In parallel to the photoinduced double bond isomerization described above, we also studied possible rotation of the stilbene moiety around the =C-C-single bond from the series of S0→S1→S0 transition trajectories. While SBR is readily observed in hemithioindigo chromophores with asymmetrically substituted phenyl rings , it cannot be resolved experimentally for the unsubstituted HTI due to the chemically Apart from the overall amount of kinetic energy gained from S1→S0 switching in the molecular mechanics models -which is indeed largest for configurations θ-C=C-= 90° -the chance of triggering SBR surely depends on the way that the excess kinetic energy is being dissipated. In solution, such dissipation involves both the HTI and nearby solvent species. In turn, HTI switching in the gas phase does permit energy dissipation to other molecules and thus leads to particularly strong enhancement of the vibrations within the HTI itself. Indeed, we found a significantly higher SBR quantum yield of 28.3 % in gas phase. This is in line with a 'hot ground state' picture in which the HTI molecule in vapor retains high kinetic energy after leaving the excited state whilst HTI in solution undergoes energy dissipation with a few picoseconds (see also supplementary information S4).