Figure shows the predictions of the SISSO models selected based on considerations of cost and accuracy as a function of the GW +BSE reference values of the triplet exciton energy. Parity plots for all other SISSO models are provided in the ESI. Similar to the optical gap, the SISSO model predictions are quite close to the reference values. The low-cost model M 3,1 has a few outliers with larger deviations from the reference values. Some of these, biphenyl, terphenyl, and PUJQIV, are the same as the optical gap outliers. 1,2,3,4-Tetraphenylbenzene (CSD reference code FOVVOB) also comprises benzene rings connected by single bonds. Biphenyl, 9,9'-bianthracenyl (CSD reference code KUBWAF01), hexabenzo(bc,ef,hi,kl,no,qr)coronene (CSD reference code HBZ-COR), and 1,12-benzoperylene (CSD reference code BNPERY) have unusually high single molecule triplet formation energy, E S T , values exceeding the GW +BSE reference values of their crystal triplet excitation energies, which causes the M 3,1 predictions to be overestimated. The intermediate cost model M 3,2 and the high-cost model M 4,3 perform better for most of these materials, except for terphenyl, which persists as an outlier, as in the case of the optical gap models.