Cu² ⁺-Activated NIR Photothermal Conversion Based on Imine Bond Photorotation for Dual-Mode Antibacterial Applications

Small organic molecule-based therapeutic systems that integrate near-infrared (NIR) photothermal activity with Cu²⁺-mediated functionality as an orthogonal therapy pathway remain scarce. Herein, we demonstrate that coordination of Cu²⁺ with a small photothermal agent induces a pronounced bathochromic shift of light absorption into the NIR region and enables effective dual-mode antibacterial activity. Two rationally designed molecules, BTAA-Me and BTAA-Et, feature a photon-driven rotating imine bond that promotes efficient non-radiative excited-state decay for high photothermal conversion, together with a bis-benzothiazole motif that serves as a selective Cu²⁺ coordination site. The resulting complex, Cu²⁺@BTAA-Et, exhibits pronounced bactericidal activity against Staphylococcus aureus and Escherichia coli under 808 nm laser irradiation, markedly outperforming either photothermal treatment with BTAA-Et or Cu²⁺ treatment alone. Static density functional theory (DFT) calculations and excited-state dynamics simulations based on time-dependent DFT (TD-DFT) systematically elucidate the underlying mechanisms. This work provides mechanistic insights into the rational design of dual-mode biomedical materials that synergistically combine photothermal effects with metal ion-mediated activity.