It is worth clarifying that, although the photoisomerization process starting from the Franck-Condon point is very fast (on the picosecond timescale), the photoisomerization rate constant is determined by a longer timescale, i.e., the wait time for photoexcitation. This wait time is determined not just by the intrinsic properties of the motor, but also by experimental settings, such as the intensity and spectrum of the light. Indeed, approaching the maximum rotation rate in this figure may require light intensities too high to be readily generated in experiments, as previously emphasized . The need for such high intensities traces to the low molar absorptivities of these compounds, about 10,000 molar -1 cm -1 ) .