Two-dimensional porphyrin- and phthalocyanine-based covalent organic frameworks

Covalent organic frameworks (COFs) represent an emerging class of porous crystalline materials and have recently shown interesting applications from catalysis to optoelectronic devices. In this review, by covering most of the reported work, we summarized the research progress of two-dimensional (2D) porphyrin- and phthalocyanine-based COFs, with highlighting the synthesis of these 2D COFs via various dynamic covalent reactions and emphasizing their potential applications in different areas.     

Covalent Organic Frameworks as Emerging Nonlinear Optical Materials

The vastness of organic synthetic strategies and knowledge of reticular chemistry have made covalent organic frameworks (COFs) one of the most chemically and structurally diverse class of materials with potential applications ranging from gas storage, molecular separation, and catalysis to energy storage and magnetism. Recently, this class of porous materials has garnered increasing interest as potential nonlinear optical (NLO) materials. Traditionally, inorganic crystals, small-molecule organic chromophores, and oligomers have been studied for their NLO response. Nevertheless, COFs offer significant advantages over existing NLO materials in terms of higher mechanical strength, thermochemical stability, and extended conjugation. Herein, we discuss crucial aspects, terminology, and measurement techniques related to NLO, followed by a critical analysis of the design principles for COFs with NLO response. Furthermore, we touch on selected potential applications of these NLO materials. Finally, future prospects and challenges of COFs as NLO materials are discussed.     

多孔有机骨架材料对顺式二醇化合物富集分离的研究进展

基于在碱性环境下硼酸能与顺式二醇化合物可逆共价结合形成稳定的五元或六元环酯,而在酸性环境下环酯开环释放顺式二醇化合物这一特性,设计合成高效、高选择性、高富集性能的硼亲和材料的研究备受关注。近年来,许多研究工作者合成了各种类型的硼亲和材料,应用于高选择性富集顺式二醇化合物。金属有机骨架(MOFs)和共价有机骨架(COFs)由于具有孔径可调、高孔隙率、高比表面积、骨架结构可调和化学及热稳定性良好等特点,被广泛应用于色谱分离和样品前处理领域。为赋予MOFs和COFs材料对顺式二醇化合物的富集选择性,各种不同结构和不同种类的硼酸修饰的MOFs和COFs被合成出来。该综述主要是对近几年来80余篇源于科学引文索引关于硼酸功能化MOFs和COFs的种类、合成方法及其应用文章的总结,包括“金属配体-片段共组装”“合成后修饰”和“自下而上”的硼酸功能化多孔材料的修饰策略,以及硼酸功能化MOFs和COFs的种类,介绍了其在化学分析和生物分析领域的发展概况和应用前景,客观评价了硼酸功能化MOFs和COFs的区别和优缺点。该文旨在让研究人员能够充分了解近几年硼酸功能化多孔有机骨架材料的研究现状、掌握合成思路和方法,为其应用提供一定的理论指导和技术支撑,为加快硼酸功能化多孔有机骨架材料的商业化脚步贡献绵薄之力。     

2020 roadmap on two-dimensional materials for energy storage and conversion

In this roadmap, two-dimensional materials including graphene, black phosporus, MXenes, covalent organic frameworks, oxides, chalcogenides, and others, are highlighted in energy storage and conversion.     

Energy Storage in Covalent Organic Frameworks: From Design Principles to Device Integration

Covalent organic frameworks(COFs) have received profound attention in recent years owing to their tailor-made porosity, large surface area and robust stability. More specifically, 2D COFs with redox-active and π electron-rich units allow efficient charge carriers hopping and ion migration, thus offering great potentials in energy storage. Herein, we present a systematic and concise overview of the recent advances in 2D COFs related to the electrochemical energy field, including supercapacitors, fuel cells, rechargeable lithium batteries, lithium-sulfur batteries, and other metal-ion batteries. In addition, a brief outlook is proposed on the challenges and prospects of COFs as electrode materials for energy storage.     

共价有机骨架的合成及其在气体吸附存储方面的应用

共价有机骨架(COFs)是一种新型的纳米结构材料,由于其独特的性质而受到人们的广泛关注.COFs的结晶.度高,孔径可调,比表面积大,具有良好的抗氧化性能和独特的分子结构,在能源、环境等方面得到了广泛的应用.COFs材料有较高的应用价值,促使人们不断努力研究其基本性质,并调控其结构和功能来提高性能.通过COFs的可设计性...     

Covalent Organic Frameworks for Energy Conversion in Photocatalysis

Intensifying energy crises and severe environmental issues have led to the discovery of renewable energy sources, sustainable energy conversion, and storage technologies. Photocatalysis is a green technology that converts eco-friendly solar energy into high-energy chemicals. Covalent organic frameworks (COFs) are porous materials constructed by covalent bonds that show promising potential for converting solar energy into chemicals owing to their pre-designable structures, high crystallinity, and porosity. Herein, we highlight recent progress in the synthesis of COF-based photocatalysts and their applications in water splitting, CO₂ reduction, and H₂O₂ production. The challenges and future opportunities for the rational design of COFs for advanced photocatalysts are discussed. This Review is expected to promote further development of COFs toward photocatalysis.     

Isostructural Three‐Dimensional Covalent Organic Frameworks

Herein, we reported the designed synthesis of three isostructural three‐dimensional covalent organic frameworks (3D COFs) with ‐H, ‐Me, or ‐F substituents, which have similar crystallinity and topology. Their crystal structures were determined by continuous rotation electron diffraction (cRED), and all three 3D COFs were found to adopt a fivefold interpenetrated pts topology. More importantly, the resolution of these cRED datasets reached up to 0.9–1.0 Å, enabling the localization of all non‐hydrogen atomic positions in a COF framework directly by 3D ED techniques for the first time. In addition, the precise control of the pore environments through the use of different functional groups led to different selectivities for CO₂ over N₂. We have thus confirmed that polycrystalline COFs can be definitely studied to the atomic level as other materials, and this study should also inspire the design and synthesis of 3D COFs with tailored pore environments for interesting applications.     

2020 roadmap on two-dimensional materials for energy storage and conversion

Energy storage and conversion have attained significant interest owing to its important applications that reduce CO₂ emission through employing green energy. Some promising technologies are included metal-air batteries, metal-sulfur batteries, metal-ion batteries, electrochemical capacitors, etc. Here, metal elements are involved with lithium, sodium, and magnesium. For these devices, electrode materials are of importance to obtain high performance. Two-dimensional (2D) materials are a large kind of layered structured materials with promising future as energy storage materials, which include graphene, black phosporus, MXenes, covalent organic frameworks (COFs), 2D oxides, 2D chalcogenides, and others. Great progress has been achieved to go ahead for 2D materials in energy storage and conversion. More researchers will join in this research field. Under the background, it has motivated us to contribute with a roadmap on ‘two-dimensional materials for energy storage and conversion.     

3D Microporous Base‐Functionalized Covalent Organic Frameworks for Size‐Selective Catalysis

The design and synthesis of 3D covalent organic frameworks (COFs) have been considered a challenge, and the demonstrated applications of 3D COFs have so far been limited to gas adsorption. Herein we describe the design and synthesis of two new 3D microporous base‐functionalized COFs, termed BF‐COF‐1 and BF‐COF‐2, by the use of a tetrahedral alkyl amine, 1,3,5,7‐tetraaminoadamantane (TAA), combined with 1,3,5‐triformylbenzene (TFB) or triformylphloroglucinol (TFP). As catalysts, both BF‐COFs showed remarkable conversion (96 % for BF‐COF‐1 and 98 % for BF‐COF‐2), high size selectivity, and good recyclability in base‐catalyzed Knoevenagel condensation reactions. This study suggests that porous functionalized 3D COFs could be a promising new class of shape‐selective catalysts.     

Challenges and perspectives of covalent organic frameworks for advanced alkali-metal ion batteries

Covalent organic frameworks(COFs) are a class of porous crystalline polymers that have been widely investigated in various fields, including energy storage, photo/electrocatalysis, drug delivery. The covalent-bond interconnection allows COFs extraordinary chemical and thermal stability, and the porous structure ensures a high ion-diffusion coefficient. These merits compensate for the drawbacks of organic electrodes that are easy to dissolve and have low charge conductivity, and promote the development of novel electrode materials with excellent performance, environmental friendliness, and low price. However, the application of COFs also encountered many problems, such as poor electronic conductivity due to the large band gap. Moreover,in some three-dimensional(3D) COFs and stacked two-dimensional(2D) COFs, the huge crystal structure, aligned ultralong channels, and numerous crystal defects usually impede ion transport, and the large molecular weights of COFs generally decrease the specific capacities. These issues are urgently needed to be solved. Here in this review, we summarize the latest progress, core challenges and coping strategies concerning with the use of COFs in alkali-metal ion batteries, discuss the impact of material structure on energy storage, and propose strategies for the construction of high-performance COF-based electrodes.     

Impact of Imine Bond Orientations on the Geometric and Electronic Structures of Imine-based Covalent Organic Frameworks

Many efforts are currently devoted to improving the stability and crystallinity of imine-based two-dimensional (2D) covalent organic frameworks (COFs) given their wide range of potential applications. The variation in the relative orientations of the imine bonds has been found to be a critical factor that impacts the stacking of the 2D COF layers, leads to the formation of isomer structures, and influences the crystallinity of the final product. Most investigations to date have focused only on the structural properties, while the role of the imine orientations on the electronic properties has not been studied systematically. Here, we explore this effect by examining how the electronic band structures, electronic couplings, and effective masses evolve when considering four isomeric structures of an imine-linked tetraphenyl-pyrene naphthalene-diimide COF. Our results provide an understanding of the impact of the imine orientations and how they need to be controlled to realize COF inter-layer stackings that can lead to efficient cross-plane electron transport. They can be used to guide the design and synthesis of imine-based COFs for applications where charge transport needs to be optimized.     

共价有机框架材料研究进展

共价有机框架材料是一类具有周期性和结晶性的有机多孔聚合物。共价有机框架材料由轻质元素通过共价键连接,拥有较低的密度、高的热稳定性以及固有的多孔性,在气体吸附、非均相催化、能量存储等研究领域有着广泛的应用潜力,引起了科学界强烈的研究兴趣。本文主要综述了近年来共价有机框架材料的最新研究进展,包括其结构设计、合成、纯化、表征以及在气体吸附,催化及光电等方面的应用,并对共价有机框架材料未来的发展趋势进行了展望。     

卟啉共价有机框架化合物的研究进展

共价有机框架化合物(COFs)是一类新兴的具有多孔结构的晶态有机聚合物,在储存与分离、催化、能量转化等领域具有广泛应用。本文介绍了一类基于卟啉单元的COFs,从框架构筑及应用开发两方面综述了这类材料的研究进展。     

Ionothermal Synthesis of Imide‐Linked Covalent Organic Frameworks

Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time‐consuming process and restricted to well‐soluble precursor molecules. Synthesis of polyimide‐linked COFs (PI‐COFs) is further complicated by the poor reversibility of the ring‐closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI‐COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene‐based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high‐temperature XRPD analysis hints to the formation of precursor–salt adducts as crystalline intermediates, which then react with each other to form the COF.     

Electroactive Organic Building Blocks for the Chemical Design of Functional Porous Frameworks (MOFs and COFs) in Electronics

Electroactive organic molecules have received a lot of attention in the field of electronics because of their fascinating electronic properties, easy functionalization and potential low cost towards their implementation in electronic devices. In recent years, electroactive organic molecules have also emerged as promising building blocks for the design and construction of crystalline porous frameworks such as metal–organic frameworks (MOFs) and covalent-organic frameworks (COFs) for applications in electronics. Such porous materials present certain additional advantages such as, for example, an immense structural and functional versatility, combination of porosity with multiple electronic properties and the possibility of tuning their physical properties by post-synthetic modifications. In this Review, we summarize the main electroactive organic building blocks used in the past few years for the design and construction of functional porous materials (MOFs and COFs) for electronics with special emphasis on their electronic structure and function relationships. The different building blocks have been classified based on the electronic nature and main function of the resulting porous frameworks. The design and synthesis of novel electroactive organic molecules is encouraged towards the construction of functional porous frameworks exhibiting new functions and applications in electronics.     

Two-dimensional Covalent Organic Frameworks: Tessellation by Synthetic Art

Covalent organic frameworks(COFs) featuring designable nanoporous structures exhibit many fascinating properties and have attracted great attention in recent years for their intriguing application potential in sensing, catalysis, gas storage and separation, optoelectronics, etc. Rational design of twodimensional(2D) COFs through judiciously selecting chemical building blocks is critical to acquiring predetermined skeleton and pore structures. In this perspective, we review the reticular synthesis of 2D COFs with different topologies, highlighting the important role of various characterization techniques in crystal structure determination. 2D COFs with simple tessellations have been widely investigated, while the synthesis of complex tessellated COFs is still a great challenge. Some recent examples of 2D COFs with novel topological structures are also surveyed.     

Strategies for Improving the Catalytic Performance of 2D Covalent Organic Frameworks for Hydrogen Evolution and Oxygen Evolution Reactions

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research.     

Three-Dimensional Chemically Stable Covalent Organic Frameworks through Hydrophobic Engineering

The development of three-dimensional (3D) covalent organic frameworks (COFs) with high chemical stability is of critical importance for their practical use. In this work, it is demonstrated that the stability of 3D COFs can be improved by periodic decoration of isopropyl groups on their backbones. Owing to the strong hydrophobicity of the alkyl groups, the resultant COFs show high crystallinity, permanent pores, and exceptional stability in harsh environments, such as strong acids (3 m HCl or 3 m H₂SO₄ for one week), a strong base (20 m NaOH for one week), and boiling water (100 °C for one month). Furthermore, these highly stable and hydrophobic COFs display excellent oil/water separation performance with >99 % separation efficiency over a wide pH range. This work demonstrates the use of alkyl decoration in 3D COFs to tune their chemical stability and expand their potential applications.