Abstract
Construction of organic semiconducting materials with in-plane π-conjugated structures and robustness through carbon-carbon bond linkages, alternatively as organic graphene analogs, is extremely desired for powerfully optoelectrical conversion. However, the poor reversibility for sp2 carbon bond forming reactions makes them unavailable for building high crystalline well-defined organic structures through a self-healing process, such as covalent organic frameworks (COFs). Here we report a scalable solution-processing approach to synthesize a family of two-dimensional (2D) COFs with trans-disubstituted C = C linkages via condensation reaction at arylmethyl carbon atoms on the basis of 3,5-dicyano-2,4,6-trimethylpyridine and linear/trigonal aldehyde (i.e., 4,4″-diformyl-p-terphenyl, 4,4′-diformyl-1,1′-biphenyl, or 1,3,5-tris(4-formylphenyl)benzene) monomers. Such sp2 carbon-jointed-pyridinyl frameworks, featuring crystalline honeycomb-like structures with high surface areas, enable driving two half-reactions of water splitting separately under visible light irradiation, comparable to graphitic carbon nitride (g-C3N4) derivatives.
Highlights
Construction of organic semiconducting materials with in-plane π-conjugated structures and robustness through carbon-carbon bond linkages, alternatively as organic graphene analogs, is extremely desired for powerfully optoelectrical conversion
The target covalent organic frameworks (COFs) were solvothermally synthesized through Knoevenagel condensation reaction between 3,5-dicyano-2,4,6-trimethylpyridine (DCTMP) and linear/trigonal aldehyde (4,4′′-diformyl-p-terphenyl, 4,4′diformyl-1,1′-biphenyl or 1,3,5-tris(4-formylphenyl)benzene) in DMF, catalyzed by the organic base piperidine
First, the pyridinyl methyl carbon atoms in DCTMP are converted to carbanions through C–H cleavage upon treatment with the base. This conversion is typically attributed to a decline in the electronic cloud density around these arylmethyl carbon atoms, which is caused by the strong electron-deficient pyridine ring that bears two electron-withdrawing cyano groups
Summary
Construction of organic semiconducting materials with in-plane π-conjugated structures and robustness through carbon-carbon bond linkages, alternatively as organic graphene analogs, is extremely desired for powerfully optoelectrical conversion. We report a scalable solution-processing approach to synthesize a family of two-dimensional (2D) COFs with trans-disubstituted C = C linkages via condensation reaction at arylmethyl carbon atoms on the basis of 3,5-dicyano-2,4,6trimethylpyridine and linear/trigonal aldehyde (i.e., 4,4′′-diformyl-p-terphenyl, 4,4′-diformyl1,1′-biphenyl, or 1,3,5-tris(4-formylphenyl)benzene) monomers Such sp[2] carbon-jointedpyridinyl frameworks, featuring crystalline honeycomb-like structures with high surface areas, enable driving two half-reactions of water splitting separately under visible light irradiation, comparable to graphitic carbon nitride (g-C3N4) derivatives. In studies on these materials, rationally designed monomers for preassembly and precise regioselective coupling polymerization act as key roles in the formation of architectures with excellent topologies In another case, we reported a 2D cyanostilbene-based covalent organic framework (COF) involving the connection of aromatic units through a carbon-carbon double bond (C = C) linkage under the Knoevenagel reaction (Fig. 1a)[8]. The appropriate energy levels of conduction and valence bands of g-C40N3-COF allow for driving two half-reactions of water splitting separately to generate hydrogen or oxygen under visible light irradiation
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