Contribution of intersystem recombination on the lifetime of radical pair produced in photoreduction of benzophenone derivatives in SDS micelle as detected by pulse-PYESR

The heavy atom effect on the radical-pair lifetime was studied on the photochemical hydrogen-abstraction reaction of benzophenone and its derivatives having halogen atoms in the phenyl group in an SDS micellar solution by using the pulse-mode product-yield-detected ESR technique. Upon introducing bromine atoms in the benzophenone frame the lifetime was shortened considerably, though no appreciable effects were found for other systems with lighter halogens. Through estimation of the several factors which may affect the lifetime of radical pair upon the halogen introduction, we concluded that the intersystem recombination, which is the geminate recombination of redical pair from the triplet state, was the main mechanism of the observed shortening of the lifetime.