The invention relates to compounds of the formula I, and to a liquid-crystalline medium, preferably having a nematic phase and negative dielectric anisotropy, which comprises one or more compounds of formula I, defined herein, for use in an electro-optical display, particularly in an active-matrix display based on the VA, ECB, PALC, FFS or IPS effect, and to the use of the compounds of the formula I for the stabilization of a liquid-crystalline medium which comprises one or more compounds of the formula II and one or more compounds of the formulae III-1 to III-4, defined herein.

The liquid crystal composition has positive dielectric anisotropy, and contains a compound contributing to high stability to heat or ultraviolet light as an additive component and a specific compound having small viscosity as a first component, and a liquid crystal display device includes the composition, and the composition may contain a specific compound having large positive dielectric anisotropy as a second component, a specific compound having high maximum temperature or small viscosity as a third component, or a specific compound having negative dielectric anisotropy as a fourth component.

The invention relates to a liquid-crystalline medium having a nematic phase and negative dielectric anisotropy which comprises a) one or more compounds of formula I ##STR00001## b) one or more compounds of formula II ##STR00002##
and c) one or more compounds selected from the compounds of formulae III-1 to III-4 ##STR00003##
in which the parameters have the meanings indicated herein, to the use thereof in an electro-optical display, particularly in an active-matrix display based on the VA, ECB, PALC, FFS or IPS effect, to displays of this type which contain a liquid-crystalline medium of this type, and to the use of the compounds of the formula I for the stabilisation of a liquid-crystalline medium which comprises one or more compounds of formula II and one or more compounds selected from the compounds of formulae III-1 to III-4.

An optical device is provided, which includes a first transparent substrate, a second transparent substrate, and a liquid-crystal material disposed between the first transparent substrate and the second transparent substrate. The liquid-crystal material includes a photo responsive material with a chemical structure of: ##STR00001##
wherein A.sup.1 is ##STR00002##
A.sup.2 and A.sup.3 are independently ##STR00003##
X is halogen. R is H, C.sub.1-12 alkyl group, or C.sub.1-12 alkoxy group. R is C.sub.1-12 alkyl group.

The invention relates to mesogenic media comprising one or more bimesogenic compounds, one or more nematogenic compound, one or more chiral compound and a compound of formula I,

R.sup.11-A.sup.11-(Z.sup.12-A.sup.12).sub.m-AGI

in which, the parameter A.sup.11, A.sup.12, Z.sup.12 and R.sup.11 have one of the meanings as given in claim 1, and to the use of these mesogenic media in liquid crystal devices and in particular in flexoelectric liquid crystal devices, as well as to liquid crystal devices comprising a liquid crystal medium according to the present invention.

An optical device is provided, which includes a first transparent substrate, a second transparent substrate, and a liquid-crystal material disposed between the first transparent substrate and the second transparent substrate. The liquid-crystal material includes a photo responsive material with a chemical structure of:

##STR00001##

wherein A.sup.1 is

##STR00002##

A.sup.2 and A.sup.3 are independently

##STR00003##

X is halogen. R is H, C.sub.1-12 alkyl group, or C.sub.1-12 alkoxy group. R is C.sub.1-12 alkyl group.

The disclosure shows a liquid crystal composition that contains a compound having an effect of preventing photolysis of the liquid crystal composition and having high solubility in the liquid crystal composition, and that satisfies at least one of characteristics such as high maximum temperature, low minimum temperature, small viscosity, suitable optical anisotropy, large positive or negative dielectric anisotropy, large specific resistance, high stability to ultraviolet light or heat, and a suitable elastic constant, etc. and so on. The disclosure shows a liquid crystal composition that contains a compound having the following azolidine ring (Q-1) or azepane ring (Q-2), a liquid crystal display device and so on. ##STR00001##

A liquid crystal composition is provided containing a compound that is effective in preventing photolysis of the liquid crystal composition, and has high solubility in the liquid crystal composition. A liquid crystal display device including the composition is also provided. The liquid crystal composition contains a compound represented by formula (1), and a liquid crystal display device uses the composition: ##STR00001##
in which, in formula (1), R.sup.1 to R.sup.8 are hydrogen or alkyl having 1 to 4 carbons; ring A.sup.1 and ring A.sup.2 are cyclohexylene, phenylene, or naphthalenediyl; Z.sup.1, Z.sup.2 and Z.sup.3 are a single bond; and a and b are independently 1 or 2, and c is 0, 1 or 2.

To provide a compound having an effect for preventing photolysis of a liquid crystal composition, and having a high solubility in the liquid crystal composition, a liquid crystal composition containing the compound, and a liquid crystal display device including the composition. The compound is represented by formula (1), a liquid crystal composition contains the compound, and a liquid crystal display device includes the composition:
M(Z-Q).sub.a(R.sup.b).sub.b(1)
wherein, in formula (1), a is 1 to 4, and b is a numerical value: (4a); M is an organic group; Z is a single bond or the like; and Q is a monovalent group represented by formula (Q-1), (Q-2) or (Q-3), in which R.sup.a and R.sup.b are hydrogen, alkyl or the like. ##STR00001##

Described herein are compounds of formula (I), and pharmaceutically acceptable salts, solvates, hydrates, isotopically labeled derivatives and radiolabeled derivative thereof, and pharmaceutical compositions thereof. Also provided are methods and kits involving the inventive compounds or compositions for detecting and imaging Tau aggregates in the brain for detection of Alzheimer's disease (AD) in a subject.