Lanthanide directed self-assembly formations of Tb(III) and Eu(III) luminescent complexes from tryptophan based pyridyl amide ligands.

The formation of self-assembly complexes between the ligands 1 (SS) and 2 (RR) and terbium or europium was undertaken and shown (using various spectroscopic titrations) to give rise to the exclusive formation of 2:1 (L:Ln) stoichiometry and not the anticipated 3:1 stoichiometry.

The effect on the lanthanide luminescence of structurally simple Eu(III) cyclen complexes upon deprotonation of metal bound water molecules and amide based pendant arms.

A series of substituted 1,4,7,10-tetraazacylcododecane ligands 1-4, possessing sensitizing nitrobenzene or naphthalene antennae, as one of the amide pendant arms, and their complexes with europium(III) were synthesised. The protonation constants and the metal ion stability constants of two of these ligands were determined by potentiometric titration. The pK(a) of the water molecules coordinated to the complexed metal ion were determined by both luminescent and potentiometric measurements. The luminescence pH dependence of a further three Eu(III) complexes, 5-7, which lack any antennae, were also studied with the aim of gaining a better understanding of the role of the metal bound water molecules in the luminescence properties of such complexes upon direct excitation of the lanthanide ion. The results from these luminescent measurements demonstrate that the Eu(III) emission was significantly modulated as a function of pH for all the complexes, which we assigned to changes occurring in the coordination environment of the ion within the cyclen system, caused by deprotonation of metal bound water molecules and/or deprotonation of pendent amide arms.

Metal-directed synthesis of enantiomerially pure dimetallic lanthanide luminescent triple-stranded helicates.

The synthesis and photophysical evaluation of two enatiomerially pure dimetallic lanthanide luminescent triple-stranded helicates is described. The two systems, formed from the chiral (R,R) ligand 1 and (S,S) ligand 2, were produced as single species in solution, where the excitation of either the naphthalene antennae or the pyridiyl units gave rise to Eu(III) emission in a variety of solvents. Excitation of the antennae also gave rise to circularly polarized Eu(III) luminescence emissions for Eu(2):1(3) and Eu(2):2(3) that were of equal intensity and opposite sign, confirming their enantiomeric nature in solution providing a basis upon which we were able to assign the absolute configurations of Eu(2):1(3) and Eu(2):2(3).

Luminescent sensing and formation of mixed f-d metal ion complexes between a Eu(iii)-cyclen-phen conjugate and Cu(ii), Fe(ii), and Co(ii) in buffered aqueous solution.

The synthesis and photophysical properties of the Eu(iii) complex , based on the use of 1,10-phenanthroline (phen) as a combined sensitizing antenna and a transition metal ion coordinating ligand, is described. The long-wavelength Eu(iii) emission from this complex was found to be highly pH sensitive, giving rise to a 'off-on-off' pH profile with maximum emission occurring within the physiological pH range. This allowed for the use of as a luminescent sensor for transition metal ions, where the titration with ions such as Cu(ii), Co(ii) and Fe(ii) gave rise to the formation of mixed f-d nuclear complexes, with concomitant changes in the photophysical properties of . Here, changes in both the ground and the singlet excited state properties of the phen antenna were observed, but the largest changes were observed for the delayed Eu emission, which was fully quenched upon titration with these ions in aqueous pH 7.4 buffered solutions. In comparison, no changes were observed in the Eu(iii) emission upon titration with ions such as Zn(ii) or group I and II ions. From these changes, we were able to demonstrate the binding stoichiometry and the binding constant for the formation of novel supramolecular complexes between and Cu(ii), Co(ii) and Fe(ii), which showed that either two or three equivalents of complexed to each of these transition metal ions, giving rise to the formation either linear f-d-f or branched f(3)-d based mixed nuclear complexes in solution.

Lanthanide luminescent anion sensing: evidence of multiple anion recognition through hydrogen bonding and metal ion coordination.

The delayed lanthanide luminescence of the terbium [Tb(III)] diaryl-urea complex 1xTb is significantly enhanced upon sensing of dihydrogenphosphate (H2PO4(-)) in CH3CN, which occurs through multiple anion binding through hydrogen bonding interactions and potential metal ion coordination to Tb(III).

pH driven self-assembly of a ternary lanthanide luminescence complex: the sensing of anions using a beta-diketonate-Eu(III) displacement assay.

The synthesis and the photophysical evaluation of a novel pH dependent lanthanide luminescent self-assembly in water between a cyclen based europium complex and a beta-diketonate is described and its use as a luminescent sensor in displacement assays for anions such as acetate, bicarbonate and lactate, where the Eu(III) emission was quenched upon anion recognition.

Supramolecular self-assembly of mixed f-d metal ion conjugates.

[reaction: see text] The synthesis of the novel Eu(III) cyclen complex, Eu1, is described. In buffered pH 7.4 water, the Eu(III) emission was "switched on" upon excitation of the Terpy antenna. In the presence of various transition-metal ions (e.g., Fe(II) and Ni(II)), both the singlet-excited state and the Eu(III) emission were quenched ("switched off"), whereas in the ground state, an MLCT band was formed, signifying the formation of stable mixed linear trimetallic f-d supramolecular self-assemblies.

Lanthanide luminescent switches: modulation of the luminescence of bis-macrocyclic based Tb(III) conjugates in water by H+, Na+ and K+.

The synthesis of four bis-macrocyclic conjugates made from the coupling of either diaza-15-crown-5 ethers (1 and 3) and diaza-18-crown-6 ethers (2 and 4) to either amide or carboxylate functionalized cyclen (1,4,7,10-tetraazacyclododecane), and their corresponding cationic Tb(III) complexes, Tb-1, Tb-2, and neutral complexes Tb-3 and Tb-4 are described. The effect on the ground, singlet excited states and the Tb(III) emission, was investigated either as a function of pH or the concentration of several Group I and II cations, upon excitation at 300 nm. The ground state and singlet excited states of the Tb(III) complexes were found to be modulated by ions such as H+, Na+ or K+, signifying the recognition of these ions by the crown ether receptors. In acidic media, below pH 4, the Tb(III) emission was highly pH sensitive, gradually increasing with large orders of magnitude of luminescence enhancements. For Tb-1 and Tb-2 complexes, the Tb(III) emission was also "switched on" in alkaline media above pH 8. At pH 7.4, the recognition of Na+ or K+ also gave rise to a significant change in the Tb(III) emission due to the modulation of the antenna-receptor moieties by these ions. For Tb-1 and Tb-3 the largest changes were seen for Na+, whereas for Tb-2 and Tb-4 the largest changes were seen for K+.

Luminescent Eu(III) and Tb(III) complexes: developing lanthanide luminescent-based devices.

This mini review gives some highlights of the work recently carried out in our research group in Dublin on the developments of lanthanide luminescent devices, where the future goal is to produce devices that can operate as sensors. A few examples demonstrate our design principles for targeting both anion and cations that are of biological or pharmaceutical relevance, where the recognition occurs in aqueous competitive media. We also discuss the possibility of developing mixed f-d metal complexes and conjugates that can be employed as novel supramolecular architectures.

Responsive lanthanide luminescent cyclen complexes: from switching/sensing to supramolecular architectures.

This article highlights some of the recent developments in the use of responsive cyclen based lanthanide luminescent devices, focusing on Eu(III), Tb(III), Nd(III) and Yb(III) complexes, where the photophysical properties, such as the excited state lifetimes, quantum yield/intensity and emission polarisation are modulated by the local chemical environment, e.g. ions and molecules, or through self-assembly of either f-f or mixed f-d cyclen complexes.

Highly selective colorimetric naked-eye Cu(II) detection using an azobenzene chemosensor.

Colorimetric azobenzene based chemosensors 1 and 2 were designed for detection of transition-metal ions such as Cu(II) under physiological pH conditions. The internal charge transfer (ICT) sensors are highly colored, absorbing in the green. For 1, the Cu(II) recognition gives rise to red-to-yellow color changes that are visible to the naked-eye and reversible upon addition of EDTA, whereas for 2, which lacks the aromatic o-methoxy chelating group, no such changes were observed.

Eu(III)-cyclen-phen conjugate as a luminescent copper sensor: the formation of mixed polymetallic macrocyclic complexes in water.

The cationic cyclen based Eu(III)-phen conjugated 1.Eu was synthesised as a chemosensor for Cu(II), where the recognition in water at pH 7.4 gave rise to quenching of the Eu(III) luminescence and the formation of tetranuclear polymetallic Cu(II)-Eu(III) macrocyclic complexes in solution where Cu(II) was bound by three 1.Eu conjugates.

H+, Na+ and K+ modulated lanthanide luminescent switching of Tb(III) based cyclen aromatic diaza-crown ether conjugates in water.

The cyclen based aromatic diaza-15-crown-5 and 18-crown-6 ether conjugates 1Tb-4Tb were designed as luminescent switches for sodium and potassium where the delayed Tb(III) emission, occurring as line-like emission bands between 490-622 nm, was 'switched on' upon recognition of these ions in pH 7.4 buffered water solution.

pH responsive Eu(III)-phenanthroline supramolecular conjugate: novel "off-on-off" luminescent signaling in the physiological pH range.

The formation of luminescent supramolecular ternary complexes in water: delayed luminescence sensing of aromatic carboxylates using coordinated unsaturated cationic heptadenatate lanthanide ion complexes.

Delayed lanthanide luminescence sensing of aromatic carboxylates using heptadentate triamide Tb(III) cyclen complexes: the recognition of salicylic acid in water.

The coordinately unsaturated terbium complexes Tb.1 and Tb.2 possess two labile metal-bound water molecules that can be displaced upon metal chelation to aromatic carboxylic anions such as salicylic acid in water, which gives rise to large enhancements in the Tb(III) luminescence.