Mechanisms of Defect Correction by Reversible Chemistries in Covalent Organic Frameworks

Reversible chemistries have been extensively explored to construct highly crystalline covalent organic frameworks (COFs) via defect correction. However, the mechanisms of defect correction that can explain the formation of products as single crystals, polycrystal/crystallites, or amorphous solids remain unknown. Herein, we employed molecular dynamics simulations combined with a polymerization model to investigate the growth kinetics of two-dimensional COFs. By virtue of the Arrhenius two-state model describing reversible reactions, we figured out the conditions in terms of active energy and binding energy for different products. Specifically, the ultraslow growth of COFs under high reversibility of reactions corresponding to low binding energies resulted in a single crystal by inhibiting the emergence of nuclei as well as correcting defects through continually dropping small defective fragments off at crystal boundaries. High bonding energies responsible for the high nucleation rate and rapid growth that incorporated defects in crystals and caused the division of crystals through defect correcting processes led to small crystallites or polycrystals. The insights into the mechanisms help us to understand and further control the growth kinetics by exploiting reversible conditions to synthesize COFs of higher quality.