Next, we analyse why there is a variation in the (anti)aromatic character of the 3 n,* states of 6-MR monoheteroaromatics. Both the E atom electronegativity and the molecular charge play roles as one can see that a low electronegativity of E and a negative charge lead to stronger aromatic character of the residual. The variation also seems to depend on the local p orbital overlap which differs among the monoheteroaromatics. For this reason, we analyzed the degree of uniformity in the π-electron distribution in the ring by calculating the root mean square deviation of π-electron distribution (RMSD()) obtained from a natural population analysis (NPA). Interestingly, there are good correlations between the MCI and RMSD() values for both S0 and 3 n,*, indicating that the more uniformly distributed the electrons, the higher the MCI values (Figure ). It is further notable that there is a reasonable correlation with the change in the RMSD() of the π-electron distribution when going from S0 to T1 and the degree of (anti)aromaticity of the residual, implying that if the -electron distribution becomes more (less) uniformly distributed upon excitation, the residual of the system will become more aromatic (antiaromatic).