Triphenylene as a Scaffold for New Molecular Materials
The work described in this thesis centres around our desire to use triphenylene as the scaffold for building new molecular materials. This has been approached in three different ways; firstly a twin linked by pyrrole units, secondly by twinning with triazoles, and finally via the formylation of triphenylene. A tetra-hexyloxysubstituted dipyrrolyltriphenylene twin had previously been synthesised in the group, however characterisation was difficult and therefore a twin with improved solubility was designed. The synthesis of tetra-decyloxysubstituted dipyrrolyltriphenylene was completed successfully, but the twinning of the compound could not be achieved. One possible explanation was interference of the long alkyl chains in the neighbouring positions to the pyrrole units. A new target precursor was designed with just two alkyl chains on the triphenylene. Previous work in the group had shown difficulties in the synthesis of the di-hexyloxysubstituted triphenylene, however with careful manipulations the synthesis was successful. New complications were found with the solubility of the di-hexyloxysubstituted dipyrrolyltriphenylene that could not be overcome. At this point crystals of the tetra-hexyloxysubstituted dipyrrolyltriphenylene twin had been obtained and full characterisation achieved. With the explosion of Click chemistry in the recent years, a twin linked by triazoles was targeted. The twin was designed from a tetra-hexyloxysubstituted diazidetriphenylene, coupled with di-hexyloxysubstituted diacetylenetriphenylene. The diacetylene triphenylene was synthesised successfully following on from the work achieved in the first project. Two routes were explored for the synthesis of the diazide. The first, a direct conversion of the dibromide to the diazide, gave no reaction. The second route was a series of manipulations starting from the dinitrotriphenylene. Some difficulties were found with the reduction of the dinitro compound to the diamine, however these were overcome using carefully controlled conditions. The corresponding diamide was synthesised to allow for full characterisation, as the diamine was found to decompose rapidly. Crystals were grown of the diamide and the x-ray structure was obtained, this showed an unexpected structure. The expected 3,6-substitution pattern had not been formed, in fact we had synthesised the 1,8-bisimide-2,7,10,11-tetrakis(hexyloxy) triphenylene. As the triazole linked triphenylene twin was not accessible, the diacetylenetriphenylene was twinned with itself. High dilution conditions were followed and the twin was successfully isolated. The twin showed no mesophase behaviour and remained stable beyond 300 oC. The third part of the thesis is based on the formylation of tetra-hexyloxysubstituted triphenylene. The formation of the triphenylene dialdehyde had previously eluded our group, however following a new protocol gave a successful synthesis. There were a number of potential compounds to investigate from this versatile precursor. We chose to target BODIPY-triphenylene hybrid compounds. Two compounds were designed, one from the dialdehyde where the BODIPY fragment would be attached via the central meso-carbon, and one from the dipyrrole where the BODIPY would be attached via the alpha positions of the pyrrole. Kryptopyrrole was used in the synthesis from the dipyrrole, to attempt to discourage potential polymer formation, however the reactions were not successful. The bis-BODIPYtriphenylene via the dialdehyde was successfully synthesised and the compound was observed for potential mesophase behaviour; it was seen to melt with decomposition at 150-160 oC. Finally, the triphenylene dialdehyde was used to synthesise a twin linked by diamines. The novel twinned structure has a central “void” region that we know to disfavour columnar organisation. The compound was observed for potential mesophase behaviour, and the twin was seen to exhibit only a stable nematic discotic mesophase up to 300 oC.
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