A Photochromic Dysprosium Compound Supported by β-Diketone Dithienylethene Ligand

Air-stable lanthanide single-molecule magnets (SMMs) with photochromic units, e.g. dithienylethene (DTE), anthracene, and polyoxometalates (POMs) have attracted considerable attentions in the field of molecular magnetism as they could increase the range of applications of magnetic molecules. However, the number of photochromic lanthanide SMMs is scarce. Inspired by a boron-based molecule featuring near-infrared absorption supported by a DTE-containing β-diketonate ligand (3ThacacH) reported by Vivian Wing-Wah Yam et al., in this work, we employed this ligand to lanthanide systems for the first time constructing an air-stable mononuclear Dy(III)-based compound, Dy(o-3Thacac)₃phen. It is a typical zero-field SMM with the anisotropy barrier approaching 100 K. Its reversible photochromic behaviors in solution were determined by UV-Vis absorption and ¹H NMR spectra. The inevitable byproducts upon UV irradiation combined with the low yield of photocyclization reaction lead to the incomplete photochromism in a solid state. However, distinct relaxation rates of quantum tunneling of the magnetization between Dy(o-3Thacac)₃phen and the irradiated sample were observed, demonstrating the feasibility of using 3ThacacH to modulate magnetodynamics. Meanwhile, this work highlights the vital roles of avoiding photoinduced byproducts, achieving photochromic single-crystal-to-single-crystal transformation, and high yields of photocyclization/photocycloreversion reaction in elucidating the photo-responsive relaxation mechanism and future device applications.