Multicomponent Linkage Engineering of Quinoline-Linked Covalent Organic Frameworks for Atmospheric-Pressure...

Developing efficient metal-free porous catalysts for the cycloaddition of CO₂ with epoxides under atmospheric-pressure conditions remains challenging because strong CO₂ affinity, efficient epoxide activation, and framework stability are difficult to integrate within a single material. Herein, we report a chemically robust bifunctional quinoline-linked covalent organic framework, Quinoline-COF_COOH, synthesized via a three-component Doebner multicomponent reaction. This approach enables the direct incorporation of CO₂-philic triazine units and Brønsted acidic carboxylic acid groups into an ordered porous framework without post-synthetic modification. Owing to the fused quinoline linkage, Quinoline-COF_COOH exhibits high crystallinity, permanent porosity, excellent chemical stability, and a surface area of 1296 m² g^-1. Compared with the imine-linked analogue, Quinoline-COF_COOH shows significantly enhanced CO₂ uptake and higher isosteric heat of adsorption (Qst = 43.2 kJ mol^-1), indicating strong framework-CO₂ interactions. Benefiting from the synergistic effect of triazine units and Brønsted acidic sites, Quinoline-COF_COOH efficiently catalyzes the cycloaddition of epoxides with CO₂ under atmospheric-pressure and metal/solvent-free conditions, achieving >99% conversion and selectivity within 6 h. Mechanistic studies and DFT calculations reveal that the carboxylic acid groups promote epoxide activation, while the triazine units facilitate CO₂ adsorption and insertion. This work highlights multicomponent linkage engineering for constructing a bifunctional COF for sustainable CO₂ conversion.