Two-photon processes in ketone photochemistry observed by time-resolved ESR spectroscopy

Abstract

Laser flash excitation of the photopolymerization initiator ω,ω-dimethoxy-ω-phenylacetophenone at 308 nm in toluene yields benzoyl and α,α-dimethoxybenzyl radicals. The latter fragment onabsorption of a second photon to methylbenzoate and methyl radicals. This explains previous contradictory results on the photochemistry of the system. Further, excitation of triplet acetone yields α-cleavage even in 2-propanol solution, where photoreduction of normal triplets is fast. The advantages of directly detected ESR to study such two-photon processes are discussed.