Probing the Selectivity of Azomethine Imine Cycloaddition to Single-Walled Carbon Nanotubes by Resonance Raman Spectroscopy

Selective covalent surface modification of single-walled carbon nanotubes (SWNTs) is of great importance to various carbon nanotube-based applications as it might offer an alternative method for enriching metallic and semiconducting nanotubes. Herein, we report on the surface modification of SWNTs through 1,3-dipolar cycloaddition of 3-phenyl-phthalazinium-1-olate, which is a stable and reactive azomethine imine. For this reaction, microwave heating was found to be more efficient than conventional and solvent-free heating. The sensitivity of cycloaddition to the molecular structure of SWNTs was probed using resonance Raman spectroscopy with three different laser excitations. Based on the obtained results, azomethine imine addition to the surface of nanotubes is selective for metallic and large-diameter semiconducting SWNTs. Thermogravimetric analysis coupled with mass spectrometry showed that fragments released at high temperatures corresponded to the phenylphthalazine group, thus confirming the covalent surface functionalization. Modified SWNTs were further characterized by X-ray photoelectron and UV/Vis-NIR spectroscopies.