Combined Skeleton and Spatial Rigidification of AIEgens in 2D Covalent Organic Frameworks for Boosted Fluorescence Emission and Sensing of Antibiotics

Fluorescent selenium covalent organic framework sensor of ofloxacin antibiotics

As the main novel pollutants in water environment, antibiotics pose great threat to human-beings. It is of pivotal significance to develop sensitive and selective sensing materials to monitor them in natural environment. For this purpose, we design and synthesize Se-based covalent organic framework (TPE-BSD-COF). It showed excellent fluorescence quenching and linear relationship, rapid response, wide detection range, and low limit-of-detection (LOD) for ofloxacin. Most importantly, it demonstrated very good selectivity without response to other typical antibiotics. Besides, ofloxacin in real environment samples was detected and excellent recovery rates were obtained. We conducted in-depth structure-activity experiments and density-function-theory (DFT) theoretical studies to unearth the fluorescence quenching mechanism. Together, this work will provide new insights into the design of fluorescent COF sensors for the detection of various environmentally interested antibiotics pollutants.

Progress in the application of functionalized covalent organic framework for bioanalysis

As a new type of crystalline porous polymer materials, covalent organic frameworks (COFs) with their unique features such as large surface area, tunable pore sizes, strong π-π stacking effect and size exclusion effects, have attracted wide attention in the analytical field. Due to the lack of catalytically active metal centers in bare COFs, functionalized COFs that are hybridized or modified with nanomaterials improve reactive activation and show better analytical performance for a variety of detection scenarios with complex analytes. Herein, we focused on the functionalized COFs used in bioanalysis ranging from nucleic acids, peptides, and proteins, to microorganisms, and discussed the functionalization strategy and unique structures and properties applied in the different stages of biosensing and advantages compared to other hybrid materials. Finally, challenges and future research directions of functionalized COFs in bioanalysis are discussed.

A near-infrared emitting covalent organic framework with AIE characteristics for light-emitting diodes

By incorporating methyl groups to introduce steric hindrance and utilizing hydroxyl groups to establish intramolecular hydrogen bonds, we synthesized a covalent organic framework (COF) with aggregation-induced emission (AIE) behavior and near-infrared (NIR) luminescence (λem = 657 nm). The integration of the innovative COF with LED chips enabled the fabrication of high-quality red and white organic phosphor-converted light-emitting diodes (LEDs). This work provides a new way to explore COFs to construct low-cost, high-performance, and eco-friendly LED devices.

Integration of ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of tetracycline based on a novel Zn (II) functionalized magnetic covalent organic framework

BACKGROUND

Based on the low volatility and refractory nature of Tetracycline (TC), excessive use leads to its continuous accumulation in water environments, posing serious risks to the ecological environment and human health. Although a very limited number of nanomaterials capable of simultaneously detecting and removing TC have been fabricated, they generally exist issues associated with a single detection signal ("on" or "off") or low adsorption rates with low adsorption capacities. As a result, it is crucial to develop a reliable technique to achieve ratiometric detection as well as rapid and efficient removal of TC.

RESULTS

Herein, a novel Zn (II) Functionalized magnetic covalent organic framework (Fe3O4@COF@Zn) was created. As the role of a fluorescent probe, it had excellent characteristics of ratiometric (F529/F436), ultrafast response (1 min), and ultra-low detection limit (16 nM). As the role of an adsorbent, it demonstrated a high capacity of adsorption (414.94 mg/g) in the pH-neutral range, fast kinetics (10 min), desirable regeneration capability, and convenient magnetic separation. By theoretical and experimental analysis, the detection and adsorption mechanism for TC was systematically revealed. Moreover, as an attempt, Fe3O4@COF@Zn showed it potential for crop remediation by adsorbing TC-contaminated water.

SIGNIFICANCE

This work demonstrates the exceptional performance of Zn-functionalized fluorescent COF for ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of TC, thereby illustrating its significant potential for the rapid monitoring and treatment of TC contamination.

Rationally design a novel Zn-MOF for fluorescent detection of nitrofuran antibiotics: The synthesis, structure and sensing applications

Nitrofuran antibiotics (NFAs) residues in waterare a persistent concern for the public due to the potential threats they pose to human health and the environment. Therefore, efficient probes that are capable of detecting trace amounts of antibiotics in real water environments have become a top priority. Herein, a novel fluorescent Zn-MOF probe (MOF-1) was revealed for the highly selective and sensitive sensing of NFAs. MOF-1 was rationally constructed with Zn(NO3)2·6H2O, 5,5'-(anthracene-9,10-diyl) diisophthalic acid (H4ADIP) and 1,3-bis(imidazol-1-ylmethyl)-benzene (mbib) by using the solvothermal method. Fluorescence sensing experiments demonstrate that MOF-1 can function as a fluorescent sensor for selective, sensitive, and rapid detection of NFAs among 15 antibiotics including ciprofloxacin (CPFX), chloramphenicol (CAP), sulfonamides and NFAs. Fluorescence titration experiments indicated that MOF-1 exhibited remarkably low detection limits of 0.19 μM, 0.26 μM, and 0.34 μM for furazolidone (FZD), furaltadone (FDH) and nitrofurazone (NFZ), respectively. Meanwhile, MOF-1 was successfully employed for NFAs detection in real samples with the recoveries of 98.7 % - 104.1 %, and a relative standard deviation below 5.1 %. Moreover, the sensing mechanism could be ascribed to the synergistic effect between the internal filtering effect and photoinduced electron transfer according to the experiment results and DFT calculations. Additionally, test strips were prepared based on MOF-1 for point of care testing of NFAs.

Fast Synthesis of Olefin-Linked Covalent Organic Frameworks via Supercritically Solvothermal Polymerization

Covalent organic frameworks (COFs) are newly emerging yet rapidly developed porous crystalline polymeric materials, which feature topological designability, structural diversity, and porosity tunability. However, most of the reported COFs hitherto are prepared by a solvothermal method, which needs a long reaction time, especially for the olefin-linked COFs, which hinders their practical applications. Herein, we report the fast growth of olefin-linked COFs synthesized by the supercritical solvothermal method under supercritical carbon dioxide conditions. Via optimization of the reaction conditions, olefin-linked COFs are prepared within 6 h, which is period much shorter than that of the traditional solvothermal method. The as-obtained COFs feature two distinct morphologies, namely, spherical and rod-like. Interestingly, the rod-like crystal shows polarized light extinction and rebrightening phenomena, indicating the high crystallinity. After being doped with I2, the obtained I2@COFTMT-PA shows a Hall mobility of 1.94 cm2 V-1 S-1, indicating its potential applications in optoelectronics. This work expands the application of the supercritically solvothermal method to the fast growth of olefin-linked COFs and solves a long-standing challenge in chemical science, which opens up opportunities for basic research as well as practical applications of olefin-linked COFs and other polymeric materials.

Covalent Organic Framework-Involved Sensors for Efficient Enrichment and Monitoring of Food Hazards: A Systematic Review

The food safety issues caused by environmental pollution have posed great risks to human health that cannot be ignored. Hence, the precise monitoring of hazard factors in food has emerged as a critical concern for the food safety sector. As a novel porous material, covalent organic frameworks (COFs) have garnered significant attention due to their large specific surface area, excellent thermal and chemical stability, modifiability, and abundant recognition sites. This makes it a potential solution for food safety issues. In this research, the synthesis and regulation strategies of COFs were reviewed. The roles of COFs in enriching and detecting food hazards were discussed comprehensively and extensively. Taking representative hazard factors in food as the research object, the expression forms and participation approaches of COFs were explored, along with the effectiveness of corresponding detection methods. Finally, the development directions of COFs in the future as well as the problems existing in practical applications were discussed, which was beneficial to promote the application of COFs in food safety and beyond.

Fluorescent Porous Materials Based on Aggregation-induced Emission for Biomedical Applications

Fluorescent porous materials based on aggregation-induced emission (AIE) are growing into a sparkling frontier in biomedical applications. Exploring those materials represents a win-win integration and has recently progressed at a rapid pace, mainly benefiting from intrinsic advantages including tunable pore size and structure, strong guest molecule encapsulation ability, superior biocompatibility, and photophysical outcomes. With the great significance and rapid progress in this area, this review provides an integrated picture on AIE luminogen-based porous materials. It encompasses inorganic, organic, and inorganic-organic porous materials, exploring fundamental concepts and the relationship between AIE performance and material design and highlighting significant breakthroughs and the latest trends in biomedical applications. In addition, some critical challenges and future perspectives in the development of AIE luminogen-based porous materials are also discussed.

Hydrazone-linked covalent organic framework functionalized with cysteine as a fluorescence sensor and Exploration of paper chip for p-nitrophenol detection

The large use and emission of p-nitrophenol (p-NP) seriously pollute the environment and endanger human health. In this work, a hydrazone-linked fluorescent covalent organic framework (BATHz-COF) was simply synthesized at room temperature and covalently linked N-acetyl-L-cysteine (NALC) via the "thiol-ene" click reaction, where carboxyl groups were introduced to improve dispersion and fluorescence intensity. As a rapid, good selectivity and reusability fluorescence sensor, the obtained COF-NALC has been used for quantitative analysis of p-NP predicated on the internal filtering effect (IFE). Under optimal conditions, COF-NALC enabled quantitative detection of p-NP with a linear range of 5-50 μM and the detection limit was 1.46 μM. The application of COF-NALC to the detection of p-NP in river water samples was successful, and the satisfactory recoveries were 98.0%-109.3%. Furthermore, the fluorescent COF paper chips constructed by in situ growth were combined with a smartphone to build a visual platform for the quick and real-time detection of p-NP, providing an excellent illustration for the development of intelligent fluorescence sensing in environmental analysis.

Covalent organic frameworks-based materials for antibiotics fluorescence detection

Antibiotics play a vital role in safeguarding people's health since most bacterial infection can be efficiently controlled and cured by treating with suitable antibiotics. However, excessive use of antibiotics in husbandry and aquaculture leaded to the pollution of eco-environment. Thus, it is important to develop simple facile methods and effective functional materials for quick on-site analysis of antibiotics. Covalent organic frameworks (COFs), as a kind of porous crystalline covalent bond linked polymers, have demonstrated its power in multiple fields. Herein, we will discuss COFs-based materials utilized as antibiotics sensors with fluorescence method. For each sensor, we will mainly discuss the mechanism for antibiotics recognition, the preparation, characterization and fluorescence sensing performance of specific antibiotics. The mechanism to illustrate the interaction between sensors and antibiotics analytes would also be stressed.

A pH-regulated fluorescence covalent organic framework for quantitative water content detection in methanol

In this paper, we designed and synthesized a two-dimensional fluorescent covalent organic framework (TAPB-DMTP-COF) for the precise determination of H2O content in methanol. The COF was synthesized using two typical monomers by grinding method, which significantly reduced the synthesis time. By adjusting the pH value of the COF suspension to 4.0, the portion of the COF material structure is disrupted, thereby mitigating π-π stacking and resolving the aggregation-caused quenching (ACQ) effect. Consequently, the non-fluorescent TAPB-DMTP-COF exhibited blue-purple fluorescence emission in methanol. At the same time, it is observed that in the presence of H2O, there is a red shift in the maximum fluorescence emission peak of TAPB-DMTP-COF, which correlates with the H2O content within a specific range. Notably, this redshift demonstrates a linear relationship with H2O content from 4% to 80% in methanol. Our work presents novel insights for efficient analysis and detection of H2O content in methanol and could be used for H2O detection in other organic solvents.

Constructing Highly Emissive Covalent Organic Frameworks for Fe3+ Ion Detection via Wall Function

Covalent organic frameworks (COFs) represent a new type of crystalline porous polymers that possess pre-designed skeletons, uniform nanopores, and ordered π structure. These attributes make them well-suited for the design of light-emitting materials. However, the majority of COFs exhibits poor luminescence due to aggregation-caused quenching (ACQ), resulting from the strong interaction between adjacent layers. To break the limitation, the building units with three methoxy groups on the walls are used to construct TM-OMe-EBTHz-COF, which suppresses the ACQ effects to improve light-emitting activity of COF. The TM-OMe-EBTHz-COF exhibits a notable emission of yellow-green luminescence in the solid state, with a remarkably high absolute quantum yield of 21.1%. The methoxy groups and hydrazine linkage form three coordination sites, contributing to excellent performance in metal ions sensing. The TM-OMe-EBTHz-COF demonstrates high sensitivity and selectivity to Fe3+ ion. Importantly, the low detection limit is below 150 nanomolar, ranking it among the best-performing Fe3+ sensor systems.

Fabrication of nanofibrous membranes decorated with metal-organic frameworks for detection of pollutants in water

The environmental pollution caused by antibiotics, Fe3+ and MnO4- pollutants is becoming increasingly serious. Polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA) were used and decorated with metal-organic frameworks (MOFs) to fabricated three kinds of nanofibrous membranes (NFMs) with different shapes and sizes were prepared by electrospinning technology using in situ growth method and mixed spinning method. The structures and properties of the above three kinds of NFMs were characterized. Among them, PAN@Co/Mn-MOF-74 NFM prepared by in-situ growth method based on PAN was a kind of nano-fluorescent NFM sensor with uniform structure and good fluorescence performance. It showed unique specificity and excellent sensitivity in the detection of ORN, Fe3+ and MnO4-. Compared with previously reported functionalized MOFs, PAN@Co/Mn-MOF-74 NFM has a lower limit of detection (LOD). This study provides a feasible technical route for the preparation of nano-fluorescent NFMs and the targeted detection of trace metal ions and antibiotics.

Ultra-fast supercritically solvothermal polymerization for large single-crystalline covalent organic frameworks

Crystalline polymer materials, e.g., hyper-crosslinked polystyrene, conjugate microporous polymers and covalent organic frameworks, are used as catalyst carriers, organic electronic devices and molecular sieves. Their properties and applications are highly dependent on their crystallinity. An efficient polymerization strategy for the rapid preparation of highly or single-crystalline materials is beneficial not only to structure-property studies but also to practical applications. However, polymerization usually leads to the formation of amorphous or poorly crystalline products with small grain sizes. It has been a challenging task to efficiently and precisely assemble organic molecules into a single crystal through polymerization. To address this issue, we developed a supercritically solvothermal method that uses supercritical carbon dioxide (sc-CO2) as the reaction medium for polymerization. Sc-CO2 accelerates crystal growth due to its high diffusivity and low viscosity compared with traditional organic solvents. Six covalent organic frameworks with different topologies, linkages and crystal structures are synthesized by this method. The as-synthesized products feature polarized photoluminescence and second-harmonic generation, indicating their high-quality single-crystal nature. This method holds advantages such as rapid growth rate, high productivity, easy accessibility, industrial compatibility and environmental friendliness. In this protocol, we provide a step-by-step procedure including preparation of monomer dispersion, polymerization in sc-CO2, purification and characterization of the single crystals. By following this protocol, it takes 1-5 min to grow sub-mm-sized single crystals by polymerization. The procedure takes ~4 h from preparation of monomer dispersion and polymerization in sc-CO2 to purification and drying of the product.

Eu3+-Modified Covalent Organic Frameworks for the Detection of a Vinyl Chloride Monomer Exposure Biomarker

The vinyl chloride monomer (VCM), a common raw material in the plastics industry, is one of the environmental pollutants to which humans are mostly exposed. Thiodiglycolic acid (TDGA) in human urine is a specific biomarker of its exposure. TDGA plays an important role in understanding the relationships between exposure to the VCM and the identification of subgroups that are at increased risk for disease diagnosis. Therefore, its detection is of great significance. Here, we designed and established a ratiometric fluorescent sensor for TDGA by using Eu3+ as a bridge connecting the covalent organic framework (COF) and the energy donor molecule 2,6-dipicolinic acid (DPA) and named it DPA/Eu@PY-DHPB-COF-COOH. The sensor not only possesses the advantages of a ratiometric fluorescent sensor that can provide built-in self-calibration to correct a variety of target-independent factors but also presents high selectivity and high sensitivity. Currently, there are only a few reports on the detection of TDGA, and to the extent of our knowledge, this report is the first work on the detection of TDGA based on a COF system; so, it has an important reference value and lays a solid foundation for designing advanced sensors of TDGA.

Lanthanide Functionalized Covalent Organic Frameworks Hybrid Materials for Luminescence Responsive Chemical Sensing

Covalent organic frameworks (COFs) possess several unique features of structural and functional chemistry, together with other modular photophysical performance, which make them candidates for luminescence responsive chemical sensing. Lanthanide (Ln3+ ) functionalized COFs hybrid materials still keep the parent COFs' virtues and also embody the abundant multiple luminescence response with both COFs and Ln3+ ions or other guest species. In this review, the summary is highlighted on the lanthanide functionalized COFs hybrid materials and their relevant systems for luminescence responsive chemical sensing. It is subdivided into five sections involving the three main topics. Firstly, the basic knowledges of COFs materials related to the luminescence responsive chemical sensing are introduced (including three sections), involving the chemistry, application and post-synthetic modification (PSM) of COFs, the luminescence and luminescence responsive chemical sensing, and the luminescence responsive chemical sensing of non-lanthanide functionalized COFs hybrids materials. Secondly, the systematic progresses are outlined on the lanthanide functionalized COFs hybrid materials in luminescence responsive chemical sensing, which is the emphasis for this review. Finally, the conclusion and prospect are given.

Dual Molecular Oxygen Activation Sites on Conjugated Microporous Polymers for Enhanced Photocatalytic Formation of Benzothiazoles

Oxidative formation of high value compounds involving active oxygen species using heterogeneous polymeric photocatalysts has become a useful tool in catalysis. Controlling the interaction between the active sites on polymer photocatalysts and oxygen molecules is still challenging due to the rather large polymer backbone structure. Here, we design a triazine-containing donor acceptor-type conjugated microporous polymer (CMP) containing dual major active sites at F and N atoms for molecular oxygen activation. Introducing fluorine atoms on the CMP backbone led to a combined effect of enhanced adsorption and electron transfer of oxygen. Time-resolved photoluminescence, electronic paramagnetic resonance spectra, and DFT calculation revealed favorable absorption energy and electron transfer kinetics between the CMP and oxygen molecules, thus efficiently generating superoxide radicals (O₂^•-) and singlet oxygen (¹O₂) as main active oxygen species. The photocatalytic activity, selectivity, and reusability of the CMP was demonstrated by the photocatalytic formation of a variety of benzothiazoles.

Carbon-Carbon Linked Organic Frameworks: An Explicit Summary and Analysis

Organic frameworks with carbon-carbon (CC) linkage are an important class of materials owing to their outstanding chemical stability and extended π-electron delocalization resulting in unique optoelectronic properties. In the first part of this review article, the design principles for the bottom-up synthesis of 2D and 3D sp/sp² CC linked organic frameworks are summarized. Representative reaction methodologies, such as Knoevenagel condensation, Aldol condensation, Horner-Wadsworth-Emmons reaction, Wittig reaction, and coupling reactions (Ullmann, Suzuki, Heck, Yamamoto, etc.) are included. This is discussed in the context of their reaction mechanism, reaction dynamics, and whether and why resulting in an amorphous or crystalline product. This is followed by a discussion of different state-of-the art bottom-up synthesis methodologies, like solvothermal, interfacial, and solid-state synthesis. In the second part, the structure-property relationships in CC linked organic frameworks with representative examples of organocatalysis, photo(electro)catalysis, energy storage and conversion, magnetism, and molecular storage and separation are analyzed. The importance of linkage type, building blocks, topology, and crystallinity of the framework material in connection with the structure-property relationship is highlighted. Finally, brief concluding remarks are presented based on the key development of bottom-up synthetic methods and provide perspectives for future development in this field.

Phenylboronic acid conjugated poly(3,4-ethylenedioxythiophene) (PEDOT) coated Ag dendrite for electrochemical non-enzymatic glucose sensing

The fern leaf-like surface topography of poly(EDOT-PBA)/Ag/Cu/GCE increases the specific surface area of the sensor, thereby enhancing the glucose sensing performance.