fotosensitizer

Photosensitizers are molecules that absorb light and, upon reaching an excited state, can initiate chemical reactions. In the presence of oxygen they commonly generate reactive oxygen species that damage biological macromolecules or drive chemical processes. Photosensitizers used in medicine operate primarily through two photochemical pathways: Type I, where electron transfer produces radicals, and Type II, where energy transfer creates singlet oxygen. The relative contribution of each pathway depends on the photosensitizer, light, oxygen availability, and environment.

Common classes include organic dyes based on porphyrins, chlorins, and phthalocyanines, as well as inorganic complexes and quantum dots. Clinically approved photosensitizers for photodynamic therapy (PDT) include porfimer sodium, temoporfin, and verteporfin; newer agents seek stronger near-infrared absorption and higher selectivity. In research, photosensitizers are used for antimicrobial PDT, photocatalysis for pollutant degradation, and initiation or control of polymerization reactions.

Key properties for effective practice include strong absorption in the red to near-infrared region (to maximize tissue penetration), high quantum yield for ROS production, selective accumulation in target tissues, and favorable pharmacokinetics with rapid clearance to minimize prolonged photosensitivity. Delivery strategies such as tumor-targeting conjugates, liposomal formulations, or nanoparticle carriers improve selectivity and distribution.

Limitations include limited light penetration depth, tumor hypoxia reducing Type II efficacy, and risk of phototoxicity to normal tissue after treatment. Overall, photosensitizers enable light-triggered therapeutic and catalytic actions and continue to be refined for deeper penetration, safety, and specificity.