We further prepared thin films of the polymers by spin-coating and their solid-state emission was characterized by absolute PLQY spectroscopy. As shown in Figure (D bottom, and F; Figure ), the solid-state emission of both linear and four-arm polymers increased with the polymer chain length. The absolute PLQYs of PDI-tetraPS with DP of 80 and 100 were 43% and 45%, respectively, while PDI-diPS (DP = 89) showed a value of 35% (Figure , G, and Table ). The polymer growth facilitated strong aggregate emission of PDI in solid state, with the four-arm structure showing a higher efficiency. Note that all emission spectra had a single peak at 625-655 nm, without any peaks appearing in the green-toyellow region. This means the strong solid-state emission in the current system is not simply due to the isolation of the PDI scaffold that facilitated the single-molecule emission as reported in other systems. The PLQY of PDI-tetraPS (DP = 62) was further enhanced from 33% to 62% by doping the polymer with 10 wt.% in a polystyrene (MW ~ 35,000 g mol -1 ) matrix, with a single red emission peak at ~610 nm still preserved (Figure ). Besides, the average exciton lifetimes of the polymer films increased from 18.7 to 26.0 ns with the increase of polymer chain length from DP = 20 to 100 (Figure , G and Table ). Notably, the absorption spectra of polymer films matched well with those obtained in DMF/H2O (5/95, v/v) (Figure and).