Coupling Rotary Motion to Helicene Inversion within a Molecular Motor

Abstract

Towards complex coupled molecular motions, the remote handedness inversion of a helicene moiety was achieved by a rotary molecular motor. The use of a specifically engineered dynamic helicene stator in a novel overcrowded-alkene second-generation molecular motor based on a fluorinated dibenzofluorene fragment allows for an unprecedented control over helicity inversion. This is achieved by the mechanical coupling of the rotation of the rotor to the helicene inversion of the stator half via a remote chirality transmission process. Thus, the unidirectional rotary motion generated upon irradiation is used to invert the dynamic stereochemistry of a helicene, leading to a 6-step cycle with eight intermediates. In this cycle, both alternation between P and M configurations of the helicene stator and dynamic thermal interconversion (paddling motion) can be achieved. In-depth computational and spectroscopic studies were performed to support the associated mechanism. The control over coupled motion and dynamic helicity offers prospects for the development of complex responsive systems.