We have studied the structural and electronic stability of a helical ribbon of flavin mononucleotide wrapping around single-walled carbon nanotubes using first-principles density-functional calculations. The helical ribbon is formed through hydrogen bonding between adjacent uracil moieties of the isoalloxazine ring and stabilized through concentric pi-pi interactions. The electronic structure calculations reveal quantum electronic stability associated with lattice registry and band alignment between the helical assembly and the (8,6) nanotube. The electronic stability plays an essential role in the experimentally observed highly selective enrichment of specific chirality tubes.

Covalent functionalization represents a promising avenue to tailor the electronic properties of carbon nanotubes. Recent experimental work has shown that cycloaddition of fluorinated olefins represents an effective approach to reduce the off-currents of mixed nanotube mats for transistor applications. We have studied the electronic structure characteristics of the corresponding [2 + 2] cycloaddition using dispersion-corrected density functional calculations. The band gap opening in chemically functionalized tubes is associated with the sp 2 to sp 3 rehybridization. Our calculation reveals that the experimentally observed suppression of metallic conductivity can be attributed to a symmetry aligned cycloaddition scheme that effectively transforms metallic tubes to semiconducting ones.

We have employed force-field molecular dynamics and first-principles calculations for the helical formation of isotactic poly(2-methoxystyrene) nanowires. Our calculation results reveal the self-assembly of left- and right-handed helical nanorods. The energy of the helical conformations depends on the chiral center as well as linkages among neighboring methoxy benzene groups. The implications of these results for understanding experimentally observed chiral asymmetry of left- and right-handed nanowires are discussed. Furthermore, we demonstrate that the coiled structures can effectively wrap around singled-walled carbon nanotubes. The electronic structure characteristics of these conformations are studied with use of first-principles calculations.

We have performed force field-based molecular dynamics and first principles density functional calculations on porphyrins and metalloporphyrins interacting with single-walled carbon nanotubes. The flattening of the porphyrin macrocycle is indicative of the self-assembly of these aromatic structures onto carbon nanotubes. An analysis of the charge distributions for conduction and valence bands reveals a distinct charge transfer behavior from the porphyrin macrocycle to the metallic or semiconducting tubes that sheds considerable light on the experimentally observed selectivity of semiconducting nanotubes.