Ru(II)-Complex-Based DNA Photocleaver Having Intense Absorption in the Phototherapeutic Window

Ru(II)-complex-based DNA photocleavers have been extensively studied for their potential application in photodynamic therapy (PDT) and photodynamic antimicrobial chemotherapy (PACT). However, their MLCT absorption maxima are generally shorter than 600 nm, limiting PDT/PACT application severely. In this work, by incorporating a 5-chloro-8-oxyquinolate-based noninnocent ligand into a merocyanine scaffold Cl-7-IVQ, we obtained a new Ru complex of this ligand, [Ru(bpy)₂(Cl-7-IVQ)]²⁺, which has intense absorption in the window 600-700 nm and enables an efficient ^•OH-mediated DNA photocleavage. This long-wavelength absorption band has a character of MLLCT transition from the hybrid Ru(dπ)-Cl-7-IVQ(π) orbital to the π*(Cl-7-IVQ) orbital and thus a contribution from the ππ* transition of the merocyanine framework, which endows the complex with a molar extinction coefficient as high as 1.73 × 10⁴ M^-1 cm^-1 at 649 nm and allows for an efficient DNA photocleavage under an irradiation of low intensity. [Ru(bpy)₂(Cl-7-IVQ)]²⁺ represents the first Ru(II)-complex-based DNA photocleaver that has an MLCT absorption maximum above 600 nm and can selectively inactivate E. coli bacterial cells over HeLa cells upon red light irradiation.