Chiral Liquid Crystalline Compounds Research Articles

ChemInform Abstract: Axial Chiral Liquid Crystals - Synthesis of Trisubstituted Allenyl Ethers.

The synthesis of racemic and enantiomerical enriched axial chiral liquid crystalline compounds incorporating a trisubstituted allene unit is described. All compounds 16–28 display the smectic C-phase and mostly also a nematic mesophase. All investigated enantiomerically enriched compounds have a ferroelectrically switchable chiral smectic SC*-phase.

Mesomorphic properties of 5boSOMH from new three rings thiobenzoate series

Phase polymorphism of a novel chiral liquid crystalline compound (S)-(+)-4-{4-(4-n-pentylbicyclo[2,2,2]octancarbonylthio)benzoyloxy}benzoate 1-methylheptyl (in short: 5boSOMH) was examined with three complementary methods: Differential Scanning Calorimetry (DSC), Polarized Light Optical Microscopy (POM) and Transmitted Light Intensity (TLI). X-Ray diffraction was used to learn about molecular arrangement in ordered phases. 5boSOMH has two enantiotropic phases: SmB* and SmA*, and exhibits solid phase polymorphism.

Characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of new chiral ( S)-5-octyloxy-2-[{4-(2-methylbuthoxy)-phenylimino(methyl]phenol liquid crystalline compound

Synthesis, characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of a new chiral liquid crystalline compound are presented in this work. This new compound has prolate molecules and exhibits the chiral smectic C* mesophase in a sufficiently large temperature interval. Two types of solid crystalline phases have been found in this compound. Typical textures and temperatures of the direct and reverse phase transitions, taking place in the compound, are given. Typical peculiarities for the first-order transition between the smectic C* mesophase and isotropic liquid have been observed.

Molecular Structure and Physical Properties of Chiral Liquid Crystalline Compounds

Influence of molecular structure on physical properties of chiral compounds is presented. It is shown that fluorinating of the achiral chain have great influence on physical properties of liquid crystalline phases. As an example, two compounds: (S)-(+)-4-(1-Metyloheptyloxy-carbonylbiphenyl) 4′-(6-perfluoropentanoyloxyhex-1-oxy) benzoate and (S)-(+)-4-(1-Metyloheptyloxycarbonylbiphenyl) 4′-(6-pentanoyloxyhex-1-oxy) benzoate have been selected. Phase transition temperatures and stability of these compounds have been studied by DSC calorimetry, texture observation, electrooptic measurements and dielectric spectroscopy. Based on these studies it was found that the SmC*–SmA* transition is a continuous one for both compounds studied.

Electro-optical and ferroelectric switching of Langmuir–Blodgett films made of a chiral smectic-C ⁎ liquid crystalline compound

Electric and electro-optical properties of a smectic liquid crystal (LC) compound formed by rod-like molecules have been investigated in the thin film sandwich geometry typically used in solid-state technology. Thin (~ 10–30 nm) Langmuir–Blodgett (LB) films of the compound (tetradecyl homologue ( n = 14) of the series p-oxybenzylidene- p′-amino-2-methylbutyl(α-cyano)cinnamate) were transferred onto glasses covered with a transparent electrode and supplied with a top electrode evaporated in vacuum. In contrast to the LC bulk, thin films of the compound manifest only a solid crystalline phase throughout the whole temperature range (20–110 °C) investigated. Ferroelectric properties of the films (covering linear electro-optic effect, pyroeffect and polarization switching) have been observed in the whole temperature range studied.

Partial resolution of racemic trans‐4‐[5‐(4‐alkoxyphenyl)‐2,5‐dimethylpyrrolidine‐1‐oxyl‐2‐yl]benzoic acids by the diastereomer method with (R)‐ or (S)‐1‐phenylethylamine

The partial resolution is described of a series of racemic trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxyl-2-yl]benzoic acids (1), which are the key intermediates for the synthesis of chiral organic radical liquid crystalline compounds and are crystallized to give racemic compounds. Racemic acid 1 [(+/-)-1] with a long alkyl chain (C7 to C13) could be resolved by the conventional diastereomeric salt formation using (R)- or (S)-1-phenylethylamine (2) as the resolving agent, whereas resolution of (+/-)-1 with a short alkyl chain (C4 to C6) was unsuccessful. Use of six equiv of (R)- or (S)-2 for the initial diastereomeric salt formation of (+/-)-1 with a C7-C13 alkyl chain, followed by recrystallization of the resulting salts once or twice, gave 2S,5S- or 2R,5R-enriched 1, respectively, in an ee range of 75-92% and with an overall recovery of 11-27%, based on the original quantity of (+/-)-1.

Phase transitions of new antiferroelectric thiobenzoate†

This article reports on the phase sequences in a new chiral liquid crystalline compound, a member of the thioester series, (S)-(+)-4-[(4-{[1-methyl]heptylcarboxyl}phenyl)-carbonylthio]phenyl-4′-decyloxy-1-benzencarboxylate, referred to as 10.OPOSMH, which has been recently synthesized. 10.OPOSMH exhibits ferro- and antiferroelectric behaviour. This compound contains three benzene rings connected with the ester and thioester central groups. The 10.OPOSMH molecule is terminated with the achiral n-decyloxy and chiral (S)-(+)-1-methylheptyl carboxylate terminal chains, where the chiral group is in para position with respect to the thioester group. This mesogen assumes the existence of antiferroelectric smectic C () and ferroelectric smectic C () phases and also the smectic chiral subphases: , and , both on heating and cooling. †This article is dedicated to Prof. Dr Jerzy A. Janik on his 80th birthday.

Ferroelectric Properties of Chiral Thiobenzoates from New Homologous Series

Chiral liquid crystalline compounds (S)-MHOBS5 and (S)-MHOBS6 from a new homologous series of the (S)-(+)-4-(1-methylheptyloxy)biphenyl 4-alkylthiobenzoates, abbreviated (S)-MHOBSn (where n denotes the number of carbon atoms in the alkyl chain) in which the chiral branched chain is attached to the biphenyl have been studied by DSC calorymetry, dielectric spectroscopy and electro-optic methods. (S)-MHOBS5 and (S)-MHOBS6 possesses a rich phase polymorphism, including enantiotropic ferroelectric smectic C phase (SmC*).

Complementary studies of de Vries type SmA ∗ phase

Two chiral liquid crystalline compounds have been investigated, namely 4-(1-methylheptyloxycarbonyl) phenyl-4′nonylbiphenyl-4-carboxylate (MHPNBC), 3-(2-fluor-octyloxy)-6-(4octyl-phenyl) pyridine (FOOPP) to study the SmA ∗–SmC ∗ transition. For both substances strong electroclinic effect is observed in the SmA ∗ phase what indicates that it is the so-called de Vries SmA ∗ phase. To study the paralectric-ferroelectric de Vries type transition electrooptic, dielectric as well as SAXS methods have been applied.

An investigation of the synthesis of chiral LCs based on the [1,2,3]‐triazole ring

The design and synthesis of chiral liquid crystalline compounds based on the [1,2,3]‐triazole heterocycle using the click chemistry modular approach is presented. The target compounds showed LC phases of type SmA, SmC* and helical N* (cholesteric). Mesomorphic behaviour was determined by polarizing optical microscopy and differential scanning calorimetry. Contact experiments indicated a right‐handed helix for the macrostructure of the cholesteric phase.

Structure of freely suspended chiral smectic films as determined by x-ray reflectivity and optical ellipsometry.

We report on a combined x-ray reflectivity and optical ellipsometry study of freely suspended smectic (Sm) films of a chiral liquid crystalline compound with the phase sequence Sm-A-Sm-C(*)(alpha)-Sm-C*-Sm-C(*)(gamma)-Sm-C(*)(A). Using tilt magnitude profiles from x-ray reflectivity as input to model the average optical properties obtained by ellipsometry, tilt direction profiles are also obtained. In this way realistic models can be elaborated for the various types of chiral Sm-C films. We find that the surface layers are more tilted than the interior layers due to surface interactions and finite size effects. For the ferrielectric Sm-C(*)(gamma) phase the tilt direction profile corresponds to a three-layer helix, in agreement with the clock model of chiral Sm-C phases. In thin films the surface interactions suppress the bulk helix structure of the Sm-C(*)(alpha) phase and a Sm-C(*)(A)-like structure is formed with an anticlinic layer-by-layer alternation of the tilt directions.

Synthesis and Liquid Crystalline Properties of (S)-[4-n-Alkyloxy-benzoyloxyphenyl]-4′-[(2-n-alkyloxy)propionyloxy]benzoate

New series of chiral liquid crystalline compounds, (S)-[4-n-alkyloxy-benzoyloxyphenyl]-4′-[(2-n-alkyloxy)propionyloxy]benzoate (QMn/m), were synthesised. Polymorphism of the new compounds was investigated by polarising microscopy and differential scanning calorimetry. All members of the homologous series showed enantiotropic SmC* and N* mesophases except one compound having the longest alkyl chain in both terminal groups. The spontaneous polarisation of these ferroelectric liquid crystalline compounds is about 110–130 nC/cm2. The temperature dependence of the dielectric permittivity was measured for all the compounds studied. Several ferroelectric binary mixtures were prepared in order to get a wide enantiotropic chiral SmC* phase at ambient temperature.

Dielectric investigations of the dynamics of the hexatic-hexatic transition in a chiral liquid crystal

We report a detailed investigation of the dynamics of the hexatic--smectic-${I}^{*}$ to hexatic--smectic-${F}^{*}$ phase transition in a chiral liquid-crystalline compound. The results show a dramatic softening of the relaxation frequency and an associated divergence of the susceptibility on approaching the transition. The temperature dependence of both these parameters can be described by a power law with an exponent equal to 1, in agreement with the theoretical predictions.

Axial Chiral Liquid Crystals-Synthesis of Trisubstituted Allenyl Ethers

The synthesis of racemic and enantiomerical enriched axial chiral liquid crystalline compounds incorporating a trisubstituted allene unit is described. All compounds 16–28 display the smectic C-phase and mostly also a nematic mesophase. All investigated enantiomerically enriched compounds have a ferroelectrically switchable chiral smectic SC*-phase.

Synthesis and Mesomorphic Properties of Chiral Biphenylol Benzoates

AbstractTen new chiral liquid crystalline compounds I1–10 of 4′ -acyl-4-biphenylol (S) -4- (2-methyl-l-butoxy) benzoates were synthesized and their mesomorphic properties were tested. They are all smectic liquid crystals with wide temperature ranges and except for compounds I1, all exhibit a Sc*phase. The influence of molecular structure on phase behavior is discussed.

Chiral liquid crystalline compounds from D-(+)-Glucose

d-(+)-Glucose was used as a starting material to prepare four potentially useful chiral liquid crystalline molecules 2, 3, 4 and 5 having multiple chiral centers in their rigid cores. It is clear that 2 indeed incorporates properties essential for ferroelectric liquid crystals, i.e., a chiral smectic C phase with an induced spontaneous polarization of about 23 nC/cm 2. Compound 3, on the other hand, shows only a nematic phase, while 4 merely shows a sharp melting point and 5 is an oil.

Odd-even effects in the thermotropic and optical properties of chiral triplet liquid crystals

Abstract A series of chiral triplet liquid crystalline compounds with a central biphenyl group to which two dihydrocholesteryl groups are attached via two flexible alkanoate spacers has been prepared and investigated. As a function of spacer length, these compounds show strong odd-even effects for the phase transition temperatures, the corresponding entropy changes and the selective reflection wavelengths associated with the chiral nematic phases. Asymmetrical compounds with one odd and one even number of methylene groups in their spacers have properties intermediate between those of symmetrical compounds with two odd or two even spacers.

ChemInform Abstract: Enantioselective Synthesis of Chiral Liquid Crystalline Compounds from Monoterpenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantioselective synthesis of chiral liquid crystalline compounds from monoterpenes

Chiral liquid crystalline compounds 1–9 have been synthesized enantioselectively from monoterpenes. The optical purities of ( S)-(−)- and ( R)-(+)-perillalcohol ( 16, 27), ( S)-(−)- and ( R)-(+)-1-pentyl-4-hydroxymethyl-1-cyclohexene ( 33, 34) and (2 S,5 S)-2-pentyl-5-hydroxymethyl-1-cyclohexanone ( 53) have been determined by 1H NMR analysis using chiral shift reagents. The mesomorphic phases and transition temperatures of compounds 2,3,5,6,7,8 and 9 have been characterized.

A new family of chiral smectic liquid crystals Synthesis and properties of liquid crystals bearing a pyridine heterocycle

Abstract A new family of chiral smectic liquid-crystalline compounds having a core structure of (Y [dbnd] C[tbnd]C or CH2CH2) have been synthesized and their thermal stabilities have been examined systematically in terms of influences of the linkage between the benzene ring and the pyridine ring, and the chain length of the terminal alkyl group.