Thioanisole triplet: Laser flash photolysis and pulse radiolysis studies

Abstract

Direct photogeneration of excited triplet states of thiophenol and its derivatives is substantially influenced by substitutions and structural changes. In this study the impact of the methyl substituent of thioanisole (a derivative of thiophenol, denoted as PhS-Me) relative to the basic molecular structure (PhS-H) on the dynamics of thioanisole triplet and its features has been explored by direct excitation (λexc. = 266 nm) and by sensitization. The T1-Tn absorption spectrum is characterized by three bands peaking at 320 nm, 360 nm and 490 nm. The triplet reactivity with triplet quenchers was determined and the triplet energy level was identified by sensitization with beta-carotene, naphthalene, and benzophenone using laser photolysis as well as solvent benzene using pulse radiolysis. The results indicate that the replacement of the hydrogen atom by the methyl substituent leads to a significant change in the thioanisole triplet properties (τ(PhSMe(T1)) = 1.20 μs, ϕT(PhSMe) = 0.35, 353 kJ mol−1 > E(PhSMe(T1)) > 287 kJ mol−1) compared with those of thiophenol (τ(PhSH(T1)) = 40 ns, ϕT(PhSH) = 0.00, E(PhSH(T1)) = 248 kJ mol−1).