Luminescent Eu(III) and Gd(III) trisbipyridine cryptates: experimental and theoretical study of the substituent effects.

Synthesis, absorption spectra and luminescebce properties of a series of lanthanide trisbipyridine cryptates Ln within R-Bpy x R-Bpy x R-Bpy, where Ln = Eu, Gd and R = H, COOH, COOCH3, CONH(CH2)2NH2 are described. Comparison of the unsubstituted parent compound with the substituted compounds shows that bipyridine substitution doesn't alter significantly the photophysical properties of the lanthanide cryptate. The absorption maximum is slightly red-shifted when three bipyridines are substituted, whereas substituting one bipyridines has a negligible effect on the absorption spectra. The experimental triplet state energy is between 21600 and 22 100 cm(-1) for the series of compounds and the luminescence lifetimes at 77 K are between 0.5 and 0.8 ms in HO2 and equal to 1.7 ms in D2O. The experimental characterizations are completed by DFT and TD-DFT calculations to assess the ability of these approaches to predict absorption maxima, triplet state energies and structural parameters of lanthanide cryptates and to characterize the electronic structure of the excited states. The calculations on the unsubstituted parent and substituted compounds show that absorption maxima and lowest 3pipi* triplet state energies can be accurately determined from density functional theory (DFT) and time-dependent (TD) DFT calculations.     

Photoacoustic spectroscopy study on intramolecular energy transfer and relaxation processes of Tb(III) complexes

The photoacoustic (PA) amplitude spectra and luminescence spectra of different Tb(III) complexes (Tb(AA)3.2H2O Na[Tb(AA)4], Tb(AA)3bpy and Tb(AA)3phen) have been measured, and the PA phase shifts of the different complexes calculated. Combined with the luminescence spectra, the PA amplitude spectra reflected the variation of the luminescence efficiency and the PA phase is directly relative to the relaxation processes. According to the variation of the luminescence efficiency and the phase shift, the intramolecular energy transfer and relaxation processes of different Tb(III) complexes were discussed.     

Nitro-functionalization and luminescence quantum yield of Eu(III) and Tb(III) benzoic acid complexes

In our pursuit of luminescent lanthanide ion-based coordination polymers, we have isolated several complexes with nitrobenzoic acid ligands and characterized these by X-ray crystallography and luminescence spectroscopy. 2-Nitrobenzoic acid reacts with Eu(III) to form 1, which crystallizes in the P-1 space group, with a = 12.385(3), b = 12.912(3), c = 17.889(4) A, alpha = 97.49(3), beta = 109.64(3) and gamma = 101.99(3) degrees . 3-Nitrobenzoic acid forms a one-dimensional coordination polymer with Eu(III), 2, which crystallizes in the triclinic space group P-1 with a = 9.7100(19), b = 10.579(2), c = 13.361(3) A, alpha = 77.41(3), beta = 88.78(3) and gamma = 88.16(3) degrees. Structures 3 and 4 correspond to the isostructural one-dimensional coordination polymers of Eu(III) and Tb(III), respectively, with the 4-nitrobenzoato anion. These crystallize in the triclinic space group P-1 with a = 9.2242(18), b = 15.102(3), c = 18.587(4) A, alpha = 75.93(3), beta = 82.88(3) and gamma = 79.00(3) degrees for 3 and a = 9.2692(19), b = 15.369(3), c = 18.353(4) A, alpha = 75.37(3), beta = 81.32(3) and gamma = 78.15(3) degrees for 4. Potentiometry, absorption and NMR spectroscopy indicate that in solution only 1 : 1 species are present. All compounds are weakly luminescent as solids and the photophysics of solutions of ligands with Ln(III) in 1 : 1 stoichiometry were studied. Quantum yields around 1 and 3% for Eu(III)-and Tb(III)-containing methanolic solutions were measured.     

Polyorganosiloxane-europium (III) host-guest inclusion system and its energy transfer luminescence

The Eu(III) ion, as a luminescent probe, is incorporated into a novel nanotube-contained polyorganosiloxane (POS), which is obtained by coupling of ladderlike polyvinylsilsesquioxane (Vi-T) with tetramethyldisiloxane (H-MM) via hydrosilylation, to form POS-Eu(III) composite. The results from fluorescent study demonstrate that the composite is actually a host-guest clathrate which includes the Eu(III) ions in the tubelike cavity of POS and moreover, the supramolecular clathrate exhibits an obvious energy transfer process which converts the UV light absorbed by POS into the visible light generated from the Eu(III) luminescence. Molecular simulation also gives support to the formation of such a clathrate and thus results in energy transfer process. Project supponed by the Research Foundation of Molecular Science Center and Director of Institute of Chemistry, the Chinese Academy of Sciences, and Foundation of Organic Solid Laboratory, the Chinese Academy of Sciences.     

Eu(III) and Tb(III) luminescence sensitized by thiophenyl-derivatized nitrobenzoato antennas

Thiophenyl-derivatized nitrobenzoic acid ligands have been evaluated as possible sensitizers of Eu(III) and Tb(III) luminescence. The resulting solution and solid-state species were isolated and characterized by luminescence spectroscopy and X-ray crystallography. The Eu(III) complex with 2-nitro-3-thiophen-3-yl-benzoic acid, 1, crystallizes in the monoclinic space group C2/c with a = 28.569(3) A, b = 17.7726(18) A, c = 17.7073(18) A, beta= 126.849(2) degrees, and V = 7194.6(13) A3. The Tb(III) complex with this ligand, 2, is isostructural, and its cell parameters are a = 29.755(6) A, b = 18.123(4) A, c = 19.519(4) A, beta= 130.35(3) degrees, and V = 8021(3) A3. Eu(III) crystallizes with 3-nitro-2-thiophen-3-yl-benzoic acid as a triclinic complex, 3, in the space group P1 with a = 11.045(2) A, b = 12.547(3) A, c = 15.500(3) A, alpha = 109.06(3)degrees, beta = 94.79(3) degrees, gamma = 107.72(3) degrees. and V = 1893.5(7) A3. With the ligand 5-nitro-2-thiophen-3-yl-benzoic acid, Eu(III) yields another molecular compound, 4, triclinic P1, with a = 10.649(2) A, b = 14.009(3) A, c = 15.205(3) A, alpha= 112.15(3) degrees, beta = 100.25(3) degrees, gamma = 106.96(3) degrees, and V = 1900.5(7) A3. All compounds dissolve in water and methanol, and the methanolic solutions are luminescent. The solution species have a metal ion-to-ligand ratio of 1:1. The quantum yields have been determined to be in the range of 0.9-3.1% for Eu(III) and 4.7-9.8% for Tb(III). The highest values of these correspond to the most intense luminescence reported for Ln(III) solutions with this type of sensitizer. The lifetimes of luminescence are in the range of 248.3-338.9 micros for Eu(III) and 208.6-724.9 micros for Tb(III). The stability constants are in the range of log 11 = 2.73-4.30 for Eu(III) and 3.34-4.18 for Tb(III) and, along with the energy migration pathways, are responsible for the reported efficiency of sensitization.     

The influence of triplet energy levels of bridging ligands on energy transfer processes in Ir(III)/Eu(III) dyads

A series of N^N,O^O-bridging ligands based on substituted 1-(pyridin-2-yl)-3-methyl-5-pyrazolone and their corresponding heteroleptic iridium(III) complexes as well as Ir-Eu bimetallic complexes were synthesized and fully characterized. The influence of the triplet energy levels of the bridging ligands on the energy transfer (ET) process from the Ir(III) complexes to Eu(III) ions in solution was investigated at 77 K in Ir(III)/Eu(III) dyads. Photophysical experiment results show the bridging ligands play an important role in the ET process. Only when the triplet energy level of the bridging ligand was lower than the triplet metal-to-ligand charge transfer ((3)MLCT) energy level of the Ir moiety, was pure emission from the Eu(III) ion observed, implying complete ET took place from the Ir moiety to the Eu(III) ion.     

Polarographic study of Eu(III)-succinate-ethylenediamine and Eu(III)-malonate-ethylenediamine mixed systems

The mixed complexes of Eu(III) with succinate (succ^2?) and malonate (mal^2?) and ethylenediamine (en) have been studied polarographically at 25°C and at constant ionic strength, μ = 0.1 (NaNO₃) and pH 6. The reduction of the complexes in each case is quasi-reversible and diffusion-controlled. In each system three mixed complexes are formed, viz. [Eu(succ)(en)]⁺, [Eu(succ)(en)2]⁺ and [Eu(succ)₂(en)]^? with stability constants log β₁₁ = 9.2, log β₁₂ = 17.5 and log β₂₁ = 11.7; and [Eu(mal)(en)]⁺, [Eu(mal)₂(en)₂]^? and [Eu(mal)₃(en)]^3? with stability constants log β₁₁ = 11.4, log β₂₂ = 19.08 and log β₃₁ = 13.5 respectively.     

Quantum efficiency of the luminescence of Eu(III), Tb(III) and Dy(III) in aqueous solutions

Summary The luminescence quantum efficiency of Eu(III), Tb(III) and Dy(III) in chloride solutions as well as complexed by aminopolyacetic acids was determined. An interpretation of the observed dependences in the system investigated has been proposed.

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Die Lumineszenz-Quantenausbeute von Eu(III), Tb(III) und Dy(III) in wäßrigen Lösungen

Zusammenfassung Die Lumineszenz-Quantenausbeute von Eu(III), Tb(III) und Dy(III) in Chloridlösung und in Komplexen mit Aminopolyessigsäuren wurde bestimmt. Eine Interpretation der beobachteten Abhängigkeiten im untersuchten System wurde vorgeschlagen.

     

Probing the binding of Tb(III) and Eu(III) to the hammerhead ribozyme using luminescence spectroscopy

BACKGROUND: Divalent metal ions serve as structural as well as catalytic cofactors in the hammerhead ribozyme reaction. The natural cofactor in these reactions is Mg(II), but its spectroscopic silence makes it difficult to study. We previously showed that a single Tb(III) ion inhibits the hammerhead ribozyme by site-specific competition for a Mg(II) ion and therefore can be used as a spectroscopic probe for the Mg(II) it replaces. RESULTS: Lanthanide luminescence spectroscopy was used to study the coordination environment around Tb(III) and Eu(III) ions bound to the structurally well-characterized site on the hammerhead ribozyme. Sensitized emission and direct excitation experiments show that a single lanthanide ion binds to the ribozyme under these conditions and that three waters of hydration are displaced from the Tb(III) upon binding the RNA. Furthermore, we show that these techniques allow the comparison of binding affinities for a series of ions to this site. The binding affinities for ions at the G5 site correlates linearly with the function Z(2)/r of the aqua ion (where Z is the charge and r is the radius of the ion). CONCLUSIONS: This study compares the crystallographic nature of the G5 metal-binding site with solution measurements and gives a clearer picture of the coordination environment of this ion. These results provide one of the best characterized metal-binding sites from a ribozyme, so we use this information to compare the RNA site with that of typical metalloproteins.     

Luminescence and energy transfer in poly(N-vinylcarbazole) blends doped by a highly anisometric Eu(III) complex

Highly fluorescent blends based on PVK (poly(N-vinylcarbazole)) doped by a new greatly anisometric Eu(III) mesogenic complex were described. The structure of the ligands in the complex was selected in such a way that its absorption maximum was close to the emission maximum of the polymer. The full-energy transfer conditions in the conjugated polymer–lanthanide complex blends were revealed. Improving luminescence efficiency of the blend occurs due to an increase in the threshold concentration of the emitting ions to prevent self-quenching phenomena. The resulting relative luminescence quantum yield of the blend increases more than twice in comparison with the individual complex. The optimized blends may be promising for application as red emitters for OLED, etc.     

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxamide derivatives and their luminescence properties

A novel ligand, N2,N6-bis[2-(3-methylpyridyl)]pyridine-2,6-dicarboxamide (L2) and the corresponding Eu(III) and Tb(III) hydrochlorate complexes have been synthesized and characterized in detail based on elemental analysis, IR and NMR. The crystal and molecular structure of the complexes was determined by X-ray crystallography. The Eu(III) and Tb(III) ions were found to coordinate to the amido nitrogen atoms and pyridine nitrogen atoms. The luminescence properties of lanthanide complexes in solid state, in different solutions and in different pH value were investigated. The result shows that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes, and the ligand (L2) is an excellent sensitizer to Tb(III) ion.     

A binaphthyl-containing Eu(III) complex and its interaction with human serum albumin: a luminescence study

On binding to human serum albumin (HSA), the Eu(III) luminescent emission enhancement of a complex containing a binaphthyl chromophore enables the determination of binding constants, showing no chiral discrimination for the (R)- (K= 8200 +/- 810 M(-1)) and (S)-enantiomers (K= 7710 +/- 460 M(-1)).     

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.     

Tremendous impact of substituent group on the extraction and selectivity to Am(III) over Eu(III) by diaryldithiophosphinic acids: experimental and DFT analysis

Comparative extraction of Am³⁺ over Eu³⁺ from nitric acid media by three dithiophosphinic acids (L) bearing different substituent aryl groups was studied. Within the experimental pH range, the distribution ratio of Am³⁺ and Eu³⁺ increases with the increase of pH due to deprotonation of the acidic extractant. Both the extraction and separation ability toward Am³⁺/Eu³⁺ by these extractants were affected drastically by the substituent aryl groups. The bis-phenyl substituted extractant shows almost no ability to extract and separate Am³⁺ from Eu³⁺, while bis(ortho-trifluoromethylphenyl) dithiophosphinic acid has the optimum extraction and separation capabilities. To help reveal the complexation and extraction behavior, the structure and bonding characters of neutral ML₃ (M?=?Am or Eu) complexes as well as the biphasic extraction reaction were studied by density functional theory (DFT). The conduct-like screening model implicit solvation model was used to simulate the extraction reaction in the aqueous-toluene biphasic system. The calculated sequence of the Gibbs free energy difference of extraction (ΔΔG ^Am/Eu_ext ) is consistent with the experimental results.

     

Role of the ancillary ligand N,N-dimethylaminoethanol in the sensitization of Eu(III) and Tb(III) luminescence in dimeric beta-diketonates

Two types of dimeric complexes [Ln2(hfa)6(mu2-O(CH2)2NHMe2)2] and [Ln(thd)2(mu2,eta2-O(CH2)2NMe2)]2 (Ln = YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) are obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the beta-diketonate. In [Tb2(hfa)6(mu2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1...Tb2 separation of 3.684(1) A. In [Tb(thd)2(mu2,eta2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1...Tb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 degrees C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield Q(L)Ln = 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped (0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the beta-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both beta-diketonates. Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.     

Particulate and soluble Eu(III)-chelates as donor labels in homogeneous fluorescence resonance energy transfer based immunoassay

Many well-established homogeneous separation free immunoassays rely on particulate label technologies. Particles generally contain a high concentration of the embedded label and they have a large surface area, which enables conjugation of a large amount of protein per particle. Eu(III)-chelate dyed nanoparticles have been successfully used as labels in heterogeneous and homogeneous immunoassays. In this study, we compared the characteristics of two homogeneous competitive immunoassays using either soluble Eu(III)-chelates or polystyrene particles containing Eu(III)-chelates as donors in a fluorescence resonance energy transfer based assay. The use of the particulate label significantly increased the obtained sensitized emission, which was generated by a single binding event. This was due to the extremely high specific activity of the nanoparticle label and also in some extent the longer Förster radius between the donor and the acceptor. The amount of the binder protein used in the assay could be decreased by 10-fold without impairing the obtainable sensitized emission, which subsequently led to improved assay sensitivity. The optimized assay using particulate donor had the lowest limit of detection (calculated using 3 × S.D. of the 0 nM standard) 50 pM of estradiol in the assay well, which was approximately 20-fold more sensitive than assays using soluble Eu(III)-chelates.     

Terminal group effects on the fluorescence spectra of Eu(III) nitrate complexes with a family of amide-based 1,10-phenanthroline derivatives

Four ligands 1,10-phenanthroline-5,6-bis(N,N-dibenzyl-1′-oxopropylamide) (L^a) 1,10-phenanthroline-5,6-bis(N-methyl-N-benzyl-1′-oxopropylamide) (L^b) 1,10-phenanthroline-5,6-bis(N-benzyl-1′-oxopropylamide) (L^c) and 1,10-phenanthroline-5,6-bis(N,N-diethyl-1′-oxopropylamide) (L^d), and their lanthanide(III) (La and Eu) complexes were synthesized. The complexes were characterized by elemental analysis, IR, fluorescence spectroscopy and conductivity. The lanthanide atoms are coordinated by O atoms from C=O, Ar–O –C and N atoms from phen With the difference of the ligands, the fluorescent intensities of the Eu(III) complexes vary regularly in the THF solution. Some factors that influence the fluorescent intensity were discussed.     

Laser-induced fluorescence study on the interaction of Eu(III) with polycarboxylates

Laser-induced fluorescence spectroscopy was applied to obtaining hydration structure of Eu(III) complexes with synthetic polycarboxylates of poly(acrylic acid), poly(maleic acid), poly(methacrylic acid), and poly(a-hydroxyacrylic acid). Dependence of (the number of water molecules in the first coordination sphere of Eu(III) ion) on pH and supporting electrolyte concentration was obtained for these complexes. The spectroscopic results show that Eu(III) is surrounded by the “cage” of polycarboxylate ligands. The pH-induced transition in conformation of poly(methacrylic acid) ligand was clearly observed in the plot vs. pH.     

Energy and substituent effects on the mass spectra of substituted benzophenones

For two competing decompositions of the same molecular ion to give products [A₁⁺] and [A₂⁺], the ratio [A₁⁺]/[A₂⁺], is equal to the ratio of rate constants for the formation of the stable ions. Thr ratios, [Y C₇H₄O⁺]/[C₇H₅O⁺], were determined for several benzophenones for electron energies from 15 to 70 eV. Plots of log [Y C₇H₄O⁺]/[C₇H₅O⁺] vs.[ω⁺] gave good straight lines at all energies. Similar correlations have been reported for log [Y C₇H₆⁺]/[C₇H₇⁺] from substituted diphenyl ethanes and are also true for substituted acetophenones, log [YøCO⁺]/[CH₃CO⁺]. A few charge exchange data were obtained which showed the same general trend as the electron-impact data and emphasize the contribution of low energy ions in the 70 eV mass spectra. Relatively poor correlations were obtained for the [Y C₆H₄⁺] and [C₆H₅⁺] ions that are formed by both one-step and two-step decompositions.     

Extraction of Eu(III) by dinonylnaphthalenesulfonic acid and synergistic effects of crown ethers and trioctylphosphine oxide

The extraction of Eu(III) by dinonylnaphthalenesulfonic acid (HDNNS) in benzene from nitrate and perchlorate solutions has been investigated. For nitrate solutions the ionic strength of the aqueous phase was kept constant at 0.1M using NaNO₃–HNO₃ mixtures. The Eu distribution was measured at different temperatures. The following stoichiometric formulae for the Eu species in benzene were derived: Eu(NO₃) (H_n–1 (DNNS)_n)₂ and Eu(H_n–1 (DNNS)_n)₃, from the nitrate and perchlorate medium respectively (n being a small number, e.g. 1, 2 or 3). The equilibrium constants were calculated and the thermodynamic parameters of the system were determined. When adding dibenzo-24-crown-8, dicyclohexyl-18-crown-6 or trioctylphosphine oxide, no synergism, but rather antagonism was observed.