Covalent organic frameworks: Design principles, synthetic strategies, and diverse applications

Covalent organic frameworks (COFs) are the emerging type of organic crystalline porous materials, prepared through reticular chemistry with building blocks featuring light elements (such as C, H, O, N, or B atoms), and connected through the covalent bond and extended into two or three dimensions. In the past few years, COFs have attracted attention for their interesting properties, including high-order porosity, structural versatility, facile surface modification, and high thermal and chemical stabilities. Accordingly, COFs are potential platforms for diverse practical implementations, including gas separation and storage, heterogeneous catalysis, chemical sensing, luminescence, electronic devices, drug delivery, and energy storage and conversion. This Review provides the overview of the design strategies and synthetic methodologies that have been used widely for the preparation of COFs, and also summarizes selected examples of their applications.