ABSTRACT
The majority of discotic materials exhibit columnar phases. Some additionally show the nematic discotic phase, but very few exhibit only the nematic phase. It is generally accepted that a fairly large, planar, and rigid core that has six or eight peripheral moieties attached is required for the generation of “discotic” mesophases. Surprisingly therefore, the nematic discotic phase was thought to be exhibited, albeit monotropically, by one of the very few discotic compounds that has only three peripheral moieties. After the discovery in 1978 of the first discogen based on hexa-substituted benzene, the natural tendency for designing and synthesizing discotic materials was to select chemical motifs that were disk-like for the core unit. This approach led almost immediately to reports on discogens based on triphenylene. Like order-disorder-order transitions in smectic phases, the phase sequences for discotic materials can exhibit disordered phases at lower temperatures changing to ordered ones at higher temperatures.
