Controllable Synthesis and Performance Modulation of 2D Covalent–Organic Frameworks

Abstract

Covalent–organic frameworks (COFs) are especially interesting and unique as their highly ordered topological structures entirely built from plentiful π‐conjugated units through covalent bonds. Arranging tailorable organic building blocks into periodically reticular skeleton bestows predictable lattices and various properties upon COFs in respect of topology diagrams, pore size, properties of channel wall interfaces, etc. Indeed, these peculiar features in terms of crystallinity, conjugation degree, and topology diagrams fundamentally decide the applications of COFs including heterogeneous catalysis, energy conversion, proton conduction, light emission, and optoelectronic devices. Additionally, this research field has attracted widespread attention and is of importance with a major breakthrough in recent year. However, this research field is running with the lack of summaries about tailorable construction of 2D COFs for targeted functionalities. This review first covers some crucial polymeric strategies of preparing COFs, containing boron ester condensation, amine‐aldehyde condensation, Knoevenagel condensation, trimerization reaction, Suzuki CC coupling reaction, and hybrid polycondensation. Subsequently, a summary is made of some representative building blocks, and then underlines how the electronic and molecular structures of building blocks can strongly influence the functional performance of COFs. Finally, conclusion and perspectives on 2D COFs for further study are proposed.

Topology-Mediated Enhanced Polaron Coherence in Covalent Organic Frameworks

“…In the presence of dopants, a single-layer trigonal COF displays an ≈2.4-fold increase in coherence numbers relative to the hexagonal topology. We believe that these results are particularly important in the context of recent experimental efforts aimed at synthesizing COFs with a high degree of crystallinity − or larger domains. , While such efforts are certainly important for achieving higher hole mobility, our analyses demonstrate that, independent of the degree of crystallinity and/or domain sizes, if the counteranions residing inside the COF pores trap the free charge carriers, the conductivity of COFs will always be lower ,,− than that measured for doped conjugated polymers. ,, Our results thus suggest that it would be important to explore the potential use of other dopants and doping techniques to achieve higher conductivities in COF films. ,, …”

Interfacial Assembly and Applications of Functional Mesoporous Materials

“…In addition, the liquid–gas interface has also been widely used for the synthesis of 2D and porous conjugated polymers . For example, in 2016, Feng and co-workers prepared highly ordered wafer-scale 2D polymer film for the applications of organic transistors as a semiconducting layer.…”

“…In addition, the liquid−gas interface has also been widely used for the synthesis of 2D and porous conjugated polymers. 252 For example, in 2016, Feng and co-workers prepared highly ordered wafer-scale 2D polymer film for the applications of organic transistors as a semiconducting layer. The preparation of atomic level monolayer involved first diffusing the porphyrin chloroform solution at an air−water interface of Langmuir−Blodgett (LB) trough to yield a submonolayer.…”

Two-dimensional metal-organic frameworks: from synthesis to bioapplications

“…Since the discovery of graphene in 2004 [ 22 , 23 ], nanomaterials with high ratios of lateral size to thickness have been widely explored in biomedical applications. Up to date, 2D nanomaterials including transition metal dichalcogenides [ 24 , 25 ], metal carbonitrides [ 26 , 27 ], black phosphorus nanosheets [ 28 , 29 ], layered double hydroxides [ 30 , 31 ], MOFs, and covalent-organic frameworks[ 32 ] have aroused tremendous research attention in both synthetic methodology and/or practical applications. In particular, 2D MOFs displayed tailored structure, adjustable composition, efficient cargo loading, and good biodegradation, making these layered materials useful for biomedical applications [ 33 ].…”