Multistate Switching of Spin Selectivity in Electron Transport through Light‐Driven Molecular Motors

It is established that electron transmission through chiral molecules depends on the electron's spin. This phenomenon, termed the chiral‐induced spin selectivity (CISS), effect has been observed in chiral molecules, supramolecular structures, polymers, and metal‐organic films. Which spin is preferred in the transmission depends on the handedness of the system and the tunneling direction of the electrons. Molecular motors based on overcrowded alkenes show multiple inversions of helical chirality under light irradiation and thermal relaxation. The authors found here multistate switching of spin selectivity in electron transfer through first generation molecular motors based on the four accessible distinct helical configurations, measured by magnetic‐conductive atomic force microscopy. It is shown that the helical state dictates the molecular organization on the surface. The efficient spin polarization observed in the photostationary state of the right‐handed motor coupled with the modulation of spin selectivity through the controlled sequence of helical states, opens opportunities to tune spin selectivity on‐demand with high spatio‐temporal precision. An energetic analysis correlates the spin injection barrier with the extent of spin polarization.
The efficiency of electrons transport through chiral systems depends on their spin. Hence, chiral molecules are spin filters. Controlling the molecules' chirality provides a way to define the spin polarization. This molecular machine performs unidirectional rotations, inverting handedness of the molecule and therefore the spin‐polarization at each stage of the rotary cycle.