Iridium(III)-Based Metal–Organic Frameworks as Multiresponsive Luminescent Sensors for Fe3+, Cr2O72–, and ATP2– in Aqueous Media

Controlled Primary Amine-Enriched SG-Bonded Papain Surface: Synthesis, Characterization, and Extraction of Protonated Dichromate

The single-step synthesis of nitro-derivatized SG using dimethyldichlorosilane in an aprotic solvent dichloromethane at 300 K is efficient and straightforward. Reduction and diazotization effectively functionalize the material for enzyme coupling at the O-carbon of the enzyme's tyrosine. The high extraction efficiency of protonated dichromate ions with a breakthrough capacity of 480 μmol·g-1 is notable. Eco-friendly elution using distilled water achieves a significant enrichment factor of 23.2. Excellent reusability (up to 900 cycles) and stable sorption efficiency (ζ ≥ 0.9) highlight the material's potential for practical applications and future research.

Two-Dimensional Lanthanide Metal-Organic Frameworks as a Platform for Sensing Pollutant and Nitrophenols Reduction

The discharge of harmful and toxic pollutants in water is destroying the ecosystem balance and human being health at an alarming rate. Therefore, the detection and removal of water pollutants by using stable and efficient materials are significant but challenging. Herein, three novel lanthanide metal-organic frameworks (Ln-MOFs), [La(L)(DMF)2(H2O)2]·H2O (LCUH-104), [Nd(L)(DMF)2(H2O)2]·H2O (LCUH-105), and [Pr(L)(DMF)2(H2O)2]·H2O (LCUH-106) [H3L = 5-(4-(tetrazol-5-yl)phenyl)isophthalic acid (H3TZI)] were solvothermally constructed and structurally characterized. In the three Ln-MOFs, dinuclear metallic clusters {Ln2} were connected by deprotonated tetrazol-containing dicarboxylate TZI3- to obtain a 2D layered framework with a point symbol of {42·84}·{46}. Their excellent chemical and thermal stabilities were beneficial to carry out fluorescence sensing and achieve the catalytic nitrophenols (NPs) reduction. Especially, the incorporation of the nitrogen-rich tetrazole ring into their 2D layered frameworks enables the fabrication of Pd nanocatalysts (Pd NPs@LCUH-104/105/106) and have dramatically enhanced catalytic activity by using the unique metal-support interactions between three Ln-MOFs and the encapsulating palladium nanoparticles (Pd NPs). Specifically, the reduction of NPs (2-NP, 3-NP, and 4-NP) in aqueous solution by Pd NPs@LCUH-104 exhibits exceptional conversion efficiency, remarkable rate constants (k), and outstanding cycling stability. The catalytic rate of Pd NPs@LCUH-104 for 4-NP is nearly 8.5 times more than that of Pd/C (wt 5%) and its turnover frequency value is 0.051 s-1, which indicate its excellent catalytic activity. Meanwhile, LCUH-105, as a multifunctional fluorescence sensor, exhibited excellent fluorescence detection of norfloxacin (NFX) (turn on) and Cr2O72- (turn off) with high selectivity and sensitivity at a low concentration, and the corresponding fluorescence enhancement/quenching mechanism has also been systematically investigated through various detection means and theoretical calculations.

Switching from Oxygen Quenching Resistance to Linear Response by Smart Luminescent Iridium(III)-Based Metal-Organic Frameworks

In this study, we utilize a photo-active Ir-metalloligand, Ir(C^N)₂(L) (C^N = 2-(2,4-difluorophenyl) pyridine, L = [2,2'-bipyridine]-5,5'-dicarboxylic acid), to assemble with CdX₂ under hydrothermal conditions, yielding highly emissive crystals of two-dimensional metal-organic frameworks (2D MOFs) (named Ir-Cd₂X_2, X = Cl, Br). The Ir-Cd₂X₂ MOFs exhibit μs-level phosphorescence lifetimes and more than 55% quantum yield (QY) at room temperature because of the rigid framework connected by Cd₂X₂ clusters. By immersing Ir-Cd₂X₂ in water solution for 5 min, a new MOF (Ir-Cd) was obtained, which is given a structure with hydrolyzed Cd-nodes by complete removal of halogen bridges as elucidated by single-crystal diffraction. Although the phosphorescence emission of pristine CdX₂ MOFs exhibits oxygen quenching resistance, the converted Ir-Cd MOF possesses sensitively oxygen-responsive ³MLCT properties, showing a K_SV value as high as 14.5 with strictly linear relation (R² = 0.995). This work differs from the traditional method for improving oxygen-sensing metrics by enhancing QY and phosphorescence lifetime in Ir complexes, while also demonstrating that the transformation in the surrounding coordination environment on adjacent metal centers can also constitute key factors for improved photoluminescence stability or responsive properties in Ir-based heteronuclear MOFs, providing clues for the development of either oxygen quenching blockers or sensors suitable for different occasions.

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 CrO₄^2-/Cr₂O₇^2- 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 Fe^III and Cr^VI ions in water as a greenest medium.

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.

Hollow terbium metal-organic-framework spheres: preparation and their performance in Fe3+ detection

Hollow metal–organic framework (MOF) micro/nanostructures have been attracting a great amount of research interest in recent years. However, the synthesis of hollow metal–organic frameworks (MOFs) is a great challenge. In this paper, by using 1,3,5-benzenetricarboxylic acid (H₃BTC) as the organic ligand and 2,5-thiophenedicarboxylic acid (H₂TDC) as the competitive ligand and protective agent, hollow terbium MOFs (Tb-MOFs) spheres were synthesized by a one-pot solvothermal method. By comparing the morphology of Tb-MOFs in the presence and absence of H₂TDC, it is found that H₂TDC plays a key role in the formation of the hollow spherical structure. Single crystal analyses and element analysis confirm that H₂TDC is not involved in the coordination with Tb³⁺. Interestingly, Tb-MOFs can be used as the luminescent probes for Fe³⁺ recognition in aqueous and N,N-dimethylformamide (DMF) solutions. In aqueous solution, the quenching constant (K_SV) is 5.8 × 10⁻⁴ M⁻¹, and the limit of detection (LOD) is 2.05 μM. In DMF, the K_SV and LOD are 9.5 × 10⁻⁴ M⁻¹ and 0.80 μM, respectively. The sensing mechanism is that the excitation energy absorption of Fe³⁺ ions reduces the energy transfer efficiency from the ligand to Tb³⁺ ions.

(a) Pictures of Tb-MOFs suspension (left) and Fe³⁺ (right) under 365 nm illumination. (b) Pictures of Fe³⁺ with (left) and without (right) Tb-MOFs. (c) Pictures of Tb-MOFs powder before (left) and after (right) Fe³⁺ adsorption.

Are luminescent Ru2+ chelated complexes selective coordinative sensors for the detection of heavy cations?

The ability of [Ru(bpy)₂(bpym)]²⁺ (bpy = 2,2'-bipyridine; bpym = 2,2'-bipyrimidine) to probe specifically heavy cations has been investigated by means of density functional theory for transition metals, group 12 elements and Pb²⁺. On the basis of the calculated Gibbs free energies of complexation in water it is shown that all reactions are favorable with negative enthalpies except for Hg²⁺, with the transition metal cations forming stable bi-metallic complexes by coordination to the bpym ligand. Comparison between the optical and photophysical properties of the Ru²⁺ probe and those of the coordination compounds does not demonstrate a high selectivity due to very similar characteristics of the absorption and emission spectra. Whereas by complexation the lowest metal-to-ligand-charge-transfer (MLCT) shoulder of [Ru(bpy)₂(bpym)]²⁺ at 462 nm is more or less shifted to the red as a function of the cation, the second MLCT band at 415 nm, less sensitive to the complexation, gains in intensity and is slightly blue-shifted. The visible MLCT emission of [Ru(bpy)₂(bpym)]²⁺ at 706 nm is altered by complexation leading to near IR (800-900 nm) emission in most of the coordination compounds. Complexation to some transition metal cations (Fe, Co, Rh and Pd) generates low-lying metal-centered (MC) excited states that quench luminescence. In contrast to the conclusion of experimental findings by Kumar et al. (Chem. Commun. 2014, 50, 8488-8490), [Ru(bpy)₂(bpym)]²⁺ cannot be proposed as a fast and selective probe for monitoring Pd²⁺ in aqueous media. Indeed, it does not possess the optical and photophysical characteristics necessary to discriminate Pd²⁺ ions over a variety of other cations.

Luminescent binuclear Zinc(II) organic framework as bifunctional water-stable chemosensor for efficient detection of antibiotics and Cr(VI) anions in water

To achieve the ultrastable LMOFs with predominant luminescent sensing performances, the aromatic π-electron mixed ligands strategy was introduced, and the ternary LMOF of {[Zn₂(HDDB)(bib)_1.5]·3H₂O}_n (1), was fabricated based on 3,5-di(2',4'-dicarboxylphenyl)benozoic acid (H₅DDB) and the N-donor of meta-bis(imidazol-1-yl)benzene (bib) under mixed solvothermal condition. LMOF 1 features the first reported 3D 3,4,4-c {6².8³.10}{6².8}₂{6³.8².10}₂ framework with 21.2 % porosity as well as high thermal and chemical stability. Further luminescent sensing showed that LMOF 1 as a bifunctional chemosensor possessing predominant detectability for sensitive detect the hexavalent chromates and nitroimidazoles/nitrofurans antibiotics in water through strong luminescent quenching effects, with excellent reusability as well as trace detection limits. Moreover, luminescent quenching mechanisms were further investigated from electron transfer and energy transfer viewpoints.

Mitochondria-targeted acridine-based dual-channel fluorescence chemosensor for detection of Sn4+ and Cr2O72- ions in water and its application in discriminative detection of cancer cells

The goal of the present work was to fabricate a new low-cost, easy-to-prepare, dual-channel fluorescence chemosensor comprised of acridine-diphenylacetyl moieties (NDA) to enable remarkable Sn⁴⁺ detection in water and biological medium. The resulting NDA-Sn⁴⁺ complex was utilized for the distinguished identification of Cr₂O₇^2- ions from other anions and biomolecules. These investigations involve the absorption, fluorescence, and electrochemical methods for the detection of Sn⁴⁺ and Cr₂O₇^2- ions in pure water. The mechanism for NDA-mediated Sn⁴⁺ detection was experimentally determined by FT-IR, NMR titrations, mass (ESI) analyses, and DFT calculations. The obtained results indicate that the NDA chemosensor possessed excellent performance characteristics including good water solubility and compatibility, quick response time (less than 10 s), high sensitivity (Sn⁴⁺ = 0.268 μM and Cr₂O₇^2- = 0.160 μM), and selectivity against coexisting metals, anions, amino acids, and peptides. The chemosensor NDA induced negligible toxicity in live cells and was successfully utilized as a biomarker for the tracking of Sn⁴⁺ in human normal and cancer cells. More importantly, NDA demonstrates distinguished recognition of Sn⁴⁺ in human cancer cells rather than in normal live cells. Additionally, NDA was shown to act as a mitochondria-targeted probe in FaDu cells.

Trinuclear Organometallic Pt-Ir-Pt Complexes: Insights into Photophysical Properties, Amino Acid Binding and Protein Sensing

The rational synthesis of trinuclear emissive organometallic complexes with two equivalent platinum(II) centres appended to the ancillary substituted 2,2'-bipyridyl ligand of the cyclometalated iridium(III) centre is reported here. The alkynyl-platinum moiety and cyclometalated iridium(III) centres have been separated through a non-conjugated CH₂ -O-CH₂ linkage. The emission titration with amino acids reveals that the complexes sense free amino acids. The luminescence sensing of BSA is thus attributed to the amino acid sensing ability of the complexes and confirmed by emission anisotropy and Far-UV CD spectral study. The decrease in α-helix in the CD spectra signifies the changes in the secondary structure of protein in presence of the complexes.

Robust Lanthanoid Picolinate-Based Coordination Polymers for Luminescence and Sensing Applications

Picolinate-based segmented dianionic ligands L₁^2- (5-((4-carboxyphenyl)ethynyl)picolinate) and L₂^2- (5,5'-(ethyne-1,2-diyl)dipicolinate) have been used in the synthesis of the highly robust and luminescent europium(III) coordination polymers [(CH₃)₂NH₂][Eu(H₂O)₂(L₁)₂] (1) and [(CH₃)₂NH₂][Eu(L₂)₂]·H₂O·CH₃COOH (2). Both 1 and 2 exhibit high selectivity for detection of nitroaromatic compounds since they act as quenchers of the Eu³⁺ emission. Stern-Volmer plots, using nitrobenzene as a quencher, yielded values of K_SV = 150 M^-1 and 160 M^-1 for 1 and 2, respectively. Luminescence studies in the presence of different metal ions indicate a high selectivity for Fe³⁺ detection, with K_SV values of 471 M^-1 and 706 M^-1 for 1 and 2, respectively. Both 1 and 2 possess extremely robust extended structures, leading to emissive properties that are stable in a wide pH range.

Iodide/metal-organic frameworks (MOF) -mediated signal amplification strategy for the colorimetric detection of H2O2, Cr2O72- and H2S

The analytical methods based on colorimetric detection of various analytes have attracted intensive interest. However, most of them display relatively low sensitivity. Herein, a novel colorimetric strategy based on iodide/metal-organic frameworks (MOF)-mediated amplification was developed for low-cost, naked-eye detection and quantification of H₂O₂,Cr₂O₇^2-, and H₂S. Cu-MOFs could catalyze the oxidation of the colorless peroxidase substrate TMB to produce a blue product. The published researches mainly focused on the immobilization or integration of a macromolecule, such as natural enzymes, to enhance MOFs catalytic abilities. The use of small molecules to improve the catalytic performance of MOFs has rarely reported. Due to the negligible steric hindrance, iodide could easily be adsorbed in the framework pore of MOFs to conduct the synergic catalytic effect, and shows a high catalytic effect. As a result, the catalytic activity of Cu-MOFs was dramatically enhanced, and thus, the nanocatalyst could act as an amplifier system for target detection. The detection limits obtained by the amplified method are 25, 30, and 0.2 nM, respectively, which are about 200-fold lower than that of the unamplified colorimetric assays. The colorimetric strategy developed herein provides a novel system for the detection of low concentrations of analytes in complex biological samples.

A Multi-response Aluminum Metal-organic Frameworks for Fluorescence Sensing of Fe3+, Sr2+, SiO32-and Toluene

A new Aluminum metal-organic frameworks(Al-MOF) based on tricarboxylate ligands(L){L = 2,2',2'-([1,3,5]-triazine-2,4,6-triimino)tribenzoic acid)} has been designed and synthesized. It can be served as a platform of multi-responsive fluorescence sensor for Fe³⁺, Sr²⁺and SiO₃^2-in water, which is mainly due to the significant enhancement effect of these ions on the fluorescence intensity of Al-MOF. Especially, Fe³⁺ions are rarely able to induce MOFs fluorescence enhancement. The limit of detection for three kinds of ions is 6.62* 10^-6M, 5.37* 10^-6M, 6.85* 10^-10M respectively. Meanwhile, It can also be used as a multi-response fluorescence probe to detect toluene in DMF solution, limit of detection is 9.16* 10^-3M respectively. The structure of Al-MOF was characterized by FTIR,¹H NMR, SEM, TAG, PXRD and element analysis. The PXRD showed that the structure of Al-MOF remained the high water stability and pH stability. The application of water samples and vegetables showed that Al-MOF had high sensitive detection for Fe³⁺ions.

An exceptionally stable luminescent cadmium(ii) metal–organic framework as a dual-functional chemosensor for detecting Cr(vi) anions and nitro-containing antibiotics in aqueous media

Based on four kinds of SBUs, a robust Cd(ii) LMOF was fabricated that possessed highly sensitive detectability as a dual-response chemosensor for Cr(vi) anions and broad-spectrum nitro-containing antibiotics in aqueous media.

Six CoII coordination polymers exhibiting UV-light-driven photocatalysis for the degradation of organic dyes

Six different Co^II coordination polymers based on a new bis-pyridyl-bis-amide and polycarboxylates were obtained, showing photocatalytic activity for organic dyes.

Improving Ion Selectivity of 1,4,7-Triazacyclononane-Based Receptor by Zinc Coordination: "Turn-On" Chemosensor for Br- and Fe3+ Ions

Ion-responsive probes have gathered significant attention because of health and environmental factors, but there are few reports on the "turn-on" mechanism of Fe³⁺ and sensitive detection of Br^- by fluorescence measurement. Herein, a green luminescence material, N-5-acetyl-2-hydroxy-benzamide-1,4,7-triazacyclononane (btacn), was successfully synthesized for the first time and comprehensively characterized. As expected, btacn exhibits high sensitive, but nonspecific, extensive interaction with Cu²⁺, Co²⁺, Zn²⁺, Mn²⁺, and Fe³⁺ ions. Therefore, to improve the specificity of the probe, we tried to synthesize transition metal complexes of btacn, but all failed except Zn(btacn)Cl₂. In addition, the preformed complex, Zn(btacn)Cl₂, was used as a special "turn-on" chemosensor for detecting trace amounts of Br^- and Fe³⁺. The electrostatic interaction with Fe³⁺ and the hydrogen bond of PhO-H···Br^- leads to obvious changes in the electronic cloud of Zn(btacn)Cl₂, which are reflected in different spectral responses.

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.

Two cadmium(II) coordination polymers as multi-functional luminescent sensors for the detection of Cr(VI) anions, dichloronitroaniline pesticide, and nitrofuran antibiotic in aqueous media

Two ternary cadmium(II) coordination polymers, with the formulas being {[Cd(tptc)_0.5(bpz)(H₂O)]·0.5H₂O}_n (CP 1), and [Cd(tptc)_0.5(bpy)]_n (CP 2), were designed through mixed ligands strategy. Benefiting from the excellent chemical stability and luminescent property, two Cd(II) CPs possessing efficient multi-functional fluorescent responses toward Cr(VI) anions, 2,6-dichloro-4-nitroaniline pesticide, and nitrofuran antibiotic in aqueous media with high sensitivity, selectivity, and excellent recyclable behaviors with the detection limits (LODs) are 235 ppb for CrO₄^2- anion, 343 ppb for Cr₂O₇^2- anion, 112 ppb for DCN pesticide, 62 ppb for NFT antibiotic for CP 1, and 173 ppb for CrO₄^2- anion, 270 ppb for Cr₂O₇^2- anion, 638 ppb for DCN pesticide, 184 ppb for NFT antibiotic for CP 2, respectively. Besides, the mechanisms of luminescence quenching were revealed from the viewpoint of internal filter effect (IFE) and photoinduced electron transfer (PET).

A Fluorescent g-C3N4 Nanosensor for Detection of Dichromate Ions

Background:

Dichromate (Cr2O7 2-) ion is one of the carcinogenic and toxic spices in environment which can easily contaminate the environment due to its high solubility in water. Therefore, a lot of attention has been focused on the detection of Cr2O7 2- with high sensitivity and selectivity.

Methods:

In present work, nitrogen-rich precursor was used for synthesizing graphitic carbon nitride (g-C3N4) nanostructures through hydrothermal oxidation of g-C3N4 nanosheets. The prepared nanostructures show two distinct fluorescence emissions centered at 368 and 450 nm which are highly sensitive toward Cr2O7 2- ions.

Results:

The as-prepared g-C3N4 was characterized by several techniques such as Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and fluorescence emission spectra. The XRD pattern of prepared nanostructures illustrated two diffraction patterns (at 13.4° and 27.6°) indicating tri-s-tri-azine-based structures. The g-C3N4 exhibited good selectivity and sensitivity toward Cr2O7 2- among other anions. According to titration test, the detection limit and stern-volmer constant (Ksv) were calculated as 40 nM and 0.13×106 M-1, respectively. The investigation of quenching mechanism shows that Cr2O7 2- may form hydrogen bonding with surface groups of g-C3N4 (such as NH2, OH and COOH) resulted in more fluorescence quenching in comparison with the pure inner filter effect.

Conclusion:

The g-C3N4 nanostructures were successfully synthesized through the hydrothermal oxidation. The as-prepared g-C3N4 can be used as a highly sensitive fluorescent probe for the selective determination of Cr2O7 2 ion among other anions. The quenching mechanism was experimentally studied. According to reliable responses in real sample tests, it can be proposed that g-C3N4 nanostructure is a suitable sensitive nanosensor for detection of Cr2O7 2 ions in aqueous media.

An oxacalix[4]arene derived dual sensing fluorescent probe for the detection of As(v) and Cr(vi) oxyanions in aqueous media

An oxacalix[4]arene-Ce(iii) complex viz. L-Ce(III) has been introduced for the selective detection of As(v) and Cr(vi) oxyanions in aqueous medium. The binding mode of L-Ce(III) + AsO₄^3-/CrO₄^2- was completely investigated with fluorometric titration, time resolve fluorescent decay and FTIR analyses. Photoinduced electron transfer (PET) and chelation-enhanced fluorescence (CHEF) play an important role in the sensing of these oxyanions. The characteristic fluorescence of the L-Ce(III) complex has been quenched by AsO₄^3- and CrO₄^2- through cascading the ligating sites. Cyclic voltammetry (CV) experiments with various scan rates suggest that the electrochemical processes on the electrodes were controlled by diffusion. Both the analytes exhibit a lower limit of detection (LOD) below their standard EPA permissible limits. Moreover, the probe successfully detects the oxyanions in environmental real samples with excellent recovery ranging from 97 to 101%.

Coordination Polymers Based on Highly Emissive Ligands: Synthesis and Functional Properties

Coordination polymers are constructed from metal ions and bridging ligands, linking them into solid-state structures extending in one (1D), two (2D) or three dimensions (3D). Two- and three-dimensional coordination polymers with potential voids are often referred to as metal-organic frameworks (MOFs) or porous coordination polymers. Luminescence is an important property of coordination polymers, often playing a key role in their applications. Photophysical properties of the coordination polymers can be associated with intraligand, metal-centered, guest-centered, metal-to-ligand and ligand-to-metal electron transitions. In recent years, a rapid growth of publications devoted to luminescent or fluorescent coordination polymers can be observed. In this review the use of fluorescent ligands, namely, 4,4'-stilbenedicarboxylic acid, 1,3,4-oxadiazole, thiazole, 2,1,3-benzothiadiazole, terpyridine and carbazole derivatives, naphthalene diimides, 4,4',4''-nitrilotribenzoic acid, ruthenium(II) and iridium(III) complexes, boron-dipyrromethene (BODIPY) derivatives, porphyrins, for the construction of coordination polymers are surveyed. Applications of such coordination polymers based on their photophysical properties will be discussed. The review covers the literature published before April 2020.

Water Stable Zn(II) Metal-Organic Framework as a Selective and Sensitive Luminescent Probe for Fe(III) and Chromate Ions

Sensing and monitoring toxic contaminants like Fe³⁺, CrO₄^2-, and Cr₂O₇^2- ions in water is very important due to their harmful effects on biological and environmental systems. Enhanced hydrolytic stability, sensitivity, and selectivity, in addition to their excellent luminescence properties, are important attributes of metal-organic framework (MOF)-based sensors for sensing applications. In this work, the water stable Zn-MOF [Zn₂(tpeb)(bpdc)₂] (where tpeb = 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene and bpdc = biphenyl-4,4'-dicarboxylic acid) was synthesized and characterized. The framework retains its crystallinity and structural integrity in harsh acidic and basic conditions (pH 4-11). Most interestingly, the Zn-MOF demonstrates a strong blue luminescence in water that can be quenched selectively only by contaminants like Fe³⁺, CrO₄^2-, and Cr₂O₇^2- ions. Higher K_sv values and low detection limits in selective luminescence quenching confirm the superior sensing performance, which is comparable to those of contemporary materials. Furthermore, in all cases, quenching efficiency remains unaltered in the presence of interfering ions, even after the compound is used in multiple cycles, which makes this MOF an attractive, reliable, and recyclable luminescent sensor material. The luminescence quenching mechanism is based on the competitive absorption and weak interactions. It is worth noting that most of the reported MOF-based sensors used for the separate sensing of Fe(III) and chromate ions are used in organic media due to their poor hydrolytic stabilities. Reports on the dual sensing of Fe(III) and chromate ions, which are also in aqueous media, are rare. Based on these results, Zn-MOF can be considered as a suitable candidate for advanced practical applications for the efficient sensing of Fe(III) and chromate ions in water.

Uranyl Organic Framework as a Highly Selective and Sensitive Turn-on and Turn-off Luminescent Sensor for Dual Functional Detection Arginine and MnO4. Inorg Chem 2020;59:5004-5017. [PMID: 32207299 DOI: 10.1021/acs.inorgchem.0c00236]

Five new uranyl coordination polymers were prepared by the hydrothermal method based on 5-nitroisophthalic acid (H₂nip) as (UO₂)(nip)(2,2'-bpy) (1), (H₂4,4'-bpy)·[(UO₂)₃(nip)₄]·(4,4'-bpy) (2), (H₂bpe)·[(UO₂)_0.5(nip)] (3), (H₂ bpp)·[(UO₂)₂-(nip)₃]·H₂O (4), and (H₂tmp)·[(UO₂)(nip)₂](5) [2,2'-bpy = 2,2'-bipyridine, 4,4'-bpy = 4,4'-bipyridine, bpe = 4,4'-vinylenedipyridine, bpp = 4,4' -trimethylenedipyridine, tmp = tetramethylpyrazine]. All of these synthesized complexes have been characterized by single crystal and powder X-ray diffraction, IR spectra, thermogravimetric analysis, elemental analysis, and luminescent properties. In particular, it is found that compounds 1 and 4 can be used as a luminescent sensor to efficiently detect arginine in aqueous solution by means of "turn-on"; the detection limits were 1.06 × 10^-6 and 6.42 × 10^-6 mol/L, respectively. Moreover, 4 can also be used as a bifunctional sensor for selective sensing of MnO₄^- anion by "turn-off". The detection limit of MnO₄^- in water was 1.79 × 10^-6 mol/L; the K_sv was 1.88 × 10⁴. The sensing effect of arginine in simulated grape juice samples and MnO₄^- in simulated river water samples was also investigated by this sensing system with high recovery. In addition, the possible mechanism of sensing arginine and MnO₄^- in the aqueous solution was discussed.

Rational design and synthesis of a stable pillar-layer NaI-organic framework as a multi-responsive luminescent sensor in aqueous solutions

A stable pillar-layer Na^I-organic framework, [Na₂(DCPB)∙(H₂O)₂]_n (namely 1), was rationally designed and synthesized by the assemble process of Na^I and 1,3-di(4'-carboxyl-phenyl)benzene (H₂DCPB). Benefiting from the luminescent property and high stability in water, the as-synthesized 1 is a potential multi-responsive luminescent sensor material toward Cr₂O₇^2-, Fe³⁺, and nitrofurazone (NFZ) in water. Ground 1 not only has the excellent detectability and selectivity but also possesses outstanding stability and circularity. The calculated K_sv values of 1 are 8.8×10³ for Fe³⁺, 9.9×10³ for Cr₂O₇^2-, and 2.7×10⁴ M^-1 for NFZ in aqueous solutions, respectively. Furthermore, 1 is able to accurately detect NFZ in real bovine serum samples through luminescence detection technology.

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.