Fac-Tris(2-phenylpyridine)iridium (III)s, covalently surrounded by six bulky host dendrons, for a highly efficient solution-processed organic light emitting device

Article abstract of DOI:10.1016/j.orgel.2011.08.015

The fully surrounded complexes by six host dendrons showed high photoluminescence quantum efficiency in a neat film, comparable to in a dilute solution. The surrounding host dendrons efficiently suppressed intermolecular interaction between central Ir complexes and prevented concentration quenching. The complex, (mCP)₆Ir, fully surrounded by six carbazole type hosts showed much better performance, compared with the complex, (DAP)₆Ir, surrounded by arylamine type hosts, because of well balanced charge injection and transporting in the devices.

Full text of DOI:10.1016/j.orgel.2011.08.015

Organic Electronics 12 (2011) 2103–2110
Contents lists available at SciVerse ScienceDirect
Organic Electronics
journal homepage: www.elsevier.com/locate/orgel
fac-Tris(2-phenylpyridine)iridium (III)s, covalently surrounded by six
bulky host dendrons, for a highly efficient solution-processed organic
light emitting device
⇑
⇑
Yong-Jin Pu , Noriaki Iguchi, Naoya Aizawa, Hisahiro Sasabe, Ken-ichi Nakayama, Junji Kido
Department of Organic Device Engineering, Yamagata University, Yonezawa, Yamagata 992-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 May 2011
Received in revised form 29 July 2011
Accepted 24 August 2011
Available online 12 September 2011
The fully surrounded complexes by six host dendrons showed high photoluminescence
quantum efficiency in a neat film, comparable to in a dilute solution. The surrounding host
dendrons efficiently suppressed intermolecular interaction between central Ir complexes
and prevented concentration quenching. The complex, (mCP)6Ir, fully surrounded by six
carbazole type hosts showed much better performance, compared with the complex,
(DAP)6Ir, surrounded by arylamine type hosts, because of well balanced charge injection
and transporting in the devices.
Keywords:
Organic light emitting device
Phosphorescence
Iridium complex
Dendrimer
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
done a lot of pioneering work on the dendrimer OLEDs
[7–9]. The dendron is bulky in volume, so that it can pre-
Organic light-emitting devices (OLEDs) have attracted a
great deal of attention because of their potentials for next
generation of flat panel displays and general lighting [1–
4]. Solution processes such as ink-jet printing are consid-
ered to have an advantage of low cost over the vacuum pro-
cess for manufacturing of large area displays or lighting. On
the other hand, the device using phosphorescent heavy me-
tal complexes such as fac-tris(2-phenylpyridine)iridium
(III) as an emitter shows much higher efficiency than the
device using a fluorescent emitter, because the phosphores-
cent complex can utilize all of singlet and triplet excitons
for the emission [5,6]. That is why the combination of the
solution-process and the phosphorescent compounds can
be an ideal choice to achieve low cost and high efficiency
in OLEDs in the future. For the solution-process, substitu-
tion of functional dendrons on the complex is one of ap-
proaches to solubilize it, and P.L. Burn group has been
vent intermolecular interaction between the emitting com-
plexes, resulting in reduction of concentration quenching
and high photoluminescence quantum efficiency (PLQE)
[9–11]. From the OLED application point of view, those den-
drons have to have enough high charge-transporting ability
for low driving voltage [12–20] and have a larger triplet en-
ergy level (T1) than that of the core complex not to quench
the triplet exciton of the complex [21,22]. In phosphores-
cent OLEDs, m-carbazolylbenzene (mCP) is one of well-
known and widely-used host materials, because its triplet
energy level is enough high (3.0 eV) to confine the phos-
phorescent emission of the iridium complex, and has bipo-
lar charge-transporting ability [23,24]. We previously
reported the phosphorescent iridium complex, (mCP)3Ir,
attached three mCP dendrons having alkyl groups, and high
efficiencies of the OLEDs using that complex [25,26]. In
(mCP)3Ir, mCP dendrons are attached on each phenyl ring
of Ir(ppy)3, and (mCP)3Ir is a facial isomer, so that the three
mCP dendrons are attached spacially same side in the com-
plex, and surround only half side of Ir(ppy)3. In this study,
we designed two type of fully surrounded Ir(ppy)3 by six
⇑
Corresponding author.
E-mail addresses: pu@yz.yamagata-u.ac.jp (Y.-J. Pu), kid@yz.yamaga-
ta-u.ac.jp (J. Kido).
1566-1199/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.orgel.2011.08.015

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Y.-J. Pu et al. / Organic Electronics 12 (2011) 2103–2110
Scheme 1. Chemical structure of the iridium complexes.
bulky dendrons, (mCP)6Ir and (DAP)6Ir (Scheme 1). Both of
the complexes showed higher PLQE in a neat film than that
of half-surrounded (mCP)3Ir and (DAP)3Ir, well-supporting
the results reported in the literature [9]. Solution-processed
OLED with (mCP)6Ir showed high efficiencies, 19 lm/W,
32 cd/A, and 12% of external quantum efficiency at
100 cd/m2, and 11 lm/W, 25 cd/A, 9.1% at 1000 cd/m2. The
energy levels of the surrounding dendrons intensely af-
fected the charge injection into the emitting layer and the
device performance.
2. Results and discussion
Scheme 2 shows synthesis route of (mCP)6Ir, (DAP)6Ir,
and (DAP)3Ir. The ligands of the complexes, 2, 5, and 6,
were synthesized via several steps of palladium catalyzed
coupling reactions. The complexes were prepared from
the two steps of complexation. First, a mixture of iridium
chloride trihydrate and excess of the ligands afforded di-
chloro bridged dimer complexes, 7, 8, and 9. Second, the
dimers were reacted by the ligands with silver trifluorom-
Scheme 2. Synthetic procedure of (DAP)3Ir, (DAP)6Ir and (mCP)6Ir: (i) 3,5-dichlorophenylboronic acid, Pd(PPh3)4, K2CO3 aq., THF, N2, reflux, (ii) di(4-(n-
butyl)phenyl)amine, Pd2(dba)3, PCy3, NaOt-Bu, toluene, N2, reflux, (iii) 2,4-dibromopyridine, Pd2(dba)3, dppf, K2CO3 aq., toluene, N2, reflux, (iv) di(4-(n-
butyl)phenyl)amine, Pd2(dba)3, P(Cy)3, NaOt-Bu, toluene, N2, reflux, (v) 3,6-di(n-butyl)carbazole, Pd(OAc)2, P(t-Bu)3, NaOt-Bu, o-xylene, N2, 120 °C, (vi)
IrCl3Á3H2O, H2O, 2-ethoxyethanol, N2, 130 °C, (vii) 2, CF3SO3Ag, diglyme, N2, 130 °C, (viii) 5, CF3SO3Ag, diglyme, N2, 130 °C, (ix) 6, CF3SO3Ag, ethyldiglyme,
N2, 150 °C.

Y.-J. Pu et al. / Organic Electronics 12 (2011) 2103–2110
2105
Fig. 1. Photoluminecence spectra of (mCP)3Ir (solid line), (mCP)6Ir
(circle), (DAP)3Ir (triangle), and (DAP)6Ir (square) in a neat film.
Fig. 2. Photoluminescent quantum efficiencies (PLQEs) of the compounds
in a neat film or a toluene solution (2 Â 10À6 mol LÀ1).
ethane sulfonate to give homoleptic functionalized com-
plexes. The complexes were fully characterized by 1H-
NMR, matrix-assisted laser desorption/ionization time-of-
flight (MALDI) mass spectrometry (MS), and elemental
analysis.
(DAP)3Ir, showed much lower PLQE in a neat film than that
in a dilute solution. These complexes are facial isomers,
therefore, in (mCP)3Ir and (DAP)3Ir, a some space around
pyridyl groups of Ir(ppy)3 core are opened and their three
dimensional structure is like a hemisphere, shown in
Fig. 3, resulting in only partial suppression of concentra-
tion-quenching in a neat film of an iridium complex. How-
ever, in (mCP)6Ir and (DAP)6Ir, the bulky host dendrons
fully surrounded Ir(ppy)3 and effectively prevented the
intermolecular interaction between Ir(ppy)3s. There are
still small amount of reduction of PLQEs from a solution
to a neat film, due to the concentration-quenching even
in the fully-substituted complexes. The substituted host
dendrons are not enough large to completely suppress
the interaction between the core complexes. Adachi et al.
reported that an average distance between iridium com-
plexes in a doped film critically influenced on PLQE [29].
Förster type energy transfer between Ir(ppy)3 cores
through an overlap of the emission and the absorption
causes a decrease of neat film PLQY. If the average distance
between iridium complexes is shorter than Förster radius,
a strong quenching occurs. The stronger quenching of
(mCP)3Ir in the neat film than that of (mCP)6Ir is due to
the shorter average distance between the cores derived
from a less number of bulky host dendrons of (mCP)3Ir
than that of (mCP)6Ir. Substitution of more branched and
larger dendrons to the core complexes are desirable to
achieve the complete suppression of concentration-
quenching.
Photoluminescence of the neat film of the complexes
fully-surrounded by the six bulky dendrons showed the
peaks around 580 nm for (mCP)6Ir and 577 nm for (DA-
P)6Ir, and the spectra were red-shifted compared with
the emission of the less-surrounded complexes around
514 nm for (mCP)3Ir and 528 nm for (DAP)3Ir (Fig. 1).
These results indicated that substitution on 3-position of
phenyl ring did not change emission color of Ir(ppy)3, but
substitution on 4-position of pyridine ring made the emis-
sion red-shifted. The emission of Ir(ppy)3 is mainly as-
cribed to triplet metal-to-ligand charge transfer (3MLCT)
transition. Its highest occupied molecular orbital (HOMO)
corresponds to d orbital of Ir and lowest unoccupied
molecular orbital (LUMO) correspond to p⁄ orbital of ppy
ligand, especially pyridine part of the ligand. That is why
electron-donating group on pyridine ring decrease the en-
ergy gap of
same electron-donating group on 3-position of phenyl ring
p–
p⁄ and LUMO level, on the other hand the
does not affect the pyridine ring because of less p-conjuga-
tion via meta-linkage [27,28].
PLQEs of the complexes in the neat film are important
parameter to estimate the shielding effect of the surround-
ing dendrons to Ir(ppy)3. PLQEs of the toluene solution and
the films were measured by using an integrating sphere
system under 331 nm excitation (Fig. 2). In a diluted solu-
tion, all complexes showed higher PLQE than 70%, which
are comparable to 85% of unsubstituted Ir(ppy)3. This re-
sult demonstrated that these surrounding dendrons are
optically inert and does not affect the emission efficiency
of Ir(ppy)3 core. The fully-surrounded complexes, (mCP)6Ir
and (DAP)6Ir, showed high PLQE even in a neat film, which
is comparable to PLQE in a dilute solution. On the other
hand, the half-surrounded complexes, (mCP)3Ir and
HOMO level of the complexes and the surrounding host
dendrons
themselves,
3,5-(3,6-di(n-butyl)carbazol-9-
yl)benzene DAP and 3,5-(N,N-di(4-(n-butyl)phenyl)amine)
benzene mCP, were estimated from ionization potentials
measured by photoelectron yield spectroscopy (Fig. 4).
LUMO levels of DAP and mCP were estimated from the dif-
ference of optically obtained energy gap and ionization po-
tential. LUMO level of the dendrimer complexes are still
unknown because the optically obtained energy gap dose

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Y.-J. Pu et al. / Organic Electronics 12 (2011) 2103–2110
Fig. 4. HOMO and LUMO levels of the surrounding host groups, DAP (fine
solid line) and mCP (fine solid line), and Ir(ppy)3 (dotted line), and HOMO
levels of the complexes (thick solid line). Chemical structure of DAP and
mCP.
Fig. 3. The optimized structures of: (a) (mCP)3Ir and (b) (mCP)6Ir by PM6
calculation. The butyl groups were replaced to hydrogen in calculation.
not correspond to HOMO–LUMO gap in the case of Ir(ppy)3
derivatives. HOMO levels of the dendrimer complexes were
close to that of Ir(ppy)3, rather than that of the surrounding
host dendrons. This result suggest that HOMO are mainly
located on the central Ir(ppy)3 group.
property than DAP dendron to improve charge balance.
The double layer devices were fabricated using B4PyMPm
as an electron transporting and hole-blocking material on
the emitting layer. DAP-surrounding complex, (DAP)3Ir
and (DAP)6Ir, showed higher current density, as well as
single layer device. This results suggest that hole current
is still excess even in the device with electron transport-
ing layer. High luminance was obtained at much lower
voltage, and the efficiency were drastically improved. In
the device with (mCP)6Ir, thickness of the emitting layer
was reduced from 60 to 40 nm to improve charge balance,
resulting in increasing efficiencies (Table 1). Current effi-
ciency of the device with (mCP)6Ir was 32 cd/A, 19 lm/
W, 12% at 100 cd/m2, and 25 cd/A, 11 lm/W, 9.1% at
1000 cd/m2. There have been several reports on solu-
tion-processed phosphorescence OLED with dendrimer
iridium complexes, and their high efficiencies, as men-
tioned in Section 1. However the most of papers empha-
sized peak efficiencies at a low current density and
luminance, and did not revealed the efficiencies at practi-
cally high luminance, e.g. for lighting application. The
efficiencies with our fully-surrounded Ir(ppy)3 are one of
high values among the solution-processed OLED ever
reported.
Single layer devices with the configuration of ITO/
poly(3,4-ethylenedioxythiophene) (PEDOT): poly(styrene
sulfonic acid) (PSS) (40 nm)/(DAP)3Ir, (DAP)6Ir, or
(mCP)6Ir (120 nm)/LiF (1 nm)/Al (100 nm) and double
layer devices with the configuration of ITO/PEDOT:PSS
(40 nm)/(DAP)3Ir, (DAP)6Ir, or (mCP)6Ir (60 nm)/bis-4,6-
(3,5-di-4-pyridylphenyl)-2-methylpyrimidine (B4PyMPm)
(60 nm)/LiF (1 nm)/Al (100 nm) were fabricated. In single
layer devices, (DAP)3Ir and (DAP)6Ir exhibited higher cur-
rent density than (mCP)6Ir, probably because HOMO level
of (DAP)3Ir and (DAP)6Ir are shallower than (mCP)6Ir to
enhance hole injection from PEDOT:PSS (Fig. 5). There-
fore, hole current should be dominant in single layer de-
vices. However, in contrast to the result of the current
density–voltage plots, (mCP)6Ir showed higher luminance
than the others. As well as the luminance, current effi-
ciencies of the single layer device with (mCP)6Ir were
much higher than those of the other two complexes. This
improvement showed that the surrounding mCP dendron
has better electron injection and/or electron transport

Y.-J. Pu et al. / Organic Electronics 12 (2011) 2103–2110
2107
a
ITO / PEDOT: PSS (40) / (DAP) Ir (120) / LiF (1) /Al (100)
ITO / PEDOT: PSS (40) / (DAP)3Ir (120) / LiF (1) /Al (100)
ITO / PEDOT: PSS (40) / (mCP)66Ir (120) / LiF (1) /Al (100)
b
ITO / PEDOT: PSS (40) / (DAP) Ir (60) / B4PyMPm (60) / LiF (1) /Al (100)
ITO / PEDOT: PSS (40) / (DAP)3Ir (60) / B4PyMPm (60) / LiF (1) /Al (100)
ITO / PEDOT: PSS (40) / (mCP)6Ir (60) / B4PyMPm (60) / LiF (1) /Al (100)
ITO / PEDOT: PSS (40) / (mCP)66Ir (40) / B4PyMPm (60) / LiF (1) /Al (100)
Fig. 5. Current density–voltage, luminance–voltage, and current efficiency–voltage characteristics of the single layer device (a) and the double layer
device (b).
Table 1
Efficiencies of the solution-processed OLEDs.
Device structure
Single layer
Compound
100 cd/m2
1000 cd/m2
Voltage (V)
gP (lm WÀ1
gC (cd AÀ1
)
gEXT (%)
Voltage (V)
gP (lm WÀ1
)
gC (cd AÀ1
)
gEXT (%)
(DAP)3Ir
(DAP)6Ir
(mCP)6Ir
(DAP)3Ir
(DAP)6Ir
(mCP)6Ir
(mCP)6Ira
–
–
–
–
–
–
–
–
–
–
–
–
13.9
10.3
4.0
10.5
6.5
5.2
0.016
0.23
2.6
0.057
12
0.071
0.75
3.2
0.19
25
0.028
0.29
1.0
0.075
9.4
13.6
6.3
14.3
8.4
7.3
0.23
1.9
0.065
7.8
11
1.0
3.8
0.30
21
25
0.39
1.1
0.11
7.8
9.1
Double layer
19
32
12
a
Thickness of emitting layer is 40 nm.
interaction between central Ir complexes and prevented
concentration quenching. Not only PLQE of the complex
but also energy levels and charge transporting property
of the surrounding host dendron are important to achieve
high efficiencies in a device. The complex, (mCP)6Ir, fully
surrounded by six carbazole type hosts showed much
better performance, compared with the complexes sur-
rounded by arylamine type hosts, because of well balanced
charge injection and transporting in the devices.
3. Conclusion
We synthesized the solution processable iridium com-
plexes for OLEDs, surrounded by diphenylamine deriva-
tives or carbazole derivatives. The fully surrounded
complexes, (DAP)6Ir and (mCP)6Ir, by six host dendrons
showed high PLQE in a neat film, comparable to their PLQE
in a dilute solution, demonstrating that the surrounding
host dendrons efficiently suppressed intermolecular

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Y.-J. Pu et al. / Organic Electronics 12 (2011) 2103–2110
(30:1) as eluent to give the compound 1 (1.26 g, 82%).
4. Experimental
4.1. Measurements
dH(400 MHz, CD2Cl2) 8.67 (1H, d, J = 4.1 Hz), 8.23 (1H, s),
8.02 (1H, d, J = 7.3 Hz), 7.82–7.76 (2H, m), 7.61–7.53 (4H,
m), 7.37 (1H, t, J = 1.8 Hz), 7.27 (1H, td, J = 5.7, 1.8 Hz). m/
z [EI] 299: (M+). Found: C, 67.74; H, 3.60; N, 4.45.
1H-NMR spectra were measured in deuterated solvents
on a JEOL ECX 400 MHz spectrometer. Mass spectra were
recorded on a JEOL JMS-K9 for electron impact-ionization
(EI) or an Applied Biosystems Voyager DE-PRO for ma-
trix-assisted laser desorption/ionization-time-of-flight
(MALDI-TOF) from dithranol (DITH) in linear or reflection
mode. Elemental analyses were carried out by the Elemen-
tal Analysis Service, Yamagata University, Japan. Thermal
gravimetric analysis (TGA) was performed on Seiko SII EX-
STAR 6000 and TGA/DTA 6200 analyzers. Differential Scan-
ning Calorimetry (DSC) was performed on a Perkin–Elmer
Diamond DSC calorimeter. Ionization potentials were mea-
sured with a photoelectron spectrometer surface analyzer
(RIKEN KEIKI AC-3). UV–visible absorption spectra were
recorded of solutions in chloroform or films on quartz with
C17H11Cl2N requires C, 68.02; H, 3.69; N, 4.67%.
2-(3-(3,5-Bis(di-(4-n-butylphenyl)amino))phenyl)phen
yl)pyridine 2: the compound 1 (0.500 g, 1.67 mmol), di(4-
(n-butyl)phenyl)amine (1.41 g, 5.00 mmol), sodium tert-
butoxide (0.721 g, 7.50 mmol), Pd2(dba)3 (0.114 g, 0.125
mmol), and P(Cy)3 (0.0701 g, 0.250 mmol) in a sealed tube
was degassed in vacuo and filled with N2. After that, de-
gassed toluene (5.0 ml) was added into the mixture, and
then the mixture was refluxed for 24 h. After the mixture
was allowed to cool to room temperature, diethylether
was added. The organic layer was washed by deionized
water, dried over magnesium sulfate, and filtered. The sol-
vent was removed in vacuo, and the residue was purified
by column chromatography over silica using chloroform
and a hexane–chloroform mixture (from 1:0 to 0:1) as elu-
ent to give the compound 2 (0.929 g, 71%). dH(400 MHz,
CD2Cl2) 8.62 (1H, d, J = 5.0 Hz), 7.97 (1H, s), 7.88 (1H, d,
J = 6.4 Hz), 7.74–7.67 (2H, m), 7.41–7.38 (2H, m), 7.22 (1H,
td, J = 5.7, 1.4 Hz), 7.04–6.97 (16H, m), 6.81 (2H, d,
J = 2.3 Hz), 6.67 (1H, t, J = 1.8 Hz), 2.52 (8H, t, J = 7.8 Hz, -
CH2CH2CH2CH3), 1.58–1.50 (8H, m, -CH2CH2CH2CH3),
1.38–1.29 (8H, m, -CH2CH2CH2CH3), 0.90 (12H, t,
J = 7.4 Hz, -CH2CH2CH2CH3). m/z [EI] 791: (M+). Found: C,
86.49; H, 7.75; N, 5.24. C57H63N3 requires C, 86.65; H, 8.04;
N, 5.32%.
4-Bromo-(2-(3-bromophenyl))pyridine 3: the mixture
of 3-bromophenylboronic acid (2.81 g, 14.0 mmol), 2,4-
dibromopyridine (3.31 g, 14.0 mmol), K2CO3 (3.87 g,
28.0 mmol), deionized water (14 ml), and toluene (60 ml)
was deoxygenated by bubbling N2 for 30 min. After that,
Pd2(dba)3 (0.385 g, 0.420 mmol) was added, and then the
mixture was refluxed for 36 h. After the mixture was al-
lowed to cool to room temperature, diethylether was
added. The organic layer was washed by deionized water,
dried over magnesium sulfate, and filtered. The solvent
was removed in vacuo, and the residue was purified by col-
umn chromatography over silica using a hexane–dichloro-
methane mixture (from 1:0 to 0:1) as eluent to give the
compound 3 (1.76 g, 40%). dH(400 MHz, CDCl3) 8.50 (1H,
d, J = 5.0 Hz), 8.14 (1H, t, J = 1.8 Hz), 7.89–7.87 (2H, m,
ArH), 7.56 (1H, d, J = 7.8 Hz), 7.43 (1H, dd, J = 5.3, 1.4 Hz),
7.34 (1H, t, J = 8.0 Hz). m/z [EI] 313: (M+), Found: C,
42.41; H, 2.02; N, 4.45. C11H7Br2N requires C, 42.21; H,
2.25; N, 4.48%.
a
Shimadzu UV-3150 spectrometer. PL spectra were
recorded on a Jobin Yvon Fluoromax-4 fluorometer. PL
quantum efficiencies were measured on a Hamamatsu
C9920-01 calibrated integrating sphere system under
nitrogen. Light emitting devices were fabricated on indium
tin oxide (ITO) coated glass substrates, which were pre-
pared by ultrasonication sequentially in detergent, metha-
nol, 2-propanol and acetone, then exposed to UV–ozone
under ambient conditions for 15 min. PEDOT:PSS was
spin-coated as an anode buffer layer on pre-cleaned ITO
substrate. On the top of PEDOT:PSS layer, dendrimers were
spin-coated from 1,2-dichloroethane or toluene solution.
The electron transporting material B4PyMPm was depos-
ited by thermal evaporation at less than 1 Â 10À4 Pa. The
aluminum cathode was deposited through a shadow mask
at less than 1 Â 10À4 Pa. The active area of each device is
2 mm  2 mm. Layer thickness calibration was performed
using a Dektak 3 surface profilometer. The EL spectra were
measured on a Hamamatsu PMA-11 photonic multichan-
nel analyzer. The current–voltage (I–V) characteristics
and luminance of the devices were measured using a
Keithley 2400 Source Meter and Konica Minolta CS-200
chromameter, respectively. External quantum efficiencies
were calculated assuming a Lambertian emission pattern
and considering all spectral features in the visible region.
5. Materials
2-(3-(3,5-Dichlorophenyl)phenyl)pyridine 1: a mixture
of 2-(3-bromophenyl)pyridine (1.20 g, 5.13 mmol), 3,5-
dichlorophenylboronic acid (1.97 g, 10.3 mmol), K2CO3
(1.42 g, 10.3 mmol), and THF (100 ml) was deoxygenated
by bubbling N2 for 30 min. After that, Pd(PPh3)4 (0.240 g,
0.208 mmol) and degassed deionized water (5.2 ml) were
added in the mixture, and then the mixture was refluxed
under N2 for 24 h. The mixture was allowed to cool to room
temperature, and then diethylether was added. The organ-
ic layer was washed by deionized water, dried over magne-
sium sulfate, and filtered. The solvent was removed in
vacuo and the residue was purified by column chromatog-
raphy over silica using a chloroform–ethyl acetate mixture
2-(3-(3,5-Dichlorophenyl)phenyl)-4-(4-(3,5-dichloroph
enyl)phenyl)pyridine 4: the compound
3
(1.75 g,
5.59 mmol), 3,5-dichlorophenylboronic acid (4.26 g,
22.3 mmol), K2CO3 (1.55 g, 11.2 mmol), deionized water
(5.6 ml), and toluene (95 ml) was deoxygenated by bubbling
N2 for 30 min. After that, Pd(PPh3)4 (0.224 g, 0.194 mmol)
was added, and then the mixture was refluxed for 24 h. After
the mixture was allowed to cool to room temperature,
diethylether was added. The organic layer was washed by
deionized water, dried over magnesium sulfate, and filtered.
The solvent was removed in vacuo, and the residue was
purified by column chromatography over silica using a hex-

Y.-J. Pu et al. / Organic Electronics 12 (2011) 2103–2110
2109
ane–chloroform mixture (from 1:0 to 0:1) as eluent to give
the compound 4 (2.01 g) as a crude. The crude product
was directly used for next step without further purification.
dH(400 MHz, CDCl3) 8.73 (1H, s), 8.18 (1H, s), 7.99 (1H, dt,
J = 7.1, 1.8 Hz), 7.84 (1H, s), 7.58–7.50 (6H, m), 7.40 (1H, t,
J = 1.8 Hz), 7.37 (1H, dd, J = 5.0, 1.8 Hz), 7.30 (1H, t,
J = 1.8 Hz).
idue was washed with K2CO3 aq. (0.33 M, 6.0 ml) and
deionized water to give crude compound 7. The crude
product was directly used for next step without further
purification.
5.1. (DPA)3Ir
2-(3-(3,5-Bis(di(4-n-butylphenyl)amino))phenyl)phen-
yl)-4-(3-(3,5-bis(di(4-n-butylphenyl)amino))phenyl)pyri-
dine 5: the mixture of di(4-n-butylphenyl)amine (18.0 g,
The mixture of 7 (0.933 g), 5 (1.25 g, 1.58 mmol), silver
trifluoromethanesulfonate (0.162 g, 0.632 mmol), and dig-
lyme (31 ml) was heated at 130 °C under N2 for 114 h.
After the mixture was allowed to cool to room tempera-
ture, insoluble part was removed by column chromatogra-
phy over silica using dichloromethane as eluent. The
solvent was removed in vacuo, and then the residue was
purified by chromatography over silica using a dichloro-
methane–hexane mixture (2:3) as eluent. Further purifica-
tion by preparative TLC using a dichloromethane–hexane
mixture (15:8) as eluent gave the complex (DPA)3Ir
(0.415 g, 31%). dH(400 MHz, CD2Cl2) 7.81–7.78 (3H), 7.60–
7.55 (6H), 7.48–7.45 (3H), 7.03–6.94 (48H, m), 6.88–6.84
(3H), 6.78–6.72 (8H), 6.66–6.59 (6H), 2.54 (24H, t,
J = 7.5 Hz, -CH2CH2CH2CH3), 1.52–1.72 (24H, m, -CH2CH2
CH2CH3), 1.32–1.52 (24H, m, -CH2CH2CH2CH3), 0.94 (36H,
t, J = 7.3 Hz, -CH2CH2CH2CH3). dC(100 MHz, CD2Cl2) 14.1,
22.7, 34.0, 35.3, 115.2, 116.1, 119.2, 122.4, 122.6, 124.4,
128.6, 129.2, 132.9, 136.5, 137.2, 137.5, 143.9, 144.4,
145.6, 147.4, 149.4, 160.8, 166.2. [MALDI:DITH] (m/z)
2559.68: (MH+). Found: C, 80.40; H, 7.17; N, 4.88.
64.0 mmol), crude
4
(3.56 g), sodium tert-butoxide
(8.85 g, 96.0 mmol), and toluene (80 ml) was deoxygen-
ated by bubbling N2 for 30 min. After that, Pd2(dba)3
(1.47 g, 1.60 mmol), PCy3 (1.79 g, 6.40 mmol) was added,
and then the mixture was refluxed for 24 h. After the mix-
ture was allowed to cool to room temperature, diethyl-
ether was added. The organic layer was washed by
deionized water, dried over magnesium sulfate, and fil-
tered. The solvent was removed in vacuo, and the residue
was purified by column chromatography over silica using
a hexane–chloroform mixture (from 1:0 to 0:1) and a hex-
ane–chloroform mixture (from 1:0 to 1:3) as eluent,
respectively, to give the compound
5 (7.30 g, 57%).
dH(400 MHz, CD2Cl2) 8.52 (1H, d, J = 5.0 Hz), 7.99 (1H, s),
7.74 (1H, s), 7.65 (1H, s), 7.36 (2H, d, J = 4.6 Hz), 7.16 (1H,
s), 7.04–6.96 (32H, m), 6.78 (4H, t, J = 2.1 Hz), 6.72 (1H, t,
J = 1.8 Hz), 6.66 (1H, t, J = 1.8 Hz) 2.51 (16H, t, J = 7.6 Hz, -
CH2CH2CH2CH3), 1.57–1.50 (16H, m, -CH2CH2CH2CH3),
1.37–1.28 (16H, m, -CH2CH2CH2CH3), 0.90 (24H, t,
J = 7.3 Hz, -CH2CH2CH2CH3). [MALDI:DITH] (m/z) 1424.9:
(MH+). Found: C, 86.55; H, 8.48; N, 4.84. C103H117N5 re-
quires C, 86.81; H, 8.28; N, 4.91%.
C171H186IrN9 requires C, 80.24; H, 7.32; N, 4.93%.
8: the mixture of 5 (2.50 g, 1.75 mmol), iridium chloride
trihydrate (0.258 g, 0.731 mmol), deionized water (12 ml),
and 2-ethoxyethanol (49 ml) was heated at 130 °C for 24 h
under N2. After the solvent was removed in vacuo, the res-
idue was washed with K2CO3 aq. (0.33 M, 38 ml) and
deionized water to give crude compound 8 (2.41 g). The
crude product was directly used for next step without fur-
ther purification.
2-(3-(3,5-Bis(3,6-di(n-butyl)carbazol-9-yl)phenyl)phe-
nyl-4-(3,5-bis(3,6-di(n-butyl)carbazol-9-yl)phenyl))pyridi
ne 6: the mixture of 3,6-di-n-butylcarbazole (7.21 g,
25.8 mmol), crude
4
(1.91 g), palladium(II) acetate
(0.231 g, 1.03 mmol), K2CO3 (10.7 g, 77.4 mmol), and o-xy-
lene (40 ml) was deoxygenated by bubbling N2 for 30 min.
After that, P(t-Bu)3 (0.75 ml, 3.10 mmol) was added, and
then the mixture was refluxed for 24 h. After the mixture
was allowed to cool to room temperature, diethylether
was added. The organic layer was washed by deionized
water, dried over magnesium sulfate, and filtered. The sol-
vent was removed in vacuo, and the residue was purified
by column chromatography over silica using a hexane–
chloroform mixture (from 1:0 to 1:1) as eluent to give
the compound 6 (3.84 g, 51%). dH(400 MHz, CD2Cl2) 8.75
(1H, d, J = 5.0 Hz), 8.45 (1H, s), 8.06 (1H, s), 8.04 (1H, d,
J = 1.8 Hz), 7.98 (2H, d, J = 1.8 Hz), 7.95 (2H, d, J = 1.8 Hz),
7.91 (8H, s), 7.88 (1H, t, J = 1.8 Hz), 7.78–7.76 (2H, m),
7.61–7.56 (2H, m), 7.49 (8H, dd, J = 8.2, 5.0 Hz), 7.22 (8H,
dt, J = 8.2, 2.0 Hz), 2.77 (16H, t, J = 7.8 Hz, -CH2CH2CH2CH3),
1.70–1.63 (16H, m, -CH2CH2CH2CH3), 1.43–1.34 (16H, m, -
CH2CH2CH2CH3), 0.93 (24H, t, J = 7.3 Hz, -CH2CH2CH2CH3),
[MALDI:DITH] (m/z) 1417.17: (MH+), Found: C, 87.14; H,
8.02; N, 4.88. C103H109N5 requires C, 87.30; H, 7.75; N,
4.94%.
5.2. (DAP)6Ir
The mixture of 8 (2.41 g), 5 (4.80 g, 3.37 mmol), silver
trifluoromethanesulfonate (0.225 g, 0.877 mmol), and dig-
lyme (15 ml) was heated at 130 °C under N2 for 192 h. The
mixture was allowed to cool to room temperature, and
then purified by column chromatography over silica using
a dichloromethane–hexane mixture (1:2 and 1:3, respec-
tively) as eluent. Further purification by preparative TLC
using a dichloromethane–hexane mixture (1:3) as eluent
gave the complex (DPA)6Ir (0.526 g, 16%). dH(400 MHz,
CD2Cl2) 7.72 (3H, s), 7.52 (3H, s), 7.31 (3H, d, J = 5.9 Hz),
7.00–6.94 (96H, m), 6.70–6.63 (21H, m), 6.59–6.55 (6H,
m), 2.51 (48H, t, J = 7.7 Hz, -CH2CH2CH2CH3), 1.57–1.50
(48H, m, -CH2CH2CH2CH3), 1.37–1.28 (48H, m, -CH2CH2
CH2CH3), 0.89 (72H, t, J = 7.3 Hz, -CH2CH2CH2CH3).
dC(100 MHz, CD2Cl2) 166.1, 161.1, 149.6, 149.3, 149.2,
147.1, 145.6, 145.1, 144.2, 140.0, 138.1, 137.4, 137.1,
133.0, 129.3, 129.2, 128.8, 124.7, 124.3, 122.3, 120.9,
116.9, 116.8, 115.98, 115.95, 115.3, 114.4, 35.2, 33.97,
33.95, 22.7, 14.0. [MALDI:DITH] (m/z) 4462.45: (MH+),
Found: C, 83.30; H, 7.83; N, 4.64. C309H348IrN15 requires
C, 83.13; H, 7.86; N, 4.71%.
7: the mixture of 2 (1.00 g, 1.27 mmol), iridium chloride
trihydrate (0.186 g, 0.527 mmol), deionized water (8.5 ml),
and 2-ethoxyethanol (36 ml) was heated at 130 °C for 24 h
under N2. After the solvent was removed in vacuo, the res-

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Y.-J. Pu et al. / Organic Electronics 12 (2011) 2103–2110
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5.3. (mCP)6Ir
The mixture of 9 (1.46 g), 6 (2.89 g, 2.03 mmol), silver
trifluoromethanesulfonate (0.498 g, 1.94 mmol), and ethyl-
diglyme (10 ml) was heated at 150 °C under N2 for 133 h.
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twice, to give the complex (mCP)6Ir (0.316 g, 16%).
dH(400 MHz, CD2Cl2) 8.28 (3H, s), 8.09 (3H, s), 7.93–7.89
(15H, m), 7.86 (24H, dd, J = 4.6, 1.4 Hz), 7.82 (3H, t,
J = 1.8 Hz), 7.61 (3H, t, J = 1.8 Hz), 7.44 (12H, d, J = 8.7 Hz),
7.40 (12H, d, J = 8.2 Hz), 7.34–7.29 (6H, m), 7.15–7.11
(27H, m), 2.72 (48H, t, J = 7.6 Hz, -CH2CH2CH2CH3), 1.67–
1.59 (48H, m, -CH2CH2CH2CH3), 1.41–1.31 (48H, m, -
CH2CH2CH2CH3), 0.92 (72H, t, J = 7.3 Hz, -CH2CH2CH2CH3).
dC(100 MHz, CD2Cl2) 166.5, 162.2, 148.0, 147.9, 145.4,
144.6, 141.3, 140.5, 139.9, 139.2, 139.0, 137.8, 135.1,
134.7, 132.0, 129.3, 126.7, 126.6, 124.8, 123.7, 123.6,
123.5, 122.9, 122.7, 121.9, 121.6, 119.6, 119.4, 117.4,
109.5, 109.3, 35.5, 34.42, 34.40, 29.7, 22.4, 13.8. [MALDI:-
DITH] (m/z) 4439.73: (MH+), Found: C, 83.58; H, 7.10; N,
4.78. C309H324N15 requires C, 83.58; H, 7.35; N, 4.73%.
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Acknowledgment
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This work was supported by Grant-in-Aid for Young
Scientists (A) No. 21685014 from MEXT, Japan.
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