Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Co2+ coordination-assisted molecularly imprinted covalent organic framework for selective extraction of ochratoxin A

Covalent organic frameworks (COFs) are attractive materials for sample pretreatment due to their tunable structures and functions. However, the precise recognition of contaminant in complex environmental matrices by COFs remains challenging owing to their insufficient specific active sites. Herein, we report Co2+ coordination-assisted molecularly imprinted flexible COF (MI-COF@Co2+) for selective recognition of ochratoxin A (OTA). The MI-COF@Co2+ was prepared via one-step polymerization of 3,3-dihydroxybenzidine, 2,4,6-tris(4-formylphenoxy)- 1,3,5-triazine, Co2+ and template. The flexible units endowed COFs with the self-adaptable ability to regulate the molecular conformation and coordinate with Co2+ to locate the imprinted cavities. The coordination interaction greatly improved the adsorption capacity and selectivity of MI-COF@Co2+ for OTA. The prepared MI-COF@Co2+ was used as solid phase extraction adsorbent for high-performance liquid chromatography determination of OTA with the detection limit of 0.03 ng mL-1 and the relative standard deviation of < 2.5 %. In addition, this method permitted interference-free determination of OTA in real samples with recovery from 89.5 % to 102.8 %. This work provides a simple way to improve the selectivity of COFs for the determination of hazardous compounds in complex environments.

Ultralight and Robust Covalent Organic Framework Fiber Aerogels

Shaping covalent organic frameworks (COFs) into macroscopic objects with robust mechanical properties and hierarchically porous structure is of great significance for practical applications but remains formidable and challenging. Herein, a general and scalable protocol is reported to prepare ultralight and robust pure COF fiber aerogels (FAGs), based on the epitaxial growth synergistic assembly (EGSA) strategy. Specifically, intertwined COF nanofibers (100-200 nm) are grown in situ on electrospinning polyacrylonitrile (PAN) microfibers (≈1.7 µm) containing urea-based linkers, followed by PAN removal via solvent extraction to obtain the hollow COF microfibers. The resultant COF FAGs possess ultralow density (14.1-15.5 mg cm-3) and hierarchical porosity that features both micro-, meso-, and macropores. Significantly, the unique interconnected structure composed of nanofibers and hollow microfibers endows the COF FAGs with unprecedented mechanical properties, which can fully recover at 50% strain and be compressed for 20 cycles with less than 5% stress degradation. Moreover, the aerogels exhibit excellent capacity for organic solvent absorption (e.g., chloroform uptake of >90 g g-1). This study opens new avenues for the design and fabrication of macroscopic COFs with excellent properties.

Thiocarbamide conversion-based nitrogen-rich covalent organic framework coatings for electro-enhanced solid-phase microextraction of bisphenols

Design and preparation of fiber coatings with excellent electrochemical performance and high polarity is significant for efficient extraction of polar targets in electro-enhanced solid-phase microextraction (EE-SPME). In this work, a combination strategy for structure regulation of covalent organic framework (COF) was proposed to fabricate a nitrogen-rich thiocarbamide linked COF coating (Thiocarbamide-TZ-DHTP) via molecular design and post-synthetic thiocarbamide conversion. The prepared COF coating possesses a large number of O, N, and S functional groups, which not only endow the coating with higher polarity but also significantly enhance its electrochemical performance. The COF coating was used for EE-SPME of polar bisphenols (BPs), demonstrating excellent enrichment efficiency and durability. Subsequently, coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS), a sensitive method was developed for determination of trace BPs. The established method possess wide linear ranges (2.0-800.0 ng L-1), good correlation coefficients (0.9985-0.9994) and low detection limits (0.1-2.0 ng L-1). Moreover, the established method had been successfully applied to detection of trace BPs in tea beverage with satisfactory recoveries (81.6 % to 118.6 %). This research provides a feasible pathway for preparing COF coating with excellent electrochemical performance and high polarity for EE-SPME.

Constructing 2D Phthalocyanine Covalent Organic Framework with Enhanced Stability and Conductivity via Interlayer Hydrogen Bonding as Electrocatalyst for CO2 Reduction

Fabricating COFs-based electrocatalysts with high stability and conductivity still remains a great challenge. Herein, 2D polyimide-linked phthalocyanine COF (denoted as NiPc-OH-COF) is constructed via solvothermal reaction between tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato nickel(II) and 2,5-diamino-1,4-benzenediol (DB) with other two analogous 2D COFs (denoted as NiPc-OMe-COF and NiPc-H-COF) synthesized for reference. In comparison with NiPc-OMe-COF and NiPc-H-COF, NiPc-OH-COF exhibits enhanced stability, particularly in strong NaOH solvent and high conductivity of 1.5 × 10-3 S m-1 due to the incorporation of additional strong interlayer hydrogen bonding interaction between the O-H of DB and the hydroxy "O" atom of DB in adjacent layers. This in turn endows the NiPc-OH-COF electrode with ultrahigh CO2-to-CO faradaic efficiency (almost 100%) in a wide potential range from -0.7 to -1.1 V versus reversible hydrogen electrode (RHE), a large partial CO current density of -39.2 mA cm-2 at -1.1 V versus RHE, and high turnover number as well as turnover frequency, amounting to 45 000 and 0.76 S-1 at -0.80 V versus RHE during 12 h lasting measurement.

Crystalline Porous Organic Cage Membranes Constructed Using Fortified Intermolecular Interactions for Molecular Sieving

Among the various types of materials with intrinsic porosity, porous organic cages (POCs) are distinctive as discrete molecules that possess intrinsic cavities and extrinsic channels capable of facilitating molecular sieving. However, the fabrication of POC membranes remains highly challenging due to the weak noncovalent intermolecular interactions and most reported POCs are powders. In this study, we constructed crystalline free-standing porous organic cage membranes by fortifying intermolecular interactions through the induction of intramolecular hydrogen bonds, which was confirmed by single-crystal X-ray analysis. To elucidate the driving forces behind, a series of terephthaldehyde building blocks containing different substitutions were reacted with flexible triamine under different conditions via interfacial polymerization (IP). Furthermore, density functional theory (DFT) calculations suggest that intramolecular hydrogen bonding can significantly boost the intermolecular interactions. The resulting membranes exhibited fast solvent permeance and high rejection of dyes not only in water, but also in organic solvents. In addition, the membrane demonstrated excellent performance in precise molecular sieving in organic solvents. This work opens an avenue to designing and fabricating free-standing membranes composed of porous organic materials for efficient molecular sieving.

Metalated covalent organic frameworks as efficient catalysts for multicomponent tandem reactions

Multicomponent tandem reactions have become indispensable synthetic methods due to their economic advantages and efficient usage in natural products and drug synthesis. The emergence of metalated covalent organic frameworks (MCOFs) has opened up new opportunities for the advancement of multicomponent tandem reactions. In contrast to commonly used homogeneous transition metal catalysts, MCOFs possess regular porosity, high crystallinity, and rich metal chelation sites that facilitate the uniform distribution and anchoring of metals within their cavities. Thus, they show extremely high activity and have recently been widely employed as catalysts for multicomponent tandem reactions. It is timely to conduct a review of MCOFs in multicomponent tandem reactions, in order to offer guidance and assistance for the synthesis of MCOF catalysts and their application in multicomponent tandem reactions. This review provides a comprehensive overview of the design and synthesis of MCOFs, their application and progress in multicomponent tandem reactions, and the primary challenges encountered during their current development with the aim of contributing to the promotion of the field.

Photosensitizing metal covalent organic framework with fast charge transfer dynamics for efficient CO2 photoreduction

Designing artificial photocatalysts for CO2 reduction is challenging, mainly due to the intrinsic difficulty of making multiple functional units cooperate efficiently. Herein, three-dimensional metal covalent organic frameworks (3D MCOFs) were employed as an innovative platform to integrate a strong Ru(ii) light-harvesting unit, an active Re(i) catalytic center, and an efficient charge separation configuration for photocatalysis. The photosensitive moiety was precisely stabilized into the covalent skeleton by using a rational-designed Ru(ii) complex as one of the building units, while the Re(i) center was linked via a shared bridging ligand with an Ru(ii) center, opening an effective pathway for their electronic interaction. Remarkably, the as-synthesized MCOF exhibited impressive CO2 photoreduction activity with a CO generation rate as high as 1840 μmol g-1 h-1 and 97.7% selectivity. The femtosecond transient absorption spectroscopy combined with theoretical calculations uncovered the fast charge-transfer dynamics occurring between the photoactive and catalytic centers, providing a comprehensive understanding of the photocatalytic mechanism. This work offers in-depth insight into the design of MCOF-based photocatalysts for solar energy utilization.

Metal-organic framework (MOF)/C-dots and covalent organic framework (COF)/C-dots hybrid nanocomposites: Fabrications and applications in sensing, medical, environmental, and energy sectors

Developing new hybrid materials is critical for addressing the current needs of the world in various fields, such as energy, sensing, health, hygiene, and others. C-dots are a member of the carbon nanomaterial family with numerous applications. Aggregation is one of the barriers to the performance of C-dots, which causes luminescence quenching, surface area decreases, etc. To improve the performance of C-dots, numerous matrices including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and polymers have been composited with C-dots. The porous crystalline structures, which are constituents of metal nodes and organic linkers (MOFs) or covalently attached organic units (COFs) provide privileged features such as high specific surface area, tunable structures, and pore diameters, modifiable surface, high thermal, mechanical, and chemical stabilities. Also, the MOFs and COFs protect the C-dots from the environment. Therefore, MOF/C-dots and COF/C-dots composites combine their features while retaining topological properties and improving performances. In this review, we first compare MOFs with COFs as matrices for C-dots. Then, the recent progress in developing hybrid MOFs/C-dots and COFs/C-dots composites has been discussed and their applications in various fields have been explained briefly.

Panchromatic Light-Harvesting Three-Dimensional Metal Covalent Organic Frameworks for Boosting Photocatalysis

Constructing artificial photocatalysts with panchromatic solar energy utilization remains an appealing challenge. Herein, two complementary photosensitizers, [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) and porphyrin dyes, have been cosensitized in metal covalent organic frameworks (MCOFs), resulting in the MCOFs with strong light absorption covering the full visible spectrum. Under panchromatic light irradiation, the cosensitized MCOFs exhibited remarkable photocatalytic H2 evolution with an optimum rate of up to 33.02 mmol g-1 h-1. Even when exposed to deep-red light (λ = 700 ± 10 nm), a commendable H2 production (0.79 mmol g-1 h-1) was still obtained. Theoretical calculation demonstrated that the [Ru(bpy)3]2+ and porphyrin modules in our MCOFs have a synergistic effect to trigger an interesting dual-channel photosensitization pathway for efficient light-harvesting and energy conversion. This work highlights the potential of combining multiple PSs in MCOFs for panchromatic photocatalysis.

A wafer scale thin film of ultra-small Sc2O3 nanocrystals on a 2D COF with high rigidity

Scandium oxide (Sc2O3) has a wide range of applications in metallurgy, chemical industry, electronics and many other high-tech fields. However, most Sc2O3 materials exist in the powder or bulk form, while nanostructured Sc2O3 has rarely been reported as there is a lack of a common method to control its dimensionality, hindering the understanding of new properties and potential applications of nano-Sc2O3 materials. In this paper, we establish a procedure to synthesize a two-dimensional (2D) Sc2O3-covalent organic framework (COF) composite film where the crystal size of Sc2O3 domains is as small as ∼3 nm. The composite film is prepared by a Schiff base condensation reaction at the sharp n-pentane/water interface using a combination of surfactant-monolayer-assisted interfacial synthesis and laminar assembly polymerization methods. Then the conditions of nucleation and uniform film formation of the 2D Sc2O3/COF are explored further. Meanwhile, an atomic force microscopy indentation test shows that the material has a high Young's modulus of 89.1 ± 3.8 GPa, which is much higher than those of the majority of reported 2D polymer materials. We further extended this synthesis method to the preparation of Yb2O3 (ytterbium oxide) and/or Er2O3 (erbium oxide)-incorporated 2D COF composite films, verifying the universality of this strategy. This work provides an opportunity to vary the dimensionality of many kinds of metal oxides and explore the potential applications of low-dimensional Sc2O3 materials.

Covalent organic framework isomers with divergent photocatalytic properties

A pair of isomeric Py-BT-COFs with the same composition, but slightly different atomic arrangements, were designed and synthesized. The minute structural variations of the Py-BT-COF isomers generated significantly different redox and photophysical properties and correspondingly led to different photocatalytic manifestations in H2 evolution and rhodamine B degradation.

Structural Regulation of Covalent Organic Frameworks for Catalysis

ConspectusChemical reactions can be promoted at lower temperatures and pressures, thereby reducing the energy input, by introducing suitable catalysts. Despite its significance, the quest for efficient and stable catalysts remains a significant challenge. In this context, addressing the efficiency of catalysts stands out as a paramount concern. However, the challenges posed by the vague structure and limited tailorability of traditional catalysts would make it highly desirable to fabricate optimized catalysts based on the understanding of structure-activity relationships. Covalent organic frameworks (COFs), a subclass of fully designed crystalline materials formed by the polymerization of organic building blocks through covalent bonds have garnered widespread attention in catalysis. The precise and customizable structures of COFs, coupled with attributes such as high surface area and facile functional modification, make COFs attractive molecular platforms for catalytic applications. These inherent advantages position COFs as ideal catalysts, facilitating the elucidation of structure-performance relationships and thereby further improving the catalysis. Nevertheless, there is a lack of systematic emphasis on and summary of structural regulation at the atomic/molecular level for COF catalysis. Consequently, there is a growing need to summarize this research field and provide deep insights into COF-based catalysis to promote its further development.In this Account, we will summarize recent advances in structural regulation achieved in COF-based catalysts, placing an emphasis on the molecular design of the structures for enhanced catalysis. Considering the unique components and structural advantages of COFs, we present the fundamental principles for the rational design of structural regulation in COF-based catalysis. This Account starts by presenting an overview of catalysis and explaining why COFs are promising catalysts. Then, we introduce the molecular design principle for COF catalysis. Next, we present the following three aspects of the specific strategies for structural regulation of COF-based catalysts: (1) By designing different functional groups and integrating metal species into the organic unit, the activity and/or selectivity can be finely modulated. (2) Regulating the linkage facilitates charge transfer and/or modulates the electronic structure of catalytic metal sites, and accordingly, the intrinsic activity/selectivity can be further improved. (3) By means of pore wall/space engineering, the microenvironment surrounding catalytic metal sites can be modulated to optimize performance. Finally, the current challenges and future developments in the structural regulation of COF-based catalysts are discussed in detail. This Account provides insight into the structural regulation of COF-based catalysts at the atomic/molecular level toward improving their performance, which would provide significant inspiration for the design and structural regulation of other heterogeneous catalysts.

Solvent Effects on Metal-free Covalent Organic Frameworks in Oxygen Reduction Reaction

Binding water molecules to polar sites in covalent organic frameworks (COFs) is inevitable, but the corresponding solvent effects in electrocatalytic process have been largely overlooked. Herein, we investigate the solvent effects on COFs for catalyzing the oxygen reduction reaction (ORR). Our designed COFs incorporated different kinds of nitrogen atoms (imine N, pyridine N, and phenazine N), enabling tunable interactions with water molecules. These interactions play a crucial role in modulating electronic states and altering the catalytic centers within the COFs. Among the synthesized COFs, the one with pyridine N atoms exhibits the highest activity, with characterized by a half-wave potential of 0.78 V and a mass activity of 0.32 A mg-1, which surpass those from other metal-free COFs. Theoretical calculations further reveal that the enhanced activity can be attributed to the stronger binding ability of *OOH intermediates to the carbon atoms adjacent to the pyridine N sites. This work sheds light on the significance of considering solvent effects on COFs in electrocatalytic systems, providing valuable insights into their design and optimization for improved performance.

12 Connecting Sites Linked Three-dimensional Covalent Organic Frameworks with Intrinsic Non-interpenetrated shp Topology for Photocatalytic H2O2 Synthesis

Developing high connectivity (>8) three-dimensional (3D) covalent organic frameworks (COFs) towards new topologies and functions remains a great challenge owing to the difficulty in getting high connectivity organic building blocks. This however represents the most important step towards promoting the diversity of COFs due to the still limited dynamic covalent bonds available for constructing COFs at this stage. Herein, highly connected phthalocyanine-based (Pc-based) 3D COFs MPc-THHI-COFs (M=H2, Ni) were afforded from the reaction between 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine M(TAPc) (M=H2, Ni) and 5,5',5'',5''',5'''',5'''''-(triphenylene-2,3,6,7,10,11-hexayl)hexa(isophthalohydrazide) (THHI) with 12 connecting sites. Powder X-ray diffraction analysis together with theoretical simulations and transmission electron microscopy reveals their crystalline nature with an unprecedented non-interpenetrated shp topology. Experimental and theoretical investigations disclose the broadened visible light absorption range and narrow optical band gap of MPc-THHI-COFs. This in combination with their 3D nanochannels endows them with efficient photocatalysis performance for H2O2 generation from O2 and H2O via 2e- oxygen reduction reaction and 2e- water oxidation reaction under visible-light irradiation (λ >400 nm). This work provides valuable result for the development of high connectivity functional COFs towards diverse application potentials.

Sustainable remediation of pesticide pollutants using covalent organic framework - A review on material properties, synthesis methods and application

Covalent organic frameworks (COF) have emerged as a potential class of materials for a variety of applications in a wide number of sectors including power storage, environmental services, and biological applications due to their ordered and controllable porosity, large surface area, customizable structure, remarkable stability, and diverse electrical characteristics. COF have received a lot of attention in recent years in the field of environmental remediation, It also find its way to eliminate the emerging pollutant from the environment notably pesticide from polluted water. This review more concentrated on the application of COF in pesticide removal by modifying COF structure, COF synthesis and material properties. To increase the adsorption ability and selectivity of the material towards certain pesticides removal, the synthesis of COF involves organic linkers with various functional groups such as amine, carboxylic acid groups etc. The COF have a high degree of stability and endurance make them suitable for intermittent usage in water treatment applications. This review manifests the novel progress where modified COFs employed in a prominent manner to remove pesticides from polluted water. Some examples of COF application in the eradication of pesticides are triformyl phenylene framework functionalized with amine groups has capacity to remove up to 50 mg/l of Organophosphorus - chlorpyrifos. COF modified to improve their photocatalytic capacity to breakdown the pesticide under visible light irradiation. COF tetraphenyl ethylene linked with carboxylic acid group shows efficient photocatalytic degradation of 90% of organochlorine insecticide endosulfan when subjected to visible light. Atrazine and imidacloprid are reduced from 100 ppm to 1 ppm in aqueous solutions by COF based on high adsorption capacity. In addition, the strategies, technique, synthesis and functional group modification design of COF are discussed.

Synthesis of surface-modified porous polysulfides from soybean oil by inverse vulcanization and its sorption behavior for Pb(II), Cu(II), and Cr(III)

Guided by efficient utilization of natural plant oil and sulfur as low-cost sorbents, it is desired to tailor the porosity and composition of polysulfides to achieve their optimal applications in the management of aquatic heavy metal pollution. In this study, polysulfides derived from soybean oil and sulfur (PSSs) with improved porosity (10.2-22.9 m2/g) and surface oxygen content (3.1-7.0 wt.%) were prepared with respect to reaction time of 60 min, reaction temperature of 170 °C, and mass ratios of sulfur/soybean oil/NaCl/sodium citrate of 1:1:3:2. The sorption behaviors of PSSs under various hydrochemical conditions such as contact time, pH, ionic strength, coexisting cations and anions, temperature were systematically investigated. PSSs presented a fast sorption kinetic (5.0 h) and obviously improved maximum sorption capacities for Pb(II) (180.5 mg/g), Cu(II) (49.4 mg/g), and Cr(III) (37.0 mg/g) at pH 5.0 and T 298 K, in comparison with polymers made without NaCl/sodium citrate. This study provided a valuable reference for the facile preparation of functional polysulfides as well as a meaningful option for the removal of aquatic heavy metals.

Phenanthroline-Decorated Covalent Organic Framework for Catalytic Synthesis of 2-Aminobenzothiazoles in Water

2-Aminobenzothiazoles are widely used in the fields of pharmaceuticals and pesticides. Herein, we report a metal-free protocol for the preparation of 2-aminobenzothiazoles by a covalent organic framework (COF) catalyzed tandem reaction. In the presence of catalytic amount of phenanthroline-decorated COF (Phen-COF), a variety of 2-aminobenzothiazoles are obtained in excellent yields by the cross-coupling of 2-iodoanilines with isothiocyanates at room temperature in water. In addition, the COF-catalyst is very stable and can be reused at least seven times without loss of its catalytic activity.

Pd NP-loaded covalent organic framework for pH-switched Pickering emulsion catalytic dechlorination

Quinoline carboxylic acid-linked and Pd nanoparticle (NP)-loaded COF nanospheres were constructed via a three-component one-pot Doebner reaction and post-synthetic metalation. The obtained Pd@DhaTAPB-COOH solid stabilizer can greatly promote the pH-switched recyclable Pickering interfacial dechlorination reaction, which sheds light on the bright future of smart Pickering emulsion catalysis.

1D Covalent Organic Frameworks Triggering Highly Efficient Photosynthesis of H2 O2 via Controllable Modular Design

The topological diversity of covalent organic frameworks (COFs) enables considerable space for exploring their structure-performance relationships. In this study, we report a sequence of novel 1D COFs (EO, ES, and ESe-COF) with typical 4-c sql topology that can be interconnected with VIA group elements (O, S, and Se) via a modular design strategy. It is found that the electronic structures, charge delivery property, light harvesting ability, and hydrophilicity of these 1D COFs can be profoundly influenced by the bridge-linked atom ordinal. Finally, EO-COF, possessing the highest quantity of active sites, the longest lifetime of the active electron, the strongest interaction with O2 , and the lowest energy barrier of O2 reduction, exhibits exceptional photocatalytic O2 -to-H2 O2 activity under visible light, with a production rate of 2675 μmol g-1  h-1 and a high apparent quantum yield of 6.57 % at 450 nm. This is the first systematic report on 1D COFs for H2 O2 photosynthesis, which enriches the topological database in reticular chemistry and promotes the exploration of structure-catalysis correlation.

Charging modulation of the pyridine nitrogen of covalent organic frameworks for promoting oxygen reduction reaction

Covalent organic frameworks (COFs) are ideal templates for constructing metal-free catalysts for the oxygen reduction reaction due to their highly tuneable skeletons and controllable porous channels. However, the development of highly active sites within COFs remains challenging due to their limited electron-transfer capabilities and weak binding affinities for reaction intermediates. Herein, we constructed highly active catalytic centres by modulating the electronic states of the pyridine nitrogen atoms incorporated into the frameworks of COFs. By incorporating different pyridine units (such as pyridine, ionic pyridine, and ionic imidazole units), we tuned various properties including dipole moments, reductive ability, hydrophilicity, and binding affinities towards reaction intermediates. Notably, the ionic imidazole COF (im-PY-BPY-COF) exhibited greater activity than the neutral COF (PY-BPY-COF) and ionic pyridine COF (ion-PY-BPY-COF). Specifically, im-PY-BPY-COF demonstrated a half-wave potential of 0.80 V in 0.1 M KOH, outperforming other metal-free COFs. Theoretical calculations and in situ synchrotron radiation Fourier transform infrared spectroscopy confirmed that the carbon atoms in the ionic imidazole rings improved the activity by facilitating binding of the intermediate OOH* and promoting the desorption of OH*. This study provides new insights into the design of highly active metal-like COF catalysts.

Enhanced As-COF nanochannels as a high-capacity anode for K and Ca-ion batteries

Covalent organic frameworks can be used for next-generation rechargeable metal-ion batteries due to their controllable spatial and chemical architectures and plentiful elemental reserves. In this study, the arsenic-based covalent organic framework (As-COF) is designed by employing the geometrical symmetry of a semiconducting phosphazene-based covalent organic framework that uses p-phenylenediamine as a linker and hexachorocyclotriphosphazene as an As-containing monomer in a C3-like spatial configuration. The As-COF with engineered nanochannels demonstrates exceptional anodic behavior for potassium (K) and calcium (Ca) ion batteries. It exhibits a high storage capacity of about 914(2039) mA h g-1, low diffusion barriers of 0.12(0.26) eV, low open circuit voltage of 0.23(0.18) V, and a minimal volume expansion of 2.41(2.32)% for K (Ca) ions. These attributes collectively suggest that As-COF could significantly advance high-capacity rechargeable batteries.

Ionic Liquid-Mediated Dynamic Polymerization for Facile Aqueous-Phase Synthesis of Enzyme-Covalent Organic Framework Biocatalysts

Utilizing covalent organic framework (COF) as a hypotoxic and porous scaffold to encapsulate enzyme (enzyme@COF) has inspired numerous interests at the intersection of chemistry, materials, and biological science. In this study, we report a convenient scheme for one-step, aqueous-phase synthesis of highly crystalline enzyme@COF biocatalysts. This facile approach relies on an ionic liquid (2 μL of imidazolium ionic liquid)-mediated dynamic polymerization mechanism, which can facilitate the in situ assembly of enzyme@COF under mild conditions. This green strategy is adaptive to synthesize different biocatalysts with highly crystalline COF "exoskeleton", as well evidenced by the low-dose cryo-EM and other characterizations. Attributing to the rigorous sieving effect of crystalline COF pore, the hosted lipase shows non-native selectivity for aliphatic acid hydrolysis. In addition, the highly crystalline linkage affords COF "exoskeleton" with higher photocatalytic activity for in situ production of H2 O2 , enabling us to construct a self-cascading photo-enzyme coupled reactor for pollutants degradation, with a 2.63-fold degradation rate as the poorly crystalline photo-enzyme reactor. This work showcases the great potentials of employing green and trace amounts of ionic liquid for one-step synthesis of crystalline enzyme@COF biocatalysts, and emphasizes the feasibility of diversifying enzyme functions by integrating the reticular chemistry of a COF.

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.

Single-Atom Catalysts on Covalent Organic Frameworks for Energy Applications

Single-atom catalysts (SACs) have been investigated and applied to energy conversion devices. However, issues of metal agglomeration, low metal loading, and substrate stability have hindered realization of the SACs' full potential. Recently, covalent organic framework (COF)-based SACs have emerged as promising materials to enable highly efficient catalytic reactions. Here, we summarize the representative COF-based SACs and their wide application in clean energy devices and conversion reactions, such as hydrogen evolution reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, and oxygen evolution reaction. Based on their catalysis conditions, these reactions are categorized into photocatalyzed and electrocatalyzed reactions. We also summarize their design strategies, including heteroatom inclusion, donor-acceptor pairs, pore engineering, interface engineering, etc. Although COF-based SACs are promising, more efforts, such as linkage engineering, functional groups, ionization, multifunctional sites for cocatalyzed systems, etc., could improve them to be the ideal SAC materials. At the end, we provide our perspectives on where the field will proceed in the next 5 years.

Nanoscale Covalent Organic Framework with Staggered Stacking of Phthalocyanines for Mitochondria-Targeted Photodynamic Therapy

Phthalocyanine photosensitizers (PSs) have shown promise in fluorescence imaging and photodynamic therapy (PDT) of malignant tumors, but their practical application is limited by the aggregation-induced quenching (AIQ) and inherent photobleaching of PSs. Herein, we report the synthesis of a two-dimensional nanoscale covalent organic framework (nCOF) with staggered (AB) stacking of zinc-phthalocyanines (ZnPc), ZnPc-PI, for fluorescence imaging and mitochondria-targeted PDT. ZnPc-PI isolates and confines ZnPc PSs in the rigid nCOF to reduce AIQ, improve photostability, enhance cellular uptake, and increase the level of reactive oxygen species (ROS) generation via mitochondrial targeting. ZnPc-PI shows efficient tumor accumulation, which allowed precise tumor imaging and nanoparticle tracking. With high cellular uptake and tumor accumulation, intrinsic mitochondrial targeting, and enhanced ROS generation, ZnPc-PI exhibits potent PDT efficacy with >95% tumor growth inhibition on two murine colon cancer models without causing side effects.

Tunable Band Engineering Management on Perovskite MAPbBr3 /COFs Nano-Heterostructures for Efficient S-S Coupling Reactions

Efficient artificial photosynthesis of disulfide bonds holds promises to facilitate reverse decoding of genetic codes and deciphering the secrets of protein multilevel folding, as well as the development of life science and advanced functional materials. However, the incumbent synthesis strategies encounter separation challenges arising from leaving groups in the ─S─S─ coupling reaction. In this study, according to the reaction mechanism of free-radical-triggered ─S─S─ coupling, light-driven heterojunction functional photocatalysts are tailored and constructed, enabling them to efficiently generate free radicals and trigger the coupling reaction. Specifically, perovskites and covalent organic frameworks (COFs) are screened out as target materials due to their superior light-harvesting and photoelectronic properties, as well as flexible and tunable band structure. The in situ assembled Z-scheme heterojunction MAPB-M-COF (MAPbBr3 = MAPB, MA+ = CH3 NH2 + ) demonstrates a perfect trade-off between quantum efficiency and redox chemical potential via band engineering management. The MAPB-M-COF achieves a 100% ─S─S─ coupling yield with a record photoquantum efficiency of 11.50% and outstanding cycling stability, rivaling all the incumbent similar reaction systems. It highlights the effectiveness and superiority of application-oriented band engineering management in designing efficient multifunctional photocatalysts. This study demonstrates a concept-to-proof research methodology for the development of various integrated heterojunction semiconductors for light-driven chemical reaction and energy conversion.

Two-Dimensional Conjugated Polymers: a New Choice For Organic Thin-Film Transistors

Organic thin-film transistors (OTFTs) as a vital component among transistors have shown great potential in smart sensing, flexible displays, and bionics due to their flexibility, biocompatibility and customizable chemical structures. Even though linear conjugated polymer semiconductors are common for constructing channel materials of OTFTs, advanced materials with high charge carrier mobility, tunable band structure, robust stability, and clear structure-property relationship are indispensable for propelling the evolution of OTFTs. Two-dimensional conjugated polymers (2DCPs), featured with conjugated lattice, tailorable skeletons, and functional porous structures, match aforementioned criteria closely. In this review, we firstly introduce the synthesis of 2DCP thin films, focusing on their characteristics compatible with the channels of OTFTs. Subsequently, the physics and operating mechanisms of OTFTs and the applications of 2DCPs in OTFTs are summarized in detail. Finally, the outlook and perspective in the field of OTFTs using 2DCPs are provided as well.

Tetraphenylethylene-Based Hydrogen-Bonded Organic Frameworks (HOFs) with Brilliant Fluorescence

By synergistically employing four key strategies: (I) introducing tetraphenylethylene groups as the central core unit with aggregation-induced emission (AIE) properties, (II) optimizing the π-conjugated length by extending the building block branches, (III) incorporating flexible groups containing ethylenic bonds, and (IV) applying crystal engineering to attain dense stacking mode and highly twisty conformation, we successfully synthesized a series of hydrogen-bonded organic frameworks (HOFs) exhibiting exceptional one/two-photon excited fluorescence. Notably, when utilizing the fluorescently superior building block L2, HOF-LIFM-7 and HOF-LIFM-8 exhibiting high quantum yields (QY) of 82.1 % and 77.1 %, and ultrahigh two-photon absorption (TPA) cross-sections of 148959.5 GM and 123901.1 GM were achieved. These materials were successfully employed in one and two-photon excited lysosome-targeting cellular imaging. It is believed that this strategy, combining building block optimization and crystal engineering, holds significant potential for guiding the development of outstanding fluorescent HOF materials.

A Nickel Anchored Covalent Organic Framework as Unimolecular Metallaphotocatalyst for Visible Light Driver C-P Bond Coupling Reaction

The urgent need to develop a sustainable and environmentally friendly method for synthesizing organophosphine compounds is underscored by their extensive applications in organic synthesis, coordination chemistry, medicinal chemistry, and photoelectric materials. Metalated covalent organic frameworks (MCOFs), which seamlessly integrate the inherent photo properties of COF with the catalytic capabilities of metal ions, offer an optimal material for efficient transformation of organics sustainably. In this study, we introduce a simple COF with nickel anchorages (Bpy-COF-NiCl2 ) as a unimolecular metallaphotocatalytic system for effective C-P bond formation. This heterogeneous photocatalyst exhibits superior catalytic performance, achieving yields of up to 95 %, and demonstrates broad substrate tolerance and functional group reactivity. Notably, the metallaphotocatalytic system has demonstrated the capability to process aryl bromides to produce the desired product, a feat not previously reported. Finally, the production and reusability test at the gram scale attests to its superior practicality for designing future organic cross-coupling reactions.

Superstructure-Induced Hierarchical Assemblies for Nanoconfined Photocatalysis

Most attempts to synthesize supramolecular nanosystems are limited to a single mechanism, often resulting in the formation of nanomaterials that lack diversity in properties. Herein, hierarchical assemblies with appropriate variety are fabricated in bulk via a superstructure-induced organic-inorganic hybrid strategy. The dynamic balance between substructures and superstructures is managed using covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) as dual building blocks to regulate the performances of hierarchical assemblies. Significantly, the superstructures resulting from the controlled cascade between COFs and MOFs create highly active photocatalytic systems through multiple topologies. Our designed tandem photocatalysis can precisely and efficiently regulate the conversion rates of bioactive molecules (benzo[d]imidazoles) through competing redox pathways. Furthermore, benzo[d]imidazoles catalyzed by such supramolecular nanosystems can be isolated in yields ranging from 70 % to 93 % within tens of minutes. The multilayered structural states within the supramolecular systems demonstrate the importance of hierarchical assemblies in facilitating photocatalytic propagation and expanding the structural repertoire of supramolecular hybrids.

Reticular framework materials for photocatalytic organic reactions

Photocatalytic organic reactions, harvesting solar energy to produce high value-added organic chemicals, have attracted increasing attention as a sustainable approach to address the global energy crisis and environmental issues. Reticular framework materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are widely considered as promising candidates for photocatalysis owing to their high crystallinity, tailorable pore environment and extensive structural diversity. Although the design and synthesis of MOFs and COFs have been intensively developed in the last 20 years, their applications in photocatalytic organic transformations are still in the preliminary stage, making their systematic summary necessary. Thus, this review aims to provide a comprehensive understanding and useful guidelines for the exploration of suitable MOF and COF photocatalysts towards appropriate photocatalytic organic reactions. The commonly used reactions are categorized to facilitate the identification of suitable reaction types. From a practical viewpoint, the fundamentals of experimental design, including active species, performance evaluation and external reaction conditions, are discussed in detail for easy experimentation. Furthermore, the latest advances in photocatalytic organic reactions of MOFs and COFs, including their composites, are comprehensively summarized according to the actual active sites, together with the discussion of their structure-property relationship. We believe that this study will be helpful for researchers to design novel reticular framework photocatalysts for various organic synthetic applications.

Engineering a molecular ruthenium catalyst into three-dimensional metal covalent organic frameworks for efficient water oxidation

The water oxidation reaction plays an important role in clean energy conversion, utilization, and storage, but mimicking the oxygen-evolving complex of photosystem II for designing active and stable water oxidation catalysts (WOCs) is still an appealing challenge. Here, we innovatively engineered a molecular ruthenium WOC as a metal complex building unit to construct a series of three-dimensional metal covalent organic frameworks (3D MCOFs) for realizing efficient oxidation catalysis. The resultant MCOFs possessed rare 3D interlocking structures with inclined interpenetration of two-dimensional covalent rhombic nets, and the Ru sites were periodically arranged in the crystalline porous frameworks. Impressively, these MCOFs showed excellent performance towards water oxidation (the O2 evolution rate is as high as 2830 nmol g-1 s-1) via the water nucleophilic attack pathway. Besides, the MCOFs were also reactive for oxidizing organic substrates. This work highlights the potential of MCOFs as a designable platform in integrating molecular catalysts for various applications.

Highly Enhancing CO2 Photoreduction by Metallization of an Imidazole-linked Robust Covalent Organic Framework

Converting CO2 into value-added chemicals to solve the issues caused by carbon emission is promising but challenging. Herein, by embedding metal ions (Co2+ , Ni2+ , Cu2+ , and Zn2+ ) into an imidazole-linked robust photosensitive covalent organic framework (PyPor-COF), effective photocatalysts for CO2 conversion are rationally designed and constructed. Characterizations display that all of the metallized PyPor-COFs (M-PyPor-COFs) display remarkably high enhancement in their photochemical properties. Photocatalysis reactions reveal that the Co-metallized PyPor-COF (Co-PyPor-COF) achieves a CO production rate as high as up to 9645 µmol g-1 h-1 with a selectivity of 96.7% under light irradiation, which is more than 45 times higher than that of the metal-free PyPor-COF, while Ni-metallized PyPor-COF (Ni-PyPor-COF) can further tandem catalyze the generated CO to CH4 with a production rate of 463.2 µmol g-1 h-1 . Experimental analyses and theory calculations reveal that their remarkable performance enhancement on CO2 photoreduction should be attributed to the incorporated metal sites in the COF skeleton, which promotes the adsorption and activation of CO2 and the desorption of generated CO and even reduces the reaction energy barrier for the formation of different intermediates. This work demonstrates that by metallizing photoactive COFs, effective photocatalysts for CO2 conversion can be achieved.

Coordination Polymers from an Amino-Functionalized Terphenyl-Tetracarboxylate Linker: Structural Multiplicity and Catalytic Properties

An amino-functionalized terphenyl-tetracarboxylic acid, 2'-amino-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H4tpta), was used as an adaptable linker to synthesize, under hydrothermal conditions, eight coordination polymers (CPs). The obtained products were formulated as [Co(μ6-H2tpta)]n (1), [Co(μ3-H2tpta)(2,2'-bipy)]n (2), [M3(μ6-Htpta)2(2,2'-bipy)2]n (M = Mn (3), Cd (4)), [Ni2(μ4-tpta)(phen)2(H2O)4]n (5), [Zn2(μ6-tpta)(phen)2]n (6), {[Zn2(μ6-tpta)(μ-4,4'-bipy)]·H2O}n (7), and [Zn2(μ6-tpta)(μ-H2biim)(H2O)2]n (8), wherein 2,2'-bipyridine (2,2'-bipy), 4,4'-bipyridine (4,4'-bipy), 1,10-phenanthroline (phen), or 2,2'-biimidazole (H2biim) are present as additional stabilizing ligands. The structural types of 1-8 vary from one-dimensional (1D) (2, 5) and two-dimensional (2D) (3, 4, 6) CPs to three-dimensional (3D) metal-organic frameworks (MOFs) (1, 7, and 8) with a diversity of topologies. The products 1-8 were investigated as catalysts in the Knoevenagel condensation involving aldehydes and active methylene derivatives (malononitrile, ethyl cyanoacetate, or tert-butyl cyanoacetate), leading to high condensation product yields (up to 99%) under optimized conditions. Various reaction conditions, substrate scope, and catalyst recycling were investigated. This work broadens the application of H4tpta as a versatile tetracarboxylate linker for the generation of diverse CPs/MOFs.

A Multifunctional Covalent Organic Framework Nanozyme for Promoting Ferroptotic Radiotherapy against Esophageal Cancer

Radiotherapy is inevitably accompanied by some degree of radiation resistance, which leads to local recurrence and even therapeutic failure. To overcome this limitation, herein, we report the room-temperature synthesis of an iodine- and ferrocene-loaded covalent organic framework (COF) nanozyme, termed TADI-COF-Fc, for the enhancement of radiotherapeutic efficacy in the treatment of radioresistant esophageal cancer. The iodine atoms on the COF framework not only exerted a direct effect on radiotherapy, increasing its efficacy by increasing X-ray absorption, but also promoted the radiolysis of water, which increased the production of reactive oxygen species (ROS). In addition, the ferrocene surface decoration disrupted redox homeostasis by increasing the levels of hydroxyl and lipid peroxide radicals and depleting intracellular antioxidants. Both in vitro and in vivo experiments substantiated the excellent radiotherapeutic response of TADI-COF-Fc. This study demonstrates the potential of COF-based multinanozymes as radiosensitizers and suggests a possible treatment integration strategy for combination oncotherapy.

Reactive oxygen nanobiocatalysts: activity-mechanism disclosures, catalytic center evolutions, and changing states

Benefiting from low costs, structural diversities, tunable catalytic activities, feasible modifications, and high stability compared to the natural enzymes, reactive oxygen nanobiocatalysts (RONBCs) have become dominant materials in catalyzing and mediating reactive oxygen species (ROS) for diverse biomedical and biological applications. Decoding the catalytic mechanism and structure-reactivity relationship of RONBCs is critical to guide their future developments. Here, this timely review comprehensively summarizes the recent breakthroughs and future trends in creating and decoding RONBCs. First, the fundamental classification, activity, detection method, and reaction mechanism for biocatalytic ROS generation and elimination have been systematically disclosed. Then, the merits, modulation strategies, structure evolutions, and state-of-art characterisation techniques for designing RONBCs have been briefly outlined. Thereafter, we thoroughly discuss different RONBCs based on the reported major material species, including metal compounds, carbon nanostructures, and organic networks. In particular, we offer particular insights into the coordination microenvironments, bond interactions, reaction pathways, and performance comparisons to disclose the structure-reactivity relationships and mechanisms. In the end, the future challenge and perspectives for RONBCs are also carefully summarised. We envision that this review will provide a comprehensive understanding and guidance for designing ROS-catalytic materials and stimulate the wide utilisation of RONBCs in diverse biomedical and biological applications.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

Current trends in the detection and removal of heavy metal ions using functional materials

The shortage of freshwater resources caused by heavy metal pollution is an acute global issue, which has a great impact on environmental protection and human health. Therefore, the exploitation of new strategies for designing and synthesizing green, efficient, and economical materials for the detection and removal of heavy metal ions is crucial. Among the various methods for the detection and removal of heavy ions, advanced functional systems including nanomaterials, polymers, porous materials, and biomaterials have attracted considerable attention over the past several years due to their capabilities of real-time detection, excellent removal efficiency, anti-interference, quick response, high selectivity, and low limit of detection. In this tutorial review, we review the general design principles underlying the aforementioned functional materials, and in particular highlight the fundamental mechanisms and specific examples of detecting and removing heavy metal ions. Additionally, the methods which enhance water purification quality using these functional materials have been reviewed, also current challenges and opportunities in this exciting field have been highlighted, including the fabrication, subsequent treatment, and potential future applications of such functional materials. We envision that this tutorial review will provide invaluable guidance for the design of functional materials tailored towards the detection and removal of heavy metals, thereby expediting the development of high-performance materials and fostering the development of more efficient approaches to water pollution remediation.

Six metal-organic architectures from a 5-methoxyisophthalate linker: assembly, structural variety and catalytic features

A methoxy-functionalized isophthalic acid, 5-methoxy isophthalic acid (H2mia), was used a versatile linker for assembling six new metal(ii) compounds under hydrothermal conditions. The obtained products were [Cu2(μ2-mia)2(phen)2(H2O)2]·2H2O (1), [Mn(μ3-mia)(phen)]n (2), [Co(μ2-mia)(2,2'-bipy)(H2O)]n·nH2O (3), [Co(μ3-mia)(μ2-4,4'-bipy)]n·nH2O (4), [Co(μ3-mia)(py)2]n (5), and [Cd(μ2-mia)(py)(H2O)2]n·nH2O (6), where phen(1,10-phenanthroline), 2,2'-bipy(2,2'-bipyridine), 4,4'-bipy(4,4'-bipyridine) or py(pyridine) were incorporated as auxiliary ligands. The crystal structures of 1-6 range from 0D (1) and 1D (2, 3, 5, 6) CPs to a 2D network (4) with a variety of topological types. The catalytic behavior of 1-6 was studied in the cyanosilylation reaction between trimethylsilyl cyanide and aldehydes, resulting in up to 99% yields of products under optimized conditions. Various reaction parameters as well as catalyst recycling and substrate scope were investigated. This study widens the use of H2mia as a versatile dicarboxylate linker for assembling a diversity of functional metal-organic architectures with remarkable structural features and catalytic properties.

Three dimensional cyclic trinuclear units based metal-covalent organic frameworks for electrochemical CO2RR

A three-dimensional metal-covalent organic framework (3D-MCOF) based on cyclic trinuclear units was synthesized using organic tetrahedral linkers and copper-based cyclic trinuclear complexes. The novel type of 3D-MCOF, named 3D-CTU-MCOF, with the ctn topology, is reported herein for the first time. Our study demonstrated enhanced electrocatalytic capacity for CO2 reduction reaction of 3D-CTU-MCOF compared to independent cyclic trinuclear units.

Synthesis of sp2 Carbon-Conjugated Covalent Organic Framework Thin-Films via Copper-Surface-Mediated Knoevenagel Polycondensation

sp2 carbon-conjugated covalent organic framework (sp2 c-COF) featured with high π-conjugation, high chemical stabilities, and designable chemical structures, are thus promising for applications including adsorption and separation, optoelectronic devices, and catalysis. For the most of these applications, large-area and continuous films are required. However, due to the needs of harsh conditions in the formation of CC bonds, classical interfacial methodologies are challenged in the synthesis of sp2 c-COFs films. Herein, a novel and robust interfacial method namely copper-surface-mediated Knoevenagel polycondensation (Cu-SMKP), is shown for scalable synthesis of sp2 c-COF films on various Cu substrates. Using this approach, large-area and continuous sp2 c-COF films could be prepared on various complicated Cu surfaces with thickness from tens to hundreds of nanometers. The resultant sp2 c-COF films on Cu substrate could be used directly as functional electrode for extraction of uranium from spiked seawater, which gives an exceptionally uptake capacity of 2475 mg g-1 . These results delineate significant synthetic advances in sp2 c-COF films and implemented them as functional electrodes for uranyl capture.

From Supramolecular Organic Cages to Porous Covalent Organic Frameworks for Enhancing Iodine Adsorption Capability by Fully Exposed Nitrogen-Rich Sites

In order to overcome the limitations of supramolecular organic cages for their incomplete accessibility of active sites in the solid state and uneasy recyclability in liquid solution, herein a nitrogen-rich organic cage is rationally linked into framework systems and four isoreticular covalent organic frameworks (COFs), that is, Cage-TFB-COF, Cage-NTBA-COF, Cage-TFPB-COF, and Cage-TFPT-COF, are successfully synthesized. Structure determination reveals that they are all high-quality crystalline materials derived from the eclipsed packing of related isoreticular two-dimensional frameworks. Since the nitrogen-rich sites usually have a high affinity toward iodine species, iodine adsorption investigations are carried out and the results show that all of them display an enhancement in iodine adsorption capacities. Especially, Cage-NTBA-COF exhibits an iodine adsorption capacity of 304 wt%, 14-fold higher than the solid sample packed from the cage itself. The strong interactions between the nitrogen-rich sites and the adsorbed iodine species are revealed by spectral analyses. This work demonstrates that, utilizing the reticular chemistry strategy to extend the close-packed supramolecular organic cages into crystalline porous framework solids, their inherent properties can be greatly exploited for targeted applications.

Modulating the Interlayer Stacking of Covalent Organic Frameworks for Efficient Acetylene Separation

Controllable modulation of the stacking modes of 2D (two-dimensional) materials can significantly influence their properties and functionalities but remains a formidable synthetic challenge. Here, an effective strategy is proposed to control the layer stacking of imide-linked 2D covalent organic frameworks (COFs) by altering the synthetic methods. Specifically, a modulator-assisted method can afford a COF with rare ABC stacking without the need for any additives, while solvothermal synthesis leads to AA stacking. The variation of interlayer stacking significantly influences their chemical and physical properties, including morphology, porosity, and gas adsorption performance. The resultant COF with ABC stacking shows much higher C2 H2 capacity and selectivity over CO2 and C2 H4 than the COF with AA stacking, which is not demonstrated in the COF field yet. Furthermore, the outstanding practical separation ability of ABC stacking COF is confirmed by breakthrough experiments of C2 H2 /CO2 (50/50, v/v) and C2 H2 /C2 H4 (1/99, v/v), which can selectively remove C2 H2 with good recyclability. This work provides a new direction to produce COFs with controllable interlayer stacking modes.

Study on Gas Sorption and Iodine Uptake of a Metal-Organic Framework Based on Curcumin

Medi-MOF-1 is a highly porous Metal-Organic framework (MOF) constructed from Zn(II) and curcumin. The obtained crystal was characterized using powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). A micrometer-sized crystal with similar morphology was successfully obtained using the solvothermal method. Thanks to its high surface area, good stability, and abound pores, the as-synthesized medi-MOF-1 could be used as a functional porous material to adsorb different gases (H₂, CO₂, CH₄, and N₂) and iodine (I₂). The activated sample exhibited a high I₂ adsorption ability of 1.936 g g^-1 at room temperature via vapor diffusion. Meanwhile, the adsorbed I₂ could be released slowly in ethanol, confirming the potential application for I₂ adsorption.

Sulfone-Modified Covalent Organic Frameworks Enabling Efficient Photocatalytic Hydrogen Peroxide Generation via One-Step Two-Electron O2 Reduction

Photocatalytic oxygen reduction reaction (ORR) offers a promising hydrogen peroxide (H2 O2 ) synthetic strategy, especially the one-step two-electron (2e- ) ORR route holds great potential in achieving highly efficient and selectivity. However, efficient one-step 2e- ORR is rarely harvested and the underlying mechanism for regulating the ORR pathways remains greatly obscure. Here, by loading sulfone units into covalent organic frameworks (FS-COFs), we present an efficient photocatalyst for H2 O2 generation via one-step 2e- ORR from pure water and air. Under visible light irradiation, FS-COFs exert a superb H2 O2 yield of 3904.2 μmol h-1  g-1 , outperforming most reported metal-free catalysts under similar conditions. Experimental and theoretical investigation reveals that the sulfone units accelerate the separation of photoinduced electron-hole (e- -h+ ) pairs, enhance the protonation of COFs, and promote O2 adsorption in the Yeager-type, which jointly alters the reaction process from two-step 2e- ORR to the one-step one, thereby achieving efficient H2 O2 generation with high selectivity.

Highly stable Ru-complex-based metal-covalent organic frameworks as novel type of electrochemiluminescence emitters for ultrasensitive biosensing

Developing novel types of high-performance electrochemiluminescence (ECL) emitters is of great significance for constructing ultrasensitive ECL sensors. Herein, a highly stable metal-covalent organic framework (MCOF), termed Ru-MCOF, has been devised and synthesized by employing a classic ECL luminophore, tris(4,4'-dicarboxylicacid-2,2'-bipyridyl)ruthenium(II) (Ru(dcbpy)₃²⁺), as building unit and applied as a novel ECL probe to construct an ultrasensitive ECL sensor for the first time. Impressively, the topologically ordered and porous architectures of the Ru-MCOF not only allow Ru(bpy)₃²⁺ units to precisely locate and homogeneously distribute in the skeleton via strong covalent bonds but also facilitate the transport of co-reactants and electrons/ions in channels to promote the electrochemical activation of both external and internal Ru(bpy)₃²⁺ units. All these features endow the Ru-MCOF with excellent ECL emission, high ECL efficiency, and outstanding chemical stability. As expected, the constructed ECL biosensor based on the Ru-MCOF as a high-efficiency ECL probe accomplishes the ultrasensitive detection of microRNA-155. Overall, the synthesized Ru-MCOF not only enriches the MCOF family but also displays excellent ECL performance and thus expands the application of MCOFs in bioassays. Considering the structural diversity and tailorability of MCOFs, this work opens a new horizon to design and synthesize high-performance ECL emitters, therefore paving a new way to develop highly stable and ultrasensitive ECL sensors and motivating further research on MCOFs.

Designing Single-Atom Active Sites on sp2 -Carbon Linked Covalent Organic Frameworks to Induce Bacterial Ferroptosis-Like for Robust Anti-Infection Therapy

With the threat posed by drug-resistant pathogenic bacteria, developing non-antibiotic strategies for eradicating clinically prevalent superbugs remains challenging. Ferroptosis is a newly discovered form of regulated cell death that can overcome drug resistance. Emerging evidence shows the potential of triggering ferroptosis-like for antibacterial therapy, but the direct delivery of iron species is inefficient and may cause detrimental effects. Herein, an effective strategy to induce bacterial nonferrous ferroptosis-like by coordinating single-atom metal sites (e.g., Ir and Ru) into the sp² -carbon-linked covalent organic framework (sp² c-COF-Ir-ppy₂ and sp² c-COF-Ru-bpy₂ ) is reported. Upon activating by light irradiation or hydrogen peroxide, the as-constructed Ir and Ru single-atom catalysts (SACs) can significantly expedite intracellular reactive oxygen species burst, enhance glutathione depletion-related glutathione peroxidase 4 deactivation, and disturb the nitrogen and respiratory metabolisms, leading to lipid peroxidation-driven ferroptotic damage. Both SAC inducers show potent antibacterial activity against Gram-positive bacteria, Gram-negative bacteria, clinically isolated methicillin-resistant Staphylococcus aureus (MRSA), and biofilms, as well as excellent biocompatibility and strong therapeutic and preventive potential in MRSA-infected wounds and abscesses. This delicate nonferrous ferroptosis-like strategy may open up new insights into the therapy of drug-resistant pathogen infection.

Recent progress in covalent organic frameworks for cancer therapy

Covalent organic frameworks (COFs) have gained tremendous interest in cancer therapy owing to their multifunctional properties, such as biocompatibility, tunable cavities, excellent crystallinity, ease of modification/functionalization, and high flexibility. These unique properties offer multiple benefits, such as high loading capacity, prevention from premature leakage, targeted delivery to the tumor microenvironment (TME), and release of therapeutic agents in a controlled manner, which makes them effective and excellent nanoplatforms for cancer therapeutics. In this review, we outline recent advances in using COFs as delivery system for chemotherapeutic agents, photodynamic therapy (PDT), photothermal therapy (PTT), sonodynamic therapy (SDT), cancer diagnostics, and combinatorial therapy for cancer therapeutics. We also summarize current challenges and future directions of this unique research field. Teaser: This review highlights recent advances in covalent organic frameworks as multifaceted nanoplatform with recent case studies for improving therapeutic outcomes for cancer therapeutics.

Experimental Validation and Computational Predictions Join Forces to Map Catalytic C-H Activation in Ferrocene Metalated Porous Organic Polymers

In recent times, a self-complementary balanced characteristic feature with the combination of both covalent bonds (structural stability) and open metal sites (single-site catalysis) introduced an advanced emerging functional nanoarchitecture termed metalated porous organic polymers (M-POPs). However, the development of M-POPs in view of the current interest in catalysis has been realized still in its infancy and remains a challenge for the years to come. In this work, we built benzothiazole-linked Fe-metalated porous organic polymer (Fc-Bz-POP) using ferrocene dicarboxaldehyde (FDC), 1,3,5-tris(4-aminophenyl) benzene (APB), and elemental sulfur (S₈) via a template-free, multicomponent, cost-effective one-pot synthetic approach. This Fc-Bz-POP is endowed with unique features including an extended network unit, isolated active sites, and catalytic pocket with a possible local structure, in which convergent binding sites are positioned in such a way that substrate molecules can be held in close proximity. Prospective catalytic application of this Fc-Bz-POP has been explored in executing catalytic allylic "C-H" bond functionalization of cyclohexene (CHX) in water at room temperature. Catalytic screening results identified that a superior performance with a CHX conversion of 95% and a 2-cyclohexene-1-ol selectivity (COL) of 80.8% at 4 h and 25 °C temperature has been achieved over Fc-Bz-POP, thereby addressing previous shortcomings of the other conventional catalytic systems. Comprehensive characterization understanding with the aid of synchrotron-based extended X-ray absorption fine structure (EXAFS) analysis manifested that the Fe atom with an oxidation state of +2 in our Fc-Bz-POP catalytic system encompasses a sandwich structural environment with the two symmetrical eclipsed cyclopentadienyl (Cp) rings, featuring nearest-neighbor (NN) Fe-C (≈2.05 Å) intramolecular bonds, as validated by the Fe L₃-edge EXAFS fitting result. Furthermore, in situ attenuated total reflection-infrared spectroscopy (ATR-IR) analysis data for liquid-phase oxidation of cyclohexene allow for the formulation of a molecular-level reaction mechanistic pathway with the involvement of specific reaction intermediates, which is initiated by the radical functionalization of the allyl hydrogen. A deep insight investigation from density functional theory (DFT) calculations unambiguously revealed that the dominant pathway from cyclohexene to 2-cyclohexene-1-ol is initiated by an allyl-H functionalization step accompanied by the formation of 2-cyclohexene-1-hydroperoxide species as the key reaction intermediate. Electronic properties obtained from DFT simulations via the charge density difference plot, Bader charge, and density of state (DOS) demonstrate the importance of the organic polymer frame structure in altering the electronic properties of the Fe site in Fc-Bz-POP, resulting in its high activity. Our contribution has great implications for the precise design of metalated porous organic polymer-based robust catalysts, which will open a new avenue to get a clear image of surface catalysis.

Ingenious Artificial Leaf Based on Covalent Organic Framework Membranes for Boosting CO2 Photoreduction

Covalent organic frameworks (COFs) hold the potential in converting CO₂ with water into value-added fuels and O₂ to save the deteriorating ecological environment. However, reaching high yield and selectivity is a grand challenge under metal-, photosensitizer-, or sacrificial reagent-free conditions. Here, inspired by microstructures of natural leaves, we designed triazine-based COF membranes with the integration of steady light-harvesting sites, efficient catalytic center, and fast charge/mass transfer configuration to fabricate a novel artificial leaf for the first time. Significantly, a record high CO yield of 1240 μmol g^-1 in a 4 h reaction, approximately 100% selectivity, and a long lifespan (at least 16 cycles) were achieved under gas-solid conditions without using any metal, photosensitizer, or sacrificial reagent. Unlike the existing knowledge, the chemical structural unit of triazine-imide-triazine and the unique physical form of the COF membrane are predominant for such a remarkable photocatalysis. This work opens a new pathway to simulating photosynthesis in leaves and may motivate relevant research in the future.