Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center

碩士 === 大同大學 === 化學工程學系(所) === 98 === There are many factors affect the properties of ferroelectric chiral smectic C phase such as chiral group, core structure, linking group, terminal chain length and optical purity. Liquid crystal molecule with extending or increasing size of lateral substituent or...

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Main Authors: Min-tzu Chuang, 莊敏慈
Other Authors: Shune-long Wu
Format: Others
Language:en_US
Published: 2010
Online Access:http://ndltd.ncl.edu.tw/handle/80428901787853981867
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description 碩士 === 大同大學 === 化學工程學系(所) === 98 === There are many factors affect the properties of ferroelectric chiral smectic C phase such as chiral group, core structure, linking group, terminal chain length and optical purity. Liquid crystal molecule with extending or increasing size of lateral substituent or incorporation of a halogen lateral substituent at chiral center may cause some degree of steric asymmetry when packed together and it is easy to form the zigzag-shaped arrangement that facilitates the formation of antiferroelectric phase while it possesses swallow-tailed structure at chiral terminal group. For these reasons, the purpose of this research is looking for a better understanding the relationship between molecular structures and mesomorphic properties. Thus, new chiral precursor, (S)-1-alkyloxy-3-chloro-2-propanols and (S)-1-(1-ethylpropoxy)-3-chloro-2-propanal containing chlomethyl chiral group were designed and synthesized by the reaction of (S)-epichlorohydrin with alcohols under the acid condition. Consequently, six homologous series of chiral compounds, (R)-1-alkyloxy-3-chloro-2-propyl 4-{4’-[(4’’-alkyloxyphenyl)phenylcarbonyloxy]} benzoates, I(m=8-12, n=3), II(m=8-12, n=4) , III(m=8-12, n=5) , IV(m=8-12, n=6) and V(m=8-12, n=8), and (R)-1-(1-ethylpropoxy)-3-chloro-2-propyl4-{4’-[(4’’- alkyloxyphenyl)phenylcarbonyloxy]}benzoates, VI(m=8-12), were preparared for the study. The effect of changing chiral groups from methyl to chloromethyl groups at asymmetric carbon, achiral alkyl chain length (m) and chiral alkyl chain length (n) of the chiral compounds on the mesomorphic and electro-optical properties were compared and discussed. In addition, the effect of changing chiral terminal alkyl chain to swallow-tailed structure on the mesophases and electro-optical properties was also investigated. The results show that with the exception of compound VI(m=8) which displays the phase sequence of Iso.-SmA*-SmC*-SmX*-Cr., the rest of compounds display the phase sequence of Iso.-SmA*-SmC*-Cr.. The comparison of chiral compounds with different chiral chain length (n=3, 4, 5, 6, 8) shows the temperature of clearing point, the melting point and the transition temperature of SmA*- SmC* decrease with increasing terminal chiral chain. The maximum magnitudes of the spontaneous polarization for the chiral compounds, I(m=8-12, n=3), II(m=8-12, n=4), III(m=8-12, n=5), IV(m=9-12, n=6) and V(m=8-12, n=8), display an odd-even effect in which compounds with even numbers (n=4, 6, 8) of chiral alkyl chain length have the larger Ps values than that with odd numbers (n=3, 5), but the optical tilt angles exhibit no significant correlation change with chiral and achiral chain length. The comparison of structurally similar chiral compounds between compounds with chloromethyl substituent and that with methyl substituent at the asymmetric carbon of the chiral groups shows that the formers have narrower temperature range of mesophases as well as SmC* phase, higher melting point and lower clearing point than the later ones. In addition, the SmX* phase was suppressed. The electro-optical measurements show that the maximum Ps values and the optical tilt angles are larger for compounds with chloromethyl group than that with methyl group. This may be presumably due to the larger size and/or electronegativity of the chlorine atom than hydrogen atom (Size: H=1.25Å, Cl=1.75Å; Electronegativity: H=2.1, Cl=3.0). When comparing structurally similar chiral swallow-tailed compounds between compounds with chloromethyl group and that with methyl group at the asymmetric carbon, the results show that the formers have wider temperature range of the SmC* phase, lower melting point and clearing point than the later ones, but the chiral swallow-tailed compounds with methyl substituent have wider temperature range of the SmCA* phase. Furthermore, the SmX* phase of the compounds with chloromethyl group only appears at short achiral alkyl chain length (m=8). Therefore, compounds with chloromethyl substituent suppress the existence of SmCA* and SmX* phases. The electro-optical measurements show that the larger size and higher electronegativity of chlorine atom (Size: H=1.25Å, Cl=1.75Å; Electronegativity: H=2.1, Cl=3.0) have no significant effect to the spontaneous polarization and the apparent tilt angle in the homolog series of swallow-tailed compounds.
author2 Shune-long Wu
author_facet Shune-long Wu
Min-tzu Chuang
莊敏慈
author Min-tzu Chuang
莊敏慈
spellingShingle Min-tzu Chuang
莊敏慈
Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center
author_sort Min-tzu Chuang
title Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center
title_short Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center
title_full Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center
title_fullStr Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center
title_full_unstemmed Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center
title_sort study on the mesophases and electro-optical properties of chiral liquid crystals possessing lateral chloromethyl substituent at chiral center
publishDate 2010
url http://ndltd.ncl.edu.tw/handle/80428901787853981867
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spelling ndltd-TW-098TTU050630022016-04-22T04:23:13Z http://ndltd.ncl.edu.tw/handle/80428901787853981867 Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center 探討具有氯化甲烷基為旋光中心側邊取代基之旋光性液晶材料的合成及其液晶相和光電性質 Min-tzu Chuang 莊敏慈 碩士 大同大學 化學工程學系(所) 98 There are many factors affect the properties of ferroelectric chiral smectic C phase such as chiral group, core structure, linking group, terminal chain length and optical purity. Liquid crystal molecule with extending or increasing size of lateral substituent or incorporation of a halogen lateral substituent at chiral center may cause some degree of steric asymmetry when packed together and it is easy to form the zigzag-shaped arrangement that facilitates the formation of antiferroelectric phase while it possesses swallow-tailed structure at chiral terminal group. For these reasons, the purpose of this research is looking for a better understanding the relationship between molecular structures and mesomorphic properties. Thus, new chiral precursor, (S)-1-alkyloxy-3-chloro-2-propanols and (S)-1-(1-ethylpropoxy)-3-chloro-2-propanal containing chlomethyl chiral group were designed and synthesized by the reaction of (S)-epichlorohydrin with alcohols under the acid condition. Consequently, six homologous series of chiral compounds, (R)-1-alkyloxy-3-chloro-2-propyl 4-{4’-[(4’’-alkyloxyphenyl)phenylcarbonyloxy]} benzoates, I(m=8-12, n=3), II(m=8-12, n=4) , III(m=8-12, n=5) , IV(m=8-12, n=6) and V(m=8-12, n=8), and (R)-1-(1-ethylpropoxy)-3-chloro-2-propyl4-{4’-[(4’’- alkyloxyphenyl)phenylcarbonyloxy]}benzoates, VI(m=8-12), were preparared for the study. The effect of changing chiral groups from methyl to chloromethyl groups at asymmetric carbon, achiral alkyl chain length (m) and chiral alkyl chain length (n) of the chiral compounds on the mesomorphic and electro-optical properties were compared and discussed. In addition, the effect of changing chiral terminal alkyl chain to swallow-tailed structure on the mesophases and electro-optical properties was also investigated. The results show that with the exception of compound VI(m=8) which displays the phase sequence of Iso.-SmA*-SmC*-SmX*-Cr., the rest of compounds display the phase sequence of Iso.-SmA*-SmC*-Cr.. The comparison of chiral compounds with different chiral chain length (n=3, 4, 5, 6, 8) shows the temperature of clearing point, the melting point and the transition temperature of SmA*- SmC* decrease with increasing terminal chiral chain. The maximum magnitudes of the spontaneous polarization for the chiral compounds, I(m=8-12, n=3), II(m=8-12, n=4), III(m=8-12, n=5), IV(m=9-12, n=6) and V(m=8-12, n=8), display an odd-even effect in which compounds with even numbers (n=4, 6, 8) of chiral alkyl chain length have the larger Ps values than that with odd numbers (n=3, 5), but the optical tilt angles exhibit no significant correlation change with chiral and achiral chain length. The comparison of structurally similar chiral compounds between compounds with chloromethyl substituent and that with methyl substituent at the asymmetric carbon of the chiral groups shows that the formers have narrower temperature range of mesophases as well as SmC* phase, higher melting point and lower clearing point than the later ones. In addition, the SmX* phase was suppressed. The electro-optical measurements show that the maximum Ps values and the optical tilt angles are larger for compounds with chloromethyl group than that with methyl group. This may be presumably due to the larger size and/or electronegativity of the chlorine atom than hydrogen atom (Size: H=1.25Å, Cl=1.75Å; Electronegativity: H=2.1, Cl=3.0). When comparing structurally similar chiral swallow-tailed compounds between compounds with chloromethyl group and that with methyl group at the asymmetric carbon, the results show that the formers have wider temperature range of the SmC* phase, lower melting point and clearing point than the later ones, but the chiral swallow-tailed compounds with methyl substituent have wider temperature range of the SmCA* phase. Furthermore, the SmX* phase of the compounds with chloromethyl group only appears at short achiral alkyl chain length (m=8). Therefore, compounds with chloromethyl substituent suppress the existence of SmCA* and SmX* phases. The electro-optical measurements show that the larger size and higher electronegativity of chlorine atom (Size: H=1.25Å, Cl=1.75Å; Electronegativity: H=2.1, Cl=3.0) have no significant effect to the spontaneous polarization and the apparent tilt angle in the homolog series of swallow-tailed compounds. Shune-long Wu 吳勛隆 2010 學位論文 ; thesis 124 en_US