Gas-phase electronic spectroscopy of nuclear spin isomer separated H₂O@C and D₂O@C

Gas-phase electronic spectra of H2O@C60+ and D2O@C60+ are presented. These data were obtained by one-photon dissociation of weakly bound helium complexes synthesised in a 3 K ion trap. Measurements were recorded in the vicinity of the 2Ag,2Bg←X2Au electronic transitions of the C60+ cage. Two-colour hole burning experiments enabled nuclear spin isomer pure data to be obtained. The spectra are rich in structure with many absorptions attributed to internal excitation of the encapsulated molecule accompanying the C60+ electronic transition. The experimental data are complemented with density functional theory calculations using the B3LYP functional and 6-31++G** basis set.</p

The dipolar endofullerene HF@C60

The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report encapsulation of hydrogen fluoride inside C60 using molecular surgery to give the endohedral fullerene HF@C60. The key synthetic step is the closure of the open fullerene cage while minimizing escape of HF. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large 1H-19F J coupling typical of an isolated species. The dipole moment of HF@C60 was estimated from the temperature-dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole

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

We present a 17O and 1H NMR study of molecular endofullerene H2O@C60 dissolved in the nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA). The 17O NMR peak is split into five components by the 17O residual quadrupolar coupling, each of which is split into a triplet by the 1H–17O residual dipolar coupling and scalar coupling. The splittings are analysed in terms of the partial alignment of the encapsulated water molecules. Order parameters describing the alignment are estimated. It is found that the preferential orientation of the endohedral water molecule has the molecular plane perpendicular to the liquid crystal director

NMR of molecular endofullerenes dissolved in a nematic liquid crystal

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

NMR lineshapes and scalar relaxation of the 17O-labelled water-endofullerene H2O@C60

The 17O isotopomer of the water-endofullerene H2O@C60 displays a remarkable proton NMR spectrum, with six well resolved peaks. These peaks are due to the J-coupling between the water protons and the 17O nucleus, which has spin-5/2. The resolution of these peaks is enabled by the suppression of water proton exchange by the fullerene cage. The six peaks display an unusual pattern of linewidths, which we model by a Liouville-space treatment of scalar relaxation due to quadrupolar relaxation of the 17O nuclei. The data are consistent with rotational diffusion of the water molecule on the sub-picosecond timescale

Gas-phase electronic spectroscopy of nuclear spin isomer separated H₂O@C₆₀+ and D₂O@C-₆₀+

Gas-phase electronic spectra of H2O@C+60 and D2O@C+60 are presented. These data were obtained by one-photon dissociation of weakly bound helium complexes synthesised in a 3 K ion trap. Mea- surements were recorded in the vicinity of the 2 Ag ,2 Bg ← X 2 Au electronic transitions of the C+60 cage. Two-colour hole burning experiments enabled nuclear spin isomer pure data to be obtained. The spectra are rich in structure with many absorptions attributed to internal excitation of the encapsulated molecule accompanying the C+60 electronic transition. The experimental data are com- plemented with density functional theory calculations using the B3LYP functional and 6-31++G∗∗ basis set

Effect of incarcerated HF on the exohedral chemical reactivity of HF@C60

The first chemical modification on the brand new endohedral HF@C60 is reported. In particular, the isomerization from optically pure (2S,5S)-cis-pyrrolidino[3,4:1,2][60]fullerene 2b to (2S,5R)-trans- pyrrolidino[3,4:1,2][60]fullerene 2b has been studied and compared with empty C60 (2a) and endohedral H2O@C60 (3). The comparative study shows a kinetic order for the isomerization process of H2O@C60 4 HF@C60 4 C60, thus confirming the effect of the incarcerated species on the zwitterionic intermediate stability

Spin-isomer conversion of water at room temperature, and quantum-rotor-induced nuclear polarization, in the water-endofullerene H2​​​O​@C60

Water exists in two forms, para and ortho, that have nuclear spin states with different symmetries. Here we report the conversion of fullerene-encapsulated para-water to ortho-water. The enrichment of para-water at low temperatures is monitored via changes in the electrical polarizability of the material. Upon rapid dissolution of the material in toluene the excess para-water converts to ortho-water. In H216O@C60 the conversion leads to a slow increase in the NMR signal. In H217O@C60 the conversion gives rise to weak signal enhancements attributed to quantum-rotor-induced nuclear spin polarization. The time constants for the spin-isomer conversion of fullerene-encapsulated water in ambient temperature solution are estimated as 30±4 s for the 16O-isotopologue of water, and 16±3 s for the 17O-isotopologue