Finally, for all diheteroaromatics, we also found a good correlation with the change in the RMSD() of the π-electron distribution when going from S0 to the 3 n,* state and the degree of (anti)aromaticity of the residual (Figure ). In particular, the -electron distributions in the 3 n,* states of 9 and 15, with two equal E atoms in para-positions, are clearly more uniform than in their isomers due to their D2h symmetry.