“…Synthesis of new PS and search for new antitumor drugs are constantly in progress. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] Among the promising ones are chlorin-based compounds, including chlorin e 6 (Ce 6 ), [21] as they meet the core requirements for the "ideal PS", [7,9,22] namely, the existence of the intense absorption band in the long-wave part of the spectrum (600-800 nm), in which biological tissues are more optically transparent (so-called "therapeutic window" [13] ); the high capacity to accumulate in the target tissue; the existence of intense fluorescence, which actually provides photodynamic effect, as well as allows to carry out fluorescence diagnostics; the storage stability and virtually no toxicity. [9] At the same time due to the characteristics (λ max = 660 ± 5 nm, ε = 41000 mol -1 •cm -1 ) chlorin-based compounds show higher depth of light penetration into tissues compared to porphyrins, [7,11,12] and the excitation coefficient of chlorins is 10 times larger than that of the porphyrins.…”