Humidity driven molecular switch based on photoluminescent DyIIICoIII single-molecule magnets

The switching of single-molecule magnet behaviour and photoluminescence by the level of humidity is presented. A functional material, {[Dy(H2O)(3)(2-pyrrolidone)(4)][Co(CN)(6)]}nH(2)O (1), based on {(DyCoIII)-Co-III} molecules was prepared. 1 exhibits two crystalline phases switchable by the humidity level at room temperature: the low humidity phase, 1(LH), stable below 42% relative humidity (RH), and the high humidity phase, 1(HH), stable above 47% RH; the 42-47% range of RH gives a unique bistable system. Both 1(LH) and 1(HH) are yellow emissive single-molecule magnets due to the intrinsic optical and magnetic properties of Dy-III complexes. The reversible single-crystal-to-single-crystal transformation from 1(HH) to 1(LH) leads to a significant slowdown of magnetic relaxation as depicted by a three-fold increase of the efficient anisotropic thermal energy barrier. The transformation from 1(HH) to 1(LH) also results in the modification of the emission characteristics, including a noticeable shift in the emission colour from almost white to yellow. Therefore, 1 is a magneto-luminescent molecular switch driven by the humidity level, also showing phase bistability for application in memory devices.