含氟三苯基雙乙炔基液晶化合物之合成

Abstract

本論文合成出兩系列含氟側取代基之三苯基雙乙炔基液晶化合物，希望藉由引進雙乙炔連接基及雙氟側取代能得到低熔點、低焓值、寬液晶相範圍及高介電異向性液晶化合物，以應用在液晶共熔混合物的調配上，進而使用在ECB模式的液晶顯示器上。 本研究合成的液晶化合物是以三苯基為核心基，雙乙炔基為連接基，末端基為烷基，所有化合物皆以微差掃描卡計和偏光顯微鏡鑑定其液晶相及相轉移溫度。所有化合物皆呈向列型液晶相。在第一系列液晶化合物中，其熔點並未如所預期的低，離室溫尚有一段距離，可能是由於分子本身太對稱所致。因此，乃增加兩末端碳鏈的差異程度，以增加分子的不對稱性，結果發現當兩末端碳鏈分別為乙基和戊基時，其熔點降低到70.2℃而均向點溫度只些微下降，使得液晶相範圍達到130℃。此外，此一系列化合物之熱焓值亦隨分子不對稱性的增加而急劇降低至3.41kcal/mole，低的熱焓值將有助於液晶共熔混合物的調配。 除了熔點稍高外，此一系列液晶化合物均達到了本研究原先預期的目標。由於含雙氟側取代，使得其De達到-5；又由於雙乙炔基的引進，使得Dn介於0.3至0.4之間。 在第二系列液晶化合物中，其熔點明顯偏高，此一原因推測是因兩末端基中有一為氟基，其對於破壞分子間末端之作用力的貢獻較小；且由於其側鏈另有一氟基側向取代，此兩氟基使得分子的極性增加，故使得其熔點較高而等向性溫度較低，且呈現出奇偶效應。此外，本研究亦探討了所合成之液晶化合物結構與其物理性質之關係。

Synthesis of a series of fluorinated bistolane was made in this reserch. We introduced the linking group of diacetylene and lateral substitution of difluoro, trying to obtain the liquid crystal with low melting point, low enthalpy, wide mesophase range, and negative dielectric anisotropic. The liquid crystal with these properties was suitable to be used in the formulation of liquid crystal mixture in the liquid crystal display with homeotropic alignment. The liquid crystal compounds in this study were with triphenyl as mesogene, diacetylene as linking group and alkyl as terminal. Their mesophase and transition temperature were characterized with DSC and OM. Their melting points were not as low as those expected, that would result from the symmetry of the molecular structure. Hence, we used more different alkyl chain as the terminal groups to destroy the molecular symmetry. With ethyl and pentyl groups as terminal groups, the compound had a melting point at 70.2 oC and lower isotropic temperature, but no obvious odd-even effect. Its mesophase range was up to 130 oC. Additionally, the enthalpies of these compounds were drastically down to 3.41 kcal/mole when their molecular symmetry reduced. The lower enthalpy will benefit the formulation of liquid crystal mixture. This series of liquid crystal was quite successful, even their melting points were a little higher. Their De up to -5 was due to the substitution of difluoro, and Dn between 0.3 and 0.4 was contributed from diacetylene. The relationship between the structure of the liquid crystal and their properties was also studied in this research.