Syntheses of two- and three-dimensional covalent organic frameworks in deep eutectic solvents

Covalent organic frameworks (COFs) constitute an emerging class of porous organic crystalline polymers with predesignable topologies and tunable functionality, and have attracted significant interest, with a wide range of potential applications. Nevertheless, the syntheses of COFs are mainly restricted to solvothermal routes that require harmful organic solvents, involve long process times, and require effort to optimize the reaction conditions with each new COF. In this work, we developed for the first time a general and simple strategy for synthesizing a series of 2D COFs (including keto-enamine, azine and hydrazone linked COFs) and imine-linked 3D COFs by using deep eutectic solvents (DESs) as green media under ambient conditions. The COFs are highly crystalline and show good surface areas, and were obtained within 2 h at room temperature in an open reaction system. More importantly, we also extended this protocol to the synthesis of a new azo-based 3D COF with a hierarchical pore structure-notable since we were not able to prepare this COF using a conventional solvothermal route.