New cholesteric liquid crystals induced by intermolecular hydrogen bonding

Cholesteric star-shaped liquid crystals induced by a maltose core: synthesis and characteristics

Tailoring the glassy mesophase range of thermotropic polyesters through copolymerization of 4,4’-bibenzoate and kinked isomer

Relative permittivity of a few H-bonded liquid crystals

Synthesis and study of liquid crystalline properties of schiff’s bases having 1,3,4-thiadiazole moiety

The photoresponsive behaviors of a smectic liquid crystal, 8CB, tuned by an azobenzene chromophore have been systematically investigated. For the smectic 8CB doped with the azobenzene chromophore, 4-n-hexyl-4′-(1-bromopropyloxy)azobenzene (AB), the smectic phase could be switched to nematic and then to isotropic phase induced by the trans-to-cisphotoisomerization of AB upon UV irradiation. For the smectic 8CB doped with AB and the chiral molecule, (S)-(−)-1, 1′-binaphthyl-2, 2′-diol (BD), the smectic phase could be switched to the cholesteric phase and then to the isotropic phase. The initial phase could be recovered when the cis isomer changed to the trans isomer upon visible irradiation. The switching of the position of reflection band of the liquid crystal mixtures could be also realized by photoisomerization. The photoresponsive behaviors are dependent on the composition ratios and the temperature performed in the study.

Photophysical, photochemical and liquid-crystalline properties of novel gallium(III) phthalocyanines

New thermotropic liquid crystalline (LC) hyperbranched (HB) polyesters containing 2,5‐diphenyl‐1,3,4‐thiadiazole (DTD) unit as mesogen in the interiors were prepared at various mole ratios (A2/B3) by melt and solution polycondensations of a dioxydiundecanol of DTD (A2) and 1,2,3‐propanetricarboxylic acid (B3) via the A2 + B3 approach and their LC and optical properties were investigated. FTIR and 1H‐NMR spectroscopies indicated that all the expected HB polyesters, which show good solubilities in organic solvents, are produced without gelation during the polymerization. Among them, the HB polymer prepared in the mole ratio of A2/B3 = 3/2 by the solution polycondensation had the highest inherent viscositiy. DSC measurents, polarizing microscope observations of optical textures, and X‐ray analyses suggested that the LC properties of HB polymers depend on the polymerization methods and the feed mole ratios. In the HB polymers prepared using the melt polycondensation, only the polymer prepared in the mole ratio of A2/B3 = 3/1 formed a highly‐ordered, tilted, crystal‐like smectic phase, but all the polymers prepared by the solution polycondensation formed highly‐ordered, tilted, smectic phases. Solution and solid‐state UV‐vis and photoluminescent (PL) spectra indicated that the HB polymers show maximum absorbances and blue‐light emission on the basis of the DTD unit, where the Stokes‐shifts were observed, probably because of intermolecular aggregation effects © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2998–3008, 2007

A homologous series of new thioalkylated double-decker cerium phthalocyanine complexes, [(CnH2n+1S)8Pc]2Ce, were synthesised and their mesomorphisms were clarified by DSC, polarized optical microscopy and X-ray diffraction. Unlike other lanthanide phthalocyanines, these double-decker cerium compounds were found by spectroscopy and X-ray crystallography to be neutral complexes. A hexagonal columnar mesophase (Colh) was exhibited by all homologues prior to melting to the isotropic liquid. Interestingly, the columnar mesophases of these compounds showed strong tendencies for spontaneous homeotropic alignment on non-treated glass substrates or ITO coated glass. The hole mobility in the Colh mesophase of the longer chain homologue was successfully measured by a TOF technique as having a value of 7 × 10−3 cm2 V−1 s−1.

Characterization of hexagonal lyotropic liquid crystal microstructure: Effects of vitamin E molecules

Synthesis and properties of PEDOT derivatives containing liquid crystalline groups

The phase behavior and optical properties of a liquid crystal (LC) composite (induced smectic phase formed by mixing two nematic LCs and one cholesteric LC) have been studied. The nematic liquid crystal 4-cyano-4′-pentyloxy biphenyl 5OCB with a strong polar terminal group was miscible with the nematic liquid crystal 4-hexyloxyphenyl-4′-pentyl benzoate HPPB having a weak polar terminal group. This binary mixture formed an induced smectic phase over a wide temperature range. The (induced smectic/cholesteric) ternary composite exhibited smectic A, cholesteric and blue phases. A novel phase was observed at the cholesteric-smectic phase transition region. The ternary system exhibited highly transparent and opaque states in the smectic and cholesteric phases, respectively, without the electric field.

Molecular organization: Chiral benzene tricarboxamides with methyl substituents at defined positions self-assemble into supramolecular polymers of preferred helicity by three-fold alpha-helical-type hydrogen bonding. The odd-even effect is operative and all derivatives are liquid crystalline showing a Col(ho) phase (see figure).Asymmetric benzene-1,3,5-tricarboxamides (aBTAs) comprising two n-octyl and one chiral methyl-alkyl side chain were synthesised and characterised. The influence of the position and the configuration of the chiral methyl group (methyl at the alpha, beta or gamma position) in the aliphatic side chains on the liquid-crystalline properties and the aggregation behaviour of the aBTAs was systematically studied and compared to symmetrical benzene-1,3,5-tricarboxamides (sBTAs). Solid-state characterisation (polarised optical microscopy, IR spectroscopy, X-ray diffraction and differential scanning calorimetry) revealed that all aBTAs show threefold, alpha-helical-type intermolecular hydrogen bonding between neighbouring molecules and exhibit a columnar hexagonal organisation from room temperature to well above 200 degrees C. Moving the chiral methyl group closer to the amide group stabilises the liquid-crystalline state, as evidenced by a higher clearing temperature and corresponding enthalpy. The self-assembly of dilute solutions of the aBTAs in methylcyclohexane ( approximately 10(-5) mol L(-1)) was investigated with circular dichroism (CD) spectroscopy. The sign of the Cotton effect demonstrated a pronounced odd-even effect, whereas the value of the molar ellipticity, Deltaepsilon, in the aBTAs was independent of the position of the methyl group. Subsequent temperature-dependent CD measurements showed that the aggregation of all aBTAs can quantitatively be described by the nucleation-growth model and that the stability of the aggregates increases when the chiral methyl group is closer to the amide moiety. The results presented herein illustrate that even small changes in the molecular structure of substituted benzene-1,3,5-tri-carboxamides affect their solid-state properties and their self-assembly behaviour in dilute solutions.

Thermotropic semi-rigid copoly(imide-carbonate)s composed of 3,4,3",4"-p-terphenyltetracarboxdi-imide and 3,4,3',4'-biphenyltetracarboxdi-imide rings

Liquid crystalline and dielectric properties of homologous series of substituted 1,3,4-oxadiazoles

This paper provides an overview of the static behavior of systems with partial orientational and positional ordering of the species. The understanding of the static behavior provides the foundation needed to understand the dynamic properties of such systems, which are described in more detail in other papers in this issue. More specifically, this paper provides an overview of the fact that species of different dimensions exhibit similar types of partial ordering of the species. This paper further provides an overview of liquid crystalline (LC) phases and molecules, including discussions of types of chemical structures (both rigid and semiflexible) in LC molecules (both nonpolymeric and polymeric); thermotropic and lyotropic LCs; nematic and multiple smectic LC phases; reentrant nematic LC phases; cholesteric LC phases and blue phases; smectic crystal phases; columnar phases; micelles and lamellar LC structures; LC phase transitions; LC glasses; viscosities of LC phases; and dynamic textures and patterns in LC phases.