Growing single crystals of two-dimensional covalent organic frameworks enabled by intermediate tracing study

Chengjun Kang,Adam K Usadi,Zhaoqiang Zhang,Lisa Saunders Baugh,Kuiwei Yang,Yuxiang Wang,Jianwen Jiang,Dan Zhao,Zhehao Huang,David C Calabro,Xiaodong Zou

doi:10.1038/s41467-022-29086-x

Chengjun Kang, Adam K Usadi + Show 9 more

Open Access

https://doi.org/10.1038/s41467-022-29086-x

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Abstract

Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals. A better understanding of the growth mechanism facilitates development of methods to grow high-quality 2D COF single crystals. Here, we take a different perspective to explore the 2D COF growth process by tracing growth intermediates. We discover two different growth mechanisms, nucleation and self-healing, in which self-assembly and pre-arrangement of monomers and oligomers are important factors for obtaining highly crystalline 2D COFs. These findings enable us to grow micron-sized 2D single crystalline COF Py-1P. The crystal structure of Py-1P is successfully characterized by three-dimensional electron diffraction (3DED), which confirms that Py-1P does, in part, adopt the widely predicted AA stacking structure. In addition, we find the majority of Py-1P crystals (>90%) have a previously unknown structure, containing 6 stacking layers within one unit cell.

Highlights

Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals
We present the growth of micron-sized 2D COF single crystals, whose structure is successfully determined by 3D electron diffraction (3DED)
The mixture was allowed to react for the different time at 65 °C, the solid COF products were quickly removed from the mixture by filtration, and the clear growth solution was subjected to mass spectroscopy (MS) measurement

Summary

Introduction

Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals. A better understanding of the growth mechanism facilitates development of methods to grow high-quality 2D COF single crystals. Covalent bonds connect the repeating units within every single COF layer; in contrast, adjacent COF layers are held together via relatively weak molecular attractions[14,15] This structural anisotropy means that the growth of 2D COF crystals requires the coordination of very different forces, including strong chemical bonds and weak molecular interactions. Self-assembly and template growth are identified as critical factors for obtaining highly crystalline COFs during the nucleation and self-healing growth stages. These criteria help us select monomers that show promise for the preparation of high-quality single crystals under well-designed conditions. We present the growth of micron-sized 2D COF single crystals, whose structure is successfully determined by 3D electron diffraction (3DED)

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