Efficient photosensitized energy transfer and near-IR fluorescence from porphyrin-SWNT complexes

Energy transfer from photoexcited porphyrin molecules to single-walled carbon nanotubes (SWNTs) has been experimentally detected for samples in aqueous Triton X-100 micellar suspensions. Addition of SWNTs to micelle-suspended porphyrin results in strong quenching of porphyrin fluorescence. Measurements of concentration-dependent quenching and spectra suggest that this process arises from formation of ground state non-covalent complexes between porphyrins and SWNTs. Optical excitation of the porphyrin generates characteristic near-IR emission from the SWNTs, indicating efficient energy transfer within the complexes. This energy transfer is deduced to occur through a Dexter-type electron exchange mechanism. Complexation of SWNTs with organic photosensitizers provides a novel way of uniformly exciting a wide range of nanotube structural species in polydisperse samples using only a single excitation wavelength.