A thermally and photoresponsive luminescent single-molecule magnet based on dysprosium-anthracene: effect of temperature on anthracene photocycloaddition.

Stimuli-responsive lanthanide-based single-molecule magnets (Ln-SMMs) are attractive for their potential in information storage, sensors and molecular devices. However, challenges remain in synergistically tuning the magnetic and optical properties of Ln-SMMs at the same temperature. Herein, we report a mononuclear dysprosium complex containing anthracene units, namely [Dy(SeCN)(NO)(depma)(4-hpy)] (1DySeCN) (depma = 9-diethylphosphonomethylanthracene, 4-hpy = 4-hydroxypyridine). It shows a thermally induced phase transition attributed to an order-disorder transition of the axial 4-hpy ligand, and a thermochromism due to a slight slipping of the anthracene pairs. Compound 1DySeCN can undergo [4 + 4] photocycloaddition reaction in a single-crystal-to-single-crystal (SC-SC) transformation manner at room temperature to form the 1D coordination polymer [Dy(SeCN)(NO)(depma)(4-hpy)] (2DySeCN), accompanied by a luminescence switch from yellow to blue-white. Meanwhile, significant changes in SMM properties are observed with the reduction of energy barrier from 334 K to 144 K and the narrowing of the butterfly-like hysteresis loop. We further investigated the effect of temperature on the photodimerization reaction of anthracene in 1DySeCN, and found that the compound can still undergo efficient photodimerization at temperatures as low as 200 K. At this temperature, the magnetic susceptibility ( ) value of the dilute compound 1DySeCN@Y also changed significantly before and after light irradiation. This study provides the first example of lanthanide-anthracene compounds synergistically modulating the magnetic and luminescent properties at the same temperature.