A controlling parameter of topological defects in two-dimensional covalent organic frameworks
You-Liang Zhu1, Huan-Yu Zhao, Cui-Liu Fu
1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China. zysun@ciac.ac.cn.
Nanoscale
|October 29, 2020
Summary
Synthesizing defect-free covalent organic frameworks (COFs) is challenging. Molecular dynamics simulations reveal that controlling monomer rotation angles (φ) significantly reduces defects, enabling high-quality crystal growth.
Area of Science:
- Materials Science
- Computational Chemistry
- Crystallography
Background:
- Synthesizing covalent organic frameworks (COFs) with long-range molecular ordering is difficult due to defect formation that disrupts crystallization.
- The fundamental causes and control mechanisms of topological defects in COFs are not well understood.
Purpose of the Study:
- To investigate the origins of topological defects during COF synthesis.
- To identify parameters that can control and minimize defect formation for high-quality crystal growth.
Main Methods:
- Molecular dynamics (MD) simulations were employed to study COF growth dynamics.
- Density functional theory (DFT) calculations were used to assess the computability of a proposed defect control parameter.
- Analysis of initial defect structures (pentagons and heptagons) for various monomer combinations ([C4 + C4], [C4 + C2], [C3 + C3], [C3 + C2]).
Main Results:
- Initial defects, such as pentagons and heptagons, were identified for specific monomer combinations and growth dynamics.
- Defect formation was significantly reduced when monomers were added to a single nucleus.
- A parameter φ, representing the range of biased rotational angle for monomer reactions, was proposed and found to have a monotonic relationship with defect population.
- Defect-free growth was achieved for all four combinations when φ < 20, independent of growth dynamics.
Conclusions:
- Controlling the rotational angle bias (φ) during monomer addition is crucial for minimizing defects in COF synthesis.
- The proposed parameter φ is computable via DFT and provides a reliable metric for screening and designing reactions for high-quality COF single crystals.
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