All the inverted gap molecules we have demonstrated here have double-bond delocalized structure with almost no bondlength alternation. This is achieved by systematically substituting the molecular cores with donors at positions with large LUMO coefficients, and, albeit to a lesser extent, with acceptors at positions with large HOMO coefficients. We thus provide a conceptual design strategy for achieving inverted singlet-triplet gaps. While the molecular cores all have high local symmetry within the ring systems, the overall molecular symmetry is often broken by the substituents. This highlights that double-bond delocalization in the conjugated molecular core is the underlying structural mechanism for inverted singlet-triplet gaps.