Interactions of small molecules and Au nanoparticles with solubilized single-wall carbon nanotubes

Oxidatively end-cut single-wall carbon nanotube (SWNT) has been solubilized (sol-SWNT) in organic solvents by refluxing in aniline and purified by silica gel chromatography. NMR analysis of sol-SWNT indicates that the ratio of nanotube carbons to aniline sites is 360:1. A hydroxy-stilbene fluorophore (trans-4-nitro-4'-hydroxy stilbene, 1) adsorbs onto sol-SWNT, but can also be demonstrably ester-coupled to the nanotube material, based on comparisons of absorbance spectra. In the combinations of I and sol-SWNT made by ester-coupling and adsorption, the fluorescences of hydroxy-stilbene and of sol-SWNT could be excited selectively and separately. When exciting (500 nm) the sol-SWNT in the presence of adsorbed hydroxystilbene, the nanotube's emission intensity decreases, but the energetics are unchanged, whereas ester-coupled hydroxy-stilbene diminishes both the sol-SWNT energy and intensity. When exciting either adsorbed (at 372 nm) or ester-coupled stilbene (at 347 nm), the stilbene emission intensities are substantially reduced, and a weak, photosensitized sol-SWNT emission could be seen. Energy transfer quenching of the stilbene by the nanotube structure produces some quantity of excited states that relax by emission. Mixed monolayer-protected Au clusters adsorb strongly onto both end-opened SWNT and sol-SWNT. Adsorption of MPCs with hydroxyl groupings in the mixed monolayer onto end-opened SWNTs occurred without change in shape of the nanotube bundles but could effect the rolling up of the more flexible sol-SWNTs. Amine-labeled MPCs were less aggressive adsorbers and the 15-20 nm nanombe bundles of sol-SWNT could be imaged, outlined with the adsorbed nanoparticles.