The spectra shown in Fig. have two obvious features. Firstly, the spectra for both DPND and DPND6 aggregates are slightly different from one another for the aggregates with more than 6 monomers, manifesting that excitonic coherence lengths in these aggregates should not excess 6 monomers during the excitation dynamic processes. Herein, we only consider the dynamic disorder effect from electron-phonon interactions but ignore the static disorder effect. It can be expected that the incorporation of static disorder should further shorten the coherence lengths. Secondly, although the DPND aggregates have two obvious peaks and the DPND6 aggregates show one dominant peak with several side peaks, roughly consistent with experimental observations, the peak widths are significantly narrower than experimental values, especially in DPND6. It is not clear for this gap between theoretical calculations and experimental observation, and it may be expected that the broadening of experimental spectra may come from the static disorder in aggregates, which is not included in the present calculations. The detailed analysis demonstrates that two absorption peaks of DPND aggregates around 2.4 and 3.0 eV should mainly come from the interaction between the FE and CT states according to the energy values of these electronic states, similar to the dimer case, and the vibrational peaks are immersed by spectral line broadening. It should be addressed that relative strengths of two peaks are inverted caused by excitonic couplings, relative to the dimer.