Multiresponsive luminescent metal-organic framework for cooking oil adulteration detection and gallium(III) sensing

A new 3D metal-organic framework {[Cd16(tr2btd)10(dcdps)16(H2O)3(EtOH)]∙15DMF}n (MOF 1, tr2btd = 4,7-di(1,2,4-triazol-1-yl)benzo-2,1,3-thiadiazole, H2dcdps = 4,4'-sulfonyldibenzoic acid) was obtained and its luminescent properties were studied. MOF 1 exhibited bright blue-green luminescence with a high quantum yield of 74 % and luminescence quenching response to a toxic natural polyphenol gossypol and luminescence enhancement response to some trivalent metal cations (Fe3+, Cr3+, Al3+ and Ga3+). The limit of gossypol detection was 0.20 µM and the determination was not interfered by the components of the cottonseed oil. The limit of detection of gallium(III) was 1.1 µM. It was demonstrated that MOF 1 may be used for distinguishing between the genuine sunflower oil and oil adulterated by crude cottonseed oil through qualitative luminescent and quantitative visual gossypol determination.

Ln-MOF-Based Hydrogel Films with Tunable Luminescence and Afterglow Behavior for Visual Detection of Ofloxacin and Anti-Counterfeiting Applications

Highly selective and sensitive quantitative detection of ofloxacin (OFX) at ultralow concentrations in aqueous media and development of new afterglow materials remains a challenge. Herein, a new 2D water-stable lanthanide metal-organic framework (NIIC-2-Tb) is proposed, which exhibits high selectivity towards OFX through the luminescence quenching with the lowest detection limit (1.1 × 10-9 M) reported to date and a fast response within 6 s. In addition, the luminescent detection of OFX by NIIC-2-Tb is not affected by typical components of blood plasma and urine. The excellent sensing effect of NIIC-2-Tb is further utilized to prepare a composite functional sensing carrageenan hydrogel material for the rapid detection of OFX in meat in real time and the first discovery of impressive afterglow in MOF-based hydrogels. This study not only presents novel Ln-MOF materials and Ln-MOF-based hydrogel films for luminescent sensing of OFX, but also demonstrates color-tunable luminescent films with afterglow, which expands the application of composite luminescent materials for detection and anti-counterfeiting.

Lanthanide complexes with a new luminescent iminophosphonamide ligand bearing phenylbenzothiazole substituents

A new iminophosphonamine Ph2P(HNPbt)(NPbt) (1, HL) bearing chromophore 2-(phen-2'-yl)-1,3-benzothiazole (Pbt) substituents was synthesized and introduced into lanthanide complexes. It was found that salt metathesis reactions between KL (2) generated in situ and LnCl3 lead to the formation of tris-iminophosphonamide complexes [LnL2]L (Ln = Y (3), Sm (4), Gd (5), Dy (6)), regardless of the 2/LnCl3 ratio. Compounds 3-6 consist of a cationic fragment [LnL2]+, where the lanthanide atom is surrounded by two rigidly κ4-coordinated ligands, and an L- anion residing in the outer coordination sphere. Iminophosphonamine 1 shows a rare excitation wavelength-dependent two-band luminescence in the solid state. For compounds containing the deprotonated form, namely potassium salt KL and complexes of Gd and Dy, a single-band luminescence with the color changing from turquoise to orange was observed. The Sm complex reveals a set of a few narrow well-resolved bands corresponding to the f-f transitions against the background of the outer-sphere ligand's emission.

Complexes on the Base of a Proton Transfer Capable Pyrimidine Derivative: How Protonation and Deprotonation Switch Emission Mechanisms

A rare example of pyrimidine-based ESIPT-capable compounds, 2-(2-hydroxyphenyl)-4-(1H-pyrazol-1-yl)-6-methylpyrimidine (HLH), was synthesized (ESIPT─excited state intramolecular proton transfer). Its reactions with zinc(II) salts under basic or acidic conditions afforded a dinuclear [Zn2LH2Cl2] complex and an ionic (H2LH)4[ZnCl4]2·3H2O solid. Another ionic solid, (H2LH)Br, was obtained from the solution of HLH acidified with HBr. In both ionic solids, the H+ ion protonates the same pyrimidinic N atom that accepts the O-H···N intramolecular hydrogen bond in the structure of free HLH, which breaks this hydrogen bond and switches off ESIPT in these compounds. This series of compounds which includes neutral HLH molecules and ionic (LH)- and (H2LH)+ species allowed us to elucidate the impact of protonation and coordination coupled deprotonation of HLH on the photoluminescence response and on altering the emission mechanism. The neutral HLH compound exhibits yellow emission as a result of the coexistence of two radiative decay channels: (i) T1 → S0 phosphorescence of the enol form and (ii) anti-Kasha S2 → S0 fluorescence of the keto form, which if feasible due to the large S2-S1 energy gap. However, owing to the efficient nonradiative decay through an energetically favorable conical intersection, the photoluminescence quantum yield of HLH is low. Protonation or deprotonation of the HLH ligand results in the significant blue-shift of the emission bands by more than 100 nm and boosts the quantum efficiency up to ca. 20% in the case of [Zn2LH2Cl2] and (H2LH)4[ZnCl4]2·3H2O. Despite both (H2LH)4[ZnCl4]2·3H2O and (H2LH)Br have the same (H2LH)+ cation in the structures, their emission properties differ significantly, whereas (H2LH)Br shows dual emission associated with two radiative decay channels: (i) S1 → S0 fluorescence and (ii) T1 → S0 phosphorescence, (H2LH)4[ZnCl4]2·3H2O exhibits only fluorescence. This difference in the emission properties can be associated with the external heavy atom effect in (H2LH)Br, which leads to faster intersystem crossing in this compound. Finally, a huge increase in the intensity of the phosphorescence of (H2LH)Br on cooling leads to pronounced luminescence thermochromism (violet emission at 300 K, sky-blue emission at 77 K).

Highly Luminescent Lanthanide Metal-Organic Frameworks with Tunable Color for Nanomolar Detection of Iron(III), Ofloxacin and Gossypol and Anti-counterfeiting Applications

Solvothermal reaction of 5,5'-(pyridine-2,6-diylbis(oxy))diisophthalic acid (H4 L) with europium(III) or terbium(III) nitrates in acetonitrile-water (1 : 1) at 120 °C gave rise to isostructural 2D coordination polymers, [Ln(HL)(H2 O)3 ]∞ (NIIC-1-Eu and NIIC-1-Tb), the layers of which are composed by eight-coordinated lanthanide(III) ions interconnected by triply deprotonated ligands HL3- . The layers are packed in the crystal without any specific intermolecular interactions between them, allowing the facile preparation of stable water suspensions, in which NIIC-1-Tb exhibited top-performing sensing properties through luminescence quenching effect with exceptionally low detection limits towards Fe3+ (LOD 8.62 nM), ofloxacin (OFX) antibiotic (LOD 3.91 nM) and cotton phytotoxicant gossypol (LOD 2.27 nM). In addition to low detection limit and high selectivity, NIIC-1-Tb features fast sensing response (within 60-90 seconds), making it superior to other MOF-based sensors for metal cations and organic toxicants. The photoluminescence quantum yield of NIIC-1-Tb was 93 %, one of the highest among lanthanide MOFs. Mixed-metal coordination polymers NIIC-1-Eux Tb1-x demonstrated efficient photoluminescence, the color of which could be modulated by the excitation wavelength and time delay for emission monitoring (within 1 millisecond). Furthermore, an original 2D QR-coding scheme was designed for anti-counterfeiting labeling of goods based on unique and tunable emission spectra of NIIC-1-Ln coordination polymers.

A Photoluminescence Study of Eu3+, Tb3+, Ce3+ Emission in Doped Crystals of Strontium-Barium Fluoride Borate Solid Solution Ba4-xSr3+x(BO3)4-yF2+3y (BSBF)

The present study is aimed at unveiling the luminescence potential of Ba4-xSr3+x(BO3)4-yF2+3y (BSBF) crystals doped with Eu3+, Tb3+, and Ce3+. Owing to the incongruent melting character of the phase, the NaF compound was used as a solvent for BSBF crystal growth. The structure of BSBF: Eu3+ with Eu2O3 concentration of about 0.7(3) wt% was solved in the non-centrosymmetric point group P63mc. The presence of Eu2O3 in BSBF: Eu3+ leads to a shift of the absorption edge from 225 nm to 320 nm. The photoluminescence properties of the BSBF: Ce3+, BSBF: Tb3+, BSBF: Eu3+, and BSBF: Eu3+, Tb3+, Ce3+ crystals have been studied. The unusual feature of europium emission in BSBF is the intensively manifested 5D0→7F0 transition at about 574 nm, which is the strongest for BSBF: Eu3+ at 370 nm excitation and for BSBF: Eu3+, Tb3+, Ce3+ at 300 nm and 370 nm excitations. No evidence of Tb3+→Eu3+ energy transfer was found for BSBF: Eu3+, Tb3+, Ce3+. The PL spectra of BSBF: Eu3+ at 77 and 300 K are similar with CIE chromaticity coordinates of (0.617; 0.378) at 300 nm excitation and (0.634; 0.359) at 395 nm excitation and low correlated color temperature which implies application prospects in the field of lightning. Due to the high intensity of 5D0→7F0 Eu3+ transition at 370 nm excitation, the BSBF: Eu3+ emission is yellow-shifted.

Ultra-low limit of luminescent detection of gossypol by terbium(III)-based metal-organic framework

The widespread use of gossypol-containing animal feed and cottonseed oil poses a great threat to water quality and livestock and human health, and there is an urgent need for a sensor for the rapid detection of trace amounts of gossypol in aqueous solutions and cottonseed oil. As a result, an unprecedented three-dimensional metal-organic framework sensor based on terbium(III) and a flexible ligand 4-(3,5-dicarboxyphenoxy)isophthalic acid (H₄L) was developed. Tb-MOF, {[Tb(H₂O)(HL)]·0.5MeCN·0.25 H₂O}_n, is highly stable in water and polar organic solvents and exhibits terbium-centered luminescence with 44% quantum yield. Suspensions of MOF in water and ethanol demonstrate a luminescence quenching response to cotton phytotoxicant gossypol with an unprecedented low detection limit of 0.76 nM and 1.89 nM, correspondingly, without interference from the components of cottonseed oil and blood plasma, making it suitable for the detection and determination of gossypol in real-life water and oil samples. Significantly, Tb-MOF is the first highly efficient sensor that uses water as a solvent to detect trace amounts of gossypol, and it can visualize and quantify gossypol in edible-grade cottonseed oil as well, which proves its great potential for practical application. In addition, Tb-MOF exhibited a detection limit for Fe³⁺ (0.23 μM) among the lowest reported for lanthanide-based MOFs in aqueous solutions so far.

4 in 1: multifunctional europium-organic frameworks with luminescence sensing properties, white light emission, proton conductivity and reverse acetylene-carbon dioxide adsorption selectivity

Lanthanide metal-organic frameworks (Ln-MOFs) combine the lanthanide luminescence characteristics and the advantages of porous materials, which can be used in various research fields by exploring their multifunctional properties. A three-dimensional water-stable and high-temperature resistant Eu-MOF [Eu(H₂O)(HL)]·0.5MeCN·0.25H₂O (H4L = 4-(3,5-dicarboxyphenoxy)isophthalic acid), demonstrating a high photoluminescence quantum yield, was synthesized and structurally characterized. In terms of luminescence, the Eu-MOF exhibits excellent selectivity and quenching sensing for Fe³⁺ (LOD = 4.32 μM) and ofloxacin, as well as color modulation with Tb³⁺ and La³⁺ to develop white LED components with high illumination efficiency (color rendering index, CRI = 90). On the other hand, narrow one-dimensional channels of the Eu-MOF decorated with COOH groups enable a rare reverse adsorption selectivity in a CO₂/C₂H₂ gas mixture. In addition, the protonated carboxyl groups in the Eu-MOF provide an efficient conducting platform for proton transfer with a conductivity value of 8 × 10^-4 S cm^-1 at 50 °C and RH 100%.

LiBa12(BO3)7F4 (LBBF) crystals doped with Eu3+, Tb3+, Ce3+: structure and luminescence properties

The luminescent properties of single crystals and polycrystalline samples of LiBa₁₂(BO₃)₇F₄ (LBBF) doped and co-doped with Eu³⁺, Tb³⁺, and Ce³⁺ have been studied in order to disclose their potential for application in white light-emitting diodes. Deciphering of LBBF:Eu³⁺ crystal structure (P4₂/mbc) makes it possible to determine the scheme of heterovalent isomorphic substitution 3Ba²⁺ ← 2Eu³⁺ + □, □ - vacancy in barium sites. Luminescent properties of LBBF crystals co-doped with Eu³⁺, Tb³⁺, Ce³⁺ and Eu³⁺, Tb³⁺ are compared. Both crystals demonstrate the luminescence close to day light with CIE coordinates and correlated color temperature (0.280; 0.305), 9232 K for LBBF:Eu³⁺,Tb³⁺,Ce³⁺ and (0.353; 0.390), 4849 K for LBBF:Eu³⁺,Tb³⁺ at 300 K at 370 nm excitation. The study of polycrystalline samples LBBF:Ce³⁺, LBBF:Tb³⁺, and LBBF:Eu³⁺, using X-ray diffraction, shows that the homogeneity regions of solid solutions differ significantly. In solid solutions LBBF:Tb³⁺ and LBBF:Eu³⁺, a gradual change in symmetry in the "tetragonal → orthorhombic → tetragonal" series takes place as the concentration of the dopant increases. When excited at a wavelength 395 nm, LBBF:Eu³⁺ samples with the content of Eu³⁺ 0.5 wt% and 2 wt% demonstrate intense red light with a high quantum yield of 63 and 60%, respectively, which allows them to be used as red components of composite phosphors for white LEDs.

Improved Synthesis of (TBA)2[W6Br14] Paving the Way to Further Study of Bromide Cluster Complexes

Octahedral cluster complexes of molybdenum and tungsten, [M₆X₈Y₆]^n- (M = Mo, W; X, Y = Cl, Br, I), are promising active components in various fields, including biomedicine and solar energy. Cluster complexes draw considerable attention due to their X-ray opacity, red/near-IR luminescence, and ability to convert triplet molecular oxygen to active singlet oxygen under UV and visible irradiation. Among the octahedral cluster complexes of molybdenum and tungsten, compounds with a {W₆Br₈}⁴⁺ core are the least studied. There are only a few examples of compounds with substituted terminal ligands, and their properties are not well understood. Among other things, this is due to more labor-intensive and expensive methods for obtaining the starting compounds in comparison with molybdenum counterparts. In this paper, we describe the synthesis of an octahedral cluster complex, (TBA)₂[W₆Br₁₄] (TBA⁺ = tetrabutylammonium), in gram quantities, starting from simple substances─W, Br₂, and Bi─in 70% yield. The formation of pentanuclear tungsten cluster complexes was recorded as a byproduct. Compounds with substituted terminal ligands (TBA)₂[W₆Br₈Y₆] (Y = NO₃, Cl, I) were obtained. We also discuss the instability of (TBA)₂[W₆Br₈(NO₃)₆] under light exposure, the optical properties of a series of compounds (TBA)₂[W₆Br₈Y₆] (Y = Cl, Br, I), and the effect of terminal ligands on the chemical shifts in ¹⁸³W NMR spectra in dimethyl sulfoxide-d₆. The presented approach to the synthesis of one of the main precursors of various bromide cluster complexes on a gram scale can stimulate the study of their properties and development of new functional materials based on them.

ESIPT-Capable 4-(2-Hydroxyphenyl)-2-(Pyridin-2-yl)-1H-Imidazoles with Single and Double Proton Transfer: Synthesis, Selective Reduction of the Imidazolic OH Group and Luminescence

1H-Imidazole derivatives establish one of the iconic classes of ESIPT-capable compounds (ESIPT = excited state intramolecular proton transfer). This work presents the synthesis of 1-hydroxy-4-(2-hydroxyphenyl)-5-methyl-2-(pyridin-2-yl)-1H-imidazole (L^OH,OH) as the first example of ESIPT-capable imidazole derivatives wherein the imidazole moiety simultaneously acts as a proton acceptor and a proton donor. The reaction of L^OH,OH with chloroacetone leads to the selective reduction of the imidazolic OH group (whereas the phenolic OH group remains unaffected) and to the isolation of 4-(2-hydroxyphenyl)-5-methyl-2-(pyridin-2-yl)-1H-imidazole (L^H,OH), a monohydroxy congener of L^OH,OH. Both L^OH,OH and L^H,OH demonstrate luminescence in the solid state. The number of OH···N proton transfer sites in these compounds (one for L^H,OH and two for L^OH,OH) strongly affects the luminescence mechanism and color of the emission: L^H,OH emits in the light green region, whereas L^OH,OH luminesces in the orange region. According to joint experimental and theoretical studies, the main emission pathway of both compounds is associated with T₁ → S₀ phosphorescence and not related to ESIPT. At the same time, L^OH,OH also exhibits S₁ → S₀ fluorescence associated with ESIPT with one proton transferred from the hydroxyimidazole moiety to the pyridine moiety, which is not possible for L^H,OH due to the absence of the hydroxy group in the imidazole moiety.

Synthesis and photophysical properties of rare earths (La, Nd, Gd, Y, Ho) complexes with silanediamido ligands bearing chelating phenylbenzothiazole chromophore

New silanediamide ligand bearing chromophore 2-phenylbenzothiazole (Pbt) groups SiMe2(HNPbt)2 (1H) was synthesized and introduced in the lanthanide complexes. It was found that independently of the stoichiometry of the salt metathesis...

Dual emission of ESIPT-capable 2-(2-hydroxyphenyl)-4-(1H-pyrazol-1-yl)pyrimidines: interplay of fluorescence and phosphorescence

ESIPT-capable pyrimidine-based compounds featuring short O–H···N intramolecular hydrogen bonds, 2-(2-hydroxyphenyl)-4-(3,5-dimethyl-1H-pyrazol-1-yl)-6-methylpyrimidine (HL1) and 2-(2-hydroxyphenyl)-4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-methylpyrimidine (HL2), were synthesized by the condensation of 4-hydrazinyl-2-(2-hydroxyphenyl)-6-methylpyrimidine with acetylacetone and dibenzoylmethane. In solution, HL1 and HL2...

Variable Dimensionality of Europium(III) and Terbium(III) Coordination Compounds with a Flexible Hexacarboxylate Ligand

A reaction between 4,4',4″-(benzene-1,3,5-triyltris(oxy))triphthalic acid (H₆L) and lanthanide(III) nitrates (Ln = Eu³⁺, Tb³⁺) in water under the same conditions gave a molecular coordination compound [Tb(H_4.5L)₂(H₂O)₅]∙6H₂O in the case of terbium(III) and a one-dimensional linear coordination polymer {[Eu₂(H₃L)₂(H₂O)₆]∙8H₂O}_n in the case of europium(III). The crystal structures of both compounds were established by single-crystal X-ray diffraction, and they were further characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. The compounds demonstrated characteristic lanthanide-centered photoluminescence. The lanthanide-dependent dimensionality of the synthesized compounds, which are the first examples of the coordination compounds of hexacarboxylic acid H₆L demonstrates its potential as a linker for new coordination polymers.

Molecular Environment Effects That Modulate the Photophysical Properties of Novel 1,3-Phosphinoamines Based on 2,1,3-Benzothiadiazole

We report synthesis, crystal structure, and photophysical properties of novel 1,3-phosphinoamines based on 4-amino-2,1,3-benzothiadiazole (NH₂-btd): Ph₂PCH(Ph)NH-btd (1) and Ph₂P(E)CH(Ph)NH-btd, (E = O (2α and 2β·thf), S (3), Se (4)). Chalcogenides 2–4 exhibit bright emissions with a major band at 519–536 nm and a minor band at 840 nm. According to TD-DFT calculations, the first band is attributed to fluorescence, while the second band corresponds to phosphorescence. In the solid state, room temperature quantum yield reaches 93% in the case of the sulphide. The compounds under study feature effects of the molecular environment on the luminescent properties, which manifest themselves in fluorosolvatochromism as well as in a luminescent response to changes in crystal packing and in contributions to aggregation effects. Specifically, transformation of solid 2β·thf to solvate-free 2β either by aging or by grinding causes crystal packing changes, and, as a result, a hypsochromic shift of the emission band. Polystyrene films doped with 2 reveal a bathochromic shift upon increasing the mass fraction from 0.2 to 3.3%, which is caused by molecular aggregation effects.

First 1-hydroxy-1H-imidazole-based ESIPT emitter with an O–H···O intramolecular hydrogen bond: ESIPT-triggered TICT and speciation in solution

Search for new types of ESIPT-capable molecules is crucial for understanding factors controlling the ESIPT photoreaction. In this paper we present combined experimental and theoretical studies of the proton transfer...

A Zn(II)-Based Sql Type 2D Coordination Polymer as a Highly Sensitive and Selective Turn-On Fluorescent Probe for Al3

A luminescent coordination polymer with the overall formula {[Zn(tr2btd)(bpdc)]∙DMF}n (where tr2btd = 4,7-di(1H-1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole; bpdc = 4,4'-biphenyldicarboxylate) was synthesized and characterized by single-crystal and powder X-ray diffraction, thermogravimetric, infrared spectroscopy, and elemental analyses. Luminescent properties of the obtained compound were studied in detail both in the solid state and as a suspension in N,N-dimethylacetamide (DMA). It was found that {[Zn(tr2btd)(bpdc)]∙DMF}n exhibits bright turquoise luminescence with excellent quantum efficiency and demonstrates turn-on fluorescence enhancement effect upon soaking in DMA Al3+ solution. Fluorescence titration experiments were carried out and the detection limit for Al3+ ions was calculated to be 120 nM, which is among the lowest reported values for similar materials. Moreover, compound demonstrated excellent selectivity and reusability, and the mechanism of the response is discussed. These results indicate that {[Zn(tr2btd)(bpdc)]∙DMF}n is a promising probe for sensitive fluorescent Al3+ detection.

Synthesis, Crystal Structure, and Luminescence of Cadmium(II) and Silver(I) Coordination Polymers Based on 1,3-Bis(1,2,4-triazol-1-yl)adamantane

Coordination polymers with a new rigid ligand 1,3-bis(1,2,4-triazol-1-yl)adamantane (L) were prepared by its reaction with cadmium(II) or silver(I) nitrates. Crystal structure of the coordination polymers was determined using single-crystal X-ray diffraction analysis. Silver formed two-dimensional coordination polymer [Ag(L)NO₃]_n, in which metal ions are linked by 1,3-bis(1,2,4-triazol-1-yl)adamantane ligands, coordinated by nitrogen atoms at positions 2 and 4 of 1,2,4-triazole rings. Layers of the coordination polymer consist of rare 18- and 30-membered {Ag₂L₂} and {Ag₄L₄} metallocycles. Cadmium(II) nitrate formed two kinds of one-dimensional coordination polymers depending on the metal-to-ligand ratio used in the synthesis. Coordination polymer [Cd(L)₂(NO₃)₂]_n was obtained in case of a 1:2 M:L ratio, while for M:L = 2:1 product {[Cd(L)(NO₃)₂(CH₃OH)]·0.5CH₃OH}_n was isolated. All coordination polymers demonstrated ligand-centered emission near 450 nm upon excitation at 370 nm.

Cinnamal Sensing and Luminescence Color Tuning in a Series of Rare-Earth Metal-Organic Frameworks with Trans-1,4-cyclohexanedicarboxylate

Three isostructural metal-organic frameworks ([Ln2(phen)2(NO3)2(chdc)2]·2DMF (Ln3+ = Y3+ for 1, Eu3+ for 2 or Tb3+ for 3; phen = 1,10-phenanthroline; H2chdc = trans-1,4-cyclohexanedicarboxylic acid) were synthesized and characterized. The compounds are based on a binuclear block {M2(phen)2(NO3)2(OOCR)4} assembled into a two-dime nsional square-grid network containing tetragonal channels with 26% total solvent-accessible volume. Yttrium (1)-, europium (2)- and terbium (3)-based structures emit in the blue, red and green regions, respectively, representing the basic colors of the standard RGB matrix. A doping of Eu3+ and/or Tb3+ centers into the Y3+-based phase led to mixed-metal compositions with tunable emission color and high quantum yields (QY) up to 84%. The bright luminescence of a suspension of microcrystalline 3 in DMF (QY = 78%) is effectively quenched by diluted cinnamaldehyde (cinnamal) solutions at millimolar concentrations, suggesting a convenient and analytically viable sensing method for this important chemical.

Intense multi-colored luminescence in a series of rare-earth metal-organic frameworks with aliphatic linkers

Two series of highly luminescent yttrium(iii), europium(iii) and terbium(iii) metal-organic frameworks containing diimine aromatic ligands and the dicarboxylate linker trans-1,4-cyclohexanedicarboxylate (chdc^2-) which can be described by the general formulas [M₂(bpy)₂(chdc)₃], where M = Y³⁺ (1), Eu³⁺ (2), and Tb³⁺ (3) and bpy = 2,2'-bipyridyl, and [M₂(phen)₂(chdc)₃], where M = Y³⁺ (4), Eu³⁺ (5), and Tb³⁺ (6) and phen = 1,10-phenanthroline, were synthesized and characterized. All compounds are based on the same dinuclear {M₂(L)₂(OOCR)₆} building blocks and possess a similar topology of the 3D framework with narrow pores. The chelate aromatic ligands act as efficient light-harvesting antennas for subsequent energy transfer to the emitting metal center (M = Eu³⁺, Tb³⁺) or intraligand photoemission (M = Y³⁺). As a result, the reported compounds display intense emission in the red (Eu³⁺), green (Tb³⁺) or blue (Y³⁺) regions representing three basic colors (RGB) of visible light. The measured quantum yields (QYs) of the solid-state luminescence for individual compounds were found to be 63% (1), 46% (2), 59% (3), 2.3% (4), 55% (5) and 49% (6). The drastic reduction of the luminescence efficiency for 4 is explained by the strong disorder of phen ligands. The high thermal stability (up to 300 °C) and exceptional moisture resistance of the bpy-based frameworks 1-3 were confirmed by TG and PXRD measurements. Various bimetal or trimetal compositions were also prepared for the bpy-series. The luminescence properties of these mixed-metal compounds depend on both the chemical composition and excitation wavelength (λ_ex). Remarkably, pure white emission with color temperature = 6126 K was achieved for [Y_1.68Eu_0.08Tb_0.24(bpy)₂(chdc)₃] at λ_ex = 360 nm with QY = 20%. The reported results suggest that the obtained coordination framework series is a convenient platform for the design of highly efficient light emitting materials with tunable properties.

A comparative study of optical properties and X-ray induced luminescence of octahedral molybdenum and tungsten cluster complexes

Octahedral W cluster complexes have more intensive X-ray excited optical luminescence than Mo ones.