Covalent organic frameworks (COFs) are crystalline porous polymers with 2D or 3D reticulated networks. Although most efforts in this field have been devoted to 2D-COFs, 3D-COFs are also receiving attention owing to their mechanical flexibility and topological diversity. In this regard, significant progress was made in 2018 by Ma et al. who successfully generated 3D imine-bonded single crystalline COFs with sizes of 50–100 μm in 30–80 days.<br/>However, for macroscale applications, generation of further large 3D-COF single crystals is desired. For this purpose, elucidation of factors influencing the growth of COF crystals is essential. Although several excellent studies on the nucleation and growth of 2D-COFs have already been reported, those of 3D-COFs have rarely been conducted until now.<br/>In this study, a strategy to use nucleation controllers to generate large 3D-COF single crystals is developed and proposed (Fig. 1). We chose a benchmark imine-based 3D-COF, COF-300 to test our strategy. Through systematic investigations in which the type of nucleation controllers was varied, a consistent correlation was found between the property of the nucleation controller and resulting crystal sizes. Consequently, we generated COF-300 single crystals of &gt;200 μm in size in 7 days.

Nucleation controller strategy to generate larger single crystals of 3D covalent organic frameworks

ACS Fall 2021

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