Bacteriochlorins and their metal complexes as NIR-absorbing photosensitizers: properties, mechanisms, and applications

Abstract Bacterichlorins possess a characteristic intense electronic absorption in the near-infrared part of the electromagnetic radiation (NIR) from 700 nm up to 900 nm, where endogenous chromophores do not absorb and which allows deep penetration through tissues. Although naturally-occurring metal complexes derived from bacteriochlorophylls are unstable and their use is limited, it is currently possible to obtain large-scale libraries of photostable synthetic compounds belonging to the bacteriochlorin family. This review presents an up-to-date overview of the most significant studies on the synthesis, spectroscopic, photochemical, and electrochemical characteristics as well as various potential applications of bacteriochlorins and their metal complexes. Particular emphasis has been given to the possibilities of their use in medicine, especially in photodynamic therapy of cancer (PDT), photodiagnosis (PD), and photodynamic inactivation (PDI) of bacteria, viruses, and fungi. The combination of (metallo)bacteriochlorins with polymeric micelles, lipoproteins, nanoparticles, and metal-organic frameworks in order to increase their efficacy is also discussed. Other potential applications of (metallo)bacteriochlorins discussed in this paper include their use as light-harvesting antennas, optical sensors, photocatalysts, and dye-sensitized solar cells for efficient solar energy conversion.