To further investigate the impact of E oligomer gap on optical gap prediction, we summarized the R 2 and MAE values for the six ML models trained using ECFP6 alone and in combination with E oligomer gap in Figure . All models achieved higher accuracy using E oligomer gap and ECFP6, with R 2 values over 0.62, compared to 0.51 for a simple linear regression model (Figure ). Notably, XGBoost emerged as the top performer with an R 2 of 0.77 and MAE of 0.065 eV. This level of accuracy falls within the experimental error margin of approximately 0.1 eV. For instance, polymer P3HT has an E exp gap between 1.9 and 2.14 eV, while PDB7 ranges from 1.6 to 1.7 eV, influenced by molecular weight, regioregularity, and processing conditions. In addition, when retrained with only ECFP6, all models had lower accuracy; for example, the XBGoost model achieved an R 2 of 0.7 and MAE of 0.075 eV.