Supermolecular Liquid Crystals - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 38

Fig. 44 Schematic representation of the local nematic structure and the helical structure
of the chiral nematic phase of dendrimer R

2-octyl, as for polypede 42 ( M W = 6889) in comparison to 41 ,theglassto
chiral nematic phase transition is lowered to a value below room tempera-
ture, and similarly the clearing point is substantially reduced. However, the
chiral nematic phase still exists over a temperature range of approximately
60 ◦ C, which is quite remarkable considering that the low molar mass equiva-
lents melt above 70 ◦ C, thus supermolecular systems provide access to liquid
crystal phases over much wider temperature ranges than the low-molar-mass
equivalents [92].
The pitch of the helix for compound 42 was found to be approximately
0.2-0.3 m, thus the material selectively reflects visible light over a wide tem-

perature range. Moreover, the pitch is relatively temperature insensitive thus
the material can be used in large area non-absorbing polarizers, or in op-
tical notch filters or reflectors. In addition, in the glassy state the helical
macrostructure of the chiral nematic phases is retained, thus similar applica-
tions are possible.
As with the terminally appended system 39 , dendritic growth of the oc-
tasilsesquioxane core allows twice the number of mesogenic units be bound
to the central scaffold. Thus, the first generation octasilsesquioxane den-
drimer 43 , see Fig. 46, which is the size of a small protein ( M W = 14653)
possessing 16 side-on attached mesogenic units, was reported [94]. After
purification of this material it was found to be monodisperse by Maldi- tof

µ