Design, synthesis, and properties of a series of charged iridium(III) complexes with a neutral bidentate ligand for deep-blue phosphorescent emitter

Article abstract of DOI:10.1016/j.jfluchem.2015.10.016

We herein report a series of charged iridium(III) complexes with a neutral bidentate ligand for blue phosphorescent emitter. A molecular design bearing a 2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine ligand proved suitable for efficient blue emission according to the comparison of photoluminescent properties of the complexes. Its Commission Internationale de L'Eclairage x,y-coordinates (CIEx,y) in solution was estimated to be (0.17, 0.18), indicating that the complex with the ligand is promising candidate for a deep-blue emitter. We further demonstrated that this complex displays blue electroluminescence by successfully integrating it in a light-emitting device.

Full text of DOI:10.1016/j.jfluchem.2015.10.016

Accepted Manuscript
Title: Design, synthesis, and properties of a series of charged
iridium(III) complexes with a neutral bidentate ligand for
deep-blue phosphorescent emitter
Author: Yusuke Takahira Eisuke Murotani Keiko Fukuda
Varun Vohra Hideyuki Murata
PII:
S0022-1139(15)30003-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2015.10.016
FLUOR 8685
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
1-8-2015
29-10-2015
31-10-2015
Please cite this article as: Y. Takahira, E. Murotani, K. Fukuda, V. Vohra, H. Murata,
Design, synthesis, and properties of a series of charged iridium(III) complexes with
a neutral bidentate ligand for deep-blue phosphorescent emitter, Journal of Fluorine
Chemistry (2015), http://dx.doi.org/10.1016/j.jfluchem.2015.10.016
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

TITLE
Design, synthesis, and properties of a series of charged iridium(III) complexes with a
neutral bidentate ligand for deep-blue phosphorescent emitter
AUTHORS
Yusuke Takahiraa,*, Eisuke Murotania, Keiko Fukudaa, Varun Vohrab,1, Hideyuki
Muratab,*
AFFILIATIONS
a Research Center, Asahi Glass Co., Ltd., 1150 Hazawa-cho, Kanagawa-ku, Yokohama,
Kanagawa 221-8755, Japan
E-mail: yusuke-takahira@agc.com
b School of Materials Science, Japan Advanced Institute of Science and Technology
(JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
E-mail: murata-h@jaist.ac.jp
1 Present address: Department of Engineering Science, Graduate School of Informatics
and Engineering, The University of Electro-Communications (UEC), 1-5-1 Chofugaoka,
Chofu, Tokyo 182-8585, Japan
GRAPHICAL ABSTRACT (synopsis)
This paper features the design, synthesis and properties of a new series of charged
iridium(III) complexes for phosphorescent emitter.
GRAPHICAL ABSTRACT
1
Page 1 of 19

HIGHLIGHTS
 A new series of charged iridum(III) complexes is synthesized.
 A deep-blue-emitting complex with an N,N-bidentate ligand is demonstrated.
 A light-emitting device based on the charged complex was successfully fabricated.
ABSTRACT
We herein report a series of charged iridium(III) complexes with a neutral bidentate
ligand for blue phosphorescent emitter. A molecular design bearing a 2-(3,
5-dimethyl-1H-pyrazol-1-yl)pyridine ligand proved suitable for efficient blue emission
according to the comparison of photoluminescent properties of the complexes. Its
Commission Internationale de L’Eclairage x,y-coordinates (CIEx,y) in solution was
estimated to be (0.17, 0.18), indicating that the complex with the ligand is a promising
candidate for a deep-blue emitter. We further demonstrated that this complex displays
blue electroluminescence by successfully integrating it in a light-emitting device.
2
Page 2 of 19

KEYWORDS (< 6 keywords)
phosphorescence; iridium complex; organic light-emitting diode
AUTHOR DECLARATION
Y.T., E.M. and K.F. are employees of Asahi Glass Co., Ltd. (AGC), and patent
applications related to this work have been filed.
3
Page 3 of 19

1. Introduction
Phosphorescent transition-metal complexes have been extensively studied due to their
potential application, particularly in light-emitting devices such as organic
light-emitting diodes (OLEDs) and light-emitting electrochemical cells (LECs) [1-3].
Phosphorescent iridium(III) complexes have attracted a great deal of attention because
of their higher luminescence efficiency over fluorescent emitter, however, the
blue-emitting phosphorescent complexes still have some drawbacks compared to their
red and green counterparts. For instance, FIrpic, which is known as the standard blue
emitter, has Commission Internationale de L’Eclairage x,y-coordinates (CIEx,y) of
(0.16, 0.29) (Figure 1, left) [4]. These coordinates correspond to a sky-blue (typically
CIEy >0.2) and cannot be considered sufficient as deep-blue emission (CIEy <0.2).
Although various types of complexes besides FIrpic have been investigated, the number
of studies reporting sufficient deep-blue emitting complexes is limited so far [5].
Among these studies, a major contribution is attributed to Lee et al. who have reported a
new
homoleptic
iridium(III)
complex,
(dfpypy)3Ir,
bearing
three
2’,6’-difluoro-2,3’-bipyridine (dfpypy) ligands [6]. Unlike FIrpic and its related
complexes based on 2-(2,4-difluorophenyl)pyridine (dfppy) surrogate, the resulting
complex exhibited deep-blue emission. The work has introduced a new ligand design,
thereby pioneering the intensive investigations on its analogous complexes (Figure 1,
right) [7].
4
Page 4 of 19

Figure 1. FIrpic and (dfpypy)3Ir
The neutral complexes such as FIrpic and (dfpypy)3Ir can be used as emitting layers in
light-emitting devices but require vacuum deposition process (dry process), which is
typically standard in the current manufacturing process. Meanwhile, charged complexes
are considered much more promising especially for large-area lighting and display
applications due to some of their additional properties: (i) the presence of ionic
species should facilitate electric charge injection from electrodes into the emission
layers, and (ii) controllable solubility based on the structure of ligands as well as anion
moiety enables solution process (wet process) fabrication of the devices. The
processability from solution such as by inkjet printing has received broad attention due
to its capability for large-area device manufacturing. During our initial studies focused
on designing a structural motif for a deep-blue emitter, we isolated a charged complex
bearing two acetonitrile molecules as ligands, exhibiting bright sky-blue emission under
UV irradiation (Scheme 1) [8]. This finding led us to envision a key structural motif of a
new series of iridum(III) complexes for efficient blue emission.
Scheme 1. Formation of a sky-blue emitting iridium(III) complex bearing two
acetonitriles as ligands. Tf = trifluoromethanesulfonyl (triflyl).
5
Page 5 of 19

We herein demonstrate the synthesis of a series of charged iridium(III) complexes
which have potential as blue phosphorescent emitters. Among them, the complex
bearing two dfpypy ligands and
a
N,N-bidentate ligand, that is
2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine, efficiently emitted to give an excellent blue
color in solution. Although the use of 2-(1H-pyrazol-1-yl)pyridine ancillary ligands is
previously reported, the emission colors of the corresponding iridium(III) complexes are
sky-blue to green [9,10]. Furthermore, we demonstrate that this complex can be
successfully integrated into light-emitting devices and therefore, not only exhibit highly
efficient photoluminescence but also electroluminescence.
2. Results and discussion
2.1 Design and synthesis of charged iridium(III) complexes
We employed a structural motif of a heteroleptic Ir(III) complex composed of two
monoanionic C,N-bidentate (C^N) ligands and another neutral X,Y-bidentate (X^Y)
ligand according to our finding described above (Figure 2).
Figure 2. Structure of charged iridium(III) complexes. Cy = cyclohexyl, Ph = phenyl,
6
Page 6 of 19

TfO = trifluorometanesulfonate (triflate). Emboldened atoms in L1−L7 would
coordinate the iridium center.
Six new complexes shown in Figure 2 were straightforwardly synthesized according to
modified literature procedures (Scheme 2) [11,12]. Iridium(III) chloride trihydrate
reacted with two equivalents of 2-(2,4-difluorophenyl)pyridine (dfppy, L1) or
2’,6’-difluoro-2,3’-bipyridine (dfpypy, L2) to afford chloro-bridged cyclometallated
iridium(III) dimer [L2Ir(-Cl)]2 (L = L1 or L2). Subsequent treatment with silver(I)
trifluorometanesulfonate followed by another X^Y ligand (L3−L7) yielded the charged
complexes in moderate to good yields (28−80%) [13]. For complexes 3 and 6,
additional chromatographic procedures on their purification steps were needed to obtain
spectroscopically pure sample and this might result in lower isolated yields (see
Experimental Section for details). These synthetic procedures are scalable, and we
thereby readily prepared complex 3 in multi-gram quantities for the following studies.
7
Page 7 of 19

Scheme 2. Synthesis of charged complexes 1−6. Reagents and conditions: (a) L1 or L2,
2-ethoxyethanol/H2O (3/1, v/v), 150 °C, 8−18 h; (b) AgOTf, CH3OH/CH2Cl2, 1/1 (v/v),
r.t., 2−5 h; (c) X^Y ligand (L3−L7), 1,2-dichloroethane, refl., 15−18 h. Yields are based
on [L2Ir(-Cl)]2.
All complexes showed certain moisture, air, and sunlight tolerances, enabling the
storage under ambient conditions without any detectable decomposition. Complex 3, for
example, was well soluble in the high boiling solvents such as N,N-dimethylformamide,
N-methyl-2-pyrrolidone, and 1,2-dichloroethane whereas toluene, xylene,
cyclopentanone, and anisole have poor to moderate solubility. On the basis of
HPLC/MS analysis, we have concluded that complex 3 used in this study contained no
detectable impurities.
2.2 Properties of charged iridium(III) complexes
Studies on photoluminescent properties of N^N-coordinated complexes have revealed
that 3 composed of two L2 and one L3 ligands is a promising candidate for deep-blue
emitter. Comparison of complexes 1 and 2 bearing different X^Y ligands indicated that
the emission wavelengths of 1 was much bluer than that of 2, emphasizing that the
electron-rich L3 would contribute to bluer emission compared to the electron-deficient
L4 (Figure 3).
8
Page 8 of 19

Figure 3. Normalized emission spectra of 1- (solid line) and 2-doped (dashed line) films
(5 wt% in poly(methyl methacrylate), room temperature, excited at 337 nm)
Another study featuring the effect of C^N ligands highlighted the superior contribution
of L2 over L1 in regard to both bluer color emission and enhanced photoluminescent
quantum yield (PLQY). The emission maximum of 3 reached the deep-blue region
(more than 15 nm-hypsochromic shift relative to 1, see Figure 4), showing efficient
contribution of L2 over its counterpart L1 Similarly to previous results presented by
Lee et al. [6]. The PLQY value of 3 display a remarkable increase reaching up to 0.83,
whereas that of 1 remains quite low (Table 1). Although complexes 1 and 3 gave high
PLQY values in 5 wt% poly(methyl methacrylate) (PMMA), we observed a drastic drop
of the value of only complex 1 in fluid solution. The relevant reason for this peculiar
observation still remains unclear. CIEx,y of 3 was notably better than that of the
sky-blue emitter FIrpic, hence underlining its potential use as a deep-blue emitter.
9
Page 9 of 19

Figure 4. Normalized emission spectra of 1 (dashed line) and 3 (solid line) (1.0 ×10−5 M
in degassed 1,2-dichloroethane, room temperature, excited at 337 nm)
Table 1. Photoluminescent properties of 1 and 3 in solution (1.0 ×10−5 M in degassed
1,2-dichloroethane, room temperature, excited at 337 nm).
Complex
PLQYa
CIEx,y

max/nm
450, 482 0.04 (0.92) (0.22, 0.25)
434, 464 0.83 (0.78) (0.17, 0.18)
1
3
FIrpicb
−
−
(0.16, 0.29)
a Values in 5 wt% PMMA film are given in the parentheses.
b See ref [4].
In order to consider the emission mechanism, we employed the molecular oxygen which
is well-known to quench triplet-state excitons. As shown in Figure 5 where we
described the drastic quenching of the emission from 3 by bubbling oxygen gas, it was
10
Page 10 of 19

clearly indicated that the emission was attributed to phosphorescence. It should also be
noted that 3 was thermally stable over 300 °C without any decomposition [14].
Figure 5. Emission spectra of 3 (1.0 ×10−5 M in 1,2-dichloroethane, room temperature,
excited at 337 nm. Nitrogen-bubbled (black line), without bubbling (gray line), and
oxygen-bubbled (dashed line) samples.
2.3 Device fabrication based on complex 3 as emitter
Several attempts for fabricating a thin film of 3 via thermal deposition were not
successful due to its thermal instability upon heating under the vacuum, probably
reflecting its charged nature. However, as the charged complexes are soluble in common
organic solvents, we fabricated light-emitting devices based on 3 through “wet process”.
Our preliminary screening for obtaining a bright emission from 3-embedded thin film
have successfully reached an optimal composition; a combination of 3/
1,3-Bis(N-carbazolyl)benzene (mCP)/Poly(methyl methacrylate) (PMMA) as
emitter/host/matrix [15]. The device architecture of the light-emitting devices were as
11
Page 11 of 19

follows (Figure 6):
ITO (150 nm)/PEDOT:PSS (30 nm)/3:mCP:PMMA (30
nm)/BAlq3 (60 nm)/LiF (1 nm)/Al(100 nm). Although the devices based on a blend
active layer containing 3 exhibited a bright emission with a maximum EQE of
approximately 0.54%, a bathochromic-shifted sky-blue electroluminescence and its
rapid emission decay within several minutes were also observed (Figure 7). A direct
analysis of the emission layer in the decayed devices by laser desorption
ionization/time-of-flight mass spectrometry (LDI-TOF MS) have suggested that no
chemical structural changes of the emitter occurred [16]. The exact reasons for the rapid
decay remained unclear, underscoring the necessary of further optimizations in both
materials and device architectures.
Figure 6. Schematic light-emitting device structure based on complex 3. Bottom-side
two layers (gray) and top-side three layers (white) were fabricated through wet and dry
processes, respectively. The concentration of complex 3 is 15 wt% with respect to the
amount of mCP.
12
Page 12 of 19

Figure 7. Current density and luminance-voltage curves (left) and electroluminescence
spectra measured at the current density of 1 mA/cm2 (right) of a light-emitting device
based on 3.
3. Conclusion
In conclusion, we have demonstrated a new, deep-blue emitting charged iridium(III)
complex based on 2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine ligand. Its CIEx,y of (0.17,
0.18) was notably superior to that of one of the standardemitter FIrpic, suggesting that
this would be a good candidate as a deep-blue emitter for light-emitting devices.
4. Experimental
4.1 General
All reagents and dry solvents used for the experiments were purchased from
Sigma-Aldrich, Kanto Chemical, Nacalai Tesque and Tokyo Chemical Industry (TCI)
and used without further purification. ASAHIKLIN AK-225 was obtained from Asahi
Glass. All solutions for photophysical experiments were degassed by gentle bubbling
13
Page 13 of 19

with nitrogen or argon for more than 30 min prior to measurement. All reactions were
carried out under a nitrogen atmosphere unless otherwise noted. 1H (300 MHz), 19F (283
MHz) and 13C (1H decoupling, 75 MHz) NMR spectra were recorded on a JEOL
JNM-AL300 FT-NMR spectrometer. 13C (1H and 19F decoupling, 100 MHz) NMR
spectra were recorded on a JEOL JNM-ECP400 FT-NMR spectrometer. Chemical shifts
 are reported in ppm units referenced to (CH3)4Si (0.0 ppm in CDCl3) or residual
19
solvent peak (2.04 ppm in acetone-d6) for 1H; CCl3F (0.0 ppm) for F; residual solvent
peak (77.0 ppm in CDCl3, 29.7 ppm in acetone-d6) for 13C. NMR data were reported as
follows: Chemical shift, integration, multiplicity (s = singlet, d = doublet, t = triplet, q =
quartet, dd = doublet of doublets, dt = doublet of triplets, ddd = doublet of doublet of
doublets,
br
=
broad,
m
=
multiplet),
and coupling constants.
Thermogravimetry-differential thermal analysis (TG-DTA) was undertaken using a
MAC Science TG-DTA200SA thermal analyzer under a nitrogen atmosphere at a
heating rate of 20 C min−1 from 20 to 600 °C. Photoluminescence spectrum, quantum
yield (PLQY) and CIEx,y coordinates were measured using a Hamamatsu C9920-02
absolute PL quantum yield measurement system (Excitation wavelength: 337 nm).
LDI-TOF MS spectra were recorded on a JEOL JMS-S3000 SpiralTOF spectrometer.
4.2 Synthesis of complexes complexes 1−6
In the first step, chloro-bridged cyclometallated iridium(III) dimers [L2Ir(-Cl)]2 (L =
L1 or L2) were synthesized from iridium(III) chloride hydrate according to the
literature procedures. [11,12] In the second step, a mixture of [L2Ir(-Cl)]2 (0.1−0.2
mmol), silver(I) trifluoromethanesulfonate (2.1 equiv), methanol/dichloromethane = 1/1
14
Page 14 of 19

(v/v, 12.5−25 mL) was stirred at ambient temperature for 2−5 h. Insoluble silver salts
were removed by passing through a short pad of Celite, washed with dichloromethane,
concentrated in vacuo. 1,2-Dichloroethane (2.5−5 mL) solution of the residue was
added L3−L7 (2.1 equiv, relative to [L2Ir(-Cl)]2) was heated at reflux for 15−18 h.
After cooling to 0 C, insoluble materials were filtered off from the reaction mixture.
Removal of the solvent gave the crude materials. The following purification procedures
afforded the charged complexes 1−6.
Complexes 1−4: Sonication in solvent (using ethyl acetate for 1; chloroform for 2;
chloroform/hexane for 3; chloroform for 4) yielded yellowish precipitate. The
precipitate was collected by filtration to give desired charged complex (1, 80%; 2, 80%;
3, 35%; 4, 49%). In the case of the isolation of 3, additional silica gel and alumina
column chromatography were required to obtain spectroscopically pure sample prior to
the sonication.
Complexes 5 and 6: Alumina column chromatography followed by sonication in
chloroform/AK-225 gave yellowish precipitate. The precipitate was collected by
filtration to give desired charged complex (5, 71%; 6; 28%). For complex 6, a repeated
procedure, that is alumina column chromatography followed by sonication, is required
to obtain spectroscopically pure sample.
4.3 Fabrication and characterization of light-emitting device based on 3
For device fabrication, glass substrates coated with a 150ꢀnm ITO layer having sheet
resistance of 10ꢀ/sq were cleaned using ultrasonication in acetone, followed by
ultrasonication in detergent, pure water, and isopropanol. Then, the substrates were
15
Page 15 of 19

placed in an ultraviolet (UV)-ozone treatment chamber for 30ꢀmin. The substrates were
then coated with a 30nm PEDOT:PSS layer by spin-coating a suspension in water
(Clevios AI4083) at a speed of 4000 rpm for 60 s. The 30 nm thick active layer was
spin-coated from a blend solution of PMMA, mCP and 3 in 1,2-dichloroethane. The
optimized PMMA:mCP ratio was 1:0.9 with a total concentration of 10 mg/ml to which
15 wt% 3 with respect to the amount of mCP was added. The samples were then placed
in a vacuum chamber and the electron injecting layer and electrodes were deposited to
finalize the devices. The finalized devices were encapsulated to avoid oxidation of the
aluminum electrodes. The current density-voltage-external quantum efficiency
characteristics of the devices were measured using a computer-controlled sourcemeter
(2400, Keithley) and an integrating sphere installed with a calibrated silicon photodiode.
The luminance and the power conversion efficiency of the OLEDs were measured using
a computer-controlled luminance meter (BM-9, TOPCON). The EL spectra of the
OLEDs were taken using a photonic multi-channel analyzer (C7473, Hamamatsu).
SUPPLEMENTARY DATA
Additional experimental procedures, TG curve of complex 3, compound
characterization data, and NMR spectra.
ACKNOWLEDGMENTS
The authors (Y.T., E.M., and K.F.) are grateful to Dr. Yoji Nakajima and Dr. Yuko
Tachibana at Asahi Glass for assistance with LDI-TOF MS.
16
Page 16 of 19

REFERENCES
[1] H. Yersin, ed., Highly Efficient OLEDs with Phosphorescent Materials, Wiley-VCH,
2007.
[2] Y. Chi, P.-T. Chou, Chem. Soc. Rev. 39 (2010) 638-655.
[3] C. Ulbricht, B. Beyer, C. Friebe, A. Winter, U.S. Schubert, Adv. Mater. 21 (2009)
4418-4441.
[4] C. Adachi, R.C. Kwong, P. Djurovich, V. Adamovich, M. A. Baldo, M.E. Thompson,
S.R. Forrest, Appl. Phys. Lett. 79 (2001) 2082-2084.
[5] K.S. Yook, J.Y. Lee, Adv. Mater. 24 (2012) 3169-3190.
[6] S.J. Lee, K. Park, K. Yang, Y. Kang, Inorg. Chem. 48 (2009) 1030-1037.
[7] Selected examples, see:
(a) S.O. Yo, U.N. Ahn, Y. Ha, S.Y. Ahn, Mol. Cryst. Liq. Cryst. 530 (2010)
116/[272]-122/[278].
(b) N. Jung, E. Lee, J. Kim, H.H.-K. Park, K. Park, Y. Kang, Bull. Korean Chem. Soc.
33 (2012) 183-188.
(c) H.R. Park, D.H. Lim, Y.K. Kim, Y. Ha, J. Nanosci. Nanotechnol. 12 (2012)
668-673.
(d) C.-H. Yang, M. Mauro, F. Polo, S. Watanabe, I. Muenster, R. Fröhlich, L. De Cola,
Chem. Mater. 24 (2012) 3684-3695.
(e) F. Kessler, R.D. Costa, D. Di Censo, R. Scopelliti, E. Ortí, H.J. Bolink, S. Meier,
W. Sarfert, M. Grätzel, M.K. Nazeeruddin, E. Baranoff, Dalt. Trans. 41 (2012)
180-191.
17
Page 17 of 19

(f) S.B. Meier, W. Sarfert, J.M. Junquera-Hernández, M. Delgado, D. Tordera, E. Ortí,
H.J. Bolink, F. Kessler, R. Scopelliti, M. Grätzel, M.K. Nazeeruddin, E. Baranoff, J.
Mater. Chem. C 1 (2013) 58-68.
(g) Y. Kang, Y.-L. Chang, J.-S. Lu, S.-B. Ko, Y. Rao, M. Varlan, Z.-H. Lu, S. Wang, J.
Mater. Chem. C 1 (2013) 441-450.
(h) F. Kessler, Y. Watanabe, H. Sasabe, H. Katagiri, M.K. Nazeeruddin, M. Grätzel, J.
Kido, J. Mater. Chem. C 1 (2013) 1070-1075.
(i) N. Darmawan, C.-H. Yang, M. Mauro, R. Fröhlich, L. De Cola, C.-H. Chang, Z.-J.
Wu, C.-W. Tai, J. Mater. Chem. C 2 (2014) 2569-2582.
[8] Schmid et al. have reported similar sovento complexes, see: B. Schmid, F.O. Garces,
R.J. Watts, Inorg. Chem. 33 (1994) 9-14.
[9] 2-(1H-pyrazoly-1-yl)pyridine-based charged iridium(III) complexes, see:
(a) [1] L. He, L. Duan, J. Qiao, R. Wang, P. Wei, L. Wang, et al., Blue-Emitting
Cationic Iridium Complexes with 2-(1H-Pyrazol-1-yl)pyridine as the Ancillary Ligand
for Efficient Light-Emitting Electrochemical Cells, Adv. Funct. Mater. 18 (2008)
2123-2131.
(b) N.M. Shavaleev, R. Scopelliti, M. Grätzel, M.K. Nazeeruddin, Inorganica Chimica
Acta Steric hindrance at metal centre quenches green phosphorescence of cationic
iridium (III) complexes with 1-(2-pyridyl)-pyrazoles, Inorganica Chim. Acta. 404
(2013) 210-214.
(c) V.A. Online, L. Duan, Y. Wei, L. He, L. Wang, Y. Qiu, Increased phosphorescent
quantum yields of controlling the counter anions, Chem. Commun. (2014) 530-532.
(d) D. Ma, L. Duan, Y. Qiu, Tetraphenylborate versus tetraimidazolylborate as
counterions for cationic iridium (III) complexes, Dalt. Trans. (2015) 8521-8528.
18
Page 18 of 19

[10] Similar 2-(1H-pyrazoly-5-yl)pyridine-based neutral iridium(III) complexes were
reported by Chi and Chou, see ref 2 and references therein.
[11] S. Sprouse, K. A. King, P. J. Spellane, R. J. Watts, J. Am. Chem. Soc., 106 (1984)
6647-6653.
[12] J. Li, P.I. Djurovich, B.D. Alleyne, I. Tsyba, N.N. Ho, R. Bau, M.E. Thompson,
Polyhedron 23 (2004) 419-428.
[13] See the experimental section for details.
[14] See the Supplementary Information.
[15] K. Fukuda, E. Murotani, Y. Takahira, V. Vohra, H. Murata, Poster presentation
#P-27, International Conference on Fluorine Chemistry 2014 Tokyo, Yokohama, Japan,
May 28-30, 2014.
[16] Y. Tachibana, Y. Nakajima, T. Isemura, K. Yamamoto, T. Satoh, J. Aoki, M. Toyoda,
Oral presentation #S22-1040, 19th International Mass Spectrometry Conference, Kyoto,
Japan, September 15-21, 2012.
19
Page 19 of 19