Chemistry of Covalent Organic Frameworks

Abstract

Linking organic molecules by covalent bonds into extended solids typically generates amorphous, disordered materials. The ability to develop strategies for obtaining crystals of such solids is of interest because it opens the way for precise control of the geometry and functionality of the extended structure, and the stereochemical orientation of its constituents. Covalent organic frameworks (COFs) are a new class of porous covalent organic structures whose backbone is composed entirely of light elements (B, C, N, O, Si) that represent a successful demonstration of how crystalline materials of covalent solids can be achieved. COFs are made by combination of organic building units covalently linked into extended structures to make crystalline materials. The attainment of crystals is done by several techniques in which a balance is struck between the thermodynamic reversibility of the linking reactions and their kinetics. This success has led to the expansion of COF materials to include organic units linked by these strong covalent bonds: B-O, C-N, B-N, and B-O-Si. Since the organic constituents of COFs, when linked, do not undergo significant change in their overall geometry, it has been possible to predict the structures of the resulting COFs, and this advantage has facilitated their characterization using powder X-ray diffraction (PXRD) techniques. It has also allowed for the synthesis of COF structures by design and for their formation with the desired composition, pore size, and aperture. In practice, the modeled PXRD pattern for a given expected COF is compared with the experimental one, and depending on the quality of the match, this is used as a starting point for solving and then refining the crystal structure of the target COF. These characteristics make COFs an attractive class of new porous materials. Accordingly, they have been used as gas storage materials for energy applications, solid supports for catalysis, and optoelectronic devices. A large and growing library of linkers amenable to the synthesis of COFs is now available, and new COFs and topologies made by reticular synthesis are being reported. Much research is also directed toward the development of new methods of linking organic building units to generate other crystalline COFs. These efforts promise not only new COF chemistry and materials, but also the chance to extend the precision of molecular covalent chemistry to extended solids.

Triazine containing N-rich microporous organic polymers for CO 2 capture and unprecedented CO 2 /N 2 selectivity

“…The CO2 philicity of the polymeric network has tremendously increased from previously reported modified polycarbazole and polytriphenylamine. CO2 uptakes of these two materials are also very comparable with previously best reported COFs [38,39], MOFs [40,41], N-doped microporous carbons [42,43], hypercrosslinked porous polymers [44][45][46] , etc. The high density of basic nitrogen sites of triazine present in the polymer network which interact with ewis acidic CO2 molecules via dipole quadrapole interaction, are responsible for huge CO2 uptake [47].…”

Optical sensing of aqueous boron based on polymeric hydroxytriphenylene derivatives

“…The family of compounds based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) have been widely used in the synthesis of discotic liquid crystals (DLC's) [11][12][13] and more recently in covalent organic frameworks (COF's), 14,15 due to their unique properties such as one-dimensional charge migration, electroluminescence, and self-assembling behaviour. The chelating properties of HHTP have been also used in optical uorescent sensing systems for boron 10 and picric acid.…”

Structure–property–activity relationships in a pyridine containing azine-linked covalent organic framework for photocatalytic hydrogen evolution

“…Synthesis 1,3,5-Phenyltriboronic acid tris(pinacol) ester (2). Bis(pinacolato)diboron (4 eq., 10 g, 39 mmol), 1,3,5-tribromobenzene (1 eq., 3.131 g, 9.75 mmol) and potassium acetate (9 eq., 8.6 g, 87.7 mmol) were added to 90 ml of 1,4-dioxane in a 250 ml ask and degassed by bubbling argon for 30 min.…”

“…2 The building blocks, aer synthesis, are reacted with each other in a reversible covalent bond forming reaction under solvothermal conditions to form a crystalline material. The rst step of the synthesis rarely uses reactions in equilibrium, leading to a plethora of organic compounds that can be tailored at will and used as building blocks.…”