For the excited state calculations, both ground-state and excited state geometries of NDI and pyrene were optimized using B3LYP/def2-SVP. In order to ensure that the true minimum is found during geometry optimization, we performed harmonic frequency calculations to ensure that no imaginary modes were observed. Vertical and adiabatic energies of the excited states were evaluated using DFT combined with multireference configuration interaction (DFT/MRCI) according to the R2016 parameterization scheme, which we have shown previously to be an efficiently model for the excitonic behavior of chromophores . For the potential energy scans, we utilized second-order approximate coupled cluster (CC2) calculations at the RI-CC2/cc-pVDZ level of theory, as DFT/MRCI did not yield the correct decay of the CT state as a function of increasing dimer separation. All calculations were carried out using the TURBOMOLE 7.2 quantum chemistry package .