新型(S)-1-甲基-2-[(2’-甲氧基)乙氧基]乙醇衍生之旋光性液晶材料的合成與光電性質之研究

Ferroelectric and Antiferroelectric Properties of Novel Chiral Liquid Crystals Derived from (S)-1-methyl-2-[(2'-methoxy)ethoxy]ethanol

李明澈(Ming-Che Li)

指導教授 ： 吳勛隆

大同大學/工程學院/化學工程學系所/碩士(2006年)

摘要

本研究主要以具有光學活性之(S)-1-methyl-2-[(2'-methoxy)ethoxy]ethanol 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：第一系列液晶材料I(m=8-12)具有SmA*-SmC*-SmX*的液晶相順序。第二系列液晶材料II(m=8-12)除了II (m=9)額外出現SmX*液晶相外，都具有SmA*-SmC*的液晶相順序。第三系列液晶材料III(m=8-12)在非旋光末端烷鏈碳數為8、9時出現 SmA*-SmCA*的液晶相順序，當碳數為10-12時出現出現SmA*-SmC*的液晶相順序。改變非旋光末端烷鏈長度’m’，可發現增加非旋光烷鏈的長度於第一、三系列液晶材料I,III (m=8-12)，SmC*相的熱穩定性會增加但是SmA*的溫度範圍卻會變窄；於第二系列液晶材料II(m=8-12)，因為SmC*-Cr.的相轉移溫度升高，因此減少了SmC*的溫度範圍。
此外,在硬核中心的苯環上導入第二、三位置氟側邊取代基會影響液晶相的生成與降低相轉移溫度、熔點及澄清點溫度。苯環第二位置之氟側邊取代基因受到遮蔽效應的影響，故部份相轉移溫度明顯的高於苯環上第三位置取代基的化合物。
光電應答的研究顯示：化合物II(m=11) 於SmC*液晶相中可得到V型光電轉換行為，而化合物III(m=9)於SmCA*液晶相中可得到U型與雙遲滯光電轉換行為。比較三系列液晶材料(m=8-12)可發現當化合物導入氟側邊取代基時，會有較低的自發性極化值與較大的傾斜角。在自發性極化值方面三系列化合物(m=9-12)最大值的介於6-16 nC/cm2，而三系列化合物(m=8-12)的傾斜角最大值介於20-30o。

關鍵字

誘電性液晶 ； 反誘電性液晶 ； 無閥V型光電轉換行為 ； 含氧烷鏈

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 optically active (S)-1-methyl-2-[(2’-methoxy) ethoxy]ethanol 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 achiral peripheral methylene chain length ‘m’ and (ii) the lateral fluoro substituents in the phenyl ring of the core.
The results showed that compounds I(m=8-12) exhibited the phases sequence of SmA*-SmC*-SmX*, compounds II(m=8-12) exhibited the phases sequence of SmA*-SmC*, while the compound II(m=9) posesses an additional SmX*. In the compounds III(m=8-12), compounds III (m=8, 9) with shorter alkyl chain displayed an enantiotropic phase sequence of SmA*-SmCA* while compounds III(m=10-12) with longer alkyl chain exhibited enantiotropic phase sequence of SmA*-SmC*. Extending achiral alkyl chain length in compounds I(m=8-12) and III(m=8-12) stabilizes the temperature ranges of SmC* phase, but suppresses the formation of SmA* phase. In compounds II(m=8-12), as the achiral alkyl chains are extended, the transition temperatures of SmC*-Cr are increased but the temperatures ranges of SmC* phase are decreased.
The compounds with lateral fluoro substituents in the phenyl ring of core could affect the formation of the mesophase, lower the transition temperatures, melting points and clearing points. Moreover, the phenyl ring with 2-fluoro substituent possesses higher transition temperature than that with 3-fluoro substituent, suggesting that molecular broadening minimized due to the sterically shielded of 2-flueoro substituent.
The electro-optical responses of chiral compound II(m=11) in the SmC* phase displayed V-shaped switching behavior, chiral compound III(m=9) in the SmCA* phase displayed U-shaped and double hysteresis loop switching behavior. Comparison of compounds I,II, III(m=8~12) clearly show that the compounds I(m=8-12) have higher Ps values than the compounds II, III(m=8-12), suggesting that compounds with the lateral fluoro substituents could suppress the polarity of the transverse dipole. The maximum Ps values of I, II, III(m=9-12) are about 6-16 nC/cm2. The compounds III(m=8-12) with 3-fluoro substituent have higher tilt angle than the compounds I, II(m=8-12). The maximum optical tilt angle values of the compounds I, II, III (m=8-12) were between 20-30o.

並列關鍵字

antiferroelectrics ； ferroelectrics ； V-shaped switching

參考文獻

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