Qinetiq Limited

Neil L Campbell

Warren L Duffy

Stephen M Kelly

Rachel P Tuffin

Steven M Kelly

Janine H Wild

A compound of formula (I): where Ris alkyl or alkenyl, Yand Yare independently selected from oxygen or sulphur, n is an integer of from 1 to 5, A is an optionally substituted phenyl or an optionally substituted cycloalkyl ring, X is a direct bond, a Calkylene, a Calkenylene, an acetylene, &#x2014;CO(O)&#x2014; or a group of sub-formula (i): where Xand Xare independently selected from a direct bond, a Calkylene, a Calkenylene, an acetylene, &#x2014;CO(O)&#x2014; and R, Rand Rare independently selected from hydrogen, halo or cyano, provided that no more than one of R, Rand Ris hydrogen. These compounds have a high dipole moment and may be used as dopants in liquid crystal mixtures.

Liquid crystal compounds

The use of a compound of formula (I) wherein Ris an alkyl or alkenyl group, either of which may be optionally interposed with one or more oxygen or sulphur atoms, Ris an alkyl or alkenyl group, Y' and Y&#x2033; are independently selected from oxygen or sulphur, n is an integer from 1 to 5, X is a direct bond or a Calkylene or Calkenylene chain, and A is group comprising one or two rings which are independently selected from aryl, heterocylic or cycloalkyl rings, and when there are two rings, they are bonded together directly or by way of a Calkylene or Calkenylene group, for increasing the u.v. stability of a liquid crystal mixture. The compounds of formula (I) are u.v. stable and are useful in liquid crystal devices which are exposed to high levels of u.v. light such as phosphor display cells. Certain compounds are novel and these form a further aspect of the invention.

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Bangor, United Kingdom

Neil L Campbell