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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 (dt)-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 dt-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-dt SWNT, FC8 displays chirality-selective SWNT dispersion. This behavior, along with various flavin helical motifs, prompts the development of criteria for 'side chain length (lS)' required for stable and dt-selective SWNT dispersion, which also explains lS-dependent dt-enrichment behavior. Moreover, SWNT dispersions with flavins with dodecyl and longer lS exhibit increased metallic (m)-SWNT, background absorption-contributing carbonaceous impurities (CIs) and preferential selectivity of s-SWNT with slightly larger dt. The increased CIs that affect the SWNT quantum yield were attributed to a solubility parameter. Furthermore, the effects of flavin lS, 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 dt-selective SWNT dispersion, wherein the FC8 ratio governs the tendency towards smaller dt. Kinetic and thermodynamic assemblies of tandem flavins result in different sorting behaviors in which wide dt-tunability was demonstrated using kinetic assembly. This study highlights the importance of appropriate side chain length and other extrinsic parameters to obtain dt-selective or high-purity s-SWNT. [ABSTRACT FROM AUTHOR]

Although solvent governed stability, selection and optical behavior of single walled carbon nanotubes (SWNTs) brought about by using specialized surfactants have importance in relation to various optoelectronic and biological applications, their origins and solvatochromism have not been thoroughly explored owing to the lack of ideal surfactant dispersing SWNTs. We show that solvent driven SWNT selection and solvatochromism occurs in SWNTs wrapped by two flavin derivatives in solvents with dielectric constants (ε) ranging from 2.3 to 80.4. Flavin-SWNT nanocomposite dispersions exhibit near-armchair and chirality-specific enrichment in lower ε aromatic solvents, and those with broader chirality selectivity are formed in higher ε solvents. Those trends are also observed by controlling flavin concentration. Consideration of optical spectra provides relative quantum yields of flavin-SWNT in each solvent, showing toluene and p -xylene dispersions as best owing to highly individualized SWNT. The selectivities and relative stabilities of the flavin-SWNT nanoconjugates are associated with the solubility parameter (δ), which controls the respective morphology of the side chains and the relative Gibbs energies of the nanoconjugates relative to those of the free flavin and SWNTs. Differences between δ of side chains vs. the media results in extended and collapsed side chain conformations in respective lower and higher ε solvents, leading to diameters (d t) selection of SWNT owing to diameter modulation of the isoalloxazine assembly. In addition, with increasing ε optical transitions of flavin/SWNT exhibit lower bathochromic shifts owing to a passivating role played by the isoalloxazine that does not take place with other surfactants. The results suggest new guidelines for the design of good SWNT dispersions that take into consideration self-association of the surfactant, conformations of side chains and the nature of the solvent. [Display omitted] [ABSTRACT FROM AUTHOR]

Despite the many advances that have been made in using anionic surfactants to disperse and sort single-walled carbon nanotubes (SWNTs) for optoelectronic applications, one-pot methods for deposition of SWNTs in a diameter (d t) and position controlled manner from as-dispersed sample are essential. Here, we designed and prepared flavin-containing self-assembled monolayers (flavin-SAMs) that can be used to assemble d t -selective individualized SWNT networks directly from SWNT dispersions by using the widely-used anionic surfactant. For a given glass substrate, the dimethallylsilane-linked azide, along with surface immobilization was employed to have Click reaction with terminal acetylene tethered to flavin group known to have strong affinity with SWNT. As demonstrated by atomic force microscopy and other methods, along successful assembly of individualized networks, the SWNTs are either fully or partially wrapped in a d t selective manner by isoalloxazine moieties tethered to the surface, displaying Langmuir isotherm adsorption behaviors in a dipping method dependent manner. The assembled SWNT network secures photoluminescence and electrical conductivity albeit its intimacy to underlying substrate and near monolayer coverage of SWNT network, respectively, and, furthermore, preferentially takes place on flavin-SAM over hydrophobic surface. Functional self-assembled monolayer captures single-walled carbon nanotube network with diameter selectivity from as-dispersed suspension. Image 1 [ABSTRACT FROM AUTHOR]