A dysprosium(III)-based triple helical-like complex as a turn-on/off fluorescence sensor for Al(III) and 4,5-dimethyl-2-nitroaniline

A novel triple helical-like complex [Dy2K2L3(NO3)2]·3DMF (1) based on a designed Schiff base N'1,N'3-bis((E)-3-ethoxy-2-hydroxybenzylidene)-malonohydrazide (H4L) was synthesized with good chemical and thermal stabilities. Single-crystal X-ray structural analysis showed that 1 presents a tetranuclear triple helical-like structure via the coordination mode of Dy : K : L with 2 : 2 : 3 stoichiometry. Fluorescence measurements showed that 1@EtOH has excellent fluorescence turn-on/off response ability for aluminium ions and 4,5-dimethyl-2-nitroaniline (DMNA) with outstanding selectivity, sensitivity, and anti-interference ability. The calculated limit of detection (LOD) values for 1@EtOH to Al3+ and DMNA were found to be 0.53 and 3.33 μM, respectively. Density functional theory (DFT) calculation showed that the fluorescence response mechanism can be explained by the photoinduced electron transfer (PET) mechanism; meanwhile, the inner filter effect (IFE) of DMNA can also affect the emission of 1@EtOH.

A portable test strip fabricated of luminescent lanthanide-functionalized metal-organic frameworks for rapid and visual detection of tetracycline antibiotics

Tetracycline antibiotics (TCs) are commonly used antibiotics in the treatment of infections, but their overuse has a negative impact on human health and ecosystems. Thus, the development of a facile and on-site visualization method for TC detection is necessary. Here, we propose the potential of using lanthanide-functionalized metal-organic framework (MOF) composites (Ag+/Tb3+@UiO-66-(COOH)2, ATUC) as a probe for the rapid detection of tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC), and doxycycline (DOX) residues, in which UiO-66-(COOH)2 (UC) could be utilized to provide an interaction microenvironment, Tb3+ as recognition units and Ag+ as a fluorescence enhancer. Upon exposure to TCs, significant luminescence quenching of ATUC excited at 255 nm was observed due to the inner filter effect (IFE) and photo-induced electron transfer (PET), and the established strategy has a detection limit (LOD) of 11.0, 20.1, 9.1, and 22.5 nM for TC, CTC, OTC, and DOX, respectively. More importantly, given its portability and conspicuous luminescence color gradation variation, a portable test strip based on ATUC was manufactured and the results could be distinguished immediately by the naked eye and smartphone analysis, allowing for on-site rapid quantitative assay of TCs, not only in the laboratory but also in a point-of-care setting.

Zinc(II)-Based Ring-and-Rod Coordination Layer as an Excitation-Wavelength-dependent Dual-Emissive Chemosensor for Discriminating Fe3+, Cr3+, and Al3+ in Water

The reactions of Zn(NO3)2, 3,6-bis(pyridin-3-yl)-9H-carbazole (bpycz), and 2,5-dihydroxyterephthalic acid (H4dhbdc) or 2-bromoterephthalic acid (Br-1,4-H2bdc) under hydro(solvo)thermal conditions yielded corresponding coordination polymers (CPs) {[Zn(H2dhbdc)(bpycz)]•0.5H2O}n (1) and [Zn(Br-1,4-bdc)(bpycz)]•2DMAc•H2O (2), respectively, with high thermal stability approaching 350 °C. CP 1 adopts a ring-and-rod layer structure, which is topologically described as a 4-connected net with the point symbol of 2•65. Two layers are interpenetrated in parallel interlocking mode to form a double 2D → 2D polyrotaxane entanglement with extra-framework void space of 19.6%. CP 2 has a non-interpenetrating ring-and-rod layer structure of 4-connected 2•65 net topology, with extra-framework void space of 16.6%. Thermally activated 1 and 2 revealed CO2 uptakes of 101.1 and 98.6 cm3 g-1, respectively, at P/P0 = 1 and 195 K. X-ray powder diffraction (XRPD) patterns confirmed that 1 and 2 both possessed high chemical stability in H2O, CH3OH, acetone, and DMF, and framework stability during gas adsorption-desorption. The H2O suspension of 1 displayed excitation-dependent dual-emissive properties, appearing at 432 nm upon excitation at 300 nm and at 528 nm upon excitation at 365 nm. Of note, 1 was capable of detection of Fe3+, Cr3+, and Al3+ ions in H2O, showing good anti-interference ability, excellent selectivity, and high sensitivity. More interesting, the dual-emissive properties make 1 to be an excellent luminescence chemosensor to screen Fe3+, Cr3+, and Al3+ from a pool of metal ions in H2O upon excitation at 300 nm via luminescence quenching effect and then discriminate Fe3+, Cr3+, and Al3+ upon excitation at 365 nm via luminescence quenching, unaltered, and enhancement responses, respectively. On the other hand, the H2O suspension of 2 demonstrated an excitation-independent emission appearing at around 430 nm, which could be utilized to sensitively detect Fe3+ and Cr3+ ions with good anti-interference ability and excellent selectivity via luminescence quenching effect. Further, 1 and 2 were recyclability and possessed cycling stability. The plausible sensing mechanisms for 1 and 2 toward Fe3+, Cr3+, and Al3+ were also explored in detail.

Aggregation-induced emission enhancement (AIEE) of tetrarhenium(I) metallacycles and their application as luminescent sensors for nitroaromatics and antibiotics

The self-assembly of tetrarhenium metallacycles [{Re(CO)₃}₂(μ-dhaq)(μ-N-N)]₂ (3a, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene; 3b, N-N = 1,3-bis(1-octylbenzimidazol-2-yl)benzene), (H₂-dhaq = 1,4-dihydroxy-9,10-anthraquinone) and [{Re(CO)₃}₂(μ-thaq)(μ-N-N)]₂ (4, N-N = 1,3-bis(1-butylbenzimidazol-2-yl)benzene), (H₂-thaq = 1,2,4-trihydroxy-9,10-anthraquinone) under solvothermal conditions is described. The metallacycles 3a,b and 4 underwent aggregation-induced emission enhancement (AIEE) in THF upon the incremental addition of water. TEM images revealed that metallacycle 3a in a 60% aqueous THF solution formed rectangular aggregates with a wide size distribution, while a 90% aqueous THF solution resulted in the formation of a mixture of nanorods and amorphous aggregates due to rapid and abrupt aggregation. UV-vis and emission spectral profiles supported the formation of nanoaggregates of metallacycles 3a,b and 4 upon the gradual addition of water to a THF solution containing metallacycles. Further studies indicated that these nanoaggregates were excellent probes for the sensitive and selective detection of nitro group containing picric acid (PA) derivatives as well as antibiotics.

Conglomerate, Racemate, and Achiral Crystals of Polymetallic Europium(III) Compounds of Bis- or Tris-β-diketonate Ligands and Circularly Polarized Luminescence Study

This work reports (a) conglomerate and racemic crystal structures of [(Δ,Δ,Δ,Δ,Δ,Δ)- or/and (Λ,Λ,Λ,Λ,Λ,Λ)-Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n coordination polymers, (b) racemic crystal structures of (Δ,Δ,Δ,Δ)-/(Λ,Λ,Λ,Λ)-Eu^III ₄(TTP)₄(bipy)₄(MEK)₂(OH₂)₂ tetrahedral clusters, and (c) the achiral crystal structure of the [Eu^III ₂(BTP)₄(OH₂)₂Na₂] _n coordination polymer (where BTP = dianionic bis-β-diketonate, TTP = trianionic tris-β-diketonate, and bipy = 2,2'-bipyridine). The screw coordination arrangement of the TTP ligand has led to the formation of homoconfigurational racemic Eu^III products. The conglomerate crystallization of [Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n appears to be caused by the presence of the sodium, Na⁺ counterions, and interactions between oxygen atoms and the trifluoromethyl unit of the TTP ligand and Na⁺ ions. All the Eu^III compounds exhibit characteristic red luminescence (⁵D₀ → ⁷F_J, J = 0-4) in solution or in the solid crystalline state. Circularly polarized luminescence (CPL) was observed in the chiral Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n species, displaying a |g _lum| value in the range of 0.15 to 0.68 at the ⁵D₀ → ⁷F₁ emission band. Subtle changes of the [Eu^III ₆(TTP)₈(OH₂)₆Na₄] _n structure which may be due to selection of twinned crystals or crystals that do not correspond to a perfect spontaneous resolution, are considered to be responsible for the variation in the observed CPL values.

Highly Efficient I2 Sorption, CO2 Capture, and Catalytic Conversion by Introducing Nitrogen Donor Sites in a Microporous Co(II)-Based Metal-Organic Framework

Recently, the development of porous absorbents for efficient CO₂ and I₂ capture has attracted considerable attention because of severe global climate change and environmental issues with the nuclear energy. Hence, a unique porous metal-organic framework (MOF), {[Co(L)]·DMF·2H₂O}_n (1, DMF = N,N-dimethylformamide) with uncoordinated N atoms was rationally constructed via using a heterofunctional 4,6-bis(4'-carboxyphenyl)pyrimidine (H₂L) linker. Interestingly, 1 exhibits exceptional properties for I₂ sorption, CO₂ capture, and catalytic conversion. Particularly, I₂ can be efficiently removed in both vapor and solution forms, and the adsorption amount can reach 676.25 and 345.28 mg g^-1, respectively. Furthermore, complex 1 displays high adsorption capacity for CO₂ (53.78 cm³ g^-1, 273 K). Consequently, 1 is expected to be a promising and practical material for environmental purification due to its excellent adsorption properties.

Regulatable Detection of Antibiotics Based on a Near-IR-Luminescent Tubelike Zn(II)-Yb(III) Nanocluster

A tubelike Zn(II)-Yb(III) cluster, [Zn6Yb5L5(HL)(NO3)4(DMF)6(EtOH)4(H2O)4] (1; DMF = N,N-dimethylformamide and EtOH = ethanol; molecular size 1.5 × 1.8 × 2.9 nm), was synthesized from a new long-chain Schiff base ligand. 1 exhibits a regulatable near-IR-luminescent response to nitrofuran antibiotics (NFAs) and fluoroquinolones with high sensitivity, which is not influenced by other antibiotics. The quenching constants of NFAs and fluoroquinolones range from 0.55 × 104 to 8.8 × 104 M-1, and the detection limits of 1 to them are from 4.2 × 10-4 to 2.6 × 10-5 M. It also shows a luminescent response to real antibiotic drugs containing NFAs and fluoroquinolones.

A Water-Stable 2-Fold Interpenetrating cds Net as a Bifunctional Fluorescence-Responsive Sensor for Selective Detection of Cr(III) and Cr(VI) Ions

Reactions of ZnSO₄∙7H₂O, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H₂bdc) afforded a luminescent coordination polymer, [Zn(Br-1,3-bdc)(NI-mbpy-34)]_n (1), under hydro(solvo)thermal conditions. Single-crystal X-ray structure analysis revealed that 1 features a three-dimensional (3-D) 2-fold interpenetrating cds (or CdSO₄) net topology with the point symbol of (6⁵·8), where the Zn(II) centers are considered as 4-connected square-planar nodes. X-ray powder diffraction (XRPD) patterns and thermogravimetric (TG) analysis confirmed that 1 shows high chemical and thermal stabilities. Notably, 1 displayed solvent dependent photoluminescence properties; the fluorescence intensity and emission maximum of 1 in different solvent suspensions varied when a solvent was changed. Furthermore, the H₂O suspension of 1 exhibited blue fluorescence emission and thus can be treated as a selective and sensitive fluorescent probe for turn-on detection of Cr³⁺ cations through absorbance caused enhancement (ACE) mechanism and turn-off detection of Cr₂O₇²⁻/CrO₄²⁻ anions through collaboration of the absorption competition and energy transfer process, with limit of detection (LOD) as low as μM scale.

A high-nuclearity Cd(ii)–Nd(iii) nanocage for the rapid ratiometric fluorescent detection of quercetin

A 32-metal Cd(ii)–Nd(iii) nanocage was constructed, and it shows rapid and stable ratiometric fluorescent response to quercetin.

Construction of a Cd8Tb4 nanoring for luminescence response to 2,6-dipicolinic acid as an anthrax biomarker

One 12-metal Cd(ii)–Tb(iii) nanoring (1.2 × 2.8 × 2.8 nm) was constructed from a flexible Schiff base ligand, and it shows luminescent response to 2,6-dipicolinic acid with high sensitivity and selectivity.

A Eu(iii) metal–organic framework based on anthracenyl and alkynyl conjugation as a fluorescence probe for the selective monitoring of Fe3+ and TNP

In this work, a luminescent metal–organic framework (Eu-MOF {[Eu₆L₆(μ₃-OH)₈(H₂O)₃]₈·H₂O}_n) was constructed by a solvothermal method with a linear organic ligand L (10-[(2-amino-4-carboxyl-phenyl)ethynyl]anthracene-9-carboxylic acid) based on anthracene and alkyne groups and using Eu³⁺ as the metal center. The MOF exhibits a stable UiO-66 crystal structure, and a six-core cluster twelve-linked secondary structural unit was successfully synthesized using 2-fluorobenzoic acid as a modulator, forming a classical fcu topology. Moreover, it exhibits good chemical stability. Interestingly, Eu-MOF exhibited high selectivity and sensitive fluorescence burst properties towards Fe³⁺ ions and 2,4,6-trinitrophenol (TNP) in DMF solution. For Fe³⁺, the K_SV value is 5.06 × 10⁵ M⁻¹ and the LOD value is 5.1 × 10⁻⁷ M. For TNP, the K_SV value is 1.92 × 10⁴ M⁻¹ and the LOD value is 1.93 × 10⁻⁶ M. In addition, Eu-MOF showed good anti-interference ability and fast response. This work provides an excellent fluorescent sensor for the detection of Fe³⁺ and 2,4,6-trinitrophenol (TNP) residues in contaminants.

In this work, Eu-MOF has been synthesized and has excellent luminescence recognition ability for Fe³⁺ and TNP with good selectivity and high sensitivity via luminescence quenching.

Nanomolar determination of nitrofurans in water via excited-state inter-ligand proton transfer

Qualification and quantification of trace organic contaminants necessitates development of highly efficient sensing system, where excited-state inter-ligand proton transfer (ESILPT) provides a feasible pathway to construct efficient chemo-sensors. Herein, a strategically synthesized lanthanide complex, Eu(DBM)₃(MeOH)₃ (briefly as Eu-DBM-MeOH; DBM = dibenzoylmethane), features two-step ESILPT processes, along with modification on molecular structure and energy band. As a result, Eu-DBM-MeOH exhibits excellent photophysical properties with characteristic luminescence of Eu³⁺ ion. Benefiting from these merits, the Eu-DBM-MeOH complex acts as ultra-sensitive chemo-sensor toward nanomolar-level nitrofuran antibiotics (nitrofurazone and nitrofurantoin) in water, by disrupting ESILPT processes. Combining the advantages on photophysical property and luminescent sensitivity, ESILPT-active compounds are expected to widen and deepen the research on complex-based luminophores, being potentially useful in trace detection and biological imaging.

One high-nuclearity Eu18 nanoring with rapid ratiometric fluorescence response to dipicolinic acid (an anthrax biomarker)

One 18-metal Eu(iii) nanoring (size: 1.0 × 2.7 × 2.7 nm) was constructed as a rapid ratiometric fluorescent probe for the detection of dipicolinic acid with high sensitivity and selectivity, by using two types of polydentate organic ligands.

Construction of a high-nuclearity Nd(III) nanoring for the NIR luminescent detection of antibiotics

One NIR luminescent 14-metal Nd(iii) nanoring (1, molecular size: 1.0 × 2.2 × 2.6 nm) was obtained from a rigid tridentate ligand, which can absorb and transfer light energy to the Nd(iii) ions. 1 shows interesting luminescence sensing activity to antibiotics, in particular to NFAs with high sensitivity due to the inner filter effect. The quenching constants and the limits of detection of 1 to NFAs are 1.05 × 104 M-1-2.33 × 104 M-1 and 3.05 μM-6.75 μM, respectively. The high fluorescence sensitivities of 1 to NFAs are not changed by the existence of other antibiotics. It also exhibits high sensitivity in the luminescent detection of NFAs contained in real antibiotic drugs.

Construction of Zn(II)/Cd(II)-Yb(III) Schiff Base Complexes for the NIR Luminescent Sensing of Fluoroquinolone Antibiotics

Two NIR luminescent Zn(II)/Cd(II)-Yb(III) complexes were obtained by the use of a Schiff base ligand with a binaphthyl backbone. Cd(II)-Yb(III) complex 2 has a triangular structure and exhibits interesting luminescent sensing activity to antibiotics, in particular to ciprofloxacin (CPFX) and norfloxacin (NFX) due to the inner filter effect. The limits of the detection of 2 to CPFX and NFX are 0.18 and 0.36 μM, respectively, and the fluorescence sensitivity is not changed with the existence of other antibiotics tested in this study.

Three Silver(I) Coordination Polymers Based on Pyridyl Ligands and Auxiliary Carboxylic Ligands: Luminescence and Efficient Sensing Properties

Easily producible sensors for harmful industrial waste compounds are of significant interest for both human health and the environment. Three novel coordination polymers, [Ag(μ-aca)(μ₄-bztpy)_1/2] (1), [Ag(μ-bza)(μ-bpa)] (2), and [Ag₂(μ-aca)₂(μ-bpa)₂]·EtOH·2H₂O (3), were assembled in this study by reactions using Ag⁺ as a node with the pyridyl ligand 1,2,4,5-tetrakis(4-pyridyl)benzene (bztpy) or 9,10-bis(4-pyridyl)anthracene (bpa) and an auxiliary chelating carboxylic ligand. Single-crystal X-ray structural analyses revealed that compound 1 has a 3D framework consisting of 1D [Ag(aca)]_∞ chains and bztpy linkers, while 2 and 3 have 2D layered structures consisting of binuclear Ag-carboxylate units and bpa linkers, respectively. Topological studies revealed that 1 has a bbf topology, while 2 and 3 are 2D [4,4] rhombic grids. The compounds were further characterized by powder X-ray diffraction, IR, elemental analysis, thermogravimetric analysis, and a luminescence study. The solids of 1-3 exhibited intense photoluminescent emission with λ_em^max at ca. 493, 472, and 500 nm, respectively. Remarkably, due to their excellent framework stability, 1 and 2 can act as multiresponsive luminescent sensors for nitrobenzene, Fe³⁺, and Cr₂O₇^2- with a high selectivity and sensitivity ascribed to their quenching effect.

High-efficient liquid exfoliation of 2D metal-organic framework using deep-eutectic solvents

The exfoliation of bulk two-dimensional metal-organic framework (MOF) into few-layered nanosheets has attracted much attention recently. In this work, an environmental-friendly route has been developed for layered-MOF (MAMS-1) delamination using deep eutectic solvent (DES), which is more sustainable and efficient alternative than conventional organic solvents for MOF nanosheet preparation. Under sonication condition, DES as solvents, the highest exfoliation rate of MAMS-1 is up to 70% with two host layers via poly(vinylpyrrolidone) (PVP) surfactant-assisted method. The presence of tert-butyl exteriors and the atomically thickness endow the MOF nanosheets stable suspension for at least one month. Due to the 2D structure and excellent stability, MAMS-1 nanosheet (MAMS-1-NS) was chosen as a good candidate to encapsulate Eu3+ cations. The obtained Eu3+@MAMS-1-NS acts as a multi-responsive luminescent sensor through fluorescence quenching, and can specifically recognize Fe3+ (LOD = 0.40 μM, KSV = 1.05 × 105 M-l), Hg2+ (LOD = 0.038 μM, KSV = 5.78 × 106 M-l), Cr2O72- (LOD = 0.33 μM, KSV = 1.55 × 105 M-l) and MnO4- (LOD = 0.088 μM, KSV = 4.49 × 105 M-l). Compared with bulk Eu3+@MAMS-1, the sensitivity of Eu3+@MAMS-1-NS is greatly improved owing to its ultrathin nanosheet morphology and highly accessible active sites on the surface.

Series of highly stable Cd(ii)-based MOFs as sensitive and selective sensors for detection of nitrofuran antibiotic

The oxygen atom of the MOF ether-bridging group acts as a Lewis base site, improving the connection and allowing the detection of 10 antibiotics through the fluorescence quenching effect.

Multifunctional photoelectric sensors and catalysts for CO2RR and Cr(vi) solution based on a series of POM-based materials

A series of POM-based materials can be used as photoelectric sensors and have high catalytic activities for CO₂RR and the reduction of Cr(vi) solution, which are significant for environmental protection and energy shortage.

Highly efficient fluorescent chemosensor for nitro antibiotic detection based on luminescent coordination polymers with 2,6-di(4-carboxyphenyl)pyrazine

A series of isostructural porous supramolecular frameworks, {[M(DCPP)(H₂O)]·(DMF)}_n, are synthesized. The as-obtained fluorescent Zn-MOF has good recognition ability towards nitro-antibiotics with low detection limits and a wide linear range.

Luminescence sensing and photocatalytic activities of four Zn(ii)/Co(ii) coordination polymers based on a pyridinephenyl bifunctional ligand

Four Zn(ii)/Co(ii) CPs act as bifunctional materials in the detection of Fe(iii) cation, Cr(vi) anion, and nitrofuran antibiotics and removal of methylene blue in aqueous media.

The construction of a multifunctional luminescent Eu-MOF for the sensing of Fe3+, Cr2O72− and amines in aqueous solution

A 3D Eu(iii)-based metal–organic framework has been synthesized as a multiresponsive chemosensor for highly sensitive and selective detection of Fe3+, Cr2O72− and amines in water.

NIR luminescent detection of quercetin based on an octanuclear Zn(ii)–Nd(iii) salen nanocluster

A NIR luminescent octanuclear Zn(ii)–Nd(iii) nanocluster 1 was constructed by the use of a salen-type Schiff base ligand. 1 exhibits a lanthanide luminescent response to Que with high sensitivity. The quenching constant of Que to the lanthanide emission is 2.6 × 10⁴ M⁻¹, and the detection limit of 1 to Que is 2.5 μM. The response behavior of 1 to Que is not affected by the existence of some potential interferents such as biomolecules.

An octanuclear Zn(ii)–Nd(iii) nanocluster was constructed by the use of a salen-type Schiff base ligand, and it shows an interesting NIR lanthanide luminescent response to quercetin with high sensitivity and selectivity.

Construction of a 18-Metal Neodymium(III) Nanoring with NIR Luminescent Sensing to Antibiotics

One 18-metal Nd(III) nanoring, [Nd₁₈(L¹)₈(HL²)₂(OAc)₂₀(MeOH)₈(EtOH)₆(H₂O)₄]·2(MeOH)·6(H₂O) (1), was constructed by the use of a hexadentate Schiff base ligand. For 1, the near-infrared (NIR) luminescence of Nd(III) was detected under the excitation of absorption band at 371 nm. The study of luminescent sensing properties exhibits that, even with the existence of other antibiotics, this Nd(III) nanoring displays high sensitivity and selectivity to nitrofuran antibiotics (NFAs). The luminescence quenching constants and limits of detection of 1 to NFAs are found to be 1.4 × 10⁴ to 3.5 × 10⁴ M^-1 and 0.9-2.2 μM, respectively.

One High-Nuclearity Cd(II)-Yb(III) Nanoring with Near-IR Luminescent Sensing to Antibiotics

One 12-metal Cd(II)-Yb(III) nanoring, [Cd₈Yb₄L₈(OAc)₈]·4OH (1), with a size of 1.2 × 2.8 × 2.8 nm was obtained from a designed flexible salen-type ligand that has eight coordination sites (O and N atoms). The near-IR emission of Yb(III) at 983 nm was detected upon the excitation of ligand-central absorption at 386 nm. This Cd(II)-Yb(III) nanoring exhibits high sensitivity to nitrofuran antibiotics (NFAs) even in the presence of other antibiotics. The quenching constants and limits of detection of NFAs are 2.5 × 10⁴-4.5 × 10⁴ M^-1 and 1.5-2.8 μM, respectively.