Eu Complexes Research Articles

Synthesis, characterization, and luminescent properties of copolymer based on derivatives of 1,2,4-triazole containing Eu(III) and Tb(III) emitters

New Eu(III) and Tb(III) hybrid materials based on N-((1-methyl-3-(pyridin-2-yl)-1H-1,2,4-triazol-5-yl)methyl)methacrylamide were synthesized and characterized as potential fluorescent emitters. Complexes of Eu(III) and Tb(III) demonstrate red and green luminescence in the visible region, respectively. The intense broad bands in the region of 270–290 nm are related to electronic transitions within pyridine-triazole-containing fragment coordinated to Ln(III) ion.

Dispersion control by using a bulky surfactant medium in the LB films for the enhancement of linearly polarized luminescence of Eu complexes

Abstract The ff transition of lanthanide ions such as Eu in the complex appears as unique energy relaxation process as luminescence after the intramolecular energy transfer from the photo-excitation of the ligand with π-electronic system. The Langmuir-Blodgett (LB) film consisting of Eu and amphiphilic naphtoic acids (NaphC15) induced the linearly polarized luminescence (LPL) with a medium, stearic acid (SA), to isolate the luminescence component by the layer structure and to keep the softness at the monolayer depositions on the quartz substrate as reported previously. Here, we used a bulky medium, 3-methyl-4-penthadecyl benzoic acid (MPBA), instead of SA, and found the Eu-NaphC15 in the LB film places more independently resulting in the 4-fold high quantum yields compared with previous system. The structures of LB films of Eu-NaphC15 with MPBA were elucidated by the measurement of synchrotron XRD and XPS. Various electronic spectra were quantitatively observed to discuss the effect molecular aggregation through much/less ππ-interaction of NaphC15 for the intensified LPL in the films.

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Inorganic Chemistry in Dalian University of Technology: Fundamental Science and Solution for Renewable Energy, Environment, Health, and Materials

Eu(III) and Cm(III) Complexation by the Aminocarboxylates NTA, EDTA, and EGTA Studied with NMR, TRLFS, and ITC-An Improved Approach to More Robust Thermodynamics.

The complex formation of Eu(III) and Cm(III) was studied via tetradentate, hexadentate, and octadentate coordinating ligands of the aminopolycarboxylate family, viz., nitrilotriacetate (NTA3-), ethylenediaminetetraacetate (EDTA4-), and ethylene glycol-bis(2-aminoethyl ether)-N,N,N',N'-tetraacetate (EGTA4-), respectively. Based on the complexones' pKa values obtained from 1H nuclear magnetic resonance (NMR) spectroscopic pH titration, complex formation constants were determined by means of the parallel-factor-analysis-assisted evaluation of Eu(III) and Cm(III) time-resolved laser-induced fluorescence spectroscopy (TRLFS). This was complemented by isothermal titration calorimetry (ITC), providing the enthalpy and entropy of the complex formation. This allowed us to obtain genuine species along with their molecular structures and corresponding reliable thermodynamic data. The three investigated complexones formed 1:1 complexes with both Eu(III) and Cm(III). Besides the established Eu(III)-NTA 1:1 and 1:2 complexes, we observed, for the first time, the existence of a Eu(III)-NTA 2:2 complex of millimolar metal and ligand concentrations. Demonstrated for thermodynamic studies on Eu(III) and Cm(III) interaction with complexones, the utilized approach is commonly applicable to many other metal-ligand systems, even to high-affinity ligands.

Reactivity of Rare-Earth Oxides in Anhydrous Imidazolium Acetate Ionic Liquids

Rare-earth metal sesquioxides (RE2O3) are stable compounds that require high activation energies in solid-state reactions or strong acids for dissolution in aqueous media. Alternatively, dissolution and downstream chemistry of RE2O3 have been achieved with ionic liquids (ILs), but typically with additional water. In contrast, the anhydrous IL 1-butyl-3-methylimidazolium acetate [BMIm][OAc] dissolves RE2O3 for RE = La–Ho and forms homoleptic dinuclear metal complexes that crystallize as [BMIm]2[RE2(OAc)8] salts. Chloride ions promote the dissolution without being included in the compounds. Since the lattice energy of RE2O3 increases with decreasing size of the RE3+ cation, Ho2O3 dissolves very slowly, while the sesquioxides with even smaller cations appear to be inert under the applied conditions. The Sm and Eu complex salts show blue and red photoluminescence and Van Vleck paramagnetism. The proton source for the dissolution is the imidazolium cation. Abstraction of the acidic proton at the C2-atom yields an N-heterocyclic carbene (imidazole-2-ylidene). The IL can be regenerated by subsequent reaction with acetic acid. In the overall process, RE2O3 is dissolved by anhydrous acetic acid, a reaction that does not proceed directly.

Circularly Polarized Luminescence from New Heteroleptic Eu(III) and Tb(III) Complexes.

The complexes [Eu(bpcd)(tta)], [Eu(bpcd)(Coum)], and [Tb(bpcd)(Coum)] [tta = 2-thenoyltrifluoroacetyl-acetonate, Coum = 3-acetyl-4-hydroxy-coumarin, and bpcd = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetate] have been synthesized and characterized from photophysical and thermodynamic points of view. The optical and chiroptical properties of these complexes, such as the total luminescence, decay curves of the Ln(III) luminescence, electronic circular dichroism, and circularly polarized luminescence, have been investigated. Interestingly, the number of coordinated solvent (methanol) molecules is sensitive to the nature of the metal ion. This number, estimated by spectroscopy, is >1 for Eu(III)-based complexes and <1 for Tb(III)-based complexes. A possible explanation for this behavior is provided via the study of the minimum energy structure obtained by density functional theory (DFT) calculations on the model complexes of the diamagnetic Y(III) and La(III) counterparts [Y(bpcd)(tta)], [Y(bpcd)(Coum)], and [La(bpcd)(Coum)]. By time-dependent DFT calculations, estimation of donor-acceptor (D-A) distances and of the energy position of the S1 and T1 ligand excited states involved in the antenna effect was possible. These data are useful for rationalizing the different sensitization efficiencies (ηsens) of the antennae toward Eu(III) and Tb(III). The tta ligand is an optimal antenna for sensitizing Eu(III) luminescence, while the Coum ligand sensitizes better Tb(III) luminescence {ϕovl = 55%; ηsens ≥ 55% for the [Tb(bpcd)(Coum)] complex}. Finally, for the [Eu(bpcd)(tta)] complex, a sizable value of glum (0.26) and a good quantum yield (26%) were measured.

Photoluminescence Properties of Eu(III) Complexes with Two Different Phosphine Oxide Structures and Their Potential uses in Micro-LEDs, Security, and Sensing Devices: A Review

Photoluminescence Properties of Eu(III) Complexes with Two Different Phosphine Oxide Structures and Their Potential uses in Micro-LEDs, Security, and Sensing Devices: A Review

Crystal-field analysis and models of Eu-emission centers with C3v symmetry in insitu Eu- and Mg-codoping GaN layers

Gallium nitride active layers co-doped in situ with magnesium and europium, GaN(Mg):Eu, show strong red photoluminescence (PL), promising for red light emitting diode (LED) application (Eu@621 nm). Polarized PL lines excited by either above or below band-gap energy for the GaN(Mg):Eu layers are assigned to the 5D0→7FJ (J = 0, 1, 2) transitions lines from several Eu centers with C3v symmetry, which consist of single line, double lines and triple lines related to splitting of 7FJ (J = 0, 1, 2) by the C3v crystal-field, respectively. Cascade luminescence line-pattern of the 5D1→7FJ (J = 0, 1, 2) transitions is a complete replica of the PL line-pattern and gives evidence of the correct assignment of the polarized PL lines. Crystal-field splitting and Zeeman splitting of the PL lines have been analysed using the C3v crystal-field equivalent operator Hamiltonian. Structural Eu models with the C3v symmetry have been proposed on the basis of the analysis: the dominant Eu center is an Eu complex with defect-free perfect surrounding: the minor Eu centers are Eu complexes accompanied by nitrogen vacancies with different charge states on the c-axis in the closest vicinity of Eu. An important role of Mg atoms in the GaN(Mg):Eu active layers has been proposed to suppress creation of gallium vacancies, giving rise to enhancement of the PL emitted from the defect-free Eu centers.

Influence of Ancillary Ligand on the Photosensitization and Photophysical Properties of Red Luminescent Tri-fluorinated Β-diketonate Eu(III) Complexes.

Highly emissive ternary Eu(III) complexes were synthesized with a tri-fluorinated β-diketone as principal ligand and heterocyclic aromatic compounds as ancillary ligands to assess their utility as an illuminating material for display devices and other optoelectronics.The general characterizations, regarding the coordinating facets of complexes were accomplished via various spectroscopic techniques. Thermal stability was investigated via TGA/DTA. Photophysical analysis was accomplished by PL studies, Band gap value, color parameters and J-O analysis. DFT calculations were performed adopting geometrically optimized structure of complexes.Superb thermal stability has been achieved in complexes, which decides their concrete candidature for display devices. The bright red luminescence of complexes is ascribed to 5D0 → 7F2 transition of Eu(III) ion. Colorimetric parameters unlocked the applicability of complexes as warm light source and J-O parameters adequately summarized the coordinating surrounding around the metal ion. Various radiative properties were also evaluated which suggested the prospective use of complexes in lasers and other optoelectronic devices. The band gap and Urbach band tail, procured from absorption spectra, revealed the semiconducting behavior of synthesized complexes. DFT studies rendered the energies of FMO and various other molecular parameters.It can be summarized from the photophysical and optical analysis of synthesized complexes that these complexes are virtuous luminescent materials and possess potentiality to be used in diverse domain of display devices.

Molecular Design of Luminescent Complexes of Eu(III): What Can We Learn from the Ligands.

The luminescent metal-organic complexes of rare earth metals are advanced materials with wide application potential in chemistry, biology, and medicine. The luminescence of these materials is due to a rare photophysical phenomenon called antenna effect, in which the excited ligand transmits its energy to the emitting levels of the metal. However, despite the attractive photophysical properties and the intriguing from a fundamental point of view antenna effect, the theoretical molecular design of new luminescent metal-organic complexes of rare earth metals is relatively limited. Our computational study aims to contribute in this direction, and we model the excited state properties of four new phenanthroline-based complexes of Eu(III) using the TD-DFT/TDA approach. The general formula of the complexes is EuL2A3, where L is a phenanthroline with -2-CH3O-C6H4, -2-HO-C6H4, -C6H5 or -O-C6H5 substituent at position 2 and A is Cl- or NO3-. The antenna effect in all newly proposed complexes is estimated as viable and is expected to possess luminescent properties. The relationship between the electronic properties of the isolated ligands and the luminescent properties of the complexes is explored in detail. Qualitative and quantitative models are derived to interpret the ligand-to-complex relation, and the results are benchmarked with respect to available experimental data. Based on the derived model and common molecular design criteria for efficient antenna ligands, we choose phenanthroline with -O-C6H5 substituent to perform complexation with Eu(III) in the presence of NO3¯. Experimental results for the newly synthesized Eu(III) complex are reported with a luminescent quantum yield of about 24% in acetonitrile. The study demonstrates the potential of low-cost computational models for discovering metal-organic luminescent materials.

Efficient Red Organic Light Emitting Diodes of Nona Coordinate Europium Tris(β-diketonato) Complexes Bearing 4'-Phenyl-2,2':6',2''-terpyridine.

Two novel nona coordinated Eu(III) complexes [Eu(btfa)3(Ph-TerPyr)] (Eu-1) and [Eu(NTA)3(Ph-TerPyr)] (Eu-2) have been synthesized and characterized. The structure of the complexes was elucidated by density functional theory (DFT) methods. The experimental photophysical properties of the complexes were investigated and complemented with theoretical calculations. Effective energy transfer (ET) pathways for the sensitized red luminescence is discussed. The complexes were tested as emitting layers (EML) in OLEDs. At the optimum doping concentration of 4 wt%, the double-EML OLEDs of Eu-1 exhibited red electroluminescence (EL) with an EQE of 4.0% and maximum brightness (B) = 1179 cd/m2, maximum current efficiency (ηc) = 5.64 cd/A, maximum power efficiency (ηp) = 4.78 lm/W with very low turn-on voltage (Vturn-on) = 3.6 V at the current density (J) of 10 mA/cm2. Interestingly, the double-EML OLEDs of Eu-2 at the optimum concentration of 3 wt%, displayed an outstanding EL performance with EQE of 7.32% and B = 838 cd/m2, ηc = 10.19 cd/A, ηp = 10.33 lm/W, and Vturn-on = 3.1 V at J =10 mA/cm2. The EL performance of this device is among the best reported for devices incorporating a europium complex as a red emitter.

Designing and Judd-Ofelt evaluation of versatile luminescent Eu (III) complexes sensitized with β-diketone ligand for multifarious applications.

The present research work entails synthesis of one binary and four ternary red light emitting Eu (III) based complexes with 3-benzylidene-2,4-pentanedione as main ligand and 1,10-phenanthroline, bathophenanthroline, neocuproine and 4,4'-dimethyl-2,2'-bipyridyl as auxiliary ligands. The Metal-Organic framework of the series was elucidated using EDAX, elemental analysis, FT-IR and 1 H-NMR. This Eu (III) series exhibit optimum thermal stability making them a promising candidate for OLED's. On the basis of emission spectra their optical parameters such as non-radiative and radiative decay rate, luminescence decay time, intrinsic quantum efficiency and Judd-Ofelt intensity parameter were determined. The mono-centric luminescence and Judd-Ofelt parameters reveals the non-existence of symmetry around the europium center. CIE chromaticity coordinates, CCT values, color purity and asymmetric ratios authenticate the color coordinates of complexes in red region. Optical band gap values lies within wide band gap semiconductors range revealing their utilization in military radars, biological labeling.

Bright LanthanideIII Triboluminescence despite Low Photoluminescence, and Dual Triboluminescence and Mechano‐Responsive Photoluminescence (Advanced Optical Materials 9/2023)

Dancers on the cover symbolize the bright green and red triboluminescence (TL) of Tb(III) and Eu(III) complexes under mechanical stimuli (clapping), despite the great contrast between their photoluminescence (PL) efficiencies under UV illumination (spotlight). In article number 2203139, Yuichi Hirai and co-workers demonstrate the existence of direct lanthanide(III) excitation processes in TL, while ligand-mediated ones dominate the PL intensity. This work presents insights for fabricating a new family of lanthanide(III)-based functional mechanophores as well as providing the key to elucidate underlying mechanisms.

Topologically devised flexible bi-aeolotropic conduction Janus-like bi-layer membrane functionalized by red-green bicolor fluorescence

To further advance the development for new-generations of high-performance, miniaturized and flexible electronic devices, it is particularly significant to research new-typed fluorescence-functionalized bi-aeolotropic conduction membrane. Herein, a unique topology optimization design philosophy is proposed, which highly integrates macroscopic with microscopic partitions to manufacture high-performance aeolotropic conduction membrane functionalized by fluorescence. Topologically devised Janus-like bi-layer membrane (JBM) with bi-aeolotropic conduction and red-green bicolor fluorescence is successfully assembled by using a bi-axis electro-spinning. [PANI/PMMA]//[Eu(TTA)3bipy/PMMA] Janus-structured micro-fiber and [PANI/PMMA]//[Tb(acac)3phen/PMMA] Janus-structured micro-fiber was respectively employed as microcosmic constructing unit to align directionally to build first layer (JBM-F) and second layer (JBM-S) of the JBM. Macroscopically, for the JBM, each layer has aeolotropic conduction, and furthermore, the conductive orientations of the two layers are vertical, and the insulated orientations are also vertical, leading in the bi-aeolotropic conduction of the JBM. The strongest conductive aeolotropism for each layer can reach 108 when the PANI/PMMA is 65%. The introduction of the Eu and Tb complexes into the Janus-structured micro-fiber gives the JBM excellent red-green bicolor fluorescence. The fluorescent traits can be employed to visualize the operational state of JBM. The high integration of Janus-structured micro-fiber possessing microcosmic partition with Janus-like bi-layer membrane possessing macrocosmic partition achieves the efficacious separation of electrical and fluorescent fillers to shun the deleterious interferences between two functions to obtain superior fluorescence and bi-aeolotropic conduction. Interestingly, the prepared flexible JBM can be applied as a reliable microcircuit interconnection, providing a basis for practical applications.

Spectral imaging in microscopy aids evaluation of the luminescent probe behaviour of europium complexes

In a series of structurally related cationic Eu(III) triamide complexes, the analysis of variations in emission lifetime and spectral signature as a function of probe environment has elucidated the nature of changes to probe speciation. The cationic complexes exhibit an intrinsic tendency to localise in cellular nucleoli or the lysosomes, providing key information in the design and evaluation of related targeted probes. Each of the three complexes studied possesses a coordinated water molecule in aqueous media, that is absent in organic solvents or is displaced by the addition of protein. The complex observed in cellulo is probably a protein-bound Eu complex.

Synthesis, solid state characterization, theoretical and experimental spectroscopic studies of the new lanthanide complexes

Three new complexes Na[Ln(pic)4]ּ⋅2.5H2O (Ln = Tb, Eu or Gd; pic = picolinate) were synthesized and characterized by infrared spectroscopy, powder X-ray diffraction and thermogravimetric analyses. The molecular structures of the complexes have been determined by single-crystal X-ray diffraction. The three isostructural lanthanide complexes crystalize in the hexagonal system with space group P6122 to Eu complex and Gd complex and space group P6522 to Tb complex. In each of the complexes, the picolinate ligands are bonded to Ln3+ and Na+ ions by different coordination modes promoting polymeric structures. The photoluminescent properties of complexes were studied and combined with theoretical studies using the density functional theory (DFT: B3LYP, PBE1PBE) and the semiempirical method AM1/Sparkle from the single crystal X-ray diffraction structures to assign a suitable model for describing the system. The B3LYP DFT functional was considered the most adequate for providing structural properties of the compounds and for describing luminescence properties. The excited triplet states (T1) and excited singlet states (S1) of the ligand were determined theoretically using Time-dependent DFT calculations (TD-DFT: B3LYP, CAM-B3LYP and LC-wPBE) and INDO/S-CIS, with the best agreement with experimental values obtained from the LC-wPBE DFT functional. The photoluminescent spectra of the complexes and their lifetime measurements were determined indicating that the Eu complex and Tb complex display different intramolecular energy transfer mechanisms with higher efficiency to ligand-to-terbium energy transfer. In addition, the experimental and theorical Judd-Ofelt intensity parameters and quantum yields of the complexes were also determined and discussed besides to a proposed 9-state diagram to describe the luminescence properties of the Eu complex. The low value of emission quantum efficiency of 5D0 emitting level of Eu(III) ion was explained by the presence of the ligand-to-metal charge transfer state (LMCT) evidenced experimentally and theoretically. A good agreement was obtained between the proposed kinetic model and experimental results showing the consistency of the set of rate equations assumed and the intramolecular pathways proposed.

Preparation, Structure, and Photophysical Behavior of Europium (III) Complexes of Decyl Alanine and Lauryl Alanine

Two Ligands (H (dec-ala) and H (dod-ala)) prepared from decyl chloride, lauroyl chloride, and amino acids (DL-alanine), reacted with Europium chloride in methanol solution, leading to two Europium (III) complexes of Eu (dec-ala)3 and Eu (dod-ala)3.Elemental analysis, NMR, and FT-IR spectra proved the elemental content, structural information of the synthesized Europium (III) complexes. The light absorption and luminescence properties were characterized by UV-vis and PL spectra analysis. Both complexes have excellent absorption capacity in the range of 200 nm-300 nm. The ideal excitation wavelengths of these complexes are at 394 nm, and the principal emission peaks are at 590 nm, 610 nm, 650 nm, and 698 nm, which correspond to 5D0 → 7F1, 5D0 →7F2, 5D0→7F3, 5D0→7F4, respectively.

Room-Temperature Ionic Liquid Cation Effects on the Structure and Stability of Anionic Lanthanide Complexes.

Room-temperature ionic liquids (RTILs) are a subset of molten salts that are liquids at room temperature and may offer an elegant, low-temperature route to predicting the properties of solvated metal complexes in their high-temperature analogues. This work studied the chemistry of chloride anion-containing RTILs to determine their similarity to inorganic molten chloride salts. The behaviors of complexes of Mn, Nd, and Eu were evaluated in a variety of chloride RTILs by absorption spectrophotometry and electrochemistry to elucidate trends in cation effects on the coordination geometry and redox properties of the solvated species. Spectrophotometric data indicated the metals are present as anionic complex (e.g., MnCl42- and NdCl63-) analogous to those observed in molten chloride salts. Strongly polarizing, charge-dense RTIL cations induced distortions to the symmetry of these complexes, resulting in lower oscillator strengths and red-shifted energies for the observed transitions. Cyclic voltammetry experiments were used to characterize the Eu(III/II) redox couple producing diffusion coefficients on the order of 10-8 cm2 s-1 and heterogeneous electron transfer rate constants ranging between 6 × 10-5 and 2 × 10-4 cm s-1. The E1/2 potentials for Eu(III/II) were also found to shift positively with increasing cation polarization power, stabilizing the Eu(II) oxidation state by removing electron density from the metal center over chloride bond networks. Both the optical spectrophotometry and electrochemistry results suggest that the polarization strength of an RTIL cation plays a major role in the geometry and stability of a metal complex.

Outersphere Approach to Increasing the Persistance of Oxygen-Sensitive Europium(II)-Containing Contrast Agents for Magnetic Resonance Imaging with Perfluorocarbon Nanoemulsions toward Imaging of Hypoxia.

Radiographic mapping of hypoxia is needed to study a wide range of diseases. Complexes of Eu(II) are a promising class of molecules to fit this need, but they are generally limited by their rapid oxidation rates in vivo. Here, a perfluorocarbon-nanoemulsion perfused with N2 , forms an interface with aqueous layers to hinder oxidation of a new perfluorocarbon-soluble complex of Eu(II). Conversion of the perfluorocarbon solution of Eu(II) into nanoemulsions results in observable differences between reduced and oxidized forms by magnetic resonance imaging both in vitro and in vivo. Oxidation in vivo occurrs over a period of ≈30min compared to <5min for a comparable Eu(II)-containing complex without nanoparticle interfaces. These results represent a critical step toward delivery of Eu(II)-containing complexes in vivo for the study of hypoxia.

Photophysical Properties of Octyl Amino Acid Europium and Terbium Complex / PVB Composite Films

The rare earth (Eu3+ and Tb3+) organic complex was doped into PVB matrix materials by solution blending physical method, and the fluorescent composite materials with different concentrations. The analysis indicates that the rare earth organic complexes are evenly distributed in the PVB organic matrix after heating and cooling treatment, and no chemical reaction occurs. The composite exhibits good thermal stability below 150°C; Emission spectrum of Eu complex /PVB films has shown an intense red emission at 615nm with an excitation at 400nm. From the Tb complex /PVB films a green emission at 542nm with an excitation at 254nm has been observed, which provides a new idea for developing fluorescent materials in many fields.