3 years ago

Effect of Reactant and Product State Decay on Ultrafast Charge-Transfer Kinetics: Violation of the Principle of Independence of Elementary Chemical Reactions

Effect of Reactant and Product State Decay on Ultrafast Charge-Transfer Kinetics: Violation of the Principle of Independence of Elementary Chemical Reactions
Anatoly I. Ivanov, Valentina A. Mikhailova
Fast decay of both the reactant and product states is shown to strongly increase the intrinsic electron transfer rate in donor–acceptor dyads. The decay is associated with redistribution/relaxation of excited vibrational states that typically participate in the reaction. Although the role of the reorganization of high-frequency vibrational modes in electron-transfer dynamics is well understood and it is commonly accepted to strongly affect the ultrafast electron transfer dynamics, the influence of the relaxation of excited vibrational states on electron transfer is not accounted for in experimental data analysis. In photoinduced electron transfer, excited states of high-frequency vibrational modes are often produced by laser pump pulse so that the ultrafast charge separation, at least partly, occurs from excited vibrational states. The charge recombination accompanying the charge separation also essentially occurs from excited vibrational states of intermediates to form a final excited vibrational state. Since the decay of the reactant state and electron transfer are two elementary chemical reactions occurring in parallel, the influence of vibrational relaxation on the intrinsic electron-transfer rate constant is a clear manifestation of the violation of the fundamental principle of chemical kinetics postulating the independence of elementary chemical reactions. The mechanism of the violation is discussed in detail. The transition probability that better characterizes the efficiency of ultrafast nonequilibrium charge recombination than the rate constant is calculated. The dependencies of the electron-transfer rate constant and the transition probability on the product decay time are predicted to be identical while on the reactant decay time to be opposite.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b06106

DOI: 10.1021/acs.jpcc.7b06106

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