Hiroki Higuchi

62.2: Invited Paper: Fast Electro‐Optical Switching in Polymer‐Stabilized Liquid Crystalline Blue Phases for Display Application

Blue phases have two major advantages over commonly used nematic phases:1) the response is much faster, 2) the zero-electric field state is optically isotropic. We demonstrate the sufficiently large electric field-induced birefringence and the micro-second response of the polymer-stabilized blue phases and the induced-isotropic phases without any surface treatment.

39.1: Invited Paper: Optically Isotropic Nano-Structured Liquid Crystal Composites for Display Applications

In this paper, we present the phase behavior and electro-optical Kerr effect of the optically isotropic liquid crystal composites, which require no surface treatment for device fabrication. Anomalously large Kerr constant, more than 10−8 mV−2 and fast response, less than sub-milli-second were observed at a room temperature.

Optically isotropic-nanostructured liquid crystal composite with high Kerr constant

The relationship between material parameters of host nematic liquid crystals (LCs) and Kerr constant of their nanostructured chiral LC composites was investigated. We made certain that the Kerr constant of nanostrutured chiral LC composites was closely related to the parameters of their host LCs, such as value of the difference of refractive index (Δn), the dielectric anisotropy (Δe), and bend to splay elastic constant ratio (K33∕K11).

Liquid crystalline blue phase I observed for a bent-core molecule and its electro-optical performance

We investigated the liquid crystalline blue phase I (BP I) observed for a nematogenic achiral bent-core molecule doped with a small percentage of a chiral additive with a high twisting power. We also observed the electro-optical performance of BP I by incorporating in-plane electric field geometry.

Fast electro-optic switching in liquid crystal blue phase II

Electro-optic switching based on the Kerr effect was investigated in detail for liquid crystal blue phase II (BPII) with different chiral pitch. The Kerr constant of BPII was found to be proportional to the cube of the chiral pitch, although the theoretical expectation was the square of the chiral pitch. In addition, there was little hysteresis in the voltage-transmittance curve of BPII. The response of BPII was found to be very fast, at less than 1 ms, in both the regions of local director reorientation and electrostriction by applied electric field.

A novel redox switch for fluorescence: drastic UV–vis and fluorescence spectral changes upon electrolysis of a hexaphenylethane derivative of 10,10′-dimethylbiacridan

The newly prepared title donor 1 has a very long CC bond [1.635(2) A], which was readily cleaved upon oxidation to give dication 2 2+ containing two 10-methylacridinium chromophores. Colorless donor 1 ( E ox +0.18 V) is non-fluorescent whereas orange dication 2 2+ ( E red −0.27 V) emits strong green fluorescence, so that, this pair can be considered as a novel redox switch for fluorescence with high electrochemical bistability.

Electrooptic response of liquid crystalline blue phases with different chiral pitches

The relationship between the electrooptic response properties and the chiral pitch of a blue phase was experimentally investigated. The Kerr constant was found to be proportional to the cube of the chiral pitch, although a theoretical square-law was expected. It was also revealed that the effect of the chiral pitch on the response time was dependent on the type of electric field-induced birefringence of the blue phase, such as local director reorientation and electrostriction. The response of the local director reorientation process was very fast at sub-millisecond and also proportional to the cube of the chiral pitch. However, in the case of the electrostriction process, the effect of the chiral pitch on the response time was insignificant and the response time was a few milliseconds.

Phase separation of monomer in liquid crystal mixtures and surface morphology in polymer-stabilized vertical alignment liquid crystal displays

The polymer-stabilized vertically aligned (PS-VA) liquid crystal display (LCD) driving mode has high potential for manufacturing low power consuming displays due to the higher transmittance and fast response as compared with the existing patterned vertically aligned and multi-domain vertically aligned modes. In this paper we have investigated the reaction mechanisms of monomer?liquid crystal blends to form a surface pre-tilt angle of liquid crystal in vertical alignment LCD associated with a fishbone electrode structure. The observed sizes of polymer bumps formed on the substrates were found to be dependent on the exposed UV wavelength and were almost equal in both top and bottom substrates. When a large UV wavelength was used, the phase separation mechanism of monomer in PS-VA mode was found nearly isotropic rather than anisotropic in contrast to the previous studies.

Effects of monomer/liquid crystal compositions on electro-optical properties of polymer-stabilized blue phase liquid crystal

A polymer-stabilized blue phase liquid crystal is one of the candidates for the next-generation display material. In this study, effects of monomer/liquid crystal compositions on electro-optical characteristics of polymer-stabilized blue phase liquid crystals were investigated. By optimizing monomer/liquid crystal compositions, lower operating voltage, reduction in hysteresis and residual birefringence were achieved. However, some technical issues remain to be overcome.

Electrochiroptical response of a hexaarylethane derivative with a helical π-skeleton: drastic UV–Vis and CD spectral changes upon electrolysis of 4′,5′-dibromodispiro[xanthene-9,9′(9′H,10′H)-phenanthrene-10′,9″-xanthene]

Upon two-electron oxidation of the title electron donor 1a, the elongated central C9–C10 bond [1.656(5) A (X-ray)] is cleaved to give the biphenyl-2,2′-diyl bis(xanthenylium) dye 2a2+, which regenerates the colorless dispiro compound 1a by two-electron reduction. The presence of isosbestic points in the UV–Vis spectra during the electrochemical oxidation of 1a to 2a2+ indicates the negligible steady-state concentration of the intermediate cation radical. Interconversion between optically resolved 1a and 2a2+ is accompanied by drastic changes in the CD spectra again with several isosbestic points, and racemization of (P)- and (M)-1a and (S)- and (R)-2a2+ does not occur at ambient conditions. This redox pair represents a new motif for the multi-output response system, where the electrochemical input is transduced into two independent spectral outputs.