Manabu Takemoto

Troponoid metallomesogens with 5-alkoxy, 5-alkoxycarbonyl, 5-alkanoyloxy, 5-alkyl, 5-alkoxy-2-amino, and 5-alkoxy-2-alkylamino substituents

Metal complexes (Cu, VO, Zn, Mn, and Ni) with 5-alkoxy-, 5-alkoxycarbonyl-, 5-alkanoyloxy-, and 5-alkyl-tropolonato structures as well as bis(5-alkoxy-2-aminotroponato)copper were synthesized. All bistropolonato Cu complexes showed ordered smectic phases such as hexatic smectic B, smectic G(J), and smectic H phases. The Zn, Mn, and Ni complexes were non-mesomorphic whereas the VO complexes with 5-alkoxy- and 5-alkanoyloxy-tropolonato groups had mesophases. Among the Cu complexes, bis(5-alkanoyloxytropolonato)copper complex had the highest clearing point. The mesomorphic properties depend on the kinds of substituents, metal ions, and heteroatoms of the core. The Cu complexes have a square planar coordination structure and the VO complexes a square pyramidal one. The thermal stability of the Cu complexes was explained by the size and symmetry of the core structure. To decrease the transition temperatures of bis(5-alkoxytropolonato)copper complexes, secondary alkoxyl groups were introduced at the C-5 positions and the two oxygen atoms of the bistropolonato core were replaced by two nitrogen atoms, which reduced the symmetry of the structure.

Dimeric liquid crystals with two troponoid mesogenic moieties: effect of the direction of the carbonyl group on the mesomorphic properties

Three twin types of troponoid liquid crystals, in which the directions of the tropone carbonyl groups are different from each other, were prepared to establish their thermal properties. Symmetrical type I dimers, in which the two tropone carbonyl groups are directed inwards, had monotropic smectic C phases, whereas two other symmetrical type IIa and IIb dimers, whose troponoid dipoles are directed outwards, were not mesomorphic except for one type IIa compound having two long terminal chains and a short alkylene spacer. Unsymmetrical type III dimers had smectic A phases. Among the dimers, unsymmetrical type III dimers had the highest clearing point when the number of atoms of the inner and outer spacers was fixed. X-ray diffraction studies of a type III dimer, in which the number of the atoms of the inner spacer was odd, showed that the molecules form an interdigitated layer structure. The binary system between type I and type IIb dimers showed an induced enantiotropic smectic A phase, in which the dipole moments of the tropone rings were cancelled.

Non‐symmetric calamitic liquid crystal dimers containing troponoid and benzenoid units

Five types of non‐symmetric calamitic dimers were synthesized to investigate the effect of the core structure and length of the spacer on mesomorphic properties. Two non‐symmetric dimers containing a troponoid and benzenoid unit showed smectic A and C phases whereas the corresponding benzenoid dimers showed no mesophase. Non‐symmetric dimers with a three‐ring system showed smectic A and C phases with higher transition temperatures than the two‐ring system. We propose packing models for these non‐symmetric dimers by considering the direction of the dipole moments of the ring structures and microsegregation between the polar units and the non‐polar chains.

Monocyclic rod-type liquid crystals; 2,5-dialkanoyloxytropones and 5-alkanoyloxy-2-alkoxytropones

Two kinds of monocyclic troponoid mesogens, 2,5-dialkanoyloxytropones (4) and 5-alkanoyloxy2-alkoxytropones (5), were prepared. The former showed monotropic smectic A phases and the virtual isotropic liquid-smectic A transitions of the latter were determined by extrapolation of results in a binary phase diagram. Comparing the mesogenic properties between the tropones 4 and the 2-alkanoyloxy-5-alkoxytropones (1), the alkanoyloxy group at C-5 enhances both the melting points and the transition temperatures of the smectic A phases. From the comparison between 5 and 1, the alkanoyloxy group at C-2 lowers the melting points.

Dimeric liquid crystals with 5‐(4‐alkoxybenzoyloxy)tropone or 4‐(4‐alkoxybenzoyloxy)phenyl cores: evaluation of the tilt angles of the cores, spacers, and side chains

Two types of symmetric dimers with 5‐(4‐alkoxybenzoyloxy)tropone cores or with 4‐(4‐alkoxybenzoyloxy)phenyl cores were synthesized to evaluate the effect of the core structure and the length of the spacer on the mesomorphic properties. The former had smectic C phases whereas the latter had smectic C and F phases. Both types of dimer showed a remarkable odd–even effect on varying the spacer on the mesomorphic properties. Comparison of the thermal stability between them demonstrated that benzenoid twins are more stable than troponoid ones. The layer spacings of the smectic C phases were measured to determine the tilt angles of the core part, the spacer, and the side chains on changing the length of the spacer and the side chains. Troponoid dimers had a larger tilt angle of the core part of the smectic C phase than benzenoid twins, which lowered the thermal stability of the troponoid. Entropy changes of the smectic C phase to the isotropic liquid showed a contrast between troponoids and benzenoids. The former had smaller values and odd–even effects than the latter, which indicated that the former troponoids had a limited number of conformers in mesophases.

Troponoid Twin Dimers with Four Rings: Synthesis and Mesomorphic Properties

Twin-type troponoids with two benzene and two tropone rings were prepared. They showed nematic phases when the inner and the side chains are short while smectic A phases appear when the inner chain becomes long. Twins with long side chains and a short inner chain had smectic C phases. From X-ray diffraction study, molecular packing models are proposed. The corresponding benzenoid twins showed nematic and smectic C phases with higher thermal stability than the troponoids.

Mesogenic Properties of Bis(5-Alkoxytropolonato)Metals

Abstract Bis(5-alkoxytropolonato) metallomesogens showed mesogenic properties when the central metal ion was a copper whereas the corresponding zinc complex was not mesogenic. The X-ray diffraction study indicated the mesophases were a smectic B phase and a higher ordered phase such as a crystal B or a smectic G phase.

Directional Effects of the Carbonyl Group on the Mesogenic Properties of Twin Troponoids

Abstract Transition temperatures of four twin types of troponoid liquid crystals, in which the direction of the tropone carbonyl groups and a kind of the spacer were different from each other, were discussed. Symmetrical twin dimers 1, in which two tropone carbonyl groups direct inside, had monotropic smectic C phases whereas another symmetrical twin dimers 3 were less mesogenic than 1. Unsymmetrical twin dimers 4 had smectic A phases. Compared their thermal stabilities, unsymmetrical 4 had the highest clearing point when the number of atoms of the inner spacer was identical.