Experimental and theoretical approaches toward anion-responsive tripod-lanthanide complexes: mixed-donor ligand effects on lanthanide complexation and luminescence sensing profiles

A new series of tripods were designed to form anion-responsive, luminescent lanthanide complexes. These tripods contain pyridine, thiazole, pyrazine, or quinoline chromophores combined with amide carbonyl oxygen and tertiary nitrogen atoms. Crystallographic and EXAFS studies of the 10-coordinated tripod-La(NO(3))(3) complexes revealed that each La(3+) cation was cooperatively coordinated by one tetradentate tripod and three bidentate NO(3)(-) anions in the crystal and in CH(3)CN. Quantum chemical calculations indicated that the aromatic nitrogen plays a significant role in lanthanide complexation. The experimentally determined stability constants of complexes of the tripod with La(NO(3))(3), Eu(NO(3))(3), and Tb(NO(3))(3) were in good agreement with the theoretically calculated interaction energies. Complexation of each tripod with lanthanide triflate gave a mixture of several lanthanide complex species. Interestingly, the addition of a coordinative NO(3)(-) or Cl(-) anion to the mixture significantly influenced the lanthanide complexation profiles. The particular combination of tripod and a luminescent Eu(3+) center gave anion-selective luminescence enhancements. Pyridine-containing tripods exhibited the highest NO(3)(-) anion-selective luminescence and thus permit naked-eye detection of the NO(3)(-) anion.     

Luminescent lanthanide complexes with stereocontrolled tris(2-pyridylmethyl)amine ligands: chirality effects on lanthanide complexation and luminescence properties

A series of tris(2-pyridylmethyl)amines including one and two asymmetric centers were synthesized in a stereo-controlled fashion as potential ligands of lanthanide cations. The reaction of chiral pyridylethyl methanesulfonates and bis(pyridylmethyl)amines occurred via an S(N)2 mechanism with complete inversion of asymmetric centers and gave the stereocontrolled tris(2-pyridylmethyl)amines, the stereochemical purity of which was ascertained by GPC, NMR, X-ray, and polarimetry experiments. They formed stable Tb(3+) and Eu(3+) complexes having 1:1, 1:2, and 1:3 stoichiometry (metal:ligand) in CH(3)CN solutions. NMR and UV titration experiments revealed that their complexation behaviors were rarely influenced by ligand chirality but significantly affected by the nature of the counteranion and the concentration ratio of metal to ligand. The Tb(3+) and Eu(3+) complexes with these tripodal ligands exhibited characteristic luminescence spectra upon excitation for pyridine chromophores (260 nm), the intensities of which were largely dependent on the ligand chirality. The meso isomer of the disubstituted tripods particularly exhibited the enhanced terbium luminescence ca. three times more than its diastereomer and un- and monosubstituted tripods. Direct excitation at the lanthanide center had similar chirality effects on the luminescence profiles, indicating that the stereochemistry of the employed ligand largely influenced the lanthanide emitting processes. Since the ligand chirality finely modified the local coordination environments around the lanthanide center, the use of stereocontrolled ligands is applicable in design of the luminescent lanthanide complexes.     

新型超分子复合发光材料四足配体铕配合物-蒙脱土的插层组装及发光性质

通过离子交换反应将四足配体铕配合物[EuL(NO3)]2+[L=1,1,1’,1’-四(吡啶-2-羧酸酯基)联三甲基丙烷]插层组装到蒙脱土(MT)层板间, 制备出一种新型的超分子复合发光材料[EuL(NO3)]2+-MT. 用元素分析、XRD、FTIR、UV-Vis和热分析对材料进行了表征, 并对其荧光性质进行了研究. 结果表明, 复合材料保持了蒙脱土良好的层柱结构特征, 其层间距d(001)值与插层配离子的直径吻合得较好, 配离子以单层形式分布于蒙脱土层板间. 在紫外光激发下, 复合材料发出较强的Eu3+特征荧光, 其相对荧光强度、荧光单色性和荧光寿命大大优于相应配合物的乙醇溶液. 复合材料中配合物的发光性能、光稳定性和热稳定性较纯配合物有明显提高.     

Colloidal nanoparticles of a europium complex with enhanced luminescent properties

We report an alternative approach, that is, forming Eu(tta)3dpbt (dpbt = 2-( N, N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine, tta = thenoyltrifluoroacetonato) nanoparticles in water/methanol mixtures, to satisfy the combined requirements of good dispersibility in water solutions and efficient long-wavelength sensitization for Eu (III) complexes to be used in biological applications. The size of Eu(tta)3dpbt colloidal particles with very high luminescent capabilities can be modulated to some extent by changing the preparation conditions. The optical excitation window for the Eu (III) luminescence of Eu(tta)3dpbt nanoparticles, extending up to 475 nm, is wider than that of Eu(tta)3dpbt molecules dissolved in toluene. This is the first example for obviously extending the sensitization window of luminescent lanthanide materials to the long-wavelength region by forming nanoparticles of a lanthanide complex. Quantum yields of Eu (III) luminescence of the prepared Eu(tta)3dpbt colloidal particles, with an average diameter of 33.1 nm, are 0.27, 0.27, 0.24, 0.19, 0.14, and 0.01 upon excitation at 402, 420, 430, 440, 450, and 475 nm, respectively. The Eu(tta)3dpbt nanoparticles exhibited excellent two-photon sensitization performance with a highest delta Phi value of 3.2 x 10(5) GM (1 GM = 10(-50) cm4 s photo(-1) particle(-1)) at the excitation wavelength of 832 nm, which is about 7 times higher than the highest value reported for the CdSe/ZnS core-shell quantum dots. The favorable luminescent properties and the good dispersibility in water solutions of the Eu(tta)3dpbt nanoparticles are very promising for the development of new luminescent nanoprobes for bioanalysis.     

Synthesis, characterization and luminescent properties of new highly luminescent organic ligand and complexes of trivalent rare earth

A novel ligand with two carboxylic groups has been synthesized. The composition and structure of the ligand were characterized by IR, (1)H NMR and MS spectrometry. The highly luminescent intensity complexes were prepared with the ligand and phen. The IR, solid state (13)C NMR and fluorescent spectra of the complex were studied. IR absorption spectra indicate that the ligand is coordinated to the Eu(3+) ion, and chemical bonds are formed between Eu(3+) ion and nitrogen atoms of phen. The fluorescent spectra illustrate that the complex has an excellent luminescence, indicating the ligand favors energy transfer to the emitting energy level of Eu(3+). The influences of pH and reaction solvent on the fluorescence intensity of the complex were also discussed.     

[（n—C4H9）4N][EuxM1—x（TTA）4]（M=La、Sm、Gd、Tb）的光致发光

合成了一类组成为[(n-C4H9)4N][EuxM1-x(TTA)4](M=La、Sm、Gd、Tb）的固体配合物，通过测定其红外光谱，X射线粉末衍射谱和荧光光谱，研究了配合物结构和发光性质随Eu^3 浓度变化的规律。红外光谱和XRD谱的分析结果表明，在体系中没有新化合物生成，而荧光光谱分析结果表明发光强度与Eu^3 浓度不成线性关系，不发光的基质配合物组分对发光有不同大小和不同类型的影响，提出一种可能的发光机制解释这一共发光现象。     

Thiolate alkylation in tripod zinc complexes: a comparative kinetic study

The biologically relevant alkylations of the thiolate ligands in tripod zinc thiolates by methyl iodide were studied kinetically. Five tripod ligands of the pyrazolyl/thioimidazolyl borate type were employed, offering N3, N2S, NS2, and S3 donor sets. For each of them, the ethyl-, benzyl-, phenyl-, and p-nitrophenylthiolate zinc complexes were investigated, yielding a total of 20 second-order rate constants. The comparison of these rate constants shows three effects: (1) the electronic effect among the thiolates, i.e., the ethanethiolates react about 3 orders of magnitude faster than the p-nitrophenylthiolates; (2) the steric effect among the pyrazolylborates, i.e., the phenyl-substituted ones react about 2 orders of magnitude faster than the tert-butyl-substituted ones; and (3) the strong acceleration by the sulfur donors in the tripods, reaching 4 orders of magnitude between the reaction times of the (N3)Zn-SR and (S3)Zn-SR complexes.     

The preparation and performance of visible-light-sensitized luminescent nanoparticles based on europium complex

Long-wavelength-sensitized luminescent materials are desired for bio-detection. In this paper, we prepared a new kind of luminescent europium nanoparticles by a co-precipitation-condensation method. The luminescent europium complex Eu（tta）3.bpt （tta = thenoyltrifluoroacetonate; bpt = 2-（N,N- di-ethylanilin-4-yl）-4,6-bis（pyrazol-l-yl）-l,3,5-triazine） was used as the active material, being encapsulated in the nanoparticles formed from 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane （PFOTS） and poly（styrene-co-methyl methacrylate） [P（ST-co-MMA）]. The prepared nanoparticles not only can be well dispersed in water but also were of high photostability. Importantly, the nanoparticles displayed maximal excitation wavelength at 425 nm as well as an extended excitation wavelength up to 480 nm and a quantum yield for Eu3＋ luminescence of 0.22 （λex= 425 nm, room temperature）.     

Crystallographic,X-ray absorption,and IR studies of solid- and solution-state structures of tris(nitrato) N,N,N',N'-tetraethylmalonamide complexes of lanthanides. Comparison with the Americium complex

To fine-tune the design of optimized donor ligands for nuclear waste actinide selective extraction, both electronic and molecular structures of the actinide complexes that are formed must be investigated. In particular, to achieve the selective complexation of transplutonium 3+ ions versus lanthanide 3+ ions is one of the major challenges, given the chemical similarities between these two f-element families. In this work, the structure of solvent-phase M(NO3)3(TEMA)2 complexes (Ln = Nd, Eu, Ho, Yb, Lu, Am; TEMA = N,N,N',N'-tetraethylmalonamide) was investigated by liquid-phase spectroscopic methods among which extended X-ray absorption fine structure played a major role. In addition, the crystal structures of the species Nd(NO3)3(TEMA)2 and Yb(NO3)3(TEMA)2 have been determined by X-ray diffraction. Nd(NO3)3(C11N2O2H22)2 crystallizes in the monoclinic system (P2(1) space group; a = 11.2627(4) A, b = 20.5992(8) A, c = 22.2126(8) A; alpha = gamma = 90 degrees, beta = 102.572(1) degrees; Z = 6), and Yb(NO3)3(C11N2O2H22)2 crystallizes in the orthorhombic system (P2(1)2(1)2(1) space group; a = 9.3542(1) A, b = 18.1148(2) A, c = 19.7675(2) A; alpha = beta = gamma = 90 degrees; Z = 4). In the solvent phase, the metal polyhedron was found to be similar to that of the solid-state complex Nd(NO3)3(TEMA)2 for M = Nd to Ho. For M = Yb and Lu, a significant elongation of one nitrate oxygen bond was observed. Comparison with measurements on the Am(NO3)3(TEMA)2 complex in ethanol has shown the similarities between the Nd3+ and Am3+ coordination spheres.     

Luminescence properties and water coordination of Eu3+ in the binary solvent mixture water/1-butyl-3-methylimidazolium chloride

The effect of relative water content on the luminescence properties and speciation of Eu3+ ions in solutions of EuCl3 in the binary solvent mixture water/[BMI]Cl is presented, where [BMI]Cl is the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride. Using luminescence techniques, the binding properties of water to Eu3+ are determined for samples with mole ratios of water-to-IL ranging from 0 to 5. Very little water binds to Eu3+ at mole ratios of water-to-IL less than 1, above which binding increases rapidly with increasing water concentration. It is shown that only certain hydration numbers for Eu3+ complexes are stable in the water/IL solutions. The data presented suggest that the Eu3+ species present are [EuClx]3-x, [EuCly(H2O)3-4]3-y, [EuClz(H2O)6]3-z, and [Eu(H2O)8-9]3+ (where x > y > z). Comparison of the positions of the 5D0<--7F0 transitions of the Eu3+ complexes in IL solution with those of model crystal systems provides insight into the extent of Cl- complexation. This study suggests that [BMI]Cl is a promising medium for luminescent lanthanide (Ln) compounds due to the low-energy phonon environment of the [LnClx]3-x complex and to the fact that moderate water contamination does not result in direct binding of water to Ln3+, which would result in luminescence quenching.     

Zn-OH2 and Zn-OH complexes with hydroborate-derived tripod ligands: a comprehensive study

The complete array of those hydrotris(pyrazolyl/thioimidazolyl)borate ligands that were developed and used in the author's laboratories, with N3, N2S, NS2, and S3 donor sets, was scanned for their ability to form Zn-OH2 and Zn-OH complexes. The coordination motifs found were Zn-OH2, Zn-OH, Zn-OH-Zn, and Zn-O2H3-Zn. Of these, the well-established Zn-OH motif was complemented with novel species bearing N3, NS2, and S3 tripods. The Zn-OH2 motif was observed only with pyrazolylborate ligands and only in unusual situations with coordination numbers higher than 4 for zinc. The new Zn-OH-Zn motif was realized for three different pyrazolylborates, for one NS2 tripod, and for two S3 tripods. Finally, it was verified that the Zn-O2H3-Zn motif again occurs only with pyrazolylborate ligands. The new complexes were identified by a total of 11 structure determinations.     

Electronic structure and luminescent properties of antimony(III) complex compounds with nitrogen containing outer-sphere organic cations

X-Ray photoelectron (XPS) and luminescent spectroscopy have been used to investigate complex compounds of antimony(III) halides with nitrogen containing organic bases. Inequality of bonds of amine and imine groups was found by XPS to disappear when complexes of antimony(III) with N,N′-diphenylguanidine (Dphg) were formed. The appearance of N1s symmetric line when transiting from Dphg to the cation N,N′-diphenylguanidine ( Dphg⁺) in complex compounds of antimony(III) testifies to this. The study performed demonstrates that electron density increment on the antimony(III) central atom (complexing agent) results in the bathochromic shift ³P₁ → ¹ S ₀ of the luminescence band of antimony(III) ion.     

Synthesis, characterization, and luminescence properties of the ternary europium complex covalently bonded to mesoporous SBA-15

A novel mesoporous SBA-15 type of hybrid material (phen-SBA-15) covalently bonded with 1,10-phenanthroline (phen) ligand was synthesized by co-condensation of tetraethoxysilane (TEOS) and the chelate ligand 5-[N,N-bis-3-(triethoxysilyl)propyl]ureyl-1,10-phenanthroline (phen-Si) in the presence of Pluronic P123 surfactant as a template. The preservation of the chelate ligand structure during the hydrothermal synthesis and the surfactant extraction process was confirmed by Fourier transform infrared (FTIR) and (29)Si MAS NMR spectroscopies. SBA-15 consisting of the highly luminescent ternary complex Eu(TTA)(3)phen (TTA = 2-thenoyltrifluoroacetone) covalently bonded to a silica-based network, which was designated as Eu(TTA)(3)phen-SBA-15, was obtained by introducing the Eu(TTA)(3).2H(2)O complex into the hybrid materials via a ligand exchange reaction. XRD, TEM, and N(2) adsorption measurements were employed to characterize the mesostructure of Eu(TTA)(3)phen-SBA-15. For comparison, SBA-15 doped with Eu(TTA)(3).2H(2)O and Eu(TTA)(3)phen complexes and SBA-15 covalently bonded with a binary europium complex with phen ligand were also synthesized, and were named SBA-15/Eu(TTA)(3), SBA-15/Eu(TTA)(3)phen, and Eu-phen-SBA-15, respectively. The detailed luminescence studies on all the materials showed that, compared with the doping sample SBA-15/Eu(TTA)(3)phen and binary europium complex functionalized sample Eu-phen-SBA-15, the Eu(TTA)(3)phen-SBA-15 mesoporous hybrid material exhibited higher luminescence intensity and emission quantum efficiency. Thermogravimetric analysis on Eu(TTA)(3)phen-SBA-15 demonstrated that the thermal stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous SBA-15 matrix.     

Polymetallic lanthanide complexes with PAMAM-naphthalimide dendritic ligands: luminescent lanthanide complexes formed in solution

Generation 3 PAMAM dendrimers functionalized with 2,3-naphthalimide chromophoric groups on the end branches were synthesized, and the formation of Eu3+ polymetallic complexes was investigated. The luminescence properties of these complexes upon binding were fully characterized. On addition of Eu3+ to the dendrimer solution, lanthanide luminescence appears. The formation of a luminescent species corresponding to a dendrimer:lanthanide ratio of 1:8 was determined by luminescence batch titration and indicated by the maximum of Eu3+ emission. This indicates an overall average coordination number of 7.5 around each lanthanide metal cation. This is the first report of such characterization in the literature. Luminescence lifetimes indicate that the metal cation is well protected from nonradiative deactivation by the dendritic structure. Despite the limited efficiency of the sensitization of Eu3+, the absolute quantum yield being 0.0006, the good protection of the eight lanthanide cations bound in the dendrimer structure and the high absorptivity leads to the red emission from Eu3+ that is easily observed in solution under irradiation with 354 nm UV light.     

Europium(III) Acrylatodibenzoylmethanate: Synthesis,Spectroscopy (IR,Luminescence), and Polymerization Properties

Eu(III) acrylatodibenzoylmethanate was synthesized with the aim of obtaining luminescent macromolecular Ln(III) complexes with chromophores. It was homo- and copolymerized with methyl methacrylate. The compounds formed were characterized by elemental analysis, luminescence, and IR spectroscopy. The luminescence intensity of the macromolecular Eu(III) complexes containing dibenzoylmethanate ions was shown to exceed the intensity of the monomeric complex by several times. The increase in the luminescence intensity when going from the monomer to copolymers is explained by the weakening of the quenching effect of the low state of the metal–ligand charge transfer.     

Schiff碱铕配合物的合成及性质

在甲醇中合成了2-乙酰基苯并咪唑缩牛磺酸Schiff碱型配体及其与Eu(Ⅲ)的配合物。 通过Eu化学和元素分析、质谱、核磁共振谱、红外光谱、激光拉曼光谱、三维荧光光谱,确定了配体与配合物的组成及结构。 Eu(Ⅲ)配合物为Eu2L3(NO3)3(L=C11H12N3O3S)。 配合物荧光发射主要是Eu3+微扰的配体发光,其次为中心Eu3+离子的窄带发射。 当λex=330.0 nm时,配合物发射Eu3+离子的特征窄带荧光;当λex=410.0 nm时,Eu3+发射λem=525.0 nm的荧光。     

Synthesis and photophysical properties of colloids fabricated by the layer-by-layer polyelectrolyte assembly onto Eu(III) complex as a core

The luminescent colloids have been synthesized through the layer-by-layer assembly of poly(sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI) onto the luminescent core. The latter has been obtained by the reprecipitation of complex Eu[(TTA)(3)1] (where TTA(-) and 1 are thenoyltrifluoroacetonate and 2-(5-chlorophenyl-2-hydroxy)-2-phenylethenyl-bis-(2-methoxyphenyl)phosphine oxide, respectively) from organic solvent to aqueous solution. The variation of Eu(III) complexes indicates the role of the complex core in the development of such core-shell colloids. Complex Eu[(TTA)(3)1] is most convenient precursor of Eu-doped luminescent nanocomposites. The fluorometric measurements at each step of the layer-by-layer polyelectrolyte assembly onto Eu[(TTA)(3)1] core, at various pHs and additives reveal the quenching of Eu-centered luminescence as a result of the interfacial interaction of the core and the dye. The AFM images and electrochemical behavior of PSS-(PEI-PSS)(n)-Eu[(TTA)(3)1] colloids deposited on the surface indicate the stability of the polyelectrolyte multilayer in the dried state.     

Time-resolved long-lived luminescence imaging method employing luminescent lanthanide probes with a new microscopy system

Superior fluorescence imaging methods are needed for detailed studies on biological phenomena, and one approach that permits precise analyses is time-resolved fluorescence measurement, which offers a high signal-to-noise ratio. Herein, we describe a new fluorescence imaging system to visualize biomolecules within living biological samples by means of time-resolved, long-lived luminescence microscopy (TRLLM). In TRLLM, short-lived background fluorescence and scattered light are gated out, allowing the long-lived luminescence to be selectively imaged. Usual time-resolved fluorescence microscopy provides fluorescence images with nanosecond resolution and has been used to image interactions between proteins, protein phosphorylation, the local pH, the refractive index, ion or oxygen concentrations, etc. Luminescent lanthanide complexes (especially europium and terbium trivalent ions (Eu3+ and Tb3+)), in contrast, have long luminescence lifetimes on the order of milliseconds. We have designed and synthesized new luminescent Eu3+ complexes for TRLLM and also developed a new TRLLM system using a conventional fluorescence microscope with an image intensifier unit for gated signal acquisition and a xenon flash lamp as the excitation source. When the newly developed luminescent Eu3+ complexes were applied to living cells, clear fluorescence images were acquired with the TRLLM system, and short-lived fluorescence was completely excluded. By using Eu3+ and Tb3+ luminescent complexes in combination, time-resolved dual-color imaging was also possible. Furthermore, we monitored changes of intracellular ionic zinc (Zn2+) concentration by using a Zn2+-selective luminescent Eu3+ chemosensor, [Eu-7]. This new imaging technique should facilitate investigations of biological functions with fluorescence microscopy, complementing other fluorescence imaging methodologies.     

Determination of fluoroquinolone antibiotics through the fluorescent response of Eu(III) based nanoparticles fabricated by layer-by-layer technique

The present work introduces the determination of fluoroquinolone antibiotics (FQs) in aqueous solutions through the fluorescent response of Eu(TTA)₃ and [Eu(TTA)₃1] (TTA⁻ and 1 are thenoyltrifluoroacetonate and phosphine oxide derivative) complexes encapsulated into the polyelectrolyte capsules fabricated through layer-by-layer deposition of poly(sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI). The variation of luminescent core, polyelectrolyte deposition and concentration conditions reveals two modes of fluorescent response on FQs of diverse structure namely the sensitization and quenching of Eu(III) centered luminescence. The obtained regularities reveal the ternary complex formation and the ligand exchange occurring at the interface of polyelectrolyte coated [Eu(TTA)₃1] based colloids as the reasons of the diverse fluorescent response of Eu(III) centered luminescence on FQs. The factors affecting the fluorescent response have been revealed, which are: the content of luminescent core, the mode of polyelectrolyte deposition, concentration and structure of FQs. The discrimination of moxifloxacin and lomefloxacin from levofloxacin, ofloxacin, difloxacin, perfloxacin through the quenching of Eu(III) luminescence in PSS-[Eu(TTA)₃1] colloids has been revealed.     

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.