title: Electron Transfer Rate Maxima at Large Donor-Acceptor Distances.
abstract: Because of their low mass, electrons can transfer rapidly over long (>15 Å) distances, but usually reaction rates decrease with increasing donor-acceptor distance. We report here on electron transfer rate maxima at donor-acceptor separations of 30.6 Å, observed for thermal electron transfer between an anthraquinone radical anion and a triarylamine radical cation in three homologous series of rigid-rod-like donor-photosensitizer-acceptor triads with p-xylene bridges. Our experimental observations can be explained by a weak distance dependence of electronic donor-acceptor coupling combined with a strong increase of the (outer-sphere) reorganization energy with increasing distance, as predicted by electron transfer theory more than 30 years ago. The observed effect has important consequences for light-to-chemical energy conversion.
authors.affiliation: Department of Chemistry, University of Basel , St. Johanns-Ring 19, 4056 Basel, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Kuss-Petermann
authors.affiliation: Department of Chemistry, University of Basel , St. Johanns-Ring 19, 4056 Basel, Switzerland.
authors.forename: Oliver S
authors.initials: OS
authors.lastname: Wenger