盤狀液晶化合物與2,3-鄰二氟苯基之二苯乙炔液晶化合物之合成

Abstract

本研究成功合成出三系列化合物：第一系列為合成以二炔基二亞甲氧基為中心之盤狀液晶，並在二亞甲氧基尾端引入可進行光聚合反應之二丙烯酸酯基，得到層列型液晶化合物8，其液晶相溫度範圍在46.1~74.8℃，且單體8對光與熱之穩定性較差，高溫下容易自行聚合。第二系列，合成以2,3-鄰二氟苯二炔基二苯基為主體之向列型棒狀液晶分子，改變2,3-鄰二氟苯基端與二苯基端之碳鏈長度，讓鄰二氟苯二炔基端烷氧基之碳數少於二苯基端的碳鏈長度，發現隨著碳數增加，熔點會隨之上升，而澄清點隨之下降，此系列化合物熔點範圍為86~113oC，澄清點溫度範圍為179~216 oC，液晶相溫度範圍在78~110 oC；其中以化合物14c的熔點和沸點溫度最高，14f最低，液晶相範圍也最窄，化合物14a則有最寬廣的液晶相溫度範圍。第三系列同樣以2,3-鄰二氟苯二炔基二苯基為主體，但相對碳鏈長度和前一系列相反，將鄰二氟苯二炔基端的碳數固定為6，二苯基端碳數分別為2與3，合成出向列型液晶化合物19a與19b，觀察到熔點與澄清點溫度均較前一系列化合物低，熔點溫度下降約20~30oC，澄清點溫度下降約50~70 oC，液晶相溫度範圍約36~57 oC之間，期望能應用在PDLC，反射式液晶顯示器，及紅外光調節器上。

Three series of liquid crystals were synthesized in this study. In the first part of this study, a rectangular liquid crystal, compound 8, with two ethynyl groups and two oxymethylene groups used to link to phenyl groups and biphenyl groups with the central phenyl core respectively exhibits smetic phases. This UV-curable liquid crystal has potential application in optical compensation film. In the second part of this study, we aim to synthesize two series of negative liquid crystals with either 4-(alkylbiphenylethynyl)-2,3-difluoro-1-alkoxybenzene (compound 14a-14f) or 4-(alkylbiphenylethynyl)-2,3-difluoro-1-n-hexylbenzene (compound 19a-19b) mesogenic core. All these two series of liquid crystals show s nematic phase. The melting points of compound 14a-14f are in the range of 86.8 to 119.5 ℃ while their isotropic temperatures are in the range from 179.6 to 215.4 ℃. Their mesogenic temperature ranges cover from 78 to 110 degrees. The milting points of compound 19a and 19b are 43.9 ℃ and 74.8 ℃ respectively while their clearing temperatures are 92 ℃ and 112 ℃. Their mesogenic temperature ranges cover from 36 to 57 degrees. They are suitable for formulating eutectic mixture and for the applications in PDLC, reflective liquid crystal display, and IR modulator.