Species enrichment of SWNTs with pyrene alkylamide derivatives: Is the alkyl chain length important?

Three similar amide-functionalized pyrene derivatives (N-methyl(18-Crown-6) pyrene1-acetamide, N-methyl(18-Crown-6)pyrene-1-butyramide and N-methyl (18-Crown-6)pyrene-1-formamide), denoted as pa-18-C-6, pb-18-C-6 and pc-18-C-6, respectively, with different alkyl chain lengths between the amide groups and pyrene moieties have been successfully synthesized and for the first time, their separation effects on single-walled carbon nanotubes (SWNTs) according to their electronic structures (metallic/semiconducting) and diameter have been demonstrated. Resonant Raman spectroscopy and UV-vis-NIR show that all three pyrene derivatives are selective to metallic SWNTs (met-SWNTs). Resonant Raman scattering (RRS) spectra also indicate that two of the pyrene derivatives, pb-18-C-6 and pc-18-C-6, are selective to large-diameter (D>1nm) met-SWNTs. The third compound, pa-18-C-6, is selective to small-diameter (D<1.03nm) met-SWNTs due to the ketone-to-enol rearrangement resulting in higher strain force relaxation; the rearrangement was shown by Fourier-transform infrared spectroscopy data. For their discrimination between different relatively large-diameter semiconducting species, RRS spectra using a 785nm laser show that pb-18-C-6 is selective to larger diameter ones while pa-18-C-6 and pc-18-C-6 have no selectivity. The selectivity for met-SWNTs in the solution is confirmed by a tenfold decline in thin film SWNT network resistivity (from 43 to 4.3Sm^-1) after depletion of metallic nanotubes by a four-pass selection procedure using pa-18-C-6 and pc-18-C-6 surfactants alternately. Further, after the four-pass selection procedure, the conductivity of a network using the supernatant SWNTs changes less when heated in air compared to another network using the precipitated SWNTs; the high conductivity stability of the network with supernatant SWNTs further confirms the high content of met-SWNTs which are resistant to carrier doping.