and). However, results from UBD calculations again corroborate that UCAM-B3LYP provides reliable aromaticity results and trends (Tables S8, S11, and S12). For the diazines 7 -9, the aromaticity in S0 (Figure ) follows the established order pyridazine (7) > pyrimidine (8) ~ pyrazine (9). Their lowest 3 n,* states are the T1 states and we find that the excitations are of similar type (Table ), although a comparison is ambiguous due to their different structures and symmetries. According to MCI, the 3 n,* state of 9 has a residual with clear aromatic character, while 7 and 8 have nonaromatic residuals (i.e., approximately half of the S0 values). Interestingly, although the largest difference in the MCI values between 7, 8, and 9 is due to the MCI-component, the MCI of 9 is also larger than those of 7 and 8, indicating a weaker -antiaromatic contribution in the 3 n,* state of 9. These findings also agree with those of a recent study on the lowest excited states of the three diazines, yet, where these states were not differentiated as n,* or * states. It was argued that the more aromatic a molecule is in its S0 state, the more antiaromatic it will be in its first excited states. Such relationships were earlier found among the * states of substituted fulvenes and related hyperconjugated compounds. However, we find that this is not valid for the diazines because 7 is more aromatic than 8 in both its S0 and T1 ( 3 n,*) states. Here, it should be stressed that the relationships between S0 aromaticity and T1 antiaromaticity only apply within compound classes (e.g., among substituted pentafulvenes), however, between compound classes there are several additional factors that impact on the excitation energies (see the Qualitative Theory section). Additionally, the relationship does not hold when the states vary in character (e.g., n,* vs. * character). Indeed, the diazines make it clear that the hypothesis that E( 3 n,*) is correlated with the (anti)aromaticity difference between S0 and the 3 n,* states is also oversimplified when regarding only isomers. Among 7 -9, the largest difference in (anti)aromaticity between the two states is found for 7 while the smallest is found for 9 (Figure ), but 7 has the lowest E( 3 n,*) (2.95 eV) and 8 the highest (4.13 eV). Further analysis reveals that the excitation energies are primarily influenced by the relative S0 energies of the three isomers because 8 is more stable than 7 by 1.03 eV (Table ), a feature that stems from repulsion between the lone-pair electrons of the two adjacent N atoms of 7. Here we explore why the 3 n,* state of 9 exhibits a highly aromatic residual according to MCI, and if the same trend among the diazines is found with magnetic and energetic aromaticity descriptors. An energy-based evidence of a higher aromatic character of the 3 n,* state of 9 than those of 7 and 8 comes from the relative energies, because 7 and 8 in their n,* states are higher in energy than 9 by, respectively, 0.21 and 0.34 eV. Additionally, and in agreement with the MCI results, the calculated MICD for 7 -9 demonstrate that only 9 exhibits a somewhat stronger diatropic β-electron ring current in its 3 n,* state compared to its S0 state. Moreover, the α-HSOMO of 9 has the least intensive paratropic contribution among 7 -9, in accordance with the values of the α-HOMO-LUMO gap (Table ). Finally, the NICS values reflect a lower paratropicity of 9 (Figure ). Taken together, electronic and energetic descriptors thus support that the 3 n,* state of 9 has some aromatic character, and the magnetic indicators reveal that 9 has the least antiaromatic T1 state among the diazines. In this context, it is notable that perfluoropyridazine in its S1 state, which is of 1 n,* character, photorearranges to the corresponding pyrazine, possibly driven by a gain in aromatic character.