Synergistic Electronic and Steric Engineering of Thiophene Donors in Covalent Organic Frameworks for Efficient CO₂...

Covalent organic frameworks (COFs), featuring broad light absorption and permanent porosity, serve as excellent supports for metal catalytic sites in photocatalytic CO₂ reduction, offering great promise for efficient and stable CO₂ photoconversion. Herein, two rationally designed thiophene-rich monomers enable the effective coupling of thiophene and benzothiadiazole units within the same COF materials, yielding D-A type COFs with bex topological structures (TTB-COF and TTP-COF). By modulating the central unit, the intramolecular built-in electric field is enhanced, and the rotational freedom of thiophene units is also constrained, leading to a wavy structure in the monolayer COF, which significantly improves the material's photocatalytic performance. Using 2,2'-bipyridine as an additive, TTB-COF-Co achieves a high CO production rate of 28.0 mmol g^-1 h^-1 with a selectivity of 88.4% in the presence of the photosensitizer [Ru(bpy)₃]Cl₂·6H₂O and the sacrificial agent triethanolamine (TEOA), being one of the best performances among COF-based catalysts. Analysis of the cumulative free energy change diagrams reveals that TTB-COF-Co lowers the energy barrier of the rate-determining step in CO₂ photoreduction, thereby demonstrating superior photocatalytic performance. This work provides a referable design strategy for constructing high-performance COF-based photocatalysts for CO₂ reduction.