Organic flux synthesis of covalent organic frameworks

It remains challenging to synthesize highly crystalline covalent organic frameworks (COFs) with poor reversible bond linkages because of the irreversible bond formation chemistry, which typically affords COFs with underrated crystallinity and porosity. Here, we report a general, green, and scalable protocol to fabricate imide-linked COFs based on organic flux-mediated syntheses. In contrast to traditional solvothermal approaches, this synthetic methodology is controllable, environment-friendly without any toxic organic solvents, and can be easily scalable to a 10-g scale. After an in-depth investigation, we prove the existence of a two-step reaction mechanism, which adjusts the formation and crystallization rate of COFs. Thus, this flux synthesis route can produce COFs with enhanced crystallinity and porosity, leading to outstanding gas sorption/separation performance. Moreover, anhydride, carboxylic, and amide monomers can all be employed to produce imide-linked COFs. This work enriches the synthesis toolboxes for COFs and presents a potential pathway to industrial-scale synthesis of COFs.