Density functional study of the¹³C NMR chemical shifts in single-walled carbon nanotubes with stone-wales defects

The ¹³C NMR chemical shifts of (7,0), (8,0), (9,0), and (10,0) single-walled carbon nanotubes (SWNTs) with Stone-Wales (SW) defects have been studied computationally using a gauge-including projector-augmented plane-wave (GIPAW) density functional theory (DFT) method. A SW-defect substantially broadens the NMR signal of a particular tube, however, in general the average shift of the non-defect carbons does not differ greatly from that of the pristine species. "Parallel" orientations of the defect site yields shifts at around 150-160 ppm from atoms in the defect site which are separated from the rest of the NMR signal. Therefore, the results indicate that ¹³C NMR might be able to detect the presence of, and perhaps even quantify the concentration of SW defects found in SWNTs. Differences in the NMR obtained for two defect orientations are analyzed by comparing the shifts of the defect atoms with those of planar and bent structures of the azupyrene molecule. Representative visualizations for the shielding tensors of the (8,0) SWNT with and without defects are also reported.