A Prospective Ultrafast Hemithioindigo Molecular Motor

The maximum speed of light-driven molecular motors is an important key-property governing not only their overall performances but also many advanced functions. Currently, special emphasis lies on increasing the rate of unidirectional rotations to surpass natural systems and harness the full potential of artificial motors. Herein, we report a new molecular setup for a prospective light-powered three-step motor based on the hemithioindigo chromophore. Comprehensive quantum chemical treatment predicts a very low energy barrier for the only thermal ratcheting step in the unidirectional 360 degrees rotation. Thus an ultrafast motion in the THz range could be possible with this motor at high light intensities and consequently a precise control of rotation speeds solely by light intensity variations could potentially be achieved. Experimental analyses using X-ray crystallography and solution spectroscopy deliver first insights into the working mechanism and show that visible-light photoswitching is feasible in both stable switching states. Additionally, significant alterations of the ground-state energies can be induced by pH changes without hampering photoswitching capabilities.