Femtosecond one- and two-color pump-probe spectroscopy of single-walled carbon nanotubes (SWNTs) in aqueous surfactant suspensions typically yields transients with superimposed photoinduced-bleach and -absorption contributions. These derive both from individualized nanotubes and bundles thereof, which complicate lifetime deconvolution and explain the wide scatter in previously reported numbers. We show that the “intrinsic” lifetimes of the lowest excited states of individualized semiconducting SWNTs can be directly determined by near-IR probing to the red of their ground state absorption onsets (corresponding to transient absorptions from first to second excited states). First excited state lifetimes were found to be (35 ± 10) ps and (56 ± 10) ps, for nanotubes having mean diameters of 0.93 and 1.3 nm, respectively. Furthermore, a fast decay component in the ps to sub-ps regime was also observed. This was tentatively attributed to in-bundle relaxation.
Comparison of the ultrafast response of HiPco- and PLV-prepared single-walled carbon nanotubes. Nominally, the same types of tubes are excited, however the profiles are different due to differing superimposed photoinduced absorption contributions resulting from different diameter distributions and bundle/defect contents
Ultrafast optical switches can be obtained by studying the ultrafast photophysics of D2O/sodium dodecylbenzene sulfonate surfactant dispersions of single-walled carbon nanotubes enriched in individual tubes (versus tube bundles). Measurements at various pump and probe wavelengths showed evidence of superimposed transient bleaching as well as induced absorption behaviour. Our results indicate that such nanotube samples manifest ultrafast pump-induced switching of probe transmission with switching times < 1 ps under appropriate conditions. Given their high photochemical and photophysical stability these materials may be suitable candidates for the development of ultrafast NIR optical switches and logic gates.
These results were obtained in collaboration with the group of Prof. M. Kappes
 H. Hippler, A.-N. Unterreiner, J.-P. Yang, S. Lebedkin and M. M. Kappes, “Evidence of ultrafast optical switching behaviour in individual single-walled carbon nanotubes”
Phys. Chem. Chem. Phys., 6, 2387-2390 (2004)
 J.-P. Yang, M. M. Kappes, H. Hippler and A.-N. Unterreiner, “Femtosecond transient absorption spectroscopy of single-walled carbon nanotubes in aqueous surfactant suspensions: Determination of the lifetime of the lowest excited state”
Phys. Chem. Chem. Phys., 7, 512-517 (2005)<