Cholesteryl-based liquid crystal dimers containing a sulfur-sulfur link in the flexible spacer

Huey-Charn Lee, Zhibao Lu, Peter A. Henderson, Marie France Achard, Wan Ahmad Kamil Mahmood, Guan-Yeow Yeap, Corrie T. Imrie

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Abstract

Seven members of the homologous series of the liquid crystal dimers, the bis(omega-(cholesteryloxycarbonyl) alkyl) disulfides, which contain a sulfur-sulfur link in the flexible spacer have been synthesised and their liquid crystal properties characterised. The dimers are referred to using the acronym Chol-n-SS-n-Chol in which n denotes the number of carbon atoms linking the cholesteryl-based groups and the sulfur atoms, and was varied between 3, 5, 6, 8, 10, 11 and 12. All seven homologues exhibit a chiral nematic phase and for the longest three members a smectic A phase was also observed. An odd-even effect is apparent in both the transition temperatures and the values of the entropy change associated with the chiral nematic-isotropic transition, Delta S-N*I/R, in which dimers with even values of n show the higher values. This is interpreted in terms of the average molecular shapes in which the C-S-S-C dihedral angle is around 90 degrees. The values of Delta S-N*I/R shown by these dimers are very small for liquid crystal dimers and this is attributed to the increased molecular biaxiality arising from the C-S-S-C dihedral angle. The smectic A phase exhibited by the homologues with n = 10, 11 and 12 is proposed to consist of an intercalated arrangement of the dimers which is driven by the mismatch in cross-sectional areas of the cholesteryl-based groups and alkyl chains.

Original languageEnglish
Pages (from-to)259-268
Number of pages10
JournalLiquid Crystals
Volume39
Issue number2
DOIs
Publication statusPublished - 2012

Keywords

  • cholesteryl
  • disulfide
  • intercalated smectic
  • liquid crystal dimers
  • odd-even effects
  • dimesogenic compounds
  • chain-length
  • behavior
  • transition
  • tetramers
  • trimers
  • phases
  • oligomers
  • monomers
  • unit

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