- 學位論文
設計與合成具有醚基結構的藍相液晶材料及其性質的探討
Design,synthesis and investigation on the blue phase liquid crystal materials with ether linkage
摘要
中文摘要 本研究是以(S)-propylene oxide為起始物合成五個系列的液晶化合物，藉由分子結構的改變，設計出具有高旋光度的藍相液晶材料，並探討(i)非旋光末端烷鏈長度‘m’，(ii)具有醚基結構的旋光烷鏈和(iii)醚基結構旋光烷鏈長度‘n’以及(iv)硬核由雙苯環取代萘環等對其液晶相及其性質的影響，以建立分子結構與液晶相的關係。五系列液晶化合物其結構如下: 實驗結果顯示:化合物I(m=6)有出現BPIII-BPII-N*的液晶相順序，化合物I(m=7)有BPII-BPI-N*的液晶相順序，化合物I(m=8, 9)有BPII-BPI-N*-TGBA*-SmA*的液晶相順序，當I(m=8)時，具有最寬廣的雙向性BPII和BPI液晶相，同時也證實了以上所合成的材料是具有高旋光度(high chirality)的液晶材料。 第二系列的化合物是將旋光部分改為具有醚基結構的旋光烷鏈，結果顯示化合物II(m=6, n=4)具有BPII-BPI-N*的液晶相順序，化合物II(m=7, 8, 9, n=4)時，則有BPII-BPI-N*-TGBA*的液晶相順序，當II(m=8, n=4)時有額外的SmA*液晶相的生成。以上所合成的化合物都具有雙向性的BPII和BPI液晶相，當m=7到m=8和m=9的時候，BPI和TGBA*液晶相的溫度範圍會隨之增加。將旋光烷鏈長度(n)延長，TGBA*液晶相的溫度範圍會降低並且在n=5和n=6時，無BPI液晶相的生成。當n=4的時具有最寬廣的挫敗相(frustrated phases)。 第五系列化合物和第二系列化合物具有相同的旋光結構，差異性在於化合物V(m)是將硬核結構由PhCOONa改為PhCOOPhPh，結果顯示化合物V(m=7, 8, 9, n=4)時，有 BPII-BPI-N*-SmC*的液晶相順序，當V(m=9, n=4)時，有BPIII液晶相的存在。相較於化合II(m)，V(m)藍相液晶相的溫度範圍降低且抑制了TGBA*液晶相的生成。 材料的物理性質如電流轉換行為、自發性極化值、介電常數皆與誘電性SmC*液晶相下量測。五個系列液晶化合物的最大值範圍介21.7-28.5 (nC/cm2)之間。結果顯示非旋光末端烷鏈長度的改變對最大Ps無顯著規則性。 總而言之，旋光材料中有PhCOONa的硬核結構與醚基結構的光學活性醇 (optically active alcohol)連接，會有較寬廣的挫敗相(frustrated phases)生成。非旋光末端烷鏈的鏈長‘m’的改變，對藍相液晶相的溫度範圍無顯著規則性。旋光烷鏈的鏈長(n)的減短,挫敗相的溫度範圍會隨之增加。五系列化合物中,II(m=7, n=4)具有最寬廣的雙向性藍相液晶相(約為12.5℃)。 關鍵字: 旋光性材料、藍相、挫敗相、光電性質、電流轉換行為、介電常數
並列摘要
ABSTRACT The primary research work of this study is an attempt to correlate the structure-property relationship of the formation of blue phases in chiral liquid crystals in terms of variation of the structure of the rigid cord, achiral alkyl chain length (m) and chiral alkyl chain length (n) possessing ether linkage attached to the chiral tail in the chiral liquid crystal materials. Thus, the optically active alcohols, 2-octanol, 1-butyloxy-2-propanol, 1-pentyloxy-2-propanol, 1-hexyloxy-2-propanol, were designed and synthesized by reacting (S)-propylene oxide with alkyl alcohols under basic condition. In consequence, five novel homologous series of chiral materials, (R)-6-(1-methylheptyloxy)naphth-2-yl 4’-octyloxybenzoate, I(m), (R)-6-(1-butyloxy-2-propyl)naphth-2-yl 4-octyloxybenzoate, II(m), (R)-6-(1-pentyloxy-2-propyl)naphth-2-yl 4-octyloxybenzoate, III(m), (R)-6-(1-hexyloxy-2-propyl)naphth-2-yl 4-octyloxybenzoate, IV(m), (R)-4-(1-butyloxy-2-propyl)biphenyl 4-octyloxybenzoate, V(m), derived from these alcohols were synthesized for the investigation of the effect of the aliphatic alkyl chain length (m), ether linking group, chiral tail alkyl chain length (n) and rigid core structures on the mesomorphic and electro-optical properties. The mesomorphic phases and their corresponding transition temperatures were primarily characterized by the microscopic textures and DSC thermograms, and the ferroelectric phases were further identified by the measurements of electric switching behavior and dielectric constant ε'. The results of compounds I(m) composed of the rigid core structure of PhCOONa and chiral group of optical activity 2-octanol, showed that compound I(m=6) exhibits the mesophases sequence of BPIII-BPII-N*, compound I(m=7) exhibits the mesophases sequence of BPII-BPI-N* and compounds I(m=8,9) exhibits the mesophases sequence of BPII-BPI-N*-TGBA*-SmA*. With the exception of I(m=8) that exists the widest temperature range of enantiotropic BPII and BPI phases, the rest of compounds in series of I(m) possess BPII and BPI phases are monotropic. Compounds I(m) display frustrated phases demonstrated that these compounds possess high chirality. The results of compound II(m=6, n=4), composed of the same rigid core structure as compound I(m) but differed in the chiral group where an additional ether linkage is introduced, shows the mesophases sequence of BPII-BPI-N*, compounds II(m=7, 8, 9, n=4) exhibit the mesophases sequence of BPII-BPI-N*-TGBA* and compound II(m=8, n=4) displayed an additional SmA* phase. All compounds posses enantiotropic BPII and BPI phases and the thermal stability of BPI and TGBA* phases increase from compounds at m=7 to m=8 and m=9. When extending the alkyl length (n) of chiral tail, the thermal stability of TGBA* phase decreases and when n=5 and 6, the BPI is suppressed. The widest temperature range of frustrated (BP and TGBA*) phases for these compounds appeared at n=4. The results of compounds V(m=7-9, n=4), composed of the same chiral group but differed in the rigid core structure (PhCOOPhPh) as compounds II(m), show the mesophases sequence of BPII-BPI-N*-SmC*, compound V(m=9, n=4) exhibit an additional BPIII phase. The thermal stability of BPII and BPI phases obtained from compounds V(m) are decreased and the TGBA* phase is suppressed as compared to that of compounds II(m). The physical properties of the chiral materials in ferroelectric SmC* phases were measured. The maximum magnitudes of spontaneous polarization measured for the materials in the SmC* phase are in the range of 21.7 to 28.5 (nC/cm2). These results also show that the maximum Ps values have no significant correlation to the change of achiral alkyl chain length (m). In conclusion, the chiral materials composed of the rigid core structure of PhCOONa and the chiral group of an additional ether linkage at terminal tail of the molecules, have higher thermal stability of frustrated (BP and TGBA*) phases. All series of compounds display that achiral alkyl chain length (m) of the molecules have no correlation to the thermal stability of the frustrated phases, nevertheless, chiral alkyl chain length (n) of molecules show an increasing in thermal stability of frustrated phases in decreasing n. Among all compounds, compound II(m=7, n=4) has the widest temperature range of enantiotropic blue phases (cal. 12.5℃). Keywords: Chiral material, Blue phase, frustrated phases, electro-optical property, switching behavior, dielectric constant ε’