Decanuclear Cluster-Based Metal–Organic Framework with a (3,11)-Connected Topology and Highly Sensitive 2,4,6-Trinitrophenol Detection

Synthesis of highly sensitive and multi-response Eu-MOF, fluorescence sensing properties and anti-counterfeiting applications

A new Europium metal-organic framework (Eu-MOF), namely [Eu(dpa) (H2O)]·0.5(bpy)·4H2O}n (H4dpa = 5-(3,4-dicarboxyphenoxy) isophenic acid, bpy = protonated 4,4'-bipyridine) was synthesized and structurally characterized by elemental analyses, infrared spectroscopy, and X-ray single-crystal diffraction analyses. Eu-MOF shows a three-dimensional network structure based on EuIII ions and (dpa)4- ligands via µ4: η1, η2, η2, η2 coordination mode. Fluorescence analysis shows that Eu-MOF has excellent fluorescence sensing characteristics, which can efficiently and sensitively detect various pollutants in water: the limit of detection (LOD) of ratiometric fluorescence detection of ANI in water was 42.9 nM, which was better than the single-peak detection limit. In addition, the peak detection limits of Eu-MOF for Flu, ORN and NB were 120 nM, 27 nM and 94 nM, respectively. In addition, XPS, LUMO orbital energy level, fluorescence lifetime, ultraviolet absorption and other principles are used to explore the mechanism of fluorescence quenching. Surprisingly, Eu-MOF not only has excellent anti- counterfeiting ability and stability, can be used as anti-counterfeiting material in life, but also has good selectivity to Flu. Eu-MOF has obvious fluorescence quenching effect on Flu on paper under ultraviolet light, which can be used for rapid in situ imaging test paper of pesticide residues.

Metal-organic frame material encapsulated Rhodamine 6G: A highly sensitive fluorescence sensing platform for the detection of picric acid contaminants in water

As a water pollutant with excellent solubility, 2,4,6-trinitrophenol (also known as picric acid, PA) poses a potential threat to the natural environment and human health, so it is crucial important to detect PA in water. In this study, a novel composite material (MIL-53(Al)@R6G) was successfully synthesized by encapsulating Rhodamine 6G into a metal-organic frame material, which was used for fluorescence detection of picric acid (PA) in water. The composite exhibits bright yellow fluorescence emission with a fluorescence quantum yield of 58.23 %. In the process of PA detection, the composite has excellent selectivity and anti-interference performance, and PA can significantly quench the fluorescence intensity of MIL-53(Al)@R6G. MIL-53(Al)@R6G has the advantages of fast detection time (20 s), wide linear range (1-100 µM) and low detection limit (4.8 nM). In addition, MIL-53(Al)@R6G has demonstrated its potential for the detection of PA in environmental water samples with satisfactory results.

MOFs as versatile scaffolds to explore environmental contaminants based on their luminescence bustle

Metal-Organic Frameworks (MOFs) with luminescent properties hold significant promise for environmental remediation. This review critically examines recent research on these materials design, synthesis, and applications, mainly focusing on their role in combating environmental pollutants. Through a comprehensive analysis of metal ions, ligands, and framework compositions, the review discusses the importance of tailored design and synthesis approaches in achieving desired luminescent characteristics. Key findings highlight the effectiveness of luminous MOFs as fluorescent sensors for a wide range of contaminants, including heavy metals, reactive species, antibiotics, and explosives. Considering all this, the review discusses future research needs and opportunities in the field of luminous MOFs. It emphasizes the importance of developing multifunctional materials, refining design methodologies, exploring sensing mechanisms, and ensuring environmental compatibility, scalability, and affordability. By providing insights into the current state of research and outlining future directions, this review is a valuable resource for researchers seeking to address environmental challenges using MOF-based solutions.

Highly sensitive fluorescent triarylimidazole derivatives for sensing of 2,4,6-trinitrophenol in aqueous solution and its application for actual environment detection

Two highly sensitive fluorescent triarylimidazole derivatives were synthesized by modifying imidazole with coumarin and large conjugate rigid plane structure. XM-F and XM-L emitted bright yellow-green fluorescent light. Their intense conjugation system generated strong π-π electrostatic interactions with TNP, accompanied by the formation of hydrogen bonds to achieve rapid detection of TNP within 25 s. The detection limits were as low as 0.049 μM and 0.071 μM, respectively. Probes had been successfully applied to rapid detection of TNP in real water samples and manufactured into portable fluorescent test strips. In view of excellent performance of XM-F, it was used to achieve real-time, portable, on-site quantitative detection of TNP by a colorimeter and a smartphone platform. In addition, XM-F also successfully processed into probe-coated TLC plates for efficient detection of fingerprints contaminated with TNP.

Explicating the recognition phenomenon of hazardous nitro-aromatic compound from contaminated environmental and cellular matrices by rationally designed pyridine-functionalized molecular probes

In the quest of recognizing hazardous nitro-aromatic compounds in water, two pyridine-functionalized Schiff-base chemosensors, DMP ((E)-N-(3,4-dimethoxybenzylidene)(pyridin-2-yl)methanamine)) and MP (4-((E)-((pyridin-2-yl)methylimino)methyl)-2-ethoxyphenol) have been synthesized to detect mutagenic 2,4,6-Trinitrophenol (TNP) in soil, water as well as cellular matrices by producing turn-off emission responses as a combined consequence of PET and RET processes. Several experimental analyses including ESI-MS, FT-IR, photoluminescence, ¹H NMR titration, and the theoretical calculations ascertained the formation and sensing efficacies of the chemosensors. The analytical substantiations revealed that structural variation of the chemosensors played a significant role in improving the sensing efficiency, which would certainly be worthwhile in developing small molecular TNP sensors. The present work depicted that the electron density within the MP framework was more than that of DMP due to the intentional incorporation of -OEt and -OH groups. As a result, MP represented a strong interaction mode towards the electron-deficient TNP with a detection limit of 39 μM.

A Dihydrotetrazine-Functionalized Metal-Organic Framework as a Highly Selective Luminescent Host-Guest Sensor for Detection of 2,4,6-Trinitrophenol

Pore decoration of metal-organic frameworks (MOFs) with functional groups is a useful strategy to attain high selectivity toward specific analytes, especially in the presence of interfering molecules with similar structures and energy levels, through selective host-guest interactions. In this work, we applied a dihydrotetrazine-decorated MOF, TMU-34, with the formula [Zn(OBA)(H₂DPT)_0.5]_n·DMF, where H₂OBA is 4,4'-oxybis(benzoic acid) and H₂DPT is 3,6-bis(pyridin-4-yl)-1,4-dihydro-1,2,4,5-tetrazine, for the highly selective detection of phenolic NACs, especially TNP (94% quenching efficiency, detection limit 8.1 × 10^-6 M, K_SV = 182663 mol L^-1), in the presence of other substituted NACs especially -NH₂-substituted NACs. Investigations reveal that the quenching mechanism is dominated by photoinduced MOF-to-TNP electron transfer through possible hydrogen-bonding interactions between the phenolic hydroxyl group of TNP and dihydrotetrazine functions of TMU-34. Despite extensive publications on the detection of TNP in the presence of other NACs, the significance of this work will be elucidated if attention is paid to the fact that TMU-34 is among the rare and highly selective MOF-based TNP sensors in the presence of -NH₂-substituted NACs as the serious interferers.

A luminescent Zn-MOF for the detection of explosives and development of fingerprints

A luminescent 3D metal-organic framework [Zn(NDA)(AMP)] = PUC1 (where, NDA = naphthalene-2,6-dicarboxylic acid and AMP = 4-aminomethyl pyridine) was synthesized under solvothermal conditions. The synthesized 3D framework was fully characterized with the help of different analytical techniques such as SCXRD, FTIR, TGA, PXRD, SEM, BET, etc. PUC1 exhibited a strong emission peak at 371 nm when excited at 290 nm and the resulting emission was efficiently quenched in the presence of various organic explosive substances like pentaerythritol tetranitrate (PETN), 2,4,6-trinitrophenyl-N-methylnitramine (Tetryl), trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX). PUC1 revealed highly sensitive and selective detection of PETN and Tetryl with high quenching constant values of 0.1 × 10⁶ and 0.12 × 10⁵ M^-1 and low detection limits of 0.315 and 0.404 μM respectively. The strong luminescent properties of PUC1 lead to its successful application in the development of latent fingermarks on different non-porous surfaces using the powder dusting method. The accuracy and applicability of the synthesized material were determined by developing fingerprints by using secretions from eccrine and apocrine glands on a glass slide and various other surfaces, followed by dusting the surfaces. The results so obtained were found to be very accurate and promising.

Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso-Hydroxylation of Arylboronic Acids

We report the synthesis and structural characterization of two coordination polymers (CPs), namely; [{Zn(L)(DMF)₄ } ⋅ 2BF₄ ]_α (1) and [{Cd(L)₂ (Cl)₂ } ⋅ 2H₂ O]_α (2) (where L=N² ,N⁶ -di(pyridin-4-yl)naphthalene-2,6-dicarboxamide). Crystal packing of 1 reveals the existence of channels running along the b- and c-axis filled by the ligated DMF and lattice anions, respectively. Whereas, crystal packing of 2 reveals that the metallacycles of each 1D chain are intercalating into the groove of adjacent metallacycles resulting in the stacking of 1D loop-chains to form a sheet-like architecture. In addition, both 1 and 2 were exploited as multifunctional materials for the detection of nitroaromatic compounds (NACs) as well as a catalyst in the ipso-hydroxylation of aryl/heteroarylboronic acids. Remarkably, 1 and 2 showed high fluorescence stability in an aqueous medium and displayed a maximum 88% and 97% quenching efficiency for 4-NPH, respectively among all the investigated NACs. The mechanistic investigation of NACs recognition suggested that the fluorescence quenching occurred via electron as well as energy transfer process. Furthermore, the ipso-hydroxylation of aryl/heteroarylboronic acids in presence of 1 and 2 gave up to 99% desired product yield within 15 min in our established protocol. In both cases, 1 and 2 are recyclable upto five cycles without any significant loss in their efficiency.

Chemically Robust and Bifunctional Co(II)-Framework for Trace Detection of Assorted Organo-toxins and Highly Cooperative Deacetalization-Knoevenagel Condensation with Pore-Fitting-Induced Size-Selectivity

Acute detection of assorted classes of organo-toxins in a practical environment is an important sustainable agenda, whereas cooperative and recyclable catalysis can mitigate hazards by minimizing energy requirements and reducing waste generation. We constructed an acid-/base-stable Co(II)-framework with a unique network topology, wherein unidirectional porous channels are decorated by anionic [Co₂(μ₂-OH)(COO)₄(H₂O)₃] secondary building units and neutral [CoN₂(COO)₂] nodes. An intense luminescent signature of the hydrolytically robust framework is harnessed for the selective, fast-responsive, and regenerable detection of two detrimental organo-aromatics, 4-aminophenol (4-AP) and 2,4,6-trinitrophenol (TNP). Alongside remarkable quenching, their nanomolar detection limits (4-AP: 99.5 nM; TNP: 67.2 nM) rank among the lowest reported values in water and corroborate their ultra-sensitivity. Density functional theory (DFT) calculations verify the electron-transfer route of sensing through portraying redistribution of energy levels of molecular orbitals in a three-dimensional network by each analyte and further envisages non-covalent host-guest interactions. Benefiting from the concurrent existence of an open-metal site and a triphenylamine-moiety-functionalized ligand, the activated framework acts as an outstandingly cooperative heterogeneous catalyst in deacetalization-Knoevenagel condensation under mild conditions. The acid-base dual catalysis is detailed for the first time from combined inputs of control experiments and DFT validations. To the best of tandem reaction, larger-sized substrate exhibits insignificant conversion, and certifies rarest pore-fitting induced size-selectivity.

Synthesis and crystal structure of oktakis(dimethylsulphoxide-κ1 O)gadolinium(III) [tetrabromido-μ2-bromido-μ2-sulfido-di-μ3-sulfido-μ4-sulfido-tetracopper(I)-tungsten(VI)], C16H48O8S12Br5Cu4GdW

C16H48O8S12Br5Cu4GdW, monoclinic, P21 (no. 4), a = 11.576(2) Å, b = 12.407(3) Å, c = 17.582(3) Å, β = 100.76(3)°, V = 2480.8(9) Å3, Z = 2, R gt(F) = 0.0446, wR ref(F 2) = 0.1169, T = 293 K.

A water-stable multi-responsive luminescent Zn-MOF sensor for detecting TNP, NZF and Cr2O72- in aqueous media

The wide prevalence of organic and inorganic pollutants in water from various industries is responsible for serious environmental problems and endangers human beings. Therefore, the search for effective methods to detect these pollutants has gained great importance. In this work, a new luminescent MOF, {[Zn(L)(bpe)_0.5]·DMF}_n (1) [H₂L = 4,4'-((naphthalene-1,4-dicarbonyl)bis(azanediyl))dibenzoic acid, bpe = 1,2-bis(4-pyridyl)ethene], was solvothermally synthesized and structurally characterized. In this MOF, Zn-SBUs (SBUs = secondary building units) were connected by acylamide-containing dicarboxylate L^2- and nitrogen-containing bpe molecules to yield a 3D porous framework with isolated DMF molecules in the pores. The activated solvent-free MOF sample (denoted as 1a) with good water-stability was obtained by the solvent-exchange and vacuum heat treatment techniques. The luminescence sensing experiments showed that 1a could sensitively, selectively and reversibly detect 2,4,6-trinitrophenol (TNP), nitrofurazone (NZF) and Cr₂O₇^2- in aqueous media, and the corresponding luminescence quenching mechanism has also been discussed. In addition, MOF 1a could quantitatively detect TNP, NZF and Cr₂O₇^2- in tap water samples, indicating that MOF 1a has the potential to detect the aforesaid pollutants in various environmental water matrices.

Phenolic nitroaromatics detection by fluorinated metal-organic frameworks: Barrier elimination for selective sensing of specific group of nitroaromatics

Many piesce of research have been performed to detect nitroaromatic-compounds (NACs) by metal-organic frameworks (MOFs). Despite extensive studies, there are still significant challenges like selective detection of specific NAC group in presence of other NACs. Here, we have integrated two functionalization strategies through decoration of pore-walls of the MOFs with trifluoromethyl groups and extension in π-conjugated system. Based on this idea, trifluoromethyl TMU-44 (with the formula [Zn₂(hfipbb)₂(L1)]_n.DMF, H₂hfipbb = 4,4'-(hexafluoroisopropylidene) bis(benzoic acid), L1 = N,N'-bis-pyridin-4-ylmethylene-benzene-1,4-diamine) and TMU-45 (with formula [Zn₂(hfipbb)₂(L2)]_n.DMF, L2 = N,N'-bis-pyridin-4-ylmethylene-naphthalene-1,5-diamine) frameworks have been synthesized. The aromatic skeleton of TMU-44 is based on phenyl rings while TMU-45 aromatic skeleton is extended by replacement of phenyl with naphthyl core. Measurements reveal that these MOFs are highly sensitive to phenolic NACs especially 2,4,6-trinitrophenol (TNP) with high quenching efficiency of 90% for TMU-44 (K_SV = 10,652 M^-1, LOD = 6.9 ppm) and 99% for TMU-45 (K_SV = 34,741 M^-1, LOD = 2.07 ppm). The proposed detection mechanism can be associated with hydrogen bonding between OH group of phenolic NACs and trifluoromethyl groups of TMU-MOFs as well as π(rich)∙∙∙π(deficient) interaction between π-conjugated backbone of TMU-frameworks and π-deficient ring of NACs.

Metal–organic frameworks constructed from an [MS4Cux]x−2 (M = W, Mo) unit: isomerization of the cluster unit induced by temperature

Two MOFs based on [WS4Cu4]2+ or unprecedented [WS4Cu6]4+·I−·[WS4Cu6]4+, and a MOF based on [MoS4Cu4]2+ with 9,10-di(pyridin-4-yl)anthracene were obtained. Temperature was important for the isomerization of [WS4Cux]x−2 in the formation of two MOFs based on [WS4Cux]x−2.

A robust 3D In–MOF with an imidazole acid ligand as a fluorescent sensor for sensitive and selective detection of Fe3+ ions

A stable In(iii)-MOF with a versatile 5-(1H-imidazol-1-yl)isophthalic acid ligand can be used as a fluorescent sensor for Fe³⁺ detection.

Two novel lead-based coordination polymers for luminescence sensing of anions, cations and small organic molecules

A novel lead-based compound is reported as a multi-responsive luminescent sensor for detecting anions, cations and small organic molecules, especially Cr₂O₇²⁻, CrO₄²⁻, Fe³⁺ and nitrobenzene.

Three AIE-ligand-based Cu(i) coordination polymers: synthesis, structures and luminescence sensing of TNP

Cu(i) CPs were constructed for the first time with the AIE ligand DPMF; they exhibited distinct architectures and efficient detection of TNP.

Efficient detection of Cr3+ and Cr2O72− using a Zn(ii) luminescent metal–organic framework

We constructed a new luminescent metal–organic framework, [Zn₂(TCBPDC)_0.5(H₂O)₂]_n·G (G = guest molecules), and realized an efficiently luminescent sensing for Cr³⁺ and Cr₂O₇²⁻.

A highly stable 8-hydroxyquinolinate-based metal–organic framework as a selective fluorescence sensor for Fe3+, Cr2O72− and nitroaromatic explosives

A novel 8-hydroxyquinolinate-based metal–organic framework exhibits excellent sensing performance toward Fe³⁺, Cr₂O₇²⁻ and nitroaromatic explosives.

Sensing organic analytes by metal–organic frameworks: a new way of considering the topic

In this review, our goal is comparison of advantageous and disadvantageous of MOFs about signal-transduction in different instrumental methods for detection of different categories of organic analytes.

Two mixed-ligand Cd(ii)–organic frameworks with unique topologies: selective luminescence sensing of TNP and Cu2+ ions with recyclable performances

Two luminescent Cd(ii)–organic frameworks exhibit unprecedented (4,4,5,5)-c and (4,4,4,6,7)-c topologies, and highly sensitive and selective sensing of 2,4,6-trinitrophenol and Cu²⁺.