Dibenzothiophene dioxide-benzofuro carbazole based bipolar host material for yellow and red phosphorescent OLEDs

Article abstract of DOI:10.1016/j.dyepig.2020.108697

2-(12H-benzofuro[3,2-a]carbazol-12-yl)dibenzo[b,d]thiophene 5,5-dioxide (DBT-INFUR) is a bipolar host material for yellow and red phosphorescent OLEDs. DBT-INFUR was designed and synthesized between dibenzothiphene acceptor and benzofuro carbazole donor with a yield of 60percent. We constructed two different devices, namely a yellow and a red phosphorescent OLEDs, and we compared the device properties with reference 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP). DBT-INFUR based yellow phosphorescent OLED device exhibited maximum current and external quantum efficiencies of 41.07 cd/A and 16.5percent, respectively and which is better than that of reference CBP based similar device (27.66 cd A, 10.15percent). DBT-INFUR based red phosphorescent OLED (12.44percent) revealed higher efficiencies when compared to the reference (7.64percent) device. The bipolar DBT-INFUR showed excellent host properties with yellow and red phosphorescent devices.

Full text of DOI:10.1016/j.dyepig.2020.108697

Dyes and Pigments 182 (2020) 108697
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Dibenzothiophene dioxide-benzofuro carbazole based bipolar host material
for yellow and red phosphorescent OLEDs
,
,
Hee Jung Janga 1, Ramanaskanda Braveentha 1, Kanthasamy Raagulana, Seung Yu Choia,
Young Hee Parka, Su Bin Oha, Il-Ji Baeb, Bo Mi Kimc, Qiong Wud **, Miyoung Kimb ***, Kyu
,
,
,
*
Yun Chaia
a Division of Bio-Nanochemistry, College of Natural Sciences, Wonkwang University, Iksan City, Chonbuk, 570-749, Republic of Korea
b Nano-Convergence Research Center, Korea Electronics Technology Institute, Jeonju, Republic of Korea
c Department of Chemical Engineering, Wonkwang University, Iksan, 570-749, Republic of Korea
d Department of Chemistry and Chemical Engineering, Hebei Normal University for Nationalities, Chengde, 067-000, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
2-(12H-benzofuro[3,2-a]carbazol-12-yl)dibenzo[b,d]thiophene 5,5-dioxide (DBT-INFUR) is a bipolar host ma-
terial for yellow and red phosphorescent OLEDs. DBT-INFUR was designed and synthesized between dibenzo-
thiphene acceptor and benzofuro carbazole donor with a yield of 60%. We constructed two different devices,
namely a yellow and a red phosphorescent OLEDs, and we compared the device properties with reference 4,40-Bis
(N-carbazolyl)-1,10-biphenyl (CBP). DBT-INFUR based yellow phosphorescent OLED device exhibited maximum
current and external quantum efficiencies of 41.07 cd/A and 16.5%, respectively and which is better than that of
reference CBP based similar device (27.66 cd A, 10.15%). DBT-INFUR based red phosphorescent OLED (12.44%)
revealed higher efficiencies when compared to the reference (7.64%) device. The bipolar DBT-INFUR showed
excellent host properties with yellow and red phosphorescent devices.
Organic light emitting diodes
Benzofuro carbazole
Bipolar host
Dibenzothiophene dioxide
1. Introduction
complexes employed as dopant, so the third-generation metal free
fluorescent dopants were introduced, and which is known as thermally
Over the past few decades, organic optoelectronic devices have
developed rapidly in terms of both device fabrication techniques and
materials design. Especially, organic light emitting diodes (OLEDs) have
shown prominent growth in commercial markets in the form of televi-
sion, mobile phones and lighting sources [1,2]. OLEDs exhibited good
advantages, such as low power consumption, wide view angle, high
brightness, color purity and possibility of fabrication in various sub-
strates [3–5]. The first-generation OLEDs used only fluorescent dopants,
which expressed low internal quantum efficiency (IQE) of 25% with only
chance of singlet emission. The IQE of 100% were achieved first time
when a heavy metal based second generation dopant was employed.
Which metal-ligand complex helped to harvest both singlet and triplet
excitons through inter system crossing (ISC) mechanism. Phosphores-
cent OLEDs posses’ major disadvantages of expensive noble metal
activated delayed fluorescence (TADF) OLEDs. Metal free dopants
showed 100% IQEs with fluorescence emission through the mechanism
of reverse inter system crossing (RISC) [6–19].
Phosphorescent OLEDs received much attention due to its high color
purity and considerable device efficiencies. The emission layer of
phosphorescent OLEDs consists of host and dopant materials [20–22].
Host-dopant combination suppress the acute triplet exciton polaron
quenching, concentration quenching and triplet-triplet annihilation
[23–28]. Host materials are major energy suppliers to the dopant ma-
terial while maintaining the charge balance at emission layer [21].
There are three types of host materials have been identified, which are
hole transport type, electron transport type and bipolar host materials
[29–34]. Hole transporting (HT) host materials build with electron
donating carbazole and diphenylamine units. 4,40-Bis(N-carbazolyl)-1,
* Corresponding author.
** Corresponding author.
*** Corresponding author.
E-mail addresses: wuqiong9308@126.com (Q. Wu), miy1kim@keti.re.kr (M. Kim), geuyoon@wonkwang.ac.kr (K.Y. Chai).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.dyepig.2020.108697
Received 21 February 2020; Received in revised form 16 May 2020; Accepted 4 July 2020
Available online 20 July 2020
0143-7208/© 2020 Elsevier Ltd. All rights reserved.

H.J. Jang et al.
Dyes and Pigments 182 (2020) 108697
Scheme 1. Synthetic scheme of starting materials DBTO-Br and DBF-INFUR.
10-biphenyl (CBP), 1,3-Bis(N-carbazolyl)benzene (mCP) and 3,3-Di
(9H-carbazol-9-yl)biphenyl (mCBP) are well-known hole transporting
type host materials [11,35–44]. Bis[2-(diphenylphosphino)phenyl]
ether oxide (DPEPO), dibenzo[b,d]furan-2,8-diylbis(diphenylphosphine
oxide) (DBFPO) and 8-Hydroxyquinoline aluminum salt (Alq3) are
identified best electron transport type (ET) host materials for phospho-
rescent and TADF OLEDs [45–49]. Moreover, pure hydrocarbon-based
design strategy proposed in OLED applications. Especially, 9,90-spi-
robifluorene (SBF) based moieties were studies with certain modifica-
tions at substituent positions. which also showed better device
performances with red, green, and blue phosphorescent OLEDs [50,51].
The ET and HT type host materials showed several drawbacks, such
as low thermal stabilities, recombination occurs towards either electron
transport layer or hole transport layer and imbalanced charges at
emission layer [52,53]. Additionally, phosphorescence emitters show
longer excited lifetime, self-quenching, and triplet polaron quenching at
high concentration, which lead to poor electroluminescent perfor-
mances. To overcome these issues, bipolar host materials were identified
with both electron donating (p type) and electron withdrawing (n type)
moieties present in a single molecule. The bipolar host materials brought
an interesting feature, such as broad charge recombination zone, well
balanced holes and electrons, thermal stabilities and well-matched
frontier molecular orbital (FMO) energies with adjacent layers
[54–59]. Additionally, one of the most key factors for a host material is
triplet energy. Host material should own higher triplet energy than the
dopant material to prevent the energy flow back [60–62]. A suitable
molecular design can fulfill the demands in order to enhance the device
efficiencies [63]. In our previous work, we designed a bipolar molecule
2

H.J. Jang et al.
Dyes and Pigments 182 (2020) 108697
Scheme 2. Synthetic route of target bipolar material DBT-INFUR.
DBTO-IN/CAR between dibenzothiophene oxide acceptor and indolo-
carbazole donor. Green phosphorescent OLED device with
DBTO-IN/CAR as host revealed excellent current and external quantum
efficiencies of 51.98 cd/A and 19.03%, respectively [53].
1.39 (s, 12H).
2.3. Synthesis of 2-(2-nitrophenyl)dibenzo[b,d]furan (DBF-Ph-N)
In this work, we designed and synthesized dibenzothiophene oxide-
benzofuro carbazole based bipolar host material 2-(12H-benzofuro[3,2-
a]carbazol-12-yl)dibenzo[b,d]thiophene 5,5-dioxide (DBT-INFUR). The
synthetic methods are shown in Scheme 1 and Scheme 2. Two different
OLED devices were fabricated with yellow and red phosphorescent
dopants to investigate the device properties. Iridium(III) bis(4-(4-tert-
butylphenyl) thieno[3,2-c]pyridinato-N,C20) acetylacetonate (PO-01-
TB) and Bis[2-(3,5-dimethylphenyl)-4-methyl -quinoline](acetylace
tonate)iridium(III) (Ir(mphmq)2(acac)) were applied as yellow and red
phosphorescent, respectively. We can expect good device performances
from yellow and red phosphorescent devices when compare to the
reference CBP host material.
A mixture of 2-(dibenzo[b,d]furan-2-yl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (DBF-BOE, 6.5 g, 22.09 mmol), 1-bromo-2-nitrobenzene
(Ph-N-Br, 4.91 g, 24.30 mmol), catalyst (Pd(PPh3)4, 0.77 g, 0.66
mmol), 2 M K2CO3 (13.82 g, 100 mmol), deionized water (50 ml),
ethanol (30 ml) and toluene (100 ml) were refluxed at 110 �C for 8 h
while stirring. After completion of the reaction, mixture was work
worked up by using deionized water and dichloromethane. Organic
layers were dried and evaporated. The crude mixture was separated by
silica column chromatography (n-Hexane and dichloromethane) to
obtain 6 g of DBF-Ph-N.
Yield: 94%; Yellow solid; 1H NMR (500 MHz, CDCl3) δ 7.93–7.94 (d,
J ¼ 7.5 Hz, 1H), 7.88–7.90 (m, 2H), 7.58–7.66 (m, 3H), 7.46–7.54 (m,
3H), 7.34–7.39 (m, 2H).
2. Experimental details
2.4. Synthesis of 12H-benzofuro[3,2-a]carbazole (DBF-INFUR)
2.1. Synthesis of 2-bromodibenzothiophene 5,5-dioxide (DBTO-Br)
A mixture of 2-(2-nitrophenyl)dibenzo[b,d]furan (DBF-Ph-N, 6g,
20.76 mmol), triethyl phospite (P(OEt)3, 70 ml) and o-dichlorobenzene
(70 ml) was refluxed at 180 �C for 24 h under inert condition. After
completion of the reaction, reaction mixture was concentrated, and
crude mixture was separated by using silica column (n-Hexane and
dichloromethane).
A mixture of 2-bromodibenzothiophene (DBT-Br, 4.0 g, 15 mmol)
and acetic acid (AcOH, 200 ml) was refluxed at 60 �C for 30 min while
stirring in a two-neck round-bottom flask equipped with a condenser.
After 30 min, 30% of hydrogen peroxide (H2O2, 100 ml) was dropped to
the reaction mixture. The reaction mixture was stirred at 80 �C for a
further 2 h. Then, a white precipitate was filtered and washed with
deionized water several times and dried to obtain 3.8 g of the dried
product DBTO-Br.
Yield: 75%; Pale white solid; 1H NMR (500 MHz, CDCl3) δ 8.55 (S,
1H), 8.14–8.16 (d, J ¼ 8.5 Hz, 1H), 8.11–8.13 (d, J ¼ 8 Hz, 1H),
8.06–8.08 (d, J ¼ 8 Hz, 1H), 7.66–7.67 (d, J ¼ 8 Hz, 1H), 7.58–7.60 (d, J
¼ 8 Hz, 1H) 7.42–7.51 (m, 5H), 7.30–7.33 (t, J ¼ 7.5 Hz, 1H).
Yield: 85%; White solid; 1H NMR (500 MHz, CDCl3) δ 7.92 (S, 1H),
7.82–7.83 (d, J ¼ 8 Hz, 1H), 7.75–7.76 (d, J ¼ 8 Hz, 1H), 7.64–7.69 (m,
3H), 7.54–7.57 (t, J ¼ 7.5, 1H); 13C NMR (500 MHz, CDCl3) δ 138.1,
136.5, 134.1, 133.6, 133.3, 131.1, 130.3, 128.7, 125.0, 123.5, 122.4,
121.8.
2.5. Synthesis of 2-(12H-benzofuro[3,2-a]carbazol-12-yl)dibenzo[b,d]
thiophene 5,5-dioxide (DBT-INFUR)
A mixture of 2-bromodibenzothiophene 5,5-dioxide (DBTO-Br, 1.0
g, 3.38 mmol), 12H-benzofuro[3,2-a]carbazole (DBF-INFUR, 1.0 g,
3.88 mmol), Pd(OAc)2 (0.05 g, 0.20 mmol), 10% t-Bu3P in toluene (0.98
ml, 4.06 mmol), NaOtBu (1.0 g, 10.40 mmol) and 80 ml of anhydrous
toluene was added in a two-neck round-bottom flask equipped with a
condenser. The mixture refluxed at 110 �C for 18 h inert atmosphere
while stirring. The crude residues were separated by a silica column and
n-hexane- dichloromethane solvent system to obtain the target molecule
DBT-INFUR of 0.96g.
2.2. Synthesis of 2-(dibenzo[b,d]furan-2-yl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (DBF-BOE)
2-bromodibenzo[b,d]furan (DBF-Br, 5 g, 20.24 mmol) was vac-
uumed for 15 min in a 250 ml round bottom flask. Anhydrous THF of
150 ml was added under inner condition, and mixture was kept stirring
under À 78 �C for 30 min. Then n-BuLi (2.5 M, 12.5 ml) was injected drop
wisely, and mixture kept stirring under the same temperature. After 1 h,
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (BOE, 7.5 ml,
36.76 mmol) was added slowly, and the reaction mixture kept overnight
to brought room temperature. The work up was held three times by
using deionized water and dichloromethane. Organic layer was dried
over anhydrous MgSO4, filtered and concentrated through rotary
evaporator. A silica column with n-Hexane: dichloromethane solvent
system used to obtain 5 g of the DBTO-BOE.
Yield: 60%; Pale yellow solid; 1H NMR (500 MHz, CDCl3) δ
8.25–8.27 (d, J ¼ 8.5 Hz, 1H), 8.18–8.19 (d, J ¼ 7.5 Hz, 1H), 8.11–8.13
(d, J ¼ 8 Hz, 1H), 7.96 (s, 1H), 7.91–7.93 (m, 1H), 7.75–7.77 (d, J ¼ 7.5
Hz, 1H), 7.55–7.64 (m, 4H), 7.37–7.44 (m, 3H), 7.25–7.31 (m, 1H),
6.92–6.95 (t, J ¼ 7.5 Hz, 1H), 6.03–6.04 (d, J ¼ 8 Hz, 1H)); 13C NMR
(500 MHz, CDCl3) δ 156.7, 155.8, 144.8, 141.4, 138.4, 137.3, 135.4,
134.2, 134.0, 131.3, 130.6, 130.5, 126.3, 125.6, 124.5, 124.0, 122.8,
122.7, 122.5, 122.1, 121.8, 121.6, 120.0, 119.8, 119.6, 11.4, 109.9,
109.0, 105.8. MS (APCI) m/z: 472.28 for C30H17NO3S [(M þ H)þ]; MS
(TOF) m/z: 471.0929 for C30H17NO3S (471.0929); Anal. Calcd for
Yield: 84%; Colorless oil; 1H NMR (500 MHz, CDCl3) δ 8.45 (S, 1H),
7.96–7.97 (d, J ¼ 8.5 Hz, 1H), 7.92–7.94 (dd, J ¼ 8.5, 1.5 Hz, 1H),
7.55–7.57 (d, J ¼ 8.5 Hz, 2H), 7.43–7.46 (m, 1H), 7.33–7.36 (m, 1H),
3

H.J. Jang et al.
Dyes and Pigments 182 (2020) 108697
Table 1
Physical properties of DBT-INFUR.
HOST
Tma (oC)
Tdb (oC)
UV–Visc (nm)
PL maxd (nm)
HOMOe (eV)
LUMOf (eV)
Egg (eV)
3.26
ETh (eV)
2.71
DBT-INFUR
236
371
297, 327
341
460i
À 5.87
À 2.61
457j
a
Melting point.
b
Thermal decomposition temperature.
UV absorption wavelength in toluene.
Photoluminescent maximum emission in THF.
Highest occupied molecular orbital energy.
Lowest unoccupied molecular orbital energy.
Energy band gap.
c
d
e
f
g
h
i
Triplet energy.
Room temperature.
j
Low temperature.
Fig. 1. Differential scanning calorimetry and thermal gravimetric analysis of DBT-INFUR.
Fig. 2. UV–Vis absorption and photoluminescent spectra of DBT-INFUR.
C30H17NO3S (%): C, 76.42; H, 3.63; N, 2.97; O, 10.18; S, 6.80. Found: C,
75.32; H, 3.62; N, 3.05; O, 9.97; S, 6.51.
3. Results and discussion
The thermal properties of DBT-INFUR were studied by thermo
gravimetric analysis (TGA) and differential scanning calorimetry (DSC)
under nitrogen atmosphere with the heating rate of 10 �C per minute. All
4

H.J. Jang et al.
Dyes and Pigments 182 (2020) 108697
Fig. 3. Frontier molecular orbital distribution of DBT-INFUR.
observed at 297, 327 and 342 nm, respectively in toluene solvent. The
short wavelength absorption about 297 nm corresponding to
transition of benzofuro carbazole moiety. The weaker absorption at long
wavelength around 327 nm attributed to n– * transition. The band gap
Table 2
π– π*
Calculation data of DBT-INFUR.
Calculation data of DBT-INFUR
Optical properties
π
energy of 3.26 eV was observed and which is almost similar with that of
indolocarbazole based DBTO-IN/CAR molecule [51]. The charge trans-
fer absorption from the benzofuro carbazole to dibenzothiophene oxide
was noticed at 342 nm. The maximum photoluminescent emission was
found at 431 and 460 nm in toluene and THF solvents, respectively. The
low temperature (77K) photoluminescent emission was recorded at 457
nm, and the triplet energy was calculated as 2.71 eV. The triplet energy
in toluene was calculated as 2.53 eV. The triplet energy is one of the
important parameters for a device to prevent the energy flow back from
the dopant material. Thus, we believe DBT-INFUR will support a great
efficiency enhancement in yellow and red phosphorescent OLED
Electrochemical properties
T1 (eV)
2.929
S1 (eV)
3.086
ΔEst (eV)
HOMO (eV)
5.97
LUMO (eV)
2.93
Band gap (eV)
3.03
0.157
data are summarized in Table 1 and depicted in Fig. 1. The thermal
decomposition of our material was observed at 371 �C for a 10% weight
reduction, and the melting point was noticed at 236 �C. These properties
can help the morphological stabilities of the device.
The UV–vis absorption and photoluminescent spectra are depicted in
Fig. 2 and summarized in Table 1. The UV absorption peaks were
Fig. 4. Device structure of yellow and red phosphorescent OLEDs. (For interpretation of the references to color in this figure legend, the reader is referred to the Web
version of this article.)
5

H.J. Jang et al.
Dyes and Pigments 182 (2020) 108697
HOMO energy level, and which was À 2.61 eV (Table 1). To investigate
the molecular orbital distribution, we performed basic density func-
tional theory DFT with a basic set of 6-31G using a Gaussian 09 [47]. The
frontier molecular orbital distributions are depicted in Fig. 3. The LUMO
distribution noticed over the electron withdrawing dibenzothiophene
oxide moiety, while HOMO distribution was over the electron donating
benzofuro carbazole unit. The dihedral angle between donor and
acceptor was calculated as 64�. But we observed a small overlapping
over the aromatic ring in dibenzothiophene oxide moiety, and which
increases the energy difference between excited singlet and triplet states
(0.15 eV). The calculation data are summarized in Table 2.
Table 3
Device characteristics of DBT-INFUR based yellow and red phosphorescent
OLEDs compare with reference CBP.
Device
Reference CBP
(Yellow
DBT-INFUR
(Yellow
Reference
CBP (Red
device)
DBT-
characteristics
INFUR
(Red
device)
device)
device)
Turn-on
voltage (V)
Current
Efficiency
(cd/A)
5.5
6.0
6.0
5.5
27.66
41.07
8.73
15.49
Power
15.80
21.50
4.57
8.85
To investigate the electroluminescent properties of our bipolar host
material DBT-INFUR, various phosphorescent OLED devices were
fabricated with red and yellow phosphorescent dopants. The yellow and
red device structures were as follow: indium tin oxide (ITO) (150 nm)/
1,4,5,8,9,11-Hexaazatriphenylenehexacarbonitrile (HATCN) (7 nm)/
4,40-Cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine](TAPC)
(43 nm)/DBT-INFUR: 10 wt% Iridium(III) bis(4-(4-tert-butylphenyl)
thieno[3,2-c]pyridinato-N,C20) acetylacetonate (PO–O1) or Bis[2-(3,5-
dimethylphenyl)-4-methyl -quinoline](acetylace tonate)iridium(III) (Ir
(mphmq)2(acac)) (20 nm)//1,3,5-Tri(m-pyridin-3-ylphenyl)benzene
Efficiency
(lm/W)
EQE (%)
CIE (x,y)
10.15
16.50
7.64
12.44
0.48, 0.50
0.49, 0.48
0.63,0.35
0.64, 0.35
devices.
The highest occupied molecular orbital (HOMO) energy level was
obtained as À 5.87 eV and which was achieved using the AC2 photo-
electron spectrometer. The lowest unoccupied molecular orbital
(LUMO) energy was calculated by adding the band gap value to the
Fig. 5. Current density-voltage and luminescence-voltage of red and yellow phosphorescent OLEDs. (For interpretation of the references to color in this figure
legend, the reader is referred to the Web version of this article.)
6

H.J. Jang et al.
Dyes and Pigments 182 (2020) 108697
Fig. 6. External quantum efficiencies of yellow and red phosphorescent OLEDs. (For interpretation of the references to color in this figure legend, the reader is
referred to the Web version of this article.)
(TmPyPB) (35 nm)/8-Quinolinolato lithium (Liq) (1.5 nm)/Aluminum
(Al) (100 nm. ITO used for anode while cathode was Al, HATCN used as
hole injecting layer (HIL), Liq for the electron injecting layer (EIL) and
TAPC as the hole transporting layer (HTL) while TmPyPB employed as
electron transport layer (ETL). Yellow and red phosphorescent dopants
were PO-O1 and Ir(mphmq)2(acac), respectively. Both yellow and red
phosphorescent OLED properties were compared with reference 4,40-Bis
(N-carbazolyl)-1,10-biphenyl (CBP) material in a similar structure. The
device structures and energy diagrams are depicted in Fig. 4.
lm/W and 10.15%). The external quantum efficiencies of red phospho-
rescent OLEDs were 12.44 and 7.64% for DBT-INFUR and reference
CBP-based devices, respectively. DBT-INFUR bipolar host materials
reveled excellent device performances with both yellow and red phos-
phorescent OLEDs while compare to the reference CBP- based similar
devices. DBT-INFUR is a potential host candidate to enhance the effi-
ciencies in yellow and red phosphorescent OLEDs.
Declaration of competing interest
The current density-voltage-luminescence performances of yellow
and red phosphorescent OLEDs are summarized in Table 3 and showed
in Figs. 5 and 6. Bipolar host DBT-INFUR based device showed higher
turn on voltage of 6 V when compared to reference device (5.5 V). But
the driving voltage of both devices were same as 7 V. The current effi-
ciency of yellow phosphorescent devices based on DBT-INFUR and CBP
was 41.07 and 27.66 cd/A, respectively. Moreover, power efficiency of
DBT-INFUR and CBP based yellow devices was 21.50 and 15.80 lm/W,
which explains that our bipolar material exhibited higher efficiencies
due its bipolar nature. The DBT-INFUR based yellow OLED devices
showed higher external quantum efficiencies of 16.50%, which is better
than that of reference device (10.15%). The red phosphorescent OLEDs
with DBT-INFUR revealed excellent device efficiencies of 15.49 cd/A
and 12.44% for current and external quantum efficiency, respectively.
The reference device with CBP host materials showed lower device
performances (8.73 cd/A and 7.64%).
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
CRediT authorship contribution statement
Hee Jung Jang: Methodology. Ramanaskanda Braveenth:
Conceptualization, Software, Investigation, Writing - original draft,
Writing - review & editing. Kanthasamy Raagulan: Data curation.
Seung Yu Choi: Methodology. Young Hee Park: Methodology. Su Bin
Oh: Software. Il-Ji Bae: Formal analysis, Data curation. Bo Mi Kim:
Resources, Funding acquisition. Qiong Wu: Investigation. Miyoung
Kim: Formal analysis. Kyu Yun Chai: Conceptualization, Resources,
Project administration, Funding acquisition.
Our bipolar host material DBT-INFUR exhibited excellent device
efficiencies with both yellow and red phosphorescent OLEDs. The bi-
polar nature of DBT-INFUR enhanced the device efficiencies while
maintain a proper charge balance at the emission layer. The CIE color
coordinates (x,y) were (0.49, 0.48) and (0.64, 0.35) for yellow and red
phosphorescent devices, respectively.
Acknowledgement
This research was supported by the Basic Science Research Program
through the National Research Foundation of Korea (NRF), funded by
the education (NRF-2016R1D1A3B01015531) and also this work was
supported by the National Research Foundation of Korea Grant funded
by the Korean Government (NRF-2017R1C1B5076425). Authors thank
Hebei Education Department Science Foundation (NO. QN2018313)
and Science Foundation of Hebei Normal University for Nationalities
(NO. 2018005) for their support.
4. Conclusion
A bipolar host material DBT-INFUR material was designed and syn-
thesized using a dibenzothiophene dioxide-benzofuro carbazole moi-
eties. Yellow phosphorescent OLEDs with our bipolar host material
exhibited excellent current, power and external quantum efficiencies of
41.07 cd/A, 21.50 lm/W and 16.50%, respectively. Which is much
higher than that of the CBP-based reference device (27.66 cd/A, 15.80
Appendix A. Supplementary data
Supplementary data related to this article can be found at https
://doi.org/10.1016/j.dyepig.2020.108697.
7

H.J. Jang et al.
Dyes and Pigments 182 (2020) 108697
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diodes doped with a red phosphorescent iridium complex. Appl Phys Lett 2002;80
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