高雙折射率液晶化合物及膽固醇型液晶之合成與鑑定

Abstract

本研究之主要目的為兩部份液晶化合物之合成。第一部份化合物為高折射率液晶化合物，選用Dibenzothiophene(DBT)為主要結構，合成具有共軛之bistolane結構，希望達到高Δn的需求。對稱系列中，以Dibenzothiophene為中心向兩旁連接上三鍵苯環的結構加上末端碳鏈；此系列的液晶熔點溫度皆在200度以上。另外，不對稱化合物在Dibenzothiophene的一端導入CN基團，另一端以三鍵苯環三鍵苯環及末端長碳鏈，中央苯環上接上乙基，此液晶分子熔點135℃,澄清點在212℃，但其呈現層列型液晶相。 第二部份化合物為膽固醇液晶之合成與HTP量測，總共合成了三類6個含旋光性團基之化合物，第一類是含有Dianhydro-D-glucitol團基的化合物，其熔點在140℃，此化合物未呈現液晶相。以此化合物為chiral dopant 所測得HTP值為119.04μm-1，是6個化合物中HTP值最高；第二類化合物則為含有(S)-(+)2-(6-Methoxy-2-naphthyl-propionic acid的兩個化合物，其未呈現液晶相；第三類含有Cholesterol的3個化合物，皆具有膽固醇液晶相。其中末端為6碳烷基之化合物4M，液晶相溫度介於148~316℃之間。其中末端為6碳烷基接上丙醯酸酯的化合物5M，液晶熔點109℃而澄清點卻超過320℃。其中末端為6個碳接上丙醯酸酯的化合物且中間苯環上有Cl側取代基的化合物6M，液晶相溫度88~294℃。由於6M化合物具有較低的膽固醇液晶相溫度，本研究以此為配方之液晶，製備成液晶盒，測量其對於可見光反射能力，探討其作為反射型偏光板之能力。

The goal of this study is aimed to synthesize several high birefringent nematic liquid crystals and cholesteric liquid crystals for display applica- tion. In the first part of this study, we synthesized two series of liquid crystals based on the dibenzothiophene core,i.e.,2-7-bis[(4-alkyl-phenyl)- ethynyl] dibenzothiophenes (Cn-PTBTP) and 2-[[4-[(4-ethyl-phenyl)-2- ethylphenyl]ethynyl]-7-cyano dibenzothiophene (CN-BTPTPC2). For the Cn-PTBTP compounds, their melting points are high than 200℃. They show both nematic and smectic phase. Their cleaning temperature are higher than 300℃. The CN-BTPTPC2 compound reveals much lower melting point. However, it exhibits only a smectic phase from 135℃ to 210℃. In the second part of this study, we synthesized six compounds based on the following three chiral groups, i.e.,dianhydro-D-glucitol,cholesterol and (S)-(+)-2-(6-Methoxy-2-naphthyl)propionic acid. Monomer taining dianhydro-D-glucitol group reveal no mesophase. However it can be used as chiral dopant. It’s helical twisting power(HTP) is 119.04 μm-1 which is highest among those of six compounds. Both momoner 2M and 3M containing (S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid show also no mesomorphic behavior. All of three monomer 4M~6M exhibit cholesteric phase. The cholesteric temperature ranges of 4M~6M are 148~316℃, 109~320℃ and 88~294℃ respectively. Since monomer 6M has the lowest meliting point, it was used to prepare the LC mixture and fabricate a LC cell. The reflection spectrum of the LC cell was measured to evaluate the possibility for the application in reflective polarizer.