R. C. Wilson

Some Three-Ring Esters Containing aFive-Membered Heteroaromatic Ring. A Comparison of Liquid Crystal Properties

Abstract Ninety compounds, over seventy of which are members of a number of homologous series of three-ring esters containing a 5-membered heteroaromatic ring, have been synthesized in order to establishhow a change in the position of the heterocyclic ring influences liquid crystal behavior when comparedwith corresponding all-benzenoid esters. The liquid crystal properties of these esters, which showconsiderable variation, are discussed. One group of compounds shows unusual phase behavior, involvingan unidentified (smectic?) phase and photomicrographs of optical textures of this phase are included.

Properties of the liquid crystals formed by certain 4′-n-alkylbiphenyl-4-yl 5-n-alkylthiophene-2-carboxylates

Abstract Thirty compounds, ten members of each of three homologous series of esters derived from 4-hydroxy-4′-n-octyl-, -nonyl-, and -decyl-biphenyl and the 5-n-alkylthiophene-2-carboxylic acids (methyl through to decyl homologues) have been prepared. The liquid crystal properties of these esters, which show extensive smectic polymorphism, have been investigated by thermal optical microscopy, differential scanning calorimetry, and miscibility studies. Four members of the corresponding 4-n-alkylbenzoates have also been prepared in order to compare their liquid crystal behaviour with the 5-n-alkylthiophene-2-carboxylate counterparts: both smectic and nematic thermal stability are higher for the 4-n-alkylbenzoates, by 30.6° and 36.8° C, respectively.

Novel bi- and ter-thiophenes exhibiting ferri- and antiferro-electric behaviour

Abstract Preliminary results of the synthesis and liquid crystalline properties of suitably substituted bi-and ter-thiophene-based chiral esters, derived from the appropriate thiophene-based carboxylic acid and either (S)-4-(1-methylheptyloxycarbonyl)phenol or (S)-1-methylheptyl-4′-hydroxybiphenyl-4-carboxylate are reported. The bithiophene ester comprising one phenyl ring exhibits monotropic smectic A, smectic C* ferro-, ferri- and antiferro-electric phase types. Increasing the number of rings, either thienyl or phenyl, increases both the melting point and thermal stability. The four ring compounds exhibit enantiotropic smectic A, smectic C* ferro-, ferri- and antiferro-electric phases together with underlying unknown phase type (SX). The identity of the SX phase is tentatively assigned as SI* following free-standing film characterisation and miscibility study.

Properties of the Liquid Crystals Formed by Certain 4′-n-Alkoxyphenyl Biphenyl -4- Carboxylates

Abstract Twelve 4′-n-alkoxyphenyl biphenyl-4-carboxylates have been prepared and their liquid crystal transition temperatures determined. Members of the homologous series were studied by differential thermal analysis and the enthalpies of fusion of the various transitions were measured. In contrast with the isomeric homologous series, the 4-biphenylyl 4′-n-alkoxybenzoates (previously reported), the 4′-n-alkoxyphenyl biphenyl-4-carboxylates do not have smectic mesophases and, in general, have lower liquid crystal transition temperatures and enthalpies of fusion. An explanation for this behaviour is offered.

The synthesis and characterisation of a novel thiophene-based liquid crystal exhibiting ferro-, ferri- and antiferro-electric phase types

The synthesis and liquid crystal properties of (R)–(–)-4-(l-methylheptyloxycarbonyl)phenyl 5-(4-decyloxyphenyl)thiophene-2-carboxylate is reported. This material exhibits the following phase types (°C): I 97.4 SA 92.2 SC* 81.4 ferri 78.8 antiferroelectric 48.6 glass state (characterised by thermal optical microscopy and differential scanning calorimetry). Results from electro-optical investigations, for example, field-induced transitions, temperature and voltage dependence and current and electro-optic response, clearly illustrate the presence of the SC* ferro-, ferri- and antiferro-electric phase types.

The synthesis and comparison of the liquid crystalline properties of certain 1-(4'-n-alkoxypolyfluorobiphenyl-4-yl)-2-(trans-4-n- pentylcyclohexyl)-ethenes and -ethanes carrying four, six or eight fluoro-substituents

The synthesis and mesomorphic properties of a variety of polyfluorinated alkylaryl-ethanes and-ethenes are reported. The number and position of the symmetrically disposed fluorosubstituents has been varied from six to four and the mesomorphic properties of the compounds are compared with those of the analogous octafluoro-substituted compounds previously reported. All the compounds are moderately low melting, mesomorphic and the type of mesophase formed is dependent upon the number and position of the fluoro- substituents. Increasing the number of fluoro-substituents from four, to six and to eight in a series of polyfluoro-alkylarylethanes decreases the mesophase thermal stability in a stepwise manner and eliminates smectic properties whilst retaining the nematic phase.

Properties of the Liquid Crystals Formed by Certain 4-(2′-Pyridyl)phenyl and 4-(4′-Pyridyl)phenyl 4″ -n-Alkoxybenzoates

Abstract Nine members of each of two homologous series of esters, the 4-(2′-pyridyl)phenyl and the 4-(4′-pyridyl)phenyl 4″-n-alkoxybenzoates, have been prepared and their liquid crystal transition temperatures measured. Both homologous series were investigated by differential thermal analysis and the enthalpy changes at the various transitions were measured. Differences in behaviour between the two series are discussed. By comparison of the transition temperatures of certain members of each series with those of corresponding 4-biphenylyl 4″-n-alkoxybenzoates, the order of the effect of the terminal phenyl, and 2- and 4-pyridyl rings in promoting the thermal stability of smectic A and nematic phases has been assessed. The nematic order differs from that reported previously for certain Schiffs bases.

The synthesis and liquid crystal properties of certain 1-(4′-n-alkoxy-2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl-4-yl)- 2-(trans-4-n-pentylcyclohexyl)-ethanes and -ethenes

Abstract The synthesis and liquid crystal properties of eight members of the homologous series of 1-(4′-n-alkoxy-2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)-ethanes and eight members of the corresponding -ethanes, which have the E-configuration, are reported. These compounds are nematic, the ethenes having a considerably mesophase higher thermal stability than the analogous ethanes.

X-ray diffraction studies of the liquid crystal phases of certain 4-n-alkoxyphenyl 4-(5-n-alkyl-2-thienyl)benzoates

Abstract The n-butyl, n-octyl, n-decyl and n-dodecyl homologues of each of the 4-n-pentyloxyphenyl, 4-n-hexyloxyphenyl and 4-n-heptyloxyphenyl 4-(5-n-alkyl-2-thienyl)benzoates have been prepared. All the homologues give rise to liquid crystal phases and their transition temperatures are reported. Phase identification was not straightforward, especially when distinguishing between some of the higher order smectic phases, and required a combination of thermal optical microscopy and X-ray diffraction studies, including powder photographs and detailed measurements of smectic layer spacings.

A study of homologation and the occurrence of an SA-SC-SA sequence of phases in the 4-n-alkoxy-3-fluorophenyl 4-(5-n-alkyl-2-thienyl)benzoates

Abstract Seventeen esters, derived from 4-n-alkoxy-3-fluorophenols and 4-(5-n-alkyl-2-thienyl)benzoic acids, have been prepared and their liquid crystal transition temperatures determined by thermal optical microscopy. On cooling the isotropic liquid, the SA-SC-SA sequence of phases reported for the octyloxy-octyl and octyloxy-nonyl esters has been observed for certain other homologues, principally members of the 4-(5-n-nonyl-2-thienyl)benzoates. For these compounds, the temperature range of occurrence of the intermediate SC phase decreases as the length of the alkoxy chain increases (for the hexyloxy-nonyl to dodecyloxy-nonyl esters) and the Sc phase is absent for the tetradecyloxy-nonyl homologue.