Nonconjugated dendritic iridium(III) complexes with tunable pyridine-based ligands: Synthesis, photophysical, electrochemical, and electroluminescent properties

Article abstract of DOI:10.1021/ic062041n

A simple synthetic route was developed for nonconjugated dendritic iridium(III) complex based on tunable pyridine-based ligands. From an intermediate 2-bromopyridyl-4-methanol, three series of polybenzyloxy dendritic pyridine-based ligands with 2-phenyl, 2-benzothienyl, and 2,4-difluorophenyl subsitituents were easily synthesized via two-step reactions (Suzuki reaction and etherifying reaction). Using these pyridine derivatives as the C∧N ligands, these dendritic iridium(III) complexes exhibiting tunable photoluminescence from blue to red were obtained. The photoluminescence quantum yields of these dendritic complexes in neat films increased with the increasing generation number of dendritic C∧N ligands. Importantly, these iridium complexes were used as dopants for successfully fabricating polymer-based electrophosphorescent light-emitting diodes (PLEDs) with the highest external quantum efficiency of 12.8%.

Full text of DOI:10.1021/ic062041n

Inorg. Chem. 2007, 46, 5518−5527
Nonconjugated Dendritic Iridium(III) Complexes with Tunable
Pyridine-Based Ligands: Synthesis, Photophysical, Electrochemical,
and Electroluminescent Properties
Xianghong Li,† Zhao Chen,‡ Qiang Zhao,† Li Shen,† Fuyou Li,*,† Tao Yi,† Yong Cao,*,‡ and
Chunhui Huang*,†
Department of Chemistry and Laboratory of AdVanced Materials, Fudan UniVersity, Shanghai
200433, People’s Republic of China, and Institute of Polymer Optoelectronic Materials and
DeVices, South China UniVersity of Technology, Guangzhou 510640, People’s Republic of China
Received October 25, 2006
A simple synthetic route was developed for nonconjugated dendritic iridium(III) complex based on tunable pyridine-
based ligands. From an intermediate 2-bromopyridyl-4-methanol, three series of polybenzyloxy dendritic pyridine-
based ligands with 2-phenyl, 2-benzothienyl, and 2,4-difluorophenyl subsitituents were easily synthesized via two-
step reactions (Suzuki reaction and etherifying reaction). Using these pyridine derivatives as the C∧N ligands,
these dendritic iridium(III) complexes exhibiting tunable photoluminescence from blue to red were obtained. The
photoluminescence quantum yields of these dendritic complexes in neat films increased with the increasing generation
number of dendritic C∧N ligands. Importantly, these iridium complexes were used as dopants for successfully
fabricating polymer-based electrophosphorescent light-emitting diodes (PLEDs) with the highest external quantum
efficiency of 12.8%.
Introduction
still the best phosphorescent dyes for OLEDs up to now.
Although the iridium(III) complexes in dilute solution at
room temperature show strong luminescence, consistent with
strong spin-orbit coupling of the iridium(III) center, the
intermolecular interaction at high concentrations leads to
dimer, excimer, or aggregate formation, which can quench
phosphorescence emission in the solid state.15-17 The
Phosphorescent heavy-metal complexes (especially irid-
ium(III) complexes) have recently attracted much attention1-12
since the pioneering work of the Thompson and Forrest
groups on the electrophosphorescent organic light-emitting
diode (OLED).13 Due to their relatively short excited-state
lifetime, high photoluminescence efficiency, and excellent
color tuning,2,14 cyclometalated iridium(III) complexes are
(8) (a) Zhao, Q.; Liu, S. J.; Shi, M.; Wang, C. M.; Yu, M. X.; Li, L.; Li,
F. Y.; Yi, T.; Huang, C. H. Inorg. Chem. 2006, 45, 6152-6160. (b)
Huang, C. H.; Li, F. Y.; Huang, W. Introduction to Organic Light-
Emitting Materials and DeVices (in Chinese); Fudan University:
Shanghai, 2005.
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Hsu, S. F.; Chen, C. H. AdV. Mater. 2005, 17, 285-289.
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T.; Yamaguchi, T. Appl. Phys. Lett. 2005, 86, 103507.
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2006, 18, 948-954.
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Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151-154.
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* To whom correspondence should be addressed. Fax: 86-21-55664621.
Tel: 86-21-55664185. E-mail: fyli@fudan.edu.cn (F.Y.L.); chhuang@
pku.edu.cn (C.H.H.).
† Fudan University.
‡ South China University of Technology.
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5518 Inorganic Chemistry, Vol. 46, No. 14, 2007
10.1021/ic062041n CCC: $37.00
© 2007 American Chemical Society
Published on Web 06/05/2007

Dendritic Ir(III) Complexes with Pyridine-Based Ligands
development of efficient OLEDs, therefore, requires a way
of controlling the intermolecular interaction. Usually, doping
cyclometalated iridium complexes into a host has been
enthusiastically investigated as the main strategy to achieve
highly efficient electrophosphorescnce devices.18-23Another
approach is to introduce dendrimers into the molecular
structures, owing to the three-dimensional hyperbranched
structure of the dendrimers.24-28
Dendrimers based on the cores of the bipyridine ruthenium
complexes29,30 and rare-earth complexes31-34 have been
studied by many groups. However, the studies on dendritic
iridium complexes are mainly limited to Samuel’s work
based on conjugated dendrimers.35-46 Through the introduc-
tion of conjugated dendrons into the pyridine-based C∧N
ligands with Suzuki coupling reactions,45 Samuel et al.
synthesized some conjugated dendritic iridium(III) complexes
and found that these dendritic complexes were beneficial to
fabricate the electroluminescence (EL) devices. However,
the obvious red-shifts of their absorption and emission bands
were observed in these conjugated iridium dendrimers, and
the possibility of color tuning is limited and the realization
of pure blue emission becomes difficult. Recently, Burn et
al.46 reported that the bathochromic problem was addressed
to some degree in the dendrimer containing 2-ethylhexyloxy
surface groups, biphenyl-based dendrons, and a fac-tri[2-
(2,4-difluorophenyl)pyridyl]iridium(III) core. This inspired
us to further synthesize appropriate nonconjugated dendritic
iridium complexes for three-color luminescent materials.
Herein, we reported a smart synthetic procedure of 2-aryl-
substituted pyridines which could easily be modified by
nonconjugated polyether dendrons. Using these dendritic
pyridine derivatives as cyclometalated C∧N ligands, the
nonconjugated dendritic iridium complexes with polyether
dendrons Ir(C∧N-Gn)2(LX) (see Scheme 1) were synthesized
and characterized by their photophysical, electrochemical,
and electroluminescent properties. Importantly, tunable pho-
toluminescence from blue to red was observed for these
dendritic iridium complexes on the basis of the pyridine-
based ligands with 2-phenyl, 2-benzothienyl, and 2,4-
difluorophenyl subsitituents.
Results and Discussion
Synthesis. It is well known that the emission color of
iridium(III) complexes depends on the chemical structure of
ligand and that the blue, green, and red emissions were
observed for the iridium(III) complexes associated with the
C∧N ligands 2,4-difluorophenylpyridine (dfp),47,48 2-phe-
nylpyridine (ppy),2 and 2-benzothienylpyridine (btp)2 (see
Scheme 1), respectively. Herein, three types of iridium(III)
complexes based on 2-arylpyridines (2-aryl ) 2-phenyl,
2-benzothienyl, and 2,4-difluorophenyl) were used as the
cores of these dendrimers to tune the phosphorescent
emission from blue to red. These dendritic C∧N ligands dfp,
ppy, and btp with polyarylether dendron via methyloxy group
were denoted as dfp-Gn, ppy-Gn, and btp-Gn (n ) 1 and 2)
(see Scheme 1), respectively.
All these dendritic C∧N ligands were synthesized through
a key intermediate of 2-bromo-4-hydroxymethylpyridine (4),
which was prepared from 2-bromo-4-methylpyridine (1) in
three steps with good overall yield of ∼65% (see Scheme
2). Because of the high reaction activity of hydroxymethyl
and bromo groups, compound 4 could be used as an
important intermediate. Through this intermediate 4, three
series of the dendritic C∧N ligands dfp-Gn, ppy-Gn, and btp-
Gn were easily synthesized through introduction of noncon-
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Inorganic Chemistry, Vol. 46, No. 14, 2007 5519

Li et al.
Scheme 1. Chemical Structures of the Dendritic Iridium Complexes Ir(C∧N-Gn)2(LX)
Scheme 2. Synthetic Route of 2-Bromopyridyl-4-methanol
Scheme 3. Two Synthetic Strategies of ppy-G1
jugated polyarylether dendrons and different aryl groups.
Two strategies were used to obtain the nonconjugated
dendritic C∧N ligands dfp-Gn, ppy-Gn, and btp-Gn. Herein,
the synthesis of ppy-G1 (as an example) is discussed in detail
(see Scheme 3). One synthetic strategy (I) of ppy-G1 was
to attach 3,5-(dibenzyl)benzyl bromide (G1-Br)31,49 to the
4-hydroxymethyl group of 4 and then to replace the bromo
group with a phenyl substituent using Kharash-coupling
reaction. However, in this way, the ether bond was partly
ruptured in Kharash reaction, resulting in a low yield (<40%)
and the formation of a byproduct, 4-hydroxymethylpyridine,
which may be attributed to the fact that the strong basic
property of the Grignard reagent facilitated the disconnection
of C-O-C bond. The other synthetic strategy (II) of ppy-
G1 (see Scheme 3) was to attach the aryl group first to
4-hydroxymethylpyridine by Suzuki reaction and then to
incorporate the dendron. Compared with the strategy (I), this
method (II) exhibited a higher overall yield (>50%) with a
relatively simple purification procedure. Similarly, the other
dendritic C∧N ligands ppy-G2, btp-Gn, and dfp-Gn (n ) 1
(49) Hawker, C. J.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1990, 112, 7638-
7647.
5520 Inorganic Chemistry, Vol. 46, No. 14, 2007

Dendritic Ir(III) Complexes with Pyridine-Based Ligands
Table 1. Photophysical Properties of the Dendritic Iridium(III) Complexes
abs (ꢀ × 104 mol-1 L cm-1
)
λem(sol)a (nm)
λ
em(film)/nm
τsola/ns
τ
film/ns
Φsol
Φfilmb(%)
a
complex
λ
Ir(dfp)2(pico)
257 (4.6), 280 (4.4), 382 (3.5), 427 (3.1)
259 (4.7), 280 (4.5), 381 (3.7), 427 (3.3)
260 (4.7), 279 (4.6), 381 (3.8), 427 (3.3)
259 (4.7), 344 (4.0), 412 (3.7), 460 (3.6), 495 (3.2)
263 (4.7), 345 (4.1), 412 (3.8), 462 (3.6), 493 (3.3)
275 (4.8), 343 (4.1), 412 (3.8), 460 (3.6), 493 (3.3)
285 (4.5), 340 (4.3), 356 (4.2), 488 (3.8)
282 (4.6), 342 (4.3), 358 (4.2), 487 (3.9)
282 (4.8), 342 (4.4), 358 (4.3), 485 (3.9)
472, 494(sh)
476, 494(sh)
476, 494(sh)
519
528
530
615, 670
619, 675
619, 674
504
517
480, 504
538
535, 580(sh)
531
619, 666
624, 680
624, 676
911
1020
1224
1130
1224
1306
2005
2510
2820
29
275
373
11
51
134
54
0.30
0.38
0.49
0.25
0.27
0.32
0.14
0.17
0.21
-
38
77
-
8
16
-
5
Ir(dfp-G1)2(pico)
Ir(dfp-G2)2(pico)
Ir(ppy)2(acac)
Ir(ppy-G1)2(acac)
Ir(ppy-G2)2(acac)
Ir(btp)2(acac)
Ir(btp-G1)2(acac)
Ir(btp-G2)2(acac)
179
895
12
a Luminescence lifetime and quantum efficiency measurements were made in THF solution at 298 K. The lifetimes have error bars of (10%, and the
luminescence quantum efficiencies in solution have error bars of (1% b The luminescence quantum efficiencies in neat films have error bars of (20%.
Table 2. Electrophosphorescent Data for the PLED Devices from Ir(ppy-Gn)2(acac) and Ir(btp-Gn)2(acac) Doped into PFO-PBD as Hosta
device
material
wt % (%)
L
max (cd/m2)
V (V)
LE (cd/A)
EQE (%)
λmax EL nm
CIE (x,y)
I
II
Ir(ppy2(acac)
2
2
4
2
4
2
2
4
2
4
12712
10529
10048
9928
18584
2403
2478
2304
1159
1285
5.8
4.8
5.1
6.3
7.7
5.8
5.8
5.8
6.5
7.7
9.5
18.8
18.0
12.9
12.5
2.4
3.3
3.8
2.4
2.5
9.5
12.8
12.4
9.5
9.5
6.0
6.0
6.0
6.0
6.3
526
530
531
532
533
620
621
621
621
619
(0.35,0.60)
(0.39,0.57)
(0.40,0.57)
(0.40,0.57)
(0.41,0.56)
(0.66,0.33)
(0.64,0.37)
(0.64,0.36)
(0.64,0.33)
(0.65,0.33)
Ir(ppy-G1)2(acac)
Ir(ppy-G1)2(acac)
Ir(ppy-G2)2(acac)
Ir(ppy-G2)2(acac)
Ir(btp)2(acac)
Ir(btp-G1)2(acac)
Ir(btp-G1)2(acac)
Ir(btp-G2)2(acac)
Ir(btp-G2)2(acac)
III
IV
V
VI
VII
VIII
IX
X
a Lmax: maximum luminance; V: operating voltage at 1 cd m-2; LE: luminance efficiency at 100 cd/m2; EQE: external quantum efficiency.
Scheme 4. Synthetic Route of the Dendritic Iridium Complexes
(a) Pd(PPh3)4, Na2CO3, PhMe, EtOH, H2O, 100 °C; (b) NaH, THF, 3 h; (c) 2-ethoxyethanol, H2O, 120 °C; (d) Na2CO3, 100 °C.
and 2) (see Scheme 1) were also obtained in moderate yields
and characterized by NMR, Maldi-TOF mass spectra, and
elemental analysis.
or pico), in the presence of sodium carbonate. The overall
yields of the dendrimers Ir(dfp-Gn)2(pico), Ir(ppy-Gn)2(acac),
and Ir(btp-Gn)2(acac) were calculated to be 60-65%, 35-
45%, and 45-60%, respectively.
All the dendritic iridium(III) complexes (see Scheme 1)
have two dendritic cyclometalated C∧N ligands and an
ancillary ligand, such as picolinic acid (pico) for Ir(dfp-Gn)2-
(pico) and acetylacetone (acac) for Ir(ppy-Gn)2(acac) and Ir-
(btp-Gn)2(acac). According to the previous literature reported
by Nonoyama,50 the synthetic method of these dendritic
iridium complexes Ir(C∧N-Gn)2(LX) involved two steps (see
Scheme 4). The cyclometalated iridium(III) µ-chloro-bridged
dimers (C∧N)2Ir(µ-Cl)2Ir(C∧N)2 were synthesized by heating
iridium chloride trihydrate (IrCl3·3H2O) with an excess of
the dendritic 2-arylpyridine derivatives (dfp-Gn, ppy-Gn, or
btp-Gn) in aqueous 2-ethoxyethanol, and then the iridium-
(III) complexes were prepared by the reaction of dimer with
the corresponding ancillary monoanionic ligands (LX ) acac
All the complexes were successfully characterized through
NMR, MALDI-TOF mass spectra, and elemental analysis.
The 1H NMR spectra of these complexes were more
complicated than those of the small molecular iridium
complexes Ir(dfp)2(pico), Ir(ppy)2(acac), and Ir(btp)2(acac).
The integral ratios of the protons of the surface phenyl groups
to the aromatic region were in agreement with the stiochi-
ometry of the dendritic complexes. The obvious proton
signals of all methylene groups were observed. Moreover,
thermal gravimetric analysis of these dendritic complexes
was also carried out at a heating rate of 10 °C/min under
nitrogen. In each case, no significant weight loss was
observed below 280 °C, indicating that introduction of the
nonconjugated dendrons to the core of 2-arylpyridine iridium-
(50) Nonoyama, K. Bull. Chem. Soc. Jpn. 1974, 47, 467.
Inorganic Chemistry, Vol. 46, No. 14, 2007 5521

Li et al.
Figure 2. Cyclic voltammograms of Ir(ppy-Gn)2(acac) (scan rate ) 50
mV s-1).
extinction coefficients of ∼4600 and 3800 M-1 cm-1,
1
respectively. In the cases of Ir(btp-Gn)2(acac), MLCT and
3MLCT were not clearly resolved, and a broad band was
observed between 435 and 525 nm. Moreover, the spectra
of the dendritic iridium complexes Ir(C∧N-Gn)2(LX) are very
similar to those of their corresponding small molecular
iridium complexes Ir(C∧N)2(LX) with the same core of the
C∧N ligand, suggesting that the dominant absorptions in the
dendritic iridium complexes Ir(C∧N-Gn)2(LX) are due to the
“Ir(C∧N)2” fragment.
Electrochemical Studies. Electrochemical properties of
Ir(dfp-Gn)2(pico), Ir(ppy-Gn)2(acac), and Ir(btp-Gn)2(acac)
(n ) 0-2) in CH2Cl2 and THF solution were studied by the
cyclic voltammetry, and the data are summarized in Table
2. As an example, Figure 2 shows the cyclic voltammograms
of Ir(ppy-Gn)2(acac) with a scan rate of 50 mV s-1.
According to the equation EHOMO(LUMO) ) -(4.80 + Eonset),55
the HOMO and LUMO energies of all complexes were
calculated and the energy gap (E) between HOMO and
LUMO can be deduced by the equation E ) LUMO -
HOMO. All complexes show reversible or quasireversible
oxidation waves in the range of 0.46-1.18 V vs Ag/AgNO3
by referencing ferrocene/ferrocenium as a standard. Accord-
ing to the previous electrochemical studies on iridium
complexes, the oxidation waves are assigned to metal-
centered IrIII/IrIVoxidation process.56 It can be seen from
Table 2 that energy gaps are similar for the dendritic iridium-
(III) complex with the same core. Therefore, introduction
of dendritic framework changed scarcely the energy gaps of
these series of iridium complexes.
Figure 1. UV-vis absorption spectra of Ir(dfp-Gn)2(pico), Ir(ppy-Gn)2-
(acac), and Ir(btp-Gn)2(acac) in THF solutions (c ) 1.0 × 10-5 mol L-1).
(III) complex hardly influenced thermal stability of the
dendritic complexes (see Supporting Information).
UV-vis Absorption Spectroscopy. The UV-vis absorp-
tion spectra of the dendritic complexes Ir(dfp-Gn)2(pico), Ir-
(ppy-Gn)2(acac), and Ir(btp-Gn)2(acac) (n ) 1 and 2) in
tetrahydrofuran (THF) solution are shown in Figure 1, and
the data are listed in Table 1. All these complexes show
intense absorption bands in the ultraviolet region at 250-
350 nm with molar extinction coefficients (ꢀ) of ∼104 mol-1
L cm-1, which are assigned to the spin-allowed πfπ*
transitions of the C∧N ligands and benzyloxy units. For these
dendritic complexes, complexation of the dendritic C∧N
ligands to the iridium cation results in little difference in
the absorption wavelengths of the ligands. However, the
molar extinction coefficient at around 270 nm increased from
the zero generation to the second generation, which is
attributed to the increased number of benzyloxy units. For
example, the ꢀ values at 270 nm for Ir(ppy)2(acac), Ir(ppy-
G1)2(acac), and Ir(ppy-G2)2(acac) were 4.30 × 104, 5.15 ×
104, and 5.60 × 104 mol-1 L cm-1 (see Figure 1),
respectively. Somewhat weaker bands at lower energies were
observed for Ir(dfp-Gn)2(pico), Ir(ppy-Gn)2(acac), and Ir-
(btp-Gn)2(acac). According to most of the previous reports
about cyclometalated complexes,51-54 these bands were
assigned to singlet and triplet metal-to-ligand charge transfer
(MLCT) transitions. For example, for Ir(ppy-Gn)2(acac), two
MLCT bands are clearly resolved at 412 and 460 nm, with
Photoluminescent Properties. The room-temperature
photoluminescence (PL) spectra of these iridium complexes
in THF solution are shown in Figure 3, and the corresponding
photophysical data are summarized in Table 1. It can be seen
that all complexes emit intense luminescence at room
temperature in THF solution. Three series of iridium
complexes Ir(dfp-Gn)2(pico), Ir(ppy-Gn)2(acac), and Ir(btp-
(51) Colombo, M. G.; Brunold, T. C.; Riedener, T.; Gu¨del, H. U. Inorg.
Chem. 1994, 33, 545-550.
(52) (a) Garces, F. O.; King, K. A.; Watts, R. J. Inorg. Chem. 1988, 27,
3464-3471. (b) Carlson, G. A.; Djurovich, P. I.; Watts, R. J. Inorg.
Chem. 1993, 32, 4483-4484.
(55) Thomas, K. R. J.; Velusamy, M.; Lin, J. T.; Chien, C. H.; Tao, Y. T.;
Wen, Y. S.; Hu, Y. H.; Chou, P. T. Inorg. Chem. 2005, 44, 5677-
5685.
(56) Wu, F. I.; Su, H. J.; Shu, C. F.; Luo, L. Y.; Diau, W. G.; Cheng, C.
H.; Duan, J. P.; Lee, G. H. J. Mater. Chem. 2005, 15, 1035-1042.
(53) Serroni, S.; Juris, A.; Campagna, S.; Venturi, M.; Denti, G.; Balzani,
V. J. Am. Chem. Soc. 1994, 116, 9086-9091.
(54) Neve, F.; Deda, M. L.; Crispini, A.; Bellusci, A.; Puntoriero, F.;
Campagna, S. Organometallics 2004, 23, 5856-5863.
5522 Inorganic Chemistry, Vol. 46, No. 14, 2007

Dendritic Ir(III) Complexes with Pyridine-Based Ligands
Figure 3. Room-temperature photoluminescence spectra of the dendritic
complexes (5 × 10-6 M) in THF solution (λex) 360 nm).
Figure 4. Photoluminescence spectra of the dendritic iridium complexes
in neat films (λex ) 360 nm).
Compared with no significant influence on the emission
properties in solution, the introduction of the polyarylether
dendrons affects greatly the solid-state emission properties
of the dendritic iridium(III) complexes. Figure 4 shows the
photoluminescence spectra of all complexes in neat films.
It can be seen from Figures 3 and 4 that these dendritic
complexes from fluid solution to solid-state film show red-
shifts of emission bands to different extent (see Table 1), in
agreement with previous result of cyclometalated iridium-
(III) MLCT emitters.2,16,45,46 Compared with the zero genera-
tion dendritic complexes, the first generation dendritic
complexes in a neat film exhibit slightly more red-shifted
emission color. An obvious shoulder band on the lower-
energy side was observed for Ir(ppy-G1)2(acac) (see Figure
4b) from fluid solution to solid-state film. Because of the
relatively small structure of first generation dendrons, the
steric bulk of the dendritic ligand was insufficient to prevent
the interaction of the ppy ligands significantly. However,
this bathochromic problem could be addressed to some
degree through introduction of the second generation den-
drons. The photoluminescence band of Ir(ppy-G2)2(acac) in
neat film overlaps nearly that of Ir(ppy)2(acac), showing that
attachment of the second generation dendron changes the
emission color slightly. In addition, it can be seen from Table
1 that the introduction of the polyarylether dendrons into
the C∧N ligands significantly improved the photolumines-
cence quantum yields (æ) and luminescence lifetimes (τ) of
the iridium complexes. For Ir(btp-Gn)2(acac), the photolu-
minescence quantum yield of Ir(btp)2(acac) in neat film was
too weak to be measured, while the corresponding quantum
yields of Ir(btp-G1)2(acac) and Ir(btp-G2)2(acac) increased
to 5% and 12%, respectively. Moreover, the luminescence
lifetimes of Ir(btp-G1)2(acac) and Ir(btp-G2)2(acac) were
Gn)2(acac) in THF solution exhibit emission bands centered
at ∼476, 520, and 619 nm (see Table 1), respectively,
indicating that they are blue, green, and red light-emitting
materials. The luminescence lifetimes (τ) of these dendritic
iridium complexes, measured at 298 K in degassed solution,
are in the range of 0.92-2.75 µs (see Table 1). Such long-
lived excited states and their sensitivity toward oxygen
indicate that the emitting states of these iridium complexes
have triplet character.2 Moreover, the photoluminescence
spectra of Ir(dfp-Gn)2(pico) and Ir(ppy-Gn)2(acac) are broad
and featureless, indicating that the emission originates
3
primarily from the MLCT state. However, fine vibronic
structures were observed in the emission spectra of Ir(btp-
Gn)2(acac), corresponding to a significant ligand3(π-π*)
contribution to the phosphorescence.57
It can be seen from Table 1 that the introduction of
polyarylether dendrons into the C∧N ligands results in a
minor perturbation on the emission properties of these
iridium(III) complexes in solution. All of the dendritic
complexes in solution with the same core of Ir(C∧N)2(LX)
show similar emission bands (see Figure 3), and no obvious
improvements on the photoluminescence quantum yields (φ)
and lifetimes of the dendritic complexes were observed with
increasing in the dendritic generation. For example, the
photoluminescence quantum yields of Ir(btp)2(acac), Ir(btp-
G1)2(acac), and Ir(btp-G2)2(acac) were calculated as 0.14,
0.17, and 0.21, respectively, corresponding to their lumi-
nescence lifetimes of 1130, 1204, and 1306 ns, respectively.
(57) (a) Sandrini, D.; Maestri, M.; Ciano, M.; Balzani, V.; Deuschel-
Cornioley, C.; von Zelewsky, A.; Jolliet, P. HelV. Chim. Acta 1988,
71, 1053. (b) Balton, C. B.; Murtaza, Z.; Shaver, R. J.; Rillema, D. P.
Inorg. Chem. 1992, 31, 3230.
Inorganic Chemistry, Vol. 46, No. 14, 2007 5523

Li et al.
Figure 5. Chemical structures of accessorial materials used in PLEDs.
lengthened to 179 and 895 ns, respectively, in comparison
with that of Ir(btp)2(acac) (τ ) 54 ns). These facts imply
that the dendron’s spread configuration weakens the inter-
molecular core-core interactions in solid state, and reduces
the probability of phosphorescence quenching.16,34
Figure 6. I-V-L characteristics for device II with the configuration of
ITO/PEDOT/PSS/PVK (40 nm)/PFO+PBD (30 wt %)/2% Ir(ppy-G1)2(acac)
(80 nm)/Ba (4 nm)/Al (120 nm) Ir(ppy-G1)2(acac). Inset: electroluminescent
spectra of device II.
Characterization of PLED Devices. Recently, polymer-
based electrophosphorescent light-emitting diodes (PLEDs)
have been paid a great deal of attention because they can be
fabricated by solution processing and suitable for large-area
and flexible display.21-23,56,59-61 Herein, two series of den-
dritic iridium(III) complexes Ir(ppy-Gn)2(acac) and Ir(btp-
Gn)2(acac) were used as emissive materials for PLEDs. The
devices consist of a multilayer configuration ITO/PEDOT/
PSS/PVK (40 nm)/PFO+PBD (30 wt %)/x% Ir-complex (80
nm)/Ba (4 nm)/Al (120 nm), where PVK is poly(vinylcar-
bazole) (see Figure 5). A thin film of PEDOT/PSS was spin-
cast onto a precleaned ITO surface and then baked at 80 °C
for 12 h under vacuum to improve hole injection and to
increase substrate smoothness. Due to good hole-transporting
properties, a layer of PVK was used as hole-transporting
layer. Poly(9,9-dioctylfluorene) (PFO) was blended with
2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD)
because PBD is a good electron-transporting material.62,63
The emitting layer, PFO-PBD (30 wt %) doped with 2%
or 4% of these iridium complexes was then spin-cast onto
the surface of PVK. Conjugated polymer PFO was chosen
as the host material because of its high fluorescent quantum
yield and good charge transporting property.
case of Ir(btp-Gn)2(acac), the variation of dendron from zero
generation to the second generation induced no obvious shifts
(∼2 nm) of electrophorescence (see Table 2 and Supporting
Information). The corresponding CIE chromaticity coordi-
nates (x, y) were about (0.64, 0.36) for Ir(btp-Gn)2(acac),
indicating that all EL devices with Ir(btp-Gn)2(acac) as
dopant showed saturated red emission.
It can also be seen from Table 2 that all PLED devices
with Ir(ppy-Gn)2(acac) as dopant exhibited excellent elec-
trophosphorescence properties. As an example, Figure 6
shows the current density (I)-voltage (V)-luminance (L)
characteristic of the device II [PVK (40 nm)/PFO+PBD (30
wt %)/2 wt % Ir(ppy-G1)2(acac) (80 nm)/Ba(4 nm)/Al (120
nm)]. The PLED device II showed the maximum luminance
of 10529 cd m-2 at 14.7 V, and the external quantum
efficiency (EQE)64 of 12.8% (see Table 2). For the device
IV of Ir(ppy-G2)2(acac) with a doping concentration of 2 wt
%, the maximum luminescence was 9928 cd m-2, and the
external quantum efficiency was 9.5%. The corresponding
CIE (Commission International de L’Eclairage) chromaticity
coordinates (x, y) were (0.39, 0.57) and (0.41, 0.56) for Ir-
(ppy-G1)2(acac) and Ir(ppy-G2)2(acac), respectively, sug-
gesting that all of Ir(ppy-Gn)2(acac) provided green emission.
Moreover, when the doping concentration of Ir(ppy-G2)2-
(acac) increased to 4 wt %, the maximum luminance of the
PLED device V reached twice that of the 2 wt % doping
concentration, and no obvious decrease in the luminous
efficiency of device V was observed.
The electroluminescence data are summarized in Table 2.
Compared the small molecular iridium complexes Ir(C∧N)2-
(LX) containing the same ancillary ligand with the corre-
sponding dendritic complexes Ir(C∧N-Gn)2(LX), no obvious
variation was observed for the electroluminescence spectra,
which means that introduction of the polyarylether dendrons
into the C∧N ligands did not alter the emissive wavelengths
of the iridium complexes significantly. For example, in the
Conclusions
In summary, we have developed a simple synthetic route
in incorporating dendrons into pyridine-based C∧N ligands
with different aryl groups via two-step reactions (Suzuki
reaction and etherifying reaction) and successfully synthe-
sized three series of nonconjugated dendritic iridium(III)
complexes based on tunable pyridine-based ligands with
2-phenyl, 2-benzothienyl, and 2,4-difluorophenyl subsititu-
(58) Kawamura, Y.; Goushi, K.; Brooks, J.; Brown, J. J.; Sadabe, H.;
Adachi, C. Appl Phys. Lett. 2005, 86, 071104.
(59) Chen, X. W.; Liao, J. L.; Liang, Y. M.; Ahmed, M. O.; Tseng, H. E.;
Chen, S. A. J. Am. Chem. Soc. 2003, 125, 636-637.
(60) Gong, X.; Ostrowski, J. C.; Bazan, G. C.; Moses, D.; Heeger, A. J.;
Liu, M. S.; Jen, A. K. Y. AdV. Mater. 2003, 15, 45-49.
(61) Jiang, C. Y.; Yang, W.; Peng, J. B.; Xiao, S.; Cao, Y. AdV. Mater.
2004, 16, 537-541.
(62) Adachi, C.; Tsutsui, T.; Saito, S. Appl. Phys. Lett. 1989, 55, 1489-
1491.
(63) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Chem. Mater.
2004, 16, 4556-4573.
(64) Forrest, S. R.; Bradley, D. D.; Thompson, M. E. AdV. Mater. 2003,
15, 1043-1048.
5524 Inorganic Chemistry, Vol. 46, No. 14, 2007

Dendritic Ir(III) Complexes with Pyridine-Based Ligands
Electrochemical Measurements. Electrochemical measurements
were carried out in a one-compartment cell under N2 atmosphere,
equipped with a glassy-carbon working electrode, a platinum wire
counter electrode, and a Ag/Ag+ reference electrode with an Eco
chemie’s Autolab. Measurements of oxidation and reduction were
undertaken in the anhydrous solution of CH2Cl2 and THF,
respectively, containing the supported electrolyte of a 0.10 mol L-1
tetrabutyl ammonium hexafluorophosphate (Bu4N+‚PF6-). The scan
ents. The emission of these dendritic complexes could be
tuned from blue to red. Interestingly, the introduction of the
nonconjugated dendrons did not significantly alter the
emissive wavelengths of the core of the iridium complexes,
but improved the solid-state luminescence quantum efficien-
cies of the iridium complexes. Moreover, by using these
iridium complexes as dopants, PLEDs were successfully
fabricated with the highest external quantum efficiency of
12.8%. Our synthetic route of nonconjugated dendritic
ligands may open up broad prospects for designing other
luminescent materials based on dendritic metal complexes.
rate was 100 or 50 mV s-1
.
Preparation of PLED Devices. An indium tin oxide (ITO) glass
substrate with a sheet resistance of 15 Ω was kindly supplied by
China Southern Glass Holding Co. Ltd. The fabrication of elec-
trophosphorescent devices followed a standard procedure. A 70 nm
thick layer of PEDOT/PSS was spin-cast onto precleaned ITO-
glass substrates. A thin layer of Ba (4 nm thick) with a 200 nm
thick Al capping layer was deposited through a shadow mask in a
chamber with a base pressure of ∼10-4 Pa. Device fabrication was
carried out in a controlled atmosphere drybox (Vacuum Atmosphere
Co.) under N2 circulation. Current density (I)-voltage (V)-
luminance (L) data were collected using a Keithley 236 source
measurement unit and a calibrated silicon photodiode. External
electroluminescence (EL) quantum efficiencies were obtained by
measuring the total light output in all directions in an integrating
sphere (IS-080, Labsphere). The luminance (cd m-2) and luminous
efficiency (cd A-1) were measured by a silicon photodiode and
calibrated using a PR-705 SpectraScan spectrophotometer (Photo
Research).
Experimental Section
Materials. Poly(ethylendioxythiophene)/poly(styrene sulfonic
acid) (PEDOT/PSS), conjugated poly(9,9-dioctylfluorene) (PFO),
2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), and
2-phenylpyridine (ppy) were purchased from Aldrich. Acetylac-
etone, 2-ethoxyethanol, 2-bromopyridine, 2-benzothienylboronic
acid, 2,4-difluorophenylboronic acid, picolinic acid, and BuLi were
obtained from Acros. IrCl3‚3H2O, Pd(PPh3)4, 2-bromo-4-methylpy-
ridine, and 3,5-dihydroxybenzyl alcohol were industrial products
and used without further purification. The Fre´chet-type dendritic
benzylic bromides [G-1]-Br and [G-2]-Br of first (n ) 1) and second
(n ) 2) generation were prepared according to the general procedure
developed by Hawer and Fre´chet.31,49 The small molecular C∧N
ligands 2-(2,4-difluorophenyl)pyridine (dfp) and 2-benzo[b]thiophe-
nylpyridine (btp) were synthesized via the Suzuki-coupling reaction,
using tetrakis(triphenylphosphine)palladium(0) and K2CO3 from
2-bromopyridine and corresponding boronic acid, according to
previous references.48,2
General Experiments. NMR spectra were recorded on Varian
Mercury Plus 400 MHz and Bruker AMX 500 MHz NMR
spectrometers. UV-visible absorption spectra were recorded using
a Shimadzu 2550 UV-vis-NIR spectrophotometer. The elemental
analyses were performed on a VarioEL III O-Element Analyzer
system. Mass spectra were obtained on a SHIMADZU matrix-
assisted laser desorption/ionization time-of-flight mass spectrometer
(MALDI-TOF-MASS). Thermal gravimetric analysis was per-
formed on a Shimadzu thermogravimetric analyzer DTG-60H at a
heating rate of 10 °C min-1 under nitrogen.
The photoluminescence spectra were measured on an Edinburgh
LFS920 fluorescence spectrophotometer. Quantum efficiency mea-
surements in THF solutions were carried out at room temperature.
Before spectra were measured, the solutions were degassed by three
freeze-pump-thaw cycles. The solution of quinine sulfate in 1
mol dm-3 sulfuric acid (Φ ) 0.56) was used as a reference.65 The
photoluminescent lifetime was recorded on a single photon counting
spectrometer from Edinburgh Instrument (FLS920) with a hydrogen-
filled pulse lamp as the excitation source. The data were analyzed
by iterative convolution of the luminescence decay profile with the
instrument response function using software package provided by
Edinburgh Instruments.
Films were spin-coated from chloroform solutions with a
dendrimer concentration of 10 mg mL-1 at 900 rpm for 1 min to
give a thickness of about 150 nm. Their photoluminescence
quantum yields in neat films were measured using an integrating
sphere (UDT, Labsphere) and Omnichrome series 56 Helium
Cadmium laser as the excitation source. The excitation wavelength
was at 325 nm.
2-Bromo-4-methoxycarbonylpyridine (3).66 A suspension of
7.4 g of 2-bromo-4-carboxypyridine (2) in 50 mL of thionyl chloride
was refluxed for 4 h under inert atmosphere. The excess of thionyl
chloride was distilled off, and the residue dried in a vacuum for 2
h. Absolute methanol (20 mL) was added, and the mixture refluxed
for 1 h. Chloroform (100 mL) was then added, and the mixture
was treated with a cold solution of sodium bicarbonate. The organic
layer was dried on anhydrous sodium sulfate and the solvent
removed in vacuum, 6.3 g of product was obtained without further
1
purification, yield: 80%; H NMR (δ, CDCl3, 400 MHz): 8.53
(d, J ) 5.2 Hz, 1H), 7.88 (d, J ) 8 Hz,1H), 7.77 (dd, J ) 1.2 Hz,
J ) 4.8 Hz, 1H), 3.96 (s, 3H).
4-Hydroxymethyl-2-bromopyridine (4). Sodium borohydride
(1.7 g) was added in one portion to a suspension of the ester 3 (6.3
g) in 200 mL of ethanol. The mixture was refluxed for 3 h and
cooled to room temperature, and then 200 mL of a saturated aqueous
ammonium chloride solution was added to decompose the excess
sodium borohydride. The ethanol was removed under vacuum, and
the precipitated solid dissolved in a minimal amount of water. The
resulting solution was extracted with ethyl acetate (5 × 200 mL)
and dried over anhydrous sodium sulfate, and the solvent was
removed under vacuum. The desired solid was obtained in 92%
yield and was used without further purification. 1H NMR (δ, CDCl3,
400 MHz): 8.25 (d, J ) 5.2 Hz, 1H), 7.35 (s, 1H), 7.20 (d, J )
4.8 Hz, 1H), 4.73 (s, 2H), 3.61 (s, 1H).
2-Phenylpyridyl-4-methanol (6). To a muxture of 5.1 g (27
mmol) of 4, 3.65 g (30 mmol) of phenylboronic acid, and 0.155 g
of Pd(PPh3)4 in deoxygenated toluene (150 mL), ethanol (15 mL)
and an aqueous solution of potassium carbonate (2 M, 30 mL) were
added. The resulting mixture was refluxed for 24 h. Cooling,
filtration, extraction with chloroform, drying over anhydrous Na2-
(66) Hamel, P.; Riendeau, D.; Brideau, C.; Chan, C.-C.; Desmarais, S.;
Delorme, D.; Dube, D.; Ducharme, Y.; Ethier, D.; Grimm, E.;
Falgueyret, J.-P.; Guay, J.; Jones, T. R.; Kwong, E.; AcAuliffe, M.;
McFarlane, C. S.; Piechuta, H.; Roumi, M.; Tagari, P.; Young, R. N.;
Girard, Y. J. Med. Chem. 1996, 40, 2866-2875.
(65) Adams, M. J.; Highfield, J. G.; Kirkbright, G. F. Anal. Chem. 1977,
49, 1850-1852.
Inorganic Chemistry, Vol. 46, No. 14, 2007 5525

Li et al.
SO4, filtration, and solvent removal afforded to a crude product
which was purified by chromatography on silica gel (light
petroleum/chloroform, v/v ) 3:1). A white powder (3.64 g) was
ppy-G1. Yield: 70%: 1H NMR (δ, CDCl3, 400 MHz): 8.66
(d, J ) 4.8 Hz, 2H), 8.01 (d, J ) 7.6 Hz, 2H), 7.72 (s, 2H), 7.49-
7.32 (m, 13H), 7.20 (d, J ) 4.8 Hz, 2H), 6.64 (s, 2H), 6.59 (s,
1H), 5.04 (s, 4H), 4.59 (s, 2H), 4.57 (s, 2H); 13C NMR (δ, CDCl3,-
100 MHz): 160.45, 157.89, 150.02, 148.54, 140.45, 139.63, 137.09,
129.32, 129.06, 128.90, 128.32, 127.83, 120.70, 118.98, 106.96,
101.82, 72.94, 70.75, 70.36; m/z [MALDI: DI]: 487.7 (M+), 595.5
(M + Ag+); Anal. Calcd for C33H29NO3 (%): C 81.29, H 5.99, N
2.87; Found: C 80.93, H 6.05, N 2.93.
ppy-G2. Yield: 73%: 1H NMR (δ, CDCl3, 400 MHz): 8.65
(d, J ) 4.8 Hz, 1H), 8.00 (d, J ) 7.6 Hz, 2H), 7.71 (s, 1H), 7.47-
7.30 (m, 23H), 7.20 (d, J ) 4.8 Hz, 1H), 6.67 (s,4H), 6.62 (s, 2H),
6.57 (s, 3H), 5.02 (s, 8H), 4.98 (s, 4H), 4.60 (s, 2H), 4.57 (s, 2H).
13C NMR (δ, CDCl3,100 MHz): 160.63, 160.53, 157.87, 150.16,
148.73, 140.74, 139.76, 139.69, 137.23, 129.50, 129.23, 129.03,
128.45, 128.02, 127.43, 120.83, 118.99, 107.13, 106.82, 101.96,
73.07, 70.89, 70.43, 70.33; m/z [MALDI: DI]: 911.9 (M+), 1019.7
(M + Ag+); Anal. Calcd for C61H53NO7 (%): C 80.33, H 5.86, N
1.54; Found: C 79.60, H 5.94, N 1.55.
btp-G1. Yield: 75%: 1HNMR (δ, CDCl3, 400 MHz): 8.59 (d,
J ) 4.8 Hz, 1H), 7.85 (s, 2H), 7.79 (m, 2H), 7.42 (m, 12H), 7.15
(d, J ) 4.8 Hz, 2H), 6.64 (s, 2H), 6.59 (s, 1H), 5.05 (s, 4H), 4.58
(s, 4H); 13CNMR (δ, CDCl3, 125 MHz): 160.21, 152.71, 149.70,
148.26, 144.74, 140.68, 140.45, 140.02, 136.80, 128.58, 128.00,
127.48, 124.48, 124.12, 122.55, 121.26, 117.65, 106.78, 101.67,
72.76, 70.24, 70.15; m/z [MALDI: DI]: 543.5 (M+), 651.5 (M +
Ag+); Anal. Calcd for C35H29NO3S (%): C 77.32, H 5.38, N 2.58;
Found: C 77.12, H 5.49, N 2.66.
btp-G2. Yield: 70%: 1HNMR (δ, CDCl3, 400 MHz): 8.59 (d,
J ) 4.8 Hz, 1H), 7.87-7.84 (m, 2H), 7.80 (s,1H), 7.78-7.76 (m,
2H), 7.42-7.30 (m, 22H), 7.17 (d, J ) 4.8 Hz, 1H), 6.69 (d, 4H),
6.65 (d, 2H), 6.57 (s, 3H), 5.02 (s, 8H), 4.99 (s, 4H), 4.59 (d, 4H);
13C NMR (CDCl3, 100 MHz): 160.45, 160.35, 152.86, 149.91,
148.62, 144.90, 140.90, 140.71, 140.31, 139.49, 137.00, 128.87,
128.31, 127.85, 125.36, 124.80, 124.46, 122.84, 121.64, 121.10,
117.88, 107.02, 106.64, 101.86, 101.78, 73.04, 70.48, 70.35, 70.25;
m/z [MALDI: DI]: 967.7 (M+), 1075.5 (M + Ag+); Anal. Calcd
for C63H53NO7S (%): C 78.16, H 5.52, N 1.45; Found: C 77.29,
H 5.43, N 1.50.
1
obtained with a yield of 73%. H NMR (δ, CDCl3, 400 MHz):
8.63 (d, J ) 5.2 Hz 1H), 7.98 (d, J ) 6.8 Hz, 1H), 7.72 (s, 1H),
7.48-7.41 (m, 3H), 7.21 (d, J ) 4.4 Hz 1H), 4.79 (s, 2H); m/z
[EI]: 185.1 (M+).
2-(2,4-Difluorophenyl)pyridyl-4-methanol (7). The similar
procedure as described for 2-phenylpyridyl-4-methanol was used.
1H NMR (δ, DMSO, 500 MHz): 8.64 (d, J ) 5.0 Hz, 1H), 8.02-
7.97 (m, 1H), 7.72 (s, 1H), 7.41-7.34 (m, 2H), 7.25-7.21 (m,
1H), 5.52 (t, J ) 5.5 Hz, 1H), 4.62 (d, J ) 6.0 Hz, 2H); 19F NMR
(δ, DMSO, 470 MHz): -108.62 to -108.69 (m, JHF ) 9.4 Hz,
JHF ) 18.8 Hz, 1F), -111.81 to -111.87 (dd, JHF ) 9.4 Hz, JHF
)
18.8 Hz, 1F).
2-(Benzo[b]thiophen-2-yl)pyridyl-4-methanol (8). A similar
1
procedure as that described for 6 was used. H NMR (δ, CDCl3,
400 MHz): 8.57 (d, J ) 5.2 Hz, 1H), 7.87 (m, 2H), 7.79 (m, 2H),
7.36 (t, J ) 4.4 Hz, 2H), 7.18 (d, J ) 5.2 Hz, 2H), 4.80 (d, J ) 5.6
Hz, 2H), 2.21 (t, J ) 6.0 Hz, 1H); m/z [EI]: 241.1 (M+); Anal.
Calcd for C14H11NOS (%): C 69.68, H 4.59, N 5.80, Found: C
69.82, H 4.68, N 5.69.
General Procedure for Synthesis of the Dendritic C∧N
Ligand. The dendritic C∧N ligands dpf-Gn, ppy-Gn, and btp-Gn
(n ) 1-2) were synthesized according to general procedure shown
in Scheme 4. The corresponding 2-arylpyridyl-4-methanol (com-
pound 6, 7, or 8) (1.0 equiv) was dissolved in anhydrous
tetrahydrofuran (THF), and NaH (excess) was added. [Gn-Br]
(n ) 1-2) (2.5 equiv) was added after H2 evolution ceased, and
the reaction was stirred under argon for 4 h. Water was added slowly
to quench any unreacted NaH, and the solution was extracted with
CH2Cl2. The organic layer was dried over anhydrous K2CO3, and
the solvent was removed under vacuum. The crude product was
applied to a silica gel column and eluted with CH2Cl2, followed
by 2-5% methanol in CH2Cl2. Yield: 50-70%.
dfp-G1. Yield: 65%: 1H NMR (δ, DMSO, 500 MHz): 8.68 (d,
J ) 4.9 Hz, 1H), 8.03-7.98 (m, 1H), 7.73 (s, 1H), 7.43-7.30 (m,
12H), 7.24 (t, J ) 7.8 Hz, 1H), 6.64 (s, 2H), 6.61 (s, 1H), 5.08 (s,
4H), 4.62 (s, 2H), 4.54 (s, 2H); 19F NMR (δ, DMSO, 470 MHz):
-108.40 to -108.47 (m, JHF ) 9.4 Hz, JHF )18.8 Hz, 1F), -111.78
to -111.84 (dd, JHF ) 9.4 Hz, JHF ) 18.8 Hz, 1F). 13C NMR (δ,
CDCl3, 125 MHz): 163.99, 163.89, 162.01, 161.91, 161.46, 161.37,
160.03, 159.47, 159.37,152.18, 150.18, 148.88, 140.90, 137.45,
132.76, 128.82, 128.22, 128.05, 124.16, 122.13, 122.06, 121.32,
112.57, 112.41, 106.84, 105.18, 104.97, 104.76, 101.60, 72.28,
70.18, 69.78; m/z [MALDI: CHCA]: 523.2 (M+); Anal. Calcd for
C33H27F2NO3 (%): C 75.70, H 5.20, N 2.68; Found: C 75.36, H
5.11, N 2.69.
dfp-G2. Yield: 70%: 1H NMR (δ, DMSO, 500 MHz): 8.66
(d, J ) 5.0 Hz, 1H), 8.02-7.99 (m, 1H), 7.73 (s,1H), 7.42-7.30
(m, 22H), 7.20 (m, 1H), 6.69 (s, 4H), 6.63- 6.60 (m, 5H), 5.06 (s,
8H), 5.01 (s, 4H), 4.62 (s, 2H), 4.54 (s, 2H), 19F NMR (δ, DMSO,
470 MHz): -108.38 to -108.45 (m, JHF ) 9.4 Hz, JHF ) 18.8
Hz, 1F), -111.73 to -111.79 (dd, JHF ) 9.4 Hz, JHF ) 18.8 Hz,
1F). 13C NMR (δ, DMSO, 100 MHz): 163.97, 163.87, 161.99,
161.89, 161.45, 161.35, 160.04, 159.93, 159.45, 159.35, 152.17,
150.19, 148.89, 140.89, 139.91, 137.38, 132.76, 132.71, 128.83,
128.26, 128.12, 124.14, 124.07, 122.14, 122.07, 121.31, 112.58,
112.41, 106.91, 105.19, 104.98, 104.77, 101.58, 72.27, 70.16, 69.80,
69.58; m/z [MALDI: CHCA]: 948.8 (M+); Anal. Calcd for
C61H51F2NO7(%): C 77.28, H 5.42, N 1.48; Found: C 76.66, H
5.72, N 1.13.
Cyclometalated Iridium Dendrimers Ir(dfp-Gn)2(pico), Ir-
(ppy-Gn)2(acac), and Ir(btp-Gn)2(acac) (n ) 1,2). According to
the Nonoyama’s method,50 cyclometalated Ir(III) µ-chloro-bridged
dimers of a general formula (C∧N)2Ir(µ-Cl)2Ir(C∧N)2 were synthe-
sized by refluxing IrCl3‚nH2O with 2.5 equiv of cyclometalating
ligands dpf-Gn, ppy-Gn, or btp-Gn in a mixture of 2-ethoxyethanol
and water (3:1, v/v).
Ir(dfp)2(pico), Ir(ppy)2(acac), and Ir(btp)2(acac) were prepared
according to previous procedures.2,10,14
General Procedure for Synthesis of the Iridium Complexes
Ir(dfp-Gn)2(pico). The corresponding chloro-bridged dimer com-
plex (dfp-Gn)2Ir(µ-Cl)2Ir(dfp-Gn)2 (0.08 mmol), 0.2 mmol of
picolinic acid, and 85-90 mg of sodium carbonate were refluxed
in an inert atmosphere in 2-ethoxyethanol for 10-12 h. After
cooling to room temperature, a colored precipitate was filtered off
and washed with water and ether. The crude product was flash
chromatographed on a silica column with THF/hexane mobile
phase, and the pure iridium complexes Ir(dfp-Gn)2(pico) were
obtained with a yield of ∼60% after solvent evaporation and drying.
1
Ir(dfp-G1)2(pico). Yellow solid, yield: 60%; H NMR (δ, d6-
DMSO, 500 MHz): 8.50 (d, J ) 6.0 Hz, 1H), 8.26 (s, 1H), 8.21
(s, 1H), 8.13 (m, 2H), 7.72 (m, 1H), 7.57 (m, 1H), 7.42 (m, 1H),
7.37-7.23 (m, 22H), 6.75-6.84 (m, 2H), 6.67-6.61 (m, 6H), 5.77
(d, J ) 8.1 Hz, 1H), 5.55 (d, J ) 8.1 Hz, 1H), 5.09 (s, 8H), 4.80
5526 Inorganic Chemistry, Vol. 46, No. 14, 2007

Dendritic Ir(III) Complexes with Pyridine-Based Ligands
(d, 4H), 4.59 (d, J ) 6.2 Hz, 4H); 19F NMR (d6-DMSO, 470
MHz): -106.66 to 106.68 (d, JHF ) 9.4 Hz, 1F), -107.44 to 107.46
(d, JHF ) 9.4 Hz, 1F), -108.83 (s, 1F), -109.37 (s, 1F); m/z
[MALDI: DI]: 1466.5 (M + Ag+); Anal. Calcd for C72H56N3O8F4-
Ir(%): C 63.61, H 4.15, N 3.09 Found: C 63.25, H 4.33, N 2.64;
TGA (5%): 332.6 °C.
(s, 4H), 4.64 (s, 4H), 1.73 (s, 6H); m/z [MALDI: DI]: 2113.7 (M+),
2221.7 (M + Ag+); Anal. Calcd for C127H111N2O16Ir (%): C 72.17,
N 1.33, H 5.29; Found: C 72.16, N 1.05, H 5.16; TGA (5%):
324.2 °C.
1
Ir(btp-G1)2(acac). Brown-red solid, yield: 60%. H NMR (δ,
CDCl3, 400 MHz): 8.38 (d, J ) 6.0 Hz, 2H), 7.60 (s, 3H), 7.58 (s,
1H), 7.44-7.30 (m, 20H), 7.04 (t, J ) 8.0 Hz, 2H), 6.99 (d, J )
6.0 Hz, 2H), 6.82 (t, J ) 7.6 Hz, 2H), 6.71 (d, J ) 2.4 Hz, 4H),
6.63 (t, J ) 2.4 Hz, 2H), 6.26 (d, J ) 8.4 Hz, 2H), 5.25 (s, 1H),
5.09 (s, 8H), 4.78 (s, 4H), 4.68 (s, 4H), 1.77 (s, 6H); m/z [MALDI:
DI]: 1376.1 (M+), 1484.2 (M + Ag+); Anal. Calcd for C75H63N2O8-
IrS2 (%): C 65.43, N 2.03, H 4.61; Found: C 65.34, N 2.11, H
4.63; TGA (5%): 289.5 °C.
1
Ir(dfp-G2)2(pico). Yellow solid, yield: 65%; H NMR (δ, d6-
DMSO, 500 MHz): 8.48 (d, J ) 6.0 Hz, 1H), 8.25 (s, 1H), 8.20
(s, 1H), 8.07 (m, 2H), 7.68 (m, 1H), 7.55-7.53 (m, 2H), 7.39-
7.23 (m, 42H), 6.68∼6.60 (m, 20H), 5.75 (d, J ) 8.0 Hz, 1H),
5.53 (d, J ) 8.1 Hz, 1H), 5.05 (s, 16H), 5.00 (s, 8H), 4.81-4.78
(m, 4H), 4.59 (d, J ) 7.0 Hz, 4H); 19F NMR (d6-DMSO, 470
MHz): -106.57 to 106.58 (d, JHF ) 9.4 Hz, 1F), -107.35 to 107.37
(d, JHF ) 9.4 Hz, 1F), -108.81 (s, 1F), -109.35 (s, 1F); m/z
[MALDI: DI]: 2317.4 (M + Ag+); Anal. Calcd for C128H104N3O16F4-
Ir(%): C 69.61, H 4.75, N 1.90; Found: C 68.85, H 4.79, N 1.44;
TGA (5%): 337.5 °C.
General Procedure for Synthesis of the Iridium Complexes
Ir(C∧N)2(acac). The corresponding chloro-bridged dimer complex
(0.08 mmol), 0.2 mmol of acetyl acetone, and 85-90 mg of sodium
carbonate were refluxed in an inert atmosphere in 2-ethoxyethanol
for 10-12 h. After cooling to room temperature, a colored
precipitate was filtered off and washed with water, hexane, and
ether. The crude product was flash chromatographed on a silica
column with a dichloromethane mobile phase, and the pure iridium
complexes Ir(C∧N)2(acac) were obtained with a yield of 40-70%
after solvent evaporation and drying.
Ir(ppy-G1)2(acac). Yellow solid, yield: 45%: 1H NMR (δ,
CDCl3, 400 MHz): 8.45 (d, J ) 5.6 Hz, 2H), 7.80 (s, 2H), 7.55
(d, J ) 7.6 Hz, 2H), 7.43-7.29 (m, 20H), 7.09 (d, J ) 6.0 Hz,
2H), 6.79 (t, J ) 7.6 Hz, 2H), 6.68 (m, 6H), 6.60 (s, 2H), 6.28 (d,
J ) 7.2 Hz, 2H), 5.20 (s, 1H), 5.07 (s, 8H), 4.71(s, 4H), 4.64 (s,
4H), 1.77 (s, 6H); m/z [MALDI: DI]: 1264.5 (M+), 1372.2 (M +
Ag+); Anal. Calcd for C71H63N2O8Ir (%): C 67.44, H 5.02, N 2.22,
Found: C 67.00, H 4.99, N 2.26; TGA (5%): 306.6 °C.
Ir(ppy-G2)2(acac). Yellow solid, yield: 40%: 1H NMR (δ,
CDCl3, 400 MHz): 8.45 (d, J ) 6.0 Hz, 2H), 7.78 (s, 2H), 7.52
(d, J ) 7.6 Hz, 2H), 7.41-7.29 (m, 40H), 7.10 (d, J ) 6.0 Hz,
2H), 6.75 (t, J ) 7.2 Hz, 2H), 6.67 (m, 14H), 6.58 (m, 6H), 6.28
(d, J ) 7.6 Hz, 2H), 5.17 (s, 1H), 5.01 (s,16H), 5.00 (s, 8H), 4.72
1
Ir(btp-G2)2(acac). Brown-red solid, yield: 60%. H NMR (δ,
CDCl3, 400 MHz): 8.38 (d, J ) 6.0 Hz, 2H), 7.61 (s, 2H), 7.56
(d, J ) 8.0 Hz, 2H), 7.40-7.29 (m, 40H), 6.99-6.95 (m, 4H),
6.78-6.68 (m, 14H), 6.60 (s,2H), 6.57 (s, 4H), 6.26 (d, J ) 8.0
Hz, 2H), 5.22 (s, 1H), 5.02 (s, 8H), 5.00 (s, 16H), 4.80 (s, 4H),
4.68 (s, 4H), 1.74 (s, 6H); m/z [MALDI: DI]: 2226.7 (M+), 2334.7
(M + Ag+); Anal. Calcd for C131H111N2O16IrS2 (%): C 70.69,
N 1.26, H 5.03; Found: C 70.84, N 1.29, H 5.08; TGA (5%):
315.5 °C.
Acknowledgment. The authors are thankful for financial
support from National Science Foundation of China (20490210
and 20501006), National High Technology Program of China
(2006AA03Z318), Shanghai Sci. Tech. Comm. (05DJ14004
and 06QH14002) and Huo Yingdong Education Foundation
(104012).
Supporting Information Available: I-V-L characteristics and
electroluminescent spectra for the PLED device with the config-
uration of ITO/PEDOT/PSS/PVK (40 nm)/PFO+PBD (30 wt %)/
x% Ir-complex (80 nm)/Ba (4 nm)/Al (120 nm) based on the
phosphorescent emitters Ir(ppy-Gn)2(acac) and Ir(btp-Gn)2(acac).
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC062041N
Inorganic Chemistry, Vol. 46, No. 14, 2007 5527