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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]

Binding affinity and thermodynamicunderstanding between a surfactantand carbon nanotube is essential to develop various carbon nanotubeapplications. Flavin mononucleotide-wrapped carbon nanotubes showinga large redshift in optical signature were utilized to determine thebinding affinity and related thermodynamic parameters of 12 differentnanotube chiralities upon exchange with other surfactants. Determinedfrom the midpoint of sigmoidal transition, the equilibrium constant(K), which is inversely proportional to the bindingaffinity of the initial surfactant-carbon nanotube, provided quantitativebinding strengths of surfactants as SDBS > SC ≈ FMN >SDS,irrespective of electronic types of SWNTs. Binding affinity of metallictubes is weaker than that of semiconducting tubes. The complex Kpatterns from semiconducting tubes show preference tocertain SWNT chiralities and surfactant-specific cooperativity accordingto nanotube chirality. Controlling temperature was effective to modulate Kvalues by 30% and enables us to probe thermodynamic parameters.Equally signed enthalpy and entropy changes produce Gibbs energy changeswith a magnitude of a few kJ/mol. A greater negative Gibbs energyupon exchange of surfactant produces an enhanced nanotube photoluminescence,implying the importance of understanding thermodynamics for designingnanotube separation and supramolecular assembly of surfactant. [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]

[Display omitted] • The synthesized POBE-BzE has capability to disperse SWNT in water and p -xylene. • POBE-BzE/SWNT can be extracted to p -xylene from water in diameter selective manner. • Partition coefficients are obtained to explain those diameter selective extractions. Aqueous two-phase extraction is instrumental for obtaining single-walled carbon nanotubes (SWNT) with uniform physical properties. This study reports that a nonionic amphiphilic poly(2-ethyloxazoline)-benzyl ether derivative (POBE-BzE) not only efficiently disperses SWNT in both water and p -xylene, but can also be utilized as a single-surfactant for partitioning SWNT in a water/ p -xylene two-phase extraction in a diameter (d t) selective manner. While individual POBE-BzE/SWNT dispersions exhibit similar photoluminescence positions from the SWNT, d t -dependency occurs according to the solvent. Upon two-phase extraction, a d t SWNT >0.9 nm was mainly extracted to the p -xylene layer, and its partition coefficient was investigated by varying the phase transfer catalyst or sodium chloride amounts, where sodium chloride served as a better transfer agent. The d t selective behavior and its partition coefficient were rationalized by the tight and loose configurations of the BzE moiety in each medium. This novel amphiphilic polymeric surfactant and two-phase extraction may be useful for sorting SWNT and other nanomaterials according to their size. [ABSTRACT FROM AUTHOR]

When the width of a graphene nanoribbon (GNR) is only a few nanometers, it possesses semiconducting properties that enable various high-end electronic applications. In this study, we report that the dense and stable dispersion of a natural graphite formed using flavin mononucleotide (FMN) as a surfactant produces GNRs as small as 10 nm in width. High-resolution transmission electron microscopy reveals GNRs with various widths, along with a graphene flake containing straight-edged GNRs and cuts, depending on substrate treatments. Such nanoribbon formation originates from sonochemical graphene unzipping with a one-dimensional FMN supramolecular ribbon as a template. Raman spectroscopy demonstrates the universal intensity ratio of D over D′ bands near 4, supporting formation of continuous edge defect. Thermal annealing enhances the optical contrast and van der Waals interactions of the graphene film, resulting in increased conductivity compared to the as-prepared graphene film, which is also better than that of reduced graphene oxide. [ABSTRACT FROM AUTHOR]