To analyze the impact of each vibrational mode on the spectra, the total reorganization energy of the S 1 is decomposed into the contribution from each normal mode. Tables and S5 in the SI detail the vibrational modes with most significant contributions for PDI-CN and PDI-F, respectively. Both PDI-CN and PDI-F exhibit that the vibrational modes lying in frequency range of 1300-1650 cm -1 predominates the vibrational contributions to the vibrational bands, which is attributed to their shared PDI backbone. The vibrational bands originate mainly from the stretching of the vinyl backbone and the in-plane bending of C-H, consistent with previous literature reports.