In Fig. and included (from CISD onward), their order inverts, with the triplet state lying higher than the dark singlet. This observation aligns with findings from more sophisticated all-electron models and is particularly noteworthy given the simplicity of the PPP approach. The bright E ′ singlet state consistently remains above the E ′ triplet state. Similar results are obtained when using substantially larger values of ε B , such as 14 eV and 20 eV (see SI Section S3). In contrast, in 3T-a, the A ′ 2 singlet is always well above both the E ′ triplet and E ′ singlet excited states, with no ST inversion observed.