A Europium(III) Complex Embedded in a Polysulfone Host Matrix: A Flexible Film with Temperature‐Responsive Ratiometric Behaviour

An emissive europium(III) complex [C 2 mim][Eu(fod) 4 ] ( 1 ; C 2 mim=1‐ethyl‐3‐methyl‐imidazolium; fod=1,1,1,2,2,3,3‐heptafluoro‐7,7‐dimethyloctane‐4,6‐dionate) was prepared. The complex shows ratiometric thermal behaviour up to 155 °C. These unusual temperature‐dependent properties arise from a solid‐solid phase transition that promotes increased contact between the anion and the cation, affecting the emission profile of the emissive anion in two different ratiometric relations. A ultrabright and flexible emissive photopolymer film was obtained using polysulfone ( PSU ) as the host matrix of 10 % (w/w) of 1 , that also induced changes on the lanthanide emissive profile with temperature. A temperature‐responsive luminescent film 1/PSU is sensitivr to heating between 100 and 155 °C. Also, the emission lifetime of 1 was not affected by confinement in PSU, while its emission quantum yield was reduced from 82 to 59 %.