Direct transition from the SmA phase to the tilted hexatic phase in liquid crystals with several lactate units

Compounds with differing numbers of lactate units in the chiral part were synthesized. For all materials, at least two smectic phases were found. In addition to the SmA, the SmC* and/or the tilted hexatic SmI*(F*) phase appear according to the length of the non-chiral alkyl chain. For the shortest non-chiral chain, a direct transition from the SmA phase to the SmI*(F*) phase has been discovered and studied. For compounds with the 2-(S)-methylbutyl alkyl chain and two lactate units in the chiral part the antiferroelectric SmC*_A phase occurs. The ferroelectric character of the hexatic phase has been confirmed even just below the SmC*_A phase.     

Antiferroelectric and ferrielectric liquid crystalline low molar mass materials and polymers

Novel liquid crystalline Low Molecular Mass (LMM) materials bearing two chiral lactate groups, as well as compounds of like structure to MHPOBC have been synthesized. All the LMM compounds exhibit the SmC*A (antiferroelectric) and/or SmC*gamma (ferrielectric) phases. The mesogens have been incorporated as pendant groups on polymer backbones of three different natures to prepare side chain liquid crystalline copolysiloxanes, homopolysiloxanes and homopolyacrylates. The investigation of the polymers by means of miscibility studies showed that the antiferro- and ferri-electric phases are strongly destabilized in the coposiloxanes and homopolysiloxanes, while in the homopolyacrylates a large temperature range mesophase is found to be miscible with the SmC*A phase. The physical properties of the mesophases and their stability, both for the LMM materials and the polymers, are presented and discussed.     

Direct transition from the SmA phase to the tilted hexatic phase in liquid crystals with several lactate units

Compounds with differing numbers of lactate units in the chiral part were synthesized. For all materials, at least two smectic phases were found. In addition to the SmA, the SmC* and/or the tilted hexatic SmI*(F*) phase appear according to the length of the non-chiral alkyl chain. For the shortest non-chiral chain, a direct transition from the SmA phase to the SmI*(F*) phase has been discovered and studied. For compounds with the 2-(S)-methylbutyl alkyl chain and two lactate units in the chiral part the antiferroelectric SmC*_A phase occurs. The ferroelectric character of the hexatic phase has been confirmed even just below the SmC*_A phase.     

New series of chiral ferroelectric liquid crystals with the keto group attached to the molecule core

Two new series of ferroelectric liquid crystals with a keto group attached to the molecular core and a lactate unit as a chiral centre were synthesized and studied. All the compounds exhibit the paraelectric SmA phase and the ferroelectric SmC * phase over very wide temperature ranges and down to room temperature. The main characteristics of the chiral ferroelectric SmC * phase, namely spontaneous polarization, spontaneous tilt angle, and dielectric constant, have been measured to establish their relationship to the length of the terminal chains. The influence of the chiral and non-chiral chain lengths on the helix pitch length is also discussed.     

New series of chiral ferroelectric liquid crystals with the keto group attached to the molecule core

Two new series of ferroelectric liquid crystals with a keto group attached to the molecular core and a lactate unit as a chiral centre were synthesized and studied. All the compounds exhibit the paraelectric SmA phase and the ferroelectric SmC* phase over very wide temperature ranges and down to room temperature. The main characteristics of the chiral ferroelectric SmC* phase, namely spontaneous polarization, spontaneous tilt angle, and dielectric constant, have been measured to establish their relationship to the length of the terminal chains. The influence of the chiral and non-chiral chain lengths on the helix pitch length is also discussed.     

New series of ferroelectric liquid crystals with two or three chiral centres exhibiting antiferroelectric and hexatic phases

New series of liquid crystals with a chiral chain containing two asymmetric carbon atoms in two lactate groups have been synthesized. Some compounds have a third asymmetric centre in an (S)-2-methylbutyl alkyl chain. All the new compounds have SmA, SmC* and hexatic phases. Two of the homologues with three chiral centres also exhibit very wide SmC_A phases and one of them a re-entrant SmC* phase. The phases are characterized by DSC, dielectric, and X-ray studies. Spontaneous polarization and tilt angle are determined for the polar phases.     

Synthesis and characterization of a chiral antiferroelectric series with new SmC A*-L transition

Two new chiral series with a tolane core: (S) 4-(1-methylheptyloxycarbonyl)phenyl (series IB) and (S) 4-(1-ethylheptyloxycarbonyl)phenyl (series IC) 4-alkanoyloxytolane-4'-carboxylates have been synthesized and characterized. All the compounds are mesomorphic, and most of them display the antiferroelectric SmC*A phase. The mesomorphic properties have been analysed by optical microscopy, DSC, helical pitch and electro-optical measurements and X-ray diffraction study. Series IB exhibits a very rich polymesomorphism with SmC*alpha, SmC*, SmC* F12, SmC* F11 and SmC*A phases, like the previously reported series IA, [(S) 4-(1-methylheptyloxycarbonyl)phenyl 4-alkyloxytolane-4-carboxylates]. Series IC is more interesting because it presents for the first time in antiferroelectric series the liquid-like phase (L phase) between the SmC*A and isotropic phases. Preliminary optical studies plead in favour of a helical short range structure for this new liquid-like L phase.     

Synthesis and characterization of a chiral antiferroelectric series with new SmC A*-L transition

Two new chiral series with a tolane core: (S) 4-(1-methylheptyloxycarbonyl)phenyl (series IB) and (S) 4-(1-ethylheptyloxycarbonyl)phenyl (series IC) 4-alkanoyloxytolane-4'-carboxylates have been synthesized and characterized. All the compounds are mesomorphic, and most of them display the antiferroelectric SmC*A phase. The mesomorphic properties have been analysed by optical microscopy, DSC, helical pitch and electro-optical measurements and X-ray diffraction study. Series IB exhibits a very rich polymesomorphism with SmC*alpha, SmC*, SmC* F12, SmC* F11 and SmC*A phases, like the previously reported series IA, [(S) 4-(1-methylheptyloxycarbonyl)phenyl 4-alkyloxytolane-4-carboxylates]. Series IC is more interesting because it presents for the first time in antiferroelectric series the liquid-like phase (L phase) between the SmC*A and isotropic phases. Preliminary optical studies plead in favour of a helical short range structure for this new liquid-like L phase.     

Variety of mesophases in compounds with an increasing number of lactate units in the chiral chain

Liquid-crystalline compounds with different numbers of lactate units, n, in the chiral part were synthesised and mesomorphic properties studied. Physical properties were compared with respect to n. In the compound with one lactate unit in the chiral part the TGBA–TGBC–SmC* phase sequence was detected. For two lactate units the antiferroelectric SmC*_A phase occurs. Finally, three-lactate material exhibits the tilted hexatic SmI*(F*) phase below the ferroelectric SmC* phase. Dielectric spectroscopy and spontaneous tilt and polarisation were measured. For the three-lactate compound the temperature dependences were analysed in the vicinity of the SmC*–hexatic phase transition, and these properties compared with the theoretically predicted behaviour.     

New ferroelectric liquid crystalline materials containing one and two lactate groups attached to the molecular core

Several new liquid crystalline materials containing one, two or three chiral centres and having one or two lactate groups in the molecular core have been synthesized. Most of the materials show the blue phase, chiral nematic phase, paraelectric smectic A phase and orthogonal hexatic smectic B phase; some possess the ferroelectric SmC* phase. A study of the mesomorphic properties has been performed using differential scanning calorimetry, optical microscopy and X-ray diffraction. The thickness of the smectic layers and the value of the average distance between the long axes of neighbouring molecules were determined. In the SmC* phase, the temperature dependence of spontaneous polarization, spontaneous tilt angle and helical pitch was measured. The influence of the number of lactate groups on mesogenic behaviour has been established.     

New antiferroelectric liquid crystalline materials containing a keto group and two lactate groups

New chiral liquid crystalline materials containing a keto group and two lactate units attached to the mesogenic core have been synthesized and studied. All the new compounds show the paraelectric SmA, ferroelectric SmC* and antiferroelectric SmC*_A phases each over rather broad temperature ranges. The properties of the phases were characterized by DSC, electro-optical and dielectric studies. The spontaneous polarization, tilt angle, helical pitch, and switching times were determined for the polar phases.     

New antiferroelectric liquid crystalline materials containing a keto group and two lactate groups

New chiral liquid crystalline materials containing a keto group and two lactate units attached to the mesogenic core have been synthesized and studied. All the new compounds show the paraelectric SmA, ferroelectric SmC* and antiferroelectric SmC*_A phases each over rather broad temperature ranges. The properties of the phases were characterized by DSC, electro-optical and dielectric studies. The spontaneous polarization, tilt angle, helical pitch, and switching times were determined for the polar phases.     

Oxadiazole-based unsymmetrical chiral liquid crystal dimers: synthesis and mesomorphic properties

The synthesis and liquid crystalline properties of novel chiral Schiff's base dimers containing the 1,3,4-oxadiazole ring are reported. The length of the terminal S-alkyl chain has been varied. All the compounds synthesised were thermally stable and exhibited enantiotropic mesomorphism, showing either SmC*–SmA–TGB–N*–BP or SmC*–SmA phase sequence.     

The effect of the alkyl chain length on the mesomorphic properties of new lactic acid derivatives

New series of lactic acid derivatives with alkyl terminal chain have been synthesised and their mesomorphic properties studied. We have varied the length of chiral and non-chiral terminal alkyl chains and found that prolonging both chains has a strong effect on the SmA*–SmC* phase transition. Most of the new materials exhibit only paraelectric SmA* phase; for homologues with a longer non-chiral chain (m ≥ 10), the ferroelectric (SmC*) phase appears below the SmA* on cooling and persists down to a room temperature. The role of the chiral terminal chain in the molecule is quite opposite – only its short length supports the existence of ferroelectric phase. Additionally, a hexatic phase appeared below the SmA*–SmC* phase sequence for several homologues at low temperatures. All materials have been studied using standard experimental techniques (differential scanning calorimetry (DSC), texture observations, polarisation and tilt angle measurements, etc.). Liquid crystalline properties of new materials have been compared with the previously prepared and studied lactic acid derivatives.     

Effect of the variation of swallow-tailed groups on the mesomorphic and electro-optical properties of chiral compounds derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid

Three homologous series of chiral swallow-tailed compounds, alkyl (S)-2-{6-[4-(4′-alkoxyphenyl)benzoyloxy]-2-naphthyl}propionates, (S)HNP(p,n,q) derived from (S)-2-(6-hydroxy-2-naphthyl)propionic acid in conjugation with a variety of swallow-tailed groups, attached to the external side of the chiral centre, have been synthesized and their mesomorphic and electro-optical properties studied. Both (S)HNP(p,1,2) and (S)HNP(p,1,3) exhibited an enantiotropic antiferroelectric SmC*_A phase. This implys that the swallow-tailed groups in the molecules favour zigzag pairing of the molecules in the smectic phase. The maximum P _S values of compounds (S)HNP(p,1,2) in the antiferroelectric phase were measured in the range 21–30 nC cm^-2; those of compounds (S)HNP(p,1,3) were in the range 15–23 nC cm^-2, indicating that these chiral compounds possess low polarity. The electro-optical response of the compounds in the antiferroelectric SmC*_A phase displayed thresholdless V-shaped switching.     

Chiral two ring compounds exhibiting antiferroelectric phases

Novel chiral two ring compounds possessing phenylethenoate moieties were synthesized and their liquid crystalline properties determined. Some of these compounds were found to exhibit SmC* γ, AF and SmC* A phases, whereas in other compounds only SmA* and SmC* phases appear. The influence of the molecular structure on the appearance of SmC* γ, AF and SmC* γ phases is discussed. The basic electro-optical properties of the homologous series of ( S )-( E )4-(1-methylheptyloxycarbonyl)phenyl 4-alkoxycinnamates, in which SmC*, SmC* γ, AF and SmC* A phases appear, were also investigated. High values of spontaneous polarization, low threshold voltages and fast switching times at room temperature were observed.     

Ferroelectric liquid crystals with a thioester linking group positioned at the chiral tail

A homologous series of chiral thioesters, hexyl (2S)-2-[6-(4-alkanoyloxyphenyl)benzoyloxy-2'-naphthyl]thiopropionates, HnPBNTP (n=7-11) was synthesized, and the mesophases and electro-optical properties were studied. All the materials possess a ferroelectric SmC* phase, which was confirmed by the switching current behaviour. It was found that compounds with a shorter alkyl chain length (n=7-9) displayed SmA* and SmC* phases, while, compounds with a longer alkyl chain length (n=10 and 11), displayed the SmC* phase exclusively. Spontaneous polarization and apparent tilt angle were also measured. The maximum P_s values are in the range 15-26 nC cm^-2, and the maximum θ values are in the range 23°-28°.     

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 fluoro-substituted chiral liquid crystals derived from (S)-lactic acid with alkoxyethanols

A homologous series of fluoro-substituted chiral liquid crystals derived from (S)-lactic acid and alkoxyethanols were prepared for investigation. Mesophases and their corresponding transition temperatures were identified by polarized optical microscopy and differential scanning calorimetry. The compounds exhibit a broad temperature range in the ferroelectric chiral smectic C (SmC*) phase; in particular, compounds with shorter alkyl chain lengths have an SmC* phase at ambient temperature. The physical properties of the ferroelectric SmC* phase, such as switching current, spontaneous polarization, optical tilt angle and electro-optical response, were also measured. The effects of fluoro substituent on the mesophases and physical properties of the chiral liquid crystals are discussed.     

New smectogens with (S)-2-methylbutyl lactate group in the terminal chain and chlorine-substituted molecular core

We report the synthesis and mesomorphic properties of new chiral materials based on (S)-2-methylbutyl lactate group in the chiral chains and a lateral substitution by a chlorine atom in the molecular core. We have studied mesomorphic properties and found that homologues with only one lactate and methylbutyl in the chain exhibit the SmC* phase in a broad temperature range. We established the spontaneous polarisation and tilt angle values. The pitch values are rather small, being within the range 360–450 nm. On the other hand, a homologue with one additional lactate in the chiral part does not exhibit the mesomorphic properties. We have tried to establish the effect of lateral substitution by comparing all studied compounds with previously prepared (S)-2-methylbutyl lactate derivatives with non-substituted molecular core.