Substituent position engineering of diphenylquinoline-based Ir(III) complexes for efficient orange and white PhOLEDs with high color stability/low efficiency roll-off using a solution-processed emission layer

Article abstract of DOI:10.1039/c5tc03004h

Three new heteroleptic Ir(iii) complexes o-LIrpic, m-LIrpic, and p-LIrpic (L = CF₃DPQ) consisting of 2,4-diphenylquinoline (DPQ) with a -CF₃ group at ortho (o)/meta (m)/para (p) positions of the metalated phenyl ring, respectively, as the main ligands were synthesized and used as emitters in phosphorescent organic light-emitting diodes (PhOLEDs). We realized that -CF₃ position extremely affects the crucial photophysical and electronic properties such as emission color, photoluminescence quantum yield (PLQY) and energy levels of these Ir(iii) complexes resulting in -CF₃ position-dependent performance of their PhOLEDs. To verify the effect of -CF₃ group position on device performance, three other Ir(iii) complexes o-LIrtmd, m-LIrtmd, and p-LIrtmd were synthesized using the same main ligands but a different ancillary ligand. In the two series of Ir(iii) complexes, the devices with m-CF₃ based complexes are outstanding in performance compared to o- or p-CF₃ based ones due to the enhanced PLQY and well suppressed non-radiative deactivations by m-substitution. Finally, the single emission layer solution-processed orange and two-component white PhOLEDs fabricated using m-LIrpic as orange emitter achieved the maximum external quantum efficiency of 17.1% (43.9 cd A^-1) and 21.1% (48.8 cd A^-1), respectively, with highly stable color coordinates and low efficiency roll-off. This is the highest efficiency reported to date for solution-processed orange PhOLEDs using a small molecular host with easily accessible emitter.

Full text of DOI:10.1039/c5tc03004h

View Article Online
View Journal
Journal of
Materials Chemistry C
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: G. Sarada, J.
Yoon, W. Cho, M. Cho, D. W. Cho, S. O. Kang, Y. Nam, J. Y. LEE and S. Jin, J. Mater. Chem. C, 2015, DOI:
10.1039/C5TC03004H.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/materialsC

Page 1 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
Substituent Position Engineering of Diphenylquinoline-based Ir(III) Complexes for
Efficient Orange and White PhOLEDs with High Color Stability/Low Efficiency Roll-Off
Using Solution-Processed Emission Layer
a
a
Ganguri Sarada,‡ Juho Yoon,‡ Woosum Cho,a Minji Cho,b Daw Won Cho,b Sang Ook Kang,b
Yeonsig Nam,c Jin Yong Lee,c and SungꢀHo Jin*a
a Department of Chemistry Education, Graduate Department of Chemical Materials, BK 21
PLUS Team for Advanced Chemical Materials, and Institute for Plastic Information and Energy
Materials, Pusan National University, Busan, 609ꢀ735, Republic of Korea,
b Department of Advanced Materials Chemistry, Korea University, Sejongꢀcity 339ꢀ700,
Republic of Korea
c Department of Chemistry, Sungkyunkwan University, Suwon 440ꢀ746, Republic of Korea
‡ These authors contributed equally to this work
*Corresponding Author Eꢀmail: shjin@pusan.ac.kr

Journal of Materials Chemistry C
Page 2 of 29
View Article Online
DOI: 10.1039/C5TC03004H
Abstract: Three new heteroleptic Ir(III) complexes o-LIrpic, m-LIrpic, and p-LIrpic
(L=CF3DPQ) consisting of 2,4ꢀdiphenylquinoline (DPQ) with a ꢀCF3 group at ortho (o)/ meta
(m)/ para (p) positions of the metalated phenyl ring, respectively, as the main ligands were
synthesized and used as emitters in phosphorescent organic lightꢀemitting diodes (PhOLEDs).
We realized that ꢀCF3 position extremely affects the crucial photophysical and electronic
properties such as emission color, photoluminescence quantum yield (PLQY) and energy levels
of these Ir(III) complexes resulting in ꢀCF3 positionꢀdependent performance of their PhOLEDs.
To verify the effect of ꢀCF3 group position on device performance, three other Ir(III) complexes
o-LIrtmd, m-LIrtmd, and p-LIrtmd were synthesized using the same main ligands but
different ancillary ligand. In the two series of Ir(III) complexes, the devices with mꢀCF3 based
complexes are outstanding in performance compared to oꢀ or pꢀCF3 based ones due to the
enhanced PLQY and well suppressed nonꢀradiative deactivations by mꢀ substitution. Finally, the
single emission layer solutionꢀprocessed orange and twoꢀcomponent white PhOLEDs fabricated
using m-LIrpic as orange emitter achieved the maximum external quantum efficiency of 17.1%
(43.9 cdAꢀ1) and 21.1% (48.8 cdAꢀ1), respectively, with highly stable color coordinates and low
efficiency rollꢀoff. This is the highest efficiency reported to date for solutionꢀprocessed orange
PhOLEDs using small molecular host with easily accessible emitter.

Page 3 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
1. Introduction
Highly efficient orange phosphorescent heavyꢀmetal complexes are indispensable for the
fabrication of monochromatic displays and twoꢀcomponent or full color white organic lightꢀ
emitting diodes (WOLEDs).1 Among the heavyꢀmetal complexes, iridium(III) complexes are
considered as the most promising phosphors in OLEDs mainly due to their high spinꢀorbit
coupling (SOC) and the ease of functionalization of cyclometalating (C^N) ligands to control the
emission colors.2 In recent years, orange phosphorescent OLEDs (PhOLEDs) using Ir(III)
complex emitters have achieved high external quantum efficiency (EQE) of about 28% in vapor
deposition process.3 Conversely, the solutionꢀprocess is most preferred method due to its low
processing cost and large scale application for practical utility.4 But the availability of highly
soluble orange Ir(III) complex emitters with easy synthetic routes are scarce and also the
efficiencies of their solutionꢀprocessed PhOLEDs are laid far behind those of the vacuumꢀ
deposited ones to date.5 Until now, the highest EQE reported for solutionꢀprocessed orange
PhOLEDs with Ir(III) complex [Ir(FlpyꢀCF3)3] emitter was 17.6% with Commission
Internationale de L’Eclairage (CIE) coordinates (0.531, 0.466).5b However, here a dendrimeric
host was used which restricts the usage of higher generation dendrimers due to their voltage
dependentꢀpoor carrier mobilities. Also the synthesis of the C^N ligand was achieved by multiꢀ
steps which limits its application in large scale.6
2,4ꢀDiphenylquinoline (DPQ)ꢀbased C^N ligands are exhibited as promising candidates for
developing efficient orange/orangeꢀred Ir(III) complexes for solutionꢀprocessed PhOLEDs due to
their elevated electronꢀaffinities, ease of synthesis and high solubility without the need of any

Journal of Materials Chemistry C
Page 4 of 29
View Article Online
DOI: 10.1039/C5TC03004H
alkyl chains.7 Based on this, recently we demonstrated a series of solutionꢀprocessable Ir(III)
complexes with different C^N ligands containing of phenylquinoline moiety.7a Amongst, the
orange PhOLEDs with emitter (DPQ)2Ir(picꢀNꢀO) showed maximum EQE of 14.2% in a ternary
host system compared to the other (perfluorinatedphenylꢀ, fluorenylꢀ, and carbazoylꢀ
phenylquinoline ligand based) Ir(III) complexes owing to its relatively high photoluminescence
quantum yield (PLQY), which illustrates the advantage of DPQ ligand over the other C^N
ligands in designing efficient phosphors. On the other hand, the energy levels of the emissive
3
states (3MLCT and/or LC) of the Ir(III) complexes can be effectively modified to obtain wideꢀ
ranging emission colors and PLQYs by the substituent effects such as electron withdrawing or
electron donating on C^N ligands and also by the substituent position effects.2c,7h As far as we
know, fineꢀtuning of PLQY and photophysical/electronic properties and hence the PhOLED
performance of the Ir(III) complexes by a simple control of the substituent position on C^N
ligand has not been much investigated.
With the aim to develop novel orange Ir(III) complexes that are easy to access synthetically,
possesses high PLQY and good solubility for realization of highly efficient solutionꢀprocessed
PhOLEDs in practical applications, we selected DPQ as C^N ligand driven by its flexible color
tunabilitiy. In this paper, we introduced trifluoromethyl (ꢀCF3) group at ortho (o)/ meta (m)/ para
(p) positions (Fig. 1) of the metalated phenyl ring of DPQ and synthesized Ir(III) complexes with
two different ancillary ligands in order to validate the effect of ꢀCF3 position on the electronic
structure of the Ir(III) complexes and consequently on performance of PhOLEDs. We realized
that the location of ꢀCF3 is very important in attaining high device performance. In particular, the
orange PhOLED fabricated with solutionꢀprocessed emission layer using the mꢀCF3 linked Ir(III)
complex, m-LIrpic, as dopant achieved the maximum EQE of 17.1% with CIE coordinates

Page 5 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
(0.528, 0.469), this is the highest EQE among the solutionꢀprocessed orange PhOLEDs using
small molecular host system (see Table S1, summary of the reported device performances) and
also this result is similar to the highest efficiency reported using dendrimeric host.5b
Furthermore, the twoꢀcomponent white PhOLEDs fabricated with m-LIrpic as orange
component demonstrated maximum EQE of 21.1%. The detailed approach and the results are
discussed hereafter.
2. Results and discussion
2.1 Synthesis and Characterization
The ꢀCF3 functionalized C^N ligands o-L, m-L, and p-L (L=CF3DPQ) based on DPQ skeleton
were prepared in single step by the acidꢀcatalyzed Friedlander condensation reaction7d of two
commercially available starting materials. The new Ir(III) complexes o-LIrpic, m-LIrpic, p-
LIrpic and o-LIrtmd, m-LIrtmd, p-LIrtmd were prepared readily following the syntheses of
the intermediate dichloroꢀbridged dimers and the reaction of the corresponding dimer with
ancillary ligands picolinate (pic) or 2,2,6,6ꢀtetramethylheptaneꢀ3,5,ꢀdiketonate (tmd) in presence
1
of Na2CO3 base (Scheme S1). All the Ir(III) complexes have been characterized by H, 13C
NMR, and high resolution mass spectroscopy [Fig. S1ꢀS2 in Supporting Information (SI)]. The
new Ir(III) complexes have good solubility in common organic solvents such as chloroform
(CHCl3), tetrahydrofuran, and chlorobenzene (CB).
2.2 Thermal and Photophysical Properties
Thermal properties of the Ir(III) complexes were evaluated using thermogravimetric analysis
(TGA) under N2 atmosphere with a scanning rate of 10oC minꢀ1. The TGA curves (Fig. S3a in
SI) of all the Ir(III) complexes exhibited reasonable thermal stabilities with decomposition
temperatures (Td), corresponding to 5% weight loss, over 300ꢀ370oC.

Journal of Materials Chemistry C
Page 6 of 29
View Article Online
DOI: 10.1039/C5TC03004H
In order to examine the effect of ꢀCF3 group position on ground and excited state properties of
the Ir(III) complexes, UV–visible absorption (Fig. 2a & 2b) and the photoluminescence (PL)
spectra (Fig. 2c & 2d) were measured in CHCl3 (10−5 M) at room temperature. The stronger
absorption peaks between 265 and 350 nm mostly represent the ligand centered 1πꢀπ* transitions.
The weaker absorption peaks between 350 and 520 nm are known to be the admixed 1MLCT and
3
3MLCT/ LC transitions where the usually spinꢀforbidden transitions of the triplet states are
allowed due to the strong SOC induced by the iridium metal.8 As shown in Fig. 2a and 2b, the
lower energy transition bands of m-LIrpic and m-LIrtmd are clearly blue shifted compared to
the oꢀ and pꢀ analogs indicating the impact of ꢀCF3 substitution position on the ground state
properties of the Ir(III) complexes.
Insets in Fig. 2c and 2d represent emission colors of the Ir(III) complexes after UVꢀ
irradiation in CHCl3. All the Ir(III) complexes emit an intense orange/orangeꢀred/red color upon
3
photoꢀexcitation. The structureless emission pattern of these Ir(III) complexes indicates MLCT
character of the emissive excited state.9 The position of ꢀCF3 on DPQ has marked changes in the
emission wavelengths of both the series of Ir(III) complexes. The PL peaks are recorded at 602,
565, 574 nm and 623, 593, 598 nm for o-LIrpic, m-LIrpic, p-LIrpic and o-LIrtmd, m-LIrtmd,
p-LIrtmd, respectively. Similar to the lower energy bands in absorption spectra, the PLmax of m-
LIrpic is hypsochromic shifted around 37 nm and 9 nm compare to the o-LIrpic and p-LIrpic,
respectively. The ꢀCF3 group at mꢀ location lowers the highest occupied molecular orbital
(HOMO) level of m-LIrpic leading to blue shift in emission.10,11 The strong polarization effect
and the large steric volume of the ꢀCF3 substituent at oꢀ position might be further reasons for
variation in the electronic distribution of o-LIrpic when compared to p-LIrpic.12 Similar

Page 7 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
tendencies in PL were also observed for o-LIrtmd, m-LIrtmd, and p-LIrtmd demonstrating the
influence of ꢀCF3 group position on emission color tuning.
As shown in Fig. S3b, the trends in film state emission spectra of all the Ir(III) complexes
were comparable to those of measured in CHCl3 except that the former are red shifted about 12ꢀ
25 nm in case of o-LIrpic, m-LIrpic, p-LIrpic and 4ꢀ7 nm in o-LIrtmd, m-LIrtmd, p-LIrtmd.
The wellꢀknown reason for less red shift in tmd based Ir(III) complexes is the bulky tBu groups
which suppress the intermolecular interactions responsible for bathochromic shift in solid state
emission.13 The PLQYs of o-LIrpic, m-LIrpic, p-LIrpic and o-LIrtmd, m-LIrtmd, p-LIrtmd
are 0.27, 0.65, 0.57 and 0.18, 0.41, 0.37, respectively, measured in dichloromethane (CH2Cl2) at
room temperature using rhodamine B (Φf = 0.68) as a standard. The transient PL analyses were
carried out for estimating the emission lifetimes of the Ir(III) complexes in CH2Cl2 at room
temperature and in 2ꢀmethyltetrahydrofuran (2ꢀMeTHF) at 77 K (Fig. S4 and Table 1). The
decay profiles of all the Ir(III) complexes are monoexponential with short emission lifetimes
ranging from 2.0ꢀ2.5 µs for o-LIrpic, m-LIrpic, p-LIrpic and 1.6ꢀ2.0 µs for o-LIrtmd, m-
LIrtmd, p-LIrtmd in CH2Cl2 representing the phosphorescence as origin of the emission.14 In
order to gain insight into the root cause for variation in PLQYs of the Ir(III) complexes, the
relaxation dynamics such as radiative and nonꢀradiative decay rate constants (Kr/Knr) were
calculated from the obtained lifetimes. In accordance with the energy gap law,15 the mꢀCF3 based
Ir(III) complexes exhibited relatively lower Knr and higher PLQYs compared to the oꢀ or pꢀCF3
based Ir(III) complexes for both the series demonstrating the substituent position effect on the
emissive properties of the Ir(III) complexes.
2.3 Electrochemical & Theoretical Calculations

Journal of Materials Chemistry C
Page 8 of 29
View Article Online
DOI: 10.1039/C5TC03004H
Cyclic voltammetry (CV) measurements were carried out to study the ꢀCF3 group position effect
on the redox properties and subsequently on the frontier orbitals of the six Ir(III) complexes. As
depicted in Fig. S5, the oxidation potentials of mꢀCF3 complexes are positiveꢀshifted in
comparison with oꢀ and pꢀCF3 analogs. As a result, the HOMO levels of mꢀ based Ir(III)
complexes are noticeably stabilized (see Table 1) causing the enhancement in band gaps. The
CV characteristics of all the Ir(III) complexes are in good agreement with the photophysical
properties. Hence, it is worth noting that a change in the location of ꢀCF3 does affect the redox
properties of these Ir(III) complexes. In order to gain insight into the structure–property
relationships, density functional theory (DFT) calculations for all the Ir(III) complexes were
carried out and the optimized HOMOs and LUMOs of these Ir(III) complexes were shown in
Fig. S6. Throughout the six Ir(III) complexes, the delocalization of HOMOs were mostly
distributed over the Ir(III) metal center and the metalated phenyl ring of DPQ, whereas the
LUMOs are mostly located on quinoline and partly on both the phenyl rings of the C^N ligands.
2.4 Electroluminescent properties of PhOLEDs
With the aim to elucidate the ꢀCF3 group position effect on EL properties of the new Ir(III)
complexes, monochromatic PhOLEDs were fabricated using the following optimized device
configuration: ITO/PEDOT:PSS (40 nm)/TAPC:DCzPPy:emitter (10 wt%, 40 nm)/TmPyPB (50
nm)/LiF (1 nm)/Al (100 nm), where TAPC is 1,1ꢀbis(4ꢀmethylphenyl)ꢀaminophenylꢀ
cyclohexane, DCzPPy is 2,6ꢀbis(3ꢀ(carbazolꢀ9ꢀyl)phenyl)pyridine, and TmPyPB is 1,3,5ꢀtris(mꢀ
pyridꢀ3ꢀylphenyl)benzene. In all the devices, TAPC:DCzPPy acts a mixed host, PEDOT:PSS
serves as hole injection layer (HIL), TmPyPB as electron transport layer (ETL), indiumꢀtin
oxide (ITO) as anode and LiF/Al as the electron injection layer and cathode. Device structure
and the energy levels of the materials involved in the fabrication of monochromatic PhOLEDs

Page 9 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
are given in Fig. 3a. Confinement of the excitons in emitting layer (EML) is expected since the
triplet energy (T1)16 of TAPC (T1=2.87 eV) and DCzPPy (T1=2.71 eV) are higher than all the
Ir(III) complexes (T1 ~ 2.08ꢀ2.21 eV, see Fig. S7a). TAPC is a unipolar (hole transporting) and
DCzPPy a bipolar (more electron transporting, less hole transporting) materials. Therefore, the
molar ratio of TAPC:DCzPPy was optimized to 4:6, respectively, for better charge balance. EML
was spin coated using CB solvent and ETL, LiF and Al were vacuum deposited on top of it. The
PL spectra of neat TAPC, DCzPPy, and TAPC:DCzPPy films are given in Fig. S7b. As
demonstrated in Fig. 3b and 3c, the deep overlap of the emission spectrum of TAPC:DCzPPy
with the MLCT absorption region of all Ir(III) complexes ensures an efficient energy transfer
from the mixed host to the Ir(III) complexes.17
The surface morphology for thin films of the mixed host (TAPC:DCzPPy) and
TAPC:DCzPPy doped with 10 wt% Ir(III) complex were analyzed using atomic force
microscopy (AFM). As shown in Fig. S8, the rootꢀmeanꢀsquare (RMS) surface roughness of the
doped EML films were similar to the undoped TAPC:DCzPPy films and even better in case of
m-LIrpic and m-LIrtmd doped films. The current densityꢀvoltageꢀ luminance (JꢀVꢀL) and EQEꢀ
luminance (ηꢀL) of the PhOLEDs based on o-LIrpic, m-LIrpic, and p-LIrpic dopants are
represented in Fig. 4a and 4b. The maximum luminance of the devices are 1592 cdmꢀ2 for o-
LIrpic, 4062 cdmꢀ2 for m-LIrpic, and 3710 cdmꢀ2 for p-LIrpic. The highest EQE of 17.1% (43.9
cdAꢀ1, 23.0 lmWꢀ1) was demonstrated by the PhOLED with m-LIrpic, while the p-LIrpic and o-
LIrpic showed 12.8% (30.1 cdAꢀ1, 13.5 lmWꢀ1) and 8.9% (13.2 cdAꢀ1, 5.2 lmWꢀ1), respectively.
Furthermore, a low efficiency rollꢀoff was recorded for m-LIrpic based device with an EQE of
about 14.7% at 1000 cdmꢀ2, i.e efficiency is retained up to 86%. The results of the
monochromatic PhOLEDs are summarized in Table 2. The device architecture also has an

Journal of Materials Chemistry C
Page 10 of 29
View Article Online
DOI: 10.1039/C5TC03004H
important role in the high performance of m-LIrpic along with its good photophysical
properties. It could be explained by considering the HOMO levels of these Ir(III) complexes
where a moderate barrier of 0.15 eV exists for hole transfer from the TAPC to the m-LIrpic,
while the remaining complexes do not have any such barrier. It is well known that the electron
mobility in organic materials is generally several orders of magnitude lower than the hole
mobility.18 From this, we strongly believe that the moderate hole barrier of m-LIrpic [0.15 eV]
balances the injection of holes in line with electrons, therefore, a high recombination of holeꢀ
electron is anticipated. In addition, introduction of ꢀCF3 at mꢀ position highly suppressed the nonꢀ
radiative deactivations and improved the PLQY of the mꢀCF3 based complexes which resulted
high efficiency in PhOLEDs.
In order to validate the aforementioned effect of ꢀCF3 group position on device
performance, PhOLEDs with another series of emitters o-LIrtmd, m-LIrtmd, and p-LIrtmd
contains tmd ancillary ligand were fabricated using the similar device configuration. Fig. 5a and
5b represent the JꢀVꢀL and ηꢀL plots of the PhOLEDs with these Ir(III) complexes. Though the
device structure and the main ligands are same, the performance of o-LIrpic, m-LIrpic, and p-
LIrpic based devices are outstanding compared to the o-LIrtmd, m-LIrtmd, and p-LIrtmd
based devices. It is beyond the scope of this paper to examine the exact reasons for the low
performance of ‘tmd’ based PhOLEDs, however, it could be partly due to the low PLQY of these
Ir(III) complexes. Interestingly, the trends in efficiency of o-LIrtmd, m-LIrtmd, and p-LIrtmd
based devices follow the structure–property relationships similar to the o-LIrpic, m-LIrpic, and
p-LIrpic. Accordingly, the PhOLEDs with m-LIrtmd show superior EQE of 6.4% (11.3 cdAꢀ1,
5.5 lmWꢀ1) than p-LIrtmd with 5.0% (7.5 cdAꢀ1, 3.4 lmWꢀ1) and o-LIrtmd with 3.7% (3.0 cdAꢀ

Page 11 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
1, 1.2 lmWꢀ1). In this scenario, it is worth stating that a subtle change in the substituent (ꢀCF3)
position on DPQ has profound impact on the PhOLED device performance.
EL spectra of the six PhOLEDs at 30 mAcmꢀ2 are shown in Fig. S9. Though the
bandwidths are broadened in EL spectra, but the ELmax are comparable to their PLmax. These
variations in the spectral bandwidth of EL compared with PL are expected to be caused by the
difference in the excitation process of the Ir(III) complexes.19 The absence of any residual
emission from TAPC:DCzPPy in EL spectra of the devices imply an effective energy transfer
from the mixed host to the Ir(III) complexes. The CIE coordinates of the monochromatic
PhOLEDs are represented in Fig. 6 and those are (0.624, 0.375), (0.535, 0.461), (0.566, 0.432)
for o-LIrpic, m-LIrpic, p-LIrpic and (0.664, 0.334), (0.596, 0.403), (0.622, 0.377) for o-
LIrtmd, m-LIrtmd, p-LIrtmd, respectively at 30 mAcmꢀ2. The confinement of the
recombination zone to the EML and the charge balance in the mixed host system are well
indicated by the stable CIE coordinates of the PhOLEDs where the shift is just (0.001, 0.001)
with increasing luminance as shown in Fig. S10.20 From the above data, it is interesting that the
PhOLEDs with m-LIrpic and p-LIrpic show orange color, m-LIrtmd shows orangeꢀred, o-
LIrpic and p-LIrtmd show red color, and o-LIrtmd shows deepꢀred color.
From the high performance of m-LIrpic based orange and [(dfpmpy)2Ir(EO2-pic)] based
blue PhOLEDs,21 it is likely to attain high efficiency in solutionꢀprocessed white OLEDs using
these materials as twoꢀcomponent emitters. Therefore, we fabricated white PhOLEDs with single
EML using ternary host system consisting of poly(vinylcarbazole) (PVK)/N,Nꢀdicarbazolylꢀ3,5ꢀ
benzene (mCP)/2,2′ꢀ(1,3ꢀphenylene)bis[5ꢀ(4ꢀtertꢀbutylphenyl)ꢀ1,3,4ꢀoxadiazole (OXDꢀ7) with
the configuration (see Fig. S11): ITO/PEDOT:PSSꢀ4083 (40 nm)/PVK:mCP:OXDꢀ7
(37.5:37.5:25) (85 wt%):blue:orange (x:y) (15 wt%) (50 nm)/1,3,5ꢀtri(1ꢀphenylꢀ1Hꢀ

Journal of Materials Chemistry C
Page 12 of 29
View Article Online
DOI: 10.1039/C5TC03004H
benzo[d]imidazolꢀ2ꢀyl)phenyl (TPBi) (30 nm)/LiF (1 nm)/Al (100 nm), where the doping ratios
of blue:orange were systematically optimized to 17:0.01 (device W1) and 17:0.015 (device W2).
W1 demonstrated a maximum EQE of 21.1% at 2000 cdmꢀ2 with a peak luminance of 12992
cdmꢀ2, also, it exhibited low rollꢀoff in efficiency with EQE 17.3% at 3000 cdmꢀ2 (Fig. 7). Very
importantly, the color coordinates of W1 are highly stable with ꢁCIEx,y (0.007, 0.009), which is
nearly independent of the driving voltage as shown in Fig. 8. All the data of white PhOLEDs are
summarized in Table 3, Fig. 7 and S12. Exchange of the HIL from PEDOT:PSSꢀ4083 to the low
conductivity PEDOT:PSSꢀ8000 might have a great potential for further enhancement of device
performance due to the improved charge balance.5b,22 In conclusion, to the best of our
knowledge, high EQE with very low rollꢀoff up to 3000 cdmꢀ2 simultaneously ultraꢀhigh color
stability in a single EML white PhOLEDs fabricated by solutionꢀprocess are seldom
reported.23,5b Finally, it is worth stating that both the orange and white PhOLEDs fabricated with
the orange phosphor m-LIrpic exhibited an excellent device performance in two separate host
systems credited to the good phophysical properties and solution processability of the new
orange emitter.
3. Conclusion
In this work, we introduced ꢀCF3 group at three different positions (oꢀ /mꢀ /pꢀ) on 2,4ꢀ
diphenylquinoline (DPQ) cyclometalating ligand and synthesized two series of highly soluble
new heteroleptic Ir(III) complexes o-LIrpic, m-LIrpic, p-LIrpic and o-LIrtmd, m-LIrtmd, p-
LIrtmd for usage in solutionꢀprocessed PhOLEDs. We observed that introduction of ꢀCF3 into
mꢀ position highly diminished the nonꢀradiative relaxations and improved the PLQY of the mꢀ
CF3 based Ir(III) complexes and also tuned the emission color from red to orange. As a result,
the performance of monochromatic PhOLEDs with both the series of Ir(III) complexes follows

Page 13 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
the order: m > p > o. Particularly, the orange PhOLED fabricated with solutionꢀprocessed
emission layer using m-LIrpic as dopant in a simple mixed host achieved the maximum
efficiency of 17.1% with low efficiency rollꢀoff and almost constant CIE coordinates (0.528,
0.469). Furthermore, the twoꢀcomponent white PhOLEDs using m-LIrpic as orange emitter
showed a peak EQE of 21.1% with strikingly low efficiency rollꢀoff with 17.3% at 3000 cdmꢀ2
and highly stable color with ꢁCIEx,y (0.007, 0.009). The overall results of these orange and
white PhOLEDs are among the best ones in solutionꢀprocessed devices. These findings
demonstrate a simple approach in fineꢀtuning the emissive properties of the Ir(III) complexes in
order to obtain highly efficient PhOLEDs for practical application of solutionꢀprocess.
Acknowledgments
This work was supported by grant fund from the National Research Foundation (NRF) (2011ꢀ
0028320) and the Pioneer Research Center Program through the NRF (2013M3C1A3065522) by
the Ministry of Science, ICT & Future Planning (MSIP) of Korea.
References
1
[a] S. Reineke, M. Thomschke, B. Lüssem and K. Leo, Rev. Mod. Phys., 2013, 85, 1245; [b]
C. Fan, L. Zhu, B. Jiang, Y. Li, F. Zhao, D. Ma, J. Qin and C. Yang, J. Phys. Chem. C,
2013, 117, 19134; [c] C.ꢀC. Chen, H.ꢀY. Lin, C.ꢀH. Li, J.ꢀH. Wu, Z.ꢀY. Tu, L.ꢀL. Lee, M.ꢀS.
Jeng, C.ꢀC. Lin, J.ꢀH. Jou and H.ꢀC. Kuo, International Journal of Photoenergy, Volume
2014, Article ID 851371, 6 pages.
2
[a] Y. H. Lee, J. Park, S.ꢀJ. Jo, M. Kim, J. Lee, S. U. Lee and M. H. Lee, Chem. Eur. J.,
2015, 21, 2052; [b] D. Liu, H. Ren, L. Deng and T. Zhang, ACS Appl. Mater. Interfaces,

Journal of Materials Chemistry C
Page 14 of 29
View Article Online
DOI: 10.1039/C5TC03004H
2013, 5, 4937; [c] Q.ꢀL. Xu, X. Liang, S. Zhang, Y.ꢀM. Jing, X. Liu, G.ꢀZ. Lu, Y.ꢀX. Zheng
and J.ꢀL. Zuo, J. Mater. Chem. C, 2015, 3, 3694.
3
[a] G. Li, Y. Feng, T. Peng, K. Ye, Y. Liu and Y. Wang, J. Mater. Chem. C, 2015, 3, 1452;
[b] G. Li, D. Zhu, T. Peng, Y. Liu, Y. Wang and M. R. Bryce, Adv. Funct. Mater., 2014, 24,
7420; [c] R. Wang, D. Liu, H. Ren, T. Zhang, H. Yin, G. Liu and J .Li, Adv. Mater., 2011,
23, 2823; [d] H.ꢀH. Chou, Y.ꢀK. Li, Y.ꢀH. Chen, C.ꢀC. Chang, C.ꢀY. Liao and C.ꢀH. Cheng,
ACS Appl. Mater. Interfaces, 2013, 5, 6168.
4 [a] X. Liu, S. Wang, B. Yao, B. Zhang, C.ꢀL. Ho, W.ꢀY. Wong, Y. Cheng and Z. Xie, Org.
Electron., 2015, 21, 1; [b] R. Wang, D. Liu, R. Zhang, L. Deng and J. Li, J. Mater. Chem.,
2012, 22, 1411; [c] T. Giridhar, T.ꢀH. Han, W. Cho, C. Saravanan, T.ꢀW. Lee and S.ꢀH. Jin,
Chem. Eur. J., 2014, 20, 8260.
5
[a] K. S. Yook and J. Y. Lee, Adv. Mater., 2014, 26, 4218; [b] B. Zhang, G. Tan, C.ꢀS. Lam,
B. Yao, C.ꢀL. Ho, L. Liu, Z. Xie, W.ꢀY. Wong, J. Ding and L. Wang, Adv. Mater., 2012, 24,
1873; [c] C. Fan and C. Yang, Chem. Soc. Rev., 2014, 43, 6439; [d] H. Xu, R. Chen, Q. Sun,
W. Lai, Q. Su, W. Huang and X. Liu, Chem. Soc. Rev., 2014, 43, 3259; [e] C.ꢀL. Ho, W.ꢀY.
Wong, G.ꢀJ. Zhou, B. Yao, Z. Xie and L.Wang, Adv. Funct. Mater., 2007, 17, 2925; [f] C.
Fan, J. Miao, B. Jiang, C. Yang, H. Wu, J. Qin and Y. Cao, Org. Electron., 2013, 14, 3392.
[a] D. A. Markelov, Y. Y. Gotlib, A. A. Darinskii, A. V. Lyulin and S. V. Lyulin, Polym.
Sci., Ser. A, 2009, 51, 331; [b] J. M. Lupton, I. D. W. Samuel, R. Beavington, M. J.
Frampton, P. L. Burn and H. Bässler, Phys. Rev. B, 2001, 63, 155206.
6
7 [a] J. Park, J.ꢀS. Park, Y. G. Park, J. Y. Lee, J. W. Kang, J. Liu, L. Dai and S.ꢀH. Jin, Org.
Electron., 2013, 14, 2114; [b] J. Ding, J. Lü, Y. Cheng, Z. Xie, L. Wang, X. Jing and F.
Wang, Adv. Funct. Mater., 2008, 18, 2754; [c] Z. Ma, J. Ding, B. Zhang, C. Mei, Y. Cheng,

Page 15 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
Z. Xie, L. Wang, X. Jing and F. Wang, Adv. Funct. Mater., 2010, 20, 138; [d] S.ꢀJ. Lee, J.ꢀS.
Park, M. Song, I. A. Shin, Y.ꢀI. Kim, J. W. Lee, J.ꢀW. Kang, Y.ꢀS. Gal, S. Kang, J. Y. Lee,
S.ꢀH. Jung, H.ꢀS. Kim, M.ꢀY. Chae and S.ꢀH. Jin, Adv. Funct. Mater., 2009, 19, 2205; [e] R.
Pode, S.ꢀJ. Lee, S.ꢀH. Jin, S. Kim and J. H. Kwon, J. Phys. D: Appl. Phys., 2010, 43,
025101; [f] M. Song, J. S. Park, M. Yoon, A. J. Kim, Y. I. Kim, Y.ꢀS. Gal, J. W. Lee and S.ꢀ
H. Jin, J. Organomet. Chem., 2011, 696, 2122; [g] J. Ding, J. Gao, Q. Fu, Y. Cheng, D. Ma
and L. Wang, Synth. Met., 2005, 155, 539; [h] X. Zhang, J. Gao, C. Yang, L. Zhu, Z. Li, K.
Zhang, J. Qin, H. You and D. Ma, J. Organomet. Chem., 2006, 691, 4312.
8 [a] H. J. Bae, J. Chung, H. Kim, J. Park, K. M. Lee, T.ꢀW. Koh, Y. S. Lee, S. Yoo, Y. Do and
M. H. Lee, Inorg. Chem., 2014, 53, 128; [b] H. K. Dahule, S. J. Dhoble, J.ꢀS. Ahn and R.
Pode, Journal of Physics and Chemistry of Solids, 2011, 72, 1524.
9
C.ꢀY. Sun, X.ꢀL. Wang, X. Zhang, C. Qin, P. Li, Z.ꢀM. Su, D.ꢀX. Zhu, G.ꢀG. Shan, K.ꢀZ.
Shao, H. Wu and J. Li, Nat. Commun., 2013, 4, 2717, DOI: 10.1038/ncomms3717.
10 [a] T. Kim, H. Kim, K. M. Lee, Y. S. Lee and M. H. Lee, Inorg. Chem., 2013, 52, 160; [b]
S.ꢀJ. Yun, H.ꢀJ. Seo, M. Song, S.ꢀH. Jin, S. K. Kang and Y.ꢀI. Kim, J. Organomet. Chem.,
2013, 724, 244.
11 J. Frey, B. F. E. Curchod, R. Scopelliti, I. Tavernelli, U. Rothlisberger, M. K. Nazeeruddin
and E. Baranoff, Dalton. Trans., 2014, 43, 5667.
12 [a] J. Wang, X. Xu, Y. Tian, C. Yao and L. Li, J. Mater. Chem. C, 2014, 2, 5036; [b] R. D.
Chambers, Organofluorine Chemistry: Fluorinated Alkenes and Reactive Intermediates,
1997, Volume 192.
13 D. H. Kim, N. S. Cho, H.ꢀY. Oh, J. H. Yang, W. S. Jeon, J. S. Park, M. C. Suh and J. H.
Kwon, Adv. Mater., 2011, 23, 2721.

Journal of Materials Chemistry C
Page 16 of 29
View Article Online
DOI: 10.1039/C5TC03004H
14 C.ꢀH. Yang, M. Mauro, F. Polo, S. Watanabe, I. Muenster, R. Fröhlich and L. D. Cola,
Chem. Mater., 2012, 24, 3684.
15 [a] X. Cao, J. Miao, M. Zhu, C. Zhong, C. Yang, H. Wu, J. Qin and Y. Cao, Chem. Mater.,
2015, 27, 96; [b] S. Okada, K. Okinaka, H. Iwawaki, M. Furugori, M. Hashimoto, T.
Mukaide, J. Kamatani, S. Igawa, A. Tsuboyama, T. Takiguchi and K. Ueno, Dalton Trans.,
2005, 1583.
16 [a] H. Sasabe and J. Kido, Chem. Mater., 2011, 23, 621; [b] Y.ꢀJ. Pu, G. Nakata, F. Satoh,
H. Sasabe, D. Yokoyama and J. Kido, Adv. Mater., 2012, 24, 1765; [c] J. S. Park, J. H. Yu,
W. S. Jeon, Y. H. Son, C. Kulshreshtha and J. H. Kwon, Journal of Information Display,
2011, 12, 51.
17 J. W. Kim, S. I. You, N. H. Kim, J.ꢀA. Yoon, K. W. Cheah, F. R. Zhu and W. Y. Kim, Sci.
Rep., 2014, 4, 7009, DOI: 10.1038/srep07009.
18 H. Yersin, Highly efficient OLEDs with Phosphorescent Materials, © 2008 WILEYꢀVCH
Verlag GmbH & Co., Page 395.
19 C.ꢀH. Fan, P. Sun, T.ꢀH. Su and C.ꢀH. Cheng, Adv. Mater., 2011, 23, 2981.
20 J.ꢀH. Lee, G. Sarada, C.ꢀK. Moon, W. Cho, K.ꢀH. Kim, Y. G. Park, J. Y. Lee, S.ꢀH. Jin and
J.ꢀJ. Kim, Adv. Opt. Mater., 2015, 3, 211.
21 W. Cho, G. Sarada, J.ꢀS. Park, Y.ꢀS. Gal, J. H. Lee and S.ꢀH. Jin, Org. Electron., 2014, 15,
2328.
22 C. Fan, Y. Li, C. Yang, H. Wu, J. Qin and Y. Cao, Chem. Mater., 2012, 24, 4581.
23 S. Wang, B. Zhang, X. Wang, J. Ding, Z. Xie and L. Wang, Adv. Opt. Mater., 2015, DOI:
10.1002/adom.201500175.

Page 17 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 1 Structures of the Ir(III) complexes and representation of substituent position.

Journal of Materials Chemistry C
Page 18 of 29
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 2 (a, b) UVꢀvisible absorption spectra; (c, d) PL spectra of the Ir(III) complexes in CHCl3
solution [Insets are photographs of emission color upon UVꢀirradiation].

Page 19 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 3 (a) Device structure of monochromatic PhOLEDs; (b, c) Representation of energy transfer
from the host to dopants (PL spectrum of TAPC:DCzPPy and absorption spectra of Ir(III)
complexes in film state).

Journal of Materials Chemistry C
Page 20 of 29
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 4 (a) Current density−voltage−luminance (J−V−L); (b) EQEꢀluminance (ηꢀL) characteristics
of monochromatic PhOLEDs with o-LIrpic, m-LIrpic, and p-LIrpic.

Page 21 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 5 (a) Current density−voltage−luminance (J−V−L); (b) EQEꢀluminance (ηꢀL) characteristics
of monochromatic PhOLEDs with o-LIrtmd, m-LIrtmd, and p-LIrtmd.

Journal of Materials Chemistry C
Page 22 of 29
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 6 1931 Commission Internationale de L’Eclairage (CIE) coordinates of the monochromatic
PhOLEDs at 30 mAcmꢀ2.

Page 23 of 29
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 7 EQEꢀluminance (ηꢀL) characteristics of white PhOLEDs.

Journal of Materials Chemistry C
Page 24 of 29
View Article Online
DOI: 10.1039/C5TC03004H
Fig. 8 EL spectra of white PhOLED at different driving voltages.

Page 25 of 29
Journal of Materials Chemistry C
Table 1 Thermal, photophysical, and electrochemical properties of the Ir(III) complexes.
a
c
c
e
Ir(III)
Td
λem
PLQY b,c
Kr
Knr
Eg
HOMO f
τ c,d
[µs]
2.2
Complex
[°C]
[nm]
602
565
574
623
593
598
[105sꢀ1] [105sꢀ1]
[eV]
2.09
2.35
2.17
1.88
2.17
2.06
/LUMO g [eV]
oꢀLIrpic
mꢀLIrpic
pꢀLIrpic
oꢀLIrtmd
mꢀLIrtmd
pꢀLIrtmd
302
362
370
364
349
335
0.27
0.65
0.57
0.18
0.41
0.37
1.23
2.60
2.85
1.13
2.05
1.95
3.32
1.40
2.15
5.13
2.95
3.32
ꢀ5.50/ꢀ3.41
ꢀ5.65/ꢀ3.30
ꢀ5.53/ꢀ 3.36
ꢀ5.28/ꢀ 3.40
ꢀ5.41/ꢀ 3.24
ꢀ5.33/ꢀ 3.27
2.5
2.0
1.6
2.0
1.9
a Measured in CHCl3 solution at room temperature (1x10ꢀ5M). b Rhodamine B (ϕpl = 0.68) in 94%
ethanol is used as reference. c Measured in CH2Cl2 at room temperature. d Excited state lifetimes.
e Optical band gaps. f Calculated from CV. g Deduced from HOMO and Eg.

Journal of Materials Chemistry C
Page 26 of 29
Table 2 EL characteristics of the monochromatic PhOLEDs with the new Ir(III) complexes
Maximum device performance
at 1000 cdmꢀ2
EQE PE
[lmWꢀ1] [cdAꢀ1]
a
Dopant
ELmax
[nm]
CIE a
[x, y]
EQE
[%]
8.9
PE
[lmWꢀ1]
5.2
LE
[cdAꢀ1]
13.2
43.9
30.1
3.0
LE
[%]
5.2
14.8
9.9
1.9
5.8
4.4
oꢀLIrpic
mꢀLIrpic
pꢀLIrpic
oꢀLIrtmd
mꢀLIrtmd
pꢀLIrtmd
2.4
16.5
9.3
0.5
4.4
2.7
7.8
38.0
23.1
1.7
602
572
580
629
597
602
(0.613, 0.383)
(0.528, 0.469)
(0.556, 0.441)
(0.663, 0.336)
(0.593, 0.405)
(0.622, 0.377)
17.1
12.8
3.7
23.0
13.5
1.2
6.4
5.5
11.3
7.5
10.3
6.7
5.0
3.4
a Values collected at a current density of 30 mAcmꢀ2.

Page 27 of 29
Journal of Materials Chemistry C
Table 3 EL characteristics of twoꢀcomponent white PhOLEDs with (dfpmpy)2Ir(EO2-pic) [blue] and m-LIrpic [orange]
Maximum device performance
at 3000 cdmꢀ2
Dopant
[B:O]
Lmax
CIE a
[x, y]
[cdmꢀ2]
EQE
[%]
PE
LE
EQE
[%]
PE
LE
[lmWꢀ1]
[cdAꢀ1]
[lmWꢀ1]
[cdAꢀ1]
(0.293,
0.395)
17:0.01 (W1)
17:0.015(W2)
21.1
15.4
18.1
13.4
48.8
36.1
17.3
12.5
15.0
10.8
40.4
29.5
12992
11990
(0.300,
0.406)
a Values collected at a current density of 30 mAcmꢀ2.

Journal of Materials Chemistry C
Page 28 of 29

Page 29 of 29
Journal of Materials Chemistry C
Table of Contents
The location of -CF3 group on 2,4-diphenylquinoline based Ir(III) complexes is found to be very important for attaining high
performance in solution-processed phosphorescent OLEDs.