Off-pathway synthesis of micron-thick, oriented 2D covalent organic framework films

Abstract

Despite the advancements in the field of 2D polymerization, the synthesis of high-quality films of oriented 2D covalent organic frameworks (2D COFs) remains a longstanding challenge. Herein, we describe a method for preparing robust, large-area, porous 2D COF films with near-perfect face-on orientation via amorphous covalent adaptable network (CAN) intermediates. Generated by solution casting, the kinetically trapped CANs undergo an unusual spontaneous alignment in response to the tensile stresses emerging during the evaporation of the solvent. A subsequent amorphous-to-crystalline transformation proceeding under solvothermal conditions converts the 3D oriented networks into porous, free-standing 2D COF films. This protocol is general and suitable for a broad range of building units and network topologies, constituting a convenient synthetic tool for assembling high-quality, oriented, robust 2D COFs.