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Sample records for charge transfer molecular

  1. Photoinduced charge and energy transfer in molecular wires.

    Science.gov (United States)

    Gilbert, Mélina; Albinsson, Bo

    2015-02-21

    Exploring charge and energy transport in donor-bridge-acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor-bridge-acceptor (D-B-A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the "molecular wire"). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor-acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor-acceptor electronic coupling and transfer rates. Several examples of donor-bridge-acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed. PMID:25212903

  2. Positron annihilation studies of some charge transfer molecular complexes

    CERN Document Server

    El-Sayed, A; Boraei, A A A

    2000-01-01

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

  3. Charge Transfer in FeO: A combined Molecular-Dynamics and Ab Initio Study

    International Nuclear Information System (INIS)

    Molecular dynamics simulations and ab initio electronic structure calculations were carried out to determine the rate of charge transfer in stoichiometric w-stite (FeO). The charge transfer of interest occurs by II/III valence interchange between nearest-neighbor Fe atoms, with the Fe(III) constituting a ''hole'' electronic defect. There are two possible nearest-neighbor charge transfers in the FeO lattice, which occur between edge-sharing or corner-sharing FeO6 octahedra. Molecular dynamics simulations predict charge transfer rates of 3.7x1011 and 1.9x109 s-1 for the edge and corner transfers, respectively, in good agreement with those calculated using an ab initio cluster approach (1.6x1011 and 8.0x108 s-1, respectively). The calculated rates are also similar to those along basal and c-axis directions in hematite (?-Fe2O3) determined previously. Therefore, as is the case for hematite, w-stite is predicted to show anisotropic electrical conductivity. Our findings indicate that a rigid ion model does not give acceptable results, thus showing the need to account for the change in polarizability of the system upon charge transfer. Our model achieves this by using a simple mechanical shell model. By calculating the electronic coupling matrix elements for many transition state configurations obtained from the molecular dynamics simulations, we found evidence that the position of the bridging oxygen atoms can greatly affect the amount electronic coupling between the donor and acceptor states. Finally, we address the effect of oxygen vacancies on the charge transfer. It was found that an oxygen vacancy not only creates a driving force for holes to transport away from the vacancy (or equivalently for electrons to diffuse toward the vacancy) but also lowers the free energy barriers for charge transfer. In addition, the reorganization energy significantly differed from the non-defective case in a small radius around the defect

  4. Cross sections for ion-molecular reactions in hydrogen systems and for charge transfer reactions of slow multiply charged ions

    International Nuclear Information System (INIS)

    Cross sections of ion-molecular reactions in hydrogen systems of H+-H2, H2+-H2 and H3+-H2 and charge transfer cross sections of multiply charged ions in atomic and molecular targets are presented in graphs and tables of the part A, B and C. All data presented for 99 collision systems have been measured systematically using an octo-pole ion beam guide (OPIG) technique till now since 1985. The part A is for ion-molecular reactions in hydrogen systems. In the lower energy region below few eV in center-of-mass systems, it is seen obviously at a glance that the ion-molecular reaction in hydrogen systems is dominated by H3+ formation process. In the energy region from few eV to few hundred eV in center-of-mass systems, many reaction channels of decay processes from intermediate molecular states seem to be opened resonantly. Some of cross section data in the part B for charge transfer reactions of low-charged ions produced by a conventional electron impact type (Nier type) ion source should be noted to strongly depend on the electron impact energy due to contamination of low lying metastable states in projectile ions. The part C is for charge transfer reactions of multiply charged ions extracted from a small type of electron beam ion source (Mini-EBIS). In measurements using the mini-EBIS, no evidence of metastable ions existing in the primary ion beam has been found except for doubly charged ion beam. The higher energy end of the present cross sections are connected with previous data in fairly good

  5. Models of charge transport and transfer in molecular switch tunnel junctions of bistable catenanes and rotaxanes

    International Nuclear Information System (INIS)

    The processes by which charge transfer can occur play a foundational role in molecular electronics. Here we consider simplified models of the transfer processes that could be present in bistable molecular switch tunnel junction (MSTJ) devices during one complete cycle of the device from its low- to high- and back to low-conductance state. The bistable molecular switches, which are composed of a monolayer of either switchable catenanes or rotaxanes, exist in either a ground-state co-conformation or a metastable one in which the conduction properties of the two co-conformations, when measured at small biases (+0.1 V), are significantly different irrespective of whether transport is dominated by tunneling or hopping. The voltage-driven generation (±2 V) of molecule-based redox states, which are sufficiently long-lived to allow the relative mechanical movements necessary to switch between the two co-conformations, rely upon unequal charge transfer rates on to and/or off of the molecules. Surface-enhanced Raman spectroscopy has been used to image the ground state of the bistable rotaxane in MSTJ-like devices. Consideration of these models provide new ways of looking at molecular electronic devices that rely, not only on nanoscale charge-transport, but also upon the bustling world of molecular motion in mechanically interlocked bistable molecules

  6. Designed self-assembly of molecular necklaces using host-stabilized charge-transfer interactions.

    Science.gov (United States)

    Ko, Young Ho; Kim, Kyungpil; Kang, Jin-Koo; Chun, Hyungphil; Lee, Jae Wook; Sakamoto, Shigeru; Yamaguchi, Kentaro; Fettinger, James C; Kim, Kimoon

    2004-02-25

    A novel approach to the noncovalent synthesis of molecular necklaces successfully led to the first quantitative self-assembly of a molecular necklace [6]MN, in which five small rings are threaded on a large ring, from 10 components. Our strategy involves the host-guest complex formation between the molecular host cucurbit[8]uril (CB[8]) and a guest molecule in which an electron donor and an electron acceptor unit are connected by a rigid linker with a proper angle, to form a cyclic oligomer through the host-stabilized intermolecular charge-transfer (CT) complex formation. In the structure of the molecular necklace [6]MN, five molecules of the guest form a cyclic framework by the intermolecular CT interactions, on which five CB[8] molecules are threaded with an arrangement reminiscent of a five-fold propeller. The molecular necklace measures approximately 3.7 nm in diameter and approximately 1.8 nm in thickness. PMID:14971915

  7. 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

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

    OpenAIRE

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

    2006-01-01

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

  9. Trifluoromethylmetallate anions as components of molecular charge transfer salts and superconductors.

    Energy Technology Data Exchange (ETDEWEB)

    Schlueter, J. A.

    1998-10-14

    Whereas polymeric and common inorganic anions frequently deprive the synthetic chemist of a chance to modify a charge transfer salt's structure through anion alterations, discrete organometallic anions provide a vast opportunity to probe the structure/property correlations of a material through rational synthetic methods. We have recently undertaken a research effort aimed at the crystallization of conducting charge transfer salts which possess modifiable, organometallic anions as the charge compensating entities. This research has been richly rewarded with the discovery of a new family of bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) based molecular superconductors. Herein is presented a summary of over twenty {kappa}(ET){sub 2}M(CF{sub 3}){sub 4}(1,1,2-trihaloethane) (M = Cu, Ag, Au) superconducting salts. Three new related salts are also reported: (ET){sub 2} [trans-Ag(CF{sub 3}),(CN){sub 2}], {kappa}{sub L}(BEDT-TSF){sub 2}Ag(CF{sub 3}){sub 4}(TCE), and {kappa}{sub L}(ET){sub 2}Ag(CF{sub 3}){sub 3}Cl(TCE).

  10. 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...

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

    CERN Document Server

    Oberhofer, H

    2009-01-01

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

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

    DEFF Research Database (Denmark)

    Stadler, Robert; Jacobsen, Karsten Wedel

    2006-01-01

    by orders of magnitude. We present a quantitative analysis of the relation between this level alignment (which can be estimated from charging free molecules) and charge transfer for bipyridine and biphenyl dithiolate (BPDT) molecules attached to gold leads based on density functional theory...... energetically higher end of the gap in the transmission function for bipyridine and at its lower end for BPDT....

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

    Science.gov (United States)

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

    2016-04-01

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

  14. Molecular structure and charge transfer contributions to nonlinear optical property of 2-Methyl-4-nitroaniline: A DFT study

    Science.gov (United States)

    Jasmine, G. Femina; Amalanathan, M.; Roy, S. Dawn Dharma

    2016-05-01

    The Charge transfer contributions to the second-order nonlinear optical properties of 2-Methyl-4-nitroaniline have been performed by means of DFT computation. The vibrational contribution studies of 2-Methyl-4-nitroaniline have also been performed using FTIR, FT-Raman analysis. More support on the experimental findings were added from the quantum chemical studies performed with DFT (B3LYP) method using 6-311++G(d,p)basis sets. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. The first order hyperpolarizability (α0) and related properties (β,α0 and Δα) of 2-Methyl-4-nitroaniline were calculated. In addition, molecular electrostatic potential (MEP), charge analysis also were investigated using theoretical calculations.

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

    Science.gov (United States)

    Sherman, David M.

    1987-01-01

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

  16. Charge-transfer with graphene and nanotubes

    OpenAIRE

    C.N.R. Rao; Rakesh Voggu

    2010-01-01

    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 ph...

  17. Structural charge transfer in the aluminophosphate molecular sieves by diffuse reflectance spectroscopy

    Science.gov (United States)

    Zanjanchi, M. A.; Rashidi, M. K.

    1999-05-01

    Influence of water adsorption in AlPO-5, SAPO-5, AlPO-11 and SAPO-11 has been studied with UV diffuse reflectance spectroscopy. The observed UV absorption spectra in the as-synthesized, template free and hydrated materials are related to the charge transfer processes between aluminum and oxygen atoms of the aluminophosphate and water molecules. As-synthesised materials show two distinct and well-defined bands at about 220 and 260-280 nm correlated to framework aluminum and organic templates, respectively. Upon calcination, the band of occluded template disappears and the band assigned to the framework aluminum shifts at about 240 nm. When the calcined samples are completely hydrated, broadening of the aluminum charge transfer band is observed. This is due to coordination of water molecules to the part of the framework aluminum. Broadening occurs more in AlPO-5 possibly because of higher water capacity and homogenity with respect to SAPO-5.

  18. Electron transfer processes of atomic and molecular doubly charged ions: information from beam experiments

    Czech Academy of Sciences Publication Activity Database

    Herman, Zdeněk

    2013-01-01

    Roč. 111, 12-13 (2013), s. 1697-1710. ISSN 0026-8976 R&D Projects: GA ČR GA203/00/0632; GA AV ČR IAA400400702 Grant ostatní: GA AV ČR(CZ) IAA440410 Institutional support: RVO:61388955 Keywords : doubly charged ions * electron transfer processes * beam experiments Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.642, year: 2013

  19. 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...

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

    Science.gov (United States)

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

    2015-08-26

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

  1. 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.

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

    International Nuclear Information System (INIS)

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

  3. Turning charge transfer on and off in a molecular interferometer with vibronic pathways.

    Science.gov (United States)

    Xiao, Dequan; Skourtis, Spiros S; Rubtsov, Igor V; Beratan, David N

    2009-05-01

    Inelastic electron-transfer kinetics in molecules with electron donor and acceptor units connected by a bridge is expected to be sensitive to bridge-localized vibronic interactions. Here, we show how inelastic electron transfer may be turned on and off in a double-slit style experiment that uses the molecule as an interferometer. We describe donor-acceptor interactions in terms of interfering vibronic coupling pathways that can be actively selected ("labeled") when pathway-specific vibrations are excited by infrared radiation. Thus, inelastic tunneling may be actively controlled, and we suggest strategies for building molecular scale quantum interferometers and switches based on this phenomenon. PMID:19435376

  4. Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

    Science.gov (United States)

    Sherman, David M.

    1987-01-01

    A molecular orbital description, based on Xα-Scattered wave calculations on a (FeTiO10)14− cluster, is given for Fe2+ → Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ → Ti4+ metal-metal charge transfer transition is 18040 cm−1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ → Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ → Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

  5. Photoinduced charge-transfer dynamics simulations in noncovalently bonded molecular aggregates.

    Science.gov (United States)

    Medrano, Carlos R; Oviedo, M Belén; Sánchez, Cristián G

    2016-06-01

    The rational design of new materials as prototype systems for organic solar cells remains challenging. Perylene diimide has emerged as a promising material to replace fullerene derivatives because of its synthetic flexibility, leading to the manipulation of their optical properties. As a result of their fused aromatic core that favors π-π stacking interactions, the aggregation of these molecules can reach highly ordered nanostructures as one-dimensional nanofibers, with a fast photoinduced charge transfer mechanism. In this article, we present an atomistic description of the photoexcited exciton dynamics in noncovalently bonded perylene diimides by time integration of the electron density in the presence of external time varying electric fields. We show that our approach is able to capture and explain the physics that underlies the charge transport mechanism through perylene diimide aggregates. PMID:27189740

  6. 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.

  7. Influences of molecular packing on the charge mobility of organic semiconductors: from quantum charge transfer rate theory beyond the first-order perturbation.

    Science.gov (United States)

    Nan, Guangjun; Shi, Qiang; Shuai, Zhigang; Li, Zesheng

    2011-05-28

    The electronic coupling between adjacent molecules is an important parameter for the charge transport properties of organic semiconductors. In a previous paper, a semiclassical generalized nonadiabatic transition state theory was used to investigate the nonperturbative effect of the electronic coupling on the charge transport properties, but it is not applicable at low temperatures due to the presence of high-frequency modes from the intramolecular conjugated carbon-carbon stretching vibrations [G. J. Nan et al., J. Chem. Phys., 2009, 130, 024704]. In the present paper, we apply a quantum charge transfer rate formula based on the imaginary-time flux-flux correlation function without the weak electronic coupling approximation. The imaginary-time flux-flux correlation function is then expressed in terms of the vibrational-mode path average and is evaluated by the path integral approach. All parameters are computed by quantum chemical approaches, and the mobility is obtained by kinetic Monte-Carlo simulation. We evaluate the intra-layer mobility of sexithiophene crystal structures in high- and low-temperature phases for a wide range of temperatures. In the case of strong coupling, the quantum charge transfer rates were found to be significantly smaller than those calculated using the weak electronic coupling approximation, which leads to reduced mobility especially at low temperatures. As a consequence, the mobility becomes less dependent on temperature when the molecular packing leads to strong electronic coupling in some charge transport directions. The temperature-independent charge mobility in organic thin-film transistors from experimental measurements may be explained from the present model with the grain boundaries considered. In addition, we point out that the widely used Marcus equation is invalid in calculating charge carrier transfer rates in sexithiophene crystals. PMID:21503350

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

    Directory of Open Access Journals (Sweden)

    S Amiri

    2016-02-01

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

  9. Cellular and molecular analysis of mutagenesis induced by charged particles of defined linear energy transfer

    Science.gov (United States)

    Zhu, L. X.; Waldren, C. A.; Vannias, D.; Hei, T. K.; Chatterjee, A. (Principal Investigator)

    1996-01-01

    Mutation induction by charged particles of defined linear energy transfer (LET) and gamma rays was scored using human-hamster hybrid AL cells. The LET values for charged particles accelerated at the Radiological Research Accelerator Facility ranged from 10 keV/microm protons to 150 keV/microm 4He ions. The induced mutant fractions at both the S1 and HGPRT loci were dependent on the dose and LET. In addition, for each dose examined, the mutant yield at the S1 locus was 30-60 fold higher than at the corresponding HGPRT locus. To determine whether the mutation spectrum was comparably dependent on dose and LET, independent S1- and HGPRT- mutants induced by 150 keV/microm 4He ions and gamma rays were isolated, and their DNA was analyzed by both Southern blotting and multiplex PCR methods. While the majority of radiation-induced mutants showed deletions of varying sizes, the relative percentage of large deletions was found to be related to both the dose and LET of the radiation examined. Using a mutation system that can detect multilocus changes, results of the present study show that radiation-induced chromosomal loss can be in the millions of base pairs.

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

    Science.gov (United States)

    Fujii, Mikiya; Yamashita, Koichi

    2013-03-01

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

  11. 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.

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

    KAUST Repository

    Domingo, Ester

    2015-04-09

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

  13. Photoinduced charge transfer and quasi-stable molecular dipole formation in poly[methyl(phenyl)silylene

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav

    Brno : University of Technology, Faculty of Chemistry, Brno, 1999, s. 29-32. ISBN 80-214-1372-7. [Workshop of Physical Chemistry Fundamentals: Dielectric Analysis of Polymers and Composites, and Related Phenomena. Brno (CZ), 20.03.1999] R&D Projects: GA AV ČR IAA1050901 Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders

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

    Science.gov (United States)

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

    2016-06-07

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

  15. Molecular electrets based on photoinduced charge transfer in poly[methyl(phenyl)silylene

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav

    Kobe: Kansai Advanced Research Center, Communications Research Laboratory, Ministry of Posts and Telecommunications, 1999, s. O-01. [Nano-Molecular Electronics Meeting 1999. Kobe (JP), 15.03.1999-16.03.1999] R&D Projects: GA AV ČR IAA1050901 Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  16. Molecular electronic states in charge transfer complex studied by x-ray absorption spectroscopy

    International Nuclear Information System (INIS)

    The electronic states of tetrathiafulvalene (TTF: TTF = C6H4S4) molecule in organic ferroelectric TTF-p-bromanil (TTF-BA: BA = C6Br4O2) and TTF crystals have been investigated by x-ray absorption spectroscopy (XAS) measurement at S K-edge. We elucidated that the peak structure at 2470.5 eV directly reflects the existence of hole in the highest occupied molecular orbital (HOMO) state of the TTF molecule in TTF-BA; that is consistent with the ionic TTF molecule (TTF+). The XAS of TTF-BA was evaluated on the basis of first-principles calculations, and the calculated spectra reproduce well the shape of experimental spectrum and the peak energy of the HOMO state.

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

    International Nuclear Information System (INIS)

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

  18. Charge transfer reactions of Kr2+ and Ne2+ ions with several molecular gases at 300 K

    International Nuclear Information System (INIS)

    Measurements are reported of the rate coefficients and product-ion distributions for the reactions of Kr2+ and Ne2+ ions with H2, N2, O2, CO, CO2 and CH4 at 300 K. The data are obtained with a selected ion flow tube (SIFT). The reaction rates are generally fast, proceeding at or near the gas kinetic limit. In the Kr2+ reactions the only mechanism observed is single charge transfer, whereas for the more energetic Ne2+ ions parallel single and double charge transfer product channels are evident, the double charge transfer channels usually being dominant. The general features of the data are discussed in relation to those previously obtained for the corresponding reactions of Ar2+ and Xe2+ ions. (orig.)

  19. Charge transferred in brush discharges

    Science.gov (United States)

    Talarek, M.; Kacprzyk, R.

    2015-10-01

    Electrostatic discharges from surfaces of plastic materials can be a source of ignition, when appear in explosive atmospheres. Incendivity of electrostatic discharges can be estimated using the transferred charge test. In the case of brush discharges not all the energy stored at the tested sample is released and the effective surface charge density (or surface potential) crater is observed after the discharge. Simplified model, enabling calculation of a charge transferred during electrostatic brush discharge, was presented. Comparison of the results obtained from the simplified model and from direct measurements of transferred charge are presented in the paper.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-08-15

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

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

    KAUST Repository

    Fonari, Alexandr

    2014-10-21

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

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

    Science.gov (United States)

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

    2016-03-01

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

  3. Probing the temperature dependence of proton transfer to charged platinum electrodes by reactive molecular dynamics trajectory studies

    International Nuclear Information System (INIS)

    We have performed reactive trajectory calculations of proton discharge on charged platinum surfaces as a function of temperature and charge. A recently developed 9-state empirical valence bond model has been employed. The temperature dependence follows an Arrhenius law with activation energies in the range of 0.1 eV. The activation energy for the discharge reaction decreases significantly with increasing driving force as modeled by an increasingly negative surface charge on the electrode. The analysis shows that the average orientation of molecules in the adsorbed water layer reacts to the approaching proton. Within increasing temperature, configurations become more prevalent which facilitate fast proton transfer by Grotthuss style proton hops from the second to the first layer. This effect becomes more pronounced near more negatively charged surfaces and leads to the computed reduction of the activation energy

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

    Indian Academy of Sciences (India)

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

    2007-03-01

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

  5. Catalysis: Quantifying charge transfer

    Science.gov (United States)

    James, Trevor E.; Campbell, Charles T.

    2016-02-01

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

  6. Molecular orbital (SCF-X-α-SW) theory of Fe2+-Mn3+, Fe3+-Mn2+, and Fe3+-Mn3+ charge transfer and magnetic exchange in oxides and silicates

    Science.gov (United States)

    Sherman, David M.

    1990-01-01

    Metal-metal charge-transfer and magnetic exchange interactions have important effects on the optical spectra, crystal chemistry, and physics of minerals. Previous molecular orbital calculations have provided insight on the nature of Fe2+-Fe3+ and Fe2+-Ti4+ charge-transfer transitions in oxides and silicates. In this work, spin-unrestricted molecular orbital calculations on (FeMnO10) clusters are used to study the nature of magnetic exchange and electron delocalization (charge transfer) associated with Fe3+-Mn2+, Fe3+-Mn3+, and Fe2+-Mn3+ interactions in oxides and silicates. 

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

    Institute of Scientific and Technical Information of China (English)

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

    2001-01-01

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

  8. 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.

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

    International Nuclear Information System (INIS)

    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

  10. Electronic couplings for molecular charge transfer: Benchmarking CDFT, FODFT, and FODFTB against high-level ab initio calculations

    International Nuclear Information System (INIS)

    We introduce a database (HAB11) of electronic coupling matrix elements (Hab) for electron transfer in 11 π-conjugated organic homo-dimer cations. High-level ab inito calculations at the multireference configuration interaction MRCI+Q level of theory, n-electron valence state perturbation theory NEVPT2, and (spin-component scaled) approximate coupled cluster model (SCS)-CC2 are reported for this database to assess the performance of three DFT methods of decreasing computational cost, including constrained density functional theory (CDFT), fragment-orbital DFT (FODFT), and self-consistent charge density functional tight-binding (FODFTB). We find that the CDFT approach in combination with a modified PBE functional containing 50% Hartree-Fock exchange gives best results for absolute Hab values (mean relative unsigned error = 5.3%) and exponential distance decay constants β (4.3%). CDFT in combination with pure PBE overestimates couplings by 38.7% due to a too diffuse excess charge distribution, whereas the economic FODFT and highly cost-effective FODFTB methods underestimate couplings by 37.6% and 42.4%, respectively, due to neglect of interaction between donor and acceptor. The errors are systematic, however, and can be significantly reduced by applying a uniform scaling factor for each method. Applications to dimers outside the database, specifically rotated thiophene dimers and larger acenes up to pentacene, suggests that the same scaling procedure significantly improves the FODFT and FODFTB results for larger π-conjugated systems relevant to organic semiconductors and DNA

  11. Charge transfer in ionic systems

    International Nuclear Information System (INIS)

    Charge transfer involving multiply charged ions in collision with atomic or molecular targets are determinant processes in controlled thermonuclear fusion research and astrophysical plasma. In such processes, an electron is generally captured in a excited state of the ion, followed by line emission. The observation of line intensities provides important information on the electron temperature, density and spacial distributions in the emitting region of the plasma. From a theoretical point of view, different approaches may be used with regard to the collisional energy range of the process. A semi-classical method is currently used at keV energies, but the description of very low-velocity processes requires a complete quantum mechanical treatment of the dynamics of both electrons and nuclei. The first approach extensively used is the resolution of the stationary close-coupling equations, but we have analyzed recently the efficiency of a time-dependent wave packet method which provides a clear and physical insight into the dynamics of the processes and may be particularly interesting for polyatomic systems since it allows the possibility of developing a fully quantal mechanical treatment for some degrees of freedom, the other ones being treated classically. The keV energy range treatment is presented on two examples pointing out the case of complex ion-atom collision systems, as well as the differences between ion-atom and ion-molecule mechanisms. In connection with translation energy spectroscopy experiments of McLaughlin et al in the 4-28 keV impact energy range, we present a complete ab-initio theoretical approach of the N4+(2s)2S + He system taking into account both single and double electron capture channels. This is an extremely complex collisional system which involves numerous channels with short range interactions and a very intricate interaction region may be observed for interatomic distances around R = 3.5 a.u.. In agreement with experimental data, the

  12. Electronic couplings for molecular charge transfer: Benchmarking CDFT, FODFT, and FODFTB against high-level ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Kubas, Adam; Blumberger, Jochen, E-mail: j.blumberger@ucl.ac.uk [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Hoffmann, Felix [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum (Germany); Heck, Alexander; Elstner, Marcus [Institute of Physical Chemistry, Karlsruhe Institute of Technology, Fritz-Haber-Weg 6, 76131 Karlsruhe (Germany); Oberhofer, Harald [Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85747 Garching (Germany)

    2014-03-14

    We introduce a database (HAB11) of electronic coupling matrix elements (H{sub ab}) for electron transfer in 11 π-conjugated organic homo-dimer cations. High-level ab inito calculations at the multireference configuration interaction MRCI+Q level of theory, n-electron valence state perturbation theory NEVPT2, and (spin-component scaled) approximate coupled cluster model (SCS)-CC2 are reported for this database to assess the performance of three DFT methods of decreasing computational cost, including constrained density functional theory (CDFT), fragment-orbital DFT (FODFT), and self-consistent charge density functional tight-binding (FODFTB). We find that the CDFT approach in combination with a modified PBE functional containing 50% Hartree-Fock exchange gives best results for absolute H{sub ab} values (mean relative unsigned error = 5.3%) and exponential distance decay constants β (4.3%). CDFT in combination with pure PBE overestimates couplings by 38.7% due to a too diffuse excess charge distribution, whereas the economic FODFT and highly cost-effective FODFTB methods underestimate couplings by 37.6% and 42.4%, respectively, due to neglect of interaction between donor and acceptor. The errors are systematic, however, and can be significantly reduced by applying a uniform scaling factor for each method. Applications to dimers outside the database, specifically rotated thiophene dimers and larger acenes up to pentacene, suggests that the same scaling procedure significantly improves the FODFT and FODFTB results for larger π-conjugated systems relevant to organic semiconductors and DNA.

  13. Optimal Control of charge transfer

    OpenAIRE

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

    2007-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-07

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

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

    International Nuclear Information System (INIS)

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

  16. Biological charge transfer via flickering resonance.

    Science.gov (United States)

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

    2014-07-15

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

  17. Effects of inter-molecular charge-transfer excitons on the external quantum efficiency of zinc-porphyrin/C60 heterojunction photovoltaic cells

    Science.gov (United States)

    Ryuzaki, Sou; Kai, Toshihiro; Toda, Yasunori; Adachi, Satoru; Onoe, Jun

    2011-04-01

    We have examined the structural effects of zinc-octaethylporphyrin [Zn(OEP)] films used as a donor on the external quantum efficiency (EQE) of organic heterojunction photovoltaic (OPV) cells [ITO/Zn(OEP)/C60/Al], and investigated what exactly causes the improvement of EQE. When the structure of the Zn(OEP) films changed from amorphous to crystalline, the maximum EQE increased from 36% to 42%, which is greater than that of around 35% for previously reported OPV cells using buffer materials (Peumans and Forrest 2001 Appl. Phys. Lett. 79 126). The crystallization of Zn(OEP) films is found to increase the number of inter-molecular charge-transfer (IMCT) excitons and to enlarge the mobility of carriers and IMCT excitons, thus significantly improving the EQE of the photoabsorption band under illumination due to the IMCT excitons.

  18. Sparfloxacin charge transfer complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and tetracyanoquinodimethane: Molecular structures, spectral, and DFT studies

    Science.gov (United States)

    Shehab, Ola R.; Mansour, Ahmed M.

    2015-08-01

    A simple, sensitive and rapid method was developed for the quantitative analysis of sparfloxacin in its pharmaceutical formulations through the formation of charge transfer complexes with π-acceptor systems. The Lambert-Beer's law was obeyed in the concentration ranges of 7-70 and 10-50 μg/mL sparfloxacin for 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and tetracyanoquinodimethane. Structural characterization of the isolated solid CT complexes was carried out by IR, 1H NMR, UV-Vis. and MS. The experimental studies were complemented by quantum chemical calculations at DFT level of theory. The electronic structures were investigated by TD-DFT calculations. Natural bond orbital analysis and molecular electrostatic potential maps were helpful in assigning the CT route. The formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy and ionization potential were calculated.

  19. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    The step from ab initio atomic and molecular properties to thermodynamic - or macroscopic - properties requires the combination of several theoretical tools. This dissertation presents constant temperature molecular dynamics with bond length constraints, a hybrid quantum mechanics...... show general (or expected) properties. Properties such as in the physical and (semi-)chemical interface between classical and quantum systems and the effects of molecular bond length constraints on the temperature during simulations. As a second step the methodology is applied to the symmetric 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 to...

  20. Gaseous charge transfer reactions of multiply charged ions

    International Nuclear Information System (INIS)

    Doubly charged ions produced in electron impact ionization have received relatively little study due to their low abundance and masking from singly charged ions which are detected at the same mass-to-charge ratio by a mass spectrometer. This interference problem was avoided by exploiting a technique in which doubly charged molecular and fragment ions are monitored using a collisional charge-exchange process where only fast singly charged product ions are allowed to reach the detector. Primary research efforts were to determine structures and energetics of multiply charged ions formed in high energy electron impact ionization processes and their reactivities in ion-molecule charge exchange interactions. Doubly charged ion mass distributions for various chemical classes (including acetylenes, alkenes, terpenes and organophosphorus compounds) were recorded and appearance energies of prominent doubly charged ions were measured. Computer molecular orbital calculations (at the MINDO/3 level) of ionic structures, energies and charge distributions were utilized to augment the analysis of experimental results

  1. Long-range charge transfer in biopolymers

    Science.gov (United States)

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

    2012-11-01

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

  2. Excitation and charge transfer in He+ + H collisions. A molecular approach including two-electron translation factors

    International Nuclear Information System (INIS)

    In a previous paper we have pointed out that the common-translation-factor (CTF) method is the only one which, at present, and within the framework of the molecular model of atomic collisions, can be shown to be both convergent and computationally fast, even for many-electron systems. In this Communication we check that this second statement is correct, presenting, for the first time, a molecular calculation involving two-electron translation factors, for He+ + H collisions. A careful study of the sensitivity of the calculated cross sections to the choice of the CTF is performed, and conclusions on that sensitivity are drawn, for several types of processes

  3. Charge Transfer and Charge Transport on the Double Helix

    OpenAIRE

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

    2003-01-01

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

  4. Frenkel and Charge-Transfer Excitons in Quasi-One-Dimensional Molecular Crystals with Strong Intermolecular Orbital Overlap

    OpenAIRE

    Hoffmann, Michael

    2000-01-01

    We present a theoretical and experimental study on the lowest electronically excited states in quasi-one-dimensional molecular crystals. The specific calculations and the experiments are performed for the model compounds MePTCDI (N-N'-dimethylperylene-3,4:9,10-dicarboximide) and TCDA(3,4:9,10-perylenetetracarboxylic dianhydride). The intermolecular interactions between nearest neighbors are quantum chemically analyzed on the basis of semi-empirical (ZINDO/S) Hartree-Fock calculations and a si...

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

    International Nuclear Information System (INIS)

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

  6. Charge transfer and transport in DNA

    OpenAIRE

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

    1998-01-01

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

  7. 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.

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

    Science.gov (United States)

    Ono, Toshikazu; Sugimoto, Manabu; Hisaeda, Yoshio

    2015-08-01

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

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

    Directory of Open Access Journals (Sweden)

    Mančal T.

    2013-03-01

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

  10. Interfacial charge transfer in nanoscale polymer transistors

    OpenAIRE

    Worne, J. H.; Giridharagopal, R.; Kelly, K. F.; Natelson, D.

    2008-01-01

    Interfacial charge transfer plays an essential role in establishing the relative alignment of the metal Fermi level and the energy bands of organic semiconductors. While the details remain elusive in many systems, this charge transfer has been inferred in a number of photoemission experiments. We present electronic transport measurements in very short channel ($L < 100$ nm) transistors made from poly(3-hexylthiophene) (P3HT). As channel length is reduced, the evolution of the contact resistan...

  11. Symmetric charge transfer cross section of uranium

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

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

    2013-01-01

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

  13. Electrical conduction in organic charge transfer complexes under pressure: A theoretical view

    Science.gov (United States)

    Singh, Yadunath

    2016-05-01

    We propose a theoretical view of temperature dependent electrical conductivity in organic charge transfer complexes and radical ion salts. Understanding of the basic conduction mechanism under high pressure in these systems is our aim. The mechanism is discussed mainly on the basis of molecular orbital overlap theory, role of charge transfer forces and charge density waves etc.

  14. 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.

  15. Intramolecular Charge Transfer States in the Condensed Phase

    Science.gov (United States)

    Williams, C. F.; Herbert, J. M.

    2009-06-01

    Time-Dependent Density Functional Theory (TDDFT) with long range corrected functionals can give accurate results for the energies of electronically excited states involving Intramolecular Charge Transfer (ICT) in large molecules. If this is combined with a Molecular Mechanics (MM) representation of the surrounding solvent this technique can be used to interpret the results of condensed phase UV-Vis Spectroscopy. Often the MM region is represented by a set of point charges, however this means that the solvent cannot repolarize to adapt to the new charge distribution as a result of ICT and so the excitation energies to ICT states are overestimated. To solve this problem an algorithm that interfaces TDDFT with the polarizable force-field AMOEBA is presented; the effect of solvation on charge transfer in species such as 4,4'dimethylaminobenzonitrile (DMABN) is discussed. M.A. Rohrdanz, K.M. Martins, and J.M. Herbert, J. Chem. Phys. 130 034107 (2008).

  16. Measurement of charge-transfer rate coefficients of He2+ with selected atomic and molecular species in high-pressure afterglows

    International Nuclear Information System (INIS)

    High-pressure, volume-dominated glow discharges for use as laser media have gained interest in the past decade as a result of the development of a variety of external ionization and discharge-stabilization techniques. In such systems, charge-transfer processes occur by way of bimolecular and termolecular reaction channels at atmospheric pressure, with the latter gaining in relative importance due to its dependence on gas pressure. Therefore, it is essential to characterize these termolecular reaction rates and recognize the fact that these reactions must be included among all other processes considering in modeling the high-pressure lasers and discharge media. This dissertation reports the measurements of bimolecular and termolecular charge-transfer reactions of He2+ into nonassociative produce channels. In this study, the population of He2+ was monitored as a function of time by detection of the N2+ (B → X) transition at 391.4 nm in high-pressure afterglows of mixed gases excited by a fast electrical-discharge system capable of operation up to 6 atm. From these data, pressure dependent rate coefficients have been extracted and subsequently resolved into contributions from bimolecular and termolecular components for reactions of He2+ with N2, O2, CO2, Ar, and Xe

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

    OpenAIRE

    Bizjak, Tanja

    2004-01-01

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

  18. Tight-binding parameters for charge transfer along DNA

    OpenAIRE

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

    2009-01-01

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

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

    OpenAIRE

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

    2000-01-01

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

  20. Charge Transfer Excitons at van der Waals Interfaces.

    Science.gov (United States)

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

    2015-07-01

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

  1. Tight-binding parameters for charge transfer along DNA

    CERN Document Server

    Hawke, L G D; Simserides, C

    2009-01-01

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

  2. Improved Charge-Transfer Fluorescent Dyes

    Science.gov (United States)

    Meador, Michael

    2005-01-01

    Improved charge-transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combinations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods. These dyes exhibit high fluorescence quantum yields -- ranging from 0.2 to 0.98, depending upon solvents and chemical structures. The wavelengths, quantum yields, intensities, and lifetimes of the fluorescence emitted by these dyes vary with (and, hence, can be used as indicators of) the polarities of solvents in which they are dissolved: In solvents of increasing polarity, fluorescence spectra shift to longer wavelengths, fluorescence quantum yields decrease, and fluorescence lifetimes increase. The wavelengths, quantum yields, intensities, and lifetimes are also expected to be sensitive to viscosities and/or glass-transition temperatures. Some chemical species -- especially amines, amino acids, and metal ions -- quench the fluorescence of these dyes, with consequent reductions in intensities, quantum yields, and lifetimes. As a result, the dyes can be used to detect these species. Another useful characteristic of these dyes is a capability for both two-photon and one-photon absorption. Typically, these dyes absorb single photons in the ultraviolet region of the spectrum (wavelengths dyes can be excited by two-photon absorption at near-infrared wavelengths (600 to 800 nm) to produce fluorescence spectra identical to those obtained in response to excitation by single photons at half the corresponding wavelengths (300 to 400 nm). While many prior fluorescent dyes exhibit high quantum yields, solvent-polarity- dependent fluorescence behavior, susceptibility to quenching by certain chemical species, and/or two-photon fluorescence, none of them has

  3. Assessment of density-functional models for organic molecular semiconductors: The role of Hartree-Fock exchange in charge-transfer processes

    International Nuclear Information System (INIS)

    The optimization of the parameters controlling the migration of holes and electrons in charge-transport processes has recently attracted much attention for the field of organic electronics. A large set of relevant results for molecular design has been largely assisted by computational modeling tools. However, the limit of applicability of approximate computational models, whose paradigm is often referred as density-functional theory (DFT), might soon be reached due to accuracy matters. The large dependence of these parameters on the chosen theoretical method is demonstrated here by systematic application of a large variety of DFT methods. They are found to lead to highly accurate results if and only if a delicate balance between exact-like and approximate DFT exchange effects is achieved; thus, predictions might strongly depend on the nature of the method being applied. This situation is solved by providing a new set of optimized exchange-correlation functionals as a good enough automated approximation for the study and design of new π-conjugated charge-carrier materials

  4. Synthesis and investigation of intra-molecular charge transfer state properties of novel donor-acceptor-donor pyridine derivatives: the effects of temperature and environment on molecular configurations and the origin of delayed fluorescence.

    Science.gov (United States)

    Aydemir, Murat; Haykır, Gülçin; Türksoy, Figen; Gümüş, Selçuk; Dias, Fernando B; Monkman, Andy P

    2015-10-14

    A novel series of donor-acceptor-donor (D-A-D) structured pyridine derivatives were synthesised and detailed photo-physical investigations were made using mainly steady-state and time-resolved spectroscopy techniques at varying temperatures. The investigations showed that the molecules have solvent polarity and temperature dependent excited-state configurations, confirmed in two different polarity solvents (295-90 K), i.e. methyl cyclohexane (MCH) and 2-methyltetrahdrofurane (2-MeTHF). In MCH, the investigations revealed dual fluorescence over the temperature range of 295-90 K. At 295 K, the ground-state configuration of the molecules has a partially twisted geometry as determined by DFT calculation, yet the emission originates totally from a locally excited (LE) state, however once the temperature is lowered to 90 K, the twisted molecular configuration is stabilised, and the emission originates from a fully-relaxed intramolecular charge transfer state (ICT), this is contrary to the systems where structural reorganisation stabilises ICT and this is frozen out at low temperatures. The DFT calculations revealed different ground state molecular configurations due to the presence of different electron-donating groups, e.g. the molecule including anthracene groups has a near 90° twisted geometry whereas the triphenylamine including molecule has a pyramidal geometrical folding, therefore, the decrease in temperature restricts the donor degree of rotational freedom. In 2-MeTHF solution, the fluorescence spectrum of both molecules is always of ICT character, but gradually red-shifts through the fluid to glass transition temperature (∼135 K), in this case, the fluorescence occurs after structural and solvent-shell relaxations, however, upon cooling below 135 K, the spectra dramatically shift back to blue giving rise to strong emission from an ICT excited-state (but not the LE state) where the molecules have unrelaxed geometries. This significant change in the nature of

  5. Charge transfer reactions in nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-07-01

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

  6. Charge transfer processes of low charge state heavy ions

    International Nuclear Information System (INIS)

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

  7. Charge Injection, Charge Trapping and Charge Transfer in Quantum-Dot Solids

    OpenAIRE

    Boehme, S.C.

    2015-01-01

    This study reports on fundamental processes in Quantum-Dot Solids, after light absorption. Transient Absorption and Time-resolved Photoluminescence spectrocopy reveal the dynamics of charge transfer and charge trapping processes. Typically, both occur on a picosecond time scale and compete with each other. We find that the efficiency of these processes depends on the Fermi level in the Quantum-Dot Solid. The latter can be controlled electrochemically, via charge injection into the Quantum-Dot...

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

    OpenAIRE

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

    2003-01-01

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

  9. Charge Redistribution and Transport in Molecular Contacts

    Science.gov (United States)

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

    2015-09-01

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

  10. Understanding charge transport in molecular electronics.

    Science.gov (United States)

    Kushmerick, J J; Pollack, S K; Yang, J C; Naciri, J; Holt, D B; Ratner, M A; Shashidhar, R

    2003-12-01

    For molecular electronics to become a viable technology the factors that control charge transport across a metal-molecule-metal junction need to be elucidated. We use an experimentally simple crossed-wire tunnel junction to interrogate how factors such as metal-molecule coupling, molecular structure, and the choice of metal electrode influence the current-voltage characteristics of a molecular junction. PMID:14976024

  11. Coronene-based charge-transfer complexes.

    Science.gov (United States)

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

    2016-08-01

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

  12. Photoinduced charge-transfer materials for nonlinear optical applications

    Science.gov (United States)

    McBranch, Duncan W.

    2006-10-24

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

  13. A charge-driven molecular water pump.

    Science.gov (United States)

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

    2007-11-01

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

  14. Fluctuation spectroscopy in organic charge transfer salts

    International Nuclear Information System (INIS)

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

  15. The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures.

    Science.gov (United States)

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Liangbo; West, Damien; Meunier, Vincent; Zhang, Shengbai

    2016-01-01

    The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs. PMID:27160484

  16. The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

    Science.gov (United States)

    Wang, Han; Bang, Junhyeok; Sun, Yiyang; Liang, Liangbo; West, Damien; Meunier, Vincent; Zhang, Shengbai

    2016-05-01

    The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.

  17. Charge transfer reaction laser with preionization means

    Science.gov (United States)

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

    1978-01-01

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

  18. 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...

  19. Mechanism of Charge Transfer from Plasmonic Nanostructures to Chemically Attached Materials.

    Science.gov (United States)

    Boerigter, Calvin; Aslam, Umar; Linic, Suljo

    2016-06-28

    Plasmonic metal nanoparticles can efficiently convert the energy of visible photons into the energy of hot charge carriers within the nanoparticles. These energetic charge carriers can transfer to molecules or semiconductors, chemically attached to the nanoparticles, where they can induce photochemical transformations. Classical models of photoinduced charge excitation and transfer in metals suggest that the majority of the energetic charge carriers rapidly decay within the metal nanostructure before they are transferred into the neighboring molecule or semiconductor, and therefore, the efficiency of charge transfer is low. Herein, we present experimental evidence that calls into question this conventional picture. We demonstrate a system where the presence of a molecule, adsorbed on the surface of a plasmonic nanoparticle, significantly changes the flow of charge within the excited plasmonic system. The nanoparticle-adsorbate system experiences high rates of direct, resonant flow of charge from the nanoparticle to the molecule, bypassing the conventional charge excitation and thermalization process taking place in the nanoparticle. This picture of charge transfer suggests that the yield of extracted hot electrons (or holes) from plasmonic nanoparticles can be significantly higher than the yields expected based on conventional models. We discuss a conceptual physical framework that allows us to explain our experimental observations. This analysis points us in a direction toward molecular control of the charge transfer process using interface and local field engineering strategies. PMID:27268233

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

    OpenAIRE

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

    2011-01-01

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

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

    International Nuclear Information System (INIS)

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

  2. Exceptional photosensitivity of a polyoxometalate-based charge-transfer hybrid material.

    Science.gov (United States)

    Liao, Jian-Zhen; Wu, Chen; Wu, Xiao-Yuan; Deng, Shui-Quan; Lu, Can-Zhong

    2016-05-31

    An unusual room-temperature light sensitivity was realized in a polyoxometalate-based hybrid material due to cooperative multicomponent molecular charge-transfer interactions taking place in this material, mainly among POMs, NDIs, and other molecules. The functional π-acidic NDI linkers and POM clusters in the discussed hybrid material were individually designed as photosensors and electron reservoirs. To propose a photo-induced charge-transfer mechanism, EPR, XPS, UV-Vis and computational studies were carried out, and indicated the presence of active charge-transfer interactions among several of the components. PMID:27192943

  3. Metal-Organic Coordination Number Determined Charge Transfer Magnitude

    Science.gov (United States)

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

    2014-03-01

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

  4. Charge-transfer excitons in DNA.

    Science.gov (United States)

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

    2008-02-21

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

  5. Effects of the charge-transfer reorganization energy on the open-circuit voltage in small-molecular bilayer organic photovoltaic devices: comparison of the influence of deposition rates of the donor.

    Science.gov (United States)

    Lee, Chih-Chien; Su, Wei-Cheng; Chang, Wen-Chang

    2016-05-14

    The theoretical maximum of open-circuit voltage (VOC) of organic photovoltaic (OPV) devices has yet to be determined, and its origin remains debated. Here, we demonstrate that VOC of small-molecule OPV devices can be improved by controlling the deposition rate of a donor without changing the interfacial energy gap at the donor/acceptor interface. The measurement of external quantum efficiency and electroluminescence spectra facilitates the observation of the existence of charge transfer (CT) states. A simplified approach by reusing the reciprocity relationship for obtaining the properties of the CT states is proposed without introducing complex techniques. We compare experimental and fitting results and propose that reorganization energy is the primary factor in determining VOC instead of either the CT energy or electronic coupling term in bilayer OPV devices. Atomic force microscopy images indicate a weak molecular aggregation when a higher deposition rate is used. The results of temperature-dependent measurements suggest the importance of molecular stacking for the CT properties. PMID:27095179

  6. Second order Born calculation for charge transfer

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  8. Atomic Pt and molecular H2O adsorptions on SrTiO3 with and without Nb-doping: Electron trapping center and mediating roles of Pt in charge transfer from semiconductor to water

    International Nuclear Information System (INIS)

    H2O adsorption on SrO-terminated SrTiO3 (0 0 1) surface has been investigated with the first-principles calculation based on DFT. An energy barrier of 0.221 eV for H2O dissociation is obtained, which illustrates a spontaneous dissociation. H and O atoms on the SrO-termination of (0 0 1) surface recombine readily. It demonstrates that Pt induces surface dipole moment and changes the surface work function. Adsorption of atomic Pt on SrO-termination of Nb-doped SrTiO3 (0 0 1) surface indicates charge transfer from the surface to Pt, i.e., Pt is negatively charged. Fukui functions illustrate the role Pt played in mediating charge transfer from (0 0 1) surface to targets adsorbed on Pt. H2O adsorption on the Pt atom supported on Nb-doped SrTiO3 confirms the charge transfer from semiconductor containing electrons to target species, which is mediated by metal. Charge transfer from negatively charged Pt to H2O weakens (activates) the H–O bonds in molecule H2O. - Graphical abstract: Pt mediates the charge transfer from SrTiO3 to H2O and can improve the efficiency of photocatalytic water splitting. Highlights: ► Pt atom is adsorbed over an O atom on the SrTiO3 (0 0 1) surface. ► H2O is dissociatively adsorbed on the surface; and H and O readily recombine as OH. ► Pt plays as electron trapping center on SrTiO3 (0 0 1) surface. Pt mediates the charge transfer from electron-doped SrTiO3 to H2O. ► Photogenerated carriers can be effectively separated due to deposited Pt.

  9. Ion momentum and energy transfer rates for charge exchange collisions

    Science.gov (United States)

    Horwitz, J.; Banks, P. M.

    1973-01-01

    The rates of momentum and energy transfer have been obtained for charge exchange collisions between ion and neutral gases having arbitrary Maxwellian temperatures and bulk transport velocities. The results are directly applicable to the F-region of the ionosphere where 0+ - 0 charge is the dominant mechanism affecting ion momentum and energy transfer.

  10. Preparation and characterization of three charge-transfer complexes

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-03-15

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

  11. Polarization and charge transfer in the hydration of chloride ions

    International Nuclear Information System (INIS)

    A theoretical study of the structural and electronic properties of the chloride ion and water molecules in the first hydration shell is presented. The calculations are performed on an ensemble of configurations obtained from molecular dynamics simulations of a single chloride ion in bulk water. The simulations utilize the polarizable AMOEBA force field for trajectory generation and MP2-level calculations are performed to examine the electronic structure properties of the ions and surrounding waters in the external field of more distant waters. The ChelpG method is employed to explore the effective charges and dipoles on the chloride ions and first-shell waters. The quantum theory of atoms in molecules (QTAIM) is further utilized to examine charge transfer from the anion to surrounding water molecules. The clusters extracted from the AMOEBA simulations exhibit high probabilities of anisotropic solvation for chloride ions in bulk water. From the QTAIM analysis, 0.2 elementary charges are transferred from the ion to the first-shell water molecules. The default AMOEBA model overestimates the average dipole moment magnitude of the ion compared to the quantum mechanical value. The average magnitude of the dipole moment of the water molecules in the first shell treated at the MP2-level, with the more distant waters handled with an AMOEBA effective charge model, is 2.67 D. This value is close to the AMOEBA result for first-shell waters (2.72 D) and is slightly reduced from the bulk AMOEBA value (2.78 D). The magnitude of the dipole moment of the water molecules in the first solvation shell is most strongly affected by the local water-water interactions and hydrogen bonds with the second solvation shell, rather than by interactions with the ion.

  12. Polarization and charge transfer in the hydration of chloride ions

    Science.gov (United States)

    Zhao, Zhen; Rogers, David M.; Beck, Thomas L.

    2010-01-01

    A theoretical study of the structural and electronic properties of the chloride ion and water molecules in the first hydration shell is presented. The calculations are performed on an ensemble of configurations obtained from molecular dynamics simulations of a single chloride ion in bulk water. The simulations utilize the polarizable AMOEBA force field for trajectory generation and MP2-level calculations are performed to examine the electronic structure properties of the ions and surrounding waters in the external field of more distant waters. The ChelpG method is employed to explore the effective charges and dipoles on the chloride ions and first-shell waters. The quantum theory of atoms in molecules (QTAIM) is further utilized to examine charge transfer from the anion to surrounding water molecules. The clusters extracted from the AMOEBA simulations exhibit high probabilities of anisotropic solvation for chloride ions in bulk water. From the QTAIM analysis, 0.2 elementary charges are transferred from the ion to the first-shell water molecules. The default AMOEBA model overestimates the average dipole moment magnitude of the ion compared to the quantum mechanical value. The average magnitude of the dipole moment of the water molecules in the first shell treated at the MP2-level, with the more distant waters handled with an AMOEBA effective charge model, is 2.67 D. This value is close to the AMOEBA result for first-shell waters (2.72 D) and is slightly reduced from the bulk AMOEBA value (2.78 D). The magnitude of the dipole moment of the water molecules in the first solvation shell is most strongly affected by the local water-water interactions and hydrogen bonds with the second solvation shell, rather than by interactions with the ion.

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

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    Dulal C. Ghosh

    2004-09-01

    Full Text Available The formation of the F3B–NH3 supermolecule by chemical interaction of its fragment parts, BF3 and NH3, and the dynamics of internal rotation about the ‘B–N’ bond have been studied in terms of parameters provided by the molecular orbital and density functional theories. It is found that the pairs of frontier orbitals of the interacting fragments have matching symmetry and are involved in the charge transfer interaction. The donation process stems from the HOMO of the donor into the LUMO of the acceptor and simultaneously, back donation stems from the HOMO of acceptor into the LUMO of the donor. The density functional computation of chemical activation in the donor and acceptor fragments, associated with the physical process of structural reorganization just prior to the event of chemical reaction, indicates that BF3 becomes more acidic and NH3 becomes more basic, compared to their separate equilibrium states. Theoretically it is observed that the chemical reaction event of the formation of the supermolecule from its fragment parts is in accordance with the chemical potential equalization principle of the density functional theory and the electronegativity equalization principle of Sanderson. The energetics of the chemical reaction, the magnitude of the net charge transfer and the energy of the newly formed bond are quite consistent, both internally and with the principle of maximum hardness, PMH. The dynamics of the internal rotation of one part with respect to the other part of the supermolecule about the ‘B–N’ bond mimics the pattern of the conformational isomerism of the isostructural ethane molecule. It is also observed that the dynamics and evolution of molecular conformations as a function of dihedral angles is also in accordance with the principle of maximum hardness, PMH. Quite consistent with spectroscopic predictions, the height of the molecule

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

    Institute of Scientific and Technical Information of China (English)

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

    2003-01-01

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

  16. Charge Transfer Based Colorimetric Detection of Silver Ion

    International Nuclear Information System (INIS)

    We have demonstrated the colorimetric chemosensor for detection of Ag+ 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; MV2+) moiety of a single sensor molecule. Under irradiation of light, Ag+ was reduced to very small silver nanoparticle by CT interaction in the presence of OEGs as flexible recognition moiety of Ag+ 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

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

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

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

    2011-01-01

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

  19. Magnetic ordering in fullerene charge-transfer complexes

    Science.gov (United States)

    Sato, Tohru; Yamabe, Tokio; Tanaka, Kazuyoshi

    1997-07-01

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

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

    Science.gov (United States)

    Edirisinghe, Neranjan; Apalkov, Vadym

    2010-03-01

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

  1. 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.

  2. On the Possibility of Superfast Charge Transfer in DNA

    OpenAIRE

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

    2013-01-01

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

  3. 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.)

  4. Controlled transfer of single charge carriers

    International Nuclear Information System (INIS)

    This paper reports on the design and operation of two devices, the turnstile and the pump, that transfer electrons one by one. They are both based on the existence of stable electrostatic configurations in arrays of ultrasmall tunnel junctions. While the turnstile only works in the normal state the pump could in principle achieve the transfer of single Cooper pairs

  5. A molecularly based theory for electron transfer reorganization energy

    International Nuclear Information System (INIS)

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

  6. Charge transfer induced activity of graphene for oxygen reduction

    Science.gov (United States)

    Shen, Anli; Xia, Weijun; Zhang, Lipeng; Dou, Shuo; Xia, Zhenhai; Wang, Shuangyin

    2016-05-01

    Tetracyanoethylene (TCNE), with its strong electron-accepting ability, was used to dope graphene as a metal-free electrocatalyst for the oxygen reduction reaction (ORR). The charge transfer process was observed from graphene to TCNE by x-ray photoelectron spectroscopy and Raman characterizations. Our density functional theory calculations found that the charge transfer behavior led to an enhancement of the electrocatalytic activity for the ORR.

  7. A Monte Carlo study of charge transfer in DNA

    OpenAIRE

    Jakobsson, Mattias; Stafström, Sven

    2008-01-01

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

  8. Charge transfer energies of tetraphenyl-porphyrin-fullerene dyads

    Science.gov (United States)

    Zope, Rajendra; Olguin, Marco; Baruah, Tunna

    2011-03-01

    Porphyrin-fullerene dyads are extensively studied for their photoinduced charge transfer properties. They form a donor-acceptor pair where the fullerene is the acceptor. Accurate theoretical estimate of the charge transfer energies in such systems has proven to be a challenge. In this study we examine the charge transfer energetics for such dyads using our recently developed density functional based excited state method which can yield reliable estimates of charge transfer energetics. In this study the effect of varying both the donor and acceptor components are studied by changing the tetra-phenyl-porphyrin (TPP) to Zn-TPP. Similarly the acceptor component is changed from C60 to C70. The structures were optimized using DFT-D3 theory at the all-electron level. Among the donor-acceptor pairs studied, we find that the ZnTPP-C60 has the lowest charge transfer energy (1.69 eV) and the TPP-C70 (2.13 eV) has the highest charge transfer energy. Supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences of the US Department of Energy through grant DE-SC0002168.

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

    Science.gov (United States)

    Omori, Yukiko; Tsuchiizu, Masahisa; Suzumura, Yoshikazu

    2011-02-01

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

  10. Molecular polarizabilities in aqueous proton transfer reactions

    International Nuclear Information System (INIS)

    Dipole polarizabilities of individual ions and molecules are computed from first principles in three condensed-phase systems: pure water, pure hydrofluoric acid, and an equimolar mixture of water and hydrofluoric acid in which HF is mostly ionized. We find that the polarizability of fluorine and oxygen centers varies linearly with the value of the bond order, which measures the local degree of advancement of the ionization reaction F-H+H2O[Fδ-·H·δ+OH2]F-+H3O+. This observation explains the validity of the Lorentz-Lorenz formula for mixtures of acids and water and could have important practical consequences concerning the construction of empirical polarizable reactive force fields. Our results are consistent with the Mulliken charge-transfer picture of proton transfer reactions. The present results also suggest that the average isotropic polarizability of a chemical entity changes substantially only when that entity is involved in charge-transfer processes.

  11. INTRAMOLECULAR CHARGE AND ENERGY TRANSFER IN MULTICHROMOPHORIC AROMATIC SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Edward C. Lim

    2008-09-09

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

  12. Theoretical treatment of charge transfer processes of relevance to astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Krstic, P.S.; Stancil, P.C.; Schultz, D.R.

    1997-12-01

    Charge transfer is an important process in many astrophysical and atmospheric environments. While numerous experimental and theoretical studies exist for H and He targets, data on other targets, particularly metals and molecules, are sparse. Using a variety of theoretical methods and computational techniques the authors are developing methods to estimate the cross sections for electron capture (charge transfer) in slow collisions of low charge state ions with heavy (Mg, Ca, Fe, Co, Ni and Zn) neutrals. In this ongoing work particular attention is paid to ascertaining the importance of double electron capture.

  13. 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.

  14. Unified description of charge transfer mechanisms and vibronic dynamics in nanoscale junctions

    OpenAIRE

    Avriller, R.

    2010-01-01

    We propose a general framework that unifies the point of view of counting statistics of transmitted (fermionic) charges as it is commonly used in the quantum transport community to the point of view of counting statics of phonons (bosons) as it is known from the field of quantum optics. As a particular example, we study on the same footing the counting statistics of electrons transfered through a molecular junction and the corresponding population dynamics of the associated molecular vibratio...

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

    Science.gov (United States)

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

    2015-10-01

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

  16. 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.

  17. 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...

  18. Light-Induced Charge Separation and Transfer in Bacteriorhodopsin

    Institute of Scientific and Technical Information of China (English)

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

    2000-01-01

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

  19. Satellite structure in laser-assisted charge-transfer cross sections

    International Nuclear Information System (INIS)

    A six-state coupled-channel calculation has been performed on the laser-assisted charge-transfer collision H++Na+hω. A greatly enhanced charge-transfer cross section is observed for low-energy collisions if the photon energy is matched to the classical satellite frequency. This frequency is determined by the location of an extremum in the difference of potential energies between the laser-pumped initial and final molecular states. The stationary-phase method has been used to reproduce the general features and the magnitude of the cross-section structure

  20. DFT and TD-DFT computation of charge transfer complex between o-phenylenediamine and 3,5-dinitrosalicylic acid

    Science.gov (United States)

    Afroz, Ziya; Alam, Mohammad Jane; Zulkarnain, Faizan, Mohd.; Ahmad, Afaq; Ahmad, Shabbir

    2016-05-01

    DFT and TD-DFT studies of o-phenylenediamine (PDA), 3,5-dinitrosalicylic acid (DNSA) and their charge transfer complex have been carried out at B3LYP/6-311G(d,p) level of theory. Molecular geometry and various other molecular properties like natural atomic charges, ionization potential, electron affinity, band gap, natural bond orbital (NBO) and frontier molecular analysis have been presented at same level of theory. Frontier molecular orbital and natural bond orbital analysis show the charge delocalization from PDA to DNSA.

  1. 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...

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

    Science.gov (United States)

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

    2013-03-01

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

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

    International Nuclear Information System (INIS)

    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

  4. On charge transfer in ion-atom collisions at intermediate collision velocities

    International Nuclear Information System (INIS)

    The authors study charge transfer at intermediate energies for multielectron ion-atom collisions within the coupled-state impact-parameter method. They point out the importance of assumptions about electronic relaxation by comparing various calculations of cross sections for KK charge transfer in F9+ + Si as a test case. In these calculations, either the unrelaxed Hamiltonian of the atomic model or a relaxed molecular Hamiltonian has been employed, and two-state atomic or molecular basis sets have been used. To correct for the inadequacy of atomic orbitals for close collisions at intermediate energies, the authors propose to add orbitals of the united atom at the two collision centers. With such an atomic basis set, quasimolecular behavior of the system is represented sufficiently well. The authors report on results for the collision system H+ + He+ for which calculations with large molecular and atomic basis sets exist

  5. Multiple-charge transfer and trapping in DNA dimers

    Science.gov (United States)

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

    2010-11-01

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

  6. 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.

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

    Science.gov (United States)

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

    2007-11-01

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

  8. The theoretical study of charge transfer through damaged DNA duplexes

    Czech Academy of Sciences Publication Activity Database

    Šebera, Jakub; Humpolíčková, Jana; Hof, Martin; Kratochvílová, Irena; Páv, Ondřej; Rosenberg, Ivan; Nencka, Radim; Tanaka, Y.; Sychrovský, Vladimír

    Nagybörzsöny : -, 2014. [CESTC 2014. Central European Symposium on Theoretical Chemistry. 21.09.2014-25.09.2014, Nagybörzsöny] R&D Projects: GA ČR GA13-27676S Institutional support: RVO:61388963 ; RVO:61388955 ; RVO:68378271 Keywords : charge transfer * 8-oxoguanine * fluorescence spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry

  9. Enhancing SERS by Means of Supramolecular Charge Transfer

    Science.gov (United States)

    Wong, Eric; Flood, Amar; Morales, Alfredo

    2009-01-01

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

  10. CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Khalil, Munira

    2014-06-27

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

  11. Positron Annihilation in Solid Charge-Transfer Complexes

    DEFF Research Database (Denmark)

    Lévay, B.; Jansen, P.

    1979-01-01

    Positron lifetime and angular correlation measurements have been carried out on 1:1 charge-transfer complexes, on their pure donor and acceptor components and on the 1:1 M mechanical mixtures of these components. Complex formation reduced the intensity of the long-lifetime component of the donor ...

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

    Science.gov (United States)

    Mazinani, Shobeir Khezr Seddigh

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

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

    Science.gov (United States)

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

    2013-09-11

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

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

    CERN Document Server

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

    2013-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

    李铁成; 刘春华; 屈一至; 刘玲; 吴勇; 王建国

    2015-01-01

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

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

    Science.gov (United States)

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

    2015-07-01

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

  17. Coarse-Grained Theory of Biological Charge Transfer with Spatially and Temporally Correlated Noise.

    Science.gov (United States)

    Liu, Chaoren; Beratan, David N; Zhang, Peng

    2016-04-21

    System-environment interactions are essential in determining charge-transfer (CT) rates and mechanisms. We developed a computationally accessible method, suitable to simulate CT in flexible molecules (i.e., DNA) with hundreds of sites, where the system-environment interactions are explicitly treated with numerical noise modeling of time-dependent site energies and couplings. The properties of the noise are tunable, providing us a flexible tool to investigate the detailed effects of correlated thermal fluctuations on CT mechanisms. The noise is parametrizable by molecular simulation and quantum calculation results of specific molecular systems, giving us better molecular resolution in simulating the system-environment interactions than sampling fluctuations from generic spectral density functions. The spatially correlated thermal fluctuations among different sites are naturally built-in in our method but are not readily incorporated using approximate spectral densities. Our method has quantitative accuracy in systems with small redox potential differences (charge delocalization and charge-transfer rates; however, in a system of units with different site energies, spatial correlations slow the fluctuations to bring units into degeneracy, in turn, slowing the charge-transfer rates. The spatial and temporal correlations of condensed phase medium fluctuations provide another source to control and tune the kinetics and dynamics of charge-transfer systems. PMID:27008541

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

    Science.gov (United States)

    Liu, Xiaoyan; Liu, Yujuan; Zheng, Yujun

    2016-02-01

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

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

    Science.gov (United States)

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

    2012-09-14

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

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

    International Nuclear Information System (INIS)

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

  1. Localized state and charge transfer in nitrogen-doped graphene

    OpenAIRE

    Joucken, Frederic; Tison, Yann; Lagoute, Jerome; Dumont, Jacques; Cabosart, Damien; Zheng, Bing; Repain, Vincent; Chacon, Cyril; Girard, Yann; Botello-Mendez, Andres Rafael; Rousset, Sylvie; Sporken, Robert; Charlier, Jean-Christophe; Henrard, Luc

    2012-01-01

    Nitrogen-doped epitaxial graphene grown on SiC(000?1) was prepared by exposing the surface to an atomic nitrogen flux. Using Scanning Tunneling Microscopy (STM) and Spectroscopy (STS), supported by Density Functional Theory (DFT) calculations, the simple substitution of carbon by nitrogen atoms has been identifi?ed as the most common doping con?guration. High-resolution images reveal a reduction of local charge density on top of the nitrogen atoms, indicating a charge transfer to the neighbor...

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

    Energy Technology Data Exchange (ETDEWEB)

    Gust, D.; Moore, T.A.

    1985-05-01

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

  3. Charge transfer efficiency improvement of a 4-T pixel by the optimization of electrical potential distribution under the transfer gate

    International Nuclear Information System (INIS)

    The charge transfer efficiency improvement method is introduced by optimizing the electrical potential distribution under the transfer gate along the charge transfer path. A non-uniform doped transfer transistor channel is introduced to provide an ascending electrical potential gradient in the transfer transistor channel. With the adjustments to the overlap length between the R1 region and the transfer gate, the doping dose of the R1 region, and the overlap length between the anti-punch-through (APT) implantations and transfer gate, the potential barrier and potential pocket in the connecting region of transfer transistor channel and the pinned photodiode (PPD) are reduced to improve the electrical potential connection. The simulation results show that the percentage of residual charges to total charges drops from 1/104 to 1/107, and the transfer time is reduced from 500 to 110 ns. This means the charge transfer efficiency is improved. (semiconductor devices)

  4. Molecular dynamics simulation of a charged biological membrane

    NARCIS (Netherlands)

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

    1996-01-01

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

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

    Science.gov (United States)

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

    2009-10-22

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

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

    Science.gov (United States)

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

    2009-09-01

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

  7. 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)

  8. Negative ion-uranium hexafluoride charge transfer reactions

    Science.gov (United States)

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

    1980-10-01

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

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

    OpenAIRE

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

    2015-01-01

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

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

    International Nuclear Information System (INIS)

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

  11. Interfacial Charge Transfer States in Condensed Phase Systems.

    Science.gov (United States)

    Vandewal, Koen

    2016-05-27

    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. PMID:26980308

  12. Effect of bridge on energy transfer and photoinduced charge separation in perylene-diimide-naphthalene-bisimide-hexathiophene based donor-bridge-acceptor triads

    Directory of Open Access Journals (Sweden)

    Tilley T.D.

    2013-03-01

    Full Text Available Femtosecond transient absorption spectroscopy is performed to assess bridge effects on energy transfer and charge separation in molecular junctions. A short, conjugated bridge can facilitate charge separation from both donor and acceptor, whereas in longer bridges charge separation only occurs from the excited donor.

  13. Unified description of charge transfer mechanisms and vibronic dynamics in nanoscale junctions.

    Science.gov (United States)

    Avriller, R

    2011-03-16

    We propose a general framework that unifies the description of counting statistics of transmitted (fermionic) charges as it is commonly used in the quantum transport community with the description of counting statistics of phonons (bosons). As a particular example, we study on the same footing the counting statistics of electrons transferred through a molecular junction and the corresponding population dynamics of the associated molecular vibrational mode. In the tunnel limit, non-perturbative results in the electron-phonon interaction are derived that unify complementary approaches based on rate equations or on the use of non-equilibrium Green functions. PMID:21335641

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

    CERN Document Server

    Kilgour, Michael

    2015-01-01

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

  15. Dynamics of the excited state intramolecular charge transfer

    International Nuclear Information System (INIS)

    -normal functions, each corresponding to the fluorescence from the LE state and ICT state. Relative populations and the average frequency of the ICT state are shown in Fig.2 and Fig.3, which represents the ICT dynamics and the subsequent solvation process, respectively. The TRF spectra illustrate unambiguously how the ICT and the solvation processes take place for laurdan dissolved in ethanol. First of all, the ICT and the solvation occur in serial. Second, the ICT proceeds in several time scales exhibiting heterogeneity of the molecular conformation in liquid. About one third of the laurdan molecules undergoes ICT immediately in much less than <50 fs time scale. Rest of them undergoes ICT by two time constants, 6.4 ps and 28 ps. The ICT state then undergoes solvation process by 47 ps time constants. Because the molecule is large and flexible, fast inertial component was not observed. In conclusion, TRF spectra in femtosecond resolution reveal detailed intramolecular charge transfer process of laurdan. The ICT process shows a series of time scales due to the conformational heterogeneity in solution. (authors)

  16. Charge redistribution and transport in molecular contacts

    Czech Academy of Sciences Publication Activity Database

    Corso, A.; Ondráček, Martin; Lotze, C.; Hapala, Prokop; Franke, K.J.; Jelínek, Pavel; Pascual, I.

    2015-01-01

    Roč. 115, č. 13 (2015), "136101-1"-"136101-5". ISSN 0031-9007 R&D Projects: GA ČR(CZ) GA14-02079S Grant ostatní: AV ČR(CZ) M100101207 Institutional support: RVO:68378271 Keywords : AFM * molecular transport * STM * DFT * molecular junction * tunneling Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.512, year: 2014

  17. Charge transfer along DNA dimers, trimers and polymers

    CERN Document Server

    Simserides, Constantinos

    2013-01-01

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

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

    Science.gov (United States)

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

    2011-06-01

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

  19. Charge Transport Phenomena in Peptide Molecular Junctions

    International Nuclear Information System (INIS)

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

  20. Charge Transport Phenomena in Peptide Molecular Junctions

    Directory of Open Access Journals (Sweden)

    Alessandra Luchini

    2008-01-01

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

  1. 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.

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

    Institute of Scientific and Technical Information of China (English)

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

    2009-01-01

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

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

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

    2013-07-01

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-28

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

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

    Science.gov (United States)

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

    2015-12-01

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

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

    Science.gov (United States)

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

    2013-03-26

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

  9. Geometric rearrangement of adsorbate driven by the charge transfer

    Energy Technology Data Exchange (ETDEWEB)

    Pavlyukh, Yaroslav; Berakdar, Jamal [Institut fuer Physik, Martin-Luther-Universitaet Halle-Wittenberg, Halle (Germany); Huebner, Wolfgang [Department of Physics and Research Center OPTIMAS, Kaiserslautern University of Technology (Germany)

    2010-05-15

    Adsorption of alkali atoms induces a significant charge redistribution in the region around the adatom. Such charge displacement is associated with a large dipole moment responsible for the interaction of adatoms and a reduction of the surface work function. In addition to these well-known effects our first principles simulations for the Na{sub 9}{sup +} cluster on the Cu(001) surface demonstrate how the charge transfer (CT) from the adsorbate to the substrate can drastically change the geometric structure of the cluster. We report on a detailed study of the adsorption process using quantum chemistry. A representation of the substrate by a cluster of 54 Cu atoms allows us to treat quantum mechanically the electronic structure of both systems, the adsorbate and the surface, on equal footing. Subsequently, we analyze the charge distribution in the composite system. Convergence of the results is verified by considering a much larger substrate cluster containing 126 Cu atoms. The role of the CT is further elucidated by the geometry optimization of the bare cluster with and without an electron deficit. It is shown that the CT drives the system to a meta-stable state which thereafter relaxes to a new configuration. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  10. Tunable charge transfer properties in metal-phthalocyanine heterojunctions

    Science.gov (United States)

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

    2016-04-01

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

  11. Molecular Transfer Printing Using Block Copolymers

    Science.gov (United States)

    Ji, Shengxiang; Liu, Chi-Chun; Liu, Guoliang; Nealey, Paul

    2009-03-01

    We report a new parallel patterning technique, molecular transfer printing (MTP), for replicating geometrically complex patterns over macroscopic areas with sub-15 nm feature dimensions, and the ability to replicate the same pattern multiple times. In MTP, inks are mixed with block copolymers (BCPs) and deposited as films on a substrate. The inks are compatible with only one block of the BCP, and sequestered into domains of nanometer scale dimensions after microphase separation. A second substrate is then placed in contact with the surface of the film. By designing the inks to react, adsorb, or otherwise interact with the second substrate, inks are transferred to the second substrate in the exact pattern of domains present at the surface of the ``master'' BCP film. Here we demonstrate high degrees of perfection on both line and dot patterns. We also show that 1) the master template can be regenerated, 2) the resultant replica can be used to direct the assembly of BCPs and as a daughter master for MTP, and 3) the master and daughter templates can be reused tens of times.

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

    Science.gov (United States)

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

    1981-10-01

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2015-04-10

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

  15. Atomic, molecular, and optical physics charged particles

    CERN Document Server

    Dunning, F B

    1995-01-01

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

  16. Excitons with charge transfer in sncl2-phthalocyanine films

    OpenAIRE

    Vertsimakha, Ya. I.; Lutsyk, P. M.

    2014-01-01

    The absorption, modulated photoreflectance, and photovoltage spectra of dichlorotin phthalocyanine (SnCl2Pc) films have been measured. These films are thermally deposited in vacuum at different substrate temperatures. The energies of charge-transfer-states (CT-states) in SnCl2Pc films (1.35, 1.52, and 2.05 eV) and the diffusion length of Frenkel excitons (130+/-30 nm) have been determined. The photosensitivity of SnCl2Pc films is comparable to that of n-type perylene derivative (MPP) layers a...

  17. Charge transfer between epitaxial graphene and silicon carbide

    OpenAIRE

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

    2010-01-01

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

  18. Optics of Chromites and Charge-Transfer Transitions

    OpenAIRE

    Andrei V. Zenkov

    2008-01-01

    Specific features of the charge-transfer (CT) states and O2p→Cr3d transitions in the octahedral (CrO6)9− 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 experi...

  19. Theoretical and experimental study of charge transfer through DNA: Impact of mercury mediated T-Hg-T base pair

    Czech Academy of Sciences Publication Activity Database

    Kratochvílová, Irena; Vala, M.; Weiter, M.; Páv, Ondřej; Šebera, Jakub; Sychrovský, Vladimír

    2015-01-01

    Roč. 22, č. 1 (2015), s. 20. ISSN 1211-5894. [Discussions in Structural Molecular Biology . Annual Meeting of the Czech Society for Structural Biology /13./. 19.03.2015-21.03.2015, Nové Hrady] Institutional support: RVO:61388963 ; RVO:68378271 Keywords : charge transfer * T-Hg-T * steady-state fluorescence Subject RIV: CF - Physical ; Theoretical Chemistry

  20. A Simple Index for Characterizing Charge Transport in Molecular Materials.

    Science.gov (United States)

    Jackson, Nicholas E; Savoie, Brett M; Chen, Lin X; Ratner, Mark A

    2015-03-19

    While advances in quantum chemistry have rendered the accurate prediction of band alignment relatively straightforward, the ability to forecast a noncrystalline, multimolecule system's conductivity possesses no simple computational form. Adapting the theory of classical resistor networks, we develop an index for quantifying charge transport in bulk molecular materials, without the requirement of crystallinity. The basic behavior of this index is illustrated through its application to simple lattices and clusters of common organic photovoltaic molecules, where it is shown to reproduce experimentally known performances for these materials. This development provides a quantitative computational means for determining a priori the bulk charge transport properties of molecular materials. PMID:26262862

  1. 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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-07-14

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

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

    Science.gov (United States)

    Kilgour, Michael; Segal, Dvira

    2015-07-01

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

  5. Dynamical Theory of Charge Transfer Between Complex Atoms and Surfaces

    Science.gov (United States)

    Chaudhuri, Basudev; Marston, Brad

    2000-03-01

    An existing dynamical quantum many-body theory of charge transfer(A. V. Onufriev and J. B. Marston, Phys. Rev. B 53), 13340 (1996); J. Merino and J. B. Marston, Phys. Rev. B 58, 6982 (1998). describes atoms with simple s-orbitals, such as alkalis and alkaline-earths, interacting with metal surfaces. The many-body equations of motion (EOM) are developed systematically as an expansion in the number of surface particle-hole excitations. Here we generalize this theory to describe atoms with richer orbital structures, such as atomic oxygen. In the simplest version of the model, only the single-particle p_z-orbitals of the atom, the ones oriented perpendicular to the surface, participate directly in resonant charge transfer as they have the largest overlap with the metallic wavefunctions. However, as the several-electron Russell-Saunders eigenstates, labeled by total angular momenta quantum numbers J, L, and S, are built out of products of single-particle orbitals, non-trivial matrix elements must be incorporated into the many-body EOM's. Comparison to recent experimental results(A. C. Lavery, C. E. Sosolik, and B. H. Cooper, Nucl. Instrum. Meth. B 157), 42 (1999); A. C. Lavery et al. to appear in Phys. Rev. B. on the scattering of low-energy oxygen ions off Cu(001) surfaces is made.

  6. Organic molecules at metal surfaces: the role of functional groups in self-assembly and charge transfer

    OpenAIRE

    Dell'Angela, Martina

    2009-01-01

    The understanding of the interaction of organic molecules with metal surfaces is crucial for tailoring the desired properties of future devices that can be employed for molecular electronics or biomedical applications. Self-assembly of complex supramolecular structures and charge transfer through molecular films or even through single molecules are some of the properties that have recently attracted much interest both for possible applications and for more fundamental studie...

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

    KAUST Repository

    El-Ballouli, Ala'a O.

    2015-11-17

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

  8. Ab initio calculation of H+He+ charge-transfer cross sections for plasma physics

    International Nuclear Information System (INIS)

    The charge-transfer in low-energy (0.25 to 150 eV/amu) H(nl)+He+(1s) collisions is investigated using a quasimolecular 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 nonadiabatic 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 on the principal and orbital quantum numbers n and l of the initial or final state. We estimate the effect of the nonadiabatic 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 an n manifold, it is only necessary to include states with n'≤n, and we discuss the limitations of our approach as the number of states increases.

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

    Science.gov (United States)

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

    2014-08-20

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

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

    Science.gov (United States)

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

    2016-03-14

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

  11. 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 V.; Christiansen, O.; Aa. Jensen, Hans Jørgen; Kongsted, Jacob

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

  12. Nanohydration of uracil: emergence of three-dimensional structures and proton-induced charge transfer.

    Science.gov (United States)

    Bacchus-Montabonel, Marie-Christine; Calvo, Florent

    2015-04-21

    Stepwise hydration of uracil has been theoretically revisited using different methods ranging from classical force fields to quantum chemical approaches. Hydration initially begins within the uracil plane but proceeds at four molecules into three-dimensional configurations or even water clusters next to the nucleobase. The relative stability between the various structures is significantly affected by zero-point energy and finite temperature (entropy) effects and also gives rise to markedly different responses to an excitation by an impinging high-energy proton. In particular, charge transfer to the molecular complex is dramatically altered in collisions toward the coating cluster but barely modified for peripheral hydration patterns. PMID:25793649

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

    International Nuclear Information System (INIS)

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

  14. Observation of quantum interference in molecular charge transport

    DEFF Research Database (Denmark)

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

    2012-01-01

    , phenomena such as giant magnetoresistance(5), Kondo effects(6) and conductance switching(7-11) have been observed in single molecules, and theorists have predicted that it should also be possible to observe quantum interference in molecular conductors(12-18), but until now all the evidence for such...... behaviour has been indirect. Here, we report the observation of destructive quantum interference in charge transport through two-terminal molecular junctions at room temperature. We studied five different rigid p-conjugated molecular wires, all of which form self-assembled monolayers on a gold surface, and...

  15. Charge transfer through single molecule contacts: How reliable are rate descriptions?

    Directory of Open Access Journals (Sweden)

    Denis Kast

    2011-08-01

    Full Text Available Background: The trend for the fabrication of electrical circuits with nanoscale dimensions has led to impressive progress in the field of molecular electronics in the last decade. However, a theoretical description of molecular contacts as the building blocks of future devices is challenging, as it has to combine the properties of Fermi liquids in the leads with charge and phonon degrees of freedom on the molecule. Outside of ab initio schemes for specific set-ups, generic models reveal the characteristics of transport processes. Particularly appealing are descriptions based on transfer rates successfully used in other contexts such as mesoscopic physics and intramolecular electron transfer. However, a detailed analysis of this scheme in comparison with numerically exact solutions is still elusive.Results: We show that a formulation in terms of transfer rates provides a quantitatively accurate description even in domains of parameter space where strictly it is expected to fail, e.g., at lower temperatures. Typically, intramolecular phonons are distributed according to a voltage driven steady state that can only roughly be captured by a thermal distribution with an effective elevated temperature (heating. An extension of a master equation for the charge–phonon complex, to effectively include the impact of off-diagonal elements of the reduced density matrix, provides very accurate solutions even for stronger electron–phonon coupling.Conclusion: Rate descriptions and master equations offer a versatile model to describe and understand charge transfer processes through molecular junctions. Such methods are computationally orders of magnitude less expensive than elaborate numerical simulations that, however, provide exact solutions as benchmarks. Adjustable parameters obtained, e.g., from ab initio calculations allow for the treatment of various realizations. Even though not as rigorously formulated as, e.g., nonequilibrium Green’s function

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

    Science.gov (United States)

    Molnar, Ferenc; Rieger, Jens

    2005-01-18

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

  17. Graphene field effect transistor as a probe of electronic structure and charge transfer at organic molecule-graphene interfaces

    DEFF Research Database (Denmark)

    Cervenka, Jiri; Budi, Akin; Dontschuk, Nikolai; Stacey, Alastair; Tadich, Anton; Rietwyk, Kevin J.; Schenk, Alex; Edmonds, Mark T.; Yin, Yuefeng; Medhekar, Nikhil; Kalbac, Martin; Pakes, Chris I.

    2015-01-01

    The electronic structure of physisorbed molecules containing aromatic nitrogen heterocycles (triazine and melamine) on graphene is studied using a combination of electronic transport, X-ray photoemission spectroscopy and density functional theory calculations. The interfacial electronic structure...... and charge transfer of weakly coupled molecules on graphene is found to be governed by work function differences, molecular dipole moments and polarization effects. We demonstrate that molecular depolarization plays a significant role in these charge transfer mechanisms even at submonolayer coverage......, particularly for molecules which possess strong dipoles. Electronic transport measurements show a reduction of graphene conductivity and charge carrier mobility upon the adsorption of the physisorbed molecules. This effect is attributed to the formation of additional electron scattering sites in graphene by...

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

    Science.gov (United States)

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

    2016-04-14

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

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

    International Nuclear Information System (INIS)

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

  20. Optics of Chromites and Charge-Transfer Transitions

    Directory of Open Access Journals (Sweden)

    Andrei V. Zenkov

    2008-08-01

    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.

  1. 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.

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

    CERN Document Server

    Ladygina, N B

    2004-01-01

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

  3. Mapping molecular motions leading to charge delocalization with ultrabright electrons

    Science.gov (United States)

    Sciaini, German

    2014-05-01

    Ultrafast diffraction has broken the barrier to atomic exploration by combining the atomic spatial resolution of diffraction techniques with the temporal resolution of ultrafast spectroscopy. X-ray free electron lasers, slicing techniques and femtosecond laser-driven X-ray and electron sources have been successfully applied for the study of ultrafast structural dynamics in a variety of samples. Yet, the application of fs-diffraction to the study of rather sensitive organic molecular crystals remains unexplored. Organic crystals are composed by weak scattering centres, often present low melting points, poor heat conductivity and are, typically, radiation sensitive. Low repetition rates (about tens of Hertz) are therefore required to overcome accumulative heating effects from the laser excitation that can degrade the sample and mask the structural dynamics. This imparts tremendous constraints on source brightness to acquire enough diffraction data before adverse photo-degradation effects have played a non-negligible role in the crystalline structure. We implemented ultra-bright femtosecond electron diffraction to obtain a movie of the relevant molecular motions driving the photo-induced insulator-to-metal phase transition in the organic charge-transfer salt (EDO-TTF)2PF6. On the first few picoseconds (0 - 10 ps) the structural evolution, well-described by three main reaction coordinates, reaches a transient intermediate state (TIS). Model structural refinement calculations indicate that fast sliding of flat EDO-TTF molecules with consecutive motion of PF6 counter-ions drive the formation of TS instead of the expected flattening of initially bent EDO-TTF moieties which seems to evolve through a slower thermal pathway that brings the system into a final high temperature-type state. These findings establish the potential of ultrabright femtosecond electron sources for probing the primary processes governing structural dynamics with atomic resolution in labile systems

  4. 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.

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

    International Nuclear Information System (INIS)

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

  6. 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.

  7. 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

  8. Charge transfer inefficiency in the pre- and post-irradiated Swept Charge Device CCD236

    International Nuclear Information System (INIS)

    This paper describes the mapping of spectral response of an e2v technologies Swept Charge Device (SCD) CCD236 pre and post irradiation with a 10 MeV equivalent proton fluence of 5.0 × 108 protons cm−2. The CCD236 is a large area (4.4 cm2) X-ray detector which will be used in India's Chandrayaan-2 Large Soft X-ray Spectrometer (CLASS) and China's Hard X-ray Modulation Telescope (HXMT). To enable the suppression of surface dark current, clocking is performed continuously resulting in a linear readout. As such the flat field illumination used to measure any change in spectral response over a conventional Charge-Coupled Devices (CCDs) is not possible. An alternative masking technique has been used to expose pinpoint regions of the device to Mn-Kα and Mn-Kβ X-rays, enabling a local map of spectral response to be built up over the device. This novel approach allows for an estimation of the Charge Transfer Inefficiency (CTI) of the device to be made by allowing the creation of a CTI scatter plot similar to that typically observed in conventional CCDs

  9. 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

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

    Science.gov (United States)

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

    2015-09-01

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

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

    Science.gov (United States)

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

    2014-12-01

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

  12. Theoretical study of the hydrated Gd3+ ion: Structure, dynamics, and charge transfer

    Science.gov (United States)

    Clavaguéra, Carine; Calvo, Florent; Dognon, Jean-Pierre

    2006-02-01

    The dynamical processes taking place in the first coordination shells of the gadolinium (III) ion are important for improving the contrast agent efficiency in magnetic-resonance imaging. An extensive study of the gadolinium (III) ion solvated by a water cluster is reported, based on molecular dynamics simulations. The AMOEBA force field [P. Y. Ren and J. W. Ponder, J. Phys. Chem. B 107, 5933 (2003)] that includes many-body polarization effects is used to describe the interactions among water molecules, and is extended here to treat the interactions between them and the gadolinium ion. In this purpose accurate ab initio calculations have been performed on Gd3+-H2O for extracting the relevant parameters. Structural data of the first two coordination shells and some dynamical properties such as the water exchange rate between the first and second coordination shells are compared to available experimental results. We also investigate the charge transfer processes between the ion and its solvent, using a fluctuating charges model fitted to reproduce electronic structure calculations on [Gd(H2O)n]3+ complexes, with n ranging from 1 to 8. Charge transfer is seen to be significant (about one electron) and correlated with the instantaneous coordination of the ion.

  13. 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 ...

  14. Optical switching of electric charge transfer pathways in porphyrin: a light-controlled nanoscale current router.

    Science.gov (United States)

    Thanopulos, Ioannis; Paspalakis, Emmanuel; Yannopapas, Vassilios

    2008-11-01

    We introduce a novel molecular junction based on a thiol-functionalized porphyrin derivative with two almost energetically degenerate equilibrium configurations. We show that each equilibrium structure defines a pathway of maximal electric charge transfer through the molecular junction and that these two conduction pathways are spatially orthogonal. We further demonstrate computationally how to switch between the two equilibrium structures of the compound by coherent light. The optical switching mechanism is presented in the relevant configuration subspace of the compound, and the corresponding potential and electric dipole surfaces are obtained by ab initio methods. The laser-induced isomerization takes place in two steps in tandem, while each step is induced by a two-photon process. The effect of metallic electrodes on the electromagnetic irradiation driving the optical switching is also investigated. Our study demonstrates the potential for using thiol-functionalized porphyrin derivatives for the development of a light-controlled nanoscale current router. PMID:21832723

  15. Optical switching of electric charge transfer pathways in porphyrin: a light-controlled nanoscale current router

    International Nuclear Information System (INIS)

    We introduce a novel molecular junction based on a thiol-functionalized porphyrin derivative with two almost energetically degenerate equilibrium configurations. We show that each equilibrium structure defines a pathway of maximal electric charge transfer through the molecular junction and that these two conduction pathways are spatially orthogonal. We further demonstrate computationally how to switch between the two equilibrium structures of the compound by coherent light. The optical switching mechanism is presented in the relevant configuration subspace of the compound, and the corresponding potential and electric dipole surfaces are obtained by ab initio methods. The laser-induced isomerization takes place in two steps in tandem, while each step is induced by a two-photon process. The effect of metallic electrodes on the electromagnetic irradiation driving the optical switching is also investigated. Our study demonstrates the potential for using thiol-functionalized porphyrin derivatives for the development of a light-controlled nanoscale current router.

  16. Ion-exchange molecularly imprinted polymer for the extraction of negatively charged acesulfame from wastewater samples.

    Science.gov (United States)

    Zarejousheghani, Mashaalah; Schrader, Steffi; Möder, Monika; Lorenz, Pierre; Borsdorf, Helko

    2015-09-11

    Acesulfame is a known indicator that is used to identify the introduction of domestic wastewater into water systems. It is negatively charged and highly water-soluble at environmental pH values. In this study, a molecularly imprinted polymer (MIP) was synthesized for negatively charged acesulfame and successfully applied for the selective solid phase extraction (SPE) of acesulfame from influent and effluent wastewater samples. (Vinylbenzyl)trimethylammonium chloride (VBTA) was used as a novel phase transfer reagent, which enhanced the solubility of negatively charged acesulfame in the organic solvent (porogen) and served as a functional monomer in MIP synthesis. Different molecularly imprinted polymers were synthesized to optimize the extraction capability of acesulfame. The different materials were evaluated using equilibrium rebinding experiments, selectivity experiments and scanning electron microscopy (SEM). The most efficient MIP was used in a molecularly imprinted-solid phase extraction (MISPE) protocol to extract acesulfame from wastewater samples. Using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) analysis, detection and quantification limits were achieved at 0.12μgL(-1) and 0.35μgL(-1), respectively. Certain cross selectivity for the chemical compounds containing negatively charged sulfonamide functional group was observed during selectivity experiments. PMID:26256920

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

    NARCIS (Netherlands)

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

    2003-01-01

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

  18. 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...... 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...... ground state by fluorescence with no electron being transferred. In the process proposed herein, charge and energy both are transferred from donor to acceptor which can further de-excite by fluorescence. The charge transfer time scale involving an actual transfer of electron is in the pico-second range....

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

    Institute of Scientific and Technical Information of China (English)

    李宏建; 彭景翠; 许雪梅; 瞿述; 罗小华; 赵楚军

    2002-01-01

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

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

    Science.gov (United States)

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

    2015-11-25

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

  1. Charge transfer and in-cloud structure of large-charge-moment positive lightning strokes in a mesoscale convective system

    Science.gov (United States)

    Lu, Gaopeng; Cummer, Steven A.; Li, Jingbo; Han, Feng; Blakeslee, Richard J.; Christian, Hugh J.

    2009-08-01

    Lightning observations in the very high frequency band and measurements of ultra low frequency magnetic fields are analyzed to investigate the charge transfer and in-cloud structure of eight positive cloud-to-ground (+CG) strokes in a mesoscale convective system. Although no high altitude images were recorded, these strokes contained large charge moment changes (1500-3200 C·km) capable of producing nighttime sprites. Even though the convective region of the storm was where the flashes originated and where the CG strokes could occur, the charge transferred to ground was mainly from the stratiform region. The post-stroke long continuing currents were connected to highly branched negative leader extension into the stratiform region. While the storm dissipated, the altitude of negative leader propagation in the stratiform area dropped gradually from 8 to 5 km, indicating that in some and perhaps all of these strokes, it was the upper positive charge in the stratiform region that was transferred.

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

    CERN Document Server

    Kitoh-Nishioka, Hirotaka

    2016-01-01

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

  3. 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

  4. Molecular Packing Determines Charge Separation in a Liquid Crystalline Bisthiophene-Perylene Diimide Donor-Acceptor Material.

    Science.gov (United States)

    Polkehn, Matthias; Tamura, Hiroyuki; Eisenbrandt, Pierre; Haacke, Stefan; Méry, Stéphane; Burghardt, Irene

    2016-04-01

    Combined electronic structure and quantum dynamical calculations are employed to investigate charge separation in a novel class of covalently bound bisthiophene-perylene diimide type donor-acceptor (DA) co-oligomer aggregates. In an earlier spectroscopic study of this DA system in a smectic liquid crystalline (LC) film, efficient and ultrafast (subpicosecond) initial charge separation was found to be followed by rapid recombination. By comparison, the same DA system in solution exhibits ultrafast resonant energy transfer followed by slower (picosecond scale) charge separation. The present first-principles study explains these contrasting observations, highlighting the role of an efficient intermolecular charge-transfer pathway that results from the molecular packing in the LC phase. Despite the efficiency of this primary charge-transfer step, long-range charge separation is impeded by a comparatively high Coulomb barrier in conjunction with small electron- and hole-transfer integrals. Quantum dynamical calculations are carried out for a fragment-based model Hamiltonian, parametrized by ab initio second-order Algebraic Diagrammatic Construction (ADC(2)) and Time-Dependent Density Functional Theory (TDDFT) electronic structure calculations. Simulations of coherent vibronic quantum dynamics for up to 156 electronic states and 48 modes are performed using the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method. Excellent agreement with experimentally determined charge separation time scales is obtained, and the spatially coherent nature of the dynamics is analyzed. PMID:26987362

  5. Theoretical estimation of the rate of photoinduced charge transfer reactions in triphenylamine C60 donor-acceptor conjugate.

    Science.gov (United States)

    Martínez, Juan Pablo; Solà, Miquel; Voityuk, Alexander A

    2016-06-01

    Fullerene-based molecular heterojunctions such as the [6,6]-pyrrolidine-C60 donor-acceptor conjugate containing triphenylamine (TPA) are potential materials for high-efficient dye-sensitized solar cells. In this work, we estimate the rate constants for the photoinduced charge separation and charge recombination processes in TPA-C60 using the unrestricted and time-dependent DFT methods. Different schemes are applied to evaluate excited state properties and electron transfer parameters (reorganization energies, electronic couplings, and Gibbs energies). The use of open-shell singlet or triplet states, several density functionals, and continuum solvation models is discussed. Strengths and limitations of the computational approaches are highlighted. The present benchmark study provides an overview of the expected performance of DFT-based methodologies in the description of photoinduced charge transfer reactions in fullerene heterojunctions. © 2016 Wiley Periodicals, Inc. PMID:26992355

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

    Science.gov (United States)

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

    2016-08-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2008-01-01

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

  8. Low-Energy Charge Transfer in Multiply-Charged Ion-Atom Collisions Studied with the Combined SCVB-MOCC Approach

    Directory of Open Access Journals (Sweden)

    B. Zygelman

    2002-03-01

    Full Text Available A survey of theoretical studies of charge transfer involving collisions of multiply-charged ions with atomic neutrals (H and He is presented. The calculations utilized the quantum-mechanical molecular-orbital close-coupling (MOCC approach where the requisite potential curves and coupling matrix elements have been obtained with the spin-coupled valence bond (SCVB method. Comparison is made among various collision partners, for equicharged systems, where it is illustrated that even for total charge transfer cross sections, scaling-laws do not exist for low-energy collisions (i.e. < 1 keV/amu. While various empirical scaling-laws are well known in the intermediateand high-energy regimes, the multi-electron configurations of the projectile ions results in a rich and varied low-energy dependence, requiring an explicit calculation for each collision-partner pair. Future charge transfer problems to be addressed with the combined SCVB-MOCC approach are briefly discussed.

  9. Theoretical and experimental study of charge transfer through DNA: Impact of mercury attached to mismatched base pairs

    Czech Academy of Sciences Publication Activity Database

    Kratochvílová, Irena; Golan, Martin; Vala, M.; Špérová, M.; Weiter, M.; Páv, Ondřej; Šebera, Jakub; Rosenberg, Ivan; Sychrovský, Vladimír

    2014-01-01

    Roč. 21, č. 1 (2014), s. 16. ISSN 1211-5894. [Discussions in Structural Molecular Biology. Annual Meeting of the Czech Society for Structural Biology /12./. 13.03.2014-15.03.2014, Nové Hrady] Institutional support: RVO:61388963 ; RVO:68378271 Keywords : metallo-DNA * T-Hg-T * steady-state fluorescence * charge transfer Subject RIV: CF - Physical ; Theoretical Chemistry

  10. 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.

  11. 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...

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Science.gov (United States)

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

    2015-10-01

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

  14. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    Energy Technology Data Exchange (ETDEWEB)

    Van Tassle, Aaron Justin

    2006-09-01

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

  15. Transient Molecular Transfer During Vacuum Testing

    Science.gov (United States)

    Perry, Radford L.

    2011-01-01

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

  16. Computing intramolecular charge and energy transfer rates using optimal modes

    International Nuclear Information System (INIS)

    In our recent work [X. Yang and E. R. Bittner, J. Phys. Chem. A 118, 5196 (2014)], we showed how to construct a reduced set of nuclear motions that capture the coupling between electronic and nuclear degrees of freedom over the course of an electronic transition. We construct these modes, referred to as “Lanczos modes,” by applying a search algorithm to find linear combinations of vibrational normal modes that optimize the electronic/nuclear coupling operator. Here, we analyze the irreducible representations of the dominant contributions of these modes and find that for the cases considered here, these belong to totally symmetric irreducible representations of the donor and acceptor moieties. Upon investigating the molecular geometry changes following the transition, we propose that the electronic transition process can be broken into two steps, in the agreement of Born-Oppenheimer approximation: a fast excitation transfer occurs, facilitated by the “primary Lanczos mode,” followed by slow nuclear relaxation on the final electronic diabatic surface

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-15

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

  18. Charge mobilities in molecular materials reversibly modified by light: towards a molecular switch

    Czech Academy of Sciences Publication Activity Database

    Nešpůrek, Stanislav; Sworakowski, J.; Wang, Geng; Toman, Petr; Bartkowiak, W.; Combellas, C.

    Arcachon : University of Bordeaux, 2004. s. P111. [International Symposium on Photochromism /4./. 12.09.2004-15.09.2004, Arcachon] R&D Projects: GA MŠk OC D14.30 Keywords : molecular switch * charge mobility * photochromism Subject RIV: BM - Solid Matter Physics ; Magnetism

  19. 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.

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

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

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

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

    Science.gov (United States)

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

    2014-12-01

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

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

    Science.gov (United States)

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

    2015-12-17

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

  3. Density functional investigation of the electronic structure and charge transfer excited states of a multichromophoric antenna

    Science.gov (United States)

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

    2016-05-01

    We report an electronic structure study of a multichromophoric molecular complex containing two of each borondipyrromethane dye, Zn-tetraphenyl-porphyrin, bisphenyl anthracene and a fullerene. The snowflake shaped molecule behaves like an antenna capturing photon at different frequencies and transferring the photon energy to the porphyrin where electron transfer occurs from the porphyrin to the fullerene. The study is performed within density functional formalism using large polarized Guassian basis sets (12,478 basis functions in total). The energies of the HOMO and LUMO states in the complex, as adjudged by the ionization potential and the electron affinity values, show significant differences with respect to their values in participating subunits in isolation. These differences are also larger than the variations of the ionization potential and electron affinity values observed in non-bonded C60-ZnTPP complexes in co-facial arrangement or end-on orientations. An understanding of the origin of these differences is obtained by a systematic study of the effect of structural strain, the presence of ligands, the effect of orbital delocalization on the ionization energy and the electron affinity. Finally, a few lowest charge transfer energies involving electronic transitions from the porphyrin component to the fullerene subunit of the complex are predicted.

  4. Spectrophotometric study of the charge transfer complexation of some porphyrin derivatives as electron donors with tetracyanoethylene

    Science.gov (United States)

    El-Zaria, Mohamed E.

    2008-01-01

    Charge transfer complexes (CTC) of 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetra(4-tolyl)porphyrin (TTP), 5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMP), Zn-5,10,15,20-tetraphenylporphyrin (Zn-TPP), and Zn-5,10,15,20-tetra(4-tolyl)porphyrin (Zn-TTP) with tetracyanoethylene (TCNE) have been studied at various temperatures in CH 2Cl 2 and CCl 4. The data are discussed in terms of equilibrium constant ( KCT), molar extinction coefficient ( ɛCT), thermodynamic standard reaction quantities (Δ G°, Δ H° and Δ S°), oscillator strength ( f), and transition dipole moment ( μ). The spectrum obtained for TPP/TCNE, TTP/TCNE, and TMP/TCNE systems shows two main absorption bands at 475 and 690 nm, which are not due to the absorption of any of the reactants. These bands are characteristic of an intermolecular charge transfer involving the overlap of the lowest unoccupied molecular orbital (LUMO) of the acceptor with the highest occupied molecular orbital (HOMO) of the donor. The results reveal that the interaction between the donors and acceptor is due to π-π * transitions by the formation of radical ion pairs. The stoichiometry of the complexes was found to be 1:1 ratio by the Job and straight line methods between donors and acceptor with the maximum absorption bands at wavelengths of 475 and 690 nm. The observed data show salvation effects on the spectral and thermodynamics properties of CTC. The ionization potential of the donors and the dissociation energy of the CTC were also determined and are found to be constant.

  5. Energy and charge transfer in ionized argon coated water clusters

    Czech Academy of Sciences Publication Activity Database

    Kočišek, Jaroslav; Lengyel, Jozef; Fárník, Michal; Slavíček, P.

    2013-01-01

    Roč. 139, č. 21 (2013), s. 214308. ISSN 0021-9606 R&D Projects: GA ČR GAP208/11/0161 EU Projects: European Commission(XE) 238671 - ICONIC Institutional support: RVO:61388955 Keywords : Charged clusters * Charged fragments * Complex reactions Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.122, year: 2013

  6. Short chain molecular junctions: Charge transport versus dipole moment

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • The role of dipole moment of organic molecules on molecular junctions has been studied. • Molecular junctions constituted using propargyl molecules of different dipole moments. • The electronic properties of the molecules were calculated using Gaussian software. • Junctions show varying rectification due to their varying dipole moment and orientation. - Abstract: The investigation of the influence of dipole moment of short chain organic molecules having three carbon atoms varying in end group on silicon surface was carried on. Here, we use three different molecules of propargyl series varying in dipole moment and its orientation to constitute molecular junctions. The charge transport mechanism in metal–molecules–semiconductor (MMS) junction obtained from current–voltage (I–V) characteristics shows the rectification behavior for two junctions whereas the other junction shows a weak rectification. The electronic properties of the molecules were calculated using Gaussian software package. The observed rectification behavior of these junctions is examined and found to be accounted to the orientation of dipole moment and electron cloud density distribution inside the molecules

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

    Indian Academy of Sciences (India)

    K Senthil Kumar; Archita Patnaik

    2013-03-01

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

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

    Directory of Open Access Journals (Sweden)

    Hong Sun

    2015-01-01

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

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

    CERN Document Server

    Wang, Xin

    2015-01-01

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

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

    Science.gov (United States)

    Wang, Xin; Liang, Shi-Dong

    2013-02-01

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

  11. A fast calculation algorithm for the charge transfer loss in CCDs

    International Nuclear Information System (INIS)

    Charge transfer loss due to deep level traps in CCDs is a common phenomenon. In single-photon counting CCDs for X-ray detection, the charge loss results in a degradation of spectroscopic resolution. The transfer loss of a signal depends on various parameters like temperature, number of transferred charges, number of charges in the preceding signals and the elapsed time between these signals. Each signal has to be corrected individually with respect to these parameters. An algorithm based on first principles of capture and emission, that allows a fast determination of the transfer loss is presented. The model was tested on calibration data of an X-ray pn-CCD of the EPIC consortium for XMM. The model describes the experimental data very well

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

    International Nuclear Information System (INIS)

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

  13. Charge transmission through a molecular wire: the role of terminal sites for the current-voltage behavior.

    Science.gov (United States)

    Petrov, E G; Zelinskyy, Ya R; May, V; Hänggi, P

    2007-08-28

    The current-voltage and the conductance-voltage characteristics are analyzed for a particular type of molecular wire embedded between two electrodes. The wire is characterized by internal molecular units where the lowest occupied molecular orbital (LUMO) levels are positioned much above the Fermi energy of the electrodes, as well as above the LUMO levels of the terminal wire units. The latter act as specific intermediate donor and acceptor sites which in turn control the current formation via the superexchange and sequential electron transfer mechanisms. According to the chosen wire structure, intramolecular multiphonon processes may block the superexchange component of the interelectrode current, resulting in a negative differential resistance of the molecular wire. A pronounced current rectification appears if (i) the superexchange component dominates the electron transfer between the terminal sites and if (ii) the multiphonon suppression of distant superexchange charge hopping events between those sites is nonsymmetric. PMID:17764286

  14. Molecular Dynamics Simulations of Nanoparticles Coated with Charged Polymers

    Science.gov (United States)

    Wen, Chengyuan; Cheng, Shengfeng

    Polymer coating is frequently used to stabilize colloidal and nano-sized particles. We employ molecular dynamics simulations to study nanoparticles coated with polymer chains that contain ionizable groups. In a polar solvent, the chains become charged with counterions dissociated. In the computational model, we treat the solvent as a uniform dielectric background and use the bead-spring model for the polymer chains. Counterions are explicitly included as mobile beads. The nanoparticle is modeled as a layer of sites uniformly distributed on a spherical surface with a certain fraction of sites serving as the tether points of the grafted polymer brush. We vary the grafting density and calculate the distribution of polymer beads and counterions around the nanoparticle. Our results indicate that charged chains adopt extended conformations because of their mutual repulsions. We further study the interactions between two polymer-coated nanoparticles and obtain the potential of mean force. We also find an interesting transition of a confined single layer of such polymer-coated nanoparticles into two layers when the confinement is removed. Results show that the brush-brush contact has a nonuniform distribution and the nanoparticles tend to form dipole-like structures.

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

    OpenAIRE

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

    2010-01-01

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

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

    OpenAIRE

    Shutthanandan V; Becker U; Ramana CV; Julien CM

    2008-01-01

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

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

    Science.gov (United States)

    Lerch, Sarah; Reinhard, Björn M

    2016-03-01

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

  18. Spectroscopic investigation and computational analysis of charge transfer hydrogen bonded reaction between 3-aminoquinoline with chloranilic acid in 1:1 stoichiometric ratio

    Science.gov (United States)

    Al-Ahmary, Khairia M.; Alenezi, Maha S.; Habeeb, Moustafa M.

    2015-10-01

    Charge transfer hydrogen bonded reaction between the electron donor (proton acceptor) 3-aminoquinoline with the electron acceptor (proton donor) chloranilic acid (H2CA) has been investigated experimentally and theoretically. The experimental work included the application of UV-vis spectroscopy to identify the charge transfer band of the formed complex, its molecular composition as well as estimating its formation constants in different solvent included acetonitrile (AN), methanol (MeOH), ethanol (EtOH) and chloroform (CHL). It has been recorded the presence of new absorption bands in the range 500-550 nm attributing to the formed complex. The molecular composition of the HBCT complex was found to be 1:1 (donor:acceptor) in all studied solvents based on continuous variation and photometric titration methods. In addition, the calculated formation constants from Benesi-Hildebrand equation recorded high values, especially in chloroform referring to the formation of stable HBCT complex. Infrared spectroscopy has been applied for the solid complex where formation of charge and proton transfer was proven in it. Moreover, 1H and 13C NMR spectroscopies were used to characterize the formed complex where charge and proton transfers were reconfirmed. Computational analysis included the use of GAMESS computations as a package of ChemBio3D Ultr12 program were applied for energy minimization and estimation of the stabilization energy for the produced complex. Also, geometrical parameters (bond lengths and bond angles) of the formed HBCT complex were computed and analyzed. Furthermore, Mullikan atomic charges, molecular potential energy surface, HOMO and LUMO molecular orbitals as well as assignment of the electronic spectra of the formed complex were presented. A full agreement between experimental and computational analysis has been found especially in the existence of the charge and proton transfers and the assignment of HOMO and LUMO molecular orbitals in the formed complex as

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-10-21

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

  1. Real-time observation of the charge transfer to solvent dynamics

    Science.gov (United States)

    Messina, Fabrizio; Bräm, Olivier; Cannizzo, Andrea; Chergui, Majed

    2013-07-01

    Intermolecular electron-transfer reactions have a crucial role in biology, solution chemistry and electrochemistry. The first step of such reactions is the expulsion of the electron to the solvent, whose mechanism is determined by the structure and dynamical response of the latter. Here we visualize the electron transfer to water using ultrafast fluorescence spectroscopy with polychromatic detection from the ultraviolet to the visible region, upon photo-excitation of the so-called charge transfer to solvent states of aqueous iodide. The initial emission is short lived (~60 fs) and it relaxes to a broad distribution of lower-energy charge transfer to solvent states upon rearrangement of the solvent cage. This distribution reflects the inhomogeneous character of the solvent cage around iodide. Electron ejection occurs from the relaxed charge transfer to solvent states with lifetimes of 100-400 fs that increase with decreasing emission energy.

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

    OpenAIRE

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

    2015-01-01

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

  3. Electrostatic sensors applied to the measurement of electric charge transfer in gas-solids pipelines

    OpenAIRE

    Woodhead, Stephen; Denham, John; Armour-Chelu, David

    2005-01-01

    This paper describes the development of a number of electric charge sensors. The sensors have been developed specifically to investigate triboelectric charge transfer which takes place between particles and the pipeline wall, when powdered materials are conveyed through a pipeline using air. A number of industrial applications exist for such gas-solids pipelines, including pneumatic conveyors, vacuum cleaners and dust extraction systems. The build-up of electric charge on pipelines and powder...

  4. Electron transfer and decay processes of highly charged iodine ions

    International Nuclear Information System (INIS)

    In the present experimental work we have investigated multi-electron transfer processes in Iq+ (q=10, 15, 20 and 25) + Ne, Ar, Kr and Xe collisions at 1.5q keV energy. The branching ratios between Auger and radiative decay channels have been measured in decay processes of multiply excited states formed by multi-electron transfer collisions. It has been shown that, in all the multi-electron transfer processes investigated, the Auger decays are far dominant over the radiative decay processes and the branching ratios are clearly characterized by the average principal quantum number of the initial excited states of projectile ions. We could express the branching ratios in high Rydberg states formed in multi-electron transfer processes by using the decay probability of one Auger electron emission. (author)

  5. Energy and charge transfer between quasi-zero-dimensional nanostructures

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Washington, DC : TechConnect, 2015, s. 71-74. ISBN 978-1-4987-4727-1. [TechConnect World Innovation . Washington, DC (US), 14.06.2015-17.06.2015] R&D Projects: GA MŠk(CZ) LD14011; GA MŠk LH12236 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : exciton transfer * electron transfer * electron-phonon interaction * quantum dots * irreversible quantum transport Subject RIV: BM - Solid Matter Physics ; Magnetism

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

    Science.gov (United States)

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

    1996-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-09-06

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, O.A.

    1978-02-01

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

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

    Institute of Scientific and Technical Information of China (English)

    R.Friedlein

    2007-01-01

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

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

    OpenAIRE

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

    2007-01-01

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

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

    Science.gov (United States)

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

    2016-01-01

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

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

    Science.gov (United States)

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

    2016-07-01

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

  14. 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.

  15. Inductive Power Transfer with Resonance for Wireless Charging of Batteries in Electric Vehicles

    OpenAIRE

    Roaldset, Johanna Ruud

    2010-01-01

    This report investigates inductive power transfer with resonance for wireless charging of electric vehicle (EV) batteries. The inspiration for the topic came from the paper Basic experimental study on helical antennas of wireless power transfer for Electric Vehicles by using magnetic resonant couplings by T. Imura, H. Okabe and Y. Hory [7]. The paper presents laboratory results of more than 97% power transfer efficiency at a distance between the coils of up to 20 cm. The coils used are air ...

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

    Science.gov (United States)

    Shimada, Toshihiro; Mochida, Michihiro; Koma, Atsushi

    1997-04-01

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

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

    Science.gov (United States)

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

    2005-01-01

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

  18. Charge transfer in the presence of a radiation field

    International Nuclear Information System (INIS)

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2013-01-01

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

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

    CERN Document Server

    Theophilou, Iris; Thanos, S

    2014-01-01

    Photoinduced charge transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for accurate and computationally inexpensive treatment of charge transfer excitations is a topic that attracts nowadays a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations (M. Tassi, I. Theophilou and S. Thanos, Int. J. Quantum Chem., {113}, 690 (2013), M. Tassi, I. Theophilou and S. Thanos, J. Chem. Phys. {138}, 124107 (2013)) to allow for the description of intermolecular charge transfer excitations. For the description of an excitation where an electron is transferred from a donor system to an acceptor one, it is necessary to keep the excited state orthogonal to the ground sate in order to avoid variational collapse. These conditions are achieved by decomposing the subspace spanned by the Hartree-Fock (HF) ground state orbitals to four subspaces: The subspace spanned ...

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

    KAUST Repository

    Ayzner, Alexander L.

    2015-01-02

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

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

    Science.gov (United States)

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

    2015-01-01

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

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

    Science.gov (United States)

    Nan, Guangjun; Zhang, Xu; Lu, Gang

    2016-06-29

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

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

    Science.gov (United States)

    Yatsuhashi, Tomoyuki; Nakashima, Nobuaki

    2010-07-22

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

  5. Thermodynamic Integration Networks and Their Application to Charge Transfer Reactions within the AauDyPI Fungal Peroxidase.

    Science.gov (United States)

    Bauß, Anna; Langenmaier, Michael; Strittmatter, Eric; Plattner, Dietmar A; Koslowski, Thorsten

    2016-06-01

    We present a computer simulation study of the thermodynamics and kinetics of charge transfer reactions within the fungal peroxidase AauDyPI from Auricularia auriculae-judae. Driving forces and reorganization energies are obtained from a thermodynamic integration scheme based upon molecular dynamics simulations. To enhance the numerical accuracy, the free energies are analyzed within a least-squares scheme of a closely knit thermodynamic network. We identify Tyr147, Tyr229, and Trp105 as oxidative agents, and find Trp377 to be a long-lived reaction intermediate. The results are compared to recent experimental findings. PMID:27182684

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-12-01

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

  7. Charge Transfer Properties Through Graphene Layers in Gas Detectors

    CERN Document Server

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

    2015-01-01

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

  8. Fullerene-Based Photoactive Layers for Heterojunction Solar Cells: Structure, Absorption Spectra and Charge Transfer Process

    Directory of Open Access Journals (Sweden)

    Yuanzuo Li

    2014-12-01

    Full Text Available The electronic structure and optical absorption spectra of polymer APFO3, [70]PCBM/APFO3 and [60]PCBM/APFO3, were studied with density functional theory (DFT, and the vertical excitation energies were calculated within the framework of the time-dependent DFT (TD-DFT. Visualized charge difference density analysis can be used to label the charge density redistribution for individual fullerene and fullerene/polymer complexes. The results of current work indicate that there is a difference between [60]PCBM and [70]PCBM, and a new charge transfer process is observed. Meanwhile, for the fullerene/polymer complex, all calculations of the twenty excited states were analyzed to reveal all possible charge transfer processes in depth. We also estimated the electronic coupling matrix, reorganization and Gibbs free energy to further calculate the rates of the charge transfer and the recombination. Our results give a clear picture of the structure, absorption spectra, charge transfer (CT process and its influencing factors, and provide a theoretical guideline for designing further photoactive layers of solar cells.

  9. Non-Markovian reduced dynamics of ultrafast charge transfer at an oligothiophene–fullerene heterojunction

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, Keith H., E-mail: keith.hughes@bangor.ac.uk [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Cahier, Benjamin [School of Chemistry, Bangor University, Bangor, Gwynedd LL57 2UW (United Kingdom); Martinazzo, Rocco [Dipartimento di Chimica Università degli Studi di Milano, v. Golgi 19, 20133 Milano (Italy); Tamura, Hiroyuki [WPI-Advanced Institute for Material Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Burghardt, Irene [Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main (Germany)

    2014-10-17

    Highlights: • Quantum dynamical study of exciton dissociation at a heterojunction interface. • The non-Markovian quantum dynamics involves a highly structured spectral density. • Spectral density is reconstructed from an effective mode transformation of the Hamiltonian. • The dynamics is studied using the hierarchical equations of motion approach. • It was found that the temperature has little effect on the charge transfer. - Abstract: We extend our recent quantum dynamical study of the exciton dissociation and charge transfer at an oligothiophene–fullerene heterojunction interface (Tamura et al., 2012) [6] by investigating the process using the non-perturbative hierarchical equations of motion (HEOM) approach. Based upon an effective mode reconstruction of the spectral density the effect of temperature on the charge transfer is studied using reduced density matrices. It was found that the temperature had little effect on the charge transfer and a coherent dynamics persists over the first few tens of femtoseconds, indicating that the primary charge transfer step proceeds by an activationless pathway.

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

    International Nuclear Information System (INIS)

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

  11. Polarization and Charge Transfer in the Hydration of Chloride Ions

    OpenAIRE

    Zhao, Zhen; Rogers, David M.; Beck, Thomas L.

    2009-01-01

    A theoretical study of the structural and electronic properties of the chloride ion and water molecules in the first hydration shell is presented. The calculations are performed on an ensemble of configurations obtained from molecular dynamics simulations of a single chloride ion in bulk water. The simulations utilize the polarizable AMOEBA force field for trajectory generation, and MP2-level calculations are performed to examine the electronic structure properties of the ions and surrounding...

  12. Charge transfer and charge conversion of K and N defect centers in Si3N4

    Science.gov (United States)

    Pacchioni, Gianfranco; Erbetta, Davide

    2000-06-01

    Charge traps in silicon nitride and their interaction have been studied by first principle density functional theory (DFT) calculations. The K0 (N3≡Si•) and N0 (Si2=N•) Si and N dangling bond centers, respectively, are electrically active paramagnetic point defects. They show an amphoteric behavior and convert into the more stable diamagnetic charged centers K- (N3≡Si-), K+ (N3≡Si+), N- (Si2=N-), and N+ (Si2=N+). The overcoordination of K+ and N+ and the electrostatic interaction with the K- or N- counterparts are important contributions to the negative-U character of the defects.

  13. Charge transfer from the n-hexadecane radical cation to cycloalkanes, alkenes and aromatics

    International Nuclear Information System (INIS)

    Charge transfer from n-hexadecane radical cations C16H34+ to solutes as cycloalkanes, alkenes and aromatics was studied by pulse radiolysis. Using ion-pair kinetics the rate constants ksub(s) of the electron transfer reactions C16H34+ + S ->sup(ks) S+ + C16H34 were determined. The electron transfer rate constants ksub(s) increase from low values for slightly exothermic reactions to a limiting value of 9 . 109 dm3 mol-1 s-1 when the electron transfer reaction is more exothermic than -0.4 eV. (orig.)

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

    Science.gov (United States)

    Behnia, Sohrab; Fathizadeh, Samira; Akhshani, Afshin

    2015-08-01

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

  15. Evaluation of Bulk Charging in Geostationary Transfer Orbit and Earth Escape Trajectories Using the Numit 1-D Charging Model

    Science.gov (United States)

    Minow, Joseph I.; Coffey, Victoria N.; Parker, Linda N.; Blackwell, William C., Jr.; Jun, Insoo; Garrett, Henry B.

    2007-01-01

    The NUMIT 1-dimensional bulk charging model is used as a screening to ol for evaluating time-dependent bulk internal or deep dielectric) ch arging of dielectrics exposed to penetrating electron environments. T he code is modified to accept time dependent electron flux time serie s along satellite orbits for the electron environment inputs instead of using the static electron flux environment input originally used b y the code and widely adopted in bulk charging models. Application of the screening technique ts demonstrated for three cases of spacecraf t exposure within the Earth's radiation belts including a geostationa ry transfer orbit and an Earth-Moon transit trajectory for a range of orbit inclinations. Electric fields and charge densities are compute d for dielectric materials with varying electrical properties exposed to relativistic electron environments along the orbits. Our objectiv e is to demonstrate a preliminary application of the time-dependent e nvironments input to the NUMIT code for evaluating charging risks to exposed dielectrics used on spacecraft when exposed to the Earth's ra diation belts. The results demonstrate that the NUMIT electric field values in GTO orbits with multiple encounters with the Earth's radiat ion belts are consistent with previous studies of charging in GTO orb its and that potential threat conditions for electrostatic discharge exist on lunar transit trajectories depending on the electrical proper ties of the materials exposed to the radiation environment.

  16. Charge transfer cross sections for Hg+, Xe+, and Cs+ in collision with various metals and carbon

    International Nuclear Information System (INIS)

    Cross sections for charge transfer between Hg+, Xe+, and Cs+ and the atomic species Fe, Mo, Al, Ti, Ta, and C have been measured in the ion energy range from 1 to 5000 eV. In general, the cross sections for charge transfer were found to be less than 2 x 10-15 cm2 for most processes over the total energy range. The one exception is Hg+ in collision with Ti. The reactants are all open shell atomic species and in most cases where the charge transfer process is exothermic, several resonant pathways exist leading to the products. Some discussion of possible reaction paths is given. The techniques used to form neutral beams of the various species studied is included

  17. Charge transfer cross sections for Hg + , Xe + , and Cs + in collision with various metals and carbon

    Science.gov (United States)

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

    1981-01-01

    Cross sections for charge transfer between Hg+, Xe+, and Cs+ and the atomic species Fe, Mo, Al, Ti, Ta, and C have been measured in the ion energy range from 1 to 5000 eV. In general, the cross sections for charge transfer were found to be less than 2×10-15 cm2 for most processes over the total energy range. The one exception is Hg+ in collision with Ti. The reactants are all open shell atomic species and in most cases where the charge transfer process is exothermic, several resonant pathways exist leading to the products. Some discussion of possible reaction paths is given. The techniques used to form neutral beams of the various species studied is included.

  18. Engineering the Charge Transfer in all 2D Graphene-Nanoplatelets Heterostructure Photodetectors

    Science.gov (United States)

    Robin, A.; Lhuillier, E.; Xu, X. Z.; Ithurria, S.; Aubin, H.; Ouerghi, A.; Dubertret, B.

    2016-05-01

    Two dimensional layered (i.e. van der Waals) heterostructures open up great prospects, especially in photodetector applications. In this context, the control of the charge transfer between the constituting layers is of crucial importance. Compared to bulk or 0D system, 2D materials are characterized by a large exciton binding energy (0.1–1 eV) which considerably affects the magnitude of the charge transfer. Here we investigate a model system made from colloidal 2D CdSe nanoplatelets and epitaxial graphene in a phototransistor configuration. We demonstrate that using a heterostructured layered material, we can tune the magnitude and the direction (i.e. electron or hole) of the charge transfer. We further evidence that graphene functionalization by nanocrystals only leads to a limited change in the magnitude of the 1/f noise. These results draw some new directions to design van der Waals heterostructures with enhanced optoelectronic properties.

  19. Engineering the Charge Transfer in all 2D Graphene-Nanoplatelets Heterostructure Photodetectors.

    Science.gov (United States)

    Robin, A; Lhuillier, E; Xu, X Z; Ithurria, S; Aubin, H; Ouerghi, A; Dubertret, B

    2016-01-01

    Two dimensional layered (i.e. van der Waals) heterostructures open up great prospects, especially in photodetector applications. In this context, the control of the charge transfer between the constituting layers is of crucial importance. Compared to bulk or 0D system, 2D materials are characterized by a large exciton binding energy (0.1-1 eV) which considerably affects the magnitude of the charge transfer. Here we investigate a model system made from colloidal 2D CdSe nanoplatelets and epitaxial graphene in a phototransistor configuration. We demonstrate that using a heterostructured layered material, we can tune the magnitude and the direction (i.e. electron or hole) of the charge transfer. We further evidence that graphene functionalization by nanocrystals only leads to a limited change in the magnitude of the 1/f noise. These results draw some new directions to design van der Waals heterostructures with enhanced optoelectronic properties. PMID:27143413

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

    DEFF Research Database (Denmark)

    Langmaack, Lasse Nicolai; Knudsen, Hans-Jørgen Høgaard

    2006-01-01

    outlet with a special mounting strap. The heat transfer is quite complex because it takes place both directly through the contact points between bulb and pipe and indirectly through the mounting strap The TXV has to react to temperature changes at the evaporator outlet. Therefore, the dynamic behavior of...... the valve (and thereby the whole refrigeration system) depends greatly on the heat transfer between the evaporator outlet tube and the charge in the bulb. In this paper a model for the overall heat transfer between the pipe and the charge is presented. Geometrical data and material properties have......The bulb of a thermostatic expansion valve (TXV) is basically a temperature-pressure converter. It senses the temperature at the outlet of the evaporator, and the substance in the bulb (charge) generates the corresponding saturation pressure inside the bulb. The bulb is mounted on the evaporator...

  1. Examination of charge transfer in Au/YSZ for high-temperature optical gas sensing

    International Nuclear Information System (INIS)

    Highlights: • A sensing mechanism for Au/YSZ high-temperature optical gas sensing films is proposed. • XPS yields potential evidence for a charge transfer based plasmonic sensing mechanism. • The mechanism involves a change in free carrier density of Au due to charge transfer. - Abstract: Au-nanoparticle incorporated oxide thin film materials demonstrate significant promise as functional sensor materials for high temperature optical gas sensing in severe environments relevant for fossil and nuclear based power generation. The Au/yttria-stabilized zirconia (YSZ) system has been extensively studied in the literature and serves as a model system for fundamental investigations that seek to better understand the mechanistic origin of the plasmonic gas sensing response. In this work, X-ray photoelectron spectroscopy techniques are applied to Au/YSZ films in an attempt to provide further experimental evidence for a proposed sensing mechanism involving a change in free carrier density of Au nanoparticles due to charge transfer

  2. Charge transfer in collisions of Beq+ (q=2-4) and Bq+ (q=3-5) ions with H

    International Nuclear Information System (INIS)

    The charge transfer reactions in collisions of Beq+(q=2-3) and Bq+(q=3-4) ions and atomic hydrogen are investigated by using the quantal molecular orbital close-coupling (QMOCC) and the two-center atomic-orbital close-coupling (TC-AOCC) methods. Total and sub-shells state-selective cross sections are calculated for low and intermediate energy region and compared with other data available. Sets of recommended cross sections, based on the QMOCC and TC-AOCC calculations, are deduced and tabulated for Be2,3+ + H and B3,4+ + H collisions, which provide important atomic data needed in the charge-exchange-recombination spectroscopy diagnostics in magnetic fusion plasmas investigation

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

    Science.gov (United States)

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

    2016-07-01

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

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

    CERN Document Server

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

    2015-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-06-07

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

  6. Photochemical charge transfer observed in nanoscale hydrogen evolving photocatalysts using surface photovoltage spectroscopy

    OpenAIRE

    Wang, J.; Zhao, J; Osterloh, FE

    2015-01-01

    © The Royal Society of Chemistry. The application of inorganic nanostructures for solar water splitting is currently limited by our understanding of photochemical charge transfer on the nanoscale, where space charge layers are less effective for carrier separation. Here we employ surface photovoltage spectroscopy to measure the internal photovoltages in single crystalline platinum/ruthenium-modified Rh-doped SrTiO3 nanocrystals for the first time. Voltages of -0.88 V and -1.13 V are found bet...

  7. Tuning the charge transfer plasmon in a metallic nanoparticle dimer bridged by a quantum dot

    Science.gov (United States)

    Kulkarni, Vikram; Manjavacas, Alejandro; Nordlander, Peter

    2015-03-01

    Localized surface plasmon resonances (LSPR) are a subject of intense experimental and theoretical research interest. LSPR have found applications in catalysis, solar energy, cancer therapy, and surface enhanced Raman spectroscopy (SERS). This is due to the exceptional light capturing and focusing capabilities of plasmonic nanostructures. An LSPR of particular interest is the charge transfer plasmon (CTP). This mode may be excited when two plasmonic nanoparticles are bridged by a conductive junction. The CTP is extraordinarily sensitive to the conductive properties of the junction. Here we perform a theoretical investigation of the CTP when two plasmonic nanoparticles are bridged by a quantum dot. All simulations are done using the time dependent density functional theory (TDDFT). By modulating the electronic structure of the quantum dot we are able to effectively turn the CTP on and off. Specifically, the CTP emerges only when a quantum dot energy level is resonant with the fermi energy of the plasmonic nanoparticles. We verify that the conductance through the junction is on the order of the quantum unit of conductance. This work is of great interest to the future design of plasmonic and molecular electronic systems. This work was supported in part by the Data Analysis and Visualization Cyberinfrastructure funded by NSF under Grant OCI-0959097.

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

    Energy Technology Data Exchange (ETDEWEB)

    Forker, Roman

    2010-07-01

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

  9. Polarization dependence of charge-transfer excitations in La2CuO4

    Science.gov (United States)

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

    2006-03-01

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

  10. Laser-plasma ion sources: application to charge-transfer X-ray lasers

    International Nuclear Information System (INIS)

    Preliminary experiments directed towards the application of laser-produced plasmas in a charge-transfer X-ray laser are described. The motivation for these is the potential of the charge-transfer process to become a highly efficient pump process due to its large cross-section and state selective nature. The experiments show bright emission of ionic lines in the soft X-ray region when a beam of ions from a laser-plasma hits a secondary target a few millimeters away. (orig.)

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

    International Nuclear Information System (INIS)

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

  12. Effects of electronic coupling and electrostatic potential on charge transport in carbon-based molecular electronic junctions

    Science.gov (United States)

    2016-01-01

    Summary Molecular junctions consisting of 2–20 nm thick layers of organic oligomers oriented between a conducting carbon substrate and a carbon/gold top contact have proven to be reproducible and reliable, and will soon enter commercial production in audio processing circuits. The covalent, conjugated bond between one or both sp2-hybridized carbon contacts and an aromatic molecular layer is distinct from the more common metal/molecule or silicon/molecule structures in many reported molecular junctions. Theoretical observations based on density functional theory are presented here, which model carbon-based molecular junctions as single molecules and oligomers between fragments of graphene. Electronic coupling between the molecules and the contacts is demonstrated by the formation of hybrid orbitals in the model structure, which have significant electron density on both the graphene and the molecule. The energies of such hybrid orbitals correlate with tunneling barriers determined experimentally, and electronic coupling between the two graphene fragments in the model correlates with experimentally observed attenuation of transport with molecular layer thickness. Electronic coupling is affected significantly by the dihedral angle between the planes of the graphene and the molecular π-systems, but is absent only when the two planes are orthogonal. Coupling also results in partial charge transfer between the graphene contacts and the molecular layer, which results in a shift in electrostatic potential which affects the observed tunneling barrier. Although the degree of partial charge transfer is difficult to calculate accurately, it does provide a basis for the “vacuum level shift” observed in many experiments, including transport and ultraviolet photoelectron spectroscopy of molecular layers on conductors. PMID:26925350

  13. Effects of electronic coupling and electrostatic potential on charge transport in carbon-based molecular electronic junctions

    Directory of Open Access Journals (Sweden)

    Richard L. McCreery

    2016-01-01

    Full Text Available Molecular junctions consisting of 2–20 nm thick layers of organic oligomers oriented between a conducting carbon substrate and a carbon/gold top contact have proven to be reproducible and reliable, and will soon enter commercial production in audio processing circuits. The covalent, conjugated bond between one or both sp2-hybridized carbon contacts and an aromatic molecular layer is distinct from the more common metal/molecule or silicon/molecule structures in many reported molecular junctions. Theoretical observations based on density functional theory are presented here, which model carbon-based molecular junctions as single molecules and oligomers between fragments of graphene. Electronic coupling between the molecules and the contacts is demonstrated by the formation of hybrid orbitals in the model structure, which have significant electron density on both the graphene and the molecule. The energies of such hybrid orbitals correlate with tunneling barriers determined experimentally, and electronic coupling between the two graphene fragments in the model correlates with experimentally observed attenuation of transport with molecular layer thickness. Electronic coupling is affected significantly by the dihedral angle between the planes of the graphene and the molecular π-systems, but is absent only when the two planes are orthogonal. Coupling also results in partial charge transfer between the graphene contacts and the molecular layer, which results in a shift in electrostatic potential which affects the observed tunneling barrier. Although the degree of partial charge transfer is difficult to calculate accurately, it does provide a basis for the “vacuum level shift” observed in many experiments, including transport and ultraviolet photoelectron spectroscopy of molecular layers on conductors.

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Paret, Stefan

    2010-02-22

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

  16. Study of the interaction of multiply charged ions and complex systems of biological interest: effects of the molecular environment

    International Nuclear Information System (INIS)

    This PhD thesis describes the experimental study of the interaction between slow multiply charged ions (tens of keV) and molecular systems of biological interest (amino acids and nucleobases). It is the aim to identify and to better understand the effect of a molecular environment on different collision induced phenomena. To do so, the time of flight spectra of cationic products emerging from collisions with isolated molecules as well as clusters are compared. It is shown that the molecular environment protects the molecule as it allows to distribute the transferred energies and charges over the whole system (global decrease of the fragmentation and quenching of some fragmentation channels). Furthermore, in the case of adenine clusters, the molecular environment weakens some intramolecular bonds. Moreover, products of chemical reactions are observed concerning proton transfer processes in hydrated cluster of adenine and the formation of peptides bonds between beta-alanine molecules in a cluster. The latter finding is studied as a function of the cluster size and type of the projectile. Some criteria for peptide bond formation, such as flexibility and geometry of the molecule, are investigated for different amino acids. (author)

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

    Science.gov (United States)

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

    2016-04-11

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

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

    KAUST Repository

    Himmelberger, Scott

    2014-10-28

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

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

    Directory of Open Access Journals (Sweden)

    Sean D Hooper

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

  20. Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.

    Science.gov (United States)

    Bazant, Martin Z

    2013-05-21

    the past 7 years, which is capable of answering these questions. The reaction rate is a nonlinear function of the thermodynamic driving force, the free energy of reaction, expressed in terms of variational chemical potentials. The theory unifies and extends the Cahn-Hilliard and Allen-Cahn equations through a master equation for nonequilibrium chemical thermodynamics. For electrochemistry, I have also generalized both Marcus and Butler-Volmer kinetics for concentrated solutions and ionic solids. This new theory provides a quantitative description of LFP phase behavior. Concentration gradients and elastic coherency strain enhance the intercalation rate. At low currents, the charge-transfer rate is focused on exposed phase boundaries, which propagate as "intercalation waves", nucleated by surface wetting. Unexpectedly, homogeneous reactions are favored above a critical current and below a critical size, which helps to explain the rate capability of LFP nanoparticles. Contrary to other mechanisms, elevated temperatures and currents may enhance battery performance and lifetime by suppressing phase separation. The theory has also been extended to porous electrodes and could be used for battery engineering with multiphase active materials. More broadly, the theory describes nonequilibrium chemical systems at mesoscopic length and time scales, beyond the reach of molecular simulations and bulk continuum models. The reaction rate is consistently defined for inhomogeneous, nonequilibrium states, for example, with phase separation, large electric fields, or mechanical stresses. This research is also potentially applicable to fluid extraction from nanoporous solids, pattern formation in electrophoretic deposition, and electrochemical dynamics in biological cells. PMID:23520980

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

    Energy Technology Data Exchange (ETDEWEB)

    1992-12-31

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

  2. Charge-transfer energy in closed-shell ion-atom interactions. [for H and Li ions in He

    Science.gov (United States)

    Alvarez-Rizzatti, M.; Mason, E. A.

    1975-01-01

    The importance of charge-transfer energy in the interactions between closed-shell ions and atoms is investigated. Ab initio calculations on H(plus)-He and Li(plus)-He are used as a guide for the construction of approximate methods for the estimation of the charge-transfer energy for more complicated systems. For many alkali ion-rate gas systems the charge-transfer energy is comparable to the induction energy in the region of the potential minimum, although for doubly charged alkaline-earth ions in rare gases the induction energy always dominates. Surprisingly, an empirical combination of repulsion energy plus asymptotic induction energy plus asymptotic dispersion energy seems to give a fair representation of the total interaction, especially if the repulsion energy is parameterized, despite the omission of any explicit charge-transfer contribution. More refined interaction models should consider the charge-transfer energy contribution.

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

    Science.gov (United States)

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

    2015-09-01

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

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

    OpenAIRE

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

    2015-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-15

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

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

    Walters, Peter L; Makri, Nancy

    2015-12-17

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

  9. 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

    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 d...

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

    Science.gov (United States)

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

    2016-07-01

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

  11. NiO: correlated band structure of a charge-transfer insulator

    Czech Academy of Sciences Publication Activity Database

    Kuneš, Jan; Anisimov, V.I.; Skornyakov, S.L.; Lukoyanov, A.V.; Vollhardt, D.

    2007-01-01

    Roč. 99, č. 15 (2007), 156404/1-156404/4. ISSN 0031-9007 Institutional research plan: CEZ:AV0Z10100521 Keywords : band structure * dynamical mean field * charge transfer insulators Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 6.944, year: 2007

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Kim S. Y.

    2013-03-01

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

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

    NARCIS (Netherlands)

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

    2015-01-01

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

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

    Science.gov (United States)

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

    2016-07-01

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

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

    Science.gov (United States)

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

    2015-10-11

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

  17. 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.

  18. Behavior of charge-transfer absorption upon passing through the neutral-ionic phase transition

    DEFF Research Database (Denmark)

    Jacobsen, Claus Schelde; Torrance, J. B.

    1983-01-01

    The charge-transfer band is determined from reflectance measurements on single crystals of TTF-chloranil from 300 to 45 K, passing through the neutral-ionic phase transition at 84 K. As the temperature is decreased from 300 K toward the transition, hnuCT decreases slowly from 0.66 to 0.55 e...

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

    NARCIS (Netherlands)

    Gorczak-Vos, N.

    2016-01-01

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

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

    CERN Document Server

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

    2010-01-01

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

  1. Correlations between molecular structure and charge distribution in organometallic complexes of lanthanoids and actinoids

    International Nuclear Information System (INIS)

    The correlation between molecular structure and charge distribution was investigated in organometallic compounds of the lanthanoid (4f-) and actinoid (5f-) elements. These compounds are suitable models for two reasons: a) they are soluble in nonpolar solvents and b) in both series, there is a possibility for continuous variation of the ionic size of the central ion. Detailed investigation of several compound-classes with different molecular symmetry, has given important information concerning the influence of the molecular structure on the macroscopic charge distribution in the molecule. The anisotropy of the charge distribution in the molecule increases with decreasing of the molecular symmetry. Contrary to predictions previously discussed in the literature, it has been shown, that the molecular symmetry primarily does not depend on sterical interactions, but on the Coulomb-interaction between the central ion and the ligand. Using different models which take into account the molecular geometry and the charge distribution, it was possible to calculate the partial electrical moments between ligand and central ion for several coordinating atoms of the used ligands. The contribution of the f-electrons to the total charge distribution around the central ion can be quantitatively calculated from the molecular polarizability and the total charge distribution of the investigated molecule. (orig./RB)

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

    Science.gov (United States)

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

    2016-06-01

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

  3. Multipole correction of atomic monopole models of molecular charge distribution. I. Peptides

    Science.gov (United States)

    Sokalski, W. A.; Keller, D. A.; Ornstein, R. L.; Rein, R.

    1993-01-01

    The defects in atomic monopole models of molecular charge distribution have been analyzed for several model-blocked peptides and compared with accurate quantum chemical values. The results indicate that the angular characteristics of the molecular electrostatic potential around functional groups capable of forming hydrogen bonds can be considerably distorted within various models relying upon isotropic atomic charges only. It is shown that these defects can be corrected by augmenting the atomic point charge models by cumulative atomic multipole moments (CAMMs). Alternatively, sets of off-center atomic point charges could be automatically derived from respective multipoles, providing approximately equivalent corrections. For the first time, correlated atomic multipoles have been calculated for N-acetyl, N'-methylamide-blocked derivatives of glycine, alanine, cysteine, threonine, leucine, lysine, and serine using the MP2 method. The role of the correlation effects in the peptide molecular charge distribution are discussed.

  4. Libraries of Extremely Localized Molecular Orbitals. 1. Model Molecules Approximation and Molecular Orbitals Transferability.

    Science.gov (United States)

    Meyer, Benjamin; Guillot, Benoît; Ruiz-Lopez, Manuel F; Genoni, Alessandro

    2016-03-01

    Despite more and more remarkable computational ab initio results are nowadays continuously obtained for large macromolecular systems, the development of new linear-scaling techniques is still an open and stimulating field of research in theoretical chemistry. In this family of methods, an important role is occupied by those strategies based on the observation that molecules are generally constituted by recurrent functional units with well-defined intrinsic features. In this context, we propose to exploit the notion of extremely localized molecular orbitals (ELMOs) that, due to their strict localization on small molecular fragments (e.g., atoms, bonds, or functional groups), are in principle transferable from one molecule to another. Accordingly, the construction of orbital libraries to almost instantaneously build up approximate wave functions and electron densities of very large systems becomes conceivable. In this work, the ELMOs transferability is further investigated in detail and, furthermore, suitable rules to construct model molecules for the computation of ELMOs to be stored in future databanks are also defined. The obtained results confirm the reliable transferability of the ELMOs and show that electron densities obtained from the transfer of extremely localized molecular orbitals are very close to the corresponding Hartree-Fock ones. These observations prompt us to construct new ELMOs databases that could represent an alternative/complement to the already popular pseudoatoms databanks both for determining electron densities and for refining crystallographic structures of very large molecules. PMID:26799516

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

    Directory of Open Access Journals (Sweden)

    Izhal Abdul Halin

    2009-11-01

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

  6. Charge-transfer dynamics in multilayered PbS and PbSe quantum dot architectures

    International Nuclear Information System (INIS)

    We demonstrate control of the charge transfer process in PbS and PbSe quantum dot assemblies. We first demonstrate efficient charge transfer from donor quantum dots to acceptor quantum dots in a multi-layer PbSe cascade structure. Then, we assemble type-I and type-II heterostructures using both PbS and PbSe quantum dots via careful control of the band alignment. In type-I structures, photo-generated carriers are transferred and localized in the smaller bandgap (acceptor) quantum dots, resulting in a significant luminescence enhancement. In contrast, a significant luminescence quenching and shorter emission lifetime confirms an efficient separation of photo-generated carriers in the type-II architecture

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

    Science.gov (United States)

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

    2016-02-01

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

  8. Study of molecular iodine-epoxy paint mass transfer

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-12-01

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

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

    CERN Document Server

    Ito, Hiroaki; Shimokawa, Naofumi

    2016-01-01

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

  10. Charge and energy transfer interplay in hybrid sensitized solar cells mediated by graphene quantum dots

    International Nuclear Information System (INIS)

    Highlights: • We report a one pot synthesis metod of GQD with controlled size and optoelectronic properties. • An improvement of common N3-DSSC characteristics is achieved when GQDs are used as co-sensitiser. • The role of GQD as cosensitisers in hybrid DSSC was investigated and the interplay between charge and energy transfer phenomena mediated by GQDs was demonstrated. • The GQDs presence determines an inhibition of the recombination processes at the TiO2/electrolyte interface. - Abstract: We explored the role of graphene quantum dots (GQDs) as co-sensitizers in hybrid dye sensitized solar cell (DSSC) architectures, focusing on various concurring mechanisms, such as: charge transfer, energy transfer and recombination rate, towards light harvesting improvement. GQDs were prepared by the hydrothermal method that allows the tuning of electronic levels and optical properties by employing appropriate precursors and synthesis conditions. The aim was to realize a type II alignment for TiO2/GQD/dye hybrid configuration, using standard N3 Ru-dye in order to improve charge transfer. When GQDs were used as co-sensitizers together with N3 Ru-dye, an improvement in power conversion efficiency was achieved, as shown by electrical measurements. The experimental analysis indicates that this improvement arises from the interplay of various mechanisms mediated by GQDs: (i) enhancement of charge separation and collection due to the cascaded alignment of the energy levels; (ii) energy transfer from GQDs to N3 Ru-dye due to the overlap between GQD photoluminescence and N3 Ru-dye absorption spectra; and (iii) reduction of the electron recombination to the redox couple due to the inhibition of the back electron transfer to the electrolyte by the GQDs

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

    DEFF Research Database (Denmark)

    Sherafatipour, Golenaz; Madsen, Morten

    Charge photocurrent generation is a key process in solar energy conversion systems. Effective dissociation of the photo-generated electron-hole pairs (excitons) has a strong influence on the efficiency of the organic solar cells. Charge dissociation takes place at the donor/acceptor interface via...... 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......-generated charges is a major limitation for the efficiency of the organic solar cells, a thorough understanding of this loss mechanism is crucial to improve the performance of the devices. Furthermore, examining this interfacial state is of great importance in order to maximize open-circuit voltage and photocurrent...

  12. Design principle for increasing charge mobility of π-conjugated polymers using regularly localized molecular orbitals

    OpenAIRE

    Terao, Jun; Wadahama, Akihisa; Matono, Akitoshi; Tada, Tomofumi; Watanabe, Satoshi; Seki, Shu; Fujihara, Tetsuaki; Tsuji, Yasushi

    2013-01-01

    The feasibility of using π-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of π-conjugated polymers by covering the π-conjugated chain with macrocycles and regularly localizing π-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, ...

  13. Suppression of Electron Transfer to Dioxygen by Charge Transfer and Electron Transfer Complexes in the FAD-dependent Reductase Component of Toluene Dioxygenase*

    Science.gov (United States)

    Lin, Tzong-Yuan; Werther, Tobias; Jeoung, Jae-Hun; Dobbek, Holger

    2012-01-01

    The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD+ at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD+. A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD+ and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductaseTOL with dioxygen and thus present a solution toward conflicting requirements. PMID:22992736

  14. Suppression of electron transfer to dioxygen by charge transfer and electron transfer complexes in the FAD-dependent reductase component of toluene dioxygenase.

    Science.gov (United States)

    Lin, Tzong-Yuan; Werther, Tobias; Jeoung, Jae-Hun; Dobbek, Holger

    2012-11-01

    The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD(+) at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD(+). A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD(+) and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductase(TOL) with dioxygen and thus present a solution toward conflicting requirements. PMID:22992736

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

    Science.gov (United States)

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

    2016-03-14

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-03-23

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

  17. Dynamical image-charge effect in molecular tunnel junctions

    DEFF Research Database (Denmark)

    Jin, Chengjun; Thygesen, Kristian Sommer

    2014-01-01

    When an electron tunnels between two metal contacts it temporarily induces an image charge (IC) in the electrodes which acts back on the tunneling electron. It is usually assumed that the IC forms instantaneously such that a static model for the image potential applies. Here we investigate how the...... finite IC formation time affects charge transport through a molecule suspended between two electrodes. For a single-level model, an analytical treatment shows that the conductance is suppressed by a factor Z(2), where Z is the quasiparticle renormalization factor, compared to the static IC approximation...

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

    Science.gov (United States)

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

    2014-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-28

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

  20. Charge transfer and structured vibrational distributions in H++CH4 low-energy collisions

    International Nuclear Information System (INIS)

    Inelastic and charge transfer collisions of protons with methane molecules have been investigated in a perpendicular-plane crossed beam experiment via the detection of the scattered protons and H atoms, respectively. Time-of-flight analysis of the protons and H atoms at scattering angles 00≤θ≤100 and collision energies 10≤E≤30 eV provided information on internal energy distributions of the CH4 and CH+4 products. Excitation of the n(ν1 ,ν3) +m (ν2 ,ν4) type vibrations, with n,m = 0, 1, 2,xxxwas found to be the most probable assignment of the observed structured energy distributions of CH4 (1 A1 ) at θ≤40. At θ>40, the energy transfer increases steeply up to the dissociation limit while the vibrational structure was no longer resolved. In the case of charge transfer, the observed narrow internal energy distributions corresponding to a most probable average internal energy of CH+4 of about 0.95 eV was centered at the recombination energy of the proton indicative of quasiresonant charge transfer. In addition, fragmentation of CH+4 formed in charge transfer collisions of H+ with CH4 was investigated in an independent experiment using mass spectrometric analysis to identify the individual fragment species. The relative intensities of the parent and fragment ions (i.e., of CH+4, CH+3, and CH+2) were found to be in good agreement with the known values of the appearance potentials of the fragment ions and the distribution of the CH+4 internal energy as obtained from the differential cross sections

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

    Science.gov (United States)

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

    2015-12-01

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

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

    International Nuclear Information System (INIS)

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

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

    CERN Document Server

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

    2008-01-01

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

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

    Science.gov (United States)

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

    2016-07-01

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

  5. Synthesis and spectrophotometric studies of charge transfer complexes of p-nitroaniline with benzoic acid in different polar solvents

    Science.gov (United States)

    Singh, Neeti; Ahmad, Afaq

    2014-09-01

    The charge transfer complexes of the donor p-nitroaniline (PNA) with the π-acceptor benzoic acid (BEA) have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using an absorption spectrophotometer. The outcome suggests that the formation of the CT-complex is comparatively high in less polar solvent. The stoichiometry of the CT-complex was found to be 1:1. The physical parameters of the CT-complex were evaluated by the Benesi-Hildebrand equation. The data are discussed in terms of the formation constant (KCT), molar extinction coefficient (ɛCT), Standard Gibbs free energy (ΔG0), oscillator strength (f), transition dipole moment (μEN), resonance energy (RN) and ionization potential (ID). The formation constant (KCT) of the complex was depends upon the nature of electron acceptor, donor, and polarity of solvents used. It is also observed that a charge transfer molecular complex is stabilized by hydrogen bonding. The formation of the complex has been confirmed by UV-visible, FT-IR, 1H NMR and TGA/DTA. The structure of the CT-complex is [(PNA)+ (BEA)-]. A general mechanism for its formation of the complex has also been proposed.

  6. Coarse Point Charge Models For Proteins From Smoothed Molecular Electrostatic Potentials.

    Science.gov (United States)

    Leherte, Laurence; Vercauteren, Daniel P

    2009-12-01

    To generate coarse electrostatic models of proteins, we developed an original approach to hierarchically locate maxima and minima in smoothed molecular electrostatic potentials. A charge-fitting program was used to assign charges to the so-obtained reduced representations. Templates are defined to easily generate coarse point charge models for protein structures, in the particular cases of the Amber99 and Gromos43A1 force fields. Applications to four small peptides and to the ion channel KcsA are presented. Electrostatic potential values generated by the reduced models are compared with the corresponding values obtained using the original sets of atomic charges. PMID:26602509

  7. Photochemical Charge Transfer and Trapping at the Interface Between an Organic Adlayer and an Oxide Semiconductor

    International Nuclear Information System (INIS)

    In this study, we identify surface sites associated with charge transfer and trapping during photo-decomposition of an organic adsorbate on the TiO2(110) surface using scanning tunneling microscopy, electron energy loss spectroscopy and photodesorption. Trimethyl acetic acid was selected because it decomposes on TiO2(110) at room temperature to form a densely packed trimethyl acetate adlayer in which each TMA group bridges two TI4+ sites and the acid proton is transfer to a bridging O2 site

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

    Science.gov (United States)

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

    2011-08-01

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

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

    OpenAIRE

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

    2006-01-01

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

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

    Science.gov (United States)

    Dutta, Dipak; Tummanapelli, Anil Kumar

    2016-08-10

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

  11. Communication: Charge-transfer rate constants in zinc-porphyrin-porphyrin-derived dyads: A Fermi golden rule first-principles-based study

    Energy Technology Data Exchange (ETDEWEB)

    Manna, Arun K.; Dunietz, Barry D., E-mail: bdunietz@kent.edu [Department of Chemistry, Kent State University, Kent, Ohio 44242 (United States)

    2014-09-28

    We investigate photoinduced charge transfer (CT) processes within dyads consisting of porphyrin derivatives in which one ring ligates a Zn metal center and where the rings vary by their degree of conjugation. Using a first-principles approach, we show that molecular-scale means can tune CT rates through stabilization affected by the polar environment. Such means of CT tuning are important for achieving high efficiency optoelectronic applications using organic semiconducting materials. Our fully quantum mechanical scheme is necessary for reliably modeling the CT process across different regimes, in contrast to the pervading semi-classical Marcus picture that grossly underestimates transfer in the far-inverted regime.

  12. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-06-05

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

  14. 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.

  15. 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.

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

    Science.gov (United States)

    Nouchi, Ryo; Kanno, Ikuo

    2005-05-01

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

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

    Science.gov (United States)

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

    2014-03-01

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

  18. Review of theories of charge transfer processes involving highly stripped heavy ions

    International Nuclear Information System (INIS)

    A review is made of various theoretical models to study charge transfer processes involving highly stripped heavy ions Asup(z+) + B → Asup((z-1)+) + B+. The limitations of applicability of these models are critically discussed. Detailed comparison is made between theories for examples of C6+ + H → C5+ + H+ and Fe26+ + H → Fe25+ + H+. Scaling rules of the charge transfer cross section with respect to Z and theoretical predictions of the distribution over the fimal states of the highly stripped heavy ion are summarized, which are important for application to nuclear fusion and to X-ray laser. The theoretical results are compared with the experimental data available at present. (author)

  19. Multiple-receptor wireless power transfer for magnetic sensors charging on Mars via magnetic resonant coupling

    Science.gov (United States)

    Liu, Chunhua; Chau, K. T.; Zhang, Zhen; Qiu, Chun; Lin, Fei; Ching, T. W.

    2015-05-01

    This paper proposes a new idea for magnetic sensors charging on Mars, which aims to effectively transmit energy from Mars Rover to distributed magnetic sensors. The key is to utilize wireless power transfer (WPT) to enable multiple receptors extracting energy from the source via magnetic resonant coupling. Namely, the energy transmitter is located on the Mars Rover, whereas the energy receptor is installed in the magnetic sensor. In order to effectively transfer the power, a resonator is installed between the transmitter and the receptors. Based on the proposed idea, the system topology, operation principle, and simulation results are developed. By performing finite element magnetic field analysis, the output power and efficiency of the proposed WPT system are evaluated. It confirms that the Mars Rover carrying with the energy transmitter is capable of loitering around the resonator, while the magnetic sensors on the receptors can be simultaneously charged according to energy-on-demand.

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

    Science.gov (United States)

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

    1977-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2012-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Dupays, A

    2004-06-01

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

  4. Molecular dynamics investigation of the ionic liquid/enzyme interface: application to engineering enzyme surface charge.

    Science.gov (United States)

    Burney, Patrick R; Nordwald, Erik M; Hickman, Katie; Kaar, Joel L; Pfaendtner, Jim

    2015-04-01

    Molecular simulations of the enzymes Candida rugosa lipase and Bos taurus α-chymotrypsin in aqueous ionic liquids 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium ethyl sulfate were used to study the change in enzyme-solvent interactions induced by modification of the enzyme surface charge. The enzymes were altered by randomly mutating lysine surface residues to glutamate, effectively decreasing the net surface charge by two for each mutation. These mutations resemble succinylation of the enzyme by chemical modification, which has been shown to enhance the stability of both enzymes in ILs. After establishing that the enzymes were stable on the simulated time scales, we focused the analysis on the organization of the ionic liquid substituents about the enzyme surface. Calculated solvent charge densities show that for both enzymes and in both solvents that changing positively charged residues to negative charge does indeed increase the charge density of the solvent near the enzyme surface. The radial distribution of IL constituents with respect to the enzyme reveals decreased interactions with the anion are prevalent in the modified systems when compared to the wild type, which is largely accompanied by an increase in cation contact. Additionally, the radial dependence of the charge density and ion distribution indicates that the effect of altering enzyme charge is confined to short range (≤1 nm) ordering of the IL. Ultimately, these results, which are consistent with that from prior experiments, provide molecular insight into the effect of enzyme surface charge on enzyme stability in ILs. PMID:25641162

  5. Semiconductor quantum dots in polyelectrolyte polymers: multilayered self-assembly and charge transfer and transport processes

    International Nuclear Information System (INIS)

    Full text: Polyacrylate-capped Q-CdS were synthesized and self-assembled as multilayers in poly(diallyldimethylammonium chloride) on different surfaces by virtue of the Coulombic attraction between the negatively charged capping agent and the cationic polyelectrolyte polymer. TEM imaging and electron diffraction measurements revealed the growth of 3-4 nm size CdS quantum crystallites, having a zinc blende lattice structure. The layer-by-layer assembly of Q-CdS in the polymer by means of consecutive surface-charge reversal was characterized using UV-visible absorption, photoluminescence, FT-IR spectroscopy and ellipsometry; revealing the linear assembly of not more than a monolayer of nanoparticles per bilayer. Photo-induced charge transfer and transport processes at these nano structured photo electrodes were studied by photoelectrochemical means, revealing novel behavior markedly different from bulk solids. In these studies, either anodic or cathodic photocurrents were measured depending on the applied potential; a behavior attributed to the quantized properties of the nanoparticles. The potential at which the photocurrent reversed in direction was found to shift by-66 mV per pH unit, tracking the shift in the redox energies of water oxidation, oxygen reduction and hydrogen evolution. Photocurrent transients were featured at the onsets of light and are attributed to surface-states mediated charge transfer. Charge transfer and transport processes at the Q-films are modeled, accounting for the bidirectional current flow and its dependence on the electrode potential, the Fermi levels of the redox couples and the nanoparticles surface

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1995-01-01

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

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

    Science.gov (United States)

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

    2016-08-25

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

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

    Directory of Open Access Journals (Sweden)

    Shutthanandan V

    2008-06-01

    Full Text Available Abstract Molybdenum disulfide (MoS2, a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM, scanning electron microscopy (SEM, transmission electron microscopy (TEM, Rutherford backscattering spectrometry (RBS, and nuclear reaction analysis (NRA. Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and

  9. Competition between covalent bonding and charge transfer at complex-oxide interfaces

    OpenAIRE

    Salafranca, Juan; Rincón, Julián; Tornos Castillo, Javier; León Yebra, Carlos; Santamaria Sánchez-Barriga, Jacobo; Dagotto, Elbio; Pennycook, Stephen J.; Varela del Arco, María

    2014-01-01

    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 $T_c$ superconductor YBa$_2$Cu$_3$O$_{7-\\delta}$ and the colossal magnetoresistance compound (La,Ca)MnO$_3$. A net transfer of electrons from manganite to cuprate with a peculiar non-monotonic charge profile is observed. Model calcula...

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

    Science.gov (United States)

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

    2008-01-01

    Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia.The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA).Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400 degrees C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant

  11. Charge transfer activation energy for alkali atoms on Re and Ta

    Science.gov (United States)

    Gładyszewski, Longin

    1993-09-01

    Ion and atom desorption energies for five alkali metals on Re and Ta were determined using the ion thermal emission noise method. The activation energies for the charge transfer process in the adsorbed state were calculated using a special energetic balance equation, which describes the surface ionization and thermal desorption effect. Energies for desorption of Li, Na, K, Rb and Cs from Re and Ta surfaces were determined by measuring the time autocorrelation function of the ion thermoemission current fluctuations.

  12. Impact of speciation on the electron charge transfer properties of nanodiamond drug carriers

    Science.gov (United States)

    Sun, Baichuan; Barnard, Amanda S.

    2016-07-01

    Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove useful in designing drug delivery systems where the release of (selected) drugs needs to be sensitive to specific conditions at the point of delivery.Unpassivated diamond nanoparticles (bucky-diamonds) exhibit a unique surface reconstruction involving graphitization of certain crystal facets, giving rise to hybrid core-shell particles containing both aromatic and aliphatic carbon. Considerable effort is directed toward eliminating the aromatic shell, but persistent graphitization of subsequent subsurface-layers makes perdurable purification a challenge. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the impact of different fractions of aromatic and aliphatic carbon on the charge transfer properties of the ensembles of bucky-diamonds. By predicting quality factors for a variety of cases, we find that perfect purification is not necessary to preserve selectivity, and there is a clear motivation for purifying samples to improve the sensitivity of charge transfer reactions. This may prove

  13. Charge transfer complexes at various donor-acceptor nanostructures in organic based solar cells

    OpenAIRE

    Piersimoni, Fortunato

    2013-01-01

    Progress in organic photovoltaics requires the development of efficient and stable materials. To achieve this goal, an understanding of the physical processes occurring at the organic/organic interface and involved in the production of photovoltage and photocurrent is needed. The present work has investigated charge transfer (CT) complex formation at organic based donoracceptor interfaces. This thesis aimed to investigate whether the CT complex is a “universal” property of organic interfaces ...

  14. Charge transfer between carbon nanotubes and sulfuric acid as determined by Raman spectroscopy

    OpenAIRE

    Puech, Pascal; Hu, Tao; Sapelkin, Andrei; Gerber, Iann; Tishkova, Victoria; Pavlenko, Ekaterina; Levine, Benjamin; Flahaut, Emmanuel; Bacsa, Wolfgang

    2012-01-01

    The spontaneous interaction between sulfuric acid and carbon nanotubes is studied using Raman spectroscopy. We are able to determine the charge transfer without any additional parameter using the spectral signature of inner and outer walls of double-wall carbon nanotubes. While for the outer wall both the lattice contraction and the nonadiabatic effects contribute to the phonon shift, only the lattice contraction contributes for the inner nanotube. For the outer nanotube, we are able to separ...

  15. Characterization and Modeling of Received Signal Strength and Charging Time for Wireless Energy Transfer

    OpenAIRE

    Uthman Baroudi; Amin-ud-din Qureshi; Samir Mekid

    2015-01-01

    Wireless sensor networks can provide effective means for monitoring and controlling a wide range of applications. Recently, tremendous effort was directed towards devising sensors powered from ambient sources such as heat, wind, and vibration. Wireless energy transfer is another source that has attractive features that make it a promising candidate for supplying power to wireless sensor nodes. This paper is concerned with characterizing and modeling the charging time and received signal stren...

  16. Charge transfer processes in CsI:Tl using near-UV light

    International Nuclear Information System (INIS)

    This paper studies charge transfer processes in CsI:Tl crystals by analyzing the bulk photo-conductivity spectra, the temperature behavior of the bulk photo-conductivity current and the shape and intensity of the activator emission pulse excited by an electron pulse beam and/or laser pulse emission at temperatures between 80 and 400 K. The Tl concentration in CsI:Tl crystals varies from 10−3–10−1 mass%. It has been determined that near-UV light induces a bulk conductivity in CsI:Tl crystals only when the Tl concentration is greater than 3×10−3 mass%. A mechanism is proposed to explain the charge transfer processes with photons whose energy is approximately half the width of the CsI band gap. Near-UV light causes charge transfer from I− to Tl+ ions, forming Tl0 centers in the 6p2P1/2 ground and 6p2P3/2 excited states. The electron, assisted by phonons, leaves the Tl0 center from either the 6p2P1/2 or 6p2P3/2 states and overcomes the 0.13 or 0.30 eV energy barrier, respectively, and subsequently populates the activator conduction sub-bands, which are found inside the band gap of CsI:Tl. The formation of activator sub-bands is possible only above the threshold Tl concentration, i.e., above 3×10−3 mass%. - Highlights: • Photoconductivity and photoluminescence of CsI:Tl • Near-UV light (3.0–3.7 eV) causes charge transfer from I− to Tl+ ions. • The Tl0 states are responsible for the photoconductivity of CsI:Tl. • Tl concentrations above 3×10−3% give rise to conductivity in the Tl sub-band

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

    Science.gov (United States)

    Berezkina, T. E.; Masyukevich, S. V.; Gall, N. R.

    2015-05-01

    We have studied the possibility of generating electricity directly by using the charge that is created in a corona discharge and transferred by airflow in the direction perpendicular to the discharge axis. Results of experimental measurements and theoretical estimations confirm this possibility. The electric power output from corona discharge in experiment was on the order of 10-3 W, which is about one-tenth of the theoretical limit. It is proposed to use this effect for creating wind-driven generators.

  18. Computational models of an inductive power transfer system for electric vehicle battery charge

    Science.gov (United States)

    Anele, A. O.; Hamam, Y.; Chassagne, L.; Linares, J.; Alayli, Y.; Djouani, K.

    2015-09-01

    One of the issues to be solved for electric vehicles (EVs) to become a success is the technical solution of its charging system. In this paper, computational models of an inductive power transfer (IPT) system for EV battery charge are presented. Based on the fundamental principles behind IPT systems, 3 kW single phase and 22 kW three phase IPT systems for Renault ZOE are designed in MATLAB/Simulink. The results obtained based on the technical specifications of the lithium-ion battery and charger type of Renault ZOE show that the models are able to provide the total voltage required by the battery. Also, considering the charging time for each IPT model, they are capable of delivering the electricity needed to power the ZOE. In conclusion, this study shows that the designed computational IPT models may be employed as a support structure needed to effectively power any viable EV.

  19. Development of highly accurate approximate scheme for computing the charge transfer integral.

    Science.gov (United States)

    Pershin, Anton; Szalay, Péter G

    2015-08-21

    The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the "exact" scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the "exact" calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature. PMID:26298117

  20. Effect of geometrical orientation on the charge transfer energetics of supramolecular (tetraphenyl)-porphyrin/fullerens dyads

    Science.gov (United States)

    Olguin, Marco; Zope, Rajendra; Baruah, Tunna

    2013-03-01

    We present our study of several low lying charge-transfer (CT) excitation energies for a widely used donor-acceptor system composed of a porphyrin-fullerene pair. The dyad systems consist of C60 and C70 acceptor systems coupled to tetraphenyl-porphyrin (TPP) and tetraphenyl-(zinc)porphyrin (ZnTPP) donor systems in a co-facial orientation. We find that replacing C60 by C70 in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV, whereas varying the donor in these complexes had marginal effect on the lowest charge transfer excitation energy. Additionally, we examined the effect of geometrical orientation on the CT energy by calculating several CT excited state energies for an end-on orientation of the porphyrin-fullerene dyads. The CT excitation energies are larger for the end-on orientation in comparison to the co-facial orientation by 0.6 eV - 0.75 eV. The difference is attributed to a reduced exciton binding energy in going from the co-facial to the end-on orientation. Supported by Office of Basic Energy Sciences of the US Department of Energy.

  1. Vibrationally resolved inelastic and charge transfer scattering of H+ by H2O

    International Nuclear Information System (INIS)

    Inelastic and charge transfer scattering of protons by water molecules at collision energies of 27.0 and 46.0 eV have been investigated in a high-resolution crossed beam experiment up to the rainbow scattering angles. Excitation of the stretching (symmetric or asymmetric) and bending mode vibrations within the electronic ground state, X 1A1, of H2O was observed in the proton energy-loss spectra. In the case of charge transfer, formation of H2O+ in the X 2B1 and A 2A1 electronic states was identified in the corresponding H-atom spectra; the vibrational states within the X and A bands were for the most part resolved and, at small angles (θ≤20), they were found to be nearly the same as in photoionization (symmetric stretch and bending mode excitation within the X state and pure bending mode excitation within the A state). The vibronic transition probabilities deviate, however, considerably from the corresponding Franck--Condon factors in favor of the enhancement of the quasiresonant states. For both the inelastic and charge transfer scattering, state-selected quantities characteristic of the detailed collision dynamics have been derived. In addition, rotational excitation superimposed on the vibrational transitions could be estimated and for both processes it was found to be of the order of 50--100 meV

  2. Development of highly accurate approximate scheme for computing the charge transfer integral

    International Nuclear Information System (INIS)

    The charge transfer integral is a key parameter required by various theoretical models to describe charge transport properties, e.g., in organic semiconductors. The accuracy of this important property depends on several factors, which include the level of electronic structure theory and internal simplifications of the applied formalism. The goal of this paper is to identify the performance of various approximate approaches of the latter category, while using the high level equation-of-motion coupled cluster theory for the electronic structure. The calculations have been performed on the ethylene dimer as one of the simplest model systems. By studying different spatial perturbations, it was shown that while both energy split in dimer and fragment charge difference methods are equivalent with the exact formulation for symmetrical displacements, they are less efficient when describing transfer integral along the asymmetric alteration coordinate. Since the “exact” scheme was found computationally expensive, we examine the possibility to obtain the asymmetric fluctuation of the transfer integral by a Taylor expansion along the coordinate space. By exploring the efficiency of this novel approach, we show that the Taylor expansion scheme represents an attractive alternative to the “exact” calculations due to a substantial reduction of computational costs, when a considerably large region of the potential energy surface is of interest. Moreover, we show that the Taylor expansion scheme, irrespective of the dimer symmetry, is very accurate for the entire range of geometry fluctuations that cover the space the molecule accesses at room temperature

  3. Dynamics of the charge transferred states relevant to magnetic phase transition in rubidium manganese hexacyanoferrate

    Energy Technology Data Exchange (ETDEWEB)

    Suemoto, T., E-mail: suemoto@issp.u-tokyo.ac.j [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi 277-8581 (Japan); Ohki, K.; Fukaya, R.; Nakajima, M. [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi 277-8581 (Japan); Tokoro, H.; Ohkoshi, S. [Department of Chemistry, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2009-12-15

    Photoinduced charge transfer dynamics in the photomagnetic material RbMn[Fe(CN){sub 6}], which exhibits a magnetic phase transition with a large hysteresis loop (230-300 K), has been investigated by observing the CN{sup -} stretching modes, which are sensitive to the valences of the adjacent transition metal ions. Mid-infrared transient absorption measurements were performed between 2013 and 2179 cm{sup -1} to observe the transient and persistent products. The sample in the high-temperature phase was excited by 400 nm laser pulses at the ligand to metal charge transfer band near the high-temperature end of the hysteresis loop. Bleach of the Fe{sup 3+}-CN{sup -}-Mn{sup 2+} band representing a decrease of the high-temperature phase and increases of the Fe{sup 2+}-CN{sup -}-Mn{sup 3+} and Fe{sup 2+}-CN{sup -}-Mn{sup 2+} bands were observed in picosecond time region, indicating a transient production of charge transferred states.

  4. Infrared photocurrent response of charge-transfer exciton in polymer bulk heterojunction

    International Nuclear Information System (INIS)

    We study the charge-transfer exciton absorption and photocurrent response in solution-processed bulk heterojunction based on poly(3-hexylthiophene) donor and (6,6)-phenyl-C61-butyric acid methyl ester acceptor in the near-infrared wavelength region. While the exciton absorption exists only for wavelength below 650 nm, direct generation of charge-transfer exciton formed between the donor and acceptor extends the absorption wavelength to 950 nm. For films with micrometer thickness, the photon-to-electron conversion efficiency is about 60% at 750 nm wavelength under reverse voltage bias and the photocurrent to dark current ratio is about 8.6 at 900 nm and remains 3.6 even at 1000 nm. Photodetector with high sensitivity covering exclusively the 650-1000 nm near infrared region can therefore be made without a low bandgap material. The charge-transfer exciton absorption coefficient and photocurrent sensitivity depend on the annealing condition which controls the donor-acceptor morphology

  5. 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.

  6. NIR and MIR charge transfer plasmons in wire-bridged antennas (Presentation Recording)

    Science.gov (United States)

    Zhang, Yue; Wen, Fangfang; Gottheim, Samuel; King, Nicholas S.; Zhang, Yu; Nordlander, Peter; Halas, Naomi J.

    2015-09-01

    We investigate optical properties of wire-bridged plasmonic nanoantennas. Here we found two spectral features: a dipolar plasmon in the visible and a Charge Transfer Plasmon (CTP) in the infrared. The CTP depends sensitively on the conductance of the junction wire, offering a controllable way for tuning the plasmon resonance to the desired wavelength regime via junction geometries. Here we use single-particle dark field spectroscopy from UV, visible to IR to identify plasmonic modes in different spectrum regimes. The simulations using Finite-difference time-domain (FDTD) method are in good agreement with experiment: Increasing the junction wire width and concurrently the junction conductance blue shifts resonance positions, and simultaneously modifies scattering strengths, the linewidth of CTP and dipolar plasmon. We notice that CTP in a much longer wavelength regime and preserving a narrow line width, an important implication for designing IR plasmons with a high quality factor for enhanced spectroscopy and sensing applications. We also extend the CTP to the IR regime by increasing the wire length to create IR plasmon while keeping the line width of the resonance. Our work offers a way for studying the charge transfer properties in plasmonic nanostructures. Not only it adds another degree in understanding the charge transfer properties in plasmonic nanostructures but also offers an optical platform for studying molecules transport at optical frequencies and related applications.

  7. A rational reduction of CI expansions: combining localized molecular orbitals and selected charge excitations.

    Science.gov (United States)

    Krah, Tim; Ben Amor, Nadia; Maynau, Daniel; Berger, J A; Robert, Vincent

    2014-07-01

    Based on localized molecular orbitals, the proposed method reduces large configuration interaction (CI) spaces while maintaining agreement with reference values. Our strategy concentrates the numerical effort on physically pertinent CI-contributions and is to be considered as a tool to tackle large systems including numerous open-shells. To show the efficiency of our method we consider two 4-electron parent systems. First, we illustrate our approach by describing the van der Waals interactions in the (H2)2 system. By systematically including local correlation, dispersion and charge transfer mechanisms, we show that 90% of the reference full CI dissociation energy of the H2 dimer is reproduced using only 3% of the full CI space. Second, the conformational cis/trans rotation barrier of the butadiene molecule is remarkably reproduced (97% of the reference value) with less than 1% of the reference space. This work paves the way to numerical strategies which afford the electronic structure determination of large open-shell systems avoiding the exponential limitation. At the same time, a physical analysis of the contents of the wave function is offered. PMID:24935105

  8. Investigation of ground state charge transfer complex between paracetamol and p-chloranil through DFT and UV-visible studies

    Science.gov (United States)

    Shukla, Madhulata; Srivastava, Nitin; Saha, Satyen

    2012-08-01

    The present report deals with the theoretical investigation on ground state structure and charge transfer (CT) transitions in paracetamol (PA)/p-chloranil (CA) complex using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) method. It is found that Cdbnd O bond length of p-chloranil increases on complexation with paracetamol along with considerable amount of charge transfer from PA to CA. TD-DFT calculations have been performed to analyse the observed UV-visible spectrum of PA-CA charge transferred complex. Interestingly, in addition to expected CT transition, a weak symmetry relieved π-π* transition in the chloranil is also observed.

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

    International Nuclear Information System (INIS)

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

  10. Final Technical Report for the Energy Frontier Research Center Understanding Charge Separation and Transfer at Interfaces in Energy Materials (EFRC:CST)

    Energy Technology Data Exchange (ETDEWEB)

    Vanden Bout, David A. [Univ. of Texas, Austin, TX (United States)

    2015-09-14

    Our EFRC was founded with the vision of creating a broadly collaborative and synergistic program that would lead to major breakthroughs in the molecular-level understanding of the critical interfacial charge separation and charge transfer (CST) processes that underpin the function of candidate materials for organic photovoltaic (OPV) and electrical-energy-storage (EES) applications. Research in these energy contexts shares an imposing challenge: How can we understand charge separation and transfer mechanisms in the presence of immense materials complexity that spans multiple length scales? To address this challenge, our 50-member Center undertook a total of 28 coordinated research projects aimed at unraveling the CST mechanisms that occur at interfaces in these nanostructured materials. This rigorous multi-year study of CST interfaces has greatly illuminated our understanding of early-timescale processes (e.g., exciton generation and dissociation dynamics at OPV heterojunctions; control of Li+-ion charging kinetics by surface chemistry) occurring in the immediate vicinity of interfaces. Program outcomes included: training of 72 graduate student and postdoctoral energy researchers at 5 institutions and spanning 7 academic disciplines in science and engineering; publication of 94 peer-reviewed journal articles; and dissemination of research outcomes via 340 conference, poster and other presentations. Major scientific outcomes included: implementation of a hierarchical strategy for understanding the electronic communication mechanisms and ultimate fate of charge carriers in bulk heterojunction OPV materials; systematic investigation of ion-coupled electron transfer processes in model Li-ion battery electrode/electrolyte systems; and the development and implementation of 14 unique technologies and instrumentation capabilities to aid in probing sub-ensemble charge separation and transfer mechanisms.

  11. Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ

    Directory of Open Access Journals (Sweden)

    Raúl García

    2015-06-01

    Full Text Available We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a π-extended tetrathiafulvalene (exTTF group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10−7 G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species.

  12. Influence of functional groups on charge transport in molecular junctions

    DEFF Research Database (Denmark)

    Mowbray, Duncan; Jones, Glenn; Thygesen, Kristian Sommer

    2008-01-01

    demonstrates how ideas from functional group chemistry may be used to engineer a molecule's transport properties, as was shown experimentally and using a semiempirical model for BDA [Nano Lett. 7, 502 (2007)]. In particular, we show that the qualitative change in conductance due to a given functional group can...... the experimental values, but good agreement is obtained after correcting for self-interaction and image charge effects. (c) 2008 American Institute of Physics....... be predicted from its known electronic effect (whether it is sigma/pi donating/withdrawing). However, the influence of functional groups on a molecule's conductance is very weak, as was also found in the BDA experiments. The calculated DFT conductances for the BDA species are five times larger than...

  13. Sprite produced by consecutive impulse charge transfers following a negative stroke: Observation and simulation

    Science.gov (United States)

    Lu, Gaopeng; Cummer, Steven A.; Tian, Ye; Zhang, Hongbo; Lyu, Fanchao; Wang, Tao; Stanley, Mark A.; Yang, Jing; Lyons, Walter A.

    2016-04-01

    On the morning of 5 June 2013, two cameras of the SpriteCam network concurrently captured a red sprite with diffuse halo over a mesoscale convective system (MCS) passing the panhandle area of Oklahoma. This sprite was produced by a negative cloud-to-ground (CG) stroke with peak current of -103 kA in a manner different from previous observations in several aspects. First of all, the causative stroke of sprite is located by the National Lightning Detection Network (NLDN) in the trailing stratiform of MCS, instead of the deep convection typically for negative sprites. Second, the sprite-producing stroke was likely the first stroke of a multistroke negative CG flash (with ≥6 CG strokes) whose evolution was mainly confined in the lower part of thunderstorm; although the parent flash of sprite might contain relatively long in-cloud evolution prior to the first stroke, there is no evidence that the negative leader had propagated into the upper positive region of thundercloud as typically observed for the sprite-producing/class negative CG strokes. Third, as shown by the simulation with a two-dimensional full-wave electrodynamic model, although the impulse charge moment change (-190 C km) produced by the main stroke was not sufficient to induce conventional breakdown in the mesosphere, a second impulse charge transfer occurred with ~2 ms delay to cause a substantial charge transfer (-290 C km) so that the overall charge moment change (-480 C km) exceeded the threshold for sprite production; this is a scenario different from the typical case discussed by Li et al. (2012). As for the source of the second current pulse that played a critical role to produce the sprite, it could be an M component whose charge source was at least 9 km horizontally displaced from the main stroke or a negative CG stroke (with weak peak current for the return stroke) that was not detected by the NLDN.

  14. Effect of medium on charge transport properties of modified poly(dA)-poly(dT) DNA molecular wire

    Science.gov (United States)

    Suhendro, D. K.; Yudiarsah, E.; Saleh, R.

    2014-09-01

    By using tight binding Hamiltonian approach, the medium's effect on charge transport properties of modified poly(dA)-poly(dT) DNA molecular wire is studied. The DNA sequences used are modified poly(dA)-poly(dT) sequence by replacing 50 base pairs randomly with GC or CG base pairs. The DNA is contacted by metallic leads at both ends. The medium's effect on DNA is modeled as backbone onsite energy disorder. The DNA is taken to be at room temperature. The charge transport properties of the two sequences are studied by calculating the transmission probabilities of the charges using the scattering and transfer matrix methods simultaneously. Then the current-voltage (I-V) characteristics are calculated from the transmission probabilities using the Landauer-Büttiker Formalism. The theoretical differential conductance curve is then calculated from the I-V characteristic curve. The I-V results show that as the backbone disorder strength increases, the maximum current decreases for both sequences. However, the threshold voltage can increase or decrease with increasing backbone disorder depending on the sequence. The transmission results show that the position of transmission peaks changed with backbone disorder strength. Comparison with previous published results using poly(dG)-poly(dC) sequence shows that in contrast to that sequence, backbone disorder can decrease the threshold voltage in one of the sequences studied. This may point to a new understanding of the interplay between environmental and sequence disorder effect on charge transport in DNA.

  15. Charge-exchange breakup of the deuteron with the production of two protons and spin structure of the amplitude of the nucleon charge transfer reaction

    International Nuclear Information System (INIS)

    In the framework of the impulse approximation, the relation between the effective cross section of the charge-exchange breakup of a fast deuteron d + a → (pp) + b and the effective cross section of the charge transfer process n + a → p + b is discussed. In doing so, the effects of the proton identity (Fermi-statistics) and of the Coulomb and strong interactions of protons in the final state are taken into account. The distribution over relative momenta of the protons, produced in the charge-exchange process d + p → (pp) + n in the forward direction, is investigated. At the transfer momenta being close to zero the effective cross section of the charge-exchange breakup of a fast deuteron, colliding with the proton target, is determined only by the spin-flip part of the amplitude of the charge transfer reaction n + p → p + n at the zero angle. It is shown that the study of the process d + p → (pp) + n in a beam of the polarized (aligned) deuterons allows one, in principle, to separate two spin-dependent terms in the amplitude of the charge transfer reaction n + p → p + n, one of which does not conserve and the other one conserves the projection of the nucleon spin onto the direction of momentum at the transition of the neutron into the proton

  16. Influence of Functional Groups on Charge Transport in Molecular Junctions

    OpenAIRE

    Mowbray, Duncan; Jones, Glenn; Thygesen, Kristian Sommer

    2008-01-01

    Using density functional theory (DFT), we analyze the influence of five classes of functional groups, as exemplified by NO2, OCH3, CH3, CCl3, and I, on the transport properties of a 1,4-benzenedithiolate (BDT) and 1,4-benzenediamine (BDA) molecular junction with gold electrodes. Our analysis demonstrates how ideas from functional group chemistry may be used to engineer a molecule's transport properties, as was shown experimentally and using a semiempirical model for BDA [Nano Lett. 7, 502 (20...

  17. The influence of negative charged centers on the hole transport in a typical molecularly doped polymer

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Charged centers are introduced into a biased sample using an electron gun. • Two-layer multiple trapping model is used to describe charge carrier transport. • Model parameters are extracted from experimental data. • Current transients rise in the preflight region due to induced space charge. • Proposed model explains the observed effects semiquantitatively. - Abstract: We have studied effects of the negative charged centers on the time of flight (TOF) curves measured in a typical hole-conducting molecularly doped polymer. The main effects are the unusual TOF (surface generation) current rise in the preflight region (be it a flat plateau or a cusp) due to the accumulated space charge and the current reduction at all times because of the monomolecular recombination. TOF-2 (bulk generation) transients are less sensitive to charged centers. Analysis of these effects has proved that charged centers do not change the carrier mobility provided that the space charge field and bimolecular recombination are properly accounted for in terms of the proposed two-layer MT model. We have shown that combination of TOF, TOF-1a and TOF-2 variants of the electron-gun based technique allows one to establish definitively the character of the charge carrier transport in MDPs

  18. An improved model of Charge Transfer Inefficiency and correction algorithm for the Hubble Space Telescope

    CERN Document Server

    Massey, Richard; Cordes, Oliver; Marggraf, Ole; Israel, Holger; Miller, Lance; Hall, David; Cropper, Mark; Prod'homme, Thibaut; Niemi, Sami-Matias

    2014-01-01

    Charge-Coupled Device (CCD) detectors, widely used to obtain digital imaging, can be damaged by high energy radiation. Degraded images appear blurred, because of an effect known as Charge Transfer Inefficiency (CTI), which trails bright objects as the image is read out. It is often possible to correct most of the trailing during post-processing, by moving flux back to where it belongs. We compare several popular algorithms for this: quantifying the effect of their physical assumptions and tradeoffs between speed and accuracy. We combine their best elements to construct a more accurate model of damaged CCDs in the Hubble Space Telescope's Advanced Camera for Surveys/Wide Field Channel, and update it using data up to early 2013. Our algorithm now corrects 98% of CTI trailing in science exposures, a substantial improvement over previous work. Further progress will be fundamentally limited by the presence of read noise. Read noise is added after charge transfer so does not get trailed - but it is incorrectly untr...

  19. 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.

  20. Transverse charge transport through DNA oligomers in large-area molecular junctions

    Science.gov (United States)

    Katsouras, Ilias; Piliego, Claudia; Blom, Paul W. M.; de Leeuw, Dago M.

    2013-09-01

    We investigate the nature of charge transport in deoxyribonucleic acid (DNA) using self-assembled layers of DNA in large-area molecular junctions. A protocol was developed that yields dense monolayers where the DNA molecules are not standing upright, but are lying flat on the substrate. As a result the charge transport is measured not along the DNA molecules but in the transverse direction, across their diameter. The electrical transport data are consistent with the derived morphology. We demonstrate that the charge transport mechanism through DNA is identical to non-resonant tunneling through alkanethiols with identical length, classifying DNA as a dielectric.

  1. Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction

    Science.gov (United States)

    Tamura, Hiroyuki; Martinazzo, Rocco; Ruckenbauer, Matthias; Burghardt, Irene

    2012-12-01

    Following up on our recent study of ultrafast charge separation at oligothiophene-fullerene interfaces [H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C 115, 10205 (2011), 10.1021/jp203174e], we present here a detailed quantum dynamical perspective on the charge transfer process. To this end, electron-phonon coupling is included non-perturbatively, by an explicit quantum dynamical treatment using the multi-configuration time-dependent Hartree (MCTDH) method. Based upon a distribution of electron-phonon couplings determined from electronic structure studies, a spectral density is constructed and employed to parametrize a linear vibronic coupling Hamiltonian. The diabatic coupling is found to depend noticeably on the inter-fragment distance, whose effect on the dynamics is here investigated. MCTDH calculations of the nonadiabatic transfer dynamics are carried out for the two most relevant electronic states and 60 phonon modes. The electron transfer process is found to be ultrafast and mediated by electronic coherence, resulting in characteristic oscillatory features during a period of about 100 fs.

  2. Hydrogen-bonded Intramolecular Charge Transfer Excited State of Dimethylaminobenzophenone using Time Dependent Density Functional Theory

    Institute of Scientific and Technical Information of China (English)

    Yu-ling Chu; Zhong Yang; Zhe-feng Pan; Jing Liu; Yue-yi Han; Yong Ding; Peng Song

    2012-01-01

    Density functional theory and time-dependent density-functional theory have been used to investigate the photophysical properties and relaxation dynamics of dimethylaminobenzophenone (DMABP) and its hydrogen-bonded DMABP-MeOH dimer.It is found that,in nonpolar aprotic solvent,the transitions from S0 to S1 and S2 states of DMABP have both n→π* and π→π* characters,with the locally excited feature mainly located on the C=O group and the partial CT one characterized by electron transfer mainly from the dimethylaminophenyl group to the C=O group.But when the intermolecular hydrogen bond C=O…H-O is formed,the highly polar intramolecular charge transfer character switches over to the first excited state of DMABP-MeOH dimer and the energy difference between the two lowlying electronically excited states increases.To gain insight into the relaxation dynamics of DMABP and DMABP-MeOH dimer in the excited state,the potential energy curves for conformational relaxation are calculated.The formation of twisted intramolecular charge transfer state via diffusive twisting motion of the dimethylamino/dimethylaminophenyl groups is found to be the major relaxation process.In addition,the decay of the S1 state of DMABP-MeOH dimer to the ground state,through nonradiative intermolecular hydrogen bond stretching vibrations,is facilitated by the formation of the hydrogen bond between DMABP and alcohols.

  3. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier

    Science.gov (United States)

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-06-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery.

  4. Energy and charge state dependences of transfer ionization to single capture ratio for fast multiply charged ions on helium

    Science.gov (United States)

    Unal, Ridvan

    The charge state and energy dependences of Transfer Ionization (TI) and Single Capture (SC) processes in collisions of multiply charged ions with He from intermediate to high velocities are investigated using coincident recoil ion momentum spectroscopy. The collision chamber is commissioned on the 15-degree port of a switching magnet, which allows the delivery of a beam with very little impurity. The target was provided from a supersonic He jet with a two-stage collimation. The two-stage, geometrically cooled, supersonic He jet has significantly reduced background contribution to the spectrum compared to a single stage He jet. In the case of a differentially pumped gas cell complex calculations based on assumptions for the correction due to the collisions with the contaminant beam led to corrections, which were up to 50%. The new setup allows one to make a direct separation of contaminant processes in the experimental data using the longitudinal momentum spectra. Furthermore, this correction is much smaller (about 8.8%) yielding better overall precision. The collision systems reported here are 1 MeV/u O(4--8)+ , 0.5--2.5 MeV/u F(4--9)+, 2.0 MeV/u Ti 15,17,18+, 1.6--1.75 MeV/u Cu18,20+ and 0.25--0.5 MeV/u I(15--25)+ ions interacting with helium. We have determined the sTIsSC ratio for high velocity highly charged ions on He at velocities in the range of 6 to 10 au and observed that the ratio is monotonically decreasing with velocity. Furthermore, we see a ratio that follows a q2 dependence up to approximately q = 9. Above q = 9 the experimental values exceed the q2 dependence prediction due to antiscreening. C. D. Lin and H. C. Tseng have performed coupled channel calculations for the energy dependence of TI and SC for F9+ + He and find values slightly higher than our measured values, but with approximately the same energy dependence. The new data, Si, Ti and Cu, go up only to q = 20 and show a smooth monotonically increasing TI/SC ratio. The TI/SC ratio for I (15

  5. Scaling of the transition temperature of hole-doped cuprate superconductors with the charge-transfer energy

    OpenAIRE

    Weber, Cédric; Yee, Chuck-Hou; Haule, Kristjan; Kotliar, Gabriel

    2011-01-01

    We use first-principles calculations to extract two essential microscopic parameters, the charge-transfer energy and the inter-cell oxygen-oxygen hopping, which correlate with the maximum superconducting transition temperature $\\Tcmax$ across the cuprates. We explore the superconducting state in the three-band model of the copper-oxygen planes using cluster Dynamical Mean-Field Theory. We find that the variation in the charge-transfer energy largely accounts for the empirical trend in $\\Tcmax...

  6. Magneto-Dielectric Effects Induced by Optically-Generated Intermolecular Charge-Transfer States in Organic Semiconducting Materials

    OpenAIRE

    Zang, Huidong; Yan, Liang; Li, Mingxing; He, Lei; Gai, Zheng; Ivanov, Ilia; Wang, Min; Chiang, Long; Urbas, Augustine; Hu, Bin

    2013-01-01

    Traditionally, magneto-dielectric effects have been developed by combining ferroelectric and magnetic materials. Here, we show a magneto-dielectric effect from optically-generated intermolecular charge-transfer states in an organic semiconducting donor:acceptor (PVK:TCNB) system. We observe in magnetic field effects of photoluminescence that a magnetic field can change singlet/triplet population ratio in intermolecular charge-transfer states. Furthermore, our theoretical analysis and experime...

  7. 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.

  8. Theoretical investigations into optical and charge transfer properties of donor-acceptor 1,8-naphthalimide derivatives as possible organic light-emitting materials

    Science.gov (United States)

    Chai, Wandong; Jin, Ruifa

    2016-01-01

    A series of D-A naphthalimide-substituted fluorene derivatives have been designed to explore their optical, electronic, and charge transport properties as charge transport and/or luminescent materials for organic light-emitting diodes (OLEDs). The frontier molecular orbitals (FMOs) analysis turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer (ICT). The calculated results show that their optical and electronic properties are affected by the substituent groups in fluorene moieties. Our results suggest that all selected candidates are promising as luminescent materials for OLEDs. In addition, all derivatives can be used as promising hole and electron transport materials while derivatives with dibenzothiophene fragment can be used as hole transport material only for OLEDs.

  9. Current-Driven Conformational Changes, Charging and Negative Differential Resistance in Molecular Wires

    OpenAIRE

    Emberly, Eldon; Kirczenow, George

    2001-01-01

    We introduce a theoretical approach based on scattering theory and total energy methods that treats transport non-linearities, conformational changes and charging effects in molecular wires in a unified way. We apply this approach to molecular wires consisting of chain molecules with different electronic and structural properties bonded to metal contacts. We show that non-linear transport in all of these systems can be understood in terms of a single physical mechanism and predict that negati...

  10. Proton and charge transfer reactions dynamics of a hydroxyflavone derivative in a polar solvent and in a cyclodextrin nanocavity

    International Nuclear Information System (INIS)

    In this work, we report on the observation of ultrafast intramolecular charge- and proton-transfer reactions of 4'-dimethylaminoflavonol (DMAF) in N,N-dimethyl formamide and in γ-cyclodextrin (γ-CD) solution. Upon femtosecond excitation an intramolecular charge transfer (ICT) reaction takes place to produce an ICT structure in ∼200 fs. This structure may undergo a proton transfer reaction to generate a zwitterionic (Z) form in 2-3 ps, or relaxes in its potential energy well, to later equilibrate with that of Z in hundreds of ps. Addition of γ-CD does not significantly affect the fast dynamics of the formed anion. The fs-emission signals of the parent molecule, 3-hydroxyflavone, indicate that the dimethyl amino group in DMAF enhances the rate constant of intermolecular proton-transfer and intramolecular charge-transfer reactions

  11. On the role of charge transfer in the stabilization of weakly bound complexes involving water and hydrogen sulphide molecules

    International Nuclear Information System (INIS)

    Graphical abstract: A charge-displacement analysis allows to quantitatively assess charge-transfer effects in hydrogen-bonded complexes. Highlights: ► We compare water with hydrogen sulphide both interacting with krypton. ► In both cases the interaction possesses a definite charge transfer component. ► Charge-transfer differs slightly in the two systems and exhibits different stereoselectivity. - Abstract: Integral cross section data for collisions of water and hydrogen sulphide molecules with noble gas atoms, measured with the same apparatus under identical conditions and analyzed by exploiting the same potential model, provided a set of internally consistent potential parameters. Their critical comparison is exploited not only to identify those systems where the intermolecular bond is not simply due to the balancing of size repulsion with dispersion and induction attraction, but also to establish the amount of bond stabilization by charge-transfer effects. Such experimental findings are analyzed through extensive and accurate ab initio calculations, addressed at discovering the relevant differences in the basic features of the potential energy surfaces. In particular, we have analyzed in detail the prototype H2S, H2O–Kr systems and found pronounced differences in the dependence of the interaction nature and energy on the relative orientation of the colliding systems. Using the recently proposed charge-displacement analysis we have been able to quantitatively assess charge-transfer effects, which differ significantly in the two systems and exhibit different stereoselectivity. This casts further light on the specificity of water interactions.

  12. Local equilibria and state transfer of charged classical particles on a helix in an electric field

    CERN Document Server

    Plettenberg, J; Zampetaki, A V; Schmelcher, P

    2016-01-01

    We explore the effects of a homogeneous external electric field on the static properties and dynamical behavior of two charged particles confined to a helix. In contrast to the field-free setup which provides a separation of the center-of-mass and relative motion, the existence of an external force perpendicular to the helix axis couples the center-of-mass to the relative degree of freedom leading to equilibria with a localized center of mass. By tuning the external field various fixed points are created and/or annihilated through different bifurcation scenarios. We provide a detailed analysis of these bifurcations based on which we demonstrate a robust state transfer between essentially arbitrary equilibrium configurations of the two charges that can be induced by making the external force time-dependent.

  13. Charge transfer in the interactions of partially stripped ions with atoms at intermediate and high energies

    International Nuclear Information System (INIS)

    The Coulomb-Born (CB) approximation has been employed to study charge transfer cross sections in collisions of Cq+, Nq+ and Oq+ (q = 1-5) with atomic hydrogen in ground state in the energy range of 30-200 keV/amu. The interaction of the active electron with the incoming projectile ion has been approximated by a model potential containing both a long-range part and a short-range part. Variations of total capture cross sections with impact energy compare favourable well with the available experimental observations and with other theoretical findings. In addition, sub-shell distributions of total capture cross sections are given in graphical form. However, we are unable to find any oscillation in the charge-state dependence of total capture cross sections. (author)

  14. Charge-sharing and electron-transfer characteristics of a gas electron multiplier (GEM)

    International Nuclear Information System (INIS)

    The charge sharing and electron-transfer process of a gas electron multiplier (GEM) with a high density of holes (60 μm in diameter at 100 μm of pitch) were examined. The GEM operated at a lower applied voltage due to the smaller size of the GEM holes; thus, a higher electric field is seen in the multiplication channels. The electron collection efficiency and the charge sharing were found to depend on the external field, as well as on the GEM voltage. The electron collection efficiency approached 90 % with a full collection of primary electrons under optimized GEM field conditions, and the range of the drift field for efficient electron collection to reach a plateau increased with the GEM voltage. The positive-ion feedback is also estimated

  15. Charge-sharing and electron-transfer characteristics of a gas electron multiplier (GEM)

    Energy Technology Data Exchange (ETDEWEB)

    Han, Sang Hyo; Kang, Hee Dong [Kyungpook National Univ., Daegu (Korea, Republic of); Kim, Yong Kyun; Moon, Byung Soo; Chung, Chong Eun [KAERI, Daejon (Korea, Republic of); Cho, Hyo Sung; Kang, Sang Mook [Yonsei Univ., Wonju (Korea, Republic of)

    2002-05-01

    The charge sharing and electron-transfer process of a gas electron multiplier (GEM) with a high density of holes (60 {mu}m in diameter at 100 {mu}m of pitch) were examined. The GEM operated at a lower applied voltage due to the smaller size of the GEM holes; thus, a higher electric field is seen in the multiplication channels. The electron collection efficiency and the charge sharing were found to depend on the external field, as well as on the GEM voltage. The electron collection efficiency approached 90 % with a full collection of primary electrons under optimized GEM field conditions, and the range of the drift field for efficient electron collection to reach a plateau increased with the GEM voltage. The positive-ion feedback is also estimated.

  16. Modeling of Charge Transfer Inefficiency in a CCD with High Speed Column Parallel Readout

    CERN Document Server

    Sopczak, Andre; Bekhouche, Khaled; Bowdery, Chris; Buttar, Craig; Damerell, Chris; Djendaoui, Dahmane; Dehimi, Lakhdar; Greenshaw, Tim; Koziel, Michal; Maneuski, Dzmitry; Nomerotski, Andrei; Stefanov, Konstantin; Tikkanen, Tuomo; Woolliscroft, Tim; Worm, Steve

    2008-01-01

    Charge Coupled Devices (CCDs) have been successfully used in several high energy physics experiments over the past two decades. Their high spatial resolution and thin sensitive layers make them an excellent tool for studying short-lived particles. The Linear Collider Flavour Identification (LCFI) collaboration is developing Column-Parallel CCDs (CPCCDs) for the vertex detector of a future Linear Collider. The CPCCDs can be read out many times faster than standard CCDs, significantly increasing their operating speed. An Analytic Model has been developed for the determination of the charge transfer inefficiency (CTI) of a CPCCD. The CTI values determined with the Analytic Model agree largely with those from a full TCAD simulation. The Analytic Model allows efficient study of the variation of the CTI on parameters like readout frequency, operating temperature and occupancy.

  17. ANISOTROPY EFFECTS IN SINGLE-ELECTRON TRANSFER BETWEEN LASER-EXCITED ATOMS AND HIGHLY-CHARGED IONS

    NARCIS (Netherlands)

    1995-01-01

    Recent collision experiments are reviewed in which one-electron transfer between laser excited target atoms and (highly charged) keV-ions has been studied. Especially results showing a dependence of the charge exchange on the initial target orbital alignment are discussed. The question to what exten

  18. Carotenoid charge transfer states and their role in energy transfer processes in LH1-RC complexes from aerobic anoxygenic phototrophs.

    Science.gov (United States)

    Šlouf, Václav; Fuciman, Marcel; Dulebo, Alexander; Kaftan, David; Koblížek, Michal; Frank, Harry A; Polívka, Tomáš

    2013-09-26

    Light-harvesting complexes ensure necessary flow of excitation energy into photosynthetic reaction centers. In the present work, transient absorption measurements were performed on LH1-RC complexes isolated from two aerobic anoxygenic phototrophs (AAPs), Roseobacter sp. COL2P containing the carotenoid spheroidenone, and Erythrobacter sp. NAP1 which contains the carotenoids zeaxanthin and bacteriorubixanthinal. We show that the spectroscopic data from the LH1-RC complex of Roseobacter sp. COL2P are very similar to those previously reported for Rhodobacter sphaeroides, including the transient absorption spectrum originating from the intramolecular charge-transfer (ICT) state of spheroidenone. Although the ICT state is also populated in LH1-RC complexes of Erythrobacter sp. NAP1, its appearance is probably related to the polarity of the bacteriorubixanthinal environment rather than to the specific configuration of the carotenoid, which we hypothesize is responsible for populating the ICT state of spheroidenone in LH1-RC of Roseobacter sp. COL2P. The population of the ICT state enables efficient S1/ICT-to-bacteriochlorophyll (BChl) energy transfer which would otherwise be largely inhibited for spheroidenone and bacteriorubixanthinal due to their low energy S1 states. In addition, the triplet states of these carotenoids appear well-tuned for efficient quenching of singlet oxygen or BChl-a triplets, which is of vital importance for oxygen-dependent organisms such as AAPs. PMID:23130956

  19. A spectroscopic study of factors affecting charge transfer at organo-metallic interfaces

    International Nuclear Information System (INIS)

    The properties of organic films produced by the Langmuir-Blodgett (LB) technique have become more widely known in the last few decades, as the variety of organic molecules suitable for this method of production has increased. One class of LB molecule receiving particular attention has been that of conjugated polymers. These organic materials exhibit an anisotropic semi-conductor like behavior along the polymer chain, making them suitable candidate materials for use in molecular electronic devices. However, the exact nature of multiple charge transport mechanisms is still an area worthy of investigation. Through the development in this work of a dosimetric device, suitable for the study of a number of different radiation types, several difficulties associated with the charge extraction from organic materials, by means of metallic electrodes, were clearly illustrated. Some of these problems were likely to have been caused by charge trapping within the film itself. However, it is the trapping at the boundary between the LB film and metallic electrode, where there is a mismatch in electronic energy levels, which has been the main investigation of this work. To that end a number of different spectroscopic investigations were undertaken in order to pinpoint various factors affecting the efficiency in the transport of charge across the interface region. Extensive low energy Positron Doppler Broadened Annihilation Spectroscopy (DBARS) measurements were made on 12-8 polydiacetylene and ω-tricosenoic acid LB films. The resulting analyses have allowed comparison of charge trapping within the different bulk films and also at the film to substrate interface. In addition to DBARS, Fourier Transform Infra-red (FTIR) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies have been used to investigate the factors affecting the carboxylic acid group at the head of the LB molecule and the role this plays in charge transport across the organo-metallic boundary. (author)

  20. Interfacial electronic charge transfer and density of states in short period Cu/Cr multilayers; TOPICAL

    International Nuclear Information System (INIS)

    Nanometer period metallic multilayers are ideal structures to investigate electronic phenomena at interfaces between metal films since interfacial atoms comprise a large atomic fraction of the samples. The Cu/Cr binary pair is especially suited to study the interfaces in metals since these elements are mutually insoluble, thus eliminating mixing effects and compound formation and the lattice mismatch is very small. This allows the fabrication of high structural quality Cu/Cr multilayers that have a structure which can be approximated in calculations based on idealized atomic arrangements. The electronic structure of the Cu and the Cr layers in several samples of thin Cu/Cr multilayers were studied using x-ray absorption spectroscopy (XAS). Total electron yield was measured and used to study the white lines at the Cu L(sub 2) and L(sub 3) absorption edges. The white lines at the Cu absorption edges are strongly related to the unoccupied d-orbitals and are used to calculate the amount of charge transfer between the Cr and Cu atoms in interfaces. Analysis of the Cu white lines show a charge transfer of 0.026 electrons/interfacial Cu atom to the interfacial Cr atoms. In the Cu XAS spectra we also observe a van Hove singularity between the L(sub 2) and L(sub 3) absorption edges as expected from the structural analysis. The absorption spectra are compared to partial density of states obtained from a full-potential linear muffin-tin orbital calculation. The calculations support the presence of charge transfer and indicate that it is localized to the first two interfacial layers in both Cu and Cr

  1. EV Charging Through Wireless Power Transfer: Analysis of Efficiency Optimization and Technology Trends

    Energy Technology Data Exchange (ETDEWEB)

    Miller, John M [ORNL; Rakouth, Heri [Delphi Automotive Systems, USA; Suh, In-Soo [Korea Advanced Institute of Science and Technology

    2012-01-01

    This paper is aimed at reviewing the technology trends for wireless power transfer (WPT) for electric vehicles (EV). It also analyzes the factors affecting its efficiency and describes the techniques currently used for its optimization. The review of the technology trends encompasses both stationary and moving vehicle charging systems. The study of the stationary vehicle charging technology is based on current implementations and on-going developments at WiTricity and Oak Ridge National Lab (ORNL). The moving vehicle charging technology is primarily described through the results achieved by the Korean Advanced Institute of Technology (KAIST) along with on-going efforts at Stanford University. The factors affecting the efficiency are determined through the analysis of the equivalent circuit of magnetic resonant coupling. The air gap between both transmitting and receiving coils along with the magnetic field distribution and the relative impedance mismatch between the related circuits are the primary factors affecting the WPT efficiency. Currently the industry is looking at an air gap of 25 cm or below. To control the magnetic field distribution, Kaist has recently developed the Shaped Magnetic Field In Resonance (SMFIR) technology that uses conveniently shaped ferrite material to provide low reluctance path. The efficiency can be further increased by means of impedance matching. As a result, Delphi's implementation of the WiTricity's technology exhibits a WPT efficiency above 90% for stationary charging while KAIST has demonstrated a maximum efficiency of 83% for moving vehicle with its On Line Vehicle (OLEV) project. This study is restricted to near-field applications (short and mid-range) and does not address long-range technology such as microwave power transfer that has low efficiency as it is based on radiating electromagnetic waves. This paper exemplifies Delphi's work in powertrain electrification as part of its innovation for the real world

  2. Assessment of asymptotically corrected model potential scheme for charge-transfer-like excitations in oligoacenes

    CERN Document Server

    Peng, Wei-Tao

    2014-01-01

    We examine the performance of the asymptotically corrected model potential scheme on the two lowest singlet excitation energies of acenes with different number of linearly fused benzene rings (up to 5), employing both the real-time time-dependent density functional theory and the frequency-domain formulation of linear-response time-dependent density functional theory. The results are compared with the experimental data and those calculated by long-range corrected hybrid functionals and others. The long-range corrected hybrid scheme is shown to outperform the asymptotically corrected model potential scheme for charge-transfer-like excitations.

  3. Metallization and charge-transfer gap closure of transition-metal iodides under pressure

    Energy Technology Data Exchange (ETDEWEB)

    Chen, A. Li-Chung

    1993-05-01

    It is shown with resistivity and near-IR absorption measurements that NiI{sub 2}, CoI{sub 2}, and FeI{sub 2} metallize under pressure by closure of the charge-transfer energy gap at pressures of 17, 10, and 23 GPa, respectively, which is close to the antiferromagnetic-diamagnetic transition in NiI{sub 2} and CoI{sub 2}. Thus, the magnetic transitions probably are caused by the metallization; in NiI{sub 2} and CoI{sub 2}, the insulator-metal transitions are first order. Moessbauer and XRD data were also collected. Figs, 46 refs.

  4. The effect of interfacial charge transfer on ferromagnetism in perovskite oxide superlattices

    International Nuclear Information System (INIS)

    The structural, magnetic, and electrical properties of superlattices composed of the ferromagnetic/metal La0.7Sr0.3MnO3 and non-magnetic/metal La0.5Sr0.5TiO3 grown on (001)-oriented SrTiO3 substrates have been investigated. Using a combination of bulk magnetometry, soft x-ray magnetic spectroscopy, and scanning transmission electron microscopy, we demonstrate that robust ferromagnetic properties can be maintained in this superlattice system where charge transfer at the interfaces is minimized. Therefore, ferromagnetism can be controlled effectively through the chemical identity and the thickness of the individual superlattice layers.

  5. Position and lifetime of atomic states close to a metal: application to resonant charge transfer

    International Nuclear Information System (INIS)

    The energy position and lifetime of atomic levels brought in front of a metal surface are the important quantities for the description of the resonant charge transfer process in atom-metal surface scattering. Recent results obtained in the non-perturbative CAM method on multielectron systems (H-, He-, C-) are discussed. They stress the importance of a proper description of the atomic system. In particular, the interaction with a metal surface is seen to reveal the differences between the different orbitals in a multielectronic system. (author)

  6. Solid State Rechargeable Organic Batteries Based on Polymer Composites of Charge-transfer Materials

    Directory of Open Access Journals (Sweden)

    R.K. Gupta

    2004-01-01

    Full Text Available Solid-state galvanic cells based on charge-transfer complexes have been extensively used. However, the low mechanical strengths of these materials have restricted their applications. To overcome this problem, the polymer composite of these materials have been prepared and used in fabrication of solid-state batteries. The pressed pellet of these materials has been used as cathode in contact with zinc as anode metal. The electrochemical characterization of these cells such as open-circuit voltages, short-circuit currents, their time and temperature dependence and rechargeability of these cells have been studied. The impedance analyses have been done to understand the nature of the electrode reaction.

  7. Dependence of kinetic rates of charge transfer on structural parameters in disordered systems

    Czech Academy of Sciences Publication Activity Database

    Menšík, Miroslav; Toman, Petr

    Praha : Czechoslovak Association for Crystal Growth (CSACG), 2014 - (Kožíšek, Z.; Nitsch, K.). s. 29 ISBN 978-80-260-6599-9. [Joint Seminar Development of Materials Science in Research and Education /24./. 08.09.2014-12.09.2014, Lednice] R&D Projects: GA MŠk LH12186; GA MŠk(CZ) LD14011 Grant ostatní: European Commission(XE) MPNS COST Action MP1202 Institutional support: RVO:61389013 Keywords : charge transfer * nanoparticles Subject RIV: BM - Solid Matter Physics ; Magnetism

  8. Pressure dependence of a charge-transfer gap and a three-band Hubbard model

    International Nuclear Information System (INIS)

    The three-band Hubbard Hamiltonian with an attractive oxygen-oxygen interaction Upp is investigated using the Hartree-Fock approximation. Such a Hamiltonian is assumed to be a generic model for CuO2 planes of high-Tc superconductors. Both superconducting and antiferromagnetic phases are found in the separate regions of the numerically obtained (Upp,δ) phase diagrams, where δ is the hole doping. It is found that the region of stability of the superconducting phase is enhanced with decreasing values of the charge-transfer gap, in good qualitative agreement with the experimental findings

  9. Charge-transfer photodissociation of adsorbed molecules via electron image states

    CERN Document Server

    Jensen, E T

    2007-01-01

    The 248nm and 193nm photodissociation of submonolayer quantities of CH$_3$Br and CH$_3$I adsorbed on thin layers of n-hexane indicate that the dissociation is caused by dissociative electron attachment from sub-vacuum level photoelectrons created in the copper substrate. The characteristics of this photodissociation-- translation energy distributions and coverage dependences show that the dissociation is mediated by an image potential state which temporarily traps the photoelectrons near the n-hexane--vacuum interface, and then the charge transfers from this image state to the affinity level of a co-adsorbed halomethane which then dissociates.

  10. Integer charge transfer at the tetrakis(dimethylamino)ethylene/Au interface

    DEFF Research Database (Denmark)

    Lindell, L.; Unge, Mikael; Osikowicz, W.; Stafstrom, S.; Salaneck, W.R.; Crispin, X.; de Jong, M.P.

    2008-01-01

    conditions, where direct overlap of the organic pi system from the metal bands is prevented due to presence of oxides and/or hydrocarbons. We present direct experimental and theoretical evidence showing that the interface energetic for such systems is governed by exchange of an integer amount of electrons.......In organic-based electronics, interfacial properties have a profound impact on device performance. The lineup of energy levels is usually dependent on interface dipoles, which may arise from charge transfer reactions. In many applications, metal-organic junctions are prepared under ambient...

  11. Formation of charge-transfer-complex in organic:metal oxides systems

    Science.gov (United States)

    Wu, S. P.; Kang, Y.; Liu, T. L.; Jin, Z. H.; Jiang, N.; Lu, Z. H.

    2013-04-01

    It is found that composite systems consisting of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) and molybdenum trioxide (MoO3) form an IR absorption band around 847 nm. It is also found that the vibrational modes of the CBP, as measured by Fourier Transform Infrared Spectroscopy, are quenched upon the formation of charge-transfer-complex (CTC) between CBP and MoO3. By examining several sets of organic:metal oxides systems, we discovered that the IR absorption band of the CTCs follow two distinct mechanisms depending on the nature and location of the HOMOs in the organic molecules.

  12. Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors

    Energy Technology Data Exchange (ETDEWEB)

    Padhiyar, Ashvin; Patel, A J; Oza, A T [Department of Physics, Sardar Patel University, Vallabh Vidyanagar-388 120, Gujarat (India)

    2007-12-05

    It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.

  13. Two-dimensional femtosecond optical spectroscopy of trapping dynamics in a charge-transfer process

    Science.gov (United States)

    Keß, Martin; Engel, Volker

    2016-04-01

    We study charge-transfer dynamics monitored by two-dimensional (2D) optical spectroscopy. The often used model consisting of two coupled diabatic electronic states in a single reaction coordinate is used to demonstrate the relation between the vibronic dynamics and the 2D-spectra. Within the employed wave-function approach, dissipation is included via a quantum-jump algorithm with explicit treatment of dephasing. States with long lifetimes which decay slowly due to the interaction with the environment are identified. Using filtered Fourier transforms, energy and time resolved information about the dissipative system dynamics can be obtained.

  14. Interfacial charge transfer behavior of conducting polymers as contact electrode for semiconductor devices

    Science.gov (United States)

    Kawakita, Jin; Fujikawa, Yuki; Nagata, Takahiro; Chikyow, Toyohiro

    2016-04-01

    As an alternative contact electrode material to metals, which is necessary for downsized semiconductor devices in 10 nm processes, an intrinsically conducting polymer was studied in terms of its interfacial charge-transfer behavior with an inorganic semiconductor. Polypyrrole as the conducting polymer was formed using an electrochemical technique on an oxide semiconductor and its electronic properties were evaluated using scanning probe microscopy. The experimental results showed that an ohmic contact was observed dynamically at local positions, although a Schottky barrier was expected in the static electronic state over the measurement area. From this research, the conducting polymer was found to be promising as a contact electrode.

  15. 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.

  16. Effective interactions between concentration fluctuations and charge transfer in chemically ordering liquid alloys

    International Nuclear Information System (INIS)

    The correlations between long-wavelength fluctuations of concentration in a liquid binary alloy are determined by a balance between an elastic strain free energy and an Ornstein-Zernike effective interaction. The latter is extracted from thermodynamic data in the case of the Li-Pb system, which is well known to chemically order with stoichiometric composition corresponding to Li4Pb. Strong attractive interactions between concentration fluctuations near the composition of chemical ordering originate from electronic charge transfer, which is estimated from the electron-ion partial structure factors as functions of composition in the liquid alloy. (author). 20 refs, 2 figs

  17. Charge-transfer induced EUV and soft X-ray emissions in the heliosphere

    OpenAIRE

    Koutroumpa, Dimitra; Lallement, Rosine; Kharchenko, V.; Dalgarno, A.; Pepino, R.; Izmodenov, V.; Quémerais, Eric

    2006-01-01

    We study the EUV/soft X-ray emission generated by charge transfer between solar wind heavy ions and interstellar neutral atoms and variations of the X-ray intensities and spectra with the line of sight direction, the observer location, the solar cycle phase and the solar wind anisotropies, and a temporary enhancement of the solar wind similar to the event observed by Snowden et al. (2004) during the XMM-Hubble Deep Field North exposure. Methods.Using recent observations of the neutral atoms c...

  18. 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.

  19. Experimental determination of charge density of 208Pb, by electron scattering at high momentum transfer

    International Nuclear Information System (INIS)

    After having recalled that elastic electron scattering allows the determination of nucleus charge density with a high precision, and that a sufficiently high momentum transfer is required for the precision of analysis methods, this research thesis presents the results obtained by an experiment performed on 208Pb with a high momentum transfer. This nucleus meets at best the approximations required by theoretical calculations. In a first part, the author discusses the use of this nucleus, discusses the available data and outlines the lacking ones. He presents the experimental installation and aspects: the linear accelerator, the scattering angle, the solid angle, the number of incident neutrons, the target thermal toughness, and the number of elastically scattered neutrons. He reports the reduction of data: experiment-based corrections, radiative corrections, spectrum deconvolution methods, data normalisation, diaphragm aperture corrections and multiple scattering corrections. The next part proposes an analysis of data, and the last one compares the obtained results with theoretical ones

  20. Measurement of charge transfer potential barrier in pinned photodiode CMOS image sensors

    Science.gov (United States)

    Chen, Cao; Bing, Zhang; Junfeng, Wang; Longsheng, Wu

    2016-05-01

    The charge transfer potential barrier (CTPB) formed beneath the transfer gate causes a noticeable image lag issue in pinned photodiode (PPD) CMOS image sensors (CIS), and is difficult to measure straightforwardly since it is embedded inside the device. From an understanding of the CTPB formation mechanism, we report on an alternative method to feasibly measure the CTPB height by performing a linear extrapolation coupled with a horizontal left-shift on the sensor photoresponse curve under the steady-state illumination. The theoretical study was performed in detail on the principle of the proposed method. Application of the measurements on a prototype PPD-CIS chip with an array of 160 × 160 pixels is demonstrated. Such a method intends to shine new light on the guidance for the lag-free and high-speed sensors optimization based on PPD devices. Project supported by the National Defense Pre-Research Foundation of China (No. 51311050301095).

  1. Beyond Vibrationally Mediated Electron Transfer: Coherent Phenomena Induced by Ultrafast Charge Separation

    CERN Document Server

    Huber, Robert; Moser, Jacques E; Grätzel, Michael; Wachtveitl, Josef

    2016-01-01

    Wave packet propagation succeeding electron transfer (ET) from alizarin dye molecules into the nanocrystalline TiO2 semiconductor has been studied by ultrafast transient absorption spectroscopy. Due to the ultrafast time scale of the ET reaction of about 6 fs the system shows substantial differences to molecular ET systems. We show that the ET process is not mediated by molecular vibrations and therefore classical ET theories lose their applicability. Here the ET reaction itself prepares a vibrational wave packet and not the electromagnetic excitation by the laser pulse. Furthermore, the generation of phonons during polaron formation in the TiO2 lattice is observed in real time for this system. The presented investigations enable an unambiguous assignment of the involved photoinduced mechanisms and can contribute to a corresponding extension of molecular ET theories to ultrafast ET systems like alizarin/TiO2.

  2. A spectroscopic study of factors affecting charge transfer at organo-metallic interfaces

    CERN Document Server

    Tucker, C E

    2001-01-01

    polydiacetylene and omega-tricosenoic acid LB films. The resulting analyses have allowed comparison of charge trapping within the different bulk films and also at the film to substrate interface. In addition to DBARS, Fourier Transform Infra-red (FTIR) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopies have been used to investigate the factors affecting the carboxylic acid group at the head of the LB molecule and the role this plays in charge transport across the organo-metallic boundary. The properties of organic films produced by the Langmuir-Blodgett (LB) technique have become more widely known in the last few decades, as the variety of organic molecules suitable for this method of production has increased. One class of LB molecule receiving particular attention has been that of conjugated polymers. These organic materials exhibit an anisotropic semi-conductor like behavior along the polymer chain, making them suitable candidate materials for use in molecular electronic devices. However,...

  3. Theory of charge transport in molecular junctions: From Coulomb blockade to coherent tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Yao-Wen; Jin, Bih-Yaw, E-mail: byjin@ntu.edu.tw [Department of Chemistry and Center for Emerging Material and Advanced Devices and Center for Quantum Science and Engineering, National Taiwan University, Taipei 10617, Taiwan (China)

    2014-08-14

    We study charge transport through molecular junctions in the presence of electron-electron interaction using the nonequilibrium Green's function techniques and the renormalized perturbation theory. In the perturbation treatment, the zeroth-order Hamiltonian of the molecular junction is composed of independent single-impurity Anderson's models, which act as the channels where charges come through or occupy, and the interactions between different channels are treated as the perturbation. Using this scheme, the effects of molecule-lead, electron-electron, and hopping interactions are included nonperturbatively, and the charge transport processes can thus be studied in the intermediate parameter range from the Coulomb blockade to the coherent tunneling regimes. The concept of quasi-particles is introduced to describe the kinetic process of charge transport, and then the electric current can be studied and calculated. As a test study, the Hubbard model is used as the molecular Hamiltonian to simulate dimeric and trimeric molecular junctions. Various nonlinear current-voltage characteristics, including Coulomb blockade, negative differential resistance, rectification, and current hysteresis, are shown in the calculations, and the mechanisms are elucidated.

  4. Theory of charge transport in molecular junctions: From Coulomb blockade to coherent tunneling

    International Nuclear Information System (INIS)

    We study charge transport through molecular junctions in the presence of electron-electron interaction using the nonequilibrium Green's function techniques and the renormalized perturbation theory. In the perturbation treatment, the zeroth-order Hamiltonian of the molecular junction is composed of independent single-impurity Anderson's models, which act as the channels where charges come through or occupy, and the interactions between different channels are treated as the perturbation. Using this scheme, the effects of molecule-lead, electron-electron, and hopping interactions are included nonperturbatively, and the charge transport processes can thus be studied in the intermediate parameter range from the Coulomb blockade to the coherent tunneling regimes. The concept of quasi-particles is introduced to describe the kinetic process of charge transport, and then the electric current can be studied and calculated. As a test study, the Hubbard model is used as the molecular Hamiltonian to simulate dimeric and trimeric molecular junctions. Various nonlinear current-voltage characteristics, including Coulomb blockade, negative differential resistance, rectification, and current hysteresis, are shown in the calculations, and the mechanisms are elucidated

  5. Molecular dynamics simulation of water between two charged layers of dipalmitoylphosphatidylserine

    NARCIS (Netherlands)

    Cascales, J.J.L.; Berendsen, H.J.C.; delaTorre, J.G.

    1996-01-01

    A molecular dynamics simulation of water between two charged layers of dipalmitoylphosphatidylserine in its liquid-crystalline state with atomic detail was carried out. From an analysis of a trajectory of 184 ps of length, we obtained information about the dynamics and structure of water between suc

  6. Transverse charge transport through DNA oligomers in large-area molecular junctions

    NARCIS (Netherlands)

    Katsouras, I.; Piliego, C.; Blom, P.W.M.; Leeuw, D.M. de

    2013-01-01

    We investigate the nature of charge transport in deoxyribonucleic acid (DNA) using self-assembled layers of DNA in large-area molecular junctions. A protocol was developed that yields dense monolayers where the DNA molecules are not standing upright, but are lying flat on the substrate. As a result

  7. Aggregation-induced emission of diarylamino-π-carborane triads: effects of charge transfer and π-conjugation.

    Science.gov (United States)

    Cho, Yang-Jin; Kim, So-Yoen; Cho, Minji; Han, Won-Sik; Son, Ho-Jin; Cho, Dae Won; Kang, Sang Ook

    2016-04-14

    Carborane-based donor-π-acceptor triads (D-π-A-π-D) bearing triarylamine moieties were synthesised. All the monomeric triads showed a blue-green emission in a dilute solution, which was assigned as an intramolecular charge-transfer (CT) emission. The intramolecular CT emission showed large Stokes shifts at a higher solvent polarity. The intramolecular CT emission further shifted to a longer wavelength with the increase in π-conjugation. Interestingly, a strong red emission was observed in highly concentrated solutions or in the solid state, which was assigned as an aggregation-induced emission (AIE). Moreover, the AIE strongly depended on solvent polarity. A large Stokes shift in AIE was attributed to the strong CT character. The changes in the dipole moment for the AIE state and monomer emission were evaluated using the Lippert-Mataga relationship. The density functional theory calculations showed that the change in electron distribution between the aryl amino group (highest occupied molecular orbital, HOMO) and the carborane moiety (lowest unoccupied molecular orbital, LUMO) indicates the intramolecular CT character, and the emission colour changes were attributed to the HOMO-LUMO energy gap controlled by the π-extension of the phenylene linker. The electrochemical properties such as oxidation and reduction potentials were consistent with theoretical calculation results. The emission properties were affected by two main factors: solvent polarity and solubility. PMID:26996491

  8. Implementation of a protein reduced point charge model toward molecular dynamics applications.

    Science.gov (United States)

    Leherte, Laurence; Vercauteren, Daniel P

    2011-11-17

    A reduced point charge model was developed in a previous work from the study of extrema in smoothed charge density distribution functions generated from the Amber99 molecular electrostatic potential. In the present work, such a point charge distribution is coupled with the Amber99 force field and implemented in the program TINKER to allow molecular dynamics (MD) simulations of proteins. First applications to two polypeptides that involve α-helix and β-sheet motifs are analyzed and compared to all-atom MD simulations. Two types of coarse-grained (CG)-based trajectories are generated using, on one hand, harmonic bond stretching terms and, on the other hand, distance restraints. Results show that the use of the unrestrained CG conditions are sufficient to preserve most of the secondary structure characteristics but restraints lead to a better agreement between CG and all-atom simulation results such as rmsd, dipole moment, and time-dependent mean square deviation functions. PMID:21800922

  9. Molecular-Based Theory for Electron-Transfer Reorganization Energy in Solvent Mixtures.

    Science.gov (United States)

    Zhuang, Bilin; Wang, Zhen-Gang

    2016-07-01

    Using statistical-field techniques, we develop a molecular-based dipolar self-consistent-field theory (DSCFT) for charge solvation in liquid mixtures under equilibrium and nonequilibrium conditions, and apply it to compute the solvent reorganization energy of electron-transfer reactions. In addition to the nonequilibrium orientational polarization, the reorganization energy in liquid mixtures is also determined by the out-of-equilibrium solvent composition around the reacting species due to preferential solvation. Using molecular parameters that are readily available, the DSCFT naturally accounts for the dielectric saturation effect and the spatially varying solvent composition in the vicinity of the reacting species. We identify three general categories of binary solvent mixtures, classified by the relative optical and static dielectric permittivities of the solvent components. Each category of mixture is shown to produce a characteristic local solvent composition profile in the vicinity of the reacting species, which gives rise to the distinctive composition dependence of the reorganization energy that cannot be predicted using the dielectric permittivities of the homogeneous solvent mixtures. PMID:27187110

  10. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

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

  11. 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.

  12. Charge transfer at carbon nanotube-graphene van der Waals heterojunctions

    Science.gov (United States)

    Liu, Yuanda; Wang, Fengqiu; Liu, Yujie; Wang, Xizhang; Xu, Yongbing; Zhang, Rong

    2016-06-01

    Carbon nanotubes and graphene are two most widely investigated low-dimensional materials for photonic and optoelectronic devices. Combining these two materials into all-carbon hybrid nanostructures has shown enhanced properties in a range of devices, such as photodetectors and flexible electrodes. Interfacial charge transfer is the most fundamental physical process that directly impacts device design and performance, but remains a subject less well studied. Here, we complemented Raman spectroscopy with photocurrent probing, a robust way of illustrating the interfacial built-in fields, and unambiguously revealed both static and dynamic (photo-induced) charge transfer processes at the nanotube-graphene interfaces. Significantly, the effects of nanotube species, i.e. metallic as opposed to semiconducting, are for the first time compared. Of all the devices examined, the graphene sheet was found to be p-type doped with (6, 5) chirality-enriched semiconducting SWNTs (s-SWNTs), while n-type doped with highly pure (>99%) metallic SWNTs (m-SWNTs). Our results provide important design guidelines for all-carbon hybrid based devices.

  13. High-impact-velocity forward charge transfer from high-Rydberg states as a classical process

    International Nuclear Information System (INIS)

    It was long ago suggested by Thomas that the charge-transfer cross section in the neighborhood of forward scattering was dominated by a double-scattering process. Thomas's analysis, which was almost completely classical, might well suggest that, in a proper quantum-mechanical study, the second Born contribution would dominate over the first, and this was ultimately found to be the case. Unfortunately, the problem which Thomas considered was charge transfer to any bound state of an incident proton from a hydrogen atom in its ground state, a problem which cannot truly be studied classically. Thomas found that the cross section behaved as r/sup -7/2/, where r is the initial electron--target-proton separation, and simply replaced r/sup -7/2/ by a0/sup -7/2/, where a0 is the Bohr radius. The result he obtained is identical in form to that obtained in the second Born approximation, but the coefficient is smaller by about a factor of ten. The more consistent procedure of replacing r/sup -7/2/ by its expectation value gives infinity for the 1s ground state, (or indeed for any state with orbital angular momentum quantum number l = 0). We show that for capture from a high-Rydberg state, that is, a state with principal quantum number n >> 1, the classical picture is not only meaningful for l not = 0, but, for l sufficiently large, becomes exact

  14. Observation of excited state charge transfer with fs/ps-CARS

    International Nuclear Information System (INIS)

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4(prime)-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4(prime)-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles

  15. Modulation of the charge transfer and photophysical properties in non-fused tetrathiafulvalene-benzothiadiazole derivatives.

    Science.gov (United States)

    Pop, Flavia; Seifert, Sabine; Hankache, Jihane; Ding, Jie; Hauser, Andreas; Avarvari, Narcis

    2015-01-28

    Bis(thiomethyl)- and bis(thiohexyl)-tetrathiafulvalene-bromo-benzothiadiazoles, containing electron donor tetrathiafulvalene (TTF) and electron acceptor benzothiadiazole (BTD) units, have been prepared by Stille coupling reactions between the TTF-SnMe3 precursors and BTD-Br2. In another series of experiments, TTF-acetylene-BTD compounds have been synthesized by Sonogashira coupling between either TTF-acetylenes and BTD-Br2 in low yields, or TTF-iodine and BTD-acetylene in moderate yields. In the compound TTF-C≡C-BTD the TTF and BTD units are coplanar in the solid state, as shown by the single crystal X-ray structure, and there is segregation in the packing between the donor and acceptor units. All the derivatives have good electron donor properties, as determined by cyclic voltammetry measurements, and they can also be reversibly reduced thanks to the presence of the BTD moiety. UV-visible spectroscopy and photophysical investigations show the presence of an intramolecular charge transfer (ICT) band and an emission band originating from the charge transfer. Both the absorption and the emission are modulated by the substitution scheme and the insertion of the acetylenic bridge. PMID:25410315

  16. 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.

  17. Momentum transfer theory of non-conservative charged particle transport in crossed electric and magnetic fields

    International Nuclear Information System (INIS)

    Momentum - transfer approximation is applied to momentum and energy balance equations describing reacting particle swarms in gases in crossed electric and magnetic fields. Transport coefficients of charged particles undergoing both inelastic and reactive, non-particle-conserving collisions with a gas of neutral molecules are calculated. Momentum - transfer theory (MTT) has been developed mainly by Robson and collaborators. It has been applied to a single reactive gas and mixtures of reactive gases in electric field only. MTT has also been applied in crossed electric and magnetic fields recently and independently of our work but the reactive collisions were not considered. Consider a swarm of electrons of charge e and mass m moving with velocity rvec v through a neutral gas under the influence of an applied electric rvec E and magnetic rvec B field. The collision processes which we shall investigate are limited to elastic, inelastic and reactive collisions of electrons with gas molecules. Here we interpret reactive collisions as collisions which produce change in number of the swarm particles. Reactive collisions involve creation (ionization by electron impact) or loss (electron attachment) of swarm particles. We consider only single ionization in approximation of the mass ratio m/m00 are masses of electrons and neutral particles, respectively. We assume that the stage of evolution of the swarm is the hydrodynamic limit (HDL). In HDL, the space - time dependence of all properties is carried by the number density n of swarm particles

  18. Ultrafast Photo-Induced Charge Transfer Unveiled by Two-Dimensional Electronic Spectroscopy

    CERN Document Server

    Bixner, Oliver; Mancal, Tomas; Hauer, Juergen; Milota, Franz; Fischer, Michael; Pugliesi, Igor; Bradler, Maximilian; Schmid, Walther; Riedle, Eberhard; Kauffmann, Harald F; Christensson, Niklas

    2012-01-01

    The interaction of exciton and charge transfer (CT) states plays a central role in photo-induced CT processes in chemistry, biology and physics. In this work, we use a combination of two-dimensional electronic spectroscopy (2D-ES), pump-probe measurements and quantum chemistry to investigate the ultrafast CT dynamics in a lutetium bisphthalocyanine dimer in different oxidation states. It is found that in the anionic form, the combination of strong CT-exciton interaction and electronic asymmetry induced by a counter-ion enables CT between the two macrocycles of the complex on a 30 fs timescale. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra, and we monitor how the excited state charge density ultimately localizes on the macrocycle closest to the counter-ion within 100 fs. A comparison with the dynamics in the radical species further elucidates how CT states modulate the electronic structure and tune fs-reac...

  19. Endoergic and resonant charge transfer excitation in He-Cu discharge

    Science.gov (United States)

    Mezei, P.; Rózsa, K.; Jánossy, M.; Apai, P.

    1987-09-01

    The intensity of Cu-II lines with upper level energies near and above those of the He ion was measured as a function of He pressure in a Cu hollow cathode tube. In this tube at low pressures the negative glow could expand above the cathode. The maximum intensity of the Cu-II 493.1 nm line was found in the low voltage, high pressure hollow cathode discharge region in accordance with a resonant charge transfer excitation process. Enhancement of the intensity of the Cu-II 436.5 nm and 417.9 nm lines was observed in the cathode glow at low pressures. Excitation of these lines is attributed to endoergic charge transfer collisions between He ions accelerated by the 2 kV tube voltage and ground state Cu atoms. The cross-section for this reaction exciting the 436.5 nm line was estimated to be of the order of 10-17 cm2.

  20. Hydrated proton and hydroxide charge transfer at the liquid/vapor interface of water

    Energy Technology Data Exchange (ETDEWEB)

    Soniat, Marielle; Rick, Steven W., E-mail: srick@uno.edu [Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 (United States); Kumar, Revati [Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70808 (United States)

    2015-07-28

    The role of the solvated excess proton and hydroxide ions in interfacial properties is an interesting scientific question with applications in a variety of aqueous behaviors. The role that charge transfer (CT) plays in interfacial behavior is also an unsettled question. Quantum calculations are carried out on clusters of water with an excess proton or a missing proton (hydroxide) to determine their CT. The quantum results are applied to analysis of multi-state empirical valence bond trajectories. The polyatomic nature of the solvated excess proton and hydroxide ion results in directionally dependent CT, depending on whether a water molecule is a hydrogen bond donor or acceptor in relation to the ion. With polyatomic molecules, CT also depends on the intramolecular bond distances in addition to intermolecular distances. The hydrated proton and hydroxide affect water’s liquid/vapor interface in a manner similar to monatomic ions, in that they induce a hydrogen-bonding imbalance at the surface, which results in charged surface waters. This hydrogen bond imbalance, and thus the charged waters at the surface, persists until the ion is at least 10 Å away from the interface.