Topology control of three-dimensional covalent organic frameworks by adjusting steric hindrance effect

Since the intrinsic topological network determines their pore characteristics and functional applications, it is important to construct 3D COFs with target topology from predesigned functional building blocks. However, when starting from precursors with same connectivity but different bulky groups, the structure and topology of 3D COFs may change, which will greatly increase the complexity of the crystal structure determination. Therefore, it is essential to understand how to control the steric hindrance effects and synthesize 3D COFs with target topology. Herein, we report the topology control of 3D COFs by adjusting steric hindrance effects of functional building blocks. Starting from a quadrilateral building block with sterically hindered phenyl groups, we have been able to achieve the target pts topology instead of the unprecedented ljh network that we reported recently by elongating the tetrahedral building block. This result clearly shows that it is promising to precisely control the topology of 3D COFs by judiciously selecting building blocks with steric hindrance and suitable dimensions.