In Fig. , panels a and e show spectra calculated at the PPP-XCISDT theory level, with the 2 A ′′ 2 dark doublet state indicated by a cross. Results are shown across a range of aza nitrogen PPP on-site energy values, ε N , spanning from -6 eV to 0 eV, while keeping U N = 15.5 eV. This range of energies encompasses scenarios from strongly electronegative nitrogen to a hypothetical situation where nitrogen electronegativity matches that of carbon, thus elucidating the role of nitrogen in these systems.