Covalent Organic Framework with Donor 1 -Acceptor-Donor 2 Motifs Regulating Local Charge of Intercalated Single Cobalt Sites for Photocatalytic CO 2 Reduction to Syngas.

Covalent organic framework (COF) has attracted increasing interest in photocatalytic CO 2 reduction, but it remains a challenge to achieve high conversion efficiency owing to the insufficient active site and fast charge recombination. Rationally optimizing the electronic structures of COF to regulate the local charge of active sites precisely is the key point to improving catalytic performance. Herein, intercalated single Co sites coordinated by imine-N motifs have been designed by using trinuclear copper-based imine-COFs with distinct electronic moieties via a molecular engineering strategy. It is confirmed that the charge delivery property and local charge distribution of these heterometallic frameworks can be profoundly influenced by electronic structures. Among these featured structures with mixed-state copper clusters, Co/Cu 3 -TPA-COF stands out for an exceptional photocatalytic CO 2 reduction activity and tunable syngas (CO/H 2 ) ratio by changing various bipyridines. Experimental and theoretical results indicate that interlayer Co-imine N motifs on the donor 1 -acceptor-donor 2 structures facilitate the formation of a highly separated electron-hole state, which effectively induces the oriented electron transfer from dual electron donors to Co centers, achieving an enhanced CO 2 activation and reduction. This work opens up an avenue for the design of high-performance COF-based catalysts for photocatalytic CO 2 reduction.