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Effect of fluorine substitution of the β-ketoiminate ancillary ligand on photophysical properties and electroluminescent ability of new iridium(III) complexes

Abstract

In this paper we report studies of the electronic structure as well as photophysical and emissive properties of family of new heteroleptic iridium(III) complexes of the general formula [Ir(bzq)2(N^O)] with N,O-donating β-ketoiminate ligands equipped with different directly fluorinated N-aryl moiety. For this purpose, a series of proper β-ketoimines were prepared, which at the subsequent step were successfully employed in the synthesis of iridium(III) phosphorescent materials. It is worth emphasizing that the developed synthetic strategy, involving the use of microwaves to accelerate of the reaction course, allows reduction of process time up to 10 minutes. All the obtained complexes were characterized by spectroscopic methods and the structures of three of them were resolved by X-Ray methods. The cyclic voltammetry measurements allowed determination of the energies of HOMO and LUMO levels of the studied complexes. Moreover, the HOMO–LUMO gaps predicted for these compounds by DFT methods showed a good correlation with the experimental values. The determined negligible influence of ligand modification on LUMO levels and only small change of HOMO levels explains the observed slight effect of different directly fluorinated N-aryl moieties on photophysical properties of the complexes. All Ir complexes were tested in host–guest type organic light emitting diodes (PhOLEDs) with poly(N–vinylcarbazole):2–tert–butylphenyl–5–biphenyl–1,3,4–oxadiazole matrix. The PhOLEDs based on all studied iridium complexes emitted green light. The most efficient phosphorescent emitter turned out to be the iridium complex with one fluorine atom substituted in para position in the phenyl ring of ancillary ligand. Diodes with the emissive layer containing 1 wt% of this emitter showed the best operating parameters: luminance about 13 000 cd/m2 and current efficiency close to 10 cd/A. A comparison of photoluminescence, electroluminescence and spectrally resolved thermoluminescence spectra of the investigated systems revealed important role of charge carrier trapping in the TL phenomena.

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Publication details

The article was received on 12 Jun 2018, accepted on 10 Jul 2018 and first published on 11 Jul 2018


Article type: Paper
DOI: 10.1039/C8TC02890G
Citation: J. Mater. Chem. C, 2018, Accepted Manuscript
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    Effect of fluorine substitution of the β-ketoiminate ancillary ligand on photophysical properties and electroluminescent ability of new iridium(III) complexes

    E. Witkowska, G. Wiosna-Sałyga, I. Głowacki, B. Orwat, M. Oh, I. Kownacki, M. Kubicki, B. Gierczyk, M. Dutkiewicz, P. Cieszko, B. Luszczynska, J. Ulanski, I. Grzelak, M. Hoffmann, P. Ledwon and M. Lapkowski, J. Mater. Chem. C, 2018, Accepted Manuscript , DOI: 10.1039/C8TC02890G

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