Synthesis and comparative photodynamic properties of two isosteric alkyl substituted zinc(II) phthalocyanines

► Two novel isosteric cationic zinc(II) phthalocyanines were synthesized for PDT. ► The sulfur-linked dye showed the best cytotoxic activity againts KB cells. ► A higher intracellular uptake was demonstrated for the sulfur-linked dye. ► A preferential localization in lysosomes was established for the sulfur-linked dye.