Before looking into the actual Z→E isomerization process, we characterized the underlying local energy configurations by separate MD simulations in the NpT ensemble (50 ns at T=300K). Figure shows the occurrence profiles h(θ) of the -C=Ctorsion angle θ, for i) HTI in the gas phase, solvation in ii) n-hexane and iii) DMSO, both at ambient conditions, respectively. As a consequence of the large torsion barrier in the S0-state, two separate profiles were derived for the Z-and E-conformers, respectively, using parallel MD runs. On this basis, the average energy difference in S0-Z and S0-E conformers was found as 0. given by the S0-Z conformer, and Boltzmann statistics at 300K would predict at most 1.4 % population of the S0-E conformer.