Photophysical and photobiological properties of natural chlorins with additional heterocyclic fragments

New substituted trimethyl ester chlorin [Formula: see text] derivatives possess pronounced fluorescent ([Formula: see text] [Formula: see text] 0,3) and photosensitizing properties ([Formula: see text] [Formula: see text] 0,6). The dyes are capable of binding with albumin (K[Formula: see text] [Formula: see text] 10 5 M[Formula: see text]. The triplet state of the dye 3 in complex with BSA showed the ability to transfer electron from the electron donor molecule (ascorbic acid). The recombination rate constant for the dye 3 anion radicals was determined (1.8 × 10 8 M[Formula: see text] s[Formula: see text]. These results show that the dye studied can act as a photosensitizer via both Type I and Type II reactions. The synthesized compounds exhibit low dark cytotoxicity at concentrations up to 50 [Formula: see text]M over 24 hours of incubation in HCT116 cells. When cells are photoexcited with a 660 nm laser, chlorins 3 and 4 cause rapid cell death at submicromolar concentrations, higher than that of the drug chlorin [Formula: see text] “Photolon”. The phototoxicity of compound 2, 5 was lower than that of “Photolon”. For the most photodynamically active compound 3, accumulation in the endoplasmic reticulum of cells and the mechanism of death are shown - rapid photo-induced necrosis.