Another property of interest for device applications is the singlet-triplet gap, i.e., the energy difference between the lowest singlet excited state and the lowest triplet excited state, both of which are included in the PAH101 dataset (see Table ). The singlet-triplet gap is a key property for organic light emitting diodes (OLEDs). Most of the electrically generated excitons in OLEDs are triplet excitons, which cannot decay radiatively to the ground state. In thermally activated delayed fluorescence (TADF) chromophores, a small singlet-triplet gap enables reverse intersystem crossing (RISC) from the lowest triplet excited state to the lowest singlet excited state, which subsequently decays to the ground state, emitting a photon. Figure shows the distribution of singlet-triplet gaps in the PAH101 dataset. Small singlet-triplet gaps are rare among between spatially separated HOMO and LUMO states are considered key to achieving small singlet-triplet gaps in TADF chromophores. With the exception of PUJQIV, the materials with the smallest singlet-triplet gaps in the PAH101 set bear no resemblance to the donor-acceptor compounds typically used for TADF. Rather, they are large PAHs with extended π systems. FACPEE, VUFHUA, and YOFCUR have segments that could lead to CT-like intramolecular excitations. GUQZUP (shown in Figure ) can be described as a graphene flake with no obvious segments. The twisted conformation it adopts in the crystal structure may contribute to orbital localization and CT-like excitations. The effect of crystal packing and intermolecular vs. intramolecular CT excitations on singlet-triplet gaps is also not well-understood and should be further investigated in relation to TADF in crystalline materials. Figure shows the distribution of the GW static dielectric constant in the PAH101 dataset. There is a prevalent perception in the organic electronic community that all organic solids have a similar dielectric constant of about 3 (we have not been able