Carborane Containing Supermolecular Liquid Crystals

In this thesis several families of supermolecular liquid crystal which contain an o-carborane cluster are described. These materials were synthesized in order to explore any effect the cluster may have upon the liquid-crystalline properties generated, in particular to see whether the cluster would drive the formation of certain phase types over others. A number of different mesogens, morphologies and chemical groups used to link the cluster to the rest of the molecules were utilized.

It was found that the presence of the cluster induces smectogenic properties in the compounds produced. Through investigation of different linking functionalities it was possible to elucidate that this effect is independent of the chemical nature of the linking group. Furthermore, this effect is also present across materials with widely varying mesogenic moieties. Through use of model compounds it was possible to determine that the smectogenic properties of the carborane cluster are unlikely to be solely caused by a steric effect, but rather must have some electronic basis.

The compounds presented here are intimately linked to other supermolecular liquid crystals which contain a rigid three-dimensional cluster component such as fullerene or silsesquioxanes. Carborane is the smallest of this family of materials to be investigated thus far. Comparison of the thermal properties of this family of related materials appears to show a general trend: a maximum in phase stability is achieved when there is an approximate match between the diameter of the cluster and the area occupied by the appended mesogens. For materials presented here this maximum was achieved when between one and two mesogens were appended and as a result the first inorganic-cluster-containing supermolecular liquid crystal which displays appreciable enatiotropic mesomorphism with a single appended mesogen has been realized.