Studies on Substituent Effect of Banana-Shaped Liquid Crystals

• Main Authors: Chin-Wei Lu, 陸勤偉
• Other Authors: 劉廣定
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/06680921909413786616

碩士 === 國立臺灣大學 === 化學研究所 === 91 === Abstract Designed molecules which might have special optical and electric properties such as ferroelectric have attracted much attention due to their potential applications. Studies in this thesis focuses on the substituent effect on the mesomorphic properties of banana-shaped liquid crystalline molecules. In 1996 Niori et al. reported on ferroelectricity in a smectic phase formed by banana-shaped Schiff-base derivatives. A major drawback of these compounds is their limited thermal, hydrolytic and photochemical stability. Therefore, we used ester-linkage in place of Schiff-base and introduced a series of functional groups to banana-shaped molecules. The results suggest that the presence of substituents destabilizes the crystal phases leading to lower the transition temperature between crystal and mesophases. It likely that e-withdrawing substituents in C-4 position of banana-shaped molecules increase intermolecular attracting forces result in liquid crystal phases be produced. In addition, bulkier substituents in the banana-shaped molecules raise intermolecular repulsions, which lead to the disappearance of mesophases. Further, it may be good for packing when substituents in C-5 position which due to phase change from isotropic to crystal directly. Finally we found that central ring of banana-shaped molecules with nitrogen were unfavorable to stabilize liquid crystal phase.