高折射率液晶化合物合成與鑑定

Abstract

本研究之主要目的為合成三個系含側向甲基及乙基取代之三苯基雙乙炔液晶化合物。第一系列化合物在中間苯環導入一乙基作為側取代基，及不對稱的雙烷基為末端基。這系列化合物的熔點可低至20-73℃，澄清點在105-141℃之間；液晶相範圍非常寬廣，可達55-97度。其中不對稱性較高的化合物在室溫即呈液晶相，其介電異方性約為0.85，雙折射率約為0.4左右。 第二系列化合物在中間苯環含一乙基為側取代基，末端基一端為烷基，另一為極性的氟基或氰基。所合成的含氟化合物，其熔點在46-75℃之間，澄清點在89-113℃之間。含氰化合物的熔點在77-102℃之間，澄清點在131-161℃之間，兩系列化合物都比前一系列有較高之相轉移溫度，主要是因其含有強極性基，尤其是氰基化合物，其介電異向性高達14，雙折射率達0.4以上。 第三系列化合物則在中間苯環含一甲基為側取代基，末端基一端為烷基，另一為極性的氟基或氰基。本系列含氟化合物的熔點在69-103℃之間，澄清點在150-183℃之間。而含氰化合物的熔點在100-148℃之間，澄清點在203-212℃之間，這一系列化合物又比第二系列化合物相轉移溫度高，由此可見導入一較大之烷基作為側取代基，可以有效的降低其熔點。本研究所合成之部份三苯基雙乙炔液晶化合物具有接近室溫之熔點、低焓值、寬廣之液晶範圍及高雙折射率，可用於調配液晶共融物，以進一步應用在PDLC，反射式液晶顯示器，及紅外光調節器上。

The goal of this study is aimed to synthesize three series of highly conjugated bistolane liquid crystals (LC) with lateral ethyl and methyl substituents. The first series of liquid crystal compounds contain a lateral ethyl substituent on the middle phenyl ring and two asymmetric alkyl groups on both ends. The synthesized liquid crystals present respectively a relatively lower melting point (20-73℃), and exhibit a very wide nematic temperature range (about 55-97degree). Their dielectric anisotropy and birefringence are 0.85 and 0.4 respectively. The second series of bistolane compounds contain a lateral ethyl on the middle phenyl ring and an alkyl on one end and a fluoro or cyano group on the other end. The fluorinated bistolane compounds exhibit melting points ranging from 46 to 75℃, and clearing points ranging from 89 to 113℃. Whereas the cyano bistolane compounds exhibit melting points ranging from 77 to 102℃, and clearing points ranging from 131 to 161℃. Both series of compounds show much higher phase transition temperatures than the dialkyl bistolane compounds. The reason could be due to the strong polar fluoro and cyano end groups. The measured dielectric anisotropy and birefringence of cyano bistolane compounds are 14 and 0.4 respectively. The third series LC compound contain a lateral methyl substituent on the middle phenyl ring and an alkyl group on one end and a fluoro or cyano group on the other end. The obtained fluorinated bistolane compounds exhibit melting points ranging from 69 to103℃, and clearing points ranging from 150 to 183℃. Whereas the cyano bistolane compounds exhibit melting points ranging from 100 to 148℃, and clearing points ranging from 203 to 212℃. If we compare this series of bistolane compounds with corresponding bistolane compound in the second series, we found that the compounds with a bulky lateral ethyl substituent show much lower phase transition temperatures. The properties of the synthesized liquid crystals which exhibit wide nematic range, small heat fusion enthalpy, high birefringence and modest viscosity are suitable for formulating eutectic mixture and for further application in PDLC, reflective liquid crystal display, and IR modulator.