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The chirality of spherical liquid crystal droplets was investigated in this study. We report the effect of confinement on blue phase III (BPIII) spheres. We investigated the behaviours of the spher...

Liquid crystal oligomers have a supermolecular structure in which two or more mesogenic units are interconnected through flexible spacers. They can form various molecular packing structures...

We prepared a homologous series of H-shaped liquid crystals I-n and investigated their phase transition properties using optical microscopy and differential scanning calorimetry. All the compounds ...

We prepared some achiral flexible liquid crystal oligomers possessing an octafluorobiphenyl unit and investigated their phase transition properties using polarising optical microscopy and differential scanning calorimetry. All the compounds showed nematic phases. The trimer with even-numbered spacers was found to exhibit coexistence of the nematic regions and the chiral nematic regions with opposite twist senses of a sample contained in a homogeneous aligned cell during a cooling process, whilst that with odd-numbered spacers did not. We discuss how the even-numbered trimer produces the helical state.

Chirality induces structural frustration in liquid crystal systems, producing various kinds of chiral frustrated phases, for example, twist grain boundary (TGB) phases, blue phases (BPs) and dark conglomerate (DC) phases. Almost all molecules exhibiting these frustrated phases have a rigid shape. Especially, a bent–core unit is regarded as a key structure for BPs and DC phases. This paper describes that some flexible liquid crystal oligomers being far from a rigid bent–core molecule stabilise these phases. The LC oligomers have a supermolecular structure in which mesogenic units are connected via flexible spacers. By designing intermolecular interactions, they can exhibit various molecular packing structures in the liquid-crystalline phases as follows: chiral dimers inducing TGB phases, U-shaped and T-shaped oligomers stabilising BPs and achiral liquid crystal trimers exhibiting DC phases. I discuss how the designed liquid crystal oligomers produce the chiral frustrated phases.

We prepared an asymmetric liquid crystal dimer possessing a terminal hydroxyl group, 2-{4-{7-[4-(4-cyanophenyl)phenyloxy]heptyloxy}phenyl}-5-(6-hydroxyhexyloxy)pyrimidine, and investigated the phase transition behaviour using polarising optical microscopy and differential scanning calorimetry. The compound exhibited an enantiotropic nematic phase. On cooling, two distinct domains were formed during the nematic-to-crystal phase transition. During heating, one domain melted at 126.4°C to the N phase, whereas the other domain changed to the N phase at 144.6°C. Therefore, the crystal and nematic phases coexisted at a temperature of 18.2 K. The coexistence behaviour characteristics depend on the cooling rate. We discuss the manner in which intermolecular interactions affect the phase transition behaviour.

To elucidate the effects of liquid crystallinity on the anticancer activity of a small mesogenic molecule, we prepared some benzoate derivatives possessing a terminal hydroxyl group and investigated their anti-proliferative activity against A549 human lung cancer cells. We also observed their molecular aggregation properties using polarised optical microscopy, differential scanning microscopy and dynamic light scattering. We discuss the structure–property relation of the benzoate derivatives. The results are explained in terms of the octanol–water partition coefficient, topological polar surface area (tPSA) and molecular aggregation ability.

We prepared some taper-shaped liquid-crystalline trimers in which two phenylpyrimidine units and a 1,4-diphenyl-2,3-difluorobenzene unit are connected to 2,4-dihdroxy benzoic acid via flexible spacers. We then investigated their liquid-crystalline properties using polarised optical microscopy, differential scanning microscopy and X-ray diffraction. 6-[4–(5-Octylpyrimidin-2-yl)phenyloxy]hexyl 2-{7-{4-[4–(4-hexylphenyl)-2,3-difluorophenyl]phenyloxy}heptanoyloxy}-4-{6-[4–(5-octylpyrimidin-2-yl)phenyloxy]hexyloxy}benzoate (1) was found to exhibit a phase sequence of isotropic liquid – nematic – intercalated smectic A – intercalated anticlinic smectic C – modulated smectic C. The structure–property relation in the taper-shaped trimers reveals that the modulated phase is induced by competition between an intercalated structure stabilised by dipole–dipole interaction and a monolayer structure by packing entropy effects. Conformational change of compound 1 induced by intermolecular interactions plays an important...

Recently, we reported that a rod-like molecule, 4-[4-(7-hydroxyheptyloxy)phenyl]-1-(4-hexylphenyl)-2,3-difluorobenzene, exhibited a nematic phase with a layered structure and smectic C phases consisting of three states. We prepared a homologous series of the rod-like molecules in which a 2,3-difluoro-1,4-diphenylbenzene unit and a hydroxyl unit are connected via a flexible methylene spacer. We investigated their physical properties using polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Although they showed nematic, smectic A and smectic C phases, the phase structures were found to depend on the flexible spacer length. Those compounds possessing a shorter spacer length than a heptyl unit exhibited bilayered smectic A and smectic C phases, whereas those possessing a longer spacer length than a heptyl unit showed conventional monolayered smectic A and smectic C phases. A nematic phase with a smectic-like layer ordering was observed for the compound poss...

After preparing a homologous series of tetrameric mesogenic compounds in which two U-shaped molecules were connected via a rigid benzene derivative or a flexible alkyl chain, we investigated their phase transition behaviour using optical microscopy, differential scanning calorimetry and X-ray diffraction analysis. The compounds possessing an alkyl spacer as the central group exhibited nematic and smectic A phases just as the corresponding U-shaped molecule did. The compound possessing a 1,2-benzene unit as the connecting group showed nematic and smectic A phases, although the compound possessing a 1,3-benzene unit exhibited only an anticlinic smectic C phase. Structure–property relations of the liquid crystalline tetramers are interpreted in terms of preorganised effects of the four mesogenic units.

We have recently reported a binaphthyl liquid crystal exhibiting on cooling a cubic blue phase over a wide temperature range. On heating, however, a chiral nematic phase appeared in place of the blue phase. To elucidate the origin of blue phase stabilisation we have prepared a homologous series of binaphthyl derivatives possessing two 2,3-difluoro-1,4-diphenylbenzene units and have investigated the phase transition behaviour and helical twisting power. A binaphthyl derivative exhibiting the blue phase was found to induce helical twist inversion in a chiral nematic mixture with a host liquid crystal, whereas other compounds without the blue phase induced short helical pitches independently of temperature. The blue phase material is thought to have two possible origins for its twisting power, which are able to stabilise the double-twist structure of the phase.

We prepared two series of liquid-crystalline oligomers composed of phenylpyrimidine based mesogenic cores, alkyl spacers and semiperfluorinated alkyl chains in one series and only alkyl chains in the second series. Their physical properties were investigated using optical microscopy, differential scanning calorimetry and X-ray diffraction measurements. The oligomers possessing a semiperfluorinated alkyl chain show a phase sequence of SmC–SmA–Col when the number of phenylpyrimidine moieties was increased. The compound possessing three phenylpyrimidine cores was found to exhibit monolayer SmA and Col phases. On the other hand, the oligomer composed of an alkyl chain and three phenylpyrimidine cores showed only a nematic phase. We discuss effects of the shape amphiphilicity and the hydrocarbon–fluorocarbon amphiphilicity on phase transition behaviour of the amphiphilic oligomers.

We prepare a series of homologues of novel binaphthyl derivatives, (R)‐2, 2′‐bis{ω‐[4‐(4‐(octyloxycarbonyl)phenyl)phenyloxycabonyl]alkyloxy}‐1, 1′‐binaphthyl [(R)‐Bi‐n], and investigate their induced helical senses and pitches in different host nematic liquid‐crystalline compounds. Pronounced odd–even effects were observed for the induced helical structure in each mixture with 5‐heptyl‐2‐(4‐hexyloxyphenyl)pyrimidine. Temperature‐dependent helical twist inversion was observed for the mixture doped with the odd members, whereas a right‐handed helix was observed for the mixture doped with the even members. On the other hand, a left‐handed helix was induced in each mixture with 4‐methyloxyphenyl 4‐pentylcyclohexane. We discuss the change in sign of the induced pitch in terms of chirality transfer from the binaphthyl derivative to a host nematic liquid crystal.

A novel liquid crystal oligomer, 4‐(4‐cyanophenyl)phenyl 4‐octyloxy‐2‐{7‐{4‐[4‐(4‐hexylphenyl)‐2,3‐difluorophenyl]phenyloxy}heptanoyloxy}benzoate, was prepared and found to exhibit a wide temperature range of a nematic phase in spite of being far from a rod‐like structure. Furthermore, the compound induced blue phases in the mixture with a chiral smectic liquid crystal. The molecular shape and its 2,3‐difluorophenyl unit play a role in stabilizing the blue phases.

Complex dielectric spectroscopy (frequency range 5 Hz–13 MHz) has been used to analyse the frequency, temperature and bias‐field dependences of the molecular dynamics of a very high‐spontaneous‐polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature‐dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X‐mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface ...

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.

Novel oligomeric compounds in which three mesogenic moieties are connected via 3,4‐dihydroxybenzoic acid or 3,5‐dihydroxybenzoic acid were prepared and the physical properties investigated. Some of the compounds were found to have a tendency to form glassy states. With respect to 4‐cyanobiphenyl‐4′‐yl 4‐octyloxy‐2‐(3,4‐bis{6‐[4‐(5‐octylpyrimidine‐2‐yl)phenyloxy]hexyloxybenzoyloxy)benzoate, it is possible to obtain a supercooled nematic phase despite it deviating from a strongly rod‐like structure. We discuss intermolecular interactions between neighbouring mesogenic parts for the appearance of the nematic phase.

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.

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.

We have designed novel liquid crystalline compounds in which two mesogenic units are connected via cis‐2‐buten‐1,4‐diol. We prepared cis‐4‐{6‐[4‐(4‐cyanophenyl)phenyloxy]hexyloxy}‐1‐{6‐[4‐(4‐methyloxy)phenyloxy]hexyloxy}‐2‐butene (6OCMBCB), cis‐1,4‐bis{6‐[4‐(4‐cyanophenyl)phenyloxy]hexyloxy}‐2‐butene (6OCCBCB) and cis‐1,4‐bis{6‐[4‐(4‐methyloxy)phenyloxy]hexyloxy}‐2‐butene (6OMMBCB), and investigated their transition properties. 6OCMBCB and 6OCCBCB exhibited nematic phases whereas 6OMMBCB showed no liquid crystalline phase. We discuss the effects of the mesogenic structure and linkage group on the transition behaviour of the dimesogenic compounds.

The phase behaviour of a dichiral liquid crystalline compound with an optically isotropic cubic phase, 2‐{4‐[(R)‐2‐fluorohexyloxy]phenyl}‐5‐{4‐[(S)‐2‐fluoro‐2‐methyldecanoyloxy]phenyl}pyrimidine, (R,S)‐FPPY, was investigated under pressures up to 100 MPa using a polarizing optical microscope equipped with a high pressure optical cell and a high pressure differential thermal analyser. (R,S)‐FPPY exhibits the isotropic liquid (I)–chiral smectic C (SmC*)–optically isotropic cubic (Cub)–chiral smectic X (SmX*)–crystal (Cr) transition sequence on cooling at pressures up to about 13 MPa, in which the SmC*–Cub transition occurs with an associated endothermic peak. The heating process of the (R,S)‐FPPY crystals showed the Cr–SmX*–Cub–I and Cr–SmX*–SmC*–I phase sequences under pressures below and above about 50 MPa, respectively. The triple point for the SmX*, Cub and isotropic liquid phases was estimated to be about 52±1 MPa, 143.0±0.5°C, indicating the upper limit of pressure for the formation of the cubic phase...

We prepared a homologous series of dimeric liquid crystals, α‐(4‐cyanobiphenyl‐4′‐yloxy)‐ω‐[4‐(5‐alkylpyrimidine‐2‐yl)phenyloxy]alkanes (mPYnOCB), in which cyanobiphenyl and phenylpyrimidine moieties are connected via a flexible central spacer. We investigated the physical properties of mPYnOCB and of binary mixtures between the dimeric compounds. The interdigitated anticlinic smectic C (SmCanti) phase was found to be induced for some binary mixtures between the dimers with a different odd‐numbered spacer. Furthermore, a striped pattern was observed in the SmCanti phase of a homeotropically aligned sample. The striped pattern was propagated when the temperature of the sample was varied. We discuss the correlation between the structure of the SmCanti phase and the appearance of the striped pattern.

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.

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.

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.

High resolution a.c. calorimetric measurements have been carried out on a liquid crystal 2-{4-[(R)-2-fluorohexyloxy]phenyl}-5-{4-[(S)-2-fluoro-2-methyldecanoyloxy]phenyl}pyrimidine (RSFPPY), determined the present measurement revealed precise temperature dependence of the heat capacity over a wide temperature range including the phase transition temperatures. The isotropic-chiral smectic C transition was anomalous in that it showed quite different behaviours depending on whether the measurement was made on heating or cooling; that is attributed to the relaxational character of the transition. A new non-transitional feature in the isotropic phase was found, corresponding to a very broad heat capacity peak over a 30 K temperature range. This indicates an existence of a new phase, possibly some kind of blue phase, at the lower temperature side of the isotropic phase. (RSFPPY), determined the present measurement revealed precise temperature dependence of

The crystal structure of the title compound, which has an optically isotropic IsoX phase with an endothermic transition on cooling from an Sm*C phase, has been determined at 230 K. The crystal has a smectic-like layer structure composed of four crystallographically independent molecules. In the layer, one-dimensional chains of tightly fitted pyrimidine rings, with N... H distances shorter than the van der Waals radii, result in the large overlapping of core moieties and further induce close contacts and stereo-specific F-methyl interactions between the chiral groups; this is considered to be responsible for the uniquely organized IsoX phase.

Novel binary mixtures have been prepared between an optically active antiferroelectric liquid crystal, (S)-4-(1-methylheptyloxycarbonyl)phenyl 4′-octyloxy-biphenyl-4-carboxylate, and an optically active twin liquid crystal, (R)-3-methyladipic acid bis[4-(5-octyl-2-(pyrimidinyl)phenyl] ester, and the liquid crystalline properties investigated. The stability of each liquid crystal phase was found to decrease by mixing these two liquid crystalline materials. Furthermore, a phase diagram between these compounds showed a clear discontinuity in phase sequences. These results indicate that the liquid crystal phases are different in nature between these materials. The mixture consisting of the antiferroelectric material (40 per cent) and the twin material (60 per cent) shows an unusual liquid crystal phase, where the texture is similar to that reported for the twist grain boundary (TGB) phase. Related binary mixtures have been prepared between optically active or racemic materials, where the chirality of...

The effect of a branched alkyl chain on molecular dynamics and ordering in a chiral smectic liquid crystal has been investigated by means of DSC, optical microscopy, powder X-ray diffraction, and solid state C-13 NMR. The introduction of a second branched alkyl chain into a S*C molecule increases the molecular tilt angle, the value of the spontaneous polarization in the S*C phase, and the SA–S*C transition enthalpy. The long-range order observed by X-ray measurements and the molecular motion detected by C-13 spin relaxation are not influenced by the branched group. On the other hand, marked NMR line broadenings for the core carbons occur in the oriented S*C phase. The results obtained suggest that the branched group affects the dynamics and ordering of the molecular core in the S*C phase through the interlayer interaction.

The effects of a second branched alkyl chain, lateral substitution, and double chiral centres on the phase transition and spontaneous polarization of the ferroelectric liquid crystal having a 2-methylalkanoyl group have been investigated. The introduction of another branched alkyl chain away from the 2-methylalkanoyl group causes a sharp SC∗-SA transition peak and also enhances the ferroelectric properties in the SC∗ phase. Since the order within the layers is liquid-like in the SC∗ phase, the alkyl chain branching away from both the chiral centre and a polar group affects the overall motion of the molecule in the SC∗ phase. In the system of a compound with double chiral centres, the existence of the chiral centre in the 2-methylalkanoyl group affects the phase transition temperatures and the magnitude of the spontaneous polarization in the SC∗ phase. On the other hand, the existence of the chiral centre in the 2-methylbutyl group only affects the stability of a more highly ordered smectic phase ...