Single-walled carbon nanotubes (SWNTs) have either chiral or achiral form, and synthesized chiral SWNTs include both leftand right-handed structures in equal amounts. Recently, a racemic mixture was found to be resolved through molecular recognition with gable-type chiral diporphyrins, namely, nanotweezers. This novel separation method for SWNTs allowed optical resolution of SWNTs for the first time. The chiral nanotweezers consist of two chiral porphyrins and rigid spacer in between. Therefore, they have potential to discriminate not only the handedness but also the diameters or alignments of the hexagons of SWNTs. We have prepared the following three types of chiral nanotweezers; m-phenylene-, 2,6-pyridylene-, and 3,6-carbazolylene-bridged diporphyrins. In the extraction of SWNTs, different selectivities have been observed among the nanotweezers. This can be attributed to the differences in their structures; namely, the dihedral angles and the distance of the two porphyrins. In this review, we would like to discuss the relationship between the structures of the nanotweezers and the results of the optical and (n,m) enrichments of the extracted SWNTs.

Review: 56 refs.