Shoichi Kutsumizu

Mesomorphic phase transitions of a series of D-phase compounds

Abstract Mesomorphic phase transitions of 4′-n-alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC) with numbers of carbons (n) in the alkoxy group ranging from 11 to 22 have been studied by differential scanning calorimetry (DSC) and polarizing optical microscopy. The D phase, a mesophase of particular interest through its being optically isotropic, was observed for the n = 17, 19, 20, 21, and 22 members of the ANBCs, as well as for the n = 16 and 18 members, as reported previously. The Sc-D phase transition temperature decreased with increasing n, so that the temperature range of the D phase extended over 64° at n = 22. In the n = 15 member, the D phase was certainly observed on first heating, but was not seen on subsequent cooling and second heating processes.

The thermotropic cubic phase: a curious mesophase

Abstract The thermotropic cubic phase has been one of the more unexplored areas in liquid crystal research and has received considerable attention over the past 10 years. A review of the recent advances in the understanding of this curious mesophase is presented, giving special attention to the well-known 4′- n -alkoxy-3′-nitrobiphenyl-4-carboxylic acid homologues and related materials. It has now become clear that the formation of the thermotropic cubic phase is realized under a delicate balance of several competitive factors.

Cubic phases of 4′-n-alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC-n)

The structure of the thermotropic cubic phases of 4′- n -alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC- n , where n indicates the number of carbon atoms in the alkoxy group) was studied by X-ray diffraction. For the homologues with n = 15, 16, 17, and 18, the cubic phase was of an Ia 3 d type, whereas the homologues with n = 19, 20, and 21 exhibited an Im 3 m cubic structure; for these seven homologues the same type of cubic structure was observed both on heating and cooling. Further lengthening of the alkoxy chain to n = 22 and 26, however, gave two types of cubic structure in the cubic phase region on heating, one with Im 3 m symmetry in the low temperature region and the other with Ia 3 d symmetry in the high temperature region. On cooling, the two homologues exhibited the Ia 3 d cubic structure only. This is the first example in the cubic phase region of a series of homologues containing two types of structure, dependent on temperature and n . Such a complicated phase diagram in the cubic region is clearly understood qualitatively in terms of Gibbs free energy-temperature diagrams. The dependence of structural parameters such as the cubic lattice constant on the alkoxy chain length n are also presented and discussed.

Cubic phases of binary systems of 4′-n-tetradecyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-14)-n-alkane

The phase behaviour of the binary systems 4′- n -tetradecyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-14)- n -alkane ( n -tetradecane or n -hexadecane) was investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The phase behaviour was a function of temperature ( T ) and the effective carbon number of the system ( n*), where n* involves carbon atoms both from the alkoxy group of ANBC-14 and from the n -alkane added. ANBC-14 shows no cubic phase, but the addition of n -alkane induced cubic phases when n*≧c. 15. An interesting point is that the type of cubic phase is Ia 3 d for 15≦n*≦17, while an Im 3 m type is formed for 18≦n*≦20. Furthermore, for n* = 22, two types of cubic phase, one with Im 3 m symmetry in the low temperature region and the other with Ia 3 d in the high temperature region, were observed both on heating and cooling. The phase diagram with respect to T and n* is very similar to that of pure one-component ANBC- n , which is a function of T and the number of carbon atoms in the alkoxy group n .

Dynamic viscoelastic properties of D-phase compounds

Abstract Dynamic viscoelastic properties were studied for two D-phase compounds, 4′- n -hexadecyloxy- and 4′- n -docosyloxy-3′ carboxylic. acids. The storage modulus ( G ′) in the D phase showed an extraordinary high value of 10 7 dyne/cm 2 , compared with that in smectic A and C phases. These viscoelastic results suggest the existence of a three-dimensional network structure constructed by rod-like micelles, as proposed by Tardieu and Billard.

X-ray studies of the self-organized structure formed by 1,2-bis(4'-n-alkoxybenzoyl)hydrazine (BABH-n) homologues. 1. Ia3d-gyroid structure

The cubic (Cub) phase structure of a thermotropic mesogen 1,2-bis(4′-n-alkoxybenzoyl)hydrazine (BABH-n, where n is the number of C atoms in the aliphatic tail) was examined by small-angle X-ray scattering. The BABH-n system exhibits two types of Cub phases, Ia3d type and Im3m type. In the phase diagram as a function of the tail length (n) the Im3m-Cub phase region (n = 13–16) was sandwiched by two Ia3d-Cub phase regions with n 16. On the basis of the triply periodic minimal surface (TPMS) picture, the Ia3d and Im3m structures are described by the gyroid (G) and doubled-P (PP) surfaces, respectively. In this paper we focused attention on the internal structure of the Ia3d-Cub phase at the molecular level. By examining how the relative intensity of the 220 reflection with respect to the 211 reference peak varies with n, we have successfully determined the position of the aliphatic tails, which are located on the G-TPMSs. As far as we know, this is the first approach to clarifying the internal structure of the thermotropic Ia3d-Cub phase. The usefulness of the systematic studies with respect to the tail length n has also been demonstrated.

Photoresponsive Toroidal Nanostructure Formed by Self-Assembly of Azobenzene-Functionalized Tris(phenylisoxazolyl)benzene

The self-assembly of tris(phenylisoxazolyl)benzene 1b with photochemically addressable azobenzene moieties produced toroidal nanostructures, the formation and dissociation of which were reversibly regulated upon photoirradiation. 1b displayed a mesogenic behavior. In the solution, the stacked assemblies along with their C3 axes were formed. In the mesophase, two molecules of 1b most likely adopted the antiparallel arrangement to stabilize the columnar organization. This assembling behavior most likely triggered the development of the supramolecular toroidal nanostructures.

Phase behaviour of the thermotropic cubic mesogens 1,2-bis-(4-n-undecyl- and 4-n-dodecyl-oxybenzoyl)hydrazine under pressure

The phase transition behaviour of two optically isotropic, thermotropic cubic mesogens 1,2-bis-(4-n-undecyloxy- and 4-n-dodecyloxy-benzoyl)hydrazine, BABH(11) and BABH(12), was investigated under hydrostatic pressures up to 300 MPa using a high pressure differential thermal analyser, a wide angle X-ray diffractometer and a polarizing optical microscope equipped with a high pressure optical cell. It is found that for BABH(11) and BABH(12), a smectic C (SmC) phase is induced between the isotropic liquid (I) and the cubic (Cub) phases by applying pressures above 10–12 and 16–17 MPa, respectively. A sea–island texture consisting of bright sand-like sea regions (SmC phase) and areas of dark islands (Cub phase) appears in the mesophase under pressures up to 140 MPa, while the sand-like texture of the SmC phase is formed predominantly on cooling under pressure. These observations indicate the destabilization of the cubic phase with increasing pressure. The phase transition sequence of BABH(11) and BABH(12), Cr–Cub–I at atmospheric pressure, changes to Cr–Cub–SmC–I under intermediate pressures and would change to Cr–SmC–I under elevated pressure.

Light‐Driven Phase Transition in a Cubic‐Phase‐Forming Binary System Composed of 4′‐n‐Docosyloxy‐3′‐nitrobiphenyl‐4‐carboxylic Acid and an Azobenzene Derivative

Binary mixtures were prepared from an azobenzene derivative and a liquid-crystal (LC) compound that exhibits smectic C (SmC) and bicontinuous cubic (Cub(bi)) LC phases. Reversible switching between the two phases in response to UV-light irradiation was observed. This light-driven SmC-to-Cub(bi) transition is the first example showing the increased dimensionality of molecular ordering with isomerization of azobenzenes (see figure).

5-N-Arylaminothiazoles as Highly Twisted Fluorescent Monocyclic Heterocycles: Synthesis and Characterization.

A series of 5-N-arylaminothiazoles was prepared by reacting thioamide dianions derived from secondary thioamides with thioformamides, followed by sequential oxidation with iodine. X-ray analyses demonstrated that they adopt structures that are highly twisted from planar conformations. Their orientations were tuned by the steric and/or electronic interactions of the substituents at their 2-, 4-, and 5-positions. The 5-aminothiazoles exhibited a range of fluorescent emissions, from blue to orange. Although the absorption spectra were independent of the polarity of the solvent, fluorescent emissions were influenced by the polarity of the solvent: in more polar solvents, the emissions were red-shifted. These phenomena were examined in terms of Lippert-Mataga plots and the change in the dipole moment between the ground and excited states. They also exhibited emissions in the solid state, again from blue to orange. Cyclic voltammetry of the 5-aminothiazoles showed reversible waves of one-electron oxidation. The half-potential of the oxidation was reduced by the introduction of electron-donating groups to the phenyl groups on the nitrogen atom at the 5-position. DFT calculations were carried out to determine the energy levels of the HOMO and LUMO. Finally, the results of TG-DTA showed that they are thermally stable.