Physical, spectroscopic, and biological properties of ruthenium and osmium photosensitizers bearing diversely substituted 4,4′-di(styryl)-2,2′-bipyridine ligands

Capitalising on the previous identification of a distyryl coordinated Ru(ii) polypyridine complex as a promising photosensitizer for photodynamic therapy, eight new complexes were synthesized by modifications of the ligands or by changing the metal coordinated. We report in this work the effects of these modifications on the physical, spectroscopic, and biological properties of the synthesized complexes. Subtle structural modifications of the distyryl ligand only had a moderate effect on the corresponding complexes' visible light absorption and singlet oxygen quantum yield. These modifications however had a significant effect on the lipophilicity, the cellular uptake and the phototoxicity of the complexes. Although the lipophilicity of the complexes had a somewhat expected effect on their cellular uptake, this last parameter could not be directly correlated to their phototoxicity, revealing other underlying phenomena. Overall, this work allowed identification of two promising ruthenium complexes as photosensitisers for photodynamic therapy and provides some guidance on how to design better photosensitizers.

Automated summary

Eight new ruthenium complexes were synthesized by modifying ligands or changing metal coordination, and their effects on physical, spectroscopic, and biological properties were studied. The modifications had moderate effects on visible light absorption and singlet oxygen quantum yield, but significant impacts on lipophilicity, cellular uptake, and phototoxicity. This work identified two promising ruthenium complexes as photosensitizers for photodynamic therapy and provided guidance for designing better photosensitizers.