Provided are a reactive mesogen that may improve display quality of a liquid crystal display, and a liquid crystal composition including the same. The reactive mesogen is represented by the following Formula:

##STR00001## where A.sub.1, A.sub.2, and A.sub.3 are each independently a substituted or unsubstituted divalent hydrocarbon ring, or a substituted or unsubstituted divalent heterocycle, L.sub.1 and L.sub.2 are each independently a direct linkage, O, S, CO, COO, OCOO, O(CH.sub.2).sub.k1, S(CH.sub.2).sub.k1, O(CF.sub.2).sub.k1, S(CF.sub.2).sub.k1, (CH.sub.2).sub.k1, CF.sub.2CH.sub.2, (CF.sub.2).sub.k1, CHCH, CFCF, CC, CHCHCOO, or (CH.sub.2).sub.k1COO(CH.sub.2).sub.k2O, Z.sub.1 and Z.sub.2 are each independently a direct linkage, O, S, CO, COO, OCOO, O(CH.sub.2).sub.m1, S(CH.sub.2).sub.m1, O(CF.sub.2).sub.m1, S(CF.sub.2).sub.m1, (CH.sub.2).sub.m1, CF.sub.2CH.sub.2, (CF.sub.2).sub.m1, CHCH, CFCF, CC, CHCHCOO, (CH.sub.2).sub.m1COO, (CH.sub.2).sub.m1COO(CH.sub.2).sub.m2O, CH(S.sub.pPa), CH.sub.2CH(S.sub.pPa), or (CH(S.sub.pPa)CH(S.sub.pPa)), Pa is a polymerizable group, B is an unsubstituted heterocycle, a substituted or unsubstituted crown ether group, or

##STR00002##

wherein T.sub.1 and T.sub.2 are each independently OH, CH.sub.3, CF.sub.3, CHF.sub.2, CH.sub.2F, CH.sub.2Br, CHBr.sub.2, CHCl.sub.2, or CH.sub.2Cl.

A liquid crystal composition including: a liquid crystal compound and a liquid crystal aligning agent including at least one compound represented by Formula 1:

##STR00001##

wherein in the Formula 1, X*, *-L.sub.1-*, *-L.sub.2-*, *-L.sub.3-*, *C*, *R*, *Y, n.sub.1, n.sub.2, and m are the same as defined in the specification.

The present invention relates to a switch element, which is thermoresponsive and which switches between a less transmissive state for radiant energy and a more transmissive state for radiant energy, and which comprises a liquid-crystalline medium. The invention furthermore relates to the use of the switch element for the regulation of radiant energy flow between interior spaces and the environment and for the regulation of the temperature of interior spaces. The invention furthermore relates to a liquid-crystalline medium, characterised in that it comprises 5-95% of a compound of the formula (I), in particular for use in the switch elements according to the invention.

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.