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 topology of donor-bridge-acceptor (DBA) molecules is probed experimentally and theoretically. The temperature dependence of photoinduced electron-transfer rate constants is analyzed with a semiclassical electron-transfer model to extract the donor/acceptor electronic coupling matrix elements \V\ and the low-frequency reorganization energy at 295 K, lambda(o),(295 K), for four rigid DBA molecules. The sensitivity of the electronic coupling \V\ to the models and parameters used to fit the data are extensively investigated. The treatment of the low-frequency reorganization energy's temperature dependence has a significant impact on the analysis. The identity of the principal coupling pathways is determined for molecular linkages that propagate symmetry allowed donor/acceptor interactions and molecular linkages that propagate symmetry forbidden donor/acceptor interactions. For the symmetry forbidden case, these analyses demonstrate that solvent molecules provide the dominant coupling pathway in the nine-bond bridge, C-shaped molecule 2 but do not significantly influence \V\ across the seven-bond, linear bridge in 1.