Excited-state reactions of triphenylpyrylium ion with cinnamate derivatives: triplet-mediated isomerization and singlet-mediated dimerization

Abstract

Excited-state reactivity of 2,4,6-triphenylpyrylium ion (TPP⁺) with cinnamates has been studied by fluorescence quenching and laser flash photolysis experiments. Electron-transfer reactions between cinnamates and excited states of TPP⁺ are reported. The pyryl radical (TPP˙) has been observed as an intermediate. In the singlet manifold, dimerization product(s) are reported and in the triplet manifold the trans–cis isomerization product is reported. Selectivity of oxygen in the product formation is observed. This is one of the few systems in which both isomerization and dimerization mechanisms are operating together through a radical cation intermediate. For the first time the dimerization of cinnamate derivatives via a radical cation is reported.