Apparently, the packing mode of PDI-tetraBr cannot be fully attributed to the H-type aggregate, possibly because of a rotational displacement in PDI stacking induced by the tetra-functionalized structure. A similar observation was reported in other star-shaped PDI molecules. The fluorescence spectra of both molecules were recorded in DMF/H2O mixtures with increasing water fraction. Conceivably, drastic fluorescence quenching was observed for both molecules in aggregates (Figures and, orange curves) due to the strong π-π stacking of the PDI scaffold. The stacking was also indicated by the enhanced transitions in the higher levels of electronic states (0-1 at ~570 nm, 0-2 at 620 nm) with respect to 0-0 transition (~540 nm) upon increasing molecular concentration (Figure and). Notably, a weak red-emission peak appeared at ~650 nm for PDI-tetraBr with a water fraction of ≥ 60%, which was not observed in PDI-diBr. In solid state, PDI-tetraBr showed a significant blueshift in emission compared to PDI-diBr (650 nm vs. 700 nm, Figure and). These results again highlight the influence of the four α-bromoisobutyryl groups on the packing configuration of PDI-tetraBr. Unfortunately, the single crystal of PDI-tetraBr suitable for structure analysis could not be obtained, likely due to the high flexibility of co-existing four α-bromoisobutyryl groups. Despite that, the significant difference between PDI-diBr and PDI-tetraBr in photophysical properties drove us to investigate whether such an effect could be observed in polymer systems, where structural distortion and CT may occur simultaneously.