Construction of Modifiable Phthalocyanine-Based Covalent Organic Frameworks with Irreversible Linking for Efficient Photocatalytic CO2 Reduction

Covalent organic frameworks (COFs) are considered promising catalysts for photocatalytic CO₂ reduction reaction (pCO₂RR) due to facilitated regulations. However, the instability of COFs with dynamic reversible covalent bonds and the limited modifiability of COFs with irreversible covalent bonds restricted the enhancement of the pCO₂RR performance. Herein, three phthalocyanine-based COFs with ether-linked, CoOP, CoPOP, and CoBOP, were successfully prepared via in situ polycondensation using modifiable bis-phthalonitrile. CoBOP achieved a record of syngas performance in pCO₂RR systems with photosensitizers and sacrificial agents (CO 83.7 mmol g^-1 h^-1 and H₂ 54.7 mmol g^-1 h^-1), surpassing most COF photocatalysts. Additionally, CoOP, CoPOP, and CoBOP exhibit stabilities in extreme environments owing to their irreversible covalent bonds. Experimental and density functional theory analyses confirm that the optimally matched the lowest unoccupied molecular orbital of the linking unit between the photosensitizer and active unit endowed CoBOP with the highest photoelectron transfer efficiency among the three catalysts, boosting its pCO₂RR activity. This work is highly instructive for designing COFs with structure-adjustable and irreversible covalent bonds.