Merging Light Harvesting and Catalysis: External Photosensitizer-Free CO ₂ -to-CO Conversion by a Copper–Phenanthroline–Pyrene Complex

The development of efficient and selective molecular systems for CO2 reduction is central to advancing carbon-neutral energy technologies. Herein, we report a pyrene-functionalized Cu(II) complex (C2) that operates as a self-sensitized photocatalyst for selective CO2-to-CO conversion under visible light, eliminating the need for external photosensitizers. The pyrene moiety serves dually as a chromophore and electron transfer mediator, facilitating intramolecular charge separation and enhancing photocatalytic performance. A nonpyrene analog (C1) was synthesized as a control to probe the role of the ligand framework. Under electrochemical conditions, C2 outperformed C1 in both activity and selectivity (TONCO ∼ 257, 88% CO, rate: 618 s–1) and achieved a TON15 h ∼ 1900 under photosensitizer-free conditions. The system also demonstrated compatibility with metal-free organic photosensitizers such as CzIPN. Mechanistic investigations employing in situ Fourier transform infrared, electron paramagnetic resonance, and transient spectroscopic techniques revealed key intermediates and elucidated charge transfer pathways. Notably, C2 maintained robust performance in aqueous solvent systems, in simulated flue gas environments, and under solar irradiation, selectively producing CO while suppressing H2 evolution. These results establish C2 as a blueprint for the rational design of self-sensitized molecular catalysts, advancing solar-driven CO2 utilization and offering a scalable route toward artificial photosynthesis and carbon management.