One-Pot Postsynthetic Linkage Modification of Imine Covalent Organic Frameworks via Iminium Activation

Abstract

Postsynthetic modification (PSM) of the linkages in covalent organic frameworks (COFs) is usually performed on isolated samples due to their incompatibility with the crystallization conditions. In this work, we report a one-pot PSM strategy that reduces imine-linked to amine-linked COFs via an iminium-activated process under acidic conditions. Using Hantzsch ester as a mild, chemoselective reductant, this method eliminates the need for isolating pristine COFs prior to transformation and shows better functional group tolerance compared to previous methods (NaBH4 and HCOOH). The resulting amine-linked COFs retain high porosity and crystallinity. As a demonstration, a H₃PO₄-loaded amine-linked pyrene COF achieves a proton conductivity of 4.9×10⁻² S cm⁻¹ at 95 °C and 80% relative humidity with a low activation energy of 0.16 eV. This one-pot strategy offers a streamlined and general approach to accessing functionalized COFs.