Electronic structures and optical properties of the IPR-violating C60X8 (X = H, F, and Cl) fullerene compounds: a computational study

Stimulated by the preparation and characterization of the isolated pentagon rule (IPR) violating chlorofullerene: C60Cl8 (Nat. Mater. 2008, 7, 790–794), we have performed a systematic investigation on the structural stabilities, electronic and optical properties of the IPR-violating C60X8 (X = H, F, and Cl) fullerene compounds via density functional theory. The large energy gaps between the highest occupied and the lowest unoccupied molecular orbitals provide a clear indication of high chemical stabilities of C60X8 derivatives, and moreover, the C60X8 molecules present great aromatic character with the negative nucleus independent chemical shift values. In the addition reactions of C60 (C2v) + 4X2 → C60X8, a series of exothermic processes are involved, with high reaction energies ranging from −71.97 to −233.16 kcal mol−1. An investigation on the electronic property shows that C60F8 and C60Cl8 could be excellent electron acceptors as a consequence of large vertical electron affinities. The density of state analysis suggests that the frontier molecular orbitals of C60X8 are mainly from the carbon orbitals of two separate annulene subunits, and the influence from X atoms is secondary. In addition, the ultraviolet-visible spectra and second-order hyperpolarizabilities of C60X8 are calculated by means of time-dependent density functional theory and a finite field approach, respectively. Both the average static linear polarizability 〈α〉 and second-order hyperpolarizability 〈γ〉 of C60X8 increase greatly compared to those of C60.