Solvent and Light Dual-Responsive Dinuclear Dy(III) Single-Molecule Magnets: Coordination and Radical Effects on Magnetic Relaxation

The controllable regulation of magnetic anisotropy and relaxation dynamics in lanthanide-based single-molecule magnets (SMMs) remains a central objective in molecular magnetism, particularly for the development of intelligent magnetic materials that require non-invasive and spatiotemporally precise control. Herein, two structurally distinct dinuclear dysprosium compounds were obtained through solvent-controlled assembly using 9-anthracenecarboxylic acid (9-HAC) as a photoactive ligand and 2,2′-biimidazole (2,2′-BIM) as an auxiliary component. The solvent-dependent coordination state of 2,2′-BIM produces markedly different Dy(III) coordination environments: in compound 1, 2,2′-BIM coordinates to the Dy(III) center, whereas in compound 2, it is protonated and remains as a lattice guest. As a result, compound 1 displays superior field-induced SMM behavior, reflecting a more favorable local ligand-field environment. Upon room-temperature light irradiation, both compounds undergo photoinduced electron transfer (PET) to generate stable organic radicals, which magnetically interact with the Dy(III) centers and attenuate the relaxation dynamics. Notably, compound 2 shows a much stronger radical-mediated effect, resulting in complete quenching of its SMM behavior after irradiation. This study proposes a dual-stimulation control method, in which the coordination environment regulated by the solvent determines the magnetic relaxation behavior and the generation of free radicals induced by light further affects the relaxation kinetics. Different from the previous PET-based photomagnetic Dy(III) systems that relied solely on light stimulation, this work introduces solvent regulation on this basis. By combining solvent-driven structural regulation with light-induced free-radical coupling, a synergistic magnetic control strategy is achieved, providing an effective approach for constructing multi-stimulation-responsive lanthanide molecular magnets with tunable relaxation kinetics.