Novel Water‐Soluble Chlorin Photosensitizers for Use in Photoelectrochemistry and Photodynamic Therapy

Water‐soluble tetra‐4‐carboxyphenylchlorins have been synthesized and characterized, including the free base dye ( H 2 C ) and its trans ‐axially ligated Sn(IV) complex ( SnC ). SnC exhibited a high singlet oxygen ( 1 O 2 ) quantum yield of 0.69 in dimethylsulfoxide (DMSO). Photodynamic therapy (PDT) activity against the MDA‐MB‐231 triple‐negative breast cancer cell line was evaluated under optimal optical irradiation conditions through 30 min irradiation with Thorlabs M625L3 (2.6 J.cm −2 ) and M660L4 (3.0 J.cm −2 ) light‐emitting diodes. A favorable IC 50 value of 5.8 µM was obtained for SnC , while a higher value of 12.1 µM was observed for H 2 C , demonstrating that water‐soluble Sn(IV) tetraarylchlorin complexes merit further in‐depth study for use as 1 O 2 photosensitizer dyes in biomedical applications. The chlorins were further investigated in photoelectrochemical studies. SnC generated higher photocurrent across most of the visible region, in agreement with the trend observed in UV–vis absorption spectroscopy. Cross‐reactivity studies showed lower photocurrent for H 2 C at wavelengths not matching its maximum. This indicates the potential suitability of these chlorins as photoactive labels for photoelectrochemical biosensors, which should be analytically validated in the future for either high‐sensitivity, single‐target detection or multiplex detection.