(688d) Nonpolar Microenvironments around Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) have a unique near-infrared fluorescence associated with their (n,m) type. Here we show that mixing aqueous suspensions with immiscible solvents results in solvatochromic shifts associated with environmental changes surrounding the SWNTs. These shifts suggest the hydrophobic region of the micelle swells with the organic solvent when mixed. We use these new microenvironments around SWNTs to investigate the photophysical properties of SWNTs in 16 nonpolar solvents and mixtures. The solvatochromic shifts follow the expected behavior from a polarizable solute in a polarizable solvent. The PL intensity is shown to be very sensitive to small concentrations of polar components. The solvatochromic shifts of the aqueous SWNT suspensions are reversible once the solvent evaporates. However, some surfactant-solvent systems show permanent changes to the NIR fluorescence emission intensity after exposure to the organic solvent. The intensity of some large diameter SWNT (n,m) types increase by more than 175%. These differences are attributed to surfactant reorganization, which can improve nanotube coverage, resulting in decreased exposure to quenching mechanisms from the aqueous phase.