Modified dipicolinic acid ligands for sensitization of europium(III) luminescence

The effect of substitution at the 4 and 3,5 positions in the pyridine ring of europium(III) pyridine-2,6-dicarboxylate complexes has been investigated with particular emphasis on sensitization of the Eu3+ ion. Sensitization of the Eu3+ 615-nm emission was achieved through excitation of the ligands in which the 4 substituent was -H, -OH, and -Cl and the 3,5 position was -H. In these cases, the ligand-to-Eu3+ ratio was confirmed as being 3:1. The sensitization was found to increase following substitution of the 4 position in the order Cl > H > OH. This is attributed to energy transfer occurring from the ligands into different Eu3+ intra-atomic energy levels, with spin selection rules governing the efficiency of this process. The Eu3+ luminescence lifetime was measured and found to vary from 1.16 to 2.90 ms depending on the excitation energy, ligand, and solvent. For the case of the 3,5-dibromo-4-hydroxy derivative, no sensitization was observed and a ligand-to-Eu3+ ratio of 1:1 was found. The solubility of these complexes in water and their long emission lifetime make them attractive for use as probes in biological systems.     

Crystal structure and luminescence of europium(III) acrylate

The atomic structure of europium acrylate crystals [Eu₂(Acr)₅OH·3H₂O]·2(0.5H₂O) was studied by X-ray analysis (a = 24.360(3) Å, b = 18.466(2) Å, c = 8.5818(9) Å, β = 96.087(2)°, space group C2/c, Z = 6, ρ_calc = 2.036 g/cm³). The crystal structure involves chains of binuclear [Eu₂(C₃H₃O₂)₅OH·3H₂O] molecules, running infinitely in the [101] direction and having pairs of C₉H₉EuO₇H₂O molecules alternating with C₆H₆EuO₄OH·2H₂O molecules that link the pairs. The infinite chains are linked by hydrogen bonds and van der Waals interactions. The thermal behavior of luminescence of the europium(III) complex is discussed.     

Anti-Stokes luminescence of europium(III)-doped lanthanum oxychloride

The anti-Stokes luminescence from the ⁵D_1,2,3 levels of Eu³⁺-doped LaOCl was observed at 300 and 77 K under dye-laser excitation to the ⁵D₀ level. A two-photon absorption from the ⁷F₀ ground level to charge-transfer states via the ⁵D₀ level was concluded to be the mechanism involved. The absorption of the first photon through the forbidden ⁵D₀→⁷F₀ transition determines the upconversion efficiency. The two-photon absorption seems to occur as an intra-ion process without interionic energy transfer.     

Effects of polarity and temperature on photoluminescence of a europium(III) chelate

The relative photoluminescence yield for (1,10-phenanthroline)europium(III) tris-thenoyltrinuoroacetonate (Eu(tta)₃Phen). an efficient enhancer of chemiluminescence, has been measured under the conditions (temperatures and solvents) specific for the oxidation of hydrocarbons. The yield is independent of viscosity and the presence of a heavy atom in the solvent, but the higher the polarity of the medium, the more the yield decreases as the temperature increases. The effect is interpreted as an acceleration of radiationless deactivation occurringvia the mechanism of electron transfer from a ligand to the excited Eu³⁺ ion.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1686–1690, July, 1996.     

Laser-induced luminescence study of europium(III) polyacrylate and polymaleate complexes

Luminescence lifetime of Eu(III) in polyacrylate and polymaleate complexes has been measured to evaluate the number of water molecules bound to the ion. The number of residual water molecules hydrated to Eu(III) in the polyacrylate and polymaleate complexes ranged from 3.5 to 4.5 when the supporting electrolyte concentration was 0.01. The residual hydration number decreased with the addition of supporting electrolyte. These results indicate that Eu(III) is surrounded by polymolecular ligands in these complexes.     

Dioxo-bridged dinuclear manganese(III) and -(IV) complexes of pyridyl donor tripod ligands: combined effects of steric substitution and chelate ring size variations on structural,spectroscopic, and electrochemical properties

The syntheses and structural, spectral, and electrochemical characterization of the dioxo-bridged dinuclear Mn(III) complexes [LMn(mo-O)(2)MnL](ClO(4))(2), of the tripodal ligands tris(6-methyl-2-pyridylmethyl)amine (L(1)) and bis(6-methyl-2-pyridylmethyl)(2-(2-pyridyl)ethyl)amine (L(2)), and the Mn(II) complex of bis(2-(2-pyridyl)ethyl)(6-methyl-2-pyridylmethyl)amine (L(3)) are described. Addition of aqueous H(2)O(2) to methanol solutions of the Mn(II) complexes of L(1) and L(2) produced green solutions in a fast reaction from which subsequently precipitated brown solids of the dioxo-bridged dinuclear complexes 1 and 2, respectively, which have the general formula [LMn(III)(mu-O)(2)Mn(III)L](ClO(4))(2). Addition of 30% aqueous H(2)O(2) to the methanol solution of the Mn(II) complex of L(3) ([Mn(II)L(3)(CH(3)CN)(H(2)O)](ClO(4))(2) (3)) showed a very sluggish change gradually precipitating an insoluble black gummy solid, but no dioxo-bridged manganese complex is produced. By contrast, the Mn(II) complex of the ligand bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine (L(3a)) has been reported to react with aqueous H(2)O(2) to form the dioxo-bridged Mn(III)Mn(IV) complex. In cyclic voltammetric experiments in acetonitrile solution, complex 1 shows two reversible peaks at E(1/2) = 0.87 and 1.70 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and the Mn(III)Mn(IV) <--> Mn(IV)(2) processes, respectively. Complex 2 also shows two reversible peaks, one at E(1/2) = 0.78 V and a second peak at E(1/2) = 1.58 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and Mn(III)Mn(IV) <--> Mn(IV)(2) redox processes, respectively. These potentials are the highest so far observed for the dioxo-bridged dinuclear manganese complexes of the type of tripodal ligands used here. The bulk electrolytic oxidation of complexes 1 and 2, at a controlled anodic potential of 1.98 V (vs Ag/AgCl), produced the green Mn(IV)(2) complexes that have been spectrally characterized. The Mn(II) complex of L(3) shows a quasi reversible peak at an anodic potential of E(p,a) of 1.96 V (vs Ag/AgCl) assigned to the oxidation Mn(II) to Mn(III) complex. It is about 0.17 V higher than the E(p,a) of the Mn(II) complex of L(3a). The higher oxidation potential is attributable to the steric effect of the methyl substituent at the 6-position of the pyridyl donor of L(3).     

Cationic rhodium hydrogenation catalysts containing chelating diphosphine ligands: effect of chelate ring size

Earlier studies on the [(1,2-bis(diphenylphosphino)ethane)rhodium]^p+-catalyzed hydrogenation of 1-hexene and methyl-(Z)-α-acetamidocinnamate have been extended to catalysts containing larger chelating diphosphine ligands, i.e., Ph₂P(CH₂)_nPPh₂, where n = 3, 4 and 5. Comparisons include measurements of equilibrium constants for the binding of the olefinic substrates to the catalysts and of the catalytic hydrogenenation rates. Some related measurements also are reported for the corresponding catalyst systems containing the chiral ligand, 4R,5R-bis(diphenylphosphinomethyl)-2,2,-dimethyldioxalane (DIOP) and non-chelating PPh₃ ligands.     

Synthesis,crystal structure,and luminescence properties of a novel europium(III) complex

A novel europium(III) complex, [Eu(C₇H₅O₂)₂(C₇H₆O₂)₂(C₁₂H₈N₂)₂Cl], was synthesized and characterized by elemental analysis and single-crystal X-ray determination. It crystallizes in the monoclinic system, space group Cc with a = 17.2814(16), b = 17.9421(17), c = 14.9971(14) Å, β = 101.6510(10)°, Z = 4, ρ _c = 1.508 g/cm³, μ = 1.496 mm^?1, the final R = 0.0516 and wR = 0.1267 for 6435 observed reflections with I > 2σ(I). Structural analysis shows that the Eu(III) atom is nine-coordinated by one chlorine atom, four N atoms of two 1,10-phenanthroline (Phen) ligands, and four O atoms from four carboxybenzene ligands, to form a distorted tricapped trigonal prism. The luminescence spectrum of the complex indicates that the intensity of the emission wavelength at 612 nm is strongest among all emission wavelengths and the second phen ligand shows an enhancement effect on the luminescence of the complex.     

Synthesis,crystal structure,and luminescence properties of a one-dimensional europium(III) polymer

In the title complex, [Eu₂(C₈H₇O₃)₆(C₁₂H₈N₂)₂] _n , which has an inversion center midway between two Eu(III) atoms of the structural unit, forms a one-dimensional polymer bridged by two mondentate, two bidentate, and two tridentate carboxylate groups with an Eu-Eu separation of 4.1853(7) Å. Each Eu atom is nine-coordinated by two N atoms of a 1,10-phenanthroline (phen) ligand and seven O atoms from six phenoxyacetate ligands, to form a distorted tricapped trigonal prismatic. The luminescence spectrum of the polymer indicates that the intensity of the emission wavelength at 619 nm is the strongest among all emission wavelengths and the second phen ligand shows an enhancement effect on the luminescence of the complex.     

Phosphine-phosphite ligands: chelate ring size vs. activity and enantioselectivity relationships in asymmetric hydrogenation

A series of new phosphine-phosphite ligands P(C)(n)OP (n = 1-4) have been synthesized and used for rhodium-catalyzed asymmetric hydrogenation of prochiral olefins in order to study the effect of the chelate ring size. Excellent ees (up to 97.5%) were obtained in the hydrogenation of dimethyl itaconate and an increase of activity and enantioselectivity was observed in the hydrogenation of (Z)-α-acetamidocinnamic acid methyl ester with the increasing length of the backbone of the ligands.     

Sensitization of Eu(III) luminescence by donor-phenylethynyl-functionalized DTPA and DO3A macrocycles

The synthesis and complexation to Eu(III) of two macrocyclic ligands functionalized donor-phenylethynyl-moieties as sensitizer is presented. The two ligands based on DTPA bis-amide ([Eu(L¹)]) and DO3A ([Na][Eu(L²)]) have been chosen because of their increased stability in water for potential applications as luminescent bioprobes for one- or two-photon excited scanning microscopy. The DTPA and DO3A ligands possess oxygen or sulfur donor atoms, respectively, connected to a triethyleneglycol (PEG) chain to ensure the water solubility. The optical properties were studied and reveal that ([Eu(L¹)]) present a lower brightness than the ([Na][Eu(L²)]) counterpart because of its inner sphere water molecule coordination that quenches the emission. On the other hand, [Na][Eu(L²)] exhibits excellent spectroscopic properties with high quantum yield ? = 0.284, and brightness B = 10,220 M^?1cm^?1(defined as ?.?). Unfortunately, the two-photon cross-section of this last complex was measured to be only 4 GM limiting its potential applications to linear microscopy.     

Complexation of lactate with neodymium(III) and europium(III) at variable temperatures: studies by potentiometry, microcalorimetry, optical absorption, and luminescence spectroscopy

The complexation of neodymium(III) and europium(III) with lactate was studied at variable temperatures by potentiometry, absorption spectrophotometry, luminescence spectroscopy, and microcalorimetry. The stability constants of three successive lactate complexes (ML(2+), ML(2)(+), and ML(3)(aq), where M stands for Nd and Eu and L stands for lactate) at 10, 25, 40, 55, and 70 °C were determined. The enthalpies of complexation at 25 °C were determined by microcalorimetry. Thermodynamic data show that the complexation of trivalent lanthanides (Nd(3+) and Eu(3+)) with lactate is exothermic and the complexation becomes weaker at higher temperatures. Results from optical absorption and luminescence spectroscopy suggest that the complexes are inner-sphere chelate complexes in which the protonated α-hydroxyl group of lactate participates in the complexation.     

Facile synthesis and luminescence properties of europium(III)-doped silica nanotubes

Photoluminescent nanomaterials had emerged as an amazing field in a wide range of applications during the past few decades. In this article, fibrous europium tartrates and photoluminescent silica nanotubes were conveniently synthesized by using sol–gel method, in which europium ions entered silica matrix. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, fourier transform infrared spectra, energy-dispersive X-ray spectroscopy and photoluminescence (PL) spectra analysis were used to characterize the growth, structure, morphology and optical property of the products. The results indicated that europium tartrates nanofibers as a template can transform tetraethylorthosilicate into silica nanotubes effectively. Meanwhile, europium(III) was transferred from the fibers to the tubes successfully. A hard template mechanism was proposed to explain the formation process of europium(III)-doped silica nanotubes. Moreover, different morphologies of silica-based nanomaterials were obtained due to varying NH₄OH addition or stirring time. PL spectra from nanofiber and nanotube show a typical emission of europium(III), and 13 % is the quenching concentration of europium(III) in silica matrix for this system. The novel silica nanotubes can be applied potentially in optical and biological areas.     

Oxygen catalyzed mobilization of iron from ferritin by iron(III) chelate ligands

Tridentate chelate ligands of 2,6-bis[hydroxy(methyl)amino]-1,3,5-triazine family rapidly release iron from human recombinant ferritin in the presence of oxygen. The reaction is inhibited by superoxide dismutase, catalase, mannitol and urea. Suggested reaction mechanism involves reduction of the ferritin iron core by superoxide anion, diffusion of iron(II) cations outside the ferritin shell, and regeneration of superoxide anions through oxidation of iron(II) chelate complexes with molecular oxygen.     

High luminescence quantum yields and long luminescence lifetime from Eu(III) complex containing two crystal water based on a new beta-diketonate ligand

New members of family of Eu(III) complex based on the thenoylacetophenone have been synthesized and characterized. The compounds were found for high metal luminescence quantum yields and long luminescence lifetime, especially for compound with two crystal water, corresponding with other compounds containing two crystal water. The result is attributed to high molar absorption coefficients of the Eu(III) complex according to UV-vis and emission spectra. The high molar absorption coefficients balance quenching effect from OH oscillators of water contained in compound.     

Sensitization of lanthanoid luminescence by organic and inorganic ligands in lanthanoid-organic-polyoxometalates

The reaction of terbium and europium salts with the lacunary polyxometalate (POM) [As(2)W(19)O(67)(H(2)O)](14-) and 2-picolinic acid (picH) affords the ternary lanthanoid-organic-polyoxometalate (Ln-org-POM) complexes [Tb(2)(pic)(H(2)O)(2)(B-β-AsW(8)O(30))(2)(WO(2)(pic))(3)](10-) (1), [Tb(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (2), and [Eu(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (3). A detailed synthetic investigation has established the conditions required to isolate pure bulk samples of the three complexes as the mixed salts H(0.5)K(8.5)Na[1]·30H(2)O, K(4)Li(4)H(4)[2]·58H(2)O, and Eu(1.66)K(7)[3]·54H(2)O, each of which has been characterized by single crystal X-ray diffraction. Complexes 2 and 3 are isostructural and can be considered to be composed of two molecules of 1 linked through an inversion center with four additional picolinate-chelated lanthanoid centers. When irradiated with a laboratory UV lamp at room temperature, compounds K(4)Li(4)H(4)[2]·58H(2)O and Eu(1.66)K(7)[3]·54H(2)O visibly luminesce green and red, respectively, while compound H(0.5)K(8.5)Na[1]·30H(2)O is not luminescent. A variable temperature photophysical investigation of the three compounds has revealed that both the organic picolinate ligands and the inorganic POM ligands sensitize the lanthanoid(III) luminescence, following excitation with UV light. However, considerably different temperature dependencies are observed for Tb(III) versus Eu(III) through the two distinct sensitization pathways.     

Chiral sensing using an achiral europium(III) complex by induced circularly polarized luminescence

[Eu(bda)(2)](-) (bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) produces intense circularly polarized luminescence (CPL) in aqueous solutions in the presence of (S)-2-pyrrolidone-5-carboxylic acid upon UV irradiation, although the molecular structure of the europium(III) complex is achiral. The mechanism for the induction of CPL was preliminarily attributed to distortions induced by association with an amino acid to generate chirality in the achiral complex. The optical anisotropy factor (g(lum) value) for the (5)D(0) → (7)F(1) transition was 0.03 in the presence of 1.0 mol dm(-3) of the amino acid. Analysis of the CPL intensity as a function of the amino acid concentration gave an association constant between those of [Eu(bda)(2)](-) and the amino acid, K(aso) = 0.55 ± 0.09 mol(-1) dm(3). These results demonstrate the potential of [Eu(bda)(2)](-) to act as a luminescent chiral-sensing reagent in microscopic spectroscopy.     

Tetracycline determination by sensitized luminescence of europium(III) sorbed on silica with chemically grafted iminodiacetic acid

The formation of mixed-ligand europium(III) complexes with tetracycline and iminodiacetic acid grafted to the surface of silica has been studied. This complex is suggested for luminescence determination of tetracycline in solutions.