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

Abstract

The structures and magnetic properties of photoresponsive 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 photoresponsive magnetic systems is the use of photochromic/photoswitchable molecules coordinated to paramagnetic metal centers to indirectly influence their magnetic properties. Herein, we present two erbium­(III)-based coordination systems: a trinuclear molecule {[ErIII(BHT)3]3(dtepy)2}.4C5H12 (1) and a 1D coordination chain {[ErIII(BHT)3(azopy)} n ·2C5H12 (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 magnetization, typical for single-molecule magnets (SMMs) as revealed by alternating current (AC) magnetic susceptibility measurements. The trinuclear compound 1 also shows an immediate color change from yellow to dark blue in response to near-UV irradiation. Such behavior is typical for the photoisomerization of the open form of the ligand into its closed form. The color change can be reversed by exposing the closed form to visible light. The chain-like compound 2, on the other hand, does not show significant signs of the expected trans–cis photoisomerization of the azopyridine in response to UV irradiation and does not appear to show photoswitching behavior.

Light‐Switchable Metal Complexes: Introducing Photoresponsive Behaviour Through Azoheteroarenes

“…[30] Again, the coordination frameworks of such bridged ligands usually show hindrance or inhibition to the photoisomerization. [31,32] Espinet and co-workers explored the photoisomerization behaviour of Au(I) and Ag(I) complexes of 2,2'-and 4,4'azopyridines. The Au(I) complex of 4,4'-azopyridine (8) showed significantly less photoisomerization (6 %) compared to the analogous derivatives of 2,2'-azopyridine, 9 (31 %) (Figure 3).…”

“…The photoisomerization of 4,4'azopyridine-based 1D coordination polymer 54 (Figure 15) prepared by Pinkowicz and co-workers was silent. [32]…”

“…Representative examples of azoheteroarene-based metal complexes exhibiting coordination polymers 52-54. [35,106,32] Figure 16. Representative examples of azoheteroarene-based metal complexes exhibiting coordination cages 55-57.…”

“…Similar to 2‐phenylazopyridine, metal complexes of the 2,2’‐ analogue also usually utilize the azo nitrogen for coordination along with the N atoms of the azobispyridines [30] . Again, the coordination frameworks of such bridged ligands usually show hindrance or inhibition to the photoisomerization [31,32] …”

A photochromic metallacycle with highly anisotropic Dy–F magnetic units

“…2 In addition, the molecular nature of these architectures makes the introduction of other functions straightforward, therefore, extending the scope of possible applications. 3 For instance, the combination of SMM behaviour and light remote control can be targeted through simple association of an anisotropic magnetic building unit and a photoactive ligand, 3 b,c such as a photochromic dithienylethene derivative 4 that can undergo reversible transformation between two, so called, open and closed isomers.…”