  Azobenzene based molecules have the property of isomerizing when illuminated.
In relation with that photoisomerization property, azobenzene containing
materials are the subject of unexplained massive mass transport. In this work
we use an idealised rectangular chromophore model to study the dependence of
the isomerization induced transport on the chromophore dimensions. Our results
show the presence of a motor arm length threshold for induced transport, which
corresponds to the host molecule size. Above the threshold, the diffusive
motions increase proportionally to the chromophore length. Intriguingly, we
find only a very small chromophore width dependence of the induced diffusive
motions. Our very simplified motor reproduces relatively well the behavior
observed using the real DR1 motor molecule, suggesting that the complex closing
procedure and the detailed shape of the motor are not necessary to induce the
molecular motions.
