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.