Optical spin-state polarization in a binuclear europium complex towards molecule-based coherent light-spin interfaces

The success of the emerging field of solid-state optical quantum information processing (QIP) critically depends on the access to resonant optical materials. Rare-earth ion (REI)-based molecular systems, whose quantum properties could be tuned taking advantage of molecular engineering strategies, are one of the systems actively pursued for the implementation of QIP schemes. Herein, we demonstrate the efficient polarization of ground-state nuclear spins—a fundamental requirement for all-optical spin initialization and addressing—in a binuclear Eu(III) complex, featuring inhomogeneously broadened $^{5}$D0 → $^{7}$F0 optical transition. At 1.4 K, long-lived spectral holes have been burnt in the transition: homogeneous linewidth (Γ$_{h}$) = 22 ± 1 MHz, which translates as optical coherence lifetime (T$_{2opt}$) = 14.5 ± 0.7 ns, and ground-state spin population lifetime (T$_{1spin}$) = 1.6 ± 0.4 s have been obtained. The results presented in this study could be a progressive step towards the realization of molecule-based coherent light-spin QIP interfaces

Definition of an intramolecular Eu‐to‐Eu energy transfer within a discrete [Eu2L] complex in solution

[Abstract] Ligand L, based on two do3a moieties linked by the methylene groups of 6,6′‐dimethyl‐2,2′‐bipyridine, was synthesized and characterized. The addition of Ln salts to an aqueous solution of L (0.01 M Tris‐HCl, pH 7.4) led to the successive formation of [LnL] and [Ln2L] complexes, as evidenced by UV/Vis and fluorescence titration experiments. Homodinuclear [Ln2L] complexes (Ln=Eu, Gd, Tb, Yb, and Lu) were prepared and characterized. The 1H and 13C NMR spectra of the Lu and Yb complexes in D2O solution (pD=7.0) showed C1 symmetry of these species in solution, pointing to two different chemical environments for the two lanthanide cations. The analysis of the chemical shifts of the Yb complex indicated that the two coordination sites present square antiprismatic (SAP) coordination environments around the metal ions. The spectroscopic properties of the [Tb2L] complex upon ligand excitation revealed conventional behavior with τH2O=2.05(1) ms and ϕH2O=51 %, except for the calculation of the hydration number obtained from the luminescent lifetimes in H2O and D2O, which pointed to a non‐integer value of 0.6 water molecules per TbIII ion. In contrast, the Eu complex revealed surprising features such as: 1) the presence of two and up to five components in the 5D0→7F0 and 5D0→7F1 emission bands, respectively; 2) marked differences between the normalized spectra obtained in H2O and D2O solutions; and 3) unconventional temporal evolution of the luminescence intensity at certain wavelengths, the intensity profile first displaying a rising step before the occurrence of the expected decay. Additional spectroscopic experiments performed on [Gd2−xEuxL] complexes (x=0.1 and 1.9) confirmed the presence of two distinct Eu sites with hydration numbers of 0 (site I) and 2 (site II), and showed that the unconventional temporal evolution of the emission intensity is the result of an unprecedented intramolecular Eu‐to‐Eu energy-transfer process. A mathematical model was developed to interpret the experimental data, leading to energy‐transfer rates of 0.98 ms−1 for the transfer from the site with q=0 to that with q=2 and vice versa. Hartree–Fock (HF) and density functional theory (DFT) calculations performed at the B3LYP level were used to investigate the conformation of the complex in solution, and to estimate the intermetallic distance, which provided Förster radii (R0) values of 8.1 Å for the energy transfer from site I to site II, and 6.8 Å for the reverse energy transfer. These results represent the first evidence of an intramolecular energy‐transfer equilibrium between two identical lanthanide cations within a discrete molecular complex in solution.Ministerio de Educación y Ciencia; CTQ2009–10721Xunta de Galicia; IN845B‐2010/06

Importance of outer-sphere and aggregation phenomena in the relaxation properties of phosphonated gadolinium complexes with potential applications as MRI contrast agents

[Abstract] A series composed of a tetra-, a tris- and a bisphosphonated ligand based on a pyridine scaffold (L4, L3 and L2, respectively) was studied within the frame of lanthanide (Ln) coordination. The stability constants of the complexes formed with lanthanide cations (Ln=La, Nd, Eu, Gd, Tb, Er and Lu) were determined by potentiometry in aqueous solutions (25.0 °C, 0.1 M NaClO4), showing that the tetraphosphonated complexes are among the most stable LnIII complexes reported in the literature. The complexation of L4 was further studied by different titration experiments using mass spectrometry and various spectroscopic techniques including UV/Vis absorption, and steady state and time-resolved luminescence (Ln=Eu and Tb). Titration experiments confirmed the formation of highly stable [LnL4] complexes. 31P NMR experiments of the LuL4 complex revealed an intramolecular interconversion process which was studied at different temperatures and was rationalized by DFT modelling. The relaxivity properties of the GdIII complexes were studied by recording their 1H NMRD profiles at various temperatures, by temperature dependent 17O NMR experiments (GdL4) and by pH dependent relaxivity measurements at 0.47 T (GdL3 and GdL2). In addition to the high relaxivity values observed for all complexes, the results showed an important second-sphere contribution to relaxivity and pH dependent variations associated with the formation of aggregates for GdL2 and GdL3. Finally, intravenous injection of GdL4 to a mouse was followed by dynamic MRI imaging at 1.5 T, which showed that the complex can be immediately found in the blood stream and rapidly eliminated through the liver and in large part through the kidneys.Torino. Compagnia di San Paolo; CSP-2012 NANOPROGL

Self‐aggregated dinuclear lanthanide(III) complexes as potential bimodal probes for magnetic resonance and optical imaging

[Abstract] Homodinuclear lanthanide complexes (Ln=La, Eu, Gd, Tb, Yb and Lu) derived from a bis‐macrocyclic ligand featuring two 2,2′,2′′‐(1,4,7,10‐tetraazacyclododecane‐1,4,7 triyl)triacetic acid chelating sites linked by a 2,6‐bis(pyrazol‐1‐yl)pyridine spacer (H2L3) were prepared and characterized. Luminescence lifetime measurements recorded on solutions of the EuIII and TbIII complexes indicate the presence of one inner‐sphere water molecule coordinated to each metal ion in these complexes. The overall luminescence quantum yields were determined (∅H2O=0.01 for [Eu2(L3)] and 0.50 for [Tb2(L3)] in 0.01 MTRIS/HCl, pH 7.4; TRIS=tris(hydroxymethyl)aminomethane), pointing to an effective sensitization of the metal ion by the bispyrazolylpyridyl unit of the ligand, especially with Tb. The nuclear magnetic relaxation dispersion (NMRD) profiles recorded for [Gd2(L3)] are characteristic of slowly tumbling systems, showing a low‐field plateau and a broad maximum around 30 MHz. This suggests the occurrence of aggregation of the complexes giving rise to slowly rotating species. A similar behavior is observed for the analogous GdIII complex containing a 4,4′ dimethyl‐2,2′‐bipyridyl spacer ([Gd2(L1)]). The relaxivity of [Gd2(L3)] recorded at 0.5 T and 298 K (pH 6.9) amounts to 13.7 mM−1 s−1. The formation of aggregates has been confirmed by dynamic light scattering (DLS) experiments, which provided mean particle sizes of 114 and 38 nm for [Gd2(L1)] and [Gd2(L3)], respectively. TEM images of [Gd2(L3)] indicate the formation of nearly spherical nanosized aggregates with a mean diameter of about 41 nm, together with some nonspherical particles with larger size.Ministerio de Educación y Ciencia; CTQ2009‐10721Xunta de Galicia; IN845B‐2010/06

Complexes de lanthanides(III) pour le développement de nouvelles sondes magnétiques et luminescentes

The simultaneous optimisation of the molecular parameters determining the relaxivity (number of coordinated water molecules, water-exchange, rotation dynamics of the whole complex, electronic relaxation, Gd(III)-proton distance) is essential to prepare efficient contrast agents. The aim of this work is on the one hand to design and study complexes with a high number of bound water molecules and to understand the influence of the coordination sphere on the stability and on the electronic relaxation and on the other hand, to use the ligand as a chromophor for the development of luminescent probes for biomedical imaging.We present the structure, the stability and the relaxivity of Gd(III) complexes of two series of tripodal ligands containing picolinate units based either on the 1,4,7-triazacyclononane ring or on a tertiary amine. These complexes show high relaxivity in water and in serum and can establish a non covalent interaction with serum albumin. The interpretation of the water proton relaxivity with the help of new relaxometric methods based on an auxiliary probe solute has allowed us to show that both the presence of the picolinate groups and the 1,4,7-triazacyclononane framework can lead to Gd(III) complexes with favourable electronic relaxation properties.This ligands have also been used for Eu(III) and Tb(III) complexation leading to strong luminescence in visible light. Other complexes derived from 8-hydroxyquinoline unit which display a very high luminescence in infrared are also studied.Afin d'accéder à des agents de contraste efficaces, il est essentiel d'optimiser simultanément les paramètres moléculaires influençant la relaxivité : nombre de molécules d'eau en première sphère de coordination, échange de l'eau, dynamique de rotation du complexe, relaxation électronique, distance Gd(III)-proton. Le but de ce travail est double. D'une part, il s'agit de concevoir et étudier des complexes possédant un nombre élevé de molécules d'eau coordinées et de comprendre l'influence de la sphère de coordination du métal sur la stabilité des complexes et la relaxation électronique. D'autre part, nous avons utilisé les ligands comme chromophores pour la mise au point de sondes luminescentes pour l'imagerie biomédicale.Nous présentons la structure, la stabilité et la relaxivité de complexes de Gd(III) de deux séries de ligands tripodes dérivés du picolinate basés, soit sur le cycle 1,4,7-triazacyclononane, soit sur un pivot amine tertiaire. Ces complexes possèdent une relaxivité élevée dans l'eau et dans le sérum et peuvent former des interactions non-covalentes avec l'albumine sérique. L'interprétation de la relaxivité des protons de l'eau au moyen de nouvelles méthodes relaxométriques basées sur l'utilisation de solutés sondes nous a permis de montrer que la présence de groupement picolinate et du cycle 1,4,7-triazacyclononane pouvait conduire à des complexes de Gd(III) possédant des propriétés de relaxation électronique favorables.Du fait de la présence de chromophores picolinate, les complexes d'Eu(III) et Tb(III) avec ces ligands donnent lieu à une luminescence intense dans le visible. D'autres complexes dérivés de l'unité 8 hydroxyquinoléine possèdent une luminescence élevée dans l'infrarouge et ont également été étudiés

Les bispidines et les ions métalliques : un mariage qui dure

International audienceCet article décrit comment, au cours de ces dernières années, la chimie des bispidines combinée à la chimie de coordination et à la radiochimie, ont ouvert la voie à un nouveau domaine d'application des bispidines : l'imagerie médicale. Deux exemples d'applications seront discutés : l'imagerie par résonance magnétique (IRM) et la tomographie à émission de positrons (TEP). Pour chacune de ces deux techniques, un ion métallique (Gd, Mn pour l'IRM ou un radioisotope pour la TEP) joue le rôle principal de « reporter » car c'est lui qui est à l'origine du signal. Cependant, ces ions ne peuvent être utilisés dans leur forme libre et doivent être « encagés » (complexés) par des molécules organiques afin de former des adduits résistants à la dissociation in vivo. Grâce à leur squelette rigide et préorganisé, les bispidines sont de bons candidats pour la complexation des métaux. Mots-clés Bispidine, agents d'imagerie, IRM, TEP, isotopes métalliques, nat/64 Cu, 68 Ga, nat/52 Mn, sondes bimodale

Complexes de lanthanides(III) pour le développement de nouvelles sondes magnétiques et luminescentes

The simultaneous optimisation of the molecular parameters determining the relaxivity (number of coordinated water molecules, water-exchange, rotation dynamics of the whole complex, electronic relaxation, Gd(III)-proton distance) is essential to prepare efficient contrast agents. The aim of this work is on the one hand to design and study complexes with a high number of bound water molecules and to understand the influence of the coordination sphere on the stability and on the electronic relaxation and on the other hand, to use the ligand as a chromophor for the development of luminescent probes for biomedical imaging.We present the structure, the stability and the relaxivity of Gd(III) complexes of two series of tripodal ligands containing picolinate units based either on the 1,4,7-triazacyclononane ring or on a tertiary amine. These complexes show high relaxivity in water and in serum and can establish a non covalent interaction with serum albumin. The interpretation of the water proton relaxivity with the help of new relaxometric methods based on an auxiliary probe solute has allowed us to show that both the presence of the picolinate groups and the 1,4,7-triazacyclononane framework can lead to Gd(III) complexes with favourable electronic relaxation properties.This ligands have also been used for Eu(III) and Tb(III) complexation leading to strong luminescence in visible light. Other complexes derived from 8-hydroxyquinoline unit which display a very high luminescence in infrared are also studied.Afin d'accéder à des agents de contraste efficaces, il est essentiel d'optimiser simultanément les paramètres moléculaires influençant la relaxivité : nombre de molécules d'eau en première sphère de coordination, échange de l'eau, dynamique de rotation du complexe, relaxation électronique, distance Gd(III)-proton. Le but de ce travail est double. D'une part, il s'agit de concevoir et étudier des complexes possédant un nombre élevé de molécules d'eau coordinées et de comprendre l'influence de la sphère de coordination du métal sur la stabilité des complexes et la relaxation électronique. D'autre part, nous avons utilisé les ligands comme chromophores pour la mise au point de sondes luminescentes pour l'imagerie biomédicale.Nous présentons la structure, la stabilité et la relaxivité de complexes de Gd(III) de deux séries de ligands tripodes dérivés du picolinate basés, soit sur le cycle 1,4,7-triazacyclononane, soit sur un pivot amine tertiaire. Ces complexes possèdent une relaxivité élevée dans l'eau et dans le sérum et peuvent former des interactions non-covalentes avec l'albumine sérique. L'interprétation de la relaxivité des protons de l'eau au moyen de nouvelles méthodes relaxométriques basées sur l'utilisation de solutés sondes nous a permis de montrer que la présence de groupement picolinate et du cycle 1,4,7-triazacyclononane pouvait conduire à des complexes de Gd(III) possédant des propriétés de relaxation électronique favorables.Du fait de la présence de chromophores picolinate, les complexes d'Eu(III) et Tb(III) avec ces ligands donnent lieu à une luminescence intense dans le visible. D'autres complexes dérivés de l'unité 8 hydroxyquinoléine possèdent une luminescence élevée dans l'infrarouge et ont également été étudiés

Complexes de lanthanides (III) pour le développement de nouvelles sondes magnétiques et luminescentes

Afin d'accéder à des agents de contraste efficaces, il est essentiel d'optimiser simultanément les paramètres moléculaires influençant la relaxivité : nombre de molécules d'eau en première sphère de coordination, échange de l'eau, dynamique de rotation du complexe, relaxation électronique, distanc Gd(III)-proton. Le but de ce travail est double. D'une part, il s'agit de concevoir et étudier des complexes possédant un nombre élevé de molécules d'eau coordinées et de comprendre l'influence de la sphère de coordination du métal sur la stabilité des complexes et la relaxation électronique. D'autn part, nous avons utilisé les ligands comme chromophores pour la mise au point de sondes luminescentes pour l'imagerie biomédicale. Nous présentons la structure, la stabilité et la relaxivité de complexes de Gd(lII) de deux séries de ligands tripodes dérivés du picolinate basés, soit sur le cycle 1,4,7 -triazacyclononane, soit sur un pivot amine tertiaire. Ces complexes possèdent une relaxivité élevée dans l'eau et dans le sérum et peuvenl former des interactions non-covalentes avec l'albumine sérique. L'interprétation de la relaxivité des protons de l'eau au moyen de nouvelles méthodes relaxométriques basées sur l'utilisation de solutés sondes nous a permis de montrer que la présence de groupement picolinate et du cycle 1,4,7triazacyclononane pouvait conduire à des complexes de Gd(lII) possédant des propriétés de relaxation électronique favorables. Du fait de la présence de chromophores picolinate, les complexes d'Eu(III) et Th(III) avec ces ligands donnent lieu à une luminescence intense dans le visible. D'autres complexes luminescents dans l'infrarouge ont également été étudiés.The simultaneous optimisation of the molecular parameters deterrnining the relaxivity (nwnber of coordinated water molecules, water-exchange, rotation dynarnics of the whole complex, electronic relaxation, Gd(III)-proton distance) is essential to prepare efficient contrast agents. The aim of this work is on the one hand to design and study complexes with a high nwnber ofbound water molecules and to understand the influence of the coordination sphere on the stability and on the electronic relaxation and on the other hand, to use the ligand as a chromophor for the developrnent of luminescent probes for biomedical imaging. We present the structure, the stability and the relaxivity of Gd(lII) complexes oftwo series of tripodalligands containing picolinate units based either 0 the 1 ,4,7-triazacyclononane ring or on a tertiary amine. These complexes show high relaxivity in water and in serum and can establish a non covalent interaction with serum albumin. The interpretation of the water proton relaxivity with the help of new relaxometric methods based on an auxiliary probe solute has allowed us to show that both the presence of the picolinate groups and the 1,4,7-triazacyclononane !Tamework can lead to Gd(lII) complexes with favourable electronic relaxation properties. This ligands have also been used for Eu(III) and Th(lII) complexation leading to strong luminescence in visible light. Other complexes derived from 8-hydroxyquinoline unit which display a very high luminescence in infrared are also studied.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Upconversion of light with molecular and supramolecular lanthanide complexes

International audienceUpconversion (UC) is the process by which the energy of multiple photons is absorbed by a compound and restored in the form of a photon of higher energy than the incident light, resulting in an anti-Stokes process. Although studied theoretically since the middle of the last century and experimentally observed in the 1960′s, the process was up to recently mainly restricted to solid state devices and ultimately to nanoparticles at the end of the century. At the same period, different researches were directed towards the possibility to observe UC at the molecular level and it is only recently that the phenomenon could be observed in discrete molecular entities in solution with still very few examples. This review aims at explaining the difficulties encountered at the molecular level compared to the solid state and summarizes the results reported to date on UC at the molecular scale