| Research Abstract |
Generally, the core structure of liquid crystals consists of at least two ring systems. Six-membered rings are used as a core moiety and a wider troponoid is less favored.
An acyl group of 2-acyloxytropones can migrate between the two oxygen atoms of C-1 and C-2, so-called [1, 9] sigmatropy, which assisted to be mesogenic. The [1, 9] sigmatropy made molecules orientated along the longer molecular axis to exhibit the mesophase. A monocyclic troponoid (1) showed a monotropic smectic A phase. A pseudo five-membered ring was formed to assist the appearance of the mesophase by the [1, 9] sigmatropy. It is anticipated that monocyclic liquid crystals have low viscosity.
The second monocyclic liquid crystals 2 also showed a monotropic smectic A phase. In order to increase the thermal stability of the monocyclic liquid crystals, a double bond was introduced into an alkyl side chain. The thermal stability of 3 was similar to that of 2. While compounds 3 (m=15, n=11 and m=18, n=11) showed a mesophase, corresponding 2 (m=15, n=13 and m=18, n=13) did not. The double bond in the side chain extended the core part of 3. Compounds with double bond (s) such as 4 and 5, therefore, would be more mesogenic than 13. Thus, the characteristic dynamic property of the seven-membered cross conjugated compounds, which does not observe in benzenoids, worked on the appearance of the mesophase.
It is noteworthy to succeed the preparation of monocyclic liquid crystals in terms of not only preparing low viscous liquid crystals, but revising that the core part of liquid crystals has to have at least two rings.
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