The Effects of Lengths of Flavin Surfactant N-10-Alkyl Side Chains on Promoting Dispersion of a High-Purity and Diameter-Selective Single-Walled Nanotube

Flavin with defined helical self-assembly helps to understand chemical designs for obtaining high-purity semiconducting (s)-single-walled carbon nanotubes (SWNT) in a diameter (d(t))-selective manner for high-end applications. In this study, flavins containing 8, 12, 16, and 20 n-alkyl chains were synthesized, and their single/tandem effects on d(t)-selective s-SWNT dispersibility were investigated at isomolarity. Flavins with n-dodecyl and longer chain lengths (FC12, FC16, and FC20) act as good surfactants for stable SWNT dispersions whereas n-octyl flavin (FC8) exhibits poor dispersibility owing to the lack of SWNT buoyancy. When used with small-d(t) SWNT, FC8 displays chirality-selective SWNT dispersion. This behavior, along with various flavin helical motifs, prompts the development of criteria for ‘side chain length (l(S))’ required for stable and d(t)-selective SWNT dispersion, which also explains l(S)-dependent d(t)-enrichment behavior. Moreover, SWNT dispersions with flavins with dodecyl and longer l(S) exhibit increased metallic (m)-SWNT, background absorption-contributing carbonaceous impurities (CIs) and preferential selectivity of s-SWNT with slightly larger d(t). The increased CIs that affect the SWNT quantum yield were attributed to a solubility parameter. Furthermore, the effects of flavin l(S), sonication bath temperature, centrifugal speed, and surfactant concentration on SWNT purity and s-/m-SWNT ratio were investigated. A tandem FC8/FC12 provides fine-tuning of d(t)-selective SWNT dispersion, wherein the FC8 ratio governs the tendency towards smaller d(t). Kinetic and thermodynamic assemblies of tandem flavins result in different sorting behaviors in which wide d(t)-tunability was demonstrated using kinetic assembly. This study highlights the importance of appropriate side chain length and other extrinsic parameters to obtain d(t)-selective or high-purity s-SWNT.