Synergistic Photomagnetic and Photomechanical Dynamics in a Dysprosium‐Based Smart Molecule

Converging photomagnetic switching and photomechanical functionalities in molecular materials is critical for next-generation adaptive technologies, yet challenged by competing demands for rigid coordination environments to suppress quantum tunneling in single-molecule magnets (SMMs) and flexible frameworks to enable macroscopic motion. Herein, photoactive 9-anthracenecarboxylic acid (HAC) is integrated into a binuclear dysprosium(III) complex, (1), which simultaneously exhibits dual light-responsive behaviors of both SMMs and macroscopic mechanical motion. The 365 nm light irradiation induces [4+4] photocycloaddition of anthracene units in 1, driving a single-crystal-to-single-crystal transformation to a 1D coordination polymer [Dy₂(HAC)₂(DMF)₂(AC)₆]n (1A). This structural reorganization boosts axial magnetic anisotropy, unlocking SMM behavior with a butterfly-shaped hysteresis loop, whereas thermal annealing regenerates the pristine structure and quenches magnetic bistability. Notably, anisotropic lattice strain from cycloaddition induces macroscopic photomechanical motions, triggering macroscopic torsional dynamics in bulk crystals and pronounced flexural deformations in thin film architectures. This work pioneers the synergistic modulation of magnetic and mechanical properties through light-driven structural dynamics in a single-component system, establishing a fundamental platform for developing intelligent materials with integrated opto-magneto-mechanical functionalities for adaptive sensing and actuation technologies.