Application of MCD spectroscopy and TD-DFT to endohedral metallofullerenes for characterization of their electronic transitions

Abstract

We describe, for the first time, the application of magnetic circular dichroism (MCD) spectroscopy and time-dependent density functional theory (TD-DFT) calculations using B3LYP and M06-2X functionals to characterize the electronic transitions of endohedral metallofullerenes (EMFs). Results revealed that the electronic transitions of La@C_2v–C₈₂, La₂@I_h–C₈₀, and Sc₃N@I_h–C₈₀ can be assigned using these techniques. Particularly, a difference in the electronic transitions between La₂@I_h–C₈₀ and Sc₃N@I_h–C₈₀, which is invisible in absorption spectra, was observed clearly in MCD spectra. The observed MCD bands agree well with the oscillator strengths calculated using the B3LYP functional. In addition, the MCD bands of La₂@I_h–C₈₀ were altered upon [5,6]-addition, demonstrating that the MCD spectroscopy is sensitive to chemical functionalization of EMFs, and that it is therefore powerful to distinguish [5,6]-adducts from pristine La₂@I_h–C₈₀, although no marked difference exists in their absorption spectra.