Structural tailoring of covalent organic frameworks with steric effects

Covalent organic frameworks(COFs) provide a unique platform with tunable structures allowing precise control of pore sizes,shapes and functions. The key to synthesizing COFs with desired structures is to precisely control the conformation and geometry of building blocks as well as the growth direction of COFs. To achieve this, steric effects are noteworthy that may have a significant impact on the assembly of COFs. Specifically, the introduction of sterically demanding substituents or bulky groups into monomers of COFs will lead to intramolecular conformational changes and intermolecular repulsions, which induce structural changes in COFs, including changes in torsion angles, interlayer distances, stacking modes and topologies of 2D COFs, and changes in spatial nodes, interpenetration and topologies of 3D COFs. This review will help to understand the impacts of steric effects on the structures of COFs and to take them into extensive consideration in the design and synthesis of COFs with novel functionalities and structural attributes.