Photoactive isomerism and magnetic relaxation dynamics in a family of β-diketonate/azopyridine-based lanthanide single-molecule magnets

Abstract

Photo-responsive lanthanide-based single-molecule magnets (Ln^III-SMMs) possess considerable potential applications in the realms of magneto-optical data storage and spintronic applications. In this work, we use β-diketonate and bpa ligand to coordinate with lanthanide ions, and obtain a family of mononuclear complexes Ln(thd)₃bpa (Ln^III = Dy^III, (1); Tb^III, (2); Er^III, (3); Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione; bpa = 2,2′-bis(4-phenylazopyridine)), where the β-diketonate provide the suitable ligand field for the construction of single-molecule magnets (SMMs), and the bpa ligand acts as the photoisomerization unit. Structural analysis reveals that all three complexes (1–3) adopt an eight-coordinate LnO₆N₂ configuration, with the metal center exhibiting a square antiprismatic (D_4d) geometry. Magnetic studies indicate that complex 1 behaves as a typical zero-field SMMs, while complex 2 is a field-induced SMMs. UV–vis spectroscopy confirms the photo-responsive behavior of complexes 1–3 in CH₂Cl₂ solution, showing that they underwent trans–cis photoisomerization. In contrast, the solid-state UV–Vis reflection spectra of the complexes under light exposure show no changes, possibly due to that the steric hindrance present of complexes in the solid state prevents the occurrence of isomerization.