NMR of molecular endofullerenes dissolved in a nematic liquid crystal

Abstract

We report the NMR of the molecular endofullerenes H@C, HO@C and HF@C dissolved in the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The H NMR lines of H and HO 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 F spectrum of HF@C dissolved in MBBA displays a doublet splitting in the nematic phase, with contributions from the H-F 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.

NMR Lineshapes and Scalar Relaxation of the Water‐Endofullerene H217O@C60

“…Details of 13 C NMR are found in the Supporting Information (SI). The 13 C spectrum shows a 110 ppb splitting between empty and filled fullerene cages, in agreement with the literature .…”

Alignment of 17O-enriched water–endofullerene H2O@C60 in a liquid crystal matrix

“…consists of a broad unresolved signal in the nematic phase and narrow lines in the isotropic phase. The background and its suppression in the nematic phase were discussed previously 17 . The H 2 16 O@C 60 spectra show the same behavior as reported previously 17 .…”

“…Both splittings show a gradual decrease with increasing temperature in the nematic phase and a discontinuity at the phase transition temperature. In the isotropic phase the pentet splitting vanishes while the triplet splitting is temperature independent and equal to the 1 H- 17 O scalar coupling.…”

“…Symmetry lowering in endofullerenes in anisotropic solvents was first observed by electron paramagnetic resonance (EPR) of the atomic endofullerenes N@C 60 and N@C 70 dissolved in the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA) 15,16 . A NMR study of H 2 @C 60 , H 2 O@C 60 and HF@C 60 in MBBA has shown clear signs of alignment of the encapsulated molecules 17 . In the anisotropic phase of the liquid crystal the 1 H lines of H 2 @C 60 and H 2 O@C 60 are split into doublets due to residual-dipolar-coupling (RDC) of the two 1 H nuclei.…”

“…Recently available 17 O-enriched H 2 O@C 60 can provide more complete information on the behavior of the encapsulated water molecule. 17 O is a quadrupolar nucleus with spin-5/2. In isotropic solvents the 1 H and 17 O spectra show splittings (into sextet and triplet respectively) due to the J OH scalar coupling 18 The NMR experiments were performed using a 500 MHz Bruker Avance III spectrometer with a standard 5 mm highresolution probe.…”