Rational design, synthesis, and characterization of deep blue phosphorescent Ir(III) complexes containing (4′-Substituted-2′- pyridyl)-1,2,4-triazole ancillary ligands

Article abstract of DOI:10.1021/jo4012514

On the basis of the results of frontier orbital considerations, 4-substituted-2′-pyridyltriazoles were designed to serve as ancillary ligands in 2-phenylpyridine main ligand containing heteroleptic iridium(III) complexes that display deep blue phosphorescence emission. The iridium(III) complexes, Ir1-Ir7, prepared using the new ancillary ligands, were found to display structured, highly quantum efficient (Φ_p = 0.20-0.42) phosphorescence with emission maxima in the blue to deep blue 448-456 nm at room temperature. In accord with predictions based on frontier orbital considerations, the complexes were observed to have emission properties that are dependent on the electronic nature of substituents at the C-4 position of the pyridine moiety of the ancillary ligand. Importantly, placement of an electron-donating methyl group at C-4′ of the pyridine ring of the 5-(pyridine-2′-yl)-3-trifluoromethyl-1,2,4-triazole ancillary ligand leads to an iridium(III) complex that displays a deep blue phosphorescence emission maximum at 448 nm in both the liquid and film states at room temperature. Finally, an OLED device, constructed using an Ir-complex containing the optimized ancillary ligand as the dopant, was found to emit deep blue color with a CIE of 0.15, 0.18, which is close to the perfect goal of 0.15, 0.15.

Full text of DOI:10.1021/jo4012514

Article
pubs.acs.org/joc
Rational Design, Synthesis, and Characterization of Deep Blue
Phosphorescent Ir(III) Complexes Containing (4′-Substituted-2′-
pyridyl)-1,2,4-triazole Ancillary Ligands
Hea Jung Park,† Ji Na Kim,† Hyun-Ji Yoo,† Kyung-Ryang Wee,‡ Sang Ook Kang,‡ Dae Won Cho,‡
and Ung Chan Yoon*,†
†Department of Chemistry, Pusan National University, Busan 609-735, Korea
‡Department of Advanced Materials Chemistry, Korea University, 2511 Sejong-ro, Sejong 339-700, Korea
S
* Supporting Information
ABSTRACT: On the basis of the results of frontier orbital considerations,
4-substituted-2′-pyridyltriazoles were designed to serve as ancillary ligands
in 2-phenylpyridine main ligand containing heteroleptic iridium(III) com-
plexes that display deep blue phosphorescence emission. The iridium(III)
complexes, Ir1−Ir7, prepared using the new ancillary ligands, were found
to display structured, highly quantum efficient (Φp = 0.20−0.42) phos-
phorescence with emission maxima in the blue to deep blue 448−456 nm at
room temperature. In accord with predictions based on frontier orbital
considerations, the complexes were observed to have emission properties
that are dependent on the electronic nature of substituents at the C-4 posi-
tion of the pyridine moiety of the ancillary ligand. Importantly, placement
of an electron-donating methyl group at C-4′ of the pyridine ring of the 5-(pyridine-2′-yl)-3-trifluoromethyl-1,2,4-triazole
ancillary ligand leads to an iridium(III) complex that displays a deep blue phosphorescence emission maximum at 448 nm in
both the liquid and film states at room temperature. Finally, an OLED device, constructed using an Ir-complex containing the
optimized ancillary ligand as the dopant, was found to emit deep blue color with a CIE of 0.15, 0.18, which is close to the perfect
goal of 0.15, 0.15.
and as a result, they do not normally effectively emit light to
form the singlet ground state.
INTRODUCTION
■
Because of numerous advantageous features including a good
viewing angle, lower power consumption and high-quality
image processing, organic light-emitting diode (OLED) based
systems are becoming next-generation display devices and solid
state light sources. In the light producing process of an OLED
system, an electron and a hole injected into the respective
LUMO and the HOMO of the organic electroluminescent layer
combine to form an exciton, which relaxes to its ground state
with emission of light. The color of the emitted light, typically
in the visible region ranging from red to blue, is determined by
the energy of the band gap between LUMO and HOMO of the
electroluminescent layer. Radiation emitted from OLEDs may
arise theoretically through either fluorescence from singlet
excited states or phosphorescence from triplet excited states of
light emitter organic molecules in the electroluminescent layer.
Since no electron-spin control mechanism operates during electrical
excitation and decay in OLEDs, electron and hole injection and
recombination occur randomly to generate approximately one
singlet exciton with an antisymmetric spin for every three triplet
excitons with a symmetric spin configuration. Because mole-
cular ground states are typically spin-antisymmetric singlets,
relaxation of singlet excitons conserves spin and efficiently
generates fluorescence emission, while triplet excitons need to
undergo spin inversion through a spin orbit coupling process,
Because of these phenomena, the energy residing in triplet
excitons is not typically used for efficient light emission in
OLEDs, and consequently, it is wasted. Thus, in an OLED,
where a fluorescent material is employed as or doped into the
electroluminescent layer, the maximum internal quantum yield
for light emission is ca. 25%. However, if the efficiency of spin−
orbit coupling in triplet excitons can be enhanced by taking
advantage of the heavy atom phenomenon, the efficiency of
intersystem crossing between triplet excited and singlet ground
state can be greatly increased. In this case, triplet excitons will
more efficiently relax to singlet ground states by phosphor-
escence emission. Thus, in an optimized OLED, all triplet
excitons are utilized for light emission, and as a result, all of the
electrogenerated singlet and triplet excitons undergo light
emission to yield a theoretically maximum internal efficiency of
100%.1,2
Materials that phosphoresce highly efficiently are typically
incorporated in electroluminescent layers of OLEDs to trans-
form triplet excitons into light. Because the spin−orbit coupling
enhancement by heavy atoms is proportional to the fourth
Received: June 20, 2013
Published: July 18, 2013
© 2013 American Chemical Society
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power of the atomic number of the atom, complexes of heavy
atoms such as platinum (Pt), iridium (Ir), europium (Eu), and
terbium (Tb) have been utilized to promote the efficiency of
intersystem crossing and phosphorescence emission.2−5 Iridium
complexes have been shown to be very effective in this regard
because they are highly phosphorescent at room temperature
and have short triplet lifetimes.6 However, thus far the develop-
ment of the phosphorescent OLEDs, which have excellent emission
quantum yields and ideal color coordinates and lifetimes, is still
at an early stage. Studies in this area have recently resulted in
the development of a blue light-emitting phosphorescent iridium
complex called FIrpic (iridium(III) bis[2-(2′,4′-difluorophenyl)-
pyridinato-N,C2′]picolinate)7 and a red light-emitting phos-
phorescent material called Ir(btp)2(acac) (iridium(III) bis[2-
(2′-benzothienyl)pyridinato-N,C2′](acetylacetonate)).3 How-
ever, much work remains to be done to improve the color purity,
efficiency, solubility and lifetime of iridium complexes used for
OLEDs.
As mentioned above, the color of light emitted by OLEDs is
determined by the energy of the band gap between the LUMO
and HOMO of the electroluminescent layer. An evaluation of
the electronic characteristics of the iridium(III) complex, tris-2-
phenylpyridnato-N,C2, Ir(ppy)3, (TPPI) shows that its LUMO
is largely localized on the pyridine ring of the main ligand
2-phenylpyridine while its HOMO is mainly localized on the
phenyl ring of the main ligand.8 As a consequence of these
properties, electron-donating groups on the pyridyl group of
the main ligand, especially at C-4, lead to an increase in
the energy of the LUMO while the presence of electron-
withdrawing groups on the phenyl ring of this ligand lowers the
energy of the HOMO. Thus, a strategy involving the
positionally selective introduction of substituents with different
electronic characters should be useful to control the energy
of the band gap and, thus, the wavelength of emission of
electroemissive substances.
Ir(III) complexes containing substituted phenylpyridnato-N,C2
main and 5-(2′-pyridyl)-3-trifluoromethyl-1,2,4-triazole ancil-
lary ligands. These complexes contain properly positioned
electron-donating substituents at the C-4 of the pyridyl moiety
of the ancillary ligand and electron-donating substituents at C-4
of the pyridine ring and electron-withdrawing groups at C-2, -3,
and -4 of the phenyl ring of the phenylpyridine main ligand. In
the studies described below, we prepared and characterized
these rationally designed Ir(III) complexes (Ir1−Ir7, Figure 1)
Figure 1. Structures of blue phosphorescent iridium(III) complexes
Ir1−Ir7 containing substituted phenylpyridine main and pyridyltria-
zole ancillary ligands.
and evaluated their photophysical properties. The results arising
from this effort demonstrate that the iridium complex
containing 5-(4′-methylpyridine-2′-yl)-3-trifluorormethyl-1,2,4-
triazolate ancillary ligand, as predicted, displays deeper blue
phosphorescence in its solution and film states at room tem-
perature than currently known complexes and that this optimal
complex can be used in the electroluminescent layer emission
of an OLED that emits deeply blue light that has color
coordinates near to the ideal value.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Designed Hetero-
leptic Iridium(III) Complexes. As stated above, an important
strategy for the design for blue phosphorescent iridium(III)
complexes that contain phenylpyridine main and variously
structured ancillary ligands focuses on control of the HOMO−
LUMO energy gap by properly positioned substituents.10
Using this approach we have designed and prepared the Ir(III)
complexes Ir1−Ir7, which contain substituted 2-phenylpyridine
main ligands and 5-(4′-substituted-pyridine-2′-yl)-3-trifluorormethyl-
1,2,4-triazolate ancillary ligands. The 2-phenylpyridine deriva-
tives, 16, 17, and 19, serving as the main ligands of the iridium
complexes, were prepared by using a slight modification of the
previously described method employing palladium-catalyzed
coupling of aryl-boronates with 2-bromopyridines (Scheme 1).9,11
Preparation of the pyridyltriazole ancillary ligands 9, 10, and 12,
required for formation of these complexes, utilized [2 + 3]
cycloaddition reactions of appropriately substituted 2-pyridylni-
triles 5 and 6 with trifluoroacetic acid hydrazide 8 (Scheme 1).12
Finally, a two-step route (Scheme 2) was utilized for prepara-
tion of the heteroleptic iridium complexes Ir1−Ir7.13 In the
sequence, IrCl3·3H2O is reacted with an excess of the desired 2-
phenylpyridine main ligand to give a μ-chlorobridged dimer,
which is then converted to the corresponding heteroleptic
complex by substitution of the bridging chlorides with the
appropriate bidentate, monoanionic 4-substituted-pyridyl tri-
azole ancillary ligand. By using this procedure, the iridium
complexes are produced as pure substances in 30−51% yields.
The single exception is Ir6, which in our hands could not be
purified completely.
Yamashita and his co-workers have shown9 that introduction
of both an electron-withdrawing trifluoromethyl (CF3) group at
C-3 and fluoro groups at C-2 and C-4 on the phenyl ring of the
phenylpyridnato-N,C2 main ligand coupled with introduction of
an electron-donating methyl group at C-4 of the pyridine ring
of the main ligand gives rise to an iridium complex that displays
an extreme blue shift in the phosphorescent emission compared
to TPPI at room temperature. Furthermore, using this sub-
stitution pattern in combination with replacement of one of
three of 2-phenylpyridine main ligand by an ancillary 5-(2′-
pyridyl)-3-trifluoromethyl-1,2,4-triazole, Yamashita devised a
blue phosphorescent iridium complex whose emission max-
imum is remarkably shorter (see below) than that of the well-
known blue emissive iridium bis(4,6-difluorophenyl-pyridinato)-
picolinate (FIrpic).
Recently we initiated investigations aimed at developing new,
blue phosphorescent iridium(III) complexes. The strategy
employed to design substances that have optimal emission char-
acteristics focused on structures that contain properly substituted
2-phenylpyridine main ligands and a variety of substituted
picolinate and pyridyltriazole ancillary ligands incorporated into
heteroleptic octahedral Ir(III) complexes. The goal of the effort
was to determine if substitution patterns in the main and
ancillary ligands could be uncovered that enable the complexes
to emit light efficiently in a deeper blue wavelength region than
do FIrpic or the complex developed by Yamashita. Guided by
expectations arising from considerations of substituent effects
on the energies of HOMOs and LUMOs, we designed several
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Scheme 1. Synthesis of Ancillary (9, 10, and 12) and Main (16, 17, and 19) Ligands
Scheme 2. Synthesis of μ-Chlorobridged Dimer Complexes 20−22 and Iridium(III) Complexes Ir1−Ir7
The synthesized iridium complexes were fully characterized
by using NMR spectroscopy and mass spectrometry. In addition,
X-ray crystallographic structure determinations were carried out
on Ir2, Ir3 and Ir5. (Figure 2, Table 1). The X-ray diffraction
results show that, as expected, iridium in the complexes is
octahedrally coordinated by the two main (2-phenylpyridine)
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Figure 2. ORTEP plots of X-ray data for iridium complexes Ir2, Ir3, and Ir5. Hydrogen atoms and solvent molecules are omitted for clarity.
and one ancillary (pyridyltriazole) ligands and that the com-
plexes have meridional configurations and consist of racemic
mixtures. In addition, the data collected for Ir1 and Ir4 matched
those previously reported for these substances by Yamashita
and co-workers.9
electron-donating methyl or methoxy substitution at C-4′ of
the 5-(pyridine-2′-yl)-3-trifluoromethyl-1,2,4-triazole ancillary li-
gand has a significant impact on the spectroscopic properties of
the heteroleptic iridium complexes. These substituents promote
modestly large (8 nm) hypsochromic shifts of the phosphor-
escence emission maximum. Particularly interesting is the fact
that complex Ir5 (emission λmax = 448 nm) displays more
deeply blue phosphorescence than that of the previously
reported9 Ir4 (λmax = 448 nm reported earlier9 and λmax = 456
nm measured in our laboratory). In addition, Ir2, which does
not contain an electron-withdrawing trifluoromethyl substitu-
ent on the main ligand, has a phosphorescence maximum 456
nm, which is similar to that of Ir4. Moreover, the presence of
the strong electron-donating N,N-dimethylamine group at C-4
of the pyridine main ligand in complex Ir7 causes a significant
13 nm bathochromic shift of the emission maximum in solution
at room temperature. Interestingly, in the film state this com-
plex displays an emission maximum that is 20 nm blue-shifted
compared to that of the substance in the solution state (Figure 5).
Measured phosphorescence lifetimes (τ) of Ir2, Ir3 and Ir5 at
Photophysical and Electrochemical Properties of Ir1−
Ir7. In Figure 3 are displayed absorption and phosphorescence
spectra of the synthesized iridium complexes Ir1−Ir7. Important
photophysical data for these substances are listed in Table 2.
In solution states, Ir1−Ir7 display weak absorption bands in the
416−426 nm region. The new iridium complexes display strong
and structured phosphorescence with emission maxima in the
deep blue or blue 448−456 nm region and with high emission
quantum efficiencies (Φp) between 0.20 and 0.42 at room
temperature (Table 1). In addition, the emission spectra of the
complexes in the film states are similar to those for the solution
states, showing that a significant bathochromic shift does not
take place as a result of π−π stacking in the latter state.
For comparison purposes, emission spectra of Ir1−Ir3 and Ir5
are given in Figure 4. Inspection of the spectra shows that
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Table 1. Crystallographic Data and Structure Refinements of Ir2, Ir3, and Ir5
identification code
empirical formula
Ir2
Ir3
Ir5
C34H24Cl2F7IrN6
912.69
C35H24Cl6F7IrN6O
1082.50
C36H22Cl2F13IrN6
1048.70
formula weight
temperature
wavelength
crystal system
space group
unit cell dimensions
a (Å)
174(2) K
0.71073 Å
monoclinic
P2(1)/n
173(2) K
293(2) K
0.71073 Å
triclinic
0.71073 Å
triclinic
P1
̅
P1
̅
11.2827(11) Å
19.8394(19) Å
14.7376(14) Å
90°
10.65690(10) Å
17.5703(2) Å
10.3490(2) Å
11.8478(2) Å
15.8534(2) Å
109.2570(10)°
91.9040(10)°
97.1330(10)°
1815.15(5) Å3
2
b (Å)
c (Å)
22.4981(4) Å
α (deg)
107.3280(10)°
β (deg)
90.385(3)°
90°
3298.8(5) Å3
94.5960(10)°
γ (deg)
102.6350(10)°
3876.06(9) Å3
volume
Z
4
4
density (calculated)
absorption coefficient
F(000)
1.838 Mg/m3
1.855 Mg/m3
1.919 Mg/m3
3.930 mm−1
1016
4.285 mm−1
3.931 mm−1
1776
2104
crystal size
theta range for data collection
index ranges
0.29 × 0.15 × 0.12 mm3
0.52 × 0.34 × 0.29 mm3
0.12 × 0.11 × 0.09 mm3
1.36−28.44°
−13 ≤ h ≤ 13
−15 ≤ k ≤ 15
−21 ≤ l ≤ 21
32416
1.72−26.00°
0.96−28.35°
−13 ≤ h ≤ 13
−24 ≤ k ≤ 24
−18 ≤ l ≤ 16
28979
−14 ≤ h ≤ 14
−23 ≤ k ≤ 23
−30 ≤ l ≤ 29
reflections collected
69348
independent reflections
completeness to theta
absorption correction
max and min transmission
refinement method
6480 [R(int) = 0.0298]
26.00° 100.0%
semiempirical from equivalents
0.6251 and 0.3706
full-matrix least-squares on F2
6480/0/461
19098 [R(int) = 0.0319]
28.35° 98.6%
semiempirical from equivalents
0.3952 and 0.2343
full-matrix least-squares on F2
19098/0/1037
9010 [R(int) = 0.0312]
28.44° 98.6%
semiempirical from equivalents
0.7187 and 0.6499
full-matrix least-squares on F2
9010/3/509
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
1.026
1.032
1.054
R1 = 0.0199, wR2 = 0.0509
R1 = 0.0215, wR2 = 0.0517
1.024 and −0.556 e Å−3
R1 = 0.0367, wR2 = 0.0901
R1 = 0.0489, wR2 = 0.0969
2.071 and −1.720 e Å−3
R1 = 0.0451, wR2 = 0.1246
R1 = 0.0501, wR2 = 0.1289
5.147 and −2.667 e Å−3
largest diff. peak and hole
77 K were 3.15, 3.57, and 3.58 μs, respectively, which are in the
similar ranges with previously reported work on a family of
iridium(III) complexes.14
HOMO and LUMO energies of −5.48 and −2.76 eV,
respectively.
OLED Device Constructed Using Iridium Complex Ir5.
The use of Ir5, the Ir(III) complex observed to display optimal
blue emission (λmax = 448 nm), as a dopant emitter in the
emissive layer of a simple OLED device was explored. The
device configuration employed is ITO/NPB (500 nm)/TAPC
(350 nm)/CDBP (100 nm)/CDBP:Ir6 (10%) (500 nm)/
Me2Si(TAZ)2 (600 nm)/LiF:Al (Figure 8). In Figure 9 are
displayed I−V−L curves and current efficiencies of the device
in comparison to one constructed employing FIr6 as the
dopant emitter (structure given in Figure 9). As can be seen by
viewing the results, the OLED device made with Ir5 emits deep
blue light corresponding to CIE (0.15, 0.18), which is very near
the perfect goal of (0.15, 0.15), although the emission efficiency
of Ir5 based OLED device is lower under the OLED
configuration comparing Fir6.
The respective HOMO and LUMO energies of complexes
Ir1−Ir7, experimentally determined by using oxidation
potential (Figure 6) and band gap data, were found to be in
the ranges of −5.48 to −5.84 eV (vs ferrocene −4.8 eV) and
−2.76 to −3.06 eV, respectively (Table 3 and Figure 7). The
results show that Ir2 and Ir3 have larger HOMO−LUMO band
gap energies than does Ir1. Thus, paralleling the results of
phosphorescence measurements, electron-donating group
substitution at C-4 of the pyridine ring of ancillary ligand
leads to lower HOMO energies and corresponding higher
LUMO energies. Interestingly, Ir2 and Ir3 possess similar
HOMO and LUMO energies to Ir4, which has an electron-
withdrawing trifluoromethyl group at C-3 of the phenyl ring of
the main ligand and is missing an electron-donating methyl
group on the ancillary ligand. Moreover, Ir5 has the lowest
HOMO energy and the largest HOMO−LUMO band gap
energy among all of the synthesized iridium complexes. This
property results from the introduction of an electron-with-
drawing trifluoromethyl group on the main ligand and an
electron-donating methyl group on the ancillary ligand. Finally,
Ir7, which contains a strongly electron-donating N,N-dimethyl-
amine group at C-4 of the pyridine ring of main ligand, has
CONCLUSIONS
■
In the effort described above, we have utilized a strategy that is
derived from frontier orbital considerations to design blue phos-
phorescent iridium(III) complexes. To explore the predicted
effects of electron-donating and -withdrawing group substitu-
ents on the emission properties of these complexes containing a
(4′-susbstituted pyridine-2′-yl)-1,2,4-triazole ancillary ligand,
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substances have high emission quantum efficiencies of 0.20−0.42
at room temperature. The results of photophysical studies with
these complexes show that introduction of an electron-donating
methyl or methoxy group at C-4 of the pyridine ring of the
ancillary ligand leads to an increase in the energy of the
HOMO−LUMO band gap and leads to a hypsochromic shift of
phosphorescence emission. In an addition, as noted previously,
introduction of an electron-withdrawing trifluoromethyl group
at C-3 of the phenyl ring of the main ligand also greatly lowers
the emission wavelength by 8 nm. The emission maximum of
Ir4 (456 nm) and Ir5 (448 nm) are 8 nm lower than those of
Ir1 (464 nm) and Ir2 (456 nm), respectively. These findings
demonstrate that Ir5 has an emission maximum that is 8 nm
shorter than that of the complex Ir4, previously described by
Yamashita and investigated thoroughly in this effort.9 In addition
to providing a potentially useful blue emitting substance for
OLED studies, the current investigation has validated a strategy
for the design of color selective emissive materials that is based
on a consideration of substituent effects on the differences in
energies of frontier (HOMO and LUMO) orbitals.
EXPERIMENTAL SECTION
■
Chemicals and Instruments. All reagents were obtained from
commercial sources and used without further purification, and solvents
were dried by using standard procedures.
1H (300 MHz) and 13C NMR (75 MHz) spectra were recorded on
CDCl3 and CD3OD as solvents, and chemical shifts are reported in
parts per million relative to CHCl3 (7.26 ppm for 1H NMR and
77.0 ppm for 13C NMR) and CH3OH (3.31 ppm for H NMR and
1
49.0 ppm for 13C NMR) as internal standards. High resolution (HRMS)
mass spectra were obtained by use of quadrupole mass analyzer,
electron impact ionization unless otherwise noted.
4-Methylpyridine N-oxide (3). This substance was prepared by
using the method of Taylor and Crovetti.15 To a solution of 4-
methylpyridine (1, 3.0 mL, 30 mmol) in glacial acetic acid (20 mL)
was added 30% hydrogen peroxide (2.9 mL, 30 mmol). The reaction
mixture was stirred at reflux for 24 h and concentrated in vacuo to
produce 3 (3.0 g, 27 mmol, 90%) as a bright yellow solid, which was
used without further purification or characterization.16
4-Methoxypyridine N-oxide (4). To a solution of 4-methox-
ylpyridine (2, 10.0 mL, 85.9 mmol) in glacial acetic acid (50 mL) was
added 30% hydrogen peroxide (8.4 mL, 85.9 mmol). The mixture was
stirred at reflux for 24 h and concentrated in vacuo giving 4 (9.6 g,
76.5 mmol, 89%) as an oil, which was used without further purification
or characterization.16
2-Cyano-4-methylpyridine (5). This substance was prepared by
using the method of Fife.17 A solution of 4-methylpyridine N-oxide
(3, 1.32 g, 12.1 mmol) in dichloromethane (10 mL) was added to
trimethylsilyl cyanide (1.8 mL, 13.6 mmol) at room temperature.
Dimethylcarbamyl chloride (1.2 mL, 13.6 mmol) in dichloromethane
Figure 3. (a) UV−vis absorption spectra, (b) phosphorescence spectra
in solution, and (c) the film states of Ir1−Ir7.
complexes Ir1−Ir7 were synthesized and structurally charac-
terized. The emission maxima of the synthesized iridium(III)
complexes are in the blue 448−464 nm region, and these
Table 2. Photophysical Properties of Blue Phosphorescent Iridium Complexes Ir1−Ir7
absorption
emission
a
a
a
b
c
d
complex MLCT*1 (nm)
MLCT*3 (nm)
λem (nm) (298 K) λem (nm) (298 K) λem (nm) (77 K) Stokes shift (cm−1
)
Φp
τ (μs)
Ir1
Ir2
Ir3
Ir4
Ir5
Ir6
Ir7
366
370
368
352
364
372
364
426
424
424
422
416
−
464, 489
456, 483
456, 484
456, 482
448, 475
459, 489, 521
469
462, 489
456, 483
456, 483
454, 481
448, 475
458, 488
449, 464
−
1923
1655
1655
1768
1717
−
0.22
0.39
0.25
0.20
0.42
−
450, 482
3.15
3.57
−
450, 484
−
444, 475
3.58
e
−
−
−
0.06
−
−
426
2153
a
b
Solution state (2.7 × 10−4 to 1.3 × 10−3 M) in dichloromethane. Film state prepared by spin coating dichloromethane solutions with PMMA (5%
wt). Measured in 2-methyltetrahydrofuran (MTHF) solution. In dichloromethane solution using Ir(tpy)3 (Φp = 0.45)10a as a reference. UV−vis
absorption and phosphorescence spectra were recorded using nonpurified Ir6.
c
d
e
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Figure 4. Phosphorescence spectra of Ir1−Ir3 and Ir5 demonstrating the effects of (a) electron-donating groups at C-4 of the pyridine ring of
ancillary ligand and (b) electron-withdrawing groups at C-3 of phenyl ring of main ligand on emission maxima.
Table 3. Frontier Orbital Properties of Blue Phosphorescent
Iridium Complexes Ir1−Ir7
a
a
b
c
complex
HOMO
LUMO
Eg(op-s)
Eg(op-t)
Ir1
Ir2
Ir3
Ir4
Ir5
−5.59
−5.65
−5.66
−5.65
−5.84
−
−2.87
−2.92
−2.93
−2.91
−3.06
−
2.97
3.00
3.00
3.02
3.07
2.91
3.07
2.72
2.73
2.73
2.74
2.78
−
d
Ir6
Ir7
−5.48
−2.76
2.72
a
HOMO energies were determined by using the voltage correspond-
ing to the onset point of oxidation and referenced to the Fc/Fc+
couple in CH2Cl2 (0.48 eV vs Ag/AgCl). Ferrocene (Fc/Fc+, −4.8
eV). Triplet LUMO energies were calculated using HOMO energies
Figure 5. Solution and film state phosphorescence spectra of Ir7.
b
and energy of the triplet-ground state band gap (Egop). Singlet optical
c
band gaps were calculated from singlet absorption band edge Triplet
(5.8 mL) was added dropwise to the resulting mixture with stirring.
The mixture was stirred at room temperature for 24 h, diluted with
10% aqueous potassium carbonate (20 mL), and stirred for 30 min.
The organic layer was separated, and aqueous layer was extracted with
dichloromethane. The combined organic layers were dried over
anhydrous Na2SO4 and concentrated in vacuo, giving a residue that
was subjected to column chromatography on silica gel (dichloro-
methane). The desired 2-cyano-4-methylpyridine (5, 1.4 g, 11.6 mmol,
96%) was obtained as a white solid: 1H NMR (CDCl3) δ 8.48 (d, 1H,
J = 5.4 Hz), 7.46 (s, 1H), 7.30 (d, 1H, J = 5.4 Hz), 2.37 (s, 3H).
2-Cyano-4-methoxylpyridine (6). A solution of 4-methoxylpyr-
idine N-oxide (4, 12.8 g, 0.1 mol) in dichloromethane (130 mL) was
added to trimethylsilyl cyanide (16.0 mL, 0.1 mmol) at room tempera-
ture. Dimethylcarbamyl chloride (11.0 mL, 0.1 mmol) in dichloro-
methane (20 mL) was then added dropwise to the mixture with
stirring. The mixture was stirred at room temperature for 24 h, diluted
with 10% aqueous potassium carbonate (100 mL), and stirred for
30 min. The organic layer was separated, and aqueous layer was
optical band gaps were calculated from triplet absorption edges.
The singlet optical band gap was recorded using unpurified Ir6.
d
extracted with dichloromethane. The combined organic layers were
dried over anhydrous Na2SO4 and concentrated in vacuo, giving a
residue that was subjected to column chromatography on silica gel
(ethyl acetate:n-hexane = 1:6). The desired 2-cyano-4-methoxylpyr-
idine (6, 10.7 g, 80.1 mmol, 80%) was obtained as a white solid:17
1H NMR (CDCl3) δ 8.50 (d, 1H, J = 5.4 Hz), 7.21 (d, 1H, J = 2.7 Hz),
6.99 (dd, 1H, J = 5.4 and 2.7 Hz), 3.90 (s, 3H).
Trifluoroacetic acid hydrazide (8). A solution of ethyl
trifluoroacetate (7, 9.0 mL, 80.0 mmol) in methanol (8.0 mL) was
stirred at 0 °C while hydrazine (90.0 mL, 0.1 mol, 1.0 M solution in
THF) was added. After 13 h, dichloromethane (100.0 mL) was added
to the solution at room temperature, and the solution was then con-
centrated in vacuo. Dichloromethane (60.0 mL) was added to the
residue, and the resulting mixture was stirred at room temperature.
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Figure 6. Cyclic voltammograms of Ir1−Ir5 and Ir7.
Figure 8. Configuration of the OLED devices using iridium complexes
Ir5 and Fir6 as dopant materials in the emissive layers (EML).
Figure 7. Energy band gap diagram of the synthesized blue
phosphorescent complexes Ir1−Ir5 and Ir7.
hydrazide (8, 2.2 g, 17.2 mmol), and the resulting mixture was stirred
at room temperature for 30 min. A solution of NaOCH3 (28 wt %) in
methanol (0.2 g) was added to mixture, which was then stirred at
reflux for 2 d. Concentration of the solution in vacuo gave a residue
that was dissolved in water. The solution was extracted with ethyl
acetate, giving an organic layer that was dried over anhydrous Na2SO4
and concentrated in vacuo. The residue was subjected to column
The formed white solid was removed by filtration, and the filtrate was
concentrated in vacuo to yield trifluoroacetic acid hydrazide (8, 6.83 g,
53.3 mmol, 67%) as a white gummy liquid:18 13C NMR (CD3OD)
δ 158.5 (q, 2JC−F = 36 Hz, CF3CONHNH2), 118.0 (q, 1JC−F = 283 Hz, CF3).
5-(4′-Methylpyridine-2′-yl)-3-trifluoromethyl-1,2,4-triazole
(9). A solution of 2-cyano-4-methylpyridine (5, 1.3 g, 9.3 mmol) in
N,N-dimethylformamide (60.0 mL) was added to trifluoroacetic acid
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Figure 9. I−V−L curves, luminescence efficiencies, and CIE coordinates of devices constructed using Ir5 and Fir6.
chromatography on silica gel (ethyl acetate:chloroform = 1:5) to give
9 (0.6 g, 2.5 mmol, 27%) as a white solid: 1H NMR (CDCl3) δ
8.70 (d, 1H, J = 5.4 Hz), 8.21 (s, 1H), 7.36 (d, 1H, J = 5.4 Hz), 2.51
(s, 3H); 13C NMR (CDCl3) δ 155.4, 155.1 (q, 2JC−F = 39 Hz, C-CF3),
150.6, 149.1, 144.5, 126.9, 123.6, 119.2 (q, 1JC−F = 268 Hz, CF3), 21.1;
HRMS (FAB) [M + H]+, Calcd for C9H8F3N4 229.0701, found
229.0703.
2-(2′,4′-Difluorophenyl)-4-picoline (16). In a 100 mL one-neck
round bottomed flask equipped with a condenser were placed 2,4-
difluorophenyl boronic acid (13, 1.1 g, 7.0 mmol), 2-bromo-4-picoline
(14, 1.2 g, 7.0 mmol), Ba(OH)2·8H2O (6.2 g, 19.5 mmol), and
Pd(PPh3)4 (0.2 g, 0.3 mmol). The flask was evacuated and filled with
N2 gas. 1,4-Dioxane (20.0 mL) and H2O (7.0 mL) were added. The
mixture was stirred at reflux for 30 h under a N2 atmosphere and
cooled to room temperature. Concentration in vacuo gave a residue
that was poured into a dichloromethane. The formed precipitate was
removed by filtration, and the filtrate was washed with 1 M NaOH
(30 mL × 2) and saturated aqueous NaCl (30 mL). The organic layer
was dried over anhydrous Na2SO4 and concentrated in vacuo, giving a
residue that was subjected to column chromatography on silica gel
(ethyl acetate:hexane = 1:6) to give 2-(2′,4′-difluorophenyl)-4-picoline
(16, 1.0 g, 4.9 mmol, 70%) as a colorless oil:9 1H NMR (CDCl3) δ
8.54 (d, 1H, J = 5.1 Hz), 7.90−7.98 (m, 1H), 7.54 (s, 1H), 7.06 (d,
1H, J = 5.1 Hz), 6.94−7.00 (m, 1H), 6.85−6.92 (m, 1H), 2.41 (s, 3H).
2-(2′4′-Difluorophenyl)-4-(dimethylamino)pyridine (17). In a
100 mL one-neck round-bottom flask equipped with a condenser were
placed 2,4-difluorophenyl boronic acid (13, 1.1 g, 6.9 mmol), 2-bromo-4-
(dimethylamino)pyridine (15, 1.2 g, 6.9 mmol), Ba(OH)2·8H2O (6.5 g,
20.6 mmol), Pd(PPh3)4 (0.4 g, 0.3 mmol), and 1,4-dioxane/H2O (1/3,
34.3 mL). The flask was evacuated and filled with N2 gas. The mixture
was stirred at reflux for 30 h under a N2 atmosphere and cooled to
room temperature. Concentration in vacuo gave a residue that was
poured into a dichloromethane (30 mL). The formed precipitate was
removed by filtration, and the filtrate was washed with satd. NaCl (aq)
(30 mL), dried over anhydrous sodium sulfate, and concentrated in
vacuo, giving a residue that was subjected to column chromatography
on silica gel (ethyl acetate:hexane = 1:2) to provide 2-(2′,4′-difluoro-
phenyl)-4-(dimethylamino)pyridine (17, 1.2 g, 5.0 mmol, 72%) as a
yellow oil:19 1H NMR (CDCl3) δ 8.30 (d, 1H, J = 5.7 Hz), 7.87−7.95
(m, 1H), 6.87−6.99 (m, 3H), 6.48 (d, 1H, J = 5.7 Hz), 3.03 (s, 6H).
2-(2′,4′-Difluoro-3′-iodophenyl)-4-picoline (18). A 2.0 M solu-
tion (12.5 mL, 25.0 mmol) of lithium diisopropylamide in heptane/
THF/ethylbenzene was added dropwise to a THF (43.0 mL) solution
of 16 (3.5 g, 10.6 mmol) at −78 °C. The resulting solution was stirred
for 1 h. Iodine (6.1 g, 24 mmol) dissolved in THF (35 mL) was added
5-(4′-Methoxypyridine-2′-yl)-3-trifluoromethyl-1,2,4-tria-
zole (10). A solution of 2-cyano-4-methoxypyridine (6, 2.0 g, 15.0 mmol)
in N,N-dimethylformamide (50.0 mL) was added to 8 (2.5 g, 19.5 mmol),
and the resulting solution was stirred at room temperature for 30 min.
A solution of NaOCH3 (28 wt %) in methanol (1.4 g) was added, and
the mixture was stirred at reflux for 3 d and concentrated in vacuo. The
residue was dissolved in water. The aqueous solution was extracted
with ethyl acetate. The organic layer was dried over anhydrous Na2SO4
and concentrated in vacuo, giving a residue that was subjected to
column chromatography on silica gel (ethyl acetate:chloroform = 1:5)
1
to give 10 (0.7 g, 3.0 mmol, 20%) as a colorless liquid: H NMR
(CDCl3) δ 8.18 (d, 1H, J = 6.3 Hz), 7.32 (s, 1H), 6.78 (d, 1H, J =
2
6.3 Hz), 4.24 (s, 3H); 13C NMR (CDCl3) δ 170.0, 152.0 (q, JC−F
=
39 Hz, C-CF3), 151.894, 146.7, 143.2, 118.8 (q, 1JC−F = 268 Hz, CF3),
114.7, 113.8, 39.1; HRMS (FAB) [M]+, Calcd for C9H7F3N4O,
244.0572, found 244.0570.
5-(Pyridine-2′-yl)-3-trifluoromethyl-1,2,4-triazole (12). A solu-
tion of 2-cyanopyridine (11, 0.93 mL, 9.6 mmol) in ethanol (30.0 mL)
was added to 8 (2.5 g, 19.5 mmol). The resulting mixture was stirred
at room temperature for 30 min and then diluted with a solution of
NaOCH3 (28 wt %) in methanol (1.4 g). The resulting solution was
stirred at reflux for 2 h and concentrated in vacuo. The residue was
heated at 130 °C for 12 h and dissolved in water. The aqueous
solution was extracted with chloroform. The organic layer was dried
over anhydrous Na2SO4 and concentrated in vacuo, giving a residue
that was subjected to column chromatography on silica gel (ethyl
acetate:chloroform = 1:5) to give 12 (1.06 g, 5.0 mmol, 52%) as a
yellow solid:12 1H NMR (CDCl3) δ 8.84 (d, 1H, J = 5.1 Hz), 8.35 (d,
1H, J = 8.1 Hz), 7.98 (ddd, 1H, J = 8.1 Hz, 8.1 Hz, 1.5 Hz), 7.54 (ddd,
1H, J = 8.1 Hz, 5.1 Hz, 1.2 Hz).
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to the solution, and the mixture was stirred for 3 h at −78 °C, warmed
to room temperature, and diluted with water (300 mL). The solution
was extracted with diethyl ether, giving an organic layer that was
washed with water (100 mL), satd. Na2S2O3 (aq) (100 mL) and satd.
NaCl (aq) (100 mL), dried over anhydrous Na2SO4, and concentrated
in vacuo. The residue was subjected to column chromatography on
silica gel (eluent = ethyl acetate:hexane = 1:6) to give 2-(2′,4′-difluoro-
3′-iodophenyl)-4-picoline (18, 5.4 g, 16.3 mmol, 65%) as a white
solid:9 1H NMR (CDCl3) δ 8.55 (d, 1H, J = 5.1 Hz), 7.90−7.98 (m, 1H),
7.55 (s, 1H), 7.10 (d, 1H, J = 5.1 Hz), 6.98−7.03 (m, 1H), 2.41 (s, 3H).
2-[2′,4′-Difluoro-3′-(trifluoromethyl)phenyl]-4-picoline (19).
A mixture of copper(I) iodide (1.7 g, 9.1 mmol) and spray-dried
anhydrous potassium fluoride (0.5 g, 9.1 mmol) was heated with a heat
gun under reduced pressure while being gently shaken until the color
changed to greenish yellow.20 After the addition of 18 (2.0 g, 6.0 mmol),
the vessel was Ar-purged, and N-methylpyrrolidinone (10 mL) and
(trifluoromethyl)trimethylsilane (1.8 mL, 12.1 mmol) were added.
The suspension was vigorously stirred for 24 h at room temperature
and poured into 28% aqueous ammonia (66 mL). The solution was
extracted with dichloromethane. The organic layer was washed with
water and brine, dried over anhydrous sodium sulfate, and concen-
trated in vacuo, giving a residue that was subjected to column
chromatography on silica gel (ethyl acetate:hexane = 1:6) yielding 2-
[2′,4′-difluoro-3′-(trifluoromethyl)phenyl]-4-picoline (19, 0.8 g, 3.1
mmol, 53%) as a colorless oil:9 1H NMR (CDCl3) δ 8.52 (d, 1H, J =
5.1 Hz), 8.08−8.16 (m, 1H), 7.53 (s, 1H), 7.03−7.09 (m, 2H), 2.37
(s, 3H).
J = 5.4 Hz), 7.00 (d, 1H, J = 5.4 Hz), 6.79 (d, 1H, J = 5.4 Hz), 6.70 (d,
1H, J = 5.4 Hz), 6.52−6.36 (m, 2H), 5.78 (dd, 1H, J = 8.4 Hz, 2.4 Hz),
5.70 (dd, 1H, J = 8.4 Hz, 2.4 Hz), 2.48 (s, 3H), 2.47 (s, 3H); HRMS
(FAB) [M]+, Calcd for C33H22F7N6Ir 828.1423, found 828.1437.
Ir3 (48%): 1H NMR (CDCl3) δ 8.04 (s, 1H), 8.00 (s, 1H), 7.72 (d,
1H, J = 2.4 Hz), 7.52 (d, 1H, J = 6.0 Hz), 7.45 (d, 1H, J = 6.0 Hz),
7.23 (d, 1H, J = 6.0 Hz), 6.77 (d, 1H, J = 6 Hz), 6.70 (d, 1H, J =
6 Hz), 6.69 (d, 1H, J = 6 Hz), 6.49−6.33 (m, 2H), 5.75 (dd, 1H, J =
8.4 Hz, 2.7 Hz), 5.68 (dd, 1H, J = 8.4 Hz, 2.7 Hz), 3.92 (s, 3H), 2.46
(s, 6H); HRMS (FAB) [M]+, Calcd for C33H22OF7N6Ir 844.1373,
found 844.1390.
Ir4 (30%):9 1H NMR (CDCl3) δ 8.88 (d, 1H, J = 5.4 Hz), 8.63
(s, 1H), 8.58 (s, 1H), 8.01−7.96 (m, 1H), 7.91−7.82 (m, 1H), 7.60
(d, 1H, J = 5.4 Hz), 6.66 (d, 1H, J = 4.8 Hz), 6.62 (d, 1H, J = 4.8 Hz),
5.75−5.62 (m, 2H), 2.47 (s, 6H).
Ir5 (51%): 1H NMR (CDCl3) δ 8.14 (s, 2H), 8.10 (s, 1H), 7.53 (d,
2H, J = 5.7 Hz), 7.28 (d, 1H, J = 5.7 Hz), 7.08 (d, 1H, J = 5.7 Hz),
6.90 (d, 1H, J = 5.7 Hz), 6.82 (d, 1H, J = 5.7 Hz), 5.89 (d, 1H, J =
10.5 Hz), 5.79 (d, 1H, J = 10.5 Hz), 2.52 (s, 6H), 2.49 (s, 3H); HRMS
(FAB) [M + H]+, Calcd for C35H21F13N6Ir 965.1249, found 965.1245.
1
Ir7 (49%): H NMR (CDCl3) δ 8.08 (s, 1H), 7.58 (d, 1H, J =
5.7 Hz), 7.44 (s, 1H), 7.38 (s, 1H), 7.21 (d, 1H, J = 6.9 Hz), 6.96 (d,
1H, J = 5.7 Hz), 6.92 (d, 1H, J = 6.9 Hz), 6.47−6.32 (m, 2H), 6.16
(dd, 1H, J = 6.9 Hz, 2.7 Hz), 6.08 (dd, 1H, J = 6.9 Hz, 2.7 Hz), 5.91
(dd, 1H, J = 8.5 Hz, 2.7 Hz), 5.86 (dd, 1H, J = 8.5 Hz, 2.7 Hz), 3.06 (s,
6H), 3.05 (s, 6H), 2.43 (s, 3H); HRMS (FAB) [M]+, Calcd for
C35H28F7N8Ir 886.1954, found 886.1960.
Optical Measurements. The absorption and photoluminescence
(PL) spectra were measured using a spectrometer and a fluorescence
spectrometer, respectively, in chloroform at room temperature. Phos-
phorescence spectra were obtained using absorption wavelengths for
their MLCT1* as excitation wavelengths in dichloromethane, and phos-
phorescence quantum yields (Φp) were estimated using a dichloro-
methane solution of Ir(tpy)3 as a standard with a known value of Φp =
0.4510a at room temperature.
Triplet Lifetime Measurements. The phosphorescence spectra
at 77 K were measured by an intensified charge-coupled device
detector equipped with a monochromator. The samples were excited
using the 355 nm pulses of the third harmonic generation from a
Q-switched nanosecond Nd:YAG laser (pulse width of 4.5 ns fwhm).
Temporal profiles were measured by a monochromator equipped with
a photomultiplier and a digital oscilloscope.
Electrochemistry. Electrochemical measurements of iridium com-
plexes Ir1−Ir7 were made by using cyclic voltammetry (CV). Cyclic
voltammograms were recorded on CHI600C in dichloromethane
(HPLC grade) solution with three electrodes consisting of a Pt disc
working electrode (2 mm diameter), a Pt wire counter electrode, and a
Ag/AgCl reference electrode at room temperature. Tetrabutylammo-
nium perchlorate and Cp2Fe/Cp2Fe+ redox couple were used as a
supporting electrolyte and a secondary internal reference (−4.8 eV),
respectively.
Crystallography. All X-ray crystallographic data were collected on
an automatic diffractometer with a graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å) and a CCD detector at ambient tempera-
ture. Thirty six frames of two-dimensional diffraction images were
collected and processed to obtain the cell parameters and orientation
matrix. The data were corrected for Lorentz and polarization effects.
Absorption effects were corrected by using the empirical method. The
structures were solved by employing direct methods (SHELXS 97)
and refined by using full-matrix least-squares techniques (SHELXL 97).
The non-hydrogen atoms were refined anisotropically, and hydrogen
atoms were placed in calculated positions and refined using a riding
model.
Synthesis of Iridium(III)-μ-Chlorobridged Dimer Complexes
20−22. Typical Procedure. A mixture of iridium(III) chloride tri-
hydrate (83.0 mg, 0.2 mmol), 2-(2′4′-difluorophenyl)-4-picoline (16,
0.12 g, 0.6 mmol) in 2-ethoxyethanol/water (4 mL; 3/1) was stirred at
reflux under a nitrogen atmosphere for 18 h. After cooling to room
temperature, the mixture was concentrated in vacuo, giving a residue
that was dissolved in water. The mixture was extracted with dichloro-
methane, and the organic layer was washed with water and brine, dried
over sodium sulfate, and concentrated in vacuo to give the iridium(III)-
μ-chlorobridged dimer complex 20. Complexes 21 and 22 were pre-
pared from the corresponding 2-phenylpyridine ligand 17 and 19,
respectively, by using a similar procedure.
1
20 (74%): H NMR (CDCl3) δ 8.91 (d, 4H, J = 5.7 Hz), 8.10
(s, 4H), 6.59 (d, 4H, J = 5.7 Hz), 6.30 (m, 4H), 5.31 (dd, 4H, J =
10.5 Hz, 2.7 Hz), 2.66 (s, 12H).
1
21 (70%): H NMR (CDCl3) δ 8.87 (d, 4H, J = 5.7 Hz), 8.21
(s, 4H), 6.70 (d, 4H, J = 5.7 Hz), 5.40 (d, 4H, J = 10.5 Hz), 2.72 (s, 12H).
22 (54%):19 1H NMR (CDCl3) δ 9.21 (d, 1H, J = 5.7 Hz), 8.86 (d,
1H, J = 5.7 Hz), 7.37 (m, 2H), 6.70−7.00 (m, 4H), 5.83 (dd, 1H, J =
5.7 Hz, 2.0 Hz), 5.35 (dd, 1H, J = 5.7 Hz, 2.0 Hz), 3.19 (s, 6H), 3.16
(s, 6H).
Synthesis of Iridium(III) Complexes Ir1−Ir7. Typical Proce-
dure. A mixture of dimer complex 20 (0.13 g, 0.11 mmol), ancillary
ligand 9 (0.06 g, 0.26 mmol), and sodium carbonate (160 mg) in
2-ethoxyethanol (7 mL) was heated at 135 °C for 24 h under a
nitrogen atmosphere. After cooling to room temperature, the solution
was concentrated in vacuo, and water was added to the residue. The
mixture was extracted with dichloromethane. The organic layer was
dried over anhydrous sodium sulfate and concentrated in vacuo, giving
a residue that was subjected to column chromatography on silica gel
(dichloromethane:hexane = 1:10). The solid obtained was recrystal-
lized from dichloromethane/hexane to give Ir2 (0.04g, 0.05 mmol,
45%) as a green yellow solid. Iridium(III) complexes Ir1 and Ir3−Ir7
were prepared from the corresponding ancillary ligands 12, 9, and 10,
respectively, by using a similar procedure.
1
Ir1 (38%): H NMR (CDCl3) δ 8.29 (d, 1H, J = 5.4 Hz), 8.06
(s, 1H), 8.04 (s, 1H), 7.57−7.73 (m, 1H) 7.56 (d, 1H, J = 5.4 Hz),
6.81 (d, 1H, J = 4.8 Hz), 6.72 (d, 1H, J = 4.8 Hz), 6.55−6.40 (m, 2H),
5.79 (dd, 1H, J = 8.4 Hz, 2.4 Hz), 5.69 (dd, 1H, J = 8.4 Hz, 2.4 Hz),
2.51 (s, 6H); HRMS (FAB) [M]+, Calcd for C32H20F7N6Ir 814.1267,
found 814.1270.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra of all previously unidentified
compounds, Phosphorescence decay spectra and detailed
crystallographic data in CIF format of crystals Ir2, Ir3, and
1
Ir2 (45%): H NMR (CDCl3) δ 8.12 (s, 1H), 8.07 (s, 1H), 8.03
(s, 1H) 7.55 (d, 1H, J = 5.4 Hz), 7.53 (d, 1H, J = 5.4 Hz), 7.25 (d, 1H,
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Ir5. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: ucyoon@pusan.ac.kr.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by National Research Foundation of
Korea Grant funded by the Korean Government
(2012R1A1A2007158 for U. C. Yoon).
REFERENCES
■
(1) Baldo, M. A.; O’Brien, D. F.; Thompson, M. E.; Forrest, S. R.
Phys. Rev. B 1999, 60, 14422.
(2) Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Pure Appl. Chem.
1999, 71, 2095.
(3) (a) Brooks, J.; Babayan, Y.; Lamansky, S.; Djurovich, P. I.; Tsyba,
I.; Bau, R.; Thompson, M. E. Inorg. Chem. 2002, 41, 3055. (b) Laskar,
I. R.; Hsu, S. F.; Chen, T. M. Polyhedron 2005, 24, 881.
(4) (a) Adachi, C.; Baldo, M. A.; Forrest, S. R.; Thompson, M. E.
Appl. Phys. Lett. 2000, 77, 904. (b) Brooks, J.; Babayan, Y.; Lamansky,
S.; Djurovich, P.; Tsyba, I.; Bau, R.; Thompson, M. E. Inorg. Chem.
2002, 41, 3055.
(5) (a) Tokito, S.; Iijima, T.; Suzuri, Y.; Kita, H.; Tsuzuki, T.; Sato, F.
Appl. Phys. Lett. 2003, 83, 569. (b) Holmes, R. J.; D’Andrade, B. W.;
Forrest, S. R.; Ren, X.; Li, J.; Thompson, M. E. Appl. Phys. Lett. 2003,
83, 3818.
(6) (a) Turro, N. J. Modern Molecular Photochemistry; The Benjamin/
Cummings Publishing Co., Inc.; Menlo Park, CA, 1978. (b) Murov, S.
L.; Carmichael, I.; Hug, G. L. Handbook of Photochemistry; Marcel
Dekker: New York, 1993.
(7) Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nature 2000, 403,
750.
(8) Hay, P. J. J. Phys. Chem. A 2002, 106, 1634.
(9) Takizawa, S.; Echizen, H.; Nishida, J.; Tsuzuki, T.; Tokito, S.;
Yamashita, Y. Chem. Lett. 2006, 35, 748.
(10) (a) Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.;
Petrov, V. A.; Wang, Y. Chem. Commun. 2001, 1494. (b) Tamayo, A.
B.; Alleyne, B. D.; Djurovich, P.; Lamansky, S.; Tsyba, I.; Ho, N. N.;
Bau, R.; Thompson, M. E. J. Am. Chem. Soc. 2003, 125, 12971.
(c) Coppo, P.; Plummer, E. A.; Cola, L. D. Chem. Commun. 2004,
1774.
(11) Sammakia, T.; Hurley, T. B. J. Org. Chem. 1999, 64, 4652.
(12) Hagiwara, K.; Aihara, T.; Tanigawa, H.; Sano, S.; Shimoda, S.;
Sano, H. Pyridyltriazole Compounds, Processes for Producing The
Same and Agricultural and Horticultural Germicides, PCT Int. Appl.
WO99/002518, Jan 21, 1999.
(13) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razaq, F.;
Kwong, R.; Tsyba, I.; Bortz, Mui, M. B.; Bau, R.; Thompson, M. E.
Inorg. Chem. 2001, 40, 1704.
(14) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho, N.
N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg. Chem.
2005, 44, 1713.
(15) Taylor, E. C.; Crovetti, A. Organic Syntheses; Rabjohn, N., Ed.;
John Wiley & Sons: New York, 1963; Collect. Vol. IV, pp 655−656.
(16) Shuman, R. T.; Ornstein, P. L.; Paschal, J. W.; Gesellchen, P. D.
J. Org. Chem. 1990, 55, 738.
(17) Fife, W. K. J. Org. Chem. 1983, 48, 1375.
(18) Sitzmann, M. E. J. Fluorine Chem. 1995, 70, 31.
(19) Jin, S. H.; Jung, O. S.; Kim, Y. I.; Hyun, M. H.; Lee, J. W.; Yoon,
U. C.; Nazeeruddin, M. K.; Klein, C.; Graetzel, M. PCT Int. Appl.
(2007), WO 2007042474.
(20) Cottet, F.; Schlosser, M. Eur. J. Org. Chem. 2002, 327.
8064
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