Ionic Liquid Crystals Based on Pyridinium Salts

This chapter describes the liquid crystalline properties of the ionic liquid crystals (ILC) based on pyridinium salts as well as their metal-containing compounds with an emphasis on the recent systems described in literature. The main factors that influence the liquid crystalline properties of pyridinium ILC are discussed. Selected thermal data are given according to mesogenic group employed and its position (either N-substitution or pyridinium ring substitution) and the number of structural cationic units (mono-, di-, or polycationic pyridinium ILC)

Liquid crystal properties resulting from synergetic effects between non-mesogenic organic molecules and a one nanometre sized octahedral transition metal cluster.

International audienceThis work presents the synthesis and studies of a red-NIR luminescent liquid crystal compound based on an octahedral metallic cluster core orthogonally bounded to six non-mesogenic organic ligands. It evidences synergetic effects between the organic and inorganic parts of the hybrid, resulting in the generation of liquid crystal properties on cooling from the isotropic melt

Enhancement of smectic C mesophase stability by using branched alkyl chains in the auxiliary ligands of luminescent Pt(II) and Pd(II) complexes.

International audienceA novel series of Pd(II) and Pt(II) complexes based on cyclometallated imine ligands and N-benzoylthiourea (BTU) derivatives as auxiliary ligands has been prepared and their liquid crystalline properties as well as photophysical properties have been investigated. The crystal structure of one cyclometallated Pt(II) complex with N-(p-F-phenyl)-N'-benzoylthiourea as a co-ligand has been solved. The liquid crystalline properties have been investigated by a combination of DSC, POM and variable temperature powder X-ray diffraction. These new metallomesogens display either a monotropic SmC phase or both SmA and SmC phases, depending on the number of alkoxy groups attached to the imine ligand, alkyl chain length or the use of branched alkoxy terminal groups. We found that the introduction of branched alkoxy terminal groups lead to lower transition temperatures and stabilization of the SmC phase in both the Pd(II) and Pt(II) complexes. While the Pd(II) complexes display no emission, the Pt(II) complexes show good emission properties in solution, in the solid state and as a PMMA film at room temperature, and their investigation is reported

Editorial: Special Issue “Liquid Crystals 2020”

This Special Issue, entitled “Liquid Crystals 2020”, is a collection of ten original research papers, including two feature papers, on theoretical and experimental advanced studies of liquid crystal science and technology [...

Differential negative resistance in the current-voltage characteristics of a new palladium(II) metallomesogen

International audienceA new palladium(II) organometallic complex with liquid crystal properties was prepared and its electrical conduction was investigated in all specific mesophases. It was established that the electrical conduction is of ionic type. The negative differential electrical resistivity was evidenced. The effect is explained by the particular characteristics of the interactions between the charge carriers and the liquid crystal in electric field. A new method for determining the activation energy is proposed, based on the analysis of the ionic current dependency on voltage. The obtained results are of interest for the design of liquid crystal devices

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

Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from <i>N</i>-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones

The synthesis and characterization of novel ionic liquid crystals based on pyridinium salts with Br− and PF6− counterions are described in this work. These pyridinium salts were derived from 4-hydroxypyridine, both by N- and O-alkylation. The 3,4,5-tri(alkyloxy)-benzyl mesogenic unit was attached to the nitrogen atom of the pyridinium ring. Alkyl chains with a different number of carbon atoms (6, 8, 10, 12 and 14) were employed in order to show the effect on the stability of mesophase. The POM (polarizing optical microscopy) and XRD (powder X-ray diffraction) studies indicated that bromide salts with shorter chains C6, C8 and C10 do not show mesomorphic properties, while longer chain analogues with C12 and C14 exhibit two enantiotropic columnar phases. Surprisingly, the pyridinium salts with the larger size PF6− counterion do not exhibit liquid crystal properties

Ionically Self-Assembled Clustomesogen with Switchable Magnetic/Luminescence Properties Containing [Re6Se8(CN)6]n- (n = 3, 4) Anionic Clusters

International audienceOctahedral anionic rhenium clusters are obtained by high-temperature solid-state chemistry synthesis as single crystals or powders within which their charge is counter balanced by alkali cations. The ceramic-like behavior of the solid-state Re6 based inorganic compound limits strongly their use in functional devices. We present herein a facile route to introduce these anionic clusters in a self-organized hybrid organic-inorganic material. By replacing alkali countercations by mesogenic organic ones, polarized optical microscopy (POM), DSC, X-ray, magnetic, fluorescence, and cyclic voltammetry techniques confirm that a lyotropic and thermotropic liquid crystal material, able to switch reversibly from a bright red NIR luminescent form to a magnetic green-colored one, is obtained