Quantum yields of singlet and triplet recombination products of singlet radical ion pairs

Abstract

The efficiencies of contact geminate recombination to either the ground or excited triplet state of neutral products are calculated for contact and remote starts of radical ion pairs initially created in the singlet state. Considering the spin-conversion in this pair as a stochastic process with given rate, the diffusional dependence of recombination and charge separation yields and corresponding efficiencies are specified. This is compared with the experimental data obtained for photo-excited perylene quenched by aromatic amines in dimethyl sulfoxide–glycerol mixtures, which allow for a wide variation of solvent viscosity with composition. The successful fitting of the theory to non-trivial viscosity dependences confirms that the spin-forbidden recombination is composed of two sequential stages. Considering that the radical-ion pair is created in the singlet state, the spin conversion should precede its recombination to the excited triplet product.