Biaxial nematic liquid crystals have attracted much attention from both fundamental and application points of view,
because the fast response based on the rotation of the minor director is expected. So far, different molecular designs have
been proposed for the emergence of the biaxial nematic phase. Among that, we have been interested in applying "preorganization"
concept on generating the biaxiality. Dimeric liquid crystal compounds have been prepared in line with
this concept in which two mesogenic parts are linked by the biphenyl connecting group. The pre-organized dimmer
shows an anomalous textural change, for vertically-aligned and free-standing film samples, at the smectic C (SmC)-
nematic (N) phase transition, in which the Schlieren texture of the SmC changes into the other Schlieren texture of the N
phase. There are two possible explanations for this textural change, i.e., the occurrence of the director change at the
SmC-N phase transition or the emergence of biaxiality in the N phase. The electric-field-induced birefringence has also
been measured in detail for investigating the biaxial nature of the sample.
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.
Aspherical mirror fabrication of HiNA set-3 projection optics was completed. By using a new polishing method, we successfully reduced low spatial frequency roughness (LSFR), mid spatial frequency roughness (MSFR) and high spatial frequency roughness (HSFR) compared with HiNA set-1 and set-2 projection optics. MSFR, which strongly affects the flare of the optics, was remarkably reduced to less than 0.2nm rms. HiNA projection optical system with the numerical aperture of 0.3 consists of two aspheric mirrors (M1 and M2). We had already fabricated two sets of the HiNA projection optics. The wavefront error (WFE) of the set-1 optics was 7.5nm rms and that of the set-2 optics was 1.9nm rms. We tried to reduce the WFE and flare in the set-3 optics. The target number of WFE of the set-3 optics was less than 1nm rms. The LSFR, MSFR and HSFR of the M1 of the set-3 optics were 0.25nm rms, 0.17nm rms and 0.10nm rms, respectively. The LSFR and MSFR are almost half values compared with those of the M1 for the set-2 optics. The HSFR was also reduced from 0.13nm rms (set-2) to 0.10nm rms (set-3). The LSFR and MSFR of the M2 were 0.25nm rms and 0.20nm rms, respectively. The estimated wavefront error calculated from these LSFR numbers is 0.7nm rms.
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.