Figure 4.

Comparison of the excited-singlet-state level ordering as calculated by semiempirical MNDO-PSDCI (mndoci) and EOM-CCSD (CCSD) coupled-cluster methods for the full chromophore (F) and the model chromophore (S) in vacuum. Note that the level ordering of the lowest four excited singlet states is invariant to the method and the complexity of the chromophore model. These levels are calculated based on the ground state geometry, and should correlate with the Franck-Condon maxima of the electronic spectra. The transition energies calculated for the second excited “1¹B_u⁺” state correlate reasonably well with the observed Franck-Condon maxima in hexane (2.72 eV (12)). The ionic versus covalent character of the states is indicated by color based on the scheme shown at upper right. The oscillator strength for excitation from the ground state is given directly above or below the state rectangle. The lowest excited singlet state generated by the MNDOCI calculations was assigned as the ICT state by Shima et al. (12).