The time dependence of the S 1 energy and the S 1 -T 1 energy gap with and without background point charges representing the solvent are shown in Figure . Figure shows that without the background point charges, PTZ-DBTO2 has similar S 1 energies in all hosts, which indicates that different environments do not alter the structure of PTZ-DBTO2 significantly differently. When the point charges are included, toluene lowers the S 1 energy most significantly. This is expected since, in the liquid state, solvent molecules can more easily re-orientate and align their dipoles with the emitter. These data are in qualitative agreement with previous discussion of the origin of the Stoke's shift in toluene, 15 with here ∼ 0.7 eV coming from interactions with the solvent (Figure ) and the remaining ∼ 0.6 eV coming from structural changes in the emitter. Of course, in the current study, both effects are extracted from a single simulation, explicitly including the environmental and temperature effects, due to the use of separate QUBE force fields for the ground and excited states of the emitter. As discussed above, PYD2 leads to a slightly stronger red-shift than CBP due to its larger dipole moment. However, the shift is much smaller than in toluene due to the more restricted solid environment.