The QUBE force field fitted to the S 0 state of PTZ-DBTO2 was used up to this point, and the same process was repeated twenty times. Ground state properties were calculated using the snapshots at the end of each S 0 state simulation cycle. The force field parameters for PTZ-DBTO2 in each of the twenty snapshots were then instantaneously swapped to the S 1 state and MD sampling was resumed for a further 100 ns. All excited state properties were calculated with snapshots extracted from the final 100 ns MD runs.