Supersaturation-Controlled Single-Crystal Growth of Covalent Organic Frameworks with Binary Solvents

The ability to rapidly produce large single crystals is crucial for advancing the applications of covalent organic frameworks (COFs). Although the modulation strategy provides a straightforward method for growing high-quality single crystals, the slow crystallization process of COFs often limits their practical use. In this study, we combined the principles of crystallization thermodynamics and kinetics with the modulation strategy to develop a binary solvent-supersaturation method, enabling the growth of single-crystal COFs in a significantly shorter time. By systematically investigating the crystal-growth kinetics across different solvent ratios, we established a diffusion-reaction growth model, highlighting the essential role of supersaturation in controlling COF crystal growth. Especially, under this crystallization guidance, elegant single crystals of COFs built with heteroatom or other functionality can also facilely obtained, which spontaneously validate the universality of the protocol. Importantly, the resulting single-crystal COFs, characterized by high structural symmetry, exhibited notable second harmonic generation (SHG) activity, which could open new avenues for future research in this field.