Title

Shape-Persistent V-Shaped Mesogens-Formation of Nematic Phases with Biaxial Order

Publication Title

Journal of Materials Chemistry

Publication Date

2006

Document Type

Article

DOI

10.1039/b605718g

Keywords

Bent Core Molecules, Homologous Series, Liquid Crystals, Aggregation, Transitions, Particles, Mixtures, Systems

Disciplines

Physics

Abstract

A homologous series of shape-persistent V-shaped molecules has been designed to form the biaxial nematic phase. Phenyleneethynylene moieties are attached to a bent fluorenone unit to create an apex angle of about 90°, which is determined from the single crystal structure. Two mesogens, one symmetric and another unsymmetric, have been synthesized by attaching a cyano group to one or both of the peripheral phenyl units, respectively. These groups introduce local dipoles essential for the formation of the nematic phases. The tendency to form a crystalline phase is reduced by laterally substituted hexyloxy chains which allow the nematic phase to be supercooled to a glassy state. Two of the three fluorenone derivatives exhibit a transition from the uniaxial nematic to the biaxial nematic phase. This transition has an undetectably small transition enthalpy, but the X-ray diffraction, polarizing optical microscopy, and conoscopy reveal the presence of the biaxial order in the low temperature nematic phase.

Comments

Available on publisher's site at http://dx.doi.org/10.1039/b605718g.

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