Two-Dimensional Metal-Organic Framework with High-Performance Single-Molecule Magnets as Nodes Showing Magnetic Coercivity Photomodulation

Addressing the spatial organization of high-performance single-molecule magnets (SMMs) and achieving stimuli-responsive switching of their magnetic bistability are pivotal challenges in molecular memory technologies, paving the way for advanced opto-magnetic devices. Herein, we utilize the photosensitive ligand 4,4′-bipyridine (BPy) as a linker to incorporate typical pentagonal-bipyramidal SMMs as nodes into a two-dimensional metal-organic framework (MOF), formulated as {[Dy_1.5(OPh)₂Cl(BPy)₃(THF)_1.5][(BPh₄)_1.5]·0.5THF}_n (1). The precise synthesis facilitates axial coordination of PhO^- and equatorial alignment of BPy, enforcing perpendicular orientations of the principal magnetic axes of Dy³⁺ ions across all Kagomé layers. Compound 1 exhibits photochromic behavior upon exposure to ultraviolet irradiation at room temperature, driven by a photoinduced electron transfer process that generates radicals. The resulting 1uv displays overall faster relaxation dynamics compared to 1, characterized by shorter relaxation times at identical temperatures within the 12-70 K range, a lower diverging temperature in field-cooled and zero-field-cooled curves (9 K for 1 vs. 6 K for 1uv), and reduced energy barriers from 1048(17)/822(46) K for 1 to 1000(9)/641(34) K for 1uv. Notably, the coercive field decreases dramatically from 4500 Oe for 1 to 1300 Oe for 1uv at 2 K, while the hysteresis loop opening temperature decreases from 20 K for 1 to 14 K for 1uv. These photoinduced changes are due to the formation of photogenerated radicals and alterations in crystal packing. This work achieves an MOF that integrate high-performance SMM behavior with magnetic coercive photomodulation, providing a design paradigm for engineering advanced SMM-MOFs with tailored photomagnetic switching.