David Lacey

The synthesis and transition temperatures of some 4,4″-dialkyl- and 4,4″-alkoxyalkyl-1,1′ :4′,1″-terphenyls with 2,3- or 2′,3′-difluoro substituents and of their biphenyl analogues

The tetrakis(triphenylphosphine) palladium (0)-catalysed coupling of arylboronic acids with aryl halides is used to prepare several 4,4″-dialkyl- and 4,4″-alkoxyalkyl-1,1′:4′,1″-terphenyls with 2,3- or 2′,3′-difluoro substituents and their related biphenyl systems. Lithiation ortho to a 1,2-difluoroaromatic unit provides the route to the 2,3-difluoroarylboronic acids.The 2,3-difluoro substituted terphenyls are low-melting liquid crystals with wide-range Sc phases and no underlying smectic phase; these compounds are excellent hosts for ferroelectric systems. The compounds with widest Sc ranges are those with the difluoro substituents in an end ring and the compounds with difluoro substituents in the central ring show more nematic character and so are useful for ECB devices.

Molecular dynamics of liquid crystalline side-chain polymers: The dielectric relaxation behaviour of a siloxan polymer in the nematic and isotropic phases

Abstract The dielectric relaxation behaviour of a liquid crystalline side-chain polymer having a siloxan backbone to which is attached an aromatic ester group via a C 5 methylene spacer has been studied in the nematic and isotropic phases. One process was observed in the isotropic phase and was characteristic of that of a glass-forming liquid. A composite process was observed in the liquid crystalline phase. In the transition range the dielectric behaviour changed continuously from that of the liquid crystal to the isotropic material. The characteristic features of the relaxations are described and their mechanisms are discussed in relation to earlier dielectric data for small molecule nematogens and for liquid crystalline side-chain polymers based on acrylate and methacrylate monomers.

Synthesis and Evaluation of Some 4,4″-Disubstituted Lateral Fluoro-1,1′:4′,1″-terphenyls

Abstract A number of laterally fluorinated 4,4″-di-n-alkyl-, 4,4″-di-n-alkoxy- and 4-n-alkyl-4″-n-alkoxy-l,r:4′,1″-terphenyls of structure (I) have been synthesised, with the lateral fluoro-substituent in the central benzene ring. The nematic and smectic thermal stabilities for all three series of compounds, have been examined. A typical example is (I), X = n–C5 HU, Y = n–C3 H7, C–N 50°C and N–I 140.6°C. For the 4,4″-di-n-alkyl-1,1′:4′,1″-terphenyls, the position of the lateral fluoro-substituent with respect to the longest n-alkyl chain is found to be important in determining the smectic behaviour of this class of compound. By using a combination of optical microscopy, X-ray diffraction and miscibility studies, the complex smectic behaviour of the higher homologues of this series has also been investigated. A comparison of the liquid crystal behaviour of the laterally fluorinated ter-phenyls of structure (I) with their non-fluorinated analogues is also given. A selected number of these compounds, have be...

Effects of Molecular Structure on the Properties of Terminally Cyano-Substituted Side Chain Liquid Crystalline Polysiloxanes

Abstract The synthesis and properties of a range of liquid crystalline side chain polysiloxanes are described. The effects of changes in chemical structure, such as lateral substitution, on the properties of these materials are discussed, and comparisons are made with the effects of similar structural changes in low molar mass materials. By selecting suitable side chains for homopolymers and copolymers, room temperature smectic, nematic and cholesteric (chiral nematic) polysiloxanes of positive dielectric anisotropy have been prepared, including the first example of a nematic siloxane homopolymer containing a cyano-group.

The Synthesis and Transition Temperatures of Some Fluoro-Substituted 4-Cyanophenyl and 4-Cyanobiphenyl-4′-yl 4-Pentyl- and 4-Butoxy-Benzoates

Abstract A series of 4-cyanophenyl 4-X-benzoates and a series of 4-cyanobiphenyl-4′-yl 4-X-benzoates (X =pentyl, butoxy) have been prepared without fluoro-substitution and with mono-fluoro to tetra-fluoro-substitution; all possible combinations of substitution patterns at the positions ortho- to the cyano group and ortho- to the carboxylate group have been obtained in an attempt to determine the structural features which are responsible for some members of these series showing very large positive values of dielectric anisotropy. The synthesis of novel precursors required for the preparation of these esters is described and the melting points and transition temperatures of the esters are discussed and an explanation is provided for the variation of TN -1 values with position and extent of fluoro-substitution.

The Synthesis of Optically Active Cyanohydrin Esters and Their Use as High Ps Dopants for Ferroelectric Displays

Abstract This paper describes the reasoning underlying the design and synthesis of a range of cyanohydrin esters, specifically as high Ps dopants of host SC materials, for use in fast switching ferroelectric displays. Full synthetic details are given for the preparation of optically pure cyanohydrin esters from naturally occurring L-amino-acids; examples derived from (a) a D-amino-acid, (b) lactic acid are also given. Such materials provide excellent dopants which in suitable SC hosts provide mixtures with wide S*C ranges, good Ps values and long pitches, which switch rapidly at room temperature and may be multiplexed at video frame rates.

Synthesis and Properties of Some Liquid Crystal Polysiloxanes with Laterally or Terminally Attached Side Chains

Abstract A series of polysiloxanes having laterally-attached mesogenic side chains and involving variations in spacer length and the nature of the two end groups are reported. The terminally-attached analogues of some of these polymers are also reported. Optical microscopy and differential scanning calorimetry were used to establish the mesomorphic properties. An explanation is proposed for the low TN-1 values observed for the polymers with laterally attached side chains.

The Synthesis and Liquid Crystal Properties of Some 2,5-Disubstituted Pyridines

Abstract The synthesis is reported of fifteen three-ring 2,5-disubstituted pyridines and two pyridine-N-oxides where the pyridine rings carry a variety of alkyl, aryl, cyclohexyl, cyclohexylethyl and fluorinated-aryl substituents. The mesomorphic transition temperatures for these compounds have been measured; all the compounds show enantiotropic phases. The different substituent effects are discussed and comparisons are made with previous work on analogous systems where the hetero-function is replaced by C-F.

Laser addressed thermo-optic effect in a novel dyed liquid-crystalline polysiloxane

Abstract Initial experimental evaluation of a novel liquid-crystalline polysiloxane for thermo-optical recording is presented. A versatile system using a single laser source has been used to gather information on the dynamics of laser addressing. To ensure the most stable, highest-contrast pixel the polymer must be heated through its biphasic region and some way into the isotropic phase. It was found that at 60°C using laser pulses of 300μs or less, write-in and selective erasure times were on the submillisecond timescale, and that bulk erasure required 1–2 min. The use of the polymer in an analogue optical store has been demonstrated and an unoptimized sensitivity of 12nJ/μm2 for 632°8 nm light was found at 24°C.

Reentrant Nematic and Injected Smectic Behaviour in Binary Mixtures Including Those of Terminally Non-Polar Compounds

Abstract Some new examples of injected smectic behaviour for binary mixtures of strong terminally polar mesogens (CBs, PCHs, BCOs, and CCHs) with a range of terminally non-polar esters are presented. Variations in the strength of the injected behaviour are discussed. Examples of S B as well as SA injection occur. Studies of mixtures of terminally non-polar 4,4″-dialkyl-2″-fluoro-p-terphenyls (I) with cyano-substituted mesogens are also described and provide an example of injection of S A and S E phases. Of greater interest is the observation that binary mixtures consisting solely of hom-ologues of (I) can exhibit reentrant nematic behaviour, providing further evidence that reentrant phenomena are not a special feature of terminally polar mesogens and their mixtures. An isomeric mixture of two compounds of structure (I) also gives an interesting case of an injected S c phase, and enhanced S c properties are recorded for other mixtures of homologues of (I). Mixtures involving alkyl/alkoxy analogues of (I) a...