Structural factors controlling the transition between columnar-hexagonal and helical mesophase in triphenylene liquid crystals

A series of novel triphenylenes has been synthesised by a combination of pa lladium catalysed coupling, oxidative cyclisation, bromination and nucleoph ilic aromatic substitution. The new derivatives are designed to have struct ures which are intermediate between the known symmetrical materials hexakis ( hexyloxy) triphenylene and hexakis( hexylthio) triphenylene. The compound s having four hexyloxy and two hexylthio substituents form only Col(h) meso phases. Triphenylenes having four hexylthio and two hexyloxy substituents a lso give Col(h) mesophases but 3,6- bis(hexyloxy)-2,7,10,11-tetrakis(hexylt hio) triphenylene 5 is unique in that it cools into a stable, more ordered phase. The low temperature phase, which appears to be indefinitely stable a t ambient temperature, is assumed to be helical based on transition enthalp y data.