We substitute at positions with LUMO coefficients, which alleviates the antiaromaticity of the core (Figure ) and stabilizes the double-bond delocalized structure as shown in Figure . In the four cases where the central six-membered ring is substituted with donors (amine-, hydroxy-, methoxy-, dimethylaminesubstituents) a negative E(S 1 -T 1 ) is attained. Substituting instead at the five-membered rings yields more negative gaps, but between S 1 and T 2 , which have the same electron configuration. Notably, E(S 1 -T 2 ) is more negative in all the tetrasubstituted molecules than in the constrained parent s-indacene. From this, we conclude that substituted molecules can potentially achieve more negative gaps than its molecular core. in Figure . The transitions involving the non-overlapping HOMO-1 and LUMO orbitals exhibit a Hund's rule violation (E(S 1 -T 2 ) = -161 meV). However, the presence of the a u HOMO that overlaps with the LUMO leads to a triplet state described by a HOMO → LUMO transition which is lower in energy, as marked in red in Figure . While the LUMO substituent patterns slightly raise the energy of the pentalene-like occupied 2b 2g orbital, it lowers the energy of the a u orbital. As a result, the B 1g excited state that exhibits the singlet-triplet inversion is below the intruding B 3u triplet in the s-indacene-4,8-diamine. In three other 4,8disubstituted cases, the B 3u triplet remains slightly below the B 1g triplet, but nonetheless the B 1g singlet is lower energy than both of them ensuring an inverted singlet-triplet gap, as listed in Figure and Table . Substitution at the five-membered rings does not have this effect, and the state-ordering of the unsubstituted D 2h s-indacene remains. This finding highlights the importance of the substitution position on the excited-state ordering in s-indacene derivatives. We thus demonstrate that the states involved in the Hund's rule violation can be manipulated to be the lowest-lying excited states through appropriate substitution patterns that results in an inverted singlet-triplet gap.