Electronic Properties of Propylamine-Functionalized Single-Walled Carbon Nanotubes

We present resonant Raman measurements on single‐walled carbon nanotubes (SWCNT) functionalized with propylamine groups at different degrees. Direct nucleophilic addition based on in situ generated primary amides is used for attaching n‐propylamine to the sidewalls of SWCNTs. The influence of the amino functionalities on the electronic structure of the nanotubes is investigated. From the Raman resonance profiles of the radial breathing modes (RBMs), the chiral indices of the corresponding tubes are assigned. We observe significant redshifts of the transition energies and a broadening of the resonance windows due to chemical modification of SWCNTs. Similar redshifts are derived from the analysis of the NIR/Vis transmission spectrum. The relative Raman intensities of the functionalized samples and the evaluation of their transmission spectra indicate a diameter dependence of the reactivity as it has been observed for other moieties. By analyzing the defect induced D mode we observe a considerable degree of functionalization accompanied by an almost unharmed tube structure, which ensures that the observed effects are mainly driven by changes of the electronic structure. Structure–property relationships in carbon nanotubes are investigated using optical spectroscopic methods. A direct nucleophilic addition, results in a significant redshift of the optical transitions together with a broadening of the resonance window (see figure). The Raman spectra indicate a reaction diameter dependence and confirm that the nanotube atomic structure is not disturbed.