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.

Carboxamide functionality grafted entangled Co(II) framework as a unique hydrogen-bond-donor catalyst in solvent-free tandem deacetalization-Knoevenagel condensation with pore-fitting-mediated size-selectivity.

Concerning environmentally benign catalysis with reduced chemical usage, less energy consumption, and waste minimization, metal-organic frameworks (MOFs) with spatially isolated task-specific functionalities not only execute atom-economic important reactions but also enable size-exclusive catalysis at the interface of structure-function synergy. Herein, we synthesized a bipillar-layer Co(II) MOF from the dicarboxylate ligand and carboxamide moiety grafted pyridyl linker. The framework contains a [Co2(COO)4N4] secondary building unit (SBU) and shows excellent hydrolytic stability due to ample non-covalent interactions among the highly conjugated aromatic struts. Notably, the carboxamide functionalities remain free and are perfectly positioned throughout the one-dimensional channels of the framework, wherein three-fold interpenetration of the structure largely increases their density along the pore wall. Benefiting from these structural features, the activated MOF acts as an unprecedented organocatalyst in tandem deacetalization-Knoevenagel condensation towards electronically assorted substrates that were additionally characterized using single-crystal X-ray diffraction. Importantly, the reaction occurs under solvent-free mild conditions, and high catalyst reusability is recorded. In this one-pot cascade reaction, substrates with molecular dimensions larger than that of the three-fold interpenetration generated optimized pore-aperture undergo insignificant conversion, and therefore a rare molecular-dimension-induced size-selectivity is demonstrated. The catalytic route is detailed based on a battery of control experiments, including juxtaposing the performance of an isostructural MOF without any linker functionalization. Compared to the common Lewis acid mediated route, the results explicitly corroborate the first-ever substrate activation via hydrogen bonding to prepare coumarin derivatives via a tandem pathway, and shed light on this futuristic unconventional catalysis using contemporary materials and avoiding major operative glitches.

Redox-Active and Urea-Engineered-Entangled MOFs for High-Efficiency Water Oxidation and Elevated Temperature Advanced CO2 Separation Cum Organic-Site-Driven Mild-Condition Cycloaddition.

Development of the multifaceted metal-organic framework (MOF) with in situ engineered task-specific sites can promise proficient oxygen evolution reaction (OER) and high-temperature adsorption cum mild-condition fixation of CO2. In fact, effective assimilation of these attributes onto a single material with advance performance characteristics is practically imperative in view of renewable energy application and carbon-footprint reduction. Herein, we developed a three-fold interpenetrated robust Co(II) framework that embraces both redox-active and hydrogen-bond donor moieties inside the microporous channel. The activated MOF demonstrates notable OER catalysis in alkaline medium via quasi-reversible Co2+/Co3+ couple and unveils low overpotential with impressive 53.5 mV/dec Tafel slope that overpowers some benchmark, commercial, as well as contemporary materials. In particular, significantly increased turnover frequency (3.313 s-1 at 400 mV) and fairly low charge-transfer resistance (3.02 Ω) compared to Co3O4, NiO, and majority of redox-active MOFs together with 91% Faradaic efficiency and notable framework durability after multiple OER cycles endorse high-performance water oxidation. Pore-wall decked urea groups benefit appreciable CO2 adsorption even at elevated temperatures with considerable MOF-CO2 interactions and exhibit recurrent capture-release cycles at diverse temperatures. Interestingly, CO2 selectivity displays radical upsurge with temperature rise, affording 40% improved CO2/N2 value of 200 at 313 K, which outperforms many porous adsorbents and delineates real-time CO2 scavenging potential. The guest-free MOF effectively catalyzes solvent-free CO2 cycloaddition with broad substrate tolerance and satisfactory reusability under relatively mild condition. Opposed to the common Lewis acid-mediated reaction, two-point hydrogen-bonding activates the substrate, as supported from controlled experiments, juxtaposing the performance of an un-functionalized MOF and fluorescence modification-derived framework-epoxide interaction, providing valuable insights on unconventional cycloaddition route in the MOF.

Dangling carboxylic-acid functionality in a fish-bone-shaped 2D framework as a hydrogen-bond-donating catalyst in Friedel-Crafts alkylation.

A two-dimensional, layer-stacked metal-organic framework (MOF) with a dangling acid functionality was developed as the first-ever example of carboxylic-acid-catalysed Friedel-Crafts alkylation with high reusability. Contrary to conventional hydrogen-bond-donating catalysis, a pair of oppositely oriented -COOH moieties acted as potential hydrogen-bonding sites, and efficiently worked for electronically assorted substrates. Control experiments including juxtaposing the performances of a post-metalated MOF and an unfunctionalized analogue explicitly authenticated the carboxylic-acid-mediated catalytic route.

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.

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.

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 Chemically Robust and Cationic Ni(II)-MOF with Nitrogen-Rich Micropores for Moisture-Tolerant CO2 Capture: Highly Regenerative and Ultrafast Colorimetric Sensor for TNP and Multiple Oxo-Anions in Water with Theoretical Revelation.

Metal-organic frameworks (MOFs) show distinctive superiority for carbon dioxide (CO2) capture and luminescent sensing of toxic pollutants over other materials, where combination of both of these properties together with improvement of hydrolytic stability and pore functionality is critical to environmental remediation applications. The Ni(II) framework [Ni2(µ2-OH)(azdc)(tpim)](NO3)·6DMA·6MeOH (CSMCRI-3) (tpim = 4,4',4″-(1H-imidazole-2,4,5-triyl)tripyridine, H2azdc = azobenzene-4,4'-dicarboxylic acid, DMA = dimethylacetamide, CSMCRI = Central Salt & Marine Chemicals Research Institute), encompassing cationic [Ni2(µ2-OH)(CO2)2] SBUs, is solvothermally synthesized from nitrogen-rich and highly fluorescent organic struts. The noninterpenetrated structure, containing free nitrogen atom affixed microporous channels, is stable in diverse organic solvents and weakly basic and acidic aqueous solutions. The activated MOF (3a) exhibits strong CO2-framework interaction and extremely selective CO2 adsorption over N2 (292.5) and CH4 (11.7). Importantly, water vapor exposure does not affect the surface area and/or multiple CO2 uptake-release cycles, signifying potential of the porous structure for long-term use under humid conditions. Aqueous-phase sensing studies illustrate extremely specific and ultrafast detection of explosive 2,4,6-trinitrophenol (TNP) via remarkable fluorescence quenching (KSV = 1.3 × 105 M-1), with a 0.25 ppm limit of detection (LOD). Furthermore, 3a serves as unique luminescent probe for highly discriminative and quick responsive detection of three noxious oxo-anions (Cr2O72-, CrO42-, MnO4-) in water via noteworthy turn-off responses and extreme low LODs (Cr2O72- 0.9; CrO42- 0.29; MnO4- 0.25 ppm). It is imperative to stress the outstanding reusability of the MOF toward multicyclic sensing of all four major water contaminants, alongside visible colorimetric changes upon individual analyte detection. Mechanistic insights in light of the electron transfer route together with density functional theory calculations portray the influence of pore functionalization in framework-analyte interactions, including alternation in energy levels, where varying degrees of contribution of energy transfer explicitly authenticates high quenching of the material.