Optical Resolution and Diameter-Based Enrichment of Single-Walled Carbon Nanotubes through Simultaneous Recognition of Their Helicity and Diameter with Chiral Monoporphyrin

We have been developing host-guest methodology for separation of single-walled carbon nanotubes (SWNTs) with gable-type diporphyrins, designated as nanotweezers. In our previous works, chiral nanotweezers have been found to discriminate left- and right-handed structures (M and P forms, respectively, defined in our previous papers) as well as (n,m) structures through preferential extraction, giving optically active SWNTs with limited (n,m) forms. Herein, we report that chiral monoporphyrin also serves as a host molecule for separating, SWNTs. When methanol was used as a solvent, chiral monoporphyrin extracted SWNTs through simultaneous recognition of their helicity and diameter, providing optically active SWNTs with enrichment of larger diameters. In ethylene glycol, on the other hand, a much larger amount of SWNTs was extracted through complexation with the chiral monoporphyrin, although the selectivity is lower than that in the case of methanol. Since the monoporphyrin can be prepared much more easily than diporphyrins, this finding may open up a practical route for large-scale separation of SWNTs through molecular recognition.