Intersystem crossing in irradiated benzene and toluene

Abstract

By use of the photosensitized (254 nm) cis-trans isomerization of butene-2 the triplet yields in liquid benzene and toluene at 25°C have been measured; they are 0.57 and 0.45. Internal conversion efficiencies are about 0.41 (benzene) and 0.48 (toluene). The effect of added xenon is to increase the triplet yield of benzene to unity. From these and similar experiments on the γ-radiation induced isomerization the rate constants for the ¹S →³S and ³S → S processes in benzene catalyzed by the spin orbit coupling effect of xenon are deduced to be 2 × 10⁸ M^–1 s^–1 and 3 × 10⁸ M^–1 s^–1 respectively. There is evidence that xenon has an effect on ionic and other processes in the high-energy radiation-induced isomerization experiments. The application of benzene and toluene as organic photosensitizers is discussed.