Three-Dimensional Covalent Organic Frameworks: From Topology Design to Applications

Abstract

Conspectus Covalent organic frameworks (COFs) represent a novel type of crystalline porous polymers with potential applications in many areas. Considering their covalent connectivity in different dimensions, COFs are classified as two-dimensional (2D) layered structures or three-dimensional (3D) networks. In particular, 3D COFs have gained increasing attention recently because of their remarkably large surface areas (>5000 m2/g), hierarchical nanopores and numerous open sites. However, it has been proven to be a major challenge to construct 3D COFs, as the main driving force for their synthesis comes from the formation of covalent bonds. In addition, there are several stones on the roads blocking the development of 3D COFs. First, the successful topology design strategies of 3D COFs have been limited to [4 + 2] or [4 + 3] condensation reactions of the tetrahedral molecules with linear or triangular building blocks in the first decade, which led to only three available topologies (ctn, bor, and dia) and strongly restricted the incorporation of some important functional units. Next, as it is very challenging to obtain large-size single crystals of 3D COFs and the same building blocks may yield many possible structures that are quite difficult to identify from simulations, their structure determination has been considered a major issue. Last, the building blocks utilized to synthesize 3D COFs are very limited, which further affects their functionalization and applications. Therefore, since it was first announced in 2007, research studies regarding 3D COFs have been underexplored for many years, and very few examples have been reported. To confront these obstacles in 3D COFs, we started contributing to this field in 2016. Considering that many interesting quadrilateral molecules (e.g., pyrene and porphyrin) cannot be easily derivatized into linear or triangular motifs, we developed a novel topology design strategy to construct 3D COFs via [4 + 4] condensation reactions of tetrahedral and quadrilateral building blocks. After many trials, we found that this is a general synthetic strategy to build 3D COFs with the new pts topology. In addition, we explored the structure determination of polycrystalline 3D COFs prepared by our developed strategy via a 3D electron diffraction technique. Moreover, we expanded the toolbox of molecular building blocks for creating 3D COFs and successfully demonstrated the functionalization of 3D COFs with characteristic properties and applications. In this Account, we summarize our above ongoing research contributions, including (i) a novel topology design strategy for the synthesis of 3D COFs; (ii) attempts to determine the crystal structure of polycrystalline 3D COFs with atomic resolution; and (iii) the diversification of building blocks and applications of functionalized 3D COFs. Overall, our studies not only offer a new paradigm of expansion in the topology design strategy and building block families of 3D COFs, but also provide an idea of future opportunities for relevant researchers ...

A 2D porphyrin-based covalent organic framework with TEMPO for cooperative photocatalysis in selective aerobic oxidation of sulfides

“…Covalent organic frameworks (COFs) represent an emerging class of crystalline materials with extended periodic structures and inherent porosity. [1][2][3][4][5] Since the seminal work reported by Yaghi and co-workers in 2005, 6 COFs have aroused extensive interest and found promising applications in gas adsorption and separation, 7,8 sensing, [9][10][11] catalysis, [12][13][14][15] optoelectronics, 16,17 energy storage 18,19 and so on. [20][21][22][23][24][25][26] Two-dimensional (2D) COFs, in which the molecular building blocks are covalently connected to form a layered structure with aligned p-columns, can particularly possess pre-organized pathways for facilitating the charge carrier transport.…”

Three‐Dimensional Covalent‐Organic Frameworks Loaded with Highly Dispersed Ultrafine Palladium Nanoparticles as Efficient Heterogeneous Catalyst

“…Three‐dimensional (3D) COFs is another important category of COFs family [28–33] . The monomers are three‐dimensionally polymerized to form 3D crystalline materials.…”

Orderly Porous Covalent Organic Frameworks-based Materials: Superior Adsorbents for Pollutants Removal from Aqueous Solutions

“…Besides the successful topology design strategies (ctn, bor, and dia) of 3D COFs, the new pts, ffc, and more topologies are also applied to build 3D COFs. 33 , 34 , 35 , 38 In 2D COFs, the extended 2D layers are composed of the periodic organic units via covalent bonds, which stack further to form a layered eclipsed structure via π-π interactions. 36 Generally, monomers with tetrahedral structure (e.g., building blocks containing sp 3 carbon or silane atom) can be used as building units to design the topology structure of 3D COFs.…”

“… 2 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 (B) Sample of topologies accessible through COF synthesis. 33 , 34 , 35 , 36 , 37 …”