Adsorption and Motion of Single Molecular Motors on TiO2(110)

Motorized molecules where an external stimulus leads to controlled motion can perform work on the atomic scale. In Feringa-type motors, controlled motion is initiated by ultraviolet light that triggers a sequence of isomerization and helical inversion steps leading to the unidirectional rotation of the motor. Studying motor molecules on solid surfaces is advantageous because molecules can be studied in real space with scanning probe microscopy, surface features act as a spatial reference, and motion can be activated by pulses from the scanning probe tip. However, commonly used metal substrates have drawbacks, notably the quenching of excited molecular states by surface conduction electrons. An alternate approach is to deposit molecular motors on semiconducting substrates, thereby removing a potential path for quenching. Here we present results on the adsorption configurations and demonstrate the motion of unidirectional Feringa molecular motors adsorbed on the wide band gap semiconductor rutile TiO2(110).