Helicity Sorting and Optical Resolution of Functionalized Single-Walled Carbon Nanotubes and Their Optical Properties

The helicity sorting and optical resolution of single-walled carbon nanotube (SWNT) derivatives were investigated to elucidate their fundamental properties and to fully understand their application scope. Herein, the helicity sorting and optical resolution of functionalized SWNTs (SWNTs-xylyl), which were prepared by reductive alkylation using 1,2-bis(bromomethyl)benzene, were achieved for the first time via gel chromatography using an agarose gel as the stationary phase. By applying a stepwise elution, three surfactant types (6,4) SWNTs-xylyl, (11,-5) SWNTs-xylyl, and (6,5) SWNTs-xylyl were successfully separated and characterized. The circular dichroism spectra of (11,-5) SWNTs-xylyl and (6,5) SWNTs-xylyl were mirror images of each other along the abscissa, confirming the successful enantiomeric separation of these functionalized SWNTs. Both of the SWNTs-xylyl enantiomers showed red-shifted near-infrared (NIR) photoluminescence (PL) peaks, which were assigned to quantum defects formed by the chemical modification process. The intensity of the red-shifted PL peak of SWNTs-xylyl significantly increased after the separation. Compared to the sample before the separation, the purified (6,5) SWNTs-xylyl exhibited a considerable red-shifted PL with reduced concentration quenching effects. Owing to these properties, the helicity sorting and optical resolution of functionalized SWNTs may have practical applications as efficient NIR optical materials.