Supermolecular Liquid Crystals - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 44

2.6
Effect of Hard Core Scaffolds - Fullerene
Apart from employing octasilsesquioxane as the central scaffold, other rigid
cage structures can be used as the central building block, for example [60]ful-
lerene. The hexa-adducts of [60]fullerene can give a spherical distribution
of mesogenic substituents about the central scaffold, and thus these types
of supermolecular material have similar topologies to those of the octa-
and hexa-substituted silsesquioxane. Not surprisingly, therefore the fullero-
dendrimers exhibit similar mesophase behavior to the silsesquioxane den-
drimers. For example, compound 45 , shown in Fig. 53 [76] is similar in
topology to supermolecule 43 showninFig.40.Material 45 exhibits a rela-
tively high glass-transition temperature, 80 ◦ C, followed by a transition to
a smectic A phase. No other liquid crystal phase is observed and the liquid
crystal state collapses to the liquid at 133 ◦ C. The octasilsesquioxane, 43 ,ex-
hibits the following phase sequence and transition temperatures; g -17.5 SmC
63.1 SmA 1 91.7 ◦ C Iso Liq. Thus it can be seen that the lower glass transi-
tion reveals the presence of smectic polymorphism. Often because of higher
glass transition temperatures or melting points, fullero-dendrimers with ter-
minally appended mesogens tend not to exhibit smectic C phases.
Terminally appended chiral mesogens have also been investigated through
the deployment of cholesteryl substituents [97]. For example, material 46 has
been prepared and shown to exhibit a smectic A phase, thus it has properties
Fig. 53 Supermolecular fullero-dendrimer 45