The mechanism of CT state-mediated singlet fission has also been used by many others to explain their experimental measurements. Essentially, the FE-CT mixed states can remarkably affect electronic absorption spectra. In our previous work, we have clearly demonstrated that the mixing between a bright FE state and a dark CT state can lead to the two absorption peaks, and the relative peak intensities are closely associated with the intermolecular distances, aggregation lengths and long-range excitation energy transfer. Indeed, the experiments have shown that the DPND thin film has an obviously enhanced absorption band in the region of 300-450 nm, quite different from DPND6, and their absorption spectra around 500-600 nm also exhibit different properties. Although those spectral differences come from the different mixing components of FE/CT states, it is still absent of the detailed spectral assignments. This paper aims to theoretically establish the detailed relationship of spectra and aggregate stacking arrangement to confirm this assignment.