Energy transfer dynamics in functionalised carbon nanotubes

Functionnalized NT are very promizing material for light harvesting applications since they combine the exceptionnal transport properties of carbon nanotubes and the versatility of organic dyes. In this study we show that a very strong interaction can be induced between porphyrin molecules and nanotubes, even in the context of non-covalent functionnalization. This interaction leads to very efficient energy tranfer from the dye to the nanotube [1,2]. We investigate its dynamics by means of broadband femtosecond transient spectroscopy. We show that the excitation of the porphyrin molecule is first followed by a internal energy conversion down to the Q band (~100fs), followed by a subpicosecond transfer to the nanotube. The population build up is observed on the lowest exciton level of the nanotube in agreement with photoluminescence measurements. Finally, we show that the quantum efficiency of this transfer can be very close to 1with an almost total quenching of the porphyrin luminescence but a strong luminescence of the nanotube. Furthermore, the transfer is clearly enhanced when pumping in resonance with the shifted Soret band of the stacked porphyrin allowing a spectrally selective investigation of the functionnalized nanotubes.