Constructing electron delocalization channels in covalent organic frameworks powering CO₂ photoreduction in water

The photocatalytic conversion of CO₂ into chemical fuels represents a promising approach for solving the future energy crisis. However, the construction of a photocatalyst simultaneously integrating a photosensitizer and molecular cocatalyst with intramolecular electron delivery is challenging. Herein, we designed covalent organic frameworks (COFs) with excellent extended conjugation and potential embedded redox active sites. The full -C = C- bridging in sp²c-COF_dpy creates and dredges the donor-acceptor channel for intramolecular electron delocalization and a cascade effect. Interestingly, CO₂ photoreduction can be carried out in water, and the optimized sp²c-COF_dpy-Co exhibits the highest activity and stability among COFs without noble metal involvement, achieving up to 17.93 mmol g⁻¹ CO with 81.4 % selectivity in a long-range reaction. Theoretical calculations and experimental data suggest that the structural advantages enable excitons to facilely reach single Co sites via the electron cascade, which provides a new concept in the nanoarchitecture of COFs for efficient CO₂ photoreduction.