Shape-Persistent V-Shaped Mesogens-Formation of Nematic Phases with Biaxial Order
Journal of Materials Chemistry
Bent Core Molecules, Homologous Series, Liquid Crystals, Aggregation, Transitions, Particles, Mixtures, Systems
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.
Lehmann, Matthias; Kang, Shin-Woong; Köhn, Christiane; Haseloh, Sönke; Kolb, Ute; Schollmeyer, Dieter; Wang, QingBing; and Kumar, Satyendra (2006). Shape-Persistent V-Shaped Mesogens-Formation of Nematic Phases with Biaxial Order. Journal of Materials Chemistry 16(44), 1326-1334. doi: 10.1039/b605718g Retrieved from http://digitalcommons.kent.edu/phypubs/88