The third singlet state (S3) is shown to be a less intense electron donation process due to an adiabatic mixture between the charge transfer and PDI Frenkel exciton. At the ground state geometry, the fourth singlet state (S4) is mapped to the localized Frenkel exciton residing on the pyrene unit. However, the emission profile shows some disagreement between the DFT/MRCI and CC2 results, where this state is ordered energetically higher in the DFT/MRCI spectrum and instead appears as an excimeric state. Any differences between the DFT/MRCI and CC2 results are seen only in the vertical excitation energies, excluding the ordering of the pyrene ππ * state at the excited state dimer geometry. While variable, this difference is <0.5 eV, with the DFT/MRCI energies always being lower. This is to be expected when comparing DFT/MRCI to other methods, as particularly when compared to CC2 energies, the wavefunction is built using the Hartree-Fock solution as opposed to the DFT solution. In general, however, any discrepancies come down to the accuracy of the initial geometry. In this case, low-lying vertical excitation energies for the S1 or S2 states differ by ∼0.3 eV. As such, one can argue that they overlap enough to both be important metrics for the heterodimer. However, in the case where the states of interest are the higherlying states such as the S3 or S4, some further care will be needed to ascertain the validity of the results.