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

Abstract

‘Dimeric’ discogens have been synthesised which have two triphenylene nuclei, each of which bears five β-OC₆H₁₃ substituents, which are linked through the remaining β positions by a flexible O(CH₂)_nO 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(CH₂)₇O. 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.

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