Endohedral confinement of dies inside carbon nanotubes : key factor for charge transfer modulation
Résumé
Encapsulating molecules inside nanotubes (called hybrid nanotubes in the following) is a common strategy to add new functionalities to the nanocontainer. The one-dimensional nature of single-walled carbon nanotubes (SWCNT) internal channels is exploited here to induce a molecular order and specific interactions which are dependent of the size of the nano container (figure 1). I present here the study of the relation between structural, vibrational and electronic properties of hybrid nanotubes encapsulating dyes. Dimethyl-quarterthiophene (4TCH3) encapsulated inside single-walled carbon nanotubes is studied by inelastic neutron scattering. The results reveal specific dynamics of the 4TCH3 modes characterized in particular by a large sensitivity in the low frequency domain of the methyl libration to the confinement. DFT based calculations consistently describe the observed phenomena and give insights on the structure of the hybrid nanotubes at low temperature where molecules preferentially interact with the nanotube wall.
We evidence also by means of Raman spectroscopy and transmission electron microscopy that the supramolecular organizations of the confined oligothiophenes depend on the nanocontainer size. Charge transfer between the dyes and the nanocontainer is shown. A strong dependence on the infrared response of the hybrid nanotube due to confinement effect is finally investigated. The 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.