Calamitic Liquid Crystals Research Articles

Structure and Dynamics of Liquid‐Crystalline Polymers with Different Molecular Architectures from Multidimensional NMR Plenary Lecture

AbstractA survey is given on the structure and dynamics of liquid‐crystalline polymers with different molecular architectures as revealed by multidimensional NMR. Specific examples discussed include semiflexible systems, rigid‐rod systems, calamitic, and discotic liquid crystals. Structural aspects include the determination of high rank order parameters, the micro‐order in frozen liquid crystals and the packing of flexible side chains. Dynamic processes discussed are local dynamics in the glassy state, conformational dynamics and collective phenomena such as the development of convective director structures and dynamic density modulations along columnar structures. It is demonstrated that advanced NMR spectroscopy yields highly specific information not available from conventional scattering, microscopic and relaxation techniques.

Enaminoketones as calamitic liquid crystals with a novel hydrogen-bonded rigid core

Abstract A series of compounds having an aminopropenone-3 group between two aromatic rings has been synthesized and thermally stable enantiotropic mesogens with properties typical of three ring liquid crystals were obtained. The mesomorphic properties of the molecules result from the presence of a rigid calamitic core stabilized by a hydrogen-bonded cis-s-cis quasi-ring form of the enaminoketone group.

Nematic–lamellar tricritical behavior and structure of the lamellar phase in the ammonium pentadecafluorooctanoate (APFO)/water system

2H NMR spectroscopy has been used to map a high-resolution (±0.04 K) phase diagram for the ammonium pentadecafluorooctanoate(APFO)/heavy water system. It is qualitatively similar to that for the CsPFO/heavy water system. In particular, it exhibits a discotic micellar nematic phase N+D intermediate to an isotropic micellar solution phase I and a lamellar phase for weight fractions of APFO between 0.395 (φ=0.278) and 0.589 (φ=0.455) and temperatures between 292.10 and 338.10 K. The N+D to lamellar transition crosses over from second to first order behavior at a tricritical point similar to the superfluid transition in 3He/4He mixtures. X-ray scattering experiments shows there to be no dramatic change in the structure of the micelle at the I to N+D and the N+D to lamellar transitions. Nematic order parameters (orientational order parameters of the discoidal micelles) have been calculated from electrical conductivity measurements. Their variation with temperature in the nematic phase and across the nematic to lamellar transition are qualitatively consistent with the behavior expected for thermotropic calamitic liquid crystals undergoing an isotropic to nematic to smectic-A sequence of transitions. It is, therefore, concluded that the transition from the N+D to the lamellar phase solely involves the propagation of long range positional ordering of the discoidal micelles into planes along the nematic director, that is, the lamellar phase is a discotic lamellar phase LD. This result reinforces previous claims about the structure of the lamellar phase of the CsPFO system as opposed to the alternative scenario of a classical lamellar phase in which the bilayers are perforated by microscopic defects. This conclusion is supported by measurements of 2H quadrupole splittings of heavy water. Similar measurements for deuterated ammonium ions show a preference for counterion binding to sites of lowest surface curvature. The fraction of counterions bound to the surface of the micelle is shown to increase as the temperature is lowered due to a growth in diameter and associated changes in surface curvature.

Amphiphilic carbohydrate-based mesogens incorporating structural features of calamitic liquid crystals

Abstract Several examples of liquid-crystalline carbohydrate derivatives incorporating a carbocyclic ring in the side chain are reported and the influence of structural variations discussed. The mesophase observed for all compounds described is smectic A and the mesophase stability is strongly affected by the linking unit between the carbocyclic and carbohydrate moieties.

ChemInform Abstract: Synthesis and Properties of Calamitic Liquid Crystals from Deoxygenated Carbohydrate Derivatives.

AbstractThe anomeric nitriles (III) and (IV) are prepared and different hydrogenation results are obtained using Pd‐C or Wilkinson catalysts.

Synthese und Eigenschaften kalamitischer Flüssigkristalle aus desoxygenierten Kohlenhydrat‐Derivaten

Synthesis and Properties of Calamitic Liquid Crystals from Deoxygenated Carbohydrate DerivativesTreatment of the L‐arabino‐ and Llyxo‐configurated glycals 1 and 7 with trimethylsily cyanide leads to the formation of the anomeric nitriles 2, 3 and 15, 17, respectively. The configurational assignments are based on hydrogenated products such as 6 or 8 and 10. Depending on the configurations of the olefinic nitril sugars, various hydrogenation results are observed using palladium/charcoal or the Wilkinson catalyst. Methanolysis provides the corresponding methyl esters. The preparation of liquid‐crystalline derivatives follows the classical route. In comparing the properties of these saccharide‐based liquid crystals with the corresponding cyclohexane derivatives, the dominant influence of the anomeric effect on the tendency for phase formation can be observed. Some of the novel derivatives show highly twisted cholesteric and wide blue phases.

Determination of the bend elastic constant and the anisotropy of diamagnetic susceptibility of lyotropic nematic calamitic liquid crystals

The bend elastic constant ${K}_{3}$ and the anisotropy of diamagnetic susceptibility ${\ensuremath{\chi}}_{a}$ of two lyotropic mixtures: potassium laurate, decanol, and water and sodium decylsulfate, decanol, and water in the nematic calamitic phase are determined. The experimental method by the action of magnetic fields in samples with and without ferrofluid. These distortions are observed in a polarizing microscope. The results of ${K}_{3}$ and ${\ensuremath{\chi}}_{a}$ are compared with the measurements of these parameters for a different lyotropic mixture.

ChemInform Abstract: Synthesis of Calamitic Liquid Crystals by Transition Metal Catalyzed Cross‐Coupling Reaction

ChemInform Abstract: Synthesis of Calamitic Liquid Crystals by Transition Metal Catalyzed Cross‐Coupling Reaction

Calamitische Flüssigkristalle: Beziehung zwischen Molekülstruktur und Mesogenität, trans-und cis-1,3,5,7-Tetraoxadecalin-Derivate [1,2] / Calamitic Liquid Crystals: Relationship Between Molecular Structure and Mesogenity, trans- and cis-1,3,5,7 -Tetraoxadecalin Derivatives [1, 2

1,3,5,7-Tetraoxadecalin has been introduced as a novel central unit into the chemistry of calamitic liquid crystals. 2e,6e-Disubstituted derivatives 3a−h and 4b, g, i of the trans or cis fused heterobicyclus, respectively, have been synthesized. Whereas most of these tram-products (3c−h) are nematic or smectic A (new “rod-like mesogens”), the cis-products (4b, g, i) are not liquid crystalline. The configurations and conformations of all compounds have been elucidated by spectroscopic methods in particular by 1H and 13C NMR. In addition the structures of 3d, 3g and 4i as representatives of both series have been confirmed by X-ray analysis. The 1,3,5,7- tetraoxadecalin unit in the non-mesomorphic ds-products exists, as expected, in the “O-inside" conformation which has been established both by 1H NMR and X-ray studies. The relationship between the chemical structure and mesomorphic behaviour of these 1,3,5,7-tetraoxadecalin derivatives is discussed, as well as the most likely structural requirements for turning the non- mesomorphic cis-products into mesomorphic ones. The name “roof-like mesogens" is proposed for this predicted new type of liquid crystals with three-dimensional geometry.