含4-(4-烷基苯)-α-甲基菧之高雙折射率液晶化合物合成研究

Abstract

本論文成功合成出四個系列以甲基菧為主要結構的液晶化合物，並探討其液晶相溫度變化。所合成的化合物大都具有寬廣的液晶相溫度範圍。第一系列化合物其結構為甲基菧苯環上接一烷基，而在另一末端苯環4位置接上異硫氰基，實驗結果顯示，此系列化合物熔點範圍約在52.6∼71.4℃之間。只有烷基碳數為己烷基時，降溫下才出現液晶相，其範圍15.6℃，為向列型液晶相。第二系列化合物其結構為甲基菧苯環上接一烷基苯，而在另一末端苯環4位置接上氨基，結果顯示：此系列化合物之熔點範圍在143.8~160.1℃之間，澄清點範圍在156.6∼195.7℃之間，熔點偏高的原因可能是分子間的氫鍵所導致。液晶相溫度範圍12.8~35.6℃之間，此系列液晶化合物均為向列型液晶相。第三系列化合物熔點範圍在81~120.1℃之間，澄清點範圍在192.8~232.3℃之間。液晶相溫度範圍99.1~133.8℃之間。第四系列化合物熔點範圍在90.7~138.8℃之間，澄清點範圍在179.9~251.5℃之間。液晶相溫度範圍83.6~133.0℃之間。第三系列化合物其熱焓值較其他系列的低，但在烷基碳數四以上時會有層列型液晶相的產生，並隨著碳數增加層列型液晶相的溫度範圍有擴張的傾向。本研究所合成之化合物。有機會應用在反射式膽固醇型及高分子分散液晶顯示器上。

Four series of liquid crystals, i.e., 4-alkyl-4’-isothiocyano-α-methyl stilbenes, 4-(4-alkylphenyl)-4’-amino-α-methylstilbenes, 4-(4-alkyl phenyl)-4’-isothiocyanato-α-methylstilbenes, and 4-(4-alkyl phenyl)-4’- cyano-α-methylstilbene, were synthesized and characterized. Most of the synthesized compounds exhibit mesomorphic properties. Some of the 4-(4-alkylphenyl)- 4-isothiocyanato-α-methylstilbene containing longer alkyl chain length (n≧4) reveal smectic phase. All obtained liquid crystals exhibit wide nematic range and high birefringence, especially the compounds with isothiocyanato group. For 4-alkylphenyl-4’-isothiocya nato-α-methylstilbenes, their melting points are in the temperature range from 52.6 to 71.4 ℃. 4-Hexylphenyl-4’- isothiocyanato-α-methylstilb ene is the only one exhibits a monotropic nematic phase. For 4-(4-alkylphenyl)-4’-amino-α-methylstilbenes, their melting points are in the temperature range from 143.8 to 160.1 ℃ and their cleaning temperature are in the temperature range from 156.6 to 195.7 ℃. The reason for these series of compounds show such high phase trnsition temperature is due to the H-bonding of amino group. Their nematic temperature ranges cover from 12.8 to 35.6 degrees. For 4-(4-alkyl phenyl)-4’-isothiocyanato-α-methylstilbenes, their melting points are in the range from 81.0 to 120.1 ℃ and their cleaning temperatures are in the range from 192.8 to 232.3 ℃. Their nematic temperature ranges cover from 99.1 to 133.8 degrees. This series of compounds exhibit a smectic phase when their terminal alkyl group longer than butyl group. For 4-(4-alkyl phenyl)-4’-cyano-α-methylstilbenes, their melting points are in the temperature range from 90.7 to 138.8 ℃ and cleaning temperatures are in the range from 179.9 to 215.5 ℃. Their nematic temperature ranges cover from 83.6 to 133.0 degrees. The liquid crystals synthesized in this study have potential applications in reflective cholesteric liquid crystal display and a polymer dispersed liquid crystal display.