Competition between geminate recombination and solvation of polar radicals following ultrafast photodissociation of bis(p-aminophenyl) disulfide

Supercontinuum probe pulses are used for studying the ultrafast photodissociation of bis(p-aminophenyl) disulfide into two p-aminophenylthiyl radicals and their subsequent geminate recombination in polar solvents. The kinetic investigations are complicated by a spectral absorption shift of the photolytically generated radicals due to solvation. The dissociation and recombination dynamics are separated from the solvation dynamics by a moment analysis of the transient spectra. Geminate recombination in polar solvents is observed only if the time scale for dielectric relaxation of the solvent is comparable to or slower than the time scale for recombination. The latter depends on the initial distance distribution of the radical pairs.