Triangular Topological 2D Covalent Organic Frameworks Constructed via Symmetric or Asymmetric “Two‐in‐One” Type Monomers

Abstract

Most of the reported covalent organic frameworks (COFs) so far are prepared from highly symmetric building blocks, which to some extent limits the expansion of COF diversity and complexity. Low-symmetric building blocks can be designed through a desymmetrized vertex strategy, which might be used to construct new topological COFs. But reports of COFs constructed by asymmetric building blocks are thus far very rare. Here, a feasible strategy to design asymmetric building blocks for COF synthesis is introduced, by simply varying the positions of functional groups in the monomer. As a proof of concept, two isomeric hexaphenylbenzene-based "two-in-one" type monomers (1,2,4-HPB-NH 2 and 1,3,5-HPB-NH 2 ) are designed and synthesized. To the authors' surprise, self-polycondensation of the asymmetric 1,2,4-HPB-NH 2 (i.e., the isomer of common C 3 -symmetric 1,3,5-HPB-NH 2 ) also affords highly crystalline COF (1,2,4-HPB-COF) similar to the symmetric 1,3,5-HPB-NH 2 counterpart with identical topological structure. The triangular porous structures of both HPB-based COFs are well resolved by powder X-ray diffraction (PXRD), theoretical simulations, nitrogen sorption, and morphologies analysis. This work demonstrates the "two-in-one" type asymmetric building blocks can also produce highly crystalline frameworks and thus provides a new structural design strategy for reticular chemistry.

Fascinating isomeric covalent organic frameworks

“…38 The mentioned concept of "from isomeric monomers to isomeric frameworks" has been extended to the synthesis of isomeric COFs with triangular pores. 39 The above examples demonstrate that the "two-in-one" strategy might be a proven and effective method for the construction of 2D constitutional isomeric COFs. Apart from synthetic solvents, catalysts would be another crucial element for the formation of periodically ordered structures of COFs.…”

Covalent Organic Frameworks for Capacitive Energy Storage: Recent Progress and Technological Challenges

“…[16a,b] The varied combinations of different monomers result in various COF structures that now can be found via several online databases. [18] 2D COFs with a planar geometry can be symmetric or asymmetric [19] , exhibiting trigonal, rhombic, tetragonal, hexagonal, or varied pore combinations (e.g., dual-pore Kagome and triple-pore Kagome), as displayed in Figure 1a. These topologies can be controlled using different combinations of monomers.…”

Triangular Heteroporous Covalent Organic Framework via a K‐Shaped “Two‐in‐One” Monomer: Targeted Synthesis and Selective Removal of Organic Pollutants

“…Among them, only a few triangular COFs have been reported that could be ascribed to the limited configuration of building units, although their unique triangular channel makes them special on precise recognition and selective transport. [14] Currently, the triangular COFs [11,12] could only be accessed through the co-polymerization of C 6 -and C 2 -symmetric building blocks or the self-polymerization of C 3 -symmetric monomers (Figure 1a). In addition, Feng et al [13] exploited the desymmetrized vertex design approach through lengthening or shortening the branches of symmetry building blocks (e.g., C 2 , C 6 ) to form the heteroporous triangular COFs, which present the rare example of the super microporous dual-triangle COFs.…”