While the inclusion of a counterion has no significant effect on the absorption lineshape of CV in polar solvent (Fig. ), its presence becomes crucial in nonpolar solvent. Fig. illustrates the distribution of the counterion along the 36 ps trajectory in toluene, where (a) shows the dependence of the S 1 -S 2 energy splitting on the counterion position. We quantify the counterion position relative to CV through the mean distance to the two nearest nitrogen atoms, as well as the dimensionless difference in the distances to both atoms, defined through the unsigned difference in distance divided by the mean distance. The purple region in Fig. (a) corresponds to almost zero splitting (i.e. degenerate S 1 and S 2 states), and for those configurations the counterion is almost equidistant from both N atoms. The maximum splitting of the excitation energies occurs when the counterion is much closer to the one of the nitrogen atoms than the other, represented by yellow to red regions on the heat map. Hence, for the contact ion pair configuration with CV, the main contribution to the energy splitting is due to the difference in the distance between the counterion and the two nitrogen atoms, since an increase in the difference in distance leads to an increase in the mean distance.