Metal Complexes in Molecular Junctions.

International audienceThe use of metal complexes to achieve conductive molecular junction with a special focus on organometallics is overviewed and illustrated with representative examples. The perspectives offered by such compounds owing to their specific properties are discussed

Polynuclear carbon-rich organometallic complexes: clarification of the role of the bridging ligand in the redox properties.

International audienceIn this Perspective, we highlight the non-innocent behaviour of the bridging ligand in organometallic polynuclear metallic complexes displaying metal-carbon σ bonds between the metallic units and a strongly coupled conjugated carbon-rich bridging ligand. With the help of representative experimental and theoretical studies on polymetallic systems, but also on monometallic complexes, we point out that the level of implication of the carbon rich ligand in the redox processes is very sensitive to the nature of (i) the metal(s), (ii) the ancillary ligands and (iii) the carbon-rich ligand itself, and that this participation is frequently found to be major. Consequently, the general denomination M((n + 1)) that is usually used for oxidized species gives the picture that only the metal density is affected, which is misleading. Moreover, for polymetallic species, these elements make the mixed valence denomination and the use of standard methodologies to rationalize intramolecular electron transfer, such as the Hush model inaccurate. Indeed, these theoretical treatments of mixed-valent complexes have at their core the assumption of metal-based redox state changes. Quantum mechanical calculations, coupled with spectroscopic methods, such as EPR spectroscopy, turn out to be a valuable suite of tools to both identify and better describe those systems with appreciable ligand redox non-innocent character. Finally, some examples and perspectives of applications for this carbon-rich type of complexes that take advantage of their peculiar electronic structure are presented

Photo-modulable Molecular Transport Junctions based on Organometallic Molecular Wires

International audiencePhoto-modulable molecular transport junctions are developed via on-wire lithography-fabricated nanogaps functionalized with a dithienylethene unit bearing two ruthenium fragments. A reversible and repeatable bi-state conductive switching upon alternate irradiation of UV and visible light can be distinctly observed. Theoretical calculations further suggest that bi-directional isomerization is due to the ruthenium moieties that modulate judiciously the electronic coupling between the photochromic part and the metal electrodes, and that the differences in electronic structure between the two isomers (open and closed states) are responsible for conductivity switching

Excited state absorption : a key phenomenon for the improvement of biphotonic based optical limiting at telecommunication wavelengths

International audienceSpectroscopic properties, two-photon absorption (TPA) and excited state absorption (ESA), of two organic cyanine dyes and of a ruthenium based organometallic cyanine are compared in order to rationalize their similar ns-optical power limiting (OPL) efficiency in the telecommunication wavelength range. The TPA contribution to the ns-OPL behavior is higher for both organic cyanines, while the main process is a TPA-induced ESA in the case of the organometallic system, in which the ruthenium induces a broadening of the NIR-ESA band and resulting in a strong spectral overlap between TPA and ESA spectra

The many facets of RuII(dppe)2 acetylide compounds

International audienceIn this contribution, we describe the various research domains in which RuII alkynyl derivatives are involved. Their peculiar molecular properties stem from a strong and intimate overlap between the metal centered d orbitals and the p system of the acetylide ligands, resulting in plethora of fascinating properties such as strong and tunable visible light absorption with a strong MLCT character  essential for sensing, photovoltaics, light‐harvesting applications or non‐linear optical properties. Likewise, the d/p mixing results in tunable redox properties at low potential due to the raising of the HOMO level, and making those compounds particularly suited to achieve redox switching of various properties associated to the acetylide conjugated ligand, such as photochromism, luminescence or magnetism, for charge transport at the molecular level and in field effect transistor devices, or charge storage for memory devices. Altogether, we show in this review the potential of RuII acetylide compounds, insisting on the molecular design and suggesting further research developments for this class of organometallic dyes, including supramolecular chemistry

Complexes organométalliques de ruthénium riches en carbone (synthèse et études de fils et interrupteurs moléculaires)

Ce travail est consacré à la synthèse et à l'étude de nouveaux complexes de ruthénium riches en carbone de type acétylure de ruthénium, pour l'élaboration de fils et commutateurs moléculaires. La première partie de ce travail est consacrée à la préparation et aux différentes études photochimiques et électrochimiques d'un complexe trimétallique de ruthénium possédant deux unités dithiényléthène (DTE) identiques. Le but est de contrôler leur fermeture successive à l'aide des stimulus lumineux et électrochimiques. La deuxième partie présente une association d'un ion d'ytterbium à un ligand possédant une unité DTE, dans le but de commuter la luminescence du centre lanthanide. Ce processus est espéré via un piégeage de la sensibilisation de l'ion lanthanide à l'aide de l'unité photochromique. Dans la troisième partie de ce travail, la synthèse et les caractérisations physico-chimiques de fils moléculaires de ruthénium sont présentées. Ces objets possédant des ligands portant des fonctions de type thiols doivent permettre une connexion de la molécule avec des surfaces métalliques d'or pour effectuer des mesures de conductivité. La dernière partie de ce manuscrit aborde la synthèse et la caractérisation de plusieurs commutateurs organométalliques possédant des réponses à des stimuli photochimiques et électrochimiques, ainsi que leur adaptation sur des surfaces métalliques. Ainsi ces molécules possèdent des fonctions d'accroches de type thiol pour leurs adaptations sur des surfaces métalliques. Nous espérons pouvoir dans un premier temps, modifier les propriétés d'absorptions UV-visible ainsi que le potentiel d'oxydation de surfaces métalliques à l'aide d'un complexe de type [Ru] DTE [Ru] S (où S représente une fonction thiol). Nous espérons également parvenir à moduler la vitesse de transfert d'électron entre une surface métallique et un centre électro-actif à l'aide d'une unité DTE insérée dans un complexe de type [Ru] DTE S. Dans un dernier temps, nous espérons pouvoir moduler la conductivité électrique de jonctions moléculaires à l'aide de complexes de type S [Ru] DTE [Ru] S et S [Ru] DTE [Ru] DTE [Ru] S.This work is devoted to the synthesis and characterization of new carbon rich ruthenium acetylide complexes to reach original molecular wires and switches. The first part of this manuscript deals with the preparation, the photoisomerisation and electrochemical studies of a ruthenium trimetallic complex bearing two identical dithienylethene (DTE) moities. The goal is to control the stepwise closing of these photochromic units using light and electrochemical stimuli. Such a control was never obtained before. The second part describes an association of an ytterbium ion and a ligand bearing a DTE unit, in order to commute the light emission of the lanthanide center. This process is expected to happen through an energy quenching by the photochromic unit. In the third part, the synthesis and the physico-chemical studies of new molecular wires bearing thiol linkers are presented. The aim is to measure the electrical conductivity of such wires in molecular junctions. The last part of this manuscript deals with the synthesis and the characterization of several multiresponsive organometallic switches for surface adaptation. In that respect, these molecules posses thiol linkers to bind surfaces. The first goal is to modify the UV-vis absorption properties and the oxidation potential of metallic surfaces with a [Ru] DTE [Ru] S type complex (S represents a thiol function). The electron transport kinetics between a surface and a redox center is also expected to be modified by light through a DTE [Ru] S complex. Finally, the electrical conductivity of molecular junctions is expected to be photochenically and electrochemically modified with S [Ru] DTE [Ru] S and S [Ru] DTE [Ru] DTE [Ru] S complexes.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Nouveaux complexes de ruthénium riches en carbone pour l'élaboration de fils et interrupteurs moléculaires originaux

rLa première partie de ce travail est consacrée à l étude de nouveaux interrupteurs moléculaires redox magnétiques, basés sur l association d unités paramagnétiques de cuivre, de manganèse, ou de radicaux nitronyle nitroxydes, avec des complexes de ruthénium de type acétylure. L objectif est d observer une modulation redox des propriétés magnétiques de ces composés. La seconde partie traite de l association de divers ions trivalents lanthanides à un complexe de ruthénium acétylure pour réaliser la première modulation redox de la luminescence des lanthanides. La troisième partie présente la synthèse et l étude de nouveaux fils moléculaires bimétalliques asymétriques dans le but d obtenir l un des premiers exemples de système asymétrique permettant une excellente délocalisation électronique dans l état oxydé. Enfin, la dernière partie aborde la synthèse et l étude de précurseurs pour le greffage sur surfaces des interrupteurs obtenus dans les parties précédentes, via la formation de SAMs.The first part of this work deals with the synthesis and characterization of new magnetic redox switches based on the association of paramagnetic units such as nitronyl nitroxide, or copper and manganese compounds with ruthenium carbon-rich acetylides. The aim was to modulate the magnetic properties by changing the oxidation state of the ruthenium center. The second part treats of the association of different trivalent lanthanide ions with acetylide carbon-rich ruthenium complexes in order to achieve the first redox modulation of lanthanide luminescence. The third part deals with the synthesis and the study of new asymmetric bimetallic molecular wires to get an efficient electronic delocalization all over the asymmetric compounds. The last part reports the synthesis and the study of new model compounds in order to further realize the grafting on gold surface of the molecular switches obtained in the first two parts. The aim was to retain the switching properties observed in solution within the SAMs.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Ruthenium-allenylidene complexes and their specific behaviour

International audienceThis review presents recent innovations in the field of stoichiometric transformations of ruthenium-allenylidene systems via synthesis and at the frontier of material science and catalysis. It especially shows new routes to the first bis-allenylidene-ruthenium and diruthenium complexes, trisallenylidene ruthenium triskelia, the use of ruthenium-allenylidene as precursors for alkenylcarbynes and indenylidenes, and the involvement of allenylidenes in the building of dinuclear ruthenium bridges with a C-7 carbon-rich bridge. (C) 2004 Elsevier B.V. All rights reserved

New coupling reactions for the construction of carbon-rich C-7 bridged di-ruthenium complexes

International audienceThis microreview summarizes our work on new reactions to obtain ruthenium(II) binuclear species with seven conjugated carbon atoms between the remote metals in very mild conditions via C-C bond formation. (i) The treatment of trans-[Cl(dppe)(2)Ru-CdropC-CdropC-SiMe3] with [Fe(C5H5)(2)]PF6 leads to an unprecedented metal-assisted [2+2] coupling reaction between C(gamma)dropC(delta) bonds to produce trans-[Cl(dppe)(2)Ru-CdropC-CdropCHC(CH2)double bondCdouble bondCdouble bondRu(dppe)(2)Cl]PF6 including a cyclobutenyl bridge. (ii) Addition of a cationic allenylidene trans-[ClRu(dppe)(2)(double bondCdouble bondCdouble bondC(CH2R1)R-2)]BF4 (R-1 = H, CH3; R-2 = CH3, Ph) on the C(gamma)dropC(delta) bond of the diyne trans-[Cl(dppe)(2)Ru-CdropC-CdropC-H] leads to ruthenium bimetallic complexes trans-[Cl(dppe)(2)Ru-CdropC-C(CH3)double bondC(R-1)-C(R-2)double bondCdouble bondCdouble bondRu(dppe)(2)Cl]BF4 containing a planar delocalized “W”-shaped C-7 bridge with tunable pendant groups. These complexes display attractive redox and optical properties with a highly delocalized charge over the conjugated carbon atoms. The crystal structures of trans-[Cl(dppe)(2)Rudouble bondCdouble bondCdouble bondC(CH3)-C(H)double bondC(CH3)-CdropC-Ru(dppe)(2)Cl]BF4 and of the annealated complex were solved. (C) 2003 Elsevier B.V. All rights reserved

Amphoteric allenylidene ruthenium complexes and the first dinuclear ruthenium species with a bis-alkenyl carbyne bridging ligand

International audienceCationic ruthenium(II) allenylidenes trans-[Cl(dppe)(2)Ru=C=C=C(CH3)R]BF4 (R = Ph, CH3) can be deprotonated to generate neutral alkenyl acetylide metal trans- [Cl(dppe)(2)Ru-CdropC-C(=CH2)R] or protonated with HBF4.Et2O to lead to dicationic ruthenium(II) carbynes trans-[Cl(dppe)(2)RudropC-CH=C(CH3)R] (BF4)(2). The latter reaction was applied to transform a conjugated bis-allenylidene bridged diruthenium complex, trans-[Cl(dppe)(2)Ru=C=C=C(CH3)-p-C6H4-(CH3)C=C=C=Ru(dppe)(2)Cl](BF4)( 2), into the first bis-alkenyl carbyne ruthenium species trans-[Cl(dppe)(2)RudropC-CH=C(CH3)-p-C6H4-(CH3)C=HC-CdropRu(dppe)(2)C l](BF4)(4)