We begin our study with the C22-PC113 dimer as a representative case where the two monomers have very similar structures and fluorescence energies (ca. 3.22 eV). The only difference between these two molecules is the sp2 nitrogen in C22, which allows us to investigate the rarely-discussed role of heteroatoms. The 4 most stable C22-PC113 exciplex structures are shown in Figure , ranked by their ascending absolute energy. Despite the geometric differences between C22-PC113 exciplex conformers, the dimers' E 5% all exhibit significant redshifts of around 0.95 eV compared to their monomers. The redshift is mainly contributed by the superexchange (SE) effect, whose amplitude is over three times larger than the other terms in Eq (6).