A liquid-crystalline medium which comprises at least one compound selected from the group of compounds of the formulae IA to IH,

##STR00001##

in which Z.sup.1 denotes a single bond, —CH.sub.2CH.sub.2—, —CH═CH—, —CH.sub.2O—, —OCH.sub.2—, —CF.sub.2O—, —OCF.sub.2—, —COO—, —OCO—, —C.sub.2F.sub.4—, —(CH.sub.2).sub.4—, —CHFCHF—, —CF.sub.2CH.sub.2—, —CH.sub.2CF.sub.2—, —C≡C—, —CF═CF—, —CH═CHCHO— or —CH.sub.2CF.sub.2O—,
and the use thereof for an active-matrix display, in particular based on the VA, PSA, PS-VA, PALC, FFS, PS-FFS, SA-VA, PS-IPS or IPS effect.

Disclosed is a novel stabilizer represented by formula I,

##STR00001##

Further disclosed is a liquid crystal composition comprising a compound of formula I. The liquid crystal composition disclosed in the present invention has a low viscosity γ.sub.1, a moderate dielectric anisotropy Δ∈, a moderate optical anisotropy Δn, and most principally a high reliability, and can achieve a quick response of liquid crystal display.

Shown is a liquid crystal composition satisfying 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 dielectric anisotropy, or has 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 negative dielectric anisotropy as a first component, and a specific compound having small viscosity as a second component, and may contain a specific compound having negative dielectric anisotropy as a third component, a specific compound having a high maximum temperature or small viscosity as a fourth component or a specific compound having a polymerizable group as an additive component.

A PSA-type liquid crystal composition includes a host liquid crystal A and a polymerizable component B, where the host liquid crystal A includes one or more liquid crystal compounds, and the polymerizable component B includes at least one compound selected from compounds of general formula I-1, general formula I-2 and general formula I-3. A liquid crystal display device includes the PSA-type liquid crystal composition above. The PSA-type liquid crystal composition has better intersolubility, cannot be crystallized at a low-temperature environment, can form a relatively stable pretilt angle after the polymerization of the polymerizable component, avoids the image sticking, and inhibits the occurrence of a display defect, such as Zara Particle, during the polymerization. ##STR00001##

A liquid-crystal (LC) medium which is based on a mixture of polar compounds and is substantially dielectrically neutral, its use for optical, electro-optical and electronic purposes, in particular as optical retarder or optical compensator in LC displays, an optical retarder or optical compensator containing the LC medium, an optical, electrooptical or electronic device containing the optical retarder or optical compensator, and a process of manufacturing the optical retarder or optical compensator.

A liquid-crystalline medium which comprises at least one compound selected from the group of compounds of the formulae IA to IH,

##STR00001##

in which Z.sup.1 denotes a single bond, —CH.sub.2CH.sub.2—, —CH═CH—, —CH.sub.2O—, —OCH.sub.2—, —CF.sub.2O—, —OCF.sub.2—, —COO—, —OCO—, —C.sub.2F.sub.4—, —(CH.sub.2).sub.4—, —CHFCHF—, —CF.sub.2CH.sub.2—, —CH.sub.2CF.sub.2—, —C≡C—, —CF═CF—, —CH═CHCHO— or —CH.sub.2CF.sub.2O—,
and the use thereof for an active-matrix display, in particular based on the VA, PSA, PS-VA, PALC, FFS, PS-FFS, SA-VA, PS-IPS or IPS effect.

Disclosed is a liquid crystal composition comprising one or more compounds represented by formula I, one or more compounds represented by formula II, and one or more compounds represented by formula III: ##STR00001##
The liquid crystal composition has simultaneously a lower rotary viscosity, a better photoelectric performance, a higher clearing point, a good low temperature performance, and less display defects. Further disclosed is a liquid crystal display element or device comprising the liquid crystal composition.

The invention relates to a liquid-crystalline medium comprising one or more compounds of the formula CC

##STR00001##

in which the groups occurring 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 vehicles, and to liquid-crystal light valves which comprise this medium and lighting devices for vehicles which contain liquid-crystal light valves of this type.

A liquid-crystalline medium which comprises at least one compound selected from the group of compounds of the formulae IA to IH, ##STR00001##
in which Z.sup.1 denotes a single bond, —CH.sub.2CH.sub.2—, —CH═CH—, —CH.sub.2O—, —OCH.sub.2—, —CF.sub.2O—, —OCF.sub.2—, —COO—, —OCO—, —C.sub.2F.sub.4—, —(CH.sub.2).sub.4—, —CHFCHF—, —CF.sub.2CH.sub.2—, —CH.sub.2CF.sub.2—, —C≡C—, —CF═CF—, —CH═CHCHO— or —CH.sub.2CF.sub.2O—,
and the use thereof for an active-matrix display, in particular based on the VA, PSA, PS-VA, PALC, FFS, PS-FFS, SA-VA, PS-IPS or IPS effect.

A stabilizer represented by formula I, wherein M represents cyclopentyl, cyclobutyl or cyclopropyl; Z.sub.1 and Z.sub.2 each independently represent a single bond, CH.sub.2, CH.sub.2CH.sub.2, O, CH.sub.2O, OCH.sub.2 or COO; ##STR00001## represents one or two of ##STR00002## and n represents 0, 1 or 2. ##STR00003##