Photophysical properties of porphyrinoid sensitizers non-covalently bound to host molecules; models for photodynamic therapy

Abstract The binding of photosensitizers to host molecules is discussed from the perspective of how the confinement in a molecular assembly influences the sensitizer’s photophysical properties. In connection with photodynamic therapy (PDT) of cancer during which the administered sensitizer necessarily interacts with the biological material the problem becomes of utmost importance. This review surveys changes of photophysical behaviour of porphyrins, metalloporphyrins and other porphyrinoid sensitizers induced by their interaction with biopolymers (proteins, nucleic acids), liposomes or synthetic sensitizer carriers (cyclodextrins, calixarenes). The structure, charge, and physicochemical properties of the sensitizer predetermine the type of interaction with the surrounding microenvironment and are manifested by changes in absorption, fluorescence, kinetics of deactivation of the excited states, and generation of singlet oxygen. As follows from the collected data, binding of the sensitizer does not restrict formation of the excited states but influences the kinetics. Various consequences of binding on the form and photophysical parameters of the sensitizers are discussed and general features of the mutual interaction are outlined.