Intramolecular Electron-Transfer Studies as a Function of Bridge Topology: The Importance of Solvent-Mediated Donor-Acceptor Electronic Coupling

Abstract

The donor-acceptor electronic coupling matrix elements, |V|, for photoinduced, intramolecular electron-transfer (ET) reactions in one linear and three C-shaped molecules have been determined from the temperature dependence of ET rate constants. The coupling matrix element in the linear molecule was found to be solvent-independent. By contrast, the coupling matrix elements in two of the three C-shaped molecules exhibit significant solvent dependence. Donor-acceptor coupling matrix elements were calculated for the linear and C-shaped molecules in the absence and presence of solvent molecules using the generalized Mulliken-Hush theory. Together, the experimental and theoretical results indicate that solvent molecules, and not the covalent bridge, mediate the electronic coupling in the C-shaped molecules. Preliminary studies of ET rate constants as a function of solvent bulk are also described.