These results indicate that the strong aggregate emission of PDI is likely due to the formation of electron donor-mediated excimer state of PDI scaffolds, benefiting from both steric hindrance and charge transfer effect brought by the polymerization of styrenic monomers. Note that charge transfer within the PDI scaffold has been reported to contribute to the excited aggregates of PDI small molecules. We speculate that the external weak electron donors introduced by polymerization may better facilitate the PDI aggregate emission via the distortion of PDI packing, as indicated by the higher quantum yield compared to small molecule systems. On the other hand, PDI small molecules with large steric hindrance from the imide position usually require multi-step organic synthesis and tedious purification by column chromatography. To reveal the key role of the styrenic units, we polymerized methyl methacrylate (MMA) using the PDI initiators and obtained PDI-diPMMA and PDI-tetraPMMA with different molecular weights (Figure ). However, the PMMA matrix showed limited emission enhancement in aggregate or solid state compared to the PS matrix, even with a four-arm structure (Figure and). In addition, PDI-tetraPBMA was also synthesized using benzyl methyl methacrylate (BMA) as the monomer. The polymer also showed strong solid-state emission with maxima at ~ 635 nm and an absolute PLQY of up to 38% (Figure ). These results indicate the potential benefits brought by the charge transfer process between phenyl groups and PDI scaffold. The lower emission enhancement brought from the PBMA matrix than the PS matrix might be due to the effect of polymer rigidity. Additionally, PDI-tetraPS (DP = 62) showed a much lower exciton lifetime τavg of ~22 ns compared to ~32 ns for both PDI-tetraPMMA (DP = 58) and PDI-tetraPBMA (DP = 52) (Figure , H, and Table ), which may be due to the more prominent charge transfer contribution from the PS matrix.