Guest-Induced Ultrasensitive Detection of Multiple Toxic Organics and Fe3+ Ions in a Strategically Designed and Regenerative Smart Fluorescent Metal-Organic Framework

Three-fold interpenetrated metal–organic framework as a multifunctional fluorescent probe for detecting 2,4,6-trinitrophenol, levofloxacin, and l-cystine

A robust Zn(ii) MOF with good chemical and thermal stability, was prepared as an effective fluorescent probe for 2,4,6-trinitrophenol (TNP), levofloxacin (LVX) and l-cystine (l-Cys) with recyclability.

Metal–organic frameworks (MOFs) as fluorescence sensors: principles, development and prospects

This review classifies the latest developments of MOF-based fluorescence sensors according to the analytes, and discusses the challenges faced by MOF-based fluorescence sensors and promotes some directions for future research.

Four MOFs with isomeric ligands as fluorescent probes for highly selective, sensitive and stable detection of antibiotics in water

Four complexes showed excellent discriminative probes for cefixime (CEF) and tetracycline (TEC) based on their sensitive fluorescence quenching. The PET and IFE effects resulted in high sensitivity and selectivity for the detection of CEF and TEC.

A novel 3D Zn-coordination polymer based on a multiresponsive fluorescent sensor demonstrating outstanding sensitivities and selectivities for the efficient detection of multiple analytes

A novel and unusual 3D luminescent coordination polymer (CP) [Zn₂(3-bpah)(bpta)(H₂O)]·3H₂O (1), where 3-bpah denotes N,N'-bis(3-pyridinecarboxamide)-1,2-cyclohexane and H₄bpta denotes 2,2',4,4'-biphenyltetracarboxylic acid, was successfully synthesized via hydrothermal methods from Zn(II) ions and 3-bpah and bpta ligands. The structure of this CP was investigated via powder X-ray diffraction (PXRD) analysis along with single crystal X-ray diffraction. Notably, 1 exhibits remarkable fluorescence behavior and stability over a wide pH range and in various pure organic solvents. More importantly, 1 can become an outstanding candidate for the selective and sensitive sensing of Fe³⁺, Mg²⁺, Cr₂O₇^2-, MnO₄^-, nitrobenzene (NB) and nitromethane (NM), at an extremely low detection limit. The changes in the fluorescence intensity exhibited by these six analytes in the presence of 1 over a wide pH range indicate that this polymer can be an excellent luminescent sensor. To the best of our knowledge, 1 is a rare example of a CP-based multiresponsive fluorescent sensor for metal cations, anions, and toxic organic solvents.

A novel 3D terbium metal-organic framework as a heterogeneous Lewis acid catalyst for the cyanosilylation of aldehyde

A novel 3D lanthanide(iii) metal-organic framework (MOF) (namely Tb-MOF), was synthesized by self-assembly from Tb(iii) ion nitrate and the rigid organic ligand H₂sbdc (H₂sbdc = 5,5-dioxo-5H-dibenzo[b,d]thiophene-3,7-dicarboxylic acid), and could work as an efficient heterogeneous catalyst for the cyanosilylation of aromatic aldehydes at room temperature. The obtained Tb-MOF has been characterized and analysed in detail by single crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis and so on. The pores of Tb-MOF provided a microenvironment that was beneficial for the substrates to be close to the Lewis acid catalytic sites. The IR spectrogram and the fluorescence titration proved that the substrates could be activated inside the channel of Tb-MOF. The heterogeneous Tb-MOF catalyst with fine catalytic efficiency exhibited a high TON (TON = 460), and could be recycled at least three times without significantly reducing its activity.

Nanomolar determination of nitrofurans in water via excited-state inter-ligand proton transfer

Qualification and quantification of trace organic contaminants necessitates development of highly efficient sensing system, where excited-state inter-ligand proton transfer (ESILPT) provides a feasible pathway to construct efficient chemo-sensors. Herein, a strategically synthesized lanthanide complex, Eu(DBM)₃(MeOH)₃ (briefly as Eu-DBM-MeOH; DBM = dibenzoylmethane), features two-step ESILPT processes, along with modification on molecular structure and energy band. As a result, Eu-DBM-MeOH exhibits excellent photophysical properties with characteristic luminescence of Eu³⁺ ion. Benefiting from these merits, the Eu-DBM-MeOH complex acts as ultra-sensitive chemo-sensor toward nanomolar-level nitrofuran antibiotics (nitrofurazone and nitrofurantoin) in water, by disrupting ESILPT processes. Combining the advantages on photophysical property and luminescent sensitivity, ESILPT-active compounds are expected to widen and deepen the research on complex-based luminophores, being potentially useful in trace detection and biological imaging.

Multifunctional MOF-based probes for efficient detection and discrimination of Pb2+, Fe3+ and Cr2O72-/CrO42

Developing metal-organic framework (MOF)-based fluorescent probes for efficient detection and discrimination of polluting ions in groundwater is vital for environmental protection and human health. In this paper, we prepared two luminescence-active transition MOFs, namely, Zn-MOF and Cd-MOF, and conducted sensing experiments. The results show that they both exhibit multiple-target detection for Fe³⁺, Pb²⁺ and Cr(VI) with high sensitivity, good anti-interference ability and good recyclability even with different frameworks. In addition, Eu³⁺-incorporated samples, Eu³⁺@MOFs, with dual-emission have been fabricated via efficient encapsulation of Eu³⁺ ions into the MOF host. As expected, Eu³⁺@MOF hybrids also act as multi-target and self-calibrated probes to selectively detect Fe³⁺ and Cr(VI) ions. However, the quenching efficiencies of the original MOFs towards Fe³⁺ are higher than those of Eu³⁺@MOFs. Thus, we could differentiate Fe³⁺, Pb²⁺ and Cr(VI) ions by comparing the changes of fluorescence emission between Eu³⁺@MOFs and the original MOFs. The recognition mechanism may be attributed to the competitive energy absorption between MOFs or Eu³⁺@MOFs and the analytes.

Inner-filter effect induced fluorescent sensor based on fusiform Al-MOF nanosheets for sensitive and visual detection of nitrofuran in milk

Developing highly sensitive and visual methods for rapid detection of antibiotics is significant to ensure food quality and safety. To meet the requirement of nitrofuran antibiotics detection, luminescent fusiform Al(III)-containing metal-organic frameworks (Al-MOF) nanosheets were successfully synthesized by one-step hydrothermal method. And then, the nanosheet served as a fluorescent probe to detect nitrofuran via the inner-filter effect mechanism. The developed sensor allowed sensitive and selective detection of nitrofuran with good linear relationships. And, the detection limit (LOD) values were estimated to be 0.53, 0.838 and 0.583 μM for nitrofurazone, nitrofurantoin and furazolidone detection, respectively. The practical application of the proposed system was verified by HPLC in spiked milk samples with satisfying recoveries ranging from 88.14 to 126.21% and low relative standard deviations of 2.85 ~ 8.13%. Moreover, we designed fluorescent test papers for semi-quantitative detection of nitrofuran via naked-eye colorimetric assay. The established method provides an alternative strategy for semiquantitative detection of nitrofuran.

Tetraphenylpyrazine-Based Manganese Metal-Organic Framework as a Multifunctional Sensor for Cu2+, Cr3+, MnO4-, and 2,4,6-Trinitrophenol and the Construction of a Molecular Logical Gate

A tetraimidazole-decorating tetraphenylpyrazine has been designed and utilized for the fabrication of a novel metal-organic framework (MOF), denoted as {Mn(Tipp)(A)₂}_n·2H₂O (TippMn, where Tipp = 2,3,5,6-tetrakis[4-[(1H-imidazol-1-yl)methyl]phenyl]pyrazine and A = deprotonation of 1,4-naphthalenedicarboxylic acid), through hydrothermal synthesis. Structural analysis reveals that TippMn possesses a 2-fold-interpenetrated 4,8-connected three-dimensional (3D) network with an unprecedented {4¹⁶·6¹²}{4⁴·6²} topology. Fluorescent spectral investigations indicate that TippMn shows discriminative fluorescence when treated by Cr³⁺ and Cu²⁺, giving an INHIBIT logical gate performance. Meanwhile, TippMn can be further used as a sensor for MnO₄^- and 2,4,6-trinitrophenol (TNP) by fluorescence quenching. Notably, the sensing processes toward Cu²⁺, Cr³⁺, MnO₄^-, and TNP are labeled with high selectivity and sensitivity, quick response, and good recyclability. It is anticipated that this MOF-based versatile sensor could shed light on the exploration of MOFs for fluorescent sensors, optical switches, etc.

High-Performance Water Harvester Framework for Triphasic and Synchronous Detection of Assorted Organotoxins with Site-Memory-Reliant Security Encryption via pH-Triggered Fluoroswitching

Atmospheric water harvesting, triphasic detection of water contaminants, and advanced antiforgery measures are among important global agendas, where metal-organic frameworks (MOFs), as an incipient class of multifaceted materials, can affect substantial development of individual properties at the interface of tailor-made fabrication. The chemically robust and microporous MOF, encompassing contrasting pore functionalization, exhibits an S-shaped water adsorption curve at 300 K with a steep pore-filling step near P/P₀ = 0.5 and shows reversible uptake-release performance. Density functional theory (DFT) studies provide atomistic-level snapshots of sequential insertion of H₂O molecules inside the porous channels and also portray H-bonding interactions with polar functional sites in the two-fold interpenetrated structure. The highly emissive attribute with an electron-pull system benefits the fast-responsive framework and highly regenerable detection of four classes of organic pollutants (2,4,6-trinitrophenol (TNP), dichloran, aniline, and nicotine) in water at a record-low sensitivity. In addition to solid-, liquid-, and vapor-phase sensing, host-guest-mediated reversible fluoroswitching is validated through repetitive paper-strip monitoring and image-based detection of food sample contamination. Structure-property synergism in the electron transfer route of sensing is justified from DFT calculations that describe the reshuffling of molecular orbital energy levels in an electron-rich network by each organotoxin, besides evidencing framework-analyte supramolecular interactions. The MOF further delineates the pH-responsive luminescence defect repair via site-specific emission modulation, wherein reversibly alternated "encrypted and decrypted" states are utilized as highly reusable anticounterfeiting labels over multiple platforms and conceptualized as artificial molecular switches. Aiming at self-calibrated, advanced security claims, a NOR-OR coupled logic gate is devised based on commensurate fluorescence-cum-real-time synchronous detection of organic and inorganic (HCl and NH₃) pollutants.

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.

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.

Mixed functionalization strategy on indium-organic framework for multiple ion detection and H2O2 turn-on sensing

A special functional group mediated functionalization platform is introduced as a new and versatile platform tool to improve the fluorescence detection performance of metal-organic frameworks (MOF). The creation of a mixed-functionalization strategy on a MOF realizes the high sensitivity detection of heavy metal ions, anions and small molecules. In this work, we have first reported a novel amino functionalized 3D indium MOF [In(BDC-NH2)(OH)]n (In1-NH2) which not only has an excellent fluorescent characteristic but also shows highly sensitive identification of Fe3+, Cu2+, Pb2+ and ClO- in water with broad linear ranges and short response times. Subsequently, based on the remaining amino group site of In1-NH2, a post-synthetic modification strategy is utilized to introduce an active boronic acid group for hydrogen peroxide detection. The obtained PBA-In1 exhibits an efficient sensing performance for hydrogen peroxide with an LOD of 0.42 μM. Given this, PBA-In1 is expected to become an effective probe to monitor the formation of metabolites in humans. In1-NH2 successfully achieves multiple ion detection and the PBA-In1 sensing platform with boronic acid functionalization may have good application prospects in biochemical research in the future.

Zn-based metal organic framework-covalent organic framework composites for trace lead extraction and fluorescence detection of TNP

A novel dual functional composite (MOF_L-TpBD) was prepared through solvothermal methods, with excellent Pb²⁺ ions separation and stable 2,4,6-Trinitrophenol (TNP) fluorescence detection performance. MOF_L-TpBD was characterized by FTIR, XRD, XPS, SEM and TGA et al. The prepared material was used to extract Pb²⁺ ions, with an adsorption capacity of 21.74 mg g^-1 calculated by Langmuir isotherm model. The limit of detection was 0.32 μg L^-1, along with a linear range from 0.7 to 12 μg L^-1 and a precision of 5.4% (1 μg L^-1, n = 9), respectively, where MOF_L-TpBD was adopted as adsorbent for Pb²⁺ ions preconcentration. The practical samples and reference water sample were measured by the provided method, with the satisfactory recoveries (91-110%) and reliable analytical results. MOF_L-TpBD was capable of fluorescent sensing of TNP, with a linear range from 0.01 to 1 mM and a limit of detection of 3.52 μM, respectively, and a precision of 3.29% was obtained (0.2 mM, n = 11). Meanwhile, the recoveries ranged from 91% to 108% in analysis of TNP for the practical samples. The designed material provided a potential candidate material for the detection of heavy metal ions and explosives in environmental water samples.

Two-dimensional nano-layered materials as multi-responsive chemosensors constructed by carbazole- and fluorene-based polyaniline-like derivatives

The development of multi-responsive chemosensors has a bright application prospect in environmental monitoring and biological diagnosis. In this paper, we report two kinds of fluorescent polyaniline-like derivatives containing of carbazole or fluorene moieties with two-dimensional (2D) nano-layered structure and their applications in the detection of Al³⁺, Fe³⁺, Cu²⁺ and HCl in different environments. Through the analysis of the structure and properties of these two 2D materials, we find that the prepared (Poly(9,9'-(9,9-dihexyl-9H-fluorene-2,7-diyl)bis(9H-carbazol-3-amine))) PDFCA material performs excellent sensing properties for above analytes. Relevant density functional theory (DFT) calculation further confirms the potential application of 2D nano-layered PDFCA material in sensing field. This study presents that 2D nano-layered PDFCA material is considerably competitive in the development of multi-responsive chemosensors, and it will greatly accelerate the research of 2D polymer materials.

Devising Mixed-Ligand Based Robust Cd(II)-Framework From Bi-Functional Ligand for Fast Responsive Luminescent Detection of Fe3+ and Cr(VI) Oxo-Anions in Water With High Selectivity and Recyclability

Environmental issue related applications have globally surfaced as hottest areas of research, wherein luminescent metal-organic frameworks (LMOFs) with functionalized pores put unique signature in real-time monitoring of multiple classes of toxic compounds, and overcome many of the challenges of conventional materials. We report a two-fold interpenetrated, mixed-ligand Cd(II)-organic framework (CSMCRI-11) [Cd_1.5(L)₂(bpy)(NO₃)]·DMF·2H₂O (CSMCRI = Central Salt and Marine Chemical Research Institute, HL = 4- (1H-imidazol-1-yl)benzoic acid, bpy = 4,4'-bipyridine) that exemplifies bipillar-layer structure with two different Cd(II) nodes, and displays notable robustness in diverse organic solvents and water. Intense luminescence signature of the activated MOF (11a) is harnessed in extremely selective and fast responsive sensing of Fe³⁺ ions in aqueous phase with notable quenching constant (1.91 × 10⁴ M^-1) and impressive 166 ppb limit of detection (LOD). The framework further serves as a highly discriminative and quick responsive scaffold for turn-off detection of two noxious oxo-anions (Cr₂O₇ ^2- and CrO₄ ^2-) in water, where individual quenching constants (CrO₄ ^2-: 1.46 × 10⁴ M^-1; Cr₂O₇ ^2-: 2.18 × 10⁴ M^-1) and LOD values (CrO₄ ^2-: 179 ppb; Cr₂O₇ ^2-: 114 ppb) rank among best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress the outstanding reusability of the MOF towards detection of all these aqueous pollutants, besides their vivid monitoring by colorimetric changes under UV-light. Mechanism of selective quenching is comprehensively investigated in light of absorption of the excitation/emission energy of the host framework by individual studied analyte.

Progress in Metal-Organic Frameworks Facilitated Mercury Detection and Removal

Metal Organic Frameworks (MOFs) are noted as exceptional candidates towards the detection and removal of specific analytes. MOFs were reported in particular for the detection/removal of environmental contaminants, such as heavy metal ions, toxic anions, hazardous gases, explosives, etc. Among heavy metal ions, mercury has been noted as a global hazard because of its high toxicity in the elemental (Hg0), divalent cationic (Hg2+), and methyl mercury (CH3Hg+) forms. To secure the environment and living organisms, many countries have imposed stringent regulations to monitor mercury at all costs. Regarding the detection/removal requirements of mercury, researchers have proposed and reported all kinds of MOFs-based luminescent/non-luminescent probes towards mercury. This review provides valuable information about the MOFs which have been engaged in detection and removal of elemental mercury and Hg2+ ions. Moreover, the involved mechanisms or adsorption isotherms related to sensors or removal studies are clarified for the readers. Finally, advantages and limitations of MOFs in mercury detection/removal are described together with future scopes.

Recyclable Luminescence Sensor for Dinotefuran in Water by Stable Cadmium-Organic Framework

Due to the widespread use of dinotefuran around the world, its impact on food and environmental safety has aroused great concern, and the establishment of a rapid and convenient approach for dinotefuran detection is necessary but challenging. Herein, we synthesized a unique three-dimensional framework {[(CH₃)₂NH₂]₂[Cd₃(BCP)₂]·10H₂O·3.5DMF}_n (1). Single-crystal X-ray analysis indicates that 1 possesses a 4,8-connected anion framework that corresponds to alb topology, with a one-dimensional rectangular channel along the c-axis with the size of 4 Å × 10 Å. Compound 1 displays satisfactory solvent and thermal stability. Luminescent investigations reveal that 1 can selectively detect dinotefuran by fluorescence quenching among other pesticides, displaying excellent anti-interference performance with common ions in water. Importantly, the limit of detection is as low as 2.09 ppm, which is far below the residual concentration of the U.S. food standard. A fluorescence quenching mechanism study shows that there exists competitive energy absorption and static quenching processes. To our knowledge, 1 is the first MOF-based fluorescence probe for dinotefuran detection.

Highly Stable Acid-Induced Emission-Enhancing Cd-MOFs: Synthesis, Characterization, and Detection of Glutamic Acid in Water and Fe Ions in Acid

Two novel 3D fluorescent metal-organic frameworks (MOFs), [Cd(L)(bbibp)]_n (1) and [Cd(L)(bbibp)_0.5]_n (2), where H₂L = 4,4'-(4,4'-bipyridine-2,6-diyl)dibenzoic acid and bbibp = 4,4'-bis(benzoimidaz-1-yl)biphenyl, were acquired through a conventional method and characterized via IR spectra, single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, powder X-ray diffraction (PXRD), scanning electron microscopy, N₂ adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The crystal framework of Cd-MOF 1 remained stable in the range of pH = 1.0-12.0. Interestingly, the emission peak of 1 showed a red shift and exhibited a fluorescence turn-on effect in an acidic environment. X-ray diffraction measurement revealed that the crystal structure of 1 remained unchanged after immersion in a pH = 1.0 solution. In addition, Cd-MOFs 1 and 2 displayed fluorescent quenching to l-glutamic acid with high sensitivity and selectivity. Meanwhile, 1 showed high selectivity in recognizing Fe³⁺ under acidic conditions, which made 1 capable of detecting Fe³⁺ in acidic industrial wastewater. Finally, the fluorescent sensing mechanism was carefully studied by PXRD, transient fluorescence lifetime, XPS, and UV spectroscopy.

Efficient chemosensors for toxic pollutants based on photoluminescent Zn(ii) and Cd(ii) metal-organic networks

Optical sensors with high sensitivity and selectivity, as important analytical tools for chemical and environmental research, can be realized by straightforward synthesis of luminescent one-, two- and three-dimensional Zn(ii) and Cd(ii) crystalline coordination arrays (CPs and MOFs). In these materials with emission centers typically based on charge transfer and intraligand emissions, the quantitative detection of specific analytes, as pesticides or anions, is probed by monitoring real-time changes in their photoluminescence and color emission properties. Pesticides/herbicides have extensive uses in agriculture and household applications. Also, a large amount of metal salts of cyanide is widely used in several industrial processes such as mining and plastic manufacturing. Acute or chronic exposure to these compounds can produce high levels of toxicity in humans, animals and plants. Due to environmental concerns associated with the accumulation of these noxious species in food products and water supplies, there is an urgent and growing need to develop direct, fast, accurate and low-cost sensing methodologies. In this critical frontier, we discuss the effective strategies, chemical stability, luminescence properties, sensitivity and selectivity of recently developed hybrid Zn(ii)/Cd(ii)-organic materials with analytical applications in the direct sensing of pesticides, herbicides and cyanide ions in the aqueous phase and organic solvents.

Three Silver(I) Coordination Polymers Based on Pyridyl Ligands and Auxiliary Carboxylic Ligands: Luminescence and Efficient Sensing Properties

Easily producible sensors for harmful industrial waste compounds are of significant interest for both human health and the environment. Three novel coordination polymers, [Ag(μ-aca)(μ₄-bztpy)_1/2] (1), [Ag(μ-bza)(μ-bpa)] (2), and [Ag₂(μ-aca)₂(μ-bpa)₂]·EtOH·2H₂O (3), were assembled in this study by reactions using Ag⁺ as a node with the pyridyl ligand 1,2,4,5-tetrakis(4-pyridyl)benzene (bztpy) or 9,10-bis(4-pyridyl)anthracene (bpa) and an auxiliary chelating carboxylic ligand. Single-crystal X-ray structural analyses revealed that compound 1 has a 3D framework consisting of 1D [Ag(aca)]_∞ chains and bztpy linkers, while 2 and 3 have 2D layered structures consisting of binuclear Ag-carboxylate units and bpa linkers, respectively. Topological studies revealed that 1 has a bbf topology, while 2 and 3 are 2D [4,4] rhombic grids. The compounds were further characterized by powder X-ray diffraction, IR, elemental analysis, thermogravimetric analysis, and a luminescence study. The solids of 1-3 exhibited intense photoluminescent emission with λ_em^max at ca. 493, 472, and 500 nm, respectively. Remarkably, due to their excellent framework stability, 1 and 2 can act as multiresponsive luminescent sensors for nitrobenzene, Fe³⁺, and Cr₂O₇^2- with a high selectivity and sensitivity ascribed to their quenching effect.

Stimuli -triggered fluoro-switching in metal-organic frameworks: applications and outlook

The design and synthesis of efficient sensor materials with fast-responsive and ultrasensitive detection ability is critical to monitor ecological safety, supervise human health, control industrial wastes, and govern food quality among others. Metal-organic frameworks (MOFs) or coordination polymers (CPs) are a new class of porous crystalline materials that have emerged in several potential applications in last two decades. In particular, applications of MOFs as sensory scaffolds for the detection of hazardous pollutants have attracted researchers due to their fabulous structural characteristics and wide range of pore environment tunability. Among several transducer procedures, the luminescence detection of a particular analyte is immensely desirable as it is easy to handle and cost effective, where visual changes in physicochemical attributes can be comprehended via a quick naked eye detection. The porous nature of MOFs facilitates the pre-concentration of target analytes within the pore structure and provides superior host-guest interaction with good detection limits when compared to conventional materials. To this end, guest-induced fluorescence switching in sensory MOFs with good recyclability and unique detectable fingerprints are of particular importance to benefit futuristic monitoring aptitudes and promises environmental remediation. In this review, we present the latest literature based on the analyte-responsive modulation of fluorescence intensity in MOFs towards the detection of target pollutants and discuss the underlying sensing mechanism, which can assist in developing new useful nano-scale devices and sensors.

Cd-Based Metal-Organic Framework for Selective Turn-On Fluorescent DMSO Residual Sensing

Dimethyl sulfoxide (DMSO) is a universally used solvent in various synthetic reactions, and trace amounts of DMSO residual are often seen on the surface of chemical product. It is difficult to quickly determine whether the residual DMSO is washed completely. This work reports a Cd^II metal-organic framework (MOF) SXU-4 which can detect trace amounts of DMSO in various solvents. Fluorescence experiments reveal its turn-on fluorescence effect toward DMSO with high selectivity and sensitivity, indicating that it can be used as an effective luminescent probe for rapid chemical product purity detection by testing the washing solution. Crystallographically characterized DMSO loaded SXU-4 (DMSO@SXU-4), in combination with computational results uncover that the enhanced DMSO-MOF conjugation through multiple DMSO-MOF supramolecule interactions and charge rearrangement are the main causes of fluorescence intensification.

A multifunctional benzothiadiazole-based fluorescence sensor for Al3+, Cr3+ and Fe3+

A benzothiadiazole-based Zn^II MOF (JXUST-3) has been synthesized, which is a good multifunctional chemosensor for the detection of Al³⁺, Cr³⁺ and Fe³⁺.

pH response of a hydroxyl-functionalized luminescent metal–organic framework based phosphor

The ligand sensitized Tb³⁺ centered emission of Tb-doped Y-based hydroxyl functionalized MOFs has been utilized for pH sensing in the visible range.

Series of highly stable Cd(ii)-based MOFs as sensitive and selective sensors for detection of nitrofuran antibiotic

The oxygen atom of the MOF ether-bridging group acts as a Lewis base site, improving the connection and allowing the detection of 10 antibiotics through the fluorescence quenching effect.

Efficient luminescence sensing in two lanthanide metal–organic frameworks with rich uncoordinated Lewis basic sites

Two novel Ln-MOFs containing uncoordinated Lewis basic sites for sensitive detection of Fe3+ ions and nitrobenzene through fluorescence quenching.

Synthesis, structure, and fluorescence properties of coordination polymers of 3,5-bis(1′,2′,4′-triazol-1′-yl) pyridine

Four coordination polymers based on 3,5-bis(1′,2′,4′-triazol-1′-yl) pyridine were synthesized. Compounds [Cd₃(btc)₂(btap)(H₂O)₆] and [Cd(oa)(btap)] exhibited high sensitivity luminescence response towards Fe³⁺, Ce³⁺, Cr₂O₇²⁻ and MnO₄⁻ in aqueous solution.

Highly efficient fluorescent chemosensor for nitro antibiotic detection based on luminescent coordination polymers with 2,6-di(4-carboxyphenyl)pyrazine

A series of isostructural porous supramolecular frameworks, {[M(DCPP)(H₂O)]·(DMF)}_n, are synthesized. The as-obtained fluorescent Zn-MOF has good recognition ability towards nitro-antibiotics with low detection limits and a wide linear range.

An ultralight charged MOF as fluoro-switchable monitor for assorted organo-toxins: size-exclusive dye scrubbing and anticounterfeiting applications via Tb3+ sensitization

The trifunctional Li(i)-MOF acts as fluoro-switchable sensor for two organo-toxins, invisible-ink based data encrypter and size–specific dye scavenger, where DFT calculations support sensing and adsorption mechanisms considering extended structure.

Two cluster-based metal–organic frameworks with selective detection of Hg2+ ion and magnetic properties

Two cluster-based metal–organic frameworks have been synthesized—one exhibits highly selective fluorescent detection of trace Hg2+ and the other shows antiferromagnetic interactions between Mn3+ ions.

A luminescent Cd(II)-metal organic frameworks combined of TPT and H3BTC detecting 2,4,6-trinitrophenol and chromate anions in aqueous

A new luminescence Cd(II)-MOF (1) ([Cd₃(BTC)₂(TPT)(H₂O)₂]·4H₂O, TPT = tris(4-pyridyl)triazine, H₃BTC = 1,3,5-benzenetricarboxylic acid) was successfully synthesized under solvothermal conditions. 1 contains 3D framework which consist of Cd atoms and btc^3- anions with the large channels along c axis. Then, tpt ligands locate in the channels by utilizing three N atoms to bridge two Cd1 atoms and one Cd2 atom. 1 not only possesses remarkable thermal stability, but also can steadily exist in different organic solvents and various acid/base solutions (pH = 3-12). Moreover, 1 can detect 2,4,6-trinitrophenol (TNP) and chromate (CrO₄^2-/Cr₂O₇^2-) anions with high selectivity and sensitivity in water via the luminescent quenching. The detection limits of 1 for TNP and CrO₄^2-/Cr₂O₇^2- are 6.23 μM and 2.13 μM/2.87 μM. The mechanism of TNP luminescence quenching may be attributed to photoinduced electron transfer and resonance energy transfer, and CrO₄^2-/Cr₂O₇^2- quenching involves resonance energy transfer and competitive absorption of light. Additionally, 1 has the great anti-interference ability and repeatability for detecting TNP and CrO₄^2-/Cr₂O₇^2-, which can display the feasibility of this material as a stable luminescent probe in aqueous system.

Improving Ion Selectivity of 1,4,7-Triazacyclononane-Based Receptor by Zinc Coordination: "Turn-On" Chemosensor for Br- and Fe3+ Ions

Ion-responsive probes have gathered significant attention because of health and environmental factors, but there are few reports on the "turn-on" mechanism of Fe³⁺ and sensitive detection of Br^- by fluorescence measurement. Herein, a green luminescence material, N-5-acetyl-2-hydroxy-benzamide-1,4,7-triazacyclononane (btacn), was successfully synthesized for the first time and comprehensively characterized. As expected, btacn exhibits high sensitive, but nonspecific, extensive interaction with Cu²⁺, Co²⁺, Zn²⁺, Mn²⁺, and Fe³⁺ ions. Therefore, to improve the specificity of the probe, we tried to synthesize transition metal complexes of btacn, but all failed except Zn(btacn)Cl₂. In addition, the preformed complex, Zn(btacn)Cl₂, was used as a special "turn-on" chemosensor for detecting trace amounts of Br^- and Fe³⁺. The electrostatic interaction with Fe³⁺ and the hydrogen bond of PhO-H···Br^- leads to obvious changes in the electronic cloud of Zn(btacn)Cl₂, which are reflected in different spectral responses.

Anionic metal-organic framework as a unique turn-on fluorescent chemical sensor for ultra-sensitive detection of antibiotics

Herein, an anionic metal-organic framework, formulated as {[Zn₃(OH)(bmipia)(H₂O)₃]₄·[Zn(H₂O)6.5]₂}_n (FCS-3), was prepared from zinc ions and semi-rigid carboxylate ligands of 5-[N,N-bis(5-methylisophthalic acid)amion] isophthalic acid (H₆bmipia) and was employed as a unique fluorescence turn-on chemical sensor for the ultra-sensitive detection of various antibiotics in the aqueous phase.

Three-component D-A hybrid heterostructures with enhanced photochromic, photomodulated luminescence and selective anion-sensing properties

As an emerging class of hybrid complexes, donor-acceptor (D-A) hybrid heterostructures with advantages of both photoactive organic and inorganic components have provided an excellent platform for the fabrication of multifunctional photoactive materials. In this context, we have demonstrated three novel host-guest D-A hybrid heterostructures, {[Ln(BCEbpy)(H₂O)₄][Co^III(CN)₆]·4H₂O}_n (1 (Eu), 2 (Dy), 3 (Sm)), based on the anionic Co(CN)₆^3- and cationic coordination layers assembled from a viologen functionalized tecton and Ln(NO)₃. Due to the introduction of an electron donor, Co^III(CN)₆^3-, the unique hybrid exhibits a highly sensitive and reversible photochromic transformation from light-yellow to brown upon UV-Vis irradiation. More interestingly, accompanied with this photochromic process, hybrid 1 simultaneously possesses a photomodulated fluorescence behaviour. In addition, hybrid 1 shows high sensitivity and selectivity towards Cr₂O₇^2- anions with a fairly small LOD of ca. 9.6 × 10^-6 M.

Amino group decorated coordination polymers for enhanced detection of folic acid

A series of fluorescent coordination polymers (CPs) {[Cd₂(CH₃-bpeb)₂(BDC)₂] CP1, (BDC)_0.5/(NH₂-BDC)_0.5-CP1, (BDC)_0.34/(NH₂-BDC)_0.66-CP1, (BDC)_0.25/(NH₂-BDC)_0.75-CP1, (BDC)_0.2/(NH₂-BDC)_0.8-CP1, (NH₂-BDC)-CP1} were prepared from conjugated ligand 4,4'-((2-methyl-1,4-phenylene)bis(ethene-2,1-diyl))bipyridine (CH₃-bpeb), terephthalic acid (BDC), aminoterephthalic acid (NH₂-BDC) and CdSO₄ under solvothermal conditions. The fluorescence of aqueous suspensions of these CPs was quenched by folic acid (FA) in a concentration dependent manner. The efficiency of quenching increasing with an increased proportion of NH₂-BDC ligand in the CP with (NH₂-BDC)-CP1 exhibiting a low detection limit of 1.7 × 10^-7 M.