Ferroelectric compounds with chiral (S)-1-methylheptyloxycarbonyl terminal chain – their miscibility and a helical pitch

Compounds with the same chiral terminal chain but different structure of rigid core and non-chiral terminal chain were added to basic highly tilted ferroelectric compound in the aim of establishing whether the miscibility of phases, especially ferroelectric phase, exists in these compounds and what are the helical pitch and tilt angle temperature dependence in bicomponent systems. In certain systems, we obtained a mixture with very short helical pitch at broad temperature range of ferroelectric phase, which open opportunities for the formulation of multicomponent mixtures for fast switching ferroelectric liquid crystals modes.     

Synthesis and physical properties of difluoroterphenyl ferroelectric liquid crystal with mixed alkenyloxy-ester terminal ends

This paper describes the synthesis and mesomorphic properties of a SmC*-forming liquid crystalline compound with potential display applications. This compound with two fluorines in the 3,3'-positions of the terphenyl core and mixed unsaturated alkoxy/ester terminal groups is synthesized in an attempt to obtain a liquid crystal with ferroelectric properties useful for display applications.     

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.     

Synthesis and characterization of chiral smectic C liquid crystalline terpolysiloxanes

A number of tailor-made side chain liquid crystalline terpolysiloxanes, containing chiral cyanohydrin ester, phenyl pyrimidine and fluorinated phenylbenzoate as the side groups, have been synthesized for potential applications as ferroelectric liquid crystal polymers. All the polysiloxanes exhibit the mesomorphic sequence of crystal-chiral smectic C-smectic A-isotropic phases.     

New ferroelectric and antiferroelectric liquid crystalline materials containing differing numbers of lactate units

A new series of chiral liquid crystalline materials having the same rigid core containing a keto group, and various numbers of ( S )-lactate groups in the chiral segment, has been synthesized and studied. All the compounds contain a branched terminal alkyl chain derived from ( S )-2-methylbutanol. The influence of the number of lactate units on mesogenic behaviour has been studied. All the compounds show the paraelectric SmA phase and the ferroelectric SmC * phase over rather wide temperature ranges. The antiferroelectric SmC * A phase was observed for the compound possessing two lactate groups.     

Effect of ferroelectric liquid crystalline quaterphenyl structure and handedness on helical pitch length in bicomponent mixtures

The aim of this paper is characterisation of mesomorphic properties and helical structure parameters: handedness and helical pitch, of two laterally substituted ferroelectric compounds and mixtures based on them. These compounds have the same quaterphenyl rigid core and the same length of non-chiral chain – eight carbon atoms, as well as the absolute configuration of chiral centre (‘R’). Base compounds differ in the kind of a substituent in a rigid core (–Cl, –CH₃). Both of them have rather low melting temperature in comparison to most of quaterphenyls, and it affects the lowering of this temperature in binary mixtures. Thus they can be used for preparation of multicomponent ferroelectric mixtures useful for application.     

Effect of alkyl chain length in the terminal ester group on mesomorphic properties of new chiral lactic acid derivatives

Two series of new liquid crystalline lactic acid derivatives with a terminal ester group have been synthesised. The effect of this ester unit and the length of its alkyl chain on the mesomorphic and dielectric properties of the compounds exhibiting a broad temperature range of chiral smectic phases have been studied. We found that the mesomorphic behaviour and phase transition temperatures are strongly affected by the molecular architecture. Depending on the alkyl chain length in the terminal ester unit, the studied materials exhibited paraelectric smectic A*, ferroelectric tilted smectic C* and antiferroelectric smectic C_A* phases over a broad temperature range. The physical properties of the compounds have been studied by optical polarising microscopy, differential scanning calorimetry, electro-optic measurements, small-angle X-ray scattering and dielectric spectroscopy. Furthermore, the homologues with short terminal alkyl chains showed a very small layer shrinkage at the transition from the orthogonal SmA* to the tilted SmC* phase, which is a characteristic feature of ‘de Vries-type’ behaviour.     

Effect of fluorination on the phase sequence,dielectric and electro-optical properties of ferroelectric and antiferroelectric mixtures

Four multicomponent room temperature mixtures were formulated using a pyrimidine-based achiral matrix as host and four terphenyl-based ester chiral compounds as dopants. Among the four mixtures, two exhibit antiferroelectric and two other exhibit ferroelectric phases at room temperature. Dopant molecules differ from each other by position and number of fluorine atom substitution at the benzoate group of the molecular rigid core. Number and location of fluorine atoms in the dopant structure show significant effect on the phase sequences as well as on different physical properties. All the mixtures found to have moderate spontaneous polarisation, high tilt angle, very fast switching time and low viscosity which are important for liquid crystal-based display applications.     

Effect of chain length and fluorination on the dielectric and electro-optic properties of three partially fluorinated biphenylyl benzoate rigid core based ferroelectric liquid crystals

Three partially fluorinated ferroelectric liquid crystals (4F4R, 4F5R and 7F3R) with biphenylyl benzoate rigid core have been investigated by frequency-dependent dielectric spectroscopy and electro-optic methods. Molecular structures of the compounds differ only by the length of the carbon chain and the number of oligomethylene spacers. 4F4R and 4F5R exhibit ferroelectric SmC* phase over a considerable temperature range and directly melts into isotropic phase, 4F4R also shows a ferroelectric type subphase. Only Goldstone mode (GM) relaxation is observed in these compounds, but no soft mode (SM). 7F3R exhibits both the SmC* and SmA* phases, has higher stability of SmC*. Both the GM and SM relaxations are observed in this case, signifying that SM relaxation is possible only when SmC* is formed on cooling from SmA*. Increase of dielectric strength and critical frequency with temperature, in all cases, has been explained in the light of generalised Landau model. Spontaneous polarisation is found to decrease with increasing flexibility, and optical tilt depends more on fluorination than on chain length.     

Synthesis and characterization of new ferroelectric liquid crystals containing a (2S)-2-[6-(4-hydroxybiphenyl-4'-carbonyloxy)-2'- naphthyl] propionate mesogenic group and oligo(oxyethylene) spacers

Three series of ferroelectric liquid crystals containing a (2S)-2-(6-(4-hydroxybiphenyl-4'-carbonyloxy)-2'-naphthyl)propionate mesogenic group and oligo(oxyethylene) spacers were synthesized. These obtained liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC), optical polarized microscopy (POM), and X-ray powder diffraction measurements. Some of these materials containing four phenyl rings of ester cores (i.e. -Ph-Ph-COO-naph-) and chiral heptyl tail exhibited a rich mesomorphic behaviour, a blue phase (BP), a cholesteric phase (Ch), a smectic A (S_A), a twist grain boundary A (TGB_A), and a chiral smectic C (S_C*) phase. Another series containing four phenyl rings of ester cores and chiral butyl and pentyl chain tails revealed only a S_A phase and a S_C* phase. Moreover, a crystal E phase was observed in the short spacer chain (n = 0 or 1) homologues of three series of compounds. Also, the mesomorphism properties were discussed as a function of spacer units, numbers of aromatic rings of core, and different terminal asymmetric moieties.     

Antiferroelectric phase in liquid crystalline compounds containing an azo group in their molecular core

Novel lactic acid derivatives containing an azo group in their molecular core have been synthesised and their mesomorphic properties established. Compounds with a short aliphatic non-chiral chain exhibited the SmA* phase and ferroelectric (FE) SmC* phase. The monotropic antiferroelectric (AF) phase was found in the homologues with a longer terminal chain. Spontaneous polarisation and tilt angle were measured for the FE and AF phases. Dielectric spectroscopy in the frequency range 1 Hz–10 MHz was carried out and dielectric properties established within the temperature range of the smectic phases. Two high frequency modes were detected in the AF phase. Small-angle X-ray measurements were conducted, and the temperature dependence of layer spacing values is established and discussed.     

New ferroelectric liquid crystals with a trifluoromethyl group

New chiral dopants, possessing a trifluoromethyl group, have been synthesized. These dopants have different polar groups, located between the chiral centre and the diphenylacetylene core. The polar part is chosen from ester, methylene ether and ether linkages. Each new chiral dopant was mixed with a non-chiral liquid crystal mixture or a ferroelectric liquid crystal mixture, and their transition temperatures and electrooptic properties measured. The largest spontaneous polarization, 4·1 nC cm^-2, was obtained at 25°C for the ferroelectric liquid crystal mixture in which the dopant, with a methylene ether linkage, was incorporated. Molecular orbital calculations (MNDO method) for the dopants show that the calculated dipole moments are correlated with the measured spontaneous polarization, and the calculated results explain the experimental results quite well. In addition, it has been found that the conformation of the chiral part is an important factor which affects the magnitude of spontaneous polarization.     

Anomalous temperature dependence of the dielectric and optical properties in ferroelectric liquid crystals

The anomalous temperature dependence of the sign of the spontaneous polarization in a biphenyl ester series of ferroelectric liquid crystals is reported. The reversal of the sign of the spontaneous polarization in the chiral smectic C phase of 2MBNCBC ((S)-2'-methylbutyl-4'-n- nonylcarbonyloxy-(l,l'-biphenyl)-l-carboxylate) is observed at T_m. This anomaly is studied in detail as functions of the length of the terminal alkyl chain, the applied electric field, the frequency and the applied hydrostatic pressure. T_m has been confirmed to depend on the length of the terminal chain and the applied pressure. However, it is independent of the applied field and the measuring frequency. In the mixture of these compounds, this anomaly is also observed.     

单取代二茂铁有机液晶的合成、结构及刚性实对介晶性影响

合成了17个未见报道的中心桥连基为酯基、C==N基,分别含有3-4个苯环,不同刚性实长度以及不同末端链长度的二茂铁化合物,并通过DSC和偏光显微镜对其介晶性进行了表征.研究表明,末端长度对相变温度和清亮温度均有影响,但对相变温度范围影响较小,而刚性实长度对其影响却很大.当刚性实达到一定长度时,末端为H原子也具有介晶性---这是第一个无柔性末端链的金属有机液晶化合物.     

Preparation and evaluation of novel ferroelectric liquid crystalline cyclic siloxane tetramers

Two series of liquid crystalline cyclic siloxane tetramers, one containing the 2-methylbutyl chiral group and the other the 1-methylheptyl chiral group, were prepared to investigate, in a systematic manner, the role of molecular structure of (a) the spacer group, (b) the mesogenic side chain and (c) the chiral end group, on the liquid crystalline behaviour of these novel tetramers. The results from this systematic structure/property correlation study clearly showed the effect of the structure of both the chiral end group and the mesogenic side chain core on the thermal properties and temperature ranges of the SmC* phase (ferroelectric) exhibited by these novel materials. By the appropriate choice of spacer group, mesogenic side chain and chiral end group, a number of cyclic siloxane tetramers exhibiting wide SmC* ranges (ferroelectricity) around room temperature were synthesized.     

Preparation and evaluation of novel ferroelectric liquid crystalline cyclic siloxane tetramers

Two series of liquid crystalline cyclic siloxane tetramers, one containing the 2-methylbutyl chiral group and the other the 1-methylheptyl chiral group, were prepared to investigate, in a systematic manner, the role of molecular structure of (a) the spacer group, (b) the mesogenic side chain and (c) the chiral end group, on the liquid crystalline behaviour of these novel tetramers. The results from this systematic structure/property correlation study clearly showed the effect of the structure of both the chiral end group and the mesogenic side chain core on the thermal properties and temperature ranges of the SmC* phase (ferroelectric) exhibited by these novel materials. By the appropriate choice of spacer group, mesogenic side chain and chiral end group, a number of cyclic siloxane tetramers exhibiting wide SmC* ranges (ferroelectricity) around room temperature were synthesized.     

Synthesis and SmC* properties of chiral liquid crystalline terephthalates

Chiral ester derivatives of terephthalic acid containing one, three, or five phenyl rings were prepared by using (S)-2-methylbutanol or (R)-2-chloropropanol as starting materials. The one-ring terephthalates did not exhibit any liquid crystalline phases, but one of them was used as a chiral dopant in ferroelectric mixtures. Elongation of the aromatic core structure to three and five phenyl rings stabilized the SmA phase, whereas a (monotropic) SmC* phase was detected in some three-ring and five-ring derivatives. In ferroelectric mixtures based on the terephthalates, spontaneous polarizations up to 340 nC cm2 were measured.     

Effect of lateral substitution by fluorine and bromine atoms in ferroelectric liquid crystalline materials containing a 2-alkoxypropanoate unit

Two homologous series of ferroelectric liquid crystalline compounds with 2-alkoxypropanoate chiral unit containing biphenyl benzoate core laterally substituted by fluorine and bromine have been synthesized and studied. All compounds possess the ferroelectric smectic C* phase over a broad temperature range. For bromine-substituted compounds values of spontaneous polarization reach high values up to 250 nC cm^-2. The effects of the lateral substitution on the phenyl ring far from the chiral centre by methyl and methoxy groups, fluorine, chlorine and bromine atoms on mesomorphic properties and on values of the spontaneous polarization are discussed.     

Four unit linking groups II. Some novel smectic C materials

About 40 diverse phenyl benzoate esters incorporating a trans-1-4-disubstituted cyclohexane ring joined to the central aromatic core by new four unit linking groups (C₄H₈, C₄H₆, C₃H₆O and C₃H₄O) have been synthesized. The effect of various lateral substituents (F, Cl, CN and Br) and especially two fluorine atoms in the 2,3-positions of the 4-n-alkoxybenzoate part of the esters has been investigated. Three homologous series of 5-n-alkyl-2-(4-phenyl)pyrimidines incorporating the same four unit linking groups have also been prepared. Many members of the ester and pyrimidine series exhibit enantiotropic smectic C mesophases at moderately elevated temperatures. Several esters and pyrimidines have been found to improve the surface alignment and temperature range of chiral smectic C mixtures for surface stabilized ferroelectric liquid crystal displays. The effect of the new four unit linking groups on the liquid crystal transition temperatures, rotational viscosity and spontaneous polarization of their host structures in a standard chiral C mixture has been studied and compared to that of analogous materials containing no central linkage and standard central linkages (-, C₂H₄, CH₂O and COO). Several lactate ester derivatives incorporating the four unit linking groups have also been prepared and been found to exhibit a moderately high spontaneous polarization.