Intensification of luminescence in quaternary europium complexes

Full text: The enhancement of luminescence in europium (III) coordination compounds can improve the quality of numerous applications as in OLED's, LED's, polymer films, etc [1]. In order to obtain highly luminescent complexes, our research group recently presented a conjecture to increase the quantum efficiency, η, in ternary europium complexes by introducing diversification of the ligands in these complexes [2]. In this work, we investigate this conjecture for another class of europium complexes: the quaternaries. The present study compares the quantum efficiency of eight complexes of the type: [Eu(DBM)4]K, [Eu(DBM)₃(β')]K, [Eu(DBM)₂(β')₂]K and a fully mixed complex [Eu(DBM,BTFA,TTA,HFAC)]K, where DBM and β' = BTFA, TTA or HFAC are the ligands. These complexes were synthesized by using a microwave reactor, and they were characterized by IR spectroscopy, ¹H and ¹⁹F NMR spectroscopy, and MALDITOF spectrometry. The η value was calculated by the software LUMPAC (1.3.1) [3] using the data obtained from spectroscopy experiments of excitation, emission, and lifetime curve. The average η value for the [Eu(DBM)₃(β')]K complexes was 32% and the average for the [Eu(DBM)₂(β')₂]K ones was 35 %, and they were less than the η value for the totally mixed complex (42%). Moreover, the totally mixed complex exhibited a η value remarkably higher than the η value for the complex with all equal ligands (9 %), a relative increase of 367%. These results showed that the more diverse ligands the complex has, the greater the η value, and this outcome opens the perspective of developing more luminescent and sensitive materials.References: [1] Koen, Binnemans, Chemical Review, 109, 4283–4374 (2009) [2] Silva, A. I., Santos, V. F., Lima, N. B., Simas, A. M., & Gonçalves, S. M., RSC Advances, 6(93), 90934-90943 (2016) [3] Dutra, José Diogo L., Thiago D. Bispo, and Ricardo O. Freire., J. of Comp. Chemistry 35.10 772-775 (2014). (author)