Towards helical-chirality-controlled molecular motors.

Photochemically driven overcrowded-alkene-based molecular motors have become ubiquitous in molecular nanotechnology due to their reliable unidirectional rotation, modular design, and responsiveness to light. For all the designs of such motors reported to this day, the directional bias of the motion is a consequence of the stereochemistry of the molecule, defined by one or multiple (pro-)chiral stereogenic centers. Such designs nevertheless suffer from incompatibility with various potential experimental conditions, involving for instance the use of strong bases or redox-stimuli. To expand the application scope of molecular motors, we envisioned to replace this point-chirality by a stable helical element, directly integrated within the structure of the molecular motor and use it as the sole inherent chiral information used to drive the unidirectional rotation of the overcrowded-alkene-based motor. Herein we report the design, synthesis, and characterization of three overcrowded-alkenes featuring a helical half, accompanied by a detailed study of their rotational properties, showing the importance of a subtle interplay of distinct isomerization processes.