When the ST gap is negative (points 1 ○ in Fig. and), the HOMO and LUMO are localized on two complementary sublattices and the HF HOMO-LUMO exchange energy K H-L is as low as -0.04 eV (2T-N) and -0.02 eV (2T-7N). In either case, the LUMO+1 orbital is doubly degenerate and is clearly not complementary to HOMO. When ∆E ST becomes positive (points 2 ○ in Fig. and), the nature of LUMO and LUMO+1 is reversed, so that the HOMO-LUMO complementarity is lost, and sizable K H-L values are calculated (-0.5 eV for 2T-N and -0.23 eV for 2T-7N). We stress that this notable reversal in the nature of LUMO and LUMO+1 is not shown by the Hückel MOs, demonstrating once again that electron correlations are the key to ST inversion.