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

A photochromic dysprosium‐based single‐molecule magnet [Dy(CyPh2PO)2(H2O)5](PMo12O40)·3CyPh2PO·H2O (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, MoVI‐to‐MoV 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 DyIII and MoV. 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.