Synthesis, structure, photophysical and electrochemical properties of series of new fac-triscyclometallated iridium complexes with carbazole or oxadiazole moieties

Article abstract of DOI:10.1016/j.ica.2012.05.010

A series of new fac-triscyclometallated iridium complexes Ir(Ln) ₃ (n = 1-6) (L₁: 2-{4-[5-phenyl-[1,3,4]oxadiazol-2-yl]- phenyl}-pyridine, L2: 2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4] oxadiazol-2-yl]- phenyl}-pyridine, L3: 9-(4-pyridin-2-yl-phenyl)-9H-carbazole, L4: 1-[4-(5-phenyl-[1,3,4]oxadiazol-2-yl)-phenyl]-isoquinoline, L5: 1-{4-[5-(4-tert-butyl-phenyl)-[1,3,4] oxadiazol-2-yl]-phenyl}-isoquinoline, L6: 9-(4-isoquinolin-1-yl-phenyl)-9H-carbazole) based on Ir(ppy)₃ (ppy = phenyl-pyridine) and Ir(piq)₃ (piq = 1-phenylisoquinoline) were synthesized from Ir(acac)₃ and corresponding ligands by a new and effective way using anthracene as a solvent. Single-crystal X-ray diffraction spectra of three complexes were studied and the iridium centers were found to adopt distorted octahedral coordination geometry. UV-Vis, photoluminescence, cyclic voltammetry were employed for studying the photophysical and electrochemical properties. These complexes exhibit intense phosphorescence in toluene solution at room temperature with high quantum efficiencies (0.07-0.58) and submicrosecond lifetimes (0.57-0.87 μs).

Full text of DOI:10.1016/j.ica.2012.05.010

Inorganica Chimica Acta 391 (2012) 50–57
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, structure, photophysical and electrochemical properties of series of new
fac-triscyclometallated iridium complexes with carbazole or oxadiazole moieties
⇑
Qiu-Lei Xu, Hong-Yan Li, Cheng-Cheng Wang, Song Zhang, Tian-Yi Li, Yi-Ming Jing, You-Xuan Zheng ,
Wei Huang , Jing-Lin Zuo, Xiao-Zeng You
⇑
State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, Center for Molecular Organic Chemistry, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210093, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new fac-triscyclometallated iridium complexes Ir(Ln)3 (n = 1–6) (L1: 2-{4-[5-phenyl-[1,3,4]
oxadiazol-2-yl]-phenyl}-pyridine, L2: 2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4] oxadiazol-2-yl]-phenyl}-
pyridine, L3: 9-(4-pyridin-2-yl-phenyl)-9H-carbazole, L4: 1-[4-(5-phenyl-[1,3,4]oxadiazol-2-yl)-phe-
nyl]-isoquinoline, L5: 1-{4-[5-(4-tert-butyl-phenyl)-[1,3,4] oxadiazol-2-yl]-phenyl}-isoquinoline, L6:
9-(4-isoquinolin-1-yl-phenyl)-9H-carbazole) based on Ir(ppy)3 (ppy = phenyl-pyridine) and Ir(piq)3
(piq = 1-phenylisoquinoline) were synthesized from Ir(acac)3 and corresponding ligands by a new and
effective way using anthracene as a solvent. Single-crystal X-ray diffraction spectra of three complexes
were studied and the iridium centers were found to adopt distorted octahedral coordination geometry.
UV–Vis, photoluminescence, cyclic voltammetry were employed for studying the photophysical and elec-
trochemical properties. These complexes exhibit intense phosphorescence in toluene solution at room
Received 20 February 2012
Received in revised form 8 May 2012
Accepted 10 May 2012
Available online 23 May 2012
Keywords:
Iridium complex
Carbazole
Oxadiazole
Synthesis
temperature with high quantum efficiencies (0.07–0.58) and submicrosecond lifetimes (0.57–0.87 ls).
Photoluminescence
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
ligands. For the realization of full-color displays and the creation
of white organic light-emitting diodes (WOLEDs), it is necessary
to develop the green, red, blue and other color region emitters.
fac-Tris(2-phenylpyridine)iridium, Ir(ppy)3, is a well-known
green emitter [7–10]. A phosphorescent OLED using Ir(ppy)3 dem-
onstrated a high performance with a maximum external quantum
efficiency of 19.2% [9].This value was comparable to the theoretical
limit of around 20% obtained from simple classical optics. fac-
Tris(1-phenyl-isoquinoline)iridium, Ir(piq)3, is an excellent red
material which has been applied in many excellent devices [11].
It is well recognized that the nature of cyclometallating ligands
can influence drastically the lowest energy emitting excited state
[12,13], adding the electron-donating or -withdrawing groups
Recently, heavy-metal complexes, particularly iridium(III) com-
plexes have received considerable attention because of their high
phosphorescence quantum efficiencies and applications in organic
light-emitting devices (OLEDs) [1–4] and luminescent biological-
labeling reagents [5,6]. The high emission efficiency is caused by
spin–orbit coupling which leads to the mixed singlet and triplet
metal-to-ligand charge-transfer states and creates the possibility
of full utilization of both the singlet and triplet excitons. Among
them, the neutral iridium(III) complexes Ir(C^N)3 containing cyclo-
metallated ligands have received extensive study because of their
application in highly efficient OLEDs with good performances
[1–4]. It is well understood that photophysical properties of the Ir
(III) complexes are strongly dependent on the character of their
frontier orbitals and the resulting highest occupied molecular orbi-
tal (HOMO) and/or lowest unoccupied molecular orbital (LUMO)
energy gap. In the Ir(C^N)3 complexes, density functional theory
calculations indicate that the HOMO is largely metal-centered,
whereas the LUMO is primarily localized on the heterocyclic rings
of the cyclometallated ligands. The emission wavelength and
excited-state lifetime can be tuned by changing cyclometallated
and different degree of p-electron conjugation into different posi-
tions of the ligands can increase or decrease the amount of electron
density at the metal center. The amount of ground state electron
density on the metal will subsequently affect the contribution of
MLCT character in the lowest energy transition, thus altering the
color of emission and radiative lifetime of the excited state of the
resulting complexes.
In 2006, Ono et al. [14] have reported some Ir(ppy)3 derivatives
containing hole-trapping moieties, such as diphenylamine, carba-
zole, and phenoxazine, with interesting photoluminescence (PL)
and electroluminescence (EL) properties. Recently, several papers
reported iridium complexes with carbazole or oxadiazole units with
good performances based on simple device structures [15–20].
⇑
Corresponding authors. Tel.: +86 25 83596775; fax: +86 25 83314502.
E-mail addresses: yxzheng@nju.edu.cn (Y.-X. Zheng), whuang@nju.edu.cn
(W. Huang).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.05.010

Q.-L. Xu et al. / Inorganica Chimica Acta 391 (2012) 50–57
51
Herein, we synthesized some fac-triscyclometallated iridium com-
plexes with carbazole or oxadiazole moieties based on Ir(ppy)3
and Ir(piq)3, Ir(L1)3–Ir(L6)3 (L1: 2-{4-[5-phenyl-[1,3,4]oxadiazol-
2-yl]-phenyl}-pyridine, L2: 2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]
oxadiazol-2-yl]-phenyl}-pyridine, L3: 9-(4-pyridin-2-yl-phenyl)-
9H-carbazole, L4: 1-[4-(5-phenyl-[1,3,4]oxadiazol-2-yl)-phenyl]-
isoquinoline, L5: 1-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-
2-yl]-phenyl}-isoquinoline, L6: 9-(4-isoquinolin-1-yl-phenyl)-
9H-carbazole). Incorporating carbazole and oxadiazole moiety into
these iridium complexes will likely increase the charge transfer
ability, subsequently simplify the devices structure and increase
the device performances.
trieved using SMART software and refined using SAINT [23] on all
observed reflections. Data was collected using a narrow-frame
method with scan widths of 0.30° in
x and an exposure time of
10 s/frame. The highly redundant data sets were reduced using
SAINT and corrected for Lorentz and polarization effects. Absorption
corrections were applied using SADABS [24] supplied by Bruker. The
structure was solved by direct methods and refined by full-matrix
least-squares on F2 using the program SHELXS-97 [25]. The positions
of metal atoms and their first coordination spheres were located
from direct-methods E-maps; other non-hydrogen atoms were
found in alternating difference Fourier syntheses and least-squares
refinement cycles and, during the final cycles, refined anisotropi-
cally. Hydrogen atoms were placed in calculated position and re-
fined as riding atoms with a uniform value of Uiso.
2. Experimental section
2.3. Synthesis
2.1. Materials and measurements
The synthesis routes of the precursors, ligands L1–L6 and com-
plexes Ir(L1)3–Ir(L6)3 are listed in Scheme 1. All the precursors
were synthesized according to the previous report [26,27]. The li-
gands used here were prepared by the modified Suzuki coupling
reactions [28]. Tetrakis(triphenylphosphine) palladium and aque-
ous sodium carbonate were used as a catalyst and a base, respec-
tively, in all the coupling reaction. The iridium complexes were
prepared with a modified method.
Ir(acac)3 and tetrakis(triphenylphosphine) palladium were pur-
chased from Kaida Co. (Shanxi, China). 2-Bromopyridine and 1-
chloroisoquinoline were obtained from Kangmanlin Chemical Co.,
(Nanjing, China). 1,3-Dimethyl-3,4,5,6-terahydro-2(1H)-pyrimidi-
none (DMPU), n-butyllithium and trimethyl borate were bought
from Alfa Aesar Co. All other reagents and chemicals were pur-
chased from commercial sources and used without further
purification.
1H NMR spectra were measured on a Bruker AM 500 spectrom-
eter. Mass spectra (MS) were obtained with ESI-MS (LCQ Fleet,
Thermo Fisher Scientific) or MALDI-TOF (Bruker Daltonic Inc.). Ele-
mental analyses for C, H, and N were performed on a Perkin–Elmer
240C analyzer. Absorption and photoluminescence spectra were
measured on a UV-3100 spectrophotometer and a Hitachi F-4600
photoluminescence spectrophotometer, respectively. The lifetime
measurements were measured with an Edinburgh Instruments
FLS920P fluorescence spectrometer in degassed toluene solutions
at 298 K. All the luminescence experiments were prepared in spec-
troscopic grade solvents.
2.3.1. General synthesis method for the intermediates and ligands
Synthesis of 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole
(P1): 4-bromobenzoyl chloride (21.95 g, 0.1 mol) was added drop-
wise to a solution of benzoyl hydrazine (13.62 g, 0.1 mol) and tri-
ethylamine (10.10 g, 0.1 mol) in chloroform (150 mL) at room
temperature (RT). The resulting mixture was stirred for 1 h and
then filtered. The collected solid was washed with water and etha-
nol to give the product N0-benzoyl-4-bromobenzohydrazide
(30.32 g, yield 95%). A mixture of N0-benzoyl-4-bromobenzo-hydra-
zide (20.00 g) and POCl3 (250 mL) in a 500 mL flask was refluxed
under nitrogen for 5 h. The excessive POCl3 was then distilled out,
and the residue was poured into water. The crude solid state prod-
uct was collected by filtration and purified by recrystallization from
chloroform/hexane to give P1 as white needlelike crystals (16.04 g,
yield: 85%). M.p.: 164–168 °C. IR (KBr, cmꢀ1): 3060, 1600, 1546,
1474, 1073, 728, 689. 1H NMR (500 MHz, CDCl3, ppm): d 8.159 (d,
2H, J = 7 Hz), 8.040 (d, 2H, J = 9 Hz), 7.710 (d, 2H, J = 8.5 Hz), 7.570
(m, 3H). MS (ESI): m/z 301.08 [M]+. Anal. Calc. for C14H9N2OBr: C,
55.84; H, 3.01; N, 9.30. Found: C, 55.87; H, 3.11; N, 9.27%.
Synthesis of 1-carbazolyl-4-bromobenzene (P5): a mixture of
carbazole (16.72 g, 0.10 mol), 1,4-dibromobenzene (23.59 g,
0.10 mol), CuI (1.90 g, 0.01 mol), 18-Crown-6 (0.88 g, 0.0033 mol),
K2CO3 (27.67 g, 0.20 mol) and DMPU (3 mL) was put into a reactor,
and then heat it at 170 °C for 13 h under nitrogen (Scheme 1). After
cooling to RT, the mixture was quenched with 1 N HCl, and the pre-
cipitate was washed with NH3ꢁH2O and water, purified with silicon
gel column chromatography using hexane as eluant (10.95 g, yield:
34%). M.p.: 152–154 °C. IR (KBr, cmꢀ1): 3056, 1496, 1452, 1230,
751. 1H NMR (500 MHz, CDCl3, ppm): d 8.175 (d, 2H, J = 7 Hz),
7.757 (d, 2H, J = 8.5 Hz), 7.495 (d, 2H, J = 8.5 Hz), 7.431 (t, 2H,
J = 7 Hz), 7.411 (d, 2H, J = 9 Hz), 7.342 (t, 2H, J = 7.5 Hz). MS(MAL-
DI-TOF): m/z 321.035 [M]+. Anal. Calc. for C18H12NBr: C, 67.10; H,
3.75; N, 4.35. Found: C, 66.93; H, 3.71; N, 4.31%.
The luminescence quantum efficiencies were calculated by
comparison of the emission intensities (integrated areas) of a stan-
dard sample (Ir(ppy)3) and the unknown sample according to the
Eq. (1) [21].
ꢀ
ꢁꢀ
ꢁꢀ
ꢁ
2
Iunk
Istd
Astd gunk
Aunk gstd
Uunk
¼
Ustd
ð1Þ
where Uunk and Ustd are the luminescence quantum yield of the
unknown sample and Ir(ppy)3, respectively. The Iunk and Istd are the
integrated emission intensities of the unknown sample and Ir(ppy)3
solution, respectively. The Aunk and Astd are the absorbance of the
unknown sample and Ir(ppy)3 solution at their excitation wave-
lengths, respectively. The gunk and gstd terms represent the refrac-
tive indices of the corresponding solvents (pure solvents were
assumed). The Ustd of Ir(ppy)3 has been revalued to be 0.4 [22].
Cyclic voltammetry measurements were conducted on a MPI-A
multifunctional electrochemical and chemiluminescent system
(Xi’an Remex Analytical Instrument Ltd., Co., China) at room tem-
perature, with a polished Pt plate as the working electrode, plati-
num thread as the counter electrode and Ag–AgNO3 (0.1 M) in
CH2Cl2 as the reference electrode, tetra-n-butylammonium per-
chlorate (0.1 M) was used as the supporting electrolyte, using
Fc+/Fc as the internal standard, the scan rate was 0.1 V/s.
General synthesis of boronic acid intermediates of P3, P4 and
P6: 30 mL anhydrous THF was injected into a flask with P1 or P2,
P5 (3.1 mmol) under nitrogen, the mixture was cooled to ꢀ50 °C.
n-Butyllithium (2.5 M in hexane, 3 mL, 2.4 mmol) was added drop-
wise via a injector, and the mixture was stirred for 2 h. Trimethyl
borate (0.31 g, 2.4 mmol) was added dropwise and the solution
was kept at ꢀ50 °C for 45 min. The reaction was allowed to warm
2.2. Crystallography
The single crystals of complexes were carried out on a Bruker
SMART CCD diffractometer using monochromated Mo K
a radiation
(k = 0.71073 Å) at room temperature. Cell parameters were re-

52
Q.-L. Xu et al. / Inorganica Chimica Acta 391 (2012) 50–57
O
Et3N
O
O
O
X
Br
+
X
Br
H2NHN
Cl
NHNH
N
N
N
N
POCl3
Li
(CH3O)3B
Br
X
B(OH)2
X
O
O
X=H ,
P1
X=H ,
P3
X=C(Me)3, P2
X=C(Me)3, P4
N
Br
N
N
N
X=H ,
L1
X
X=C(Me)3, L2
Pd(PPh3)4
O
N
Cl
N
X=H
L4
L5
N
X=C(Me)3,
X
Pd(PPh3)4
O
N
DMPU, CuI
18-Crown-6
Br
N
N
+
P5
Br
Br
N
H
N
N
Br
Pd(PPh3)4
L3
Li
(CH3O)3B
N
B(OH)2
N
Cl
N
P6
N
Pd(PPh3)4
L6
R
R
R
R
or
+ Ir(acac)3
Ir
or
Ir
N
N2, 300 oC
N
N
N
3
3
Ir(L1)3-Ir(L6)3
Scheme 1. Synthetic route to ligands L1–L6 and corresponding Ir complexes.
to RT slowly before 2 N HCl solution (2 mL) addition. When the mix-
ture reached RT, the THF and H2O was evaporated to provide a solid,
which was purified with alumina gel column chromatography (ace-
tate/petroleum ether = 2:1 as eluant) and give white solid. P3:
yield: 35%. 1H NMR (500 MHz, DMSO, ppm) d 8.34 (s, 2H), 8.16
(dd, J = 7.6, 1.4 Hz, 2H), 8.11 (d, J = 8.1 Hz, 2H), 8.03 (d, J = 8.0 Hz,
2H), 7.66 (q, J = 6.2 Hz, 3H). P4: yield: 42%. 1H NMR (500 MHz,
DMSO, ppm) d 8.34 (s, 2H), 8.09 (dd, 4H, J = 12.3, 8.3 Hz), 8.02 (d,
2H, J = 7.9 Hz), 7.66 (d, 2H, J = 8.4 Hz), 1.34 (s, 9H). P6: yield: 45%.
1H NMR (500 MHz, DMSO, ppm) d 8.25 (d, 4H, J = 8.5 Hz), 8.11 (d,
2H, J = 8.2 Hz), 7.61 (d, 2H, J = 8.2 Hz), 7.48–7.39 (m, 4H), 7.30
(ddd, 2H, J = 7.9, 5.8, 2.3 Hz).
A mixture of the boronic acid intermediates of P3, P4 and P6
(0.96 mmol), 4.8 mL NaCO3 (2 M), 10 mL toluene and 5 mL ethanol
solution was refluxed for 0.5 h under N2, then (0.04 g, 3% mmol)
Pd(PPh3)4 in 5 mL toluene and 0.1 mL 2-bromopyridine or 1-
chloroisoquinoline were injected to the solution and stirred for
24 h at 110 °C. After cooling, the reaction mixture was poured into
water (10 mL), and ethyl acetate (10 mL) was added. The organic
layer was separated and the aqueous layer was extracted with
ethyl acetate (2 ꢂ 10 mL). The combined organic solutions were
dried with Na2SO4 and concentrated. The residue was chromato-
graphed on silica gel (ethyl acetate/petroleum ether = 1:3 as
eluant) to give the corresponding ligands with different yields.

Q.-L. Xu et al. / Inorganica Chimica Acta 391 (2012) 50–57
53
2-{4-[5-phenyl-[1,3,4]oxadiazol-2-yl]-phenyl}-pyridine
(L1).
1228, 1163, 1109, 970, 825, 748, 715, 680. Anal. Calc. for
C27H20N2: C, 87.07; H, 5.41; N, 7.52. Found: C, 87.07; H, 5.38; N,
7.55%.
Yield: 75%. M.p.: > 300 °C. 1H NMR (500 MHz, CDCl3, ppm): d 8.79
(d, 1H, J = 4.6 Hz), 8.29 (d, 2H, J = 8.4 Hz), 8.27–8.16 (m, 4H), 7.87
(d, 2H, J = 3.4 Hz), 7.59 (d, 3H, J = 6.7 Hz), 7.35 (dd, 1H, J = 8.7,
4.4 Hz). 13C NMR (500 MHz, CDCl3, ppm): d 164.67, 164.39,
155.92, 149.88, 142.33, 137.01, 131.79, 129.09, 127.51, 127.31,
126.98, 124.11, 123.86, 122.92, 120.86. MS (ESI): m/z
(%) = 300(100) [M+]. IR (cmꢀ1): 3048 (C@C–H), 1611, 1539, 1466,
1434 (C@C, C@N, C@O), 1331, 1258, 1154, 998, 852, 790, 769,
684. Anal. Calc. for C19H13N3O: C, 76.42; H, 4.38; N, 14.04. Found:
C, 76.40; H, 4.41; N, 14.10%.
2.3.2. General synthesis method for the complex Ir(L)3
Under nitrogen, Ir(acac)3, three equivalents of the relevant li-
gand and five equivalents of the anthracene were added into a
sealed stainless steel reactor and heated to 300 °C for 24 h. The
crude product was chromatographed on alumina gel (ethyl ace-
tate/petroleum ether, 2:1) to give target powder product. Anthra-
cene here is used as a solvent at 300 °C.
2-{4-[5-(4-tert-Butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-
pyridine (L2). Yield: 75%. M.p.: > 300 °C. 1H NMR (500 MHz, CDCl3,
ppm) d 8.76 (d, 1H, J = 8.0 Hz), 8.26 (d, 2H, J = 14.5 Hz), 8.19 (d, 2H,
J = 14 Hz), 8.10 (d, 2H, J = 14.5 Hz), 7.83 (d, 2H, J = 7.5 Hz), 7.57 (d,
2H, J = 14.5 Hz), 7.32 (dd, 1H, J = 7.5, 3 Hz), 1.38 (s, 9H). 13C NMR
(500 MHz, CDCl3, ppm): d 164.77, 164.18, 155.97, 155.45, 149.68,
142.33, 137.01, 130.70, 127.50, 126.98, 126.31, 124.80, 124.46,
123.96, 121.43, 120.64, 119.82, 34.97, 31.12. MS (ESI): m/z
(%) = 356 (100) [M+]. IR (cmꢀ1): 3056 (C@C–H), 2960, 2900, 2854
(C–H), 1601, 1536, 1480, 1463 (C@C, C@N, C@O), 1302, 1267,
1096, 887, 873, 834, 756, 640. Anal. Calc. for C23H21N3O: C,
77.72; H, 5.96; N, 11.82. Found: C, 77.73; H, 5.94; N, 11.83%.
9-(4-Pyridin-2-yl-phenyl)-9H-carbazole (L3). Yield: 80%.
M.p.: > 300 °C. 1H NMR (500 MHz, CDCl3, ppm) d 8.79 (d, 1H,
J = 4.8 Hz), 8.27 (d, 2H, J = 8.5 Hz), 8.19 (d, 2H, J = 7.7 Hz), 7.86 (s,
2H), 7.73 (d, 2H, J = 8.5 Hz), 7.52 (d, 2H, J = 8.2 Hz), 7.46 (t, 3H,
J = 7.6 Hz). 13C NMR (500 MHz, CDCl3, ppm): d 156.59, 149.90,
140.77, 138.42, 136.96, 128.45, 127.22, 126.07, 123.56, 122.43,
120.57, 120.39, 120.13, 109.89. MS (ESI): m/z (%) = 320(100) [M+].
IR (cmꢀ1): 3035 (C@C–H), 1726, 1572, 1452 (C@C), 1362, 1211,
1096, 896, 813, 755, 643. Anal. Calc. for C23H18N2: C, 85.68; H,
5.63; N, 8.69. Found: C, 85.70; H, 5.62; N, 8.70%.
1-[4-(5-Phenyl-[1,3,4]oxadiazol-2-yl)-phenyl]-isoquinoline
(L4). Yield: 72%. M.p.: > 300 °C. 1H NMR (500 MHz, CDCl3, ppm) d
8.66 (d, 1H, J = 9.5 Hz), 8.34 (d, 2H, J = 14.5 Hz), 8.27–8.16 (m,
2H), 8.12 (d, 1H, J = 14 Hz), 7.93 (t, 3H, J = 21 Hz), 7.75 (dd, 2H,
J = 13, 6.6 Hz), 7.67–7.54 (m, 4H). 13C NMR (500 MHz, CDCl3,
ppm): d 164.77, 164.39, 159.27, 142.90, 142.30, 136.91, 131.82,
130.76, 130.27, 129.12, 127.62, 127.22, 126.94, 126.56, 123.99,
123.89, 120.55. MS (ESI): m/z (%) = 350 (100) [M+]. IR (cmꢀ1):
3054 (C@C–H), 1610, 1546, 1493,1407 (C@C, C@N, C@O), 1358,
1268, 1064, 968, 819, 834, 757, 696. Anal. Calc. for C23H15N3O: C,
79.07; H, 4.33; N, 12.03. Found: C, 79.05; H, 4.34; N, 12.04%.
1-{4-[5-(4-tert-Butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-
isoquinoline (L5). Yield: 74%. M.p.: > 300 °C. 1H NMR (500 MHz,
CDCl3, ppm) d 8.68 (d, 1H, J = 5.7 Hz), 8.35 (d, 2H, J = 8.2 Hz), 8.13
(d, 3H, J = 8.4 Hz), 7.94 (dd, 3H, J = 14.4, 8.2 Hz), 7.76 (dd, 2H,
J = 14.7, 6.5 Hz), 7.62 (dd, J = 15.6, 3H, 7.9 Hz), 1.41 (s, 9H). 13C
NMR (500 MHz, CDCl3, ppm): d 164.88, 164.18, 159.32, 155.46,
142.78, 142.30, 136.91, 130.73, 130.26, 129.10, 127.60, 127.21,
127.00, 126.87, 126.57, 126.10, 124.11, 121.07, 120.53, 35.12,
31.14. MS (ESI): m/z (%) = 406 (100) [M+]. IR (cmꢀ1): 3052 (C@C–
H), 2970, 2902, 2868 (C–H), 1622, 1563, 1496, 1454 (C@C, C@N,
C@O), 1358, 1268, 1064, 1018, 980, 858, 829, 745, 716, 691. Anal.
Calc. for C27H23N3O: C, 79.97; H, 5.72; N, 10.36. Found: C, 79.81;
H, 5.70; N, 10.38%.
Ir(L1)3. Orange solid, yield: 50%, M.p.: > 300 °C. 1H NMR
(500 MHz, CDCl3, ppm) d 8.04 (d, J = 8.1 Hz, 3H), 7.96 (d, 3H,
J = 9.6 Hz), 7.87 (d, 3H, J = 8.2 Hz), 7.77 (m, 12H), 7.54 (s, 3H),
7.44 (m, 9H), 7.08 (t, 3H, J = 6.3 Hz). 13C NMR (500 MHz, CDCl3,
ppm): d 165.25, 164.96, 164.03, 160.23, 147.48, 147.35, 136.98,
134.99, 131.49, 129.03, 126.77, 126.60, 124.60, 123.96, 123.31,
120.33, 120.04, 119.05. MS (MALDI-TOF): m/z 1087 (M+), 789
([M–ligand]+). IR (cmꢀ1): 3050, 1620, 1542,1470, 1436, 1342,
1259, 1161, 995, 846, 794, 771, 690. Anal. Calc. for C57H36IrN9O3:
C, 62.97; H, 3.34; N, 11.60. Found: C, 62.96; H, 3.36; N, 11.59%.
Ir(L2)3. Orange solid, yield: 60%, M.p.: > 300 °C. 1H NMR
(500 MHz, CDCl3, ppm) d 7.98 (d, J = 8.3 Hz, 3H), 7.92 (d, 3H,
J = 8.1 Hz), 7.83 (d, 3H, J = 8.2 Hz), 7.71 (dd, 15H, J = 16.9, 7.9 Hz),
7.36 (d, 6H, J = 8.4 Hz), 7.04 (t, 3H, J = 6.3 Hz), 1.28 (s, 27H). 13C
NMR (500 MHz, CDCl3, ppm): d 165.30, 164.89, 164.18, 160.04,
154.94, 147.39, 147.34, 136.77, 134.94, 126.34, 125.97, 124.52,
124.43, 123.22, 121.10, 119.94, 119.29, 34.95, 31.07. MS (MALDI-
TOF): m/z 1255(M+), 902 ([M–ligand]+). IR (cmꢀ1): 3060, 2961,
2902, 2861, 1606, 1547, 1495, 1473, 1428, 1302, 1268, 1098,
1068, 845, 790, 745, 727, 563. Anal. Calc. for C69H60IrN9O3: C,
66.01; H, 4.82; N, 10.04. Found: C, 65.97; H, 4.84; N, 10.06%.
Ir(L3)3. Yellow solid, yield: 77%, M.p.: > 300 °C. 1H NMR
(500 MHz, CDCl3, ppm) d 7.98 (dd, 9H, J = 7.7, 3.7 Hz), 7.83 (d,
3H, J = 8.3 Hz), 7.79 (d, 3H, J = 5.1 Hz), 7.70 (t, 3H, J = 8.3 Hz), 7.24
(d, 3H, J = 2.0 Hz), 7.03 (ddd, 18H, J = 9.7, 8.3, 4.6 Hz), 6.91 (s,
6H). 13C NMR (500 MHz, CDCl3, ppm): d 165.14, 162.16, 147.92,
143.39, 139.83, 138.02, 137.91, 132.86, 126.08, 123.88, 122.97,
120.46, 120.10, 119.95, 117.65, 110.2. MS (MALDI-TOF): m/z
1156 (M+), 835 ([M–ligand]+). IR (cmꢀ1): 3038, 1741, 1577, 1455
(C = C), 1366, 1219, 1168, 1109, 914, 783, 751, 657. Anal. Calc. for
C
69H51IrN6: C, 71.67; H, 4.45; N, 7.27. Found: C, 71.65; H, 4.46;
N, 7.28%.
Ir(L4)3. Red solid, yield: 70%, M.p.: > 300 °C. 1H NMR (500 MHz,
CDCl3, ppm) d 9.03 (d, 3H, J = 8.3 Hz), 8.46 (d, 3H, J = 8.4 Hz), 8.07
(d, 3H, J = 8.4 Hz), 7.83 (d, 9H, J = 6.5 Hz), 7.76 (p, 6H, J = 6.1 Hz),
7.64 (d, 3H, J = 1.7 Hz), 7.48 (m, 9H), 7.43 (d, 3H, J = 6.2 Hz), 7.32
(d, 3H, J = 6.1 Hz). 13C NMR (500 MHz, CDCl3, ppm): d 166.45,
164.73, 164.20, 163.86, 148.96, 139.73, 136.78, 135.03, 131.52,
130.83, 130.46, 129.07, 128.37, 127.34, 127.24, 126.96, 126.64,
124.23, 123.86, 121.79, 119.34, 118.64. MS (MALDI-TOF): m/z
1237 (M+), 889 ([M–ligand]+). IR (cmꢀ1): 3056, 1615, 1552, 1495,
1424, 1361, 1270, 1067, 967, 883, 835, 765 696. Anal. Calc. for
C69H42IrN9O3: C, 66.98; H, 3.42; N, 10.19. Found: C, 67.01; H,
3.43; N, 10.15%.
Ir(L5)3. Red solid, yield: 75%, M.p.: > 300 °C. 1H NMR (500 MHz,
CDCl3, ppm) d 9.02 (d, J = 7.9 Hz, 3H), 8.43 (d, J = 8.4 Hz, 3H), 8.04
(dd, J = 8.4, 1.6 Hz, 3H), 7.83 (m, 3H), 7.75 (dd, J = 4.9, 3.3 Hz, 15H),
7.41 (dd, J = 13.6, 7.3 Hz, 9H), 7.28 (s, 3H), 1.32 (s, 27H). 13C NMR
(500 MHz, CDCl3, ppm): d 166.50, 164.68, 164.33, 163.58, 154.97,
148.89, 139.67, 136.76, 134.98, 130.78, 130.42, 128.31, 127.29,
126.91, 126.39, 126.02, 124.37, 121.67, 121.12, 118.87, 34.99,
31.11. MS (MALDI-TOF): m/z 1404 (M+), 1001 ([M–ligand]+). IR
(cmꢀ1): 3054, 2959, 2901, 2865, 1614, 1539, 1492, 1441, 1380,
1264 1141, 1102, 848, 810, 727, 672. Anal. Calc. for C81H66IrN9O3:
C, 69.21; H, 4.73; N, 8.97. Found: C, 69.27; H, 4.70; N, 8.94%.
9-(4-Isoquinolin-1-yl-phenyl)-9H-carbazole (L6). Yield: 80%.
M.p.: > 300 °C. 1H NMR (500 MHz, CDCl3, ppm) d 8.72 (d, 1,H
J = 5.7 Hz), 8.33 (d, 1H, J = 8.4 Hz), 8.20 (d, 2H, J = 7.7 Hz), 8.02 (t,
3H, J = 8.6 Hz), 7.82 (m, 4H), 7.72 (t, 1H, J = 7.5 Hz), 7.60 (d, 2H,
J = 8.2 Hz), 7.49 (t, 2H, J = 7.6 Hz), 7.35 (t, 2H, J = 7.3 Hz). 13C NMR
(500 MHz, CDCl3, ppm): d 159.77, 142.38, 140.83, 138.70, 138.17,
137.02, 131.56, 130.25, 127.52, 127.35, 127.23, 126.93, 126.71,
126.10, 123.59, 120.41, 120.30, 120.18, 109.92. MS (ESI): m/z
(%) = 370(100) [M+]. IR (cmꢀ1): 3040, 1602, 1515, 1450, 1360,

54
Q.-L. Xu et al. / Inorganica Chimica Acta 391 (2012) 50–57
Ir(L6)3. Red solid, yield: 80%, M.p.: > 300 °C. 1H NMR (500 MHz,
For crystals Ir(L2)3 and Ir(L3)3, the Ir–C and Ir–N distances are a lit-
tle smaller than that of Ir(L4)3, which means there is stronger
attachment between iridium and the ppy basement. The phenyl
and pyridine group in crystal Ir(L3)3 almost coplanar with a very
small torsion angles [N(1)–C(6)–C(5)–C(3) = 0.69°] between two
rings. The X-ray shows a large dihedral angle [C(13)–C(12)–
N(10)–C(14) = 46.0°] between the carbazole and the ppy ring since
the carbazole group is a rigid plane. Comparing to Ir(L3)3, Ir(L2)3
and Ir(L4)3 are more flexible. For crystal Ir(L2)3, the torsion angles
between oxadiazole moiety and phenyl group (C(13)–C(12)–
C(19)–O(3)) and (O(3)–C(58)–C(38)–C(63)) are about 12.1° and
ꢀ23.0°, respectively. The Ir–C and Ir–N distances of crystal
Ir(L4)3 are similar with that of Ir(piq)3.
CDCl3, ppm) d 9.11 (d, 3H, J = 8.3 Hz), 8.42 (d, 3H, J = 8.5 Hz), 7.95
(d, 6H, J = 7.7 Hz), 7.87 (d, 3H, J = 8.2 Hz), 7.78 (m, 6H), 7.66 (d,
3H, J = 6.2 Hz), 7.38 (d, 3H, J = 2.1 Hz), 7.32 (d, 3H, J = 6.2 Hz),
7.06 (m, 9H), 6.97 (d, 6H, J = 8.2 Hz), 6.86 (t, 6H, J = 7.3 Hz). 13C
NMR (500 MHz, CDCl3, ppm): d 166.81, 165.55, 143.74, 140.22,
138.71, 136.86, 133.87, 131.05, 130.54, 129.76, 127.94, 127.57,
127.32, 126.69, 125.47, 123.22, 120.71, 119.57, 119.32, 117.68,
110.58. MS (MALDI-TOF): m/z 1306 (M+), 935 ([M–ligand]+). IR
(cmꢀ1): 3049, 1569, 1539, 1449 1377, 1223, 1152, 802, 753, 718,
681. Anal. Calc. for C81H57IrN6: C, 74.46; H, 4.40; N, 6.43. Found:
C, 74.48; H, 4.41; N, 6.44%.
3. Results and discussion
3.3. Photophysical properties
3.1. Synthesis
The UV–Vis absorption spectra of the complexes in toluene at
1 ꢂ 10ꢀ5 M are shown in Fig. 2, and the electronic absorption data
are listed in Table 3. In common with most Ir(III) complexes, the
absorption spectra can be divided into two regions. All complexes
display strong absorption bands below 360 nm with extinction coef-
ficients in the order of 104 Mꢀ1 cmꢀ1, moderately intense absorption
bands in the range 360–460 nm, and weak absorption bands above
460 nm. The intense peaks in the short wavelength region are as-
In popular methods, triscyclometallated Ir(III) complexes can be
prepared with three synthetic routes [29] by treating Ir(acac)3 with
3 equivalents of the free ligand in glycerol at refluxing tempera-
tures or from the appropriate b-diketonate derivative [(C^N)2Ir
(O^O), O^O = b-diketone] or dichloro-bridged dimer [(C^N)2Ir
(l-Cl)2Ir(C^N)2], by heating the Ir complex with a 2–3-fold excess
of cyclometallating ligand in glycerol. Although these synthesis
methods work equally well for some ligands, it is hard to control
the reaction conditions and complicated to purify the target triscy-
clometallated Ir(III) complexes due to the exits of high boiling
point glycerol solvent and the byproducts. In this study, Ir(acac)3
with 3 equivalents of the free ligand together with some anthra-
cene were put into a stainless steel reactor. The reactor was sealed
in a nitrogen atmosphere and then was kept at 300 °C for one day
and the anthracene was used as solvent at high temperature. There
is nearly no byproduct in this reaction because the mer-triscyclo-
metallated Ir(III) complex can be transferred to fac-triscyclometal-
lated one. Because the starting materials and anthracene have good
solubility in popular solvents, it is convenient to get the pure fac-
triscyclometallated Ir(III) complexes with good yield.
signed to spin-allowed intraligand 1LC (
p
?
p
⁄) transitions which
closely resemble the spectra of the free ligands. According to the pre-
vious study [29–33], both ligand-to-ligand charge transfer (LLCT)
and metal-to-ligand charge transfer (MLCT, d
p
(Ir) ?
p
⁄ (ligand))
may contribute to the visible-region charge transfer (CT) bands.
Therefore, we believe that the moderately intense absorptions at
ca. 360–460 nm and weak absorptions above 460 nm may receive
contributions from LLCT, spin allowed 1MLCT and spin forbidden
3MLCT transitions for complexes Ir(L1)3-Ir(L6)3. The spin–orbit cou-
pling is enhanced by the presence of closely-spaced
p
?
p
⁄ and
MLCT states and the heavy-atom effect of Ir center [34,35]. When
the tert-butyl group were introduced, the complexes Ir(L1)3 and
Ir(L2)3, Ir(L4)3 and Ir(L5)3 show the same absorption position and
intensity suggesting that this substitute at this position does not af-
fect the energy state in the complexes.
3.2. Crystal structures of Ir(L2)3, Ir(L3)3 and Ir(L4)3
The photoluminescence spectra of the complexes in toluene at
room temperature are also shown in Fig. 2 and the corresponding
photophysical data of the iridium complexes are summarized in
Table 3. The compounds were separated into two groups, the Ir(p-
py)3 based family, Ir(L1)3–Ir(L3)3, and the Ir(piq)3 based family,
Ir(L4)3–Ir(L6)3. The former shows green and yellowish green color
centered at ca. 503–540 nm and the later displays red emission lo-
cated at ca. 611–631 nm. Comparing to the reference complexes
Ir(ppy)3 and Ir(piq)3, the carbazole contained compounds show a
little blue shift and the oxadiazole ones exhibit a remarked
The single crystal of Ir(L2)3 was obtained from the CH2Cl2 solu-
tion and Ir(L3)3, Ir(L4)3 were got from the mixture solution of
CH2Cl2 and ethanol. Fig. 1 shows the ORTEP views and coordination
polyhedrons of Ir(L2)3, Ir(L3)3 and Ir(L4)3, respectively. The crys-
tallographic refinement parameters of Ir(L2)3, Ir(L3)3 and Ir(L4)3
are summarized in Table 1. Selected relevant bond parameters
are listed in Table 2.
All the complexes exhibit facial octahedral coordination geom-
etry and a 3-fold rotational axis passing through the iridium atom.
Fig. 1. ORTEP drawing of complexes Ir(L2)3, Ir(L3)3, Ir(L4)3 and their coordination polyhedron. Ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted
for clarity.

Q.-L. Xu et al. / Inorganica Chimica Acta 391 (2012) 50–57
55
Table 1
Crystallographic data for complexes Ir(L2)3, Ir(L3)3 and Ir(L4)3.
Ir(L2)3
Ir(L3)3ꢁCH2Cl2
Ir(L4)3
Formula
Formula weight
T (K)
C71H74IrO5N9
1325.59
293(2)
C74H54Cl11N6Ir
1609.36
296(2)
C70H46IrN9O4
1269.36
291(2)
k (Å)
0.71073
0.71073
0.71073
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
Triclinic
P1
Monoclinic
P2(1)/c
Monoclinic
P2(1)/c
ꢀ
13.3786(14)
14.2595(15)
19.506(2)
76.614(2)
78.801(2)
62.855(2)
3024.5(6)
2
13.877(2)
25.106(4)
20.836(3)
90.00
109.45
90.00
6844.6(18)
4
1.562
14.995(3)
23.141(5)
22.515(5)
90
122.14
90
6615(2)
4
1.275
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalcd (g/cm3)
1.374
2.141
l
(Mo K
a
) (mmꢀ1
)
2.429
2.070
F(000) (e)
1360
3216
2552
Crystal size (mm)
0.15 ꢂ 0.14 ꢂ 0.13
0.10 ꢂ 0.15 ꢂ 0.14
0.13 ꢂ 0.11 ꢂ 0.10
Reflections collected
Unique
17652
36856
33311
12330
0.910
13412
1.002
11643
1.006
Goodness-of-fit (GOF) on F2
R1, wR2 [I > 2
R1, wR2 (all data)
CCDC No.
r
(I)]
0.0628, 0.1165
0.1152, 0.1350
837670
0.0534, 0.1432
0.0672, 0.1500
837671
0.0541, 0.1787
0.0897, 0.1870
837672
w(Fo ꢀ Fc2)2/
R .
w(Fo2)]1/2
a
2
R1
=
R
||Fo| ꢀ |Fc||/
R
Fo|. wR2b = [
R
Table 2
Selected bond distances (Å) and angles (°) for Ir(L2)3, Ir(L3)3 and Ir(L4)3.
Ir(L2)3
Ir(1)–C(3)
N(1)–C(6)
C(13)–C(3)–Ir(1)
N(1)–C(6)–C(5)–C(3)
1.983(6)
1.358(2)
126.9(7)
2.5(3)
Ir(1)–N(1)
N(1)–Ir(1)–C(3)
C(6)–N(1)–Ir(1)
2.131(1)
78.8(4)
114.0(8)
12.1(2)
C(4)–N(1)
C(5)–C(3)–Ir(1)
C(4)–N(1)–Ir(1)
O(3)–C(58)–C(38)–C(63)
1.348(8)
117.5(9)
126.6(1)
ꢀ23.0(7)
C(13)–C(12)–C(19)–O(3)
Ir(L3)3
Ir(1)–C(3)
N(1)–C(6)
C(13)–C(3)–Ir(1)
N(1)–C(6)–C(5)–C(3)
1.985(8)
1.354(5)
114.6(2)
0.69
Ir(1)–N(1)
2.137(4)
79.0(5)
126.0(2)
46.0(8)
C(4)–N(1)
1.344(5)
116.0(7)
128.4(1)
178.1(4)
N(1)–Ir(1)–C(3)
C(4)–N(1)–Ir(1)
C(13)–C(12)–N(10)–C(14)
C(5)–C(3)–Ir(1)
C(6)–N(1)–Ir(1)
N(10)–C(14)–C(15)–C(19)
Ir(L4)3
Ir(1)–C(3)
N(4)–C(25)
C(38)–C(3)–Ir(1)
N(4)–C(25)–C(34)–C(3)
2.019(1)
1.334(8)
126.3(2)
ꢀ7.9(1)
Ir(1)–N(4)
2.138(4)
77.8(6)
122.5(9)
6.62
C(29)–N(4)
1.366(6)
116.2(3)
116.5(6)
ꢀ19.34
N(4)–Ir(1)–C(3)
C(29)–N(4–Ir(1)
C(38)–C(37)–C(29)–O(2)
C(34)–C(3)–Ir(1)
C(25)–N(4)–Ir(1)
O(2)–C(40)–C(41–C(42)
Ir(ppy)3
Ir(L1)3, Ir(L2)3
Ir(L3)3
a
b
Ir(ppy)3
Ir(L1)3, Ir(L2)3
Ir(L3)3
Ir(piq)3
Ir(piq)3
Ir(L4)3, Ir(L5)3
Ir(L6)3
Ir(L4)3, Ir(L5)3
Ir(L6)3
300
350
400
450
500
550
500
550
600
650
700
750
800
Wavelength (nm)
Wavelength (nm)
Fig. 2. The UV–Vis absorption spectra (a) and photoluminescence emission spectra (b) of the complexes in toluene at 1 ꢂ 10ꢀ5 M with the excitation wavelength of 440 nm.
bathochromic shift. It was reported that the effects should be as
follows: the energy of the
tion of an electron-donating moiety (carbazole) and lowered by the
Similar to the absorption spectra, the butyl group have no effect
on the photoluminescence character, so complexes Ir(L1)3 and
Ir(L2)3 have the same photoluminescence spectra, so do Ir(L4)3
p
⁄ orbital is heightened by the introduc-
presence of an electron-withdrawing moiety (oxadiazole) [36].
and Ir(L5)3. The observed phosphorescence lifetimes (sp) of the

56
Q.-L. Xu et al. / Inorganica Chimica Acta 391 (2012) 50–57
Table 3
Photophysical data of Ir(III) complexes in degassed toluene solutions.
c
f
Complex
Absorptiona k (nm) ( , 10ꢀ3 L molꢀ1 cmꢀ1
e
)
Excitation
Emission
Uem
Lifetime
kre
knr
b
d
k (nm)
kmax (nm)
CIE (x, y)
sp
(
ls)
106 sꢀ1
106 sꢀ1
3g
Ir(ppy)3
Ir(L1)3
Ir(L2)3
Ir(L3)3
Ir(piq)3
Ir(L4)3
Ir(L5)3
Ir(L6)3
289(62.6), 349(20.1), 380(23.3), 410(14.9), 456(5.2), 488(2.0)
315(96.9), 398(17.3), 448(6.4), 480(3.1), 529(0.1)
315(96.9), 398(17.3), 448(6.4), 480(3.1), 529(0.1)
290(31.7), 347(43.4), 387(21.6), 449(1.7)
324(21.5), 353(13.8), 429(9.0), 477(6.4), 594(1.8)
331(49.9), 350(46.4), 367(36.7), 439(12.5), 488(6.7), 551(0.8)
331(49.9), 350(46.4), 367(36.7), 439(12.5), 488(6.7), 551(0.8)
290(31.7), 347(43.4), 387(21.7), 449(1.67)
371
374
374
370
371
368
368
370
508
540
540
503
621
631
630
611
(0.26,0.67)
(0.38,0.60)
(0.37,0.61)
(0.22,0.64)
(0.57,0.42)
(0.68,0.31)
(0.67,0.32)
(0.64,0.35)
0.40
0.37
0.36
0.58
0.22
0.16
0.16
0.07
2.00
0.84
0.86
0.82
1.12
0.61
0.66
0.71
2.0
0.4
0.4
0.7
0.2
0.2
0.2
0.1
3.0
0.7
0.7
0.5
0.7
1.3
1.3
1.3
22
a
b
c
d
e
f
Absorption spectra were measured in aerated toluene solution at 300 K.
CIE (x, y) is the Commission Internationale de L’Eclairge (CIE) color coordinates.
Quantum yield in degassed toluene near 10ꢀ5 M measured with 468 nm excitation relative value on the basis of Ir(ppy)3 as the quantum yield is 0.4.
Luminescence lifetimes ( p) were measured in N2-saturated CHCl3 in dark room.
Radiative rate constant calculated from kr =
Nonradiative rate constant calculated from knr = 1/sp ꢀ kr.
s
U/sp.
complexes at the room-temperature lifetimes are in the range of
sub-microseconds ( p = 0.61–0.86 s, Table 3 and Fig. S1), which
are indicative of the phosphorescent origin for the excited states
in each case. As has been reported, the phosphorescence lifetime
is a key factor that causes triplet–triplet annihilation for Ir com-
6.0x10-6
4.0x10-6
s
l
2.0x10-6
0.0
Ir(L1)3
Ir(L2)3
Ir(L3)3
Ir(L4)3
Ir(L5)3
Ir(L6)3
plexes in the OLEDs operation. The longer of sp the material usually
leads to more significant triplet–triplet annihilation [37]. Such
short lifetimes of our complexes can increase spin-state mixing
and reduce the chance of device efficiency decay. We further
probed the photophysical properties of the complexes by measur-
ing their PL quantum yields (Up) in dilute degassed toluene solu-
tions at room temperature. The attachment of carbazole into
framework of the Ir(ppy)3 will greatly increase the photolumines-
cence intensity and the quantum efficiency Up. However, neither
carbazole nor oxadiazole have effect on improving the Up of
Ir(piq)3 group, but reducing it unexpected, from 0.22 to 0.07. By
-2.0x10-6
-4.0x10-6
-6.0x10-6
0.4
0.6
0.8
1.0
1.2
1.4
Voltage (V)
Fig. 3. Cyclovoltammety (CV) diagram of complexes Ir(L1)3–Ir(L6)3 (5 ꢂ 10ꢀ4 M) in
dichloromethane solution of n-Bu4NClO4 (0.1 M) at a sweep rate of 0.1 V/s using
ferrocene as the internal standard.
using Up
calculate the radiative (kr) and nonradiative (knr) decay rates from
Up and p, where the intersystem-crossing yield (UISC) is typically
= UISC{kr/(kr + knr)} and s
p = (kr + knr)–1, it is possible to
Table 4
s
Electrochemical properties for complexes Ir(L1)3–Ir(L6)3.
assumed to be 1.0 for metal phosphors with strong heavy-atom ef-
fect. All the complexes have reasonably similar knr values, while
the kr values for the Ir(ppy)3 based complexes are higher than that
of the Ir(piq)3 based family, which can be expected from the com-
parable quantum efficiencies and lifetimes for both series of
compounds.
Complex
Eox/Va
HOMOb
LUMOc
Eg (eV)
Ir(L1)3
Ir(L2)3
Ir(L3)3
Ir(L4)3
Ir(L5)3
Ir(L6)3
0.93
0.88
0.79
0.90
0.91
0.80
ꢀ5.47
ꢀ5.41
ꢀ5.33
ꢀ5.43
ꢀ5.43
ꢀ5.33
ꢀ3.14
ꢀ3.07
ꢀ2.79
ꢀ3.4
2.33
2.34
2.53
2.04
2.04
2.13
ꢀ3.4
ꢀ3.2
a
0.1 M [Bu4N]ClO4 in CH2Cl2 vs a Fc/Fc+ couple.
The HOMO level was calculated by using the energy level of the ferrocene value
3.4. Electrochemical properties
b
of 4.8 eV below the vacuum level.
The electrochemical properties of the complexes Ir(L1)3–Ir(L6)3
were studied by cyclic voltammetry (Fig. 3) using ferrocene as the
internal standard and the results are listed in Table 4. Because of
the limited range available in CH2Cl2 and the inability of our instru-
ment to measure the reduction potentials in the range from ꢀ2.7 to
ꢀ3.5 V, we obtained only the oxidation potentials for our com-
pounds. During the anodic scan in CH2Cl2, each of the Ir(III) com-
plexes exhibit a reversible oxidation with the redox potential in
the region of 0.79 and 0.93 V; we attribute this positive oxidation
potential to the metal-centered Ir(III)/Ir(IV) oxidation couple, in
accordance with the reported cyclometallated Ir(III) systems
[38,39]. The complexes with oxadiazole moiety have higher oxida-
tion potential than that with carbazole because carbazole is an
electron-donating unit, but oxadiazole is an electron-withdrawing
moiety. On the basis of the potentials of the oxidation and reduc-
tion couples, the HOMO and LUMO energy levels of complexes
were estimated with regard to the energy level of the ferrocene ref-
erence (4.8 eV below the vacuum level) [40,41] by the equations
EHOMO = ꢀ(4.80 + Eonset) and ELUMO = Eg + EHOMO [42]. The HOMO
c
Estimated from the HOMO and band-gap energies (ELUMO = Eg + EHOMO).
energies of the two groups are similar (about ꢀ5.4 eV), and the
LUMO difference is bigger (2.79–3.4 eV). Complexes Ir(L1)3 and
Ir(L2)3 almost have the similar Eg, HOMO and LUMO energies
and complexes Ir(L4)3 and Ir(L5)3 even have the same correspond-
ing energy data, suggested that the t-butyl group don’t have obvi-
ous effect on their electrochemical properties. We also find the
Ir(piq)3 group has relative lower energy gap and tend to be oxi-
dized easily as reported, which agree with the red shift of emission
spectrum.
4. Conclusions
In conclusion, we synthesized and characterized several new
cyclometallated iridium(III) complexes by incorporating hole-
transporting carbazole or electron-transporting oxadiazole
moieties. By using Ir(acac)3 with three equivalents of the free

Q.-L. Xu et al. / Inorganica Chimica Acta 391 (2012) 50–57
57
[11] A. Tsuboyama, H. Iwawaki, M. Furugori, T. Mukaide, J. Kamatani, S. Igawa, T.
Moriyama, S. Miura, T. Takiguchi, S. Okada, M. Hoshino, K. Ueno, J. Am. Chem.
Soc. 125 (2003) 12971.
[12] K.P. Balashev, M.V. Puzyk, V.S. Kotlyar, M.V. Kulikova, Coord. Chem. Rev. 159
(1997) 109.
[13] Z. He, W.-Y. Wong, X. Yu, H.-S. Kwok, Z. Lin, Inorg. Chem. 45 (2006) 10922.
[14] K. Ono, M. Joho, K. Saito, M. Tomura, Y. Matsushita, S. Naka, H. Okada, H.
Onnagawa, Eur. J. Inorg. Chem. (2006) 3676.
[15] L. Chen, Z. Ma, J. Ding, L. Wang, X. Jing, F. Wang, Chem. Commun. 47 (2011)
9519.
ligand together with some anthracene as solvent in a reactor under
nitrogen at 300 °C for one day, the pure fac-triscyclometallated
Ir(III) complexes can be obtained convenient with good yield. The
Ir(ppy)3 based compounds, Ir(L1)3–Ir(L3)3, show green or yellow-
ish green color centered at ca. 503–540 nm and the Ir(piq)3 based
complexes, Ir(L4)3–Ir(L6)3, display red emission located at ca. 611–
631 nm due to the MLCT emission. The complexes Ir(L1)3–Ir(L3)3
with carbazole or oxadizole show efficient photoluminescence
emission and high quantum efficiency Up, which indicate they
are potential materials for the application in OLEDs.
[16] J.-X. Cai, T.-L. Ye, X.-F. Fan, C.-M. Han, H. Xu, L.-L. Wang, D.-G. Ma, Y. Lin, P.-F.
Yan, J. Mater. Chem. 21 (2011) 15405.
[17] H.-J. Seo, M. Song, S.-H. Jin, J.H. Choi, S.-J. Yun, Y.-I. Kim, RSC Advances 1 (2011)
755.
[18] D. Wang, J. Wang, H.-L. Fan, H.-F. Huang, Z.-Z. Chu, X.-C. Gao, D.-C. Zou, Inorg.
Chim. Acta 370 (2011) 340.
Acknowledgments
[19] M. Song, J.S. Park, M. Yoon, A.J. Kim, Y.-I. Kim, Y.-S. Gal, J.W. Lee, S.-H. Jin, J.
Organomet. Chem. 696 (2011) 2122.
[20] T. Malinauskas, M. Daskeviciene, K. Kazlauskas, H.-C. Su, J.V. Grazulevicius, S.
Jursenas, C.-C. Wu, V. Getautis, Tetrahedron 67 (2011) 1852.
[21] D.P. Rillema, D.G. Taghdiri, D.S. Jones, C.D. Keller, L.A. Worl, T.J. Meyer, H.A.
Levy, Inorg. Chem. 26 (1987) 578.
This work was supported by the National Natural Science Foun-
dation of China (Grant Nos. 20971067 and 21021062), the Major
State Basic Research Development Program (2011CB808704).
[22] K.A. King, P.J. Spellane, R.J. Watts, J. Am. Chem. Soc. 107 (1985) 1431.
[23] SAINT-Plus, version 6.02; Bruker Analytical X-ray System, Madison, WI, 1999.
[24] G.M. Sheldrick, SADABS: An empirical absorption correction program, Bruker
Analytical X-ray Systems, Madison, WI, 1996.
[25] G.M. Sheldrick, SHELXTL-97, Universität of Göttingen, Göttingen, Germany, 1997.
[26] Q. Zhang, J.S. Chen, Y.X. Cheng, L.X. Wang, D.G. Ma, X.B. Jing, F.S. Wang, J.
Mater. Chem. 14 (2004) 895.
[27] Z. Peng, Z. Bao, M.E. Galvin, Adv. Mater. 10 (1998) 680.
[28] O. Lohse, P. Thevenin, E. Waldvogel, Synlett 1 (1999) 45.
[29] A.B. Tamayo, B.D. Alleyne, P.I. Djurovich, S. Lamansky, I. Tsyba, N.N. Ho, R. Bau,
M.E. Thompson, J. Am. Chem. Soc. 125 (2003) 7377.
[30] K. Dedeian, P.I. Djurovich, F.O. Garces, G. Carlson, R.J. Watts, Inorg. Chem. 30
(1991) 1685.
Appendix A. Supplementary material
CCDC 837670 (Ir(L2)3), 837671 (Ir(L3)3) and 837672 (Ir(L4)3)
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.ica.
2012.05.010.
[31] M.G. Colombo, T.C. Brunold, T. Riedener, H.U. Gudel, Inorg. Chem. 33 (1994)
545.
References
[32] S. Serroni, A. Juris, S. Campagna, M. Venturi, G. Denti, V. Balzani, J. Am. Chem.
Soc. 116 (1994) 9086.
[33] A. Mamo, I. Stefio, M.F. Parisi, A. Credi, M. Venturi, C. Di Pietro, S. Campagna,
Inorg. Chem. 36 (1997) 5947.
[34] Y. Wang, N. Herron, V.V. Grushin, D. LeCloux, V. Petrov, Appl. Phys. Lett. 79
(2001) 449.
[35] F.O. Garces, K.A. King, R.J. Watts, Inorg. Chem. 27 (1988) 3464.
[36] X. Gong, P.K. Ng, W.K. Chan, Adv. Mater. 10 (1998) 1337.
[37] S. Reineke, K. Walzer, K. Leo, Phys. Rev. B 75 (2007) 125328.
[38] S. Bettington, M. Tavasli, M.R. Bryce, A. Beeby, H. Al-Attar, A.P. Monkman,
Chem. Eur. J. 13 (2007) 1423.
[1] S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, H.E. Lee, C. Adachi, P.E.
Burrows, S.R. Forrest, M.E. Thompson, J. Am. Chem. Soc. 123 (2001) 4304.
[2] K.R.J. Thomas, M. Velusamy, J.T. Lin, C.H. Chien, Y.T. Tao, Y.S. Wen, Y.H. Hu, P.T.
Chou, Inorg. Chem. 44 (2005) 5677.
[3] S.C. Chan, M.C.W. Chan, Y. Wang, C.M. Che, K.K. Cheung, N. Zhu, Chem. Eur. J. 7
(2001) 4180.
[4] W. Lu, B.X. Mi, M.C.W. Chan, Z. Hui, C.M. Che, N. Zhu, S.T. Lee, J. Am. Chem. Soc.
126 (2004) 4958.
[5] K.K.W. Lo, C.K. Chung, T.K.M. Lee, L.H. Lui, K.H.K. Tsang, N. Zhu, Inorg. Chem. 42
(2003) 6886.
[39] M.K. Nazeeruddin, R.T. Wegh, Z. Zhou, C. Klein, Q. Wang, F.D. Angelis, S.
Fantacci, M. Grätzel, Inorg. Chem. 45 (2006) 9245.
[40] M. Thelakkat, H.-W. Schmidt, Adv. Mater. 10 (1998) 219.
[41] R.S. Ashraf, M. Shahid, E. Klemm, M. Al-Ibrahim, S. Sensfuss, Macromol. Rapid
Commun. 27 (2006) 1454.
[6] K.K.W. Lo, C.K. Li, J.S.Y. Lau, Organometallics 24 (2005) 4594.
[7] M.A. Baldo, S. Lamansky, P.E. Burrows, M.E. Thompson, S.R. Forrest, Appl. Phys.
Lett. 75 (1999) 4.
[8] C. Adachi, Appl. Phys. Lett. 77 (2000) 904.
[9] M. Ikai, S. Tokito, Y. Sakamoto, T. Suzuki, Y. Taga, Appl. Phys. Lett. 79 (2001)
156.
[42] R. Zhu, G.A. Wen, J.C. Feng, R.F. Chen, L. Zhao, H.P. Yao, Q.L. Fan, W. Wei, B.
Peng, W. Huang, Macromol. Rapid Commun. 26 (2005) 1729.
[10] S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, R. Kwong, I. Tsyba, M.
Bortz, B. Mui, R. Bau, M.E. Thompson, Inorg. Chem. 40 (2001) 1704.