Ultra-Fast Synthesis of Single-Crystalline Three-Dimensional Covalent Organic Frameworks and Their Applications in Polarized Optics

The applications of covalent crystalline materials face a chronic challenge of the efficient and precise construction of a highly or single-crystalline product by polymerization, especially for three-dimensional covalent organic frameworks (3D COFs) featuring highly complex crystalline porous structures. Here, we demonstrate the first example of minutes growth of 3D COF single crystals, in which supercritical CO2 as the solvent extremely accelerates the precise construction of 3D covalent networks. The crystal growth rate of 3D COFs reaches 35 μm min–1, and single crystals with sizes up to 110 μm are polymerized within 1–5 min, which have unique optical properties such as polarized photoluminescence, polarized second-harmonic generation, and so on. Considering this, as well as environmental friendliness and industrial compatibility, the supercritically solvothermal polymerization holds great promise in future applications.