Dehydration‐Assisted Rapid Modulated Synthesis of Monodisperse Covalent Organic Framework Single Crystals With Tunable Sizes

The effective control over mesoscale features of covalent organic framework (COF) single crystals is important for definitive structural analysis, systematic structure-performance study, and elucidating crystallization mechanisms. However, the rapid synthesis of COF single crystals with uniform but flexibly tunable size remains a challenge on account of the complicated process of crystallization. Here, we report a dehydration-assisted modulated strategy enabling the rapid synthesis of single-crystalline imine-linked three-dimensional (3D) COFs (COF-300, COF-303, and COF-320). The strategy stems from a systematic study on the role of water in solvothermal and aniline-modulated syntheses of COF-300 using 1,4-dioxane as solvent. Kinetic analyses reveal that the hydrolysis reaction reduces the efficiency of the imine-exchange reaction in regulating the reversible imine bond formation, thereby retarding crystallization in modulated synthesis. Based on this finding, a dehydrated modulated strategy employing hydratable benzonitrile as solvent was developed and flexibly combined with simple adjustments to reaction temperature, solvent, and static/stirring conditions to achieve rapid synthesis of COF-300 single crystals with uniform size tunable from 213 nm to 44.3 µm within 1∼3 h. Crystal size-dependent iodine sorption measurements demonstrate that shortening microporous diffusion paths can accelerate adsorption/desorption kinetics and enhance sorption capacity.