Probing single-walled carbon nanotube defect chemistry using resonance Raman spectroscopy

Using state-of-the-art time-dependent density functional theory and employing the complex polarization propagator theory, we compute the UV-vis absorption and resonance Raman (RR) spectra of pristine and H- and F-decorated single-walled carbon nanotubes (SWCNTs). We find that H- and F-functionalization brightens a low energy exciton that couples the SWCNT local-defect chemistry to its extended π network. Surprisingly, the energy of the strongly light absorbing π-π⁎ excitation (S11S) and the Raman shift of the radial breathing mode (RBM) are not very sensitive to the presence of the defects, and to a lesser degree their type. In contrast, the RR intensities of the RBM resonance profile are reduced by two orders of magnitude upon functionalization due to changes in the dynamic polarizabilities. Additionally, the resonance profile shows sensitivity to the defect chemistry where the H-functionalized CNTs have a factor ≈4 larger intensities than F-functionalized CNTs in the near resonance region. Despite the differences in the nature of the local defects, our findings are in good agreement with recent experiments on individual SWCNTs with well controlled topological defects. The study shows that photoluminescence is not sensitive to low concentrations of defects, but RR spectroscopy provides a powerful ultra-sensitive tool to identify and categorize CNT defects.