Toward azo-linked covalent organic frameworks by developing linkage chemistry via linker exchange

Abstract

Exploring new linkage chemistry for covalent organic frameworks (COFs) provides a strong driving force to promote the development of this emerging class of crystalline porous organic materials. Herein we report a strategy to synthesize COFs with azo linkage, one of the most important functional unit in materials science but having not yet been exploited as a linkage of COFs. This strategy is developed on the basis of in situ linker exchange, by which imine-linked COFs are completely transformed into azo-linked COFs (Azo-COFs). Moreover, distinct properties of Azo-COFs from their corresponding imine-linked precursors are observed, indicating unique property of Azo-COFs. This strategy provides a useful approach to develop new linkage chemistry for COFs. It also has established a synthetic method for azo-linked COFs, which not only enriches the family of COFs but also offers a platform to explore properties and applications of this class of crystalline porous conjugated polymers.

Sulfonic-coordinated Co–N–C solid acid catalysts for high-performance solvent regeneration for efficient carbon capture

“…Fourier transform extended X-ray adsorption fine structure (FT-EXAFS) spectroscopy was performed to obtain more detailed information on the coordination structure of Co on the sulfo-COF support [43].…”

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

“…The three-component Strecker reaction, aza-Diels-Alder reaction, Debus-Radziszewski reaction, sulfur cyclization reaction, Groebke-Blackburn-Bienayme ´reaction, A 3 -coupling reaction, and Kabachnik-Fields reaction have been used for COF synthesis with a-aminonitrile, 40 quinoline, 40 benzimidazole, 41 benzothiazole, 42 imidazo[1,2a]pyridine, 43 propargylamine 44 and a-aminophosphonate 45 linkages, respectively. In addition, the construction of COFs linked by amine, 46,47 amide 48,49 benzothiazole, 50 and azo 51 moieties based on post-synthetic modification of imine-linked COFs greatly enriched the variety of COFs.…”

Aromatic Amine-Functionalized Covalent Organic Frameworks (COFs) for CO2/N2 Separation

“…Additionally, the exchange of building blocks (linker exchange) in already existing, crystalline frameworks opens the possibility to synthesize COFs with improved crystallinity or make COFs accessible that were not accessible via condensation of the respective building blocks. , Qian et al reported the first COF-to-COF linker exchange by replacing 1,4-phenylenediamine (PA) with benzidine (BD) in an imine-linked COF, which yielded an almost complete transformation . The linker-exchange strategy was applied to achieve, among others, different COF linkages, ,− changes in the pore hierarchy and size by different linker symmetries, − the transformation of linear polymers into COFs , or 3D into 2D COFs, and the introduction of functional groups into the framework …”