Optical Properties of New Terbium(III) Ternary Complexes Containing Anionic 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and Neutral Sensitizers in Solution, Solid and PMMA Thin Films: Intra and Interphase Colour Tuning

Four new terbium(III) ternary complexes, [Tb(fod)₃ (indazole)] (1), [Tb(fod)₃ (tptz)] (2), [Tb(fod)₃ (impy)] (3) and [Tb(fod)₃ (tppo)₂ ] (4) with 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, (Hfod) and N and O donors are synthesized and structurally characterized. The photoluminescence of the complexes are studied in solid, chloroform solution and thin PMMA hybrid films (PMMA is a poly(methyl methacrylate)). The ligand-based emission is dominant in solution of 3 and 4. The effect of ancillary ligands on the photoluminescence of terbium(III) ion is investigated. The mechanism of energy transfer is discussed and correlates the luminescence of acceptor terbium ion with the triplet state energy level of donor ligands. Among the four complexes studied, the luminescence from 1 is most intense followed by 2, 4 and 3. The Commission International de I'Eclairage (CIE) color coordinates of these complexes are calculated and presented. The complexes 3 and 4 show intraphase color tuning when excited under different UV wavelengths. The emission color of [Tb(fod)₃ (tppo)₂ ] (4) changes from pure blue to turquoise green via almost pure white under 360, 328 and 280 nm UV excitation wavelengths respectively. The [Tb(fod)₃ (impy)] (3) show similar results. The complex [Tb(fod)₃ (tptz)] (2) displays interphase color tuning from yellow (solution) to turquoise green (solid) and fascinatingly incorporation of complex in PMMA polymer generates white light under same excitation wavelength (360 nm).

Lanthanide complexes based on a conjugated pyridine carboxylate ligand: structures, luminescence and magnetic properties

Three lanthanide compounds have been synthesized, namely, {[Dy₂(bpda)₃(H₂O)₃]₄·2H₂O}(Dy-1), {[Sm(bpda)₂·(H₂O)]·H₂O}_n (Sm-2) and {[Tb₂(bpda)₃(H₂O)₃]₄·2H₂O} (Tb-3) (H₂bpda = 2,2′-bipyridine-6,6′-dicarboxylic acid). Their structures were determined by single crystal X-ray diffraction and characterized by elemental analysis, infrared spectroscopy and thermogravimetric analysis. Dy-1 and Tb-3 are isostructural with a conjugate bimolecular four-nuclear cluster structure constructed with intramolecular hydrogen bonds and they form a 3D supramolecular structure with intermolecular hydrogen bonding. Sm-2 is a one-dimensional chain structure and is further connected by intricate hydrogen bonds into a three-dimensional supramolecular structure. These three compounds exhibit significant characteristic luminescence from the ligand to the central Ln(iii) ion, which is found by solid-state photoluminescence measurement. Sm-2 exhibits a long luminescence lifetime and high fluorescence quantum yield. A slow relaxation phenomenon is observed for the dysprosium compound by measuring the alternating-current susceptibility at low temperature and the underlying mechanism was further confirmed by theoretical calculations.

The structures, fluorescence and magnetic properties of series three lanthanide complexes have been investigated. Dysprosium complex exhibit the single-molecule behavior.

Tuning the luminescence properties of lanthanide coordination polymers with Ag@SiO2 nanoparticles

A series of core-shell Ag@SiO₂ nanoparticles with different core diameters and shell thicknesses have been prepared by a modified-Stöber method. They provide a facile route to tune the luminescence intensities, lifetimes and quantum efficiencies of lanthanide coordination polymers in the solid powder state. The coordination polymers [Tb₂(p-PTA)₃(H₂O)₂]_n, [Tb₂(o-PTA)₃(H₂O)₂]_n, [Eu₂(p-PTA)₃(H₂O)₂]_n and [Eu₂(o-PTA)₃(H₂O)₂]_n (PTA = phthalic acid) are synthesized and subsequently bound to the surface of Ag@SiO₂ nanoparticles. The luminescence intensities of the lanthanide complexes are enhanced as high as 10.8 times. The enhancement times depend on the core diameter and shell thickness of the Ag@SiO₂ nanoparticles. Importantly, by simply controlling the ratios between the complexes and the nanoparticles, the luminescence intensities, lifetimes and quantum efficiencies of the lanthanide complexes can be tuned in wide ranges. Typically, the luminescence lifetime of [Eu₂(p-PTA)₃(H₂O)₂]_n powder increases from 451 μs to 783 μs when 300 μL Ag@SiO₂ solution is added. Meanwhile, the luminescence quantum efficiency of the complex increases from 32.1% to 40.9%. The change of the luminescence properties of the lanthanide coordination polymers can be ascribed to the surface plasmon resonance effect of the Ag@SiO₂ nanoparticles as well as the decrease of the nonradiative decay rates of the complexes.

Fluorescence enhancement of europium complexes by core-shell Ag@SiO₂ nanoparticles

Three kinds of core-shell Ag@SiO2 nanoparticles with shell thickness of around 10, 15, and 25 nm, respectively, have been prepared by modified Stöber method and used for fluorescence enhancement. Six kinds of europium complexes with halobenzoic acid have been synthesized. Elemental analysis and lanthanide coordination titration show that the complexes have the compositions of Eu(p-XBA)3·H2O and Eu(o-XBA)3·2H2O (X=F, Cl, Br). The fluorescence spectra investigation indicates that the introduction of Ag@SiO2 nanoparticles into the europium complexes' solution can significantly enhance the fluorescence intensities of the complexes. The sequence of enhancement factors for halobenzoic acid complexes with different halogen atoms is F<Cl<Br, and the fluorescence enhancement factors increase as the excitation wavelength of complexes increase. When the thickness of the SiO2 shell is 25 nm, the fluorescence intensity of the europium complexes can reach a maximum enhancement factor of 5.1. The fluorescence enhancement mechanism may be the metal-enhanced fluorescence resulting from surface plasmon resonance of nanoparticles. And the nanoparticles near the complexes can effectively prevent complexes from the interaction with the solvent molecules, leading to a decrease of nonradiative energy transfer and the suppression of luminescence quench.

Synthesis, crystal structure and fluorescence properties of terbium complexes with phenoxyacetic acid and 2,4,6-tris-(2-pyridyl)-s-triazine

Two complexes of Tb(3+), Gd(3+) /Tb(3+) and one heteronuclear crystal Gd(3+)/Tb(3+) with phenoxyacetic acid (HPOA) and 2,4,6-tris-(2-pyridyl)-s-triazine (TPTZ) have been synthesized. Elemental analysis, rare earth coordination titration, inductively coupled plasma atomic emission spectrometry (ICP-AES) and thermogravimetric analysis-differential scanning calorimetry (TG-DSC) analysis show that the two complexes are Tb2 (POA)6 (TPTZ)2 · 6H2O and TbGd(POA)6 (TPTZ)2 · 6H2O, respectively. The crystal structure of TbGd(POA)6 (TPTZ)2 · 2CH3OH was determined using single-crystal X-ray diffraction. The monocrystal belongs to the triclinic system with the P-1 space group. In particular, each metal ion is coordinately bonded to three nitrogen atoms of one TPTZ and seven oxygen atoms of three phenoxyacetic ions. Furthermore, there exist two coordinate forms between C6H5OCH2COO(-) and the metal ions in the crystal. One is a chelating bidentate, the other is chelating and bridge coordinating. Fluorescence determination shows that the two complexes possess strong fluorescence emissions. Furthermore, the fluorescence intensity of the Gd(3+)/Tb(3+) complex is much stronger than that of the undoped complex, which may result from a decrease in the concentration quench of Tb(3+) ions, and intramolecular energy transfer from the ligands coordinated with Gd(3+) ions to Tb(3+) ions.