Simultaneous Discrimination of Handedness and Diameter of Single-Walled Carbon Nanotubes (SWNTs) with Chiral Diporphyrin Nanotweezers Leading to Enrichment of a Single Enantiomer of (6,5)-SWNTs

TLDR

Separation of single‑walled carbon nanotubes by handedness is a growing research focus. The authors aim to separate SWNT enantiomers using chiral diporphyrin nanotweezers. They designed nanotweezers 1 composed of two chiral porphyrins bridged by phenanthrene to simultaneously discriminate tube diameter and handedness based on (n,m) selectivity. The nanotweezers selectively enriched the (6,5)-SWNT enantiomer, achieving 67 % enantiomeric excess and isolating a single stereoisomer from CoMoCAT‑SWNTs.

Abstract

Separation of single-walled carbon nanotubes (SWNTs) according to their handedness has been attracting growing interest. Our methodology to separate the enantiomers of SWNTs is based on molecular recognition with chiral diporphyrin nanotweezers. Herein, we report novel nanotweezers 1 consisting of two chiral porphyrins and phenanthrene in between. These nanotweezers 1 are rationally designed to discriminate diameter and handedness simultaneously by taking into account the relationship between the (n, m) selectivity and the structures of previously reported chiral nanotweezers. Owing to the relatively narrow cleft made by two porphyrins, the nanotweezers 1 showed high selectivity toward (6,5)-SWNTs possessing the smallest diameter among the major components of CoMoCAT−SWNTs. In addition, the chiral diporphyrin 1 discriminated the left- and right-handed structures of (6,5)-SWNTs, providing high enantiomeric excess (67% ee on the basis of the (6,5)-SWNTs with high optical purity recently reported by Weisman). In conclusion, only the single stereoisomer of (6,5)-SWNTs was highly enriched through the extraction of CoMoCAT−SWNTs with phenanthrene-bridged chiral diporphyrin nanotweezers 1.