Palladium nanoparticles covered with liquid-crystal molecules were prepared by UV irradiation of an alcohol solution of palladium(II) acetate in the presence of liquid-crystal molecules. The prepared Pd nanoparticles have an average diameter of 2.5 nm. A twisted nematic (TN) liquid-crystal device (LCD) was fabricated by doping with Pd nanoparticles covered with another kind of nematic liquid-crystal molecules. In this device the sign of the dielectric anisotropy (Δε) of the liquid-crystal molecules, which cover Pd nanoparticles, is opposite to that of nematic liquid-crystal molecules, which work as the host of the device (Δε>0). The TN-LCD cell fabricated in this research exhibits a frequency modulation response to an applied alternative voltage wave form.

We report the reduction of threshold voltage, V th , of twisted nematic liquid crystal devices by doping the nanoparticles of MgO and SiO 2 . The results are well explained by inserting the experimentally determined values of elastic constants and dielectric anisotropy in the formula, where both of these quantities decrease due to the existence of these nanoparticles. The V th decrease approximately as ffiffi ffi S p , where S being the order parameter. The S is also shown to decrease by doping nanoparticles.

We have investigated the generation of the pretilt angles for nematic liquid crystal (5CB) aligned in the cells using rubbed polyimide (PI) films containing trifluoromethyl moieties as a function of rubbing strength (RS). In order to characterize the films, we have conducted an analysis of the surface atomic concentration of fluorine (F) relative to that of carbon (C), F/C(%) with an electron spectroscopy for chemical analysis (ESCA) in the shallow surface region at the depth of 3 and 12 nm. It is shown that the F/C ratio at a depth of 3 nm decreases with RS, and that the observed pretilt angle shows a high value approaching 45° in the weak RS region, and tends to decrease with increasing RS. The existence of the trifluoromethyl moiety in the special PI, and its appearance in the surface region are considered to be responsible for the generation of high pretilt angles at low RS region since a surface covered by fluorine atoms has a low surface energy and the van der Waals dispersion force is thought to be dominant and hence perpendicular LC alignment is expected. With increasing RS the surface concentration of fluorine atoms decreases and repeated triangles will be formed; a combination of the dispersion force and steric interaction between LC molecules and these structures may cause a medium or low pretilted LC conformation.

Intrinsic optical transitions of lower Davydov excitons in thiophene/phenylene co-oligomer ͑TPCO͒ crystals were investigated. Lower Davydov excitons are either optically allowed or forbidden depending on the number of thiophene rings constituting the TPCOs. The TPCO molecules are orientated nearly parallel to each other like H aggregates and are aligned in herringbone fashion within a crystalline layer. The transition selection rules are dominated by the components of the molecular transition dipole moments lying in the herringbone planes of the respective crystals. The selection rules at the exciton band bottoms of the TPCOs differ from those of oligothiophenes in spite of these two compounds having similar molecular structures. The selection rules vary drastically with the molecular alignment because of the H aggregation. TPCO and oligothiophene crystals are treated as H aggregates as a first approximation. This treatment is very useful for understanding the optical transitions of conjugated materials.