Time-resolved studies of individual molecular rotors

Abstract

Thioether molecular rotors show great promise as nanoscale models for exploringthe fundamental limits of thermally and electrically driven molecular rotation.By using time-resolved measurements which increase the time resolution of thescanning tunneling microscope we were able to record the dynamics of individualthioether molecular rotors as a function of surface structure, rotor chemistry,thermal energy and electrical excitation. Our results demonstrate that the localsurface structure can have a dramatic influence on the energy landscape that themolecular rotors experience. In terms of rotor structure, altering the length of therotor’s alkyl tails allowed the origin of the barrier to rotation to be more fullyunderstood. Finally, time-resolved measurement of electrically excited rotation revealedthat vibrational excitation of a C–H bond in the rotor’s alkyl tail is an efficientchannel with which to excite rotation, and that the excitation is a one-electronprocess.