Ercules E.S. Teotonio

Influence of the N-[methylpyridyl]acetamide ligands on the photoluminescent properties of Eu(III)-perchlorate complexes

Abstract This work reports the synthesis, characterization and spectroscopic studies of Eu(III)-perchlorate complexes with amide ligands derived from N -[ x -methylpyridyl]acetamide where x =3, 4 and 6. The Eu(ClO 4 ) 3 3( x -mpa) complexes were characterized by elemental analyses, molar conductance, TG analyses and vibrational spectroscopy. Raman and infrared data show that the perchlorate ion, (ClO 4 − ), is bonded to Eu(III) as a monodentate ligand and that in these three complexes water molecules are not coordinated to the rare earth ion. The profiles of the emission spectra of the complexes with 3- and 4-mpa ligands are very similar but they differ from the complex containing 6-mpa ligand. This spectroscopic behavior can be rationalized in terms of the Ω λ ( λ =2 and 4) and R 02 experimental intensity parameters. The values of Ω 2 (∼6.5×10 −20 cm 2 ) in these complexes are smaller than in Eu(III)-TTA compounds ( Ω 2 ∼35.0×10 −20 cm 2 ), indicating that in the former case the rare earth ion is in a chemical environment less polarizable. Lifetime and emission quantum efficiency measurements for the emitting level 5 D 0 were carried out and the results are discussed.

Luminescence investigation of the Sm(III)-β-diketonates with sulfoxides, phosphine oxides and amides ligands

Abstract In this paper we report on a photoluminescent investigation of complexes involving Sm 3+ -β-diketonates with sulfoxides, phosphine oxides and amides ligands. In the synthesis of the coordination compounds we used samarium tris(thenoyltrifluoroacetonate) dihydrated precursor with the following ligands (L): DBSO and PTSO sulfoxides; TPPO phosphine oxide and (PHA) N -phenylacetamide. They have shown high orange luminescence characteristic of the Sm 3+ ion. The emission spectra of the Sm 3+ -complexes present narrow bands arising from the 4 G 5/2 → 6 H J ( J =5/2, 7/2, 9/2, 11/2) transitions with the hypersensitive 4 G 5/2 → 6 H 9/2 transition as a prominent group. It is observed an efficient intramolecular energy transfer from the triplet state (T) of the ligands to the emitting 4 G 5/2 state of the Sm 3+ ion. The experimental intensity parameters ( η Sm and η Eu ) for the Sm and Eu complexes have been determined and compared. The lifetimes ( τ ) of the emitting level 4 G 5/2 of the Sm-complexes are approximately 10 times higher than in the precursor compound [Sm(TTA) 3 ·(H 2 O) 2 ] indicating that radiative processes are operative in all the compounds due to the absence of multiphonon relaxation by coupling with the OH oscillators.

Luminescence Investigations on Eu(III) Thenoyltrifluoroacetonate Complexes with Amide Ligands

The influence of amide ligands on the photoluminescent behavior of tris(thenoyltrifluoroacetonate)- europium(III) in the solid state is reported. Elemental analysis showed that these compounds have the following formulas [Eu(TTA)3·(ANL)2] and [Eu(TTA)3·PZA], where ANL = acetanilide and PZA = pyrazinamide. The photoluminescence spectra of the complexes recorded in the range 420-720 nm at 77 K show narrow bands arising from the 5D0 → 7F J transitions (where J = 0-4), under excitation at 394 nm. Based on the emission spectra and luminescence decay curves the intensity parameters (Ωλ), lifetime (τ) and emission quantum efficiency (η) were determined. The Ω2 values indicate that the Eu3+ion in these complexes is in a highly polarizable chemical environment. The higher value of η (60%) obtained for the complex with the ANL ligand, in comparison with the complex with the PZA ligand (30%), indicates a more efficient deactivation of the Eu3+ion in the [Eu(TTA)3·PZA] complex.

Synthesis and photophysical study of highly luminescent coordination compounds of rare earth ions with thenoyltrifluoroacetonate and AZT.

This work presents the study of the interaction between zidovudine (AZT) and rare earth (RE) ions with thenoyltrifluoroacetonate (TTA). The complexes [RE(TTA)(3) x (AZT)(2)] (where RE(III)=Eu and Gd) were prepared by reaction between the [RE(TTA)(3) x (H(2)O)(2)] precursors and AZT dissolved in acetone in the molar ratio 1:2. The obtained luminescent materials were characterized by microanalyses (C, H, N), complexometric titration, IR spectroscopy, X-ray powder diffraction and thermal analysis (DSC and TG/DTG). The luminescence data indicate that the substitution of the two water molecules by AZT in the europium complex causes an intensification of luminescence corresponding to the (5)D(0) -->(7)F(J) (J=0-4) transitions associated with one of the site symmetries. Based on the luminescence spectrum of the Eu(III)-compound the Omega(lambda) experimental intensity parameters (lambda=2 and 4) were calculated for the electronic transitions (5)D(0)-->(7)F(2, 4). The Omega(2) intensity parameter for this new compound is higher than for the precursor compound, suggesting an effective interaction between the AZT and the chemical environment of the Eu(III) ion. Luminescence data confirm that the AZT complex and precursor compound have a comparable emission quantum efficiency.

Steady-state luminescence investigation of the binding of Eu(III) and Tb(III) ions with synthetic peptides derived from plant thionins.

This work reports Eu(III) and Tb(III) luminescence titrations in which the lanthanide ions were used as spectroscopic probes for Ca(II) ions to determine the metal binding ability of Ac-NESVKEEGGW-NH(2) and Ac-NESVKEDGGW-NH(2). These decapeptides correspond to the putative calcium binding region of the plant antifungal proteins SI-alpha1 from Sorghum bicolor and of Zeathionin from Zea mays, respectively. The luminescence spectra for the Eu(III)-decapeptide system (red emission) with the excitation at the Trp band at 280 nm showed an enhancement of the intensities of the 5D(0)-->7F(J) transitions (where J=0-4) with increments of Eu(III) ion concentration. The photoluminescence titration data of the terbium ion (green emission) in the decapeptide solutions showed intensification of the 5D(4)-->7F(J) transitions (J=0-6), similar to that observed for the Eu(III) ion. Thus, energy transfer from Ac-NESVKEEGGW-NH(2) and Ac-NESVKEDGGW-NH(2) to the trivalent lanthanide ions revealed that these peptides are capable of binding to these metal ions with association constants of the order of 10(5) M(-1). The amino acid derivative Ac-Trp-OEt also transferred energy to Tb(III) and Eu(III) ions as judged from the quenching of tryptophan luminescence. However, the energy transfers were significantly lower. Taken together the luminescence titration data indicated that Ac-NESVKEEGGW-NH(2) and Ac-NESVKEDGGW-NH(2) bind efficiently to both trivalent lanthanide ions and that these ions may be used as probes to distinguish an anionic peptide from a neutral amino acid derivative.

Photoluminescence behavior of the Sm3+ and Tb3+ ions doped into the Gd2(WO4)3 matrix prepared by the Pechini and ceramic methods

The Gd2(WO4)3:RE3+ compounds (where RE3+ = Sm and Tb) were prepared by the Pechini and ceramic methods and characterized by X-ray diffraction and infrared spectroscopy. These rare earth materials present high orange (Sm3+-compound) and green (Tb3+-compound) luminescence intensity under UV radiation. The excitation spectra of these compounds presented broad bands arising from ligand-to-metal charge transfer (O®W and O®RE3+) and narrow bands from 4f-intraconfigurational transitions. The excitation spectra of Tb3+ system also exhibit broad bands attributed to the interconfigurational transition (4f-5d). The emission spectra exhibited the 4G5/2®6HJ (J = 5/2, 7/2, 9/2 and 11/2) and 5D4® 7FJ (J = 0-6) transitions (direct excitation), for the systems doped with Sm3+ and Tb3+, respectively, while a broad band assigned to the LMCT (O®W) is observed when the excitation is monitored on the O®W LMCT state around 270 nm. The experimental intensity parameters hSm and hEu present similar behaviors, suggesting that the Sm3+ ion is in a highly polarizable chemical environment with similar covalent character of the metal-donor atom interaction to the tungstate doped europium system. The cross-relaxation process from the 5D3 to the 5D4 levels of the Gd2(WO4)3:Tb3+ system has been also reported.

Synthesis and luminescent properties of supramolecules of β-diketonate of Eu(III) and crown ethers as ligands

This work reports the synthesis and luminescence behavior of the diaquatris(thenoyltrifluoracetonate)europium(III) with dibenzol8-crown-6 (DB18C6) and 18-crown-6 (18C6), in the solid state. The new compounds Eu(TTA) 3 (H 2 O) 2 (DB18C6) 2 and Eu(TTA) 3 (H 2 O) 2 (18C6) 2 were characterized by elemental analysis, infrared spectroscopy, thermalanalysis and scattering electronic microscopy. The emission spectra show narrow emission bands that arise from the 5 D 0 → 7 F J transitions (J = 0-4) of the Eu 3+ ion. The spectral data of the Eu(TTA) 3 (H 2 O) 2 (DB18C6) 2 and Eu(TTA) 3 (H 2 O) 2 (18C6) 2 compounds present, respectively, one and two peaks assigned to the 5 D 0 → 7 F 0 transition ( ∼ 578 nm), suggesting one and two sites of symmetry around the metal ion. In addition, the luminescence decay curves of these DB18C6 and 18C6 systems were better fitted by a mono- and bi-exponential decays, respectively. The values of the experimental intensity parameters (Ω λ ) indicate that the europium ion in the complexes is in a highly polarizable chemical environment. The values of emission quantum efficiencies for the two Eu(III)-supramolecular compounds are similar (η = 26%).

Red-green emitting and superparamagnetic nanomarkers containing Fe3O4 functionalized with calixarene and rare earth complexes.

The design of bifunctional magnetic luminescent nanomaterials containing Fe3O4 functionalized with rare earth ion complexes of calixarene and β-diketonate ligands is reported. Their preparation is accessible through a facile one-pot method. These novel Fe3O4@calix-Eu(TTA) (TTA = thenoyltrifluoroacetonate) and Fe3O4@calix-Tb(ACAC) (ACAC = acetylacetonate) magnetic luminescent nanomaterials show interesting superparamagnetic and photonic properties. The magnetic properties (M-H and ZFC/FC measurements) at temperatures of 5 and 300 K were explored to investigate the extent of coating and the crystallinity effect on the saturation magnetization values and blocking temperatures. Even though magnetite is a strong luminescence quencher, the coating of the Fe3O4 nanoparticles with synthetically functionalized rare earth complexes has overcome this difficulty. The intramolecular energy transfer from the T1 excited triplet states of TTA and ACAC ligands to the emitting levels of Eu(3+) and Tb(3+) in the nanomaterials and emission efficiencies are presented and discussed, as well as the structural conclusions from the values of the 4f-4f intensity parameters in the case of the Eu(3+) ion. These novel nanomaterials may act as the emitting layer for the red and green light for magnetic light-converting molecular devices (MLCMDs).

Knoevenagel Condensation of Aldehydes and Ketones with Malononitrile Catalyzed by Amine Compounds-Tethered Fe3O4@SiO2 Nanoparticles

A new magnetic nanoparticle supported-catalyst was developed for the Knoevenagel condensation between malononitrile and several aldehydes. The Fe3O4@SiO2-3N (where 3N = N1-(3-trimethoxysilylpropyl)diethylenetriamine) catalyst was characterized by XRD, infrared spectroscopy, and thermogravimetric analysis. The reactions provide excellent yields in a shorter reaction time in relation to others reported in the literature. The catalyst was easily recovered and reused until six times without significant loss of its catalytic capacity.Graphical Abstract

Low Temperature Synthesis of Luminescent RE2O3:Eu3+ Nanomaterials Using Trimellitic Acid Precursors

[RE(TLA)·(H2O)n:Eu3+] (RE3+: Y, Gd and Lu; TLA: trimellitic acid) precursor complexes were synthesized by an one step aqueous co-precipitation method. After annealing for 1 h, RE2O3:Eu3+ nanophosphors were formed through the benzenetricarboxylate low temperature thermolysis method (500-1000 oC). The compounds were characterized by using different techniques [elemental analysis (CHN), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG/DTG), X-ray powder diffraction (XPD) and scanning electron microscope (SEM)]. The XPD data indicated that the Y2O3:Eu3+ materials have crystallite size range from 11 to 62 nm. The SEM and transmission electron microscopy (TEM) images show that the annealed materials keep morphological similarities with the precursor complexes. The photoluminescence properties were studied based on the excitation and emission spectra, and luminescence decay lifetimes of the 5D0 emitting level of the Eu3+ ion. The experimental intensity parameters (Ωλ), lifetimes (τ), as well as radiative (Arad) and non-radiative (Anrad) decay rates were calculated and discussed. The RE2O3:Eu3+ phosphors (RE: Y3+ and Lu3+) annealed at 500 to 1000 oC have emission quantum efficiency (intrinsic quantum yield) values from 60 to 82%, indicating that this material can be potentially used for optical markers applications.