Photodynamic inactivation of Candida albicans sensitized by a series of novel axially di-substituted silicon (IV) phthalocyanines

The photodynamic activities against Candida albicans have been evaluated for seven silicon (IV) phthalocyanines modified axially by different functional groups. The effects of the axial substituents on the spectroscopic, photochemical, cellular uptake, and photobiological properties of these silicon phthlaocyanines have been revealed. The dicationic compounds 2 and 4, having two quaternary ammonium groups at the axial positions, exhibit the highest antifungal photocytotoxicity with an IC90 of 61–66 μM, which can be ascribed to their high singlet oxygen quantum yield, non-aggregation nature, effective cellular uptake, and intracellular distribution pattern (localizing preferentially in the mitochondria). By comparison, compounds 2 and 4 show a higher photodynamic inactivation of C. albicans cells than methylene blue (MB), a known antifungal photosensitizer. The IC90 values against C. albicans for 2 and 4 are ca. 8 times lower than that for MB. These results indicate that the dicationic silicon phthalocyanines 2 and 4 are interesting candidates as antifungal photosensitizers for future studies.

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► Photodynamic inactivation of Candida albicans by a series of SiPcs was studied.
► The structure–activity relationship of these silicon phthalocyanines was discussed.
► The dicationic SiPcs 2 and 4 exhibit the highest antifungal photocytotoxicity.
► 2 and 4 show ca. 8 times higher photoactivities than methylene blue.