The creation of persistent glassy columnar discotic liquid crystals using ‘dimeric’ discogens

‘Dimeric’ discogens have been synthesised which have two triphenylene nuclei, each of which bears five β-OC 6 H 13 substituents, which are linked through the remaining β positions by a flexible O(CH 2 ) n O polymethylene chain (n=3-16). Calculations show that the minimum chain length for bridging between columns in the Col h phase of these compounds is O(CH 2 ) 7 O. It was found that only those dimers for which n>7 formed a Col h phase. This mesophase can be supercooled into a metastable glass which is relatively hard and in which the columnar order and orientation is retained. These glasses revert to the crystalline state within a few hours but we have shown that longer-lasting Col h glasses can be engineered through introducing an extra degree of disorder into the glass by making the ‘dimers’ subtly unsymmetrical. These ‘dimers’ either have differently substituted triphenylene rings at the two ends of the linking chain or an amide group within the chain itself. They give Col h aligned glasses which last for months at room temperature.