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Molecules of columnar liquid crystals (CLCs) typically consisting of a rigid aromatic core and flexible alkyl chains, can form a columnar mesophase by self-assembly. This self assembly of the molecules in the columns are driven by π-π interactions among the aromatic cores, while the alkyl chains fill the intercolumnar space. Among other promising features of CLCs for applications, the characteristic one dimensional (1D) charge transport feature, due to π orbitals with delocalized electrons, qualifies CLCs for variety of electronic application. In this work, selected different columnar liquid crystals (CLCs) were systematically studied in order to elucidate their structure, phase behavior, molecular dynamics and conductivity. It is aimed to gain an understanding of the structure-dynamics property relationships of the CLCs. The systems chosen in this study corresponds to hexakis(n-alkyloxy)triphenylene based discotic liquid crystals (DLCs), which are extensively studied model systems and considered as “working horse” of the CLC research. In addition to the selected triphenylene based CLCs, dipole functionalized CLCs related to these selected CLCs and columnar ionic liquid crystals (ILCs) were chosen due to the interest of both scientific and application points of view. The research work is focused on two different states of columnar liquid crystalline systems, which are “CLCs in the bulk state” and “a CLC under nanoconfinement”. On the one hand, for the investigations of CLCs in the bulk state, unfunctionalized as well as mono-dipole functionalized triphenylene-based DLCs, triphenylene crown ether-based DLCs and columnar ILCs were studied. On the other hand, for the investigations of a CLC under nanoconfinement, an unfunctionalized triphenylene-based DLC confined into cylindrical nanopores was investigated. All CLCs studied in this work form a hexagonal columnar (Colh) mesophase. The main experimental techniques applied for this study are differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS), specific heat spectroscopy (SHS) employing differential AC-chip calorimetry and temperature modulated DSC (TMDSC), as well as fast scanning calorimetry (FSC). In addition, different complementary techniques were also used, including thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), polarizing optical microscopy (POM), and X-ray diffraction (XRD). In the first part of the thesis regarding the investigations on the different CLCs in the bulk state, the mesomorphic properties of the CLCs were explored using POM and XRD. The POM and XRD investigations evidenced the characteristic mesomorphic properties of the Colh mesophases formed. Moreover, an amorphous halo in the XRD pattern was observed for all systems studied, which indicates nanophase separation between the substituents filling the intercolumnar area and the columns formed by the cores. The phase behavior of the CLCs was explored conducting conventional DSC measurements. The phase transition temperatures and enthalpies were determined. The DSC investigations showed that all CLCs studied, except one of the materials, have a plastic crystalline (Cry) phase, a Colh mesophase and an isotropic (Iso) phase upon heating from 173 K. Furthermore, at least one thermal glass transition was detected by DSC for all CLCs. For the triphenylene based DLCs, two different thermal glass transitions were found. The molecular dynamics taking place in these systems as well as the conductivity were probed using BDS in a broad frequency and temperature range. Additionally, the glassy dynamics were studied using advanced calorimetric techniques; SHS and FSC. Hence, an understanding of the molecular dynamics was obtained from different perspectives. The investigations revealed a γ process and α-processes (multiple glassy dynamics) for all CLCs studied in this work. The γ processes probed by BDS are assigned to the PE-like localized fluctuations of the methyl groups of the alkyl chains filling the intercolumnar area. Among the multiple glassy dynamics detected (α1-, α2-, α3- and α4 processes), the α1-processes observed for all CLCs are attributed to the PE like cooperative fluctuations taking place in the alkyl chains. Moreover, other glass dynamics (α2-, α3- and α4 processes) detected by BDS are ambiguously attributed to the cooperative fluctuations of the cores. Different possibilities of the molecular assignment of these glassy dynamics are proposed and further discussed in the thesis. In addition to the relaxation processes, a conductivity contribution was observed by BDS for all CLCs. In order to quantify the conductivity contribution as well as to reveal the conductivity mechanism, the conductivity contribution was analyzed in detail and discussed. In the second part of the thesis regarding the investigations on a CLC under nanoconfinement, a triphenylene based DLC confined into cylindrical nanopores of anodic aluminum oxide and silica membranes, having pore sizes from 161 nm down to 12 nm, was studied. n Octcylphosphonic acid (OPA) and n octadecylphosphonic acid (ODPA) modifications were used to graft the hydrophilic inner walls of the pores with alkyl chains, consequently, the hydrophobic pore walls were obtained. The study considers both unmodified and modified pore walls. The phase behavior under the nanoconfinement was explored using DSC. The DSC investigations elucidated the pore size dependencies of the phase transition temperatures and enthalpies. The collective orientational order (dominating molecular ordering) under the confinement was probed using BDS. The molecular ordering under the nanoconfinement was deduced to be pore size and surface chemistry dependent. The results evidenced that the dominating planar axial configuration, only configuration suitable for electronic applications, was successfully achieved by both OPA and ODPA modifications for most of the pore sizes probed., Moleküle von kolumnaren Flüssigkristallen (CLCs), die typischerweise aus einem starren aromatischen Kern und flexiblen Alkylketten bestehen, können durch Selbstorganisation eine kolumnaren Mesophase bilden. Die Selbstorganisation der Moleküle in den Säulen wird durch π-π-Interaktionen zwischen den aromatischen Kernen bewirkt, während die Alkylketten, die den zwischenkolumnaren Raum füllen. Neben anderen vielversprechenden Anwendungsmöglichkeit von CLCs qualifiziert die charakteristische eindimensionale (1D) Ladungstransportfunktion aufgrund von π-Orbitalen mit delokalisierten Elektronen die CLCs für eine Vielzahl von elektronischen Anwendungen. In dieser Arbeit wurden ausgewählte verschiedene kolumnare Flüssigkristalle (CLCs) systematisch untersucht, um ihre Struktur, ihr Phasenverhalten, ihre Molekulardynamik und ihre Leitfähigkeit zu verstehen. Ziel ist es, ein Verständnis der strukturdynamischen Eigenschaftsbeziehungen der CLCs zu gewinnen. Die in dieser Studie ausgewählten Systeme entsprechen hexakis(n-alkyloxy)triphenylenbasierten diskotischen Flüssigkristallen (DLCs), die umfassend untersuchte Modellsysteme sind und als "Arbeitspferd" der CLC-Forschung gelten. Zusätzlich zu den ausgewählten triphenylenbasierten CLCs wurden aufgrund des wissenschaftlichen und anwendungsbezogenen Interesses dipolfunktionalisierte CLCs in Bezug auf diese ausgewählten CLCs und kolumnare ionische Flüssigkristalle (ILCs) ausgewählt. Die Forschungsarbeiten konzentrieren sich auf zwei verschiedene Zustände kolumnarer flüssigkristalliner Systeme, den "CLCs im Volumentzustand" und "ein CLC unter Nanoconfinement". Zum einen wurden für die Untersuchung von CLCs im Volumentzustand sowohl unfunktionalisierte als auch mono Dipol funktionalisierte triphenylenbasierte DLCs, triphenylenkronenetherbasierte DLCs und kolumnare ILCs ausgewertet. Andererseits wurde für die Untersuchungen eines CLC unter Nanoconfinement ein unfunktionalisiertes DLC auf Triphenylenbasis untersucht, das in zylindrischen Nanoporen eingeschlossen werde. Alle CLCs, die in dieser Arbeit untersucht wurden, bilden eine hexagonal geordnete flüssigkristalline Mesophase. Die wichtigsten experimentellen Techniken, die für diese Studie verwendet werden, sind die Differential-Scanning-Kalorimetrie (DSC), die dielektrische Breitbandspektroskopie (BDS), die spezifische Wärmespektroskopie (SHS) mit differentieller AC-Chip-Kalorimetrie und die temperaturmodulierte DSC (TMDSC) sowie die Fastscan-Kalorimetrie (FSC). Darüber hinaus wurden auch unterschiedliche komplementäre Techniken eingesetzt, darunter die thermogravimetrische Analyse (TGA), die Fourier-Transformations-Infrarotspektroskopie (FTIR), die optische Polarisationsmikrokopie (POM) und die Röntgendiffraktion (XRD). Im ersten Teil der Arbeit der Untersuchungen an den verschiedenen CLCs im Massenzustand wurden die mesomorphen Eigenschaften der CLCs mit POM und XRD studiert. Die POM- und XRD-Untersuchungen zeigten die charakteristischen mesomorphen Eigenschaften der gebildeten hexagonal geordnete flüssigkristalline Mesophase. Darüber hinaus wurde ein amorpher Halogen im XRD-Spektrum für alle untersuchten Systeme beobachtet, was auf eine Nanophasentrennung zwischen den Substituenten, die den interkolumnaren Bereich ausfüllen, und den von den Kernen gebildeten Säulen hinweist. Das Phasenverhalten der CLCs wurde weiter durch konventionelle DSC-Messungen untersucht. Die Phasenübergangstemperaturen und Enthalpien wurden bestimmt. Die DSC-Untersuchungen zeigten, dass alle untersuchten CLCs, mit Ausnahme eines der Materialien, eine plastisch kristalline (Cry)-Phase, eine hexagonal geordnete flüssigkristalline Mesophase und eine isotrope (Iso)-Phase beim Erwärmen von 173 K zu hohen Temperaturen aufweisen. Außerdem wurde mindestens ein thermischer Glasübergang mittels DSC für alle CLCs nachgewiesen. Für die triphenylenbasierten DLCs wurden zwei unterschiedliche thermische Glasübergänge gefunden.Die in diesen Systemen stattfindende Molekulardynamik sowie die Leitfähigkeit wurden mit BDS in einem breiten Frequenz- und Temperaturbereich untersucht. Zusätzlich wurde die glasartige Dynamik mit modernen kalorimetrischen Techniken wie SHS und FSC untersucht. Daher wurde ein Verständnis der molekularen Dynamik aus verschiedenen Perspektiven gewonnen. Die Untersuchungen zeigten einen γ-Prozess und α-Prozesse (multiple glasartige Dynamik) für alle in dieser Arbeit untersuchten CLCs. Die von BDS untersuchten γ Prozesse sind den PE-ähnlichen lokalisierten Fluktuationen der interkolumnaren Bereich füllenden Alkylketten zugeordnet. Die multiple glasartige Dynamik (α1-, α2-, α3- und α4-Prozesse) werden für alle CLCs beobachteten α1 Prozesse dem PE zugeschrieben, wie kooperative Schwankungen in den Alkylketten. Darüber hinaus werden andere durch BDS nachgewiesene Glasdynamiken (α2-, α3- und α4-Prozesse) mehrdeutig auf die kooperativen Fluktuationen der Kerne zugeordnet. Verschiedene Möglichkeiten der molekularen Zuordnung dieser glasartigen Dynamik werden vorgeschlagen und in der Arbeit weiter diskutiert. Zusätzlich zu den Relaxationsprozessen wurde durch die BDS ein Leitfähigkeitsbeitrag für alle CLCs beobachtet. Um den Leitfähigkeitsbeitrag zu quantifizieren und den Leitfähigkeitsmechanismus aufzuzeigen, wurde der Leitfähigkeitsbeitrag detailliert analysiert und diskutiert. Im zweiten Teil der Arbeit wurde ein DLC auf Triphenylenbasis untersucht, das in zylindrischen Nanoporen von anodischen Aluminiumoxid- und Silica-Membranen mit Porengrößen von 161 nm bis 12 nm eingeschlossen wurde. n-Octcylphosphonsäure- (OPA) und n-Octadecylphosphonsäure (ODPA)-Modifikationen wurden verwendet, um die hydrophilen Innenwände der Poren mit Alkylketten zu hydrophobieren. Die Studie betrachtet sowohl unveränderte als auch modifizierte Porenwände. Das Phasenverhalten unter der Nanoconfinement wurde mit Hilfe von DSC untersucht. Die DSC-Untersuchungen erhellten die Porengrößenabhängigkeiten der Phasenübergangstemperaturen und Enthalpien. Die kollektive Orientierungsordnung (dominierende molekulare Ordnung) unter Confinement wurde mit Hilfe von BDS untersucht. Die molekulare Ordnung unter dem Nanoconfinement ist abhängig von der Porengröße und der Oberflächenchemie. Die Ergebnisse zeigten, dass die dominierende planare axiale Konfiguration, die nur für elektronische Anwendungen geeignet ist, erfolgreich durch OPA- und ODPA-Modifikationen für die meisten der untersuchten Porengrößen erreicht wurde.

Novel liquid crystalline Janus dendrimers that combine a mesogenic block and an electroactive block have been synthesised. The mesogenic block is based on two third-generation Percec-type dendrons bearing six or eight terminal dodecyloxy alkyl chains, whereas the electroactive blocks are formed by one or two carbazole units. The liquid crystal behaviour was investigated by polarised-light optical microscopy, differential scanning microscopy and X-ray diffraction. The Janus dendrimers with one electroactive unit exhibited cubic or columnar liquid crystal phases, whereas the Janus dendrimers with two electroactive units did not show liquid crystalline behaviour. The UV-vis absorption and emission properties of the Janus dendrimers were investigated. The spectra suggested the existence of π-π stacking and the formation of aggregates in the solid state. Electrodeposition of the carbazole-containing dendrimers afforded semi-globular particles in which the number of electropolymerizable units and the flexible or rigid character of the linker have a decisive influence in the particle size., This work was supported by the MINECO-FEDER funds (project CTQ2015-70174), Gobierno de Aragón-FSE (Research Group E47_17R).

Novel columnar liquid crystals whose molecular structures consist of a C star-shaped 1,3,5-triazine unit as a central core, and three pendant 2-phenyl-5-(di-, and/or tri-n-alkoxyphenyl)-1,3,4-thiadiazole arms, containing ether connecting groups, variable number and positions of linear alkoxy chains were synthesised and their mesomorphic properties were studied by differential scanning calorimetry, polarised optical microscopy and X-ray diffraction. The mesomorphic properties were found to be dependent on the length, position and number of the peripheral alkoxy chains. Most compounds form enantiotropic hexagonal columnar phases. These compounds also show photoluminescent properties in the visible region with good quantum yields. Photophysical studies were realised in solution and in solid state. Also, solvatofluorochromism and cyclic voltammetry studies were performed., This research was supported by FONDECYT (1100140), 'Vicerrectoría de Investigación' of the University of concepción, the Spanish project CTQ2012-35692 and FEDER funds.

El concepto de Cable Molecular ha sido muy explorado tanto sintéticamente como teóricamente en los últimos lustros. Los polímeros de coordinación (centros metálicos conectados por ligandos puente apropiados) son potencialmente aptos para desempeñar esta función. Si bien se han sintetizado sistemas con alta movilidad de carga, en general su procesamiento resulta aún dificultoso. Una posible vía para remontar este inconveniente es el procesamiento desde una fase cristal liquido, orientable en escala macroscópica. En el presente trabajo de Tesis Doctoral se sintetizaron polímeros de coordinación en base a Carboxilatos Bimetálicos de Rodio y Rutenio, interconectados por ligandos diversos, tales como Ligandos Nitrogenados Bidentados (Tetrazina, Fenazina y Bipiridina), Carboxilatos o Haluros. La elección de tales centros bimetálicos se basa en su conocida habilidad para generar fases Cristal Líquido y en la estructura electrónica que los compuestos de Rutenio presentan. Luego de caracterizarlos, se estudiaron sus propiedades Cristal Líquido, y se procesaron como fibras orientadas los complejos más promisorios. Finalmente, se midió la conductividad eléctrica de estas fibras. The concept of Molecular Wire has been widely explored both sintetically and theoretically in the past lustra. Coordination polymers (metallic centres connected by suitable bridging ligands) are potentially able to fulfill this role. Although systems with high charge mobility have been synthesized, their processing still remains difficult. A possible way to overcome this inconvenience is processing from a liquid crystalline phase, macroscopically oriented. In the present Doctoral Thesis work, coordination polymers based on Rhodium and Ruthenium carboxylates and Bidentate Nitrogenated Ligands (such as Tetrazine, Phenazine and Bipyridine) have been synthesized. The choice of these metallic centers lays in their known ability to generate Liquid Crystal phases and the electronic structure presented by Ruthenium compounds. After their characterization, their Liquid Crystal properties were studied, and the most promising complexes were processed as oriented fibers. Finally, the electrical conductivity of these fibers was measured. Fil: Rossi, Leonardo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Los cristales líquidos columnares (CLC) resultan atractivos por la posibilidad de aprovechar su organización supramolecular para transportar carga o energía en dispositivos moleculares. La organización en fases CLC puede explicarse en forma simplificada a partir de la competencia entre interacciones ordenadoras entre los cores moleculares y la tendencia al desorden de las cadenas alifáticas periféricas. Sin embargo, esta descripción resulta insuficiente para explicar ciertos aspectos estructurales como, por ejemplo, el rol que juega la naturaleza de los conectores, o aún de las mismas cadenas, en la determinación de tales estructuras. Para avanzar en la comprensión de dicha influencia, trabajamos en dos direcciones. Por un lado, comenzamos a explorar sistemas basados en interacciones de puente halógeno (XB). Hasta el momento no se han reportado mesógenos discóticos basados en esta interacción, por lo que realizamos diversos ensayos de cocristalización, empleando grupos centrales prodiscóticos que fueran potenciales donores múltiples de XB, y aceptores monodentados que pudieran eventualmente incorporar cadenas alifáticas. Estudiamos los sólidos obtenidos y, en los casos en que obtuvimos cristales, resolvimos y analizamos sus estructuras. A partir de la necesidad de usar tanto donores como aceptores fuertes, y de la dificultad encontrada para lograr la policoordinación, planteamos posibles nuevos enfoques con los que avanzar a futuro. Por otro lado, nos enfocamos en sistemas columnares basados en carboxilatos bimetálicos que forman polímeros de coordinación. En este caso, analizamos cómo afecta a las propiedades CL la incorporación de grupos funcionales o bloques moleculares que puedan proveer interacciones adicionales entre las unidades binucleares. Así, sintetizamos, caracterizamos y estudiamos las propiedades CL de complejos de Ru y/o Rh de: alcoxibenzoatos con dodecilsulfato como ligando axial; benzoatos con cadenas oxietilénicas en lugar de alquílicas; alcanoiloxibenzoatos; derivados de ácidos biliares; alcoxihalobenzoatos. Los resultados hallados fueron diversos: algunos de los compuestos presentaron fases ColH termotrópicas, transiciones a fases cúbicas y/o liotropismo, mientras que en otros casos no presentaron ningún tipo de comportamiento mesomórfico. Analizamos en todos los casos la influencia de los grupos funcionales incorporados sobre estas propiedades CL y, cuando la información estructural obtenida lo permitió, propusimos modelos de organización supramolecular. Columnar liquid crystals (CLC) are interesting because its supramolecular organization can be used to transport charge or energy on molecular devices. The organization in CLC phases can be explained by competition between ordering interactions involving molecular cores and the disorder tendency provided by the conformational liberty of the peripheral aliphatic chains. However, this description level isn’t enough to explain a set of structural aspects such as the role that the nature of connectors between core and chains, or even of chains itself, plays in those structures. To have a better understanding of such influence, we’ve worked on two directions. On one hand, we started to explore halogen bonding (XB) based systems. So far, discotic mesogens based on XB interactions hasn’t been reported, so we’ve made several cocristalization essays, with prodiscotic central groups that could act eventually as multiple XB donors, and monodentate acceptors that could eventually incorporate aliphatic chains. We studied the obtained solids and, when crystals were achieved, we solved and analyzed their structures. Considering that both strong XB donors and acceptors are needed, and the difficulty found to achieve policoordination, we propose new approaches for future studies. On the other hand, we focused on columnar systems based on bimetallic carboxylates that form coordination polymers. In this case, we analyzed how LC properties are affected by the inclusion of functional groups or molecular blocks that may provide aditional interactions to binuclear units. Thus, we synthesized, characterized and studied LC properties of Ru and/or Rh complexes of: alcoxybenzoates with dodecylsulfate as axial ligand; benzoates with oxyethylene chains instead of alkyl chains; alcanoyloxybenzoates; bile acids derivatives; alcoxyhalobenzoates. Results were dissimilar: some compounds showed thermotropic ColH phases, transitions to cubic phases and/or lyotropic behaviour, while some others showed no mesomorphic behaviour at all. In all cases, we analyzed the influence of the incorporated functional groups over this LC properties, and we proposed supramolecular organization models when the obtained structural information allowed it. Fil: Raffo, Pablo Alejandro. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

International audience; The electrical responses of a columnar liquid crystal (a diimidodiester derivative of benzo[ghi]perylene) depositedeither by spin-coating or by thermal evaporation into a typical OLED device are compared. For the spin-coated film, homeotropic alignment was induced by thermal annealing, which enhanced the charge carrier mobility significantly. For the evaporated films, homeotropic alignment could not be obtained by annealing. However, a degree of rectification higher than 3 orders of magnitude was achieved, even without annealing, with an electrical response similar to the response of the aligned spin-coated film. A trap-limited space−charge-limited current model was used to extract the charge carrier mobility directly from the current−voltage curves. Grazing incidence wide-angle X-ray scattering confirmed the homeotropic alignment of the annealed spin-coated film, whereas the columns are mostly oriented parallel to the surface in the evaporated case. In a field-effect transistor with bottom-gate bottom-contact geometry, the evaporated film exhibited a typical behavior of an n-type transistor. The degree of intermolecular order is thereby strongly dependent on the deposition method where vacuum deposition leads to a higher order. This higher order, however, impedes reorientation by annealing of the evaporated film but leads to improved charge transport between the electrodes even without homeotropic alignment of columnar liquid crystal.

3 pages; International audience; This Letter reports the determination of the singlet exciton diffusion length (LD) for a thermotropic discotic columnar liquid crystal (CLC) in both non-oriented and homeotropically oriented (columns perpendicular to the substrate) samples. Experimental results based on photoluminescence measurements indicate that LD is only slightly dependent on the liquid crystal orientation. Conversely, studies of ITO/ CLC (50 nm)/Al Schottky-type devices formed by non-oriented and oriented liquid crystalline films show an increase in the photocurrent by a factor of 16, due to the homeotropic alignment. This improvement is attributed to both increased light absorption and charge-carrier mobility.

The incoherent quasi-elastic neutron scattering from the heptyl and octyl derivatives of the acta-alkylphthalocyanines, CnPcH2, in their crystalline and liquid crystalline (discotic columnar) phases has been measured. Diffusive motion is observed on the 10-10 to 10-12 s timescale. This is interpreted as alkyl chain motion. A detailed comparison of the mesophase data for C7PcH2 has been made with the predictions of the rotational isomeric state model, and an 2 extra motion on this timescale has been invoked, which probably is a localized translational motion. A small discontinuity in the elastic fraction of the quasi-elastic scattering is consistent with a change in the molecular tilt at the transition between the two Dhd phases.

9 pages; International audience; Discotic molecules comprising a rigid aromatic core and flexible side chains have been promisingly applied in OLEDs as self-organizing organic semiconductors. Due to their potentially high charge carrier mobility along the columns, device performance can be readily improved by proper alignment of columns throughout the bulk. In the present work, the charge mobility was increased by 5 orders of magnitude due to homeotropic columnar ordering induced by the boundary interfaces during thermal annealing in the mesophase. State-of-the-art diodes were fabricated using spin-coated films whose homeotropic alignment with formation of hexagonal germs was observed by polarizing optical microscopy. The photophysical properties showed drastic changes at the mesophase-isotropic transition, which is supported by the gain of order observed by X-ray diffraction. The electrical properties were investigated by modeling the current−voltage characteristics by a space-charge-limited current transport with a field dependent mobility.

11 pages; International audience; Two key parameters for the performance of an organic photovoltaic cell are the exciton diffusion length and the charge carrier mobility. Considering these paramaters, columnar liquid crystals, with strong pi-orbital overlap between neighbouring cores, are promising materials. We describe our strategy towards the synthesis of both donor- and acceptor-type materials exhibiting a hexagonal columnar mesophase at the operating temperature range of the cell, including room temperature. We present the alignment behaviour of these materials when submitted to a thermal annealing, and, in particular, an approach to obtain thin open films with homeotropic orientation.

2 pages; International audience; In this work, we report the achievement of a homeotropically (or face-on) oriented bilayer formed by a pair of discotic materials designed with specific properties: selective solubility, adjusted transition temperatures, and room temperature hexagonal columnar liquid-crystalline phase. The homeotropic orientation of the bilayer which is only a few hundred nanometers thick is performed by solution-processed deposition followed by thermal annealing in the geometry of open supported films and is evidenced by X-ray scattering. This represents the first proof of principle of an organic heterojunction based on two oriented columnar liquid crystal layers.

7 pages; International audience; The structure and the orientation of thermotropic hexagonal columnar liquid crystals are studied by grazing incidence X-ray diffraction (GIXD) for different discotic compounds in the geometry of open supported thin films. Whatever the film deposition mode (either spin-coating or vacuum evaporation) and the film thickness, a degenerate planar alignment with the liquid crystalline columns parallel to the substrate is found. However, if a specific thermal process is applied to the liquid crystal film, homeotropic anchoring (columns normal to the interface) can be stabilized in a metastable state.

During this thesis, I worked out and validated a novel synthetic route to a new series of oligoperi-naphthylenic chromophores. Our approach is based on the assembling of two easily accessible building blocks - one central, the other terminal - via a coupling reaction followed by a multiple cyclodehydrogenation in a strongly basic medium. Smoothly further functionalised by esterification at each end, these dyes display a liquidcrystalline behaviour. We succeeded in elaborating columnar liquid crystals that strongly absorb the long wavelengths of the visible light while displaying their mesophase at room temperature., Au cours de cette thèse, j'ai mis au point et validé une voie de synthèse inédite donnant accès à une nouvelle famille de chromophores oligo-péri-naphtyléniques. Notre approche repose sur le couplage de deux briques facilement synthétisables (l'une centrale, l'autre terminale), puis sur une réaction de cyclodéshydrogénation multiple en milieu fortement basique. Aisément fonctionnalisés ensuite par estérification à leurs extrémités, ces colorants présentent un comportement cristallin liquide. Nous avons ainsi réussi à élaborer des cristaux liquides colonnaires absorbant fortement les grandes longueurs d'onde de la lumière visible tout en présentant leur mésophase à température ambiante.