Directionality Reversal and Shift of Rotational Axis in a Hemithioindigo Macrocyclic Molecular Motor

Molecular motors are central driving units for nanomachinery and control of their directional motions is of fundamental importance for their functions. Light-driven variants use an easy to provide, easy to dose, and waste free fuel with high energy content, which makes them particularly interesting for many applications. Typically, light-driven molecular motors work via rotations around dedicated chemical bonds (e.g. double bonds) where directionality of the rotation is dictated by the steric effects of asymmetry in close vicinity to the rotation axis. In this work we show how unidirectional rotation around a virtual axis can be realized by reprogramming a molecular motor. To this end, a classical light-driven motor is restricted by macrocyclization and its intrinsic directional rotation is transformed into a directional rotation of the macrocyclic chain in the opposite direction. Further, solvent polarity changes allow to toggle the function of this molecular machine between a directional motor and a non-directional photoswitch. In this way a new concept for the design of molecular motors is delivered together with an elaborate control over their motions and functions by simple solvent changes. The possibility of sensing the environmental polarity and correspondingly adjusting directionality of motions opens up a next level of control and responsiveness to light-driven nanoscopic motors.