Weitere Untersuchungen zum Mechanismus der photodynamischen Wirkung von Farbstoffen

Flash photolytic studies of the transient intermediates produced in the flash excitation of an aqueous buffered solution of the photosensitizing dye “thiopyronine” were undertaken in order to obtain direct insight into the reaction mechanism of the photosensitizing action of the dye. As had been expected from the structural similarity to a well-known photosensitizer, methylene blue, previously reported on, the flash excitation of thiopyronine, in a deaerated buffered solution at pH 7.4 without any substrate, produced three transient intermediates: a triplet-state (Dt), a half-oxidized form (Oxd), and a half-reduced form or semiquinone (Red) of the dye. Red and Oxd were generated simultaneously through electron tansfer reactions, i.e., Dt+Dt→Red+Oxd and Dt+D→Red+Oxd, where D is the dye in the ground state. Thiopyronine solutions containing some reducing and oxidizing agents were studied in order to identify the intermediates. The absorption spectra of these intermediates were identified, and their reaction mechanism studied. The rate constants of some elementary processes obtained are: Dt→k1=2.36×103sec−1 Dt+Dt→k′=7.69×108m−1sec−1 Dt+D→k″=7.69×108m−1sec−1 Red+Red→k6=(1–2)×109m−1sec−1 Oxd→k7=(1–3)×103sec−1 Dt+EDTA→k8=1.6×107m−1sec−1 Dt+ATU→k9≈small Oxd+ATU→k10(2–5)×106m−1small The high efficieny of thiopyrinine in its Photodynamic effect was discussed in connection with the high quantum yield of triplet-state production and the high reversibility of the high reversibility of the photochemical redox reaction of the dye.

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Weitere Untersuchungen zum Mechanismus der photodynamischen Wirkung von Farbstoffen

Cited by 3 publications

References 5 publications

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Studies of the Transient Intermediates of a Thiopyronine Aqueous Solution under Flash Excitation

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