Supermolecular Liquid Crystals - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 24

Fig. 26 Local structure of the chiral smectic C ∗ phase

showed a crystalline solid at lower temperatures. As the chiral group chosen
was 2-methylbutyl, the chiral nematic phase was not iridescent, because the
pitch of the chiral phase was too long. In addition, the smectic C ∗ phase is ex-
pected to be ferroelectric, however, the polarization would be expected to be
relatively small because of the weak dipole at the stereogenic center.
The laterally appended dendrimer, 32 , shown in Fig. 27, as expected ex-
hibits a chiral nematic phase, with smectic mesophase formation being sup-
pressed. The clearing point is almost 50 ◦ C lower, whereas the melting point
is only 25 ◦ C lower in comparison to the terminally appended system. This
demonstrates that lateral appendages of the mesogens causes disruption to
the intermolecular packing, thereby destabilizing mesophase formation. The
local structure of the chiral nematic phase is thus shown in Fig. 28.
In the synthesis of the dendrimers it is more difficult to attach the den-
drons with laterally appended mesogens to the scaffold than it is to attach the
dendrons with terminally appended mesogens. This may be associated with
the effects of a higher degree of crowding produced by the laterally attached
mesogens. This forces the issue of dispersity, but in a controlled way, it is pos-
sible to prepare a dendrimer with only three dendrons rather than the four
that are possible, as shown in Fig. 29. The three-armed product, 33 , possesses
a nematic phase with a similar structure to that shown in Fig. 28 for the four-
armed dendrimer. Remarkably, the melting points and clearing points of the