An EPR study of the photogeneration of hydroxyl radicals in aqueous solutions of octakis(pyridiniomethyl)phthalocyaninotitanyl octachloride

The possibility of the photogeneration of hydroxyl radicals by means of a direct oxidation of water by a metal-containing phthalocyanine complex via excitation of its Q-band in aqueous solutions under anaerobic conditions was demonstrated for the first time. The efficiency of the photosensitizer (octakis(pyridiniomethyl)phthalocyaninotitanyl octachloride) was found to increase in the presence of oxygen from air due to the formation of an additional amount of (OH)-O-. radicals from superoxide-anions, which, in turn, arise as a result of electron transfer from the reduced form of molecules of the photosensitizer to oxygen molecules. The quantum yields of hydroxyl radicals in deaerated and aerated solutions were estimated at (0.5 +/- 0.1) x 10(-4) and (1.1 +/- 0.2) x 10(-4), respectively.