Spontaneous polymer alignment enabling the synthesis of oriented 2D covalent organic framework films

Abstract Despite the rapid progress in the field of 2D polymerisation, the fabrication of high-quality films of 2D covalent organic frameworks (2D COFs) remains a longstanding challenge. Herein, we describe a two-stage method for preparing mechanically robust, large-area, porous, highly oriented, imine-linked 2D COF films from kinetically trapped, amorphous covalent adaptable network (CAN) films. The protonated imine-linked CANs are generated by solution casting and 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 to porous, free-standing 2D COF films. This protocol is applicable to a broad range of building units and a variety of 2D COF topologies. Our results provide a convenient and general synthetic tool for the assembly of high-quality 2D COFs films suitable for the construction of molecularly precise, oriented, robust, porous materials with tailorable properties.