Understanding Noncovalent Interactions of Small Molecules with Carbon Nanotubes.

We combine experimental methods, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations in the quantitative analysis of noncovalent interactions between (6,5)-enriched single-walled carbon nanotubes (SWNTs), as hosts, and a set of pyrene derivatives with different electronic properties and surface areas, as guests. The experiments and calculations were carried out in two solvents with markedly different polarities, namely 1,1',2,2'-tetrachloroethane (TCE) and N,N-dimethylformamide (DMF). Our results show that dispersion forces govern the supramolecular association of small molecules with (6,5)-SWNTs, with negligible contributions from ground-state charge-transfer effects. In the nonpolar solvent (TCE), the binding constants are highly correlated with the contact area between the SWNT and the guests. In the polar solvent (DMF), the binding constants show a complex dependence on the chemical nature of the pyrene substituents, as demonstrated by MD simulations with the explicit inclusion of solvent molecules. The solvation of the small molecules is shown to play a leading role in the binding process. Remarkably, the binding constants obtained from the MD simulations for the five guest molecules correlate with those derived from experiment. Furthermore, the MD simulations also reveal the structure of the adsorbed guest from low to high SWNT surface coverage.