Copolymer-Controlled Diameter-Selective Dispersion of Semiconducting Single-Walled Carbon Nanotubes

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Abstract

The ability of a series of strictly alternating copolymers to selectively enwrap single-walled carbon nanotubes (SWNTs) is investigated. Seven copolymers comprising either fluorene or carbazole subunits separated by naphthalene, anthracene, and anthraquinone spacers are obtained in good yields via a Suzuki cross-coupling protocol. The 1,5-linked naphthalene, anthracene, and anthraquinone units are introduced to favor a spiral conformation of the polymer backbone in order to improve its SWNT wrapping features. Particularly high yields of polymers are obtained using the naphthalene-1,5-ditriflate precursor, highlighting the potential of bifunctional aryltriflates as precursors of copolymers. All polymers disperse HiPco SWNTs in toluene. The obtained dispersions are purified by density gradient centrifugation and their compositions are analyzed by photoluminescence (PL) spectroscopy. In their dispersing ability the polymers display more or less pronounced SWNT diameter selectivity. In particular, poly(9,9-didodecylfluorene-2,7-diyl-alt-anthracene-1,5-diyl) (P2) exhibits a strong selectivity toward SWNTs having a diameter of ≥0.95 nm, including close-to-zigzag nanotubes. SWNT dispersions of P2 are further analyzed by absorbance and Raman scattering spectroscopy. The diameter selectivity is attributed to the anthracene-1,5-diyl subunit. In order to combine diameter selectivity with the preference for large chiral angles as shown by polyfluorene, the number of fluorene subunits in the polymer backbone is doubled in P7. Indeed, to some extent, the combination of both selectivities is observed in its dispersing behavior.

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