Synthesis of a Homologous Series of Alkyl Lumazines and their Application to the Dispersion of Carbon Nanotubes

In this thesis, the synthesis of a series of alkyl lumazine surfactants (LCn) is reported. Their application to the dispersion of both CoMoCAT and HiPco single-walled carbon nanotubes (SWNTs) is examined in detail and the thermal stability and chirality selection properties of dispersions made with these surfactants were compared both between themselves and with an alkyl flavin surfactant (FC12). Lumazine alkyl chain length exhibited some control over the quality and the quantity of SWNTs dispersed. LC10 was deemed most appropriate for comparison with FC12 based on considerations of solubility and nanotube individualization. Although the lumazines were less diameter-selective than the flavins, they still appeared to favor smaller-diameter tubes (<1 >nm) as compared to the FC12. The helix formed by FC12 on the surfaces of SWNTs is shown to be preserved in LCn surfactants by the existence of a sigmoidal decay in SWNT fluorescence intensity upon heating SWNT dispersions, which is the same in form as the decay exhibited by FC12-wrapped SWNTs. This decay, however, occurs at a slightly higher (~4°C) temperature and more sharply for LCn. The sum total of these properties indicates that the smaller unit size of the LCn and the lower π-π stacking ability as compared to FC12 enable greater flexibility in supramolecular assembly, resulting in lower selectivity and the selection of smaller SWNTs, and that the more electron-poor, lower π-π stacking lumazine forms a helix that is more cohesive than one made from flavins, yet with individual molecules that are more easily separated from the SWNT once the helix is ruptured.