LONG-DISTANCE CHARGE RECOMBINATION WITHIN RIGID MOLECULAR ASSEMBLIES IN NONDIPOLAR SOLVENTS

The lifetimes of the charge-separated states formed on photoexcitation of rigid donor-insulator-acceptor molecules with variable edge-to-edge separation from 5 to 15 angstrom have been measured in the nondipolar solvents trans-decalin, benzene, dioxane, and their admixtures by using the time-resolved microwave conductivity (TRMC) technique. The lifetime is governed by two recombination pathways: direct to the ground state and indirect via the locally excited donor. The latter becomes increasingly important as the separation distance increases and/or the driving force for charge separation decreases. Very large solvent effects are found. Data are presented on the effects of changing the donor and acceptor groups and of modifying the norbornyl type sigma-bonded bridges.