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Sample records for charge-transfer excited states

  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. Coherence, energy and charge transfers in de-excitation pathways of electronic excited state of biomolecules in photosynthesis

    DEFF Research Database (Denmark)

    Bohr, Henrik; Malik, F. Bary

    2013-01-01

    The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin–chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used F¨orster–Dexter th...

  3. Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

    Science.gov (United States)

    Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

    2001-01-01

    The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

  4. 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.

  5. 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.

  6. Is dipole moment a valid descriptor of excited state's charge-transfer character?

    Science.gov (United States)

    Petelenz, Piotr; Pac, Barbara

    2013-11-20

    In the ongoing discussion on excited states of the pentacene crystal, dipole moment values have been recently invoked to gauge the CT admixture to excited states of Frenkel parentage in a model cluster. In the present paper, a simple dimer model is used to show that, in general, the dipole moment is not a valid measure of the CT contribution. This finding eliminates some apparent disagreement between the computational results published by different research groups. The implications of our results and other related aspects of cluster-type quantum chemistry calculations are discussed in the context of the standing literature dispute concerning the mechanism of singlet fission in the pentacene crystal, notably the role of charge transfer contributions vs the involvement of an excimer-like doubly excited intermediate (D state).

  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. Charge-Transfer Excited States in Aqueous DNA: Insights from Many-Body Green's Function Theory

    Science.gov (United States)

    Yin, Huabing; Ma, Yuchen; Mu, Jinglin; Liu, Chengbu; Rohlfing, Michael

    2014-06-01

    Charge-transfer (CT) excited states play an important role in the excited-state dynamics of DNA in aqueous solution. However, there is still much controversy on their energies. By ab initio many-body Green's function theory, together with classical molecular dynamics simulations, we confirm the existence of CT states at the lower energy side of the optical absorption maximum in aqueous DNA as observed in experiments. We find that the hydration shell can exert strong effects (˜1 eV) on both the electronic structure and CT states of DNA molecules through dipole electric fields. In this case, the solvent cannot be simply regarded as a macroscopic screening medium as usual. The influence of base stacking and base pairing on the CT states is also discussed.

  9. Evaluating Electronic Couplings for Excited State Charge Transfer Based on Maximum Occupation Method ΔSCF Quasi-Adiabatic States.

    Science.gov (United States)

    Liu, Junzi; Zhang, Yong; Bao, Peng; Yi, Yuanping

    2017-02-14

    Electronic couplings of charge-transfer states with the ground state and localized excited states at the donor/acceptor interface are crucial parameters for controlling the dynamics of exciton dissociation and charge recombination processes in organic solar cells. Here we propose a quasi-adiabatic state approach to evaluate electronic couplings through combining maximum occupation method (mom)-ΔSCF and state diabatization schemes. Compared with time-dependent density functional theory (TDDFT) using global hybrid functional, mom-ΔSCF is superior to estimate the excitation energies of charge-transfer states; moreover it can also provide good excited electronic state for property calculation. Our approach is hence reliable to evaluate electronic couplings for excited state electron transfer processes, which is demonstrated by calculations on a typical organic photovoltaic system, oligothiophene/perylenediimide complex.

  10. The role of hydrogen bonding in excited state intramolecular charge transfer.

    Science.gov (United States)

    Chipem, Francis A S; Mishra, Anasuya; Krishnamoorthy, G

    2012-07-07

    Intramolecular charge transfer (ICT) that occurs upon photoexcitation of molecules is a vital process in nature and it has ample applications in chemistry and biology. The ICT process of the excited molecules is affected by several environmental factors including polarity, viscosity and hydrogen bonding. The effect of polarity and viscosity on the ICT processes is well understood. But, despite the fact that hydrogen bonding significantly influences the ICT process, the specific role of hydrogen bonding in the formation and stabilization of the ICT state is not unambiguously established. Some literature reports predicted that the hydrogen bonding of the solvent with a donor promotes the formation of a twisted intramolecular charge transfer (TICT) state. Some other reports stated that it inhibits the formation of the TICT state. Alternatively, it was proposed that the hydrogen bonding of the solvent with an acceptor favors the TICT state. It is also observed that a dynamic equilibrium is established between the free and the hydrogen bonded ICT states. This perspective focuses on the specific role played by hydrogen bonding of the solvent with the donor and the acceptor, and by proton transfer in the ICT process. The utility of such influence in molecular recognition and anion sensing is discussed with a few recent literature examples in the end.

  11. 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...

  12. 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.

  13. Fundamental studies of interfacial excited-state charge transfer in molecularly tethered semiconductor nanoassemblies

    Science.gov (United States)

    Youker, Diane Greer

    The research presented in this dissertation focuses on elucidating the parameters affecting dynamics and yield of electron transfer reactions in semiconducting nanoparticle assemblies through the use of time-resolved spectroscopy. In particular, the dissertation focuses on photoinduced electron injection in assemblies of CdSe, CdS, or PbS quantum dots covalently bound to either metal oxide films or each other through the use of bifunctional molecular linkers. Chapter 2 elucidates the influence of electronic coupling on excited-state electron transfer from CdS quantum dots to TiO2 nanoparticles via molecular linkers with phenylene bridges. We establish that the efficiency of electron injection from CdS quantum dots to TiO2 nanoparticle varies dramatically with electronic coupling, which can be controlled by tuning the properties of molecular linkers. Chapter 3 presents the role of excitation energy on interfacial electron transfer in tethered assemblies of CdSe quantum dots and TiO2 nanoparticles. Through this work, we determined that injection efficiency from band-edge states is independent of excitation energy. However, the efficiency of injection from trap-states decreases at lower-energy excitation. We attribute the decrease to a lower energy distribution of emissive trap-states from which injection is less efficient. Chapter 4 presents the observation of multiphasic electron injection dynamics from photoexcited PbS quantum dots to TiO2 nanoparticles. In this collaborative study with Dr. Masumoto from the University of Tsukuba we observed electron injection on multiple timescales. We determined that electron injection occurred in this system through two different mechanisms. The first involved injection from thermalized PbS excited states and the second through injection of hot electrons through Auger recombination of biexcitons that creates high lying excitonic states. Chapter 5 investigates charge transfer in covalently bound quantum dot assemblies. We utilize

  14. Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer, Photoisomerization and Fluorescence Probe Properties.

    Science.gov (United States)

    Hota, Prasanta Kumar; Singh, Anil Kumar

    2014-07-27

    Numerous studies of donor-acceptor conjugated linear polyenes have been carried out with the goal to understand the exact nature of the excited state electronic structure and dynamics. In this article we discuss our endeavours with regard to the excited state intramolecular charge transfer, photoisomerization and fluorescence probe properties of various donor-acceptor substituted compounds of diphenylpolyene [Ar(CH = CH) n Ar] series and ethenylindoles.

  15. Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

    Directory of Open Access Journals (Sweden)

    Ritesh Nandy

    2010-10-01

    Full Text Available Several 2-(phenylethynyltriphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different polarity. For a given derivative, solvent polarity had minimal effect on the absorption maxima. However, for a given solvent the absorption maxima red shifted with increasing conjugation of the substituent. The fluorescence emission of these derivatives was very sensitive to solvent polarity. In the presence of strongly electron withdrawing (–CN and strongly electron donating (–NMe2 substituents large Stokes shifts (up to 130 nm, 7828 cm−1 were observed in DMSO. In the presence of carbonyl substituents (–COMe and –COPh, the largest Stokes shift (140 nm, 8163 cm−1 was observed in ethanol. Linear correlation was observed for the Stokes shifts in a Lippert–Mataga plot. Linear correlation of Stokes shift was also observed with ET(30 scale for protic and aprotic solvents but with different slopes. These results indicate that the fluorescence emission arises from excited state intramolecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending upon the nature of the substituent on the phenyl ring. HOMO–LUMO energy gaps have been estimated from the electrochemical and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations.

  16. Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Barry; Sun, Haitao; Govind, Niranjan; Kowalski, Karol; Autschbach, Jochen

    2015-07-14

    Criteria to assess charge-transfer (CT) and `CT-like' character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals is compared with with coupled-cluster (CC) benchmarks. The test set includes an organic CT complex, two `push-pull' donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT, which has led to the concept of `CT-like' excitations. However, `CT-like' excitations are not like charge transfer, and the improvements are not obtained for the right reasons. The triplet excitation energies are underestimated for all systems, often severely. For the `CT-like' candidates, when going from a non-hybrid to an LC functional the error in the singlet-triplet (S/T) separation changes from negative to positive, providing error compensation. For the cyanine, the S/T separation is too large with all functionals, leading to the best error compensation for non-hybrid functionals.

  17. Multiple analyte response and molecular logic operations by excited-state charge-transfer modulation in a bipyridine integrated fluorophore.

    Science.gov (United States)

    Sreejith, Sivaramapanicker; Divya, Kizhumuri P; Manojkumar, T K; Ajayaghosh, Ayyappanpillai

    2011-02-01

    The tunable excited-state properties of a new donor-π-acceptor-π-donor-type fluorophore 1 with a bipyridyl moiety and its ability to respond to different analytes in solution and on paper microchannels are described. Furthermore, the multiple analyte response of fluorophore 1 has been exploited to perform multiple logic operations. Molecule 1, by virtue of its excited-state charge transfer, exhibits solvatochromism and reversible modulation of its emission in response to multiple chemical inputs, thus resulting in different fluorescent signals. The intraligand charge-transfer (ILCT) emission of 1 at 574 nm has been modulated to three emission outputs by using different chemical inputs, such as Zn(2+), H(+), and ethylenediaminetetraacetic acid (EDTA). Thus, different logic operations such as AND, 2-input-INH, 3-input-INH, IMP, and a combination of these logic operations could be achieved.

  18. Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Kjær, Kasper Skov; Alonso-Mori, Roberto

    2017-01-01

    state lifetime of iron based complexes due to spin crossover-the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand...... iron complexes with four cyanide (CN-;) ligands and one 2,2′-bipyridine (bpy) ligand. This enables MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL......-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. We...

  19. Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

    Science.gov (United States)

    Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

    2015-08-11

    The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

  20. Charge-transfer state excitation as the main mechanism of the photodarkening process in ytterbium-doped aluminosilicate fibres

    Energy Technology Data Exchange (ETDEWEB)

    Bobkov, K K; Rybaltovsky, A A; Vel' miskin, V V; Likhachev, M E; Bubnov, M M; Dianov, E M [Fiber Optics Research Center, Russian Academy of Sciences, Moscow (Russian Federation); Umnikov, A A; Gur' yanov, A N; Vechkanov, N N [G.G.Devyatykh Institute of Chemistry of High-Purity Substances, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation); Shestakova, I A [Open Joint-Stock Company M.F. Stel' makh Polyus Research Institute, Moscow (Russian Federation)

    2014-12-31

    We have studied photodarkening in ytterbium-doped fibre preforms with an aluminosilicate glass core. Analysis of their absorption and luminescence spectra indicates the formation of stable Yb{sup 2+} ions in the glass network under IR laser pumping at a wavelength λ = 915 nm and under UV irradiation with an excimer laser (λ = 193 nm). We have performed comparative studies of the luminescence spectra of the preforms and crystals under excitation at a wavelength of 193 nm. The mechanism behind the formation of Yb{sup 2+} ions and aluminium – oxygen hole centres (Al-OHCs), common to ytterbium-doped YAG crystals and aluminosilicate glass, has been identified: photoinduced Yb{sup 3+} charge-transfer state excitation. (optical fibres)

  1. 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.

  2. Excited state intramolecular charge transfer reaction in non-aqueous reverse micelles: Effects of solvent confinement and electrolyte concentration

    Indian Academy of Sciences (India)

    Tuhin Pradhan; Harun Al Rasid Gazi; Biswajit Guchhait; Ranjit Biswas

    2012-03-01

    Steady state and time resolved fluorescence emission spectroscopy have been employed to investigate the effects of solvent confinement and electrolyte concentration on excited state intramolecular charge transfer (ICT) reaction in 4-(1-pyrrolidinyl) benzonitrile (P5C), 4-(1-piperidinyl) benzonitrile (P6C), and 4-(1-morpholenyl) benzonitrile (M6C) in AOT/n-heptane/acetonitrile and AOT/n-heptane/methanol reverse micelles. Dramatic confinement effects have been revealed via a huge reduction (factor ranging between 100 and 20) over bulk values of both equilibrium and reaction rate constants. A strong dependence on the size of the confinement () of these quantities has also been observed. dependent average static dielectric constant, viscosity and solvation time-scale have been determined. Estimated dielectric constants for confined methanol and acetonitrile show a decrease from the respective bulk values by a factor of 3-5 and viscosities increased by a factor of 2 at the highest considered. Addition of electrolyte at = 5 for acetonitrile is found to produce a linear increase of confined solvent viscosity but leads to a non-monotonic electrolyte concentration dependence of average solvation time. Reaction rate constant is found to decrease linearly with electrolyte concentration for P5C and P6C but non-monotonically for M6C, the highest decrease for all the molecules being ∼ 20% over the value in the absence of added electrolyte in the solvent pool. The observed huge reduction in reaction rate constant is attributed to the effects of decreased solution polarity, enhanced viscosity and slowed-down solvent reorganization of the solvent under confinement in these non-aqueous reverse micelles.

  3. Excited state charge transfer reaction in (mixed solvent + electrolyte) systems: Role of reactant-solvent and reactant-ion interactions

    Indian Academy of Sciences (India)

    Harun Al Rasid Gazi; Ranjit Biswas

    2011-05-01

    Fluorescence spectroscopic techniques have been used to study the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in two sets of mixed solvents, (1-propanol + ethyl acetate) and (propylene carbonate + acetonitrile), in the absence and presence of a strong electrolyte, lithium perchlorate. These two sets of mixed solvent systems represent binary solvent mixtures of low and high polarities, respectively. Density, sound velocity and viscosity measurements indicate that these two mixed solvent systems are structurally different. Stronger ion-reactant interaction is evidenced in the mole fraction independence of emission frequencies in electrolyte solutions of low polar binary solvent mixtures. For both these mixtures, the reaction driving force (- ) decreases with increase in mole fraction of the relatively less polar solvent component of the mixture. Interestingly, - increases significantly on addition of electrolyte in low polar mixtures and exhibits mixture composition dependence but, in contrast, - in high polar mixtures does not sense variation in mixture composition in presence of electrolyte. This insensitivity to mixture composition for high polar mixtures is also observed for the measured reaction time constant. In addition, the reaction time constant does not sense the presence of electrolyte in the high polar solvent mixtures. The reaction time constant in low polar mixtures, which becomes faster on addition of electrolyte, lengthens on increasing the mole fraction of the relatively less polar solvent component of the mixture. These observations have been qualitatively explained in terms of the measured solvent reorganization energy and reaction driving force by using expressions from the classical theory of electron transfer reaction.

  4. Charge-transfer pipi* excited state in the 7-azaindole dimer. A hybrid configuration interactions singles/time-dependent density functional theory description.

    Science.gov (United States)

    Gelabert, Ricard; Moreno, Miquel; Lluch, José M

    2006-01-26

    The hybrid configuration interaction singles/time dependent density functional theory approach of Dreuw and Head-Gordon [Dreuw, A.; Head-Gordon, M. J. Am. Chem. Soc. 2004, 126, 4007] has been applied to study the potential energy landscape and accessibility of the charge-transfer pipi* excited state in the dimer of 7-azaindole, which has been traditionally considered a model for DNA base pairing. It is found that the charge-transfer pipi* excited state preferentially stabilizes the product of a single proton transfer. In this situation, the crossing between this state and the photoactive electronic state of the dimer is accessible. It is found that the charge-transfer pipi* excited state has a very steep potential energy profile with respect to any single proton-transfer coordinate and, in contrast, an extremely flat potential energy profile with respect to the stretch of the single proton-transfer complex. This is predicted to bring about a pair of rare fragments of the 7-azaindole dimer, physically separated and hence having very long lifetimes. This could have implications in the DNA base pairs of which the system is an analogue, in the form of replication errors.

  5. Excited state intramolecular charge transfer reaction of 4-(morpholenyl) benzonitrile in solution: Effects of hetero atom in the donor moiety

    Indian Academy of Sciences (India)

    Tuhin Pradhan; Harun Al Rasid Gazi; Ranjit Biswas

    2010-07-01

    An intramolecular charge transfer (ICT) molecule with an extra hetero atom in its donor moiety has been synthesized in order to investigate how ICT reaction is affected by hetero atom replacement. Photo-physical and photo-dynamical properties of this molecule, 4-(morpholenyl)benzonitrile (M6C), have been studied in 20 different solvents. The correlation between the reaction driving force (- ) and activation barrier ( #) has been explored in order to understand the solvent effects (static and dynamic) on the photo-excited ICT reaction in this molecule. A Kramer’s model analysis of the experimentally observed reaction rate constants indicates a solvent-averaged activation barrier of ∼ 4 in the absence of solvent dynamical control. The reaction in M6C is therefore not a barrier-less reaction but close to the limit where conventional kinetics might break down.

  6. Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies

    Science.gov (United States)

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

    2015-02-01

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

  7. Twisted intramolecular charge transfer states : rotationally resolved fluorescence excitation spectra of 4,4 '-dimethylaminobenzonitrile in a molecular beam

    NARCIS (Netherlands)

    Nikolaev, A.E.; Myszkiewicz, G.; Berden, G.; Meerts, W.L.; Pfanstiel, J.F.; Pratt, D.W.

    2005-01-01

    We report the observation at high resolution of seven vibronic bands that appear within similar to200 cm(-1) of the electronic origin in the S-1-S-0 fluorescence excitation spectrum of 4,4(')-dimethylaminobenzonitrile (DMABN) in a molecular beam. Surprisingly, each band is found to be split into two

  8. Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-). Theoretical evidence for a competitive charge transfer mechanism.

    Science.gov (United States)

    Hu, Zhenming; Boyd, Russell J; Nakatsuji, Hiroshi

    2002-03-20

    Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-) complexes have been investigated using the B3LYP and the symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theoretical methods. All the dicarbonyl complexes have singlet ground electronic states with large singlet-triplet separations. Thermal dissociations of CO from the parent dicarbonyls are energetically unfavorable. CO thermal dissociation is an activation process for [Cl(2)Rh(CO)(2)](-) while it is a repulsive potential for CpM(CO)(2). The natures of the main excited states of CpM(CO)(2) and [Cl(2)Rh(CO)(2)](-) are found to be quite different. For [Cl(2)Rh(CO)(2)](-), all the strong transitions are identified to be metal to ligand CO charge transfer (MLCT) excitations. A significant feature of the excited states of CpM(CO)(2) is that both MLCT excitation and a ligand Cp to metal and CO charge transfer excitation are strongly mixed in the higher energy states with the latter having the largest oscillator strength. A competitive charge transfer excited state has therefore been identified theoretically for CpRh(CO)(2) and CpIr(CO)(2). The wavelength dependence of the quantum efficiencies for the photoreactions of CpM(CO)(2) reported by Lees et al. can be explained by the existence of two different types of excited states. The origin of the low quantum efficiencies for the C-H/S-H bond activations of CpM(CO)(2) can be attributed to the smaller proportion of the MLCT excitation in the higher energy states.

  9. An Accurate and Linear Scaling Method to Calculate Charge-Transfer Excitation Energies and Diabatic Couplings

    CERN Document Server

    Pavanello, Michele; Visscher, Lucas; Neugebauer, Johannes

    2012-01-01

    Quantum--Mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this goal for those charge transfer excitations that take place between non-covalently bound molecules. In particular, we present a method that scales linearly with the number of non-covalently bound molecules in the system and is based on a two-pronged approach: The molecular electronic structure of broken-symmetry charge-localized states is obtained with the Frozen Density Embedding formulation of subsystem Density-Functional Theory; subsequently, in a post-SCF calculation, the full-electron Hamiltonian and overlap matrix elements among the charge-localized states are evaluated with an algorithm which takes full advantage of the subsystem DFT density partitioning technique. The method is benchmarked against Coupled-Cluster calculations and achieves chemical accuracy for the systems considered...

  10. Both intra- and interstrand charge-transfer excited states in aqueous B-DNA are present at energies comparable to, or just above, the (1)pipi* excitonic bright states.

    Science.gov (United States)

    Lange, Adrian W; Herbert, John M

    2009-03-25

    Vertical electronic excitations in model systems representing single- and double-stranded B-DNA are characterized using electronic structure theory, including both time-dependent density functional theory (TD-DFT) and correlated wave function techniques. Previous TD-DFT predictions of charge-transfer (CT) states well below the optically bright (1)pipi* states are shown to be artifacts of the improper long-range behavior of standard density-functional exchange approximations, which we rectify here using a long-range correction (LRC) procedure. For nucleobase dimers (hydrogen-bonded or pi-stacked), TD-LRC-DFT affords vertical excitation energies in reasonable agreement with the wave function methods, not only for the (1)npi* and (1)pipi* states but also for the CT states, and qualitatively reproduces well-known base-stacking effects on the absorption spectrum of DNA. The emergence of (1)pipi* Frenkel exciton states, localized on a single strand, is clearly evident, and these states (rather than low-energy CT states) are primarily responsible for the fact that DNA's absorption spectrum exhibits a red tail that is absent in monomer absorption spectra. For B-DNA in aqueous solution, the low-energy tail of the CT band (representing both intra- and interstrand CT states) appears at energies comparable to those of the optically bright (1)pipi* exciton states. In systems with more than one base pair, we also observe the emergence of delocalized, interstrand CT excitations, whose excitation energies may be significantly lower than the lowest CT excitation in a single base pair. Together, these observations suggest that a single Watson-Crick base pair is an inadequate model of the photophysics of B-DNA.

  11. What is the "best" atomic charge model to describe through-space charge-transfer excitations?

    Science.gov (United States)

    Jacquemin, Denis; Le Bahers, Tangui; Adamo, Carlo; Ciofini, Ilaria

    2012-04-28

    We investigate the efficiency of several partial atomic charge models (Mulliken, Hirshfeld, Bader, Natural, Merz-Kollman and ChelpG) for investigating the through-space charge-transfer in push-pull organic compounds with Time-Dependent Density Functional Theory approaches. The results of these models are compared to benchmark values obtained by determining the difference of total densities between the ground and excited states. Both model push-pull oligomers and two classes of "real-life" organic dyes (indoline and diketopyrrolopyrrole) used as sensitisers in solar cell applications have been considered. Though the difference of dipole moments between the ground and excited states is reproduced by most approaches, no atomic charge model is fully satisfactory for reproducing the distance and amount of charge transferred that are provided by the density picture. Overall, the partitioning schemes fitting the electrostatic potential (e.g. Merz-Kollman) stand as the most consistent compromises in the framework of simulating through-space charge-transfer, whereas the other models tend to yield qualitatively inconsistent values.

  12. Identifying interfacial charge transfer states in organic heterostructures (Conference Presentation)

    Science.gov (United States)

    Arndt, Andreas P.; Gerhard, Marina; Howard, Ian A.; Koch, Martin; Lemmer, Ulrich

    2016-09-01

    Charge transfer (CT) states play evidently an important role at the interface of organic heterostructures but their identification and characterization is often experimentally less obvious and challenging. We studied two exemplary material systems which both represented a benchmark within the research of organic photovoltaics at their time: the homopolymer P3HT blended with PC61BM and the copolymer PTB7 blended with PC71BM. In both heterostructures, we could identify a distinct CT state emission by the use of NIR time-resolved photoluminescence (PL) [1], [2]. The selectivity of this technique enables us to clearly probe the energetics and dynamics of weak emitting interfacial states and therefore to prove differences in the CT state characteristics between the two systems. We went beyond this previous work and investigated the time and temperature dependent emission anisotropy as well as the electric field dependence of the time-resolved PL for both blends and the pristine polymers, respectively. In both cases the CT state emission clearly deviates from the one of the primarily excited singlet excitons: the emission anisotropy reveals an additional relaxation pathway for the exciton which is connected with a change of the transition dipole moment of the emission, and under applied bias different quenching thresholds can give access to varying binding energies of the emissive excitons involved. Finally, we think that our findings demonstrate how interfacial CT state emission can be clearly identified as such and how it can be unambiguously distinguished from singlet exciton emission.

  13. Interplay between excited-state intramolecular proton transfer and charge transfer in flavonols and their use as protein-binding-site fluorescence probes

    Energy Technology Data Exchange (ETDEWEB)

    Sytnik, A.; Gormin, D.; Kasha, M. (Florida State Univ., Tallahassee, FL (United States))

    1994-12-06

    A comparative study is presented of competitive fluorescences of three flavonols, 3-hydroxyflavone, 3,3[prime],4[prime],7-tetrahydroxyflavone (fisetin), and 4[prime]-diethylamino-3-hydroxyflavone (DHF). The normal fluorescence S[sub 1] [yields] S[sub 0] (400-nm region) is largely replaced by the proton-transfer tautomer fluorescence S[prime][sub 1] [yields] S[prime][sub 0] in the 550-nm region for all three of the flavonols in aprotic solvents at room temperature. For DHF in polar solvents the normal fluorescence becomes a charge-transfer fluorescence (460-500 nm) which competes strongly with the still dominant proton-transfer fluorescence (at 570 nm). In protic solvents, and at 77 K, the interference with intramolecular hydrogen bonding gives rise to greatly enhanced normal fluorescence, lowering the quantum yield of proton-transfer fluorescence. The utility of DHF as a discriminating fluorescence probe for protein binding sites is suggested by the strong dependence of the charge-transfer fluorescence on polarity of the environment and by various static and dynamic parameters of the charge-transfer and proton-transfer fluorescence which can be determined. 49 refs., 6 figs., 1 tab.

  14. 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.

  15. Spectroscopy of charge transfer states in Mg1 - x Ni x O

    Science.gov (United States)

    Churmanov, V. N.; Sokolov, V. I.; Pustovarov, V. A.; Gruzdev, N. B.; Mironova-Ulmane, N.

    2016-10-01

    Photoluminescence and photoluminescence excitation spectra of solid solution Mg1- x Ni x O ( x = 0.008) have been analyzed. The contributions of charge transfer electronic states and nonradiative Auger relaxation to the formation of the photoluminescence spectrum are discussed.

  16. Charge transfer and excitation in H++CH3 collisions below 10keV

    Science.gov (United States)

    Nagao, Masatoshi; Hida, Ken-Nosuke; Kimura, Mineo; Rai, Sachchida N.; Liebermann, Heinz-Peter; Buenker, Robert J.; Suno, Hiroya; Stancil, Phillip C.

    2008-07-01

    Charge transfer and electronic excitation in collisions of H+ ions with CH3 from a few tens of eV up to 10keV are theoretically investigated. The adiabatic potential energy curves and corresponding wave functions are calculated by using the multireference single- and double-excitation configuration interaction method, and the scattering dynamics is studied based on the semiclassical impact parameter molecular-orbital close-coupling approach. Charge-transfer cross sections are found to be large and rather energy-dependent over the entire energy region studied. Electronic excitation is also energy-dependent with a sharp increase from below 10-17to10-16cm2 . Most of the molecular products produced through charge transfer or excitation are known to be unstable and undergo fragmentation producing various hydrocarbon radical species. Hence, identification of fragmented species and their production mechanism are important for spectroscopic analysis.

  17. Ground-state charge transfer as a mechanism for surface-enhanced Raman scattering

    Science.gov (United States)

    Lippitsch, Max E.

    1984-03-01

    A model is presented for the contribution of ground-state charge transfer between a metal and adsorbate to surface-enhanced Raman scattering (SERS). It is shown that this contribution can be understood using the vibronic theory for calculating Raman intensities. The enhancement is due to vibronic coupling of the molecular ground state to the metal states, the coupling mechanism being a modulation of the ground-state charge-transfer energy by the molecular vibrations. An analysis of the coupling operator gives the selection rules for this process, which turn out to be dependent on the overall symmetry of the adsorbate-metal system, even if the charge transfer is small enough for the symmetry of the adsorbate to remain the same as that of the free molecule. It is shown that the model can yield predictions on the properties of SERS, e.g., specificity to adsorption geometry, appearance of forbidden bands, dependence on the applied potential, and dependence on the excitation wavelength. The predictions are in good agreement with experimental results. It is also deduced from this model that in many cases atomic-scale roughness is a prerequisite for the observation of SERS. A result on the magnitude of the enhancement can only be given in a crude approximation. Although in most cases an additional electromagnetic enhancement seems to be necessary to give an observable signal, this charge-transfer mechanism should be important in many SERS systems.

  18. Charge transfer transitions in the excitation spectra of PrX{sub 3}:Ce{sup 3+} (X=Cl, Br) scintillators

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, A.M. [GE Global Research, 1 Research Circle, K1 4A24, Niskayuna, NY 12309 (United States)], E-mail: srivastava@crd.ge.com

    2009-01-15

    The Cl{sup -}{yields}Pr{sup 3+} charge transfer transition is identified to occur in the excitation spectrum of PrCl{sub 3}:Ce{sup 3+} at 211 nm (47,393 cm{sup -1}). A model based on the dissociation of the charge transfer state is proposed to explain the presence of the ligand-to-Pr{sup 3+} charge transfer transition band in the excitation spectrum of PrX{sub 3}:Ce{sup 3+} (X=Cl, Br) when the Ce{sup 3+} emission is monitored00.

  19. Tuning the role of charge-transfer states in intramolecular singlet exciton fission through side-group engineering

    Science.gov (United States)

    Lukman, Steven; Chen, Kai; Hodgkiss, Justin M.; Turban, David H. P.; Hine, Nicholas D. M.; Dong, Shaoqiang; Wu, Jishan; Greenham, Neil C.; Musser, Andrew J.

    2016-12-01

    Understanding the mechanism of singlet exciton fission, in which a singlet exciton separates into a pair of triplet excitons, is crucial to the development of new chromophores for efficient fission-sensitized solar cells. The challenge of controlling molecular packing and energy levels in the solid state precludes clear determination of the singlet fission pathway. Here, we circumvent this difficulty by utilizing covalent dimers of pentacene with two types of side groups. We report rapid and efficient intramolecular singlet fission in both molecules, in one case via a virtual charge-transfer state and in the other via a distinct charge-transfer intermediate. The singlet fission pathway is governed by the energy gap between singlet and charge-transfer states, which change dynamically with molecular geometry but are primarily set by the side group. These results clearly establish the role of charge-transfer states in singlet fission and highlight the importance of solubilizing groups to optimize excited-state photophysics.

  20. Interfacial Charge Transfer States in Condensed Phase Systems

    Science.gov (United States)

    Vandewal, Koen

    2016-05-01

    Intermolecular charge transfer (CT) states at the interface between electron-donating (D) and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. CT states efficiently generate charge carriers for some D-A combinations, and others show high fluorescence quantum efficiencies. These properties are exploited in organic solar cells, photodetectors, and light-emitting diodes. This review summarizes experimental and theoretical work on the electronic structure and interfacial energy landscape at condensed matter D-A interfaces. Recent findings on photogeneration and recombination of free charge carriers via CT states are discussed, and relations between CT state properties and optoelectronic device parameters are clarified.

  1. 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)

  2. Multicolour Emission States from Charge Transfer between Carbon Dots and Surface Molecules

    Directory of Open Access Journals (Sweden)

    Shengliang Hu

    2017-02-01

    Full Text Available The emissive states of carbon dots have been tuned by controlling the charge transfer process. The carbon dots couple with molecules, which are made of a benzene ring and different heteroatom substituents, through amino-carboxylic bonds that are generally identified as charge transfer promoters at the interface. New ways of radiative recombination are created due to the transfer of photo-excited electrons from carbon dots to the lowest unoccupied molecular orbital (LUMO of the grafted molecules. By variation of the molecular orbital energy levels via heteroatom substituents in the benzene ring, the different optical properties and emission colors of the carbon dots were presented. This work opens up new opportunities for the application of carbon dots since different heteroatom substituents could lead to many possibilities for conjugation with drugs and biomolecules.

  3. Frenkel and Charge-Transfer Excitations in Donor-acceptor Complexes from Many-Body Green's Functions Theory.

    Science.gov (United States)

    Baumeier, Björn; Andrienko, Denis; Rohlfing, Michael

    2012-08-14

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

  4. 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

    for charge{transfer character, we furthermore conrm that the di¿erence between excitation energies calculated with TDDFT and with the Tamm-Danco¿ approximation (TDA) to TDDFT is indeed correlated with the charge-transfer character of a given electronic transition both in vacuo and in solution...

  5. 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.

    2016-03-01

    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.

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

    Science.gov (United States)

    Vandewal, Koen; Albrecht, Steve; Hoke, Eric T.; Graham, Kenneth R.; Widmer, Johannes; Douglas, Jessica D.; Schubert, Marcel; Mateker, William R.; Bloking, Jason T.; Burkhard, George F.; Sellinger, Alan; Fréchet, Jean M. J.; Amassian, Aram; Riede, Moritz K.; McGehee, Michael D.; Neher, Dieter; Salleo, Alberto

    2014-01-01

    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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

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

    DEFF Research Database (Denmark)

    Sherafatipour, Golenaz; Madsen, Morten

    charge transfer (CT) excitons, which is Coulombically bound interfacial electron- hole pairs residing at the donor/acceptor heterojunctions. The CT state represents an intermediate state between the exciton dissociation and recombination back to the ground state. Since the recombination of photo...... at the donor/acceptor interface is detected. As a less studied system, we examine here the interfacial charge transfer state recombination in DBP:C70 thin-films. The weak EL from the small molecule solar cell biased in the forward direction gives valuable information about the CT state recombination, from...... 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...

  13. 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.

  14. The intramolecular charge transfer state in carbonyl-containing polyenes and carotenoids.

    Science.gov (United States)

    Enriquez, Miriam M; Fuciman, Marcel; LaFountain, Amy M; Wagner, Nicole L; Birge, Robert R; Frank, Harry A

    2010-09-30

    Numerous femtosecond time-resolved optical spectroscopic experiments have reported that the lifetime of the low-lying S(1) state of carbonyl-containing polyenes and carotenoids decreases with increasing solvent polarity. The effect becomes even more pronounced as the number of double bonds in the conjugated π-electron system decreases. The effect has been attributed to an intramolecular charge transfer (ICT) state coupled to S(1), but it is still not clear what the precise molecular nature of this state is, and how it is able to modulate the spectral and dynamic properties of polyenes and carotenoids. In this work, we examine the nature of the ICT state in three substituted polyenes: crocetindial, which contains two terminal, symmetrically substituted carbonyl groups in conjugation with the π-electron system, 8,8'-diapocarotene-8'-ol-8-al, which has one terminal conjugated carbonyl group and one hydroxyl group, and 8,8'-diapocarotene-8,8'-diol, which has two terminal, symmetrically positioned, hydroxyl groups but no carbonyls. Femtosecond time-resolved optical spectroscopic experiments on these molecules reveal that only the asymmetrically substituted 8,8'-diapocarotene-8'-ol-8-al exhibits any substantial effect of solvent on the excited state spectra and dynamics. The data are interpreted using molecular orbital theory which shows that the ICT state develops via mixing of the low-lying S(1) (2(1)A(g)-like) and S(2) (1(1)B(u)-like) excited singlet states to form a resultant state that preferentially evolves in polar solvent and exhibits a very large (∼25 D) dipole moment. Molecular dynamics calculations demonstrate that the features of the ICT state are present in ∼20 fs.

  15. Small-signal charge transfer inefficiency experiments explained by the McWhorter interface state model

    NARCIS (Netherlands)

    Penning De Vries, René G.M.; Wallinga, Hans

    1984-01-01

    The small-signal charge transfer inefficiency (SCTI) of a surface-channel CCD has been studied. The experimentally observed behavior of the SCTI could not be explained by the conventional interface state model. Using the McWhorter model for the interface states, which assumes a distribution of the s

  16. Theoretical Study of the Charge-Transfer State Separation within Marcus Theory

    DEFF Research Database (Denmark)

    Volpi, Riccardo; Nassau, Racine; Nørby, Morten Steen

    2016-01-01

    We study, within Marcus theory, the possibility of the charge-transfer (CT) state splitting at organic interfaces and a subsequent transport of the free charge carriers to the electrodes. As a case study we analyze model anthracene-C60 interfaces. Kinetic Monte Carlo (KMC) simulations on the cold...

  17. Low-energy state-selective charge transfer by multiply charged ions

    NARCIS (Netherlands)

    Lubinski, G; Juhasz, Z; Morgenstern, R; Hoekstra, R

    2001-01-01

    We present a combined rf-guided ion beam and photon emission spectroscopy method, which facilitates state-selective charge-transfer measurements at energies of direct relevance for astrophysics and fusion-plasma diagnostics and modeling. Ion energies have been varied from 1000 eV/amu down to energie

  18. Charge transfer to ground-state ions produces free electrons

    Science.gov (United States)

    You, D.; Fukuzawa, H.; Sakakibara, Y.; Takanashi, T.; Ito, Y.; Maliyar, G. G.; Motomura, K.; Nagaya, K.; Nishiyama, T.; Asa, K.; Sato, Y.; Saito, N.; Oura, M.; Schöffler, M.; Kastirke, G.; Hergenhahn, U.; Stumpf, V.; Gokhberg, K.; Kuleff, A. I.; Cederbaum, L. S.; Ueda, K.

    2017-01-01

    Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne2+ produced after Ne 1s photoionization in Ne-Kr mixed clusters.

  19. Comparative study on contribution of charge-transfer collision to excitations of iron ion between argon radio-frequency inductively-coupled plasma and nitrogen microwave induced plasma

    Energy Technology Data Exchange (ETDEWEB)

    Satoh, Kozue; Wagatsuma, Kazuaki, E-mail: wagatuma@imr.tohoku.ac.jp

    2015-06-01

    various excitation levels. • We find a non-thermal behavior of the high-lying energy levels in MIP which deviates from the normal distribution. • This non-thermal behavior would be caused by charge-transfer collisions with the ground state of nitrogen molecule ion.

  20. Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Yang [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States); Aggelen, Helen van [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States); Department of Inorganic and Physical Chemistry, Ghent University, 9000 Ghent (Belgium); Yang, Weitao, E-mail: weitao.yang@duke.edu [Department of Chemistry and Department of Physics, Duke University, Durham, North Carolina 27708 (United States)

    2013-12-14

    Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.

  1. Double, Rydberg and charge transfer excitations from pairing matrix fluctuation and particle-particle random phase approximation.

    Science.gov (United States)

    Yang, Yang; van Aggelen, Helen; Yang, Weitao

    2013-12-14

    Double, Rydberg, and charge transfer (CT) excitations have been great challenges for time-dependent density functional theory (TDDFT). Starting from an (N ± 2)-electron single-determinant reference, we investigate excitations for the N-electron system through the pairing matrix fluctuation, which contains information on two-electron addition/removal processes. We adopt the particle-particle random phase approximation (pp-RPA) and the particle-particle Tamm-Dancoff approximation (pp-TDA) to approximate the pairing matrix fluctuation and then determine excitation energies by the differences of two-electron addition/removal energies. This approach captures all types of interesting excitations: single and double excitations are described accurately, Rydberg excitations are in good agreement with experimental data and CT excitations display correct 1/R dependence. Furthermore, the pp-RPA and the pp-TDA have a computational cost similar to TDDFT and consequently are promising for practical calculations.

  2. Charge transfer state in DBP:C70 organic solar cells

    DEFF Research Database (Denmark)

    Sherafatipour, Golenaz; Benduhn, Johannes; Spoltore, Donato

    -acceptor interface via delocalized charge-transfer (CT) states, which represents an intermediate state between the exciton dissociation and recombination back to the ground state. In this work we perform the electroluminescence (EL) created by bimolecular free career recombination and sensitive external quantum....... Electroluminescence from charge transfer states in polymer solar cells. J. Am. Chem. Soc. 131, 11819–11824 (2009)....... efficiency measurements (sEQE) in DBP:C70 based SCs as a less studied system in order to study the energy and effect of CT states on degradation of the devices2. The results from these measurements reveal valuable information about the loss mechanism during the aging experiment as well as the energy...

  3. Nonlinear lattice relaxation of photogenerated charge-transfer excitation in halogen-bridged mixed-valence metal complexes. II. Polaron channel

    Science.gov (United States)

    Mishima, A.; Nasu, K.

    1989-03-01

    The one-dimensional extended Peierls-Hubbard model with half-filled-band electrons is studied in order to clarify the lattice relaxation path of the photogenerated charge-transfer excitation in halogen-bridged mixed-valence metal complexes. The ground and excited states are calculated within mean-field theory for electrons and the adiabatic approximation for phonons. It is concluded that the main origin of the photoinduced absorption is a distant pair of the hole-polaron and the electron-polaron. This distant pair is created not from the ground state of the self-trapped exciton (STE), but from the excited states of the STE through their autodissociation. This is consistent with the experiment on the excitation energy dependence of the photoinduced absorption yield.

  4. 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

  5. The effect of thermal motion on the electron localization in metal-to-ligand charge transfer excitations in [Fe(bpy)3](2+).

    Science.gov (United States)

    Domingo, Alex; Sousa, Carmen; de Graaf, Coen

    2014-12-21

    Accurate electronic structure calculations of the lowest excited states have been performed on twenty snapshots of a molecular dynamics simulation of [Fe(bpy)3](2+) dissolved in water. The thermal motion distorts the structure of the complex from its average D3 symmetry, causing the localization on one bipyridine ligand of the excited electron in the metal-to-ligand charge transfer (MLCT) state. The excitation energy is about 0.25 eV lower than that for the delocalized description of the MLCT state and is in good agreement with experiments. The composition of the MLCT band is carefully analyzed and the effect of thermal motion on the mechanism of light-induced spin crossover is discussed.

  6. 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...

  7. Solvent electronic polarization effects on a charge transfer excitation studied by the mean-field QM/MM method

    Energy Technology Data Exchange (ETDEWEB)

    Nakano, Hiroshi [Department of Molecular Engineering, Kyoto University, Kyoto Daigaku Katsura, Kyoto 615-8510 (Japan); Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Kyoto 615-8245 (Japan)

    2015-12-31

    Electronic polarization effects of a medium can have a significant impact on a chemical reaction in condensed phases. We discuss the effects on the charge transfer excitation of a chromophore, N,N-dimethyl-4-nitroaniline, in various solvents using the mean-field QM/MM method with a polarizable force field. The results show that the explicit consideration of the solvent electronic polarization effects is important especially for a solvent with a low dielectric constant when we study the solvatochromism of the chromophore.

  8. Quantum dynamics of vibrational excitations and vibrational charge transfer processes in H+ + O2 collisions at collision energy 23 eV

    Indian Academy of Sciences (India)

    Saieswari Amaran; Sanjay Kumar

    2009-09-01

    Quantum mechanical study of vibrational state-resolved differential cross sections and transition probabilities for both the elastic/inelastic and the charge transfer processes have been carried out in the H+ + O2 collisions at the experimental collision energy of 23 eV. The quantum dynamics has been performed within the vibrational close-coupling rotational infinite-order sudden approximation framework employing our newly obtained quasi-diabatic potential energy surfaces corresponding to the ground and the first excited electronic states which have been computed using ab initio procedures and Dunning’s correlation consistent-polarized valence triple zeta basis set at the multireference configuration interaction level of accuracy. The present theoretical results for elastic/inelastic processes provide an overall agreement with the available state-selected experimental data, whereas the results for the charge transfer channel show some variance in comparison with those of experiments and are similar to the earlier theoretical results obtained using model effective potential based on projected valence bond method and using semi-empirical diatomics-in-molecules potential. The possible reason for discrepancies and the likely ways to improve the results are discussed in terms of the inclusion of higher excited electronic states into the dynamics calculation.

  9. 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.

  10. The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C60 molecular triad

    Science.gov (United States)

    Olguin, Marco; Basurto, Luis; Zope, Rajendra R.; Baruah, Tunna

    2014-05-01

    We present a detailed study of charge transfer (CT) excited states for a large number of configurations in a light-harvesting Carotenoid-diaryl-Porphyrin-C60 (CPC60) 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 CPC60 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 C60-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five different CPC60 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.

  11. The effect of solvent polarity on the balance between charge transfer and non-charge transfer pathways in the sensitization of singlet oxygen by pipi triplet states.

    Science.gov (United States)

    Schmidt, Reinhard

    2006-05-11

    A large set of literature kinetic data on triplet (T(1)) sensitization of singlet oxygen by two series of biphenyl and naphthalene sensitizers in solvents of strongly different polarity has been analyzed. The rate constants and the efficiencies of singlet oxygen formation are quantitatively reproduced by a model that assumes the competition of a non-charge transfer (nCT) and a CT deactivation channel. nCT deactivation occurs from a fully established spin-statistical equilibrium of (1)(T(1)(3)Sigma) and (3)(T(1)(3)Sigma) encounter complexes by internal conversion (IC) to lower excited complexes that dissociate to yield O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)), and O(2)((3)Sigma(g)(-)). IC of (1,3)(T(1)(3)Sigma) encounter complexes is controlled by an energy gap law that is generally valid for the transfer of electronic energy to and from O(2). (1,3)(T(1)(3)Sigma) nCT complexes form in competition to IC (1)(T(1)(3)Sigma) and (3)(T(1)(3)Sigma) exciplexes if CT interactions between T(1) and O(2) are important. The rate constants of exciplex formation depend via a Marcus type parabolic model on the corresponding free energy change DeltaG(CT), which varies with sensitizer triplet energy, oxidation potential, and solvent polarity. O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)), and O(2)((3)Sigma(g)(-)) are formed in the product ratio (1/6):(1/12):(3/4) in the CT deactivation channel. The balance between nCT and CT deactivation is described by the relative contribution p(CT) of CT induced deactivation calculated for a sensitizer of known triplet energy from its quenching rate constant. It is shown how the change of p(CT) influences the quenching rate constant and the efficiency of singlet oxygen formation in both series of sensitizers. p(CT) is sensitive to differences of solvent polarity and varies for the biphenyls and the naphthalenes as sigmoidal with DeltaG(CT). This quantitative model represents a realistic and general mechanism for the quenching of pipi triplet states by O

  12. Influence of charge transfer state on Eu3+ luminescence in LaAlO3, by high pressure spectroscopy

    Science.gov (United States)

    Behrendt, Mirosław; Mahlik, Sebastian; Grinberg, Marek; Stefańska, Dagmara; Dereń, Przemysław J.

    2017-01-01

    The contribution presents spectroscopic characterization of LaAlO3 doped with 0.5 mol %. Eu3+. We measured steady state luminescence, luminescence excitation spectra, as well as the time resolved spectra and luminescence kinetics. The experiments were performed at high hydrostatic pressure applied in diamond anvil cell (DAC) which was changed from ambient to 250 kbar. We found that for all pressures the emission from the 5D0 and 5D1 excited emitting state of Eu3+ was delayed in time after excitation pulse whilst emission from the 5D2 appear immediately after excitation. At pressure above 12 kbar the strong magnification of the luminescence lines related to the transitions from the 5D3 state which were very weak at ambient condition is observed. The emission decay of the 5D3 luminescence become slower when pressure is increased. All these effects are attributed to pressure-induced increase of the energy of the ground electronic configuration 4f6 of the Eu2+ with respect to the valence band edge which results in the charge transfer state, and 5D3 level crossing.

  13. Topological charge transfer in frequency doubling of fractional orbital angular momentum state

    Science.gov (United States)

    Ni, R.; Niu, Y. F.; Du, L.; Hu, X. P.; Zhang, Y.; Zhu, S. N.

    2016-10-01

    Nonlinear frequency conversion is promising for manipulating photons with orbital angular momentum (OAM). In this letter, we investigate the second harmonic generation (SHG) of light beams carrying fractional OAM. By measuring the OAM components of the generated second harmonic (SH) waves, we find that the integer components of the fundamental beam will interact with each other during the nonlinear optical process; thus, we figure out the law for topological charge transfer in frequency doubling of the fractional OAM state. Theoretical predictions by solving the nonlinear coupled wave equations are consistent with the experimental results.

  14. Time-dependent transition density matrix for visualizing charge-transfer excitations in photoexcited organic donor-acceptor systems

    Science.gov (United States)

    Li, Yonghui; Ullrich, Carsten

    2013-03-01

    The time-dependent transition density matrix (TDM) is a useful tool to visualize and interpret the induced charges and electron-hole coherences of excitonic processes in large molecules. Combined with time-dependent density functional theory on a real-space grid (as implemented in the octopus code), the TDM is a computationally viable visualization tool for optical excitation processes in molecules. It provides real-time maps of particles and holes which gives information on excitations, in particular those that have charge-transfer character, that cannot be obtained from the density alone. Some illustration of the TDM and comparison with standard density difference plots will be shown for photoexcited organic donor-acceptor molecules. This work is supported by NSF Grant DMR-1005651

  15. 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.

  16. 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.

  17. 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.

  18. Dissociation of charge-transfer states at donor-acceptor interfaces of organic heterojunctions

    Science.gov (United States)

    Inche Ibrahim, M. L.

    2017-02-01

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

  19. Analysis of the magnetic coupling in binuclear systems. III. The role of the ligand to metal charge transfer excitations revisited

    Science.gov (United States)

    Calzado, Carmen J.; Angeli, Celestino; Taratiel, David; Caballol, Rosa; Malrieu, Jean-Paul

    2009-07-01

    In magnetic coordination compounds and solids the magnetic orbitals are essentially located on metallic centers but present some delocalization tails on adjacent ligands. Mean field variational calculations optimize this mixing and validate a single band modelization of the intersite magnetic exchange. In this approach, due to the Brillouin's theorem, the ligand to metal charge transfer (LMCT) excitations play a minor role. On the other hand the extensive configuration interaction calculations show that the determinants obtained by a single excitation on the top of the LMCT configurations bring an important antiferromagnetic contribution to the magnetic coupling. Perturbative and truncated variational calculations show that contrary to the interpretation given in a previous article [C. J. Calzado et al., J. Chem. Phys. 116, 2728 (2002)] the contribution of these determinants to the magnetic coupling constant is not a second-order one. An analytic development enables one to establish that they contribute at higher order as a correlation induced increase in the LMCT components of the wave function, i.e., of the mixing between the ligand and the magnetic orbitals. This larger delocalization of the magnetic orbitals results in an increase in both the ferro- and antiferromagnetic contributions to the coupling constant.

  20. Effect of Molecular Packing and Charge Delocalization on the Nonradiative Recombination of Charge-Transfer States in Organic Solar Cells

    KAUST Repository

    Chen, Xian Kai

    2016-09-05

    In organic solar cells, a major source of energy loss is attributed to nonradiative recombination from the interfacial charge transfer states to the ground state. By taking pentacene–C60 complexes as model donor–acceptor systems, a comprehensive theoretical understanding of how molecular packing and charge delocalization impact these nonradiative recombination rates at donor–acceptor interfaces is provided.

  1. Combination of transient 2D-IR experiments and ab initio computations sheds light on the formation of the charge-transfer state in photoexcited carbonyl carotenoids.

    Science.gov (United States)

    Di Donato, Mariangela; Segado Centellas, Mireia; Lapini, Andrea; Lima, Manuela; Avila, Francisco; Santoro, Fabrizio; Cappelli, Chiara; Righini, Roberto

    2014-08-14

    The excited state dynamics of carbonyl carotenoids is very complex because of the coupling of single- and doubly excited states and the possible involvement of intramolecular charge-transfer (ICT) states. In this contribution we employ ultrafast infrared spectroscopy and theoretical computations to investigate the relaxation dynamics of trans-8'-apo-β-carotenal occurring on the picosecond time scale, after excitation in the S2 state. In a (slightly) polar solvent like chloroform, one-dimensional (T1D-IR) and two-dimensional (T2D-IR) transient infrared spectroscopy reveal spectral components with characteristic frequencies and lifetimes that are not observed in nonpolar solvents (cyclohexane). Combining experimental evidence with an analysis of CASPT2//CASSCF ground and excited state minima and energy profiles, complemented with TDDFT calculations in gas phase and in solvent, we propose a photochemical decay mechanism for this system where only the bright single-excited 1Bu(+) and the dark double-excited 2Ag(-) states are involved. Specifically, the initially populated 1Bu(+) relaxes toward 2Ag(-) in 200 fs. In a nonpolar solvent 2Ag(-) decays to the ground state (GS) in 25 ps. In polar solvents, distortions along twisting modes of the chain promote a repopulation of the 1Bu(+) state which then quickly relaxes to the GS (18 ps in chloroform). The 1Bu(+) state has a high electric dipole and is the main contributor to the charge-transfer state involved in the dynamics in polar solvents. The 2Ag(-) → 1Bu(+) population transfer is evidenced by a cross peak on the T2D-IR map revealing that the motions along the same stretching of the conjugated chain on the 2Ag(-) and 1Bu(+) states are coupled.

  2. Excited states

    CERN Document Server

    Lim, Edward C

    1974-01-01

    Excited States, Volume I reviews radiationless transitions, phosphorescence microwave double resonance through optical spectra in molecular solids, dipole moments in excited states, luminescence of polar molecules, and the problem of interstate interaction in aromatic carbonyl compounds. The book discusses the molecular electronic radiationless transitions; the double resonance techniques and the relaxation mechanisms involving the lowest triplet state of aromatic compounds; as well as the optical spectra and relaxation in molecular solids. The text also describes dipole moments and polarizab

  3. Further evidence for charge transfer complexes in brown carbon aerosols from excitation-emission matrix fluorescence spectroscopy.

    Science.gov (United States)

    Phillips, Sabrina M; Smith, Geoffrey D

    2015-05-14

    The light-absorbing fraction of organic molecules in ambient aerosols, known as "brown carbon," is an important yet poorly characterized component. Despite the fact that brown carbon could alter the radiative forcing of aerosols significantly, identification of specific chromophores has remained challenging. We recently demonstrated that charge transfer (CT) complexes formed in organic molecules could be responsible for a large fraction of absorption observed in water-extracted ambient particulate matter.1 In the present study, we use excitation-emission matrix fluorescence spectroscopy to further corroborate the importance of CT complexes in defining aerosol optical properties. Monotonically increasing and decreasing quantum yields, decreasing Stokes shifts, and red-shifting emission maxima are observed from ambient particulate matter collected in Athens, Georgia, strongly suggesting that a superposition of independent chromophores is not sufficient to explain brown carbon absorption and fluorescence. Instead, we show that a model in which such chromophores are energetically coupled to a dense manifold of CT complexes is consistent with all of the observations. Further, we suggest that a significant fraction of the observed fluorescence originates from CT complexes and that their contribution to brown carbon absorption is likely greater than we reported previously.

  4. Excitation and charge transfer in low-energy hydrogen atom collisions with neutral atoms: Theory, comparisons, and application to Ca

    CERN Document Server

    Barklem, Paul S

    2016-01-01

    A theoretical method for the estimation of cross sections and rates for excitation and charge transfer processes in low-energy hydrogen atom collisions with neutral atoms, based on an asymptotic two-electron model of ionic-covalent interactions in the neutral atom-hydrogen atom system, is presented. The calculation of potentials and non-adiabatic radial couplings using the method is demonstrated. The potentials are used together with the multi-channel Landau-Zener model to calculate cross sections and rate coefficients. The main feature of the method is that it employs asymptotically exact atomic wavefunctions, which can be determined from known atomic parameters. The method is applied to Li+H, Na+H, and Mg+H collisions, and the results compare well with existing detailed full-quantum calculations. The method is applied to the astrophysically important problem of Ca+H collisions, and rate coefficients are calculated for temperatures in the range 1000-20000 K.

  5. The interplay between neutral exciton and charge transfer states in single-strand polyadenine: a quantum dynamical investigation.

    Science.gov (United States)

    Santoro, Fabrizio; Improta, Roberto; Avila, Francisco; Segado, Mireia; Lami, Alessandro

    2013-08-01

    We investigate the quantum dynamics of the internal conversion of excitons into charge transfer (CT) states in single-strand oligomers of adenine (An) of different length (n up to 10 units) excited by a short-time laser pulse. Calculations are based on a model vibronic Hamiltonian whose parameters are fitted to accurate time-dependent density functional theory (TD-DFT) calculations, which was shown to reproduce the experimental absorption spectrum with the increase of n. As a first step, we analyze the impact of the vibrational motion on the population transfer in the dimer, highlighting that it causes loss of coherence and slows down the dynamics. For longer oligomers we resort to a simplified approach considering only electronic states and solving the equation of motion for the density matrix driven by inter-state couplings. In this way we are able also to include phenomenologically dephasing terms that mainly simulate intra-molecular effects, and lifetimes of local excitations mimicking monomer-like decay processes. Relaxation effects, whose role is to drive the system towards the thermal equilibrium allowing population exchange among states, are deliberately not considered here, since the focus is on very short-time dynamics. We consider both the cases of an instantaneous and of a finite-time (full width at half maximum 50 fs) laser pulse. According to our calculations, the photoexcited oligomers exhibit a complex dynamics and CT population rises on a 20-30 fs timescale and it persists even on the picosecond timescale. CT population increases with the length of the oligomer and it is only weakly dependent on the relative stability of CT and exciton states (within a range of 1500 cm(-1)). The chain length already modifies the photoexcited dynamics for A2 and A4 systems, but this effect saturates for small n so that the A10 oligomer is also representative of longer chains.

  6. Proton-transfer mediated quenching of pyrene/indole charge-transfer states in isooctane solutions.

    Science.gov (United States)

    Altamirano, Marcela S; Bohorquez, María del Valle; Previtali, Carlos M; Chesta, Carlos A

    2008-01-31

    The fluorescence quenching of pyrene (Py) by a series of N-methyl and N-H substituted indoles was studied in isooctane at 298 K. The fluorescence quenching rate constants were evaluated by mean of steady-state and time-resolved measurements. In all cases, the quenching process involves a charge-transfer (CT) mechanism. The I(o)/I and tau(o)/tau Stern-Volmer plots obtained for the N-H indoles show a very unusual upward deviation with increasing concentration of the quenchers. This behavior is attributed to the self-quenching of the CT intermediates by the free indoles in solution. The efficiency of quenching of the polyaromatic by the N-H indoles increases abruptly in the presence of small amount of added pyridine (or propanol). A detailed analysis of the experimental data obtained in the presence of pyridine provides unambiguous evidence that the self-quenching process involves proton transfer from the CT states to indoles.

  7. Charge transfer and triplet states in OPV materials and devices (Presentation Recording)

    Science.gov (United States)

    Dyakonov, Vladimir

    2015-10-01

    Electron back transfer (EBT), potentially occurring after electron transfer from donor to acceptor may populate the lower lying donor or acceptor triplet state and serve as recombination channel.[1] Here we report on studies of charge transfer and triplet states in blends of highly efficient benzodithiophene PTB7 polymer in combination with the fullerene-derivative PC71BM using the spin sensitive optically detected magnetic resonance (ODMR) technique and compare the results with those obtained in P3HT (poly(3- hexylthiophene):PC61BM blends. Although PTB7:PC71BM absorbers yield much higher power conversion efficiencies in solar cells exceeding 7%, we found a significant increase of triplet exciton generation, which was absent in the P3HT based blends. We discuss this observation within the EBT scenario with the emphasis on the influence of morphology, fullerene load, HOMO/LUMO energy and presence of additives (DIO). Suppressing the EBT process by morphology and/or energetics of polymer and molecules is important to achieve the full potential of highly efficient OPV materials. [1] M. Liedtke, et al., JACS 133, 9088 (2011).

  8. Probing of Charge Transfer States at Buried Organic Interfaces with Even-Order Spectroscopy

    Science.gov (United States)

    Pandey, Ravindra; Moon, Aaron; Roberts, Sean

    Organic thin film photovoltaics (OPV) are an emerging economically competitive technology that combines manufacturing adaptability, low-cost processing and a lightweight, flexible device end-product. At junctions formed between organic electron-donating and electron-accepting materials, the abrupt change in the dielectric properties can strongly perturb the density of states of the OPV. This can substantially alter the driving force for charge transfer between these materials. Electronic Sum Frequency Generation (ESFG), owing to its inherent interfacial sensitivity, is ideally suited to probe buried interfaces. Here, we report the ESFG spectra of Copper Phthalocyanine (CuPc) films, deposited on SiO2 measured for both reflection and transmission geometries. Three peaks are observed that roughly correlate with resonances that comprise CuPc's Q-band absorption but display slight shifts and amplitude changes with respect to CuPc's bulk absorption spectrum. Experimental results are compared with calculations based on a thin film interference model that accounts for ESFG emitted from both the CuPc:Air and CuPc:SiO2 interface as well as contributions to the signal from higher order source terms from the bulk. The model reveals a difference in the density of states between the two interfaces and suggests that by combining experimental transmission and reflection data it is possible to separate bulk and interfacial contributions to ESFG spectra.

  9. Explicit solvent DRF INDOs/CIS computations of charge transfer state energetics in a pyrenyldeoxyuridine nucleoside model.

    Science.gov (United States)

    Van Duijnen, Piet Th; Netzel, Thomas L

    2006-02-16

    In this work we present calculated absorption and emission spectra in acetonitrile (MeCN) solution of N-acetyl-1-aminopyrene (PAAc, a spectroscopic model compound) and N-(1-pyrenyl)-1-methyluracil-5-carboxamide (PAU(Me), a computational model for 5-(N-carboxyl-1-aminopyrenyl)-2'-deoxyuridine (PAdU)). The computational method used--the discrete reaction field approach (DRF)--combines a quantum mechanical (QM) description of the solute (here DFT and INDOs/CIS, i.e., the INDO parametrization for spectroscopy) with a classical, molecular mechanics (MM) description of the solvent molecules. The latter are modeled with point charges representing the permanent charge distribution and polarizabilities to account for many-body interactions among the solute and other solvent molecules. Molecular dynamics is used to sample the degrees of freedom of the solution around several solute conformations each in two electronic excited states. This leads to a large number of solute/solvent configurations from which 800 are selected for each excited state and collected into a single ensemble by means of proper Boltzmann averaging. DRF INDOs/CIS applied to the selected solute/solvent configurations give simulated absorption and emission band spectra--each based on 15,200 calculated transitions--that compare well with experimental results. For example, the much broader absorption and emission bands in PAdU compared with PAAc are reproduced, and the simulated emission spectra of PAU(Me) agree well with broad (380-550 nm) charge transfer (CT) emission seen for PAdU in MeCN. The observed multiexponential fluorescence decay profiles for PAdU in different polar solvents are interpreted in terms of solute/solvent conformational heterogeneity here generated in the MD simulations for PAU(Me) in MeCN. Additionally, the simulations demonstrate the mixing of the forbidden Py*+/dU*- CT states with allowed pyrenyl 1(pi,pi*) states.

  10. Direct and charge transfer state mediated photogeneration in polymer-fullerene bulk heterojunction solar cells

    Science.gov (United States)

    Mingebach, M.; Walter, S.; Dyakonov, V.; Deibel, C.

    2012-05-01

    We investigated photogeneration yield and recombination dynamics in blends of poly(3-hexyl thiophene) (P3HT) and poly[2-methoxy-5 -(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) with [6,6]-phenyl-C61butyric acid methyl ester (PC61BM) by means of temperature dependent time delayed collection field measurements. In MDMO-PPV:PC61BM, we find a strongly field dependent polaron pair dissociation which can be attributed to geminate recombination in the device. Our findings are in good agreement with field dependent photoluminescence measurements published before, supporting a scenario of polaron pair dissociation via an intermediate charge transfer state. In contrast, polaron pair dissociation in P3HT:PC61BM shows only a very weak field dependence, indicating an almost field independent polaron pair dissociation or a direct photogeneration. Furthermore, we found Langevin recombination for MDMO-PPV:PC61BM and strongly reduced Langevin recombination for P3HT:PC61BM.

  11. 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.

  12. Understanding the charge-transfer state and singlet exciton emission from solution-processed small-molecule organic solar cells.

    Science.gov (United States)

    Ran, Niva A; Kuik, Martijn; Love, John A; Proctor, Christopher M; Nagao, Ikuhiro; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2014-11-19

    Electroluminescence (EL) from the charge-transfer state and singlet excitons is observed at low applied voltages from high-performing small-molecule bulk-heterojunction solar cells. Singlet emission from the blends emerges upon altering the processing conditions, such as thermal annealing and processing with a solvent additive, and correlates with improved photovoltaic performance. Low-temperature EL measurements are utilized to access the physics behind the singlet emission.

  13. Luminescence from the ligand to metal charge transfer state of the neptunyl (V) ion and its complexes in solution

    Energy Technology Data Exchange (ETDEWEB)

    Bradshaw, Rebecca; Sykes, Daniel; Faulkner, Stephen [University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford (United Kingdom); Natrajan, Louise S; Livens, Francis R [Centre for Radiochemistry Research, School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Taylor, Robin J, E-mail: Stephen.Faulkner@chem.ox.ac.uk [Central Laboratory, National Nuclear Laboratory, Sellafield, Seascale, Cumbria, CA20 1PG (United Kingdom)

    2010-03-15

    The photophysical properties of the neptunyl (V) ion in aqueous solution have been studied using time-resolved luminescence spectroscopy. While any f-f transitions in emission are too weak to detect using available technology, the ligand to metal charge transfer state is emissive in the visible part of the spectrum. Both the aquo ion and its complexes with bidentate ligands exhibit biexponential decay kinetics, which can be rationalised by slow exchange on the timescale of the experiment.

  14. Charge-transfer (CT) orbitals for the one-electron description of CT excitations in a wide range of donor-acceptor separations

    Science.gov (United States)

    Gritsenko, O. V.

    2017-01-01

    A transformation of the virtual Kohn-Sham orbitals is proposed to a set of charge-transfer orbitals (CTOs) adapted to description of CT excitations. The CTO scheme offers a simple estimate of the CT excitation energy with an orbital energy difference. This estimate reproduces well the reference values of the configuration interaction (CI) method in a wide range of donor-acceptor separations in the paradigmatic He -Be complex. CTO-based orbital energy and shape indices are proposed to assess the suitability of the CT description with virtual orbitals of a given basis set. Both indices yield correct trends for the Kohn-Sham and Hartree-Fock orbitals.

  15. Intermolecular-charge-transfer-induced fluorescence quenching in protic solvent

    Science.gov (United States)

    Lin, Tao; Liu, Xiaojun; Lou, Zhidong; Hou, Yanbing; Teng, Feng

    2016-11-01

    The fluorescence quenching of fluorenone in protic solvent has been extensively investigated, and the intermolecular hydrogen bond was found to play a crucial role. Unfortunately, the mechanism at atomic level is still not clear. In the present work, we theoretically put forward the charge transfer along the hydrogen bond in the excited states. The vertical excitation energies of the fluorenone-methanol complex as well as the potential energy profiles and surfaces of the vertical excited states and charge transfer states were calculated by using the ab initio electronic-structure methods. The photochemical reactions occurring in the diverse charge transfer states were compared and their decisiveness to the fluorescence quenching was discussed in the paper.

  16. 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.

  17. 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.

  18. Charge-transfer excitations in low-gap systems under the influence of solvation and conformational disorder: Exploring range-separation tuning

    Energy Technology Data Exchange (ETDEWEB)

    Queiroz, Thiago B. de, E-mail: thiago.branquinho-de-queiroz@uni-bayreuth.de; Kümmel, Stephan [Theoretical Physics IV, University of Bayreuth, D-95440 Bayreuth (Germany)

    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.

  19. Ground-state oxygen holes and the metal-insulator transition in the negative charge-transfer rare-earth nickelates

    Science.gov (United States)

    Bisogni, Valentina; Catalano, Sara; Green, Robert J.; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N.; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten

    2016-10-01

    The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal-insulator transition in terms of bond disproportionation.

  20. 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.

  1. Primary optical excitations and excited-state interaction energies in sexithiophene

    NARCIS (Netherlands)

    Loi, MA; Martin, C; Chandrasekhar, HR; Chandrasekhar, M; Graupner, W; Garnier, F; Mura, A; Bongiovanni, G

    2002-01-01

    Based on a unique combination of angle-resolved transmission spectroscopy and transmission data at high pressure, we identify the primary photoexcitations and the relevant excited-state interaction energies in a sexithiophene crystal. Optical excitations include charge-transfer excitons and Davydov

  2. Magneto-photocurrent in organic photovoltaic cells; the effect of short-lived charge transfer states

    Science.gov (United States)

    Ehrenfreund, Eitan; Devir-Wolfman, A.; Khachatryan, B.; Gautam, B.; Tessler, N.; Vardeny, Z. V.

    2014-03-01

    The spin degrees of freedom are responsible for the magnetic field effects in organic devices at low magnetic fields. The MFE is formed via a variety of spin-mixing mechanisms, such as the hyperfine (typical strength: Bhf<0.003 T), triplet-polaron or triplet-triplet (Btrip<0.1 T) interactions, that limit the response by their respective strength. We report on magneto-photocurrent (MPC) response of bulk hetero-junction organic photovoltaic cells in an extended field range B =0.00005 - 8 Tesla, and found that spin mixing mechanisms are still operative even at the highest fields. In fact, the response MPC(B) can be divided into three main regions, each with a different sign: sharp response that increases with B up to B1 ~ 0.04 T; broad response that decreases with B in the range from B1 to B2 ~ 0.3-0.7 T; and even broader response that increases above B2; this response does not saturate even at 8.5 T. We attribute the latter MPC component to short-lived charge transfer excitons (CTE) where spin-mixing is caused by the difference of the donor/acceptor g factors; a mechanism that is increasingly more effective at high magnetic field. Supported by the US-Israel BSF.

  3. Assessment of Charge-Transfer Excitations in Organic Dyes obtained from TD-srDFT Based on Long-Range MP2 and MCSCF Wave Functions

    CERN Document Server

    Hedegård, Erik D; Knecht, Stefan; Fromager, Emmanuel; Jensen, Hans Jørgen Aa

    2013-01-01

    Charge transfer excitations can be described within TD-DFT, not only by means of long-range corrected exchange functionals but also with a combination of wave function theory and TD-DFT based on range separation. The latter approach enables a rigorous formulation of multi-determinantal TD-DFT schemes where excitation classes, which are absent in conventional TD-DFT spectra (like for example double excitations), can be addressed. This paper investigates the combination of both the long-range MCSCF and SOPPA ans\\"atze with a short-range DFT (srDFT) description. We find that the combinations of SOPPA or MCSCF with TD-DFT yield better results than could be expected from the pure wave function schemes. For the Time-Dependent MCSCF short-range DFT ansatz (TD-MC-srDFT) excitation energies calculated over a larger benchmark set of molecules with predominantly single reference character yield good agreement with their reference values, and are in general comparable to the long-range corrected functional CAM-B3LYP. The...

  4. 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.

  5. Conformational control of benzophenone-sensitized charge transfer in dinucleotides.

    Science.gov (United States)

    Merz, Thomas; Wenninger, Matthias; Weinberger, Michael; Riedle, Eberhard; Wagenknecht, Hans-Achim; Schütz, Martin

    2013-11-14

    Charge transfer in DNA cannot be understood without addressing the complex conformational flexibility, which occurs on a wide range of timescales. In order to reduce this complexity four dinucleotide models 1X consisting of benzophenone linked by a phosphodiester to one of the natural nucleosides X = A, G, T, C were studied in water and methanol. The theoretical work focuses on the dynamics and electronic structure of 1G. Predominant conformations in the two solvents were obtained by molecular dynamics simulations. 1G in MeOH adopts mainly an open geometry with a distance of 12–16 Å between the two aromatic parts. In H2O the two parts of 1G form primarily a stacked conformation yielding a distance of 5–6 Å. The low-lying excited states were investigated by electronic structure theory in a QM/MM environment for representative snapshots of the trajectories. Photo-induced intramolecular charge transfer in the S1 state occurs exclusively in the stacked conformation. Ultrafast transient absorption spectroscopy with 1X reveals fast charge transfer from S1 in both solvents with varying yields. Significant charge transfer from the T1 state is only found for the nucleobases with the lowest oxidation potential: in H2O, charge transfer occurs with 3.2 × 10(9) s(-1) for 1A and 6.0 × 10(9) s(-1) for 1G. The reorganization energy remains nearly unchanged going from MeOH to the more polar H2O. The electronic coupling is rather low even for the stacked conformation with H(AB) = 3 meV and explains the moderate charge transfer rates. The solvent controls the conformational distribution and therefore gates the charge transfer due to differences in distance and stacking.

  6. Hydrogen Bonds in Excited State Proton Transfer

    Science.gov (United States)

    Horke, D. A.; Watts, H. M.; Smith, A. D.; Jager, E.; Springate, E.; Alexander, O.; Cacho, C.; Chapman, R. T.; Minns, R. S.

    2016-10-01

    Hydrogen bonding interactions between biological chromophores and their surrounding protein and solvent environment significantly affect the photochemical pathways of the chromophore and its biological function. A common first step in the dynamics of these systems is excited state proton transfer between the noncovalently bound molecules, which stabilizes the system against dissociation and principally alters relaxation pathways. Despite such fundamental importance, studying excited state proton transfer across a hydrogen bond has proven difficult, leaving uncertainties about the mechanism. Through time-resolved photoelectron imaging measurements, we demonstrate how the addition of a single hydrogen bond and the opening of an excited state proton transfer channel dramatically changes the outcome of a photochemical reaction, from rapid dissociation in the isolated chromophore to efficient stabilization and ground state recovery in the hydrogen bonded case, and uncover the mechanism of excited state proton transfer at a hydrogen bond, which follows sequential hydrogen and charge transfer processes.

  7. 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.

  8. 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.

  9. Asymptotic correction of the exchange-correlation kernel of time-dependent density functional theory for long-range charge-transfer excitations.

    Science.gov (United States)

    Gritsenko, Oleg; Baerends, Evert Jan

    2004-07-08

    Time-dependent density functional theory (TDDFT) calculations of charge-transfer excitation energies omegaCT are significantly in error when the adiabatic local density approximation (ALDA) is employed for the exchange-correlation kernel fxc. We relate the error to the physical meaning of the orbital energy of the Kohn-Sham lowest unoccupied molecular orbital (LUMO). The LUMO orbital energy in Kohn-Sham DFT--in contrast to the Hartree-Fock model--approximates an excited electron, which is correct for excitations in compact molecules. In CT transitions the energy of the LUMO of the acceptor molecule should instead describe an added electron, i.e., approximate the electron affinity. To obtain a contribution that compensates for the difference, a specific divergence of fxc is required in rigorous TDDFT, and a suitable asymptotically correct form of the kernel fxc(asymp) is proposed. The importance of the asymptotic correction of fxc is demonstrated with the calculation of omegaCT(R) for the prototype diatomic system HeBe at various separations R(He-Be). The TDDFT-ALDA curve omegaCT(R) roughly resembles the benchmark ab initio curve omegaCT CISD(R) of a configuration interaction calculation with single and double excitations in the region R=1-1.5 A, where a sizable He-Be interaction exists, but exhibits the wrong behavior omegaCT(R)excitations in compact systems and fxc(asymp) for weakly interacting fragments and suitable interpolation expressions are considered.

  10. Ultrafast investigation of photoinduced charge transfer in aminoanthraquinone pharmaceutical product

    Science.gov (United States)

    Zhang, Song; Sun, Simei; Zhou, Miaomiao; Wang, Lian; Zhang, Bing

    2017-01-01

    We investigated the mechanism of intramolecular charge transfer and the following radiationless dynamics of the excited states of 1-aminoanthraquinone using steady state and time-resolved absorption spectroscopy combined with quantum chemical calculations. Following photoexcitation with 460 nm, conformational relaxation via twisting of the amino group, charge transfer and the intersystem crossing (ISC) processes have been established to be the major relaxation pathways responsible for the ultrafast nonradiative of the excited S1 state. Intramolecular proton transfer, which could be induced by intramolecular hydrogen bonding is inspected and excluded. Time-dependent density functional theory (TDDFT) calculations reveal the change of the dipole moments of the S0 and S1 states along the twisted coordinate of the amino group, indicating the mechanism of twisted intra-molecular charge transfer (TICT). The timescale of TICT is measured to be 5 ps due to the conformational relaxation and a barrier on the S1 potential surface. The ISC from the S1 state to the triplet manifold is a main deactivation pathway with the decay time of 28 ps. Our results observed here have yield a physically intuitive and complete picture of the photoinduced charge transfer and radiationless dynamics in anthraquinone pharmaceutial products. PMID:28233835

  11. The role of emissive charge transfer states in two polymer-fullerene organic photovoltaic blends : tuning charge photogeneration through the use of processing additives

    NARCIS (Netherlands)

    Clarke, Tracey M.; Peet, Jeff; Lungenschmied, Christoph; Drolet, Nicolas; Lu, Xinhui; Ocko, Benjamin M.; Mozer, Attila J.; Loi, Maria Antonietta

    2014-01-01

    The role of charge transfer (CT) states in organic photovoltaic systems has been debated in the recent literature. In this paper the device performances of two structurally analogous polymers PDTSiTTz (also known as KP115) and PCPDTTTz blended with PCBM are investigated, focusing on the effect the p

  12. Block-Localized Wavefunction (BLW) Based Two-State Approach for Charge Transfers between Phenyl Rings.

    Science.gov (United States)

    Mo, Yirong; Song, Lingchun; Lin, Yuchun; Liu, Minghong; Cao, Zexing; Wu, Wei

    2012-03-13

    The block-localized wave function (BLW) method is the simplest and most efficient variant of ab initio valence bond (VB) theory which defines electron-localized resonance states following the conventional VB concepts. Here, a BLW-based two-state approach is proposed to probe the charge/hole transfer reactions within the Marcus-Hush model. With this approach, both the electronic coupling and reorganization energies can be derived at the ab initio level. Pilot applications to the electron/hole transfers between two phenyl rings are presented. Good exponential correlation between the electronic coupling energy and the donor-acceptor distance is shown, whereas the inner-sphere reorganization shows little geometric dependency. Computations also support the assumption in Marcus theory that the thermal electron transfer barrier (ΔG*), which is a sum of the reaction barrier (ΔEa) for electron/hole transfer and the coupling energy (VAB), is a quarter of the reorganization energy (λ).

  13. 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.

  14. Investigation of the charge-transfer in photo-excited nanoparticles for CO2 reduction in non-aqueous media

    Directory of Open Access Journals (Sweden)

    Dimitrijević Nada M.

    2013-01-01

    Full Text Available Photoinduced charge separation in TiO2 and Cu2O semiconductor nanoparticles was examined using Electron Paramagnetic Resonance spectroscopy in order to get insight into the photocatalytic reduction of CO2 in nonaqueous media. For dissolution/grafting of CO2 we have used carboxy-PEG4-amine, and as a solvent poly(ethylene glycol 200. We have found that, in this system, reduction of CO2 starts at potential of -0.5 V vs Ag/AgCl, which is significantly more positive than the potential for electrochemical reduction of CO2 in most organic solvents and water (-2.0 V vs. Ag/AgCl. The electron transfer from excited nanoparticles to CO2 is governed both by thermodynamic and kinetic parameters, namely by the redox potential of conduction band electrons and adsorption/binding of CO2 on the surface of nanoparticles.

  15. Charge transfer excitation of trivalent rare earth ions Sm/sup 3+/, Eu/sup 3+/, Gd/sup 3+/, Ho/sup 3+/, Er/sup 3+/ and Yb/sup 3+/ emission in BaFCl crystals

    Energy Technology Data Exchange (ETDEWEB)

    Su, M.Z.; Sun, X.P.

    1987-01-01

    The charge transfer type excitation spectra of trivalent rare earth ions Sm/sup 3+/, Eu/sup 3+/, Gd/sup 3+/, Ho/sup 3+/, Er/sup 3+/ and Yb/sup 3+/ emission in BaFCl crystals have been studied. The charge transfer type emissions of Ho/sup 3+/, Er/sup 3+/ and Yb/sup 3+/ in BaFCl have also been observed in addition to that of Eu/sup 3+/. The energy of charge transfer band of these RE/sup 3+/ ions were estimated experimentally and also calculated by Jorgensen's refined electron spin-pairing energy theory. Both the experimental and calculated values coincide well.

  16. Charge transfer of edge states in zigzag silicene nanoribbons with Stone–Wales defects from first-principles

    Energy Technology Data Exchange (ETDEWEB)

    Ting, Xie [College of Mathematics and Statistics, Chongqing University, Chongqing 401331 (China); School of Mathematics and Statistic, Chongqing University of Technology, Chongqing 400054 (China); Rui, Wang, E-mail: rcwang@cqu.edu.cn [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China); State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Science, Beijing 100190 (China); Shaofeng, Wang [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China); Xiaozhi, Wu, E-mail: xiaozhiwu@cqu.edu.cn [Institute for Structure and Function and Department of Physics, Chongqing University, Chongqing 400044 (China)

    2016-10-15

    Highlights: • The properties of SW defects in silicene and ZSNRs are obtained. • The SW defects at the edge of ZSNRs induce a sizable gap. • The charge transfer of edge states is resulted from SW defects in ZSNRS. - Abstract: Stone–Wales (SW) defects are favorably existed in graphene-like materials with honeycomb lattice structure and potentially employed to change the electronic properties in band engineering. In this paper, we investigate structural and electronic properties of SW defects in silicene sheet and its nanoribbons as a function of their concentration using the methods of periodic boundary conditions with first-principles calculations. We first calculate the formation energy, structural properties, and electronic band structures of SW defects in silicene sheet, with dependence on the concentration of SW defects. Our results show a good agreement with available values from the previous first-principles calculations. The energetics, structural aspects, and electronic properties of SW defects with dependence on defect concentration and location in edge-hydrogenated zigzag silicene nanoribbons are obtained. For all calculated concentrations, the SW defects prefer to locate at the edge due to the lower formation energy. The SW defects at the center of silicene nanoribbons slightly influence on the electronic properties, whereas the SW defects at the edge of silicene nanoribbons split the degenerate edge states and induce a sizable gap, which depends on the concentration of defects. It is worth to find that the SW defects produce a perturbation repulsive potential, which leads the decomposed charge of edge states at the side with defect to transfer to the other side without defect.

  17. Surface-state-mediated charge-transfer dynamics in CdTe/CdSe core-shell quantum dots.

    Science.gov (United States)

    Rawalekar, Sachin; Kaniyankandy, Sreejith; Verma, Sandeep; Ghosh, Hirendra N

    2011-06-20

    Herein, we report the synthesis of aqueous CdTe/CdSe type-II core-shell quantum dots (QDs) in which 3-mercaptopropionic acid is used as the capping agent. The CdTe QDs and CdTe/CdSe core-shell QDs are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), steady-state absorption, and emission spectroscopy. A red shift in the steady-state absorption and emission bands is observed with increasing CdSe shell thickness over CdTe QDs. The XRD pattern indicates that the peaks are shifted to higher angles after growth of the CdSe shell on the CdTe QDs. HR-TEM images of both CdTe and CdTe/CdSe QDs indicate that the particles are spherical, with a good shape homogeneity, and that the particle size increases by about 2 nm after shell formation. In the time-resolved emission studies, we observe that the average emission lifetime (τ(av)) increases to 23.5 ns for CdTe/CdSe (for the thickest shell) as compared to CdTe QDs (τ(av) =12 ns). The twofold increment in the average emission lifetime indicates an efficient charge separation in type-II CdTe/CdSe core-shell QDs. Transient absorption studies suggest that both the carrier cooling and the charge-transfer dynamics are affected by the presence of traps in the CdTe QDs and CdTe/CdSe core-shell QDs. Carrier quenching experiments indicate that hole traps strongly affect the carrier cooling dynamics in CdTe/CdSe core-shell QDs.

  18. Charge transfer mechanism for the formation of metallic states at the KTaO3/SrTiO3 interface

    KAUST Repository

    Nazir, Safdar

    2011-03-29

    The electronic and optical properties of the KTaO3/SrTiO3 heterointerface are analyzed by the full-potential linearized augmented plane-wave approach of density functional theory. Optimization of the atomic positions points at subordinate changes in the crystal structure and chemical bonding near the interface, which is due to a minimal lattice mismatch. The creation of metallic interface states thus is not affected by structural relaxation but can be explained by charge transfer between transition metal and oxygen atoms. It is to be expected that a charge transfer is likewise important for related interfaces such as LaAlO3/SrTiO3. The KTaO3/SrTiO3 system is ideal for disentangling the complex behavior of metallic interface states, since almost no structural relaxation takes place.

  19. Correlational analysis of Eu3+ charge transfer state using La effective charge in La-based mixed-anion host compounds

    Science.gov (United States)

    Yoshimatsu, Ryo; Okada, Masahiro; Ishigaki, Tadashi; Watanabe, Shinta; Honma, Tetsuo; Ohmi, Koutoku

    2017-03-01

    A prediction of the Eu3+ charge transfer state (E CT) was attempted in La-based mixed-anion host compounds. We paid attention to La3OF3S2:Eu, since it is expected to have a more covalent La site than La2O2S. The La effective charge (La EC) was proposed as the index factor of covalency and/or ionicity. The correlation between the experimental E CT and the calculated La EC was systematically analyzed for La2S3, LaFS, La2O2S, La2O3, LaOF, and LaF3 host materials, and good approximation was obtained using the single exponential function with a variable number of La ECs. According to the fitting curve, the E CT of La3OF3S2:Eu was predicted to be 5.8 and 2.1 eV for Eu3+ centers activated at ionic and covalent sites, respectively. To confirm the prediction accuracy, La3OF3S2:Eu phosphor powder samples were synthesized by solid-state reaction. From the photoluminescence excitation and absorption measurements, the E CT values of about 4.7 eV (ionic La site) and 2.4 eV (covalent La site) were obtained. Even though the energy difference between the predicted and experimental values is large for the higher E CT, La EC is the useful index factor for estimating E CT. In addition, it indicates that the estimation can be applied to phosphor materials having multication sites.

  20. Donor-to-Donor vs Donor-to-Acceptor Interfacial Charge Transfer States in the Phthalocyanine-Fullerene Organic Photovoltaic System.

    Science.gov (United States)

    Lee, Myeong H; Dunietz, Barry D; Geva, Eitan

    2014-11-06

    Charge transfer (CT) states formed at the donor/acceptor heterointerface are key for photocurrent generation in organic photovoltaics (OPV). Our calculations show that interfacial donor-to-donor CT states in the phthalocyanine-fullerene OPV system may be more stable than donor-to-acceptor CT states and that they may rapidly recombine, thereby constituting a potentially critical and thus far overlooked loss mechanism. Our results provide new insight into processes that may compete with charge separation, and suggest that the efficiency for charge separation may be improved by destabilizing donor-to-donor CT states or decoupling them from other states.

  1. Excited states v.6

    CERN Document Server

    Lim, Edward C

    1982-01-01

    Excited States, Volume 6 is a collection of papers that discusses the excited states of molecules. The first paper discusses the linear polyene electronic structure and potential surfaces, considering both the theoretical and experimental approaches in such electronic states. This paper also reviews the theory of electronic structure and cites some experimental techniques on polyene excitations, polyene spectroscopic phenomenology, and those involving higher states of polyenes and their triplet states. Examples of these experimental studies of excited states involve the high-resolution one-pho

  2. Local pair natural orbitals for excited states

    Science.gov (United States)

    Helmich, Benjamin; Hättig, Christof

    2011-12-01

    We explore how in response calculations for excitation energies with wavefunction based (e.g., coupled cluster) methods the number of double excitation amplitudes can be reduced by means of truncated pair natural orbital (PNO) expansions and localized occupied orbitals. Using the CIS(D) approximation as a test model, we find that the number of double excitation amplitudes can be reduced dramatically with minor impact on the accuracy if the excited state wavefunction is expanded in state-specific PNOs generated from an approximate first-order guess wavefunction. As for ground states, the PNO truncation error can also for excitation energies be controlled by a single threshold related to generalized natural occupation numbers. The best performance is found with occupied orbitals which are localized by the Pipek-Mezey localization. For a large test set of excited states we find with this localization that already a PNO threshold of 10-8-10-7, corresponding to an average of only 40-80 PNOs per pair, is sufficient to keep the PNO truncation error for vertical excitation energies below 0.01 eV. This is a significantly more rapid convergence with the number doubles amplitudes than in domain-based local response approaches. We demonstrate that the number of significant excited state PNOs scales asymptotically linearly with the system size in the worst case of completely delocalized excitations and sub-linearly whenever the chromophore does not increase with the system size. Moreover, we observe that the flexibility of state-specific PNOs to adapt to the character of an excitation allows for an almost unbiased treatment of local, delocalized and charge transfer excited states.

  3. Local pair natural orbitals for excited states.

    Science.gov (United States)

    Helmich, Benjamin; Hättig, Christof

    2011-12-07

    We explore how in response calculations for excitation energies with wavefunction based (e.g., coupled cluster) methods the number of double excitation amplitudes can be reduced by means of truncated pair natural orbital (PNO) expansions and localized occupied orbitals. Using the CIS(D) approximation as a test model, we find that the number of double excitation amplitudes can be reduced dramatically with minor impact on the accuracy if the excited state wavefunction is expanded in state-specific PNOs generated from an approximate first-order guess wavefunction. As for ground states, the PNO truncation error can also for excitation energies be controlled by a single threshold related to generalized natural occupation numbers. The best performance is found with occupied orbitals which are localized by the Pipek-Mezey localization. For a large test set of excited states we find with this localization that already a PNO threshold of 10(-8)-10(-7), corresponding to an average of only 40-80 PNOs per pair, is sufficient to keep the PNO truncation error for vertical excitation energies below 0.01 eV. This is a significantly more rapid convergence with the number doubles amplitudes than in domain-based local response approaches. We demonstrate that the number of significant excited state PNOs scales asymptotically linearly with the system size in the worst case of completely delocalized excitations and sub-linearly whenever the chromophore does not increase with the system size. Moreover, we observe that the flexibility of state-specific PNOs to adapt to the character of an excitation allows for an almost unbiased treatment of local, delocalized and charge transfer excited states.

  4. Photophysical studies of dipolar organic dyes that feature a 1,3-cyclohexadiene conjugated linkage: the implication of a twisted intramolecular charge-transfer state on the efficiency of dye-sensitized solar cells.

    Science.gov (United States)

    Chen, Kuan-Fu; Chang, Che-Wei; Lin, Ju-Ling; Hsu, Ying-Chan; Yeh, Ming-Chang P; Hsu, Chao-Ping; Sun, Shih-Sheng

    2010-11-15

    A detailed study of the synthesis and photophysical properties of a new series of dipolar organic photosensitizers that feature a 1,3-cyclohexadiene moiety integrated into the π-conjugated structural backbone has been carried out. Dye-sensitized solar cells (DSSCs) based on these structurally simple dyes have shown appreciable photo-to-electrical energy conversion efficiency, with the highest one up to 4.03 %. Solvent-dependent fluorescence studies along with the observation of dual emission on dye 4 b and single emission on dyes 4 a and 32 suggest that dye 4 b possesses a highly polar emissive excited state located at a lower-energy position than at the normal emissive excited state. A detailed photophysical investigation in conjunction with computational studies confirmed the twisted intramolecular charge-transfer (TICT) state to be the lowest emissive excited state for dye 4 b in polar solvents. The relaxation from higher-charge-injection excited states to the lowest TICT state renders the back-electron transfer process a forbidden one and significantly retards the charge recombination to boost the photocurrent. The electrochemical impedance under illumination and transient photovoltage decay studies showed smaller charge resistance and longer electron lifetime in 4 b-based DSSC compared to the DSSCs with reference dyes 4 a and 32, which further illustrates the positive influence of the TICT state on the performance of DSSCs.

  5. Excited states 2

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 2 is a collection of papers that deals with molecules in the excited states. The book describes the geometries of molecules in the excited electronic states. One paper describes the geometries of a diatomic molecule and of polyatomic molecules; it also discusses the determination of the many excited state geometries of molecules with two, three, or four atoms by techniques similar to diatomic spectroscopy. Another paper introduces an ordered theory related to excitons in pure and mixed molecular crystals. This paper also presents some experimental data such as those invo

  6. Excited states in DNA strands investigated by ultrafast laser spectroscopy.

    Science.gov (United States)

    Chen, Jinquan; Zhang, Yuyuan; Kohler, Bern

    2015-01-01

    Ultrafast laser experiments on carefully selected DNA model compounds probe the effects of base stacking, base pairing, and structural disorder on excited electronic states formed by UV absorption in single and double DNA strands. Direct π-orbital overlap between two stacked bases in a dinucleotide or in a longer single strand creates new excited states that decay orders of magnitude more slowly than the generally subpicosecond excited states of monomeric bases. Half or more of all excited states in single strands decay in this manner. Ultrafast mid-IR transient absorption experiments reveal that the long-lived excited states in a number of model compounds are charge transfer states formed by interbase electron transfer, which subsequently decay by charge recombination. The lifetimes of the charge transfer states are surprisingly independent of how the stacked bases are oriented, but disruption of π-stacking, either by elevating temperature or by adding a denaturing co-solvent, completely eliminates this decay channel. Time-resolved emission measurements support the conclusion that these states are populated very rapidly from initial excitons. These experiments also reveal the existence of populations of emissive excited states that decay on the nanosecond time scale. The quantum yield of these states is very small for UVB/UVC excitation, but increases at UVA wavelengths. In double strands, hydrogen bonding between bases perturbs, but does not quench, the long-lived excited states. Kinetic isotope effects on the excited-state dynamics suggest that intrastrand electron transfer may couple to interstrand proton transfer. By revealing how structure and non-covalent interactions affect excited-state dynamics, on-going experimental and theoretical studies of excited states in DNA strands can advance understanding of fundamental photophysics in other nanoscale systems.

  7. Semiconduction properties of some polyene-iodine charge-transfer complexes and their application in solid-state batteries

    Energy Technology Data Exchange (ETDEWEB)

    Sen, S.; Pal, P.; Misra, T.N. (Indian Association for the Cultivation of Science, Calcutta (India). Dept. of Spectroscopy)

    1993-03-01

    The conjugated polyenes [beta]-carotene, lutein, retinoic acid and [beta]-apo-8'-carotenal are shown to form charge-transfer (CT) complexes with the electron acceptor iodine. The conductivity increases by several orders of magnitude and the activation energy decreases on CT complex formation. Using these complexes as cathodic material, batteries with the configuration Mg/(polyene-iodine CT complex)/graphite are developed. Different battery parameters are evaluated. The effects of ambient temperature and humidity on battery performance are also studied. Results show that a [beta]-apo-8'-carotenal-1[sub 2] based battery has the maximum power density and longest self-life and is suitable for use as a micro-electronic gadget energizer. (author)

  8. Excited states 4

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 4 is a collection of papers that deals with the excited states of molecular activity. One paper investigates the resonance Raman spectroscopy as the key to vibrational-electronic coupling. This paper reviews the basic theory of Raman scattering; it also explains the derivation of the Raman spectra, excitation profiles, and depolarization ratios for simple resonance systems. Another paper reviews the magnetic properties of triplet states, including the zero-field resonance techniques, the high-field experiments, and the spin Hamiltonian. This paper focuses on the magnetic

  9. 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.

  10. Nonradiative charge transfer in collisions of protons with rubidium atoms

    Institute of Scientific and Technical Information of China (English)

    Yan Ling-Ling; Qu Yi-Zhi; Liu Chun-Hua; Zhang Yu; Wang Jian-Guo; Buenker Robert J

    2012-01-01

    The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10-3 keV 10 keV.The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region.The importance of rotational coupling for chargetransfer process is stressed.Compared with the radiative charge-transfer process,nonradiative charge transfer is a dominant mechanism at energies above 15 eV.The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail.The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

  11. 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.

  12. Ultrafast charge transfer via a conical intersection in dimethylaminobenzonitrile.

    Science.gov (United States)

    Fuss, Werner; Pushpa, Kumbil Kuttan; Rettig, Wolfgang; Schmid, Wolfram E; Trushin, Sergei A

    2002-04-01

    The L(a)-like S2 state (2A) of 4-(dimethylamino)benzonitrile was pumped at 267 nm in the gas phase at 130 degrees C. Nonresonant multiphoton ionization at 800 nm with mass-selective detection then probed the subsequent processes. Whereas ionization at the Franck-Condon geometry only gave rise to the parent ion, fragmentation increased on motion towards the charge-transfer (CT) state. This useful difference is ascribed to a geometry-dependent resonance in the ion. The time constants found are interpreted by ultrafast (approximately 68 fs) relaxation through a conical intersection to both the CT and the L(b)-type S1 state (1B). Then the population equilibrates between these two states within 1 ps. From there the molecule relaxes within 90 ps to a lower excited state which can only be a triplet state (T(n)) and then decomposes within 300 ps. Previous experiments either investigated only 1B --> CT relaxation-which does not take place in the gas phase or nonpolar solvents for energetic reasons--or, starting from S2 excitation, typically had insufficient time resolution (>1 ps) to detect the temporary charge transfer. Only recently temporary population of the CT state was found in a nonpolar solvent (Kwok et al., J. Phys. Chem. A. 2000, 104, 4188), a result fully consistent with our mechanism. We also show that S2 --> S1 relaxation does not occur vertically but involves an intermediate strong geometrical distortion, passing through a conical intersection.

  13. K-shell excitation by K- to L-shell charge transfer in slow Krsup(q+)-Kr and Xesup(q+)-Xe collisions

    Energy Technology Data Exchange (ETDEWEB)

    Schuch, R.; Justiniano, E.; Hoffmann, R. (Heidelberg Univ. (Germany, F.R.). Physikalisches Inst.); Schadt, W.; Schmidt-Boecking, H. (Frankfurt Univ. (Germany, F.R.). Inst. fuer Kernphysik); Mokler, P.H.; Bosch, F.; Schoenfeldt, W.A.; Stachura, Z. (Gesellschaft fuer Schwerionenforschung m.b.H., Darmstadt (Germany, F.R.))

    1983-06-14

    K vacancy production probabilities with decelerated highly-charged Krsup(q+) (2.8 MeV u/sup -1/) on Kr and Xesup(q+) (3.6 MeV u/sup -1/) on Xe were measured by particle-photon coincidences. The impact-parameter-dependent probabilities reveal a dramatic change in shape and absolute height as soon as the projectile bears L-shell vacancies. From a comparison with calculations it is concluded that K- to L-shell charge transfer can be described, even in the heavy collision system Xe on Xe, by the 2p..pi..-2psigma rotational coupling mechanism when the relativistic energy splitting is taken into account. Deviations from a statistical distribution of the projectile L vacancies between the molecular levels are found.

  14. Unusually Slow Electron Cooling to Charge-Transfer State in Gradient CdTeSe Alloy Nanocrystals Mediated through Mn Atom.

    Science.gov (United States)

    Debnath, Tushar; Maiti, Sourav; Ghosh, Hirendra N

    2016-04-07

    We have synthesized Mn-doped CdTeSe gradient alloy nanocrystals (NCs) by a colloidal synthetic method, and charge carrier dynamics have been revealed through ultrafast transient absorption (TA) spectroscopy. Due to the reactivity difference between Te and Se, a CdTe-rich core and CdSe-rich shell have been formed in the CdTeSe alloy with the formation of a gradient type II core-shell structure. Electron paramagnetic resonance studies suggest Mn atoms are located in the surface of the alloy NCs. Steady-state optical absorption and emission studies suggest formation of a charge-transfer (CT) state in which electrons are localized in a CdSe-rich shell and holes are localized in a CdTe-rich core which appears in the red region of the spectra. Electron transfer in the CT state is found to take place in the Marcus inverted region. To understand charge-transfer dynamics in the CdTeSe alloy NCs and to determine the effect of Mn doping on the alloy, ultrafast transient absorption studies have been carried out. In the case of the undoped alloy, formation of the CT state is found to take place through electron relaxation to the conduction band of the CT state with a time of 600 fs and through hole relaxation (from the CdSe-rich state to the CdTe-rich state) to the valence band of the CT state with a time scale of 1 ps. However, electron relaxation in the presence of Mn dopants takes place initially via an electron transfer to the Mn 3d state (d(5)) followed by transfer from the Mn 3d state (d(6)) to the CT state, which has been found to take place with a >700 ps time scale in addition to the hole relaxation time of 2 ps. Charge recombination time of the CT state is found to be extremely slow in the Mn-doped CdTeSe alloy NCs as compared to the undoped one, where the Mn atom acts as an electron storage center.

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

    KAUST Repository

    Sini, Gjergji

    2011-03-08

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

  16. Electronic excited states and relaxation dynamics in polymer heterojunction systems

    Science.gov (United States)

    Ramon, John Glenn Santos

    The potential for using conducting polymers as the active material in optoelectronic devices has come to fruition in the past few years. Understanding the fundamental photophysics behind their operations points to the significant role played by the polymer interface in their performance. Current device architectures involve the use of bulk heterojunctions which intimately blend the donor and acceptor polymers to significantly increase not only their interfacial surface area but also the probability of exciton formation within the vicinity of the interface. In this dissertation, we detail the role played by the interface on the behavior and performance of bulk heterojunction systems. First, we explore the relation between the exciton binding energy to the band offset in determining device characteristics. As a general rule, when the exciton binding energy is greater than the band offset, the exciton remains the lowest energy excited state leading to efficient light-emitting properties. On the other hand, if the offset is greater than the binding energy, charge separation becomes favorable leading to better photovoltaic behavior. Here, we use a Wannier function, configuration interaction based approach to examine the essential excited states and predict the vibronic absorption and emission spectra of the PPV/BBL, TFB/F8BT and PFB/F8BT heterojunctions. Our results underscore the role of vibrational relaxation in the formation of charge-transfer states following photoexcitation. In addition, we look at the relaxation dynamics that occur upon photoexcitation. For this, we adopt the Marcus-Hush semiclassical method to account for lattice reorganization in the calculation of the interconversion rates in TFB/F8BT and PFB/F8BT. We find that, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, a regeneration pathway to the optically active lowest excitonic state in TFB/F8BT is possible via thermal repopulation from the exciplex. Finally

  17. Excited states in electron-transfer reaction products : ultrafast relaxation dynamics of an isolated acceptor radical anion.

    OpenAIRE

    D. A. Horke; Roberts, G.M.; Verlet, J. R. R.

    2011-01-01

    The spectroscopy and ultrafast relaxation dynamics of excited states of the radical anion of a representative charge-transfer acceptor molecule, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, have been studied in the gas phase using time-resolved photoelectron spectroscopy. The photoelectron spectra reveal that at least two anion excited states are bound. Time-resolved studies show that both excited states are very short-lived and internally convert to the anion ground state, with the ...

  18. Description of the Charge Transfer States at the Pentacene/C60 Interface: Combining Range-Separated Hybrid Functionals with the Polarizable Continuum Model

    KAUST Repository

    Zheng, Zilong

    2016-06-24

    Density functional theory (DFT) approaches based on range-separated hybrid functionals are currently methods of choice for the description of the charge-transfer (CT) states in organic donor/acceptor solar cells. However, these calculations are usually performed on small-size donor/acceptor complexes and as result do not account for electronic polarization effects. Here, using a pentacene/C60 complex as a model system, we discuss the ability of long-range corrected (LCR) hybrid functionals in combination with the polarizable continuum model (PCM) to determine the impact of the solid-state environment on the CT states. The CT energies are found to be insensitive to the interactions with the dielectric medium when a conventional time-dependent DFT/PCM (TDDFT/PCM) approach is used. However, a decrease in the energy of the CT state in the framework of LRC functionals can be obtained by using a smaller range-separated parameter when going from an isolated donor/acceptor complex to the solid-state case.

  19. The Roles of Structural Order and Intermolecular Interactions in Determining Ionization Energies and Charge-Transfer State Energies in Organic Semiconductors

    KAUST Repository

    Graham, Kenneth

    2016-08-17

    The energy landscape in organic semiconducting materials greatly influences charge and exciton behavior, which are both critical to the operation of organic electronic devices. These energy landscapes can change dramatically depending on the phases of material present, including pure phases of one molecule or polymer and mixed phases exhibiting different degrees of order and composition. In this work, ultraviolet photoelectron spectroscopy measurements of ionization energies (IEs) and external quantum efficiency measurements of charge-transfer (CT) state energies (ECT) are applied to molecular photovoltaic material systems to characterize energy landscapes. The results show that IEs and ECT values are highly dependent on structural order and phase composition. In the sexithiophene:C60 system both the IEs of sexithiophene and C60 shift by over 0.4 eV while ECT shifts by 0.5 eV depending on molecular composition. By contrast, in the rubrene:C60 system the IE of rubrene and C60 vary by ≤0.11 eV and ECT varies by ≤0.04 eV as the material composition varies. These results suggest that energy landscapes can exist whereby the binding energies of the CT states are overcome by energy offsets between charges in CT states in mixed regions and free charges in pure phases. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Charge transfer of edge states in zigzag silicene nanoribbons with Stone-Wales defects from first-principles

    Science.gov (United States)

    Ting, Xie; Rui, Wang; Shaofeng, Wang; Xiaozhi, Wu

    2016-10-01

    Stone-Wales (SW) defects are favorably existed in graphene-like materials with honeycomb lattice structure and potentially employed to change the electronic properties in band engineering. In this paper, we investigate structural and electronic properties of SW defects in silicene sheet and its nanoribbons as a function of their concentration using the methods of periodic boundary conditions with first-principles calculations. We first calculate the formation energy, structural properties, and electronic band structures of SW defects in silicene sheet, with dependence on the concentration of SW defects. Our results show a good agreement with available values from the previous first-principles calculations. The energetics, structural aspects, and electronic properties of SW defects with dependence on defect concentration and location in edge-hydrogenated zigzag silicene nanoribbons are obtained. For all calculated concentrations, the SW defects prefer to locate at the edge due to the lower formation energy. The SW defects at the center of silicene nanoribbons slightly influence on the electronic properties, whereas the SW defects at the edge of silicene nanoribbons split the degenerate edge states and induce a sizable gap, which depends on the concentration of defects. It is worth to find that the SW defects produce a perturbation repulsive potential, which leads the decomposed charge of edge states at the side with defect to transfer to the other side without defect.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zanni, Martin Thomas [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    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.

  2. 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.

  3. Charge Transfer Dissociation (CTD) Mass Spectrometry of Peptide Cations: Study of Charge State Effects and Side-Chain Losses

    Science.gov (United States)

    Li, Pengfei; Jackson, Glen P.

    2017-01-01

    1+, 2+, and 3+ precursors of substance P and bradykinin were subjected to helium cation irradiation in a 3D ion trap mass spectrometer. Charge exchange with the helium cations produces a variety of fragment ions, the number and type of which are dependent on the charge state of the precursor ions. For 1+ peptide precursors, fragmentation is generally restricted to C-CO backbone bonds (a and x ions), whereas for 2+ and 3+ peptide precursors, all three backbone bonds (C-CO, C-N, and N-Cα) are cleaved. The type of backbone bond cleavage is indicative of possible dissociation channels involved in CTD process, including high-energy, kinetic-based, and ETD-like pathways. In addition to backbone cleavages, amino acid side-chain cleavages are observed in CTD, which are consistent with other high-energy and radical-mediated techniques. The unique dissociation pattern and supplementary information available from side-chain cleavages make CTD a potentially useful activation method for the structural study of gas-phase biomolecules.

  4. Low-Lying ππ* States of Heteroaromatic Molecules: A Challenge for Excited State Methods.

    Science.gov (United States)

    Prlj, Antonio; Sandoval-Salinas, María Eugenia; Casanova, David; Jacquemin, Denis; Corminboeuf, Clémence

    2016-06-14

    The description of low-lying ππ* states of linear acenes by standard electronic structure methods is known to be challenging. Here, we broaden the framework of this problem by considering a set of fused heteroaromatic rings and demonstrate that standard electronic structure methods do not provide a balanced description of the two (typically) lowest singlet state (La and Lb) excitations. While the Lb state is highly sensitive to correlation effects, La suffers from the same drawbacks as charge transfer excitations. We show that the comparison between CIS/CIS(D) can serve as a diagnostic for detecting the two problematic excited states. Standard TD-DFT and even its spin-flip variant lead to inaccurate excitation energies and interstate gaps, with only a double hybrid functional performing somewhat better. The complication inherent to a balanced description of these states is so important that even CC2 and ADC(2) do not necessarily match the ADC(3) reference.

  5. Altering intra- to inter-molecular hydrogen bonding by dimethylsulfoxide: A TDDFT study of charge transfer for coumarin 343

    Science.gov (United States)

    Liu, Xiaochun; Yin, Hang; Li, Hui; Shi, Ying

    2017-04-01

    DFT and TDDFT methods were carried out to investigate the influences of intramolecular and intermolecular hydrogen bonding on excited state charge transfer for coumarin 343 (C343). Intramolecular hydrogen bonding is formed between carboxylic acid group and carbonyl group in C343 monomer. However, in dimethylsulfoxide (DMSO) solution, DMSO 'opens up' the intramolecular hydrogen bonding and forms solute-solvent intermolecular hydrogen bonded C343-DMSO complex. Analysis of frontier molecular orbitals reveals that intramolecular charge transfer (ICT) occurs in the first excited state both for C343 monomer and complex. The results of optimized geometric structures indicate that the intramolecular hydrogen bonding interaction is strengthened while the intermolecular hydrogen bonding is weakened in excited state, which is confirmed again by monitoring the shifts of characteristic peaks of infrared spectra. We demonstrated that DMSO solvent can not only break the intramolecular hydrogen bonding to form intermolecular hydrogen bonding with C343 but also alter the mechanism of excited state hydrogen bonding strengthening.

  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.

  7. Intramolecular Charge Transfer and Solvation of Photoactive Molecules with Conjugated Push-Pull Structures.

    Science.gov (United States)

    Zhu, Huaning; Wang, Xian; Ma, Renjun; Kuang, Zhuoran; Guo, Qianjin; Xia, Andong

    2016-10-18

    A comparative investigation on the photophysical properties and solvation-related ICT dynamics of three push-pull compounds containing different donors including carbazole, triphenylamine and phenothiazine, was performed. The steady-state spectra and theoretical calculations show the charge transfers from the central donors to the acceptors at each side. The characterization of the extent of charge transfer was determined by various means, including estimation of the dipole moment, the electron density distribution of HOMO and LUMO, CDD and change in Gibb's free energy, which show the charge transfer strength to be in the order PDHP > BDHT > PDHC. This suggests that the electron-donating ability of the donor groups plays a crucial role in the charge transfer in these compounds. The TA data show the excited-state relaxation dynamics follow a sequential model: FC→ICT→ICT'→S0 , and are affected by the solvent polarity. The results presented here demonstrate that the compound with a higher degree of ICT characteristic interacts more strongly with stronger polar solvent molecules, which can accelerate the solvation and spectral evolution to lower energy levels. The A-π-D-π-A architectures with prominent ICT characteristics based on carbazole, triphenylamine and phenothiazine might be potential scaffolds for light-harvesting and photovoltaic devices. These results are of value for understanding structure-property relationships and the rational design of functional materials for photoelectric applications.

  8. Intramolecular Charge Transfer in Arylpyrazolines

    Institute of Scientific and Technical Information of China (English)

    WANG Ming-Liang; LIU Ju-Zheng; XU Chun-Xiang

    2006-01-01

    @@ Arylpyrazoline microparticles dispersed in water are synthesized and their absorption spectra are compared with those in solution. It is found that the absorbance of pyrazoline group in solution of 5-aryl arylpyrazoline is far greater than that in solution of arylpyrazolines with no 5-aryl group. This hyperchromic effect is intensified in 5-aryl arylpyrazoline microparticles. It is indicated that intramolecular charge transfer exists between pyrazoline group and 5-aryl group and this kind of interaction is increased in their microparticles.

  9. Two-State Intramolecular Charge Transfer (ICT) with 3,5-Dimethyl-4-(dimethylamino)benzonitrile (MMD) and Its Meta-Isomer mMMD. Ground State Amino Twist Not Essential for ICT.

    Science.gov (United States)

    Druzhinin, Sergey I; Galievsky, Victor A; Demeter, Attila; Kovalenko, Sergey A; Senyushkina, Tamara; Dubbaka, Srinivas R; Knochel, Paul; Mayer, Peter; Grosse, Christian; Stalke, Dietmar; Zachariasse, Klaas A

    2015-12-10

    From X-ray structure analysis, amino twist angles of 90.0° for 2,4-dimethyl-3-(dimethylamino)benzonitrile (mMMD), 82.7° for 4-(di-tert-butylamino)benzonitrile (DTABN), and 88.7° for 6-cyanobenzoquinuclidine (CBQ) are determined, all considerably larger than the 57.4° of 3,5-dimethyl-4-(dimethylamino)benzonitrile (MMD). This large twist leads to lengthening of the amino-phenyl bond, 143.5 pm (mMMD), 144.1 pm (DTABN), 144.6 pm (CBQ), and 141.4 pm (MMD), as compared with 136.5 pm for the planar 4-(dimethylamino)benzonitrile (DMABN). As a consequence, the electronic coupling between the amino and phenyl subgroups in mMMD, DTABN, CBQ, and MMD is much weaker than in DMABN, as seen from the strongly reduced molar absorption coefficients. The fluorescence spectrum of MMD in n-hexane at 25 °C consists of two emissions, from a locally excited (LE) and an intramolecular charge transfer (ICT) state, with a fluorescence quantum yield ratio Φ'(ICT)/Φ(LE) of 12.8. In MeCN, a single ICT emission is found. With mMMD in n-hexane, in contrast, only LE fluorescence is observed, whereas the spectrum in MeCN originates from the ICT state. These differences are also seen from the half-widths of the overall fluorescence bands, which in n-hexane are larger for MMD than for mMMD, decreasing with solvent polarity for MMD and increasing for mMMD, reflecting the disappearance of LE and the onset of ICT in the overall spectra, respectively. From solvatochromic measurements the dipole moments μe(ICT) of MMD (16 D) and mMMD (15 D) are obtained. Femtosecond excited state absorption (ESA) spectra at 22 °C, together with the dual (LE + ICT) fluorescence, reveal that MMD in n-hexane undergoes a reversible LE ⇄ ICT reaction, with LE as the precursor, with a forward rate constant ka = 5.6 × 10(12) s(-1) and a back-reaction kd ∼ 0.05 × 10(12) s(-1). With MMD in the strongly polar solvent MeCN, ICT is faster: ka = 10 × 10(12) s(-1). In the case of mMMD in n-hexane, the ESA spectra show

  10. Charge-transfer processes in semiconductor colloids

    Science.gov (United States)

    Kamat, Prashant V.; Gopidas, K. R.

    1990-04-01

    A picosecond transient absorption spectroscopy technique has been employed to probe the charge transfer processes in Ti02 semiconductor colloids. The trapping of electrons at the TiO surface (Ti4+ sitesY was characterized from the appearance of a broad absorption in the region of 550-750 nm following the 355-nm laser pulse excitation of Ti02 colloids. The lifetime of these trapped charge carriers increased upon incorporation of a hole scavenger in the colloidal semiconductor system. The mechanistic and kinetic details of the charge injection from excited CdS into a large bandgap semiconductor such as AgI and Ti02 have also been inves-' t i ga ted.

  11. Multi-pathway excited state relaxation of adenine oligomers in aqueous solution: a joint theoretical and experimental study.

    Science.gov (United States)

    Banyasz, Akos; Gustavsson, Thomas; Onidas, Delphine; Changenet-Barret, Pascale; Markovitsi, Dimitra; Improta, Roberto

    2013-03-11

    The singlet excited states of adenine oligomers, model systems widely used for the understanding of the interaction of ultraviolet radiation with DNA, are investigated by fluorescence spectroscopy and time-dependent (TD) DFT calculations. Fluorescence decays, fluorescence anisotropy decays, and time-resolved fluorescence spectra are recorded from the femtosecond to the nanosecond timescales for single strand (dA)20 in aqueous solution. These experimental observations and, in particular, the comparison of the fluorescence behavior upon UVC and UVA excitation allow the identification of various types of electronic transitions with different energy and polarization. Calculations performed for up to five stacked 9-methyladenines, taking into account the solvent, show that different excited states are responsible for the absorption in the UVC and UVA spectral domains. Independently of the number of bases, bright excitons may evolve toward two types of excited dimers having π-π* or charge-transfer character, each one distinguished by its own geometry and spectroscopic signature. According to the picture arising from the joint experimental and theoretical investigation, UVC-induced fluorescence contains contribution from 1) exciton states with a different degree of localization, decaying within a few ps, 2) "neutral" excited dimers decaying on the sub-nanosecond timescale, being the dominant species, and 3) charge-transfer states decaying on the nanosecond timescale. The majority of the photons emitted upon UVA excitation are related to charge-transfer states.

  12. Assessment of charge-transfer excitations with time-dependent, range-separated density functional theory based on long-range MP2 and multiconfigurational self- consistent field wave functions

    DEFF Research Database (Denmark)

    Hedegård, Erik D.; Jensen, Hans Jørgen Aagaard; Knecht, Stefan;

    2013-01-01

    formulation of multi-determinantal TD-DFT schemes where excitation classes, which are absent in conventional TD-DFT spectra (like for example double excitations), can be addressed. This paper investigates the combination of both the long-range Multi-Configuration Self-Consistent Field (MCSCF) and Second Order...... TD-MC-srDFT and performs slightly better against the reference data for this small subset. Beyond the proof-of-principle calculations comprising the first part of this contribution, we additionally studied the low-lying singlet excited states (S1 and S2) of the retinal chromophore. The chromophore...... displays multireference character in the ground state and both excited states exhibit considerable double excitation character, which in turn cannot be described within standard TD-DFT, due to the adiabatic approximation. However, a TD-MC-srDFT approach can account for the multireference character...

  13. Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

    Science.gov (United States)

    Skourtis, Spiros S.; Prytkova, Tatiana; Beratan, David N.

    2012-01-01

    This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH−-containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH−, upon photo-excitation of FADH− with 350–450 nm light. We compute the lowest singlet excited states of FADH− in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH− that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron- acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH− - thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green’s function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH− causes a π → π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH− - to - dimer electronic coupling, thus inducing rapid electron transfer. PMID:23226907

  14. Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

    Science.gov (United States)

    Skourtis, Spiros S.; Prytkova, Tatiana; Beratan, David N.

    2007-12-01

    This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH--containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH-, upon photo-excitation of FADH- with 350-450 nm light. We compute the lowest singlet excited states of FADH- in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH- that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron-acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH--thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green's function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH- causes a π→π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH--to-dimer electronic coupling, thus inducing rapid electron transfer.

  15. 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.

  16. Charge-displacement analysis for excited states

    Energy Technology Data Exchange (ETDEWEB)

    Ronca, Enrico, E-mail: enrico@thch.unipg.it; Tarantelli, Francesco, E-mail: francesco.tarantelli@unipg.it [Istituto CNR di Scienze e Tecnologie Molecolari, via Elce di Sotto 8, I-06123 Perugia (Italy); Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, via Elce di Sotto 8, I-06123 Perugia (Italy); Pastore, Mariachiara, E-mail: chiara@thch.unipg.it; Belpassi, Leonardo; De Angelis, Filippo [Istituto CNR di Scienze e Tecnologie Molecolari, via Elce di Sotto 8, I-06123 Perugia (Italy); Angeli, Celestino; Cimiraglia, Renzo [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Ferrara, via Borsari 46, I-44100 Ferrara (Italy)

    2014-02-07

    We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.

  17. 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.

  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. 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.

  20. 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.

  1. 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....

  2. Proton transfer assisted charge transfer phenomena in photochromic Schiff bases and effect of -NEt2 groups to the anil Schiff bases.

    Science.gov (United States)

    Jana, Sankar; Dalapati, Sasanka; Guchhait, Nikhil

    2012-11-15

    Photochromic Schiff bases 5-diethylamino-2-[(4-diethylamino-benzylidene)-hydrazonomethyl]-phenol (DDBHP) and N,N'-bis(4-N,N-diethylaminosalisalidene) hydrazine (DEASH) with both the proton and charge transfer moieties have been synthesized, and their photophysical properties such as excited state intramolecular charge transfer (ICT) and proton transfer (ESIPT) processes have been reported on the basis of steady-state and time-resolved spectral measurement in various solvents. The ground-state six-membered intramolecular hydrogen bonding network at the proton transfer site accelerates the ESIPT process for these compounds. Both the compounds show large Stokes-shifted emission bands for proton transfer and charge transfer processes. The hydrogen bonding solvents play a crucial role in these photophysical processes. Excited-state dipole moment of DDBHP and DEASH calculated by the solvatochromic method supports the polar character of the charge transfer excited state. Introduction of -NEt(2) groups to the reported salicylaldehyde azine (SAA) Schiff base results an increase in fluorescence lifetime from femtosecond to picosecond time scale for the proton transfer process.

  3. Excited states in electron-transfer reaction products: ultrafast relaxation dynamics of an isolated acceptor radical anion.

    Science.gov (United States)

    Horke, Daniel A; Roberts, Gareth M; Verlet, Jan R R

    2011-08-04

    The spectroscopy and ultrafast relaxation dynamics of excited states of the radical anion of a representative charge-transfer acceptor molecule, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, have been studied in the gas phase using time-resolved photoelectron spectroscopy. The photoelectron spectra reveal that at least two anion excited states are bound. Time-resolved studies show that both excited states are very short-lived and internally convert to the anion ground state, with the lower energy state relaxing within 200 fs and a near-threshold valence-excited state relaxing on a 60 fs time scale. These excited states, and in particular the valence-excited state, present efficient pathways for electron-transfer reactions in the highly exergonic inverted region which commonly displays rates exceeding predictions from electron-transfer theory.

  4. Quasi-solid state polymer electrolytes for dye-sensitized solar cells. Effect of the electrolyte components variation on the triiodide ion diffusion properties and charge-transfer resistance at platinum electrode

    Energy Technology Data Exchange (ETDEWEB)

    Nazmutdinova, G.; Sensfuss, S.; Schroedner, M. [Thuringian Institute for Textile and Plastics Research, Breitscheidstrasse 97, 07407 Rudolstadt (Germany); Hinsch, A. [Fraunhofer Institute for Solar Energy Systems, Heidenhofstrasse 2, 79110 Freiburg (Germany); Sastrawan, R. [Freiburg Materials Research Center FMF, Stefan-Meier-Street 21, 79104 Freiburg (Germany); Gerhard, D.; Himmler, S.; Wasserscheid, P. [Friedrich-Alexander-University, Egerlandstrasse 3, 91058 Erlangen (Germany)

    2006-11-30

    Quasi-solid state polymer electrolytes have been prepared from poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) as gelator for 1-ethyl-3-methylimidazolium based ionic liquids (with anions like trifluoromethanesulfonate [EMIM][TfO], bis(trifluoromethanesulfonyl)imide [EMIM][Tf{sub 2}N]) and polyacrylonitrile (PAN) for gelation of 1-ethyl-3-methylimidazolium dicyanamide [EMIM][DCA] as well as I{sup -}/I{sub 3}{sup -} as the redox couple. All electrolytes exhibit high ionic conductivity in the range of 10{sup -3} S/cm. The effect of gelation, redox couple concentration, I{sup -}/I{sub 3}{sup -} ratio, choice of cations and additives on the triiodide diffusion and charge-transfer resistance of the platinum/electrolyte interface (R{sub ct}) were studied. The apparent diffusion coefficient of triiodide ion (D(I{sub 3}{sup -})) at various iodide/triiodide ratios in liquid and gelified electrolytes has been calculated from measurements of the diffusion limited current (I{sub lim}) in electrochemical cell resembling the set-up of a dye-sensitized solar cell. The charge-transfer resistance of the platinum/electrolyte interface as well as the capacitance of the electrical double layer (C{sub dl}) have been calculated from impedance measurements. Electrolytes with reduced content of polymer (2.5 wt.%) were doped with Al{sub 2}O{sub 3} particles of different sizes (50 nm, 300 nm, 1 {mu}m). The dispersion of the particles proceeds by speedy stirring of the hot electrolyte and the addition of PAN provides a homogeneous suspension. The addition of Al{sub 2}O{sub 3} particles causes a slight increase of the triiodide diffusion constants. Furthermore the suggested enhancement of the charge transfer rate shows a dependence on the size of the particles. (author)

  5. Intramolecular Charge Transfer of Carotene-porphyrin-fullerene Triad: Sequential or Superexchange Cechanism

    Institute of Scientific and Technical Information of China (English)

    SUN,Yu; CHEN,Yue-Hui; LI,Yuan-Zuo; LI,Yong-Qing; MA,Feng-Cai

    2008-01-01

    As an excellent artificial photosynthetic reaction center,the carotene (C)-porphyrin (P)-fullerene (F) triad was extensively investigated experimentally.To reveal the mechanism of the intramolecular charge transfer (ICT) on the mimic of photosynthetic solar energy conversion (such as singlet energy transfer between pigments,and photoinduced electron transfer from excited singlet states to give long-lived charge-separated states),the ICT mechanisms of C-P-F triad on the exciton were theoretically studied with quantum chemical methods as well as the 2D and 3D real space analysis approaches.The results of quantum chemical methods reveal that the excited states are the ICT states,since the densities of HOMO are localized in the carotene or porphyrin unit,and the densities of LUMO are localized in the fullerene unit.Furthermore,the excited states should be the intramolecular superexchange charge transfer (ISCT) states for the orbital transition from the HOMO whose densities are localized in the carotene to the LUMO whose densities are localized in the fullerene unit.The 3D charge difference densities can clearly show that some excited states are ISCT excited states,since the electron and hole are resident in the fullerene and carotene units,respectively.From the results of the electron-hole coherence of the 2D transition density matrix,not only 3D results are supported,but also the delocalization size on the exciton can be observed.These phenomena were further interpreted with non-linear optical effect.The large changes of the linear and non-linear polarizabilities on the exciton result in the charge separate states,and if their changes are large enough,the ICT mechanism can become the ISCT on the exciton.

  6. 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.

  7. Enhanced Three-Photon Absorption by Symmetric Twisted Intramolecular Charge Transfer

    Institute of Scientific and Technical Information of China (English)

    GUO Fu-Quan; YANG Jun; ZHANG Qi-Jin; MING Hai

    2005-01-01

    @@ We report on a novel organic chromophore with symmetric twisted intramolecular charge transfer (TICT) state on excitation. The properties of nonlinear transmission induced by three-photon absorption (3PA) are demonstrated pumped with nanosecond laser pulse. Large 3PA cross sections as high as the order of 10-74 cm6s2have been obtained for nanosecond and picosecond laser pulses at 1064 nm from intensity-dependent transmission measurements. Similar two emissive behaviours from one-photon and three-photon excited fluorescence spectra indicate that the linear and nonlinear fluorescences share the same TICT relaxation process from the excited states. The intensity dependence of upconversion fluorescence on the incident intensity obeys the cubic law that characterizes the three-photon absorption.

  8. Excited State Dynamics of Protonated Phenylalanine and Tyrosine: Photo-Induced Reactions Following Electronic Excitation.

    Science.gov (United States)

    Féraud, Géraldine; Broquier, Michel; Dedonder, Claude; Jouvet, Christophe; Grégoire, Gilles; Soorkia, Satchin

    2015-06-11

    The electronic spectroscopy and the electronic excited state properties of cold protonated phenylalanine and protonated tyrosine have been revisited on a large spectral domain and interpreted by comparison with ab initio calculations. The protonated species are stored in a cryogenically cooled Paul trap, maintained at ∼10 K, and the parent and all the photofragment ions are mass-analyzed in a time-of-flight mass spectrometer, which allows detecting the ionic species with an improved mass resolution compared to what is routinely achieved with a quadrupole mass spectrometer. These new results emphasize the competition around the band origin between two proton transfer reactions from the ammonium group toward either the aromatic chromophore or the carboxylic acid group. These reactions are initiated by the coupling of the locally excited ππ* state with higher charge transfer states, the positions and coupling of which depend on the conformation of the protonated molecules. Each of these reaction processes gives rise to specific fragmentation channels that supports the conformer selectivity observed in the photofragmentation spectra of protonated tyrosine and phenylalanine.

  9. 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.

  10. Tracking excited-state charge and spin dynamics in iron coordination complexes

    DEFF Research Database (Denmark)

    Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe

    2014-01-01

    to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)(3)](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate......Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons(1-4). But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited...... states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics(5) and the flux limitations of ultrafast X-ray sources(6,7). Such a situation exists for archetypal poly-pyridyl iron complexes, such as [Fe(2...

  11. Excited-state relaxation in π-conjugated polymers

    Science.gov (United States)

    Frolov, S. V.; Bao, Z.; Wohlgenannt, M.; Vardeny, Z. V.

    2002-05-01

    We study ultrafast relaxation processes of odd- (Bu) and even-parity (Ag) exciton states in poly(p-phenylene vinylene) derivatives. The Bu states are studied using a regular two-beam pump-and-probe spectroscopy, which can monitor vibronic relaxation and exciton diffusion. In order to observe the Ag states, a three-beam femtosecond transient spectroscopy is developed, in which two different excitation pulses successively generate odd-parity (1Bu) excitons at 2.2 eV and then reexcite them to higher Ag states. We are able to distinguish two different classes of Ag states: one class (mAg) experiences ultrafast internal conversion back to the lowest singlet exciton, whereas the other class (kAg) in violation of the Vavilov-Kasha's rule undergoes a different relaxation pathway. The excitons subsequently dissociate into long-lived polaron pairs, which results in emission quenching with the action spectrum similar to that of the intrinsic photoconductivity. We conclude that the Ag states above 3.3 eV (kAg) are charge-transfer states, that mediate carrier photogeneration.

  12. Charge transfer in collisions of H+ with Li (1s22s, 2pz): TD-MADNESS approach

    Science.gov (United States)

    Domínguez-Gutiérrez, F. J.; Krstić, P. S.

    2016-10-01

    In this work we carry out a study of the single-electron charge transfer process for H+ collisions with atomic neutral lithium, in its ground and first excited state, at 1-25 keV amu-1. For this, we solve numerically the time dependent Schrödinger equation to the defined accuracy by using a multi-resolution adaptive approach, thus removing the uncertainties connected to a basis size and spatial and temporal numeric mesh size. We approximate the atomic lithium target by a single electron model in a frozen-core pseudo-potential while the projectile follows a straight line trajectory. Within these approximations we report new benchmark data for charge transfer cross sections to n = 2, and 3 states of hydrogen from 1s22s and 1s22pz of Li. Available theoretical and experimental data in the literature are in reasonable agreement with our results.

  13. Ultrafast excited state dynamics of Pt(II) chromophores bearing multiple infrared absorbers.

    Science.gov (United States)

    Glik, Elena A; Kinayyigit, Solen; Ronayne, Kate L; Towrie, Michael; Sazanovich, Igor V; Weinstein, Julia A; Castellano, Felix N

    2008-08-04

    The paper reports the synthesis, structural characterization, electrochemistry, ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopy associated with two independent d (8) square planar Pt(II) diimine chromophores, Pt(dnpebpy)Cl 2 ( 1) and Pt(dnpebpy)(C[triple bond]Cnaph) 2 ( 2), where dnpebpy = 4,4'-(CO 2CH 2- (t) Bu) 2-2,2'-bipyridine and CCnaph = naphthylacetylide. The neopentyl ester substitutions provided markedly improved complex solubility relative to the corresponding ethyl ester which facilitates synthetic elaboration as well as spectroscopic investigations. Following 400 nm pulsed laser excitation in CH 2Cl 2, the 23 cm (-1) red shift in the nu C=O vibrations in 1 are representative of a complex displaying a lowest charge-transfer-to-diimine (CT) excited state. The decay kinetics in 1 are composed of two time constants assigned to vibrational cooling of the (3)CT excited-state concomitant with its decay to the ground state (tau = 2.2 +/- 0.4 ps), and to cooling of the formed vibrationally hot ground electronic state (tau = 15.5 +/- 4.0 ps); we note that an assignment of the latter to a ligand field state cannot be excluded. Ultrafast TA data quantitatively support these assignments yielding an excited-state lifetime of 2.7 +/- 0.4 ps for the (3)CT excited-state of 1 and could not detect any longer-lived species. The primary intention of this study was to develop a Pt (II) complex ( 2) bearing dual infrared spectroscopic tags (C[triple bond]C attached to the metal and CO (ester) attached to the diimine ligand) to independently track the movement of charge density in different segments of the molecule following pulsed light excitation. Femtosecond laser excitation of 2 in CH 2Cl 2 at 400 nm simultaneously induces a red-shift in both the nu C=O (-30 cm (-1)) and the nu C[triple bond]C (-61 cm (-1)) vibrations. The TRIR data in 2 are consistent with a charge transfer assignment, and the significant decrease of the energy of the nu

  14. Satellite lines at the ionization threshold in charge transfer systems

    Science.gov (United States)

    Wardermann, W.; von Niessen, W.

    1992-01-01

    This article deals with the possibility of low-energy ionizations of reduced intensity for larger organic molecules. Possible mechanisms which may lead to this phenomenon are outlined and the necessary structural features are discussed. The lowest ionization energies of some organic unsaturated nitro and nitroso compounds are calculated by the ADC(3) ab initio many-body Green's function method. The π-electron system consists either of fused five- and six-membered rings or of two fused five-membered rings with a variable number of heteroatoms. Some of the molecules contain exocylic double bonds and some are substituted with the donor groups -NH 2, -OH and -NHOH. The strongest many-body effects are found for the nitroso compounds, where in one case the spectral line at the ionization threshold has lost more than 40% of its intensity to satellites. We study the many-body effects at or close to the ionization threshold for these compounds. A particular mechanism which involves the screening of localized valence holes by charge transfer excitations appears to be capable of influencing the profile and intensities of the ionization spectrum already at the ionization threshold. The effect leads to strongly reduced relative intensities of the bands and may cause the appearance of satellite bands nearly at the ionization threshold. The spectral changes in the outermost valence region are discussed by using a simple model calculation in terms of ground-state electronic properties of the molecules.

  15. Excited-State Dipole and Quadrupole Moments: TD-DFT versus CC2.

    Science.gov (United States)

    Jacquemin, Denis

    2016-08-09

    The accuracies of the excited-state dipole and quadrupole moments obtained by TD-DFT are assessed by considering 16 different exchange-correlation functionals and more than 30 medium and large molecules. Except for excited-state presenting a significant charge-transfer character, a relatively limited dependency on the nature of the functional is found. It also turns out that while DFT ground-state dipole moments tend to be too large, the reverse trend is obtained for their excited-state counterparts, at least when hybrid functionals are used. Consequently, the TD-DFT excess dipole moments are often too small, an error that can be fortuitously corrected for charge-transfer transition by selecting a pure or a hybrid functional containing a small share of exact exchange. This error-cancelation phenomena explains the contradictory conclusions obtained in previous investigations. Overall, the largest correlation between CC2 and TD-DFT excess dipoles is obtained with M06-2X, but at the price of a nearly systematic underestimation of this property by ca. 1 D. For the excess quadrupole moments, the average errors are of the order of 0.2-0.6 D·Å for the set of small aromatic systems treated.

  16. Communication: Exciton analysis in time-dependent density functional theory: How functionals shape excited-state characters.

    Science.gov (United States)

    Mewes, Stefanie A; Plasser, Felix; Dreuw, Andreas

    2015-11-01

    Excited-state descriptors based on the one-particle transition density matrix referring to the exciton picture have been implemented for time-dependent density functional theory. State characters such as local, extended ππ(∗), Rydberg, or charge transfer can be intuitively classified by simple comparison of these descriptors. Strong effects of the choice of the exchange-correlation kernel on the physical nature of excited states can be found and decomposed in detail leading to a new perspective on functional performance and the design of new functionals.

  17. Probing the Locality of Excited States with Linear Algebra.

    Science.gov (United States)

    Etienne, Thibaud

    2015-04-14

    This article reports a novel theoretical approach related to the analysis of molecular excited states. The strategy introduced here involves gathering two pieces of physical information, coming from Hilbert and direct space operations, into a general, unique quantum mechanical descriptor of electronic transitions' locality. Moreover, the projection of Hilbert and direct space-derived indices in an Argand plane delivers a straightforward way to visually probe the ability of a dye to undergo a long- or short-range charge-transfer. This information can be applied, for instance, to the analysis of the electronic response of families of dyes to light absorption by unveiling the trend of a given push-pull chromophore to increase the electronic cloud polarization magnitude of its main transition with respect to the size extension of its conjugated spacer. We finally demonstrate that all the quantities reported in this article can be reliably approximated by a linear algebraic derivation, based on the contraction of detachment/attachment density matrices from canonical to atomic space. This alternative derivation has the remarkable advantage of a very low computational cost with respect to the previously used numerical integrations, making fast and accurate characterization of large molecular systems' excited states easily affordable.

  18. Linear, third- and fifth-order nonlinear spectroscopy of a charge transfer system coupled to an underdamped vibration

    CERN Document Server

    Dijkstra, Arend G

    2015-01-01

    We study hole, electron and exciton transport in a charge transfer system in the presence of underdamped vibrational motion. We analyze the signature of these processes in the linear and third-, and fifth-order nonlinear electronic spectra. Calculations are performed with a numerically exact hierarchical equations of motion method for an underdamped Brownian oscillator spectral density. We find that combining electron, hole and exciton transfer can lead to non-trivial spectra with more structure than with excitonic coupling alone. Traces taken during the waiting time of a two-dimensional spectrum are dominated by vibrational motion and do not reflect the electron, hole, and exciton dynamics directly. We find that the fifth-order nonlinear response is particularly sensitive to the charge transfer process. While third-order 2D spectroscopy detects the correlation between two coherences, fifth-order 2D spectroscopy (2D population spectroscopy) is here designed to detect correlations between the excited states du...

  19. Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment.

    Science.gov (United States)

    Kreitner, Christoph; Heinze, Katja

    2016-09-21

    Deactivation pathways of the triplet metal-to-ligand charge transfer ((3)MLCT) excited state of cyclometalated polypyridine ruthenium complexes with [RuN5C](+) coordination are discussed on the basis of the available experimental data and a series of density functional theory calculations. Three different complex classes are considered, namely with [Ru(N^N)2(N^C)](+), [Ru(N^N^N)(N^C^N)](+) and [Ru(N^N^N)(N^N^C)](+) coordination modes. Excited state deactivation in these complex types proceeds via five distinct decay channels. Vibronic coupling of the (3)MLCT state to high-energy oscillators of the singlet ground state ((1)GS) allows tunneling to the ground state followed by vibrational relaxation (path A). A ligand field excited state ((3)MC) is thermally accessible via a (3)MLCT →(3)MC transition state with the (3)MC state being strongly coupled to the (1)GS surface via a low-energy minimum energy crossing point (path B). Furthermore, a (3)MLCT →(1)GS surface crossing point directly couples the triplet and singlet potential energy surfaces (path C). Charge transfer states either with higher singlet character or with different orbital parentage and intrinsic symmetry restrictions are thermally populated which promote non-radiative decay via tunneling to the (1)GS state (path D). Finally, the excited state can decay via phosphorescence (path E). The dominant deactivation pathways differ for the three individual complex classes. The implications of these findings for isoelectronic iridium(iii) or iron(ii) complexes are discussed. Ultimately, strategies for optimizing the emission efficiencies of cyclometalated polypyridine complexes of d(6)-metal ions, especially Ru(II), are suggested.

  20. 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.

  1. Theoretical description of photo-doping in Mott and charge-transfer insulators

    Science.gov (United States)

    Eckstein, Martin

    2012-02-01

    Many aspects of photo-excited insulator-to-metal transitions in Mott and charge-transfer systems are theoretically not well understood: How is the photo-doped state related to a chemically doped state? On what timescale do we expect the formation of quasiparticles? To describe the electronic dynamics of Mott insulators, we have used nonequilibrium dynamical mean-field theory (DMFT) in combination with Quantum Monte Carlo and various weak and strong-coupling [1] techniques. In the talk, I will briefly present the current status of this approach and of related cluster approaches for nonequilibrium. I will then discuss results for the photo-doping in the Hubbard model, and in a in a p-d model for charge-transfer insulators. When the onsite Coulomb repulsion U is much larger than the hopping, rapid thermalization of the pump-excited Mott insulator is inhibited by the energetic stabilization of doublon-hole pairs [2], and various types of non-thermal states can arise. Immediately after the excitation process, the system of doublons and holes is too hot to form quasiparticle states, but coupling to a heat-bath of phonons can drive the system into a metallic state with well developed doublon and hole bands. Close to the metal-insulator transition, on the other hand, when U is of the order as the hopping, doublons and holes rapidly thermalize due to the electron-electron interaction, which makes the system a bad metal rather than a Fermi liquid. [4pt] [1] M. Eckstein and Ph. Werner, Phys. Rev. B 82, 115115 (2010).[0pt] [2] M. Eckstein and Ph. Werner, Phys. Rev. B 84, 035122 (2011).

  2. Solvent-mediated electron hopping: long-range charge transfer in IBr-(CO2) photodissociation.

    Science.gov (United States)

    Sheps, Leonid; Miller, Elisa M; Horvath, Samantha; Thompson, Matthew A; Parson, Robert; McCoy, Anne B; Lineberger, W Carl

    2010-04-09

    Chemical bond breaking involves coupled electronic and nuclear dynamics that can take place on multiple electronic surfaces. Here we report a time-resolved experimental and theoretical investigation of nonadiabatic dynamics during photodissociation of a complex of iodine monobromide anion with carbon dioxide [IBr-(CO2)] on the second excited (A') electronic state. Previous experimental work showed that the dissociation of bare IBr- yields only I- + Br products. However, in IBr-(CO2), time-resolved photoelectron spectroscopy reveals that a subset of the dissociating molecules undergoes an electron transfer from iodine to bromine 350 femtoseconds after the initial excitation. Ab initio calculations and molecular dynamics simulations elucidate the mechanism for this charge hop and highlight the crucial role of the carbon dioxide molecule. The charge transfer between two recoiling atoms, assisted by a single solvent-like molecule, provides a notable limiting case of solvent-driven electron transfer over a distance of 7 angstroms.

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

    Science.gov (United States)

    Babb, James F.; McLaughlin, B. M.

    2017-02-01

    Radiative charge exchange collisions between a carbon atom {{C}}({}3P) and a helium ion {{He}}+({}2S), 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 interstellar photon dominated regions and in x-ray dominated regions, where the abundance of {{He}}+ affects the abundance of {CO}.

  4. 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.

  5. 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.

  6. 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...

  7. Excited state Intramolecular Proton Transfer in Anthralin

    DEFF Research Database (Denmark)

    Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens

    1998-01-01

    Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results in an unus......Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results......, associated with an excited-state intramolecular proton transfer process....

  8. Opposites Attract: Organic Charge Transfer Salts

    Science.gov (United States)

    van de Wouw, Heidi L.; Chamorro, Juan; Quintero, Michael; Klausen, Rebekka S.

    2015-01-01

    A laboratory experiment is described that introduces second-year undergraduate organic chemistry students to organic electronic materials. The discovery of metallic conductivity in the charge transfer salt tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) is a landmark result in the history of organic electronics. The charge transfer…

  9. Charge-transfer crystallites as molecular electrical dopants

    Science.gov (United States)

    Méndez, Henry; Heimel, Georg; Winkler, Stefanie; Frisch, Johannes; Opitz, Andreas; Sauer, Katrein; Wegner, Berthold; Oehzelt, Martin; Röthel, Christian; Duhm, Steffen; Többens, Daniel; Koch, Norbert; Salzmann, Ingo

    2015-10-01

    Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi-Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites--rather than individual acceptor molecules--should be regarded as the dopants in such systems.

  10. Charge transfer in Li/CFx-silver vanadium oxide hybrid cathode batteries revealed by solid state 7Li and 19F nuclear magnetic resonance spectroscopy

    Science.gov (United States)

    Sideris, Paul J.; Yew, Rowena; Nieves, Ian; Chen, Kaimin; Jain, Gaurav; Schmidt, Craig L.; Greenbaum, Steve G.

    2014-05-01

    Solid state 7Li and 19F magic angle spinning nuclear magnetic resonance (MAS NMR) experiments are conducted on several cathodes containing CFx-Silver vanadium oxide (CFx-Ag2V4O11) hybrid cathodes discharged to 50% depth of discharge (DoD) and stored at their open-circuit voltage for a period of one and three months. Three carbonaceous sources for the CFx phase are investigated: petroleum coke-based, fibrous, and mixed fibrous. For each hybrid cathode, a measurable increase in the relative amount of lithium fluoride is observed after a three month resting period in both the 7Li and 19F NMR spectra. These changes are attributed to lithium ion migration from the silver vanadium oxide to the CFx phase during the resting period, and help clarify the mechanism behind high power handling capability of this cathode.

  11. Multimode optical fibers: steady state mode exciter.

    Science.gov (United States)

    Ikeda, M; Sugimura, A; Ikegami, T

    1976-09-01

    The steady state mode power distribution of the multimode graded index fiber was measured. A simple and effective steady state mode exciter was fabricated by an etching technique. Its insertion loss was 0.5 dB for an injection laser. Deviation in transmission characteristics of multimode graded index fibers can be avoided by using the steady state mode exciter.

  12. The mechanisms of Excited states in enzymes

    DEFF Research Database (Denmark)

    Petersen, Frederic Nicolas Rønne; Bohr, Henrik

    2010-01-01

    Enzyme catalysis is studied on the basis of excited state processes, which are of electronic, vibrational and thermal nature. The ways of achieving the excited state, such as photo-absorption and ligand binding, are discussed and exemplified by various cases of enzymes.......Enzyme catalysis is studied on the basis of excited state processes, which are of electronic, vibrational and thermal nature. The ways of achieving the excited state, such as photo-absorption and ligand binding, are discussed and exemplified by various cases of enzymes....

  13. 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

  14. Excited states rotational effects on the behavior of excited molecules

    CERN Document Server

    Lim, Edward C

    2013-01-01

    Excited States, Volume 7 is a collection of papers that discusses the excited states of molecules. The first paper reviews the rotational involvement in intra-molecular in vibrational redistribution. This paper analyzes the vibrational Hamiltonian as to its efficacy in detecting the manifestations of intra-molecular state-mixing in time-resolved and time-averaged spectroscopic measurements. The next paper examines the temporal behavior of intra-molecular vibration-rotation energy transfer (IVRET) and the effects of IVRET on collision, reaction, and the decomposition processes. This paper also

  15. Characterization of adsorption and electronic excited states of quercetin on titanium dioxide nanoparticles

    Science.gov (United States)

    Zdyb, Agata; Krawczyk, Stanisław

    2016-03-01

    Adsorption of quercetin on colloidal titanium dioxide nanoparticles in ethanol and its excited-state electronic structure were investigated by means of electronic and vibrational spectroscopies. The changes in electronic charge redistribution as reflected by the dipole moment difference, ∆μ, between the ground and excited electronic states were measured with electroabsorption spectroscopy and analyzed using results of TD DFT computations. Adsorption of quercetin causes a red shift of its absorption spectrum. Raman spectra of quercetin analyzed with reference to analogous data for morin indicate binding of quercetin through the hydroxy groups of the catechol moiety. The difference dipole moment, which is 5.5 D in free quercetin, increases to 11.8 D in opposite direction in adsorbed quercetin, and is associated with charge-transfer to the Ti atom. The computed transition energy, intensity, vector Δμ and molecular orbitals involved in the electronic transition at different molecular configurations indicate a bidentate chelating mode of binding of quercetin.

  16. Excited State Properties of Fluorine-Substituted Hexabenzocoronene: A Quantum-Chemical Characterization

    Institute of Scientific and Technical Information of China (English)

    LI Yuan-Zuo; SUN Yu; LI Yong-Qing; MA Feng-Cai

    2006-01-01

    The first fluorine-substituted hexabenzocoronene has been synthesized and its electronic structure and optical properties have been reported [Q. Zhang, et al., Org. Lett.7 (2005) 5019]. In this letter, the electronic structure and excited state properties of the fluorine-substituted hexabenzocoronene are studied with quantum chemistry method as well as the transition and the charge difference densities. The transition densities show the orientations and strength of the dipole moments and the charge difference densities reveal the orientation and results of the intramolecular charge transfer. The calculated transition energies and oscillator strengths are consistent with the experimental data, and the theoretical results of transition and charge difference densities are valuable to understanding the excited state properties of the fluorine-substituted hexabenzocoronene.

  17. 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.

  18. Ultrafast twisting motions and intramolecular charge-transfer reaction in a cyanine dye trapped in molecular nanocavities

    Science.gov (United States)

    Fayed, T. A.; Organero, J. A.; Garcia-Ochoa, I.; Tormo, L.; Douhal, A.

    2002-09-01

    Emission properties of the cyanine dye, 1-(2-naphthyl)-2-ethenyl-(2-benzothiazolium) iodide, in aqueous nanocavities offered by cyclodextrins and in a film of a polymeric matrix were studied by means of steady-state and picosecond time-resolved emission spectroscopy. The results show the occurrence of a fast twisting motion and a subsequent intramolecular charge-transfer reaction. The initial step can be prevented by the size of the nanocavity which governs the spectral position of the fluorescence band and lifetime of the excited encapsulated host.

  19. Unrestricted density functional theory based on the fragment molecular orbital method for the ground and excited state calculations of large systems

    Energy Technology Data Exchange (ETDEWEB)

    Nakata, Hiroya, E-mail: nakata.h.ab@m.titech.ac.jp [Center for Biological Resources and Informatics, Tokyo Institute of Technology, B-62 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501 (Japan); RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Fedorov, Dmitri G. [NRI, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Yokojima, Satoshi [RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Tokyo University of Pharmacy and Life Sciences, 1423-1 Horinouchi, Hachioji-shi, Tokyo 192-0392 (Japan); Kitaura, Kazuo [Graduate School of System Informatics, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501 (Japan); Sakurai, Minoru [Center for Biological Resources and Informatics, Tokyo Institute of Technology, B-62 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501 (Japan); Nakamura, Shinichiro [RIKEN, Research Cluster for Innovation, Nakamura Lab, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

    2014-04-14

    We extended the fragment molecular orbital (FMO) method interfaced with density functional theory (DFT) into spin unrestricted formalism (UDFT) and developed energy gradients for the ground state and single point excited state energies based on time-dependent DFT. The accuracy of FMO is evaluated in comparison to the full calculations without fragmentation. Electronic excitations in solvated organic radicals and in the blue copper protein, plastocyanin (PDB code: 1BXV), are reported. The contributions of solvent molecules to the electronic excitations are analyzed in terms of the fragment polarization and quantum effects such as interfragment charge transfer.

  20. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    -molecular mechanics scheme, and tools to analyse statistical data and generate relative free energies and free energy surfaces. The methodology is applied to several charge transfer species and reactions in chemical environments - chemical in the sense that solvent, counter ions and substrate surfaces are taken...... in to account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems...... and asymmetric charge transfer reactions between several first-row transition metals in water. The results are compared to experiments and rationalised with classical analytic expressions. Shortcomings of the methods are accounted for with clear steps towards improved accuracy. Later the analysis is extended...

  1. Photophysical study of some 3-benzoylmethyleneindol-2-ones and estimation of ground and excited states dipole moments from solvatochromic methods using solvent polarity parameters

    Science.gov (United States)

    Saroj, Manju K.; Sharma, Neera; Rastogi, Ramesh C.

    2012-03-01

    3-Benzoylmethyleneindol-2-ones, isatin based chalcones containing donor and acceptor moieties that exhibit excited-state intramolecular charge transfer, have been studied in different solvents by absorption and emission spectroscopy. The excited state behavior of these compounds is strongly dependent on the nature of substituents and the environment. These compounds show multiple emissions arising from a locally excited state and the two states due to intramolecular processes viz. intramolecular charge transfer (ICT) and excited state intramolecular proton transfer (ESIPT). Excited-state dipole moments have been calculated using Stoke-shifts of LE and ICT states using solvatochromic methods. The higher values of dipole moments obtained lead to support the formation of ICT state as one of the prominent species in the excited states of all 3-benzoylmethyleneindol-2-ones. The correlation of the solvatochromic Stokes-shifts with the microscopic solvent polarity parameter (ETN) was found to be superior to that obtained using bulk solvent polarity functions. The absorption and florescence spectral characteristics have been also investigated as a function of acidity and basicity (Ho/pH) in aqueous phase.

  2. 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.

  3. Multiple-Resonance Local Wave Functions for Accurate Excited States in Quantum Monte Carlo.

    Science.gov (United States)

    Zulfikri, Habiburrahman; Amovilli, Claudio; Filippi, Claudia

    2016-03-08

    We introduce a novel class of local multideterminant Jastrow-Slater wave functions for the efficient and accurate treatment of excited states in quantum Monte Carlo. The wave function is expanded as a linear combination of excitations built from multiple sets of localized orbitals that correspond to the bonding patterns of the different Lewis resonance structures of the molecule. We capitalize on the concept of orbital domains of local coupled-cluster methods, which is here applied to the active space to select the orbitals to correlate and construct the important transitions. The excitations are further grouped into classes, which are ordered in importance and can be systematically included in the Jastrow-Slater wave function to ensure a balanced description of all states of interest. We assess the performance of the proposed wave function in the calculation of vertical excitation energies and excited-state geometry optimization of retinal models whose π → π* state has a strong intramolecular charge-transfer character. We find that our multiresonance wave functions recover the reference values of the total energies of the ground and excited states with only a small number of excitations and that the same expansion can be flexibly used at very different geometries. Furthermore, significant computational saving can also be gained in the orbital optimization step by selectively mixing occupied and virtual orbitals based on spatial considerations without loss of accuracy on the excitation energy. Our multiresonance wave functions are therefore compact, accurate, and very promising for the calculation of multiple excited states of different character in large molecules.

  4. 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.

  5. 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.

  6. Effect of intramolecular charge transfer on fluorescence and singlet oxygen production of phthalocyanine analogues.

    Science.gov (United States)

    Vachova, Lenka; Novakova, Veronika; Kopecky, Kamil; Miletin, Miroslav; Zimcik, Petr

    2012-10-14

    Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two dialkylamino substituents (donors) and six alkylsulfanyl or aryloxy substituents (non-donors). The dialkylamino substituents were responsible for ICT that deactivated excited states and led to considerable decrease of fluorescence and singlet oxygen quantum yields. Photophysical and photochemical properties were compared to corresponding macrocycles that do not bear any donor centers. The data showed high feasibility of ICT in the tetrapyrazinoporphyrazine macrocycle and significantly lower efficiency of this deactivation process in the tribenzopyrazinoporphyrazine type molecules. Considerable effect of non-donor peripheral substituents on ICT was also described. The results imply that tetrapyrazinoporphyrazines may be more suitable for development of new molecules investigated in applications based on ICT.

  7. Rapid excited state structural reorganization captured by pulsed x-rays.

    Energy Technology Data Exchange (ETDEWEB)

    Chen, L. X.; Jennings, G.; Liu, T.; Gosztola, D. J.; Hessler, J. P.; Scaltrito, D. V.; Meyer, G. J.; Johns Hopkins Univ.

    2002-09-11

    Visible light excitation of [CuI(dmp)2](BArF), where dmp is 2,9-dimethyl-1,10-phenanthroline and BArF is tetrakis(3,5-bis(trifluoromethylphenyl))borate, in toluene produces a photoluminescent, metal-to-ligand charge-transfer (MLCT) excited state with a lifetime of 98 {+-} 5 ns. Probing this state within 14 ns after photoexcitation with pulsed X-rays establishes that a CuII center, borne in a CuI geometry, binds an additional ligand to form a five-coordinate complex with increased bond lengths and a coordination geometry of distorted trigonal bipyramid. The average Cu-N bond length increases in the excited state by 0.07 Angstroms. The transiently formed five-coordinate MLCT state is photoluminescent under the condition studied, indicating that the absorptive and emissive states have distinct geometries. The data represent the first X-ray characterization of a molecular excited state in fluid solution on a nanosecond time scale.

  8. Excited States in Staggered Meson Propagators

    CERN Document Server

    Bernard, C; De Tar, C; Gottlieb, Steven; Gregory, E B; Heller, U M; Osborn, J; Sugar, R; Toussaint, D; Louis, St; Gottlieb, Steven

    2003-01-01

    We report on preliminary results from multi-particle fits to meson propagators with three flavors of light dynamical quarks. We are able to measure excited states in propagators with pion quantum numbers, which we interpret as the pion 2S state, and is evidence of locality of the action. In the a_0 (0^{++}) propagators we find evidence for excited states which are probably the expected decay channels, pi+eta and K+Kbar.

  9. Ultrafast excited state dynamics of tris-(2,2'-bipyridine) Ruthenium (II)

    Energy Technology Data Exchange (ETDEWEB)

    Yeh, Alvin T.W. [Univ. of California, Berkeley, CA (United States)

    2000-03-01

    Time resolved anisotropy measurements and time dependent transient absorption measurements are used to study the evolution of the photoexcited Franck-Condon state to the formation of the long-lived triplet metal-to-ligand charge-transfer (3MLCT) state in tris-(2,2’-bipyridine) ruthenium. [Ru(bpy)3]2+ represents a large class of inorganic compounds with interesting and potentially applicable photophysical properties. These compounds have generated much interest in the inorganic chemistry community because their photophysical properties are easily manipulated by synthetic chemistry methods. However, little remains known about the processes which govern the evolution horn initial photoexcitation to the formation of the long-lived excited state.

  10. Super-iron Nanoparticles with Facile Cathodic Charge Transfer

    Energy Technology Data Exchange (ETDEWEB)

    M Farmand; D Jiang; B Wang; S Ghosh; D Ramaker; S Licht

    2011-12-31

    Super-irons contain the + 6 valence state of iron. One advantage of this is that it provides a multiple electron opportunity to store additional battery charge. A decrease of particle size from the micrometer to the nanometer domain provides a higher surface area to volume ratio, and opportunity to facilitate charge transfer, and improve the power, voltage and depth of discharge of cathodes made from such salts. However, super-iron salts are fragile, readily reduced to the ferric state, with both heat and contact with water, and little is known of the resultant passivating and non-passivating ferric oxide products. A pathway to decrease the super-iron particle size to the nano-domain is introduced, which overcomes this fragility, and retains the battery capacity advantage of their Fe(VI) valence state. Time and power controlled mechanosynthesis, through less aggressive, dry ball milling, leads to facile charge transfer of super-iron nanoparticles. Ex-situ X-ray Absorption Spectroscopy is used to explore the oxidation state and structure of these iron oxides during discharge and shows the significant change in stability of the ferrate structure to lower oxidation state when the particle size is in the nano-domain.

  11. A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Wenlan; Köhn, Andreas [Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart (Germany); InnovationLab GmbH, Speyerer St. 4, D-69115 Heidelberg (Germany); Lunkenheimer, Bernd [InnovationLab GmbH, Speyerer St. 4, D-69115 Heidelberg (Germany); Institute of Physical Chemistry, University of Mainz, Duesbergweg 10-14, D-55128 Mainz (Germany); Settels, Volker; Engels, Bernd [Institute of Physical and Theoretical Chemistry, University of Würzburg, Emil-Fischer-St. 42, D-97074 Würzburg (Germany); Fink, Reinhold F. [Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, D-72076 Tübingen (Germany)

    2015-08-28

    We present a general method for analyzing the character of singly excited states in terms of charge transfer (CT) and locally excited (LE) configurations. The analysis is formulated for configuration interaction singles (CIS) singly excited wave functions of aggregate systems. It also approximately works for the second-order approximate coupled cluster singles and doubles and the second-order algebraic-diagrammatic construction methods [CC2 and ADC(2)]. The analysis method not only generates a weight of each character for an excited state, but also allows to define the related quasi-diabatic states and corresponding coupling matrix elements. In the character analysis approach, we divide the target system into domains and use a modified Pipek-Mezey algorithm to localize the canonical MOs on each domain, respectively. The CIS wavefunction is then transformed into the localized basis, which allows us to partition the wavefunction into LE configurations within domains and CT configuration between pairs of different domains. Quasi-diabatic states are then obtained by mixing excited states subject to the condition of maximizing the weight of one single LE or CT configuration (localization in configuration space). Different aims of such a procedure are discussed, either the construction of pure LE and CT states for analysis purposes (by including a large number of excited states) or the construction of effective models for dynamics calculations (by including a restricted number of excited states). Applications are given to LE/CT mixing in π-stacked systems, charge-recombination matrix elements in a hetero-dimer, and excitonic couplings in multi-chromophoric systems.

  12. Elucidation of the Relationships between H-Bonding Patterns and Excited State Dynamics in Cyclovalone

    Directory of Open Access Journals (Sweden)

    Marco Lamperti

    2014-08-01

    Full Text Available Cyclovalone is a synthetic curcumin derivative in which the keto-enolic system is replaced by a cyclohexanone ring. This modification of the chemical structure might in principle result in an excited state that is more stable than that of curcumin, which in turn should produce an enhanced phototoxicity. Indeed, although curcumin exhibits photosensitized antibacterial activity, this compound is characterized by very fast excited-state dynamics which limit its efficacy as a photosensitizer. In previous works we showed that the main non-radiative decay pathway of keto-enolic curcuminoids is through excited-state transfer of the enolic proton to the keto-oxygen. Another effective deactivation pathway involves an intermolecular charge transfer mechanism occurring at the phenyl rings, made possible by intramolecular H-bonding between the methoxy and the hydroxyl substituent. In this paper we present UV-Vis and IR absorption spectra data with the aim of elucidating the intramolecular charge distribution of this compound and its solvation patterns in different environments, with particular focus on solute-solvent H-bonding features. Moreover, we discuss steady state and time-resolved fluorescence data that aim at characterizing the excited-state dynamics of cyclovalone, and we compare its decay photophysics to that of curcumin. Finally, because during the characterization procedures we found evidence of very fast photodegradation of cyclovalone, its photostability in four organic solvents was studied by HPLC and the corresponding relative degradation rates were calculated.

  13. Laser controlled charge-transfer reaction at low temperatures

    CERN Document Server

    Petrov, Alexander; Kotochigova, Svetlana

    2016-01-01

    We study the low-temperature charge transfer reaction between a neutral atom and an ion under the influence of near-resonant laser light. By setting up a multi-channel model with field-dressed states we demonstrate that the reaction rate coefficient can be enhanced by several orders of magnitude with laser intensities of $10^6$ W/cm$^2$ or larger. In addition, depending on laser frequency one can induce a significant enhancement or suppression of the charge-exchange rate coefficient. For our intensities multi-photon processes are not important.

  14. Visualization of Metal-to-Ligand and Ligand-to-Ligand Charge Transfer in Metal-Ligand Complexes

    Institute of Scientific and Technical Information of China (English)

    Yong Ding; Jian-xiu Guo; Xiang-si Wang; Sha-sha Liu; Feng-cai Ma

    2009-01-01

    Three methods including the atomic resolved density of state, charge difference density, and the transition density matrix are used to visualize metal to ligand charge transfer (MLCT) in ruthenium(Ⅱ) ammine complex. The atomic resolved density of state shows that there is density of Ru on the HOMOs. All the density is localized on the ammine, which reveals that the excited electrons in the Ru complex are delocalized over the ammine ligand. The charge difference density shows that all the holes are localized on the Ru and the electrons on the ammine. The localization explains the MLCT on excitation. The transition density matrix shows that there is electron-hole coherence between Ru and ammine. These methods are also used to examine the MLCT in Os(bpy)(p0p)Cl ("Osp0p"; bpy=2,2'-bipyridyl; p0p=4,4'-bipyridyl) and the ligand-to-ligand charge transfer (LLCT) in Alq3. The calculated results show that these methods are powerful to examine MLCT and LLCT in the metal-ligand system.

  15. 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.

  16. Rearrangements in ground and excited states

    CERN Document Server

    de Mayo, Paul

    1980-01-01

    Rearrangements in Ground and Excited States, Volume 3 presents essays on the chemical generation of excited states; the cis-trans isomerization of olefins; and the photochemical rearrangements in trienes. The book also includes essays on the zimmerman rearrangements; the photochemical rearrangements of enones; the photochemical rearrangements of conjugated cyclic dienones; and the rearrangements of the benzene ring. Essays on the photo rearrangements via biradicals of simple carbonyl compounds; the photochemical rearrangements involving three-membered rings or five-membered ring heterocycles;

  17. 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.

  18. Photoinduced intramolecular charge transfer of sodium 4-(N,N-dimethylamino)benzenesulfonate

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A new dual fluorescent N,N-dimethylaniline derivative, sodium 4-(N,N-dimethylamino)- benzenesulfonate (SDMAS), is reported. In SDMAS, the electron acceptor is linked to the phenyl ring via a sulfur atom at the para-position of the electron donor. It was found that SDMAS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as formamide, methanol and acetonitrile. In organic solvents only a single-band emission at ca.360 nm was observed in the short wavelength region. The dual fluorescence of SDMAS in water was found at 365 and 475 nm, respectively. Introduction of organic solvent such as ethanol, acetonitrile, and 1,4-dioxane into aqueous solution of SDMAS leads to blue-shift and quenching of the long-wavelength emission. Measurements of steady-state and picosecond time-resolved fluorescence indicate that the long wavelength fluorescence is emitted from a charge transfer (CT) state that is populated from the locally excited (LE) state, with the latter giving off the short wavelength fluorescence. The fact that a highly polar solvent is required to bring out the dual fluorescence suggests that the CT process of SDMAS has a high activation energy (Ea). In supporting this assumption the time-resolved fluorescence measurements give an Ea of 15.35 kJ.mol-1. It was assumed that the participation of the sulfur atom d-orbital in the conjugation of sulfonate group with phenyl ring and the strong twisting and inverting of the dimethylamino plane relative to the phenyl ring could be the reasons for the high activation energy. A molecular configuration change upon charge transfer in water was suggested for SDMAS based on the thermodynamic data. SDMAS reported here represents the example of the dual fluorescent amine substituted aromatic sulfonate.

  19. Near resonant charge transfer in the reaction F(+) + CO - F + CO(+)

    Science.gov (United States)

    Kusunoki, I.; Ishikawa, T.

    1985-06-01

    Charge transfer reactions in the F(+) + CO system were investigated using a F(+) ion beam in the energy range 10-300 eVlab. The electronically excited product CO(+) A2Pi(i) was observed by the emission from the A-X transitions. At low collisional energy the dominant product is in the vibrational level v' = 5. The reaction cross section sigma(5) is about 1 A-sq at 12 eVc.m. and decreases with increasing collision energy. The large cross section at v' = 5 can be interpreted by near-resonant charge-transfer reactions. The rotational temperature of the product is about 300 K, which is the temperature of the reactant CO gas. For the resonant charge transfer, the translational energy is not effective, but the electronic and vibrational energy couple with each other strongly.

  20. Linear interpolation method in ensemble Kohn-Sham and range-separated density-functional approximations for excited states

    DEFF Research Database (Denmark)

    Senjean, Bruno; Knecht, Stefan; Jensen, Hans Jørgen Aa

    2015-01-01

    of range separation and use of the slope of the linearly interpolated ensemble energy, rather than orbital energies. The range-separated approach is appealing, as it enables the rigorous formulation of a multideterminant state-averaged DFT method. In the exact theory, the short-range density functional......-independent) ground-state short-range exchange-correlation functional is used in this context, curvature appears, thus leading to an approximate weight-dependent excitation energy. In order to obtain unambiguous approximate excitation energies, we propose to interpolate linearly the ensemble energy between...... promising results have been obtained for both single (including charge transfer) and double excitations with spin-independent short-range local and semilocal functionals. Even at the Kohn-Sham ensemble DFT level, which is recovered when the range-separation parameter is set to 0, LIM performs better than...

  1. Momentum-Dependent Charge Transfer Excitations in Sr{sub {bold 2}}CuO {sub {bold 2}}Cl{sub {bold 2}} Angle-Resolved Electron Energy Loss Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Y.Y.; Zhang, F.C.; Dravid, V.P.; Ng, K.K.; Klein, M.V.; Schnatterly, S.E.; Miller, L.L. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States)]|[Science and Technology Center for Superconductivity, Northwestern University, Evanston, Illinois 60208 (United States)]|[Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221 (United States)]|[Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)]|[Department of Physics, Science and Technology Center for Superconductivity, University of Illinois, Urbana, Illinois 61801 (United States)]|[Department of Physics, University of Virginia, Charlottesville, Virginia 22901 (United States)]|[Ames Laboratory, Iowa State University, Ames, Iowa 50011 (United States)

    1996-08-01

    Electron-hole pair excitations in the insulating cuprates Sr{sub 2}CuO{sub 2}Cl{sub 2} were investigated by angle-resolved electron energy loss spectroscopy. The optically allowed and optically forbidden transitions were observed to be strongly anisotropic in Cu-O{sub 2} plane. The former show a large energy dispersion {approximately}1.5 eV along [110], and the latter appear at a higher energy position ({approximately}4.5 eV) only along [100], but not along [110]. We interpret these results as transitions involving excitons. A small exciton model is examined to explain both the observed features. {copyright} {ital 1996 The American Physical Society.}

  2. Photophysics of trioxatriangulenium ion. Electrophilic reactivity in the ground state and excited singlet state

    DEFF Research Database (Denmark)

    Reynisson, J.; Wilbrandt, R.; Brinck, V.

    2002-01-01

    of the long wavelength absorption band. A strong fluorescence is observed at 520 nm (tau(n) = 14.6 ns, phi(n) = 0.12 in deaerated acetonitrile). The fluorescence is quenched by 10 aromatic electron donors predominantly via a dynamic charge transfer mechanism, but ground state complexation is shown...

  3. Coherent dynamics of mixed Frenkel and Charge Transfer Excitons in Dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene Thin Films: The Importance of Hole Delocalization

    CERN Document Server

    Fujita, Takatoshi; Sawaya, Nicolas P D; Aspuru-Guzik, Alan

    2016-01-01

    Charge transfer states in organic semiconductors play crucial roles in processes such as singlet fission and exciton dissociation at donor/acceptor interfaces. Recently, a time-resolved spectroscopy study of dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene (DNTT) thin films provided evidence for the formation of mixed Frenkel and charge-transfer excitons after the photoexcitation. Here we investigate optical properties and excitation dynamics of the DNTT thin films by combining ab initio calculations and a stochastic Schrodinger equation. Our theory predicts that the low-energy Frenkel exciton band consists of 8 to 47% CT character. The quantum dynamics simulations show coherent dynamics of Frenkel and CT states in 50 fs after the optical excitation. We demonstrate the role of charge delocalization and localization in the mixing of CT states with Frenkel excitons as well as the role of their decoherence.

  4. Structural dynamics of a noncovalent charge transfer complex from femtosecond stimulated Raman spectroscopy.

    Science.gov (United States)

    Fujisawa, Tomotsumi; Creelman, Mark; Mathies, Richard A

    2012-09-06

    Femtosecond stimulated Raman spectroscopy is used to examine the structural dynamics of photoinduced charge transfer within a noncovalent electron acceptor/donor complex of pyromellitic dianhydride (PMDA, electron acceptor) and hexamethylbenzene (HMB, electron donor) in ethylacetate and acetonitrile. The evolution of the vibrational spectrum reveals the ultrafast structural changes that occur during the charge separation (Franck-Condon excited state complex → contact ion pair) and the subsequent charge recombination (contact ion pair → ground state complex). The Franck-Condon excited state is shown to have significant charge-separated character because its vibrational spectrum is similar to that of the ion pair. The charge separation rate (2.5 ps in ethylacetate and ∼0.5 ps in acetonitrile) is comparable to solvation dynamics and is unaffected by the perdeuteration of HMB, supporting the dominant role of solvent rearrangement in charge separation. On the other hand, the charge recombination slows by a factor of ∼1.4 when using perdeuterated HMB, indicating that methyl hydrogen motions of HMB mediate the charge recombination process. Resonance Raman enhancement of the HMB vibrations in the complex reveals that the ring stretches of HMB, and especially the C-CH(3) deformations are the primary acceptor modes promoting charge recombination.

  5. Resonant charge transfer at dielectric surfaces

    CERN Document Server

    Marbach, Johannes; Fehske, Holger

    2012-01-01

    We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable nitrogen molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green's function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for aluminum oxide, magnesium oxide, silicon oxide, and diamond at several kinetic energies of the projectile. With the exception of magnesium oxide the coefficients turn out to be of the order of...

  6. 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...

  7. 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...

  8. Comprehensive investigation of the excited-state dynamics of push-pull triphenylamine dyes as models for photonic applications.

    Science.gov (United States)

    Ishow, Eléna; Clavier, Gilles; Miomandre, Fabien; Rebarz, Mateusz; Buntinx, Guy; Poizat, Olivier

    2013-09-07

    A series of emitting push-pull triarylamine derivatives, models of their widely used homologues in photonics and organic electronics, was investigated by steady-state and time-resolved spectroscopy. Their structural originality stems from the sole change of the electron-withdrawing substituent X (-H: 1, -CN: 2, -NO2: 3, -CHC(CN)2: 4), giving rise to efficient emission tuning from blue to red upon increasing the X electron-withdrawing character. All compounds are highly fluorescent in alkanes. The more polar compounds 2-4 undergo considerable Stokes shift and emission quenching in polar solvents. Femtosecond transient absorption data allowed us to identify the nature of the emissive state which varies as a function of the compound and surrounding polarity. A long-lived ππ* excited state with weak charge transfer character was found for 1. This excited state evolves into a long-lived ICT state with red-shifted emission for 2 in polar solvents. For 3 and 4, the ICT state is directly populated in all solvents. Long-lived and emissive in n-hexane, it relaxes in toluene to a new ICT' conformation with stronger charge transfer character and enhanced Stokes shift. In more polar THF, ethanol, and nitrile solvents, ICT relaxes to a dark excited state ICT'' with viscosity-dependent kinetics (ICT'' state lifetime drops with increasing solvent polarity (150 ps for 3 in THF, 8.5 ps in butyronitrile, 1.9 ps in acetonitrile), denoting an efficient radiationless deactivation to the ground state (back charge transfer). This result reveals a very small S0-S1 energy gap at the relaxed ICT'' geometry, with a possible close-lying S0-S1 conical intersection, which suggests that the ICT → ICT'' process results from a structural change involving a large-amplitude molecular distortion. This fast structural change can account for the strong fluorescence quenching observed for 3 and 4 in polar solvents. Finally, the magnitude of intersystem crossing between the singlet and triplet excited

  9. Comparative assessment of density functional methods for evaluating essential parameters to simulate SERS spectra within the excited state energy gradient approximation

    Science.gov (United States)

    Mohammadpour, Mozhdeh; Jamshidi, Zahra

    2016-05-01

    The prospect of challenges in reproducing and interpretation of resonance Raman properties of molecules interacting with metal clusters has prompted the present research initiative. Resonance Raman spectra based on the time-dependent gradient approximation are examined in the framework of density functional theory using different methods for representing the exchange-correlation functional. In this work the performance of different XC functionals in the prediction of ground state properties, excitation state energies, and gradients are compared and discussed. Resonance Raman properties based on time-dependent gradient approximation for the strongly low-lying charge transfer states are calculated and compared for different methods. We draw the following conclusions: (1) for calculating the binding energy and ground state geometry, dispersion-corrected functionals give the best performance in comparison to ab initio calculations, (2) GGA and meta GGA functionals give good accuracy in calculating vibrational frequencies, (3) excited state energies determined by hybrid and range-separated hybrid functionals are in good agreement with EOM-CCSD calculations, and (4) in calculating resonance Raman properties GGA functionals give good and reasonable performance in comparison to the experiment; however, calculating the excited state gradient by using the hybrid functional on the hessian of GGA improves the results of the hybrid functional significantly. Finally, we conclude that the agreement of charge-transfer surface enhanced resonance Raman spectra with experiment is improved significantly by using the excited state gradient approximation.

  10. Photoinduced intramolecular charge transfer in push-pull polyenes: effects of solvation, electron-donor group, and polyenic chain length.

    Science.gov (United States)

    Akemann, Walther; Laage, Damien; Plaza, Pascal; Martin, Monique M; Blanchard-Desce, Mireille

    2008-01-17

    Subpicosecond absorption spectroscopy is used to characterize the primary photoinduced processes in a class of push-pull polyenes bearing a julolidine end group as the electron donor and a diethylthiobarbituric acid end group as the electron acceptor. The excited-state decay time and relaxation pathway have been studied for four polyenes of increasing chain length (n = 2-5 double bonds) in aprotic solvents of different solvation time, polarity, and viscosity. Intramolecular charge transfer (ICT) leading to a transient state of cyanine-like structure (fully conjugated with no bond length alternation) is observed in all polar solvents at a solvent dependent rate, but the reaction is not observed in cyclohexane, a nonpolar solvent. In polar solvents, the reaction time increases with the average solvation time but remains slightly larger, except in the viscous solvent triacetin. These facts are interpreted as an indication that both solvent reorganization and internal restructuring are involved in the ICT-state formation. The observed photodynamics resemble those we previously found for another class of polyenes bearing a dibutylaniline group as the donor, including a similar charge-transfer rate in spite of the larger electron donor character of the julolidine group. This observation brings further support to the proposal that an intramolecular coordinate is involved in the charge-transfer reaction, possibly a torsional motion of the donor end group. On the other hand, relaxation of the ICT state leads to cis-trans isomerization or crossing to the triplet state, depending on the length of the polyenic chain. In dioxane, tetrahydrofuran, and triacetin, the ICT state of the shorter chains (n = 2, 3) relaxes to the isomer with a viscosity-dependent rate, while that of the longer ones (n = 4, 5) leads to the triplet state with a viscosity-independent rate, as expected. In acetonitrile, the ICT-state lifetime is generally much shorter. A change from photoisomerization to

  11. Excited-state charge coupled proton transfer reaction in dipole-functionalized salicylideneaniline

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Kew-Yu, E-mail: kyuchen@fcu.edu.tw; Hu, Jiun-Wei

    2015-03-15

    Based on design and synthesis of salicylideneaniline derivatives 1–4, we demonstrate an exceedingly useful system to investigate the excited-state intramolecular charge transfer (ESICT) coupled with excited-state intramolecular proton transfer (ESIPT) reaction via the dipolar functionality of Schiff base salicylideneaniline. In solid and aprotic solvents 1–4 exist mainly as E conformers that possess a strong intramolecular six-membered-ring hydrogen bond. Compounds 2–4 exhibit solely a long-wavelength proton-transfer tautomer emission, while dipole-functionalized Schiff base 1 exhibits remarkable dual emission due to the different solvent-polarity environments between ESICT and ESIPT states. Moreover, the geometric structures, frontier molecular orbitals (MOs) and the potential energy curves for 1–4 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations. - Highlights: • A dipole-functionalized salicylideneaniline derivative was synthesized. • The Schiff base exhibits remarkable dual emission. • A novel ESICT/ESIPT coupled system was created.

  12. On the nature of an excited state

    CERN Document Server

    Blossier, Benoit

    2016-01-01

    In many lattice simulations with dynamical quarks, radial or orbital excitations of hadrons lie near multihadron thresholds: it makes the extraction of excited states properties more challenging and can introduce some systematics difficult to estimate without an explicit computation of correlators using interpolating fields strongly coupled to multihadronic states. In a recent study of the strong decay of the first radial excitation of the $B^*$ meson, this issue has been investigated and we have clues that a diquark interpolating field $\\bar{b} \\gamma^i q$ is very weakly coupled to a $B \\pi$ $P$-wave state while the situation is quite different if we consider an interpolating field of the kind $\\bar{b} \

  13. 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

  14. The investigation of excited state proton transfer mechanism in water-bridged 7-azaindole

    Science.gov (United States)

    Zhang, Yong-Jia; Zhao, Jin-Feng; Li, Yong-Qing

    2016-01-01

    Based on the time-dependent density functional theory (TDDFT), the excited-state intermolecular proton transfer (ESIPT) mechanism of water-bridged 7-azaindole has been investigated theoretically. The calculations of primary bond lengths and the IR vibrational spectra between the S0 state and the S1 state that verified the intramolecular hydrogen bond were strengthened. The fact that reproduced experimental absorbance and fluorescence emission spectra well theoretically demonstrate that the TDDFT theory we adopted is reasonable and effective. In addition, intramolecular charge transfer based on the frontier molecular orbitals demonstrated the indication of the ESIPT reaction. The constructed potential energy curves of ground state and the first excited state based on keeping the H2···O3 and H6···N7 distances fixed at a series of values have been used to illustrate the ESIPT process. A relative lower barrier of 5.94 kcal/mol in the S1 state potential energy curve for type II (lower than that of 9.82 kcal/mol in the S1 state for type I) demonstrates that type II ESIPT process occurs firstly in 7Al-2H2O complex.

  15. Nodal Variational Principle for Excited States

    CERN Document Server

    Zahariev, Federico; Levy, Mel

    2016-01-01

    It is proven that the exact excited-state wavefunction and energy may be obtained by minimizing the energy expectation value of a trial wave function that is constrained only to have the correct nodes of the state of interest. This excited-state nodal minimum principle has the advantage that it requires neither minimization with the con- straint of wavefunction orthogonality to all lower eigenstates nor the antisymmetry of the trial wavefunctions. It is also found that the minimization over the entire space can be partitioned into several in- terconnected minimizations within the individual nodal regions, and the exact excited-state energy may be obtained by a minimization in just one or several of these nodal regions. For the proofs of the the- orem, it is observed that the many-electron eigenfunction, restricted to a nodal region, is equivalent to a ground state wavefunction of one electron in a higher dimensional space; and an explicit excited-state energy variational expression is obtained by generalizing...

  16. Electronic Excited States of Tungsten(0) Arylisocyanides

    OpenAIRE

    2015-01-01

    W(CNAryl)_6 complexes containing 2,6-diisopropylphenyl isocyanide (CNdipp) are powerful photoreductants with strongly emissive long-lived excited states. These properties are enhanced upon appending another aryl ring, e.g., W(CNdippPh^(OMe)_2)_6; CNdippPh^(OMe)_2 = 4-(3,5-dimethoxyphenyl)-2,6-diisopropylphenylisocyanide (Sattler et al. J. Am. Chem. Soc. 2015, 137, 1198−1205). Electronic transitions and low-lying excited states of these complexes were investigated by time-dependent density fun...

  17. Computing Correct Truncated Excited State Wavefunctions

    CERN Document Server

    Bacalis, N C; Zang, J; Karaoulanis, D

    2016-01-01

    We demonstrate that, if a truncated expansion of a wave function is small, then the standard excited states computational method, of optimizing one root of a secular equation, may lead to an incorrect wave function - despite the correct energy according to the theorem of Hylleraas, Undheim and McDonald - whereas our proposed method [J. Comput. Meth. Sci. Eng. 8, 277 (2008)] (independent of orthogonality to lower lying approximants) leads to correct reliable small truncated wave functions. The demonstration is done in He excited states, using truncated series expansions in Hylleraas coordinates, as well as standard configuration-interaction truncated expansions.

  18. 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 (<50 fs) dynamics of β carotene and peridinin. The studies show evidence for a structurally displaced intermediate in both cases and strong 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.

  19. 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

  20. State-specific transport properties of partially ionized flows of electronically excited atomic gases

    Science.gov (United States)

    Istomin, V. A.; Kustova, E. V.

    2017-03-01

    State-to-state approach for theoretical study of transport properties in atomic gases with excited electronic degrees of freedom of both neutral and ionized species is developed. The dependence of atomic radius on the electronic configuration of excited atoms is taken into account in the transport algorithm. Different cutoff criteria for increasing atomic radius are discussed and the limits of applicability for these criteria are evaluated. The validity of a Slater-like model for the calculation of state-resolved transport coefficients in neutral and ionized atomic gases is shown. For ionized flows, a method of evaluation for effective cross-sections of resonant charge-transfer collisions is suggested. Accurate kinetic theory algorithms for modelling the state-specific transport properties are applied for the prediction of transport coefficients in shock heated flows. Based on the numerical observations, different distributions over electronic states behind the shock front are considered. For the Boltzmann-like distributions at temperatures greater than 14,000 K, an important effect of electronic excitation on the partial thermal conductivity and viscosity coefficients is found for both neutral and ionized atomic gases: increasing radius of excited atoms causes a strong decrease in these transport coefficients. Similarly, the presence of electronically excited states with increased atomic radii leads to reduced diffusion coefficients. Nevertheless the overall impact of increasing effective cross-sections on the transport properties just behind the shock front under hypersonic reentry conditions is found to be minor since the populations of high-lying electronic energy levels behind the shock waves are low.

  1. Strategic modulation of the photonic properties of conjugated organometallic Pt-Ir polymers exhibiting hybrid CT-excited states.

    Science.gov (United States)

    Soliman, Ahmed M; Zysman-Colman, Eli; Harvey, Pierre D

    2015-04-01

    Polymer 6, ([trans-Pt(PBu3 )2 (C≡C)2 ]-[Ir(dFMeppy)2 (N^N)](PF6 ))n , (([Pt]-[Ir](PF6 ))n ; N^N = 5,5'-disubstituted-2,2'-bipyridyl; dFMeppy = 2-(2,4-difluoro-phenyl)-5-methylpyridine) is prepared along with model compounds. These complexes are investigated by absorption and emission spectroscopy and their photophysical and electrochemical properties are measured and compared with their corresponding non fluorinated complexes. Density functional theory (DFT) and time-dependent DFT computations corroborate the nature of the excited state as being a hybrid between the metal-to-ligand charge transfer ((1,3) MLCT) for the trans-Pt(PBu3 )2 (C≡CAr)2 unit, [Pt] and the metal-to-ligand/ligand-to-ligand' charge transfer ((1,3) ML'CT/LL'CT) for [Ir] with L = dFMeppy. Overall, the fluorination of the phenylpyridine group expectedly does not change the nature of the excited state but desirably induces a small blue shift of the absorption and emission bands along a slight decrease in emission quantum yields and lifetimes.

  2. Estimation of Ground-State and Singlet Excited-State Dipole Moments of Substituted Schiff Bases Containing Oxazolidin-2-one Moiety through Solvatochromic Methods.

    Science.gov (United States)

    Kumari, Rekha; Varghese, Anitha; George, Louis

    2017-01-01

    Absorption and fluorescence studies on novel Schiff bases (E)-4-(4-(4-nitro benzylideneamino)benzyl)oxazolidin-2-one (NBOA) and (E)-4-(4-(4-chlorobenzylidene amino)benzyl)oxazolidin-2-one (CBOA) were recorded in a series of twelve solvents upon increasing polarity at room temperature. Large Stokes shift indicates bathochromic fluorescence band for both the molecules. The photoluminescence properties of Schiff bases containing electron withdrawing and donating substituents were analyzed. Intramolecular charge transfer behavior can be studied based on the influence of different substituents in Schiff bases. Changes in position and intensity of absorption and fluorescence spectra are responsible for the stabilization of singlet excited-states of Schiff base molecules with different substituents, in polar solvents. This is attributed to the Intramolecular charge transfer (ICT) mechanism. In case of electron donating (-Cl) substituent, ICT contributes largely to positive solvatochromism when compared to electron withdrawing (-NO2) substituent. Ground-state and singlet excited-state dipole moments of NBOA and CBOA were calculated experimentally using solvent polarity function approaches given by Lippert-Mataga, Bakhshiev, Kawskii-Chamma-Viallet and Reichardt. Due to considerable π- electron density redistribution, singlet excited-state dipole moment was found to be greater than ground-state dipole moment. Ground-state dipole moment value which was determined by quantum chemical method was used to estimate excited-state dipole moment using solvatochromic correlations. Kamlet-Abboud-Taft and Catalan multiple linear regression approaches were used to study non-specific solute-solvent interaction and hydrogen bonding interactions in detail. Optimized geometry and HOMO-LUMO energies of NBOA and CBOA have been determined by DFT and TD-DFT/PCM (B3LYP/6-311G (d, p)). Mulliken charges and molecular electrostatic potential have also been evaluated from DFT calculations.

  3. Triplet excited state properties in variable gap π-conjugated donor–acceptor–donor chromophores

    KAUST Repository

    Cekli, Seda

    2016-02-12

    A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

  4. Paramagnetic excited vortex states in superconductors

    Science.gov (United States)

    Gomes, Rodolpho Ribeiro; Doria, Mauro M.; Romaguera, Antonio R. de C.

    2016-06-01

    We consider excited vortex states, which are vortex states left inside a superconductor once the external applied magnetic field is switched off and whose energy is lower than of the normal state. We show that this state is paramagnetic and develop here a general method to obtain its Gibbs free energy through conformal mapping. The solution for any number of vortices in any cross-section geometry can be read off from the Schwarz-Christoffel mapping. The method is based on the first-order equations used by Abrikosov to discover vortices.

  5. Excited singlet states of "hairpin" polyenes

    OpenAIRE

    Froelich, Wolfgang; Dewey, Harry J.; Deger, Hans; Dick, Bernhard; Klingensmith, Kenneth A.; Puettmann, Wilhelm; Vogel, Emanuel; Hohlneicher, Georg; Michl, Josef

    1983-01-01

    The synthesis and UV-visible, polarized-fluorescence and MCD spectra of 6 U-shaped hairpin polyenes (e.g., I) are reported. Qual. arguments and results of p-electron calcns. permit the identification of 4 excited singlet states and their assignment to mixts. of singly and doubly excited configurations. The hairpin polyenes represent a link between the all-trans-polyenes on the 1 hand and the annulenes and acenes on the other; they have the topol. of the former and a geometry near that of the ...

  6. Elementary charge-transfer processes in mesoscopic conductors

    NARCIS (Netherlands)

    Vanević, M.; Nazarov, Y.V.; Belzig, W.

    2008-01-01

    We determine charge-transfer statistics in a quantum conductor driven by a time-dependent voltage and identify the elementary transport processes. At zero temperature unidirectional and bidirectional single-charge transfers occur. The unidirectional processes involve electrons injected from the sour

  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. STIRAP on helium: Excitation to Rydberg states

    Science.gov (United States)

    Yuan, Deqian

    Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S→33P→nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of ~ 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable ~790 nm IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S → 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections.

  9. 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)

    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.

  10. Internal charge transfer based ratiometric interaction of anionic surfactant with calf thymus DNA bound cationic surfactant: Study I

    Science.gov (United States)

    Mukherjee, Abhijit; Chaudhuri, Tandrima; Moulik, Satya Priya; Banerjee, Manas

    2016-01-01

    Cetyl trimethyl ammonium bromide (CTAB) binds calf thymus (ct-) DNA like anionic biopolymers electrostatically and established equilibrium both in the ground as well as in excited state in aqueous medium at pH 7. Anionic sodium dodecyl sulfate (SDS) does not show even hydrophobic interaction with ct-DNA at low concentration. On contrary, SDS can establish well defined equilibrium with DNA bound CTAB in ground state where the same CTAB-DNA isosbestic point reappears. First report of internal charge transfer (ICT) based binding of CTAB with ct-DNA as well as ICT based interaction of anionic SDS with DNA bound CTAB that shows dynamic quenching contribution also. The reappearance of anodic peak and slight increase in cathodic peak current with increasing concentration (at lower range) of anionic SDS, possibly reflect the release of CTAB from DNA bound CTAB by SDS.

  11. Internal charge transfer based ratiometric interaction of anionic surfactant with calf thymus DNA bound cationic surfactant: Study I.

    Science.gov (United States)

    Mukherjee, Abhijit; Chaudhuri, Tandrima; Moulik, Satya Priya; Banerjee, Manas

    2016-01-01

    Cetyl trimethyl ammonium bromide (CTAB) binds calf thymus (ct-) DNA like anionic biopolymers electrostatically and established equilibrium both in the ground as well as in excited state in aqueous medium at pH 7. Anionic sodium dodecyl sulfate (SDS) does not show even hydrophobic interaction with ct-DNA at low concentration. On contrary, SDS can establish well defined equilibrium with DNA bound CTAB in ground state where the same CTAB-DNA isosbestic point reappears. First report of internal charge transfer (ICT) based binding of CTAB with ct-DNA as well as ICT based interaction of anionic SDS with DNA bound CTAB that shows dynamic quenching contribution also. The reappearance of anodic peak and slight increase in cathodic peak current with increasing concentration (at lower range) of anionic SDS, possibly reflect the release of CTAB from DNA bound CTAB by SDS.

  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. Spectroscopy of equilibrium and nonequilibrium charge transfer in semiconductor quantum structures

    Science.gov (United States)

    Rössler, C.; Burkhard, S.; Krähenmann, T.; Röösli, M.; Märki, P.; Basset, J.; Ihn, T.; Ensslin, K.; Reichl, C.; Wegscheider, W.

    2014-08-01

    We investigate equilibrium and nonequilibrium charge-transfer processes by performing high-resolution transport spectroscopy. Using electrostatically defined quantum dots for energy-selective emission and detection, we achieved very high spectral resolution and a high degree of tunability of relevant experimental parameters. Most importantly, we observe that the spectral width of elastically transferred electrons can be substantially smaller than the linewidth of a thermally broadened Coulomb peak. This finding indicates that the charge-transfer process is fast compared to the electron-phonon interaction time. By drawing an analogy to double quantum dots, we argue that the spectral width of the elastic resonance is determined by the lifetime broadening hΓ of the emitter and detector states. Good agreement with the model is found also in an experiment in which the charge transfer is in the regime hΓ≫kBT. By performing spectroscopy below the Fermi energy, we furthermore observe elastic and inelastic transfer of holes.

  14. Optical studies of the charge transfer complex in polythiophene/fullerene blends for organic photovoltaic applications

    Science.gov (United States)

    Drori, T.; Holt, J.; Vardeny, Z. V.

    2010-08-01

    We studied the photophysics of regioregular polythiophene/ C61 (RR-P3HT/PCBM) blend films utilized for organic photovoltaic applications using the femtosecond transient and steady-state photomodulation techniques with above-gap and below-gap pump excitations and electroabsorption spectroscopy. We provide strong evidence for the existence of charge transfer complex (CTC) state in the blend that is formed deep inside the optical gap of the polymer and fullerene constituents, which is clearly revealed in the electroabsorption spectrum with an onset at 1.2 eV. We identify this “midgap” band as the lowest lying CTC state formed at the interfaces separating the polymer and fullerene phases. With above-gap pump excitation the primary photoexcitations in the blend are excitons and polarons in the polymer domains that are generated within the experimental time resolution (150 fs), having distinguishable photoinduced absorption (PA) bands in the mid-IR. The photogenerated excitons subsequently decay within ˜10ps , consistent with the polymer weak photoluminescence in the blend. In contrast, with below-gap pump excitation, a new PA band in the mid-IR is generated within our time resolution, which is associated with photogenerated species that decay into polarons at much later times; also no PA of excitons is observed. We interpret the photoexcitations as CT excitons, which with below-gap pump excitation are resonantly generated on the CTC states at the interfaces, as the first step for polaron generation, without involving intrachain excitons in the polymer phase. We found that the polarons generated with below-gap pump excitation are trapped at the interfaces with relatively long lifetime, and thus may generate polarons on the polymer chains and fullerene molecules with a different mechanism than with above-gap excitation. In any case the interfacial polarons generated with below-gap excitation do not substantially contribute to the photocurrent density in photovoltaic

  15. Linear and third- and fifth-order nonlinear spectroscopies of a charge transfer system coupled to an underdamped vibration

    Energy Technology Data Exchange (ETDEWEB)

    Dijkstra, Arend G., E-mail: arend.dijkstra@mpsd.mpg.de, E-mail: tanimura@kuchem.kyoto-u.ac.jp [Max Planck Institute for the Structure and Dynamics of Matter, Hamburg (Germany); Tanimura, Yoshitaka, E-mail: arend.dijkstra@mpsd.mpg.de, E-mail: tanimura@kuchem.kyoto-u.ac.jp [Department of Chemistry, Kyoto University, Kyoto (Japan)

    2015-06-07

    We study hole, electron, and exciton transports in a charge transfer system in the presence of underdamped vibrational motion. We analyze the signature of these processes in the linear and third-, and fifth-order nonlinear electronic spectra. Calculations are performed with a numerically exact hierarchical equations of motion method for an underdamped Brownian oscillator spectral density. We find that combining electron, hole, and exciton transfers can lead to non-trivial spectra with more structure than with excitonic coupling alone. Traces taken during the waiting time of a two-dimensional (2D) spectrum are dominated by vibrational motion and do not reflect the electron, hole, and exciton dynamics directly. We find that the fifth-order nonlinear response is particularly sensitive to the charge transfer process. While third-order 2D spectroscopy detects the correlation between two coherences, fifth-order 2D spectroscopy (2D population spectroscopy) is here designed to detect correlations between the excited states during two different time periods.

  16. Linear and third- and fifth-order nonlinear spectroscopies of a charge transfer system coupled to an underdamped vibration.

    Science.gov (United States)

    Dijkstra, Arend G; Tanimura, Yoshitaka

    2015-06-01

    We study hole, electron, and exciton transports in a charge transfer system in the presence of underdamped vibrational motion. We analyze the signature of these processes in the linear and third-, and fifth-order nonlinear electronic spectra. Calculations are performed with a numerically exact hierarchical equations of motion method for an underdamped Brownian oscillator spectral density. We find that combining electron, hole, and exciton transfers can lead to non-trivial spectra with more structure than with excitonic coupling alone. Traces taken during the waiting time of a two-dimensional (2D) spectrum are dominated by vibrational motion and do not reflect the electron, hole, and exciton dynamics directly. We find that the fifth-order nonlinear response is particularly sensitive to the charge transfer process. While third-order 2D spectroscopy detects the correlation between two coherences, fifth-order 2D spectroscopy (2D population spectroscopy) is here designed to detect correlations between the excited states during two different time periods.

  17. Photoinduced intramolecular charge transfer of sodium 4-(N,N-dimethylamino)benzenesulfonate

    Institute of Scientific and Technical Information of China (English)

    林丽榕; 江云宝

    2000-01-01

    A new dual fluorescent N,N-dimethylaniline derivative, sodium 4-(N,N-dimethylamino)-benzenesulfonate (SDMAS), is reported. In SDMAS, the electron acceptor is linked to the phenyl ring via a sulfur atom at the para-position of the electron donor. It was found that SDMAS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as formamide, methanol and acetonitrile. In organic solvents only a single-band emission at ca.360 nm was observed in the short wavelength region. The dual fluorescence of SDMAS in water was found at 365 and 475 nm, respectively. Introduction of organic solvent such as ethanol, acetonitrile, and 1,4-dioxane into aqueous solution of SDMAS leads to blue-shift and quenching of the long-wavelength emission. Measurements of steady-state and picosecond time-resolved fluorescence indicate that the long wavelength fluorescence is emitted from a charge transfer (CT) state that is populated from the locally excited (LE) state, with the latter giving off the

  18. Quantum Monte Carlo Treatment of the Charge Transfer and Diradical Electronic Character in a Retinal Chromophore Minimal Model.

    Science.gov (United States)

    Zen, Andrea; Coccia, Emanuele; Gozem, Samer; Olivucci, Massimo; Guidoni, Leonardo

    2015-03-10

    The penta-2,4-dieniminium cation (PSB3) displays similar ground state and first excited state potential energy features as those of the retinal protonated Schiff base (RPSB) chromophore in rhodopsin. Recently, PSB3 has been used to benchmark several electronic structure methods, including highly correlated multireference wave function approaches, highlighting the necessity to accurately describe the electronic correlation in order to obtain reliable properties even along the ground state (thermal) isomerization paths. In this work, we apply two quantum Monte Carlo approaches, the variational Monte Carlo and the lattice regularized diffusion Monte Carlo, to study the energetics and electronic properties of PSB3 along representative minimum energy paths and scans related to its thermal cis–trans isomerization. Quantum Monte Carlo is used in combination with the Jastrow antisymmetrized geminal power ansatz, which guarantees an accurate and balanced description of the static electronic correlation thanks to the multiconfigurational nature of the antisymmetrized geminal power term, and of the dynamical correlation, due to the presence of the Jastrow factor explicitly depending on electron–electron distances. Along the two ground state isomerization minimum energy paths of PSB3, CASSCF calculations yield wave functions having either charge transfer or diradical character in proximity of the two transition state configurations. Here, we observe that at the quantum Monte Carlo level of theory, only the transition state with charge transfer character can be located. The conical intersection, which becomes highly sloped, is observed only if the path connecting the two original CASSCF transition states is extended beyond the diradical one, namely by increasing the bond-length-alternation (BLA). These findings are in good agreement with the results obtained by MRCISD+Q calculations, and they demonstrate the importance of having an accurate description of the static and

  19. Excited-state relaxation of some aminoquinolines

    Directory of Open Access Journals (Sweden)

    2006-01-01

    Full Text Available The absorption and fluorescence spectra, fluorescence quantum yields and lifetimes, and fluorescence rate constants ( k f of 2-amino-3-( 2 ′ -benzoxazolylquinoline (I, 2-amino-3-( 2 ′ -benzothiazolylquinoline (II, 2-amino-3-( 2 ′ -methoxybenzothiazolyl-quinoline (III, 2-amino-3-( 2 ′ -benzothiazolylbenzoquinoline (IV at different temperatures have been measured. The shortwavelength shift of fluorescence spectra of compounds studied (23–49 nm in ethanol as the temperature decreases (the solvent viscosity increases points out that the excited-state relaxation process takes place. The rate of this process depends essentially on the solvent viscosity, but not the solvent polarity. The essential increasing of fluorescence rate constant k f (up to about 7 times as the solvent viscosity increases proves the existence of excited-state structural relaxation consisting in the mutual internal rotation of molecular fragments of aminoquinolines studied, followed by the solvent orientational relaxation.

  20. Rearrangements in ground and excited states

    CERN Document Server

    de Mayo, Paul

    1980-01-01

    Rearrangements in Ground and Excited States, Volume 2 covers essays on the theoretical approach of rearrangements; the rearrangements involving boron; and the molecular rearrangements of organosilicon compounds. The book also includes essays on the polytopal rearrangement at phosphorus; the rearrangement in coordination complexes; and the reversible thermal intramolecular rearrangements of metal carbonyls. Chemists and people involved in the study of rearrangements will find the book invaluable.

  1. Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping

    KAUST Repository

    Begum, Raihana

    2016-12-17

    Since compelling device efficiencies of perovskite solar cells have been achieved, investigative efforts have turned to understand other key challenges in these systems, such as engineering interfacial energy-level alignment and charge transfer (CT). However, these types of studies on perovskite thin-film devices are impeded by the morphological and compositional heterogeneity of the films and their ill-defined surfaces. Here, we use well-defined ligand-protected perovskite nanocrystals (NCs) as model systems to elucidate the role of heterovalent doping on charge-carrier dynamics and energy level alignment at the interface of perovskite NCs with molecular acceptors. More specifically, we develop an in situ doping approach for colloidal CsPbBr3 perovskite NCs with heterovalent Bi3+ ions by hot injection to precisely tune their band structure and excited-state dynamics. This synthetic method allowed us to map the impact of doping on CT from the NCs to different molecular acceptors. Using time-resolved spectroscopy with broadband capability, we clearly demonstrate that CT at the interface of NCs can be tuned and promoted by metal ion doping. We found that doping increases the energy difference between states of the molecular acceptor and the donor moieties, subsequently facilitating the interfacial CT process. This work highlights the key variable components not only for promoting interfacial CT in perovskites, but also for establishing a higher degree of precision and control over the surface and the interface of perovskite molecular acceptors.

  2. Charge transfer and mixed-valence behavior in phtalocyanine-dimer cations.

    Science.gov (United States)

    Monari, Antonio; Evangelisti, Stefano; Leininger, Thierry

    2010-09-28

    Phtalocyanine compounds deserved a considerable interest in recent times, particularly because of their possible use in the field of nanoelectronics. In particular, the charge mobility (of both electrons and holes) in phtalocyanine stacked arrangements has been recently extensively investigated. The present work focuses on the study of the hole-transfer mechanism between two phtalocyanine monomers. For an interdisk distance larger than 4.5 bohrs, the eclipsed dimer exhibits a mixed-valence behavior, with a saddle point transition state separating two equivalent minima. This behavior, however, is strongly dependent on the relative angle between the disks. In particular, the mixed-valence character of the compound is strongly enhanced for arrangements that are far from the eclipsed geometry. Moreover, for values of the angle close to π/8 and 3π/8, the ground and excited transition states have exactly the same energy, thus implying the presence of a conical intersection. These results can have deep implication in the charge transfer along phtalocyanine chains.

  3. Charge Transfer Fluctuations as a Signal for QGP

    OpenAIRE

    Shi, Lijun; Jeon, Sangyong

    2005-01-01

    In this work, the charge transfer fluctuation which was previously used for $pp$ collisions is proposed for relativistic heavy-ion collisions as a QGP probe. We propose the appearance of a local minimum at midrapidity for the charge transfer fluctuation as a signal for a QGP. Within a two-component neutral cluster model, we demonstrate that the charge transfer fluctuation can detect the presence of a QGP as well as the size of the QGP in the rapidity space. We also show that the forward-backw...

  4. Theoretical investigation on dual fluorescence and intramolecular charge transfer of 5-phenyl-5H-phenanthridin-6-one

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Quantum-chemical calculations with the time-dependent density function theory (TDDFT) have been carried out for 5-phenyl-5H-phenanthridin-6-one (PP). For this molecule, dual fluorescence and in- tramolecular charge transfer (ICT) were experimentally observed. The B3LYP functional with 6-311+G (2d, p) basis set has been used for the theoretical calculations. The solvent effects have been described within the polarizable continuum model (PCM). Ground-state geometry optimization reveals that the phenyl/phenanthridinone dihedral angle equals 90.0°, a nearly perpendicular structure. Vertical ab- sorption energy calculations characterize the lower singlet excited states both in gas phase and in solvents. It can be found that the lower excited states have locally excitation (LE) feature. Through constructing the potential energy curves of both isolated and solvated systems describing the LE→ICT reaction and fluorescence emission, we obtain the enthalpy difference ΔH between the LE and ICT states, energy barrier Ea, and energy difference δEFC, indicating the structural changes taking place during the ICT reaction. Potential curve and calculated emission energies for both isolated and sol- vated systems show a dual fluorescence phenomenon, consisting of a LE emission band and a red-shifted ICT band. Our calculations including the solvent effects indicate that the dual fluorescence is brought about by the change in molecular structure connected with the planarization of the twisted N-phenylphenanthridinone during the ICT reaction.

  5. Identification of excited states in conjugated polymers

    CERN Document Server

    Hartwell, L J

    2003-01-01

    This thesis reports quasi steady state photoinduced absorption measurements from three conjugated polymers: polypyridine (PPy), polyfluorene (PFO) and the emeraldine base (EB) form of polyaniline. The aim of these experiments was to determine the nature of the photoexcited states existing in these materials in the millisecond time domain, as this has important consequences for the operation of real devices manufactured using these materials. The results from the photoinduced absorption experiments are closely compared with published results from pulse radiolysis experiments. In all cases there is very good correspondence between the two data sets, which has enabled the photoexcited states to be assigned with a high degree of confidence. Quasi steady-state photoinduced absorption involves the measurement of the change in absorption of a material in response to optical excitation with a laser beam. The changes in absorption are small, so a instrument was developed and optimised for each different sample. Lock-i...

  6. Holographic Construction of Excited CFT States

    CERN Document Server

    Christodoulou, Ariana

    2016-01-01

    We present a systematic construction of bulk solutions that are dual to CFT excited states. The bulk solution is constructed perturbatively in bulk fields. The linearised solution is universal and depends only on the conformal dimension of the primary operator that is associated with the state via the operator-state correspondence, while higher order terms depend on detailed properties of the operator, such as its OPE with itself and generally involve many bulk fields. We illustrate the discussion with the holographic construction of the universal part of the solution for states of two dimensional CFTs, either on $R \\times S^1$ or on $R^{1,1}$. We compute the 1-point function both in the CFT and in the bulk, finding exact agreement. We comment on the relation with other reconstruction approaches.

  7. Excited state molecular structure determination in disordered media using laser pump/x-ray probe time-domain x-ray absorption spectroscopy.

    Energy Technology Data Exchange (ETDEWEB)

    Chen, L. X.; Chemistry

    2003-01-01

    Advances in X-ray technologies provide opportunities for solving structures of photoexcited state molecules with short lifetimes. Using X-ray pulses from a modern synchrotron source, the structure of a metal-to-ligand-charge-transfer (MLCT) excited state of CuI(dmp)2+ (dmp 1/4 2,9-dimethyl-1,10-phenanthroline) was investigated by laser pump/X-ray probe X-ray absorption fine structure (LPXP-XAFS) in fluid solution at room temperature on a nanosecond time scale. The experimental requirements for such pump-probe XAFS are described in terms of technical challenges: (1) conversion of optimal excited state population, (2) synchronization of the pump laser pulse and probe Xray pulse, and (3) timing of the detection. Using a laser pump pulse for the photoexcitation, a photoluminescent MLCT excited state of CuI(dmp)2(BArF), (dmp 1/4 2,9-dimethyl-1,10-phenanthroline), BArF 1/4 tetrakis(3,5-bis(trifluoromethylphenyl)borate) with a lifetime of 98{+-}5 ns was created. Probing the structure of this state at its optimal concentration using an X-ray pulse cluster with a total duration of 14.2 ns revealed that (1) a Cu{sup II} center was generated via a whole charge transfer; (2) the copper in the MLCT state bound an additional ligand to form a penta-coordinate complex with a likely trigonal bipyramidal geometry; and (3) the average Cu-N bond length increases in the MLCT excited state by 0.07 . In contrast to previously reported literature, the photoluminescence of this pentacoordinate MLCT state was not quenched upon ligation with the fifth ligand. On the basis of experimental results, we propose that the absorptive and emissive states have distinct geometries. The results represent X-ray characterization of a molecular excited state in fluid solution on a nanosecond time scale.

  8. Tetrathiafulvalene-1,3,5-triazines as (multi)donor-acceptor systems with tunable charge transfer: structural, photophysical, and theoretical investigations.

    Science.gov (United States)

    Pop, Flavia; Riobé, François; Seifert, Sabine; Cauchy, Thomas; Ding, Jie; Dupont, Nathalie; Hauser, Andreas; Koch, Marius; Avarvari, Narcis

    2013-05-06

    Palladium-catalyzed cross-coupling reactions between chlorinated 1,3,5-triazines (TZ) and tetrathiafulvalene (TTF) trimethyltin derivatives afford mono- and C3 symmetric tris(TTF)-triazines as donor-acceptor compounds in which the intramolecular charge transfer (ICT) is modulated by the substitution scheme on TTF and TZ and by chemical or electrochemical oxidation. The TTF-TZ-Cl2 and (SMe)2TTF-TZ-Cl2 derivatives show fully planar structures in the solid state as a consequence of the conjugation between the two units. Electrochemical and photophysical investigations, supported by theoretical calculations, clearly demonstrate that the lowest excited state can be ascribed to the intramolecular charge transfer (ICT) π(TTF)→π*(TZ) transition. The tris(TTF) compound [(SMe)2TTF]3-TZ shows fluorescence when excited in the ICT band, and the emission is quenched upon oxidation. The radical cations TTF(+•) are easily observed in all of the cases through chemical and electrochemical oxidation by steady-state absorption experiments. In the case of [(SMe)2TTF]3-TZ, a low energy band at 5000 cm(-1), corresponding to a coupling between TTF(+•) and TTF units, is observed. A crystalline radical cation salt with the TTF-TZ-Cl2 donor and PF6(-) anion, prepared by electrocrystallization, is described.

  9. Cyanide anion sensing mechanism of 1,3,5,7-tetratolyl aza-BODIPY: Intramolecular charge transfer and partial configuration change

    Science.gov (United States)

    Bhat, Haamid R.; Jha, Prakash C.

    2017-02-01

    The cyanide anion sensing mechanism of 1,3,5,7-tetratolyl aza-BODIPY (1) has been rigorously investigated using density functional theory and time dependent-density functional theory methods. Mulliken charge distribution and Natural Bond Orbital analysis reveals that cyanide addition may occur at both electrophilic centers with equal probability. The molecular orbital analysis reveals that first excited state (S1) of 1 is a local excited state with π-π∗ transition, whereas for 2 (the cyano form of 1), S1 , a charge-separation state, is found to be responsible for the intramolecular charge transfer (ICT) process which in conjunction with partial configuration change induces fluorescence stimulation in 2.

  10. 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.

  11. PROPENSITY RULES IN Ar—IMPACT EXCITATION OF H— IN DOUBLY EXCITED STATES

    Institute of Scientific and Technical Information of China (English)

    NaotoKoyama; MotoiMaeda; 等

    1990-01-01

    We have theoretically investigated excitation processes of H- ions in the doubly excited states by Ar-impact,using the impulse approximation and employing the hyperspherical wavefunctions.We have found that the H- ion in the double excited states tends to conserve its initial states as a “floppy linear triatomic molecule” during excitation processes except for the restriction arising from the Pauli exclusion principle for two atomic electrons.

  12. Carbazole-containing light- emitting polymers: Properties of excited states

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A series of light-emitting conjugated polymers alternatively involving carbazole and bivinylene arylene moieties in the main chain were synthesized via Wittig-Horner type copolymerization. The photoinduced charge transfer process relating to these polymers was investigated by using the technique of fluorescence spectroscopy. The interaction between excited copolymers and C60 in benzene solution was studied. The fluorescence quenching can be well described by the "sphere-of-action" mechanism. It is believed that two basic steps are involved in the quenching process, i.e. the diffusion of excitation within the conjugated polymers and the dissociation of the exctions trapped by fullerene. The radius of the sphere-of-action can be related to the excitation diffusion length, which depends on the lifetime of the exciton. The dynamic fluorescence quenching of the copolymers by another quencher, 1,4-dicyanobenzene (DCB) was also surveyed. Copolymers with different chain conformations show different temperature effects in the dynamic quenching. A planar conformation is beneficial for the quenching via bimolecular collision.

  13. Excited states of muonium in atomic hydrogen

    Indian Academy of Sciences (India)

    V S Kulhar

    2006-06-01

    Muonium formation in excited states in muon-hydrogen charge-exchange collision is investigated using a method developed in a previous paper. Differential cross-section results are found to resemble positronium formation cross-section results of positron-hydrogen charge-exchange problem. Forward differential and integrated cross-sections are computed for muon energy of 2 keV and higher. Total muonium formation cross-sections are computed using Jackson and Schiff scaling rules. Muonium formation cross-section results obtained from proton-hydrogen charge-exchange cross-section results, using velocity scaling are compared with the results of the present calculation.

  14. The intermolecular charge transfer integral as an indicator of future success in organic photovoltaics (Conference Presentation)

    Science.gov (United States)

    Collison, Christopher J.; Zheng, Chenyu; Hestand, Nicholas J.; Jalan, Ishita; Cody, Jeremy A.; Spano, Frank C.

    2016-09-01

    In recent years, higher power conversion efficiencies have been measured using "push-pull" or Donor-Acceptor (D-A) type compounds designed to specifically address bandgap and energy level requirements. Yet, a strong prescription is fundamentally lacking that improves materials for the set of all critical properties (including exciton diffusion rate and charge transport/ mobility) that combine to provide optimal performance. We will present our newest theoretical models that simulate the morphology-based spectroscopy for a series of squaraines, compounds representative of the total set of D-A type OPV-targets. The theory will describe how morphological and molecular structure influences i) the absorption spectrum, ii) the excited states and iii) the intermolecular charge transfer integral (ICTI). In particular, the ICTI's role in exciton diffusion and carrier mobility will be explored. Using device data that correlates with the ICTI variation, we will explain how this parameter must be considered in future design of new easily-purified, consistently processable, low-band-gap small molecules targeted for large scale OPV manufacture.

  15. 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.

  16. The polaron: Ground state, excited states, and far from equilibrium

    Energy Technology Data Exchange (ETDEWEB)

    Trugman, S.A. [Los Alamos National Lab., NM (United States). Theory Div.; Bonca, J. [Univ. of Ljubljana (Slovenia)]|[Jozef Stefan Inst., Ljubljana (Slovenia)

    1998-12-01

    The authors describe a variational approach for solving the Holstein polaron model with dynamical quantum phonons on an infinite lattice. The method is simple, fast, extremely accurate, and gives ground and excited state energies and wavefunctions at any momentum k. The method can also be used to calculate coherent quantum dynamics for inelastic tunneling and for strongly driven polarons far from equilibrium.

  17. Experimental and Quantum-Chemical Study of Electronically Excited States of Protolytic Isovanillin Species

    Science.gov (United States)

    Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Yu.

    2014-05-01

    Methods of electronic spectroscopy and quantum chemistry are used to compare protolytic vanillin and isovanillin species. Three protolytic species: anion, cation, and neutral are distinguished in the ground state of the examined molecules. Vanillin and isovanillin in the ground state in water possess identical spectral characteristics: line positions and intensities in the absorption spectra coincide. Minima of the electrostatic potential demonstrate that the deepest isomer minimum is observed on the carbonyl oxygen atom. However, investigations of the fluorescence spectra show that the radiative properties of isomers differ. An analysis of results of quantum-chemical calculations demonstrate that the long-wavelength ππ* transition in the vanillin absorption spectra is formed due to electron charge transfer from the phenol part of the molecule to oxygen atoms of the methoxy and carbonyl groups, and in the isovanillin absorption spectra, it is formed only on the oxygen atom of the methoxy group. The presence of hydroxyl and carbonyl groups in the structure of the examined molecules leads to the fact that isovanillin in the ground S0 state, the same as vanillin, possesses acidic properties, whereas in the excited S1 state, they possess basic properties. A comparison of the рKа values of aqueous solutions demonstrates that vanillin possesses stronger acidic and basic properties in comparison with isovanillin.

  18. Ensemble DFT Approach to Excited States of Strongly Correlated Molecular Systems.

    Science.gov (United States)

    Filatov, Michael

    2016-01-01

    Ensemble density functional theory (DFT) is a novel time-independent formalism for obtaining excitation energies of many-body fermionic systems. A considerable advantage of ensemble DFT over the more common Kohn-Sham (KS) DFT and time-dependent DFT formalisms is that it enables one to account for strong non-dynamic electron correlation in the ground and excited states of molecular systems in a transparent and accurate fashion. Despite its positive aspects, ensemble DFT has not so far found its way into the repertoire of methods of modern computational chemistry, probably because of the perceived lack of practically affordable implementations of the theory. The spin-restricted ensemble-referenced KS (REKS) method is perhaps the first computationally feasible implementation of the ideas behind ensemble DFT which enables one to describe accurately electronic transitions in a wide class of molecular systems, including strongly correlated molecules (biradicals, molecules undergoing bond breaking/formation), extended π-conjugated systems, donor-acceptor charge transfer adducts, etc.

  19. Relaxed excited states of color centers

    Energy Technology Data Exchange (ETDEWEB)

    Baldacchini, G.

    1992-12-31

    Color centers in alkali halides display an optical cycle which has been, and it is still today, a model case for similar processes in other materials. Moreover, the luminescence of some color centers is so efficient that it has been used in laser applications. However, the quantum state from which the emission of light is originated, the so called relaxed excited state (RES), is not very well known. Indeed, in spite of the wealth of experimental results collected and of the theoretical approaches attempted, an exact description of the RES is still missing. This paper, confined mainly to F centers which are the simplest point defects in crystals, contains a review of the main experimental evidences which has some light on the nature of the RES, with special emphasis on the latest magneto-optical experiments. Also, a description of the theoretical models is attempted whenever required by a particular argument.

  20. Photolysis of benzophenone with two-step two-laser excitation

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The first laser excites a molecule to a lower triplet state and another sequential laser excites it resonantly to higher triplet states or makes it ionization. This two-step two-laser method provides a novel way to study the electron transfer or charge transfer of excited molecules. The higher excited benzophenone and its radical cation can be observed under the time-resolved ab sorption method when it was excited to lower triplet state by one laser and another one exciting it to higher triplet states resonantly. The higher excited benzophenone molecules undergoing inter molecular hydrogen abstraction with iso-propylalcohol molecules are faster than the lower ones.

  1. Lowest excited states and optical absorption spectra of donor-acceptor copolymers for organic photovoltaics: a new picture emerging from tuned long-range corrected density functionals.

    Science.gov (United States)

    Pandey, Laxman; Doiron, Curtis; Sears, John S; Brédas, Jean-Luc

    2012-11-01

    Polymers with low optical gaps are of importance to the organic photovoltaics community due to their potential for harnessing a large portion of the solar energy spectrum. The combination along their backbones of electron-rich and electron-deficient fragments contributes to the presence of low-lying excited states that are expected to display significant charge-transfer character. While conventional hybrid functionals are known to provide unsatisfactory results for charge-transfer excitations at the time-dependent DFT level, long-range corrected (LRC) functionals have been reported to give improved descriptions in a number of systems. Here, we use such LRC functionals, considering both tuned and default range-separation parameters, to characterize the absorption spectra of low-optical-gap systems of interest. Our results indicate that tuned LRC functionals lead to simulated optical-absorption properties in good agreement with experimental data. Importantly, the lowest-lying excited states (excitons) are shown to present a much more localized nature than initially anticipated.

  2. Lowest excited states and optical absorption spectra of donor–acceptor copolymers for organic photovoltaics: a new picture emerging from tuned long-range corrected density functionals

    KAUST Repository

    Pandey, Laxman

    2012-01-01

    Polymers with low optical gaps are of importance to the organic photovoltaics community due to their potential for harnessing a large portion of the solar energy spectrum. The combination along their backbones of electron-rich and electron-deficient fragments contributes to the presence of low-lying excited states that are expected to display significant charge-transfer character. While conventional hybrid functionals are known to provide unsatisfactory results for charge-transfer excitations at the time-dependent DFT level, long-range corrected (LRC) functionals have been reported to give improved descriptions in a number of systems. Here, we use such LRC functionals, considering both tuned and default range-separation parameters, to characterize the absorption spectra of low-optical-gap systems of interest. Our results indicate that tuned LRC functionals lead to simulated optical-absorption properties in good agreement with experimental data. Importantly, the lowest-lying excited states (excitons) are shown to present a much more localized nature than initially anticipated. © 2012 the Owner Societies.

  3. 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

  4. Ab initio treatment of ion-induced charge transfer dynamics of isolated 2-deoxy-D-ribose.

    Science.gov (United States)

    Bacchus-Montabonel, Marie-Christine

    2014-08-21

    Modeling-induced radiation damage in biological systems, in particular, in DNA building blocks, is of major concern in cancer therapy studies. Ion-induced charge-transfer dynamics may indeed be involved in proton and hadrontherapy treatments. We have thus performed a theoretical approach of the charge-transfer dynamics in collision of C(4+) ions and protons with isolated 2-deoxy-D-ribose in a wide collision energy range by means of ab initio quantum chemistry molecular methods. The comparison of both projectile ions has been performed with regard to previous theoretical and experimental results. The charge transfer appears markedly less efficient with the 2-deoxy-D-ribose target than that with pyrimidine nucleobases, which would induce an enhancement of the fragmentation process in agreement with experimental measurements. The mechanism has been analyzed with regard to inner orbital excitations, and qualitative tendencies have been pointed out for studies on DNA buiding block damage.

  5. 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.

  6. How much double excitation character do the lowest excited states of linear polyenes have?

    Science.gov (United States)

    Starcke, Jan Hendrik; Wormit, Michael; Schirmer, Jochen; Dreuw, Andreas

    2006-10-01

    Doubly excited states play important roles in the low-energy region of the optical spectra of polyenes and their investigation has been subject of theoretical and experimental studies for more than 30 years now and still is in the focus of ongoing research. In this work, we address the question why doubly excited states play a role in the low-energy region of the optical spectrum of molecular systems at all, since from a naive point of view one would expect their excitation energy approximately twice as large as the one of the corresponding single excitation. Furthermore, we show that extended-ADC(2) is well suited for the balanced calculation of the low-lying excited 21Ag-, 11Bu- and 11Bu+ states of long all- trans polyenes, which are known to possess substantial double excitation character. A careful re-investigation of the performance of TDDFT calculations for these states reveals that the previously reported good performance for the 21Ag- state relies heavily on fortuitous cancellation of errors. Finally, the title question is answered such that for short polyenes the lowest excited 21Ag- and 11Bu- states can clearly be classified as doubly excited, whereas the 11Ag- ground state is essentially represented by the (ground-state) HF determinant. For longer polyenes, in addition to increasing double excitation contributions in the 21Ag- and 11Bu- states, the ground state itself aquires substantial double excitation character (45% in C 22H 24), so that the transition from the ground state to these excited states should not be addressed as the excitation of two electrons relative to the 11Ag- ground state.

  7. 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.

  8. 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) ...

  9. Ab initio calculation of H + He$^+$ charge transfer cross sections for plasma physics

    CERN Document Server

    Loreau, J; Lauvergnat, D; Desouter-Lecomte, M; Vaeck, N

    2010-01-01

    The charge transfer in low energy (0.25 to 150 eV/amu) H($nl$) + He$^+(1s)$ collisions is investigated using a quasi-molecular approach for the $n=2,3$ as well as the first two $n=4$ singlet states. The diabatic potential energy curves of the HeH$^+$ molecular ion are obtained from the adiabatic potential energy curves and the non-adiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge transfer cross section in the principal and orbital quantum numbers $n$ and $l$ of the initial or final state. We estimate the effect of the non-adiabatic rotational couplings, which is found to be important even at energies below 1 eV/amu. However, the effect is small on the total cross sections at energies below 10 eV/amu. We observe that to calculate charge transfer cross sections in a $n$ manifold, it is only necessary to include states with $n^{\\prime}\\leq n$...

  10. Excitation and ionization of hydrogen Rydberg states in a plasma

    Energy Technology Data Exchange (ETDEWEB)

    Glab, W.; Nayfeh, M.H.

    1982-08-01

    Hydrogen Rydberg states in a hydrogen plasma are optically excited from the plasma-excited n = 2 state. Photoionization and optogalvanic, which are due to electron-impact ionization and other collisional processes, are used to monitor the Rydberg states. This process may be used to study collisional ionization of the Rydberg states.

  11. Excitation and ionization of hydrogen Rydberg states in a plasma.

    Science.gov (United States)

    Glab, W; Nayfeh, M H

    1982-08-01

    Hydrogen Rydberg states in a hydrogen plasma are optically excited from the plasma-excited n = 2 state. Photoionization and optogalvanic ionization, which is due to electron-impact ionization and other collisional processes, are used to monitor the Rydberg states. This process may be used to study collisional ionization of the Rydberg states.

  12. 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.

  13. Influence of ligand substitution on excited state structural dynamics in Cu(I) bis-phenanthroline complexes.

    Energy Technology Data Exchange (ETDEWEB)

    Lockard, J. V.; Kabehie, S.; Zink, J. I.; Smolentsev, G.; Soldatov, A.; Chen, L. X. (Chemical Sciences and Engineering Division); (Northwestern Univ.); (Univ. of California at Los Angeles); (Southern Federal Univ.); (Lund Univ.)

    2010-01-01

    This study explores the influences of steric hindrance and excited state solvent ligation on the excited state dynamics of Cu{sup I} diimine complexes. Ultrafast excited state dynamics of Cu(I)bis(3,8-di(ethynyltrityl)-1,10-phenanthroline) [Cu{sup I}(detp){sub 2}]{sup +} are measured using femtosecond transient absorption spectroscopy. The steady state electronic absorption spectra and measured lifetimes are compared to those of Cu(I)bis(1,10-phenanthroline), [Cu{sup I}(phen){sub 2}]{sup +}, and Cu(I)bis(2-9-dimethyl-1,10-phenanthroline), [Cu{sup I}(dmp){sub 2}]{sup +}, model complexes to determine the influence of different substitution patterns of the phenanthroline ligand on the structural dynamics associated with the metal to ligand charge transfer excited states. Similarities between the [Cu{sup I}(detp){sub 2}]{sup +} and [Cu{sup I}(phen){sub 2}]{sup +} excited state lifetimes were observed in both coordinating and noncoordinating solvents and attributed to the lack of steric hindrance from substitution at the 2- and 9-positions. The solution-phase X-ray absorption spectra of [Cu{sup I}(detp){sub 2}]{sup +}, [Cu{sup I}(phen){sub 2}]{sup +}, and [Cu{sup I}(dmp){sub 2}]{sup +} are reported along with finite difference method calculations that are used to determine the degree of ground state dihedral angle distortion in solution and to account for the pre-edge features observed in the XANES region.

  14. Excited State Properties of Hybrid Perovskites.

    Science.gov (United States)

    Saba, Michele; Quochi, Francesco; Mura, Andrea; Bongiovanni, Giovanni

    2016-01-19

    Metal halide perovskites have come to the attention of the scientific community for the progress achieved in solar light conversion. Energy sustainability is one of the priorities of our society, and materials advancements resulting in low-cost but efficient solar cells and large-area lighting devices represent a major goal for applied research. From a basic point of view, perovskites are an exotic class of hybrid materials combining some merits of organic and inorganic semiconductors: large optical absorption, large mobilities, and tunable band gap together with the possibility to be processed in solution. When a novel class of promising semiconductors comes into the limelight, lively discussions ensue on the photophysics of band-edge excitations, because just the states close to the band edge are entailed in energy/charge transport and light emission. This was the case several decades ago for III-V semiconductors, it has been up to 10 years ago for organics, and it is currently the case for perovskites. Our aim in this Account is to rationalize the body of experimental evidence on perovskite photophysics in a coherent theoretical framework, borrowing from the knowledge acquired over the years in materials optoelectronics. A crucial question is whether photon absorption leads to a population of unbound, conductive free charges or instead excitons, neutral and insulating bound states created by Coulomb interaction just below the energy of the band gap. We first focus on the experimental estimates of the exciton binding energy (Eb): at room temperature, Eb is comparable to the thermal energy kBT in MAPbI3 and increases up to values 2-3kBT in wide band gap MAPbBr3 and MAPbCl3. Statistical considerations predict that these values, even though comparable to or larger than thermal energy, let free carriers prevail over bound excitons for all levels of excitation densities relevant for devices. The analysis of photophysics evidence confirms that all hybrid halide

  15. Excited State Dynamics in Carbon Nanotubes

    Science.gov (United States)

    Miyamoto, Yoshiyuki

    2004-03-01

    Carbon nanotube, one of the most promising materials for nano-technology, still suffers from its imperfection in crystalline structure that will make performance of nanotube behind theoretical limit. From the first-principles simulations, I propose efficient methods to overcome the imperfection. I show that photo-induced ion dynamics can (1) identify defects in nanotubes, (2) stabilize defected nanotubes, and (3) purify contaminated nanotubes. All of these methods can be alternative to conventional heat treatments and will be important techniques for realizing nanotube-devices. Ion dynamics under electronic excitation has been simulated with use of the computer code FPSEID (First-Principles Simulation tool for Electron Ion Dynamics) [1], which combines the time-dependent density functional method [2] to classical molecular dynamics. This very challenging approach is time-consuming but can automatically treat the level alternation of differently occupied states, and can observe initiation of non-adiabatic decay of excitation. The time-dependent Kohn-Sham equation has been solved by using the Suzuki-Trotter split operator method [3], which is a numerically stable method being suitable for plane wave basis, non-local pseudopotentials, and parallel computing. This work has been done in collaboration with Prof. Angel Rubio, Prof. David Tomanek, Dr. Savas Berber and Mina Yoon. Most of present calculations have been done by using the SX5 Vector-Parallel system in the NEC Fuchu-plant, and the Earth Simulator in Yokohama Japan. [1] O. Sugino and Y. Miyamoto, Phys. Rev. B59, 2579 (1999); ibid, B66 089901(E) (2001) [2] E. Runge and E. K. U. Gross, Phys. Rev. Lett. 52, 997 (1984). [3] M. Suzuki, J. Phys. Soc. Jpn. 61, L3015 (1992).

  16. Charge transfer to a semi-esterified bifunctional phenol

    Energy Technology Data Exchange (ETDEWEB)

    Brede, O.; Hermann, R.; Orthner, H. [Leipzig Univ. (Germany)

    1996-03-01

    The charge transfer from solvent radical cations of n-butyl chloride and cyclohexane to 2-butyl-6(3`-t-butyl-2`-hydroxy-5`-methylbenzyl)-4-methyl-phenylac rylate (GM) yields in the first step phenoxyl radicals as well as acrylate radical cations of this semi-acrylated bifunctional phenol. Subsequently an intramolecular charge transfer from the acrylate radical cation to the phenol group takes place. Because of the instability of phenol radical cations, under our experimental conditions (nanosecond pulse radiolysis, non-polar solvents, room temperature) phenoxyl radicals are the only observable products of phenol ionization. (author).

  17. Excited State Spectra and Dynamics of Phenyl-Substituted Butadienes

    DEFF Research Database (Denmark)

    Wallace-Williams, Stacie E.; Schwartz, Benjamin J.; Møller, Søren

    1994-01-01

    A combination of steady-state and dynamic spectral measurements are used to provide new insights into the nature of the excited-state processes of all-trans-1,4-diphenyl-1,3-butadiene and several analogs: 1,4-diphenyl- 1,3-cyclopentadiene, 1,1,4,4-tetraphenylbutadiene, 1,2,3,4-tetraphenyl-1,3-cyc...... indicate that phenyl torsional motion is not important to the excited-state dynamics and reveal alternative excited-state reaction pathways. The results demonstrate how molecular systems that are structually similar can exhibit different electronic properties and excited-state dynamics....

  18. Spectroscopic Studies of Doping and Charge Transfer in Single Walled Carbon Nanotubes and Lead Sulfide Quantum Dots

    Science.gov (United States)

    Haugen, Neale O.

    The use of single wall carbon nanotubes (SW-CNTs) in solar photovoltaic (PV) devices is a relatively new, but quickly growing field. SW-CNTs have found application as transparent front contacts, and high work function back contacts in thin film solar PV. For the utility of SW-CNTs to be fully realized, however, controllable and stable doping as well as long term protection from doping must be achieved. Spectroscopic techniques facilitate detailed investigations of the intrinsic and variable properties of semiconductor materials without the issues of contact deposition and the possibility of sample contamination. Detailed spectroscopic analysis of the doping induced changes in the optical properties of SW-CNTs has revealed normally hidden excited state transitions in large diameter single walled carbon nanotubes for the first time. Spectroscopic monitoring of the degree of doping in SW-CNTs made possible studies of the dopant complex desorption and readsorption energies and kinetics. The long term protection from doping of SW-CNTs exposed to ambient laboratory conditions was achieved as a result of the more detailed understanding of the doping processes and mechanisms yielded by these spectroscopic studies. The application of SW-CNTs to other roles in solar PV devices was another goal of this research. Efficient collection of photogenerated charge carriers in semiconductor quantum dot (QD) based solar photovoltaic devices has been limited primarily by the poor transport properties and high density of recombination sites in the QD films. Coupling semiconductor QDs to nanomaterials with better transport properties is one potential solution to the poor transport within the QD films. This portion of the work investigated the possibility of charge transfer occurring in nano-heterostructures (NHSs) of PbS QDs and SW-CNTs produced through spontaneous self-assembly in solution. Electronic coupling in the form of charge transfer from the QDs to the SW-CNTs is unambiguously

  19. Surface-enhanced photoinduced charge transfer processes in metal-molecule nanoclusters

    OpenAIRE

    Centeno, Silvia P.; Ruano, Cristina; Román-Pérez, Jéssica; López-Tocón, Isabel; Soto, Juan; Otero, Juan Carlos

    2013-01-01

    This work deals with the unexplained efficiency of the electrode potential (EV) in tuning the energy of Charge Transfer (ECT) electronic states of hybrid systems formed by molecules and metal nanostructures. Huge energy gains (G) of up to 5 eV/V observed in electrochemical SERS experiences have been tentatively explained by a local increase of the electric potential at specific adsorption sites.[1] This gain, which is in conflict with the classical picture of the metal-adsorbate CT mechanism ...

  20. Excited-State Effective Masses in Lattice QCD

    Energy Technology Data Exchange (ETDEWEB)

    George Fleming, Saul Cohen, Huey-Wen Lin

    2009-10-01

    We apply black-box methods, i.e. where the performance of the method does not depend upon initial guesses, to extract excited-state energies from Euclidean-time hadron correlation functions. In particular, we extend the widely used effective-mass method to incorporate multiple correlation functions and produce effective mass estimates for multiple excited states. In general, these excited-state effective masses will be determined by finding the roots of some polynomial. We demonstrate the method using sample lattice data to determine excited-state energies of the nucleon and compare the results to other energy-level finding techniques.

  1. Critical Assessment of TD-DFT for Excited States of Open-Shell Systems: I. Doublet-Doublet Transitions.

    Science.gov (United States)

    Li, Zhendong; Liu, Wenjian

    2016-01-12

    A benchmark set of 11 small radicals is set up to assess the performance of time-dependent density functional theory (TD-DFT) for the excited states of open-shell systems. Both the unrestricted (U-TD-DFT) and spin-adapted (X-TD-DFT) formulations of TD-DFT are considered. For comparison, the well-established EOM-CCSD (equation-of-motion coupled-cluster with singles and doubles) is also used. In total, 111 low-lying singly excited doublet states are accessed by all the three approaches. Taking the MRCISD+Q (multireference configuration interaction with singles and doubles plus the Davidson correction) results as the benchmark, it is found that both U-TD-DFT and EOM-CCSD perform well for those states dominated by singlet-coupled single excitations (SCSE) from closed-shell to open-shell, open-shell to vacant-shell, or closed-shell to vacant-shell orbitals. However, for those states dominated by triplet-coupled single excitations (TCSE) from closed-shell to vacant-shell orbitals, both U-TD-DFT and EOM-CCSD fail miserably due to severe spin contaminations. In contrast, X-TD-DFT provides balanced descriptions of both SCSE and TCSE. As far as the functional dependence is concerned, it is found that, when the Hartree-Fock ground state does not suffer from the instability problem, both global hybrid (GH) and range-separated hybrid (RSH) functionals perform grossly better than pure density functionals, especially for Rydberg and charge-transfer excitations. However, if the Hartree-Fock ground state is instable or nearly instable, GH and RSH tend to underestimate severely the excitation energies. The SAOP (statistically averaging of model orbital potentials) performs more uniformly than any other density functionals, although it generally overestimates the excitation energies of valence excitations. Not surprisingly, both EOM-CCSD and adiabatic TD-DFT are incapable of describing excited states with substantial double excitation characters.

  2. Excited state dynamics of 9,9'-bianthryl in room temperature ionic liquids as revealed by picosecond time-resolved fluorescence study

    Indian Academy of Sciences (India)

    Dinesh Chandra Khara; Aniruddha Paul; Kotni Santhosh; Anunay Samanta

    2009-05-01

    Picosecond time-resolved fluorescence measurements have been carried out on 9,9'-bianthryl in three imidazolium ionic liquids to probe the excited state dynamics. In the early time-scale, the fluorescence spectra of bianthryl have been found to consist of emission from both locally excited (LE) and charge transfer (CT) states. The LE → CT relaxation time, as estimated from the decay of the fluorescence intensity of the LE emission, is found to vary between 230 and 390 ps, while the average solvent relaxation time, as estimated from the analysis of time-dependent fluorescence Stokes shift, is found to vary between 620 ps and 1840 ps, depending on the viscosity of the ionic liquids. The results confirm that while in conventional less viscous solvents the CT formation kinetics of bianthryl occurs simultaneously with the solvation dynamics, in ionic liquids the two processes mostly occur in different time scales.

  3. Systematics of α -decay transitions to excited states

    Science.gov (United States)

    Delion, D. S.; Dumitrescu, A.

    2015-08-01

    We systematize the available experimental material concerning α -decay transitions to low-lying excited states in even-even and odd-mass emitters. We generalize our previous theoretical prediction concerning the linear dependence between hindrance factors and the excitation energy for transitions in even-even α emitters. Thus, we show that α intensities for transitions to excited states depend linearly upon the excitation energy for all known even-even and odd-mass α emitters. It turns out that the well-known Viola-Seaborg law for α -decay transitions between ground states can be generalized for transitions to excited states. This rule can be used to predict any α -decay half-life to a low-lying excited state.

  4. Direct detection of photoinduced charge transfer complexes in polymer fullerene blends

    Science.gov (United States)

    Behrends, Jan; Sperlich, Andreas; Schnegg, Alexander; Biskup, Till; Teutloff, Christian; Lips, Klaus; Dyakonov, Vladimir; Bittl, Robert

    2012-03-01

    We report transient electron paramagnetic resonance (trEPR) measurements with submicrosecond time resolution performed on a polymer:fullerene blend consisting of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) at low temperatures. The trEPR spectrum immediately following photoexcitation reveals signatures of spin-correlated polaron pairs. The pair partners (positive polarons in P3HT and negative polarons in PCBM) can be identified by their characteristic g values. The fact that the polaron pair states exhibit strong non-Boltzmann population unambiguously shows that the constituents of each pair are geminate, i.e., originate from one exciton. We demonstrate that coupled polaron pairs are present even several microseconds after charge transfer and suggest that they embody the intermediate charge transfer complexes that form at the donor/acceptor interface and mediate the conversion from excitons into free charge carriers.

  5. 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.

  6. Correlating electronic and vibrational motions in charge transfer systems

    Energy Technology Data Exchange (ETDEWEB)

    Khalil, Munira [Univ. of Washington, Seattle, WA (United States)

    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.

  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. 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.

  9. 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.

  10. Radially Excited States of 1P Charmonium and X(3872)

    CERN Document Server

    Chen, Y; Liu, Y; Ma, J; Zhang, J; Chen, Ying; Liu, Chuan; Liu, Yubin; Ma, Jianping; Zhang, Jianbo

    2007-01-01

    The first excited states of charmonium in $0^{++}$, $1^{++}$, $1^{+-}$ channels are numerically investigated with lattice QCD of improved gauge and Wilson fermion actions, formulated on anisotropic lattices. Having determined the mass of ground states, the masses of excited states can be extracted by a constrained curve fitting algorithm which gives the masses 3.825(88) GeV, 3.853(57) GeV, and 3.858(70) Gev for the first excited states in $0^{++}$, $1^{++}$, $1^{+-}$ channels, respectively. A node structure is also observed in the Bethe-Salpeter wave-function of the $1^{++}$ state. The mass of the radically excited $1^{++}$ state is close to the mass of the newly observed X(3872). It indicates that X(3872) can be the first excited state of $\\chi_{c1}$.

  11. 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.

  12. Ghost-interaction correction in ensemble density-functional theory for excited states with and without range separation

    Science.gov (United States)

    Alam, Md. Mehboob; Knecht, Stefan; Fromager, Emmanuel

    2016-07-01

    Ensemble density-functional theory (eDFT) suffers from the so-called "ghost-interaction" error when approximate exchange-correlation functionals are used. In this work, we present a rigorous ghost-interaction correction (GIC) scheme in the context of range-separated eDFT. The method relies on an exact decomposition of the ensemble short-range exchange-correlation energy into a multideterminantal exact exchange term, which involves the long-range interacting ensemble density matrix, instead of the Kohn-Sham (KS) one, and a complementary density-functional correlation energy. A generalized adiabatic connection formula is derived for the latter. In order to perform practical calculations, the complementary correlation functional is simply modeled by its ground-state local density approximation (LDA), while long-range interacting ground- and excited-state wave functions are obtained self-consistently by combining a long-range configuration-interaction calculation with a short-range LDA potential. We show that the GIC reduces the curvature of approximate range-separated ensemble energies drastically while providing considerably more accurate excitation energies, even for charge-transfer and double excitations. Interestingly, the method performs well also in the context of standard KS-eDFT, which is recovered when the range-separation parameter is set to 0.

  13. Excited electronic states and spectroscopy of unsymmetrically substituted polyenes

    Science.gov (United States)

    Itoh, Takao

    2013-09-01

    α-Methyl-ω-phenylpolyenes, Me-(CH=CH)N-Ph, (MPPNs) with N = 2, 3, and 4 were synthesized. Fluorescence, absorption, and excitation spectra of MPPNs have been measured under different conditions along with those of β-methylstyrene. It is shown that there is a forbidden singlet (π, π*) excited state located at energies below the absorbing state for MPPNs with N = 3 and 4. Excitation energies of these polyenes are determined as a function of N. Quantitative analysis of the temperature dependence of the relative intensity of the fluorescence spectrum and its solvent shift behavior extract estimates of the various physical parameters that characterize excitation energies and excited-state dynamical behavior of MPPN with N = 3. The singlet excited states of the MPPNs were compared with those of the α,ω-diphenylpolyenes and α,ω-dimethylpolyenes.

  14. Electronic excited states responsible for dimer formation upon UV absorption directly by thymine strands: joint experimental and theoretical study.

    Science.gov (United States)

    Banyasz, Akos; Douki, Thierry; Improta, Roberto; Gustavsson, Thomas; Onidas, Delphine; Vayá, Ignacio; Perron, Marion; Markovitsi, Dimitra

    2012-09-12

    The study addresses interconnected issues related to two major types of cycloadditions between adjacent thymines in DNA leading to cyclobutane dimers (TTs) and (6-4) adducts. Experimental results are obtained for the single strand (dT)(20) by steady-state and time-resolved optical spectroscopy, as well as by HPLC coupled to mass spectrometry. Calculations are carried out for the dinucleoside monophosphate in water using the TD-M052X method and including the polarizable continuum model; the reliability of TD-M052X is checked against CASPT2 calculations regarding the behavior of two stacked thymines in the gas phase. It is shown that irradiation at the main absorption band leads to cyclobutane dimers (TTs) and (6-4) adducts via different electronic excited states. TTs are formed via (1)ππ* excitons; [2 + 2] dimerization proceeds along a barrierless path, in line with the constant quantum yield (0.05) with the irradiation wavelength, the contribution of the (3)ππ* state to this reaction being less than 10%. The formation of oxetane, the reaction intermediate leading to (6-4) adducts, occurs via charge transfer excited states involving two stacked thymines, whose fingerprint is detected in the fluorescence spectra; it involves an energy barrier explaining the important decrease in the quantum yield of (6-4) adducts with the irradiation wavelength.

  15. Description of excited states in [Re(Imidazole)(CO)3 (Phen)](+) including solvent and spin-orbit coupling effects: Density functional theory versus multiconfigurational wavefunction approach.

    Science.gov (United States)

    Fumanal, Maria; Daniel, Chantal

    2016-10-15

    The low-lying electronic excited states of [Re(imidazole)(CO)3 (phen)](+) (phen = 1,10-phenanthroline) ranging between 420 nm and 330 nm have been calculated by means of relativistic spin-orbit time-dependent density functional theory (TD-DFT) and wavefunction approaches (state-average-CASSCF/CASPT2). A direct comparison between the theoretical absorption spectra obtained with different methods including SOC and solvent corrections for water points to the difficulties at describing on the same footing the bands generated by metal-to-ligand charge transfer (MLCT), intraligand (IL) transition, and ligand-to-Ligand- charge transfer (LLCT). While TD-DFT and three-roots-state-average CASSCF (10,10) reproduce rather well the lowest broad MLCT band observed in the experimental spectrum between 420 nm and 330 nm, more flexible wavefunctions enlarged either by the number of roots or by the number of active orbitals and electrons destabilize the MLCT states by introducing IL and LLCT character in the lowest part of the absorption spectrum. © 2016 Wiley Periodicals, Inc.

  16. Preresonance Raman studies of metal-to-ligand charge transfer in (NH sub 3 ) sub 4 Ru(2,2 prime -bpy) sup 2+. In situ bond length changes, force constants, and reorganization energies

    Energy Technology Data Exchange (ETDEWEB)

    Doorn, S.K.; Hupp, J.T. (Northwestern Univ., Evanston, IL (USA))

    1989-06-21

    As a prototype for charge-transfer reactions in general, the intense metal-to-ligand charge-transfer transition occurring in Ru(NH{sub 3}){sub 4}(bpy){sup 2+} (bpy = 2,2{prime}-bipyridine) has been examined experimentally by resonance and preresonance Raman spectroscopy and analytically by time-dependent scattering theory. To their knowledge, the present example represents the first application of the theory to charge-transfer problems. From the experiments and corresponding theory, the normal-coordinate changes accompanying the transition have been calculated. Both metal-ligand and intraligand bonds are found to distort significantly. When the distortion data are combined with the observed vibrational frequencies, a mode-by-mode assessment of the inner-shell reorganization energy is possible. Further experiments, in which the nature of the solvent is systematically varied, show that selected force constants (and therefore selected components of the internal reorganization energy) are modulated significantly (ca. 6-11 %) by ligand-solvent hydrogen bonding. Finally, variations in the nature of the solvent are found to shift ground- and/or excited-state energies in such a way as to either enhance or attenuate the occurrence of net photochemistry.

  17. Three-photon excitation of hydrogen Rydberg states.

    Science.gov (United States)

    Glab, W L; Nayfeh, M H

    1983-01-01

    A three-photon process using radiation at 2430 and 3660 A and with a 1s-2s two-photon resonance is used to excite atomic hydrogen from the ground state to Rydberg states of high principal quantum number. Collision-induced ionization is used to monitor the excitation.

  18. Three-photon excitation of hydrogen Rydberg states

    Energy Technology Data Exchange (ETDEWEB)

    Glab, W.L.; Nayfeh, M.H.

    1983-01-01

    A three-photon process using radiation at 2430 and 3660 A and with a 1s-2s two-photon resonance is used to excite atomic hydrogen from the ground state to Rydberg states of high principal quantum number. Collision-induced ionization is used to monitor the excitation.

  19. DILEPTON YIELD FROM THE DECAY OF EXCITED SI-28 STATES

    NARCIS (Netherlands)

    BACELAR, JC; BUDA, A; BALANDA, A; KRASZNAHORKAY, A; VANDERPLOEG, H; SUJKOWSKI, Z; VANDERWOUDE, A

    1994-01-01

    The first dilepton yield measurements from excited nuclear states obtained with a new Positron-Electron Pair Spectroscopic Instrument (PEPSI) are reported. Nuclear states in Si-28, with an initial excitation energy E* = 50 MeV, were populated via the isospin T = 0 reaction He-4 + Mg-24 and the mixed

  20. Exact ensemble density-functional theory for excited states

    CERN Document Server

    Yang, Zeng-hui; Pribram-Jones, Aurora; Burke, Kieron; Needs, Richard J; Ullrich, Carsten A

    2014-01-01

    We construct exact Kohn-Sham potentials for the ensemble density-functional theory (EDFT) of excited states from the ground and excited states of helium. The exchange-correlation potential is compared with current approximations, which miss prominent features. The ensemble derivative discontinuity is tested, and the virial theorem is proven and illustrated.

  1. Experimental Investigation of Excited-State Lifetimes in Atomic Ytterbium

    Energy Technology Data Exchange (ETDEWEB)

    Bowers, C.J.; Budker, D.; Commins, E.D.; DeMille, D.; Freedman, S.J.; Nguyen, A.-T.; Shang, S.-Q.; /UC, Berkeley; Zolotorev, M.; /SLAC

    2011-11-15

    Lifetimes of 21 excited states in atomic Yb were measured using time-resolved fluorescence detection following pulsed laser excitation. The lifetime of the 4f{sup 14}5d6s {sup 3}D{sub 1} state, which is of particular importance for a proposed study of parity nonconservation in atoms, was measured to be 380(30) ns.

  2. 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.

  3. Role of Excited States In High-order Harmonic Generation

    Science.gov (United States)

    Beaulieu, S.; Camp, S.; Descamps, D.; Comby, A.; Wanie, V.; Petit, S.; Légaré, F.; Schafer, K. J.; Gaarde, M. B.; Catoire, F.; Mairesse, Y.

    2016-11-01

    We investigate the role of excited states in high-order harmonic generation by studying the spectral, spatial, and temporal characteristics of the radiation produced near the ionization threshold of argon by few-cycle laser pulses. We show that the population of excited states can lead either to direct extreme ultraviolet emission through free induction decay or to the generation of high-order harmonics through ionization from these states and recombination to the ground state. By using the attosecond lighthouse technique, we demonstrate that the high-harmonic emission from excited states is temporally delayed by a few femtoseconds compared to the usual harmonics, leading to a strong nonadiabatic spectral redshift.

  4. Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate

    CERN Document Server

    Gibson, Andrew J; Handrup, Karsten; Weston, Matthew; Mayor, Louise C; O'Shea, James N

    2014-01-01

    The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4'-dicarboxylato)-ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy (RPES) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2&3 in the excited state but not from the LUMO, therefore enabling core-hole clock analysis, which gives an upper limit of $6.0\\pm$2.5fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells (DSSC), which may lead to reduced recombination effe...

  5. Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate.

    Science.gov (United States)

    Gibson, Andrew J; Temperton, Robert H; Handrup, Karsten; Weston, Matthew; Mayor, Louise C; O'Shea, James N

    2014-06-21

    The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4'-dicarbo-xylato)-ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy, and near edge X-ray absorption fine structure spectroscopy. Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2 and 3 in the excited state but not from the LUMO, therefore enabling core-hole clock analysis, which gives an upper limit of 6.0 ± 2.5 fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells, which may lead to reduced recombination effects and improved efficiencies of future devices.

  6. Charge transfer from an adsorbed ruthenium-based photosensitizer through an ultra-thin aluminium oxide layer and into a metallic substrate

    Energy Technology Data Exchange (ETDEWEB)

    Gibson, Andrew J.; Temperton, Robert H.; Handrup, Karsten; Weston, Matthew; Mayor, Louise C.; O’Shea, James N., E-mail: james.oshea@nottingham.ac.uk [School of Physics and Astronomy and Nottingham Nanotechnology and Nanoscience Centre (NNNC), University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2014-06-21

    The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4′-dicarbo-xylato) -ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy, and near edge X-ray absorption fine structure spectroscopy. Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2 and 3 in the excited state but not from the LUMO, therefore enabling core-hole clock analysis, which gives an upper limit of 6.0 ± 2.5 fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells, which may lead to reduced recombination effects and improved efficiencies of future devices.

  7. Nonadiabatic excited-state molecular dynamics: On-the-fly limiting of essential excited states

    Science.gov (United States)

    Nelson, Tammie; Naumov, Artem; Fernandez-Alberti, Sebastian; Tretiak, Sergei

    2016-12-01

    The simulation of nonadiabatic dynamics in extended molecular systems involving hundreds of atoms and large densities of states is particularly challenging. Nonadiabatic coupling terms (NACTs) represent a significant numerical bottleneck in surface hopping approaches. Rather than using unreliable NACT cutting schemes, here we develop "on-the-fly" state limiting methods to eliminate states that are no longer essential for the non-radiative relaxation dynamics as a trajectory proceeds. We propose a state number criteria and an energy-based state limit. The latter is more physically relevant by requiring a user-imposed energy threshold. For this purpose, we introduce a local kinetic energy gauge by summing contributions from atoms within the spatial localization of the electronic wavefunction to define the energy available for upward hops. The proposed state limiting schemes are implemented within the nonadiabatic excited-state molecular dynamics framework to simulate photoinduced relaxation in poly-phenylene vinylene (PPV) and branched poly-phenylene ethynylene (PPE) oligomers for benchmark evaluation.

  8. Ultrafast excited state relaxation in long-chain polyenes

    Energy Technology Data Exchange (ETDEWEB)

    Antognazza, Maria Rosa, E-mail: mariarosa.antognazza@polimi.it [Center for Nano Science and Technology of IIT-PoliMI, via Pascoli 70/3, 20133 Milano (Italy); Lueer, Larry [National Laboratory for Ultrafast and Ultraintense Optical Science, CNR-INFM, Dipartimento di Fisica, Politecnico di Milano, P.za L. da Vinci 32, 20133 Milano (Italy); Madrid Institute of Advanced Studies, IMDEA Nanociencia, Faculdad de Ciencias, Av. Tomas y Valiente 7, 28049 Madrid (Spain); Polli, Dario [National Laboratory for Ultrafast and Ultraintense Optical Science, CNR-INFM, Dipartimento di Fisica, Politecnico di Milano, P.za L. da Vinci 32, 20133 Milano (Italy); Christensen, Ronald L. [Department of Chemistry, Bowdoin College, Brunswick, ME 04011 (United States); Schrock, Richard R. [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Lanzani, Guglielmo [Center for Nano Science and Technology of IIT-PoliMI, via Pascoli 70/3, 20133 Milano (Italy); National Laboratory for Ultrafast and Ultraintense Optical Science, CNR-INFM, Dipartimento di Fisica, Politecnico di Milano, P.za L. da Vinci 32, 20133 Milano (Italy); Cerullo, Giulio [National Laboratory for Ultrafast and Ultraintense Optical Science, CNR-INFM, Dipartimento di Fisica, Politecnico di Milano, P.za L. da Vinci 32, 20133 Milano (Italy)

    2010-07-19

    Graphical abstract: Excited state dynamics of a long-chain polyene studied by femtosecond pump-probe spectroscopy. - Abstract: We present a comprehensive study, by femtosecond pump-probe spectroscopy, of excited state dynamics in a polyene that approaches the infinite chain limit. By excitation with sub-10-fs pulses resonant with the 0-0 S{sub 0} {yields} S{sub 2} transition, we observe rapid loss of stimulated emission from the bright excited state S{sub 2}, followed by population of the hot S{sub 1} state within 150 fs. Vibrational cooling of S{sub 1} takes place within 500 fs and is followed by decay back to S{sub 0} with 1 ps time constant. By excitation with excess vibrational energy we also observe the ultrafast formation of a long-living absorption, that is assigned to the triplet state generated by singlet fission.

  9. CoPc and CoPcF16 on gold: Site-specific charge-transfer processes

    Directory of Open Access Journals (Sweden)

    Fotini Petraki

    2014-04-01

    Full Text Available Interface properties of cobalt(II phthalocyanine (CoPc and cobalt(II hexadecafluoro-phthalocyanine (CoPcF16 to gold are investigated by photo-excited electron spectroscopies (X-ray photoemission spectroscopy (XPS, ultraviolet photoemission spectroscopy (UPS and X-ray excited Auger electron spectroscopy (XAES. It is shown that a bidirectional charge transfer determines the interface energetics for CoPc and CoPcF16 on Au. Combined XPS and XAES measurements allow for the separation of chemical shifts based on different local charges at the considered atom caused by polarization effects. This facilitates a detailed discussion of energetic shifts of core level spectra. The data allow the discussion of site-specific charge-transfer processes.

  10. Inelastic scattering of {sup 9}Li and excitation mechanism of its first excited state

    Energy Technology Data Exchange (ETDEWEB)

    Al Falou, H. [Astronomy and Physics Department, Saint Mary' s University, Halifax, Nova Scotia B3H 3C3 (Canada); TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Kanungo, R., E-mail: ritu@triumf.ca [Astronomy and Physics Department, Saint Mary' s University, Halifax, Nova Scotia B3H 3C3 (Canada); Andreoiu, C.; Cross, D.S. [Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Davids, B.; Djongolov, M. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Gallant, A.T. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Department of Physics, University of British Columbia, British Columbia V6T 1Z4 (Canada); Galinski, N.; Howell, D. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Kshetri, R.; Niamir, D. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Orce, J.N. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Department of Physics, University of the Western Cape, P/B X17, Bellville, ZA-7535 (South Africa); Shotter, A.C. [Department of Physics and Astronomy, University of Edinburgh, Edinburgh (United Kingdom); Sjue, S. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Tanihata, I. [Research Center for Nuclear Physics, Osaka University, Mihogaoka, Ibaraki, Osaka 567 0047 (Japan); Thompson, I.J. [Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States); Triambak, S. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Uchida, M. [Astronomy and Physics Department, Saint Mary' s University, Halifax, Nova Scotia B3H 3C3 (Canada); Walden, P. [TRIUMF, Vancouver, British Columbia V6T 2A3 (Canada); Wiringa, R.B. [Physics Division, Argonne National Laboratory, Argonne, IL 60439 (United States)

    2013-04-25

    The first measurement of inelastic scattering of {sup 9}Li from deuterons at the ISAC facility is reported. The measured angular distribution for the first excited state confirms the nature of excitation to be an E2 transition. The quadrupole deformation parameter is extracted from an analysis of the angular distribution.

  11. Bogoliubov Excited States and the Lyth Bound

    CERN Document Server

    Aravind, Aditya; Paban, Sonia

    2014-01-01

    We show that Bogoliubov excited scalar and tensor modes do not alleviate Planckian evolution during inflation if one assumes that $r$ and the Bogoliubov coefficients are approximately scale invariant. We constrain the excitation parameter for the scalar fluctuations, $\\beta$, and tensor perturbations, $\\tilde{\\beta}$, by requiring that there be at least three decades of scale invariance in the scalar and tensor power spectrum. For the scalar fluctuations this is motivated by the observed nearly scale invariant scalar power spectrum. For the tensor fluctuations this assumption may be shown to be valid or invalid by future experiments.

  12. Ultrafast Excited-State Dynamics of Diketopyrrolopyrrole (DPP)-Based Materials: Static versus Diffusion-Controlled Electron Transfer Process

    KAUST Repository

    Alsulami, Qana

    2015-06-25

    Singlet-to-triplet intersystem crossing (ISC) and photoinduced electron transfer (PET) of platinum(II) containing diketopyrrolopyrrole (DPP) oligomer in the absence and presence of strong electron-acceptor tetracyanoethylene (TCNE) were investigated using femtosecond and nanosecond transient absorption spectroscopy with broadband capabilities. The role of platinum(II) incorporation in those photophysical properties was evaluated by comparing the excited-state dynamics of DPP with and without the metal centers. The steady-state measurements reveal that platinum(II) incorporation facilitates dramatically the interactions between DPP-Pt(acac) and TCNE, resulting in charge transfer (CT) complex formation. The transient absorption spectra in the absence of TCNE reveal ultrafast ISC of DPP-Pt(acac) followed by their long-lived triplet state. In the presence of TCNE, PET from the excited DPP-Pt(acac) and DPP to TCNE, forming the radical ion pairs. The ultrafast PET which occurs statically from DPP-Pt(acac) to TCNE in picosecond regime, is much faster than that from DPP to TCNE (nanosecond time scale) which is diffusion-controlled process, providing clear evidence that PET rate is eventually controlled by the platinum(II) incorporation.

  13. Excited-State Photophysics in a Low Band Gap Polymer with High Photovoltaic Efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Miller, Stephen A. [Univ. of North Carolina, Chapel Hill, NC (United States); Stuart, Andrew C. [Univ. of North Carolina, Chapel Hill, NC (United States); Womick, Jordan M. [Univ. of North Carolina, Chapel Hill, NC (United States); Zhou, Huaxing [Univ. of North Carolina, Chapel Hill, NC (United States); You, Wei [Univ. of North Carolina, Chapel Hill, NC (United States); Moran, Andrew M. [Univ. of North Carolina, Chapel Hill, NC (United States)

    2010-12-27

    We report an experimental investigation of a newly synthesized polymer, PNDT-DTPyT, with a 1.55 eV band gap tuned for optimal photovoltaic performance. Several time-resolved optical spectroscopies are used to examine fundamental photophysics in pure polymer films. Clear signatures of a distribution in photoexcitation sizes are found in steady state absorption and fluorescence measurements conducted from 100 to 300 K. Electronic structure calculations are combined with an empirical model to establish that, on average, the excitations span less than two repeat units because of strong interactions with the surrounding environment. These strong vibronic interactions are attributed to the charge transfer nature of the excitation, which involves a significant change in the spatial charge distribution. Femtosecond transient grating (TG) measurements find energy transfer processes occurring with roughly 1 and 10 ps time constants. This distinction in time scales most likely has a geometric origin (e.g., processes involving stacked and nonstacked neighbors). Fluorescence quenching and TG experiments show that the addition of PCBM to blends composed of both PNDT-DTPyT and PCBM correlates with an increase in the charge separation efficiency following photoexcitation. This increase in charge separation efficiency is caused by a reduction in the average distance that photoexcitations in the polymer must traverse before injecting electrons into PCBM. Photovoltaic power conversion efficiencies measured for the films are consistent with this interpretation, where a maximum efficiency of 4.1% is found for the 1:1 blend of polymer and PCBM. Overall, the present study covers several fundamental processes taking place in photovoltaic devices from the primary events surrounding the creation of photoexcitations in the polymer to their deactivation at the PCBM interface.

  14. Effect of Aperiodicity on the Charge Transfer Through DNA Molecules

    Science.gov (United States)

    Ghosh, Angsula; Chaudhuri, Puspitapallab

    The effect of aperiodicity on the charge transfer process through DNA molecules is investigated using a tight-binding model. Single-stranded aperiodic Fibonacci polyGC and polyAT sequences along with aperiodic Rudin-Shapiro poly(GCAT) sequences are used in the study. Based on the tight-binding model, molecular orbital calculations of the DNA chains are performed and ionization potentials compared, as this might be relevant to understanding the charge transfer process. Charges migrate through the sequences in a multistep hopping process. Results for current conduction through aperiodic sequences are compared with those for the corresponding periodic sequences. We find that dinucleotide aperiodic Fibonacci sequences decrease the current while tetranucleotide aperiodic Rudin-Shapiro sequences increase the current when compared with the corresponding periodic sequences. The conductance in all cases decays exponentially as the sequence length increases.

  15. Charge transfer properties of pentacene adsorbed on silver: DFT study

    Energy Technology Data Exchange (ETDEWEB)

    N, Rekha T.; Rajkumar, Beulah J. M., E-mail: beulah-rajkumar@yahoo.co.in [PG & Research Department of Physics, Lady Doak College, Madurai 625002 (India)

    2015-06-24

    Charge transfer properties of pentacene adsorbed on silver is investigated using DFT methods. Optimized geometry of pentacene after adsorption on silver indicates distortion in hexagonal structure of the ring close to the silver cluster and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles. Theoretically simulated absorption spectrum has a symmetric surface plasmon resonance peak around 486nm corresponding to the transfer of charge from HOMO-2 to LUMO. Theoretical SERS confirms the process of adsorption, tilted orientation of pentacene on silver surface and the charge transfers reported. Localization of electron density arising from redistribution of electrostatic potential together with a reduced bandgap of pentacene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices.

  16. Integrated Charge Transfer in Organic Ferroelectrics for Flexible Multisensing Materials.

    Science.gov (United States)

    Xu, Beibei; Ren, Shenqiang

    2016-09-01

    The ultimate or end point of functional materials development is the realization of strong coupling between all energy regimes (optical, electronic, magnetic, and elastic), enabling the same material to be utilized for multifunctionalities. However, the integration of multifunctionalities in soft materials with the existence of various coupling is still in its early stage. Here, the coupling between ferroelectricity and charge transfer by combining bis(ethylenedithio)tetrathiafulvalene-C60 charge-transfer crystals with ferroelectric polyvinylidene fluoride polymer matrix is reported, which enables external stimuli-controlled polarization, optoelectronic and magnetic field sensing properties. Such flexible composite films also display a superior strain-dependent capacitance and resistance change with a giant piezoresistance coefficient of 7.89 × 10(-6) Pa(-1) . This mutual coupled material with the realization of enhanced couplings across these energy domains opens up the potential for multisensing applications.

  17. Role of charge transfer configurations in LaMnO3, CaMnO3, and CaFeO3.

    Science.gov (United States)

    Sadoc, Aymeric; Broer, Ria; de Graaf, Coen

    2007-04-01

    A simple scheme is proposed to analyze the N-electron wave function obtained in embedded cluster calculations in valence bond terms such as ligand-to-metal charge transfer and non-charge-transfer determinants. The analysis is based on a unitary transformation of pairs of natural orbitals to optimal atomiclike orbitals. The procedure is applied to compare the degree of ionicity in NiO and MnO and to explain the existence or absence of Jahn-Teller distortions in LaMnO3, CaMnO3, and CaFeO3. The authors find that the ground state of LaMnO3 is dominated by non-charge-transfer configurations, whereas the charge transfer configurations dominate the ground state wave function in the other two perovskites.

  18. The one-electron description of excited states: Natural excitation orbitals of density matrix theory and Kohn-Sham orbitals of density functional theory as ideal orbitals

    Science.gov (United States)

    van Meer, R.; Gritsenko, O. V.; Baerends, E. J.

    2015-10-01

    Linear response density matrix functional theory has been shown to solve the main problems of time-dependent density functional theory (deficient in case of double, charge transfer and bond breaking excitations). However, the natural orbitals preclude the description of excitations as (approximately) simple orbital-to-orbital transitions: many weakly occupied 'virtual' natural orbitals are required to describe the excitations. Kohn-Sham orbitals on the other hand afford for many excitations such a simple orbital description. In this communication we show that a transformation of the set of weakly occupied NOs can be defined such that the resulting natural excitation orbitals (NEOs) restore the single orbital transition structure for excitations generated by the linear response DMFT formalism.

  19. [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.

  20. Conformational control of benzophenone-sensitized charge transfer in dinucleotides

    OpenAIRE

    Merz, Thomas; Wenninger, Matthias; Weinberger, Michael; Riedle, Eberhard; Wagenknecht, Hans-Achim; Schuetz, Martin

    2013-01-01

    Charge transfer in DNA cannot be understood without addressing the complex conformational flexibility, which occurs on a wide range of timescales. In order to reduce this complexity four dinucleotide models 1X consisting of benzophenone linked by a phosphodiester to one of the natural nucleosides X = A, G, T, C were studied in water and methanol. The theoretical work focuses on the dynamics and electronic structure of 1G. Predominant conformations in the two solvents were obtained by molecula...

  1. 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.

  2. Population of highly excited intermediate resonance states by electron transfer and excitation

    Energy Technology Data Exchange (ETDEWEB)

    Schuch, R. (Manne Siegbahn Institute of Physics, S-104 05 Stockholm, Sweden (SE)); Justiniano, E. (Department of Physics, East Carolina University, Greenville, North Carolina 27858-4353 (USA)); Schulz, M.; Datz, S.; Dittner, P.F.; Giese, J.P.; Krause, H.F.; Schoene, H.; Vane, R. (Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6377 (USA)); Shafroth, S. (Department of Physics, North Carolina University, Chapel Hill, North Carolina 27599-3255 (USA))

    1991-05-01

    Coincidences between two sulfur {ital K} x rays were detected from collisions of hydrogenlike S ions with H{sub 2} gas in the projectile energy range between 150 and 225 MeV. These {ital K} x rays are emitted in the decay of doubly excited states formed in the collisions via transfer and excitation. The excitation function for two coincident {ital K}{beta} transitions peaks at about 175 MeV, slightly above the expected {ital KMM} resonance energy for resonant transfer and excitation (RTE). This demonstrates the occurrence of {Delta}{ital N}{ge}2 transitions (i.e., {ital KMM} and higher resonances) in the RTE process. The cross sections for the population of the very highly excited states are higher than those predicted by theoretical calculations that use dielectronic recombination rates folded with the Compton profile for the bound electrons.

  3. Unveiling the excited state energy transfer pathways in peridinin-chlorophyll a-protein by ultrafast multi-pulse transient absorption spectroscopy.

    Science.gov (United States)

    Redeckas, Kipras; Voiciuk, Vladislava; Zigmantas, Donatas; Hiller, Roger G; Vengris, Mikas

    2017-04-01

    Time-resolved multi-pulse methods were applied to investigate the excited state dynamics, the interstate couplings, and the excited state energy transfer pathways between the light-harvesting pigments in peridinin-chlorophyll a-protein (PCP). The utilized pump-dump-probe techniques are based on perturbation of the regular PCP energy transfer pathway. The PCP complexes were initially excited with an ultrashort pulse, resonant to the S0→S2 transition of the carotenoid peridinin. A portion of the peridinin-based emissive intramolecular charge transfer (ICT) state was then depopulated by applying an ultrashort NIR pulse that perturbed the interaction between S1 and ICT states and the energy flow from the carotenoids to the chlorophylls. The presented data indicate that the peridinin S1 and ICT states are spectrally distinct and coexist in an excited state equilibrium in the PCP complex. Moreover, numeric analysis of the experimental data asserts ICT→Chl-a as the main energy transfer pathway in the photoexcited PCP systems.

  4. Origin of ultrafast excited state dynamics of 1-nitropyrene.

    Science.gov (United States)

    Murudkar, Sushant; Mora, Aruna K; Singh, Prabhat K; Nath, Sukhendu

    2011-10-01

    Time-resolved emission measurements in subpicosecond time domain have been carried out for 1-nitropyrene in different solvents to understand the mechanism for the observed ultrafast decay of its first excited singlet state. Excited-state dynamics of 1-nitropyrene is found to be independent of the solvent viscosity. This result contradicts the proposition in the literature (J. Phys. Chem. A 2007, 111, 552) that the ultrafast decay in 1-nitropyrene is due to the large amplitude torsional motion of the nitro group around the pyrene moiety. Excited-state dynamics of 1-nitropyrene in solvents with different dielectric constants shows that excited-state lifetime suddenly increases after a certain value of the dielectric constant. Detailed quantum chemical calculations have been carried out to understand the process that is responsible for the observed effect of the dielectric constant on the excited-state dynamics of 1-nitropyrene. It is seen that the excited-state lifetime and the singlet-triplet energy gap follow similar variation with the dielectric constant of the medium. Such a correlation between the excited-state lifetime and the singlet-triplet energy gap supports the fact that the observed ultrafast decay for 1-nitropyrene is due to an efficient intersystem crossing rather than to the torsional motion of the nitro group as proposed in the literature.

  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. Photoionization of excited states of neon-like Mg III

    Indian Academy of Sciences (India)

    Narendra Singh; Man Mohan

    2002-04-01

    The close coupling -matrix method is used to calculate cross-sections for photoionization of Mg III from its first three excited states. Configuration interaction wave functions are used to represent two target states of Mg III retained in the -matrix expansion. The positions and effective quantum numbers for the Rydberg series converging to the excited state 2226 \\ 2 of the residual ion, are predicted.

  7. A Simple Hubbard Model for the Excited States of Dibenzoterrylene

    CERN Document Server

    Sadeq, Z S

    2016-01-01

    We use a simple Hubbard model to characterize the electronic excited states of the dibenzoterrylene (DBT) molecule; we compute the excited state transition energies and oscillator strengths from the ground state to several singlet excited states. We consider the lowest singlet and triplet states of the molecule, examine their wavefunctions, and compute the density correlation functions that describe these states. We find that the DBT ground state is mostly a closed shell singlet with very slight radical character. We predict a relatively small singlet-triplet splitting of 0.75 eV, which is less than the mid-sized -acenes but larger than literature predictions for this state; this is because the Hubbard interaction makes a very small correction to the singlet and triplet states.

  8. Photoinduced intramolecular charge transfer process of betaine pyridinium: A theoretical spectroscopic study

    Science.gov (United States)

    Perrier, Aurélie; Aloïse, Stéphane; Pawlowska, Zuzanna; Sliwa, Michel; Maurel, François; Abe, Jiro

    2011-10-01

    Using Time-Dependent Density Functional Theory and taking into account bulk solvent effects, we investigate the absorption and emission spectra of a betaine pyridinium molecule, the 2-(1-pyridinio) benzimidazolate (SBPa). This molecule exhibits strong photoinduced intramolecular charge transfer (ICT). We have identified two different electronic states involved, respectively, in the strong bathochromic ICT absorption band (S 2) and in the moderate emission band (S 1). The ICT process is analyzed in terms of charge distribution and dipole moment evolutions upon photoexcitation. These results are compared with steady-state spectroscopic measurements.

  9. 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.

  10. Photo-modulated thin film transistor based on dynamic charge transfer within quantum-dots-InGaZnO interface

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiang [Electronic Science and Engineering School, Southeast University, Nanjing (China); National Center for Nanoscience and Technology, Beijing (China); Yang, Xiaoxia; Liu, Mingju [National Center for Nanoscience and Technology, Beijing (China); Tao, Zhi; Wei, Lei, E-mail: lw@seu.edu.cn; Li, Chi, E-mail: lichi@seu.edu.cn; Zhang, Xiaobing; Wang, Baoping [Electronic Science and Engineering School, Southeast University, Nanjing (China); Dai, Qing, E-mail: daiq@nanoctr.cn [National Center for Nanoscience and Technology, Beijing (China); London Center for Nanotechnology, University College London, London WC1H 0AH (United Kingdom); Nathan, Arokia [Electronic Science and Engineering School, Southeast University, Nanjing (China); London Center for Nanotechnology, University College London, London WC1H 0AH (United Kingdom)

    2014-03-17

    The temporal development of next-generation photo-induced transistor across semiconductor quantum dots and Zn-related oxide thin film is reported in this paper. Through the dynamic charge transfer in the interface between these two key components, the responsibility of photocurrent can be amplified for scales of times (∼10{sup 4} A/W 450 nm) by the electron injection from excited quantum dots to InGaZnO thin film. And this photo-transistor has a broader waveband (from ultraviolet to visible light) optical sensitivity compared with other Zn-related oxide photoelectric device. Moreover, persistent photoconductivity effect can be diminished in visible waveband which lead to a significant improvement in the device's relaxation time from visible illuminated to dark state due to the ultrafast quenching of quantum dots. With other inherent properties such as integrated circuit compatible, low off-state current and high external quantum efficiency resolution, it has a great potential in the photoelectric device application, such as photodetector, phototransistor, and sensor array.

  11. Spectroscopic probing of location and dynamics of an environment-sensitive intramolecular charge transfer probe within liposome membranes.

    Science.gov (United States)

    Paul, Bijan Kumar; Guchhait, Nikhil

    2011-11-15

    The present work demonstrates the interaction of an intramolecular charge transfer (ICT) probe 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) with liposome membranes of dimyristoyl-L-α-phosphatidylcholine (DMPC) and dimyristoyl-L-α-phosphatidylglycerol (DMPG) studied by steady-state absorption, emission and time-resolved emission techniques. A huge hypsochromic shift together with remarkable enhancement of fluorescence quantum yield of the polarity sensitive ICT emission of DPDAME upon interaction with the lipids has been rationalized in terms of incorporation of the probe into hydrophobic interior of the lipids. Compelling evidences for penetration of the probe into the hydrocarbon interior of the lipids have been deduced from intertwining different experimental results e.g., micropolarity in the immediate vicinity of the probe in lipid environments, steady-state anisotropy, red-edge excitation shift (REES), fluorescence quenching experiments and time-resolved measurements. The rotational relaxation dynamics study of the membrane-bound probe unveils the impartation of high degree of motional rigidity. Wavelength-selective emission behaviour paves way for monitoring of solvent-relaxation in the membranes. Overall, the ICT probe DPDAME displays its commendable sensitivity in deciphering the microheterogeneous environments of liposomal membranes of DMPC and DMPG and promises a new membrane-polarity sensitizing probe.

  12. Fluorescence excitation involving multiple electron transition states of N{sub 2} and CO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Wu, C.Y.R.; Chen, F.Z.; Hung, T.; Judge, D.L. [Univ. of Southern California, Los Angeles, CA (United States)

    1997-04-01

    The electronic states and electronic structures of N{sub 2} and CO{sub 2} in the 8-50 eV energy region have been studied extensively both experimentally and theoretically. In the energy region higher than 25 eV there exists many electronic states including multiple electron transition (MET) states which are responsible for producing most of the dissociative photoionization products. The electronic states at energies higher than 50 eV have been mainly determined by Auger spectroscopy, double charge transfer, photofragment spectroscopy and ion-ion coincidence spectroscopy. The absorption and ionization spectra of these molecules at energies higher than 50 eV mainly show a monotonic decrease in cross section values and exhibit structureless features. The decay channels of MET and Rydberg (or superexcited) states include autoionization, ionization, dissociative ionization, predissociation, and dissociation while those of single ion and multiple ion states may involve predissociation. and dissociation processes. The study of fluorescence specifically probes electronically excited species resulting from the above-mentioned decay channels and provides information for understanding the competition among these channels.

  13. The role of charge transfer in the oxidation state change of Ce atoms in the TM13-CeO2(111) systems (TM = Pd, Ag, Pt, Au): a DFT + U investigation.

    Science.gov (United States)

    Tereshchuk, Polina; Freire, Rafael L H; Ungureanu, Crina G; Seminovski, Yohanna; Kiejna, Adam; Da Silva, Juarez L F

    2015-05-28

    Despite extensive studies of transition metal (TM) clusters supported on ceria (CeO2), fundamental issues such as the role of the TM atoms in the change in the oxidation state of Ce atoms are still not well understood. In this work, we report a theoretical investigation based on static and ab initio molecular dynamics density functional theory calculations of the interaction of 13-atom TM clusters (TM = Pd, Ag, Pt, Au) with the unreduced CeO2(111) surface represented by a large surface unit cell and employing Hubbard corrections for the strong on-site Coulomb correlation in the Ce f-electrons. We found that the TM13 clusters form pyramidal-like structures on CeO2(111) in the lowest energy configurations with the following stacking sequence, TM/TM4/TM8/CeO2(111), while TM13 adopts two-dimensional structures at high energy structures. TM13 induces a change in the oxidation state of few Ce atoms (3 of 16) located in the topmost Ce layer from Ce(IV) (itinerant Ce f-states) to Ce(III) (localized Ce f-states). There is a charge flow from the TM atoms to the CeO2(111) surface, which can be explained by the electronegativity difference between the TM (Pd, Ag, Pt, Au) and O atoms, however, the charge is not uniformly distributed on the topmost O layer due to the pressure induced by the TM13 clusters on the underlying O ions, which yields a decrease in the ionic charge of the O ions located below the cluster and an increase in the remaining O ions. Due to the charge flow mainly from the TM8-layer to the topmost O-layer, the charge cannot flow from the Ce(IV) atoms to the O atoms with the same magnitude as in the clean CeO2(111) surface. Consequently, the effective cationic charge decreases mainly for the Ce atoms that have a bond with the O atoms not located below the cluster, and hence, those Ce atoms change their oxidation state from IV to III. This increases the size of the Ce(III) compared with the Ce(IV) cations, which builds-in a strain within the topmost Ce layer, and

  14. Excited-state dynamics in diketopyrrolopyrrole-based copolymer for organic photovoltaics investigated by transient optical spectroscopy

    Science.gov (United States)

    Matsuzaki, Hiroyuki; Furube, Akihiro; Katoh, Ryuzi; Pratap Singh, Samarendra; Sonar, Prashant; Williams, Evan Laurence; Vijila, Chellappan; Sandhya Subramanian, Gomathy; Gorelik, Sergey; Hobley, Jonathan

    2014-01-01

    We investigate the photoexcited state dynamics in a donor-acceptor copolymer, poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene} (pDPP-TNT), by picosecond fluorescence and femtosecond transient absorption spectroscopies. Time-resolved fluorescence lifetime measurements of pDPP-TNT thin films reveal that the lifetime of the singlet excited state is 185 ± 5 ps and that singlet-singlet annihilation occurs at excitation photon densities above 6 × 1017 photons/cm3. From the results of singlet-singlet annihilation analysis, we estimate that the single-singlet annihilation rate constant is (6.0 ± 0.2) × 10-9 cm3 s-1 and the singlet diffusion length is ~7 nm. From the comparison of femtosecond transient absorption measurements and picosecond fluorescence measurements, it is found that the time profile of the photobleaching signal in the charge-transfer (CT) absorption band coincides with that of the fluorescence intensity and there is no indication of long-lived species, which clearly suggests that charged species, such as polaron pairs and triplet excitons, are not effectively photogenerated in the neat pDPP-TNT polymer.

  15. Study of excited nucleon states at EBAC: status and plans

    Energy Technology Data Exchange (ETDEWEB)

    Hiroyuki Kamano

    2009-12-01

    We present an overview of a research program for the excited nucleon states in Excited Baryon Analysis Center (EBAC) at Jefferson Lab. Current status of our analysis of the meson production reactions based on the unitary dynamical coupled-channels model is summarized, and the N* pole positions extracted from the constructed scattering amplitudes are presented. Our plans for future developments are also discussed.

  16. Molecular and vibrational structure of tetroxo d0 metal complexes in their excited states. a study based on time-dependent density functional calculations and Franck-Condon theory.

    Science.gov (United States)

    Jose, Linta; Seth, Michael; Ziegler, Tom

    2012-02-23

    We have applied time dependent density functional theory to study excited state structures of the tetroxo d(0) transition metal complexes MnO(4)(-), TcO(4)(-), RuO(4), and OsO(4). The excited state geometry optimization was based on a newly implemented scheme [Seth et al. Theor. Chem. Acc. 2011, 129, 331]. The first excited state has a C(3v) geometry for all investigated complexes and is due to a "charge transfer" transition from the oxygen based HOMO to the metal based LUMO. The second excited state can uniformly be characterized by "charge transfer" from the oxygen HOMO-1 to the metal LUMO with a D(2d) geometry for TcO(4)(-), RuO(4), and OsO(4) and two C(2v) geometries for MnO(4)(-). It is finally found that the third excited state of MnO(4)(-) representing the HOMO to metal based LUMO+1 orbital transition has a D(2d) geometry. On the basis of the calculated excited state structures and vibrational modes, the Franck-Condon method was used to simulate the vibronic structure of the absorption spectra for the tetroxo d(0) transition metal complexes. The Franck-Condon scheme seems to reproduce the salient features of the experimental spectra as well as the simulated vibronic structure for MnO(4)(-) generated from an alternative scheme [Neugebauer J. J. Phys. Chem. A 2005, 109, 1168] that does not apply the Franck-Condon approximation.

  17. Vibronic coupling in the excited-states of carotenoids.

    Science.gov (United States)

    Miki, Takeshi; Buckup, Tiago; Krause, Marie S; Southall, June; Cogdell, Richard J; Motzkus, Marcus

    2016-04-28

    The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S2 to the optically dark state S1. Extending this picture, some additional dark states (3A(g)(-) and 1B(u)(-)) and their interaction with the S2 state have also been suggested to play a major role in the ultrafast deactivation of carotenoids and their properties. Here, we investigate the interaction between such dark and bright electronic excited states of open chain carotenoids, particularly its dependence on the number of conjugated double bonds (N). We focus on the ultrafast wave packet motion on the excited potential surface, which is modified by the interaction between bright and dark electronic states. Such a coupling between electronic states leads to a shift of the vibrational frequency during the excited-state evolution. In this regard, pump-degenerate four-wave mixing (pump-DFWM) is applied to a series of carotenoids with different numbers of conjugated double bonds N = 9, 10, 11 and 13 (neurosporene, spheroidene, lycopene and spirilloxanthin, respectively). Moreover, we demonstrate in a closed-chain carotenoid (lutein) that the coupling strength and therefore the vibrational shift can be tailored by changing the energy degeneracy between the 1B(u)(+) and 1B(u)(-) states via solvent interaction.

  18. Ultrafast excited state relaxation in long-chain polyenes

    Science.gov (United States)

    Antognazza, Maria Rosa; Lüer, Larry; Polli, Dario; Christensen, Ronald L.; Schrock, Richard R.; Lanzani, Guglielmo; Cerullo, Giulio

    2010-07-01

    We present a comprehensive study, by femtosecond pump-probe spectroscopy, of excited state dynamics in a polyene that approaches the infinite chain limit. By excitation with sub-10-fs pulses resonant with the 0-0 S 0 → S 2 transition, we observe rapid loss of stimulated emission from the bright excited state S 2, followed by population of the hot S 1 state within 150 fs. Vibrational cooling of S 1 takes place within 500 fs and is followed by decay back to S 0 with 1 ps time constant. By excitation with excess vibrational energy we also observe the ultrafast formation of a long-living absorption, that is assigned to the triplet state generated by singlet fission.

  19. 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.

  20. The examination of berberine excited state by laser flash photolysis

    Science.gov (United States)

    Cheng, Lingli; Wang, Mei; Zhao, Ping; Zhu, Hui; Zhu, Rongrong; Sun, Xiaoyu; Yao, Side; Wang, Shilong

    2009-07-01

    The property of the excited triplet state of berberine (BBR) was investigated by using time-resolved laser flash photolysis of 355 nm in acetonitrile. The transient absorption spectra of the excited triplet BBR were obtained in acetonitrile, which have an absorption maximum at 420 nm. And the ratio of excitation to ionization of BBR in acetonitrile solvent was calculated. The self-decay and self-quenching rate constants, and the absorption coefficient of 3BBR* were investigated and the excited state quantum yield was determined. Furthermore utilizing the benzophenone (BEN) as a triplet sensitizer, and the β-carotene (Car) as an excited energy transfer acceptor, the assignment of 3BBR* was further confirmed and the related energy transfer rate constants were also determined.

  1. Interface charge transfer process in ZnO:Mn/ZnS nanocomposites

    Science.gov (United States)

    Stefan, M.; Toloman, D.; Popa, A.; Mesaros, A.; Vasile, O. R.; Leostean, C.; Pana, O.

    2016-03-01

    ZnO:Mn/ZnS nanocomposites were prepared by seed-mediated growth of ZnS QDs onto the preformed ZnO:Mn nanoparticles. The formation of the nanocomposite structure has been evidenced by XRD, HRTEM, and XPS. The architecture of the nanocomposite with outer ZnS QDs around ZnO:Mn cores is sustained by the sulfur and oxygen depth profiles resulted from XPS. When the two components are brought together, the band gap of ZnS component decreases while that of ZnO:Mn increases. It is the result of interface charge transfer from ZnO:Mn to ZnS QDs. Here ZnO:Mn valence states are extended through the interface into unoccupied gap states of ZnS. The energy band setup is modified from a type II into a type I band alignment. The process is accompanied by enhancement of composite UV emission of PL spectra as compared to its counterparts. The charge transfer from valence band also determines the increase of the core-polarization effect of s shell electrons at Mn2+ nucleus, thus determining the increase of the hyperfine field through the reduction of the covalency degree of Zn(Mn)-O bonds. The quantum confinement in ZnS QDs promotes the ferromagnetic coupling of singly occupied states due to Zn vacancies determining a superparamagnetic behavior of the ensemble. When the nanocomposites are formed, due to interface charge transfer effects, an increased number of filled cation vacancies in ZnS QDs develop, thus disrupting the pre-existing ferromagnetic coupling between spins resulting in a significant reduction of the overall saturation magnetization. The possibility to modulate nanocomposite properties by controlling the interface interactions may be foreseen in these types of materials.

  2. Efficiency of intramolecular electron transfer from the second excited state of the donor in molecular triads D-A1-A2

    Science.gov (United States)

    Feskov, S. V.; Ivanov, A. I.

    2016-01-01

    It is found that intramolecular and intermolecular electron transfer from the second singlet excited state of the donor in all molecular dyads studied up to now is accompanied by ultrafast recombination into the first excited state, resulting in a low quantum yield of the thermalized state with separated charges. The ultrafast photoinduced intramolecular charge transfer in donor‒acceptor 1‒acceptor 2 molecular triads is studied to ascertain the possibilities of increasing the quantum yield of ionic state. It is demonstrated that nonthermal (hot) electron transfer from the primary acceptor to the secondary acceptor can, in parallel with relaxation of a polar solvent, efficiently suppress the ultrafast recombination of charges into the first excited state of the donor and increase the yield of the ionic state. It is established that the angle between the directions of reaction coordinates corresponding to the electron transfer from the donor to the primary acceptor and from the primary acceptor to the secondary acceptor play the most important role in describing these processes. It is concluded that the value of this angle is governed by the ratio between the reorganization energies of the three possible electron transfers in the triad and can vary within wide limits. The parametric regions with maximum quantum yield of the thermalized ionic state are revealed. The strong effect the geometry of a studied triad has on charge separation efficiency is observed.

  3. Excited-state intramolecular hydrogen bonding of compounds based on 2-(2-hydroxyphenyl)-1,3-benzoxazole in solution: a TDDFT study.

    Science.gov (United States)

    Li, Hui; Liu, Yufang; Yang, Yonggang; Yang, Dapeng; Sun, Jinfeng

    2014-12-10

    The excited-state properties of intramolecular hydrogen bonding in the compounds based on 2-(2-hydroxyphenyl)-1,3-benzoxazole (6 and its tautomers 6a and 6b) have been investigated using theoretical methods. According to the geometric optimization and IR spectra in the ground and excited states calculated by density functional theory (DFT) and time-dependent DFT (TD-DFT) methods respectively, the type of intramolecular hydrogen bonding N⋯HO in 6 and 6a is demonstrated to be significantly strengthened, while NH⋯O in the tautomers 6a and 6b are proved to be sharply weakened upon excitation to excited state S1. The calculated absorption peaks of 6 are in good accordance with the experimental results. Moreover, other compounds based on 6 that R1 and R2 are both substituted as well as that only R1 is substituted are investigated to understand the effect of substituent on intramolecular hydrogen bonding. It is found that the hydrogen bond strength can be controlled by the inductive field effect of the substituent. In addition, the intramolecular charge transfers (ICT) of the S1 state for 6 and its tautomers 6a and 6b were theoretically investigated by analyses of molecular orbital.

  4. Peroxyacetyl radical: Electronic excitation energies, fundamental vibrational frequencies, and symmetry breaking in the first excited state

    Energy Technology Data Exchange (ETDEWEB)

    Copan, Andreas V.; Wiens, Avery E.; Nowara, Ewa M.; Schaefer, Henry F.; Agarwal, Jay, E-mail: jagarwal@uga.edu [Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602 (United States)

    2015-02-07

    Peroxyacetyl radical [CH{sub 3}C(O)O{sub 2}] is among the most abundant peroxy radicals in the atmosphere and is involved in OH-radical recycling along with peroxyacetyl nitrate formation. Herein, the ground (X{sup ~}) and first (A{sup ~}) excited state surfaces of cis and trans peroxyacetyl radical are characterized using high-level ab initio methods. Geometries, anharmonic vibrational frequencies, and adiabatic excitation energies extrapolated to the complete basis-set limit are reported from computations with coupled-cluster theory. Excitation of the trans conformer is found to induce a symmetry-breaking conformational change due to second-order Jahn-Teller interactions with higher-lying excited states. Additional benchmark computations are provided to aid future theoretical work on peroxy radicals.

  5. Charge transfer in keV O+(4S,2D,2P)-He collisions

    Science.gov (United States)

    Lindsay, B. G.; Stebbings, R. F.

    2003-02-01

    Absolute differential cross sections (DCSs) are reported for charge-transfer scattering of (1 5)-keV O+(4S) ground-state and O+(2D,2P) metastable-state ions by helium atoms at angles between 0.2° and 6.3° in the laboratory frame. Estimated ground-state and metastable-state total cross sections are derived from these measurements. The present ground-state cross sections agree satisfactorily with previous measurements for energies above 2 keV and the metastable-state cross sections are consistent with the mixed-state data of Kusakabe et al. [J. Phys. Soc. Japan 59, 1987 (1990)]. The large differences between the ground- and metastable-state cross sections predicted by theory are not observed.

  6. Investigation into chromophore excited-state coupling in allophycocyanin

    Science.gov (United States)

    Zheng, Xiguang; Zhao, Fuli; Wang, He Z.; Gao, Zhaolan; Yu, Zhenxin; Zhu, Jinchang; Xia, Andong; Jiang, Lijin

    1994-08-01

    Both theoretical and experimental studies are presented on chromophore excited-state coupling in linker-free allophycocyanin (APC), one of the antenna phycobiliproteins in algal photosynthesis. A three-site-coupling model has been introduced to describe the exciton interaction mechanism amoung the excited (beta) chromophore in APC, and the exciton energy splitting is estimated. Picosecond polarized fluorescence experiments both on monomeric and trimeric APC isolated from alga Spirulina platensis have been performed. The experimental results show that APC monomer and trimer exhibit remarkedly different spectropic characteristics, and satisfy the suggestion of strong excited- state coupling among chromophores in APC.

  7. 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...

  8. 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.

  9. 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.

  10. Density Relaxation in Time-Dependent Density Functional Theory: Combining Relaxed Density Natural Orbitals and Multireference Perturbation Theories for an Improved Description of Excited States.

    Science.gov (United States)

    Ronca, Enrico; Angeli, Celestino; Belpassi, Leonardo; De Angelis, Filippo; Tarantelli, Francesco; Pastore, Mariachiara

    2014-09-09

    Making use of the recently developed excited state charge displacement analysis [E. Ronca et al., J. Chem. Phys. 140, 054110 (2014)], suited to quantitatively characterize the charge fluxes coming along an electronic excitation, we investigate the role of the density relaxation effects in the overall description of electronically excited states of different nature, namely, valence, ionic, and charge transfer (CT), considering a large set of prototypical small and medium-sized molecular systems. By comparing the response densities provided by time-dependent density functional theory (TDDFT) and the corresponding relaxed densities obtained by applying the Z-vector postlinear-response approach [N. C. Handy and H. F. Schaefer, J. Chem. Phys. 81, 5031 (1984)] with those obtained by highly correlated state-of-the-art wave function calculations, we show that the inclusion of the relaxation effects is imperative to get an accurate description of the considered excited states. We also examine what happens at the quality of the response function when an increasing amount of Hartree-Fock (HF) exchange is included in the functional, showing that the usually improved excitation energies in the case of CT states are not always the consequence of an improved description of their overall properties. Remarkably, we find that the relaxation of the response densities is always able to reproduce, independently of the extent of HF exchange in the functional, the benchmark wave function densities. Finally, we propose a novel and computationally convenient strategy, based on the use of the natural orbitals derived from the relaxed TDDFT density to build zero-order wave function for multireference perturbation theory calculations. For a significant set of different excited states, the proposed approach provided accurate excitation energies, comparable to those obtained by computationally demanding ab initio calculations.

  11. Excited States of the divacancy in SiC

    Science.gov (United States)

    Bockstedte, Michel; Garratt, Thomas; Ivady, Viktor; Gali, Adam

    2014-03-01

    The divacancy in SiC - a technologically mature material that fulfills the necessary requirements for hosting defect based quantum computing - is a good candidate for implementing a solid state quantum bit. Its ground state is isovalent to the NV center in diamond as demonstrated by density functional theory (DFT). Furthermore, coherent manipulation of divacancy spins in SiC has been demonstrated. The similarities to NV might indicate that the same inter system crossing (ICS) from the high to the low spin state is responsible for its spin-dependent fluorescent signal. By DFT and a DFT-based multi-reference hamiltonian we analyze the excited state spectrum of the defects. In contrast to the current picture of the spin dynamics of the NV center, we predict that a static Jahn-Teller effect in the first excited triplet states governs an ICS both with the excited and ground state of the divacancy.

  12. Microwave spectroscopy of furfural in vibrationally excited states

    Science.gov (United States)

    Motiyenko, R. A.; Alekseev, E. A.; Dyubko, S. F.

    2007-07-01

    The results of microwave spectrum investigation of the excited vibrational states of furfural in the frequency range between 49 and 149 GHz are reported. In total 15 excited vibrational states (9 for trans-furfural and 6 for cis-furfural) were assigned and analyzed. Six of the 15 investigated states were assigned for the first time. Accurate values of rigid rotor and quartic centrifugal distortion constants of asymmetric top Hamiltonian have been determined for 13 excited states. Also for some states several sextic and octic level constants were needed in order to fit the data within experimental accuracy. The vt = 3 and vs = 1, va = 1 states of trans-furfural were found to be strongly perturbed and only rotational transitions with low Ka values can be reliably identified in this study.

  13. Characterizing RNA Excited States using NMR Relaxation Dispersion

    Science.gov (United States)

    Xue, Yi; Kellogg, Dawn; Kimsey, Isaac J; Sathyamoorthy, Bharathwaj; Stein, Zachary W; McBrairty, Mitchell; Al-Hashimi, Hashim M.

    2016-01-01

    Changes in RNA secondary structure play fundamental roles in the cellular functions of a growing number of non-coding RNAs. This chapter describes NMR-based approaches for characterizing microsecond-to-millisecond changes in RNA secondary structure that are directed toward short-lived and low-populated species often referred to as “excited states”. Compared to larger-scale changes in RNA secondary structure, transitions towards excited states do not require assistance from chaperones, are often orders of magnitude faster, and are localized to a small number of nearby base pairs in and around non-canonical motifs. Here we describe a procedure for characterizing RNA excited states using off-resonance R1ρ NMR relaxation dispersion utilizing low-to-high spin-lock fields (25–3000 Hz). R1ρ NMR relaxation dispersion experiments are used to measure carbon and nitrogen chemical shifts in base and sugar moieties of the excited state. The chemical shift data is then interpreted with the aid of secondary structure prediction to infer potential excited states that feature alternative secondary structures. Candidate structures are then tested by using mutations, single-atom substitutions, or by changing physiochemical conditions, such as pH and temperature, to either stabilize or destabilize the candidate excited state. The resulting chemical shifts of the mutants or under different physiochemical conditions are then compared to those of the ground and excited state. Application is illustrated with a focus on the transactivation response element (TAR) from the human immune deficiency virus type 1 (HIV-1), which exists in dynamic equilibrium with at least two distinct excited states. PMID:26068737

  14. A cubic scaling algorithm for excited states calculations in particle-particle random phase approximation

    CERN Document Server

    Lu, Jianfeng

    2016-01-01

    The particle-particle random phase approximation (pp-RPA) has been shown to be capable of describing double, Rydberg, and charge transfer excitations, for which the conventional time-dependent density functional theory (TDDFT) might not be suitable. It is thus desirable to reduce the computational cost of pp-RPA so that it can be efficiently applied to larger molecules and even solids. This paper introduces an $O(N^3)$ algorithm, where $N$ is the number of orbitals, based on an interpolative separable density fitting technique and the Jacobi-Davidson eigensolver to calculate a few low-lying excitations in the pp-RPA framework. The size of the pp-RPA matrix can also be reduced by keeping only a small portion of orbitals with orbital energy close to the Fermi energy. This reduced system leads to a smaller prefactor of the cubic scaling algorithm, while keeping the accuracy for the low-lying excitation energies.

  15. Excited-state Halo of 14C

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Neutron capture processes on carbon isotope play an important role in astrophysics ranging fromnucleosynthesis in the stellar helium and carbon burning stages to possibly inhomogeneous big bangmodels. The capture rate in astrophysical environments strongly depends on the structure of these carbonnuclei. For example, the first 1/2+ state in 13C is a neutron halo state, and these results in an enormous

  16. Targeting excited states in all-trans polyenes with electron-pair states

    Science.gov (United States)

    Boguslawski, Katharina

    2016-12-01

    Wavefunctions restricted to electron pair states are promising models for strongly correlated systems. Specifically, the pair Coupled Cluster Doubles (pCCD) ansatz allows us to accurately describe bond dissociation processes and heavy-element containing compounds with multiple quasi-degenerate single-particle states. Here, we extend the pCCD method to model excited states using the equation of motion (EOM) formalism. As the cluster operator of pCCD is restricted to electron-pair excitations, EOM-pCCD allows us to target excited electron-pair states only. To model singly excited states within EOM-pCCD, we modify the configuration interaction ansatz of EOM-pCCD to contain also single excitations. Our proposed model represents a simple and cost-effective alternative to conventional EOM-CC methods to study singly excited electronic states. The performance of the excited state models is assessed against the lowest-lying excited states of the uranyl cation and the two lowest-lying excited states of all-trans polyenes. Our numerical results suggest that EOM-pCCD including single excitations is a good starting point to target singly excited states.

  17. 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.

  18. 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.

  19. Negative thermal expansion induced by intermetallic charge transfer.

    Science.gov (United States)

    Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

    2015-06-01

    Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu3Fe4O12 and LaCu3Fe4-x Mn x O12, as well as in Bi or Ni substituted BiNiO3. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding -70 × 10(-6) K(-1) near room temperature, in the temperature range which can be controlled by substitution.

  20. Turn-on fluorescence probes based on pyranine/viologen charge-transfer complexes for the determination of nucleotides

    Energy Technology Data Exchange (ETDEWEB)

    Schäferling, Michael, E-mail: Michael.schaeferling@utu.fi; Lang, Thomas; Schnettelker, Annette

    2014-10-15

    The formation of ground state charge-transfer complexes between pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid) and viologen (paraquat) derivatives is utilized for the design of novel fluoroionophores for the determination of phosphate species, particularly of nucleotides. The strong quenching of the pyranine fluorescence by viologen-type charge transfer acceptors can be countermanded if these are functionalized with triethylammonium groups that serve as recognition elements for phosphate anions. We report on the fluorogenic responses of these water-soluble molecular probes in presence of different phosphates. Absorbance measurements give additional information on the charge transfer complex formation and the interaction with nucleotides. The experimental data show that these aggregates form attractive, simple and versatile fluorescence turn-on probes for nucleoside triphosphates. The reversibility of the fluorescence response is demonstrated by means of an enzymatic model assay using ATPase for the decomposition of adenosine triphosphate. - Highlights: • Pyranine/viologen charge-transfer complexes as molecular probe for ATP recognition. • Fluorescence turn on mechanism. • Selective compared to other nucleotides and phosphate anions. • Fast and reversible response applicable to monitor enzymatic reactions.

  1. Charge transfer interactions of a Ru(II) dye complex and related ligand molecules adsorbed on Au(111)

    Energy Technology Data Exchange (ETDEWEB)

    Britton, Andrew J.; Weston, Matthew; O' Shea, James N. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Nottingham Nanotechnology and Nanoscience Centre (NNNC), University of Nottingham, Nottingham NG7 2RD (United Kingdom); Taylor, J. Ben; Rienzo, Anna; Mayor, Louise C. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2011-10-28

    The interaction of the dye molecule, N3 (cis-bis(isothiocyanato)bis(2,2{sup '}-bipyridyl-4,4{sup '}-dicarboxylato) -ruthenium(II)), and related ligand molecules with a Au(111) surface has been studied using synchrotron radiation-based electron spectroscopy. Resonant photoemission spectroscopy (RPES) and autoionization of the adsorbed molecules have been used to probe the coupling between the molecules and the substrate. Evidence of charge transfer from the states near the Fermi level of the gold substrate into the lowest unoccupied molecular orbital (LUMO) of the molecules is found in the monolayer RPES spectra of both isonicotinic acid and bi-isonicotinic acid (a ligand of N3), but not for the N3 molecule itself. Calibrated x-ray absorption spectroscopy and valence band spectra of the monolayers reveals that the LUMO crosses the Fermi level of the surface in all cases, showing that charge transfer is energetically possible both from and to the molecule. A core-hole clock analysis of the resonant photoemission reveals a charge transfer time of around 4 fs from the LUMO of the N3 dye molecule to the surface. The lack of charge transfer in the opposite direction is understood in terms of the lack of spatial overlap between the {pi}*-orbitals in the aromatic rings of the bi-isonicotinic acid ligands of N3 and the gold surface.

  2. Tunable Excited-State Properties and Dynamics as a Function of Pt–Pt Distance in Pyrazolate-Bridged Pt(II) Dimers

    Energy Technology Data Exchange (ETDEWEB)

    Brown-Xu, Samantha E.; Kelley, Matthew S. J.; Fransted, Kelly A.; Chakraborty, Arnab; Schatz, George C.; Castellano, Felix N.; Chen, Lin X.

    2016-02-04

    The influence of molecular structure on excited state properties and dynamics of a series of cyclometalated platinum dimers was investigated through a combined experimental and theoretical approach using femtosecond transient absorption (fs TA) spectroscopy and density functional theory (DFT) calculations. The molecules have the general formula [Pt(ppy)(µ-R2pz)]2 where ppy = 2-phenylpyridine, pz = pyrazolate and R = H, Me, Ph, or tBu, and are strongly photoluminescent at room temperature. The distance between the platinum centers in this A frame geometry can be varied depending on the steric bulk of the bridging pyrazolate ligands that exert structural constraints and compress the Pt-Pt distance. At large Pt-Pt distances there is little interaction between the subunits and the chromophore behaves similar to a monomer with excited states described as mixtures of ligand-centered and metal-to-ligand charge transfer (LC/MLCT) transitions. When the Pt(II) centers are brought closer together with bulky bridging ligands, they interact through their orbitals and the S1 and T1 states are best characterized as metal metal to ligand charge transfer (MMLCT) in character. The results of the fs TA experiments reveal that intersystem crossing (ISC) occurs on ultrafast timescales (τS1 < 200 fs) while there are two relaxation processes occurring within the triplet manifold, τ1 = 0.5 – 3.2 ps and τ2 = 20 – 70 ps; the longer time constants correspond to the presence of bulkier bridging ligands. DFT calculations illustrate that the Pt-Pt distances further contract in the T1 3MMLCT states, therefore slower relaxation may be related to a larger structural reorganization. Subsequent investigations using faster time resolution are planned to measure the ISC process as well as to identify any potential coherent interaction(s) between the platinum centers that may occur.

  3. Excited state correlations of the finite Heisenberg chain

    Science.gov (United States)

    Pozsgay, Balázs

    2017-02-01

    We consider short range correlations in excited states of the finite XXZ and XXX Heisenberg spin chains. We conjecture that the known results for the factorized ground state correlations can be applied to the excited states too, if the so-called physical part of the construction is changed appropriately. For the ground state we derive simple algebraic expressions for the physical part; the formulas only use the ground state Bethe roots as an input. We conjecture that the same formulas can be applied to the excited states as well, if the exact Bethe roots of the excited states are used instead. In the XXZ chain the results are expected to be valid for all states (except certain singular cases where regularization is needed), whereas in the XXX case they only apply to singlet states or group invariant operators. Our conjectures are tested against numerical data from exact diagonalization and coordinate Bethe Ansatz calculations, and perfect agreement is found in all cases. In the XXX case we also derive a new result for the nearest-neighbour correlator , which is valid for non-singlet states as well. Our results build a bridge between the known theory of factorized correlations, and the recently conjectured TBA-like description for the building blocks of the construction.

  4. Shape vibrations and quasiparticle excitations in the lowest 0+ excited state of the Erbium isotopes

    CERN Document Server

    Chen, Fang-Qi

    2016-01-01

    The ground and first excited 0+ states of the {156-172}Er isotopes are analyzed in the framework of the generator coordinate method. The shape parameter beta is used to generate wave functions with different deformations which together with the two-quasiparticle states built on them provide a set of states. An angular momentum and particle number projection of the latter spawn the basis states of the generator coordinate method. With this ansatz and using the separable pairing plus quadrupole interaction we obtain a good agreement with the experimental spectra and E2 transition rates up to moderate spin values. The structure of the wave functions suggests that the first excited 0+ states in the soft Er isotopes are dominated by shape fluctuations, while in the well deformed Er isotopes the two-quasiparticle states are more relevant. In between both degrees of freedom are necessary .

  5. Dielectric controlled excited state relaxation pathways of a representative push-pull stilbene: a mechanistic study using femtosecond fluorescence up-conversion technique.

    Science.gov (United States)

    Rafiq, Shahnawaz; Sen, Pratik

    2013-02-28

    Femtosecond fluorescence up-conversion technique was employed to reinvestigate the intriguing dependence of fluorescence quantum yield of trans-4-dimethylamino-4(')-nitrostilbene (DNS) on dielectric properties of the media. In polar solvents, such as methanol and acetonitrile, the two time components of the fluorescence transients were assigned to intramolecular charge transfer (ICT) dynamics and to the depletion of the ICT state to the ground state via internal conversion along the torsional coordinate of nitro moiety. The viscosity independence of the first time component indicates the absence of any torsional coordinate in the charge transfer process. In slightly polar solvent (carbon tetrachloride) the fluorescence transients show a triple exponential behavior. The first time component was assigned to the formation of the ICT state on a 2 ps time scale. Second time component was assigned to the relaxation of the ICT state via two torsion controlled channels. First channel involves the torsional motion about the central double bond leading to the trans-cis isomerization via a conical intersection or avoided crossing. The other channel contributing to the depopulation of ICT state involves the torsional coordinates of dimethylanilino and∕or nitrophenyl moieties and leads to the formation of a conformationally relaxed state, which subsequently relaxes back to the ground state radiatively, and is responsible for the high fluorescence quantum yield of DNS in slightly polar solvents such as carbon tetrachloride, toluene, etc. The excited singlet state which is having a dominant π-π∗ character may also decay via intersystem crossing to the n-π∗ triplet manifold and thus accounts for the observed triplet yield of the molecule in slightly polar solvents.

  6. Polarization Enhanced Charge Transfer: Dual-Band GaN-Based Plasmonic Photodetector

    Science.gov (United States)

    Jia, Ran; Zhao, Dongfang; Gao, Naikun; Liu, Duo

    2017-01-01

    Here, we report a dual-band plasmonic photodetector based on Ga-polar gallium nitride (GaN) for highly sensitive detection of UV and green light. We discover that decoration of Au nanoparticles (NPs) drastically increases the photoelectric responsivities by more than 50 times in comparition to the blank GaN photodetector. The observed behaviors are attributed to polarization enhanced charge transfer of optically excited hot electrons from Au NPs to GaN driven by the strong spontaneous polarization field of Ga-polar GaN. Moreover, defect ionization promoted by localized surface plasmon resonances (LSPRs) is also discussed. This novel type of photodetector may shed light on the design and fabrication of photoelectric devices based on polar semiconductors and microstructural defects.

  7. The effect of solvent additives on morphology and excited-state dynamics in PCPDTBT:PCBM photovoltaic blends.

    Science.gov (United States)

    Etzold, Fabian; Howard, Ian A; Forler, Nina; Cho, Don M; Meister, Michael; Mangold, Hannah; Shu, Jie; Hansen, Michael Ryan; Müllen, Klaus; Laquai, Frédéric

    2012-06-27

    The dependence of the thin film morphology and excited-state dynamics for the low-bandgap donor-acceptor copolymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) in pristine films and in blends (1:2) with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) on the use of the solvent additive 1,8-octanedithiol (ODT) is studied by solid-state nuclear magnetic resonance (NMR) spectroscopy and broadband visible and near-infrared pump-probe transient absorption spectroscopy (TAS) covering a spectral range from 500-2000 nm. The latter allows monitoring of the dynamics of excitons, bound interfacial charge-transfer (CT) states, and free charge carriers over a time range from femto- to microseconds. The broadband pump-probe experiments reveal that excitons are not only generated in the polymer but also in PCBM-rich domains. Depending on the morphology controlled by the use of solvent additives, polymer excitons undergo mainly ultrafast dissociation (photovoltaic devices.

  8. Charge Transfer Based Colorimetric Detection of Silver Ion

    Energy Technology Data Exchange (ETDEWEB)

    Han, Seung Choul; Kim, Kwang Seob; Choi, Soon Kyu; Oh, Jinho; Lee, Jae Wook [Dong-A Univ., Busan (Korea, Republic of)

    2014-05-15

    We have demonstrated the colorimetric chemosensor for detection of Ag{sup +} via formation of nanoparticles which is based on the intramolecular CT interaction between the electron-rich (2,6-dialkoxynaphthalene; Np) moiety and the electron-deficient (methyl viologen; MV{sup 2+}) moiety of a single sensor molecule. Under irradiation of light, Ag{sup +} was reduced to very small silver nanoparticle by CT interaction in the presence of OEGs as flexible recognition moiety of Ag{sup +} and stabilizer for Ag nanoparticles, thus Ag nanoparticles resulted to reddish brown in the color change of sensor solution, gradually. Therefore, the charge-transfer interaction between an electron-deficient and an electron-rich units existing at a sensor molecule can be regarded as a new and efficient method to construct various colorimetric chemosensors. Donor.acceptor interactions or charge transfer (CT) interactions are an important class of non-covalent interactions and have been widely exploited in self-assembling systems. Beyond molecular chemistry, supramolecular chemistry aims at constituting highly complex, functional chemical systems from components held together by intermolecular forces. Chemosensors are the molecules of abiotic origin that bind selectively and reversibly with the analyte with concomitant change in one or more properties of the system. The recognition and signaling of ionic and neutral species of varying complexity is one of the most intensively studied areas of contemporary supramolecular chemistry.

  9. Energy and charge transfer in nanoscale hybrid materials.

    Science.gov (United States)

    Basché, Thomas; Bottin, Anne; Li, Chen; Müllen, Klaus; Kim, Jeong-Hee; Sohn, Byeong-Hyeok; Prabhakaran, Prem; Lee, Kwang-Sup

    2015-06-01

    Hybrid materials composed of colloidal semiconductor quantum dots and π-conjugated organic molecules and polymers have attracted continuous interest in recent years, because they may find applications in bio-sensing, photodetection, and photovoltaics. Fundamental processes occurring in these nanohybrids are light absorption and emission as well as energy and/or charge transfer between the components. For future applications it is mandatory to understand, control, and optimize the wide parameter space with respect to chemical assembly and the desired photophysical properties. Accordingly, different approaches to tackle this issue are described here. Simple organic dye molecules (Dye)/quantum dot (QD) conjugates are studied with stationary and time-resolved spectroscopy to address the dynamics of energy and ultra-fast charge transfer. Micellar as well as lamellar nanostructures derived from diblock copolymers are employed to fine-tune the energy transfer efficiency of QD donor/dye acceptor couples. Finally, the transport of charges through organic components coupled to the quantum dot surface is discussed with an emphasis on functional devices.

  10. On the accuracy of the general, state-specific polarizable-continuum model for the description of correlated ground- and excited states in solution.

    Science.gov (United States)

    Mewes, Jan-Michael; Herbert, John M; Dreuw, Andreas

    2017-01-04

    Equilibrium and non-equilibrium formulations of the state-specific polarizable-continuum model (SS-PCM) are evaluated in combination with correlated ground- and excited-state densities provided by the algebraic-diagrammatic construction method (ADC) for the polarization propagator via the computationally efficient intermediate-state representation (ISR) formalism. Since the influence of the SS-PCM onto quantum-chemical method is naturally limited to the presence of the apparent surface charges in the one-electron Hamiltonian and hence fully contained in the polarized MOs, the herein presented solvent model can be combined with all implemented orders and variants of ADC. Employing ADC/SS-PCM, the symmetric, ionized dimers of neon, ethene and nitromethane are investigated. Their broken-symmetry wavefunctions exhibit a low-lying charge-transfer state that is symmetry-equivalent to the ground state. This curious though ultimately artificial feature is convenient as it allows for a direct comparison of ADC/SS-PCM for the CT state to the Møller-Plesset/PCM description of the ground state. The agreement down to 0.02 eV for a wide range of dielectric constants validates the ADC/SS-PCM approach. Eventually, the relaxed potential-energy surfaces of the ground and lowest excited states of 4-(N,N)-dimethylaminobenzonitrile in cyclohexane and acetonitrile are computed, and it is demonstrated that the ADC(2)/SS-PCM approach affords excellent agreement with experimental fluorescence data. Only at the ADC(3) level of theory, however, the experimentally observed solvent-dependent dual fluorescence can be explained.

  11. 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.

  12. Impact of Substituents on Excited-State and Photosensitizing Properties in Cationic Iridium(III) Complexes with Ligands of Coumarin 6.

    Science.gov (United States)

    Takizawa, Shin-Ya; Ikuta, Naoya; Zeng, Fanyang; Komaru, Shohei; Sebata, Shinogu; Murata, Shigeru

    2016-09-01

    A series of bis-cyclometalated cationic iridium (Ir) complexes were synthesized employing two coumarin 6 ligands and a 2,2'-bipyridine (bpy) with various substituents as new sensitizers, realizing both features of strong visible-light absorption and long-lived excited state. Complexes 2-4, with electron-donating methyl and methoxy groups, absorbed visible light strongly (ε: 126 000-132 000 M(-1) cm(-1)) and exhibited room-temperature phosphorescence with remarkably long lifetimes (21-23 μs) in dichloromethane. In contrast, the excited state of prototype complex 1 without any substituents was short-lived, particularly in highly polar acetonitrile. Phosphorescence of complex 5 with the strong electron-withdrawing CF3 groups was too weak to be detected at room temperature even in less polar dichloromethane. The triplet energies of their coumarin ligand-centered ((3)LC) phosphorescent states were almost invariable, demonstrating that selective tuning of the excited-state lifetime is possible through this "simple chemical modification of the bpy ligand" (we name it the "SCMB" method). The spectroscopic and computational investigations in this study suggest that a potential source of the nonradiative deactivation is a triplet ligand-to-ligand charge-transfer state ((3)LLCT state, coumarin 6 → bpy) and lead us to conclude that the energy level of this dark (3)LLCT state, as well as its thermal population, is largely dependent on the substituents and solvent polarity. In addition, the significant difference in excited-state lifetime was reflected in the photosensitizing ability of complexes 1-5 in visible-light-driven hydrogen generation using sodium ascorbate and a cobalt(III) diglyoxime complex as an electron donor and a water-reduction catalyst, respectively. This study suggests that the SCMB method should be generally effective in controlling the excited state of other bis-cyclometalated cationic Ir(III) complexes.

  13. Neutron halos in the excited states for N=127 isotones

    Institute of Scientific and Technical Information of China (English)

    SUN Qin; GUO Jian-You

    2009-01-01

    Properties of the ground states and the excited states of N=127 isotones are investigated by using the nonlinear relativistic mean field theory with the interactions PK1. By analyzing the rms of proton and neutron, the single particle energies of valence nucleon and the density distributions of neutron, proton and the last neutron, it can be found that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 209Pb. It is also predicted that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 207Hg, 208Tl, 210Bi and 211Po.

  14. Super-atom molecular orbital excited states of fullerenes.

    Science.gov (United States)

    Johansson, J Olof; Bohl, Elvira; Campbell, Eleanor E B

    2016-09-13

    Super-atom molecular orbitals are orbitals that form diffuse hydrogenic excited electronic states of fullerenes with their electron density centred at the centre of the hollow carbon cage and a significant electron density inside the cage. This is a consequence of the high symmetry and hollow structure of the molecules and distinguishes them from typical low-lying molecular Rydberg states. This review summarizes the current experimental and theoretical studies related to these exotic excited electronic states with emphasis on femtosecond photoelectron spectroscopy experiments on gas-phase fullerenes.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  15. Excited states of Ne isoelectronic ions: SAC-CI study

    Energy Technology Data Exchange (ETDEWEB)

    Das, A.K.; Ehara, M.; Nakatsuji, H. [Kyoto Univ. (Japan). Faculty of Engineering

    2001-02-01

    Excited states of the s, p, and d symmetries up to principal quantum number n = 4 are studied for the first eight members of Ne isoelectronic sequence (Ne to Cl{sup 7+}) by the SAC-CI (symmetry-adapted-cluster configuration-interaction) method. The valence STO basis sets of Clementi et al. and the optimized excited STO are used by the STO-6G expansion method. The calculated transition energies agree well with the experimental values wherever available. (orig.)

  16. Ultrafast excited-state intramolecular proton transfer of aloesaponarin I.

    Science.gov (United States)

    Nagaoka, Shin-ichi; Uno, Hidemitsu; Huppert, Dan

    2013-04-25

    Time-resolved emission of aloesaponarin I was studied with the fluorescence up-conversion and time-correlated single-photon-counting techniques. The rates of the excited-state intramolecular proton transfer, of the solvent and molecular rearrangements, and of the decay from the excited proton-transferred species were determined and interpreted in the light of time-dependent density functional calculations. These results were discussed in conjunction with UV protection and singlet-oxygen quenching activity of aloe.

  17. Ultrafast charge transfer between MoTe2 and MoS2 monolayers

    Science.gov (United States)

    Pan, Shudi; Ceballos, Frank; Bellus, Matthew Z.; Zereshki, Peymon; Zhao, Hui

    2017-03-01

    High quality and stable electrical contact between metal and two-dimensional materials, such as transition metal dichalcogenides, is a necessary requirement that has yet to be achieved in order to successfully exploit the advantages that these materials offer to electronics and optoelectronics. MoTe2, owing to its phase changing property, can potentially offer a solution. A recent study demonstrated that metallic phase of MoTe2 connects its semiconducting phase with very low resistance. To utilize this property to connect other two-dimensional materials, it is important to achieve efficient charge transfer between MoTe2 and other semiconducting materials. Using MoS2 as an example, we report ultrafast and efficient charge transfer between MoTe2 and MoS2 monolayers. In the transient absorption measurements, an ultrashort pump pulse is used to selectively excite electrons in MoTe2. The appearance of the excited electrons in the conduction band of MoS2 is monitored by using a probe pulse that is tuned to the resonance of MoS2. We found that electrons transfer to MoS2 on a time scale of at most 0.3 ps. The transferred electrons give rise to a large transient absorption signal at both A-exciton and B-exciton resonances due to the screening effect. We also observed ultrafast transfer of holes from MoS2 to MoTe2. Our results suggest the feasibility of using MoTe2 as a bridge material to connect MoS2 and other transition metal dichalcogenides, and demonstrate a new transition metal dichalcogenide heterostructure involving MoTe2, which extends the spectral range of such structures to infrared.

  18. Quantum dynamics of the charge transfer in C{sup +} + S at low collision energies

    Energy Technology Data Exchange (ETDEWEB)

    Chenel, Aurelie; Mangaud, Etienne; Justum, Yves; Desouter-Lecomte, Michele [Laboratoire de Chimie Physique, Bat 349, Univ-ParisSud et CNRS-UMR8000, F-91405 Orsay Cedex (France); Talbi, Dahbia [Groupe de Recherche en Astronomie et Astrophysique du Languedoc, Universite de Montpellier II et CNRS-UMR5024, Place Eugene Bataillon, F-34095 Montpellier Cedex 05 (France); Bacchus-Montabonel, Marie-Christine, E-mail: michele.desouter-lecomte@u-psud.f [Laboratoire de Spectrometrie Ionique et moleculaire, Universite de Lyon I et CNRS-UMR5579, 43 Bd du 11 Novembre 1918, F-69622 Villeurbanne Cedex (France)

    2010-12-28

    Following a recent semiclassical investigation by Bacchus-Montabonel and Talbi (2008 Chem. Phys. Lett. 467 28), the C{sup +}(2s{sup 2}2p){sup 2}P + S(3s{sup 2}3p{sup 4}){sup 3}P charge transfer process involved in the modellization of the interstellar medium chemistry and its reverse reaction are revisited by combining a wave packet approach and semiclassical dynamics in a quasimolecular approach for doublet and quartet states. New radial non-adiabatic coupling matrix elements have been calculated and the mixed treatment gives access to new precise values of the rate coefficients for the direct and reverse charge transfer processes. For this system, quantum and semiclassical results are in good agreement even at low collision kinetic energies. The dominance of the quartet states in the process is confirmed. In the quantum treatment, the collision matrix elements are extracted from wave packets by the flux method with an absorbing potential. The formation of resonances due to a centrifugal barrier is illustrated.

  19. Excited-state dynamics of astaxanthin aggregates

    Science.gov (United States)

    Fuciman, Marcel; Durchan, Milan; Šlouf, Václav; Keşan, Gürkan; Polívka, Tomáš

    2013-05-01

    Astaxanthin forms three types of aggregates in hydrated dimethyl sulfoxide (DMSO). In DMSO/water ratio of 1:1, a red-shifted J-aggregate with maximum at 570 nm is generated, while a ratio of 1:9 produces blue-shifted H-aggregates with peaks at 386 nm (H1) and 460 nm (H2). Monomeric astaxanthin in DMSO has an S1 lifetime of 5.3 ps, but a long-lived (33 ps) S∗ signal was also identified. Aggregation changes the S1 lifetimes to 17 ps (H1), 30 ps (H2), and 14 ps (J). Triplet state of astaxanthin, most likely generated via singlet homofission, was observed in H1 and H2 aggregates.

  20. State-Selective Excitation of Quantum Systems via Geometrical Optimization.

    Science.gov (United States)

    Chang, Bo Y; Shin, Seokmin; Sola, Ignacio R

    2015-09-08

    We lay out the foundations of a general method of quantum control via geometrical optimization. We apply the method to state-selective population transfer using ultrashort transform-limited pulses between manifolds of levels that may represent, e.g., state-selective transitions in molecules. Assuming that certain states can be prepared, we develop three implementations: (i) preoptimization, which implies engineering the initial state within the ground manifold or electronic state before the pulse is applied; (ii) postoptimization, which implies engineering the final state within the excited manifold or target electronic state, after the pulse; and (iii) double-time optimization, which uses both types of time-ordered manipulations. We apply the schemes to two important dynamical problems: To prepare arbitrary vibrational superposition states on the target electronic state and to select weakly coupled vibrational states. Whereas full population inversion between the electronic states only requires control at initial time in all of the ground vibrational levels, only very specific superposition states can be prepared with high fidelity by either pre- or postoptimization mechanisms. Full state-selective population inversion requires manipulating the vibrational coherences in the ground electronic state before the optical pulse is applied and in the excited electronic state afterward, but not during all times.

  1. Two-Mode Excited Entangled Coherent State: Nonclassicality and Entanglement

    Science.gov (United States)

    Zhang, Hao-Liang; Wu, Jia-Ni; Liu, Cun-Jin; Hu, Yin-Quan; Hu, Li-Yun

    2017-03-01

    Two-mode excited entangled coherent states (TME-ECSs) are introduced by operating repeatedly the photon-excited operator on the ECSs. It is shown that the normalization constant is related to the product of two Laguerre polynomials. The influence of the operation on nonclassical behaviour of the ECSs is investigated in terms of cross-correlation function, anti-bunching effect and the negativity of Wigner function, which show that nonclassical properties can be enhanced. In addition, inseparability properties of the TME-ECSs are discussed by using Bell inequality and concurrence. It is found that the degree of quantum entanglement of even ECSs increases with the increase of the total excited photon number, and the violation of Bell inequality can be present for both even and odd case only when the total excited photon numbers are even and odd, respectively.

  2. Highly Efficient Visible-to-NIR Luminescence of Lanthanide(III) Complexes with Zwitterionic Ligands Bearing Charge-Transfer Character: Beyond Triplet Sensitization.

    Science.gov (United States)

    Pan, Mei; Du, Bin-Bin; Zhu, Yi-Xuan; Yue, Mei-Qin; Wei, Zhang-Wen; Su, Cheng-Yong

    2016-02-12

    Two zwitterionic-type ligands featuring π-π* and intraligand charge-transfer (ILCT) excited states, namely 1,1'-(2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene)dipyridinium-4-olate (TMPBPO) and 1-dodecylpyridin-4(1 H)-one (DOPO), have been prepared and applied to the assembly of lanthanide coordination complexes in an effort to understand the ligand-direction effect on the structure of the Ln complexes and the ligand sensitization effect on the luminescence of the Ln complexes. Due to the wide-band triplet states plus additional ILCT excitation states extending into lower energy levels, broadly and strongly sensitized photoluminescence of f→f transitions from various Ln(3+) ions were observed to cover the visible to near-infrared (NIR) regions. Among which, the Pr, Sm, Dy, and Tm complexes simultaneously display both strong visible and NIR emissions. Based on the isostructural feature of the Ln complexes, color tuning and single-component white light was achieved by preparation of solid solutions of the ternary systems Gd-Eu-Tb (for TMPBPO) and La-Eu-Tb and La-Dy-Sm (for DOPO). Moreover, the visible and NIR luminescence lifetimes of the Ln complexes with the TMPBPO ligand were investigated from 77 to 298 K, revealing a strong temperature dependence of the Tm(3+) ((3) H4 ) and Yb(3+) ((2) F5/2 ) decay dynamics, which has not been explored before for their coordination complexes.

  3. First-principles Calculation of Excited State Spectra in QCD

    Energy Technology Data Exchange (ETDEWEB)

    Jozef Dudek,Robert Edwards,Michael Peardon,David Richards,Christopher Thomas

    2011-05-01

    Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi-hadron contributions, and describe a recent calculation of the I=2 pion-pion energy-dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.

  4. Accurate Excited State Geometries within Reduced Subspace TDDFT/TDA.

    Science.gov (United States)

    Robinson, David

    2014-12-09

    A method for the calculation of TDDFT/TDA excited state geometries within a reduced subspace of Kohn-Sham orbitals has been implemented and tested. Accurate geometries are found for all of the fluorophore-like molecules tested, with at most all valence occupied orbitals and half of the virtual orbitals included but for some molecules even fewer orbitals. Efficiency gains of between 15 and 30% are found for essentially the same level of accuracy as a standard TDDFT/TDA excited state geometry optimization calculation.

  5. Coherent excitation of a single atom to a Rydberg state

    DEFF Research Database (Denmark)

    Miroshnychenko, Yevhen; Gaëtan, Alpha; Evellin, Charles

    2010-01-01

    We present the coherent excitation of a single Rubidium atom to the Rydberg state 58d3/2 using a two-photon transition. The experimental setup is described in detail, as are experimental techniques and procedures. The coherence of the excitation is revealed by observing Rabi oscillations between...... ground and Rydberg states of the atom. We analyze the observed oscillations in detail and compare them to numerical simulations which include imperfections of our experimental system. Strategies for future improvements on the coherent manipulation of a single atom in our settings are given....

  6. Extended Holstein polaron model for charge transfer in dry DNA

    Institute of Scientific and Technical Information of China (English)

    Liu Tao; Wang Yi; Wang Ke-Lin

    2007-01-01

    The variational method is applied to the study of charge transfer in dry DNA by using an extended Holstein small polaron model in two cases: the site-dependent finite-chain discrete case and the site-independent continuous one. The treatments in the two cases are proven to be consistent in theory and calculation. Discrete and continuous treatments of Holstein model both can yield a nonlinear equation to describe the charge migration in an actual long-range DNA chain.Our theoretical results of binding energy Eb, probability amplitude of charge carrier φ and the relation between energy and charge-lattice coupling strength are in accordance with the available experimental results and recent theoretical calculations.

  7. Graphene nonvolatile memory prototype based on charge-transfer mechanism

    Science.gov (United States)

    Lv, Hongming; Wu, Huaqiang; Huang, Can; Wang, Yuda; Qian, He

    2014-04-01

    A graphene nonvolatile memory (GNVM) prototype based on charge transfer between the graphene layer and the NH2(CH2)3Si(OEt)3 (APTES) self-assembled monolayer (SAM) is demonstrated. Graphene was transferred to an APTES-SAM-engineered SiO2 substrate and patterned into bottom-gate transistors. Owing to the charge trapping/detrapping property of the nitrogen atoms in APTES, a significant and reproducible transfer curve hysteresis is observed. Memory performance metrics, including retention and endurance, are reported. Comparisons between vacuum and ambient environment test results indicate air absorbates’ detrimental effect. Loss of nonvolatile storage is explained on the basis of a two-layer tunneling junction model, which sheds light on further device improvement through aminosilane molecule structure optimization.

  8. 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...

  9. 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.

  10. Discrete electrostatic charge transfer by the electrophoresis of a charged droplet in a dielectric liquid.

    Science.gov (United States)

    Im, Do Jin; Ahn, Myung Mo; Yoo, Byeong Sun; Moon, Dustin; Lee, Dong Woog; Kang, In Seok

    2012-08-14

    We have experimentally investigated the electrostatic charging of a water droplet on an electrified electrode surface to explain the detailed inductive charging processes and use them for the detection of droplet position in a lab-on-a-chip system. The periodic bouncing motion of a droplet between two planar electrodes has been examined by using a high-resolution electrometer and an image analysis method. We have found that this charging process consists of three steps. The first step is inductive charge accumulation on the opposite electrode by the charge of a droplet. This induction process occurs while the droplet approaches the electrode, and it produces an induction current signal at the electrometer. The second step is the discharging of the droplet by the accumulated induced charge at the moment of contact. For this second step, there is no charge-transfer detection at the electrometer. The third step is the charging of the neutralized droplet to a certain charged state while the droplet is in contact with the electrode. The charge transfer of the third step is detected as the pulse-type signal of an electrometer. The second and third steps occur simultaneously and rapidly. We have found that the induction current by the movement of a charged droplet can be accurately used to measure the charge of the droplet and can also be used to monitor the position of a droplet under actuation. The implications of the current findings for understanding and measuring the charging process are discussed.

  11. 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...

  12. 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.

  13. Charge Transfer and Ionization by Intermediate-Energy Heavy Ions

    Energy Technology Data Exchange (ETDEWEB)

    Toburen, L. H. [East Carolina University; McLawhorn, S. L. [East Carolina University; McLawhorn, R. A. [East Carolina University; Evans, N. L. [East Carolina University; Justiniano, E. L. B. [East Carolina University; Shinpaugh, J. L. [East Carolina University; Schultz, David Robert [ORNL; Reinhold, Carlos O [ORNL

    2006-11-01

    The use of heavy ion beams for microbeam studies of mammalian cell response leads to a need to better understand interaction cross sections for collisions of heavy ions with tissue constituents. For ion energies of a few MeV u-1 or less, ions capture electrons from the media in which they travel and undergo subsequent interactions as partially 'dressed' ions. For example, 16 MeV fluorine ions have an equilibrium charge of 7+, 32 MeV sulphur ions have an equilibrium charge of approx. 11+, and as the ion energies decrease the equilibrium charge decreases dramatically. Data for interactions of partially dressed ions are extremely rare, making it difficult to estimate microscopic patterns of energy deposition leading to damage to cellular components. Such estimates, normally obtained by Monte Carlo track structure simulations, require a comprehensive database of differential and total ionisation cross sections as well as charge transfer cross sections. To provide information for track simulation, measurement of total ionisation cross sections have been initiated at East Carolina University using the recoil ion time-of-flight method that also yields cross sections for multiple ionisation processes and charge transfer cross sections; multiple ionisation is prevalent for heavy ion interactions. In addition, measurements of differential ionisation cross sections needed for Monte Carlo simulation of detailed event-by-event particle tracks are under way. Differential, total and multiple ionisation cross sections and electron capture and loss cross sections measured for C+ ions with energies of 100 and 200 keV u-1 are described.

  14. Charge transfer and ionisation by intermediate-energy heavy ions.

    Science.gov (United States)

    Toburen, L H; McLawhorn, S L; McLawhorn, R A; Evans, N L; Justiniano, E L B; Shinpaugh, J L; Schultz, D R; Reinhold, C O

    2006-01-01

    The use of heavy ion beams for microbeam studies of mammalian cell response leads to a need to better understand interaction cross sections for collisions of heavy ions with tissue constituents. For ion energies of a few MeV u(-1) or less, ions capture electrons from the media in which they travel and undergo subsequent interactions as partially 'dressed' ions. For example, 16 MeV fluorine ions have an equilibrium charge of 7(+), 32 MeV sulphur ions have an equilibrium charge of approximately 11(+), and as the ion energies decrease the equilibrium charge decreases dramatically. Data for interactions of partially dressed ions are extremely rare, making it difficult to estimate microscopic patterns of energy deposition leading to damage to cellular components. Such estimates, normally obtained by Monte Carlo track structure simulations, require a comprehensive database of differential and total ionisation cross sections as well as charge transfer cross sections. To provide information for track simulation, measurement of total ionisation cross sections have been initiated at East Carolina University using the recoil ion time-of-flight method that also yields cross sections for multiple ionisation processes and charge transfer cross sections; multiple ionisation is prevalent for heavy ion interactions. In addition, measurements of differential ionisation cross sections needed for Monte Carlo simulation of detailed event-by-event particle tracks are under way. Differential, total and multiple ionisation cross sections and electron capture and loss cross sections measured for C(+) ions with energies of 100 and 200 keV u(-1) are described.

  15. Computational studies on the excited states of luminescent platinum(II) alkynyl systems of tridentate pincer ligands in radiative and nonradiative processes.

    Science.gov (United States)

    Lam, Wai Han; Lam, Elizabeth Suk-Hang; Yam, Vivian Wing-Wah

    2013-10-09

    Platinum(II) alkynyl complexes of various tridentate pincer ligands, [Pt(trpy)(C≡CR)](+) (trpy = 2,2':6',2″-terpyridine), [Pt(R'-bzimpy)(C≡CR)](+) (R'-bzimpy = 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine and R' = alkyl), [Pt(R'-bzimb)(C≡CR)] (R'-bzimb = 1,3-bis(N-alkylbenzimidazol-2'-yl)benzene and R' = C4H9), have been found to possess rich photophysical properties. The emission in dilute solutions of [Pt(trpy)(C≡CR)](+) originated from a triplet alkynyl-to-tridentate pincer ligand-to-ligand charge transfer (LLCT) excited state, with mixing of a platinum-to-tridentate pincer ligand metal-to-ligand charge transfer (MLCT) excited state, while that of [Pt(R'-bzimb)(C≡CR)] originated from a triplet excited state of intraligand (IL) character of the tridentate ligand mixed with a platinum-to-tridentate ligand MLCT character. Interestingly, both emissions were observed in [Pt(R'-bzimpy)(C≡CR)](+) in some cases. In addition, [Pt(R'-bzimb)(C≡CR)] displayed a photoluminescence quantum yield higher than that of [Pt(R'-bzimpy)(C≡CR)](+). Computational studies have been performed on the representative complexes [Pt(trpy)(C≡CPh)](+) (1), [Pt(R'-bzimpy)(C≡CPh)](+) (2), and [Pt(R'-bzimb)(C≡CPh)] (3), where R' = CH3 and Ph = C6H5, to provide an in-depth understanding of the nature of their emissive origin as well as the radiative and nonradiative processes. In particular, the factors governing the ordering of the triplet excited states and radiative decay rate constants of the emissive state ((3)ES) have been examined. The potential energy profiles for the deactivation process from the (3)ES via triplet metal-centered ((3)MC) states have also been explored. This work reveals for the first time the potential energy profiles for the thermal deactivation pathway of square planar platinum(II) complexes.

  16. A Neutron Halo in 12B Excited State

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Nonlinear relativistic mean field(RMF) theory with a new effective interaction NL3 has been used to investigate the bulk properties of 12B nucleus and its daughter nuclei. The results obtained in RMF indicate one neutron halo in 12B nucleus at an excited state. The density distribution of neutrons in the excited state of 12B has a long tail and the nucleon in 2s1/2 state has very small separation energy. The rms radius of halo neutron is about twice larger than that of matter. Meanwhile, it becomes more apparent that nuclear halo is a general feature of loosely bound nuclei. As the binding energy becomes smaller, to form a bound state the nucleon tends to occupy a state with a low angular momentum. It

  17. Charge transfer effects on the Fermi surface of Ba0.5K 0.5Fe2As2

    KAUST Repository

    Nazir, Safdar

    2011-01-31

    Ab-initio calculations within density functional theory are performed to obtain a more systematic understanding of the electronic structure of iron pnictides. As a prototypical compound we study Ba0.5K 0.5Fe2As2 and analyze the changes of its electronic structure when the interaction between the Fe2As 2 layers and their surrounding is modified. We find strong effects on the density of states near the Fermi energy as well as the Fermi surface. The role of the electron donor atoms in iron pnictides thus cannot be understood in a rigid band picture. Instead, the bonding within the Fe2As 2 layers reacts to a modified charge transfer from the donor atoms by adapting the intra-layer Fe-As hybridization and charge transfer in order to maintain an As3- valence state. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Octupole correlations in excited 0{sup +} states of the actinides

    Energy Technology Data Exchange (ETDEWEB)

    Spieker, Mark; Endres, Janis; Zilges, Andreas [Institute for Nuclear Physics, University of Cologne (Germany); Bucurescu, Dorel; Pascu, Sorin; Zamfir, Nicolae-Victor [Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest (Romania); Faestermann, Thomas [Physik Department, Technische Universitaet Muenchen, Munich (Germany); Hertenberger, Ralf; Wirth, Hans-Friedrich [Fakultaet fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, Munich (Germany)

    2014-07-01

    New experimental data has once again shown the importance of the octupole degree of freedom in the actinides. To further study possible admixtures of double-octupole structures to the wave function of positive-parity states, a high-resolution (p,t) experiment on {sup 242}Pu has been recently performed at the Q3D magnetic spectrograph in Munich. Excited 0{sup +} states were populated in {sup 240}Pu up to an excitation energy of 3 MeV. The new data allowed for a stringent test of the predictions of the spdf interacting boson model. In order to find possible double-octupole 0{sup +} candidates in the actinides, the signature of close-lying first and second excited 0{sup +} states has been proposed. It is found that the observation of this signature coincides with an E1 γ-decay of the first excited 0{sup +} state, while this state is strongly populated in the (p,t) reaction.

  19. Electronically excited negative ion resonant states in chloroethylenes

    Energy Technology Data Exchange (ETDEWEB)

    Khvostenko, O.G., E-mail: khv@mail.ru; Lukin, V.G.; Tuimedov, G.M.; Khatymova, L.Z.; Kinzyabulatov, R.R.; Tseplin, E.E.

    2015-02-15

    Highlights: • Several novel dissociative negative ion channels were revealed in chloroethylenes. • The electronically excited resonant states were recorded in all chloroethylenes under study. • The states were assigned to the inter-shell types, but not to the core-excited Feshbach one. - Abstract: The negative ion mass spectra of the resonant electron capture by molecules of 1,1-dichloroethylene, 1,2-dichloroethylene-cis, 1,2-dichloroethylene-trans, trichloroethylene and tetrachloroethylene have been recorded in the 0–12 eV range of the captured electron energy using static magnetic sector mass spectrometer modified for operation in the resonant electron capture regime. As a result, several novel low-intensive dissociation channels were revealed in the compounds under study. Additionally, the negative ion resonant states were recorded at approximately 3–12 eV, mostly for the first time. These resonant states were assigned to the electronically excited resonances of the inter-shell type by comparing their energies with those of the parent neutral molecules triplet and singlet electronically excited states known from the energy-loss spectra obtained by previous studies.

  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. Excited state tautomerization of 7-azaindole catalyzed by pyrazole

    Science.gov (United States)

    Karmakar, Shreetama; Mukherjee, Moitrayee; Chakraborty, Tapas

    2013-03-01

    Pyrazole, a five member cyclic azole, is reported here as an efficient catalyst for excited state tautomeric conversion of 7-azaindole. In hydrocarbon solution the two compounds efficiently form a doubly hydrogen-bonded 1:1 cyclic complex whose association constant value is found comparable with 7-azaindole dimerization constant, and according to B3LYP/6-311G++∗∗ calculation the binding energies of the complex and dimer are nearly same. In the excited state (S1), the TDDFT calculation predicts tautomer of the complex to be 13.4 kcal/mol more stable than normal form. Fluorescence spectra reveal that upon UV excitation the complex emits exclusively from the tautomeric form.

  2. Cationic dye-sensitized degradation of sodium hyaluronate through photoinduced electron transfer in the upper excited state.

    Science.gov (United States)

    Kojima, M; Takahashi, K; Nakamura, K

    2001-09-01

    The formation of ground-state complexes of methylene blue (MB) and thionine (TN) with sodium hyaluronate (NaHA) was clearly observed by means of absorption spectra in aqueous solution. Irradiation of the complexes using 313 nm light caused significant degradation of NaHA under oxygen and argon. However, the use of visible light over 400 nm, which gives the lowest excited singlet state of the cationic dyes, caused no degradation. MB and TN were more efficient sensitizers for the degradation of NaHA than rose bengal (RB), although RB is a more efficient singlet oxygen (1O2) sensitizer than the cationic dyes. Under similar conditions the polysaccharides with carboxyl groups, such as alginic acid and polygalacturonic acid, also photodecomposed. However, the polysaccharides without carboxyl groups, such as pullulan and methyl cellulose, did not. The irradiation of the polysaccharides in the presence of powdered titanium dioxide as a photocatalyst to generate the hydroxyl radical (.OH) in aerated aqueous solution caused the fragmentation of all the polymers. It was confirmed that methyl viologen, an electron-accepting sensitizer, formed a charge-transfer complex with NaHA, the irradiation of which caused the efficient degradation of NaHA. In the presence of beta- and gamma-cyclodextrins the MB- and TN-sensitized photodegradation of NaHA was markedly suppressed. This was probably due to the formation of the inclusion complexes comprising the cationic dyes and the cyclodextrins. On the basis of the results obtained we propose that the cationic dye-sensitized degradation of NaHA involves a photoinduced electron-transfer process between the upper excited dyes and the ground-state NaHA and that .OH and 1O2 do not participate in the degradation.

  3. Photo-induced charge transfer and relaxation of persistent charge carriers in polymer/nanocrystal composites for applications in hybrid solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Heinemann, Marc Daniel; Zutz, Folker; Kolny-Olesiak, Joanna; Borchert, Holgert; Riedel, Ingo; Parisi, Juergen [University of Oldenburg, Department of Physics, Energy and Semiconductor Research Laboratory, Oldenburg (Germany); Maydell, Karsten von [EWE Research Center for Energy Technology, Oldenburg (Germany)

    2009-12-09

    The photo-induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3-hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc-CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and [6,6]-phenyl C{sub 61}-butyric acid methyl ester (PCBM) are studied as well. The light-induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo-induced absorption (PIA) and light-induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo-excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long-term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc-CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  4. Estimation of correlation energy for excited-states of atoms

    CERN Document Server

    Hemanadhan, M

    2014-01-01

    The correlation energies of various atoms in their excited-states are estimated by modelling the Coulomb hole following the previous work by Chakravorty and Clementi. The parameter in the model is fixed by making the corresponding Coulomb hole to satisfy the exact constraint of charge neutrality.

  5. Size dependent deactivation of the excited state of DHICA

    DEFF Research Database (Denmark)

    Gauden, Magdalena; Pezzella, Alessandro; Panzella, Lucia;

    2008-01-01

    Melanin is a natural pigment mainly responsible for the protection of skin and eyes from UV damage. 5,6- dihydroxyindole- 2 carboxylic acid (DHICA) is a key melanin building block. We have investigated the excited state dynamics of DHICA as well as its derivatives and oligomeric units using...

  6. Lowest energy excited singlet state of isolated cis-hexatriene

    NARCIS (Netherlands)

    Kohler, B.E.; Song, K.; Buma, W.J.

    1991-01-01

    In a previous letter [J. Chem. Phys. 92, 4622 (1990)] we reported the first observation of the 2 1Ag state of cis-hexatriene in a supersonic jet expansion by using resonance enhanced multiphoton ionization spectroscopy. Here, the vibrational analysis of the 1 1Ag2 1Ag excitation spectrum of cis-hexa

  7. Optical Switching Using Transition from Dipolar to Charge Transfer Plasmon Modes in Ge2Sb2Te5 Bridged Metallodielectric Dimers

    Science.gov (United States)

    Ahmadivand, Arash; Gerislioglu, Burak; Sinha, Raju; Karabiyik, Mustafa; Pala, Nezih

    2017-01-01

    Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state. PMID:28205643

  8. Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce4+ charge transfer transition

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Ce4+-doped Ca2SnO4 with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce4+ ions doped in Ca2SnO4 occupy the Sn4+ sites. The excitation and emission spectra of Ca2Sn1-xCexO4 appear to have broad bands with peaks at ~ 268nm and ~442nm, respectively. A long excited-state lifetime (~ 83μs) for the emission from Ca2Sn1-xCexO4 suggests that the luminescence originates from a ligand-to-metal Ce4+ charge transfer (CT). The luminescent properties of Ca2Sn1-xCexO4 have been compared with those of Sr2CeO4, which is the only material reported so far to show Ce4+ CT luminescence. More interestingly, it is observed that the emission intensity of Ca2Sn1-xCexO4 with a small doping concentration (x ~ 0.03) is comparable to that of Sr2CeO4 in which the concentration of active centre is 100%.

  9. Excited-state quantum phase transition in the Rabi model

    Science.gov (United States)

    Puebla, Ricardo; Hwang, Myung-Joong; Plenio, Martin B.

    2016-08-01

    The Rabi model, a two-level atom coupled to a harmonic oscillator, can undergo a second-order quantum phase transition (QPT) [M.-J. Hwang et al., Phys. Rev. Lett. 115, 180404 (2015), 10.1103/PhysRevLett.115.180404]. Here we show that the Rabi QPT accompanies critical behavior in the higher-energy excited states, i.e., the excited-state QPT (ESQPT). We derive analytic expressions for the semiclassical density of states, which show a logarithmic divergence at a critical energy eigenvalue in the broken symmetry (superradiant) phase. Moreover, we find that the logarithmic singularities in the density of states lead to singularities in the relevant observables in the system such as photon number and atomic polarization. We corroborate our analytical semiclassical prediction of the ESQPT in the Rabi model with its numerically exact quantum mechanical solution.

  10. Direct excitation of butterfly states in Rydberg molecules

    Science.gov (United States)

    Lippe, Carsten; Niederpruem, Thomas; Thomas, Oliver; Eichert, Tanita; Ott, Herwig

    2016-05-01

    Since their first theoretical prediction Rydberg molecules have become an increasing field of research. These exotic states originate from the binding of a ground state atom in the electronic wave function of a highly-excited Rydberg atom mediated by a Fermi contact type interaction. A special class of long-range molecular states, the butterfly states, were first proposed by Greene et al.. These states arise from a shape resonance in the p-wave scattering channel of a ground state atom and a Rydberg electron and are characterized by an electron wavefunction whose density distribution resembles the shape of a butterfly. We report on the direct observation of deeply bound butterfly states of Rydberg molecules of 87 Rb. The butterfly states are studied by high resolution spectroscopy of UV-excited Rydberg molecules. We find states bound up to - 50 GHz from the 25 P1/2 , F = 1 state, corresponding to binding lengths of 50a0 to 500a0 and with permanent electric dipole moments of up to 500 Debye. This distinguishes the observed butterfly states from the previously observed long range Rydberg molecules in rubidium.

  11. Photocatalysis with CdSe nanoparticles in confined media: mapping charge transfer events in the subpicosecond to second timescales.

    Science.gov (United States)

    Harris, Clifton; Kamat, Prashant V

    2009-03-24

    Photoinduced charge transfer events between 3 nm diameter CdSe semiconductor nanocrystals and an electron acceptor, MV2+, have been probed in the subpicosecond-microseconds-seconds time scale by confining the reactants in an AOT/heptane reverse micelle. The probe molecule, methyl viologen (MV2+) interacts with the excited CdSe nanoparticle and quenches its emission effectively. The ultrafast electron transfer to MV2+, as monitored from the exciton bleaching recovery of CdSe and the formation of MV+* radical, is completed with an average rate constant of 2.25x10(10) s(-1). Under steady state irradiation (450 nm) the accumulation of MV+* is seen with a net quantum yield of 0.1. Mediation of the electron transfer through TiO2 nanoparticles is achieved by coupling them with the CdSe-MV2+ system within the reverse micelle. This coupling of two semiconductor nanoparticles increases the quantum yield of MV2+ reduction by a factor of 2. The dual roles of TiO2 as an electron shuttle and a rectifier are elucidated by transient absorption spectroscopy and steady state photolysis. The presence of both TiO2 and MV2+ in the reverse micelle creates a synergistic effect to enhance the electron transfer rate constant by an order of magnitude. The time-resolved events that dictate the production and stabilization of electron transfer product provide an insight into the photocatalytic systems that are potentially important in solar hydrogen production and photocatalytic remediation.

  12. Encapsulation of 3-hydroxyflavone and fisetin in β-cyclodextrins: Excited state proton transfer fluorescence and molecular mechanics studies

    Science.gov (United States)

    Banerjee, Anwesha; Sengupta, Pradeep K.

    2006-06-01

    Excited-state intramolecular proton-transfer (ESIPT) and dual emission properties (emission profile, anisotropy and decay kinetics) of 3-hydroxyflavone (a synthetic, model flavonol) and fisetin (3,7,3',4'-OH-flavone, a therapeutically active plant flavonol) have been exploited to study their encapsulation in nano-cavities comprising of natural and chemically modified β-cyclodextrins. In the presence of β-CDs, both the flavonols show significantly enhanced relative yields (along with changes in other emission parameters) of the tautomer emission. In addition, for fisetin, large blue shifts are observed for the normal emission (which has significant charge transfer character). From these we infer that the flavonols are encaged in predominantly hydrophobic micro-environments, where external hydrogen bonding perturbations (interfering with the intrinsic ESIPT), and dipolar relaxation effects, are minimized. This is further explained from results of molecular mechanics calculations which indicate selectivity in orientation of the encapsulated flavonols. Moreover, chemical modification of the β-CDs is found to profoundly influence the binding affinities of the guest flavonols.

  13. Optimized resonating valence bond state in square lattice: correlations & excitations

    Directory of Open Access Journals (Sweden)

    Z Nourbakhsh

    2009-09-01

    Full Text Available We consider RVB state as a variational estimate for the ground state of Heisenberg antiferromagnet in square lattice. We present numerical calculation of energy, spin-spin correlation function and spin excitation spectrum. We show, that the quantum flactuations reduce of magnetization respect to Neel order. Our results are in good agreement with other methods such as spin-wave calculation and series expansions.

  14. Ghost interaction correction in ensemble density-functional theory for excited states with and without range separation

    CERN Document Server

    Alam, Md Mehboob; Fromager, Emmanuel

    2016-01-01

    Ensemble density-functional theory (eDFT) suffers from the "ghost-interaction" (GI) error when approximate exchange-correlation functionals are used. In this letter, we present a rigorous GI correction (GIC) in the context of multideterminantal range-separated eDFT. The method, which relies on a double generalized adiabatic connection for ensembles, is equally applicable to standard Kohn-Sham eDFT. We show that GIC reduces the curvature of approximate ensemble energies drastically while providing considerably more accurate excitation energies, even for charge-transfer and double excitations.

  15. On the excited-state multi-dimensionality in cyanines

    Science.gov (United States)

    Dietzek, Benjamin; Brüggemann, Ben; Persson, Petter; Yartsev, Arkady

    2008-03-01

    Vibrational coherences in a photoexcited cyanine dye are preserved for the time-scale of diffusive torsional motion to the bottom of the excited-state potential. The coherently excited modes are virtually unaffected by solvent friction and thus distinct from the bond-twisting motion, which is strongly coupled to the surrounding solvent. We correlate the modes apparent in the resonance Raman and the four-wave mixing signal of 1,1'-diethyl-2,2'-cyanine with the understanding of optimal control of isomerization. In turn, the experimental results illustrate that optimal control might be used to obtain vibrational information complementary to conventional spectroscopic data.

  16. Charge-transfer character of the low-energy Chl a Q(y) absorption band in aggregated light harvesting complexes II.

    Science.gov (United States)

    Kell, Adam; Feng, Ximao; Lin, Chen; Yang, Yiqun; Li, Jun; Reus, Michael; Holzwarth, Alfred R; Jankowiak, Ryszard

    2014-06-12

    One of the key functions of the major light harvesting complex II (LHCII) of higher plants is to protect Photosystem II from photodamage at excessive light conditions in a process called "non-photochemical quenching" (NPQ). Using hole-burning (HB) spectroscopy, we investigated the nature of the low-energy absorption band in aggregated LHCII complexes - which are highly quenched and have been established as a good in vitro model for NPQ. Nonresonant holes reveal that the lowest energy state (located near 683.3 nm) is red-shifted by ~4 nm and significantly broader (by a factor of 4) as compared to nonaggregated trimeric LHCII. Resonant holes burned in the low-energy wing of the absorption spectrum (685-710 nm) showed a high electron-phonon (el-ph) coupling strength with a Huang-Rhys factor S of 3-4. This finding combined with the very low HB efficiency in the long-wavelength absorption tail is consistent with a dominant charge-transfer (CT) character of the lowest energy transition(s) in aggregated LHCII. The value of S decreases at shorter wavelengths (energy excitonic state is strongly mixed with the CT states. Our findings support the mechanistic model in which Chl-Chl CT states formed in aggregated LHCII are intermediates in the efficient excited state quenching process (M. G. Müller et al., Chem. Phys. Chem. 2010, 11, 1289-1296; Y. Miloslavina et al., FEBS Lett. 2008, 582, 3625-3631).

  17. Sub-50 fs excited state dynamics of 6-chloroguanine upon deep ultraviolet excitation.

    Science.gov (United States)

    Mondal, Sayan; Puranik, Mrinalini

    2016-05-18

    The photophysical properties of natural nucleobases and their respective nucleotides are ascribed to the sub-picosecond lifetime of their first singlet states in the UV-B region (260-350 nm). Electronic transitions of the ππ* type, which are stronger than those in the UV-B region, lie at the red edge of the UV-C range (100-260 nm) in all isolated nucleobases. The lowest energetic excited states in the UV-B region of nucleobases have been investigated using a plethora of experimental and theoretical methods in gas and solution phases. The sub-picosecond lifetime of these molecules is not a general attribute of all nucleobases but specific to the five primary nucleobases and a few xanthine and methylated derivatives. To determine the overall UV photostability, we aim to understand the effect of more energetic photons lying in the UV-C region on nucleobases. To determine the UV-C initiated photophysics of a nucleobase system, we chose a halogen substituted purine, 6-chloroguanine (6-ClG), that we had investigated previously using resonance Raman spectroscopy. We have performed quantitative measurements of the resonance Raman cross-section across the Bb absorption band (210-230 nm) and constructed the Raman excitation profiles. We modeled the excitation profiles using Lee and Heller's time-dependent theory of resonance Raman intensities to extract the initial excited state dynamics of 6-ClG within 30-50 fs after photoexcitation. We found that imidazole and pyrimidine rings of 6-ClG undergo expansion and contraction, respectively, following photoexcitation to the Bb state. The amount of distortions of the excited state structure from that of the ground state structure is reflected by the total internal reorganization energy that is determined at 112 cm(-1). The contribution of the inertial component of the solvent response towards the total reorganization energy was obtained at 1220 cm(-1). In addition, our simulation also yields an instantaneous response of the first

  18. MULTIPLY CHARGED IONS COLLISIONS WITH ATOMS INTO EXCITED STATES

    Institute of Scientific and Technical Information of China (English)

    PanGuangyan

    1990-01-01

    The emission spectra in collisions between Ions and Atoms have been measured by an Optical Multichannel Analysis System (OMA).The experimental results demonstrate that there are two channels of excitation in collision between single charged ions and atoms and three channels of excitation in collision between double charged ions and atoms.Emission cross cestions and excitation cross sections have been obtained.K.Kadota et al and R.Shingal et al suggested that,under the appropriate conditions,the H42+-Li and He2++Na collision systems can be used efficiently to produce a laser of Lyman-α(30,4nm) and Lyman-β(25.6nm)lines via cascade to He+(2P)state.

  19. Observation of the First Excited State in 23O

    CERN Document Server

    Frank, N; Baumann, T; Bazin, D; Brown, J; DeYoung, P A; Finck, J E; Gade, A; Hinnefeld, J; Howes, R; Lecouey, J -L; Luther, B; Peters, W A; Scheit, H; Thoennessen, M

    2007-01-01

    The first excited state in neutron-rich 23O was observed in a (2p1n) knock-out reaction from 26Ne on a beryllium target at a beam energy of 86 MeV/A. The state is unbound with respect to neutron emission and was reconstructed from the invariant mass from the 22O fragment and the neutron. It is unbound by 45(2) keV corresponding to an excitation energy of 2.8(1) MeV. The non-observation of further resonances implies a predominantly direct reaction mechanism of the employed three-nucleon-removal reaction which suggests the assignment of the observed resonance to be the 5/2+ hole state.

  20. Optical nanoscopy with excited state saturation at liquid helium temperatures

    Science.gov (United States)

    Yang, B.; Trebbia, J.-B.; Baby, R.; Tamarat, Ph.; Lounis, B.

    2015-10-01

    Optical resolution of solid-state single quantum emitters at the nanometre scale is a challenging step towards the control of delocalized states formed by strongly and coherently interacting emitters. We have developed a simple super-resolution optical microscopy method operating at cryogenic temperatures, which is based on optical saturation of the excited state of single fluorescent molecules with a doughnut-shaped beam. Sub-10 nm resolution is achieved with extremely low excitation intensities, a million times lower than those used in room-temperature stimulated emission depletion microscopy. Compared with super-localization approaches, our technique offers a unique opportunity to super-resolve single molecules with overlapping optical resonance frequencies and paves the way to the study of coherent interactions between single emitters and to the manipulation of their degree of entanglement.

  1. Embedding potentials for excited states of embedded species.

    Science.gov (United States)

    Wesolowski, Tomasz A

    2014-05-14

    Frozen-Density-Embedding Theory (FDET) is a formalism to obtain the upper bound of the ground-state energy of the total system and the corresponding embedded wavefunction by means of Euler-Lagrange equations [T. A. Wesolowski, Phys. Rev. A 77(1), 012504 (2008)]. FDET provides the expression for the embedding potential as a functional of the electron density of the embedded species, electron density of the environment, and the field generated by other charges in the environment. Under certain conditions, FDET leads to the exact ground-state energy and density of the whole system. Following Perdew-Levy theorem on stationary states of the ground-state energy functional, the other-than-ground-state stationary states of the FDET energy functional correspond to excited states. In the present work, we analyze such use of other-than-ground-state embedded wavefunctions obtained in practical calculations, i.e., when the FDET embedding potential is approximated. Three computational approaches based on FDET, that assure self-consistent excitation energy and embedded wavefunction dealing with the issue of orthogonality of embedded wavefunctions for different states in a different manner, are proposed and discussed.

  2. Charge Transfer Characteristics and Initiation Mechanisms of Long Delayed Sprites

    Science.gov (United States)

    Li, J.; Cummer, S. A.; Lyons, W. A.; Nelson, T. E.

    2007-12-01

    Simultaneous measurements of high altitude optical emissions and the magnetic field produced by sprite-associated lightning discharges enable a close examination of the link between low altitude lightning process and high altitude sprite process. In this work, we report results of the coordinated analysis of high speed (1000--10000 frames per second) sprite video and wideband (0.1 Hz to 30 kHz) magnetic field measurements made simultaneously at the Yucca Ridge Field Station and Duke University during the June through August 2005 campaign period. During the observation period, the high speed camera detected 83 sprite events in 67 TLE sequences, which are caused by the same number of +CGs. 46% of these sprite events are delayed more than 10 ms after the lightning return stroke. With the estimated lightning source current moment waveform, we computed the continuing current amplitude and total charge transfer characteristics of the long delayed sprites (>10 ms delay). Our calculation shows the total charge moment change of the long delayed sprites can vary from several hundred C km to more than ten thousand C km. All the long delayed sprites are related with intense continuing current bigger than 2 kA. This continuing current provides about 50% to 90% of the total charge transfer. However, a bigger continuing current does not necessarily mean a shorter time delay. This indicates that other processes also involved in the sprite initiation for long delayed sprites. In our observations, the sferic burst, a high frequency noise caused by intra-cloud activity, is always accompanied by a slow intensification in the lightning source current before the time of sprite initiation. Thus we used the lightning source current as an input and employed a 2-D FDTD model to numerically simulate the electric field at different altitudes and compare it with the breakdown field. Including the effect of the electron mobility dependence on electric field, the simulation results showed that

  3. Controlling Excited-State Contamination in Nucleon Matrix Elements

    CERN Document Server

    Yoon, Boram; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank

    2016-01-01

    We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size $32^3 \\times 64$ generated using the rational hybrid Monte Carlo algorithm at $a=0.081$~fm and with $M_\\pi=312$~MeV. The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a two-state fit to data at multiple values of the source-sink separation $t_{\\rm sep}$. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost-effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of $t_{\\rm sep}$ needed to demonstrate convergence of the isovector charges of the nucleon to the $t_...

  4. Controlling excited-state contamination in nucleon matrix elements

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Boram; Gupta, Rajan; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank

    2016-06-01

    We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2+1 flavor ensemble with lattices of size $32^3 \\times 64$ generated using the rational hybrid Monte Carlo algorithm at $a=0.081$~fm and with $M_\\pi=312$~MeV. The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a two-state fit to data at multiple values of the source-sink separation $t_{\\rm sep}$. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost-effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of $t_{\\rm sep}$ needed to demonstrate convergence of the isovector charges of the nucleon to the $t_{\\rm sep} \\to \\infty $ estimates is presented.

  5. Excited state dynamics of the astaxanthin radical cation

    Science.gov (United States)

    Amarie, Sergiu; Förster, Ute; Gildenhoff, Nina; Dreuw, Andreas; Wachtveitl, Josef

    2010-07-01

    Femtosecond transient absorption spectroscopy in the visible and NIR and ultrafast fluorescence spectroscopy were used to examine the excited state dynamics of astaxanthin and its radical cation. For neutral astaxanthin, two kinetic components corresponding to time constants of 130 fs (decay of the S 2 excited state) and 5.2 ps (nonradiative decay of the S 1 excited state) were sufficient to describe the data. The dynamics of the radical cation proved to be more complex. The main absorption band was shifted to 880 nm (D 0 → D 3 transition), showing a weak additional band at 1320 nm (D 0 → D 1 transition). We found, that D 3 decays to the lower-lying D 2 within 100 fs, followed by a decay to D 1 with a time constant of 0.9 ps. The D 1 state itself exhibited a dual behavior, the majority of the population is transferred to the ground state in 4.9 ps, while a small population decays on a longer timescale of 40 ps. Both transitions from D 1 were found to be fluorescent.

  6. Controlling excited-state contamination in nucleon matrix elements

    Science.gov (United States)

    Yoon, Boram; Gupta, Rajan; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank; Nucleon Matrix Elements NME Collaboration

    2016-06-01

    We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2 +1 -flavor ensemble with lattices of size 323×64 generated using the rational hybrid Monte Carlo algorithm at a =0.081 fm and with Mπ=312 MeV . The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a 2-state fit to data at multiple values of the source-sink separation tsep. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of tsep needed to demonstrate convergence of the isovector charges of the nucleon to the tsep→∞ estimates is presented.

  7. 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.

  8. Reexamination of the excited states of C12

    Science.gov (United States)

    Freer, M.; Boztosun, I.; Bremner, C. A.; Chappell, S. P. G.; Cowin, R. L.; Dillon, G. K.; Fulton, B. R.; Greenhalgh, B. J.; Munoz-Britton, T.; Nicoli, M. P.; Rae, W. D. M.; Singer, S. M.; Sparks, N.; Watson, D. L.; Weisser, D. C.

    2007-09-01

    An analysis of the C12(C12,3α)C12 reaction was made at beam energies between 82 and 106 MeV. Decays to both the ground state and the excited states of Be8 were isolated, allowing states of different characters to be identified. In particular, evidence was found for a previously observed state at 11.16 MeV. An analysis of the angular distributions of the unnatural parity states at 11.83 and 13.35 MeV, previously assigned Jπ=2-, calls into question the validity of these assignments, suggesting that at least one of the states may correspond to Jπ=4-. Evidence is also found for 1- and 3- strengths associated with broad states between 11 and 14 MeV.

  9. Electronic spectra and photophysics of platinum(II) complexes with alpha-diimine ligands - Solid-state effects. I - Monomers and ligand pi dimers

    Science.gov (United States)

    Miskowski, Vincent M.; Houlding, Virginia H.

    1989-01-01

    Two types of emission behavior for Pt(II) complexes containing alpha-diimine ligands have been observed in dilute solution. If the complex also has weak field ligands such as chloride, ligand field (d-d) excited states become the lowest energy excited states. If only strong field ligands are present, a diimine 3(pi-pi/asterisk/) state becomes the lowest. In none of the cases studied did metal-to-ligand charge transfer excited state lie lowest.

  10. Multiconfiguration Pair-Density Functional Theory Is as Accurate as CASPT2 for Electronic Excitation.

    Science.gov (United States)

    Hoyer, Chad E; Ghosh, Soumen; Truhlar, Donald G; Gagliardi, Laura

    2016-02-04

    A correct description of electronically excited states is critical to the interpretation of visible-ultraviolet spectra, photochemical reactions, and excited-state charge-transfer processes in chemical systems. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory and a new kind of density functional called an on-top density functional. Here, we show that MC-PDFT with a first-generation on-top density functional performs as well as CASPT2 for an organic chemistry database including valence, Rydberg, and charge-transfer excitations. The results are very encouraging for practical applications.

  11. Negative-parity nucleon excited state in nuclear matter

    Science.gov (United States)

    Ohtani, Keisuke; Gubler, Philipp; Oka, Makoto

    2016-10-01

    Spectral functions of the nucleon and its negative-parity excited state in nuclear matter are studied by using QCD sum rules and the maximum entropy method (MEM). It is found that in-medium modifications of the spectral functions are attributed mainly to density dependencies of the and condensates. The MEM reproduces the lowest-energy peaks of both the positive- and negative-parity nucleon states at finite density up to ρ ˜ρN (normal nuclear matter density). As the density grows, the residue of the nucleon ground state decreases gradually while the residue of the lowest negative-parity excited state increases slightly. On the other hand, the positions of the peaks, which correspond to the total energies of these states, are almost density independent for both parity states. The density dependencies of the effective masses and vector self-energies are also extracted by assuming phenomenological mean-field-type propagators for the peak states. We find that, as the density increases, the nucleon effective mass decreases while the vector self-energy increases. The density dependence of these quantities for the negative-parity state on the other hand turns out to be relatively weak.

  12. Lifetimes and structure of excited states of 115Sb

    Science.gov (United States)

    Lobach, Yu. N.; Bucurescu, D.

    1998-06-01

    Lifetimes of excited states of 115Sb were measured by the Doppler shift attenuation method in the (α,2nγ) reaction at Eα = 27.2 MeV. The experimental level scheme and the electromagnetic transition probabilities have been interpreted in terms of the interacting boson-fermion model. A reasonable agreement with the experiment was obtained for the positive-parity states. The experimental data also show the applicability of the cluster-vibrational model for the mixing of two 9/2+ states having different intrinsic configurations.

  13. A charge-transfer surface enhanced Raman scattering model from time-dependent density functional theory calculations on a Ag10-pyridine complex.

    Science.gov (United States)

    Birke, Ronald L; Znamenskiy, Vasiliy; Lombardi, John R

    2010-06-07

    Vibrational frequency calculations were made for a Ag(10)-pyridine vertex complex with density functional theory (DFT) for static simulated spectra and with time-dependent DFT (TD-DFT) for preresonance and resonance simulated spectra using both B3LYP/LANL2DZ and BP86/TZP methodologies. In addition, 40 excited states of the complex were calculated and assigned symmetry based on a C(2v) symmetry of the optimized complex found with B3LYP/LANL2DZ. Molecular orbital isosurfaces show that the excited states involve both Ag(10) intercluster excitations and charge-transfer (CT) excitations between the Ag nanocluster and the pyridine molecule. An excitation around 500 nm involving CT from the Ag cluster to pyridine was found in both calculations. For free pyridine, the relative average deviations between unscaled calculated and experimental results were 1.5 cm(-1) for BP86 and 3.1 cm(-1) for the B3LYP calculations. For the complex, simulated spectra at a variety of excitation wavelengths were calculated. In the case of 514 nm excitation, the simulated Raman cross section from the TD-DFT calculations (near the CT resonance) was plotted versus Raman shift frequency and compared with an experimental surface enhanced Raman scattering (SERS) spectrum obtained on an oxidation-reduction cycle, ORC roughened Ag electrode. The BP86 TD-DFT calculation with finite damping term showed a better fit to experimental spectrum with respect to both relative intensities and frequencies. The average deviation of the unscaled BP86 calculations for 16 bands in the experimental spectrum was 13.0 cm(-1). The calculated spectrum in both cases shows many contributions from nontotally symmetric as well as totally symmetric modes, indicating the contribution of Herzberg-Teller (HT) scattering. The simulated intensities of the Raman modes of different symmetry from Ag(10)-pyridine can be correlated with HT intensity borrowing from excited states of given symmetry and decent oscillator strength. These

  14. Versatile charge transfer through anthraquinone films for electrochemical sensing applications

    Energy Technology Data Exchange (ETDEWEB)

    Venarusso, Luna B. [Department of Chemistry, Universidade Federal de Mato Grosso do Sul, Caixa Postal 549, Campo Grande, MS 79070-900 (Brazil); Tammeveski, Kaido [Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu (Estonia); Maia, Gilberto, E-mail: gilberto.maia@ufms.br [Department of Chemistry, Universidade Federal de Mato Grosso do Sul, Caixa Postal 549, Campo Grande, MS 79070-900 (Brazil)

    2011-10-01

    Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to study the effect of anthraquinone (AQ) films on the charge transfer rate of {beta}-nicotinamide adenine dinucleotide (NAD{sup +}), dopamine (DA), and ferricyanide on glassy carbon (GC) electrodes in solutions of different pH. Maximum blocking action on the Fe(CN){sub 6}{sup 3-} redox probe was observed at pH 7 and open-circuit potential (OCP). However, maximum electron hopping effect was observed at pH 9 at both -0.58 V and -0.85 V for Fe(CN){sub 6}{sup 3-}, pH 7 at -0.58 V for NAD{sup +}, and pH 9 at -0.58 V for DA, suggesting that electron hopping in AQ films on a GC surface is dependent on both pH and electrode potential. These findings lend support for the application of these films in the detection of soluble redox probes such as NAD{sup +} and DA at biological pH values (from 7 to 9).

  15. 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.

  16. Controlling autoionization in strontium two-electron-excited states

    Science.gov (United States)

    Fields, Robert; Zhang, Xinyue; Dunning, F. Barry; Yoshida, Shuhei; Burgdörfer, Joachim

    2016-05-01

    One challenge in engineering long-lived two-electron-excited states, i.e., so-called planetary atoms, is autoionization. Autoionization, however, can be suppressed if the outermost electron is placed in a high- n, n ~ 300 - 600 , high- L state because such states have only a very small overlap with the inner electron, even when this is also excited to a state of relatively high n and hence of relatively long lifetime. Here the L-dependence of the autoionization rate for high- n strontium Rydberg atoms is examined during excitation of the core ion 5 s 2S1 / 2 - 5 p 2P3 / 2 transition. Measurements in which the angular momentum of the Rydberg electron is controlled using a pulsed electric field show that the autoionization rate decreases rapidly with increasing L and becomes very small for values larger than ~ 20 . The data are analyzed with the aid of calculations undertaken using complex scaling. Research supported by the NSF and Robert A. Welch Foundation.

  17. Origin of the Red Shift for the Lowest Singlet π → π* Charge-Transfer Absorption of p-Nitroaniline in Supercritical CO2.

    Science.gov (United States)

    Hidalgo, Marcelo; Rivelino, Roberto; Canuto, Sylvio

    2014-04-08

    The origin of the unusual solvatochromic shift of p-nitroaniline (PNA) in supercritical carbon dioxide (SCCO2) is theoretically investigated on the basis of experimental data. Ab initio quantum chemistry calculations have been employed to unveil the interaction of CO2 with this archetypical molecule. It is demonstrated that the nitro group of PNA works as an electron-donating site binding to the electron-deficient carbon atom of CO2, most probably via a Lewis acid-base interaction. Moreover, a cooperative C-H···O hydrogen bond seems to act as an additional stabilizing source during the solvation process of PNA in SCCO2. To support the influence of solute-solvent specific interactions on the lowest singlet π → π* charge-transfer excitation, we perform a sequential Monte Carlo time-dependent density functional theory simulation to evaluate the excited states of PNA in SCCO2 (T = 315 K, ρ = 0.81 g/cm(3)). A critical assessment of this simulation, compared to calculations carried out within the polarized continuum model, gives strong evidence that our proposed complexes are important in describing the solvatochromic shift of PNA in SCCO2. The calculated red shift from the gas phase accounts for 66% to 80% (depending on the degree of complexation) of the experimental data. Finally, these results also alleviate possible failures commonly attributed to long-range corrected functionals in reproducing the solvatochromism of PNA.

  18. The electronic excited states of green fluorescent protein chromophore models

    Science.gov (United States)

    Olsen, Seth Carlton

    We explore the properties of quantum chemical approximations to the excited states of model chromophores of the green fluorescent protein of A. victoria. We calculate several low-lying states by several methods of quantum chemical calculation, including state-averaged complete active space SCF (CASSCF) methods, time dependent density functional theory (TDDFT), equation-of motion coupled cluster (EOM-CCSD) and multireference perturbation theory (MRPT). Amongst the low-lying states we identify the optically bright pipi* state of the molecules and examine its properties. We demonstrate that the state is dominated by a single configuration function. We calculate zero-time approximations to the resonance Raman spectrum of GFP chromophore models, and assign published spectra based upon these.

  19. Competition between covalent bonding and charge transfer at complex-oxide interfaces.

    Science.gov (United States)

    Salafranca, Juan; Rincón, Julián; Tornos, Javier; León, Carlos; Santamaria, Jacobo; Dagotto, Elbio; Pennycook, Stephen J; Varela, Maria

    2014-05-16

    Here we study the electronic properties of cuprate-manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor YBa2Cu3O7-δ and the colossal magnetoresistance compound (La,Ca)MnO3. A net transfer of electrons from manganite to cuprate with a peculiar nonmonotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales.

  20. 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...

  1. 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.

  2. Charge transfer adducts of metal complexes of π-donor ligands with I 2 and TCNQ

    Science.gov (United States)

    Bera, T. R.; Sen, D.; Ghosh, R.

    1989-01-01

    Copper(II) and nickel(II) biguanides and O-alkyl-1-amidinourea can act as donors for the formation of charge transfer (CT) adducts with I 2 and tetracyanoquinodimethane (TNCQ) as acceptors. Iodine adducts are characterized both in solid and solution states whereas TCNQ adducts obtain only in solution. Appearance of a broad band at 355 nm for iodine adducts and at 335 nm for TNCQ adducts and shifting of i.r. frequencies support the formation of donor acceptor associates. Elemental analysis establishes 1:1 stoichiometry of the solid adducts. The K and ɛ values determined by modified Benesi—Hildebrand, Scott and Rose—Drago equations are found to be of the order of 10 4 and 10 3 respectively at 298 K in methanol. The solvent effect on the K values is discussed in terms of coupled solute-solute and solute-solvent equilibria.

  3. Annealing bounds to prevent further Charge Transfer Inefficiency increase of the Chandra X-ray CCDs

    Science.gov (United States)

    Monmeyran, Corentin; Patel, Neil S.; Bautz, Mark W.; Grant, Catherine E.; Prigozhin, Gregory Y.; Agarwal, Anuradha; Kimerling, Lionel C.

    2016-12-01

    After the front-illuminated CCDs on board the X-ray telescope Chandra were damaged by radiation after launch, it was decided to anneal them in an effort to remove the defects introduced by the irradiation. The annealing led to an unexpected increase of the Charge Transfer Inefficiency (CTI). The performance degradation is attributed to point defect interactions in the devices. Specifically, the annealing at 30 °C activated the diffusion of the main interstitial defect in the device, the carbon interstitial, which led to its association with a substitutional impurity, ultimately resulting in a stable and electrically active defect state. Because the formation reaction of this carbon interstitial and substitutional impurity associate is diffusion limited, we recommend a higher upper bound for the annealing temperature and duration of any future CCD anneals, that of -50 °C for one day or -60 °C for a week, to prevent further CTI increase.

  4. Ultracold, radiative charge transfer in hybrid Yb ion - Rb atom traps

    CERN Document Server

    McLaughlin, B M; Lane, I C; McCann, J F

    2014-01-01

    Ultracold hybrid ion-atom traps offer the possibility of microscopic manipulation of quantum coherences in the gas using the ion as a probe. However, inelastic processes, particularly charge transfer can be a significant process of ion loss and has been measured experimentally for the Yb$^{+}$ ion immersed in a Rb vapour. We use first-principles quantum chemistry codes to obtain the potential energy curves and dipole moments for the lowest-lying energy states of this complex. Calculations for the radiative decay processes cross sections and rate coefficients are presented for the total decay processes. Comparing the semi-classical Langevin approximation with the quantum approach, we find it provides a very good estimate of the background at higher energies. The results demonstrate that radiative decay mechanisms are important over the energy and temperature region considered. In fact, the Langevin process of ion-atom collisions dominates cold ion-atom collisions. For spin dependent processes \\cite{kohl13} the...

  5. Negative-parity nucleon excited state in nuclear matter

    CERN Document Server

    Ohtani, Keisuke; Oka, Makoto

    2016-01-01

    Spectral functions of the nucleon and its negative parity excited state in nuclear matter are studied using QCD sum rules and the maximum entropy method (MEM). It is found that in-medium modifications of the spectral functions are attributed mainly to density dependencies of the $\\langle \\bar{q}q \\rangle $ and $\\langle q^{\\dagger}q \\rangle $ condensates. The MEM reproduces the lowest-energy peaks of both the positive and negative parity nucleon states at finite density up to $\\rho \\sim \\rho_N$ (normal nuclear matter density). As the density grows, the residue of the nucleon ground state decreases gradually while the residue of the lowest negative parity excited state increases slightly. On the other hand, the positions of the peaks, which correspond to the total energies of these states, are almost density independent for both parity states. The density dependencies of the effective masses and vector self-energies are also extracted by assuming the mean-field green functions for the peak states. We find that,...

  6. Excitation energies with time-dependent density matrix functional theory: Singlet two-electron systems.

    Science.gov (United States)

    Giesbertz, K J H; Pernal, K; Gritsenko, O V; Baerends, E J

    2009-03-21

    Time-dependent density functional theory in its current adiabatic implementations exhibits three striking failures: (a) Totally wrong behavior of the excited state surface along a bond-breaking coordinate, (b) lack of doubly excited configurations, affecting again excited state surfaces, and (c) much too low charge transfer excitation energies. We address these problems with time-dependent density matrix functional theory (TDDMFT). For two-electron systems the exact exchange-correlation functional is known in DMFT, hence exact response equations can be formulated. This affords a study of the performance of TDDMFT in the TDDFT failure cases mentioned (which are all strikingly exhibited by prototype two-electron systems such as dissociating H(2) and HeH(+)). At the same time, adiabatic approximations, which will eventually be necessary, can be tested without being obscured by approximations in the functional. We find the following: (a) In the fully nonadiabatic (omega-dependent, exact) formulation of linear response TDDMFT, it can be shown that linear response (LR)-TDDMFT is able to provide exact excitation energies, in particular, the first order (linear response) formulation does not prohibit the correct representation of doubly excited states; (b) within previously formulated simple adiabatic approximations the bonding-to-antibonding excited state surface as well as charge transfer excitations are described without problems, but not the double excitations; (c) an adiabatic approximation is formulated in which also the double excitations are fully accounted for.

  7. On the nature of highly vibrationally excited states of Thiophosgene

    CERN Document Server

    Keshavamurthy, Srihari

    2011-01-01

    In this work an analysis of the highly vibrationally excited states of thiophosgene (SCCl$_{2}$) is made in order to gain insights into some of the experimental observations and spectral features. The states analyzed herein lie in a spectrally complex region where strong mode mixings are expected due to the overlap of several strong anharmonic Fermi resonances. Two recent techniques, a semiclassical angle space representation of the eigenstates and the parametric variation of the eigenvalues (level-velocities) are used to identify eigenstate sequences exhibiting common localization characteristics. Preliminary results on the influence of highly excited out-of-plane bending modes on the nature of the eigenstates suggest a possible bifurcation in the system.

  8. On the nature of highly vibrationally excited states of thiophosgene

    Indian Academy of Sciences (India)

    Srihari Keshavamurthy

    2012-01-01

    In this work an analysis of the highly vibrationally excited states of thiophosgene (SCCl2) is made in order to gain insights into some of the experimental observations and spectral features. The states analysed here lie in a spectrally complex region where strong mode mixings are expected due to the overlap of several strong anharmonic Fermi resonances. Two recent techniques, a semiclassical angle space representation of the eigenstates and the parametric variation of the eigenvalues (level-velocities) are used to identify eigenstate sequences exhibiting common localization characteristics. Preliminary results on the influence of highly excited out-of-plane bending modes on the nature of the eigenstates suggest a possible bifurcation in the system.

  9. Precision study of excited state effects in nucleon matrix elements

    Energy Technology Data Exchange (ETDEWEB)

    Dinter, Simon; Drach, Vincent; Jansen, Karl; Renner, Dru B. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC; Alexandrou, Constantia [Cyprus Univ., Nicosia (Cyprus). Dept. of Physics; The Cyprus Insitute, Nicosia (Cyprus). Computation-Based Science and Technology Research Center; Constantinou, Martha [Cyprus Univ., Nicosia (Cyprus). Dept. of Physics

    2011-08-15

    We present a dedicated analysis of the influence of excited states on the calculation of nucleon matrix elements. This calculation is performed at a fixed value of the lattice spacing, volume and pion mass that are typical of contemporary lattice computations. We focus on the nucleon axial charge, g{sub A}, for which we use about 7,500 measurements, and on the average momentum of the unpolarized isovector parton distribution, left angle x right angle {sub u-d}, for which we use about 23,000 measurements. All computations are done employing N{sub f}=2+1+1 maximally-twisted-mass Wilson fermions and using nonperturbatively calculated renormalization factors. Excited state e ects are shown to be negligible for g{sub A}, whereas they lead to an O(10%) downward shift for left angle x right angle {sub u-d}. (orig.)

  10. The effects of doubly excited states on ionization balance

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The effects of highly doubly excited states on ionization balance are investigated. In the calculation, A Collisional-Radiative model in Detailed-Configuration-Accounting (DCA) is applied to population calculations for NLTE plasmas. Configuration-averaged rate coefficients that needed in the rate equations are obtained based on the first order perturbation theory. The Hatree-Fock-Slater self-consistent-field method is used to calculate the electron wave functions. The mean ionization stage of high-Z plasma Lu is presented. The comparison shows that the mean ionization stage increases more than 3 stages when doubly excited states 5l6l' and 5l5l' are not included in the population calculations.

  11. Stark spectrum of barium in highly excited Rydberg states

    Institute of Scientific and Technical Information of China (English)

    Yang Hai-Feng; Gao Wei; Cheng Hong; Liu Xiao-Jun; Liu Hong-Ping

    2013-01-01

    We present observations of Stark spectra of barium in highly excited Rydberg states in the energy region around n =35.The one-photon excitation concerns the π transition.The observed Stark spectra at electric fields ranging from 0 to 60 V·cm-1 are well explained by the diagonalization of the Hamiltonian incorporating the core effects.From the Stark maps,the anti-crossings between energy levels are identified experimentally and theoretically.The time of flight spectra at the specified Stark states are recorded,where the deceleration and acceleration of barium atoms are observed.This is very consistent with the prediction derived from the Stark maps from the point of view of energy conservation.

  12. 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.

  13. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Morherr, Antonia, E-mail: morherr@stud.uni-frankfurt.de [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Witt, Sebastian [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Chernenkaya, Alisa [Graduate School Materials Science in Mainz, 55128 Mainz (Germany); Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz (Germany); Bäcker, Jan-Peter [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Schönhense, Gerd [Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz (Germany); Bolte, Michael [Institut für anorganische Chemie, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany); Krellner, Cornelius [Physikalisches Institut, Goethe-Universität Frankfurt am Main, 60438 Frankfurt am Main (Germany)

    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-F{sub 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 π-conjugated donor molecules.

  15. 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...

  16. Charge Transfer as a Probe for the Interfacial Properties of Quantum Dot-Ligand Complexes

    Science.gov (United States)

    Weinberg, David Joseph

    This dissertation describes the study of charge transfer interactions between colloidal quantum dots (QDs) and molecular redox partners in the context of both fundamental investigations of charge recombination mechanisms in nanocrystal-molecule systems, and as a technique to probe the properties of the QD ligand shell. Charge separation in a system of CdS nanocrystals and organic hole acceptors results in the formation of a spin-correlated radical ion pair. Interrogating this photogenerated species with EPR and magnetic field effect transient absorption techniques reveals that the charge recombination dynamics of this donor-acceptor system are dictated by the radical pair intersystem crossing mechanism on the nanosecond timescale. These experiments also indicate that the photoinjected electron localizes at a CdS QD surface trap state, and the coupling between the electron and hole in this spin-correlated system is low. Additional studies involving the CdS QDs and organic hole acceptors are proposed which would investigate the exchange of charge and energy within the nanocrystal organic adlayer. Collisional charge transfer interactions between substituted benzoquinone molecules and PbS QDs coated with mixed monolayers of oleic acid and perfluorodecanethiol are monitored via photoluminescence and transient absorption spectroscopies. These experiments reveal that partially fluorinated ligand shells are less permeable to solution phase molecules and offer greater protection of the nanocrystal surface than their aliphatic counterparts. Only a small amount of fluorinated surfactant ( 20% surface coverage) is necessary to profoundly change the permeability of the ligand shell, and the protective nature of these fluorinated molecules is likely a combination of the molecular volume and oleophobicity of these ligands. Follow up work is discussed which would elucidate the influence of solvent and extent of surfactant fluorination on the permeability of these ligand shells, as

  17. Nonlinear Optical Spectroscopy of Excited States in Polyfluorene

    CERN Document Server

    Tong, M; Vardeny, Z V

    2006-01-01

    We used a variety of nonlinear optical (NLO) spectroscopies to study the singlet excited states order, and primary photoexcitations in polyfluorene; an important blue emitting p-conjugated polymer. The polarized NLO spectroscopies include ultrafast pump-probe photomodulation, two-photon absorption, and electroabsorption. For completeness we also measured the linear absorption and photoluminescence spectra. We found that the primary photoexcitations in polyfluorene are singlet excitons.

  18. Excited states in large molecular systems through polarizable embedding

    DEFF Research Database (Denmark)

    List, Nanna Holmgaard; Olsen, Jógvan Magnus Haugaard; Kongsted, Jacob

    2016-01-01

    In this perspective, we provide an overview of recent work within the polarizable embedding scheme to describe properties of molecules in realistic environments of increasing complexity. After an outline of the theoretical basis for the polarizable embedding model, we discuss the importance of us...... theory. We finally discuss aspects related to two recent extensions of the model (i) effective external field and (ii) polarizable density embedding emphasizing their importance for efficient yet accurate description of excited-state properties in complex environments....

  19. First observation of excited states in 173Hg93

    CERN Document Server

    O'Donnell, D; Scholey, C; Bianco, L; Capponi, L; Carroll, R J; Darby, I G; Donosa, L; Drummond, M; Ertugral, F; Greenlees, P T; Grahn, T; Hauschild, K; Herzan, A; Jakobsson, U; Jones, P; Joss, D T; Julin, R; Juutinen, S; Ketelhut, S; Labiche, M; Leino, M; Lopez-Martens, A; Mullholland, K; Nieminen, P; Peura, P; Rahkila, P; Rinta-Antila, S; Ruotsalainen, P; Sandzelius, M; Saren, J; Saygi, B; Simpson, J; Sorri, J; Thornthwaite, A; Uusitalo, J

    2012-01-01

    The neutron-deficient nucleus 173Hg has been studied following fusion-evaporation reactions. The observation of gamma rays decaying from excited states are reported for the first time and a tentative level scheme is proposed. The proposed level scheme is discussed within the context of the systematics of neighbouring neutron-deficient Hg nuclei. In addition to the gamma-ray spectroscopy, the alpha decay of this nucleus has been measured yielding superior precision to earlier measurements.

  20. Unnatural parity resonance states in positron-excited hydrogen scattering

    Institute of Scientific and Technical Information of China (English)

    Ma Jia; Zhou Ya-Jun; Wang Yuan-Cheng

    2012-01-01

    The coupled-channels optical method for positron scattering has been applied to investigate resonance states with unnatural parities in a positron-excited hydrogen system.The positronium formation channels and continuum channel are included via a complex equivalent local potential.Resonance states with angular momenta L =1 to L =2 and parities (-1)L+1 are calculated.Resonance energies and widths are reported and compared with other theoretical calculations.We found that the opening positronium formation channels play an important role in forming nondipole Feshbach resonances.

  1. Modular Hamiltonian for Excited States in Conformal Field Theory.

    Science.gov (United States)

    Lashkari, Nima

    2016-07-22

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Z_{n} replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories.

  2. Modular Hamiltonian of Excited States in Conformal Field Theory

    CERN Document Server

    Lashkari, Nima

    2015-01-01

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the replica Z_n symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories.

  3. Static polarizabilities for excited states within the spin-conserving and spin-flipping equation-of-motion coupled-cluster singles and doubles formalism: Theory, implementation, and benchmarks

    Science.gov (United States)

    Nanda, Kaushik D.; Krylov, Anna I.

    2016-11-01

    We present the theory and implementation for calculating static polarizabilities within the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) framework for electronically excited states and its spin-flip variant. We evaluate the second derivatives of the EOM-CCSD Lagrangian with respect to electric-field perturbations. The relaxation of reference molecular orbitals is not included. In our approach, the wave function amplitudes satisfy the 2n + 1 rule and the amplitude-response Lagrange multipliers satisfy the 2n + 2 rule. The new implementation is validated against finite-field and CCSD response-theory calculations of the excited-state polarizabilities of pyrimidine and s-tetrazine. We use the new method to compute static polarizabilities of different types of electronic states (valence, charge-transfer, singlets, and triplets) in open- and closed-shell systems (uracil, p-nitroaniline, methylene, and p-benzyne). We also present an alternative approach for calculating excited-state static polarizabilities as expectation values by using the EOM-CCSD wave functions and energies in the polarizability expression for an exact state. We find that this computationally less demanding approach may show differences up to ˜30 % relative to the excited-state polarizabilities computed using the analytic-derivative formalism.

  4. Static polarizabilities for excited states within the spin-conserving and spin-flipping equation-of-motion coupled-cluster singles and doubles formalism: Theory, implementation, and benchmarks.

    Science.gov (United States)

    Nanda, Kaushik D; Krylov, Anna I

    2016-11-28

    We present the theory and implementation for calculating static polarizabilities within the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) framework for electronically excited states and its spin-flip variant. We evaluate the second derivatives of the EOM-CCSD Lagrangian with respect to electric-field perturbations. The relaxation of reference molecular orbitals is not included. In our approach, the wave function amplitudes satisfy the 2n + 1 rule and the amplitude-response Lagrange multipliers satisfy the 2n + 2 rule. The new implementation is validated against finite-field and CCSD response-theory calculations of the excited-state polarizabilities of pyrimidine and s-tetrazine. We use the new method to compute static polarizabilities of different types of electronic states (valence, charge-transfer, singlets, and triplets) in open- and closed-shell systems (uracil, p-nitroaniline, methylene, and p-benzyne). We also present an alternative approach for calculating excited-state static polarizabilities as expectation values by using the EOM-CCSD wave functions and energies in the polarizability expression for an exact state. We find that this computationally less demanding approach may show differences up to ∼30% relative to the excited-state polarizabilities computed using the analytic-derivative formalism.

  5. 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.)

  6. The investigation of interactions in the excited state of flavins using time-resolved spectroscopy

    NARCIS (Netherlands)

    Visser, A.J.W.G.

    1975-01-01

    In paper I the results obtained with a very short (3 nsec) intense laser pulse as excitation source are described. This pulse excites such a large amount of flavin molecules into higher excited singlet and triplet states that changes in absorption of these higher excited states can be analyzed with

  7. Quantum Entanglement of Locally Excited States in Maxwell Theory

    CERN Document Server

    Nozaki, Masahiro

    2016-01-01

    In 4 dimensional Maxwell gauge theory, we study the changes of (Renyi) entangle-ment entropy which are defined by subtracting the entropy for the ground state from the one for the locally excited states generated by acting with the gauge invariant local operators on the state. The changes for the operators which we consider in this paper reflect the electric-magnetic duality. The late-time value of changes can be interpreted in terms of electromagnetic quasi-particles. When the operator constructed of both electric and magnetic fields acts on the ground state, it shows that the operator acts on the late-time structure of quantum entanglement differently from free scalar fields.

  8. Excited-State Properties of Molecular Solids from First Principles

    Science.gov (United States)

    Kronik, Leeor; Neaton, Jeffrey B.

    2016-05-01

    Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion.

  9. Highly luminescent Sm(III) complexes with intraligand charge-transfer sensitization and the effect of solvent polarity on their luminescent properties.

    Science.gov (United States)

    Lo, Wai-Sum; Zhang, Junhui; Wong, Wing-Tak; Law, Ga-Lai

    2015-04-20

    Samarium complexes with the highest quantum yields to date have been synthesized, and their luminescence properties were studied in 12 solvents. Sensitization via a nontriplet intraligand charge-transfer pathway was also successfully demonstrated in solution states with good quantum yields.

  10. Ground and excited state proton transfer of the bioactive plant flavonol robinetin in a protein environment: spectroscopic and molecular modeling studies.

    Science.gov (United States)

    Pahari, Biswa Pathik; Chaudhuri, Sudip; Chakraborty, Sandipan; Sengupta, Pradeep K

    2015-02-12

    We performed spectroscopic and molecular modeling studies to explore the interaction of the bioactive plant flavonol robinetin (3,7,3',4',5'-OH flavone), with the carrier protein human serum albumin (HSA). Multiparametric fluorescence sensing, exploiting the intrinsic "two color" fluorescence of robinetin (comprising excited state intramolecular proton transfer (ESIPT) and charge transfer (CT) emissions) reveals that binding to HSA significantly affects the emission and excitation profiles, with strongly blue-shifted (∼29 nm) normal fluorescence and remarkable increase in the ESIPT fluorescence anisotropy (r) and lifetime (τ). Flavonol-induced HSA (tryptophan) fluorescence quenching data yield the dynamic quenching constant (KD) as 5.42 × 10(3) M(-1) and the association constant (Ks) as 5.59 × 10(4) M(-1). Time-resolved fluorescence anisotropy decay studies show dramatic (∼170 times) increase in the rotational correlation time (τ(rot)), reflecting greatly enhanced restrictions in motion of robinetin in the protein matrix. Furthermore, prominent induced circular dichroism (ICD) bands appear, indicating that the chiral environment of HSA strongly perturbs the electronic transitions of the intrinsically achiral robinetin molecule. Molecular docking calculations suggest that robinetin binds in subdomain IIA of HSA, where specific interactions with basic residues promote ground state proton abstraction and stabilize an anionic species, which is consistent with spectroscopic observations.

  11. Initial state-resolved excited state absorption spectroscopy of ZBLAN:Ho3+ glass

    Science.gov (United States)

    Piatkowski, D.; Wisniewski, K.; Koepke, C.; Piramidowicz, R.; Klimczak, M.; Malinowski, M.

    2008-12-01

    Phase-sensitive and frequency-resolved detection techniques are used for the initial state-resolved excited state absorption (ESA) measurements in ZBLAN:Ho3+ glass. Both experimental techniques were applied simultaneously in a broad spectral range (550 1750 nm) for the first time. Estimated results are compared and discussed in detail. A simple kinetic model, used for qualitative considerations, is presented and successfully compared with the experimental data. The measured spectra will be useful for identifying new up-conversion excitation channels in the considered system, where ESA transitions originating from several excited levels are observed.

  12. Application of spectroscopy and super-resolution microscopy: Excited state

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharjee, Ujjal [Iowa State Univ., Ames, IA (United States)

    2016-02-19

    Photophysics of inorganic materials and organic molecules in complex systems have been extensively studied with absorption and emission spectroscopy.1-4 Steady-state and time-resolved fluorescence studies are commonly carried out to characterize excited-state properties of fluorophores. Although steady-state fluorescence measurements are widely used for analytical applications, time-resolved fluorescence measurements provide more detailed information about excited-state properties and the environment in the vicinity of the fluorophore. Many photophysical processes, such as photoinduced electron transfer (PET), rotational reorientation, solvent relaxation, and energy transfer, occur on a nanosecond (10-9 s) timescale, thus affecting the lifetime of the fluorophores. Moreover, time-resolved microscopy methods, such as lifetimeimaging, combine the benefits of the microscopic measurement and information-rich, timeresolved data. Thus, time-resolved fluorescence spectroscopy combined with microscopy can be used to quantify these processes and to obtain a deeper understanding of the chemical surroundings of the fluorophore in a small area under investigation. This thesis discusses various photophysical and super-resolution microscopic studies of organic and inorganic materials, which have been outlined below.

  13. Photoluminescence characteristics of Pr{sup 3+} in ThO{sub 2}: interplay of defects in a photo-induced charge transfer

    Energy Technology Data Exchange (ETDEWEB)

    Godbole, S.V. E-mail: shvagod@yahoo.co.in; Dhobale, A.R.; Sastry, M.D.; Lu, C.-H.; Page, A.G

    2003-12-01

    Photo-luminescence studies of Pr{sup 3+} activated thorium oxide phosphor have revealed that mainly {sup 3}P{yields}{sup 3}H{sub 4} and {sup 1}D{sub 2}{yields}{sup 3}H{sub 4} transitions with life-time of 30 and 600 {mu}s are observed in this sample. An exponential reduction in the emission intensity of Pr{sup 3+} ions was observed on following continuous excitation with 275 nm corresponding to the f-d transition band of Pr{sup 3+} ions. Such a reduction in emission intensity was observed at all temperatures investigated in the range 90-330 K. The emission intensity recovered partially on dark storage only above 180 K. The recovery of emission intensity was also observed on the illumination of pre-exposed sample to light in the wavelength region 300-430 nm. Following illumination with 275 nm, Pr{sup 3+} activated thorium oxide phosphor has displayed a weak thermally stimulated luminescence. These results thus suggest that the optical excitation dynamically changes the state of the system under observation, and that changes are occurring in the valence state of Pr ions due to e/h transfer process on 275-nm exposure. On dark storage and also on 365-nm illumination of the pre-exposed sample, e/h traps recombine to cause emission signal recovery. The analysis of data on reduction in intensity obtained with exposure to 275 nm suggests the likelihood of the of Pr{sup 3+} ions existing at three different sites. The activation energies associated with the release of electrons from excited Pr{sup 3+} ions at different sites were determined from the temperature dependence of the photo-induced charge transfer process.

  14. Intramolecular charge transfer with crystal violet lactone in acetonitrile as a function of temperature: reaction is not solvent-controlled.

    Science.gov (United States)

    Druzhinin, Sergey I; Demeter, Attila; Zachariasse, Klaas A

    2013-08-22

    Intramolecular charge transfer (ICT) with crystal violet lactone (CVL) in the excited singlet state takes place in solvents more polar than n-hexane, such as ethyl acetate, tetrahydrofuran, and acetonitrile (MeCN). In these solvents, the fluorescence spectrum of CVL consists of two emission bands, from a locally excited (LE) and an ICT state. The dominant deactivation channel of the lowest excited singlet state is internal conversion, as the quantum yields of fluorescence (0.007) and intersystem crossing (0.015) in MeCN at 25 °C are very small. CVL is a weakly coupled electron donor/acceptor (D/A) molecule, similar to an exciplex (1)(A(-)D(+)). A solvatochromic treatment of the LE and ICT emission maxima results in the dipole moments μe(LE) = 17 D and μe(ICT) = 33 D, much larger than those previously reported. This discrepancy is attributed to different Onsager radii and spectral fluorimeter calibration. The LE and ICT fluorescence decays of CVL in MeCN are double exponential. As determined by global analysis, the LE and ICT decays at 25 °C have the times τ2 = 9.2 ps and τ1 = 1180 ps, with an amplitude ratio of 35.3 for LE. From these parameters, the rate constants ka = 106 × 10(9) s(-1) and kd = 3.0 × 10(9) s(-1) of the forward and backward reaction in the LE ⇄ ICT equilibrium are calculated, resulting in a free enthalpy difference ΔG of -8.9 kJ/mol. The amplitude ratio of the ICT fluorescence decay equals -1.0, which signifies that the ICT state is not prepared by light absorption in the S0 ground state, but originates exclusively from the directly excited LE precursor. From the temperature dependence of the fluorescence decays of CVL in MeCN (-45 to 75 °C), activation energies E(a) = 3.9 kJ/mol (LE → ICT) and E(d) = 23.6 kJ/mol (ICT → LE) are obtained, giving an enthalpy difference ΔH (= E(a) - E(d)) of -19.7 kJ/mol, and an entropy difference ΔS = -35.5 J mol(-1) K(-1). These data show that the ICT reaction of CVL in MeCN is not barrierless

  15. Evidences from electron momentum spectroscopy for ultra-fast charge transfers and structural reorganizations in a floppy molecule: Ethanol

    Energy Technology Data Exchange (ETDEWEB)

    Deleuze, Michael S; Hajgato, Balazs; Morini, Filippo, E-mail: michael.deleuze@uhasselt.b [Theoretical Chemistry, Department SBG, Hasselt University, Agoralaan Gebouw D, B-3590 Diepenbeek (Belgium)

    2009-11-01

    Calculations of electron momentum distributions employing advanced Dyson orbital theories and statistical thermodynamics beyond the RRHO approximation fail to quantitatively reproduce the outermost momentum profile inferred from experiments on ethanol employing high resolution Electron Momentum Spectroscopy [1]. Study of the influence of nuclear dynamics in the initial ground state and final ionized state indicates that this discrepancy between theory and experiment reflects a charge transfer occurring during an ultra-fast dissociation of the ethanol radical cation into a methyl radical and H{sub 2}C=O-H{sup +}.

  16. Metastable excited states of OBr2- and OCl2- dianions

    Science.gov (United States)

    Noorisafa, Zeinab; Sabzyan, Hassan; Keshavarz, Elham

    2014-11-01

    Electronic stabilities, structures, properties, and spectroscopic constants of the halogen oxide dianions OBr2- and OCl2- and their singly charged anions which are of astrophysical and laboratory interests have been studied. The X2Σ states of OBr2- and OCl2- are metastable with PECs having smooth wells with minima located at R = 1.859 Å and 1.776 Å, and Coulomb barriers of 40402.54987 cm-1 and 43746.63462 cm-1 heights located at RRCB = 2.100 Å and 1.922 Å, respectively, both without any vibrational states. While, the B2Σ state of OBr2- and the A2Σ state of OCl2- are metastable with PECs having wells deep enough to suite several bound states, with minima located at Re = 1.773 Å and 1.6430 Å, and Coulomb barriers of 191437.45813 cm-1 and 180550.70294 cm-1 heights located at RRCB = 2.658 Å and 2.4480 Å, with De = 1.26470 eV and 1.60837 eV, respectively. The OBr- and OCl- singly charged anions are stable in their ground states. Based on the calculated Frank-Condon factors, it is concluded that metastable excited state OBr2- and OCl2- dianions and ground state OBr- and OCl- singly charged anions can be formed via electron capture processes.

  17. Ultrafast Structural Rearrangements in the MLCT Excited State for Copper(I) bis-Phenanthrolines in Solution

    Energy Technology Data Exchange (ETDEWEB)

    Shaw, G B; Grant, C D; Shirota, H; Castner Jr., E W; Meyer, G J; Chen, L X

    2006-10-05

    Ultrafast excited state structural dynamics of [Cu{sup I}(dmp){sub 2}]{sup +} (dmp = 2,9-dimethyl-1,10-phenanthroline) have been studied to identify structural origins of transient spectroscopic changes during the photoinduced metal-to-ligand-charge-transfer (MLCT) transition that induces an electronic configuration change from Cu(I) (3d{sup 10}) to Cu(II) (3d{sup 9}). This study has important connections with the flattening of the Franck-Condon state tetrahedral geometry and the ligation of Cu(II)* with the solvent observed in the thermally equilibrated MLCT state by our previous laser-initiated time-resolved x-ray absorption spectroscopy (LITR-XAS) results. To better understand the structural photodynamics of Cu(I) complexes, we have studied both [Cu{sup I}(dmp){sub 2}]{sup +} and [Cu{sup I}(dpp){sub 2}]{sup +} (dpp = 2,9-diphenyl-1,10-phenanthroline) in solvents with different dielectric constants, viscosities and thermal diffusivities by transient absorption spectroscopy. The observed spectral dynamics suggest that a solvent-independent inner-sphere relaxation process is occurring despite the large amplitude motions due to the flattening of the tetrahedral coordinated geometry. The singlet fluorescence dynamics of photoexcited [Cu{sup I}(dmp){sub 2}]{sup +} were measured in the coordinating solvent acetonitrile, using the fluorescence upconversion method at different emission wavelengths. At the bluest emission wavelengths, a prompt fluorescence lifetime of 66 fs is attributed to the excited state deactivation processes due to the internal conversion and intersystem crossing at the Franck-Condon state geometry. The differentiation between the prompt fluorescence lifetime with the tetrahedral Franck-Condon geometry and that with the flattened tetrahedral geometry uncovers an unexpected ultrafast flattening process in the MLCT state of [Cu{sup I}(dmp){sub 2}]{sup +}. These results provide guidance for future x-ray structural studies on ultrafast time scale, as

  18. 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].

  19. Excited-state proton transfer of firefly dehydroluciferin.

    Science.gov (United States)

    Presiado, Itay; Erez, Yuval; Simkovitch, Ron; Shomer, Shay; Gepshtein, Rinat; Pinto da Silva, Luís; Esteves da Silva, Joaquim C G; Huppert, Dan

    2012-11-08

    Steady-state and time-resolved emission techniques were used to study the protolytic processes in the excited state of dehydroluciferin, a nonbioluminescent product of the firefly enzyme luciferase. We found that the ESPT rate coefficient is only 1.1 × 10(10) s(-1), whereas those of d-luciferin and oxyluciferin are 3.7 × 10(10) and 2.1 × 10(10) s(-1), respectively. We measured the ESPT rate in water-methanol mixtures, and we found that the rate decreases nonlinearly as the methanol content in the mixture increases. The deprotonated form of dehydroluciferin has a bimodal decay with short- and long-time decay components, as was previously found for both D-luciferin and oxyluciferin. In weakly acidic aqueous solutions, the deprotonated form's emission is efficiently quenched. We attribute this observation to the ground-state protonation of the thiazole nitrogen, whose pK(a) value is ~3.

  20. Excited states above the proton threshold in {sup 26}Si

    Energy Technology Data Exchange (ETDEWEB)

    Komatsubara, T. [Institute for Basic Science (IBS), Rare Isotope Science Project, Yuseong-gu Daejeon (Korea, Republic of); Kubono, S.; Ito, Y. [RIKEN, Saitama (Japan); Hayakawa, T.; Shizuma, T. [Japan Atomic Energy Agency, Tokai, Ibaraki (Japan); Ozawa, A.; Ishibashi, Y. [University of Tsukuba, Institute of Physics, Tsukuba, Ibaraki (Japan); Moriguchi, T. [National Cerebral and Cardiovascular Center Research Institute, Suita, Osaka (Japan); Yamaguchi, H.; Kahl, D. [University of Tokyo, Wako Branch, Center for Nuclear Study (CNS), Wako, Saitama (Japan); Hayakawa, S. [Laboratori Nazionali del Sud-INFN, Catania (Italy); Nguyen Binh, Dam [Vietnamese Academy for Science and Technology, Institute of Physics, Hanoi (Viet Nam); Chen, A.A.; Chen, J. [McMaster University, Hamilton, Ontario (Canada); Setoodehnia, K. [University of Notre Dame, Department of Physics, Notre Dame, Indiana (United States); Kajino, T. [National Astronomical Observatory, Tokyo (Japan); University of Tokyo, Department of Astronomy, Graduate School of Science, Tokyo (Japan)

    2014-09-15

    The level scheme above the proton threshold in {sup 26}Si is crucial for evaluating the {sup 25}Al(p, γ){sup 26}Si stellar reaction, which is important for understanding the astrophysical origin of the long-lived cosmic radioactivity {sup 26}Al(T{sub 1/2} = 7.17 x 10{sup 5} y) in the Galaxy. The excited states in {sup 26}Si have been studied using an in-beam γ-ray spectroscopy technique with the {sup 24}Mg({sup 3}He, nγ){sup 26}Si reaction. γ-rays with energies up to 4.6 MeV emitted from excited states in {sup 26}Si have been measured using large volume HPGe detectors. The spin-parity of one of the most important states reported recently at 5890.0keV has been assigned as 0{sup +} by γ-γ angular correlation measurements in this work. (orig.)