A thermochromic europium(iii) 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) 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.

A Europium(III) Complex with an Unusual Anion–Cation Interaction: A Luminescent Molecular Thermometer for Ratiometric Temperature Sensing

“…In this context, this work presents the temperature dependence of the photophysical spectral properties of a tetrakis-1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionate (FOD) Eu 3 + anionic complex with thermochromism in the visible range. An unusual thermochromic behaviour, similar to the previously observed for [P 6,6,6,14 ][Eu(FOD) 4 ], [21] [P 6,6,6,14 ] + is trihexyltetradecylphosphonium cations, was also identified in the [CHOL][Eu(FOD) 4 ] complex (1; CHOL = choline), foreseeing the design of new luminescent temperature probes. An equilibrium reflecting a temperature-dependent degree of asymmetry on the coordination of the Eu 3 + ion leads to a dramatic change in the intensity of the hypersensitive transition 5 D 0 !…”

“…The red shift of the maximum intensity can be explained by the structural modification of the coordinated β‐diketonate ligand induced by temperature increase . For the [P 6,6,6,14 ][Eu(FOD) 4 ] ionic liquid, it was observed a gradual colour change from the familiar light yellow to a deep red at temperatures close to 80 °C, attributed to partial β‐diketonate decomplexation, with concomitant establishment of a strong anion‐cation interaction .…”

A Reusable Eu3+ Complex for Naked‐Eye Discrimination of Methanol from Ethanol with a Ratiometric Fluorimetric Equilibrium in Methanol/Ethanol Mixtures

“…[18] ESI-MS confirms the presence of this neutral organic compound while Eu 3+ is hepta-coordinated with three FODunits plus one 2,4,6trimethylphenolate unit. between 574-578 nm corresponds to the phosphorane like compound P 6,6,6,14 FOD formed during the 2,4,6-trimethylphenolate addition to the complex [P 6,6,6,14 ][Eu(FOD) 4 ] (Scheme 1).…”

“…[18] According to the preformed solubility tests, this organic purple compound was more stable (maintained the pinkish color) in MeOH than in EtOH (although after ethanol evaporation the color was regained again). [18] According to the preformed solubility tests, this organic purple compound was more stable (maintained the pinkish color) in MeOH than in EtOH (although after ethanol evaporation the color was regained again).…”

“…[3,17] Also, we recently reported that the [P 6,6,6,14 ][Eu(FOD) 4 ] ionic liquid undergoes a disturbance in the coordination sphere of the Eu 3+ ion, with a disruption of the local symmetry when heated up to ca. [18] This can be explained by the fact that the inclusion of fluorine substituents in the organic ligand, with a high electron-withdrawing effect, reduces the charge density on the oxygen atoms inducing partial dissociation of one of the ligands. [18] This can be explained by the fact that the inclusion of fluorine substituents in the organic ligand, with a high electron-withdrawing effect, reduces the charge density on the oxygen atoms inducing partial dissociation of one of the ligands.…”