Crystallization of Dimensional Isomers in Covalent Organic Frameworks

Dimensionalisomers, defined in reticular chemistry as frameworksconsisting of identical molecular building blocks but extended intwo or three dimensions (2D or 3D), are an important type of frameworkisomers that have never been isolated. Herein, we report the crystallizationof dimensional isomers in covalent organic frameworks (COFs) for thefirst time. By polymerization of the same molecular building blocksat different temperatures, both 2D and 3D COFs were successfully constructeddue to the temperature-induced conformational changes of precursorsfrom planar to tetrahedral. In addition, the non-fluorescent 2D COFcan be gradually converted into the fluorescent 3D COF by increasingthe temperature under solvothermal conditions. Therefore, it is reasonableto crystallize the dimensional isomers of reticular materials by controllingthe conformation of molecular building blocks, and more examples canbe expected. Since the obtained dimensional isomers show differentproperties and functions, this work will definitely motivate us todesign reticular materials for target applications in the future.