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.