Journal
DYES AND PIGMENTS
Volume 203, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.dyepig.2022.110300
Keywords
Hexafluoroacetylacetone; Lanthanide tetrakis complexes; Red emission; Red and orange electroluminescence
Funding
- Majestys Trust Fund for Strategic Research
- HM's Trust Fund
- Universita di Perugia [SR/SQU/SCI/CHEM/21/01]
- MIUR (Progetto AMIS-Dipartimenti di Eccellenza)
- National Natural Science Foundation of China
- Youth Innovation Promotion Association of the Chinese Academy of Sciences
- Hong Kong Research Grants Council [21771172]
- Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials [2013150]
- Hong Kong Poly-technic University [153058/19P]
- Research Institute for Smart Energy (RISE) [2019B121205002]
- Endowed Professorship in Energy [1-ZE1C]
- Engineering and Physical Sciences Research Council (EPSRC)
- [847S]
- [EP/K004956/1]
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A series of novel lanthanide metal complexes have been synthesized and characterized. These complexes exhibit good photophysical properties and can be applied as dopants in organic light-emitting diodes.
A series of tetrakis lanthanide complexes with the general formula [Ln(hfaa)(4)](-)(DpaH)(+) [Ln = (Sm-1), (Eu-1) and (Tb-1)], hfaa = hexafluroacetylacetonate and Dpa - 2,2 '-dipyridylamine] has been synthesized by the reaction of LnCl3, hfaa and Dpa in the presence of ammonia solution (25%). The complexes have been characterized by analytical and spectroscopic methods. The solution molecular structure of the complexes was elucidated by one- and two-dimensional NMR spectroscopy which shows that the DpaH+ cation retains a close interaction with the lanthanide anion in solution. The crystal structure of Eu-1, determined by single crystal Xray diffraction, confirms this intermolecular interaction in the solid-state through a N-HMIDLINE HORIZONTAL ELLIPSISO hydrogen bond of 2.187 A. In the [Eu(hfaa)(4)]- anion the EuO8 coordination polyhedron has a distorted triangular dodecahedron geometry with approximate D-2d-symmetry around the metal centre. Photophysical, thermal, and electroluminescent properties of the complexes have been investigated. The Sm-1 and Eu-1 complexes displayed efficient typical red emission with a sizeable photoluminescence quantum yield (PLQY) while Tb-1 displayed near-white light emission. The complexes have been used as dopants to fabricate single- and double-emitting layer (EML) OLEDs through the thermal evaporation method. At the optimum doping concentration, double-EML Eu-1 based device displayed orange electroluminescence (EL) with a brightness (B) of 417 cd/m(2) and very low Vturn-on = 3.4 V. Interestingly, the Sm-1 based single-EML device exhibited pure red emission with the Commission internationale de l'e acute accent clairage [(CIE)(x,y) = 0.613, 0.321], which is rare. The Sm-1 based device performance [B =145 cd/ m(2), current efficiency (eta(c)) = 0.35 cd/A, power efficiency (eta(p)) = 0.15 lm/W with an external quantum efficiency (EQE) = 0.3% and Vturn-on = 7.1 V] surpassed that of the only reported Sm-based single red-OLED (R-OLED).
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