| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 89 === The effects of polyether side chains on the mesomorphic properties of b-diketone-derived liquid crystalline complexes have been investigated. When compared with the corresponding complexes having alkoxy side chains, polyether side chains lower the clearing point of the complexes. In addition, the temperature effect has been observed for some b-diketone complexes that have eight side chains: namely, a Dhd phase was observed at high temperature and a Drd one at low temperature. The chain length also affects the mesophases for complexes that have ten side chains, where a Dhd phase was observed for those with short side chains but a Drd phase for those with long side chains. Based on the fact that oxygen atoms can lower the clear point of liquid crystalline complexes, we also introduce an oxygen atom into the perfluoroalkyl side chains for some Schiff's base-derived liquid crystals. The results indicate that the more is the fluorine atom in the side chains, the more stable is the smectic phase. In addition, the introduction of oxygen atoms lowers the temperature for liquid crystalline phases. However, the fluorophobic effect is small and thus the temperature range of liquid crystalline phase cannot be dramatically increased when the distance between the side-chain fluorine atoms and the benzene ring is beyond a certain threshold. The oxygen effect on the pyrimidine derivatives is different. The increase of oxygen atoms in the side chains causes inefficient molecular packing, which is unfavorable for the formation of liquid crystalline phases.
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