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

Abstract

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 (C_2v) + 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.