Molecular Rotor Functionalized with a Photoresponsive Brake

A molecular motor that has been previously
shown to rotate when
fueled by electrons through a scanning tunneling microscope tip has
been functionalized with a terarylene photochrome fragment on its
rotating subunit. Photoisomerization has been performed under UV irradiation.
Variable-temperature 1H NMR and UV–vis studies demonstrate
the rotational motion and its braking action after photoisomerization.
The braking action can be reversed by thermal heating. Once the rigid
and planar closed form is obtained, the rotation is effectively slowed
at lower temperature, making this new rotor a potential motor with
an independent response to electrons and light.