N -heterocyclic carbenes: Versatile second cyclometalated ligands for neutral iridium(III) heteroleptic complexes

Article abstract of DOI:10.1021/ic501949h

With 2-(2,4-difluorophenyl)pyridine (dfppy) as the first cyclometalated ligand and different monoanionic N-heterocyclic carbenes (NHCs) as the second cyclometalated ligands, 16 blue or greenish-blue neutral iridium(III) phosphorescent complexes, (dfppy)

Full text of DOI:10.1021/ic501949h

Article
pubs.acs.org/IC
N‑Heterocyclic Carbenes: Versatile Second Cyclometalated Ligands
for Neutral Iridium(III) Heteroleptic Complexes
†
†
‡
†
†
†
†
Tian-Yi Li, Xiao Liang, Liang Zhou, Chen Wu, Song Zhang, Xuan Liu, Guang-Zhao Lu,
†
,†
†
Li-Sha Xue, You-Xuan Zheng,* and Jing-Lin Zuo
†State Key Laboratory of Coordination Chemistry, Collaborative Innovation Center of Advanced Microstructures, Center for
Molecular Organic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China
‡
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun, 130022, P. R. China
*
S Supporting Information
ABSTRACT: With 2-(2,4-difluorophenyl)pyridine (dfppy) as
the first cyclometalated ligand and different monoanionic N-
heterocyclic carbenes (NHCs) as the second cyclometalated
ligands, 16 blue or greenish-blue neutral iridium(III)
phosphorescent complexes, (dfppy) Ir(NHC), were synthe-
2
sized efficiently. The obtained Ir(III) complexes display typical
phosphorescence of 455−485 nm with quantum yields up to
0
.73. By modifying the phenyl moiety in the NHCs with
electron-withdrawing substituents (e.g., −F or −CF ) or
3
replacing it with N-heteroaromatic rings (pyridine or
pyrimidine), the HOMO−LUMO gaps are broadened, and
the emissions shift to the more blue region accordingly.
Furthermore, to extend the application scope of NHCs as the
second cyclometalated ligands, five other Ir(III) complexes
from blue to red were synthesized with different first
cyclometalated ligands. Finally, the organic light-emitting
diodes using one blue emitter exhibit a maximum current
−1
efficiency of 37.83 cd A , an external quantum efficiency of
−2
1
0.3%, and a maximum luminance of 8709 cd m . Our results demonstrate that NHCs as the second cyclometalated ligands are
good candidates for the achievement of efficient phosphorescent Ir(III) complexes and corresponding devices.
1
. INTRODUCTION
phenyl ring with pyridine was effectual. According to the
4
structure−property relationship, Yang and co-workers devel-
Phosphorescent iridium(III) complexes are the favorable
choices for organic light-emitting diodes (OLEDs) due to the
high efficiency and stability. With active design of ligands,
phosphorescent Ir(III) complexes could exhibit a wide emission
range from near-ultraviolet to red. Recently, many high-
performance single-color and white devices employing Ir(III)
phosphors as emissive dopants have been reported. However,
the research on blue Ir(III) complexes is still vital because the
devices with such emitters seldom show satisfying performances
owing to the inherent contradiction between emission energy
and photoluminescent quantum yield (PLQY).
From greenish-blue to deep blue, the seeking for blue
materials is continuous and tough. Since the frontier molecular
orbitals (FMOs), especially the highest occupied molecular
oped blue Ir(III) complexes with fluorinated 1,3,4-oxadiazole
5
1
derivatives as cyclometalated ligands. Kang and co-workers
reported a blue homoleptic complex Ir(dfpypy) containing
3
2
fluorine-substituted bipyridine ligand of 2′,6′-difluoro-2,3′-
6
bipyridine. Another strategy is to increase the LUMO energies
3
by introducing the electron-donating groups into the pyridine
ring. Wu and co-workers introduced electron-donating
methoxy groups into the pyridine ring and achieve emission
7
at 452 nm. Using bipyridine ligand with methyl substitute,
Kido and co-workers reported a pure blue emitter and the
relevant devices, whose emission peak is at 454 nm with high
1−
power efficiency (30 lm W ) and external quantum efficiency
8
(
17%). Replacement of pyridyl fragment in phenylpyridine
ligands with other N-heterocyclic moieties, such as pyrazole,
triazole, imidazole, have also been proved an efficient way to
achieve blue emitters, since the LUMO energy levels are high
orbital (HOMO) and the lowest unoccupied molecular orbital
4
(
LUMO), are crucial for the photophysical properties, some
popular strategies aiming to broaden the HOMO−LUMO gap
are adopted to tune the emission to blue. To lower the HOMO
energy of Ir(III) complexes, attaching the electron withdrawing
moieties to the cyclometalated phenyl ring or replacing the
Received: August 13, 2014
Published: December 11, 2014
©
2014 American Chemical Society
161
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
Scheme 1. Chemical Structures and Synthetic Routes of the Ligands and Complexes
9
enough for blue emission in these materials. De Cola and co-
workers synthesized a series blue emitters with bipyridine main
ligand and pyridyl−azole ancillary ligands. They display
efficient genuine blue phosphorescence at ∼440 nm at room
phenylpyridine derivatives. The use of a dimer precursor [Ir(μ-
Cl)(COD) ] (COD = 1,5-cyclooctadiene) was reported with
2
2
18
high yields for the synthesis of some Ir(NHC)
but the mixed fac/mer-Ir(NHC) products with similar polarity
hindered the further development.
In this study, with N-heteroleptic carbenes as the second
complexes,
3
3
10
temperature with high quantum yield. As reported by our
group and others, although most ancillary ligands do not make
a contribution to the lowest excited state directly, ancillary
ligands with strong fields can help to increase the HOMO−
LUMO energy gap and improve the device performances. For
example, iridium(III)bis(4,6-difluorophenyl-pyridinato)-
cyclometalated ligands, a series of new type of (C^N) Ir(NHC)
2
phosphors were synthesized efficiently. First, using dfppy (2-
11
(
1
2,4-difluorophenyl)pyridine) as the first cyclometalated ligand,
6 blue or greenish-blue complexes were obtained in good
1
2
yields (Scheme 1). Considering that the NHCs have noticeable
contributions to the HOMOs of the complexes, the NHCs
were modified with phenyl, naphthalene, electron-withdrawing
substituents, and N-heteroaromatic rings to investigate the
relationship between the ligand structures and the photo-
physical properties. Second, by changing the first cyclo-
metalated ligands, another five Ir(III) complexes from blue to
red were synthesized. Finally, the OLEDs constructed with one
blue emitter of them show interesting performances. Hence, we
found a much easier and efficient method to introduce precious
NHC ligands into neutral iridium phosphors, and our results
picolinate (FIrpic)
and iridium(III)bis(4,6-difluoro-
13
phenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6) are effi-
cient blue emitters due to their distinctive ancillary ligands.
With the σ-donating N-heterocyclic carbene ligands (NHCs),
Ir(III) complexes with high triplet energy gaps can be used as
blue emitters for OLEDs and electrochemical cells. Thompson
and Forrest first reported the facial and meridional isomers fac/
mer-Ir(pmb)3 and fac/mer-Ir(pmi)3 (pmb = 1-phenyl-3-
methylbenzimidazole, pmi = 1-phenyl-3-methyl imidazole)
exhibiting luminescence at ca. 380 nm. Chi and co-workers
reported the (dfbmb) Ir(fptz) (dfbmb = 1-(2,4-difluoroben-
zyl)-3-methylbenzimidazolium, fptz = 2-(3-(trifluoromethyl)-
H-1,2,4-triazol-5-yl)pyridine) complex with a pyridyl triazole
14
2
demonstrate that the (C^N) Ir(NHC) configuration is a
2
versatile and promising structure for interesting neutral
phosphorescent Ir(III) complexes.
1
ancillary ligand showing emission at 458 nm with a high
15
quantum yield of 0.73. Cheng and co-workers focused on
neutral bis-carbene Ir(III) complexes, which covered a wide
range of emission color from red to blue by changing the
ancillary ligands. Recently, Baranoff and co-workers success-
fully synthesized charged iridium complexes presenting fine-
tunable emissions from near-UV to red with different
cyclometalated ligands and found that the NHCs show a
2
. EXPERIMENTAL SECTION
General Information. An electrospray ionization (ESI) mass
spectrometer (LCQ fleet, Thermo Fisher Scientific) was used to
record mass spectra (MS) for the carbene ligands. High-resolution
1
6
(
HR) mass spectra (Agilent 6540 UHD Accurate-Mass Q-TOF LC/
1
MS) were recorded for the complexes. H NMR spectra were
measured on a Bruker AM 500 spectrometer. UV−visible absorption
and photoluminescence spectra were obtained using a Shimadzu UV-
17
subsidiary tunable effect on the emission color.
3
100 and a Hitachi F-4600 spectrophotometer, respectively. The
However, because of the difficulty of synthesis, in the past
decade only several neutral carbene-based Ir(III) complexes
have been reported, and few emitters showed interesting device
phosphorescence quantum yields were determined in nitrogen-
deaerated CH Cl2 solutions at 298 K against fac-Ir(ppy) as a
2
3
19
reference (Φ = 0.40). The decay lifetimes were determined on an
Edinburgh Instruments FLS-920 fluorescence spectrometer in
P
performances. The direct synthetic route for Ir(NHC) starting
3
from carbene iodized salt precursors and IrCl ·3H O resulted in
degassed CH Cl2 solutions at room temperature. A conventional
3
2
2
a lower yield compared with the moderately high yield of
three-electrode configuration, consisting of a polished Pt plate working
1
62
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
a
electrode, a Pt wire counter electrode, and a reference electrode of Ag/
Scheme 2
AgNO (0.1 M) in MeCN, was used to record cyclic voltammetry data
3
in nitrogen-deaerated CH CN solution with 0.1 M [Bu N]ClO as the
3
4
4
supporting electrolyte and ferrocene as internal standard at a scan rate
−1
of 50 mV s . The HOMO and LUMO energy levels were calculated
using the equation HOMO (eV) = Eox − EFc/Fc+ + 4.8 and LUMO
(
eV) = Ered − E
+ 4.8.
Fc/Fc+
X-ray Crystallography. The crystallographic data were collected
on a Siemens SMART CCD diffractometer (Bruker Daltonic Inc.) at
room temperature using graphite-monochromated Mo Kα radiation (λ
=
0.710 73 Å). The cell parameters were retrieved using SMART
20
software and refined using SAINT on all observed reflections.
Absorption corrections were performed with SADABS supplied by
21
Bruker. All the calculations for the structure determination were
22
carried out using the SHELXTL package. Initial atomic positions
were located by Patterson method using XS program, and the
structures of the complexes were refined anisotropically by the least-
squares method. Hydrogen atoms were fixed in calculated positions
and refined as riding atoms with uniform Uiso values.
Theoretical Calculation. The density functional theory (DFT)
and time-dependent DFT (TD-DFT) calculations were carried out
23
with Gaussian 09 software package. The geometries of the ground
state (S ) were fully optimized with the B3LYP exchange-correlation
0
24
25
functional using the LANL2DZ basis set for iridium atom and the
-31G** basis set for the other atoms both in vacuum and in
CH Cl (C-PCM solvent model). Vibrational frequency calculations
2
6
6
27
2
2
were performed to validate that they are minima on potential energy
surface. On the basis of the optimized S molecular structures in
0
2
8
solvent, TD-DFT calculation was performed, with M062x functional
and the same combination of basis sets, to determine the vertical
transition characters and to simulate the UV−vis absorption spectra.
Solvent effect was also considered by using C-PCM model. Frontier
molecular orbitals were visualized using GaussView, and their
quantified compositions in percentage on different parts were given
by QMForge. GaussSum 2.2 was used to broaden the vertical
transitions into simulated spectra, which were then compared with
experimental data through Gaussian distribution with full width at half-
a
(
a) The chemical structures and the synthetic routes of iridium
complexes with different C^N cyclometalated ligands and L5a
precursor. (b) The chemical structures of the reported iridium
complexes cited in Table 2.
−1
maximum = 4000 cm .
the intermediate product and the same molar quantity of CH I were
3
Fabrication of the OLEDs Device. Indium tin oxide (ITO)
dissolved in 5 mL of tetrahydrofuran (THF) and stirred for 12 h. The
NHC precursor as iodized salt was filtered and washed with THF
giving the product as white powder.
−1
coated glass with a sheet resistance of 15 Ω sq was used as the anode
substrate. Successively, 1,1-bis(4-(di-p-tolylamino)phenyl)cyclohexane
(
3
TAPC, 40 nm), phosphorescent emitter doped in N,N′-dicarbazolyl-
,5-benzene host (mCP, 20 nm), 1,3,5-tri(m-pyrid-3-yl-phenyl)-
L1a. 2-Bromonaphthalene (4.12 g) and 1.18 g of benzimidazole
1
gave 1.79 g of product (yield: 46%). H NMR (500 MHz, deuterated
benzene (TmPyPB,40 nm), LiF (1 nm), and Al (100 nm) were
evaporated on the substrate. Current density−voltage−luminance (J−
V−L) characteristics were measured by using a programmable Keithley
source measurement unit (Keithley 2400 and Keithley 2000) with a
silicon photodiode.
Synthesis and Characterization. All the synthesis experiments
were carried out under nitrogen, and solvents were dried prior to use.
All the μ-chloro-bridged dimer complexes used in this work, namely,
dimethylsulfoxide (DMSO-d )) δ 10.29 (s, 1H), 8.48 (s, 1H), 8.34 (d,
6
J = 8.7 Hz, 1H), 8.19 (dd, J = 18.9, 7.0 Hz, 3H), 7.95 (dd, J = 15.7, 5.0
Hz, 2H), 7.78 (ddd, J = 13.9, 12.1, 7.0 Hz, 4H), 4.24 (s, 3H). MS
+
+
(ESI): calcd. for [M − I] (C H N ) m/z = 259.12, found 259.25.
18
15
2
L1b. 2-Bromonaphthalene (4.12 g) and 0.68 g of imidazole gave
2.17 g of product (yield: 65%). H NMR (500 MHz, DMSO-d ) δ
1
6
9.95 (s, 1H), 8.44 (s, 2H), 8.24 (d, J = 8.8 Hz, 1H), 8.06 (dd, J = 17.1,
10.4 Hz, 3H), 7.90 (d, J = 8.8 Hz, 1H), 7.68 (dq, J = 13.2, 6.5 Hz, 2H),
+
+
2
[
(
(
(
(dfppy) Ir(μ-Cl)] , [(4-tfmpiq) Ir(μ-Cl)] (4-tfmpiq = 1-(4-
4.02 (s, 3H). MS (ESI): calcd. for [M − I] (C H N ) m/z =
2
2
2
2
14 13
trifluoromethyl)phenyl)isoquinoline), [(dbthppy) Ir(μ-Cl)]2
209.11, found 209.17.
2
dbthppy = 2-(dibenzo[b,d]thiophen-4-yl)pyridine), [(4-tfmppy) Ir-
L2a. Bromobenzene (3.12 g) and 1.18 g of benzimidazole gave 1.65
2
1
μ-Cl)]2 (4-tfmppy = 2-(4-(trifluoromethyl)phenyl)pyridine), [(3-
g of product (yield: 49%). H NMR (500 MHz, DMSO-d ) δ 10.15 (s,
6
tfmppy) Ir(μ-Cl)]2 (3-tfmppy = 2-(3-(trifluoromethyl)phenyl)-
1H), 8.17 (d, J = 8.3 Hz, 1H), 7.89−7.68 (m, 8H), 4.19 (s, 3H). MS
2
+
+
pyridine), and [(dfpypy) Ir(μ-Cl)] , were synthesized according to
(ESI): calcd. for [M − I] (C H N ) m/z = 209.11, found 209.25.
2
2
14 13
2
the reported methods by heating IrCl ·3H O (1 equiv) and relevant
L2b. Bromobenzene (3.12 g) and 0.68 g of imidazole gave 1.37 g of
product (yield: 48%). H NMR (500 MHz, DMSO-d ) δ 9.82 (s, 1H),
3
2
1
cyclometalated ligand (2.2 equiv) in 2-ethoxyethanol and water (v/v =
6
2
9
3
/1) at 110 °C. Chemical structures and synthetic procedures of the
8.31 (s, 1H), 7.99 (s, 1H), 7.80 (d, J = 7.7 Hz, 2H), 7.67 (t, J = 7.8 Hz,
2H), 7.59 (t, J = 7.4 Hz, 1H), 3.98 (s, 3H). MS (ESI): calcd. for [M −
Ir(III) complexes (Ir1a-Ir8a/Ir1b-Ir8b and Ir9-Ir13) are shown in
+
+
Schemes 1 and 2.
I] (C H N ) m/z = 159.09, found 159.17.
10
11
2
General Synthesis of Carbene Precursors. A mixture of
benzimidazole or imidazole (10.0 mmol), brominated benzene
L3a. 1-Bromo-4-fluorobenzene (3.48 g) and 1.18 g of benzimida-
zole gave 1.66 g of product (yield: 47%). 1H NMR (500 MHz,
derivative (20.0 mmol), K CO3 (20.0 mmol, 2.76 g), CuI (1.0
DMSO-d ) δ 10.14 (s, 1H), 8.17 (d, J = 8.1 Hz, 1H), 7.92 (dd, J = 8.2,
2
6
mmol, 0.19 g), 18-crown-6 (0.10 g), and DMPU (1,3-dimethyl-3,4,5,6-
tetrahydro-2(1H)-pyrimidinone, 3 mL) was heated at 190 °C for 12 h
in a sealed stainless reactor under nitrogen. The mixture was extracted
with 200 mL of ethyl ether, and column chromatography (eluent =
ethyl ether/hexane 1:1.5 v/v) gave the intermediate product. Then,
4.6 Hz, 2H), 7.77 (dt, J = 15.3, 8.0 Hz, 3H), 7.64 (t, J = 8.5 Hz, 2H),
+
+
4.19 (s, 3H). MS (ESI): calcd. for [M − I] (C H FN ) m/z =
14
12
2
227.10, found 227.25.
L3b. 1-Bromo-4-fluorobenzene (3.48 g) and 0.68 g of imidazole
1
gave 1.47 g of product (yield: 48%). H NMR (500 MHz, DMSO-d )
6
1
63
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
δ 9.74 (s, 1H), 8.26 (s, 1H), 7.96 (s, 1H), 7.85 (dd, J = 8.8, 4.5 Hz,
8.0 Hz, 1H), 8.18 (d, J = 8.2 Hz, 1H), 8.14 (d, J = 5.3 Hz, 1H), 8.02 (t,
J = 7.1 Hz, 2H), 7.86−7.75 (m, 2H), 7.64 (d, J = 7.8 Hz, 1H), 7.53 (t,
J = 7.6 Hz, 1H), 7.45 (t, J = 7.6 Hz, 1H), 7.30 (dd, J = 19.7, 7.4 Hz,
2H), 7.26−7.19 (m, 1H), 6.98 (s, 3H), 6.82−6.66 (m, 2H), 6.05 (d, J
= 7.5 Hz, 1H), 5.66 (d, J = 8.1 Hz, 1H), 3.45 (s, 3H). HR electron
2
H), 7.56 (t, J = 8.7 Hz, 2H), 3.96 (s, 3H). MS (ESI): calcd. for [M −
+ +
I] (C H FN ) m/z = 177.08, found 177.17.
10
10
2
L4a. 1-Bromo-4-(trifluoromethyl)benzene (4.48 g) and 1.18 g of
1
benzimidazole gave 2.13 g of product (yield: 53%). H NMR (500
+
+
MHz, DMSO-d ) δ 10.25 (s, 1H), 8.19 (d, J = 8.4 Hz, 3H), 8.11 (d, J
impact (EI) MS Calcd: m/z 831.1717 for [M + H] (C H F IrN ),
6
40 26 4 4
=
8.3 Hz, 2H), 7.94 (d, J = 8.3 Hz, 1H), 7.80 (dt, J = 29.0, 7.5 Hz,
found: m/z 831.1714.
+
+
2
=
H), 4.22 (s, 3H). MS (ESI): calcd. for [M − I] (C H F N ) m/z
Ir1b. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.27 g L1b, and 0.16 g of
15
12
3
2
2
1
277.09, found 277.25.
L4b. 1-Bromo-4-(trifluoromethyl)benzene (4.48 g) and 0.68 g of
silver(I) oxide gave 0.25 g of product(yield: 41%). H NMR (500
MHz, DMSO-d ) δ 8.27 (d, J = 41.1 Hz, 3H), 8.16 (d, J = 7.7 Hz, 1H),
6
1
imidazole gave 2.17 g of product (yield: 61%). H NMR (500 MHz,
7.97 (t, J = 28.4 Hz, 3H), 7.88−7.75 (m, 2H), 7.67 (dd, J = 42.5, 24.4
Hz, 2H), 7.39−7.30 (m, 1H), 7.30−7.22 (m, 1H), 7.20 (d, J = 6.9 Hz,
1H), 7.04 (dd, J = 26.8, 18.9 Hz, 2H), 6.93 (s, 1H), 6.82−6.62 (m,
2H), 5.82−5.65 (m, 1H), 3.31 (s, 3H). HR EI-MS Calcd: m/z
DMSO-d ) δ 9.93 (s, 1H), 8.40 (s, 1H), 8.15−7.98 (m, 5H), 3.99 (s,
6
+
+
2
3
H). MS (ESI): calcd. for [M − I] (C H F N ) m/z = 227.08,
11
10
3
found 227.17.
+
+
L5a. 1-Bromo-3-(trifluoromethyl)benzene (4.48 g) and 1.18 g of
781.1561 for [M + H] (C H F IrN ), found: m/z 781.1561.
36 24 4 4
1
benzimidazole gave 1.83 g of product (yield: 45%). H NMR (500
MHz, DMSO-d ) δ 10.23 (s, 1H), 8.29 (s, 1H), 8.20 (t, J = 9.1 Hz,
Ir2a. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.30 g L2a, and 0.16 g of
2
1
silver(I) oxide gave 0.37 g of product (yield: 60%). H NMR (500
6
2
H), 8.13 (d, J = 7.8 Hz, 1H), 8.03 (t, J = 7.9 Hz, 1H), 7.89 (d, J = 8.3
MHz, DMSO-d ) δ 8.40 (d, J = 7.7 Hz, 1H), 8.25 (dd, J = 15.9, 8.5 Hz,
6
Hz, 1H), 7.86−7.79 (m, 1H), 7.79−7.71 (m, 1H), 4.21 (s, 3H). MS
2H), 8.08 (d, J = 5.3 Hz, 1H), 7.99 (dd, J = 17.2, 6.7 Hz, 2H), 7.84−
7.78 (m, 1H), 7.58 (t, J = 11.6 Hz, 2H), 7.40 (dd, J = 17.5, 9.9 Hz,
2H), 7.10−6.96 (m, 3H), 6.78 (t, J = 6.7 Hz, 1H), 6.70 (t, J = 11.0 Hz,
2H), 6.62 (d, J = 7.3 Hz, 1H), 6.03 (d, J = 7.4 Hz, 1H), 5.59 (d, J = 7.9
+
+
(
ESI): calcd. for [M − I] (C H F N ) m/z = 277.09, found 277.25.
15
12
3
2
L5b. 1-Bromo-3-(trifluoromethyl)benzene (4.48 g) and 0.68 g of
1
imidazole gave 1.60 g of product (yield: 45%). H NMR (500 MHz,
DMSO-d ) δ 9.93 (s, 1H), 8.41 (d, J = 1.6 Hz, 1H), 8.25 (s, 1H), 8.14
+
Hz, 1H), 3.42 (s, 3H). HR EI-MS Calcd: m/z 781.1561 for [M + H]
6
+
(
d, J = 7.9 Hz, 1H), 8.04−7.87 (m, 3H), 3.99 (s, 3H). MS (ESI): calcd.
(C H F IrN ), found: m/z 781.1560.
36
24
4
4
+
+
for [M − I] (C H F N ) m/z = 227.08, found 227.17.
Ir2b. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.25 g L2b, and 0.16 g of
11
10
3
2
2
1
L6a. 3-Bromopyridine (3.14 g) and 1.18 g of benzimidazole gave
silver(I) oxide gave 0.38 g of product (yield: 66%). H NMR (500
1
1.25 g of product (yield: 37%). H NMR (500 MHz, DMSO-d ) δ
MHz, DMSO-d ) δ 8.21 (d, J = 8.4 Hz, 1H), 8.14 (d, J = 8.4 Hz, 1H),
6
6
9
.62 (s, 1H), 9.10 (d, J = 5.8 Hz, 1H), 9.00 (d, J = 8.3 Hz, 1H), 8.77
8.04 (s, 1H), 8.00 (d, J = 5.6 Hz, 1H), 7.94 (d, J = 5.7 Hz, 1H), 7.81
(dt, J = 15.7, 7.7 Hz, 2H), 7.46 (d, J = 7.7 Hz, 1H), 7.26 (s, 1H), 7.08−
7.01 (m, 2H), 6.91 (t, J = 7.5 Hz, 1H), 6.72 (t, J = 7.1 Hz, 1H), 6.69−
6.60 (m, 2H), 6.54 (d, J = 7.0 Hz, 1H), 6.00 (d, J = 7.7 Hz, 1H), 5.64
(d, J = 8.3 Hz, 1H), 3.15 (s, 3H). HR EI-MS Calcd: m/z 731.1404 for
(
s, 1H), 8.39 (t, J = 7.1 Hz, 1H), 7.93 (d, J = 8.0 Hz, 1H), 7.86 (d, J =
.7 Hz, 1H), 7.49−7.40 (m, 2H), 4.49 (s, 3H). MS (ESI): calcd. for
7
+
+
[
M − I] (C H N ) m/z = 210.10, found 210.25.
13
12
3
L6b. 3-Bromopyridine (3.14 g) and 0.68 g of imidazole gave 1.38 g
1
+
+
of product (yield: 48%). H NMR (500 MHz, DMSO-d ) δ 9.85 (s,
[M + H] (C H F IrN ), found: m/z 731.1403.
6
32 22 4 4
1
H), 9.04 (d, J = 2.5 Hz, 1H), 8.96 (dd, J = 14.8, 7.2 Hz, 1H), 8.79 (d,
Ir3a. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.31 g L3a, and 0.16 g of
silver(I) oxide gave 0.36 g of product (yield: 56%). H NMR (500
2
1
J = 4.4 Hz, 1H), 8.35 (s, 1H), 8.25 (d, J = 8.2 Hz, 1H), 7.74 (dd, J =
+
8
.2, 4.8 Hz, 1H), 3.99 (s, 3H). MS (ESI): calcd. for [M − I]
MHz, DMSO-d ) δ 8.38 (d, J = 7.6 Hz, 1H), 8.32 (d, J = 7.9 Hz, 1H),
6
+
(C H N ) m/z = 160.09, found 160.25.
8.30−8.22 (m, 2H), 8.22−8.17 (m, 1H), 8.09 (d, J = 5.5 Hz, 1H), 7.93
(d, J = 5.7 Hz, 1H), 7.85 (dd, J = 13.9, 7.1 Hz, 2H), 7.60 (d, J = 7.5
Hz, 2H), 7.47−7.37 (m, 2H), 7.06 (t, J = 6.4 Hz, 1H), 7.01 (t, J = 6.3
Hz, 1H), 6.78 (d, J = 11.2 Hz, 2H), 6.00 (d, J = 7.6 Hz, 1H), 5.60 (d, J
= 8.0 Hz, 1H), 3.41 (s, 3H). HR EI-MS Calcd: m/z 799.1476 for [M +
9
10
3
L7a. 5-Bromopyrimidine (3.16 g) and 1.18 g of benzimidazole gave
1
1.45 g of product (yield: 43%). H NMR (500 MHz, DMSO-d ) δ
6
1
0.29 (s, 1H), 9.53 (s, 1H), 9.40 (s, 2H), 8.21 (d, J = 8.2 Hz, 1H), 8.01
(
d, J = 8.2 Hz, 1H), 7.83 (t, J = 7.7 Hz, 1H), 7.77 (t, J = 7.7 Hz, 1H),
+
+
+
4
2
.25 (s, 3H). MS (ESI): calcd. for [M − I]+ (C12H11N4 ) m/z =
H] (C H F IrN ), found: m/z 799.1473.
36 23 5 4
11.10, found 211.25.
Ir3b. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.27 g L3b, and 0.16 g of
2
1
L7b. 5-Bromopyrimidine (3.16 g) and 0.68 g of imidazole gave 1.15
silver(I) oxide gave 0.32 g of product (yield: 54%). H NMR (500
1
g of product (yield: 40%). H NMR (500 MHz, DMSO-d ) δ 9.90 (s,
MHz, DMSO-d ) δ 8.22 (d, J = 8.0 Hz, 1H), 8.17 (d, J = 8.7 Hz, 1H),
6
6
1
3
1
H), 9.40 (s, 1H), 9.31 (s, 2H), 8.38 (s, 1H), 8.04 (s, 1H), 4.01 (s,
8.04 (s, 1H), 7.94 (dd, J = 11.7, 5.6 Hz, 2H), 7.84 (dd, J = 18.3, 8.0
Hz, 2H), 7.52 (dd, J = 6.8, 4.4 Hz, 1H), 7.27 (s, 1H), 7.08 (t, J = 5.7
Hz, 2H), 6.74−6.61 (m, 3H), 6.15 (d, J = 8.7 Hz, 1H), 5.98 (d, J = 7.7
Hz, 1H), 5.64 (d, J = 8.2 Hz, 1H), 3.14 (s, 3H). HR EI-MS Calcd: m/z
+
+
H). MS (ESI): calcd. for [M − I] (C H N ) m/z = 161.08, found
8
9
4
61.08.
L8a. 5-Bromo-2-(trifluoromethyl)pyrimidine (4.52 g) and 1.18 g of
1
+
+
benzimidazole gave 1.59 g of product (yield: 39%). H NMR (500
749.1310 for [M + H] (C H F IrN ), found: m/z 749.1309.
32 21 5 4
MHz, DMSO-d ) δ 10.25 (s, 1H), 9.63 (s, 2H), 8.22 (d, J = 8.3 Hz,
Ir4a. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.35 g L4a, and 0.16 g of
silver(I) oxide gave 0.40 g of product (yield: 58%). H NMR (500
6
2
1
1
H), 8.11 (d, J = 8.2 Hz, 1H), 7.86−7.81 (m, 2H), 3.32 (s, 3H). MS
+
+
(
ESI): calcd. for [M − I] (C H F N ) m/z = 279.09, found 279.17.
MHz, DMSO-d ) δ 8.44 (d, J = 7.8 Hz, 1H), 8.26 (d, J = 8.5 Hz, 1H),
13
10
3
4
6
L8b. 5-Bromo-2-(trifluoromethyl)pyrimidine (4.52 g) and 0.68 g of
8.19 (d, J = 8.0 Hz, 2H), 8.11 (d, J = 5.5 Hz, 1H), 7.91−7.81 (m, 3H),
7.63 (d, J = 7.6 Hz, 1H), 7.53−7.40 (m, 2H), 7.35 (d, J = 8.0 Hz, 1H),
7.07 (t, J = 6.2 Hz, 1H), 7.01 (t, J = 6.3 Hz, 1H), 6.85 (s, 1H), 6.75
(dd, J = 24.8, 13.0 Hz, 2H), 5.99 (d, J = 7.5 Hz, 1H), 5.60 (d, J = 8.0+
Hz, 1H), 3.44 (s, 3H). HR EI-MS Calcd: m/z 849.1435 for [M + H]
1
imidazole gave 2.06 g of product (yield: 58%). H NMR (500 MHz,
DMSO-d ) δ 10.05 (s, 1H), 9.61 (s, 2H), 8.46 (s, 1H), 8.10 (s, 1H),
6
+
+
4
2
.05 (s, 3H). MS (ESI): calcd. for [M − I] (C H F N ) m/z =
29.07, found 229.17.
General Synthesis of Iridium Complexes. A mixture of the μ-
9
8
3
4
+
(C H F IrN ), found: m/z 849.1435.
37
23
7
4
chloro-bridged dimer (0.4 mmol), the relative NHC precursors (0.88
Ir4b. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.31 g L4b, and 0.16 g of
silver(I) oxide gave 0.33 g of product (yield: 52%). H NMR (500
2
1
mmol) and Ag O (0.70 mmol) was heated at 120 °C in 10 mL of 2-
2
ethoxyethanol for 12 h protected from light. After the distillation of
the solvent, the crude product was dissolved in CH Cl , and gray
MHz, DMSO-d ) δ 8.23 (d, J = 8.1 Hz, 1H), 8.17 (s, 2H), 7.94 (d, J =
6
5.9 Hz, 1H), 7.90−7.80 (m, 3H), 7.67 (d, J = 8.2 Hz, 1H), 7.34 (s,
1H), 7.26 (d, J = 8.0 Hz, 1H), 7.08 (q, J = 6.4 Hz, 2H), 6.79 (s, 1H),
6.75−6.62 (m, 2H), 5.96 (d, J = 7.7 Hz, 1H), 5.65 (d, J = 8.1 Hz, 1H)+,
3.17 (s, 3H). HR EI-MS Calcd: m/z 799.1278 for [M + H]
2
2
precipitate was filtered off. The filtrate was condensed and column
chromatography (eluent = ethyl ether/hexane = 1.5:1 v/v) gave
terminal product as yellow powder. All the target products were
recrystallized from CH Cl and MeOH.
+
(C H F IrN ), found: m/z 799.1278.
2
2
33 21
7
4
Ir1a. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.34 g L1a, and 0.16 g of
silver(I) oxide gave 0.26 g of product (yield: 39%). H NMR (500
Ir5a. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.35 g L5a, and 0.16 g of
silver(I) oxide gave 0.46 g of product (yield: 67%). H NMR (500
2
2
1
1
MHz, DMSO-d ) δ 8.71 (d, J = 8.0 Hz, 1H), 8.50 (s, 1H), 8.25 (d, J =
MHz, DMSO-d ) δ 8.34 (d, J = 8.1 Hz, 1H), 8.25 (d, J = 8.1 Hz, 1H),
6
6
1
64
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
8
7
7
1
1
8
.19 (d, J = 8.1 Hz, 1H), 8.09 (s, 2H), 7.85 (dd, J = 18.3, 5.5 Hz, 3H),
.63 (d, J = 7.8 Hz, 1H), 7.50 (t, J = 7.5 Hz, 1H), 7.47−7.41 (m, 1H),
.12 (d, J = 7.3 Hz, 1H), 7.06 (t, J = 5.6 Hz, 1H), 7.01 (d, J = 5.8 Hz,
H), 6.84 (d, J = 7.2 Hz, 1H), 6.78−6.68 (m, 2H), 5.99 (d, J = 7.4 Hz,
H), 5.59 (d, J = 7.7 Hz, 1H), 3.43 (s, 3H). HR EI-MS Calcd: m/z
= 18.4, 8.2 Hz, 2H), 7.90 (d, J = 5.7 Hz, 1H), 7.69 (d, J = 7.9 Hz, 1H),
7.52 (t, J = 7.7 Hz, 1H), 7.47 (t, J = 7.6 Hz, 1H), 7.17 (dd, J = 13.2, 6.6
Hz, 3H), 6.82 (d, J = 7.4 Hz, 1H), 6.04 (s, 1H), 5.62 (s, 1H), 3.47 (s,
+
+
3H). HR EI-MS Calcd: m/z 851.1340 for [M + H] (C H F IrN ),
3
5
21
7
6
found: m/z 851.1339.
(3-tfmppy) Ir(L5a) (Ir10). [(3-tfmppy) Ir(μ-Cl)] (0.53 g), 0.35 g
+
+
49.1435 for [M + H] (C H F IrN ), found: m/z 849.1433.
37
23
7
4
2
2
2
Ir5b. [(dfppy) Ir(μ-Cl)]2 (0.49 g), 0.31 g L5b, and 0.16 g of
of L5a, and 0.16 g of silver(I) oxide gave 0.47 g of product (yield:
2
1
1
silver(I) oxide gave 0.38 g of product (yield: 59%). H NMR (500
64%). H NMR (500 MHz, DMSO-d ) δ 8.40 (d, J = 7.7 Hz, 1H),
6
MHz, DMSO-d ) δ 8.28 (s, 1H), 8.23 (d, J = 8.6 Hz, 1H), 8.16 (d, J =
8.33 (d, J = 6.3 Hz, 2H), 8.21 (s, 1H), 8.14−8.05 (m, 3H), 8.00 (t, J =
8.7 Hz, 1H), 7.86−7.79 (m, 1H), 7.59 (dd, J = 16.5, 8.9 Hz, 2H), 7.43
(dd, J = 13.6, 6.5 Hz, 2H), 7.10 (dd, J = 21.3, 11.5 Hz, 3H), 7.05−6.99
(m, 2H), 6.98−6.91 (m, 1H), 6.82−6.71 (m, 1H), 6.34 (dd, J = 19.3,
7.6 Hz, 1H), 3.36 (s, 3H). HR EI-MS Calcd: m/z 913.1559 for [M +
6
7.9 Hz, 1H), 7.92 (d, J = 5.6 Hz, 1H), 7.88 (d, J = 5.7 Hz, 1H), 7.84 (t,
J = 11.8 Hz, 3H), 7.32 (s, 1H), 7.08 (dd, J = 12.7, 6.5 Hz, 2H), 7.04 (d,
J = 7.5 Hz, 1H), 6.75 (d, J = 7.5 Hz, 1H), 6.68 (dd, J = 22.2, 11.5 Hz,
2
H), 5.96 (d, J = 7.7 Hz, 1H), 5.64 (d, J = 8.2 Hz, 1H), 3.16 (s, 3H).
+
+
+
+
HR EI-MS Calcd: m/z 799.1278 for [M + H] (C H F IrN ),
H] (C39
(4-tfmppy)
of L5a, and 0.16 g of silver(I) oxide gave 0.49 g of product (yield:
H
25
F
2
9
IrN
4
), found: m/z 913.1561.
Ir(μ-Cl)] (0.53 g), 0.35 g
2
33
21
7
4
found: m/z 799.1279.
Ir6a. [(dfppy) Ir(μ-Cl)] (0.49 g), 0.30 g of L6a, and 0.16 g of
Ir(L5a) (Ir11). [(4-tfmppy)
2
2
2
1
1
silver(I) oxide gave 0.34 g of product (yield: 55%). H NMR (500
67%). H NMR (500 MHz, DMSO-d ) δ 8.33 (t, 2H), 8.27 (d, J = 8.1
6
MHz, CDCl ) δ 8.38−8.20 (m, 2H), 8.03 (dd, J = 15.5, 6.9 Hz, 1H),
Hz, 1H), 8.13 (dd, J = 13.9, 6.9 Hz, 2H), 8.09−8.02 (m, 2H), 7.92 (d,
J = 5.8 Hz, 1H), 7.91−7.82 (m, 2H), 7.61 (d, J = 8.0 Hz, 1H), 7.49 (t,
J = 7.7 Hz, 1H), 7.42 (t, J = 7.6 Hz, 1H), 7.22 (d, J = 7.8 Hz, 2H), 7.14
(t, J = 6.6 Hz, 1H), 7.08 (d, J = 6.9 Hz, 2H), 6.77 (d, J = 12.1 Hz, 2H),
6.38 (s, 1H), 3.34 (s, 3H). HR EI-MS Calcd: m/z 913.1559 for [M +
3
7
7
6
.91−7.53 (m, 6H), 7.37 (d, J = 13.4 Hz, 2H), 7.10−7.00 (m, 1H),
.00−6.90 (m, 1H), 6.89−6.64 (m, 2H), 6.50−6.41 (m, 1H), 6.40−
.11 (m, 2H), 5.66 (dd, J = 47.9, 8.4 Hz, 1H), 2.80 (s, 3H). HR EI-MS
+
+
Calcd: m/z 782.1513 for [M + H] (C H F IrN ), found: m/z
35
23
4
5
+
+
7
82.1507.
H] (C39H F IrN ), found: m/z 913.1555.
25 9 4
Ir6b. [(dfppy) Ir(μ-Cl)] (0.49 g), 0.25 g of L6b, and 0.16 g of
(dbthppy)2Ir(L5a) (Ir12). [(dbthppy)2Ir(μ-Cl)]2 (0.60 g), 0.35 g of
2
2
1
silver(I) oxide gave 0.30 g of product (yield: 51%). H NMR (500
L5a, and 0.16 g of silver(I) oxide gave 0.42 g of product (yield: 53%).
1
MHz, CDCl ) δ 8.27 (ddd, J = 31.9, 22.5, 7.7 Hz, 3H), 7.89−7.51 (m,
H NMR (500 MHz, DMSO-d ) δ 8.43 (d, J = 8.2 Hz, 1H), 8.36 (t, J
6
3
5
1
H), 7.05 (d, J = 21.7 Hz, 1H), 6.85 (t, J = 34.7 Hz, 2H), 6.66 (d, J =
9.0 Hz, 1H), 6.53−6.23 (m, 3H), 5.84−5.51 (m, 2H), 3.20 (s, 3H).
= 7.8 Hz, 2H), 8.31 (d, J = 5.7 Hz, 1H), 8.15 (d, J = 7.0 Hz, 2H), 8.11
(d, J = 6.2 Hz, 2H), 8.06 (d, J = 7.5 Hz, 2H), 8.00 (d, J = 8.5 Hz, 3H),
7.84 (d, J = 7.8 Hz, 2H), 7.57−7.51 (m, 2H), 7.47−7.39 (m, 6H), 7.12
(dt, J = 12.5, 6.6 Hz, 2H), 7.00 (t, J = 6.8 Hz, 1H), 6.82 (d, J = 7.4 Hz,
+
+
HR EI-MS Calcd: m/z 732.1357 for [M + H] (C H F IrN ),
31
21
4
5
found: m/z 732.1355.
Ir7a. [(dfppy) Ir(μ-Cl)] (0.49 g), 0.29 g of L7a, and 0.16 g of
+
1H), 3.32 (s, 3H). HR EI-MS Calcd: m/z 989.1566 for [M + H]
2
2
1
+
silver(I) oxide gave 0.39 g of product (yield: 63%). H NMR (500
(C49
H
31
F
3
IrN
(4-tfmpiq)
L5a, and 0.16 g of silver(I) oxide gave 0.45 g of product as deep red
4
S
2
), found: m/z 989.1562.
Ir(μ-Cl)] (0.62 g), 0.35 g of
2
MHz, DMSO-d ) δ 8.40 (d, J = 7.8 Hz, 1H), 8.24 (d, J = 8.3 Hz, 1H),
2
Ir(L5a) (Ir13). [(4-tfmpiq)
2
6
8.17 (d, J = 8.6 Hz, 1H), 8.08 (d, J = 5.1 Hz, 1H), 8.00 (d, J = 8.0 Hz,
1
1H), 7.97 (d, J = 5.8 Hz, 1H), 7.83 (dd, J = 16.9, 8.7 Hz, 2H), 7.60 (d,
powder (yield: 56%). H NMR (500 MHz, CDCl ) δ 8.95−8.86 (m,
3
J = 7.7 Hz, 1H), 7.46−7.37 (m, 2H), 6.99 (t, J = 6.1 Hz, 1H), 6.78 (t, J
2H), 8.32 (d, J = 8.3 Hz, 1H), 8.26 (d, J = 8.3 Hz, 1H), 8.11 (d, J = 8.3
Hz, 1H), 8.00 (t, J = 7.9 Hz, 1H), 7.83 (dd, J = 20.8, 7.1 Hz, 3H), 7.74
(dt, J = 12.8, 4.9 Hz, 4H), 7.42−7.36 (m, J = 11.6, 7.3 Hz, 3H), 7.31
(dt, J = 17.8, 8.9 Hz, 5H), 7.26−7.21 (m, 2H), 7.02 (dd, J = 11.8, 6.4
Hz, 2H), 3.47 (s, 3H). HR EI-MS Calcd: m/z 1035.1692 for [M +
=
=
7.1 Hz, 1H), 6.75−6.66 (m, 2H), 6.61 (d, J = 7.1 Hz, 1H), 6.03 (d, J
7.5 Hz, 1H), 5.59 (d, J = 8.2 Hz, 1H), 3.42 (s, 3H). HR EI-MS
+
+
Calcd: m/z 783.1466 for [M + H] (C H F IrN ), found: m/z
34
22
4
6
7
83.1464.
+
+
Ir7b. [(dfppy) Ir(μ-Cl)] (0.49 g), 0.25 g of L7b, and 0.16 g of
Na] (C47H F IrN Na ), found: m/z 1035.1691.
28 9 4
2
2
1
silver(I) oxide gave 0.45 g of product (yield: 76%). H NMR (500
MHz, DMSO-d ) δ 9.80 (s, 1H), 9.23 (d, J = 8.4 Hz, 1H), 9.15 (s,
3. RESULTS AND DISCUSSION
6
1
2
H), 8.32 (d, J = 4.9 Hz, 1H), 8.29−8.21 (m, 2H), 8.20−8.10 (m,
H), 8.02 (d, J = 20.4 Hz, 2H), 7.51 (s, 1H), 7.38 (s, 1H), 6.76 (dd, J
Molecular Design, Synthesis, and Chemical Charac-
terization. The iodized carbene precursors were prepared by
the modified Ullmann coupling reaction of benzimidazole or
imidazole with the corresponding bromonaphthalene, bromo-
benzene, bromopyridine, or bromopyrimidine derivatives,
followed by N-methylation with iodomethane. Then, the target
Ir(III) complexes were synthesized by heating the mixture of
=
20.1, 10.1 Hz, 1H), 6.70−6.59 (m, 1H), 5.71 (d, J = 7.8 Hz, 1H),
5.46 (d, J = 7.6 Hz, 1H), 3.31 (s, 3H). HR EI-MS Calcd: m/z
+
+
733.1309 for [M + H] (C H F IrN ), found: m/z 733.1309.
30
20
4
6
Ir8a. [(dfppy) Ir(μ-Cl)] (0.49 g), 0.35 g of L8a, and 0.16 g of
2
2
1
silver(I) oxide gave 0.32 g of product (yield: 47%). H NMR (500
MHz, DMSO-d ) δ 9.80 (d, J = 5.6 Hz, 1H), 9.58 (d, J = 5.5 Hz, 1H),
6
8
.79 (s, 1H), 8.32 (d, J = 8.4 Hz, 1H), 8.27 (d, J = 8.3 Hz, 1H), 8.22 (t,
J = 7.8 Hz, 1H), 8.14 (t, J = 7.7 Hz, 1H), 7.89 (d, J = 7.5 Hz, 1H), 7.85
d, J = 7.8 Hz, 1H), 7.68 (t, J = 6.5 Hz, 1H), 7.58 (t, J = 6.5 Hz, 1H),
.41 (m, J = 7.2 Hz, 2H), 6.85 (t, J = 10.8 Hz, 1H), 6.79 (t, J = 10.8
Hz, 1H), 5.75 (d, J = 8.2 Hz, 1H), 5.09 (d, J = 8.6 Hz, 1H), 3.32 (s,
Ir(III) μ-chloro-bridged dimer, NHC precursors, and Ag O in
2
15
2
-ethoxyethanol. According to the previous reports, during
(
7
the process of the formation of Ir(III) complexes, 2 mol NHC
precursors coordinate with 1 mol Ag(I) in situ forming the
carbene coordination structures. Then, the silver carbene
complexes were reacted directly with the μ-chloro-bridged
dimers performing the transition of the carbene ligands to the
iridium center. Also, the silver cation promoted the progress
due to the formation of AgCl.
+
+
3
H). HR EI-MS Calcd: m/z 851.1340 for [M + H] (C H F IrN ),
35 21 7 6
found: m/z 851.1332.
Ir8b. [(dfppy) Ir(μ-Cl)] (0.49 g), 0.31 g of L8b, and 0.16 g of
2
2
1
silver(I) oxide gave 0.32 g of product (yield: 49%). H NMR (500
MHz, DMSO-d ) δ 8.76 (s, 1H), 8.30−8.23 (m, 2H), 8.16 (d, J = 8.2
6
Hz, 1H), 7.88 (dd, J = 18.9, 10.7 Hz, 3H), 7.77 (d, J = 4.8 Hz, 1H),
The results from DFT calculations suggest that the
modification on the phenyl moiety of the NHCs makes a
distinctive difference on the FMOs and photophysical proper-
ties of the complexes. On the basis of this theoretical guideline,
7
6
1
.45 (s, 1H), 7.10 (dd, J = 13.2, 6.3 Hz, 2H), 6.71 (t, J = 10.2 Hz, 1H),
.63 (t, J = 10.4 Hz, 1H), 5.90 (d, J = 6.0 Hz, 1H), 5.58 (d, J = 6.8 Hz,
+
H), 3.21 (s, 3H). HR EI-MS Calcd: m/z 801.1183 for [M + H]
+
(C H F IrN ), found: m/z 801.1184.
31
19
7
6
electron-withdrawing moieties (−CF , −F) and N-heteroar-
(
dfpypy) Ir(L5a) (Ir9). [(dfpypy) Ir(μ-Cl)] (0.49 g), 0.35 g of L5a,
3
2
2
2
1
omatic rings (pyridine, pyrimidine) are introduced into NHCs
for larger HOMO−LUMO gap and emission hypsochromic
shift. Meanwhile, the replacement of phenyl ring with more
and 0.16 g of silver(I) oxide gave 0.35 g of product (yield: 51%). H
NMR (500 MHz, DMSO-d ) δ 8.38 (d, J = 8.1 Hz, 1H), 8.27 (d, J =
6
8.2 Hz, 1H), 8.19 (dd, J = 13.7, 7.1 Hz, 2H), 8.12 (s, 1H), 7.96 (dd, J
1
65
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
conjugated naphthalene ring is expected to gain a bathochromic
shift. Here, 16 blue or greenish-blue iridium complexes
(HR MS, ESI). As shown in Figure 1, single peaks (marked
with asterisk at 10.29 ppm for L1a and at 10.25 ppm for L4a)
with integral of one hydrogen in high field can be assigned to
(
(
dfppy) Ir(L1a∼L8a) (Ir1a∼Ir8a) and (dfppy) Ir(L1b∼L8b)
2
2
1
Ir1b∼Ir8b) containing second cyclometalated NHC ligands
the pro-carbenic proton in the H NMR spectra of the NHC
were synthesized in good yields (39−76%). Furthermore,
another five complexes (Ir9−Ir13) with different first cyclo-
metalated ligands from blue to red were synthesized to confirm
the extensive application of NHC as a second cyclometalated
ligand and the corresponding effects on emission properties.
The synthesized Ir(III) complexes were characterized with
precursors because of the electron-withdrawing effect of cation
together with the shielding effect of the imidazole conjunction
structure. After the complexes were formed, these signals
disappeared. This further confirmed the formation of the
carbene−Ir structures.
The structures of the Ir(III) phosphors were further
confirmed by the single-crystal X-ray diffraction analysis. Ten
crystals (CCDC numbers: 986474−986483) were obtained
either by solvent diffusion (MeOH into CH Cl solutions for
1
H NMR (Figure 1) and high-resolution mass spectroscopy
2
2
Ir2a, Ir2b, Ir3a, Ir3b, Ir4a, Ir5a, Ir5b, Ir8b, and Ir9) or by
controlled sublimation (Ir11) under high vacuum atmosphere.
The perspective diagrams of these complexes were depicted in
Figure 2. The corresponding crystallographic data were
collected in Supporting Information, Table S1, and the selected
bond lengths and angles were listed in Supporting Information,
Table S2. In the coordination sphere, the iridium center
coordinates to two C^N ligands and one NHC ligand. The
C^N ligands adopt a mutually eclipsed configuration, with the
N atoms residing at the trans and cis locations for C atoms. All
the coordination bonds are longer than 2.00 Å. The Ir−C1
bonds are in the range of 2.019 to 2.110 Å, and the Ir−C2
bonds are slightly longer than Ir−C1 bonds (except Ir8b),
demonstrating a stable coordination via electrons donated by
carbene C: atoms. As a result of the five-membered structure of
imidazole ring, C1−Ir−C2 angles are all less than 90°, and
some are even less than 80°. The N1−Ir−N2 angles are ∼170°,
presenting an obviously distorted octahedral geometry around
the iridium center. These structural characteristics can also be
found in other reported Ir(III) complexes with neutral
30
NHCs.
Electrochemistry and DFT/TD-DFT Calculation. The
redox properties and HOMO/LUMOs of the emitters have
impact on the charge transport ability and the OLED structure.
To investigate the NHCs effect, cyclic voltammetry measure-
ments were performed on Ir1a-Ir8a and Ir1b-Ir8b. The
HOMO/LUMOs calculated with ferrocene as standard
reference were listed in Supporting Information, Table S3.
During the anodic scan in MeCN, each complex exhibits a
1
Figure 1. H NMR spectra of L1a/Ir1a (top) and L4a/Ir4a (bottom).
Figure 2. Perspective diagrams of X-ray crystal structures of studied complexes with dfppy ligand. (Thermal ellipsoids shown at 40% probability
level; H atoms and solvent molecules are omitted for clarity.) Labels are added on the atoms bonded to the iridium center.
1
66
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
partial reversible process with strong oxidation peaks and
unobvious reduction peaks, which could be assigned to metal-
centered Ir(III)/Ir(IV) redox couple (Supporting Information,
Figure S1). When the phenyl unit in carbene ligands was
replaced, the oxidation and reduction potentials of Ir complexes
were positive-shifted. This phenomenon was also observed in
iridium complexes with ancillary ligands, which account for a
11f
relatively large proportion of the HOMOs. In the negative
potential scan range, all the complexes show quasi-reversible
redox peaks mainly due to the reduction of dfppy ligands. From
Supporting Information, Table S3, it could be found that from
Ir1a to Ir5a and from Ir1b to Ir5b, the substitution of electron-
withdrawing substitutes caused a positive shift in Eox at ∼100
mV. Consequently, the HOMOs are stabilized, and the
ΔE(
gaps (Eox − E ) are broadened, which
HOMO−LUMO)
red
31
agree with Barnard and Hogan’s results. Furthermore, when
the phenyl rings are replaced by pyridine and pyrimidine rings,
the HOMOs are further stabilized, and the ΔE(
HOMO−LUMO)
gaps are much larger in Ir6a/Ir6b, Ir7a/Ir7b, and Ir8a/Ir8b.
These results are well-consistent with the shifts of emission
peaks of these complexes. Supported by the theoretical
calculation results and also proved by the following photo-
physical properties measurements, our molecular design of the
NHCs indeed can tune the emission of the iridium phosphors,
which turns out to be a rational and useful design method. This
trend is further reproduced by the following theoretical
calculation results and is reflected in the variation of the
emission spectra.
Figure 3. Schematic representations of the calculated FMOs of Ir1a−
Ir8a (a) and Ir1b−Ir8b (b).
Information about the energy level and electronic structure
of the FMOs was provided by the computational calculations.
The results are helpful for the assignment of the electron
transition characteristics and the discussion on the photo-
physical variations. Thus, the ground-state geometries of all the
Ir(III) complexes were fully optimized using DFT method with
B3LYP functional. The energies and the compositions of the
FMOs are collected in Supporting Information, Table S4, and
the contour plots of HOMOs and LUMOs are listed in
Supporting Information, Figure S2. Furthermore, Figure 3
schematically illustrates the changing trend of these orbitals.
TD-DFT calculations were based on the optimized ground-
state structures and certain vertical transitions, which could
reveal the nature of different UV−vis absorption bands that
were selected in Supporting Information, Table S5.
From Supporting Information, Table S4, it can be found that
the LUMOs have similar compositions and are located mainly
on the two dfppy ligands (∼93%). Therefore, the LUMOs are
exactly the same. However, the HOMOs present a clear
variation trend that is consistent with our molecular design.
Since the π orbital energy of the naphthyl is higher-lying, the
HOMOs of Ir1a/Ir1b, which have the largest contributions
from the NHCs, are the highest ones. With the replacement of
naphthyl by phenyl and with electron-withdrawing fluorine/
trifluoromethyl-substituted phenyl, due to the stabilization
effect, the HOMOs decrease to a certain extent in Ir2a/Ir2b−
Ir5a/Ir5b. The following alternation of phenyl moiety to
pyridyl and pyrimidyl moieties further minimizes the
occupation ratios of NHCs in HOMOs, and the energy levels
are lowered from Ir6a/Ir6b to Ir8a/Ir8b, gradually.
Figure 4. UV−vis absorption spectra of Ir1a−Ir8a (a) and Ir1b−Ir8b
Photophysical Property. The absorption and emission
spectra of all complexes measured at room temperature or 77 K
in CH Cl solution were given in Figures 4 and 5, and the
−6
(
b). All the spectra were measured in CH Cl (5 × 10 M) at room
2
2
temperature.
2
2
photophysical data were summarized in Table 1. All the
dfppy) Ir(NHC) complexes show broad and intense absorp-
(
2
1
67
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
Figure 5. Emission spectra of Ir1a−Ir8a (a) and Ir1b−Ir8b (b) at room temperature. The normalized emission spectra of Ir1a−Ir8a (c) and Ir1b−
−
5
Ir8b (d) at 77 K. All the samples are in the deaerated CH Cl solutions (5 × 10 M).
2
2
Table 1. Photophysical Properties of Ir1a−Ir8a and Ir1b−Ir8b
a
b
absorption at 298 K
emission at 298 K
MeCN
emission at 77 K
λem (nm)
3
c
complex
λabs (ε) (nm (×10− L mol−1 cm−1))
CH Cl2
τ (μs)
ΦPL
λmax (nm)
2
Ir1a
Ir1b
Ir2a
Ir2b
Ir3a
Ir3b
Ir4a
Ir4b
Ir5a
Ir5b
Ir6a
Ir6b
Ir7a
Ir7b
Ir8a
Ir8b
250 (72.7)
485
481
488
494
494
484
480
474
477
472
475
474
475
474
476
472
1.9
2.1
1.7
1.8
1.9
1.8
1.8
1.9
1.9
1.8
1.9
1.8
1.9
1.7
1.7
1.9
0.06
0.14
0.26
0.65
0.37
0.73
0.30
0.57
0.51
0.69
0.63
0.61
0.28
0.33
0.11
0.32
481, 515, 556
482, 519, 557
470, 475, 482
478, 503(sh)
455, 486
249 (52.1), 381 (4.7)
483
485
483
248 (54.1), 291 (27.1), 329 (11.4), 380 (5.2)
228 (48.0), 262 (37.3), 384 (5.0)
251 (50.4), 293 (25.7), 379 (4.9)
250 (39.3), 381 (5.0)
470, 490(sh)
473, 491(sh)
465, 486(sh)
469, 487(sh)
465, 485(sh)
469, 488(sh)
474, 499
471, 500
255 (51.7), 290 (26.0), 375 (5.7)
233 (46.2), 260 (38.7), 378 (5.7)
249 (57.2), 285 (31.8), 377 (6.4)
232 (47.6), 263 (44.0), 378 (5.9)
256 (51.2), 375 (4.5)
452, 462, 484
469, 490
462, 493
467, 496
469, 499
254 (42.0), 376 (4.8)
473, 498
470, 502
255(43.3), 291(24.2), 380(3.9)
256 (32.9), 377 (3.7)
471, 498
465, 496
471, 497
471, 501
252 (39.1), 373 (2.7)
470, 499
468, 498
251 (37.1), 372 (4.8)
455, 479
457, 481
451, 463, 482
a
−6
b
−5
c
Measured in CH Cl solutions (∼5 × 10 M). Measured in deaerated solutions (∼5 × 10 M), λ = 380 nm, sh = shoulder. Take fac-Ir(ppy)
2
2
ex
3
−5
in CH Cl as reference (∼5 × 10 M, ΦPL = 0.40).
2
2
tions between 230 and 280 nm which can be assigned to spin
allowed π−π* ligand centered (LC) transitions involving the
dfppy and NHCs. The moderate absorption bands between
clarified and confirmed by the TD-DFT calculations (Support-
ing Information, Figure S3, Table S5) for completeness. All the
complexes own alike S → S transitions in the same range of
1
0
n
3
00−400 nm are corresponding to the spin allowed metal to
wavelength with similar oscillator strength. This confirms the
resemblance of UV−vis absorption spectra of these complexes.
For phosphorescent emitters used in OLEDs, significant
mixing of the lowest triplet and higher-lying singlet excited
states caused by efficient SOC is in favor of high
phosphorescent quantum efficiency. Meanwhile, strong SOC
effect can drastically shorten the emission decay time and
depress the triplet−triplet annihilation. The emission spectra in
CH Cl exhibit maximum peaks in the range of 455−485 nm
1
ligand charge-transfer ( MLCT) transitions, partially over-
lapped by the broad LC absorptions. The weak absorption tails
after 400 nm can be assigned as the theoretically forbidden
3
MLCT transitions, caused by the large spin orbital coupling
(
SOC) that was introduced by iridium center. No distinct
difference is observed in absorption profiles for all the
complexes, indicating the similar electronic and vibrational
structures of the ground states (S ) and the first excited states
0
2
2
(
S1). The detailed assignments of the absorption spectra are
generated from the electronic 0−0 transition between the
1
68
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
lowest triplet excited state to the ground state, making them
blue or greenish-blue phosphors. The emission at lower energy
range (∼490 nm) might stem from overlapping vibrational
Different Color Emitters with Carbene Ligand. Because
the NHCs are σ-donating ligands with high triplet energy levels,
most neutral and cationic iridium complexes are blue
phosphorescent emitters. To demonstrate that they are versatile
second cyclometalated ligands for neutral Ir(III) phosphors,
L5a was chosen to prepare another five complexes with
different C^N cyclometalated ligands, namely, 2′,6′-difluoro-
2,3′-bipyridine (dfpypy), 2-(3-(trifluoromethyl)phenyl) pyri-
dine (3-tfmppy), 2-(4-(trifluoromethyl)phenyl)pyridine (4-
tfmppy), 2-(dibenzo[b,d]thiophen-4-yl) pyridine (dbthppy),
and 1-(4-(trifluoromethyl)phenyl) isoquinoline (4-tfmpiq), to
cover the emission range from blue to red. The chemical
structures of these complexes and reported complexes with
corresponding C^N ligands and conventional ancillary ligands
(e.g., acac, pic, and tpip (tetraphenylimidodiphosphinate)) for
references are presented in Scheme 2. The single-crystal
structures of Ir9 and Ir11 were depicted in Figure 6. The UV−
3
2
satellites. All the emission spectra are obviously less
13
structured than that of FIr6 but are much better resolved
than that of fac-Ir(ppy) (ppy = 2-phenylpyridinate) in similar
3
3
3
conditions. This indicates that the MLCT characters involved
in the emitting T states of different complexes are various, but
1
significant, since a dominant MLCT character in T usually
1
leads to large inhomogeneity and low-energy lying metal−
ligand vibrational satellites, smearing out the spectrum below
34
the electronic original emission.
Obviously, in Figure 5, both at room temperature and 77 K,
the emission spectra of Ir2a/Ir2b are less structured without
shoulder peaks compared with the others. These differences are
generated from the nature of these two complexes determined
by their chemical structures. To our knowledge, the iridium
phosphors with pure MLCT emission states will present a
broad and structureless emission, such as fac-Ir(ppy) , which
3
has a broad emission even at very low temperature. Ir2a/Ir2b
present a broad emission at 77 K demonstrating that the
emission states of these two complexes are mainly dominated
by MLCT characters. The other complexes, namely, Ir1a/Ir1b
and Ir3a-Ir8a/Ir3b-Ir8b, are slightly structured at room
temperature and highly structured at 77 K. These again
demonstrate that their emission states are hybrid states with
3
3
major MLCT and minor ILCT characters.
Although the theoretical calculation results indicate that the
HOMOs and LUMOs are further stabilized and the
Figure 6. Perspective diagrams of X-ray crystal structures of Ir9 and
Ir11. (Thermal ellipsoids shown at 40% probability level; H atoms and
solvent molecules are omitted for clarity.) Labels are added on the
atoms bonded to the iridium center.
ΔE
are broadened, when the phenyl moiety is
HOMO−LUMO
replaced by pyridyl or pyrimidyl in Ir6a/Ir6b, Ir7a/Ir7b, and
Ir8a, their emission peaks are shown at ∼470 nm without
obvious hypsochromic shifts. It may result from the
vis absorption spectra and photoluminescent spectra of these
complexes were shown in Figure 7. Their photophysical data
were collected in Table 2. As shown in Figure 7, all the
complexes own intense absorption bands in high-energy range
assigned to LC charge transfer and low-energy absorption
bands generated by MLCT. The emission peaks of these
complexes are in a wide range from 464 to 603 nm, and all the
emissions are structureless, indicating the MLCT character of
their emission states.
stabilization of the emissive T excited states simultaneously.
1
Although broad ΔE
are favorable to hypsochromic
HOMO−LUMO
shifts, the excited states are not necessarily arising from the
HOMO to LUMO excitations. However, it is noteworthy that
Ir8b has a significant hypsochromic shift and the first emission
peak is 457 nm, suggesting that this emission may come from a
higher-lying emissive state in energy. This hypothesis can be
proved by its emission spectrum at 77 K, in which the first
emission peak at ambient temperature splits into two peaks of
According to the TD-DFT calculations, the lowest allowed
transitions generate from a combination of HOMO−1
451 and 463 nm together with another peak at 482 nm. The
latter two peaks are comparable with those in other complexes,
and the first peak is generated from a higher-lying hybrid
emissive state. Most of the Ir(III) phosphors have satisfying
photoluminescence quantum efficiencies up to 0.73.
(d +π
) → LUMO (π* ) and HOMO (d +π ) →
dfpypy Ir L5a
Ir
dfpypy
L U M O f o r I r 9 a n d f r o m o n l y H O M O
(d +πfirst cyclometalated ligand) → LUMO (π*first cyclometalated ligand
)
Ir
for Ir5a and Ir10-Ir13. The S → S transition absorption
0
1
To demonstrate that the Ir(III) complexes are promising
emitters for OLEDs, we measured the photoluminescent
spectra of all the blue and greenish-blue complexes doped in
widely used host material of mCP with the concentration of 10
wt %, and the amorphous films were excited by the maximum
exciting wavelength of 320 nm for pure mCP (Supporting
Information, Figure S4). From this figure, we found the doped
amorphous films present the emission peaks of the iridium
complexes, and the emission of the mCP at 361 nm cannot be
observed. The results demonstrate that the energy transfer from
the host material to the dopants is complete. Also, we found
that Ir5b has the highest photoluminescent intensity and
efficiency among all the spectra recorded at the same
conditions. These results make it convincing that the iridium
phosphors reported in this manuscript are suitable for OLEDs,
and Ir5b is a promising emitter.
peaks locate at 285.6, 304.4, 312.2, 321.5, 334.3, and 364.7 nm
for Ir9, Ir5a, Ir10, Ir11, Ir12, and Ir13, respectively. The result
correspond to the emission sequence.
To evaluate the effects exerted by NHCs on the photo-
physical properties, the photoluminescence of these complexes
was compared with some reported Ir(III) emitters. Because of
the stronger ligand field induced by carbene than by acac and
tpip, the separation of the iridium d orbitals is larger.
Consequently, in the comparisons of Ir10/Ir10-r, Ir11/Ir11-
r, and Ir13/Ir13-r, the emission peaks of the formers are about
30 nm shorter than the latter references. Moreover, the
quantum yields of the synthesized couples are comparable or
even better than reported ones. Meanwhile, we found that the
emission peak of Ir5a is 5 nm shorter than that of FIrpic,
suggesting that L5a has comparable ligand field strength to that
of pic. However, in the case of Ir9/Ir9-r, since the T energy
1
1
69
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
phenyl)cyclohexane, 40 nm)/Ir5b (9 wt %): mCP (20 nm)/
TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF
(
1 nm)/Al (100 nm) was fabricated with optimized dopant
concentration of 9 wt % as an example to evaluate the
electroluminescence (EL) performances of our carbene-based
emitters. The energy diagrams of the device, as well as the
molecular structures of the materials used, are shown in Figure
8
. Obviously, the HOMO/LUMO levels of the Ir5b complex
are all within that of host material mCP. The LUMO (−3.11
eV) of the Ir5b complex is even lower than that of the electron-
transport material TmPyPB. So, a good carrier trapping is
expected in the device, which is the dominant EL mechanism.
Furthermore, holes and electrons will be well-confined within
the doped light-emitting layer.
The EL spectrum current density (J) and luminance (L)
versus voltage (V), luminance versus current efficiency (ηc)
characteristics of the device are also shown in Figure 8. The
device emits blue light with the EL emission peak at 470 nm.
The emission spectra are almost invariant of the current density
and are very close to the PL spectrum of the Ir5b complex in
CH Cl solution, indicating that the EL emission of the device
2
2
originates from the triplet excited states of the phosphor. The
turn-on voltage (Vturn‑on) of this device is 3.4 V, and the
maximum η and external quantum efficiency (η ) are 37.83 cd
c
ext
−1
A
and 10.3%, respectively. The maximum luminance (Lmax)
of 8709 cd m can be obtained at 11.7 V. The performances
are even comparable to that of the devices using the famous sky
−2
Figure 7. Normalized UV−vis absorption (a) and emission spectra (b)
in CH Cl at ambient temperature for Ir9, Ir5a, Ir10, Ir11, Ir12, and
2
2
35
Ir13.
blue emitter FIrpic as the emitter.
We believe the relative good device performances are due to
the low LUMO energy level and good electron mobility of the
Ir5b complex because the dopant acts as the hole and electron
traps to retard the motion of both types of carriers. The low
LUMO level of the dopant is particularly important for the
reason that the hole mobility of the TAPC is higher than the
Table 2. Photophysical Properties of the Synthesized and
Reported Iridium Complexes with Relevant C^N Ligands
a
a
absorption
photoluminescence
λ
(ε)
−1
τ
abs
(nm (×10− L mol cm−1))
3
complex
λmax (nm) (μs)
ΦPL
36
electron mobility of the TmPyPB, and the excitons
Ir9
239 (50.8), 278 (36.6)sh, 363 (3.9)
246 (42.0), 377 (4.3), 443 (0.4)
249 (57.2), 285 (31.8), 377 (6.4)
255 (43.16), 282 (26.0)sh,
464
457/459
465
2.1
1.8
1.9
1.9
0.09
0.67
0.51
0.83
accumulation is expected in hole-blocking layer near the
interface of emitting layer (Ir complex: mCP)/TmPyPB due to
3
8
Ir9-r
Ir5a
37
3
9
the high energy barrier between TmPyPB and mCP. The
accumulation of excitons is expected to cause the serious
triplet−triplet annihilation (TTA) and triplet−polaron annihi-
lation (TPA) of the Ir(III) complexes, and low efficiency
consequently. In our case, the LUMO level of the dopant is
lower than that of the mCP, and the TmPyPB will benefit the
electron-transport properties. The good electron mobility of
the phosphorescent emitter would facilitate the injection and
transport of electrons, which broadens the recombination zone,
balances the distribution of holes and electrons, and reduces
leakage current, particularly for the high doping concentration,
FIrpic
470
3
77 (5.3), 455 (0.4)
247 (51.3), 285 (30.7)sh, 331 (9.1),
90 (3.4)
268 (39.3), 293 (24.2), 342 (7.1),
54 (2.3)
252 (52.1), 289 (28.4)sh, 329 (9.8),
72 (6.2), 433 (2.4)
270 (55.4), 359 (10.2), 408 (4.1),
58 (3.4)
Ir10
478
502
496
524
1.9
2.1
1.7
1.9
0.25
0.07
0.32
0.23
3
1
1c
1c
Ir10-r
Ir11
4
3
1
Ir11-r
4
b
Ir12
249 (72.5), 307 (61.1), 413 (3.6)
230 (82.7), 277 (24.7)sh,
512
603
1.8
2.1
0.30
0.62
Ir13
3
34 (11.8)
41
leading to the suppressed TTA, TPA effects, and improved
4
0
Ir13-r
309, 343, 397 (5.2), 468 (4.5)
631
c
0.31
recombination probability and device efficiency.
a
b
Recorded in CH Cl at ambient temperature. There is no reported
2
2
But the device showed serious efficiency roll-off at higher
brigtness due to two posibilities. One is the stability problem of
the complexes. But most of the iridium complexes with F/CF3
units can be sublimated to form crystals. Another reason is the
population of the excited state of the blue emitter. The long
lifetime of the blue Ir(III) complexes will cause serious triplet−
triplet annihilation (especially in high dopant concentration)
and triplet−polaron annihilation (especially at high current
density). An ∼2 μs lifetime for our complexes perhaps is a
problem. In our future work we will try to synthesize the
iridium phosphors with reduced lifetime based on cyclo-
metalated NHCs.
c
analogous iridium phosphor with dbthppy cyclometalated ligand. Not
reported.
6
level of the dfpypy is very high, the ligand field effect generated
by the carbene ligand is limited, and the emission states of them
are both dominated by the MLCT character. Therefore, no
obvious hypsochromatic shift was observed.
Electroluminescence Performance. Because the complex
Ir5b has the similar emission to that of Ir5a and even higher
efficiency in both solution and amorphous film, the OLED with
the structure of ITO/TAPC (1,1-bis(4-(di-p-tolylamino)-
1
70
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
Figure 8. (a) Energy level diagrams of HOMO and LUMO levels (relative to vacuum level) and molecular structures for materials investigated; (b)
EL spectrum; (c) J−V−L curves; (d) η −L curve.
c
4
. CONCLUSION
ASSOCIATED CONTENT
Supporting Information
■
*
S
In summary, by using monoanionic NHCs as the second
cyclometalated ligands, a series of iridium complexes of the new
type, (C^N) Ir(NHC), have been successfully synthesized.
X-ray crystallographic data of the complexes in CIF format,
tabulated crystal information and structure data, cyclic
voltammograms, theoretical calculation results and emission
spectra of Ir1a/1b to Ir8a/8b in mCP thin film, and the decay
curves of the complexes. This material is available free of charge
via the Internet at http://pubs.acs.org.
2
They are good models for investigating the NHC effect on the
emitting properties. By modifying the NHCs, the HOMO
composition and energy could be controlled. Consequently, the
emission peaks of 16 blue or greenish-blue emitters were
tunable within tens of nanometers at ∼470 nm. Additionally,
with the use of different C^N ligands, another five emitters
nearly covering all the visible wavelength range from 464 to 603
nm were also prepared. More importantly, the OLED with Ir5b
AUTHOR INFORMATION
Corresponding Author
*E-mail: yxzheng@nju.edu.cn.
Notes
■
exhibits good performances with a maximum η of 37.83 cd
The authors declare no competing financial interest.
c
−2
−1
A , an η of 10.3%, and an Lmax of 8709 cd m . The NHC is
ext
ACKNOWLEDGMENTS
a kind of versatile and ideal ligand for neutral Ir(III)
phosphorescent complexes with different colors. Our study
suggests that the Ir(III) complexes with NHCs as the second
cyclometalated ligands have several advantages: (1) easy
synthetic chemical accessibility; (2) NHCs have strong ligand
field, which can tune the emission in a wide range; (3) the
■
This work was supported by the National Natural Science
Foundation of China (21371093, 21201161, 91433113), the
Major State Basic Research Development Program
(
2011CB808704, 2013CB922101, 2014CB643802), and the
Natural Science Foundation of Jiangsu Province
(
BK20130054).
devices using (C^N) Ir(NHC) as the emitter show good
2
performances. Although most of the materials reported are sky-
blue emitters, we have demonstrated that the replacement of
ancillary ligands with NHCs can indeed adjust the emission
peak wavelength. Further work on new materials and OLEDs
with second cyclometalated NHCs aiming at true blue and full
color, high efficiency, and low-efficiency roll off, is underway in
our laboratory.
REFERENCES
■
(
1) (a) Adachi, C.; Baldo, M. A.; Forrest, S. R.; Thompson, M. E.
Appl. Phys. Lett. 2000, 77, 904−906. (b) Lamansky, S.; Djurovich, P.;
Murphy, D.; Abdel-Razzaq, F.; Lee, H. E.; Adachi, C.; Burrows, P. E.;
Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304−
4
312. (c) Muller, C. D.; Falcou, A.; Reckefuss, N.; Rojahn, M.;
Wiederhirn, V.; Rudati, P.; Frohne, H.; Nuyken, O.; Becker, H.;
Meerholz, K. Nature 2003, 421, 829−833. (d) Holder, E.; Langeveld,
1
71
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
B. M. W.; Schubert, U. S. Adv. Mater. 2005, 17, 1109−1121.
(13) Holmes, R. J.; D’Andrade, B. W.; Forrest, S. R.; Ren, X.; Li, J.;
Thompson, M. E. Appl. Phys. Lett. 2003, 83, 3818−3820.
(14) Sajoto, T.; Djurovich, P. I.; Tamayo, A.; Yousufuddin, M.; Bau,
R.; Thompson, M. E.; Holmes, R. J.; Forrest, S. R. Inorg. Chem. 2005,
44, 7992−8003.
(
(
e) Wong, W. Y.; Ho, C. L. Coord. Chem. Rev. 2009, 253, 1709−1758.
f) Xiao, L. X.; Chen, Z. J.; Qu, B.; Luo, J. X.; Kong, S.; Gong, Q. H.;
Kido, J. J. Adv. Mater. 2011, 23, 926−952. (g) Costa, R. D.; Orti, E.;
Bolink, H. J.; Monti, F.; Accorsi, G.; Armaroli, N. Angew. Chem., Int.
Ed. 2012, 51, 8178−8211. (h) Lee, S.; Kim, S. O.; Shin, H.; Yun, H. J.;
Yang, K.; Kwon, S. K.; Kim, J. J.; Kim, Y. H. J. Am. Chem. Soc. 2013,
(15) Chang, C. F.; Cheng, Y. M.; Chi, Y.; Chiu, Y. C.; Lin, C. C.; Lee,
G. H.; Chou, P. T.; Chen, C. C.; Chang, C. H.; Wu, C. C. Angew.
Chem., Int. Ed. 2008, 47, 4542−4545.
1
35, 14321−14328.
2) (a) You, Y. M.; Park, S. Y. J. Am. Chem. Soc. 2005, 127, 12438−
2439. (b) Zhou, G. J.; Ho, C. L.; Wong, W. Y.; Wang, Q.; Ma, D. G.;
Wang, L. X.; Lin, Z. Y.; Marder, T. B.; Beeby, A. Adv. Funct. Mater.
008, 18, 499−511. (c) Yang, X. L.; Sun, N.; Dang, J. S.; Huang, Z.;
(
1
(16) (a) Hsieh, C. H.; Wu, F. I.; Fan, C. H.; Huang, M. J.; Lu, K. Y.;
Chou, P. Y.; Yang, Y. H. O.; Wu, S. H.; Chen, I. C.; Chou, S. H.;
Wong, K. T.; Cheng, C. H. Chem.Eur. J. 2011, 17, 9180−9187.
(b) Lu, K. Y.; Chou, H. H.; Hsieh, C. H.; Yang, Y. H. O.; Tsai, H. R.;
Tsai, H. Y.; Hsu, L. C.; Chen, C. Y.; Chen, I. C.; Cheng, C. H. Adv.
Mater. 2011, 23, 4933−4937.
2
Yao, C. L.; Xu, X. B.; Ho, C. L.; Zhou, G. J.; Ma, D. G.; Zhao, X.;
Wong, W. Y. J. Mater. Chem. C 2013, 1, 3317−3326. (d) Baranoff, E.;
Bolink, H. J.; Constable, E. C.; Delgado, M.; Haussinger, D.;
Housecroft, C. E.; Nazeeruddin, M. K.; Neuburger, M.; Orti, E.;
Schneider, G. E.; Tordera, D.; Walliser, R. M.; Zampese, J. A. Dalton
Trans. 2013, 42, 1073−1087.
(17) (a) Kessler, F.; Costa, R. D.; Di Censo, D.; Scopelliti, R.; Orti,
E.; Bolink, H. J.; Meier, S.; Sarfert, W.; Gratzel, M.; Nazeeruddin, M.
K.; Baranoff, E. Dalton Trans. 2012, 41, 180−191. (b) Meier, S. B.;
Sarfert, W.; Junquera-Hernandez, J. M.; Delgado, M.; Tordera, D.;
Orti, E.; Bolink, H. J.; Kessler, F.; Scopelliti, R.; Gratzel, M.;
Nazeeruddin, M. K.; Baranoff, E. J. Mater. Chem. C 2013, 1, 58−68.
(18) Chien, C. H.; Fujita, S.; Yamoto, S.; Hara, T.; Yamagata, T.;
Watanabe, M.; Mashima, K. Dalton Trans. 2008, 916−923.
(19) King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem. Soc. 1985,
107, 1431−1432.
(
3) (a) Liu, S. J.; Zhao, Q.; Deng, Y.; Xia, Y. J.; Lin, J.; Fan, Q. L.;
Wang, L. H.; Huang, W. J. Phys. Chem. C 2007, 111, 1166−1175.
b) Zhou, G. J.; Wong, W. Y.; Yao, B.; Xie, Z. Y.; Wang, L. X. Angew.
(
Chem., Int. Ed. 2007, 46, 1149−1151. (c) Gather, M. C.; Kohnen, A.;
Meerholz, K. Adv. Mater. 2011, 23, 233−248. (d) Zhuang, J. Y.; Li, W.
F.; Su, W. M.; Liu, Y.; Shen, Q.; Liao, L. S.; Zhou, M. Org. Electron.
2
013, 14, 2596−2601. (e) Sasabe, H.; Nakanishi, H.; Watanabe, Y.;
Yano, S.; Hirasawa, M.; Pu, Y. J.; Kido, J. Adv. Funct. Mater. 2013, 23,
550−5555. (f) Wang, J.; Liu, J.; Huang, S. J.; Wu, X. K.; Shi, X. D.;
(20) SAINT-Plus, version 6.02; Bruker Analytical X-ray Systems:
Madison, WI, 1999.
(21) Sheldrick, G. M. SADABS, An empirical absorption correction
5
Chen, C. P.; Ye, Z. C.; Lu, J. G.; Su, Y. K.; He, G. F.; Zheng, Y. X. Org.
Electron. 2013, 14, 2854−2858. (g) Fan, C.; Miao, J. S.; Jiang, B.; Yang,
C. L.; Wu, H. B.; Qin, J. G.; Cao, Y. Org. Electron. 2013, 14, 3392−
program; Bruker Analytical X-ray Systems: Madison, WI, 1996.
(22) Sheldrick, G. M. SHELXTL-97; Universitat
̈ ̈
of Gottingen:
Gottingen, Germany, 1997.
̈
3
398.
4) Chen, Z. Q.; Bian, Z. Q.; Huang, C. H. Adv. Mater. 2010, 22,
534−1539.
5) Chen, L. Q.; You, H.; Yang, C. L.; Ma, D. G.; Qin, J. G. Chem.
Commun. 2007, 1352−1354.
6) Lee, S. J.; Park, K. M.; Yang, K.; Kang, Y. Inorg. Chem. 2009, 48,
030−1037.
7) Wu, L. L.; Yang, C. H.; Sun, I. W.; Chu, S. Y.; Kao, P. C.; Huang,
H. H. Organometallics 2007, 26, 2017−2023.
8) Kessler, F.; Watanabe, Y.; Sasabe, H.; Katagiri, H.; Nazeeruddin,
M. K.; Graetzel, M.; Kido, J. J. Mater. Chem. C 2013, 1, 1070−1075.
9) (a) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.; Lamansky, S.;
Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. J. Am. Chem. Soc.
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino., J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
Revision A.01; Gaussian, Inc.: Wallingford, CT, 2009.
(
1
(
(
1
(
(
(
2
003, 125, 7377−7387. (b) Lo, S. C.; Shipley, C. P.; Bera, R. N.;
Harding, R. E.; Cowley, A. R.; Burn, P. L.; Samuel, I. D. W. Chem.
Mater. 2006, 18, 5119−5129. (c) He, L.; Qiao, J.; Duan, L.; Dong, G.
F.; Zhang, D. Q.; Wang, L. D.; Qiu, Y. Adv. Funct. Mater. 2009, 19,
(24) (a) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37,
785−789. (b) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652.
(c) Hay, P. J. J. Phys. Chem. A 2002, 106, 1634−1641.
(25) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299−310.
(26) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon,
M. S.; Defrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654−3665.
(27) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995−2001.
(28) Zhao, Y.; Truhlar, D. G. J. Phys. Chem. A 2006, 110, 5121−5129.
(29) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem.
Soc. 1984, 106, 6647−6653.
(30) Monti, F.; Kessler, F.; Delgado, M.; Frey, J.; Bazzanini, F.;
Accorsi, G.; Armaroli, N.; Bolink, H. J.; Orti, E.; Scopelliti, R.;
Nazeeruddin, M. K.; Baranoff, E. Inorg. Chem. 2013, 52, 10292−10305.
(31) Stringer, B. D.; Quan, L. M.; Barnard, P. J.; Wilson, D. J. D.;
Hogan, C. F. Organometallics 2014, 33, 4860−4872.
(32) Rausch, A. F.; Thompson, M. E.; Yersin, H. Inorg. Chem. 2009,
48, 1928−1937.
(33) (a) Finkenzeller, W. J.; Yersin, H. Chem. Phys. Lett. 2003, 377,
299−305. (b) Hofbeck, T.; Yersin, H. Inorg. Chem. 2010, 49, 9290−
9299.
(34) (a) Wilde, A. P.; Watts, R. J. J. Phys. Chem. 1991, 95, 622−629.
(b) Colombo, M. G.; Brunold, T. C.; Riedener, T.; Gudel, H. U.;
Fortsch, M.; Burgi, H. B. Inorg. Chem. 1994, 33, 545−550.
2
950−2960.
10) Yang, C. H.; Mauro, M.; Polo, F.; Watanabe, S.; Muenster, I.;
Froehlich, R.; Cola, L. D. Chem. Mater. 2012, 24, 3684−3695.
11) (a) Zhu, Y. C.; Zhou, L.; Li, H. Y.; Xu, Q. L.; Teng, M. Y.;
Zheng, Y. X.; Zuo, J. L.; Zhang, H. J.; You, X. Z. Adv. Mater. 2011, 23,
041−4046. (b) Li, H. Y.; Zhou, L.; Teng, M. Y.; Xu, Q. L.; Lin, C.;
Zheng, Y. X.; Zuo, J. L.; Zhang, H. J.; You, X. Z. J. Mater. Chem. C
013, 1, 560−565. (c) Xu, Q. L.; Wang, C. C.; Li, T. Y.; Teng, M. Y.;
(
(
4
2
Zhang, S.; Jing, Y. M.; Yang, X.; Li, W. N.; Lin, C.; Zheng, Y. X.; Zuo,
J. L.; You, X. Z. Inorg. Chem. 2013, 52, 4916−4925. (d) Wang, C. C.;
Jing, Y. M.; Li, T. Y.; Xu, Q. L.; Zhang, S.; Li, W. N.; Zheng, Y. X.;
Zuo, J. L.; You, X. Z.; Wang, X. Q. Eur. J. Inorg. Chem. 2013, 5683−
5
693. (e) Li, T. Y.; Liang, X.; Wu, C.; Xue, L. S.; Xu, Q. L.; Zhang, S.;
Liu, X.; Zheng, Y. X.; Wang, X.-Q. J. Organomet. Chem. 2014, 755,
10−119. (f) Li, H. Y.; Li, T. Y.; Teng, M. Y.; Xu, Q. L.; Zhang, S.; Jin,
Y. M.; Liu, X.; Zheng, Y. X.; Zuo, J. L. J. Mater. Chem. C 2014, 2,
116−1124.
12) (a) Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.;
Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Appl. Phys. Lett. 2001,
9, 2082−2084. (b) Holmes, R. J.; Forrest, S. R.; Tung, Y. J.; Kwong,
R. C.; Brown, J. J.; Garon, S.; Thompson, M. E. Appl. Phys. Lett. 2003,
2, 2422−2424.
1
1
(
7
8
1
72
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173

Inorganic Chemistry
Article
(
35) (a) Shih, P. I.; Chien, C. H.; Chuang, C. Y.; Shu, C. F.; Yang, C.
H.; Chen, J. H.; Chi, Y. J. Mater. Chem. 2007, 17, 1692−1698. (b) Hsu,
F. M.; Chien, C. H.; Shu, C. F.; Lai, C. H.; Hsieh, C. C.; Wang, K. W.;
Chou, P. T. Adv. Funct. Mater. 2009, 19, 2834−2843. (c) Hsu, F. M.;
Chien, C. H.; Shih, P. I.; Shu, C. F. Chem. Mater. 2009, 21, 1017−
1
022. (d) Rothmann, M. M.; Haneder, S.; Da Como, E.; Lennartz, C.;
Schildknecht, C.; Strohriegl, P. Chem. Mater. 2010, 22, 2403−2410.
e) Cui, L. S.; Liu, Y.; Yuan, X. D.; Li, Q.; Jiang, Z. Q.; Liao, L. S. J.
(
Mater. Chem. C 2013, 1, 8177−8185. (f) Han, C. M.; Zhao, F. C.;
Zhang, Z.; Zhu, L. P.; Xu, H.; Li, J.; Ma, D. G.; Yan, P. F. Chem. Mater.
2
013, 25, 4966−4976. (g) Wagner, D.; Hoffmann, S. T.; Heinemeyer,
U.; Munster, I.; Kohler, A.; Strohriegl, P. Chem. Mater. 2013, 25,
758−3765. (h) Deng, L. J.; Li, J. Y.; Wang, G. X.; Wu, L. Z. J. Mater.
Chem. C 2013, 1, 8140−8145.
36) Fong, H. H.; Lun, K. C.; So, S. K. Chem. Phys. Lett. 2002, 353,
3
(
4
(
(
07−413.
37) Parker, I. D. J. Appl. Phys. 1994, 75, 1656−1666.
38) Kang, Y.; Chang, Y. L.; Lu, J. S.; Ko, S. B.; Rao, Y. L.; Varlan, M.;
Lu, Z. H.; Wang, S. N. J. Mater. Chem. C 2013, 1, 441−450.
39) Rausch, A. F.; Thompson, M. E.; Yersin, H. J. Phys. Chem. A
009, 113, 5927−5932.
40) Fang, K. H.; Wu, L. L.; Huang, Y. T.; Yang, C. H.; Sun, I. W.
Inorg. Chim. Acta 2006, 359, 441−450.
41) (a) Kalinowski, J.; Stampor, W.; Mezyk, J.; Cocchi, M.; Virgili,
(
2
(
(
D.; Fattori, V.; Di Marco, P. Phys. Rev. B 2002, 66, 235321. (b) Jeon,
W. S.; Park, T. J.; Kim, S. Y.; Pode, R.; Jang, J.; Kwon, J. H. Appl. Phys.
Lett. 2008, 93, 063303.
1
73
dx.doi.org/10.1021/ic501949h | Inorg. Chem. 2015, 54, 161−173