Theoretical Study on the Structure and Spectral Properties of Two Classical C72 Isomers and Their Newly Endohedral Cluster Fullerenes.

Two non-IPR fullerenes, Cs-#10528C72 and D2-#10611C72, and their corresponding endohedral fullerenes, Dy2O@Cs-#10528C72 and UCCe@D2-#10611C72, have been analyzed using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) spectra, as well as optimized geometric structures at the density functional theory (DFT) level. The spectral components of the total spectra corresponding to carbon atoms in different local environments have been examined. Then, the ultraviolet-visible (UV-vis) absorption spectroscopy of the two derivatives, Dy2O@Cs-#10528C72 and UCCe@D2-#10611C72, was theoretically simulated using the time-dependent density functional theory (TD-DFT) approach, and the calculations are consistent with the experimental results. The findings reveal a notable isomer dependence in the XPS and NEXAFS spectra, while the UV-vis spectra are useful for differentiating the structural isomers. Furthermore, the Quantum Theory of Atoms-in-Molecules (QTAIM) and the noncovalent interaction (NCI) analysis further elucidated the bonding nature and interaction characteristics between the encapsulated metal cluster and the carbon cage. Consequently, this study concludes that both X-ray and UV-vis spectroscopies are important theoretical tools for probing the electronic properties and conducting structural analysis of fullerene-based materials, while also providing valuable information for further experimental and theoretical research on fullerenes.