biostudies-literatureUnknown11(1)Li JDivalent europium 5d-4f transition has aroused great attention in many fields, in a way of doping Eu²⁺ ions into inorganic solids. However, molecular Eu²⁺ complexes with 5d-4f transition are thought to be too air-unstable to explore their applications. In this work, we synthesized four Eu²⁺-containing azacryptates EuX₂-N_n (X = Br, I, n = 4, 8) and systematically studied the photophysical properties in crystalline samples and solutions. Intriguingly, the EuX₂-N₈ complexes exhibit near-unity photoluminescence quantum yield, good air-/thermal-stability and mechanochromic property (X = I). Furthermore, we proved the application of Eu²⁺ complexes in organic light-emitting diodes (OLEDs) with high efficiency and luminance. The optimized device employing EuI₂-N₈ as emitter has the best performance as the maximum luminance, current efficiency, and external quantum efficiency up to 25470 cd m^-2, 62.4 cd A^-1, and 17.7%, respectively. Our work deepens the understanding of structure-property relationship in molecular Eu²⁺ complexes and could inspire further research on application in OLEDs.Nature communications5218https://www.ebi.ac.uk/biostudies/studies/S-EPMC7562750biostudies-literatureHighly efficient and air-stable Eu(II)-containing azacryptates ready for organic light-emitting diodes.PMC7562750Liu HLiu ZLi JSun BZhan GBian ZZhao ZWang LfalseHighly efficient and air-stable Eu(II)-containing azacryptates ready for organic light-emitting diodes.Divalent europium 5d-4f transition has aroused great attention in many fields, in a way of doping Eu²⁺ ions into inorganic solids. However, molecular Eu²⁺ complexes with 5d-4f transition are thought to be too air-unstable to explore their applications. In this work, we synthesized four Eu²⁺-containing azacryptates EuX₂-N_n (X = Br, I, n = 4, 8) and systematically studied the photophysical properties in crystalline samples and solutions. Intriguingly, the EuX₂-N₈ complexes exhibit near-unity photoluminescence quantum yield, good air-/thermal-stability and mechanochromic property (X = I). Furthermore, we proved the application of Eu²⁺ complexes in organic light-emitting diodes (OLEDs) with high efficiency and luminance. The optimized device employing EuI₂-N₈ as emitter has the best performance as the maximum luminance, current efficiency, and external quantum efficiency up to 25470 cd m^-2, 62.4 cd A^-1, and 17.7%, respectively. Our work deepens the understanding of structure-property relationship in molecular Eu²⁺ complexes and could inspire further research on application in OLEDs.2020-01-01T00:00:00Z2020 Oct2024-02-15T09:14:17.043Z2020-10-29T10:51:29ZS-EPMC75627503306057310.1038/s41467-020-19027-x