含氟三苯基單乙炔及反式α-甲基二苯乙烯液晶化合物之合成

Abstract

本研究之主要目的為合成五系列分別含雙苯基乙炔及α位置甲基取代二苯乙烯之液晶化合物。第一系列化合物在中心核兩端分別導入烷基及氟原子，其中烷基含2~6個碳，此系列化合物的熔點在169~176℃之間，澄清點在188~210℃之間，液晶相範圍在13~36℃。 第二系列化合物在兩端苯環上分別導入不對稱烷基，其中一邊烷基含3~6個碳，此系列化合物的熔點在130~147℃之間，澄清點在195~209℃之間，液晶相範圍在61~65℃。由於本系列不像第一系列化合物，導入氟原子這種強極性基作為末端基，使得本系列的熔點及澄清點比第一系列化合物低。 第三系列化合物在兩端分別導入氟原子及烷基，其中烷基含4~6個碳，中間苯環導入側向甲基，形成含側向甲基之液晶化合物，此系列化合物的熔點在66~80℃之間，澄清點在124~142℃之間，液晶相範圍在53~67℃，由於側向甲基的影響，破壞了液晶化合物的排列，所以使此系列的液晶化合物有較低的熔點及澄清點。 第四系列化合物具有二苯乙烯結構，在雙鍵上具有甲基取代基，分子兩端分別導入氟原子及烷基，其中烷基含4~6個碳，本系列化合物沒有呈現液晶相。 第五系列化合物亦具有二苯乙烯結構，在雙鍵上具有甲基取代基，分子兩端分別導入氟原子及烷基，其中烷基含3~5個碳原子，此系列化合物的熔點在96~105℃之間，澄清點在119~133℃之間，液晶相範圍在22~28℃。 本研究合成之數個系列液晶化合物，均具有多個苯環及乙炔或乙烯所以具有較高的雙折射率，加上氟末端基的導入，使其介電異方性也會增加，有潛力應用於反射式液晶顯示元件中。

The goal of this study is aimed to synthesize several series of highly conjugated triphenylacetylene and alpha-methyl stilbene based liquid crystals(LC). The first series of liquid crystals containing a fluoro and an alkyl groups on both ends are named as 1-(4-fluorobiphenyl) -2(4-alkylphenyl) acetylene.The alkyl groups contain 2 to 6 methylene units.The synthesized liquid crystals exhibit melting points ranging from 169 to 176℃, and clearing temperatures ranging from 188 to 210℃.Their nematic temperature ranges are about 13 to 36℃. The second series of liquid crystals containing an ethyl and an alkyl gropus on both ends are named as 1-(4-ethylbiphenyl)-2-(4-alkylphenyl) acetylene. The synthesized liquid crystals exhibit melting points ranging from 130 to 147℃,and clearing temperatures ranging from 195 to 209℃. Their nematic temperature ranges are about 61 to 65℃.Because of the lack of the strong polar fluoro group, this series of compounds show lower melting points and clearing temperatures than those of the first series of compounds. The third series of liquid crystals containing a fluoro and an alkyl groups on both ends and lateral methyl substituent on the middle phenyl ring are named as 1-(4-fluoro-3’-methyl biphenyl)-2-(4-alkylphenyl) acetylene.The synthesized liquid crystals exhibit melting points ranging from 66 to 80℃, and clearing temperatures ranging from 124 to 142℃. Their nematic temperature ranges are about 53 to 67℃. In comparison of these compounds in this series with the first two series, we found that this series of compounds with a lateral methyl substituent exhibit much lower phase transition temperatures. The fourth series of compounds containing a fluoro and an alkyl groups on both ends of the trans alpha-methyl stilbene based structure are named as (E)-1-(4-alkylphenyl)-2-fluorophenyl propene. The alkyl groups contain 4 to 6 methylene units. The synthesized compounds exhibit melting points ranging from 9 to 42℃. This series of compounds reveal no mesomorphic property. The fifth series of liquid crystals containing a fluoro and an alkylphenyl groups on both ends of the trans alpha-methyl stilbene based structure are named as (E)-1-(4-alkylbiphenyl)-2-fluorophenyl propene. The alkyl groups contain 3 to 5 methylene units. The synthesized liquid crystals exhibit melting points ranging from 96 to 105℃, and clearing temperatures ranging from 119 to 133℃. Their nematic temperature ranges are about 22 to 28℃. All of the synthesized liquid crystals which exhibit wide nematic ranges , small heat fusion enthalpy, high birefringence are suitable for formulating eutectic mixtures for the application of reflective type liquid crystal displays.