Supermolecular Liquid Crystals - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 36

Fig. 41 Schematic drawing of the bilayer structure of the smectic A phase of multipede
39 . The 16 mesogenic units (cylinders and spheres which represent the cyano groups) per
molecule are accommodated in the layers without the introduction of curvature in the
packing of the mesogenic units together

macrostructure. Furthermore, the material exhibits an extraordinarily long
temperature range for the chiral nematic phase. A transition from a glassy
state to the chiral nematic phase occurs near to room temperature and then
the phase extends over 90 degrees before transforming to the isotropic liquid
at 116.9 ◦ C [92].
The local structure of the chiral nematic phase is shown in Fig. 44 where
the supermolecules are depicted as having rod-like/tubular structures where
the mesogenic units are expected to intermingle between the supermolecules.
The chiral nematic phase will have a helical macrostructure superimposed
upon the local nematic ordering as shown in the figure. Remarkably, the ma-
terial has a helical pitch of approximately 2 m, which is a relatively short

pitch considering the size of the polypede, and approximately the same as the
pitch that would be produced by the individual mesogenic units without spac-
ers being attached. However, unlike the situation for the mesogenic units, the
pitch is relatively temperature insensitive. Thus the surface of the polypede
acts as a molecular recognition surface, in a similar way to recognition sur-

µ