Effects of n → π* Orbital Interactions on Molecular Rotors: The Control and Switching of Rotational Pathway and Speed.

The role of n → π* orbital interactions in the rotational pathway and barrier of biaryl-based molecular rotors was elucidated through a combined experimental and computational study. The n → π* interaction in the transition state can lead to the acceleration of rotors. The competition between the n → π* interaction and hydrogen bonding further enabled the reversal of the pathway and greasing/braking the rotor in response to acid/base stimuli, thereby creating a switchable molecular rotor.