Synthesis and optoelectronic properties of a heterobimetallic Pt(ii)-Ir(iii) complex used as a single-component emitter in white PLEDs

Article abstract of DOI:10.1039/c2dt12027e

To tune aggregation/excimer emission and obtain a single active emitter for white polymer light-emitting devices (PLEDs), a heterobimetallic Pt(ii)-Ir(iii) complex of FIr(pic)-C₆DBC₆-(pic)PtF was designed and synthesized, in which C<

Full text of DOI:10.1039/c2dt12027e

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 2972
www.rsc.org/dalton
PAPER
Synthesis and optoelectronic properties of a heterobimetallic Pt(II)–Ir(III)
complex used as a single-component emitter in white PLEDs†
Xiaoshuang Li, Yu Liu, Jian Luo, Zhiyong Zhang, Danyan Shi, Qing Chen, Yafei Wang,* Juan He,
Jianming Li, Gangtie Lei and Weiguo Zhu*
Received 25th October 2011, Accepted 13th December 2011
DOI: 10.1039/c2dt12027e
To tune aggregation/excimer emission and obtain a single active emitter for white polymer light-emitting
devices (PLEDs), a heterobimetallic Pt(II)–Ir(III) complex of FIr(pic)-C6DBC6-(pic)PtF was designed and
synthesized, in which C6DBC6 is a di(phenyloxyhexyloxy) bridging group, FIr(pic) is an iridium(III) bis
[(4,6-difluorophenyl)pyridinato-N,C2′] (picolinate) chromophore and FPt(pic) is a platinum(II) [(4,6-
difluorophenyl)pyridinato-N,C2′] (picolinate) chromophore. Its physical and opto-electronic properties
were investigated. Interestingly, the excimer emission was efficiently controlled by this heterobimetallic
Pt(II)–Ir(III) complex compared to the PL profile of the mononuclear FPt(pic) complex in the solid state.
Near-white emissions were obtained in the single emissive layer (SEL) PLEDs using this heterobimetallic
Pt(II)–Ir(III) complex as a single dopant and poly(vinylcarbazole) as a host matrix at dopant concentrations
from 0.5 wt% to 2 wt%. This work indicates that incorporating a non-planar iridium(III) complex into the
planar platinum(II) complex can control aggregation/excimer emissions and a single phosphorescent
emitter can be obtained to exhibit white emission in SEL devices.
These single phosphorescent emitters mainly contain copolymers
Introduction
with different phosphors,17–19 and small molecular compounds
with a mononuclear platinum complex unit.20–23 By mixing the
blue-emitting monomolecule and its aggregation/excimer emis-
Since Kido and his coworkers reported the first white organic
light-emitting diode in 1994,1 white organic and polymer light-
emitting diodes (OLEDs/PLEDs) have attracted tremendous
attention in both academic and industrial communities for their
intrinsic characteristics, such as low driving voltages, non-glare
light, homogenous illumination, and for their potential appli-
cations in energy saving solid-state lighting sources.2 Up to now,
various white OLEDs/PLEDs with single-emissive-layers
(SEL),1,3,4 multiple-emissive-layers (MEL),5 tandems,6–9 and
microcavity structures,10,11 have been reported. In these devices,
the SEL-based white OLEDs and PLEDs can be made with a
simple process technique and were considered a class of promis-
ing commercial lighting sources.
sions, or different phosphor emissions, the SEL OLEDs/PLEDs
exhibit white or near-white emissions. However, it is more
difficult to present pure white emission in SEL devices
with single small molecular phosphorescent emitters than
copolymers.
As the structure and optoelectronic properties of the single
small molecular active emitters are easily tuned in order to
control the formation of the aggregation/excimer and to obtain
stable white emission, we previously reported an alkyltrifluor-
ene-modified mononuclear platinum complex and another dinuc-
lear cyclometalated platinum(II) complex of (dfppy)2-Pt2(dipic)
as single active emitters in white SEL PLEDs.4 In this paper, to
further study the structure–property relationship of the platinum-
containing complexes, we designed and synthesized a heterobi-
metallic platinum–iridium complex of FIr(pic)-C6DBC6-(pic)
PtF, in which the C6DBC6 is a di(phenyloxyhexyloxy) bridged
group. FIr(pic) and FPt(pic), blue-emitting phosphorescent chro-
mophores, are iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,
C2′] (picolinate) and platinum(II) [(4,6-difluorophenyl)-pyridi-
nato-N,C2′](picolinate), respectively. Here, incorporating an
unconjugated C6DBC6 unit between the FIr(pic) and FPt(pic)
chromophores is expected to efficiently manage intramolecular
energy transfer, and partly control the excimer formation as the
biphenyl unit in C6DBC6 has a distorted configuration. Introdu-
cing a non-planar iridium complex unit into the planar platinum
There are often two approaches to construct the emitting layer
in the SEL-based white OLEDs/PLEDs. The first way is doping
multi-emitters with various emissive colors into
a host
matrix.12–16 However, this type of device has an inherent color
stability problem as the blue emitters have shorter lifetimes than
the green and red ones. The second way is employing only a
single emitter with a wide-band emission in a host matrix.17–23
College of Chemistry, Key Lab of Environment-Friendly Chemistry and
Application in Ministry of Education, Xiangtan University, Xiangtan,
411105, China. E-mail: zhuwg18@126.com, qij8304@hotmail.com;
Fax: +86 731 58292251; Tel: +86 731 58298280
†Electronic supplementary information (ESI) available. See DOI:
10.1039/c2dt12027e
2972 | Dalton Trans., 2012, 41, 2972–2978
This journal is © The Royal Society of Chemistry 2012

View Article Online
complex is hoped to further tune aggregation/excimer formation.
The synthetic route of this FIr(pic)-C6DBC6-(pic)PtF complex is
shown in Scheme 1. Its photophysical, electrochemical and elec-
troluminescent properties were studied. The results showed that
this heterobimetallic platinum–iridium complex presented stable
near-white emission in the SEL PLEDs using poly(N-vinylcarba-
zole) (PVK) as a host matrix at different dopant concentrations
from 0.5 wt% to 2 wt%. Therefore, attaching a non-planar blue-
emitting iridium complex to a planar blue-emitting platinum
complex by the unconjugated C6DBC6 unit can effectively tune
the aggregation/excimer formation and a single active phosphor-
escent emitter can be obtained to exhibit white emission in SEL-
based PLEDs.
ether-forming reaction under a strict ratio of 4,4′-dihydroxybi-
phenyl and methyl 3-(6-bromohexyloxy) picolinate. Picolinic
acid derivative 4 was obtained by a hydrolysis of methyl picoli-
nate derivative 3 in sodium carbonate aqueous solution and
methanol. The mononuclear Pt(II) complex 9 was synthesized by
a debridging reaction of the chloride-bridged dimer 8 in the pres-
ence of sodium carbonate. The heterobimetallic platinum–
iridium complex of FIr(pic)-C6DBC6-(pic)PtF was obtained by
a similar ether-forming reaction between compounds 7 and 9, in
which DMF was used as the solvent instead of acetone to
improve the solubility of reactants. The molecular structure of
1
FIr(pic)-C6DBC6-(pic)PtF was confirmed by H NMR spectra
and elemental analysis.
Results and discussion
Photophysical properties
Synthesis and characterization
The UV-vis absorption spectra of FIr(pic)-C6DBC6-(pic)PtF,
FIr(pic) and FPt(pic) in dichloromethane (DCM) are shown in
Fig. 1, and their UV-vis absorption data are listed in Table 1.
Similar UV-vis absorption spectra with a strong high-lying
Compounds of 1, 2, 5, 8, FIr(pic) and FPt(pic) were prepared
following literature procedures.4a,24–26 The methyl picolinate
derivative 3 with a hydroxyl was synthesized via a Williamson
Scheme 1 Synthetic route of the heterobimetallic cyclometalated platinum–iridium complex of FIr(pic)-C6DBC6-(pic)PtF.
This journal is © The Royal Society of Chemistry 2012 Dalton Trans., 2012, 41, 2972–2978 | 2973

View Article Online
degassed DCM at room temperature using FIr(pic) as the stan-
dard (ΦPL = 0.60).29 This indicates that the heterobimetallic
platinum–iridium complex has a higher emission efficiency than
FPt(pic) in DCM. To further understand the effect of the uncon-
jugated C6DBC6 linking unit clearly in FIr(pic)-C6DBC6-(pic)
PtF, the PL spectrum of a mixture of FPt(pic) and FIr(pic) was
examined in DCM for comparison and shown in Figure S1.† A
analogous PL spectrum with a 2 nm blue shift is found for the
mixture instead of FIr(pic)-C6DBC6-(pic)PtF at 10−5 M in
DCM. However, we found that the mixture film exhibited much
weaker emission compared to that of the FIr(pic)-C6DBC6-(pic)-
PtF neat film. It implies that the unconjugated C6DBC6 linking
unit plays an important role in the emission.
On the other hand, the PL spectra in the neat films display
only a minor red shift for FIr(pic)-C6DBC6-(pic)PtF and
FIr(pic) compared to their corresponding PL spectra in DCM.
The maximum emission peaks around 495 nm and 502 nm are
observed in the PL spectra for FIr(pic)-C6DBC6-(pic)PtF and
FIr(pic) in their neat films, respectively. However, a significantly
red-shifted PL spectrum with an emission peak around 599 nm
is exhibited only for FPt(pic) in its neat film. The remarkably
different PL spectra between FIr(pic)-C6DBC6-(pic)PtF and
FPt(pic) in their neat films can be ascribed to their different
aggregated state. A non-planar structure of the FIr(pic) unit and
a distorted unconjugated linkage of the C6DBC6 unit make their
resulting heterobimetallic platinum–iridium complex hardly
aggregate in the neat film. Therefore, it is difficult for FIr(pic)-
C6DBC6-(pic)PtF to give aggregation/excimer emissions under
this solid state.
Fig. 1 UV/vis absorption spectra of FIr(pic)-C6DBC6-(pic)PtF,
FIr(pic) and FPt(pic) in dilute DCM (10−5 M) at 298 K.
absorption band below 300 nm and a weak low-lying absorption
band between 350 nm and 450 nm are observed for FIr(pic)-
C6DBC6-(pic)PtF and FIr(pic), in which the high-lying absorp-
tion band is assigned to be ligand-centered (LC) π–π* electron
transition, and the low-lying absorption band is attributed to the
mixing singlet and triplet metal-to-ligand charge transfer
(MLCT) transitions.27a However, FPt(pic) exhibited two new
moderate absorption peaks in the range of 328 nm–350 nm.
These moderate absorption peaks probably originate from the
intraligand π–π* electron transition and the ligand to ligand
charge transfer (LLCT) transition.27b Compared to the UV-vis
absorption spectrum of FPt(pic), the absorption peaks of the
intraligand π–π* and LLCT transitions from this heterobimetallic
platinum–iridium complex have not been observed. This implies
that incorporating a non-planar FIr(pic) unit into a planar plati-
num complex by the unconjugated C6DBC6 unit can reduce the
molecular aggregation and result in the disappearance of absorp-
tion from the LLCT transition for the resulting heterobimetallic
platinum–iridium complex in DCM.
The photoluminescence (PL) spectra of FIr(pic)-C6DBC6-
(pic)PtF, FIr(pic) and FPt(pic) in DCM and their neat films are
shown in Fig. 2 and their PL data are also listed in Table 1.
Almost identical PL spectra are observed between the heterobi-
metallic platinum–iridium complex and the mono-nuclear
FIr(pic) complex at 10−5 M in DCM. For FIr(pic)-C6DBC6-
(pic)PtF, an intense emission peak at 469 nm with a shoulder at
496 nm is presented. According to the literature,28 this blue
emission is assigned to the mixing singlet and triplet MLCT
transitions of this complex. We noted that the FIr(pic)-C6DBC6-
(pic)PtF complex has a PL quantum yield (ΦPL) of 0.53 in
Thermal and dispersibility properties
The thermal properties were examined by thermgravimetric
analysis (TGA) under a nitrogen atmosphere at a scan rate of
20 °C min−1. The thermal decomposition temperatures at 292 °C
were observed for FIr(pic)-C6DBC6-(pic)PtF. This means that
FIr(pic)-C6DBC6-(pic)PtF has high stability at the same time.
In order to make clear their dispersibility in a polymer matrix,
the films of FIr(pic)-C6DBC6-(pic)PtF, FIr(pic) and FPt(pic)
doped into PVK at 1 wt% doping concentration were made. The
surface morphologies were recorded by atomic force microscopy
(AFM) and are shown in Fig. 3. Roughnesses with Ra
=
0.45 nm, 0.37 nm and 0.34 nm are observed in the FIr(pic)-
C6DBC6-(pic)PtF, FIr(pic) and FPt(pic)-doped films, respect-
ively. Therefore, this heterobimetallic cyclometalated platinum–
iridium complex likewise has a good dispersibility in the PVK
matrix.
Table 1 Photophysical and electrochemical properties of FIr(pic)-C6DBC6-(pic)PtF, FIr(pic) and FPt(pic)
Compounds
UV-vis (nm)
Emission (nm)a
Emission (nm)b
EHOMO (eV)
ELUMO (eV)
Eg (eV)
FIr(pic)
FPt(pic)
FIr(pic)-C6DBC6-(pic)PtF
258, 385
250, 328 352, 385
250, 280 374
471, 496
475, 502
469, 496
501
599
495
−5.62
−6.63
−5.51
−3.20
−3.46
−3.08
2.42
3.17
2.43
a Measured in DCM at room temperature. b Measured in the neat film at room temperature.
2974 | Dalton Trans., 2012, 41, 2972–2978
This journal is © The Royal Society of Chemistry 2012

View Article Online
Fig. 2 PL spectra of FIr(pic)-C6DBC6-(pic)PtF, FIr(pic) and FPt(pic)
in DCM (10−5 M) and their neat films at 298 K.
Electrochemical properties
The electrochemical behaviors of FIr(pic)-C6DBC6-(pic)PtF
were investigated by cyclic voltammetry (CV), and the resulting
CV data are listed in Table 1. A reversible onset oxidation poten-
tial (Eox) in a range from 1.23 to 1.25 V and an onset reduction
potential (Ered) in a range from −1.16 to −1.18 V were observed.
Based on the literature, the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital (LUMO)
energy levels (EHOMO and ELUMO) were calculated by the fol-
lowing equation: EHOMO = −(Eox + 4.34), ELUMO = −(Ered
+
4.34).30 As a result, the HOMO and LUMO energy levels are
located at −5.51 eV and −3.08 eV for FIr(pic)-C6DBC6-(pic)
PtF, respectively. Compared to FIr(pic) and FPt(pic), this hetero-
bimetallic platinum–iridium complex presented incremental
EHOMO and ELUMO levels.
Electroluminescence properties
The electroluminescence (EL) spectra of the FIr(pic)-C6DBC6-
(pic)PtF-doped PVK devices at the different dopant concen-
trations from 0.5 wt% to 2 wt% at 10 V are shown in Fig. 4, and
their CIE chromaticity diagrams are also inserted in Fig. 4. Four
distinct emission peaks at 410, 474, 500 and 598 nm are
observed in these EL spectra, in which the emission peaks at
474 and 500 nm are assigned to both chromophores of the
iridium and platinum complexes, and the emission peak at
598 nm is attributed to the excimers. Compared to the reported
mononuclear platinum complex or its analogous dinuclear plati-
num complexes,4 the FIr(pic)-C6DBC6-(pic)PtF complex exhib-
ited a decreased excimer emission at the dopant concentrations
from 0.5 wt% to 2 wt% in the PLEDs. Furthermore, with
increasing dopant concentrations, the excimer emission wea-
kened little by little. This decreased excimer emission is attribu-
ted to the combined effects of a non-planar structure of the
FIr(pic) unit and a distortedly unconjugated linkage of the
C6DBC6 unit. As a result, a near-white emission was observed
in the devices at low dopant concentrations from 0.5 wt% to
2.0 wt% under 10V, which corresponds to CIE coordinates from
(0.24, 0.30) to (0.22, 0.36). In addition, the EL spectra have a
minor change with increasing driving voltages from 9 V to 14 V
in the device at 0.5 wt% doping concentration (Fig. 5). The
Fig. 3 Atomic force microscope images for the complex-doped PVK
films (70 nm) at 1wt% doping concentration. (a) FIr(pic)-C6DBC6-(pic)
PtF, (b) FIr(pic) and (c) FPt(pic).
highest luminance of 245 cd m−2 and a current efficiency of 0.04
cd A−1 is achieved in the device at a 1 wt% doping level,
respectively. Although these preliminary results are inferior to
those of the reported white OLEDs, to the best of our knowl-
edge, this is the first example on a heterobimetallic platinum–
iridium complex as a single-emitting component in white
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2972–2978 | 2975

View Article Online
heterobimetallic platinum–iridium complex as a single active
emitter. This work provides another way to obtain the SEL-
based white PLEDs by employing the heterobimetallic plati-
num–iridium complex as a single phosphorescent emitter. In
order to further improve the efficiency, we are carrying out
studies on device optimization.
Experimental
Methods
All 1H NMR spectra were acquired using a Bruker Dex-400
NMR instrument. UV absorption spectra were recorded with a
HP-8453UV-visible system. PL spectra were recorded on a fluor-
escence spectrophotometer (HITACHI-850). Cyclic voltammetry
was carried out on a CHI660A electrochemical workstation
in a 0.1 mol L−1 tetrabutylammonium hexafluorophosphate
(Bu4NPF6) acetonitrile solution at a 100 mV s−1 scan rate under
nitrogen protection. A micro-platinum spar (ø = 0.8 mm), a plati-
num wire and KCl saturated Hg/HgO were used as the work
electrode, counter electrode and reference electrode, respectively.
The thermogravimetric analysis (TGA) was carried out with a
NETZSCH STA449 from 25 °C to 700 °C at a 20 °C min−1
heating rate under a nitrogen atmosphere.
Fig. 4 EL spectra and CIE 1931 chromaticity diagrams of the FIr(pic)-
C6DBC6-(pic)PtF-doped PLEDs at different dopant concentrations from
0.5 wt% to 2 wt%.
Device fabrication and characterization
Electroluminescence spectra were recorded with an InstaSpec IV
CCD system (Oriel). Luminance was measured with a Si photo-
diode and calibrated by a PR-705 SpectraScan spectropho-
tometer (Photo Research). The SEL devices were fabricated with
a structure of ITO/PEDOT : PSS (40–50 nm)/emitting layer
(70–75 nm)/CsF (1.5 nm)/Al (100 nm), in which indium tin
oxide (ITO) and poly(3,4-ethylenedioxy-thiophene)-poly
(styrenesulfonate) (PEDOT : PSS) (Bayer AG) were used as the
anode and hole-injection layer. Cesium fluoride (CsF) and Al
were employed as the electron-injection layer and cathode,
respectively. The emitting layer consists of the FIr(pic)-
C6DBC6-(pic)PtF dopant and PVK host matrix. The dopant
weight concentrations vary from 0.5 wt%, 1 wt% to 2 wt%.
Fig. 5 EL spectra and CIE 1931 chromaticity diagrams of the FIr(pic)-
C6DBC6-(pic)-PtF-doped PLEDs at 0.5 wt% dopant concentration
under different applied voltages.
PLEDs. Compared to the mononuclear cyclometalated platinum
complex of FPt(pic) and the homobimetallic platinum complex
of (dfppy)2Pt2(dipic),4 as expected, introducing a non-planar
iridium complex into the planar platinum complex by an uncon-
jugated linkage of the C6DBC6 unit plays a more important role
in controlling aggregation/excimer emissions for their resulting
heterobimetallic platinum–iridium complex. Therefore, this
FIr(pic)-C6DBC6-(pic)PtF complex exhibited a more decreased
excimer emission than (dfppy)2Pt2(dipic) and FPt(pic) in the
devices and should become another promising single phosphor-
escent emitter to exhibit white-emission in the SEL-based
PLEDs.
Synthesis of FIr(pic)-C6DBC6-(pic)PtF
General information. All solvents were carefully dried and
distilled prior to use. Commercially available reagents were used
without further purification unless otherwise stated. All reactions
were performed under a nitrogen atmosphere and were monitored
by thin-layer chromatography (TLC). Flash column chromato-
graphy and preparative TLC were carried out using silica gel
from Merck (200–300 mesh).
Methyl-3-(6-(4′-hydroxybiphenyl-4-oxy)hexyloxy)picolinate
(3). A mixture of compound 2 (1.7 g, 5 mmol), biphenyl-4,4′-
diol (1.5 g, 7.5 mmol), potassium carbonate (3.7 g, 27 mmol),
potassium iodide (0.1 g, 0.6 mmol) and 100 mL acetone were
stirred at 65 °C for 48 h. After the mixture was cooled to room
temperature (RT), 100 mL deionized water was added. The
formed precipitate was filtered off, and washed with water, fol-
lowed by ethanol. The precipitate was then purified on a silica
Conclusions
In summary, a heterobimetallic platinum–iridium complex of
FIr(pic)-C6DBC6-(pic)PtF was prepared. Introducing a non-
planar FIr(pic) unit into the planar FPt(pic) unit by an unconju-
gated linkage can effectively control the excimer emission for
the heterobimetallic platinum–iridium complex. Near-white
emission was obtained in the SEL-based PLEDs using this
2976 | Dalton Trans., 2012, 41, 2972–2978
This journal is © The Royal Society of Chemistry 2012

View Article Online
column using a mixture of hexane and ethyl acetate (1 : 2, v/v)
as eluent to provide compound 3 (1.3 g, 61.9%) as a white solid.
1H NMR (DMSO, 400 MHz) δ: 9.42 (s, 1H), 8.17 (d, J = 4.19
Hz, 1H), 7.66 (d, J = 8.5 Hz, 1H), 7.40–7.63 (m, 5H), 6.95 (d, J
= 8.41 Hz, 2H), 6.81 (d, J = 8.28 Hz, 2H), 4.10 (t, J = 6.10 Hz,
2H), 3.98 (t, J = 6.3 Hz, 2H), 3.83 (s, 3H), 1.75–1.82 (m, 4H),
1.26–1.37 (m, 4H).
1H), 5.53 (d, J = 6.6 Hz, 1H), 4.11 (t, J = 6.5 Hz, 2H), 3.43
(t, J = 6.7 Hz, 2H), 1.89–1.99 (m, 4H), 1.23–1.27 (m, 4H).
Platinum[II][(4,6-difluorophenyl)-pyridinato-N,C2]
[3-(6-(4′-hydroxybiphenyl-4-oxy)hexyloxy)picolinate] (9)
A mixture of platinum dimer 8 (0.21 g, 0.25 mmol), compound
4 (0.26 g, 0.62 mmol), sodium carbonate (0.33 g, 3.1 mmol)
and 15 mL 2-ethoxylethanol was stirred at 100 °C for 12 h.
After the mixture was cooled to RT, 30 mL deionized water was
added. The resulting precipitate was filtered off, and washed
with water, followed by hexane. The precipitate was then dried
and purified on a silica column using a mixture of hexane and
ethyl acetate (1 : 8, v/v) as eluent to present compound 9 (0.18 g,
3-(6-(4′-Hydroxybiphenyl-4-oxy)hexyloxy)picolinic acid (4). A
mixture of compound 3 (0.5 g, 1.19 mmol), 10 mL sodium car-
bonate aqueous solution (2 M) and 50 mL methanol were stirred
at 70 °C for 6 h. After the mixture was cooled to RT, 20 mL HCl
solution (2 M) was added (pH = 2). The resulting precipitate
was filtered off, washed with water, and by ethanol to present
compound 4 (0.38 g, 76.0%) as a white solid. 1H NMR (DMSO,
400 MHz) δ: 13.09 (s, 1H), 9.42 (s, 1H), 8.17 (d, J = 4.19 Hz,
1H), 7.66 (d, J = 8.5 Hz, 1H), 7.40–7.63 (m, 5H), 6.95 (d, J =
8.41 Hz, 2H), 6.82 (d, J = 8.28 Hz, 2H), 4.10 (t, J = 6.10 Hz,
2H), 3.98 (t, J = 6.3 Hz, 2H), 1.72–1.84 (m, 4H), 1.24–1.34 (m,
4H).
1
89.6%) as a yellow solid. H NMR (DMSO, 400 MHz) δ: 9.42
(s, 1H), 9.08 (d, J = 6.63 Hz, 2H), 8.18 (d, J = 4.19 Hz, 2H),
7.95–8.02 (m, 2H), 7.70–7.73 (m, 1H), 7.41–7.54 (m, 5H), 6.95
(d, J = 8.41 Hz, 2H), 6.82 (d, J = 8.28 Hz, 2H), 6.62–6.67 (m,
1H), 4.09 (t, J = 6.10 Hz, 2H), 3.98 (t, J = 6.3 Hz, 2H),
1.72–1.84 (m, 4H), 1.24–1.34 (m, 4H).
Iridium[III]bis[(4,6-difluorophenyl)-pyridinato-N,C2][(3-
hydroxy)picolinate] (6). A mixture of iridium trichloride hydrate
(0.3 g, 0.85 mmol), compound 5 (0.5 g, 2.62 mmol), 15 mL 2-
ethoxyethanol and 5 mL deionized water were stirred at 100 °C
for 12 h. After the mixture was cooled to RT, the resulting pre-
cipitate was filtered off, washed with water, followed by hexane
to provide chloro-bridged dimer as a yellow solid. Then the
mixture of the chloro-bridged dimer (0.35 g, 0.28 mmol), 3-
hydroxypicolinic acid (0.11 g, 0.84 mmol), sodium carbonate
(0.45 g, 4.2 mmol) and 30 mL 2-ethoxyethanol was stirred at
130 °C for 12 h. After the mixture was cooled to RT, 20 mL
deionized water and 5 mL HCl solution (2 M) were added (pH =
6), the resulting precipitate was filtered off, and washed with
water, followed by hexane. The precipitate was then purified on
a silica column using a mixture of hexane and ethyl acetate
(2 : 1, v/v) as the eluent to present the compound 6 (0.49 g,
Heterobimetallic iridium–platinum complex of FIr(pic)-
C6DBC6-(pic)PtF. A mixture of iridium complex 7 (0.09 g,
0.1 mmol), platinum complex 9 (0.08 g, 0.1 mmol), cesium car-
bonate (0.17 g, 0.5 mmol), potassium iodide (0.01 g,
0.06 mmol) and 10 mL of DMF was stirred at 80 °C for 30 h.
After the mixture was cooled to RT, 30 mL deionized water was
added, and the resulting mixture was extracted with DCM
(30 mL × 3). The organic layer was combined and then dried
over anhydrous MgSO4. After removal of the solvent, the
residue was purified on a silica column using a mixture of
hexane and ethyl acetate (1 : 10, v/v) as eluent to provide
FIr(pic)-C6DBC6-(pic)PtF (0.058 g, 36.2%) as a yellow solid.
1H NMR: (CDCl3, 400 MHz) δ: 8.83 (d, J = 5.5 Hz, 3H),
8.23–8.25 (m, 4H), 7.72–7.80 (m, 5H), 7.40–7.49 (m, 4H),
7.21–7.33 (m, 6H), 7.00–7.02 (m, 4H), 6.65 (t, J = 1.6 Hz, 2H),
6.40–6.53 (m, 2H), 5.81 (d, J = 8.64 Hz, 1H), 5.53 (d, J = 6.6
Hz, 1H), 4.16 (t, J = 6.5 Hz, 2H), 3.90 (t, J = 6.8 Hz, 2H), 3.58
(t, J = 6.5 Hz, 2H), 3.44 (t, J = 6.5 Hz, 2H), 1.84–1.99 (m, 6H),
1.23–1.27 (m, 12H). Anal. calcd for C69H56F6IrN5O8Pt: C,
52.31; H, 3.54; N, 4.42; Found: C, 52.51; H, 3.74; N, 4.56%.
1
86.1%) as a yellow solid. H NMR (CDCl3, 400 MHz) δ: 13.59
(s, 1H), 8.70 (d, J = 5.4 Hz, 1H), 8.23–8.68 (m, 2H), 7.80 (t, J =
7.76 Hz, 2H), 7.44–7.50 (m, 2H), 7.24–7.29 (m, 4H), 7.0 (d, J =
5.2 Hz, 1H), 6.40–6.54 (m, 2H), 5.81 (d, J = 8.64 Hz, 1H), 5.59
(d, J = 6.6 Hz, 1H).
Iridium[III]bis[(4,6-difluorophenyl)-pyridinato-N,C2]
[3-(6-bromohexyloxy)picolinate](7)
Acknowledgements
A mixture of compound 6 (0.5 g, 0.7 mmol), 1,6-dibromohexane
(1.6 g, 6.56 mmol), cesium carbonate (1.0 g, 3.0 mmol), potass-
ium iodide (0.1 g, 0.6 mmol) and 15 mL acetone was stirred at
65 °C for 6 h. After the mixture was cooled to RT, 20 mL dei-
onized water was added. The resulting mixture was extracted
with DCM (30 mL × 3). The organic layer was combined and
dried over anhydrous MgSO4. After removal of the solvent, the
residue was purified on a silica column using a mixture of
hexane and ethyl acetate (1 : 4, v/v) as eluent to obtain the com-
Financial support from the National Natural Science Foundation
of China (50973093, 20872124, 21172187 and 20772101), the
Specialized Research Fund and the New Teachers Fund for the
Doctoral Program of Higher Education of China (2009 430111
0004, 200805301013), the Scientific Research Fund of Hunan
Provincial Education Department (10A119, 11CY023, 10B112),
the Science Foundation of Hunan Province (2009FJ2002), the
Open Project Program of Key Laboratory of Environmentally
Friendly Chemistry and Applications of Ministry of Education
(09HJYH06), and the Postgraduate Science Foundation for Inno-
vation in Hunan Province (CX2011B263, CX2009B124) is
acknowledged.
1
pound of 7 (0.53 g, 85.5%) as a yellow solid. H NMR (CDCl3,
400 MHz) δ: 8.84 (d, J = 5.2 Hz, 1H), 8.23–8.29 (m, 2H), 7.76
(t, J = 7.64 Hz, 2H), 7.41–7.50 (m, 3H), 7.21–7.23 (m, 2H),
6.99–7.01 (m,1H), 6.40–6.53 (m, 2H), 5.81 (d, J = 8.64 Hz,
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2972–2978 | 2977

View Article Online
13 L. Hou, L. Duan, J. Qiao, D. Q. Zhang, G. F. Dong, L. D. Wang and
Y. Qiu, Org. Electron., 2010, 11, 1344.
References
14 X. H. Yang, Z. X. Wang and G. E. Jabbour, Appl. Phys. Lett., 2008, 93,
193305.
15 Q. Wang, J. Q. Ding, D. G. Ma, Y. X. Cheng, L. X. Wang and
F. S. Wang, Adv. Mater., 2009, 21, 2397.
16 H. B. Wu, J. H. Zou, F. Liu, L. Wang, A. Mikhailovsky, G. C. Bazan,
W. Yang and Y. Cao, Adv. Mater., 2008, 20, 696.
17 J. Liu, Y. Cheng, Z. Xie, Y. Geng, L. Wang, X. Jing and F. Wang, Adv.
Mater., 2008, 20, 1357.
18 (a) J. Jiang, Y. Xu, W. Yang, R. Guan, Z. Liu, H. Zhen and Y. Cao, Adv.
Mater., 2006, 18, 1769; (b) Y. H. Xu, R. Guan, J. X. Jiang, W. Yang,
H. Y. Zhen, J. B. Peng and Y. Cao, J. Polym. Sci., Part A: Polym. Chem.,
2008, 46, 453.
19 M. J. Park, J. H. Kwak, J. H. Lee, I. H. Jung, H. Kong, C. H. Lee, D.
H. Hwang and H. K. Shim, Macromolecules, 2010, 43, 1379.
20 X. H. Yang, Z. X. Wang, S. Madakuni, J. Li and G. E. Jabbour, Adv.
Mater., 2008, 20, 2405.
1 J. Kido, K. Hongawa, K. Okuyama and K. Nagai, Appl. Phys. Lett.,
1994, 64, 815.
2 (a) M. C. Gather, H. Köhnen and K. Meerholz, Adv. Mater., 2011, 23,
233; (b) H. H. Sasabe and J. Kido, Chem. Mater., 2011, 23, 621;
(c) S. H. Kim, S. Park, J. E. Kwon and S. Y. Park, Adv. Funct. Mater.,
2011, 21, 644.
3 (a) B. W. D’Andrade, R. J. Holmes and S. R. Forrest, Adv. Mater., 2004,
16, 624; (b) J. Kido, K. Hongawa, K. Okuyama and K. Nagai, Appl.
Phys. Lett., 1994, 64, 815; (c) J. Huang, G. Li, E. Wu, Q. Xu and
Y. Yang, Adv. Mater., 2006, 18, 114; (d) P.-I. Shih, C.-F. Shu, Y.-L. Tung
and Y. Chi, Appl. Phys. Lett., 2006, 88, 251110; (e) H. A. Attar, A.
P. Monkman, M. Tavasli, S. Bettington and M. R. Bryce, Appl. Phys.
Lett., 2005, 86, 121101.
4 (a) Y. F. Wang, Y. Liu, X. S. Li, H. R. Qi, M. X. Zhu, L. Wang, G. T. Lei,
Q. L. Wei, W. G. Zhu, J. B. Peng and Y. Cao, Org. Electron., 2010, 11,
1954; (b) Y. F. Wang, X. P. Deng, Y. Liu, M. J. Ni, M. Liu, T. Tan, X. Li,
W. Zhu and Y. Cao, Tetrahedron, 2011, 67, 2118.
21 B. W. D’Andrade, J. Brooks, V. Adamovich, M. E. Thompson and
S. R. Forrest, Adv. Mater., 2002, 14, 1032.
5 (a) J. Kido, M. Kimura and K. Nagai, Science, 1995, 267, 1332;
(b) S. L. Lai, S. L. Tao, M. Y. Chan, T. W. Ng, M. F. Lo, C. S. Lee,
X. H. Zhang and S. T. Lee, Org. Electron., 2010, 11, 1511; (c) C. L. Ho,
W. Y. Wang, Q. Wang, D. G. Ma, L. X. Wang and Z. Y. Lin, Adv. Funct.
Mater., 2008, 18, 928; (d) Y. Zhang, F. Huang and A. K. J. Jen, Appl.
Phys. Lett., 2008, 92, 5063303; (e) Y. R. Sun and S. R. Forrest, Appl.
Phys. Lett., 2007, 91, 263503.
22 E. L. Williams, K. Haavisto, J. Li and G. E. Jabbour, Adv. Mater., 2007,
19, 197.
23 J. Kalinowski, M. Cocchi, D. Virgili, V. Fattori and J. A. G. Williams,
Adv. Mater., 2007, 19, 4000.
24 J. Y. Cho, K. Y. Suponitsky, J. Li, T. V. Timofeeva, S. Barlow and
S. R. J. Marder, J. Organomet. Chem., 2005, 690, 4090.
25 S. Lamansky, M. E. Thompson, V. Adamovich, P. I. Djurovich,
C. Adachi, M. A. Baldo, S. R. Forrest, R. U. S. Kwong, Patent
20050214576 (2005)
6 C. C. Chang, J. F. Chen, S. W. Hwang and C. H. Chen, Appl. Phys. Lett.,
2005, 87, 253501.
7 Z. L. Shen, P. E. Burrows, V. Bulovic, S. R. Forrest and M. E. Thompson,
Science, 1997, 276, 2009.
8 C. J. Liang and W. C. H. Choy, J. Organomet. Chem., 2009, 694, 2712.
9 H. Kanno, R. J. Holmes, Y. Sun, S. K. Cohen and S. R. Forrest, Adv.
Mater., 2006, 18, 339.
26 T. H. Kwon, M. K. Kim, J. Kwon, D. Y. Shin, S. J. Park, C. L. Lee, J.
J. Kim and J. I. Hong, Chem. Mater., 2007, 19, 3673.
27 (a) V. N. Kozhevnikov, M. C. Durrant and J. A. G. Williams, Inorg.
Chem., 2011, 50, 6304; (b) V. L. Whittle and J. A. Gareth Williams,
Inorg. Chem., 2008, 47, 6596.
10 A. Dodabalapur, L. J. Rothberg, T. M. Miller and E. W. Kwock, Appl.
Phys. Lett., 1994, 64, 2486.
28 A. F. Rausch, H. H. Homeier, P. H. Djurovich and M. E. Thompson,
Proc. SPIE–Int. Soc. Opt. Eng., 2007, 6655, 66550F.
11 A. Dodabalapur, L. J. Rothberg, R. H. Jordan, T. M. Miller, R. E. Slesher
and J. M. Phillips, J. Appl. Phys., 1996, 80, 6954.
12 Y. Niu, M. S. Liu, J. W. Ka, J. Bardeker, M. T. Zin, R. Schofield, Y. Chi
and A. K. Y. Jen, Adv. Mater., 2007, 19, 300.
29 C. Adachi, R. C. Kwong, P. Djurovich, V. Adamovich, M. A. Baldo,
M. E. Thompson and S. R. Forrest, Appl. Phys. Lett., 2001, 79, 2082.
30 Z. J. Si, J. Li, B. Li, Z. R. Hong, S. Y. Liu and W. L. Li, J. Phys. Chem.
C, 2008, 112, 3920.
2978 | Dalton Trans., 2012, 41, 2972–2978
This journal is © The Royal Society of Chemistry 2012