Covalent Organic Polymers and Frameworks for Fluorescence-Based Sensors

An imine COF as a dual-functional fluorescent sensing platform for vitamin K1 and water

Luminescent covalent organic frameworks (LCOFs) with large π-conjugated system were a family of crystalline porous materials with promising applications. However, the actual application and quenching mechanisms of the LCOFs with dual-functionality remain poor understood. Here, a micro-mesoporous luminescent covalent organic framework (LCOF-DT) with high crystallinity and good stability was prepared by the solvothermal method using 1, 3, 5-tri-(4-aminophenyl) benzene and 2, 5-dihydroxyterephthalaldehyde as monomers through Schiff base condensation reaction. The LCOF-DT exhibited not only a good sensitivity and colorimetric visualization for water in conventional organic solvents over a relatively broad linear range (0 %-50 %) but also showed exceptional fluorescent recognition capability for vitamin K1, even in the presence of 17 different competing substrates. Additionally, a sensitive, specific, rapid, and practical fluorescent method for vitamin K1 detection in the commercially vitamin K1 tablets was developed. Based on the aforementioned research, designing covalent organic frameworks with multifunctional fluorescent response would be a tendency in the further application of detection technology.

Preparation of the conjugated hypercrosslinked polymers containing phenylenediamine and phenylenetriamine derivatives for fluorescent sensing of three nitrophenols

Hypercrosslinked polymers (HCPs) are the most promising porous organic polymers for large-scale production due to their easy preparation, extensive raw material source, good stability, and large specific surface area. However, due to the lack of extended conjugability, their application in fluorescence sensing is limited. Herein, three conjugated hypercrosslinked polymers (the conjugated HCPs: TPPDA-DMB, TDPAB-DMB, and MTDAB-DMB) were easily prepared by the Friedel-Craft arylation reactions with phenylenediamine or phenylenetriamine derivatives and p-dimethoxybenzene (DMB). The extended conjugated structures and the 3D networks give the conjugated HCPs excellent fluorescence properties and fluorescence sensing performance for nitrophenols. TPPDA-DMB can sense 2,4-dinitrophenol (DNP) and picric acid (PA) with KSV values of 1.31 × 104 and 1.43 × 104 L mol-1, TDPAB-DMB can sense PA and o-nitrophenol (o-NP) with KSV values of 9.97 × 103 and 7.54 × 103  L mol-1, and MTDAB-DMB can sense DNP and PA with KSV values of 2.42 × 103 and 1.01 × 104 L mol-1, respectively. Experiments and theoretical calculations show that the fluorescence quenching mechanisms of the nitrophenols to the conjugated HCPs include electron transfer and energy transfer processes.

Construction of carboxyl-functionalized hyper-cross-linked porous polymers using waste polystyrene for effective adsorption of phenolic contaminants

The extensive presence of phenolic organic contaminants (POCs) poses a serious threat to humans. Meanwhile, the upcycling/reusing of waste polystyrene to reduce the exponential growth of plastic pollution is a very important environmental issue. Addressing these demands, a series of carboxyl-functional hypercrosslinked polymers (labeled PP-HCPs) were constructed by knitting waste polystyrene with pyromellitic dianhydride at different ratios through a one-step Friedel-Crafts reaction for effective adsorption of POCs. Among the prepared PP-HCPs, PP-HCP2 displayed a large specific surface area with high adsorption capacity (37.3 mg g-1) for POCs. Using PP-HCP2 as solid phase extraction sorbent, six POCs were effectively extracted from water and peach drink samples, then subjected to high-performance liquid chromatography-ultraviolet detection. The method demonstrated good linearity in the range of 0.03-100.0 ng mL-1 for water samples and 0.06-100.0 ng mL-1 for peach drinks under optimum experimental conditions. At a signal-to-noise ratio of 3, low detection limits were found to be 0.01-0.10 ng mL-1 for water samples and 0.02-0.15 ng mL-1 for peach drinks. Good accuracy and repeatability were achieved with recoveries of 85.3-111.8 % and the relative standard deviations below 8.6 %. The PP-HCP2-based approach can be employed as a dependable and sensitive tool to detect POCs in water and peach drink samples. This work delivers a simple and economically viable approach to fabricate carboxyl-functional HCPs by converting waste foam into high-value-added sorbent, with great significance for sustainable development.

A Conjugated Porous Organic Polymer as a Metal-Free Bifunctional Electrocatalyst for Enhanced Water Splitting

A conjugated porous organic polymer (SMCOP-4) with imine linkage and triazine functional moiety was rationally designed and synthesized by an imine condensation reaction. The π-conjugated network of SMCOP-4 facilitates electron mobility, enhancing electrochemical activity. Metal-free electrocatalyst SMCOP-4 shows superior performance for HER and OER with a low overpotential of 139 mV and 295 mV, respectively, at 10 mA cm-2 current density and with small Tafel slopes in alkaline electrolytes. Along with the low overpotential values, the electrocatalyst is highly stable at electrochemical conditions. Further, density functional theory calculations were carried out to identify the most active sites in catalyzing the HER and OER on the SMCOP-4 catalyst.

Construction of Luminescent Three-Dimensional Covalent Organic Frameworks for Molecular Decoding of Wide Organic Compounds

Constructing highly conjugated three-dimensional covalent organic frameworks (3D COFs), particularly those with luminescent features, remains a significant challenge. In this work, we successfully synthesized a 3D COF, named 3D-Py-SP-COF, using a rigid and orthogonal spirobifluorene building block for the spatial 3D structure construction and planar pyrene as luminescent units. The incorporation of the pyrene and the unique rigid 3D network structure endow 3D-Py-SP-COF with fluorescent properties. The successful formation of this 3D COF was verified by FT-IR, solid-state 13C CP-MAS NMR. Structural simulations based on the experimental powder X-ray diffraction analysis revealed that 3D-Py-SP-COF adopted a two-fold interpenetrated pts topology. The highly conjugated porous framework and fluorescent nature allow precise detection and localization of more than two dozen volatile organic compounds (VOCs), including aromatics, alcohols, and other commonly encountered industrial VOCs.

A BODIPY-Containing Covalent Organic Framework as a Highly Porous Photosensitizer for Environmental Remediation and Pollutants Adsorption

The direct incorporation of borondipyrromethene (BODIPY) subunits into the structural backbone of covalent organic frameworks (COFs) gives facile access to porous photosensitizers but is still a challenging task. Here, we introduce β-ketoenamine-linked BDP-TFP-COF, which crystallizes in AA-stacking mode with hcb topology. A comprehensive characterization reveals high crystallinity and enhanced stability in a variety of solvents, excellent mesoporosity (SABET=1042 m2 g-1), broad light absorption in the visible region, and red emission upon the exfoliation of few-layer COF nanosheets. The versatility of multifunctional BODIPY-COFs is highlighted in various applications. Pollutants Bisphenol A (BPA, qmax=426 mg g-1) and Methylene Blue (MB, qmax=96 mg g-1) have been efficiently removed from H2O. Fluorescence quenching or enhancement of exfoliated BDP-TFP-COF nanosheets have been utilized for dual-mode sensing of MB or NEt3, respectively. Ultimately, the photosensitizing effect of the BODIPY units is retained in the COF. Thus, BPD-TFP-COF was established as a metal-free triplet photosensitizer, which efficiently oxidized a mustard gas simulant under visible light irradiation.

Interface engineering of supported palladium electrocatalyst with covalent organic polymer towards oxygen reduction reaction

Interface engineering is an important strategy to improve the oxygen reduction reaction (ORR) performance of metal-based electrocatalysts. However, how to develop efficient and abundant interface is still a challenge. Herein, the three-dimensional mesoporous metal oxide-supported Pd-based catalyst was prepared and its ORR activity was further improved through the interfacial modification with microporous covalent organic polymer. Due to the meso/microporous structure and optimized organic-inorganic interface, the as-obtained catalyst could provide abundant active sites and suitable electronic structure, which makes it as a superior catalyst toward alkaline ORR. The surface modified Pd catalyst shows an improved half-wave potential (E1/2) from 0.84 V to 0.86 V and an improved limiting current density (JL) from 5.8 mA cm-2 to 6.0 mA cm-2. Moreover, the developed catalyst has excellent methanol tolerance and stability during the long-time cycling. When it was used as cathodic electrocatalyst in zinc-air battery, a peak power density of 106 mW cm-2 could be achieved and the battery maintains excellent stability during cycling tests over 45 h, which is better than the benchmarked commercial Pt/C catalyst. This study provides an efficient interface engineering strategy for constructing active and stable electrocatalysts, which may be useful in ORR and other energy-related conversions.

A review of research progress on COF-based biosensors in pathogen detection

Despite the availability of various detection tools, the rapid identification and accurate detection of pathogens remain a major challenge in public health management. Covalent organic frameworks (COFs), which are crystalline conjugated organic polymers with considerable application potential, offer unique advantages in several fields owing to their highly ordered structure, large specific surface area, stable chemical properties, and tunable pore microenvironment. In recent years, with the rapid development of biosensing technology, COF application in the field of pathogen detection has attracted extensive attention. Herein, the properties, applications, and synthesis methods of COFs are briefly described, and the application types and basic principles of COFs in building an efficient and sensitive pathogen detection platform are emphatically discussed. Overall, we analyze the current challenges associated with COF-based biosensors in pathogen detection and look forward to their broad application prospects in biomedicine and public health in future.

Covalent organic frameworks in cancer theranostics: advancing biomarker detection and tumor-targeted therapy

In recent years, covalent organic frameworks (COFs) have garnered considerable attention in the field of onco-nanotechnology as a new type of nanoporous construct due to their promising physicochemical properties, ease of modification, and ability to be coupled with several moieties and therapeutic molecules. They can not only be used as biocompatible nanocarriers to deliver therapeutic payloads to the tumor zone selectively but can also be combined with a variety of therapeutic modalities to achieve the desired treatments. This review comprehensively presented recent achievements and progress in COF-based cancer diagnosis, detection, and cancer therapy to provide a better prospect for further research. Herein our primary emphasis lies on exploring the application of COFs as potential sensors for cancer-derived biomarkers that have received comparatively less attention in previous discussions. While the utilization of COFs in solid tumor therapy has faced significant challenges in scientific research and clinical applications, we reviewed the most promising features that underscore their potential in cancer theranostics.

Heavy-Atom-Free Covalent Organic Frameworks for Organic Room-Temperature Phosphorescence via Förster and Dexter Energy Transfer Mechanism

Covalent organic frameworks (COFs), with their accessible nanoscale porosity, selectable building blocks, and precisely engineered topology, offer unique benefits in the design of room-temperature phosphorescent (RTP) materials. However, their potential has been limited by phosphorescence quenching caused by interlayer π-π stacking interactions. This paper presents a novel strategy to enhance RTP in heavy-atom-free COFs by employing a donor-acceptor (D-A) system that leverages the Förster resonance energy transfer (FRET) and Dexter energy transfer (DET) mechanisms. Among the materials investigated, the best-performing COF exhibits a phosphorescence lifetime of 4.35 ms at room temperature. Spectral analysis, structural analysis, and theoretical calculations indicate the presence of intralayer FRET processes as well as interlayer DET processes within the D-A COF system. Potential anti-counterfeiting applications are explored by exploiting the unique phosphorescent properties of these materials. Additionally, the inherent permanent porosity of COFs presents new opportunities for future development and application. This strategy offers many promising prospects for advancing the RTP technology in COF materials and broadens their potential applications in various fields.

Covalently Coupling Carbon Quantum Dots for Photoluminescence Red Shift Response to pH

Conventional fluorescent pH sensors, despite offering high sensitivity and rapid response, are limited by their reliance on fluorescence intensity changes, hindering applications requiring precise wavelength control. Here, we present a pH sensing strategy based on cross-linked carbon quantum dots (CCL-CQDs) displaying a remarkable pH-dependent red shift in the fluorescence emission wavelength. Amino- and carboxyl-functionalized CQDs were synthesized via a one-step hydrothermal method and further assembled into CCL-CQDs through the condensation reaction between amino groups and glutaraldehyde. The CCL-CQDs displayed excellent pH sensitivity, with their fluorescence emission wavelength exhibiting a linear red shift upon increasing pH (from 2.29 to 7.16). The results of mechanism exploration revealed that H+ induced the cleavage of C═N bonds in the CCL-CQD structure, leading to the formation of -COOH groups and increased surface-oxidized carbon content. This enhanced oxidation generated more surface defects, triggering a wavelength shift in surface-state-related fluorescence emission. This study demonstrates the successful synthesis of pH-sensitive CCL-CQDs with an excellent fluorescence detection performance.

A Fluorescent Covalent Organic Cage for Ultrafast Detection of Picric Acid and HCl Vapor Sensing

Covalent organic cages (COCs) have recently gained massive attention owing to their solution processability and structural flexibility. Herein, we report an amine-linked fluorescent COC (COC2) synthesized by adopting dynamic covalent imine chemistry followed by imine bond reduction and characterized with different spectroscopic techniques. The COC2 was utilized for highly sensitive, selective, and ultrafast detection of picric acid at the nanomolar level. The fluorescence quenching efficiency of PA towards the COC2 is 98.6 %, with a detection limit of 2.7 nM. PA sensing with the COC2, coated on a TLC plate and paper strip, exhibited an outstanding fluorescence quenching property. Furthermore, the COC2 unveiled solid-state acidochromism upon exposure to HCl acid fumes and was transferred back to the original form on exposure to NH3 vapors.

Covalent Organic Framework as Selective Fluorescence Sensors for Cancer Inducing Volatile Organic Compounds

Certain volatile organic compounds (VOCs), such as formaldehyde, acetone, and ethanol, are overexpressed in some terminal diseases like cancer, diabetes, Alzheimer's, etc. Therefore, high-precision detection and quantification of VOCs is imperative for early diagnosis of such detrimental diseases. Non-invasive and accurate fluorescence-based detection of such analytes has garnered widespread attention. The inherent luminescent properties of covalent organic frameworks (COFs), resulting from their extensive π-conjugation, have made them suitable for sensing applications. Structural tunability and strong covalent linkers facilitate sensing by COFs. Appropriate choices of linker and skeletal units of the COF can help detect various biologically important analytes selectively. The most common linkers used in this regard is the imine linker, which can undergo excellent hydrogen bonding with different protic VOCs e. g., ethanol, methanol, etc. Besides imine detection, hydrogen bonding also proved useful for detection of aldehydes. Suitable combinations of donors and acceptors enable the COFs to have specific charge transfer interactions with many electron-rich and electron-poor VOCs. In this review, we have highlighted the syntheses of selective COFs incorporating linkers designed for sensing cancer-inducing VOCs. A detailed discussion of the interaction mechanisms between COFs and these VOCs is provided, along with examples from recent literature in this field.

Emissive Hydrazone-Linked Covalent Organic Frameworks as Highly Sensitive and Selective Sensor for the Hydrazine Detection

Covalent Organic Frameworks (COFs) exhibit a range of exceptional attributes, including notable porosity, outstanding stability, and a precisely tuned π-conjugated network, rendering them highly promising candidates for fluorescence sensors applications. In this study, the synthesis of two emissive hydrazone-linked COFs designed for hydrazine detection is presented. The partially conjugated structure of the hydrazone linkage effectively weakens the fluorescence quenching processes induced by aggregation. Additionally, the incorporation of flexible structural components further reduces conjugation, thereby enhancing luminescent efficiency. Remarkably, these COFs possess a significant abundance of heteroatoms, enabling distinctive interactions with hydrazine molecules, which in turn results in exceptional selectivity and sensitivity for hydrazine detection. The detection limit of these COFs reaches the nanomolar range, surpassing all previously reported COFs, thereby underscoring their superior performance in chemical sensing applications.

Anthracene-Based Endoperoxides as Self-Sensitized Singlet Oxygen Carriers for Hypoxic-Tumor Photodynamic Therapy

Singlet oxygen is a crucial reactive oxygen species (ROS) in photodynamic therapy (PDT). However, the hypoxic tumor microenvironment limits the production of cytotoxic singlet oxygen through the light irradiation of PDT photosensitizers (PSs). This restriction poses a major challenge in improving the effectiveness of PDT. To overcome this challenge, researchers have explored the development of singlet oxygen carriers that can capture and release singlet oxygen in physiological conditions. Among these developments, anthracene-based endoperoxides, initially discovered almost 100 years ago, have shown the ability to generate singlet oxygen controllably under thermal or photo stimuli. Recent advancements have led to the development of a new class of self-sensitized anthracene-endoperoxides, with potential applications in enhancing PDT effects for hypoxic tumors. This review discusses the current research progress in utilizing self-sensitized anthracene-endoperoxides as singlet oxygen carriers for improved PDT. It covers anthracene-conjugated small organic molecules, metal-organic complexes, polymeric structures, and other self-sensitized nano-structures. The molecular structural designs, mechanisms, and characteristics of these systems will be discussed. This review aims to provide valuable insights for developing high-performance singlet oxygen carriers for hypoxic-tumor PDT.

Emissive Covalent Organic Frameworks: Improved Fluorescence via Flexible Building Blocks and Selective Sensing of Nitroaromatic Explosives

2D covalent organic frameworks (COFs) are attractive for fluorescence sensing due to their lightweight, robust, and highly ordered porous structures. However, the highly conjugated structures between adjacent layers of covalent organic frameworks can often result in aggregation-caused quenching (ACQ) properties. Here, the study designs two flexible hydrazone-linked COFs to suppress ACQ effects, thereby enhancing their luminescent activities. Furthermore, the high density of nitrogen and oxygen atoms on these flexible walls serves as binding sites for hydrogen bonding interactions, indicating sensitivity and selectivity towards 2,4,6-trinitrophenol detection.

Sensitive and Discriminative Fluorescent Detection of Volatile Primary Aliphatic Diamine Vapors from Monoamines

The discriminative detection of volatile primary aliphatic diamines (VPADs) is a relevant and timely issue. This paper explores the distinctive optical features of H-type and J-type aggregates on paper-based (PB) films, namely H-PB and J-PB films, respectively, of a Lewis acidic Zn(salen)-type complex upon chemisorption of vapors of ditopic VPADs versus those of monotopic volatile amines. While volatile monotopic Lewis bases upon chemisorption give rise to mono-adducts accompanied by enhancement of the fluorescence, in contrast, VPADs act as ditopic bases forming di-adducts with distinct optical properties, leading to fluorescence quenching. This behavior enables the sensitive and discriminative detection of VPAD vapors from those of volatile monoamines. For example, for ethylenediamine (EDA), using J-PB films, sensitive detection is achieved with a LOD down to 6.6 ppm, lower than the OSHA permissible exposure limit of 10 ppm for EDA, and a linear dynamic range up to 100 ppm. Instead, H-PB films enable the detection of EDA vapors at higher ppm concentrations (up to 3000 ppm) with a linearity of up to 1000 ppm. Thus, the combination of both H-PB and J-PB films of the Zn(salen)-type complex represents a unique example of the sensitive and discriminative detection of EDA vapors in such a wide concentration range.

Diffusion limited synthesis of wafer-scale covalent organic framework films for adaptative visual device

Synthesizing high-crystalline covalent organic framework films is highly desired to advance their applications in two-dimensional optoelectronics, but it remains a great challenge. Here, we report a diffusion-limited synthesis strategy for wafer-scale uniform covalent organic framework films, in which pre-deposited 4,4',4″,4‴-(1,3,6,8-Tetrakis(4-aminophenyl) pyrene is encapsulated on substrate surface with a layer of covalent organic framework prepolymer. The polymer not only prevents the dissolution of precursor, but limits the reaction with terephthalaldehyde dissolved in solution, thereby regulating the polymerization process. The size depends on growth substrates, and 4-inch films have been synthesized on silicon chips. Their structure, thickness, patterning and crystallization degree can be controlled by adjusting building blocks and polymerization chemistries, and molybdenum disulfide have been used as substrates to construct vertical heterostructure. The measurements reveal that using covalent organic framework as a photosensitive layer, the heterojunction displays enhanced photoelectric performance, which can be used to simulate the adaptative function of visual system.

In Situ Fluorescent Visualization of the Interfacial Layer of Induced Crystallization in Polyvinyl Chloride

Despite the remarkable progress in the modification and application of polyvinyl chloride (PVC), developing processing aids for the induced crystallization of PVC and characterizing its interfacial layer remain challenges. Herein, we propose a new polymeric nucleating agent, polyamidea12-graft-styrene-maleic anhydride copolymer (PA12-g-SMA), which possesses high compatibility and crystallinity, effectively improving the crystallinity to 15.1%, the impact strength to 61.03 kJ/m2, and the degradation temperature of PVC to 267 °C through a single and straightforward processing step. Additionally, after the introduction of two different fluorescent sensors in PA12-g-SMA and PVC, the interfacial layer of the induced crystallization can be monitored in situ via a confocal laser scanning microscope (CLSM). This study highlights a rare strategy for significantly enhancing the physical properties of rigid PVC through simply adding a polymeric nucleating agent during processing, while also emphasizing the importance of visualizing the interfacial layer to understand various polymer crystallization processes.

Fabrication of Ag Nanoparticle-Embedded Covalent Organic Frameworks for Oil Gel with Long-Term Stability and High Lubrication Performance

In previous reports, covalent organic frameworks (COFs) have demonstrated significant potential as lubricant additives. Herein, we embedded Ag nanoparticles in the DT-COF (polycondensation polymer of 2,5-dihydroxyterephthalaldehyde and 4,4',4″-(1,3,5-triazine-2,4,6-triyl) trianiline) matrix via the ball milling method and utilized this composite (Ag@DT-COF) as an additive for supermolecule oil gel. The low molecular weight gelator effectively mitigates the dispersion challenges of COFs in lubricant oil, while the embedded Ag nanoparticles enhance the repairing effect and antipressure performance of the lubricant. The resulting Ag@DT-COF gel exhibits a reduction in the average friction coefficient and wear volume of base oil by 46.0% and 87.5%, respectively, and increases the load-carrying capacity to 750 N. The remarkable tribological properties are attributed to the easy adsorption of DT-COF, antiwear characteristic of Ag nanoparticles, and the gelator that ensures the long-term stability of oil gel.

Influence of Carbon-Nitride Dot-Emitting Species and Evolution on Fluorescence-Based Sensing and Differentiation

Carbon dots have attracted widespread interest for sensing applications based on their low cost, ease of synthesis, and robust optical properties. We investigate structure-function evolution on multiemitter fluorescence patterns for model carbon-nitride dots (CNDs) and their implications on trace-level sensing. Hydrothermally synthesized CNDs with different reaction times were used to determine how specific functionalities and their corresponding fluorescence signatures respond upon the addition of trace-level analytes. Archetype explosives molecules were chosen as a testbed due to similarities in substituent groups or inductive properties (i.e., electron withdrawing), and solution-based assays were performed using ratiometric fluorescence excitation-emission mapping (EEM). Analyte-specific quenching and enhancement responses were observed in EEM landscapes that varied with the CND reaction time. We then used self-organizing map models to examine EEM feature clustering with specific analytes. The results reveal that interactions between carbon-nitride frameworks and molecular-like species dictate response characteristics that may be harnessed to tailor sensor development for specific applications.

Construction of 2-azidacetic acid functionalized high-crystallinity fluorescent covalent organic framework: Applications in mitoxantrone and Fe3+ sensing and adsorption

Due to the dual functions of fluorescence detection and adsorption, fluorescent covalent organic frameworks (COFs) have attracted significant attention. However, common fluorescent COFs often exhibit unsatisfactory fluorescence properties and selectivity, coupled with poor solution dispersibility, which limit their effectiveness in detection and adsorption applications. In response, a novel post-modified fluorescent COF (named AZC-COF) was synthesized by connecting a fluorescent COF (COF-TB) with 2-azidacetic acid through a copper-catalyzed aide-alkyne cycloaddition (CuAAC) reaction. AZC-COF demonstrated excellent solution dispersibility and robust green fluorescence, boasting an absolute fluorescence quantum yield (QY) of 7.58%, which was 13.5 times higher than that of COF-TB. Furthermore, leveraging the active carboxylic acid and triazole sites, AZC-COF exhibited remarkable binding abilities for mitoxantrone (MIX) and Fe3+, enabling sensitive detection and efficient adsorption of them. In contrast, due to the absence of these functional sites, COF-TB showed poor detection and enrichment capabilities for MIX and Fe3+. The impressive detection and adsorption efficiencies of MIX and Fe3+ in environmental water, aquatic organism (fish) and plasma samples underscore the potential of AZC-COF as a detection-adsorption platform. Additionally, AZC-COF demonstrated low toxicity and hemolytic activity, alongside promising potential for cell imaging and detection of MIX and Fe3+, highlighting its considerable application prospect in biological systems.

Hydrazone-Linked Donor-Acceptor Covalent Organic Polymer as a Heterogeneous Photocatalyst for C-S Bond Formation

In the realm of solar energy utilization, there is a growing focus on designing and implementing effective photocatalytic systems, for the conversion of solar energy into valuable chemical fuels. The potential of Covalent Organic Polymers (COPs) as photocatalysts for visible-light-driven organic transformation has been widely investigated, positioning them as promising candidates in this field. In the design of COPs, introducing a donor-acceptor arrangement facilitates the transfer of electrons from the donor to the acceptor, creating a charge transfer complex and leading to enhanced conductivity and improved charge separation. Here we present a novel hydrazone-linked covalent organic polymer ETBC-PyHz containing TPE donor and pyridine acceptor. Utilizing this, an efficient method has been developed for an oxidative cross-coupling reaction involving C-S bond formation. This process involves arylhydrazines and arenethiols, and results in the production of unsymmetrical diaryl sulfides via the formation of aryl and thioarene radicals. This conversion holds significant importance because the byproducts produced during the process are nitrogen and water, making it environmentally benign.

A novel organic chromo-fluorogenic optical sensor for detecting chromium ions

Sensing trivalent chromium ion (Cr(III)) is widely applied in different areas, such as clinical analysis, marine, environmental monitoring, or even chemical industry applications. Cr(III) has a significant role in the physiological process of human life. It is classified as an essential micronutrient for living organisms. Herein, we developed and designed a novel optical Cr(III) ions sensor film. The investigated sensor has a relatively small dynamic range of 1.24 × 10-3 to 0.5 μM. We report a highly sensitive optical sensor film for Cr(III) ions based on diethyl 3,4-diaminothieno[2,3-b]thiophene-2,5-dicarboxylate (3D) probe. The optical characteristics of the chemical probe exhibit substantial emission at 460 nm under 354 nm excitation. Besides, the interaction of the Cr(III) ions with 3D involves a complex formation with a 2:1 (metal: ligand) ratio, which is convoyed by the main peak enhancement that centered at 460 nm of 3D, and the main peak is red-shifted to 480 nm. The easily discernible fluorescence enhancement effect is a defining characteristic of the complexation reaction between the 3D probe and Cr(III). On the basis of the substantial fluorescence mechanism caused by the formation of a (Cr(III)-3D complex, which inhibits the photo-induced electron transfer (PET) process, the devised optical sensor was proposed. This film exhibits exceptional sensitivity and selectivity due to its notable fluorescence properties, stock shift of less than 106 nm, and detection capabilities at a significantly low detection limit of 0.37 × 10-3 μM. The detection procedure is executed by utilizing a physiological pH medium (pH = 7.4) with a relative standard deviation RSDr (1 %, n = 3). In addition, the 3D sensor demonstrates a high degree of affinity for Cr(III), as determined by the calculation of its binding constant to be 1.40 × 106. We present an impressive optical sensor that is constructed upon a three-dimensional molecule.

Nitrogen-Rich Covalent Organic Polymer for Metal-Free Tandem Catalysis and Postmetalation-Actuated High-Performance Water Oxidation

Development of high-performing catalytic materials for selective and mild chemical transformations through adhering to the principles of sustainability remains a central focus in modern chemistry. Herein, we report the template-free assembly of a thermochemically robust covalent organic polymer (COP: 1) from 2,2'-bipyridine-5,5'-dicarbonyl dichloride and 2,4,6-tris(4-aminophenyl)triazine as [2 + 3] structural motifs. The two-dimensional (2D) layered architecture contains carboxamide functionality, delocalized π-cloud, and free pyridyl-N site-decked pores. Such trifunctionalization benefits this polymeric network exhibiting tandem alcohol oxidation-Knoevenagel condensation. In contrast to common metal-based catalysts, 1 represents a one of a kind metal-free alcohol oxidation reaction via extended π-cloud delocalization-mediated free radical pathway, as comprehensively supported from diverse control experiments. In addition to reasonable recyclability and broad substrate scope, the mild reaction condition underscores its applicability in benign synthesis of valuable product benzylidene malononitrile. Integration of 2,2'-bipyridyl units in this 2D COP favors anchoring non-noble metal ions to devise 1-M (M: Ni2+/ Co2+) that demonstrate outstanding electrochemical oxygen evolution reaction in alkaline media with high chronoamperometric stability. Electrochemical parameters of both 1-Co and 1-Ni outperform some benchmark, commercial, as well as a majority of contemporary OER catalysts. Specifically, the overpotential and Tafel slope (280 mV, 58 mV/dec) for 1-Ni is better than 1-Co (360 mV, 78 mV/dec) because of increased charge accumulation as well as a higher number of active sites compared to the former. In addition, the turnover frequency of 1-Ni is found to be 6 times higher than that of 1-Co and ranks among top-tier water oxidation catalysts. The results provide valuable insights in the field of metal-free tandem catalysis as well as promising electrochemical water splitting at the interface of task-specific functionality fuelling in polymeric organic networks.

Self-assembled dipeptide confined in covalent organic polymers for fluorescence sensing of tryptamine in fermented meat products

Diphenylalanine(FF)-Zn self-assembly (FS) confined in covalent organic polymers (FS@COPs) with efficient fluorescence was synthesized for fluorescence sensing of biogenic amines, which was one of the most important indicators for monitoring food freshness. FS@COPs combined excellent biodegradability of self-assembled dipeptide with chemical stability, porosity and targeted site recognition of COPs. With an optimal excitation wavelength of 360 nm and an optimal emission wavelength of 450 nm, FS@COPs could be used as fluorescence probes to rapidly visualize and highly sensitive determination of tryptamine (Try) within 15 min, and the linear range was from 40 to 900 μg L-1 with a detection limit of 63.08 μg kg-1. Importantly, the FS@COPs showed a high fluorescence quantum yield of 11.28%, and good stability, solubility, and selectivity, which could successfully achieve the rapid, accurate and highly sensitive identification of Try. Furthermore, we revealed the mechanism of FS@COPs for fluorescence sensing of targets. The FS@COPs system was applied to the fluorescence sensing of Try in real samples and showed satisfactory accuracy of 93.02%-105.25%.

Ionic Covalent Organic Framework as a Dual Functional Sensor for Temperature and Humidity

Visual sensing of humidity and temperature by solids plays an important role in the everyday life and in industrial processes. Due to their hydrophobic nature, most covalent organic framework (COF) sensors often exhibit poor optical response when exposed to moisture. To overcome this challenge, the optical response is set out to improve, to moisture by incorporating H-bonding ionic functionalities into the COF network. A highly sensitive COF, consisting of guanidinium and diformylpyridine linkers (TG-DFP), capable of detecting changes in temperature and moisture content is fabricated. The hydrophilic nature of the framework enables enhanced water uptake, allowing the trapped water molecules to form a large number of hydrogen bonds. Despite the presence of non-emissive building blocks, the H-bonds restrict internal bond rotation within the COF, leading to reversible fluorescence and solid-state optical hydrochromism in response to relative humidity and temperature.

Carbon dots and covalent organic frameworks based FRET immunosensor for sensitive detection of Escherichia coli O157:H7

The combination of carbon dots (CDs) with covalent organic frameworks (COFs) was used to design an innovative sensor based on fluorescence resonance energy transfer (FRET) for the detection of Escherichia coli O157:H7 (E. coli O157:H7) in food samples. Carbon dots were used as fluorescence donors, covalent organic frameworks as fluorescence acceptors. The antibody (Ab) specific to E. coli O157:H7 was used to form a CD-Ab-COF immunosensor by linking CDs and COFs. The antibody was specifically bound with E. coli O157:H7, which caused the connection between CDs and COFs to be interrupted, and the carbon dots exhibited fluorescence restoration. The sensor exhibited a linear detection range spanning from 0 to 106 CFU/mL, with the limit of detection (LOD) of 7 CFU/mL. The analytical performance of the developed immunosensor was evaluated using spiked food samples with different concentrations of E. coli O157:H7, validating the capability of assessing risks in food testing.

Tuning the Pyridine Units in Vinylene-Linked Covalent Organic Frameworks Boosting 2e- Oxygen Reduction Reaction

The N-doped carbon materials are supposed to be the efficient oxygen reduction reaction (ORR) catalysts with the undefined N-doped carbon ring groups. It is essential to well define the role of the nitrogen atoms of these carbon structures in active behavior. Even though, the covalent organic frameworks (COFs) with precise structures are well developed, but unable to exclude the polar linkages influence. This study presents a series of pyridine-containing COFs linked via nonpolar carbon-carbon double bonds (C = C). Their catalytic activity and selectivity for 2e- ORR are successfully modulated by locating the embedded pyridine nitrogen in the backbones through the linking modes of pyridine moieties within the frameworks. Such phenomena can be attributed to their different binding abilities toward O2, leading to the different binding strength of the intermediate OH* to the catalytic sites, also verified by the theoretical calculation. This work provides us a new insight to design high-efficiency ORR catalysts through the exact location of pyridine nitrogen.

Covalent organic frameworks (COFs) as carrier for improved drug delivery and biosensing applications

Porous organic frameworks (POFs) represent a significant subclass of nanoporous materials in the field of materials science, offering exceptional characteristics for advanced applications. Covalent organic frameworks (COFs), as a novel and intriguing type of porous material, have garnered considerable attention due to their unique design capabilities, diverse nature, and wide-ranging applications. The unique structural features of COFs, such as high surface area, tuneable pore size, and chemical stability, render them highly attractive for various applications, including targeted and controlled drug release, as well as improving the sensitivity and selectivity of electrochemical biosensors. Therefore, it is crucial to comprehend the methods employed in creating COFs with specific properties that can be effectively utilized in biomedical applications. To address this indispensable fact, this review paper commences with a concise summary of the different methods and classifications utilized in synthesizing COFs. Second, it highlights the recent advancements in COFs for drug delivery, including drug carriers as well as the classification of drug delivery systems and biosensing, encompassing drugs, biomacromolecules, small biomolecules and the detection of biomarkers. While exploring the potential of COFs in the biomedical field, it is important to acknowledge the limitations that researchers may encounter, which could impact the practicality of their applications. Third, this paper concludes with a thought-provoking discussion that thoroughly addresses the challenges and opportunities associated with leveraging COFs for biomedical applications. This review paper aims to contribute to the scientific community's understanding of the immense potential of COFs in improving drug delivery systems and enhancing the performance of biosensors in biomedical applications.

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.

Selective Capturing of the CO2 Emissions Utilizing Ecological (3-Mercaptopropyl)trimethoxysilane-Coated Porous Organic Polymers in Composite Materials

Capturing carbon dioxide (CO2) is still a major obstacle in the fight against climate change and the reduction of greenhouse gas emissions. To address this problem, we employed a simple Friedel-Crafts alkylation to investigate the effectiveness of porous organic polymers (POPs) based on triphenylamine (TPA) and trihydroxy aryl terms derived from chloranil (CH), designated as TPA-CH POP. We then treated the TPA-CH POP with (3-mercaptopropyl)trimethoxysilane (3-MPTS), forming a TPA-CH POP-SH nanocomposite to enhance CO2 capture. Utilizing FTIR, solid-state NMR, SEM, TEM, along with XPS techniques, the molecular makeup, morphological characteristics, as well as physical features of TPA-CH POP and the TPA-CH POP-SH nanocomposite were thoroughly explored. Upon scorching to 800 °C, the TPA-CH POP-SH nanocomposite demonstrated more thermal durability over TPA-CH POP, achieving a char yield of up to 71.5 wt.%. The TPA-CH POP-SH nanocomposite displayed a 2.5-times better CO2 capture, as well as a comparable adsorption capacity of 48.07 cm3 g-1 at 273 K. Additionally, we found that the TPA-CH POP-SH nanocomposite exhibited an improved CO2/nitrogen (N2) selectivity versus the original TPA-CH POP. Typical enthalpy changes for CO2 capture were somewhat increased by the 3-MPTS coating, indicating greater binding energies between CO2 molecules and the adsorbent surface. Our outcomes demonstrate that a TPA-CH POP composite coated with MPTS is a viable candidate for effective CO2 capture uses. Our findings encourage the investigation of different functional groups and optimization strategies.

Stranski-Krastanov Growth of Two-Dimensional Covalent Organic Framework Films

Insights into the formation mechanisms of two-dimensional covalent organic frameworks (2D COFs) at both the in-plane and interlayer levels are essential for improving material quality and synthetic methodology. Here, we report the controllable preparation of 2D COF films via on-surface synthesis and investigate the growth mechanism using atomic force microscopy. Monolayer, bilayer, and layer-plus-island multilayer COF films were successfully constructed on hexagonal boron nitride in a controlled manner. The porphyrin-based COF films grow in the Stranski-Krastanov mode, i.e., a uniform bilayer COF film can be formed through layer-by-layer growth in the initial stage followed by island growth starting from the third layer. Furthermore, fluorescence quenching caused by π-π stacking interactions between 2D COF neighboring layers was revealed. These results provide new perspectives on the synthesis of high-quality 2D COF films with controllable thickness and morphology, paving the way for a diverse range of applications.

Approaching Tryptophan-Derived Polynorbornene Fluorescent Chemosensors: Synthesis, Characterization, and Sensing Ability for Biomedical Applications as Biomarkers for Detecting Fe2+ Ions

We present a novel group of tryptophan (Trp)-based fluorescent polymeric probes synthesized via ring-opening metathesis polymerization (ROMP) of Trp-derived norbornene monomers. These probes, in mono- and disubstituted forms, incorporate amide and ester anchoring groups. The quantity of Trp substituents did not affect fluorescence selectivity but influenced quenching percentage. Poly-diamide-Trp, Poly-monoamide-Trp, Poly-diester-Trp, and Poly-monoester-Trp probes displayed selective detection of Fe2+ and Fe3+ ions with fluorescence on-off characteristics. Poly-diamide-Trp and Poly-monoamide-Trp exhibited a limit of detection (LOD) for Fe2+ and Fe3+ ions of 0.86-11.32 μM, while Poly-diester-Trp and Poly-monoester-Trp showed higher LODs (21.8-108.7 μM). These probes exhibited high selectivity over Fe2+, a crucial metal ion in the body known for its redox properties causing oxidative stress and cell damage. Cell cytotoxicity tests in various cell types confirmed biocompatibility. Additionally, Poly-diamide-Trp displayed excellent cell permeability and iron ion detection in EA.hy926 cells, suggesting potential for bioimaging and clinical applications.

Fluorescent covalent organic frameworks - promising bioimaging materials

Fluorescent covalent organic frameworks (COFs) have emerged as promising candidates for imaging living cells due to their unique properties and adjustable fluorescence. In this mini-review, we provide an overview of recent advancements in fluorescent COFs for bioimaging applications. We discuss the strategies used to design COFs with desirable properties such as high photostability, excellent biocompatibility, and pH sensitivity. Additionally, we explore the various ways in which fluorescent COFs are utilized in bioimaging, including cellular imaging, targeting specific organelles, and tracking biomolecules. We delve into their applications in sensing intracellular pH, reactive oxygen species (ROS), and specific biomarkers. Furthermore, we examine how functionalization techniques enhance the targeting and imaging capabilities of fluorescent COFs. Finally, we discuss the challenges and prospects in the field of fluorescent COFs for bioimaging in living cells, urging further research in this exciting area.

Size-Dependent Deformation and Competition H-Bond Site-Induced Individual Fluorescence Response of a Single-Crystal Three-Dimensional Covalent Organic Framework

Understanding the individual fluorescence response mechanism of covalent organic frameworks (COFs) at a single-crystal level is of great significance for the rational design of COF-based microsensors but unreachable because all previous COF-based sensors are performed with average fluorescence response behavior of various sized polycrystalline COFs. Herein, we design to explore the fluorescence response of a monodisperse single-crystal COF and further reveal the individual heterogeneity of the response mechanism. Three-dimensional single-crystal COF-301 (SCOF-301) with an intramolecular H-bond-induced excited-state intramolecular proton-transfer effect is selected as a proof-of-concept SCOF. With ethanol, benzene, and ammonia as model analytes, three different deformation and competition H-bond site-induced fluorescence response mechanisms related to crystal size are revealed. Small single particles of SCOF-301 (SSCOF-301) exhibit a more flexible structure, leading to the dominant role of deformation in the fluorescence response of small-sized SSCOF-301. The decreasing flexibility of SSCOF-301 with the increase of crystal size results in involvement of competition of the H-bond site to the fluorescence response besides deformation. Further increase of the crystal size makes the large-sized SSCOF-301 difficult to deform; thus, the competition of the H-bond site dominates the fluorescence response. This work provides a deep understanding of the individual fluorescence response mechanism of COFs to guide the design of a functional COF sensor with suitable size and mechanism for different structural analytes.

Tailoring ammonia capture in MOFs and COFs: A multi-scale and machine learning comprehensive investigation of functional group modification

Our study aims to examine the impact of ligand functionalization on the ammonia adsorption properties of MOFs and COFs, by combining multi-scale calculations with machine learning techniques. Density Functional Theory calculations were performed to investigate the interactions between ammonia (NH3) and a comprehensive set of 48 strategically chosen functional groups. In all of the cases, it is observed that functionalized rings exhibit a stronger interaction with ammonia molecule compared to unfunctionalized benzene, while -O2Mg demonstrates the highest interaction energy with ammonia (15 times stronger than the bare benzene). The trend obtained from the thorough DFT screening is verified via Grand Canonical Monte-Carlo calculations by employing interatomic potentials derived from quantum chemical calculations. Isosteric heat of adsorption plots provide a comprehensive elucidation of the adsorption process, and important insights can be taken for studies in fine-tuning materials for ammonia adsorption. Furthermore, a proof of concept machine learning (ML) analysis is conducted, which demonstrates that ML can accurately predict NH3 binding energies despite the limited amount of data. The findings derived from our multi-scale methodology indicate that the functionalization strategy can be utilized to guide synthesis towards MOFs, COFs, or other porous materials for enhanced NH3 adsorption capacity.

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.

Ionic Polyimine-Based Composite Membrane with Inductive and Complexation Synergistic Effects for Sensitive and On-Site Fluorescent Detection of Volatile Iodine

Along with the development of nuclear power, concerns about radioactive emissions and the potential for nuclear leakage have been widely raised, particularly of harmful iodine isotopes. However, as a significant component of nuclear air waste, the enrichment and detection of air-dispersed gaseous iodine remain a challenge. In this work, it is focused on developing an attraction-immobilization-detection strategy-based fluorescence method for the on-site detection of volatile iodine, by employing a photoluminescent ionic polyimine network-polyvinylpyrrolidone (IPIN-PVP) composite membrane. This strategy synergizes ion-induced dipole interactions from IPIN and complexation effects from PVP, allowing effective iodine enrichment and immobilization. As a result, the optimized IPIN-PVP membrane exhibits rapid response times of 5 s and a low detection limit of 4.087 × 10-8 m for gaseous iodine. It also introduces a portable handheld detection device that utilizes the composite membrane, offering a practical solution for real-time on-site detection of volatile iodine. This innovation enhances nuclear safety measures and disaster management by providing rapid and reliable iodine detection capabilities.

Designing State-of-the-Art Gas Sensors: From Fundamentals to Applications

Gas sensors are crucial in environmental monitoring, industrial safety, and medical diagnostics. Due to the rising demand for precise and reliable gas detection, there is a rising demand for cutting-edge gas sensors that possess exceptional sensitivity, selectivity, and stability. Due to their tunable electrical properties, high-density surface-active sites, and significant surface-to-volume ratio, nanomaterials have been extensively investigated in this regard. The traditional gas sensors utilize homogeneous material for sensing where the adsorbed surface oxygen species play a vital role in their sensing activity. However, their performance for selective gas sensing is still unsatisfactory because the employed high temperature leads to the poor stability. The heterostructures nanomaterials can easily tune sensing performance and their different energy band structures, work functions, charge carrier concentration and polarity, and interfacial band alignments can be precisely designed for high-performance selective gas sensing at low temperature. In this review article, we discuss in detail the fundamentals of semiconductor gas sensing along with their mechanisms. Further, we highlight the existed challenges in semiconductor gas sensing. In addition, we review the recent advancements in semiconductor gas sensor design for applications from different perspective. Finally, the conclusion and future perspectives for improvement of the gas sensing performance are discussed.

Transforming Thermally Activated Delayed Fluorescence to Room-Temperature Phosphorescence through Modulation of the Donor in Charge-Transfer Cocrystals

A cocrystallization strategy is used through incorporation of 1,2,4,5-tetracyanobenzene (TCNB) as an acceptor with halogen-substituent thioxanthone (TX) derivatives as donors. The resulting cocrystals TT-R (R = H, F, Cl, Br, or I) transform the thermally activated delayed fluorescence emission in the TT-H, TT-F, and TT-Cl cocrystals to room-temperature phosphorescence in the TT-Br and TT-I cocrystals. Definite crystal packing structures demonstrate a 1:1 alternative donor-acceptor stacking in the TT-H cocrystal, a 2:1 alternative donor-acceptor stacking in the TT-F and TT-Cl cocrystals, and a separate stacking of donor and acceptor in the TT-Br and TT-I cocrystals. A transformation law can be revealed that with an increase in atomic number from H, F, Cl, Br, to I, the cocrystals show the structural transformation of the number of aggregated TX-R molecules from monomers to dimers and finally to multimers. This work will facilitate an understanding of the effect of halogen substituents on the crystal packing structure and luminescence properties in the cocrystals.

Donor-Acceptor Interactions Enhanced Colorimetric Sensors for Both Acid and Base Vapor Based on Two-Dimensional Covalent Organic Frameworks

Due to the high surface area and uniform porosity of covalent organic frameworks (COFs), they exhibit superior properties in capturing and detecting even trace amounts of gases in the air. However, the COFs materials that possess dual detected functionality are still less reported. Here, an imine-based COF containing thiophene as a donor and triazine as an acceptor to form spatial-distribution-defined D-A structures was prepared. D-A system between thiophene and triazine facilitates the charge transfer process during the protonation process of the imine and the triazine units. The obtained COF exhibits simultaneous sensing ability toward both acidic and alkaline vapors with obvious colorimetric sensing functionality.

Synthesis of polymer dots as fluorescent nanoprobe for the detection of Ponceau 4R, an additive color abuse in food

Abusing organic dyes in industrial food products is an important issue in many countries. Rapid chemical sensing of these compounds can be of great importance during the industrial life of humans. In this work, we synthesized a new fluorescent polymer dot and successfully applied it as an optical probe for the detection of red color abuse in foodstuffs. Ponceau 4R is a red organic dye additive that is used in some foodstuffs such as tomato sauces or pastes. It is too hazardous to human health. Detection of such abusage is challenging. The development of π-conjugated polymer dots having a bright emission band at visible can be a promising probe for the detection of food color additives. A variety of methods and monomers were previously used for their synthesis. Here, the Suzuki Coupling method was employed. The limit of detection (LOD) of the method was obtained 16 nmol L-1 for the detection of Ponceau 4R.

Porous organic polymers-based fluorescent chemosensors for Fe(III) ions-a functional mimic of siderophores

Extended organic polymers such as amorphous Covalent Organic Polymers (COPs) and crystalline Covalent Organic Frameworks (COFs) are emerging functional polymeric materials that have recently been shown promises as luminescent materials for chemosensing applications. A wide variety of luminescence COPs and COFs have been synthesized and successfully used as fluorescence-sensing materials for hazardous environmental pollutants and toxic contaminants. This review exemplifies various COPs and COFs-based fluorescence sensors for selective sensing of Fe(III) ions. The fluorescence sensors are sorted according to their structural features and each section provides a detailed discussion on the synthesis and fluorescence sensing ability of different COPs and COFs towards Fe(III) ions. Also, this review highlights the limitations of the existing organic polymer-based chemosensors and future perspectives on translating COPs and COFs-based fluorescence sensors for the practical detection of Fe(III) ions.

Strategic design of a rare trigonal symmetric luminescent covalent organic framework by linker modification

We designed a trigonal symmetric imine-linked covalent organic framework (COF), TFPC-DAB, with control over the angularity of the building units, where a bent C2-symmetric diamine, such as 1,3-diaminobenzene (1,3-DAB or DAB), with an exo-angle of 120° was used instead of those with an exo-angle of 180°, in combination with a C3-symmetric trialdehyde, such as tri(4-formylphenoxy)cyanurate (TFPC). Its synthesis was accomplished by reacting the building units in a mixture of mesitylene/dioxane/6 M acetic acid under solvothermal conditions. The phase purity, thermal stability, and porosity of TFPC-DAB were established by various analytical techniques. Utilizing the Density Functional Tight Binding (DFTB+) simulation and Pawley refinement, the best fit of the small angle x-ray pattern was found to have an AA stacking of TFPC-DAB in the trigonal space group P3 with low refinement parameters. Such smart materials are in huge demand to detect hazardous corrosive chemicals, such as HCl and NH3. The dual features of electron deficient π-acidic triazine moiety and heteroatoms (N/O) from TFPC and electron rich phenyl units from DAB embodied in the framework enhance its luminescent property and thereby make it suitable for solvent-based HCl and NH3 sensing. The detection limits for HCl and NH3 in methanol were found to be 14 and 82 ppb, respectively. The effect of solvent polarity on the sensing studies was observed with much lower detection limits in dioxane: 2.5 and 11 ppb for HCl and NH3, respectively. A detailed theoretical calculation using density functional theory and configurational bias Monte Carlo modules was conducted for understanding interactions between the COF and HCl or NH3 analytes.

N, S-Codoped Carbon Dots-Based Reusable Solvatochromic Organogel Sensors for Detecting Organic Solvents

The visualization and analysis of organic solvents using fluorescent sensors are crucial, given their association with environmental safety and human health. Conventional fluorescent sensors are typically single-use sensors and they often require sophisticated measurement instruments, which limits their practical and diverse applications. Herein, we develop solvatochromic nitrogen and sulfur codoped carbon dots (NS-CDs)-based organogel sensors that display color changes in response to different solvents. NS-CDs are synthesized using a solvothermal method to produce monodispersed particles with exceptional solubility in various organic solvents. NS-CDs exhibit distinct photoluminescent emission spectra that correlate with the solvent polarity, and the solvent-dependent photoluminescent mechanism is investigated in detail. To highlight the potential application of solvatochromic NS-CDs, portable and low-cost NS-CDs-embedded organogel sensors are fabricated. These sensors exhibit highly robust solvatochromic performance despite repeated solvent switches, thus ensuring consistent and reliable measurements in practical applications. This study provides valuable insights into the solvatochromism of carbon dots and opens up new avenues for designing real-time organic solvent sensing platforms.

A PEDOT enhanced covalent organic framework (COF) fluorescent probe for in vivo detection and imaging of Fe3

Simple and accurate in vivo monitoring of Fe3+ is essential for gaining a better understanding of its role in physiological and pathological processes. A novel fluorescent probe was synthesized via in situ solid-state polymerization of 3,4-ethylenedioxythiophene (PEDOT) in the pore channels of a covalent organic framework (COF). The PEDOT@COF fluorescent probe exhibited an absolute quantum yield (QY) 3 times higher than COF. In the presence of Fe3+ the PEDOT@COF 475 nm fluorescence emission, 365 nm excitation, is quenched within 180 s. Fluorescence quenching is linear with Fe3+ in the concentration range of 0-960 μM, with a detection limit of 0.82 μM. The fluorescence quenching mechanism was attributed to inner filter effect (IEF), photoinduced electron transfer (PET) and static quenching (SQE) between PEDOT@COF and Fe3+. A paper strip-based detector was designed to facilitate practical applicability, and the PEDOT@COF probe successfully applied to fluorescence imaging of Fe3+ levels in vivo. This work details a tool of great promise for enabling detailed investigations into the role of Fe3+ in physiological and pathological diseases.

Chemical Sensors Based on Covalent Organic Frameworks

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

Ratiometric Fluorescent Detection of Chromium(III) Based on One-Dimensional Imine-Linked Covalent Organic Framework

Chromium (Cr3+) as a highly toxic pollutant has aroused much attention due to its wide industrial applications. Covalent organic frameworks (COFs) have been considered as one of the most promising metal ion sensors due to their open pore channels and abundant adsorption sites. Herein, a novel luminescent one-dimensional COF (Py-An COF) was constructed by the condensation of 5'-(anthracen-9-yl)-[1,1':3',1″-terphenyl]-4,4″-dicarbaldehyde (An-2CHO) and 1,3,6,8-tetrakis(p-aminophenyl) pyrene (PyTTA). The resulting COF showed high crystallinity, comparative high surface area, and good thermal stability, which can be utilized for Cr3+ fluorescent sensors with high sensitivity and selectivity. Furthermore, the coordination between Schiff-base N atoms and Cr3+ inhibits the photoinduced electron transfer (PET) process, resulting in the enhanced fluorescence intensity of chromophores (436 nm) and decreased the fluorescence intensity of Py-An COF (512 nm) simultaneously, which eventually realizes a highly efficient ratiometric fluorescent sensor for trace Cr3+. Compared with other porous fluorescent materials, Py-An COF possesses a lower detection limit, higher sensitivity, and better selectivity. This work provides strategic guidance for the design of COFs as ratiometric fluorescence sensors.

Covalent organic frameworks: Pioneering remediation solutions for organic pollutants

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