In this study, we rationally designed an oligomer model to represent CP materials based on their fundamental characteristics. The two-step procedure to construct the oligomer structure is depicted in Figure with polymer PTB7 as an example. In the first step, we replaced the long alkyl side chains with methyl groups since alkyl side chains primarily affect solubility. This substitution enables efficient computational simulations while maintaining similar electronic and optical properties. As the conjugated backbone contributes most to the electronic properties of CPs, following side chain truncation, we replicated the monomer to form an oligomer structure, such as dimer or trimer. Previous studies suggested that using oligomer structures-such as a dimer, trimer, or tetramer, which extends the conjugated backbone chains to capture the characteristic of πelectron delocalization-enhances the predictive accuracy of DFT methods for experimental gaps, compared to employing monomer. Given the limited understanding of the correlation between the conjugation length of backbone chain and the electronic properties of CPs, we tested various polymer structures and established two guidelines for constructing oligomers (see Note S4 for details): the oligomer should contain at least four aromatic blocks linked by C-C single bonds along the backbone chain; (2) the oligomer should consist of at least six aromatic rings. Additionally, after side chain truncation, the obtained monomer can be regarded as an oligomer if it simultaneously contains more than four aromatic blocks and more than eight aromatic rings.