Synergic Light-Induced Electron Transfer and [4 + 4] Cycloaddition toward Switchable Photoluminescence and Single-Molecule Magnet Behavior in a Dy4 Cubane

Abstract Molecular materials possessing switchable magneto-optical properties are of great interest for their potential applications in spintronics and molecular devices. However, switching their photoluminescence (PL) and single-molecule magnet (SMM) behavior via light-induced structural changes still constitutes a formidable challenge. Herein, a series of cubane structures were synthesized via self-assembly of anthracene acid and rare-earth ions under hydrothermal conditions. Upon Xe lamp irradiation at room temperature, all complexes exhibited obvious photochromic phenomena and complete PL quenching, which were realized via the synergistic effect of photogenerated radicals and [4 + 4] photocycloaddition of Ac components, with the quenched PL showing the largest fluorescence intensity change (99.72%) in electron-transfer photochromic materials. A reversible decoloration process was unexpectedly achieved via mechanical grinding stemming from the relaxation of photogenerated radicals. Moreover, an SMM behavior in the Dy analog appeared after room-temperature irradiation owing to the photocycloaddition of Ac ligands and photogenerated stable radicals changed the electrostatic ligand field and magnetic couplings. This work realizes for the first time complete PL quenching and photoinduced SMM behavior via simultaneous modulation of photocycloaddition and photogenerated radicals in one system, providing a dynamical switch for the construction of multifunctional polymorphic optical response materials and optical storage devices.