ABSTRACT
Interest in phthalocyanines (Pc) as second-generation photosensitizers for photodynamic therapy (PDT) started in 1985 following the report that some of these compounds are efficient photosensitizers in mammalian cells, and pointing out their advantages over hematoporphyrin derivative. The use of Pc in PDT is still in preclinical stages, and much still remains to be revealed. This chapter reviewS these agents’ basic photobiology, structure-activity relation, and mechanisms of action in various systems. The quantum yield and lifetime of the excited triplet state, which is the important state for useful photochemistry, depend on two main factors: the aggregation state and the central metal ion. Photocytotoxicity of Pc depends on the presence of molecular oxygen. As expected, the extent of cell photoinactivation is proportional to the total light fluence. One of the major effects of the central metal ion is on the lifetime of the triplet state. In general, Pes that contain paramagnetic metals have short triplet lifetimes, making them inefficient photosensitizers for PDT.
