Oligofluorene main-chain length-dependence on one-pot extraction of chirality-selective semiconducting single-walled carbon nanotubes

Abstract

Abstract Polyfluorene and their derivatives are noted for being fascinating dispersants for single-walled carbon nanotubes (SWCNTs) because they selectively solubilize semiconducting (sem-) SWCNTs. However, the selective extraction mechanism of this unique behavior has not yet been fully clarified. In this paper, we describe a unique SWCNT solubilization behavior using 12 fluorene oligomers with different main-chain lengths (FOn, n = 2∼30), in which n is the number of fluorene-repeating unit. Sonication of SWCNTs using these oligofluorenes in toluene was found to solubilize SWCNTs when the main-chain length was longer than n = 12. Raman spectra revealed that selective sem-SWCNT extraction occurred when using the FOn with n ≥ 18, while, when using FOn (n = 12, 15), both sem- and metallic (met-) SWCNTs were solubilized. The (n,m)chiralites of the extracted SWCNTs using the fluorene oligomers differed from those using a homopolymer, poly(9,9′-di-n-octylfluorene) (PFO); that is, PFO extracted (9,7)SWCNTs well, while only FO30 slightly dissolved the (9,7)tubes, and when using other FOn (n = 12∼27), no (9,7)tubes were solubilized. The present study demonstrated the importance of the main-chain length of the oligofluorenes on selected chirality extraction of sem-SWCNTs, which is useful for designing fluorene-based compounds with selective extraction of sem-SWCNTs with a specific (n,m) chirality.