The functionalization of nanoparticles is nowadays a standard procedure for many applications. Carbon nanotubes are no exception, and their functionalization has become an important part of the research effort these past decades. Nevertheless, there is still a lack of knowledge concerning the efficiency of the grafting processes, and more specifically concerning the question of the competition between covalent and non-covalent grafting when functionalized for example with aromatic fluorescent molecules. In a previous article, we investigated the grafting of fluorescein isothiocyanate onto double-walled carbon nanotubes. In order to explore the influence of the geometry of the fluorophore on the efficiency of the grafting processes, this work investigated the grafting of a streptocyanine onto the same carbon nanotubes using a combination of X-ray photoelectron spectroscopy, inelastic neutron scattering spectroscopy and computational simulations. The selected streptocyanine presents a very different geometry compared to FITC. Nevertheless, we show that, as in the case of FITC, both covalent and non-covalent grafting occurred simultaneously and that a comparable fraction of the fluorophore remained simply adsorbed onto the DWNTs despite thorough washings, indicating that the geometry of the streptocyanine did not exhibit the expected influence on the grafting process efficiency.