From these plots, a few patterns become evident. Low error molecules are more likely to be aromatic, potentially with sequential attached rings, for both S 1 and T 1 . In contrast, S 1 high overestimation, S 1 high underestimation, and T 1 high underestimation molecules are likely to be not aromatic, with some unconventional molecular structures included in these groups. In particular, the S 1 overestimation group includes 5 and 7 C-ring molecules, and both S 1 and T 1 underestimation include charged N atoms. There are some aromatic substructures in the T 1 overestimation molecules, but they are attached to the bulk structure with a rotatable bond. This overestimation could be a result of the 3D structure generation, since only limited conformer analysis is conducted and potentially the lowest energy conformer was not achieved. To clarify the effect of this versus an inherent inaccuracy in the excited state energy calculation of xTB-sTDA, a more intensive conformer search could be an avenue of future work. Further substructure analysis of each error category, including most common scaffolds and most common fragments based on RDKit, is provided in SI Section VIII.