Third-Order Nonlinear Optical Properties of Endohedral Fullerene (H2)2@C70and (H2O)2@C70Accompanied by the Prospective of Novel (HF)2@C70

In view of the experimental observation of (H2)2@C70and (H2O)2@C70, it has been suggested that hydrogen fluoride (HF) dimer can be completely localized within the sub-nanospace inside the fullerene C70cage. With the aim of quantum chemical prospective of (HF)2@C70, electronic structure calculations of C60hosting H2, HF, and H2O monomers, as well as C70hosting H2, HF, and H2O monomers and dimers, were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population, and interaction energy calculation. The F–H···F bonding energy inside C70was estimated at −13.25 kcal/mol, which is smaller than that of free dimer in the gas phase (−8.37 kcal/mol). Exploration of various featured properties suggests that (HF)2@C70may be also regarded as a unique system composed of both inter- and intramolecular interactions like (H2)2@C70and (H2O)2@C70. In addition, absorption spectroscopy and linear and nonlinear optical coefficients of C60hosting H2, HF, and H2O monomers, as well as C70hosting H2, HF, and H2O monomers and dimers, have also been forecasted. The results show that there is almost no influence of embedded H2, HF, and H2O monomers and dimers on the peak wavelength of absorption spectra for C60and C70. Endohedral C70possesses the larger second hyperpolarizabilities with respect to that of endohedral C60, indicating that the effect of cage size is effective in the second hyperpolarizabilities of endohedral fullerenes. The study will benefit not only the designation and the syntheses of the novel molecular (HF)2@C70but also the understanding of the structures and properties of endohedral fullerenes.