Structure and Switching in Bent-Shaped Molecular Liquid Crystal Systems with Two Mesogenic Groups Linked by Alkylene Spacer

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Abstract
Structure and switching behavior were studied in liquid crystals consisting of bent-shaped molecules with the linkage of an alkylene spacer, m(O)AMnAM(O)m, where m and n are carbon numbers of end and spacer chains, respectively. All the compounds exhibit a fan-shaped texture without a fringe structure in their smectic phase, different from the texture of conventional bent (banana)-shaped liquid crystals. In 12AM5AM12, two switching current peaks indicating the antiferroelectric phase were observed. The spontaneous polarization was about 600 nC/cm2. The color change due to the birefringence change is associated with the switching, though the extinction direction between crossed polarizers remains the same. This clearly proves that the bent-molecules do not tilt with respect to the layer normal. In the dielectric measurements, there exist two relaxations at 600 kHz and below 100 Hz and they are suppressed by a biased voltage. Structure and switching in the other systems, 80AM5AMO8, are also described briefly.