Of the two other diheteroaromatics with E ≠ E' (13 and 14), it is only 14 that exhibits a sufficiently aromatic character in S0 to satisfy our aromaticity criterion (MCI ≥ 0.0358). The 3 n,* state of 14 resembles that of 3, whereby also this excitation can be described as that of a monoheteroaromatic. Further support for this interpretation comes from the shape of the formal n orbital involved in the n,* excitation since it has a marked localization at the anionic C atom (Figure ). With regard to 13, it has a nonaromatic S0 state, yet, is still interesting as its MCI value in 3 n,* is significantly higher than half the S0 value. Thus, the MCI( 3 n,*)tot value is intermediate between that of 5 and 1. Furthermore, the 3 n,* states are the T1 states of both 13 and 14, and the singly occupied n orbitals are equally localized at the two heteroatoms while the corresponding orbital which is unoccupied in the excited state is heavily localized at the least electronegative heteroatom, in line with the hypothesis above. On the other hand, the extent of aromaticity is determined by the -orbital overlap, and since O only provides a poor -overlap it leads to a very significant attenuation of the aromaticity in 13. To no surprise, the shape of the highest singly occupied lone-pair orbital and the extent of aromaticity of the 3 n,* state are not linked. Thus, when considering the orbitals, the lowest 3 n,* of 13 resembles that of 1 while its extent of aromaticity resembles that of 5.