Recognition and one-pot extraction of right- and left-handed semiconducting single-walled carbon nanotube enantiomers using fluorene-binaphthol chiral copolymers

Synthesized single-walled carbon nanotubes (SWNTs) are mixtures of right- and left-handed helicity and their separation is an essential topic in nanocarbon science. In this paper, we describe the separation of right- and left-handed semiconducting SWNTs from as-produced SWNTs. Our strategy for this goal is simple: we designed copolymers composed of polyfluorene and chiral bulky moieties because polyfluorenes with long alkyl-chains are known to dissolve only semiconducting SWNTs and chiral binaphthol is a so-called BINAP family that possesses a powerful enantiomer sorting capability. In this study, we synthesized 12 copolymers, (9,9-dioctylfluorene-2,7-diyl)x((R)- or (S)-2,2'-dimethoxy-1,1'-binaphthalen-6,6-diyl)y, where x and y are copolymer composition ratios. It was found that, by a simple one-pot sonication method, the copolymers are able to extract either right- or left-handed semiconducting SWNT enantiomers with (6,5)- and (7,5)-enriched chirality. The separated materials were confirmed by circular dichroism, vis-near IR and photoluminescence spectroscopies. Interestingly, the copolymer showed inversion of SWNT enantiomer recognition at higher contents of the chiral binaphthol moiety. Molecular mechanics simulations reveal a cooperative effect between the degree of chirality and copolymer conformation to be responsible for these distinct characteristics of the extractions. This is the first example describing the rational design and synthesis of novel compounds for the recognition and simple sorting of right- and left-handed semiconducting SWNTs with a specific chirality.