Red-Light-Driven Ru(II) Photocatalysts Enable Dual Oxidation of NADH and Glutathione in Living Cells

Abstract Intracellular photocatalysis has emerged as a promising strategy to disrupt cancer redox homeostasis, yet most photoredox systems remain limited by oxygen dependence and deactivation by intracellular thiols, particularly glutathione (GSH). Here we report PEGylated Ru(II) terpyridine complexes that function as visible-light photocatalysts, and catalytically oxidize both NADH and GSH through complementary Type I and Type II pathways. The complexes exhibit broad visible-light absorption, aqueous stability, and activity in biologically relevant media. Stern–Volmer quenching experiments and electrochemical studies are consistent with excited-state electron transfer from NADH and GSH, while ROS studies reveal singlet oxygen, superoxide, and hydrogen peroxide during catalysis. Unexpectedly, glutathione enhances rather than suppresses photocatalytic activity, supporting its participation in catalyst turnover. NADH oxidation is maintained in oxygen-limited solution. In cancer cells, red-light irradiation disrupts the intracellular NAD+/NADH balance, depletes glutathione, and amplifies oxidative stress, resulting in selective photocytotoxicity. Comparative studies further reveal that intracellular performance depends not only on catalytic efficiency in solution but also on catalyst photostability and accessibility to cellular redox pools. Together, these findings establish terpyridine-based Ru(II) photocatalysts as an effective strategy for disrupting intracellular redox balance and provide new insight into glutathione-assisted photocatalysis in biological systems.