α-Halogenation of triphenylene-based discotic liquid crystals: towards a chiral nucleus

In an attempt to prepare chiral discotic liquid crystals based on a helically twisted triphenylene nucleus a route has been developed for the introduction of a-fluoro, -chloro and -bromo substituents and it is shown that multiple a-halogenation is also possible. The monosubstituted derivatives all show enhanced mesophase stability whilst formation of the mesophase is suppressed for the polyhalogenated derivatives. Rather surprisingly, reaction of 2,3,6,7,10,11-hexahexyloxytriphenylene (HAT6) with iodine monochloride results in chlorination rather than iodination.