Red and green light activatable ruthenium complexes for singlet oxygen-driven photo-functional applications

Ruthenium photosensitizers bearing bis-(2,6-diquinolin-8-yl) pyridine (DQP) and carboxylated terpyridine exhibit intense visible-light absorption (ε = 85 400 M^-1 cm^-1 at 500 nm) and long-lived excited states that efficiently transfer energy to molecular oxygen to generate singlet oxygen (¹O₂). Carboxylation of the terpyridine scaffold imposes a strong electronic perturbation, bathochromically shifting the absorption manifold to 670 nm, stabilizing the triplet state, and extending lifetimes to 208 ns. In combination with the wide-bite-DQP donor, these effects reinforce metal-to-ligand charge-transfer and markedly enhance ¹O₂ generation. The tri-carboxylterpyridine complex emerges as the most active photosensitizer, delivering a ¹O₂ quantum yield of 88% under green excitation and inducing 60-70% apoptosis in colorectal carcinoma cells (HCT-116) under green and red light. These chromophores also mediate efficient visible-light-driven photooxidation of diphenyl anthracene, α-terpinene, dihydroxynaphthalene, 2-furfural, and 1,3-cyclohexadiene, affording moderate to high yields of oxygenated products.