![]() ![]() Owing to special well-defined stable structures together with tailored functionalities, they have attracted numerous interests since 2005 and promised widespread applications ranging from gas separation to photoelectronics 10, 11, 15, 16, 17, 18, 19, 20. ![]() ![]() and the interaction strength between intra- and inter-layers of two-dimensional (2D) COFs differ by several orders of magnitude 3, 10, 11, 14. They have highly complex structures with different topologies, pore structures, linkages, functional groups, etc. As a type of crystalline porous polymers, covalent organic frameworks (COFs) are obtained by atomically precise integration of organic building blocks via strong covalent bonds in a highly ordered periodic manner 10, 11, 14, 15, 16. Therefore, although covalent bond ensures higher stability of crystalline materials in the application, it brings single-crystal polymerization a puzzling contradiction between growth time and product quality, causing dilemma in not only researches but also applications of these materials 2, 7, 10, 11. Considerable long-time is consumed for the polymerization along with reversible error-correction of the covalent lattices 4, 6, 7, 10, 11, 12, 13. To obtain high-quality single crystals, it is necessary to decelerate the polymerization and prolong the growth time 8, 9. Under a mild condition of polymerization in solvent, the challenge becomes more critical 2, 4, 5, 7. Single-crystal growth normally requires harsh conditions such as high temperatures or pressures 7. Compared with other crystals, crystalline materials constructed via covalent bonds face a greater challenge in efficient and precise production, since the formation and breakage of strong covalent bonds have lower reversibility than other linkages 2, 3, 4, 5, 6. It is generally considered that the growth of a single crystal is much more time-consuming than amorphous or polycrystalline materials 1. ![]() This work overcomes traditional concept on low efficiency of single-crystal polymerization, and holds great promise for future applications owing to its efficiency, industrial compatibility, environmental friendliness and universality for different crystalline structures and linkage bonds. Although it is the fastest single-crystal polymerization, the growth in sc-CO 2 leads to not only the largest crystal size of 2D COFs, but also higher quality with improved photoconductivity performance. Here, we find supercritical CO 2 (sc-CO 2) accelerates single-crystal polymerization by 10,000,000 folds, and produces two-dimensional (2D) COF single crystals with size up to 0.2 mm within 2~5 min. To produce μm-sized single crystals, the growth time is prolonged to >15 days, far away from the requirements in practical applications. Efficiently producing high-quality single crystals by polymerization in solvent remains as an unsolved issue in chemistry, especially for covalent organic frameworks (COFs) with highly complex structures.
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