Highly Crystalline Helical Covalent Organic Frameworks

Controllable synthesis of highly crystalline covalent organic frameworks (COFs) with unique structures is important for fundamental research and their practical applications. Herein, we report highly crystalline helical COFs, termed helical-COFTP-Py, synthesized through the Schiff base condensation of 1,3,6,8-tetra(4-aminophenyl)-pyrene and terephthalaldehyde via supercritically solvothermal polymerization in supercritical carbon dioxide (sc-CO2) as the reaction medium. The reaction conditions that affect the formation of the helical product are investigated. We find that the interlayer rotation is triggered by the adsorption of CO2, revealing the important role of sc-CO2 in the formation of helical crystals. In addition, when 2,5-dihydroxyterephthalaldehyde (DHTP) is used as the monomer, the resultant COFDHTP-Py crystals feature a rod-like morphology without a helical structure, indicating the role of interlayer hydrogen bonds in locking the adjacent layers and hindering the interlayer rotation. The helical COF crystals prepared in this work feature high crystallinity, large size, and helical one-dimensional channels, holding promising applications in chiral resolution and ion separation.