THE TRIPLET AND RADICAL SPECIES OF HAEMATOPORPHYRIN AND SOME OF ITS DERIVATIVES

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Abstract
Abstract— Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0‐acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate).After 347 nm irradiation in water containing 2% Triton X‐100, haematoporphyrin forms the triplet state (φT= 0.92) and photoionises monophotonically (φI= 0.03). For the O‐acyl derivatives, φT approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates (k1˜104s‐1) and oxygen quenching constants (kQ˜1.5times109M‐1s‐1) for the triplet state have been measured. The difference and corrected spectra for the semi‐reduced species in methanol and semi‐oxidised species in aqueous Triton X‐100 are presented.The photophysical characteristics in fluid solution of haematoporphyrin and its 0‐acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins.

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