Optically Active Bimesogens Incorporating Branched Central Spacers

In the current fascination with liquid crystalline dimers, bimesogens and oligomers the role of the central spacer in these systems has perhaps been somewhat neglected. In compound 1, a phenyl 4-cyanobenzoate bimesogen, the central spacer incorporates a methyl group at the 2- position and is therefore chiral. The helical twisting power of 1, measured in both 5CB and E7, was found to be 0.36 and 0.35 μm-1 wt%-1 respectively. Compound 1 exhibited a monotropic chiral nematic phase, however no twist-bend modulated phase was observed. We prepared a number of analogues of 1 incorporating different mesogenic units and observe that those with a small aspect ratio are non mesogenic, whereas those with larger aspect ratios variously exhibit chiral nematic, TB, SmC and SmB phases

Mesophase structure and behaviour in bulk and restricted geometry of a dimeric compound exhibiting a nematic-nematic transition

We present structural studies of a dimeric compound composed of a central heptyl spacer linking two mesogens consisiting of terphenyl units at which two adjacent fluoro groups are attached to each central ring. The terminal rings are linked to pentyl chains as terminal groups. The material exhibits a nematic-nematic transition and a low temperature modulated phase. The higher temperature nematic phase was found to exhibit an anomaly of the bend elastic constant similar to that of the dimers with N-Ntb phase sequence, and the physical properties of the low-temperature nematic phase are similar to those of the known Ntb materials. The structure of the low-temperature modulated smectic/columnar phase is described together with its ability to form freely suspended films and fibres. The relation of the modulated structure to the fibre formation and to the appearance of the labyrinthine instability in freely-suspended films is discussed

A liquid-crystalline fullerene–oligophenylenevinylene dyad which displays columnar mesomorphism

The design, synthesis and liquid-crystalline properties of a family of hybrid compounds which are built from rod-like (oligophenylenevinylene) and disc-like [poly(benzyl ether)] units are reported. All compounds form columnar phases within broad temperature ranges; the mesophases are stable even below room temperature. Weak photovoltaic effect was observed for the C60–OPV dyad. For the molecule having a terminal OH group, frustration of the hexagonal packing was observed and gave rise to a rare phase sequence. For this material, a columnar phase with trigonal symmetry and doubling of the crystallographic lattice was found below the hexagonal columnar phase