Dysprosium Complexes Incorporating Halogen-Substituted Anthracene: Piezochromism and Single-Molecule Magnet Properties

Lanthanide-based single-molecule magnets (Ln-SMMs) showing stimuli-responsive changes in photoluminescence (PL) and magnetic properties are attractive for their potential applications in information storage and molecular devices. In this work, we report two mononuclear complexes, namely, Dy(SCN)2(NO3)(Cl-depma)2(4-hpy)2 (Dy-Cl) and Dy(SCN)2(NO3)(Br-depma)2(4-hpy)2 (Dy-Br), where X-depma represents 10-X-9-diethylphosphinomethylanthracene (X = Cl, Br) and 4-hpy is 4-hydroxypyridine. Both contain face-to-face π-π-interacted anthracene rings and exhibit yellow-green excimer emission. Unlike the other related Dy–anthracene complexes without a halogen substituent, Dy-Cl and Dy-Br cannot undergo photocycloaddition reaction under UV-light irradiation. However, they exhibited remarkable grinding-induced changes in luminescence. Magnetic studies revealed that Dy-Cl and Dy-Br show SMM behavior under zero dc field with the effective energy barriers (Ueff/kB) of 259 K and 264 K, respectively. We also investigated the effect of pressure on the magnetic properties of Dy-Br and observed a reduction in the magnetization value, narrowing of the butterfly-shaped hysteresis loop, and acceleration of the magnetic relaxation under 1.09 GPa. The results demonstrate that introducing a halogen substituent into an anthracene group may pose significant influences on the photophysical and photochemical properties of the complexes. In addition, pressure may be a promising external stimulus to modulate the PL and SMM behaviors of Dy–anthracene complexes.