Thermal and Electrooptical Properties of Ferroelectric Liquid Crystals Having OH Groups
作者:Kazuo Sugiyama、Koichi Kato、Kohei Shiraishi
DOI:10.1246/bcsj.64.1652
日期:1991.5
Four kinds of ferroelectric liquid crystals (FLCs) possessing OH groups, ((S)-2-methylbutyl 4-[4-(11-hydroxyundecyloxy)benzylideneamino]cinnamate 4a, (S)-2-methylbutyl 4-[4-(11-hydroxyundecyloxy)-2-hydroxybenzylideneamino]cinnamate 4b, (S)-2-hydroxypropyl 4-[4-(11-hydroxyundecyloxy)benzylideneamino]cinnamate 4c, and (S)-2-hydroxypropyl 4-[4-(11-hydroxyundecyloxy)-2-hydroxybenzylideneamino]cinnamate 4d) were prepared in order to understand how the introduction of OH groups in FLCs affect the phase behavior and electrooptical effects. α,ω-Diols 4c and 4d show a higher transition temperature of the smectic A (SA) phase than do ω-hydroxyl compounds 4a and 4b. Comparing 4b and 4d both of which have an OH group at the o-position of the benzylidene group with 4a and 4c, the former samples show a higher SA-isotropization (I) transition temperature than do the latter ones. It is suggested from IR spectroscopic results that inter- and intramolecular hydrogen bonding contribute to the stabilization of the SA phase. The order of the helical pitch in the chiral smectic C (Sc*) phase was found to be 4b>4a>4d>4c within 1.8–6.6 μm. From an electrooptical effect due to a deformation of the helical structure in the Sc phase, the rise time of the surface director (τsr) and the rise time of the bulk director (τbr) were measured to be as follows: τsr are 850, 1500, 30, and 70 μs, and τbr are 12, 100, 0.17, and 0.35 ms for 4a, 4b, 4c, and 4d, respectively. It was found that the intramolecular hydrogen bonding results in a slower optical response time, whereas intermolecular hydrogen bonding results in a faster one.
四种具有氢氧基(OH)团的铁电液晶(FLC)被制备,以了解在FLC中引入OH基团如何影响相行为和电光效应。这些液晶分别为((S)-2-甲基丁基 4-[4-(11-羟基十一烷氧基)苯亚胺基]肉桂酸酯 4a、(S)-2-甲基丁基 4-[4-(11-羟基十一烷氧基)-2-羟基苯亚胺基]肉桂酸酯 4b、(S)-2-羟基丙基 4-[4-(11-羟基十一烷氧基)苯亚胺基]肉桂酸酯 4c 和 (S)-2-羟基丙基 4-[4-(11-羟基十一烷氧基)-2-羟基苯亚胺基]肉桂酸酯 4d。α,ω-二醇 4c 和 4d 的层状相(SA)相转变温度高于ω-羟基化合物 4a 和 4b。比较4b和4d这两种在苯亚胺基o位具有OH基团的样品与4a和4c,前者在SA-各向同性(I)转变温度上高于后者。红外光谱结果表明,分子内和分子间氢键对SA相的稳定有贡献。发现螺旋层状相(Sc*)中的螺距顺序为4b>4a>4d>4c,范围在1.8–6.6微米。由于Sc相中螺旋结构的形变引起的电光效应,测得表面导向器(τsr)和体导向器(τbr)的上升时间分别为:4a、4b、4c 和 4d 的 τsr 分别为850、1500、30、70微秒,τbr 分别为12、100、0.17、0.35毫秒。研究发现,分子内氢键导致光学响应时间变慢,而分子间氢键则导致光学响应时间变快。