Mechanochemical crystallization of covalent organic frameworks: from the linkage up

Covalent organic frameworks (COFs) are conventionally synthesized under solvothermal conditions, requiring toxic or high-boiling solvents, long reaction times, and sealed, pressurized environments. Mechanochemistry offers a solvent-free, energy-efficient alternative to a broad spectrum of organic synthesis. Its extension to COFs has accelerated over the last five years, demonstrating potential for synthetic simplification, bulk production, and diverse macromorphology; however, reaction types remain limited by our understanding of linkage formation and crystallization within this new reaction space. Imine and imine-derived COFs are particularly well studied due to their relatively simple crystallization and potential for enhanced stability and diverse functionality. However, successful translation from solution-phase to solid-state systems involves (1) demonstrating bond formation and (2) optimizing crystallization, a two-step process that is sparsely understood when it comes to imine derivation and often relies on conditions set by synthesis of the solution-phase COF equivalent, leaving researchers with incompatible chemical environments and little guidance on mechanical specifications. The presented review aims to explore mechanochemical formation of imine and imine-derived COFs through reaction parameters for both model compounds and supramolecular structures. The current landscape of imine-derived linkages will be summarized, separating transformations into three crystallization strategies to easily assess linkage potential for de novo reactions and post-synthetic modifications (PSMs). Additionally, by highlighting direct comparisons between reaction conditions in and out of solution, this review will underline key connections across synthetic methods and may serve as a guide in the selection of appropriate chemical and mechanical factors for initial precursor and COF screenings. Ultimately, the literature highlighted in this review will lower the barrier of entry, facilitating efficient design of mechanochemical syntheses for imine-derived COFs from the linkage up.