Variations in bile salt surfactant structure allow tuning of the sorting of single-wall carbon nanotubes by aqueous two-phase extraction.

Being some of the most efficient agents to individually solubilize single-wall carbon nanotubes (SWCNTs), bile salt surfactants (BSS) represent the foundation for the surfactant-based structure sorting and spectroscopic characterization of SWCNTs. In this work, we investigate three BSS in their ability to separate different SWCNT chiral structures by aqueous two-phase extraction (ATPE): sodium deoxycholate (DOC), sodium cholate (SC) and sodium chenodeoxycholate (CDOC). The small difference in their chemical structure (just one hydroxyl group) leads to significant differences in their stacking behavior on SWCNT walls with different diameter and chiral structure that, in turn, has direct consequences for the chiral sorting of SWCNTs using these BSS. By performing several series of systematic ATPE experiments, we reveal that, in general, the stacking of DOC and CDOC is more enantioselective than the stacking of SC on the SWCNT walls, while SC has a clear diameter preference for efficiently solubilizing the SWCNTs in comparison to DOC and CDOC. Moreover, combining sodium dodecylsulfate with SC allows for resolving the ATPE sorting transitions of empty and water-filled SWCNTs for a number of SWCNT chiralities. We also show that addition of SC to combinations of DOC and sodium dodecylbenzenesulfonate can enhance separations of particular chiralities.

Diameter-Dependent Optical Absorption and Excitation Energy Transfer from Encapsulated Dye Molecules toward Single-Walled Carbon Nanotubes.

The hollow cores and well-defined diameters of single-walled carbon nanotubes (SWCNTs) allow for creation of one-dimensional hybrid structures by encapsulation of various molecules. Absorption and near-infrared photoluminescence-excitation (PLE) spectroscopy reveal that the absorption spectrum of encapsulated 1,3-bis[4-(dimethylamino)phenyl]-squaraine dye molecules inside SWCNTs is modulated by the SWCNT diameter, as observed through excitation energy transfer (EET) from the encapsulated molecules to the SWCNTs, implying a strongly diameter-dependent stacking of the molecules inside the SWCNTs. Transient absorption spectroscopy, simultaneously probing the encapsulated dyes and the host SWCNTs, demonstrates this EET, which can be used as a route to diameter-dependent photosensitization, to be fast (sub-picosecond). A wide series of SWCNT samples is systematically characterized by absorption, PLE, and resonant Raman scattering (RRS), also identifying the critical diameter for squaraine filling. In addition, we find that SWCNT filling does not limit the selectivity of subsequent separation protocols (including polyfluorene polymers for isolating only semiconducting SWCNTs and aqueous two-phase separation for enrichment of specific SWCNT chiralities). The design of these functional hybrid systems, with tunable dye absorption, fast and efficient EET, and the ability to remove all metallic SWCNTs by subsequent separation, demonstrates potential for implementation in photoconversion devices.