A thermochromic europium(<scp>iii</scp>) room temperature ionic liquid with thermally activated anion–cation interactions

Abstract

We report the first example of an observable and reversible case of thermochromism due to the interaction of an alkylphosphonium (P_6,6,6,14)⁺ with a β-diketonate (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate-fod) of an europium(iii) tetrakis-β-diketonate room temperature ionic liquid. This thermochromism is characterized by the conversion of a light yellow viscous liquid, at room temperature, to a reddish substance close to 80 °C. The reversibility of this optical effect was highlighted by the thermal stability of the Eu(iii) complex.