Trans-A₂B₂-Type Metalloporphyrin-Based Donor-Acceptor Covalent Organic Frameworks for Efficient Photocatalytic CO₂...

The sunlight-driven CO₂ cycloaddition to aziridines represents a promising strategy for CO₂ resource utilization, offering a green alternative to conventional thermally driven fixation approach that typically requires high temperatures and/or elevated pressures. Inspired by the exceptional light-absorption properties of porphyrin derivatives and the enhanced charge separation afforded by a donor-acceptor (D-A) configuration, two porphyrin-based D-A type covalent organic frameworks (COFs), including metal-free m-DBPA-COF and metallized m-NiDBPA-COF are synthesized through acid-catalyzed Schiff base reaction between electron donor (tris(4-aminophenyl)amine) and electron acceptor (trans-A₂B₂-type m-DBP-CHO or m-NiDBP-CHO) units. The incorporation of trans-A₂B₂-type metalloporphyrin markedly enhances the transfer and separation of photoinduced charge carriers through ligand-to-metal charge transfer (LMCT) and the electron push-pull characteristic inherent in D-A configurations. Moreover, the incorporated Ni ions provide Lewis acidic sites that facilitate substrate interactions. Encouragingly, under visible light-assisted and mild conditions (1 atm CO₂ with no heating required), m-NiDBPA-COF exhibited remarkable photocatalytic performance, achieving a reaction rate of 4.13 mol mol^-1 h^-1, which is comparable to that of most thermal catalysts in catalyzing the CO₂ cycloaddition to aziridines. Overall, the study not only provides a guide for the design of porphyrin-based COF photocatalysts, but also offers a green route to address the CO₂-related resource utilization issues.