A new selective fluorogenic probe for trivalent cations

A highly efficient, selective, reversible and ultra-sensitive fluorescence "Turn-ON" chemosensor for aluminium ions by a novel Schiff base

The synthesis of a Schiff base-based chemosensor, denoted as H6L, was accomplished through the condensation reaction of Isophthalohydrazide and 2,6-dihydroxybenzaldehyde in an ethanol solvent. The resulting compound was further characterized using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, as well as high-resolution mass spectrometry (HRMS). Extensive research has been conducted on several facets of metal sensing phenomena, revealing that the Schiff base H6L demonstrates discerning and expeditious fluorescence sensing characteristics specifically towards Al (III) in acetonitrile. The purported method detects Al (III) can be ascribed to the suppression of photo-induced electron transfer (PET) and the enhanced chelation-induced fluorescence (CHEF). The stoichiometry of metal-ligand complexes (2:1) was determined using Job's plots titrations, HRMS and subsequently confirmed using NMR titration studies. The H6L sensors demonstrated remarkable fluorescence sensing capabilities in acetonitrile, with a low detection limit (LOD) of 0.44 μM. This LOD is suitably low for the detection of Al3+, which is commonly found in many environmental and biological systems. Fluorescence lifetime measurement provides additional evidence of complexation of H6L with Al (III). The reversibility of the sensor was demonstrated through the introduction of pyrophosphate (PPi), which forms a complex with aluminium ions, thereby releasing the chemo sensor for subsequent utilization. The findings suggest that H6L has the potential to serve as a viable probe for the detection and identification of Al3+ ions.

Selective Adsorption of Dyes and Fe3+ Sensing via Tb3+ Incorporation in an Anionic Cadmium-Organic Framework

A three-dimensional (3D) anionic cadmium-organic framework, namely [(CH3)2NH2][Cd1.5(DMTDC)2] ⋅ 2DMA ⋅ 0.5H2O (Cd-MOF; DMA=N,N-dimethylacetamide), was successfully synthesized under solvothermal conditions by using a linear thienothiophene-containing dicarboxylate ligand, 3,4-dimethylthieno [2,3-b]-thiophene-2,5-dicar-boxylic acid (H2DMTDC). Single-crystal X-ray diffraction analysis reveals that Cd-MOF exhibits a 3D anionic framework with pcu α-Po topology, featuring rectangle and rhombus-shaped channels along b- and c- axis direction. Cd-MOF demonstrates selective adsorption of cationic dyes over anionic and neutral dyes. Additionally, Tb3+-loaded Cd-MOF serves as a fast-response fluorescence sensor for the sensitive detection of Fe3+ ions with a low limit of detection (8.90×10-7 M) through fluorescence quenching.

Exploitation of a 1D coordination polymer as a portable kit for an eye-catching fluorometric response towards sensing of trivalent cations

The development and utilization of coordination polymers (CPs) have drawn interest for potential applications in different fields. Detection of metal ions in efficient and selective manners is an important field of research. It paves the way to protect human health by balancing toxic metal ions and biologically active metal ions in the atmosphere. In this regard, a new one-dimensional (1D) 4-(1-naphthylvinyl)pyridine (4-nvp) based CP [Cd(NCS)2(4-nvp)2]n (1) was synthesized and characterized structurally by single-crystal X-ray diffraction. Interestingly, this 1D CP underwent supramolecular aggregation via π⋯π stacking interactions, which specifically generated an environment for a potent "turn on" response in the presence of trivalent cations (Fe3+, Al3+, and Cr3+) in the nanomolar range but remained silent in the presence of other metal ions. Density functional theory (DFT) computations and X-ray photoelectron spectroscopy (XPS) were performed to establish the sensing phenomena. Fascinatingly, utilizing the sensitivity of 1 in an aqueous medium, a hands-on portable cotton swab kit was developed for instant identification of these three important trivalent metal cations.

Selective and pH-Independent Detection of Ba2+ in Water by a Benzo-21-crown-7-Functionalized BODIPY

Herein, we report on highly Ba2+ selective fluorescence sensing in water by a fluorescent probe consisting of a benzo-21-crown-7 as a Ba2+ binding unit (ionophore) and a tetramethylated BODIPY fluorophore as a fluorescence reporter. This fluorescent probe showed a Ba2+ induced fluorescence enhancement (FE) by a factor of 12±1 independently of the pH value and a high Ba2+ sensitivity with a limit of detection (LOD) of (17.2±0.3) μM. Moreover, a second fluorescent probe consisting of the same BODIPY fluorophore, but a benzo-18-crown-6 as a cation-responsive binding moiety, showed an even higher FE upon Ba2+ complexation by a factor of 85±3 and a lower LOD of (13±3) μM albeit a lower Ba2+ selectivity. The fluorescence sensing mechanism of Ba2+ was further investigated by time-resolved fluorescence as well as transient absorption spectroscopy (TAS) and it turned out that within these probes a blocking of a photoinduced electron transfer (PET) by Ba2+ is very likely responsible for the FE.

Fluorescent deactivation behaviors based on ESIPT and TICT of novel double target fluorescent probe and its sensing mechanism for Al3+/Mg2+: A TD-DFT study

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods with integral equation formula polarized continuum model (IEFPCM), the fluorescent behavior and recognizing mechanism of probe N'-((1-hydroxynaphthalen-2-yl)methylene)isoquinoline-3-carbohydrazide (NHMI) for Al³⁺/Mg²⁺ ion were investigated in more detail. Excited state intramolecular proton transfer (ESIPT) process in probe NHMI occurs in the stepwise pattern. The proton H₅ of enol structure (E1) firstly moves from O₄ to N₆ to form single proton-transfer (SPT2) structure, and then the proton H₂ of SPT2 transfers from N₁ to N₃ to form the stable double proton-transfer (DPT) structure. Subsequently, the transformation from DPT to its isomer (DPT1) induces the twisted intramolecular charge transfer (TICT) process. Two non-emissive TICT states (TICT1 and TICT2) were obtained, and TICT2 state quenches the fluorescence observed in the experiment. With the addition of aluminum (Al³⁺) or magnesium (Mg²⁺) ion, TICT process is prohibited by the coordination interaction between NHMI and Al³⁺/Mg²⁺, and the strong fluorescent signal is turned on. For probe NHMI, the twisted C-N single bond of acylhydrazone part leads to the TICT state. This sensing mechanism may inspire researchers to develop new probes from a different direction.

Trivalent metal ion sensor enabled bioimaging and quantification of vaccine-deposited Al3+ in lysosomes

Extracellular metallic debris is deposited into the well-known 'recycle bins' of the cells named lysosomes. The accumulation of unwanted metal ions can cause dysfunction of hydrolyzing enzymes and membrane rupturing. Thus, herein, we synthesized rhodamine-acetophenone/benzaldehyde derivatives for the detection of trivalent metal ions in aqueous media. In solution, the synthesized probes exhibited a 'turn-on' colorimetric and fluorometric response upon complexation with trivalent metal ions (M³⁺). Mechanistically, M³⁺ chelation enables the appearance of a new emission band at approximately 550 nm, which verifies the disruption of the closed ring and the restoration of conjugation on the xanthene core in rhodamine 6G derivatives. Exclusive localization of the biocompatible probes at the lysosomal compartment favored the quantification of deposited Al³⁺. Moreover, the novelty of the work lies in the detection of Al³⁺ deposited in the lysosome that originated from hepatitis B vaccines, which shows their efficiency for near future in vivo applications.

Schiff Bases: A Versatile Fluorescence Probe in Sensing Cations

Metal cations such as Zn²⁺, Al³⁺, Hg²⁺, Cd²⁺, Sn²⁺, Fe²⁺, Fe³⁺ and Cu²⁺ play important roles in biology, medicine, and the environment. However, when these are not maintained in proper concentration, they can be lethal to life. Therefore, selective sensing of metal cations is of great importance in understanding various metabolic processes, disease diagnosis, checking the purity of environmental samples, and detecting toxic analytes. Schiff base probes have been largely used in designing fluorescent sensors for sensing metal ions because of their easy processing, availability, fast response time, and low detection limit. Herein, an in-depth report on metal ions recognition by some Schiff base fluorescent sensors, their sensing mechanism, their practical applicability in cell imaging, building logic gates, and analysis of real-life samples has been presented. The metal ions having biological, industrial, and environmental significance are targeted. The compiled information is expected to prove beneficial in designing and synthesis of the related Schiff base fluorescent sensors.

Multi-crosslinked network chitosan films containing caffeic acid and Fe3+ with high anti-oxidation and anti-UV abilities

In this study, caffeic acid (CA) and Fe³⁺ were added to chitosan solution to prepare chitosan/caffeic acid/Fe³⁺ (CCAF) composite films. CA was used to introduce covalent bonds and hydrogen bonds. Fe³⁺ was used to introduce metal coordination bonds which combined with hydrogen bond and covalent bonds to form a multi-crosslinked system to enhance the tensile strength (TS), improve the antioxidant properties and UV resistance performance. The results showed that the TS of chitosan/caffeic acid (CCA) film with the addition of 0.3 mmol CA was increased by 36.6 % compared with pure chitosan film. The TS of the CCAF film increased from 42.6 MPa to 73.9 MPa with an increase of 73.5 %. The free radical scavenging rate of CCA film and CCAF film, in comparison to pure chitosan film, were improved by 155.7 % and 148.24 %, respectively. The UV resistance property of the CCAF solution was tested at 365 nm and the results showed that the UV barrier rate reached 99.99 %. The water vapor transmission (WVT) and water vapor permeability (WVP) of CCAF film both showed a 25.71 % reduction compared to that of the chitosan film. Besides, the composite film also showed excellent antibacterial properties, which provided the possibility for more applications.

A colorimetric sensing probe for chromium (III) ion based on domino like reaction

In this work, a gold nanobipyramid@Ag nanorod (AuNBP@Ag NR)-based sensor platform was developed for the quantitative, visual, and sensitive detection of Cr³⁺ ions in aqueous solutions. This assay provides quantitative detection of Cr³⁺, which relies on the absorbance change of AuNBP@Ag NRs due to morphological change of the AuNBP@Ag NRs induced by Cr³⁺. When AuNBP@Ag NRs and Cr³⁺ mix, the coordination reaction of the carboxyl groups of citrate and Cr³⁺ occurs, which leads to the collapse of Ag shell nanorods, similar to the domino effect, and obvious color changes from yellow to pink can be observed by the naked eye. When combined with UV-vis spectrophotometer-based colorimetric detection, a detection limit of 8.7 nM for Cr³⁺ in ultrapure water was achieved. With the advantages of high sensitivity, selectivity, and performance, we anticipate that the sensor will be helpful for the on-site, quantitative detection of Cr³⁺ ions in water samples.

Water-soluble optical sensors: keys to detect aluminium in biological environment

Metal ion plays a critical role from enzyme catalysis to cellular health and functions. The concentration of metal ions in a living system is highly regulated. Among the biologically relevant metal ions, the role and toxicity of aluminium in specific biological functions have been getting significant attention in recent years. The interaction of aluminium and the living system is unavoidable due to its high earth crust abundance, and the long-term exposure to aluminium can be fatal for life. The adverse Al3+ toxicity effects in humans result in various diseases ranging from cancers to neurogenetic disorders. Several Al3+ ions sensors have been developed over the past decades using the optical responses of synthesized molecules. However, only limited numbers of water-soluble optical sensors have been reported so far. In this review, we have confined our discussion to water-soluble Al3+ ions detection using optical methods and their utility for live-cell imaging and real-life application.

Heterometallic Dual-Liganded AE-Ln-CPs Luminescent Probes for Efficient Sensing of Fe(III) Ions

Iron ion is widely present in the environment and in biological systems, and are indispensable trace elements in living organisms, so development of an efficient and simple sensor for sensing Fe(III) ions has attracted much attention. Here, six heterometallic AE-Ln coordination polymers (CPs) [Ln₂ (pda)₄(Hnda)₂Ca₂(H₂O)₂]·MeOH (Ln = Eu (1), Tb (2); H₂pda = 2,6-pyridinedicarboxylic acid, H₂nda = 2,3-naphthalenedicarboxylic acid), [Ln (pda)₂ (nda)AE₂(HCOO)(H₂O)] (AE = Sr, Ln = Eu (3), Tb (4); AE = Ba, Ln = Eu (5), Tb (6)) with two-dimensional (2D) layer structures were synthesized by hydrothermal method. All of them were characterized by elemental analysis, XRD, IR, TG, as well as single crystal X-ray diffraction. They all show infinite 2D network structure, where complexes 1 and 2 are triclinic with space group of P1¯, while 3-6 belong to the monoclinic system, space group P2_1/n. The solid-state fluorescence lifetimes of complexes 1, 3 and 5 are τ_obs1 = 1930.94, 2049.48 and 2,413.04 µs, respectively, and the quantum yields Ф_total are 63.01, 60.61, 87.39%, respectively, which are higher than those of complexes 2, 4 and 6. Complexes 1-6 all exhibited efficient fluorescence quenching response to Fe³⁺ ions in water, and were not interfered by the following metal ions: Cu²⁺, Cd²⁺, Mg²⁺, Ni²⁺, Co²⁺, Ca²⁺, Ba²⁺, Sr²⁺, Li⁺, Na⁺, K⁺, Al³⁺, Fe²⁺, Pb²⁺, Cr³⁺, Mn²⁺ and Zn²⁺. The quenching coefficient K_SV for complexes 1-6 is 1.41 × 10⁵ M⁻¹, 7.10 × 10⁴ M⁻¹, 1.70 × 10⁵ M⁻¹, 1.57 × 10⁵ M⁻¹, 9.37 × 10⁴ M⁻¹, 1.27 × 10⁵ M⁻¹, respectively. The fluorescence quenching mechanism of these complexes towards Fe³⁺ ions was also investigated. It is possible that the weak interaction formed between the complexes and the Fe³⁺ ions reduce the energy transfer from the ligand to the Ln³⁺ ion, producing the emission burst effect. This suggests that complexes 1-6 can be candidate for efficient luminescent sensor of Fe³⁺.

A stable lanthanum-based metal-organic framework as fluorescent sensor for detecting TNP and Fe3+ with hyper-sensitivity and ultra-selectivity

A new Lanthanum-based luminescent metal-organic framework, {[La(H₂O)₄(HL)]·H₂O} (1), has been successfully synthesized by employing 3,3',5,5'-azodioxybenzenetetracarboxylic acid (H₄L) as a rigid organic linker through the solvothermal reactions. 1 exhibits a two-dimensional (2D) layered structure and a three-dimensional (3D) supramolecular structure is formed by hydrogen bonds between the layers. Stability studies indicate that 1 has good chemical stability and thermostability. Meanwhile, the K_sv values for TNP is 4.61 × 10⁴ M^-1 with the LOD of 4.13 × 10^-6 M and the K_sv value for Fe³⁺ is 1.22 × 10⁴ M^-1 with the LOD of 1.72 × 10^-5 M, respectively, which demonstrated that 1 exhibits high sensitivity and excellent selectivity for the detection of TNP and Fe³⁺via fluorescence quenching. Significantly, 1 shows high regenerability after five recycling progress for sensing Fe³⁺. The possible mechanisms associated with the luminescent quenching are discussed in detail through some relevant experiments and tests, as well as the DFT calculations. Based on the above excellent properties of 1, it will have extremely potential to be used as a dual functional sensor for both detecting TNP and Fe³⁺ in aqueous solution, simultaneously.

A Highly Stable Eu−MOF Multifunctional Luminescent Sensor for the Effective Detection of Fe3+, Cr2O72−/CrO42− and Aspartic Acid in Aqueous Systems

Heavy metal ions were common pollutants in water pollution. Amino acids, as important substances in organisms, participate in many life activities. The detection of heavy metal ions and amino acids...

Double noncovalent network chitosan/hyperbranched polyethylenimine/Fe3+ films with high toughness and good antibacterial activity

The application of pure chitosan films is significantly limited due to their poor mechanical properties. In this study, a novel type of chitosan/hyperbranched polyethylenimine (CHP) and chitosan/hyperbranched polyethylenimine/Fe³⁺ (CHPF) films with high toughness and good antibacterial activity were prepared through a noncovalent crosslinking method. From the tensile test results, the strain and toughness of the CHP film increased by 798.1% and 292.3%, respectively, compared with pure chitosan film, after the addition of 20% hyperbranched polyethylenimine (HPEI). The addition of trace metal iron ions (3 mg) forms a metal coordination bond with the amine group on HPEI, as well as the hydroxyl group and amine group on chitosan, and develops a double noncovalent bond network structure with hydrogen bonding, which further enhances the mechanical tensile strength of the chitosan-based film, with an increase of 48.4%. Interestingly, HPEI and Fe³⁺ can be used as switches to increase and decrease the fluorescence property of chitosan, respectively. Furthermore, the CHP and CHPF films showed good antibacterial activity against S. aureus and E. coli.

Double noncovalent network chitosan/hyperbranched polyethylenimine/Fe³⁺ films.

Assembly of a Zn(II) coordination polymer of tetrapyridyl tetraene ligands for selective sensing of CrO42- and Fe3+ in water via luminescence quenching and enhancement

Four Zn(II)-based coordination polymers (CPs), [Zn(4-tkpvb)(FB)2] (CP1), [Zn(4-tkpvb)(CB)2] (CP2), [Zn(4-tkpvb)(BB)2] (CP3) and [Zn(4-tkpvb)(NTP)]n (CP4), were prepared from solvothermal reactions of Zn(NO3)2•6H2O with 1,2,4,5-tetrakis((E)-2-(pyridin-4-yl)vinyl)benzene (4-tkpvb) in the presence of 3-florobenzoic acid...

Highly selective fluorescent turn-on-off sensing of OH-, Al3+ and Fe3+ ions by tuning ESIPT in metal organic frameworks and mitochondria targeted bio-imaging

Herein we report a multifunctional high performance metal organic framework (Zn-DHNDC MOF) based chemosensor that displays an exceptional excited state intramolecular proton transfer (ESIPT) tuned fluorescence turn-on-off response for OH-, Al3+ and Fe3+ ions along with mitochondria targeted bio-imaging. Properly tuning ESIPT as well as the hydroxyl group (-OH) allows Zn-DHNDC MOF to optimize and establish chelation enhanced fluorescence (CHEF) and chelation enhanced quenching (CHEQ) based sensing mechanisms. The MOF benefits from acid-base interactions with the ions which generate a turn-on bluish green fluorescence (λ Em 492 nm) for OH-, an intense turn-on green fluorescence (λ Em 528 nm) for Al3+ and a turn-off fluorescence quenching response for Fe3+ ions. The aromatic -OH group indeed plays its part in triggering CHEF and CHEQ processes responsible for the turn-on-off events. Low limits of detection (48 nM of OH-, 95 nM for Al3+, 33 nM for Fe3+ ions), high recyclability and fast response time (8 seconds) further assist the MOF to implement an accurate quantitative sensing strategy for OH-, Al3+ and Fe3+ ions. The study further demonstrates the MOF's behaviour in cellular medium by subjecting it to live cell confocal microscopy. Along with a bio-compatible nature the MOF exhibited successful accumulation inside the mitochondria of MCF7 cancer cells, which defines it as a significant bio-marker. Therefore the present work successfully represents the multidisciplinary nature of Zn-DHNDC MOFs, primarily in sensing and biomedical studies.

Devising Mixed-Ligand Based Robust Cd(II)-Framework From Bi-Functional Ligand for Fast Responsive Luminescent Detection of Fe3+ and Cr(VI) Oxo-Anions in Water With High Selectivity and Recyclability

Environmental issue related applications have globally surfaced as hottest areas of research, wherein luminescent metal-organic frameworks (LMOFs) with functionalized pores put unique signature in real-time monitoring of multiple classes of toxic compounds, and overcome many of the challenges of conventional materials. We report a two-fold interpenetrated, mixed-ligand Cd(II)-organic framework (CSMCRI-11) [Cd_1.5(L)₂(bpy)(NO₃)]·DMF·2H₂O (CSMCRI = Central Salt and Marine Chemical Research Institute, HL = 4- (1H-imidazol-1-yl)benzoic acid, bpy = 4,4'-bipyridine) that exemplifies bipillar-layer structure with two different Cd(II) nodes, and displays notable robustness in diverse organic solvents and water. Intense luminescence signature of the activated MOF (11a) is harnessed in extremely selective and fast responsive sensing of Fe³⁺ ions in aqueous phase with notable quenching constant (1.91 × 10⁴ M^-1) and impressive 166 ppb limit of detection (LOD). The framework further serves as a highly discriminative and quick responsive scaffold for turn-off detection of two noxious oxo-anions (Cr₂O₇ ^2- and CrO₄ ^2-) in water, where individual quenching constants (CrO₄ ^2-: 1.46 × 10⁴ M^-1; Cr₂O₇ ^2-: 2.18 × 10⁴ M^-1) and LOD values (CrO₄ ^2-: 179 ppb; Cr₂O₇ ^2-: 114 ppb) rank among best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress the outstanding reusability of the MOF towards detection of all these aqueous pollutants, besides their vivid monitoring by colorimetric changes under UV-light. Mechanism of selective quenching is comprehensively investigated in light of absorption of the excitation/emission energy of the host framework by individual studied analyte.

Porphyrin-Based Metal-Organic Framework Probe: Highly Selective and Sensitive Fluorescent Turn-On Sensor for M3+ (Al3+, Cr3+, and Fe3+) Ions

The development of porphyrin-based metal-organic frameworks (MOFs) has attracted significant interest in the scientific community in recent years because of their versatile applications particularly in optical and electronic fields. In this study, a highly selective and sensitive fluorescent turn-on sensor using a porphyrinic MOF, Tb-TCPP, is presented, which displays a 10-fold fluorescence enhancement in the presence of Al³⁺, Cr³⁺, and Fe³⁺ ions. The detection limit is in the nM region. For the Al³⁺ ion, it could be visually detected at concentrations as low as 5 mM within 15 min. Tb-TCPP could also be used as an indicator for acidic or alkaline solutions at pH values of >9 and <3. The studies on the detection mechanism illustrate that cation exchange proceed between Tb-TCPP and these M³⁺ ions, and consequently, energy transfer from TCPP to Tb³⁺ is suppressed and π*-π energy transfer of the porphyrin ligand is significantly enhanced.

Two series of Ln-MOFs by solvent induced self-assembly demonstrating the rapid selective sensing of Mg2+ and Fe3+ cations

Two series of lanthanide-based metal-organic frameworks, namely {[Ln(BIPA-TC)0.5(DMA)2(NO3)]·DMA·H2O}n (1-Ln, Ln = Eu, Dy, Sm, Nd) and {[Ln2(BIPA-TC)1.5(DMA)3(H2O)2]·2DMA·2H2O}n (2-Ln, Ln = Eu, Dy, Sm, Nd), were successfully constructed via a solvent regulation strategy based on a π-electron rich tetra-carboxylate ligand (H4BIPA-TC). 1-Ln shows a 4-connected lvt topology with the point symbol of {42·84}, but 2-Ln displays a new 4,4,6-connected wxk1 topology with the point symbol of {43·83}4{46·66·83}2{86}. The solid-state luminescence property and the microporous nature of Eu-MOFs (1-Eu and 2-Eu) indicate that they can potentially be used as luminescent sensors. Fluorescence measurements indicate that Fe3+ exhibits the quenching effect for 1-Eu with the quenching efficiency of 93.1%. 2-Eu is the first MOF sensor for Mg2+ with the lowest detection limit of 1.53 × 10-10 mol L-1 and displays good recyclable capability. Simultaneously, in the presence of other metal ions (Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pd2+, Al3+, Cr3+and Fe3+), 2-Eu can maintain the selective sensing of Mg2+, indicating its potential for Mg2+ turn-on sensing.

Pore-Functionalized and Hydrolytically Robust Cd(II)-Metal-Organic Framework for Highly Selective, Multicyclic CO2 Adsorption and Fast-Responsive Luminescent Monitoring of Fe(III) and Cr(VI) Ions with Notable Sensitivity and Reusability

Metal-organic frameworks (MOFs) show a distinctive pre-eminence over other heterogeneous systems for adsorption of carbon dioxide (CO₂) gas and fluorescence detection of water contaminating ions, where integration of both these attributes along with enhancement of pore functionality and water stability is crucial for potential applications related to environmental remediation. Pore functionalization has been achieved in a 2-fold interpenetrated, mixed-ligand Cd(II)-framework [Cd_1.5(L)₂(bpy)(NO₃)]·2DMF·2H₂O (CSMCRI-5) (HL = 4-(4-carboxyphenyl)-1,2,4-triazole, bpy = 4,4'-bipyridine, DMF = dimethylformamide, CSMCRI = Central Salt & Marine Chemicals Research Institute) by utilizing a bifunctional ligand HL. The bpy-pillared framework, containing diverse Cd(II) nodes, optimum sized voids, and free N-atom affixed one-dimensional porous channels, shows notable structural robustness in diverse organic solvents and water. In spite of a negligible surface area, the activated MOF (5a) exhibits good CO₂ uptake and highly selective CO₂ adsorption over N₂ (259.94) and CH₄ (14.34) alongside minor loss during multiple CO₂ adsorption-desorption cycles. Luminescence studies demonstrate extremely selective and ultrafast sensing of Fe³⁺ ions in the aqueous phase with notable quenching (1.13 × 10⁴ M^-1) as well as an impressive 98 ppb limit of detection (LOD). Importantly, Fe³⁺ detection is exclusively retained under simulated physiological conditions. The framework further serves as a quick-responsive scaffold for toxic CrO₄^2- and Cr₂O₇^2- anions, where individual quenching constants (CrO₄^2-: 1.73 × 10⁴ M^-1; Cr₂O₇^2-: 5.42 × 10⁴ M^-1) and LOD values (CrO₄^2-: 280 ppb; Cr₂O₇^2-: 320 ppb) rank among the best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress vivid monitoring of all these aqueous pollutants by a handy paper-strip method, besides outstanding applicability of 5a toward their recyclable detection. Mechanism of selective quenching is comprehensively investigated in light of the absorption of the excitation/emission energy of the host framework by an individual studied analyte.

Zinc(ii)-based coordination polymer encapsulated Tb3+ as a multi-responsive luminescent sensor for Ru3+, Fe3+, CrO4 2-, Cr2O7 2- and MnO4. RSC Adv 2020;10:6022-6029. [PMID: 35497449 PMCID: PMC9049217 DOI: 10.1039/c9ra09541a]

A zinc(ii)-based coordination polymer (CP), namely [Zn(modbc)2] n (Zn-CP) (modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4'-bipyridine-5-carbonitrile), has been synthesized and characterized. Single-crystal structural determination reveals that Zn-CP is a two-dimensional framework structure with tetranuclear homometallic Zn4(modbc)4 units cross-linked by modbc. The excellent luminescence as well as good stability of Zn-CP do not enable it to have selective sensing capability for different ions. After encapsulation of Tb3+ in Zn-CP, the as-obtained fluorescent functionalized Tb3+@Zn-CP maintained excellent luminescence as well as stability, which made it a highly selective and sensitive multiresponsive luminescent sensor for Ru3+, Fe3+, CrO4 2-, Cr2O7 2-, and MnO4 - with high sensitivity, good anti-interference performance, and quick response time (∼10 s). The detection limits are 0.27 μM, 0.57 μM, 0.10 μM, 0.43 μM and 0.15 μM, respectively. A possible sensing mechanism was discussed in detail.

Two d10 luminescent metal-organic frameworks as dual functional luminescent sensors for (Fe3+,Cu2+) and 2,4,6-trinitrophenol (TNP) with high selectivity and sensitivity

Two luminescent 3D supramolecular structures [Cd3(L)2(2,2-bipy)2](DMF)3(CH3CH2OH)2(H2O) (1) and [Zn3(L)2(2,2-bipy)2(DMF)2](DMF)2(CH3CH2OH)2(H2O) (2) (H3L = 4,4',4''-nitrilotribenzoic acid) have been successfully synthesized under solvothermal conditions using Cd(NO3)2·4H2O or Zn(NO3)2·6H2O as the metal sources, and 4,4',4''-nitrilotribenzoic acid (H3L), 2,2-bipy as the ligands in DMF solvent. Compound 1 displays a bi-nodal (2,3,6)-coordinated net with {83}2{86·126·163}{8}6 topology, compound 2 can be described as a (3,6)-connected 2-nodal net with kgd topology. The phase purity of compound 1 and 2 is characterized by X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. Compound 1 and 2 can serve as effective luminescent sensors for Fe3+, Cu2+ and TNP via luminescent quenching.

Two tetranuclear Cd-based metal–organic frameworks for sensitive sensing of TNP/Fe3+ in aqueous media and gas adsorption

Two Cd-MOFs were solvothermally synthesized by mixed-ligand strategy. 1 has the largest adsorption selectivity for CO₂. Furthermore, 1 and 2 present sensitive sensing for TNP/Fe³⁺ in water or soil samples.

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⁺.

A highly stable 8-hydroxyquinolinate-based metal–organic framework as a selective fluorescence sensor for Fe3+, Cr2O72− and nitroaromatic explosives

A novel 8-hydroxyquinolinate-based metal–organic framework exhibits excellent sensing performance toward Fe³⁺, Cr₂O₇²⁻ and nitroaromatic explosives.