Solution-processable highly efficient deep-red and orange organic light-emitting diodes based on multi-functional Ir(III) complexes

Article abstract of DOI:10.1039/c7tc02557b

A heteroleptic deep-red iridium(iii) complex, TPQIr-HT, based on thiophene-phenylquinoline (TPQ), and orange Ir(iii) complexes, m-CF₃DPQIr-HT and m-CF₃DPQIr-ET based on diphenylquinoline (DPQ), are designed by attaching a carbazole-based hole transporting (HT) group and an oxadiazole (OXD)-based electron transporting (ET) group to the parent Ir(iii) complexes, TPQIr and m-CF₃DPQIr. The Ir(iii) complexes TPQIr-HT show a deep-red emission peak at 612 nm, similar to that of TPQIr, whereas m-CF₃DPQIr-HT and m-CF₃DPQIr-ET show an orange emission peak at 567 ± 1 nm, which is similar to that of m-CF₃DPQIr. The newly functionalized Ir(iii) complexes show improved device performance compared to the Ir(iii) complexes, TPQIr and m-CF₃DPQIr, without the additional functional groups. The phosphorescent organic light-emitting diodes (PhOLEDs) fabricated using a deep-red Ir(iii) complex, TPQIr-ET, achieved a maximum external quantum efficiency (EQE) of 17.47% using GraHIL as the hole injection layer (HIL). Similarly, the orange Ir(iii) complex, m-CF₃DPQIr-HT, achieved a maximum EQE of 21.61%.

Full text of DOI:10.1039/c7tc02557b

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Solution-Processable Highly Efficient Deep-Red and Orange Organic Light-Emitting
Diodes Based on Multi-functional Ir(III) Complexes
‡a
‡a
Woosum Cho,
Ganguri Sarada, Athithan Maheshwaran,a YeongꢀSoon Gal,b Yeonsig
Nam,c Jin Yong Lee*c, and SungꢀHo Jin*a
aDepartment of Chemistry Education, Graduate Department of Chemical Materials and
Institute for Plastic Information and Energy Materials, Pusan National University, Busan,
46241, Republic of Korea, *Eꢀmail: shjin@pusan.ac.kr
aDepartment of Fire Safety, Kyungil University, Gyeongsangbukꢀdo 38428, Republic of
Korea
cDepartment of Chemistry, Sungkyunkwan University, Suwon 16419, Republic of Korea, *Eꢀ
mail: jinylee@skku.edu
‡ These authors contributed equally to this work
1

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Abstract: The heteroleptic deepꢀred iridium(III) complex, TPQIrꢀHT based on thiopheneꢀ
phenylquinoline (TPQ), and orange Ir(III) complexes, mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET
based on diphenylquinoline (DPQ), were designed by attaching a carbazoleꢀbased hole
transporting (HT) group and an oxadiazole (OXD)ꢀbased electron transporting (ET) group to
the parent Ir(III) complexes, TPQIr and mꢀCF3DPQIr. The Ir(III) complexes TPQIrꢀHT
showed a deepꢀred emission peak at 612 nm, similar to that of TPQIr, whereas mꢀCF3DPQIrꢀ
HT and mꢀCF3DPQIrꢀET showed an orange emission peak at 567±1 nm, which is similar to
that of mꢀCF3DPQIr. The newly functionalized Ir(III) complexes showed improved device
performance compared to the Ir(III) complexes, TPQIr and mꢀCF3DPQIr, without the
additional functional groups. The phosphorescent organic lightꢀemitting diodes (PhOLEDs)
fabricated using the deepꢀred Ir(III) complex, TPQIrꢀET, achieved a maximum external
quantum efficiency (EQE) of 17.47% using GraHIL as the hole injection layer (HIL).
Similarly, the orange Ir(III) complex, mꢀCF3DPQIrꢀHT, achieved a maximum EQE of
21.61%.
2

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1. Introduction
Solutionꢀprocessed phosphorescent organic lightꢀemitting diodes (PhOLEDs) have
attracted great interest for cost effective and largeꢀarea manufacturing of solidꢀstate lighting
and displays sources.1ꢀ5 Ir(III) complexes are considered most promising emitters in OLEDs
due to their high quantum yields, strong spinꢀorbit couplings, short triplet lifetimes, and
emission color tunability from blue to deepꢀred.6,7 Deepꢀred phosphorescent emitters and
PhOLEDs with Commission International de L’Eclairage (CIE) ≥ 0.67 are still rare, despite
extensive efforts applying novel dopant and host materials to attain high performance
solutionꢀprocessed deepꢀred PhOLEDs.8ꢀ11 Recently, deepꢀred and orange PhOLEDs using
Ir(III) complex emitters achieved a high external quantum efficiency (EQE) of about 26 and
28%, respectively, through vapor deposition processes.12ꢀ17 The performance of solutionꢀ
processed PhOLEDs is still inferior to the vacuumꢀdeposited counterparts in terms of
efficiency, turnꢀon voltages (Von) and efficiency rollꢀoff at high current densities.18ꢀ22 Highly
efficient orange phosphorescent emitters are indispensable for the fabrication of twoꢀ
component white OLEDs.23ꢀ27
Many research groups have focused on the design and synthesis of novel solutionꢀ
processable deepꢀred and orange emitting phosphors with different design strategies. For
example, Cao et al. reported a series of Ir(III) complexes through the incorporation of hole
transporting (HT) triphenylamine units and/or electron transporting (ET) phosphine oxide
groups to the cyclometalating (C^N) ligand phenylisoquinoline. Among them, one phosphor
(R2) showed a maximum EQE of 7.6% with CIE coordinates of (0.68, 0.30).28 Xie et al.
synthesized Ir(htꢀ5htꢀpy)2(acac), by introducing hexyl side chain on the ligand to improve
3

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miscibility with the host materials to form a homogeneous emissive layer, which exhibited a
decent EQE of 8.2% with satisfactory CIE coordinates of (0.68, 0.31) for saturated red
emission.29
In our previous works, we reported deepꢀred emitting solutionꢀprocessable Ir(III)
complexes oꢀCF3DPQIrtmd based on diphenylquinoline (DPQ),30 (FPQ)2Ir(picꢀNꢀO) based
on fluorenylꢀphenylquinoline (FPQ),31 and (EOꢀCzꢀPQ)2Ir(acac) based on carbazolyl (Cz)ꢀ
phenylquinoline (PQ)32 ligands. Their PhOLEDs exhibited EQEs of 3.7, 8.9 and 4.74% with
CIE coordinates of (0.663, 0.336), (0.660, 0.338) and (0.65, 0.34), respectively. We also
reported a thiopheneꢀphenylquinoline (TPQ)ꢀbased highly efficient solutionꢀprocessable
homoleptic Ir(III) complex, Ir(ThꢀPQ)3, with deepꢀred CIE coordinates (0.64, 0.34).33 Using
the same C^N ligand (TPQ), we have also reported a deepꢀred emitting heteroleptic Ir(III)
complex, TPQIrꢀET,34 by incorporating an ET functional moiety, oxadiazole (OXD) unit,
onto the ancillary ligand. TPQIrꢀET achieved a high EQE of 20.59% in solutionꢀprocessed
PhOLEDs with CIE coordinates (0.673, 0.323) due to the balanced charge carrier injection by
the ET functional group. In addition, we reported the orange emitting solutionꢀprocessable
Ir(III) complexes mꢀCF3DPQIrpic, pꢀCF3DPQIrpic and (DPQ)2Ir(picꢀNꢀO) using DPQꢀbased
C^N ligands and their PhOLEDs exhibited EQEs of 17.1, 12.8 and 14.2%, respectively.30,31
Here, we synthesized a new deepꢀred heteroleptic Ir(III) complex, TPQIrꢀHT (Scheme 2),
suitable for solution process, by incorporating an HT functional group, (9ꢀ(3ꢀ(9Hꢀcarbazolꢀ9ꢀ
yl)phenyl)ꢀ3ꢀethylꢀ9Hꢀcarbazol) (mCP), onto the ancillary ligand to facilitate charge balance
in the emitting layer (EML). We also synthesized new orange emitting heteroleptic Ir(III)
complexes, mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET (Scheme 3), for solution process by
incorporating ET and HT functional groups on the ancillary ligand. The PhOLED of TPQIrꢀ
HT furnished deepꢀred CIE coordinates of (0.67, 0.32) and a high EQE of 17.47%. Also, the
4

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PhOLEDs of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET exhibited common orange CIE
coordinates of (0.54, 0.46) and a high EQE of 21.61 and 18.39%, respectively.
2. Experimental
2.1 General information
All chemicals and reagents were purchased from Aldrich Chemical Co. and used without
further purification. Compound 1, TPQIrꢀCl in Scheme 2 34,35; compound 6, mCPCH2Br and
OXDCH2Br in Scheme 3 were synthesized using the reported procedures.35,36 1H NMR
spectra were recorded on a Varian Mercury Plus 300 MHz spectrometer in CDCl3 using
tetramethylsilane as an internal standard. Thermal gravimetric analysis (TGA) was carried
o
out by Mettler Toledo TGA/SDTA 851e under N2 atmosphere at a heating rate of 10 C/min.
The UV–vis absorption and the fluorescence spectra were recorded with JASCO V–570 and
Hitachi F–4500 fluorescence spectrophotometers at room temperature (RT), respectively.
Cyclic voltammetry (CV) measurements were performed with a CHI 600C potentiostat (CH
Instruments) at a scan rate of 100 mV/s using anhydrous dichloromethane (CH2Cl2) and 0.1
M tetrabutylammonium tetrafluoroborate (TBABF4) as the solvent and electrolyte,
respectively, at RT. A platinum disc was used as the working electrode, a platinum wire as the
counter electrode, and a Ag/AgCl as the reference electrode. The potentials were referenced
to the ferrocene/ferrocenium redox couple (Fc/Fc+). A sublimated grade of 4,4’,4”ꢀtris(Nꢀ
carbazolyl)ꢀtriphenylamine (TCTA), 1,3,5ꢀtris(Nꢀphenylbenzimidazoleꢀ2ꢀyl)benzene (TPBi),
4,4’ꢀcyclohexylidenebis[N,Nꢀbis(4ꢀmethylphenyl)benzenamine] (TAPC), and 2,6ꢀbis(3ꢀ(9Hꢀ
Carbazolꢀ9ꢀyl)phenyl)pyridine (26DCzPPy) were purchased from OSM and used as the host
materials for the EMLs of the orange and deepꢀred emitting PhOLEDs. A sublimated grade of
1,3,5ꢀtri[(3ꢀpytidyl)ꢀphenꢀ3ꢀyl]benzene (TmPyPB) purchased from OSM was used as an ET
layer (ETL). The process of fabrication and characterizations of PhOLEDs are described in
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supporting information (SI).
2.2 Synthesis of 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazole-3-carbaldehyde (2).
Phosphoryl chloride (200 mmol) was added dropwise into N,Nꢀdimethylformamide (DMF,
200 mmol) in an ice bath. The mixture was stirred at RT for 1 h and a solution of 1,3ꢀdi(9Hꢀ
carbazolꢀ9ꢀyl)benzene (1, 3.27 g, 8 mmol) in 10 mL of DMF was added. The reaction
mixture was heated at 130 °C with stirring for 24 h and then poured into ice water. After
neutralizing with a base, the mixture was extracted with chloroform (CHCl3). The organic
layer was dried over anhydrous Na2SO4 and the solvent was removed by distillation under
vacuum. The solid residue was purified by column chromatography on silica gel
(hexane:ethyl acetate (EtOAc), 4:1 v/v) to obtain a whitishꢀyellow solid, 2 (1.92 g, 55%). 1H
NMR (300 MHz, CDCl3): δ (ppm) 10.13 (s, 1H), 8.69 (s, 1H), 8.24ꢀ8.21 (d, 1H), 8.17ꢀ8.15 (d,
2H), 8.00ꢀ7.98 (d, 1H), 7.90ꢀ7.87 (m, 1H), 7.80 (m, 2H), 7.70ꢀ7.68 (d, 2H), 7.60ꢀ7.56 (m,
4H), 7.47ꢀ7.42 (m, 3H), 7.35ꢀ7.30 (t, 2H).
2.3 Synthesis of (9-(3-(9H-carbazol-9-yl)-9H-carbazol-3-yl)methanol (mCPCH2OH).
To a solution of compound 2 (1.92 g 4.34 mmol) in ethanol (40 mL) and CH2Cl2 (40 mL),
NaBH4 was added slowly at RT. The reaction mixture was stirred for 3 h at RT and then
poured into water (70 mL) and extracted with CH2Cl2. The organic layer was washed with
water, dried over Na2SO4 and concentrated under vacuum to get the crude product. The
desired product, mCPCH2OH, was obtained as a colorless solid (1.8 g, 94%) upon
recrystallization in toluene. 1H NMR (300 MHz, CDCl3): δ (ppm) 8.15 (s, 4H), 7.85ꢀ7.78 (m,
2H), 7.70ꢀ7.69 (m, 2H), 7.53ꢀ7.44 (m, 8H), 7.34ꢀ7.26 (m, 3H), 4.88 (d, 2H), 1.78 (s, 1H).
2.4 Synthesis of bis[4-phenyl-2-(thiophen-2-yl)quinoline]iridium (9-(3-(9H-carbazol-9-
yl)-9H-carbazol-3-yl) piconlinate (TPQIr-HT).
A mixture of TPQIrꢀCl (1.50 g, 1.63 mmol), mCPCH2OH (1.07 g, 2.45 mmol), and K2CO3
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(2.18 g, 16.3 mmol) in DMF (20 mL) was stirred at 80 oC under N2 atmosphere for 12 h. The
resulting mixture was cooled to RT followed by the addition of cold water and further
extracted with CH2Cl2. The organic layer was dried over anhydrous Na2SO4 and then the
solvent was evaporated under reduced pressure. The solid crude product was purified by
column chromatography on silica gel (EtOAc:CH2Cl2:hexane, 3:5:2 v/v/v) to furnish a red
1
powder, TPQIrꢀHT (0.78 g, 36%). H NMR (300 MHz, CDCl3): δ (ppm) 8.15 (s, 4H), 7.85ꢀ
7.78 (m, 2H), 7.70ꢀ7.69 (m, 2H), 7.53ꢀ7.44 (m, 8H), 7.34ꢀ7.26 (m, 3H), 4.88 (s, 2H), 1.78 (s,
1H). Anal. calcd for C75H48IrN5O3S2: C, 68.06; H, 3.66; N, 5.29; found C, 67.91; H, 3.60; N,
5.23.
2.5 Synthesis of bi[4-phenyl-2-(3-(trifluoromethyl)phenyl)quinoline]iridium piconlinate
hydroxyl (m-CF3DPQIr-OH) (7).
The dimer (2 g, 1.08 mmol) and 3ꢀhydroxypicolinic acid (0.752 g, 5.41 mmol) were mixed
with Na2CO3 (1.14 g, 10.92 mmol) in 2ꢀethoxyethanol (50 mL). The mixture was stirred for
12 h at RT under N2 atmosphere. After completion of the reaction, the mixture was poured
into water and extracted with CH2Cl2, dried over anhydrous Na2SO4 and the solvent was
evaporated under vacuum. The residue was then purified by column chromatography on
silica gel (hexane:EtOAc, 6:4 v/v) to furnish compound mꢀCF3DPQIrꢀOH (7) as a dark
orange solid (0.66 g, 60%). 1H NMR (300 MHz, CDCl3): δ (ppm) 13.28 (s, 1H), 8.70ꢀ8.67 (d,
J=9.3 Hz, 1H), 8.16 (s, 1H), 8.08 (m, 3H), 7.89ꢀ7.86 (d, J=7.5 Hz, 2H), 7.63 (s, 11H), 7.48ꢀ
7.34 (m, 4H), 7.26ꢀ7.22 (m, 2H), 7.03ꢀ7.01 (m, 3H), 6.93ꢀ6.90 (d, J=8.7 Hz, 1H), 6.50ꢀ6.47
(d, 1H).
2.6 Synthesis of bi[4-phenyl-2-(3-(trifluoromethyl)phenyl)quinoline]iridium (9-(3-(9H-
carbazol-9-yl)-9H-carbazol-3-yl) piconlinate (m-CF3DPQIr-HT).
A mixture of mꢀCF3DPQIrꢀOH (0.5 g, 0.486 mmol), mCPCH2Br and Cs2CO3 (0.32 g,
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0.973 mmol) in acetone (25 mL) was refluxed for 8 h under N2 atmosphere. After cooling to
RT, the solvent was evaporated and the residue was dissolved in CH2Cl2. The organic phase
was washed with water, dried with Na2SO4 and purified using flash chromatography on silica
gel (hexane:EtOAc, 3:2 v/v) to afford m-CF3DPQIrꢀHT as a dark orange solid (0.42 g,
1
60%). H NMR (300 MHz, CDCl3): δ (ppm) 8.99ꢀ8.96 (d, J=8.7 Hz, 1H), 8.17ꢀ8.08 (q, J=27
Hz, 6H), 8.03ꢀ8.01 (d, J=6 Hz, 2H), 7.78ꢀ7.70 (m, 3H), 7.66ꢀ7.58 (m, 15H), 7.45ꢀ7.36 (m,
10H), 7.30ꢀ7.28 (m, 5H), 7.05ꢀ6.96 (q, J=26.4 Hz, 2H), 6.88ꢀ6.86 (d, J=6.9 Hz, 1H), 6.80ꢀ
6.75 (t, J=14.7 Hz, 1H), 6.65ꢀ6.60 (t, J=14.7 Hz, 1H), 6.41ꢀ6.39 (d, J=7.8 Hz, 1H), 5.22 (s,
2H). Anal. calcd for C81H50F6IrN5O3: C, 67.21; H, 3.48; N, 4.84; found C, 67.30; H, 3.42; N,
4.79.
2.7 Synthesis of bi[4-phenyl-2-(3-(trifluoromethyl)phenyl)quinoline]iridium 4-(4-(5-
phenyl-1,3,4- oxadiazol-2-yl)phenoxy)picolinate (m-CF3DPQIr-ET).
A mixture of mꢀCF3DPQIrꢀOH (0.5 g, 0.486 mmol), OXDCH2Br, and Cs2CO3 (0.32 g,
0.973mmol) in acetone (25 mL) was refluxed for 8 h under N2 atmosphere. After cooling to
RT, the solvent was evaporated and the residue was dissolved in CH2Cl2. The organic phase
was washed with water, dried over Na2SO4 and purified using flash chromatography on silica
1
gel (hexane:EtOAc, 4:2 v/v) to afford m-CF3DPQIrꢀET as an orange solid (0.43 g, 70%). H
NMR (300 MHz, CDCl3): δ (ppm) 9.02ꢀ8.99 (d, J=9.3 Hz, 1H), 8.16ꢀ8.01 (m, 8H), 7.92ꢀ7.89
(t, J =17.4 Hz, 2H), 7.67ꢀ7.55 (m, 16H), 7.41ꢀ7.48 (m, 4H), 7.19 (m, 2H), 7.05ꢀ7.00 (q, 2H),
6.91 (m, 2H), 6.45ꢀ6.42 (d, J=9 Hz, 1H), 5.18 (s, 2H). Anal. calcd for C65H40F6IrN5O4: C,
61.90; H, 3.20; N, 5.55; found C, 61.81; H, 3.16; N, 5.63.
3. Results and discussion
The three Ir(III) complexes, TPQIrꢀHT, mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET, were
successfully synthesized according to the routes shown in Schemes 2 and 3. The molecular
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1
structures were thoroughly characterized by H NMR spectroscopy and elemental analysis.
TPQIrꢀHT, mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET showed moderate thermal stability with
decomposition temperatures (ꢁT5%, corresponding to 5% weight loss) comparable to those of
TPQIr and mꢀCF3DPQIr (Fig. S1). As shown in Fig. 1, UV−vis absorption and
photoluminance (PL) spectra of TPQIr, TPQIrꢀHT, TPQIrꢀET, mꢀCF3DPQIr, mꢀCF3DPQIrꢀ
HT and mꢀCF3DPQIrꢀET measured at RT in CHCl3 solution (10ꢀ5 M) and in film state,
resemble the UVꢀvis absorption and PL spectrum of the parent Ir(III) complexes, TPQIr and
mꢀCF3DPQIr. The introduction of mCP and OXD groups on picolinic acid did not affect the
ground or emissive excited state energies of the Ir(III) complexes. The strong absorption
1
peaks at 300 and 350 nm can be assigned to the spinꢀallowed π−π* bands of the C^N
ligands. The lowꢀenergy broad bands between 430 and 560 nm were attributed to the metalꢀ
3
toꢀligand charge transfer excitations, 1MLCT and MLCT, representing the strong spinꢀorbit
coupling effects induced by the heavy metal center. Upon irradiation, TPQIrꢀHT emitted
bright red light at the maximum PL (PLmax) of 612 nm, which was slightly red shifted from
TPQIr and TPQIrꢀET (Fig. 1a). Also mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET emitted bright
orange light at the PLmax of 567ꢀ568 nm, which was slightly red shifted from mꢀCF3DPQIr
(Fig. 1b). Thermal, photophysical and electrochemical properties of the new Ir(III) complexes
are presented in Table 1.
The PL quantum yield (ΦPL) of TPQIrꢀHT, mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET were
measured in degassed CHCl3 solution at RT using Ir(pic)2(acac) (ΦPL = 0.20 in CHCl3) as
standard. TPQIrꢀHT exhibited ΦPL of 0.20, compared to 0.68 and 0.66 for mꢀCF3DPQIrꢀHT
and mꢀCF3DPQIrꢀET, respectively. CV analysis was carried out for TPQIrꢀHT, mꢀCF3DPQIrꢀ
HT and mꢀCF3DPQIrꢀET to find the highest occupied molecular orbital (HOMO) energy
level and the lowest unoccupied molecular orbital (LUMO) energy level. The experimental
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HOMO energies were ꢀ5.24, ꢀ5.41 and ꢀ5.42 eV and the LUMO were ꢀ3.29, ꢀ3.11 and ꢀ3.10
eV for TPQIrꢀHT, mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET (Fig. S2), respectively. Both the
HOMO and LUMO levels of TPQIrꢀHT were very close to the corresponding energy levels
of TPQIr and TPQIrꢀET.34 HOMO and LUMO of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET
were almost the same as the corresponding energy levels of mꢀCF3DPQIr30, indicating that
the introduction of either an carbazoleꢀbased HT or OXDꢀbased ET group on the ancillary
ligand did not greatly influence the frontier orbital energy levels of these Ir(III) complexes,
similar to their photophysical properties.
The density functional theory (DFT) analysis for Ir(III) complexes was performed with the
suite of Gaussian09 programs using B3LYP functional with 6ꢀ31G(d) basis set for C, H, N, O,
F, and S, and LANL2DZ for Ir atom.37 The HOMO electron density of TPQIrꢀHT was
majorly distributed over the Ir(III) metal and on the thiopheneꢀquinoline rings of TPQ, while
the LUMO was located on the phenylquinoline of TPQ (Fig. S3). This shows that MLCT
probably contributed to the transition properties. To clearly understand the spatial distribution
of the frontier molecular orbitals, the contour plots of HOMO to HOMOꢀ2 and LUMO to
LUMO+2 of mꢀCF3DPQIr, mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET are given in Fig. S4, Fig.
S5 and Fig. S6, respectively, and the calculated energies are summarized in Table S1. In
general, for the three orange Ir(III) complexes, the LUMOs were mainly located on picolinic
acid and the mꢀCF3DPQ main ligand. The HOMOs and HOMOꢀ1 of mꢀCF3DPQIr and mꢀ
CF3DPQIrꢀET were located largely on the metal center and the ꢀCF3 substituted phenyl ring
of the cyclometalating ligands. Conversely, the HOMO and HOMOꢀ1 of mꢀCF3DPQIrꢀHT
were located entirely on mCP, which reveals the intramolecular energy transfer from mCP to
the Ir(III) complex unit.33,36 Noticeably, the metal atom contributed HOMO and HOMOꢀ1 for
mꢀCF3DPQIr and mꢀCF3DPQIrꢀET (Fig. 4 and 6), whereas it contributed HOMOꢀ2 for mꢀ
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CF3DPQIrꢀHT. Hence, this in depth analysis of the molecular orbitals (HOMO to HOMOꢀ2
and LUMO to LUMO+2) implies the MLCT character of the transitions.
The electron and hole mobilities of TPQIrꢀHT were measured by using the spaceꢀcharge
limited current (SCLC)39 method with a device configuration of ITO/LiF (10 nm)/Ir(III)
complex (100 nm)/LiF (1 nm)/Al (100 nm) for the electronꢀonly device and an
ITO/PEDOT:PSS (40 nm)/Ir(III) complex (100 nm)/MoO3 (5 nm)/Al (100 nm) for the holeꢀ
only device. The electron and hole mobilities of TPQIr and TPQIrꢀET were also measured by
the same method (Table S2). The current density versus voltage (JꢀV2) plots for the devices
are shown in Fig. S7. The electron and hole mobilities of TPQIrꢀHT were 8.72 x 10ꢀ5 and
2.84 x 10ꢀ4 cm2/V s, respectively. This result clearly shows that tethering an mCP unit to the
Ir(III) complex not only improved the hole mobility but also the electron mobility, as
compared with TPQIr. The mobility results of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET also
followed the same trend of TPQIrꢀHT and TPQIrꢀET, i.e., the electron and hole mobilities of
mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET were 3.22 x 10ꢀ5 and 6.02 x 10ꢀ4 cm2/V s and 4.73 x
10ꢀ4 and 8.32 x 10ꢀ5 cm2/V s, respectively. S. ꢀW. Lin et al. reported that hole and electron
mobilities of mCP are in the order of 10ꢀ4 cm2/V s and also reported that mCP’s hole mobility
is higher than electron mobility.40 However, the carrier mobilities of TPQIr and mꢀCF3DPQIr
is lower compared to mCP. Thus by the attachment of mCPꢀbased HT unit, the carrier
mobilities of both electron and hole is improved.
In order to evaluate the PhOLEDs performance of TPQIrꢀHT as an emitter, we fabricated
deepꢀred PhOLEDs with a simple device structure containing a solutionꢀprocessed hole
injection layer (HIL) and EML (Fig. 2a). The device configuration adopted in this study was
an ITO/GraHIL/TCTA:TPBi:Ir(III) complex (10 wt %)/TmPyPB/LiF/Al, where TCTA:TPBi
acts as the mixed cohost for the EML. Here, GraHIL, a selfꢀorganized polymeric gradient
11

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HIL, composed of PEDOT:PSS and a perfluorinated oligomer with a low surface energy
tetrafluorethyleneꢀperfluoroꢀ3,6ꢀdioxaꢀ4ꢀmethylꢀ7ꢀocteneꢀsulfonic acid oligomer (PFI) in 2:1
weight ratio,41ꢀ43 was used as HIL. GraHIL has a gradient work function, which gradually
increases from ~4.8 to ~5.63 eV due to the selfꢀorganization of PFI. This phenomenon is very
important to realize an efficient hole injection into the EML by reducing the injection barrier
at the HIL/EML interface.41 Therefore, the deepꢀred PhOLEDs do not require an additional
layer for hole injection between HIL and EML. TmPyPB was used as ETL. We also
fabricated control devices using TPQIr and TPQIrꢀET as dopants to compare the effect of the
mCP group on the device performance.
As anticipated, GraHILꢀbased deepꢀred PhOLEDs showed better performance than did the
deepꢀred PhOLEDs, where PEDOT:PSS was used as HIL (Table 2 and Table S3), due to the
reduced injection barrier for the former one resulting in low Von. For instance, the turnꢀon
voltage (Von) of the GraHILꢀbased deepꢀred PhOLEDs was about 4.2 V, while the Von of the
PEDOT:PSSꢀbased deepꢀred PhOLEDs was in the range of 6.7ꢀ7.0 V (Fig. S8). Data of the
deepꢀred PhOLEDs containing PEDOT:PSS are provided in Table S3. Fig. 2b and 2c shows
the current densityꢀvoltageꢀluminance (JꢀVꢀL) and current efficiencyꢀJꢀpower efficiency (CEꢀ
JꢀPE) characteristics of the deepꢀred PhOLEDs using GraHIL. The CE and PE of the
optimized deepꢀred PhOLED of TPQIrꢀHT were 15.87 cd/A and 5.05 lm/W, respectively,
which were higher than those of CE (11.53 cd/A) and PE (4.26 lm/W) of TPQIr. Similarly,
the deepꢀred PhOLED of TPQIrꢀHT exhibited a maximum EQE of 17.47%, compared to
13.70% for TPQIr (Fig. 3a). This is one of the best EQEs reported for solutionꢀprocessed
red/deepꢀred PhOLEDs (see Table S4, which summarizes the reported device performances).
The high hole and electron mobility of TPQIrꢀHT relative to TPQIr resulted in good charge
balance in EML, which enhanced the performance of TPQIrꢀHT in PhOLEDs. However, the
12

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deepꢀred PhOLED of TPQIrꢀET showed better performance (EQE: 21.48%) than did TPQIrꢀ
HT in the similar device structure. Mobility study revealed that TPQIrꢀETꢀbased deepꢀred
PhOLED had better electron mobility than hole mobility, which was reversed from the case
of the TPQIrꢀHTꢀbased device. Actually, the mobility of electronꢀcarriers is several orders of
magnitude lower than that of holeꢀcarriers in organic materials.44 Therefore, the introduction
of the ET group into the Ir(III) complex enhanced the mobility of the low mobile electron
carriers, and thus balanced the injected charge carriers in the EML.
The orange PhOLEDs exhibited a similar trend to the deepꢀred PhOLEDs as shown in
Table
3.
The
device
configuration
adopted
in
this
study
was
ITO/PEDOT:PSS/TAPC:26DCzPPy:Ir(III) complex (10 wt%)/TmPyPB/LiF/Al, where
TAPC:26DCzPPy acts as the mixed cohost for the EML. We also fabricated a control device
using mꢀCF3DPQIr as the dopant to compare the effect of mCP and OXD groups on device
performance.
The JꢀVꢀL and CEꢀJꢀPE characteristics of the orange PhOLEDs doped with mꢀCF3DPQIrꢀ
HT and mꢀCF3DPQIrꢀET are summarized in Fig. 2e and 2f. The CE and PE of the optimized
orange PhOLEDs of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET were 52.16 cd/A and 24.56 lm/W
and 46.59 cd/A and 21.03 lm/W, respectively, which were higher than those of the CE (44.23
cd/A) and PE (19.85 lm/W) of mꢀCF3DPQIr. Also, the orange PhOLEDs of mꢀCF3DPQIrꢀHT
and mꢀCF3DPQIrꢀET exhibited maximum EQEs of 21.61 and 18.39%, compared to 17.34%
for mꢀCF3DPQIr (Fig. 3d). This is one of the highest EQEs reported for solutionꢀprocessed
orange PhOLEDs (see Table S5, which summarizes the reported device performances). The
improvement in performance of the orange PhOLEDs of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀ
ET compared to the PhOLED of mꢀCF3DPQIr was attributed to the good charge balance in
EML.
13

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In addition, good solubility and thin film formability of the EML materials are also
important factors for the fabrication of high performance solutionꢀprocessed PhOLEDs.
Therefore, we analyzed the surface morphology of the EML films consisting of TPQIr,
TPQIrꢀHT, TPQIrꢀET, mꢀCF3DPQIr, mꢀCF3DPQIrꢀHT, and mꢀCF3DPQIrꢀET using atomic
force microscopy (AFM). The rootꢀmeanꢀsquare (RMS) surface roughness values were 0.30,
0.34, 0.40, 0.41, 0.40, and 0.43 nm for TPQIr, TPQIrꢀHT, TPQIrꢀET, mꢀCF3DPQIr, mꢀ
CF3DPQIrꢀHT, and mꢀCF3DPQIrꢀET, respectively (Fig. S9). This suggests that the thin film
formability of TPQIrꢀHT and mꢀCF3DPQIrꢀHT is better than that of TPQIrꢀET and mꢀ
CF3DPQIrꢀET, respectively, in EML due to the better solubility of the carbazole (mCP) than
the OXD moiety in chlorobenzene. The deepꢀred PhOLEDs, irrespective of the dopant, HIL
and luminance range, exhibited the same electroluminescence (EL) peak at 624 nm (Fig. 3b)
and the CIE coordinates of (0.67, 0.32) (Fig. 3c) representing the saturated deepꢀred emission,
which is highly sought after for deepꢀblue emission.
The CIE coordinates and the efficiency of TPQIrꢀHT were better than our previously
reported solutionꢀprocessed PhOLEDs containing phenylquinolineꢀbased deepꢀred emitting
heteroleptic Ir(III) complexes such as oꢀLIrtmd,30 (FPQ)2Ir(picꢀNꢀO)31 and (EOꢀCVzꢀ
PhQ)2Ir(acac).32 Similarly, the orange PhOLEDs exhibited the same EL peak at 575 nm (Fig.
3e) and the same CIE coordinates of (0.54, 0.46) (Fig. 3f), irrespective of the dopant and
luminance range.
4. Conclusion
In summary, we attached an mCPꢀbased HT unit and an OXDꢀbased ET unit to the
heteroleptic Ir(III) complexes, TPQIr and mꢀCF3DPQIr, to achieve a good charge balance in
EML by improving the HT and ET properties of TPQIrꢀHT, mꢀCF3DPQIrꢀHT and mꢀ
CF3DPQIrꢀET as compared with the parent Ir(III) complexes, TPQIr and mꢀCF3DPQIr. As a
14

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dopant, the new Ir(III) complex, TPQIrꢀHT, showed deepꢀred EL in solutionꢀprocessed
PhOLEDs. Introduction of the mCP moiety improved the carrier mobilities and device
performance relative to TPQIr, without affecting the deepꢀred CIE coordinates (0.67, 0.32).
We achieved a high EQE of 17.47% for the deepꢀred PhOLED of TPQIrꢀHT, which is
superior to the performance of TPQIr (EQE: 13.70%). As dopants, the new Ir(III) complexes,
mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET, also showed orange EL in solutionꢀprocessed
PhOLEDs. We achieved high EQEs of 21.64% and 18.39 % for the orange PhOLED of mꢀ
CF3DPQIrꢀHT and mꢀCF3DPQIrꢀET, respectively, which is higher than that of mꢀCF3DPQIr
(EQE: 17.34%). The overall results of these PhOLEDs with multiꢀfunctional Ir(III)
complexes show that the introduction of new functional units (HT/ET) is an effective method
to improve the device performance.
Acknowledgment
W. Cho and G. Sarada contributed equally to this work. This work was supported by the
Pioneer Research Center Program through the National Research Foundation of Korea
funded by the Ministry of Science, ICT & Future Planning (MSIP) of Korea (NRFꢀ
2013M3C1A3065522).
References
1. T. Qin, J. Ding, M. Baumgarten, L. Wang and K. Mullen, Macromol. Rapid
Commun., 2012, 33, 1036.
2. C.ꢀL. Ho, H. Li and W.ꢀY. Wong, J. Organomet. Chem., 2014, 751, 261.
3. X. Xu, X. Yang, J. Zhao, G. Zhou and W.ꢀY. Wong, Asian J. Org. Chem. 2015, 4,
394.
15

Journal of Materials Chemistry C
Page 16 of 28
View Article Online
DOI: 10.1039/C7TC02557B
4. X. Dai, Z. Zhang, Y. Jin, Y. Niu, H. Cao, X. Liang, L. Chen, J. Wang and X. Peng,
Nature, 2014, 515, 96.
5. J. Ding, J. Lu, Y. Cheng, Z. Xie, L. Wang, X. Jing and F. Wang, Adv. Funct. Mater.,
2008, 18, 2754.
6. Y. You, S. Y. Park, Dalton Trans., 2009, 1267.
7. G. J. Hedley, A. Ruseckas, I. D.W. Samuel, Chem. Phys. Lett., 2008, 450, 292.
8. R. Wang, D. Liu, R. Zhang, L. Deng and J. Li, J. Mater. Chem., 2012, 22, 1411.
9. Y.ꢀL. Deng, L.ꢀS. Cui, Y. Liu, Z.ꢀK. Wang, Z.ꢀQ. Jiang and L.ꢀS. Liao, J. Mater.
Chem. C, 2016, 4, 1250.
10. S. Cao, L. Hao, W.ꢀY. Lai, H. Zhang, Z. Yu, X. Zhang, X. Liu and W. Huang, J.
Mater. Chem. C, 2016, DOI: 10.1039/c6tc00856a.
11. M. Zhu, Y. Li, S. Hu, C. Li, C. Yang, H. Wu, J. Qin and Y. Cao, Chem. Commun.,
2012, 48, 2695.
12. B. Jiang, Y. Gu, J. Qin, X. Ning, S. Gong, G. Xie and C. Yang, J. Mater. Chem. C,
2016, 4, 3492.
13. X. Liu, B. Yao, Z. Zhang, X. Zhao, B. Zhang, W.ꢀY. Wong, Y. Cheng and Z. Xie, J.
Mater. Chem. C, 2016, 4, 5787.
14. G. Li, Y. Feng, T. Peng, K. Ye, Y. Liu and Y. Wang, J. Mater. Chem. C, 2015, 3,
1452.
15. G. Li, D. Zhu, T. Peng, Y. Liu, Y. Wang and M. R. Bryee, Adv. Funct. Mater., 2014,
24, 7420.
16. R. Wang, D. Liu, H. Ren, T. Zhang, H. Yin, G. Liu and J. Li, Adv. Mater., 2011, 23,
2823.
17. H.ꢀH. Chou, Y.ꢀK. Li, Y.ꢀH. Chen, C.ꢀC. Chang, C.ꢀY. Liao and C.ꢀH. Cheng, ACS
16

Page 17 of 28
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C7TC02557B
Appl. Mater. Interfaces, 2013, 5, 6168.
18. H. Fukagawa, T. Shimizu, H. Hanashima, Y. Osada, M. Suzuki, H. Fujikake, Adv.
Mater., 2012, 24, 5099.
19. K.ꢀH. Kim, J.ꢀL. Liao, S. W. Lee, B. Sim, C.ꢀK. Moon, G.ꢀH. Lee, H. J. Kim, Y. Chi,
J.ꢀJ. Kim, Adv. Mater., 2016, 28, 2526.
20. M.ꢀC. Tang, C. K.ꢀM. Chan, D. P.ꢀK. Tsang, Y.ꢀC. Wong, M. M.ꢀY. Chan, K. M.ꢀC.
Wong and V. W.ꢀW. Yam, Chem. Eur. J, 2014, 20, 15233.
21. X. Yang, X. Xu, J. Zhao, J. Dang, Z. Huang, X. Yan, G. Zhou and D. Wang, Inorg.
Chem., 2014, 53, 12986.
22. 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.
23. S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K. Watzer, B. Lussem and K. Leo,
Nature, 2009, 459, 234.
24. C. Fan, L. Zhu, B. Jiang, Y. Li, F. Zhao, D. Ma, J. Qin and C. Yang, J. Phys. Chem.
C, 2013, 117, 19134.
25. C.ꢀC. Chen, H.ꢀY. Lin, C.ꢀH. Li, J.ꢀH. Wu, Z.ꢀY. Yu, L.ꢀL. Lee, M.ꢀS. Jeng, C.ꢀC.
Lin, J.ꢀH. Jou and H.ꢀC. Kuo, Int. J. Photoenergy, 2014, 6. article ID 851371.
26. H. Wu, G. Zhou, J. Zou, C. ꢀL. Ho, W. ꢀY. Wong, W. Yang, J. Peng and Y. Cao, Adv.
Mater., 2009, 21, 4181.
27. B. Zhang, G. Tan, C. ꢀS. Lam, B. Yao, C. ꢀLam. Ho, L. Liu, Z. Xie, W. ꢀY. Wong, J.
Ding and L. Wang, Adv. Mater., 2012, 24, 1873.
28. M. Zhu, Y. Li, B. Jiang, S. Gong, H. Wu, J. Qin, Y. Cao and C. Yang, Org. Electron.,
2015, 26, 400.
29. X. Liu, S. Wang, B. Yao, B. Zhang, C.ꢀL. Ho, W.ꢀY. Wong, Y. Cheng and Z. Xie
17

Journal of Materials Chemistry C
Page 18 of 28
View Article Online
DOI: 10.1039/C7TC02557B
Org. Electron., 2015, 21, 1.
30. G. Sarada, J. Yoon, W. Cho, M. Cho, D. W. Cho, S. O. Kang, Y. Nam, J. Y. Lee and
S.ꢀH. Jin, J. Mater. Chem. C, 2016, 4, 113.
31. 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.
32. 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.
33. T. Giridhar, T.ꢀH. Han, W. Cho, C. Saravanan, T.ꢀW. Lee and S.ꢀH. Jin, Chem. –Eur.
J., 2014, 20, 8260.
34. T. Giridhar, C. Saravanan, W. Cho, Y. G. Park, J. Y. Lee and S.ꢀH. Jin, Chem.
Commun., 2014, 50, 4000.
35. T.ꢀH. Kwon, M. K. Kim, J. Kwon, D.ꢀY. Shin, S. J. Park, C.ꢀL. Lee, J.ꢀJ. Kim and J.ꢀI.
Hong, Chem. Mater., 2007, 19. 3673.
36. Z. Si, J. Li, B. Li, F. Zhao, S. Liu and W. Li, Inorg. Chem., 2007, 46, 6155.
37. M. J. Frisch, et al., Al, Gaussian 09, Revision A. 1, Gaussian Inc, Wallingford, CT,
2009.
38. C. Yao, J. Li, J. Wang, X. Xu, R. Liu, L. Li, J. Mater. Chem. C, 2015, 3, 8675.
39. C. ꢀG. Zhen, Y. ꢀF. Dai, W. ꢀJ. Zeng, Z. Ma, Z. ꢀK. Chen, J. Kieffer, Adv. Funct.
Mater., 2011, 21, 699.
40. J.ꢀH. Jou, W.ꢀB. Wang, S.ꢀZ. Chen, J.ꢀJ. Shyue, M.ꢀF. Hsu, C.ꢀW. Lin, S.ꢀM. Shen,
C.ꢀJ. Wang, C.ꢀP. Liu, C.ꢀT. Chen, M.ꢀF. Wu and S.ꢀW. Liu, J. Mater. Chem., 2010,
20, 8411.
41. T. ꢀW. Lee, Y. Chung, O. Kwon, J. ꢀJ. Park, Adv. Funct. Mater., 2007, 17, 390.
18

Page 19 of 28
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C7TC02557B
42. T. ꢀH. Han, M. ꢀR. Choi, S. ꢀY. Woo, S. ꢀY. Min, C. ꢀL. Lee, T. ꢀW. Lee, Adv. Mater.,
2012, 24, 1487.
43. T. ꢀH. Han, Y. Lee, M. ꢀR. Choi, S. ꢀH. Woo, S. ꢀH. Bae, B. H. Hong, J. ꢀH. Ahn, T. ꢀ
W. Lee, Nat. Photonics, 2012, 6, 105.
44. H. Yersin, Highly efficient OLEDs with Phosphorescent Materials, WILEYꢀVCH
Verlag GmbH & Co., 2008, p. 395.
N
O
O
N
N
N
O
N
N
O
O
N
N
O
N
Ir
Ir
Ir
O
N
S
O
S
S
O
2
2
2
TPQIr-ET
TPQIr
TPQIr-HT
Present work
Our previous work
19

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N
N
O
N
N
N
O
N
N
O
N
N
N
O
O
Ir
Ir
O
Ir
O
O
O
2
F3C
F3C
2
F3C
2
m-CF3DPQIr
Our previous work
m-CF3DPQIr-HT
m-CF3DPQIr-ET
Present work
Scheme 1. Molecular structures of TPQIrꢀHT, TPQIr, TPQIrꢀET, mꢀCF3DPQIrꢀHT, mꢀ
CF3DPQIrꢀET, and mꢀCF3DPQIr.
20

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O
O
NH2
IrCl3.3H2O
DPP, m-Cresol
140 oC, 12h
N
S
2-Ethoxyethanol/H2O (3:1)
140 oC, 20 h
S
TPQ
2-Ethoxyethanol
rt, 12 h, K2CO3
Cl
S
Cl
Cl
N
N
O
Ir
N
Ir
Ir
O
OH
N
N
O
S
S
2
2
Cl
2
TPQIr-Cl
N
DMF, 80 o
12 h, K2CO3
C
N
O
HO
O
N
N
N
Ir
N
S
O
2
mCPCH2OH
TPQIr-HT
H
N
HO
NaBH4
O
N
N
N
N
N
POCl3
N
Br
Br
CuI, K3PO4
1,2 trans cyclohexane
Dioxane, 105 oC
DMF, rt-130 o
C
EtOH, CH2Cl2
rt
mCPCH2OH
1
2
Scheme 2. Synthetic route of TPQIrꢀHT.
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O
O
IrCl3.H2O
Dpp, m-cresol
Cl
N
N
N
Ir
Ir
NH2
2-Ethoxyethanol:water (3:1)
140 °C, 20 h
140 °C, 12 h
CF3
3
Cl
CF3
F3C
4
2
F3C
2
6
5
N
2-Ethoxyethanol,
rt, 12 h, Na2CO3
HO
OH
O
Br
N
N
O
O
O
O
N
OH
N
N
O
N
Ir
N
mCPCH2Br
Ir
F3C
Cs2CO3, acetone,
Reflux
F3C
m-CF3DPQIr-OH
2
N
2
m-CF3DPQIr-HT
Cs2CO3, acetone,
Reflux
Br
O
N
N
OXDCH2Br
O
O
N
O
N
Ir
O
N
F3C
N
2
m-CF3DPQIr-ET
Scheme 3. Synthetic route of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET.
22

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1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
TPQIr
TPQIr-HT / solution
TPQIr-ET / solution
TPQIr
TPQIr-HT / film
TPQIr-ET / film
/ solution
(a)
1.0
0.8
0.6
0.4
0.2
0.0
/ film
300
400
500
600
700
800
Wavelength (nm)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
m
-CF3DPQIr
/ sol
(b)
m
m
m
m
m
-CF3DPQIr-HT / sol
-CF3DPQIr-ET / sol
-CF3DPQIr
/ film
-CF3DPQIr-HT / film
-CF3DPQIr-ET / film
300
400
500
600
700
800
Wavelength (nm)
Fig. 1 (a) UVꢀvisible absorption and PL spectra of TPQIrꢀHT in comparison with TPQIr and
TPQIrꢀET and (b) UVꢀvisible absorption and PL spectra of mꢀCF3DPQIrꢀHT, mꢀCF3DPQIrꢀ
ET in comparison with mꢀCF3DPQIr.
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(d)
(a)
104
105
104
103
102
101
300
500
,
,
,
m
m
m
-CF3DPQIr
,
,
,
TPQIr
TPQIr-HT
TPQIr-ET
-CF3DPQIr-HT
-CF3DPQIr-ET
250
200
150
100
50
400
300
200
100
0
103
102
101
100
(b)
(e)
100
14
0
0
2
4
6
8
10
12
14
0
2
4
6
8
10
12
Voltage (V)
Voltage (V)
60
40
20
0
60
30
25
20
15
10
5
30
,
,
,
m-CF3DPQIr
(f)
(c)
,
,
,
TPQIr
TPQIr-HT
TPQIr-ET
m-CF3DPQIr-HT
-CF3DPQIr-ET
25
20
15
10
5
40
20
0
m
0
0
-20
-20
-5
-5
0
40
80
120
160
200
240
0
30
60
90
120
150
Current density (mA/cm2)
Current density (mA/cm2)
Fig. 2. (a) Energy level diagram, (b) JꢀVꢀL characteristics, and (c) CEꢀJꢀPE of TPQIrꢀHT in
comparison with TPQIr and TPQIrꢀET and (d) energy level diagram, (e) JꢀVꢀL characteristics,
and (f) CEꢀJꢀPE of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET in comparison with mꢀCF3DPQIr.
24

Page 25 of 28
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C7TC02557B
30
25
20
15
10
5
25
TPQIr
TPQIr-HT
TPQIr-ET
(d)
m
m
m
-CF3DPQIr
(a)
-CF3DPQIr-HT
-CF3DPQIr-ET
20
15
10
5
0
0
0
500 1000 1500 2000 2500 3000
Luminance (cd/m2)
0
2000 4000 6000 8000 10000 12000
Luminance (cd/m2)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
TPQIr
TPQIr-HT
TPQIr-ET
m
m
m
-CF3DPQIr
(b)
(e)
1.0
0.8
0.6
0.4
0.2
0.0
-CF3DPQIr-HT
-CF3DPQIr-ET
At 30 mA/cm2
500
At 30 mA/cm2
500
400
600
700
800
400
600
Wavelength (nm)
700
800
Wavelength (nm)
(c)
(f)
Fig. 3 (a) EQE vs. luminance, (b) EL spectra, and (c) CIE coordinates (at 30 mA/cm2) of
TPQIrꢀHT in comparison with TPQIr and TPQIrꢀET and (d) EQE vs. luminance, (e) EL
spectra, and (f) CIE coordinates (at 30 mA/cm2) of mꢀCF3DPQIrꢀHT and mꢀCF3DPQIrꢀET in
comparison with mꢀCF3DPQIr.
25

Journal of Materials Chemistry C
Page 26 of 28
Table 1. Thermal, photophysical and electrochemical data of Ir(III) complexes.
a
b
c
d
e
Td
λabs
λem
λem
ΦPL
HOMO/LUMOf
(eV)
Egg
(eV)
1.95
1.93
1.96
2.13
2.13
2.14
Ir(III) complex
(oC)
338
327
350
362
320
321
(nm)
(nm)
610
612
610
566
568
567
(nm)
625
626
625
583
584
583
(%)
0.22
0.18
0.20
0.65
0.68
TPQIr
302, 350, 480
295, 344, 473
299, 349, 480
274, 340, 455
280, 339, 457
281, 341, 453
ꢀ5.23/ꢀ3.24
ꢀ5.24/ꢀ3.29
ꢀ5.25/ꢀ3.27
ꢀ5.39/ꢀ3.11
ꢀ5.41/ꢀ3.11
ꢀ5.42/ꢀ3.10
TPQIrꢀHT
TPQIrꢀET
mꢀCF3DPQIr
mꢀCF3DPQIrꢀHT
mꢀCF3DPQIrꢀET
0.66
a
o
b
Temperature with 5% mass loss measured by TGA with a heating rate of 10 C/min under N2. Measured in CHCl3 solution at 1.0 x 10ꢀ5 M
c
d
concentration. Maximum emission wavelength measured in CHCl3 solution at 1.0 x 10ꢀ5 M concentration. Maximum emission wavelength
measured in a film state. e Measured in 1.0 x 10ꢀ5 M CHCl3 solution relative to Ir(piq)2(acac) (ΦPL = 0.20) with 420 nm excitation. f Determined
from the onset of CV oxidation and reduction calculated HOMO and LUMO level. g Optical band gap determined from the film state of UVꢀvis
absorption edge value.
26

Page 27 of 28
Journal of Materials Chemistry C
Table 2. Device performances of deepꢀred PhOLEDs with Ir(III) complexes.
Doping concentration
Dopant
Turn ona
(V)
EQEb
(%)
CEb
(cd/A)
11.51
14.04
17.44
11.53
15.87
19.70
10.70
13.68
15.99
PEb
(lm/W)
4.02
4.41
5.17
4.26
5.05
5.62
3.96
4.60
5.08
Luminanceb
(cd/m2)
1907
CIE at 100 cd/m2
(x, y)
(%)
8
TPQIr
TPQIrꢀHT
TPQIrꢀET
TPQIr
4.28
4.31
4.35
4.27
4.28
4.25
4.22
4.34
4.28
11.89
14.20
18.38
13.70
17.47
21.48
11.52
14.51
17.63
(0.67, 0.32)
(0.67, 0.32)
(0.67, 0.32)
(0.67, 0.32)
(0.67, 0.32)
(0.67, 0.32)
(0.67, 0.32)
(0.67, 0.32)
(0.67, 0.32)
8
1860
8
2092
10
10
10
12
12
12
2521
TPQIrꢀHT
TPQIrꢀET
TPQIr
1901
2345
2422
TPQIrꢀHT
TPQIrꢀET
2118
2355
a At 1 cd/m2. b Maximum efficiency.
27

Journal of Materials Chemistry C
Page 28 of 28
Table 3. Device performances of orange PhOLEDs with Ir(III) complexes.
Doping concentration
Dopant
Turn ona
(V)
EQEb
(%)
CEb
(cd/A)
41.16
44.89
42.51
44.23
52.16
46.59
40.57
48.36
44.83
PEb
(lm/W)
16.30
18.85
16.45
19.85
24.56
21.03
18.28
22.79
20.17
Luminanceb
(cd/m2)
10015
9132
CIE at 100 cd/m2
(x, y)
(wt%)
8
mꢀCF3DPQIr
mꢀCF3DPQIrꢀHT
mꢀCF3DPQIrꢀET
mꢀCF3DPQIr
4.52
4.58
4.56
4.54
4.63
4.55
4.60
4.69
4.61
15.73
17.52
16.68
17.34
21.64
18.39
16.17
19.53
17.71
(0.54, 0.46)
(0.54, 0.46)
(0.54, 0.46)
(0.54, 0.46)
(0.54, 0.46)
(0.54, 0.46)
(0.54, 0.46)
(0.54, 0.46)
(0.54, 0.46)
8
8
8780
10
10
10
12
12
12
10820
9137
mꢀCF3DPQIrꢀHT
mꢀCF3DPQIrꢀET
mꢀCF3DPQIr
9427
9464
mꢀCF3DPQIrꢀHT
mꢀCF3DPQIrꢀET
8924
8890
a At 1 cd/m2. b Maximum efficiency.
28