Low-Coordinate Erbium(III) Single-Molecule Magnets with Photochromic Behavior

The structure and magnetic properties of photo-responsive magnets can be controlled or fine-tuned by visible light irradiation which makes them appealing as candidates for ternary memory devices: photochromic and photomagnetic at the same time. One of the strategies for photo-responsive magnetic systems is the use of photochromic/photoswitchable molecules coordinated to paramagnetic metal centers to in-directly influence their magnetic properties. Herein, we present two erbium(III) based coordination systems: a trinuclear molecule {[ErIII(BHT)3]3(dtepy)2}.3C5H12 (1) and a 1-D coordination chain {[ErIII(BHT)3(azopy)}nnC5H12 (2), where the bridging photochromic ligands belong to the class of diarylethenes: 1,2-bis(2-methyl-5-pyridyl)thie-3-yl)perfluorocyclopentene (dtepy) and 4,4'-azopyridine (azopy), respectively (BHT = 2,6-di-tert-butyl-4-methylphenolate). Both compounds show slow dynamics of the magnetization, typical for single-molecule magnets (SMMs) as revealed by alternating current (AC) magnetic susceptibility measurements. The trinuclear compound 1, shows also an immediate color change from yellow to dark blue in response to near-UV irradiation. Such a behavior is typical for the photo-isomerization of the open-form of the ligand o-dtepy ligand into its closed-form c-dtepy. The color change can be reversed by exposing the c-dtepy to visible light. The chain-like compound 2, on the other hand, does not show significant signs of the expected trans-cis photoisomerization in response to UV irradiation and does not appear to show photoswitching behavior.