A compound represented by Formula (1):

##STR00001## R.sup.1 is hydrogen or an alkyl group that may be substituted; rings A.sup.1 to A.sup.2 are cyclohexylene or phenylene that may be substituted; a is 0 to 4; Z.sup.1 is a single bond or an alkylene group that may be substituted; Sp.sup.1 to Sp.sup.3 are a single bond or an alkylene that may be substituted; M.sup.1 to M.sup.4 are H, F, Cl, or an alkyl group that may be substituted; R.sup.2 and R.sup.3 are hydrogen, a group represented by Formula (1-a), or an alkyl group having 1 to 5 carbon atoms that may be substituted; and at least one of R.sup.2 and R.sup.3 is a group represented by Formula (1-a);

##STR00002## Sp.sup.4 is a single bond or an alkylene group that may be substituted; R.sup.4 and R.sup.5 are hydrogen or an alkyl group; and at least one of R.sup.4 and R.sup.5 is an alkyl group.

The invention relates to a liquid-crystalline medium which comprises at least one compound of the formula I, ##STR00001## in which R.sup.1 and R.sup.1* each, independently of one another, denote an alkyl or alkoxy radical having 1 to 15 C atoms, where, in addition, one or more CH.sub.2 groups in these radicals may each be replaced, independently of one another, by ##STR00002##
in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, A.sup.1 denotes ##STR00003## L.sup.1 denotes F, Cl, CF.sub.3, OCF.sub.3 or CHF.sub.2,
and to the use thereof for electro-optical purposes, in particular for shutter glasses, 3D applications, in TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, PS-FFS and PS-VA-IPS displays.

A liquid crystal composition without requiring an alignment film or alignment treatment on a substrate. The problem is solved by a low molecular weight polar compound capable of homogeneously aligning a liquid crystal medium relative to the substrate, for example, a low molecular weight polar compound represented by formula (1):

M-P(1)

In formula (1), M is a nonpolar group having 1 or more carbons, and P is a polar group.

Liquid crystal compound satisfying at least one of physical properties such as high stability to heat or light, high maximum temperature, high clearing point, low minimum temperature of liquid crystal phase, small viscosity, suitable optical-anisotropy, large negative dielectric-anisotropy, suitable elastic constant and good compatibility with other liquid crystal compounds; liquid crystal composition containing the compound; and liquid crystal display device including the composition. Compound represented by formula (1), wherein R.sup.1 is alkyl having 1 to 15 carbons; R.sup.2 is alkyl having branched-chain and 3 to 15 carbons; A.sup.1, A.sup.2 are independently 1,2-cyclopropylene; Z.sup.1, Z.sup.2 are independently single bond or alkylene having 1 to 15 carbons; L.sup.1, L.sup.2 are fluorine, chlorine, OCF.sub.3 or OCH.sub.2F; X.sup.1, X.sup.2 are oxygen or sulfur; and a is 0 or 1, b is 0 or 1, and sum of a and b is 0, 1 or 2.

##STR00001##

Compound (1) is provided.

R.sup.1-MES-Sp.sup.1-P.sup.1(1)

In compound (1), R.sup.1 is alkyl having 1 to 15 carbons; MES is a mesogen group having an at least one ring; Sp.sup.1 is a single bond or alkylene having 1 to 10 carbons, and in the alkylene, at least one hydrogen is replaced by group (1a); P.sup.1 is group (1e) or (1f);

##STR00001##

wherein, M.sup.1, M.sup.2, M.sup.3 and M.sup.4 are hydrogen; Sp.sup.2 and Sp.sup.3 are a single bond or alkylene having 1 to 10 carbons; R.sup.2 is alkyl having 1 to 15 carbons; R.sup.3 is group (1g), (1h) or (1i);

##STR00002##

wherein, Sp.sup.4 and Sp.sup.5 are a single bond or alkylene having 1 to 10 carbons; S.sup.1 is >CH, and S.sup.2 is >C<; and X is OH.

A liquid crystal display device having a liquid crystal composition, requiring neither an alignment film nor alignment treatment on a substrate. The problem is solved by a low molecular weight polar compound for homogeneously aligning a liquid crystal medium relative to the substrate, for example, the low molecular weight polar compound represented by formula (1).

Formula 95

M-P(1)

In formula (1), M is a nonpolar group having 1 or more carbons, and P is a polar group.

A liquid crystal composition without requiring an alignment film or alignment treatment on a substrate. The problem is solved by a low molecular weight polar compound capable of homogeneously aligning a liquid crystal medium relative to the substrate, for example, a low molecular weight polar compound represented by formula (1).

M-P(1)

In formula (1), M is a nonpolar group having 1 or more carbons, and P is a polar group.

A liquid crystal composition for dimming that satisfies at least one of characteristics such as a high maximum temperature, a low minimum temperature, a small viscosity, a large optical anisotropy and a large positive dielectric anisotropy, or that is suitably balanced between at least two of these characteristics, and a liquid crystal dimming device including this composition. A liquid crystal composition for dimming that includes a specific compound having a large positive dielectric anisotropy as a first component and that may include a specific compound having a high maximum temperature or a low minimum temperature as a second component and a specific compound having a large dielectric anisotropy in the minor axis direction as a third component.

Shown 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 specific compound having large positive dielectric anisotropy as a first component and a specific compound having small viscosity as a second component, and the composition may contain a specific compound having high maximum temperature or small viscosity as a third component, a specific compound having positive dielectric anisotropy as a fourth component, or a specific compound having negative dielectric anisotropy as a fifth component.

The invention relates to a liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, characterised in that it comprises one or more compounds of the formula I in a total concentration of 40%,

##STR00001##

in which the parameters have the meanings indicated in claim 1, and to the use of the liquid-crystalline medium for electro-optical purposes, in particular in liquid-crystal light valves for lighting devices for motor vehicles, and to liquid-crystal light valves which comprise this medium and lighting devices for motor vehicles which contain such liquid-crystal light valves.