Fumitaka Ogasawara

Novel T-shaped Chiral Oligomers with a Wide Temperature Range of a Blue Phase

The crystal structure of (S)-1-methylheptyl-4′-{4-octyloxy-2-{11-[4-(5-hexylpyrimidin-2-yl)phenoxy]undecanoyloxy}benzoyloxy}biphenyl-4-carboxylate, which has a relatively wide temperature range of blue phase III on cooling, has been determined. The molecule was found to form a λ-shaped structure. We have prepared a homologous series of the chiral oligomers and investigated effects of structure on appearance of the blue phase. All compounds were found to show a phase sequence of Iso-BP-N*-glass on cooling. The structure-property correlations reveal that (1) chirality does not affect on the Iso-BP transition temperature, (2) increasing chirality destabilizes the N* phase, and (3) the longer spacer lowers the BP-N* transition temperature.

Synthesis and physical properties of novel S‐shaped liquid crystal oligomers

We prepared novel S‐shaped liquid crystal oligomers, the 4,4′‐bis(ω‐(2‐(ω‐(4‐(cyanophenyl)phenyloxy)alkyloxy)phenyloxy)alkyloxybiphenyls (S‐n ), and investigated their transition behaviour. The oligomer with even‐numbered spacers (S‐6) exhibited a nematic phase, whereas the oligomer with odd‐numbered spacers (S‐7) exhibited nematic and smectic A phases. Transition properties of the S‐shaped oligomers are compared with those of the corresponding monomeric and U‐shaped dimeric compounds. The entropy changes associated with the I–N transition for the oligomers were found to have small values, similar to that of the monomeric compound. A biaxial smectic phase was induced below the SmA phase in some binary mixtures of S‐6 and a phenylpyrimidine derivative (8‐PYP‐6O). On the other hand, the SmA phase was stabilized in the mixtures of S‐7 and 8‐PYP‐6O. We discuss the transition behaivour of the S‐shaped oligomers in terms of their molecular shape.

Structure-Property Correlations of Novel S-Shaped Liquid Crystal Oligomers

Transition properties of a homologous series of novel S-shaped oligomers on varying the spacer length, core structure and linking group were investigated. All the S-shaped oligomers showed a nematic (N) phase on cooling. Formation of the N phase is interpreted in terms of the length to diameter (L/D) ratio, indicating that intramolecular core-core interaction plays an important role in stabilizing N phases. A non-symmetric S-shaped oligomer possessing cyanobiphenyl and phenylpyrimidine moieties exhibited enantiotropic N and smectic A (SmA) phases. The high stability of the SmA phase results from intermolecular interactions between the unlike mesogenic moieties. We discuss physical properties of the S shaped system that has structure within structure.

Synthesis and physical properties of novel liquid crystal oligomers possessing polar terminal groups

A homologous series of novel liquid crystal oligomers possessing 4‐fluorobiphenyl and 4‐trifluoromethoxyphenyl benzoate moieties was prepared and the physical properties investigated. The dimesogenic compounds, 4‐trifluoromethoxyphenyl 4‐{6‐[4‐(4‐fluorophenyl)phenyloxy]alkoxy}benzoates, exhibited nematic (N) and smectic A (SmA) phases. Pronounced odd–even effects were seen, not only for the phase transition but also for the induced dielectric anisotropy in the N phase of the mixture with a host material, on varying the spacer length of the dimeric compounds. The λ–shaped trimesogenic compound, 4‐trifluoromethoxyphenyl 3,4‐bis{6‐[4‐(4‐fluorophenyl)phenyloxy]hexyloxy}benzoate, was found to show monotropic N and SmA phases. We discuss oligomeric effects of the mesogenic moieties on the phase transition behaviour, and on the induced dielectric anisotropy.

Molecular Organization of Preorganized S-Shaped Oligomers in the Liquid Crystalline Phases

We prepared a homologous series of S-shaped oligomers, 4,4′-bis(ω-(2-(ω-(4-(cyanophenyl)phenyloxy)alkyloxy)phenyloxy)alkyloxy)biphenyl [ I-(m,n) ], and investigated effects of the spacer length on the phase transition behavior. I-(7,7), I-(8,8), I-(9,9) and I-(7,9) showed nematic (N) and smectic A (SmA) phases, whereas I-(6,6) and I-(6,9) showed only an N phase. The melting behavior was found to depend on the parity of the spacer ( m ). The liquid-crystalline phases of I-(8,8) and I-(6,9) are monotropic, however, those of I-(9,9) and I-(7,9) are enantiotropic. X-ray diffraction measurements of I-(7,7), I-(8,8) and I-(7,9) indicate that the S-shaped oligomers exist as a close-packed structure in the monolayer SmA phase.

Synthesis and Electrooptic Properties of a Novel U-Shaped Mesogenic Molecule

A novel U-shaped liquid-crystalline molecule where two polar mesogenic groups are connected via catechol, 1-6-(3,4-difluorophenyloxy)hexyloxy-2-6-[4-(4-fluorophenyl)phenyloxy]hexyloxybenzene, was prepared and the electrooptic properties were investigated. The threshold voltage of a nematic mixture consisted of a host liquid crystal (LC) and 10 wt% of the U-shaped compound was found to be markedly lower than that of the host LC. We discuss the structure-property correlation of the U-shaped mesogenic system.

Chiral Additive Effects on Bend Growth Rate for an Optically Compensated Bend-Mode Liquid Crystal Display

We investigated bend growth processes for an optically compensated bend (OCB)-mode liquid crystal display. The bend growth consists of two transformations. i.e., the transformation from symmetric splay alignment to bend alignment and that from asymmetric splay alignment to bend alignment. We observed the temperature dependence of bend growth processes and detected the asymmetric splay-to-bend transformation at 0 °C. We investigated the kinetic effects of a chiral additive on the bend growth processes in three directions, i.e., the same as, and opposite and perpendicular to the rubbing direction. The chiral additive did not affect the symmetric splay-to-bend transformation, however, it was found to accelerate the asymmetric splay-to-bend transformation in all three directions. This acceleration is attributed to the chirality-induced coexistence of top and bottom splay alignments in the asymmetric splay regions.

Synthesis and physical properties of novel fluorine-containing U-shaped compounds

We prepared a homologous series of novel fluorine-containing U-shaped mesogenic compounds and investigated the electrooptical properties of a mixture with a nematic liquid crystal for an optically compensated bend (OCB) mode liquid crystal display. A U-shaped compound, 1,2-bis[6-(3,4,5-trifluorophenyloxy)hexyloxy]benzene, was found to enhance the dielectric anisotropy of the mixture. A critical voltage (VCR) at a splay to bend transition of a nematic mixture consisting of a host liquid crystal and 5 wt % U-shaped compound was found to be lower than that of the host liquid crystal. We discuss the effects of the molecular structure of the U-shaped compounds on the electrooptical properties of the mixture.