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1

Charge-displacement analysis via natural orbitals for chemical valence: charge transfer effects in coordination chemistry.  

PubMed

We recently devised a simple scheme for analyzing on quantitative grounds the Dewar-Chatt-Duncanson donation and back-donation in symmetric coordination complexes. Our approach is based on a symmetry decomposition of the so called Charge-Displacement (CD) function quantifying the charge flow, upon formation of a metal (M)-substrate (S) bond, along the M-S interaction axis and provides clear-cut measures of donation and back-donation charges in correlation with experimental observables [G. Bistoni et al., Angew. Chem., Int. Ed. 52, 11599 (2013)]. The symmetry constraints exclude of course from the analysis most systems of interest in coordination chemistry. In this paper, we show how to entirely overcome this limitation by taking advantage of the properties of the natural orbitals for chemical valence [M. Mitoraj and A. Michalak, J. Mol. Model. 13, 347 (2007)]. A general scheme for disentangling donation and back-donation in the CD function of both symmetric and non-symmetric systems is presented and illustrated through applications to M-ethyne (M = Au, Ni and W) coordination bonds, including an explicative study on substrate activation in a model reaction mechanism. PMID:25725717

Bistoni, Giovanni; Rampino, Sergio; Tarantelli, Francesco; Belpassi, Leonardo

2015-02-28

2

Charge-displacement analysis via natural orbitals for chemical valence: Charge transfer effects in coordination chemistry  

NASA Astrophysics Data System (ADS)

We recently devised a simple scheme for analyzing on quantitative grounds the Dewar-Chatt-Duncanson donation and back-donation in symmetric coordination complexes. Our approach is based on a symmetry decomposition of the so called Charge-Displacement (CD) function quantifying the charge flow, upon formation of a metal (M)-substrate (S) bond, along the M-S interaction axis and provides clear-cut measures of donation and back-donation charges in correlation with experimental observables [G. Bistoni et al., Angew. Chem., Int. Ed. 52, 11599 (2013)]. The symmetry constraints exclude of course from the analysis most systems of interest in coordination chemistry. In this paper, we show how to entirely overcome this limitation by taking advantage of the properties of the natural orbitals for chemical valence [M. Mitoraj and A. Michalak, J. Mol. Model. 13, 347 (2007)]. A general scheme for disentangling donation and back-donation in the CD function of both symmetric and non-symmetric systems is presented and illustrated through applications to M-ethyne (M = Au, Ni and W) coordination bonds, including an explicative study on substrate activation in a model reaction mechanism.

Bistoni, Giovanni; Rampino, Sergio; Tarantelli, Francesco; Belpassi, Leonardo

2015-02-01

3

Charge Transfer Reactions  

NASA Astrophysics Data System (ADS)

Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

Dennerl, Konrad

2010-12-01

4

Charge Transfer Reactions Induce Born-Oppenheimer Breakdown in Surface Chemistry: Applications of Double Resonance Spectroscopy in Molecule-Surface Scattering  

NASA Astrophysics Data System (ADS)

Atomic and molecular interactions constitute a many-body quantum problem governed fundamentally only by the Coulomb forces between many electrons and nuclei. While simple to state, computers are simply not fast enough to solve this problem by brute force, except for the simplest examples. Combining the Born-Oppenheimer Approximation (BOA) with Density Functional Theory (DFT), however, allows theoretical simulations of extraordinarily complex chemical systems including molecular interactions at solid metal surfaces, the physical basis of surface chemistry. This lecture describes experiments demonstrating the limits of the BOA/DFT approximation as it relates to molecules interacting with solid metal surfaces. One of the most powerful experimental tools at our disposal is a form of double resonance spectroscopy, which allows us to define the quantum state of the molecule both before and after the collision with the surface, providing a complete picture of the resulting energy conversion processes. With such data, we are able to emphasize quantitative measurements that can be directly compared to first principles theories that go beyond the Born-Oppenheimer approximation. One important outcome of this work is the realization that Born-Oppenheimer breakdown can be induced by simple charge transfer reactions that are common in surface chemistry. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach and A. M. Wodtke Nature {433}(7025), 503-505 (2005) Y. H. Huang, C. T. Rettner, D. J. Auerbach and A. M. Wodtke Science {290}(5489), 111-114 (2000) R. Cooper, I. Rahinov, Z. S. Li, D. Matsiev, D. J. Auerbach and A. M. Wodtke Chemical Science {1}(1), 55-61 (2010) J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach and A. M. Wodtke PCCP {13}(1), 97-99 (2011).

Wodtke, Alec M.

2013-06-01

5

Intramolecular Charge Transfer in Arylpyrazolines  

Microsoft Academic Search

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

Ming-Liang Wang; Ju-Zheng Liu; Chun-Xiang Xu

2006-01-01

6

Facilely and efficiently tuning metal-organic nanostructures of a charge-transfer complex based on a water controlled nanoreaction and the chemistry of 7,7,8,8-tetracyanoquinodimethane (TCNQ)  

NASA Astrophysics Data System (ADS)

Metal-organic charge-transfer complexes based on 7,7,8,8-tetracyanoquinodimethane (TCNQ) have received considerable attention because of their unique solid-state physical properties for potential applications in nanoscale opto-electronic devices. To address the challenge in preparing novel metal-TCNQ (MTCNQ) nanostructures, here we introduce a facile and efficient way for synthesizing MTCNQ, taking Ni[TCNQ]2(H2O)2 as an example. By finely tuning the amount of water added into TCNQ solution, well-ordered and large-scale patterns of Ni[TCNQ]2(H2O)2 were successfully obtained in a controllable manner. This facile method will not only be beneficial for the tailored preparation of nanoscale MTCNQ complexes, but also enrich the chemistry of TCNQ.

Song, Jingyi; Ji, Zhuoyu; Nie, Qiong; Hu, Wenping

2014-02-01

7

Charge Transfer Reactions in Porous Materials  

E-print Network

with Monte Carlo methods is discussed in Chapter 2. In Chapter 3, infrared spectra of a model proton-transfer complex calculated using mixed quantum-classical molecular dynamics are calculated. These studies indicate that charge transfer dynamics...

Mitchell-Koch, Katie Rose

2008-08-15

8

Direct visualization of the charge transfer in conjugated polymers  

NASA Astrophysics Data System (ADS)

Ion-induced charge-transfer states in conjugated polyelectrolytes were experimentally investigated by Justin M. Hodgkiss and his co-workers [J Am Chem Soc, 2009, 131(25): 8913]. In this work, charged and neutral conjugated polyelectrolytes were further studied with quantum chemistry methods. The calculation result shows that the absorption spectra are roughly in visible and ultraviolet light regions, and the two absorption peaks are located in the wavelength span 300-400 nm for charged polyelectrolytes. However, in neutral conjugated polyelectrolytes, the peaks of the absorption spectra showed a blue shift compared with those of the charged polyelectrolytes. Charge transfer (CT) properties of the studied compounds were also investigated with both the three-dimensional real-space analysis method of transition and charge difference densities, and the two-dimensional real-space analysis method of transition density matrices based on the simulated absorption spectra. The calculation results revealed the charge transfer in conjugated polyelectrolytes on the excitation states.

Li, Yan; Li, YuanZuo; Dong, Bin; Yang, ZhiLin

2011-06-01

9

Charge transfer between ND3 ... and phenol  

E-print Network

Charge transfer between ND3 ¿ ,, 2 ¿ ... and phenol Ho-Tae Kim, Richard J. Green, and Scott L by intracomplex proton transfer. The calculated barrier to interconversion depends on the level of theory to be a significant barrier separating the ring and hydrogen-bonded geometries, although still well below the energy

Anderson, Scott L.

10

Kinetics of charge transfer in lithium intercalation  

SciTech Connect

Because of their efficiency as cathodic materials in secondary lithium batteries, the metal oxides intercalated with lithium are of great interest to many researchers. The lithium intercalation reaction may be observed by either an electrochemical or a chemical reaction mechanism. The authors previous Mossbauer Spectroscopic study of Li{sub y}Fe{sub 2}O{sub 3} confirmed that lithium intercalation in Fe{sub 2}O{sub 3} both chemically and electrochemically have the same structure characterization. Although the intercalated compounds have been prepared, few charge transfer process studies between the lithium and metal oxides electrode have been reported. Deciphering the mechanism for charge transfer during electrochemical intercalation is highly significant for advancing the use of such cathodic materials. In the present work, a step potential experiment has been developed for investigating the charge transfer behavior of n-BuLi on Fe{sub 2}O{sub 3} electrodes.

Hu, Z.; Du, G.; Wu, H. [Fudan Univ., Shanghai (China). Dept. of Chemistry

1994-12-31

11

Charge-transfer magnetoelectrics of polymeric multiferroics.  

PubMed

The renaissance of multiferroics has yielded a deeper understanding of magneto-electric coupling of inorganic single-phase multiferroics and composites. Here, we report charge-transfer polymeric multiferroics, which exhibit external field-controlled magnetic, ferroelectric, and microwave response, as well as magneto-dielectric coupling. The charge-transfer-controlled ferroic properties result from the magnetic field-tunable triplet exciton which has been validated by the dynamic polaron-bipolaron transition model. In addition, the temperature-dependent dielectric discontinuity and electric-field-dependent polarization confirms room temperature ferroelectricity of crystalline charge-transfer polymeric multiferroics due to the triplet exciton, which allows the tunability of polarization by the photoexcitation. PMID:24654686

Qin, Wei; Jasion, Daniel; Chen, Xiaomin; Wuttig, Manfred; Ren, Shenqiang

2014-04-22

12

Simulations of charge transfer in Electron Multiplying Charge Coupled Devices  

NASA Astrophysics Data System (ADS)

Electron Multiplying Charge Coupled Devices (EMCCDs) are a variant of traditional CCD technology well suited to applications that demand high speed operation in low light conditions. On-chip signal amplification allows the sensor to effectively suppress the noise introduced by readout electronics, permitting sub-electron read noise at MHz pixel rates. The devices have been the subject of many detailed studies concerning their operation, however there has not been a study into the transfer and multiplication process within the EMCCD gain register. Such an investigation has the potential to explain certain observed performance characteristics, as well as inform further optimisations to their operation. In this study, the results from simulation of charge transfer within an EMCCD gain register element are discussed with a specific focus on the implications for serial charge transfer efficiency (CTE). The effects of operating voltage and readout speed are explored in context with typical operating conditions. It is shown that during transfer, a small portion of signal charge may become trapped at the semiconductor-insulator interface that could act to degrade the serial CTE in certain operating conditions.

Bush, N.; Stefanov, K.; Hall, D.; Jordan, D.; Holland, A.

2014-12-01

13

Building model systems to understand Proton-Coupled Electron Transfer in heme : spectroscopic investigation of charge transfer to axially bound diimide acceptors  

E-print Network

Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry, which allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are ...

Hanson, Christina J

2013-01-01

14

Charge transfer reactions in Xe plasma expansion  

NASA Astrophysics Data System (ADS)

Charge transfer reactions of fast Xe ions with hydrocarbons including methane (CH4), ethene (C2H4), and propane (C3H8) are studied by adding these hydrocarbon gases into a cross flowing Xe plasma expansion. Branching ratios and relative reaction rates for the charge transfers of fast Xe+ with each of the three hydrocarbon gases are measured under different rf powers of the inductively coupled Xe discharge. For CH4/Xe system, we find that fast Xe+ reacts readily with CH4 generating CH4+ and CH3+ in a ratio of 1:0.56, with an estimated rate coefficient of (2.3±0.3)×10-10cm3/s at 75W rf power which slowly increases to (2.9±0.3)×10-10cm3/s at 250W (error bars reflect only the uncertainties due to the unknown extent of the ion recombination that follows the charge transfer reaction). These observed charge transfer reactions are made possible by the kinetically excited Xe ions produced by free expansion of the plasma. For the C2H4/Xe system product ions C2H4+ and C2H2+ are observed, and for C3H8/Xe, C2H4+ and C2H5+ and minor product ions including C2H2+ and C3H7+ are observed.

Jiao, C. Q.; Garscadden, A.; Ganguly, B. N.

2007-04-01

15

Dynamical Treatment of Charge Transfer through Duplex Nucleic Acids Containing Modified Adenines  

PubMed Central

We address the issue of whether chemical alterations of nucleobases are an effective tool to modulate charge transfer through DNA molecules. Our investigation uses a multi-level computational approach based on classical molecular dynamics and quantum chemistry. We find yet another evidence that structural fluctuations are a key factor to determine the electronic structure of double-stranded DNA. We argue that the electronic structure and charge transfer ability of flexible polymers is the result of a complex intertwining of various structural, dynamical and chemical factors. Chemical intuition may be used to design molecular wires, but this is not the sole component in the complex charge transfer mechanism through DNA. PMID:24060008

Brancolini, Giorgia; Migliore, Agostino; Corni, Stefano; Fuentes-Cabrera, Miguel; Luque, F. Javier; Di Felice, Rosa

2014-01-01

16

Variable Charge Soils: Mineralogy and Chemistry  

SciTech Connect

Soils rich in particles with amphoteric surface properties in the Oxisols, Ultisols, Alfisols, Spodosols and Andisols orders (1) are considered variable charge soils (2). The term “variable charge” is used to describe organic and inorganic soil constituents with reactive surface groups whose charge varies with pH, ionic concentration and composition of the soil solution. Such groups are the surface carboxyl, phenolic and amino functional groups of organic materials in soils, and surface hydroxyl groups of Fe and Al oxides, allophane and imogolite. The hydroxyl surface groups are also present on edges of some phyllosilicate minerals such as kaolinite, mica, and hydroxyl-interlayered vermiculite. The variable charge is developed on the surface groups as a result of adsorption or desorption of ions that are constituents of the solid phase, i.e., H+, and the adsorption or desorption of solid-unlike ions that are not constituents of the solid. Highly weathered soils usually undergo isoeletric weathering and reach a “zero net charge” stage during their development. They have a slightly acidic to acidic soil solution pH, which is close to either point of zero net charge (PZNC) (3) or point of zero salt effect (PZSE) (3). They are characterized by high abundances of minerals with a point of zero net proton charge (PZNPC) (3) at neutral and slightly basic pHs; the most important being Fe and Al oxides and allophane. Under acidic conditions, the surfaces of these minerals are net positively charged. In contrast, the surfaces of permanent charge phyllosilicates are negatively charged regardless of ambient conditions. Variable charge soils therefore, are heterogeneous charge systems. The coexistence and interactions of oppositely charged surfaces or particles confers a different pattern of physical and chemical behavior on the soil, relatively to a homogeneously charged system of temperate regions. In some variable charge soils (Oxisols and some Ultisols developed on ferromagnesian-rich parent materials) the surfaces of phyllosilicates are coated to a lesser or greater extent by amorphous or crystalline, oppositely charged nanoparticles of Fe and Al oxides. These coatings exhibit a high reactive surface area and help cementing larger particles with one another. As a result of these electrostatic interactions, stable microaggregates that are difficult to disperse are formed in variable charge soils. Most of highly weathered soils have reached the “advanced stage” of Jackson-Sherman weathering sequence that is characterized by the removal of Na, K, Ca, Mg, and Fe(II), the presence of Fe and Al polymers, and very dilute soil solutions with an ionic strength (IS) of less than 1 mmol L-1. The inter-penetration or overlapping of the diffuse double layers on oppositely charged surfaces may occur in these dilute systems. These diffuse layer interactions may affect the magnitude of the effective charge, i.e., the counter-ion charge (4). In addition, salt adsorption, which is defined as the simultaneous adsorption in equivalent amounts of the cation and anion of an electrolyte with no net release of other ions into the soil solution, appears to be a common phenomenon in these soils. They act as cation- and anion-exchangers and as salt-sorbers. The magnitude of salt adsorption depends strongly on initial IS in the soil solution and the presence in appreciable amounts of oppositely charged surfaces. Among the authors that have made illustrious contributions towards a better understanding of these fascinating soil systems are S. Matson, R.K. Schofield, van Olphen, M.E. Sumner, G.W. Thomas, G.P. Gillman, G. Uehara, B.K.G. Theng, K. Wada, N.J. Barrow, J.W. Bowden, R.J. Hunter and G. Sposito. This entry is mainly based on publications by these authors.

Qafoku, Nik; Van Ranst, Eric; Noble, Andrew; Baert, Geert

2003-11-01

17

Accumulative electron transfer: multiple charge separation in artificial photosynthesis.  

PubMed

To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru(II)-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme. PMID:22470977

Karlsson, Susanne; Boixel, Julien; Pellegrin, Yann; Blart, Errol; Becker, Hans-Christian; Odobel, Fabrice; Hammarström, Leif

2012-01-01

18

Biological charge transfer via flickering resonance  

PubMed Central

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

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

2014-01-01

19

Experiments on charge transfer across Coulomb islands  

NASA Astrophysics Data System (ADS)

Preliminary experiments on controlled charge transfer across tunnel junctions of small aluminium islands have been performed. We fabricate samples by conventional e-beam lithography using a converted SEM and measurements are carried out in a compact plastic dilution refrigerator fitting inside a 2” necked transport dewar. Experiments to test the effect of a coherent electro-acoustic wave on the I-V curve are in progress.

Pekola, J. P.; Kira, G. M.; Ma¨kela¨, T.; Paalanen, M. A.

1994-02-01

20

Pattern classification using charge transfer devices  

NASA Technical Reports Server (NTRS)

The feasibility of using charge transfer devices in the classification of multispectral imagery was investigated by evaluating particular devices to determine their suitability in matrix multiplication subsystem of a pattern classifier and by designing a protype of such a system. Particular attention was given to analog-analog correlator devices which consist of two tapped delay lines, chip multipliers, and a summed output. The design for the classifier and a printed circuit layout for the analog boards were completed and the boards were fabricated. A test j:g for the board was built and checkout was begun.

1980-01-01

21

Charge transfer-mediated singlet fission.  

PubMed

Singlet fission, the splitting of a singlet exciton into two triplet excitons in molecular materials, is interesting not only as a model many-electron problem, but also as a process with potential applications in solar energy conversion. Here we discuss limitations of the conventional four-electron and molecular dimer model in describing singlet fission in crystalline organic semiconductors, such as pentacene and tetracene. We emphasize the need to consider electronic delocalization, which is responsible for the decisive role played by the Mott-Wannier exciton, also called the charge transfer (CT) exciton, in mediating singlet fission. At the strong electronic coupling limit, the initial excitation creates a quantum superposition of singlet, CT, and triplet-pair states, and we present experimental evidence for this interpretation. We also discuss the most recent attempts at translating this mechanistic understanding into design principles for CT state-mediated intramolecular singlet fission in oligomers and polymers. PMID:25648486

Monahan, N; Zhu, X-Y

2015-04-01

22

Charge Transfer Cross Sections for Dysprosium and Cerium  

Microsoft Academic Search

Symmetric charge transfer cross sections between singly ionized ions and their parent atoms were measured for dysprosium and cerium in the impact energy range of 100 2000 eV. The primary ion beam was extracted from a laser ion source in which the atoms were ionized by laser resonant photo-ionization. The slow ions produced in the charge transfer reaction and the

Koji Tamura; Hajime Adachi; TakemasaShibata TakemasaShibata

1999-01-01

23

Charge Transfer Model of Atomic Ordering in Complex Perovskite Alloys  

E-print Network

Charge Transfer Model of Atomic Ordering in Complex Perovskite Alloys Zhigang Wu and Henry Krakauer-based perovskite alloys. The model allows charge transfer between A sites and is a generalization of Bellaiche Pb-based and Ba-based complex perovskite alloys. It yields smaller structural energy differences

Wu, Zhigang

24

PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE  

E-print Network

PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE G.MALOVICHKO, V of crystals from barium titanate (BT) family make them promising candidates for various applications@uos.de; vgrachev@uos.de; schirmer@uos.de Abstract The results of the study of charge transfer processes in barium

Malovichko, Galina

25

Charge transfer, surface charging, and overlayer-induced faceting J. G. Che* and C. T. Chan  

E-print Network

Charge transfer, surface charging, and overlayer-induced faceting J. G. Che* and C. T. Chan to analyze the change of surface energy of metallic surfaces upon surface charging. We then studied surface charging is main driving mechanism in view of such an empirical correlation. Our results show

Che, Jingguang

26

Mechanisms of proton transfer in proteins: Localized charge transfer versus delocalized soliton transfer  

PubMed Central

Proton translocation coupled to redox chemistry is ubiquitous for membrane enzymes involved in energy generation in cells. In such enzymes, proton transport occurs in special proton conducting channels, which consist of a series of protonatable groups of the protein connected by chains of mobile water molecules. Here we discuss two possible mechanisms of proton transport along such structures: diffusion of a localized charge and delocalized soliton transitions, in which several protons are collectively shifted along a chain of hydrogen bonds. PMID:19391991

Stuchebrukhov, Alexei A.

2010-01-01

27

Charge transfer between reduced graphene oxide sheets on insulating substrates  

NASA Astrophysics Data System (ADS)

Understanding the electrical communications between graphene sheets placed on insulating substrates is of great value to rational design of functional graphene nanoelectronics. In this paper, we report charge transfer between reduced graphene oxide (rGO) sheets separated in hundreds of nanometers on insulating substrates. We found that the rGO sheet collects charges from the adjacent charged rGO sheet through the dielectric surfaces. The efficiency of charge transfer between the separated rGO sheets is dependent on their separation distance, gap length, and the substrate type. The findings suggest that the charge interflow should not be neglected in a graphene circuit.

Shen, Yue; Zhang, Xueqiang; Wang, Ying; Zhou, Xuejiao; Hu, Jun; Guo, Shouwu; Zhang, Yi

2013-07-01

28

Contributions of charge-density research to medicinal chemistry  

PubMed Central

This article reviews efforts in accurate experimental charge-density studies with relevance to medicinal chemistry. Initially, classical charge-density studies that measure electron density distribution via least-squares refinement of aspherical-atom population parameters are summarized. Next, interaction density is discussed as an idealized situation resembling drug–receptor interactions. Scattering-factor databases play an increasing role in charge-density research, and they can be applied both to small-molecule and macromolecular structures in refinement and analysis; software development facilitates their use. Therefore combining both of these complementary branches of X-ray crystallography is recommended, and examples are given where such a combination already proved useful. On the side of the experiment, new pixel detectors are allowing rapid measurements, thereby enabling both high-throughput small-molecule studies and macromolecular structure determination to higher resolutions. Currently, the most ambitious studies compute intermolecular interaction energies of drug–receptor complexes, and it is recommended that future studies benefit from recent method developments. Selected new developments in theoretical charge-density studies are discussed with emphasis on its symbiotic relation to crystallography. PMID:25485126

Dittrich, Birger; Matta, Chérif F.

2014-01-01

29

Imaging charge transfer in iodomethane upon x-ray photoabsorption.  

PubMed

Studies of charge transfer are often hampered by difficulties in determining the charge localization at a given time. Here, we used ultrashort x-ray free-electron laser pulses to image charge rearrangement dynamics within gas-phase iodomethane molecules during dissociation induced by a synchronized near-infrared (NIR) laser pulse. Inner-shell photoionization creates positive charge, which is initially localized on the iodine atom. We map the electron transfer between the methyl and iodine fragments as a function of their interatomic separation set by the NIR-x-ray delay. We observe signatures of electron transfer for distances up to 20 angstroms and show that a realistic estimate of its effective spatial range can be obtained from a classical over-the-barrier model. The presented technique is applicable for spatiotemporal imaging of charge transfer dynamics in a wide range of molecular systems. PMID:25035485

Erk, Benjamin; Boll, Rebecca; Trippel, Sebastian; Anielski, Denis; Foucar, Lutz; Rudek, Benedikt; Epp, Sascha W; Coffee, Ryan; Carron, Sebastian; Schorb, Sebastian; Ferguson, Ken R; Swiggers, Michele; Bozek, John D; Simon, Marc; Marchenko, Tatiana; Küpper, Jochen; Schlichting, Ilme; Ullrich, Joachim; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

2014-07-18

30

A surface acoustic wave /SAW/ charge transfer imager  

NASA Technical Reports Server (NTRS)

An 80 MHz, 2-microsecond surface acoustic wave charge transfer device (SAW-CTD) has been fabricated in which surface acoustic waves are used to create traveling longitudinal electric fields in the silicon substrate and to replace the multiphase clocks of charge coupled devices. The traveling electric fields create potential wells which will carry along charges that may be stored in the wells; the charges may be injected into the wells by light. An optical application is proposed where the SAW-CTD structure is used in place of a conventional interline transfer design.

Papanicolauo, N. A.; Lin, H. C.

1981-01-01

31

Control of emission by intermolecular fluorescence resonance energy transfer and intermolecular charge transfer.  

PubMed

Control of emission by intermolecular fluorescence resonant energy transfer (IFRET) and intermolecular charge transfer (ICT) is investigated with the quantum-chemistry method using two-dimensional (2D) and three-dimensional (3D) real space analysis methods. The work is based on the experiment of tunable emission from doped 1,3,5-triphenyl-2-pyrazoline (TPP) organic nanoparticles (Peng, A. D.; et al. Adv. Mater. 2005, 17, 2070). First, the excited-state properties of the molecules, which are studied (TPP and DCM) in that experiment, are investigated theoretically. The results of the 2D site representation reveal the electron-hole coherence and delocalization size on the excitation. The results of 3D cube representation analysis reveal the orientation and strength of the transition dipole moments and intramolecular or intermolecular charge transfer. Second, the photochemical quenching mechanism via IFRET is studied (here "resonance" means that the absorption spectrum of TPP overlaps with the fluorescence emission spectrum of DCM in the doping system) by comparing the orbital energies of the HOMO (highest occupied molecular orbital) and the LUMO (lowest unoccupied molecular orbital) of DCM and TPP in absorption and fluorescence. Third, for the DCM-TPP complex, the nonphotochemical quenching mechanism via ICT is investigated. The theoretical results show that the energetically lowest ICT state corresponds to a pure HOMO-LUMO transition, where the densities of the HOMO and LUMO are strictly located on the DCM and TPP moieties, respectively. Thus, the lowest ICT state corresponds to an excitation of an electron from the HOMO of DCM to the LUMO of TPP. PMID:16686468

Sun, Mengtao; Pullerits, Tõnu; Kjellberg, Pär; Beenken, Wichard J D; Han, Keli

2006-05-18

32

Energy versus charge transfer in ?-conjugated polymer:fullerene blends  

NASA Astrophysics Data System (ADS)

The article is focused on the detailed elucidation of fluorescence quenching by charge and/or energy transfer in ?-conjugated polymers. The processes were studied in blends of MDMO-PPV, Tg-PPV, PCDTBT and PCBTDPP with fullerenes PC60BM and PC70BM in chlorobenzene. Fluorescence quenching was evaluated by the Perrin equation for static quenching and quenching sphere radiuses were calculated. These radiuses were found to be the same as the Förster critical distances for resonance energy transfer. It was concluded that energy transfer prevails over charge transfer under the conditions where the donor and acceptor are not in close contact.

Heinrichova, Patricie; Vala, Martin; Weiter, Martin

2014-01-01

33

Improved Charge-Transfer Fluorescent Dyes  

NASA Technical Reports Server (NTRS)

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 < 400 nm) and emit photons in the long-wavelength ultraviolet, visible, and, when dissolved in some solvents, near-infrared regions. In addition, these 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 the combination of all of these attributes. Because the present dyes do have all of these attributes, they have potential utility as molecular probes in a variety of applications. Examples include (1) monitoring curing and deterioration of polymers; (2) monitoring protein expression; (3) high-throughput screening of drugs; (4) monitoring such chemical species as glucose, amines, amino acids, and metal ions; and (5) photodynamic therapy of cancers and other diseases.

Meador, Michael

2005-01-01

34

Charge-transfer collisions for polarized ion sources  

SciTech Connect

Charge-transfer processes relevant to polarized ion sources are discussed and results are summarized. The primary atom discussed is hydrogen, with particulr emphasis on H/sup -/ formation. Heavier negative ions are briefly discussed.

Schlachter, A.S.

1983-06-01

35

ChargeTransfer EAM Studies of Kinesin Molecular Motor  

E-print Network

of faithfully representing reactive interactions and charge transfer among constituent atomic and molecular enables an `iterative loop' in which information about forces and the effects of changes in the local of highquality firstprinciples electronic structure calculations performed for key configurational

Maccabe, Barney

36

Photoreactivity of metal-to-ligand charge transfer excited states  

Microsoft Academic Search

Generally, transition metal complexes in metal-to-ligand charge transfer (MLCT) excited states are considered to be less reactive than in other states (e.g. ligand field, ligand-to-metal charge transfer) because the orbitals which participate in MLCT transitions are frequently of the ? type and, thus, less involved in strong bonding interactions. However, contrary to these expectations, numerous complexes, in particular the organometallic

Arnd Vogler; Horst Kunkely

1998-01-01

37

Multiferroicity of carbon-based charge-transfer magnets.  

PubMed

A new type of carbon charge-transfer magnet, consisting of a fullerene acceptor and single-walled carbon nanotube donor, is demonstrated, which exhibits room temperature ferromagnetism and magnetoelectric (ME) coupling. In addition, external stimuli (electric/magnetic/elastic field) and the concentration of a nanocarbon complex enable the tunabilities of the magnetization and ME coupling due to the control of the charge transfer. PMID:25389110

Qin, Wei; Gong, Maogang; Chen, Xiaomin; Shastry, Tejas A; Sakidja, Ridwan; Yuan, Guoliang; Hersam, Mark C; Wuttig, Manfred; Ren, Shenqiang

2015-01-27

38

D/sup -/ production by charge transfer in metal vapors  

SciTech Connect

Fast D/sup -/ ions can be produced from D/sup +/ by multiple charge-transfer collisions in a metal-vapor target. Experimental cross sections and thick-target D/sup -/ yields are presented and discussed. The high D/sup -/ yield experimentally observed from charge transfer in cesium vapor is consistent with recent low-energy cross-section calculations and measurements.

Schlachter, A.S.

1980-10-01

39

Phonons and charge-transfer excitations in HTS superconductors  

SciTech Connect

Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs.

Bishop, A.R.

1989-01-01

40

Charge transfer during individual collisions in ice growing by riming  

NASA Technical Reports Server (NTRS)

The charging of a target by riming in the wind was studied in the temperature range of (-10, -18 C). For each temperature, charge transfers of both signs are observed and, according to the environmental conditions, one of them prevails. The charge is more positive as the liquid water concentration is increased at any particular temperature. It is found that even at the low impact velocities used (5 m/s) there is abundant evidence of fragmentation following the collision.

Avila, Eldo E.; Caranti, Giorgio M.

1991-01-01

41

XAFS study of charge transfer in intercalation compounds  

Microsoft Academic Search

An intercalation process is a reversible topotactic reaction in which a guest species occupies empty sites in a solid structure. A charge transfer is always observed between the guest and the host. An accurate knowledge of this electronic exchange, i.e. how many electrons are transferred and on which electronic level, can only be obtained from precise electronic band structure calculations.

Guy Ouvrard; Ziyu Wu

1997-01-01

42

INTRAMOLECULAR CHARGE AND ENERGY TRANSFER IN MULTICHROMOPHORIC AROMATIC SYSTEMS  

SciTech Connect

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.

Edward C. Lim

2008-09-09

43

Charge transfer reactions in nematic liquid crystals  

SciTech Connect

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.

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

44

Charge-transfer magnets: multiferroicity of carbon-based charge-transfer magnets (adv. Mater. 4/2015).  

PubMed

Carbon charge-transfer complexes offer great potential for next generation organic multiferroics. On page 734, S. Ren and co-workers demonstrate room temperature magnetoelectric coupling of nanocarbon charge-transfer magnets. In the image magnetic field effects on optoelectronic and dipole properties of nanocarbon complexes are shown, which would be critical for the development of all-organic multifunctional smart devices. PMID:25607918

Qin, Wei; Gong, Maogang; Chen, Xiaomin; Shastry, Tejas A; Sakidja, Ridwan; Yuan, Guoliang; Hersam, Mark C; Wuttig, Manfred; Ren, Shenqiang

2015-01-01

45

Theoretical treatment of charge transfer processes of relevance to astrophysics  

SciTech Connect

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.

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

1997-12-01

46

Coherent ultrafast charge transfer in an organic photovoltaic blend.  

PubMed

Blends of conjugated polymers and fullerene derivatives are prototype systems for organic photovoltaic devices. The primary charge-generation mechanism involves a light-induced ultrafast electron transfer from the light-absorbing and electron-donating polymer to the fullerene electron acceptor. Here, we elucidate the initial quantum dynamics of this process. Experimentally, we observed coherent vibrational motion of the fullerene moiety after impulsive optical excitation of the polymer donor. Comparison with first-principle theoretical simulations evidences coherent electron transfer between donor and acceptor and oscillations of the transferred charge with a 25-femtosecond period matching that of the observed vibrational modes. Our results show that coherent vibronic coupling between electronic and nuclear degrees of freedom is of key importance in triggering charge delocalization and transfer in a noncovalently bound reference system. PMID:24876491

Falke, Sarah Maria; Rozzi, Carlo Andrea; Brida, Daniele; Maiuri, Margherita; Amato, Michele; Sommer, Ephraim; De Sio, Antonietta; Rubio, Angel; Cerullo, Giulio; Molinari, Elisa; Lienau, Christoph

2014-05-30

47

Conformational control of benzophenone-sensitized charge transfer in dinucleotides.  

PubMed

Charge transfer in DNA cannot be understood without addressing the complex conformational flexibility, which occurs on a wide range of timescales. In order to reduce this complexity four dinucleotide models 1X consisting of benzophenone linked by a phosphodiester to one of the natural nucleosides X = A, G, T, C were studied in water and methanol. The theoretical work focuses on the dynamics and electronic structure of 1G. Predominant conformations in the two solvents were obtained by molecular dynamics simulations. 1G in MeOH adopts mainly an open geometry with a distance of 12–16 Å between the two aromatic parts. In H2O the two parts of 1G form primarily a stacked conformation yielding a distance of 5–6 Å. The low-lying excited states were investigated by electronic structure theory in a QM/MM environment for representative snapshots of the trajectories. Photo-induced intramolecular charge transfer in the S1 state occurs exclusively in the stacked conformation. Ultrafast transient absorption spectroscopy with 1X reveals fast charge transfer from S1 in both solvents with varying yields. Significant charge transfer from the T1 state is only found for the nucleobases with the lowest oxidation potential: in H2O, charge transfer occurs with 3.2 × 10(9) s(-1) for 1A and 6.0 × 10(9) s(-1) for 1G. The reorganization energy remains nearly unchanged going from MeOH to the more polar H2O. The electronic coupling is rather low even for the stacked conformation with H(AB) = 3 meV and explains the moderate charge transfer rates. The solvent controls the conformational distribution and therefore gates the charge transfer due to differences in distance and stacking. PMID:24084688

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

2013-11-14

48

The study of surface acoustic wave charge transfer device  

NASA Technical Reports Server (NTRS)

A surface acoustic wave-charge transfer device, consisting of an n-type silicon substrate, a thermally grown silicon dioxide layer, and a sputtered film of piezoelectric zinc oxide is proposed as a means of circumventing problems associated with charge-coupled device (CCD) applications in memory, signal processing, and imaging. The proposed device creates traveling longitudinal electric fields in the silicon and replaces the multiphase clocks in CCD's. The traveling electric fields create potential wells which carry along charges stored there. These charges may be injected into the wells by light or by using a p-n junction as in conventional CCD's.

Papanicolaou, N.; Lin, H. C.

1978-01-01

49

Reptation Quantum Monte Carlo calculation of charge transfer: The Na-Cl dimer  

NASA Astrophysics Data System (ADS)

The phenomenon of ion pairing in aqueous solutions is of widespread importance in chemistry and physics, and charge transfer between the ions plays a significant role. We examine the performance of quantum Monte Carlo (QMC) calculations for describing the charge transfer behavior in a NaCl dimer. The influence of the fermion nodes is investigated by obtaining the electron density using the reptation Monte Carlo approach. The fermion nodes are given by single-particle orbitals in Slater-Jastrow trial wavefunctions. We consider the single-particle orbitals from Hartree-Fock and density functional theory calculations with several exchange-correlation approximations. Appreciable dependence of the charge transfer on the fixed-node approximation was found although the total energy was found to be rather insensitive. Our work shows that a careful examination of the fixed-node approximation is necessary for quantifying charge transfer in QMC calculations even when other properties such as reaction energetics are insensitive to the approximation.

Yao, Yi; Kanai, Yosuke

2015-01-01

50

Charge Transfer and Support Effects in Heterogeneous Catalysis  

SciTech Connect

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/TiO{sub 2} 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 TiO{sub 2}. The yield for this phenomenon is on the order of 10{sup ?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/TiO{sub 2} 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 D{sub 2} compared to H{sub 2}, contrary to what is expected given the higher mass of D{sub 2}. Reversible changes in the rectification factor of the diode are observed when switching between D{sub 2} and H{sub 2}. 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 H{sub 2} oxidation. Absorption of the light in the Si, combined with the band bending at the interface, gives rise to a steady?state flow of hot holes to the surface. This leads to a decrease in turnover on the surface, an effect which is enhanced when a reverse bias is applied to the diode. Similar experiments were carried out for CO oxidation. On Pt/Si diodes, the reaction rate was found to increase when a forward bias was applied. When the diode was exposed to visible light and a reverse bias was applied, the rate was instead decreased. This implies that a flow of negative charges to the surface increases turnover, while positive charges decrease it. Charge flow in an oxide supported metal catalyst can be modified even without designing the catalyst as a solid state electronic device. This was done by doping stoichiometric and nonstoichiometric TiO{sub 2} films with F, and using the resulting oxides as supports for Pt films. In the case of stoichiometric TiO{sub 2}, F was found to act as an n?type dopant, creating a population of filled electronic states just below the conduction band, and dramatically increasing the conductivity of the oxide film. The electrons in those states can transfer to surface O, activating it for reaction with CO, and leading to increased turnover for CO oxidation. This reinforces the hypothesis that CO oxidation is activated by a flow of negative charges to the surface. The same set of catalysts was used for methanol oxidation. The electronic properties of the TiO{sub 2} films again correlated with the turnover rates, but also with selectivity. With stoichiometric TiO{sub 2} as the support, F?doping caused an increase in selectivity toward the formation of partial oxidation products, formaldehyde and methyl formate, versus the total oxidation product, CO{sub 2}. With non?stoichiometric TiO{sub 2}, F?doping had the reverse effect. Ambient Pressure X?Ray Photoelectron Spectroscopy was used to investigate this F?doping effect in reaction conditions. In O2 alone, and in CO oxidation conditions, the O1s spectrum showed a high binding energy peak that correlated in intensity with the activity of the different films: for stoichiomet

Hervier, Antoine

2011-12-21

51

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

SciTech Connect

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.

Zanni, Martin T.

1999-12-17

52

Are hydrogen-bonded charge transfer crystals room temperature ferroelectrics?  

PubMed

We present a theoretical investigation of the anomalous ferroelectricity of mixed-stack charge transfer molecular crystals, based on the Peierls-Hubbard model, and first-principles calculations for its parametrization. This approach is first validated by reproducing the temperature-induced transition and the electronic polarization of TTF-CA, and then applied to a novel series of hydrogen-bonded crystals, for which room temperature ferroelectricity has recently been claimed. Our analysis shows that the hydrogen-bonded systems present a very low degree of charge transfer and hence support a very small polarization. A critical reexamination of experimental data supports our findings, shedding doubts on the ferroelectricity of these systems. More generally, our modeling allows the rationalization of general features of the ferroelectric transition in charge transfer crystals and suggests design principles for materials optimization. PMID:25526158

D'Avino, Gabriele; Verstraete, Matthieu J

2014-12-01

53

Are Hydrogen-Bonded Charge Transfer Crystals Room Temperature Ferroelectrics?  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of the anomalous ferroelectricity of mixed-stack charge transfer molecular crystals, based on the Peierls-Hubbard model, and first-principles calculations for its parametrization. This approach is first validated by reproducing the temperature-induced transition and the electronic polarization of TTF-CA, and then applied to a novel series of hydrogen-bonded crystals, for which room temperature ferroelectricity has recently been claimed. Our analysis shows that the hydrogen-bonded systems present a very low degree of charge transfer and hence support a very small polarization. A critical reexamination of experimental data supports our findings, shedding doubts on the ferroelectricity of these systems. More generally, our modeling allows the rationalization of general features of the ferroelectric transition in charge transfer crystals and suggests design principles for materials optimization.

D'Avino, Gabriele; Verstraete, Matthieu J.

2014-12-01

54

Solvents effects on charge transfer from quantum dots.  

PubMed

To predict and understand the performance of nanodevices in different environments, the influence of the solvent must be explicitly understood. In this Communication, this important but largely unexplored question is addressed through a comparison of quantum dot charge transfer processes occurring in both liquid phase and in vacuum. By comparing solution phase transient absorption spectroscopy and gas-phase photoelectron spectroscopy, we show that hexane, a common nonpolar solvent for quantum dots, has negligible influence on charge transfer dynamics. Our experimental results, supported by insights from theory, indicate that the reorganization energy of nonpolar solvents plays a minimal role in the energy landscape of charge transfer in quantum dot devices. Thus, this study demonstrates that measurements conducted in nonpolar solvents can indeed provide insight into nanodevice performance in a wide variety of environments. PMID:25751367

Ellis, Jennifer L; Hickstein, Daniel D; Schnitzenbaumer, Kyle J; Wilker, Molly B; Palm, Brett B; Jimenez, Jose L; Dukovic, Gordana; Kapteyn, Henry C; Murnane, Margaret M; Xiong, Wei

2015-03-25

55

33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.  

Code of Federal Regulations, 2012 CFR

...in charge of shoreside transfer operations: Qualifications...person may serve, and the operator of the waterfront facility...in charge of shoreside transfer operations supervises a transfer, the operator shall certify in...

2012-07-01

56

33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.  

Code of Federal Regulations, 2011 CFR

...in charge of shoreside transfer operations: Qualifications...person may serve, and the operator of the waterfront facility...in charge of shoreside transfer operations supervises a transfer, the operator shall certify in...

2011-07-01

57

33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.  

Code of Federal Regulations, 2014 CFR

...in charge of shoreside transfer operations: Qualifications...person may serve, and the operator of the waterfront facility...in charge of shoreside transfer operations supervises a transfer, the operator shall certify in...

2014-07-01

58

33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.  

Code of Federal Regulations, 2013 CFR

...in charge of shoreside transfer operations: Qualifications...person may serve, and the operator of the waterfront facility...in charge of shoreside transfer operations supervises a transfer, the operator shall certify in...

2013-07-01

59

Multiple-charge transfer and trapping in DNA dimers  

SciTech Connect

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)] 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.

Tornow, Sabine; Zwicknagl, Gertrud [Institut fuer Mathematische Physik, TU Braunschweig, 38106 Braunschweig (Germany); Bulla, Ralf [Institut fuer Theoretische Physik, Universitaet zu Koeln, 50937 Koeln (Germany); Anders, Frithjof B. [Theoretische Physik II, TU Dortmund, 44221 Dortmund (Germany)

2010-11-15

60

Charge-transfer in quasilinear push-pull polyene chains  

NASA Astrophysics Data System (ADS)

We used a TD-DFT approach relying on range-separated hybrids to evaluate the photon induced charge-transfer of substituted polyene oligomers of increasingly long chains. Several exchange-correlation functionals have been considered. Push, pull and push-pull systems containing up to 20 unit cells have been compared. A cooperative, but non additive, impact of the donor and acceptor groups is found. In long oligomers, the changes in the electronic density are mainly located on the central segment and not on the terminal electroactive groups, but the charge-transfer distance remains large, which contrasts with most push-pull compounds.

Anne, Fréderic B.; Purpan, Florent D.; Jacquemin, Denis

2013-08-01

61

Bioexcimers as Precursors of Charge Transfer and Reactivity in Photobiology  

NASA Astrophysics Data System (ADS)

Accurate CASPT2//CASSCF calculations show that ?-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.

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

2007-11-01

62

Charge localization and charge transfer in the Bebq2 monomer and dimer.  

PubMed

The geometrical structure and electronic properties of bis(10-hydroxybenzo[h]quinolinato)beryllium (Bebq2) molecule and its dimer both in the neutral and in the positively and negatively charged states were studied using quantum-chemical calculations. It is found that the excess charge in the charged systems is localized on one of the hydroxybenzoquinoline ligands. Structural changes in charged Bebq2 are pronounced in the charged ligand and nearly negligible in the neutral ligand. Charge transfer from the charged ligand to a neutral one can proceed either within a single Bebq2 monomer molecule or between the different monomers in the Bebq2 dimer. The corresponding hopping integrals were estimated as half the excitation energy from the ground to the first excited state of either the monomer or the dimer calculated at the avoided crossing point. PMID:25107360

Safonov, Andrei A; Bagaturyants, Alexander A

2014-08-01

63

Disulfide bond formation involves a quinhydrone-type charge-transfer complex.  

PubMed

The chemistry of disulfide exchange in biological systems is well studied. However, the detailed mechanism of how oxidizing equivalents are derived to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers oxidizing equivalents through DsbA to secreted proteins. DsbB becomes reoxidized by reducing quinones that are part of the membrane-bound electron-transfer chains. It is this quinone reductase activity that links disulfide bond formation to the electron transport system. We show here that purified DsbB contains the spectral signal of a quinhydrone, a charge-transfer complex consisting of a hydroquinone and a quinone in a stacked configuration. We conclude that disulfide bond formation involves a stacked hydroquinone-benzoquinone pair that can be trapped on DsbB as a quinhydrone charge-transfer complex. Quinhydrones are known to be redox-active and are commonly used as redox standards, but, to our knowledge, have never before been directly observed in biological systems. We also show kinetically that this quinhydrone-type charge-transfer complex undergoes redox reactions consistent with its being an intermediate in the reaction mechanism of DsbB. We propose a simple model for the action of DsbB where a quinhydrone-like complex plays a crucial role as a reaction intermediate. PMID:14612576

Regeimbal, James; Gleiter, Stefan; Trumpower, Bernard L; Yu, Chang-An; Diwakar, Mithun; Ballou, David P; Bardwell, James C A

2003-11-25

64

Disulfide bond formation involves a quinhydrone-type charge–transfer complex  

PubMed Central

The chemistry of disulfide exchange in biological systems is well studied. However, the detailed mechanism of how oxidizing equivalents are derived to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers oxidizing equivalents through DsbA to secreted proteins. DsbB becomes reoxidized by reducing quinones that are part of the membrane-bound electron-transfer chains. It is this quinone reductase activity that links disulfide bond formation to the electron transport system. We show here that purified DsbB contains the spectral signal of a quinhydrone, a charge–transfer complex consisting of a hydroquinone and a quinone in a stacked configuration. We conclude that disulfide bond formation involves a stacked hydroquinone–benzoquinone pair that can be trapped on DsbB as a quinhydrone charge–transfer complex. Quinhydrones are known to be redox-active and are commonly used as redox standards, but, to our knowledge, have never before been directly observed in biological systems. We also show kinetically that this quinhydrone-type charge–transfer complex undergoes redox reactions consistent with its being an intermediate in the reaction mechanism of DsbB. We propose a simple model for the action of DsbB where a quinhydrone-like complex plays a crucial role as a reaction intermediate. PMID:14612576

Regeimbal, James; Gleiter, Stefan; Trumpower, Bernard L.; Yu, Chang-An; Diwakar, Mithun; Ballou, David P.; Bardwell, James C. A.

2003-01-01

65

Vortex-driven charge transfer between partially coalescing droplets  

NASA Astrophysics Data System (ADS)

Oppositely charged drops fail to coalesce above a critical field strength, despite the attractive force between the opposite charges. Here we report the existence of a critical ionic conductivity below which oppositely charged drops only partially coalesce. The degree of coalescence of water drops in oil can be tuned from complete coalescence at low field strengths to complete non-coalescence at high field strengths, thus providing external control over the size of the resulting daughter droplet. Strikingly, in this regime the size and charge of the daughter droplet are both independent of the conductivity. We present evidence suggesting the charge transfer is instead dominated by convection associated with the capillary-driven penetration of a vortex into the larger drop, and we demonstrate that the size of the daughter droplet is consistent with a scaling model based on a balance between capillary-driven inertia and electrostatic repulsion.

Ristenpart, William; Creasey, J. C.; Hamlin, B. S.

2011-11-01

66

Molecular charge-transfer interaction with single-layer graphene  

Microsoft Academic Search

While the effect of electrochemical doping on single-layer graphene (SG) with holes and electrons has been investigated, the effect of charge-transfer doping on SG has not been examined hitherto. Effects of varying the concentration of electron donor and acceptor molecules such as tetrathiafulvalene (TTF) and tetracyanoethylene (TCNE) on SG produced by mechanical exfoliation as well as by the reduction of

Dattatray J. Late; Anupama Ghosh; Biswanath Chakraborty; A. K. Sood; Umesh V. Waghmare; C. N. R. Rao

2011-01-01

67

CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS  

SciTech Connect

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.

Khalil, Munira

2014-06-27

68

Full counting statistics of charge transfer in Coulomb blockade systems  

Microsoft Academic Search

Full counting statistics (FCS) of charge transfer in mesoscopic systems has recently become a subject of significant interest, since it proves to reveal an important information about the system which can be hardly assessed by other means. While the previous research mostly addressed the FCS of noninteracting systems, the present paper deals with the FCS in the limit of strong

D. A. Bagrets; Yu. V. Nazarov

2003-01-01

69

Enhancing SERS by Means of Supramolecular Charge Transfer  

NASA Technical Reports Server (NTRS)

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.

Wong, Eric; Flood, Amar; Morales, Alfredo

2009-01-01

70

Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines  

SciTech Connect

The FTIR spectra of charge transfer complexes of purines and pyrimidines with organic acceptors such as TCNQ, TCNE, DDQ, chloranil and iodine are obtained and studied in the present work. Adenine, guanine, thymine, cytosine and uracil are the purines and pyrimidines which are found as constituent of DNA and RNA. Charge transfer induced hydrogen bonding is concluded on the basis of indirect transitions observed in the infrared range in these CTCs. Some CTCs show gaussian bands revealing delocalization of charge carriers. The CTCs show interband transition in three-dimensions rather than two-dimensions unlike CTCs of amino acids. There is no extended hydrogen bonded network spanning the whole crystal. This leads to indirect transition due to locally deformed lattice furnishing a phonon-assisted transition.

Rathod, Pravinsinh I.; Oza, A. T. [Department Of Physics, Sardar Patel University, Vallabh Vidyanagar, Gujarat, 388120 (India)

2011-10-20

71

Space-Charge Transfer in Hybrid Inorganic-Organic Systems  

NASA Astrophysics Data System (ADS)

We discuss density functional theory calculations of hybrid inorganic-organic systems that explicitly include the global effects of doping (i.e., position of the Fermi level) and the formation of a space-charge layer. For the example of tetrafluoro-tetracyanoquinodimethane on the ZnO(0001¯) surface we show that the adsorption energy and electron transfer depend strongly on the ZnO doping. The associated work function changes are large, for which the formation of space-charge layers is the main driving force. The prominent doping effects are expected to be quite general for charge-transfer interfaces in hybrid inorganic-organic systems and important for device design.

Xu, Yong; Hofmann, Oliver T.; Schlesinger, Raphael; Winkler, Stefanie; Frisch, Johannes; Niederhausen, Jens; Vollmer, Antje; Blumstengel, Sylke; Henneberger, Fritz; Koch, Norbert; Rinke, Patrick; Scheffler, Matthias

2013-11-01

72

33 CFR 127.1301 - Persons in charge of transfers for the facility: Qualifications and certification.  

Code of Federal Regulations, 2012 CFR

... (1) Has at least 48 hours' transfer experience with each LHG being transferred...b) Before a person in charge of transfers for a waterfront facility handling LHG supervises a transfer of LHG, the operator of the facility shall certify...

2012-07-01

73

33 CFR 127.1301 - Persons in charge of transfers for the facility: Qualifications and certification.  

Code of Federal Regulations, 2010 CFR

... (1) Has at least 48 hours' transfer experience with each LHG being transferred...b) Before a person in charge of transfers for a waterfront facility handling LHG supervises a transfer of LHG, the operator of the facility shall certify...

2010-07-01

74

33 CFR 127.1301 - Persons in charge of transfers for the facility: Qualifications and certification.  

Code of Federal Regulations, 2014 CFR

... (1) Has at least 48 hours' transfer experience with each LHG being transferred...b) Before a person in charge of transfers for a waterfront facility handling LHG supervises a transfer of LHG, the operator of the facility shall certify...

2014-07-01

75

33 CFR 127.1301 - Persons in charge of transfers for the facility: Qualifications and certification.  

Code of Federal Regulations, 2013 CFR

... (1) Has at least 48 hours' transfer experience with each LHG being transferred...b) Before a person in charge of transfers for a waterfront facility handling LHG supervises a transfer of LHG, the operator of the facility shall certify...

2013-07-01

76

33 CFR 127.1301 - Persons in charge of transfers for the facility: Qualifications and certification.  

Code of Federal Regulations, 2011 CFR

... (1) Has at least 48 hours' transfer experience with each LHG being transferred...b) Before a person in charge of transfers for a waterfront facility handling LHG supervises a transfer of LHG, the operator of the facility shall certify...

2011-07-01

77

Measurements of charge transfer efficiency in a proton-irradiated swept charge device  

NASA Astrophysics Data System (ADS)

Charged Coupled Devices (CCDs) have been successfully used in several low energy X-ray astronomical satellites over the past two decades. Their high energy resolution and high spatial resolution make them a perfect tool for low energy astronomy, such as observing the formation of galaxy clusters and the environment around black holes. The Low Energy X-ray Telescope (LE) group is developing a Swept Charge Device (SCD) for the Hard X-ray Modulation Telescope (HXMT) satellite. A SCD is a special low energy X-ray CCD, which can 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) with a proton-irradiated SCD have been performed at a range of operating temperatures. The SCD is irradiated by 3 × 108cm-2 10 MeV protons.

Wang, Yu-Sa; Yang, Yan-Ji; Chen, Yong; Liu, Xiao-Yan; Cui, Wei-Wei; Xu, Yu-Peng; Li, Cheng-Kui; Li, Mao-Shun; Han, Da-Wei; Chen, Tian-Xiang; Huo, Jia; Wang, Juan; Li, Wei; Hu, Wei; Zhang, Yi; Lu, Bo; Yin, Guo-He; Zhu, Yue; Zhang, Zi-Liang

2014-06-01

78

Active pixel sensor with intra-pixel charge transfer  

NASA Technical Reports Server (NTRS)

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

1995-01-01

79

Active pixel sensor with intra-pixel charge transfer  

NASA Technical Reports Server (NTRS)

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

2003-01-01

80

Active pixel sensor with intra-pixel charge transfer  

NASA Technical Reports Server (NTRS)

An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

2004-01-01

81

Donor-acceptor ligand-to-ligand charge-transfer coordination complexes of nickel(II).  

PubMed

A family of charge-transfer chromophores comprising square-planar nickel(II) complexes with one catecholate donor ligand and one ?-diimine acceptor ligand is reported. The nine new chromophores were prepared using three different catecholate ligands and three different ?-diimine ligands. Single-crystal X-ray diffraction studies on all members of the series confirm a catecholate donor-nickel(II)-?-diimine acceptor electronic structure. The coplanar arrangement of donor and acceptor ligands manifests an intense ligand-to-ligand charge-transfer (LL'CT) absorption band that can be tuned incrementally from 650 nm (1.9 eV) to 1370 nm (0.9 eV). Electrochemical studies of all nine complexes reveal rich redox chemistry with two one-electron reduction processes and two one-electron oxidation processes. For one dye, both the singly reduced anion and the singly oxidized cation were prepared, isolated, and characterized by EPR spectroscopy to confirm ligand-localization of the redox processes. The optical and electrochemical properties of these new complexes identify them as attractive candidates for charge-transfer photochemistry and solar-energy conversion applications. PMID:25100175

Kramer, Wesley W; Cameron, Lindsay A; Zarkesh, Ryan A; Ziller, Joseph W; Heyduk, Alan F

2014-08-18

82

Space charge segregation at grain boundaries in titanium dioxide: 1. Relationship between lattice defect chemistry and space charge potential  

Microsoft Academic Search

The electrical potential difference between the interface and the bulk in TiO[sub 2] is obtained as a function of temperature, oxygen pressure, and acceptor or donor doping from a space charge model that explicitly includes the high-temperature lattice defect chemistry. Using defect equilibrium constants for TiO[sub 2] from previous literature studies, it is shown that for a space charge determined

Jeri Ann S. Ikeda; Yet-Ming Chiang

1993-01-01

83

A quantitative view of charge transfer in the hydrogen bond: the water dimer case.  

PubMed

The hydrogen bond represents a fundamental intermolecular interaction that binds molecules in vapor and liquid water. A crucial and debated aspect of its electronic structure and chemistry is the charge transfer (CT) accompanying it. Much effort has been devoted, in particular, to the study of the smallest prototype system, the water dimer, but even here results and interpretations differ widely. In this paper, we reassess CT in the water dimer by using charge-displacement analysis. Besides a reliable estimate of the amount of CT (14.6 me) that characterizes the system, our study provides an unambiguous context, and very useful bounds, within which CT effects may be evaluated, crucially including the associated energy stabilization. PMID:25044753

Ronca, Enrico; Belpassi, Leonardo; Tarantelli, Francesco

2014-09-15

84

Laboratory Studies of Thermal Energy Charge Transfer of Multiply Charged Ions in Astrophysical Plasmas  

NASA Technical Reports Server (NTRS)

The laser ablation/ion storage facility at the UNLV Physics Department has been dedicated to the study of atomic and molecular processes in low temperature plasmas. Our program focuses on the charge transfer (electron capture) of multiply charged ions and neutrals important in astrophysics. The electron transfer reactions with atoms and molecules is crucial to the ionization condition of neutral rich photoionized plasmas. With the successful deployment of the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Chandra X-ray Observatory by NASA high resolution VUV and X-ray emission spectra fiom various astrophysical objects have been collected. These spectra will be analyzed to determine the source of the emission and the chemical and physical environment of the source. The proper interpretation of these spectra will require complete knowledge of all the atomic processes in these plasmas. In a neutral rich environment, charge transfer can be the dominant process. The rate coefficients need to be known accurately. We have also extended our charge transfer measurements to KeV region with a pulsed ion beam. The inclusion of this facility into our current program provides flexibility in extending the measurement to higher energies (KeV) if needed. This flexibility enables us to address issues of immediate interest to the astrophysical community as new observations are made by high resolution space based observatories.

Kwong, Victor H. S.

2003-01-01

85

Charge-transfer complexes of phenylephrine with nitrobenzene derivatives  

NASA Astrophysics Data System (ADS)

The molecular charge-transfer complexes of phenylephrine with picric acid and m-dinitrobenzene have been studied and investigated by IR, 1H NMR electronic spectra in organic solvents and buffer solutions, respectively. Simple and selective methods are proposed for the determination of phenylephrine hydrochloride in bulk form and in tablets. The two methods are based on the formation of charge-transfer complexes between drug base as a n-donor (D) and picric acid, m-dinitrobenzene as ?-acceptor (A). The products exhibit absorption maxima at 497 and 560 nm in acetonitrile for picric acid and m-dinitrobenzene, respectively. The coloured product exhibits an absorption maximum at 650 nm in dioxane. The sensitive kinetic methods for the determination phynylephrine hydrochloride are described. The method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time at 20 min.

El-Mossalamy, E. H.

2004-04-01

86

Excited-state intramolecular charge transfer in 9-aminoacridine derivative.  

PubMed

A new fluorochromic dye was obtained from the reaction of 9-aminoacridine with ethyl-2-cyano-3-ethoxyacrylate. It displays complex fluorescence that is ascribed to normal emission from the acridine chromophore in addition to excited-state intramolecular charge transfer (ESICT) formed upon light excitation. The analysis of the fluorescence decays in different solvents reveals two short-lived components in the range of 80-450 ps and 0.7-3.2 ns, ascribed to the formation and decay of the intramolecular charge transfer (ICT) state, in addition to a third component of about 9.0 ns, which is related to the normal emission from the acridine singlet excited state, probably in an enol-imine tautomeric form. The ICT emission is readily quenched by water addition to polar solvents, and this effect is ascribed to changes in the keto-amine/enol-imine equilibrium of this fluorochromic dye. PMID:16833932

Pereira, Robson Valentim; Garcia Ferreira, Ana Paula; Gehlen, Marcelo Henrique

2005-07-14

87

The charge transfer characteristic of porphyrin Langmuir-Blodgett films  

NASA Astrophysics Data System (ADS)

The ordered porphyrin Langmuir-Blodgett (LB) films were prepared under different surface pressures. The UV-vis absorption spectrum, infrared spectrum, cyclic voltammetry and constant potential jump were used for testing. UV-vis spectra showed that under the surface pressure of approx. 10 mN/m, the ordered porphyrin LB films formed were demonstrated by infrared spectra. With the order degree of LB films strengthened, the charge transfer and storage of porphyrin LB films enhanced. And it was measured by electrochemical method. IR spectrum proves that both the interaction of porphyrin rings (the rings can form the head-to-head structure) and that of hydroxyl groups (the groups can form the feet-to-feet structure) in porphyrin LB ordered films can affect the charge transfer characteristics of porphyrin films.

Qi, P.; Li, Z. H.; Zhou, Y.; Wang, F.; Du, Y.; Zhang, L. Q.; Li, G.; Zhang, H. Z.

2013-08-01

88

The driving forces for twisted or planar intramolecular charge transfer.  

PubMed

A D-A (donor-acceptor)-type chromophore may twist or flatten in its excited state to form a TICT (twisted intramolecular charge transfer) state or a PICT (planar intramolecular charge transfer) state, respectively. What is the driving force behind this twisting or planarization? Which geometry will occur for a certain D-A chromophore? To answer these questions, both fragment orbital interaction and excited state energy decomposition analyses were performed on several classical TICT/PICT molecules. Three driving forces were identified, namely, energy gap, hole-electron interactions, and excited state relaxation. The contributions of these driving forces in various types of molecules were analyzed to determine how the molecular structure affects them. The energy gap difference between the twisted and planar geometries was found to play a decisive role in most situations. Thus, evaluating the frontier orbital interactions between the donor and acceptor effectively predicts whether chromophores planarize or twist in the excited state. PMID:25759940

Zhong, Cheng

2015-04-14

89

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

PubMed Central

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 significant increase in size associated with a decrease in density with further annealing. PMID:18534025

Ramana, CV; Becker, U; Shutthanandan, V; Julien, CM

2008-01-01

90

Understanding charge transfer in carbon nanotube-fullerene bulk heterojunctions.  

PubMed

Semiconducting single-walled carbon nanotube/fullerene bulk heterojunctions exhibit unique optoelectronic properties highly suitable for flexible, efficient, and robust photovoltaics and photodetectors. We investigate charge-transfer dynamics in inverted devices featuring a polyethylenimine-coated ZnO nanowire array infiltrated with these blends and find that trap-assisted recombination dominates transport within the blend and at the active layer/nanowire interface. We find that electrode modifiers suppress this recombination, leading to high performance. PMID:25797180

Gong, Maogang; Shastry, Tejas A; Cui, Qiannan; Kohlmeyer, Ryan R; Luck, Kyle A; Rowberg, Andrew; Marks, Tobin J; Durstock, Michael F; Zhao, Hui; Hersam, Mark C; Ren, Shenqiang

2015-04-01

91

Energy and charge transfer in ionized argon coated water clusters  

SciTech Connect

We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H{sub 2}O){sub n} clusters resulting in the ionization threshold above ?15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar{sup +} and water occurs above the threshold; at higher electron energies above ?28 eV, an excitonic transfer process between Ar{sup +}* and water opens leading to new products Ar{sub n}H{sup +} and (H{sub 2}O){sub n}H{sup +}. On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H{sub 2}O){sub n}H{sub 2}{sup 2+} and (H{sub 2}O){sub n}{sup 2+} ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.

Ko?išek, J., E-mail: kocisek@jh-inst.cas.cz, E-mail: michal.farnik@jh-inst.cas.cz, E-mail: petr.slavicek@vscht.cz; Lengyel, J.; Fárník, M., E-mail: kocisek@jh-inst.cas.cz, E-mail: michal.farnik@jh-inst.cas.cz, E-mail: petr.slavicek@vscht.cz [J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague (Czech Republic); Slaví?ek, P., E-mail: kocisek@jh-inst.cas.cz, E-mail: michal.farnik@jh-inst.cas.cz, E-mail: petr.slavicek@vscht.cz [Department of Physical Chemistry, Institute of Chemical Technology, Technická 5, 16628 Prague 6 (Czech Republic)

2013-12-07

92

Cooperative phenomena associated with electron and proton transfer in quinhydrone charge-transfer crystal  

NASA Astrophysics Data System (ADS)

Studies of the IR vibrational spectroscopy of single crystals of the H-bonded quinhydrone charge-transfer complexes show that a new phase transition occurs upon application of hydrostatic pressure, associated with the proton transfer in the 2D proton lattice. The temperature- and pressure-induced changes in the O-H vibrational spectra are accounted for in terms of the melting of the proton lattice due to the proton tunneling effect.

Mitani, T.; Saito, G.; Urayama, H.

1988-05-01

93

Reflection mechanism for generating spin transfer torque without charge current  

NASA Astrophysics Data System (ADS)

A reflection mechanism for generating spin-transfer torque is proposed. It is due to interference of bias-driven nonequilibrium electrons incident on a switching junction, with the electrons reflected from an insulating barrier inserted in the junction after the switching magnet. It is shown, using the rigorous Keldysh formalism, that this out-of-plane torque T? is proportional to an applied bias and is as large as the torque in a conventional junction generated by a strong charge current. However, the charge current and the in-plane torque T? are almost completely suppressed by the insulating barrier. This junction thus offers the highly applicable possibility of bias-induced switching of magnetization without charge current.

Autès, G.; Mathon, J.; Umerski, A.

2012-03-01

94

Spin-dependent charge transfer state design rules in organic photovoltaics.  

PubMed

Charge transfer states play a crucial role in organic photovoltaics, mediating both photocurrent generation and recombination losses. In this work, we examine recombination losses as a function of the electron-hole spacing in fluorescent charge transfer states, including direct monitoring of both singlet and triplet charge transfer state dynamics. Here we demonstrate that large donor-acceptor separations minimize back transfer from the charge transfer state to a low-lying triplet exciton 'drain' or the ground state by utilizing external pressure to modulate molecular spacing. The triplet drain quenches triplet charge transfer states that would otherwise be spin protected against recombination, and switches the most efficient origin of the photocurrent from triplet to singlet charge transfer states. Future organic solar cell designs should focus on raising the energy of triplet excitons to better utilize triplet charge transfer mediated photocurrent generation or increasing the donor-acceptor spacing to minimize recombination losses. PMID:25762410

Chang, Wendi; Congreve, Daniel N; Hontz, Eric; Bahlke, Matthias E; McMahon, David P; Reineke, Sebastian; Wu, Tony C; Bulovi?, Vladimir; Van Voorhis, Troy; Baldo, Marc A

2015-01-01

95

Spin-dependent charge transfer state design rules in organic photovoltaics  

NASA Astrophysics Data System (ADS)

Charge transfer states play a crucial role in organic photovoltaics, mediating both photocurrent generation and recombination losses. In this work, we examine recombination losses as a function of the electron-hole spacing in fluorescent charge transfer states, including direct monitoring of both singlet and triplet charge transfer state dynamics. Here we demonstrate that large donor–acceptor separations minimize back transfer from the charge transfer state to a low-lying triplet exciton ‘drain’ or the ground state by utilizing external pressure to modulate molecular spacing. The triplet drain quenches triplet charge transfer states that would otherwise be spin protected against recombination, and switches the most efficient origin of the photocurrent from triplet to singlet charge transfer states. Future organic solar cell designs should focus on raising the energy of triplet excitons to better utilize triplet charge transfer mediated photocurrent generation or increasing the donor–acceptor spacing to minimize recombination losses.

Chang, Wendi; Congreve, Daniel N.; Hontz, Eric; Bahlke, Matthias E.; McMahon, David P.; Reineke, Sebastian; Wu, Tony C.; Bulovi?, Vladimir; van Voorhis, Troy; Baldo, Marc A.

2015-03-01

96

Photochemistry and charge transfer chemistry of the platinum group elements  

SciTech Connect

During the past 3 years, progress was made in elucidating the excited state structures of Pt(diimine)(dithiolate) complexes, while more recent efforts focused on the photochemistry of these complexes and electronic structure of other dithiolate systems. A carbonyl-Ir-maleonitrile dithiolate complex is also studied.

Eisenberg, R.

1992-12-01

97

Chemistry and charge transfer phenomena in water cluster cations  

Microsoft Academic Search

The present paper discusses three case studies of water cluster cation stability and reactivity by FT-ICR technique: (1) HCl reactions with protonated water clusters that reveal mechanisms of ionic solvation and evaporative recombination, (2) the black body radiation induced fragmentation of hydrated magnesium, Mg+(H2O)n, that leads to mono-hydroxide formation and evaporation of a hydrogen atom once that a critical size

Christian Berg; Uwe Achatz; Martin Beyer; Stefan Joos; Gerhard Albert; Thomas Schindler; Gereon Niedner-Schatteburg; Vladimir E. Bondybey

1997-01-01

98

Chemistry and charge transfer phenomena in water cluster cations  

NASA Astrophysics Data System (ADS)

The present paper discusses three case studies of water cluster cation stability and reactivity by FT-ICR technique: (1) HCl reactions with protonated water clusters that reveal mechanisms of ionic solvation and evaporative recombination, (2) the black body radiation induced fragmentation of hydrated magnesium, Mg+(H2O)n, that leads to mono-hydroxide formation and evaporation of a hydrogen atom once that a critical size of n = 17 is reached, and (3) the fragmentation of hydrated aluminum cations, Al+(H2O)n, which leads to the formation of aluminum di-hydroxide and evaporation of a hydrogen molecule at a critical size of about 22 water molecules. Solvation shell effects and possible clathrate-like structures are discussed together with the liquid- versus solid-like character of the clusters. Future investigations are proposed.

Berg, Christian; Achatz, Uwe; Beyer, Martin; Joos, Stefan; Albert, Gerhard; Schindler, Thomas; Niedner-Schatteburg, Gereon; Bondybey, Vladimir E.

1997-11-01

99

Photochemistry and charge transfer chemistry of the platinum group elements  

SciTech Connect

Significant progress has been made on the photochemistry and photophysics of platinum group element dithiolate complexes. The specific systems under investigation are square planar complexes of Pt(II) containing a dithiolate chelate and two other donor groups to complete the coordination sphere. The donor groups may be amines, imines, phosphines, phosphites or olefins, and they can be either monodentate or joined together as part of a chelate ring.

Eisenberg, R.

1991-12-01

100

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

PubMed

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 properties of contacted surfaces. For example, in the case of a silicon-on-insulator field effect transistors are in contact with PDMS and subsequent delamination leads to threshold voltage shifts that exceed 500 mV. PMID:21526803

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

2011-06-01

101

Charge Transfer and Ionization by Intermediate-Energy Heavy Ions  

SciTech Connect

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

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

2006-11-01

102

Charge transfer and ionisation by intermediate-energy heavy ions.  

PubMed

The use of heavy ion beams for microbeam studies of mammalian cell response leads to a need to better understand interaction cross sections for collisions of heavy ions with tissue constituents. For ion energies of a few MeV u(-1) or less, ions capture electrons from the media in which they travel and undergo subsequent interactions as partially 'dressed' ions. For example, 16 MeV fluorine ions have an equilibrium charge of 7(+), 32 MeV sulphur ions have an equilibrium charge of approximately 11(+), and as the ion energies decrease the equilibrium charge decreases dramatically. Data for interactions of partially dressed ions are extremely rare, making it difficult to estimate microscopic patterns of energy deposition leading to damage to cellular components. Such estimates, normally obtained by Monte Carlo track structure simulations, require a comprehensive database of differential and total ionisation cross sections as well as charge transfer cross sections. To provide information for track simulation, measurement of total ionisation cross sections have been initiated at East Carolina University using the recoil ion time-of-flight method that also yields cross sections for multiple ionisation processes and charge transfer cross sections; multiple ionisation is prevalent for heavy ion interactions. In addition, measurements of differential ionisation cross sections needed for Monte Carlo simulation of detailed event-by-event particle tracks are under way. Differential, total and multiple ionisation cross sections and electron capture and loss cross sections measured for C(+) ions with energies of 100 and 200 keV u(-1) are described. PMID:17132666

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

2006-01-01

103

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

SciTech Connect

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 D{sub 6h} 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 D{sub 2} eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D{sub 1}, D{sub 2} (N{sup +}-Phenyl, N-Phenyl{sup +}). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an oscillation of the spin density – charge migration – between the N atom and the phenyl ring with a period of 4 fs. When the nuclear motion becomes coupled, this oscillation persists in a damped form, followed by an effective charge transfer after 30 fs.

Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A. [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)] [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)

2013-07-28

104

Charge transfer in proton-hydrogen collisions under Debye plasma  

NASA Astrophysics Data System (ADS)

The effect of plasma environment on the 1s ? nlm charge transfer, for arbitrary n, l, and m, in proton-hydrogen collisions has been investigated within the framework of a distorted wave approximation. The effect of external plasma has been incorporated using Debye screening model of the interacting charge particles. Making use of a simple variationally determined hydrogenic wave function, it has been possible to obtain the scattering amplitude in closed form. A detailed study has been made to investigate the effect of external plasma environment on the differential and total cross sections for electron capture into different angular momentum states for the incident energy in the range of 20-1000 keV. For the unscreened case, our results are in close agreement with some of the most accurate results available in the literature.

Bhattacharya, Arka; Kamali, M. Z. M.; Ghoshal, Arijit; Ratnavelu, K.

2015-02-01

105

On the use of Bader's atomic charges for the evaluation of charge transfers between ground and excited states  

NASA Astrophysics Data System (ADS)

In this letter, we assess to what extent Bader's atomic charges are appropriate to quantify charge transfers in photon absorption processes. We actually underline the fundamental role of the atomic dipole moment, which is indeed involved in the change of the electron density polarization upon excitation. This contribution cannot be neglected and enables to reproduce the total transition dipole moments with full accuracy if an enough tight integration quadrature is used. As this scheme allows separating intra-atomic density reorganization and interatomic charge transfer, it is well suited to describe through-space charge-transfer excitations.

Tognetti, Vincent; Joubert, Laurent

2013-02-01

106

Importance of Charge Transfer Excitations in DNA Electron Spectrum:  

NASA Astrophysics Data System (ADS)

Electron spectra of DNA model compounds, adenosine-thymidine and guanosine-cytidine nucleoside base pairs, as well as the relevant homogeneous stacked base pair steps in A-DNA and B-DNA conformations, were investigated using ZINDO semiempirical quantum-chemical method. This work confirms that, in DNA with intact Watson-Crick hydrogen bonding and base stacking, the highest occupied molecular orbitals (HOMO) are residing on purine base residues, whereas the lowest unoccupied molecular orbitals (LUMO) — on pyrimidine base residues. In general, the present results are satisfactorily comparable with the available experimental data. The role of charge transfer excitations in the polymer DNA 260 nm spectral band is discussed.

Starikov, E. B.

107

Modulating unimolecular charge transfer by exciting bridge vibrations.  

PubMed

Ultrafast UV-vibrational spectroscopy was used to investigate how vibrational excitation of the bridge changes photoinduced electron transfer between donor (dimethylaniline) and acceptor (anthracene) moieties bridged by a guanosine-cytidine base pair (GC). The charge-separated (CS) state yield is found to be lowered by high-frequency bridge mode excitation. The effect is linked to a dynamic modulation of the donor-acceptor coupling interaction by weakening of H-bonding and/or by disruption of the bridging base-pair planarity. PMID:19928957

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

2009-12-23

108

Kinematics of charge transfer: Ar^++H2  

E-print Network

) an intimate-collision mechanism which results in large-angle scattering and which produces H; in a broad range of vibrational states. I. INTRODUCTION Because of the familiar problem of detecting very low (i. e., quasithermal) energy product ions, little... 63 meV below Ar+(lPSf2) and the v' =2 state is only 13 meV below Ar+(2p1f2 ). We shall refer to the formation of H; in these states as quasiresonant charge transfer (RCT), while formation of H; in higher vibrational states will be considered...

Hierl, Peter M.; Pacak, V.; Herman, Z.

1977-01-01

109

Photoinduced charge-transfer materials for nonlinear optical applications  

DOEpatents

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 C60 acceptor layers.

McBranch, Duncan W.

2006-10-24

110

On the Acid-Base Chemistry of Permanently Charged Minerals  

E-print Network

complexation model, which superposes a thermodynamic description of acid-base reactions such as oxides results chiefly from acid- base reactions. The variations in the surface charge as a function of p of the mean electrical potential at the surface on the energetics of the acid-base reactions (4). As seen

Morel, François M. M.

111

Photoinduced Charge and Energy Transfer Processes in Molecular Aggregates  

SciTech Connect

This project involved the experimental probing of the electronic excited states generated by photoinduced (center-to-center) electron and energy transfer processes in several classes of transition metal donor/acceptor (D/A) complexes. Some of the general properties inferred from these studies should be useful in the design of new systems for energy conversion applications. Pursuit of the project goals has involved the determination of electron transfer efficiencies and the detailed study of variations in the electronic spectra of D/A complexes. This has resulted in the study of some very fundamental issues of photoinduced charge transfer and the identification of some of the constraints on its efficiency. The experimental studies of the competition between the degradative non-radiative unimolecular relaxation of transition metal excited states and their transfer of charge from these excited states to external acceptors have involved a range of techniques such as transient decay kinetics, photoacoustic calorimetry and transient or stationary state spectroscopy. The substrates synthesized for these studies were selected to provide model systems, or series of model systems to probe the validity of models of electronic excited states and their reactivity. The work during the last few years has focused largely, but not exclusively, on the use of emission spectral band shapes to probe the properties of charge transfer (CT) excited states. Bandshape variations are one of the very few approaches for systematically probing electronic excited states and good band shape resolution is necessary in order to gain information about the structural variations that correlate with excited state reactivity. Differences in molecular structure correlate with differences in chemical reactivity, and the variations in emission bandshapes are well known to relate to variations in the molecular structural differences between the excited and ground electronic states. However, it is has been rarely noticed that configurational mixing of the lowest energy excited state with other electronic states leads to unique distortions of the lowest energy excited state which result in modifications in the vibronic structure and bandshape of the emission. We have used the emission sideband shapes to evaluate patterns of ground state-excited state and excited state-excited state configurational mixing in some simple series of complexes.

John F. Endicott

2009-10-20

112

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

E-print Network

Charge transfer and in-cloud structure of large-charge-moment positive lightning strokes 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 (1500­3200 CÁkm) capable

Cummer, Steven A.

113

Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes  

Microsoft Academic Search

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of

Amy E. Childress; Menachem Elimelech

1996-01-01

114

Charge transfer and injection barrier at the metal-organic interfaces  

NASA Astrophysics Data System (ADS)

The metal-organic interface plays a critical role in determining the functionality and performance of many innovative organic based devices. It has attracted extensive research interests in recent years. This thesis presents investigations of the electronic structures of organic materials, such as tris-(8-hydroxyquinoline) aluminum (Alq3) and copper phthalocyanine (CuPc), during their interface formation with metals. The characterization is accomplished by X-ray and ultraviolet photoelectron spectroscopes (XPS and UPS) and inverse photoelectron spectroscopy (IPES). As discussed herein, both occupied and unoccupied electronic states at the interfaces are carefully examined in different aspects. In Chapter 4, the charge transfer and chemical reaction at various metal/Alq3 interfaces are investigated using XPS and UPS to study the electron injection into the Alga film. Electron transfer from the low work function metal and Al/LiF(CsF) bilayer to the Alga has been observed. The role of the dielectric and possible chemistry at the interface are discussed in comparison of the low work function metals. Further in Chapter 5, the origin of the metal-interface dipole and the estimation of charge injection barrier is explored using several organic materials. A thermodynamic equilibrium model is extended to explain the relation between the charge transfer process ad the interface dipole. Further, in Chapter 6 the combination of XPS, UPS and IPES detailed the evolution of both occupied and unoccupied energy states during the alkali metal doping. The energy gap modification in organic due to metal doping is observed directly for the spectra. Chapter 7 provides stability study of the organic thin films under x-ray and UV light. The results verify the usability of UPS and XPS for the organic materials used in the thesis. Chapter 7 also shows the secondary ion mass spectroscopy results of metal diffusion in organic thin films.

Yan, Li

2002-09-01

115

Smart CMOS Charge Transfer Readout Circuit for Time Delay and Integration Arrays  

Microsoft Academic Search

This paper presents a novel CMOS charge transfer readout circuit for X-ray time delay and integration (TDI) arrays with a depth of 64. The proposed circuit uses a charge transfer readout similar to CCD; thus, the summing of the signal charges can be implemented easily compared with other typical CMOS readout circuits for TDI arrays. The weakness of TDI arrays

Chul Bum Kim; Byung-Hyuk Kim; Yong Soo Lee; Han Jung; Hee Chul Lee

2006-01-01

116

Dynamics of charge transfer states on metal surfaces: The competition between reactivity and quenching  

E-print Network

Dynamics of charge transfer states on metal surfaces: The competition between reactivity. In particular we are interested in positive charge transfer from a metal surface to molecular or atomic oxygen adsorbed on the surface. Once the negatively charged oxygen on the surface loses an electron it becomes

Zeiri, Yehuda

117

Surface Science 425 (1999) 114 Non-adiabatic charge transfer process of oxygen on  

E-print Network

Surface Science 425 (1999) 1­14 Non-adiabatic charge transfer process of oxygen on metal surfaces November 1998 Abstract The dynamics of charge transfer processes of oxygen on metal surfaces a different charged oxygen species. Empirical universal potential energy functions have been constructed

Zeiri, Yehuda

118

Nanocrystal/J-aggregate constructs : chemistry, energy transfer, and applications  

E-print Network

The interaction of light with matter is one of the most central subjects to modern chemistry. Two types of materials, semiconductor nanocrystals and J-aggregates of cyanine dyes, have been developed chiefly due to their ...

Walker, Brian J. (Brian Jacob)

2011-01-01

119

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

E-print Network

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 ...

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

2015-01-01

120

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

PubMed

In the ongoing discussion on excited states of the pentacene crystal, dipole moment values have been recently invoked to gauge the CT admixture to excited states of Frenkel parentage in a model cluster. In the present paper, a simple dimer model is used to show that, in general, the dipole moment is not a valid measure of the CT contribution. This finding eliminates some apparent disagreement between the computational results published by different research groups. The implications of our results and other related aspects of cluster-type quantum chemistry calculations are discussed in the context of the standing literature dispute concerning the mechanism of singlet fission in the pentacene crystal, notably the role of charge transfer contributions vs the involvement of an excimer-like doubly excited intermediate (D state). PMID:24138489

Petelenz, Piotr; Pac, Barbara

2013-11-20

121

Ultracold, radiative charge transfer in hybrid Yb ion - Rb atom traps  

E-print Network

Ultracold hybrid ion-atom traps offer the possibility of microscopic manipulation of quantum coherences in the gas using the ion as a probe. However, inelastic processes, particularly charge transfer can be a significant process of ion loss and has been measured experimentally for the Yb$^{+}$ ion immersed in a Rb vapour. We use first-principles quantum chemistry codes to obtain the potential energy curves and dipole moments for the lowest-lying energy states of this complex. Calculations for the radiative decay processes cross sections and rate coefficients are presented for the total decay processes. Comparing the semi-classical Langevin approximation with the quantum approach, we find it provides a very good estimate of the background at higher energies. The results demonstrate that radiative decay mechanisms are important over the energy and temperature region considered. In fact, the Langevin process of ion-atom collisions dominates cold ion-atom collisions. For spin dependent processes \\cite{kohl13} the...

McLaughlin, B M; Lane, I C; McCann, J F

2014-01-01

122

Monte Carlo model for describing charge transfer in irradiated CCDs  

NASA Astrophysics Data System (ADS)

Radiation exposure of CCD devices degrades the charge transfer inefficiency (CTI) by the creation of electron trap sights within the bulk silicon. The presence of electron traps tend to smear the signal of a point-like image. This affects CCDs used in star trackers where sub-pixel centroiding is required for accurate pointing knowledge. To explore the effects of radiation damage in CCD devices, we have developed a Monte-Carlo model for simulating charge transfer in buried channel CCDs. The model is based on the Shockley-Read-Hall generation-recombination theory. The CTI in CCD devices was measured before and after exposure to mono-energetic 61 MeV protons. Our data show that displacement damage in the bulk silicon increases the CTI of the CCD device. CTI was measure don irradiated CCD devices at various temperatures form -10 to -150 C, thus providing estimates of the electron trap energy levels created in the CCD silicon. The dominate post-radiation rap energy level was the silicon E-center found to be at an energy of 0.46 eV, which is in good agreement with other published values. To fit our data over the complete temperature range, we also required electron traps of 0.36 eV and 0.21 eV. Our model also includes the effects of charge cloud growth with signal volume and clocking rates of the CCD device. Determining the types and levels of radiation a CCD device will encounter during its operational life is very important for choosing CCD operating parameters.

Gallagher, Dennis J.; Demara, Raymond; Emerson, Gary; Frame, Wayne W.; Delamere, Alan W.

1998-04-01

123

Ab initio study of charge-transfer dynamics in collisions of C{sup 2+} ions with hydrogen chloride  

SciTech Connect

Ab initio quantum chemistry molecular calculations followed by a semiclassical dynamical treatment in the keV collision energy range have been developed for the study of the charge-transfer process in collisions of C{sup 2+} ions with hydrogen chloride. The mechanism has been investigated in detail in connection with avoided crossings between states involved in the reaction. A simple mechanism driven by a strong nonadiabatic coupling matrix element has been pointed out for this process. A comparative analysis with the halogen fluoride target corresponding to a similar electronic configuration shows a quite different charge-transfer mechanism leading to a very different behavior of the cross sections. Such behavior may be correlated to specific nonadiabatic interactions observed in these collision systems.

Rozsalyi, E.; Vibok, A. [Department of Theoretical Physics, University of Debrecen, P.O. Box 5, H-4010 Debrecen (Hungary); Bene, E. [Institute of Nuclear Research, Hungarian Academy of Sciences, P.O. Box 51, H-4001 Debrecen (Hungary); Halasz, G. J. [Department of Information Technology, University of Debrecen, P.O. Box 12, H-4010 Debrecen (Hungary); Bacchus-Montabonel, M. C. [Laboratoire de Spectrometrie Ionique et Moleculaire, Universite de Lyon (Lyon I), CNRS-UMR5579, 43 Bd. du 11 Novembre 1918, F-69622 Villeurbanne Cedex (France)

2011-05-15

124

Charge Transfer Efficiency and Charge Injection in the HST/WFC3 UVIS Detectors  

NASA Astrophysics Data System (ADS)

Devices in low-earth orbit are particularly susceptible to the cumulative effects of radiation damage and the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS detectors, installed on HST in May 2009, are no exception. Such damage not only generates new hot pixels but also degrades the charge transfer efficiency (CTE), causing a loss in source flux due to charge traps as well as a systematic shift in the object centroid as the trapped charge is slowly released during readout. Based on an analysis of both internal and external monitoring data, we provide an overview of the consequences of the more than 2.5 years of radiation damage to the WFC3 CCD cameras. The advantages and disadvantages of available mitigation options are discussed, including use of the WFC3 charge injection capability, a mode now available to observers, and the status of an empirical correction similar to the one adopted for the HST Advanced Camera for Surveys (ACS).

Baggett, Sylvia M.; Noeske, K.; Anderson, J.; Biretta, J.; Borders, T.; Bushouse, H.; Khozhurina-Platais, V.; MacKenty, J.; Petro, L.; WFC3 Team

2012-01-01

125

Fingerprint of fractional charge transfer at metal/organic interface  

E-print Network

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 physisorbed molecules. This phenomenon is unambiguously recognizable by a non-rigid shift of the core-level main lines while the occupied states at the interface stay mostly unperturbed, and the unoccupied states experience pronounced changes. The experimental results are corroborated by first-principles calculations.

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

2015-02-06

126

Experimental study of low-energy charge transfer in nitrogen  

NASA Technical Reports Server (NTRS)

Total charge transfer cross sections were obtained for the N2(+)-N2 system with relative translational ion energies between 9 and 441 eV. Data were obtained to examine the dependence of total cross section on ion energy. The effect of ion excitation on the cross sections was studied by varying the electron ionization energy in the mass spectrometer ion source over an electron energy range between 14.5 and 32.1 eV. The dependence of total cross section on the neutralization chamber gas pressure was examined by obtaining data at pressure values from 9.9 to 0.000199 torr. Cross section values obtained were compared with experimental and theoretical results of other investigations.

Smith, A.

1979-01-01

127

Radiative charge transfer in Ne2+ + He collisions  

NASA Astrophysics Data System (ADS)

The optical potential and semiclassical methods have been applied to the studies of radiative charge transfer in collisions of ground-state and metastable Ne2+ ions with neutral helium. Cross sections are presented with relative collision energies between 0.1 meV and 10 keV. For all transitions concerned, the cross sections display rich resonance structures in the low-energy region. From the calculated cross sections, rate coefficients are obtained with temperatures between 10 and 20 × 106 K and are found to be in agreement with available experimental data. The multireference single- and double-excitation configuration-interaction (MRD-CI) method was used to obtain the relevant adiabatic molecular potentials and dipole transition matrix elements.

Zhao, L. B.; Wang, J. G.; Stancil, P. C.; Gu, J. P.; Liebermann, H.-P.; Buenker, R. J.; Kimura, M.

2006-12-01

128

Photoinduced Charge Transfer from Titania to Surface Doping Site  

PubMed Central

We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO2. Charge transfer from the photo-excited TiO2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO2 nanorod and catalytic site. A slab of TiO2 represents a fragment of TiO2 nanorod in the anatase phase. Titanium to ruthenium replacement is performed in a way to match the symmetry of TiO2 substrate. One molecular layer of adsorbed water is taken into consideration to mimic the experimental conditions. It is found that these adsorbed water molecules saturate dangling surface bonds and drastically affect the electronic properties of systems investigated. The modeling is performed by reduced density matrix method in the basis of Kohn-Sham orbitals. A nano-catalyst modeled through replacement defect contributes energy levels near the bottom of the conduction band of TiO2 nano-structure. An exciton in the nano-rod is dissipating due to interaction with lattice vibrations, treated through non-adiabatic coupling. The electron relaxes to conduction band edge and then to the Ru cite with faster rate than hole relaxes to the Ru cite. These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting. PMID:23795229

Inerbaev, Talgat; Hoefelmeyer, James D.; Kilin, Dmitri S.

2013-01-01

129

Interface charge transfer in polypyrrole coated perovskite manganite magnetic nanoparticles  

NASA Astrophysics Data System (ADS)

Different hybrid structures were obtained by coating magnetic nanoparticles of perovskite type manganite at optimal doping (La0.67Sr0.33MnO3,LSMO) with different quantities of polypyrrole (PPy). The amorphous layer of polypyrrole surrounding the crystalline magnetic core was observed by high resolution transmission electron microscopy (HRTEM) and analyzed by using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements in near edge structure (XANES) techniques. By analyzing the magnetic behavior of the samples one can observe that the surface modification of magnetic nanoparticles by PPy results in an increase in the saturation magnetization of the composites. The process is ascribed to paired electrons transferred from the delocalized ? states of the PPy into the outer disordered layers of the manganite. The analysis of pre-edge peak of the Mn K-edge XANES spectra in the case of PPy coated LSMO nanoparticles indicates that the charge transfer between polymer and nanoparticles is (directed) going to missing or distorted oxygen positions, hence increasing the 3d electrons' mobility and orbital hybridization between the neighboring manganese ion. As a consequence, within the surface layers of LSMO nanoparticles, both energy bands disrupted the structure, and the double exchange process between Mn ions was reestablished determining the saturation magnetizations and pre-edge features increase, respectively.

Pana, O.; Soran, M. L.; Leostean, C.; Macavei, S.; Gautron, E.; Teodorescu, C. M.; Gheorghe, N.; Chauvet, O.

2012-02-01

130

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

NASA Astrophysics Data System (ADS)

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-K? and Mn-K? 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.

Smith, P. H.; Gow, J. P. D.; Pool, P.; Holland, A. D.

2015-03-01

131

Reversible Phase Transfer of Nanoparticles Based on Photoswitchable Host–Guest Chemistry  

PubMed Central

An azobenzene-containing surfactant was synthesized for the phase transfer of ?-cyclodextrin (?-CD)-capped gold nanoparticles between water and toluene phases by host–guest chemistry. With the use of the photoisomerization of azobenzene, the reversible phase transfer of gold nanoparticles was realized by irradiation with UV and visible light. Furthermore, the phase transfer scheme was applied for the quenching of a reaction catalyzed by gold nanoparticles, as well as the recovery and recycling of the gold nanoparticles from aqueous solutions. This work will have significant impact on materials transfer and recovery in catalysis and biotechnological applications. PMID:24524295

2015-01-01

132

Real-time simulations of photoinduced coherent charge transfer and proton-coupled electron transfer.  

PubMed

Photoinduced electron transfer (ET) and proton-coupled electron transfer (PCET) are fundamental processes in natural phenomena, most noticeably in photosynthesis. Time-resolved spectroscopic evidence of coherent oscillatory behavior associated with these processes has been reported both in complex biological environments, as well as in biomimetic models for artificial photosynthesis. Here, we consider a few biomimetic models to investigate these processes in real-time simulations based on ab initio molecular dynamics and Ehrenfest dynamics. This allows for a detailed analysis on how photon-to-charge conversion is promoted by a coupling of the electronic excitation with specific vibrational modes and with proton displacements. The ET process shows a characteristic coherence that is linked to the nuclear motion at the interface between donor and acceptor. We also show real-time evidence of PCET in a benzimidazole-phenol redox relay. PMID:25224924

Eisenmayer, Thomas J; Buda, Francesco

2014-10-20

133

Bonding and charge transfer in nitrogen-donor uranyl complexes: insights from NEXAFS spectra.  

PubMed

We investigate the electronic structure of three newly synthesized nitrogen-donor uranyl complexes [(UO2)(H2bbp)Cl2], [(UO)2(Hbbp)(Py)Cl], and [(UO2)(bbp)(Py)2] using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments and simulations. The complexes studied feature derivatives of the tunable tridentate N-donor ligand 2,6-bis(2-benzimidazyl)pyridine (bbp) and exhibit discrete chemical differences in uranyl coordination. The sensitivity of the N K-edge X-ray absorption spectrum to local bonding and charge transfer is exploited to systematically investigate the evolution of structural as well as electronic properties across the three complexes. A thorough interpretation of the measured experimental spectra is achieved via ab initio NEXAFS simulations based on the eXcited electron and Core-Hole (XCH) approach and enables the assignment of spectral features to electronic transitions on specific absorbing sites. We find that ligand-uranyl bonding leads to a signature blue shift in the N K-edge absorption onset, resulting from charge displacement toward the uranyl, while changes in the equatorial coordination shell of the uranyl lead to more subtle modulations in the spectral features. Theoretical simulations show that the flexible local chemistry at the nonbinding imidazole-N sites of the bbp ligand is also reflected in the NEXAFS spectra and highlights potential synthesis strategies to improve selectivity. In particular, we find that interactions of the bbp ligand with solvent molecules can lead to changes in ligand-uranyl binding geometry while also modulating the K-edge absorption. Our results suggest that NEXAFS spectroscopy combined with first-principles interpretation can offer insights into the coordination chemistry of analogous functionalized conjugated ligands. PMID:25330350

Pemmaraju, C D; Copping, Roy; Wang, Shuao; Janousch, Markus; Teat, Simon J; Tyliszcak, Tolek; Canning, Andrew; Shuh, David K; Prendergast, David

2014-11-01

134

Charge-transfer metal-insulator transitions in the spin-1 2 Falicov-Kimball model  

E-print Network

ARTICLES Charge-transfer metal-insulator transitions in the spin-1 2 Falicov-Kimball model Woonki-coordination-number Bethe lattice in the thermodynamic limit. This model is a paradigm for a charge-transfer metal-insulator transition, where the occupancy of localized and delocalized electronic orbitals rapidly changes at the metal-insulator

Freericks, Jim

135

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

SciTech Connect

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.

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

2008-04-02

136

Molecular orbital (SCF-X??-SW) theory of Fe2+-Mn3+, Fe 3+-Mn 2+, and Fe3+-Mn3+ charge transfer and magnetic exchange in oxides and silicates  

USGS Publications Warehouse

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. -from Author

Sherman, D.M.

1990-01-01

137

Wire transfer of charge packets using a CCD-BBD structure for charge-domain signal processing  

NASA Technical Reports Server (NTRS)

A structure for the virtual transfer of charge packets across metal wires is described theoretically and is experimentally verified. The structure is a hybrid of charge-coupled device (CCD) and bucket-brigade device (BBD) elements and permits the topological crossing of charge-domain signals in low power signal processing circuits. A test vehicle consisting of 8-, 32-, and 96-stage delay lines of various geometries implemented in a double-poly, double-metal foundry process is used to characterize the wire-transfer operation. Transfer efficiency ranging between 0.998 and 0.999 is obtained for surface n-channel devices with clock cycle times in the range from 40 ns to 0.3 ms. Transfer efficiency as high as 0.9999 is obtained for buried n-channel devices. Good agreement is found between experiment and simulation.

Fossum, Eric R.

1991-01-01

138

Charge-transfer reactions in atom scattering from ionic surfaces: A time-dependent wavepacket approach  

E-print Network

Charge-transfer reactions in atom scattering from ionic surfaces: A time-dependent wavepacket with the electrostatic image charge in the metal surface, as indicated in Fig. 1(a). For low workfunction surfaces resonant with the valence band of the surface, but the image attraction is small (at least for singly-charged

Zeiri, Yehuda

139

Charge Transfer Process During Collision of Riming Graupel Pellet with Small Ice Crystals within a Thundercloud  

NASA Technical Reports Server (NTRS)

A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.

Datta, Saswati; De, Utpal K.; Goswami, K.; Jones, Linwood

1999-01-01

140

Pseudoparticle approach for charge-transferring molecule-surface collisions  

NASA Astrophysics Data System (ADS)

Based on a semiempirical generalized Anderson-Newns model, we construct a pseudoparticle description for electron emission due to deexcitation of metastable molecules at surfaces. The pseudoparticle approach allows us to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both channels are open. This is, for instance, the case when a metastable N2(3?u+) molecule hits a diamond surface. Using nonequilibrium Green functions and physically motivated approximations to the self-energies of the Dyson equations, we derive a system of rate equations for the probabilities with which the metastable N2(3?u+) molecule, the molecular ground state N2(1?g+), and the negative ion N2-(2?g) can be found in the course of the scattering event. From the rate equations, we also obtain the spectrum of the emitted electron and the secondary electron emission coefficient. Our numerical results indicate the resonant tunneling process undermining the source of the Auger channel, which therefore contributes only a few percent to the secondary electron emission.

Marbach, Johannes; Bronold, Franz Xaver; Fehske, Holger

2012-09-01

141

Charge transfer in Sr Zintl template on Si(001)  

NASA Astrophysics Data System (ADS)

The formation of the half monolayer (ML) Sr Zintl template layer on Si(001) is investigated in a combined experimental and theoretical work consisting of in situ reflection high energy electron diffraction, in situ x-ray photoelectron spectroscopy (XPS), and density functional theory. Starting with clean 2 × 1 reconstructed Si(001), we demonstrate that Sr deposition leads to a charge transfer from the metal to the Si substrate resulting in the disappearance of the asymmetry of Si dimers—an essential structural change that enables direct perovskite epitaxy on Si, and likely, other semiconductors. XPS reveals an unexpected shift to higher binding energy of the Si 2p core-level components, including the bulk. This unusual behavior is attributed to final state effects using first principles calculations. As measured by ultraviolet photoelectron spectroscopy, the deposition of 0.5 ML of Sr lowers the work function of the system by 1.35 eV, and is in good agreement with our theoretical calculations.

Choi, Miri; Posadas, Agham B.; Seo, Hosung; Hatch, Richard C.; Demkov, Alexander A.

2013-01-01

142

Charge-transfer complexes of 4-methylpiperidine with ?- and ?-acceptors  

NASA Astrophysics Data System (ADS)

The solid charge-transfer (CT) molecular complexes formed in the reaction of the electron donor 4-methylpiperidine (4MP) with the ?-electron acceptor iodine and ?-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) have been investigated spectrophotometrically in chloroform at 25 °C. These were characterized through electronic and infrared spectra as well as elemental and thermal analysis. The obtained results showed that the formed solid CT-complexes have the formulas [(4MP) I]+I-3, [(4MP)(DDQ)2] and [(4MP)(TBCHD)] and with TCNQ the adduct [TCMPQDM] is obtained through N-substitution reaction in full agreement with the known reaction stoichiometries in solution as well as the elemental measurements. The formation constant KCT, molar extinction coefficient ?CT, free energy change ?G0, CT energy ECT and the ionization potential Ip have been calculated for the CT-complexes [(4MP) I]+I-3, [(4MP)(DDQ)2] and [(4MP)(TBCHD)].

AlQaradawi, Siham Y.; Mostafa, Adel; Bazzi, Hassan S.

2015-01-01

143

Nematic and spin-charge orders driven by hole-doping a charge-transfer insulator  

NASA Astrophysics Data System (ADS)

Recent experimental discoveries have brought a diverse set of broken symmetry states to the center stage of research on cuprate superconductors. Here, we focus on a thematic understanding of the diverse phenomenology by exploring a strong-coupling mechanism of symmetry breaking driven by frustration of antiferromagnetic (AFM) order. We achieve this through a variational study of a three-band model of the CuO2 plane with Kondo type exchange couplings between doped oxygen holes and classical copper spins. Two main findings from this strong-coupling multi-band perspective are (1) that the symmetry hierarchy of spin stripe, charge stripe, intra-unit-cell nematic order and isotropic phases are all accessible microscopically within the model, (2) many symmetry-breaking patterns compete with energy differences within a few meV per Cu atom to produce a rich phase diagram. These results indicate that the diverse phenomenology of broken-symmetry states in hole-doped AFM charge-transfer insulators may indeed arise from hole-doped frustration of antiferromagnetism.

Fischer, Mark H.; Wu, Si; Lawler, Michael; Paramekanti, Arun; Kim, Eun-Ah

2014-09-01

144

'Tunable' positive and negative surface charges on a capillary wall: exploiting the Immobiline chemistry.  

PubMed

The Immobiline (weak acrylamido acids and bases) chemistry has been applied to the covalent attachment of a positively (or, if needed, negatively) charged layer onto the inner surface of the silica wall. In particular, the following basic Immobilines have been used: pK 6.2, pK 7.0, pK 8.5 and pK 9.3. In order to avoid pK changes, the charged Immobilines are mixed with neutral acrylamido derivatives (in particular the highly resistant and hydrophilic N-acryloyl aminoethoxyethanol) so as to form a co-polymer having a 1:5 molar ratio (charged to neutral). The mu(eo) vs. pH curves have a slope opposite to that of a naked capillary and fan out on the pH scale following the titration curves of the different weak bases. Such chemistry allows the covalent attachment of charged species having known pK values and offering controlled charged densities on the wall. However, with the atomic force microscope, it is found that such soft coatings (whether charged or neutral) do not seem to provide complete coverage of the surface: naked patches of fused silica are found interdispersed among the polymer-coated ones. A good solution is a hybrid bonded and dynamic coating, obtained by adding short chain linear polyacrylamides to the background electrolyte. Good separations of polycations [poly(L-histidine)] and of histones are reported up to pH 5.7. PMID:8796483

Capelli, L; Ermakov, S V; Righetti, P G

1996-05-14

145

The coordination and atom transfer chemistry of titanium porphyrin complexes  

SciTech Connect

Preparation, characterization, and reactivity of ({eta}{sup 2}- alkyne)(meso-tetratolylpoprphrinato)titanium(II) complexes are described, along with inetermetal oxygen atom transfer reactions involving Ti(IV) and Ti(III) porphyrin complexes. The {eta}{sup 2}- alkyne complexes are prepared by reaction of (TTP)TiCl{sub 2} with LiAlH{sub 4} in presence of alkyne. Structure of (OEP)Ti({eta}{sup 2}-Ph-C{triple_bond}C-Ph) (OEP=octaethylporphryin) was determined by XRD. The compounds undergo simple substitution to displace the alkyne and produce doubly substituted complexes. Structure of (TTP)Ti(4-picoline){sub 2} was also determined by XRD. Reaction of (TTP)Ti{double_bond}O with (OEP)Ti-Cl yields intermetal O/Cl exchange, which is a one-electron redox process mediated by O atom transfer. Also a zero-electron redox process mediated by atom transfer is observed when (TTP)TiCl{sub 2} is reacted with (OEP)Ti{double_bond}O.

Hays, J.A.

1993-11-05

146

Experimental and theoretical studies of charge transfer and deuterium ion transfer between D2O+ and C2H4.  

PubMed

The charge transfer and deuterium ion transfer reactions between D(2)O(+) and C(2)H(4) have been studied using the crossed beam technique at relative collision energies below one electron volt and by density functional theory (DFT) calculations. Both direct and rearrangement charge transfer processes are observed, forming C(2)H(4) (+) and C(2)H(3)D(+), respectively. Independent of collision energy, deuterium ion transfer accounts for approximately 20% of the reactive collisions. Between 22 and 36 % of charge transfer collisions occur with rearrangement. In both charge transfer processes, comparison of the internal energy distributions of products with the photoelectron spectrum of C(2)H(4) shows that Franck-Condon factors determine energy disposal in these channels. DFT calculations provide evidence for transient intermediates that undergo H/D migration with rearrangement, but with minimal modification of the product energy distributions determined by long range electron transfer. The cross section for charge transfer with rearrangement is approximately 10(3) larger than predicted from the Rice-Ramsperger-Kassel-Marcus isomerization rate in transient complexes, suggesting a nonstatistical mechanism for H/D exchange. DFT calculations suggest that reactive trajectories for deuterium ion transfer follow a pathway in which a deuterium atom from D(2)O(+) approaches the pi-cloud of ethylene along the perpendicular bisector of the C-C bond. The product kinetic energy distributions exhibit structure consistent with vibrational motion of the D-atom in the bridged C(2)H(4)D(+) product perpendicular to the C-C bond. The reaction quantitatively transforms the reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the deuterium ion is transferred in a configuration in which both the breaking and the forming bonds are extended. PMID:15303914

Liu, Li; Cai, Xiaohui; Li, Yue; Richards O'Grady, Elizabeth; Farrar, James M

2004-08-22

147

Electrostatic Deposition of Pesticide Sprays onto Ionizing Targets: Charge and Mass-Transfer Analysis  

Microsoft Academic Search

Electrostatic deposition of charged pesticide sprays onto biological targets may be undesirably limited under certain operational conditions by gaseous-discharge currents induced to flow between the incoming charged spray cloud and grounded points on the target (e.g. leaf tips). Spray deposition and charge transfer onto idealized target models as functions of target characteristics and intensity of spray-droplet charging are quantified experimentally

S. Edward Law

1982-01-01

148

Ligand dissociation mediated charge transfer observed at colloidal W18O49 nanoparticle interfaces.  

PubMed

Understanding charge transfer dynamics through the ligand shell of colloidal nanoparticles has been an important pursuit in solar energy conversion. While charge transport through ligand shells of nanoparticle films has been studied intensely in static dry and electrochemical systems, its influence on charge transfer kinetics in dispersed colloidal systems has received relatively less attention. This work reports the oxidation of amine passivated tungsten oxide nanoparticles by an organically soluble tris-(1,10-phenanthroline) iron(III) derivative. By following the rate of this oxidation optically via the production of the ferroin derivative under various reaction conditions and particle derivatizations, we are able to show that the fluxional ligand shells on dispersed, colloidal nanoparticles provide a separate and more facile pathway for charge transfer, in which the rate-limiting step for charge transfer is the ligand dissociation. Since such ligand shells are frequently required for nanoparticle stability, this observation has significant implications for colloidal nanoparticle photocatalysis. PMID:24564847

Grauer, David C; Alivisatos, A Paul

2014-03-11

149

Charge transfer during intracloud lightning from a time-dependent multidipole model  

NASA Astrophysics Data System (ADS)

A time-dependent, multidipole (TDMD) model has been developed to show the charge transfer during intracloud (IC) flashes with high time and space resolution. This model combines high-speed electric field measurements from a balloon-borne instrument (Esonde) and three-dimensional lightning maps from the New Mexico Tech Lightning Mapping Array (LMA). The result is a time-varying spatial distribution of charge along lightning channels, which reveals several details about charge transfer during IC flashes. For example, a flash in 2004 initially deposited negative charge in one region and later transferred part of it to another region at a lower altitude where the negative leader was more highly branched. A flash in 2007 shows charge distributions along a main channel and two short branches; each of the three channels had different charges per unit length of channel.

Lu, Gaopeng; Winn, W. P.; Sonnenfeld, R. G.

2011-02-01

150

Measurement of Electromagnetic Radiation Emitted during Rapid Intramolecular Electron Transfer  

E-print Network

, photosynthesis, artificial photosynthesis, redox chemistry, photography, xerog- raphy, and other processes all the electromagnetic (EM) waveform broadcast by the charge-transfer process itself. Intermolecular and intramo- lecular

151

One-center charge transfer transitions in manganites  

NASA Astrophysics Data System (ADS)

In the framework of a rather conventional cluster approach which combines the crystal field and the ligand field models we have considered different charge transfer (CT) states and O 2p-Mn 3d CT transitions in MnO9-6 octahedra. The many-electron dipole transition matrix elements were calculated using the Racah algebra for the cubic point group. Simple ``local'' approximation allowed us to calculate the relative intensity for all dipole-allowed ?-? and ?-? CT transitions. We present a self-consistent description of the CT bands in insulating stoichiometric LaMn3+O3 compound with the only Mn3+ valent state and idealized octahedral MnO9-6 centers which allows us to substantially correct the current interpretation of the optical spectra. Our analysis shows the multiband structure of the CT optical response with the weak low-energy edge at 1.7 eV, associated with forbidden t1g(?)-eg transition and a series of the weak and strong dipole-allowed high-energy transitions starting from 2.5 and 4.5 eV, respectively, and extending up to nearly 11 eV. The most intensive features are associated with two strong composite bands near 4.6-4.7 and 8-9 eV, respectively, resulting from the superposition of the dipole-allowed ?-? and ?-? CT transitions. These predictions are in good agreement with experimental spectra. The experimental data points to a strong overscreening of the crystal field parameter Dq in the CT states of MnO9-6 centers.

Moskvin, A. S.

2002-05-01

152

25th anniversary article: 25 years of fullerene research in electron transfer chemistry.  

PubMed

The past 25 years have served as a test bed for exploring the chemistry and physics, in general, and the electron transfer chemistry, in particular, of low-dimensional carbon. Nevertheless, the new realm started with the advent of fullerenes, followed in chronological order by carbon nanotubes, and, more recently, by graphene. The major thrust of this Review article is to historically recap the versatility of fullerenes regarding the design, the synthesis, and the tests as an electroactive building block in photosynthetic reaction mimics, photovoltaics, and catalysis. PMID:24532250

Kirner, Sabrina; Sekita, Michael; Guldi, Dirk M

2014-03-12

153

Discrepancy between hadron matter and quark-gluon matter in net charge transfer fluctuation  

E-print Network

A parton and hadron cascade model, PACIAE, is employed to investigate the net charge transfer fluctuation within $|\\eta|$=1 in Au+Au collisions at $\\sqrt{s_{NN}}$=200 GeV. It is turned out that the observable of net charge transfer fluctuation, $\\kappa$, in hadronic final state (HM) is nearly a factor of 3 to 5 larger than that in initial partonic state (QGM). However, only twenty percent of the net charge transfer fluctuation in the QGM can survive the hadronization

Dai-Mei Zhou; Xiao-Mei Li; Bao-Guo Dong; Ben-Hao Sa

2006-02-08

154

Direct observation of ion transfer in contact charging between a metal and a polymer  

NASA Astrophysics Data System (ADS)

Triboelectric charging between metals and insulators is usually thought to involve electron transfer. Doping some polymers with a small amount of salt can significantly change their charging properties, even reversing the sign to which they charge upon contact with a given metal. We show by means of secondary-ion mass spectrometry that ions of the salt are transferred across the interface in contacts between a doped polymer and a metal. Specifically, we observe a transfer of bromine ions when polystyrene doped with a small amount of the salt cetylpyridinium bromide is contacted to an indium surface.

Mizes, H. A.; Conwell, E. M.; Salamida, D. P.

1990-04-01

155

Electrospray Charging of Minerals: Surface Chemistry and Applications to High-Velocity Microparticle Impacts  

NASA Astrophysics Data System (ADS)

Electrospray is a soft ionization technique commonly used to charge large biomolecules; it has, however, also been applied to inorganic compounds. We are extending this technique to mineral microparticles. Electrospray-charged mineral microparticles are interesting in the context of surface science because surface chemistry dictates where and how charge carriers can bond to mineral surfaces. In addition, using electrospray to charge mineral particles allows these particles to be electrostatically accelerated as projectiles in high- and hyper-velocity impacts. Since current techniques for producing high- and hyper-velocity microparticle impacts are largely limited to metal or metal-coated projectiles, using minerals as projectiles is a significant innovation. Electrospray involves three steps: creation of charged droplets containing solute/particles, evaporation and bifurcation of droplets, and desolvation of the solute/particles. An acidified solution is slowly pumped through a needle in a strong DC field, which causes the solution to break into tiny, charged droplets laden with protons. Solvent evaporates from the electrosprayed droplets as they move through the electric field toward a grounded plate, causing the charge on the droplet to increase relative to its mass. When the electrosprayed droplet’s charge becomes such that the droplet is no longer stable, it bifurcates, and each of the resulting droplets carries some of the original droplet’s charge. Evaporation and bifurcation continues until the solute particle is completely desolvated. The result is a protonated solute molecule or particle. We built an instrument that electrosprays particles into vacuum and measures them using an image charge detector. Mineral microparticles were prepared by grinding natural mineral samples to ~2 µm diameter. These microparticles are then added to a 4:1 methanol:water solution to create a 0.005% w/v suspension. The suspension is electrosprayed into vacuum, where the charge detector measures the electrosprayed mineral particles’ speed and charge. Quartz microparticles have been successfully electrosprayed. Variation in quartz microparticles’ charge as a function of pH is being evaluated. In addition, we are studying how to completely desolvate electrosprayed mineral particles. Desolvation is not trivial and often requires more than the passive passage of the droplets from the needle to the grounded plate and into vacuum. We are testing two desolvation methods: a heated beam tube and a heated capillary. Preliminary data suggests we have achieved complete desolvation with a hot beam tube. Although quartz’s surface chemistry is rather unique, successful electrospray of quartz microparticles strongly suggests that other minerals may also be electrosprayed. We are preparing olivine samples for electrospray. In addition, an instrument that creates high-velocity microparticle impacts using electrospray-charged mineral microparticles is being developed. This instrument will not only permit minerals to be used as projectiles, but also allows direction characterization of chemical speciation occurring during microparticle impacts.

Daly, T.; Call, S.; Austin, D. E.

2010-12-01

156

Peierls transitions in ionic organic charge-transfer crystals with spin and charge degrees of freedom.  

PubMed

The quasi-one-dimensional electronic structure of organic charge-transfer (CT) salts rationalizes Peierls transitions in mixed or segregated stacks of pi-electron donors (D) and acceptors (A). A microscopic Peierls-Hubbard model, HCT, is presented for CT salts with mixed stacks (Drho+Arho-)n and ionicity rho > 0.7. Dimerization opens a Peierls gap that, due to electron correlation, is the singlet-triplet gap, EST. In contrast to spin-Peierls systems, such as Heisenberg spin chains with rho = 1 and TSP < 20 K, Peierls transitions in CT salts with rho < 1 occur at higher TP and involve both spin and charge degrees of freedom. Linear electron-phonon coupling and an adiabatic approximation for a harmonic lattice are used to model the dimerization amplitude deltaT for T < TP, the magnetic (spin) susceptibility chiT, and the relative infrared intensity of totally symmetric molecular modes. Exact thermodynamics of HCT for stacks up to N = 12 sites are applied to two CT salts with TP approximately 50 and 120 K whose magnetism and infrared have not been modeled previously and to CT salts with inaccessibly high TP > 350 K whose description has been difficult. Ionic CT salts are correlated Peierls systems with a degenerate ground state (GS) at T = 0 whose elementary excitations are spin solitons, while dimerized ion-radical stacks that support triplet-spin excitons have nondegenerate GS. In less ionic CT salts, modulation of HCT parameters on cooling or under pressure leads to Peierls and/or neutral-ionic transitions of the GS, without appreciable thermal population of excited states. Correlations change the gap equation that relates EST at T = 0 to TP compared to free electrons, and size convergence is fast in stacks with large delta0 and high TP. PMID:16986864

Bewick, S A; Soos, Z G

2006-09-28

157

Computational insights into the charge relaying properties of ?-turn peptides in protein charge transfers.  

PubMed

Density functional theory calculations suggest that ?-turn peptide segments can act as a novel dual-relay elements to facilitate long-range charge hopping transport in proteins, with the N terminus relaying electron hopping transfer and the C terminus relaying hole hopping migration. The electron- or hole-binding ability of such a ?-turn is subject to the conformations of oligopeptides and lengths of its linking strands. On the one hand, strand extension at the C-terminal end of a ?-turn considerably enhances the electron-binding of the ?-turn N terminus, due to its unique electropositivity in the macro-dipole, but does not enhance hole-forming of the ?-turn C terminus because of competition from other sites within the ?-strand. On the other hand, strand extension at the N terminal end of the ?-turn greatly enhances hole-binding of the ?-turn C terminus, due to its distinct electronegativity in the macro-dipole, but does not considerably enhance electron-binding ability of the N terminus because of the shared responsibility of other sites in the ?-strand. Thus, in the ?-hairpin structures, electron- or hole-binding abilities of both termini of the ?-turn motif degenerate compared with those of the two hook structures, due to the decreased macro-dipole polarity caused by the extending the two terminal strands. In general, the high polarity of a macro-dipole always plays a principal role in determining charge-relay properties through modifying the components and energies of the highest occupied and lowest unoccupied molecular orbitals of the ?-turn motif, whereas local dipoles with low polarity only play a cooperative assisting role. Further exploration is needed to identify other factors that influence relay properties in these protein motifs. PMID:25430869

Zhang, Ru; Liu, Jinxiang; Yang, Hongfang; Wang, Shoushan; Zhang, Meng; Bu, Yuxiang

2015-02-01

158

Unstable, metastable, or stable halogen bonding interaction involving negatively charged donors? A statistical and computational chemistry study.  

PubMed

The noncovalent halogen bonding could be attributed to the attraction between the positively charged ?-hole and a nucleophile. Quantum mechanics (QM) calculation indicated that the negatively charged organohalogens have no positively charged ?-hole on their molecular surface, leading to a postulation of repulsion between negatively charged organohalogens and nucleophiles in vacuum. However, PDB survey revealed that 24% of the ligands with halogen bonding geometry could be negatively charged. Moreover, 36% of ionizable drugs in CMC (Comprehensive Medicinal Chemistry) are possibly negatively charged at pH 7.0. QM energy scan showed that the negatively charged halogen bonding is probably metastable in vacuum. However, the QM calculated bonding energy turned negative in various solvents, suggesting that halogen bonding with negatively charged donors should be stable in reality. Indeed, QM/MM calculation on three crystal structures with negatively charged ligands revealed that the negatively charged halogen bonding was stable. Hence, we concluded that halogen bonding with negatively charged donors is unstable or metastable in vacuum but stable in protein environment, and possesses similar geometric and energetic characteristics as conventional halogen bonding. Therefore, negatively charged organohalogens are still effective halogen bonding donors for medicinal chemistry and other applications. PMID:25390886

Yang, Zhuo; Xu, Zhijian; Liu, Yingtao; Wang, Jinan; Shi, Jiye; Chen, Kaixian; Zhu, Weiliang

2014-12-11

159

Electron transfer dynamics and excited state branching in a charge-transfer platinum(II) donor-bridge-acceptor assembly.  

PubMed

A linear asymmetric Pt(ii) trans-acetylide donor-bridge-acceptor triad designed for efficient charge separation, NAP[triple bond, length as m-dash]Pt(PBu3)2[triple bond, length as m-dash]Ph-CH2-PTZ (), containing strong electron acceptor and donor groups, 4-ethynyl-N-octyl-1,8-naphthalimide (NAP) and phenothiazine (PTZ) respectively, has been synthesised and its photoinduced charge transfer processes characterised in detail. Excitation with 400 nm, ?50 fs laser pulse initially populates a charge transfer manifold stemming from electron transfer from the Pt-acetylide centre to the NAP acceptor and triggers a cascade of charge and energy transfer events. A combination of ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopies, supported by UV-Vis/IR spectroelectrochemistry, emission spectroscopy and DFT calculations reveals a self-consistent photophysical picture of the excited state evolution from femto- to milliseconds. The characteristic features of the NAP-anion and PTZ-cation are clearly observed in both the TRIR and TA spectra, confirming the occurrence of electron transfer and allowing the rate constants of individual ET-steps to be obtained. Intriguingly, has three separate ultrafast electron transfer pathways from a non-thermalised charge transfer manifold directly observed by TRIR on timescales ranging from 0.2 to 14 ps: charge recombination to form either the intraligand triplet (3)NAP with 57% yield, or the ground state, and forward electron transfer to form the full charge-separated state (3)CSS ((3)[PTZ(+)-NAP(-)]) with 10% yield as determined by target analysis. The (3)CSS decays by charge-recombination to the ground state with ?1 ns lifetime. The lowest excited state is (3)NAP, which possesses a long lifetime of 190 ?s and efficiently sensitises singlet oxygen. Overall, molecular donor-bridge-acceptor triad demonstrates excited state branching over 3 different pathways, including formation of a long-distant (18 Å) full charge-separated excited state from a directly observed vibrationally hot precursor state. PMID:25361227

Scattergood, Paul A; Delor, Milan; Sazanovich, Igor V; Bouganov, Oleg V; Tikhomirov, Sergei A; Stasheuski, Alexander S; Parker, Anthony W; Greetham, Gregory M; Towrie, Michael; Davies, E Stephen; Meijer, Anthony J H M; Weinstein, Julia A

2014-12-21

160

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

E-print Network

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 isotopes of Sulfur, colliding with H$^{+}$ and D$^{+}$ ions and comparison is made to a number of other collision systems.

G Shen; P C Stancil; J G Wang; J F McCann; B M McLaughlin

2015-02-25

161

Charge transfer kinetics at the solid–solid interface in porous electrodes  

E-print Network

Interfacial charge transfer is widely assumed to obey the Butler–Volmer kinetics. For certain liquid–solid interfaces, the Marcus–Hush–Chidsey theory is more accurate and predictive, but it has not been applied to porous ...

Bai, Peng

162

Charge transfer across transition-metal oxide interfaces: Emergent conductance and electronic structure  

NASA Astrophysics Data System (ADS)

We perform density functional theory plus dynamical mean-field theory calculations to investigate internal charge transfer in a superlattice composed of alternating layers of vanadate and manganite perovskite and Ruddlesden-Popper structure materials. We show that the electronegativity difference between vanadium and manganese causes moderate charge transfer from VO2 to MnO2 layers in both perovskite and Ruddlesden-Popper-based superlattices, leading to hole doping of the VO2 layer and electron doping of the MnO2 layer. Comparison of the perovskite and Ruddlesden-Popper-based heterostructures shows that apical oxygen motion in the perovskite superlattice enhances charge transfer. Our first principles simulations demonstrate that the combination of internal charge transfer and quantum confinement provided by heterostructuring is a powerful approach to engineering electronic structure and tailoring correlation effects in transition metal oxides.

Chen, Hanghui; Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.

2014-12-01

163

Charge Transfer through Single-Stranded Peptide Nucleic Acid Composed of Thymine Nucleotides  

E-print Network

Charge Transfer through Single-Stranded Peptide Nucleic Acid Composed of Thymine Nucleotides Amit; In Final Form: February 18, 2008 Self-assembled monolayers (SAMs) of single-stranded peptide nucleic acids. Peptide nucleic acid (PNA) is an analo

Borguet, Eric

164

Formation of H/sup -/ by charge transfer in alkaline-earth vapors  

SciTech Connect

Progress since the last symposium on the study of H/sup -/ formation by charge transfer in alkaline-earth vapors is reported. High yields are obtained at low energies, in agreement with theoretical predictions.

Schlachter, A.S.; Morgan, T.J.

1983-12-05

165

The role of charge-transfer states in energy transfer and dissipation within natural and artificial bacteriochlorophyll proteins  

NASA Astrophysics Data System (ADS)

Understanding how specific protein environments affect the mechanisms of non-radiative energy dissipation within densely assembled chlorophylls in photosynthetic protein complexes is of great interest to the construction of bioinspired solar energy conversion devices. Mixing of charge-transfer and excitonic states in excitonically interacting chlorophylls was implicated in shortening excited states' lifetimes, but its relevance to active control of energy dissipation in natural systems is under considerable debate. Here we show that the degree of fluorescence quenching in two similar pairs of excitonically interacting bacteriochlorophyll derivatives is directly associated with increasing charge-transfer character in the excited state, and that the protein environment may control non-radiative dissipation by affecting the mixing of charge-transfer and excitonic states. The capability of local protein environments to determine the fate of excited states, and thereby to confer different functionalities to excitonically coupled dimers substantiates the dimer as the basic functional element of photosynthetic enzymes.

Wahadoszamen, Md.; Margalit, Iris; Ara, Anjue Mane; van Grondelle, Rienk; Noy, Dror

2014-10-01

166

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

NASA Astrophysics Data System (ADS)

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.

Wang, Xin; Liang, Shi-Dong

2013-02-01

167

Intrinsic charge trapping in organic and polymeric semiconductors: a physical chemistry perspective  

SciTech Connect

We aim to understand the origins of intrinsic charge carrier traps in organic and polymeric semiconductor materials from a physical chemistry perspective. In crystalline organic semiconductors, we point out some of the inadequacies in the description of intrinsic charge traps using language and concepts developed for inorganic semiconductors. In ?-conjugated polymeric semiconductors, we suggest the presence of a two-tier electronic energy landscape, a bimodal majority landscape due to two dominant structural motifs and a minority electronic energy landscape from intrinsic charged defects. The bimodal majority electronic energy landscape results from a combination of amorphous domains and microcrystalline or liquid-crystalline domains. The minority tier of the electronic density of states is comprised of deep Coulomb traps embedded in the majority electronic energy landscape. This minority electronic energy landscape may dominate transport properties at low charge carrier densities, such as those expected for organic photovoltaic devices, while the bimodal majority electronic energy landscape becomes significant at high carrier densities, that is, in organic field effect transistors.

Zhu, Xiaoyang; Barbara, Paul F.; Kaake, Loren

2010-01-01

168

The design and operation of practical charge-transfer transversal filters  

Microsoft Academic Search

Some of the design considerations for charge-transfer split-electrode transversal filters are discussed. Clock frequency, filter length, and chip area are important design parameters. The relationship of these parameters to filter performance and accuracy is described. Both random and tap weight quantization errors are considered, and the optimum filter length is related to tap weight error. A parallel charge-transfer channel, which

RICHARD D. BAERTSCH; WILLIAM E. ENGELER; HOWARD S. GOLDBERG; CHARLES M. PUCKETTE; JEROME J. TIEMANN

1976-01-01

169

Charge Transfer Interaction and Hydrogen Bonding between Vitamine K1 and Dihydrovitamine K1  

NASA Astrophysics Data System (ADS)

We studied visible and infrared spectra, in particular their temperature dependence, of Vitamine K1 oil dissolving dihydrovitamine K1. Vitamine K1 and dihydrovitamine K1 were found to form charge transfer complexes and hydrogen bonds in the mixture. A co-crystal of Dihydrovitamine K1 and Vitamine K1 with charge transfer interaction and hydrogen bonding was shown to grow in a narrow temperature range near -20°C.

Nagahira, Yukio; Matsuki, Kazunori; Fukutome, Hideo

1981-01-01

170

Electronic reorganization triggered by electron transfer: The intervalence charge transfer of a Fe(3+) /Fe(2+) bimetallic complex.  

PubMed

The key role of the molecular orbitals in describing electron transfer processes is put in evidence for the intervalence charge transfer (IVCT) of a synthetic nonheme binuclear mixed-valence Fe(3+) /Fe(2+) compound. The electronic reorganization induced by the IVCT can be quantified by controlling the adaptation of the molecular orbitals to the charge transfer process. We evaluate the transition energy and its polarization effects on the molecular orbitals by means of ab initio calculations. The resulting energetic profile of the IVCT shows strong similarities to the Marcus' model, suggesting a response behaviour of the ensemble of electrons analogue to that of the solvent. We quantify the extent of the electronic reorganization induced by the IVCT process to be 11.74 eV, a very large effect that induces the crossing of states reducing the total energy of the transfer to 0.89 eV. © 2015 Wiley Periodicals, Inc. PMID:25739890

Domingo, Alex; Angeli, Celestino; de Graaf, Coen; Robert, Vincent

2015-04-30

171

Charge transfer emission in coumarin 343 sensitized TiO{sub 2} nanoparticle: A direct measurement of back electron transfer  

SciTech Connect

Electron injection and back electron transfer dynamics in coumarin 343 (C-343) adsorbed on TiO{sub 2} nanoparticles are studied by picosecond transient absorption and time-resolved fluorescence spectroscopy. The direct detection of electrons in the nanoparticles and the parent cation are monitored using picosecond transient absorption spectroscopy, and the corresponding dynamics of the adsorbate are monitored by time-resolved absorption spectra of the cation radical of C-343 in the visible region. When the electron returns from the nanoparticles to the present cation, a low quantum yield red-shifted charge transfer emission is observed. Measuring the charge transfer emission lifetimes by a picosecond time-resolved fluorimeter, the author gets an exact rate of back electron transfer reaction from the nanoparticle to the parent cation.

Ghosh, H.N.

1999-11-25

172

Charge Transfer Efficiency modeling/measurements as function of CCD pixel rate  

SciTech Connect

We have developed a charge transport model for predicting the effects on Charge Transfer Efficiency (CTE) of Charge Coupled Devices (CCDs) as functions of number of transfers, pixel charge flow rate, and magnitude in the CCD`s vertical and horizontal charge transport mediums. The model uses carrier lifetime an mobility criteria to establish pixel speed arguments and limitations for various CCD architectures. The model is compared with experimental measurements obtained using strobed single pixel illumination and a variant of the deferred charge tail technique while independently varying the CCD pixel rates for both the vertical and horizontal readout phases. The generic model is discussed and applied to specific real CCDs. Agreement between predicted performance and actual measured performance is presented.

Yates, G.J.; Gallegos, R.; Pena, C. [Los Alamos National Lab., NM (United States); Zagarino, P. [Sharpenit, Ellwood, CA (United States)

1995-09-01

173

Electronic and Nuclear Factors in Charge and Excitation Transfer  

SciTech Connect

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

Piotr Piotrowiak

2004-09-28

174

Negatively charged self-assembling DNA\\/poloxamine nanospheres for in vivo gene transfer  

Microsoft Academic Search

Over the past decade, numerous nonviral cationic vectors have been synthesized. They share a high density of positive charges and efficiency for gene transfer in vitro. However, their positively charged surface causes instability in body fluids and cytotoxi- city, thereby limiting their efficacy in vivo. Therefore, there is a need for developing alternative molecular structures. We have examined tetrabranched amphi-

Bruno Pitard; Mahajoub Bello-Roufai; Olivier Lambert; Peggy Richard; Lea Desigaux; Sarah Fernandes; Caroline Lanctin; Helene Pollard; Mehdi Zeghal; Pierre-Yves Rescan; Denis Escande

2004-01-01

175

Energy transfer through a multi-layer liner for shaped charges  

Microsoft Academic Search

This invention relates to the determination of parameters for selecting materials for use as liners in shaped charges to transfer the greatest amount of energy to the explosive jet. Multi-layer liners constructed of metal in shaped charges for oil well perforators or other applications are selected in accordance with the invention to maximize the penetrating effect of the explosive jet

Saul Skolnick; Albert Goodman

1985-01-01

176

Charge transfer from delocalized excited states in a bulk heterojunction material  

NASA Astrophysics Data System (ADS)

Charge generation in an organic photovoltaic blend was investigated using transient absorption spectroscopy. In films of pure electron donating material, subpicosecond spectral oscillations were observed and assigned to torsional modes associated with excited state relaxation and localization. These modes are systematically suppressed in the presence of fullerene, indicating that a significant fraction of charge transfer occurs prior to excited state localization.

Kaake, Loren G.; Moses, Daniel; Heeger, Alan J.

2015-02-01

177

Temperature dependence conductivity in organic charge transfer complexes: A theoretical view  

NASA Astrophysics Data System (ADS)

We propose a theoretical view of temperature dependent conductivity in organic charge transfer complexes and radical ion salts with symmetric and asymmetric donor molecules over a wide range of temperature. This phenomenon can be understand on the basis on the current carriers, 3-D effects, scattering by defects and impurities, formation of charge density waves (CDW) and soliton propagation etc.

Singh, Yadunath

2013-06-01

178

Ultrafast charge transfer in operating bulk heterojunction solar cells.  

PubMed

The ultrafast charge generation process in organic solar cell devices is investigated by transient reflection spectroscopy on five state-of-the-art bulk heterojunction systems. The charge generation process in operating devices is found to be a combination of an ultrafast generation mechanism over several hundred femto-seconds and a slow process from pico-seconds to nanoseconds, limited by exciton diffusion dynamics. In addition, the lack of electric field dependence in the charge dynamics rules out geminate recombination as an important loss mechanism. PMID:25677734

Zhong, Chengmei; Choi, Hyosung; Kim, Jin Young; Woo, Han Young; Nguyen, Thanh Luan; Huang, Fei; Cao, Yong; Heeger, Alan J

2015-03-01

179

Photovoltage Bleaching in Bulk Heterojunction Solar Cells through Occupation of the Charge Transfer State  

E-print Network

We observe a strong peak in the capacitive photocurrent of a MDMO-PPV / PCBM bulk heterojunction solar cell for excitation below the absorbance threshold energy. Illumination at the peak energy blocks charge capture at other wavelengths, and causes the photovoltage to drop dramatically. These results suggest that the new peak is due to a charge transfer state, which provides a pathway for charge separation and photocurrent generation in the solar cell.

Shah, Hemant; Bansal, Tanesh; Alphenaar, Bruce

2010-01-01

180

Chemistry  

NSDL National Science Digital Library

Finds ChemEd DL resources related to the sections of the General Chemistry textbook, Chemistry, by Kenneth W. Whitten, Raymond E. Davis, M. Larry Peck, George G. Stanley published by Brooks/Cole, 2010.

181

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory  

PubMed Central

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

2011-01-01

182

A parametric study of shock jump chemistry, electron temperature, and radiative heat transfer models in hypersonic flows  

E-print Network

A PARAMETRIC STUDY OF SHOCK JUMP CHEMISTRY, ELECTRON TEMPERATURE, AND RADIATIVE HEAT TRANSFER MODELS IN HYPERSONIC FLOWS A Thesis by ROBERT BRIAN GREENDYKE Submitted to the Graduate College of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE August 1988 Major Subject: Aerospace Engineering A PARAMETRIC STUDY OF SHOCK JUMP CHEMISTRY, ELECTRON TEMPERATURE, AND RADIATIVE HEAT TRANSFER MODELS IN HYPERSONIC FLOWS A Thesis by ROBERT BRIAN...

Greendyke, Robert Brian

1988-01-01

183

Single and double charge transfer of He(2+) ions with molecules at near-thermal energies  

NASA Technical Reports Server (NTRS)

Rate coefficients were measured for charge-transfer reactions of He(2+) ions with H2, N2, O2, CO, CO2, and H2O. The experiments were carried out using a selected-ion drift-tube mass spectrometer. Total rate coefficients are found to be very large and are generally close to the limiting Langevin capture rate coefficients or the corresponding ADO-model (Su and Bowers, 1973) coefficients. The product-ion spectra indicate that both single and double charge transfer and possibly transfer ionization occur in these reactions.

Tosh, R. E.; Johnsen, R.

1993-01-01

184

Time delay and integration detectors using charge transfer devices  

NASA Technical Reports Server (NTRS)

An imaging system comprises a multi-channel matrix array of CCD devices wherein a number of sensor cells (pixels) in each channel are subdivided and operated in discrete intercoupled groups of subarrays with a readout CCD shift register terminating each end of the channels. Clock voltages, applied to the subarrays, selectively cause charge signal flow in each subarray in either direction independent of the other subarrays. By selective application of four phase clock voltages, either one, two or all three of the sections subarray sections cause charge signal flow in one direction, while the remainder cause charge signal flow in the opposite direction. This creates a form of selective electronic exposure control which provides an effective variable time delay and integration of three, six or nine sensor cells or integration stages. The device is constructed on a semiconductor sustrate with a buried channel and is adapted for front surface imaging through transparent doped tin oxide gates.

Mccann, D. H.; White, M. H.; Turly, A. P.

1981-01-01

185

The effects of charge transfer on the aqueous solvation of ions  

SciTech Connect

Ab initio-based charge partitioning of ionic systems results in ions with non-integer charges. This charge-transfer (CT) effect alters both short- and long-range interactions. Until recently, the effects of CT have been mostly neglected in molecular dynamics (MD) simulations. The method presented in this paper for including charge transfer between ions and water is consistent with ab initio charge partitioning and does not add significant time to the simulation. The ions of sodium, potassium, and chloride are parameterized to reproduce dimer properties and aqueous structures. The average charges of the ions from MD simulations (0.900, 0.919, and -0.775 for Na{sup +}, K{sup +}, and Cl{sup -}, respectively) are consistent with quantum calculations. The hydration free energies calculated for these ions are in agreement with experimental estimates, which shows that the interactions are described accurately. The ions also have diffusion constants in good agreement with experiment. Inclusion of CT results in interesting properties for the waters in the first solvation shell of the ions. For all ions studied, the first shell waters acquire a partial negative charge, due to the difference between water-water and water-ion charge-transfer amounts. CT also reduces asymmetry in the solvation shell of the chloride anion, which could have important consequences for the behavior of chloride near the air-water interface.

Soniat, Marielle; Rick, Steven W. [Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 (United States)

2012-07-28

186

The effects of charge transfer on the aqueous solvation of ions  

NASA Astrophysics Data System (ADS)

Ab initio-based charge partitioning of ionic systems results in ions with non-integer charges. This charge-transfer (CT) effect alters both short- and long-range interactions. Until recently, the effects of CT have been mostly neglected in molecular dynamics (MD) simulations. The method presented in this paper for including charge transfer between ions and water is consistent with ab initio charge partitioning and does not add significant time to the simulation. The ions of sodium, potassium, and chloride are parameterized to reproduce dimer properties and aqueous structures. The average charges of the ions from MD simulations (0.900, 0.919, and -0.775 for Na+, K+, and Cl-, respectively) are consistent with quantum calculations. The hydration free energies calculated for these ions are in agreement with experimental estimates, which shows that the interactions are described accurately. The ions also have diffusion constants in good agreement with experiment. Inclusion of CT results in interesting properties for the waters in the first solvation shell of the ions. For all ions studied, the first shell waters acquire a partial negative charge, due to the difference between water-water and water-ion charge-transfer amounts. CT also reduces asymmetry in the solvation shell of the chloride anion, which could have important consequences for the behavior of chloride near the air-water interface.

Soniat, Marielle; Rick, Steven W.

2012-07-01

187

Effects of Surface Modification and Moisture on the Rates of Charge Transfer between Metals and Organic Materials  

E-print Network

Effects of Surface Modification and Moisture on the Rates of Charge Transfer between Metals of contact charging resulting from the rolling of millimeter-sized metallic spheres on flat surfaces The transfer of charge that occurs when two surfaces are brought into contact (with or without friction

Prentiss, Mara

188

Energy and charge transfer in organic light-emitting diodes: A soluble quinacridone study  

NASA Astrophysics Data System (ADS)

A soluble derivative of quinacridone, N,N'-di-isoamyl quinacridone (DIQA), has been synthesized and used to study the mechanisms of Förster energy transfer and charge transfer in organic light-emitting diodes (OLEDs) based on 8-hydroxyquinoline (Alq3). Quantum efficiencies and spectra were measured for both photoluminescence (PL) and electroluminescence (EL) for films of poly(9-vinylcarbazole) (PVK) doped with Alq3 and DIQA. Both PL and EL showed an efficiency enhancement in films of PVK:Alq3:DIQA compared to films of PVK:Alq3. However, the optimal DIQA doping concentration was found to be lower for EL than for PL. Examination of the spectra revealed that more emission originated from DIQA for EL than for PL at a given doping level. We conclude that Förster energy transfer from Alq3 to DIQA occurs in both cases of PL and EL, but that charge transfer to DIQA occurs in the operation of the OLED resulting in additional pathways to DIQA emission. Ultraviolet photoelectron spectroscopy measurements showed that electron transfer from Alq3 to DIQA, hole transfer from PVK to DIQA, and hole transfer from Alq3 to DIQA are all energetically favorable processes. These results suggest that charge transfer is an important mechanism in the efficiency enhancement seen in OLEDs based on a host-dopant scheme, and that both the electronic properties and the optical properties of the dopant material are important parameters for device optimization.

Shaheen, S. E.; Kippelen, B.; Peyghambarian, N.; Wang, J.-F.; Anderson, J. D.; Mash, E. A.; Lee, P. A.; Armstrong, N. R.; Kawabe, Y.

1999-06-01

189

Ultrafast charge- and energy-transfer dynamics in conjugated polymer: cadmium selenide nanocrystal blends.  

PubMed

Hybrid nanocrystal-polymer systems are promising candidates for photovoltaic applications, but the processes controlling charge generation are poorly understood. Here, we disentangle the energy- and charge-transfer processes occurring in a model system based on blends of cadmium selenide nanocrystals (CdSe-NC) with poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) using a combination of time-resolved absorption and luminescence measurements. The use of different capping ligands (n-butylamine, oleic acid) as well as thermal annealing allows tuning of the polymer-nanocrystal interaction. We demonstrate that energy transfer from MDMO-PPV to CdSe-NCs is the dominant exciton quenching mechanism in nonannealed blends and occurs on ultrafast time scales (<1 ps). Upon thermal annealing electron transfer becomes competitive with energy transfer, with a transfer rate of 800 fs independent of the choice of the ligand. Interestingly, we find hole transfer to be much less efficient than electron transfer and to extend over several nanoseconds. Our results emphasize the importance of tuning the organic-nanocrystal interaction to achieve efficient charge separation and highlight the unfavorable hole-transfer dynamics in these blends. PMID:24490650

Morgenstern, Frederik S F; Rao, Akshay; Böhm, Marcus L; Kist, René J P; Vaynzof, Yana; Greenham, Neil C

2014-02-25

190

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

NASA Astrophysics Data System (ADS)

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 ?m 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 ?s is achieved and 31% of image lag was reduced by using the proposed process techniques.

Zhongxiang, Cao; Quanliang, Li; Ye, Han; Qi, Qin; Peng, Feng; Liyuan, Liu; Nanjian, Wu

2014-11-01

191

Spectrophotometric study of the charge transfer complex between 2-amino-4-picoline with chloranilic acid  

NASA Astrophysics Data System (ADS)

Charge transfer complex formation between 2-amino-4-picoline (2A4P) as the electron donor with chloranilic acid (CLA) as the electron acceptor has been studied spectrophotometrically in different polar solvents included acetone (AcN), ethanol (EtOH) and acetonitrile (AN). The molecular composition of the formed complex was recognized utilizing Job's, photometric and conductometric titration methods to be 1:1. The formation constants and molecular extinction coefficients were estimated using Benesi-Hildebrand equation; they recorded high values confirming high stability of the formed complex. Moreover, the results showed that the complex is more stable in acetone with lower electric permittivity compared with ethanol or acetonitrile of higher ones. The values of some spectroscopic physical parameters like oscillator strength f, transition dipole moment ?, resonance energy RN, charge transfer energy ECT, dissociation energy W, ionization potential IP and standard free energy ?Go were determined and evaluated. The solid complex was isolated and its molecular composition was determined by elemental analysis to be 1:1. Furthermore, the solid complex was characterized using FTIR and 1H NMR measurements. They confirmed the presence of proton transfer beside charge transfer in the obtained complex. Molecular orbital calculations utilizing GAMESS computations were carried out to predict infrared spectra. They also confirmed the presence of proton transfer beside charge transfer in the formed complex.

Alghanmi, Reem M.; Al-Attas, Amirah S.; Habeeb, Moustafa M.

2013-02-01

192

Photophysics of charge transfer in a polyfluorene/violanthrone blend  

NASA Astrophysics Data System (ADS)

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 .

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

2005-01-01

193

Photophysics of charge transfer in a polyfluorene\\/violanthrone blend  

Microsoft Academic Search

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

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

2005-01-01

194

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

NASA Astrophysics Data System (ADS)

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 powdered materials can lead to electrostatic discharge and so is of interest from a safety viewpoint. The charging of powders can also adversely affect their mechanical handling characteristics and so is of interest to handling equipment engineers. The paper presents the design of the sensors, the design of the electric charge test rig and electric charge measurement test results.

Woodhead, S. R.; Denham, J. C.; Armour-Chelu, D. I.

2005-01-01

195

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

PubMed Central

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

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

2002-01-01

196

Charge Transfer Properties Through Graphene Layers in Gas Detectors  

E-print Network

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.

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

2015-03-23

197

Charge Transfer Properties Through Graphene Layers in Gas Detectors  

E-print Network

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.

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

198

Horizontal versus vertical charge and energy transfer in hybrid assemblies of semiconductor nanoparticles  

PubMed Central

Summary We studied the photoluminescence and time-resolved photoluminescence from self-assembled bilayers of donor and acceptor nanoparticles (NPs) adsorbed on a quartz substrate through organic linkers. Charge and energy transfer processes within the assemblies were investigated as a function of the length of the dithiolated linker (DT) between the donors and acceptors. We found an unusual linker-length-dependency in the emission of the donors. This dependency may be explained by charge and energy transfer processes in the vertical direction (from the donors to the acceptors) that depend strongly on charge transfer processes occurring in the horizontal plane (within the monolayer of the acceptor), namely, parallel to the substrate. PMID:23019559

Gotesman, Gilad; Guliamov, Rahamim

2012-01-01

199

Fermi level pinning and the charge transfer contribution to the energy of adsorption at semiconducting surfaces  

SciTech Connect

It is shown that charge transfer, the process analogous to formation of semiconductor p-n junction, contributes significantly to adsorption energy at semiconductor surfaces. For the processes without the charge transfer, such as molecular adsorption of closed shell systems, the adsorption energy is determined by the bonding only. In the case involving charge transfer, such as open shell systems like metal atoms or the dissociating molecules, the energy attains different value for the Fermi level differently pinned. The Density Functional Theory (DFT) simulation of species adsorption at different surfaces, such as SiC(0001) or GaN(0001) confirms these predictions: the molecular adsorption is independent on the coverage, while the dissociative process adsorption energy varies by several electronvolts.

Krukowski, Stanis?aw, E-mail: stach@unipress.waw.pl [Institute of High Pressure Physics, Polish Academy of Sciences, Soko?owska 29/37, 01-142 Warsaw (Poland); Interdisciplinary Centre for Modelling, University of Warsaw, Pawi?skiego 5a, 02-106 Warsaw (Poland); Kempisty, Pawe?; Strak, Pawe?; Sakowski, Konrad [Institute of High Pressure Physics, Polish Academy of Sciences, Soko?owska 29/37, 01-142 Warsaw (Poland)

2014-01-28

200

Laboratory Studies of Thermal Energy Charge Transfer of Silicon and Iron Ions in Astrophysical Plasmas  

NASA Technical Reports Server (NTRS)

The laser ablation/ion storage facility at the UNLV Physics Department is dedicated to the study of atomic processes in low temperature plasmas. Our current program is directed to the study of charge transfer of multiply charged ions and neutrals that are of importance to astrophysics at energies less than 1 eV (about 10(exp 4) K). Specifically, we measure the charge transfer rate coefficient of ions such as N(2+), Si(3+), Si(3+), with helium and Fe(2+) with molecular and atomic hydrogen. All these ions are found in a variety of astrophysical plasmas. Their electron transfer reactions with neutral atoms can affect the ionization equilibrium of the plasma.

Kwong, Victor H. S.

1997-01-01

201

A Novel Approach to Simulate a Charge Transfer in DNA Repair by an Anacystis nidulans Photolyase  

PubMed Central

An Anacystis nidulans photolyase enzyme containing two chromophore cofactors was simulated for a photoreaction DNA repairing process via molecular dynamics (MD) method. A novel approach has been introduced for the electron transfer between the FAD (flavin adenine dinucleotide; flavin) molecule and CPD (cyclobutane pyrimidine dimer). This approach involves four simulation stages with different charges for the FAD and CPD fragments and a role of a charged state of the active cofactor was qualified during the MD modeling. Observations show that flavin has actively participated in a charge transfer process, thereby involving the conformational changes of the DNA and CPD substrate fragment. The DNA conformation behavior has shown to correlate with the electron transfer from flavin to CPD. This is manifested on the similarities of the DNA repairing process by excision repair of the UV photoproducts. PMID:24772194

Dushanov, E.B.; Kholmurodov, Kh.T.

2014-01-01

202

Cross sections of charge transfer between a Gd atom and its singly charged positive ion in metastable states close to the ground state  

Microsoft Academic Search

The charge-transfer cross sections between a gadolinium atom and its singly charged positive ion in metastable states have been measured with a crossed-beam apparatus. The primary ions are produced by photo- ionization with a tunable dye laser. The populations of primary ions in excited states have been measured by the laser-induced fluorescence method. By measuring the populations, the charge-transfer cross

M. Hashida; S. Sakabe; Y. Izawa

1996-01-01

203

Importance of charge transfer and polarization effects for the modeling of uranyl-cation complexes  

SciTech Connect

The structures, energies, and charges of uranyl cation complexes with water molecules, nitrate ion, and carbonate ions were determined using Hartree-Fock, second-order Moeller-Plesset (MP2) perturbation theory, and density functional theory (DFT) ab initio quantum chemical methods. Reasonable agreement with experimentally determined structures was found. Significant polarization of the ligands as well as charge transfer to the uranyl ion was observed in the complexes. The dissociation energy curves for the complexes were also determined at the MP2 level of theory. Attempts to reproduce these curves with molecular mechanical models with fixed atomic point charges failed, showing that an appropriate force field for these systems must include polarization and charge-transfer effects.

Hemmingsen, L.; Amara, P.; Ansoborlo, E.; Field, M.J.

2000-05-04

204

Note: Charge transfer in a hydrated peptide group is determined mainly by its intrinsic hydrogen-bond energetics  

SciTech Connect

Charge transfer in a hydrogen-bonded N-methylacetamide(H{sub 2}O){sub 3} system is obtained from ?B97X-D/6-31++G** and CHelpG atomic charge calculations of individual peptide-water interactions as well as that of the entire complex. In the latter, the electron transfer to water is 0.19 e, influenced primarily by the hydrogen bonds to the C=O group. The values of such charge transfer are paralleled by the corresponding intrinsic hydrogen-bond energies. These results support the desirability of incorporating charge transfer in molecular mechanics energy functions.

Mirkin, Noemi G.; Krimm, Samuel [LSA Biophysics, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109-1055 (United States)] [LSA Biophysics, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109-1055 (United States)

2014-01-28

205

Modeling of charge transfer processes to understand photophysical signatures: The case of Rhodamine 110  

NASA Astrophysics Data System (ADS)

Photophysical signatures, namely absorption and emission energies, lifetime and quantum yields, have been computed through TD-DFT approaches and compared with experimental counterparts for the Rhodamine 110 dye in aqueous solution. Thanks to a new protocol of analysis, based on the use of very promising electronic based indices, it has been possible to investigate the interplay between Rhodamine 110 dye's structure, degree of charge transfer upon excitation, and fluorescence signatures. This combined analysis is very promising to support the understanding of charge transfer based mechanisms affecting dyes photophysics.

Savarese, Marika; Raucci, Umberto; Netti, Paolo A.; Adamo, Carlo; Ciofini, Ilaria; Rega, Nadia

2014-08-01

206

Ion-atom charge-transfer reactions and a hot intercloud medium. [in interstellar space  

NASA Technical Reports Server (NTRS)

An investigation is conducted concerning the ionization equilibrium of carbon in a hot intercloud medium (ICM), taking into account various charge-transfer reactions. Attention is given to problems related to observations of carbon along the lines of sight to several unreddened stars. It is pointed out that the observed underabundance of C III and overabundance of C I can be consistent with the presence of a hot, partially ionized ICM, provided that two of the charge-transfer reactions considered are rapid at thermal energies.

Steigman, G.

1975-01-01

207

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

SciTech Connect

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

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

2012-05-14

208

Charge transfer effects in molecule-negative ion complexes induced by core ionization  

NASA Astrophysics Data System (ADS)

A variety of charge transfer effects can take place as a result of core ionization of anion-molecule complexes. As specific examples we study the core ionization of Na-H2O and Cl-H2O clusters using an ab initio Green's function method. The site-localized character of the electron distribution in the ground state of these weakly bound clusters favors a transfer of an electron from the negative atomic ion to the H2O molecular unit upon ionization of the O1s core level. The charge transferred screens the created core hole giving rise to the appearance of low-lying satellites which are completely absent in the spectrum of the isolated H2O molecule. Energies and intensities of the charge-transfer satellites are found to depend strongly on the chemical type of the atomic anion. While the bandshape of the O1s-1 spectrum of Cl-H2O is very similar to that of isolated H2O, the spectrum of Na-H2O has virtually nothing to do with the core-ionization spectrum of the water molecule. Interestingly, the charge-transfer satellites seen in the O1s core-ionization spectrum of the Cl-H2O cluster can be well related to states in the O1s core-excitation spectrum of the isolated H2O molecule. The physics of core ionization of the clusters is discussed in detail.

Streltsov, A. I.; Dobrodey, N. V.; Cederbaum, L. S.

2003-08-01

209

Switching to a reversible proton motion in a charge-transferred dye.  

PubMed

We report on the steady-state, pico- and femtosecond time-resolved emission studies of 6-amino-2-(2-methoxyphenyl)benzoxazole (6A-MBO) and 6-amino-2-(2-hydroxyphenyl)benzoxazole (6A-HBO) in different solvents. We observed an intramolecular charge transfer (ICT) reaction following by slow (relatively) solvent relaxation, which happened in the same time domain for both molecules. The ultrafast ICT reaction happens in 80-140 fs whereas the solvent relaxation occurs in 0.5-1.1 ps. In 6A-MBO the excited CT species has a lifetime of ?2.5 ns. However, in 6A-HBO and after the ICT reaction, a reversible excited-state intramolecular proton transfer (ESIPT) reaction takes place in the formed enol charge transfer (ECT*) species producing a keto (K*) type tautomer. Depending on the solvent, the forward ESIPT reaction (ECT* ? K*) happens in 40-175 ps while that of the reverse one (ECT* ? K*) occurs in 240-990 ps. Kinetic isotopic effect (OH/OD exchange) study in acetone shows that the reversible ESIPT reaction occurs via tunneling, while we suggest that in acetonitrile solution it evolves along the IHB and solvent coordinates. Our results show a reversible proton motion coupled to charge-transfer reactions opening the way to new explorations of charge- and proton-transfer dynamics and spectroscopy. PMID:25523413

Gutierrez, Mario; Alarcos, Noemí; Liras, Marta; Sánchez, Félix; Douhal, Abderrazzak

2015-01-15

210

Interstellar Chemistry Gets More Complex With New Charged-Molecule Discovery  

NASA Astrophysics Data System (ADS)

Astronomers using data from the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) have found the largest negatively-charged molecule yet seen in space. The discovery of the third negatively-charged molecule, called an anion, in less than a year and the size of the latest anion will force a drastic revision of theoretical models of interstellar chemistry, the astronomers say. Molecule formation Formation Process of Large, Negatively-Charged Molecule in Interstellar Space CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for page of graphics and detailed information "This discovery continues to add to the diversity and complexity that is already seen in the chemistry of interstellar space," said Anthony J. Remijan of the National Radio Astronomy Observatory (NRAO). "It also adds to the number of paths available for making the complex organic molecules and other large molecular species that may be precursors to life in the giant clouds from which stars and planets are formed," he added. Two teams of scientists found negatively-charged octatetraynyl, a chain of eight carbon atoms and one hydrogen atom, in the envelope of gas around an old, evolved star and in a cold, dark cloud of molecular gas. In both cases, the molecule had an extra electron, giving it a negative charge. About 130 neutral and about a dozen positively-charged molecules have been discovered in space, but the first negatively-charged molecule was not discovered until late last year. The largest previously-discovered negative ion found in space has six carbon atoms and one hydrogen atom. "Until recently, many theoretical models of how chemical reactions evolve in interstellar space have largely neglected the presence of anions. This can no longer be the case, and this means that there are many more ways to build large organic molecules in cosmic environments than have been explored," said Jan M. Hollis of NASA's Goddard Space Flight Center (GSFC). Ultraviolet light from stars can knock an electron off a molecule, creating a positively-charged ion. Astronomers had thought that molecules would not be able to retain an extra electron, and thus a negative charge, in interstellar space for a significant time. "That obviously is not the case," said Mike McCarthy of the Harvard-Smithsonian Center for Astrophysics. "Anions are surprisingly abundant in these regions." Remijan and his colleagues found the octatetraynyl anions in the envelope of the evolved giant star IRC +10 216, about 550 light-years from Earth in the constellation Leo. They found radio waves emitted at specific frequencies characteristic of the charged molecule by searching archival data from the GBT, the largest fully-steerable radio telescope in the world. Another team from the Harvard-Smithsonian Center for Astrophysics (CfA) found the same characteristic emission when they observed a cold cloud of molecular gas called TMC-1 in the constellation Taurus. These observations also were done with the GBT. In both cases, preceding laboratory experiments by the CfA team showed which radio frequencies actually are emitted by the molecule, and thus told the astronomers what to look for. "It is essential that likely interstellar molecule candidates are first studied in laboratory experiments so that the radio frequencies they can emit are known in advance of an astronomical observation," said Frank Lovas of the National Institute of Standards and Technology (NIST). Both teams announced their results in the July 20 edition of the Astrophysical Journal Letters. "With three negatively-charged molecules now found in a short period of time, and in very different environments, it appears that many more probably exist. We believe that we can discover more new species using very sensitive and advanced radio telescopes such as the GBT, once they have been characterized in the laboratory," said Sandra Bruenken of the CfA. "Further detailed studies of anions, including astronomical observations, laboratory studies, and theo

2007-07-01

211

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

NASA Technical Reports Server (NTRS)

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.

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

2007-01-01

212

Probing Electronic, Structural, and Charge Transfer Properties of Organic Semiconductor/Inorganic Oxide Interfaces Using Field-Effect Transistors  

NASA Astrophysics Data System (ADS)

Interfaces between organic semiconductors and inorganic oxides provide the functionality for devices including field-effect transistors (FETs) and organic photovoltaics. Organic FETs are sensitive to the physical structure and electronic properties of the few molecular layers of material at the interface between the semiconducting channel and the gate dielectric, and provide quantitative information such as the field-effect mobility of charge carriers and the concentration of trapped charge. In this thesis, FET interfaces between organic small-molecule semiconductors and SiO2, and donor/acceptor interfaces between organic small-molecules and the wide bandgap semiconductor ZnO are studied using electrical measurements of field-effect transistor devices. Monolayer-scale films of dihexyl sexithiophene are shown to have higher hole mobility than other monolayer organic semiconductors, and the origin of the high mobility is discussed. Studies of the crystal structure of the monolayer using X-ray structural probes and atomic force microscopy reveal the crystal structure is different in the monolayer regime compared to thicker films and bulk crystals. Progress and remaining challenges are discussed for in situ X-ray diffraction studies of the dynamic changes in the local crystal structure in organic monolayers due to charge carriers generated during the application of electric fields from the gate electrode in working FETs. Studies were conducted of light sensitive organic/inorganic interfaces that are modified with organic molecules grafted to the surface of ZnO nanoparticles and thin films. These interfaces are models for donor/acceptor interfaces in photovoltaics. The process of exciton dissociation at the donor/acceptor interface was sensitive to the insulating or semiconducting molecules grafted to the ZnO, and the photoinduced charge transfer process is measured by the threshold voltage shift of FETs during illumination. Charge transfer between light sensitive donor molecules based on rhenium bipyridine complexes and ZnO thin films was measured using FETs, revealing the role of positive trapped charge in persistent photoconductivity in donor sensitized ZnO. The carboxylic acid attachment chemistry, used to anchor the donor molecules, is demonstrated to enhance the conductivity of ZnO thin films. The mechanism for the enhanced conductivity is linked to the passivation of defects on the surface of the ZnO.

Spalenka, Josef Wade

213

Structure-property relationships for three indoline dyes used in dye-sensitized solar cells: TDDFT study of visible absorption and photoinduced charge-transfer processes.  

PubMed

The electronic structures of three D-A-?-A indoline dyes (WS-2, WS-6, and WS-11) used in dye-sensitized solar cells (DSSCs) were studied by performing quantum chemistry calculations. The coplanarity of the A-?-A segment and distinct noncoplanarity of the indoline donor part of each dye were confirmed by checking the calculated geometric parameters. The relationships between molecular modifications and the optical properties of the dyes were derived in terms of the partial density of states, absorption spectrum, frontier molecular orbital, and excited-state charge transfer. 3D real-space analysis of the transition density (TD) and charge difference density (CDD) was also performed to further investigate the excited-state features of the molecular systems, as they provide visualized physical pictures of the charge separation and transfer. It was found that modifying the alkyl chain of the bridge unit near the acceptor unit is an efficient way to decrease dye aggregation and improve DSSC efficiency. Inserting a hexylthiophene group next to the donor unit leads to a complicated molecular structure and a decrease in the charge-transfer ability of the system, which has an unfavorable impact on DSSC performance. PMID:24154611

Li, Huixing; Chen, Maodu

2013-12-01

214

Charge transfer events in semiconducting single-wall carbon nanotubes.  

PubMed

Electron-donating ferrocene units have been attached to SWNTs, with different degrees of functionalization. By means of a complementary series of novel spectroscopic techniques (i.e., steady-state and time-resolved), we have documented that mutual interactions between semiconducting SWNT and the covalently attached electron donor (i.e., ferrocene) lead, in the event of photoexcitation, to the formation of radical ion pairs. In the accordingly formed radical ion pairs, oxidation of ferrocene and reduction of SWNT were confirmed by spectroelectrochemistry. It is, however, shown that only a few semiconducting SWNTs [i.e., (9,4), (8,6), (8,7), and (9,7)] are susceptible to photoinduced electron transfer processes. These results are of relevant importance for the development of SWNT-based photovoltaics. PMID:22039995

Oelsner, Christian; Herrero, M Antonia; Ehli, Christian; Prato, Maurizio; Guldi, Dirk M

2011-11-23

215

Photophysical studies of metal to ligand charge transfer involving quadruply bonded complexes of molybdenum and tungsten.  

PubMed

Photoinduced metal-to-ligand charge transfer transitions afford numerous applications in terms of photon energy harvesting. The majority of metal complexes studied to date involve diamagnetic systems of d(6), d(8), and d(10) transition metals. These typically have very short-lived, ?100 fs, singlet metal to ligand charge transfer ((1)MLCT) states that undergo intersystem crossing to triplet metal to ligand charge transfer ((3)MLCT) states that are longer lived and are responsible for much of the photophysical studies. In contrast, the metal-metal quadruply bonded complexes of molybdenum and tungsten supported by carboxylate, O2CR, and related amidinate ligands (RN)2C(R') have relatively long-lived (1)MLCT states arising from M2? to L?* transitions. These have lifetimes in the range 1-20 ps prior to intersystem crossing to T1 states that may be (3)MLCT or (3)MM??* with lifetimes of 1-100 ns and 1-100 ?s, respectively. The M2 quadruply bonded complexes take the form M2L4 or M2L4-nL'n where n = 1-3. Thus, in their photoexcited MLCT states, these compounds pose the question of how the charge resides on the ligands. This Account reviews the current knowledge of how charge is positioned with time in S1 and T1 states with the aid of active IR reported groups located on the ligands, for example, C?X multiple bonds (X = C, N, or O). Several examples of localized and delocalized charge distributions are noted along with kinetic barriers to the interconversion of MLCT and ??* states. On the 50th anniversary of the recognition of the MM quadruple bond, these complexes are revealing some remarkable features in the study of the photophysical properties of metal-ligand charge transfer states. PMID:25695495

Chisholm, Malcolm H; Brown-Xu, Samantha E; Spilker, Thomas F

2015-03-17

216

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches  

NASA Astrophysics Data System (ADS)

Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

Wasielewski, M. R.

217

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches  

SciTech Connect

Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

Wasielewski, M.R.

1992-08-01

218

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches  

SciTech Connect

Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

Wasielewski, M.R.

1992-01-01

219

Optimal control of charge transfer Jan Werschnika and Eberhard K.U. Grossa  

E-print Network

of the laser by T.H. Maiman in 1960 physicists and chemists dream about coherently controlling quantum systemsOptimal control of charge transfer Jan Werschnika and Eberhard K.U. Grossa aFreie Universit is calculated with the help of quantum optimal control theory employing a time-dependent formulation

Gross, E.K.U.

220

Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies  

NASA Technical Reports Server (NTRS)

We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

Havener, C. C.; Vane, C. R.; Krause, H. F.; Stancil, P. C.; Mroczkowski, T.; Savin, D. W.

2002-01-01

221

PHYSICAL REVIEW B 86, 115417 (2012) Pseudoparticle approach for charge-transferring molecule-surface collisions  

E-print Network

to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both percent to the secondary electron emission. DOI: 10.1103/PhysRevB.86.115417 PACS number(s): 34.35.+a, 34 of surface reactions is of fundamental interest. It represents a quantum impurity problem where a finite many

Fehske, Holger

222

Coherent Electronic and Nuclear Dynamics for Charge Transfer in 1-Ethyl-4-(carbomethoxy)pyridinium Iodide  

E-print Network

charge transfer between iodide and 1-ethyl-4-(carbomethoxy)- pyridinium ions. Pump-probe signal by the Kramers-Kronig transformation, which allows the dispersive component of the polarization response in electroluminescent devices,12-16 and large quantum yield (but modest thermodynamic efficiency) in photosynthesis17

Scherer, Norbert F.

223

Quenching of Lanthanide Emission by Intervalence Charge Transfer in Crystals Containing Closed Shell Transition Metal Ions  

Microsoft Academic Search

The quenching of the luminescence originating from the excited states P0 and D2 of Pr and D3 and D4 of Tb has been studied in oxide crystals containing closed shell transition metal ions, such as titanates, vanadates, niobates, and tantalates. It has been shown that the emission from these excited states can be quenched by an intervalence charge transfer mechanism.

Philippe Boutinaud; Piotr Putaj; Rachid Mahiou; Enrico Cavalli; Adolfo Speghini; Marco Bettinelli

2007-01-01

224

Charge-transfer complexes of plastoquinone and alpha-tocopherol quinone in vitro.  

PubMed

It has been found that plastoquinone (PQ) and alpha-tocopherol quinone (alpha-TQ) can form quinhydrone-type charge-transfer complexes on PQH2 and alpha-TQH2, respectively, both in the crystalline state and in solutions of organic solvents. The charge-transfer spectra of PQ/PQH2 mixtures in hydrophobic solvents showed two bands: one at 349-358 nm, the other at 430-440 nm, one charge-transfer band at 351-355 nm occurring in water-miscible solvents. The intensity ratio of these two bands varied with changing PQ/PQH2 ratio. The charge-transfer spectra of alpha-TQ/alpha-TQH2 mixtures in all solvents investigated showed one peak at 361-367 nm and a broad shoulder within the range 400-540 nm, whose shape varied depending on the solvent used. In the infrared spectrum of PQ and alpha-TQ (1700-1600 cm(-1)) splitting of the carbonyl band occurred and was caused by the presence of two peak. In the spectra of quinhydrones the splitting disappeared, this being brought about by the appearance of a new peak at the position of splitting, which originated from the complexed quinones. The possibility of the formation of such complexes in thylakoid membranes is discussed. PMID:17010919

Kruk, J

1988-06-01

225

Water Channel of Horseradish Peroxidase Studied by the Charge-Transfer Absorption Band of Ferric Heme  

E-print Network

Water Channel of Horseradish Peroxidase Studied by the Charge-Transfer Absorption Band of Ferric The heme of horseradish peroxidase is buried in the protein, but a channel from the protein surface connects the aqueous solution to the heme site. Ferric horseradish peroxidase has an absorption band at 640

Sharp, Kim

226

Ionic Electrets: Electrostatic Charging of Surfaces by Transferring Mobile Ions upon Contact  

E-print Network

elementary charge per 2000 nm2 ) and close to the theoretical limit imposed by the dielectric breakdown electret is proportional to its surface area; the dielectric breakdown of air appears to limit the amount, in the absence of bulk liquid, to another material upon contact. According to the ion-transfer model of contact

Prentiss, Mara

227

Charge Transfer and Vibrational Excitation in Molecule-Surface Collisions: Trajectorized Quantum Theory  

Microsoft Academic Search

Vibrational excitation of diatomic molecules scattered from solid surfaces is considered. Emphasis is placed on a mechanism in which charge transfer between the molecule and surface creates a temporary molecular ion. A classical mechanics analysis of this effect has been presented previously. Here a mixed picture is offered in which the center-of-mass translational motion is treated classically with a trajectory

J. W. Gadzuk; S. Holloway

1985-01-01

228

Enhanced Charge-Transfer Kinetics by Anion Surface Modi cation of Kyu-Sung Park,,  

E-print Network

Enhanced Charge-Transfer Kinetics by Anion Surface Modi cation of LiFePO4 Kyu-Sung Park,, Penghao on global warming and air pollution, alternative energy sources at an a ordable price are urgently needed acceptable, but also a relief from distributed sources of air pollution. LiFePO4 o ers a cathode alternative

Henkelman, Graeme

229

Polarization and Charge-Transfer Effects in Aqueous Solution via Ab Initio QM/MM Simulations  

E-print Network

component of these calculations is intermolecular potential functions that describe intermolecular in the potential energy function is a major goal in the development of next-generation force fields.3 Furthermore energy is the dominant many-body effect in computing intermolecular interactions, whereas charge transfer

Minnesota, University of

230

Formation of H/sup -/ by charge transfer in alkaline-earth vapors  

SciTech Connect

Progress on the study of H/sup -/ formation by charge transfer in alkaline-earth vapors is reported. The H/sup -/ equilibrium yield in strontium vapor reaches a maximum of 50% at an energy of 250 eV/amu, which is the highest H/sup -/ yield reported to date.

Schlachter, A.S.; Morgan, T.J.

1983-10-01

231

Transition-State Charge Transfer Reveals Electrophilic, Ambiphilic, and Nucleophilic Carbon-Hydrogen Bond Activation  

E-print Network

functionalized products.1 For alkane oxidation reactions, Pt, Pd, Hg, and Au metal catalysts have been exploited and magni- tude of charge transfer (CT) bonding between metal/ligand com- plexes and alkane C-H bonds of insertion and substitution C-H activation TSs that were analyzed, including oxidative addition, -bond

Goddard III, William A.

232

Stark-effect spectroscopy of the heme charge-transfer bands of deoxymyoglobin  

SciTech Connect

The authors report the Stark spectra of the Soret, Q, and charge-transfer bands of deoxymyoglobin. The data show that band III has charge-transfer character but that the magnitude of the charge displacement is significantly smaller than expected or than what is observed for band I or even the Soret or Q bands. The data also show that symmetry breaking of iron-protoporphyrin IX in myoglobin produces a larger difference dipole moment in the Soret transition when compared to the dimethyl ester of protoporphyrin IX. The results lend further credence to the hypothesis that the electrostatic environment of the heme pocket in myoglobin is important in modifying the properties of the heme transitions, and they provide a basis for quantitative analysis of the static and time-dependent band shifts observed in response to environmental electrostatic perturbations and ligand binding dynamics.

Franzen, S.; Woodruff, W.H. [Los Alamos National Lab., NM (United States). Bioscience and Biotechnology Group] [Los Alamos National Lab., NM (United States). Bioscience and Biotechnology Group; Moore, L.J.; Boxer, S.G. [Stanford Univ., CA (United States). Dept. of Chemistry] [Stanford Univ., CA (United States). Dept. of Chemistry

1999-04-22

233

Photoexcitation of electronic instabilities in one-dimensional charge-transfer systems  

NASA Astrophysics Data System (ADS)

We investigate the real-time dynamics of photoexcited electronic instabilities in a charge-transfer system model, using the time-dependent density matrix renormalization group method. The model of choice was the quarter-filled one-dimensional extended Peierls-Hubbard Hamiltonian interacting with classical few-cycle electromagnetic radiation. The results show that only one electronic instability drives the main features of the photogenerated time-dependent behavior. Indeed, the photoresponse of the system shows a large enhancement of the 4kF (bond and charge) instability whereas the 2kF state remains largely unaffected. This conclusion holds regardless of the nature of the optical excitations and whether the system is perturbed resonantly or not. Our results suggest potential applications of charge-transfer systems with slow phononic dynamics as optoelectronic switching devices.

Rincón, Julián; Al-Hassanieh, K. A.; Feiguin, Adrian E.; Dagotto, Elbio

2014-10-01

234

Interaction and charge transfer between isolated thylakoids and multi-walled carbon nanotubes.  

PubMed

Charge separation in photosynthetic light reactions has gained much interest in an attempt to fabricate biological photovoltaic devices through integration of photosynthetic material and conducting electrodes. Direct interaction between thylakoids, as representatives of photosynthetic materials, and multi-walled carbon nanotubes (MWCNTs) is expected to increase charge transfer. Thylakoids are isolated from spinach leaf chloroplasts and pristine MWCNTs are dispersed in Triton X-100 (TX-100) as a surfactant to retain their electronic properties through non-covalent interactions. The Raman and UV-Vis spectra suggest close interactions between the thylakoids and the MWCNTs. Stable thylakoids including the embedded protein subunits and light harvesting antennas can be detected from the non-shifted 680 nm absorbance peak. The 50% fluorescence quenching in the MWCNTs-thylakoids preparation as compared to thylakoids alone using single wavelength excitation suggests charge transfer between the thylakoids and the MWCNTs. PMID:25531101

Dewi, Herlina Arianita; Sun, Gengzhi; Zheng, Lianxi; Lim, Sierin

2015-02-01

235

Hot charge-transfer excitons set the time limit for charge separation at donor/acceptor interfaces in organic photovoltaics.  

PubMed

Photocurrent generation in organic photovoltaics (OPVs) relies on the dissociation of excitons into free electrons and holes at donor/acceptor heterointerfaces. The low dielectric constant of organic semiconductors leads to strong Coulomb interactions between electron-hole pairs that should in principle oppose the generation of free charges. The exact mechanism by which electrons and holes overcome this Coulomb trapping is still unsolved, but increasing evidence points to the critical role of hot charge-transfer (CT) excitons in assisting this process. Here we provide a real-time view of hot CT exciton formation and relaxation using femtosecond nonlinear optical spectroscopies and non-adiabatic mixed quantum mechanics/molecular mechanics simulations in the phthalocyanine-fullerene model OPV system. For initial excitation on phthalocyanine, hot CT excitons are formed in 10(-13)?s, followed by relaxation to lower energies and shorter electron-hole distances on a 10(-12)?s timescale. This hot CT exciton cooling process and collapse of charge separation sets the fundamental time limit for competitive charge separation channels that lead to efficient photocurrent generation. PMID:23223125

Jailaubekov, Askat E; Willard, Adam P; Tritsch, John R; Chan, Wai-Lun; Sai, Na; Gearba, Raluca; Kaake, Loren G; Williams, Kenrick J; Leung, Kevin; Rossky, Peter J; Zhu, X-Y

2013-01-01

236

Camptothecins guanine interactions: mechanism of charge transfer reaction upon photoactivation  

NASA Astrophysics Data System (ADS)

The potent activity exhibited by the antitumoral camptothecin (CPT) and its analog irinotecan (CPT-11) is known to be related to a close contact between the drug and the nucleic acid base guanine. This specificity of interaction between these two chromophores was examined by following changes in the photophysical properties of the drug using steady-state as well as time-resolved absorption and fluorescence methods. The observed effects on absorption, fluorescence emission and singlet excited state lifetimes give evidence for the occurrence of a stacking complex formation restricted to the quinoline part of CPT or CPT-11 and the guanine base but also with the adenine base. The triplet excited state properties of the drugs have been also characterized in absence and in presence of guanosine monophosphate and reveal the occurrence of an electron transfer from the guanine base to the drug. Support for this conclusion was obtained from the studies of a set of biological targets of various oxido-reduction potentials, adenosine monophosphate, cytidine, cytosine, tryptophan, tyrosine and phenylalanine. This finding gives an interpretation of the CPT-induced guanine photolesions previously reported in the literature. These data taken together are discussed in connection with the drug activity. The stacking complex CPT/guanine is necessary but not sufficient to explain the role of the chirality and of the lactone structure in the function of the drug. A stereospecific interaction with the enzyme topoisomerase I seems necessary to stabilize the stacking complex. The first experiments using time-resolved fluorescence by two-photon excitation confirms that CPT does not bind to the isolated enzyme.

Steenkeste, K.; Guiot, E.; Tfibel, F.; Pernot, P.; Mérola, F.; Georges, P.; Fontaine-Aupart, M. P.

2002-01-01

237

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

PubMed Central

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. PMID:22303133

Shafie, Suhaidi; Kawahito, Shoji; Halin, Izhal Abdul; Hasan, Wan Zuha Wan

2009-01-01

238

Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches  

NASA Astrophysics Data System (ADS)

We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual ?? molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

Ramakrishnan, Raghunathan; Nest, Mathias

2015-01-01

239

Energy transfer versus charge separation in type-II hybrid organic-inorganic nanocomposites.  

PubMed

Hybrid organic-inorganic nanomaterials have the potential of providing synergetic properties. Blends of semiconductor nanocrystals and conjugated polymers in particular promise novel optoelectronic properties. Effective design of tailored optoelectronic properties requires a deep understanding of the photophysics of these composite materials, which includes charge separation and Dexter and Förster energy transfer. We performed a detailed and quantitative spectroscopic investigation of a type II aligned hybrid system consisting of a blue emitting conducting polymer and CdTe nanocrystals. Although charge separation is expected from the type II alignment, we find a dominant (70% efficiency) energy transfer process. We discuss all possible de-excitation pathways for the excitons in terms of the alignment of energy levels, time scales, and physical geometry of the system. This allows us to conclude that energy transfer occurs via the Förster mechanism and provides a clear guideline for the design of novel hybrid materials. PMID:19507819

Lutich, Andrey A; Jiang, Guoxin; Susha, Andrei S; Rogach, Andrey L; Stefani, Fernando D; Feldmann, Jochen

2009-07-01

240

Intramolecular charge transfer character in tetrathiafulvalene-annulated porphyrinoids: effects of core modification and protonation.  

PubMed

The synthesis, characterization, and photophysical and electrochemical properties of a novel tetrathiafulvalene (TTF)-annulated core-modified porphyrin (1) and its expanded rubyrin analogue (2) are described. The sulfur core modifications in 1 and 2 allow a feasible intramolecular charge transfer from the TTF fragments to the central conjugated core as inferred from comparative spectroscopic and electrochemical measurements. DFT calculations also support the intramolecular charge transfer nature of 1 and 2 upon excitation. Further the electronic perturbation of the TTF-annulated porphyrins was achieved by protonation, giving rise to a drastic change in the optical features with an extremely low energy band in the NIR region. The pronounced electron accepting ability of the macrocyclic core of the dicationic species (H21(2+) and H22(2+)) resulted in the thermally excited electron transfer occurring at room temperature as elucidated by EPR spectroscopy. PMID:25738190

Bolligarla, Ramababu; Ishida, Masatoshi; Shetti, Vijayendra S; Yamasumi, Kazuhisa; Furuta, Hiroyuki; Lee, Chang-Hee

2015-04-14

241

Reduction of Charge Transfer Loss in Atomic Laser Isotope Separation by Production of Excited Ions through Autoionization Levels  

Microsoft Academic Search

A new technique to reduce charge transfer loss when extracting ions from photoionized plasma has been developed, thereby increasing the efficiency of atomic vapor laser isotope separation (AVLIS). By selecting autoionization levels, specific isotopes are ionized to the excitation levels of the ions. Cross sections for charge transfer between specific excited ions and ground state atoms are smaller than those

Masahiro TOOMA; Manabu UENO; Kinya KOBAYASHI; Kazuki TSUCHIDA; Kazumichi SUZUKI

1996-01-01

242

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

243

Reaction dynamics and proton coupled electron transfer: studies of tyrosine-based charge transfer in natural and biomimetic systems.  

PubMed

In bioenergetic reactions, electrons are transferred long distances via a hopping mechanism. In photosynthesis and DNA synthesis, the aromatic amino acid residue, tyrosine, functions as an intermediate that is transiently oxidized and reduced during long distance electron transfer. At physiological pH values, oxidation of tyrosine is associated with a deprotonation of the phenolic oxygen, giving rise to a proton coupled electron transfer (PCET) reaction. Tyrosine-based PCET reactions are important in photosystem II, which carries out the light-induced oxidation of water, and in ribonucleotide reductase, which reduces ribonucleotides to form deoxynucleotides. Photosystem II contains two redox-active tyrosines, YD (Y160 in the D2 polypeptide) and YZ (Y161 in the D1 polypeptide). YD forms a light-induced stable radical, while YZ functions as an essential charge relay, oxidizing the catalytic Mn?CaO? cluster on each of four photo-oxidation reactions. In Escherichia coli class 1a RNR, the ?2 subunit contains the radical initiator, Y122O•, which is reversibly reduced and oxidized in long range electron transfer with the ?2 subunit. In the isolated E. coli ?2 subunit, Y122O• is a stable radical, but Y122O• is activated for rapid PCET in an ?2?2 substrate/effector complex. Recent results concerning the structure and function of YD, YZ, and Y122 are reviewed here. Comparison is made to recent results derived from bioengineered proteins and biomimetic compounds, in which tyrosine-based charge transfer mechanisms have been investigated. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. PMID:25260243

Barry, Bridgette A

2015-01-01

244

Lead methylammonium triiodide perovskite-based solar cells: an interfacial charge-transfer investigation.  

PubMed

This work reports on an investigation into interfacial charge transfer in CH3NH3PbI3 perovskite solar cells by using anatase TiO2 nanocuboids enclosed by active {100} and {001} facets. The devices show 6.0 and 8.0% power conversion efficiency with and without hole-transport material. Transient photovoltage/photocurrent decay and charge extraction, as well as impedance spectroscopy measurements, reveal that carbon materials are effective counter electrodes in perovskite solar cells. The photogenerated charges are observed to be stored in mesoporous TiO2 film under illumination and in the CH3NH3PbI3 layer in the dark. The use of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-MeOTAD) as a hole-transport material accelerates interfacial charge recombination between the photogenerated electrons and holes. PMID:25213607

Xu, Xiaobao; Zhang, Hua; Cao, Kun; Cui, Jin; Lu, Jianfeng; Zeng, Xianwei; Shen, Yan; Wang, Mingkui

2014-11-01

245

Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter  

NASA Technical Reports Server (NTRS)

An imaging device formed as a monolithic complementary metal oxide semiconductor Integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

Fossum, Eric R. (Inventor); Mendis, Sunetra K. (Inventor); Pain, Bedabrata (Inventor); Nixon, Robert H. (Inventor); Zhou, Zhimin (Inventor)

2000-01-01

246

Model for the charge-transfer probability in helium nanodroplets following electron-impact ionization  

SciTech Connect

A theoretical model has been developed to describe the probability of charge transfer from helium cations to dopant molecules inside helium nanodroplets following electron-impact ionization. The location of the initial charge site inside helium nanodroplets subject to electron impact has been investigated and is found to play an important role in understanding the ionization of dopants inside helium droplets. The model is consistent with a charge migration process in small helium droplets that is strongly directed by intermolecular forces originating from the dopant, whereas for large droplets (tens of thousands of helium atoms and larger) the charge migration increasingly takes on the character of a random walk. This suggests a clear droplet size limit for the use of electron-impact mass spectrometry for detecting molecules in helium droplets.

Ellis, Andrew M.; Yang Shengfu [Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)

2007-09-15

247

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

NASA Astrophysics Data System (ADS)

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 [1-3]. 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 [4]. 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 optimization of the performance of molecular photovoltaic devices. I will present the state of the art in this field and discuss the mechanisms of polaron pair generation and recombination in the novel low band gap polymer-fullerene blends as well as in high-efficiency SC.[4pt] [1] C. Deibel, T. Strobel, V. Dyakonov, Phys. Rev. Lett. 103, 036402 (2009).[0pt] [2] C. Deibel, T. Strobel, and V. Dyakonov, Adv. Mater. 22, 4097 (2010).[0pt] [3] C. Deibel, and V. Dyakonov, Rep. Prog. Phys. 73, 096401 (2010).[0pt] [4] M. Liedtke, et al., JACS 133, 9088 (2011).

Dyakonov, Vladimir

2013-03-01

248

Temperature-dependent kinetics of charge transfer, hydrogen-atom transfer, and hydrogen-atom expulsion in the reaction of CO+ with CH4 and CD4.  

PubMed

We have determined the rate constants and branching ratios for the reactions of CO(+) with CH4 and CD4 in a variable-temperature selected ion flow tube. We find that the rate constants are collisional for all temperatures measured (193-700 K for CH4 and 193-500 K for CD4). For the CH4 reaction, three product channels are identified, which include charge transfer (CH4(+) + CO), H-atom transfer (HCO(+) + CH3), and H-atom expulsion (CH3CO(+) + H). H-atom transfer is slightly preferred to charge transfer at low temperature, with the charge-transfer product increasing in contribution as the temperature is increased (H-atom expulsion is a minor product for all temperatures). Analogous products are identified for the CD4 reaction. Density functional calculations on the CO(+) + CH4 reaction were also conducted, revealing that the relative temperature dependences of the charge-transfer and H-atom transfer pathways are consistent with an initial charge transfer followed by proton transfer. PMID:24588097

Melko, Joshua J; Ard, Shaun G; Johnson, Ryan S; Shuman, Nicholas S; Guo, Hua; Viggiano, Albert A

2014-09-18

249

Direct Observation of Charge Transfer at a MgO(111) Surface A. Subramanian,1,* L. D. Marks,1  

E-print Network

Direct Observation of Charge Transfer at a MgO(111) Surface A. Subramanian,1,* L. D. Marks,1 O on the polar (111) surface of MgO and refine the valence charge distribution. The surface is nonstoichiometric. The partial charges that we obtain for the surface atoms are in reasonable agreement with empirical bond

Marks, Laurence D.

250

Site-specific probing of charge transfer dynamics in organic photovoltaics  

NASA Astrophysics Data System (ADS)

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 C60 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 (C60) 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 C60 layer is readily observed as a completely reversible, transient shift of the C60 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.

Arion, Tiberiu; Neppl, Stefan; Roth, Friedrich; Shavorskiy, Andrey; Bluhm, Hendrik; Hussain, Zahid; Gessner, Oliver; Eberhardt, Wolfgang

2015-03-01

251

Phosphopeptide Anion Characterization via Sequential Charge Inversion and Electron Transfer Dissociation  

PubMed Central

Sequential ion/ion reactions have been used to characterize phosphopeptides present in relatively simple peptide mixtures, including one generated from the tryptic digestion of ?-casein. The phosphopeptides in these mixtures gave rise to either low or no signals via positive ion electrospray ionization. Strong signals, however, were generated in the negative ion mode. An initial ion/ion reaction that employed multiply-protonated amino-terminated dendrimers converted phosphopeptide anions to the doubly protonated species. The doubly charged cations were then subjected to ion/ion electron transfer to induce dissociation. Electron transfer dissociation of doubly positive charged phosphopeptides yields characteristic c- and z-type fragment ions by dissociation of the N-C? bond along the peptide backbone while preserving the labile post-translational modifications. These results illustrate the ability to alter ion charge after ion formation and prior to structural interrogation. Phosphopeptides provide an example where it can be difficult to form strong doubly charged cation signals directly when they are present in mixtures, which, as a result, precludes the use of electron transfer dissociation as a structural probe. The sequential ion/ion reaction process described here, therefore, can provide a new capability for structural interrogation in phosphoproteomics. PMID:16737238

Gunawardena, Harsha P.; Emory, Joshua F.; McLuckey, Scott A.

2008-01-01

252

Charge transfer and optical phonon mixing in few-layer graphene chemically doped with sulfuric acid  

NASA Astrophysics Data System (ADS)

Chemical doping is expected to substantially increase the density of free charge carriers by charge transfer and modify the Fermi level and screening effect of doped materials. Here, along with Raman identification of 3 and 4 graphene layers by a 633-nm laser excitation, we investigated charge transfer and optical phonon mixing in few layer graphenes in detail by utilizing sulfuric acid as an electron-acceptor dopant. Sulfuric acid molecules are found to be only physically adsorbed on the surface layers of graphenes without intercalations. The top and bottom layers of bilayer graphene can be intentionally doped differently by concentrated sulfuric acid. The difference of the hole doping between the top and bottom layers results in phonon mixing of symmetric and antisymmetric modes in bilayer graphene. The Raman frequency evolution with the doping level is in agreement with recent ab initio density-functional theory calculations [P. Gava, M. Lazzeri, A. M. Saitta, and F. Mauri, Phys. Rev. B 80, 155422 (2009)10.1103/PhysRevB.80.155422]. Chemical doping by adsorption-induced charge transfer offers a way to study the electronic and vibrational behaviors of few layer graphenes at high-carrier concentration.

Zhao, Weijie; Tan, Pingheng; Zhang, Jun; Liu, Jian

2010-12-01

253

Ultrafast spectroscopic signature of charge transfer between single-walled carbon nanotubes and C60.  

PubMed

The time scales for interfacial charge separation and recombination play crucial roles in determining efficiencies of excitonic photovoltaics. Near-infrared photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g., C60). However, little is known about crucial photochemical events that occur on femtosecond to nanosecond time scales at such heterojunctions. Here, we present transient absorbance measurements that utilize a distinct spectroscopic signature of charges within SWCNTs, the absorbance of a trion quasiparticle, to measure both the ultrafast photoinduced electron transfer time (?pet) and yield (?pet) in photoexcited SWCNT–C60 bilayer films. The rise time of the trion-induced absorbance enables the determination of the photoinduced electron transfer (PET) time of ?pet ? 120 fs, while an experimentally determined trion absorbance cross section reveals the yield of charge transfer (?pet ? 38 ± 3%). The extremely fast electron transfer times observed here are on par with some of the best donor:acceptor pairs in excitonic photovoltaics and underscore the potential for efficient energy harvesting in SWCNT-based devices. PMID:25019648

Dowgiallo, Anne-Marie; Mistry, Kevin S; Johnson, Justin C; Blackburn, Jeffrey L

2014-08-26

254

Unexpectedly similar charge transfer rates through benzo-annulated bicyclo[2.2.2]octanes.  

PubMed

A 4-(pyrrolidin-1-yl)phenyl electron donor and 10-cyanoanthracen-9-yl electron acceptor are attached via alkyne linkages to the bridgehead carbon atoms of bicyclo[2.2.2]octane and all three benzo-annulated bicyclo[2.2.2]octanes. The sigma-system of bicyclo[2.2.2]octane provides a scaffold having nearly constant bridge geometry on which to append multiple, weakly interacting benzo pi-bridges, so that the effect of incrementally increasing numbers of pi-bridges on electron transfer rates can be studied. Surprisingly, photoinduced charge transfer rates measured by transient absorption spectroscopy in toluene show no benefit from increasing the number of bridge pi-systems, suggesting dominant transport through the sigma-system. Even more surprisingly, the significant changes in hybridization undergone by the sigma-system as a result of benzo-annulation also appear to have no effect on the charge transfer rates. Natural Bond Orbital analysis is applied to both sigma- and pi-communication pathways. The transient absorption spectra obtained in 2-methyltetrahydrofuran (MTHF) show small differences between the benzo-annulated molecules that are attributed to changes in solvation. All charge transfer rates increase significantly upon cooling the MTHF solutions to their glassy state. This behavior is rationalized using combined molecular dynamics/electronic structure trajectories. PMID:18500799

Goldsmith, Randall H; Vura-Weis, Josh; Scott, Amy M; Borkar, Sachin; Sen, Ayusman; Ratner, Mark A; Wasielewski, Michael R

2008-06-18

255

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

PubMed Central

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 the neutral-ionic state crossing in, for example, hydrogen halides or alkali halides, the path from separated reactants to the conical intersection region is uphill and the charge-transferred state is a biradical. The lowest-energy adiabatic singlet state shows at least two minima along a single approach path of Ca to the ? system: (i) a van der Waals complex with a doubly occupied highest molecular orbital, denoted , and a small negative charge on Ca and (ii) an open-shell singlet (biradical) at intermediate approach (Ca?C distance ?2.5–2.7 ?) with molecular orbital structure ?1?2, where ?2 is an orbital showing significant charge transfer form Ca to the ?-system, leading to a one-electron multicentered bond. A third minimum (iii) at shorter distances along the same path corresponding to a closed-shell state with molecular orbital structure has also been found; however, it does not necessarily represent the ground state at a given Ca?C distance in all three systems. The topography of the lowest adiabatic singlet potential energy surface is due to the one- and two-electron bonding patterns in Ca-? complexes. PMID:21037111

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

2010-01-01

256

Charge transfer tuning by chemical substitution and uniaxial pressure in the organic complex tetramethoxypyrene–tetracyanoquinodimethane  

NASA Astrophysics Data System (ADS)

In the search for novel organic charge transfer salts with variable charge transfer degree we study the effects of two modifications to the recently synthesized donor-acceptor Tetramethoxypyrene (TMP)-Tetracyanoquinodimethane (TCNQ). One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of TMP-F4TCNQ and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules alternately stacked (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP-TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our bandstructure calculations confirm the one-dimensional behavior of TMP-F4TCNQ with pro- nounced dispersion only along the stacking axis. Infrared measurements illustrating the CN vibration frequency shift in F4TCNQ suggest however no improvement on the degree of charge transfer in TMP-F4TCNQ with respect to TMP-TCNQ. In both complexes about 0.1 is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on designed TMP-TCNQ and TMP-F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP-TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer.

Rudloff, Milan; Ackermann, Kai; Huth, Michael; Jeschke, Harald O.; Tomic, Milan; Valentí, Roser; Wolfram, Benedikt; Bröring, Martin; Bolte, Michael; Chercka, Dennis; Baumgarten, Martin; Müllen, Klaus

257

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

SciTech Connect

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.

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

2014-04-28

258

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

PubMed

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. PMID:24784248

Theophilou, Iris; Tassi, M; Thanos, S

2014-04-28

259

Nonadiabatic dynamics of charge transfer and singlet fission at the pentacene/C60 interface.  

PubMed

Charge carrier multiplication in organic heterojunction systems, a process known as singlet fission (SF), holds promise for development of solar cells with enhanced photon-to-electron yields, and therefore it is of substantial fundamental interest. The efficiency of photovoltaic devices based on this principle is determined by complex dynamics involving key electronic states coupled to particular nuclear motions. Extensive experimental and theoretical studies are dedicated to this topic, generating multiple opinions on the nature of such states and motions, their properties, and mechanisms of the competing processes, including electron-phonon relaxation, SF, and charge separation. Using nonadiabatic molecular dynamics, we identify the key steps and mechanisms involved in the SF and subsequent charge separation, and build a comprehensive kinetic scheme that is consistent with the existing experimental and theoretical results. The ensuing model provides time scales that are in excellent agreement with the experimental observations. We demonstrate that SF competes with the traditional photoinduced electron transfer between pentacene and C60. Efficient SF relies on the presence of intermediate dark states within the pentacene subsystem. Having multiexciton and charge transfer character, these states play critical roles in the dynamics, and should be considered explicitly when explaining the entire process from the photoexcitation to the final charge separation. PMID:24397723

Akimov, Alexey V; Prezhdo, Oleg V

2014-01-29

260

Impact of distributions and mixtures on the charge transfer properties of graphene nanoflakes  

NASA Astrophysics Data System (ADS)

Many of the promising new applications of graphene nanoflakes are moderated by charge transfer reactions occurring between defects, such as edges, and the surrounding environment. In this context the sign and value of properties such as the ionization potential, electron affinity, electronegativity and chemical hardness can be useful indicators of the efficiency of graphene nanoflakes for different reactions, and can help identify new application areas. However, as samples of graphene nanoflakes cannot necessarily be perfectly monodispersed, it is necessary to predict these properties for polydispersed ensembles of flakes, and provide a statistical solution. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the charge transfer properties of different types of ensembles where restrictions have been placed on the diversity of the structures. By predicting quality factors for a variety of cases, we find that there is a clear motivation for restricting the sizes and suppressing certain morphologies to increase the selectivity and efficiency of charge transfer reactions; even if samples cannot be completely purified.Many of the promising new applications of graphene nanoflakes are moderated by charge transfer reactions occurring between defects, such as edges, and the surrounding environment. In this context the sign and value of properties such as the ionization potential, electron affinity, electronegativity and chemical hardness can be useful indicators of the efficiency of graphene nanoflakes for different reactions, and can help identify new application areas. However, as samples of graphene nanoflakes cannot necessarily be perfectly monodispersed, it is necessary to predict these properties for polydispersed ensembles of flakes, and provide a statistical solution. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the charge transfer properties of different types of ensembles where restrictions have been placed on the diversity of the structures. By predicting quality factors for a variety of cases, we find that there is a clear motivation for restricting the sizes and suppressing certain morphologies to increase the selectivity and efficiency of charge transfer reactions; even if samples cannot be completely purified. Electronic supplementary information (ESI) available: Details of computational simulations and specific results. Comparison of the expectation values of quality factors for ensemble properties based on different statistical distributions. See DOI: 10.1039/c4nr06123c

Shi, Hongqing; Rees, Robert J.; Per, Manolo C.; Barnard, Amanda S.

2015-01-01

261

Two-level system with a thermally fluctuating transfer matrix element: Application to the problem of DNA charge transfer  

NASA Astrophysics Data System (ADS)

Charge transfer along the base-pair stack in DNA is modeled in terms of thermally assisted tunneling between adjacent base pairs. The key element of the approach in this paper is the notion that this tunneling between base pairs that fluctuate significantly from their nominal orientation is rate limited by the requirement of optimal alignment. We focus on this aspect of the process by modeling two adjacent base pairs in terms of a classical damped oscillator subject to thermal fluctuations as described by a Fokker-Planck equation. We find that the process is characterized by two time scales, a result that is in accord with the experimental findings.

D'Orsogna, Maria R.; Rudnick, Joseph

2002-10-01

262

Forster Resonance Energy Transfer and Conformational Stability of Proteins: An Advanced Biophysical Module for Physical Chemistry Students  

ERIC Educational Resources Information Center

Protein folding is an exploding area of research in biophysics and physical chemistry. Here, we describe the integration of several techniques, including absorption spectroscopy, fluorescence spectroscopy, and Forster resonance energy transfer (FRET) measurements, to probe important topics in protein folding. Cytochrome c is used as a model…

Sanchez, Katheryn M.; Schlamadinger, Diana E.; Gable, Jonathan E.; Kim, Judy E.

2008-01-01

263

Molecular control of photoexcited charge transfer and recombination at a quaterthiophene/zinc oxide interface  

SciTech Connect

Nonadiabatic quantum molecular dynamics simulations are performed to study photoexcited charge transfer (CT) and charge recombination (CR) at an interface between a conjugated oligomer donor, quaterthiophene (QT), and an inorganic acceptor (ZnO). Simulations reveal a detrimental effect of static disorder in QT conformation on the efficiency of hybrid QT/ZnO solar cells due to increased CR. On the contrary, dynamic disorder (i.e., fluctuation of carbon-hydrogen bonds in QT) is essential for high efficiency by assisting CT. The separate controllability of CT and CR at the molecular level has impacts on molecular design for efficient solar cells and explains recent experimental observations.

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

2012-05-14

264

Molecular control of photoexcited charge transfer and recombination at a quaterthiophene/zinc oxide interface  

NASA Astrophysics Data System (ADS)

Nonadiabatic quantum molecular dynamics simulations are performed to study photoexcited charge transfer (CT) and charge recombination (CR) at an interface between a conjugated oligomer donor, quaterthiophene (QT), and an inorganic acceptor (ZnO). Simulations reveal a detrimental effect of static disorder in QT conformation on the efficiency of hybrid QT/ZnO solar cells due to increased CR. On the contrary, dynamic disorder (i.e., fluctuation of carbon-hydrogen bonds in QT) is essential for high efficiency by assisting CT. The separate controllability of CT and CR at the molecular level has impacts on molecular design for efficient solar cells and explains recent experimental observations.

Mou, Weiwei; Ohmura, Satoshi; Shimojo, Fuyuki; Nakano, Aiichiro

2012-05-01

265

Photochemical charge separation in zeolites: Electron transfer dynamics, nanocrystals and zeolitic membranes. Final technical report  

SciTech Connect

Aluminosilicate zeolites provide an excellent host for photochemical charge separation. Because of the constraints provided by the zeolite, the back electron transfer from the reduced acceptor to the oxidized sensitizer is slowed down. This provides the opportunity to separate the charge and use it in a subsequent reaction for water oxidation and reduction. Zeolite-based ruthenium oxide catalysts have been found to be efficient for the water splitting process. This project has demonstrated the usefulness of zeolite hosts for photolytic splitting of water.

Dutta, Prabir K.

2001-09-30

266

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

PubMed

Interfacial charge transfer is widely assumed to obey the Butler-Volmer kinetics. For certain liquid-solid interfaces, the Marcus-Hush-Chidsey theory is more accurate and predictive, but it has not been applied to porous electrodes. Here we report a simple method to extract the charge transfer rates in carbon-coated LiFePO4 porous electrodes from chronoamperometry experiments, obtaining curved Tafel plots that contradict the Butler-Volmer equation but fit the Marcus-Hush-Chidsey prediction over a range of temperatures. The fitted reorganization energy matches the Born solvation energy for electron transfer from carbon to the iron redox site. The kinetics are thus limited by electron transfer at the solid-solid (carbon-Li(x)FePO4) interface rather than by ion transfer at the liquid-solid interface, as previously assumed. The proposed experimental method generalizes Chidsey's method for phase-transforming particles and porous electrodes, and the results show the need to incorporate Marcus kinetics in modelling batteries and other electrochemical systems. PMID:24699391

Bai, Peng; Bazant, Martin Z

2014-01-01

267

Aspects of artificial photosynthesis. Photosensitized electron transfer and charge separation in redox active surfactant aggregates  

Microsoft Academic Search

Photosensitized electron transfer and charge separation have been demonstrated by steady-state and nanosecond laser flash photolysis in the presence of redox active surfactant aggregates prepared from CHâ==C(CHâ)-COO(CHâ)ââ(CâHâN\\/sup +\\/)âCHâ,Br⁻,I⁻ (RMV\\/sup 2 +\\/). Tris(2,2'-bipyridine)ruthenium chloride (Ru(bpy)â\\/sup 2 +\\/) has been used as a sensitizer. Forward electron transfer from excited Ru(bpy)â\\/sup 2 +\\/ to RMV\\/sup 2 +\\/ aggregates has been shown to be

Kazue Kurihara; Pietro Tundo; Janos H. Fendler

1983-01-01

268

Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin  

SciTech Connect

Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

2014-03-03

269

Energy and charge transfer dynamics between Alq3 and CdSeS nanocrystals.  

PubMed

The photoluminescence properties of the blend films consisting of organic small molecules and nanocrystals (NCs)--Alq3 and CdSeS NCs--were studied by steady-state and time-resolved photoluminescence (PL) spectroscopy with different excited wavelengths. Both the fluorescence intensity and lifetime are intensively dependent on the NC concentration. The detailed analysis of experiment data proves that Forster energy transfer from the Alq3 to the NCs exists simultaneously with the charge transfer and both compete with each other in the blend films. PMID:20355648

Zhang, Shuping; Liu, Yuqiang; Yang, Yanqiang

2010-03-01

270

Chemistry control and corrosion mitigation of heat transfer salts for the fluoride salt reactor (FHR)  

SciTech Connect

The Molten Salt Reactor Experiment (MSRE) was a prototype nuclear reactor which operated from 1965 to 1969 at Oak Ridge National Laboratory. The MSRE used liquid fluoride salts as a heat transfer fluid and solvent for fluoride based {sup 235}U and {sup 233}U fuel. Extensive research was performed in order to optimize the removal of oxide and metal impurities from the reactor's heat transfer salt, 2LiF-BeF{sub 2} (FLiBe). This was done by sparging a mixture of anhydrous hydrofluoric acid and hydrogen gas through the FLiBe at elevated temperatures. The hydrofluoric acid reacted with oxides and hydroxides, fluorinating them while simultaneously releasing water vapor. Metal impurities such as iron and chromium were reduced by hydrogen gas and filtered out of the salt. By removing these impurities, the corrosion of reactor components was minimized. The Univ. of Wisconsin - Madison is currently researching a new chemical purification process for fluoride salts that make use of a less dangerous cleaning gas, nitrogen trifluoride. Nitrogen trifluoride has been predicted as a superior fluorinating agent for fluoride salts. These purified salts will subsequently be used for static and loop corrosion tests on a variety of reactor materials to ensure materials compatibility for the new FHR designs. Demonstration of chemistry control methodologies along with potential reduction in corrosion is essential for the use of a fluoride salts in a next generator nuclear reactor system. (authors)

Kelleher, B. C.; Sellers, S. R.; Anderson, M. H.; Sridharan, K.; Scheele, R. D. [Dept. of Engineering Physics, Univ.of Wisconsin - Madison, 1500 Engineering Drive, Madison, WI 53706 (United States)

2012-07-01

271

Ligand(s)-to-metal charge transfer as a factor controlling the equilibrium constants of late first-row transition metal complexes: revealing the Irving-Williams thermodynamical series.  

PubMed

A unified relationship between the experimental formation constants and the ligand(s)-to-metal charge transfer values of versatile ligand complexes of late transition series first-row bivalent metal ions is uncovered. The latter property not only explicates the Irving-Williams series but also rationalizes quantitatively Pearson's concept of hard and soft acids and bases by correlating the gas-phase to aqueous solution-phase chemistry in a broad sense. PMID:25414118

Varadwaj, Pradeep R; Varadwaj, Arpita; Jin, Bih-Yaw

2015-01-14

272

Charge transfer in proton-helium collisions from low to high energy  

NASA Astrophysics Data System (ADS)

The cross section for charge transfer in proton-helium collisions has been computed in the energy range from 10 eV/u up to 10 MeV/u. Four different methods (full quantal time-independent and time-dependent methods, molecular and atomic basis set semi-classical approaches) valid in different energy regimes have been used to calculate the partial and total cross section for single-electron capture. The results are compared with previous theoretical calculations and experimental measurements and the different theoretical methods used are shown to be complementary for describing the charge transfer reaction. A fit of the cross section, valid for collision energies from 10 eV/u up to 10 MeV/u is presented based on these results.

Loreau, J.; Ryabchenko, S.; Vaeck, N.

2014-07-01

273

Charge-transfer induced magnetic field effects of nano-carbon heterojunctions.  

PubMed

Room temperature magnetic field effects have not been definitively observed in either single-walled carbon nanotubes (SWCNTs) or C?? under a small magnetic field due to their weak hyperfine interaction and slight difference of g-factor between positive and negative polarons. Here, we demonstrate charge-transfer induced magnetic field effects in nano-carbon C??-SWCNT bulk heterojunctions at room temperature, where the mechanism of magnetic field effects is verified using excited state transition modeling. By controlling SWCNT concentrations and interfacial interactions, nano-carbon heterojunctions exhibit tunability of charge-transfer density and room temperature magnetoconductance of 2.8% under 100?mT external magnetic field. External stimuli, such as electric field and photoexcitation, also play an important role in controlling the magnetic field effects of nano-carbon heterojunctions, which suggests that these findings could enable the control of optoelectronic properties of nano-carbon heterojunctions. PMID:25146555

Qin, Wei; Gong, Maogang; Shastry, Tejas; Hersam, Mark C; Ren, Shenqiang

2014-01-01

274

Charge-Transfer Induced Magnetic Field Effects of Nano-Carbon Heterojunctions  

NASA Astrophysics Data System (ADS)

Room temperature magnetic field effects have not been definitively observed in either single-walled carbon nanotubes (SWCNTs) or C60 under a small magnetic field due to their weak hyperfine interaction and slight difference of g-factor between positive and negative polarons. Here, we demonstrate charge-transfer induced magnetic field effects in nano-carbon C60-SWCNT bulk heterojunctions at room temperature, where the mechanism of magnetic field effects is verified using excited state transition modeling. By controlling SWCNT concentrations and interfacial interactions, nano-carbon heterojunctions exhibit tunability of charge-transfer density and room temperature magnetoconductance of 2.8% under 100 mT external magnetic field. External stimuli, such as electric field and photoexcitation, also play an important role in controlling the magnetic field effects of nano-carbon heterojunctions, which suggests that these findings could enable the control of optoelectronic properties of nano-carbon heterojunctions.

Qin, Wei; Gong, Maogang; Shastry, Tejas; Hersam, Mark C.; Ren, Shenqiang

2014-08-01

275

Charge Transfer in Collisions of C{sup +} with H and H{sup +} with C  

SciTech Connect

Charge transfer rate coefficients for collisions of C{sup +} with H and H{sup +} with C are presented for temperatures from 30,000 to 10{sup 7} K and from 10 to 10{sup 7} K, respectively. The rate coefficients were calculated from recommended cross sections deduced in a recent theoretical and experimental investigation that took into account previous measurements. Nonadiabatic radial coupling is the dominant mechanism for both reactions above {approximately}50,000 K, but for lower temperatures the reaction of H{sup +} with C proceeds primarily by radiative charge transfer. Implications, due to the magnitude of the rate coefficients, for various astrophysical environments are discussed. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}

Stancil, P.C.; Havener, C.C.; Krstic, P.S.; Schultz, D.R. [Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6372 (United States)] [Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6372 (United States); Kimura, M. [School of Allied Health Sciences, Yamaguchi University, Ube, Yamaguchi 755, Japan and Department of Physics, Rice University, Houston, TX 77251 (United States)] [School of Allied Health Sciences, Yamaguchi University, Ube, Yamaguchi 755, Japan and Department of Physics, Rice University, Houston, TX 77251 (United States); Gu, J.; Hirsch, G.; Buenker, R.J. [Theoretische Chemie, Bergische Universitaet-Gesamthochschule Wuppertal, Gaussstrasse 20, D-42097 Wuppertal (Germany)] [Theoretische Chemie, Bergische Universitaet-Gesamthochschule Wuppertal, Gaussstrasse 20, D-42097 Wuppertal (Germany); Zygelman, B. [W. M. Keck Laboratory for Computational Physics, Department of Physics, University of Nevada, Las Vegas, NV 89154-4002 (United States)] [W. M. Keck Laboratory for Computational Physics, Department of Physics, University of Nevada, Las Vegas, NV 89154-4002 (United States)

1998-08-01

276

Cross sections for charge transfer between mercury ions and other metals  

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

277

Intermediate vibronic coupling in charge transfer states: Comprehensive calculation of electronic excitations in sexithiophene crystal  

NASA Astrophysics Data System (ADS)

A comprehensive theory of linear vibronic coupling in a coupled manifold of Frenkel and charge-transfer states in an infinite molecular crystal is presented and applied for sexithiophene. The approach, valid in the intermediate-coupling regime, includes up to three-particle terms of the Philpott expansion, with the vibronic wavefunctions represented in the Lang-Firsov basis. As a stringent test, the scheme is used to reproduce the complete set of available sexithiophene absorption and electroabsorption spectra within a unified theoretical framework. The input is based primarily on independent calculations and to some extent on independent experiments, with explicit fitting contained within the limits set by the estimated inherent errors of a priori parameter estimates. Reasonably good quantitative agreement with experimental spectra is achieved. The results resolve some existing interpretational ambiguities and expose some peculiarities of electric field effect on vibronic eigenstates of Frenkel parentage, highlighting the role of charge-transfer interactions.

Stradomska, Anna; Kulig, Waldemar; Slawik, Micha?; Petelenz, Piotr

2011-06-01

278

Production and destruction of D/sup -/ by charge transfer in metal vapors  

SciTech Connect

Experimental studies of D/sup -/ collisions are of interest for basic physics, where experimental results can be used to test theoretical models for charge transfer, and for applications to ion sources for accelerators and for heating magnetically confined plasmas of interest for fusion. The high D/sup -/ yield from charge transfer in a thick cesium-vapor target is consistent with recent cross-section calculations and measurements. Recent theoretical calculations of cross sections in thick alkaline-earth-vapor targets, leading to prediction of a large D/sup -/ yield at low energy, have been partially confirmed in recent measurements, in which a D/sup -/ yield of 50% was observed at a D energy of 500 eV.

Schlachter, A.S.

1981-06-01

279

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

SciTech Connect

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.

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

280

Charge-Transfer Induced Magnetic Field Effects of Nano-Carbon Heterojunctions  

PubMed Central

Room temperature magnetic field effects have not been definitively observed in either single-walled carbon nanotubes (SWCNTs) or C60 under a small magnetic field due to their weak hyperfine interaction and slight difference of g-factor between positive and negative polarons. Here, we demonstrate charge-transfer induced magnetic field effects in nano-carbon C60-SWCNT bulk heterojunctions at room temperature, where the mechanism of magnetic field effects is verified using excited state transition modeling. By controlling SWCNT concentrations and interfacial interactions, nano-carbon heterojunctions exhibit tunability of charge-transfer density and room temperature magnetoconductance of 2.8% under 100?mT external magnetic field. External stimuli, such as electric field and photoexcitation, also play an important role in controlling the magnetic field effects of nano-carbon heterojunctions, which suggests that these findings could enable the control of optoelectronic properties of nano-carbon heterojunctions. PMID:25146555

Qin, Wei; Gong, Maogang; Shastry, Tejas; Hersam, Mark C.; Ren, Shenqiang

2014-01-01

281

Photoinduced Magnetism Caused by Charge-Transfer Excitations in Tetracyanoethylene-Based Organic Magnets  

NASA Astrophysics Data System (ADS)

The photoinduced magnetism in Mn-tetracyanoethylene (TCNE) molecule-based magnets is ascribed to charge-transfer excitations from manganese to TCNE. Charge-transfer energies are calculated using density functional theory; photoinduced magnetization is described using a model Hamiltonian based on a double-exchange mechanism. Photoexciting electrons from the manganese core spins into the lowest unoccupied orbital of TCNE with photon energies around 3 eV increase the magnetization through a reduction of the canting angle of the manganese core spins for an average electron density on TCNE less than one. When photoexciting with a smaller energy, divalent TCNE molecules are formed. The delocalization of the excited electron causes a local spin flip of a manganese core spin.

Erdin, Serkan; van Veenendaal, Michel

2006-12-01

282

Charge transfer complex in diketopyrrolopyrrole polymers and fullerene blends: Implication for organic solar cell efficiency  

NASA Astrophysics Data System (ADS)

Copolymers based on diketopyrrolopyrrole (DPP) have recently gained potential in organic photovoltaics. When blended with another acceptor such as PCBM, intermolecular charge transfer occurs which may result in the formation of charge transfer (CT) states. We present here the spectral photocurrent characteristics of two donor-acceptor DPP based copolymers, PDPP-BBT and TDPP-BBT, blended with PCBM to identify the CT states. The spectral photocurrent measured using Fourier-transform photocurrent spectroscopy (FTPS) and monochromatic photocurrent (PC) methods are compared with P3HT:PCBM, where the CT state is well known. PDPP-BBT:PCBM shows a stable CT state while TDPP-BBT does not. Our analysis shows that the larger singlet state energy difference between TDPP-BBT and PCBM along with the lower optical gap of TDPP-BBT obliterates the formation of a midgap CT state resulting in an enhanced photovoltaic efficiency over PDPP-BBT:PCBM.

Moghe, D.; Yu, P.; Kanimozhi, C.; Patil, S.; Guha, S.

2012-02-01

283

Analytical study for the charge-transfer complexes of losartan potassium  

Microsoft Academic Search

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 ?-acceptor iodine and various ?-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

Ibrahim A. Darwish

2005-01-01

284

Mixed Exciton–Charge-Transfer States in Photosystem II: Stark Spectroscopy on Site-Directed Mutants  

PubMed Central

We investigated the electronic structure of the photosystem II reaction center (PSII RC) in relation to the light-induced charge separation process using Stark spectroscopy on a series of site-directed PSII RC mutants from the cyanobacterium Synechocystis sp. PCC 6803. The site-directed mutations modify the protein environment of the cofactors involved in charge separation (PD1, PD2, ChlD1, and PheD1). The results demonstrate that at least two different exciton states are mixed with charge-transfer (CT) states, yielding exciton states with CT character: (PD2?+PD1??ChlD1)?673nm and (ChlD1?+PheD1??)?681nm (where the subscript indicates the wavelength of the electronic transition). Moreover, the CT state PD2+PD1? acquires excited-state character due to its mixing with an exciton state, producing (PD2+PD1?)??684nm. We conclude that the states that initiate charge separation are mixed exciton-CT states, and that the degree of mixing between exciton and CT states determines the efficiency of charge separation. In addition, the results reveal that the pigment-protein interactions fine-tune the energy of the exciton and CT states, and hence the mixing between these states. This mixing ultimately controls the selection and efficiency of a specific charge separation pathway, and highlights the capacity of the protein environment to control the functionality of the PSII RC complex. PMID:22853895

Romero, Elisabet; Diner, Bruce A.; Nixon, Peter J.; Coleman, Wiliam J.; Dekker, Jan P.; van Grondelle, Rienk

2012-01-01

285

Ultrafast structural pathway of charge transfer in n,n,n',n'-tetramethylethylenediamine.  

PubMed

We have explored the ultrafast molecular structural dynamics associated with charge transfer in N,N,N',N'-tetramethylethylenediamine using Rydberg fingerprint spectroscopy in conjunction with self-interaction corrected density functional theory. Excitation at 239 nm prepares the molecule in the Franck-Condon region of the 3s state with the charge localized on one of the two amine groups. As seen from the time-dependent Rydberg electron binding energies, the pathway of the rapidly ensuing dynamics leads through several structurally distinct conformers with various degrees of charge localization before reaching the fully charge-delocalized structure on a picosecond time scale. At several steps along the reaction path, the transient structures are identified through a comparison of the spectroscopically observed binding energies with computed values. The molecular structure is seen to evolve dynamically from an initially folded conformer to the stretched form that supports charge delocalization before an equilibrium sets in with forward and backward time constants of 1.19 (0.14) and 2.61 (0.31) ps, respectively. A coherent wavepacket motion in the charge-localized state with a period of 270 (17) fs and damping of 430 (260) fs is observed and tentatively assigned to the nitrogen umbrella motion. The damping time constant indicates the rate of the energy flow into other vibrations that are not activated by the optical excitation. PMID:25714009

Cheng, Xinxin; Zhang, Yao; Gao, Yan; Jónsson, Hannes; Weber, Peter M

2015-03-26

286

Aspects of artificial photosynthesis. Photosensitized electron transfer and charge separation in cationic surfactant vesicles  

Microsoft Academic Search

Electron transfer and charge separation have been investigated in cationic dioctadecyldimethylammonium chloride (DODAC) vesicles by laser spectroscopy. h-Methylphenothiazine (MPTH) and its long-chain analogue, N-dodecylphenothiazine (DPTH), were used as electron donors, while a surfactant derivative of tris(2,2'-bipyridine)ruthenium perchlorate, RuCââ(bpy)â\\/sup 2 +\\/, acted as the photoactive electron acceptor, DODAC vesicles organized these donor and acceptor molecules. RuCââ(bpy)â\\/sup 2 +\\/ molecules were anchored

Pierre P. Infelta; Michael Graetzel; Janos H. Fendler

1980-01-01

287

Charge transfer in collisions of Be3+ ions with H atoms  

NASA Astrophysics Data System (ADS)

The nonradiative charge-transfer processes for the Be3+(1s)+H(1s) collisions are investigated by the quantum-mechanical molecular orbital close-coupling method in the energy range of 0.01-10 keV/u. The radiative charge-transfer cross sections are calculated by the optical potential and semiclassical methods in the energy range 10-6-103 eV/u. The needed molecular data are obtained by the ab initio multireference single- and double-excitation configuration interaction method. Total and state-selective cross sections are presented and compared with other available theoretical data. Our calculation agrees well with the atomic orbital close-coupling results of Liu [L. Liu, D. Jakimovski, J. G. Wang, and R. K. Janev, J. Phys. BJPAPEH0953-407510.1088/0953-4075/43/14/144005 43, 144005 (2010)], but there exist some discrepancies with the semiclassical molecular orbital close-coupling results of Shimakura [N. Shimakura, J. Phys. BJPAMA40953-407510.1088/0953-4075/21/13/015 21, 2485 (1988)]. The present results show that the capture to Si2+(1s3l) states is dominant in the whole energy range with the exception of a narrow range of 2-4 keV/u. Rotational couplings play an important role not only in the state-selective cross sections, but also in the total charge-transfer results. At energies below 40 eV/u, the radiative charge transfer exceeds the nonradiative process.

Liu, C. H.; Wang, J. G.

2013-04-01

288

Ink-jet printing of organic metal electrodes using charge-transfer compounds  

Microsoft Academic Search

In this work the authors fabricated patterned thin films made of highly conductive organic charge-transfer complexes using the ink-jet printing technique. The overprinted films of BO9(C14-TCNQ)4 exhibit low sheet resistivity and are available for carrier injection and interconnection of organic field-effect transistors (FETs). The performance of pentacene thin film FETs, where the top contact and bottom contact are ink-jet-printed organic

M. Hiraoka; T. Hasegawa; Y. Abe; T. Yamada; Y. Tokura; H. Yamochi; G. Saito; T. Akutagawa; T. Nakamura

2006-01-01

289

Photo-induced charge transfer in fullerene-oligothiophene dyads - A quantum-chemical study  

NASA Astrophysics Data System (ADS)

The excited states of fullerene-oligothiophene dyads were studied by quantum-chemical methods in respect of their theoretical suitability as solar-cell materials. Compared to the constituents a significant extension of the absorption spectra to the red has been found caused by optically excitable charge transfer states. These states seem to be responsible for the low energy conversion efficiency of fullerene-oligothiophene dyads in photovoltaic devices.

Beenken, Wichard J. D.

2009-02-01

290

Statistics of charge transfer through impurities in strongly correlated 1D metals  

Microsoft Academic Search

We review recent advances in the field of full counting statistics (FCS) of charge transfer through impurities imbedded into strongly correlated one-dimensional metallic systems, modelled by Tomonaga-Luttinger liquids (TLLs). We concentrate on the exact analytic solutions for the cumulant generating function (CGF), which became available recently and apply these methods in order to obtain the FCS of a non-trivial contact

A. Komnik; B. Trauzettel; U. Weiss

2007-01-01

291

Imidazole as a parent ?-conjugated backbone in charge-transfer chromophores  

PubMed Central

Summary Research activities in the field of imidazole-derived push–pull systems featuring intramolecular charge transfer (ICT) are reviewed. Design, synthetic pathways, linear and nonlinear optical properties, electrochemistry, structure–property relationships, and the prospective application of such D-?-A organic materials are described. This review focuses on Y-shaped imidazoles, bi- and diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain. PMID:22423270

Kulhánek, Ji?í

2012-01-01

292

Photo-induced charge transfer in molecular materials based on Prussian blue analogs: A photoacoustic study  

Microsoft Academic Search

Photoacoustic spectra of molecular materials based on the assembling of the [Fe(CN)6] molecular block were recorded and evaluated. An intense absorption band around 600 nm was observed for compounds where the valence of the involved metals allows charge transfer through the CN ligand (inner photo-induced redox reactions). In the absence of this transition, only the signal corresponding to d-d transitions

S. Stolik; E. Reguera; S. A. Tomás; F. Sánchez-Sinencio

2005-01-01

293

Charge-Transfer Excitations Steer the Davydov Splitting and Mediate Singlet Exciton Fission in Pentacene  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments.

Beljonne, D.; Yamagata, H.; Brédas, J. L.; Spano, F. C.; Olivier, Y.

2013-05-01

294

Charge-transfer excitations steer the Davydov splitting and mediate singlet exciton fission in pentacene.  

PubMed

Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments. PMID:23767738

Beljonne, D; Yamagata, H; Brédas, J L; Spano, F C; Olivier, Y

2013-05-31

295

Ultrafast interfacial charge transfer dynamics in dye-sensitized and quantum dot solar cell  

NASA Astrophysics Data System (ADS)

Dye sensitized solar cell (DSSC) appeared to be one of the good discovery for the solution of energy problem. We have been involved in studying ultrafast interfacial electron transfer dynamics in DSSC using femtosecond laser spectroscopy. However it has been realized that it is very difficult to design and develop higher efficient one, due to thermodynamic limitation. Again in DSSC most of the absorbed photon energy is lost as heat within the cell, which apart from decreasing the efficiency also destabilizes the device. It has been realized that quantum dot solar cell (QDSC) are the best bet where the sensitizer dye molecules can be replaced by suitable quantum dot (QD) materials in solar cell. The quantum-confinement effect in semiconductors modifies their electronic structure, which is a very important aspect of these materials. For photovoltaic applications, a long-lived charge separation remains one of the most essential criteria. One of the problems in using QDs for photovoltaic applications is their fast charge recombination caused by nonradiative Auger processes, which occur predominantly at lower particle sizes due to an increase in the Coulomb interaction between electrons and holes. Various approaches, such as the use of metal-semiconductor composites, semiconductor-polymer composite, and semiconductor core-shell heterostructures, have been attempted to minimize the fast recombination between electrons and holes. To make higher efficient solar devices it has been realised that it is very important to understand charge carrier and electron transfer dynamics in QD and QD sensitized semiconductor nanostructured materials. In the present talk, we are going to discuss on recent works on ultrafast electron transfer dynamics in dye-sensitized TiO2 nanoparticles/film [1-12] and charge (electron/hole) transfer dynamics in quantum dot core-shell nano-structured materials [13-17].

Ghosh, Hirendra N.

2013-02-01

296

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

NASA Astrophysics Data System (ADS)

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 potential difference between the PMMA and the stainless steel. Furthermore, the current in air using the dual coaxial glass pipes was less than that using the ejector.

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

2012-12-01

297

A study of different modes of charge transfer to ground in upward lightning  

NASA Astrophysics Data System (ADS)

We examined simultaneous measurements of currents and close electric field changes, as well as high-speed video images, associated with pulses superimposed on the initial continuous current (ICC pulses) and M-components following return strokes in upward flashes initiated from the Gaisberg Tower in Austria. For tower-initiated lightning, upward leaders often create multiple branches below the cloud base that can facilitate initiation of transients at relatively low heights along the grounded channel carrying ICC of some tens to hundreds of amperes. In this situation, a conducting channel is present, which is necessary for the M-component mode of charge transfer to ground, but the excitation wave (leader), after entering the channel, cannot form a long-front downward M-wave, because of the relatively short distance between the entry (junction) point and the strike-object top. Clearly, two parallel channels, one previously existing and the other newly formed (or rejuvenated) are involved in the charge transfer, and there is a common channel section between the junction point and the strike object. We use the term "mixed mode of charge transfer to ground", to indicate that in the case of low junction point the "classical" M-component mode is not possible, even though a conducting channel to ground (an attribute of the M-component mode) is present. The mixed mode scenario is also applicable to impulsive processes during continuing currents following return strokes in upward lightning.

Zhou, Helin; Rakov, Vladimir A.; Diendorfer, Gerhard; Thottappillil, Rajeev; Pichler, Hannes; Mair, Martin

2015-04-01

298

Heme photolysis occurs by ultrafast excited state metal-to-ring charge transfer.  

PubMed

Ultrafast time-resolved resonance Raman spectra of carbonmonoxy hemoglobin (Hb), nitroxy Hb, and deoxy Hb are compared to determine excited state decay mechanisms for both ligated and unligated hemes. Transient absorption and Raman data provide evidence for a sequential photophysical relaxation pathway common to both ligated and unligated forms of Hb* (photolyzed heme), in which the excited state 1Q decays sequentially: 1Q-->Hb*I-->Hb*II-->Hb ground state. Consistent with the observed kinetics, the lifetimes of these states are <50 fs, approximately 300 fs, and approximately 3 ps for 1Q, Hb*I, and Hb*II, respectively. The transient absorption data support the hypothesis that the Hb*I state results from an ultrafast iron-to-porphyrin ring charge transfer process. The Hb*II state arises from porphyrin ring-to-iron back charge transfer to produce a porphyrin ground state configuration a nonequilibrium iron d-orbital population. Equatorial d-pi* back-bonding of the heme iron to the porphyrin during the lifetime of the Hb*II state accounts for the time-resolved resonance Raman shifts on the approximately 3 ps time scale. The proposed photophysical pathway suggests that iron-to-ring charge transfer is the key event in the mechanism of photolysis of diatomic ligands following a porphyrin ring pi-pi* transition. PMID:11325737

Franzen, S; Kiger, L; Poyart, C; Martin, J L

2001-05-01

299

Charge Transfer in Collisions between Diatomic Molecular Ions and Atomic Hydrogen Using Merged Beams  

SciTech Connect

A merged-beams technique is used to measure charge transfer (CT) cross sections for the (O2+,D) and (CO+,D) systems from 2 keV/u to 20 eV/u, which covers a wide range of energy: high energies where the collision is ro-vibrationally frozen to low energies where ro-vibrational modes become important. At high energies where the differences in the Q-values of the CT process can be neglected, the cross sections all converge to (7.5 0.5) x 10-16 cm2 at 2 keV/u and are consistent with a H2+ + H calculation which assumes the ro-vibrational modes are frozen. Toward lower velocities, (O2+,D) and (CO+,D) have consistently similar cross sections, as one might expect from the comparison of their characteristic vibrational time, but diverge below 60eV/u. In contrast, previously reported merged-beams measurements for (D2+,H), a system with fewer electrons on the molecular core, no electronic excited states and with relatively less charge transfer channels, shows a decreasing cross section toward lower energies. These different trends are compared to merged-beams measurements of charge transfer for several 4+ atomic ions that have a different number of electrons on the core.

Andrianarijaona, V. M. [Pacific Union College; Draganic, Ilija N [ORNL; Seely, D. G. [Albion College; Havener, Charles C [ORNL

2011-01-01

300

The charge transfer characteristic of tetraphenylporphyrin iron chloride Langmuir-Blodgett films  

NASA Astrophysics Data System (ADS)

The charge transfer characteristic of tetraphenylporphyrin iron (III) chloride (FeP) Langmuir-Blodgett (LB) films on the surface of the ITO glass electrode was reported. When the cyclic voltammetry (CV) scanning was running, the charge transfer characteristic was controlled by the oxidation-reduction process of Fe(III)/Fe(II). The charge transfer characteristic was related to the following factors: the cross-sectional area, relative to the electrode, of FeP as the electron donor (or acceptor). The greater the cross-sectional area of the aggregation of FeP as the electron donor (or acceptor) was, the larger the number of the donated (or accepted) electrons was. The projected area of the cross-section on the ITO electrode. The greater the projected area was, the larger the number of the donated (or accepted) electrons was. The distance between the center of the electron donor (or acceptor) of FeP and the surface of ITO electrode. The smaller the distance was, the greater the rate of donating (or accepting) electrons was. The monolayer coverage, which formed because of the FeP lying on the ITO surface in the form of the monomer and aggregate, was more sensitive to detect oxygen.

Du, Y.; Li, Z. H.; Qi, P.; Wang, F.; Liu, D.

2013-11-01

301

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

PubMed

Organic charge transfer cocrystals are inexpensive, modular, and solution-processable materials that are able, in some instances, to exhibit properties such as optical nonlinearity, (semi)conductivity, ferroelectricity, and magnetism. Although the properties of these cocrystals have been investigated for decades, the principal challenge that researchers face currently is to devise an efficient approach which allows for the growth of high-quality crystalline materials, in anticipation of a host of different technological applications. The research reported here introduces an innovative design, termed LASO-lock-arm supramolecular ordering-in the form of a modular approach for the development of responsive organic cocrystals. The strategy relies on the use of aromatic electronic donor and acceptor building blocks, carrying complementary rigid and flexible arms, capable of forming hydrogen bonds to amplify the cocrystallization processes. The cooperativity of charge transfer and hydrogen-bonding interactions between the building blocks leads to binary cocrystals that have alternating donors and acceptors extending in one and two dimensions sustained by an intricate network of hydrogen bonds. A variety of air-stable, mechanically robust, centimeter-long, organic charge transfer cocrystals have been grown by liquid-liquid diffusion under ambient conditions inside 72 h. These cocrystals are of considerable interest because of their remarkable size and stability and the promise they hold when it comes to fabricating the next generation of innovative electronic and photonic devices. PMID:25369425

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

2014-12-10

302

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

E-print Network

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

J. Loreau; K. Sodoga; D. Lauvergnat; M. Desouter-Lecomte; N. Vaeck

2010-06-02

303

Charge transfer inefficiency in the Hubble Space Telescope since Servicing Mission 4  

NASA Astrophysics Data System (ADS)

We update a physically motivated model of radiation damage in the Hubble Space Telescope Advanced Camera for Surveys/Wide Field Channel, using data up to mid-2010. We find that charge transfer inefficiency increased dramatically before shuttle Servicing Mission 4, with ~1.3 charge traps now present per pixel. During detector readout, charge traps spuriously drag electrons behind all astronomical sources, degrading image quality in a way that affects object photometry, astrometry and morphology. Our detector readout model is robust to changes in operating temperature and background level, and can be used to iteratively remove the trailing by pushing electrons back to where they belong. The result is data taken in mid-2010 that recovers the quality of imaging obtained within the first six months of orbital operations.

Massey, Richard

2010-11-01

304

Charge transfer collisions of Si^3+ with H at low energies  

NASA Astrophysics Data System (ADS)

Charge transfer of positively charged ions with atomic hydrogen is important not only in magnetically confined plasmas between impurity ions and H atoms from the chamber walls influences the overall ionization balance and effects the plasma cooling but also in astrophysics, where it plays a key role in determining the properties of the observed gas. It also provides a recombination mechanism for multiply charged ions in X-ray ionized astronomical environments. We report an investigation using the molecular-orbital close-coupling (MOCC) method, both quantum mechanically and semi-classically, in the adiabatic representation. Ab initio adiabatic potentials and coupling matrix elements--radial and angular--are calculated using the MRD-CI method. Comparison of our results with other theoretical as well as experimental findings will be discussed.

Joseph, D. C.; Gu, J. P.; Saha, B. C.

2009-11-01

305

Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO2(110).  

PubMed

The d-orbital contribution from the transition metal centers of phthalocyanine brings difficulties to understand the role of the organic ligands and their molecular frontier orbitals when it adsorbs on oxide surfaces. Here we use zinc phthalocyanine (ZnPc)/TiO(2)(110) as a model system where the zinc d-orbitals are located deep below the organic orbitals leaving room for a detailed study of the interaction between the organic ligand and the substrate. A charge depletion from the highest occupied molecular orbital is observed, and a consequent shift of N1s and C1s to higher binding energy in photoelectron spectroscopy (PES). A detailed comparison of peak shifts in PES and near-edge X-ray absorption fine structure spectroscopy illustrates a slightly uneven charge distribution within the molecular plane and an inhomogeneous charge transfer screening between the center and periphery of the organic ligand: faster in the periphery and slower at the center, which is different from other metal phthalocyanine, e.g., FePc/TiO(2). Our results indicate that the metal center can substantially influence the electronic properties of the organic ligand at the interface by introducing an additional charge transfer channel to the inner molecular part. PMID:22519339

Yu, Shun; Ahmadi, Sareh; Sun, Chenghua; Adibi, Pooya Tabib Zadeh; Chow, Winnie; Pietzsch, Annette; Göthelid, Mats

2012-04-21

306

Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO2(110)  

NASA Astrophysics Data System (ADS)

The d-orbital contribution from the transition metal centers of phthalocyanine brings difficulties to understand the role of the organic ligands and their molecular frontier orbitals when it adsorbs on oxide surfaces. Here we use zinc phthalocyanine (ZnPc)/TiO2(110) as a model system where the zinc d-orbitals are located deep below the organic orbitals leaving room for a detailed study of the interaction between the organic ligand and the substrate. A charge depletion from the highest occupied molecular orbital is observed, and a consequent shift of N1s and C1s to higher binding energy in photoelectron spectroscopy (PES). A detailed comparison of peak shifts in PES and near-edge X-ray absorption fine structure spectroscopy illustrates a slightly uneven charge distribution within the molecular plane and an inhomogeneous charge transfer screening between the center and periphery of the organic ligand: faster in the periphery and slower at the center, which is different from other metal phthalocyanine, e.g., FePc/TiO2. Our results indicate that the metal center can substantially influence the electronic properties of the organic ligand at the interface by introducing an additional charge transfer channel to the inner molecular part.

Yu, Shun; Ahmadi, Sareh; Sun, Chenghua; Adibi, Pooya Tabib Zadeh; Chow, Winnie; Pietzsch, Annette; Göthelid, Mats

2012-04-01

307

Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO{sub 2}(110)  

SciTech Connect

The d-orbital contribution from the transition metal centers of phthalocyanine brings difficulties to understand the role of the organic ligands and their molecular frontier orbitals when it adsorbs on oxide surfaces. Here we use zinc phthalocyanine (ZnPc)/TiO{sub 2}(110) as a model system where the zinc d-orbitals are located deep below the organic orbitals leaving room for a detailed study of the interaction between the organic ligand and the substrate. A charge depletion from the highest occupied molecular orbital is observed, and a consequent shift of N1s and C1s to higher binding energy in photoelectron spectroscopy (PES). A detailed comparison of peak shifts in PES and near-edge X-ray absorption fine structure spectroscopy illustrates a slightly uneven charge distribution within the molecular plane and an inhomogeneous charge transfer screening between the center and periphery of the organic ligand: faster in the periphery and slower at the center, which is different from other metal phthalocyanine, e.g., FePc/TiO{sub 2}. Our results indicate that the metal center can substantially influence the electronic properties of the organic ligand at the interface by introducing an additional charge transfer channel to the inner molecular part.

Yu Shun; Ahmadi, Sareh; Adibi, Pooya Tabib Zadeh; Chow, Winnie; Goethelid, Mats [Materials Physics, ICT, Royal Institute of Technology, Electrum 229, SE-16440 Stockholm (Sweden); Sun, Chenghua [University of Queensland, ARC Centre of Excellence for Functional Nanomaterials and Centre for Computational Molecular Science, Australia Institute for Bioengineering and Nanotechnology, University of Queensland, Qld 4072 (Australia); Pietzsch, Annette [Max-lab, Lund University, Box 118, SE- 22100 Lund (Sweden)

2012-04-21

308

Tuning the entanglement between orbital reconstruction and charge transfer at a film surface  

PubMed Central

The interplay between orbital, charge, spin, and lattice degrees of freedom is at the core of correlated oxides. This is extensively studied at the interface of heterostructures constituted of two-layer or multilayer oxide films. Here, we demonstrate the interactions between orbital reconstruction and charge transfer in the surface regime of ultrathin (La,Sr)MnO3, which is a model system of correlated oxides. The interactions are manipulated in a quantitative manner by surface symmetry-breaking and epitaxial strain, both tensile and compressive. The established charge transfer, accompanied by the formation of oxygen vacancies, provides a conceptually novel vision for the long-term problem of manganites—the severe surface/interface magnetization and conductivity deterioration. The oxygen vacancies are then purposefully tuned by cooling oxygen pressure, markedly improving the performances of differently strained films. Our findings offer a broad opportunity to tailor and benefit from the entanglements between orbit, charge, spin, and lattice at the surface of oxide films. PMID:24569650

Cui, B.; Song, C.; Li, F.; Wang, G. Y.; Mao, H. J.; Peng, J. J.; Zeng, F.; Pan, F.

2014-01-01

309

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

SciTech Connect

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 the earlier work of Wu and Van Voorhis [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 Ru{sup 2+}-Ru{sup 3+} 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. The smaller value for the reorganization free energy can be explained by the fact that the Ru-O distances of the divalent and trivalent Ru hexahydrates are predicted to be more similar in the electron transfer complex than for the separated aqua ions.

Oberhofer, Harald; Blumberger, Jochen [Department of Chemistry, University of Cambridge, Cambridge CB2 1EW (United Kingdom)

2009-08-14

310

Chemistry  

NSDL National Science Digital Library

These sites willhelp you gain greater understanding of Chemistry! Weather is also available Three areas to be on the test. STUDY HARD!!!! Equations Types of Equations Types of Equations text/htmlMichigan Teacher Network Matter Density of solids Density of solids text/htmlICSD ScienceZone Metals Kidneys and Metals Problem Set Kidneys and Metals Problem Set image/tiffCenter for Digital Curriculum Research POTENTIAL SURROGATE METALS FOR INCINERATOR TRIAL BURNS POTENTIAL SURROGATE METALS FOR INCINERATOR TRIAL BURNS text/html Let it snow Interactive Weather Maker Interactive Weather Maker urlexample ...

Riley

2006-04-22

311

Calculations of [ital Q] values in single- and double-charge-transfer collisions of highly charged ions with atoms  

SciTech Connect

Close-coupling calculations are carried out for the [ital Q] values for electron capture processes in collisions of multiply charged ions with atoms over a broad range of energies. For single-capture processes the results for N[sup 7+]+He and O[sup 8+]+He collisions are in good agreement with the experimental data of Wu [ital et] [ital al]. [preceding paper, Phys. Rev. A 50, 502 (1994)]. To compare with the experimental [ital Q] values for the transfer ionization (TI) and the true double-capture (TDC) processes, an independent-electron model was used to calculate double-electron-capture cross sections. By combining with the calculated average fluorescence yields, the theoretical [ital Q] values for TI and TDC processes are also found to be in fair agreement with the experimental data. We also compared the [ital Q] values calculated by the close-coupling method and by the classical-trajectory Monte Carlo method.

Chen, Z.; Lin, C.D. (Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601 (United States)); Toshima, N. (Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305 (Japan))

1994-07-01

312

Charge transfer by electronic excitation: Direct measurement by high resolution spectroscopy in the gas phase.  

PubMed

We report a quantitative measurement of the amount of charge that is transferred when the single ammonia complex of the photoacid beta-naphthol (2HNA) is excited by light. The measurement was made by comparing the permanent electric dipole moments of cis-2HNA in its ground (S(0)) and excited (S(1)) states, determined by Stark-effect studies of its fully resolved S(1)<--S(0) electronic spectrum. While the increase in electron transfer from the donor (NH(3)) to the acceptor (2HN) upon excitation is small ( approximately 0.05e), it is sufficient to redshift the electronic spectrum of the complex by approximately 600 cm(-1) ( approximately 0.1 eV). Thereby explored is the incipient motion of the acid-base complex along the excited state (electron-coupled) proton transfer coordinate. PMID:19968329

Fleisher, A J; Morgan, P J; Pratt, D W

2009-12-01

313

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

USGS Publications Warehouse

A molecular orbital description, based on X??-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(t2 g) and Ti(t2 g) 3 d orbitals. ?? 1987 Springer-Verlag.

Sherman, D.M.

1987-01-01

314

Synergetic approach to many-body problems: From scattering charge transfer to arrays of quantum dots  

NASA Astrophysics Data System (ADS)

We call synergetic an approach in which the use of analytical and numerical methods interweave, the results naturally complimenting each other. Analytical results improve numerical approximations and vice versa. We apply this philosophy to two particularly interesting many-body problems involving charge transfer. First, we consider charge transfer between alkali atoms and metallic scattering surfaces. The question is this: what is the final charge state of an atom scattered off a metal surface as a function of its initial state and other experimental parameters, such as atom's velocity and surface work function? We use a generalized time-dependent Newns-Anderson Hamiltonian which includes electron spin, multiple atomic orbitals with image shifted levels, intra-atomic Coulomb repulsion, and resonant exchange. A variational electronic many-body wave function solves the dynamical problem. The wave function consists of sectors with either zero, one, or two particle-hole pairs: the wave function ansatz is equivalent to a 1/N expansion (we set N = 2 for the physical case of electrons). The equations of motion are integrated numerically without further approximation. The solution shows loss-of-memory--the final charge state is independent of the initial one--in agreement with theoretical and experimental expectations. We develop a picture of probability flow between different sectors of the Hilbert space, and show that retaining sectors up to the second order in 1/N is sufficient for an accurate description of charge transfer. As further tests of the theory, we reproduce the experimentally observed peak in the excited neutral Li(2p) occupancy at intermediate work functions starting from different initial conditions. We include Auger processes by adding two-body interaction terms to the many-body Hamiltonian. Preliminary experimental evidence for an upturn in the Li(2p) occupancy at the lowest work-functions may be explained by Auger transitions. Next, we turn our attention to a different class of physical systems which involve charge transfer, namely arrays of semiconducting quantum dots. The physics of these structures is rich, as novel phases are attainable. We find conditions under which enhanced symmetry characterized by the group SU(4) occurs in isolated semiconducting quantum dots. A Hubbard model then describes a pillar array of coupled dots and at half-filling it can be mapped onto a SU(4) spin chain, which has a reach phase diagram. The chain spontaneously dimerizes which we confirm numerically by using a recent numerical technique--the Density Matrix Renormalization Group (DMRG). We suggest further improvements to the method. Our DMRG analysis also shows that this state is robust to perturbations which break SU(4) symmetry. We propose ways to experimentally verify the phases.

Onufriev, Alexey Vlad

315

Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes.  

PubMed

The Born-Oppenheimer approximation refers to the assumption that the nuclear and electronic wave functions describing a molecular system evolve and can be determined independently. It is now well-known that this approximation often breaks down and that nuclear-electronic (vibronic) coupling contributes greatly to the ultrafast photophysics and photochemistry observed in many systems ranging from simple molecules to biological organisms. In order to probe vibronic coupling in a time-dependent manner, one must use spectroscopic tools capable of correlating the motions of electrons and nuclei on an ultrafast time scale. Recent developments in nonlinear multidimensional electronic and vibrational spectroscopies allow monitoring both electronic and structural factors with unprecedented time and spatial resolution. In this Account, we present recent studies from our group that make use of different variants of frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy, a pulse sequence combining electronic and vibrational excitations in the form of a UV-visible pump, a narrowband (12 cm(-1)) IR pump, and a broadband (400 cm(-1)) IR probe. In the first example, T-2DIR is used to directly compare vibrational dynamics in the ground and relaxed electronic excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine) and Ru(4,4'-diethylester-2,2'-bipyridine)2(NCS)2, prototypical charge transfer complexes used in photocatalytic CO2 reduction and electron injection in dye-sensitized solar cells. The experiments show that intramolecular vibrational redistribution (IVR) and vibrational energy transfer (VET) are up to an order of magnitude faster in the triplet charge transfer excited state than in the ground state. These results show the influence of electronic arrangement on vibrational coupling patterns, with direct implications for vibronic coupling mechanisms in charge transfer excited states. In the second example, we show unambiguously that electronic and vibrational movement are coupled in a donor-bridge-acceptor complex based on a Pt(II) trans-acetylide design motif. Time-resolved IR (TRIR) spectroscopy reveals that the rate of electron transfer (ET) is highly dependent on the amount of excess energy localized on the bridge following electronic excitation. Using an adaptation of T-2DIR, we are able to selectively perturb bridge-localized vibrational modes during charge separation, resulting in the donor-acceptor charge separation pathway being completely switched off, with all excess energy redirected toward the formation of a long-lived intraligand triplet state. A series of control experiments reveal that this effect is mode specific: it is only when the high-frequency bridging C?C stretching mode is pumped that radical changes in photoproduct yields are observed. These experiments therefore suggest that one may perturb electronic movement by stimulating structural motion along the reaction coordinate using IR light. These studies add to a growing body of evidence suggesting that controlling the pathways and efficiency of charge transfer may be achieved through synthetic and perturbative approaches aiming to modulate vibronic coupling. Achieving such control would represent a breakthrough for charge transfer-based applications such as solar energy conversion and molecular electronics. PMID:25789559

Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Weinstein, Julia A

2015-04-21

316

Charge transfer dissociation (CTD) mass spectrometry of peptide cations using kiloelectronvolt helium cations.  

PubMed

A kiloelectronvolt beam of helium ions is used to ionize and fragment precursor peptide ions starting in the 1+ charge state. The electron affinity of helium cations (24.6 eV) exceeds the ionization potential of protonated peptides and can therefore be used to abstract an electron from--or charge exchange with--the isolated precursor ions. Kiloelectronvolt energies are used, (1) to overcome the Coulombic repulsion barrier between the cationic reactants, (2) to overcome ion-defocussing effects in the ion trap, and (3) to provide additional activation energy. Charge transfer dissociation (CTD) of the [M+H](+) precursor of Substance P gives product ions such as [M+H](2+•) and a dominant series of a ions in both the 1+ and 2+ charge states. These observations, along with the less-abundant a + 1 ions, are consistent with ultraviolet photodissociation (UVPD) results of others and indicate that C-C(?) cleavages are possible through charge exchange with helium ions. Although the efficiencies and timescale of CTD are not yet suitable for on-line chromatography, this new approach to ion activation provides an additional potential tool for the interrogation of gas phase ions. PMID:25231159

Hoffmann, William D; Jackson, Glen P

2014-11-01

317

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

SciTech Connect

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

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

2014-01-07

318

Formation of a green-form TTF-CA charge transfer complex confirmed with terahertz transmission spectrum  

NASA Astrophysics Data System (ADS)

The green polymorph of tetrathiafulvalene-p-chloranil (TTF-CA) charge transfer complex was synthesized by grinding fine powders of TTF and CA. The polymorph was identified using terahertz spectroscopy.

Tanno, Takenori; Oohashi, Takahiro

319

Spectroscopic study of excited state intramolecular charge transfer in ethyl ester of N,N?-Dimethylaminonaphthyl-(acrylic)-acid  

NASA Astrophysics Data System (ADS)

In this work, we have studied the twisted intramolecular charge transfer process in ethyl ester of N, N'-Dimethylaminonaphthyl-(acrylic)-acid (EDMANA) using absorption and emission spectroscopy. Single conformer of EDMANA present in the ground state gives rise to local and charge transfer emission in different solvents. Solvatochromic effect on the Stokes shifted emission band clearly indicates the charge transfer character of the emitting singlet excited state. Considering twisted intramolecular charge transfer model, the ground and excited state properties of EDMANA have been evaluated along the donor and acceptor twisting coordinates separately using density functional theory (DFT) and time dependent density functional theory (TDDFT), respectively, with B3LYP functional and 6-31G basis set. The effect of solvent on the spectral properties has been explored theoretically at the same level with time dependent density functional theory-polarized continuum model (TDDFT-PCM) and the theoretical results support the solvent polarity dependent Stokes shifted emission of EDMANA molecule.

Singh, Rupashree Balia; Mahanta, Subrata; Kar, Samiran; Guchhait, Nikhil

2007-12-01

320

First Year Chemistry Laboratory Courses for Distance Learners: Development and Transfer Credit Acceptance  

ERIC Educational Resources Information Center

In delivering chemistry courses by distance, a key challenge is to offer the learner an authentic and meaningful laboratory experience that still provides the rigour required to continue on in science. To satisfy this need, two distance general chemistry laboratory courses appropriate for Bachelor of Science (B.Sc.) students, including chemistry…

Brewer, Sharon E.; Cinel, Bruno; Harrison, Michelle; Mohr, Christina L.

2013-01-01

321

On the Photometric Consequences of Charge-Transfer Inefficiency in WFPC2  

E-print Network

Charge-transfer effects in photometry with Wide Field Planetary Camera 2 aboard the Hubble Space Telescope are investigated by a comparison of WFPC2 observations with groundbased photometry for the Galactic globular clusters omega Centauri and NGC 2419. Simple numerical formulae describing the fraction of lost signal as functions of position on the detector, stellar brightness, and the diffuse sky brightness recorded in an image are presented, and the resulting corrections are compared to those previously derived by Whitmore & Heyer (1997, Instrument Science Report WFPC2 97-08). Significant lost-charge effects are seen that are proportional to both the Y coordinate (i.e., the number of shifts along the parallel register during readout) and the X coordinate (number of shifts along the serial register). The percentage of charge lost decreases as the star brightness or the diffuse sky brightness increases. Charge losses during the brief period when WFPC2 was operated at a temperature of -76 degrees C were approximately 85% greater, but apart from that no significant change in the charge transfer losses with time during the first 3.5 years of WFPC2's mission is evident, except possibly a weak effect for the very faintest star images. These results are quite similar to those of Whitmore & Heyer, which were based on a much smaller data set, but there are some differences in detail. Even with the present set of corrections, additional sources of calibration uncertainty which I am unable identify or characterize with the available data probably limit the external accuracy of photometry from WFPC2 to of order 1-2%.

Peter B. Stetson

1998-10-02

322

Coherence, Energy and Charge Transfers in De-Excitation Pathways of Electronic Excited State of Biomolecules in Photosynthesis  

NASA Astrophysics Data System (ADS)

The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin-chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used Förster-Dexter theory, which does not allow for charge transfer, is a special case of B-A theory. The latter could, under appropriate circumstances, lead to excimers.

Bohr, Henrik G.; Malik, F. Bary

2013-11-01

323

Charge transfer between a laser-cooled ion and a thermal atom in a radio-frequency trap  

Microsoft Academic Search

The charge transfer process between a laser-cooled magnesium ion and a thermal barium atom in a radio-frequency ion trap in extremely low energy regime is observed. The merit of using the trap is that the generated ions are also confined in the trap. The occurrence of the charge transfer process is confirmed by the detection of the laser-induced fluorescence from

Taro Hasegawa; Tadao Shimizu

2000-01-01

324

Effects of partial charge-transfer solute -- solvent interactions in absorption spectra of aromatic hydrocarbons in aqueous and alcoholic solutions  

E-print Network

A method for study of charge-transfer interactions between solute molecules and solvent based on the comparison of the ratios of spectral shifts of different electronic transitions in solute molecules in chemically inert solvent is proposed. The method is applicable to molecules that do not change their dipole moment on excitation. As an example, a presence of charge transfer interactions in higher electronic states of aromatic hydrocarbons (benzene, phenanthrene, and naphthalene) dissolved in water and alcohols was demonstrated.

Ar'ev, I A; Solovieva, E A

2013-01-01

325

Effects of partial charge-transfer solute -- solvent interactions in absorption spectra of aromatic hydrocarbons in aqueous and alcoholic solutions  

E-print Network

A method for study of charge-transfer interactions between solute molecules and solvent based on the comparison of the ratios of spectral shifts of different electronic transitions in solute molecules in chemically inert solvent is proposed. The method is applicable to molecules that do not change their dipole moment on excitation. As an example, a presence of charge transfer interactions in higher electronic states of aromatic hydrocarbons (benzene, phenanthrene, and naphthalene) dissolved in water and alcohols was demonstrated.

I. A. Ar'ev; N. I. Lebovka; E. A. Solovieva

2013-03-03

326

Charge-Transfer States and Upper Limit of the Open-Circuit Voltage in Polymer:Fullerene Organic Solar Cells  

Microsoft Academic Search

The power conversion efficiency of polymer:fullerene bulk heterojunction solar cells depends on the generated photocurrent and photovoltage. Here we show, using the thermodynamic theory of detailed balance, that the photovoltage in particular is limited by the presence of polymer:fullerene material interaction, resulting in the formation of a weak donor-acceptor charge transfer complex (CTC). Excited CTCs, or charge transfer (CT) states,

Koen Vandewal; Kristofer Tvingstedt; Jean V. Manca; Olle Inganas

2010-01-01

327

A combined experimental and theoretical study on photoinduced intramolecular charge transfer in trans-ethyl p-(dimethylamino)cinamate  

Microsoft Academic Search

Intramolecular charge transfer (ICT) behavior of trans-ethyl p-(dimethylamino)cinamate (EDAC) in various solvents has been studied by steady-state absorption and emission, picosecond time-resolved fluorescence spectroscopy and femtosecond transient absorption experiments as well as time-dependent density functional theory (TDDFT). Large fluorescence spectral shift in more polar solvents indicates an efficient charge transfer from the donor site to the acceptor moiety in the

T. Sanjoy Singh; S. Mitra; A. K. Chandra; N. Tamai; S. Kar

2008-01-01

328

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

SciTech Connect

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).

Schlueter, J. A.

1998-10-14

329

Ultrafast dynamics of solvation and charge transfer in a DNA-based biomaterial.  

PubMed

Charge migration along DNA molecules is a key factor for DNA-based devices in optoelectronics and biotechnology. The association of a significant amount of water molecules in DNA-based materials for the intactness of the DNA structure and their dynamic role in the charge-transfer (CT) dynamics is less documented in contemporary literature. In the present study, we have used a genomic DNA-cetyltrimethyl ammonium chloride (CTMA) complex, a technological important biomaterial, and Hoechest 33258 (H258), a well-known DNA minor groove binder, as fluorogenic probe for the dynamic solvation studies. The CT dynamics of CdSe/ZnS quantum dots (QDs; 5.2?nm) embedded in the as-prepared and swollen biomaterial have also been studied and correlated with that of the timescale of solvation. We have extended our studies on the temperature-dependent CT dynamics of QDs in a nanoenvironment of an anionic, sodium bis(2-ethylhexyl)sulfosuccinate reverse micelle (AOT RMs), whereby the number of water molecules and their dynamics can be tuned in a controlled manner. A direct correlation of the dynamics of solvation and that of the CT in the nanoenvironments clearly suggests that the hydration barrier within the Arrhenius framework essentially dictates the charge-transfer dynamics. PMID:24665050

Choudhury, Susobhan; Batabyal, Subrata; Mondol, Tanumoy; Sao, Dilip; Lemmens, Peter; Pal, Samir Kumar

2014-05-01

330

Charge-transfer-based Gas Sensing Using Atomic-layer MoS2  

PubMed Central

Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules. PMID:25623472

Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho

2015-01-01

331

Charge-transfer-based gas sensing using atomic-layer MoS2.  

PubMed

Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules. PMID:25623472

Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M; Kim, Dong-Ho

2015-01-01

332

An improved model of charge transfer inefficiency and correction algorithm for the Hubble Space Telescope  

NASA Astrophysics Data System (ADS)

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 per cent 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 untrailed during post-processing.

Massey, Richard; Schrabback, Tim; Cordes, Oliver; Marggraf, Ole; Israel, Holger; Miller, Lance; Hall, David; Cropper, Mark; Prod'homme, Thibaut; Niemi, Sami-Matias

2014-03-01

333

Fowler-Nordheim tunneling induced charge transfer plasmons between nearly touching nanoparticles.  

PubMed

Reducing the gap between two metal nanoparticles down to atomic dimensions uncovers novel plasmon resonant modes. Of particular interest is a mode known as the charge transfer plasmon (CTP). This mode has been experimentally observed in touching nanoparticles, where charges can shuttle between the nanoparticles via a conductive path. However, the CTP mode for nearly touching nanoparticles has only been predicted theoretically to occur via direct tunneling when the gap is reduced to ~0.4 nm. Because of challenges in fabricating and characterizing gaps at these dimensions, experiments have been unable to provide evidence for this plasmon mode that is supported by tunneling. In this work, we consider an alternative tunneling process, that is, the well-known Fowler-Nordheim (FN) tunneling that occurs at high electric fields, and apply it for the first time in the theoretical investigation of plasmon resonances between nearly touching nanoparticles. This new approach relaxes the requirements on gap dimensions, and intuitively suggests that with a sufficiently high-intensity irradiation, the CTP can be excited via FN tunneling for a range of subnanometer gaps. The unique feature of FN tunneling induced CTP is the ability to turn on and off the charge transfer by varying the intensity of an external light source, and this could inspire the development of novel quantum devices. PMID:23215253

Wu, Lin; Duan, Huigao; Bai, Ping; Bosman, Michel; Yang, Joel K W; Li, Erping

2013-01-22

334

Quantitative femtosecond charge transfer dynamics at organic/electrode interfaces studied by core-hole clock spectroscopy.  

PubMed

Organic semiconductor materials have important applications in organic electronics and other novel hybrid devices. In these devices, the transport of charge carriers across the interfaces between organic molecules and electrodes plays an important role in determining the device performance. Charge transfer dynamics at the organic/electrode interface usually occurs at the several femtoseconds timescale, and quantitative charge transfer dynamics data can been inferred using synchrotron-based core-hole clock (CHC) spectroscopy. In this research news, we have reviewed recent progress in the applications of CHC spectroscopy on the quantitative characterization of charge transfer dynamics at organic/electrode interfaces. By examining charge transfer dynamics at different types of interface, from weakly interacting van der Waals-type interfaces to interfaces with strong covalent bonds, we discuss a few factors that have been found to affect the charge transfer dynamics. We also review the application of CHC spectroscopy to quantify through-bonds and through-space charge transport in organic molecules. PMID:24692009

Cao, Liang; Gao, Xing-Yu; Wee, Andrew T S; Qi, Dong-Chen

2014-12-10

335

Non-Radiative Relaxation of Electronically Excited DNA Oligomers: Proton Coupled Charge Transfer  

NASA Astrophysics Data System (ADS)

We address possible relaxation mechanisms of electronically excited DNA oligomers with a combined quantum mechanics/molecular mechanics (QM/MM) approach. Using long-range corrected density functional theory (LRC-DFT), we show that charge transfer (CT) states between neighboring nucleobases appear at energies just above optically bright ^{1}??^{ast} excitonic states in aqueous solution. In double stranded DNA systems, both intrastrand and interstrand CT states are observed. It has been hypothesized that excitonic states may decay via a conical intersection into a CT state on a subpicosecond timescale. The proximity in energy of such states in out calculations appears consistent with this claim. Assuming that such a non-radiative mechanism occurs, we investigate subsequent relaxation of CT states by constructing and optimizing the geometry of model CT systems with constrained density functional theory (CDFT). We find that CT states relax in double stranded DNA through proton transfer across Watson-Crick base pairs with little to no energy barrier. Furthermore, the ground state energy shifts upwards along this reaction coordinate to nearly the same as that of the proton coupled charge transfer state, creating the possibility for a non-radiative pathway to the ground state. Q. Wu and T. Van Voorhis Phys. Rev. A (2005)

Lange, Adrian W.; Herbert, John M.

2009-06-01

336

Engineering Interfacial Photo-Induced Charge Transfer Based on Nanobamboo Array Architecture for Efficient Solar-to-Chemical Energy Conversion.  

PubMed

Engineering interfacial photo-induced charge transfer for highly synergistic photocatalysis is successfully realized based on nanobamboo array architecture. Programmable assemblies of various components and heterogeneous interfaces, and, in turn, engineering of the energy band structure along the charge transport pathways, play a critical role in generating excellent synergistic effects of multiple components for promoting photocatalytic efficiency. PMID:25704499

Wang, Xiaotian; Liow, Chihao; Bisht, Ankit; Liu, Xinfeng; Sum, Tze Chien; Chen, Xiaodong; Li, Shuzhou

2015-04-01

337

P3HT:PCBM Bulk-Heterojunctions: Observing Interfacial and Charge Transfer States with Surface Photovoltage Spectroscopy  

E-print Network

P3HT:PCBM Bulk-Heterojunctions: Observing Interfacial and Charge Transfer States with Surface photocurrent by trapping charge carriers or by inducing electric fields.26-30 We recently applied surface Supporting Information ABSTRACT: Surface photovoltage (SPV) spectra are reported for separate films of (6

Osterloh, Frank

338

The influences of the transfer method and particle surface chemistry on the dispersion of nanoparticles in nanocomposites  

NASA Astrophysics Data System (ADS)

The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS).The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS). Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr31846f

Pravaz, Olivier; Droz, Benoît; Schurtenberger, Peter; Dietsch, Hervé

2012-10-01

339

Photophysics and charge transfer in donor-acceptor triblock copolymer photovoltaic materials  

NASA Astrophysics Data System (ADS)

Efficient conversion of solar energy to electricity in low-cost organic photovoltaic (OPV) devices requires the complex interplay between multiple processes and components over various length and time scales. Optimizing device morphology to ensure efficient exciton diffusion and charge transport as well as ensuring efficient charge photogeneration is necessary to achieve optimum performance in new materials. The conjugated polymer electron donor PFM (poly(9,9-diocetyluorene-co-bis-N,N-(4-methylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine)) and electron acceptor F8BT (poly[(9,9-di-n-octyluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)), comprise the novel triblock copolymer PFM-F8BT-PFM. This copolymer is designed to phase separate on the 20-30 nm scale, a domain size ideal for maximizing exciton collection at the donor-acceptor interface. Using steady-state and ultrafast spectroscopic characterization including high repetition rate transient absorption spectroscopy, the dynamics of charge and energy transfer of the component polymers and the triblock co-polymer have been investigated. The results demonstrate that for the homopolymers solvent dependent exciton transport processes dominate, while in the triblock copolymer solutions transient spectroscopy provides evidence for interfacial charge separation.

Schwarz, Kyra N.; Jones, David J.; Smith, Trevor A.; Ghiggino, Kenneth P.

2014-10-01

340

Energy transfer through a multi-layer liner for shaped charges  

DOEpatents

This invention relates to the determination of parameters for selecting materials for use as liners in shaped charges to transfer the greatest amount of energy to the explosive jet. Multi-layer liners constructed of metal in shaped charges for oil well perforators or other applications are selected in accordance with the invention to maximize the penetrating effect of the explosive jet by reference to four parameters: (1) Adjusting the explosive charge to liner mass ratio to achieve a balance between the amount of explosive used in a shaped charge and the areal density of the liner material; (2) Adjusting the ductility of each layer of a multi-layer liner to enhance the formation of a longer energy jet; (3) Buffering the intermediate layers of a multi-layer liner by varying the properties of each layer, e.g., composition, thickness, ductility, acoustic impedance and areal density, to protect the final inside layer of high density material from shattering upon impact of the explosive force and, instead, flow smoothly into a jet; and (4) Adjusting the impedance of the layers in a liner to enhance the transmission and reduce the reflection of explosive energy across the interface between layers.

Skolnick, Saul (Albuquerque, NM); Goodman, Albert (Albuquerque, NM)

1985-01-01

341

Sequential protonation of meso-(p-(dimethylamino)phenyl)porphyrins. Charge-transfer excited states producing hyperporphyrins  

SciTech Connect

Successive protonation by trifluoroacetic acid of meso-tetraphenylporphyrin derivatives bearing one, two, or four p-dimethylamino groups gives rise to new types of spectra. With one free amino group, the spectrum of the centrally protonated porphyrin shows a strong far-red band, a broad, flat absorption in the visible, and a less intense Soret band. With two or more free amino groups, the Soret band of the centrally protonated porphyrin is further split into two components. Complete protonation, including the peripheral amino groups, in all cases restores the spectral structure of the unsubstituted tetraphenylporphyrin dication. The spectra of the dianions of tetraanilino- and tetraphenylporphyrins are also similar. These results, and the related behavior of p-oxyphenylporphyrins and protonated Schiff base porphyrins, lead to a general interpretation of hyperporphyrin spectra in terms of charge-transfer excited states, involving charge movement either into or out of the porphyrin ring. 26 refs., 4 figs., 2 tabs.

Ojadi, E.C.A. (Brandeis Univ., Waltham, MA (United States) Univ. of Massachusetts, Dartmouth, MA (United States)); Linschitz, H.; Droupadi, P.R.; Wang, W. (Brandeis Univ., Waltham, MA (United States)); Gouterman, M. (Univ. of Washington, Seattle, WA (United States)); Walter, R.I. (Univ. of Illinois, Chicago, IL (United States)); Lindsey, J.S.; Wagner, R.W. (Carnegie-Mellon Univ., Pittsburgh, PA (United States))

1993-12-16

342

Influence of an electrical potential on the charge transfer kinetics of bacteriorhodopsin  

PubMed Central

The adsorption of bacteriorhodopsin(bR)-containing purple membranes (PM) to black lipid membranes (BLM) was used to study the charge translocation kinetics of bR upon flash excitation. The discharge of the PM-BLM system after charging upon illumination is found to proceed quite slowly (discharge time up to several minutes) but is considerably accelerated by addition of the protonophore FCCP. Therefore, the dependence of the proton transfer kinetics in bR on electrical potentials generated by preceding flashes of varying repetition rate and intensity was investigated. The kinetics are slowed down with increasing flash intensity as well as repetition rate. This effect is partly abolished by small amounts of FCCP. A new model is introduced which takes into account the instantaneous feedback of the electrical potential on the kinetics of the pump current. It explains the observed deviations from first-order kinetics and renders an approach with “distributed kinetics” unnecessary. PMID:19431767

Kleinschmidt, Christoph; Hess, Benno

1990-01-01

343

Efficient photoinduced charge transfer in TiO2 nanorod/conjugated polymer hybrid materials  

NASA Astrophysics Data System (ADS)

The mechanisms of photoinduced charge transfer in composites of TiO2 nanorods with a conjugated polymer (poly(2-methoxy-5-(2'-ethyl)(hexyloxy) 1,4-phenylenevinylene) (MEH-PPV) have been investigated by steady-state, time-resolved photoluminescence (PL) spectroscopy and photoluminescence excitation (PLE) spectroscopy. Efficient charge separation takes place at the TiO2-nanorod/polymer interfaces when the polymer is excited, leading to quenching of the photoluminescence efficiency ? and shortening of the measured lifetime ?PL. In addition, the low-temperature absorption and photoluminescence spectra show that the inclusion of TiO2 nanorods in polymer can reduce disorder in conformation and enhance conjugation in the polymer chain. A photovoltaic solar cell device based on the MEH-PPV/TiO2-nanorod composite material is also presented, which shows a two order increase in short-circuit current JSC compared to that based on the pristine MEH-PPV.

Lin, Yu-Ting; Zeng, Tsung-Wei; Lai, Wei-Zong; Chen, Chun-Wei; Lin, Yun-Yue; Chang, Yu-Sheng; Su, Wei-Fang

2006-12-01

344

Adsorption of colloidal platinum nanoparticles to supports: charge transfer and effects of electrostatic and steric interactions.  

PubMed

Adsorption of colloidal nanoparticles to surfaces and supports is a convenient approach to heterogeneous catalysts, polymer additives, or wastewater treatment. We investigated the adsorption efficiency of laser-generated and initially ligand-free platinum nanoparticles to TiO2 supports as a function of pH, ionic strength, and ligand surface coverage. The nanoparticle adsorption is dominantly controlled by electrostatic interactions: if the pH of the suspension is between the isoelectric point of the nanoparticles and the support, nanoparticles are adsorbed and transfer a net charge to the support. This charge-driven adsorption is not affected by steric repulsion due to various ligands attached to the nanoparticle surface. In addition to electrostatic interactions, colloidal stability given by moderate ionic strengths and pH values above the isoelectric point of nanoparticles are prerequisites for colloidal deposition. PMID:25226205

Marzun, Galina; Streich, Carmen; Jendrzej, Sandra; Barcikowski, Stephan; Wagener, Philipp

2014-10-14

345

Compton scattering and charge transfer in Er substituted DyAl2  

NASA Astrophysics Data System (ADS)

A unique applicability of Compton spectroscopy in probing the electronic states of rare earth aluminides using high energy (662 keV) ?-rays is reported. We have measured first-ever Compton profiles of Dy1-xErxAl2 (x=0, 0.2) using 20Ci 137Cs Compton spectrometer. The charge reorganization in Dy1-xErxAl2 (x=0, 0.2), on the formation of compound, has been discussed using the valence band Compton profile data. The experimental Compton profile data unambiguously establish charge transfer from Al to Dy (Dy and Er) on formation of x=0.0 (0.2) compound, which is in tune with spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) calculations. A reasonable agreement between SPR-KKR based Compton profiles and the experimental data show applicability of the Green function method in predicting the electronic properties of rare earth compounds.

Ahuja, B. L.; Mohammad, F. M.; Mohammed, S. F.; Sahariya, Jagrati; Mund, H. S.; Heda, N. L.

2015-02-01

346

Aspects of artificial photosynthesis. Photosensitized electron transfer and charge separation in redox active surfactant aggregates  

SciTech Connect

Photosensitized electron transfer and charge separation have been demonstrated by steady-state and nanosecond laser flash photolysis in the presence of redox active surfactant aggregates prepared from CH/sub 2/==C(CH/sub 3/)-COO(CH/sub 2/)/sub 11/(C/sub 5/H/sub 4/N/sup +/)/sub 2/CH/sub 3/,Br/sup -/,I/sup -/ (RMV/sup 2 +/). Tris(2,2'-bipyridine)ruthenium chloride (Ru(bpy)/sub 3//sup 2 +/) has been used as a sensitizer. Forward electron transfer from excited Ru(bpy)/sub 3//sup 2 +/ to RMV/sup 2 +/ aggregates has been shown to be faster than that from Ru(bpy)/sub 3//sup 2 +/ to methylviologen (MV/sup 2 +/) in homogeneous solutions. Conversely, the undesirable back-reaction between the reduced electron acceptor RMV/sup +/ and the oxidized sensitizer Ru(bpy)/sub 3//sup 3 +/ has been found to be considerably retarded compared to the reaction between MV/sup +/ and Ru(bpy)/sub 3//sup 2 +/. Further, unlike MV/sup +/., RMV/sup +/. decayed by a two-step process. These results have been rationalized in terms of a mechanism which requires most of the photosensitized forward electron transfer to occur on the surface of RMV/sup 2 +/ aggregates. Subsequently, some of the oxidized sensitizer escapes the potential field of RMV/sup 2 +/ and charge recombination is retarded by electrostatic repulsions between the positively charged aggregates and Ru(bpy)/sub 3//sup 3 +/. 10 figures, 1 table.

Kurihara, K.; Tundo, P.; Fendler, J.H.

1983-09-15

347

Theoretical Investigation of OCN(-) Charge Transfer Complexes in Condensed Phase Media: Spectroscopic Properties in Amorphous Ice  

NASA Technical Reports Server (NTRS)

Density functional theory (DFT) calculations of cyanate (OCN(-)) charge-transfer complexes were performed to model the "XCN" feature observed in interstellar icy grain mantles. OCN(-) charge-transfer complexes were formed from precursor combinations of HNCO or HOCN with either NH3 or H2O. Three different solvation strategies for realistically modeling the ice matrix environment were explored, including (1) continuum solvation, (2) pure DFT cluster calculations, and (3) an ONIOM DFT/PM3 cluster calculation. The model complexes were evaluated by their ability to reproduce seven spectroscopic measurements associated with XCN: the band origin of the OCN(-) asymmetric stretching mode, shifts in that frequency due to isotopic substitutions of C, N, O, and H, plus two weak features. The continuum solvent field method produced results consistent with some of the experimental data but failed to account for other behavior due to its limited capacity to describe molecular interactions with solvent. DFT cluster calculations successfully reproduced the available spectroscopic measurements very well. In particular, the deuterium shift showed excellent agreement in complexes where OCN(-) was fully solvated. Detailed studies of representative complexes including from two to twelve water molecules allowed the exploration of various possible solvation structures and provided insights into solvation trends. Moreover, complexes arising from cyanic or isocyanic acid in pure water suggested an alternative mechanism for the formation of OCN(-) charge-transfer complexes without the need for a strong base such as NH3 to be present. An extended ONIOM (B3LYP/PM3) cluster calculation was also performed to assess the impact of a more realistic environment on HNCO dissociation in pure water.

Park, Jin-Young; Woon, David E.

2004-01-01

348

Interfacial electronic charge transfer and density of states in short period Cu/Cr multilayers  

SciTech Connect

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 multilayers studied were fabricated by magnetron sputtering and consist of bilayers from 1.9 mn to 3.3 mn. X-ray diffraction, cross-section TEM and plan-view TEM show the Cu layers to have a BCC structure Cu in contrast to its equilibrium FCC structure. 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 confirm the presence of charge transfer and indicate that it is localized to the first two interfacial layers in both Cu and Cr.

Bello, A.F.; Van Buuren, T.; Kepesis, J.E.; Barbee, T.W., Jr.

1998-04-01

349

Bidirectional diffusion of ammonium and sodium cations in forward osmosis: role of membrane active layer surface chemistry and charge.  

PubMed

Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4(+)) and sodium (Na(+)) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes. PMID:25418020

Lu, Xinglin; Boo, Chanhee; Ma, Jun; Elimelech, Menachem

2014-12-16

350

Charge Density Quantification of Polyelectrolyte Polysaccharides by Conductometric Titration: An Analytical Chemistry Experiment  

ERIC Educational Resources Information Center

An easy analytical method for determination of the charge density of polyelectrolytes, including polysaccharides and other biopolymers, is presented. The basic principles of conductometric titration, which is used in the pulp and paper industry as well as in colloid and interface science, were adapted to quantify the charge densities of a…

Farris, Stefano; Mora, Luigi; Capretti, Giorgio; Piergiovanni, Luciano

2012-01-01

351

Thermal energy charge transfer between S2+ and H2, N2, and CO  

NASA Astrophysics Data System (ADS)

We measured the charge transfer rate coefficients for the reactions S2++H2?products, S2++N2?products, and S2++CO?products using a radio frequency trap. S2+ ions are produced by laser ablation of a solid tungsten disulfide target. We derive the rate coefficient of the reaction from the decay rate of the stored ions in the trap. The rate coefficients for the above three reactions are 1.58(0.13)×10-9 cm3 s-1 at Tequiv=1077 K, and 1.67(0.12)×10-9 and 1.78(0.13)×10-9 cm3 s-1 at Tequiv=6462 K.

Chen, De; Gao, H.; Kwong, Victor H.

2003-11-01

352

On the charge transfer between single-walled carbon nanotubes and graphene  

NASA Astrophysics Data System (ADS)

It is important to understand the electronic interaction between single-walled carbon nanotubes (SWNTs) and graphene in order to use them efficiently in multifunctional hybrid devices. Here, we deposited SWNT bundles on graphene-covered copper and SiO2 substrates by chemical vapor deposition and investigated the charge transfer between them by Raman spectroscopy. Our results revealed that, on both copper and SiO2 substrates, graphene donates electrons to the SWNTs, resulting in p-type doped graphene and n-type doped SWNTs.

Rao, Rahul; Pierce, Neal; Dasgupta, Archi

2014-08-01

353

Direct observation of charge transfer region at interfaces in graphene devices  

SciTech Connect

Nanoscale spectromicroscopic characterizing technique is indispensable for realization of future high-speed graphene transistors. Highly spatially resolved soft X-ray photoelectron microscopy measurements have been performed using our '3D nano-ESCA' (three-dimensional nanoscale electron spectroscopy for chemical analysis) equipment in order to investigate the local electronic states at interfaces in a graphene device structure. We have succeeded in detecting a charge transfer region at the graphene/metal-electrode interface, which extends over {approx}500 nm with the energy difference of 60 meV. Moreover, a nondestructive depth profiling reveals the chemical properties of the graphene/SiO{sub 2}-substrate interface.

Nagamura, Naoka [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Horiba, Koji; Oshima, Masaharu [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 5-7, Goban-cho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Toyoda, Satoshi [Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan) [Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 5-7, Goban-cho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Kurosumi, Shodai; Shinohara, Toshihiro [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Fukidome, Hirokazu; Suemitsu, Maki [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)] [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Nagashio, Kosuke; Toriumi, Akira [Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2013-06-17

354

Assessment of asymptotically corrected model potential scheme for charge-transfer-like excitations in oligoacenes  

E-print Network

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.

Wei-Tao Peng; Jeng-Da Chai

2014-08-14

355

Study of charge transfer complexes of menadione (vitamin K 3) with a series of anilines  

NASA Astrophysics Data System (ADS)

Menadione (vitamin K 3) has been shown to form charge transfer complexes with N, N-dimethyl aniline, N, N-dimethyl p-toluidine and N, N-dimethyl m-toluidine in CCl 4 medium. The CT transition energies are well correlated with the ionisation potentials of the anilines. The formation constants of the complexes have been determined at a number of temperatures from which the enthalpies and entropies of formation have been obtained. The formation constants exhibit a very good linear free energy relationship (Hammett) at all the temperatures studied.

Pal, Purnendu; Saha, Avijit; Mukherjee, Asok K.; Mukherjee, Dulal C.

2004-01-01

356

Utility of ? -acceptor reagents for spectrophotometric determination of sulphonamide drugs via charge-transfer complex formation  

Microsoft Academic Search

A simple, sensitive and accurate spectrophotometric method for the determination of sulphonamides (sulphamethoxazole (SMZ),\\u000a sulphaguanidine (SGD), sulphaquinoxaline sodium (SQX), sulphametrole (SMR), and sulphadimidine sodium (SDD)) has been developed.\\u000a The charge-transfer reactions between sulphonamides as n-electron donors and 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone\\u000a (chloranilic acid, p-CLA) as ?-acceptors resulting in highly coloured complexes were studied. Experimental conditions for these CT

Faten Ahmed Nour El-Dien; Gehad Genidy Mohamed; Eman Yossri Frag

2009-01-01

357

Charge transfer interactions and nonlinear optical properties of push pull chromophore benzaldehyde phenylhydrazone: A vibrational approach  

NASA Astrophysics Data System (ADS)

FT Raman and IR spectra of the crystallized nonlinear optic (NLO) molecule, benzaldehyde phenylhydrazone (BPH) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies of BPH have been investigated with the help of B3LYP density functional theory (DFT) method. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). From the optimized geometry, the decrease in C-N bond length indicates the electron delocalization over the region of the molecule. The vibrational analysis confirm the charge transfer interaction between the phenyl rings through ?Cdbnd N-N? skeleton.

Ravikumar, C.; Joe, I. Hubert; Jayakumar, V. S.

2008-07-01

358

Orientation dependence of charge transfer for C{sub 60} on Cu(100)  

SciTech Connect

Scanning tunneling microscopy was used to characterize the lowest unoccupied molecular orbitals (LUMO), up to LUMO+3, of individual C{sub 60} molecules within monolayer films on Cu(100). On this surface C{sub 60} orients in four distinct configurations with respect to the substrate. Tunneling spectroscopy and spectroscopic imaging were used to identify the energies and spatial distributions of the molecular orbitals. We find that the LUMO shifts by {approx}200 meV depending on the orientation of the molecule, which suggests charge transfer between the surface and molecule is orientation dependent. Orientation-dependent shifts were also observed for the higher unoccupied molecular orbitals.

Daughton, D. R.; Gupta, J. A. [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States)

2011-03-28

359

Scale-model charge-transfer technique for measuring enhancement factors  

NASA Technical Reports Server (NTRS)

Determination of aircraft electric field enhancement factors is crucial when using airborne field mill (ABFM) systems to accurately measure electric fields aloft. SRI used the scale model charge transfer technique to determine enhancement factors of several canonical shapes and a scale model Learjet 36A. The measured values for the canonical shapes agreed with known analytic solutions within about 6 percent. The laboratory determined enhancement factors for the aircraft were compared with those derived from in-flight data gathered by a Learjet 36A outfitted with eight field mills. The values agreed to within experimental error (approx. 15 percent).

Kositsky, J.; Nanevicz, J. E.

1991-01-01

360

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

PubMed

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

Bacchus-Montabonel, Marie-Christine; Calvo, Florent

2015-04-01

361

Formation of charge-transfer-complex in organic:metal oxides systems  

NASA Astrophysics Data System (ADS)

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.

Wu, S. P.; Kang, Y.; Liu, T. L.; Jin, Z. H.; Jiang, N.; Lu, Z. H.

2013-04-01

362

Spectrophotometric determination of terfenadine in pharmaceutical preparations by charge-transfer reactions  

Microsoft Academic Search

A simple, rapid and accurate method for the spectrophotometric determination of terfenadine has been developed. The proposed method based on the charge-transfer reactions of terfenadine, as n-electron donor, with 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, p-CLA) as ?-acceptors to give highly colored complexes. The experimental conditions such as reagent concentration, reaction solvent and time have been

Elmorsy Khaled

2008-01-01

363

Metal-insulator transition in PF6 doped polypyrrole: interchain charge transfer versus electronic correlation  

E-print Network

We performed dielectric spectroscopy on polypyrrole near the metal-insulator transition (MIT) down to 2 K. We evaluate the dependence of the plasma frequency and the scattering time (t) on the distance to the MIT, characterized by the Fermi-level relative to the band-edge of extended states, E_F-E_c. Especially the strong decrease of t with increasing E_F-E_c is in conflict with the usually applied models for the MIT. Although morphology and disorder are important, the MIT is Mott-Hubbard-like being dominated by the competition of interchain charge transfer and electronic correlation.

H. C. F. Martens; H. B. Brom; R. Menon

2001-01-12

364

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

SciTech Connect

Au-nanoparticle incorporated oxide thin film materials demonstrate significant promise as functionalsensor materials for high temperature optical gas sensing in severe environments relevant for fossil andnuclear based power generation. The Au/yttria-stabilized zirconia (YSZ) system has been extensivelystudied in the literature and serves as a model system for fundamental investigations that seek to betterunderstand the mechanistic origin of the plasmonic gas sensing response. In this work, X-ray photoelec-tron spectroscopy techniques are applied to Au/YSZ films in an attempt to provide further experimentalevidence for a proposed sensing mechanism involving a change in free carrier density of Au nanoparticles due to charge transfer.

Baltrus, John P. [U.S. DOE; Ohodnicki, Paul R. [U.S. DOE

2014-01-01

365

Direct optical generation of long-range charge-transfer states in organic photovoltaics.  

PubMed

Direct optical excitation of long-range charge-transfer (CT) states in organic photovoltaics is shown to be feasible, a fact that is ascribed to the very low but non-vanishing oscillator strength of each individual transition and the much higher density of states (DOS) as compared with their short-range counterparts. This finding provides a new framework to interpret the low-energy absorption spectra of photovoltaic devices and to correlate this property with the optoelectronic conversion process in working devices. PMID:25044396

Ma, Haibo; Troisi, Alessandro

2014-09-17

366

Estimation of instantaneous heat transfer coefficients for a direct-injection stratified-charge rotary engine  

NASA Technical Reports Server (NTRS)

The main objective of this report was to derive equations to estimate heat transfer coefficients in both the combustion chamber and coolant pasage of a rotary engine. This was accomplished by making detailed temperature and pressure measurements in a direct-injection stratified-charge rotary engine under a range of conditions. For each sppecific measurement point, the local physical properties of the fluids were calculated. Then an empirical correlation of the coefficients was derived by using a multiple regression program. This correlation expresses the Nusselt number as a function of the Prandtl number and Reynolds number.

Lee, C. M.; Addy, H. E.; Bond, T. H.; Chun, K. S.; Lu, C. Y.

1987-01-01

367

Single CuTCNQ charge transfer complex nanowire as ultra high responsivity photo-detector.  

PubMed

We report ultra large photo responsivity ? (ratio of photo-generated current to absorbed power) in a single nanowire (NW) device made from a single strand of a nanowire (diameter ~30nm and length ~200nm) of an organomettalic semiconducting charge transfer complex material of CuTCNQ. The device shows responsivity of 8x10(4) A/Watt at 1 volt applied bias with an enhancement over the dark current exceeding 10(5) at zero bias. The observed photo current has a spectral dependence that strongly follows the main absorption peak (close to 405 nm) showing the primary role of absorbed photo-generated carriers. PMID:24663833

Basori, Rabaya; Das, K; Kumar, Prashant; Narayan, K S; Raychaudhuri, A K

2014-03-10

368

Correlation between charge transfer exciton recombination and photocurrent in polymer/fullerene solar cells  

SciTech Connect

We correlate carrier recombination via charge transfer excitons (CTEs) with the short circuit current, J{sub sc}, in polymer/fullerene solar cells. Near infrared photoluminescence spectroscopy of CTE in three blends differing for the fullerene acceptor, gives unique insights into solar cell characteristics. The energetic position of the CTE is directly correlated with the open-circuit voltage, V{sub oc}, and more important J{sub sc} decreases with increasing CTE emission intensity. CTE emission intensity is discussed from the perspective of blend morphology. The work points out the fundamental role of CTE recombination and how optical spectroscopy can be used to derive information on solar cell performances.

Hallermann, Markus; Da Como, Enrico; Feldmann, Jochen [Photonics and Optoelectronics Group, Department of Physics, CeNS Ludwig-Maximilians-University, 80799 Munich (Germany); Izquierdo, Marta; Filippone, Salvatore; Martin, Nazario [Department of Organic Chemistry, Universidad Complutense de Madrid, 28040 Madrid (Spain); Juechter, Sabrina; Hauff, Elizabeth von [Institute of Physics, Energy and Semiconductor Research Laboratory, University of Oldenburg, 26111 Oldenburg (Germany)

2010-07-12

369

On the charge transfer between single-walled carbon nanotubes and graphene  

SciTech Connect

It is important to understand the electronic interaction between single-walled carbon nanotubes (SWNTs) and graphene in order to use them efficiently in multifunctional hybrid devices. Here, we deposited SWNT bundles on graphene-covered copper and SiO{sub 2} substrates by chemical vapor deposition and investigated the charge transfer between them by Raman spectroscopy. Our results revealed that, on both copper and SiO{sub 2} substrates, graphene donates electrons to the SWNTs, resulting in p-type doped graphene and n-type doped SWNTs.

Rao, Rahul, E-mail: rrao@honda-ri.com; Pierce, Neal; Dasgupta, Archi [Honda Research Institute USA, Columbus, Ohio 43212 (United States)

2014-08-18

370

Charge transfer fluorescence and f-f luminescence in ytterbium compounds  

NASA Astrophysics Data System (ADS)

Luminescence and excitation spectra as well as decay kinetics are presented for the charge transfer (CT) luminescence of Lu 3Al 5O 12, Y 3Ga 5O 12 and YAlO 3 crystals doped by Yb 3+ in various concentrations, the CT luminescence properties are compared to those of Y 3Al 5O 12-Yb. For the first time the excitation spectra of the intraconfigurational 2F 5/2 ? 2F 7/2 luminescence of Yb 3+ ions in YAG, LuAG and YAP in the region of the CT absorption band and in the fundamental absorption range up to 20 eV were measured, possible mechanisms of the energy transfer to Yb 3+ 4f states are discussed.

Kamenskikh, I. A.; Guerassimova, N.; Dujardin, C.; Garnier, N.; Ledoux, G.; Pedrini, C.; Kirm, M.; Petrosyan, A.; Spassky, D.

2003-10-01

371

Aspects of artificial photosynthesis. Photosensitized electron transfer and charge separation in cationic surfactant vesicles  

SciTech Connect

Electron transfer and charge separation have been investigated in cationic dioctadecyldimethylammonium chloride (DODAC) vesicles by laser spectroscopy. h-Methylphenothiazine (MPTH) and its long-chain analogue, N-dodecylphenothiazine (DPTH), were used as electron donors, while a surfactant derivative of tris(2,2'-bipyridine)ruthenium perchlorate, RuC/sub 18/(bpy)/sub 3//sup 2 +/, acted as the photoactive electron acceptor, DODAC vesicles organized these donor and acceptor molecules. RuC/sub 18/(bpy)/sub 3//sup 2 +/ molecules were anchored onto the surface of the vesicles, while MPTH molecules were distributed among the hydrophobic bilayers of the vesicles. The metal to ligand charge transfer excited state of the ruthenium complex, RuC/sub 18/(bpy)/sub 3//sup 2 +/*, readily accepted an electron from MPTH to give MPTH/sup +/ and RuC/sub 18/(bpy)/sub 3//sup +/. First, there is a rapid geminate recombination at the very site of the generation of the cation radical. Second, some of the MPTH/sup +/. Escapes into the vesicle entrapped water pools and, owing to spatial confinement, the combination occurs at the inner surface of the vesicles. Finally, a part of MPTH/sup +/. Escapes into the bulk aqueous solution where it survives for extended periods (>>1 ms). MPTH and NaCl affect the outer surface charge density of the vesicles. The amounts of MPTH/sup +/. produced and that expelled into the bulk aqueous solution were maximized in the presence of 1.0 x 10/sup -3/ M NaCl. Under this condition there was still a sufficient electrostatic repulsion between MPTH/sup +/. and the charged surface of the vesicles to slow down considerably the undesirable charge recombination reactions. Carrying out the electron transfer using DPTH resulted only in short-lived DPTH/sup +/. in low concentrations. The long hydrocarbon chain on this molecule prevented the expulsion of this cation radical from the vesicle. Relevance of this study to light-induced photochemical energy conversion is discussed.

Infelta, P.P.; Graetzel, M.; Fendler, J.H.

1980-02-27

372

EV Charging Through Wireless Power Transfer: Analysis of Efficiency Optimization and Technology Trends  

SciTech Connect

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 program geared toward a safer, greener and more connected driving. Moreover, it draws from and adds to Dr. Andrew Brown Jr.'s SAE books 'Active Safety and the Mobility Industry', 'Connectivity and Mobility Industry', and 'Green Technologies and the Mobility Industry'. Magnetic resonant coupling is the foundation of modern wireless power transfer. Its efficiency can be controlled through impedance matching and magnetic field shaping. Current implementations use one or both of these control methods and enable both stationary and mobile charging with typical efficiency within the 80% and 90% range for an air gap up to 25 cm.

Miller, John M [ORNL; Rakouth, Heri [Delphi Automotive Systems, USA; Suh, In-Soo [Korea Advanced Institute of Science and Technology

2012-01-01

373

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

SciTech Connect

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

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

1994-12-06

374

TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4?-dimethylaminoflavonol in ethanol solvent  

NASA Astrophysics Data System (ADS)

Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4?-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF-EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3-C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule.

Wang, Ye; Shi, Ying; Cong, Lin; Li, Hui

2015-02-01

375

TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4'-dimethylaminoflavonol in ethanol solvent.  

PubMed

Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4'-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF-EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3-C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule. PMID:25282020

Wang, Ye; Shi, Ying; Cong, Lin; Li, Hui

2015-02-25

376

Charge transfer satellite in Pr@C82 metallofullerene observed using resonant x-ray emission spectroscopy  

NASA Astrophysics Data System (ADS)

Resonant x-ray emission spectroscopy (RXES) was performed on the metallofullerene Pr@C82 at the PrL3 absorption edge. We verify not only nearly three-electron charge transfers from the metal to the cage but also back-electron transfer observed as a charge transfer satellite. The results are compared to theoretical calculations with a single-impurity Anderson model. Theory shows that the electronic structure of endohedral atom in the cage is atomiclike. The satellite structure originates from the charge transfer, i.e., dynamical screening effect, induced by the core-hole potential in the final state rather than from the valence fluctuation of the rare-earth metal in the ground state. We also performed the RXES measurement of Pr2O3 for comparison.

Yamaoka, H.; Sugiyama, H.; Kubozono, Y.; Kotani, A.; Nouchi, R.; Vlaicu, A. M.; Oohashi, H.; Tochio, T.; Ito, Y.; Yoshikawa, H.

2009-11-01

377

Vectorial doping-promoting charge transfer in anatase TiO2 {0 0 1} surface  

NASA Astrophysics Data System (ADS)

Doping-induced visible-light adsorption is often considered as the main reason for the enhanced photocatalytic activity of TiO2. However, this work provides a new understanding on the effect of doping on the photocatalytic activity of TiO2. The investigation on the C-F codoped anatase TiO2 {0 0 1} surface reveals that the impurity C and F atoms prefer to substitute for the outmost O atoms in the TiO2 {0 0 1} surface rather than those in the bulk TiO2. The exhibited vectorial doping of C and F atoms in TiO2 {0 0 1} surface produces a conducting layer with low electric resistance, which can promote the charge transfer in the photocatalytic reaction. This effectively inhibits the undesirable bulk recombination of photogenerated electron and hole. Hence, the optimized charge transfer in the C-F codoped TiO2 {0 0 1} surface makes a great contribution to the enhanced photocatalytic activity of TiO2. Further, the surface doping treatment is a potential method to improve the performance of photocatalyst.

Zhou, Peng; Wu, Jionghua; Yu, Weilai; Zhao, Guanghui; Fang, Guojia; Cao, Shaowen

2014-11-01

378

Observation of excited state charge transfer with fs/ps-CARS  

SciTech Connect

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.

Blom, Alex Jason

2009-08-01

379

Optimal control of charge transfer for slow H+ + D collisions with shaped laser pulses.  

PubMed

We show that optimally shaped laser pulses can beneficially influence charge transfer in slow H(+)+D collisions. Time-dependent wave packet optimal control simulations are performed based on a two-state adiabatic Hamiltonian. Optimal control is performed using either an adaptive or a fixed target to obtain the desired laser control field. In the adaptive target scheme, the target state is updated according to the renormalized fragmentary yield in the exit channel throughout the optimization process. In the fixed target scheme, the target state in the exit channel is a normalized outgoing Gaussian wave packet located at a large internuclear separation. Both approaches produced excellent optimal outcomes, far exceeding that achieved in the field-free collisional charge transfer. The adaptive target scheme proves to be more efficient, and often with complex final wave packet. In contrast, the fixed target scheme, although more slowly convergent, is found to produce high fidelity for the desired target wave packet. The control mechanism in both cases utilizes bound vibrational states of the transient HD(+) complex. PMID:24606358

Zhang, Wei; Shu, Chuan-Cun; Ho, Tak-San; Rabitz, Herschel; Cong, Shu-Lin

2014-03-01

380

Synthesis and characterization of highly conductive charge-transfer complexes using positron annihilation spectroscopy  

NASA Astrophysics Data System (ADS)

Molecular charge-transfer complexes of the tetramethylethylenediamine (TMEDA) with picric acid (Pi-OH), benzene-1,4-diol (QL), tin(IV) tetrachloride (SnCl4), iodine, bromine, and zinc chloride (ZnCl2) have been synthesized and investigated by elemental and thermal analysis, electronic, infrared, Raman and proton-NMR, energy-dispersive X-ray spectroscopy, X-ray powder diffraction and positron annihilation lifetime spectroscopy, and scanning electron microscopy. In this work, three types of acceptors ?-acceptors (Pi-OH and QL), ?-acceptors (iodine and bromine), and vacant orbital acceptors (SnCl4 and ZnCl2) were covered. The results of elemental analysis indicated that the CT complexes were formed with ratios 1:1 and 1:2 for QL, SnCl4, and ZnCl2 acceptors and iodine, Pi-OH, and Br2 acceptors, respectively. The type of chelating between the TMEDA donor and the mentioned acceptors depends upon the behavior of both items. The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, and the power of acceptors. The correlation between these parameters and the molecular weight and biological activities of studied complexes was also observed. Regarding the electrical properties, the AC conductivity and the dielectric coefficients were measured as a function of frequency at room temperature. The TMEDA charge-transfer complexes were screened against antibacterial (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa) and antifungal (Aspergillus flavus and Candida albicans) activities.

Adam, Abdel Majid A.; Refat, Moamen S.; Sharshar, T.; Heiba, Z. K.

381

Charge-transfer complexes of sulfamethoxazole drug with different classes of acceptors  

NASA Astrophysics Data System (ADS)

The charge-transfer complexes of the donor sulfamethoxazole (SZ) with iodine (I 2), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil (CHL) and picric acid (PA) have been studied spectrophotometrically in chloroform or methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CT-complexes in case of four acceptors. The stoichiometry of the complexes was found to be 1:1 ratio by molar ratio method between donor and acceptor with maximum absorption bands (CT band). The data are discussed in terms of formation constant ( KCT), molar extinction coefficient ( ?CT), standard free energy (? G°), oscillator strength (ƒ), transition dipole moment ( ?), resonance energy ( RN) and ionization potential ( ID). The results indicate that the formation constant ( KCT) for the complexes were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used. IR, 1H NMR, mass spectra, UV-Vis techniques, elemental analyses (CHN) and TG-DTG investigation were used to characterize the four sulfamethoxazole charge-transfer complexes.

Refat, Moamen S.; El-Korashy, Sabry A.; El-Deen, Ibrahim M.; El-Sayed, Shaima M.

2010-09-01

382

Lead-iodide nanowire perovskite with methylviologen showing interfacial charge-transfer absorption: a DFT analysis.  

PubMed

Methylviologen lead-iodide perovskite (MVPb2I6) is a self-assembled one-dimensional (1-D) material consisting of lead-iodide nanowires and intervening organic electron-accepting molecules, methylviologen (MV(2+)). MVPb2I6 characteristically shows optical interfacial charge-transfer (ICT) transitions from the lead-iodide nanowire to MV(2+) in the visible region and unique ambipolar photoconductivity, in which electrons are transported through the three-dimensional (3-D) organic network and holes along the 1-D lead-iodide nanowire. In this work, we theoretically study the electronic band-structure and photocarrier properties of MVPb2I6 by density functional theory (DFT) calculations. Our results clearly confirm the experimentally reported type-II band alignment, whose valence band mainly consists of 5p (I) orbitals of the lead-iodide nanowires and the conduction band of the lowest unoccupied molecular orbital of MV(2+). The DFT calculation also reveals weak charge-transfer interactions between the lead-iodide nanowires and MV(2+). In addition, the electronic distributions of the valence and conduction bands indicate the 3-D transport of electrons and 1-D transport of holes, supporting the reported experimental result. PMID:25050419

Fujisawa, Jun-ichi; Giorgi, Giacomo

2014-09-01

383

Modulation of the charge transfer and photophysical properties in non-fused tetrathiafulvalene-benzothiadiazole derivatives.  

PubMed

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

Pop, Flavia; Seifert, Sabine; Hankache, Jihane; Ding, Jie; Hauser, Andreas; Avarvari, Narcis

2015-01-28

384

Electronic interactions and charge transfers of metal atoms and clusters on oxide surfaces.  

PubMed

Understanding the interaction of small metal clusters and isolated atoms with oxide surfaces is crucial in order to rationalize the properties of heterogeneous catalysts composed of sub-nanometer metal particles dispersed on an oxide support. The interaction with the oxide surface can significantly alter the original properties of the metal deposit. In particular, the occurrence and the direction of charge transfer at the metal/oxide interface determine the chemical activity of the supported catalyst. The charge transfer depends on a number of factors like the nature of the oxide (reducible or non-reducible), the surface exposed, the presence of defects, the nature of the supported metal, etc. In this article we describe the most important conceptual aspects of the electronic metal-support interaction, a phenomenon related to the direct modification of the metal nano-particle determined by the formation of chemical bonds at the interface with the oxide. For metal nano-particles with a size of about 1 nm or below these effects become dominant although difficult to identify experimentally. PMID:23287900

Pacchioni, Gianfranco

2013-02-14

385

An Integrated Professional and Transferable Skills Course for Undergraduate Chemistry Students  

ERIC Educational Resources Information Center

Upon graduation, chemistry majors often find themselves inadequately prepared for the "real world" that awaits them when they join the workplace. Some employers find chemistry graduates lacking written- and oral-communication skills, critical-thinking skills, group-work skills, as well as the ability to efficiently analyze data and retrieve…

Ashraf, S. Salman; Marzouk, Sayed A. M.; Shehadi, Ihsan A.; Murphy, Brian M.

2011-01-01

386

33 CFR 155.715 - Contents of letter of designation as a person-in-charge of the transfer of fuel oil.  

Code of Federal Regulations, 2012 CFR

...PREVENTION REGULATIONS FOR VESSELS Transfer Personnel, Procedures, Equipment...person-in-charge of the transfer of fuel oil. The letter...person-in-charge of the transfer of fuel oil and state that...formal instruction from the operator or agent of the vessel...

2012-07-01

387

33 CFR 155.715 - Contents of letter of designation as a person-in-charge of the transfer of fuel oil.  

Code of Federal Regulations, 2011 CFR

...PREVENTION REGULATIONS FOR VESSELS Transfer Personnel, Procedures, Equipment...person-in-charge of the transfer of fuel oil. The letter...person-in-charge of the transfer of fuel oil and state that...formal instruction from the operator or agent of the vessel...

2011-07-01

388

33 CFR 155.715 - Contents of letter of designation as a person-in-charge of the transfer of fuel oil.  

Code of Federal Regulations, 2013 CFR

...PREVENTION REGULATIONS FOR VESSELS Transfer Personnel, Procedures, Equipment...person-in-charge of the transfer of fuel oil. The letter...person-in-charge of the transfer of fuel oil and state that...formal instruction from the operator or agent of the vessel...

2013-07-01

389

33 CFR 155.715 - Contents of letter of designation as a person-in-charge of the transfer of fuel oil.  

Code of Federal Regulations, 2014 CFR

...PREVENTION REGULATIONS FOR VESSELS Transfer Personnel, Procedures, Equipment...person-in-charge of the transfer of fuel oil. The letter...person-in-charge of the transfer of fuel oil and state that...formal instruction from the operator or agent of the vessel...

2014-07-01

390

Unravelling the mechanism of photoinduced charge transfer processes in lead iodide perovskite solar cells  

NASA Astrophysics Data System (ADS)

Lead halide perovskites have recently been used as light absorbers in hybrid organic-inorganic solid-state solar cells, with efficiencies as high as 15% and open-circuit voltages of 1 V. However, a detailed explanation of the mechanisms of operation within this photovoltaic system is still lacking. Here, we investigate the photoinduced charge transfer processes at the surface of the perovskite using time-resolved techniques. Transient laser spectroscopy and microwave photoconductivity measurements were applied to TiO2 and Al2O3 mesoporous films impregnated with CH3NH3PbI3 perovskite and the organic hole-transporting material spiro-OMeTAD. We show that primary charge separation occurs at both junctions, with TiO2 and the hole-transporting material, simultaneously, with ultrafast electron and hole injection taking place from the photoexcited perovskite over similar timescales. Charge recombination is shown to be significantly slower on TiO2 than on Al2O3 films.

Marchioro, Arianna; Teuscher, Joël; Friedrich, Dennis; Kunst, Marinus; van de Krol, Roel; Moehl, Thomas; Grätzel, Michael; Moser, Jacques-E.

2014-03-01

391

Microgravity and Charge Transfer in the Neuronal Membrane: Implications for Computational Neurobiology  

NASA Technical Reports Server (NTRS)

Evidence from natural and artificial membranes indicates that the neural membrane is a liquid crystal. A liquid-to-gel phase transition caused by the application of superposed electromagnetic fields to the outer membrane surface releases spin-correlated electron pairs which propagate through a charge transfer complex. The propagation generates Rydberg atoms in the lipid bilayer lattice. In the present model, charge density configurations in promoted orbitals interact as cellular automata and perform computations in Hilbert space. Due to the small binding energies of promoted orbitals, their automata are highly sensitive to microgravitational perturbations. It is proposed that spacetime is classical on the Rydberg scale, but formed of contiguous moving segments, each of which displays topological equivalence. This stochasticity is reflected in randomized Riemannian tensor values. Spacetime segments interact with charge automata as components of a computational process. At the termination of the algorithm, an orbital of high probability density is embedded in a more stabilized microscopic spacetime. This state permits the opening of an ion channel and the conversion of a quantum algorithm into a macroscopic frequency code.

Wallace, Ron

1995-01-01

392

Quantum effects in energy and charge transfer in an artificial photosynthetic complex  

E-print Network

We investigate the quantum dynamics of energy and charge transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex.This complex consists of six light-harvesting chromophores and an electron-acceptor fullerene. To describe quantum effects on a femtosecond time scale, we derive the set of exact non-Markovian equations for the Heisenberg operators of this photosynthetic complex in contact with a Gaussian heat bath. With these equations we can analyze the regime of strong system-bath interactions, where reorganization energies are of the order of the intersite exciton couplings. We show that the energy of the initially-excited antenna chromophores is efficiently funneled to the porphyrin-fullerene reaction center, where a charge-separated state is set up in a few picoseconds, with a quantum yield of the order of 95%. In the single-exciton regime, with one antenna chromophore being initially excited, we observe quantum beatings of energy between two resonant antenna chromophores with a decoherence time of $\\sim$ 100 fs. We also analyze the double-exciton regime, when two porphyrin molecules involved in the reaction center are initially excited. In this regime we obtain pronounced quantum oscillations of the charge on the fullerene molecule with a decoherence time of about 20 fs (at liquid nitrogen temperatures). These results show a way to directly detect quantum effects in artificial photosynthetic systems.

Pulak Kumar Ghosh; Anatoly Yu. Smirnov; Franco Nori

2011-06-30

393

Quantum effects in energy and charge transfer in an artificial photosynthetic complex  

SciTech Connect

We investigate the quantum dynamics of energy and charge transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex. This complex consists of six light-harvesting chromophores and an electron-acceptor fullerene. To describe quantum effects on a femtosecond time scale, we derive the set of exact non-Markovian equations for the Heisenberg operators of this photosynthetic complex in contact with a Gaussian heat bath. With these equations we can analyze the regime of strong system-bath interactions, where reorganization energies are of the order of the intersite exciton couplings. We show that the energy of the initially excited antenna chromophores is efficiently funneled to the porphyrin-fullerene reaction center, where a charge-separated state is set up in a few picoseconds, with a quantum yield of the order of 95%. In the single-exciton regime, with one antenna chromophore being initially excited, we observe quantum beatings of energy between two resonant antenna chromophores with a decoherence time of {approx}100 fs. We also analyze the double-exciton regime, when two porphyrin molecules involved in the reaction center are initially excited. In this regime we obtain pronounced quantum oscillations of the charge on the fullerene molecule with a decoherence time of about 20 fs (at liquid nitrogen temperatures). These results show a way to directly detect quantum effects in artificial photosynthetic systems.

Ghosh, Pulak Kumar [Advanced Science Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Smirnov, Anatoly Yu.; Nori, Franco [Advanced Science Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, Michigan 41109-1040 (United States)

2011-06-28

394

Quantum effects in energy and charge transfer in an artificial photosynthetic complex  

NASA Astrophysics Data System (ADS)

We investigate the quantum dynamics of energy and charge transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex. This complex consists of six light-harvesting chromophores and an electron-acceptor fullerene. To describe quantum effects on a femtosecond time scale, we derive the set of exact non-Markovian equations for the Heisenberg operators of this photosynthetic complex in contact with a Gaussian heat bath. With these equations we can analyze the regime of strong system-bath interactions, where reorganization energies are of the order of the intersite exciton couplings. We show that the energy of the initially excited antenna chromophores is efficiently funneled to the porphyrin-fullerene reaction center, where a charge-separated state is set up in a few picoseconds, with a quantum yield of the order of 95%. In the single-exciton regime, with one antenna chromophore being initially excited, we observe quantum beatings of energy between two resonant antenna chromophores with a decoherence time of ˜100 fs. We also analyze the double-exciton regime, when two porphyrin molecules involved in the reaction center are initially excited. In this regime we obtain pronounced quantum oscillations of the charge on the fullerene molecule with a decoherence time of about 20 fs (at liquid nitrogen temperatures). These results show a way to directly detect quantum effects in artificial photosynthetic systems.

Ghosh, Pulak Kumar; Smirnov, Anatoly Yu.; Nori, Franco

2011-06-01

395

Modeling the electrical conduction in DNA nanowires: Charge transfer and lattice fluctuation theories  

NASA Astrophysics Data System (ADS)

An analytical approach is proposed for the investigation of the conductivity properties of DNA. The charge mobility of DNA is studied based on an extended Peyrard-Bishop-Holstein model when the charge carrier is also subjected to an external electrical field. We have obtained the values of some of the system parameters, such as the electron-lattice coupling constant, by using the mean Lyapunov exponent method. On the other hand, the electrical current operator is calculated directly from the lattice operators. Also, we have studied Landauer resistance behavior with respect to the external field, which could serve as the interface between chaos theory tools and electronic concepts. We have examined the effect of two types of electrical fields (dc and ac) and variation of the field frequency on the current flowing through DNA. A study of the current-voltage (I -V ) characteristic diagram reveals regions with a (quasi-)Ohmic property and other regions with negative differential resistance (NDR). NDR is a phenomenon that has been observed experimentally in DNA at room temperature. We have tried to study the affected agents in charge transfer phenomena in DNA to better design nanostructures.

Behnia, S.; Fathizadeh, S.

2015-02-01

396

Radiation-induced charge transfer inefficiency in charge-coupled devices: Sentinel-4 CCD pre-development as a case study  

NASA Astrophysics Data System (ADS)

Energetic particles in space damage electronic components, and in particular affect the capability of Charge-Coupled Devices (CCD) to transfer photo-generated charge packets to the output node. If not properly accounted for either during the instrument design process or in the mission data processing pipeline, radiation-induced Charge Transfer Inefficiency (CTI) causes image distortion, decreases the signal-to-noise ratio, and ultimately leads to bias in the measurement carried out. CTI is a well-identified error budget contributor for mission operating in the photon-starving regime like space telescopes dedicated to Astronomy, but is less studied in the context of Earth Observation missions. We present a study conducted during the Sentinel-4/UVN CCD pre-development to provide a first assessment of the CTI effects on the Sentinel-4 measurements.

Prod'homme, T.; Belloir, J.-M.; Weber, H.; Bazalgette Courrèges-Lacoste, G.; Meynart, R.; Nowicki-Bringuier, Y.-R.; Caron, J.; Levillain, Y.; Woffinden, C.; Lord, B.; Mackie, R.

2014-10-01

397

Mechanism of redox-active ligand-assisted nitrene-group transfer in a Zr(IV) complex: direct ligand-to-ligand charge transfer preferred.  

PubMed

The mechanism of the nitrene-group transfer reaction from an organic azide to isonitrile catalyzed by a Zr(IV) d(0) complex carrying a redox-active ligand was studied by using quantum chemical molecular-modeling methods. The key step of the reaction involves the two-electron reduction of the azide moiety to release dinitrogen and provide the nitrene fragment, which is subsequently transferred to the isonitrile substrate. The reducing equivalents are supplied by the redox-active bis(2-iso-propylamido-4-methoxyphenyl)-amide ligand. The main focus of this work is on the mechanism of this redox reaction, in particular, two plausible mechanistic scenarios are considered: 1)?the metal center may actively participate in the electron-transfer process by first recruiting the electrons from the redox-active ligand and becoming formally reduced in the process, followed by a classical metal-based reduction of the azide reactant. 2)?Alternatively, a non-classical, direct ligand-to-ligand charge-transfer process can be envisioned, in which no appreciable amount of electron density is accumulated at the metal center during the course of the reaction. Our calculations indicate that the non-classical ligand-to-ligand charge-transfer mechanism is much more favorable energetically. Utilizing a series of carefully constructed putative intermediates, both mechanistic scenarios were compared and contrasted to rationalize the preference for ligand-to-ligand charge-transfer mechanism. PMID:25470137

Ghosh, Soumya; Baik, Mu-Hyun

2015-01-19

398

Ground- and excited-state dipole moments of some nitroaromatics: Evidence for extensive charge transfer in twisted nitrobenzene systems  

NASA Astrophysics Data System (ADS)

Electro-optical absorption measurements have been made on four model nitroaromatics to determine the effect of twisting of the donor-acceptor single bond on the charge-transfer characteristics in the Franck-Condon excited states. Observed ground- and excited-state dipole moments of nitromesitylene, which has been treated experimentally as the nonplanar analogue of planar nitrobenzene, indicate that electronic excitation of twisted nitrobenzene results in a nearly full unit charge transfer from donor (benzene) to the acceptor (nitro) group (??=18.3 D). On the other hand, in planar nitrobenzene and nitronaphthalene the charge transfer is more delocalized over the whole molecular skeleton, resulting in normal changes in dipole moment (??=5-10 D). In the analogous anthracene system, i.e., 9-nitroanthracene, the charge transfer upon electronic excitation is extremely low (??=1.7 D), which is reflected by its very small change in the dipole moment. Therefore, it is evident that the charge-transfer processes in the twisted molecules are quite different for different aromatic ring systems. Simple molecular-orbital calculations satisfactorily explain the reason for such differences on the basis of their highest occupied molecular-orbital (HOMO) and lowest unoccupied molecular-orbital (LUMO) characteristics. Transition moment directions have also been obtained experimentally and compared with the theoretically predicted directions based on the symmetry properties of the HOMO and LUMO. Agreement is found in all cases studied.

Sinha, Hemant K.; Yates, Keith

1990-11-01

399

Magneto-Dielectric Effects Induced by Optically-Generated Intermolecular Charge-Transfer States in Organic Semiconducting Materials  

PubMed Central

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 experimental evidence indicate that the singlets and triplets in charge-transfer states have stronger and weaker electrical polarizations, respectively. Therefore, the observed magneto-dielectric effect can be attributed to magnetically-dependent singlet/triplet ratio in intermolecular charge-transfer states. In principle, a magneto-dielectric effect can be generated through two different channels based on magneto-polarization and magneto-current effects when the singlet/triplet ratio in intermolecular charge-transfer states is changed by a magnetic field. We find, from the simulation of dielectric effects, that magneto-polarization and magneto-current effects play primary and secondary roles in the generation of magneto-dielectric effect. PMID:24084983

Zang, Huidong; Yan, Liang; Li, Mingxing; He, Lei; Gai, Zheng; Ivanov, Ilia; Wang, Min; Chiang, Long; Urbas, Augustine; Hu, Bin

2013-01-01

400

Mechanism of charge transfer/disproportionation in LnCu3Fe4O12 (Ln = lanthanides)  

NASA Astrophysics Data System (ADS)

The Fe-Cu intersite charge transfer and Fe charge disproportionation are interesting phenomena observed in some LnCu3Fe4O12 (Ln = lanthanides) compounds containing light and heavy Ln atoms, respectively. We show that a change in the spin state is responsible for the intersite charge transfer in the light Ln compounds. At the high-spin state, such systems prefer an unusual Cu d8 configuration, whereas at the low-spin state they retreat to the normal Cu d9 configuration through a charge transfer from Fe to the Cu 3dxy orbital. We find that the strength of the crystal-field splitting and the relative energy ordering between Cu 3dxy and Fe 3d states are the key parameters determining the intersite charge transfer (charge disproportionation) in light (heavy) Ln compounds. It is further proposed that the size of Ln affects the on-site interaction strength of Cu 3d states, leading to a strong modification of the Cu L3-edge spectrum, as observed by the x-ray-absorption spectroscopy.

Rezaei, N.; Hansmann, P.; Bahramy, M. S.; Arita, R.

2014-03-01

401

Tunneling in Chromatium chromatophores: detection of a Hopfield charge-transfer band  

SciTech Connect

A weak charge-transfer band has been observed in the cytochrome c-P/sub 870/ electron-transfer reaction in Chromatium vinosum chromatophores at 10 K and at 85 K. First, the intermediate acceptor, I, was trapped in the reduced state by lowering the redox potential at room temperature, then illuminating with white light at low temperature for 20 min. Next, illumination by broadband infrared (1-3 ..mu..m, 6.5 kW/m/sup 2/) for 4 hr at 10 K decreased the I/sup -/ electron spin resonance signal by 30%. One-hour infrared illumination at 85 K decreased the cytochrome c Soret band shift by 10%. The effect of infrared was to promote the system from the ground vibrational state with the electron on P/sub 870/ to an excited vibrational state with the electron on cytochrome c. The absorption band peak is near 2 ..mu..m, and the integrated cross section is approx. =6 x 10/sup -3/ eV.M/sup -1/.cm/sup -1/. These values are consistent with small (0.02 nm) nuclear motion and with electron-transfer rates measured in the dark. 23 references, 3 figures.

Goldstein, R.F.; Bearden, A.

1984-01-01

402

Regressed relations for forced convection heat transfer in a direct injection stratified charge rotary engine  

NASA Technical Reports Server (NTRS)

Currently, the heat transfer equation used in the rotary combustion engine (RCE) simulation model is taken from piston engine studies. These relations have been empirically developed by the experimental input coming from piston engines whose geometry differs considerably from that of the RCE. The objective of this work was to derive equations to estimate heat transfer coefficients in the combustion chamber of an RCE. This was accomplished by making detailed temperature and pressure measurements in a direct injection stratified charge (DISC) RCE under a range of conditions. For each specific measurement point, the local gas velocity was assumed equal to the local rotor tip speed. Local physical properties of the fluids were then calculated. Two types of correlation equations were derived and are described in this paper. The first correlation expresses the Nusselt number as a function of the Prandtl number, Reynolds number, and characteristic temperature ratio; the second correlation expresses the forced convection heat transfer coefficient as a function of fluid temperature, pressure and velocity.

Lee, Chi M.; Schock, Harold J.

1988-01-01

403

Charge transfer structure-reactivity dependence of fullerene-single-walled carbon nanotube heterojunctions.  

PubMed

Charge transfer at the interface between single-walled carbon nanotubes (SWCNTs) of distinct chiral vectors and fullerenes of various molecular weights is of interest both fundamentally and because of its importance in emerging photovoltaic and optoelectronic devices. One approach for generating isolated, discretized fullerene-SWCNT heterojunctions for spectroscopic investigation is to form an amphiphile, which is able to disperse the latter at the single-SWCNT level in aqueous solution. Herein, we synthesize a series of methanofullerene amphiphiles, including derivatives of C60, C70, and C84, and investigated their electron transfer with SWCNT of specific chirality, generating a structure-reactivity relationship. In the cases of two fullerene derivatives, lipid-C61-polyethylene glycol (PEG) and lipid-C71-PEG, band gap dependent, incomplete quenching was observed across all SWCNT species, indicating that the driving force for electron transfer is small. This is further supported by a variant of Marcus theory, which predicts that the energy offsets between the nanotube conduction bands and the C61 and C71 LUMO levels are less than the exciton binding energy in SWCNT. In contrast, upon interfacing nanotubes with C85 methanofullerene, a complete quenching of all semiconducting SWCNT is observed. This enhancement in quenching efficiency is consistent with the deeper LUMO level of C85 methanofullerene in comparison with the smaller fullerene adducts, and suggests its promise as for SWCNT-fullerene heterojunctions. PMID:23848070

Hilmer, Andrew J; Tvrdy, Kevin; Zhang, Jingqing; Strano, Michael S

2013-08-14

404

The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions  

NASA Astrophysics Data System (ADS)

Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9?-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:-[6,6]-phenyl-C61-butyric acid methyl ester (PCDTBT:PC61BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix.

Krinichnyi, V. I.; Yudanova, E. I.; Denisov, N. N.

2014-07-01

405

The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions.  

PubMed

Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9?-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:-[6,6]-phenyl-C61-butyric acid methyl ester (PCDTBT:PC61BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix. PMID:25084955

Krinichnyi, V I; Yudanova, E I; Denisov, N N

2014-07-28

406

Charge efficiency of Ni/H2 cells during transfer orbit of Telstar 4 satellites  

NASA Technical Reports Server (NTRS)

The TELSTAR 4 communication satellites being manufactured by Martin Marietta Astro Space (Astro Space) for AT&T are three axis stabilized spacecraft scheduled to be launched on expendable vehicles such as the Atlas or Ariane rockets. Typically, these spacecraft consist of a box that holds the electronics and supports the antenna reflectors and the solar array wings. The wings and reflectors are folded against the sides of the box during launch and the spacecraft is spun for attitude control in that phase; they are then deployed after achieving the final orbit. The launch phase and transfer orbits required to achieve the final geosynchronous orbit typically take 4 to 5 days during which time the power required for command, telemetry, attitude control, heaters, etc., is provided by two 50 AH nickel hydrogen batteries augmented by the exposed outboard solar panels. In the past, this situation has presented no problem since there was a considerable excess of power available from the array. In the case of large high powered spacecraft such as TELSTAR 4, however, the design power levels in transfer orbit approach the time-averaged power available from the exposed surface area of the solar arrays, resulting in a very tight power margin. To compound the difficulty, the array output of the spinning spacecraft in transfer orbit is shaped like a full wave rectified sine function and provides very low charging rates to the batteries during portions of the rotation. In view of the typically low charging efficiency of alkaline nickel batteries at low rates, it was decided to measure the efficiency during a simulation of the TELSTAR 4 conditions at the expected power levels and temperatures on three nickel hydrogen cells of similar design. The unique feature of nickel hydrogen cells that makes the continuous measurement of efficiency possible is that hydrogen is one of the active materials and thus, cell pressure is a direct measure of the state of charge or available capacity. The pressure is measured with a calibrated strain gage mounted on the outside of the pressurized cell.

Fang, W. C.; Maurer, Dean W.; Vyas, B.; Thomas, M. N.

1994-01-01

407

Demystifying Introductory Chemistry. Part 3: Ionization Energies, Electronegativity, Polar Bonds, and Partial Charges.  

ERIC Educational Resources Information Center

Shows how ionization energies provide a convenient method for obtaining electronegativity values that is simpler than the conventional methods. Demonstrates how approximate atomic charges can be calculated for polar molecules and how this method of determining electronegativities may lead to deeper insights than are typically possible for the…

Spencer, James; And Others

1996-01-01

408

Metal-to-metal charge transfer transitions - Interpretation of visible-region spectra of the moon and lunar materials  

NASA Technical Reports Server (NTRS)

Prominent bands in the spectral profiles of Fe-Ti phases in lunar samples have been attributed to charge-transfer transitions between Fe and Ti cations, and a model is presented for calculating charge transfer energies from energy levels computed by the SCF-X(alpha) scattered wave molecular orbital method for isolated MO6 octahedral coordination clusters containing Fe(2+), Fe(3+), Ti(3+), and Ti(4+) cations. The calculated charge transfer energy for the Fe(2+) to Ti(4+) transition correlates well with a measured spectral feature around 0.6 micron in ilmenite, and, since ilmenite is a major constituent of mare basalts and dark-mantling material, the observed darkness and blueness of the regolith in lunar black spots is attributed primarily to this transition. The Ti(3+) to Ti(4+) transition is thought to contribute to some phases.

Loeffler, B. M.; Burns, R. G.; Tossell, J. A.

1975-01-01

409

The low-energy, charge-transfer excited states of 4-amino-4-prime-nitrodiphenyl sulfide  

NASA Technical Reports Server (NTRS)

Absorption and emission spectra of 4-amino-4-prime-nitrodiphenyl sulfide in polar and nonpolar solvents were used to characterize and assign the low-energy excited states of the molecule. Fluorescence-excitation anisotropy spectra and fluorescence quantum yields were also used to characterize the photophysics of these states. The lowest-energy fluorescent singlet state was determined to be an intramolecular charge transfer (ICT) state involving transfer of a full electron charge from the amino to the nitro group yielding a dipole moment of about 50 D. A low-energy, intense absorption band is assigned as a transition to a different ICT state involving a partial electron charge transfer from sulfur to the nitro group.

O'Connor, Donald B.; Scott, Gary W.; Tran, Kim; Coulter, Daniel R.; Miskowski, Vincent M.; Stiegman, Albert E.; Wnek, Gary E.

1992-01-01

410

Are hot charge transfer states the primary cause of efficient free-charge generation in polymer:fullerene organic photovoltaic devices? A kinetic Monte Carlo study.  

PubMed

Kinetic Monte Carlo simulations are used to examine the effect of high-energy, 'hot' delocalised charge transfer (HCT) states for donor:acceptor and mixed:aggregate blends, the latter relating to polymer:fullerene photovoltaic devices. Increased fullerene aggregation is shown to enhance charge generation and short-circuit device current - largely due to the increased production of HCT states at the aggregate interface. However, the instances where HCT states are predicted to give internal quantum efficiencies in the region of 50% do not correspond to HCT delocalisation or electron mobility measured in experiments. These data therefore suggest that HCT states are not the primary cause of high quantum efficiencies in some polymer:fullerene OPVs. Instead it is argued that HCT states are responsible for the fast charge generation seen in spectroscopy, but that regional variation in energy levels are the cause of long-term, efficient free-charge generation. PMID:24943036

Jones, Matthew L; Dyer, Reesha; Clarke, Nigel; Groves, Chris

2014-10-14

411

Chronoamperometry at micropipet electrodes for determination of diffusion coefficients and transferred charges at liquid/liquid interfaces.  

PubMed

Chronoamperometry was carried out at liquid/liquid interfaces supported at the tip of micropipet electrodes for direct determination of the diffusion coefficient of a species in the outer solution. The diffusion coefficient was used for subsequent determination of the transferred charges per species from the diffusion-limited steady-state current. A large tip resistance of the micropipets causes prolonged charging current so that the faradic current can be measured accurately only at a long-time regime (typically t > 5 ms). At the same time, the long-time current response at the interfaces surrounded by a thin glass wall of the pipets is enhanced by diffusion of the species from behind the pipet tip. Therefore, numerical simulations of the long-time chronoamperometric response were carried out using the finite element method for accurate determination of diffusion coefficients. Validity of the simulation results was confirmed by studying simple transfer of tetraethylammonium ion. The technique was applied for transfer/adsorption reactions of the natural polypeptide protamine and also for Ca2+ and Mg2+ transfers facilitated by ionophore ETH 129. With the diffusion coefficient of protamine determined to be (1.2 +/- 0.1) x 10(-6) cm(2)/s, the ionic charge transferred by each protamine molecule was obtained as +20 +/- 1, which is close to the excess positive charge of protamine. Also, the diffusion coefficient of ETH 129 was determined to demonstrate that each ionophore molecule transfers +0.67 and +1 charge per Ca2+ and Mg2+ transfer, respectively, which corresponds to formation of 1:3 and 1:2 complexes with the respective ions. PMID:15362923

Yuan, Yi; Wang, Lei; Amemiya, Shigeru

2004-09-15

412

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

NASA Astrophysics Data System (ADS)

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.

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

413

An Ultra-Thin Molecular Superconductor Made from Charge Transfer Complexes  

NASA Astrophysics Data System (ADS)

A class of charge transfer molecular systems having a D2A arrangement (D = donor, A = accepter) exhibit superconductivity in the bulk and are often termed ``unusual superconductors'' based on the different nature of their superconducting states as compared to convention BCS superconductors. In this study we have formed an ultra-thin (BETS)2-GaCl4 molecular superconductor consisting of a single sheet of layered molecules composed of individual GaCl4 sandwiched between the chains of a double domino stacked BETS on a Ag(111) surface. Amazingly, the superconducting gap can still be detected in such an ultra-thin molecular layer, and the shape of the gap reveals a d-wave pairing symmetry. Moreover, real space STM spectroscopic images provide direct evidence of the superconducting site as the BETS chains. In stark contrast to the high Tc superconductors, the spectroscopic maps clearly display nanoscale electronic order indicating robust superconducting properties at this extreme spatial limit..

Clark, Kendal; Hassenien, A.; Khan, S.; Braun, K.-F.; Tanaka, H.; Hla, S.-W.

2010-03-01

414

Use of charge-transfer complex formation for the spectrophotometric determination of nortriptyline.  

PubMed

Three simple and selective methods are proposed for the determination of nortriptyline hydrochloride in bulk form and in tablets. The first two methods are based on the formation of charge-transfer complexes between the drug base as a n-donor and quinhydrone or p-chloranil as pi-acceptor. The products exhibit absorption maxima at 497 and 560 nm in acetonitrile for quinhydrone and p-chloranil, respectively. The third method is based on the interaction of N-alkylvinylamine formed from the condensation of the free secondary amine group and acetaldehyde with p-chloranil to give a vinylamino substituted quinone. The coloured product exhibits an absorption maximum at 650 nm in dioxane. All variables were studied to optimize reaction conditions. Beer's law was obeyed and the relative standard deviations were found to be less than 1.5%. The methods have been applied to the analysis of nortriptyline hydrochloride in the bulk drug and in tablets. PMID:11204939

Attia, F M

2000-01-01

415

Identifying the magnetoconductance responses by the induced charge transfer complex states in pentacene-based diodes  

NASA Astrophysics Data System (ADS)

We investigate the magnetoconductance (MC) responses in photocurrent, unipolar injection, and bipolar injection regimes in pentacene-based diodes. Both photocurrent and bipolar injection contributed MC responses show large difference in MC line shape, which are attributed to triplet-polaron interaction modulated by the magnetic field dependent singlet fission and the intersystem crossing of the polaron pair, respectively. By blending 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane into pentacene, all the MC responses are suppressed but the MC response at unipolar injection regime is enhanced, which is attributed to the induced charge transfer complex states (CT complex states). This work identify the MC responses between single carrier contributed MC and exciton related MC by the induced CT complex states.

Huang, Wei-Shun; Lee, Tsung-Hsun; Guo, Tzung-Fang; Huang, J. C. A.; Wen, Ten-Chin

2012-07-01

416

II-utility of fluorine-19 NMR spectroscopy for investigation of charge transfer complexes  

NASA Astrophysics Data System (ADS)

Fluorine and proton chemical shifts for the griseofulvin oxime—fluoranil complex are reported. 1H, 19F-NMR spectra prove the course of the charge transfer complex formation. Due to redistribution of the electron density, the protons of the donor are slightly shifted towards a lower field where deshielding has occurred. Signals of the 19F-NMR spectra of fluoranil complex showed a positive value for the upfield shift of the fluorine resonance due to a shielding effect. Fluoranil (tetrafluoro-2,5-cyclohexadiene-1,4-dione) has a high electron-accepting ability with respect to the functional groups containing heteroatoms. The complete qualitative and quantitative chemical characterization of the resulting complex has been studied.

El-Adl, Sobhy

1994-11-01

417

Effect of. gamma. -cyclodextrin on the intramolecular charge transfer processes in aminocoumarin laser dyes  

SciTech Connect

Steady-state and time-resolved studies on the emission properties of three 7-(diethylamino)coumarin laser dyes (I-III) in aqueous {gamma}-cyclodextrin ({gamma}-CD) solutions are reported. On addition of {gamma}-CD, fluorescence maxima of all the three dyes shift to higher energy, with a huge enhancement of the yield of intramolecular charge transfer (ICT) emission for the flexible ones (I and II) and a very slight enhancement for the rigid analogue III. The results are explained in terms of the concept of polarity-dependent twisted ICT rates. It is proposed that twisted ICT, the main nonradiative process in the excited ICT states of these dyes, is severely restricted inside the {gamma}-cyclodextrin cavity because of the reduced polarity. This is responsible for the enhancement of fluorescence from the ICT state.

Nag, A.; Chakrabarty, T.; Bhattacharyya, K. (Indian Association for the cultivation of Science, Calcutta (India))

1990-05-17

418

Charge-induced distortion and stabilization of surface transfer doped porphyrin films  

SciTech Connect

The interaction between zinc-tetraphenylporphyrin (ZnTPP) and fullerenes (C{sub 60} and C{sub 60}F{sub 48}) are studied using ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM). Low temperature STM reveals highly ordered ZnTPP monolayers on Au(111). In contrast to C{sub 60}, a submonolayer coverage of C{sub 60}F{sub 48} results in long-range disorder of the underlying single ZnTPP layer and distortion of individual ZnTPP molecules. This is induced by substantial charge transfer at the organic-organic interface, revealed by the interface energetics from UPS. However, a second layer of ZnTPP prevents C{sub 60}F{sub 48} guests from breaking the self-assembled porphyrin template. This finding is important for understanding the growth behaviour of “bottom-up” functional nanostructures involving strong donor-acceptor heterojunctions in molecular electronics.

Smets, Y.; Stark, C. B.; Wright, C. A.; Pakes, C. I. [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia)] [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia); Lach, S.; Schmitt, F.; Ziegler, C. [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern (Germany)] [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern (Germany); Wanke, M. [Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz (Germany)] [Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz (Germany); Ley, L. [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia) [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia); Institut für Technische Physik, Universität Erlangen-Nürnberg, 91058 Erlangen (Germany)

2013-07-28

419

Spectrophotometric determination of bisoprolol in pharmaceutical preparations by charge transfer reactions  

NASA Astrophysics Data System (ADS)

A simple, rapid and sensitive method for the spectrophotometric determination, of bisoprolol was developed. The proposed methods were based on the charge-transfer reactions of bisoprolol, as n-electron donor, with 7,7,8,8-tetracyanoqumodimethane (TCNQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as ?-acceptors to give highly colored complexes. The proposed methods were validated according to the ICH guidelines with respect to linearity, limit of detection, limit of quantification, accuracy, precision, recovery and specificity. Beer's law is obeyed over the concentration ranges of 10-60 and 10-80 ?g/mL bisoprolol with TCNQ and DDQ, respectively. The proposed methods were successfully applied to the assay of bisoprolol in pharmaceutical preparations.

Ulu, Sevgi Tatar; Kel, Elif

2012-06-01

420

Topological phase transition and gate-controlled charge transfer in minimal topological-spin qubit circuit  

NASA Astrophysics Data System (ADS)

We propose a minimal topological-spin qubit circuit to investigate the non-Abelian rotations within the degenerate ground-state manifold, as well as the topological phase transition and charge transfer. From a quantum dot, the state of the Majorana system can be read out. Along with the splitting of the degenerate ground-state manifold of a topological qubit, a topological phase transition is observed, showing the existence of a Majorana fermion. By choosing the phase difference across the dots, the non-Abelian rotations and the required energetically degenerate state in the qubit can be achieved, which results in universal quantum computation. Moreover, on the basis of the measurement of the electron in quantum dots and topological qubit, this demonstrates that topologically protected tunnel braids between dots and MBSs are critical to non-Abelian rotations.

Wang, Zhen-Hua; Kuang, Xiao-Yu; Zhong, Ming-Min; Yang, Zai-Xiu; Li, Hui

2014-06-01

421

Synthesis, characterization and biological studies of a charge transfer complex: 2-Aminopyridinium-4-methylbenzenesulfonate.  

PubMed

A single crystal charge transfer (CT) complex, 2-aminopyridinium-4-methylbenzenesulfonate (APTS) was synthesized and recrystallized by slow solvent evaporation solution growth method at room temperature. The complex has been characterized with the elemental analysis, UV-visible, infrared (IR), (1)H and (13)C nuclear magnetic resonance (NMR) spectra. Thermogravimetric (TG) and differential thermal analysis (DTA) were reported the thermal behaviour of the complex. Single crystal XRD studies showed that the orthorhombic nature of the crystal with space group Pbca. The biological activities of CT complex, such as DNA binding and antioxidant activity has been carried out. The results indicated that the compound could interact with DNA through intercalation and show significant capacity of scavenging with 2,2-diphenyl-2-picryl-hydrazyl (DPPH). PMID:25796016

Vadivelan, Ganesan; Saravanabhavan, Munusamy; Murugesan, Venkatesan; Sekar, Marimuthu

2015-06-15

422

Real-time cumulant approach for charge-transfer satellites in x-ray photoemission spectra  

NASA Astrophysics Data System (ADS)

X-ray photoemission spectra generally exhibit satellite features beyond the main peak due to many-body excitations. However, the satellites associated with charge-transfer excitations in correlated materials have proved difficult to calculate from first principles and their interpretation has been controversial. Here we show that these satellites can be attributed to local density fluctuations in response to a suddenly created core hole. Our approach is based on a cumulant representation of the core-hole Green's function with a real-time, time-dependent density functional theory calculation of the cumulant. This approach includes effects that cannot be accounted for by cluster methods and yields a direct real-space, real-time interpretation. Illustrative results for TiO2 and NiO are in good agreement with XPS experiment.

Kas, J. J.; Vila, F. D.; Rehr, J. J.; Chambers, S. A.

2015-03-01

423

Enhanced nonlinear optical response of an endohedral metallofullerene through metal-to-cage charge transfer  

NASA Astrophysics Data System (ADS)

A new mechanism for increasing the third-order nonlinear optical susceptibility, ?(3), is described for endohedral metallofullerenes. A two to three orders of magnitude increase in the nonlinear response is reported for degenerate four-wave mixing experiments conducted with solutions of Er2@C82 (isomer III) relative to empty-cage fullerenes. A value of -8.7×10-32esu is found for the molecular susceptibility, ?xyyx, of Er2@C82 compared to previously reported values of ?xxxx=3×10-34 esu and ?xyyx=4×10-35 esu for C60. The results confirm the importance of the metal-to-cage charge-transfer mechanism for enhancing the nonlinear optical response in endohedral metallofullerenes.

Heflin, J. R.; Marciu, D.; Figura, C.; Wang, S.; Burbank, P.; Stevenson, S.; Dorn, H. C.

1998-06-01

424

Optical charge transfer for the dope in GaAs  

SciTech Connect

It is concluded that the chromium dope is amphoteric in behavior on the basis of the spectra, kinetics, and lux-ampere characteristics of the absorption and photoconductivity induced by 1.15-um IR laser radiation in high-resistance specimens of GaAs. It is assumed that the additional IR illumination produces optical charge transfer in the chromium in accordance with Cr/sup 3 +/3d/sup 3/ + h..nu.. ..-->.. Cr/sup 2 +/3d/sup 4/ + Cr/sup 4 +/3d/sup 2/. The photoneutralization of the Cr/sup 4 +/3d/sup 2/ centers is responsible for additional optical-absorption and photoconductivity bands appearing in the long-wave region. The kinetic equations for these centers are solved, which describes the experimental results satisfactorily. It is suggested that chromium may compensate not only shallow donors in GaAs but also shallow acceptors.

Vakulenko, O.V.; Skirda, A.S.; Skryshevskii, V.A.

1984-05-01

425

Symmetric charge-transfer cross sections of IIIa rare-earth-metal elements  

SciTech Connect

Symmetric charge-transfer cross sections of IIIa rare-earth-metal elements (Sc, Y, and Gd) in the impact energy range of 30 to 1000 eV were measured for the first time. The experiments were performed with a crossed-beam apparatus that featured primary ion production by photoionization with a tunable dye laser. Comparing the cross sections of IIIa rare-earth-metal elements ({sigma}{sub Sc}, {sigma}{sub Y}, and {sigma}{sub Gd}) with those of alkali metals or helium {sigma}{sub 0}, we found that {sigma}{sub 0{approx_equal}{sigma}Sc}<{sigma}{sub Y}<{sigma}{sub Gd{approx_equal}}2{sigma}{sub 0}at an impact energy of 1000 eV.

Hashida, Masaki; Sakabe, Shuji; Izawa, Yasukazu [ARCBS, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan) and Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8502 (Japan); Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871 (Japan) and Institute for Laser Technology, 2-6 Yamadaoka, Suita, Osaka 565-0871 (Japan)

2011-03-15

426

Spectroscopic detection of ozone-olefin charge-transfer complexes in cryogenic matrices  

SciTech Connect

When ozone-olefin mixtures are codeposited in argon or krypton matrices, broad intense visible-UV absorptions appear that are clearly due to the long-sought ozone-olefin charge-transfer (C-T) complexes. With olefins tetramethylethylene, trimethylethylene, cis- and trans-2-butene, isobutylene, and propene, the maximum absorptions appear, respectively, at 500, 388, 400, 407, 388, and 345 nm. As is usual for C-T absorptions, these wavelengths provide values of {upsilon}{sub max}(C-T) that correlate with the olefin ionization potentials. As the matrix temperature is raised, ozonolysis begins; kinetic measurements give activation energies of 1.0 {plus minus} 0.4 kcal/mol for the krypton matrix reaction between ozone and cis- or trans-2-butene.

Singmaster, K.A. (San Jose State Univ., CA (USA)); Pimentel, G.C. (Univ of California, Berkeley (USA))

1990-06-28

427

Field and chirality effects on electrochemical charge transfer rates: spin dependent electrochemistry.  

PubMed

This work examines whether electrochemical redox reactions are sensitive to the electron spin orientation by examining the effects of magnetic field and molecular chirality on the charge transfer process. The working electrode is either a ferromagnetic nickel film or a nickel film that is coated with an ultrathin (5-30 nm) gold overlayer. The electrode is coated with a self-assembled monolayer that immobilizes a redox couple containing chiral molecular units, either the redox active dye toluidine blue O with a chiral cysteine linking unit or cytochrome c. By varying the direction of magnetization of the nickel, toward or away from the adsorbed layer, we demonstrate that the electrochemical current depends on the orientation of the electrons' spin. In the case of cytochrome c, the spin selectivity of the reduction is extremely high, namely, the reduction occurs mainly with electrons having their spin-aligned antiparallel to their velocity. PMID:25752750

Mondal, Prakash Chandra; Fontanesi, Claudio; Waldeck, David H; Naaman, Ron

2015-03-24

428

The exact forces on classical nuclei in non-adiabatic charge transfer  

NASA Astrophysics Data System (ADS)

The decomposition of electronic and nuclear motion presented in Abedi et al. [Phys. Rev. Lett. 105, 123002 (2010)] yields a time-dependent potential that drives the nuclear motion and fully accounts for the coupling to the electronic subsystem. Here, we show that propagation of an ensemble of independent classical nuclear trajectories on this exact potential yields dynamics that are essentially indistinguishable from the exact quantum dynamics for a model non-adiabatic charge transfer problem. We point out the importance of step and bump features in the exact potential that are critical in obtaining the correct splitting of the quasiclassical nuclear wave packet in space after it passes through an avoided crossing between two Born-Oppenheimer surfaces and analyze their structure. Finally, an analysis of the exact potentials in the context of trajectory surface hopping is presented, including preliminary investigations of velocity-adjustment and the force-induced decoherence effect.

Agostini, Federica; Abedi, Ali; Suzuki, Yasumitsu; Min, Seung Kyu; Maitra, Neepa T.; Gross, E. K. U.

2015-02-01

429

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

PubMed

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. PMID:25524825

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

2014-01-01

430

Charge transfer in graphene oxide-dye system for photonic applications  

SciTech Connect

The fluorescence of a standard dye Rhodamine 6G (R6G) in solution decreases on addition of reduced graphene oxide (rGO). The absorption spectra and lifetime measurements confirm that no excited-state but a ground-state complex formation is responsible for this effect. For silver decorated rGO (Ag-rGO), the quenching efficiency and ground state complex formation process is small. Z-scan measurements have been done to study the optical nonlinearity at 532 nm under ps time scale. Remarkable reduction in the saturable absorption (SA) effect of R6G indicates no nonlinear contribution from the ground state complex. The results have been explained with varying charge transfer rates and non-fluorescence nature of the complex.

Bongu, Sudhakara Reddy, E-mail: bisht@iitm.ac.in; Bisht, Prem B., E-mail: bisht@iitm.ac.in [Department of Physics, Indian Institute of Technology Madras, Chennai, 600036 (India); Thu, Tran V.; Sandhu, Adarsh [EIIRIS, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku, Toyohashi 441-8580 (Japan)

2014-02-20

431

Charge Transfer Between Ground-State Si(3+) and He at Electron-Volt Energies  

NASA Technical Reports Server (NTRS)

The charge-transfer rate coefficient for the reaction Si(3+)(3s(sup 2)S) + He yields products is measured by means of a combined technique of laser ablation and ion storage. A cylindrical radio-frequency ion trap was used to store Si(3+) ions produced by laser ablation of solid silicon targets. The rate coefficient of the reaction was derived from the decay rate of the ion signal. The measured rate coefficient is 6.27(exp +0.68)(sub -0.52) x 10(exp -10)cu cm/s at T(sub equiv) = 3.9 x 10(exp 3)K. This value is about 30% higher than the Landau-Zener calculation of Butler and Dalgarno and is larger by about a factor of 3 than the recent full quantal calculation of Honvault et al.

Fang, Z.; Kwong, Victor H. S.

1997-01-01

432

The exact forces on classical nuclei in non-adiabatic charge transfer  

E-print Network

The decomposition of electronic and nuclear motion presented in~[A. Abedi, N. T. Maitra, and E. K. U. Gross, Phys. Rev. Lett. 105, 123002 (2010)] yields a time-dependent potential that drives the nuclear motion and fully accounts for the coupling to the electronic subsystem. Here we show that propagation of an ensemble of independent classical nuclear trajectories on this exact potential yields dynamics that are essentially indistinguishable from the exact quantum dynamics for a model non-adiabatic charge transfer problem. We point out the importance of step and bump features in the exact potential that are critical in obtaining the correct splitting of the quasiclassical nuclear wave packet in space after it passes through an avoided crossing between two Born-Oppenheimer surfaces, and analyze their structure. Lastly, an analysis of the exact potentials in the context of trajectory surface hopping procedure is presented, including preliminary investigations of velocity-adjustment, and the force-induced decoherence effect.

Federica Agostini; Ali Abedi; Yasumitsu Suzuki; Seung Kyu Min; Neepa T. Maitra; E. K. U. Gross

2015-01-31

433

Ultrafast twisting dynamics of thioflavin-T: spectroscopy of the twisted intramolecular charge-transfer state.  

PubMed

Understanding the excited-state properties of thioflavin-T (ThT) has been of immense importance, because of its efficient amyloid-sensing ability related to neurodegenerative disorders. The excited-state dynamics of ThT is studied by using sub-pico- and nanosecond time-resolved transient absorption techniques as well as density functional theory (DFT)/time-dependent DFT calculations. Barrierless twisting around the central C-C bond between two aromatic moieties is the dominant process that contributes to the ultrafast dynamics of the S1 state. The spectroscopic properties of the intramolecular charge-transfer state are characterized for the first time. The energetics of the S0 and S1 states has also been correlated with the experimentally observed spectroscopic parameters and structural dynamics. A longer-lived transient state populated with a very low yield has been characterized as the triplet state. PMID:25251013

Ghosh, Rajib; Palit, Dipak K

2014-12-15

434

Charge transfer complex states in diketopyrrolopyrrole polymers and fullerene blends: Implications for organic solar cell efficiency  

NASA Astrophysics Data System (ADS)

The spectral photocurrent characteristics of two donor-acceptor diketopyrrolopyrrole (DPP)-based copolymers (PDPP-BBT and TDPP-BBT) blended with a fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were studied using Fourier-transform photocurrent spectroscopy (FTPS) and monochromatic photocurrent (PC) method. PDPP-BBT:PCBM shows the onset of the lowest charge transfer complex (CTC) state at 1.42 eV, whereas TDPP-BBT:PCBM shows no evidence of the formation of a midgap CTC state. The FTPS and PC spectra of P3HT:PCBM are also compared. The larger singlet state energy difference of TDPP-BBT and PCBM compared to PDPP-BBT/P3HT and PCBM obliterates the formation of a midgap CTC state resulting in an enhanced photovoltaic efficiency over PDPP-BBT:PCBM.

Moghe, D.; Yu, P.; Kanimozhi, C.; Patil, S.; Guha, S.