Photoinduced electron transfer in mixed-valence compounds: Beyond the golden rule regime

Abstract

The short-time charge transfer evolution following photoexcitation in mixed valence compounds is studied using path integral calculations. Due to the large nonadiabatic coupling, path integral calculations using direct path summation techniques are inadequate, and charge transfer dynamics can only be computed using a transfer matrix technique developed by Makri and Makarov. The resulting relaxation is considerably slower than that predicted by low-order perturbation theory. The effects of the solvent on the decay process, and the validity of the golden rule to predict the dynamics of the decay process are investigated. The effects of preparing an initial state that is not a rovibrational state of the acceptor potential energy surface is also examined. These exact calculations show that the large electronic mixing gives rise to very fast oscillations in the electronic state population as the wave function oscillates coherently between the donor and acceptor. This is followed by a slower relaxation induced by the coupling to the dissipative solvent modes, which occurs on time scales ≤100 fs. This information provides insight into the mechanism for oscillations observed in time-resolved transient spectra of these compounds, and suggests substantial limitations of the golden rule picture. © 1998 American Institute of Physics.