ORBITAL SYMMETRY EFFECTS ON INTRAMOLECULAR CHARGE RECOMBINATION

Quantum yields and lifetimes were determined for charge transfer fluorescence accompanying the charge recombination, that follows photoinduced charge separation, in a series of four rigid D-bridge-A systems (1-4) each with overall molecular C(s) symmetry and an effective bridge length of eight sigma bonds. From these data the electronic coupling (H(cr)) between the ground state and the charge separated state was calculated. In 2-4 charge recombination is "symmetry allowed" and for these systems H(cr) is consistently larger than for the "symmetry forbidden" charge recombination in 1. The results obtained indicate that such symmetry effects could modify the overall rate of intramolecular electron transfer by about one order of magnitude.