Super-structures produced in the smectic molecular organization are reviewed, and the origin for the structures discussed,
in which it is emphasized that the frustration plays an important role in the emergence of the super-structures. Properties
and structures of mysterious smectic phases possessing chirality-induced super-structures are introduced, including
smectic blue and smectic Q (SmQ) phases that possess three dimensional (3D) structures. The molecular design on
stabilizing the 3D structure is proposed. The molecular orientations in the 3D structures are not so sensitive to the
external electric field due to an intricate smectic ordering, thus it has been difficult to imagine practical applications of
these structures. The SmQ compound possessing an azobenzene core in the molecular structure is designed and the
liquid-crystalline properties and photoresponse investigated. By means of the photoisomerization of the azobenzene
moiety, we demonstrate that the 3D structure of the SmQ phase can be controlled by light as an external stimulus,
suggesting a possibility for new applications utilizing the liquid-crystalline 3D structure.
An optically active liquid crystal compound, bis-[4’-(1-methylheptyloxy-carbonyl)-4-biphenyl] terephthalate, possessing two chiral centers at both peripheral ends was prepared, and the liquid-crystalline properties investigated. This compound showed a liquid crystal phase with a 3D superstructure of the defects, i.e., the smectic Q (SmQ) phase, between the antiferroelectric and isotropic liquid phases. Complicated x-ray diffraction spots appeared in the small angle region in the SmQ phase due to the formation of the 3D network of the defects, however, only broad scattering was observed in the wide angle region. Reducing the number of phenyl rings of this compound decreased the stability of the SmQ phase, thus the resulting compound just exhibited the antiferroelectric phase. Even in the isotropic phase above the SmQ or antiferroelectric phase of these compounds, a clear x-ray diffraction scattering was detected in the small angle region, suggesting a possible molecular pre-organization in the isotropic phase. Contact studies showed that another liquid crystal superstructure, i.e., a twist grain boundary phase, was induced by mixing these chiral compounds or by mixing the antiferroelectric compound with an achiral compound. Helical structures induced in the nematic phase were also examined for these and the related chiral compounds.
Novel non-symmetric dimeric liquid crystal, 1-(4-cyanobiphenyl-4'-yloxy)-11-[2-(4-octylphenyl)pyrimidine-5-yloxy]undecane (8YP11OCB), has been prepared and the physical properties investigated by means of optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction and dielectric measurements. The crystal structure has been determined to understand microscopic behavior of the compound. Electro-optical properties for 8YP11OCB were compared to those for 1-(4-cyanobiphenyl-4'-yloxy)-11-[4-(5-octylpyrimidine-2-yl)phenyl-4"-oxy]undecane (8PY11OCB). 8YP11OCB with smaller dielectric anisotropy than 8PY11OCB was found to show a lower threshold voltage in the smectic A phase than 8PY11OCB. Crystal structure of 8YP11OCB indicates that three types of core-core interactions exist and that the enthalpy gained by the specific interactions stabilizes the molecular packing with large free volume in the SmA phase.