Akihisa Yamaguchi

Phase transition behaviour of novel Y‐shaped liquid crystal oligomers

We have designed novel liquid crystal oligomers in which three mesogenic units are connected via 3,5‐dihydroxybenzoic acid. 4‐Cyanobiphenyl‐4′‐yl 3,5‐bis{6‐[4‐(5‐octylpyrimidin‐2‐yl)phenyloxy]hexyloxy}benzoate and 4‐(5‐octylpyrimidine‐2‐yl)phenyl 3,5‐bis{6‐[4‐(5‐octylpyrimidine‐2‐yl)phenyloxy]hexyloxy}benzoate have been prepared, and their physical properties investigated by optical microscopy and differential scanning calorimetry. The Y‐shaped liquid crystal oligomers were found to show a direct phase transition from isotropic liquid to anticlinic SmC (SmCanti) phase.

Kinetically induced intermolecular association: unusual enthalpy changes in the nematic phase of a novel dimeric liquid-crystalline moleculeElectronic supplementary information (ESI) available: photomicrographs of the nematic phase formed by BOPPHB on ...

A novel dimeric liquid-crystalline molecule in which two mesogenic groups are connected via catechol was found to have smectic-like layer ordering in the nematic phase, and unusual enthalpy changes were observed in the nematic phase on heating from the monotropic smectic C phase.

Unusual smectic phases organized by novel λ-shaped mesogenic molecules

A homologous series of novel λ-shaped mesogenic compounds in which three mesogenic groups are connected to 3, 4-dihydroxybenzoic acid has been prepared and their physical properties investigated by means of optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. The λ-shaped compounds studied showed unusual smectic phases. 4-Cyanobiphenyl-4′-yl 3,4-bis{6-[4-(5-octylpyrimidin-2-yl)phenyloxy]hexyloxy}benzoate was found to realize an incommensurate SmA (SmAinc) phase. A “uniform planarly” aligned sample of 2-(4-octylphenyl)pyrimidin-5-yl 3,4-bis{6-[4-(5-octylpyrimidin-2-yl)phenyloxy]hexyloxy} benzoate showed a Schlieren-like texture in the smectic phase. We discuss structural effects of the λ-shaped compounds on molecular organization in liquid-crystalline phases.

Odd–even effects in the phase transition behaviour of novel U‐shaped liquid crystals

A homologous series of U‐shaped dimeric liquid crystals in which two mesogenic groups are connected via catechol has been prepared and the effects of terminal alkyl chains, alkyl spacers and core structures on the transition properties investigated by means of optical microscopy and differential scanning calorimetry. The phase sequence exhibits a pronounced odd–even effect as the length and parity of the spacers is varied, in which the even members favour the nematic and smectic C phases, whereas the odd members favour the nematic and smectic A phases. We discuss the transition behaviour of the U‐shaped compounds in terms of molecular shape.

Synthesis and physical properties of novel liquid crystal trimers containing resorcinol as a linking unit

A homologous series of novel liquid crystal trimers in which cyanobiphenyl and phenylpyrimidine moieties are connected via resorcinol was prepared and their physical properties investigated. 3‐{6‐[4‐(4‐Cyanophenyl)phenyl]hexyloxy}‐1‐{6‐[4‐(5‐octylpyrimidine‐2‐yl)phenyl]hexyloxy}benzene, compound I‐(6,6), was found to show monotropic nematic, smectic A and anticlinic smectic C (SmCanti) phases. We investigated the effects of the spacer length and the linking group on the phase transition behaviour. In addition, trimers with identical mesogenic units were prepared and their physical properties compared with those containing two different mesogens. Only the meta‐substituted trimers showed the SmCanti phase despite its reduced tendency to exhibit liquid crystallinity than the ortho‐ and para‐substituted trimers.

Physical properties of a novel chiral material possessing a binaphthyl group

A novel chiral dimeric compound, (R)‐2,2′‐bis{6‐[4‐(5‐octylpyrimidine‐2‐yl)phenyloxy]hexyloxy}‐1,1′‐binaphthyl (1), has been prepared and its physical properties investigated. Compound 1 was found to show a monotropic smectic A phase. A twist grain boundary phase was observed in binary mixtures of compound 1 and its corresponding monomeric liquid crystal, 5‐octyl‐2‐(4‐hexyloxyphenyl)pyrimidine (8‐PYP‐6O). Pitch measurements in a mixture with a host material revealed that the binaphthyl dimer induces a stronger helical structure in the N* phase than in the SmC* phase. We also measured helical pitch values in N* and SmC* phases induced by other twin materials with a chiral centre. We discuss characteristic effects of axial chirality in liquid crystalline phases in comparison with that of centres of chilarity.

Influence of the Alkyl Spacer Length on the Phase Transition Behaviour of the λ-Shaped Liquid Crystal

ABSTRACT We reported that a novel λ-shaped liquid-crystalline molecule I-6 in which a cyanobiphenyl and two phenylpyrimidine groups are connected to 3, 4-dihydroxybenzoic acid exhibits an incommensurate SmA phase. In the present study, we have prepared the homologous series of the λ-shaped molecules I-n ( n = 4 , 5 , 7 , 8 , 9 , 12 ) and investigated effect of the spacer length on the phase transition behaviour. Compounds I-4 , I-8 and I-12 with an even member of atoms in spacer showed the phase sequences of N-SmA-Cr or SmA-Cr. On the other hand, the odd members I-7 and I-9 showed the phase sequence of N-SmA-SmCanti-Cr.

Phase Transition Behaviour of Amphiphilic Supermolecules Possessing a Semiperfluorinated Alkyl Chain

Recently we have found that a novel amphiphilic compound, 1H, 1H, 2H, 2H-heptadecafluoro-1-decyl 3, 4, 5- tris[6-(4′-cyanobiphenyl-4-yloxy)hexyloxy]benzoate, exhibited the phase sequence of isotropic liquid -smectic A-bicontinuous cubic-crystal. In this study, we have prepared compounds possessing biphenyl groups or alkyl chains instead of the cyanobiphenyl groups of the amphiphilic compound and investigated their liquid-crystalline properties using optical microscopy and differential scanning calorimetry. The compound possessing the biphenyl groups was found to exhibit a columnar phase, however, the compound possessing the alkyl chains did not show any liquid-crystalline phase. We discuss the structure-property relationship in the amphiphilic oligomers.

Novel liquid crystal trimers exhibiting a monolayer smectic C phase containing strong macroscopic fluctuations

We prepared a homologous series of novel liquid crystal trimers, 1,4‐bis(4‐{ω‐[4‐(5‐dodecylpyrimidine‐2‐yl)phenyloxy]alkyloxyphenyl}carbonyloxy)benzene, I‐(m, n), and investigated their physical properties using optical microscopy, differential scanning calorimetry and X‐ray diffraction. All the compounds exhibited enantiotropic nematic (N) and smectic C (SmC) phases. Pronounced odd–even effects were apparent for the transition properties on varying the spacer length. X‐ray diffraction measurements suggest that the SmC phase has a monolayer structure in which the molecular long axis is tilted to the layer normal. Furthermore, formation of defect‐lines was observed for the SmC phases.

Frustration Caused by Competition Between Interlayer and Intralayer Interactions in a Dichiral Liquid Crystal

We reported that a dichiral liquid crystal 2-{4-[(R)-2-fluorohexyloxy]phenyl}-5-4-[(S)-2-fluoro-2-methyldecanoy]phenyl}pyrimidine (1) upon cooling exhibits an endothermic transition from a chiral smectic C phase to an optically isotropic phase (IsoX). We have investigated transition behaviour of a binary mixture between 1 and the corresponding monochiral liquid crystal without the IsoX phase, 2-[4-[hexyloxy]phenyl}-5-4-{[(S)-2-fluoro-2-methylnonanoyl]phenyl}pyrimidine (2). In the phase diagram clear hysteresis was observed in appearance of the IsoX phase between heating and cooling.