Intramolecular Electron Transfer in Mixed-valence Triarylamines PDF Download
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Author: Kelly Lancaster
Publisher:
ISBN:
Category : Charge exchange
Languages : en
Pages :
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Book Description
Mixed-valence compounds are of interest as model systems for the study of electron transfer reactions. The intramolecular electron transfer processes and patterns of charge delocalization in such compounds depend on the interplay between the electronic (V) and the vibronic (L) coupling. One can obtain both parameters from a Hush analysis of the intervalence band that arises upon optical intramolecular electron transfer if the band is intense and well-separated from other bands. This is quite often the case for mixed-valence triarylamines. As such, both Hush analysis and simulation of the intervalence band are widely used to classify these compounds as charge localized (class-II) or delocalized (class-III). Yet one must estimate the diabatic electron transfer distance (R) to calculate V in the Hush formalism. For mixed-valence triarylamines, R is commonly taken as the N-N distance; we show this to be a poor approximation in many cases. The activation barrier to thermal intramolecular electron transfer in a class-II mixed-valence compound is also related to the parameters V and L. Thus, if one can capture the rate of thermal electron transfer at multiple temperatures, then two experimental methods exist by which to extract the microscopic parameters. One technique that is widely used for organic mixed-valence compounds is variable-temperature electron spin resonance (ESR) spectroscopy. But this method is only rarely used to determine thermal electron transfer rates in mixed-valence triarylamines, as the electron transfer in most of the class-II compounds with distinct intervalence bands is too fast to observe on the ESR timescale. We show, for the first time, that one can use ESR spectroscopy to measure thermal electron transfer rates in such compounds. Simulation of ESR spectra based on density functional theory calculation and comparison with optical data also uncover the nature (i.e., adiabatic or nonadiabatic) of the electron transfer process.
Author: Kelly Lancaster
Publisher:
ISBN:
Category : Charge exchange
Languages : en
Pages :
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Book Description
Mixed-valence compounds are of interest as model systems for the study of electron transfer reactions. The intramolecular electron transfer processes and patterns of charge delocalization in such compounds depend on the interplay between the electronic (V) and the vibronic (L) coupling. One can obtain both parameters from a Hush analysis of the intervalence band that arises upon optical intramolecular electron transfer if the band is intense and well-separated from other bands. This is quite often the case for mixed-valence triarylamines. As such, both Hush analysis and simulation of the intervalence band are widely used to classify these compounds as charge localized (class-II) or delocalized (class-III). Yet one must estimate the diabatic electron transfer distance (R) to calculate V in the Hush formalism. For mixed-valence triarylamines, R is commonly taken as the N-N distance; we show this to be a poor approximation in many cases. The activation barrier to thermal intramolecular electron transfer in a class-II mixed-valence compound is also related to the parameters V and L. Thus, if one can capture the rate of thermal electron transfer at multiple temperatures, then two experimental methods exist by which to extract the microscopic parameters. One technique that is widely used for organic mixed-valence compounds is variable-temperature electron spin resonance (ESR) spectroscopy. But this method is only rarely used to determine thermal electron transfer rates in mixed-valence triarylamines, as the electron transfer in most of the class-II compounds with distinct intervalence bands is too fast to observe on the ESR timescale. We show, for the first time, that one can use ESR spectroscopy to measure thermal electron transfer rates in such compounds. Simulation of ESR spectra based on density functional theory calculation and comparison with optical data also uncover the nature (i.e., adiabatic or nonadiabatic) of the electron transfer process.
Author: Jody Ann Roberts
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Yuwu Zhong
Publisher: John Wiley & Sons
ISBN: 3527349804
Category : Science
Languages : en
Pages : 517
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Book Description
Mixed-Valence Systems Comprehensive overview on the advanced development of mixed-valence chemistry Mixed-Valence Systems: Fundamentals, Synthesis, Electron Transfer, and Applications covers all topics related to the theory and experimental results of mixed-valence systems, including the design, synthesis, and applications of mixed-valence compounds containing inorganic, organometallic and organic redox-active centers. The text also covers the recent advances in mixed-valence chemistry, including the development of new mixed-valence systems, transition of mixed valency, better understanding of the spectral characteristics of intervalence charge transfer, and controllable electron transfer related to molecular electronics. In Mixed-Valence Systems, readers can expect to find detailed information on sample topics such as: Characterization and evaluation of mixed-valence systems, electron paramagnetic resonance spectroscopy, and electrochemical methods Optical analysis, important issues in mixed-valence chemistry, transition of mixed valency from localized to delocalized, and solvent control of electron transfer Theoretical background, potential energy surfaces from classical two-state model, and quantum description of the potential energy surfaces Reorganization energies, electronic coupling matrix element and the transition moments, generalized Mulliken–Hush theory, and analysis of the band shape of intervalence charge transfer Strengthening the relationship of mixed-valence electron transfer and molecular electronics, Mixed-Valence Systems is of immense value to researchers and professionals working in the field of electron transfer, molecular electronics, and optoelectronics.
Author: Teng-Yuan Dong
Publisher:
ISBN:
Category :
Languages : en
Pages : 694
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Book Description
Author: Peter Henry Dinolfo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The primary focus of this thesis is the examination of intramolecular electron transfer processes in mixed valence compounds. Rhenium based supramolecular coordination chemistry has been used create a number of highly symmetrical structures that contain cofacially arranged, redox active ligands. When reduced by an odd number of electrons, the molecules belong to an unusual class of mixed valence compounds where the ligands are the degenerate redox centers, i.e. Ligand-Centered Mixed Valency. Inter-ligand electronic communication in these systems is controlled by direct donor/acceptor orbital overlap rather than by superexchange through the molecular framework. As shown by X-ray crystallography and semiempirical modeling, the spectroscopically determined electronic coupling strengths are consistent with geometrical configurational differences between the cofacial ligand pairs. In a number of cases, electroabsorbance (Stark) spectroscopy has been employed to directly evaluate the adiabatic charge transfer distances. Depending the geometrical arrangement of the redox active ligand pairs, the degree of electronic communication can be tuned from non-interacting (Robin-Day Class I), to fully delocalized (Class III).
Author: Lauge J. Schäffer
Publisher:
ISBN:
Category : Cobalt compounds
Languages : en
Pages : 90
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Book Description
Author: Starla Demorest Glover
Publisher:
ISBN: 9781124703428
Category :
Languages : en
Pages : 175
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Book Description
Investigations into the dynamics of picosecond electron transfer in a series of mixed valence systems of the type [Ru3([mu]3-O)(OAc)6(py)(CO)-([mu]2-BL)- Ru3([mu]3-O)(OAc)6(py)(CO)]−1, where BL = 1,4-pyrazine or 4,4'-bipyridine and py = 4-dimethylaminopyridine, pyridine, or 4-cyanopyridine are described. Solvent and temperature dependence into the rate of ground state intramolecular electron transfer is probed by infrared analysis of [nu](CO) bandshapes where simulated rate constants yield to rates ranging from 4 E 11 to 3 E 12 s-1. Correlations between rate constants and solvent properties including solvent reorganization energy, optical and static dielectric constants, microscopic solvent polarity, viscosity, principal rotational moments of inertia, and solvent dipolar relaxation times, have been examined. Correlations revealed a marked lack of dependence on electron transfer rates with respect to solvent thermodynamic parameters, and a strong dependence on solvent dynamic parameters. This is consistent with electron transfers having very low activation barriers that approach zero. Temperature dependent studies revealed electron transfer rates accelerated as the freezing points of solvent solutions were approached with a sharp increase in the rate of electron transfer upon freezing. This has been attributed to a localized-to-delocalized transition in these mixed valence ions at the solvent phase transition. This non-Arrhenius behavior is explained in terms of decoupling the slower solvent motions involved in the frequency factor, [nu]N, which weights faster vibrational promoter modes that increase the value of [nu]N. Solvent and temperature dependence of optically induced intramolecular electron transfer is probed by analysis of intervalence charge transfer bands in NIR spectra. The application of a semi-classical three-state model for mixed valency best describes the electronic spectra wherein is the appearance of two intervalence bands; a band which has metal-to-metal-charge-transfer character and another having metal-to-ligand-charge-transfer character. This three-state model fully captures the observed spectroscopic behavior where the MBCT transition increases in energy and the MMCT band decreases in energy as electronic communication increases through the series of mixed valence ions. The solvent and temperature dependence of the MBCT and MMCT electronic transitions is found to persist as coalescence of infrared vibrational spectra suggest ground state delocalization on the vibrational timescale. The solvent and temperature dependence of the MBCT and MMCT electronic transitions defines the mixed valence complexes as lying at the borderline of delocalization. Fine tuning the electronic coupling in the series of dimers has allowed for the resolution of a full Class II, early Class II/III, late Class II/III to Class III systems and the influence of solvent dynamics in each regime. These investigations have prompted the redefinition of borderline Class II/III mixed valency to account for outer sphere (solvent) contributions to electron transfer; in nearly delocalized systems, solvent dynamics localized otherwise delocalized electronic ground states. Further, studies explore the origins and dynamics behind spectral coalescence of vibrational [nu] (CO) bandshapes in [Ru3([mu]3-O)(OAc)6(py)(CO)-([mu]2-BL)- Ru3([mu]3-O)(OAc)6(py)(CO)]−1 systems and a picosecond isomerization in square pyramidal Ru(S2C4F6)(P(C6H5)3)2(CO) system.
Author: Casey Hughes Londergan
Publisher:
ISBN:
Category :
Languages : en
Pages : 320
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Book Description
Author: Michael K. Johnson
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 496
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Book Description
Identifies unifying concepts applicable to electron transfer between metal centers in both solid-state materials and biological systems. The 23 contributions cover such topics as: peptides and proteins; inorganic complexes; and theoretical and experimental aspects of solid state transfer. For materials scientists, solid state scientists, and biochemists. Annotation copyrighted by Book News, Inc., Portland, OR
Author: Achim Müller
Publisher: Elsevier Publishing Company
ISBN:
Category : Science
Languages : en
Pages : 420
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Book Description
Various aspects of electron and proton transfer in chemistry and biology are described in this volume. The joint presentation was chosen for two reasons. Rapid electron and proton transfer govern cellular energetics in both the most primitive and higher organisms with photosynthetic and heterotrophic lifestyles. Further, biology has become the area where the various disciplines of science, which were previously diversified, are once again converging. The book begins with a survey of physicochemical principles of electron transfer in the gas and solid phase, with thermodynamic and photochemical driving force. Inner and outer sphere mechanisms and the coupling of electron transfer to nuclear rearrangements are reviewed. These principles are applied to construct artificial photosynthesis, leading to biological electron transfer involving proteins with transition metal and/or organic redox centres. The tuning of the free energy profile on the reaction trajectory through the protein by single amino acids or by the larger ensemble that determines the electrostatic properties of the reaction path is one major issue.Another one is the transformation of one-electron to paired-electron steps with protection against hazardous radical intermediates. The diversity of electron transport systems is represented in various chapters with emphasis on photosynthesis, respiration and nitrogenases. The book will be of interest to scientists in chemistry, physics and the life sciences.
