Démonstrateurs des potentialités applicatives des clustomésogènes

Clustomesogens are a new class of hybrid liquid crystals developed since 2008 in our laboratory. They are a combination of an inorganic core, namely transition metal clusters, linked with promesogenic organic ligands through covalent or electrostatic interactions. These hybrid materials associate liquid crystals self-assembling abilities to the metallic clusters intrinsic properties. This work present octahedral molybdenum cluster based clustomesogens, emitting, through phosphorence mechanisms, in the deep red area and exhibiting 10% to 50% quantum efficiency. These materials are produced via an ionic approach by replacing the alkali cations of the ternary solid state compounds with tailored promesogenic organic ones. The ambition of this work is to rationalize the structures-properties relationship to control, at the nanometric scale, the clustomesogens organization. This approach allows us to observe nematic liquid crystalline phases over a wide range of temperatures. As these compounds are miscible with commercial nematic liquid crystals, we could envision their use as emissive species in the design of electroswitchable luminescent liquid crystal cells. By changing the type and concentration of commercial liquid crystals, we could adjust the operating temperature range as well as the viscosity of the mixture. We also establish that it is possible to modulate the clustomesogens' photoluminescence by 50% by applying an alternative electric field, as in display devices. In the last part of this work, we study the integration of clustomesogens as the emissive species into electroluminescent diodes. Being able to control their structure should allow their use in lighting devices. These works pave the way for using Molybdenum clustomesogens as an alternative to inorganic compounds presently used as red light emitters.Les clustomésogènes sont une nouvelle classe de cristaux liquides hybrides multifonctionnels découverts dans l'équipe CSM de l'Institut des Sciences Chimiques de Rennes en 2008. Ils sont constitués d'un cœur inorganique - des clusters de métaux de transition - auquel sont associés, de manière covalente ou électrostatique, des ligands organiques pro-mésogéniques. Ces matériaux hybrides associent les propriétés d'auto-assemblage des cristaux liquides aux propriétés intrinsèques des clusters métalliques. Le présent travail s'articule autour de clustomésogènes contenant des clusters octaédriques de molybdène, phosphorescents dans le rouge-proche infra-rouge, et aux rendements quantiques compris entre 10% et 50%. Ils sont synthétisés par approche ionique en vue de leur intégration dans des dispositifs optiques. La démarche consiste à rationaliser les relations structures-propriétés afin de contrôler l'arrangement des clustomésogènes à l'échelle nanométrique. Nous créons ainsi des états nématiques sur de larges gammes de température. Le transfert de ces systèmes dans des cellules électro-optiques est renforcé par leur miscibilité dans un certain nombre de cristaux liquides commerciaux. La nature et la concentration de ces derniers permet l'ajustement des températures de fonctionnement et le contrôle de la viscosité de l'état cristal-liquide. Nous montrons qu'il est possible de faire commuter l'intensité de photoluminescence des clustomésogènes de 50% par l'application d'un champ alternatif à la manière des systèmes d'affichage. L'intégration au sein de diodes électroluminescentes constitue le dernier volet de ce travail. La maîtrise de leur structure permet d'envisager leur potentiel dans des dispositifs d'éclairage. L'ensemble de ces études ouvre la voie aux clustomésogènes de molybdène comme alternative réaliste aux émetteurs inorganiques rouges actuels

Electroswitchable red-NIR luminescence of ionic clustomesogen containing nematic liquid crystalline devices.

International audienceWe describe in this work several polyionic hybrid mol. compds. combining, by electrostatic interactions, liq. cryst. ammonium cations and tailor made molybdenum hexanuclear dianionic cluster units. All hybrids show nematic liq. cryst. behavior below 100 °C, no matter the nature of the metallic cluster apical and inner ligands. They also retain the shiny deep red photoluminescence properties of their parent cluster in the nematic phase. This nematic phase remains however quite viscous for all compds. and mixing them with com. available nematic LCs seems mandatory to integrate them into electroswitchable devices. This particularity conducted us to insert the best candidate in terms of homogeneity and stability of the clustomesogen/com. LC mixt. into a LC cell and study the behavior toward the application of an elec. stimulus. We show that the application of 30 V AC voltage allows observing a reversible modulation of the photoluminescence signal by about 52%. This work presents the first deep red photoluminescent transition metal cluster contg. device directed towards optoelectronic applications

Étude de la respiration « nitrate-NO » dans l’interaction symbiotique entre Medicago truncatula et Sinorhizobium meliloti: A la recherche d’un transporteur de nitrite mitochondria

Symbiosis between legume plants and nitrogen-fixing bacteria (rhizobium) constitute a major issue to reduce nitrogen fertilization in crops. Central function of nodules is the enzymatic reduction of atmospheric nitrogen (N2) into ammoniac (NH4+) by the bacterial nitrogenise, and the subsequent assimilation in the plant cell. This highly energy-consuming process is a paradox as occurring in hypoxied tissue where mitochondrial respiration -the main ATP source- is strongly reduced. The question rose how the ATP required for cellular functioning is generated into nodules. Based on recent observations on hypoxied roots, we rose the hypothesis that, in nodules, ATP is formed trough a cyclic respiration -called nitrate-NO respiration- that consists in four steps: 1) nitrate reductase (NR) reduces nitrate (NO3-) into nitrite (NO2-) in the cytosol ; 2) NO2- is transported from cytosol into mitochondria using transporter(s) protein(s) ; 3) electrons of mitochondrial transfer chain reduces NO2- into nitric oxide (NO), thus allowing respiration functioning and ATP formation ; and 4) NO freely diffuses from mitochondria to cytosol to be oxidized back into NO3- through leghemoglobine (Lb) action. During this thesis, we showed, using Medicago truncatula-Sinorhizobium meliloti system as a model, that NRs and electron transfer chains from both plant and bacterial partners were involved in NO production of functioning nodules. NR activity was also showed to be crucial to maintain high energetic status required for nitrogen fixation. The second aim was to characterized nitrite transport across purified root mitochondria. Then, mitochondrial nitrite transporter candidate(s) were investigated. An in silico strategy searching for predicted proteins in M. truncatula genome, potentially localized to mitochondria, that shared homologous sequences with known transporters was conducted. 6 candidates were chosen at the end of this analysis. Membrane mitochondria proteins were identified using mass spectrometry (MS) analysis, revealing 3 new candidates. The expression profile in normoxied and hypoxied roots and nodules was characterized for the 9 candidates retained. Two of them showed particularly promising patterns. Finally, sub-cellular localization and tissular expression during nodule development were analyzed for some candidates that shared interesting expression patterns.Les symbioses entre les légumineuses et les bactéries fixatrices d’azote (rhizobium) représentent un enjeu majeur pour la réduction des intrants azotés en agriculture. La réduction de l'azote moléculaire (N2) en ammonium (NH4+) par la nitrogénase bactérienne, puis son assimilation par la cellule végétale constituent la fonction centrale des nodosités symbiotiques. Ce processus, très coûteux en énergie, présente le paradoxe de se produire dans un organe très appauvri en oxygène, ce qui conduit à fortement réduire la respiration mitochondriale, principale source d'ATP. La question se posait donc de savoir par quels mécanismes l'ATP nécessaire au fonctionnement cellulaire est régénéré au sein de la nodosité. Sur la base d'observations récentes faites dans les racines en hypoxie, nous avons posé l'hypothèse selon laquelle, dans la nodosité fixatrice d'azote, une partie de l'ATP est régénérée par le biais d'une respiration cyclique (respiration nitrate-NO) en quatre étapes: 1) le nitrate (NO3-) est réduit en nitrite (NO2-) dans le cytosol par la nitrate réductase (NR); 2) le NO2- est transporté du cytosol dans la mitochondrie par l'intermédiaire d'un (ou plusieurs) transporteur(s); 3) le NO2- est réduit en oxyde nitrique (NO) par les électrons de la chaîne respiratoire (permettant ainsi le fonctionnement de la respiration et la régénération de l'ATP); et 4) le NO diffuse librement vers le cytosol où il est oxydé en NO3- par la leghémoglobine (Lb). Au cours de ce travail de thèse, mené sur le modèle Medicago truncatula-Sinorhizobium meliloti, nous avons d'abord montré que les nitrate réductases et les chaînes de transfert d'électron des deux partenaires, végétal et bactérien, sont impliquées dans la production de NO dans les nodosités fonctionnelles. Nous avons également montré que l'activité nitrate réductase est nécessaire au maintien d'un état énergétique élevé permettant la fixation de l'azote. Dans un second temps, nous avons entrepris de caractériser le transport du nitrite chez des mitochondries purifiées de racines. L’objectif était ensuite d’identifier un ou plusieurs candidats pour le transport du nitrite dans les mitochondries. Pour cela, sur la base d'homologies de séquence avec des transporteurs déjà identifiés et de séquences d'adressage putatives, une recherche in silico des protéines prédites de M. truncatula a été conduite. Cette analyse a permit de sélectionner 6 candidats avec une localisation possible aux mitochondries. L’analyse par spectrométrie de masse des protéines présentes sur les membranes des mitochondries a révélé 3 autres candidats. L'expression des 9 candidats retenus a été caractérisée en situation de normoxie et d’hypoxie dans les racines et les nodosités. Cela a permis de mettre en évidence deux profils intéressants. Enfin, l'étude de l’adressage subcellulaire et l’expression tissulaire au cours du développement de la nodosité ont été débutés pour certains des candidats retenus sur leur profil d’expression et ceux obtenus par spectrométrie de masse

Clustomesogen containing demonstrative devices

Les clustomésogènes sont une nouvelle classe de cristaux liquides hybrides multifonctionnels découverts dans l'équipe CSM de l'Institut des Sciences Chimiques de Rennes en 2008. Ils sont constitués d'un cœur inorganique - des clusters de métaux de transition - auquel sont associés, de manière covalente ou électrostatique, des ligands organiques pro-mésogéniques. Ces matériaux hybrides associent les propriétés d'auto-assemblage des cristaux liquides aux propriétés intrinsèques des clusters métalliques. Le présent travail s'articule autour de clustomésogènes contenant des clusters octaédriques de molybdène, phosphorescents dans le rouge-proche infra-rouge, et aux rendements quantiques compris entre 10% et 50%. Ils sont synthétisés par approche ionique en vue de leur intégration dans des dispositifs optiques. La démarche consiste à rationaliser les relations structures-propriétés afin de contrôler l'arrangement des clustomésogènes à l'échelle nanométrique. Nous créons ainsi des états nématiques sur de larges gammes de température. Le transfert de ces systèmes dans des cellules électro-optiques est renforcé par leur miscibilité dans un certain nombre de cristaux liquides commerciaux. La nature et la concentration de ces derniers permet l'ajustement des températures de fonctionnement et le contrôle de la viscosité de l'état cristal-liquide. Nous montrons qu'il est possible de faire commuter l'intensité de photoluminescence des clustomésogènes de 50% par l'application d'un champ alternatif à la manière des systèmes d'affichage. L'intégration au sein de diodes électroluminescentes constitue le dernier volet de ce travail. La maîtrise de leur structure permet d'envisager leur potentiel dans des dispositifs d'éclairage. L'ensemble de ces études ouvre la voie aux clustomésogènes de molybdène comme alternative réaliste aux émetteurs inorganiques rouges actuels.Clustomesogens are a new class of hybrid liquid crystals developed since 2008 in our laboratory. They are a combination of an inorganic core, namely transition metal clusters, linked with promesogenic organic ligands through covalent or electrostatic interactions. These hybrid materials associate liquid crystals self-assembling abilities to the metallic clusters intrinsic properties. This work present octahedral molybdenum cluster based clustomesogens, emitting, through phosphorence mechanisms, in the deep red area and exhibiting 10% to 50% quantum efficiency. These materials are produced via an ionic approach by replacing the alkali cations of the ternary solid state compounds with tailored promesogenic organic ones. The ambition of this work is to rationalize the structures-properties relationship to control, at the nanometric scale, the clustomesogens organization. This approach allows us to observe nematic liquid crystalline phases over a wide range of temperatures. As these compounds are miscible with commercial nematic liquid crystals, we could envision their use as emissive species in the design of electroswitchable luminescent liquid crystal cells. By changing the type and concentration of commercial liquid crystals, we could adjust the operating temperature range as well as the viscosity of the mixture. We also establish that it is possible to modulate the clustomesogens' photoluminescence by 50% by applying an alternative electric field, as in display devices. In the last part of this work, we study the integration of clustomesogens as the emissive species into electroluminescent diodes. Being able to control their structure should allow their use in lighting devices. These works pave the way for using Molybdenum clustomesogens as an alternative to inorganic compounds presently used as red light emitters

Liquid Crystal Elastomers—A Path to Biocompatible and Biodegradable 3D-LCE Scaffolds for Tissue Regeneration

The development of appropriate materials that can make breakthroughs in tissue engineering has long been pursued by the scientific community. Several types of material have been long tested and re-designed for this purpose. At the same time, liquid crystals (LCs) have captivated the scientific community since their discovery in 1888 and soon after were thought to be, in combination with polymers, artificial muscles. Within the past decade liquid crystal elastomers (LCE) have been attracting increasing interest for their use as smart advanced materials for biological applications. Here, we examine how LCEs can potentially be used as dynamic substrates for culturing cells, moving away from the classical two-dimensional cell-culture nature. We also briefly discuss the integration of a few technologies for the preparation of more sophisticated LCE-composite scaffolds for more dynamic biomaterials. The anisotropic properties of LCEs can be used not only to promote cell attachment and the proliferation of cells, but also to promote cell alignment under LCE-stimulated deformation. 3D LCEs are ideal materials for new insights to simulate and study the development of tissues and the complex interplay between cells

Highly Tunable Circularly Polarized Emission of an Aggregation-Induced Emission Dye Using Helical Nano- and Microfilaments as Supramolecular Chiral Templates

International audienceAggregation-induced emission (AIE)-based circularly polarized luminescence (CPL) has been recognized as a promising pathway for developing chiroptical materials with high luminescence dissymmetry factors (|g(lum)|). Here, we propose a method for the construction of a thermally tunable CPL-active system based on a supramolecular self-assembly approach that utilizes helical nano- or microfilament templates in conjunction with an AIE dye. The CPL properties of the ensuing ensembles are predominantly determined by the intrinsic geometric differences among the various filament templates such as their overall dimensions (width, height, and helical pitch) and the area fraction of the exposed aromatic segments or sublayers. The proposed mechanism is based on the collective data acquired by absorption, steady state and time-resolved fluorescence, absolute quantum yield, and CPL measurements. The highest |g(lum)| value for the most promising dual-modulated helical nanofilament templates in the present series was further enhanced, reaching up to |g(lum)| = 0.25 by confinement in the appropriate diameter of anodized aluminum oxide (AAO) nanochannels. It is envisioned that this methodology will afford new insights into the design of temperature-rate indicators or anti-counterfeiting tags using a combination of structural color by the nano- and microfilament templates and the AIE property of the guest dye

Transition metal clusters containing luminescent hybrid liquid crystal in the design of electroswitchable devices

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Voltage-Driven Photoluminescence Modulation of Liquid-Crystalline Hybridized ZnO Nanoparticles

International audienceLiquid-crystalline hybrid nanomaterials have been obtained by grafting mesogenic units around luminescent ZnO nanocrystals of 5 nm in diameter. Modifying the mesogenic density around the inorganic core allows the modulation of the liquid-crystalline behavior and its miscibility in commercial liquid crystal (LC). The strong blue photoluminescence observed for the hybrids can be modulated by applying a voltage on a LC cell containing commercial LC and 10 wt % of hybrid

Controlling the Structure and Morphology of Organic Nanofilaments Using External Stimuli.

In our continuing pursuit to generate, understand, and control the morphology of organic nanofilaments formed by molecules with a bent molecular shape, we here report on two bent-core molecules specifically designed to permit a phase or morphology change upon exposure to an applied electric field or irradiation with UV light. To trigger a response to an applied electric field, conformationally rigid chiral (S,S)-2,3-difluorooctyloxy side chains were introduced, and to cause a response to UV light, an azobenzene core was incorporated into one of the arms of the rigid bent core. The phase behavior as well as structure and morphology of the formed phases and nanofilaments were analyzed using differential scanning calorimetry, cross-polarized optical microscopy, circular dichroism spectropolarimetry, scanning and transmission electron microscopy, UV-vis spectrophotometry, as well as X-ray diffraction experiments. Both bent-core molecules were characterized by the coexistence of two nanoscale morphologies, specifically helical nanofilaments (HNFs) and layered nanocylinders, prior to exposure to an external stimulus and independent of the cooling rate from the isotropic liquid. The application of an electric field triggers the disappearance of crystalline nanofilaments and instead leads to the formation of a tilted smectic liquid crystal phase for the material featuring chiral difluorinated side chains, whereas irradiation with UV light results in the disappearance of the nanocylinders and the sole formation of HNFs for the azobenzene-containing material. Combined results of this experimental study reveal that in addition to controlling the rate of cooling, applied electric fields and UV irradiation can be used to expand the toolkit for structural and morphological control of suitably designed bent-core molecule-based structures at the nanoscale