Thien-2-yl substituted chlorins as photosensitizers for photodynamic therapy and photodynamic antimicrobial chemotherapy

The synthesis and characterization of meso-tetra(thien-2-yl)chlorin (1) and meso-tetra(5-bromothien-2-yl)chlorin (2) is reported. These dyes have red-shifted absorption maxima compared to those of the analogous meso-tetraphenylchlorin (3). 1 and 2 have Q bands at 660 and 664 nm, respectively, singlet oxygen quantum yields of 0.60 and 0.64 and exhibit good photostability. The triplet states were found to have lifetimes of 8.6 μs in N2 purged DMF. Time-dependent cellular uptake of chlorins reached a maximum in MCF-7 cancer cells after 12 h. Upon irradiation with a Thorlabs M660L3 LED (280 mW cm−2), 2 exhibited better photocytotoxicity with an IC50 value of 2.7 μM against MCF-7 cells. The 2ʹ,7ʹ-dichlorodihydrofluorescein diacetate (DCFDA) assay provided evidence for intracellular generation of reactive oxygen species. Photodynamic inactivation of bacteria by the chlorins was also studied. 2 exhibits better activity with log reduction values of 7.42 and 8.34 towards Staphylococcus aureus and Escherichia coli, respectively, under illumination for 60 min at 660 nm with a Thorlabs M660L3 LED (280 mW cm−2). These results demonstrate that 2 is a promising candidate for future in vivo experiments and merits further in-depth investigation