Patent ID: 7423151

Claim:
A compound of the formula (I) where X is —CH═CH—, —CR═CH—, —CR═CR—, N—H, N—R 1 , O, S or Se; R is the same or different at each occurrence and is F, Cl, Br, NO 2 , CN, a straight-chain or branched or cyclic alkyl or alkoxy group having from 1 to 20 carbon atoms, in each of which one or more nonadjacent CH 2 groups may be replaced by —O—, —S—, —NR 1 , or —CONR 2 —, and in each of which one or more hydrogen atoms may be replaced by F or an aryl or heteroaryl group having from 4 to 14 carbon atoms which may be substituted by one or more nonaromatic radicals R; R 1 and R 2 are the same or different and are each H or an aliphatic or aromatic hydrocarbon radical having from 1 to 20 carbon atoms, a is, 0 1, 2, 3or 4, b is 0, 1 or 2, whose purity (determined by means of HPLC) is more than 99%.