Exciplex Mechanism of Excited-State Electron Transfer Reactions

Abstracts Terenin Memorial International Symposium on Photochemistry and Photophysics of Molecules and Ions, July 29 - August 2, 1996, v. 2, p. 234.

ABSTRACT. The evidences are obtained for the mechanism of transient formation of exciplexes with partial electron transfer and relatively long lifetimes (up to 10-60 ns) in excited-state electron transfer reactions in polar media rather than for direct complete electron transfer after preliminary reorganization of the reactants and medium as it was supposed by conventional Marcus mechanism. Therefore electron transfer occurs by gradual shift of an electron density form the donor to acceptor concerted with the reorganization of the reactants and medium.
Transient formation of exciplexes, in contrast to conventional mechanism, provides adequate quantitative description of experimental peculiarities of excited-state electron transfer reactions, in particular small (and sometimes even negative) activation enthalpies, quantum yields of radical ion and triplet formation, effects of the solvent polarity, and even better coincidence with the experimental data for the dependence of apparent rate constants on the driving force of electron transfer.

Laboratory of Photochemistry