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Issue 27, 2014
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Substituent effect on the electroluminescence efficiency of amidinate-ligated bis(pyridylphenyl) iridium(iii) complexes

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Abstract

This paper reports the synthesis, structure, and photophysical and electrophosphorescence properties of heteroleptic amidinate/bis(pyridylphenyl) iridium(III) complexes having different substituents on the nitrogen atoms of the amidinate ancillary ligands. The reaction of bis(pyridylphenyl) iridium(III) chloride [(ppy)2Ir(μ-Cl)]2 with the lithium salt of various amidinate ligands Li{(NR)(NR′)CPh} at 80 °C gave in 60–80% yields the corresponding heteroleptic bis(pyridylphenyl)/amidinate iridium(III) complexes having a general formula [(ppy)2Ir{(NR)(NR′)CPh}], where R = R′ = iPr (1), R = R′ = t-Bu (2), R = Et, R′ = t-Bu (3), and R = Et, R′ = (CH2)3N(CH3)2 (4). These heteroleptic iridium(III) complexes exhibited bright yellowish-green phosphorescence emission with moderate photoluminescence (PL) quantum yields (ΦPL = 0.16–0.34) and short phosphorescence lifetimes of 0.98–1.18 μs in toluene solution at room temperature. Organic light-emitting diodes (OLEDs) were fabricated by the use of these complexes as phosphorescent dopants in various concentrations (x = 5–100 wt%) in the 4,4′-N,N′-dicarbazolylbiphenyl (CBP) host. Because of the steric hindrance of the amidinate ligands, no significant intermolecular interaction was observed in these complexes, thus leading to the reduction of self-quenching and triple–triplet annihilation at high currents/luminance. A significant influence of the substituents in the amidinate ligands on the electroluminescence efficiency was observed. Among these complexes, complex (2), which contains the bulky t-butyl group on the amidinate nitrogen atoms, showed the highest current efficiency (ηc: up to 116 cd A−1), power efficiency (ηp: up to 72.2 lm W−1) and external quantum efficiency (ηext; up to 16.3%).

Graphical abstract: Substituent effect on the electroluminescence efficiency of amidinate-ligated bis(pyridylphenyl) iridium(iii) complexes

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Article information


Submitted
25 Dec 2013
Accepted
03 Apr 2014
First published
04 Apr 2014

J. Mater. Chem. C, 2014,2, 5317-5326
Article type
Paper
Author version available

Substituent effect on the electroluminescence efficiency of amidinate-ligated bis(pyridylphenyl) iridium(III) complexes

V. K. Rai, M. Nishiura, M. Takimoto and Z. Hou, J. Mater. Chem. C, 2014, 2, 5317
DOI: 10.1039/C3TC32553A

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