Enhanced singlet oxygen generation of a soft salt through efficient energy transfer between two ionic metal complexes

In this study, a soft salt complex based photosensitizer has been developed for photodynamic therapy (PDT) of cancer cells. The iridium(III) complex [Ir(L)(L′)]3+(PF6−)3 (C1) with L and L′ being terpyridine ligands (L = 4′-phenyl-2,2′:6′,2′′-terpyridine, L′ = 3-([2,2′:6′,2′′-terpyridin]-4′-yl)-9-hexyl-9H-carbazole) was chosen as the cationic component, and the iridium(III) complex [Ir(dfppy)2CN2]−Bu4N+ (A1) was selected as the anionic component. Complexes C1 and A1 are directly connected through electrostatic interaction to form a soft salt based photosensitizer (S1), which exhibited an enhanced singlet oxygen generation rate because of efficient energy transfer between two ionic metal complexes. Furthermore, this novel photosensitizer was successfully applied in photodynamic therapy (PDT) of cancer cells for the first time.