Enhancing Photocatalytic CO₂ Reduction to Multicarbon Fuels via Hydrophobic Donor-(π-Acceptor) Covalent Organic Frameworks

Covalent organic frameworks (COFs) have emerged as promising candidates for photocatalytic CO2 reduction, yet achieving high efficiency for C2+ (C2H4, C3H6) products remains challenging due to inherent hydrophilicity and rapid charge recombination. We synthesized three isostructural COFs by polymerizing 2,4,6-triformylphloroglucinol with fluorine-tuned amine monomers. Strategic fluorination induces in-plane hydrogen bonding to lock π-conjugated acceptor (A) units, forming a donor-(π-acceptor) (D-(π-A)) architecture that suppresses electron–hole recombination postexcitation while enhancing charge carrier mobility through π-A coplanarity. Concurrently, fluorination creates a hydrophobic surface to mitigate CO2 mass-transfer limitations, elevating local CO2 concentration and optimizing proton availability at the three-phase interface. The multifluorinated COF demonstrates exceptional photocatalytic activity for CO2-to-propylene conversion, exhibiting 18.1-fold and 1.5-fold enhancements over its nonfluorinated and monofluorinated counterparts, respectively. This work establishes fluorination as a dual-functional strategy to simultaneously regulate electronic structures and surface properties in COFs, providing new pathways for solar-driven synthesis of multicarbon chemicals from sustainable C1 feedstocks while contributing to ecological sustainability.