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

Abstract

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 solidsolid 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 ultra-bright 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 %.

Lanthanide-based complexes as efficient physiological temperature sensors

“…The bands in the ranges 600-1200 cm -1 and 800-970 cm -1 are due to the stretching modes of the C-C and C-F bonds, respectively. Similar observations were obtained with the Eu analogue, [C2mim][Eu(fod)4]; [24] heating does not affect the infrared profile of the [C2mim][Tb(fod)4], but unlike the former, there is no discernible broadening of the peaks associated with increased motion of adjacent atoms, which might indicate a more rigid structure (Figure S3). 1@PMMA: 10% (w/w) of 1 was dissolved in CH2Cl2 and added to a solution of PMMA in tetrahydrofuran.…”

“…[23] Figure were discussed in detail in our previous work and were not considered relevant for the observed thermochromism of [C2mim][Tb(fod)4]0.99985:[C2mim][Eu(fod)4]0.00015. [24] The solid-state emission spectra of 1 were recorded between 450 and 650 nm, under excitation of the ligand absorption band at 350 nm, from 25 to 75 ºC with 1 ºC steps between 35 and 45 ºC. Upon heating, the fluorescence intensity of Tb III decreases dramatically, while that of Eu III decreases at a much slower rate.…”

“…Assuming the optical properties of [C2mim][Eu(fod)4], [24] the option of using an extremely low ratio of Eu/Tb stems from the fact that a highly emissive Eu III complex could hide the Tb III signal. Despite the intense green luminescence, the intrinsic quantum yield (Ф) of the Tb III complex is only 2% and is surprisingly low compared with other Tb III diketonate complexes [13,28] or its Eu III analogue, which presents a value for ФEu of 82%.…”

“…-150 ºC. [24] Poly(methylmethacrylate), known as acrylic glass owing to its transparency and chemical stability, presents some advantages over other organic polymers, including protection from water, high transparency, good optical properties and improved photostability under UV irradiation of the guest complexes.…”