Synthesis and mesomorphic properties of 4-n-alkoxy 4'-[4-((4-n-alkoxy-2,3,5,6-tetrafluoro-phenyl)ethynyl)benzyloxy]benzoates

Two series of tolane-based liquid crystals have been prepared that incorporate a tetrafluorophenyl moiety and a flexible methyl ether bond into the core structure. The mesomorphic properties have been studied by polarizing microscopic textural observation and DSC measurements. By comparison with their non-fluorinated analogues, the effect of tetrafluorophenylene on mesomorphic behaviour has been discussed in this paper.     

Synthesis and mesomorphic properties of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoates

A series of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoate liquid crystals have been synthesized. Their phase transition temperatures have been measured by optical polarizing microscopy and confirmed by DSC. The results show that a highly fluorinated terminal chain impairs mesomorphic properties.     

Synthesis and mesomorphic properties of fluorinated phenyl 4-[(4-n-alkoxy-2,3-difluorophenyl)ethynyl]benzoates

Three series of fluorinated phenyl 4-[(4-n-alkoxy-2,3-difluorophenyl)ethynyl]benzoate liquid crystals have been synthesized. Their phase transition temperatures were measured by texture observation in a polarizing microscope and confirmed by DSC. Their mesomorphic properties and fluoro-substituent effects were studied in detail.     

Synthesis and mesomorphic properties of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoates

A series of 4-[(4-n-polyfluoroalkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]phenyl fluoro-substituted benzoate liquid crystals have been synthesized. Their phase transition temperatures have been measured by optical polarizing microscopy and confirmed by DSC. The results show that a highly fluorinated terminal chain impairs mesomorphic properties.     

Synthesis and mesomorphic properties of 4-alkyl-3,4'-disubstituted biphenyls and terphenyls

Liquid-crystalline 4-alkyl-3-chloro(methyl)-4'-substituted biphenyls and terphenyls have been synthesized. Investigation of the mesomorphic properties of these compounds shows that unlike their unsubstituted analogues they form a liquid-crystalline phase at a lower temperature and over a narrower temperature range.     

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.     

Synthesis and mesomorphic properties of fluorinated phenyl 4‐[(4‐n‐alkoxy‐2,3‐difluorophenyl)ethynyl]benzoates

Three series of fluorinated phenyl 4‐[(4‐n‐alkoxy‐2,3‐difluorophenyl)ethynyl]benzoate liquid crystals have been synthesized. Their phase transition temperatures were measured by texture observation in a polarizing microscope and confirmed by DSC. Their mesomorphic properties and fluoro‐substituent effects were studied in detail.     

Properties of thermotropic liquid crystals induced by hydrogen bonding between pyridyl-1,2,4-oxadiazole derivatives and benzoic acid, 4-chlorobenzoic acid or 4-methylbenzoic acid

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 3-(4-pyridyl)-5-(4-n-alkoxy)phenyl-1,2,4-oxadiazoles with benzoic acid, 4-chlorobenzoic acid or 4-methylbenzoic acid. Neither the oxadiazole derivatives nor the carboxylic acids are mesomorphic, but the H-bonded complexes are. Their liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction.     

Solid-phase combinatorial syntheses of mesomorphic 4-alkoxyphenyl 4-alkoxybenzoylaminobenzoates

Eighteen two-ring and 100 three-ring benzenoid amides were synthesised using a solid-phase combinatorial method involving acylation or benzoylation and palladium(0)-catalysed carbonylation of a secondary amine, obtained by the reductive amination of 4-iodoaniline and a backbone amide linker. The purity of the products obtained was high enough for investigation of their thermal properties. All the three-ring derivatives were shown to be mesomorphic, but the two-ring derivatives were not. The mesomorphic behaviour and the transition temperatures of the three-ring derivatives were virtually identical to those of samples obtained by liquid-phase synthesis and purified by column chromatography and recrystallisation.     

Mesomorphic properties of 4-(polyfluoroalkoxycarbonyl)phenyl 4-(4-n-heptoxy-2,3,5,6-tetrafluorophenyl)benzoates

A series of 4-(polyfluoroalkoxycarbonyl)phenyl 4-(4-n-heptoxy-2,3,5,6-tetrafluorophenyl)benzoates were synthesized and observed using DSC and optical polarizing microscopy. The results show that they are not mesogens. Their mesomorphic properties were compared with similar compounds containing no aromatic fluorine substituents.     

Supramolecular liquid crystals induced by intermolecular hydrogen bonding between benzoic acid and 4-(alkoxyphenylazo) pyridines

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid. None of the pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. Their liquid crystalline properties were investigated by DSC, polarizing optical microscopy, FTIR spectroscopy and powder X-ray diffraction. The complexes exhibit enantiotropic smectic C phases.     

Supramolecular liquid crystals induced by intermolecular hydrogen bonding between benzoic acid and 4-(alkoxyphenylazo) pyridines

Supramolecular liquid crystalline complexes have been obtained from binary mixtures of 4-(alkoxyphenylazo) pyridines and 4-octyloxylbenzoic acid. None of the pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. Their liquid crystalline properties were investigated by DSC, polarizing optical microscopy, FTIR spectroscopy and powder X-ray diffraction. The complexes exhibit enantiotropic smectic C phases.     

Synthesis and mesomorphic properties of resorcyl di[4-(4-alkoxy-2,3-difluorophenyl)ethynyl]benzoate: a novel achiral antiferroelectric banana-shaped mesogen

Two resorcyl di[4-(4-alkoxy-2,3-difluorophenyl)ethynyl]benzoate liquid crystals were prepared and their mesomorphic properties observed and measured. Achiral antiferroelectric phases were seen with increasing length of the hydrocarbon terminal chains.     

Mesomorphic properties of 4-(polyfluoroalkoxycarbonyl)phenyl 4-(4-n-heptoxy-2,3,5,6-tetrafluorophenyl)benzoates

A series of 4-(polyfluoroalkoxycarbonyl)phenyl 4-(4-n-heptoxy-2,3,5,6-tetrafluorophenyl)benzoates were synthesized and observed using DSC and optical polarizing microscopy. The results show that they are not mesogens. Their mesomorphic properties were compared with similar compounds containing no aromatic fluorine substituents.     

Synthesis and mesomorphic properties of resorcyl di[4-(4-alkoxy-2,3-difluorophenyl)ethynyl]benzoate: a novel achiral antiferroelectric banana-shaped mesogen

Two resorcyl di[4-(4-alkoxy-2,3-difluorophenyl)ethynyl]benzoate liquid crystals were prepared and their mesomorphic properties observed and measured. Achiral antiferroelectric phases were seen with increasing length of the hydrocarbon terminal chains.     

Synthesis and mesomorphic properties of some homologues of fluorinated 4-chlorobenzoate-tolanes

Three homologues series of 4-chloro-substituted benzoate-tolanes were prepared. Thermal optical microscopy and DSC analysis show that these compounds are liquid crystalline. The effect on the mesomorphic properties of different positions of the perfluorophenyl in the molecular core unit is discussed.     

Synthesis and mesomorphic properties of some esters of trans-4-n-alkoxycinnamic and trans-4-n-alkoxy-alpha-methylcinnamic acids exhibiting ferroelectric and antiferroelectric phases

The synthesis and mesomorphic properties of several homologues of (S)-(+)-1-methylheptyl 4-[4(trans-4-n-alkoxycinnamoyloxy)benzoyloxy]benzoates (series I) and (S)-(+)-1-methylheptyl 4-[4-(trans-4-n-alkoxy-alpha-methylcinnamoyloxy)benzoyloxy]benzoates (series II) are described. The influence of the alpha -methyl group on the different mesophases and the clearing temperatures has been evaluated. Many homologues of both the series show a ferroelectric chiral smectic C (SmC*) phase while the antiferroelectric smectic C phase (SmC*A) is exhibited by compounds of series I. The mesophases have been identified by optical polarizing microscopy, differential scanning calorimetry and miscibility studies. The spontaneous polarization, the helical pitch and the tilt angle of two of the compounds have also been measured.     

Synthesis and mesomorphic properties of some fluorinated phenyl 4-[(4-n-alkoxyphenyl)ethynyl]benzoates

Eight homologous series of fluorinated phenyl 4-[(4-n-alkoxyphenyl)ethynyl]benzoates have been synthesized. Textural observations by polarizing microscopy and DSC measurements of the phase transitions show that most of these compounds are thermotropic liquid crystals with nematic and smectic A phases; furthermore, several show monotropic high order smectic phases. The results showed that the SmA phase is enhanced with increasing degree of fluorosubstitution on the para- and meta-positions of the terminal phenyl groups. The mesomorphic properties of these compounds are also affected by the direction of ester bonds. The effect of triple bonds is also discussed.     

Synthesis and mesomorphic properties of perfluorinated rod-like liquid crystals with sulphur-containing spacers

In order to determine the influence of 'sulphur-containing' spacers on the formation of mesophases in low molecular mass compounds, we have examined the mesomorphic behaviour of molecules which consists of a 4-biphenyl unit linked to an unbranched fluorinated chain via a short spacer including at least a sulphur atom. The synthesis of these compounds has been carried out from 2-F-butylethyl iodide or from the 2-F-alkylethyl mercaptans in the case of the F-hexyl and F-octyl tails. The mesomorphic properties have been characterized by polarized light microscopy and by differential thermal analysis showing the peculiar contribution of each of the spacers. The influence of the fluorinated chain and the shape of the connector on the stability of the mesophases has been investigated. The compounds with a thioether or a hemithioacetal spacer showed no mesomorphic properties, whereas the structures with a thioester spacer showed a very interesting enantiotropic behaviour of the smectic A type over a wide temperature range. Furthermore from the series exhibiting liquid crystalline behaviour, increasing the number of fluoromethylene units simultaneously increases both the melting and the clearing temperature. These mesomorphic properties within the fluorinated series are compared with those of their monocatenar hydrocarbon homologues.     

Synthesis and mesomorphic properties of perfluorinated rod-like liquid crystals with sulphur-containing spacers

In order to determine the influence of 'sulphur-containing' spacers on the formation of mesophases in low molecular mass compounds, we have examined the mesomorphic behaviour of molecules which consists of a 4-biphenyl unit linked to an unbranched fluorinated chain via a short spacer including at least a sulphur atom. The synthesis of these compounds has been carried out from 2-F-butylethyl iodide or from the 2-F-alkylethyl mercaptans in the case of the F-hexyl and F-octyl tails. The mesomorphic properties have been characterized by polarized light microscopy and by differential thermal analysis showing the peculiar contribution of each of the spacers. The influence of the fluorinated chain and the shape of the connector on the stability of the mesophases has been investigated. The compounds with a thioether or a hemithioacetal spacer showed no mesomorphic properties, whereas the structures with a thioester spacer showed a very interesting enantiotropic behaviour of the smectic A type over a wide temperature range. Furthermore from the series exhibiting liquid crystalline behaviour, increasing the number of fluoromethylene units simultaneously increases both the melting and the clearing temperature. These mesomorphic properties within the fluorinated series are compared with those of their monocatenar hydrocarbon homologues.