Superexchange‐Assisted Through‐Bridge Electron Transfer: Electronic and Dynamical Aspects

The effects of electronic structure on bridge‐assisted electron transfer are considered. Using static perturbation theory, time‐dependent perturbation theory, and direct time‐dependent dynamics within generalized tight binding models, we examine the role of energy gaps, relative energetics of donor and acceptor orbitals with hole‐type and electron‐type superexchange sites, damping and dephasing, and overall energetics in electron transfer. We find that a generalization of the simple McConnell relationship to nonresonant transfer can in fact be made, but that no simple formula describes all limits; this is important in applications to a number of systems, including photosynthetic reaction centers, in which such superexchange occurs. The dynamical studies indicate some important and unexpected phenomena: these include quantum interferences between different pathways, recurrences and oscillations, and competitive effects of hole‐type and electron‐type superexchange. We suggest that direct dynamical study, as has begun to appear from several laboratories, provides an excellent way to visualize the intermediate state contributions to intramolecular electron transfer processes.