Luminescent Metal-organic Framework Research Articles

Inner filter effect on amino-functionalized metal-organic framework for the selective detection of tetracycline

The use of tetracycline (TC) for the treatment of infectious diseases caused by bacteria has been humongous over the past few decades. However, the presence of untreated TC in freshwater leads to antimicrobial resistance. To prevent this concern from damaging the freshwater system, a stable sensor with high selectivity and rapid detection towards TC is desirable. Metal-Organic Frameworks (MOFs) are organic-inorganic hybrid structures with excellent stability, multifunctional ability, and tuneable pore structure that find extensive applications in detection techniques. The structural adaptability, excellent porosity and large surface area of MOFs prove advantageous in terms of adsorption of antibiotics. With this insight, a highly stable Zn-based Luminescent Metal-Organic Framework (LMOF) for the selective detection of tetracycline was developed. It is worth mentioning that, the LMOF-based sensor showed no depreciation in luminescence activity and can be reused more than 10 times. Moreover, a very low detection limit of 0.11 μM and a Stern-Volmer quenching constant (Ksv) value of 1.16 × 104 M−1 indicate its sensitivity precision towards TC detection. A significant inner filter effect of TC was observed in addition to adsorption of TC on the MOF through hydrogen bonding. Further, test strips based on IRMOF-3 showed satisfactory recovery in real-time samples. Thus, the stimuli-responsive sensor reports a simple strategy for excellent sensing performance towards TC.

PH-Stable Luminescent Metal-Organic Frameworks for the Selective Detection of Aqueous-Phase FeIII and CrVI Ions.

The development of chemically stable metal-organic framework (MOF)-based luminescent platforms for toxic ion detection in an aqueous medium is highly challenging because most of the classical MOFs are prone to water degradation, and that is the reason why most of the MOF-based luminescent sensors use a nonaqueous medium for sensing. In this contribution, we report two new water-stable luminescent MOFs (Zn-MOF-1 and Zn-MOF-2), assembled from a mixed-ligand synthesis approach. Because of the presence of a hydrophobic trifluoromethyl group to the backbone and stronger metal-N coordination, these MOFs exhibit excellent stability not only in water but also in acidic/alkaline aqueous solutions (pH = 3-10). Here, we report a green sensing approach by exploiting the significant reduction in photoluminescence of these MOFs in the presence of toxic ions. Fe3+ and CrO42-/Cr2O72- ions could be traced with a detection limit (LOD) in the micromolar range (0.045 and 0.745/0.33 μM for Zn-MOF-1; 125.2 and 114.2/83.5 μM for Zn-MOF-2). The mechanistic study reveals that competitive absorption of the excitation energy coupled with fluorescent resonance energy transfer are responsible for the turn-off quenching. The anti-interference ability and recyclability along with the pH stability gave these MOFs high potential to be used as practical sensors toward FeIII and CrVI ions in water as a greenest medium.

Efficient nitro-aromatic sensor via highly luminescent Zn-based metal-organic frameworks

Highly stable zinc-based luminescent metal-organic framework (LMOF) [(Zn2-(NDC)2(bpy)·Gx) where NDC-2,6-naphthalene dicarboxylic acid, bpy - 4,4' bipyridine, and G - guest solvent molecules] is synthesized via solvothermal method at different synthesizing temperatures (120, 150 and 180∘C) for the detection of nitro-aromatics. Sample structure and presence of ligands is confirmed by X-ray diffraction and FTIR measurements, respectively. The photoluminescence properties of synthesized LMOF samples show the strong emission intensity in ethanol at 376 nm when it is excited at 240 nm. The detection limit is calculated using fluorescence quenching for the various nitro-analytes (2,4-DNP, 2-Nitrotoulene, 4-Nitrophenol, and Nitrobenzene) revealed that it is least for the sample synthesized at 150∘C with the maximum percentage in fluorescence decay. The thermal stability of as-synthesized samples is analysed using thermogravimetry analysis (TGA) which reveals that sample synthesized at 150∘C is the most stable sample. The TGA analysis also shows that on further heating from 526∘C to 980∘C decomposition of zinc metal and formation of zinc oxide takes place. FE-SEM confirms the cuboidal morphology with an average particle size of 12.62 nm, corroborated by the TEM analysis. The fluorescence quenching mechanism is explained on the basis of dipole-dipole and π-stacked interactions between the MOF and nitro-aromatics that play a prominent role in the sensing of nitro-analytes. Synthesized MOF samples show excellent recyclability in fluorescence quenching even after the fourth cycle, i.e. more than 95% and is sensitive to detect nitro-aromatics even upto 0.284 µM, and the results can generalize the explosive sensor technology and sensing various nitro-based pollutants.

Multi-step tandem functionalization assembly of MOFs-based hybrid polymeric films for color tuning luminescence and responsive sensing on organic vapors

Metal-organic frameworks (MOFs) are a promising class of porous crystalline materials which can be functionalized by versatile postsynthetic modification (PSM) for further practical applications. Whereas, such crystalline nature of MOFs stands as a serious obstacle to their desired shaping and manufacture for further practical applications. Herein, a multi-step tandem functionalization assembly strategy is employed to fabricate a luminescent MOF-based hybrid polymeric film to endow the luminescent MOFs with processability and applicability. In detail, Eu3+ ions are introduced into ZnMOF-5-NH2 frameworks to create a red emitting-center firstly. Next, methacrylic anhydride is incorporated to react with amino functional groups of Eu-ZnMOF-5-NH2 to obtain Eu-MOF-L with unsaturated bonds by a covalent PSM strategy. Finally, the copolymerization reaction took place between Eu-MOF-L and monomers (butyl methacrylate) which initiated by benzoyl peroxide. The polymeric hybrid film (Eu-MOF-L@PBMA film) is soft, flexible, and homogeneous. The physical characterization and the luminescence properties of these hybrid materials were studied in details. The multi-color luminescence of these hybrids and their polymeric hybrid films are tuned by optimizing the critical parameters to serve as a white-light emitting device. Furthermore, Eu-MOF-L@PBMA film is utilized for the detection of volatile organic vapors. In terms of their distinct color variation, an effective dual-readout method assists in sensing volatile organic vapors, especially organic amine vapors.

Solvent-free synthesis of hierarchical Tb3+-doped Yttrium benzene-1,3,5-tricarboxylate metal organic framework nanosheets for fast and highly sensitive fluorescence detection of Fe3+ and Cr2O72− ions

Controllable synthesis of luminescent metal-organic frameworks (MOFs) having the merits of ease preparation, outstanding sensitivity and stability is of great significance for exploring their efficient sensing applications. Herein, we report a hierarchical terbium-doped yttrium-benzene-1,3,5-tricarboxylate MOF nanosheet via solvent-free synthetic strategy with a topological structure of MIL-78. The fluorescence property of the hierarchical Tb3+-doped Y-based MOF nanosheets can be tuned by adjusting the molar ratio of Tb3+ to Y3+ ions, and the Tb0.5Y0.5-MOF nanosheet-like morphology with the optimum characteristic Tb3+ ion green emission exhibited great potential acting as fluorescence probe for highly sensitive Fe3+ and Cr2O72− detection. The Tb3+-doped Y-MOF nanosheets show a fast response time of less than 1 s for Fe3+ ions. They also have low detection limits of 0.40 and 0.26 µM toward Fe3+ and Cr2O72− ions, respectively, as well as excellent stability. This work paves the way to explore intriguing hierarchical MOF-based luminescent materials for efficient fluorescence sensing applications.

Design and syntheses of two luminescent metal-organic frameworks for detecting nitro-antibiotic, Fe3+ and Cr2O72-

Two zinc(II)–coordination polymers, namely [Zn2(L1)2(bpa)(H2O)2]·2(H2O) (1) and [Zn(L1)(bpp)] (2) (where L1 ​= ​5-(2-cyanophenoxy) isophthalic acid; bpa ​= ​1,2-bis(4-pyridine)-ethane; and bpp ​= ​1,3-bis(1)pyridyl propane) have been synthesized under hydrothermal conditions. Both as-synthesized samples were characterized by element analysis, powder X-ray diffraction, infrared spectrum, thermogravimetric analysis and single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic crystal system with P–1 space group, and compound 2 belongs to the P21/n space group of monoclinic system. Both Zn-MOFs have good luminescent properties for rapidly detecting nitro-antibiotics, Cr2O72− and Fe3+ in water with high selectivity and sensitivity. Therefore, both Zn-MOFs materials are promising luminescent sensors in the detection of target analytes in water.

Multi-responsive luminescent MOF sensor for Fe3+, CrO42− and Cr2O72− in aqueous solution based on phenylenediacetate and bis-imidazole ligand

Two metal-organic frameworks (MOFs), namely, [Zn2(m-2mbix)(HEA)2·2H2O]n (1) and { [Ni(m-2mbix)(HEA)]·3H2O}n (2) (m-2mbix = 1,3-bis(2-methylimidazol-1-ylmethyl)benzene, H2HEA = 1,2-phenylenediacetic acid), respectively, were successfully synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction analysis, elemental analysis, infrared spectroscopy and thermogravimetric analysis. Single crystal structures revealed that 1 and 2 were two-dimensional structure and two-dimensional (4,4)-topological layer structure, respectively. In addition, the complex 1 can function as a turn-off luminescent sensor to sensitively and selectively sensing Fe3+, CrO42− and Cr2O72− ions in aqueous media.

Imparting down/up-conversion dual channels fluorescence to luminescence metal-organic frameworks by carbon dots-induced for fluorescence sensing.

The rapid and simple synthesis of highly efficient multi-emission luminescent metal-organic frameworks (LMOFs) with down/up-conversion fluorescence properties becomes critical in potential optical sensing. Here, we present a luminescent dual-ligand co-assisted strategy to one-pot prepare LMOFs for multiplex fluorescence sensing using carbon dots (CDs) and 2-methylimidazole (2-MIM) as dual-ligand to induce Zn2+ on zeolitic imidazolate framework-8 surface (CDs/MIM-Zn). The CDs/MIM-Zn exhibited efficient fluorescence-enhanced dual channels triple-emission with Stokes and anti-Stokes type excitation profiles. With the assistance of Stokes and anti-Stokes type optical property of CDs and the intrinsic porosity of MOFs structure, a rapid and sensitive dual-channel detection excited at 370nm and 790nm was performed to fluorescence turn off-on detect metal ions and reduced glutathione in real blood samples with the satisfactory recoveries of 98.3-106.4%. The dual channels triple-emission strategy ensured multiplex detection of more analytes in parallel.

Modulating Photo- and Radioluminescence in Tb(III) Cluster-Based Metal–Organic Frameworks

Luminescent metal–organic frameworks (MOFs) are of interest for sensing, theranostics, dosimetry, and other applications. The use of lanthanoids in MOF nodes allows for intrinsic metal-based luminescence. In this work, a facile route for modulating the photoluminescent and radioluminescent properties of Tb(III)-based MOFs is reported. By using Tb(III) cluster nodes as X-ray attenuators, and organic linkers with varying excited state energies as sensitizers, MOFs with metal-based, linker-based, and metal+linker-based photo- and radioluminescence are reported.

Achieving gas pressure-dependent luminescence from an AIEgen-based metal-organic framework

Materials exhibiting aggregation-induced emission (AIE) behaviour enable strong emission in solid state and can respond to various external stimuli, which may facilitate the development of materials for optical sensing, bioimaging or optoelectronic devices. Herein, we use an AIE luminogen 2’,5’-diphenyl-[1,1’:4’,1”-terphenyl]-4,4”-dicarboxylic acid as the ligand to prepare an AIEgen-based MOF (metal-organic framework) named FJI-H31. FJI-H31 exhibits bright luminescence under ambient conditions (under air and at room temperature), but almost no emission is observed under vacuum. Our investigation shows that the emission intensity displays a smooth and reversible enhancement with increased gas pressure, which may be attributed to the restriction of intramolecular motion brought by structural deformation under pressure stimulus. Unlike most pressure-responsive MOFs, the luminescence reverts to its original state once gas pressure recovers. By virtue of its unique optical properties, a luminescent MOF with sensing ability of gas-pressure is realized.

Metal-Organic Frameworks in Mixed-Matrix Membranes for High-Speed Visible-Light Communication.

Mixed-matrix membranes (MMMs) based on luminescent metal-organic frameworks (MOFs) and emissive polymers with the combination of their unique advantages have great potential in separation science, sensing, and light-harvesting applications. Here, we demonstrate MMMs for the field of high-speed visible-light communication (VLC) using a very efficient energy transfer strategy at the interface between a MOF and an emissive polymer. Our steady-state and ultrafast time-resolved experiments, supported by high-level density functional theory calculations, revealed that efficient and ultrafast energy transfer from the luminescent MOF to the luminescent polymer can be achieved. The resultant MMMs exhibited an excellent modulation bandwidth of around 80 MHz, which is higher than those of most well-established color-converting phosphors commonly used for optical wireless communication. Interestingly, we found that the efficient energy transfer further improved the light communication data rate from 132 Mb/s of the pure polymer to 215 Mb/s of MMMs. This finding not only showcases the promise of the MMMs for high-speed VLC but also highlights the importance of an efficient and ultrafast energy transfer strategy for the advancement of data rates of optical wireless communication.

Multiresponsive luminescent probe for Fe3+, CrO4 2- and Cr2O7 2- in aqueous solution based on N,N’-bis-pyridin-2-ylmethylene-hydrazine and phthalate ligands

One new luminescent metal-organic framework (LMOF), {[Cd2(L) (BDC)2(H2O)2]·4H2O}n (1) (L = N,N’-bis-pyridin-2-ylmethylene-hydrazine, H2BDC = phthalic acid), was synthesized and structurally characterized by single-crystal X-ray diffraction analysis, elemental analysis, infrared spectroscopy and thermogravimetric analysis. Complex 1 exhibits two-dimensional (6,3)-topological layer structures that are further stabilized by hydrogen bonds into a 3 D architecture. Luminescence experiments showed that 1 can act as a turn-off luminescent probe for the sensitive and selective detection of Fe3+, CrO4 2-, and Cr2O7 2- ions. The detection limits as well as the possible quenching mechanism was also explored.

A luminescent Eu3+-functionalized MOF for sensitive and rapid detection of tetracycline antibiotics in swine wastewater and pig kidney

Tetracyclines (TCs), a type of antibiotics, are widely used in human therapy and animal husbandry. Public concerns about tetracyclines residues have been raised due to their negative impact on the environment and food, causing bacterias drug resistance and human health concerns. In this work, a luminescent europium MOF (EuUCBA) is constructed via post-synthetic attachment of Eu3+ into a UiO-66 type MOF. The luminescent of EuUCBA exhibits high stability in aqueous media in the pH range of 4–11. Among 36 common veterinary drugs, the synthesized probe is highly selective and sensitive to six tetracyclines with low detection limits of 0.118 μM, 0.228 μM, 0.102 μM, 0.138 μM, 0.206 μM, and 0.078 μM for oxytetracycline (OTC), chlortetracycline (CTC), methylenetetracycline (MTC), minocycline (MOC), tetracycline (TC), and doxycycline (DOXY), respectively. Furthermore, the probe shows good anti-interference ability and fast response. Finally, EuUCBA was successfully to detect DOXY in swine wastewater and pig kidney with good recoveries. This work provides an excellent fluorescent sensor for highly selective and rapid detection of TCs residues in wastewater and complex biological samples.

Novel pyrazole-based carboxylate ligand as a building block for assembling lanthanides in luminescent 2D and 3D MOFs

New pyrazole-based carboxylic ligand 1-(carboxymethyl)-1H-pyrazole-3,5-dicarboxylic acid (H3L) as well as its lanthanide complexes [LnL(H2O)2]n, Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8) and [LnL(H2O)]n, Ln = Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14) have been prepared and studied. Compounds 1–8 represent a 3D polymer structure while 9–14 are 2D-polymers. Lanthanide-centered luminescence of compounds 4–9 is studied in detail. It is shown that high energy triplet level of H3L ligand (27100 cm−1) is able to sensitize not only the yellow-green luminescence of Tb3+ and Dy3+ ions, but also the red-orange luminescence of Sm3+ and Eu3+. NIR-luminescence of the neodymium complex 4 is possible upon direct excitation through the f-f transition of the Nd3+ ion.

Cooperation between Eu MOF and glycerol for luminescent sensing of nerve agent mimic vapor

There is a global interest in developing rapid and reliable sensing methods for vapors of extremely toxic nerve agent weapons due to public safety and national security concerns. Luminescence detection is regarded as an attractive way to meet the demand for fast reporting as well as disturbance avoidance. In this study, the potentials of Ln-based luminescent metal-organic framework (MOF) for nerve agent sensing is demonstrated and the cooperation with glycerol is developed as a facile method for sensitivity and selectivity enhancement. Specifically, a layer structural pyrazole-functionalized Eu MOF based sensing film, exhibits 1.6-fold enhancement of ligand fluorescence and 50% quenching of Eu emission in the presence of glycerol after 20 ​s of exposure to saturated vapor of nerve agent simulant. The film not only achieves a detection limit as low as 0.7 ​ppm but shows selectivity versus common interferences like NH3. Mechanism study indicates that phosphorylation of –OH from glycerol occurs accompanied with the protonation of pyrazole group, much similar to the initial inhibition of acetylcholinesterase by nerve agents.

Evaluation of the morphology and chelating agent excess in the design of luminescent metalorganic framework of europium thenoyltrifluoroacetone

Metal-organic frameworks (MOFs) have been synthesized using several elements, including the rare-earth. Research on luminescent diketones as an efficient alternative for the generation of OLEDs has increased in recent years, however, the evaluation of parameters such as morphology or excess of the cheating agent is not completely studied. In this work, the synthesis of thenoyltrifluoroacetone (TTA) combined with europium at the different chelating agent and rare earth ratio is presented, founding a change in morphology directed related with optical performance, structural analysis was performed using x-ray diffraction (XRD), and was observed a monoclinic structure in Eu 15% and Eu 20% samples. Morphological analysis was done with scanning electron microscopy (SEM). The TTA5Eu sample presented an irregular morphology with nanometric particles embedded, the TTA15Eu had a morphology of agglomerated particles, and TTA20Eu sample the morphology changes radically to an angular morphology. Nanowires were present in the sample of 25% Eu3+. The chemical properties were determined using Fourier transform infrared spectroscopy (FTIR), and the optical properties were measured by photoluminescence (FL). The results showed vibration bands and stretching of the thiophene group, without apparent change due to the chelation of the Eu3+.

Smart Tetraphenylethene-Based Luminescent Metal-Organic Frameworks with Amide-Assisted Thermofluorochromics and Piezofluorochromics.

Luminescent metal–organic frameworks (MOFs) are appealing for the design of smart responsive materials, whereas aggregation‐induced emission (AIE) fluorophores with twisted molecular rotor structure provide exciting opportunities to construct MOFs with new topology and responsiveness. Herein, it is reported that elongating AIE rotor ligands can render the newly formed AIE MOF (ZnETTB) (ETTB = 4',4''',4''''',4'''''''‐(ethene‐1,1,2,2‐tetrayl)tetrakis(([1,1'‐biphenyl]‐3,5‐dicarboxylic acid))) with more elasticity, more control for intramolecular motion, and specific amide‐sensing capability. ZnETTB shows specific host–guest interaction with amide, where N,N‐diethylformamide (DEF), as an example, is anchored through C—H···O and C—H···π bonds with Zn cluster and ETTB8− ligand, respectively. DEF anchoring reduces both the distortion level and the intramolecular motions of ETTB8− ligand to lead a blueshifted and intensified emission for DEF ∈ ZnETTB. Moreover, amide anchoring also affords the DEF ∈ ZnETTB with the excellent thermofluorochromic behavior, and further increases the piezofluorochromic sensitivity at low‐pressure ranges on the basis of its elastic framework. This work is one of the rare examples of amide‐responsive smart materials, which shall shed new lights on design of smart MOFs with twisted AIE rotors for further sensing and detection applications.

Tailoring a luminescent metal − organic framework precise inclusion of Pt-Aptamer nanoparticle for noninvasive monitoring Parkinson's disease

Pathologic α-synuclein (α-Syn) has been implicated as a significant causal agent of Parkinson's disease (PD). Thus, α-Syn is an important target for the development of diagnostic tests and therapeutics for PD. In this work, a fluorescence “turn-on” strategy based on a Tb- luminescent metal−organic framework probe (Tb-MOF@Pt-Aptamer) is developed for the noninvasive monitor of α-Syn via oral delivery. To overcome the harsh gut conditions, acid-stable luminescent Tb-MOF capsules are found to excellently protect aptamer on the surface of Pt nanoparticle via precise pore size of luminescent Tb-MOF. When the α-Syn exists on the gut, the α-Syn can be specially recognized with aptamer in Tb-based luminescent MOF probe. Then Pt-Aptamer/α-Syn complex is released into the gut leading to the notable “turn-on” fluorescence signal to the probe. Additionally, the integrity of luminescent Tb-MOF is retained along the gut and is drained in the feces. Detecting fecal fluorescence intensity may provide a solution to PD detection. The noninvasive fluorescence “turn-on” strategy is a great promising detection progress for the early and potential therapeutics diagnosis of PD.

Unfolding the Role of Building Units of MOFs with Mechanistic Insight Towards Selective Metal Ions Detection in Water.

The potential emergence of fluorescence-based techniques has propelled research towards developing probes that can sense trace metal ions specifically. Although luminescent metal-organic frameworks (MOFs) are well suited for this application, the role of building blocks towards detection is not fully understood. In this work, a systematic screening by varying number of Lewis basic (pyridyl-N atoms) sites is carried out in a series of isostructural, robust UiO-67 MOFs, and targeting a model metal ion-Fe3+ . All the three fluorescent MOFs are seen to present quenching response towards Fe3+ ions in water. However, UiO-67@N exhibits highly selective and sensitive response, whereas emission of both UiO-67 and UiO-67@NN is quenched by several metal ions. Detailed experimental and theoretical mechanistic investigation is carried out in addition to demonstration of UiO-67@N being able to sense trace amount of Fe3+ ions in synthetic biological water sample. Further, UiO-67@N based mixed-matrix membrane (MMM) has been prepared and employed to mimic the real time Fe3+ ions detection in water.

Ultrasound Irradiation Assisted Synthesis of Luminescent Nano Amide-Functionalized Metal-Organic Frameworks; Application Toward Phenol Derivatives Sensing.

Two nano amide-functionalized metal-organic frameworks (MOFs) with molecular formula [Co(oba) (bpta)]·(DMF)2 TMU-50 and [Co2(oba)2 (bpfn)]·(DMF)2.5 TMU-51 obtained under ultrasonic method without any surfactants. The only difference between the two selected amide functionalized pillar ligands, N,N′-bis(4-pyridinyl)-terephthalamide (bpta), and N,N′-bis-(4-pyridylformamide)-1,5-naphthalenediamine (bpfn), is related to the naphthyl group, which led to the different luminescence properties of the nano frameworks. In this study, the special ability of the luminescent nano MOFs were investigated to sensitize nitroaromatic compounds. Due to its unique and porous framework, Nano TMU-50 shows a good sensitivity towards nitro phenol by strong fluorescence emission with a detection limit of 2 × 10–3 mM−1. Both nano MOF structures were characterized via many analyses such as powder X-ray diffraction, Field Emission Scanning Electron Microscopy (FE-SEM), elemental analysis, and FTIR spectroscopy. Moreover, the effect of a number of important parameters including initial reagent concentrations, power of ultrasound, time on morphology, and size of nano structures were examined. According to the fluorescence titration results, the activated nano-TMU-50 detected NP selectively with a quick response.