Formation of Two-Dimensional Covalent Organic Frameworks and the Impact of Defects

Two-dimensional (2D) covalent organic frameworks (COFs) are a class of crystalline and porous polymers being explored in electronic and energy storage devices. So far, these materials are prone to defects, which have restricted their usage. Utilizing kinetic Monte Carlo and molecular dynamics simulations, we modeled the formation of 2D COFs at the atomic and molecular levels. Our results revealed the factors impacting the nucleation and growth of these 2D crystals. In particular, we established a quantitative model describing their non-classical crystallization processes, providing insights into growing high-quality 2D COF crystals. Our atomistic simulations showed that monomer addition and island coalescence contribute to forming 2D COF crystals. We also studied the mechanisms underlying the formation of vacancy and dislocation defects during polymerization. Additionally, using the density functional-based tight binding method and molecular dynamics simulations, we investigated the impact of defects on the electronic band structures and mechanical properties of 2D COFs. These results inform the design and fabrication of 2D COFs for various applications.