Helical Discotic Liquid Crystals

The structural properties of ten helicenebisquinones that have side chains differing in number and structure are analyzed by means of polarized light microscopy, differential thermal analysis, and X-ray diffraction. All the derivatives whose side chains are bonded to the helical cores by ether linkages assemble into hexagonally arrayed columns, even when the number of side chains is only two, but not all form true liquid crystalline phases. Those that have three unsymmetrically disposed side chains do, and when these side chains are dodecyloxymethoxy groups, the clearing temperatures are as low as 107 °C, which is 125 °C lower than that of the only previously studied nonracemic helicenebisquinone. Differences in side chain chirality affect the melting characteristics moderately, but they affect the packing arrangements, as analyzed by X-ray diffraction, insignificantly. A set of models is proposed to account for the differences in the materials' properties.