The composition contains a specific compound having a high maximum temperature and a low minimum temperature as a first component and has negative dielectric anisotropy, and may further contain a specific compound having large negative dielectric anisotropy as a second component, a specific compound having a high maximum temperature or small viscosity as a third component, a specific compound having large negative dielectric anisotropy as a fourth component and a specific compound having a polymerizable group as an additive component.

Provided is a liquid crystal compound satisfying at least one of physical properties such as high stability to heat and light, a high clearing point (or high maximum temperature), low minimum temperature of a liquid crystal phase, small viscosity, suitable optical anisotropy, large dielectric anisotropy, a suitable elastic constant and excellent compatibility with other liquid crystal compounds, a liquid crystal composition containing the compound and a liquid crystal display device including the composition. A compound, represented by formula (1): ##STR00001##
wherein, in formula (1), R.sup.1 is alkoxy having 1 to 9 carbons or the like; R.sup.2 is alkenyl having 2 to 10 carbons; Z.sup.1 and Z.sup.2 are independently a single bond, CH.sub.2CH.sub.2, CHCH or the like; and a and b are independently 0 or 1.

The present invention provides a liquid crystal display device with reduced power consumption as well as reduced flicker. The liquid crystal display device is one in a transverse electric field mode, including: paired substrates; a photo-alignment film disposed on at least one of the substrates; a horizontal alignment liquid crystal layer disposed between the substrates; and pixels arranged in a matrix form, the liquid crystal layer containing liquid crystal molecules with a bicyclohexyl skeleton and liquid crystal molecules with a difluorobenzene skeleton, the liquid crystal layer having negative anisotropy of dielectric constant, one of the substrates including TFTs disposed in the respective pixels, the TFTs each including a semiconductor layer that contains an oxide semiconductor, the liquid crystal display device having a frame rate of lower than 50 Hz.

The liquid crystal composition contains a compound contributing to high stability to heat or ultraviolet light, has negative dielectric anisotropy and has a nematic phase, and may contain a specific compound having high negative dielectric anisotropy as a first component, a specific compound having a high maximum temperature or small viscosity as a second component, and a specific compound having a polymerizable group.

Provided are a compound having an effect on preventing photolysis of a liquid crystal composition, and high solubility in the liquid crystal composition, a liquid crystal composition containing the compound and a liquid crystal display device including the composition.

A compound is represented by formula (1), a liquid crystal composition contains the compound and a liquid crystal display device uses the composition.

##STR00001##

In formula (1), for example, R1 is alkyl having 1 to 10 carbons; R2 is hydrogen, hydroxy, oxy radical or alkyl; ring A1, ring A2 and ring A3 are independently 1,4-cyclohexylene, 1,4-phenylene or pyridine-2,5-diyl; Z1 and Z2 are independently a single bond or alkylene; and a and b are independently 0 or 1.

Provided are a liquid crystal composition satisfying at least one of characteristics such as high maximum temperature, low minimum temperature, small viscosity, suitable optical anisotropy and large dielectric anisotropy, or having a suitable balance regarding at least two of the characteristics, and an AM device including the composition.

The liquid crystal composition contains a quencher as a first additive, and may contain a specific compound having large negative dielectric anisotropy as a first component, a specific compound having high maximum temperature or small viscosity as a second component, or a specific compound having a polymerizable group as a second additive.

The invention relates to a liquid-crystalline medium which comprises at least one compound of the formula I,

##STR00001##

in which R.sup.1, R.sup.1*, rings A and B, Z.sup.1, L.sup.1, L.sup.2, a and b have the meanings indicated in Claim 1, and to the use thereof for an active-matrix display, in particular based on the VA, PSA, PS-VA, PALC, FFS, PS-FFS, IPS or PS-IPS effect.

Provided are a liquid-crystal-medium having stability to heat, light and so forth, a wide liquid-crystal-phase temperature-range and significantly large dielectric-anisotropy and developing an optically isotropic liquid-crystal-phase; and various optical-devices used in a wide temperature-range, having short response-time, a large contrast-ratio and low drive-voltage and suppressing decrease in an effective dielectric-constant in a high-frequency range.

A Liquid-crystal composition contains achiral-component T containing at least one compound selected from a first component represented by formula (1) and at least one compound selected from a second component represented by formula (2) or (3) and a chiral-agent to develop optically-isotropic liquid-crystal-phase:

##STR00001##

In formula (1), R.sup.1: alkyl, ring A.sup.1: 1,4-cyclohexylene, ring B.sup.1: 1,4-phenylene, L.sup.11 to L.sup.14: fluorine, Y.sup.1: fluorine, n.sup.1: 1 or 2, R.sup.2: alkyl, Z.sup.21 and Z.sup.22: single-bond or CF.sub.2O, L.sup.21 to L.sup.23: fluorine, Y.sup.2: fluorine, R.sup.3: alkyl, Z.sup.31 and 2.sup.32: single-bond or CF.sub.2O, L.sup.31 to L.sup.34: fluorine, Y.sup.3: fluorine, for example.

To show a liquid crystal compound satisfying at least one of physical properties such as a high stability to heat, light or the like, a high clearing point, a low minimum temperature of a liquid crystal phase, a small viscosity, a suitable optical anisotropy, a large dielectric anisotropy, a suitable elastic constant and an excellent compatibility with other liquid crystal compounds, a liquid crystal composition containing the compound and a liquid crystal display device including the composition. A compound represented by formula (1): ##STR00001## wherein, in formula (1), for example, R.sup.1 is alkyl having 1 to 15 carbons; ring A.sup.1 and ring A.sup.2 are 1,4-cyclohexylene, 1,4-cyclohexenylene, 1,4-phenylene, 1,4-phenylene in which at least one piece of hydrogen is replaced by halogen, tetrahydropyran-2,5-diyl or 1,3-dioxane-2,5-diyl; Z.sup.1 and Z.sup.2 are a single bond or CF.sub.2O; L.sup.1, L.sup.2 and L.sup.3 are halogen or hydrogen; and a is 0 to 3.

Described is a liquid crystal composition which satisfies at least one of such characteristics as high upper limit temperature of the nematic phase, low lower limit temperature of the nematic phase, low viscosity, adequate optical anisotropy, large negative dielectric anisotropy, high resistivity, high stability to ultraviolet light and high stability to heat, or which has an adequate balance between at least two of the above-mentioned characteristics. Also described is an AM element having a short response time, high voltage holding ratio, high contrast ratio, long life and the like. The liquid crystal composition contains a specific compound having a large negative dielectric anisotropy and a low lower limit temperature as a first component, a specific compound having a low viscosity or a high upper limit temperature as a second component, and a specific compound having a polymerizable group as a third component. The AM element contains the composition.