Résumé
Middle infrared response on a carbon nanotube is very weak because this homonuclear allotrope of carbon does not bear permanent dipoles. Nevertheless, a significant number of infrared phonons are predicted by the group theory. Encapsulating molecules inside nanotubes (called hybrid nanotubes in the following) is a common strategy to add new functionalities. The one-dimensional nature of single-walled carbon nanotubes (SWCNT) internal channels has been exploited here to induce a molecular order and specific interactions which are dependent of the size of the nano container (figure).Here we report the discovery of a strong dependence on the infrared response of the hybrid nanotube due to confinement effect when dimethylquaterthiophenes are encapsulated inside SWCNTs1. Results are compared to experiments performed on nanotubes where dyes are π-stacked at the outer surface. Surprisingly, the confinement properties lead to an exaltation of the infrared absorption response in the carbon nanotubes from dye molecule interactions. Thanks to the comparison between the experimental investigations and DFT calculations, we elucidate the origin of the large enhancement of this infrared absorption and demonstrate that interactions between conjugated oligomers and nanotubes can be probed.