Site-Memory-Triggered Reversible Acronym Encryption in a Nitrogen-Rich Pore-Partitioned MOF for Ultrasensitive Monitoring of Roxarsone and Dichloran over Multiple Platform

Stimuli-responsive emission color modulation in fluorescent metal-organic frameworks (MOFs) promises luminescence-ink-based security application, while task-specific functionality-engineered pores can aid fast-responsive, discriminative, and ultralow detection of harmful organo-aromatics in the aqueous phase. Considering practical applicability, a self-calibrated fluoro-switch between encrypted and decrypted states is best suited for antiforgery measures, whereas image-based monitoring of organo-toxins by repetitive and handy methods over multiple platforms endorses in-field sensory potential. Herein, we constructed a mixed-ligand based chemically stable and bilayered-pillar MOF from -NH2-hooked pyridyl linker and tricarboxylate ligand that embraces negatively charged [Cd3(μ2-OH)(COO)6] node and shows pore-space-partitioning by nitrogen-rich flanked organic struts. Owing to the presence of a self-calibrating triazolylamine moiety-grafted auxiliary linker, this anionic MOF delineates reversible and multicyclic fluoro-swapping between protonated-encrypted and deprotonated-decrypted domains in the alternative presence of acid and base. Such pH-triggered, site-specific luminescence variation is utilized to construct highly regenerative anticounterfeiting labels for vivid acronym encryption. The intense fluorescence signature of the material is further harnessed in extremely selective and quick responsive sensing of harmful feed additive roxarsone (ROX) and dichloran (DCNA) pesticide in highly recyclable fashion with significant quenching and nanomolar limits of detection (ROX: 52 ppb; DCNA: 26.8 ppb). Notably, the ultrasensitive fluoro-detection of both these organo-toxins is successfully demonstrated via a handy paper-strip method as well as on the vegetable surface for real-time monitoring. Comprehensive density functional theory studies validate the electron transfer mechanism through redistribution of molecular orbital energy levels by each of the targeted analytes in this electron-rich framework besides evidencing MOF-analyte supramolecular interactions.

Coordination Unsaturation and Basic Site-Immobilized Nanochannel in a Chemorobust MOF for 3-Fold-Increased High-Temperature Selectivity and Fixation of CO2 under Mild Conditions with Nanomolar Recognition of Roxarsone

A multifaceted metal-organic framework (MOF) with task-specific site-engineered pores can promise high-temperature and moisture-tolerant capture and non-redox fixation of CO2 under mild conditions as well as ultrasensitive detection of carcinogenic contaminants in water. Herein, we report a pillar-bilayered MOF that holds a nanochannel with contrasting functionalities for both these sustainable applications with improved performance characteristics. The twofold entangled robust framework exhibits CO2 adsorption at elevated temperatures with considerable MOF-gas interaction. Interestingly, CO2 selectivity unveils nearly a 3-fold improvement upon the rise of temperature, affording a CO2/N2 value of 820 at 313 K, which outperforms many porous adsorbents. Additionally, breakthrough simulation establishes complete separation and attests the potential of this MOF in the separation of flue gas mixture. Importantly, minor CO2 loss during multiple capture-release cycles and under a relative humidity of 75% promise practical usability of the material. Density functional theory (DFT) not only portrays the atomistic level snapshots of temperature-triggered CO2 inclusion inside this microporous vessel alongside the role of diverse CO2-philic sites but also validates the basis of N2-phobicity of an azo-functionalized linker on such increased selectivity. The guest-free MOF further demonstrates non-redox and recyclable CO2 fixation with wide epoxide tolerance under solvent-free mild conditions and even works at atmospheric pressure and room temperature. The crucial roles of high-density acid-base sites in both adsorption and catalysis are supported by control experiments and by comparing the activity of an unfunctionalized MOF. The hydrolytic stability and strong luminescence signature benefit the framework in aqueous-phase selective and fast responsive detection of detrimental roxarsone (ROX) with high quenching (7.56 × 104 M-1) and very low sensitivity (68 nM). Apart from varying degrees of an energy-transfer mechanism, the fluorosensing of ROX is comprehensively supported by in-depth DFT studies that manifest alteration of MOF energy levels in the presence of organoarsenic compounds and depict MOF-analyte supramolecular interactions.

Detection Enhancement of One Multifunctional Cd-Metal-Organic Framework toward Tetracycline Antibiotics by Simply Mixing Eu3+ in Suspension

It is necessary to find more simple methods to improve the detection selectivity and sensitivity of antibiotics. Herein, we constructed a novel three-dimensional (3D) Cd-MOF LCU-117 assembled from p-terphenyl-4,2″,5″,4'-tetracarboxylic acid, which showed a special 3D helical structure with carboxylic acid ligands and nitrogen-containing ligands crossing each other vertically. Luminescence measurements indicated that LCU-117 has high selectivity and sensitivity toward Eu³⁺ through the ratiometric effect. Meanwhile, this complex itself could detect antibiotics oxytetracycline (OTC) through the turn-off mechanism. When Eu³⁺ was added in suspensions of LCU-117 (noted as Eu³⁺@LCU-117), the detection toward OTC was enhanced significantly and visually. The sensing mechanism was investigated in detail by various measurements and theoretical calculations. LCU-117 has a good effect on the logic gate, potential fingerprint detection, and mixed-matrix membranes (MMMs). The practical application for monitoring OTC in water samples also provided a satisfactory result.

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.

Triphenylbenzene functionalized polyhedral oligomeric silsesquioxane fluorescence sensor for the selective analysis of trace nitrofurazone in aquatic product and cosmetics

Nitrofurazone (NFZ) is carcinogenic and mutagenic to human in long-term ingestion, and it is prohibited to be added in food. In this work, a novel triphenylbenzene (TPB) functionalized fluorescent hybrid porous polymers (POSS@TPB) was constructed by using polyhedral oligomeric silsesquioxane (POSS) as the rigid group and TPB as the core unit of high fluorescence. The morphology and physicochemical properties of POSS@TPB were characterized in detail. Moreover, the synergistic effect of inner filter effect and photoinduced electron transfer is verified by experimental and simulation results. After condition optimization, a NFZ analysis method based on POSS@TPB probe was established with a linear range of 0.4-16.5 mg/L and a detection limit of 0.13 mg/L. In addition, the fluorescent probe has good stability, anti-interference and considerable reusability. At the same time, the selective analysis of trace NFZ in aquatic product and cosmetics was carried out with satisfied recoveries of 87%-110.6% and relative standard deviation less than 4.1%. And the results were verified by high-performance liquid chromatography method. Overall, this fluorescence sensor has excellent performance in NFZ analysis, which provides a broad application prospect for the repeatable and selective residue NFZ analysis in aquatic product and cosmetics.

Selective and Multicyclic CO2 Adsorption with Visible Light-Driven Photodegradation of Organic Dyes in a Robust Metal-Organic Framework Embracing Heteroatom-Affixed Pores

Pore environment modulation with polarizing groups is one of the essential prerequisites for selective carbon dioxide (CO₂) adsorption in metal-organic frameworks (MOFs), wherein judicious installation of the photocatalytic feature can promise visible light-triggered degradation of toxic organic dye molecules. However, astute amalgamation of both these attributes over a single MOF is rather rare, yet much anticipated in view of sustainable applications. Pore engineering is effectively harnessed in a Zn(II)-based three-dimensional (3D) MOF, CSMCRI-16 (CSMCRI = Central Salt and Marine Chemicals Research Institute), through mixed-ligand assembly of a N-rich linker (L), 4,4'-oxybis(benzoic acid) (H₂oba) ligand, and [Zn₂(CO₂)₄N₂] paddle-wheel secondary building units (SBUs). The noninterpenetrated structure contains unbound nitrogen and accessible oxygen atom-decorated porous channels and exhibits admirable stability in diverse organic solvents, open air, and at elevated temperatures. The heteroatom-decorated porous channels facilitated excellent CO₂ uptake in the activated MOF (16a) with high selectivity over N₂ (CO₂/N₂: 155.3) at 273 K. The framework further exhibits reasonable CO₂ affinity and multicyclic CO₂ sorption recurrence without a significant loss in the uptake capacity. Benefitting from the presence of the [Zn₂(CO₂)₄N₂] cluster in conjugation with π-conjugated organic ligands, the extended 3D network revealed an optical band gap energy of 2.55 eV, which makes the MOF an efficient photocatalyst toward the degradation of the cationic dyes crystal violet (CV) and methylene blue (MB) in the presence of a simple 40 W visible light lamp without any assistance of external oxidants. The catalyst exhibits multicyclic performance and short reaction time in addition to the fact that catalytic efficiencies (CV: 97.2%, MB: 97.8%) are comparable to those of contemporary materials.

Brønsted Acid-Functionalized Ionic Co(II) Framework: A Tailored Vessel for Electrocatalytic Oxygen Evolution and Size-Exclusive Optical Speciation of Biothiols

Metal-organic frameworks (MOFs) not only combine globally demanded renewable energy generation and environmental remediation onto a single platform but also rationalize structure-performance synergies to devise smarter materials with remarkable performance. The robust and non-interpenetrated cationic MOF exemplifies a unique bifunctional scaffold for the efficient electrochemical oxygen evolution reaction (OER) and ultrasensitive monitoring of biohazards. The microporous framework containing Brønsted acid-functionalized [Co₂(μ₂-OH)(CO₂)₂] secondary building units (SBUs) exhibits remarkable OER performance in 1 M KOH, requiring 410 mV overpotential to obtain 10 mA cm^-2 anodic current density, and a low Tafel slope of 55 mV/dec with 93.1% Faradaic efficiency. Apart from the high turnover frequency and electrochemically assessable surface area, steady OER performance over 500 cycles under potentiodynamic and potentiostatic conditions result in long-term catalyst durability. The highly emissive attribute from nitrogen-rich fluorescent struts benefits the MOF in recyclable and selective fluoro-detection of three biothiols (l-cysteine, homocysteine, and glutathione) in water with a fast response time. In addition to colorimetric monitoring in the solid and solution phases, control experiments validate size-exclusive biothiol speciation through molecular-dimension-mediated pore diffusion. The role of SBUs in the OER mechanism is detailed from density functional theory-derived free energy analysis, which also validates the importance of accessible N-sites in sensing via portraying framework-analyte supramolecular interactions.

A water-stable Zn4O-based MOF decorated with carbazolyl chromophores for multi-responsive fluorescence sensing of Fe3+, Cr2O72− and nitro-compounds

A MOF with strong deep blue light emission and high quantum efficiency has high selectivity and sensitivity for detecting 2,6-dichloro-4-nitroaniline.

Urea-engineering mediated hydrogen-bond donating Friedel−Crafts alkylation of indoles and nitroalkenes in dual-functionalized and microporous metal-organic framework with high recyclability and pore-fitting-induced size-selectivity

As an effective alternative to Lewis acid activation, hydrogen-bond donating (HBD) organo-catalysis denotes a powerful construction tool to important classes of carbon–carbon bonds, wherein metal-organic frameworks (MOFs) alleviate issues like...

An yttrium-organic framework based on a hexagonal prism second building unit for luminescent sensing of antibiotics and highly effective CO2 fixation

An yttrium-organic framework based on a hexagonal prism second building unit was constructed from nonanuclear yttrium(iii) and 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine for the luminescent sensing of antibiotics and highly effective CO2 fixation.

A low-dimensional N-rich coordination polymer as an effective fluorescence sensor for 2,4,6-trinitrophenol detection in an aqueous medium

Stable one-dimensional coordination polymer is used as a highly selective sensor for the detection of TNP.

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.

Intrinsic-Unsaturation-Enriched Biporous and Chemorobust Cu(II) Framework for Efficient Catalytic CO2 Fixation and Pore-Fitting Actuated Size-Exclusive Hantzsch Condensation with Mechanistic Validation

Carbon dioxide (CO₂) utilization and one-pot Hantzsch condensation denote two important protocols pertinent to sustainable agenda because of the obvious advantages like reduction in chemical usage, short reaction time, and minimum waste generation. To this end, the astute combination of optimum-sized pore structure with built-in Lewis acid center in metal-organic frameworks (MOFs) can bring about such reactions under energetically favorable conditions and offer a step forward to size-exclusive catalysis. The chemoresistant and twofold interpenetrated Cu(II) framework CSMCRI-13 (CSMCRI = Central Salt & Marine Chemicals Research Institute) is built from a C₃-symmetric tricarboxylate ligand and an N,N'-donor linker that undergo incisive amalgamation of the paddle-wheel [Cu₂(COO)₄] secondary building unit (SBU) and the intrinsically unsaturated Cu(II) node with four coordination. The microporous structure features a dual-pore containing cage-like network with free oxygen-atom-enriched cavities and exhibits appreciable CO₂ adsorption with moderate MOF-CO₂ interaction in activated form (13a). Benefitting from both, the coordinatively frustrated metal center containing MOF acts as a highly synergistic and solvent-free catalyst in CO₂ cycloaddition reaction under an 8 bar CO₂ pressure at 70 °C in 6 h. The catalyst furnished admirable reactivity and fair recyclability with a wide range of substrates, wherein sterically encumbered and long-chain epoxides produced poor conversion. This MOF further executes highly regenerable Hantzsch condensation reaction under mild condition with superior activity to contemporary materials, where most of the 1,4-dihydropyridine derivatives are additionally characterized through the single-crystal X-ray diffraction analysis. Importantly, mechanistic proof of the tricomponent condensation involving built-in Lewis acid sites is validated from several control experiments and in-depth analytical studies. To the best of the single-step multicomponent reaction, substrate molecules having incompatible molecular dimension to that of pore size of the framework resulted insignificant conversion and demonstrated the first-ever pore-fitting-induced size selectivity in Hantzsch condensation.

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.

Advancement in functionalized luminescent frameworks and their prospective applications as inkjet-printed sensors and anti-counterfeit materials

Supramolecular luminescent frameworks with conjugated architectures exhibits interesting photophysical properties with phenomenal chemical and thermal stability. This has instigated global researchers towards its extensive application in toxic analyte detection and the formulation of anti-counterfeit materials. In correlation with this present scenario, luminescent metal-organic frameworks (LMOFs), possessing tailorable structural and functional properties and exceptional physicochemical features, have been categorized as emerging 'smart materials'. Interestingly, LMOFs have assisted in the rapid development of an effectual sensing platform and swift fabrication of anti-counterfeit materials on desirable substrates with the aid of 'Inkjet Printing', which is a viable, low-cost, and high-resolution technology. Inkjet printing is an excellent material deposition technique in the modern era owing to its easy settling over flexible substrates, simplistic emergence of large area image patterns with improved throughput, minimal cost, explicit resolution, and least waste generation. The present review provides state-of-the-art progress on LMOFs based (i) luminescent security ink fabrication with static and dynamic multinodal luminescent materials and (ii) sensory device formulation for the easy and instantaneous recognition of hazardous analytes through the 'Inkjet Printing' technology. This techno-chemical integration will be certainly beneficial to prevent the growth of counterfeit materials and monitor the bioaccumulation of hazardous analytes in our ecological system.

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.

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.

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.

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.