Conversion of Imine to Oxazole and Thiazole Linkages in Covalent Organic Frameworks

Advanced Postsynthetic Modification of COF: Elevating Hydrophilicity for Efficient Doxorubicin Delivery

Covalent organic frameworks (COFs) show great potential as drug delivery systems (DDSs) due to their customizable structures, stability, and capacity for pore surface functionalization. However, their natural hydrophobicity limits their dispersion in water, posing challenges for biological applications. We address this issue by initially reducing a COF (Az-COF) to an amine-linked form (Az-AL-COF) and subsequently sulfonating it to obtain Az-AL-SO3H-COF, a water-dispersible derivative. Water contact angle (WCA) analysis confirmed increased hydrophilicity across the series of 84.5, 61.2, and 54.7° for Az-COF, Az-AL-COF, and Az-AL-SO3H-COF, respectively. Using doxorubicin (Dox) as a model drug, the modified COFs exhibited pH-sensitive drug release, with greater release at acidic pH (5.6) compared to neutral pH (7.4). Cytotoxicity assays revealed that Az-AL-SO3H-COF was biocompatible with normal cells (MCF-10) while effectively suppressing the growth of cancer cells (MDA-MB-231). The Dox-loaded sulfonated COF (Dox@Az-AL-SO3H-COF) showed selective cytotoxicity against cancer cells, highlighting its potential as a pH-responsive, biocompatible DDS for cancer treatment.

Semiconducting Covalent Organic Frameworks

Semiconductors form the foundational bedrock of modern electronics and numerous cutting-edge technologies. Particularly, semiconductors crafted from organic building blocks hold immense promise as next-generation pioneers, thanks to their vast array of chemical structures, customizable frontier orbital energy levels and bandgap structures, and easily adjustable π electronic properties. Over the past 50 years, advancements in chemistry and materials science have facilitated extensive investigations into small organic π compounds, oligomers, and polymers, resulting in a rich library of organic semiconductors. However, a longstanding challenge persists: how to organize π building units or chains into well-defined π structures, which are crucial for the performance of organic semiconductors. Consequently, the pursuit of methodologies capable of synthesizing and/or fabricating organic semiconductors with ordered structures has emerged as a frontier in organic and polymeric semiconductor research. In this context, covalent organic frameworks (COFs) stand out as unique platforms allowing for the covalent integration of organic π units into periodically ordered π structures, thus facilitating the development of semiconductors with extended yet precisely defined π architectures. Since their initial report in 2008, significant strides have been made in exploring various chemistries to develop semiconducting COFs, resulting in a rich library of structures, properties, functions, and applications. This review provides a comprehensive yet focused exploration of the general structural features of semiconducting COFs, outlining the basic principles of structural design, illustrating the linkage chemistry and synthetic strategies based on typical one-pot polymerization reactions to demonstrate the growth of bulk materials, nanosheets, films, and membranes. By elucidating the interactions between COFs and various entities such as photons, phonons, electrons, holes, ions, molecules, and spins, this review categorizes semiconducting COFs into nine distinct sections: semiconductors, photoconductors, light emitters, sensors, photocatalysts, photothermal conversion materials, electrocatalysts, energy storage electrodes, and radical spin materials, focusing on disclosing structure-originated properties and functions. Furthermore, this review scrutinizes structure-function correlations and highlights the unique features, breakthroughs, and challenges associated with semiconducting COFs. Furnished with foundational knowledges and state-of-the-art insights, this review predicts the fundamental issues to be addressed and outlines future directions for semiconducting COFs, offering a comprehensive overview of this rapidly evolving and remarkable field.

Expanded Synthesis of 3D Covalent Organic Frameworks via Linker Exchange for Efficient Photocatalytic Aerobic Oxidation

Despite recent progress in 3D covalent organic frameworks (3D-COFs), their design and synthesis still pose significant challenges, mainly due to a limited mechanistic understanding of their synthesis. Herein, a linker exchange approach has been utilized to synthesize a series of new 3D-COFs by first preparing an imine-linked 3D-COF followed by exchanging with selected linear diamine linkers. This approach can be widely applicable to different types of diamines, enabling rational-designed synthesis of 3D frameworks that are previously inaccessible via direct polymerization in a one-pot reaction. Mechanistic aspects associated with the improved 3D-COF synthesis via the linker exchange approach, are investigated by density functional theory calculations, in which the possibility of the departure of the leaving linker is a spontaneous process with a decrease in enthalpy. Catalytic and computational results revealed that incorporating benzoxazole moiety into the 3D-COF frameworks enables a significant increase in the capability of visible-light-driven catalysis. The overall findings of the present study will pave the way toward the development of 3D-COFs with tunable structures and functions for other promising and challenging applications.

Two-Dimensional Heteropore Covalent Organic Frameworks: From Construction to Functions

ConspectusCovalent organic frameworks (COFs) represent a fascinating class of crystalline porous polymers constructed from organic building blocks linked by covalent bonds. Benefiting from their high crystallinity, large surface area, and ease of functionalization, COFs have demonstrated significant potential across various fields, including gas adsorption, luminescence, sensing, catalysis, energy storage, nanomedicine, etc. In the first decade of COF development, only those with homogeneous porosity have been constructed, and thus, their topological structures are quite limited. An exciting progress in the field of COFs is the emergence of two-dimensional (2D) COFs with hierarchical porosity, known as heteropore COFs, which have garnered considerable attention in recent years. Heteropore COFs are deliberately designed to integrate different types of pores into a single framework, resulting in heterogeneous porosity that imparts captivating properties and functions. Compared to their homopore counterparts, heteropore COFs offer a compelling platform for creating hierarchically structured porous materials, thanks to their distinctive multicompartment architectures and different pore environments. Since we achieved the construction of the first heteropore COF featuring both micropores and mesopores in 2014, substantial advancements have been achieved in the realm of heteropre COFs over the past decade, considerably increasing the topological diversity of 2D COFs. In this Account, we summarize our contributions to the development of 2D heteropore COFs. First, we review representative design strategies for the construction of 2D heteropore COFs, including the angle-specific-vertex, heterostructural-mixed-linker, multiple-linking-site, and desymmetrization-design strategies and their combinations as well as the dynamic covalent chemistry-mediated linker exchange strategy. Based on these strategies, heteroporous frameworks with two, three, and four different kinds of pores and different types of linkages have been successfully fabricated. Next, we discuss the properties and applications of heteropore COFs, including those shared with their homopore counterparts and unique ones originating from their hierarchical porous structures. Our research has shown that heteropore COFs have inherited the common features from their homopore counterparts and exhibited application potentials in gas adsorption, chemical sensing, environmental remediation, etc. More importantly, the multicompartment architecture and heterogeneous pore environment of heteropore COFs offer distinct benefits, for which exclusive applications and unique properties of heteropore COFs distinct from those of homopore COFs have been demonstrated. Finally, we highlight the current challenges and future directions of heteropore COFs, with an emphasis on the development of structural design and synthetic methodologies, precise structural characterization, and the exploration of unique properties and advanced applications. We believe that this Account will offer valuable insights into the design and synthesis of COFs with heteroporous structures, thereby accelerating their applications across a wide range of interdisciplinary research areas.

Photothermal Catalytic Synthesis of Sulfonic Acid Functionalized Covalent Organic Framework Achieved by COF-to-COF Transformation for Photocatalysis

Although photothermal catalysis is a clean, efficient, and green approach to access organic products, its application in the synthesis and transformation of covalent organic frameworks (COFs) remains unprecedented. Herein, we report the photothermal catalytic synthesis of C─C bond linked COF under visible light, which can be a reusable photocatalyst to highly promote oxidation of benzyl amines. Furthermore, we have developed a new postsynthetic modification strategy to construct COFs by photoinduced thermally-driven hydroamination via crystal-to-crystal transformation. The obtained COF containing sulfonic acid group showed an excellent catalytic performance in promoting aerobic oxidation of alkyl arenes under mild reaction conditions. These results not only enrich the COF synthetic methodology but also open a new route to access COFs in a green and sustainable way.

Transforming 2D Imine into 3D Thiazole Covalent Organic Frameworks by Conjugated Connectors: Fully Conjugated Photocatalysts

We developed a robust three-dimensional (3D) covalent organic framework (COF), fully conjugated in both the planar (x, y) and interlayer (z) directions, using a one-pot sulfurization process. We converted the two-dimensional (2D) imine-linked COF (Py-BDA-COF) to the 3D thiazole-linked COF (3D-Py-BDA-S-COF). In the interlayer direction (z-axis), the alternating covalently bound acetylene and ethylene arrangements serve as conjugated connectors ("pillars") and create a fully conjugated and very robust COF in all three dimensions. On top of this, the presence of the sulfur lone pair electrons in the thiazole rings considerably enhances the electron delocalization degree of the frameworks. The 3D-Py-BDA-S-COF is successfully evaluated in the photocatalytic reduction of nitrobenzene.

Advances in synthetic strategies for two-dimensional conjugated polymers

Two-dimensional conjugated polymers (2D CPs) are typically represented by 2D conjugated covalent organic frameworks (COFs) that consist of covalently cross-linked linear conjugated polymers, which possess extended in-plane π-conjugation and out-of-plane electronic couplings. The precise incorporation of molecular building blocks into ordered polymer frameworks through (semi)reversible 2D polycondensation methodologies enables the synthesis of novel polymer semiconductors with designable and predictable properties for various (opto)electronic, spintronic, photocatalytic, and electrochemical applications. Linkage chemistry lays the foundation for this class of synthetic materials and provides a library for subsequent investigations. In this review, we summarize recent advances in synthetic strategies for 2D CPs. By exploring synthetic approaches and the intricate interplay between chemical structure, the efficiency of 2D conjugation, and related physicochemical properties, we are expected to guide readers with a general background in synthetic chemistry and those actively involved in electronic device research. Furthermore, the discussion will appeal to researchers intrigued by the prospect of uncovering novel physical phenomena or mechanisms inherent in these emerging polymer semiconductors. Finally, future research directions and perspectives of highly crystalline and processable 2D CPs for electronics and other cutting-edge fields are discussed.

Ultrastable Imidazole-linked Porous Organic Cages for Ammonia Capture and Detection

Here, we report the facile synthesis of imidazole-linked porous organic cages (IPOCs) via an in situ cyclization reaction protocol. Specifically, three IPOCs with [2+4] lantern-like structures and one with a [3+6] triangular prism structure were successfully prepared through condensation reactions between tetraformyl-functionalized calix[4]arene and bis(o-phenylenediamine) monomers in a single pot. Notably, these IPOCs exhibit high porosity, with Brunauer-Emmett-Teller (BET) specific surface areas reaching up to 1162 m2 g-1. Moreover, they demonstrate excellent chemical stability in both strong acidic and alkaline solutions. Furthermore, IPOC-2 and IPOC-4 display a remarkable NH3 capturing capability, with uptakes of up to 11.5 mmol g-1 at 1 bar and 298 K, surpassing most reported porous organic materials. Additionally, IPOC-1 exhibits highly efficient fluorescent quenching sensing of aqueous NH3, with a detection limit as low as 3.35×10-6 M. These findings strongly suggest the potential for widespread use of imidazole linkages in the development of robust functional porous organic cage materials for diverse applications.

Bioinspired Photo-Thermal Catalytic System Using Covalent Organic Framework-Based Aerogel for Synchronous Seawater Desalination and H2O2 Production

Efficient utilization of solar energy is widely regarded as a crucial solution to addressing the energy crisis and reducing reliance on fossil fuels. Coupling photothermal and photochemical conversion can effectively improve solar energy utilization yet remains challenging. Here, inspired by the photosynthesis system in green plants, we report herein an artificial solar energy converter (ASEC) composed of light-harvesting units as solar collector and oriented ionic hydrophilic channels as reactors and transporters. Based on such architecture, the obtained ASEC (namely ASEC-NJFU-1) can efficiently realize parallel production of freshwater and H2O2 from natural seawater under natural light. The total solar energy conversion (SEC) of ASEC-NJFU-1 reaches up to 8047 kJ m-2 h-1, corresponding to production rates of freshwater and H2O2 are 3.56 kg m-2-1 h-1 and 19 mM m-2 h-1, respectively, which is a record-high value among all photothermal-photocatalytic systems reported to date. Mechanism investigation of combining spectrum and experimental studies indicated that the high SEC performance for ASEC-NJFU-1 was attributed to the presence of plant bioinspired architecture with carbon nanotubes as solar-harvestor and COF-based oriented aerogel as reactors and transporters. Our work thus establishes a novel artificial photosynthesis system for highly efficient solar energy utilization.

Industrialization of Covalent Organic Frameworks

Covalent organic frameworks (COFs) have attracted broad interest because of their well-defined, customizable, highly stable, and porous structures. COFs have shown significant potential for various practical applications, such as gas storage/purification, drug purification, water treatment, catalysis, and battery applications. Scaling up COFs is highly desirable to meet industrial application demands but is hindered by the limitations of synthesis methods and the high cost of reactants. Recently, emerging green synthesis methods, such as mechanochemical synthesis and flux synthesis, have offered promising solutions to these challenges (e.g., ton-scale production of COFs has been achieved by companies recently). This Perspective provides an overview of the state of the art with respect to the industrial production of COFs and discusses factors influencing the large-scale production of COFs. Directions and opportunities for improving the performance and sustainability of COFs toward industrial applications are also emphasized.

Mesoporous Acridinium-Based Covalent Organic Framework for Long-lived Charge-Separated Exciton Mediated Photocatalytic [4+2] Annulation

Readily tuneable porosity and redox properties of covalent organic frameworks (COFs) result in highly customizable photocatalysts featuring extended electronic delocalization. However, fast charge recombination in COFs severely limits their photocatalytic activities. Herein a new mode of COF photocatalyst design strategy to introduce systematic trap states is programmed, which aids the formation and stabilization of long-lived charge-separated excitons. Installing cationic acridinium functionality in a pristine electron-rich triphenylamine COF via postsynthetic modification resulted in a semiconducting photocatalytic donor-acceptor dyad network that performed rapid and efficient oxidative Diels-Alder type [4+2] annulation of styrenes and alkynes to fused aromatic compounds under the atmospheric condition in good to excellent yields. Large mesopores of ≈4 nm diameter ensured efficient mass flow within the COF channel. It is confirmed that the catalytic performance of COF originates from the ultra-stable charge-separated excitons of 1.9 nm diameter with no apparent radiative charge-recombination pathway, endorsing almost a million times better photo-response and catalysis than the state-of-the-art.

Functionalized Graphene via a One-Pot Reaction Enabling Exact Pore Sizes, Modifiable Pore Functionalization, and Precision Doping

Functionalizing graphene with exact pore size, specific functional groups, and precision doping poses many significant challenges. Current methods lack precision and produce random pore sizes, sites of attachment, and amounts of dopant, leading to compromised structural integrity and affecting graphene's applications. In this work, we report a strategy for the synthesis of functionalized graphitic materials with modifiable nanometer-sized pores via a Pictet-Spengler polymerization reaction. This one-pot, four-step synthesis uses concepts based on covalent organic frameworks (COFs) synthesis to produce crystalline two-dimensional materials that were confirmed by PXRD, TEM measurements, and DFT studies. These new materials are structurally analogous to doped graphene and graphene oxide (GO) but, unlike GO, maintain their semiconductive properties when fully functionalized.

Pyrene-based covalent organic frameworks (PyCOFs): a review

Recently, pyrene-based covalent organic frameworks (PyCOFs) have aroused great interest because the large planar structure of the pyrene unit could effectively enhance the interlayer π-π interaction and promote the separation and migration of carriers, significantly improving the crystallinity and photoelectrical properties of PyCOFs. Since the first PyCOF-containing boroxate linkage was reported in 2008 by the Yaghi group, many PyCOFs with different kinds of linkages have been reported, exhibiting great potential applications in different fields such as adsorption/separation, chemical sensing, catalysis, energy storage, etc. However, as far as we know, the reviews related to PyCOFs are rare, although PyCOFs have been widely reported to show promising applications. Thus, it is right time and important for us to systematically summarize the research advance in PyCOFs, including the synthesis with different linkages and applications. Moreover, the prospects and obstacles facing the development of PyCOFs are discussed. We hope that this review will provide new insights into PyCOFs that can be explored for more attractive functions or applications.

Designing Heterocyclic Covalent Organic Frameworks with Tunable Electronic Structures for Efficient Electrosynthesis of Hydrogen Peroxide

The electrocatalytic production of hydrogen peroxide (H2O2) through the two-electron oxygen reduction reaction (2e- ORR) has garnered significant research attention in recent years due to its numerous appealing advantages, such as being eco-friendly and exhibiting high energy conversion efficiency. Metal-free carbon materials with specific catalytic sites have been recognized as potential electrocatalysts for 2e- ORR; however, the design of highly efficient catalysts with well-defined structures and long-term stability for large-scale H2O2 production remains unsatisfactory. In this study, three covalent organic frameworks (COFs) - imine-linked LZU-1, oxazole-linked LZU-190, and thiazole-linked LZU-190(S), are successfully synthesized to explore their catalytic activity in electrocatalytic H2O2 production. Among these, the carbon sites LZU-190(S) are predominantly activated by the introduced adjacent heteroatoms via electronic effects, resulting in much higher H2O2 selectivity compared to the oxazole and imine linkages. This work provides new insights into developing COFs-based electrocatalysts for efficient H2O2 generation.

Self-Exfoliating Benzotristriazine Macrocyclic Network: A New 2D Material for High-Performance Electrochemical Energy Storage

Aza-fused aromatic π-conjugated networks are an important class of 2D graphitic analogs, which are generally constructed using aromatic precursors. Herein, the study describes a new synthetic approach and electrochemical properties of a self-exfoliating benzotristriazine 2D network (BTTN) constructed using aliphatic precursors, under relatively mild conditions. The obtained BTTN exhibits a nanodisc-like morphology, the self-exfoliation tendency of which is ascribed to the presence of structurally different macrocycles with high electronic repulsion between the layers. The benzotristriazine repeat units of BTTN is electroactive and holds higher carbon/nitrogen ratio when compared with the conventional graphitic aza-fused π-conjugated networks. The self-exfoliated BTTN nanodiscs show excellent electrochemical energy storage of 485 and 333 F g-1 at 1 A g-1 in three-electrode and two-electrode measurements, respectively. BTTN in a symmetric coin-cell architecture exhibits a high specific energy value of 46 Wh kg-1 at a power density of 1 kW kg-1 and shows excellent cyclic stability of 96% for 10 000 and 90% for 30 000 charge-discharge cycles at a higher current density of 5 A g-1, surpassing the device performance of most of the reported all-organic pseudocapacitive 2D networks.

Engineering Screw Dislocations in Covalent Organic Frameworks

We report the application of a Pictet-Spengler reaction to the synthesis of covalent organic frameworks (COFs) using functionalized terephthalaldehydes. The COFs produced show an increased propensity to generate screw dislocations and produce multilayered flakes when compared with other 2D-COFs. Using HRTEM, definitive evidence for screw dislocations was obtained and is presented. The effects on separations using these materials in membranes are also reported.

Ultrahigh Responsivity and Robust Semiconducting Fiber Enabled by Molecular Soldering-Governed Defect Engineering for Smart Textile Optoelectronics

Semiconducting fibers (SCFs) are of significant interest to design next-generation wearable and comfortable optoelectronics that seamlessly integrate with textiles. However, the practical applications of current SCFs are always limited by poor optoelectronic performance and low mechanical robustness caused by uncontrollable multiscale structural defects. Herein, a versatile in situ molecular soldering-governed defect engineering strategy is proposed to construct ultrahigh responsivity and robust wet-spun MoS2 SCFs, by using a π-conjugated dithiolated molecule to simultaneously patch microscale sulfur vacancies within MoS2 nanosheets, diminish mesoscale interlayer voids/wrinkles, promote macroscale orientation, build long-range photoelectron percolation bridges, and provide n-doping effect. The derived MoS2 SCFs exhibit over two orders of magnitude higher responsivity (144.3 A W-1) than previously reported fiber photodetectors, 37.3-fold faster photoresponse speed (52 ms) than pristine counterpart, and remarkable bending robustness (retain 94.2% of the initial photocurrent after 50 000 bending-flattening cycles). Such superior robustness and photodetection capacity of MoS2 SCFs further enable large-scale weaving of reliable smart textile optoelectronic systems, such as direction-identifiable wireless light alarming system, modularized mechano-optical communication system, and indoor light-controlled IoT system. This work offers a universal strategy for the scalable production of mechanically robust and high-performance SCFs, opening up exciting possibilities for large-scale integration of wearable optoelectronics.

Rigid covalent organic frameworks with thiazole linkage to boost oxygen activation for photocatalytic water purification

Owing to their capability to produce reactive oxygen species (ROS) under solar irradiation, covalent organic frameworks (COFs) with pre-designable structure and unique architectures show great potentials for water purification. However, the sluggish charge separation, inefficient oxygen activation and poor structure stability in COFs restrict their practical applications to decontaminate water. Herein, via a facile one-pot synthetic strategy, we show the direct conversion of reversible imine linkage into rigid thiazole linkage can adjust the π-conjugation and local charge polarization of skeleton to boost the exciton dissociation on COFs. The rigid linkage can also improve the robustness of skeleton and the stability of COFs during the consecutive utilization process. More importantly, the thiazole linkage in COFs with optimal C 2p states (COF-S) effectively increases the activities of neighboring benzene unit to directly modulate the O2-adsorption energy barrier and improve the ROS production efficiency, resulting in the excellent photocatalytic degradation efficiency of seven toxic emerging contaminants (e.g. degrading ~99% of 5 mg L-1 paracetamol in only 7 min) and effective bacterial/algal inactivation performance. Besides, COF-S can be immobilized in continuous-flow reactor and in enlarged reactor to efficiently eliminate pollutants under natural sunlight irradiation, demonstrating the feasibility for practical application.

Construction of Benzoxazine-linked One-Dimensional Covalent Organic Frameworks Using the Mannich Reaction

Covalent polymerization of organic molecules into crystalline one-dimensional (1D) polymers is effective for achieving desired thermal, optical, and electrical properties, yet it remains a persistent synthetic challenge for their inherent tendency to adopt amorphous or semicrystalline phases. Here we report a strategy to synthesize crystalline 1D covalent organic frameworks (COFs) composing quasi-conjugated chains with benzoxazine linkages via the one-pot Mannich reaction. Through [4+2] and [2+2] type Mannich condensation reactions, we fabricated stoichiometric and sub-stoichiometric 1D covalent polymeric chains, respectively, using doubly and singly linked benzoxazine rings. The validity of their crystal structures has been directly visualized through state-of-the-art cryogenic low-dose electron microscopy techniques. Post-synthetic functionalizations of them with a chiral MacMillan catalyst produce crystalline organic photocatalysts that demonstrated excellent catalytic and recyclable performance in light-driven asymmetric alkylation of aldehydes, affording up to 94 % enantiomeric excess.

Robust Nitrogen-Doped Microporous Carbon via Crown Ether-Functionalized Benzoxazine-Linked Porous Organic Polymers for Enhanced CO2 Adsorption and Supercapacitor Applications

Nitrogen-doped carbon materials, characterized by abundant microporous and nitrogen functionalities, exhibit significant potential for carbon dioxide capture and supercapacitors. In this study, a class of porous organic polymer (POP) were successfully synthesized by linking Cr-TPA-4BZ-Br4 and tetraethynylpyrene (Py-T). The model benzoxazine monomers of Cr-TPA-4BZ and Cr-TPA-4BZ-Br4 were synthesized using the traditional three-step method [involving CH═N formation, reduction by NaBH4, and Mannich condensation]. Subsequently, the Sonogashira coupling reaction connected the Cr-TPA-4BZ-Br4 and Py-T monomers, forming Cr-TPA-4BZ-Py-POP. The successful synthesis of Cr-TPA-4BZ-Br4 and Cr-TPA-4BZ-Py-POP was confirmed through various analytical techniques. After verifying the successful synthesis of Cr-TPA-4BZ-Py-POP, carbonization and KOH activation procedures were conducted. These crucial steps led to the formation of poly(Cr-TPA-4BZ-Py-POP)-800, a carbon material with a structure akin to graphite. In practical applications, poly(Cr-TPA-4BZ-Py-POP)-800 exhibited a noteworthy CO2 adsorption capacity of 4.4 mmol/g, along with specific capacitance values of 397.2 and 159.2 F g-1 at 0.5 A g-1 (measured in a three-electrode cell) and 1 A g-1 (measured in a symmetric coin cell), respectively. These exceptional dual capabilities stem from the optimal ratio of heteroatom doping. The outstanding performance of poly(Cr-TPA-4BZ-Py-POP)-800 microporous carbon holds significant promise for addressing contemporary energy and environmental challenges, making substantial contributions to both sectors.

Tunable 2D Conjugated Porous Organic Polymer Films for Precise Molecular Nanofiltration and Optoelectronics

Structural design of 2D conjugated porous organic polymer films (2D CPOPs), by tuning linkage chemistries and pore sizes, provides great adaptability for various applications, including membrane separation. Here, four free-standing 2D CPOP films of imine- or hydrazone-linked polymers (ILP/HLP) in combination with benzene (B-ILP/HLP) and triphenylbenzene (TPB-ILP/HLP) aromatic cores are synthesized. The anisotropic disordered films, composed of polymeric layered structures, can be exfoliated into ultrathin 2D-nanosheets with layer-dependent electrical properties. The bulk CPOP films exhibit structure-dependent optical properties, triboelectric nanogenerator output, and robust mechanical properties, rivaling previously reported 2D polymers and porous materials. The exfoliation energies of the 2D CPOPs and their mechanical behavior at the molecular level are investigated using density function theory (DFT) and molecular dynamics (MD) simulations, respectively. Exploiting the structural tunability, the comparative organic solvent nanofiltration (OSN) performance of six membranes having different pore sizes and linkages to yield valuable trends in molecular weight selectivity is investigated. Interestingly, the OSN performances follow the predicted transport modeling values based on theoretical pore size calculations, signifying the existence of permanent porosity in these materials. The membranes exhibit excellent stability in organic solvents at high pressures devoid of any structural deformations, revealing their potential in practical OSN applications.

Constrution of Quinazoline-Linked Covalent Organic Frameworks via a Multicomponent Reaction for Photocatalysis

Quinazoline (Qz)-linked covalent organic frameworks (COFs) have been constructed via a three-component reaction of ortho-acylanilines, benzaldehydes and NH4OAc. The structure of Qz-COFs has been confirmed by solid-state nuclear magnetic resonance spectroscopy, Fourier transform infrared and powder X-ray diffraction patterns. The Qz-COFs possess high chemical stability, showing good endurance to strong acid, strong base, oxidant, reductant and other conditions. Particularly, Qz-COF-3 can catalyze the aerobic photooxidation of toluene and other compounds containing C(sp3)-H bonds.

Covalent Organic Framework/Graphene Hybrids: Synthesis, Properties, and Applications

To address current energy crises and environmental concerns, it is imperative to develop and design versatile porous materials ideal for water purification and energy storage. The advent of covalent organic frameworks (COFs), a revolutionary terrain of porous materials, is underscored by their superlative features such as divinable structure, adjustable aperture, and high specific surface area. However, issues like inferior electric conductivity, inaccessible active sites impede mass transfer and poor processability of bulky COFs restrict their wider application. As a herculean stride forward, COF/graphene hybrids amalgamate the strengths of their constituent components and have in consequence, enticed significant scientific intrigue. Herein, the current progress on the structure and properties of graphene-based materials and COFs are systematically outlined. Then, synthetic strategies for preparing COF/graphene hybrids, including one-pot synthesis, ex situ synthesis, and in situ growth, are comprehensively reviewed. Afterward, the pivotal attributes of COF/graphene hybrids are dissected in conjunction with their multifaceted applications spanning adsorption, separation, catalysis, sensing, and energy storage. Finally, this review is concluded by elucidating prevailing challenges and gesturing toward prospective strides within the realm of COF/graphene hybrids research.

Synthetic Strategies to Extended Aromatic Covalent Organic Frameworks

π-Conjugated materials are highly attractive owing to their unique optical and electronic properties. Covalent organic frameworks (COFs) offer a great opportunity for precise arrangement of building units in a π-conjugated crystalline matrix and tuning of the properties through choice of functionalities or post-synthetic modification. With this review, we aim at summarizing both the most representative as well as emerging strategies for the synthesis of π-conjugated COFs. We give examples of direct synthesis using large, π-extended building blocks. COFs featuring fully conjugated linkages such as vinylene, pyrazine, and azole are discussed. Then, post-synthetic modification methods that result in the extension of the COF π-system are reviewed. Throughout, mechanistic insights are presented when available. In the context of their utilization as film devices, we conduct a concise survey of the prominent COF layer deposition techniques reported and their aptness for the deposition of fused aromatic systems.

The Transfer Dehydrogenation Method Enables a Family of High Crystalline Benzimidazole-linked Cu (II)-phthalocyanine-based Covalent Organic Frameworks Films

Heterocycle-linked phthalocyanine-based COFs with close-packed π-π conjugated structures are a kind of material with intrinsic electrical conductivity, and they are considered to be candidates for photoelectrical devices. Previous studies have revealed their applications for energy storage, gas sensors, and field-effect transistors. However, their potential application in photodetector is still not fully studied. The main difficulty is preparing high-quality films. In our study, we found that our newly designed benzimidazole-linked Cu (II)-phthalocyanine-based COFs (BICuPc-COFs) film can hardly formed with a regular aerobic oxidation method. Therefore, we developed a transfer dehydrogenation method with N-benzylideneaniline (BA) as a mild reagent. With this in hand, we successfully prepared a family of high crystalline BICuPc-COFs powders and films. Furthermore, both of these new BICuPc-COFs films showed high electrical conductivity (0.022-0.218 S/m), higher than most of the reported COFs materials. Due to the broad absorption and high conductivity of BICuPc-COFs, synaptic devices with small source-drain voltage (VDS=1 V) were fabricated with response light from visible to near-infrared. Based on these findings, we expect this study will provide a new perspective for the application of conducting heterocycle-linked COFs in synaptic devices.

Robust Thiazole-Linked Covalent Organic Frameworks for Water Sensing with High Selectivity and Sensitivity

The rational design of covalent organic frameworks (COFs) with hydrochromic properties is of significant value because of the facile and rapid detection of water in diverse fields. In this report, we present a thiazole-linked COF (TZ-COF-6) sensor with a large surface area, ultrahigh stability, and excellent crystallinity. The sensor was synthesized through a simple three-component reaction involving amine, aldehyde, and sulfur. The thiazole and methoxy groups confer strong basicity to TZ-COF-6 at the nitrogen sites, making them easily protonated reversibly by water. Therefore, TZ-COF-6 displayed color change visible to the naked eye from yellow to red when protonated, along with a red shift in absorption in the ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) when exposed to water. Importantly, the water-sensing process was not affected by polar organic solvents, demonstrating greater selectivity and sensitivity compared to other COF sensors. Therefore, TZ-COF-6 was used to detect trace amounts of water in organic solvents. In strong polar solvents, such as N,N-dimethyl formamide (DMF) and ethanol (EtOH), the limit of detection (LOD) for water was as low as 0.06% and 0.53%, respectively. Even after 8 months of storage and 15 cycles, TZ-COF-6 retained its original crystallinity and detection efficiency, displaying high stability and excellent cycle performance.

Metal-Organic Frameworks for Water Harvesting and Concurrent Carbon Capture: A Review for Hygroscopic Materials

As water scarcity becomes a pending global issue, hygroscopic materials prove a significant solution. Thus, there is a good cause following the structure-performance relationship to review the recent development of hygroscopic materials and provide inspirational insight into creative materials. Herein, traditional hygroscopic materials, crystalline frameworks, polymers, and composite materials are reviewed. The similarity in working conditions of water harvesting and carbon capture makes simultaneously addressing water shortages and reduction of greenhouse effects possible. Concurrent water harvesting and carbon capture is likely to become a future challenge. Therefore, an emphasis is laid on metal-organic frameworks (MOFs) for their excellent performance in water and CO2 adsorption, and representative role of micro- and mesoporous materials. Herein, the water adsorption mechanisms of MOFs are summarized, followed by a review of MOF's water stability, with a highlight on the emerging machine learning (ML) technique to predict MOF water stability and water uptake. Recent advances in the mechanistic elaboration of moisture's effects on CO2 adsorption are reviewed. This review summarizes recent advances in water-harvesting porous materials with special attention on MOFs and expects to direct researchers' attention into the topic of concurrent water harvesting and carbon capture as a future challenge.

COF-Based Photocatalysts for Enhanced Synthesis of Hydrogen Peroxide

Covalent Organic Frameworks (COFs), with their intrinsic structural regularity and modifiable chemical functionality, have burgeoned as a pivotal material in the realm of photocatalytic hydrogen peroxide (H2O2) synthesis. This article reviews the recent advancements and multifaceted approaches employed in using the unique properties of COFs for high-efficient photocatalytic H2O2 production. We first introduced COFs and their advantages in the photocatalytic synthesis of H2O2. Subsequently, we spotlight the principles and evaluation of photocatalytic H2O2 generation, followed by various strategies for the incorporation of active sites aiming to optimize the separation and transfer of photoinduced charge carriers. Finally, we explore the challenges and future prospects, emphasizing the necessity for a deeper mechanistic understanding and the development of scalable and economically viable COF-based photocatalysts for sustainable H2O2 production.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Covalent Organic Frameworks: Cutting-Edge Materials for Carbon Dioxide Capture and Water Harvesting from Air

The implacable rise of carbon dioxide (CO2 ) concentration in the atmosphere and acute water stress are one of the central challenges of our time. Present-day chemistry is strongly inclined towards more sustainable solutions. Covalent organic frameworks (COFs), attributable to their structural designability with atomic precision, functionalizable chemical environment and robust extended architectures, have demonstrated promising performances in CO2 trapping and water harvesting from air. In this Review, we discuss the major developments in this field as well as sketch out the opportunities and shortcomings that remain over large-scale COF synthesis, device engineering, and long-term performance in real environments.

Chemical Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks (COFs) are a type of crystalline porous polymer composed of light elements through strong covalent bonds. COFs have attracted considerable attention due to their unique designable structures and excellent material properties. Currently, COFs have shown outstanding potential in various fields, including gas storage, pollutant removal, catalysis, adsorption, optoelectronics, and their research in the sensing field is also increasingly flourishing. In this review, we focus on COF-based sensors. Firstly, we elucidate the fundamental principles of COF-based sensors. Then, we present the primary application areas of COF-based sensors and their recent advancements, encompassing gas, ions, organic compounds, and biomolecules sensing. Finally, we discuss the future trends and challenges faced by COF-based sensors, outlining their promising prospects in the field of sensing.

Crystalline Polyphenylene Covalent Organic Frameworks

The synthesis of crystalline polyphenylene covalent organic frameworks (COFs) was accomplished by linking fluorinated tris(4-acetylphenyl)benzene building units using aldol cyclotrimerization. The structures of the two COFs, reported here, were confirmed by powder X-ray diffraction techniques, Fourier transform infrared, and solid-state 13C CP/MAS NMR spectroscopy. The results showed that the COFs were porous and chemically stable in corrosive, harsh environments for at least 1 week. Accordingly, postsynthetically modified derivatives of these COFs using primary amines showed CO2 uptake from air and flue gas.

Covalent organic frameworks: Pioneering remediation solutions for organic pollutants

Covalent Organic Frameworks (COFs) have emerged as a promising class of crystalline porous materials with customizable structures, high surface areas, and tunable functionalities. Their unique properties make them attractive candidates for addressing environmental contamination caused by pharmaceuticals, pesticides, industrial chemicals, persistent organic pollutants (POPs), and endocrine disruptors (EDCs). This review article provides a comprehensive overview of recent advancements and applications of COFs in removing and remedying various environmental contaminants. We delve into the synthesis, properties, and performance of COFs and their potential limitations and future prospects.

A Phosphine-Amine-Linked Covalent Organic Framework with Staggered Stacking Structure for Lithium-Ion Conduction

In-plane ionic conduction over two-dimensional (2D) materials is desirable for flexible electronics. Exfoliating 2D covalent organic frameworks (COFs) towards a few layers is highly anticipated, whereas most examples remain robust via π-stacking against the interlayered dislocation. Herein, we synthesize a phosphine-amine-linked 2D COF by a nucleophilic substitution reaction of phosphazene with amines. The synthesized COF is crystalline, and stacks in an AB-staggered fashion, wherein the AB dual layers are interlocked by embedding P-Cl bonds from one to another layer, and the non-interlocked layers are readily delaminated. Therefore, in situ post-quaternization over phosphazene can improve the ionization of backbones, accompanied by layered exfoliation. The ultrathin nanosheets can decouple lithium salts for fast solid-state ion transport, achieving a high conductivity and low activation energy. Our findings explore the P-N substitution reaction for COF crystallization and demonstrate that the staggered stacking 2D COFs are readily exfoliated for designing solid electrolytes.

Synthesis of stable and efficient amide-based covalent organic frameworks fiber coatings for the improved solid-phase microextraction of polar aromatic amines

BACKGROUND

Developing facile and general functionalization strategies to improve the durability of covalent organic framework (COF) coatings and their affinity for polar targets is of great significance for solid-phase microextraction (SPME) technology.

RESULTS

In this work, a facile and general amidation strategy was developed for conversion from reversible (imine) to irreversible (amide) linkages in COF coatings. After the amidation, the durability of the obtained amide-linked covalent organic framework (Am-P-COF) coating was greatly improved, and the adsorption efficiency for polar aromatic amines (AAs) was also significantly increased. Moreover, this strategy is also applicable to the amidation of other two COF coatings, showing good general applicability. The obtained Am-P-COF coated fiber was used for SPME, and then coupled with gas chromatography tandem mass spectrometry (GC-MS/MS) to detect AAs. Under the optimal SPME conditions (extraction temperature: 50 °C, extraction time: 30 min, stirring rate: 600 rpm, pH: 8, NaCl concentration: 5.0 mg mL-1, desorption temperature: 290 °C and desorption time: 10 min), a detection method for trace AAs was established. The established method possess wide linear ranges (0.5-500.0 ng L-1), good correlation coefficients (0.9986-0.9993) and low detection limits (0.1-0.5 ng L-1). Moreover, the established method had also been successfully applied to detection of trace AAs in bottled tea beverage and plastic bags packed tea with satisfactory recoveries (83.5 %-116.8 %).

SIGNIFICANCE AND NOVELTY

This research provides a facile and general pathway for increasing the durability of COF coatings and affinity to the polar AAs. The detection method based on the obtained fibers possesses high sensitivity, satisfactory reproducibility and good precision.

Recent advances in the utilization of covalent organic frameworks (COFs) as electrode materials for supercapacitors

Due to their excellent stability, ease of modification, high specific surface area, and tunable redox potentials, covalent organic frameworks (COFs) as potential electrodes in supercapacitors (SCs) have raised much research interest because these materials can enable the achievement of high electric double-layer supercapacitance and high pseudocapacitance. Here, the design strategies and SC applications of COF-based electrode materials are summarized. The detailed principles are introduced first, followed by discussions on strategies with diverse examples. The updated advances in design and applications are also discussed. Finally, in the outlook section, we provide some guidelines on the rational design of COF-based electrode materials for high-performance SCs, which we hope will inspire novel concepts for COF-based supercapacitors.

Double-Walled Covalent Organic Frameworks with High Stability

Double-walled covalent organic frameworks, consisting of two same building blocks parallel to each other forming ladder-shape linkers, could enhance the stability of the frameworks and increase the density of functional sites, thus making them suitable for various applications. In this study, two double-walled covalent organic frameworks, namely DW-COF-1 and DW-COF-2, were successfully synthesized via imine condensation. The resulting DW-COFs exhibited a honeycomb topology, high crystallinity and stability. Particularly, DW-COF-2 showed excellent resistance toward boiling water, strong acid, and strong base, due to its double-walled structure, which limits the exposure of labile imine bonds to external chemical environments. The DW-COFs showed high porosity near 900 m2 /g, making them suitable for gas storage/separation. The selective gas adsorption experiments showed that at 273 K and 1 atm pressure, DW-COF-1 and DW-COF-2 exhibited a good IAST selectivity towards CO2 /N2 (15/85) adsorption, with selectivity values of 121.3 and 56.4 for CO2 over N2 , respectively.

Linkage Transformations in a Three-Dimensional Covalent Organic Framework for High-Capacity Adsorption of Perfluoroalkyl Substances

Despite their many advantages, covalent organic frameworks (COFs) built from three-dimensional monomers are synthetically difficult to functionalize. Herein, we provide a new synthetic approach to the functionalization of a three-dimensional covalent organic framework (COF-300) by using a series of solid-state linkage transformations. By reducing the imine linkages of the framework to amine linkages, we produced a more hydrolytically stable material and liberated a nucleophilic amino group, poised for further functionalization. We then treated the amine-linked COF with diverse electrophiles to generate a library of functionalized materials, which we tested for their ability to adsorb perfluoroalkyl substances (PFAS) from water. The framework functionalized with dimethylammonium groups, COF-300-dimethyl, adsorbed more than 250 mg of perfluorooctanoic acid (PFOA) per 1 g of COF, which represents an approximately 14,500-fold improvement over that of COF-300 and underscores the importance of electrostatic interactions to PFAS adsorption performance. This work provides a conceptually new approach to the design and synthesis of functional three-dimensional COFs.

Recent Progress in Design Principles of Covalent Organic Frameworks for Rechargeable Metal-Ion Batteries

Covalent organic frameworks (COFs) are acknowledged as a new generation of crystalline organic materials and have garnered tremendous attention owing to their unique advantages of structural tunability, frameworks diversity, functional versatility, and diverse applications in drug delivery, adsorption/separation, catalysis, optoelectronics, and sensing, etc. Recently, COFs is proven to be promising candidates for electrochemical energy storage materials. Their chemical compositions and structures can be precisely tuned and functionalized at the molecular level, allowing a comprehensive understanding of COFs that helps to make full use of their features and addresses the inherent drawback based on the components and functions of the devices. In this review, the working mechanisms and the distinguishing advantages of COFs as electrodes for rechargeable Li-ion batteries are discussed in detail. Especially, principles and strategies for the rational design of COFs as advanced electrode materials in Li-ion batteries are systematically summarized. Finally, this review is structured to cover recent explorations and applications of COF electrode materials in other rechargeable metal-ion batteries.

Construction of Thiadiazole-Linked Covalent Organic Frameworks via Facile Linkage Conversion with Superior Photocatalytic Properties

The establishment of facile synthetic routes to engineer covalent organic frameworks (COFs) with fully conjugated structure and excellent stability is highly desired for practical applications in optoelectronics and photocatalysis. Herein, a novel linkage conversion strategy is reported to prepare crystalline thiadiazole-linked COFs via thionation, cyclization, and oxidation of N-acylhydrazole bonds with Lawesson's reagent (LR). The as-prepared thiadiazole-linked COFs not only remain porosity and crystallinity, but enhance its chemical stability. Furthermore, thiadiazole-linked COFs are more favorable to lower exciton binding energy and promote π-electron delocalization over the whole reticular framework than N-acylhydrazone-linked COFs. Notably, the extended π-conjugation structure and decent crystallinity of the resulting TDA-COF are reflected by its higher photocatalytic H2 evolution rate (61.3 mmol g-1 in 5 h) in comparison with that (7.5 mmol g-1 ) of NAH-COF.

Gradient Channel Segmentation in Covalent Organic Framework Membranes with Highly Oriented Nanochannels

Covalent organic frameworks (COFs) offer an exceptional platform for constructing membrane nanochannels with tunable pore sizes and tailored functionalities, making them promising candidates for separation, catalysis, and sensing applications. However, the synthesis of COF membranes with highly oriented nanochannels remains challenging, and there is a lack of systematic studies on the influence of postsynthetic modification reactions on functionality distribution along the nanochannels. Herein, we introduced a "prenucleation and slow growth" approach to synthesize a COF membrane featuring highly oriented mesoporous channels and a high Brunauer-Emmett-Teller surface area of 2230 m2 g-1. Functional moieties were anchored to the pore walls via "click" reactions and coordinated with Cu ions to serve as segmentation functions. This led to a remarkable H2/CO2 separation performance that surpassed the Robeson upper bound. Moreover, we found that the functionalities distributed along the nanochannels could be influenced by functionality flexibility and postsynthetic reaction rate. This strategy paved the way for the accurate design and construction of COF-based artificial solid-state nanochannels with high orientation and precisely controlled channel environments.

Simple and Efficient Hydrogen Bond-Assisted Unit Exchange for Constructing Highly Soluble Covalent Organic Frameworks

The majority of COFs synthesized using current methods exist as insoluble powders, which is unfavorable for processing and molding and greatly limits their practical applications. The syntheses of solution-processable or soluble COFs are challenging but hold immense promise and potential. Herein, for the first time, we have developed a simple and high-efficiency solvothermal-treated unit exchange approach to convert insoluble COF powders into smaller, highly soluble COFs via a hydrogen bond-assisted strategy. Due to the enhanced backbone-solvent hydrogen-bonding interactions between COFs and protic solvents and the effect of grain size reduction, the COFs after unit exchange can be easily dissolved in various protic solvents while remaining as insoluble powders in nonprotic solvents. The obtained soluble COFs exhibit remarkable fluorescence quenching upon detection of iodine in aqueous solution, with a detection limit as low as 75 nM, and can be fabricated into membranes for the efficient treatment of iodine-contaminated solutions.

Covalent organic frameworks for CO2 capture: from laboratory curiosity to industry implementation

CO2 concentration in the atmosphere has increased by about 40% since the 1960s. Among various technologies available for carbon capture, adsorption and membrane processes have been receiving tremendous attention due to their potential to capture CO2 at low costs. The kernel for such processes is the sorbent and membrane materials, and tremendous progress has been made in designing and fabricating novel porous materials for carbon capture. Covalent organic frameworks (COFs), a class of porous crystalline materials, are promising sorbents for CO2 capture due to their high surface area, low density, controllable pore size and structure, and preferable stabilities. However, the absence of synergistic developments between materials and engineering processes hinders achieving the qualitative leap for net-zero emissions. Considering the lack of a timely review on the combination of state-of-the-art COFs and engineering processes, in this Tutorial Review, we emphasize the developments of COFs for meeting the challenges of carbon capture and disclose the strategies of fabricating COFs for realizing industrial implementation. Moreover, this review presents a detailed and basic description of the engineering processes and industrial status of carbon capture. It highlights the importance of machine learning in integrating simulations of molecular and engineering levels. We aim to stimulate both academia and industry communities for joined efforts in bringing COFs to practical carbon capture.

A Porous Crystalline Nitrone-Linked Covalent Organic Framework

Herein, we report the synthesis of a nitrone-linked covalent organic framework, COF-115, by combining N, N', N', N'''-(ethene-1, 1, 2, 2-tetrayltetrakis(benzene-4, 1-diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid-state 13 C multi cross-polarization magic angle spinning NMR spectroscopy of the 13 C-isotope-labeled COF-115 and Fourier-transform infrared spectroscopy. The permanent porosity of COF-115 was evaluated through low-pressure N2 , CO2 , and H2 sorption experiments. Water vapor and carbon dioxide sorption analysis of COF-115 and the isoreticular imine-linked COF indicated a superior potential of N-oxide-based porous materials for atmospheric water harvesting and CO2 capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF-115 to the associated amide-linked material was successfully demonstrated.

Single Site Coordination Enabled Construction of Metal-Diketimine-Linked Covalent Organic Frameworks for Boosted Electrooxidation of Biomass Derivative

Aromatic aldehydes are widely used for the construction of covalent organic frameworks (COFs). However, due to the high flexibility, high steric hindrance, and low reactivity, it remains challenging to synthesize COFs using ketones as building units, especially the highly flexible aliphatic ones. Here, the single nickel site coordination strategy is reported to lock the configurations of the highly flexible diketimine to transform discrete oligomers or amorphous polymers into highly crystalline nickel-diketimine-linked COFs (named as Ni-DKI-COFs). The strategy has been successfully extended to the synthesis of a series of Ni-DKI-COFs by the condensation of three flexible diketones with two tridentate amines. Thanks to the ABC stacking model with high amount and easily accessible single nickel (II) sites on their 1D channels, Ni-DKI-COFs are exploited as well-defined electrocatalyst platforms for efficiently electro-upgrading biomass-derived 5-Hydroxymethylfurfural (HMF) into value-added 2,5-furandicarboxylic acid (FDCA) with a 99.9% yield and a 99.5% faradaic efficiency as well as a high turnover frequency of 0.31 s-1 .

Large-Scale Synthesis of Covalent Organic Frameworks: Challenges and Opportunities

Connecting organic building blocks by covalent bonds to design porous crystalline networks has led to covalent organic frameworks (COFs), consequently transferring the flexibility of dynamic linkages from discrete architectures to extended structures. By virtue of the library of organic building blocks and the diversity of dynamic linkages and topologies, COFs have emerged as a novel field of organic materials that propose a platform for tailor-made complex structural design. Progress over the past two decades in the design, synthesis, and functional exploration of COFs in diverse applications successively established these frameworks in materials chemistry. The large-scale synthesis of COFs with uniform structures and properties is of profound importance for commercialization and industrial applications; however, this is in its infancy at present. An innovative designing and synthetic approaches have paved novel ways to address future hurdles. This review article highlights the fundamental of COFs, including designing principles, coupling reactions, topologies, structural diversity, synthetic strategies, characterization, growth mechanism, and activation aspects of COFs. Finally, the major challenges and future trends for large-scale COF fabrication are outlined.

A fluorescence biosensor based on DNA aptamers-COF for highly selective detection of ATP and thrombin

Due to their distinctive physical, chemical, electrical, and optical properties as well as their prospective uses, 2D covalent organic framework (COF) have attracted much attention. Herein, TaTPA-COF was effectively synthesized from the condensation of TTA and TFPA using a facile solvothermal method and characterized by SEM image, FT-IR spectra, and PXRD pattern. The generated bulk TaTPA-COF materials combined with DNA aptamers are utilized as the acceptor (quencher) for the highly sensitive and selective detection of adenosine 5'-triphosphate (ATP) and thrombin, with a novel fluorescence biosensing platform and a proof-of-concept application.

Recent Advances in the Use of Covalent Organic Frameworks as Heterogenous Photocatalysts in Organic Synthesis

Organic photochemistry is intensely developed in the 1980s, in which the nature of excited electronic states and the energy and electron transfer processes are thoroughly studied and finally well-understood. This knowledge from molecular organic photochemistry can be transferred to the design of covalent organic frameworks (COFs) as active visible-light photocatalysts. COFs constitute a new class of crystalline porous materials with substantial application potentials. Featured with outstanding structural tunability, large porosity, high surface area, excellent stability, and unique photoelectronic properties, COFs are studied as potential candidates in various research areas (e.g., photocatalysis). This review aims to provide the state-of-the-art insights into the design of COF photocatalysts (pristine, functionalized, and hybrid COFs) for organic transformations. The catalytic reaction mechanism of COF-based photocatalysts and the influence of dimensionality and crystallinity on heterogenous photocatalysis performance are also discussed, followed by perspectives and prospects on the main challenges and opportunities in future research of COFs and COF-based photocatalysts.