Salts of Lanthanide(III) Hexafluoroacetylacetonates [Ln = Sm(III), Eu(III) and Tb(III)] with Dipyridylammonium Cations: Synthesis, Characterization, Photophysical Properties and OLED Fabrication

Rashid Ilmi, Danyang Zhang, Leonardo Tensi, Houda Al-Sharji, Nawal K. Al-Rasbi, Alceo Macchioni, Liang Zhou, Wai-Yeung Wong, Paul Raithby, Muhammad S Khan

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Abstract

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 LnCl 3, 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 X-ray diffraction, confirms this intermolecular interaction in the solid-state through a N–H⋯O hydrogen bond of 2.187 Å. In the [Eu(hfaa) 4] - anion the EuO 8 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 V turn-on = 3.4 V. Interestingly, the Sm-1 based single-EML device exhibited pure red emission with the Commission internationale de l'éclairage [(CIE) x,y = 0.613, 0.321], which is rare. The Sm-1 based device performance [B = 145 cd/m 2, current efficiency (η c) = 0.35 cd/A, power efficiency (η p) = 0.15 lm/W with an external quantum efficiency (EQE) = 0.3% and V turn-on = 7.1 V] surpassed that of the only reported Sm-based single red-OLED (R-OLED).

Original languageEnglish
Article number110300
JournalDyes and Pigments
Volume203
Early online date4 Apr 2022
DOIs
Publication statusPublished - 31 Jul 2022

Bibliographical note

Funding Information:
MSK acknowledges His Majesty's Trust Fund for Strategic Research (Grant No. SR/SQU/SCI/CHEM/21/01) for funding. RI thanks HM's Trust Fund for a postdoctoral fellowship. AM thanks Università di Perugia and MIUR (“Progetto AMIS–Dipartimenti di Eccellenza”) for funding. LZ is grateful for the financial aid from the National Natural Science Foundation of China (21771172), Youth Innovation Promotion Association of the Chinese Academy of Sciences (2013150). WYW thanks the Hong Kong Research Grants Council ( PolyU 153058/19P), Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials (2019B121205002), Hong Kong Polytechnic University (1-ZE1C), Research Institute for Smart Energy (RISE) and the Endowed Professorship in Energy from Ms Clarea Au (847S) for the financial support. PRR is grateful to the Engineering and Physical Sciences Research Council (EPSRC) for continued funding (Grant EP/K004956/1).

Keywords

  • Hexafluoroacetylacetone
  • Lanthanide tetrakis complexes
  • Red and orange electroluminescence
  • Red emission

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Process Chemistry and Technology

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