Dynamics of electron transfer

When one places an electron into the donor molecule, the equilibrium fast polarization, which is purely electronic forms first. Being independent of the electron position, it is unimportant for the dynamics of electron transfer. Afterward the average slow polarization Pg, arises that corresponds to the initial (0 charge distribution (the electron in the donor). The interaction of the electron with this polarization stabilizes the electron state in the donor (with respect to that in the isolated donor molecule) (i.e., its energy level is lowered) (Fig. 34.1). At the same time, a given configuration of slow, inertial polarization destabilizes the electron state (vacant) in the acceptor (Fig. 34.1). Therefore, even for identical reactants, the electron energy levels in the donor and acceptor are different at the initial equilibrium value of slow polarization. 

Having obtained the charge-localized state, the dynamics of electron transfer can be treated as a time-dependent configuration interaction problem [356, 362-364], In this case the two configurations would be taken as the left... 

Part C. Dynamics of Electron Transfer Across Polypeptides by Stephan S. Isied (Rutgers University)... 

A special case of a non-adiabatic reaction is electron transfer. The dynamics of electron-transfer processes have been studied extensively, and the most robust model used to describe... 

The dynamics of electron-transfer at the interfaces of Ti02/Dye 2/electrolyte are summarized in Fig. 20.7. Two forward electron-transfer steps are much faster than the corresponding reverse electron-transfer (charge recombination) on the order of 103 to 106. The results well explain the high rjei value due to the efficient and vectorial electron-transfer in Dye 2-sensitized DSC. 

Dynamics of Electron Transfer Processes on Semiconducting Catalysts... 

Photoinitiated and optical electron-transfer processes and their relationship to corresponding ground-state thermal processes provide important new tests of theory, especially when comparisons are made for a given DBA system, of charge separation (CS) and charge recombination (CR), or of thermal and optical electron transfer (e.g., [27]). Photoinitiated processes have also been valuable in providing access to the dynamics of electron transfer in the activationless and inverted kinetic regimes (e.g., [43, 44]). 

The reader may desire an explanation of the low values of y derived by Barton and coworkers [30, 131, 137-140] from fluorescence quenching data for systems in which the dynamics of electron transfer have not been directly measured. In most cases, the absolute efficiency (quantum yield) of the quenching processes studied in these systems is rather low, and thus they may represent long-range electron transfer by mechanisms other than superexchange, such as to those described by Felts et al. [125], Davis and colleagues [126], and Okada et al. [127]. However, the author considers that it is highly unlikely that such processes occur with rate constants > 10 s . In view of the complex nature of these systems, the author is loath to offer a detailed interpretation, and refers the reader to commentaries by others who have been directly involved in this research [13, 15]. 

Thus, the kinetics of diffusion-controlled bimolecular electron-transfer reactions in the micellar interiors differ from that in the homogeneous solution. Numerous data have shown that Eq. 9 reproduces the dynamics of electron-transfer reactions within micelle interiors [80]. Diffusion coefficients (D) estimated from Eqs. 8 and 9 are very similar to those obtained by independent measurements. For example, Eq. 8 gave ku = 7.5 X 10 s for electron transfer from excited pyrene to CH2I2 in SDS micelles [79b]. One estimates from Eq. 8, with = 20 A and ai = 1.5 (calculated assuming d = 7 A), a value of Z) = 1.3 x 10 cm s, nearly identical with the experimentally determined value of Z) = lO " cm s [45]. 

Warshel, A. and Hwang, J.-K. (1986). Simulation of the dynamics of electron transfer reactions in polar solvents semiclassical trajectories and dispersed polaron approaches. 

Hicks, J.I., Zamborini, F.P., and Murray, R.W. (2002) Dynamics of electron transfers between electrodes and monolayers of nanoparticles. 

Tianquan Lian received his BS degree from Xiamen University in 1985, his MS degree from the Chinese Academy of Sciences in 1988 and his PhD from the University of Pennsylvania in 1993. After postdoctoral training in the University of California at Berkeley, he joined the faculty of chemistry department at Emory University in 1996. He was promoted to associate professor in 2002 and full professor in 2005. He has been a recipient of the NSF CAREER award and the Sloan fellowship. His research interest is focused on the ultrafast dynamics of nanomaterials and interfaces. He is particularly interested in fundamental physical chemistry problems related to nanomaterials-based solar energy conversion concepts and devices. These problems include the dynamics of electron transfer, energy transfer, vibrational energy relaxation and solvation at interfaces and in nanomaterials. 

Simulation of the Dynamics of Electron Transfer Reactions in Polar Solvents Semidassical Trajectories and Dispersed Polaron Approaches,... 

Dynamics of Electron Transfer Pathways in Redox Proteins... 

In this chapter we will highlight recent experimental data on the picosecond dynamics of electron localization and solvation in polar liquids and on the ultrafast radiationless transitions that accompany laser excitation of e in the same systems. The specific issues we address concern (1) the mechanism for electron localization in polar liquids, (2) the molecular description of the solvation process in forming the cluster, and (3) the dynamics of electron transfer following photodetachment of an electron from its cluster. 

We conclude this article on a note of optimistic speculation. Clearly the above results on solvated electrons establish the potential of ultrashort laser pulses to probe the fundamental details of the dynamics of electron transfer reactions, which will be the cornerstone for the development of microscopic theories of electron dynamics in the condensed phase. Electrons are ubiquitous species, and the practical reflection of this appears in research areas such as photosynthesis, dielectric breakdown, fast optical... 

In many biological systems, electron transfer takes place between redox couples present in media with different dielectric properties. Electrochemical studies at the ITIES enable one to address systematically the effect of polarization and specific properties of the electrolyte medium on the dynamics of electron transfer. This knowledge has particular relevance in processes involving redox phase transfer catalysis. 

Hendrickson and co-workers have continued to probe the dynamics of electron transfer in molecular systems in the solid state. Mossbauer and specific-heat data on biferrocenium [(C5H5)Fe(C5H4 C5H4)Fe(C5H5)] salts indicate that intramolecular electron transfer is controlled by lattice dynamics. The tri-iodide salts show valence localization up to 350 K by Mbssbauer data. The room-temperature crystal structure is centrosymmetric and evidently disordered. 

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