Photoinduced electron transfer in the paraquat–thiourea molecular complex

Abstract

The bipyridinium ion paraquat forms a 1 : 1 association complex with thiourea in aqueous solution. Excitation in the region 360–440 nm with a high-intensity pulse causes transient changes in the visible absorption spectrum which are completely reversible within 10 s. A study of the time evolution of the absorption spectrum indicates that the primary photoproducts are the paraquat radical cation and the thiourea radical cation. Subsequent dimerization of thiourea radicals produces formamidine disulphide, which, along with thiourea radicals, reacts with paraquat radicals to regenerate the association complex.