Unique (3,4,10)-Connected Lanthanide–Organic Framework as a Recyclable Chemical Sensor for Detecting Al3+

Construction of olefinic coordination polymer single crystal platforms: precise organic synthesis, in situ exploration of reaction mechanisms and beyond

Olefin [2+2] photocycloaddition reactions based on coordination-bond templates provide numerous advantages for the selective synthesis of cyclobutane compounds. This review outlines the recent advances in the design and construction of single crystal platforms of olefinic coordination polymers for precise organic synthesis, in situ exploration of reaction mechanisms, and possible developments as comprehensively as possible. Numerous examples are presented to illustrate how the arrangements of the olefin pairs influence the solid-state photoreactivity and examine the types of cyclobutane products. Furthermore, the photocycloaddition reaction mechanisms are investigated by combining advanced techniques such as single crystal X-ray diffraction, powder X-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, fluorescence spectroscopy, laser scanning confocal microscopy and theoretical calculations. Finally, potential applications resulting from promising physicochemical properties before and after photoreactions are discussed, and existing challenges and possible solutions are also proposed.

Iodine Adsorption-Desorption-Induced Structural Transformation and Improved Ag+ Turn-On Luminescent Sensing Performance of a Nonporous Eu(III) Metal-Organic Framework

Posttreatment of pristine metal-organic frameworks (MOFs) with suitable vapor may be an effective way to regulate their structures and properties but has been less explored. Herein, we report an interesting example in which a crystalline nonporous Eu(III)-MOF was transferred to a porous amorphous MOF (aMOF) via iodine vapor adsorption-desorption posttreatment, and the resulting aMOF showed improved turn-on sensing properties with respect to Ag+ ions. The crystalline Eu-MOF, namely, Eu-IPDA, was assembled from Eu(III) and 4,4'-{4-[4-(1H-imidazol-1-yl)phenyl]pyridine-2,6-diyl}dibenzoic acid (H2IPDA) and exhibited a two-dimensional (2D) coordination network based on one-dimensional secondary building blocks. The close packing of the 2D networks gives rise to a three-dimensional supramolecular framework without any significant pores. Interestingly, the nonporous Eu-IPDA could absorb iodine molecules when Eu-IPDA crystals were placed in iodine vapor at 85 °C, and the adsorption capacity was 1.90 g/g, which is comparable to those of many MOFs with large BET surfaces. The adsorption of iodine is attributed to the strong interactions among the iodine molecule, the carboxy group, and the N-containing group and leads to the amorphization of the framework. After immersion of the iodine-loaded Eu-IPDA in EtOH, approximately 89.7% of the iodine was removed, resulting in a porous amorphous MOF, denoted as a-Eu-IPDA. In addition, the remaining iodine in the a-Eu-IPDA framework causes strong luminescent quenching in the fluorescence emission region of the Eu(III) center when compared with that in Eu-IPDA. The luminescence intensity of a-Eu-IPDA in water suspensions was significantly enhanced when Ag+ ions were added, with a detection limit of 4.76 × 10-6 M, which is 1000 times that of pristine Eu-IPDA. It also showed strong anti-interference ability over many common competitive metal ions and has the potential to sense Ag+ in natural water bodies and traditional Chinese medicine preparations. A mechanistic study showed that the interactions between Ag+ and the absorbed iodine, the carboxylate group, and the N atoms all contribute to the sensing performance of a-Eu-IPDA.

Highly Luminescent Eu3+-Incorporated Zr-MOFs as Fluorescence Sensors for Detection of Hazardous Organic Compounds in Water and Fruit Samples

Considering the risk of toxic organic compounds to both human health and the environment, highly luminescent Eu3+-incorporated amino-functionalized zirconium metal-organic frameworks, namely, Eu/MOF and Eu@MOF were synthesized via the solvothermal method. The synthesized luminescent europium-incorporated MOFs act as outstanding sensor materials for diphenylamine and dinitrobenzene detection in water and fruit samples. The synergistic effect of Eu3+ metal ions and amino-functionalized MOFs enhances the luminescent properties of the MOFs improving the fluorescence sensing ability toward the analytes. The enhancement in the detection capacity of the Eu3+-incorporated sensors than the sole MOF toward toxic organic compounds was confirmed using the Stern-Volmer equation of limit of detection (LOD) measurements along with fluorescence lifetime measurements. The sensors exhibited turn-on fluorometric detection toward their respective analytes due to the inner filter effect. The plausible fluorescence sensing mechanism has been studied. The DFT calculations have been integrated to study the structure, stability, and charge transfer processes.

Sensitive Current Sensor Based on a Lanthanide Framework with Lewis Basic Bipyridyl Sites for Cu2+ Detection

A new Yb-based three-dimensional metal-organic framework with free Lewis basic sites, [Yb₂(ddbpdc)₃(CH₃OH)₂] (referred to as ACBP-6), from YbCl₃ and (6R,8R)-6,8-dimethyl-7,8-dihydro-6H-[1,5]dioxonino[7,6-b:8,9-b']dipyridine-3,11-dicarboxylic acid (H₂ddbpdc) was synthesized by a conventional solvothermal method. Two Yb³⁺ are connected by three carboxyl groups to form the [Yb₂(CO₂)₅] binuclear unit, which is further bridged by two carboxyl moieties to produce a tetranuclear secondary building unit. With further ligation of the ligand ddbpdc^2-, a 3-D MOF with helical channels is constructed. In the MOF, Yb³⁺ only coordinates with O atoms, leaving the bipyridyl N atoms of ddbpdc^2- unoccupied. The unsaturated Lewis basic sites make this framework possible to coordinate with other metal ions. After growing the ACBP-6 in situ into a glass micropipette, a novel current sensor is formed. This sensor shows high selectivity and a high signal-to-noise ratio toward Cu²⁺ detection with a detection limit of 1 μM, due to the stronger coordination ability between the Cu²⁺ and the bipyridyl N atoms.

Ortho Effects of Tricarboxylate Linkers in Regulating Topologies of Rare-Earth Metal-Organic Frameworks

A linker design strategy is developed to attain novel polynuclear rare-earth (RE) metal-organic frameworks (MOFs) with unprecedented topologies. We uncover the critical role of ortho-functionalized tricarboxylate ligands in directing the construction of highly connected RE MOFs. The acidity and conformation of the tricarboxylate linkers were altered by substituting with diverse functional groups at the ortho position of the carboxyl groups. For instance, the acidity difference between carboxylate moieties resulted in forming three hexanuclear RE MOFs with novel (3,3,3,10,10)-c wxl, (3,12)-c gmx, and (3,3,3,12)-c joe topologies, respectively. In addition, when a bulky methyl group was introduced, the incompatibility between the net topology and ligand conformation guided the co-appearance of hexanuclear and tetranuclear clusters, generating a novel 3-periodic MOF with a (3,3,8,10)-c kyw net. Interestingly, a fluoro-functionalized linker prompted the formation of two unusual trinuclear clusters and produced a MOF with a fascinating (3,8,10)-c lfg topology, which could be gradually replaced by a more stable tetranuclear MOF with a new (3,12)-c lee topology with extended reaction time. This work enriches the polynuclear clusters library of RE MOFs and unveils new opportunities to construct MOFs with unprecedented structural complexity and vast application potential.

Inner transition metal-modulated metal organic frameworks (IT-MOFs) and their derived nanomaterials: a strategic approach towards stupendous photocatalysis

Photocatalysis, as an amenable and effective process, can be adopted for pollution remediation and to alleviate the ongoing energy crisis. In this case, recently, metal organic frameworks (MOFs) have attracted increasing attention in the field of photocatalysis owning to their unique characteristics including large specific surface area, tuneable pore architecture, mouldable framework composition, tuneable band structure, and exceptional photon absorption tendency complimented with superior anti-recombination of excitons. Among the plethora of frameworks, inner transition metal based-MOFs (IT-MOFs) have started to garner significant traction as photocatalysts due to their distinct characteristics compared to conventional transition metal-based frameworks. Typically, IT-MOFs have the tendency to generate high nuclearity clusters and possess abundant Lewis acidic sites, together with mixed valency, which aids in easily converting redox couples, thereby making them a suitable candidate for various photocatalytic reactions. Therefore, in this contribution, we aim to summarise the excellent photocatalytic performance of IT-MOFs and their composites accompanied by a thorough discussion of their topological changes with a variation in the structure of the metal cluster, fabrication routes, morphological features, and physico-chemical properties together with a brief discussion of computational findings. Moreover, we attempt to explore the scientific understanding of the functionalities of IT-MOFs and their composites with detailed mechanistic pathways for in-depth clarity towards photocatalysis. Furthermore, we present a comprehensive analysis of IT-MOFs for various crucial photocatalytic applications such as H₂/O₂ evolution, organic pollutant degradation, organic transformation, and N₂ and CO₂ reduction. In addition, we discuss the measures employed to enhance their performance with some future directions to address the challenges with IT-MOF-based nanomaterials.

A dual-function [Ru(bpy)3]2+ encapsulated metal organic framework for ratiometric Al3+ detection and anticounterfeiting application

In this work, a novel composite material (HPU-24@Ru) has been prepared by combining a blue-emission Cd-based metal-organic framework (MOF, [Cd₂(TCPE)(DMF)(H₂O)₃]_n, HPU-24) with a red-emission tris (2,2'-bipyridine) dichlororuthenium(II) hexahydrate ([Ru(bpy)₃]²⁺) molecule for ratiometric fluorescence sensing of Al³⁺ ions in aqueous medium and high-level dynamic anticounterfeiting application. The luminescence measurement results indicated that the fluorescence intensity of HPU-24 at 446 nm showed a red shift in the presence of Al³⁺ ions, and the new peak appeared at 480 nm and continued to increase with an increase in Al³⁺ ion concentration. Meanwhile, the fluorescence intensity of [Ru(bpy)₃]²⁺ almost showed no change. The detection limit was calculated as 11.63 μM, which was better than that for the MOF-based Al³⁺ ions in some reported examples in aqueous media and achieved through strong electrostatic interactions between HPU-24@Ru and Al³⁺ ions. Moreover, owing to the particularity of the tetrastyryl structure in HPU-24, HPU-24@Ru showed intriguing temperature-dependent emission behavior. This unique structure provides the composite material HPU-24@Ru with attributes for high-level information encryption that make it difficult for counterfeiters to identify all of the right decryption measures.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Dinuclear Lanthanide Compound as a Promising Luminescent Probe for Al3+ Ions

Luminescent probes have wide applications in biological system analysis and environmental science. Here, one novel luminescent dinuclear europium compound with a crown ether analogous ligand was synthesized through a solvent-thermal reaction. Through transformation, upon the addition of Al³⁺ ions to the N,N'-dimethyl formamide solution of the europium compound, the luminescent intensity of the characteristic emission of Eu³⁺ decreased, and a new emission peak appeared at 346 nm and increased rapidly. The luminescent investigation indicated that it could act as a highly sensitive and selective luminescent probe for Al³⁺ ions. Moreover, mass spectrometry and single-crystal X-ray diffraction confirmed the formation of a new more stable trinuclear aluminium compound during the sensing process.

A pH-Stable TbIII-Based Metal-Organic Framework as a Turn-On and Blue-Shift Fluorescence Sensor toward Benzaldehyde and Salicylaldehyde in Aqueous Solution

A new polydentate tetracarboxylic acid with a benzothiadiazole unit (4',4'''-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid), H₄BTDBA) has been used to prepare a pH-stable three-dimensional Tb^III-based metal-organic framework (MOF) with the formula {[(CH₃)₂NH₂]_0.7[Tb₂(BTDBA)_1.5(lac)_0.7(H₂O)₂]·solvents}_n (Hlac = lactic acid, JXUST-19). JXUST-19 exhibits a new (4,4,12)-connected topology based on tetranuclear [Tb₄] clusters. JXUST-19 can remain stable when soaked in water for at least 1 week and in aqueous solutions with various pH values (2-12) for 24 h. Fluorescence study indicates JXUST-19 can be employed as a rare turn-on and blue-shift MOF sensor toward benzaldehyde (BZ) and salicylaldehyde (SA). To date, JXUST-19 represents the first Tb^III-based turn-on MOF sensor toward salicylaldehyde in aqueous solution, and the fluorescence enhancement and naked-eye detection of BZ have been rarely reported. In addition, JXUST-19 based fluorescent test papers, light-emitting diode lamp beads, and portable composite films were developed to realize naked-eye detection of BZ and SA, which has great potential in practical applications.

Seven Ln(III) coordination polymers with two kinds of geometric coordination but the same 3D topological property: luminescence sensing and magnetic property

Two series of seven lanthanide metal coordination polymers (Ln-CPs) formulated as {[Ln(dttpa)_1.5(H₂O)₂]·H₂O}_n [Ln = La³⁺ (1), Ce³⁺ (2), Nd³⁺ (3), Sm³⁺ (4) and Eu³⁺ (5)] and {[Ln (dttpa)_1.5(H₂O)]·xH₂O}_n [Ln = Tb³⁺ (6) and Er³⁺ (7), x = 0.75] have been successfully constructed using Ln³⁺ ions and 2,5-di(1H-1,2,4-triazol-1-yl)terephthalic acid (H₂dttpa) via a hydrothermal method. Their 3D structures are fully characterised by Fourier transform infrared (FT-IR) spectroscopy, X-ray single-crystal analyses, powder diffraction analyses (PXRD), elemental analyses (EAs) and thermogravimetric analyses (TGAs). All Ln-CPs display the same topological property with the point symbol of {4²·8⁴}{4⁴·6²}₂{4⁹·6⁶}₂, and crystallize in the triclinic space group P1̄. Interestingly, Eu-CP (5) effectively sensitizes the visible emission of Tb³⁺ and shows high selectivity and stable response with the lowest detection limit of 9.88 nM. Furthermore, Tb-CP (6) acts as a good luminescence sensor to detect nitrobenzene (NB) with a detection limit of 12.5 nM. In addition, the magnetic susceptibility measurement for Er-CP (7) further shows that compounds constructed by dttpa^2- are a kind of promising functional material.

Luminescent Dimeric Oxalate-Bridged Eu3+/Tb3+-Implanted Arsenotungstates: Tunable Emission, Energy Transfer, and Detection of Ba2+ Ion in Aqueous Solution

Two cases of lanthanide (Ln)-implanted arsenotungstates, K₁₇Na₂H₅[{(As₂W₁₉O₆₇(H₂O))Ln(H₂O)₂}₂(C₂O₄)]·87H₂O (Ln = Eu (1), Ln = Tb (2)) and their codoped derivatives Eu_xTb_1-x-POM (x = 0.01 (3), x = 0.04 (4), x = 0.1 (5), x = 0.2 (6)) were prepared and further characterized by powder X-ray diffraction, infrared spectra, and thermogravimetric analyses. An X-ray structural analysis of 1 and 2 indicates that they both present a dimeric oxalate-bridged Ln³⁺-implanted lanthanide arsenotungstate polyanion structure. Under the O → W LMCT excitation at 265 nm of arsenotungstate polyanions, the emissions of Ln³⁺ ions in 1 and 2 are sensitized and the lifetimes are prolonged. Codoped compounds 3-6 demonstrate a color-tunable emission from green to red by adjusting the Eu³⁺/Tb³⁺ ratio. Emission spectra and time-resolved emission spectroscopic studies were performed for 3 to further authenticate the energy transfer processes from excited arsenotungstates to the Eu³⁺ and Tb³⁺ metal ions and also between the Eu³⁺ and Tb³⁺ centers. More interestingly, 1 is an effective fluorescent probe for the recognition and detection of Ba²⁺ ions in aqueous solution. The optical properties of the Ln-implanted arsenotungstate compounds not only expressly reveal distinctive energy transfer processes in those compounds but also broaden the application of POM-based materials in the fluorescence sensing field.

A Benzothiadiazole-Based Eu3+ Metal-Organic Framework as the Turn-On Luminescent Sensor toward Al3+ and Ga3+ with Potential Bioimaging Application

The design and preparation of novel multifunctional lanthanide metal-organic frameworks (Ln-MOFs) have been arisen widespread attention. In particular, Ln-MOFs have shown great luminescence potential in chemical sensing. Herein, a new benzothiadiazole-based Eu-MOF {[(CH₃)₂NH₂][Eu(BTDB)₂]·2H₂O}_n (JXUST-11) was obtained based on 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid (H₂BTDB), which exhibits a chain-based three-dimensional framework. Moreover, JXUST-11 is considered as a photoluminescent sensor to identify Al³⁺ and Ga³⁺ ions by fluorescence enhancement with the detection limits of 2.9 and 10.2 ppm, severally. Importantly, Al³⁺ and Ga³⁺ can be discerned with the naked eye by color change under a natural lamp. In addition, a portable MOF film based on JXUST-11 was developed for Al³⁺ and Ga³⁺ detection. This is the first Ln-MOF that can be employed as a naked-eye fluorescent probe to identify Ga³⁺. Interestingly, JXUST-11 is also capable of detecting Al³⁺ and Ga³⁺ in living cells.

Design of an antenna effect Eu(III)-based metal-organic framework for highly selective sensing of Fe3

Highly selective sensing of Fe³⁺ is very important due to its great effect on biological systems. A novel ligand [1,1':4',1'':4'',1''':4''',1''''-quinquephenyl]-2,2'',2'''',5''-tetracarboxylic acid (H₄qptca) was designed and successfully obtained for the first time via three steps in high total yields according to the absorption spectrum of Fe³⁺. The europium(III)-based metal-organic framework derived from H₄qptca, {[Eu(qptca)_1/2(H₂qptca)_1/2(H₂O)₂]·DMF}_n (referred to as SLX-1), was then synthesized and used as a water-stable and highly selective luminescent sensor for Fe³⁺ in aqueous solution with a comparable detection limit using Ln-MOF probes (6.45 μM) through the antenna effect of SLX-1. Furthermore, the luminescence quenching mechanism was also proposed as a competitive absorption mechanism.

Luminescent Covalent Organic Frameworks for Biosensing and Bioimaging Applications

Luminescent covalent organic frameworks (LCOFs) have attracted significant attention due to their tunability of structures and photophysical properties at molecular level. LCOFs are built to highly ordered and periodic 2D or 3D framework structures through covalently assembling with various luminophore building blocks. Recently, the advantages of LCOFs including predesigned properties of structure, unique photoluminescence, hypotoxicity and good biocompatibility and tumor penetration, broaden their applications in biorelated fields, such as biosensing, bioimaging, and drug delivery. A specific review that analyses the advances of LCOFs in the field of biosensing and bioimaging is thus urged to emerge. Here the construction of LCOFs is reviewed first. The synthetic chemistry of LCOFs highlights the key role of chemical linkages, which not only concrete the building blocks but also affect the optical properties and even can act as the responsive sites for potential sensing applications. How to brighten LCOFs are clarified through description of structure managements. The ability to utilize the luminescence of LCOFs for applications in biosensing and bioimaging is discussed using state-of-the-art examples of varied practical goals. A prospect finally addresses opportunities and challenges the development of LCOFs facing from chemistry, physics to the applications, according to their current progress.

Fluorescence and electrochemical detection of iodine vapor in the presence of high humidity using Ln-based MOFs

Efficient detection of toxic radioiodine species emitted by nuclear-related activities and accidents is crucial for the health of the human body and safety of the environment. Herein we report that a series of stable Ln-based MOFs with BTC linkers (Ln-BTCs) could provide dual fluorescence and electrochemical response of iodine vapor in the presence of humidity. Iodine molecules could be attracted by the oxygen sites of carboxylate linkers and confined in the cavities of Ln-BTCs. Due to the photoinduced electron transfer effect, the fluorescence of Ln-BTCs is quenched drastically in the presence of iodine. Meanwhile, the conductivity of Ln-BTCs could reach an increase of 107 fold in magnitude after iodine trapping. Water molecules could also be trapped in Ln-BTCs, having interacted with the frameworks via hydrogen bonds, and reduce the iodine uptake capacity, but they cannot alter the fluorescence and conductive properties of Ln-BTCs as distinctly as iodine molecules could. Besides, Raman mapping suggests a diffusion coefficient of 1.5 × 10-14 m2 s-1 for iodine transport in the porous Eu-BTC. The dual fluorescence and electrochemical signal outputs show high sensitivity and attractive ability to reduce false positives, which could be useful for potential integration for sensing radioiodine vapor.

Porous Anionic Co(II) Metal-Organic Framework, with a High Density of Amino Groups, as a Superior Luminescent Sensor for Turn-on Al(III) Detection

Accumulation of high concentrations of Al(III) in body has a direct impact on health and therefore, the trace detection of Al(III) has been a matter for substantial concern. An anionic metal organic framework ({[Me₂ NH₂ ]_0.5 [Co(DATRz)_0.5 (NH₂ BDC)] ⋅ xG}_n ; 1; HDATRz=3,5-diamino-1,2,4-triazole, H₂ NH₂ -BDC=2-amino-1,4-benzenedicarboxylic acid, G=guest molecule) composed of two types of secondary building units (SBU) and channels of varying sizes was synthesized by employing a rational design mixed ligand synthesis approach. Free -NH₂ groups on both the ligands are immobilized onto the pore surface of the MOF which acts as a superior luminescent sensor for turn-on Al(III) detection. Furthermore, the large channels could allow the counter-ions to pass through and get exchanged to selectively detect Al(III) in presence of other seventeen metal ions with magnificent luminescence enhancement. The observed limit of detection is as low as 17.5 ppb, which is the lowest among the MOF-based sensors achieved so far. To make this detection approach simple, portable and economic, we demonstrate MOF filter paper test for real time naked eye observation.

Response of a Zn(II)-based metal-organic coordination polymer towards trivalent metal ions (Al3+, Fe3+ and Cr3+) probed by spectroscopic methods

A new zinc-based two-dimensional coordination polymer, [Zn(5-AIP)(Ald-4)]·H2O (5-AIP = 5-amino isophthalate, Ald-4 = aldrithiol-4), 1, has been synthesized at room temperature by the layer diffusion technique. Single-crystal X-ray diffraction analysis of 1 showed a two-dimensional bilayer structure. An aqueous suspension of 1 upon excitation at 300 nm displayed an intense blue emission at 403 nm. The luminescence spectra were interestingly responsive and selective to Al3+, Cr3+ and Fe3+ ions even in the presence of other interfering ions. The calculated detection limits for Al3+, Cr3+ and Fe3+ were 0.35 μM ([triple bond, length as m-dash]8.43 ppb), 0.46 μM ([triple bond, length as m-dash]22.6 ppb) and 0.30 μM ([triple bond, length as m-dash]15.85 ppb), respectively. Notably, with the cumulative addition of Al3+ ions, the luminescence intensity at 403 nm decreased steadily with a gradual red shift up to 427 nm. Afterward, this red shifted peak showed a turn-on effect upon further addition of Al3+ ions. On the other hand, for Cr3+ and Fe3+ ions, there was only drastic luminescence quenching and a large red shift up to 434 nm. This indicated the formation of a complex between 1 and these metal ions, which was also supported by the UV-Visible absorption spectra of 1 that showed the appearance of a new band at 280 nm in the presence of these three metal ions. The FTIR spectra revealed that these ions interacted with the carboxylate oxygen atom of 5-AIP and the nitrogen atom of the Ald-4 ligand in the structure. The luminescence lifetime decay analysis manifested that a charge-transfer type complex was formed between 1 and Cr3+ and Fe3+ ions that resulted in huge luminescence quenching due to the efficient charge transfer involving the vacant d-orbitals, whereas for Al3+ ions having no vacant d-orbital, turn-on of luminescence occurred because of the increased rigidity of 1 upon complexation.

A Photoluminescent Cd(II) Coordination Polymer with Potential Active Sites Exhibiting Multiresponsive Fluorescence Sensing for Trace Amounts of NACs and Fe3+ and Al3+ Ions

The elaborately designed π-electron-rich fluorescent ligand 1,4-bis(1-carboxymethylene-4-imidazolyl)benzene (H₂L), possessing bifunctional groups including the carboxylate groups (building units) and 4-imidazoyl groups (N-donor potential active sites) has been employed to construct fluorescent coordination polymers. A luminescent sensor, namely [Cd(L)(phen)₂]·5H₂O (1), was obtained, which has a one-dimensional structure. The fluorescent material shows a blue emission maximum at 457 nm with a luminescence lifetime of 488 ns and a quantum yield (QY) of 4.56%. Significantly, 1 serves as a promising multiresponsive luminescent sensor to detect trace nitroaromatic compounds (NACs) with the limits of detection (LOD) of 7.21 × 10^-8, 1.85 × 10^-5, and 1.15 × 10^-5 mol/L for 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), and 4-nitrophenol (4-NP), respectively. Furthermore, CP 1 exhibits fluorescent turn-off and turn-on sensing behavior for Fe³⁺ and Al³⁺ metal ions with trace amounts of 1.05 × 10^-7 and 1.13 × 10^-7 mol/L, respectively. Experimental methods and theoretical calculations were employed to elucidate the sensing mechanism in detail.

Recent progresses in luminescent metal-organic frameworks (LMOFs) as sensors for the detection of anions and cations in aqueous solution

The discharge of excessive metal ions and anions into water bodies leads to the serious pollution of water and environment, which in turn has a certain impact on industry, agriculture, and human life. Because of the unique advantages of luminescent metal-organic frameworks (LMOFs), they have been successfully explored as various fluorescent probes to quickly and effectively detect these pollutants. This perspective not only introduces the design strategy and classification of LMOFs, especially the construction methods of water-stable LMOFs, but also reports the latest progresses in some LMOFs between 2016 and 2020 as well as expounds the mechanisms of LMOFs for detecting anions and cations. Moreover, the luminescence properties of LMOFs are related to the selection of metal ions, the structure of organic ligands, the pore size, and the interaction of guest molecules. Finally, the further development of LMOFs is summarized and prospected in this field.

Selective and recyclable tandem sensing of PO43- and Al3+ by a water-stable terbium-based metal-organic framework

Herein, a luminescent water-stable terbium-based metal-organic framework (MOF) {[Tb(Cmdcp)(H₂O)₃]₂(NO₃)₂·5H₂O}_n (1, H₃CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide) has been synthesized and used for the recyclable sensing of PO₄^3- and Al³⁺ in tandem. MOF 1 acts as a fluorescent sensor for PO₄^3- by the luminescence "turn-off" mechanism with high selectivity over other anions, such as F^-, Cl^-, Br^-, I^-, NO₃^-, H₂PO₄^-, HSO₄^-, HCO₃^-, HSO₃^-, SO₄^2-, CO₃^2- and HPO₄^2-. The formed PO₄^3-@1 complex further acts as the Al³⁺ sensor with the luminescence "turn-on" mechanism, also with high selectivity over diverse inorganic cations of Fe²⁺, Mn²⁺, Co²⁺, Ni²⁺, Hg²⁺, Na⁺, K⁺, Li⁺, Ag⁺, Mg²⁺, Ca²⁺, Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺. The detection process for both PO₄^3- and Al³⁺ can be directly observed with naked eyes under the UV light at 365 nm. The detection limits for PO₄^3- and Al³⁺ are 1.1 μM and 6.6 μM, respectively. Such a sensing cycle is further transferable to urine and serum samples with a satisfactory near-quantitative recovery, highlighting its good potential in biologically relevant applications.

Luminescence modulation, near white light emission, selective luminescence sensing, and anticounterfeiting via a series of Ln-MOFs with a π-conjugated and uncoordinated lewis basic triazolyl ligand

A series of Ln-MOFs with π-conjugated and uncoordinated lewis basic triazolyl ligand have luminescence modulation, near white light emission, selective luminescence sensing, and anticounterfeiting.

The influence of linker substitution on the fluorescence responsive sensing of isostructural coordination polymers: visual turn-on, ratiometric, and turn-off sensing in water

Linker substituents show great impacts on the luminescence properties and sensing performances of isostructural coordination polymers, causing turn-on or ratiometric sensing of Fe³⁺, Al³⁺, and Cr³⁺ and turn-off sensing of CrO₄²⁻ and Cr₂O₇²⁻.

A metal–organic framework featuring highly sensitive fluorescence sensing for Al3+ ions

A new fluorescent MOF can detect Al3+ ions with high selectivity and sensitivity via turn-off effect and emission color change.

Intriguing pH-modulated Luminescence Chameleon System based on Postsynthetic Modified Dual-emitting Eu3+@Mn-MOF and Its Application for Histidine Chemosensor

Due to the disruption by other nonanalyte factors, single-emission probes have been limited in complicated detecting systems. In this work, a pH-modulated luminescence chameleon system based on lanthanide-based MOF (Eu³⁺@Mn-MOF), with stable structure and miraculous dual-emitting fluorescent properties, was synthesized by a postsynthetic modification (PSM) strategy of a simple hydrothermal and agitation method. Amazingly, not only can the Eu³⁺@Mn-MOF emit a broad emission at 500 nm attributed to the ligand-based fluorescence emission but it can also exhibit the characteristic emission of Eu³⁺ ions responding to the antenna effect. Moreover, the Eu³⁺@Mn-MOF displays an interesting luminescence color transition between acidic and basic solutions. Inspired by this phenomenon, a pH-modulated luminescence chameleon system was first constructed and employed to detect histidine, a kind of basic amino acid for a variety of biological matters, causing a unique fluorescence signal of the ratio-dependent color to change from yellow to light pink which differs from the color change of other water-soluble amino acids. Therefore, Eu³⁺@Mn-MOF can be as a practical pH-modulated luminescence chameleon system chemsensor for sensing histidine with low detection limit, high sensitivity, and rapid sensing time. In conclusion, the postsynthetic modified Eu³⁺@Mn-MOF has outstanding applications in the fields of chemical detection and human health.

Novel alkaline earth metal–organic frameworks with thiophene groups for selective detection of Fe3+

This work demonstrates that the alkaline earth ion radii play an important role in coordination numbers and topologies for constructing MOFs, and these MOFs can be used as fast-response fluorescence sensors for the detection of Fe³⁺.

Rare-earth metal–organic frameworks: from structure to applications

In the past 30 years, rare-earth metal–organic frameworks (MOFs) have been gaining attention owing to their diverse chemical structures, and tunable properties.

Sonochemical synthesis of microscale Zn(ii)-MOF with dual Lewis basic sites for fluorescent turn-on detection of Al3+ and methanol with low detection limits

A microscale Zn-MOF containing dual Lewis basic sites for the efficient bifunctional fluorescent detection of Al³⁺ and methanol.