transfer processes are studied for Arq+ + Ne (q = 8, 9, 11, 12) collisions by using multi-parameter coincidence techniques. Various electron transfer processes are identified experimentally and the related cross-sections are measured. The dependence of transfer ionization cross-sections on the recoil charge states is compared with the results from the modified molecular classical overbarrier model. It is found that the modified model described the experimental results reasonably.

  13. 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

    2004-09-01

    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

  14. Magnetic ordering in fullerene charge-transfer complexes

    Science.gov (United States)

    Sato, Tohru; Yamabe, Tokio; Tanaka, Kazuyoshi

    1997-07-01

    We have determined the ground states of the charge-transfer (CT) complexes in which the energy levels of the highest occupied molecular orbital (HOMO) of donors and the lowest unoccupied MO (LUMO) of acceptors are closely located, and examined some fullerene complexes consisting of C60, C70, tetrakis(dimethylamino)ethylene (TDAE), and 1,1',3,3'-tetramethyl-Δ2,2'-bi(imidazolidine) (TMBI). The observed magnetic properties of TDAE-C60, TMBI-C60, and TDAE-C70 can be accounted for by employing realistic parameters. The effective Hamiltonian including up to the fourth-order perturbation has also been derived in the fourfold degenerate model space. The effective Hamiltonian can plausibly reproduce the magnetic phase diagram obtained by the variational treatment of TDAE-C60. It has been shown that the third and the fourth processes contribute to the stabilization of the antiferromagnetic state.

  15. Enhanced charge transfer by phenyl groups at a rubrene/C{sub 60} interface

    Energy Technology Data Exchange (ETDEWEB)

    Mou Weiwei; Hattori, Shinnosuke; Nomura, Ken-ichi; Nakano, Aiichiro [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Ohmura, Satoshi; Shimojo, Fuyuki [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

    2012-05-14

    Exciton dynamics at an interface between an electron donor, rubrene, and a C{sub 60} acceptor is studied by nonadiabatic quantum molecular dynamics simulation. Simulation results reveal an essential role of the phenyl groups in rubrene in increasing the charge-transfer rate by an order-of-magnitude. The atomistic mechanism of the enhanced charge transfer is found to be the amplification of aromatic breathing modes by the phenyl groups, which causes large fluctuations of electronic excitation energies. These findings provide insight into molecular structure design for efficient solar cells, while explaining recent experimental observations.

  16. Enhanced charge transfer by phenyl groups at a rubrene/C60 interface.

    Science.gov (United States)

    Mou, Weiwei; Ohmura, Satoshi; Hattori, Shinnosuke; Nomura, Ken-ichi; Shimojo, Fuyuki; Nakano, Aiichiro

    2012-05-14

    Exciton dynamics at an interface between an electron donor, rubrene, and a C(60) acceptor is studied by nonadiabatic quantum molecular dynamics simulation. Simulation results reveal an essential role of the phenyl groups in rubrene in increasing the charge-transfer rate by an order-of-magnitude. The atomistic mechanism of the enhanced charge transfer is found to be the amplification of aromatic breathing modes by the phenyl groups, which causes large fluctuations of electronic excitation energies. These findings provide insight into molecular structure design for efficient solar cells, while explaining recent experimental observations. PMID:22583307

  17. Electric field induced charge transfer through single and double-stranded DNA polymer molecules

    OpenAIRE

    Ramos, Marta M. D.; Correia, Helena M. G.

    2011-01-01

    The charge transfer through single-stranded and double-stranded DNA polymer molecules has been the subject of numerous experimental and theoretical studies concerning their applications in molecular electronics. However, the underlying mechanisms responsible for their different electrical conductivity observed in the experiments are poorly understood. Here we use a self-consistent quantum molecular dynamics method to study the effect of an applied electric field along the molecular axis on ch...

  18. Charge transfer along DNA molecule within Peyrard-Bishop-Holstein model

    Science.gov (United States)

    Edirisinghe, Neranjan; Apalkov, Vadym

    2010-03-01

    Charge transport through DNA molecule is important in many areas ranging from DNA damage repair to molecular nanowires. It is now widely accepted that a phonon mediated hopping of a charge carrier plays a major role in charge transport through DNA. In the present study we investigate system dynamics within Peyrard-Bishop-Holstein model for the charge transfer between donor and acceptor sites. We found that an escape time of a charge, trapped at the donor state of the DNA strand, is very sensitive to the initial value of H-bond stretching. This suggests importance of ensemble averaging. Moreover sharp phase transitions were observed for escape time in parameter space of transfer integrals and phonon-charge coupling constant.

  19. Charge Transfer and Catalysis at the Metal Support Interface

    Energy Technology Data Exchange (ETDEWEB)

    Baker, Lawrence Robert [Univ. of California, Berkeley, CA (United States)

    2012-07-31

    Kinetic, electronic, and spectroscopic characterization of model Pt–support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts. This dissertation builds on extensive existing knowledge of metal–support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge flow and presents solid-state devices and doped supports as novel methods for obtaining electronic control over catalytic reaction kinetics.

  20. On the Possibility of Superfast Charge Transfer in DNA

    OpenAIRE

    Lakhno, V. D.; Sultanov, V. B.

    2013-01-01

    Numerous experiments on charge transfer in DNA yield a contradictory picture of the transfer: on the one hand they suggest that it is a very slow process and the charge is almost completely localized on one Watson-Crick pair, but on the other hand they demonstrate that the charge can travel a very large distance. To explain this contradiction we propose that superfast charge transitions are possible between base pairs on individual DNA fragments resulting in the establishment of a quasi-equil...

  1. Probing charge transfer and hot carrier dynamics in organic solar cells with terahertz spectroscopy

    Science.gov (United States)

    Cunningham, Paul D.; Lane, Paul A.; Melinger, Joseph S.; Esenturk, Okan; Heilweil, Edwin J.

    2016-04-01

    Time-resolved terahertz spectroscopy (TRTS) was used to explore charge generation, transfer, and the role of hot carriers in organic solar cell materials. Two model molecular photovoltaic systems were investigated: with zinc phthalocyanine (ZnPc) or alpha-sexathiophene (α-6T) as the electron donors and buckminsterfullerene (C60) as the electron acceptor. TRTS provides charge carrier conductivity dynamics comprised of changes in both population and mobility. By using time-resolved optical spectroscopy in conjunction with TRTS, these two contributions can be disentangled. The sub-picosecond photo-induced conductivity decay dynamics of C60 were revealed to be caused by auto-ionization: the intrinsic process by which charge is generated in molecular solids. In donor-acceptor blends, the long-lived photo-induced conductivity is used for weight fraction optimization of the constituents. In nanoscale multilayer films, the photo-induced conductivity identifies optimal layer thicknesses. In films of ZnPc/C60, electron transfer from ZnPc yields hot charges that localize and become less mobile as they thermalize. Excitation of high-lying Franck Condon states in C60 followed by hole-transfer to ZnPc similarly produces hot charge carriers that self-localize; charge transfer clearly precedes carrier cooling. This picture is contrasted to charge transfer in α-6T/C60, where hole transfer takes place from a thermalized state and produces equilibrium carriers that do not show characteristic signs of cooling and self-localization. These results illustrate the value of terahertz spectroscopic methods for probing charge transfer reactions.

  2. Self-interaction and charge transfer in organic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Koerzdoerfer, Thomas

    2009-12-18

    This work concentrates on the problem of self-interaction, which is one of the most serious problems of commonly used approximative density functionals. As a major result of this work, it is demonstrated that self-interaction plays a decisive role for the performance of different approximative functionals in predicting accurate electronic properties of organic molecular semiconductors. In search for a solution to the self-interaction problem, a new concept for correcting commonly used density functionals for self-interaction is introduced and applied to a variety of systems, spanning small molecules, extended molecular chains, and organic molecular semiconductors. It is further shown that the performance of functionals that are not free from self-interaction can vary strongly for different systems and observables of interest, thus entailing the danger of misinterpretation of the results obtained from those functionals. The underlying reasons for the varying performance of commonly used density functionals are discussed thoroughly in this work. Finally, this thesis provides strategies that allow to analyze the reliability of commonly used approximations to the exchange-correlation functional for particular systems of interest. This cumulative dissertation is divided into three parts. Part I gives a short introduction into DFT and its time-dependent extension (TDDFT). Part II provides further insights into the self-interaction problem, presents a newly developed concept for the correction of self-interaction, gives an introduction into the publications, and discusses their basic results. Finally, the four publications on self-interaction and charge-transfer in extended molecular systems and organic molecular semiconductors are collected in Part III. (orig.)

  3. Charge transfer and emergent phenomena of oxide heterostructures

    Science.gov (United States)

    Chen, Hanghui

    Charge transfer is a common phenomenon at oxide interfaces. We use first-principles calculations to show that via heterostructuring of transition metal oxides, the electronegativity difference between two dissimilar transition metal ions can lead to high level of charge transfer and induce substantial redistribution of electrons and ions. Notable examples include i) enhancing correlation effects and inducing a metal-insulator transition; ii) tailoring magnetic structures and inducing interfacial ferromagnetism; iii) engineering orbital splitting and inducing a non-cuprate single-orbital Fermi surface. Utilizing charge transfer to induce emergent electronic/magnetic/orbital properties at oxide interfaces is a robust approach. Combining charge transfer with quantum confinement and expitaxial strain provides an appealing prospect of engineering electronic structure of artificial oxide heterostructures. This research was supported by National Science Foundation under Grant No. DMR-1120296.

  4. A Monte Carlo study of charge transfer in DNA

    OpenAIRE

    Jakobsson, Mattias; Stafström, Sven

    2008-01-01

    A model describing charge (hole) transport in DNA has been developed. The individual charge transfer steps in the transport process are described by Marcus theory modified to account for electron delocalization over adjacent identical nucleobases. Such a modification, as well as introducing a distance dependence in the reorganization energy, is necessary in order to reach an agreement with the observed transfer rates in well defined model systems to DNA. Using previously published results as ...

  5. SEMICONDUCTOR DEVICES: Simulation for signal charge transfer of charge coupled devices

    Science.gov (United States)

    Zujun, Wang; Yinong, Liu; Wei, Chen; Benqi, Tang; Zhigang, Xiao; Shaoyan, Huang; Minbo, Liu; Yong, Zhang

    2009-12-01

    Physical device models and numerical processing methods are presented to simulate a linear buried channel charge coupled devices (CCDs). The dynamic transfer process of CCD is carried out by a three-phase clock pulse driver. By using the semiconductor device simulation software MEDICI, dynamic transfer pictures of signal charges cells, electron concentration and electrostatic potential are presented. The key parameters of CCD such as charge transfer efficiency (CTE) and dark electrons are numerically simulated. The simulation results agree with the theoretic and experimental results.

  6. INTRAMOLECULAR CHARGE AND ENERGY TRANSFER IN MULTICHROMOPHORIC AROMATIC SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Edward C. Lim

    2008-09-09

    A concerted experimental and computational study of energy transfer in nucleic acid bases and charge transfer in dialkylaminobenzonitriles, and related electron donor-acceptor molecules, indicate that the ultrafast photoprocesses occur through three-state conical interactions involving an intermediate state of biradical character.

  7. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    The step from ab initio atomic and molecular properties to thermodynamic - or macroscopic - properties requires the combination of several theoretical tools. This dissertation presents constant temperature molecular dynamics with bond length constraints, a hybrid quantum mechanics...... to show general (or expected) properties. Properties such as in the physical and (semi-)chemical interface between classical and quantum systems and the effects of molecular bond length constraints on the temperature during simulations. As a second step the methodology is applied to the symmetric...... structure modes. This is for a large iridium-iridium dimer complex which shows a dramatic structural (and vibrational) change upon electronic excitation....

  8. Conducting charge-transfer salts based on neutral π-radicals

    NARCIS (Netherlands)

    Bryan, C.D.; Fleming, R.M.; Glarum, S.H.; Haddon, R.C.; Oakley, R.T.; Palstra, T.T.M.; Perel, A.S.; Schneemeyer, L.F.; Waszczak, J.V.; Cordes, A.W.

    1993-01-01

    Most molecular conductors rely on charge transfer to create carriers. For example, the ET salts are hole-doped whereas the C60 salts are electron-doped. Neutral radical species in which bands are formed by π-orbital overlap would be expected to have half-filled bands and thus to be conducting, but n

  9. Charge Transfer Dynamics from Photoexcited Semiconductor Quantum Dots

    Science.gov (United States)

    Zhu, Haiming; Yang, Ye; Wu, Kaifeng; Lian, Tianquan

    2016-05-01

    Understanding photoinduced charge transfer from nanomaterials is essential to the many applications of these materials. This review summarizes recent progress in understanding charge transfer from quantum dots (QDs), an ideal model system for investigating fundamental charge transfer properties of low-dimensional quantum-confined nanomaterials. We first discuss charge transfer from QDs to weakly coupled acceptors within the framework of Marcus nonadiabatic electron transfer (ET) theory, focusing on the dependence of ET rates on reorganization energy, electronic coupling, and driving force. Because of the strong electron-hole interaction, we show that ET from QDs should be described by the Auger-assisted ET model, which is significantly different from ET between molecules or from bulk semiconductor electrodes. For strongly quantum-confined QDs on semiconductor surfaces, the coupling can fall within the strong coupling limit, in which case the donor-acceptor interaction and ET properties can be described by the Newns-Anderson model of chemisorption. We also briefly discuss recent progress in controlling charge transfer properties in quantum-confined nanoheterostructures through wavefunction engineering and multiple exciton dissociation. Finally, we identify a few key areas for further research.

  10. Energy Transfer in molecular devices

    CERN Document Server

    Caraglio, M

    2014-01-01

    Protein machines often exhibit long range interplay between different sites in order to achieve their biological tasks. We investigate and characterize the non--linear energy localization and the basic mechanisms of energy transfer in protein devices. By studying two different model protein machines, with different biological functions, we show that genuinely non--linear phenomena are responsible for energy transport between the different machine sites involved in the biological functions. The energy transfer turns out to be extremely efficient from an energetic point of view: by changing the energy initially provided to the model device, we identify a well defined range of energies where the time for the energy transport to occur is minimal and the amount of transferred energy is maximum. Furthermore, by introducing an implicit solvent, we show that the energy is localized on the internal residues of the protein structure, thus minimizing the dissipation.

  11. Mean-Field Theory of Intra-Molecular Charge Ordering in (TTM--TTP)I3

    Science.gov (United States)

    Omori, Yukiko; Tsuchiizu, Masahisa; Suzumura, Yoshikazu

    2011-02-01

    We examine an intra-molecular charge-ordered (ICO) state in the multi-orbital molecular compound (TTM--TTP)I3 on the basis of an effective two-orbital model derived from ab initio calculations. Representing the model in terms of the fragment molecular-orbital (MO) picture, the ICO state is described as the charge disproportionation on the left and right fragment MOs. By applying the mean-field theory, the phase diagram of the ground state is obtained as a function of the inter-molecular Coulomb repulsion and the intra-molecular transfer integral. The ICO state is stabilized by large inter-fragment Coulomb interactions, and the small intra-molecular transfer energy between two fragment MOs. Furthermore, we examine the finite-temperature phase diagram. The relevance to the experimental observations in the molecular compound of (TTM--TTP)I3 is also discussed.

  12. On the Possibility of Superfast Charge Transfer in DNA

    CERN Document Server

    Lakhno, V D

    2013-01-01

    Numerous experiments on charge transfer in DNA yield a contradictory picture of the transfer: on the one hand they suggest that it is a very slow process and the charge is almost completely localized on one Watson-Crick pair, but on the other hand they demonstrate that the charge can travel a very large distance. To explain this contradiction we propose that superfast charge transitions are possible between base pairs on individual DNA fragments resulting in the establishment of a quasi-equilibrium charge distribution during the time less than that of charge solvation. In other words, we hypothesize these states irrespective of the nature of a mechanism responsible for their establishment, whether it be a hopping mechanism, or a band mechanism, or superexchange, or polaron transport, etc., leaving aside the debates of which one is more advantageous. We discuss qualitative differences between the charge transfer in a dry DNA and that in a solution. In a solution, of great importance is the charge solvation whi...

  13. Dynamics of Charge Transfer in Ordered and Chaotic Nucleotide Sequences

    CERN Document Server

    Fialko, N S

    2013-01-01

    Charge transfer is considered in systems composed of a donor, an acceptor and bridge sites of (AT) nucleotide pairs. For a bridge consisting of 180 (AT) pairs, three cases are dealt with: a uniform case, when all the nucleotides in each strand are identical; an ordered case, when nucleotides in each DNA strand are arranged in an orderly fashion; a chaotic case, when (AT) and (TA) pairs are arranged randomly. It is shown that in all the cases a charge transfer from a donor to an acceptor can take place. All other factors being equal, the transfer is the most efficient in the uniform case, the ordered and chaotic cases are less and the least efficient, accordingly. The results obtained are in agreement with experimental data on long-range charge transfer in DNA.

  14. A molecularly based theory for electron transfer reorganization energy

    International Nuclear Information System (INIS)

    Using field-theoretic techniques, we develop a molecularly based dipolar self-consistent-field theory (DSCFT) for charge solvation in pure solvents under equilibrium and nonequilibrium conditions and apply it to the reorganization energy of electron transfer reactions. The DSCFT uses a set of molecular parameters, such as the solvent molecule’s permanent dipole moment and polarizability, thus avoiding approximations that are inherent in treating the solvent as a linear dielectric medium. A simple, analytical expression for the free energy is obtained in terms of the equilibrium and nonequilibrium electrostatic potential profiles and electric susceptibilities, which are obtained by solving a set of self-consistent equations. With no adjustable parameters, the DSCFT predicts activation energies and reorganization energies in good agreement with previous experiments and calculations for the electron transfer between metallic ions. Because the DSCFT is able to describe the properties of the solvent in the immediate vicinity of the charges, it is unnecessary to distinguish between the inner-sphere and outer-sphere solvent molecules in the calculation of the reorganization energy as in previous work. Furthermore, examining the nonequilibrium free energy surfaces of electron transfer, we find that the nonequilibrium free energy is well approximated by a double parabola for self-exchange reactions, but the curvature of the nonequilibrium free energy surface depends on the charges of the electron-transferring species, contrary to the prediction by the linear dielectric theory

  15. A molecularly based theory for electron transfer reorganization energy

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, Bilin; Wang, Zhen-Gang, E-mail: zgw@cheme.caltech.edu [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States)

    2015-12-14

    Using field-theoretic techniques, we develop a molecularly based dipolar self-consistent-field theory (DSCFT) for charge solvation in pure solvents under equilibrium and nonequilibrium conditions and apply it to the reorganization energy of electron transfer reactions. The DSCFT uses a set of molecular parameters, such as the solvent molecule’s permanent dipole moment and polarizability, thus avoiding approximations that are inherent in treating the solvent as a linear dielectric medium. A simple, analytical expression for the free energy is obtained in terms of the equilibrium and nonequilibrium electrostatic potential profiles and electric susceptibilities, which are obtained by solving a set of self-consistent equations. With no adjustable parameters, the DSCFT predicts activation energies and reorganization energies in good agreement with previous experiments and calculations for the electron transfer between metallic ions. Because the DSCFT is able to describe the properties of the solvent in the immediate vicinity of the charges, it is unnecessary to distinguish between the inner-sphere and outer-sphere solvent molecules in the calculation of the reorganization energy as in previous work. Furthermore, examining the nonequilibrium free energy surfaces of electron transfer, we find that the nonequilibrium free energy is well approximated by a double parabola for self-exchange reactions, but the curvature of the nonequilibrium free energy surface depends on the charges of the electron-transferring species, contrary to the prediction by the linear dielectric theory.

  16. Light-Induced Charge Separation and Transfer in Bacteriorhodopsin

    Institute of Scientific and Technical Information of China (English)

    HUANG Yu-Hua; LI Qing-Guo; ZHAO You-Yuan; ZHANG Zhong-Bin; OU-YANG Xiao-Ping; GONG Qin-Gan; CHEN Ling-Bing; LI Fu-Ming; LIU Jian; DING Jian-Dong

    2000-01-01

    The photo-voltage signals in bacteriorhodopsin(bR) excited by 1064nm pulse laser are different from those by 532 or 355 nm. It shows that the positive and negative photoelectric signals are produced by the motion of the positive and negative charges, respectively, and more energy is needed for producing the positive charges than the negative. The mechanism of light-induced charge generation and charge transfer in bR was studied and analyzed by measuring the photoelectric signals with different impedance of measuring circuit and different pulse-width of 532 nm laser as pump light.

  17. Strongly Dichroic Organic Films via Controlled Assembly of Modular Aromatic Charge-Transfer Liquid Crystals.

    Science.gov (United States)

    Bé, Ariana Gray; Tran, Cheryl; Sechrist, Riley; Reczek, Joseph J

    2015-10-01

    The formation of highly anisotropic organic thin films based on the designed self-assembly of mixed-stack liquid crystals is reported. A series of alkoxyanthracene donors is combined in a modular fashion with a naphthalenediimide acceptor to generate new charge-transfer columnar liquid crystals. Materials characterization and molecular modeling provides insight into structure-function relationships in these organic materials that lead to the striking bulk dichroic properties of certain molecular assemblies. PMID:26375256

  18. Failures of TDDFT in describing the lowest intramolecular charge-transfer excitation in para-nitroaniline

    DEFF Research Database (Denmark)

    Eriksen, Janus J.; Sauer, Stephan P. A.; Mikkelsen, Kurt Valentin;

    2013-01-01

    We investigate the failure of Time{Dependent Density Functional Theory (TDDFT) with the CAM{B3LYP exchange{correlation (xc) functional coupled to the Polarizable Embedding (PE) scheme (PE-CAM-B3LYP) in reproducing the solvatochromic shift of the lowest intense charge{transfer excitation in para...... to benchmark results of TDDFT calculations with CAM-B3LYP for intramolecular charge{transfer excitations in molecular systems similar to pNA against higher{level ab initio wave function methods, like, e.g., CCSD, prior to their use. Using the calculated change in dipole moment upon excitation as a measure...

  19. Solvation-driven charge transfer and localization in metal complexes.

    Science.gov (United States)

    Rondi, Ariana; Rodriguez, Yuseff; Feurer, Thomas; Cannizzo, Andrea

    2015-05-19

    In any physicochemical process in liquids, the dynamical response of the solvent to the solutes out of equilibrium plays a crucial role in the rates and products: the solvent molecules react to the changes in volume and electron density of the solutes to minimize the free energy of the solution, thus modulating the activation barriers and stabilizing (or destabilizing) intermediate states. In charge transfer (CT) processes in polar solvents, the response of the solvent always assists the formation of charge separation states by stabilizing the energy of the localized charges. A deep understanding of the solvation mechanisms and time scales is therefore essential for a correct description of any photochemical process in dense phase and for designing molecular devices based on photosensitizers with CT excited states. In the last two decades, with the advent of ultrafast time-resolved spectroscopies, microscopic models describing the relevant case of polar solvation (where both the solvent and the solute molecules have a permanent electric dipole and the mutual interaction is mainly dipole-dipole) have dramatically progressed. Regardless of the details of each model, they all assume that the effect of the electrostatic fields of the solvent molecules on the internal electronic dynamics of the solute are perturbative and that the solvent-solute coupling is mainly an electrostatic interaction between the constant permanent dipoles of the solute and the solvent molecules. This well-established picture has proven to quantitatively rationalize spectroscopic effects of environmental and electric dynamics (time-resolved Stokes shifts, inhomogeneous broadening, etc.). However, recent computational and experimental studies, including ours, have shown that further improvement is required. Indeed, in the last years we investigated several molecular complexes exhibiting photoexcited CT states, and we found that the current description of the formation and stabilization of CT

  20. Charge transfer in the cold Yb$^+$ + Rb collisions

    CERN Document Server

    Sayfutyarova, Elvira R; Yakovleva, Svetlana A; Belyaev, Andrey K

    2013-01-01

    Charge-transfer cold Yb$^+$ + Rb collision dynamics is investigated theoretically using high-level {\\it ab initio} potential energy curves, dipole moment functions and nonadiabatic coupling matrix elements. Within the scalar-relativistic approximation, the radiative transitions from the entrance $A^1\\Sigma^+$ to the ground $X^1\\Sigma^+$ state are found to be the only efficient charge-transfer pathway. The spin-orbit coupling does not open other efficient pathways, but alters the potential energy curves and the transition dipole moment for the $A-X$ pair of states. The radiative, as well as the nonradiative, charge-transfer cross sections calculated within the $10^{-3}-10$ cm$^{-1}$ collision energy range exhibit all features of the Langevin ion-atom collision regime, including a rich structure associated with centrifugal barrier tunneling (orbiting) resonances. Theoretical rate coefficients for two Yb isotopes agree well with those measured by immersing Yb$^+$ ion in an ultracold Rb ensemble in a hybrid trap....

  1. Ga Nanoparticle/Graphene Platforms: Plasmonic and Charge Transfer Interactions

    Science.gov (United States)

    Yi, Congwen; Kim, Tong-Ho; Yang, Yang; Losurdo, Maria; Brown, April S.

    2013-03-01

    Metal nanoparticle (NP) - graphene multifunctional platforms are of great interest for numerous applications, such as sensing and catalysis, and for fundamental studies on charge transfer and light-matter interactions. To understand platform-photon interactions, it is important to articulate the coupling of photon-based excitations, such as the interaction between plasmons in each of the material components, as well as their charge-based interactions dependent upon the energy alignment at the metal/graphene interface. Herein, we use liquid metal Ga nanoparticles, which can be deposited at 300K on graphene, to explore the surface-enhanced Raman spectroscopy modulation induced by the NPs,. The localized charge transfer between Ga NPs and graphene are investigated, and enhancement of the graphene Raman modes is correlated with metal coverage the transfer of electrons from Ga to graphene creating local regions of enhanced electron concentration which modify the electron-phonon interaction in graphene.

  2. Multiple-charge transfer and trapping in DNA dimers

    Science.gov (United States)

    Tornow, Sabine; Bulla, Ralf; Anders, Frithjof B.; Zwicknagl, Gertrud

    2010-11-01

    We investigate the charge transfer characteristics of one and two excess charges in a DNA base-pair dimer using a model Hamiltonian approach. The electron part comprises diagonal and off-diagonal Coulomb matrix elements such a correlated hopping and the bond-bond interaction, which were recently calculated by Starikov [E. B. Starikov, Philos. Mag. Lett. 83, 699 (2003)10.1080/0950083031000151374] for different DNA dimers. The electronic degrees of freedom are coupled to an ohmic or a superohmic bath serving as dissipative environment. We employ the numerical renormalization group method in the nuclear tunneling regime and compare the results to Marcus theory for the thermal activation regime. For realistic parameters, the rate that at least one charge is transferred from the donor to the acceptor in the subspace of two excess electrons significantly exceeds the rate in the single charge sector. Moreover, the dynamics is strongly influenced by the Coulomb matrix elements. We find sequential and pair transfer as well as a regime where both charges remain self-trapped. The transfer rate reaches its maximum when the difference of the on-site and intersite Coulomb matrix element is equal to the reorganization energy which is the case in a guanine/cytosine (GC)-dimer. Charge transfer is completely suppressed for two excess electrons in adenine/thymine (AT)-dimer in an ohmic bath and replaced by damped coherent electron-pair oscillations in a superohmic bath. A finite bond-bond interaction W alters the transfer rate: it increases as function of W when the effective Coulomb repulsion exceeds the reorganization energy (inverted regime) and decreases for smaller Coulomb repulsion.

  3. PHOTOINDUCED CHARGE TRANSFER POLYMERIZATION OF STYRENE INITIATED BY ELECTRON ACCEPTOR

    Institute of Scientific and Technical Information of China (English)

    CAO Weixiao; ZHANG Peng; FENG Xinde

    1995-01-01

    Photoinduced charge transfer polymerization of styrene(St) with electron acceptor as initiator was investigated. In case of fumaronitrile (FN) or maleic anhydride (MA) as initiator the polymerization takes place regularly, whereas the tetrachloro-1, 4-benzenequinone (TCQ), 2, 3-dichloro-5, 6-dicyano-1, 4-benzenequinone (DDQ) . or tetracyano ethylene (TCNE) as initiator the polymerization proceeds reluctantly only after the photoaddition reaction. A mechanism was proposed that free radicals would be formed following the charge and proton transfer in the exciplex formed between St and electron acceptors.

  4. Bioexcimers as Precursors of Charge Transfer and Reactivity in Photobiology

    Science.gov (United States)

    Serrano-Andrés, Luis; Merchán, Manuela; Roca-Sanjuán, Daniel; Olaso-González, Gloria; Rubio, Mercedes

    2007-11-01

    Accurate CASPT2//CASSCF calculations show that π-stacked interactions in different biochromophores such as DNA nucleobases or porphyrin-quinone pairs yield excimer-like situations which behave as precursors of processes like charge transfer or photoreactivity. Examples are the transfer of charge between a reduced pheophytin and an accepting quinone molecule, process that trigger the sequence of electron transfer phenomena in photosynthetic photosystem II, the electron transfer between adjacent DNA nucleobases in a strand of oligonucleotides, and the photodimerization taking place in cytosine pairs leading to cyclobutanecytosine mutants. These processes take place through nonadiabatic photochemical mechanisms whose evolution is determined by the presence and accessibility of conical intersections and other surface crossings between different electronic states.

  5. [Dynamics of charge transfer along an oligonucleotide at finite temperature].

    Science.gov (United States)

    Lakhno, V D; Fialko, N S

    2004-01-01

    The quantum-statistical approach was used to describe the charge transfer in nucleotide sequences. The results of numerical modeling for hole transfer in the GTTGGG sequence with background temperature noise are given. It was shown that, since guanine has an oxidation potential lower than thymine, the hole created at the G donor in this sequence passes through the thymine barrier into the guanine triplet (acceptor) at a time of approximately 10 ps at a temperature of 37 degrees C.

  6. Enhancing SERS by Means of Supramolecular Charge Transfer

    Science.gov (United States)

    Wong, Eric; Flood, Amar; Morales, Alfredo

    2009-01-01

    In a proposed method of sensing small quantities of molecules of interest, surface enhanced Raman scattering (SERS) spectroscopy would be further enhanced by means of intermolecular or supramolecular charge transfer. There is a very large potential market for sensors based on this method for rapid detection of chemical and biological hazards. In SERS, the Raman signals (vibrational spectra) of target molecules become enhanced by factors of the order of 108 when those molecules are in the vicinities of nanostructured substrate surfaces that have been engineered to have plasmon resonances that enhance local electric fields. SERS, as reported in several prior NASA Tech Briefs articles and elsewhere, has remained a research tool and has not yet been developed into a practical technique for sensing of target molecules: this is because the short range (5 to 20 nm) of the field enhancement necessitates engineering of receptor molecules to attract target molecules to the nanostructured substrate surfaces and to enable reliable identification of the target molecules in the presence of interferants. Intermolecular charge-transfer complexes have been used in fluorescence-, photoluminescence-, and electrochemistry-based techniques for sensing target molecules, but, until now, have not been considered for use in SERS-based sensing. The basic idea of the proposed method is to engineer receptor molecules that would be attached to nanostructured SERS substrates and that would interact with the target molecules to form receptor-target supramolecular charge-transfer complexes wherein the charge transfer could be photoexcited.

  7. Charge transfer devices. Citations from the NTIS data base

    Science.gov (United States)

    Reed, W. E.

    1980-04-01

    The technology, design, fabrication, and applications of charge transfer devices are presented in the cited research reports. Applications include imaging, signal processing, detectors, filters, amplifiers, and memory devices. This updated bibliography contains 107 abstracts, all of which are new entries to the previous edition.

  8. CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Khalil, Munira

    2014-06-27

    The goal of this research program was to measure coupled electronic and nuclear motions during photoinduced charge transfer processes in transition metal complexes by developing and using novel femtosecond spectroscopies. The scientific highlights and the resulting scientific publications from the DOE supported work are outlined in the technical report.

  9. Measurements of Charge Transfer Efficiency in a Proton-irradiated Swept Charge Device

    CERN Document Server

    YuSa, Wang; XiaoYan, Liu; WeiWei, Cui; YuPeng, Xu; ChengKui, Li; MaoShun, Li; DaWei, Han; TianXiang, Chen; Jia, Huo; Juan, Wang; Wei, Li; Wei, Hu; Yi, Zhang; Bo, Lu; GuoHe, Yin; Yue, Zhu; ZiLiang, Zhang

    2013-01-01

    Charge Coupled Devices (CCDs) have been successfully used in several low energy X-ray astronomical satellite over the past two decades. Their high energy resolution and high spatial resolution make them an perfect tool for low energy astronomy, such as formation of galaxy clusters and environment of black holes. The Low Energy X-ray Telescope (LE) group is developing Swept Charge Device (SCD) for the Hard X-ray Modulation Telescope (HXMT) satellite. SCD is a special low energy X-ray CCD, which could be read out a thousand times faster than traditional CCDs, simultaneously keeping excellent energy resolution. A test method for measuring the charge transfer efficiency (CTE) of a prototype SCD has been set up. Studies of the charge transfer inefficiency (CTI) have been performed at a temperature range of operation, with a proton-irradiated SCD.

  10. A tetrastable naphthalenediimide: anion induced charge transfer, single and double electron transfer for combinational logic gates.

    Science.gov (United States)

    Ajayakumar, M R; Hundal, Geeta; Mukhopadhyay, Pritam

    2013-09-11

    Herein we demonstrate the formation of the first tetrastable naphthalenediimide (NDI, 1a) molecule having multiple distinctly readable outputs. Differential response of 1a to fluoride anions induces intramolecular charge transfer (ICT), single/double electron transfer (SET/DET) leading to a set of combinational logic gates for the first time with a NDI moiety. PMID:23752683

  11. Conformationally Gated Charge Transfer in DNA Three-Way Junctions.

    Science.gov (United States)

    Zhang, Yuqi; Young, Ryan M; Thazhathveetil, Arun K; Singh, Arunoday P N; Liu, Chaoren; Berlin, Yuri A; Grozema, Ferdinand C; Lewis, Frederick D; Ratner, Mark A; Renaud, Nicolas; Siriwong, Khatcharin; Voityuk, Alexander A; Wasielewski, Michael R; Beratan, David N

    2015-07-01

    Molecular structures that direct charge transport in two or three dimensions possess some of the essential functionality of electrical switches and gates. We use theory, modeling, and simulation to explore the conformational dynamics of DNA three-way junctions (TWJs) that may control the flow of charge through these structures. Molecular dynamics simulations and quantum calculations indicate that DNA TWJs undergo dynamic interconversion among "well stacked" conformations on the time scale of nanoseconds, a feature that makes the junctions very different from linear DNA duplexes. The studies further indicate that this conformational gating would control charge flow through these TWJs, distinguishing them from conventional (larger size scale) gated devices. Simulations also find that structures with polyethylene glycol linking groups ("extenders") lock conformations that favor CT for 25 ns or more. The simulations explain the kinetics observed experimentally in TWJs and rationalize their transport properties compared with double-stranded DNA. PMID:26266714

  12. Resonant charge transfer in slow Li+-Li(2s) collisions

    Institute of Scientific and Technical Information of China (English)

    李铁成; 刘春华; 屈一至; 刘玲; 吴勇; 王建国

    2015-01-01

    The resonant charge transfer process for Li+–Li(2s) collision is investigated by the quantum-mechanical molecular orbital close-coupling (QMOCC) method and the two-center atomic-orbital close-coupling (AOCC) method in an energy range of 1.0 eV/u–104 eV/u. Accurate molecular structure data and charge transfer cross sections are given. Both the all-electron model (AEM) and one-electron model (OEM) are used in the QMOCC calculations, and the discrepancies between the two models are analyzed. The OEM calculation can also give a reliable prediction of the cross sections for energies below 1 keV/u.

  13. Charge transfer mobility of naphthodithiophenediimide derivative: Normal-mode and bond length relaxation analysis

    Science.gov (United States)

    Liu, Xiaoyan; Liu, Yujuan; Zheng, Yujun

    2016-02-01

    In this letter, the charge transfer mobility of naphthalenediimide (NDTI) derivative is investigated. By employing the normal-mode analysis and bond length relaxation analysis, the influences of chemical elements on reorganization energies and intermolecular electronic couplings are investigated in NDTI derivative. The results show that the introduction of atom O would decrease reorganization energy in hole-hopping process and increase electronic coupling. This analysis encourages the molecular and material design in organic semiconductors.

  14. Synthetic system mimicking the energy transfer and charge separation of natural photosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Gust, D.; Moore, T.A.

    1985-05-01

    A synthetic molecular triad consisting of a porphyrin P linked to both a quinone Q and a carotenoid polyene C has been prepared as a mimic of natural photosynthesis for solar energy conversion purposes. Laser flash excitation of the porphyrin moiety yields a charge-separated state Csup(+.)-P-Qsup(-.) within 100 ps with a quantum yield of more than 0.25. This charge-separated state has a lifetime on the microsecond time scale in suitable solvents. The triad also models photosynthetic antenna function and photoprotection from singlet oxygen damge. The successful biomimicry of photosynthetic charge separation is in part the result of multistep electron transfers which rapidly separate the charges and leave the system at high potential, but with a considerable barrier to recombination.

  15. Nonadiabatic couplings and charge transfer study in H + CS+ collision using time-dependent quantum dynamics

    Science.gov (United States)

    Kaur, Rajwant; Dhilip Kumar, T. J.

    2015-11-01

    Experiments have reported the high stability of HCS+ ion and inhibit to decompose over the range of collision energies. In this study, the various energy transfer channels of atomic H collision with CS+ molecular ion has been performed by ab initio computations at the multireference configuration interaction/aug-cc-pVQZ level of theory. The ground and several low-lying excited electronic state potential energy surfaces in three different molecular orientations, namely, two collinear configurations with, (1) H approaching the S atom (γ = 0°), (2) H approaching the C atom (γ = 180°) and one perpendicular configuration, (3) H approaching the centre of mass of CS (γ = 90°) with the diatom fixed at the equilibrium bond length, have been obtained. Nonadiabatic effects with Landau-Zener coupling leading to avoided crossings are observed between the ground- and the first-excited states in γ = 90° orientation, and also between the first- and second-excited states in γ = 180° orientation. Quantum dynamics have been performed to study the charge transfer using time-dependent wave packet method on the diabatic potential energy surfaces. The probability of charge transfer is found to be highest with 42% in γ = 180°. The high charge transfer probability result in the formation of H+ + CS channel which ascertains the high stability of HCS+ ion.

  16. Charge Transfer Channels in Formation of Exciplex in Polymer Blends

    Institute of Scientific and Technical Information of China (English)

    DOU Fei; ZHANG Xin-Ping

    2011-01-01

    The strong dependence of photoluminescence of charge transfer excited states or exciplex in a blend film of poly(9,9'-dioctylBuorene-co-benzothiadiazole) (F8BT) and poly(9,9'-dioctyl6uorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-l,4- phenylenediamine) (PFB) on the excitation wavelengths and morphology is investigated. The experimental results reveal that electron transfer in the LUMOs from PFB to F8BT is more efficient than hole transfer in the HOMOs from PFB to F8BT for the formation of exciplex at the interfacial junctions between these two types of molecules in the blend Sim. Furthermore, energy transfer from the blue-emitting PFB to the green-emitting F8BT at the interfaces introduces an additional two-step channel and thus enhances the formation of an exciplex. This is important for understanding of charge generation and separation in organic bulk heterojunctions and for design of optoelectronic devices.%@@ The strong dependence of photoluminescence of charge transfer excited states or exciplex in a blend film of poly(9,9'-dioctylfluorene-co-benzothiadiazole)(F8BT)and poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine)(PFB)on the excitation wavelengths and morphology is investigated.The experimental results reveal that electron transfer in the LUMOs from PFB to F8BT is more efficient than hole transfer in the HOMOs from PFB to F8BT for the formation of exciplex at the interfacial junctions between these two types of molecules in the blend film.Furthermore,energy transfer from the blue-emitting PFB to the green-emitting F8BT at the interfaces introduces an additional two-step channel and thus enhances the formation of an exciplex.This is important for understanding of charge generation and separation in organic bulk heterojunctions and for design of optoelectronic devices.

  17. Negative ion-uranium hexafluoride charge transfer reactions

    Science.gov (United States)

    Streit, Gerald E.; Newton, T. W.

    1980-10-01

    The flowing afterglow technique has been used to study the process of charge transfer from selected negative ions (F-, Cl-, Br-, I-, SF6-) to UF6. The sole ionic product in all cases was observed to be UF6-. Data analysis was complicated by an unexpected coupling of chemical and diffusive ion loss processes when UF6- product ions were present. The rate coefficients for the charge transfer processes are (k in 10-9 cm3 molecule-1 s-1) F-, 1.3; Cl-, 1.1; Br-, 0.93; I-, 0.77; and SF6-, 0.69. The rate constants agree quite well with the classical Langevin predictions.

  18. Charge transfer in conjugated oligomers encapsulated into carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Almadori, Y.; Alvarez, L.; Michel, T.; Le Parc, R.; Bantignies, J.L.; Hermet, P.; Sauvajol, J.L. [Laboratoire Charles Coulomb UMR 5521, Universite Montpellier 2, 34095 Montpellier (France); Laboratoire Charles Coulomb UMR 5521, CNRS, 34095 Montpellier (France); Arenal, R. [Laboratoire d' Etude des Microstructures, CNRS-ONERA, 92322 Chatillon (France); Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, U. Zaragoza, 50018 Zaragoza (Spain); Babaa, R. [Laboratoire de Chimie des Surfaces et Interfaces, CEA, IRAMIS, SPCSI, 91191 Gif-sur-Yvette Cedex (France); Chemical Engineering Department, University of Technology PETRONAS, UTP, Ipoh-Perak (Malaysia); Jouselme, B.; Palacin, S. [Laboratoire de Chimie des Surfaces et Interfaces, CEA, IRAMIS, SPCSI, 91191 Gif-sur-Yvette Cedex (France)

    2011-11-15

    This study deals with a hybrid system consisting in quaterthiophene derivative encapsulated inside single-walled and multi-walled carbon nanotubes. Investigations of the encapsulation step are performed by transmission electron microscopy. Raman spectroscopy data point out different behaviors depending on the laser excitation energy with respect to the optical absorption of quaterthiophene. At low excitation energy (far from the oligomer resonance window) there is no significant modification of the Raman spectra before and after encapsulation. By contrast, at high excitation energy (close to the oligomer resonance window), Raman spectra exhibit a G-band shift together with an important RBM intensity loss, suggesting a significant charge transfer between the inserted molecule and the host nanotubes. Those results suggest a photo induced process leading to a significant charge transfer. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Molecular Models for Conductance in Junctions and Electrochemical Electron Transfer

    Science.gov (United States)

    Mazinani, Shobeir Khezr Seddigh

    This thesis develops molecular models for electron transport in molecular junctions and intra-molecular electron transfer. The goal is to identify molecular descriptors that afford a substantial simplification of these electronic processes. First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured conductance of a tunneling junction decreases as a function of the calculated molecular polarizability for several systems, a result consistent with the idea of a molecule as a polarizable dielectric. A model based on a macroscopic extension of the Clausius-Mossotti equation to the molecular domain and Simmon's tunneling model is developed to explain this correlation. Despite the simplicity of the theory, it paves the way for further experimental, conceptual and theoretical developments in the use of molecular descriptors to describe both conductance and electron transfer. Second, the conductance of several biologically relevant, weakly bonded, hydrogen-bonded systems is systematically investigated. While there is no correlation between hydrogen bond strength and conductance, the results indicate a relation between the conductance and atomic polarizability of the hydrogen bond acceptor atom. The relevance of these results to electron transfer in biological systems is discussed. Hydrogen production and oxidation using catalysts inspired by hydrogenases provides a more sustainable alternative to the use of precious metals. To understand electrochemical and spectroscopic properties of a collection of Fe and Ni mimics of hydrogenases, high-level density functional theory calculations are described. The results, based on a detailed analysis of the energies, charges and molecular orbitals of these metal complexes, indicate the importance of geometric constraints imposed by the ligand on molecular properties such as acidity and electrocatalytic activity. Based on model calculations of

  20. Charge transfer in energetic Li^2+ - H collisions

    Science.gov (United States)

    Mancev, I.

    2008-07-01

    The total cross sections for charge transfer in Li^2+ - H collisions have been calculated, using the four-body first Born approximation with correct boundary conditions (CB1-4B) and four-body continuum distorted wave method (CDW-4B) in the energy range 10 - 5000 keV/amu. Present results call for additional experimental data at higher impact energies than presently available.

  1. Fingerprint of fractional charge transfer at metal/organic interface

    OpenAIRE

    Savu, Sabine-A.; Biddau, Giulio; Pardini, Lorenzo; Bula, Rafael; Bettinger, Holger F; Draxl, Claudia; Chassé, Thomas; Casu, M. Benedetta

    2015-01-01

    Although physisorption is a widely occurring mechanism of bonding at the organic/metal interface, contradictory interpretations of this phenomenon are often reported. Photoemission and X-ray absorption spectroscopy investigations of nanorods of a substituted pentacene, 2,3,9,10-tetrafluoropentacene, deposited on gold single crystals reveal to be fundamental to identify the bonding mechanisms. We find fingerprints of a fractional charge transfer from the clean metal substrate to the physisorbe...

  2. Transfer of momentum, mass and charge in heavy ion collisions

    International Nuclear Information System (INIS)

    A model for the first two phases of heavy ion collisions based on the transport of single nucleons through the window between the two scattering nuclei is described in some detail. It is pointed out that the model can account simultaneously for a large portion of the energy transfer from relative to intrinsic motion and for the observed variances in mass and charge numbers for reaction times up to the order of 10-21 s. (P.L.)

  3. Rovibrationally selected ion-molecule collision study using the molecular beam vacuum ultraviolet laser pulsed field ionization-photoion method: charge transfer reaction of N2(+)(X 2Σg+; v+ = 0-2; N+ = 0-9) + Ar.

    Science.gov (United States)

    Chang, Yih Chung; Xu, Yuntao; Lu, Zhou; Xu, Hong; Ng, C Y

    2012-09-14

    We have developed an ion-molecule reaction apparatus for state-selected absolute total cross section measurements by implementing a high-resolution molecular beam vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) ion source to a double-quadrupole double-octopole ion-guide mass spectrometer. Using the total cross section measurement of the state-selected N(2)(+)(v(+), N(+)) + Ar charge transfer (CT) reaction as an example, we describe in detail the design of the VUV laser PFI-PI ion source used, which has made possible the preparation of reactant N(2)(+)(X (2)Σ(g)(+), v(+) = 0-2, N(+) = 0-9) PFI-PIs with high quantum state purity, high intensity, and high kinetic energy resolution. The PFI-PIs and prompt ions produced in the ion source are shown to have different kinetic energies, allowing the clean rejection of prompt ions from the PFI-PI beam by applying a retarding potential barrier upstream of the PFI-PI source. By optimizing the width and amplitude of the pulsed electric fields employed to the VUV-PFI-PI source, we show that the reactant N(2)(+) PFI-PI beam can be formed with a laboratory kinetic energy resolution of ΔE(lab) = ± 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (E(cm)'s) down to thermal energies. Absolute total rovibrationally selected cross sections σ(v(+) = 0-2, N(+) = 0-9) for the N(2)(+)(X (2)Σ(g)(+); v(+) = 0-2, N(+) = 0-9) + Ar CT reaction have been measured in the E(cm) range of 0.04-10.0 eV, revealing strong vibrational enhancements and E(cm)-dependencies of σ(v(+) = 0-2, N(+) = 0-9). The thermochemical threshold at E(cm) = 0.179 eV for the formation of Ar(+) from N(2)(+)(X; v(+) = 0, N(+)) + Ar was observed by the measured σ(v(+) = 0), confirming the narrow ΔE(cm) spread achieved in the present study. The σ(v(+) = 0-2; N(+)) values obtained here are compared with previous experimental and theoretical results. The theoretical predictions

  4. Rovibrationally selected ion-molecule collision study using the molecular beam vacuum ultraviolet laser pulsed field ionization-photoion method: Charge transfer reaction of N2+(X 2Σg+; v+= 0–2; N+= 0–9) + Ar

    International Nuclear Information System (INIS)

    We have developed an ion-molecule reaction apparatus for state-selected absolute total cross section measurements by implementing a high-resolution molecular beam vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) ion source to a double-quadrupole double-octopole ion-guide mass spectrometer. Using the total cross section measurement of the state-selected N2+(v+, N+) + Ar charge transfer (CT) reaction as an example, we describe in detail the design of the VUV laser PFI-PI ion source used, which has made possible the preparation of reactant N2+(X 2Σg+, v+= 0–2, N+= 0–9) PFI-PIs with high quantum state purity, high intensity, and high kinetic energy resolution. The PFI-PIs and prompt ions produced in the ion source are shown to have different kinetic energies, allowing the clean rejection of prompt ions from the PFI-PI beam by applying a retarding potential barrier upstream of the PFI-PI source. By optimizing the width and amplitude of the pulsed electric fields employed to the VUV-PFI-PI source, we show that the reactant N2+ PFI-PI beam can be formed with a laboratory kinetic energy resolution of ΔElab=± 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (Ecm’s) down to thermal energies. Absolute total rovibrationally selected cross sections σ(v+= 0–2, N+= 0–9) for the N2+(X 2Σg+; v+= 0–2, N+= 0–9) + Ar CT reaction have been measured in the Ecm range of 0.04–10.0 eV, revealing strong vibrational enhancements and Ecm-dependencies of σ(v+= 0–2, N+= 0–9). The thermochemical threshold at Ecm= 0.179 eV for the formation of Ar+ from N2+(X; v+= 0, N+) + Ar was observed by the measured σ(v+= 0), confirming the narrow ΔEcm spread achieved in the present study. The σ(v+= 0–2; N+) values obtained here are compared with previous experimental and theoretical results. The theoretical predictions calculated based on the Landau-Zener-Stückelberg formulism are found to be

  5. Molecular dynamics simulation of a charged biological membrane

    NARCIS (Netherlands)

    López Cascales, J.J.; García de la Torre, J.; Marrink, S.J.; Berendsen, H.J.C.

    1996-01-01

    A molecular dynamics simulation of a membrane with net charge in its liquid-crystalline state was carried out. It was modeled by dipalmitoylphosphatidylserine lipids with net charge, sodium ions as counterions and water molecules. The behavior of this membrane differs from that was shown by other me

  6. New type of dual solid-state thermochromism: modulation of intramolecular charge transfer by intermolecular pi-pi interactions, kinetic trapping of the aci-nitro group, and reversible molecular locking.

    Science.gov (United States)

    Naumov, Pance; Lee, Sang Cheol; Ishizawa, Nobuo; Jeong, Young Gyu; Chung, Ihn Hee; Fukuzumi, Shunichi

    2009-10-22

    When heated above room temperature, some crystalline polymorphs of the 1,3-bis(hydroxyalkylamino)-4,6-dinitrobenzenes (BDBn, n = 2-5), bis(hydroxyalkyl) analogues of the intramolecular charge-transfer molecule 1,3-diamino-4,6-dinitrobenzene, exhibit "dual" thermochromism: gradual color change from yellow to orange at lower temperatures, and sharp color change from orange to red at higher temperatures. These two thermochromic changes are related to different solid-state processes. When allowed to cool to room temperature, the yellow color of the thermochromic molecules with different alkyl length (n) is recovered with unexpectedly different kinetics, the order of the respective rate constants ranging from 10(-7)-10(-6) s(-1) for BDB2 to about 0.1 s(-1) in the case of BDB3. The thermochromic mechanism and the reasons behind the different kinetics were clarified on the basis of detailed crystallographic characterization, kinetic thermoanalysis, and spectroscopic study of eight crystalline forms (seven polymorphs and one solvate). It was found that the polymorphism is due to the possibility of "locking" and "unlocking" of the alkyl arms by formation of a strong intramolecular hydrogen bond between the hydroxyl groups at their hydroxyl termini. The locking of BDB2, with shortest alkyl arms, is reversible and it can be controlled thermally; either of the two conformations can be obtained in the solid state by proper thermal treatment. By use of high temperature in situ single crystal X-ray diffraction analysis of BDB3, direct evidence was obtained that the gradual thermochromic change is related to increased distance and weakened pi-pi interactions between the stacked benzene rings: the lattice expands preferably in the stacking direction, causing enhanced oscillator strength and red shift of the absorption edge of the intramolecular charge transfer transition. The second, sharp thermochromic change had been assigned previously to solid-solid phase transition triggered

  7. New Type of Dual Solid-State Thermochromism: Modulation of Intramolecular Charge Transfer by Intermolecular π-π Interactions, Kinetic Trapping of the Aci-Nitro Group, and Reversible Molecular Locking

    Science.gov (United States)

    Naumov, Panče; Lee, Sang Cheol; Ishizawa, Nobuo; Jeong, Young Gyu; Chung, Ihn Hee; Fukuzumi, Shunichi

    2009-09-01

    When heated above room temperature, some crystalline polymorphs of the 1,3-bis(hydroxyalkylamino)-4,6-dinitrobenzenes (BDBn, n = 2-5), bis(hydroxyalkyl) analogues of the intramolecular charge-transfer molecule 1,3-diamino-4,6-dinitrobenzene, exhibit "dual" thermochromism: gradual color change from yellow to orange at lower temperatures, and sharp color change from orange to red at higher temperatures. These two thermochromic changes are related to different solid-state processes. When allowed to cool to room temperature, the yellow color of the thermochromic molecules with different alkyl length (n) is recovered with unexpectedly different kinetics, the order of the respective rate constants ranging from 10-7-10-6 s-1 for BDB2 to about 0.1 s-1 in the case of BDB3. The thermochromic mechanism and the reasons behind the different kinetics were clarified on the basis of detailed crystallographic characterization, kinetic thermoanalysis, and spectroscopic study of eight crystalline forms (seven polymorphs and one solvate). It was found that the polymorphism is due to the possibility of "locking" and "unlocking" of the alkyl arms by formation of a strong intramolecular hydrogen bond between the hydroxyl groups at their hydroxyl termini. The locking of BDB2, with shortest alkyl arms, is reversible and it can be controlled thermally; either of the two conformations can be obtained in the solid state by proper thermal treatment. By use of high temperature in situ single crystal X-ray diffraction analysis of BDB3, direct evidence was obtained that the gradual thermochromic change is related to increased distance and weakened π-π interactions between the stacked benzene rings: the lattice expands preferably in the stacking direction, causing enhanced oscillator strength and red shift of the absorption edge of the intramolecular charge transfer transition. The second, sharp thermochromic change had been assigned previously to solid-solid phase transition triggered by

  8. Quantum information transfer between topological and conventional charge qubits

    Science.gov (United States)

    Jun, Li; Yan, Zou

    2016-02-01

    We propose a scheme to realize coherent quantum information transfer between topological and conventional charge qubits. We first consider a hybrid system where a quantum dot (QD) is tunnel-coupled to a semiconductor Majorana-hosted nanowire (MNW) via using gated control as a switch, the information encoded in the superposition state of electron empty and occupied state can be transferred to each other through choosing the proper interaction time to make measurements. Then we consider another system including a double QDs and a pair of parallel MNWs, it is shown that the entanglement information transfer can be realized between the two kinds of systems. We also realize long distance quantum information transfer between two quantum dots separated by an MNW, by making use of the nonlocal fermionic level formed with the pared Majorana feimions (MFs) emerging at the two ends of the MNW. Furthermore, we analyze the teleportationlike electron transfer phenomenon predicted by Tewari et al. [Phys. Rev. Lett. 100, 027001 (2008)] in our considered system. Interestingly, we find that this phenomenon exactly corresponds to the case that the information encoded in one QD just returns back to its original place during the dynamical evolution of the combined system from the perspective of quantum state transfer. Project supported by the National Natural Science Foundation of China (Grant No. 11304031).

  9. Charge transfer along DNA dimers, trimers and polymers

    CERN Document Server

    Simserides, Constantinos

    2013-01-01

    The transfer of electrons and holes along DNA dimers, trimers and polymers is described at the base-pair level, using the relevant on-site energies of the base-pairs and the hopping parameters between successive base-pairs. The temporal and spatial evolution of carriers along a $N$ base-pair DNA segment is determined, solving a system of $N$ coupled differential equations. Useful physical quantities are calculated including the pure mean carrier transfer rate $k$, the inverse decay length $\\beta$ used for exponential fit ($k = k_0 \\textrm{exp}(-\\beta d)$) of the transfer rate as a function of the charge transfer distance $d = N \\times$ 3.4 {\\AA} and the exponent $\\eta$ used for a power law fit ($k = k_0' N^{-\\eta}$) of the transfer rate as function of the number of monomers $N$. Among others, the electron and hole transfer along the polymers poly(dG)-poly(dC), poly(dA)-poly(dT), GCGCGC..., ATATAT... is studied. $\\beta$ ($\\eta$) falls in the range $\\approx$ 0.2 - 2 {\\AA}$^{-1}$ (1.7 - 17), $k_0$ ($k_0'$) is us...

  10. Efficient charge generation by relaxed charge-transfer states at organic interfaces

    KAUST Repository

    Vandewal, Koen

    2013-11-17

    Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy. © 2014 Macmillan Publishers Limited.

  11. Nanocontact electrification: patterned surface charges affecting adhesion, transfer, and printing.

    Science.gov (United States)

    Cole, Jesse J; Barry, Chad R; Knuesel, Robert J; Wang, Xinyu; Jacobs, Heiko O

    2011-06-01

    Contact electrification creates an invisible mark, overlooked and often undetected by conventional surface spectroscopic measurements. It impacts our daily lives macroscopically during electrostatic discharge and is equally relevant on the nanoscale in areas such as soft lithography, transfer, and printing. This report describes a new conceptual approach to studying and utilizing contact electrification beyond prior surface force apparatus and point-contact implementations. Instead of a single point contact, our process studies nanocontact electrification that occurs between multiple nanocontacts of different sizes and shapes that can be formed using flexible materials, in particular, surface-functionalized poly(dimethylsiloxane) (PDMS) stamps and other common dielectrics (PMMA, SU-8, PS, PAA, and SiO(2)). Upon the formation of conformal contacts and forced delamination, contacted regions become charged, which is directly observed using Kelvin probe force microscopy revealing images of charge with sub-100-nm lateral resolution. The experiments reveal chemically driven interfacial proton exchange as the dominant charging mechanism for the materials that have been investigated so far. The recorded levels of uncompensated charges approach the theoretical limit that is set by the dielectric breakdown strength of the air gap that forms as the surfaces are delaminated. The macroscopic presence of the charges is recorded using force-distance curve measurements involving a balance and a micromanipulator to control the distance between the delaminated objects. Coulomb attraction between the delaminated surfaces reaches 150 N/m(2). At such a magnitude, the force finds many applications. We demonstrate the utility of printed charges in the fields of (i) nanoxerography and (ii) nanotransfer printing whereby the smallest objects are ∼10 nm in diameter and the largest objects are in the millimeter to centimeter range. The printed charges are also shown to affect the electronic

  12. Charge and Energy Dependences of Ionization and Transfer for Helium in Collisions with Fast Charged Projectiles

    Institute of Scientific and Technical Information of China (English)

    FU Hong-Bin; WANG Bao-Hong; DING Bao-Wei; LIU Zhao-Yuan

    2009-01-01

    The classical method within the independent electron model is employed to investigate (i) charge dependences of single and double ionization for helium by various charged ions Aq+ (q = 1 - 8) at impact energies of 0.64 and 1.44 MeV/u, respectively, (ii) energy dependences of transfer ionization for helium by 0.5-3 MeV/u A8,9+ ions impact. The Lenz-Jensen model of the atom is applied instead of the Bohr model of the atom, and the impact-parameter dependences are also introduced into the calculations. Satisfactory agreement is found between theoretical and experimental data.

  13. Charge transport in molecular junctions: From tunneling to hopping with the probe technique

    CERN Document Server

    Kilgour, Michael

    2015-01-01

    We demonstrate that a simple phenomenological approach can be used to simulate electronic conduction in molecular wires under thermal effects induced by the surrounding environment. This "Landauer-B\\"uttiker's probe technique" can properly replicate different transport mechanisms: phase coherent nonresonant tunneling, ballistic behavior, and hopping conduction, to provide results consistent with experiments. Specifically, our simulations with the probe method recover the following central characteristics of charge transfer in molecular wires: (i) The electrical conductance of short wires falls off exponentially with molecular length, a manifestation of the tunneling (superexchange) mechanism. Hopping dynamics overtakes superexchange in long wires demonstrating an ohmic-like behavior. (ii) In off-resonance situations, weak dephasing effects facilitate charge transfer. Under large dephasing the electrical conductance is suppressed. (iii) At high enough temperatures, $k_BT/\\epsilon_B>1/25$, with $\\epsilon_B$ as ...

  14. Observation of quantum interference in molecular charge transport

    DEFF Research Database (Denmark)

    Guedon, Constant M.; Valkenier, Hennie; Markussen, Troels;

    2012-01-01

    for such behaviour has been indirect. Here, we report the observation of destructive quantum interference in charge transport through two-terminal molecular junctions at room temperature. We studied five different rigid p-conjugated molecular wires, all of which form self-assembled monolayers on a gold surface...

  15. Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

    Science.gov (United States)

    Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A.

    2013-07-01

    Coupled electron-nuclear dynamics, implemented using the Ehrenfest method, has been used to study charge migration with fixed nuclei, together with charge transfer when nuclei are allowed to move. Simulations were initiated at reference geometries of neutral benzene and 2-phenylethylamine (PEA), and at geometries close to potential energy surface crossings in the cations. Cationic eigenstates, and the so-called sudden approximation, involving removal of an electron from a correlated ground-state wavefunction for the neutral species, were used as initial conditions. Charge migration without coupled nuclear motion could be observed if the Ehrenfest simulation, using the sudden approximation, was started near a conical intersection where the states were both strongly coupled and quasi-degenerate. Further, the main features associated with charge migration were still recognizable when the nuclear motion was allowed to couple. In the benzene radical cation, starting from the reference neutral geometry with the sudden approximation, one could observe sub-femtosecond charge migration with a small amplitude, which results from weak interaction with higher electronic states. However, we were able to engineer large amplitude charge migration, with a period between 10 and 100 fs, corresponding to oscillation of the electronic structure between the quinoid and anti-quinoid cationic electronic configurations, by distorting the geometry along the derivative coupling vector from the D6h Jahn-Teller crossing to lower symmetry where the states are not degenerate. When the nuclear motion becomes coupled, the period changes only slightly. In PEA, in an Ehrenfest trajectory starting from the D2 eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D1, D2 (N+-Phenyl, N-Phenyl+). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an

  16. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer.

    Science.gov (United States)

    Yao, Yi; Berkowitz, Max L; Kanai, Yosuke

    2015-12-28

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na(+) and K(+) ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

  17. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

    International Nuclear Information System (INIS)

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na+ and K+ ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications

  18. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Yi; Berkowitz, Max L., E-mail: maxb@unc.edu, E-mail: ykanai@unc.edu; Kanai, Yosuke, E-mail: maxb@unc.edu, E-mail: ykanai@unc.edu [Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 (United States)

    2015-12-28

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na{sup +} and K{sup +} ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

  19. Digitized charge transfer magnitude determined by metal-organic coordination number.

    Science.gov (United States)

    Yang, Hung-Hsiang; Chu, Yu-Hsun; Lu, Chun-I; Yang, Tsung-Han; Yang, Kai-Jheng; Kaun, Chao-Cheng; Hoffmann, Germar; Lin, Minn-Tsong

    2013-03-26

    Well-ordered metal-organic nanostructures of Fe-PTCDA (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride) chains and networks are grown on a Au(111) surface. These structures are investigated by high-resolution scanning tunneling microscopy. Digitized frontier orbital shifts are followed in scanning tunneling spectroscopy. By comparing the frontier energies with the molecular coordination environments, we conclude that the specific coordination affects the magnitude of charge transfer onto each PTCDA in the Fe-PTCDA hybridization system. A basic model is derived, which captures the essential underlying physics and correlates the observed energetic shift of the frontier orbital with the charge transfer. PMID:23451803

  20. Charge Transport Phenomena in Peptide Molecular Junctions

    Directory of Open Access Journals (Sweden)

    Alessandra Luchini

    2008-01-01

    Full Text Available Inelastic electron tunneling spectroscopy (IETS is a valuable in situ spectroscopic analysis technique that provides a direct portrait of the electron transport properties of a molecular species. In the past, IETS has been applied to small molecules. Using self-assembled nanoelectronic junctions, IETS was performed for the first time on a large polypeptide protein peptide in the phosphorylated and native form, yielding interpretable spectra. A reproducible 10-fold shift of the I/V characteristics of the peptide was observed upon phosphorylation. Phosphorylation can be utilized as a site-specific modification to alter peptide structure and thereby influence electron transport in peptide molecular junctions. It is envisioned that kinases and phosphatases may be used to create tunable systems for molecular electronics applications, such as biosensors and memory devices.

  1. Charge transfer reaction of multi-charged oxygen ions with O2

    Science.gov (United States)

    Holzscheiter, H. M.; Church, D. A.

    1981-10-01

    The reaction rates for charge transfer from O2 to doubly and triply charged oxygen atoms are measured in a demonstration of the measurement capabilities of a system at ultrahigh vacuum with low-energy magnetically confined ions. Ions were produced by electron impact ionization of gas within a Penning-type ion trap, with selective removal of unwanted ionization states by radio-frequency resonant excitation. Ion number mass-to-charge ratio spectra obtained at partial pressures of O2 from 9.9 x 10 to the -9th to 1.5 x 10 to the -7th torr yield rate constants of 1.0 x 10 to the -9th cu cm/sec and 2.5 x 10 to the -9th cu cm/sec for the O(2+) and O(3+) reactions, respectively. Measurements made at a 30% increase of the effective axial well depth of the trap demonstrate that the rate constant is essentially energy independent in the energy range studies, implying that the O(2+) cross section for charge transfer has an inverse velocity dependence of the Langevin type, despite a reaction rate lower than the Langevin valve.

  2. Tunable charge transfer properties in metal-phthalocyanine heterojunctions

    Science.gov (United States)

    Siles, P. F.; Hahn, T.; Salvan, G.; Knupfer, M.; Zhu, F.; Zahn, D. R. T.; Schmidt, O. G.

    2016-04-01

    Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of different organic materials to create organic heterostructures which combine the electrical capabilities of each material. This opens the possibility to precisely engineer and tune new electrical properties. In particular, similar transition metal phthalocyanines demonstrate hybridization and charge transfer properties which could lead to interesting physical phenomena. Although, when considering device dimensions, a better understanding and control of the tuning of the transport properties still remain in the focus of research. Here, by employing conductive atomic force microscopy techniques, we provide an insight about the nanoscale electrical properties and transport mechanisms of MnPc and fluorinated phthalocyanines such as F16CuPc and F16CoPc. We report a transition from typical diode-like transport mechanisms for pure MnPc thin films to space-charge-limited current transport regime (SCLC) for Pc-based heterostructures. The controlled addition of fluorinated phthalocyanine also provides highly uniform and symmetric-polarized transport characteristics with conductance enhancements up to two orders of magnitude depending on the polarization. We present a method to spatially map the mobility of the MnPc/F16CuPc structures with a nanoscale resolution and provide theoretical calculations to support our experimental findings. This well-controlled nanoscale tuning of the electrical properties for metal transition phthalocyanine junctions stands as key step for future phthalocyanine-based electronic devices, where the low dimension charge transfer, mediated by transition metal atoms could be intrinsically linked to a transfer of magnetic moment or spin.Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of

  3. Superconductivity and charge transfer excitations in high T c superconductors

    Science.gov (United States)

    Balseiro, C. A.; Alascio, B.; Gagliano, E.; Rojo, A.

    We present some numerical results to show that in a simple model which includes Cu3d and O 2p orbitals together with inter and intra atomic correlations pairing between holes can occur due to charge transfer excitations. We present also a simple approximation to derive an effective Hamiltonian containing an interaction between particles which is attractive for some values of the different microscopic parameters. Nous présentons des résultats numériques qui montrent que dans un modèle simple, incluant les orbitales 3d du cuivre et 2p de l'oxygène, avec une interaction coulombienne interatomique et intra-atomique, les trous peuvent s'apparier à cause des excitations de transfert de charge. Nous présentons aussi une approximation simple pour obtenir un Hamiltonien effectif contenant une interaction entre particules qui peut être attractive pour certaines valeurs des paramètres microscopiques.

  4. Charge transfer and polarization screening at organic-metal interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Peisert, Heiko; Kolacyak, Daniel; Chasse, Thomas [University of Tuebingen (Germany). Institute of Physical and Theoretical Chemistry

    2009-07-01

    Core hole screening effects at organic/metal interfaces were studied using core level X-ray photoemission spectroscopy (XPS), x-ray excited Auger electron spectroscopy (XAES) and valence band ultraviolet photoemission spectroscopy (UPS). The comparison of energetic shifts in XPS and XAES enables the estimation of electronic relaxation energy (screening ability). Magnesium phthalocyanine (MgPc), zinc phthalocyanine (ZnPc) and perfluorinated zinc phthalocyanine (ZnPcF16) evaporated on single crystalline Au(100) were used as model molecules. Two different features in the metal Auger spectra can be clearly separated for (sub-)monolayer coverages while only minor changes of the shape of corresponding photoemission features are observed. In contrast, Auger spectra of fluorine in ZnPcF16 do not show different components for ultrathin films. Applying a dielectric continuum model, the major screening mechanism cannot be described sufficiently by polarization screening due to mirror charges, significant contributions by charge transfer screening have to be considered.

  5. Ab initio charge-carrier mobility model for amorphous molecular semiconductors

    Science.gov (United States)

    Massé, Andrea; Friederich, Pascal; Symalla, Franz; Liu, Feilong; Nitsche, Robert; Coehoorn, Reinder; Wenzel, Wolfgang; Bobbert, Peter A.

    2016-05-01

    Accurate charge-carrier mobility models of amorphous organic molecular semiconductors are essential to describe the electrical properties of devices based on these materials. The disordered nature of these semiconductors leads to percolative charge transport with a large characteristic length scale, posing a challenge to the development of such models from ab initio simulations. Here, we develop an ab initio mobility model using a four-step procedure. First, the amorphous morphology together with its energy disorder and intermolecular charge-transfer integrals are obtained from ab initio simulations in a small box. Next, the ab initio information is used to set up a stochastic model for the morphology and transfer integrals. This stochastic model is then employed to generate a large simulation box with modeled morphology and transfer integrals, which can fully capture the percolative charge transport. Finally, the charge-carrier mobility in this simulation box is calculated by solving a master equation, yielding a mobility function depending on temperature, carrier concentration, and electric field. We demonstrate the procedure for hole transport in two important molecular semiconductors, α -NPD and TCTA. In contrast to a previous study, we conclude that spatial correlations in the energy disorder are unimportant for α -NPD. We apply our mobility model to two types of hole-only α -NPD devices and find that the experimental temperature-dependent current density-voltage characteristics of all devices can be well described by only slightly decreasing the simulated energy disorder strength.

  6. Proton-Coupled Electron Transfer: Moving Together and Charging Forward

    OpenAIRE

    Hammes-Schiffer, Sharon

    2015-01-01

    Proton-coupled electron transfer (PCET) is ubiquitous throughout chemistry and biology. This Perspective discusses recent advances and current challenges in the field of PCET, with an emphasis on the role of theory and computation. The fundamental theoretical concepts are summarized, and expressions for rate constants and kinetic isotope effects are provided. Computational methods for calculating reduction potentials and pK a’s for molecular electrocatalysts, as well as insights into linear c...

  7. Charge transfer between epitaxial graphene and silicon carbide

    OpenAIRE

    Kopylov, S; A. Tzalenchuk; Kubatkin, Sergey; Fal'ko, V. I.

    2010-01-01

    We analyze doping of graphene grown on SiC in two models which differ by the source of charge transferred to graphene, namely, from SiC surface and from bulk donors. For each of the two models, we find the maximum electron density induced in monolayer and bilayer graphene, which is determined by the difference between the work function for electrons in pristine graphene and donor states on/in SiC, and analyze the responsivity of graphene to the density variation by means of electrostatic gate...

  8. Modulating unimolecular charge transfer by exciting bridge vibrations.

    Science.gov (United States)

    Lin, Zhiwei; Lawrence, Candace M; Xiao, Dequan; Kireev, Victor V; Skourtis, Spiros S; Sessler, Jonathan L; Beratan, David N; Rubtsov, Igor V

    2009-12-23

    Ultrafast UV-vibrational spectroscopy was used to investigate how vibrational excitation of the bridge changes photoinduced electron transfer between donor (dimethylaniline) and acceptor (anthracene) moieties bridged by a guanosine-cytidine base pair (GC). The charge-separated (CS) state yield is found to be lowered by high-frequency bridge mode excitation. The effect is linked to a dynamic modulation of the donor-acceptor coupling interaction by weakening of H-bonding and/or by disruption of the bridging base-pair planarity.

  9. Optics of Chromites and Charge-Transfer Transitions

    Directory of Open Access Journals (Sweden)

    Andrei V. Zenkov

    2008-01-01

    Full Text Available Specific features of the charge-transfer (CT states and O2p→Cr3d transitions in the octahedral (CrO69− complex are considered in the cluster approach. The reduced matrix elements of the electric-dipole transition operator are calculated on many-electron wave functions of the complex corresponding to the initial and final states of a CT transition. Modeling the optic spectrum of chromites has yielded a complicated CT band. The model spectrum is in satisfactory agreement with experimental data which demonstrates the limited validity of the generally accepted concept of a simple structure of CT spectra.

  10. Coupled quantum-classical method for long range charge transfer: relevance of the nuclear motion to the quantum electron dynamics

    International Nuclear Information System (INIS)

    Charge and excitonic-energy transfer phenomena are fundamental for energy conversion in solar cells as well as artificial photosynthesis. Currently, much interest is being paid to light-harvesting and energy transduction processes in supramolecular structures, where nuclear dynamics has a major influence on electronic quantum dynamics. For this reason, the simulation of long range electron transfer in supramolecular structures, under environmental conditions described within an atomistic framework, has been a difficult problem to study. This work describes a coupled quantum mechanics/molecular mechanics method that aims at describing long range charge transfer processes in supramolecular systems, taking into account the atomistic details of large molecular structures, the underlying nuclear motion, and environmental effects. The method is applied to investigate the relevance of electron–nuclei interaction on the mechanisms for photo-induced electron–hole pair separation in dye-sensitized interfaces as well as electronic dynamics in molecular structures. (paper)

  11. Coupled quantum-classical method for long range charge transfer: relevance of the nuclear motion to the quantum electron dynamics.

    Science.gov (United States)

    da Silva, Robson; Hoff, Diego A; Rego, Luis G C

    2015-04-10

    Charge and excitonic-energy transfer phenomena are fundamental for energy conversion in solar cells as well as artificial photosynthesis. Currently, much interest is being paid to light-harvesting and energy transduction processes in supramolecular structures, where nuclear dynamics has a major influence on electronic quantum dynamics. For this reason, the simulation of long range electron transfer in supramolecular structures, under environmental conditions described within an atomistic framework, has been a difficult problem to study. This work describes a coupled quantum mechanics/molecular mechanics method that aims at describing long range charge transfer processes in supramolecular systems, taking into account the atomistic details of large molecular structures, the underlying nuclear motion, and environmental effects. The method is applied to investigate the relevance of electron-nuclei interaction on the mechanisms for photo-induced electron-hole pair separation in dye-sensitized interfaces as well as electronic dynamics in molecular structures. PMID:25767107

  12. Charge Transfer and Triplet States in High Efficiency OPV Materials and Devices

    Science.gov (United States)

    Dyakonov, Vladimir

    2013-03-01

    The advantage of using polymers and molecules in electronic devices, such as light-emitting diodes (LED), field-effect transistors (FET) and, more recently, solar cells (SC) is justified by the unique combination of high device performance and processing of the semiconductors used. Power conversion efficiency of nanostructured polymer SC is in the range of 10% on lab scale, making them ready for up-scaling. Efficient charge carrier generation and recombination in SC are strongly related to dissociation of the primary singlet excitons. The dissociation (or charge transfer) process should be very efficient in photovoltaics. The mechanisms governing charge carrier generation, recombination and transport in SC based on the so-called bulk-heterojunctions, i.e. blends of two or more semiconductors with different electron affinities, appear to be very complex, as they imply the presence of the intermediate excited states, neutral and charged ones. Charge transfer states, or polaron pairs, are the intermediate states between free electrons/holes and strongly bound excitons. Interestingly, the mostly efficient OLEDs to date are based on the so-called triplet emitters, which utilize the triplet-triplet annihilation process. In SC, recent investigations indicated that on illumination of the device active layer, not only mobile charges but also triplet states were formed. With respect to triplets, it is unclear how these excited states are generated, via inter-system crossing or via back transfer of the electron from acceptor to donor. Triplet formation may be considered as charge carrier loss channel; however, the fusion of two triplets may lead to a formation of singlet excitons instead. In such case, a generation of charges by utilizing of the so far unused photons will be possible. The fundamental understanding of the processes involving the charge transfer and triplet states and their relation to nanoscale morphology and/or energetics of blends is essential for the

  13. Charge and energy transfer in a bithiophene perylenediimide based donor-acceptor-donor system for use in organic photovoltaics.

    Science.gov (United States)

    Wenzel, Jan; Dreuw, Andreas; Burghardt, Irene

    2013-07-28

    The elementary charge and excitation energy transfer steps in a novel symmetric donor-acceptor-donor triad first described in Roland et al. Phys. Chem. Chem. Phys., 2012, 14, 273, consisting of a central perylenediimide moiety as a potential electron acceptor and two identical electron rich bithiophene compounds, have been investigated using quantum chemical methodology. These elementary processes determine the applicability of such systems in photovoltaic devices. The molecular structure, excited states and the photo-physical properties are investigated using smaller model systems and including solvation effects. The donor and acceptor π-systems are separated by an ethyl bridge such that the molecular orbitals are either located on the donor or acceptor moiety making the identification of locally excited versus charge transfer states straightforward. Using excited state geometry optimizations, the mechanism of photo-initiated charge separation could be identified. Geometry relaxation in the excited donor state leads to a near-degeneracy with the locally excited acceptor state, entailing strong excitonic coupling and resonance energy transfer. This energy transfer process is driven by planarization and bond length alternation of the donor molecule. Geometry relaxation of the locally excited acceptor state in turn reveals a crossing with the energetically lowest charge transfer excited state. The energetic position of the latter depends in a sensitive fashion on the solvent. This provides an explanation of the sequential process observed in the experiment, favoring ultrafast (∼130 fs) formation of the excited acceptor state followed by slower (∼3 ps scale) formation of the charge separated state.

  14. Atomic, molecular, and optical physics charged particles

    CERN Document Server

    Dunning, F B

    1995-01-01

    With this volume, Methods of Experimental Physics becomes Experimental Methods in the Physical Sciences, a name change which reflects the evolution of todays science. This volume is the first of three which will provide a comprehensive treatment of the key experimental methods of atomic, molecular, and optical physics; the three volumes as a set will form an excellent experimental handbook for the field. The wide availability of tunable lasers in the pastseveral years has revolutionized the field and lead to the introduction of many new experimental methods that are covered in these volumes. Traditional methods are also included to ensure that the volumes will be a complete reference source for the field.

  15. Molecular Thermodynamics of Charged Hard-Dumbbell Fluids

    Institute of Scientific and Technical Information of China (English)

    秦原; 刘洪来; 胡英

    2001-01-01

    Chemical potentials of charged hard-dumbbell fluids are obtained by Monte Carlo simulations using Widom's test-particle method, corresponding compressibility factors are achieved by integration of chemical potentials at different densities. A molecular thermodynamic model is also developed for these charged hard-dumbbell fluids where the residual Helmholtz function is composed of two terms: a reference term responsible for the charged hard spheres and a bonding contribution measuring the sticky interactions between positive and negative hard ions.Model predictions are in good agreement with simulation results.

  16. Charge transport in molecular junctions: From tunneling to hopping with the probe technique

    Energy Technology Data Exchange (ETDEWEB)

    Kilgour, Michael; Segal, Dvira, E-mail: dsegal@chem.utoronto.ca [Chemical Physics Theory Group, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6 (Canada)

    2015-07-14

    We demonstrate that a simple phenomenological approach can be used to simulate electronic conduction in molecular wires under thermal effects induced by the surrounding environment. This “Landauer-Büttiker’s probe technique” can properly replicate different transport mechanisms, phase coherent nonresonant tunneling, ballistic behavior, and hopping conduction. Specifically, our simulations with the probe method recover the following central characteristics of charge transfer in molecular wires: (i) the electrical conductance of short wires falls off exponentially with molecular length, a manifestation of the tunneling (superexchange) mechanism. Hopping dynamics overtakes superexchange in long wires demonstrating an ohmic-like behavior. (ii) In off-resonance situations, weak dephasing effects facilitate charge transfer, but under large dephasing, the electrical conductance is suppressed. (iii) At high enough temperatures, k{sub B}T/ϵ{sub B} > 1/25, with ϵ{sub B} as the molecular-barrier height, the current is enhanced by a thermal activation (Arrhenius) factor. However, this enhancement takes place for both coherent and incoherent electrons and it does not readily indicate on the underlying mechanism. (iv) At finite-bias, dephasing effects may impede conduction in resonant situations. We further show that memory (non-Markovian) effects can be implemented within the Landauer-Büttiker’s probe technique to model the interaction of electrons with a structured environment. Finally, we examine experimental results of electron transfer in conjugated molecular wires and show that our computational approach can reasonably reproduce reported values to provide mechanistic information.

  17. Charge transport in molecular junctions: From tunneling to hopping with the probe technique

    Science.gov (United States)

    Kilgour, Michael; Segal, Dvira

    2015-07-01

    We demonstrate that a simple phenomenological approach can be used to simulate electronic conduction in molecular wires under thermal effects induced by the surrounding environment. This "Landauer-Büttiker's probe technique" can properly replicate different transport mechanisms, phase coherent nonresonant tunneling, ballistic behavior, and hopping conduction. Specifically, our simulations with the probe method recover the following central characteristics of charge transfer in molecular wires: (i) the electrical conductance of short wires falls off exponentially with molecular length, a manifestation of the tunneling (superexchange) mechanism. Hopping dynamics overtakes superexchange in long wires demonstrating an ohmic-like behavior. (ii) In off-resonance situations, weak dephasing effects facilitate charge transfer, but under large dephasing, the electrical conductance is suppressed. (iii) At high enough temperatures, kBT/ɛB > 1/25, with ɛB as the molecular-barrier height, the current is enhanced by a thermal activation (Arrhenius) factor. However, this enhancement takes place for both coherent and incoherent electrons and it does not readily indicate on the underlying mechanism. (iv) At finite-bias, dephasing effects may impede conduction in resonant situations. We further show that memory (non-Markovian) effects can be implemented within the Landauer-Büttiker's probe technique to model the interaction of electrons with a structured environment. Finally, we examine experimental results of electron transfer in conjugated molecular wires and show that our computational approach can reasonably reproduce reported values to provide mechanistic information.

  18. Overcoming the Cut-Off Charge Transfer Bandgaps at the PbS Quantum Dot Interface

    KAUST Repository

    El-Ballouli, Ala'a O.

    2015-11-17

    Light harvesting from large size of semiconductor PbS quantum dots (QDs) with a bandgap of less than 1 eV is one of the greatest challenges precluding the development of PbS QD-based solar cells because the interfacial charge transfer (CT) from such QDs to the most commonly used electron acceptor materials is very inefficient, if it occurs at all. Thus, an alternative electron-accepting unit with a new driving force for CT is urgently needed to harvest the light from large-sized PbS QDs. Here, a cationic porphyrin is utilized as a new electron acceptor unit with unique features that bring the donor–acceptor components into close molecular proximity, allowing ultrafast and efficient electron transfer for QDs of all sizes, as inferred from the drastic photoluminescence quenching and the ultrafast formation of the porphyrin anionic species. The time-resolved results clearly demonstrate the possibility of modulating the electron transfer process between PbS QDs and porphyrin moieties not only by the size quantization effect but also by the interfacial electrostatic interaction between the positively charged porphyrin and the negatively charged QDs. This approach provides a new pathway for engineering QD-based solar cells that make the best use of the diverse photons making up the Sun\\'s broad irradiance spectrum.

  19. Charge-transfer interactions between TCNQ and silver clusters Ag20 and Ag13.

    Science.gov (United States)

    Chen, Jing; Zhang, Hanyu; Liu, Xianhu; Yuan, Chengqian; Jia, Meiye; Luo, Zhixun; Yao, Jiannian

    2016-03-14

    Interactions between tetracyanoquinodimethane (TCNQ) and two typical silver clusters Ag13 and Ag20 are studied by first-principles DFT calculations. Charge transfer (CT) from silver clusters to TCNQ molecules initiates the Ag-N bond formation at selective sites resulting in the formation of different isomers of Ag13-TCNQ and Ag20-TCNQ complexes. We show here a comprehensive spectroscopic analysis for the two CT complexes on the basis of Raman and infrared activities. Furthermore, frontier molecular orbital (FMO) and natural bond orbital (NBO) analysis of the complexes provides a vivid illustration of electron cloud overlap and interactions. The behavior of TCNQ adsorbed on the tetrahedral Ag20 cluster was even found in good agreement with the experimental measurement of TCNQ molecules on a single-crystal Ag(111) surface. This study not only endeavors to clarify the charge-transfer interactions of TCNQ with silver, but also presents a finding of enhanced charge transfer between Ag13 and TCNQ indicating potential for candidate building blocks of granular materials. PMID:26888771

  20. Charge-transfer complexes and their role in exciplex emission and near-infrared photovoltaics.

    Science.gov (United States)

    Ng, Tsz-Wai; Lo, Ming-Fai; Fung, Man-Keung; Zhang, Wen-Jun; Lee, Chun-Sing

    2014-08-20

    Charge transfer and interactions at organic heterojunctions (OHJs) are known to have critical influences on various properties of organic electronic devices. In this Research News article, a short review is given from the electronic viewpoint on how the local molecular interactions and interfacial energetics at P/N OHJs contribute to the recombination/dissociation of electron-hole pairs. Very often, the P-type materials donate electrons to the N-type materials, giving rise to charge-transfer complexes (CTCs) with a P(δ+) -N(δ-) configuration. A recently observed opposite charge-transfer direction in OHJs is also discussed (i.e., N-type material donates electrons to P-type material to form P(δ-) -N(δ+) ). Recent studies on the electronic structures of CTC-forming material pairs are also summarized. The formation of P(δ-) -N(δ+) -type CTCs and their correlations with exciplex emission are examined. Furthermore, the potential applications of CTCs in NIR photovoltaic devices are reviewed. PMID:24799189

  1. Total and differential cross sections for charge transfer in He2+-He+ collisions: trajectory effects

    International Nuclear Information System (INIS)

    Cross sections have been computed for charge transfer in collisions between 4He+ and 4He2+ ions for centre-of-mass collision energies 0.21 ≤ E ≤ 2.50 keV. The semi-classical impact parameter method was employed, with a basis of atomic orbitals modified by plane-wave translation factors. Both rectilinear and Coulomb trajectories were used, and the differential cross sections were found to be sensitive to the assumed form of trajectory. Comparison is made with molecular orbital calculations by previous workers. (author)

  2. Deuteron-proton charge exchange reaction at small transfer momentum

    CERN Document Server

    Ladygina, N B

    2004-01-01

    The charge-exchange reaction pd -> npp at 1 GeV projectile proton energy is studied. This reaction is considered in a special kinematics, when the transfer momentum from the beam proton to fast outgoing neutron is close to zero. Our approach is based on the Alt-Grassberger-Sandhas formulation of the multiple-scattering theory for the three-nucleon system. The matrix inversion method has been applied to take account of the final state interaction (FSI) contributions. The differential cross section, tensor analyzing power $C_{0,yy}$, vector-vector $C_{y,y}$ and vector-tensor $C_{y,xz}$ spin correlation parameters of the initial particles are presented. It is shown, that the FSI effects play a very important role under such kinematical conditions. The high sensitivity of the considered observables to the elementary nucleon-nucleon amplitudes has been obtained.

  3. Charge transfer excitons in C60-dimers and polymers

    CERN Document Server

    Harigaya, K

    1996-01-01

    Charge-transfer (CT) exciton effects are investigated for the optical absorption spectra of crosslinked C60 systems by using the intermediate exciton theory. We consider the C60-dimers, and the two (and three) molecule systems of the C60-polymers. We use a tight-binding model with long-range Coulomb interactions among electrons, and the model is treated by the Hartree-Fock approximation followed by the single-excitation configuration interaction method. We discuss the variations in the optical spectra by changing the conjugation parameter between molecules. We find that the total CT-component increases in smaller conjugations, and saturates at the intermediate conjugations. It decreases in the large conjugations. We also find that the CT-components of the doped systems are smaller than those of the neutral systems, indicating that the electron-hole distance becomes shorter in the doped C60-polymers.

  4. [Spectrophotometric determination of cinnarizine based on charge-transfer reaction].

    Science.gov (United States)

    Xu, B; Zhao, F; Tong, S

    1999-12-01

    The charge-transfer (CT) complex formed between cinnarizine as the donor and 7, 7, 8, 8-Tetracyanoquinodimethane (TCNQ) as the acceptor in acetone-methanol has been studied by spectrophotometric method. Beer's law is obeyed in the range of 0-18 microg x mL(-1) of cinnarizine. The apparent molar absorptivity of CT complex at 743 nm is 1.58 x 10(4) L x mol(-1) x cm(-1). The composition of CT complex is found to be 1 : 1 by Bent-French and Job's methods. The relative standard deviation is less than 3% (n = 10). The method has been applied to the determination of cinnarizine in tablets with satisfactory results. PMID:15822327

  5. Self-interaction effects on charge-transfer collisions

    CERN Document Server

    Quashie, Edwin E; Andrade, Xavier; Correa, Alfredo A

    2016-01-01

    In this article, we investigate the role of the self-interaction error in the simulation of collisions using time-dependent density functional theory (TDDFT) and Ehrenfest dynamics. We compare many different approximations of the exchange and correlation potential, using as a test system the collision of $\\mathrm{H^+ + CH_4}$ at $30~\\mathrm{eV}$. We find that semi-local approximations, like PBE, and even hybrid functionals, like B3LYP, produce qualitatively incorrect predictions for the scattering of the proton. This discrepancy appears because the self-interaction error allows the electrons to jump too easily to the proton, leading to radically different forces with respect to the non-self-interacting case. From our results, we conclude that using a functional that is self-interaction free is essential to properly describe charge-transfer collisions between ions and molecules in TDDFT.

  6. Dual Fluorescence in GFP Chromophore Analogues: Chemical Modulation of Charge Transfer and Proton Transfer Bands.

    Science.gov (United States)

    Chatterjee, Tanmay; Mandal, Mrinal; Das, Ananya; Bhattacharyya, Kalishankar; Datta, Ayan; Mandal, Prasun K

    2016-04-14

    Dual fluorescence of GFP chromophore analogues has been observed for the first time. OHIM (o-hydroxy imidazolidinone) shows only a charge transfer (CT) band, CHBDI (p-cyclicamino o-hydroxy benzimidazolidinone) shows a comparable intensity CT and PT (proton transfer) band, and MHBDI (p-methoxy o-hydroxy benzimidazolidinone) shows a higher intensity PT band. It could be shown that the differential optical behavior is not due to conformational variation in the solid or solution phase. Rather, control of the excited state electronic energy level and excited state acidity constant by functional group modification could be shown to be responsible for the differential optical behavior. Chemical modification-induced electronic control over the relative intensity of the charge transfer and proton transfer bands could thus be evidenced. Support from single-crystal X-ray structure, NMR, femtosecond to nanosecond fluorescence decay analysis, and TDDFT-based calculation provided important information and thus helped us understand the photophysics better. PMID:26998908

  7. "Like-charge attraction" between anionic polyelectrolytes: molecular dynamics simulations.

    Science.gov (United States)

    Molnar, Ferenc; Rieger, Jens

    2005-01-18

    "Like-charge attraction" is a phenomenon found in many biological systems containing DNA or proteins, as well as in polyelectrolyte systems of industrial importance. "Like-charge attraction" between polyanions is observed in the presence of mobile multivalent cations. At a certain limiting concentration of cations, the negatively charged macroions cease to repel each other and even an attractive force between the anions is found. With classical molecular dynamics simulations it is possible to elucidate the processes that govern the attractive behavior with atomistic resolution. As an industrially relevant example we study the interaction of negatively charged carboxylate groups of sodium polyacrylate molecules with divalent cationic Ca2+ counterions. Here we show that Ca2+ ions initially associate with single chains of polyacrylates and strongly influence sodium ion distribution; shielded polyanions approach each other and eventually "stick" together (precipitate), contrary to the assumption that precipitation is initially induced by intermolecular Ca2+ bridging. PMID:15641856

  8. Orbital dependent ultrafast charge transfer dynamics of ferrocenyl-functionalized SAMs on gold studied by core-hole clock spectroscopy

    International Nuclear Information System (INIS)

    Understanding the charge transport properties in general of different molecular components in a self-assembled monolayer (SAM) is of importance for the rational design of SAM molecular structures for molecular electronics. In this study, we study an important aspect of the charge transport properties, i.e. the charge transfer (CT) dynamics between the active molecular component (in this case, the ferrocenyl moieties of a ferrocenyl-n-alkanethiol SAM) and the electrode using synchrotron-based core-hole clock (CHC) spectroscopy. The characteristic CT times are found to depend strongly on the character of the ferrocenyl-derived molecular orbitals (MOs) which mediate the CT process. Furthermore, by systemically shifting the position of the ferrocenyl moiety in the SAM, it is found that the CT characteristics of the ferrocenyl MOs display distinct dependence on its distance to the electrode. These results demonstrate experimentally that the efficiency and rate of charge transport through the molecular backbone can be modulated by resonant injection of charge carriers into specific MOs. (paper)

  9. Photoconductive response in organic charge transfer interfaces with high quantum efficiency.

    Science.gov (United States)

    Alves, Helena; Pinto, Rui M; Maçôas, Ermelinda S

    2013-01-01

    Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications, such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior improved performance when compared with materials in a more disordered form. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. Here we report the first example of photoconductive behaviour of single-crystal charge-transfer interfaces. The system composed of rubrene and 7,7,8,8-tetracyanoquinodimethane presents a responsivity reaching 1 AW(-1), corresponding to an external quantum efficiency of nearly 100%. This result opens the possibility of using organic single-crystal interfaces in photonic applications. PMID:23673627

  10. A Model of Charge Transfer Excitons: Diffusion, Spin Dynamics, and Magnetic Field Effects

    CERN Document Server

    Lee, Chee Kong; Willard, Adam P

    2016-01-01

    In this letter we explore how the microscopic dynamics of charge transfer (CT) excitons are influenced by the presence of an external magnetic field in disordered molecular semiconductors. This influence is driven by the dynamic interplay between the spin and spatial degrees of freedom of the electron-hole pair. To account for this interplay we have developed a numerical framework that combines a traditional model of quantum spin dynamics with a coarse-grained model of stochastic charge transport. This combination provides a general and efficient methodology for simulating the effects of magnetic field on CT state dynamics, therefore providing a basis for revealing the microscopic origin of experimentally observed magnetic field effects. We demonstrate that simulations carried out on our model are capable of reproducing experimental results as well as generating theoretical predictions related to the efficiency of organic electronic materials.

  11. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS2

    International Nuclear Information System (INIS)

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS2 upon adsorption of various gas molecules (H2, O2, H2O, NH3, NO, NO2, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS2 with a low degree of charge transfer and accept charge from the monolayer, except for NH3, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS2 are not significantly altered upon adsorption of H2, H2O, NH3, and CO, whereas the lowest unoccupied molecular orbitals of O2, NO, and NO2 are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS2. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS2. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides

  12. Doping graphene films via chemically mediated charge transfer

    Directory of Open Access Journals (Sweden)

    Ishikawa Ryousuke

    2011-01-01

    Full Text Available Abstract Transparent conductive films (TCFs are critical components of a myriad of technologies including flat panel displays, light-emitting diodes, and solar cells. Graphene-based TCFs have attracted a lot of attention because of their high electrical conductivity, transparency, and low cost. Carrier doping of graphene would potentially improve the properties of graphene-based TCFs for practical industrial applications. However, controlling the carrier type and concentration of dopants in graphene films is challenging, especially for the synthesis of p-type films. In this article, a new method for doping graphene using the conjugated organic molecule, tetracyanoquinodimethane (TCNQ, is described. Notably, TCNQ is well known as a powerful electron accepter and is expected to favor electron transfer from graphene into TCNQ molecules, thereby leading to p-type doping of graphene films. Small amounts of TCNQ drastically improved the resistivity without degradation of optical transparency. Our carrier doping method based on charge transfer has a huge potential for graphene-based TCFs.

  13. Charge Transfer and Support Effects in Heterogeneous Catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Hervier, Antoine [Univ. of California, Berkeley, CA (United States)

    2011-12-21

    The kinetic, electronic and spectroscopic properties of two-dimensional oxide-supported catalysts were investigated in order to understand the role of charge transfer in catalysis. Pt/TiO2 nanodiodes were fabricated and used as catalysts for hydrogen oxidation. During the reaction, the current through the diode, as well as its I-V curve, were monitored, while gas chromatography was used to measure the reaction rate. The current and the turnover rate were found to have the same temperature dependence, indicating that hydrogen oxidation leads to the non-adiabatic excitation of electrons in Pt. A fraction of these electrons have enough energy to ballistically transport through Pt and overcome the Schottky barrier at the interface with TiO2. The yield for this phenomenon is on the order of 10-4 electrons per product molecule formed, similar to what has been observed for CO oxidation and for the adsorption of many different molecules. The same Pt/TiO2 system was used to compare currents in hydrogen oxidation and deuterium oxidation. The current through the diode under deuterium oxidation was found to be greater than under hydrogen oxidation by a factor of three. Weighted by the difference in turnover frequencies for the two isotopes, this would imply a chemicurrent yield 5 times greater for D2 compared to H2, contrary to what is expected given the higher mass of D2. Reversible changes in the rectification factor of the diode are observed when switching between D2 and H2. These changes are a likely cause for the differences in current between the two isotopes. In the nanodiode experiments, surface chemistry leads to charge flow, suggesting the possibility of creating charge flow to tune surface chemistry. This was done first by exposing a Pt/Si diode to visible light while using it as a catalyst for H2 oxidation. Absorption of the light in the Si, combined with

  14. Looking at bulk-heterojunction organic photovoltaics from two viewpoints: morphology development and charge transfer

    Science.gov (United States)

    Van den Brande, Niko; Demir, Fatma; Geerlings, Paul; Van Mele, Bruno; Van Lier, Gregory; Van Assche, Guy

    2012-06-01

    In this paper, a combined experimental and theoretical study was performed on the P3HT:PCBM system used in organic photovoltaics. Fast-scanning differential chip calorimetry, an advanced thermal analysis technique, was used to simulate the thermal annealing used in the production of P3HT:PCBM solar cells to increase the degree of crystallinity, and thus efficiency. The main advantage of this technique for stuying the thermal annealing are the very high rates of heating and cooling that can be used, up to 106 K.s-1, permitting one to avoid crystallization during cooling. In parallel with the experimental study, the charge transfer between donor (P3HT) and acceptor (PCBM) at the interface is studied using density functional theory. The charge separation between donor and acceptor present for the ground state of the combined system, diminished when the first triplet was investigated. This was explained by the formation of a bridge state, formed after population by the LUMO with one electron. Such a molecular orbital can facilitate charge transfer.

  15. Structure and dynamics of a dizinc metalloprotein: effect of charge transfer and polarization.

    Science.gov (United States)

    Li, Yong L; Mei, Ye; Zhang, Da W; Xie, Dai Q; Zhang, John Z H

    2011-08-25

    Structures and dynamics of a recently designed dizinc metalloprotein (DFsc) (J. Mol. Biol. 2003, 334, 1101) are studied by molecular dynamics simulation using a dynamically adapted polarized force field derived from fragment quantum calculation for protein in solvent. To properly describe the effect of charge transfer and polarization in the present approach, quantum chemistry calculation of the zinc-binding group is periodically performed (on-the-fly) to update the atomic charges of the zinc-binding group during the MD simulation. Comparison of the present result with those obtained from simulations under standard AMBER force field reveals that charge transfer and polarization are critical to maintaining the correct asymmetric metal coordination in the DFsc. Detailed analysis of the result also shows that dynamic fluctuation of the zinc-binding group facilitates solvent interaction with the zinc ions. In particular, the dynamic fluctuation of the zinc-zinc distance is shown to be an important feature of the catalytic function of the di-ion zinc-binding group. Our study demonstrates that the dynamically adapted polarization approach is computationally practical and can be used to study other metalloprotein systems.

  16. Relation between Nonlinear Optical Properties of Push-Pull Molecules and Metric of Charge Transfer Excitations.

    Science.gov (United States)

    List, Nanna Holmgaard; Zaleśny, Robert; Murugan, N Arul; Kongsted, Jacob; Bartkowiak, Wojciech; Ågren, Hans

    2015-09-01

    We establish the relationships between the metric of charge transfer excitation (Δr) for the bright ππ* state and the two-photon absorption probability as well as the first hyperpolarizability for two families of push-pull π-conjugated systems. As previously demonstrated by Guido et al. (J. Chem. Theory Comput. 2013, 9, 3118-3126), Δr is a measure for the average hole-electron distance upon excitation and can be used to discriminate between short- and long-range electronic excitations. We indicate two new benefits from using this metric for the analyses of nonlinear optical properties of push-pull systems. First, the two-photon absorption probability and the first hyperpolarizability are found to be interrelated through Δr; if β ∼ (Δr)(k), then roughly, δ(TPA) ∼ (Δr)(k+1). Second, a simple power relation between Δr and the molecular hyperpolarizabilities of push-pull systems offers the possibility of estimating properties for longer molecular chains without performing calculations of high-order response functions explicitly. We further demonstrate how to link the hyperpolarizabilities with the chain length of the push-pull π-conjugated systems through the metric of charge transfer. PMID:26575913

  17. Experimental and modeling study on charge storage/transfer mechanism of graphene-based supercapacitors

    Science.gov (United States)

    Ban, Shuai; Jing, Xie; Zhou, Hongjun; Zhang, Lei; Zhang, Jiujun

    2014-12-01

    A symmetrical graphene-based supercapacitor is constructed for studying the charge-transfer mechanism within the graphene-based electrodes using both experiment measurements and molecular simulation. The in-house synthesized graphene is characterized by XRD, SEM and BET measurements for morphology and surface area. It is observed that the electric capacity of graphene electrode can be reduced by both high internal resistance and limited mass transfer. Computer modeling is conducted at the molecular level to characterize the diffusion behavior of electrolyte ions to the interior of electrode with emphasis on the unique 2D confinement imposed by graphene layers. Although graphene powder poses a moderate internal surface of 400 m2 g-1, the capacitance performance of graphene electrode can be as good as that of commercial activated carbon which has an overwhelming surface area of 1700 m2 g-1. An explanation to this abnormal correlation is that graphene material has an intrinsic capability of adaptively reorganizing its microporous structure in response to intercalation of ions and immergence of electrolyte solvent. The accessible surface of graphene is believed to be dramatically enlarged for ion adsorption during the charging process of capacitor.

  18. Radiative charge transfer lifetime of the excited state of (NaCa)$^+$

    CERN Document Server

    Makarov, O P; Michels, H J; Smith, W W; Makarov, Oleg P.

    2003-01-01

    New experiments were proposed recently to investigate the regime of cold atomic and molecular ion-atom collision processes in a special hybrid neutral-atom--ion trap under high vacuum conditions. The collisional cooling of laser pre-cooled Ca$^+$ ions by ultracold Na atoms is being studied. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A$^1\\Sigma^+$ state of the (NaCa)$^+$ molecular system. We calculate the rate coefficient for radiative charge transfer using a semiclassical approach. The dipole radial matrix elements between the ground and the excited states, and the potential curves were calculated using Complete Active Space Self-Consistent field and M\\"oller-Plesset second order perturbation theory (CASSCF/MP2) with an extended Gaussian basis, 6-311+G(3df). The semiclassical charge transfer rate coefficient was averaged over a thermal Maxwellian distribution. In addition we also present elastic collision cross sections and the spin-exchange cross section. The ra...

  19. Charge transport in columnar stacked triphenylenes: Effects of conformational fluctuations on charge transfer integrals and site energies

    NARCIS (Netherlands)

    Senthilkumar, K.; Grozema, F.C.; Bickelhaupt, F.M.; Siebbeles, L.D.A.

    2003-01-01

    Values of charge transfer integrals, spatial overlap integrals and site energies involved in transport of positive charges along columnar stacked triphenylene derivatives are provided. These parameters were calculated directly as the matrix elements of the Kohn–Sham Hamiltonian, defined in terms of

  20. Radiative charge transfer in cold and ultracold Sulfur atoms colliding with Protons

    CERN Document Server

    Shen, G; Wang, J G; McCann, J F; McLaughlin, B M

    2015-01-01

    Radiative decay processes at cold and ultra cold temperatures for Sulfur atoms colliding with protons are investigated. The MOLPRO quantum chemistry suite of codes was used to obtain accurate potential energies and transition dipole moments, as a function of internuclear distance, between low-lying states of the SH$^{+}$ molecular cation. A multi-reference configuration-interaction (MRCI) approximation together with the Davidson correction is used to determine the potential energy curves and transition dipole moments, between the states of interest, where the molecular orbitals (MO's) are obtained from state-averaged multi configuration-self-consistent field (MCSCF) calculations. The collision problem is solved approximately using an optical potential method to obtain radiative loss, and a fully two-channel quantum approach for radiative charge transfer. Cross sections and rate coefficients are determined for the first time for temperatures ranging from 10 $\\mu$ K up to 10,000 K. Results are obtained for all ...

  1. Proton-Coupled Electron Transfer: Moving Together and Charging Forward.

    Science.gov (United States)

    Hammes-Schiffer, Sharon

    2015-07-22

    Proton-coupled electron transfer (PCET) is ubiquitous throughout chemistry and biology. This Perspective discusses recent advances and current challenges in the field of PCET, with an emphasis on the role of theory and computation. The fundamental theoretical concepts are summarized, and expressions for rate constants and kinetic isotope effects are provided. Computational methods for calculating reduction potentials and pKa's for molecular electrocatalysts, as well as insights into linear correlations and non-innocent ligands, are also described. In addition, computational methods for simulating the nonadiabatic dynamics of photoexcited PCET are discussed. Representative applications to PCET in solution, proteins, electrochemistry, and photoinduced processes are presented, highlighting the interplay between theoretical and experimental studies. The current challenges and suggested future directions are outlined for each type of application, concluding with an overall view to the future. PMID:26110700

  2. Energy and Charge Transfer from Guest to Host in Doped Organic Electroluminescent Devices

    Institute of Scientific and Technical Information of China (English)

    李宏建; 彭景翠; 许雪梅; 瞿述; 罗小华; 赵楚军

    2002-01-01

    The luminescence properties of doped organic electroluminescent devices are explained by means off Hamiltonian model. The results show that there is a corresponding relation between the amount of transferred charge and the change of the energy originating from charge transfer, and the relation can be influenced by dopant concentration.As the amount of transferred charge increases, the total energy decreases and the luminescence intensity increases.Therefore, we deduce that the energy transfer from guest to host may be derived from the charge transfer. For a given organic electroluminescent device, the maximum value of the conductivity can be observed in a specific dopant concentration. The calculated results show that the greater the transferred charges, the higher the conductivities in doped organic electroluminescent devices. The results agree basically with experimental results.

  3. Charge-Transfer in Time-Dependent Density Functional Theory: Insights from the Asymmetric Hubbard Dimer

    CERN Document Server

    Fuks, J I

    2013-01-01

    We show that an asymmetric two-fermion two-site Hubbard model illustrates the essential features of long-range charge-transfer dynamics in a real-space molecule. We apply a resonant field that transfers one fermion from one site to the other. Via constrained search we find the exact ground-state exchange-correlation functional, and use it to propagate the Kohn-Sham system, giving the first "adiabatically-exact" calculation of time-resolved charge-transfer. This propagation fails to properly transfer charge. We analyze why by comparing the exact and adiabatically-exact potentials and discuss the role of the derivative discontinuity. The implication for real-space molecules is that even the best possible adiabatic approximation, despite capturing non-local step features relevant to dissociation and charge-transfer excitations, cannot capture fully time-resolved charge-transfer dynamics.

  4. Molecular Dipole Moment Computed with Ab Initio MKS Charges

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Molecular dipole moments computed at the levels of HF/STO-3G, HF/6-31G(d, p), HF/6-311+G(2d, 2p), MP2/6-31G(d, p) and MP2/6-311+G(2d, 2p) have been investigated. HF/6-311+G(2d, 2p) was found to be the relatively good choice to compute MKS charges for reproducing the experimental values of molecular dipole moments. Root mean square deviation of computed dipole moments for 21 small polar molecules is about 0.1969 D.

  5. Charge Transfer and Support Effects in Heterogeneous Catalysis

    Energy Technology Data Exchange (ETDEWEB)

    Hervier, Antoine [Univ. of California, Berkeley, CA (United States)

    2011-12-21

    The kinetic, electronic and spectroscopic properties of two-dimensional oxide-supported catalysts were investigated in order to understand the role of charge transfer in catalysis. Pt/TiO2 nanodiodes were fabricated and used as catalysts for hydrogen oxidation. During the reaction, the current through the diode, as well as its I-V curve, were monitored, while gas chromatography was used to measure the reaction rate. The current and the turnover rate were found to have the same temperature dependence, indicating that hydrogen oxidation leads to the non-adiabatic excitation of electrons in Pt. A fraction of these electrons have enough energy to ballistically transport through Pt and overcome the Schottky barrier at the interface with TiO2. The yield for this phenomenon is on the order of 10-4 electrons per product molecule formed, similar to what has been observed for CO oxidation and for the adsorption of many different molecules. The same Pt/TiO2 system was used to compare currents in hydrogen oxidation and deuterium oxidation. The current through the diode under deuterium oxidation was found to be greater than under hydrogen oxidation by a factor of three. Weighted by the difference in turnover frequencies for the two isotopes, this would imply a chemicurrent yield 5 times greater for D2 compared to H2, contrary to what is expected given the higher mass of D2. Reversible changes in the rectification factor of the diode are observed when switching between D2 and H2. These changes are a likely cause for the differences in current between the two isotopes. In the nanodiode experiments, surface chemistry leads to charge flow, suggesting the possibility of creating charge flow to tune surface chemistry. This was done first by exposing a Pt/Si diode to visible light while using it as a catalyst for H2 oxidation. Absorption of the light in the Si, combined with

  6. Proton-Coupled Electron Transfer: Moving Together and Charging Forward

    Energy Technology Data Exchange (ETDEWEB)

    Hammes-Schiffer, Sharon

    2015-06-25

    Proton-coupled electron transfer (PCET) is ubiquitous throughout chemistry and biology. This Perspective discusses recent advances and current challenges in the field of PCET, with an emphasis on the role of theory and computation. The fundamental theoretical concepts are summarized, and expressions for rate constants and kinetic isotope effects are provided. Computational methods for calculating reduction potentials and pKa’s for molecular electrocatalysts, as well as methods for simulating the nonadiabatic dynamics of photoinduced processes, are also described. Representative applications to PCET in solution, proteins, electrochemistry, and photoinduced processes are presented, highlighting the interplay between theoretical and experimental studies. The current challenges and suggested future directions are outlined for each type of application, concluding with an overall view to the future. The work described herein was supported by National Science Foundation Grant CHE-13-61293 (theory development), National Institutes of Health Grant GM056207 (soybean lipoxygenase), Center for Chemical Innovation of the National Science Foundation Solar Fuels Grant CHE-1305124 (cobalt catalysts), Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (nickel catalysts), and Air Force Office of Scientific Research Award No. FA9550-14-1-0295 (photoinduced PCET).

  7. Dynamic Peptide Library for the Discovery of Charge Transfer Hydrogels.

    Science.gov (United States)

    Berdugo, Cristina; Nalluri, Siva Krishna Mohan; Javid, Nadeem; Escuder, Beatriu; Miravet, Juan F; Ulijn, Rein V

    2015-11-25

    Coupling of peptide self-assembly to dynamic sequence exchange provides a useful approach for the discovery of self-assembling materials. In here, we demonstrate the discovery and optimization of aqueous, gel-phase nanostructures based on dynamically exchanging peptide sequences that self-select to maximize charge transfer of n-type semiconducting naphthalenediimide (NDI)-dipeptide bioconjugates with various π-electron-rich donors (dialkoxy/hydroxy/amino-naphthalene or pyrene derivatives). These gel-phase peptide libraries are characterized by spectroscopy (UV-vis and fluorescence), microscopy (TEM), HPLC, and oscillatory rheology and it is found that, of the various peptide sequences explored (tyrosine Y-NDI with tyrosine Y, phenylalanine F, leucine L, valine V, alanine A or glycine G-NH2), the optimum sequence is tyrosine-phenylalanine in each case; however, both its absolute and relative yield amplification is dictated by the properties of the donor component, indicating cooperativity of peptide sequence and donor/acceptor pairs in assembly. The methodology provides an in situ discovery tool for nanostructures that enable dynamic interfacing of supramolecular electronics with aqueous (biological) systems. PMID:26540455

  8. Single Molecule Spectroelectrochemistry of Interfacial Charge Transfer Dynamics In Hybrid Organic Solar Cell

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Shanlin [Univ. of Alabama, Tuscaloosa, AL (United States)

    2014-11-16

    Our research under support of this DOE grant is focused on applied and fundamental aspects of model organic solar cell systems. Major accomplishments are: 1) we developed a spectroelectorchemistry technique of single molecule single nanoparticle method to study charge transfer between conjugated polymers and semiconductor at the single molecule level. The fluorescence of individual fluorescent polymers at semiconductor surfaces was shown to exhibit blinking behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and semiconductor substrates. The similarities in molecular conformation suggest that the observed differences in blinking activity are due to charge transfer between fluorescent polymer and semiconductor, which provides additional pathways between states of high and low fluorescence quantum efficiency. Similar spectroelectrochemistry work has been done for small organic dyes for understand their charge transfer dynamics on various substrates and electrochemical environments; 2) We developed a method of transferring semiconductor nanoparticles (NPs) and graphene oxide (GO) nanosheets into organic solvent for a potential electron acceptor in bulk heterojunction organic solar cells which employed polymer semiconductor as the electron donor. Electron transfer from the polymer semiconductor to semiconductor and GO in solutions and thin films was established through fluorescence spectroscopy and electroluminescence measurements. Solar cells containing these materials were constructed and evaluated using transient absorption spectroscopy and dynamic fluorescence techniques to understand the charge carrier generation and recombination events; 3) We invented a spectroelectorchemistry technique using light scattering and electroluminescence for rapid size determination and studying electrochemistry of single NPs in an

  9. Quantum State Transfer between Charge and Flux Qubits in Circuit-QED

    Institute of Scientific and Technical Information of China (English)

    WU Qin-Qin; LIAO Jie-Qiao; KUANG Le-Man

    2008-01-01

    @@ We propose a scheme to implement quantum state transfer in a hybrid circuit quantum electrodynamics (QED)system which consists of a superconducting charge qubit, a flux qubit, and a transmission line resonator (TLR).It is shown that quantum state transfer between the charge qubit and the flux qubit can be realized by using the TLR as the data bus.

  10. Charge-Transfer Matrix Elements by FMO-LCMO Approach: Hole Transfer in DNA with Parameter Tuned Range-Separated DFT

    CERN Document Server

    Kitoh-Nishioka, Hirotaka

    2016-01-01

    A scheme for computing charge-transfer matrix elements with the linear combination of fragment molecular orbitals and the 'nonempirically tuned range-separated' density functional is presented. It takes account of the self-consistent orbital relaxation induced by environmental Coulomb field and the exchange interaction in fragment pairs at low computational scaling along the system size. The accuracy was confirmed numerically on benchmark systems of imidazole and furane homo-dimer cations. Applications to hole transfers in DNA nucleobase pairs and in a $\\pi$-stack adenine octomer highlight the effects of orbital relaxation.

  11. Architecture of a charge-transfer state regulating light harvesting in a plant antenna protein.

    Science.gov (United States)

    Ahn, Tae Kyu; Avenson, Thomas J; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K; Bassi, Roberto; Fleming, Graham R

    2008-05-01

    Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). We found evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a delocalized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can "tune" the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophyll-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

  12. Crystal growth of new charge-transfer salts based on π-conjugated donor molecules

    Science.gov (United States)

    Morherr, Antonia; Witt, Sebastian; Chernenkaya, Alisa; Bäcker, Jan-Peter; Schönhense, Gerd; Bolte, Michael; Krellner, Cornelius

    2016-09-01

    New charge transfer crystals of π-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure are reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-Fx, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the crystal structure and by infrared spectroscopy on single crystals. With these three different acceptor strengths and the two sets of donor materials, it is possible to investigate the distribution of the charge transfer systematically. This helps to understand the charge transfer process in this class of materials with π-conjugated donor molecules.

  13. ARCHITECTURE OF A CHARGE-TRANSFER STATE REGULATING LIGHT HARVESTING IN A PLANT ANTENNA PROTEIN

    Energy Technology Data Exchange (ETDEWEB)

    Fleming, Graham; Ahn, Tae Kyu; Avenson, Thomas J.; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K.; Bassi, Roberto; Fleming, Graham R.

    2008-04-02

    Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge-transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). In this work, we present evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a de-localized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can `tune? the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophylls-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

  14. Crystal Growth of new charge-transfer salts based on $\\pi$-conjugated molecules

    CERN Document Server

    Morherr, Antonia; Chernenkaya, Alisa; Bäcker, Jan-Peter; Schönhense, Gerd; Bolte, Michael; Krellner, Cornelius

    2016-01-01

    New charge transfer crystals of $\\pi$-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure is reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-F$_x$, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the crystal structure and by infrared spectroscopy on single crystals. With these three different acceptor strengths and the two sets of donor materials, it is possible to investigate the distribution of the charge transfer systematically. This helps to understand the charge transfer process in this class of materials with $\\pi$-conjug...

  15. Vascular permeability in a human tumour xenograft: molecular charge dependence.

    Science.gov (United States)

    Dellian, M; Yuan, F; Trubetskoy, V S; Torchilin, V P; Jain, R K

    2000-05-01

    Molecular charge is one of the main determinants of transvascular transport. There are, however, no data available on the effect of molecular charge on microvascular permeability of macromolecules in solid tumours. To this end, we measured tumour microvascular permeability to different proteins having similar size but different charge. Measurements were performed in the human colon adenocarcinoma LS174T transplanted in transparent dorsal skinfold chambers in severe combined immunodeficient (SCID) mice. Bovine serum albumin (BSA) and IgG were fluorescently labelled and were either cationized by conjugation with hexamethylenediamine or anionized by succinylation. The molecules were injected i.v. and the fluorescence in tumour tissue was quantified by intravital fluorescence microscopy. The fluorescence intensity and pharmacokinetic data were used to calculate the microvascular permeability. We found that tumour vascular permeability of cationized BSA (pI-range: 8.6-9.1) and IgG (pI: 8.6-9.3) was more than two-fold higher (4.25 and 4.65x10(-7) cm s(-1)) than that of the anionized BSA (pI approximately 2.0) and IgG (pI: 3.0-3.9; 1.11 and 1.93x10(-7) cm s(-1), respectively). Our results indicate that positively charged molecules extravasate faster in solid tumours compared to the similar-sized compounds with neutral or negative charges. However, the plasma clearance of cationic molecules was approximately 2x faster than that of anionic ones, indicating that the modification of proteins enhances drug delivery to normal organs as well. Therefore, caution should be exercised when such a strategy is used to improve drug and gene delivery to solid tumours.

  16. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    Energy Technology Data Exchange (ETDEWEB)

    Van Tassle, Aaron Justin [Univ. of California, Berkeley, CA (United States)

    2006-01-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  17. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    Energy Technology Data Exchange (ETDEWEB)

    Van Tassle, Aaron Justin

    2006-09-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  18. Multiple Charge Transfer States at Ordered and Disordered Donor/Acceptor Interfaces

    Science.gov (United States)

    Fusella, Michael; Verreet, Bregt; Lin, Yunhui; Brigeman, Alyssa; Purdum, Geoffrey; Loo, Yueh-Lin; Giebink, Noel; Rand, Barry

    The presence of charge transfer (CT) states in organic solar cells is accepted, but their role in photocurrent generation is not well understood. Here we investigate solar cells based on rubrene and C60 to show that CT state properties are influenced by molecular ordering at the donor/acceptor (D/A) interface. Crystalline rubrene films are produced with domains of 100s of microns adopting the orthorhombic phase, as confirmed by grazing incidence XRD, with the (h00) planes parallel to the substrate. C60 grown atop these films adopts a highly oriented face-centered cubic phase with the (111) plane parallel to the substrate. For this highly ordered system we have discovered the presence of four CT states. Polarized external quantum efficiency (EQE) measurements assign three of these to crystalline origins with the remaining one well aligned with the disordered CT state. Varying the thickness of a disordered blend of rubrene:C60 atop the rubrene template modulates the degree of crystallinity at the D/A interface. Strikingly, this process alters the prominence of the four CT states measured via EQE, and results in a transition from single to multiple electroluminescence peaks. These results underscore the impact of molecular structure at the heterojunction on charge photogeneration.

  19. Molecular Weight and Charge Density Asymmetry in Polyelectrolyte Complexation

    Science.gov (United States)

    Audus, Debra; Fredrickson, Glenn; Duechs, Dominik

    2009-03-01

    We investigate the phase diagram of oppositely charged polymers in a good solvent using a field-theoretic model. Mean-field solutions fail to predict the experimentally observed macroscopic phase separation into a solvent-rich phase and a dense liquid aggregate of polymers - a ``complex coacervate.'' We therefore study the model within a one-loop approximation, which accounts for Gaussian fluctuations in electrostatic and chemical potentials. Our particular focus is the effect of molecular weight, ionic strength, and charge asymmetry on the phase envelope. A set of dimensionless parameters is identified that dictate the size and shape of the two-phase region. Our results should be helpful in guiding experimental studies of coacervation.

  20. Manipulating the proton transfer process in molecular complexes: synthesis and spectroscopic studies.

    Science.gov (United States)

    Panja, Sumit Kumar; Dwivedi, Nidhi; Saha, Satyen

    2016-08-01

    The proton transfer process in carefully designed molecular complexes has been investigated directly in the solid and solution phase. SCXRD studies have been employed to investigate the N-H-O bonding interaction sites of the molecular complexes, with additional experimental support from FTIR and Raman spectroscopic studies, to gain information on the relative position of hydrogen in between the N and O centers. Further, the proton transfer process in solution is studied using UV-Visible spectroscopy through monitoring the intramolecular charge transfer (ICT) process in these molecular complexes, which is primarily governed by the number of electron withdrawing groups (nitro groups) on proton donor moieties (NP, DNP and TNP). It is found that the magnitude of the ICT process depends on the extent of proton transfer, which on the other hand depends on the relative stabilities of the constituent species (phenolate species). A correlation is observed between an increase in the number of nitro groups and an increase in the melting point of the molecular complexes, indicating the enhancement of ionic character due to the proton transfer process. The aliphatic H-bonding is identified and monitored using (1)H-NMR spectroscopy, which reveals that the identity of molecular complexes in solution interestingly depends on the extent of proton transfer, in addition to the nature of the solvents. The aliphatic C-H-O H-bonding interaction between the oxygen atom of the nitro group and the alkyl hydrogen in piperidinium was also found to play a significant role in strengthening the primary interaction involving a hydrogen transfer process. The conductivity of the molecular complexes increases with an increase in the number of nitro groups, indicating the enhancement in ionic character of the molecular complexes. PMID:27424765

  1. CHARGE-TRANSFER AND ENERGY-TRANSFER IN THE PHOTO-INDUCED COPOLYMERIZATION OF 2-VINYLNAPHTHALENE WITH MALEIC ANHYDRIDE

    Institute of Scientific and Technical Information of China (English)

    LI Tong; LUO Bin; LI Shanjun; CHU Guobei

    1990-01-01

    The initiation mechanism of the copolymerization of 2-vinylnaphthalene with maleic anhydride was studied under irradiation of 365 nm. The excited complex was formed from ( 1 ) the local excitation of 2-vinylnaphthalene followed by the charge-transfer interaction with maleic anhydride and ( 2 ) the excitation of the ground state charge-transfer complex, and then it collapsed to 1,4-tetramethylene biradical for initiation. A 1:1 alternating copolymer was formed in different monomer feeds. Addition of benzophenone could greatly enhance the rate of copolymerization through energy-transfer mechanism.

  2. Molecular Dipole Osmosis Based on Induced Charge Electro-Osmosis

    Science.gov (United States)

    Sugioka, Hideyuki

    2016-09-01

    We propose a novel mechanism of producing a large nonlinear electrokinetic vortex flow around a nonconductive polar molecule in an electrolyte. That is, a large nonlinear electrokinetic slip velocity is derived by considering a local giant permittivity due to a molecular electric dipole moment with induced-charge electro-osmosis (ICEO). Different from the conventional ICEO theory, our theory predicts that a nonconductive biomaterial, such as a base of a deoxyribonucleic acid (DNA) molecule, has a significantly high ICEO flow velocity because of its large local permittivity. We consider that our findings will contribute markedly to promising biomedical applications.

  3. Synthesis of a novel perylene diimide derivative and its charge transfer interaction with C60

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A novel organic electron acceptor, N,N′-dipyrimidinyl-3,4,9,10-perylene-tetracarboxylic diimide (DMP), was designed and synthesized. The molecular structure was characterized by FTIR spectrum and elemental analysis. By cyclic voltammetry measurements, DMP was found to possess a lower LUMO energy level than N,N′-diphenyl-3,4,9,10-perylene-tetracarboxylic diimide due to the stronger electron-withdrawing pyrimidinyl group than the phenyl group. Fluorescence quenching is observed in a dual-layer film consisting of a DMP layer and a C60 layer and was attributed to the charge transfer at the interface due to the energy level offset between DMP and C60.

  4. Bottom-up formation of endohedral mono-metallofullerenes is directed by charge transfer

    Science.gov (United States)

    Dunk, Paul W.; Mulet-Gas, Marc; Nakanishi, Yusuke; Kaiser, Nathan K.; Rodríguez-Fortea, Antonio; Shinohara, Hisanori; Poblet, Josep M.; Marshall, Alan G.; Kroto, Harold W.

    2014-12-01

    An understanding of chemical formation mechanisms is essential to achieve effective yields and targeted products. One of the most challenging endeavors is synthesis of molecular nanocarbon. Endohedral metallofullerenes are of particular interest because of their unique properties that offer promise in a variety of applications. Nevertheless, the mechanism of formation from metal-doped graphite has largely eluded experimental study, because harsh synthetic methods are required to obtain them. Here we report bottom-up formation of mono-metallofullerenes under core synthesis conditions. Charge transfer is a principal factor that guides formation, discovered by study of metallofullerene formation with virtually all available elements of the periodic table. These results could enable production strategies that overcome long-standing problems that hinder current and future applications of metallofullerenes.

  5. Influence of Coherent Tunneling and Incoherent Hopping on the Charge Transfer Mechanism in Linear Donor-Bridge-Acceptor Systems.

    Science.gov (United States)

    Li, Guangqi; Govind, Niranjan; Ratner, Mark A; Cramer, Christopher J; Gagliardi, Laura

    2015-12-17

    The mechanism of charge transfer has been observed to change from tunneling to hopping with increasing numbers of DNA base pairs in polynucleotides and with the length of molecular wires. The aim of this paper is to investigate this transition by examining the population dynamics using a tight-binding Hamiltonian with model parameters to describe a linear donor-bridge-acceptor (D-B-A) system. The model includes a primary vibration and an electron-vibration coupling at each site. A further coupling of the primary vibration with a secondary phonon bath allows the system to dissipate energy to the environment and reach a steady state. We apply the quantum master equation (QME) approach, based on second-order perturbation theory in a quantum dissipative system, to examine the dynamical processes involved in charge-transfer and follow the population transfer rate at the acceptor, ka, to shed light on the transition from tunneling to hopping. With a small tunneling parameter, V, the on-site population tends to localize and form polarons, and the hopping mechanism dominates the transfer process. With increasing V, the population tends to be delocalized and the tunneling mechanism dominates. The competition between incoherent hopping and coherent tunneling governs the mechanism of charge transfer. By varying V and the total number of sites, we also examine the onset of the transition from tunneling to hopping with increasing length.

  6. Influence of Coherent Tunneling and Incoherent Hopping on the Charge Transfer Mechanism in Linear Donor-Bridge-Acceptor Systems.

    Science.gov (United States)

    Li, Guangqi; Govind, Niranjan; Ratner, Mark A; Cramer, Christopher J; Gagliardi, Laura

    2015-12-17

    The mechanism of charge transfer has been observed to change from tunneling to hopping with increasing numbers of DNA base pairs in polynucleotides and with the length of molecular wires. The aim of this paper is to investigate this transition by examining the population dynamics using a tight-binding Hamiltonian with model parameters to describe a linear donor-bridge-acceptor (D-B-A) system. The model includes a primary vibration and an electron-vibration coupling at each site. A further coupling of the primary vibration with a secondary phonon bath allows the system to dissipate energy to the environment and reach a steady state. We apply the quantum master equation (QME) approach, based on second-order perturbation theory in a quantum dissipative system, to examine the dynamical processes involved in charge-transfer and follow the population transfer rate at the acceptor, ka, to shed light on the transition from tunneling to hopping. With a small tunneling parameter, V, the on-site population tends to localize and form polarons, and the hopping mechanism dominates the transfer process. With increasing V, the population tends to be delocalized and the tunneling mechanism dominates. The competition between incoherent hopping and coherent tunneling governs the mechanism of charge transfer. By varying V and the total number of sites, we also examine the onset of the transition from tunneling to hopping with increasing length. PMID:26554424

  7. Restricted Photochemistry in the Molecular Solid State: Structural Changes on Photoexcitation of Cu(I) Phenanthroline Metal-to-Ligand Charge Transfer (MLCT) Complexes by Time-Resolved Diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Makal, Anna; Benedict, Jason; Trzop, Elzbieta; Sokolow, Jesse; Fournier, Bertrand; Chen, Yang; Kalinowski, Jaros; #322; aw A.; Graber, Tim; Henning, Robert; Coppens, Philip (UC); (Buffalo)

    2015-10-15

    The excited-state structure of Cu{sup I}[(1,10-phenanthroline-N,N') bis(triphenylphosphine)] cations in their crystalline [BF{sub 4}] salt has been determined at both 180 and 90 K by single-pulse time-resolved synchrotron experiments with the modified polychromatic Laue method. The two independent molecules in the crystal show distortions on MLCT excitation that differ in magnitude and direction, a difference attributed to a pronounced difference in the molecular environment of the two complexes. As the excited states differ, the decay of the emission is biexponential with two strongly different lifetimes, the longer lifetime, assigned to the more restricted molecule, becoming more prevalent as the temperature increases. Standard deviations in the current Laue study are very much lower than those achieved in a previous monochromatic study of a Cu(I) 2,9-dimethylphenanthroline substituted complex (J. Am. Chem. Soc. 2009, 131, 6566), but the magnitudes of the shifts on excitation are similar, indicating that lattice restrictions dominate over the steric effect of the methyl substitution. Above all, the study illustrates emphatically that molecules in solids have physical properties different from those of isolated molecules and that their properties depend on the specific molecular environment. This conclusion is relevant for the understanding of the properties of molecular solid-state devices, which are increasingly used in current technology.

  8. Molecular co-catalyst accelerating hole transfer for enhanced photocatalytic H2 evolution

    Science.gov (United States)

    Bi, Wentuan; Li, Xiaogang; Zhang, Lei; Jin, Tao; Zhang, Lidong; Zhang, Qun; Luo, Yi; Wu, Changzheng; Xie, Yi

    2015-10-01

    In artificial photocatalysis, sluggish kinetics of hole transfer and the resulting high-charge recombination rate have been the Achilles' heel of photocatalytic conversion efficiency. Here we demonstrate water-soluble molecules as co-catalysts to accelerate hole transfer for improved photocatalytic H2 evolution activity. Trifluoroacetic acid (TFA), by virtue of its reversible redox couple TFA./TFA-, serves as a homogeneous co-catalyst that not only maximizes the contact areas between co-catalysts and reactants but also greatly promotes hole transfer. Thus K4Nb6O17 nanosheet catalysts achieve drastically increased photocatalytic H2 production rate in the presence of TFA, up to 32 times with respect to the blank experiment. The molecular co-catalyst represents a new, simple and highly effective approach to suppress recombination of photogenerated charges, and has provided fertile new ground for creating high-efficiency photosynthesis systems, avoiding use of noble-metal co-catalysts.

  9. Direct electrochemical detection of PCR product based on charge transfer through DNA

    Institute of Scientific and Technical Information of China (English)

    ZHAO Hongtao; ZHANG Zhijie; JU Huangxian

    2005-01-01

    @@ Human genome project and genetic identification for inherited diseases will definitely have a profound impact on the diagnosis of diseases[1], which calls for rapid and accurate assays of DNA. Among different types of sensors, electrochemical DNA biosensors offer a promising alternative means[2,3]. Recent efforts to elucidate the mechanism of charge transfer in DNA have demonstrated that the charge transfer is sensitive to the perturbation in base stack[4,5]. Long-range charge transfer in DNA therefore has been showing great potential application in the development of DNA-based biosensors, especially in the study of single nucleotide polymorphs[7―10].

  10. Charge transfer at organic-organic heterojunctions, and remote doping of a pentacene transistor

    Science.gov (United States)

    Zhao, Wei

    Organic-organic heterojunctions (OOHs) are the fundamental building blocks of organic devices, such as organic light-emitting diodes, organic photovoltaic cells, and photo detectors. Transport of free electrons and holes, exciton formation, recombination or dissociation, and various other physical processes all take place in OOHs. Understanding the electronic structures of OOH is critical for studying device physics and further improving the performance of organic devices. This work focuses on the electronic structure, i.e., the energy level alignment, at OOHs, investigated by ultraviolet and inverse photoemission spectroscopy (UPS and IPES). The weak interaction that generally prevails at OOH interfaces leads to small interface dipoles of 0˜0.5eV. The experimental observations on the majority of OOHs studied can be semi-quantitatively predicted by the model derived from the induced density of interface states and charge neutrality level (IDIS/CNL). However, we also find that the electronic structure of interfaces between two small-band-gap semiconductors, e.g., using copper phthalocyanine (CuPc) as the donor and a tris(thieno)-hexaazatriphenylene derivative (THAP) as the acceptor, is strongly influenced by changes in the substrate work function. In these cases, the charge transfer that takes place at the interface is governed by thermodynamic equilibrium, dominating any subtle interaction due to IDIS/CNL. The impact of doping on the energy level alignment of OOHs is also studied. The charges donated by the dopant molecules transfer from the parent doped layer to the adjacent undoped layer, taking advantage of the molecular level offset, and are then spatially separated from the dopant molecules. Remote doping, based on this charge transfer mechanism, is demonstrated with the heterojunction formed between pentacene and N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'bisphenyl-4,4'diazine (alpha-NPD) p-doped with tris[1,2-bis(trifluoromethyl) ethane-1,2-dithiolene] (Mo

  11. Transient Molecular Transfer During Vacuum Testing

    Science.gov (United States)

    Perry, Radford L.

    2011-01-01

    A common question in contamination budgeting involves the loss of collected volatiles during ambient I&T activity under vacuum and the resultant cross-contamination from outgassing. (1) How much of the material collected under ambient conditions evaporates under vacuum? (2) Why do pristine surfaces sometimes show increased molecular contamination after vacuum bakeout? (3) How much of the collected molecular contamination is transient (i.e. migratory) and how much is permanent? Measuring the transient deposition may be accomplished using a thermally passive QCM

  12. Thermodynamic, kinetic and electronic structure aspects of a charge-transfer active bichromophoric organofullerene

    Indian Academy of Sciences (India)

    K Senthil Kumar; Archita Patnaik

    2013-03-01

    Our recent work on charge transfer in the electronically push-pull dimethylaminoazobenzene-fullerene C60 donor-bridge-acceptor dyad through orbital picture revealed charge displacement from the n(N=N) (non-bonding) and (N=N) type orbitals centred on the donor part to the purely fullerene centred LUMOs and (LUMO+n) orbitals, delocalized over the entire molecule. Consequently, this investigation centres around the kinetic and thermodynamic parameters involved in the solvent polarity dependent intramolecular photo-induced electron transfer processes in the dyad, indispensable for artificial photosynthetic systems. A quasi-reversible electron transfer pathway was elucidated with electrode-specific heterogeneous electron transfer rate constants.

  13. Topological Effects of Charge Transfer in Telomere G-Quadruplex Mechanism on Telomerase Activation and Inhibition

    Science.gov (United States)

    Wang, Xin; Liang, Shi-Dong

    2013-02-01

    We explore the charge transfer in the telomere G-Quadruplex (TG4) DNA theoretically by the nonequilibrium Green's function method, and reveal the topological effect of the charge transport in TG4 DNA. The consecutive TG4 (CTG4) is semiconducting with 0.2 0.3 eV energy gap. Charges transfer favorably in the CTG4, but are trapped in the nonconsecutive TG4 (NCTG4). The global conductance is inversely proportional to the local conductance for NCTG4. The topological structure transition from NCTG4 to CTG4 induces abruptly 3nA charge current, which provide a microscopic clue to understand the telomerase activated or inhibited by TG4. Our findings reveal the fundamental property of charge transfer in TG4 and its relationship with the topological structure of TG4.

  14. Topological effects of charge transfer in telomere G-quadruplex: Mechanism on telomerase activation and inhibition

    CERN Document Server

    Wang, Xin

    2015-01-01

    We explore charge transfer in the telomere G-Quadruplex (TG4) DNA theoretically by the nonequilibrium Green's function method, and reveal the topological effect of charge transport in TG4 DNA. The consecutive TG4(CTG4) is semiconducting with 0.2 ~ 0.3eV energy gap. Charges transfers favorably in the consecutive TG4, but are trapped in the non-consecutive TG4 (NCTG4). The global conductance is inversely proportional to the local conductance for NCTG4. The topological structure transition from NCTG4 to CTG4 induces abruptly ~ 3nA charge current, which provide a microscopic clue to understand the telomerase activated or inhibited by TG4. Our findings reveal the fundamental property of charge transfer in TG4 and its relationship with the topological structure of TG4.

  15. Electrical resistivity study of some organic charge transfer complexes under pressure

    International Nuclear Information System (INIS)

    Electrical resistivity study of the organic charge transfer complexes tetramethyl benzidine - TCNQ and tetramethyl p-phenylene diamine - TCNQ has been carried out up to pressure 80 kilobar. Using the structural aspect, a conduction mechanism under pressure is suggested. (author)

  16. Electronic and Nuclear Factors in Charge and Excitation Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Piotr Piotrowiak

    2004-09-28

    We report the and/or state of several subprojects of our DOE sponsored research on Electronic and Nuclear Factors in Electron and Excitation Transfer: (1) Construction of an ultrafast Ti:sapphire amplifier. (2) Mediation of electronic interactions in host-guest molecules. (3) Theoretical models of electrolytes in weakly polar media. (4) Symmetry effects in intramolecular excitation transfer.

  17. Metal-organic charge transfer can produce biradical states and is mediated by conical intersections

    OpenAIRE

    Tishchenko, Oksana; Li, Ruifang; Truhlar, Donald G.

    2010-01-01

    The present paper illustrates key features of charge transfer between calcium atoms and prototype conjugated hydrocarbons (ethylene, benzene, and coronene) as elucidated by electronic structure calculations. One- and two-electron charge transfer is controlled by two sequential conical intersections. The two lowest electronic states that undergo a conical intersection have closed-shell and open-shell dominant configurations correlating with the 4s2 and 4s13d1 states of Ca, respectively. Unlike...

  18. Quantum Plasmonics: Optical Monitoring of DNA-Mediated Charge Transfer in Plasmon Rulers.

    Science.gov (United States)

    Lerch, Sarah; Reinhard, Björn M

    2016-03-01

    Plasmon coupling between DNA-tethered gold nanoparticles is investigated by correlated single-particle spectroscopy and transmission electron microscopy for interparticle separations between 0.5 and 41 nm. Spectral characterization reveals a weakening of the plasmon coupling due to DNA-mediated charge transfer for separations up to 2.8 nm. Electromagnetic simulations indicate a coherent charge transfer across the DNA. PMID:26789736

  19. Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

    OpenAIRE

    Shutthanandan V; Becker U; Ramana CV; Julien CM

    2008-01-01

    Abstract Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer me...

  20. Single-crystal organic charge-transfer interfaces probed using Schottky-gated heterostructures.

    Science.gov (United States)

    Gutiérrez Lezama, Ignacio; Nakano, Masaki; Minder, Nikolas A; Chen, Zhihua; Di Girolamo, Flavia V; Facchetti, Antonio; Morpurgo, Alberto F

    2012-09-01

    Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the heterointerfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN(2) single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behaviour from room temperature to ~150 K, and remains as high as ~1 cm(2) V(-1) s(-1) at 30 K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively on the basis of the heterostructure band diagram. These results elucidate the electronic structure of rubrene/PDIF-CN(2) interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors. PMID:22820687

  1. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Bhargavi, R.; Nair, Geetha G., E-mail: geeraj88@gmail.com, E-mail: skpras@gmail.com; Krishna Prasad, S., E-mail: geeraj88@gmail.com, E-mail: skpras@gmail.com [Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore 560013 (India); Majumdar, R.; Bag, Braja G. [Department of Chemistry and Chemical Technology, Vidyasagar University, Midnapore (W) 721 102 (India)

    2014-10-21

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  2. Integer versus Fractional Charge Transfer at Metal(/Insulator)/Organic Interfaces: Cu(/NaCl)/TCNE

    OpenAIRE

    Hofmann, O.; Rinke, P.; Scheffler, M.; Heimel, G.

    2015-01-01

    Semilocal and hybrid density functional theory was used to study the charge transfer and the energy-level alignment at a representative interface between an extended metal substrate and an organic adsorbate layer. Upon suppressing electronic coupling between the adsorbate and the substrate by inserting thin, insulating layers of NaCl, the hybrid functional localizes charge. The laterally inhomogeneous charge distribution resulting from this spontaneous breaking of translational symmetry is re...

  3. Charge Transfer and Surface Scattering at Cu/C_60 Planar Interfaces

    Science.gov (United States)

    Hebard, A. F.; Ruel, R. R.; Eom, C. B.

    1996-03-01

    Thin films of Cu and C_60 have been sequentially deposited onto insulating substrates in high vacuum and studied using in situ resistivity measurements during deposition. Different regimes of behavior, which manifest the transfer of electrons from the Cu metal across the planar interface to the C_60, are identified. For example, in the continuous film limit, in which the Cu is thick enough to have a size-effect resistivity proportional to the reciprocal of the film thickness, the presence of an adjacent C_60 monolayer gives rise to an increase in resistance. This resistance increase is quantitatively described by a scattering model in which the interfacial diffuse scattering cross section is found to be 5Åthe approximate area of a face of the molecular cage. In a second regime of behavior, in which the ultra-thin Cu films have a morphology of coalescing islands, the presence of an adjacent C_60 monolayer, doped by charge transfer from the metal, creates a shunting path with sheet resistance ~8000Ω/Box accompanied by a pronounced decrease in resistance. The inferred room-temperature resistivity is more than a factor of two less than that of the 3-dimensional alkali-metal-doped compounds, A_3C_60 (A=K,Rb).

  4. Analytical study for the charge-transfer complexes of losartan potassium

    Energy Technology Data Exchange (ETDEWEB)

    Darwish, Ibrahim A. [Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Assiut University, Assiut 71526 (Egypt)]. E-mail: iadarwish@yahoo.com

    2005-09-06

    Studies were carried out, for the first time, to investigate the charge-transfer reactions of losartan potassium (LOS-K) as n-electron donor with the {sigma}-acceptor iodine and various {pi}-acceptors: 7,7,8,8-tetracyanoquinodimethane, 1,3,5-trinitrobenzene, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, p-chloranilic acid, tetracyanoethylene, 2,3,5,6-tetrabromo-1,4-benzoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, and 2,4,7-trinitro-9-fluorenone. Different colored charge-transfer complexes and radical anions were obtained. Different variables affecting the reactions were studied and optimized. The formed complexes and the site of interaction were examined by UV-vis, IR, and {sup 1}H NMR techniques, and computational molecular modeling. The formation of the colored complexes were utilized in the development of simple, rapid and accurate spectrophotometric methods for the analysis of LOS-K in pure form as well as in its pharmaceutical tablets. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9985-0.9998) were found between the absorbances and the concentrations of LOS-K in the range of 2-200 {mu}g ml{sup -1}. The limits of assays detection ranged from 0.61 to 19.65 {mu}g ml{sup -1}. No interference could be observed from the co-formulated hydrochlorothiazide (HCTZ), as well as from the additives commonly present in the tablets. The methods were successfully applied to the analysis of tablets from different manufacturers that contain LOS-K, alone or combined with HCTZ, with good accuracy and precision; the recovery percentages ranged from 98.96 {+-} 1.62% to 101.58 {+-} 1.29%. The results were compared favourably with the reported method.

  5. Parasitic components from charge transfer in neutral beams for fusion

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, O.A.

    1978-02-01

    Charge exchange within accelerating grids in neutral beam systems produces parasitic beam components which degrade the performance of the systems. These components also change the plasma confinement properties at the target. This note discusses parasitic beams produced in three types of grid systems: (1) TFTR/MFTF sources, (2) accel-decel grids for low energy beams, and (3) the JSC negative ion system.

  6. [Combined hopping-superexchange mechanism of charge transfer in DNA; a model with nearest interactions].

    Science.gov (United States)

    Lakhno, V D; Sultanov, V B

    2007-01-01

    In the framework of the earlier developed combined hopping-superexchange mechanism of charge transfer in DNA, a model with all nearest interactions between nucleobases is proposed. It is shown that the transfer rates for various types of nucleotide sequences calculated within this model are in a good agreement with experimental data.

  7. Heat transfer from the evaporator outlet to the charge of thermostatic expansion valves

    DEFF Research Database (Denmark)

    Langmaack, Lasse Nicolai; Knudsen, Hans-Jørgen Høgaard

    2006-01-01

    The bulb of a thermostatic expansion valve (TXV) is basically a temperature-pressure converter. It senses the temperature at the outlet of the evaporator, and the substance in the bulb (charge) generates the corresponding saturation pressure inside the bulb. The bulb is mounted on the evaporator...... of the valve (and thereby the whole refrigeration system) depends greatly on the heat transfer between the evaporator outlet tube and the charge in the bulb. In this paper a model for the overall heat transfer between the pipe and the charge is presented. Geometrical data and material properties have been kept...

  8. Theoretical and experimental evidence on charge transfer phenomenon of Th(IV) hydrolysis in aqueous medium

    International Nuclear Information System (INIS)

    The present work reports one of the hydrolysis products of thorium is certainly undergoing charge transfer electronic transition. To study electronic transition of this species, absorbance was measured in the concentration range of Th(IV) ions from 1x10-8 M to 1x10-5 M in the absorption wavelength range of 190 nm to 400 nm. Absorbance was observed only in a narrow concentration range of 9.0x10-7 M to 6x10-6 M Th(lV) at 203 nm having molar extinction coefficient (ε) of 1x106 L.mol-1.cm-1. Above and below this concentration range, absorption peak was not observed. The mass spectra study shows that the molecular ion peak is appearing at value 298.8 and it is close to molecular weight of Th(OH)4. Further, theoretical absorption spectra of all possible species of Th(IV) hydrolysis were calculated using Gaussian 03 programme. Geometry optimizations were performed by time-dependent density functional theory (TD-DFT) at the Becker's three parameterized Lee-Yang-Par (B3LYP) and Stuttgart-Dresden effective core potentials basis set (SDD) was used. (author)

  9. Solvent effects on charge spatial extent in DNA and implications for transfer.

    OpenAIRE

    Mantz, Y. A.; Gervasio, F. L.; Laino, T.; Parrinello, M.

    2007-01-01

    To clarify the role played by water in facilitating long-range DNA charge transport, carefully designed, state-of-the-art, self-interaction corrected density-functional quantum mechanical and molecular mechanical (SIC-QM/MM) simulations are performed for the first time on two ionized adenine:thymine bridge models in explicit water solvent at finite temperature. For random solvent configurations, the charge is partially delocalized. However, a charge localization on different, well-separated a...

  10. Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene.

    Science.gov (United States)

    Alexander-Webber, J A; Huang, J; Maude, D K; Janssen, T J B M; Tzalenchuk, A; Antonov, V; Yager, T; Lara-Avila, S; Kubatkin, S; Yakimova, R; Nicholas, R J

    2016-01-01

    Epitaxial graphene has proven itself to be the best candidate for quantum electrical resistance standards due to its wide quantum Hall plateaus with exceptionally high breakdown currents. However one key underlying mechanism, a magnetic field dependent charge transfer process, is yet to be fully understood. Here we report measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to an almost linear increase in carrier density with magnetic field. This behaviour is strong evidence for field dependent charge transfer from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels we model the densities of donor states and predict the field dependence of charge transfer in excellent agreement with experimental results, thus providing a guide towards engineering epitaxial graphene for applications such as quantum metrology. PMID:27456765

  11. Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene

    Science.gov (United States)

    Alexander-Webber, J. A.; Huang, J.; Maude, D. K.; Janssen, T. J. B. M.; Tzalenchuk, A.; Antonov, V.; Yager, T.; Lara-Avila, S.; Kubatkin, S.; Yakimova, R.; Nicholas, R. J.

    2016-07-01

    Epitaxial graphene has proven itself to be the best candidate for quantum electrical resistance standards due to its wide quantum Hall plateaus with exceptionally high breakdown currents. However one key underlying mechanism, a magnetic field dependent charge transfer process, is yet to be fully understood. Here we report measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to an almost linear increase in carrier density with magnetic field. This behaviour is strong evidence for field dependent charge transfer from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels we model the densities of donor states and predict the field dependence of charge transfer in excellent agreement with experimental results, thus providing a guide towards engineering epitaxial graphene for applications such as quantum metrology.

  12. Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

    KAUST Repository

    Gruenewald, Marco

    2015-02-11

    We investigate the prototypical hybrid interface formed between PTCDA and conductive n-doped ZnO films by means of complementary optical and electronic spectroscopic techniques. We demonstrate that shallow donors in the vicinity of the ZnO surface cause an integer charge transfer to PTCDA, which is clearly restricted to the first monolayer. By means of DFT calculations, we show that the experimental signatures of the anionic PTCDA species can be understood in terms of strong hybridization with localized states (the shallow donors) in the substrate and charge back-donation, resulting in an effectively integer charge transfer across the interface. Charge transfer is thus not merely a question of locating the Fermi level above the PTCDA electron-transport level but requires rather an atomistic understanding of the interfacial interactions. The study reveals that defect sites and dopants can have a significant influence on the specifics of interfacial coupling and thus on carrier injection or extraction.

  13. A Molecular Dynamic Simulation of Hydrated Proton Transfer in Perfluorosulfonate Ionomer Membranes (Nafion 117

    Directory of Open Access Journals (Sweden)

    Hong Sun

    2015-01-01

    Full Text Available A molecular dynamic model based on Lennard-Jones Potential, the interaction force between two particles, molecular diffusion, and radial distribution function (RDF is presented. The diffusion of the hydrated ion, triggered by both Grotthuss and vehicle mechanisms, is used to study the proton transfer in Nafion 117. The hydrated ion transfer mechanisms and the effects of the temperature, the water content in the membrane, and the electric field on the diffusion of the hydrated ion are analyzed. The molecular dynamic simulation results are in good agreement with those reported in the literature. The modeling results show that when the water content in Nafion 117 is low, H3O+ is the main transfer ion among the different hydrated ions. However, at higher water content, the hydrated ion in the form of H+(H2O2 is the main transfer ion. It is also found that the negatively charged sulfonic acid group as the fortified point facilitates the proton transfer in Nafion 117 better than the free water molecule. The diffusion of the hydrated ion can be improved by increasing the cell temperature, the water content in Nafion, and the electric field intensity.

  14. Charge Transfer and Bonding Strength in Lithium-intercalated Polyaromatic Hydrocarbons Studied by Photoelectron Spectroscopy

    Institute of Scientific and Technical Information of China (English)

    R.Friedlein

    2007-01-01

    1 Results The potential applications of small-, medium-and large-size polyaromatic hydrocarbons for charge and energy storage in lithium metal and lithium ion batteries are discussed. In order to find the best carbon-based electrode materials, the specific roles of the molecular and solid-state contributions have to be understood. For the molecular contributions, a semi-quantitative method is proposed to compare the charge storage capability of polyaromatic hydrocarbon molecules. A compilation of result...

  15. Controllable Quantum State Transfer Between a Josephson Charge Qubit and an Electronic Spin Ensemble

    Science.gov (United States)

    Yan, Run-Ying; Wang, Hong-Ling; Feng, Zhi-Bo

    2016-01-01

    We propose a theoretical scheme to implement controllable quantum state transfer between a superconducting charge qubit and an electronic spin ensemble of nitrogen-vacancy centers. By an electro-mechanical resonator acting as a quantum data bus, an effective interaction between the charge qubit and the spin ensemble can be achieved in the dispersive regime, by which state transfers are switchable due to the adjustable electrical coupling. With the accessible experimental parameters, we further numerically analyze the feasibility and robustness. The present scheme could provide a potential approach for transferring quantum states controllably with the hybrid system.

  16. Photophysics of charge transfer in a polyfluorene/violanthrone blend

    Science.gov (United States)

    Cabanillas-Gonzalez, J.; Virgili, T.; Lanzani, G.; Yeates, S.; Ariu, M.; Nelson, J.; Bradley, D. D. C.

    2005-01-01

    We present a study of the photophysical and photovoltaic properties of blends of violanthrone in poly[9, 9-bis (2-ethylhexyl)-fluorene-2, 7-diyl ] (PF2/6) . Photoluminescence quenching and photocurrent measurements show moderate efficiencies for charge generation, characteristic of such polymer/dye blends. Pump-probe measurements on blend films suggest that while ˜47% of the total exciton population dissociates within 4ps of photoexcitation, only ˜32% subsequently results in the formation of dye anions. We attribute the discrepancy to the likely formation of complex species with long lifetimes, such as stabilized interface charge pairs or exciplexes. This conclusion is supported by the appearance of a long lifetime component of 2.4ns in the dynamics of the photoinduced absorption signal associated to polarons in photoinduced absorption bands centered at 560nm .

  17. Charge transfer in the presence of a radiation field

    International Nuclear Information System (INIS)

    In the first Borm approximation, the dressing modification in laser-assisted charge exchange collision is investigated. The cross sections for electron capture by a proton from dressed atomic hydrogen and dressed helium targets are calculated within a wide energy range. Theoretical results show that with impact energy increasing, the dressing effect leads to increasingly significant cross-section modifications. The modified capture cross sections are increasing functions of the ratio of laser strength to frequency. (author)

  18. Analysis of incomplete charge transfer effects in a CMOS image sensor

    Institute of Scientific and Technical Information of China (English)

    Han Liqiang; Yao Suying; Xu Jiangtao; Xu Chao; Gao Zhiyuan

    2013-01-01

    A method to judge complete charger transfer is proposed for a four-transistor CMOS image sensor with a large pixel size.Based on the emission current theory,a qualitative photoresponse model is established to the preliminary prediction.Further analysis of noise for incomplete charge transfer predicts the noise variation.The test pixels were fabricated in a specialized 0.18μm CMOS image sensor process and two different processes of buried N layer implantation are compared.The trend prediction corresponds with the test results,especially as it can distinguish an unobvious incomplete charge transfer.The method helps us judge whether the charge transfer time satisfies the requirements of the readout circuit for the given process especially for pixels of a large size.

  19. The lowest-energy charge-transfer state and its role in charge separation in organic photovoltaics.

    Science.gov (United States)

    Nan, Guangjun; Zhang, Xu; Lu, Gang

    2016-06-29

    Energy independent, yet higher than 90% internal quantum efficiency (IQE), has been observed in many organic photovoltaics (OPVs). However, its physical origin remains largely unknown and controversial. The hypothesis that the lowest charge-transfer (CT) state may be weakly bound at the interface has been proposed to rationalize the experimental observations. In this paper, we study the nature of the lowest-energy CT (CT1) state, and show conclusively that the CT1 state is localized in typical OPVs. The electronic couplings in the donor and acceptor are found to determine the localization of the CT1 state. We examine the geminate recombination of the CT1 state and estimate its lifetime from first principles. We identify the vibrational modes that contribute to the geminate recombination. Using material parameters determined from first principles and experiments, we carry out kinetic Monte Carlo simulations to examine the charge separation of the localized CT1 state. We find that the localized CT1 state can indeed yield efficient charge separation with IQE higher than 90%. Dynamic disorder and configuration entropy can provide the energetic and entropy driving force for charge separation. Charge separation efficiency depends more sensitively on the dimension and crystallinity of the acceptor parallel to the interface than that normal to the interface. Reorganization energy is found to be the most important material parameter for charge separation, and lowering the reorganization energy of the donor should be pursued in the materials design. PMID:27306609

  20. The lowest-energy charge-transfer state and its role in charge separation in organic photovoltaics.

    Science.gov (United States)

    Nan, Guangjun; Zhang, Xu; Lu, Gang

    2016-06-29

    Energy independent, yet higher than 90% internal quantum efficiency (IQE), has been observed in many organic photovoltaics (OPVs). However, its physical origin remains largely unknown and controversial. The hypothesis that the lowest charge-transfer (CT) state may be weakly bound at the interface has been proposed to rationalize the experimental observations. In this paper, we study the nature of the lowest-energy CT (CT1) state, and show conclusively that the CT1 state is localized in typical OPVs. The electronic couplings in the donor and acceptor are found to determine the localization of the CT1 state. We examine the geminate recombination of the CT1 state and estimate its lifetime from first principles. We identify the vibrational modes that contribute to the geminate recombination. Using material parameters determined from first principles and experiments, we carry out kinetic Monte Carlo simulations to examine the charge separation of the localized CT1 state. We find that the localized CT1 state can indeed yield efficient charge separation with IQE higher than 90%. Dynamic disorder and configuration entropy can provide the energetic and entropy driving force for charge separation. Charge separation efficiency depends more sensitively on the dimension and crystallinity of the acceptor parallel to the interface than that normal to the interface. Reorganization energy is found to be the most important material parameter for charge separation, and lowering the reorganization energy of the donor should be pursued in the materials design.

  1. Characterizing reactions to fabricate thin films of charge transfer complexes by synchrotron photoelectron spectroscopy: A case study of DCNQI-Cu

    Science.gov (United States)

    Shimada, Toshihiro; Mochida, Michihiro; Koma, Atsushi

    1997-04-01

    Ultraviolet photoelectron spectroscopy with various photon energies using synchrotron radiation was used to characterize chemical reactions associated with thin film growth of organic charge transfer complex (DMe-DCNQI) 2Cu. Other molecular systems H 2Pc, CuPc and C 60 were also studied to clarify the origin of the systematic relation between the spectra and the incident photon energy. Characteristic photon energy dependence of the photo-ionization cross section of molecular orbitals is useful to analyze the intermolecular reactions.

  2. Bonding and charge transfer plasmons of conductively bridged nanoparticles: The effects of junction conductance and nanoparticle morphology

    Science.gov (United States)

    Koya, Alemayehu Nana; Lin, Jingquan

    2016-09-01

    A detailed study of charge transfer plasmon properties of conductively bridged nanoparticles is essential for designing artificial molecules and developing plasmonic sensors. In this report, we demonstrate spectral tuning and control of local field responses of conductively bridged and compositionally homogeneous plasmonic nanoparticles of various shapes and sizes. The scattering spectral peaks of connected nanoparticles are tuned by controlling inter-particle feed-gap, junction conductance, and nanoparticle morphology. The far-field spectral responses are further tuned by increasing the number of nanoparticles from dimer to trimer, and a generalized expression for charge transfer plasmon peak shift with junction geometry is developed for various shapes of nanotrimers. The corresponding near-field distributions of the linked nanoparticles also exhibit remarkable features. Specifically, the local field profiles of dimer nanoparticles calculated at the charge transfer wavelengths show strong interaction between the nanoparticles. On the other hand, in the bridged symmetrical nanotrimers, the central nanoparticles act as a bridge and only the rest two of the nanoparticles show bright modes. These findings suggest that using conductively bridged nanoaggregates could play a significant role in tuning far-field spectral responses of plasmonic nanostructures for practical applications in molecular sensing.

  3. Spectroscopic analysis and charge transfer interaction studies of 4-benzyloxy-2-nitroaniline insecticide: A density functional theoretical approach

    Science.gov (United States)

    Arul Dhas, D.; Hubert Joe, I.; Roy, S. D. D.; Balachandran, S.

    2015-01-01

    A widespread exploration on the intra-molecular charge transfer interaction through an efficient π-conjugated path from a strong electron-donor group (amino) to a strong electron-acceptor group (nitro) has been carried out using FTIR, FT-Raman, UV-Vis, fluorescence and NMR spectra on insecticide compound 4-benzyloxy-2-nitroaniline. Density functional theory method is used to determine optimized molecular geometry, harmonic vibrational wavenumbers and intensities using 6-311G(d,p) basis set by means of Gaussian 09W program suit. A comprehensive investigation on the sp2 to sp3 hybridization and non-planarity property has been performed. Natural bond orbital analysis is used to study the existence of C-H⋯O, N-H⋯O and C-H⋯π proper and improper hydrogen bonds. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. A complete assignment of the experimental absorption peaks in the ultraviolet region has also been performed. Isotropic chemical shifts of 13C, 1H, 15N and 18O NMR and nuclear spin-spin coupling constants have been computed using the gauge-invariant atomic orbital method. The biological activity of substituent amino and nitro groups are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.

  4. Charge Transfer Properties Through Graphene Layers in Gas Detectors

    CERN Document Server

    Thuiner, P; Jackman, R.B.; Müller, H.; Nguyen, T.T.; Oliveri, E.; Pfeiffer, D.; Resnati, F.; Ropelewski, L.; Smith, J.A.; van Stenis, M.; Veenhof, R.

    2015-01-01

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical, electrical and optical properties. For the first time graphene layers suspended on copper meshes were installed into a gas detector equipped with a gaseous electron multiplier. Measurements of low energy electron and ion transfer through graphene were conducted. In this paper we describe the sample preparation for suspended graphene layers, the testing procedures and we discuss the preliminary results followed by a prospect of further applications.

  5. Comparison of two models for bridge-assisted charge transfer

    CERN Document Server

    Schreiber, M; Kleinekathöfer, U

    1999-01-01

    Based on the reduced density matrix method, we compare two different approaches to calculate the dynamics of the electron transfer in systems with donor, bridge, and acceptor. In the first approach a vibrational substructure is taken into account for each electronic state and the corresponding states are displaced along a common reaction coordinate. In the second approach it is assumed that vibrational relaxation is much faster than the electron transfer and therefore the states are modeled by electronic levels only. In both approaches the system is coupled to a bath of harmonic oscillators but the way of relaxation is quite different. The theory is applied to the electron transfer in ${\\rm H_2P}-{\\rm ZnP}-{\\rm Q}$ with free-base porphyrin (${\\rm H_2P}$) being the donor, zinc porphyrin (${\\rm ZnP}$) being the bridge and quinone (${\\rm Q}$) the acceptor. The parameters are chosen as similar as possible for both approaches and the quality of the agreement is discussed.

  6. Process techniques of charge transfer time reduction for high speed CMOS image sensors

    International Nuclear Information System (INIS)

    This paper proposes pixel process techniques to reduce the charge transfer time in high speed CMOS image sensors. These techniques increase the lateral conductivity of the photo-generated carriers in a pinned photodiode (PPD) and the voltage difference between the PPD and the floating diffusion (FD) node by controlling and optimizing the N doping concentration in the PPD and the threshold voltage of the reset transistor, respectively. The techniques shorten the charge transfer time from the PPD diode to the FD node effectively. The proposed process techniques do not need extra masks and do not cause harm to the fill factor. A sub array of 32 × 64 pixels was designed and implemented in the 0.18 μm CIS process with five implantation conditions splitting the N region in the PPD. The simulation and measured results demonstrate that the charge transfer time can be decreased by using the proposed techniques. Comparing the charge transfer time of the pixel with the different implantation conditions of the N region, the charge transfer time of 0.32 μs is achieved and 31% of image lag was reduced by using the proposed process techniques. (semiconductor devices)

  7. Formation and fragmentation of quadruply charged molecular ions by intense femtosecond laser pulses.

    Science.gov (United States)

    Yatsuhashi, Tomoyuki; Nakashima, Nobuaki

    2010-07-22

    We investigated the formation and fragmentation of multiply charged molecular ions of several aromatic molecules by intense nonresonant femtosecond laser pulses of 1.4 mum with a 130 fs pulse duration (up to 2 x 10(14) W cm(-2)). Quadruply charged states were produced for 2,3-benzofluorene and triphenylene molecular ion in large abundance, whereas naphthalene and 1,1'-binaphthyl resulted only in up to triply charged molecular ions. The laser wavelength was nonresonant with regard to the electronic transitions of the neutral molecules, and the degree of fragmentation was strongly correlated with the absorption of the singly charged cation radical. Little fragmentation was observed for naphthalene (off-resonant with cation), whereas heavy fragmentation was observed in the case of 1,1'-binaphthyl (resonant with cation). The degree of H(2) (2H) and 2H(2) (4H) elimination from molecular ions increased as the charge states increased in all the molecules examined. A striking difference was found between triply and quadruply charged 2,3-benzofluorene: significant suppression of molecular ions with loss of odd number of hydrogen was observed in the quadruply charged ions. The Coulomb explosion of protons in the quadruply charged state and succeeding fragmentation resulted in the formation of triply charged molecular ions with an odd number of hydrogens. The hydrogen elimination mechanism in the highly charged state is discussed.

  8. Formation and fragmentation of quadruply charged molecular ions by intense femtosecond laser pulses.

    Science.gov (United States)

    Yatsuhashi, Tomoyuki; Nakashima, Nobuaki

    2010-07-22

    We investigated the formation and fragmentation of multiply charged molecular ions of several aromatic molecules by intense nonresonant femtosecond laser pulses of 1.4 mum with a 130 fs pulse duration (up to 2 x 10(14) W cm(-2)). Quadruply charged states were produced for 2,3-benzofluorene and triphenylene molecular ion in large abundance, whereas naphthalene and 1,1'-binaphthyl resulted only in up to triply charged molecular ions. The laser wavelength was nonresonant with regard to the electronic transitions of the neutral molecules, and the degree of fragmentation was strongly correlated with the absorption of the singly charged cation radical. Little fragmentation was observed for naphthalene (off-resonant with cation), whereas heavy fragmentation was observed in the case of 1,1'-binaphthyl (resonant with cation). The degree of H(2) (2H) and 2H(2) (4H) elimination from molecular ions increased as the charge states increased in all the molecules examined. A striking difference was found between triply and quadruply charged 2,3-benzofluorene: significant suppression of molecular ions with loss of odd number of hydrogen was observed in the quadruply charged ions. The Coulomb explosion of protons in the quadruply charged state and succeeding fragmentation resulted in the formation of triply charged molecular ions with an odd number of hydrogens. The hydrogen elimination mechanism in the highly charged state is discussed. PMID:20578764

  9. DNA in a Dissipative Environment: A Charge Transfer Approach

    Science.gov (United States)

    Behnia, Sohrab; Fathizadeh, Samira; Akhshani, Afshin

    2015-08-01

    Conductivity properties of DNA molecule is investigated in a simple, chemically specific approach, that is intimately related to the Su-Schrieffer-Heeger (SSH) model. In the SSH model, the non-diagonal matrix element dependent on intersite displacements is considered and there is a coupling between the charge and lattice deformation along DNA helix. In order to study the evolution of the electrical current flowing through DNA in the presence of external electrical field, the electrical current is directly extracted from the dynamical equations. Ranges of electrical field and hopping constant value are estimated using MLE approach. The model is studied by means of I-V characteristic diagrams and the environmental effects is conducted through a phonon bath using different lengths of DNA. The NDR and quasi-Ohmic regions are observed.

  10. Carotenoid to chlorophyll energy transfer in the peridinin–chlorophyll-a–protein complex involves an intramolecular charge transfer state

    Science.gov (United States)

    Zigmantas, Donatas; Hiller, Roger G.; Sundström, Villy; Polívka, Tomáš

    2002-01-01

    Carotenoids are, along with chlorophylls, crucial pigments involved in light-harvesting processes in photosynthetic organisms. Details of carotenoid to chlorophyll energy transfer mechanisms and their dependence on structural variability of carotenoids are as yet poorly understood. Here, we employ femtosecond transient absorption spectroscopy to reveal energy transfer pathways in the peridinin–chlorophyll-a–protein (PCP) complex containing the highly substituted carotenoid peridinin, which includes an intramolecular charge transfer (ICT) state in its excited state manifold. Extending the transient absorption spectra toward near-infrared region (600–1800 nm) allowed us to separate contributions from different low-lying excited states of peridinin. The results demonstrate a special light-harvesting strategy in the PCP complex that uses the ICT state of peridinin to enhance energy transfer efficiency. PMID:12486228

  11. Charge Transfer Properties Through Graphene for Applications in Gaseous Detectors

    CERN Document Server

    Franchino, S; Hall-Wilton, R.; Jackman, R.B.; Muller, H.; Nguyen, T.T.; de Oliveira, R.; Oliveri, E.; Pfeiffer, D.; Resnati, F.; Ropelewski, L.; Smith, J.; van Stenis, M.; Streli, C.; Thuiner, P.; Veenhof, R.

    2016-01-01

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical and electrical properties. Regarded as the thinnest and narrowest conductive mesh, it has drastically different transmission behaviours when bombarded with electrons and ions in vacuum. This property, if confirmed in gas, may be a definitive solution for the ion back-flow problem in gaseous detectors. In order to ascertain this aspect, graphene layers of dimensions of about 2x2cm$^2$, grown on a copper substrate, are transferred onto a flat metal surface with holes, so that the graphene layer is freely suspended. The graphene and the support are installed into a gaseous detector equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency properties to electrons and ions are studied in gas as a function of the electric fields. The techniques to produce the graphene samples are described, and we report on preliminary tests of graphene-coated GEMs.

  12. Charge transfer properties through graphene for applications in gaseous detectors

    Science.gov (United States)

    Franchino, S.; Gonzalez-Diaz, D.; Hall-Wilton, R.; Jackman, R. B.; Muller, H.; Nguyen, T. T.; de Oliveira, R.; Oliveri, E.; Pfeiffer, D.; Resnati, F.; Ropelewski, L.; Smith, J.; van Stenis, M.; Streli, C.; Thuiner, P.; Veenhof, R.

    2016-07-01

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical and electrical properties. Regarded as the thinnest and narrowest conductive mesh, it has drastically different transmission behaviours when bombarded with electrons and ions in vacuum. This property, if confirmed in gas, may be a definitive solution for the ion back-flow problem in gaseous detectors. In order to ascertain this aspect, graphene layers of dimensions of about 2×2 cm2, grown on a copper substrate, are transferred onto a flat metal surface with holes, so that the graphene layer is freely suspended. The graphene and the support are installed into a gaseous detector equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency properties to electrons and ions are studied in gas as a function of the electric fields. The techniques to produce the graphene samples are described, and we report on preliminary tests of graphene-coated GEMs.

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

    KAUST Repository

    Ayzner, Alexander L.

    2015-01-02

    © 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.

  14. Mechanism of charge transfer and its impacts on Fermi-level pinning for gas molecules adsorbed on monolayer WS{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Changjie; Zhu, Huili, E-mail: hlzhu@jmu.edu.cn [Department of Physics, School of Science, Jimei University, Xiamen 361021 (China); Yang, Weihuang [Division of Physics and Applied Physics, School of Physical and Mathematical Science, Nanyang Technological University, Singapore 637371 (Singapore)

    2015-06-07

    Density functional theory calculations were performed to assess changes in the geometric and electronic structures of monolayer WS{sub 2} upon adsorption of various gas molecules (H{sub 2}, O{sub 2}, H{sub 2}O, NH{sub 3}, NO, NO{sub 2}, and CO). The most stable configuration of the adsorbed molecules, the adsorption energy, and the degree of charge transfer between adsorbate and substrate were determined. All evaluated molecules were physisorbed on monolayer WS{sub 2} with a low degree of charge transfer and accept charge from the monolayer, except for NH{sub 3}, which is a charge donor. Band structure calculations showed that the valence and conduction bands of monolayer WS{sub 2} are not significantly altered upon adsorption of H{sub 2}, H{sub 2}O, NH{sub 3}, and CO, whereas the lowest unoccupied molecular orbitals of O{sub 2}, NO, and NO{sub 2} are pinned around the Fermi-level when these molecules are adsorbed on monolayer WS{sub 2}. The phenomenon of Fermi-level pinning was discussed in light of the traditional and orbital mixing charge transfer theories. The impacts of the charge transfer mechanism on Fermi-level pinning were confirmed for the gas molecules adsorbed on monolayer WS{sub 2}. The proposed mechanism governing Fermi-level pinning is applicable to the systems of adsorbates on recently developed two-dimensional materials, such as graphene and transition metal dichalcogenides.

  15. Photoinduced charge transfer involving a MoMo quadruply bonded complex to a perylene diimide.

    Science.gov (United States)

    Alberding, Brian G; Brown-Xu, Samantha E; Chisholm, Malcolm H; Epstein, Arthur J; Gustafson, Terry L; Lewis, Sharlene A; Min, Yong

    2013-04-21

    Evidence, based on femtosecond transient absorption and time resolved infrared spectroscopy, is presented for photoinduced charge transfer from the Mo2δ orbital of the quadruply bonded molecule trans-Mo2(T(i)PB)2(BTh)2, where T(i)PB = 2,4,6-triisopropyl benzoate and BTh = 2,2'-bithienylcarboxylate, to di-n-octyl perylene diimide and di-n-hexylheptyl perylene diimide in thin films and solutions of the mixtures. The films show a long-lived charge separated state while slow back electron transfer, τBET ~ 500 ps, occurs in solution.

  16. The description of charge transfer in fast negative ions scattering on water covered Si(100) surfaces

    Science.gov (United States)

    Chen, Lin; Qiu, Shunli; Liu, Pinyang; Xiong, Feifei; Lu, Jianjie; Liu, Yuefeng; Li, Guopeng; Liu, Yiran; Ren, Fei; Xiao, Yunqing; Gao, Lei; Zhao, Qiushuang; Ding, Bin; Li, Yuan; Guo, Yanling; Chen, Ximeng

    2016-11-01

    Doping has significantly affected the characteristics and performance of semiconductor electronic devices. In this work, we study the charge transfer processes for 8.5-22.5 keV C- and F- ions scattering on H2O-terminated p-type Si(100) surfaces with two different doping concentrations. We find that doping has no influence on negative-ion formation for fast collisions in this relatively high energy range. Moreover, we build a model to calculate negative ion fractions including the contribution from positive ions. The calculations support the nonadiabatic feature of charge transfer.

  17. Polarization dependence of charge-transfer excitations in La2CuO4

    Science.gov (United States)

    Lu, Li; Chabot-Couture, Guillaume; Hancock, Jason; Vajk, Owen; Yu, Guichuan; Ishii, Kenji; Mizuki, Jun'ichiro; Casa, Diego; Gog, Thomas; Greven, Martin

    2006-03-01

    We have carried out an extensive resonant inelastic x-ray scattering (RIXS) study of La2CuO4 at the Cu K-edge. Multiple charge-transfer excitations have been identified using the incident photon energy dependence of the cross section and studied carefully with polarizations E//c and E //ab. An analysis of the incident photon energy dependence, the polarization dependence, as well as the K-edge absorption spectra, indicates that the RIXS spectra reveal rich physics about the K-edge absorption process and momentum-dependent charge-transfer excitations in cuprates.

  18. Fluorescence behavior of intramolecular charge transfer state in trans-ethyl p-(dimethylamino)cinamate

    International Nuclear Information System (INIS)

    Steady-state and time-resolved emission studies have been performed to investigate the intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino)cinamate (EDAC) in various solvents. Large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the excited state compared to the ground state. The excited state properties in hydrogen-bonding solvents are markedly different from other solvents indicating the possible competition of intermolecular hydrogen bond formation with the electron donor site and ICT

  19. Photoinduced charge transfer within polyaniline-encapsulated quantum dots decorated on graphene.

    Science.gov (United States)

    Nguyen, Kim Truc; Li, Dehui; Borah, Parijat; Ma, Xing; Liu, Zhaona; Zhu, Liangliang; Grüner, George; Xiong, Qihua; Zhao, Yanli

    2013-08-28

    A new method to enhance the stability of quantum dots (QDs) in aqueous solution by encapsulating them with conducting polymer polyaniline was reported. The polyaniline-encapsulated QDs were then decorated onto graphene through π-π interactions between graphene and conjugated polymer shell of QDs, forming stable polyaniline/QD/graphene hybrid. A testing electronic device was fabricated using the hybrid in order to investigate the photoinduced charge transfer between graphene and encapsulated QDs within the hybrid. The charge transfer mechanism was explored through cyclic voltammetry and spectroscopic studies. The hybrid shows a clear response to the laser irradiation, presenting a great advantage for further applications in optoelectronic devices.

  20. Electronic coupling effects and charge transfer between organic molecules and metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Forker, Roman

    2010-07-01

    We employ a variant of optical absorption spectroscopy, namely in situ differential reflectance spectroscopy (DRS), for an analysis of the structure-properties relations of thin epitaxial organic films. Clear correlations between the spectra and the differently intense coupling to the respective substrates are found. While rather broad and almost structureless spectra are obtained for a quaterrylene (QT) monolayer on Au(111), the spectral shape resembles that of isolated molecules when QT is grown on graphite. We even achieve an efficient electronic decoupling from the subjacent Au(111) by inserting an atomically thin organic spacer layer consisting of hexa-peri-hexabenzocoronene (HBC) with a noticeably dissimilar electronic behavior. These observations are further consolidated by a systematic variation of the metal substrate (Au, Ag, and Al), ranging from inert to rather reactive. For this purpose, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is chosen to ensure comparability of the molecular film structures on the different metals, and also because its electronic alignment on various metal surfaces has previously been studied with great intensity. We present evidence for ionized PTCDA at several interfaces and propose the charge transfer to be related to the electronic level alignment governed by interface dipole formation on the respective metals. (orig.)

  1. Geometry and quadratic nonlinearity of charge transfer complexes in solution: a theoretical study.

    Science.gov (United States)

    Mukhopadhyay, S; Pandey, Ravindra; Das, Puspendu K; Ramasesha, S

    2011-01-28

    In this paper, we have computed the quadratic nonlinear optical (NLO) properties of a class of weak charge transfer (CT) complexes. These weak complexes are formed when the methyl substituted benzenes (donors) are added to strong acceptors like chloranil (CHL) or di-chloro-di-cyano benzoquinone (DDQ) in chloroform or in dichloromethane. The formation of such complexes is manifested by the presence of a broad absorption maximum in the visible range of the spectrum where neither the donor nor the acceptor absorbs. The appearance of this visible band is due to CT interactions, which result in strong NLO responses. We have employed the semiempirical intermediate neglect of differential overlap (INDO∕S) Hamiltonian to calculate the energy levels of these CT complexes using single and double configuration interaction (SDCI). The solvent effects are taken into account by using the self-consistent reaction field (SCRF) scheme. The geometry of the complex is obtained by exploring different relative molecular geometries by rotating the acceptor with respect to the fixed donor about three different axes. The theoretical geometry that best fits the experimental energy gaps, β(HRS) and macroscopic depolarization ratios is taken to be the most probable geometry of the complex. Our studies show that the most probable geometry of these complexes in solution is the parallel displaced structure with a significant twist in some cases.

  2. Evidence of Delocalization in Charge-Transfer State Manifold for Donor:Acceptor Organic Photovoltaics.

    Science.gov (United States)

    Guan, Zhiqiang; Li, Ho-Wa; Zhang, Jinfeng; Cheng, Yuanhang; Yang, Qingdan; Lo, Ming-Fai; Ng, Tsz-Wai; Tsang, Sai-Wing; Lee, Chun-Sing

    2016-08-24

    How charge-transfer states (CTSs) assist charge separation of a Coulombically bound exciton in organic photovoltaics has been a hot topic. It is believed that the delocalization feature of a CTS plays a crucial role in the charge separation process. However, the delocalization of the "hot" and the "relaxed" CTSs is still under debate. Here, with a novel frequency dependent charge-modulated electroabsorption spectroscopy (CMEAS) technique, we elucidate clearly that both "hot" and "relaxed" CTSs are loosely bound and delocalized states. This is confirmed by comparing the CMEAS results of CTSs with those of localized polaron states. Our results reveal the role of CTS delocalization on charge separation and indicate that no substantial delocalization gradient exists in CTSs.

  3. Transverse Schottky spectra and beam transfer functions of coasting ion beams with space charge

    International Nuclear Information System (INIS)

    A study of the transverse dynamics of coasting ion beams with moderate space charge is presented in this work. From the dispersion relation with linear space charge, an analytic model describing the impact of space charge on transverse beam transfer functions (BTFs) and the stability limits of a beam is derived. The dielectric function obtained in this way is employed to describe the transverse Schottky spectra with linear space charge as well. The difference between the action of space charge and impedances is highlighted. The setup and the results of an experiment performed in the heavy ion synchrotron SIS-18 at GSI to detect space-charge effects at different beam intensities are explicated. The measured transverse Schottky spectra and BTFs are compared with the linear space-charge model. The stability diagrams constructed from the BTFs are presented. The space-charge parameters evaluated from the Schottky and BTF measurements are compared with estimations based on measured beam parameters. The impact of collective effects on the Schottky and BTF diagnostics is also investigated through numerical simulations. For this purpose the self-field of beams with linear and non-linear transverse density-distributions is computed on a twodimensional grid. The noise of the random particle distribution causes fluctuations of the dipole moment of the beam which produce the Schottky spectrum. BTFs are simulated by exciting the beam with transverse kicks. The simulation results are used to verify the space-charge model. (orig.)

  4. Transverse Schottky spectra and beam transfer functions of coasting ion beams with space charge

    Energy Technology Data Exchange (ETDEWEB)

    Paret, Stefan

    2010-02-22

    A study of the transverse dynamics of coasting ion beams with moderate space charge is presented in this work. From the dispersion relation with linear space charge, an analytic model describing the impact of space charge on transverse beam transfer functions (BTFs) and the stability limits of a beam is derived. The dielectric function obtained in this way is employed to describe the transverse Schottky spectra with linear space charge as well. The difference between the action of space charge and impedances is highlighted. The setup and the results of an experiment performed in the heavy ion synchrotron SIS-18 at GSI to detect space-charge effects at different beam intensities are explicated. The measured transverse Schottky spectra and BTFs are compared with the linear space-charge model. The stability diagrams constructed from the BTFs are presented. The space-charge parameters evaluated from the Schottky and BTF measurements are compared with estimations based on measured beam parameters. The impact of collective effects on the Schottky and BTF diagnostics is also investigated through numerical simulations. For this purpose the self-field of beams with linear and non-linear transverse density-distributions is computed on a twodimensional grid. The noise of the random particle distribution causes fluctuations of the dipole moment of the beam which produce the Schottky spectrum. BTFs are simulated by exciting the beam with transverse kicks. The simulation results are used to verify the space-charge model. (orig.)

  5. State-to-state dynamics of molecular energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Gentry, W.R.; Giese, C.F. [Univ. of Minnesota, Minneapolis (United States)

    1993-12-01

    The goal of this research program is to elucidate the elementary dynamical mechanisms of vibrational and rotational energy transfer between molecules, at a quantum-state resolved level of detail. Molecular beam techniques are used to isolate individual molecular collisions, and to control the kinetic energy of collision. Lasers are used both to prepare specific quantum states prior to collision by stimulated-emission pumping (SEP), and to measure the distribution of quantum states in the collision products by laser-induced fluorescence (LIF). The results are interpreted in terms of dynamical models, which may be cast in a classical, semiclassical or quantum mechanical framework, as appropriate.

  6. [Time-resolved optical studies of charge relaxation and charge transfer at electrode interfaces

    Energy Technology Data Exchange (ETDEWEB)

    1992-12-31

    Key components were identified in a quantitative model of carrier relaxation in semiconductor electrodes: nonlinear aspects of nonradiative and radiative recombination, effect of space charge field on carrier dynamics, self-absorption effects in direct gas semiconductors, and influence of surface state population kinetics on charge carrier recombination. For CdSe, the first three are operative (no direct proof of the last one). A realistic kinetic model for carrier recombination in the bulk of CdSe was used which includes important nonlinear effects, both radiative and nonradiative. The change in interfacial recombination velocity with the chemical nature of the sinterface was studied (n-CdSe/silane interfaces). Temperature effect (278 to 328 K) on fluorescence decay of n-CdSe in contact with 0.5 M KOH was found to be weak. An analytical solution was obtained for time-resolved fluoresence from electrodes under potential bias, and is being tested. Fluorescence work on a different material, CdS, indicate different recombination kinetics; this material was used to directly pump an optical transition of a surface state.

  7. Effect of Surface Charge on Surface-Initiated Atom Transfer Radical Polymerization from Cellulose Nanocrystals in Aqueous Media.

    Science.gov (United States)

    Zoppe, Justin O; Xu, Xingyu; Känel, Cindy; Orsolini, Paola; Siqueira, Gilberto; Tingaut, Philippe; Zimmermann, Tanja; Klok, Harm-Anton

    2016-04-11

    Cellulose nanocrystals (CNCs) with different charge densities were utilized to examine the role of electrostatic interactions on surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media. To this end, growth of hydrophilic uncharged poly(N,N-dimethylacrylamide) (PDMAM) brushes was monitored by electrophoresis, (1)H NMR spectroscopy, and dynamic light scattering (DLS). Molecular weight and polydispersity of PDMAM brushes was determined by GPC analysis of hydrolytically cleaved polymers. Initiator and polymer brush grafting densities, and thus, initiator efficiencies were derived from elemental analysis. Higher initiator efficiency of polymer brush growth was observed for CNCs with higher anionic surface sulfate half-ester group density, but at the expense of high polydispersity caused by inefficient deactivation. PDMAM grafts with number-average molecular weights up to 530 kDa and polydispersity indices Cu-mediated SI-CRP are analogous to those conducted in solution. PMID:26901869

  8. Anomalous charge and negative-charge-transfer insulating state in cuprate chain-compound KCuO_2

    OpenAIRE

    Choudhury, D.; Rivero, P.; Meyers, D.; Liu, X.; Cao, Y; Middey, S.; Whitaker, M. J.; Barraza-Lopez, S.; Freeland, J. W.; Greenblatt, M.; Chakhalian, J.

    2015-01-01

    Using a combination of X-ray absorption spectroscopy experiments with first principle calculations, we demonstrate that insulating KCuO_2 contains Cu in an unusually-high formal-3+ valence state, the ligand-to-metal (O to Cu) charge transfer energy is intriguingly negative (Delta~ -1.5 eV) and has a dominant (~60%) ligand-hole character in the ground state akin to the high Tc cuprate Zhang-Rice state. Unlike most other formal Cu^{3+} compounds, the Cu 2p XAS spectra of KCuO_2 exhibits pronoun...

  9. Charge transfer in a sharply nonuniform electric field mediated by swirling liquid flow with minimal hydraulic resistance

    Science.gov (United States)

    Nagorny, V. S.; Smirnovsky, A. A.; Chernyshev, A. S.; Kolodyazhny, D. Yu.

    2015-09-01

    A scheme of a fuel nozzle with "needle-plane" electrode system, the location of which enables one to minimize the imparted hydraulic resistance, is proposed. We consider the processes of charge transfer in a sharply inhomogeneous electric field in order to estimate the amount of charge coming out of the channel. For this purpose, we used the OpenFOAM software package, modified to account for the electrohydrodynamic effects. By using the k-ω SST turbulence model within an axial-symmetrical RANS problem, the vortex liquid flow and charge transfer are calculated. The impact of vorticity degree on the processes of charge transfer is studied. It is found that the charge flowing out of the calculation domain is about 80% of the injected charge. The vorticity degree in the above range of values has little effect on the process of charge transfer.

  10. Changes in wetting and contact charge transfer by femtosecond laser-ablation of polyimide

    Energy Technology Data Exchange (ETDEWEB)

    Guo, X.D., E-mail: xiaodong.guo@uib.no [Department of Physics and Technology, Allegaten 55, 5020 Bergen, University of Bergen (Norway); Dai, Y.; Gong, M. [Department of Physics, Shanghai 200444, Shanghai University (China); Qu, Y.G. [Center for Geobiology, Allegaten 41, 5020 Bergen, University of Bergen (Norway); Helseth, L.E. [Department of Physics and Technology, Allegaten 55, 5020 Bergen, University of Bergen (Norway)

    2015-09-15

    Highlights: • Laser ablation significantly reduced the triboelectric charging of polyimide films. • Hierarchical micro/nanostructures formed on the surface of the sample. • Structural anisotropy leads to spatially varying contact angles of water droplets. • Raman spectroscopy revealed a carbonization of the polyimide sample. • The corresponding loss of insulation may explain the reduction of charge transfer. - Abstract: In this study it is demonstrated that the triboelectric charging of polyimide thin films is significantly reduced by using a femtosecond laser to nanostructure its. It is found that the contact charge transfer between laser-ablated Kapton and aluminum is almost negligible, and even much lower than the significant current occurring when non-treated Kapton touches the metal. Scanning electron microscopy demonstrates that laser ablation produces a hierarchical micro and nanostructure, and it is found that the structural anisotropy leads to spatially varying contact angles of water droplets residing on the surface. Raman spectra suggest that the centers of the laser-ablated tracks are carbonized; therefore, the loss of insulation can be responsible for the reduction of charge transfer.

  11. Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

    Science.gov (United States)

    Grisolia, M. N.; Varignon, J.; Sanchez-Santolino, G.; Arora, A.; Valencia, S.; Varela, M.; Abrudan, R.; Weschke, E.; Schierle, E.; Rault, J. E.; Rueff, J.-P.; Barthélémy, A.; Santamaria, J.; Bibes, M.

    2016-05-01

    At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions at and between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

  12. Elastic, excitation, ionization and charge transfer cross sections of current interest in fusion energy research

    Energy Technology Data Exchange (ETDEWEB)

    Schultz, D.R.; Krstic, P.S. [Oak Ridge National Lab. TN (United States). Physics Div.

    1997-01-01

    Due to the present interest in modeling and diagnosing the edge and divertor plasma regions in magnetically confined fusion devices, we have sought to provide new calculations regarding the elastic, excitation, ionization, and charge transfer cross sections in collisions among relevant ions, neutrals, and isotopes in the low-to intermediate-energy regime. We summarize here some of our recent work. (author)

  13. Quantum-Classical Path Integral Simulation of Ferrocene-Ferrocenium Charge Transfer in Liquid Hexane.

    Science.gov (United States)

    Walters, Peter L; Makri, Nancy

    2015-12-17

    We employ the quantum-classical path integral methodology to simulate the outer sphere charge-transfer process of the ferrocene-ferrocenium pair in liquid hexane with unprecedented accuracy. Comparison of the simulation results to those obtained by mapping the solvent on an effective harmonic bath demonstrates the accuracy of linear response theory in this system. PMID:26673195

  14. Solvent-induced reversible solid-state colour change of an intramolecular charge-transfer complex.

    Science.gov (United States)

    Li, Ping; Maier, Josef M; Hwang, Jungwun; Smith, Mark D; Krause, Jeanette A; Mullis, Brian T; Strickland, Sharon M S; Shimizu, Ken D

    2015-10-11

    A dynamic intramolecular charge-transfer (CT) complex was designed that displayed reversible colour changes in the solid-state when treated with different organic solvents. The origins of the dichromatism were shown to be due to solvent-inclusion, which induced changes in the relative orientations of the donor pyrene and acceptor naphthalenediimide units. PMID:26299357

  15. Charge-Transfer Complex of p-Aminodiphenylamine with Maleic Anhydride: Spectroscopic, Electrochemical, and Physical Properties.

    Science.gov (United States)

    Karaca, Erhan; Kaplan Can, Hatice; Bozkaya, Uğur; Özçiçek Pekmez, Nuran

    2016-07-01

    A new charge-transfer complex and the amide formed by the interaction between the electron donor of the p-aminodiphenylamine and the electron acceptor of maleic anhydride are investigated by spectroscopic methods. The amidation reaction is caused by proton and charge transfer between the maleic anhydride and p-aminodiphenylamine molecules. The Benesi-Hildebrand equation is used to determine the formation constant, the molar extinction coefficient and the standard Gibbs free energy of the complex by using UV/Vis spectroscopy. To reveal the electronic and spectroscopic properties of these molecules, theoretical computations are performed on the structures of maleic anhydride, p-aminodiphenylamine and the conformers of their charge-transfer complex. The charge-transfer complex and amidation reaction mechanism are also confirmed by IR and NMR spectroscopy and HRMS. The nature of the maleic anhydride-p-aminodiphenylamine complex is characterized by cyclic voltammetry, thermogravimetric analysis, XRD and SEM. Solid microribbons of this complex show higher thermal stability than p-aminodiphenylamine. PMID:26990700

  16. Determination of Interfacial Charge-Transfer Rate Constants in Perovskite Solar Cells.

    Science.gov (United States)

    Pydzińska, Katarzyna; Karolczak, Jerzy; Kosta, Ivet; Tena-Zaera, Ramon; Todinova, Anna; Idígoras, Jesus; Anta, Juan A; Ziółek, Marcin

    2016-07-01

    A simple protocol to study the dynamics of charge transfer to selective contacts in perovskite solar cells, based on time-resolved laser spectroscopy studies, in which the effect of bimolecular electron-hole recombination has been eliminated, is proposed. Through the proposed procedure, the interfacial charge-transfer rate constants from methylammonium lead iodide perovskite to different contact materials can be determined. Hole transfer is faster for CuSCN (rate constant 0.20 ns(-1) ) than that for 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD; 0.06 ns(-1) ), and electron transfer is faster for mesoporous (0.11 ns(-1) ) than that for compact (0.02 ns(-1) ) TiO2 layers. Despite more rapid charge separation, the photovoltaic performance of CuSCN cells is worse than that of spiro-OMeTAD cells; this is explained by faster charge recombination in CuSCN cells, as revealed by impedance spectroscopy. The proposed direction of studies should be one of the key strategies to explore efficient hole-selective contacts as an alternative to spiro-OMeTAD. PMID:27253726

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

    DEFF Research Database (Denmark)

    Sherafatipour, Golenaz; Madsen, Morten

    which the maximum open-circuit voltage can be estimated, and further can be used in the modeling and optimization of the OPV devices. [1] C. Deibe, T. Strobe, and V. Dyakonov, “Role of the charge transfer state in organic donor-acceptor solar cells,” Adv. Mater., vol. 22, pp. 4097–4111, 2010. [2] K...

  18. Coherent nuclear wave packet dynamics of laurdan launched by intramolecular charge transfer

    Directory of Open Access Journals (Sweden)

    Kim S. Y.

    2013-03-01

    Full Text Available Coherent nuclear wave packets in the product state launched by the ultrafast intramolecular charge transfer are observed by time-resolved fluorescence with 40 fs time resolution. Direct information on reaction coordinates and structural changes can be obtained.

  19. Mechanism and Dynamics of Charge Transfer in Donor-Bridge-Acceptor Systems

    NARCIS (Netherlands)

    Gorczak-Vos, N.

    2016-01-01

    Photoinduced charge transfer in organic materials is a fundamental process in various biological and technological areas. Donor-bridge-acceptor (DBA) molecules are used as model systems in numerous theoretical and experimental work to systematically study and unravel the underlying mechanisms of cha

  20. On the relation between local and charge-transfer exciton bindingenergies in organic photovoltaic materials

    NARCIS (Netherlands)

    de Gier, Hilde Dorothea; Braam, Henderika; Havenith, Remco

    2015-01-01

    In organic photovoltaic devices two types of excitons can be generated for which different binding energies can be defined: the binding energy of the local exciton generated immediately after light absorption on the polymer and the binding energy of the charge-transfer exciton generated through the

  1. Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads

    KAUST Repository

    Whited, Matthew T.

    2012-01-01

    We report the synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage. Both molecules undergo symmetry-breaking intramolecular charge transfer in the excited state, and the directly linked dyad serves as a visible-light-absorbing analogue of 9,9′-bianthryl.

  2. A schematic model for energy and charge transfer in the chlorophyll complex

    DEFF Research Database (Denmark)

    Bohr, Henrik; Malik, F.B.

    2011-01-01

    A theory for simultaneous charge and energy transfer in the carotenoid-chlorophyll-a complex is presented here and discussed. The observed charge transfer process in these chloroplast complexes is reasonably explained in terms of this theory. In addition, the process leads to a mechanism to drive...... an electron in a lower to a higher-energy state, thus providing a mechanism for the ejection of the electron to a nearby molecule (chlorophyll) or into the environment. The observed lifetimes of the electronically excited states are in accord/agreement with the investigations of Sundström et al....... and are in the range of pico-seconds and less. The change in electronic charge distribution in internuclear space as the system undergoes an electronic transition to a higher-energy state could, under appropriate physical conditions, lead to oscillating dipoles capable of transmitting energy from the carotenoid-chlorophylls...

  3. Role of Molecular Weight Distribution on Charge Transport in Semiconducting Polymers

    KAUST Repository

    Himmelberger, Scott

    2014-10-28

    © 2014 American Chemical Society. Model semiconducting polymer blends of well-controlled molecular weight distributions are fabricated and demonstrated to be a simple method to control intermolecular disorder without affecting intramolecular order or degree of aggregation. Mobility measurements exhibit that even small amounts of low molecular weight material are detrimental to charge transport. Trends in charge carrier mobility can be reproduced by a simple analytical model which indicates that carriers have no preference for high or low molecular weight chains and that charge transport is limited by interchain hopping. These results quantify the role of long polymer tie-chains and demonstrate the need for controlled polydispersity for achieving high carrier mobilities.

  4. Ultrafast charge transfer in MoS2/WSe2 p–n Heterojunction

    Science.gov (United States)

    Peng, Bo; Yu, Guannan; Liu, Xinfeng; Liu, Bo; Liang, Xiao; Bi, Lei; Deng, Longjiang; Chien Sum, Tze; Loh, Kian Ping

    2016-06-01

    Atomically thin and sharp van der Waals heterojunction can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) onto n-type molybdenum disulfide (MoS2). Theory predicts that stacked MoS2 and WSe2 monolayer forms type II p–n junction, creating a built-in electric field across the interface which facilitates electron–hole separation and transfer. Gaining insights into the dynamics of charge transfer across van der Waals heterostructure is central to understanding light-photocurrent conversion at these ultrathin interfaces. Herein, we investigate the exciton dissociation and charge transfer in a MoS2/WSe2 van der Waals hetero-structure. Our results show that ultrafast electron transfer from WSe2 to MoS2 take place within 470 fs upon optical excitation with 99% charge transfer efficiency, leading to drastic photoluminescence quenching and decreased lifetime. Our findings suggest that van der Waals heterostructure may be useful as active components in ultrafast optoelectronic devices.

  5. Broadband Tunable Microlasers Based on Controlled Intramolecular Charge-Transfer Process in Organic Supramolecular Microcrystals.

    Science.gov (United States)

    Dong, Haiyun; Wei, Yanhui; Zhang, Wei; Wei, Cong; Zhang, Chunhuan; Yao, Jiannian; Zhao, Yong Sheng

    2016-02-01

    Wavelength tunable micro/nanolasers are indispensable components for various photonic devices. Here, we report broadband tunable microlasers built by incorporating a highly polarized organic intramolecular charge-transfer (ICT) compound with a supramolecular host. The spatial confinement of the ICT dye generates an optimized energy level system that favors controlled population distribution between the locally excited (LE) state and the twisted intramolecular charge-transfer (TICT) state, which is beneficial for significantly broadening the tailorable gain region. As a result, we realized a wide tuning of lasing wavelength in the organic supramolecular microcrystals based on temperature-controlled population transfer from the LE to TICT state. The results will provide a useful enlightenment for the rational design of miniaturized lasers with desired performances. PMID:26756966

  6. Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses.

    Science.gov (United States)

    Boll, Rebecca; Erk, Benjamin; Coffee, Ryan; Trippel, Sebastian; Kierspel, Thomas; Bomme, Cédric; Bozek, John D; Burkett, Mitchell; Carron, Sebastian; Ferguson, Ken R; Foucar, Lutz; Küpper, Jochen; Marchenko, Tatiana; Miron, Catalin; Patanen, Minna; Osipov, Timur; Schorb, Sebastian; Simon, Marc; Swiggers, Michelle; Techert, Simone; Ueda, Kiyoshi; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

    2016-07-01

    Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I(21+). The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse. PMID:27051675

  7. Non-Linearity in Wide Dynamic Range CMOS Image Sensors Utilizing a Partial Charge Transfer Technique

    Directory of Open Access Journals (Sweden)

    Izhal Abdul Halin

    2009-11-01

    Full Text Available The partial charge transfer technique can expand the dynamic range of a CMOS image sensor by synthesizing two types of signal, namely the long and short accumulation time signals. However the short accumulation time signal obtained from partial transfer operation suffers of non-linearity with respect to the incident light. In this paper, an analysis of the non-linearity in partial charge transfer technique has been carried, and the relationship between dynamic range and the non-linearity is studied. The results show that the non-linearity is caused by two factors, namely the current diffusion, which has an exponential relation with the potential barrier, and the initial condition of photodiodes in which it shows that the error in the high illumination region increases as the ratio of the long to the short accumulation time raises. Moreover, the increment of the saturation level of photodiodes also increases the error in the high illumination region.

  8. Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

    Directory of Open Access Journals (Sweden)

    Rebecca Boll

    2016-07-01

    Full Text Available Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse.

  9. A new battery-charging method suggested by molecular dynamics simulations

    CERN Document Server

    Hamad, Ibrahim Abou; Wipf, D; Rikvold, P A; 10.1039/b920970k

    2010-01-01

    Based on large-scale molecular dynamics simulations, we propose a new charging method that should be capable of charging a Lithium-ion battery in a fraction of the time needed when using traditional methods. This charging method uses an additional applied oscillatory electric field. Our simulation results show that this charging method offers a great reduction in the average intercalation time for Li+ ions, which dominates the charging time. The oscillating field not only increases the diffusion rate of Li+ ions in the electrolyte but, more importantly, also enhances intercalation by lowering the corresponding overall energy barrier.

  10. Coarse-grained molecular dynamics simulation of binary charged lipid membranes: Phase separation and morphological dynamics

    CERN Document Server

    Ito, Hiroaki; Shimokawa, Naofumi

    2016-01-01

    Biomembranes, which are mainly composed of neutral and charged lipids, exhibit a large variety of functional structures and dynamics. Here, we report a coarse-grained molecular dynamics (MD) simulation of the phase separation and morphological dynamics in charged lipid bilayer vesicles. The screened long-range electrostatic repulsion among charged head groups delays or inhibits the lateral phase separation in charged vesicles compared with neutral vesicles, suggesting the transition of the phase-separation mechanism from spinodal decomposition to nucleation or homogeneous dispersion. Moreover, the electrostatic repulsion causes morphological changes, such as pore formation, and further transformations into disk, string, and bicelle structures, which are spatiotemporally coupled to the lateral segregation of charged lipids. Based on our coarse-grained MD simulation, we propose a plausible mechanism of pore formation at the molecular level. The pore formation in a charged-lipid-rich domain is initiated by the p...

  11. Site-specific probing of charge transfer dynamics in organic photovoltaics

    Energy Technology Data Exchange (ETDEWEB)

    Arion, Tiberiu; Roth, Friedrich [Center for Free-Electron Laser Science/DESY, Notkestraße 85, D-22607 Hamburg (Germany); Neppl, Stefan; Shavorskiy, Andrey; Bluhm, Hendrik; Gessner, Oliver [Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Hussain, Zahid [ALS, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Eberhardt, Wolfgang [Center for Free-Electron Laser Science/DESY, Notkestraße 85, D-22607 Hamburg (Germany); ALS, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Institute of Optics and Atomic Physics, TU Berlin, Straße des 17. Juni 135, D-10623 Berlin (Germany)

    2015-03-23

    We report the site-specific probing of charge-transfer dynamics in a prototype system for organic photovoltaics (OPVs) by picosecond time-resolved X-ray photoelectron spectroscopy. A layered system consisting of approximately two monolayers of C{sub 60} deposited on top of a thin film of Copper-Phthalocyanine (CuPC) is excited by an optical pump pulse and the induced electronic dynamics are probed with 590 eV X-ray pulses. Charge transfer from the electron donor (CuPC) to the acceptor (C{sub 60}) and subsequent charge carrier dynamics are monitored by recording the time-dependent C 1s core level photoemission spectrum of the system. The arrival of electrons in the C{sub 60} layer is readily observed as a completely reversible, transient shift of the C{sub 60} associated C 1s core level, while the C 1s level of the CuPC remains unchanged. The capability to probe charge transfer and recombination dynamics in OPV assemblies directly in the time domain and from the perspective of well-defined domains is expected to open additional pathways to better understand and optimize the performance of this emerging technology.

  12. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid.

    Science.gov (United States)

    Rury, Aaron S; Sorenson, Shayne; Dawlaty, Jahan M

    2016-03-14

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm(-1) oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology. PMID:26979698

  13. Control of intrachain charge transfer in model systems for block copolymer photovoltaic materials.

    Science.gov (United States)

    Johnson, Kerr; Huang, Ya-Shih; Huettner, Sven; Sommer, Michael; Brinkmann, Martin; Mulherin, Rhiannon; Niedzialek, Dorota; Beljonne, David; Clark, Jenny; Huck, Wilhelm T S; Friend, Richard H

    2013-04-01

    We report the electronic properties of the conjugated coupling between a donor polymer and an acceptor segment serving as a model for the coupling in conjugated donor-acceptor block copolymers. These structures allow the study of possible intrachain photoinduced charge separation, in contrast to the interchain separation achieved in conventional donor-acceptor blends. Depending on the nature of the conjugated linkage, we observe varying degrees of modification of the excited states, including the formation of intrachain charge transfer excitons. The polymers comprise a block (typically 18 repeat units) of P3HT, poly(3-hexyl thiophene), coupled to a single unit of F8-TBT (where F8 is dioctylfluorene, and TBT is thiophene-benzothiadiazole-thiophene). When the P3HT chain is linked to the TBT unit, we observe formation of a localized charge transfer state, with red-shifted absorption and emission. Independent of the excitation energy, this state is formed very rapidly (<40 fs) and efficiently. Because there is only a single TBT unit present, there is little scope for long-range charge separation and it is relatively short-lived, <1 ns. In contrast, when the P3HT chain and TBT unit are separated by the wider bandgap F8 unit, there is little indication for modification of either ground or excited electronic states, and longer-lived charge separated states are observed.

  14. Decellular biological scaffold polymerized with PEDOT for improving peripheral nerve interface charge transfer.

    Science.gov (United States)

    Frost, Christopher M; Cederna, Paul S; Martin, David C; Shim, Bong Sup; Urbanchek, Melanie G

    2014-01-01

    Regenerative peripheral nerve interfaces (RPNIs) are for signal transfer between peripheral nerves inside the body to controllers for motorized prosthetics external to the body. Within the residual limb of an amputee, surgical construction of a RPNI connects a remaining peripheral nerve and spare muscle. Nerve signals become concentrated within the RPNI. Currently metal electrodes implanted on the RPNI muscle transfer signals but scarring around metal electrodes progressively diminishes charge transfer. Engineered materials may benefit RPNI signal transfer across the neural interface if they lower the power and charge density of the biologically meaningful signals. Poly3,4-ethylenedioxythiophene (PEDOT) is known to mediate ionic potentials allowing excitation across a critical nerve gap. We hypothesize that the capacity of an interface material to conduct electron mediated current is significantly increased by polymerized coating of PEDOT. SIS was either used plain or after PEDOT coating by electrochemical polymerization. Muscle forces are a direct representation of stimulating current distribution within an RPNI. In situ muscle forces were measured for the same muscle by electrically stimulating: a) the muscle's innervating nerve, b) directly on the muscle, c) on plain SIS laid on the muscle, and d) on SIS polymerized with PEDOT laid on the muscle. Electro-chemically coating PEDOT on SIS resulted in a thin, flexible material. PEDOT coated SIS distributed electrical stimulation more efficiently than SIS alone. Conductive polymer containing biological material allowed ionic signal distribution within the RPNI like muscle at lower charge density. PMID:25569986

  15. Charge-dependent dissociation of insulin cations via ion/ion electron transfer

    Science.gov (United States)

    Liu, Jian; Gunawardena, Harsha P.; Huang, Teng-Yi; McLuckey, Scott A.

    2008-10-01

    The dissociation reactions of various charge states of insulin cations obtained directly from nano-electrospray were investigated as a result of ion/ion electron transfer from azobenzene anions. Data were collected with and without simultaneous ion trap collisional excitation of the first generation charge-reduced product during the ion/ion reaction period. Neither separation of the two constituent chains nor cleavages within the loop defined by the disulfide bridges were observed under normal electron transfer dissociation (ETD) conditions for any of the charge states studied. However, substantial sequence coverage (exocyclic region: 82.6%; entire protein: 38.8%) outside the ring structure was obtained for insulin +6, while only limited coverage (exocyclic: 43.5%; entire protein: 20.4%) was observed for insulin +5 and no dissociation, aside from low abundance side-chain losses, was noted for insulin +4 and +3 in the normal ETD spectra. When the first generation charge-reduced precursor ions were subjected to collisional activation during the ion/ion reaction period, higher sequence coverages were obtained for both insulin +5 (entire protein: 34.7%) and +4 (entire protein: 20.4%) with backbone cleavages occurring within the loop defined by the disulfide bonds. Dissociation of insulin +3 was not significantly improved by the additional activation. Separation of the two constituent chains resulting from cleavages of both of the two disulfide bridges that link the chains was observed for insulin +6, +5, and +4 when the charge-reduced species were activated. The dissociation of disulfide linkages in this study suggests that as the charge state decreases, disulfide bond cleavages dominate over N-C[alpha] bond cleavages in the electron transfer dissociation process.

  16. Analytical Study for the Charge-Transfer Complexes of Rosuvastatin Calcium with π-Acceptors

    Directory of Open Access Journals (Sweden)

    Nourah Z. Alzoman

    2013-07-01

    Full Text Available Studies were carried out to investigate the charge-transfer (CT reaction of ROS-Ca, as a n-electron donor with various p-acceptors: tetracyanoethylene, p-chloranilic acid, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, 2,3,5,6-tetrabromo-1,4-benzoquinone, 1,3,5-trinitrobenzene, 2,3,5,6-tetrachloro-1,4-benzoquinone, 7,7,8,8-tetracyano-quinodimethane, and 2,4,7-trinitro-9-fluorenone. Different colored CT complexes were obtained. The reaction mechanism and site of interaction were determined by ultraviolet-visible spectrophotometric techniques and computational molecular modeling. The formation of the colored complexes was utilized in the development of simple, rapid and accurate spectrophotometric methods for the determination of ROS-Ca. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9984–0.9995 were found between the absorbances and the concentrations of ROS-Ca in the range of 2–200 mg mL−1. The limits of detection ranged from 0.41 to 12.24 mg mL−1. No interference could be observed from the additives commonly present in the tablets or from the drugs that are co-formulated with ROS-Ca in its combined formulations. The methods were successfully applied to the analysis of tablets with good accuracy and precision; the recovery percentages ranged from 99.54–100.46 ± 1.58–1.82%. The results were compared favorably with the reported method. The proposed methods are practical and valuable for routine application in quality control laboratories for determination of ROS-Ca in its bulk form and tablets.

  17. Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme

    Energy Technology Data Exchange (ETDEWEB)

    Theophilou, Iris, E-mail: i.theophilou@fz-juelich.de [Peter Grunberg Institut (PGI) Forschungszentrum Jülich, D-52425 Jülich (Germany); Tassi, M.; Thanos, S. [Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, ‘Demokritos’ National Center for Scientific Research, 15310 Athens (Greece)

    2014-04-28

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.

  18. A molecular study of microbe transfer between distant environments.

    Directory of Open Access Journals (Sweden)

    Sean D Hooper

    Full Text Available BACKGROUND: Environments and their organic content are generally not static and isolated, but in a constant state of exchange and interaction with each other. Through physical or biological processes, organisms, especially microbes, may be transferred between environments whose characteristics may be quite different. The transferred microbes may not survive in their new environment, but their DNA will be deposited. In this study, we compare two environmental sequencing projects to find molecular evidence of transfer of microbes over vast geographical distances. METHODOLOGY: By studying synonymous nucleotide composition, oligomer frequency and orthology between predicted genes in metagenomics data from two environments, terrestrial and aquatic, and by correlating with phylogenetic mappings, we find that both environments are likely to contain trace amounts of microbes which have been far removed from their original habitat. We also suggest a bias in direction from soil to sea, which is consistent with the cycles of planetary wind and water. CONCLUSIONS: Our findings support the Baas-Becking hypothesis formulated in 1934, which states that due to dispersion and population sizes, microbes are likely to be found in widely disparate environments. Furthermore, the availability of genetic material from distant environments is a possible font of novel gene functions for lateral gene transfer.

  19. Reversible Tuning of Interfacial and Intramolecular Charge Transfer in Individual MnPc Molecules.

    Science.gov (United States)

    Zhong, Jian-Qiang; Wang, Zhunzhun; Zhang, Jia Lin; Wright, Christopher A; Yuan, Kaidi; Gu, Chengding; Tadich, Anton; Qi, Dongchen; Li, He Xing; Lai, Min; Wu, Kai; Xu, Guo Qin; Hu, Wenping; Li, Zhenyu; Chen, Wei

    2015-12-01

    The reversible selective hydrogenation and dehydrogenation of individual manganese phthalocyanine (MnPc) molecules has been investigated using photoelectron spectroscopy (PES), low-temperature scanning tunneling microscopy (LT-STM), synchrotron-based near edge X-ray absorption fine structure (NEXAFS) measurements, and supported by density functional theory (DFT) calculations. It is shown conclusively that interfacial and intramolecular charge transfer arises during the hydrogenation process. The electronic energetics upon hydrogenation is identified, enabling a greater understanding of interfacial and intramolecular charge transportation in the field of single-molecule electronics. PMID:26528623

  20. Fe1+-Fe2+ charge transfer process after 57Co decay in ZnTe

    International Nuclear Information System (INIS)

    We have performed Moessbauer absorption and emission experiments on 57Fe impurities in ZnTe. A transient Fe1+ charge state has been observed below 130K in the emission spectra. The dynamics of the Fe1+-Fe2+ charge transfer was shown to obey an activation process with an activation energy of 0.09eV. Low temperature Raman relaxation rates within the Fe2+ spin-orbit levels are found to be at least 100 times faster in ZnTe than in ZnS

  1. Measurements of Charge Transfer Inefficiency in a CCD with High-Speed Column Parallel Readout

    CERN Document Server

    Sopczak, Andre; Damerell, Chris; Greenshaw, Tim; Koziel, Michal; Stefanov, Konstantin; Tikkanen, Tuomo; Woolliscroft, Tim; Worm, Steve

    2008-01-01

    Charge Coupled Devices (CCDs) have been successfully used in several high energy physics experiments over the past two decades. Their high spatial resolution and thin sensitive layers make them an excellent tool for studying short-lived particles. The Linear Collider Flavour Identification (LCFI) collaboration is developing Column-Parallel CCDs (CPCCDs) for the vertex detector of a future Linear Collider. The CPCCDs can be read out many times faster than standard CCDs, significantly increasing their operating speed. A test stand for measuring the charge transfer inefficiency (CTI) of a prototype CPCCD has been set up. Studies of the CTI have been performed at a range of readout frequencies and operating temperatures.

  2. Control over the charge transfer in dye-nanoparticle decorated graphene

    Science.gov (United States)

    Bongu, Sudhakara Reddy; Veluthandath, Aneesh V.; Nanda, B. R. K.; Ramaprabhu, Sundara; Bisht, Prem B.

    2016-01-01

    Charge transfer interaction between silver decorated graphene and three differently charged dyes, cationic (rhodamine 6G), neutral (rhodamine B) and anionic (fluorescein 27) has been studied. The ground state association constants have been evaluated and changes in the fluorescence intensity and lifetimes have been obtained in two solvents. Strength of complex-formation has been found to be higher with the cationic molecule in water. In a higher viscosity solvent, the ground state complex formation is restricted. Local field of localized surface plasmons of nanoparticles adsorbed on the graphene sheets leads to enhanced absorption and fluorescence of fluorescein 27.

  3. Ultracold magnetically tunable interactions without radiative-charge-transfer losses between Ca+, Sr+, Ba+, and Yb+ ions and Cr atoms

    Science.gov (United States)

    Tomza, Michał

    2015-12-01

    The Ca+, Sr+, Ba+, and Yb+ ions immersed in an ultracold gas of the Cr atoms are proposed as experimentally feasible heteronuclear systems in which ion-atom interactions at ultralow temperatures can be controlled with magnetically tunable Feshbach resonances without charge transfer and radiative losses. Ab initio techniques are applied to investigate electronic-ground-state properties of the (CaCr)+, (SrCr)+, (BaCr)+, and (YbCr)+ molecular ions. The potential energy curves, permanent electric dipole moments, and static electric dipole polarizabilities are computed. The spin-restricted open-shell coupled-cluster method restricted to single, double, and noniterative triple excitations and the multireference configuration-interaction method restricted to single and double excitations are employed. The scalar relativistic effects are included within the small-core energy-consistent pseudopotentials. The leading long-range induction and dispersion interaction coefficients are also reported. Finally, magnetic Feshbach resonances between the Ca+, Sr+, Ba+, and Yb+ ions interacting with the Cr atoms are analyzed. The present proposal opens the way towards robust quantum simulations and computations with ultracold ion-atom systems free of radiative charge-transfer losses.

  4. Excited state intramolecular proton transfer and charge transfer dynamics of a 2-(2'-hydroxyphenyl)benzoxazole derivative in solution.

    Science.gov (United States)

    Kim, Chul Hoon; Park, Jaehun; Seo, Jangwon; Park, Soo Young; Joo, Taiha

    2010-05-13

    Excited state intramolecular proton transfer (ESIPT) and subsequent intramolecular charge transfer (ICT) dynamics of a 2-(2'-hydroxyphenyl)benzoxazole derivative conjugated with an electron withdrawing group (HBOCE) in solutions and a polymer film has been investigated by femtosecond time-resolved fluorescence (TRF) and TRF spectra measurements without the conventional spectral reconstruction method. TRF with high enough resolution (benzoxazole groups is invoked to account for the dispersive ESIPT dynamics in liquids. From the TRF spectra of both the enol and keto isomers, we have identified the ICT reaction of the keto isomer occurring subsequent to the ESIPT. The ICT proceeds also by two time constants of near instantaneous and 2.7 ps. Since the ICT dynamics of HBOCE is rather close to the polar solvation dynamics, we argue that the ICT is barrierless and determined mostly by the solvent fluctuation.

  5. Multi-Stimuli-Responsive Charge-Transfer Hydrogel for Room-Temperature Organic Ferroelectric Thin-Film Devices.

    Science.gov (United States)

    Pandeeswar, Makam; Senanayak, Satyaprasad P; Narayan, K S; Govindaraju, T

    2016-07-01

    The possibility of designing programmable thin-film supramolecular structures with spontaneous polarization widens the utility of facile supramolecular chemistry. Although a range of low molecular mass molecular single crystals has been shown to exhibit ferroelectric polarization, demonstration of stimuli-responsive, thin-film, solution-processable supramolecular ferroelectric materials is rare. We introduce aromatic π-electron donor-acceptor molecular systems responsive to multiple stimuli that undergo supramolecular chiral mixed-stack charge-transfer (CT) coassembly through the tweezer-inclusion-sandwich process supported by hydrogen-bonding interactions. The structural synergy originating from hydrogen-bonding and chiral CT interactions resulted in the development of spontaneous unidirectional macroscopic polarization in the crystalline nanofibrous hydrogel network, under ambient conditions. Moreover, the tunability of these interactions with optical, mechanical, thermal, and electrical stimuli allowed the design of multistate thin-film memory devices. Our design strategy of the supramolecular motif is expected to help the development of new molecular engineering strategies for designing potentially useful smart multicomponent organic electronics. PMID:27305598

  6. Charge transfer kinetics at the solid-solid interface in porous electrodes

    Science.gov (United States)

    Bai, Peng; Bazant, Martin Z.

    2014-04-01

    Interfacial charge transfer is widely assumed to obey the Butler-Volmer kinetics. For certain liquid-solid interfaces, the Marcus-Hush-Chidsey theory is more accurate and predictive, but it has not been applied to porous electrodes. Here we report a simple method to extract the charge transfer rates in carbon-coated LiFePO4 porous electrodes from chronoamperometry experiments, obtaining curved Tafel plots that contradict the Butler-Volmer equation but fit the Marcus-Hush-Chidsey prediction over a range of temperatures. The fitted reorganization energy matches the Born solvation energy for electron transfer from carbon to the iron redox site. The kinetics are thus limited by electron transfer at the solid-solid (carbon-LixFePO4) interface rather than by ion transfer at the liquid-solid interface, as previously assumed. The proposed experimental method generalizes Chidsey’s method for phase-transforming particles and porous electrodes, and the results show the need to incorporate Marcus kinetics in modelling batteries and other electrochemical systems.

  7. Charge-transfer complexes of pyrimidine Schiff bases with aromatic nitro compounds

    Science.gov (United States)

    Issa, Yousry M.; El Ansary, A. L.; Sherif, O. E.; Hassib, H. B.

    2011-08-01

    Charge-transfer (CT) complexes of pyrimidine Schiff bases, derived from condensation of 2-aminopyrimidine and substituted benzaldehydes, with some aromatic polynitro compounds were prepared and investigated using IR, UV, visible and 1H NMR spectroscopy. For all solid complexes, the main interaction between the donor and acceptor molecules takes place through the π-π* interaction. Strong and some weak acidic acceptors, in addition interact through proton transfer from the acceptor molecule to the basic centre of the electron donor. Also, an n-π* transition was detected in some complexes.

  8. Femtosecond Heterodyne Transient Grating Spectroscopic Studies of Intramolecular Charge Transfer Character of Peridinin and Peridinin Analogs

    Science.gov (United States)

    Bishop, Michael; Khosravi, Soroush; Obaid, Razib; Whitelock, Hope; Carroll, Ann Marie; Lafountain, Amy; Frank, Harry; Beck, Warren; Gibson, George; Berrah, Nora

    2016-05-01

    The peridinin chlorophyll-a protein is a light harvesting complex found in several species of dinoflagellates. Peridinin absorbs strongly in the mid-visible spectral region and, despite the lack of a strong permanent dipole moment in its lowest energy excited state, is able to transfer excitation energy quickly and efficiently to chlorophyll-a. It is believed that the high efficiency arises from the development of intramolecular charge-transfer (ICT) character upon photoexcitation. Recently, heterodyne transient grating spectroscopy has been used to study the ultrafast (Grant No. DE-SC0012376.

  9. Charge transfer via a two-strand superexchange bridge in DNA

    OpenAIRE

    X. F. Wang(Henan Normal University, Xinxiang, P. R. China); Chakraborty, Tapash

    2006-01-01

    Charge transfer in a DNA duplex chain is studied by constructing a system with virtual electrodes connected at the ends of each DNA strand. The systeym is described by the tight-binding model and its transport is analyzed by the transfer matrix method. The very weak distance dependence in long (G:C)(T:A)_M(G:C)_3 DNA chain observed in experiment [B. Giese, et al., Nature 412, 318 (2001)] is explained by a unistep two-strand superexchange bridge without the need for the multi-step thermally-in...

  10. Effect of Surface Charge on Surface-Initiated Atom Transfer Radical Polymerization from Cellulose Nanocrystals in Aqueous Media.

    Science.gov (United States)

    Zoppe, Justin O; Xu, Xingyu; Känel, Cindy; Orsolini, Paola; Siqueira, Gilberto; Tingaut, Philippe; Zimmermann, Tanja; Klok, Harm-Anton

    2016-04-11

    Cellulose nanocrystals (CNCs) with different charge densities were utilized to examine the role of electrostatic interactions on surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media. To this end, growth of hydrophilic uncharged poly(N,N-dimethylacrylamide) (PDMAM) brushes was monitored by electrophoresis, (1)H NMR spectroscopy, and dynamic light scattering (DLS). Molecular weight and polydispersity of PDMAM brushes was determined by GPC analysis of hydrolytically cleaved polymers. Initiator and polymer brush grafting densities, and thus, initiator efficiencies were derived from elemental analysis. Higher initiator efficiency of polymer brush growth was observed for CNCs with higher anionic surface sulfate half-ester group density, but at the expense of high polydispersity caused by inefficient deactivation. PDMAM grafts with number-average molecular weights up to 530 kDa and polydispersity indices interfacial region at the onset of polymerization is proposed. The results presented here could have implications for other substrates that present surface charges and for the assumption that the kinetics of Cu-mediated SI-CRP are analogous to those conducted in solution.

  11. Study of molecular iodine-epoxy paint mass transfer

    Energy Technology Data Exchange (ETDEWEB)

    Belval-Haltier, E. [Inst. de Protection et Surete Nucleaire, IPSN, CEN Cadarache, St. Paul-lez-Durance (France)

    1996-12-01

    The mass transfer phenomena may have a significant influence on the quantity of I{sub 2} which could be released following a severe accident of a nuclear power plant and specially the mass transfer of iodine onto containment surfaces. So, the objective of the present work was to evaluate which phase limited the adsorption process of iodine onto gaseous epoxy paint under a range of conditions which may be relevant to a severe reactor accident. In this aim, a series of experiments was conducted in which the sorption kinetics of molecular iodine, labelled with {sup 131}I, was measured by monitoring continuously the accumulation of this species on the epoxy surface. For each test condition, the initial deposition velocity was determined and the corresponding gas phase mass transfer, kg, was estimated by using the heat transfer analogy for a laminar flow passing over a flat plate. Then, the surface reaction rate, Kr, was deduced from these two values. Experiments performed indicated that iodine adsorption onto epoxy paint is highly dependent on temperature, relative humidity of the carrier gas and moisture content of the painted coupon. In dry air flow conditions, the adsorption of iodine onto paint was found to increase with temperature and to be limited by the surface reaction rate, Kr. The I{sub 2} adsorption rate was found to increase with the humidity of carrier gas and in some studied conditions, the initial deposition velocity appeared to be controlled by gas phase mass transfer rather than surface interaction. The same phenomenon has been observed with an increase of the initial water content of the painted coupon. (author) 6 figs., 1 tab., 8 refs.

  12. Dynamical image-charge effect in molecular tunnel junctions

    DEFF Research Database (Denmark)

    Jin, Chengjun; Thygesen, Kristian Sommer

    2014-01-01

    When an electron tunnels between two metal contacts it temporarily induces an image charge (IC) in the electrodes which acts back on the tunneling electron. It is usually assumed that the IC forms instantaneously such that a static model for the image potential applies. Here we investigate how...

  13. Dependence of charge transfer phenomena during solid-air two-phase flow on particle disperser

    Science.gov (United States)

    Tanoue, Ken-ichiro; Suedomi, Yuuki; Honda, Hirotaka; Furutani, Satoshi; Nishimura, Tatsuo; Masuda, Hiroaki

    2012-12-01

    An experimental investigation of the tribo-electrification of particles has been conducted during solid-air two-phase turbulent flow. The current induced in a metal plate by the impact of polymethylmethacrylate (PMMA) particles in a high-speed air flow was measured for two different plate materials. The results indicated that the contact potential difference between the particles and a stainless steel plate was positive, while for a nickel plate it was negative. These results agreed with theoretical contact charge transfer even if not only the particle size but also the kind of metal plate was changed. The specific charge of the PMMA particles during solid-air two-phase flow using an ejector, a stainless steel branch pipe, and a stainless steel straight pipe was measured using a Faraday cage. Although the charge was negative in the ejector, the particles had a positive specific charge at the outlet of the branch pipe, and this positive charge increased in the straight pipe. The charge decay along the flow direction could be reproduced by the charging and relaxation theory. However, the proportional coefficients in the theory changed with the particle size and air velocity. Therefore, an unexpected charge transfer occurred between the ejector and the branch pipe, which could not be explained solely by the contact potential difference. In the ejector, an electrical current in air might have been produced by self-discharge of particles with excess charge between the nickel diffuser in the ejector and the stainless steel nozzle or the stainless steel pipe due to a reversal in the contact potential difference between the PMMA and the stainless steel. The sign of the current depended on the particle size, possibly because the position where the particles impacted depended on their size. When dual coaxial glass pipes were used as a particle disperser, the specific charge of the PMMA particles became more positive along the particle flow direction due to the contact

  14. Spectroscopic and computational investigations on the origin of charge transfer between included neutral guest molecules and a functionalized anionic layered host.

    Science.gov (United States)

    Dutta, Dipak; Tummanapelli, Anil Kumar

    2016-08-10

    Layered double hydroxides (LDHs) or anionic clays are an important class of ion-exchange materials, well known for drug and gene delivery and several other applications including catalysis, bioactive nanocomposite, electroactive and photoactive materials. Their structure is based on positively charged brucite-like inorganic sheets with the interlamellar space being occupied by charge-compensating exchangeable anions. In spite of having a vast scope many of the applications of LDHs are restricted as their host-guest chemistry is limited to ion-exchange reactions. Recently we have shown for the first time that charge-transfer interactions can be used as a driving force for the insertion of neutral guest molecules (ortho- and para-chloranil) within the galleries of an Mg-Al LDH by forming a charge-transfer complex with aniline pre-intercalated as p-aminobenzoate anion. Here, we have performed quantum chemical calculations in combination with molecular dynamics simulations to elucidate the nature of interactions, arrangement and the evaluation of electronic and Raman spectral signatures of the chloranil charge-transfer complex included within the galleries of the Mg-Al LDH. The natural bond orbital (NBO) analysis has been used to understand the nature and origin of the unidirectional charge-transfer that lead to the unusual insertion of chloranil in the galleries of the Mg-Al LDH. The NBO analysis reveals that a considerable amount of electronic charge redistribution occurs from the p-aminobenzoate to the chloranil during latter's insertion within the LDH galleries with a very negligible amount of back donation. This work is expected to pave the way for understanding the host-guest chemistry and targeted and controlled delivery of poorly soluble drugs. PMID:27461409

  15. Cross sections for charge transfer between mercury ions and other metals

    Science.gov (United States)

    Vroom, D. A.; Rutherford, J. A.

    1977-01-01

    Cross sections for charge transfer between several ions and metals of interest to the NASA electro propulsion program have been measured. Specifically, the ions considered were Hg(+), Xe(+) and Cs(+) and the metals Mo, Fe, Al, Ti, Ta, and C. Measurements were made in the energy regime from 1 to 5,000 eV. In general, the cross sections for charge transfer were found to be less than 10 to the minus 15 power sq cm for most processes over the total energy range. Exceptions are Hg(+) in collision with Ti and Ta. The results obtained for each reaction are given in both graphical and numerical form in the text. For quick reference, the data at several ion velocities are condensed into one table given in the summary.

  16. Charge-transfer-directed radical substitution enables para-selective C-H functionalization

    Science.gov (United States)

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-08-01

    Efficient C-H functionalization requires selectivity for specific C-H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C-H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C-H functionalization reactions.

  17. Charge transfer and formation of conducting C60 monolayers at C60/noble-metal interfaces

    Science.gov (United States)

    Nouchi, Ryo; Kanno, Ikuo

    2005-05-01

    The resistance of a conducting C60 monolayer formed on a polycrystalline Ag film was found to be 0.7±0.1kΩ by in situ resistance measurements. By another series of in situ resistance measurements, the surface scattering cross sections, whose magnitude represents the relative amount of transferred charge, were evaluated as 100Å2 for C60/Au, and 150Å2 for C60/Cu and C60/Ag systems. However, comparison with previous results obtained for monolayers formed on Au and Cu films showed that the resistances of conducting C60 monolayers do not show a simple dependence on the transferred charge. Atomic force microscopy measurements revealed that the grain size of the underlying noble metals also plays an important role.

  18. Short-Range Charge Transfer Between Oxide Based Superconductor-Ferromagnetic Metal Interfaces

    Science.gov (United States)

    Chien, Te-Yu; Kourkoutis, L. F.; Chakhalian, J.; Muller, D.; Freeland, J. W.

    2014-03-01

    Unlike the conventional superconductor (S) and ferromagnetic metal (F) interface, the understanding of the proximity effect between oxide-based S and F is still unclear. One particular question relates to the charge transfer length scale between S and F layers, which resulted from the lack of an appropriate experimental tool. In this talk, we show that by combining the cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S) along with scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS), the charge transfer length scale at the interfaces between YBa Cu O -δ(YBCO) and La3Ca3MnO (LCMO) was revealed to have upper limit of 1 nm.

  19. Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zanni, Martin T.

    1999-12-17

    This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents.

  20. Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

    International Nuclear Information System (INIS)

    This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents

  1. Isotope effect in charge-transfer collisions of H with He{sup +}

    Energy Technology Data Exchange (ETDEWEB)

    Loreau, J.; Dalgarno, A. [Institute for Theoretical Atomic, Molecular and Optical Physics, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138 (United States); Ryabchenko, S. [Northern (Arctic) Federal University, 17 Severnaya Dvina Emb., 163002 Arkhangelsk (Russian Federation); Laboratoire de Chimie Quantique et Photophysique, Universite Libre de Bruxelles (ULB), CP160/09, 1050 Bruxelles (Belgium); Vaeck, N. [Laboratoire de Chimie Quantique et Photophysique, Universite Libre de Bruxelles (ULB), CP160/09, 1050 Bruxelles (Belgium)

    2011-11-15

    We present a theoretical study of the isotope effect arising from the replacement of H by T in the charge-transfer collision H(n=2) + He{sup +}(1s) at low energy. Using a quasimolecular approach and a time-dependent wave-packet method, we compute the cross sections for the reaction including the effects of the nonadiabatic radial and rotational couplings. For H(2s) + He{sup +}(1s) collisions, we find a strong isotope effect at energies below 1 eV/amu for both singlet and triplet states. We find a much smaller isotopic dependence of the cross section for H(2p) + He{sup +}(1s) collisions in triplet states, and no isotope effect in singlet states. We explain the isotope effect on the basis of the potential energy curves and the nonadiabatic couplings, and we evaluate the importance of the isotope effect on the charge-transfer rate coefficients.

  2. Charge-transfer-directed radical substitution enables para-selective C–H functionalization

    Science.gov (United States)

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-08-01

    Efficient C–H functionalization requires selectivity for specific C–H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C–H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C–H functionalization reactions.

  3. Oxidation and Metal-Insertion in Molybdenite Surfaces: Evaluation of Charge-Transfer Mechanisms and Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Ramana, Chintalapalle V.; Becker, U.; Shutthanandan, V.; Julien, C. M.

    2008-06-05

    Molybdenum sulfide (MoS2), an important representative member of the layered transition-metal dichalcogenides, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and industrial science and technology. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. On the other hand understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is quite important to utilize these minerals in technological applications. Furthermore, such a detailed investigation of thermal oxidation behavior and intercalation process will provide a basis to further explore and model the mechanism of adsorption of metal ions on to geomedia. Therefore, the present work was performed to understand the oxidation and intercalation processes of molybdenite surfaces. The results obtained, using a wide variety of analytical techniques, are presented and discussed in this paper.

  4. Semilocal and Hybrid Density Embedding Calculations of Ground-State Charge-Transfer Complexes

    CERN Document Server

    Laricchia, S; Della Sala, F; 10.1063/1.4795825

    2013-01-01

    We apply the frozen density embedding method, using a full relaxation of embedded densities through a freeze-and-thaw procedure, to study the electronic structure of several benchmark ground-state charge-transfer complexes, in order to assess the merits and limitations of the approach for this class of systems. The calculations are performed using both semilocal and hybrid exchange-correlation (XC) functionals. The results show that embedding calculations using semilocal XC functionals yield rather large deviations with respect to the corresponding supermolecular calculations. Due to a large error cancellation effect, however, they can often provide a relatively good description of the electronic structure of charge-transfer complexes, in contrast to supermolecular calculations performed at the same level of theory. On the contrary, when hybrid XC functionals are employed, both embedding and supermolecular calculations agree very well with each other and with the reference benchmark results. In conclusion, fo...

  5. Muon transfer from muonic hydrogen to heavier atoms; Transfert de charge muonique

    Energy Technology Data Exchange (ETDEWEB)

    Dupays, A

    2004-06-01

    This work concerns muon transfer from muonic hydrogen to heavier atoms. Recently, a method of measurement of the hyperfine structure of ground-state muonic hydrogen based on the collision energy dependence of the muon transfer rate to oxygen has been proposed. This proposal is based on measurements which where performed at the Paul Scherrer Institute in the early nineties which indicate that the muon transfer from muonic hydrogen to oxygen increases by a factor of 4 going from thermal to 0.12 eV energies. The motivation of our calculations was to confirm this behaviour. To study the collision energy dependence of the muon transfer rate, we have used a time-independent close-coupling method. We have set up an hyperspherical elliptic formalism valid for nonzero total angular momentum which allows accurate computations of state-to-state reactive and charge exchange processes. We have applied this formalism to muon-transfer process to oxygen and neon. The comparison with experimental results is in both cases excellent. Finally, the neon transfer rate dependence with energy suggests to use neon instead of oxygen to perform a measurement of the hyperfine structure of muonic hydrogen. The results of accurate calculations of the muon transfer rates from muonic protium and deuterium atoms to nitrogen, oxygen and neon are also reported. Very good agreement with measured rates is obtained and for the three systems, the isotopic effect is perfectly reproduced. (author)

  6. Ligand-induced dependence of charge transfer in nanotube-quantum dot heterostructures.

    Science.gov (United States)

    Wang, Lei; Han, Jinkyu; Sundahl, Bryan; Thornton, Scott; Zhu, Yuqi; Zhou, Ruiping; Jaye, Cherno; Liu, Haiqing; Li, Zhuo-Qun; Taylor, Gordon T; Fischer, Daniel A; Appenzeller, Joerg; Harrison, Robert J; Wong, Stanislaus S

    2016-08-25

    As a model system to probe ligand-dependent charge transfer in complex composite heterostructures, we fabricated double-walled carbon nanotube (DWNT)-CdSe quantum dot (QD) composites. Whereas the average diameter of the QDs probed was kept fixed at ∼4.1 nm and the nanotubes analyzed were similarly oxidatively processed, by contrast, the ligands used to mediate the covalent attachment between the QDs and DWNTs were systematically varied to include p-phenylenediamine (PPD), 2-aminoethanethiol (AET), and 4-aminothiophenol (ATP). Herein, we have put forth a unique compilation of complementary data from experiment and theory, including results from transmission electron microscopy (TEM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Raman spectroscopy, electrical transport measurements, and theoretical modeling studies, in order to fundamentally assess the nature of the charge transfer between CdSe QDs and DWNTs, as a function of the structure of various, intervening bridging ligand molecules. Specifically, we correlated evidence of charge transfer as manifested by changes and shifts associated with NEXAFS intensities, Raman peak positions, and threshold voltages both before and after CdSe QD deposition onto the underlying DWNT surface. Importantly, for the first time ever in these types of nanoscale composite systems, we have sought to use theoretical modeling to justify and account for our experimental results. Our overall data suggest that (i) QD coverage density on the DWNTs varies, based upon the different ligand pendant groups used and that (ii) the presence of a π-conjugated carbon framework within the ligands themselves coupled with the electron affinity of their pendant groups collectively play important roles in the resulting charge transfer from QDs to the underlying CNTs. PMID:27368081

  7. Charge-transfer gap closure in transition-metal halides under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Chen, A.L.; Yu, P.Y.

    1995-01-01

    Insulator-to-metal transition induced by pressure has been studied in three transition metal iodides: NiI{sub 2}, CoI{sub 2} and FeI{sub 2} using optical absorption and resistivity measurements at room temperature. Comparisons between the results obtained by these two techniques suggested that the closure of the charge-transfer gap is the principal mechanism responsible for the insulator-to-metal transition in these materials.

  8. Obtaining electricity by direct transfer of charge generated in corona discharge

    Science.gov (United States)

    Berezkina, T. E.; Masyukevich, S. V.; Gall, N. R.

    2015-05-01

    We have studied the possibility of generating electricity directly by using the charge that is created in a corona discharge and transferred by airflow in the direction perpendicular to the discharge axis. Results of experimental measurements and theoretical estimations confirm this possibility. The electric power output from corona discharge in experiment was on the order of 10-3 W, which is about one-tenth of the theoretical limit. It is proposed to use this effect for creating wind-driven generators.

  9. Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

    Directory of Open Access Journals (Sweden)

    Shutthanandan V

    2008-06-01

    Full Text Available Abstract Molybdenum disulfide (MoS2, a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM, scanning electron microscopy (SEM, transmission electron microscopy (TEM, Rutherford backscattering spectrometry (RBS, and nuclear reaction analysis (NRA. Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and

  10. Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics.

    Science.gov (United States)

    Ramana, C V; Becker, U; Shutthanandan, V; Julien, C M

    2008-01-01

    Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia.The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA).Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400 degrees C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant

  11. Impact of speciation on the electron charge transfer properties of nanodiamond drug carriers

    Science.gov (United States)

    Sun, Baichuan; Barnard, Amanda S.

    2016-07-01

    Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove useful in designing drug delivery systems where the release of (selected) drugs needs to be sensitive to specific conditions at the point of delivery.Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove

  12. Computational models of an inductive power transfer system for electric vehicle battery charge

    Science.gov (United States)

    Anele, A. O.; Hamam, Y.; Chassagne, L.; Linares, J.; Alayli, Y.; Djouani, K.

    2015-09-01

    One of the issues to be solved for electric vehicles (EVs) to become a success is the technical solution of its charging system. In this paper, computational models of an inductive power transfer (IPT) system for EV battery charge are presented. Based on the fundamental principles behind IPT systems, 3 kW single phase and 22 kW three phase IPT systems for Renault ZOE are designed in MATLAB/Simulink. The results obtained based on the technical specifications of the lithium-ion battery and charger type of Renault ZOE show that the models are able to provide the total voltage required by the battery. Also, considering the charging time for each IPT model, they are capable of delivering the electricity needed to power the ZOE. In conclusion, this study shows that the designed computational IPT models may be employed as a support structure needed to effectively power any viable EV.

  13. Coarse Point Charge Models For Proteins From Smoothed Molecular Electrostatic Potentials.

    Science.gov (United States)

    Leherte, Laurence; Vercauteren, Daniel P

    2009-12-01

    To generate coarse electrostatic models of proteins, we developed an original approach to hierarchically locate maxima and minima in smoothed molecular electrostatic potentials. A charge-fitting program was used to assign charges to the so-obtained reduced representations. Templates are defined to easily generate coarse point charge models for protein structures, in the particular cases of the Amber99 and Gromos43A1 force fields. Applications to four small peptides and to the ion channel KcsA are presented. Electrostatic potential values generated by the reduced models are compared with the corresponding values obtained using the original sets of atomic charges. PMID:26602509

  14. Density functional theory for the description of charge-transfer processes at TTF/TCNQ interfaces

    KAUST Repository

    Van Regemorter, Tanguy

    2012-09-15

    In the field of organic electronics, a central issue is to assess how the frontier electronic levels of two adjacent organic layers align with respect to one another at the interface. This alignment can be driven by the presence of a partial charge transfer and the formation of an interface dipole; it plays a key role for instance in determining the rates of exciton dissociation or exciton formation in organic solar cells or light-emitting diodes, respectively. Reliably modeling the processes taking place at these interfaces remains a challenge for the computational chemistry community. Here, we review our recent theoretical work on the influence of the choice of density functional theory (DFT) methodology on the description of the charge-transfer character in the ground state of TTF/ TCNQ model complexes and interfaces. Starting with the electronic properties of the isolated TTF and TCNQ molecules and then considering the charge transfer and resulting interface dipole in TTF/TCNQ donor-acceptor stacks and bilayers, we examine the impact of the choice of DFT functional in describing the interfacial electronic structure. Finally, we employ computations based on periodic boundary conditions to highlight the impact of depolarization effects on the interfacial dipole moment. © Springer-Verlag 2012.

  15. Development of highly accurate approximate scheme for computing the charge transfer integral.

    Science.gov (United States)

    Pershin, Anton; Szalay, Péter G

    2015-08-21

    The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the "exact" scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the "exact" calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature. PMID:26298117

  16. Charge-transfer complexes of 4-nitrocatechol with some amino alcohols

    Science.gov (United States)

    Baniyaghoob, Sahar; Najafpour, Mohammad Mahdi; Boghaei, Davar M.

    2010-03-01

    Charge-transfer (CT) complexes formed from the reactions of 4-nitropyrocatechol (4-nCat) as an electron acceptor with four amino alcohols: 2-aminoethanol, 1-amino-2-propanol, 4-aminobutanol and N-(2-hydroxyethyl)-1,3-diaminopropane (NHEDAP) as electron donors, have been studied spectrophotometrically in H 2O and H 2O/EtOH at 20, 25, 30, 35 and 40 °C. The calculated values of the oscillator strength and transition moment confirm the formation of CT-complexes. The thermodynamic and spectroscopic parameters were also evaluated for the formation of CT-complexes. The equilibrium constants ranged from 9.00 to 2.20 l mol -1 (M -1). These interactions are exothermic and have relatively large standard enthalpy and entropy changes (Δ H values ranged from -15.58 to -3.10 kJ mol -1; Δ S ranged from 26.81 to -3.25 J K -1 mol -1). The solid CT-complexes have been synthesized and characterized by IR, NMR, mass spectrometry and thermal analysis. The photometric titration curves and other spectrometric data for the reactions indicated that the data obtained refer to the formation of 1:1 charge-transfer complex of [(4-nCat) (NHEDAP)] and 1:2 charge-transfer complexes of other amino alcohols [(4-nCat) (amino alcohol) 2]. The effect of alkali and alkaline earth metals on increasing the equilibrium constant of the CT-complexation was also investigated.

  17. Structure and electronic spectra of purine-methyl viologen charge transfer complexes.

    Science.gov (United States)

    Jalilov, Almaz S; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A; Schatz, George C; Lewis, Frederick D

    2014-01-01

    The structure and properties of the electron donor-acceptor complexes formed between methyl viologen and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and (1)H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well-described by time-dependent DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2'-deoxyguanosine 3'-monophosphate (DAD'DAD' type) and 7-deazaguanosine (DAD'ADAD' type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors.

  18. Development of highly accurate approximate scheme for computing the charge transfer integral

    Energy Technology Data Exchange (ETDEWEB)

    Pershin, Anton; Szalay, Péter G. [Laboratory for Theoretical Chemistry, Institute of Chemistry, Eötvös Loránd University, P.O. Box 32, H-1518 Budapest (Hungary)

    2015-08-21

    The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the “exact” scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the “exact” calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature.

  19. Rate limiting activity of charge transfer during lithiation from ionic liquids

    Science.gov (United States)

    Rodrigues, Marco-Tulio F.; Lin, Xinrong; Gullapalli, Hemtej; Grinstaff, Mark W.; Ajayan, Pulickel M.

    2016-10-01

    Given the increased use of room temperature ionic liquid electrolytes in Li-ion batteries, due to their non-flammability and negligible volatility, this study evaluates the lithiation kinetics to understand and improve the rate performance of Li-ion batteries. Lithium titanate spinel is used as a model electrode and the electrolyte is composed of LiTFSI and TFSI-coordinated alkoxy-modified phosphonium ionic liquid. Based on the analysis of activation energies for each process, we report that the charge-transfer reaction at the electrode/electrolyte interface is the rate-limiting step for cell operation. This finding is further supported by the observation that a 50-fold decrease in charge-transfer resistance at higher temperatures leads to a significant performance improvement over that of a traditional organic electrolyte at room temperature. Charge-transfer resistance and electrolyte wetting on the electrode surface are critical processes for optimal battery performance, and such processes need to be included when designing new ionic liquids in order to exceed the power density obtained with the use of current carbonate-based electrolytes.

  20. NIR and MIR charge transfer plasmons in wire-bridged antennas (Presentation Recording)

    Science.gov (United States)

    Zhang, Yue; Wen, Fangfang; Gottheim, Samuel; King, Nicholas S.; Zhang, Yu; Nordlander, Peter; Halas, Naomi J.

    2015-09-01

    We investigate optical properties of wire-bridged plasmonic nanoantennas. Here we found two spectral features: a dipolar plasmon in the visible and a Charge Transfer Plasmon (CTP) in the infrared. The CTP depends sensitively on the conductance of the junction wire, offering a controllable way for tuning the plasmon resonance to the desired wavelength regime via junction geometries. Here we use single-particle dark field spectroscopy from UV, visible to IR to identify plasmonic modes in different spectrum regimes. The simulations using Finite-difference time-domain (FDTD) method are in good agreement with experiment: Increasing the junction wire width and concurrently the junction conductance blue shifts resonance positions, and simultaneously modifies scattering strengths, the linewidth of CTP and dipolar plasmon. We notice that CTP in a much longer wavelength regime and preserving a narrow line width, an important implication for designing IR plasmons with a high quality factor for enhanced spectroscopy and sensing applications. We also extend the CTP to the IR regime by increasing the wire length to create IR plasmon while keeping the line width of the resonance. Our work offers a way for studying the charge transfer properties in plasmonic nanostructures. Not only it adds another degree in understanding the charge transfer properties in plasmonic nanostructures but also offers an optical platform for studying molecules transport at optical frequencies and related applications.

  1. Computational Studies on Structural, Excitation, and Charge-Transfer Properties of Ureidopeptidomimetics.

    Science.gov (United States)

    Joy, Sherin; Sureshbabu, Vommina V; Periyasamy, Ganga

    2016-07-14

    Peptides with ureido group enclosing backbones are considered peptidomimetics and are known for their higher stabilities, biocompatibilities, antibiotic, inhibitor, and charge-transduction activities. These peptidomimetics have some unique applications, which are quite different from those of natural peptides. Hence, it is imperative to appreciate their properties at a microscopic level. In this regard, this work outlines, in detail, the charge transfer (CT) properties, hole-migration dynamics, and electronic structures of various experimentally comprehended ureidopeptidomimetic models using density functional theory (DFT). Time-dependent DFT and complete active space self-consistent field computations on basic models provide the necessary evidence for the viability of CT from the end enfolding the ureido group to the other end with a carboxylate entity. This donor-to-acceptor CT has been reflected in excitation studies, in which the higher intensity band corresponds to CT from the π orbital of the ureido group to the π* orbital of the carboxylate entity. Further, hole-migration studies have shown that charge can evolve from the ureido end, whereas the hole generated at the carboxylate end does not migrate. However, hole migration has been reported to occur from both ends (amino and carboxylate ends) in glycine oligopeptides, and our studies show that the ability to transfer and migrate charge can be tuned by modifying the donor and acceptor functional groups in both the neutral and cationic charge states. We have analyzed the possibility of hole migration following ionization using DFT-based wave-packet propagation and found its occurrence on a ∼2-5 fs time scale, which reflects the charge-transduction ability of peptidomimetics. PMID:27314639

  2. Ultracold magnetically tunable interactions without radiative charge transfer losses between Ca$^+$, Sr$^+$, Ba$^+$, and Yb$^+$ ions and Cr atoms

    CERN Document Server

    Tomza, Michał

    2015-01-01

    The Ca$^+$, Sr$^+$, Ba$^+$, and Yb$^+$ ions immersed in an ultracold gas of the Cr atoms are proposed as experimentally feasible heteronuclear systems in which ion-atom interactions at ultralow temperatures can be controlled with magnetically tunable Feshbach resonances without charge transfer and radiative losses. \\textit{Ab initio} techniques are applied to investigate electronic-ground-state properties of the (CaCr)$^+$, (SrCr)$^+$, (BaCr)$^+$, and (YbCr)$^+$ molecular ions. The potential energy curves, permanent electric dipole moments, and static electric dipole polarizabilities are computed. The spin restricted open-shell coupled cluster method restricted to single, double, and noniterative triple excitations, RCCSD(T), and the multireference configuration interaction method restricted to single and double excitations, MRCISD, are employed. The scalar relativistic effects are included within the small-core energy-consistent pseudopotentials. The leading long-range induction and dispersion interaction co...

  3. Molecular dynamics investigation of the ionic liquid/enzyme interface: application to engineering enzyme surface charge.

    Science.gov (United States)

    Burney, Patrick R; Nordwald, Erik M; Hickman, Katie; Kaar, Joel L; Pfaendtner, Jim

    2015-04-01

    Molecular simulations of the enzymes Candida rugosa lipase and Bos taurus α-chymotrypsin in aqueous ionic liquids 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium ethyl sulfate were used to study the change in enzyme-solvent interactions induced by modification of the enzyme surface charge. The enzymes were altered by randomly mutating lysine surface residues to glutamate, effectively decreasing the net surface charge by two for each mutation. These mutations resemble succinylation of the enzyme by chemical modification, which has been shown to enhance the stability of both enzymes in ILs. After establishing that the enzymes were stable on the simulated time scales, we focused the analysis on the organization of the ionic liquid substituents about the enzyme surface. Calculated solvent charge densities show that for both enzymes and in both solvents that changing positively charged residues to negative charge does indeed increase the charge density of the solvent near the enzyme surface. The radial distribution of IL constituents with respect to the enzyme reveals decreased interactions with the anion are prevalent in the modified systems when compared to the wild type, which is largely accompanied by an increase in cation contact. Additionally, the radial dependence of the charge density and ion distribution indicates that the effect of altering enzyme charge is confined to short range (≤1 nm) ordering of the IL. Ultimately, these results, which are consistent with that from prior experiments, provide molecular insight into the effect of enzyme surface charge on enzyme stability in ILs. PMID:25641162

  4. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    Science.gov (United States)

    Rüfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  5. Ultrafast charge-transfer in organic photovoltaic interfaces: geometrical and functionalization effects.

    Science.gov (United States)

    Santos, Elton J G; Wang, W L

    2016-09-21

    Understanding the microscopic mechanisms of electronic excitation in organic photovoltaic cells is a challenging problem in the design of efficient devices capable of performing sunlight harvesting. Here we develop and apply an ab initio approach based on time-dependent density functional theory and Ehrenfest dynamics to investigate photoinduced charge transfer in small organic molecules. Our calculations include mixed quantum-classical dynamics with ions moving classically and electrons quantum mechanically, where no experimental external parameter other than the material geometry is required. We show that the behavior of photocarriers in zinc phthalocyanine (ZnPc) and C60 systems, an effective prototype system for organic solar cells, is sensitive to the atomic orientation of the donor and the acceptor units as well as the functionalization of covalent molecules at the interface. In particular, configurations with the ZnPc molecules facing on C60 facilitate charge transfer between substrate and molecules that occurs within 200 fs. In contrast, configurations where ZnPc is tilted above C60 present extremely low carrier injection efficiency even at longer times as an effect of the larger interfacial potential level offset and higher energetic barrier between the donor and acceptor molecules. An enhancement of charge injection into C60 at shorter times is observed as binding groups connect ZnPc and C60 in a dyad system. Our results demonstrate a promising way of designing and controlling photoinduced charge transfer on the atomic level in organic devices that would lead to efficient carrier separation and maximize device performance.

  6. Ultrafast charge-transfer in organic photovoltaic interfaces: geometrical and functionalization effects.

    Science.gov (United States)

    Santos, Elton J G; Wang, W L

    2016-09-21

    Understanding the microscopic mechanisms of electronic excitation in organic photovoltaic cells is a challenging problem in the design of efficient devices capable of performing sunlight harvesting. Here we develop and apply an ab initio approach based on time-dependent density functional theory and Ehrenfest dynamics to investigate photoinduced charge transfer in small organic molecules. Our calculations include mixed quantum-classical dynamics with ions moving classically and electrons quantum mechanically, where no experimental external parameter other than the material geometry is required. We show that the behavior of photocarriers in zinc phthalocyanine (ZnPc) and C60 systems, an effective prototype system for organic solar cells, is sensitive to the atomic orientation of the donor and the acceptor units as well as the functionalization of covalent molecules at the interface. In particular, configurations with the ZnPc molecules facing on C60 facilitate charge transfer between substrate and molecules that occurs within 200 fs. In contrast, configurations where ZnPc is tilted above C60 present extremely low carrier injection efficiency even at longer times as an effect of the larger interfacial potential level offset and higher energetic barrier between the donor and acceptor molecules. An enhancement of charge injection into C60 at shorter times is observed as binding groups connect ZnPc and C60 in a dyad system. Our results demonstrate a promising way of designing and controlling photoinduced charge transfer on the atomic level in organic devices that would lead to efficient carrier separation and maximize device performance. PMID:27314747

  7. Investigation of the contact charge transfer absorption of organic solvents with oxygen for use in oxygen determination.

    Science.gov (United States)

    Choi, M F; Hawkins, P

    1995-07-01

    The contact charge transfer (CCT) absorption spectra of dimethylsulphoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), ethanol, methanol, water, benzene (Bz), N,N'-diethylaniline (DEA), N,N'-dimethyl-p-toluidine (DMT) and N,N'-diethyl-p-toluidine with molecular oxygen have been investigated. These solvents form strong ultraviolet/visible CCT absorption spectra with intensities that are related to the partial pressure of the applied oxygen. DMSO, DMF, DMA, Bz, DEA and DMT are shown to form 1:1 molecular contact complexes with molecular oxygen. A simple oxygen sensing system is described using CCT absorption spectroscopy of DMT at a wavelength of 400 nm, with a gas flow rate of 60 cm(3) min(-1) through the solvent in a cuvette with a pathlength of 1 cm. Inexpensive plastic fibres are used to relay the light from a xenon lamp source to the cuvette and back to a photo-detector. The response of the sensing system to changes in oxygen concentration is reversible, non-linear and in good agreement with the Beer-Lambert law. The most sensitive response region is from 0 to 20% O(2) with a change in signal level of about 35%. The solvent used shows no deterioration in performance over a long period and can be used to determine gaseous oxygen concentrations from 0 to 100%. It does not respond to carbon dioxide.

  8. Final Technical Report for the Energy Frontier Research Center Understanding Charge Separation and Transfer at Interfaces in Energy Materials (EFRC:CST)

    Energy Technology Data Exchange (ETDEWEB)

    Vanden Bout, David A. [Univ. of Texas, Austin, TX (United States)

    2015-09-14

    Our EFRC was founded with the vision of creating a broadly collaborative and synergistic program that would lead to major breakthroughs in the molecular-level understanding of the critical interfacial charge separation and charge transfer (CST) processes that underpin the function of candidate materials for organic photovoltaic (OPV) and electrical-energy-storage (EES) applications. Research in these energy contexts shares an imposing challenge: How can we understand charge separation and transfer mechanisms in the presence of immense materials complexity that spans multiple length scales? To address this challenge, our 50-member Center undertook a total of 28 coordinated research projects aimed at unraveling the CST mechanisms that occur at interfaces in these nanostructured materials. This rigorous multi-year study of CST interfaces has greatly illuminated our understanding of early-timescale processes (e.g., exciton generation and dissociation dynamics at OPV heterojunctions; control of Li+-ion charging kinetics by surface chemistry) occurring in the immediate vicinity of interfaces. Program outcomes included: training of 72 graduate student and postdoctoral energy researchers at 5 institutions and spanning 7 academic disciplines in science and engineering; publication of 94 peer-reviewed journal articles; and dissemination of research outcomes via 340 conference, poster and other presentations. Major scientific outcomes included: implementation of a hierarchical strategy for understanding the electronic communication mechanisms and ultimate fate of charge carriers in bulk heterojunction OPV materials; systematic investigation of ion-coupled electron transfer processes in model Li-ion battery electrode/electrolyte systems; and the development and implementation of 14 unique technologies and instrumentation capabilities to aid in probing sub-ensemble charge separation and transfer mechanisms.

  9. Sprite produced by consecutive impulse charge transfers following a negative stroke: Observation and simulation

    Science.gov (United States)

    Lu, Gaopeng; Cummer, Steven A.; Tian, Ye; Zhang, Hongbo; Lyu, Fanchao; Wang, Tao; Stanley, Mark A.; Yang, Jing; Lyons, Walter A.

    2016-04-01

    On the morning of 5 June 2013, two cameras of the SpriteCam network concurrently captured a red sprite with diffuse halo over a mesoscale convective system (MCS) passing the panhandle area of Oklahoma. This sprite was produced by a negative cloud-to-ground (CG) stroke with peak current of -103 kA in a manner different from previous observations in several aspects. First of all, the causative stroke of sprite is located by the National Lightning Detection Network (NLDN) in the trailing stratiform of MCS, instead of the deep convection typically for negative sprites. Second, the sprite-producing stroke was likely the first stroke of a multistroke negative CG flash (with ≥6 CG strokes) whose evolution was mainly confined in the lower part of thunderstorm; although the parent flash of sprite might contain relatively long in-cloud evolution prior to the first stroke, there is no evidence that the negative leader had propagated into the upper positive region of thundercloud as typically observed for the sprite-producing/class negative CG strokes. Third, as shown by the simulation with a two-dimensional full-wave electrodynamic model, although the impulse charge moment change (-190 C km) produced by the main stroke was not sufficient to induce conventional breakdown in the mesosphere, a second impulse charge transfer occurred with ~2 ms delay to cause a substantial charge transfer (-290 C km) so that the overall charge moment change (-480 C km) exceeded the threshold for sprite production; this is a scenario different from the typical case discussed by Li et al. (2012). As for the source of the second current pulse that played a critical role to produce the sprite, it could be an M component whose charge source was at least 9 km horizontally displaced from the main stroke or a negative CG stroke (with weak peak current for the return stroke) that was not detected by the NLDN.

  10. A rational reduction of CI expansions: combining localized molecular orbitals and selected charge excitations.

    Science.gov (United States)

    Krah, Tim; Ben Amor, Nadia; Maynau, Daniel; Berger, J A; Robert, Vincent

    2014-07-01

    Based on localized molecular orbitals, the proposed method reduces large configuration interaction (CI) spaces while maintaining agreement with reference values. Our strategy concentrates the numerical effort on physically pertinent CI-contributions and is to be considered as a tool to tackle large systems including numerous open-shells. To show the efficiency of our method we consider two 4-electron parent systems. First, we illustrate our approach by describing the van der Waals interactions in the (H2)2 system. By systematically including local correlation, dispersion and charge transfer mechanisms, we show that 90% of the reference full CI dissociation energy of the H2 dimer is reproduced using only 3% of the full CI space. Second, the conformational cis/trans rotation barrier of the butadiene molecule is remarkably reproduced (97% of the reference value) with less than 1% of the reference space. This work paves the way to numerical strategies which afford the electronic structure determination of large open-shell systems avoiding the exponential limitation. At the same time, a physical analysis of the contents of the wave function is offered. PMID:24935105

  11. Ultrafast dynamics of solvation and charge transfer in a DNA-based biomaterial.

    Science.gov (United States)

    Choudhury, Susobhan; Batabyal, Subrata; Mondol, Tanumoy; Sao, Dilip; Lemmens, Peter; Pal, Samir Kumar

    2014-05-01

    Charge migration along DNA molecules is a key factor for DNA-based devices in optoelectronics and biotechnology. The association of a significant amount of water molecules in DNA-based materials for the intactness of the DNA structure and their dynamic role in the charge-transfer (CT) dynamics is less documented in contemporary literature. In the present study, we have used a genomic DNA-cetyltrimethyl ammonium chloride (CTMA) complex, a technological important biomaterial, and Hoechest 33258 (H258), a well-known DNA minor groove binder, as fluorogenic probe for the dynamic solvation studies. The CT dynamics of CdSe/ZnS quantum dots (QDs; 5.2 nm) embedded in the as-prepared and swollen biomaterial have also been studied and correlated with that of the timescale of solvation. We have extended our studies on the temperature-dependent CT dynamics of QDs in a nanoenvironment of an anionic, sodium bis(2-ethylhexyl)sulfosuccinate reverse micelle (AOT RMs), whereby the number of water molecules and their dynamics can be tuned in a controlled manner. A direct correlation of the dynamics of solvation and that of the CT in the nanoenvironments clearly suggests that the hydration barrier within the Arrhenius framework essentially dictates the charge-transfer dynamics.

  12. An improved model of Charge Transfer Inefficiency and correction algorithm for the Hubble Space Telescope

    CERN Document Server

    Massey, Richard; Cordes, Oliver; Marggraf, Ole; Israel, Holger; Miller, Lance; Hall, David; Cropper, Mark; Prod'homme, Thibaut; Niemi, Sami-Matias

    2014-01-01

    Charge-Coupled Device (CCD) detectors, widely used to obtain digital imaging, can be damaged by high energy radiation. Degraded images appear blurred, because of an effect known as Charge Transfer Inefficiency (CTI), which trails bright objects as the image is read out. It is often possible to correct most of the trailing during post-processing, by moving flux back to where it belongs. We compare several popular algorithms for this: quantifying the effect of their physical assumptions and tradeoffs between speed and accuracy. We combine their best elements to construct a more accurate model of damaged CCDs in the Hubble Space Telescope's Advanced Camera for Surveys/Wide Field Channel, and update it using data up to early 2013. Our algorithm now corrects 98% of CTI trailing in science exposures, a substantial improvement over previous work. Further progress will be fundamentally limited by the presence of read noise. Read noise is added after charge transfer so does not get trailed - but it is incorrectly untr...

  13. Photoinduced Intramolecular Charge Transfer in Donor-acceptor Dyad and Donor-bridge-acceptor Triad

    Institute of Scientific and Technical Information of China (English)

    Yong Ding; Yuan-zuo Li; Feng-cai Ma

    2008-01-01

    The ground and excited state properties of the [60]fullerene,diphenylbenzothiadiazole-triphenylamine (PBTDP-TPA) dyad and fullerene-diphenylbenzothiadiazole-triphenylamine (fullerene-PBTDP-TPA) triad were investigated theoretically using density functional theory with B3LYP functional and 3-21G basis set and time-dependent density functional theory with B3LYP functional and STO-3G basis set as well as 2D and 3D real space analysis methods.The 2D site representation reveals the electron-hole coherence on exci- tation.The 3D transition density shows the orientation and strength of the transition dipole moment,and the 3D charge difference density gives the orientation and result of the intramolecular charge transfer.Also, photoinduced intermolecular charge transfer (ICT) in PBTDP-TPA-fullerene triad are identified with 2D and 3D representations,which reveals the mechanisms of ICT in donor-bridge-acceptor triad on excitation. Besides that we also found that the direct superexchange ICT from donor to acceptor (tunneling through the bridge) strongly promotes the ICT in the donor-bridge-acceptor triad.

  14. Geometry and quadratic nonlinearity of charge transfer complexes in solution using depolarized hyper-Rayleigh scattering.

    Science.gov (United States)

    Pandey, Ravindra; Ghosh, Sampa; Mukhopadhyay, S; Ramasesha, S; Das, Puspendu K

    2011-01-28

    We report large quadratic nonlinearity in a series of 1:1 molecular complexes between methyl substituted benzene donors and quinone acceptors in solution. The first hyperpolarizability, β(HRS), which is very small for the individual components, becomes large by intermolecular charge transfer (CT) interaction between the donor and the acceptor in the complex. In addition, we have investigated the geometry of these CT complexes in solution using polarization resolved hyper-Rayleigh scattering (HRS). Using linearly (electric field vector along X direction) and circularly polarized incident light, respectively, we have measured two macroscopic depolarization ratios D=I(2ω,X,X)/I(2ω,Z,X) and D(')=I(2ω,X,C)/I(2ω,Z,C) in the laboratory fixed XYZ frame by detecting the second harmonic scattered light in a polarization resolved fashion. The experimentally obtained first hyperpolarizability, β(HRS), and the value of macroscopic depolarization ratios, D and D('), are then matched with the theoretically deduced values from single and double configuration interaction calculations performed using the Zerner's intermediate neglect of differential overlap self-consistent reaction field technique. In solution, since several geometries are possible, we have carried out calculations by rotating the acceptor moiety around three different axes keeping the donor molecule fixed at an optimized geometry. These rotations give us the theoretical β(HRS), D and D(') values as a function of the geometry of the complex. The calculated β(HRS), D, and D(') values that closely match with the experimental values, give the dominant equilibrium geometry in solution. All the CT complexes between methyl benzenes and chloranil or 1,2-dichloro-4,5-dicyano-p-benzoquinone investigated here are found to have a slipped parallel stacking of the donors and the acceptors. Furthermore, the geometries are staggered and in some pairs, a twist angle as high as 30° is observed. Thus, we have demonstrated in

  15. Influence of functional groups on charge transport in molecular junctions

    DEFF Research Database (Denmark)

    Mowbray, Duncan; Jones, Glenn; Thygesen, Kristian Sommer

    2008-01-01

    demonstrates how ideas from functional group chemistry may be used to engineer a molecule's transport properties, as was shown experimentally and using a semiempirical model for BDA [Nano Lett. 7, 502 (2007)]. In particular, we show that the qualitative change in conductance due to a given functional group can...... the experimental values, but good agreement is obtained after correcting for self-interaction and image charge effects. (c) 2008 American Institute of Physics....... be predicted from its known electronic effect (whether it is sigma/pi donating/withdrawing). However, the influence of functional groups on a molecule's conductance is very weak, as was also found in the BDA experiments. The calculated DFT conductances for the BDA species are five times larger than...

  16. Energy and charge state dependences of transfer ionization to single capture ratio for fast multiply charged ions on helium

    Science.gov (United States)

    Unal, Ridvan

    The charge state and energy dependences of Transfer Ionization (TI) and Single Capture (SC) processes in collisions of multiply charged ions with He from intermediate to high velocities are investigated using coincident recoil ion momentum spectroscopy. The collision chamber is commissioned on the 15-degree port of a switching magnet, which allows the delivery of a beam with very little impurity. The target was provided from a supersonic He jet with a two-stage collimation. The two-stage, geometrically cooled, supersonic He jet has significantly reduced background contribution to the spectrum compared to a single stage He jet. In the case of a differentially pumped gas cell complex calculations based on assumptions for the correction due to the collisions with the contaminant beam led to corrections, which were up to 50%. The new setup allows one to make a direct separation of contaminant processes in the experimental data using the longitudinal momentum spectra. Furthermore, this correction is much smaller (about 8.8%) yielding better overall precision. The collision systems reported here are 1 MeV/u O(4--8)+ , 0.5--2.5 MeV/u F(4--9)+, 2.0 MeV/u Ti 15,17,18+, 1.6--1.75 MeV/u Cu18,20+ and 0.25--0.5 MeV/u I(15--25)+ ions interacting with helium. We have determined the sTIsSC ratio for high velocity highly charged ions on He at velocities in the range of 6 to 10 au and observed that the ratio is monotonically decreasing with velocity. Furthermore, we see a ratio that follows a q2 dependence up to approximately q = 9. Above q = 9 the experimental values exceed the q2 dependence prediction due to antiscreening. C. D. Lin and H. C. Tseng have performed coupled channel calculations for the energy dependence of TI and SC for F9+ + He and find values slightly higher than our measured values, but with approximately the same energy dependence. The new data, Si, Ti and Cu, go up only to q = 20 and show a smooth monotonically increasing TI/SC ratio. The TI/SC ratio for I (15

  17. Effect of medium on charge transport properties of modified poly(dA)-poly(dT) DNA molecular wire

    Science.gov (United States)

    Suhendro, D. K.; Yudiarsah, E.; Saleh, R.

    2014-09-01

    By using tight binding Hamiltonian approach, the medium's effect on charge transport properties of modified poly(dA)-poly(dT) DNA molecular wire is studied. The DNA sequences used are modified poly(dA)-poly(dT) sequence by replacing 50 base pairs randomly with GC or CG base pairs. The DNA is contacted by metallic leads at both ends. The medium's effect on DNA is modeled as backbone onsite energy disorder. The DNA is taken to be at room temperature. The charge transport properties of the two sequences are studied by calculating the transmission probabilities of the charges using the scattering and transfer matrix methods simultaneously. Then the current-voltage (I-V) characteristics are calculated from the transmission probabilities using the Landauer-Büttiker Formalism. The theoretical differential conductance curve is then calculated from the I-V characteristic curve. The I-V results show that as the backbone disorder strength increases, the maximum current decreases for both sequences. However, the threshold voltage can increase or decrease with increasing backbone disorder depending on the sequence. The transmission results show that the position of transmission peaks changed with backbone disorder strength. Comparison with previous published results using poly(dG)-poly(dC) sequence shows that in contrast to that sequence, backbone disorder can decrease the threshold voltage in one of the sequences studied. This may point to a new understanding of the interplay between environmental and sequence disorder effect on charge transport in DNA.

  18. Hydrogen-bonded Intramolecular Charge Transfer Excited State of Dimethylaminobenzophenone using Time Dependent Density Functional Theory

    Institute of Scientific and Technical Information of China (English)

    Yu-ling Chu; Zhong Yang; Zhe-feng Pan; Jing Liu; Yue-yi Han; Yong Ding; Peng Song

    2012-01-01

    Density functional theory and time-dependent density-functional theory have been used to investigate the photophysical properties and relaxation dynamics of dimethylaminobenzophenone (DMABP) and its hydrogen-bonded DMABP-MeOH dimer.It is found that,in nonpolar aprotic solvent,the transitions from S0 to S1 and S2 states of DMABP have both n→π* and π→π* characters,with the locally excited feature mainly located on the C=O group and the partial CT one characterized by electron transfer mainly from the dimethylaminophenyl group to the C=O group.But when the intermolecular hydrogen bond C=O…H-O is formed,the highly polar intramolecular charge transfer character switches over to the first excited state of DMABP-MeOH dimer and the energy difference between the two lowlying electronically excited states increases.To gain insight into the relaxation dynamics of DMABP and DMABP-MeOH dimer in the excited state,the potential energy curves for conformational relaxation are calculated.The formation of twisted intramolecular charge transfer state via diffusive twisting motion of the dimethylamino/dimethylaminophenyl groups is found to be the major relaxation process.In addition,the decay of the S1 state of DMABP-MeOH dimer to the ground state,through nonradiative intermolecular hydrogen bond stretching vibrations,is facilitated by the formation of the hydrogen bond between DMABP and alcohols.

  19. Beyond vibrationally mediated electron transfer: interfacial charge injection on a sub-10-fs time scale

    Science.gov (United States)

    Huber, Robert; Moser, Jacques E.; Gratzel, Michael; Wachtveitl, Josef L.

    2003-12-01

    The electron transfer (ET) from organic dye molecules to semiconductor-colloidal systems is characterized by a special energetic situation with a charge transfer reaction from a system of discrete donor levels to a continuum of acceptor states. If these systems show a strong electronic coupling they are amongst the fastest known ET systems with transfer times of less than 10 fs. In the first part a detailed discussion of the direct observation of an ET reaction with a time constant of about 6 fs will be given, with an accompanying argumentation concerning possible artifacts or other interfering signal contributions. In a second part we will try to give a simple picture for the scenario of such superfast ET reactions and one main focus will be the discussion of electronic dephasing and its consequences for the ET reaction. The actual ET process can be understood as a kind of dispersion process of the initially located electron into the colloid representing a real motion of charge density from the alizarin to the colloid.

  20. Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction

    Science.gov (United States)

    Tamura, Hiroyuki; Martinazzo, Rocco; Ruckenbauer, Matthias; Burghardt, Irene

    2012-12-01

    Following up on our recent study of ultrafast charge separation at oligothiophene-fullerene interfaces [H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C 115, 10205 (2011), 10.1021/jp203174e], we present here a detailed quantum dynamical perspective on the charge transfer process. To this end, electron-phonon coupling is included non-perturbatively, by an explicit quantum dynamical treatment using the multi-configuration time-dependent Hartree (MCTDH) method. Based upon a distribution of electron-phonon couplings determined from electronic structure studies, a spectral density is constructed and employed to parametrize a linear vibronic coupling Hamiltonian. The diabatic coupling is found to depend noticeably on the inter-fragment distance, whose effect on the dynamics is here investigated. MCTDH calculations of the nonadiabatic transfer dynamics are carried out for the two most relevant electronic states and 60 phonon modes. The electron transfer process is found to be ultrafast and mediated by electronic coherence, resulting in characteristic oscillatory features during a period of about 100 fs.

  1. Scaling of the transition temperature of hole-doped cuprate superconductors with the charge-transfer energy

    OpenAIRE

    Weber, Cédric; Yee, Chuck-Hou; Haule, Kristjan; Kotliar, Gabriel

    2011-01-01

    We use first-principles calculations to extract two essential microscopic parameters, the charge-transfer energy and the inter-cell oxygen-oxygen hopping, which correlate with the maximum superconducting transition temperature $\\Tcmax$ across the cuprates. We explore the superconducting state in the three-band model of the copper-oxygen planes using cluster Dynamical Mean-Field Theory. We find that the variation in the charge-transfer energy largely accounts for the empirical trend in $\\Tcmax...

  2. Studies on the interfacial charge transfer processes of nanocrystalline CdSe thin film electrodes by intensity modulated photocurrent spectroscopy

    Institute of Scientific and Technical Information of China (English)

    张敬波; 林原; 尹峰; 肖绪瑞

    2000-01-01

    Interfacial charge transfer kinetics of the nanocrystalline CdSe thin film electrodes have been studied in sodium polysulfide solutions by intensity modulated photocurrent spectroscopy (IMPS). The interfacial direct and indirect charge transfer and recombination processes were analyzed in terms of the parameters: normalized steady state photocurrents and surface state lifetimes obtained by measuring the IMPS responses under different applied potentials and different solution concentrations. IMPS responses of polycrystalline CdSe thin film electrodes were also presented for comparison.

  3. Energy transfer through a multi-layer liner for shaped charges

    Science.gov (United States)

    Skolnick, Saul; Goodman, Albert

    1985-01-01

    This invention relates to the determination of parameters for selecting materials for use as liners in shaped charges to transfer the greatest amount of energy to the explosive jet. Multi-layer liners constructed of metal in shaped charges for oil well perforators or other applications are selected in accordance with the invention to maximize the penetrating effect of the explosive jet by reference to four parameters: (1) Adjusting the explosive charge to liner mass ratio to achieve a balance between the amount of explosive used in a shaped charge and the areal density of the liner material; (2) Adjusting the ductility of each layer of a multi-layer liner to enhance the formation of a longer energy jet; (3) Buffering the intermediate layers of a multi-layer liner by varying the properties of each layer, e.g., composition, thickness, ductility, acoustic impedance and areal density, to protect the final inside layer of high density material from shattering upon impact of the explosive force and, instead, flow smoothly into a jet; and (4) Adjusting the impedance of the layers in a liner to enhance the transmission and reduce the reflection of explosive energy across the interface between layers.

  4. Theoretical investigations into optical and charge transfer properties of donor-acceptor 1,8-naphthalimide derivatives as possible organic light-emitting materials

    Science.gov (United States)

    Chai, Wandong; Jin, Ruifa

    2016-01-01

    A series of D-A naphthalimide-substituted fluorene derivatives have been designed to explore their optical, electronic, and charge transport properties as charge transport and/or luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbitals (FMOs) analysis 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 substituent groups in fluorene moieties. Our results suggest that all selected candidates are promising as luminescent materials for OLEDs. In addition, all derivatives can be used as promising hole and electron transport materials while derivatives with dibenzothiophene fragment can be used as hole transport material only for OLEDs.

  5. 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

    2014-12-04

    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.

  6. Local equilibria and state transfer of charged classical particles on a helix in an electric field

    CERN Document Server

    Plettenberg, J; Zampetaki, A V; Schmelcher, P

    2016-01-01

    We explore the effects of a homogeneous external electric field on the static properties and dynamical behavior of two charged particles confined to a helix. In contrast to the field-free setup which provides a separation of the center-of-mass and relative motion, the existence of an external force perpendicular to the helix axis couples the center-of-mass to the relative degree of freedom leading to equilibria with a localized center of mass. By tuning the external field various fixed points are created and/or annihilated through different bifurcation scenarios. We provide a detailed analysis of these bifurcations based on which we demonstrate a robust state transfer between essentially arbitrary equilibrium configurations of the two charges that can be induced by making the external force time-dependent.

  7. Charge Transfer Complexes of Polymers%高分子电荷转移复合物

    Institute of Scientific and Technical Information of China (English)

    赵扬; 邱家白

    1986-01-01

    @@ 电荷转移复合物(charge transfer complex, CTC)的研究,始于本世纪二十年代。然而对CTC理论的阐述,及其实际应用方面,长期未取得实质性进展。1952年R. S. Mulliken在J. H. Hildebrand的实验基础上首创共振模型,引入电荷转移(charge transfer,CT)这一术语,奠定了CTO的理论基础。从此,对CT现象的研究不断深入,开拓的领域日益广阔,已成为世界性的研究课题。

  8. Charge transfer in the interactions of partially stripped ions with atoms at intermediate and high energies

    International Nuclear Information System (INIS)

    The Coulomb-Born (CB) approximation has been employed to study charge transfer cross sections in collisions of Cq+, Nq+ and Oq+ (q = 1-5) with atomic hydrogen in ground state in the energy range of 30-200 keV/amu. The interaction of the active electron with the incoming projectile ion has been approximated by a model potential containing both a long-range part and a short-range part. Variations of total capture cross sections with impact energy compare favourable well with the available experimental observations and with other theoretical findings. In addition, sub-shell distributions of total capture cross sections are given in graphical form. However, we are unable to find any oscillation in the charge-state dependence of total capture cross sections. (author)

  9. Modeling of Charge Transfer Inefficiency in a CCD with High Speed Column Parallel Readout

    CERN Document Server

    Sopczak, Andre; Bekhouche, Khaled; Bowdery, Chris; Buttar, Craig; Damerell, Chris; Djendaoui, Dahmane; Dehimi, Lakhdar; Greenshaw, Tim; Koziel, Michal; Maneuski, Dzmitry; Nomerotski, Andrei; Stefanov, Konstantin; Tikkanen, Tuomo; Woolliscroft, Tim; Worm, Steve

    2008-01-01

    Charge Coupled Devices (CCDs) have been successfully used in several high energy physics experiments over the past two decades. Their high spatial resolution and thin sensitive layers make them an excellent tool for studying short-lived particles. The Linear Collider Flavour Identification (LCFI) collaboration is developing Column-Parallel CCDs (CPCCDs) for the vertex detector of a future Linear Collider. The CPCCDs can be read out many times faster than standard CCDs, significantly increasing their operating speed. An Analytic Model has been developed for the determination of the charge transfer inefficiency (CTI) of a CPCCD. The CTI values determined with the Analytic Model agree largely with those from a full TCAD simulation. The Analytic Model allows efficient study of the variation of the CTI on parameters like readout frequency, operating temperature and occupancy.

  10. Engineering interfacial photo-induced charge transfer based on nanobamboo array architecture for efficient solar-to-chemical energy conversion.

    Science.gov (United States)

    Wang, Xiaotian; Liow, Chihao; Bisht, Ankit; Liu, Xinfeng; Sum, Tze Chien; Chen, Xiaodong; Li, Shuzhou

    2015-04-01

    Engineering interfacial photo-induced charge transfer for highly synergistic photocatalysis is successfully realized based on nanobamboo array architecture. Programmable assemblies of various components and heterogeneous interfaces, and, in turn, engineering of the energy band structure along the charge transport pathways, play a critical role in generating excellent synergistic effects of multiple components for promoting photocatalytic efficiency. PMID:25704499

  11. ANISOTROPY EFFECTS IN SINGLE-ELECTRON TRANSFER BETWEEN LASER-EXCITED ATOMS AND HIGHLY-CHARGED IONS

    NARCIS (Netherlands)

    1995-01-01

    Recent collision experiments are reviewed in which one-electron transfer between laser excited target atoms and (highly charged) keV-ions has been studied. Especially results showing a dependence of the charge exchange on the initial target orbital alignment are discussed. The question to what exten

  12. Transverse charge transport through DNA oligomers in large-area molecular junctions

    Science.gov (United States)

    Katsouras, Ilias; Piliego, Claudia; Blom, Paul W. M.; de Leeuw, Dago M.

    2013-09-01

    We investigate the nature of charge transport in deoxyribonucleic acid (DNA) using self-assembled layers of DNA in large-area molecular junctions. A protocol was developed that yields dense monolayers where the DNA molecules are not standing upright, but are lying flat on the substrate. As a result the charge transport is measured not along the DNA molecules but in the transverse direction, across their diameter. The electrical transport data are consistent with the derived morphology. We demonstrate that the charge transport mechanism through DNA is identical to non-resonant tunneling through alkanethiols with identical length, classifying DNA as a dielectric.

  13. Carotenoid charge transfer states and their role in energy transfer processes in LH1-RC complexes from aerobic anoxygenic phototrophs.

    Science.gov (United States)

    Šlouf, Václav; Fuciman, Marcel; Dulebo, Alexander; Kaftan, David; Koblížek, Michal; Frank, Harry A; Polívka, Tomáš

    2013-09-26

    Light-harvesting complexes ensure necessary flow of excitation energy into photosynthetic reaction centers. In the present work, transient absorption measurements were performed on LH1-RC complexes isolated from two aerobic anoxygenic phototrophs (AAPs), Roseobacter sp. COL2P containing the carotenoid spheroidenone, and Erythrobacter sp. NAP1 which contains the carotenoids zeaxanthin and bacteriorubixanthinal. We show that the spectroscopic data from the LH1-RC complex of Roseobacter sp. COL2P are very similar to those previously reported for Rhodobacter sphaeroides, including the transient absorption spectrum originating from the intramolecular charge-transfer (ICT) state of spheroidenone. Although the ICT state is also populated in LH1-RC complexes of Erythrobacter sp. NAP1, its appearance is probably related to the polarity of the bacteriorubixanthinal environment rather than to the specific configuration of the carotenoid, which we hypothesize is responsible for populating the ICT state of spheroidenone in LH1-RC of Roseobacter sp. COL2P. The population of the ICT state enables efficient S1/ICT-to-bacteriochlorophyll (BChl) energy transfer which would otherwise be largely inhibited for spheroidenone and bacteriorubixanthinal due to their low energy S1 states. In addition, the triplet states of these carotenoids appear well-tuned for efficient quenching of singlet oxygen or BChl-a triplets, which is of vital importance for oxygen-dependent organisms such as AAPs. PMID:23130956

  14. Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer salts

    DEFF Research Database (Denmark)

    Sing, M.; Schwingenschlögl, U.; Claessen, R.;

    2003-01-01

    diagnostic tool. We show that the observation of generic one-dimensional signatures in photoemission spectra of the valence band close to the Fermi level can be strongly affected by surface effects. Especially, great care must be exercised taking evidence for an unusual one-dimensional many-body state......We have thoroughly characterized the surfaces of the organic charge-transfer salts TTF-TCNQ and (TMTSF)(2)PF6 which are generally acknowledged as prototypical examples of one-dimensional conductors. In particular x-ray-induced photoemission spectroscopy turns out to be a valuable nondestructive...

  15. Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors

    Energy Technology Data Exchange (ETDEWEB)

    Padhiyar, Ashvin; Patel, A J; Oza, A T [Department of Physics, Sardar Patel University, Vallabh Vidyanagar-388 120, Gujarat (India)

    2007-12-05

    It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.

  16. Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors

    Science.gov (United States)

    Padhiyar, Ashvin; Patel, A. J.; Oza, A. T.

    2007-12-01

    It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.

  17. Charge transfer in energetic Li2+-H and He+-He+ collisions

    Science.gov (United States)

    Mančev, I.

    2009-02-01

    The total cross sections for charge transfer in Li2+-H and He+-He+ collisions have been calculated, using the four body first Born approximation with correct boundary conditions (CB1-4B) and four body continuum distorted wave method (CDW-4B) in the energy range 10-5000 keV/amu. The role of dynamic electron correlations is examined as a function of the impact energy. The present results call for additional experimental data at higher impact energies than presently available.

  18. Metallization and charge-transfer gap closure of transition-metal iodides under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Chen, A. Li-Chung

    1993-05-01

    It is shown with resistivity and near-IR absorption measurements that NiI{sub 2}, CoI{sub 2}, and FeI{sub 2} metallize under pressure by closure of the charge-transfer energy gap at pressures of 17, 10, and 23 GPa, respectively, which is close to the antiferromagnetic-diamagnetic transition in NiI{sub 2} and CoI{sub 2}. Thus, the magnetic transitions probably are caused by the metallization; in NiI{sub 2} and CoI{sub 2}, the insulator-metal transitions are first order. Moessbauer and XRD data were also collected. Figs, 46 refs.

  19. Examination of charge transfer in Au/YSZ for high-temperature optical gas sensing

    Energy Technology Data Exchange (ETDEWEB)

    Baltrus, John P. [U.S. DOE; Ohodnicki, Paul R. [U.S. DOE

    2014-01-01

    Au-nanoparticle incorporated oxide thin film materials demonstrate significant promise as functionalsensor materials for high temperature optical gas sensing in severe environments relevant for fossil andnuclear based power generation. The Au/yttria-stabilized zirconia (YSZ) system has been extensivelystudied in the literature and serves as a model system for fundamental investigations that seek to betterunderstand the mechanistic origin of the plasmonic gas sensing response. In this work, X-ray photoelec-tron spectroscopy techniques are applied to Au/YSZ films in an attempt to provide further experimentalevidence for a proposed sensing mechanism involving a change in free carrier density of Au nanoparticles due to charge transfer.

  20. Assessment of asymptotically corrected model potential scheme for charge-transfer-like excitations in oligoacenes

    CERN Document Server

    Peng, Wei-Tao

    2014-01-01

    We examine the performance of the asymptotically corrected model potential scheme on the two lowest singlet excitation energies of acenes with different number of linearly fused benzene rings (up to 5), employing both the real-time time-dependent density functional theory and the frequency-domain formulation of linear-response time-dependent density functional theory. The results are compared with the experimental data and those calculated by long-range corrected hybrid functionals and others. The long-range corrected hybrid scheme is shown to outperform the asymptotically corrected model potential scheme for charge-transfer-like excitations.

  1. Charge-transfer induced EUV and soft X-ray emissions in the heliosphere

    OpenAIRE

    Koutroumpa, Dimitra; Lallement, Rosine; Kharchenko, V.; Dalgarno, A.; Pepino, R.; Izmodenov, V.; Quémerais, Eric

    2006-01-01

    We study the EUV/soft X-ray emission generated by charge transfer between solar wind heavy ions and interstellar neutral atoms and variations of the X-ray intensities and spectra with the line of sight direction, the observer location, the solar cycle phase and the solar wind anisotropies, and a temporary enhancement of the solar wind similar to the event observed by Snowden et al. (2004) during the XMM-Hubble Deep Field North exposure. Methods.Using recent observations of the neutral atoms c...

  2. Indolizino[5,6-b]quinoxaline Derivatives: Intramolecular Charge Transfer Characters and NIR Fluorescence.

    Science.gov (United States)

    Kojima, Mitsuru; Hayashi, Hironobu; Aotake, Tatsuya; Ikeda, Shinya; Suzuki, Mitsuharu; Aratani, Naoki; Kuzuhara, Daiki; Yamada, Hiroko

    2015-11-01

    Indolizino[5,6-b]quinoxaline derivatives (1 a and 1 b) with a push-pull structure were prepared to show intramolecular charge-transfer properties. Compounds 1 a and 1 b are strongly fluorescent in aprotic solvents while symmetrical derivatives (2 a and 2 b) were non-fluorescent. The π-expanded α-α linked dimer (10) of indolizino[5,6-b]quinoxaline 1 b was serendipitously obtained to show NIR absorption over 800 nm and the fluorescence edge reached to 1400 nm.

  3. Two-dimensional femtosecond optical spectroscopy of trapping dynamics in a charge-transfer process

    Science.gov (United States)

    Keß, Martin; Engel, Volker

    2016-04-01

    We study charge-transfer dynamics monitored by two-dimensional (2D) optical spectroscopy. The often used model consisting of two coupled diabatic electronic states in a single reaction coordinate is used to demonstrate the relation between the vibronic dynamics and the 2D-spectra. Within the employed wave-function approach, dissipation is included via a quantum-jump algorithm with explicit treatment of dephasing. States with long lifetimes which decay slowly due to the interaction with the environment are identified. Using filtered Fourier transforms, energy and time resolved information about the dissipative system dynamics can be obtained.

  4. Charge-transfer photodissociation of adsorbed molecules via electron image states

    CERN Document Server

    Jensen, E T

    2007-01-01

    The 248nm and 193nm photodissociation of submonolayer quantities of CH$_3$Br and CH$_3$I adsorbed on thin layers of n-hexane indicate that the dissociation is caused by dissociative electron attachment from sub-vacuum level photoelectrons created in the copper substrate. The characteristics of this photodissociation-- translation energy distributions and coverage dependences show that the dissociation is mediated by an image potential state which temporarily traps the photoelectrons near the n-hexane--vacuum interface, and then the charge transfers from this image state to the affinity level of a co-adsorbed halomethane which then dissociates.

  5. Nanometer scale carbon structures for charge-transfer systems and photovoltaic applications.

    Science.gov (United States)

    Guldi, Dirk M

    2007-03-28

    This article surveys and highlights the integration of nanometer scale carbon structures--in combination with chromophores that exhibit (i) significant absorption cross section throughout the visible part of the solar spectrum and (ii) good electron donating power--into novel electron donor-acceptor conjugates (i.e., covalent) and hybrids (i.e., non-covalent). The focus of this article is predominantly on performance features--charge-transfer and photovoltaic--of the most promising solar energy conversion systems. Besides documenting fundamental advantages as they emerge around nanometer scale carbon structures, critical evaluations of the most recent developments in the fields are provided.

  6. Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface

    DEFF Research Database (Denmark)

    Lindell, L.; Unge, Mikael; Osikowicz, W.;

    2008-01-01

    In organic-based electronics, interfacial properties have a profound impact on device performance. The lineup of energy levels is usually dependent on interface dipoles, which may arise from charge transfer reactions. In many applications, metal-organic junctions are prepared under ambient...... conditions, where direct overlap of the organic pi system from the metal bands is prevented due to presence of oxides and/or hydrocarbons. We present direct experimental and theoretical evidence showing that the interface energetic for such systems is governed by exchange of an integer amount of electrons....

  7. Excited state intramolecular charge transfer reaction in 4-(1-azetidinyl)benzonitrile: Solvent isotope effects

    Indian Academy of Sciences (India)

    Tuhin Pradhan; Piue Ghoshal; Ranjit Biswas

    2009-01-01

    Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several other properties such as quantum yield and radiative rates have been found to be insensitive to the solvent isotope substitution in all these solvents. The origin of the solvent isotope insensitivity of the reaction is discussed and correlated with the observed slowing down of the solvation dynamics upon isotope substitution.

  8. Formation of an intermolecular charge-transfer compound in UHV codeposited tetramethoxypyrene and tetracyanoquinodimethane

    DEFF Research Database (Denmark)

    Medjanik, K.; Perkert, S.; Naghavi, S.;

    2010-01-01

    Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP -TCNQ ) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS......). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d =0.894nm and d =0.677nm). A softening of the CN stretching vibration (redshift by 7 cm⊃-1) of TCNQ is visible in the IR spectra, being indicative of a CT on the order of 0.3e from TMP...

  9. Charge transfer and penning ionization of dopants in or on helium nanodroplets exposed to EUV radiation.

    Science.gov (United States)

    Buchta, Dominic; Krishnan, Siva R; Brauer, Nils B; Drabbels, Marcel; O'Keeffe, Patrick; Devetta, Michele; Di Fraia, Michele; Callegari, Carlo; Richter, Robert; Coreno, Marcello; Prince, Kevin C; Stienkemeier, Frank; Moshammer, Robert; Mudrich, Marcel

    2013-05-30

    Helium nanodroplets are widely used as a cold, weakly interacting matrix for spectroscopy of embedded species. In this work, we excite or ionize doped He droplets using synchrotron radiation and study the effect onto the dopant atoms depending on their location inside the droplets (rare gases) or outside at the droplet surface (alkali metals). Using photoelectron-photoion coincidence imaging spectroscopy at variable photon energies (20-25 eV), we compare the rates of charge-transfer to Penning ionization of the dopants in the two cases. The surprising finding is that alkali metals, in contrast to the rare gases, are efficiently Penning ionized upon excitation of the (n = 2)-bands of the host droplets. This indicates rapid migration of the excitation to the droplet surface, followed by relaxation, and eventually energy transfer to the alkali dopants.

  10. Measurement of charge transfer potential barrier in pinned photodiode CMOS image sensors

    Science.gov (United States)

    Chen, Cao; Bing, Zhang; Junfeng, Wang; Longsheng, Wu

    2016-05-01

    The charge transfer potential barrier (CTPB) formed beneath the transfer gate causes a noticeable image lag issue in pinned photodiode (PPD) CMOS image sensors (CIS), and is difficult to measure straightforwardly since it is embedded inside the device. From an understanding of the CTPB formation mechanism, we report on an alternative method to feasibly measure the CTPB height by performing a linear extrapolation coupled with a horizontal left-shift on the sensor photoresponse curve under the steady-state illumination. The theoretical study was performed in detail on the principle of the proposed method. Application of the measurements on a prototype PPD-CIS chip with an array of 160 × 160 pixels is demonstrated. Such a method intends to shine new light on the guidance for the lag-free and high-speed sensors optimization based on PPD devices. Project supported by the National Defense Pre-Research Foundation of China (No. 51311050301095).

  11. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier

    Science.gov (United States)

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-06-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery.

  12. A spectroscopic study of factors affecting charge transfer at organo-metallic interfaces

    CERN Document Server

    Tucker, C E

    2001-01-01

    polydiacetylene and omega-tricosenoic acid LB films. The resulting analyses have allowed comparison of charge trapping within the different bulk films and also at the film to substrate interface. In addition to DBARS, Fourier Transform Infra-red (FTIR) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies have been used to investigate the factors affecting the carboxylic acid group at the head of the LB molecule and the role this plays in charge transport across the organo-metallic boundary. The properties of organic films produced by the Langmuir-Blodgett (LB) technique have become more widely known in the last few decades, as the variety of organic molecules suitable for this method of production has increased. One class of LB molecule receiving particular attention has been that of conjugated polymers. These organic materials exhibit an anisotropic semi-conductor like behavior along the polymer chain, making them suitable candidate materials for use in molecular electronic devices. However,...

  13. Current-Driven Conformational Changes, Charging and Negative Differential Resistance in Molecular Wires

    OpenAIRE

    Emberly, Eldon; Kirczenow, George

    2001-01-01

    We introduce a theoretical approach based on scattering theory and total energy methods that treats transport non-linearities, conformational changes and charging effects in molecular wires in a unified way. We apply this approach to molecular wires consisting of chain molecules with different electronic and structural properties bonded to metal contacts. We show that non-linear transport in all of these systems can be understood in terms of a single physical mechanism and predict that negati...

  14. Beyond Vibrationally Mediated Electron Transfer: Coherent Phenomena Induced by Ultrafast Charge Separation

    CERN Document Server

    Huber, Robert; Moser, Jacques E; Grätzel, Michael; Wachtveitl, Josef

    2016-01-01

    Wave packet propagation succeeding electron transfer (ET) from alizarin dye molecules into the nanocrystalline TiO2 semiconductor has been studied by ultrafast transient absorption spectroscopy. Due to the ultrafast time scale of the ET reaction of about 6 fs the system shows substantial differences to molecular ET systems. We show that the ET process is not mediated by molecular vibrations and therefore classical ET theories lose their applicability. Here the ET reaction itself prepares a vibrational wave packet and not the electromagnetic excitation by the laser pulse. Furthermore, the generation of phonons during polaron formation in the TiO2 lattice is observed in real time for this system. The presented investigations enable an unambiguous assignment of the involved photoinduced mechanisms and can contribute to a corresponding extension of molecular ET theories to ultrafast ET systems like alizarin/TiO2.

  15. First-Principle Framework for Total Charging Energies in Electrocatalytic Materials and Charge-Responsive Molecular Binding at Gas-Surface Interfaces.

    Science.gov (United States)

    Tan, Xin; Tahini, Hassan A; Seal, Prasenjit; Smith, Sean C

    2016-05-01

    Heterogeneous charge-responsive molecular binding to electrocatalytic materials has been predicted in several recent works. This phenomenon offers the possibility of using voltage to manipulate the strength of the binding interaction with the target gas molecule and thereby circumvent thermochemistry constraints, which inhibit achieving both efficient binding and facile release of important targets such as CO2 and H2. Stability analysis of such charge-induced molecular adsorption has been beyond the reach of existing first-principle approaches. Here, we draw on concepts from semiconductor physics and density functional theory to develop a first principle theoretical approach that allows calculation of the change in total energy of the supercell due to charging. Coupled with the calculated adsorption energy of gas molecules at any given charge, this allows a complete description of the energetics of the charge-induced molecular adsorption process. Using CO2 molecular adsorption onto negatively charged h-BN (wide-gap semiconductor) and g-C4N3 (half metal) as example cases, our analysis reveals that - while adsorption is exothermic after charge is introduced - the overall adsorption processes are not intrinsically spontaneous due to the energetic cost of charging the materials. The energies needed to overcome the barriers of these processes are 2.10 and 0.43 eV for h-BN and g-C4N3, respectively. This first principle approach opens up new pathways for a more complete description of charge-induced and electrocatalytic processes. PMID:27067063

  16. Aggregation-induced emission of diarylamino-π-carborane triads: effects of charge transfer and π-conjugation.

    Science.gov (United States)

    Cho, Yang-Jin; Kim, So-Yoen; Cho, Minji; Han, Won-Sik; Son, Ho-Jin; Cho, Dae Won; Kang, Sang Ook

    2016-04-14

    Carborane-based donor-π-acceptor triads (D-π-A-π-D) bearing triarylamine moieties were synthesised. All the monomeric triads showed a blue-green emission in a dilute solution, which was assigned as an intramolecular charge-transfer (CT) emission. The intramolecular CT emission showed large Stokes shifts at a higher solvent polarity. The intramolecular CT emission further shifted to a longer wavelength with the increase in π-conjugation. Interestingly, a strong red emission was observed in highly concentrated solutions or in the solid state, which was assigned as an aggregation-induced emission (AIE). Moreover, the AIE strongly depended on solvent polarity. A large Stokes shift in AIE was attributed to the strong CT character. The changes in the dipole moment for the AIE state and monomer emission were evaluated using the Lippert-Mataga relationship. The density functional theory calculations showed that the change in electron distribution between the aryl amino group (highest occupied molecular orbital, HOMO) and the carborane moiety (lowest unoccupied molecular orbital, LUMO) indicates the intramolecular CT character, and the emission colour changes were attributed to the HOMO-LUMO energy gap controlled by the π-extension of the phenylene linker. The electrochemical properties such as oxidation and reduction potentials were consistent with theoretical calculation results. The emission properties were affected by two main factors: solvent polarity and solubility. PMID:26996491

  17. Short-lived charge-transfer excitons in organic photovoltaic cells studied by high-field magneto-photocurrent.

    Science.gov (United States)

    Devir-Wolfman, Ayeleth H; Khachatryan, Bagrat; Gautam, Bhoj R; Tzabary, Lior; Keren, Amit; Tessler, Nir; Vardeny, Z Valy; Ehrenfreund, Eitan

    2014-07-29

    The main route of charge photogeneration in efficient organic photovoltaic cells based on bulk hetero-junction donor-acceptor blends involves short-lived charge-transfer excitons at the donor-acceptor interfaces. The cell efficiency is critically affected by the charge-transfer exciton recombination and dissociation processes. By measuring the magneto-photocurrent under ambient conditions at room temperature, we show here that magnetic field-induced spin-mixing among the charge-transfer exciton spin sublevels occurs in fields up to at least 8.5 Tesla. The resulting magneto-photocurrent increases at high fields showing non-saturating behaviour up to the highest applied field. We attribute the observed high-field spin-mixing mechanism to the difference in the donor-acceptor g-factors. The non-saturating magneto-photocurrent response at high field indicates that there exist charge-transfer excitons with lifetime in the sub-nanosecond time domain. The non-Lorentzian high-field magneto-photocurrent response indicates a dispersive decay mechanism that originates due to a broad distribution of charge-transfer exciton lifetimes.

  18. Ultrafast Photo-Induced Charge Transfer Unveiled by Two-Dimensional Electronic Spectroscopy

    CERN Document Server

    Bixner, Oliver; Mancal, Tomas; Hauer, Juergen; Milota, Franz; Fischer, Michael; Pugliesi, Igor; Bradler, Maximilian; Schmid, Walther; Riedle, Eberhard; Kauffmann, Harald F; Christensson, Niklas

    2012-01-01

    The interaction of exciton and charge transfer (CT) states plays a central role in photo-induced CT processes in chemistry, biology and physics. In this work, we use a combination of two-dimensional electronic spectroscopy (2D-ES), pump-probe measurements and quantum chemistry to investigate the ultrafast CT dynamics in a lutetium bisphthalocyanine dimer in different oxidation states. It is found that in the anionic form, the combination of strong CT-exciton interaction and electronic asymmetry induced by a counter-ion enables CT between the two macrocycles of the complex on a 30 fs timescale. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra, and we monitor how the excited state charge density ultimately localizes on the macrocycle closest to the counter-ion within 100 fs. A comparison with the dynamics in the radical species further elucidates how CT states modulate the electronic structure and tune fs-reac...

  19. Endoergic and resonant charge transfer excitation in He-Cu discharge

    Science.gov (United States)

    Mezei, P.; Rózsa, K.; Jánossy, M.; Apai, P.

    1987-09-01

    The intensity of Cu-II lines with upper level energies near and above those of the He ion was measured as a function of He pressure in a Cu hollow cathode tube. In this tube at low pressures the negative glow could expand above the cathode. The maximum intensity of the Cu-II 493.1 nm line was found in the low voltage, high pressure hollow cathode discharge region in accordance with a resonant charge transfer excitation process. Enhancement of the intensity of the Cu-II 436.5 nm and 417.9 nm lines was observed in the cathode glow at low pressures. Excitation of these lines is attributed to endoergic charge transfer collisions between He ions accelerated by the 2 kV tube voltage and ground state Cu atoms. The cross-section for this reaction exciting the 436.5 nm line was estimated to be of the order of 10-17 cm2.

  20. Observation of excited state charge transfer with fs/ps-CARS

    Energy Technology Data Exchange (ETDEWEB)

    Blom, Alex Jason [Iowa State Univ., Ames, IA (United States)

    2009-01-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4'-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  1. Observation of excited state charge transfer with fs/ps-CARS

    International Nuclear Information System (INIS)

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4(prime)-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4(prime)-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles

  2. Charge-transfer optical absorption mechanism of DNA:Ag-nanocluster complexes

    Science.gov (United States)

    Longuinhos, R.; Lúcio, A. D.; Chacham, H.; Alexandre, S. S.

    2016-05-01

    Optical properties of DNA:Ag-nanoclusters complexes have been successfully applied experimentally in Chemistry, Physics, and Biology. Nevertheless, the mechanisms behind their optical activity remain unresolved. In this work, we present a time-dependent density functional study of optical absorption in DNA:Ag4. In all 23 different complexes investigated, we obtain new absorption peaks in the visible region that are not found in either the isolated Ag4 or isolated DNA base pairs. Absorption from red to green are predominantly of charge-transfer character, from the Ag4 to the DNA fragment, while absorption in the blue-violet range are mostly associated to electronic transitions of a mixed character, involving either DNA-Ag4 hybrid orbitals or intracluster orbitals. We also investigate the role of exchange-correlation functionals in the calculated optical spectra. Significant differences are observed between the calculations using the PBE functional (without exact exchange) and the CAM-B3LYP functional (which partly includes exact exchange). Specifically, we observe a tendency of charge-transfer excitations to involve purines bases, and the PBE spectra error is more pronounced in the complexes where the Ag cluster is bound to the purines. Finally, our results also highlight the importance of adding both the complementary base pair and the sugar-phosphate backbone in order to properly characterize the absorption spectrum of DNA:Ag complexes.

  3. Modulation of the charge transfer and photophysical properties in non-fused tetrathiafulvalene-benzothiadiazole derivatives.

    Science.gov (United States)

    Pop, Flavia; Seifert, Sabine; Hankache, Jihane; Ding, Jie; Hauser, Andreas; Avarvari, Narcis

    2015-01-28

    Bis(thiomethyl)- and bis(thiohexyl)-tetrathiafulvalene-bromo-benzothiadiazoles, containing electron donor tetrathiafulvalene (TTF) and electron acceptor benzothiadiazole (BTD) units, have been prepared by Stille coupling reactions between the TTF-SnMe3 precursors and BTD-Br2. In another series of experiments, TTF-acetylene-BTD compounds have been synthesized by Sonogashira coupling between either TTF-acetylenes and BTD-Br2 in low yields, or TTF-iodine and BTD-acetylene in moderate yields. In the compound TTF-C≡C-BTD the TTF and BTD units are coplanar in the solid state, as shown by the single crystal X-ray structure, and there is segregation in the packing between the donor and acceptor units. All the derivatives have good electron donor properties, as determined by cyclic voltammetry measurements, and they can also be reversibly reduced thanks to the presence of the BTD moiety. UV-visible spectroscopy and photophysical investigations show the presence of an intramolecular charge transfer (ICT) band and an emission band originating from the charge transfer. Both the absorption and the emission are modulated by the substitution scheme and the insertion of the acetylenic bridge. PMID:25410315

  4. Charge transfer at carbon nanotube-graphene van der Waals heterojunctions

    Science.gov (United States)

    Liu, Yuanda; Wang, Fengqiu; Liu, Yujie; Wang, Xizhang; Xu, Yongbing; Zhang, Rong

    2016-06-01

    Carbon nanotubes and graphene are two most widely investigated low-dimensional materials for photonic and optoelectronic devices. Combining these two materials into all-carbon hybrid nanostructures has shown enhanced properties in a range of devices, such as photodetectors and flexible electrodes. Interfacial charge transfer is the most fundamental physical process that directly impacts device design and performance, but remains a subject less well studied. Here, we complemented Raman spectroscopy with photocurrent probing, a robust way of illustrating the interfacial built-in fields, and unambiguously revealed both static and dynamic (photo-induced) charge transfer processes at the nanotube-graphene interfaces. Significantly, the effects of nanotube species, i.e. metallic as opposed to semiconducting, are for the first time compared. Of all the devices examined, the graphene sheet was found to be p-type doped with (6, 5) chirality-enriched semiconducting SWNTs (s-SWNTs), while n-type doped with highly pure (>99%) metallic SWNTs (m-SWNTs). Our results provide important design guidelines for all-carbon hybrid based devices.

  5. Label-Free Acetylcholine Image Sensor Based on Charge Transfer Technology for Biological Phenomenon Tracking

    Science.gov (United States)

    Takenaga, Shoko; Tamai, Yui; Okumura, Koichi; Ishida, Makoto; Sawada, Kazuaki

    2012-02-01

    A 32 ×32 charge-transfer enzyme-type acetylcholine (ACh) image sensor array was produced for label-free tracking of images of ACh distribution and its performance in repeatable measurements without enzyme deactivation was examined. The proposed sensor was based on a charge-transfer-type pH image sensor, which was modified using an enzyme membrane (acetylcholine esterase, AChE) for each pixel. The ACh image sensor detected hydrogen ions generated by the ACh-AChE reaction. A polyion complex membrane composed of poly(L-lysine) and poly(4-styrenesulfonate) was used to immobilize the enzyme on the sensor. The improved uniformity and adhesion of the polyion complex membrane were evaluated in this study. As a result, temporal and spatial fluctuations of the ACh image sensor were successfully minimized using this approach. The sensitivity of the sensor was 4.2 mV/mM, and its detection limit was 20 µM. In five repeated measurements, the repeatability was 8.8%.

  6. Momentum transfer theory of non-conservative charged particle transport in crossed electric and magnetic fields

    International Nuclear Information System (INIS)

    Momentum - transfer approximation is applied to momentum and energy balance equations describing reacting particle swarms in gases in crossed electric and magnetic fields. Transport coefficients of charged particles undergoing both inelastic and reactive, non-particle-conserving collisions with a gas of neutral molecules are calculated. Momentum - transfer theory (MTT) has been developed mainly by Robson and collaborators. It has been applied to a single reactive gas and mixtures of reactive gases in electric field only. MTT has also been applied in crossed electric and magnetic fields recently and independently of our work but the reactive collisions were not considered. Consider a swarm of electrons of charge e and mass m moving with velocity rvec v through a neutral gas under the influence of an applied electric rvec E and magnetic rvec B field. The collision processes which we shall investigate are limited to elastic, inelastic and reactive collisions of electrons with gas molecules. Here we interpret reactive collisions as collisions which produce change in number of the swarm particles. Reactive collisions involve creation (ionization by electron impact) or loss (electron attachment) of swarm particles. We consider only single ionization in approximation of the mass ratio m/m00 are masses of electrons and neutral particles, respectively. We assume that the stage of evolution of the swarm is the hydrodynamic limit (HDL). In HDL, the space - time dependence of all properties is carried by the number density n of swarm particles

  7. Molecular dynamics simulation of water between two charged layers of dipalmitoylphosphatidylserine

    NARCIS (Netherlands)

    Cascales, J.J.L.; Berendsen, H.J.C.; delaTorre, J.G.

    1996-01-01

    A molecular dynamics simulation of water between two charged layers of dipalmitoylphosphatidylserine in its liquid-crystalline state with atomic detail was carried out. From an analysis of a trajectory of 184 ps of length, we obtained information about the dynamics and structure of water between suc

  8. Transverse charge transport through DNA oligomers in large-area molecular junctions

    NARCIS (Netherlands)

    Katsouras, I.; Piliego, C.; Blom, P.W.M.; Leeuw, D.M. de

    2013-01-01

    We investigate the nature of charge transport in deoxyribonucleic acid (DNA) using self-assembled layers of DNA in large-area molecular junctions. A protocol was developed that yields dense monolayers where the DNA molecules are not standing upright, but are lying flat on the substrate. As a result

  9. Model calculation of the charge transfer in low-energy He+ scattering from metallic surfaces

    International Nuclear Information System (INIS)

    Charge-transfer mechanisms in low-energy helium-scattering spectroscopy are analyzed by using an Anderson-like description of the time-dependent collisional process, which allows us to include several electronic bands of extended and localized nature in the solid. The Hamiltonian parameters are obtained from a Hartree-Fock self-consistent-field calculation of the He-target atom dimeric system. We examine in particular cases such as Ca and Ga linear chain substrates. We found that at velocities large enough, the localized state in the solid contributes to the He+ neutralization, showing the characteristic oscillatory behavior of the nonadiabatic charge exchange between localized states, in agreement with other calculations. In the range of low velocities we found that if the hybridization between the He orbital and the localized states in the solid is able to produce the formation of an antibonding state having a predominant weight of the He-1s orbital, this promotes the charge exchange between the Helium and the extended bandstates of the solid

  10. How well can Charge Transfer Inefficiency be corrected? A parameter sensitivity study for iterative correction

    CERN Document Server

    Israel, Holger; Prod'homme, Thibaut; Cropper, Mark; Cordes, Oliver; Gow, Jason; Kohley, Ralf; Marggraf, Ole; Niemi, Sami; Rhodes, Jason; Short, Alex; Verhoeve, Peter

    2015-01-01

    Radiation damage to space-based Charge-Coupled Device (CCD) detectors creates defects which result in an increasing Charge Transfer Inefficiency (CTI) that causes spurious image trailing. Most of the trailing can be corrected during post-processing, by modelling the charge trapping and moving electrons back to where they belong. However, such correction is not perfect -- and damage is continuing to accumulate in orbit. To aid future development, we quantify the limitations of current approaches, and determine where imperfect knowledge of model parameters most degrade measurements of photometry and morphology. As a concrete application, we simulate $1.5\\times10^{9}$ "worst case" galaxy and $1.5\\times10^{8}$ star images to test the performance of the Euclid visual instrument detectors. There are two separable challenges: If the model used to correct CTI is perfectly the same as that used to add CTI, $99.68$ % of spurious ellipticity is corrected in our setup. This is because readout noise is not subject to CTI,...

  11. Implementation of a protein reduced point charge model toward molecular dynamics applications.

    Science.gov (United States)

    Leherte, Laurence; Vercauteren, Daniel P

    2011-11-17

    A reduced point charge model was developed in a previous work from the study of extrema in smoothed charge density distribution functions generated from the Amber99 molecular electrostatic potential. In the present work, such a point charge distribution is coupled with the Amber99 force field and implemented in the program TINKER to allow molecular dynamics (MD) simulations of proteins. First applications to two polypeptides that involve α-helix and β-sheet motifs are analyzed and compared to all-atom MD simulations. Two types of coarse-grained (CG)-based trajectories are generated using, on one hand, harmonic bond stretching terms and, on the other hand, distance restraints. Results show that the use of the unrestrained CG conditions are sufficient to preserve most of the secondary structure characteristics but restraints lead to a better agreement between CG and all-atom simulation results such as rmsd, dipole moment, and time-dependent mean square deviation functions. PMID:21800922

  12. Charge Transfer Dynamics in Semiconductor Quantum Dots Relevant to Solar Hydrogen Production

    Science.gov (United States)

    Krauss, Todd

    Artificial conversion of sunlight to chemical fuels has attracted attention for several decades as a potential source of clean, renewable energy. For example, in light-driven proton reduction to molecular hydrogen, a light-absorbing molecule (the photosensitizer) rapidly transfers a photoexcited electron to a catalyst for reducing protons. We recently found that CdSe quantum dots (QDs) and simple aqueous Ni2+ salts in the presence of a sacrificial electron donor form a highly efficient, active, and robust system for photochemical reduction of protons to molecular hydrogen. To understand why this system has such extraordinary catalytic behavior, ultrafast transient absorption (TA) spectroscopy studies of electron transfer (ET) processes from the QDs to the Ni catalysts were performed. CdSe QDs transfer photoexcited electrons to a Ni-dihydrolipoic acid (Ni-DHLA) catalyst complex extremely fast and with high efficiency. Even under high fluence, the relative fraction of TA signal due to ET remains well over 80%, and depopulation from exciton-exciton annihilation is minimal (6%). We also found that increasing QD size and/or shelling the core CdSe QDs with a shell of CdS slowed the ET rate, in agreement with the relative efficiency of photochemical H2 generation. The extremely fast ET provides a fundamental explanation for the exceptional photocatalytic H2 activity of the CdSe QD/Ni-DHLA system and guides new directions for further improvements.

  13. On combining Thole's induced point dipole model with fixed charge distributions in molecular mechanics force fields.

    Science.gov (United States)

    Antila, Hanne S; Salonen, Emppu

    2015-04-15

    The Thole induced point dipole model is combined with three different point charge fitting methods, Merz-Kollman (MK), charges from electrostatic potentials using a grid (CHELPG), and restrained electrostatic potential (RESP), and two multipole algorithms, distributed multipole analysis (DMA) and Gaussian multipole model (GMM), which can be used to describe the electrostatic potential (ESP) around molecules in molecular mechanics force fields. This is done to study how the different methods perform when intramolecular polarizability contributions are self-consistently removed from the fitting done in the force field parametrization. It is demonstrated that the polarizable versions of the partial charge models provide a good compromise between accuracy and computational efficiency in describing the ESP of small organic molecules undergoing conformational changes. For the point charge models, the inclusion of polarizability reduced the the average root mean square error of ESP over the test set by 4-10%.

  14. Optical properties of poly(3-hexylthiophene) and interfacial charge transfer between poly(3-hexylthiophene) and titanium dioxide in composites

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Long; Zhang, Jianling [State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Polymer Research Institute of Sichuan University, Chengdu 610065 (China); Wang, Weiwei [State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Polymer Research Institute of Sichuan University, Chengdu 610065 (China); Institut des Matériaux Jean Rouxel, University of Nantes, CNRS, 2 rue de la Houssinière, 44322 Nantes (France); Yang, Haigang [State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Polymer Research Institute of Sichuan University, Chengdu 610065 (China); Reisdorffer, Frederic [Institut des Matériaux Jean Rouxel, University of Nantes, CNRS, 2 rue de la Houssinière, 44322 Nantes (France); Nguyen, Thien-Phap, E-mail: Thien-Phap.Nguyen@cnrs-imn.fr [Institut des Matériaux Jean Rouxel, University of Nantes, CNRS, 2 rue de la Houssinière, 44322 Nantes (France); Dan, Yi, E-mail: danyi@scu.edu.cn [State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Polymer Research Institute of Sichuan University, Chengdu 610065 (China)

    2015-03-15

    The optical properties of poly(3-hexylthiophene) (P3HT), in pristine form or with added anatase titanium dioxide (TiO{sub 2}) nanoparticles have been investigated, and the interfacial charge transfer between P3HT and TiO{sub 2} have been studied by steady-state luminescence spectroscopy analysis. The photoluminescence results revealed that incorporation of TiO{sub 2} nanoparticles in concentrations up to 0.3 mM significantly enhanced the luminescence intensity of P3HT when exposing to light of energy higher than TiO{sub 2} bandgap. The observed variation suggested an energy transfer from TiO{sub 2} nanoparticles to P3HT. Meanwhile, when P3HT/TiO{sub 2} composites were exposed to light of energy below TiO{sub 2} bandgap, TiO{sub 2} nanoparticles gradually quench the fluorescence of P3HT, demonstrating the injection of excited electrons from lowest unoccupied molecular orbit of P3HT to the conduction band of TiO{sub 2}. - Highlights: • Optical properties of P3HT, in pristine form or with added TiO{sub 2} were investigated. • Excitation above TiO{sub 2} bandgap produces a remarkable increase in P3HT emission. • The enhancement is attributed to transfer of excitation energy from TiO{sub 2} to P3HT. • TiO{sub 2} quenches P3HT emission when composites are excited below TiO{sub 2} bandgap. • The quench is due to the injection of excitons from LUMO of P3HT to CB of TiO{sub 2}.

  15. A non-adiabatic wavepacket dynamical study of the low energy charge transfer process in the S{sup 3+} + H collision

    Energy Technology Data Exchange (ETDEWEB)

    Labuda, Marta, E-mail: marta@mif.pg.gda.pl [Faculty of Applied Physics and Mathematics, Gdansk University of Technology, ul. Narutowicza 11/12, 80233 Gdansk (Poland); Gonzalez-Vazquez, Jesus [Instituto de Quimica Fisica Rocasolano, CSIC, C/ Serrano 119, 28006 Madrid (Spain); Martin, Fernando [Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Instituto Madrileno de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid (Spain); Gonzalez, Leticia [Institute of Theoretical Chemistry, University of Vienna, Waehringerstrasse 17, 1090 Vienna (Austria)

    2012-05-25

    Highlights: Black-Right-Pointing-Pointer S{sup 3+} + H charge transfer process. Black-Right-Pointing-Pointer Low energy collision in the [1-10] eV range. Black-Right-Pointing-Pointer Non-adiabatic wavepacket quantum dynamical study. Black-Right-Pointing-Pointer 2D time-dependent wavepacket approach in the femtosecond time scale. - Abstract: The collisional system S{sup 3+} + H {yields} S{sup 2+} + H{sup +} has been studied using a time-dependent wavepacket methodology in two-dimensions. Using available potential energy surfaces and coupling matrix elements obtained from multireference ab initio calculations, five non-adiabatically coupled electronic states of {sup 1}{Pi} symmetry have been included in the dynamical simulations. The collision has been studied in the low energy regime of 1-10 eV. The wavepacket treatment accounts for the description of the collision including all possible impact parameters simultaneously in all spatial directions of the considered plane. The molecular movie of the scattered products arising from charge transfer yields the angular distribution and the total charge transfer probability vs. initial kinetic energy of the projectile. A detailed analysis of the forward, sideways, and backward scattering mechanisms showing different patterns is presented.

  16. FAST TRACK COMMUNICATION: Effects of charge transfer interaction of graphene with electron donor and acceptor molecules examined using Raman spectroscopy and cognate techniques

    Science.gov (United States)

    Voggu, Rakesh; Das, Barun; Sekhar Rout, Chandra; Rao, C. N. R.

    2008-11-01

    The effects of the interaction of few-layer graphene with electron donor and acceptor molecules have been investigated by employing Raman spectroscopy, and the results compared with those from electrochemical doping. The G-band softens progressively with increasing concentration of tetrathiafulvalene (TTF) which is an electron donor, while the band stiffens with increasing concentration of tetracyanoethylene (TCNE) which is an electron acceptor. Interaction with both TTF and TCNE broadens the G-band. Hole and electron doping by electrochemical means, however, stiffen and sharpen the G-band. The 2D-band position is also affected by interaction with TTF and TCNE. More importantly, the intensity of the 2D-band decreases markedly with the concentration of either. The ratio of intensities of the 2D-band and G-band decreases with an increase in TTF or TCNE concentration, and provides a means for carrier titration in the charge transfer system. Unlike the intensity of the 2D-band, that of the D-band increases on interaction with TTF or TCNE. All of these effects occur due to molecular charge transfer, also evidenced by the occurrence of charge transfer bands in the electronic absorption spectra. The electrical resistivity of graphene varies in opposite directions on interaction with TTF and TCNE, the resistivity depending on the concentration of either compound.

  17. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

    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 ...

  18. The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Krinichnyi, V. I., E-mail: kivirus@gmail.com; Yudanova, E. I.; Denisov, N. N. [Kinetics and Catalysis, Institute of Problems of Chemical Physics, Chernogolovka 142432 (Russian Federation)

    2014-07-28

    Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′, 3′-benzothiadiazole)]:-[6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PCDTBT:PC{sub 61}BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix.

  19. Probing the Nature of Charge Transfer at Nano-Bio Interfaces: Peptides on Metal Oxide Nanoparticles.

    Science.gov (United States)

    Tarakeshwar, Pilarisetty; Palma, Julio L; Holland, Gregory P; Fromme, Petra; Yarger, Jeffery L; Mujica, Vladimiro

    2014-10-16

    Characterizing the nano-bio interface has been a long-standing endeavor in the quest for novel biosensors, biophotovoltaics, and biocompatible electronic devices. In this context, the present computational work on the interaction of two peptides, A6K (Ac-AAAAAAK-NH2) and A7 (Ac-AAAAAAA-NH2) with semiconducting TiO2 nanoparticles is an effort to understand the peptide-metal oxide nanointerface. These investigations were spurred by recent experimental observations that nanostructured semiconducting metal oxides templated with A6K peptides not only stabilize large proteins like photosystem-I (PS-I) but also exhibit enhanced charge-transfer characteristics. Our results indicate that α-helical structures of A6K are not only energetically more stabilized on TiO2 nanoparticles, but the resulting hybrids also exhibit enhanced electron transfer characteristics. This enhancement can be attributed to substantial changes in the electronic characteristics at the peptide-TiO2 interface. Apart from understanding the mechanism of electron transfer (ET) in peptide-stabilized PS-I on metal oxide nanoparticles, the current work also has implications in the development of novel solar cells and photocatalysts.

  20. Metal Ion Enhanced Charge Transfer in a Terpyridine-bis-Pyrene System

    Directory of Open Access Journals (Sweden)

    Luisa De Cola

    2009-05-01

    Full Text Available The synthesis, electrochemical and photophysical properties of a branched molecule 3,5-bis(pyrene-1-yl-4'-phenyl-2,2':6',2''-terpyridine are reported. Spectroscopy in different solvents reveals that an optical electron transfer from the pyrene donor to the terpyridyl electron acceptor can occur in polar media, as the system displays both charge transfer (CT absorption and CT emission. Furthermore, the study of the zinc complex as well as the bis-protonated form shows an enhancement of the electron transfer character of the system, by an increase of the acceptor strength. This is accompanied by a large increase of the non-radiative processes. With sub-nanosecond transient absorption spectroscopy, the CT state, consisting of the pyrene radical cation and the terpyridine radical anion, has been detected. At room temperature, the study of the nanosecond transient absorption spectra reveals the formation of a low-lying triplet excited state that we attribute to the pyrene moiety through which the CT state decays. At 77K, the absence of the terpyridine triplet emission also suggests the population of a low-lying triplet state of the pyrene unit.

  1. Charge-transfer excitations in low-gap systems under the influence of solvation and conformational disorder: Exploring range-separation tuning

    Science.gov (United States)

    de Queiroz, Thiago B.; Kümmel, Stephan

    2014-08-01

    Charge transfer excitations play a prominent role in the fields of molecular electronics and light harvesting. At the same time they have developed a reputation for being hard to predict with time-dependent density functional theory, which is the otherwise predominant method for calculating molecular structure and excitations. Recently, it has been demonstrated that range-separated hybrid functionals, in particular with an "optimally tuned" range separation parameter, describe charge-transfer excitations reliably for different molecules. Many of these studies focused on molecules in vacuum. Here we investigate the influence of solvation on the electronic excitations of thiophene oligomers, i.e., paradigm low gap systems. We take into account bulk solvation using a continuum solvation model and geometrical distortions from molecular dynamics. From our study, three main findings emerge. First, geometrical distortions increase absorption energies by about 0.5 eV for the longer thiophene oligomers. Second, combining optimal tuning of the range separation parameter with a continuum solvation method is not straightforward and has to be approached with great care. Third, optimally tuned range-separated hybrids without a short-range exchange component tend to inherit undesirable characteristics of semi-local functionals: with increasing system size the range separation parameter takes a smaller value, leading to a functional of effectively more semi-local nature and thus not accurately capturing, e.g., the saturation of the optical gap with increasing system size.

  2. Charge-transfer excitations in low-gap systems under the influence of solvation and conformational disorder: Exploring range-separation tuning

    International Nuclear Information System (INIS)

    Charge transfer excitations play a prominent role in the fields of molecular electronics and light harvesting. At the same time they have developed a reputation for being hard to predict with time-dependent density functional theory, which is the otherwise predominant method for calculating molecular structure and excitations. Recently, it has been demonstrated that range-separated hybrid functionals, in particular with an “optimally tuned” range separation parameter, describe charge-transfer excitations reliably for different molecules. Many of these studies focused on molecules in vacuum. Here we investigate the influence of solvation on the electronic excitations of thiophene oligomers, i.e., paradigm low gap systems. We take into account bulk solvation using a continuum solvation model and geometrical distortions from molecular dynamics. From our study, three main findings emerge. First, geometrical distortions increase absorption energies by about 0.5 eV for the longer thiophene oligomers. Second, combining optimal tuning of the range separation parameter with a continuum solvation method is not straightforward and has to be approached with great care. Third, optimally tuned range-separated hybrids without a short-range exchange component tend to inherit undesirable characteristics of semi-local functionals: with increasing system size the range separation parameter takes a smaller value, leading to a functional of effectively more semi-local nature and thus not accurately capturing, e.g., the saturation of the optical gap with increasing system size

  3. Charge-transfer excitations in low-gap systems under the influence of solvation and conformational disorder: exploring range-separation tuning.

    Science.gov (United States)

    de Queiroz, Thiago B; Kümmel, Stephan

    2014-08-28

    Charge transfer excitations play a prominent role in the fields of molecular electronics and light harvesting. At the same time they have developed a reputation for being hard to predict with time-dependent density functional theory, which is the otherwise predominant method for calculating molecular structure and excitations. Recently, it has been demonstrated that range-separated hybrid functionals, in particular with an "optimally tuned" range separation parameter, describe charge-transfer excitations reliably for different molecules. Many of these studies focused on molecules in vacuum. Here we investigate the influence of solvation on the electronic excitations of thiophene oligomers, i.e., paradigm low gap systems. We take into account bulk solvation using a continuum solvation model and geometrical distortions from molecular dynamics. From our study, three main findings emerge. First, geometrical distortions increase absorption energies by about 0.5 eV for the longer thiophene oligomers. Second, combining optimal tuning of the range separation parameter with a continuum solvation method is not straightforward and has to be approached with great care. Third, optimally tuned range-separated hybrids without a short-range exchange component tend to inherit undesirable characteristics of semi-local functionals: with increasing system size the range separation parameter takes a smaller value, leading to a functional of effectively more semi-local nature and thus not accurately capturing, e.g., the saturation of the optical gap with increasing system size.

  4. Dipole-mediated rectification of intramolecular photoinduced charge separation and charge recombination.

    Science.gov (United States)

    Bao, Duoduo; Upadhyayula, Srigokul; Larsen, Jillian M; Xia, Bing; Georgieva, Boriana; Nuñez, Vicente; Espinoza, Eli M; Hartman, Joshua D; Wurch, Michelle; Chang, Andy; Lin, Chung-Kuang; Larkin, Jason; Vasquez, Krystal; Beran, Gregory J O; Vullev, Valentine I

    2014-09-17

    Controlling charge transfer at a molecular scale is critical for efficient light harvesting, energy conversion, and nanoelectronics. Dipole-polarization electrets, the electrostatic analogue of magnets, provide a means for "steering" electron transduction via the local electric fields generated by their permanent electric dipoles. Here, we describe the first demonstration of the utility of anthranilamides, moieties with ordered dipoles, for controlling intramolecular charge transfer. Donor-acceptor dyads, each containing a single anthranilamide moiety, distinctly rectify both the forward photoinduced electron transfer and the subsequent charge recombination. Changes in the observed charge-transfer kinetics as a function of media polarity were consistent with the anticipated effects of the anthranilamide molecular dipoles on the rectification. The regioselectivity of electron transfer and the molecular dynamics of the dyads further modulated the observed kinetics, particularly for charge recombination. These findings reveal the underlying complexity of dipole-induced effects on electron transfer and demonstrate unexplored paradigms for molecular rectifiers. PMID:25162490

  5. Photoinduced Charge Transfer at Metal Oxide/Oxide Interfaces Prepared with Plasma Enhanced Atomic Layer Deposition

    Science.gov (United States)

    Kaur, Manpuneet

    LiNbO3 and ZnO have shown great potential for photochemical surface reactions and specific photocatalytic processes. However, the efficiency of LiNbO3 is limited due to recombination or back reactions and ZnO exhibits a chemical instability in a liquid cell. In this dissertation, both materials were coated with precise thickness of metal oxide layers to passivate the surfaces and to enhance their photocatalytic efficiency. LiNbO 3 was coated with plasma enhanced atomic layer deposited (PEALD) ZnO and Al2O3, and molecular beam deposited TiO2 and VO2. On the other hand, PEALD ZnO and single crystal ZnO were passivated with PEALD SiO2 and Al2O3. Metal oxide/LiNbO3 heterostructures were immersed in aqueous AgNO3 solutions and illuminated with ultraviolet (UV) light to form Ag nanoparticle patterns. Alternatively, Al2O3 and SiO2/ZnO heterostructures were immersed in K3PO 4 buffer solutions and studied for photoelectrochemical reactions. A fundamental aspect of the heterostructures is the band alignment and band bending, which was deduced from in situ photoemission measurements. This research has provided insight to three aspects of the heterostructures. First, the band alignment at the interface of metal oxides/LiNbO 3, and Al2O3 or SiO2/ZnO were used to explain the possible charge transfer processes and the direction of carrier flow in the heterostructures. Second, the effect of metal oxide coatings on the LiNbO3 with different internal carrier concentrations was related to the surface photochemical reactions. Third is the surface passivation and degradation mechanism of Al2O 3 and SiO2 on ZnO was established. The heterostructures were characterized after stability tests using atomic force microscopy (AFM), scanning electron microscopy (SEM), and cross-section transmission electron microscopy (TEM). The results indicate that limited thicknesses of ZnO or TiO2 on polarity patterned LiNbO3 (PPLN) enhances the Ag+ photoinduced reduction process. ZnO seems more efficient

  6. Position-Dependent Extension of π-Conjugation in D-π-A Dye Sensitizers and the Impact on the Charge-Transfer Properties

    OpenAIRE

    Wielopolski, Mateusz; Kim, Jong-Hyung; Jung, Young-Sam; Yu, Young-Jae; Kay, Kwang-Yol; Thomas W. Holcombe; Zakeeruddin, Shaik M.; Grätzel, Michael; Moser, Jacques-E.

    2013-01-01

    A series of five organic donor-π-bridge-acceptor (D-π-A) sensitizers is investigated within the context of their photoinduced charge-transfer properties. Thereby, the focus is set on the impact of structural modifications of the molecular architecture on the π-systems of the dyes. In particular, two different modes of systematic extension of the sensitizers’ π-systems, namely, (i) within the electron donating site and (ii) within the π-bridge, are investigated by means of steady-state and tim...

  7. Charging system using solar panels and a highly resonant wireless power transfer model for small UAS applications

    Science.gov (United States)

    Hallman, Sydney N.; Huck, Robert C.; Sluss, James J.

    2016-05-01

    The use of a wireless charging system for small, unmanned aircraft system applications is useful for both military and commercial consumers. An efficient way to keep the aircraft's batteries charged without interrupting flight would be highly marketable. While the general concepts behind highly resonant wireless power transfer are discussed in a few publications, the details behind the system designs are not available even in academic journals, especially in relation to avionics. Combining a highly resonant charging system with a solar panel charging system can produce enough power to extend the flight time of a small, unmanned aircraft system without interruption. This paper provides an overview of a few of the wireless-charging technologies currently available and outlines a preliminary design for an aircraft-mounted battery charging system.

  8. A nanoscale study of charge extraction in organic solar cells: the impact of interfacial molecular configurations

    Science.gov (United States)

    Tang, Fu-Ching; Wu, Fu-Chiao; Yen, Chia-Te; Chang, Jay; Chou, Wei-Yang; Gilbert Chang, Shih-Hui; Cheng, Horng-Long

    2014-11-01

    In the optimization of organic solar cells (OSCs), a key problem lies in the maximization of charge carriers from the active layer to the electrodes. Hence, this study focused on the interfacial molecular configurations in efficient OSC charge extraction by theoretical investigations and experiments, including small molecule-based bilayer-heterojunction (sm-BLHJ) and polymer-based bulk-heterojunction (p-BHJ) OSCs. We first examined a well-defined sm-BLHJ model system of OSC composed of p-type pentacene, an n-type perylene derivative, and a nanogroove-structured poly(3,4-ethylenedioxythiophene) (NS-PEDOT) hole extraction layer. The OSC with NS-PEDOT shows a 230% increment in the short circuit current density compared with that of the conventional planar PEDOT layer. Our theoretical calculations indicated that small variations in the microscopic intermolecular interaction among these interfacial configurations could induce significant differences in charge extraction efficiency. Experimentally, different interfacial configurations were generated between the photo-active layer and the nanostructured charge extraction layer with periodic nanogroove structures. In addition to pentacene, poly(3-hexylthiophene), the most commonly used electron-donor material system in p-BHJ OSCs was also explored in terms of its possible use as a photo-active layer. Local conductive atomic force microscopy was used to measure the nanoscale charge extraction efficiency at different locations within the nanogroove, thus highlighting the importance of interfacial molecular configurations in efficient charge extraction. This study enriches understanding regarding the optimization of the photovoltaic properties of several types of OSCs by conducting appropriate interfacial engineering based on organic/polymer molecular orientations. The ultimate power conversion efficiency beyond at least 15% is highly expected when the best state-of-the-art p-BHJ OSCs are combined with present arguments

  9. Molecular-Based Theory for Electron-Transfer Reorganization Energy in Solvent Mixtures.

    Science.gov (United States)

    Zhuang, Bilin; Wang, Zhen-Gang

    2016-07-01

    Using statistical-field techniques, we develop a molecular-based dipolar self-consistent-field theory (DSCFT) for charge solvation in liquid mixtures under equilibrium and nonequilibrium conditions, and apply it to compute the solvent reorganization energy of electron-transfer reactions. In addition to the nonequilibrium orientational polarization, the reorganization energy in liquid mixtures is also determined by the out-of-equilibrium solvent composition around the reacting species due to preferential solvation. Using molecular parameters that are readily available, the DSCFT naturally accounts for the dielectric saturation effect and the spatially varying solvent composition in the vicinity of the reacting species. We identify three general categories of binary solvent mixtures, classified by the relative optical and static dielectric permittivities of the solvent components. Each category of mixture is shown to produce a characteristic local solvent composition profile in the vicinity of the reacting species, which gives rise to the distinctive composition dependence of the reorganization energy that cannot be predicted using the dielectric permittivities of the homogeneous solvent mixtures. PMID:27187110

  10. Spreading of a Unilamellar Liposome on Charged Substrates: A Coarse-Grained Molecular Simulation.

    Science.gov (United States)

    Kong, Xian; Lu, Diannan; Wu, Jianzhong; Liu, Zheng

    2016-04-19

    Supported lipid bilayers (SLBs) are able to accommodate membrane proteins useful for diverse biomimetic applications. Although liposome spreading represents a common procedure for preparation of SLBs, the underlying mechanism is not yet fully understood, particularly from a molecular perspective. The present study examines the effects of the substrate charge on unilamellar liposome spreading on the basis of molecular dynamics simulations for a coarse-grained model of the solvent and lipid molecules. Liposome transformation into a lipid bilayer of different microscopic structures suggests three types of kinetic pathways depending on the substrate charge density, that is, top-receding, parachute, and parachute with wormholes. Each pathway leads to a unique distribution of the lipid molecules and thereby distinctive properties of SLBs. An increase of the substrate charge density results in a magnified asymmetry of the SLBs in terms of the ratio of charged lipids, parallel surface movements, and the distribution of lipid molecules. While the lipid mobility in the proximal layer is strongly correlated with the substrate potential, the dynamics of lipid molecules in the distal monolayer is similar to that of a freestanding lipid bilayer. For liposome spreading on a highly charged surface, wormhole formation promotes lipid exchange between the SLB monolayers thus reduces the asymmetry on the number density of lipid molecules, the lipid order parameter, and the monolayer thickness. The simulation results reveal the important regulatory role of electrostatic interactions on liposome spreading and the properties of SLBs. PMID:27019394

  11. Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions.

    Science.gov (United States)

    Yan, Haijun; Bergren, Adam Johan; McCreery, Richard; Della Rocca, Maria Luisa; Martin, Pascal; Lafarge, Philippe; Lacroix, Jean Christophe

    2013-04-01

    In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d  16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling.

  12. Correlation between the Open-Circuit Voltage and Charge Transfer State Energy in Organic Photovoltaic Cells.

    Science.gov (United States)

    Zou, Yunlong; Holmes, Russell J

    2015-08-26

    In order to further improve the performance of organic photovoltaic cells (OPVs), it is essential to better understand the factors that limit the open-circuit voltage (VOC). Previous work has sought to correlate the value of VOC in donor-acceptor (D-A) OPVs to the interface energy level offset (EDA). In this work, measurements of electroluminescence are used to extract the charge transfer (CT) state energy for multiple small molecule D-A pairings. The CT state as measured from electroluminescence is found to show better correlation to the maximum VOC than EDA. The difference between EDA and the CT state energy is attributed to the Coulombic binding energy of the CT state. This correlation is demonstrated explicitly by inserting an insulating spacer layer between the donor and acceptor materials, reducing the binding energy of the CT state and increasing the measured VOC. These results demonstrate a direct correlation between maximum VOC and CT state energy.

  13. Photoinduced charge transfer and acetone sensitivity of single-walled carbon nanotube-titanium dioxide hybrids.

    Science.gov (United States)

    Ding, Mengning; Sorescu, Dan C; Star, Alexander

    2013-06-19

    The unique physical and chemical properties of single-walled carbon nanotubes (SWNTs) make them ideal building blocks for the construction of hybrid nanostructures. In addition to increasing the material complexity and functionality, SWNTs can probe the interfacial processes in the hybrid system. In this work, SWNT-TiO2 core/shell hybrid nanostructures were found to exhibit unique electrical behavior in response to UV illumination and acetone vapors. By experimental and theoretical studies of UV and acetone sensitivities of different SWNT-TiO2 hybrid systems, we established a fundamental understanding on the interfacial charge transfer between photoexcited TiO2 and SWNTs as well as the mechanism of acetone sensing. We further demonstrated a practical application of photoinduced acetone sensitivity by fabricating a microsized room temperature acetone sensor that showed fast, linear, and reversible detection of acetone vapors with concentrations in few parts per million range. PMID:23734594

  14. Identifying the magnetoconductance responses by the induced charge transfer complex states in pentacene-based diodes

    Science.gov (United States)

    Huang, Wei-Shun; Lee, Tsung-Hsun; Guo, Tzung-Fang; Huang, J. C. A.; Wen, Ten-Chin

    2012-07-01

    We investigate the magnetoconductance (MC) responses in photocurrent, unipolar injection, and bipolar injection regimes in pentacene-based diodes. Both photocurrent and bipolar injection contributed MC responses show large difference in MC line shape, which are attributed to triplet-polaron interaction modulated by the magnetic field dependent singlet fission and the intersystem crossing of the polaron pair, respectively. By blending 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane into pentacene, all the MC responses are suppressed but the MC response at unipolar injection regime is enhanced, which is attributed to the induced charge transfer complex states (CT complex states). This work identify the MC responses between single carrier contributed MC and exciton related MC by the induced CT complex states.

  15. Effects of acid concentration on intramolecular charge transfer reaction of 4-(azetidinyl) benzonitrile in solution

    Indian Academy of Sciences (India)

    Biswajit Guchhait; Tuhin Pradhan; Ranjit Biswas

    2014-01-01

    Effects of acid concentration on excited state intramolecular charge transfer reaction of 4-(azetidinyl) benzonitrile (P4C) in aprotic (acetonitrile and ethyl acetate) and protic (ethanol) solvents have been studied by means of steady state absorption and fluorescence, and time resolved fluorescence spectroscopic techniques. While absorption and fluorescence bands of P4C have been found to be shifted towards higher energy with increasing acid concentration in acetonitrile and ethyl acetate, no significant dependence has been observed in ethanolic solutions. Reaction rate becomes increasingly slower with acid concentration in acetonitrile and ethyl acetate. In contrast, acid in ethanolic solutions does not produce such an effect on reaction rate. Time-dependent density functional theory calculations have been performed to understand the observed spectroscopic results.

  16. Charge transfer state in DBP:C70 organic solar cells

    DEFF Research Database (Denmark)

    Sherafatipour, Golenaz; Benduhn, Johannes; Spoltore, Donato;

    Organic solar cells (OSC) are green solar energy technology, which can be fabricated from organic compounds with cheep techniques and on flexible or transparent substrates such as plastic or glass. OSCs are cost efficient, and lightweight devices that can exhibit high power conversion efficiency...... of the CT states from which the maximum open circuit can be calculated and will set the base for modeling and optimizing the stability of the solar cells. 1. Cao, H. et al. Recent progress in degradation and stabilization of organic solar cells. J. Power Sources 264, 168–183 (2014). 2. Tvingstedt, K. et al....... Electroluminescence from charge transfer states in polymer solar cells. J. Am. Chem. Soc. 131, 11819–11824 (2009)....

  17. Charge-transfer interaction mediated organogels from 18β-glycyrrhetinic acid appended pyrene

    Directory of Open Access Journals (Sweden)

    Jun Hu

    2013-12-01

    Full Text Available We describe herein the two-component charge-transfer (CT interaction induced organogel formation with 18β-glycyrrhetinic acid appended pyrene (GA-pyrene, 3 as the donor, and 2,4,7-trinitrofluorenone (TNF, 4 as the acceptor. The use of TNF (4 as a versatile electron acceptor in the formation of CT gels is demonstrated through the formation of gels in a variety of solvents. Thermal stability, stoichiometry, scanning electron microscopy (SEM, optical micrographs, and circular dichroism (CD are performed on these CT gels to investigate their thermal and assembly properties. UV–vis, fluorescence, mass spectrometric as well as variable-temperature 1H NMR experiments on these gels suggest that the CT interaction is one of the major driving forces for the formation of these organogels.

  18. Mechanisms for charge-transfer processes at electrode/solid-electrolyte interfaces.

    Energy Technology Data Exchange (ETDEWEB)

    Chueh, William; El Gabaly Marquez, Farid; Whaley, Josh A.; McCarty, Kevin F.; McDaniel, Anthony H.; Farrow, Roger L.

    2011-11-01

    This report summarizes the accomplishments of a Laboratory-Directed Research and Development (LDRD) project focused on developing and applying new x-ray spectroscopies to understand and improve electric charge transfer in electrochemical devices. Our approach studies the device materials as they function at elevated temperature and in the presence of sufficient gas to generate meaningful currents through the device. We developed hardware and methods to allow x-ray photoelectron spectroscopy to be applied under these conditions. We then showed that the approach can measure the local electric potentials of the materials, identify the chemical nature of the electrochemical intermediate reaction species and determine the chemical state of the active materials. When performed simultaneous to traditional impedance-based analysis, the approach provides an unprecedented characterization of an operating electrochemical system.

  19. Strong screening in photoemission at interfaces between organic semiconductors and gold: polarization effects versus charge transfer

    Energy Technology Data Exchange (ETDEWEB)

    Kolacyak, Daniel; Peisert, Heiko; Chasse, Thomas [Universitaet Tuebingen, Institut fuer Physikalische Chemie (Germany); Petershans, Andre [Forschungszentrum Karlsruhe, Institut fuer Technische Chemie (Germany)

    2008-07-01

    We studied electronic polarization effects at organic/metal interfaces using combined photoemission spectroscopy (PES) and X-ray excited Auger electron spectroscopy (XAES) as a function of the organic layer thickness. As a model system, sandwich structures of metall-phthalocyanines (e.g consisting of PcMg and PcZn) were deposited on gold. It was found, that the screening of the photohole is remarkably increased for molecules directly at the interface whereas further layers are affected weakly. This may be caused by a fast charge transfer across the interface as a result of the photoionization due to the overlap organic/metal wave functions. Furthermore, differences in the screening were found for buried molecules and molecules on the surface of the organic film ascribed to different polarization energies. The influence of the morphology and orientation was studied by comparing different substrates: polycrystalline gold foil and single crystalline Au(100).

  20. Intramolecular Charge-Transfer Interaction of Donor-Acceptor-Donor Arrays Based on Anthracene Bisimide.

    Science.gov (United States)

    Iwanaga, Tetsuo; Ogawa, Marina; Yamauchi, Tomokazu; Toyota, Shinji

    2016-05-20

    We designed anthracene bisimide (ABI) derivatives having two triphenylamine (TPA) groups as donor units at the 9,10-positions to form a novel π-conjugated donor-acceptor system. These compounds and their analogues with ethynylene linkers were synthesized by Suzuki-Miyaura and Sonogashira coupling reactions, respectively. In UV-vis spectra, the linker-free derivatives showed broad absorption bands arising from intramolecular charge-transfer interactions. Introducing ethynylene linkers resulted in a considerable red shift of the absorption bands. In fluorescence spectra, the ethynylene derivatives showed intense emission bands at 600-650 nm. Their photophysical and electrochemical properties were compared with those of the corresponding mono TPA derivatives on the basis of theoretical calculations and cyclic voltammetry to evaluate the intramolecular electronic interactions between the donor and acceptor units.

  1. The effect of interfacial charge transfer on ferromagnetism in perovskite oxide superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Yang, F. [Univ. of California, Davis, CA (United States). Department of Chemical Engineering and Materials Science; Gu, M. [Univ. of California, Davis, CA (United States). Department of Chemical Engineering and Materials Science; Arenholz, E. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS); Browning, N. D. [Univ. of California, Davis, CA (United States). Department of Molecular and Cellular Biology; Takamura, Y. [Univ. of California, Davis, CA (United States). Department of Chemical Engineering and Materials Science

    2012-01-05

    We investigate the structural, magnetic, and electrical properties of superlattices composed of the ferromagnetic/metal La0.7Sr0.3MnO3 and non-magnetic/metal La0.5Sr0.5TiO3 grown on (001)-oriented SrTiO3 substrates. Using a combination of bulk magnetometry, soft x-ray magnetic spectroscopy, and scanning transmission electron microscopy, we demonstrate that robust ferromagnetic properties can be maintained in this superlattice system where charge transfer at the interfaces is minimized. Thus, ferromagnetism can be controlled effectively through the chemical identity and the thickness of the individual superlattice layers.

  2. When hole extraction determines charge transfer across metal-organic-metal structure

    Science.gov (United States)

    Govor, L. V.; Reiter, G.; Parisi, J.

    2016-03-01

    We examined the charge transfer in metal-organic-metal structure, where the contact resistance of the extracting interface is larger than the resistance of the organic crystalline material and the resistance of the injecting interface. If direct tunneling (low voltage) and Fowler-Nordheim tunnelling (high voltage) across both interfaces take place, part of the injected holes remains located in the organic crystal because of the blocking action of the extracting interface, but not because of traps within the organic crystalline material (which was negligible). If Fowler-Nordheim tunneling across the injecting interface and direct tunneling across the extracting interface take place for high voltages, the latter leads to the deviation of the total current-voltage characteristic from the power law I∼ Vγ with γ>2 to Ohm's law with γ≃1.0 .

  3. Creation of recognition sites for organophosphate esters based on charge transfer and ligand exchange imprinting methods.

    Science.gov (United States)

    Say, Ridvan

    2006-10-01

    This manuscript describes a method for the selective binding behavior of paraoxan and parathion compounds on surface imprinted polymers which were prepared using both charge transfer (CT) (methacryloyl-antipyrine, MAAP) and ligand-exchange (LE) (methacryloyl-antipyrine-gadalonium, MAAP-Gd) monomers. These polymers were prepared in the presence of azobisisobutyronitrile (AIBN) as an initiator and crosslinking EDMA and were imprinted with organophosphate esters. Influence of CT and LE imprinting on the creation of recognition sites toward paraoxan and parathion was determined applying adsorption isotherms. The effect of initial concentration of paraoxan and parathion, adsorption time and imprinting efficiency on adsorption selectivity for MIP-CT and MIP-LE was investigated. Association constant (K(ass)), number of accessible sites (Q(max)), relative selectivity coefficient (k') and binding ability were also evaluated.

  4. Restoration of Conductivity with TTF-TCNQ Charge-Transfer Salts

    Energy Technology Data Exchange (ETDEWEB)

    Odom, Susan A.; Caruso, Mary M.; Finke, Aaron D.; Prokup, Alex M.; Ritchey, Joshua A.; Leonard, Francois; White, Scott R.; Sottos, Nancy R.; Moore, Jeffrey S.

    2010-05-03

    The formation of the conductive TTF-TCNQ (tetrathiafulvalene–tetracyanoquinodimethane) charge-transfer salt via rupture of microencapsulated solutions of its individual components is reported. Solutions of TTF and TCNQ in various solvents are separately incorporated into poly(urea-formaldehyde) core–shell microcapsules. Rupture of a mixture of TTF-containing microcapsules and TCNQ-containing microcapsules results in the formation of the crystalline salt, as verified by FTIR spectroscopy and powder X-ray diffraction. Preliminary measurements demonstrate the partial restoration of conductivity of severed gold electrodes in the presence of TTF-TCNQ derived in situ. This is the first microcapsule system for the restoration of conductivity in mechanically damaged electronic devices in which the repairing agent is not conductive until its release.

  5. Spectroscopic studies of charge transfer complexes between colchicine and some π acceptors

    Science.gov (United States)

    Arslan, Mustafa; Duymus, Hulya

    2007-07-01

    Charge transfer complexes between colchicine as donor and π acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ), p-chloranil ( p-CHL) have been studied spectrophotometrically in dichloromethane at 21 °C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515 nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi-Hildebrand and van't Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used.

  6. Synthesis, characterization and biological studies of a charge transfer complex: 2-Aminopyridinium-4-methylbenzenesulfonate

    Science.gov (United States)

    Vadivelan, Ganesan; Saravanabhavan, Munusamy; Murugesan, Venkatesan; Sekar, Marimuthu

    2015-06-01

    A single crystal charge transfer (CT) complex, 2-aminopyridinium-4-methylbenzenesulfonate (APTS) was synthesized and recrystallized by slow solvent evaporation solution growth method at room temperature. The complex has been characterized with the elemental analysis, UV-visible, infrared (IR), 1H and 13C nuclear magnetic resonance (NMR) spectra. Thermogravimetric (TG) and differential thermal analysis (DTA) were reported the thermal behaviour of the complex. Single crystal XRD studies showed that the orthorhombic nature of the crystal with space group Pbca. The biological activities of CT complex, such as DNA binding and antioxidant activity has been carried out. The results indicated that the compound could interact with DNA through intercalation and show significant capacity of scavenging with 2,2-diphenyl-2-picryl-hydrazyl (DPPH).

  7. Atomic data for neutron-capture elements III. Charge transfer rate coefficients for low-charge ions of Ge, Se, Br, Kr, Rb, and Xe

    CERN Document Server

    Sterling, N C

    2011-01-01

    We present total and final-state resolved charge transfer (CT) rate coefficients for low-charge Ge, Se, Br, Kr, Rb, and Xe ions reacting with neutral hydrogen over the temperature range 10^2--10^6 K. Each of these elements has been detected in ionized astrophysical nebulae, particularly planetary nebulae. CT rate coefficients are a key ingredient for the ionization equilibrium solutions needed to determine total elemental abundances from those of the observed ions. A multi-channel Landau Zener approach was used to compute rate coefficients for projectile ions with charges q=2-5, and for singly-charged ions the Demkov approximation was utilized. Our results for five-times ionized species are lower limits, due to the incompleteness of level energies in the NIST database. In addition, we computed rate coefficients for charge transfer ionization reactions between the neutral species of the above six elements and ionized hydrogen. The resulting total and state-resolved CT rate coefficients are tabulated and availa...

  8. Molecular level energy and electron transfer processes at nanocrystalline titanium dioxide interfaces

    Science.gov (United States)

    Farzad, Fereshteh

    This thesis describes photo-induced molecular electron and energy transfer processes occurring at nanocrystalline semiconductor interfaces. The Introductory Chapter provides background and describes how these materials may be useful for solar energy conversion. In Chapter 2, results describing excitation of Ru(deeb)(bpy)2 2+, bis(2,2'-bipyridine)(2,2'-bipyridine-4,4 '-diethylester)ruthenium(II) hexafluorophosphate, bound to nanocrystalline TiO2 thin films, immersed in an acetonitrile bath are presented. The data indicates that light excitation forms predominately long-lived metal-to-ligand charge-transfer, MLCT, excited states under these conditions. Modeling of the data as a function of irradiance has been accomplished assuming parallel unimolecular and bimolecular excited state deactivation processes. The quantum yield for excited state formation depends on the excitation irradiance, consistent with triplet-triplet annihilation processes that occur with k > 1 x 108 s-1. Chapter 3 extends the work described in Chapter 2 to LiClO4 acetonitrile solutions. Li+ addition results in a red shift in the MLCT absorption and photoluminescence, PL, and a concentration dependent quenching of the PL intensity on TiO2. The Li+ induced spectroscopic changes were found to be reversible by varying the electrolyte composition. A second-order kinetic model quantified charge recombination transients. A model is proposed wherein Li+ ion adsorption stabilizes TiO2 acceptor states resulting in energetically more favorable interfacial electron transfer. The photophysical and photoelectrochemical properties of porous nanocrystalline anatase TiO2 electrodes modified with Ru(deeb)(bpy)2 2+, Os(deeb)(bpy)22+, and mixtures of both are described in Chapters 4 and 5. In regenerative solar cells with 0.5 M LiI/0.05 M I2 acetonitrile electrolyte, both compounds efficiently inject electrons into TiO2 producing monochromatic incident photon-to-current efficiencies (IPCE), IPCE (460 nm) = 0.70 + 0

  9. Resonant charge transfer of hydrogen Rydberg atoms incident at a Cu(100) projected band-gap surface

    CERN Document Server

    Gibbard, J A; Kohlhoff, M; Rennick, C J; So, E; Ford, M; Softley, T P

    2015-01-01

    The charge transfer (ionization) of hydrogen Rydberg atoms (principal quantum number $n=25-34$) incident at a Cu(100) surface is investigated. Unlike fully metallic surfaces, where the Rydberg electron energy is degenerate with the conduction band of the metal, the Cu(100) surface has a projected bandgap at these energies, and only discrete image states are available through which charge transfer can take place. Resonant enhancement of charge transfer is observed at hydrogen principal quantum numbers for which the Rydberg energy matches the energy of one of the image states. The integrated surface ionization signals show clear periodicity as the energies of states with increasing $n$ come in and out of resonance with the image states. The velocity dependence of the surface ionization dynamics is also investigated. Decreased velocity of the incident H atom leads to a greater mean distance of ionization and a lower field required to extract the ion. The surface-ionization profiles (signal versus applied field) ...

  10. New Developments in Charge Transfer Multiplet Calculations: Projection Operations, Mixed-Spin States and pi-Bonding

    Energy Technology Data Exchange (ETDEWEB)

    de Groot, F.M.F.; /Utrecht U.; Hocking, R.K.; /Stanford U., Chem. Dept.; Piamonteze, C.; /LBL, Berkeley; Hedman, B.; Hodgson, K.O.; Solomon, E.I.; /Stanford U., Chem. Dept.

    2007-01-02

    This paper presents a number of new additions to the charge transfer multiplet calculations as used in the calculation of L edge X-ray absorption spectra of 3d and 4d transition metal systems, both oxides and coordination compounds. The focus of the paper is on the consequences of the optimized spectral simulations for the ground state, where we make use of a recently developed projection technique. This method is also used to develop the concept of a mixed-spin ground state, i.e. a state that is a mixture of a high-spin and low-spin state due to spin-orbit coupling combined with strong covalency. The charge transfer mechanism to describe {pi}-bonding uses the mixing of the metal-to-ligand charge transfer (MLCT) channel in addition to the normal CT channel and allows for the accurate simulation of {pi}-bonding systems, for example cyanides.

  11. Atomistic and Molecular Effects in Electric Double Layers at High Surface Charges.

    Science.gov (United States)

    Lee, Jonathan W; Mani, Ali; Templeton, Jeremy A

    2015-07-14

    The Poisson-Boltzmann theory for electrolytes near a charged surface is known to be invalid due to unaccounted physics associated with high ion concentration regimes. To investigate this regime, fluids density functional theory (f-DFT) and molecular dynamics (MD) simulations were used to determine electric surface potential as a function of surface charge. Based on these detailed computations, for electrolytes with nonpolar solvent, the surface potential is shown to depend quadratically on the surface charge in the high charge limit. We demonstrate that modified Poisson-Boltzmann theories can model this limit if they are augmented with atomic packing densities provided by MD. However, when the solvent is a highly polar molecule, water in this case, an intermediate regime is identified in which a constant capacitance is realized. Simulation results demonstrate the mechanism underlying this regime, and for the salt water system studied here, it persists throughout the range of physically realistic surface charge densities so the potential's quadratic surface charge dependence is not obtained. PMID:26079793

  12. Self-Consistent Determination of Atomic Charges of Ionic Liquid through a Combination of Molecular Dynamics Simulation and Density Functional Theory.

    Science.gov (United States)

    Ishizuka, Ryosuke; Matubayasi, Nobuyuki

    2016-02-01

    A self-consistent scheme is developed to determine the atomic partial charges of ionic liquid. Molecular dynamics (MD) simulation was conducted to sample a set of ion configurations, and these configurations were subject to density functional theory (DFT) calculations to determine the partial charges. The charges were then averaged and used as inputs for the subsequent MD simulation, and MD and DFT calculations were repeated until the MD results are not altered any more. We applied this scheme to 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide ([C1mim][NTf2]) and investigated its structure and dynamics as a function of temperature. At convergence, the average ionic charges were ±0.84 e at 350 K due to charge transfer among ions, where e is the elementary charge, while the reduced ionic charges do not affect strongly the density of [C1mim][NTf2] and radial distribution function. Instead, major effects are found on the energetics and dynamics, with improvements of the overestimated heat of vaporization and the too slow motions of ions observed in MD simulations using commonly used force fields.

  13. The influence of the vinyl terminal group on the poly(para-phenylenevinylene) charge transfer integrals.

    Science.gov (United States)

    Ottonelli, Massimo; Duce, Daniele; Thea, Sergio; Dellepiane, Giovanna

    2013-07-01

    The charge transport properties of organic semiconductors are one of the foremost limiting factors in technological applications of these materials, which are becoming important competitors with respect to the inorganic semiconductors. In fact, conjugated organic molecules are used at present as active materials in different types of devices. For this reason, the theoretical study of the electron and hole mobility, carried out in order to give hints for the design of new molecules or for the optimization of their supramolecular organization, is a task of great interest. Here, we present the results of a quantum chemical study, in the framework of the Marcus and density functional theories, on the effects of terminal groups (when they directly interact with the pi-conjugated system of the organic semiconductors) on the charge carriers mobility of organic semiconductors. In particular, using a representative oligomer of poly(para-phenylenevinylene) as a model system, we have found that strong effects on the predicted values of the intramolecular transfer integrals as well as on their dependence on the supramolecular organizations occur, when the vinyl moiety (as ending group) is taken into account.

  14. Defect and charge transfer studies on hybrid solar cells with silicon nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Niesar, Sabrina; Fabian, Wolfgang; Erhard, Nadine; Stegner, Andre; Brandt, Martin; Stutzmann, Martin [Walter Schottky Institut, Technische Universitaet Muenchen, 85748 Garching (Germany); Herrmann, Daniel; Riedle, Eberhard [Ludwig-Maximilians-Universitaet Muenchen, 80538 Muenchen (Germany); Pereira, Rui [University of Aveiro, 3810-193 Aveiro (Portugal); Wiggers, Hartmut [Institut fuer Verbrennung und Gasdynamik, Universitaet Duisburg-Essen, 47057 Duisburg (Germany)

    2011-07-01

    Hybrid inorganic nanoparticle-polymer solar cells are a promising alternative to purely organic devices due to the broad spectral range of absorption of the inorganic material. In this work, a combination of P3HT and silicon nanocrystals (Si-ncs), which are synthesized in a microwave plasma reactor, is studied. In particular, we focus on methods to decrease the concentration of silicon dangling bond defects which negatively affect the electronic properties of the hybrid solar cells. HF etching in combination with vacuum annealing at 200 C leads to the lowest defect densities. Conductivity measurements in vacuum show that the defect reduction results in improved electrical properties of Si-nc thin films. Electron paramagnetic resonance and Fourier transform infrared spectroscopy are used to study the stability of the different post-growth treatments. The charge transfer across the organic-inorganic interface is investigated via broadband-femtosecond optical pump-probe spectroscopy. We find that the addition of the Si-ncs leads to an increase of the charge separation as compared to pure P3HT.

  15. Charge Transfer in Light Effect Under Visible Radiation in an Ozoniser Discharge

    Directory of Open Access Journals (Sweden)

    S.V. Salvi

    2006-11-01

    Full Text Available Two fresh discharge vessels (1 and 2 of Siemen’s ozoniser type having the same height butdifferent surface-to-volume ratios have been fabricated by enclosing argon at 10 mm mercury.By immersing these in electrolytic solution and by subjecting these to a definite high 50 Hz acvoltage, the discharge count rates in dark (Cf D and under light (Cf L have been determinedusing a scaler held at different bias-voltages. The plot of the ratio (C1f / C2f D and (C1f / C2f Lof discharge counts versus pulse height (bias-voltage shows that this ratio for a constantpotential of 3.5 kV (rms is initially large in value, then rapidly decreases to a minimum. It is alsoobserved that more is the surface-to-volume ratio, more is the magnitude of net effect of irradiation.Further, the pulse height analysis shows that the charge carried by the pulses to the electrodes(charge transfer decreases under illumination. A possible mechanism to explain the net effectof the discharge current ratio in the light of pulse height measurements is discussed.

  16. Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations

    CERN Document Server

    Goudfrooij, P; Maíz-Appelániz, J; Kimble, R A; Goudfrooij, Paul; Bohlin, Ralph C.; Maiz-Apellaniz, Jesus; Kimble, Randy A.

    2006-01-01

    A variety of on-orbit imaging and spectroscopic observations are used to characterize the Charge Transfer Efficiency (CTE) of the Charge-Coupled Device (CCD) of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. A set of formulae is presented to correct observations of point sources for CTE-related loss of signal. For data taken in imaging mode, the CTE loss is parametrized in terms of the location of the source on the CCD, the source signal level within the measurement aperture, the background level, and the time of observation. For spectroscopic data, it is found that one additional parameter is needed to provide an adequate calibration of the CTE loss, namely the signal in the point spread function located between the signal extraction box and the read-out amplifier. The effect of the latter parameter is significant for spectra taken using the G750L or G750M gratings of STIS. The algorithms presented here correct flux calibration inaccuracies due to CTE losses as large as 30...

  17. Photophysical study of a charge transfer oxazole dye in micelles: Role of surfactant headgroups

    Energy Technology Data Exchange (ETDEWEB)

    Maiti, Jyotirmay [Department of Chemistry, West Bengal State University, Barasat, Kolkata 700126 (India); Sarkar, Yeasmin; Parui, Partha Pratim [Department of Chemistry, Jadavpur University, Kolkata 700032 (India); Chakraborty, Sandipan [Department of Microbiology, University of Calcutta, Kolkata 700019 (India); Biswas, Suman [Department of Chemistry, West Bengal State University, Barasat, Kolkata 700126 (India); Das, Ranjan, E-mail: ranjan.das68@gmail.com [Department of Chemistry, West Bengal State University, Barasat, Kolkata 700126 (India)

    2015-07-15

    Photophysics of 5-(4′′-dimethylaminophenyl)-2-(4′-sulfophenyl)oxazole, sodium salt (DMO) which undergoes intramolecular charge transfer in the excited state was studied in micelles. In the cationic and the nonionic micelles, significantly higher fluorescence quantum yield is observed in comparison to the anionic micelles, due to much lower accessibility of DMO to the water molecules in the former micelles than the latter. Time-resolved fluorescence decays were characterized by a fast (τ{sub 1}) and a slow (τ{sub 2}) component of decay in all the micelles. The fast decay component (τ{sub 1}) increases significantly in going from the anionic micelles to the cationic micelles, because of the poorly hydrated headgroup region of the latter micelles compared to the former. Furthermore, much higher value of the slow component of decay (τ{sub 2}) is observed for the cationic and the neutral micelles than the anionic micelles. This is attributed to the increased penetration of water molecules into the micellar core of the anionic micelles compared to the cationic and the neutral micelles. - Highlights: • Photophysics of the fluorophore are remarkably different in the cationic and the anionic micelles. • Differential hydration of the surfactant headgroups gives rise to significantly different fluorescence quantum yield and lifetime in oppositely charged micelles. • Electrostatic interactions fine tune location of the fluorophore in the micelle–water interface of ionic micelles.

  18. Transition Metal Substitution Effects on Metal-to-Polyoxometalate Charge Transfer.

    Science.gov (United States)

    Glass, Elliot N; Fielden, John; Huang, Zhuangqun; Xiang, Xu; Musaev, Djamaladdin G; Lian, Tianquan; Hill, Craig L

    2016-05-01

    A series of hetero-bimetallic transition metal-substituted polyoxometalates (TMSPs) were synthesized based on the Co(II)-centered ligand [Co(II)W11O39](10-). The eight complex series, [Co(II)(M(x)OHy)W11O39]((12-x-y)-) (M(x)OHy = V(IV)O, Cr(III)(OH2), Mn(II)(OH2), Fe(III)(OH2), Co(II)(OH2), Ni(II)(OH2), Cu(II)(OH2), Zn(II)(OH2)), of which six are reported for the first time, was synthesized starting from [Co(III)W11O39](9-) and studied using spectroscopic, electrochemical, and computational techniques to evaluate the influence of substituted transition metals on the photodynamics of the metal-to-polyoxometalate charge transfer (MPCT) transition. The bimetallic complexes all show higher visible light absorption than the plenary [Co(II)W12O40](6-) and demonstrate the same MPCT transition as the plenary complex, but they have shorter excited-state lifetimes (sub-300 ps in aqueous media). The decreased lifetimes are rationalized on the basis of nonradiative relaxation due to coordinating aqua ligands, increased interaction with cations due to increased negative charge, and the energy gap law, with the strongest single factor appearing to be the charge on the anion. The most promising results are from the Cr- and Fe-substituted systems, which retain excited-state lifetimes at least 50% of that of [Co(II)W12O40](6-) while more than tripling the absorbance at 400 nm. PMID:27082443

  19. Large impact of reorganization energy on photovoltaic conversion due to interfacial charge-transfer transitions.

    Science.gov (United States)

    Fujisawa, Jun-ichi

    2015-05-14

    Interfacial charge-transfer (ICT) transitions are expected to be a novel charge-separation mechanism for efficient photovoltaic conversion featuring one-step charge separation without energy loss. Photovoltaic conversion due to ICT transitions has been investigated using several TiO2-organic hybrid materials that show organic-to-inorganic ICT transitions in the visible region. In applications of ICT transitions to photovoltaic conversion, there is a significant problem that rapid carrier recombination is caused by organic-inorganic electronic coupling that is necessary for the ICT transitions. In order to solve this problem, in this work, I have theoretically studied light-to-current conversions due to the ICT transitions on the basis of the Marcus theory with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. An apparent correlation between the reported incident photon-to-current conversion efficiencies (IPCE) and calculated reorganization energies was clearly found, in which the IPCE increases with decreasing the reorganization energy consistent with the Marcus theory in the inverted region. This activation-energy dependence was systematically explained by the equation formulated by the Marcus theory based on a simple excited-state kinetic scheme. This result indicates that the reduction of the reorganization energy can suppress the carrier recombination and enhance the IPCE. The reorganization energy is predominantly governed by the structural change in the chemical-adsorption moiety between the ground and ICT excited states. This work provides crucial knowledge for efficient photovoltaic conversion due to ICT transitions. PMID:25892453

  20. Charge transport and transfer processes in CuInS2 nanocrystal-based hybrid solar cells

    OpenAIRE

    Miranti, Rany

    2015-01-01

    Colloidally synthesized CIS NCs are investigated in this work for their charge transport and charge transfer properties. By post-synthesis removal and replacement of the different types of ligands surrounding the CIS NCs, these properties can found be enhanced - especially by a combination of successive solution-phase and post-deposition ligand exchanges, which is derived from results obtained by measurements in combination with different polymers as active layer blends for BHJ solar cells. A...

  1. A how-to approach for a 3D simulation of charge transfer characteristics in a gas electron multiplier (GEM)

    CERN Document Server

    Sharma, A

    1999-01-01

    In this paper a detailed description of how to simulate charge transfer processes in a gaseous device is presented, taking the gas electron multiplier (GEM) as an example. A 3-dimensional simulation of the electric field and avalanche is performed. Results on charge transport are compared to experiment and agree within experimental errors; the avalanche mechanism and positive ion feedback are studied. The procedures used in the simulation are described in detail, and program scripts are appended. (15 refs).

  2. Interfacial charge-transfer transitions in a TiO2-benzenedithiol complex with Ti-S-C linkages.

    Science.gov (United States)

    Fujisawa, Jun-ichi; Muroga, Ryuki; Hanaya, Minoru

    2015-11-28

    Interfacial charge-transfer (ICT) transitions between organic materials and inorganic semiconductors are a new mechanism for light absorption at organic-semiconductor interfaces. ICT transitions cause one-step interfacial charge separation without loss of energy. This feature is potentially useful to realize efficient organic-inorganic hybrid solar cells. ICT transitions have been examined by employing titanium dioxide (TiO2) nanoparticles chemisorbed with π-conjugated molecules via Ti-O-C linkages. Here, we report ICT transitions in a TiO2 and 1,2-benzenedithiol (BDT) complex with Ti-S-C linkages. BDT adsorbs on TiO2 by the bridging bidentate coordination of the sulfur atoms to surface titanium atoms. The TiO2-BDT complex shows ICT transitions from the BDT moiety to the conduction band of TiO2 in the visible region. The ICT transitions occur by orbital overlaps between the d orbitals of the surface titanium atoms and the π orbitals of the benzene ring. Our density-functional-theory (DFT) analysis reveals that the 3p valence orbitals of the sulfur bridging atoms contribute to more than 50% of the highest occupied molecular orbital (HOMO) and the 3d-3p(sulfur)-π interaction via the Ti-S-C linkage enhances the electronic mixing between the titanium atoms and the benzene moiety as compared to the 3d-2p(oxygen)-πvia the Ti-O-C linkage. This result indicates the important role of the heavier-atom linkers for strong organic-inorganic electronic couplings. PMID:26486297

  3. Environment Dependent Charge Potential for Water

    OpenAIRE

    Muralidharan, Krishna; Valone, Steven M.; Atlas, Susan R.

    2007-01-01

    We present a new interatomic potential for water captured in a charge-transfer embedded atom method (EAM) framework. The potential accounts for explicit, dynamical charge transfer in atoms as a function of the local chemical environment. As an initial test of the charge-transfer EAM approach for a molecular system, we have constructed a relatively simple version of the potential and examined its ability to model the energetics of small water clusters. The excellent agreement between our resul...

  4. Evaluation of intramolecular charge transfer state of 4-, -dimethylamino cinnamaldehyde using time-dependent density functional theory

    Indian Academy of Sciences (India)

    Surajit Ghosh; K V S Girish; Subhadip Ghosh

    2013-07-01

    Intramolecular charge transfer of 4-,-dimethylamino cinnamaldehyde (DMACA) in vacuum and in five different aprotic solvents has been studied by using time-dependent density functional theory (TDDFT). Polarizable continuum model (PCM) was employed to consider solvent-solute interactions. The potential energy curves were constructed at different torsional angle of ,-dimethylamino moiety with respect to the adjacent phenyl ring. A large bathochromic shift in our calculated emission and absorption energies for polar solvents is a clear reminiscent of charge transfer nature of the excited state. Finally, the reported results are in agreement with experimental findings.

  5. Scanning electrochemical microscopy. 38. Application of SECM to the study of charge transfer through bilayer lipid membranes.

    Science.gov (United States)

    Tsionsky, M; Zhou, J; Amemiya, S; Fan, F R; Bard, A J; Dryfe, R A

    1999-10-01

    The use of the scanning electrochemical microscope (SECM) to probe the kinetics of charge-transfer processes at bilayer lipid membranes (BLM) is presented. Analysis of the SECM tip response demonstrates that an unmodified BLM behaves as an insulator, whereas a BLM doped with iodine shows some positive feedback. The SECM technique thus allows one to probe processes at a BLM and determine the kinetics of the charge-transfer process. The SECM can also be used to determine the shape of the BLM. PMID:10660439

  6. The Effect of Interfacial Geometry on Charge-Transfer States in the Phthalocyanine/Fullerene Organic Photovoltaic System.

    Science.gov (United States)

    Lee, Myeong H; Geva, Eitan; Dunietz, Barry D

    2016-05-19

    The dependence of charge-transfer states on interfacial geometry at the phthalocyanine/fullerene organic photovoltaic system is investigated. The effect of deviations from the equilibrium geometry of the donor-donor-acceptor trimer on the energies of and electronic coupling between different types of interfacial electronic excited states is calculated from first-principles. Deviations from the equilibrium geometry are found to destabilize the donor-to-donor charge transfer states and to weaken their coupling to the photoexcited donor-localized states, thereby reducing their ability to serve as charge traps. At the same time, we find that the energies of donor-to-acceptor charge transfer states and their coupling to the donor-localized photoexcited states are either less sensitive to the interfacial geometry or become more favorable due to modifications relative to the equilibrium geometry, thereby enhancing their ability to serve as gateway states for charge separation. Through these findings, we eludicate how interfacial geometry modifications can play a key role in achieving charge separation in this widely studied organic photovoltaic system.

  7. The Effect of Interfacial Geometry on Charge-Transfer States in the Phthalocyanine/Fullerene Organic Photovoltaic System.

    Science.gov (United States)

    Lee, Myeong H; Geva, Eitan; Dunietz, Barry D

    2016-05-19

    The dependence of charge-transfer states on interfacial geometry at the phthalocyanine/fullerene organic photovoltaic system is investigated. The effect of deviations from the equilibrium geometry of the donor-donor-acceptor trimer on the energies of and electronic coupling between different types of interfacial electronic excited states is calculated from first-principles. Deviations from the equilibrium geometry are found to destabilize the donor-to-donor charge transfer states and to weaken their coupling to the photoexcited donor-localized states, thereby reducing their ability to serve as charge traps. At the same time, we find that the energies of donor-to-acceptor charge transfer states and their coupling to the donor-localized photoexcited states are either less sensitive to the interfacial geometry or become more favorable due to modifications relative to the equilibrium geometry, thereby enhancing their ability to serve as gateway states for charge separation. Through these findings, we eludicate how interfacial geometry modifications can play a key role in achieving charge separation in this widely studied organic photovoltaic system. PMID:26237431

  8. Hydrogen-transfer and charge-transfer in photochemical and radiation induced reactions. Progress report, November 1, 1975--October 31, 1976

    International Nuclear Information System (INIS)

    The relative importance of light absorption, quenching of triplet, and hydrogen transfer repair has been examined in retardation by mercaptans of photoreduction of aromatic ketones by alcohols. In the reduction of benzophenone by 2-propanol, retardation is efficient and, after correction for the first two effects, is due entirely to hydrogen-transfer repair, as indicated by deuterium labeling. In reduction of acetophenone by α-methylbenzyl alcohol, repair by hydrogen transfer is also operative. In reduction of benzophenone by benzhydrol, retardation is less efficient and is due to quenching, as the ketyl radical does not abstract hydrogen from mercaptan rapidly in competition with coupling. Deuterium isotope effects are discussed in terms of competitive reactions. Photoreduction of benzophenone by 2-butylamine and by triethylamine is retarded by aromatic mercaptans and disulfides. Of the retardation not due to light absorption and triplet quenching by the sulfur compounds, half is due to hydrogen-transfer repair, as indicated by racemization and deuterium labeling. The remainder is attributed to quenching by the sulfur compound of the charge-transfer-complex intermediate. Photoreduction by primary and secondary amines, but not by tertiary amines, is accelerated by aliphatic mercaptans. The acceleration is attributed to catalysis of hydrogen transfer by the mercaptan in the charge-transfer complex. The effect is large in hydrocarbon solvent, less in polar organic solvents and absent in water

  9. Correlation between charge transfer and exchange coupling in carbon-based magnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Anh Tuan, E-mail: tuanna@hus.edu.vn [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Science and Technology Department, Vietnam National University, Hanoi, 144 Xuan Thuy, Cau Giay, Hanoi (Viet Nam); Japan Advanced Institute of Science and Technology, 1-1, Asahidai, Nomi, Ishikawa, 923-1292 Japan (Japan); Nguyen, Van Thanh; Nguyen, Huy Sinh [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Pham, Thi Tuan Anh [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Faculty of Science, College of Hai Duong, Nguyen Thi Due, Hai Duong (Viet Nam); Do, Viet Thang [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Ha Noi (Viet Nam); Faculty of Science, Haiphong University, 171 Phan Dang Luu, Kien An, Hai Phong (Viet Nam); Dam, Hieu Chi [Japan Advanced Institute of Science and Technology, 1-1, Asahidai, Nomi, Ishikawa, 923-1292 Japan (Japan)

    2015-10-15

    Several forms of carbon-based magnetic materials, i.e. single radicals, radical dimers, and alternating stacks of radicals and diamagnetic molecules, have been investigated using density-functional theory with dispersion correction and full geometry optimization. Our calculated results demonstrate that the C{sub 31}H{sub 15} (R{sub 4}) radical has a spin of ½. However, in its [R{sub 4}]{sub 2} dimer structure, the net spin becomes zero due to antiferromagnetic spin-exchange between radicals. To avoid antiferromagnetic spin-exchange of identical face-to-face radicals, eight alternating stacks, R{sub 4}/D{sub 2m}/R{sub 4} (with m = 3-10), were designed. Our calculated results show that charge transfer (Δn) between R{sub 4} radicals and the diamagnetic molecule D{sub 2m} occurs with a mechanism of spin exchange (J) in stacks. The more electrons that transfer from R{sub 4} to D{sub 2m}, the stronger the ferromagnetic spin-exchange in stacks. In addition, our calculated results show that Δn can be tailored by adjusting the electron affinity (E{sub a}) of D{sub 2m}. The correlation between Δn, E{sub a}, m, and J is discussed. These results give some hints for the design of new ferromagnetic carbon-based materials.

  10. Hydrogenase/ferredoxin charge-transfer complexes: effect of hydrogenase mutations on the complex association.

    Science.gov (United States)

    Long, Hai; King, Paul W; Ghirardi, Maria L; Kim, Kwiseon

    2009-04-23

    The [FeFe]-hydrogenases in the green alga Chlamydomonas reinhardtii utilize photogenerated electrons to reduce protons into hydrogen gas. The electrons are supplied from photosystem I and transferred to the [FeFe]-hydrogenase through specific hydrogenase-ferredoxin association. To understand how structural and kinetic factors control the association better, we used Brownian dynamics simulation methods to simulate the charge-transfer complex formation between both native and in silico mutants of the [FeFe]-hydrogenase HYDA2 and the [2Fe2S]-ferredoxin FDX1 from C. reinhardtii . The changes in binding free energy between different HYDA2 mutants and the native FDX1 were calculated by the free-energy perturbation method. Within the limits of our current models, we found that two HYDA2 mutations, T99K(H) and D102K(H), led to lower binding free energies and higher association rate with FDX1 and are thus promising targets for improving hydrogen production rates in engineered organisms. PMID:19317477

  11. Correlation between charge transfer and exchange coupling in carbon-based magnetic materials

    Directory of Open Access Journals (Sweden)

    Anh Tuan Nguyen

    2015-10-01

    Full Text Available Several forms of carbon-based magnetic materials, i.e. single radicals, radical dimers, and alternating stacks of radicals and diamagnetic molecules, have been investigated using density-functional theory with dispersion correction and full geometry optimization. Our calculated results demonstrate that the C31H15 (R4 radical has a spin of ½. However, in its [R4]2 dimer structure, the net spin becomes zero due to antiferromagnetic spin-exchange between radicals. To avoid antiferromagnetic spin-exchange of identical face-to-face radicals, eight alternating stacks, R4/D2m/R4 (with m = 3-10, were designed. Our calculated results show that charge transfer (Δn between R4 radicals and the diamagnetic molecule D2m occurs with a mechanism of spin exchange (J in stacks. The more electrons that transfer from R4 to D2m, the stronger the ferromagnetic spin-exchange in stacks. In addition, our calculated results show that Δn can be tailored by adjusting the electron affinity (Ea of D2m. The correlation between Δn, Ea, m, and J is discussed. These results give some hints for the design of new ferromagnetic carbon-based materials.

  12. Femtosecond Heterodyne Transient Grating Spectroscopic Studies of Intramolecular Charge Transfer Character of Peridinin and Peridinin Analogs

    Science.gov (United States)

    Bishop, Michael; Khosravi, Soroush; Obaid, Razib; Whitelock, Hope; Carroll, Ann Marie; Lafountain, Amy; Frank, Harry; Beck, Warren; Gibson, George; Berrah, Nora

    2016-05-01

    The peridinin chlorophyll-a protein is a light harvesting complex found in several species of dinoflagellates. Peridinin absorbs strongly in the mid-visible spectral region and, despite the lack of a strong permanent dipole moment in its lowest energy excited state, is able to transfer excitation energy quickly and efficiently to chlorophyll-a. It is believed that the high efficiency arises from the development of intramolecular charge-transfer (ICT) character upon photoexcitation. Recently, heterodyne transient grating spectroscopy has been used to study the ultrafast (ICT character in the case of peridinin, but up to now the work has not provided appropriate control experiments. The present experiments examine peridinin and two peridinin analogs, S1-peridinin and S2-peridinin. S1-peridinin is reported to have greatly diminished ICT character, and S2-peridinin is reported to have little-or-no ICT character. Heterodyne transient grating data will be presented and provide a more unambiguous characterization spectral and kinetic properties associated with the peridinin ICT state. Funded by the DoE-BES, Grant No. DE-SC0012376.

  13. The dynamics of energy and charge transfer in lead sulfide quantum dot solids

    Energy Technology Data Exchange (ETDEWEB)

    Lingley, Zachary [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States); Lu, Siyuan [Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States); Madhukar, Anupam, E-mail: madhukar@usc.edu [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States); Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States)

    2014-02-28

    We report on a systematic time-resolved photoluminescence study of the competing energy and charge transfer rates in PbS QDs of differing sizes in the same QD solid as a function of both temperature and ligand-controlled different inter-QD average separations. This complements previous studies that typically varied only one parameter and reveals new aspects while also confirming some known features. For the smallest PbS QDs, the dominant decay process is nonradiative resonant energy transfer (NRET) to adjacent larger dots for all separations but at a rate that increases with decreasing temperature. For the largest QDs, NRET being forbidden, the decay is found to be exponential in the inter-QD separation consistent with carrier tunneling but, for each fixed tunneling distance, exhibiting a thermally activated tunneling carrier population with the activation energy dependent upon the ligand length controlling the inter-QD separation. A consistent understanding of this expanded and rich decay rate behavior of both large and small QDs, we show, can be obtained by accounting for the ligand length dependent (a) dielectric environment of the QD solid modeled using an effective medium description, (b) the energy cost of dissociating the exciton into electron and hole in neighboring QDs, and (c) the potential participation of midgap states. Implications of the findings for NRET based photovoltaics are discussed.

  14. Thickness dependent charge transfer states and dark carriers density in vacuum deposited small molecule organic photocell

    Science.gov (United States)

    Shekhar, Himanshu; Tzabari, Lior; Solomeshch, Olga; Tessler, Nir

    2016-10-01

    We have investigated the influence of the active layer thickness on the balance of the internal mechanisms affecting the efficiency of copper phthalocyanine - fullerene (C60) based vacuum deposited bulk heterojunction organic photocell. We fabricated a range of devices for which we varied the thickness of the active layer from 40 to 120 nm and assessed their performance using optical and electrical characterization techniques. As reported previously for phthalocyanine:C60, the performance of the device is highly dependent on the active layer thickness and of all the thicknesses we tried, the 40 nm thin active layer device showed the best solar cell characteristic parameters. Using the transfer matrix based optical model, which includes interference effects, we calculated the optical power absorbed in the active layers for the entire absorption band, and we found that this cannot explain the trend with thickness. Measurement of the cell quantum efficiency as a function of light intensity showed that the relative weight of the device internal processes changes when going from 40 nm to 120 nm thick active layer. Electrical modeling of the device, which takes different internal processes into account, allowed to quantify the changes in the processes affecting the generation - recombination balance. Sub gap external quantum efficiency and morphological analysis of the surface of the films agree with the model's result. We found that as the thickness grows the density of charge transfer states and of dark carriers goes up and the uniformity in the vertical direction is reduced.

  15. 2013 MOLECULAR ENERGY TRANSFER GORDON RESEARCH CONFERENCE (JANUARY 13-18, 2013 - VENTURA BEACH MARRIOTT, VENTURA CA

    Energy Technology Data Exchange (ETDEWEB)

    Reid, Scott A. [Marquette University

    2012-10-18

    Sessions covered all areas of molecular energy transfer, with 10 sessions of talks and poster sessions covering the areas of :  Energy Transfer in Inelastic and Reactive Scattering  Energy Transfer in Photoinitiated and Unimolecular Reactions  Non-adiabatic Effects in Energy Transfer  Energy Transfer at Surfaces and Interfaces  Energy Transfer in Clusters, Droplets, and Aerosols  Energy Transfer in Solution and Solid  Energy Transfer in Complex Systems  Energy Transfer: New vistas and horizons  Molecular Energy Transfer: Where Have We Been and Where are We Going?

  16. Surface charge-transfer complex formation of catechol on titanium(IV) oxide and the application to bio-sensing.

    Science.gov (United States)

    Murata, Yusuke; Hori, Hiroshige; Taga, Atsushi; Tada, Hiroaki

    2015-11-15

    Adsorption properties of 2-hydroxyphenol (catechol) on TiO2 particles has been studied at 298K. The adsorption proceeds from the aqueous solution with the Langmuir type behavior. Diffuse reflectance infrared spectra of the catechol-adsorbed TiO2 suggested that catechol is adsorbed on TiO2 solution via the chelation to the surface Ti ions. The adsorption induces a strong absorption in the whole visible region, of which intensity increases with an increase in the adsorption amount. Photoelectrochemical experiments and molecular orbital calculations indicate that the absorption stems from the charge-transfer (CT) transition from the HOMO of catechol to the conduction band of TiO2. Time courses for the adsorption of catechol on mesoporous TiO2 nanocrystalline film-coated glass was traced by measuring the change in the absorbance of the CT band, and analyzed on the basis of the Langmuir model. This study would present a new simple technique for sensing of important biomolecules bearing the catechol moiety. PMID:26247381

  17. Solid-state thermochromism and phase transitions of charge transfer 1,3-diamino-4,6-dinitrobenzene dyes.

    Science.gov (United States)

    Lee, Jong Hoon; Naumov, Pance; Chung, Ihn Hee; Lee, Sang Cheol

    2011-09-01

    The lower 1,3-bis(hydroxyalkylamino) homologues of the strong intramolecular X-type charge transfer (CT) system 1,3-diamino-4,6-dinitrobenzene (DADNB) exhibit reversible color change in the solid state from yellow at room temperature (RT) to orange and red at high temperature (HT). To investigate the structural prerequisites for occurrence of this phenomenon, we prepared 10 new derivatives of DADNB where the hydroxyalkyl arms at the amino groups were replaced with substituents having different electronic and steric profiles. Two of the new materials exhibit sharp and reversible thermochromic change in the solid state: when heated, the bis(aminoethyl) derivative (DADNB-1) undergoes color change from orange-red to brown, while one of the three polymorphs of the bisphenyl product (DADNB-2) changes its color from red to yellow. The physicochemical analysis and the crystal structures of seven of these compounds, one of which is trimorphic, confirmed that both phenomena are due to solid-solid phase transitions. The brown high-temperature phase of DADNB-1 presents the first example where the absorption is shifted beyond the red region. Form C of DADNB-2 is the first material of this group that exhibits "negative" thermochromism, where the high-temperature phase absorbs at lower wavelength than the low-temperature one. The results demonstrate the potentials of these simple and easily accessible organic molecular materials for thermal switching of the optical properties by utility of intermolecular interactions to modulate the intramolecular CT.

  18. Theoretical rationalization of the singlet-triplet gap in OLEDs materials: impact of charge-transfer character.

    Science.gov (United States)

    Moral, M; Muccioli, L; Son, W-J; Olivier, Y; Sancho-García, J C

    2015-01-13

    New materials for OLED applications with low singlet-triplet energy splitting have been recently synthesized in order to allow for the conversion of triplet into singlet excitons (emitting light) via a Thermally Activated Delayed Fluorescence (TADF) process, which involves excited-states with a non-negligible amount of Charge-Transfer (CT). The accurate modeling of these states with Time-Dependent Density Functional Theory (TD-DFT), the most used method so far because of the favorable trade-off between accuracy and computational cost, is however particularly challenging. We carefully address this issue here by considering materials with small (high) singlet-triplet gap acting as emitter (host) in OLEDs and by comparing the accuracy of TD-DFT and the corresponding Tamm-Dancoff Approximation (TDA), which is found to greatly reduce error bars with respect to experiments thanks to better estimates for the lowest singlet-triplet transition. Finally, we quantitatively correlate the singlet-triplet splitting values with the extent of CT, using for it a simple metric extracted from calculations with double-hybrid functionals, that might be applied in further molecular engineering studies. PMID:26574215

  19. Calculations of state-selective differential cross sections for charge transfer in collisions between O3+ and H2

    Institute of Scientific and Technical Information of China (English)

    Chi Bao-Qian; Liu Ling; Wang Jian-Guo

    2008-01-01

    The non-dissociative charge-transfer processes in collisions between O3+ and H2 are investigated by using the quantum-mechanical molecular-orbital coupled-channel (QMOCC) method. The adiabatic potentials and radial cou-pling matrix elements.utilized in the QMOCC calculations are obtained with the spin-coupled valence-bond approach. Electronic and vibrational state-selective differential cross sections are presented for projectile energies of 0.1, 1.0 and 10.0 eV/u in the H2 orientation angles of 45° and 89°. The electronic and the vibrational state-selective differential cross sections show similar behaviours: they decrease as the scattering angle increases, and beyond a specific angle the oscillating structures appear. Moreover, it is also found that the vibrational state-selective differential cross sections are strongly orientation-dependent, which provides a possibility to determine the orientations of molecule H2 by identifying the vibrational state-selective differential scattering processes.

  20. Solid-state thermochromism and phase transitions of charge transfer 1,3-diamino-4,6-dinitrobenzene dyes.

    Science.gov (United States)

    Lee, Jong Hoon; Naumov, Pance; Chung, Ihn Hee; Lee, Sang Cheol

    2011-09-01

    The lower 1,3-bis(hydroxyalkylamino) homologues of the strong intramolecular X-type charge transfer (CT) system 1,3-diamino-4,6-dinitrobenzene (DADNB) exhibit reversible color change in the solid state from yellow at room temperature (RT) to orange and red at high temperature (HT). To investigate the structural prerequisites for occurrence of this phenomenon, we prepared 10 new derivatives of DADNB where the hydroxyalkyl arms at the amino groups were replaced with substituents having different electronic and steric profiles. Two of the new materials exhibit sharp and reversible thermochromic change in the solid state: when heated, the bis(aminoethyl) derivative (DADNB-1) undergoes color change from orange-red to brown, while one of the three polymorphs of the bisphenyl product (DADNB-2) changes its color from red to yellow. The physicochemical analysis and the crystal structures of seven of these compounds, one of which is trimorphic, confirmed that both phenomena are due to solid-solid phase transitions. The brown high-temperature phase of DADNB-1 presents the first example where the absorption is shifted beyond the red region. Form C of DADNB-2 is the first material of this group that exhibits "negative" thermochromism, where the high-temperature phase absorbs at lower wavelength than the low-temperature one. The results demonstrate the potentials of these simple and easily accessible organic molecular materials for thermal switching of the optical properties by utility of intermolecular interactions to modulate the intramolecular CT. PMID:21790159