Theoretical study on electronic structures and spectroscopic regularities of ethylated single-walled carbon nanotubes

The electronic structures of a series of ethylated single-walled carbon nanotubes (SWCNTs) were studied using density; function theory (DFT) at B3LYP/6-31G(d) level. The bond vertical to the main axis of the SWCNT was predicted to be the most thermodynamically stable additive site by ethylene. The energy gaps of the ethylated SWCNTs decrease with the decrease in the symmetries after the addition. The C-C and C=C stretching vibrations in the IR spectra of the ethylated SWCNTs, compared with those in the IR spectra of the pristine SWCNTs, are red-shifted. The chemical shifts at 172.9 ppm of the bridged carbon atoms in the NMR spectrum of (3,3)-C2H4(v) (C36C2H4) are shifted downfield in comparison with those at 144.7 ppm of the same carbon atoms in (3,3) (C-36). Meanwhile, (3,3)-C2H4(v) (C36C2H4) shows a weakened anti-aromaticity owing to a nuclear independent chemical shift (NICS) at 3.6 ppm, relative to the NICS value at 6.3 ppm of (3,3) (C-36).