When the electron-vibration coupling is not taken into account, each absorption peak in Figure : The experimental (orange dashed line) and calculated vibronic absorption (upper) and CD (lower) spectra of PDI-CN (left) and PDI-F (right) tetramers. The blue and green solid lines denote the calculated spectra with and without electron-vibration coupling, respectively. The theoretical spectra of two tretamers are red-shifted by 806 and 1210 cm -1 , respectively, to align with the experimental results. Gaussian lineshape with FWHM of 806 and 968 cm -1 was employed, respectively. circularly polarized light. From a quantum chemistry perspective, this phenomenon arises from the splitting of energy-degenerate states due to electronic dipole-dipole interactions between excitons, leading to oppositely signed rotatory strengths. In the vibronic absorption spectrum of PDI-CN, compared to the monomer, most of the vibrational peaks corresponding to the sophisticated structure have been smeared out, but four main peaks (18000, 19350, 21054, 22500 cm -1 ) still appear. In comparison to the pure electronic spectrum, the exciton states with significant oscillator strengths undergo strong vibronic coupling, resulting in the splitting and formation of weaker vibrational shoulder peaks. Similar splitting is also observed in the CD spectrum, occurring near the positions of the strongest positive and negative signals. Additionally, unlike in the pure electronic spectrum, the sign reversal in the CD spectrum does not correspond to the position of the strongest absorption peak but rather occurs near the vibrational shoulder peak, which is consistent with experimental observations. Finally, the characteristic positive signal at low energy and negative signal at high energy in the CD spectrum, combined with the fact that exciton coupling between fragments is positive, indicates that PDI-CN can form right-handed helical H-type aggregates in a mixed solution of methanol as a non-solvent and N,N-dimethylformamide(DMF) as a good solvent. For PDI-F aggregates, the exciton coupling between fragments is positive, and its CD spectrum exhibits characteristics that are completely opposite to those of PDI-CN aggregates. This suggests that PDI-F can form left-handed helical H-type aggregates in a mixed solution of methanol and dichloroethane (DCE). As shown in Figure , in the absorption spectrum, there are three prominent vibronic absorption peaks located at 17710, 20000, and 22000 cm -1 . Similar splitting occurs at the location of the maximum difference absorption.