Atomically Engineered Acridine Derivatives Serve as Metal‐Free and Self‐Sensitized Catalysts for Solar‐Driven CO 2 to Formic Acid with High‐Efficiency and Near‐Perfect Selectivity

Abstract Achieving efficient and selective light‐driven CO 2 conversion to formic acid is a significant scientific challenge, particularly when utilizing purely organic, metal‐free, and earth‐abundant element‐based molecule photocatalysts. Herein, we first reported the discovery of acridine derivatives (DADN , PXZN , and PTZN ) as new‐type, metal‐free, self‐sensitized molecule catalysts that enabled exceptional performance in solar‐driven CO 2 reduction to formic acid. Notably, the atomically engineered sulfur‐containing heterocycle PTZN demonstrated unprecedented formate yield rate of 47.8 mmol g −1 h −1 and >99% selectivity in a photocatalytic system using 1,3‐dimethyl‐1 H ‐benzo[ d ]imidazol‐3‐ium (BI + ) as proton and electron relay. The superior activity of PTZN was revealed to arise from its synergistic combination of strong CO 2 ‐binding affinity (−0.195 eV), prolonged charge‐separated states (11 ns), and robust CO 2 electronic coupling (2.51 eV). Comprehensive studies including in situ electron spin resonance, in situ infrared, and transient absorption spectroscopy unambiguously unveiled a direct single electron transfer process from the excited singlet‐state acridine derivatives to CO 2 , generating CO 2 ·− . Moreover, a hydrogen atom transfer process utilizing in situ generated BIH as a hydrogen atom carrier enabled the conversion of CO 2 ·− to formic acid. This work establishes the first demonstration of a sequential proton–electron transfer mechanism in acridine‐based photocatalysis, resolving long‐standing challenges in proton and electron delivery during CO 2 activation.