As demonstrated above, our two-step procedure for oligomer model construction through side chain truncation and backbone extension significantly improves the linear correlation between E DF T gap and E exp gap , increasing the R 2 value from 0.15 to 0.51 (see Figure ). Particularly, side chain truncation largely reduces computational cost, which is beneficial for high-throughput screening. Although less impactful on electronic properties than the conjugated backbone, alkyl side chains still require consideration in order to further improve the prediction accuracy of experimentally measured optical gaps. Consequently, we applied two categories of descriptors for ML modeling: DFT calculated HOMO-LUMO gaps of modified oligomers to represent the extended backbone, and molecular features from SMILES strings of monomers to capture the effect of alkyl side chains.