Starting with the three azaphosphinines 10 -12 in their 3 n,* states computed at UCCSD(T) level, we found that these exhibit some multiconfigurational character (T1 diagnostics > 0.044, the threshold for open-shell species) . Accordingly, we explored these species also at UBD and CASSCF levels and found that multiconfigurational character does not impact on the results (see sections 2.1, 3.1, and 3.6 of the Supporting Information). Indeed, the trend in the MCI values computed with UCAM-B3LYP agrees with that of UBD.