The discovery of discotic liquid crystals in 1977 by Chandrasekhar has led to an ever increasing interest in the preparation of new discotic mesogens. Research on the potential application of such systems has, however, been held back mostly by synthetic and purification difficulties to obtain enough of the required pure materials. The work described in this thesis (Chapter 2) concerns the synthesis of macrodiscotic structures which led to the formation novel discotic liquid crystalline systems. Nonplanar substituted phthalocyanines have been described by Simon and were found to be mesogenic. We expected that planarising these systems (formation of triphenylene) would have the effect of changing both the absorption (shift to longer wavelength due to extra conjugation) and the mesogenic properties (due to formation of large discs). The syntheses of triphenylenophthalocyanines were achieved using palladium catalysed aryl-aryl cross-coupling as key step in the syntheses. The end materials were characterised and tend to be mesogenic. After the successful synthesis of the triphenylenophthalocyanines, we were in a position to further extend the n-system of our phthalocyanines and the molecules targeted were perylenophthalocyanines (Chapter 3). The syntheses were achieved through a cyc1oaddition reaction as key step. In this case, however, none of the perylenophthalocyanines were liquid crystalline. 3: 1 phthalocyanines were also prepared and tend to be non-mesogenic. A senes of mixed hexyloxy-Ihexylthio-triphenylenes has also been synthesised to determine the structural features governing the formation of helical mesophases shown by HHTI (Chapter 4). It has been shown that four sulphide substituents (plus two alkoxides) are required to induce the additional, more ordered phase. Furthermore, the position of substitution is crucial for its formation. Also, the synthesis and characterization of a series of triphenylenes has been described in which 2, 4 or 6 of the alkyloxy chains of parent hexa(hexyloxy)triphenylene are replaced by heptyl chains (giving mixed alkyl-alkyloxy triphenylenes). This series provides a direct comparison to the derivatives which gives to the rare helical phase. Finally, the synthesis of a few novel triphenylene molecules expected to be on the boundaries between the traditional rod-shaped and disc-shaped structure were achieved. Some of these compounds formed discotic mesophases.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:398494 |
| Date | January 2003 |
| Creators | Gopee, Hemant |
| Publisher | University of East Anglia |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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