Retention of intrinsic electronic properties of soluble single-walled carbon nanotubes after a significant degree of sidewall functionalization by the bingel reaction

Sidewalls of acid-treated, shortened single-walled carbon nanotubes (SWNTs) with long alkyl chains at the open ends and defect sites have been functionalized by Bingel reaction to examine the structures and spectroscopic properties in detail for the first time. The microwave-assisted Bingel reaction has been successfully applied to the sidewall functionalization of which the reaction rate is ca. 50 times faster than that under the conventional conditions. The degree of the sidewall functionalization (one diester unit per 75-300 carbon atoms of SWNTs) was found to be controllable by changing the output power of the microwave under the same temperature. Atomic force microscopy and transmission electron microscopy showed the progressive exfoliation of the SWNT bundles by the double chemical modification. Resonant Raman and UV-vis-NIR absorption spectroscopies revealed that the electronic properties of SWNT are largely retained after a significant degree of sidewall modification by the Bingel reaction without apparent selective reactivity for metallic and semiconducting SWNTs. This is in remarkable contrast with the conventional sidewall functionalization of SWNTs leading to the loss of their electronic properties (one functional group per 10-100 carbon atoms on the sidewall). Thus, our covalent functionalization methodology can provide SWNT materials with both excellent solubility and inherent electronic properties which are highly desirable in solution-phase processing for the fabrication of SWNT-based molecular devices.