Unconventional Fast Room Temperature Synthesis of Covalent Organic Framework Single Crystals Unveiling Precise Structural Insights

Two-dimensional covalent organic frameworks (COFs) are a special kind of crystalline polymers produced by the polycondensation reaction of organic linkers. However, the polymerization is often uncontrolled and conventionally yields polycrystalline powders. For that reason, the development of new methods to obtain single-crystalline COFs is an urgent need. Herein, we report a modulated, room-temperature, and fast synthesis of a highly fluorinated COF where the reaction conditions were systematically analyzed to yield single-crystalline rods of around three microns. The increase in crystal size enabled the analysis of precise structural features such as the mechanical properties or the different aggregation states of the bidimensional framework. In addition, the reaction mechanism was computationally elucidated, and the roles of the modulator agent and the catalyst were analyzed, confirming the critical importance of trifluoroacetic acid and 2,3,5,6-tetrafluoroaniline in modulating Schiff base bond formation and, consequently, the crystallinity of the resulting COF. This study reveals new insights into the crystallization of high-quality 2D COFs.