USE OF MODERN ELECTRON-TRANSFER THEORIES TO DETERMINE ELECTRONIC COUPLING MATRIX-ELEMENTS IN INTRAMOLECULAR SYSTEMS

The dependence of the donor/acceptor electronic coupling on the topolo gy of donor-bridge-acceptor (DBA) molecules is probed experimentally a nd theoretically. The temperature dependence of photoinduced electron- transfer rate constants is analyzed with a semiclassical electron-tran sfer model to extract the donor/acceptor electronic coupling matrix el ements \V\ and the low-frequency reorganization energy at 295 K, lambd a(o),(295 K), for four rigid DBA molecules. The sensitivity of the ele ctronic coupling \V\ to the models and parameters used to fit the data are extensively investigated. The treatment of the low-frequency reor ganization energy's temperature dependence has a significant impact on the analysis. The identity of the principal coupling pathways is dete rmined for molecular linkages that propagate symmetry allowed donor/ac ceptor interactions and molecular linkages that propagate symmetry for bidden donor/acceptor interactions. For the symmetry forbidden case, t hese analyses demonstrate that solvent molecules provide the dominant coupling pathway in the nine-bond bridge, C-shaped molecule 2 but do n ot significantly influence \V\ across the seven-bond, linear bridge in 1.