Spectroscopic distinction of carbon nanobelts and nanohoops

Among nanocarbon materials prepared via organic synthesis, carbon nanobelts (NBs), such as cyclacenes and cyclophenacenes, and carbon nanohoops (NHs), such as cycloparaphenylenes, are starting materials for preparing carbon nanotubes with controlled structures. Herein, X-ray photoelectron spectroscopy (XPS) and Raman spectra of zigzag NBs (ZNBs), armchair NBs (ANBs) and NHs were simulated using a computational method and calibrated against the experimental spectra of NHs with 6 and 12 benzenes. The XPS results showed that the C1s peak positions for the ZNBs were at binding energies (BEs) at least 0.5 eV higher than those for the ANBs and NHs. As the diameter increased, the peak position was shifted to higher BEs for the ZNBs but to lower BEs for the ANBs and NHs, because of the change of highest occupied molecular orbital and lowest unoccupied molecular orbital energies. The Raman spectroscopic analysis revealed that there were distinct characteristic modes for each type of structure, i.e., the C–H vibrational band for the ZNBs, the G band for the ANBs, and the D band for the NHs. As the diameter increased, the positions of these characteristic bands and the radial breathing modes were shifted. These results indicate that NBs and NHs can be distinguished using XPS and Raman spectroscopy.