Nonclassical Crystallization of Covalent Organic Frameworks Guided by Exogenous Noncovalent Interactions

Nonclassical crystallization has been proposed as a process that breaks through the traditional monomer attachment mode and is widely used to change the crystallization kinetics and the products of various materials. However, the rapid kinetic self-assembly caused by the low crystallization barrier poses a great challenge in elucidating and regulating the control forces and mechanisms of this process. Here, we report for the first time the introduction of additional alkyl amines as a source of exogenous noncovalent interactions in the synthesis of covalent organic frameworks (COFs), thereby regulating the nonclassical crystallization of COFs. The introduction of exogenous noncovalent interactions guides the initial kinetic self-assembly to form intermediate one-dimensional (1D) nanotubes, which prolongs the kinetic assembly stage. We reveal and regulate the crystallization mechanism of nonclassical synergistic competition of COFs based on exogenous noncovalent interactions and endogenous covalent and π-π interactions. In addition, we demonstrate the "seed-germination-growth-maturity" mimicry growth process of COFs by using time-dependent morphological characterization techniques. We have realized the control of exogenous noncovalent interactions by changing the flexibility of supramolecular interactions and prepared a variety of COFs with different superstructures but with the same topology. We also verified through an amine monomer expansion experiment that this strategy has a certain adaptability. Finally, we preliminarily explored the adsorption potential of NNCOFs for anions such as ReO₄^-/TcO₄^-. This work emphasizes the understanding and control of crystallization mechanisms in crystalline materials, which will provide new perspectives in materials science and separation chemistry.