Masamitsu Ishitobi

Novel high birefringence dibenzothiophenylacetylene liquid crystals

We have designed, synthesized and evaluated dibenzothiophenylacetylene homologues as new heterocyclic molecules which were expected to have high δα values and short wavelength UV absorption spectra. The dibenzothiophenyl acetylene homologues exhibited wide nematic phase ranges and had very high extrapolated δn of over 0.6 and directly measured values of 0.5. The compounds with two dibenzothiophenyl rings were colourless, so that we have succeeded in obtaining colourless super-high δn liquid crystals. We have also analysed the contribution of the transition band to the refractive indices and the birefringence. From the analysis, the main origins of δn for compounds 1 and 2 are lower MOs than the HOMO and this results in the compatibility of large δn and lack of colour. The dibenzothiophenylacetylene compounds behaved according to our design expectations.

Highly Anisotropic Molecular Materials for LCD

Abstract Two kinds of novel molecular materials with high optical anisotropy were synthesized and evaluated. Liquid crystalline phenylacetylene derivatives, which have mesogen of a 1,4-Bis(phenylethynyl)benzene, not only showed high δn but also were stable for heating or light. Triphenodioxazine derivatives were highly dichroic in guest-host liquid crystal mixtures, where they also showed vivid color due to a sharp peak in absorption spectra. Hence, these molecules possibly improve visual performance of some reflection type liquid crystal displays (LCDs).

Experimental determination of molecular polarizability anisotropy of nematogens by depolarized Rayleigh light scattering

The anisotropy of molecular polarizability Δα of several nematogens has been determined by depolarized Rayleigh light scattering. The experimentally determined values were found to be noticeably smaller than those obtained by MOPAC calculation. Δα values determined from order parameter S and refractive indices show reasonably good agreement with those determined in the present experiment. This result warns us that Δα calculated by MOPAC, particularly at a finite wavelength, may be larger than the true value.

Highly Oriented J-Aggregates of Nitroazo Dye and Its Surface-Induced Chromism

Highly oriented J-aggregates of a nitroazo dye were obtained in solid thin films on aligned poly(tetrafluoroethylene) surfaces. During film deposition on a friction-transferred poly(tetrafluoroethylene) layer, a sharp peak grew in the polarized absorption spectra around 613 nm, which was red-shifted 117 nm from the peak in dilute dichloromethane solution. The peak showed remarkable optical anisotropy: dichroic ratios D of up to 22 were observed, and the intrinsic D value should substantially exceed this value. These results indicate that the peak is attributable to highly oriented J-aggregates. On glass, however, H-like aggregates grew, exhibiting an absorption peak at 410 nm. Hence, the substrate surface induced the remarkable chromism observed as a 203 nm red shift.

A Novel Monte Carlo Method for Liquid Crystal using Extended Inter-Molecular Potential (EIMP)

Abstract A novel Monte Carlo (MC) simulation method using Extended Inter-molecular Potential (EIMP) for liquid crystal (LC) systems is reported. The EIMP is calculated, prior to the MC calculation, as interaction energy between two molecules that are located in various configurations. The MC method using the EIMP enables to carry out a calculation of even a system within many molecules in short CPU time. It is applied to the systems that consist of 750–1000 molecules of typical LCs (4-n-alkyl-4′-cyanobiphenyls; nCBs). Several phases are successfully reproduced and order parameters of them agree with the experiments.