A thermochromic europium(III) room temperature ionic liquid with thermally activated anion-cation interactions

We report the first example of an observable and reversible case of thermochromism due to the interaction of an alkylphosphonium (P-6,P-6,P-6,P-14)(+) with a beta-diketonate (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane- 4,6-dionate-fod) of an europium(III) tetrakis-beta-diketonate room temperature ionic liquid. This thermochromismis characterized by the conversion of a light yellow viscous liquid, at room temperature, to a reddish substance close to 80 degrees C. The reversibility of this optical effect was highlighted by the thermal stability of the Eu(III) complex.