Surface coating- and light-controlled oxygen doping of carbon nanotubes

Tuning the optical properties of single-wall carbon nanotubes (SWCNTs) via oxygen doping has been a simple and effective approach to create fluorescent quantum emitters. We performed oxygen doping of SWCNTs in water utilizing chirality-pure (6,5) enantiomers with different surface coatings of DNA and surfactants by ultraviolet (UV) light irradiation. We found the reaction to be primarily dependent on the wavelength of UV light and the specific coating material on the nanotube surface. Particularly, DNA coatings react more readily with the reactive oxygen species that is photochemically produced under short-wavelength UV light than SWCNTs, preventing oxygen doping of nanotubes from occurring. The surface coverage of SWCNTs created by coating materials plays a weaker role in controlling the reaction efficiency of oxygen doping. This is demonstrated clearly by the lack of oxygen doping for two (6,5) enantiomers wrapped by DNA with drastically different surface coverages. These findings reveal important mechanisms of oxygen doping of SWCNTs, providing methods of controlling optical properties of nanotubes for developing unique applications.