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Unexpected Liquid Crystalline Behaviour of Three-Ring Bent-Core Mesogens: Bis(4-Subst.-Phenyl) 2-Methyl-Iso-Phthalates
Chemical Physics Publications (2012)
  • Wolfgang Weissflog
  • Ute Baumeister
  • Maria-Gabriela Tamba
  • Gerhard Pelzl
  • Horst Kresse
  • Rudolf Friedemann
  • Gunther Hempel
  • Ricardo Kurz
  • Matthias Roos
  • Kurt Merzwiler
  • Antal Jakli, Kent State University - Kent Campus
  • Cuiyu Zhang, Kent State University - Kent Campus
  • Nicholas Diorio, Kent State University - Kent Campus
  • Ralf Stannarius
  • Alexey Eremin
  • Ulrike Kornek
Abstract

Three-ring bent-core bis(4-subst.-phenyl) 2-methyl-iso-phthalates exhibiting nematic, SmA and SmC phases are reported. The occurring mesophases have been identified by their optical textures and X-ray diffraction measurements which give also geometrical structural parameters like layer spacing and molecular tilt. Quantum chemical calculations on single molecules and X-ray structure analysis in the crystalline state indicate wide opening angles (about 155 degrees) of the molecular legs due to the lateral methyl group in position 2 of the central phenyl ring. However solid state NMR spectroscopy in the liquid crystalline phases finds stronger molecular bending (bending angle to be about 138 degrees in the SmA and about 146 degrees in the nematic phase). Dielectric and SHG measurements give evidence that in the SmA phase a polar structure can be induced by application of an electric field which disappears in the isotropic liquid phase. The electric field not only leads to a slight textural change even in the SmA phase but also polar-type electric current response (P-S about 200 nC cm(-2)) is observed. This unusual electro-optical behaviour is discussed on the basis of the orientation of polar clusters formed by the bent molecules. In the paper we not only attempt to characterize the mesophases and to describe their physical properties, but we also show that these types of molecules represent the borderline between bent-shaped and calamitic liquid crystals.

Keywords
  • Carboxyl Connecting Groups,
  • Banana-Shaped Compounds,
  • 2 Ester Groups,
  • Spontaneous Polarization,
  • Substituted Phenylbenzoates,
  • Dielectric-Relaxation,
  • Molecular Arrangement,
  • Mesophase Behavior,
  • Calamitic Mesogens,
  • Phase
Disciplines
Publication Date
January 25, 2012
Publisher Statement
Available on publisher's site at http://dx.doi.org/10.1039/c2sm07064b
Citation Information
Wolfgang Weissflog, Ute Baumeister, Maria-Gabriela Tamba, Gerhard Pelzl, et al.. "Unexpected Liquid Crystalline Behaviour of Three-Ring Bent-Core Mesogens: Bis(4-Subst.-Phenyl) 2-Methyl-Iso-Phthalates" Chemical Physics Publications Vol. 8 Iss. 9 (2012)
Available at: http://works.bepress.com/antal_jakli/9/