The purpose of the invention is to control, by using a colorless alignment control monomer, the alignment of liquid crystal molecules of a liquid crystal display element that does not include an alignment film, and to provide a liquid crystal composition with which the colorless alignment control monomer exhibits excellent compatibility. The invention uses a liquid crystal display element that comprises an alignment control monomer including an aromatic ester that undergoes photo-Fries rearrangement by light irradiation, and that employs a liquid crystal composition having a negative dielectric anisotropy. The invention also uses the liquid crystal composition.

Provided is a compound represented by formula (1) described below.

##STR00001##

In formula (1), a and b are independently 0, 1 or 2, and expressions: 0a+b3 hold, ring A.sup.1, ring A.sup.2, ring A.sup.3 and ring A.sup.4 are independently 1,4-cyclohexylene, for example, Z.sup.1, Z.sup.2, Z.sup.3, Z.sup.4 and Z.sup.3 are independently a single bond, alkylene having 1 to 10 carbons, or the like, Sp.sup.1 and Sp.sup.2 are independently a single bond, alkylene having 1 to 10 carbons, or the like, and P.sup.1 and P.sup.2 are independently a specific polymerizable group.

Disclosed is a liquid crystal composition comprising one or more compounds represented by formula I and/or formula II and one or more compounds represented by formula III: ##STR00001##
wherein the definition of each substituent is given. The composition involved in the present invention has a low viscosity .sub.1, a high clearing point Tni and a large optical anisotropy n, and can realize a rapid response of liquid crystal display.

The present invention provides a compound represented by formula (i), a liquid crystal composition using the compound, and a liquid crystal display device using the liquid crystal composition. The compound represented by formula (i) has a partial structure K.sup.i1 represented by any of general formulas (K-1) to (K-17) and further has ring B having at least two P-Sp- groups. Therefore, when used for a liquid crystal composition, the compound adsorbs to substrates sandwiching the liquid crystal composition (liquid crystal layer) and allows liquid crystal molecules to be held such that they are aligned in a vertical direction without a PI layer, and improved alignment stability and low-temperature storage stability can be achieved.

The liquid crystal display device of the disclosure has: a first substrate; a plurality of pixel electrodes formed on the first substrate; a second substrate; a counter electrode formed on the second substrate and facing the pixel electrode; a liquid crystal layer including a liquid crystal composition between the pixel electrode and the counter electrode; and an alignment control layer formed of a polymer containing an alignable monomer that is one component of the liquid crystal composition, in which the alignment control layers are each formed on a side of the first substrate and on a side of the second substrate. The alignable monomer is a polymerizable polar compound having a mesogen moiety formed of at least one ring, and a polar group.

A negative dielectric anisotropy liquid crystal composition having one or more A-R.sub.0B compounds represented by formula I above as a first component, and one or more compounds represented by formula II above as a second component: ##STR00001##
The liquid crystal composition has a good stability against light and heat, a lower viscosity, a wider refractive index that may be achieved by adjusting the monomer ratio, and a higher clearing point (a very wide service temperature range). The liquid crystal composition has a higher light transmittance, thus allowing a display device to have a higher brightness or an energy saving effect.

The present invention relates to a liquid crystal (LC) medium comprising polymerisable compounds, to a process for its preparation, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, and to LC displays comprising it.

Disclosed is a liquid crystal display device comprising an array substrate and an opposite substrate arranged facing the array substrate, wherein the structure of said array substrate comprises elongated and evenly spaced slit electrodes and electrode gaps between the slit electrodes, and said opposite substrate comprises a bulk electrode; and further comprises a liquid crystal composition between said array substrate and the opposite substrate. The liquid crystal display device has a higher light transmittance, such that more backlight passes through the liquid crystal display device, resulting in the liquid crystal display device having a higher luminance.

A liquid crystal composition that satisfies at least one of characteristics such as a high maximum temperature, a low minimum temperature, a wide temperature range of a liquid crystal phase, a small viscosity, a large optical anisotropy, a large positive or negative dielectric anisotropy, a large specific resistance, a high stability to light, a high stability to heat and a large elastic constant or that is suitably balanced between at least two of these characteristics. The means is use of a liquid crystal composition that includes a specific compound having a high maximum temperature or a small viscosity as a first component, and that may include a specific compound having a large positive dielectric anisotropy as a second component, or a specific compound having a large negative dielectric anisotropy as a third component or a specific compound having a polymerizable group as a first additive.

A liquid crystal composition that satisfies at least one of characteristics such as a high maximum temperature, a low minimum temperature, a small viscosity, a suitable optical anisotropy and a large negative dielectric anisotropy, or that has a suitable balance between at least two of these characteristics, and an AM device including this composition. The nematic liquid crystal composition includes a specific compound having a large negative dielectric anisotropy as a first component and a specific compound having a small viscosity as a second component, and may include a specific compound having a negative dielectric anisotropy as a third component, and a specific compound having a high maximum temperature or a small viscosity as a fourth component, or a specific compound having a polymerizable group as an additive.