Fig. 5. Energy, structure and detailed working mechanism of AMM ±n.

a, The full reaction scheme including all experimental rate constants/quantum yields (given as an average over at least two independent experiments) for the molecular machine operation at 10 °C shows the light-driven winding (blue; relative standard deviation ~10%), nucleophile-catalysed unwinding (brown; relative standard deviation ~35%) and sequence-specific unwinding (grey; relative standard deviation ~15%, solid arrow represents experimentally observed relaxation from +3 to +2, while dotted arrows indicate that further, sequence-specific relaxation at 10 °C is not viable). An increasing number of crossings decreases the winding and increases the unwinding process. Note that the rates for the nucleophile-catalysed unwinding are all in a narrow range irrespective of the winding-induced strain. This can be rationalized when considering that the nucleophilic attack at the imine carbon atom is likely the rate-determining step in this reaction, while the subsequent ring-opening and unwinding steps are fast and thus do not affect the kinetics of the amine–imine exchange. b, Calculated energies of the most stable conformer of motors −1 to +3 in the gas phase relative to 0. A higher number of crossings increases the electronic energy of the system. Experimentally, the system was found to reach up to +3 crossings. c,d, Representative structures of one possible conformer of species 0 (c) and +3 (d). The energies and structures in Fig. 5b–d were calculated at the M06-2X/def-SVP//GFN-xTB level of theory.