Luminescent Ternary Complexes Research Articles

Time-Resolved Terbium-Based Probe for the Detection of Zinc(II) Ions: Investigation of the Formation of a Luminescent Ternary Complex.

Because of their unique photochemical and photophysical properties, luminescent lanthanide-based complexes have long captivated chemists. In recent years, the number of reports of luminescent lanthanide complex-based probes for monitoring of biological and environmental processes has dramatically increased, namely, because of their selectivity for particular analytes, lower limits of detection, and the fact that they allow monitoring of analytes in real time. Lanthanide-based probes need to be paired with an appropriate antenna/sensitizer to allow maximum energy transfer, with the antenna typically covalently attached to the stable lanthanide chelate. We have recently investigated "dark" lanthanide-based probes where the sensitizer is not covalently linked to the lanthanide chelate. Herein we report the use of a luminescent lanthanide-based probe system for the detection of Zn2+ ions based on the formation of a ternary complex between a "dark" terbium complex, lumazine, and Zn2+. The terbium(III)-based probe incorporates a 1,4,7,10-tetraazacyclododecane-1,4,7,10-triacetic acid macrocyclic chelator covalently attached to a cyclen moiety, which is the Zn2+ ion binding group. In the presence of Zn2+ ions and lumazine (a strongly UV-absorbing sensitizer), a 1:1:1 ternary complex forms. The resulting complex is highly luminescent and selective for Zn2+ ions over other cations of environmental significance. Furthermore, with a limit of detection of 1.2 μM, this probe can detect the level of chronic zinc(II) concentrations denoted by the U.S. Environmental Protection Agency.

Hierarchical Self‐Assembly of Luminescent EuIII Complexes on Silicon

AbstractWe have combined the metal‐coordinating features of phenanthroline with the remarkable complexing properties of tetraphosphonate (Tiiii) cavitands towards N‐methylammonium salts with the aim of assembling novel luminescent ternary complexes. The formation of such complexes was first tested in solution: the charged sarcosine derivative 1, bearing a phenanthroline moiety, was complexed by the cavitand Tiiii‐A, followed by coordination of EuIII–tris(β‐diketonate) complex 2. The occurrence of the self‐assembly has been proven by NMR spectroscopy, mass spectrometry and photophysical measurements. The transfer of this binding protocol to the surface showed the complete orthogonality of these interactions, as verified by control experiments on complexation‐inactive surfaces. The formation of the ternary complexes on the silicon surface was monitored by means of X‐ray photoelectron spectroscopy and luminescence spectroscopy. The emission properties of the silicon‐bound Si‐Tiiii‐B·1·2 and the corresponding ternary complex Tiiii‐A·1·2 in solution are similar, which indicates that the transfer of the self‐assembly process onto silicon does not significantly perturb the EuIII coordination environment. The self‐assembly protocol illustrated here can be extended to a wide variety of lanthanide ions and can be implemented for applications in sensing, bioimaging and optoelectronic devices.

The role of cadmium(II) bridges in the self-assembly with lanthanide(III) and thiacalix[4]arene (TCAS) to selectively form a luminescent ternary CdII2·TbIII2·TCAS2 complex

The ability of metal ions to self-assemble to form luminescent ternary complexes with TbIII and thiacalix[4]arene-p-tetrasulfonate (TCAS) was investigated, as exemplified by AgI in AgI2·TbIII2·TCAS2 and AgI2·TbIII·TCAS2 at pH 6.5 and 10, respectively. Among FeIII, NiII, ZnII, PdII, CdII, HgII, TlI, and PbII metals, only CdII resulted in more intense luminescence than a TbIII–TCAS binary system, which occurs at pH values of ∼6.5 and suggests the formation of a ternary complex. Determination of the molar ratio and electrospray-ionization mass spectrometry results revealed that the species formed at pH 6.5 was CdII2·TbIII2·TCAS2. Analogous to the solid-state structure of AgI2·TbIII2·TCAS2, CdII2·TbIII2·TCAS2 should also adopt a double-cone structure with the cyclic tetrametal CdII–CdII–TbIII–TbIII core sandwiched by two cone-shaped TCAS ligands that are connected by two S–CdII–S linkages at the two adjacent S atoms in TCAS. However, the CdII system did not form a ternary complex like AgI2·TbIII·TCAS2 at higher pH values; this is because the S–CdII–S linkages are shorter than S–AgI–S, which brings the two TCAS ligands closer together and ejects TbIII. In aqueous solutions CdII2·TbIII2·TCAS2 exhibited the following photophysical properties: a luminescence quantum yield (Φ) of 0.15 and lifetime (τ) of 1.12ms; these values are very close to those obtained for AgI2·TbIII2·TCAS2. The number of water molecules coordinated to TbIII was determined to be 2.2, which is identical to the number coordinated to TbIII in AgI2·TbIII2·TCAS2. Together, these results elucidate the structural similarities of CdII2·TbIII2·TCAS2 and AgI2·TbIII2·TCAS2. Other LnIII species (i.e., NdIII and YbIII) also afforded ternary complexes with the same stoichiometry, which shows that it is the CdII bridges that restrict the self-assembly to CdII2·LnIII2·TCAS2.

N‐Heterocyclic Tridentate Aromatic Ligands Bound to [Ln(hexafluoroacetylacetonate)3] Units: Thermodynamic, Structural, and Luminescent Properties

Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac(-)) and neutral, semi-rigid, tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands (Lk) to trivalent lanthanide atoms (Ln(III)). The solid-state structures of [Ln(Lk)(hfac)(3)] (Ln=La, Eu, Lu) showed that [Ln(hfac)(3)] behaved as a neutral six-coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron-withdrawing trifluoromethyl substituents limited charge-neutralization and favored cascade complexation with Lk; 3) nine-coordination was preserved for [Ln(Lk)(hfac)(3)] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of [Eu(Lk)(hfac)(3)], the ternary system Ln(III)/hfac(-)/Lk is a promising candidate for the planned metal-loading of preformed multi-tridentate polymers.

A supramolecular sensing system for AgIat nanomolar levels by the formation of a luminescent AgI–TbIII–thiacalix[4]arene ternary complex

The first example of the detection of AgI ions using supramolecular chemistry is demonstrated, in which two thiacalix[4]arene ligands are linked by analyte AgI ions and then coordinate to TbIII ions to form a luminescent ternary complex, AgI2·TbIII2·TCAS2, enabling the detection of AgI at concentrations as low as 3.2×10−9 M.

Exceptionally Long-Lived Luminescence Emitted from TbIII Ion Caged in an AgI–TbIII–Thiacalix[4]arene Supramolecular Complex in Water

The compositions and photophysical properties of luminescent ternary complexes of thiacalix[4]arene-p-sulfonate (TCAS), Tb(III), and Ag(I) ions were determined. At pH 6, Ag(I) (2)Tb(III) (2)TCAS(2) formed. Moreover, at pH 10, in the presence of a 20-fold excess of Ag(I) and a 50-fold excess of TCAS with respect to Tb(III), Ag(I) (2)Tb(III)TCAS(2) formed as the main luminescent species. The structure of these complexes was proposed: two TCAS ligands are linked by two S-Ag(I)-S linkages to adopt a double-cone supramolecular structure. Furthermore, each Tb(III) ion in the former complex accepts O(-), S, O(-) donation, whereas in the latter, the Tb(III) center accepts eightfold O(-) donation. The luminescence quantum yield (Phi) of Ag(I) (2)Tb(III) (2)TCAS(2) (0.16) was almost equal to that of Tb(III)TCAS, but the luminescence lifetime tau of the former (=1.09 ms) was larger than that of the latter. For Ag(I) (2)Tb(III)TCAS(2), the yield Phi (=0.11) was small, which is attributed to the low efficiency of photosensitization (eta=0.11). However, the tau value (4.61 ms) was exceptionally large and almost equal to the natural luminescence lifetime of Tb(III) (4.7 ms), which is due to the absence of coordinating water molecules (q=0.1). This is compatible with the proposed structure in which the Tb(III) ion is shielded by a supramolecular cage that expels coordinated water molecules responsible for luminescence quenching.

Construction, Characterization, and Photoluminescence of Mesoporous Hybrids Containing Europium(III) Complexes Covalently Bonded to SBA-15 Directly Functionalized by Modified β-Diketone

Novel organic−inorganic mesoporous luminescent hybrid materials were prepared by linking the binary and ternary Eu3+ complexes to the functionalized ordered mesoporous SBA-15 with the modified 1-(2-naphthoyl)-3,3,3-trifluoroacetonate (NTA) by co-condensation of tetraethoxysilane (TEOS) in the presence of Pluronic P123 surfactant as a template. 1-(2-Naphthoyl)-3,3,3-trifluoroacetonate (NTA) grafted to the coupling agent 3-(triethoxysilyl)propyl isocyanate (TEPIC) was used as the precursor for the preparation of mesoporous materials. SBA-15 consisting of the highly luminescent ternary complex Eu(NTA)3bpy covalently bonded to the silica-based network, which was designated as Eu(NTA−SBA-15)3bpy, was obtained by introducing EuCl3 and 2,2‘-bipyridine (bpy) complex into the hybrid material via a ligand-exchange reaction. In addition, for comparison, SBA-15 doped with Eu(NTA)3·2H2O and Eu(NTA)3bpy complexes and SBA-15 covalently bonded with the binary Eu3+ complex with NTA ligand were also synthesized, denoted as...

A Dinuclear Lanthanide Complex for the Recognition of Bis(carboxylates): Formation of Terbium(III) Luminescent Self-Assembly Ternary Complexes in Aqueous Solution

The synthesis and photophysical properties of a coordinatively unsaturated cationic dinuclear terbium complex, 2.Tb(2), that can detect the presence of mono- or bis(carboxylates) in buffered aqueous solution at physiological pH is described. Full ligand synthesis and structural characterization of 2.Na(2) are also described. Spectroscopic measurements determined that each Tb(III) metal center has two metal-bound water molecules (q = 2). The recognition or sensing of N,N-dimethylaminocarboxylic acid, 4, and the bis(carboxylate) terephthalic acid, 5, which can also function as sensitizing antennae, was found to occur through the binding of these carboxylates to the metal center via the displacement of the metal bound water molecules. This gave rise to the formation of luminescent ternary complexes in solution in 2:1 or 1:1 (ion:2.Tb(2)) stoichiometry, respectively. Aliphatic bis(carboxylates) also bind to 2.Tb(2) where the selectivity for the ion recognition and stoichiometry was dictated by the structure of the anion, being most selective for pimelic acid, 6. Binding of either l- or d-tartaric acid gave rise to the formation ternary complex formation, with 2:1 stoichiometry, where the ion recognition resulted in quenching of the lanthanide emission.

Self-assembly of luminescent ternary complexes between seven-coordinate lanthanide(iii) complexes and chromophore bearing carboxylates and phosphonates

Luminescent lanthanide complexes have been prepared by exploiting the interaction between lanthanide DO3A complexes and chromophore bearing carboxylates or phosphonates. This interaction can be utilised to probe the choice of sensitising chromophore suited to a given lanthanide. Furthermore, ternary complexes obtained from chromophore appended carboxylates dissociate in the presence of phosphate, while those obtained from phosphonates do not.

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.

Crown ether lanthanide complexes as building blocks for luminescent ternary complexes

Lanthanide complexes of the macrocyclic ligands 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane- N, N′-diacetic acid (H 2(dacda)) and 1,4,7,10-tetraoxa-13-azacyclopentadecane-13-acetic acid (H(macma)) have been isolated and characterised. The photophysical properties of the red and green emissive, Eu(III) and Tb(III), respectively, complexes have been elucidated. Upon addition of mono- or bi-dentate aromatic carboxylates or dibenzoylmethide in solutions of the Eu(III) macrocycles triggering of the lanthanide emission is observed. The formation of the ternary complex between the lanthanide macrocycle and the sensitiser is controlled by the available coordinaton sites of the lanthanide macrocycle prior to the binding event.