Automatic Sorting of Single-Chirality Single-Wall Carbon Nanotubes Using Hydrophobic Cholates: Implications for Multicolor Near-Infrared Optical Technologies

Single-chirality separation of single-wall carbon nanotubes (SWCNTs) is important for taking advantage of the inherent high performance of SWCNTs. Mixed surfactant systems containing cholate derivatives have commonly been used for single-chirality separation, but the chirality selection resolution remains low. This study systematically investigates the effect of cholate derivatives on chirality selection in adsorption chromatography to improve the resolution. Comparative experiments using seven cholate derivatives reveal that the separation results highly depend on the hydrophobicity of the derivative, and the highly hydrophobic cholates can achieve the highest-resolution selectivity. All separation results can be explained by hydrophobic interactions. Finally, these findings are used to maximize the single-chirality separation resolution. As a result, 20 specific chirality-enriched nanotubes, including 11 high-purity single-chirality species, can be automatically sorted from one bottle of nanotube solution. The obtained (n,m) species exhibit a variety of excitation and emission wavelengths and are useful for near-infrared optical technologies where the choice of optical transition wavelengths is limited. In particular, (7,5) and (7,6) [or (9,4), (8,6), and (8,7)] SWCNTs are useful as near-infrared phosphors for multicolor bioimaging.