Finally, we employed NMSSE with respect to the model Hamiltonian to simulate the vibrationally-resolved absorption and CD spectra of PDI-CN aggregates with the size ranging from 2 to 9 units. As illustrated in Figure , significant changes were observed in the vibronic absorption spectra of the aggregates compared to that of the monomer. With increasing aggregate size, the position of the strongest absorption peak shifted, and the characteristic odd-even alternation pattern in the spectra gradually diminished. Interestingly, this oddeven characteristic was well preserved in the vibronic ECD spectra, indicating that the ECD spectroscopy is more sensitive to the aggregate size, intermolecular distance and packing way. Notably, after incorporating vibronic effects, the CD signal intensity for odd-numbered segments surpassed that of even-numbered segments, with a marked change in the relative intensities of the two peaks in the 20,000-22,000 cm -1 range as the number of segments increases. Specifically, in the trimer, the relative intensities of these peaks were nearly identical, whereas in greater aggregate, the higher energy peak was significantly enhanced. Gaussian lineshape with FWHM set to 806 cm -1 was employed.