Separation of semiconducting single-walled carbon nanotubes by using a long-alkyl-chain benzenediazonium compound

We designed and synthesized 4-dodecyloxybenzenediazonium tetrafluoroborate (1), which preferentially reacts with metallic single-walled carbon nanotubes (SWNTs) by kinetic control. We first determined the suitable experimental conditions for the preferential reaction of 1 with individually dissolved SWNTs by monitoring the decrease in absorbance for the metallic SWNT in the range of 400-650 nm in the absorption spectrum of the SWNTs. The reacted SWNTs were thoroughly rinsed with THF to obtain THF-insoluble SWNTs. The Raman spectrum of the THF-insoluble SWNTs showed a strong peak near 180 cm^-1, which corresponds to a semiconducting breathing band. The metallic breathing bands (≈ 220 cm^-1) and Breit-Wingner-Fano (BWF) modes (1520 cm ^-1) corresponding to the metallic SWNTs were much weaker than those of the pristine SWNTs. We also confirmed that metallic peaks in the range of 400-650 nm in the absorption spectrum of THF-insoluble SWNTs that were individually dissolved in an aqueous micelle of sodium cholate were almost nondetectable. All the results indicate that the THF-insoluble SWNTs are semiconducting.