Facile Fabrication of an AIE-Active Metal-Organic Framework for Sensitive Detection of Explosives in Liquid and Solid Phases

A dysprosium(III)-based triple helical-like complex as a turn-on/off fluorescence sensor for Al(III) and 4,5-dimethyl-2-nitroaniline

A novel triple helical-like complex [Dy2K2L3(NO3)2]·3DMF (1) based on a designed Schiff base N'1,N'3-bis((E)-3-ethoxy-2-hydroxybenzylidene)-malonohydrazide (H4L) was synthesized with good chemical and thermal stabilities. Single-crystal X-ray structural analysis showed that 1 presents a tetranuclear triple helical-like structure via the coordination mode of Dy : K : L with 2 : 2 : 3 stoichiometry. Fluorescence measurements showed that 1@EtOH has excellent fluorescence turn-on/off response ability for aluminium ions and 4,5-dimethyl-2-nitroaniline (DMNA) with outstanding selectivity, sensitivity, and anti-interference ability. The calculated limit of detection (LOD) values for 1@EtOH to Al3+ and DMNA were found to be 0.53 and 3.33 μM, respectively. Density functional theory (DFT) calculation showed that the fluorescence response mechanism can be explained by the photoinduced electron transfer (PET) mechanism; meanwhile, the inner filter effect (IFE) of DMNA can also affect the emission of 1@EtOH.

Solvent- and pH-Stable Eu(III)-Based Metal-Organic Framework with Phosphate-Ratio Fluorescence Sensing and Significant Proton Conduction

Lanthanide-based metal-organic frameworks show good potential for applications due to their unique structures and functional properties. A highly thermally and acid-base stable Eu-MOF was synthesized by a solvothermal method with the molecular formula {[(CH3)2NH2]2[Eu2(NDDP)2(H2O)2]·H2O}n (Eu-MOF, H4NDDP = 5,5'-(naphthalene-2,6-diyl)diisophthalic acid). Eu-MOF takes a three-dimensional (4,4,8)-connected topology. The water molecules involved in the coordination, free water molecules, and [(CH3)2NH2]+ cations in the pore can be used as proton carriers. The proton conductivity attains 1.25 × 10-4 S cm-1 at room temperature and 2.42 × 10-3 S cm-1 at 70 °C and 98% relative humidity. Combined with the dual-emission properties from the ligands and Eu(III) ions enables Eu-MOF to be used as a ratiometric fluorescent sensor for phosphate efficiently and rapidly, with a limit of detection of 0.12 μM in the Tris-HCl buffer solution. These results provide a new approach for the construction of MOFs with high proton conductivity and a ratiometric fluorescence response.

Eu3+-Functionalized MOFs for the simple and rapid 5-Hydroxymethylfurfural determination in food

5-Hydroxymethylfurfural (5-HMF) is an important product of the Maillard reaction and can be used as a quality indicator of food. 5-HMF has been found in studies to be harmful to human health. In this study, a highly selective and anti-interference fluorescent sensor Eu@1 is constructed based on Eu3+-functionalized Hf-based MOF for monitoring 5-HMF in a variety of food products. Eu@1 shows high selectivity, low LOD (8.46 μM), fast response time, and repeatability for 5-HMF. More importantly, after adding 5-HMF to milk, honey and apple juice samples, the probe Eu@1 is proved to be successfully in sensing 5-HMF in the above food samples. Therefore, this study provides a dependable and efficient alternative for the detection of 5-HMF in food samples.

New opportunities for cyclodextrins in supramolecular assembly: metal organic frameworks, crystalline self-assembly, and catalyzed assembly

Cyclodextrins (CDs) are widely used macrocycles in supramolecular assembly due to their easy availability, versatile functionality and excellent biocompatibility. Although they are well-known for forming host-guest complexes with a wide range of guests and this host-guest chemistry has long been utilized in industry and academia, new opportunities have arisen in recent years, particularly in supramolecular assembly. In the present review, we will first provide a basic introduction to CDs and then summarize their emerging roles in the fields of supramolecular chemistry and materials. This includes their involvement in hybrid frameworks with inorganic components such as metal ions and polyoxometalates, crystalline self-assembly with amphiphilic molecules, and their new possibility of "catassembly" and induced chiral supramolecular structures that have previously been overlooked. Finally, we will comment on the future perspectives of CDs to inspire more ideas and efforts, with the aim of promoting diverse applications of CDs in supramolecular materials.

Enhancing propellant performance through intermolecular interactions: cyclodextrin-based MOF loading in nitrocellulose

Metal-organic frameworks (MOFs) offer promising opportunities for modifying energetic materials due to their micro-porous structure and high performance. In this study, we present a novel green MOF named cyclodextrin-MOF (CD-MOF), which incorporates potassium ions, synthesized using a simple methanol vapor diffusion approach. The CD-MOF incorporates potassium ions and enhances propellant performance through intermolecular force optimization with nitrocellulose (NC). Molecular dynamics simulations reveal stronger interactions between the CD-MOF and NC. The loading of the CD-MOF within NC forms a stable structure with resistance to migration and defense against crystalline precipitation and water absorption. Notably, in static combustion and pyrolysis tests, the CD-MOF exhibits efficient flame and flash inhibition. The thermal degradation and cauterization of the CD-MOF resulted in the formation of a complex microporous material capable of absorbing flammable and harmful gases such as CO, NO, NO2, and N2O. These findings shed light on the superior performance of the CD-MOF compared to conventional inorganic salts, and the comprehensive characterization and molecular simulations provide insights into the unique properties and applications of the CD-MOF, emphasizing its significant contribution to the field of green propellants.

Cu2+ assisted carnation-like fluorescent metal-organic framework for triple-mode detection of glyphosate in food samples

Herein, by employing a novel synthesized ligand H₂L, a flower-like luminescent metal-organic framework IRMOF-3-L was constructed for developing a triple-mode sensor for glyphosate (Glyp) detection. The ligand H₂L was designed to contain three functional parts, which endowed the resulted IRMOF-3-L with peroxidase-like activity and unique fluorescence property, as well as specific combining capacity for Cu²⁺ to quench its fluorescence. The quenched fluorescence of IRMOF-3-L/Cu²⁺ could be recovered by Glyp to realize fluorescence detection of Glyp. Besides, the peroxidase activity of IRMOF-3-L/Cu²⁺ could also be inhibited by Glyp, and result in the decrease of catalysate oxTMB, concurrently reducing the changes of colorimetric and SERS signal. Therefore, the fluorescent/colorimetric/SERS triple-mode based detection of Glyp was favorably realized, and the detection limits were calculated as low as 0.738, 2.26 and 0.186 nM, respectively. Furthermore, a portable test strips-smartphone sensing platform was constructed for point of care testing of Glyp in food samples.

Humidity Sensors Based on Metal-Organic Frameworks

Humidity sensors are important in industrial fields and human activities. Metal-organic frameworks (MOFs) and their derivatives are a class of promising humidity-sensing materials with the characteristics of a large specific surface area, high porosity, modifiable frameworks, and high stability. The drawbacks of MOFs, such as poor film formation, low electrical conductivity, and limited hydrophilicity, have been gradually overcome with the development of material science. Currently, it is moving towards a critical development stage of MOF-based humidity sensors from usability to ease of use, of which great challenges remain unsolved. In order to better understand the related challenges and point out the direction for the future development of MOF-based humidity sensors, we reviewed the development of such sensors based on related published work, focusing on six primary types (impedance, capacitive, resistive, fluorescent, quartz crystal microbalance (QCM), and others) and analyzed the sensing mechanism, material design, and sensing performance involved, and presented our thoughts on the possible future research directions.

Nanoreactor Based on Cyclodextrin for Direct Electrocatalyzed Ammonia Synthesis

The high-efficiency transition metal-free electrocatalytic nitrate reduction reaction (NO₃^-RR) for ammonia synthesis has received more attention because of its green and environmentally friendly characteristics. Here, we report an efficient electrochemical NH₃ synthesis directly from purely organic macrocyclic compounds α-, β-, and γ-cyclodextrins (CDs)-catalyzed transition metal-free electroreduction of nitrate under ambient conditions. In comparison with α-, and β-CDs, parent γ-CD presented uncommon catalytic performance with a relatively higher NH₃ yield that can reach up to 2.28 mg h^-1 cm^-2 with a Faradaic efficiency (FE) of 63.2% at -0.9 V versus a reversible hydrogen electrode in alkaline medium, and the potassium ion-coordinated γ-CD complex can achieve a maximum NH₃ production rate up to 4.66 mg h^-1 cm^-2 with an NH₃ FE of 79.3%. Further comparison with permethyl-γ-CD, d-glucose, and poly(vinyl alcohol) for the NO₃^-RR indicated that the typical torus-shaped cyclic conformation and edge hydroxyl groups of parent CDs play important roles in the electrocatalytic process. The K⁺-mediated 3D γ-CD-K⁺ frameworks containing six CDs as nanoreactors greatly strengthen the enrichment effect of nitrate through hydrogen-bonding interaction and electrostatic interaction and promote the mass transfer, thus leading to the efficient NO₃^-RR in an alkaline electrolyte. This work provides a convenient, green, and economic method for high-performance NO₃^-RR, which has potential applications in the fields of environment, energy, and industry.

Dual-Color 2D Lead-Organic Framework with Two-Fold Interlocking Structures for the Detection of Nitrofuran Antibiotics and 2,6-Dichloro-4-nitroaniline

The misuse of organic pollutants such as nitrofuran antibiotics (NFAs) and 2,6-dichloro-4-nitroaniline (DCN) has become a hot topic of global concern, and developing rapid, efficient, and accurate techniques for detecting NFAs and pesticides in water is a major challenge. Here, we designed a novel lead-based anion 2D metal-organic framework (MOF){[(CH₃)₂NH₂]₂[Pb(TCBPE)(H₂O)₂]}_n (F3) with interlocking structures, in which TCBPE stands for 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene. Powder X-ray diffraction and thermogravimetric analysis revealed that F3 has excellent chemical and solvent stability. It is worth noting that F3 has a grinding discoloration effect. The solvent-protected grinding approach achieved F3B with a high quantum yield (QY = 73.77%) and blue fluorescence, while the direct grinding method produced F3Y with a high quantum yield (QY = 37.27%) and yellow-green fluorescence. Importantly, F3B can detect NFAs in water rapidly and sensitively while remaining unaffected by other antibiotics. F3Y can identify DCN in water quickly and selectively while remaining unchanged by other pesticides. F3B demonstrated high selectivity and rapid response to NFAs at a limit of detection (LOD) as low as 0.26 μM, while F3Y indicated high selectivity and responded quickly to DCN in water at an LOD as low as 0.14 μM. The method was successfully applied to detect NFAs in actual water samples of the fish tanks and ponds as well as the pesticide DCN in soil samples. The recovery rates were 97.0-105.15% and 102.2-106.48%, and the relative standard deviations were 0.63-1.45% and 0.29-1.69%, respectively. In addition, F3B and F3Y can be made into fluorescent test papers for the visual detection of NFAs and DCN, respectively. Combined with experiments and density functional theory calculations, the mechanism of fluorescence quenching of MOFs by target analytes was also revealed.

Dual-Ligand Strategy Employing Rigid 2,5-Thiophenedicarboxylate and 1,10-Phenanthroline as Coligands for Solvothermal Synthesis of Eight Lanthanide(III) Coordination Polymers: Structural Diversity, DFT Study, and Exploration of the Luminescent Tb(III) Coordination Polymer as an Efficient Chemical Sensor for Nitroaromatic Compounds

Lanthanide coordination polymers (Ln-CPs) are potential chemosensors when fabricated to depict a detectable change in optical properties on interaction with target analytes. This work investigates the interaction of nitroaromatic compounds with Ln-CPs leading to induced changes in fluorescence emission intensity, a crucial strategy to develop a selective and sensitive system for the sensing of nitroaromatics. Approaching toward this objective, solvothermal reactions of 2,5-thiophenedicarboxylic (2,5-TDC) acid, 1,10-phenanthroline (1,10-Phen), and Ln(NO₃)₃·xH₂O are carried out to assemble eight Ln(III) coordination polymers [Ln₂(2,5-TDC)₃(1,10-Phen)₂(H₂O)₂] [Ln = Pr (1), Nd (2)], {[Tb(2,5-TDC)_1.5(1,10-Phen)(H₂O)]·DMF} (3), and [Ln(2,5-TDC)_1.5(1,10-Phen)]·xH₂O (Ln = Tb (4), Dy (5), Ho (6), Er (7), and Yb (8)); x = 0 for CP 4, 5, 6, and 8 and x = 1 for CP 7 with two different space groups and dimensions. The as-synthesized polymers 1-8 are characterized by powder X-ray crystallography, infrared spectroscopy, and thermogravimetric analysis. The structure-corroborated density functional theory (DFT) studies are done on the selected CPs to investigate the interactions between different structural motifs of the assembled CPs. The luminescence properties of CP 4 are explored in detail and are found to be highly sensitive for the detection of p-nitrotoluene as indicated by the most intensive fluorescence quenching with the lowest limit of detection (0.88 ppm) and high quenching constant (4.3 × 10⁴ M^-1). Other nitro compounds (viz., o-nitrobenzaldehyde, m-nitroaniline, picric acid, m-dinitrobenzene, p-nitrophenol, and p-nitroaniline) are also screened for potential sensing by CP 4.

An Overview of the Design of Metal-Organic Frameworks-Based Fluorescent Chemosensors and Biosensors

Taking advantage of high porosity, large surface area, tunable nanostructures and ease of functionalization, metal-organic frameworks (MOFs) have been popularly applied in different fields, including adsorption and separation, heterogeneous catalysis, drug delivery, light harvesting, and chemical/biological sensing. The abundant active sites for specific recognition and adjustable optical and electrical characteristics allow for the design of various sensing platforms with MOFs as promising candidates. In this review, we systematically introduce the recent advancements of MOFs-based fluorescent chemosensors and biosensors, mainly focusing on the sensing mechanisms and analytes, including inorganic ions, small organic molecules and biomarkers (e.g., small biomolecules, nucleic acids, proteins, enzymes, and tumor cells). This review may provide valuable references for the development of novel MOFs-based sensing platforms to meet the requirements of environment monitoring and clinical diagnosis.

Assembly of a Heterotrimetallic Zn2Dy2Ir Pentanuclear Complex toward Multifunctional Molecular Materials

Rational selection of metal ions and organic ligands to synthesize metal-organic complexes (MOCs) is necessary for constructing multifunctional materials. Herein, we have obtained a novel heterotrimetallic Zn₂Dy₂Ir pentanuclear MOC by the assembly of Dy^III, luminescent Zn^II(valpn), and [Ir^III(H₂L)(ppy)₂]Cl metalloligands (Hppy = 2-phenylpyridine, H₂L = 2,2'-bipyridine-5,5'-di-p-benzoic acid). Single-crystal structural analysis shows that the central [Ir^III(L)(ppy)₂]^- bridges two ZnDy moieties using two carboxylates of L^2-. Measurements of organic light-emitting diodes (OLEDs) show that the maximum luminance is 284.2 cd/m² and the turn-on voltage is 6 V. Magnetic studies reveal that Zn₂Dy₂Ir is a field-induced single-molecule magnet (SMM) with an energy barrier of 19.1(2) K under a 2 kOe dc field. Zn₂Dy₂Ir shows luminescence sensing with a quenching efficiency of up to 99.0% for 2,4,6-trinitrophenol (TNP).

Cyclodextrin metal-organic frameworks and derivatives: recent developments and applications

While there is a tremendous amount of scientific research on metal organic frameworks (MOFs) for gas storage/separation, catalysis and energy storage, the development and application of biocompatible MOFs still poses major challenges. In general, they can be synthesised from various biocompatible linkers and metal ions but particularly cyclodextrins (CDs) as cyclic oligosaccharides are an astute choice for the former. Although the field of CD-MOF materials is still in the early stages and their design and fabrication comes with many hurdles, the benefits coming from CDs built in a porous framework are exciting. Versatile host-guest complexation abilities, high encapsulation capacity and hydrophilicity are among the valuable properties inherent to CDs and offer extended and novel applications to MOFs. In this review, we provide an overview of the state-of-the-art synthesis, design, properties and applications of these materials. Initially, a rationale for the preparation of CD-based MOFs is provided, based on the chemical and structural properties of CDs and including their advantages and disadvantages. Further on, the review exhaustively surveys CD-MOF based materials by categorising them into three sub-classes, namely (i) CD-MOFs, (ii) CD-MOF hybrids, obtained via combination with external materials, and (iii) CD-MOF-derived materials prepared under pyrolytic conditions. Subsequently, CD-based MOFs in practical applications, such as drug delivery and cancer therapy, sensors, gas storage, (enantiomer) separations, electrical devices, food industry, and agriculture, are discussed. We conclude by summarizing the state of the art in the field and highlighting some promising future developments of CD-MOFs.

Electrochemiluminescent sensor based on an aggregation-induced emission probe for bioanalytical detection

In recent years, with the rapid development of electrochemiluminescence (ECL) sensors, more luminophores have been designed to achieve high-throughput and reliable analysis. Impressively, after the proposed fantastic concept of "aggregation-induced electrochemiluminescence (AIECL)" by Cola, the application of AIECL emitters provides more abundant choices for the further improvement of ECL sensors. In this review, we briefly report the phenomenon, principle and representative applications of aggregation-induced emission (AIE) and AIECL emitters. Moreover, it is noteworthy that the cases of AIECL sensors for bioanalytical detection are summarized in detail, from 2017 to now. Finally, inspired by the applications of AIECL emitters, relevant prospects and challenges for AIECL sensors are proposed, which is of great significance for exploring more advanced bioanalytical detection technology.

Machine learning-assisted array from fluorescent conjugated microporous polymers for multiple explosives recognition

The fluorescent properties of conjugated microporous polyphenylene (CMPs) were tuned through a wide range by inclusion of small amount of comonomer as chromophore in the network. The multi-color CMPs were used for explosives sensing and demonstrated broad sensitivity (ranging from -0.01888 μM^-1 to -0.00467 μM^-1) and LODs (ranging from 31.0 nM to 125.3 nM) against thirteen explosive compounds including nitroaromatics (NACs), nitramines (NAMs) and nitrogen-rich heterocycles (NRHCs). The CMPs were also developed as a sensor array for discrimination of thirteen explosives, specifically including NT, p-DNB, DNT, TNT, TNP, TNR, RDX, HMX, CL-20, FOX-7, NTO, DABT and DHT. By using classical statistical method "Linear Discriminant Analysis (LDA)", the thirteen explosives at a fixed concentration were completely discriminated and unknown test samples were indentied with 88% classification accuracy. Moreover, explosives in different concentrations and the mixtures of explosives were also successfully classified. Compared with LDA, Machine Learning algorithms have significant advantages in analyzing the array-based sensing data. Different Machine Learning models for pattern recognition have also been implemented and discussed here and much higher accuracy (96% for "neural network") can be achieved in predicting unknown test samples after training.

Unearth the Luminescence Potential of Metal-Organic Frameworks: Adopting a Feasible Strategy to Fabricate One Ratiometric Fluorescence Sensor for Monitoring Both 1-Hydroxypyrene and Cu2

In this work, a novel luminescent hybrid material with double emission centers (Eu(TTA)_0.2@9-1-UMOF) is successfully prepared, adopting a feasible design strategy. Initially, the second ligand 1,2,4-benzenetricarboxylic acid (H₃BTC) is encapsulated based on a solid solution approach, which effectively improves the ligand-based emission intensity of the original LMOF and provides functional sites for introducing the second luminescent center; then, Eu³⁺ as the red emission source is loaded into the frameworks through a coordination post-synthetic modification method; finally, to balance the emission intensity at 613 nm (Eu³⁺) and 465 nm (1,4-naphthalenedicarboxylic acid (H₂NDC)), 2-thenoyltrifluoroacetone (TTA) as a powerful antenna is introduced. Given the outstanding luminescence properties and structural stability of Eu(TTA)_0.2@9-1-UMOF, it is further developed as a ratiometric sensor for detecting 1-hydroxypyrene (1-HP, the biomarker of polycyclic aromatic hydrocarbons (PAHs)) and Cu²⁺, which promotes the pre-diagnosis of human health. Notably, Eu(TTA)_0.2@9-1-UMOF exhibits excellent selective recognition ability for both 1-HP and Cu²⁺ with high sensitivity (LOD = 4.06 × 10^-6 mg/mL, 3.85 × 10^-7 mol/L, respectively) and fast response speed. In addition, Eu(TTA)_0.2@9-1-UMOF as a fluorescent probe shows great potential for the determination of 1-HP and Cu²⁺ in actual samples. More importantly, this work widens the road for the development of dual/multiple LMOF-based sensors for analytical applications.

Construction of highly energetic metal-organic frameworks with a nitrobenzene derivative

Three metal–organic frameworks [CdL(DMF)]n 1, {[CuL(H2O)(DMF)]•DMF•0.5H2O}n 2 and [Nd(HL)L(DMF)3]n 3 have been synthesized with a nitrobenzene derivative 4-((5-hydroxy-2,4-dinitrophenoxy)methyl)-3-nitrobenzoic acid (H2L). Compound 1 has a dense three-dimensional framework with 1D Cd...

Recent Advances of Porous Materials Based on Cyclodextrin

Porous materials have attracted significant attention because of their rising applications in many fields. Cyclodextrins (CDs) are suitable building units in the fabrication of porous materials owing to their intrinsic nanoporous structure, easy modification, and biocompatibility, which may result in the formation of CD-based organic frameworks (including cyclodextrin metal-organic frameworks (CD-MOFs) and cyclodextrin covalent organic frameworks (CD-COFs)), and CD-based polymer hybrid porous materials. This review focuses on the recent progress in the fabrication and applications of CD-based porous materials with novel structures and functionalities.

Structural Design of Low Toxicity Metal-Organic Frameworks for Multifunction Detection of Organic and Inorganic Contaminants from Water

Metal-organic frameworks (MOFs)-based sensors for monitoring toxic substances in wastewater have attracted great attention due to the efficient and reliable performance. Here, we has synthesized two novel zinc-based MOFs [Zn(ttb)₂(H₂O)₂]_n (Zn1-ttb) and {[Zn(ttb)₂]·0.5CH₃CN}_n (Zn2-ttb) through changing the polarity of reaction solvents and finally obtained target 2D MOF material [Zn(ttb)(bdc)_0.5]_n(Zn3-ttb-bdc) by successfully introducing an ancillary ligand H₂bdc (Httb = 1-(triazo-1-ly)-4-(tetrazol-5-ylmethyl)benzene, H₂bdc = 1,4-benzenedicarboxylic acid). As-prepared Zn3-ttb-bdc exhibits high water and chemical stability as well as excellent fluorescence property. Due to the -COOH binding sites from H₂bdc, Zn3-ttb-bdc shows high sensitivity and a rapid luminescent response to a representative organic micropollutant trinitrophenol (TNP) and inorganic pollutants (Fe³⁺ and Cr₂O₇^2-) in wastewater. The mechanisms of multifunctional detection abilities of Zn3-ttb-bdc toward different types of pollutants are further studied. This work presents the structural design in preparing MOF materials for multifunctional detection performance, thus opening new perspectives for emerging MOF-based sensors as environmental monitors.

Highly selective detection of TNP over other nitro compounds in water: the role of selective host–guest interactions in Zr-NDI MOF

A fluorescent Zr-NDI based MOF shows the selective sensing of TNP in water, over other classes of nitro compounds. DFT studies reveal favourable host–guest interactions behind this phenomenon.