Claude Picard

Quantum chemistry-based interpretations on the lowest triplet state of luminescent lanthanides complexes. Part 1. Relation between the triplet state energy of hydroxamate complexes and their luminescence properties

In this paper, we evaluate the potential use of theoretical calculations to obtain an energy scale of the lowest ligand-centred triplet excited state in luminescent terbium(III) complexes. In these complexes, non-radiative deactivation of the terbium emitting state via a back-energy transfer process (T1<--Tb(5D4)) is a common quenching process. Consequently the prediction of the energy gap between these two excited states should be useful for programming highly luminescent Tb(III) systems. We report on a strategy based upon experimental and theoretical investigations of the excited state properties of a series of four simple aromatic hydroxamate ligands coordinated to Tb(III) and Gd(III) ions. By using previously reported crystallographic data, the structural and energies properties of these systems were investigated in the ground and first excited triplet states at the density functional theory (DFT) level of calculations. Our theoretical results are consistent with a triplet excited state T1 which is localised on one ligand only and whose the energy level is independent of the lanthanide ion nature (Tb(III), Gd(III)). A good agreement between the calculated adiabatic transition energies and experimental data derived from emission spectra is obtained when a corrective term is considered. These satisfactory results are an indication that this type of modelling can lead to discriminate in terms of the position of the lowest ligand triplet energy level the best antenna among a family of chromophoric compounds. In addition this theoretical approach has provided indications that the difference between the adiabatic transition energies of all the investigated complexes can be mainly explained by metal-ligand electrostatic interactions. The influence of the number of antennae on the quantum yield and the luminescence lifetime is discussed.

Mono(di)nuclear Europium(III) Complexes of Macrobi(tri)cyclic Cryptands Derived from Diazatetralactams as Luminophores in Aqueous Solution

To increase the excellent light-emitting properties of the Eu3+ ion, macrobicyclic and macrotricyclic ligands 7 – 10, incorporating a 18-membered tetralactam ring (acting as a lanthanide binding site) and a sensitizer group (2,2′-bipyridine or 2,2′-bipyridine 1,1′-dioxide moiety), were synthesized. The mononuclear and dinuclear europium cryptates derived from these ligands were isolated and characterized. Their luminescent properties and those of the corresponding cryptates containing a phenanthroline group (see 11 and 12) were examined in H2O and D2O solutions at 77 and 300 K. It results that the tetralactam moiety plays a major role in the efficient shielding of the complexed Eu3+ ion from the water environment. The cryptands incorporating the bipyridine unit are the most promising labels according to their photophysical properties (excitation maxima, emission decay lifetime, relative luminescent yield). In contrast with literature data, introduction of N-oxide groups in the bipyridine chromophore weakens the luminescence properties of the cryptate.

Novel terpyridine macrocyclic complexing agent and luminescence of its neutral Ln(III) complexes (Ln=Eu, Tb, Sm, Dy) in aqueous solution

Abstract A very convenient synthesis of an 18-membered triaza-macrocyclic ligand bearing one endocyclic terpyridine unit and three acetate pendant groups is reported. This nonadentate ligand forms very stable neutral lanthanide complexes in aqueous solution and efficiently shields the metal ion from the water environment. In this medium the Eu(III) and Tb(III) complexes are strongly fluorescent through an energy-transfer luminescence pathway (τ∼1 ms and Φ∼20%).

Macrocyclic polyether tetralactams II : a study of their binding properties with alkaline - earth cations

Abstract Solvent extractions of alkali and alkaline-earth picrates were carried out in a waterchloroform system using newly synthesized tetralactams containing dimethyleneoxy moieties. These ligands display excellent extracting properties for Ca 2+ , Ba 2+ , and Sr 2+ cations. Some of the less lipophilic derivatives have greater preference for Ba 2+ vs. Na + and Zn 2+ and, to a lesser extent, K + , Mg 2+ and Ca 2+ . In addition, the stability constants were determined for the 1:1 and 1:2 M 2+ :tetralactam complexes by UV spectrophotometry in THF solution. In each series of tetralactams log K S values as high as 6 were observed for Ca 2+ , Sr 2+ and Ba 2+ ions. The 18-, 21- and 24- membered tetralactams complex preferentially Sr 2+ , Ca 2+ and Ba 2+ cations respectively.

Styrylbenzodiazinones 3. Chromo- and fluoroionophores derived from monoaza-15-crown-5. Photophysical and complexing properties

Abstract The photophysical and complexing properties of two chromo- and fluoroionophores derived from the monoaza-15-crown-5 and styrylbenzodiazinones are studied by UV spectrophotometry and spectrofluorometry. Their comparison with those of BOZ-crown and DCM-crown analogous dyes shows the specificity of the benzodiazinone moiety on these properties. The occurrence of twisted intramolecular charge transfer states by internal rotation around the ArCN bond and the effects of biological metallic ions are discussed.

A click procedure with heterogeneous copper to tether technetium-99m chelating agents and rhenium complexes. Evaluation of the chelating properties and biodistribution of the new radiolabelled glucose conjugates.

An efficient protocol was developed to tether chelating agents and rhenium complexes onto a glucoside scaffold with a heterogeneous copper catalyst via click chemistry. The supported catalyst avoids the formation of unwanted copper complexes during the cyclisation step. The possibility to graft a pre-chelated M(CO)(3) core by click chemistry onto a biomolecule was highlighted for the first time. (99m)Tc(CO)(3)-glucoconjugates displayed excellent in vitro stability, a fast in vivo blood clearance and a low specific organ uptake or long-term retention in spleen and stomach.

New Macrobicycles Containing a Tetralactam Moiety: Template Synthesis and Study of their Binding with Lanthanides

Abstract The synthesis of macrobicyclic cryptands 1 , 2 from an 18-membered diazatetralactam and 6,6′-bis(bromomethyl)-2,2′-bipyridine or 2,6-bis(3-bromomethyl-1-pyrazolyl)pyridine has been investigated using various metal carbonates. The analysis of the distribution products by gel permeation chromatography showed that macrocyclization process was markedly conditioned by cation template effects. Optimum yields were obtained for Li + and Na + in the preparation of 1 and 2 , respectively. The cryptate structure of the corresponding complexes of Ln(III) (Ln=Eu, Tb, Gd) is discussed on the basis of spectroscopic and photophysical data.

Time‐Resolved Luminescence in Aqueous Solution − New Europium Labels Derived from Macro(bi)cyclic Ligands with Aminocarboxylic Units

A new family of macro(bi)cyclic ligands has been designed and synthesized, with the goal of developing lanthanide labels suitable for time-resolved luminescence-based biological applications. They are constructed from diamide (3) or tetralactam (4) complexing moieties associated with an intracyclic 2,2′-bipyridine chromophore and two exocyclic carboxylic groups. The luminescence properties of their Eu3+ complexes were studied in aqueous solution. In this medium, noticeable enhancements in the lifetime and quantum yield were observed, in comparison with those of other bipyridine-based ligands considered interesting as luminescent labels. The effects of coordinated water molecules, LMCT states, and ligand triplet state energy on the nonradiative deactivation processes to the ground state were examined. According to these results and in view of the stability of these complexes in aqueous solutions, the [Eu(3)]+ complex may be considered as a promising luminescent bioprobe.

Macrocyclic polyether tetralactams I : synthesis and cyclization studies

Abstract A three-step method for the synthesis of new 18, 21 or 24-membered macrocyclic tetralactams with two dimethyleneoxy moieties is described. The method consists in the ring closure of a bis-secondary amine with a diamide diacid activated by the thiazolidine-2-thione group. The cyclization does not require high dilution techniques and provides the expected tetralactams in good yields, ranging from 42% to 73%. This synthetic pathway leads to dissymmetrical or symmetrical molecules with substituents of variable lipophilicity.

Luminescence of Eu3+ and Tb3+ Complexes of Two Macrobicyclic Ligands Derived from a Tetralactam Ring and a Chromophoric Antenna

Two macrobicyclic ligands derived from an 18-membered tetralactam ring and 2,2′-bipyridine or 2,6-bis(pyrazol-1-yl)pyridine moieties, 1 and 2, respectively, form stable complexes with GdIII, EuIII, and TbIII ions in aqueous solution. The ligand-based luminescence is retained in the GdIII cryptates, whereas this radiative deactivation is quenched in the EuIII and TbIII cryptates by ligand-to-metal energy transfer, resulting in the usual metal-centered emission spectra. Singlet- and triplet-state energies, emission-decay lifetimes, and luminescence yields were measured. [Tb⊂1]3+ cryptate shows a long luminescence lifetime (τ=1.12 ms) and a very high metal luminescence quantum yield (Φ=0.25) in comparison with those reported in the literature for Tb3+ complexes sensitized by a bipyridine chromophore. By comparison to [Ln⊂1]3+, [Ln⊂2]3+ presents markedly lower luminescence properties, due to worse interaction between the 2,6-bis(pyrazol-1-yl)pyridine unit and the metal ion. Moreover, the luminescent metal and the triplet ligand energy levels of [Eu⊂2]3+ do not match. The effects of H2O molecules coordinated to the metal centre and of thermally activated decay processes on nonradiative deactivation to the ground-state are also reported.