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Title page for etd-0628110-123640


URN etd-0628110-123640 Statistics This thesis had been viewed 1404 times. Download 5 times.
Author Min-tzu Chuang
Author's Email Address No Public.
Department Chemical Engineering
Year 2009 Semester 2
Degree Master Type of Document Master's Thesis
Language English Page Count 124
Title Study on the Mesophases and Electro-optical Properties of Chiral Liquid Crystals Possessing Lateral Chloromethyl Substituent at Chiral Center
Keyword
  • Ferroelectric liquid crystal
  • new chiral compounds
  • new chiral compounds
  • Ferroelectric liquid crystal
  • Abstract 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.
    Advisor Committee
  • Shune-long Wu - advisor
  • Mei-ching Yu - co-chair
  • Tien-jung Chen - co-chair
  • Files indicate in-campus access only
    Date of Defense 2010-04-30 Date of Submission 2010-06-28


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