Lanthanide Emission Research Articles

Lanthanide near infrared imaging in living cells with Yb 3+ nano metal organic frameworks

We have created unique near-infrared (NIR)-emitting nanoscale metal-organic frameworks (nano-MOFs) incorporating a high density of Yb(3+) lanthanide cations and sensitizers derived from phenylene. We establish here that these nano-MOFs can be incorporated into living cells for NIR imaging. Specifically, we introduce bulk and nano-Yb-phenylenevinylenedicarboxylate-3 (nano-Yb-PVDC-3), a unique MOF based on a PVDC sensitizer-ligand and Yb(3+) NIR-emitting lanthanide cations. This material has been structurally characterized, its stability in various media has been assessed, and its luminescent properties have been studied. We demonstrate that it is stable in certain specific biological media, does not photobleach, and has an IC50 of 100 μg/mL, which is sufficient to allow live cell imaging. Confocal microscopy and inductively coupled plasma measurements reveal that nano-Yb-PVDC-3 can be internalized by cells with a cytoplasmic localization. Despite its relatively low quantum yield, nano-Yb-PVDC-3 emits a sufficient number of photons per unit volume to serve as a NIR-emitting reporter for imaging living HeLa and NIH 3T3 cells. NIR microscopy allows for highly efficient discrimination between the nano-MOF emission signal and the cellular autofluorescence arising from biological material. This work represents a demonstration of the possibility of using NIR lanthanide emission for biological imaging applications in living cells with single-photon excitation.

Relations between structure and physicooptical properties of Eu3+ and Tb3+ tetraphosphonates

The crystal structure of the Tb3+ complex with ethylenediaminetetra(methylenephosphonic acid) (H8EDTMP) was determined and it was found that the compound is isostructural with the previously studied [C(NH2)3]7[Eu(EDTMP)(CO3)]⋅10H2O crystal. The Eu3+ and Tb3+ complexes with trans-cyclohexane-1,2-diamine-N,N,N′,N′-tetrakis(methylenephosphonic acid) (H8CDTMP) of known crystal structures were also obtained. As it results from the X-ray analyses both tetraphosphonate ligands (EDTMP and CDTMP) bind the Ln3+ ion with 2 nitrogen atoms and 4 oxygen atoms in such a way that only one oxygen atom from each phosphonate group is linked with the central ion. The coordination sphere is completed by two oxygen atoms of the bidendate carbonate anion in the case of Ln3+–EDTMP complexes, whereas two monomeric Ln3+–CDTMP complex anions are connected by two hydroxyl ions and one water molecule. The spectroscopic (FTIR and emission) studies of crystals are presented and discussed with respect to their structures. It was shown that OH oscillators present in the inner-sphere of Eu3+ and Tb3+ complexes with CDTMP do not quench lanthanide emission. The reasons of that are three very short hydrogen bonds (∼2Å) formed between two hydroxyl groups and a water molecule. The luminescence lifetimes and quantum yields of lanthanide tetraphosphonates were compared with those obtained for Ln3+ tetracarboxylates.

Incorporation and Luminescence of Yb3+ in CdSe Nanocrystals

Doping quantum dots (QDs) with lanthanide ions is promising to combine the efficient sharp line emission of lanthanides with the strong and size-tunable absorption of QDs. Incorporating lanthanide ions in II-VI QDs remains challenging, however, here we report successful coupling of CdSe QDs with the lanthanide ion Yb(3+). Our spectroscopic results demonstrate that Yb(3+) ions are first adsorbed on the CdSe surface and subsequently incorporated in the nanocrystalline semiconductor particles by growing a Se shell. Evidence for incorporation is provided by the fine structure of the CdSe QDs absorption in the excitation spectrum of the Yb(3+) emission at 1000 nm and the long lifetime of the Yb(3+) emission after shell overgrowth. Sensitized Yb(3+) infrared emission may find application in optical amplifiers, solar concentrators, and bioimaging. The method described is a promising strategy for incorporating lanthanide ions in other II-VI QDs.

Color and Brightness Tuning in Heteronuclear Lanthanide Terephthalate Coordination Polymers

AbstractHeteronuclear lanthanide terephthalate coordination polymers with the general chemical formula [Ln2–2xLn′2x(bdc)3(H2O)4]∞, for which bdc2– symbolizes benzene‐1,4‐dicarboxylate (or terephthalate) and Ln and Ln′ represent trivalent rare earth ions, were synthesized and structurally characterized. Analysis of the Y/Lu compounds by 89Y and 13C solid‐state NMR spectroscopy was carried out, and the results support the hypothesis of randomly distributed lanthanide ions. The spectroscopic and colorimetric properties of this family of compounds were investigated in detail. The resulting data demonstrate that this series of compounds presents highly tunable luminescence properties and clearly indicate that intermetallic deactivation processes play an important role in the emission mechanism. Playing with intermetallic distances allows one to tune the color and the brightness of the lanthanide emission in these coordination polymers.

New Molecular Motif for Recognizing Sialic Acid Using Emissive Lanthanide–Macrocyclic Polyazacarboxylate Complexes: Deprotonation of a Coordinated Water Molecule Controls Specific Binding

A new molecular motif--lanthanide-macrocyclic polyazacarboxylate hexadentate complexes, Ln(3+)-ABNOTA--was found to specifically bind to sialic acid with strong emission enhancement and high affinity. The selectivity toward sialic acid over other monosaccharides was one of the highest among artificial receptors. Also, the novel binding mechanism was investigated in detail; binding selectivity is controlled by interactions between sialic acid and both the central metal and a hydroxyl group produced by deprotonation of a coordinated water molecule in the Ln(3+) complex.

A novel white-luminescent ternary europium hybrids with phenanthroline functionalized periodic mesoporous organosilicas (PMOs) and 2-methyl-9-hydroxyphenalenone

Abstract The molecular linkage (phenSi) is modified from 5-amino-1,10-phenanthroline (phenNH 2 ) by 3-(triethoxysilyl)-propyl isocyanate (TESPIC). Then phenNH 2 functionalized periodic mesoporous organosilica (PMO) hybrids are synthesized by linking ternary europium complexes with phenSi linkage and 2-methyl-9-hydroxyphenalenone (MHPO), which use co-condensation method in the presence of Pluronic P123 surfactant as a template. The europium PMO hybrid system (denoted as Eu(MHPO) 3 phen-PMO(NO 3 ) 3 ) has been characterized in detail, whose results reveal that these hybrids have uniformity in the mesopore structure. It is worthy pointing out that the europium hybrids show emission of both europium ion and phen functionalized PMOs, which can be integrated into the close white luminescence. This provides us a strategy to obtain white emissive lanthanide hybrids.

Direct Modulation of Lanthanide Emission at Sub-Lifetime Scales

The long lifetime of lanthanide emitters can present a challenge for conventional pump-based modulation schemes, where the maximum switching speed is limited by the decay time of the excited state. However, spontaneous emission can also be controlled through the local optical environment. Here, we demonstrate a direct modulation scheme enabled by dynamic control of the local density of optical states (LDOS). Specifically, we exploit the LDOS differences between electric and magnetic dipole transitions near a metal mirror and demonstrate that rapid nanometer-scale mirror displacements can modulate the emission spectra of trivalent europium ions within their excited state lifetime. The dynamic LDOS modulation presented here can be readily extended to faster optical modulation schemes and applied to other long-lived emitters to control the direction, polarization, and spectrum of spontaneous emission at sublifetime scales.

Design of red/green emissive lanthanide activated nano-materials by supersonic and microwave co-irradiations

ZnSnO3:Eu3+ and Sr1−xCaxMoO4:Tb3+ nanocrystals with controlled shape have been assembled in the presence of two driving forces (supersonic microwave co-assistance, abbreviated as SMC) simultaneously in less than 60min at very low temperature (80°C). Scanning Electronic Microscope (SEM) images further supported the existence of cubic crystals and shuttle-like structures. More interestingly, Eu(III) ion has been encapsulated into zinc stannate for the first time and ZnSnO3:Eu3+ can exhibit red emissions excited by long wavelength (395nm). Similarly, it was found that Sr1−xCaxMoO4:Tb3+ had striking green luminescence. The parameters to improve the optical properties have been studied in detail. This convenient approach may be applicable to construct other phosphors with well-defined crystalline structures.

Dendrimers as Nd3+ ligands: Effect of Generation on the Efficiency of the Sensitized Lanthanide Emission

We have designed two novel dendrimers with cyclam cores with appended poly(amido amine) (PAMAM) dendrons, decorated at the periphery with four and eight dansyl chromophores, respectively. The photophysical properties of the dendrimers and their Nd(3+) complexes have been investigated. The energy-transfer efficiency to the lanthanide ions from these dendrimers has been studied as a function of the generation. It has been observed that an increase in the dendrimer generation as well as the number of amide units enhances the energy transfer to the lanthanide ion.

Preparation and photophysical studies of [Ln(hfac)3DPEPO], Ln = Eu, Tb, Yb, Nd, Gd; interpretation of total photoluminescence quantum yields

Synthesis and photophysical characterisation of [Ln(hfac)3DPEPO] complexes (with Ln = Eu, Tb, Yb, Nd, Gd) has been carried out to investigate the factors responsible for the variation in total photoluminescence quantum yield within this family of emissive lanthanide complexes. Electronic absorption and emission spectroscopy, in conjunction with DFT calculations of the excited state of the Eu complex, elucidate the role of each ligand in the sensitisation of the lanthanide through the antenna effect. The X-ray crystal structure of [Gd(hfac)3DPEPO] has been determined and shows an 8-coordinate environment around the Gd and a ten-membered chelate ring involving the DPEPO ligand. Total photoluminescence quantum yields were measured to be 6%, 1% and 2% for Ln = Tb, Nd and Yb, respectively, in comparison with around 80% for Ln = Eu. The lower quantum yield for Nd and Yb, compared with Eu, can be attributed to more efficient quenching of the excited Ln state by high-energy oscillations within the ligands, whereas the lower quantum yield for Tb is assigned to a combination of poor energy transfer from the ligand excited state to the Tb and longer radiative lifetime.

Near-Infrared Emission of Lanthanide(III) Texaphyrin Complexes

Lanthanide texaphyrin derivatives containing Er3+, Nd3+, and Yb3+ ions exhibit near-IR emission from the f–f transition of the lanthanide ions. Both the triplet transient difference absorption spectral measurement and singlet oxygen generation measurement suggest energy transfer from the macrocyclic ligand to the lanthanide ions. Electron-transfer mechanism could also play a role in the NIR emission of Yb–Tex complex.

Synthesis of Chlorin-Sensitized Near Infrared-Emitting Lanthanide Complexes

Lanthanide (Yb(3+), Nd(3+)) complexes equipped with red-absorbing hydroporphyrin (chlorin) antennae were synthesized and characterized. The syntheses are scalable, highly modular, and enable the introduction of different chlorins functionalized with a single reactive group (COOH or NH(2)). Absorption maxima were dependent on chlorin substitution pattern (monomeso aryl or dimeso aryl) and metalation state (free base or zinc chelate). The complexes benefit from dual chlorin (610-639 nm) and lanthanide (980 or 1065 nm for Yb- or Nd-complexes, respectively) emission in the biologically relevant red and near IR region of the spectrum.

Synthesis, crystal structure and luminescence of novel Eu3+, Sm3+ and Gd3+ complexes of 1,3,5- and 1,2,4-triazines

New Eu3+, Sm3+ and Gd3+ complexes of triazine ligands 2,4,6-tri(2-pyridyl)-1,3,5-triazine, 3,5,6-tri(2-pyridyl)-1,2,4-triazine and 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine were synthesized. The structure of five of them was established by single crystal X-ray crystallography. Various aspects of the triazine ligands such as steric interactions, deviation from the planarity and coordination mode define the structure of the complexes. The 1H NMR spectra of the solutions of Eu3+ and Sm3+ molecules showed broad paramagnetic shifted peaks assigned to the protons of the ligated triazines. The powder EPR spectra of the Gd3+ complexes exhibited a broad peak centered at g=2. All Eu3+ and Sm3+ complexes display characteristic lanthanide emission upon UV excitation. The enhancement of the luminescence is attributed to the effective energy transfer from the triazine ligand to the lanthanide ion. 1,2,4-Triazines show to be better sensitizers for Eu3+ and Sm3+ than the 1,3,5-triazine ligand. Co-coordination of the triazines with β-diketonate ligands further enhances the luminescence of the lanthanides. This enhancement was attributed to the synergistic effect of the two ligands and/or the decrease of the vibrational quenching processes.

Strong blue and white photoluminescence emission of BaZrO3 undoped and lanthanide doped phosphor for light emitting diodes application

In this paper, we report the obtained strong broadband blue photoluminescence (PL) emission centered at 427nm for undoped BaZrO3 observed after 266nm excitation of submicron crystals prepared by hydrothermal/calcinations method. This emission is enhanced with the introduction of Tm3+ ions and is stronger than the characteristic PL blue emission of such lanthanide. The proposed mechanism of relaxation for host lattice emission is based on the presence of oxygen vacancies produced during the synthesis process and the charge compensation due to the difference in the electron valence between dopant and substituted ion in the host. Brilliant white light emission with a color coordinate of (x=0.29, y=0.32) was observed by combining the blue PL emission from the host with the green and red PL emission from Tb3+ and Eu3+ ions, respectively. The color coordinate can be tuned by changing the ratio between blue, green and red band by changing the concentration of lanthanides.

Structure and luminescence of a 2-dimensional 2,3-pyridinedicarboxylate coordination polymer constructed from lanthanide(III) dimers

A new two-dimensional lanthanide coordination polymer, [Ln(C7H3NO4)(C7H4NO4)(H2O)]n (Ln=trivalent Pr, Nd, Sm, Eu, and Tb) has been hydrothermally synthesized from reaction with 2,3-pyridinedicarboxylic acid. The compound crystallizes in the P21/c space group and is built from sheets composed of carboxylate-bridged Ln dimers stacked along the [100] direction and held together by hydrogen bonding between carboxylic acid groups. The organic component is successful at sensitizing lanthanide emission in the Sm, Eu, and Tb compounds with quantum yields experimentally determined of 0.60, 4.6, and 2.6%, respectively.

New Cross-Linking Quinoline and Quinolone Derivatives for Sensitive Fluorescent Labeling

A variety of contemporary analytical platforms, utilized in technical and biological applications, take advantage of labeling the objects of interest with fluorescent tracers—compounds that can be easily and sensitively detected. Here we describe the synthesis of new fluorescent quinoline and quinolone compounds, whose light emission can be conveniently tuned by simple structural modifications. Some of these compounds can be used as sensitizers for lanthanide emission in design of highly sensitive luminescent probes. In addition, we also describe simple efficient derivatization reactions that allow introduction of amine- or click-reactive cross-linking groups into the fluorophores. The reactivity of synthesized compounds was confirmed in reactions with low molecular weight nucleophiles, or alkynes, as well as with click-reactive DNA-oligonucleotide containing synthetically introduced alkyne groups. These reactive derivatives can be used for covalent attachment of the fluorophores to various biomolecules of interest including nucleic acids, proteins, living cells and small cellular metabolites. Obtained compounds are characterized using NMR, steady-state fluorescence spectroscopy as well as UV absorption spectroscopy.Electronic supplementary materialThe online version of this article (doi:10.1007/s10895-012-1039-z) contains supplementary material, which is available to authorized users.

Evaluation of quinoline as a remote sensitiser for red and near-infrared emissive lanthanide(iii) ions in solution and the solid state

In order to evaluate quinoline as a remote sensitiser, we have prepared a DTPA based ligand, H3L, bearing quinoline bisamide arms for the complexation of a range of lanthanide(III) ions to give the neutral complexes LnLwhere Ln(3+) = Y(3+), Eu(3+), Sm(3+), Tb(3+), Er(3+), Yb(3+), Nd(3+), Gd(3+). Detection of the phosphorescence signal exhibited by the GdLcomplex at 77 K confirmed that the triplet energy level of the sensitiser at 21,190 cm(-1) was suitable for the indirect population of a range of lanthanide luminescent states. A full photophysical analysis of the complexes reveals that SmL and EuL display red emission when excited through the ligand-based absorption band centred at 330 nm, extending the excitation to violet light around 370 nm. We demonstrate that quinoline sensitizes near-infrared emission in the YbL, ErL and NdL complexes, in powder form as well as in solution. Most importantly, the luminescence for YbL and NdL was sufficiently efficient to be detected in non-deuterated solvent.

ChemInform Abstract: Design and Synthesis of Near‐Infrared Emissive Lanthanide Complexes Based on Macrocyclic Ligands

AbstractReview: about 100 refs.

Design and Synthesis of Near‐Infrared Emissive Lanthanide Complexes Based on Macrocyclic Ligands

AbstractThis review firstly summarizes our recent work on the preparation and photophysical properties of cationic or neutral lanthanide(III) monoporphyrinate complexes, as well as some bridging dinuclear complexes, in which the porphyrinate anion can sensitize the NIR emission of NdIII, YbIII and ErIII ions by serving as an antenna that absorbs visible light and transfers the energy to the excited state of the lanthanide(III) ion, followed by relaxation through the NIR emission. Next, several d–f heterobimetallic diporphyrin complexes, in which a transition metal (M = Zn, Pd, and Pt) porphyrinate moiety serves as a donor by transferring its energy to the Yb3+ ion and enhances the NIR emission, are described. In addition, the synthesis and photophysical properties of some GdIII porphyrinate complexes and monophthalocyaninato lanthanide complexes are also described in this contribution. Apart from the above compounds, we also discuss the construction of multidecker multimetallic lanthanide Schiff base assemblies, which demonstrate that these varieties of salen‐type Schiff base ligands can stabilize LnIII centers and provide the antenna for lanthanide luminescence. By taking advantage of the absorption and emission properties of transition‐metal Schiff base complexes, multinuclear and polynuclear ZnII–LnIII Schiff base complexes have also been constructed with improved luminescence properties.

Effect of varying lanthanide local coordination sphere on luminescence properties illustrated by selected inorganic and organic rare earth complexes synthesized in sol–gel host glasses

Inorganic and organic ligands were carefully selected to illustrate the effect of modifications in the local field environment around the rare earth lanthanide (III) on its emission properties. In this article two strategies were employed to enhance emission of lanthanides encapsulated in sol–gel glass. (i) Changing the symmetry around the lanthanide, which was diagnosed by changing the local environment around the lanthanide using different inorganic counter ions (acetate, nitrate and chloride) these ligands differ in their affinity toward the lanthanide first coordination sphere. The ligand that penetrates the lanthanide more results in more asymmetric environment and thus results in higher emission. The aim of this part was to demonstrate the change of symmetry on emission in the absence of energy transfer. Our results indicate that the acetate ion has the highest affinity toward the first coordination sphere followed by the nitrate while the chloride showed the lowest affinity. Penetration by the ligands ofthe lanthanide also results in removing OH quenchers surrounding the lanthanide and this further explains the boost in emission. (ii) A bulky organic ligand that forms a complex with the lanthanide is used. The organic ligand separates the lanthanide ion from inner O–H oscillators. In this case the chelating organic chromophore with suitable photophysical properties was employed to sensitize the lanthanide and thus energy transfer occurs via the antenna effect. The organic ligand absorbs UV light, then energy is transferred to the lanthanide and finally the lanthanide emits in the visible region. The first coordination environment surrounding europium was controlled by the ligand selection and the outer sphere was modified by doping the synthesized complexes in an optically transparent sol–gel glass host. The glass network carefully prepared by sol–gel process is effective in preventing free oxygen and water from attacking lanthanide -complexes without loss of luminescence. Emission spectroscopy measurements of the doped silica specimens confirmed the variation of Eu (III) emission depending on the first coordination sphere surrounding the europium ion. The encapsulation of the europium complexes was performed for two reasons: (i) to improve the stability of red phosphor with efficient and high color-purity characteristics under ultraviolet excitation and (ii) this work provides a framework for preparing transparent composite glasses that are robust hosts to study the fundamental interactions between nano-materials and light.