Primary photophysical processes in benzene. Part 2.—Monomer studies

Abstract

Triplet yields for benzene excited at 254 nm in dilute solution (0.112 M) in cyclohexane have been measured, and internal conversion yields estimated, by the but-2-ene isomerization technique, as a function of temperature; for example, at 45°C, ϕ_TM= 0.14 and ϕ_ICM= 0.82. Using data from a previous paper, the temperature dependence of the three major decay processes, intersystem crossing, internal conversion, and fluorescence for the monomeric form of excited singlet benzene have been calculated. Intersystem crossing has an activation energy of 0.097 eV and a pre-exponential factor of 3.2 × 10⁸ s^–1. The triplet lifetime in 0.112 M benzene solutions at 45°C is estimated to be 21 ns. Internal conversion increases with temperature and, assuming a simplified mechanism, has an activation energy of 0.325 eV with an associated pre-exponential factor of 7.9 × 10¹² s^–1.