Photochemical α-cleavage and hydrogen abstraction in deoxybenzoin: a laser spectroscopy investigation

Abstract

Transient absorptions in the range 380–500 nm in deoxybenzoin are investigated for the first time by nanosecond laser spectroscopy. This study gives evidence for absorption by a triplet state, and by benzoyl and benzyl radicals. Photoreduction of the triplet state and generation of a ketyl radical are also obtained. This enables some peculiar results of the polymerization of vinyl monomers photoinduced by deoxybenzoin to be explained. Our results show that deoxybenzoin exhibits a peculiar behaviour since the two photoprocesses occur with the same efficiency. Hydrogen abstraction and α-cleavage rate constants, quenching rate constants of the species by oxygen, lifetimes of the transients, and absorption spectra are derived. The influence of the solvent is discussed as a function of the excited states involved. A complete diagram of the evolution of the energy levels is thus obtained.