Spectrophotometric Determination of Trace Amount of Total FeII/FeIII and Live Cell Imaging of a Carboxylato Zn(II) Coordination Polymer

The coordination polymer, (Zn(II)-CP, 1), {[Zn(2,6-NDC)(4-Cltpy)](H₂O)₄} (1) (2,6-H₂NDC = 2,6-naphthalene dicarboxylic acid and 4-Cltpy = 4'-chloro-[2,2';6',2″]terpyridine) is structurally characterized by single crystal X-ray diffraction measurement and other physicochemical studies (PXRD, FTIR, thermal analysis, microanalytical data). 4-Cltpy acts as end-capping ligand, and NDC^2- is a carboxylato bridging motif to constitute ZnN₃O₂ distorted trigonal bipyramid core that propagates to construct 1D chain. The coordination polymer, 1, detects total iron (Fe³⁺ and Fe²⁺) in aqueous solution by visual color change, colorless to pink. Absorption spectrophotometric technique in aqueous medium measures the limit of detection (LOD) 0.11 μM (Fe²⁺) and 0.15 μM (Fe³⁺), and binding constants (K_d) are 6.7 × 10⁴ M^-1 (Fe³⁺) and 3.33 × 10⁴ M^-1 (Fe²⁺). Biocompatibility of 1 is examined in live cells, and intracellular Fe²⁺ and Fe³⁺ are detected in MDA-MB 231 cells. Zn(II) substitution is assumed upon addition of Fe^III/Fe^II solution to the suspension of the coordination polymer, 1, in water-acetonitrile (41:1) (LZn^II + Fe^III/II → LFe^III + Zn^II, where L is defined as coordinated ligands), which is accompanied by changing from colorless to pink at room temperature. The color of the mixture may be assumed to the charge transfer transition from carboxylate-O to Cltpy via Fe(II/III) bridging center (carboxylate-O-Fe-CltPy). The product isolated from the reaction is finally characterized as Fe(III)@1-CP. It is presumed that product Fe(II)@1-CP may undergo fast aerial oxidation to transform Fe(III)@1-CP. The Fe^III exchanged framework (Fe(III)@1-CP) has been characterized by PXRD, IR, TGA and energy dispersive X-ray analysis (EDX)-SEM. The MTT assay calculates the cell viability (%), and the tolerance limit is 100 μM to total Fe²⁺ and Fe³⁺.

A Top-Down Approach and Thermal Characterization of Luminescent Hybrid BPA.DA-MMA@Ln2L3 Materials Based on Lanthanide(III) 1H-Pyrazole-3,5-Dicarboxylates

In this study, novel hybrid materials exhibiting luminescent properties were prepared and characterized. A top-down approach obtained a series of polymeric materials with incorporated different amounts (0.1; 0.2; 0.5; 1, and 2 wt.%) of dopants, i.e., europium(III) and terbium(III) 1H-pyrazole-3,5-dicarboxylates, as luminescent sources. Methyl methacrylate and bisphenol A diacrylate monomers were applied for matrix formation. The resulting materials were characterized using Fourier transform infrared spectroscopy (FTIR) and thermal analysis methods (TG-DTG-DSC, TG-FTIR) in air and nitrogen atmosphere, as well as by luminescence spectroscopy. The homogeneity of the resulting materials was investigated by means of optical microscopy. All obtained materials exhibited good thermal stability in both oxidizing and inert atmospheres. The addition of lanthanide(III) complexes slightly changed the thermal decomposition pathways. The main volatile products of materials pyrolysis are carbon oxides, water, methyl methacrylic acid and its derivatives, bisphenol A, 4-propylphenol, and methane. The luminescence properties of the lanthanide complexes and the prepared hybrid materials were investigated in detail.

In situ formation and dispersion of lanthanide complexes in wormlike micelles

Lanthanide-containing, water-based fluids normally suffer from low photoluminescent (PL) and/or colloidal stability, which greatly hinders their applications. Herein, we report the preparation of PL fluids which contain in situ formed europium complexes in aqueous solution. The strategy first relies on the construction of wormlike micelles by mixing a zwitterionic surfactant (tetradecyldimethylaminoxide, C₁₄DMAO) and a tridentate ligand for a lanthanide cation (2,6-dipicolinic acid, DPA) in water. The addition of the dual-functionalized DPA to an aqueous solution of C₁₄DMAO (100 mol L^-1) induced non-monotonic rheological changes, with the expected formation of a pseudogemini surfactant at a DPA-to-C₁₄DMAO molar ratio of approximately 1 : 2. When a third component of EuCl₃ is introduced to this system, complexes formed in situ between Eu³⁺ and DPA, resulting in bright red-emission. Besides DPA, C₁₄DMAO is also involved in the complexation, which squeezes out water molecules and greatly improves the PL stability of the fluid. The synergetic effect among Eu³⁺, DPA and C₁₄DMAO leads to the high colloidal stability of the fluid, opening the door for a wide range of potential applications. Further tests indicate that this strategy can be easily expanded to other lanthanide cations such as Tb³⁺.

Amino acid derivative-based Ln-metallohydrogels with multi-stimuli responsiveness and applications

Metallohydrogels and lanthanide (Ln) fluorescent materials have gained much attention recently. In this study, we designed and synthesized a facile gelator of a phenylalanine-based derivative containing an indazole group (namely IZF). It was found that IZF can self-assemble to form hydrogel at pH ≤ 7. Meanwhile, IZF and Tb³⁺/Eu³⁺ can co-assemble to generate IZF-Tb and IZF-Eu metallohydrogels with green and red fluorescence, respectively, at pH 8-11, with excellent multi-stimuli responsiveness. The bimetallic hydrogels of IZF-Tb/Eu exhibit different colors under UV light by adjusting the ratio of Tb³⁺ and Eu³⁺. Moreover, white light emission was achieved with IZF-Tb/Eu bimetallic gels through doping carbon dots (CDs) by tailoring the stoichiometric ratio of Ln-complex and CDs. Remarkably, IZF-Tb and IZF-Eu could be used as fluorescent inks with excellent stability. This study indicates that the amino acid derivative-based Ln-metallohydrogels are excellent candidates for constructing information storage and multiple anti-counterfeiting materials.

Two luminescent film sensors constructed from new lanthanide coordination polymers for ratiometric detection of Zn2+ and NH3 in water and their white emission properties

Two luminescent film sensors constructed from new lanthanide coordination polymers based on a new tetra-monodentated ligand for ratiometric detection of Zn2+ and NH3 in water were developed.

Lanthanide Polyoxometalate Based Water-Jet Film with Reversible Luminescent Switching for Rewritable Security Printing

Luminescent security printing is of particular importance in the information era. However, the use of conventional paper still carries a lot of economic and environmental issues. Therefore, developing new environmentally friendly security printing material with a low cost is imperative. To achieve the aforementioned goals, novel lanthanide polyoxometalate doped gelatin/glycerol films with high transparency, high strength, and good flexibility have been developed via a solution-casting method. The electrostatic interaction between zwitterionic gelatin and polyoxometalate was confirmed by attenuated total reflection Fourier transform infrared spectroscopy. Luminescent spectra and digital images indicated that the films exhibited reversible luminescent switching properties through association and dissociation of hydrogen bonds between glycerol and water molecules, allowing its potential application as water-jet rewritable paper for luminescent security printing. Furthermore, the printed information can be conveniently "erased" by heating, and the film can be reused for printing. The film exhibited excellent ability to be both rewritten and re-erased. A QR code pattern and hybrid printing were employed to improve the security of information. In addition, the rewritable films possessed excellent regeneration ability and low toxicity, as well as good stability against UV irradiation and organic solvents. The water-jet rewritable film based on lanthanide polyoxometalate for luminescent security printing, to the best of our knowledge, has not yet been reported up to date. This work provides an attractive alternative strategy on fabricating rewritable films for luminescent security printing in terms of cutting down the cost, simplifying the preparation process, and protecting the environment.

Ultra-trace level detection of Cu2+ in an aqueous medium by novel Zn(ii)-dicarboxylato–pyridyl coordination polymers and cell imaging with HepG2 cells

Fluorescent 1D Zn(ii) coordination polymers are aggregated via noncovalent interactions. The emission of the CPs is exclusively quenched by Cu²⁺ and the LOD is at μM range. In aqueous medium internalization CPs within HepG2 cells is detected by microscopic cell image using Cu²⁺.

Synthesis and characterization of poly(methyl methacrylate) co-doped with Tb(tmhd)3 - Rhodamine B for luminescent optical fiber applications

Currently, there is a growing interest in the development of multi-colored materials based on the combination of two or more systems (organic or inorganic) as a strategy to take advantage of their combined physical or chemical properties. These multi-colored materials have found potential applications as sensors, amplifiers, and optical fibers. In this work, the physical characteristics of poly(methyl methacrylate) (PMMA) doped with Terbium(III)-tris-(2,2,6,6-tetramethyl-3,5-heptanedionate) (Tb(tmhd)₃) at 1.57-1.58 mmol and Rhodamine B (RhB) at different concentrations were analyzed. The emission obtained from these samples (multichromophoric samples) varied as function of RhB concentration due to an efficient energy transfer process (33-65%). The role of PMMA as inert matrix that assists in the recombination process was confirmed by FTIR and Raman spectra analysis. Moreover, an improvement in thermal resistance of the materials was observed due to the presence of the dopants during the polymerization process.

Two-dimensional square-grid iron(ii) coordination polymers showing anion-dependent spin crossover behavior

Two Fe(ii)-based coordination polymers [Fe(tpmd)2(NCS)2]·5.5H2O (1) and [Fe(tpmd)2(NCSe)2]·7H2O (2) with the framework of square-grid type have been assembled from FeSO4·7H2O, N,N,N',N'-tetrakis(pyridin-4-yl)methanediamine (tpmd), and KNCS/KNCSe in methanol and characterized. By utilizing two pyridine groups of a tpmd ligand, 1 and 2 are formed in two-dimensional layered structures through coordination of octahedral iron(ii) ions with the tpmd to NCS-/NCSe- ligands in which they have a supramolecular isomorphous conformation. 1 shows a paramagnetic behavior between 2 and 300 K, while 2 exhibits two-step spin crossover (ca. 145 and 50 K) in the temperature range due to the coordination of NCSe- ligands. At 300 K 2 is fully high-spin state. However, at 100 K 2 becomes ca. 50% high spin and 50% low spin iron(ii) ions, which is verified by magnetic moments. In the structural analysis of 2 at 100 K, two different layers are observed with different bond distances around iron(ii) ions in which the layers are stacked alternately.

White-Light Emitting Di-Ureasil Hybrids

White-light emitting materials have emerged as important components for solid state lighting devices with high potential for the replacement of conventional light sources. Herein, amine-functionalized organic-inorganic di-ureasil hybrids consisting of a siliceous skeleton and oligopolyether chains codoped with lanthanide-based complexes, with Eu3+ and Tb3+ ions and 4,4'-oxybis(benzoic acid) and 1,10-phenanthroline ligands, and the coumarin 1 dye were synthesized by in situ sol⁻gel method. The resulting luminescent di-ureasils show red, green, and blue colors originated from the Eu3+, Tb3+, and C1 emissions, respectively. The emission colors can be modulated either by variation of the relative concentration between the emitting centers or by changing the excitation wavelength. White light emission is achieved under UV excitation with absolute quantum yields of 0.148 ± 0.015, 0.167 ± 0.017, and 0.202 ± 0.020 at 350, 332, and 305 nm excitation, respectively. The emission mechanism was investigated by photoluminescence and UV⁻visible absorption spectroscopy, revealing an efficient energy transfer from the organic ligands to the Ln3+ ions and the organic dye, whereas negligible interaction between the dopants is discerned. The obtained luminescent di-ureasils have potential for optoelectronic applications, such as in white-light emitting diodes.

A two-dimensional cadmium(II) coordination polymer constructed from 4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylate and 1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylate ligands

Crystals of poly[[aqua[μ₃-4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylato-κ⁵O¹O^1':N³,O⁴:O⁵][μ₄-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylato-κ⁷N³,O⁴:O⁴,O^4':O¹,O^1':O¹]cadmium(II)] monohydrate], {[Cd₂(C₁₅H₁₄N₂O₄)(C₁₆H₁₄N₂O₆)(H₂O)]·H₂O}_n or {[Cd₂(Hcpimda)(cpima)(H₂O)]·H₂O}_n, (I), were obtained from 1-(4-carboxybenzyl)-2-propyl-1H-imidazole-4,5-dicarboxylic acid (H₃cpimda) and cadmium(II) chloride under hydrothermal conditions. The structure indicates that in-situ decarboxylation of H₃cpimda occurred during the synthesis process. The asymmetric unit consists of two Cd²⁺ centres, one 4-carboxy-1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-5-carboxylate (Hcpimda^2-) anion, one 1-(4-carboxylatobenzyl)-2-propyl-1H-imidazole-4-carboxylate (cpima^2-) anion, one coordinated water molecule and one lattice water molecule. One Cd²⁺ centre, i.e. Cd1, is hexacoordinated and displays a slightly distorted octahedral CdN₂O₄ geometry. The other Cd centre, i.e. Cd2, is coordinated by seven O atoms originating from one Hcpimda^2- ligand and three cpima^2- ligands. This Cd²⁺ centre can be described as having a distorted capped octahedral coordination geometry. Two carboxylate groups of the benzoate moieties of two cpima^2- ligands bridge between Cd2 centres to generate [Cd₂O₂] units, which are further linked by two cpima^2- ligands to produce one-dimensional (1D) infinite chains based around large 26-membered rings. Meanwhile, adjacent Cd1 centres are linked by Hcpimda^2- ligands to generate 1D zigzag chains. The two types of chains are linked through a μ₂-η² bidentate bridging mode from an O atom of an imidazole carboxylate unit of cpima^2- to give a two-dimensional (2D) coordination polymer. The simplified 2D net structure can be described as a 3,6-coordinated net which has a (4³)₂(4⁶.6⁶.8³) topology. Furthermore, the FT-IR spectroscopic properties, photoluminescence properties, powder X-ray diffraction (PXRD) pattern and thermogravimetric behaviour of the polymer have been investigated.

Multifunctional Lanthanide-Based Metal-Organic Frameworks with a Polyheterotopic Ligand: Doped with Ytterbium(III) for Luminescence Enhancement and Selective Dye Adsorption

The chemistry of metal-organic frameworks has been progressing fast with its exciting potential in multifunctional applications. A series of three-dimensional lanthanide-based metal-organic frameworks, {[Ln(HTPO)(NO3 )(H2 O)]⋅x(CH3 CN)⋅y(H2 O)}n (Ln=Eu (1), Tb (2), Gd (3), Sm (4), Dy (5), Nd (6)), {[Eu(TPO)(HCOO)0.5 ]⋅(H3 O)0.5 }n (7), {[Eu(TPO)(DMF)]⋅(solv)x }n (8; DMF= N,N-dimethylformamide), and {[Eu(TPO)(DMA)]⋅(solv)x }n (9; DMA=dimethylacetamide) were synthesized with semirigid C3 -symmetric ligand tris(4-carboxylphenyl)phosphine oxide (H3 TPO). In these frameworks, the H3 TPO ligand exists in a totally different configuration. Framework 1 exhibits good breathing properties for absorbing more guest molecules through a solvent-induced single-crystal-to-single-crystal (SC-SC) transformation involving a configuration transformation of the organic linker in the framework. The ytterbium ion was doped into 1 to improve the luminescent performance (lifetime and quantum yield) of the red europium emission. Among a series of Eu1-x Ybx TPO samples, Eu0.88 Yb0.12 TPO showed enhanced luminescence intensity (≈5.1 times that of the pure europium system), and the lifetime increased from 1073.08 to 1236.57 μs. Moreover, the porosity of these frameworks allows them to efficiently adsorb dye molecules with high selectivity and efficiency.

Octahedral Yb(iii) complexes embedded in [CoIII(CN)6]-bridged coordination chains: combining sensitized near-infrared fluorescence with slow magnetic relaxation

The rare octahedral Yb^III complexes formed in the bimetallic Yb–Co chains reveal significant magnetic anisotropy and photoluminescence activity in the near-infrared range.