NMR of molecular endofullerenes dissolved in a nematic liquid crystal

Abstract

We report the NMR of the molecular endofullerenes H₂@C₆₀, H₂O@C₆₀ and HF@C₆₀ dissolved in the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The ¹H NMR lines of H₂ and H₂O display a doublet splitting due to residual dipole–dipole coupling. The dipolar splitting depends on temperature in the nematic phase and vanishes above the nematic–isotropic phase transition. The ¹⁹F spectrum of HF@C₆₀ dissolved in MBBA displays a doublet splitting in the nematic phase, with contributions from the ¹H–¹⁹F dipole–dipole coupling and J-coupling. The phenomena are analyzed using a model in which the fullerene cages acquire a geometrical distortion, either through interaction with the liquid crystal environment, or through their interaction with the endohedral molecules. The distorted cages become partially oriented with respect to the liquid crystal director, and the endohedral molecules become partially oriented with respect to the distorted cages.