Synthesis and characterization of cyclometalated iridium(III) complexes containing pyrimidine-based ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.04.011

New pyrimidine derivatives (pyr) have been synthesized using palladium-catalyzed Suzuki coupling reaction. These compounds can undergo cyclometalation with iridium trichloride to form bis-cyclometalated iridium complexes, (pyr)₂Ir(acac) (acac =

Full text of DOI:10.1016/j.jorganchem.2009.04.011

Journal of Organometallic Chemistry 694 (2009) 2757–2769
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of cyclometalated iridium(III) complexes
containing pyrimidine-based ligands
Cing-Fong Lin a, Wei-Sheng Huang b, Hsien-Hsin Chou b, Jiann T. Lin a,b,
*
a Department of Chemistry, National Central University, Chungli 320, Taiwan
b Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
New pyrimidine derivatives (pyr) have been synthesized using palladium-catalyzed Suzuki coupling
reaction. These compounds can undergo cyclometalation with iridium trichloride to form bis-cyclometa-
lated iridium complexes, (pyr)2Ir(acac) (acac = acetylacetonate; pyr = cyclometalated pyr). The substitu-
ents at the both cyclometalated phenyl ring and pyrimidine ring were found to affect both
electrochemical and photophysical properties of the complexes. Computation results on these complexes
are consistent with the electrochemical and photophysical data. The complexes are green-emitting with
good solution quantum yields at ꢀ0.30. Light-emitting devices using these complexes as dopants were
fabricated, and the device performance at 100 mA/cm2 are moderate: 9 (17 481 cd/m2, 4.8%, 18 cd/A,
5.1 lm/W); 10 (18 704 cd/m2, 4.9%, 18.9 cd/A, 4.7 lm/W); 13 (20 942 cd/m2, 5.4%, 21.0 cd/A, 6.1 lm/W).
Ó 2009 Elsevier B.V. All rights reserved.
Received 10 February 2009
Received in revised form 1 April 2009
Accepted 2 April 2009
Available online 19 April 2009
Keywords:
Iridium(III) complexes
Phosphorescence
Pyrimidine
Light-emitting diodes
1. Introduction
been used in materials such as liquid crystals [13] and OLEDs [14].
Pyrimidine is expected to be more electron-deficient than its pyri-
Transition-metal-based phosphorescent complexes have re-
ceived considerable attention in recent years because of their poten-
tial application in organic light-emitting diode (OLED) [1]. Strong
spin–orbital coupling induced by the heavier metal ion results in
mixing of the singlet and triplet excited states and leads to high
phosphorescence efficiency due to removal of the spin-forbidden
constraint of the radiative relaxation of triplet state [2]. Among
phosphorescent metal complexes, iridium(III) complexes appear
to be the most intensively explored owing to their easy syntheses
and excellent color tunability [3]. A large number of iridium com-
plexes reported in literature contained two cyclometalated ligands,
such as 2-phenylpyridine [4], quinozaline [5], phenyltriazole [6] and
2-phenylbenzoimidazole [7], together with an auxiliary ligand such
as acetylacetonate (acac) or picolinate (pic). High performance
phosphorescent OLEDs were achieved using these phosphorescent
dyes as dopants in a small molecule [5–8] or polymer host [9].
We have been interested in the development of new phosphores-
cent metal complexes for applications in OLEDs. Series of complexes
with cyclometalated benzimidazole-based [7a,10] and lepidine-
based [11] ligands were successfully synthesized and OLEDs using
these complexes were also demonstrated. In this report, we ex-
tended our research to cyclometalated pyrimidine-based ligands.
Pyrimidine, an important motif in natural products [12], has also
dine congener which has been used to construct electron-transport-
ing materials [15]. Cyclometalation with pyrimidine-containing
ligands may possibly afford complexes which are color tunable
and capable of electron transporting. In this article, we systemati-
cally designed and synthesized a series of new pyrimidine-based
iridium complexes which have cyclometalated electron-donating
(4-tert-butyl, 4-methoxy, 2-thiophenyl) or electron-withdrawing
(4-trifluormethyl, 4-fluoro, 3-trifluoromethyl) aromatic rings at
positions 2 and/or 5 of the pyrimidine moiety. To our knowledge,
there were only two reports on pyrimidine-based iridium complex
with cyclometalated aromatic ring residing at position 4 of the
pyrimidine moiety [16]. The electrochemical, photophysical and
electrophosphorescent properties of these iridium complexes will
be discussed.
2. Results and discussion
2.1. Synthesis of the materials
The synthetic routes and chemical structures of the pyrimidine
derivatives are shown in Scheme 1 and Chart 1 respectively. The
starting material, 5-bromo-2-iodopyrimidine, was synthesized by
following the literature procedures [17]. The preparation of pyrim-
idine ligands (abbreviated as pyr) involved a two-step synthesis
from 5-bromo-2-iodopyrimidine: (1) carbon–carbon bond forma-
tion via palladium-catalyzed Suzuki cross-coupling with the corre-
sponding arylboronic acid at the iodo-substituted carbon; (2) a
* Corresponding author. Address: Department of Chemistry, National Central
University, Chungli 320, Taiwan. Tel.: +886 2 27898522; fax: +886 2 27831237.
E-mail address: jtlin@chem.sinica.edu.tw (J.T. Lin).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.04.011

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C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
Pd(PPh3)4, Na2CO3,
N
N
N
toluene, THF, H2O
Ar1
Br
Ar1
B(OH)2
Br
I
+
N
Pd(PPh3)4, Na2CO3,
Pt(Bu)3 toluene,
THF, H2O
N
N
Ar2
Ar1
B(OH)2
Br
Ar1
Ar2
+
N
N
,
,
,
Ar1, Ar2 =
CF3
F
1 Ar1 = Ar2 = i
2 Ar1 = ii, Ar2 = i
3 Ar1 = iii, Ar2 = i
4 Ar1 = iv, Ar2 = i
5 Ar1 = v, Ar2 = i
6 Ar1 = v, Ar2 = ii
7 Ar1 = v, Ar2 = vi
i
iii
ii
CF3
S
OMe
,
,
v
iv
vi
Ar2
Ar2
Ar2
S / H2O
(3:1)
O
O
+
IrCl3. nH2O
1-7
N
N
N
N
N
N
Cl
Cl
4 HCl
+
O
O
Ir
Ir
Ir
Na2CO3, S
Ar1
n H2O
Ar1
Ar1
S= 2-methoxyethanol
2
2
2
8 from 1, 9 from 2
10 from 3, 11 from 4
12 from 5, 13 from 6
14 from 7
Scheme 1. Synthetic of the pyrimidine ligands and their iridium complexes.
F C
3
F
MeO
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Ir
Ir
N
Ir
N
MeO
F
Ir
F C
O
3
O
O
O
O
O
O
O
9
10
11
8
CF
3
S
CF
CF
3
3
N
CF
3
N
N
F C
3
N
N
N
N
N
N
F C
3
N
N
F
C
Ir
3
N
Ir
O
O
O
O
S
O
O
CF
3
14
13
12
Chart 1. Molecular structures of compound 8–14.
second Suzuki coupling with another arylboronic acid at the bro-
mo-substituted carbon. A bulky phosphine, PtBu3, was adding as
the cocatalyst [14a]. The preparation of cyclometalated iridium
complexes, (pyr)2Ir(acac) (pyr is the cyclometalated ligand), in-
volved a two-step synthesis: (1) IrCl3 ꢁ nH2O reacted with pyr to
form a chloro-bridged dimmer; (2) the dimer was then treated with
2,4-pentanedione in the presence of base to form (pyr)2Ir(acac).
molecular orbitals (HOMOs) in (pyr)2Ir(acac) were calculated rela-
tive to ferrocene (Fc) which has a value of ꢂ4.8 eV with respect to
the vacuum level [18]. The HOMO energies in combination with
the optical bandgaps derived from the absorption band edges were
used to calculate the energies of the lowest unoccupied molecular
orbitals (LUMOs) of the iridium complexes. Both HOMO and LUMO
energies are collected in Table 1.
No chemically reversible reduction waves were detected for
(pyr)2Ir(acac). In comparison, a quasi-reversible one-electron oxi-
dation wave ranging from 772 to 1424 mV (versus Ag/AgNO3)
was observed in each complex. This is attributed to the oxidation
of the iridium(III) based on previous electrochemical studies and
theoretical calculations [6,19]. These values appear to be high com-
pared to those of (ppy)2Ir(acac) (ppy = 2-phenylpyridine) [20],
2.2. Electrochemical properties
The electrochemical properties of (pyr)2Ir(acac) were studied
using cyclic voltammetry (CV), and the electrochemical data are
summarized in Table 1. The cyclic voltammograms of the com-
plexes are shown in Fig. 1. The energies of the highest occupied

C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
2759
Table 1
Photophysical and electrochemical data for (pyr)2Ir(acac) and pyr.
a
b
c
f
i
Compounds
kabs (log
e)
(nm)
kem (nm)
Up
sd
(l
s)
sr,
e l
s
Eox (mV)
HOMOg (eV)
LUMOh (eV)
Eg (eV)
1
2
296 (4.9)
292 (4.9)
3
4
5
6
290 (4.96)
306 (4.97)
291 (4.92)
282 (4.94)
313 (4.97)
7
8
9
277 (4.93), 307 (4.5), 380 (4.0), 438 (3.8)
304 (4.92), 380 (4.3), 435 (4.0), 472 (3.5)
306 (4.91), 367 (4.2), 418 (4.0)
275 (5.07), 318 (4.90), 376 (4.2), 430 (3.1)
275 (5.07), 301 (4.91), 375 (4.0), 425 (3.8)
277 (5.05), 378 (4.4), 425 (4.0), 462 (3.8)
327 (4.8), 385 (4.07), 446 (3.5)
544
542
522
532
526
531
558
0.28
0.29
0.34
0.32
0.27
0.32
0.052
1.16
2.39
2.15
2.26
1.49
1.30
4.18
4.13
8.24
6.32
7.06
5.52
4.06
80.4
772 (110)
1047 (110)
994 (100)
855 (120)
1360 (110)
1422 (100)
1387 (110)
ꢂ5.28
ꢂ5.55
ꢂ5.50
ꢂ5.35
ꢂ5.86
ꢂ5.92
ꢂ5.88
3.0
2.28
2.27
2.40
2.41
2.33
2.33
2.25
3.29
3.10
2.92
3.26
3.32
3.37
10
11
12
13
14
a
Measured in CH2Cl2 10ꢂ5 M at 298 K.
Recorded in toluene solutions at 298 K. Excitation wavelength was 400 nm for all iridium compounds.
Quantum yield was measured with respect to coumarin (Uem = 0.63 in acetonitrile).
Measured at 298 K. Excitation wavelength was 350 nm.
e is the absorption coefficient.
b
c
d
e
f
sr = s/Up.
Oxidation potentials reported are referenced to Ag/AgNO3. The values in parenthesis are the difference between the cathodic and anodic peaks. Conditions of cyclic
voltammetric measurements: platinum working electrode; Ag/AgNO3 reference electrode. Scan rate: 100 mV/s. Electrolyte: tetrabutylammonium hexafluorophosphate.
g
HOMO levels calculated from CV potentials using ferrocene as a standard [HOMO = ꢂ 4.8 + (EFc ꢂ Eox)].
h
LUMO levels derived via equation Eg = LUMO ꢂ HOMO.
i
Eg: bandgap. Eg was obtained from the absorption spectra.
(ppy)3Ir [21,22] and analogues, and (ppy)2Ir(L)+ (L = 2,20-bipyri-
dine) and analogues [23] as well. The highest occupied molecular
orbital (HOMO) of (ppy)2Ir(acac) was demonstrated to consist prin-
Y
X
3
4
2
N
cipally of a mixture of the 5d orbital of Ir and the phenyl-p orbital
N
5
1
of ppy [24]. Accordingly, variation of the substituents at the cyclo-
metalated phenyl ring will affect the oxidation potential of the irid-
ium ion in the congeners of (ppy)2Ir(acac) [20]. The HOMO of
(pyr)2Ir(acac) also consists mainly of the 5d of Ir and the cyclo-
6
Ir
3'
N
N
6'
2'
1'
metalated phenyl-p orbital based on the computation results (vide
X
4'
O
O
5'
infra). Therefore, the oxidation potential of Ir(III) in (pyr)2Ir(acac) is
expected to have a similar trend with that of (ppy)2Ir(acac). Com-
plexes 12 and 9 have an electron-withdrawing CF3 unit at positions
4 and 3 (Fig. 2) of the cyclometalated phenyl ring, respectively.
However, the former has a higher oxidation potential (1360 versus
1047 mV). This may be rationalized by the larger Hammett param-
Y
Fig. 2. The structure of (pyr)2Ir(acac) with labeling at the cyclometalated phenyl
ring.
eter
r of CF3 unit in 12, which is at the para position of the Ir atom
[25] and more effectively depletes the electron density of the Ir
atom. Complexes 8–11, having a different substituent at position
3 (Fig. 2) of the cyclometalated phenyl ring, have the oxidation
potentials in the order of
8 (772 mV) < 11 (855 mV) < 10
(994 mV) < 9 (1047 mV). This is consistent with the order of Ham-
mett parameter rmeta [25], CMe3 (ꢂ0.09) < OMe (0.10) < F
(0.34) < CF3 (0.46). The substituent at position 4 (meta to the li-
gated nitrogen atom) of the pyrimidine ring in pyr also affects
the oxidation potential of the iridium ion, though to a lesser extent.
For complexes 12–14 which have a different substituent at posi-
tion 4 of the pyrimidine ring, the oxidation potentials increase in
the order of 12 (1360 mV) < 14 (1387 mV) < 13 (1422 mV). This is
consistent with the order of Hammett parameter for the meta-sub-
stituent. Possibly more electron-deficient nitrogen atom lowers the
energy level of the metal because of stronger metal-to-ligand
charge-transfer.
30
8
20
9
10
10
0
11
13
-10
2.3. Photophysical properties
12
The photophysical data of pyr and (pyr)2Ir(acac) are collected in
Table 1. Absorption spectra for selected free ligands and (pyr)2
Ir(acac) complexes are shown in Fig. 3. The strong absorption
bands of the pyr ligands observed at about 250ꢂ350 nm with high
-20
14
-30
extinction coefficients (e
> 80 000 Mꢂ1 cmꢂ1) are mainly due to
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
p–p* transitions. Ligands with electron-donating substituents such
as OMe (4) and thiophene ring (7) have a longer absorption
Voltage (V)
wavelength than others, possibly there exists weak charge-transfer
Fig. 1. Cyclic voltammograms of 8–14, measured in CH2Cl2.

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C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
180000
b
a
100000
80000
60000
40000
20000
0
160000
2
9
140000
120000
100000
80000
60000
40000
20000
0
3
4
10
11
13
300
400
500
300
400
500
wavelength (nm)
Wavelength (nm)
Fig. 3. Absorption spectra of compounds in CH2Cl2 (a) pyr ligands and (b) (pyr)2Ir(acac).
from these electron donors to the electron-deficient acceptor,
pyrimidine. Ligand (6) with two electron-withdrawing substitu-
ents, CF3, appears to have the shortest absorption wavelength.
The strong absorption bands of complexes (pyr)2Ir(acac) at about
250ꢂ380 nm with high extinction coefficients are assigned to the
metalated ligand, i.e., lowering of the HOMO level. Conversely,
CF3 group at positions 3 and 5 of the cyclometalated phenyl ring
will render position 1 of the aromatic ring less electron deficient.
We observed similar phenomena: kem (12) < kem (9) It was also re-
ported that fluorine atom behaved differently from CF3 group be-
cause of its mesomeric and inductive nature [26]. Indeed, the
complex 10 was found to have a shorter emission wavelength than
not only 9, but also 8 which has an inductive-only electron-donat-
ing tert-butyl group in position 3. It is believed that the shorter
emission wavelength of 11 (kem = 532 nm) than 8 (kem = 544 nm)
is due to the mesomeric and inductive nature of the OMe group
[25]. These results are also supported by the molecular orbital cal-
culations (vide infra). Complexes 12ꢂ14 have the same cyclometa-
lated phenyl ring but different substituents at position 5 of the
pyrimidine. The order of kem values, 12 < 13 < 14, implies that the
LUMO level also plays an important role in color tuning. Though
the substituent at position 5’ of pyrimidine can only have inductive
effect on the ligated nitrogen (vide supra) of pyrimidine, it is be-
lieved that the thiophene ring is beneficial to lowering the energy
p–p* transitions of the pyr ligands by comparison with the absorp-
tion spectra of the corresponding pyr ligands. The absorption
bands at 380ꢂ520 nm can be assigned to the spin-allowed me-
tal-to-ligand charge-transfer (1MLCT) and the spin-forbidden
3MLCT bands. As aforementioned, the substituent affects the
HOMO energy level in the complexes. The LUMO energy level,
being delocalized over the whole ligand
p orbitals (vide infra), is
also affected by the substituent. Therefore, it is less easy to ratio-
nalize the trend of 1MLCT and 3MLCT energies.
The pyr ligands emit in the violet-blue region. In contrast, the
emission wavelengths of (pyr)2Ir(acac) fall in the range of
kem = 522–558 nm, which vary with the structures of the cyclo-
metalated ligands. All phosphorescence spectra of (pyr)2Ir(acac)
are shown in Fig. 4. The prominent vibronic feature of the emission
spectra indicates that there is significant mixing of the 3MLCT and
of the p* orbital of pyr ligand via delocalization.
3
*
pp transitions. It was reported that an inductive-only electron-
withdrawing CF3 group at positions 4 and 2 of the cyclometalated
phenyl ring (Fig. 2) will lead to electron deficiency of position 1 and
result in hypsochromic shift of the emission [26]. Such an outcome
Except for 14 (Up = 0.052), most of (pyr)2Ir(acac) exhibit good
solution phosphorescence quantum yields (Up = 0.28–0.34) at
room temperature under air free condition, indicating that there
exists strong spin–orbit coupling. The relatively low quantum yield
of 14 is supported by the significantly larger non-radiative decay
rate constant than the radiative constant (22 versus
1.2 ꢃ 104 sꢂ1). The observed phosphorescence lifetimes of ca.
was attributed to the lowering of the
r
-donation from the cyclo-
1.16–4.18
deduce the radiative lifetimes of 4.14–80.4
Uem. The complexes should be appropriate for phosphores-
ls in degassed toluene for all complexes were used to
1.0
0.8
0.6
0.4
0.2
0.0
ls via the equation
8
9
sr = s/
10
11
12
13
14
cent OLEDs because of their short excited state lifetimes and high
phosphorescence quantum yields.
2.4. MO calculation
Molecular orbital calculations using Q-Chem (see Experimental
section) [27] on selected complexes were carried out to gain more
insight into the photophysical properties of the complexes. The
features of the three highest occupied (HOMO, HOMO ꢂ 1, and
HOMO ꢂ 2) and the three lowest unoccupied (LUMO, LUMO + 1,
and LUMO + 2) frontier orbitals mainly involved in the transition
are depicted in Fig. 5, and the description and energy gaps of each
transition are listed in Table 2. The electron densities of the HOMO
and HOMO ꢂ 1 are located mainly on the metal, acetylacetonate
and the cyclometalated phenyl ring, whereas the LUMO and
500
550
600
650
700
Wavelength (nm)
Fig. 4. Phosphorescence spectra of all complexes in toluene at 298 K.

C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
2761
Fig. 5. Selected frontier orbitals for (pyr)2Ir(acac).
LUMO + 1 are distributed on the whole cyclometalated ligand. The
dominance of the HOMO ? LUMO transition in the S0 ? T1 transi-
12–14, have HOMO energy levels in the order of 12 (ꢂ5.36 eV) > 14
(ꢂ5.42 eV) > 13 (ꢂ5.63 eV). These results clearly meet the trend of
Hammett parameters and the electrochemical data (vide supra).
The order of the calculated triplet energy, 14 < 9 ꢄ 8 < 13
< 11 < 10 ꢄ 12, is only slightly different from the experimental re-
sults of 14 < 8 ꢄ 9 < 11 ꢄ 13 < 12 < 10.
tion points that both MLCT and
p–p* transitions have significant
contributions. For complexes 8–12, the HOMO energy level (Chart
2) is more stabilized with increasing electron-withdrawing ability
of substitutents at position 3 of the cyclometalated phenyl ring: 11
(ꢂ4.82 eV) ꢄ 8 (ꢂ4.84 eV) > 10 (ꢂ5.09 eV) > 9 (ꢂ5.28 eV). Further-
more, the substituent at position 4 of the cyclometalated phenyl
ring has a larger effect on the HOMO energy level than that at posi-
tion 3. Consequently, an electron-deficient CF3 group at position 4
of the ligated phenyl group features more stabilizing HOMO orbital
and larger energy gap of the complex than that at position 3 of the
same phenyl group. This is evidenced by the lower HOMO energy
(ꢂ5.36 eV) and larger energy gap (3.43 eV) of 12 compared to 9
(ꢂ5.28 and 3.35 eV). The measured oxidation potentials and band-
gaps are in support of these computation results. Complexes with
varied substituents at position 5’ of the pyrimidine ring of pyr, e.g.,
TD-DFT calculation at the same level were also performed to
give more detailed information of aforementioned complexes,
and the description and energy gaps of each transition are listed
in Table 2 (see computational methodology). The lowest-lying
allowed transitions (S1) are excited mainly from HOMO to
LUMO/LUMO + 1 with considerable oscillator strength (0.072–
0.108), assigned to the p–p* transition of pyr ligand. On the other
hand, the two lowest-lying T1 and T2 transitions of all iridium
analogues are constituted of transitions mainly from HOMO/
HOMO ꢂ 1 to LUMO/LUMO + 1 (63–85%) and non-negligible
contribution (5–7%) from HOMO ꢂ 2/HOMO ꢂ 3 to LUMO/

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C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
Fig. 5 (continued)
LUMO + 1. These are also ascribed to a mixture of 3MLCT charge-
transfer and ligand-centered 3pp* transitions. It is interesting that
both T1 and T2 transitions of 11 have small contribution (17%) from
HOMO ꢂ 1, indicating that the ligand-centered 3pp* transition also
has some charge-transfer character because of the electron-donat-
ing nature of the methoxy group. Also, the HOMO ꢂ 1 orbital has
notable contribution form the acac ligand in all complexes.
A comparison is made between the complexes in this study and
their pyrimidine isomers where the non-ligated nitrogen atom of
the pyrimidine is at position 50 instead of 30. Incorporation of a
CF3 unit at position 40 shifts the emission to the red [16]. A
homoleptic Ir complex derived from pyrimidine isomer, 3,
6-bis(phenyl)pyridazine, was reported to emit green light. The
emission was tuned to red by replacement of pyridazine with
phthalazine [28]. Compared to the substituent at position 3, the
substituent at position 4 is expected to have more electronic
influence on position 1 because HOMO has population at position
4 instead of 3. We therefore seek for the possibility of blue-shifting
the kem values in these complexes by replacing the CF3 unit in 12
with a CN unit (the complex is abbreviated as A). Though there is

C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
2763
Fig. 5 (continued)
lowering of the HOMO level, the LUMO level is lowered by nearly
the same extent (Table 2). Consequently, complexes 12 and A have
comparable kem values. Hypsochromic shift of the emission is ob-
served upon incorporation of an electron-donating dimethylamino
unit at position 40 of A (the complex is abbreviated as B) due to its
strong inductive influence on the ligated nitrogen atom at the para
position. More dramatic hypsochromic shift of the emission is ob-
served only upon replacing the tert-butylphenyl unit at position 5’
and the hydrogen atom at position 40 of 12 by a hydrogen atom and
dimethylamino unit, respectively (the complex is abbreviated as
C). Obviously, the LUMO energy level is raised significantly upon
removal of tert-butylphenyl unit because the LUMO is populated
fluorene (BPAPF) (40 nm)/6 wt% (pyr)2Ir(acac) doped in 4,40-N,
N-dicarbarzolebiphenyl (CBP) (30 nm)/2,9-dimethyl-4,7-diphe-
nyl-1,10-phenanthroline (BCP) (10 nm)/tris(8-hydroxyquinoline)
aluminum (Alq3) (30 nm)/Mg:Ag; where BPAPF [29] was used
the hole-transporting layer, CBP as the host material, BCP as the
hole and exciton blocking layer, and Alq3 as the electron-trans-
porting layer. Fig. 6 shows the configurations of the devices and
the molecular structures of the compounds used in these devices.
The performance parameters of the EL devices are collected in
Table 3 and the EL spectra of these devices are shown in Fig. 7.
All the devices emitted light characteristic of (pyr)2Ir(acac) which
ranged from 532 to 550 nm and had narrow full width at half
maximum (FWHM).
through the three aromatic rings in 8–14. In contrast, a strong
donating substituent at position 4 of the cyclometalated phenyl
ring and a strong
-withdrawing substituent at position 40 of the
p-
All devices exhibited turn-on voltages at 3.5ꢂ4.0 V. The device
performances are shown in Figs. 8 and 9 which depicts the cur-
rent–voltage–luminance properties, external quantum efficiencies,
and power efficiencies versus current density, respectively. The
performance of the devices at a current density of 100 mA/cm2 is
p
pyrimidine ring (Fig. 2) will have opposite effect.
2.5. Electroluminescent properties
moderate:
9
(17 481 cd/m2, 4.8%, 18 cd/A, 5.1 lm/W); 10
Three of the iridium complexes were selected for device fabri-
cation. The device structures used are similar to those in our ear-
lier report [7a]: ITO/9,9-bis{4-[di(p-biphenyl)aminophenyl]}-
(18 704 cd/m2, 4.9%, 18.9 cd/A, 4.7 lm/W); 13 (20 942 cd/m2, 5.4%,
21.0 cd/A, 6.1 lm/W). Though the performance of the devices is
better than those of normal green-emitting fluorescence OLEDs,

2764
C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
Fig. 5 (continued)
it is inferior to that of (ppy)2Ir(acac)-based green-emitting OLED
of similar device configuration [30]. With optimized device
configurations, the green-emitting OLEDs based on (ppy)2Ir(acac)
can have external quantum efficiency as high as ꢀ19% [2c,31].
Such an outcome may be due to inefficient trapping of the holes
in the three complexes due to their insufficiently high HOMO
levels (5.50–5.92 eV) compared to that of the CBP host (HOMO =
5.5 eV), which renders direct exciton formation in the complexes
less efficient. The efficiencies of the devices dropped rapidly
with increased applied voltage possibly due to the increased
opportunity for triplet–triplet annihilation of the phosphor-
bound excitons. Therefore, optimization of the device configura-
tion is necessary for (pyr)2Ir(acac) in order to have practical
applications.
3. Conclusion
In summary, we have synthesized and characterized new irid-
ium(III) complexes using pyrimidine derivatives as the cyclometa-
lated ligands and b-diketonate as the ancillary ligand. Hammett
parameters nicely rationalize the trend of the oxidation of the Ir
center and the emission wavelength in these complexes. Color-tun-
ing can be achieved via appropriate variation of the substituents at
the pyridimine ligands, which is also evidenced from the computa-
tion results. The complexes emit in the range of kmax = 522–558 nm
in toluene with solution quantum yields ranging from 0.05 to 0.32.
The EL devices using these complexes as the dopants in CBP, BPAPF
and Alq3 as the hole- and electron-transporting layers, respectively,
and BCP as the hole-blocking layer, exhibited moderate perfor-

C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
2765
Table 2
0.00
Calculated lower-lying transitions of (pyr)2Ir(acac).a
Compounds
State
T1
Assignmentsb
Ecal (eV)
kcal (nm)
fc
-1.12
-1.00
-2.00
-3.00
-4.00
-5.00
-6.00
-7.00
-1.17
-1.39
-1.39
-1.06
-1.28
-1.52
-1.52
-1.42
-1.63
-1.66
-1.47
-1.55
8
H3 ? L (6%)
H ? L (17%)
H ? L1 (67%)
H ? L (65%)
H ? L1 (19%)
H ? L (79%)
H ? L1 (11%)
H ? L2 (5%)
H ? L (11%)
H ? L1 (80%)
H3 ? L1 (6%)
H ? L (83%)
H3 ? L (7%)
H ? L1 (85%)
H ? L (93%)
H ? L1 (92%)
H2 ? L1 (8%)
H ? L (74%)
H2 ? L (10%)
H ? L1 (72%)
H ? L (89%)
H ? L2 (7%)
H ? L1 (89%)
H ? L3 (6%)
H2 ? L (8%)
H1 ? L1 (17%)
H ? L (63%)
H3 ? L (5%)
H2 ? L1 (6%)
H1 ? L (17%)
H ? L1 (64%)
H ? L (85%)
H ? L2 (10%)
H ? L1 (88%)
H ? L3 (7%)
H2 ? L1 (8%)
H ? L (79%)
H2 ? L (9%)
H ? L1 (79%)
H ? L (91%)
H ? L2 (6%)
H ? L1 (91%)
H3 ? L1 (7%)
H ? L (81%)
H3 ? L (7%)
H ? L1 (83%)
H ? L (92%)
H ? L1 (91%)
H3 ? L (7%)
H2 ? L1 (15%)
H ? L (67%)
H3 ? L1 (7%)
H2 ? L (18%)
H ? L1 (64%)
H ? L (93%)
H ? L1 (91%)
H2 ? L1 (9%)
H ? L (79%)
H2 ? L (11%)
H ? L1 (78%)
H ? L (92%)
H ? L1 (93%)
H3 ? L1 (5%)
H ? L (79%)
H3 ? L (8%)
H1 ? L (6%)
H ? L1 (69%)
H ? L (96%)
H ? L1 (94%)
H ? L (83%)
H3 ? L (6%)
H ? L1 (78%)
H ? L (97%)
H ? L1 (94%)
2.40
517.9
0.000
-1.61
-1.69
-1.58
-1.90
-1.93
-1.66
-1.90
-1.93
-1.77
-2.10
-2.15
-1.85
-2.10
-2.12
-1.99
-2.31
-2.34
T2
S1
2.40
2.64
517.3
470.0
0.000
0.072
S2
T1
T2
2.66
2.39
2.41
466.0
519.3
514.9
0.020
0.000
0.000
-4.82
-4.84
9
-5.09
-5.20
-5.36
-5.22
-5.52
-5.80
-5.25
-5.50
-5.28
-5.69
-6.12
-5.36
-5.66
-5.36
-5.77
-6.18
-5.42
-5.50
-5.82
-5.55
-5.63
-6.04
-5.80
-6.15
-5.85
-5.99
-6.34
S1
S2
T1
2.67
2.72
2.48
464.8
456.4
499.9
0.106
0.005
0.000
-6.50
10
8
9
10
11
12
13
14
A
B
C
T2
S1
S2
T1
2.51
2.76
2.82
2.46
495.3
449.3
440.4
503.8
0.000
0.094
0.007
0.000
Chart 2. Schematic representation of the calculated electronic structure in the gas-
phase for complexes 8–14.
Mg: Ag
11
Alq3 (30 nm)
BCP (10 nm)
T2
2.47
502.3
0.000
6 wt% (pyr)2Ir(acac) in
CBP (30 nm)
S1
S2
T1
T2
S1
2.76
2.79
2.49
2.50
2.74
450.4
444.9
498.9
496.4
452.5
0.079
0.009
0.000
0.000
0.093
BPAPF (40 nm)
ITO
12
Glass
S2
T1
2.80
2.42
443.9
512.7
0.006
0.000
13
14
N
N
N
N
T2
2.43
510.0
0.000
S1
S2
T1
2.66
2.71
2.34
467.2
457.5
531.4
0.096
0.007
0.000
CBP
BPAPF
T2
2.36
526.0
0.000
O
Ph
Ph
Al
S1
S2
T1
2.63
2.70
2.49
471.3
459.0
498.9
0.108
0.007
0.000
N
N
N
A
B
3
CH3
H3C
T2
2.51
494.8
0.000
BCP
Alq3
S1
S2
T1
2.75
2.81
2.62
450.9
441.2
473.9
0.092
0.007
0.000
Fig. 6. The configurations of the OLED devices, and the molecular structures of the
compounds used in the devices.
T2
2.68
463.8
0.000
mance. The best performance data are found in 13-based device:
20 942 cd/m2, 5.4%, 21.0 cd/A, 6.1 lm/W at 100 mA/cm2.
S1
S2
T1
T2
2.88
3.01
2.71
2.77
430.6
412.7
457.2
447.7
0.107
0.008
0.000
0.000
C
4. Experimental section
S1
S2
2.98
3.09
417.0
401.1
0.069
0.001
4.1. General information
a
The 1H NMR spectra were recorded on a Bruker AMX400 spec-
trometer. FAB-mass spectra were collected on a JMS-700 double
focusing mass spectrometer (JEOL, Tokyo, Japan) with a resolution
of 3000 for low resolution and 8000 for high resolution (5% valley
Results are based on gas-phase TD-DFT calculation.
H = HOMO, L = LUMO, H1 = the next highest occupied molecular orbital, or
b
HOMO ꢂ 1, H2 = HOMO ꢂ 2, L1 = LUMO + 1, L2 = LUMO + 2. In parentheses is the
population of a pair of MO excitations.
c
Oscillator strength.

2766
C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
Table 3
700
Electrophophorescence data for (pyr)2Ir(acac) complexes.
9
10
13
Compound
9
10
13
600
500
400
300
200
100
Von (V)
3.8
4.0
3.5
Lmax (cd/m2)
(V at Lmax (V))
kem (nm)
61 201
(15.0)
550
0.43, 0.56
66
8.46
18.56
30.0
42 769
(15.0)
532
0.34, 0.62
60
7.44
14.89
28.8
70 673
(15.0)
542
0.38, 0.60
66
8.02
16.11
31.3
CIE (x,y)
fwhm (nm)
gext,max (%)
gp,max (lm/W)
gc,max (cd/A)
L (cd/m2)*
gext (%)*
17 481
4.8
5.1
18 704
4.9
4.7
20 942
5.4
6.1
0
gp (lm/W)*
gc (cd/A)*
80000
18.0
18.9
21.0
0
2
4
6
8
10
12
14
16
70000
60000
50000
40000
30000
20000
10000
0
Lmax, maximum luminance; L, luminance; Von, turn-on voltage; V, voltage; gext,max
maximum external quantum efficiency; p,max, maximum power efficiency; gc,max
maximum current efficiency; ext, external quantum efficiency;
,
,
g
9
g
g
p, power effi-
10
ciency; gc, current efficiency; fwhm, full width at half maximum.
13
*
At a current density of 100 mA/cm2.
1.0
0.8
0.6
0.4
0.2
0.0
9
10
13
0
2
4
6
8
10
12
14
16
Voltage (V)
Fig. 8. I–V–L characteristics for the devices.
taken as the average of three separate determinations and were
reproducible within 10%. Luminescence lifetimes were determined
on an Edinburgh FL920 time-correlated pulsed single-photon-
35
300
400
500
600
700
800
30
9
10
Wavelength (nm)
25
20
15
10
5
13
Fig. 7. EL spectra of the devices for selected complexes.
definition). For FAB-mass spectra, the source accelerating voltage
was operated at 10 kV with a Xe gun, using 3-nitrobenzyl alcohol
as the matrix. MALDI-mass spectra were collected on a Voyager
DE-PRO (Applied Biosystem, Houston, USA) equipped with a nitro-
gen laser (337 nm) and operated in the delayed extraction reflector
mode. Elemental analyses were performed on a Perkin–Elmer 2400
CHN analyzer. Cyclic voltammetry experiments were performed
with a BHI-621B electrochemical analyzer. All measurements were
carried out at room temperature with a conventional three-elec-
trode configuration consisting of a platinum working electrode,
an auxiliary electrode, and a nonaqueous Ag/AgNO3 reference elec-
trode. The E1/2 values were determined as 1/2(Eap þ Epc ), where Epa
and Ecp are the anodic and cathodic peak potentials, respectively.
The solvent used was CH2Cl2 and the supporting electrolyte was
0.1 M tetrabutylammonium hexafluorophosphate. Electronic
absorption spectra were obtained on a Cary 50 Probe UV–Vis spec-
trometer. Emission spectra were recorded in deoxygenated solu-
tions at 298 K by a JASCO FP-6500 fluorescence spectrometer.
The emission spectra were collected on samples with o.d. ꢀ 0.1
at the excitation wavelength. UV–Vis spectra were checked before
and after irradiation to monitor any possible sample degradation.
Emission maxima were reproducible within 2 nm. Luminescence
0
9
0
100
200
300
400
500
600
700
8
7
6
5
4
3
2
1
0
9
10
13
0
100
200
300
400
500
600
700
Current density (mA/cm2)
quantum yields
(Uem) were calculated relative to coumarin
(Uem = 0.63 in acetonitrile). Luminescence quantum yields were
Fig. 9. External quantum efficiencies and power efficiencies of the devices.

C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
2767
counting instrument. Samples were degassed via freeze-thaw-
4.3. General procedure for the synthesis of (pyr)2Ir(acac)
pump cycle at least three times prior to measurements. Samples
were excited at 337 nm from a nitrogen pulsed flashlamp with
1 ns FWHM pulse duration transmitted through a Czerny–Turner
design monochromator. Emission was detected at 90° via a second
Czerny–Turner design monochromator onto a thermoelectrically
cooled red-sensitive photomultiplier tube. The resulting photon
counts were stored on a microprocessor-based multichannel ana-
lyzer. The instrument response function was profiled using a scat-
ter solution and subsequently deconvoluted from the emission
data to yield an undisturbed decay. Nonlinear least square fittings
of the decay curves were performed with the Levenburg–Marqu-
ardt algorithm and implemented by the Edinburgh Instruments
F900 software. The reported values represent the average of at
least three readings.
.
To a flask containing IrCl3 nH2O (176 mg, 0.50 mmol) and 1.0
equiv. of pyr ligands, a 3:1 mixture of 2-ethoxyethanol and water
(25 mL) was added. The mixture was then refluxed for 48 h and
cooled to room temperature. After cooling, the reaction was
quenched by water and the resulting mixture was washed with
acetone and hexanes. The solid formed was collected by filtration
and pumped dry to give the crude product of the l-chloro-bridged
Ir(III) dimer. This crude product was mixed with Na2CO3 (0.30 g,
3.0 mmol), 2,4-pentanedione (0.30 g, 3.0 mmol) and 2-methoxy-
ethanol (20 mL) in a flask. The mixture was then heated to reflux
for 24 h. After cooling, the reaction was quenched by water and
the mixture was extracted with CH2Cl2. The combined extracts
were then washed with brine, dried over MgSO4, and evaporated
to dryness. The crude product was purified by column chromatog-
raphy on a silica gel column using a mixture of CH2Cl2 and hexanes
(1:1 by volume) as the eluent.
4.2. General procedure for the syntheses of pyrimidine ligands
Pyrimidine ligands were obtained via sequential palladium-cat-
alysed Suzuki cross-coupling reactions with appropriate arylbornic
acid. A mixture of arylboronic acid (10 mmol), 5-bromo-2-iodopyr-
imidine (2.85 g, 10 mmol), Na2CO3 (10 ml, 2 M in H2O, 20 mmol),
and Pd(PPh3)4 (115 mg, 1.0 mol%) and toluene (25 ml) was refluxed
for 24 h under nitrogen. The resulting mixture was allowed to cool
to room temperature, diluted with CH2Cl2 (10 mL) and extracted
with brine. Combined organic extracts were dried over MgSO4.
The concentrated crude intermediate was purified by column chro-
matography on silica gel and eluted with CH2Cl2/hexanes. The
intermediate then underwent a second Suzuki cross-coupling reac-
tion with another arylboronic acid under similar condition except
that PtBu3 was added as the cocatalyst.
2,5-Bis-(4-tert-butyl-phenyl)-pyrimidine (1): White powders.
Yield = 70%. 1H NMR (400 MHz, CDCl3): d 8.99 (s, 2H, pyrimidine),
8.38 (d, 2H, J = 8.4 Hz, C6H4), 7.53 (m, 6H, C6H4), 1.36 (s, 18H,
CH3). FABMS: m/z 345.2 (M+H)+.
5-(4-tert-Butyl-phenyl)-2-(4-trifluoromethyl-phenyl)-pyrimidine
(2): White powders. Yield = 70%. 1H NMR (400 MHz, CDCl3): d 9.02
(s, 2H, pyrimidine), 8.60 (d, 2H, J = 7.6 Hz, C6H4CF3), 7.75 (d, 2H,
J = 7.6 Hz, C6H4CF3), 7.57 (m, 4H, C6H4), 1.37 (s, 9H, CH3). FABMS:
m/z 357.2 (M+H)+.
Compound 8: Orange powders. Yield = 12%. 1H NMR (400 MHz,
CDCl3):
d 8.95 (d, 2H, J = 2.8 Hz, pyrimidine), 8.89 (d, 2H,
J = 2.8 Hz, pyrimidine), 7.84 (d, 2H, J = 8.4 Hz, C6H3), 7.56 (s, 8H,
C6H4), 6.93 (d, 2H, J = 8.4 Hz, C6H3), 6.33 (s, 2H, C6H3), 5.19 (s, 1H,
acac-CH), 1.79 (s, 6H, acac-CH3), 1.37 (s, 18H, CH3), 1.05 (s, 18H,
CH3). FABMS: m/z 978.4 (M+). Anal. Calc. for C53H61N4O2Ir: C,
65.07; H, 6.28; N, 5.73. Found: C, 64.86; H, 6.08; N, 5.71%.
Compound 9: Yellow–orange powders. Yield = 21%. 1H NMR
(400 MHz, CDCl3): d 9.06 (s, 2H, pyrimidine), 8.86 (s, 2H, pyrimi-
dine), 8.07 (d, 2H, J = 8.4 Hz, C6H3CF3), 7.58 (d, 8H, J = 1.2 Hz,
C6H4CF3), 7.14 (d, 2H, J = 8.4 Hz, C6H3CF3), 6.52 (s, 2H, C6H3CF3),
5.28 (s, 1H, acac-CH), 1.82 (s, 6H, acac-CH3), 1.37 (s, 18H, CH3).
FABMS: m/z 1002.0 (M+). Anal. Calc. for C47H43F6N4O2Ir: C, 56.33;
H, 4.33; N, 5.59. Found: C, 56.07; H, 4.21; N, 5.38%.
Compound 10: Yellow powders. Yield = 12%. 1H NMR (400 MHz,
CDCl3): d 8.99 (d, 2H, J = 2.8 Hz, pyrimidine), 8.79 (d, 2H, J = 2.8 Hz,
pyrimidine), 7.98 (td, 2H, J = 8.8 and 2.4 Hz, C6H3F), 7.57 (s, 8H,
C6H4), 6.62 (td, 2H, J = 8.8 and 2.4 Hz, C6H3F), 5.98 (d, 1H,
J = 2.4 Hz, C6H3F), 5.96 (d, 1H, J = 2.4 Hz, C6H3F), 5.30 (s, 1H, acac-
CH), 1.82 (s, 6H, acac-CH3), 1.37 (s, 18H, CH3). FABMS: m/z 902.2
(M+). Anal. Calc. for: C45H43F2N4O2Ir: C, 59.92; H, 4.80; N, 6.21.
Found: C, 60.09; H, 4.60; N, 6.00%.
5-(4-tert-Butyl-phenyl)-2-(4-fluoro-phenyl)-pyrimidine
(3):
Compound 11: Yellow powders. Yield = 31%. H NMR (400 MHz,
CDCl3): d 8.92 (d, 2H, J = 2.8 Hz, pyrimidine), 8.80 (d, 2H,
White powders. Yield = 92%. 1H NMR (400 MHz, CDCl3): d 8.98 (s,
2H, pyrimidine), 8.46–8.44 (m, 2H, C6H4F), 7.57–7.52 (m, 4H,
C6H4), 7.5 (td, 2H, J = 8.8 and 2.4 Hz, C6H4F), 1.35 (s, 9H, CH3). FAB-
MS: m/z 306.1 (M+).
J = 2.8 Hz, pyrimidine), 7.91 (d, 2H, J = 8.4 Hz, C6H3), 7.55 (s, 8H,
C6H4), 6.49 (d, 2H, J = 8.4 Hz, C6H3), 5.87 (s, 2H, C6H3), 5.22 (s, 1H,
acac-CH), 3.57 (s, 6H, OCH3), 1.81 (s, 6H, acac-CH3), 1.37 (s, 18H,
CH3). FABMS: m/z 926.2 (M+). Anal. Calc. for: C47H49N4O4Ir: C,
60.95; H, 5.33; N, 6.05. Found: C, 60.70; H, 4.97; N, 5.75%.
Compound 12: Yellow powders. Yield = 12%. 1H NMR (400 MHz,
CDCL3): d 9.06 (d, 2H, J = 2.8 Hz, pyrimidine), 8.86 (s, 2H, J = 2.8 Hz,
pyrimidine), 8.23 (s, 2H, C6H3CF3), 7.58 (s, 8H, C6H4), 6.99 (d, 2H,
J = 8.0 Hz, C6H3CF3), 6.47 (d, 2H, J = 8.0 Hz, C6H3CF3), 5.28 (s, 1 H,
acac-CH), 1.82 (s, 6H, acac-CH3), 1.37 (s, 18H, CH3). FABMS: m/z
1002.5 (M+). Anal. Calc. for: C47H43F2F6N4O2Ir: C, 56.33; H, 4.33;
N, 5.59. Found: C, 56.73; H, 4.49; N, 5.43%.
5-(4-tert-Butyl-phenyl)-2-(4-methoxy-phenyl)-pyrimidine
(4):
White powders. Yield = 76%. 1H NMR (400 MHz, CDCl3): d 8.98 (s,
2H, pyrimidine), 8.41 (dd, 2H, J = 8.8 and 2.0 Hz, C6H4OMe), 7.56–
7.51 (m, 4H, C6H4), 7.00 (dd, 2H, J = 8.8 and 2.0 Hz, C6H4OCH3),
3.88 (s, 3H, OCH3), 1.36 (s, 9H, CH3). FABMS: m/z 319.2 (M+H)+.
5-(4-tert-Butyl-phenyl)-2-(3-trifluoromethyl-phenyl)-pyrimidine (5):
White powders. Yield = 73%. 1H NMR (400 MHz, CDCl3): d 9.02 (s,
2H, pyrimidine), 8.82 (s, 1H, C6H4CF3), 8.66 (d, 1H, J = 7.6 Hz,
C6H4CF3), 7.73 (d, 1H, J = 7.6 Hz, C6H4CF3), 7.58 (m, 5H, C6H4 and
C6H4CF3), 1.37 (s, 9H, CH3). FABMS: m/z 357.1 (M+H)+.
Compound 13: Yellow powders. Yield = 26%. 1H NMR (400 MHz,
CDCl3): d 9.09 (d, 2H, J = 2.8 Hz, pyrimidine), 8.86 (d, 2H, J = 2.8 Hz,
pyrimidine), 8.27 (s, 2H, C6H3CF3), 7.86–7.73 (m, 8H, C6H4CF3), 7.03
(d, 2H, J = 8.0 Hz, C6H3CF3), 6.47 (d, 2H, J = 8.0 Hz, C6H3CF3), 5.32 (s,
1 H, acac-CH), 1.84 (s, 6H, acac-CH3). FABMS: m/z 1026.2 (M+).
Anal. Calc. for C41H25F12N4O2Ir: C, 48.00; H, 2.46; N, 5.46. Found:
C, 48.12; H, 2.41; N, 5.42%.
2-(3-Trifluoromethyl-phenyl)-5-(4-trifluoromethyl-phenyl)-pyrim-
idine (6): White powders. Yield = 67%. 1H NMR (400 MHz, CDCl3): d
9.04 (s, 2H, pyrimidine), 8.79 (s, 1H, C6H4CF3), 8.69 (d, 1H,
J = 7.6 Hz, C6H4CF3), 7.76 (m, 5H, C6H4CF3 and C6H4), 7.63 (t, 1H,
J = 8.0 Hz, C6H4CF3). FABMS: m/z 369.1 (M+H)+.
5-Thiophen-2-yl-2-(3-trifluoromethyl-phenyl)-pyrimidine
(7):
White powders. Yield = 65%.1H NMR (400 MHz, CDCl3): d 9.02 (s,
2 H, pyrimidine), 8.75 (s, 1H, C6H4CF3), 8.65 (d, 1H, J = 7.6 Hz,
C6H4CF3), 7.73 (d, 1H, J = 7.6 Hz, C6H4CF3), 7.61 (t, 1H, J = 7.6 Hz,
C6H4CF3), 7.45–7.44 (m, 2H, thiophene), 7.17 (t, 1H, J = 4.0 Hz, thi-
ophene). FABMS: m/z 307.2 (M+H)+.
Compound 14: Orange powders. Yield = 22%. 1H NMR (400 MHz,
CDCl3): d 9.05 (d, 2H, J = 2.8 Hz, pyrimidine), 8.83 (d, 2H, J = 2.8 Hz,
pyrimidine), 8.21 (s, 2H, C6H3CF3), 7.47 (m, 4H, thiophene), 7.19 (t,
2H, J = 3.6 Hz, thiophene), 7.00 (d, 2H, J = 8.0 Hz, C6H3CF3), 6.47 (d,
2H, J = 8.0 Hz, C6H3CF3), 5.31 (s, 1H, acac-CH), 1.87 (s, 6H, acac-

2768
C.-F. Lin et al. / Journal of Organometallic Chemistry 694 (2009) 2757–2769
CH3). FABMS: m/z 901.9 (M+). Anal. Calc. for C35H23F6N4O2S2Ir: C,
46.61; H, 2.57; N, 6.21. Found: C, 46.73; H, 2.74; N, 5.96%.
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Compound BCP (2.9-dimethyl-4,7-diphenyl-1,10-phenanthro-
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Geometrical optimization of the molecules at density functional
level was carried out with Q-Chem [27] software using B3LYP
exchange-correlation functional. The CRENBL basis set with rela-
tivistic effective potential is applied to the iridium atom [35],
where 6-31G* basis set is applied to the rest of the atoms. The
gas-phase time-dependent DFT (TD-DFT) calculations at the same
level were performed on the basis of the geometry in the ground
state. TD-DFT calculations were previously employed to character-
ize excited states with charge-transfer character [36]. In some
cases underestimation of the excitation energies was observed
[36,37]. We have also performed the TD-DFT calculations at the
same level using GAUSSIAN 03 program suite. The results show that
inclusion of the solvent effect, e.g., toluene, CH2Cl2 and acetonitrile,
only slightly affect the kcal despite using either PCM or C-PCM
solvation model. Therefore, in the present work, we use TD-DFT
(calculated with Q-Chem) to characterize the electronic configura-
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Acknowledgements
We gratefully acknowledge support from the National Science
Council, Academia Sinica, and National Central University.
(b) J.R. Durrant, S.A. Haque, E. Palomares, Chem. Commun. (2006) 3279;
(c) Y. Shao, L.F. Molnar, Y. Jung, J. Kussmann, C. Ochsenfeld, S.T. Brown,
A.T.B. Gilbert, L.V. Slipchenko, S.V. Levchenko, D.P. O’Neill, R.A. DiStasio Jr.,
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