Symmetric Variation of Monomers for Constructing 1D/2D Imine-Based Covalent Organic Frameworks

Synthetic control of topology connectivity is the crowning achievement for covalent organic framework(COF)fabrications.Although a large number of one-,two-,and three-dimensional(1D,2D,and 3D)COFs have been reported,their topology structure constructions are restricted to the use of symmetric monomers with the purpose of increasing the crystallinity and/or porosity.Herein,three imine-linked COFs with different topology nets(namely,sql-b and sql-c)were constructed by symmetric variation of monomers via the condensation of a tetra-amine monomer with a D2h-symmetry and lower C_(2v)-symmetric dialdehyde monomers,bearing a phenolic hydroxyl group at different positions.The results indicated that a reasonable introduction of the phenolic hydroxyl group could effectively tune the topological structure of COFs at the molecular level during the crystallization stage.Particularly,the remarkable difference in the dye uptake ability between these COF materials indicated that the fabricated specific pore geometries,as well as different steric hindrance and H-bonding interactions,played a pivotal role in accessing molecules in the solution.Therefore,this work might boost the explorations of COF materials with expected topologies and pore geometries from conventional monomers through bottom-up synthesis methodology by molecular designing and engineering.

Covalent organic frameworks catalyzed by organic Lewis acid

We report the synthesis of covalent organic framework(COF)crystals with organic Lewis acid instead of the conventional use of Br?nsted acid or inorganic Lewis acid.Specifically,tris(pentafluorophenyl)borane was applied for the growth of seven imine COFs:TAPB-PDA-,TAPB-2,5-DMTA-,TAPB-2,3-DMTA-,TAPT-PDA-,TAPT-2,5-DMTA-,TAPT-2,3-DMTA-COF with hcb topology and varied in functional groups,as well as a new one,COF-820,with sql topology.All these COFs were obtained at room temperature.Their high crystallinity and porosity demonstrate the versatility of the organic Lewis acid as a catalyst.Bulky organic Lewis acid was found critical for the production of COF-820,while its absence resulted in the formation of a different COF,4PE-1P-COF,with kgm topology using the same building blocks.Such steric effect,typical for organic catalysts,provides a new way to regulate the topology of COFs and their future design.