The long-range-corrected wB97X-D3 was used in all calculations to obtain the correct 1/r asymptotic behavior in charge transfer excitation, because global hybrid GGA functionals, such as B3LYP, suffer from serious qualitative errors as reflected in the huge discrepancy between the exciton model and the TDDFT (Figure ). The compact 6-31G* basis set was used because the calculated dimer fluorescence energy only deviates from the 6-311++G** calculated results by 0.045 eV on average for the TDM-parallel C22-X series (Figure ), negligible compared to the typical 0.20 eV discrepancy between TDDFT and experiments. As the basis set superposition error (BSSE) may impact the accuracy of ΔE %A!B , we employed the counterpoise correction 87 in every calculation of ΔE %A!B by replacing one of the monomers with ghost atoms.