含側向取代基之三苯基雙乙炔系列晶化合物之合成研究

Abstract

本論文合成了數個系列含側向取代甲基的末端不對稱烷基及末端氟基之三苯基雙乙炔液晶化合物，交測其液晶相溫度之變化。所合成之化合物大都具有寬廣的液晶相溫度和較低的熔解焓值，應可應用在液晶共融混合物的調配上。 本研究第一部份是有關含末端不對稱烷基之液晶化合物的合成與鑑定。這些化合物是由 4-碘甲苯胺與4-烷基苯乙炔作耦反全合應，再經由重氮化後以碘取代，所得的碘化物再與另一個4-烷基苯乙炔作耦合反應最後生成所需之不對稱產物。所有化合物皆呈現向列型液晶相，且熔點都隨著烷基長度的加長而有降低的趨勢。側向取代甲基的加入更使得熔點大幅度的下降，並伴隨液晶相溫度範圍的加寬。另一方面靠近側向取代基的末端烷基長度如較另一端的末端烷基來得短可有較低的熔點。另外在雙折射率上有一較高的值。 本研究第二部份是有關含末端氟基的液晶化合物之合成與鑑定，所有化合物皆呈現向列型液晶相，除了末端烷基為乙基時的熔點較丙基低外，其餘化合物的熔點皆隨著末端烷基的加長而呈現出下降的趨勢，其均向性溫度則出現奇偶效應，但其熔解焓均較第一系列液晶化合物高；在光電特性上，此系列同時具有高的介電異向性及雙折射率值。本研究並詳細地探討了所合成液晶化合物化學結構與其液晶性質之關係。

Several series of new asymmetric and fluorinated triphenyl-diacetylenes are synthesized and characterized. These synthesized compounds which exhibit respectively a wider temperature range of mesohase, and a small melting enthalpy are suitable for formulating LC eutectic mixtures. The first pat of this thesis described the synthesis and characterization of a series of compounds containing asymmatric alkyl terminal groups. 4-lodotoluidine was coupled with 4-alkylphenylacetylene, followed by diazotization and iodination to forma 4-[2-(4-alkylphenyl)-1-ethynyl]-2-iodotoluene which was further coupled with 4- alkyl-phenylacetylene to yield the asymmetric triphenyl-diacetylene compounde. All the obtained compounds exhibit respectively a nematic phase. Their clear temperatures decrease with increasing the length of alkyl groups. The results demonstrate that introducing an lateral methyl group into the mesogemic core decreases dramatically the melting points of teh obtained compounds and also increases their temrperature range of the nematic phase. Furthermore, the chain lengths of two terminal alkyl groups located at each side of mesogenic core have profound effect on the melting points of the obtained compounds. The synthesis and characterization of a series of fluorinated triphenyldiaceylenes were described in the second part of this study. All obtained compounds reveals respectively a nematic phase. Their melting points decrease as the terminal alkyl chain length increase. However, the melting enthalpies of this serise of the compounds are larger than those of previous series of compounds. In this study, the detailed structure-properties relationship of the obtained compounds is discussed.