In the S 0 sampling cycle shown in Figure , PTZ-DBTO2 started in the equatorial configuration, switched into the axial configuration at around 1.8 ns, and transformed back into the equatorial state at 3 ns. This distribution can be explained by the low energy barrier between the two conformers, which is only about 2 kcal/mol (0.087 eV) in vacuum. For the first 5 ns (dashed line), the emitter is modelled in the S 0 state, before switching to the S 1 state force field. Note that simulations in the solid state hosts include an initial heating phase to equilibrate the system. The relative populations of the two conformations in each of the hosts after 5 ns of each of the twenty MD runs are summarised in Table . Thus, although the two conformations of PTZ-DBTO2 are very similar in energy in vacuum, transfer to either solution or the solid state seems to promote a higher population of the equatorial structure.