Simultaneous enrichments of optical purity and (n,m) abundance of SWNTs through extraction with 3,6-carbazolylene-bridged chiral diporphyrin nanotweezers.

Abstract

Since structural control of single-walled carbon nanotubes (SWNTs) leads to control of their physical properties, isolation and synthesis of specific (n,m) structures of SWNTs have been extensively investigated in view of their technological applications. In this context, we developed a novel method for separating SWNTs through molecular recognition with chiral gable-type diporphyrins designated as "nanotweezers". The method allowed us to obtain optically active SWNTs, namely, the chiral SWNTs enriched in either left- or right-handed helical form, for the first time. In this paper, we describe prominent optical enrichment of (7,5)-SWNTs through preferential extraction with chiral 3,6-carbazolylene-bridged nanotweezers as well as simultaneous enrichment of the abundance of (7,5)- and (8,4)-SWNTs. The (n,m) enrichment through this extraction is considered to result from the diameter differentiation of the nanotweezers, suggested by the complex structures in the theoretical calculations. That is, carbazolylene-bridged nanotweezers encapsulate a SWNT deeply enough to recognize the diameter of (7,5)-SWNTs. The deep contact is considered to realize the discrimination of the small diameter difference even less than 0.10 nm. This is a significant progress toward the separation of single species of SWNTs consisting of single (n,m) structure with one helicity.