set as implemented in the Q-Chem 5.1 package. All structures are optimized at the ωB97X-D/def2-TZVP level using Gaus-sian16. As in previous studies, we only see a small basis set dependence in near-planar conjugated molecules (Figure ). Finally, we note EOM-CCSD appears to potentially give slightly more positive gaps and thus provides a conservative assessment of singlet-triplet gaps in conjugated molecules. For example, the singlet-triplet gap (E(S 1 -T 1 )) of azulene was determined experimentally to be 49 meV, which is 6 meV below the value obtained with EOM-CCSD/cc-pVDZ, 55 meV. Azupyrene has previously been suggested as an inverted gap molecule. And yet, despite having a double-bond delocalized structure and negligible HOMO-LUMO overlap, it has a positive gap of +26 meV at the EOM-CCSD/cc-pVDZ level. In accordance with the Heilbronner strategy, we substitute azupyrene with archetypical donor substituents (-OH, -OMe, -NH 2 , NMe 2 ) at positions with significant LUMO coefficients, and with electron withdrawing substituents (-CN, -CF 3 ) at positions with large HOMO coefficients, as shown in Figure . In this way, we find several new cases of substituted azupyrenes with a lower singlet-triplet gap than the parent compound. Most notably, we find that azupyrene-3,5,8,10-tetraol and azupyrene-1,2,6,7tetracarbonitrile have an inverted singlet-triplet gap at the EOM-CCSD/cc-pVDZ level.