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 d irect oxidation of water by a metal-containing phthalocyanine complex via e xcitation of its Q-band in aqueous solutions under anaerobic conditions was demonstrated for the first time. The efficiency of the photosensitizer (oc takis(pyridiniomethyl)phthalocyaninotitanyl octachloride) was found to incr ease in the presence of oxygen from air due to the formation of an addition al amount of (OH)-O-. radicals from superoxide-anions, which, in turn, aris e as a result of electron transfer from the reduced form of molecules of th e photosensitizer to oxygen molecules. The quantum yields of hydroxyl radic als in deaerated and aerated solutions were estimated at (0.5 +/- 0.1) x 10 (-4) and (1.1 +/- 0.2) x 10(-4), respectively.