Linker Engineering as a Topological Switch in Covalent Organic Frameworks with Single Ni Sites for Photocatalytic CO ₂ Reduction

Abstract Highly selective photoconversion of CO 2 into value‐added fuels is crucial yet still restricted by efficacious catalysts with established structure‐activity correlations. Herein, through a linker rigidity‐flexibility modulation strategy utilizing rigid pyrene or relatively flexible biphenyl as parts of motifs, two covalent organic frameworks (COFs) with topological divergence bearing Ni single atoms are obtained for efficient CO 2 photoreduction. Pyrene‐containing Ni‐BPYP‐COF with hit topology manifests an impressive CO generation rate of 21.1 mmol g −1 h −1 , outperforming biphenyl‐incorporating Ni‐BPYA‐COF with bex topology by 2.5‐fold. Notably, even under simulated flue gas conditions (15% CO 2 ), Ni‐BPYP‐COF maintains outstanding activity, yielding CO at 15.4 mmol g −1 h −1 (≈100% selectivity). Extensive experimental and theoretical studies reveal that, despite the comparable NiN 2 O 4 catalytic sites, the greater conjugation and irregular hexagonal tessellation of the Ni‐BPYP‐COF enhance its ability to harvest visible light, augment dipole moments that are beneficial for charge separation, and allow for precise tuning of the d ‐band center position, facilitating CO 2 activation and the generation of * CO intermediates. The findings underscore the synergistic interaction between linker‐governed conjugation and topology in modulating the electronic structure of COFs, thereby improving CO 2 photoreduction activity and providing insights for developing selective photocatalysts.