Photosensitizer

Photosensitizers are light absorbers that alter the course of a photochemical reaction. They usually are catalysts. Photosensitizers have been used as light-responsive drugs with their imaging capabilities, easy synthesis, tunable energy levels, and biocompatibility, which make them an innovative tool for therapeutic approaches in treatment of various cancers. Among different methods for cancer therapy, photodynamic therapy (PDT) using a photosensitizer can take advantage of penetrated light into a targeted tissue for improving tumor control. The PDT comprises of three major components; photosensitizer, oxygen, and light source of appropriate wavelength, which when act together, generate a photochemical reaction. Depending on the part of the body being treated, the photosensitizing agent is either administered into the bloodstream through a vein or placed directly on the skin. By irradiation light on the targeted area, the excited photosensitizer emits energy in the form of heat and exhibits intersystem crossing (ISC), leading to the formation of reactive oxygen species (ROS) in triplet state.
Photosensitizers can function by many mechanisms, sometimes they donate an electron to the substrate, sometimes they abstract a hydrogen atom from the substrate. At the end of this process, the photosensitizer returns to its ground state, where it remains chemically intact, poised to absorb more light. One branch of chemistry which frequently utilizes photosensitizers is polymer chemistry, using photosensitizers in reactions such as photopolymerization, photocrosslinking, and photodegradation. Photosensitizers are also used to generate prolonged excited electronic states in organic molecules with uses in photocatalysis, photon upconversion and photodynamic therapy. Generally, photosensitizers absorb electromagnetic radiation consisting of infrared radiation, visible light radiation, and ultraviolet radiation and transfer absorbed energy into neighboring molecules^[1][2].

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