Photochromic Dysprosium Single‐Molecule Magnet Featuring Reversible Redox Transformation of Polyoxomolybdate Moiety

Abstract A photochromic dysprosium‐based single‐molecule magnet [Dy(CyPh 2 PO) 2 (H 2 O) 5 ](PMo 12 O 40 ) ⋅ 3CyPh 2 PO⋅H 2 O ( 1‐Dy ) is synthesized via cocrystal engineering of a polyoxomolybdate (POMo) anion and an Ising‐type cation with pseudo pentagonal bipyramidal geometry. Upon ultraviolet irradiation, Mo VI ‐to‐Mo V single‐electron photoreduction occurs in the POMo moiety, resulting in significant changes of optical and magnetic properties. The emergence of intervalence charge‐transfer transitions in heteropoly blue state 1‐Dy* facilitates photothermal conversion in near‐infrared region. Meanwhile, the coercive field of hysteresis loop is altered from 0.72 T ( 1‐Dy ) to 0.04 T ( 1‐Dy* ) at 2 K, which might be contributed to the magnetic interaction between Dy III and Mo V . After dark treatment, 1‐Dy* can convert to the initial state with the recovery of magnetic memory effect. These results presented herein provide a blueprint for developing versatile opto‐magnetic materials via the coupling of photochemical regulation and magnetic interaction.