Luminescent Metal-organic Framework Research Articles

Tuning the sensitization pathway T1→5DJ in Eu-based MOF through modification of the antenna ligand. A theoretical approach via multiconfigurational quantum calculations

The current study demonstrates the possibility of improving the efficiency of Eu3+ sensitization in an Eu-based MOF, labelled as EuL-R, by modifying the antenna ligand. The electronic structure of seven antenna ligand derivatives with the form R-4-(pyrimidin-5-yl) benzoic acid (L-R) ligand derivates was thoroughly examined in this research. Also, the most likely energy transfer channels for the sensitization pathway of Eu3+ ions in the EuL-R systems (R: CH3, –OH, –SH and –NH2) was studied. The efficiency in the intersystem crossing (ISC) process from S1 to T1 in the antenna make plausible a subsequent energy transfer to the emissive state in the Eu3+. This process was studied via multireference CASSCF/NEVPT2 calculations due to the multiconfigurational character of Eu3+ ions. Based on Latva and Reindhout's empirical rules, the 4-(2-(thiophen-2-yl)pyrimidin-5-yl)benzoic acid (L6) was chosen as efficient antenna for the sensitization process in this system. In conclusion, it was discovered that including the thiophenyl group at the L antenna (L6), increased the energy gaps S1→T1 and T1→5DJ (Eu3+) to an optimal range for the ISC and subsequent energy transfer. Finally, a deeply understanding of the sensitization and emission mechanisms was possible from the excited-state dynamics analysis of the L6 antenna, via fluorescence, inter-system crossing (ISC), phosphorescence, and kF, kISC, and kP, rates calculations. This study therefore highlights the importance of a thorough theoretical procedure via a robust quantum mechanical tool to guide the development of novel luminescent lanthanide-based MOFs.

An enhanced-stability metal–organic framework of NH2-MIL-101 as an improved fluorescent and colorimetric sensor for nitrite detection based on diazotization reaction

Nitrite ion (NO2-) is a typical contaminant that can cause severe damage to the human body. Diazotization-based fluorimetric methods used for the efficient and selective detection of NO2- under a strong acidic condition remain a huge challenge. In this study, a specific nanoprobe was developed through the functionalization of the luminescent MOF of NH2-MIL-101 with Polyvinylidene fluoride/polyvinylpyrrolidone (PVDF/PVP) for detecting NO2- based on diazotization reaction. After functionalization, the resultant NH2-MIL-101 @PVDF/PVP exhibited enhanced stability even under a strong acidic condition and featured higher fluorescence intensity. Because NO2- reacted with the -NH2 group of the probe to form diazonium salt, a significant fluorescence signal was obtained. With the addition of N-(1-Naphthyl) ethylenediamine, the diazonium salt significantly changed from colorless to a purple-red color under direct sunlight. The developed dual-signal readout sensor exhibited high sensitivity, high selectivity, and good linearity in the range of 0.67–20 μM with a limit of detection of 0.67 μM. Owing to the unique properties of MOFs, the proposed sensor was characterized by simple preparation, high sensitivity, and fast response kinetics compared with the traditional sensing reagents. This study provides a potential strategy for fabricating smart fluorimetric probes used for nitrite detection.

Terbium-based metal organic framework and its immobilized nanofibrous membrane for selective detection and efficient removal of phosphate

The detection and removal of phosphate were advantageous means to predict and mitigate eutrophication of aquatic ecosystems. In this study, a luminescent rod-like terbium-based metal organic frameworks (MOFs) had been synthesized successfully via facile hydrothermal reaction for convenient and efficient detection and adsorption of phosphate. Specifically, the Tb-based MOFs (Tb-BTC) exhibited high selectivity for sensing of phosphate through fluorescence quenching mechanism with the quenching constant values (Ksv) of 1.18 × 104 M−1 and low limit of detection (LOD) of 2.97 μM. Simultaneously, Tb-BTC also possessed superior adsorption ability for phosphate based on Langmuir isotherm model and pseudo-second-order kinetic model determining that the maximum adsorption capacity reached up to 222.2 mg/g with equilibrium time of 30 min. More significantly, Tb-BTC nanoparticle could be stably integrated into polyacrylonitrile (PAN) nanofibers for constructing hierarchically hybrid nanofibrous membrane (PAN/TB) through electrospinning to further improve its operability and recoverability. And the obtained customized membrane maintained selective detection for phosphate with visual LOD of 3 × 10−4 M and good capture of phosphate with the maximum adsorption capacity of 111.3 mg/g, respectively. Therefore, this study provided prospective candidate for detection and removal of phosphate making contribution at a certain level to predict and attenuate water eutrophication.

Spectral, thermal, structural and DFT studies of new luminescent heterobimetallic MOF of lead and sodium based on diglycolic acid ligand having unusual coordination environment for photodegradation and antibacterial applications

Single crystals of a new bimetallic MOF of diglycolic acid ligand with different metals such as sodium and lead have been synthesized via the gel-diffusion method. The Single crystal X-ray diffraction studies revealed that an unusual coordination environment arises due to the mutual coordination of both sodium and lead metals. The grown crystals was further characterized by FTIR, PXRD, TG-DTG, BET, and Photoluminescence studies. DFT studies of the bimetallic MOF implies a high electrophilicity index (5.3148 eV) that predicts high biomolecular binding capacity of the molecule. The complex under study has a hardness value of 1.7645 eV, indicating that the material is hard. The simulated PXRD is in good agreement with the experimental PXRD pattern which confirms the structural integrity of crystals within the bulk. The antibacterial activity as well as the degradation property of the material towards methylene blue was also studied in detail. The photocatalytic degradation and biological studies suggest that the grown crystals are found to be an effective material for the degradation of organic pollutant methylene blue and can be used for antimicrobial applications.

A Multimodal Ratiometric Luminescent Thermometer Based on a Single-Dysprosium Metal–Organic Framework

The design of high-performance luminescent MOF thermometers with multi-operation modes has been long sought but remains a formidable challenge. In this work, for the first time, we present a multimodal luminescent ratiometric thermometer based on the single-lanthanide metal-organic framework (MOF) DyTPTC-2Me (H4TPTC-2Me = 2',5'-dimethyl-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid). It not only has the characteristic luminescence of Dy3+ in which the atomic transitions from the 4I15/2 and 4F9/2 states (thermally coupled energy levels, TCELs) are included but also emits ligand fluorescence due to the efficient energy back-transfer of Dy3+ to the ligand, thus allowing accurate non-invasive determination of temperature by different modes. In particular, the TCEL-based emissions of the Dy3+ ions give ideal signals for measuring the temperature in the 303-423 K range. The emissions of the ligand and Dy3+ (4F9/2 → 6H13/2) are used for temperature sensing in the range of 423 to 503 K. Both two modes feature promising thermometric performance, including high relative sensitivity, high temperature resolution, and excellent repeatability. Their combination is thus beneficial to achieve more accurate temperature detection over a broad temperature range, which can broaden the application scope of the ratiometric luminescent thermometers.

Eu3+-anchoring Zirconium-organic framework for enhancing fluorescence sensing detection sensitivity towards Cr(VI) ions

Heavy metal ion Cr(VI) content has been regarded as one of the most important indicators for discharged industrial wastewater. However, effective identification and detection of Cr(VI) analytes with high sensitivity and selectivity from various water environments remains a significant challenge. In this study, a novel luminescent material (labelled as Eu@Zr-MOF) with high water stability was assembled by post-modification of a zirconium-organic framework with lanthanide Eu3+ ions. And the coordination bonds binding between Eu3+ ions and carboxyl O atoms of Zr-MOF were confirmed by XPS technique. After Eu3+ ions were successfully immobilized within the Zr-MOF lattice, Eu@Zr-MOF exhibits a bright red fluorescence signal which was inherited from the unique luminescent feature of embedded Eu3+ ions. Notably, Eu@Zr-MOF can be deployed as a reliable photochemical sensor for quantitative fluorescence quenching detection of Cr2O72− ions based on the emission peak at 618 nm, showing rather high sensitivity (KSV = 6.746 × 104 M−1) and ultra low detection limit (DL = 5.71 ppb) which has been enhanced more than 3 times compared with pristine Zr-MOF. This study provides a reliable reference for the preparation of novel luminescent MOFs platform for efficient recognition and detection of Cr(VI) analytes.

Dual-Emission Metal–Organic Framework for Highly Selective Ratiometric Sensing of Lithium(I) Ions in Aqueous Solution

The development of highly selective and sensitive detection methods for lithium ions in various environments, such as aqueous or battery application, is highly sought. However, it remains elusive due to the small radius and weak coordination ability of lithium ions. Considering a metal–organic framework (MOF) possesses plentiful open coordination sites and an adjustable pore size, the well-designed MOF would be an ideal platform for the selective detection of Li+. Herein, a novel dual-emission luminescent metal–organic framework with three-dimensional structure, namely, Co–HIAT, was prepared by the hydrothermal method and structurally characterized. The Co–HIAT MOF displays the ligand-based emission at 340 nm and the charge transition emission between the metal ions and ligand at 410 nm simultaneously. Hence, the first example of ratiometric fluorescence detecting of Li+ can be achieved by measuring the ratio of fluorescence at 410 to 340 nm in the fluorescent spectra of the Co–HIAT, which exhibits the outstanding sensitivity and selectivity, giving a detection limit down to 0.17 μM. Detailed experimental studies showed that the sensing mechanism involves the strong interactions of Li+ with the reasonable hydroxyl and carboxyl oxygen atoms in the Co–HIAT framework, which is responsible for the ratiometric change in fluorescence emission properties in the inclusion of Li+. It is worth noting that electrochemical experiments further confirmed its superior affinity for lithium ions. This work represents an important and feasible pathway to design MOFs for the detection of Li+.

Simulation monitoring of tetracyclines in wastewater based on fluorescence image processing and machine learning classifier

Antibiotics, as an emerging pollutant, have attracted extensive attention due to their trace residues and toxic side effects in the environment. Here, we constructed a new detection mechanism for tetracyclines in sewage by online trace sensing through machine learning (ML) algorithm and image fingerprint extraction method. The image fingerprint information was obtained from the blue to red specific fluorescence response generated by the interaction between the luminescent metal-organic framework (MOF) with tetracyclines, which greatly improved the ability against background interference. Fluorescence images of samples with different concentrations were collected, and the RGB mean value of sample images was extracted through the program as "fingerprint information". Then k-means clustering model (KCM) and hierarchical clustering model (HCM) were constructed to analyze the differences in fingerprint information of samples with different concentrations by clustering analysis method in machine learning. The clustering results showed good clustering characteristics of samples with similar concentrations, which provided reliable support for rapid detection while avoiding the use of expensive large instruments and time-consuming analysis methods.

Paper-based fluorometric sensing of malachite green using synergistic recognition of aptamer-molecularly imprinted polymers and luminescent metal–organic frameworks

Herein, a paper-based fluorescence sensor based on the metal-organic frameworks capped with aptamer and molecular imprinted polymer (MOF-Apt@MIP) was designed for malachite green (MG) and realized sensitive detection by using digital image colorimetry with the aid of smartphone. The green fluorescence terbium MOF-76 was prepared and used as a carrier to conjugate with MG specific aptamer. MG, as template molecule, was subsequently added into MOF-Apt to generate MIP layer under the action of co-polymerization process. With the addition of MG, the fluorescence of MOF-Apt@MIP was quenched because MG was synergistically bound with aptamer and MIP and induced photo-induced electron transfer (PET) effect. Then, the obtained MOF-Apt@MIP probe was applied to a circle pattern paper and measured by a smartphone, in which color recognition software was installed to read out the RGB values of the acquired images. The detection limit for paper-based detection was 0.1 ng/mL. This point of care testing (POCT) method was applied to detect MG in fish and water samples with recoveries in 94.0–105.6 %. This method endows synergistic binding effect of aptamer and MIP, enhancing the detection sensitivity and specificity, and the paper-based detection with smartphone facilitate the on-site monitoring. It is expected that this sensor will be of great significance for the detection and monitoring of illegal additive in food stuffs.

A highly sensitive and specific luminescent MOF determines nitric oxide production and quantifies hydrogen sulfide-mediated inhibition of nitric oxide in living cells.

The synthesis of a novel carboxylate-type organic linker-based luminescent MOF (Zn(H2L) (L1)) (named PUC2) (H2L = 2-aminoterephtalic acid, L1 = 1-(3-aminopropyl) imidazole) is reported by the solvothermal method and comprehensively characterized using single-crystal XRD, PXRD, FTIR, TGA, XPS, FESEM, HRTEM, and BET. PUC2 selectively reacts with nitric oxide (▪NO) with a detection limit of 0.08µM, and a quenching constant (0.5 × 104M-1) indicating a strong interaction with ▪NO. PUC2 sensitivity remains unaffected by cellular proteins or biologically relevant metals (Cu2+/ Fe3+/Mg2+/ Na+/K+/Zn2+), RNS/ROS, or H2S to score ▪NO in living cells. Lastly, we used PUC2 to demonstrate that H2S inhibition increases ▪NO production by ~ 14-30% in various living cells while exogenous H2S suppresses ▪NO production, indicating that the modulation of cellular ▪NO production by H2S is rather generic and not restricted to a particular cell type. In conclusion, PUC2 can successfully detect ▪NO production in living cells and environmental samples with considerable potential for its application in improving the understanding of the role of ▪NO in biological samples and study the inter-relationship between ▪NO and H2S.

Metal organic framework-based tricolor fluorescence imprinted sensor for rapid intelligent detection of homovanillic acid

Homovanillic acid (HVA) is one of the main metabolites of catecholamines in the body. Abnormal levels of HVA in urine and serum are associated with neuroblastoma and Parkinson's disease. Herein, a smartphone-assisted tricolor fluorescence imprinted sensor was proposed with one-pot synthesis strategy for the intelligent determination of HVA in serum and urine. In this study, luminescent metal–organic framework was used as reference probe, while green-emitting CdTe and red-emitting CdTe were used as response probes. With increasing HVA concentration, the green-emitting CdTe and red-emitting CdTe fluorescence were gradually quenched, while the blue fluorescence of metal–organic framework remained stability. The tricolor fluorescence imprinted sensor extends the color variations range for visual detection with dynamic detection range (0.05–180 µM). The fluorescence imprinted sensor exhibits a lower detection limit of 15 nM and rapid response within 2 min. Interestingly, a portable smart sensing platform was designed by integrating the tricolor fluorescence imprinted polymer and a smartphone assisted device to achieve on-site accurate analysis HVA with a detection limit of 34 nM. The sensing platform was applied to in situ monitoring of HVA in serum and urine with satisfactory results, providing a new method for visual intelligent detection of HVA.

A high selective Zn-based luminescent metal-organic framework for fluorescence sensing detecting iron(III) and trinitrophenol

A high selective Zn-based luminescent metal-organic framework for fluorescence sensing detecting iron(III) and trinitrophenol

A 12-Connected [Y4((μ3-OH)4]8+ Cluster-Based Luminescent Metal-Organic Framework for Selective Turn-on Detection of F- in H2O.

Fluoride ion (F-) is one of the most hazardous elements in potable water. Over intake of F- can give rise to dental fluorosis, kidney failure, or DNA damage. As a result, developing affordable, equipment-free and credible approaches for F- detection is an important task. In this work, a new three dimensional rare earth cluster-based metal-organic framework assembled from lanthanide Y(III) ion, and a linear multifunctional ligand 3-nitro-4,4'-biphenyldicarboxylic acid, formulated as {[Y(μ3-OH)]4[Y(μ3-OH)(μ2-H2O)0.25(H2O)0.5]4[μ4-nba]8}n (1), where H2nba = 3-nitro-4,4'-biphenyldicarboxylic acid, has been hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. X-ray diffraction structural analysis revealed that 1 crystallizes in tetragonal system with P4¯21m space group, and features a 3D framework with 1D square 18.07(3)2 Å2 channels running along the [0,0,1] or c-axis direction. The structure of 1 is built up of unusual eight-membered rings formed by two types of {Y4O4} clusters connected to each other via 12 μ4-nba2- and 4 μ3-OH- ligands. Three crystallographic independent Y3+ ions display two coordinated configurations with a seven-coordinated distorted monocapped trigonal-prism (YO7) and an eight-coordinated approximately bicapped trigonal-prism (YO8). 1 is further stabilized through O-H⋯O, O-H⋯N, C-H⋯O, and π⋯π interactions. Topologically, MOF 1 can be simplified as a 12-connected 2-nodal Au4Ho topology with a Schläfli symbol {420·628·818}{43}4 or a 6-connected uninodal pcu topology with a Schläfli symbol {412·63}. The fluorescent sensing application of 1 was investigated to cations and anions in H2O. 1 exhibits good luminescence probing turn-on recognition ability toward F- and with a limit detection concentration of F- down to 14.2 μM in aqueous solution (Kec = 11403 M-1, R2 = 0.99289, σ = 0.0539). The findings here provide a feasible detection platform of LnMOFs for highly sensitive discrimination of F- in aqueous media.

A functional cobalt-organic framework constructed by triphenylamine tricarboxylate: Detect nitroaromatics by fluorescence sensing and UV-shielding

Luminescent metal-organic frameworks (LMOF) with ligand-modified are a promising strategy to be applied to fabricate chemical sensors. Herein, a novel Co (II) metal-organic framework (Co-MOF), namely Co [(NTB) bpy] (NTB = 4,4′4″-tricarboxylic acid triphenylamine, bpy = 4,4 ′-bipyridyl), was successfully synthesized with excellent water stability and fluorescence properties. Due to the propeller structure of NTB ligands, a special topological structure of Co-MOF was shown: {24.416.68}{2}4. It was proved that Co-MOF has great stability by soaking in different solvents for two weeks. Remarkably, the fluorescence quenching experiment verified that Co-MOF has excellent fluorescence sensor performance. Trinitrophenol, 2,4-dinitrophenol, and 2-amino-4-nitrotoluene (10−5 M) with LOD of 9.00 × 10−5, 5.40 × 10−5 and 5.07 × 10−6 M can be detected via the process of fluorescence enhancement and quenching. Throughout the investigation, the mechanics of fluorescence quenching was performed. Due to the excellent UV absorption capacity of Co-MOF, it was a promising application to combine low-dimensional nanomaterials with sustainable biomass materials. A hybrid films of Co-MOF and cellulose acetate (CA) was generated. The hybrid films had highly transparency in the visible wavelength range and excellent UV-shielding ability owing to the CA/Co-MOF hybrid films enhanced the UV absorption capacity of Co-MOF.

“Two-in-one” dual-function luminescent MOF hydrogel for onsite ultra-sensitive detection and efficient enrichment of radioactive uranium in water

In consideration of the severe hazards of radioactive uranium pollution and the growing demand of uranium resources, the novel sensor/adsorbent composite was creatively developed to integrate the dual functions for on-site detection of uranium contamination and efficient recovery of uranium resources. By hybridizing the luminescent 3D terbium (III) metal–organic framework (Tb–MOF) with sodium alginate (SA) gel using terbium (III) as cross-linker, the Tb-MOF/Tb-AG was fabricated with multi-luminescence centers and sufficient binding sites for uranium. Notably, the ultra-high sensitivity with detection limit as low as 1.2 ppt was achieved, which was 4 orders of magnitude lower than the uranium contamination standard in drinking water (USEPA) and even comparable to the sensitivity of the ICP-MS. Furthermore, the very wide quantification range (1.0 ×10−9-5.0 ×10−4 mol/L), remarkable adsorption capacity (549.0 mg/g) and outstanding anti-interference ability have been achieved without sophisticated sample preparation procedures. Applied in complex natural water samples from Uranium Tailings and the Pearl River, this method has shown good detection accuracy. The ultra high sensitivity and great adsorption capacity for uranium could be ascribed to the synergistic coordination, hydrogen bonding and ion exchange between uranium and Tb-MOF/Tb-AG. The mechanisms were explored by infrared spectroscopy, batch experiments, X-ray photoelectron studies and energy dispersive spectroscopic studies. In addition, the Tb-MOF/Tb-AG can be reused for uranium adsorption.

Fabrication of Two Luminescent Imidazolyl Cadmium-Organic Frameworks and Their Sensing Mechanism for 2,6-Dichloro-4-nitroaniline.

2,6-Dichloro-4-nitroaniline, alias dicloran (DCN), is a broad-spectrum pesticide that can cause irreversible damage to the human body. Therefore, it is of great significance to develop a technology for the rapid and convenient detection of DCN. Luminescent metal organic frameworks have attracted extensive attention in the field of sensing and detection due to their excellent optical properties. In this study, two kinds of 2D Cd-MOFs (CdMOF-1 and CdMOF-2) were developed for the detection of residual DCN in the environment. Both CdMOFs exhibit excellent solvent and acid-base stability and can respond to DCN quickly and sensitively in a short time (30 s). CdMOFs not only have good selectivity and anti-interference toward DCN but also have good reusability. Under the conditions of DCN concentrations of 1-15 and 0.3-30 μM, the change in fluorescence intensity of CdMOF-1 and CdMOF-2 showed a good linear relationship with DCN concentration (R2 = 0.999/0.991), and the detection limits were 0.36 and 0.12 μM, respectively. Through ultraviolet-visible absorption spectroscopy (UV-Vis), X-ray photoelectron spectroscopy, fluorescence lifetime, and density functional theory calculations, it is revealed that the fluorescence quenching mechanisms of DCN for two kinds of Cd-MOFs are competitive absorption and photoinduced electron transfer, and there may be a weak π-π interaction. Finally, it is demonstrated that by using two types of fluorescent CdMOFs to make the fluorescent test paper and detect actual soil, these can be applied to the actual scene and achieve onsite real-time detection.

Recent Advances in Luminescent Metal-Organic Frameworks for Detection of Gas and Volatile Organic Molecules

Gas molecules and volatile compounds in the air affect product purity and health. Because of increasing demand for better quality of life and health in industrial and general environments, timely detection of abnormal gas releases and poisonous compound volatilization is essential. Luminescence metal-organic frameworks (LMOFs) are materials with tunable pore sizes, defined structures, and luminescence properties, which have been widely reported as sensor materials for detecting various compounds. Here, luminescence mechanisms of LMOFs are reviewed and interactions between the host and guest molecules are explained at the molecular level. On the basis of these relationships, the state-of-the-art LMOF-based sensors for various common gas molecules (including H2O, O2, COx, and NOx) and volatile organic compounds (VOCs) are further described in depth. This review may benefit the further development of LMOFs and accelerate their practical application in various sensor combinations.

Metal–organic framework (MOF)-based fluorescence “turn-on” sensors

The various potential sensing application by luminescent MOFs.

Dual-response fluorescence sensing of H2PO4- and CO32- using AJP filter paper based on a pH-stable CdII-based luminescent metal-organic framework.

A new CdII-based luminescent metal-organic framework (LMOF) with the formula {[Cd(BIBT)(NDC)]·solvents}n (JXUST-32, BIBT = 4,7-bi(1H-imidazol-1-yl)benzo-[2,1,3]thiadiazole and H2NDC = 2,6-naphthalenedicarboxylic acid) was successfully synthesized by a solvothermal method. JXUST-32 shows a two-dimensional (4,4)-connected network and exhibits significant fluorescence red shift and slight enhancement for H2PO4- and CO32- sensing with detection limits of 0.11 and 0.12 μM, respectively. In addition, JXUST-32 has good thermal stability, chemical stability and recyclability. Significantly, JXUST-32 represents a fluorescence red-shift dual response MOF sensor for H2PO4- and CO32- detection and the analytes can be identified by the naked eye, aerosol jet printing filter paper, light-emitting diode beads and luminescent films.

Nano vs. bulk: surfactant-controlled photophysical and morphological features of luminescent lanthanide MOFs

Surfactant-assisted nano-synthesis and post-synthetic modification of three archetype bulk MOFs illuminate the size-dependent morphological and photophysical property changes of nanoMOFs.