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.