In a brief history of the discovery of antiferroelectricity in liquid crystals, the important role played by tristable switching, i.e. an electric field induced phase transition from antiferroelectric SCA* to ferroelectric SC*, has been emphasised and the antiferroelectric herringbone structure of SCA* has been presented. Then we have explained how to identify the subphases in the SC* region, e.g. SCγ*, SCα*; the clarification of the subphase structures is essential for understanding antiferroelectricity in liquid crystals. After summarizing the evidence for the SCA* structure presented, we have suggested the pair formation of transverse dipole moments in adjacent smectic layers as the cause of its antiferroelectricity, showing that the smectic layer is much closer to the usual picture of molecules lying on equidistant planes; the packing entropy due to the sinusoidal density wave character stabilizes ferroelectric SC*. The competition between the interactions stabilizing SCA* and SC* is responsible for the occurrence of several varieties of ferrielectric and antiferroelectric subphases, which constitutes the Devil's staircase. We have further suggested that the essentials of the SCα* phase are its considerably reduced ability to form SCA* and SC*. At least when the spontaneous polarization is zero, SCα* is a smectic C-like phase with molecular tilting that is non-correlated on the visible wavelength scale When the spontaneous polarization is not zero, as suggested by Prost and Bruinsma recently, a novel type of Coulomb interaction between smectic layers due to the collective polarization fluctuations causes the antiferroelectricity in the high-temperature region of SCα*; the competition between this antiferroelectricity and the SC* ferroelectricity may form another staircase, causing the complexity in SCα*. Applications and some future problems have been described in the final section.

Antiferroelectric chiral smectic liquid crystals

The invention is to provide a liquid crystal composition that satisfies at least one of characteristics such as a high maximum temperature of a nematic phase, a low minimum temperature of a nematic phase, a small viscosity, a large optical anisotropy, a large positive dielectric anisotropy, a large specific resistance, a large elastic coefficient, a high stability to ultraviolet light and heat, or that is suitably balanced between at least two of the characteristics. As the liquid crystal display device containing the compositions is to provide an AM device that has a short response time, a large voltage holding ratio, a large contrast ratio, a long service life and so forth, thus it can be used for the liquid crystal projector, liquid crystal television and so forth.

Liquid crystal composition and liquid crystal display device

Disclosed are: a liquid crystal composition, which satisfies at least one property selected from a high upper-limit temperature in a nematic phase, a low lower-limit temperature in a nematic phase, a low viscosity, high optical anisotropy, high dielectric anisotropy, a high specific resistivity, high stability to ultraviolet ray, high stability to heat and the like, or which has an adequate balance between at least two properties selected from the above-mentioned properties; and an AM element having a short response time, a high voltage holding ratio, a high contrast ratio, a long service life and the like. Specifically disclosed are: a liquid crystal composition which comprises a specific pentacyclic compound having high optical anisotropy and high dielectric anisotropy as the first component, a specific compound having a low viscosity as the second component, and a specific tetracyclic compound having a high upper-limit temperature as the third component, and which has a nematic phase; and a liquid crystal display element comprising the composition.

Liquid crystal composition and liquid crystal display element

Liquid crystal (LC) media based on a mixture of polar compounds having negative dielectric anisotropy, their use in electro-optical displays, especially those having active matrix addressing based on the ECB (electrically controlled birefringence) or VA (vertically aligned) mode or similar modes, and LC displays of these types, are described.

Liquid crystal medium

Molecular orientational structures in MHPOBC were studied by means of conoscope observation. Contrary to a ferroelectric response of the conoscope to an electric field in the smectic C* phase, the conoscopic figure in the antiferroelectric smectic CA* phase does not shift its center and is biaxial with its optic plane perpendicular to the field direction. This conoscope change is only due to a dielectric contribution, indicating the existence of the inherent threshold in the electric field induced transition to the ferroelectric phase. In between the ferroelectric and antiferroelectric phases, a kind of ferrielectric phase was clearly distinguished in the field response of the conoscopic figure; the shift of the conoscope center perpendicular to the applied field and the biaxial optic plane parallel to the field suggest a novel molecular orientational structure.

Molecular Orientational Structures in Ferroelectric, Ferrielectric and Antiferroelectric Smectic Liquid Crystal Phases as Studied by Conoscope Observation

Chiral smectic C compounds having an ester group in the central core, an optically active tail group (alkoxy or alkoxycarbonyl), and an electronegative substituent (halogen or cyano) ortho to the chiral tail were synthesized. The effect of the ortho substitution on the characteristics, especially on spontaneous polarization (Ps), was examined. When the chiral tail is a 1-methylheptyloxy group the lateral substituent increases Ps relative to the unsubstituted analogue. In the case of 1-methylheptyloxycarbonyl tail group, however, the lateral substituent decreases Ps relative to the unsubstituted. These effects of lateral substituents are explained in terms of chemical structure of a single molecule, i. e., by taking statistical weight of conformers and the associated electric dipole moments into account.

Chiral smectic C liquid crystals having an electronegative substituent ortho to the chiral tail group - a study of a factor determining the magnitude of spontaneous polarization

A novel optically active liquid crystal compound and a liquid crystal composition containing the same are provided, which compound is expressed by the formula ##STR1## wherein R 1 is alkyl or alkoxy of 4-18 C; R 2 is alkyl, alkoxy, acyl or alkoxymethyl of 4-18C; but either one of R 1 or R 2 is an optically active group; either one of X 1 or X 2 is halogen atom and the other is H; m and n each are 0 or 1 and m+n is 0 or 1.

Halogen-containing, optically active liquid crystal compound and liquid crystal composition containing same

A novel chiral liquid crystal compound having an optically active group which affords a superior response rate when used as a liquid crystal display element, and a liquid crystal composition containing the same are provided, which chiral liquid crystal compound is expressed by the formula ##STR1## wherein R represents an alkyl group of 1 to 18 carbon atoms; R* represents an optically active alkyl group of 4 to 15 carbon atoms; X represents single bond, --O--, ##STR2## Y represents --CH2 O-- or --OCH2 --; Z represents single bond, --O--, ##STR3## and m and n each represent 1 or 2.

Liquid crystal compound having methyleneoxy group and composition containing same

The present invention provides a liquid crystalline compound having a difluoropropyleneoxy group as a bonding group, which is represented by Formula (1): wherein R1 and R2 each independently represent hydrogen, halogen, a cyano group or an alkyl group having 1 to 20 carbon atoms; rings A1 to A5 each independently represent a 1,4-cyclohexylene group, a 1,4-cyclohexenylene group or a 1,4-phenylene group; Z1 to Z4 each independently represent a single bond, —CH2CH2—, —CH2O—, —OCH2—, —COO—, —OCO—, —CH═CH—, —C≡C—, —CF2O— or —OCF2—; Y1, Y2, Y3 and Y4 each independently represent hydrogen or fluorine; and k, l, m and n each independently represent 0 or 1. This liquid crystalline compound has a large absolute value (|Δe|) of a dielectric anisotropy and shows a relatively small refractive anisotropy. The present invention further provides a liquid crystal composition comprising this compound which makes it possible to drive display elements of various modes at a low voltage, and a liquid crystal display element containing this liquid crystal composition.

Liquid crystalline compound having a difluoropropyleneoxy group as bonding group, liquid crystal composition and liquid crystal display element

A novel optically active compound suitable for use in a display mode utilizing a ferroelectric liquid crystal, and a chiral smectic liquid crystal composition containing the same are provided, which novel optically active compound is expressed by the formula ##STR1## wherein R represents an alkyl group of 2 to 15 carbon atoms; X represents CN group or a halogen atom; Y and Z each represent a halogen atom or hydrogen atom, but either one of Y and Z is hydrogen atom; l is 1 or 2; m is 0 or 1; and a symbol * shows that the carbon atom having this symbol attached thereto constitutes an optically active center.

Kazutoshi Miyazawa

Papers

Chiral smectic C liquid crystals having an electronegative substituent ortho to the chiral tail group - a study of a factor determining the magnitude of spontaneous polarization

Halogen-containing, optically active liquid crystal compound and liquid crystal composition containing same

Liquid crystal compound having methyleneoxy group and composition containing same

Liquid crystalline compound having a difluoropropyleneoxy group as bonding group, liquid crystal composition and liquid crystal display element

Novel optically active compound and liquid crystal composition containing same