Novel silicon(IV) phthalocyanines containing piperidinyl moieties: Synthesis and in vitro antifungal photodynamic activities

•A series of SiPcs axially substituted with piperidinyl moieties has been synthesized.•The structure–activity relationships of these compounds has been discussed.•The methylation of piperidinyl groups can enhance the photosensitizing activities.•The cellular uptake toward C. albicans decreased after the methylation.•One of cationic compounds shows the highest photocytotoxicity against C. albicans.

A new series of silicon(IV) phthalocyanines (SiPcs) axially di-substituted with piperidinyl moieties (compounds 1, 2a, and 3a) and their N-methylated derivatives (compounds 2b and 3b) have been synthesized and characterized. Meanwhile, an analogue di-substituted with cyclohexyl groups (compound 4) has also been prepared as a control. The antifungal photoactivities of these SiPcs toward Candida albicans were found to follow the order: 2b ＞ 3a ≈ 3b ＞ 1 ≈ 2a ＞ 4. The structure–activity relationship of these phthalocyanines has been discussed by investigating their photophysical and photochemical properties, partition coefficient, and cellular uptake. The cationic phthalocyanine 2b shows the highest photodynamic activity against C. albicans causing 4 log10 reduction of this fungus at 100 μM, which could be attributed to its high singlet oxygen yields, less aggregation in aqueous media, and relatively efficient cellular uptake.

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