Nonclassical Crystallization of Covalent Organic Frameworks Guided by Exogenous Noncovalent Interactions

Area of Science:

• Materials Science
• Crystallization Science
• Supramolecular Chemistry

Background:

• Nonclassical crystallization offers an alternative to traditional monomer attachment, influencing material kinetics and products.
• Rapid self-assembly in nonclassical crystallization presents challenges in understanding and controlling underlying mechanisms.
• Covalent organic frameworks (COFs) are a class of materials where controlling crystallization is crucial for tailored properties.

Purpose of the Study:

• To investigate the regulation of nonclassical crystallization in COFs using exogenous noncovalent interactions.
• To elucidate the synergistic competition mechanism governing COF crystallization.
• To demonstrate a method for controlling COF superstructure formation while maintaining topology.

Main Methods:

• Introduction of alkyl amines as exogenous noncovalent interaction sources during COF synthesis.
• Utilizing time-dependent morphological characterization to observe COF growth dynamics.
• Modifying supramolecular interaction flexibility to control crystallization outcomes.
• Amine monomer expansion experiments to assess strategy adaptability.

Main Results:

• Exogenous noncovalent interactions guided self-assembly into intermediate 1D nanotubes, prolonging the kinetic stage.
• A synergistic competition mechanism involving exogenous and endogenous interactions was revealed and regulated.
• A "seed-germination-growth-maturity" growth process was mimicked and characterized.
• Diverse COF superstructures with consistent topology were synthesized by tuning noncovalent interactions.
• Preliminary exploration of NNCOFs for ReO4-/TcO4- anion adsorption was conducted.

Conclusions:

• Exogenous noncovalent interactions are effective in controlling nonclassical crystallization of COFs.
• The study provides insights into the crystallization mechanisms of COFs, enabling superstructure control.
• This approach offers new perspectives for materials science and separation chemistry, particularly in anion adsorption.