Abstract
Single-wall carbon nanotubes non-covalently functionalized with porphyrin molecules have proven to be a very promising light harvesting system either for energy or charge transfer. In this paper we investigate the dynamics of this coupling at a sub-picosecond time-scale, by means of transient absorption spectroscopy. We show that the ground state recovery time of the porphyrin is reduced by several orders of magnitude in the compound compared to the case of pristine porphyrin. Concomitantly, a strong bleaching signal is observed on the optical resonances of the nanotubes showing an ultrafast population buildup upon excitation of the porphyrin. We conclude that the energy transfer occurs on a time-scale shorter than 100 fs. Two-color measurements show that higher excited states of the nanotubes are populated on the same time-scale raising the point of the transfer mechanism. We briefly discuss two possible mechanisms.