The Role Played by Orbital Energetics in Solvent Mediated Electronic Coupling†

Electron-transfer rates are measured for three supramolecular species, which contain an electron donor, electron acceptor, and rigid connecting bridge. Two of the species are linear and the third species is C-shaped. The latter topology produces a 10 Å wide, solvent accessible gap between the donor and the acceptor units. This molecular design allows the dependence of the electron-transfer rate on the solvent's electronic character to be evaluated. The results display a strong correlation between the energy of the solvent's lowest unoccupied molecular orbital and the magnitude of solvent mediated electronic coupling in systems with electronically excited donors. The variation of the electronic coupling with solvent modulates transfer rate constants by more than an order of magnitude.