新型乳酸衍生旋光性含硫烷鏈之液晶材料的合成與光電性質之研究

Syntheis and Properties of New Chiral Liquid Crystals Derived from (S)-Lactic Acid with 2-(Methylsulfanyl)-1-ethanol

蔡明允(Ming-Yun Tasi)

指導教授 ： 吳勛隆

大同大學/工程學院/化學工程學系所/碩士(2005年)

摘要

本研究主要是在說明旋光性層列相液晶其結構與性質之間的關係，以 (S)-lactic acid 為起始物合成一系列旋光性液晶材料，並分別探討（i）非旋光末端烷鏈長度’m’及（ii）在硬核中心導入氟側邊取代基對於液晶相及物理光電特性的影響，以建立分子結構與旋光液晶相的關係。
實驗結果顯示：第一、二系列液晶材料 I (m=8~12)、II (m=8~12)均出現SmA*和SmC*兩種液晶相。在第三系列III (m=10~12)出現了N*, TGBA*, SmA* 和SmC* 四種液晶相。改變非旋光末端烷鏈長度’m’，發現隨著非旋光末端烷鏈長度’m’的增加，液晶相的溫度範圍隨之降低，即澄清點溫度隨著降低、結晶點溫度隨著升高；在硬核中心的苯環上導入第二位置氟側邊取代基會降低相轉移溫度、熔點、澄清點溫度及自發性極化值。
三系列液晶化合物在SmC*液晶相進行光電量測時顯示在改變溫度和頻率下第I(m=9)和II(m=8, 9)可得到V型轉換行為，而電流轉換行為的量測結果則不會受到非旋光末端烷鏈長度’m’ 的改變和在硬核中心導入氟側邊取代基而有太大的差異。三系列(m=9~12)的自發性極化值最大值介於62.92~85.92 nC/cm2 和傾斜角最大值介於24o~32o。
綜合以上結果得知：苯環第二位置氟側邊取代之乳酸衍生旋光性液晶材料，具有寬廣溫度範圍，熔點可達室溫範圍的誘電性液晶相並且在光電量測產生V型光電轉換行為。

關鍵字

誘電性液晶

並列摘要

The primary of this research work was an attempt to elucidate the correlation between structure and property in the chiral smectic liquid crystal. A homologous series of chiral materials derived from (S)-lactic acid has been successfully synthesized and the structures-property relationship investigated in the chiral liquid crystal system. The target compounds were modified independently by (i) the nonchiral peripheral methylene chain length ‘m’ and (ii) the lateral substitution group in the core.
Chiral materials of two series I(m=8~12) and II(m=8~12) displayed enantiotropic mesophases of the SmA* and SmC* phases. The shorter chain members III(m=8, 9) of the third series III(m=8~12) displayed an enantiotropic phase sequence of SmA* and SmC* phases while the longer chain members III(m=10~12) exhibited enantiotropic phase sequence of N*, TGBA*, SmA* and SmC* phases. With the increasing nonchiral methylene chain lengths ‘m’, the temperature range of the mesophase decreases, and the clearing point decreases and the crystal point increases. The materials with lateral 2-fluoro substitution in the phenyl ring of core could depress the formation of mesophase, lowering the transition temperature, melting point, clearing point and Ps values.
The electro-optical response in the series of chiral materials in the SmC* phase displayed typical ferroelectric hysteresis loop or hysteresis-free, V-shaped switching property upon various applied frequencies and temperatures. The maximum Ps values of I(m=9~11), II(m=9~11) and III(m=9~11) vary form 62.92~85.92 nC/cm2 and the maximum optical tilt angle values of the compounds I, II, III(m=9~11) were between 24o~32o.
In conclusion, the results indicated that the chiral alklysulfanyl chain materials derived from (S)-lactic acid with the lateral 2-fluoro substitution in the phenyl ring of core was favorable for the formation of the wide temperature range of the ferroelectric phase. V-shaped switching behaviors appear in the SmC* phase of the chiral materials of the series I(m=9) and II(m=8, 9).

並列關鍵字

liquid crystal

參考文獻

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