Covalent Organic Frameworks: Design, Synthesis, and Functions

Abstract

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures. Unlike other polymers, a significant feature of COFs is that they are structurally predesignable, synthetically controllable, and functionally manageable. In principle, the topological design diagram offers geometric guidance for the structural tiling of extended porous polygons, and the polycondensation reactions provide synthetic ways to construct the predesigned primary and high-order structures. Progress over the past decade in the chemistry of these two aspects undoubtedly established the base of the COF field. By virtue of the availability of organic units and the diversity of topologies and linkages, COFs have emerged as a new field of organic materials that offer a powerful molecular platform for complex structural design and tailor-made functional development. Here we target a comprehensive review of the COF field, provide a historic overview of the chemistry of the COF field, survey the advances in the topology design and synthetic reactions, illustrate the structural features and diversities, scrutinize the development and potential of various functions through elucidating structure−function correlations based on interactions with photons, electrons, holes, spins, ions, and molecules, discuss the key fundamental and challenging issues that need to be addressed, and predict the future directions from chemistry, physics, and materials perspectives.

Electroactive Organic Building Blocks for the Chemical Design of Functional Porous Frameworks (MOFs and COFs) in Electronics

“…Metal-organic frameworks (MOFs) [11][12][13] and covalento rganic frameworks (COFs) [14][15][16] have emerged in the past two decades as promising crystalline porousm aterials for gas storagea nd separation, catalysis, energy storage, sensing, and many other applications, due to their remarkable chemical, structurala nd functional versatility,a sc ompared to other conventional materials, such as zeolites or activated carbon.W hereas MOFs are constructed from multitopic organicl igandsa nd metal nodes connected by coordinationb onds, COFs consist of purely organic and lightweightb uildingb locks linked by strong covalent bonds (Figure 1). In both cases, highly ordered and tuneable networks with large surfacea rea may be obtained, while stability, crystallinity and scalability are critical parameters concerning industrial applications.…”

Synthesis of Robust MOFs@COFs Porous Hybrid Materials via an Aza‐Diels–Alder Reaction: Towards High‐Performance Supercapacitor Materials

“…An in-depth analysis of MOF-Uio-66-NH 2 and COF-LZU1 substructures of MOF@COF-LZU1 indicates that the 13 Cs pectra of the latter should not differ significantly from individual ones of the neat MOF-Uio-66-NH 2 and COF-LZU1. In fact, the chemical shifts are essentially due to electronic surrounding at nucleus level and only minor changes on carbon site from MOF@COF-LZU1 relative to MOF-Uio-66-NH 2 and COF-LZU1 can be expected, it is natural to observe no changes between spectra from MOF@-COF-LZU1 versus the sum of MOF-Uio-66-NH 2 and COF-LZU1 (Supporting Information, Figure S8 and Table S1).…”

“…Solid-state NMR structural analysis of such materials are usually obtained on the basis of classical mono-dimensional 1 Ht o 13 Cc ross-polarization magic-angle-spinning experiments (CP/MAS) [22,31] and discussions rely exclusively on isotropic chemical shifts measurements that provides structural information at nucleus level. Unlike in solution, and despite improved sample crystallinity,the 13 Cresonances are rather broad in the solid-state and easily overlap.S uch features may render assignments of signals difficult, leading in turn to misinterpretation, in particular in the case of MOFs and COFs in which quaternary and CH chemical shifts are piled up in the same small crowded zone (ca. 110 to 160 ppm).…”

“…To circumvent this potential problem, we performed more advanced experiments including 13 Cs pectral edition, [32] 1 H ultra-fast MAS direct polarization ( 1 HD P/MAS) and 1 H/ 13 C frequency shifted Lee-Goldburg HETCOR ( 1 H/ 13 CF SLG HETCOR). [33] Thel atter allows to detect spatial proximities between 1 Ha nd 13 Ca nd may be tuned to select short internuclear distances like CH to distant quaternaries.Moreover, further to its enhanced resolution with respect to monodimensional spectra, it may separate spin-systems belonging to different molecules and proves useful when residual reagents also overlap peaks of interest (Supporting Information, Figures S4-S7). On the basis of this bundle of information complete assignments of the investigated species were possible ( Figure 2) on both proton and carbon sides providing astrong evidence for reactions completion (see the Supporting Information for detailed assignments).…”

“…[12] On the other hand, COFs exhibit much higher thermal and chemical stability owing to the all-covalent nature of the architecture in which the small molecular units are held together by strong covalent bonds,s uch as B À O, C = N, B À N, C=C, and BÀOÀSiC. [13] Thegreat variety and programmability of covalent bonds between the COF building units,which can be obtained by exploiting various synthetic organic reactions, enables chemical engineering of COF surface areas,p ore sizes,a nd crystal structure forming 2D or 3D crystalline functional architectures. [14] More recently,MOFs@COFs hybrid structures have been developed as an ew type of multifunctional porous materials by introducing the as-prepared MOF into the synthetic process of COF.S uch materials contain the structural traits and combine the advantages of individual components thereby yielding highest performances in gas separation, [15,19] (photo)catalysis, [16,21,22] aptasensors, [17] and lithium storage.…”