Phototransformations of porphyrins in aqueous and micellar media.

Porphyrin photoproducts with absorption maxima at 640 and 660 nm are formed in aqueous and micellar solutions during light exposure. Changes in the dimethoxyhaematoporphyrin (DMHp) Soret band on irradiation suggest that the photoproduct (640 nm) formation is conditioned by the "sandwich"-type self-associates. The formation of the photoproduct (660 nm) in micellar haematoporphyrin (Hp) and photosan-3 (PS) solutions and its formation in small amounts in phosphate-buffered solution (PBS), is related to the presence of covalently linked porphyrin structures and/or interaction with surfactant molecules. PS is the most photostable of the three investigated porphyrins. Its photostability is probably due to the presence of covalently linked "sandwich"-type aggregates.