Photophysical properties of porphyrins in biological membranes.

This review illustrates the photophysical properties of some porphyrins, especially those used for biomedical applications, in relation to their photosensitizing efficiency in biological membranes. Porphyrin absorption and luminescence properties are mainly examined. The factors influencing the affinity of porphyrins for biological membranes, including the dye hydrophobicity, the charge and aggregation state, the pH of the medium and the physicochemical properties of the dye environment, are discussed. These factors determine the differences in the photophysical properties of porphyrins in biological membranes. Particular attention is paid to the porphyrin aggregation state: only monomeric species and possibly planar end-to-end aggregates are endowed with significant photosensitizing ability. Many conclusions presented are based on data obtained on membrane model systems such as micelles or liposomes which can mimic specific situations occurring in cells.