Recognition and One-Pot
Extraction of Right- and Left-Handed
Semiconducting Single-Walled Carbon Nanotube Enantiomers Using Fluorene-Binaphthol
Chiral Copolymers
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Abstract
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)<i>x</i>((<i>R</i>)- or (<i>S</i>)-2,2′-dimethoxy-1,1′-binaphthalen-6,6-diyl)<i>y</i>, where <i>x</i> and <i>y</i> 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