bacteriochlorin

Bacteriochlorin is a class of tetrapyrrolic macrocycles closely related to porphyrins. It denotes a reduced form of porphyrin in which the macrocycle has undergone additional hydrogenation relative to chlorin, resulting in a dihydro-porphyrin-type skeleton. This increased saturation alters the electronic structure and typically shifts absorption to longer wavelengths than chlorin derivatives, with strong absorption extending into the red to near-infrared region in many cases. The changes in conjugation also influence photophysical properties such as fluorescence and photostability.

Natural occurrence: Bacteriochlorins occur in certain photosynthetic bacteria as components of bacteriochlorophylls. In these organisms, the bacteriochlorin-type macrocycle participates in light harvesting under low-light or anaerobic conditions, enabling absorption of near-infrared light that complements other pigments in the photosynthetic apparatus.

Synthesis and derivatives: Chemists prepare bacteriochlorins by selective hydrogenation of porphyrin or chlorin precursors, or by chemical modification of bacteriochlorophyll derivatives. Catalytic hydrogenation under mild conditions or other reduction strategies are used to introduce the additional saturation required to form the bacteriochlorin framework. Substituents may be appended to tune solubility, aggregation behavior, and photophysical properties for specific applications.

Applications: Due to their near-infrared absorption and often favorable singlet oxygen generation, bacteriochlorin derivatives are explored as photosensitizers for photodynamic therapy and antimicrobial photodynamic inactivation. They are also investigated as fluorescent imaging agents in research settings and can be incorporated into targeting constructs to improve tissue selectivity.

See also: chlorin, porphyrin, bacteriochlorophyll.