De Novo Synthesis of Covalent Organic Frameworks: A Principle for Topology Selection and Profound π Electronic Effects.

Covalent organic frameworks are a class of crystalline porous polymers with well-defined skeletons and ordered pores, making them attractive for structural design and synthesis. Progress in chemistry over the past two decades has greatly enabled our capability of designed synthesis of framework materials. However, a key fundamental issue that how reaction systems select a specific topology from isomers and what structural parameters determine the formation of the topology remains unclear. Here, we unveil a feasible design strategy for the selective formation of polygonal topology in the framework synthesis. We focused on tetragonal and Kagome topologies as they are the most challenging topology isomers to be selectively synthesized. We observed that electron-deficient monomers form Kagome frameworks and electron-rich units produce tetragonal skeletons. This finding provides the structural guidance for de novo synthesis of Kagome and tetragonal frameworks selectively. Remarkably, the framework topology exerts profound electronic effects on photoconductivity and photocatalytic activity, leading to the finding of exceptional hydrogen evolution systems.