The magnetic circular dichroism (MCD) and absorption studies of 1,8-naphthalimide. The theoretical analysis in terms of density functional (DF) and coupled cluster (CC) theories

The vibronic coupling theory based on the Franck–Condon (FC) approach was applied to study the absorption and magnetic circular dichroism (MCD) spectra of 1,8-naphthalimide in the excitation region corresponding to the low-energy 1A1 → 2A1 and 1A1 → 1B1 transitions. The computations carried out in terms of PBE0 and CC2 methods have shown that the vertical excitation energies of 2A1 and 1B1 states and Franck–Condon parameters from CC2/aug-cc-pVDZ computation lead to a very good agreement with the experiment. MCD analysis suggests that the vibronic coupling effects between 2A1 and 1B1 states may be responsible for observed minor discrepancies between the theoretical and empirical MCD spectra.