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

Abstract

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]}·nH₂O (1), based on {Dy^IIICo^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.