Metal-Free Photocatalytic CO2 Reduction to Formate Driven by Visible Light via a Consecutive Photoinduced Electron Transfer Mechanism.

Realizing efficient and selective photocatalytic CO2 reduction (PCO2R) using metal-free organic systems under visible light remains a significant challenge. Here, we report the first metal-free, self-sensitized molecular photocatalyst capable of driving visible-light-induced CO2-to-HCOO- conversion via a consecutive photoinduced electron transfer (ConPET) mechanism. The rationally designed BPI-OMe, featuring an electron-donating group, demonstrates exceptional performance under visible light irradiation, achieving a formate production rate of 27.51 mmol g-1 h-1 with > 99% selectivity. This outstanding activity stems from its optimized electronic properties: a low excitation energy (2.98 eV), a long-lived charge-separated anion radical state (τ = 806.94 ns), a high-energy SOMO level (-3.47 eV), and strong CO2 binding affinity (-0.147 eV). In situ ESR and ultrafast spectroscopic analyses reveal the ConPET process: sequential photon absorption enables electron transfer from ascorbic acid to BPI-OMe, generating BPI-OMe, followed by electron delivery to CO2 to form CO2 -, which is subsequently converted to formate through a hydrogen atom transfer. This work not only represents a breakthrough in metal-free PCO2R but also provides a general molecular design strategy based on multi-photon charge accumulation for enabling challenging solar-to-chemical transformations.