Liquid crystals supra molecular

Fig. 49 (a) Examples of Janus-type bis-dendrons and (b) model of the self-assembly in a core-shell columnar LC structure [154]. Reproduced with permission [154, Bioinspired supra-molecular liquid crystals, Fig. 3], copyright 2006, The Royal Society... 

The most simple molecular topology of such systems reported so far is a tetrahedral supermolecule obtained by reacting tetrakis(dimethylsiloxy)-silane with alkenyloxy-cyanobiphenyls (Fig. 22), as discussed previously. Such tetramers exhibit smectic A liquid crystal phases [179]. For such end-on materials, microsegregation at the molecular level favors the formation of the smectic A phases in preference to the nematic phase exhibited by the mesogenic monomers themselves. The use of different polyhedral silox-ane systems (Fig. 24) or the Ceo polyhedron as the template for multi- and polypedal hexakis(methano)fullerenes (Fig. 70) substituted with a large number of terminally attached mesogenic groups confirm the same tendency to the formation of smectic A phases (vide supra). 

In the fledgling field of super- and supra-molecular liquid crystals, many different terms have been introduced which describe some of the same structures. Figure 1 shows some classical molecular architectures that can be used to describe the gross structures of super- and supra-molecular liquid crystals. For example, two mesogenic units, i.e., molecular entities that can be deployed in material design in order to induce mesophase formation, can... 

The bi- and trinuclear bis- and tris-cw-enaminoketonato complexes investigated by Pyzuk et al. also represent an interesting approach in designing new molecular species forming liquid crystals, with a perfect control of the location of active sites within the mesophase, thus allowing for specific interactions to take place. The choice of enaminoketone as template ligands was dictated by their relative ease of synthesis, formation of chemically stable mesomorphic complexes vide supra), and facile shape modification. 

A new type of thermotropic supramolec-ular liquid crystal obtained by molecular recognition processes through hetero-inter-molecular hydrogen bonds, which function between different and independent molecules species, were reported by Kato and Frechet [11-13] and Lehn and co-workers [14,15] in 1989 and 1993. After these findings, a wide variety of structures of molecular complexes has been prepared by supra-molecular self-assembly. 

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