We note that the Stoke's shift in toluene for the current work is still 0.4 eV smaller than the experimental value. The discrepancy could be caused by the fact that the solvent is only included as point charges in the QM calculation. Thus, only approximate electrostatic interactions between PTZ-DBTO2 and its environment are accounted for, neglecting other factors such as dipole-induced dipole interactions. Additionally, we showed in the previous section that there is rapid exchange between the axial and equatorial conformations of the molecule in the S 0 state on this time scale. A slightly higher proportion of the axial conformation would be expected to give a higher absorption energy and, hence, an increased computed Stoke's shift.