Laser flash photolysis of haematoporphyrins in some homogeneous and heterogeneous environments

Abstract

Nanosecond laser flash photolysis has been used to generate and characterise the triplet state of haematoporphyrin in a number of homogeneous and microheterogeneous environments. First-order triplet decay rate constants lie in the range (1–3)× 10⁴ s^–1 in detergents and homogeneous environments but are higher [(4–6)× 10⁴ s^–1] in liposomal and cellular environments. Values of the singlet–triplet extinction coefficients reflect the degree of aggregation of the haematoporphyrin in the various environments and imply that aggregation is extensive in phosphate buffers, liposomal and cellular environments but is small in detergents and homogeneous solution. Quantum yields for triplet formation are near unity for all the systems studied.