A butterfly-like yellow luminescent Ir(III) complex and its application in highly
efficient polymer light-emitting devices†
Lei Fu,
a
Mei Pan,
*
a
Yan-Hu Li,
b
Hong-Bin Wu,
b
Hai-Ping Wang,
a
Cheng Yan,
a
Kang Li,
a
Shi-Chao Wei,
a
Zi Wang
a
and Cheng-Yong Su
*
a
Received 27th July 2012, Accepted 3rd September 2012
DOI: 10.1039/c2jm34992b
A novel butterfly-like Ir(
III) complex is designed, synthesized, and characterized for highly efficient
yellow phosphorescent polymer-based light-emitting diodes (PLEDs). The device shows a maximum
external quantum efficiency of 19.2%, luminance efficiency of 40 cd A
1
and Commission International
de L’Eclairage (CIE) color coordinates of (0.49, 0.50) at J ¼ 1.2 mA cm
2
.
Introduction
Ir(III) complexes are one kind of promising phosphorescent
emitters which have attracted intensive study in recent years.
1
Due to their efficient intersystem crossing owing to the large
spin–orbital coupling mediated by the heavy metal core, Ir(
III)
complexes feature unmatched photoluminescence efficiencies,
relatively short (ms range) phosphorescence lifetimes and
versatile color tuning abilities via ligand control. Typically, Ir(
III)
complexes can emit blue to red phosphorescence upon opto- or
electro-stimulating.
2–4
However, reports of yellow luminescent
Ir(
III) complexes remain relatively rare. In recent years, due to the
emerging demand for white light illumination, mixing yellow
with blue luminescence or phosphorescence has become an
important choice in the fabrication of white light emitting diodes
(LEDs).
5–7
Furthermore, yellow constitutes one of the most
sensitive colors to human eyes and is widely used in traffic
signals, wild field rescues or art decoration. Therefore, the
fabrication of yellow light emitting Ir(
III) complexes is quite
essential in both the scientific and the practical view. Due to this,
the application of efficiently emitting Ir(
III) complexes in poly-
mer-based light emitting diodes (PLEDs) has made significant
progress in recent years. Compared with the standard vacuum
evaporation-based organic light emitting diodes (OLEDs),
PLEDs feature improved large-area display or illumination
ability, as well as facile and inexpensive solution processing
methods. However, until now, PLEDs still faced the problem of
the relatively low device efficiency of fluorescent polymer-emit-
ting layers. One solution is that the mixture of phosphorescent
Ir(
III) complexes in polymer-emitting layers may provide a
significant breakthrough in obtaining both large display area and
high device efficiency.
8
In this regard, improvement of the
luminance efficiency (F
p
) is a prerequisite for the successful
application of Ir(
III) complex based PLEDs. However, other
factors such as the electron or hole transport and injection
abilities, solubilities, and film-forming properties of Ir(
III)
complex will also affect the electroluminesence (EL) performance
of the PLED devices significantly. In this article, we report a
butterfly-like bright yellow luminescent Ir(
III) complex based on
a carbazole-substituted tridentate N^C^N ligand. Its application
in PLEDs gives a maximum external quantum efficiency of
19.2%, which is among the highest quantum efficiency for yellow
light PLED ever reported.
9
Experimental
General details
The
1
H NMR spectra were recorded on a Varian/Mercury-Plus 300
NMR spectrometer using tetramethylsilane (TMS) as an internal
reference. Elemental analyses (C, H, N) were tested on a Vario EL
instrument. Mass spectra were determined by AccuTOF CS JMS-
T100CS spectrometer. UV-Vis absorption spectra were measured
on a Shimadzu UV-2450 spectrometer. The photoluminescence
(PL) spectra were recorded on an Edinburgh Analytical Instru-
ments FLS920 spectrometer. The emission quantum yield of the
complex was measured in degassed CH
2
Cl
2
solution, using
Rhodamine 6G in degassed ethanol as the standard. Cyclic vol-
tammetry (CV) was performed on a CHI760D electrochemical
workstation at room temperature using 0.1 mol L
1
tetra(n-butyl)
ammonium hexafluorophosphate (TBAP) as the supporting elec-
trolyte and degassed CH
2
Cl
2
as the solvent. The ferrocenium/
ferrocene couple was used as the internal standard.
a
MOE Laboratory of Bioinorganic and Synthetic Chemistry/KLGHEI of
Environment and Energy Chemistry, State Key Laboratory of
Optoelectronic Materials and Technologies, School of Chemistry and
Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275,
China. E-mail: panm@mail.sysu.edu.cn; cesscy@mail.sysu.edu.cn; Fax:
+86 20-8411-5178
b
Institute of Polymer Optoelectronic Materials and Devices, State Key
Laboratory of Optoelectronic Functional Materials and Devices, South
China University of Technology, Guangzhou 510640, P. R. China
† Electronic supplementary information (ESI) available:
Crystallographic information, TG curve, PL spectra. See DOI:
10.1039/c2jm34992b
22496 | J. Mater. Chem., 2012, 22, 22496–22500 This journal is ª The Royal Society of Chemistry 2012
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