Supermolecular Liquid Crystals - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 3

Fig. 1 Templates for the design of liquid-crystalline supermolecular materials. The meso-
genic units are shown as various shapes, however, the materials may be constructed with
mesogenic units of the same type. In this case, many of the constructions shown are
essentially dendritic
be tied end to end to give linear supermolecular materials. If the mesogenic
groups are the same, then they are called dimers or bimesogens ,butiftheyare
different, they are referred to as dimesogens . The mesogenic units may also be
tied together laterally, rather than end to end, or they may have terminal units
tied to lateral units to give T-shaped dimers or T-shaped dimesogens ,asshown
in Fig. 1 [25].
Figure 2 shows some examples of liquid-crystalline dimers where the
liquid crystal units are identical [28-30]. In the first example, the cyanobi-
phenyl mesogenic moieties are joined together with a simple aliphatic chain.
These materials exhibit unusual odd-even effects for the clearing point tran-
sition temperatures where the liquid crystal phases melt to the amorphous
liquid. Generally, for such systems, the homologues that have connecting
spacer chains with an even number of methylene units have much higher
clearing points in comparison to the systems with an odd number of methy-
lene units. This is because the odd members tend to have bent conformational
structures which induce disorder into the mesophase structure, whereas
the even members tend to have linear structures that support mesophase
formation.