To illustrate the redistribution of electron density that occurs during the S0 → S1 transition, the electron density differences between the NMOs involved in this transition are also plotted for each conformer 1a–1d, in Fig. 4. The initial S0 → S1 excitation of conformer 1a has π → π* character on the axle of the motor, consistent with the idea that the initial dynamics are governed by softening of the axle double bond followed by rotation.22 This transition also involves considerable change in electron density on the stator, which is consistent with the narrow and well-defined absorption spectra reported for neutral molecular motors based on substituted fluorenes.22,57 The characteristics of this charge redistribution are maintained when considering conformers 1b–1c. In terms of key NMOs, the S0 → S1 transition is dominated by a transfer of population from NMO 98, which is localised on the stator, to NMO 103, which is also localised on the stator but has significant π* anti-bonding character on the axle double bond (Table 2 and ESI†).