Luminescent Properties of Europium(III) Complexes with Quinaldic Acid and Sulfur–Containing Neutral Ligands

The luminescent heteroligand complexes of europium(III) with quinaldic acid and sulfur-containing neutral ligands Eu(Quin)3∙D∙3H2O (Quin–quinaldic acid, D–dimethyl sulfoxide or dihexyl sulfoxide) and Eu(Quin)3∙3H2O have been obtained. Their composition and structure have been determined. The thermal and spectral-luminescent properties of the heteroligand europium(III) complexes have been studied. The quinaldate ion has been found to coordinate to the europium(III) ion as a bidentate ligand. The Stark structure of 5D0–7Fj (j = 0, 1, 2) transitions in the low-temperature luminescence spectra of the europium(III) complexes has been analyzed     

The luminescence response of diamine-liganded europium complexes upon resonant and pre-resonant excitation

The luminescence of four europium thenoyltrifluoroacetonate complexes containing diamine ligands is studied in solutions. The compounds are resonantly excited in the ligand absorption band by means of high-power nanosecond UV laser pulses. Additionally, a continuous light source is also used for resonant, as well as pre-resonant excitation of the complexes. The luminescence response characterizes the synthesized europium coordination complexes as emissive compounds suitable for fluorometric applications. Related to the possible usefulness of the diamine-liganded Eu complexes as luminescent labels for sensing and imaging of biological molecules, the luminescence response of these compounds upon UV excitation was probed also in aqueous media.     

Luminescense properties of new complexes of Eu(III) and Tb(III) with heterotopic ligands

As a result of coordination between ligands L and L' and europium(III) and terbium(III) ions, the new architectures were formed. The formulae of the complexes have been assigned on the basis of the spectroscopic data in solution and microanalyses. The europium complexes show excellent luminescence properties with high quantum yield (1b-Eu(3)L(2)) and effective intramolecular energy transfer from the ligand to the Eu(III) ions.     

Computational study of pH‐responsive di‐lanthanide complexes

Lanthanide complexes have found extensive use as luminescent probes for biological and medical investigations. Recently, a di‐europium complex that exhibits pH‐dependent luminescence‐decay was reported, and the ligand in that complex includes a large number of ionizable sites. To better understand the pH‐dependence of luminescence‐decay of this complex, the pK _a's of all tautomers of the di‐Lu³⁺ version of this complex were calculated computationally. The calculated Boltzmann‐averaged pK _a's of the complex are 5.85, ?0.21, and ?1.47 for the di‐Lu³⁺ complex in its first, second, and third protonation states, respectively. These pK _a values across protonation states indicate that changes in luminescence‐decay rate at physiologically relevant pH may be related to first protonation event of the complex exclusively.     

Coordination compounds of europium(III) and samarium(III) dibenzoylmethanates with 5-phenyl-2-(2′-pyridyl)-7,8-benzo-6,5-dihydro-1,3,6-triazaindolizine

Novel heteroligand europium(III) and samarium(III) complexes with dibenzoylmethane (HDBM) and 5-phenyl-2-(2??-pyridyl)-7,8-benzo-6,5-dihydro-1,3,6-triazaindolizine (L), Ln(DBM)₃L (Ln = Eu, Sm), were synthesized. The structure of the europium complex was determined by X-ray diffraction. It was shown that the use of L as an auxiliary ligand increases the luminescence intensity of lanthanides severalfold as compared with analogous complexes containing phenanthroline as the second ligand.     

Highly luminescent, triple- and quadruple-stranded, dinuclear Eu, Nd, and Sm(III) lanthanide complexes based on bis-diketonate ligands

The bis(beta-diketone) ligands 1,3-bis(3-phenyl-3-oxopropanoyl)benzene, H(2)L(1) and 1,3-bis(3-phenyl-3-oxopropanoyl) 5-ethoxy-benzene, H(2)L(2), have been prepared for the examination of dinuclear lanthanide complex formation and investigation of their properties as sensitizers for lanthanide luminescence. The ligands bear two conjugated diketonate binding sites linked by a 1,3-phenylene spacer. The ligands bind to lanthanide(III) or yttrium(III) ions to form neutral homodimetallic triple stranded complexes [M(2)L(1)(3)] where M = Eu, Nd, Sm, Y, Gd and [M(2)L(2)(3)], where M = Eu, Nd or anionic quadruple-stranded dinuclear lanthanide units, [Eu(2)L(1)(4)](2-). The crystal structure of the free ligand H(2)L(1) has been determined and shows a twisted arrangement of the two binding sites around the 1,3-phenylene spacer. The dinuclear complexes have been isolated and fully characterized. Detailed NMR investigations of the complexes confirm the formation of a single complex species, with high symmetry; the complexes show clear proton patterns with chemical shifts of a wide range due to the lanthanide paramagnetism. Addition of Pirkle's reagent to solutions of the complexes leads to splitting of the peaks, confirming the chiral nature of the complexes. Electrospray and MALDI mass spectrometry have been used to identify complex formulation and characteristic isotope patterns for the different lanthanide complexes have been obtained. The complexes have high molar absorption coefficients (around 13 x 10(4) M(-1)cm(-1)) and display strong visible (red or pink) or NIR luminescence upon irradiation at the ligand band around 350 nm, depending on the choice of the lanthanide. Emission quantum yield experiments have been performed and the luminescence signals of the dinuclear complexes have been found to be up to 11 times more intense than the luminescence signals of the mononuclear analogues. The emission quantum yields and the luminescence lifetimes are determined to be 5% and 220 micros for [Eu(2)L(1)(3)], 0.16% and 13 micros for [Sm(2)L(1)(3)], and 0.6% and 1.5 micros for [Nd(2)L(1)(3)]. The energy level of the ligand triplet state was determined from the 77 K spectrum of [Gd(2)L(1)(3)]. The bis-diketonate ligand is shown to be an efficient sensitizer, particularly for Sm and Nd. Photophysical studies of the europium complexes at room temperature and 77 K show the presence of a thermally activated deactivation pathway, which we attribute to ligand-to-metal charge transfer (LMCT). Quenching of the luminescence from this level seems to be operational for the Eu(III) complex but not for complexes of Sm(III) and Nd(III), which exhibit long lifetimes. The quadruple-stranded europium complex has been isolated and characterized as the piperidinium salt of [Eu(2)L(1)(4)](2-). Compared with the triple-stranded Eu(III) complex in the solid state, the quadruple-stranded complex displays a more intense emission signal with a distinct emission pattern indicating the higher symmetry of the quadruple-stranded complex.     

Synthesis and infrared and luminescence spectra of rare earth complexes with a new hexapodal ligand

Solid complexes of rare earth nitrates and picrates with a new hexapodal ligand, 1,2,3,4,5,6-hexa{[(2'-benzylamino-formyl)phenoxyl]methyl}-benzene (L) have been prepared. These complexes were characterized by elemental analysis, IR and molar conductivity. At the same time, the luminescence properties of the Eu(III) and Tb(III) nitrates and picrates complexes in solid state were also investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of europium and terbium ions. The influence of the counter anion on the luminescent intensity was also discussed.     

Synthesis,characterization and luminescence properties of Eu(III) and Tb(III) complexes with novel pyrazole derivatives and 1,10-phenanthroline

Two novel pyrazole-derived ligands, 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)picolinic acid (CDPA) and 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)-N-phenylpicolinamide (CDPP) were prepared by 3,6-dichloropicolinic acid (DCPA). Their complexes with terbium(III) and europium(III) were synthesized. The complexes were characterized by elemental analysis, infrared spectra, ¹H NMR and TG–DTG. Furthermore, the above complexes using 1,10-phenanthroline as a secondary ligand were also synthesized and characterized. The luminescence properties of these complexes in solid state were investigated. The results suggested that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes and the fluorescence of the complexes with 1,10-phenanthroline as a secondary ligand was prominently stronger than that of complexes without this ligand., and the three ligand (DCPA), (CDPP) and (CDPA) are excellent sensitizers to Eu(III) and Tb(III) ion.     

Efficient sensitization of europium, ytterbium, and neodymium functionalized tris-dipicolinate lanthanide complexes through tunable charge-transfer excited states

A series of push-pull donor-pi-conjugated dipicolinic acid ligands and related tris-dipicolinate europium and lutetium complexes have been prepared. The ligands present broad absorption and emission transitions in the visible spectral range unambiguously assigned to charge-transfer transitions (CT) by means of time-dependent density functional theory calculations. The photophysical properties (absorption, emission, luminescence quantum yield, and lifetime) of the corresponding europium complexes were thoroughly investigated. Solvatochromism and temperature effects clearly confirm that Eu(III) sensitization directly occurs from the ligand CT state. In addition, modulation of the energy of the CT donating state by changing the nature of the donor fragment allows the optimal energy of the antennae for europium sensitization to be determined, and this optimal energy was found to be close to the (5)D 1 accepting state. Finally, this CT sensitization process has been successfully extended to near-infrared emitters (neodymium and ytterbium).     

Increased antenna effect of the lanthanide complexes by control of a number of terdentate N-donor pyridine ligands

Three europium complexes with the terdentate N-donor ligand 2,6-bis(1H-pyrazol-3-yl)pyridine (L) have been synthesized, and their crystal structures have been determined. The ligand/metal ratios in these complexes are 3, 2, and 1. The photophysical properties of the complexes indicate more efficient ligand sensitization of europium emission for the homoleptic complex.     

Modulating the photophysical properties of azamacrocyclic europium complexes with charge-transfer antenna chromophores

Two europium complexes with bis(bipyridine) azamacrocyclic ligands featuring pendant arms with or without π-conjugated donor groups are synthesized and fully characterized by theoretical calculations and NMR spectroscopy. Their photophysical properties, including two-photon absorption, are investigated in water and in various organic solvents. The nonfunctionalized ligand gives highly water-stable europium complexes featuring bright luminescence properties but poor two-photon absorption cross sections. On the other hand, the europium complex with an extended conjugated antenna ligand presents a two-photon absorption cross section of 45 GM at 720 nm but is poorly luminescent in water. A detailed solvent-dependent photophysical study indicates that this luminescence quenching is not due to the direct coordination of O-H vibrators to the metal center but to the increase of nonradiative processes in a protic solvent induced by an internal isomerization equilibrium.     

Lanthanide-sensitized luminescence for the detection of tetracyclines

Organic chelates of lanthanide ions, priviously used to enhance the detection sensitivity of the ions, are now used for the sensitive detection of the ligands. When complexed with europium(III), tetracycline displays the broad-banded absorption characteristics of an organic ligand. The excited ligand undergoes intersystem crossing to a triplet state, and then transfers its energy to a 4f level within the europium(III) ion. the resulting narrow, line-like luminescence of the europium(III) ion has a peak intensity ten times greater than the peak intensity of the uncomplexed ligand. This lanthanide-sensitized luminescence technique is used to quantify tetracycline and two of its analogues. Detection limits are in the nanogram range. Experimental conditions are discussed.     

Luminescence studies of europium chelates with increasing benzene ring substituents ligand-doped polymer

The luminescence properties of four europium chelates with increasing benzene ring substituents ligand in poly(methylmethacrylate) (PMMA) have been investigated by fluorescence emission spectra and lifetime measurements. According to the fluorescence emission spectra, the Judd-Ofelt parameters Omega2, Omega4 of europium chelates-doped PMMA have been calculated and the radiative properties were also presented. It showed that the increase of benzene ring substituents in ligand can increase the metastable state lifetime tau(m), the luminescence quantum yield eta and the stimulated emission cross-section sigma of 5D0-->7F2 transition.     

Structural characterization of shielded isomeric europium complexes with metal-metal contact

New luminescent isomeric europium(III) complexes with carboxylic carbonyl group coordination (I and II) have been prepared by solvothermal synthesis using the ligand 2,2'-bipyridine-4,4'-dicarboxylic acid (bpdc), with the nonradiatively shielded Eu3+ coordination sphere completed by dimethyl sulfoxide ligands. The room temperature IR spectra and Eu3+ luminescence spectra do not provide a definitive distinction between I and II, but low-temperature luminescence can give a clear identification.     

Influence of the Nature of Carboxylic Acid on the Luminescence and Spectral Properties of (Carboxylato)bis(dibenzoylmethanato)europium(III) Complexes

A series of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes containing anions of both saturated and unsaturated carboxylic acids were synthesized to compare the luminescence and spectral properties of heteroligand Eu(III) complexes. (Carboxylato)bis(dibenzoylmethanato)europium(III) complexes with unsaturated acid anions were synthesized for the first time. The compounds obtained were characterized using elemental analysis and luminescence and IR spectroscopy. These studies revealed two types of influence of the nature of an acid substituent on the luminescence spectra of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes. The anomalous Stark structure of the luminescence spectra of one group of compounds is attributed to the charge transfer state at 77 K.     

脂肪酸铕配合物掺杂聚乙烯、聚丙烯和聚苯乙烯光致发光复合材料

合成了正己酸铕、正辛酸铕、月桂酸铕和硬脂酸铕4种不同碳链链长的脂肪酸铕配合物,通过哈克转矩流变仪将铕配合物(质量分数1%)机械掺杂于3种不同透明度的聚乙烯(PE)、聚丙烯(PP)和聚苯乙烯(PS)通用树脂中,制备了系列铕配合物掺杂聚合物光致发光复合材料,考察了配体、配合物、聚合物基体对复合材料的外观、透明性及其荧光性能的影响。 结果表明,4种脂肪酸铕配合物及其掺杂的复合材料在紫外光的激发下均在593、617 nm处发射强的Eu3+离子5D0→7F1、5D0→7F2跃迁的特征荧光;脂肪酸配体的碳链长短对铕配合物及复合材料的发光影响较小;PE、PP复合材料发光颜色与红光铕配合物相同,PS复合材料因基体PS和Eu3+离子的发光共同作用而呈现了玫瑰红的荧光发射。     

Luminescence of europium(III) β-diketonate complexes in a Nafion membrane

EuL₃ · phen complex compounds (L is benzoylacetone, dibenzoylmethane, or thenoyltrifluoroacetone; phen is 1,10-phenanthroline) were synthesized in a perfluorosulfonic membrane. The results of adsorption measurements suggest that the complexes experience steric hindrances in the membrane pores. The luminescence from intercalates is sensitized due to the increase in the degree of population of the ⁵ D ₀ excited state of europium(III) caused by the transfer of energy from the ligands. Depending on the type of β-diketonate ligand, the adsorption of water on the modified membrane can enhance or suppress the luminescence from the complex.     

Luminescence determination of europium microquantities after its preconcentration on polyurethane foam

Sorption of the mixed-ligand complexes of europium(III) with thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline (Phen) on polyurethane foam (PUF) has been studied by a luminescence method. The optimum conditions of sorption have been found. The sorbate composition on PUF has been determined (the Eu:TTA:Phen ratio was 1:3:1). Luminescence spectra of the europium complexes in solution and on PUF at 77 K have been investigated. It was concluded that the character of the Eu³⁺ coordination both in solution and on the sorbent is the same. Stability constants for the complexes in solution (lg K = 8.4) and on the sorbent (lg K = 5.5) have been calculated. The decrease of the stability of the complex on PUF is explained by the deformation of the complex molecule in the sorbent phase. Sorption coefficients for europium (245) and scandium (2.35) and the coefficient of selectivity for europium in Sc₂O₃ (102.3) have been determined. A method for the sorption-luminescence determination of europium in Sc₂O₃ with a lower limit of contents determined of 1 × 10⁻⁶⁰% has been developed.     

Synthesis and luminescence properties of lanthanide complexes with a new aryl amide bifunctional bridging ligand

A new aryl amide type bifunctional bridging ligand 4,4'-bis{[(2'-benzylaminoformyl)phenoxyl]methyl}-1,1'-biphenyl (L) and its complexes with lanthanide ions (Ln=Pr, Eu, Gd, Tb, Ho, Er) were synthesized and characterized by elemental analysis, infrared spectra, conductivity measurements and thermal analysis. At the same time, the luminescence properties of the Eu and Tb complexes in acetone solutions were investigated. Under the excitation of UV light, these two complexes exhibited characteristic emission of europium and terbium ions. And the lowest triplet state energy level T1 of this ligand matches better to the lowest resonance energy level of Tb(III) than to Eu(III) ion.     

Two-photon antenna effect induced in octupolar europium complexes

The synthesis of new chromophore-based pyridine-dicarboxamide ligands and related D3 symmetric europium(III) complexes is described. The photophysical properties of the ligands and the complexes were thoroughly investigated and interpreted on the basis of theoretical calculations (TD-DFT). Finally, the luminescence of Eu(III) was sensitized by two-photon absorption of the ligand, illustrating the two-photon antenna effect phenomenon.