LASER-FLASH PHOTOLYSIS STUDIES OF BENOXAPROFEN AND ITS ANALOGS .1. YIELDS OF TRIPLET-STATES AND SINGLET OXYGEN IN ACETONITRILE SOLUTIONS

The photochemistry of benoxaprofen(BP) and four of its analogues in ac etonitrile has been investigated using both steady-state and laser-fla sh photolysis. On steady-state photolysis, all compounds decarboxylate d, 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 extinc tion coefficients of around 25 000 dm3 mol-1 cm-1. Furthermore, all th e compounds underwent intersystem crossing with efficiencies of around 0.4. Direct measurements of the time-resolved luminescence from singl et oxygen (1DELTA(g)) using benzophenone as a triplet-state sensitizer in aerated solutions of benoxaprofen and its analogues, indicated tha t the efficiency of singlet oxygen formation (S(DELTA)) was close to u nity. These results imply that the singlet-oxygen quantum yields are c lose to 0.4.