Effects of several lanthanide trichloride hydrates on the melting behavior and spherulitic superstructure of poly(ethylene oxide)

Binary mixtures of poly(ethylene oxide) (PEO) with the trichloride hydrates of lanthanum, cerium, europium, terbium, and ytterbium have been studied with calorimetry, polarized optical microscopy, and infrared spectroscopy. Melting‐point depression of the PEO‐rich phase occurs in all cases. At sufficiently high concentrations of the low molecular weight lanthanide complex, crystallization of the polymer is absent. The lighter lanthanides with larger ionic radii, such as lanthanum and cerium, are more effective in suppressing PEO crystallization from solution or the molten state because they are more oxophilic. The spherulitic superstructure of PEO disappears at rather low concentrations of the lanthanide salts, between 2 and 8 mol % Ln³⁺. Lanthanum and terbium are most efficient at disrupting the formation of PEO spherulites, and europium is least efficient. Infrared spectroscopy identifies twisting and wagging vibrational absorptions of CH₂ groups in the polymer that are sensitive to the morphologies of these mixtures. Modifications of the PEO infrared absorbances in the presence of these five lanthanide salts correlate more closely with the presence or absence of major PEO melting, not the formation of a spherulitic superstructure. The phase behavior is rather simple, with no evidence of eutectic solidification upon cooling from the molten state. Multiple melting endotherms are observed in the differential scanning calorimetry heating traces of binary mixtures containing 8 mol % Yb³⁺ and between 10 and 20 mol % Eu³⁺, but the concentration dependence of these first‐order endothermic transitions is not characteristic of eutectic phase behavior. The presence of trivalent cations, such as Eu³⁺ or Yb³⁺, in these complexes perturbs the crystallization kinetics of PEO upon cooling from the molten state, as well as the melting behavior upon heating. Ion–dipole or electrostatic interactions between the lanthanide cation and the ether oxygen of PEO might alter the surface free energy at the periphery of the crystalline lamellae and perturb the chain‐folding characteristics of PEO. Consequently, coupling between the amorphous matrix and the PEO crystallites is strengthened, and this provides stability for the existence of multiple‐chain‐folded crystals composed of rather thin lamellae that could be responsible for multiple melting behavior. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2200–2213, 2003     

Single-Ion Conduction and Electrochemical Characteristics of Poly (Oxyethylene)/ Lithium Methoxy Oligo(Oxyethylene) Sulfate Blend

Abstract

The ion conduction of a blend of poly(oxyethylene) (PEO) and lithium methoxy oligo(oxyethylene) sulfate (SAL₈) and its electrochemical characteristics were studied. The maximum ambient conductivity of the blend reaches 1.2 × 10^?6 S/cm. The blend exhibits single-ion conduction, excellent mechanical performance, and electrochemical stability. A battery of Li/PEO + SAL₈/Li_1+xV₃O₈ has a constant discharge capacity at different discharge current densities up to a certain voltage, while the discharge capacity of Li/P (MEO_16-AM) + LiClO₄/Li_1+xV₃O₈ decreases with an increase of the discharge current density.     

A Series of Carboxylic‐Functionalized Ionic Liquids and their Solubility for Lanthanide Oxides

Herein we report the synthesis of propanoic acid functionalized ionic liquids (ILs) with various lengths of alkyl chain on the imidazole ring. The synthesized propanoic acid functionalized ILs were used to dissolve Eu₂O₃ (or Tb₄O₇) due to the formation of europium(III) (or terbium(III)) carboxylate, aimed to get soft luminescent materials combining the properties of ILs and attractive luminescent properties of lanthanide ions. The luminescent behavior of Eu³⁺ and Tb³⁺ in the ILs were investigated by luminescence spectroscopy. The affect of the alkyl chain on the luminescent behavior (the asymmetry parameter (R), the lifetime of ⁵D₀, and the ⁵D₀ quantum efficiency) of Eu³⁺ has been discussed.     

Eu(fod)3 binding on the 1H‐NMR spectra of bis(2′‐ethylbenzoate)ethylene glycol podands

The complexing and selective binding constants of Eu(fod)₃ with bis(2′‐ethylbenzoate)ethylene glycol podands having one to four oxyethylene groups was observed on their ¹H‐NMR spectra at 250 MHz and 295 K in CDCl₃. The Eu(fod)₃ interaction displayed the selective binding role of oxygen on H₂C–O–CH₂ backbones with referring the ¹H chemical shifts. The estimated equilibrium constants, K_a, of 1:1 ratio of interactions were in accordance with the Eu(fod)₃ ionic radii to bind the oxygen sites depending on the size and conformation of the esters. Esters having one or two ethyleneoxy groups gave mainly 2:2 complexes using ester sites. The minimum lanthanide‐podand ester distance displayed the maximum stability so that ester with four oxyethylene groups was found to bind the Eu(fod)₃ moderately, whereas ester with three oxyethylene groups showed a large induced chemical shift due to the stability of Eu³⁺ complexes with larger ethyleneoxy groups. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation,Characterization and Luminescence Study of Chitosan Membrane and Powder Forms with Eu3 + and Tb3 +

Chitosan membranes with trivalent lanthanide ion Eu^{3 +} were prepared at a ratio of 3:1 w/w (chitosan:lanthanide). There was no membrane formation at a ratio of 1:1 w/w (chitosan: Eu^{3 +} or Tb^{3 +}); in this case a white solid powder was obtained. Both chitosan compounds were characterized by elemental analysis (CHN), thermal analysis (TG/DTG), scanning electron microscopy (SEM) and luminescence spectroscopy. CHN analysis was performed only for chitosan compounds in powder form, suggesting that these compounds have the general formula QUILn.6H₂O, where QUI = Chitosan and Ln = Eu^{3 +} or Tb^{3 +}. The results of TG/DTG curves for chitosan membranes with Eu^{3 +} ion indicate that the introduction of this metal into the chitosan structure causes gradual degradation in residual carbons, showing lower weight loss in the Eu^{3 +} membranes compared to pure chitosan membrane. Analysis of luminescence demonstrated that chitosan membranes with Eu^{3 +} ion exhibit emission in the visible region, showing emission bands from chitosan and Eu^{3 +} moieties. For chitosan with Eu^{3 +} and Tb^{3 +} ions compounds, in powder form, the analysis of luminescence suggested that chitosan is not transferring energy to the lanthanide ion; however, the chemical region where the lanthanide ion is found breaks the selection rules and favors the emission of these ions.     

Fluorescence Properties of Europium and Terbium Triundecylenate-Containing Polymers and Solutions

Europium triundecylenate, Eu(UA)₃, and terbium triundecylenate, Tb(UA)₃, were prepared by the method described in our previous paper. Either Eu(UA)₃ or Tb(UA)₃ was dissolved in methacrylic acid (<20%) and copolymerized as a crosslinker with methyl methacrylate (>80) by bulk polymerization in molds made of two glass plates. The fluorescence spectroscopy of these Eu- or Tb-containing polymers under ultraviolet/visible excitation light was investigated. The fluorescence spectroscopy of solutions of Eu(UA)₃ or Tb(UA)₃ in methacrylic acid was measured and compared with that of the solid-state Eu- or Tb-containing polymers. The fluorescence excitation and emission spectra of the solutions and polymers showed the characteristic features of free Eu³⁺ or Tb³⁺. The lifetime fluorescence of the solutions and polymers with Eu³⁺ are also included.     

Synthesis and Luminescence of Eu‐N2,N6‐Bis(2‐hydroxyethyl)pyridine‐2,6‐dicarboxamide Complexes Containing Mesoporous Material

Ligand N²,N⁶‐bis(2‐hydroxyethyl)pyridine‐2,6‐dicarboxamide (L=BHPC) was synthesized and used to construct lanthanide‐based mesoporous material Eu‐L‐MCM‐41. In the structure of resulting Eu‐L‐MCM‐41, Eu³⁺ was chelated by BHPC, and the Eu‐L complexes were anchored into the forming MCM‐41 host by the reaction between the hydroxyl group and active Si‐OH. The mesoporous material Eu‐L‐MCM‐41 was characterized by UV, IR, small‐angle X‐ray diffraction (SAXRD) patterns, nitrogen adsorption/desorption isotherms, TGA and fluorescence spectra. The results indicate that ligand and Eu³⁺ have been introduced into the MCM‐41 host, and Eu‐L‐MCM‐41 exhibits characteristic luminescence of Eu³⁺.     

Laser spectroscopic study of multiple Eu3+ sites and their crystal fields in YAlG crystals

Resonance fluorescence spectra are excited from a single crystal of curopium doped yttrium aluminum garnet. An analysis from the energy spectrum shows that the spectra are due to trivalent europuim ions occupying two different sites in the unit cell and a crystal field analysis reveals that these ions at these sites experience fields of orthorhombic and axial symmetry. The former is that expected if Eu³⁺ replaces the Y³⁺ at the orthorhombic d sites, the latter if the lanthanide ion replaces the Al³⁺ ions at the a sites (with a distorted C_3i symmetry), there are indications that Eu³⁺ prefers the a over the d sites.     

EXAFS, SAXS and Eu3+ Luminescence Spectroscopy of Sol-Gel Derived Siloxane-Polyethyleneoxide Hybrids

Hybrid Eu³⁺-doped silica-poliethyleneoxide (PEO) nanocomposites with covalent bonds between the inorganic (siloxane) and organic (PEO) phases have been obtained by sol-gel process. These materials are transparent, flexible and present high Eu³⁺ luminescence output. Their luminescence properties, local environment around europium ions and structure have been investigated as a function of europium content. EXAFS measurements indicate that the increase in Eu-doping induces a decrease in Eu³⁺ coordination number. An increase in symmetry degree around the metal ion is also observed for increasing Eu³⁺ concentration, while non radiative decay paths from the ⁵D₀ excited state become more important. SAXS results suggest the preferential interaction of europium ions with ether-type oxygens of the polymer chains. However, the existence of interactions between the cations and the carbonyl groups from urea bridges located at the siloxane-PEO interface can not be excluded.     

Solubility, diffusion coefficient and ionic conductivity of alkyl viologens in poly(ethylene oxide) and its derivatives

A series of alkyl viologens RV (R denotes ethyl, butyl, hexyl, heptyl, and dodecyl) was dissolved in poly(ethylene oxide) (PEO) oligomers (average molar masses of 200, 300, 400, 600 and 1000 g mol⁻¹). The solubility of RV in PEO oligomers decreased with increasing alkyl chain length of RV and the molar mass of PEO. Cyclic voltammograms of RV in PEO containing 0.50 M LiClO₄ clearly show two redox waves. The ionic conductivity of PEO oligomers containing RV decreased with increasing alkyl chain length, suggesting the migration of RV itself in the PEO oligomers. Potential step chronoamperometry was used to obtain the apparent diffusion coefficient of RV in the PEO oligomers. The ionic conductivity has a linear relationship with the apparent diffusion coefficient regardless of the RV species, the PEO molar mass and the temperature. RV was shown to act as a redox mediator in PEO oligomers as long as the ionic conductivity of the PEO was high. Poly(oligo(oxyethylene) methacrylate) (PMEO) was used as a solid solvent for a series of alkyl viologens. Since PMEO is an excellent ion-conducting polymer, RV was confirmed to be an effective redox mediator in this PMEO. It was concluded in this study that ionic conductivity in the polymer matrix could be used as an effective parameter for prediction of the diffusion coefficient of charged organic molecules.     

Characterization and properties of Eu3+-doped CdWO4 prepared by a hydrothermal method

Eu³⁺-doped CdWO₄ was prepared for the first time by a hydrothermal method. The structure, morphology, and luminescence of the Eu³⁺-doped CdWO₄ were characterized. TEM results revealed that the pure CdWO₄ was a nanorod with a width of about 50 nm. The photoluminescent properties of Eu³⁺-doped CdWO₄ complexes indicated energy transfer from WO₄ ^2? groups to Eu³⁺ and suggested effective doping of Eu³⁺ into the lattice of CdWO₄. The photocatalytic activity of CdWO₄ and Eu³⁺-doped CdWO₄ was investigated by the photodegradation of methyl orange (MO). Eu³⁺-doped CdWO₄ had enhanced photocatalytic activity in the photodegradation of MO. The hydroxyl radical was detected by the terephthalic acid photoluminescence (TA-PL) method, and the regular change revealed that the hydroxyl radical may be the active species.     

CATIONIC CONDUCTIVITY FOR THE CROSSLINKED P [OLIGO (OXYETHYLENE) METHACRYLATE-COoMETHACRYLOYL ALKYLSULFONIC ACID LITHIUM]

Crosslinked copolymers with single Li~+-ionic conductivity were prepared from oligo (oxyethylene) methacrylate (MEO_n), methacryloyl alkylsulfonic acid lithium (SAMLi), and oligo (oxyethylene) dimethacrylate (DMEO_n). Li~+-ionic conductivity of the copolymer is improved by crosslinking and presented as a function of polymerization degree (n) in MEO_n, comonomeric salt concentration (O/Li), and crosslinking degree. The crosslinked copolymer P (0.7 MEO_(14)-0.3DMEO_(14)-SHMLi) without other small molecular additives exhibits an optimum Li~+-ionic conductivity of 1.2×10~(-6) S/cm at 25℃. Dc polarization test in the cell composed of Li/copolymer/Li shows a constant dc ionic conductivity which closes gradually to the ac one with decreasing dc polarization potential.     

Lanthanide(III)‐Based Multicolor Luminescent Hybrid Gel for Amine Sensing

Bridged polysilsesquioxanes (BPs) show great potential in the development of lanthanide‐based luminescent materials, owing to their capacity to loading lanthanide complexes with high concentration and their flexible processability. A novel BP precursor, consisting of a C ₃‐symmetrical benzene central core moiety, capable of sensitizing the luminescence of Eu³⁺ and Tb³⁺ is reported. Tunable, full‐color luminescent gels were facilely prepared by mixing the as‐synthesized precursor and Ln³⁺ ions in appropriate solvents. By either changing the Eu³⁺/Tb³⁺ molar ratio or altering the excitation wavelength, the emission colors of the final gels can be finely tuned. Additionally, the yellow‐colored emissive gel with a molar ratio of Eu³⁺ to Tb³⁺ of 0.5 can be used as an effective ratiometric luminescent sensor for distinguishing amines with lower pK _a (<5) from those with higher pK _a (>9).     

Fluorimetry and differential scanning calorimetry analysis of ionomers with low Eu3+ contents

Fluorimetry and differential scanning calorimetry have been used to characterize ionomers that were synthesized by copolymerization of methyl methacrylate, methacrylic acid, and europium methacrylate (EMA). Under excitation of UV light at 375 nm no self-quenching was found in fluorescence of EMA-containing ionomers at 615 nm within the Eu³⁺ concentration range of 1.6 × 10⁻² to 11.49 × 10⁻² mol %, which means that the distance between two Eu³⁺ ions is larger than 50 Å. In the same concentration range self-quenching took place in europium octanoate (EOA)-containing ionomers in which EOA was doped as an additive. Only one T_g was found for both kinds of polymers within the concentration range of Eu³⁺ ions. For all ion contents studied, T_g values were essentially independent of ion content and values were slightly higher for the EMA containing ionomers. © 1997 John Wiley & Sons, Inc.     

Three Lanthanide Metal‐Organic Frameworks Based on an Ether‐Decorated Polycarboxylic Acid Linker: Luminescence Modulation,CO2 Capture and Conversion Properties

Three new isostructural 3D lanthanide metal–organic frameworks (Ln‐MOFs), {H[LnL(H₂O)]?2 H₂O}_n ( 1‐Ln ) (Ln=Eu³⁺, Gd³⁺ and Tb³⁺), based on infinite lanthanide‐carboxylate chains were constructed by employing an ether‐separated 5,5′‐oxydiisophthalic acid (H₄L) ligand under solvothermal reaction. 1‐Eu and 1‐Tb exhibit strong red and green emission, respectively, through the antenna effect, as demonstrated through a combination of calculation and experimental results. Moreover, a series of dichromatic doped 1‐Eu_xTb_y MOFs were fabricated by introducing different concentrations of Eu³⁺ and Tb³⁺ ions, and they display an unusual variation of luminescent colors from green, yellow, orange to red. 1‐Eu with channels decorated by ether O atoms and the open metal sites displays good performance for CO₂ capture and conversion between CO₂ and epoxides into cyclic carbonates.     

DNA binding and antibacterial properties of ternary lanthanide complexes with salicylic acid and phenanthroline

Twelve ternary lanthanide complexes RE(sal)₃phen (RE³⁺ = La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Tm³⁺, Yb³⁺, Lu³⁺, sal = salicylic acid, phen = phenanthroline) were prepared. Interactions between the complexes and calf thymus DNA (ct‐DNA) were investigated using UV–visible spectrophotometry, fluorescence quench experiment and viscosity measurement. Hypochromicity and red shift of the absorption spectra of complexes were observed in the presence of DNA. The enhanced emission intensity of ethidium bromide (EB) in the presence of DNA was quenched by the addition of lanthanide complexes, which indicated that the lanthanide complexes displaced EB from its binding sites in DNA. Based on the systematic research of the binding constant (K_b) and the fluorescence quenching constant (K_q) of the 12 complexes, we found that the complexes with smaller lanthanide ion radius had stronger binding abilities with DNA. Viscosity measurement showed that the relative viscosity of the DNA solution was enhanced with increasing the amounts of the complexes. All these results suggested that the complexes could bind to DNA and the major binding mode was intercalative binding. Moreover, all these complexes exhibited excellent antibacterial abilities against Escherichia coli. Also, the antibacterial activities of complexes with heavy rare earth were higher than those of complexes with light rare earth. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis, characterization and spectroscopic studies of copolymer of styrene with 4-oxe-4(P-hydroxyl phenylamino) but-2-enoic acid and corresponding fluorescent macromolecular lanthanide(III) complexes

Copolymer of styrene with 4-oxe-4(P-hydroxyl phenylamino) but-2-enoic acid (PSHPEA) and its luminescent lanthanide complexes Ln-PSHPEA (Ln = La, Eu, Tb and Y) were synthesized and characterized by means of elemental analysis, FT-IR, thermogravimetric analysis and fluorescence determination. The results showed that the carboxylic groups on the chain of the copolymer acted as bidentate ligands coordinated to lanthanide ions, but the amido carbonyl groups, amino N and hydroxy groups had not taken part in coordination; the coordination degree of -COO⁻/Ln³⁺ which determined the content of metal ions in the macromolecular complexes, was closely dependent on both the pH value of the solution and the molar ratio of St to 4-oxe-4(P-hydroxyl phenylamino) but-2-enoic acid in the polymer ligand. The fluorescence determination showed that the complexes exhibited characteristic fluorescence with comparatively high brightness and good mono-chromaticity. Typical relationship between emission intensity and Ln³⁺ ions content in macromolecular complexes exhibited some extent of fluorescence concentration quenching in our studies. The emission intensity of Tb-PSHPEA complexes was much stronger than that of Eu-PSHPEA complexes, which was attributed to especial effectivity in transferring energy from the lowest triplet energy level of the ligand onto the excited state (⁵D₀) of Tb³⁺ ion than that (⁵D₄) of Eu³⁺ ion.     

The preparation,characterization, photoelectrochemical and photocatalytic properties of lanthanide metal-ion-doped TiO2 nanoparticles

Lanthanide metal-ion-doped TiO₂ nanoparticles were prepared with hydrothermal method and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP) and fluorescence spectrum. The results showed that a small part of metal ions entered into the lattice of TiO₂ and others adsorbed on the surface of TiO₂. The photoelectrochemical and photocatalytic properties of these lanthanide metal-ion-doped TiO₂ nanoparticles were investigated and the results showed that the photoresponse of Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ electrodes were much larger and that of Sm³⁺-doped TiO₂ electrode was a little larger than that of undoped TiO₂ electrode, indicating that the photogenerated carriers were separated more efficiently in Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ nanoparticles than in undoped TiO₂ nanoparticles. The photocatalytic degradation of rhodamine B (RB) was conducted in the suspension of lanthanide metal-ion-doped TiO₂ nanoparticles, and its first-order reaction rate constant (k) and average initial rate (r_ini) were significantly higher in the presence of Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ nanoparticles than those in the presence of undoped TiO₂ nanoparticles. The enhanced photocatalytic degradation rate of RB in the presence of Eu³⁺-, La³⁺-, Nd³⁺- and Pr³⁺-doped TiO₂ nanoparticles is attributed to increased charge separation in these systems. The effect of the content of La³⁺ on the reaction parameters (k and r_ini) was also investigated and the result showed that there was an optimal value (ca. 0.5%) of the content of La³⁺ to make the rate constant (k) and average initial rate (r_ini) reach the maxima.     

The Role of Ligand Topology in the Decomplexation of Luminescent Lanthanide Complexes by Dipicolinic Acid

In this study, we present the aqueous solution behavior of two luminescent lanthanide antenna complexes (Eu³⁺? 1 , Dy³⁺? 9 ) with different ligand topologies in the presence of dipicolinic acid (DPA, pyridine‐2,6‐dicarboxylic acid). Macrocyclic (1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid, DO3A, 9 ) and acyclic (1,4,7‐triazaheptane‐1,1,7,7‐tetraacetic acid, DTTA, 1 ) ligands have been selected to form a ratiometric pair in which Dy³⁺? 9 acts as a reference and Eu³⁺? 1 acts as a probe for the recognition of DPA. The pair of luminescent complexes in water reveals the capability to work as a DPA luminescent sensor. The change of emission intensity of Eu³⁺ indicates the occurrence of a new sensitization path for the lanthanide cation through excitation of DPA. NMR evidence implies the presence of free 1 and mass spectrometry shows the formation of emitting [EuDPA₂]^? as a result of a ligand exchange reaction.     

Poly(vinylamine) complexes with f‐block salts from the lanthanide series that exhibit significant glass‐transition temperature enhancement

Six f‐block salts from the lanthanide series form complexes with poly(vinyl amine) and increase the glass‐transition temperature of the polymer. Results for poly(vinylamine) complexes with EuCl₃(H₂O)₆ and TbCl₃(H₂O)₆ surpass those for d⁷ cobalt complexes that were studied previously. The glass‐transition temperature increases by 49 °C per mol % Eu³⁺ and 50 °C per mol % Tb³⁺, up to 2 mol % of the f‐block cations. At 5 mol % Eu³⁺, T_g is slightly higher than 250 °C with no visual evidence of thermal degradation of either component in the complex. This corresponds to a T_g enhancement of almost 200 °C with respect to the undiluted polymer. The increases in T_g for these lanthanide complexes with poly(vinylamine) obey the following trend: up to 2 mol % of the f‐block cation. With the exception of Gd(CH₃COO)₃, which contains different anionic ligands than all of the other trichlorides, this trend correlates inversely with the highest dehydration/dehydrochlorination temperature of each undiluted lanthanide salt, as measured via calorimetry above the melting point and verified by thermogravimetry. Waters of hydration and amino sidegroups undergo ligand substitution in the coordination sphere of the lanthanides. Since lanthanide cations are classified as hard acids, it is not unreasonable that they form complexes with the nitrogen lone pair in the amino sidegroup of the polymer, which is classified as a hard base. Micro‐clustering of several amino side groups reduces chain mobility significantly in the vicinity of each metal center, produces coordination crosslinks, and increases T_g. Complementary solution studies reveal that hydrogels form with swelling ratios between 20 and 50 at Eu³⁺ mole fractions between 0.01 and 0.05 with respect to poly(vinylamine). Infrared spectroscopic observations suggest that the amino nitrogen lone pair in poly(vinylamine) interacts with these lanthanide metal centers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1931–1938, 2000