Laser-flash photolysis studies of benoxaprofen and its analogues 1. Yields of triplet states and singlet oxygen in acetonitrile solutions

Abstract

The photochemistry of benoxaprofen(BP) and four of its analogues in acetonitrile has been investigated using both steady-state and laser-flash photolysis. On steady-state photolysis, all compounds decarboxylated, albeit in small quantum yields. The fluorescence yields were found to be in the range 0.4–0.6. The triplet-triplet absorption spectra of all the compounds studied show absorption maxima at 410 nm with extinction coefficients of around 25 000 dm 3 mol −1 cm −1. Furthermore, all the compounds underwent intersystem crossing with efficiencies of around 0.4. Direct measurements of the time-resolved luminescence from singlet oxygen ( 1Δ g) using benzophenone as a triplet-state sensitizer in aerated solutions of benoxaprofen and its analogues, indicated that the efficiency of singlet oxygen formation (S Δ) was close to unity. These results imply that the singlet-oxygen quantum yields are close to 0.4.