Visualization of Light‐Induced Rotational Movement in Crystal: Exploring the Mechanism of Viologen‐Containing Molecular Machines

Abstract Constructing effective light‐driven crystal molecular machines and exploring their mechanisms of movement are vital for the development of molecular machines. These explorations afford an Mn ²⁺ metal‐organic framework (MOF)crystal, marking the first instance of a viologen‐containing crystalline MOF capable of exhibiting reversible light‐driven rotational motion. Structural analysis indicates that the rotation of the bipyridine units initiates with a transformation in the coordination configuration of the manganese ion, which subsequently alters the dihedral angle of the bipyridine from −6.7° to −46.8°. This rotation is facilitated through a single bond and involves a transition state with the dihedral angle approaching 0° during the radical phase of the viologen. This result not only elucidates the mechanism by which photo‐induced electron transfer propels the controlled rotation of biaryl groups within crystalline MOFs but also highlights the great potential of viologen‐containing crystalline MOFs as molecular machines.