Long-Range Electron Tunneling in Aqueous and Organic Glasses

Abstract

Photoinduced electron transfer (ET) reactions have been investigated in glassy media at 77 K. Distance decay parameters for electron tunneling through water, 2-methyltetrahydrofuran, and toluene have been determined through measurements of donor luminescence quenching by randomly dispersed electron acceptors. Remarkably different long-range ET efficiencies in the three solvents are in accord with the predictions of a super exchange model of distant electronic couplings. We conclude that tunneling energy effects play an important role in long-range ET reactions, and further that the coupling drops off very rapidly across van der Waals gaps betwee nmolecules in glasses.