The key natural molecular orbitals (NMOs) involved in the photoexcitation and subsequent rotation of the motor from 1a to 1b, i.e. the NMOs in which there is a significant change in the natural orbital occupation (NOO) between the ground state and the first electronically excited singlet state are listed in Table 2 and in the ESI.† Note that we only consider S1 in our discussions below because for the lowest energy 1a conformer, the oscillator strength of S2 is significantly lower than that of S1 and the VEE of S2 is higher than the photon energies corresponding to 320–298 nm, suggesting that it does not play a significant role in the excited state dynamics following excitation in this range.