A Unidirectional Surface-Anchored N‑Heterocyclic Carbene Rotor
mediaposted on 01.07.2020, 13:04 by Jindong Ren, Matthias Freitag, Christian Schwermann, Anne Bakker, Saeed Amirjalayer, Andreas Rühling, Hong-Ying Gao, Nikos L. Doltsinis, Frank Glorius, Harald Fuchs
A molecular rotor based on N-heterocyclic carbenes (NHCs) has been rationally designed following theoretical predictions, experimentally realized, and characterized. Utilizing the structural tunability of NHCs, a computational screening protocol was first applied to identify NHCs with asymmetric rotational potentials on a surface as a prerequisite for unidirectional molecular rotors. Suitable candidates were then synthesized and studied using scanning tunneling microscopy/spectroscopy (STM/STS), analytical theoretical models, and molecular dynamics simulations. For our best NHC rotor featuring a mesityl N substituent on one side and a chiral naphthylethyl substituent on the other, unidirectional rotation is driven by inelastic tunneling of electrons from the NHC to the STM tip. While electrons preferentially tunnel through the mesityl N substituent, the chiral naphthylethyl substituent controls the directionality. Such NHC-based surface rotors open up new possibilities for the design and construction of functionalized molecular systems with high catalytic applicability and superior stability compared with other classes of molecular rotors.