ON THE SEPARATION OF STATIC AND DYNAMIC SOLVENT EFFECTS FOR ELECTRON-TRANSFER REACTIONS

Recent studies of electron transfer (ET) reactions in polar solvents have shown that solvent dynamics, in addition to solvent statics, can have a dramatic effect on the rate. ET reactions were analyzed with the aim of suggesting methods that permit a separation of solvent static and dynamic effects on the rate. Two schemes that can separate these effects are (1) the measurement of ET charge separation (typically a normal regime reaction) and charge recombination (typically an inverted regime reaction) rates in the same solvent and (2) the variation of the static (transition state) rate in a given solvent, as induced by altering the electronic coupling via a series of donor-acceptor complexes at different fixed distances. To emphasize dynamical effects, the static rate contribution should be large, and therefore in the adiabatic, strong electronic coupling limit of Marcus theory. We obtain an expression for the solvent dynamically influenced rate, for the inverted ET regime, which can describe this limit as well as all degrees of electronic coupling. It has the form of a consecutive reaction scheme, the steps being diffusion along the reaction coordinate followed by surface crossing (the static rate contribution), as was obtained previously for the nonadiabatic static rate case.