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Framework crystallization is an unresolved challenge in the chemistry of covalent organic frameworks (COFs) due to the poorly controlled simultaneous polymerization and crystallization processes. Here, we report the first morphogenesis of COF mesocrystals with two-dimensional hexagonal p6m symmetry through the combination of alkyl amine as a dynamic modulator and 2,4,6- triformylresorcinol imine as an asymmetrical building block. The amine modulator depresses the lateral growth of 2D sheets, and the slow kinetics combined with the asymmetrical conformation of 2,4,6-triformylresorcinol imine lead to the formation of transient imine macrocycles, which further undergo mesoscale self-assembly into nanotubular structures. The nanotubular structures tend to join together into rod-like bundles with ordered hexagonal rods, which finally grow into uniform hexagonal COF mesocrystals. The present strategy opens a nonclassical nucleation and crystal growth approach to create COFs with unexplored mesocrystal structures, which further extends the scope of crystalline framework materials and provides a new strategy for crystal morphogenesis.

The formation of mesostructured polymer and carbon single-crystals is very difficult due to increased complexity of the energy hypersurface and the role of slowed-down kinetics. Here we reported the synthesis of ordered mesostructured phloroglucinol-formaldehyde single crystals through mesoscale self-assembly of reactive monomicelles under acidic conditions which were traditionally thought very difficult to control the morphology because of the rapid polymerization rate. Polymeric and carbon single crystals from unusual curved hexagonal rods and spindles with two-dimensional hexagonal mesostructures, to previously unreported lozenge single-crystal sheets with lamellar mesostructures were obtained. Contrary to the literature reports, the lamellar mesostructured lozenge single-crystal sheets were successfully transformed to graphene-like layered carbons after calcination under 800 °C, and they can be further exfoliated into unprecedented high-quality single-layered carbon nanoribbons. These results unambiguously expanded our understanding about mesocrystals, and opened up new avenues for the efficient production of single-layered carbon nanoribbons which possess promising applications in electrochemical devices.