Non-symmetric liquid crystal dimers containing an isoflavone moiety

Tze-Nee Chan, Zhibao Lu, Wan-Sinn Yam, Guan-Yeow Yeap, Corrie T. Imrie

Research output: Contribution to journalArticle

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Abstract

The first series of liquid crystal dimers to contain an isoflavone-based moiety has been prepared, the alpha-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-omega-(4-methoxyazobenzene-4'-oxy)alkanes. All eight members of this homologous series exhibit an enantiotropic nematic phase. The nematic-isotropic transition temperatures and associated entropy changes exhibit a dramatic dependence on the length and parity of the flexible spacer. This characteristic behaviour for a homologous series of liquid crystal dimers has been interpreted in terms of how the flexible alkyl spacer controls the average molecular shape. A comparison of the transitional properties of this series with those of the symmetric parent dimers, the alpha,omega-bis(4-methoxyazobenzene-4'-oxy) alkanes, reveals that replacing a methoxyazobenzene unit by the isoflavone-based group reduces the melting point but increases the nematic-isotropic transition temperature. Three other non-symmetric dimers are reported: 1-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-9-(4-cyanobiphenyl-4'-oxy) nonane, 1-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy)-10-(4-nitroazobenzene-4'-oxy) decane and cholesteryl 11-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy) undecanoate. The former two show enantiotropic nematic behaviour while the latter exhibits an enantiotropic chiral nematic phase. Again, when compared with the parent symmetric dimer, a reduction in melting point is observed while the clearing temperature is increased. The trend in the melting points is accounted for in terms of the difficulties associated with packing the non-symmetric dimers into a crystalline lattice compared to the symmetric dimers. The physical significance of the increase in the clearing temperatures is not yet clear.

Original languageEnglish
Pages (from-to)393-402
Number of pages10
JournalLiquid Crystals
Volume39
Issue number3
Early online date13 Feb 2012
DOIs
Publication statusPublished - 2012

Keywords

  • isoflavone
  • liquid crystal dimers
  • odd-even effects
  • non-symmetric
  • banana-calamitic dimers
  • charge-transfer groups
  • mesomorphic properties
  • mesogenic properties
  • mesophase behavior
  • cholesterol
  • derivatives
  • monomers
  • trimers
  • tetramers

Cite this

Non-symmetric liquid crystal dimers containing an isoflavone moiety. / Chan, Tze-Nee; Lu, Zhibao; Yam, Wan-Sinn; Yeap, Guan-Yeow; Imrie, Corrie T.

In: Liquid Crystals, Vol. 39, No. 3, 2012, p. 393-402.

Research output: Contribution to journalArticle

Chan, Tze-Nee ; Lu, Zhibao ; Yam, Wan-Sinn ; Yeap, Guan-Yeow ; Imrie, Corrie T. / Non-symmetric liquid crystal dimers containing an isoflavone moiety. In: Liquid Crystals. 2012 ; Vol. 39, No. 3. pp. 393-402.
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abstract = "The first series of liquid crystal dimers to contain an isoflavone-based moiety has been prepared, the alpha-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-omega-(4-methoxyazobenzene-4'-oxy)alkanes. All eight members of this homologous series exhibit an enantiotropic nematic phase. The nematic-isotropic transition temperatures and associated entropy changes exhibit a dramatic dependence on the length and parity of the flexible spacer. This characteristic behaviour for a homologous series of liquid crystal dimers has been interpreted in terms of how the flexible alkyl spacer controls the average molecular shape. A comparison of the transitional properties of this series with those of the symmetric parent dimers, the alpha,omega-bis(4-methoxyazobenzene-4'-oxy) alkanes, reveals that replacing a methoxyazobenzene unit by the isoflavone-based group reduces the melting point but increases the nematic-isotropic transition temperature. Three other non-symmetric dimers are reported: 1-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-9-(4-cyanobiphenyl-4'-oxy) nonane, 1-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy)-10-(4-nitroazobenzene-4'-oxy) decane and cholesteryl 11-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy) undecanoate. The former two show enantiotropic nematic behaviour while the latter exhibits an enantiotropic chiral nematic phase. Again, when compared with the parent symmetric dimer, a reduction in melting point is observed while the clearing temperature is increased. The trend in the melting points is accounted for in terms of the difficulties associated with packing the non-symmetric dimers into a crystalline lattice compared to the symmetric dimers. The physical significance of the increase in the clearing temperatures is not yet clear.",
keywords = "isoflavone, liquid crystal dimers, odd-even effects, non-symmetric, banana-calamitic dimers, charge-transfer groups, mesomorphic properties, mesogenic properties, mesophase behavior, cholesterol, derivatives, monomers, trimers, tetramers",
author = "Tze-Nee Chan and Zhibao Lu and Wan-Sinn Yam and Guan-Yeow Yeap and Imrie, {Corrie T.}",
note = "Acknowledgements CTI and GYY gratefully acknowledge the funding of this research under a PMI2 Research Co-operation (British Council) award. GYY would also like to thank Universiti Sains Malaysia for providing the supporting funding through RU Research Grant (No. 1001/PKIMIA/811159).",
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AU - Chan, Tze-Nee

AU - Lu, Zhibao

AU - Yam, Wan-Sinn

AU - Yeap, Guan-Yeow

AU - Imrie, Corrie T.

N1 - Acknowledgements CTI and GYY gratefully acknowledge the funding of this research under a PMI2 Research Co-operation (British Council) award. GYY would also like to thank Universiti Sains Malaysia for providing the supporting funding through RU Research Grant (No. 1001/PKIMIA/811159).

PY - 2012

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N2 - The first series of liquid crystal dimers to contain an isoflavone-based moiety has been prepared, the alpha-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-omega-(4-methoxyazobenzene-4'-oxy)alkanes. All eight members of this homologous series exhibit an enantiotropic nematic phase. The nematic-isotropic transition temperatures and associated entropy changes exhibit a dramatic dependence on the length and parity of the flexible spacer. This characteristic behaviour for a homologous series of liquid crystal dimers has been interpreted in terms of how the flexible alkyl spacer controls the average molecular shape. A comparison of the transitional properties of this series with those of the symmetric parent dimers, the alpha,omega-bis(4-methoxyazobenzene-4'-oxy) alkanes, reveals that replacing a methoxyazobenzene unit by the isoflavone-based group reduces the melting point but increases the nematic-isotropic transition temperature. Three other non-symmetric dimers are reported: 1-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-9-(4-cyanobiphenyl-4'-oxy) nonane, 1-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy)-10-(4-nitroazobenzene-4'-oxy) decane and cholesteryl 11-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy) undecanoate. The former two show enantiotropic nematic behaviour while the latter exhibits an enantiotropic chiral nematic phase. Again, when compared with the parent symmetric dimer, a reduction in melting point is observed while the clearing temperature is increased. The trend in the melting points is accounted for in terms of the difficulties associated with packing the non-symmetric dimers into a crystalline lattice compared to the symmetric dimers. The physical significance of the increase in the clearing temperatures is not yet clear.

AB - The first series of liquid crystal dimers to contain an isoflavone-based moiety has been prepared, the alpha-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-omega-(4-methoxyazobenzene-4'-oxy)alkanes. All eight members of this homologous series exhibit an enantiotropic nematic phase. The nematic-isotropic transition temperatures and associated entropy changes exhibit a dramatic dependence on the length and parity of the flexible spacer. This characteristic behaviour for a homologous series of liquid crystal dimers has been interpreted in terms of how the flexible alkyl spacer controls the average molecular shape. A comparison of the transitional properties of this series with those of the symmetric parent dimers, the alpha,omega-bis(4-methoxyazobenzene-4'-oxy) alkanes, reveals that replacing a methoxyazobenzene unit by the isoflavone-based group reduces the melting point but increases the nematic-isotropic transition temperature. Three other non-symmetric dimers are reported: 1-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-9-(4-cyanobiphenyl-4'-oxy) nonane, 1-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy)-10-(4-nitroazobenzene-4'-oxy) decane and cholesteryl 11-(4'-methoxy- 3-phenyl-4H-1-benzopyran-4-one-7-oxy) undecanoate. The former two show enantiotropic nematic behaviour while the latter exhibits an enantiotropic chiral nematic phase. Again, when compared with the parent symmetric dimer, a reduction in melting point is observed while the clearing temperature is increased. The trend in the melting points is accounted for in terms of the difficulties associated with packing the non-symmetric dimers into a crystalline lattice compared to the symmetric dimers. The physical significance of the increase in the clearing temperatures is not yet clear.

KW - isoflavone

KW - liquid crystal dimers

KW - odd-even effects

KW - non-symmetric

KW - banana-calamitic dimers

KW - charge-transfer groups

KW - mesomorphic properties

KW - mesogenic properties

KW - mesophase behavior

KW - cholesterol

KW - derivatives

KW - monomers

KW - trimers

KW - tetramers

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DO - 10.1080/02678292.2012.658712

M3 - Article

VL - 39

SP - 393

EP - 402

JO - Liquid Crystals

JF - Liquid Crystals

SN - 0267-8292

IS - 3

ER -