It is worth emphasizing that the ∼ 8 kcal mol -1 of free energy available from THI is only a fraction of the 80 kcal mol -1 energy provided by a photon from the 355 nm laser used in the experiments . As a consequence, it is of interest to consider how to improve the energy efficiency. One possibility may be to modify the structure in a manner that makes the metastable form less stable, without degrading other key parameters. This would probably bring the additional benefit of lowering the THI barrier and thus increasing the rotation rate. It might also be possible to collect power not only from THI but also from the photoisomerization step, as noted above.