The photophysical properties of three photosensitizers—dimegine, photoditazine, and radachlorin—have been comparatively examined. For dimegine and photoditazine, two techniques have been used to measure the singlet oxygen generation quantum yields and the quenching constants of singlet oxygen by dimegine and photoditazine, as well as the dimegine fluorescence quantum yield.

We compare the photostability of one porphyrin and two chlorine photosensitizers. We show that a higher photostability of dimegine compared to photoditazine and radachlorin is determined both by their different chemical natures and by the fact that the aggregation ability of porphyrin dyes is higher than that of chlorine dyes, which in the solution leads to efficient formation of dimers and higher-order complexes.

A comparative study of the influence of an aqueous medium properties on the aggregation of dimegine, photoditazine and radachlorin was carried out. A nonlinear dependence of the molar extinction on the concentration of the photosensitizer in solution was noted, moreover to varying degrees for the dosage form of the solution and solutions prepared using lyophilized photosensitizer powders. It has been shown that the use of surfactants (Pluronic F-127 and polyvinylpyrrolidone) within certain limits reduces the problems associated with the aggregation of the studied photosensitizers.