A new tris β-diketonate europium(III) [Eu(btfa)₃Py-Im] (Eu-1) complex (4,4,4-trifluoro-1-phenyl-1,3-butanedione (btfa) and 2-(2-pyridyl)benzimidazole (Py-Im)] has been synthesized and characterized by analytical and spectroscopic methods complemented by X-ray crystallography1. Single crystal X-ray diffraction analysis shows that Eu-1 is octacoordinated (Fig.1) and the coordination sphere is composed of a EuO₆N₂ core with a trigonal dodecahedral (D_2d) geometry. Photophysical properties of Eu-1 were analyzed in detail and with the help of the experimental photoluminescence data (Fig.1) and theoretical modelling, energy transfer rates were calculated, and an energy transfer mechanism is proposed for Eu-1. Finally, the complex was used as the emitting layer (EML) to fabricate OLEDs. Eight OLEDs, of which four single-EML and four double-EML with varying doping concentrations, were fabricated via thermal evaporation method using Eu-1 as the EML. Under the optimum conditions, a highly monochromatic bright red emission (CIEx,y = 0.640, 0.311) with brightness (B) = 896 cd/m2, current efficiency (ηc) = 2.26 cd/A, power efficiency (ηp) = 1.92 lm/W and external quantum efficiency (EQE) = 1.6% at very low V_turn-on = 3.4 V was obtained (Fig.1).

Acknowledgements: M.S.K. acknowledges His Majesty’s Trust Fund for Strategic Research (Grant no. SR/SQU/SCI/CHEM/21/01) and The Ministry of Higher Education, Research and Innovation (MoHERI), Oman (Grant no.: RC/RG-SCI/CHEM/20/01).

Reference:

1. Ilmi, R.; Zhang, D.; Dutra, J. D. L.; Dege, N.; Zhou, L.; Wong, W.-Y.; Raithby, P. R.; Khan, M. S., A tris β-diketonate europium(III) complex based OLED fabricated by thermal evaporation method displaying efficient bright red emission. Org. Electron. 2021, 96, 106216.