Photophysical studies of tetratolylporphyrin photosensitizers for potential medical applications

A group of meso-substituted synthetic tetratolylporphyrins was investigated by the methods of absorption and fluorescence spectroscopies as well as steady-state and time-resolved photothermal spectroscopies. The experiments were carried out in the air, oxygen or nitrogen atmospheres, at two temperatures. The details concerning the fast and slow deactivation processes of excitation energy of the dyes were studied. The estimated quantum yield of fluorescence and the efficiency of (S1–T1) intersystem crossing process give a possibility to evaluate the population yield and quenching rate of the triplet state, important for the therapeutic application, mostly mediated by the T1-state. For tetrapyrrole with the carboxyphenyl group substituted in meso-position, the triplet state yield was the highest, of 0.86–0.94, whereas the porphyrin with aminophenyl group seemed to be efficient singlet oxygen generators (0.81–0.99) with a high rate constant of its excited triplet state quenching by molecular oxygen.