Eu Complexes Research Articles

Current Development of Lanthanide Complexes for Biomedical Applications.

Luminescent molecule-based bioimaging system is widely used for precise localization and distinction of cancer/tumor cells. Luminescent lanthanide (Ln(III)) complexes offer long-lived (sub-millisecond time scale) and sharp (FWHM <10 nm) emission, arising from the forbidden 4f-4f electronic transitions. Luminescent Ln(III) complex-based bioimaging has emerged as a promising option for both in vitro and in vivo visualizations. In this mini-review, the historical development and recent significant progress of luminescent Ln(III) probes for bioapplications are introduced. The recent studies are mainly focused on three points: (i) the structural modifications of Ln(III) complexes in both macrocyclic and small ligands, (ii) the acquirement of high resolution luminescence images of cancer/tumor cells and (iii) the constructions of ratiometric biosensors. Furthermore, our recent study is explained as a new Cancer GPS (cancer grade probing for determining tumor grade through photophysical property analyses of intracellular Eu(III) complex.

Theoretical Study of Am(III) and Eu(III) Separation by a Bipyridyl Phosphate Ligand.

Actinide An(III) and lanthanide Ln(III) are known to exhibit similar chemical properties; thus, it is difficult to distinguish them in the separation of highly radioactive waste liquids. One potential method to efficiently separate actinides and lanthanides involves the design and development of phosphorus-oxygen-bonded ligands with solvent extraction separation. Here, a bipyridine phosphate ligand with two isopropyl and phosphate groups is introduced to selectively extract actinides. The electronic structure, bonding properties, thermodynamic behavior, and quantum theory of atoms in molecules (QTAIM) of Am(III) and Eu(III) complexes with the bipyridine phosphate ligands were analyzed by using density functional theory (DFT) calculations. The analysis demonstrates that the Am-N bond exhibits stronger covalent characteristics than the Eu-N bond, indicating that the bipyridine phosphate ligand had better selectivity for Am(III) than for Eu(III) in terms of binding affinity. The thermodynamic analysis established the complex [ML(NO3)2(H2O)2]+ as the most stable species during the complexation process. The results indicate great potential for utilizing the bipyridine phosphate ligand for the effective separation of An(III)/Ln(III) in spent fuel reprocessing experiments.

Photophysical analysis and Judd–Ofelt calculation of Eu (III) complexes: Influence of various neutral ligands on luminescent properties

This article presents the preparation and characterization of a series of four tris-β-diketonate Eu(III) complexes with formulation of [Eu(tfaa)3(L)n], tfaa denotes the 1,1,1-trifluoroacetylacetone, L to monodentate or bidentate neutral ligand with nitrogen and oxygen as donor atom and n can be 1 and 2. The characterization of synthesized complexes was done using infrared spectroscopy, thermo-gravimetric analysis and proton NMR spectroscopy. UV–vis absorption, photoluminescence as well as time-resolved luminescence spectroscopies were also employed to examine the spectroscopic features of ternary complexes. The proton NMR and IR spectral information has suggested the bonding of organic moieties to the Eu(III) ion. The chemical shift obtained for the protons of primary and secondary moieties are shifted in an opposite direction. The band gap values (optical and electronic) suggest the semiconducting nature of prepared europium complexes. The trivalent ion centered emission is shown by all the prepared complexes on excitation under UV-light. The hypersensitive peak situated at about 612 nm responsible for red emission is corresponding to 5D0→7F2 transition and found to be sensitive to the chelating environment present at around emissive ion. Red emanating europium materials have acquired significant utilization in OLEDs, flat panel displays and solid state electronics.

Comprehensive Photophysical and Nonlinear Spectroscopic Study of Thioanisolyl‐Picolinate Triazacyclononane Lanthanide Complexes

AbstractDetailed photophysical studies of luminescent lanthanide complexes are presented and elaborated using a newly developed thioanisolyl‐picolinate antenna and the related tacn macrocyclic ligand. The new ligand proved to sensitise Nd(III), Sm(III), Eu(III) and Yb(III) emission. Eu(III) complex showed complete energy transfer, yielding high quantum yield (44 %) and brightness, while the Tb(III) analogue underwent a thermally activated back‐energy transfer, resulting in a strong oxygen quenching of the triplet excited state. Transient absorption spectroscopy measurements of Gd(III), Tb(III) and Eu(III) compounds confirmed the sensitization processes upon the charge‐transfer antenna excitation. The triplet excited state lifetime of the Tb(III) complex was 5‐times longer than that of the Gd(III) analogue. In contrast, the triplet state was totally quenched by the energy transfer to the 4f‐metal ion in the Eu(III) species. Nonlinear two‐photon absorption highlighted efficient biphotonic sensitization in Eu(III) and Sm(III) complexes. In case of the Nd(III) compound, one‐photon absorption in 4f–4f transitions was predominant, despite the excitation at the antenna two‐photon band. This phenomenon was due to the Nd(III) 4f–4f transitions overlapping with the wavelength‐doubled absorption of the complex.

Comprehensive performance of polycarbonate films doped with Tb(III) and Eu(III) complexes

AbstractIn order to expand the application of biobased polycarbonate in optical components, a series of isosorbide polycarbonate (PICC)/rare earth ion complex fluorescent composites were prepared by using PICC as a macromolecular ligand and Eu3+ and Tb3+ as rare earth luminescence centers. The coordination system between rare earth ions and PICC was investigated by Fourier transform infrared spectroscopy, DSC and TGA. On adjusting the ratio of Eu3+ and Tb3+, a PICC/rare earth ion composite with adjustable fluorescence color was obtained. Also, the thermal, mechanical and optical properties of a series of PICC/rare earth ion fluorescent films with different ratios were tested. A transparent fluorescent composite material with excellent mechanical properties and tunable fluorescent colors has been prepared. © 2024 Society of Industrial Chemistry.

Synthesis, Spectroscopy and Biological Activities of Some Trivalent Lanthanide Complexes of Octadecyl N-salicylaldimine (ONsal)

A series of Ln(III) complexes of octadecyl N-salicylaldimine (ONsal) were synthesized and characterized by CHN analysis, magnetic moment, conductivity, thermoanalytical and spectroscopic methods. Elemental and thermal analysis data confirmed the formation of heptacoordinated [Ln(ONsal)2Cl2(H2O)]Cl complexes where Ln = Ce3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, which is further supported by the respective mass spectra. The ligand acts as a neutral bidentate species coordinating through azomethine nitrogen and phenolic O-atom. The linkage of one H2O molecule in all the complexes has been inferred from the thermal analysis. All the Ln(III) complexes are paramagnetic in nature and act as 2:1 electrolyte in 0.002 M DMF at 25 ºC. The complexes of Sm(III), Eu(III) and Tb(III) display luminescent properties. The powder XRD patterns of Nd(III) and Dy(III) complexes could be successfully indexed for monoclinic crystal systems, while the diffraction lines of Eu(III) complex are indexed for a triclinic crystal system. Methanolic solutions of the ligand and complexes were checked for α-glucosidase and α-amylase inhibitory properties where some of the Ln(III) complexes show significant α-glucosidase inhibitory potency while only Tb(III) complex shows inhibition against α-amylase.

Enhancing the Selectivity of Trivalent Actinide over Lanthanide Using Asymmetrical Phenanthroline Diamide Ligands.

Phenanthroline diamide ligands have been widely used in the separation of trivalent actinides and lanthanides, but little research has focused on extractants with asymmetrical substitutes. Two novel asymmetrical phenanthroline-based ligands N2,N2,N9-triethyl-N9-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DE-ET-DAPhen) and N2-ethyl-N9,N9-dioctyl-N2-tolyl-1,10-phenanthroline-2,9-dicarboxamide (DO-ET-DAPhen) were first synthesized in this work, whose extraction ability and complexation mechanism to trivalent actinides [An(III)] and lanthanides [Ln(III)] were systematically investigated. The ligands dissolved in n-octanol exhibit good extraction ability and high selectivity toward Am(III) in acidic solutions. The complexation mechanism of the ligands with Ln(III) in solution and solid state was analyzed using slope analysis, 1H NMR spectrometric titration, ESI-MS, and calorimetric titration. It is revealed that the ligands complex with Am(III)/Eu(III) with 1:1 stoichiometry. The stability constant (log β) of the complexation reaction of Eu(III) with DE-ET-DAPhen determined by UV-vis spectrophotometric and calorimetric titration is higher than that of DO-ET-DAPhen, indicating the stronger complexation ability of DE-ET-DAPhen. Meanwhile, the calorimetric titration results show that the complexation process is exothermic with a decreased entropy. The structures of 1:1 complexes of Eu(III) and Nd(III) with DE-ET-DAPhen were analyzed through single-crystal X-ray diffraction. This work proves that ligands containing asymmetrical functional groups are promising for An(III)/Ln(III) separation, which shows great significance in efficient extractants designed for the spent nuclear fuel reprocessing process.

Structure-changeable luminescent Eu(III) complex as a human cancer grade probing system for brain tumor diagnosis.

Accurate determination of human tumor malignancy is important for choosing efficient and safe therapies. Bioimaging technologies based on luminescent molecules are widely used to localize and distinguish active tumor cells. Here, we report a human cancer grade probing system (GPS) using a water-soluble and structure-changeable Eu(III) complex for the continuous detection of early human brain tumors of different malignancy grades. Time-dependent emission spectra of the Eu(III) complexes in various types of tumor cells were recorded. The radiative rate constants (kr), which depend on the geometry of the Eu(III) complex, were calculated from the emission spectra. The tendency of the kr values to vary depended on the tumor cells at different malignancy grades. Between T = 0 and T = 3h of invasion, the kr values exhibited an increase of 4% in NHA/TS (benign grade II gliomas), 7% in NHA/TSR (malignant grade III gliomas), and 27% in NHA/TSRA (malignant grade IV gliomas). Tumor cells with high-grade malignancy exhibited a rapid upward trend in kr values. The cancer GPS employs Eu(III) emissions to provide a new diagnostic method for determining human brain tumor malignancy.

Photoluminescence lifetime stability studies of β-diketonate europium complexes based phenanthroline derivatives in poly(methyl methacrylate) films.

In this work, five phenanthroline derivatives substituted with different methyl groups have been selected to synthesize β-diketonate-based europium complexes to check the influence of the substitutions on the degradation effect of those complexes in poly(methyl methacrylate) (PMMA) films. The photophysical properties of Eu(III) complexes, including absorbance, excitation, and emission have been carefully investigated in solution, solid-state, and doped in PMMA film. In all these states, the complexes exhibit an impressive red emission at 614 nm with a high photoluminescence quantum yield of up to 85 %. The films have been exposed under outdoor, indoor, and dark storage stability lifetime conditions for 1200 hours. The photoluminescence measurements recorded every 400, 800, and 1200 hours demonstrated that the film containing europium complex with phenanthroline ligand substituted by a high number of methyl groups (Eu(TTA)3L5) showed good photoluminescent stability in indoor and dark conditions, and exhibited better resistance to degradation in outdoor conditions compared to other complexes. This study has proved that phenanthroline ligands could be tuned chemically leading to better stability of those types of complexes in films which can be end-used for future stable optoelectronic devices such as luminescent solar concentrators.

Stability trend analysis of light lanthanide complexes with a fluorophenyl-dipicolinamide: A quantum chemical study

Extracting lanthanides (Ln) from actinides (An) is a crucial step in reprocessing spent nuclear fuel, and the interaction between ligands and Ln inevitably deserves careful study. In this study, we employ density functional theory (DFT) calculations to analyze the stability trend of trivalent light lanthanides (Ln (III), from La(III) to Eu(III)) complexes with N,N'‑diethyl-N,N'-di(para)fluorophenyl-2,6-dipicolinamide (FDPA), which has emerged as a promising ligand in Ln-An separation. The bond length, nature of bonding and electronic energy density properties of Ln-N and Ln-O bonds have been investigated. The quantum theory of atoms in molecules calculation shows that Ln(III)-FDPA complexes are stable, via closed-shell interactions. The Gibbs free energy changes (∆G) of La(III), Pr(III), Pm(III), Sm(III), and Eu(III) complexes with FDPA are approximately -0.07 Kcal/mol. In contrast, the ∆G values of Ce(III) and Nd(III) complexes with FDPA are 1.534 and 0.781 Kcal/mol, respectively. These findings indicate that La(III), Pr(III), Pm(III), Sm(III), and Eu(III) can be excellently extracted by FDPA from acidic solvents, whereas Ce(III) and Nd(III) do not. Our study contributes to a better understanding of the mechanism of lanthanide complexes and provides guidance for the design of ligands that can effectively discriminate lanthanides in nuclear waste reprocessing.

Formation of N,N,N',N'-tetramethylethylenediamine via coupling of the two charge reversed C-N bonds of Me3NO in the presence of an Eu(II) bis(trimethylsilyl)amide complex.

An N,N,N',N'-tetramethylethylenediamine (TMEDA) complex of Eu(II) was synthesized via an unprecedented self-aminomethylation of Me3NO in the presence of Eu[N(SiMe3)2]2(THF)2. The neutral TMEDA ligand is formed via the coupling of two charge reversed carbon centres from the same precursor Me3NO. In contrast, the reactions of LnII[N(SiMe3)2]2(THF)2 (Ln = Yb, Sm) with Me3NO led to the oxygen-bridged dinuclear complexes of Ln(III).

Induced chiroptical properties of helical Eu(iii) complex by electrostatic interaction with DNA

CPL activity was successfully induced from a helical Eu(iii) complex, EuLCOOH, by electrostatic interaction with DNA in aqueous solutions.

Synthesis, structure and luminescence of two europium complexes of diphenylimidazophenanthrolines

A dinuclear Eu(iii) complex with long photoluminescence lifetime was synthesized via hydrothermal nitrile hydrolysis and nitro to amino transformation.

Slow magnetic relaxation and luminescence properties in β-diketonate lanthanide(iii) complexes. Preparation of Eu(iii) and Yb(iii) OLED devices

Six β-diketonate compounds [Ln(btfa)3(4,4′-dinonylbipy)] Ln = Sm, Eu, Tb, Dy, Er and Yb are reported. Magnetic and Luminescence study is also filed. The Eu and Yb complexes were successfully used as emitters in multilayer vacuum-deposited OLEDs.

Fine tuning the steric hindrance of the Eu(ii) tris(pyrazolyl)borate complex for a blue organic light-emitting diode

A sky-blue OLED based on a Eu(ii) complex Eu–tBu shows an EQEmax of 15.7% and a Lmax of 52 240 cd m−2.

A terpyridyl-imidazole based europium tris-(β-diketonate) complex as an efficient molecular luminescent thermometer and single component white light emitter via synergy in energy transfer between ligands and Eu3.

The thermosensing and thermochromic behavior of one of our recently reported terpyridyl-imidazole based ternary europium tris-(β-diketonate) complexes of the composition [Eu(tta)3(tpy-HImzphen)] (tta = 2-thenoyltrifluoroacetone and tpy-HImzphen = 2-(4-[2,2':6',2''] terpyridin-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole) has been thoroughly investigated in this work. The said Eu(III) complex exhibits magnificent thermosensing as well as thermochromic properties and can be recommended as an excellent temperature sensor in a wide temperature domain of 273-343 K in terms of both emission intensity ratio (Sm = 5.78% K-1 at Tm = 343 K, δT = 0.012 K) and lifetime values (Sm = 3.36% K-1 at Tm = 333 K, δT = 0.009 K) or even in terms of its emitting color (red at 268 K, violet at 303 K, and blue at 343 K). Additionally, it displays remarkable solvent-induced luminescence behavior by displaying various emitting colors instead of its sole characteristic red emission upon varying the nature of the solvent. Finally, amalgamating these two features, we are able to attain white light emission (Commission Internationale de l'Eclairage coordinates: x = 0.34, y = 0.38) at 283 K from a single component. A plausible energy transfer mechanism has also been proposed in light of the existence of the ligand-to-metal charge transfer (LMCT) state as the quencher.

Complexes of rare earth metals with bromine-substituted (benzoxazolyl)naphtholate ligands as emissive materials

A series of complexes [Ln(NpBrOON)3]2 (Ln = Nd, Eu, Gd, Yb) were synthesized by the reaction of the corresponding lanthanide silylamides with 2-(2-benzoxazol-2-yl)-7-bromo-3-naphthol. The structure of the initial phenol, Eu and Yb complexes was established using X-ray diffraction analysis, which showed that the resulting compounds have a centrosymmetric dimeric structure. All the obtained complexes in the solid state upon excitation by light with a wavelength of 365 nm revealed ligand-centered photoluminescence (PL) in the visible region of 450–700 nm. The complexes of Nd and Yb in addition exhibit the metal-ctntered emission in the near-infrared (NIR) region of high intensity.

Electrofluorochromism based on the valence change of europium complexes in electrochemical devices with Prussian blue as the counter electrode.

The electrofluorochromism of Eu complexes based on the valence change between Eu3+ and Eu2+ is demonstrated in a two-electrode electrochemical device consisting of Prussian blue (PB) as the counter electrode. This study aims to improve the electrofluorochromic (EFC) performance of luminescence switching between Eu3+ and Eu2+ by enhancing the electrochemical reactivity of the EFC device. By introducing a PB film as a counter electrode in a two-electrode device, the redox reaction of Eu3+/2+ is promoted because of charge compensation by the counter PB film. The increase in the reaction charge enables faster changes in the photoluminescence from Eu3+ to Eu2+ and an increase in the blue luminescence intensity from the Eu2+ state. This approach achieves a lowered driving voltage, accelerates the electrochemical redox reaction of the Eu complex, and enhances the reversibility of the valence change of the Eu ion.

Thermodynamics of the Eu(III)-Mg-SO4-H2O and Eu(III)-Na-SO4-H2O systems. Part II: spectroscopy experiments, complexation and Pitzer/SIT models.

A time-resolved laser fluorescence spectroscopy (TRLFS) study was carried out to investigate the Eu(III)-SO4 complexation at room temperature over a wide range of Na2SO4 concentrations (0-2 mol kg-1). Spectroscopic observations confirm the step-wise formation of the aqueous complexes Eu(SO4)+, Eu(SO4)2- and Eu(SO4)33- over the investigated Na2SO4 concentrations. Combining TRLFS data obtained in this study and solubility data reported in Part I of this work for the Eu2(SO4)3-Na2SO4-H2O and Eu2(SO4)3-MgSO4-H2O systems, thermodynamic and activity models were derived based on the SIT and Pitzer formalisms. A combination of the geochemical calculation codes PhreeqC (SIT), PhreeSCALE (Pitzer) and the parameter estimation code PEST was used to determine the solubility products of Eu2(SO4)3·8H2O(cr) and Na2Eu2(SO4)4·2H2O(cr), stability constants of the Eu(III)-SO4 complexes (β0i), and the specific binary and ternary interaction parameters (εij, β(0)ij, β(1)ij, Cϕij, θik, Ψijk) for both activity models. The thermodynamic constants determined in this work are discussed with reference to values available in the literature.

High-performance white light-emitting diodes based on Efficient Trivalent Europium molecular complex

Trivalent Europium-based monochromatic red emissive phosphors are necessary constituents to comprehend high-performance solid-state lighting (SSL) devices. Here, in the present study, we report efficient molecular Eu(III) based red-emitting complexes Eu(TTA)3-TPA-DPA-Ph/t-Butyl...