2D Conjugated Covalent Organic Frameworks: Defined Synthesis and Tailor-Made Functions

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers and have received tremendous attention and research interest. COFs can be classified into two-dimensional (2D) and three-dimensional (3D) analogues. Resembling the architectures of porous graphene, 2D conjugated COFs have exhibited promising prospects in many fields, such as gas storage and separation, heterogeneous catalysis, sensing, photocatalysis, environmental remediation, drug delivery, energy storage and conversion, and so forth. However, efficient structural design for high-throughput production of crystalline 2D COFs remains challenging.In this Account, we summarize our recent contributions to the design, synthesis, and application exploration of 2D conjugated COFs. First, we raised an efficient "two-inone" strategy for the facile synthesis of 2D imine COFs with good reproducibility and solvent adaptability. Thanks to this elaborate molecular design strategy, we could easily modulate the topology of COFs and fabricate COF films. In addition, we developed two approaches to stabilize the 2D conjugated COFs by using planar building blocks and donor−acceptor structures. We also proposed a skeleton engineering strategy to design COFs as electrode materials, through which redox-active orthoquinone moieties were stepwise-incorporated in the skeletons of isostructural 2D imine-linked COFs. This strategy enabled systematic investigations on a series of 2D conjugated COFs with analogous structures but different numbers of active sites for energy storage, which provides a good platform to unveil the underlying structure−property relationships. In addition, we recently developed a new kind of arylamine-linked 2D conjugated COFs. The electroactive diphenylamine linkages endowed these 2D conjugated COFs with extended conjugation and improved stability, which also conferred these COFs with excellent pseudocapacitive energy storage performance. Moreover, tailor-made sulfur-rich COFs were introduced that were synthesized by selective introduction of polysulfide or sulfonyl groups on the COF skeletons and were used for Li storage and proton conduction. At the end, the key challenges of 2D conjugated COFs toward practical applications and their future prospects are suggested. We hope that this Account will evoke new inspirations and innovative work in the field of 2D conjugated COFs in the near future, especially in some burgeoning and interdisciplinary research areas.

Metal-related electrocatalysts for Li–CO2batteries: an overview of the fundamentals to explore future-oriented strategies

“…As a new class of heterogeneous catalysts, COFs have the advantages of highly ordered pore structures, tunable pore size, large specific surface area, diverse synthesis methods, and easy functional modification. 130–134 The reasons why COFs can be used as cathode catalysts for Li–CO 2 batteries are as follows: (1) the channels of COFs can be flexibly designed to provide favourable support for the transport of Li + and CO 2 ; (2) the structure of COFs can be functionalized by using different functional groups or metals; (3) COFs can form a synergistic effect with other materials to further improve the electrochemical performance and stability of the battery. 135 Recently, Jiang et al 136 successfully exfoliated quinone-based COFs into large-scale and ultrathin MnO 2 /2,6-diaminoanthraquinone-2,4,6-triformylphloroglucinol (DQTP) COF-nanosheet (NS) hybrid materials as cathode catalysts for Li–CO 2 batteries (Fig.…”

Comprehensive Review for an Efficient Charge Transfer in Single Atomic Site Catalyst/Organic Polymers toward Photocatalytic CO2 Reduction

“…COFs are a class of crystalline porous organic polymers formed by the reversible covalent bonds between the cores and linkers and are extended 2D or 3D structures. [246][247][248] These reversible bonds help COFs reconstruct the defects, thus forming COFs with a highly crystalline structure. The advent of COF in 2005 finally opened up opportunities for synthesizing fully tunable organic polymers in terms of chemical compositions and structure orders.…”

COF-based artificial probiotic for modulation of gut microbiota and immune microenvironment in inflammatory bowel disease

“…16,20 As an emerging class of porous crystalline materials, covalent organic frameworks (COFs) with well-dened porosity, tunable composition, ultrahigh surface area and excellent biocompatibility have been developed as salient materials for separation, catalysis, sensing, drug delivery, and other biomedical applications. [21][22][23][24][25][26][27] Particularly, Schiff base-linked COFs have attracted great attention because of their interesting physical and chemical properties. 28 Furthermore, it is worth noting that due to the highly active imine (-C]N) bond, the Schiff base and its derivatives possess excellent antioxidant activity.…”