Blue Phosphorescence with High Quantum Efficiency Engaging the Trifluoromethylsulfonyl Group to Iridium Phenylpyridine Complexes

Article abstract of DOI:10.1021/acs.inorgchem.9b02672

Incorporation of an electron-withdrawing -SO₂CF₃ substituent to cyclometalating C^N-phenylpyridine (ppy) ligand resulted in an expected blue-shifted phosphorescence in the corresponding homoleptic Ir(ppySCF₃)₃ c

Full text of DOI:10.1021/acs.inorgchem.9b02672

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Blue Phosphorescence with High Quantum Efficiency Engaging the
Trifluoromethylsulfonyl Group to Iridium Phenylpyridine Complexes
Jin-Hyoung Kim, So-Yoen Kim, Seol Jang, Seungjun Yi, Dae Won Cho,* Ho-Jin Son,*
and Sang Ook Kang*
Department of Advanced Materials Chemistry, Korea University, Sejong 30019, Korea
*
S Supporting Information
ABSTRACT: Incorporation of an electron-withdrawing
SO CF substituent to cyclometalating C^N-phenylpyridine
−
2
3
(
ppy) ligand resulted in an expected blue-shifted phosphor-
escence in the corresponding homoleptic Ir(ppySCF3)3
complex, showing the emission of λem = 464 nm at 300 K.
One of its heteroleptic derivatives, modified by a pyrazolyl
borate LX ligand, Ir(ppySCF ) (bor), exhibited further blue-
3
2
shifted phosphorescence of λem = 460 nm at 300 K. Cyclic
voltammograms (CVs) and density-functional theory (DFT)
calculations supported the efficacy of the electron-with-
drawing capability of the SO CF3 substituent lowering
2
HOMO energy and obtained widened bandgaps and resumed
blue emissions for all of the iridium complexes studied. The
homoleptic complexes of both substituents, Ir(ppySCF ) and Ir(ppySF) , reached the higher quantum yields (Φ ) of (0.89
3
3
3
PL
and 0.72), respectively. Similarly, emission quantum yields (Φ ) of the heteroleptic derivatives were reported to be (0.75, 0.83,
PL
and 0.87) for Ir(ppySCF ) (acac), Ir(ppySCF ) (bor), and Ir(ppySCF ) (pic), respectively. Emission kinetics support the
3
2
3 2
3 2
enhanced quantum efficiency when k and k values are compared between Ir(ppySCF ) and Ir(ppySF) , and both values
r
nr
3 3
3
favorably contribute to attaining a higher quantum efficiency for Ir(ppySCF ) . Among solution-processed multilayered devices
3
3
having an ITO/PEDOT:PSS/TCTA:Ir dopant (10:1, w/w)/TmPyPB/Liq/Al structure, a heteroleptic dopant, Ir-
ppySCF ) (bor), exhibited better device performance, reporting an external quantum efficiency (EQE) of 1.14%, current
(
3
2
−
1
−1
efficiency (CE) of 2.31 cd A , and power efficiency (PE) of 1.21 lm W , together with blue chromaticity of CIE = (0.16,
x,y
0
.32).
INTRODUCTION
Scheme 1. Blue Emission Tuning via the Incorporation of
Electron-Withdrawing Groups on the C^N-Phenyl Pyridine
■
Among the remaining tasks in OLED material development,
securing a highly efficient blue phosphorescent dopant has been
one of the major challenges.
(
ppy) Ligand and Variation of the Ancillary Group (L^X)
1
−15
The choice of phosphorescent
transition metal and engaging it through bidentate ligands with
conjugated σ-donor and π-acceptor functionalities were a
1
,4,9,16−19
common synthetic strategy.
However, even before
attempting exotic ligand design, a well-known bandgap
adjustment from phenylpyridine (ppy) ligand has not yet been
fully addressed in terms of ligand derivatization and its
correlation to the photophysical property of the resulting
iridium dopant. For example, the most popular strategy to obtain
blue-emitting phosphorescent Ir complex has been set up by
incorporating an electron-withdrawing group (EWG) at the
phenyl moiety of ppy ligand, as shown in Scheme 1. The EWG
can stabilize the highest occupied molecular orbital (HOMO),
Recently, it has been realized that the fluoro sulfonyl (−SO F)
2
group is stronger than any other of the EWGs mentioned above,
and the utility of this functional ligand thus produced the
corresponding Ir complexes exhibiting blue-shifted phosphor-
4
,9,19
resulting in an increased bandgap of Ir complexes.
Several
2
0−27
EWGs, such as fluorine (−F),
trifluoromethyl
4
,20,25−32
33−35
36−39
(−CF3),
nitro (−NO ),
cyano (−CN),
have been used to induce such blue
emissions from Ir(III) complexes.
and
2
4
0−48
sulfonyl (−SO R)
Received: September 5, 2019
2
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 2. Molecular Structures of Sulfonyl Group-Substituted Iridium(III) Complexes
escence. Additionally, a higher phosphorescence quantum
efficiency of those iridium complexes was reported, and its
EXPERIMENTAL SECTION
■
The general information for the Experimental Section, details for the
instrumentation, DFT and TD-DFT calculation, X-ray crystallography,
the device fabrication, and the synthesis of ppySF are provided in the
Supporting Information.
origin was proven to be the stronger σ-bond at C −Ir, and
Ph
3
hence destabilizing the MC state originating from the
48
corresponding σ*-orbital of C −Ir. To further support this
argument that the stronger the electron-withdrawing power it
has, the more stabilized HOMO that is attributed to it, and yet
Ph
Synthesis of 3-Bromophenyl Trifluoromethyl Sulfide (L1).
Under an N
is dropwise added to a DMF solvent (5 mL) containing NaH (0.25 g,
0.57 mol) and stirred at 20 °C for 15 min. The reaction mixture is
atmosphere, 3-bromobenzenethiol (2.00 g, 10.58 mmol)
2
3
the more destabilized MC state it bears, the Hammett value
1
(
σ ) of −SO CF is 0.96, and larger than that of −SO F, 0.91.
p
2
3
2
further exposed to CF I gas, until its color becomes yellow. The yellow
3
Our motivation of introducing the most EWD group, −SO CF ,
2
3
crude product is extracted with CH Cl and dried over anhydrous
2
2
lies in confirmation of the substituent effect, which not only
portrays the known structure and property relationship but also
realizes how much deeper blue color coordinate and/or
emission quantum efficiency we can achieve from the
substitution.
MgSO . After solvent evaporation under reduced pressure, the
4
remaining residue is purified by silica gel chromatography using
1
CH Cl /n-hexane as eluent, to give L1. Yield 20% (0.54 g). H NMR
2
2
(
7
300.1 MHz, CDCl ): δ 7.82 (s, 1H), (7.64−7.58) (m, 2H), 7.31 (t, J =
3
.2 Hz, 1H). ESI-MS (m/z): calcd. for C H BrF S: 255.9169, found [M
7 4 3
+
Since our earlier work dealt only with a series of the
+ H] : 256.9876.
Synthesis of 1-Bromo-3-(trifluoromethylsulfonyl)benzene
L2). Under an N atmosphere, the mixture of acetic acid (36 mL),
heteroleptic iridium dopants from the −SO F substitution,
2
4
8
(
Ir(ppySF) (LX), this work is rather comprehensive and
2
2
L1 (0.1 g, 0.39 mmol), and hydrogen peroxide (12 mL) is heated at 120
C for 3 h. After cooling to RT, the crude product is extracted with
CH Cl and dried over anhydrous Na SO . After solvent evaporation
includes the remaining homoleptic complex, Ir(ppySF) , as
3
°
well. Scheme 2 shows that a complete set comprising both
2
2
2
4
−
SO F and −SO CF groups is in the list. The synthesis of all
2
2
3
under reduced pressure, the remaining residue is purified by silica gel
the SO F derivatives is nontrivial, and most of the products were
2
chromatography using CH Cl /n-hexane as eluent, to give L2. Yield
2
2
fully characterized, including the X-ray structures of all of the
heteroleptic complexes. Within the scope of the elucidation of
wide bandgap and emission enhancement, the following
experimental protocols have been established in this work.
First, HOMO energy control by either −SO F or −SO CF has
1
9
7
8% (0.11 g). H NMR (300.1 MHz, CDCl ): δ 8.17 (s, 1H), (8.00−
.95) (m, 2H), 7.56 (t, J = 8.1 Hz, 1H). ESI-MS (m/z): calcd. for
3
+
C H BrF O S: 287.9067, found [M + H] : 288.9124.
7
4
3
2
Synthesis of 2-(3-(Trifluoromethylsulfonyl)phenyl)pyridine
(ppySCF ). Under an N atmosphere, Pd(PPh (0.48 g, 5 mol %) is
)
3 4
2
2
3
3
2
added to a dried, degassed toluene (40 mL) containing L2 (2.42 g, 8.37
mmol) and 2-(tributylstannyl)pyridine (3.08 g, 8.37 mmol). The
reaction mixture is refluxed at 110 °C for 16 h. After cooling to RT, the
solvent is removed under reduced pressure. The dark residue is purified
by silica gel chromatography using ethyl acetate/n-hexane as eluent, to
been measured by CV and confirmed from the serial DFT
calculations. Second, steady-state photochemistry and photo-
dynamic studies estimated the efficacy of the dopants produced
by the −SO CF substitution. From those approaches, the blue
2
3
phosphorescence origin from the −SO CF substitution and
1
2
3
give ppySCF . Yield 63% (1.51 g). H NMR (300.1 MHz, CDCl ): δ
3
3
their excited state properties have been unveiled. Also, albeit the
most efficient device had not been manufactured due to the
unsublimable nature of the blue dopants produced, the choice
from the heteroleptic complex, Ir(ppySCF ) (bor), proves to
8
=
(
.76 (d, J = 4.8 Hz, 1H), 8.75 (s, 1H), 8.54 (d, J = 7.8 Hz, 1H), 8.08 (d, J
7.8 Hz, 1H), (7.87−7.77) (m, 3H), 7.37 (t, J = 5.7 Hz, 1H). ESI-MS
+
m/z): calcd. for C H F NO S: 287.0228, found [M + H] : 288.0124.
12 8 3 2
3
2
Synthesis of Ir(ppySCF ) . A glycerol solvent (5 mL) containing
3 3
be a better option for the electroluminescence device fabricated.
ppySCF (0.95 g, 3.3 mmol) and Ir(acac) (0.49 g, 1.0 mmol) is
3
3
B
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Scheme 3. Synthetic Route to the Cyclometalating Ligands (ppySF and ppySCF3)
a
Conditions: (i) Pd(PPh ) , toluene, 110 °C, 16 h (72% yield); (ii) CF I, NaH, DMF, 20 °C, 15 min (20% yield); (iii) acetic acid, H O , 120 °C,
3
4
3
2
2
3
h (98% yield); (iv) Pd(PPh ) , toluene, N , reflux, 16 h (63% yield).
3 4 2
Scheme 4. Synthetic Routes to the Ir(III) Complexes (Ir(ppySF) , Ir(ppySCF ) , Ir(ppySCF ) (acac), Ir(ppySCF ) (pic), and
3
3 3
3 2
3 2
a
Ir(ppySCF ) (bor))
3
2
a
Conditions: (i) Ir(acac) , glycerol, N , reflux, 24 h (39% yield); (ii) IrCl ·xH O, 2-ethoxyethanol/water (3:1, v/v), 100 °C, 8 h; (iii) Ir(acac) ,
3
2
3
2
3
glycerol, N , reflux, 24 h (42% yield); (iv) acetylacetone, Na CO , 2-ethoxyethanol, 100 °C, 8 h (65% yield); (v) picolinic acid, Na CO , 2-
2
2
3
2
3
ethoxyethanol, 100 °C, 8 h (52% yield); (vi) AgOTF, CH Cl /CH OH, room temperature, 2 h; (vii) potassium tetrakis(1-pyrazolyl)borate,
2
2
3
CH CN, 100 °C, 12 h (24% yield).
3
C
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 1. Crystal structures of Ir(ppySCF ) (acac), Ir(ppySCF ) (pic), and Ir(ppySCF ) (bor). H atoms have been omitted for clarity. ORTEP
3
2
3
2
3 2
49
drawings are provided in Figures S14−S16 of the SI.
refluxed under a N atmosphere for 24 h. After cooling to RT, the
containing the crude brown residue and potassium tetrakis(1-
2
reaction mixture is poured into H O. The resulting precipitate is
pyrazolyl)borate (0.34 g, 1.08 mmol) was refluxed at 100 °C for 12 h
2
collected by filtration and washed with H O and n-hexane. The crude
under N atmosphere. After cooling to RT, the crude product is
2
2
yellow powder is purified by silica gel chromatography using ethyl
acetate/n-hexane as eluent, to give Ir(ppySCF ) . Yield 42% (0.44 g).
extracted with CH Cl and dried over anhydrous MgSO . After
evaporation under reduced pressure, the remaining residue is purified
2
2
4
3
3
1
H NMR (300.1 MHz, CDCl ): δ 8.19 (s, 3H), 8.12 (d, J = 8.4 Hz, 3H),
by silica gel chromatography using ethyl acetate/n-hexane as eluent, to
3
1
7
3
.88 (t, J = 7.6 Hz, 3H), 7.51 (d, J = 4.8 Hz, 3H), 7.37 (d, J = 8.1 Hz,
give Ir(ppySCF
3
)
2
(bor) as a light yellow solid. Yield 24% (0.09 g). H
H), 7.17 (t, J = 6.2 Hz, 3H), 6.98 (d, J = 8.1 Hz, 3H). ESI-MS (m/z):
NMR (300.1 MHz, CDCl
3
): δ 8.13 (s, 2H), 7.97 (d, J = 7.8 Hz, 2H),
+
calcd. for C H F IrN O S : 1051.0078, found [M] : 1051.2353.
7.77 (t, J = 7.5 Hz, 2H), 7.72 (s, 2H), (7.38−7.31) (m, 4H), 7.18 (d, J =
2.1 Hz, 2H), 6.94 (t, J = 6.6 Hz, 2H), 6.74 (s, 2H), 6.46 (d, J = 7.8 Hz,
36
21
9
3
6 3
Synthesis of Ir(ppySF) . A procedure analogous to the preparation
3
of Ir(ppySCF ) was used starting from ppySF (0.36 g, 1.52 mmol) and
2H), 6.26 (s, 2H), 6.17 (s, 2H), 6.05 (s, 2H). ESI-MS (m/z): calcd. for
3
3
+
Ir(acac) (0.25 g, 0.51 mmol). The product Ir(ppySF) was obtained as
C
H
36
26BF
6
IrN10
O
4
S
2
: 1,044.1206, found [M] : 1,044.7211.
3
3
1
a yellow powder. Yield 39% (0.18 g). H NMR (300.1 MHz, DMSO-
d6): δ 8.60 (d, J = 8.1 Hz, 3H), 8.49 (s, 3H), 8.01 (t, J = 7.2 Hz, 3H),
RESULTS AND DISCUSSION
■
7
3
.55 (d, J = 5.4 Hz, 3H), 7.46 (d, J = 7.2 Hz, 3H), 7.38 (t, J = 6.3 Hz,
H), 6.91 (d, J = 8.1 Hz, 3H). ESI-MS (m/z): calcd. for
Synthesis and Characterization. The trifluoromethylsul-
fonyl-substituted cyclometalating C^N ligand (ppySCF ) was
prepared in three steps in an analogous manner to the synthesis
of 2-(3-fluorosulfonylphenyl)pyridine (ppySF) (Scheme 3).
The trifluoromethylsulfonyl group (−SO CF ) in the bromo-
phenyl moiety was introduced by treatment of 3-bromobenze-
+
C H F IrN O S : 901.0174, found [M] : 901.0791.
33
21
3
3
6
3
3
Synthesis of [(ppySCF ) IrCl] . IrCl ·xH O (0.5 g, 1.42 mmol) is
3
2
2
3
2
added to the 8 mL of 2-ethoxyethanol/water mixture solvent (3:1, v/v)
48
containing ppySCF (1.02 g, 3.55 mmol) and refluxed at 100 °C under
3
2
3
N atmosphere for 8 h. After cooling to RT, the addition of H O (50
2
2
mL) gives a light-yellow precipitate. The yellow solids precipitated are
filtered out and washed with cold n-hexane. The crude product was
used for the next reaction, without further purification.
nethiol and CF I gas in DMF followed by oxidation of sulfur
3
with H O and acetic acid. The ppySCF ligand was obtained
2
2
3
Synthesis of Ir(ppySCF ) (acac). Under a N atmosphere,
using the Stille-type cross-coupling reaction of 1-bromo-3-
((trifluoromethyl)sulfonyl)benzene and 2-(tributylstannyl)-
pyridine in a yield of 63% (Scheme 3).
3
2
2
[
0
(ppySCF ) IrCl] (0.57 g, 0.36 mmol), acetylacetone (0.072 mL,
3 2 2
.72 mmol), and Na CO (0.13 g, 1.23 mmol) are added to the 2-
2 3
ethoxyethanol solvent (10 mL) and heated at 100 °C for 8 h. After
With the cyclometalating ligands in hand, the final homoleptic
Ir(ppySF) and Ir(ppySCF ) were synthesized from treating
cooling to RT, the reaction mixture is poured into H O. The resulting
2
3
3 3
precipitate is collected by filtration and washed with H O and n-hexane.
2
Ir(acac) with ligands (ppySF and ppySCF ) (3.3 equiv) in
3
3
The crude yellow powder is purified by silica gel chromatography using
ethyl acetate/n-hexane as eluent, to give Ir(ppySCF ) (acac). Yield
19
moderate yields of 39 and 42%, respectively (Scheme 4). For
the preparation of the heteroleptic Ir(III) complexes, the
3
2
1
6
8
2
1
5% (0.20 g). H NMR (300.1 MHz, CDCl ): δ 8.48 (d, J = 6 Hz, 2H),
3
dichloro-bridged iridium dimer, [(ppySCF ) IrCl] , was
.07 (d, J = 9.3 Hz, 4H), 7.95 (t, J = 7.8 Hz, 2H), 7.38 (t, J = 6.6 Hz,
H), 7.20 (d, J = 7.8 Hz, 2H), 6.52 (d, J = 8.4 Hz, 2H), 5.29 (s, 1H),
.82 (s, 6H). ESI-MS (m/z): calcd. for C H F IrN O S : 864.0374,
3
2
2
synthesized by reaction of IrCl ·xH O and the cyclometalating
3 2
ppySCF ligand. Subsequently, the cleavage of dichloro-bridged
2
9
21
6
2
6
2
3
+
found [M] : 864.0515.
Synthesis of Ir(ppySCF ) (pic). Under a N atmosphere,
iridium dimer with the corresponding ancillary ligands (acac,
pic, and bor) produced the desired heteroleptic Ir-
3
2
2
[
(ppySCF ) IrCl] (0.57 g, 0.36 mmol), picolinic acid (0.09 g, 0.72
3 2 2
(
ppySCF ) (LX) dopants (LX = acac, pic, and bor) in moderate
3 2
mmol), and Na CO (0.13 g, 1.26 mmol) are added to the 2-
2
3
yields of (24−65)% (Scheme 4). All compounds were fully
characterized by H NMR spectroscopy and ESI-mass
ethoxyethanol solvent (10 mL) and heated at 100 °C for 8 h. After
1
cooling to RT, the reaction mixture is poured into H O. The resulting
2
spectrometry (see the Experimental Section and Figures S1−
S13 of the Supporting Information).
precipitates are filtered out and washed with H O and n-hexane. The
2
crude yellow powder is purified by silica gel chromatography using ethyl
acetate/n-hexane as eluent, to give Ir(ppySCF ) (pic). Yield 52% (0.16
X-ray Crystallographic Analysis. Figure 1 shows molec-
ular structures of Ir(ppySCF ) (acac), Ir(ppySCF ) (pic), and
3
2
1
g). H NMR (300.1 MHz, CDCl ): δ 8.83 (d, J = 5.1 Hz, 1H), 8.37 (d, J
3
3 2
3 2
=
7
7
7.5 Hz, 1H), (8.18−7.91) (m, 6H), 7.62 (d, J = 4.2 Hz, 1H), (7.50−
Ir(ppySCF ) (bor) analyzed via X-ray crystallography of single
3 2
.45) (m, 2H), (7.41−7.29) (m, 4H), 7.20 (t, J = 6.9 Hz, 1H), 6.72 (d,
crystals grown in CH Cl solution. Crystal symmetries were
2
2
.8 Hz, 1H), 6.45 (d, J = 7.8 Hz, 1H). ESI-MS (m/z): calcd. for
determined as follows: an orthorhombic space group Pccn for
+
C H F IrN O S : 887.0170, found [M + H] : 888.0231.
3
0
18
6
3
6 2
Ir(ppySCF ) (acac), a trigonal space group P3
̅
for Ir-
̅
ppySCF ) (pic), and a triclinic space group P1 for Ir-
3 2
3
2
Synthesis of Ir(ppySCF ) (bor). Under a N atmosphere, the
3
2
2
(
(
mixture of [(ppySCF ) IrCl] (0.57 g, 0.36 mmol) and silver
3
2
2
ppySCF ) (bor). Their molecular structures contained trans-
trifluoromethanesulfonate (AgOTF, 0.19 g, 0.72 mmol) is added to
the 30 mL of CH Cl /CH OH mixture solvent (3:1, v/v) and stirred at
3 2
N,N of pyridine moieties and cis-C,C geometry of phenyl
moieties in the cyclometalated ligand. The lateral angle for trans
2
2
3
RT for 2 h. After the salts precipitated are filtered out, the filtrate was
concentrated under reduced pressure. A CH CN solution (10 mL)
N−Ir−N was 176.4(3)° for Ir(ppySCF ) (acac), 175.5(5)° for
3
3 2
D
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
1
Ir(ppySCF ) (pic), and 172.0(2)° for Ir(ppySCF ) (bor).
ligand charge transfer ( MLCT) transition in the singlet state. A
3
2
3 2
3
Lateral trans N−Ir−N bonds were bent from linear structures.
spin-forbidden triplet MLCT ( MLCT) band was observed at
In particular, Ir(ppySCF ) (bor) was largely distorted, due to
wavelengths (420−483) nm with very weak absorbance.
Although heteroleptic Ir complexes contained two identical
cyclometalated ligands as the chromophore, their absorption
spectra were strongly affected by the ancillary ligand. Their onset
positions in the absorption spectra varied substantially, as shown
in the enlarged spectra of Figure 2a. The onset of Ir-
(ppySCF ) (acac) was observed at longer wavelength than in
other complexes. The onset of Ir(ppySCF ) (bor) was
observed at the shortest wavelength. Such an ancillary ligand
effect resembles those found in the −SO F congeners.
For homoleptic complexes, the absorption spectrum of
Ir(ppySCF ) was observed at shorter wavelength compared
to that of Ir(ppySF) , indicating that a strong EWG might have
increased the bandgap. LC bands of Ir(ppySCF3)3 and
Ir(ppySF) were observed at around 275 nm. They were
more intense than those of heteroleptic complexes as shown in
Figure 2b, probably due to one more ppy ligands in the
homoleptic complex. The onset wavelengths of MLCT
3
2
the bulky bor ancillary ligand.
Bond lengths between iridium and donor atoms of ancillary
ligands were longer than those of the main ligand, as listed in
Table 1. This means that the ancillary ligand was less tightly
Table 1. Bond Distances (Å) between Ir and Donor Atoms of
Ligands in Heteroleptic Ir Complexes
3 2
3
2
Ir(ppySCF ) (acac)
Ir(ppySCF ) (pic)
Ir(ppySCF ) (bor)
48
3
2
3
2
3 2
2
Ir−Cph
1.991(7)
Ir−Cph
1.966(2)
.935(2)
2.043(1)
.046(1)
2.144(1)
2.144(1)
Ir−Cph
1.993(6)
2.009(5)
2.045(4)
2.049(4)
2.140(5)
2.158(5)
1
3
3
Ir−Npy
2.047(7)
2.140(5)
Ir−Npy
Ir−Npy
3
2
1
Ir−Oacac
Ir−Npic
Ir−Opic
Ir−Nbor
3
bound to the Ir center, compared to the main ligand. Indeed,
bond lengths of Ir−O and Ir−N of the ancillary ligand were in
the ranges (2.140(5)−2.144(1)) and (2.140(5)−2.158(5)) Å,
3
absorption for Ir(ppySCF ) and Ir(ppySF) were (471 and
3
3
3
473) nm, respectively.
respectively. Ir−N bond lengths of the main ligand were in the
py
Steady-State Phosphorescence Properties. Figure 3
range (2.043(1)−2.049(4)) Å, which were less deviated by the
ancillary ligand. This may be attributed to the axial formation of
trans N −Ir−N bonds. However, Ir−C bond lengths varied
shows the steady-state photoluminescence (PL) spectra
measured at (300 and 77) K. The strong blue emission
originated from triplet excited states with both the π−π* and
MLCT characteristics. The photophysical properties of
heteroleptic complexes were significantly affected by variation
in ancillary ligands. Emission maxima of heteroleptic Ir-
py
py
ph
in the range (1.935(2)−2.009(5)) Å, indicating that the
ancillary ligands and their donor atoms resulted in different
31,48
electronic and steric environments.
Ir(ppySCF ) (bor) had
3 2
the longest Ir−C bond length, probably due to the distorted
ph
(
(
ppySCF ) (acac), Ir(ppySCF ) (pic), and Ir-
3 2 3 2
structure caused by the bulky ancillary ligand.
ppySCF ) (bor) were observed at (485, 469, and 460) nm,
3
2
Steady-State Absorption Properties. Relating to pre-
respectively. Such blue-shifts induced by changes in ancillary
groups from -acac to -bor could be explained as degrees of
stabilization of the Ir metal center. The electron-withdrawing
ability of the ancillary ligand is increased in the order of acac <
pic < bor. These trends are in line with those reported for other
heteroleptic Ir complexes.
At 300 K, the emission maximum of Ir(ppySCF ) was 464
vious examples of the heteroleptic iridium complexes of the type
48
Ir(ppySF) (LX) with a −SO F group at ppy ligand, Figure 2a
2
2
31,48
3
3
nm, which was blue-shifted by 6 nm compared to that of
Ir(ppySF) (470 nm). Such a hypsochromic shift might be due
3
to a slightly increased electron-withdrawing ability of the
−
SO CF substituent, compared with that of the −SO F
2
3
2
substituent in the phenyl moiety. Consequently, a substituent
change from −SO F to −SO CF resulted in a larger bandgap of
2
2
3
the series of heteroleptic Ir complexes (see Table 2).
At 77 K, Ir complexes showed a well-developed vibronic
structure in emission spectra with a rigidochromic shift to
shorter wavelengths of about (5−10) nm, compared with those
at 300 K, as shown in Figure 3b. Usually, solvent reorganization
is significantly impeded in a rigid matrix. Thus, the emission is
50
observed at higher energy regions at 77 K. The 0−0 emission
Figure 2. UV−vis absorption spectra of (a, upper) heteroleptic Ir(III)
complexes (Ir(ppySCF ) (acac), Ir(ppySCF ) (pic), and Ir-
bands of heteroleptic complexes (Ir(ppySCF ) (acac), Ir-
3
2
3
2
3
2
(ppySCF ) (pic), and Ir(ppySCF ) (bor)) were (475, 463,
3 2 3 2
(
ppySCF ) (bor)) and (b, lower) homoleptic Ir(III) complexes
Ir(ppySCF ) and Ir(ppySF) ).
3 2
and 455) nm, respectively. The 0−1 emission bands were
observed at longer wavelengths, as listed in Table 2. The spacing
(
3 3 3
(
Δv
) between 0−0 and 0−1 vibronic bands was in the range
0−01
−1
0
shows absorption spectra of their analogues of Ir-
(1,410−1,530) cm , which might correspond to C−C
stretching modes between phenyl and pyridyl rings or to the
stretching of aromatic rings.
(
(
ppySCF ) (acac), Ir(ppySCF ) (pic), and Ir-
3
2
3 2
5
1,52
ppySCF ) (bor) in CH Cl at 300 K. These absorption
In the heteroleptic complexes,
3
2
2
2
−
1
spectra showed strong bands at <320 nm that could be
attributed to the π−π* transition of ppy ligands [ligand
centered ( LC) transition]. The broad absorption band at
the Δν
value was 1,411 cm for Ir(ppySCF ) (acac),
0
0−01
3 2
1
−1
−1
1,474 cm for Ir(ppySCF ) (pic), and 1,528 cm for
3
2
1
Ir(ppySCF ) (bor) with increasing order of acac < pic < bor
ancillary ligands.
3 2
(
320−420) nm could be assigned to the spin-allowed metal-to-
E
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 3. Emission spectra of Ir complexes (a) in anaerobic CH Cl (at 300 K, λ = 355 nm) and (b) in a glassy 2-methyltetrahydrofuran matrix (at 77
2
2
ex
K, λ = 355 nm).
ex
Table 2. Photophysical and Electrochemical Parameters of Ir Complexes
Em. at 300 K
Em. at 77 K
opt
λp
τp
k
k
τp
[μs]
E
ELUMO/E
E
ELUMO/E
E (theo)
r
nr
ox
[eV]
HOMO
g
HOMO
[eV] (theo)
g
Complexes
[nm] [μs]
ϕPL [10 s−1] [10 s−1] λp [nm]
5
5
[eV]
a
[eV]
b
c
[eV]
c
Ir(ppySCF ) (acac)
485
469
460
464
470
1.40
1.98
3.58
1.41
1.53
0.75
0.87
0.83
0.89
0.72
5.36
4.39
2.32
6.31
4.71
1.79
0.66
0.48
0.78
1.83
475, 509
463, 497
455, 489
457, 491
461, 495
3.47
3.01
4.07
2.26
2.44
0.86
1.04
1.17
0.90
0.87
−3.05/−5.66
−3.16/−5.84
−3.24/−5.97
−2.99/−5.70
−2.98/−5.67
2.61
2.68
2.73
2.71
2.69
−2.09/−5.90
−2.27/−6.05
−2.26/−6.28
−2.25/−6.18
−2.30/−6.23
3.81
3.78
4.02
3.93
3.93
3
2
Ir(ppySCF ) (pic)
3
2
Ir(ppySCF ) (bor)
3
2
Ir(ppySCF3)3
Ir(ppySF)3
a
The HOMO level was determined using the following equation: E
(eV) = −e(E + 4.8). The LUMO level was determined using the
HOMO
ox
opt
b
opt
following equation: E
measured at 77 K. The values were obtained from the DFT calculation results.
(eV) = e(EHOMO + Eg ). The Eg values were calculated using the maximum wavelength of the 0−0 emission band
LUMO
c
At 77 K, the 0−0 emission band of Ir(ppySCF ) was
the color purity of Ir(ppySCF ) (acac) was superior to the
3 2
others. At 300 K, S values of all Ir complexes were in the range
(0.69−0.75), suggesting that structural displacement occurred
3
3
observed at 457 nm, which was blue-shifted compared to that of
Ir(ppySF) at 461 nm. The Δv values of homoleptic
3
00−01
−
1
Ir(ppySCF ) and Ir(ppySF) were (1,518 and 1,500) cm ,
easily in the excited triplet state. Moreover, at 300 K, Δv
3
3
3
00−01
respectively. The change in Δv0
value implies that the C−C
values were increased in the order of Ir(ppySCF ) (acac) (968
0−01
3 2
−
1
−1
bond strength is affected by the electron-withdrawing ability and
bulkiness of the ancillary ligand. The Δv0 value correlates
cm ), Ir(ppySCF ) (pic) (1,234 cm ), and Ir-
(ppySCF ) (bor) (1,365 cm ). On the other hand, Δv
3 2
−
1
0−01
3 2
00−01
−1
−
1
directly with the color purity of the emission spectra. Color
value.
values were 1,269 cm for Ir(ppySCF ) and 1,169 cm for
3 3
purity deteriorates with increasing Δv0
Ir(ppySF) . The Δv
values at 300 K were smaller than those
at 77 K. This means that structural displacement and the main
deactivation process can occur through lower energy vibrations
0−01
3
00−01
Another important factor affecting color purity is the Huang−
Rhys factor S, which represents the structural distortion ΔQ
51,53,54
between excited and ground states.
S is defined as the
at 300 K. Phosphorescence quantum yields (Φ ) were
PL
intensity ratio of the 0−0 and 0−1 vibrational band in I /I . At
determined in the range (0.72−0.89) at 300 K, as listed in
0
1
00
7
7 K, the S values of Ir(ppySCF ) (acac), Ir(ppySCF ) (pic),
Table 2.
3 2 3 2
and Ir(ppySCF ) (bor) were (0.41, 0.45, and 0.48), respec-
Photodynamic Properties. Figure 3 shows the emission
decay profiles measured in anaerobic CH Cl at (300 and 77) K.
3
2
tively. The S values for Ir(ppySCF ) and Ir(ppySF) were
3
3
3
2
2
(
0.45 and 0.56), respectively. In terms of Δν00−01 and S values,
Table 2 shows that the phosphorescence emission lifetimes (τp)
F
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
−1
56
were in the range (1.40−1.98) μs, except for Ir-
(500−600) cm . While Ir(ppySCF ) and Ir(ppySF) retain
3
3
3
(
ppySCF ) (bor) of 3.58 μs, which was remarkably longer
a similar ligand structure, the vibrational relaxation of
3
2
than other complexes. The τ (4.07 μs) of Ir(ppySCF ) (bor)
in the 2-methyl tetrahydrofuran (MTHF) matrix at 77 K was
Ir(ppySCF ) through OSO motion may be efficiently
p
3 2
3 3
inhibited by bulky −CF , rather than −F. As a result, the k
3
nr
also longer than those of other complexes of (2.26−3.47) μs
value of Ir(ppySCF ) is ca. 2.35-fold smaller than that of
3 3
(
Table 2).
Ir(ppySF) . The Φ for Ir(ppySCF ) is slightly higher (ca.
3
PL
3 3
Radiative (k ) and nonradiative (k ) rate constants were
1.24-fold) compared to that of Ir(ppySF) , as listed in Table 2.
r
nr
3
calculated using the following equation: k = Φ /τ and k =
This may be due to the larger k value (ca. 1.34-fold) of
r
PL
p
nr
r
(
1/τ ) − k . The k values for Ir complexes were at least 2.5-fold
Ir(ppySCF ) than that of Ir(ppySF) . This implies that the
p
r
r
3 3
3
greater than the k values. This result indicates that the primary
distinct decrease in knr for Ir(ppySCF3)3 has no direct
nr
deactivation process involves radiative phosphorescence,
although the nonradiative pathway is non-negligible. The knr
value of Ir(ppySF)3 was 2-fold greater than that of Ir-
correlation with the increasing k value but helps support the
r
enhanced Φ efficiency of Ir(ppySCF3)3.
PL
Electrochemical Properties. Figure 5 shows the electro-
(
ppySCF ) . Table 2 shows that the k values increased in the
chemical behaviors that were examined by cyclic voltammetry
3
3
nr
order Ir(ppySCF ) (bor) < Ir(ppySCF ) (pic) < Ir-
3
2
3 2
(
ppySCF ) (acac). This trend can be interpreted based on
3 2
the energy gap. The k value is usually governed by the energy
gap, as depicted in the following eq 1:
nr
55
ln(k ) ∝ (−γ/ℏω ) × (ΔE)
(1)
nr
M
where, γ is expressed in terms of molecular parameters, ω is the
M
maximum and dominant vibrational frequency, and ΔE
T−S
represents the energy gap between the excited triplet and
ground states.
In this work, experimental energy gaps were determined from
the 0−0 vibronic peaks of the corresponding phosphorescence
3
at 300 K. Figure 4 shows that the ln(k ) of the MLCT state
nr
Figure 5. Cyclic voltammograms of Ir(III) complexes (1 mM) in the
oxidation sides in CH CN in the presence of 0.1 M TBAP; scan rate of
3
−
1
1
00 mV s .
(
CV). All iridium compounds exhibited a reversible oxidation
process in CH CN solution. Oxidation waves may be assigned to
the Ir /Ir redox couple. The onset potentials of oxidation
waves were in the range (0.86−1.17) V vs Fc/Fc for the five
complexes. For homoleptic complexes, the oxidation potential
3
III
IV
57
+
(
0.90 V) of Ir(ppySCF ) was more stable than that of
3 3
Ir(ppySF) (0.87 V), indicating that the −SO CF substituent
3
2
3
stabilized the HOMO level more than the −SO F substituent.
2
Figure 4. Relationship between ln(k ) and the energy gap (ΔET−S) of
nr
For heteroleptic complexes, the oxidation potentials of
homoleptic complexes (Ir(ppySCF ) and Ir(ppySF) ) and hetero-
3
3
3
Ir(ppySCF ) (acac), Ir(ppySCF ) (pic), and Ir-
leptic complexes (Ir(ppySCF ) (acac), Ir(ppySCF ) (pic), and
3
2
3 2
3
2
3 2
+
Ir(ppySCF ) (bor)).
(ppySCF ) (bor) were (0.86, 1.04, and 1.17) V vs Fc/Fc ,
3 2
3
2
respectively. Change of the ancillary ligand resulted in different
oxidation potential. Ancillary ligands can modulate the physical
properties of heteroleptic complexes due to their intrinsic ligand
field strength and electronic interaction with the central metal
ion. Usually, a stronger field strength of ancillary ligand has a
directly proportional relationship with its π-acceptor properties
that strengthens the back-bonding ability, leading to a
hypsochromic shift in phosphorescence emission. This ancillary
increased linearly for the ΔE values of both homoleptic and
T−S
heteroleptic complexes. Despite fewer data, γ/ℏω values were
M
−
1
estimated from the slope values as follows: −27.72 eV for
homoleptic, and −12.53 eV for heteroleptic Ir complexes,
which were close to the low vibrational energy of ca. (290 and
−1
−
1
6
44) cm , respectively. This result indicates that the non-
58
radiative deactivation process might have been promoted
through low-frequency vibrational relaxation.
effect is reported for well-known Ir complexes. Indeed, the
emission maxima of three known heteroleptic Ir complexes
In the case of heteroleptic complexes, it is difficult to specify
(FIr(acac), FIr(pic), and Fir6 (FIr(bor); FIr(LX) = (C^N) Ir-
(LX) (C^N = 2-(2,4-difluorophenyl)pyridine)) were observed
2
−
1
which vibration modes are involved in ca. 290 cm , because
many vibration modes are gathered in the range. However, the
vibration of homoleptic complexes of ca. 644 cm− might be
specified as the asymmetric and symmetric OSO
deformation modes, which are usually observed in the range
at (484, 472, and 458) nm, respectively (see the corresponding
1
21,59,60
structures in Figure S17 of the SI).
In this work, the
hypsochromic shift in the phosphorescence spectra was
observed in the order Ir(ppySCF ) (acac) > Ir-
3
2
G
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 6. Frontier molecular orbitals (HOMO and LUMO) of Ir(III) complexes in their optimized geometries in singlet state. E values indicate the
g
bandgap energy between the HOMO and the LUMO.
(
ppySCF ) (pic) > Ir(ppySCF ) (bor). Therefore, we could
ligand plays an important role in energy gap control. The order
of HOMO and LUMO levels is denoted in the scheme of the
fabricated structure of the OLED device, which will be discussed
later.
3
2
3 2
easily deduce that the field strength of the ancillary ligand
increased in the order acac (O^O) < pic (O^N) < bor (N^N).
The Ir(III) complexes containing strong ligand-field ancillary
ligand showed large oxidation potential value.
Table 2 summarizes the oxidation potentials of Ir complexes.
The HOMO was calculated using the following eq 2 with
standard ferrocene value of −4.8 eV to vacuum level:
Density Functional Theory (DFT) Calculations. To
further improve our understanding of their structural, electronic,
and photophysical properties, DFT and TD-DFT investigations
were carried out in both singlet (S , ground) and triplet (T ,
0
1
excited) states. Theoretical calculations were performed using
EHOMO (eV) = −(Eoxonset − EFc/Fc + 4.8) eV
+
61
(2)
the Gaussian 09 program. We applied a B3LYP function with
LANL2DZ basis set for Ir atom and 6-31G(d,p) basis set for
Using the CV data, HOMO levels were determined to be in the
range −(5.66−5.97) eV, as listed in Table 2. The LUMO level
can usually be determined by using the reduction onset potential
in the CV spectrum, but we could not obtain the reduction
potentials of Ir complexes due to their limited CV window.
However, the three complexes (Ir(ppySCF ) (bor), Ir-
62−64
other atoms.
Preferentially, we performed geometry
optimization under C and C symmetries for heteroleptic and
1
3
homoleptic complexes, respectively. Figure 6 shows the frontier
molecular orbitals (FMO) and their energy levels of Ir
complexes. The HOMO was localized on the iridium center
and extended to the phenyl moiety of the cyclometalating ligand.
The LUMO was mainly localized on the pyridine moiety of the
cyclometalating ligand, with a small portion of the d orbital
character of the iridium center. The HOMO was mainly
localized on the ortho- and para-sites of the phenyl ring with
respect to the iridium atom, while orbital nodes were at the meta-
sites of the phenyl ring. The LUMO predominantly resided on
the two meta-sites relative to the iridium center, showing nodes
at the ortho- and para-sites. The HOMO was also found in the
ancillary ligand. However, the LUMO had no orbital
distribution in the same position. When a substituent was
attached at the position having significant electron density in the
MO, strong electronic interaction was possible through this
particular position. However, a substituent introduced at the
node position of the MO showed weak interaction with the main
chromophore. Therefore, the substitution on the para-site of the
phenyl-moiety of ppy ligand had more influence on the
electronic structure of the HOMO, in line with the results of
electrochemical characterization.
3
2
(
ppySCF ) , and Ir(ppySF) ) show a tiny irreversible peak in
3 3 3
the reduction potentials but due to their low intensity and
obscurity, it is not use for the calculation of LUMO energy
level.Therefore, we determined the LUMO level using optical
bandgap based on the following empirical relationship (eq 3):
ELUMO (eV) = −(EHOMO − Egopt)
(3)
where Egopt was the optical energy bandgap. In this study, we
determined the Eg values using the maximum wavelength of
the 0−0 emission band measured at 77 K. The E values of
Ir(ppySCF ) (acac), Ir(ppySCF ) (pic), and Ir-
opt
opt
g
3
2
3 2
(
ppySCF ) (bor) were (2.61, 2.68, and 2.73) eV, respectively.
3 2
opt
The Eg values of Ir(ppySCF ) and Ir(ppySF) were (2.71
3 3
3
and 2.69) eV, respectively. The LUMO levels were in the range
(2.98−3.24) eV, as listed in Table 2. The HOMO and LUMO
levels of homoleptic Ir(ppySCF ) were slightly more stabilized
−
3
3
than those of Ir(ppySF) . In the case of heteroleptic complexes,
both HOMO and LUMO levels shifted to lower energy in the
3
following order: Ir(ppySCF ) (acac) > Ir(ppySCF ) (pic) >
The difference in Hammett parameter was only 0.05 between
−SO F and −SO CF substituents at the para position of the
3
2
3 2
Ir(ppySCF ) (bor). Since the energy shifts of the HOMO levels
3
2
2
2
3
were larger than those of the LUMO levels, the energy gaps
between HOMO and LUMO increased in the same order of
Ir(ppySCF ) (acac) < Ir(ppySCF ) (pic) < Ir-
phenyl ring. However, Ir(ppySCF ) and Ir(ppySF) showed
3 3 3
significant differences in E , emission maxima, and the
ox
calculated ΔHOMO. Meanwhile, heteroleptic Ir complexes
had additional electron-withdrawing capacity of ancillary ligands
3
2
3 2
(
ppySCF ) (bor). These results indicate that the ancillary
3
2
H
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 7. Optimized triplet excited state structures and the highest singly occupied molecular orbital (HSOMO) and the lowest singly occupied
molecular orbital (LSOMO) of Ir(III) complexes.
Figure 8. Structures of device with energy levels of materials and chemical structures of the materials used.
(
bor > pic > acac) bound to the iridium center. As a result,
were (6−9)%. This result indicates that the MLCT transitions
involved in emissions originated from cyclometalating ligands.
Tables S2−S6 of the SI give the dominant electronic
transitions and oscillator strengths as determined by TD-DFT
calculation. The lowest energy transition for Ir complexes was
calculated at around 450 nm with zero oscillation strength,
corresponding to the transition between the HOMO and the
LUMO. This is a perfect forbidden transition for the triplet
manifold in the theoretical calculation. Other significantly
intense bands corresponded to transitions in the singlet state.
Simulated absorption bands also matched well with the
experimental ones, as shown in Figure S18 of the SI. The
calculated HOMO energy levels showed similar trends under
the altered oxidation potentials in CV spectra, as shown in
Figure 5. However, the HOMO energy level of Ir(ppySCF3)3
Ir(ppySCF ) (bor) exhibited a larger HOMO energy stabiliza-
tion than Ir(ppySCF ) (pic) or Ir(ppySCF ) (acac). However,
LUMO energy stabilization was limited by less MO contribution
of the ancillary ligand. For homoleptic complexes, the
contributions of iridium to HOMOs of Ir(ppySCF ) and
3
2
3
2
3 2
3
3
Ir(ppySF) were about (58 and 57)%, respectively, as listed in
3
Table S1 of the SI. On the other hand, the contribution of their
ligand to LUMOs was about 98%. Therefore, the lowest energy
transition from HOMO to LUMO is a characteristic MLCT
transition. Iridium contributions of (49−53)% to the HOMOs
of heteroleptic complexes were slightly lower than their
corresponding contributions to the HOMOs of homoleptic
complexes (Table S1 of the SI). The contribution of ancillary
ligands was very low at (5−9)%, suggesting that the ancillary
ligands had no role in MLCT transitions. On the other hand, the
total contributions of iridium and ancillary ligands to LUMOs
was calculated to be slightly higher than that of Ir(ppySF) . The
3
LUMO energy levels were in the range −(2.09−2.30) eV, in
I
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 9. Performances of the devices bearing series of Ir(III) complexes. (a) J−V−L characteristics, (b) current efficiency (CE)−current density (J)
curves, (c) power efficiency (PE)−current density (J) curves, and (d) external quantum efficiency (EQE) as a function of current density (J).
Table 3. Electroluminescence Characteristics of OLEDs
a
b
c
d
e
f
Dopant
Von (V)
λpeak (nm)
EQE (%)
CE (Cd/A)
PE (lm/W)
CIE
Ir(ppySCF ) (bor)
Ir(ppySCF3)3
Ir(ppySF)3
6.40
10.25
11.45
466, 497
470, 498
477(sh), 505
1.14
0.74
0.71
2.31
1.68
1.89
1.21
0.41
0.56
(0.16, 0.32)
(0.24, 0.44)
(0.26, 0.48)
3
2
a
b
c
d
e
f
Turn-on voltage at 1 nit. Peak wavelength at 1 nit. Max external quantum efficiency. Max current efficiency. Max power efficiency. The
commission internationale de L’Eclairage (CIE) coordinates at 1 nit.
which the energy variation of LUMO was smaller, compared to
the HOMO variation.
nm)/Liq (1 nm)/Al (150 nm, cathode). The poly(3,4-
ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:
PSS) was used as hole injection layer (HIL). The emitting
layer consisted of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as
host materials, and Ir complexes were used as phosphorescent
dopants. The host material TCTA has specific properties of wide
Structures in the triplet state were optimized using the
unrestricted B3LYP (UB3LYP) method with the same basis set
under triplet multiplicity. Figure 7 shows the frontier orbitals
and their energy levels of optimized structures in the triplet state.
The highest singly occupied molecular orbital (HSOMO)
distributions in the lowest-lying triplet state were similar to the
LUMO distributions in the singlet state. The triplet HSOMO
existed at lower energy level than the singlet LUMO energy
level. For heteroleptic Ir complexes, the HSOMO levels were
stabilized in the order Ir(ppySCF ) (acac) > Ir-
bandgap (3.3 eV), high glass transition temperature (T ),
g
6
6,67
moderate hole-transporting ability, and high triplet energy.
The 1,3,5-tris(3-pyridyl-3-phenyl)benzene (TmPyPB) and 8-
quinolinolato lithium (Liq) were used as the electron transport
layer (ETL) and the electron injection layer (EIL), respectively.
They were deposited by thermal evaporation onto the emitting
layer under high vacuum. The triplet energies of TCTA (2.86
eV) and TmPyPB (2.8 eV) were higher than those of the triplet
state of Ir complexes, which facilitated efficient energy transfer
from hosts to dopants. Figure 9 depicts the current density (J)−
voltage−luminance (J−V−L), current efficiency−current den-
sity, power efficiency−current density, and EQE−current
density of the fabricated OLED devices. Table 3 summarizes
the performances of these devices. Among them, Ir-
(ppySCF ) (bor) exhibited a turn-on voltage of 6.40 V with
3
2
(
ppySCF ) (pic) > Ir(ppySCF ) (bor). The lowest singly
3 2 3 2
occupied molecular orbital (LSOMO) distribution resembled
the HOMO distribution, in which the orbital was located on the
iridium ion and the phenyl moiety of the cyclometalating ligand.
This means that the emission originated from the HSOMO state
has the MLCT character of the triplet manifold.
Device Performance. OLED devices bearing Ir complexes
were fabricated through a partial solution process. Their
electroluminescent (EL) characteristics were then investigated.
Bulky −SO F and −SO CF groups may suppress the self-
3
2
its device performance characterized by external quantum yield
2
2
3
−
1
quenching and triplet−triplet annihilation (TTA) between
(EQE) of 1.14%, current efficiency (CE) of 2.31 cd A , and
65
1−
complexes in the OLED device. Thus, we did not observe any
significant concentration dependency of dopant. Figure 8 shows
the structures of devices: ITO (150 nm, anode)/PEDOT:PSS
power efficiency (PE) of 1.21 lm W .
Figure 10 shows the EL spectra of the Ir complexes that were
measured at similar wavelength to the photoluminescence (PL)
spectra. However, the EL spectra were less structured compared
(
40 nm)/TCTA:Ir complexes (30 nm: 10 wt %)/TmPyPB (35
J
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
CONCLUSIONS
■
To achieve blue phosphorescence, we developed new homo-/
heteroleptic Ir complexes using a combination of cyclo-
metalating C^N ligand bearing −SO F and −SO CF
2
2
3
substituents and ancillary ligands, such as acac, pic, and bor.
As a result of fine-tuning of EWG (−SO -R) from −SO F to
2
2
−
SO CF , the emission maximum of homoleptic Ir(ppySCF )
having stronger EWG was blue-shifted by 6 nm compared to
2
3
3
3
Ir(ppySF) . In addition, Ir(ppySCF ) (Φ = 0.89) showed
3
3 3
PL
higher quantum efficiency compared with Ir(ppySF) (Φ =
3
PL
0.72), which had been elaborated by the larger k value (ca. 1.34-
r
fold) of Ir(ppySCF ) than that of Ir(ppySF) . For heteroleptic
3
3
3
complexes, further modification with variation of ancillary
ligands from acac to bor generated a hypsochromic shift in the
emission spectra. Among them, Ir(ppySCF ) (bor) emitted
3
2
largely blue-shifted phosphorescence that might be due to the
synergistic effect of combining SO CF -substituted C^N
Figure 10. Electroluminescence spectra of devices bearing Ir(III)
2
3
cyclometalating ligand and ancillary ligand bor. These trends
are consistent with increased HOMO−LUMO bandgap and
discernible HOMO stabilization, which were confirmed by
photophysical and electrochemical analysis and DFT calcu-
dopants recorded at 1 nit.
to those in the glassy matrix at 77 K, or even in solution at 300 K.
In particular, the EL spectra of homoleptic Ir complexes changed
drastically in the relative intensity of vibronic bands. Although
the host and ETL materials were also emissive chromophores,
no emission peaks were detected in the EL spectra. This result
indicated that energy transfer occurred efficiently from the host
to the dopant emitter in these OLED devices. The EL spectra
slightly shifted to the longer wavelength (ca. (1−7) nm) than the
photoluminescence (PL) spectra in solution (Table 3). Table 3
shows the Commission International de L’Eclairage (CIE) color
coordinates of these OLED devices.
For the devices bearing homoleptic and heteroleptic Ir
complex dopants, EL spectra and CIE coordinates were
distinguished by both the main and ancillary ligands. Among
them, the device bearing Ir(ppySCF ) (bor) showed bluer CIE
lation. All SO R-substituted Ir complexes exhibited high
2
emission quantum yields of (0.72−0.89) in anaerobic CH Cl
2
2
at 300 K. Therefore, we fabricated OLED devices using these Ir
complexes as dopants. Among them, the Ir(ppySCF ) (bor)
3
2
OLED device showed potential blue phosphorescence charac-
terized by the bluest chromaticity with CIEx,y = (0.16, 0.32).
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b02672.
■
*
S
́
Experimental details; NMR spectra; ESI-mass spectra;
crystallographic data, optimized geometries, and TD-
DFT assignment; X-ray crystallographic data (PDF)
3
2
coordinate (0.16, 0.32), and its EL spectrum displayed the
shortest wavelength, compared with the others. However, its
device performance was not optimized, because its device
fabrication was limited, due to the unsublimable nature of Ir
complexes. The poor performances of our fabricated devices
when compared to the results reported in typical OLED devices
based on the sublimable materials are thought to be caused by
the drawbacks of the solution processed method such as the lack
of optimal alignment of energy level derived from limitation of
multilayer deposition, poor film morphology, and easy
Accession Codes
CCDC 1919505, 1919522, and 1919544 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: sangok@korea.ac.kr.
*E-mail: dwcho@korea.ac.kr.
*E-mail: hjson@korea.ac.kr.
■
68
crystallization upon spin-coating. Regarding the relatively
low performance relative to the results of similar solution-
processed OLED device, such discrepancy might be due to
different manufacture conditions and process parameters
because the overall performance of the OLED device is generally
variable according to the device fabrication conditions including
the thickness of the common layers, such as HIL (PE-
DOT:PSS), host material (TCTA), and doping degree (wt %)
of Ir dopant in the emitting layer. Indeed, unlike material used in
a previous report, we used the blue-emitting Ir(III) dopant series
and TmPyPB as dopant and ETL material instead of green-
emitting BPyPmIr and TPBI (2,2′,2″-(1,3,5-benzinetriyl)-
ORCID
Jin-Hyoung Kim: 0000-0002-5709-0399
So-Yoen Kim: 0000-0001-9392-7195
Dae Won Cho: 0000-0002-4785-069X
Ho-Jin Son: 0000-0003-2069-1235
Sang Ook Kang: 0000-0002-3911-7818
Notes
69
The authors declare no competing financial interest.
tris(1-phenyl-1-H-benzimidazole)), respectively. Above all, a
less smooth alignment of HOMO levels between PEDOT:PSS
ACKNOWLEDGMENTS
This work was supported by the MOTIE (Ministry of Trade,
Industry & Energy (10051379) and KDRC (Korea Display
(
5.2 eV) and TCTA (5.9 eV), which weakens its hole injection
■
ability in the device, is thought to be the biggest reason for low
performance.
K
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Research Corporation) support program for the development of
future devices technology for display industry, the International
Science, the Functional Districts of the Science Belt support
program, Ministry of Science, ICT and Future Planning
(17) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee,
H.-E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E.
Highly phosphorescent bis-cyclometalated iridium complexes: Syn-
thesis, photophysical characterization, and use in organic light emitting
diodes. J. Am. Chem. Soc. 2001, 123, 4304−4312.
(
2015K000287), and the Basic Science Research Program
(18) Tsuboyama, A.; Iwawaki, H.; Furugori, M.; Makaide, T.;
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education (NRF-
Kamatani, J.; Igawa, S.; Moriyama, T.; Miura, S.; Takiguchi, T.; Okada,
S.; Hoshino, M.; Ueno, K. Homoleptic cyclometalated iridium
complexes with highly efficient red phosphorescence and application
to organic light-emitting diode. J. Am. Chem. Soc. 2003, 125, 12971−
12979.
2
014R1A6A1030732 and NRF-2019R1A2C1010431).
REFERENCES
■
(19) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.; Lamansky, S.;
(
1) Yersin, H. Highly Efficient OLEDs with Phosphorescent Materials;
Wiley-VCH: Berlin, 2007.
Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. Synthesis and
characterization of facial and meridional tris-cyclometalated Iridium-
(
2) Forrest, S. R. Excitons and the lifetime of organic semiconductor
devices. Philos. Trans. R. Soc., A 2015, 373, 20140320−20140326.
3) Lee, J.; Jeong, C.; Batagoda, T.; Coburn, C.; Thompson, M. E.;
(
III) complexes. J. Am. Chem. Soc. 2003, 125, 7377−7387.
(
20) Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.;
(
Petrov, V. A.; Wang, Y. New, efficient electroluminescent materials
based on organometallic Ir complexes. Chem. Commun. 2001, 1494−
1495.
Forrest, S. R. Hot excited state management for long-lived blue
phosphorescent organic light-emitting diodes. Nat. Commun. 2017, 8,
1
5566−15574.
4) Chi, Y.; Chou, P.-T. Transition-metal phosphors with cyclo-
metalating ligands: fundamentals and applications. Chem. Soc. Rev.
010, 39, 638−655.
5) Xiao, L.; Chen, Z.; Qu, B.; Luo, J.; Kong, S.; Gong, Q.; Kido, J.
(
(21) Adachi, C.; Kwong, R. C.; Djurovich, P. I.; Adamovich, V.; Baldo,
M. A.; Thompson, M. E.; Forrest, S. R. Endothermic energy transfer: A
mechanism for generating very efficient high-energy phosphorescent
emission in organic materials. Appl. Phys. Lett. 2001, 79, 2082−2084.
(22) Holmes, R. J.; Forrest, S. R.; Tung, Y.-J.; Kwong, R. C.; Brown, J.
J.; Garon, S.; Thompson, M. E. Blue organic electrophosphorescence
using exothermic host−guest energy transfer. Appl. Phys. Lett. 2003, 82,
2422−2424.
2
(
Recent progresses on materials for electrophosphorescent organic light-
emitting devices. Adv. Mater. 2011, 23, 926−952.
(
6) Fu, H.; Cheng, Y.-M.; Chou, P.-T.; Chi, Y. Feeling blue? Blue
phosphors for OLEDs. Mater. Today 2011, 14, 472−479.
7) Zhang, Y.; Lee, J.; Forrest, S. R. Tenfold increase in the lifetime of
blue phosphorescent organic light-emitting diodes. Nat. Commun.
014, 5, 5008−5014.
8) Lee, J.; Chen, H.-F.; Batagoda, T.; Coburn, C.; Djurovich, P. I.;
(
(23) Coppo, P.; Plummer, E. A.; De Cola, L. Tuning Iridium(III)
phenylpyridine complexes in the “almost blue” region. Chem. Commun.
2004, 1774−1775.
2
(
(24) Ragni, R.; Plummer, E. A.; Brunner, K.; Hofstraat, J. W.; Babudri,
F.; Farinola, G. M.; Naso, F.; De Cola, L. Blueemittingiridiumcom-
plexes: synthesis, photophysics and phosphorescent devices. J. Mater.
Chem. 2006, 16, 1161−1170.
Thompson, M. E.; Forrest, S. R. Deep blue phosphorescent organic
light-emitting diodes with very high brightness and efficiency. Nat.
Mater. 2016, 15, 92−98.
(
9) Im, Y.; Byun, S. Y.; Kim, J. H.; Lee, D. R.; Oh, C. S.; Yook, K. S.;
(25) Sajjad, M. T.; Sharma, N.; Pal, A. K.; Hassan, K.; Xie, G.; Kolln, L.
̈
Lee, J. Y. Recent progress in high-efficiency blue-light-emitting
materials for organic light-emitting diodes. Adv. Funct. Mater. 2017,
S.; Hanan, G. S.; Samuel, I. D. W.; Zysman-Colman, E. Controlling the
emission efficiency of blue-green Iridium(III) phosphorescent emitters
and applications in solution-processed organic light-emitting diodes. J.
Mater. Chem. C 2016, 4, 8939−8946.
2
(
7, 1603007−1603030.
10) Kim, S.; Bae, H. J.; Park, S.; Kim, W.; Kim, J.; Kim, J. S.; Jung, Y.;
Sul, S.; Ihn, S.-G.; Noh, C.; Kim, S.; You, Y. Degradation of blue-
phosphorescent organic light-emitting devices involves exciton-
induced generation of polaron pair within emitting layers. Nat.
Commun. 2018, 9, 1211−1221.
(26) Sarma, M.; Tsai, W.-L.; Lee, W.-K.; Chi, Y.; Wu, S.-H.; Chou, P.-
T.; Wong, K.-T. Anomalously long-lasting blue PhOLED featuring
phenyl-pyrimidine cyclometalated Iridium emitter. Chem. 2017, 3,
4
(
61−476.
(
11) Li, X.; Zhang, J.; Zhao, Z.; Wang, L.; Yang, H.; Chang, Q.; Jiang,
27) Chen, Z.; Wang, L.; Ho, C.-L.; Chen, S.; Suramitr, S.;
N.; Liu, Z.; Bian, Z.; Liu, W.; Lu, Z.; Huang, C. Deep blue
phosphorescent organic light-emitting diodes with CIEy value of 0.11
and external quantum efficiency up to 22.5%. Adv. Mater. 2018, 30,
Plucksacholatarn, A.; Zhu, N.; Hannongbua, S.; Wong, W.-Y. Smart
design on the cyclometalated ligands of Iridium(III) complexes for
facile tuning of phosphorescence color spanning from deep-blue to
near-infrared. Adv. Opt. Mater. 2018, 6, 1800824−1800833.
1
(
705005−1705012.
12) Kuo, H.-H.; Zhu, Z.-L.; Lee, C.-S.; Chen, Y.-K.; Liu, S.-H.; Chou,
(28) Takizawa, S.-Y.; Echizen, H.; Nishida, J.-I.; Tsuzuki, T.; Tokito,
P.-T.; Jen, A. K.-Y; Chi, Y. Bis-tridentate Iridium(III) phosphors with
very high photostability and fabrication of blue-emitting OLEDs. Adv.
Sci. 2018, 5, 1800846−1800852.
S.; Yamashita, Y. Finely-tuned blue-phosphorescent iridium complexes
based on 2-phenylpyridine derivatives and application to polymer
organic light-emitting device. Chem. Lett. 2006, 35, 748−749.
(
13) Shin, H.; Ha, Y. H.; Kim, H.-G.; Kim, R.; Kwon, S.-K.; Kim, Y.-
(29) Takizawa, S.-Y.; Nishida, J.-I.; Tsuzuki, T.; Tokito, S.; Yamashita,
H.; Kim, J.-J. Controlling horizontal dipole orientation and emission
spectrum of Ir complexes by chemical design of ancillary ligands for
efficient deep-blue organic light-emitting diodes. Adv. Mater. 2019, 31,
Y. Phosphorescent iridium complexes based on 2-phenylimidazo[1,2-
a]pyridine ligands: tuning of emission color toward the blue region and
application to polymer light-emitting devices. Inorg. Chem. 2007, 46,
1
(
808102−1808107.
4
(
308−4319.
14) Chen, Y.-K.; Kuo, H.-H.; Luo, D.; Lai, Y.-N.; Li, W.-C.; Chang,
30) Xu, M.; Zhou, R.; Wang, G.; Xiao, Q.; Du, W.; Che, G. Synthesis
C.-H.; Escudero, D.; Jen, A.K.-Y.; Hsu, L.-Y.; Chi, Y. Phenyl- and
pyrazolyl-functionalized pyrimidine: versatile chromophore of bis-
tridentate Ir(III) phosphors for organic light-emitting diodes. Chem.
Mater. 2019, 31, 6453−6464.
and characterization of phosphorescent iridium complexes containing
trifluoromethyl-substituted phenyl pyridine based ligands. Inorg. Chim.
Acta 2008, 361, 2407−2412.
15) Na, H.; Canada, L. M.; Wen, Z.; Wu, J. I-C.; Teets, T. S. Mixed-
̃
(31) Cho, Y.-J.; Kim, S.-Y.; Kim, J.-H.; Crandell, D. W.; Baik, M.-H.;
(
carbene cyclometalated iridium complexes with saturated blue
Lee, J.; Kim, C. H.; Son, H.-J.; Han, W.-S.; Kang, S. O. Important role of
ancillary ligand in the emission behaviours of blue-emitting heteroleptic
Ir(III) complexes. J. Mater. Chem. C 2017, 5, 4480−4487.
(32) Pal, A. K.; Krotkus, S.; Fontani, M.; Mackenzie, C. F. R.; Cordes,
D. B.; Slawin, A. M. Z.; Samuel, I. D. W.; Zysman-Colman, E. High-
efficiency deep-blue-emitting organic light-emitting diodes based on
luminescence. Chem. Sci. 2019, 10, 6254−6260.
(
16) Yersin, H.; Rausch, A. F.; Czerwieniec, R.; Hofbeck, T.; Fischer,
T. The triplet state of organo-transition metal compounds. triplet
harvesting and singlet harvesting for efficient OLEDs. Coord. Chem. Rev.
2011, 255, 2622−2652.
L
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Iridium(III) carbene complexes. Adv. Mater. 2018, 30, 1804231−
emitting Iridium(III) complexes and solution-processable PhOLEDs.
DaltonTrans. 2017, 46, 10996−11007.
1
804240.
(
33) Aoki, S.; Matsuo, Y.; Ogura, S.; Ohwada, H.; Hisamatsu, Y.;
(48) Kim, J.-H.; Kim, S.-Y.; Cho, Y.-J.; Son, H.-J.; Cho, D. W.; Kang, S.
O. A detailed evaluation for the nonradiative processes in highly
phosphorescent Iridium(III) complexes. J. Phys. Chem. C 2018, 122,
4029−4036.
Moromizato, S.; Shiro, M.; Kitamura, M. Regioselective aromatic
substitution reactions of cyclometalated Ir(III) complexes: synthesis
and photochemical properties of substituted Ir(III) complexes that
exhibit blue, green, and red color luminescence emission. Inorg. Chem.
(49) Farrugia, L. J. ORTEP-3 for Windows - a version of ORTEP-III
with a graphical user interface (GUI). J. Appl. Crystallogr. 1997, 30,
565−565.
2
(
011, 50, 806−818.
34) Kando, A.; Hisamatsu, Y.; Ohwada, H.; Itoh, T.; Moromizato, S.;
Kohno, M.; Aoki, S. Photochemical properties of red-emitting
tris(cyclometalated) Iridium(III) complexes having basic and nitro
groups and application to pH sensing and photoinduced cell death.
Inorg. Chem. 2015, 54, 5342−5357.
(50) Tamayo, A. B.; Garon, S.; Sajoto, T.; Djurovich, P. I.; Tsyba, I.
M.; Bau, R.; Thompson, M. E. Cationic bis-cyclometalated Iridium(III)
diimine complexes and their use in efficient blue, green, and red
electroluminescent devices. Inorg. Chem. 2005, 44, 8723−8732.
(51) Son, M. R.; Cho, Y.-J.; Son, H.-J.; Cho, D. W.; Kang, S. O. A
spectroscopic study on the satellite vibronic band in phosphorescent Pt-
complexes with high colour purity. Phys. Chem. Chem. Phys. 2017, 19,
32670−32677.
(52) Cho, Y.-J.; Kim, S.-Y.; Son, H.-J.; Han, W.-S.; Cho, D. W.; Kang,
S. O. Comprehensive spectroscopic studies of cis and trans isomers of
red-phosphorescent heteroleptic Iridium(III) complexes. J. Photochem.
Photobiol., A 2018, 356, 673−680.
(53) Yersin, H.; Donges, D. Low-lying electronic states and
photophysical properties of organometallic Pd(II) and Pt(II)
compounds. Modern research trends presented in detailed case studies.
Top. Curr. Chem. 2001, 214, 81−186.
(54) Huang, K.; Rhys, A. Theory of light absorption and non-radiative
transition in F-centres. Philos. Trans. R. Soc. A 1950, 204, 406−423.
(55) Wilson, J. S.; Chawdhury, N.; Al-Mandhary, M. R. A.; Younus,
(
35) Tamura, Y.; Hisamatsu, Y.; Kumar, S.; Itoh, T.; Sato, K.; Kuroda,
R.; Aoki, S. Efficient synthesis of tris-heteroleptic Iridium(III)
2
+
complexes based on the Zn promoted degradation of tris-cyclo-
metalated Iridium(III) complexes and their photophysical properties.
Inorg. Chem. 2017, 56, 812−833.
(
36) Hisamatsu, Y.; Aoki, S. Design and synthesis of blue-emitting
cyclometalated Iridium(III) complexes based on regioselective
functionalization. Eur. J. Inorg. Chem. 2011, 2011, 5360−5369.
(
37) Kozhevnikov, V. N.; Dahms, K.; Bryce, M. R. Nucleophilic
substitution of fluorine atoms in 2,6-difluoro-3-(pyridin-2-yl) benzoni-
trile leading to soluble blue-emitting cyclometalated Ir(III) complexes.
J. Org. Chem. 2011, 76, 5143−5148.
(
38) Kim, S. H.; Jang, J.; Lee, S. J.; Lee, J. Y. Deep blue phosphorescent
organic light-emitting diodes using a Si based wide bandgap host and an
Ir dopant with electron withdrawing substituents. Thin Solid Films
2
(
008, 517, 722−726.
M.; Khan, M. S.; Raithby, P. R.; Kohler, A.; Friend, R. H. The energy
̈
39) Jeon, S. O.; Jang, S. E.; Son, H. S.; Lee, J. Y. External quantum
gap law for triplet states in Pt-containing conjugated polymers and
monomers. J. Am. Chem. Soc. 2001, 123, 9412−9417.
efficiency above 20% in deep blue phosphorescent organic light-
emitting diodes. Adv. Mater. 2011, 23, 1436−1441.
(
(56) Sekkal, M.; Legrand, P. A spectroscopic investigation of the
−
1
40) Ragni, R.; Orselli, E.; Kottas, G. S.; Omar, O. H.; Babudri, F.;
carrageenans and agar in the 1500−100 cm spectral range.
Pedone, A.; Naso, F.; Farinola, G. M.; De Cola, L. Iridium(III)
complexes with sulfonyl and fluorine substituents: synthesis, stereo-
chemistry and effect of functionalisation on their photophysical
properties. Chem. - Eur. J. 2009, 15, 136−148.
Spectrochim. Acta 1993, 49, 209−221.
(57) Nazeeruddin, M. K.; Wegh, R. T.; Zhou, Z.; Klein, C.; Wang, Q.;
De Angelis, F.; Fantacci, S.; Gratzel, M. Efficient green-blue-light-
̈
emitting cationic iridium complex for light-emitting electrochemical
cells. Inorg. Chem. 2006, 45, 9245−9250.
(
41) Tordera, D.; Bunzli, A. M.; Pertegas, A.; Junquera-Hernandez, J.
̈
́ ́
M.; Constable, E. C.; Zampese, J. A.; Housecroft, C. E.; Ortí, E.; Bolink,
H. J. Efficient green-light-emitting electrochemical cells based on ionic
Iridium complexes with sulfone-containing cyclometalating ligands.
Chem. - Eur. J. 2013, 19, 8597−8609.
(58) Li, J.; Djurovitch, P. I.; Alleyene, B. D.; Yousufuddin, M.; Ho, N.
N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Synthetic
control of excited-state properties in cyclometalated Ir(III)complexes
using ancillary ligands. Inorg. Chem. 2005, 44, 1713−1727.
(59) Holmes, R. J.; D’Andrade, B. W.; Forrest, S. R.; Ren, X.; Li, J.;
Thompson, M. E. Efficient, deep-blue organic electrophosphorescence
by guest charge trapping. Appl. Phys. Lett. 2003, 83, 3818−3820.
(60) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Tsyba, I.; Ho, N. N.; Bau,
R.; Thompson, M. E. Synthesis and characterization of cyclometalated
Ir(III) complexes with pyrazolyl ancillary ligands. Polyhedron 2004, 23,
419−428.
(
42) Constable, E. C.; Ertl, C. D.; Housecroft, C. E.; Zampese, J. A.
Green-emitting Iridium(III) complexes containing sulfanyl-or sulfone-
functionalized cyclometallating 2-phenylpyridine ligands. DaltonTrans.
2
(
014, 43, 5343−5356.
43) Ertl, C. D.; Cerda,
Bolink, H. J.; Constable, E. C.; Neuburger, M.; Ortí, E.; Housecroft, C.
J.; Junquera-Hernandez, J. M.; Pertegas, A.;
́ ́ ́
̂
̂
+
E. Colour tuning by the ring roundabout: [Ir(CN) (NN)] emitters
2
with sulfonyl-substituted cyclometallating ligands. RSC Adv. 2015, 5,
(61) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.;
Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.;
Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.;
Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A.
J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma,
K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
4
(
2815−42827.
44) Zhao, J.; Yu, Y.; Yang, X.; Yan, X.; Zhang, H.; Xu, X.; Zhou, G.;
Wu, Z.; Ren, Y.; Wong, W. Y. Phosphorescent Iridium(III) complexes
bearing fluorinated aromatic sulfonyl group with nearly unity
phosphorescent quantum yields and outstanding electroluminescent
properties. ACS Appl. Mater. Interfaces 2015, 7, 24703−24714.
(
45) Zhang, W.; Luo, Y.; Xu, Y.; Li, W.; Shen, W. Theoretical
investigation and design of highly efficient blue phosphorescent
Iridium(III) complexes bearing fluorinated aromatic sulfonyl groups.
ChemPhysChem 2016, 17, 4149−4157.
(
46) Benjamin, H.; Zheng, Y.; Batsanov, A. S.; Fox, M. A.; Al-Attar, H.
A.; Monkman, A. P.; Bryce, M. R. Sulfonyl-substituted heteroleptic
cyclometalated Iridium(III) complexes as blue emitters for solution-
processable phosphorescent organic light emitting diodes. Inorg. Chem.
̈
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, Revision D.01; Gaussian, Inc.:
Wallingford, CT, 2009.
(62) Hay, P. J.; Wadt, W. R. Ab initio effective core potentials for
molecular calculations. Potentials for K to Au including the outermost
core orbitals. J. Chem. Phys. 1985, 82, 299−310.
2
(
016, 55, 8612−8627.
47) Benjamin, H.; Fox, M. A.; Batsanov, A. S.; Al-Attar, H. A.; Li, C.;
̂
Ren, Z.; Monkman, A. P.; Bryce, M. R. Pyridylpyrazole NN ligands
combined with sulfonyl-functionalised cyclometalating ligands for blue-
M
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
63) Lee, C.; Yang, W.; Parr, R. G. Development of the colle-salvetti
correlation-energy formula into a functional of the electron density.
Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789.
(
64) Becke, A. D. Density-functional thermochemistry. III. The role of
exact exchange. J. Chem. Phys. 1993, 98, 5648−5652.
(
65) Li, H.-Y.; Zhou, L.; Teng, M.-Y.; Xu, Q.-L.; Lin, C.; Zheng, Y.-X.;
Zuo, J.-L.; Zhang, H.-J.; You, X.-Z. Highly efficient green phosphor-
escent OLEDs based on a novel iridium complex. J. Mater. Chem. C
2
(
013, 1, 560−565.
66) Reineke, S.; Schwartz, G.; Leo, K. Reduced efficiency roll-off in
phosphorescent organic light emitting diodes by suppression of triplet-
triplet annihilation. Appl. Phys. Lett. 2007, 91, 123508−123510.
(
67) Tao, Y.; Yang, C.; Qin, J. Organic host materials for
phosphorescent organic light-emitting diodes. Chem. Soc. Rev. 2011,
0, 2943−2970.
68) Jou, J.-H.; Sahoo, S.; Dubey, D. K.; Yadav, R. A. K.;
4
(
Swayamprabha, S. S.; Chavhan, S. D. Molecule-based monochromatic
and polychromatic OLEDs with wet-process feasibility. J. Mater. Chem.
C 2018, 6, 11492−11518.
(
69) Yang, X.; Feng, Z.; Dang, J.; Sun, Y.; Zhou, G.; Wong, W.-Y. High
performance solution-processed organic yellow light-emitting devices
and fluoride ion sensors based on a versatile phosphorescent Ir(III)
complex. Mater. Chem. Front. 2019, 3, 376−384.
N
DOI: 10.1021/acs.inorgchem.9b02672
Inorg. Chem. XXXX, XXX, XXX−XXX