The creation of long-lasting glassy columnar discotic liquid crystals using 'dimeric' discogens

'Dimeric' discogens have been synthesised which have two triphenylene nucle i, each of which bears five beta-OC6H13 substituents, which are linked thro ugh the remaining beta positions by a flexible O (CH2)(n)O polymethylene ch ain (n = 3-16). Calculations show that the minimum chain length for bridgin g between columns in the Col(h) phase of these compounds is O (CH2)(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 h ard and in which the columnar order and orientation is retained. These glas ses revert to the crystalline state within a few hours but we have shown th at longer-lasting Col(h) glasses can be engineered through introducing an e xtra degree of disorder into the glass by making the 'dimers' subtly unsymm etrical. These 'dimers' either have differently substituted triphenylene ri ngs 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 tem perature.