| Summary: | 碩士 === 國立高雄師範大學 === 化學系 === 98 === Five series of liquid crystal compounds were synthesized to study the influence of the structure of terminal group or substituent group on the mesogenic behavior of calamitic liquid crystals and bent-shaped liquid crystals. These target molecules are summarized in the following table.
The important results of their mesogenic properties are summarized as follows.
In series 1~3, the phenyl terminal group is substituted by π-electron excessive heterocyclic aromatic groups, containing thiophene ring and furan ring. They exhibit some liquid crystal phases. The liquid crystal phase sequence is I-SmA-SmC-SmX-Cr.These point out that rigid aromatic heterocyclic for ring can also produce liquid crystal phases. The shorter the alkoxyalkyl chain is, the clearing temperature is increasing, and the narrower is the temperature ranges of SmC phase even disappear.
In series 4, because of clearing temperature is too high and the compounds were slowly decomposed before clearing temperature. SmA and SmC phases can be identified by polarized optical microscope.
In series 5, the bromo-substituent in the 4-position of the isophthalic acid can effectively reduce the clearing temperature. But the temperature range of B2 phase will be narower. From electro-optical investigations, the mesophase was identified as a B2 phase and containes ferroelectric properties, Ps= 368 nC/cm.
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