Covalent Organic Frameworks via In Situ Monomer Release for Humid CO 2 Uptake

Achieving high crystallinity and porosity in covalent organic frameworks (COFs) remains a major challenge, particularly for robust azine-linked systems, where limited bond reversibility hinders framework ordering. While several strategies have improved the crystallinity in imine-linked COFs, analogous advances in azine-linked frameworks are still lacking. Here, we present a kinetic modulation strategy based on the in situ slow release of hydrazine via the trifluoroacetic acid (TFA)-mediated hydrolysis of a tetrazine precursor during the COF synthesis. Using this approach, we successfully synthesized two crystalline azine-linked COFs incorporating either a nonplanar bicarbazole or a planar pyrene core. This method enhances structural order, as evidenced by narrowed full width at half-maximum (FWHM) values in PXRD and higher surface areas compared to the COFs prepared with direct hydrazine hydrate addition. Time-resolved UV-vis and PXRD analyses elucidate the role of reaction kinetics in framework evolution. Notably, the resulting COFs exhibit S-shaped water vapor adsorption isotherms with minimal uptake below 40% relative humidity (RH), reflecting their hydrophobic backbones. More importantly, CO₂ uptake remains largely unaffected at 40% RH, and dynamic breakthrough experiments confirm that H₂O does not interfere with CO₂ adsorption under these conditions. This work establishes a generalizable route for crystallinity enhancement in kinetically trapped COFs and offers promising materials for gas separation under humid environments.