Use of Modern Electron Transfer Theories To Determine Electronic Coupling Matrix Elements in Intramolecular Systems

Abstract

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, λo(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.