Dibenzo[: B, d] furan and dibenzo [b, d] thiophene molecular dimers as hole blocking materials for high-efficiency and long-lived blue phosphorescent organic light-emitting diodes

Article abstract of DOI:10.1039/c9tc02689d

Novel hole blocking materials (HBMs) based on dibenzo[b,d]furan and dibenzo[b,d]thiophene molecular dimers have been rationally designed and synthesized for high-efficiency and long-lived blue phosphorescent organic light-emitting diodes (PhOLEDs). Therma

Full text of DOI:10.1039/c9tc02689d

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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
View Article Online
DOI: 10.1039/C9TC02689D
Journal of Materials Chemistry C
PAPER
Dibenzo[b,d]furan and Dibenzo[b,d]thiophene Molecular Dimers
as Hole Blocking Materials for High-Efficiency and Long-Lived Blue
Phosphorescent Organic Light-Emitting Diodes†
Received 00th January 20xx,
Accepted 00th January 20xx
Seokhoon Jang, Kyung Hyung Lee, Jun Yeob Lee and Youngu Lee *a
a
b
*b
DOI: 10.1039/x0xx00000x
Novel hole blocking materials (HBMs) based on dibenzo[b,d]furan and dibenzo[b,d]thiophene molecular dimers have been
www.rsc.org/
rationally designed and synthesized for high-efficiency and long-lived blue phosphorescent organic light-emitting diodes
(PhOLEDs). Thermal, optical, and electrochemical analyses show that [2,2 ′ -bidibenzo[b,d]furan]-6,6 ′ -
diylbis(diphenylphosphine oxide) (DBF-d-PO), [2,2′-bidibenzo[b,d]thiophene]-6,6′-diylbis(diphenylphosphine oxide) (DBT-d-
PO), 6,6′-di(pyridine-3-yl)-2,2′-bidibenzo[b,d]furan (DBF-d-Py), and 6,6′-di(pyridine-3-yl)-2,2′-bidibenzo[b,d]thiophene (DBT-
d-Py) possess high thermal stability, deep highest occupied molecular orbital energy levels (-6.61 –-6.95 eV), and high triplet
energy (E ) (2.68 – 2.95 eV). Blue PhOLEDs with DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py exhibit low turn-on and
T
operating voltages, excellent external quantum efficiency, and high current and power efficiencies. A blue PhOLED with DBF-
d-Py shows the best efficiency with a maximum external quantum efficiency of 24.3%, a maximum current efficiency of 44.3
-1
-1
cd A , and a maximum power efficiency of 46.4 lm W . In addition, it exhibits an outstanding external quantum efficiency
-2
-2
of 22.4% at a practical luminance of 1000 cd m and a very high maximum luminance of 88,953 cd m at 12 V. Furthermore,
blue PhOLEDs with DBF-d-Py and DBT-d-Py exhibit highly improved lifetimes compared with the conventional HBM, BmPyPB,
because of the efficient hole blocking by the deep HOMO energy level and the high thermal stability stabilizing hole blocking
layer morphology.
introduced between the EML and ETL to prevent the holes and
1
9-24
Introduction
triplet excitons from migrating into the ETL.
HBMs such as 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-
phenyl-4H-1,2,4-triazole (TAZ), 1,3-bis(3,5-dipyrid-3-yl-
phenyl)benzene (BmPyPB), and 1,3,5-tri(m-pyrid-2-yl-phenyl)-
Phosphorescent organic light-emitting diodes (PhOLEDs),
which can use both singlet and triplet excitons for
luminescence, have been widely applied in commercial and
research areas.1 Red and green PhOLEDs have satisfactory
efficiency and lifetime, but blue phosphorescent ones still do
2
5-27
benzene (TmPyPB), have been developed.
However, they
-7
possess low thermal stability; hence, they tend to undergo
phase transition during PhOLED driving, which is a great
obstacle to the development of the PhOLED with a long
8
-
not have an acceptable performance for commercialization.
1
3
One of the best ways to enhance the efficiency of blue
2
8-30
lifetime.
have recently been used as core molecular structures for
PhOLED materials because of their high E and excellent
Lee et al. reported HBMs
Dibenzo[b,d]furan and dibenzo[b,d]thiophene
PhOLEDs is to introduce a hole blocking layer (HBL) between
the emitting layer (EML) and the electron transporting layer
4-18
T
(
ETL).1
If the highest occupied molecular orbital (HOMO)
3
1-33
electron transporting ability.
energy level of the ETL is not sufficiently deeper than that of
the EML, the holes in the EML can be leaked into the ETL. In
addition, if the triplet energy (E ) of the ETL is lower than that
T
of the EML, the triplet excitons of the EML can be quenched by
the ETL. Therefore, the leakage of holes and triplet excitons
from the EML reduces device efficiency and lifetime. The HBL
based on 2,6-disubstituted dibenzo[b,d]furan and
dibenzo[b,d]thiophene for blue PhOLEDs, showing an external
quantum efficiency (ηext) of approximately 24%. However,
the long-term stability is not sufficient for practical blue
PhOLED devices. Therefore, HBMs with excellent device
stability and high efficiency must be developed.
Increasing the material stability while maintaining high
efficiency is a challenging task and requires a different
approach to the design of conventional PhOLED materials.
Therefore, designing molecules that satisfy thermal properties
1
9
T
with a deep HOMO energy level and high E needs to be
a. Department of Energy Science & Engineering, DGIST, 333, Techno Jungang-daero,
Hyeonpung-eup, Dalseong-gun, Daegu, 42988, Republic of Korea.
E-mail: youngulee@dgist.ac.kr; Tel: +82-53-785-6414; Fax: +82-53-785-6409
School of Chemical Engineering, Sungkyunkwan University, 2066, Seobu-ro,
Jangan-gu, Suwon-si, Gyeonggi-do, 16419, Republic of Korea.
E-mail: leej17@skku.edu
as well as HOMO energy levels and E
dimers consisting of two
dibenzo[b,d]thiophene molecules jointed by a covalent bond
can maximize thermal properties without a large E reduction.
is essential. Molecular
dibenzo[b,d]furan or
T
b.
†
Electronic
Supplementary
Information
(ESI)
available.
See
T
DOI:10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 2018
J. Mater. Chem. C, 2018, 00, 1-3 | 1
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Page 2 of 11
Paper
Journal of Materials of Chemistry C
View Article Online
DOI: 10.1039/C9TC02689D
Scheme 1 Synthetic routes of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py.
The incorporation of electron-withdrawing groups (EWGs) is
characteristics indicate that DBF-d-Py and DBT-d-Py with
pyridine EWGs have better electron mobility than DBF-d-PO
and DBT-d-PO with phosphine oxide EWGs. Blue PhOLEDs with
DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py as HBLs exhibit
low turn-on and operating voltages, excellent external
quantum efficiency, and high current and power efficiencies.
A blue PhOLED with DBF-d-Py shows the best efficiency with a
maximum external quantum efficiency (ηext,max) of 24.3%, a
essential
in
designing
dibenzo[b,d]furan
or
dibenzo[b,d]thiophene molecular dimers as effective HBMs.
For example, heteroaromatic segments containing a nitrogen
atom, such as pyridine, pyrimidine, triazole, and oxadiazole
3
4-38
have been used as EWGs.
By introducing these kinds of
EWGs, the HOMO energy level of HBMs can be deepened,
thereby effectively preventing hole diffusion from the EML to
the ETL. Moreover, electrons from the ETL can be easily
injected into the EML without the charge accumulation in the
HBL because of intermolecular interactions such as
-1
maximum current efficiency (ηce,max) of 44.3 cd A , and a
-1
maximum power efficiency (ηpe,max) of 46.4 lm W . It also
exhibits an outstanding ηext of 22.4% at a practical luminance
-2
intermolecular
hydrogen
bonds.
In
addition,
of 1000 cd m and a very high maximum luminance of 88,953
-2
diphenylphosphine oxide or diphenylsilyl groups can be
cd m at 12 V. Furthermore, blue PhOLEDs with DBF-d-Py and
DBT-d-Py exhibit a highly improved lifetime compared with the
conventional HBM, BmPyPB, with a pyridine electron
transport unit and a phenyl core structure.
introduced to increase the E
T
and the bandgap (E
g
) of the
by
HBMs.2
1,39-41
This can prevent the reduction of E
and E
T
g
disrupting the conjugation of aromatic molecules. However, if
the molecular conjugation breaks, the requirements for
energy levels can be achieved, but the charge mobility is
generally reduced.
Results and discussion
In this work, we design and synthesize novel HBMs based on
dibenzo[b,d]furan and dibenzo[b,d]thiophene molecular
We designed novel HBMs based on dibenzo[b,d]furan and
dibenzo[b,d]thiophene molecular dimers to achieve excellent
thermal stability and high E values. Two dibenzo[b,d]furan or
T
dibenzo[b,d]thiophene segments were connected through the
meta-positions of each segment to form molecular dimers.
Therefore, the thermal stability can be increased without
dimers,
[2,2
′
-bidibenzo[b,d]furan]-6,6
′
-
diylbis(diphenylphosphine oxide) (DBF-d-PO), [2,2 ′ -
bidibenzo[b,d]thiophene]-6,6
oxide) (DBT-d-PO), 6,6
′
-diylbis(diphenylphosphine
-di(pyridine-3-yl)-2,2 -
′
′
bidibenzo[b,d]furan (DBF-d-Py), and 6,6′-di(pyridine-3-yl)-2,2′-
bidibenzo[b,d]thiophene (DBT-d-Py), for blue PhOLEDs with
high-efficiencies and long lifetimes. We successfully
synthesized dimeric intermediates using dibenzo[b,d]furan
and dibenzo[b,d]thiophene segments and incorporated
pyridine and phosphine oxide functional groups as EWGs for
the HBMs. A computational simulation was used to investigate
decreasing E
introduced
T
. Pyridine and phosphine oxide EWGs were
into the dibenzo[b,d]furan and
dibenzo[b,d]thiophene dimers for deep HOMO energy levels
and excellent electron transporting properties.
Scheme 1 depicts the synthetic routes of DBF-d-PO, DBT-d-
PO,
DBF-d-Py,
and
DBT-d-Py.
First,
6-bromo-2-
iododibenzo[b,d]furan (compound 1) and 6-bromo-2-
iododibenzo[b,d]thiophene (compound 1′) were synthesized
the
optimal
structure,
orbital
distribution,
and
physicochemical properties of the HBMs. Thermal, optical, and
electrochemical analyses show that DBF-d-PO, DBT-d-PO, DBF-
d-Py, and DBT-d-Py possess high thermal stability, deep HOMO
from
bromodibenzo[b,d]thiophene.
bromodibenzo[b,d]furan-2-yl)-4,4,5,5-tetramethyl-1,3,2-
4-bromodibenzo[b,d]furan
and
4-
Subsequently,
2-(6-
T
energy levels (-6.61 – -6.95 eV), and high E (2.68 – 2.95 eV)
dioxaborolane
(compound
2)
and
2-(6-
values. Moreover, their electron-only device (EOD)
2
| J. Name., 2012, 00, 1-3
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Journal of Material Chemistry C
Paper
View Article Online
DOI: 10.1039/C9TC02689D
Fig. 1 Optimized molecular structures, HOMO and LUMO distributions, and calculated bandgaps of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py.
bromodibenzo[b,d]thiophene-2-yl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane) (compound 2 ′) were prepared through the
Miyaura borylation. Next, though the Suzuki reaction, 6,6 ′-
dibromo-2,2 ′ -bidibenzo[b,d]furan (compound 3) and 6,6 ′ -
dibromo-2,2 ′-bidibenzo[b,d]thiophene (compound 3 ′) were
synthesized by reacting compound 1 (or 1′) with compound 2
and DBT-d-PO with phosphine oxide EWGs. The LUMO
distributions of the phosphine oxide-based compounds were
completely blocked in the central dibenzo[b,d]furan and
dibenzo[b,d]thiophene dimers, but those of DBF-d-Py and
DBT-d-Py were greatly extended toward the pyridine EWGs.
The electron density of DBF-d-Py and DBT-d-Py was higher
than that of DBF-d-PO and DBT-d-PO; hence, the electron
transporting ability of DBF-d-Py and DBT-d-Py is expected to
be better than that of DBF-d-PO and DBT-d-PO.
Conventional OLEDs are fabricated by thermal vacuum
evaporation; thus, the thermal stability of the synthesized
HBMs must be investigated. In addition, when OLEDs are
driven, the change in thin film morphology caused by the
endothermic process is critical to the efficiency and lifetime of
the OLEDs. Therefore, OLED materials with high thermal
stability must be developed. Fig. 2, S12, and Table 1 show the
thermogravimetric analysis (TGA), differential scanning
calorimetry (DSC), and differential thermal analysis (DTA)
(or 2 ′). Two bromo functional groups of compound 3 and 3 ′
were substituted to diphenylphosphines. Finally, DBF-d-PO
and DBT-d-PO were successfully synthesized by oxidizing the
diphenylphosphines. DBF-d-Py and DBT-d-Py were synthesized
by reacting compound 3 and 3 ′ with pyridine-3-boronic acid
through the Suzuki reaction. All the synthesized compounds
were confirmed by gas chromatography - mass spectrometry
(GC-MS) and nuclear magnetic resonance (NMR) spectrometry.
DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py were highly
purified using a train sublimator.
The molecular calculations of DBF-d-PO, DBT-d-PO, DBF-d-Py,
and DBT-d-Py were conducted using the density functional
theory simulation based on Becke, three-parameter, Lee-
Yang-Parr (B3LYP) 6-31G* as a basis set. Fig. 1 depicts the
optimized molecular structure, HOMO and lowest unoccupied
molecular orbital (LUMO) distribution, and energy levels of
DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py. For DBF-d-PO
and DBF-d-Py, the dihedral angles between the two
d
results. The decomposition temperature (T ) values of DBF-d-
PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py were 484, 514, 380,
o
and 400 C, respectively. The DSC results showed that DBF-d-
PO and DBT-d-PO had high glass transition temperature (T
values of 142 and 162 C, respectively. The DTA measurement
g
)
o
results exhibited that DBF-d-Py and DBT-d-Py had T
g
values of
o
o
o
dibenzo[b,d]furan segments were 40.5
and 40.1 ,
134 and 135 C, respectively. Moreover, to investigate the
thermal stability and morphological durability against thermal
stress, an atomic force microscopy (AFM) study of HBM films
was performed. AFM images of DBF-d-PO, DBT-d-PO, DBF-d-
Py and DBT-d-Py films were measured before and after
respectively. For DBT-d-PO and DBT-d-Py, the dihedral angles
between the two dibenzo[b,d]thiophene segments were
o
equally calculated at 39.3 . Significant distortions between the
dibenzo[b,d]furan and dibenzo[b,d]thiophene molecular
dimers may result in a reduced degree of the effective
o
thermal annealing treatment (85 C, 24 h). As shown in Fig. S13
conjugation in the molecular orbital. Thus, the decrease of E
and E can be minimized while maximizing the thermal stability.
In addition, the dihedral angles of DBF-d-PO and DBF-d-Py
were larger than those of DBT-d-PO and DBT-d-Py, suggesting
g
and S14, before thermal annealing treatment, the root-mean-
square roughness (Rrms) values of DBF-d-PO, DBT-d-PO, DBF-d-
Py, and DBT-d-Py films were 0.274, 0.283, 0.302 and 0.287 nm,
respectively. After thermal annealing treatment for 24 h, the
T
E
g
and E
T
of DBF-d-PO and DBF-d-Py were higher than those of
Rrms values of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py
DBT-d-PO and DBT-d-Py. For DBF-d-Py and DBT-d-Py with two
pyridine EWGs, their HOMO distributions extended to
electron-deficient pyridine segments such that both
compounds had deeper HOMO energy levels than DBF-d-PO
films were 0.278, 0.288, 0.306, and 0.320 nm, respectively.
They showed a negligible change in their Rrms values before
and after thermal annealing treatment, indicating that they
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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Paper
Journal of Materials of Chemistry C
possess high thermal and morphological stability against heat.
Therefore, it is expected that DBF-d-PO, DBT-d-PO, DBF-d-Py,
View Article Online
DOI: 10.1039/C9TC02689D
Table 1 Physical properties of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py.
a/T
[oC]
λ
d
λ
e
λ
f
E
g
E
h
HOMO /LUMO
[eV]
i
j
T
d
g
max,abs
onset,abs
max,FL
g
T
HBMs
[nm]
[nm]
[nm]
[eV]
[eV]
DBF-d-PO
DBT-d-PO
DBF-d-Py
DBT-d-Py
484/142b
258
254
246
256
351
370
350
374
367
387
366
379
3.53
3.35
3.54
3.32
2.95
2.70
2.74
2.68
-6.75/-3.22
-6.61/-3.26
-6.95/-3.41
-6.71/-3.39
b
514/162
380/134
c
c
400/135
a
obtained from TGA. b obtained from DSC. c measured from DTA. measured from UV-vis absorption spectrum. e measured from the absorption onset in film.
d
f
measured from fluorescent emission spectrum. deduced from absorption onset in film. h estimated from phosphorescent spectrum. estimated from the LUMO energy
level and E
g
i
. j estimated from the reduction potential in CV.
g
Fig. 2 TGA traces of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py with a heating
o
-1
rate of 10 C min .
and DBT-d-Py can maintain a uniform and stable film
morphology during device operation.
The optical properties of DBF-d-PO, DBT-d-PO, DBF-d-Py, and
DBT-d-Py were investigated by UV-vis absorption
spectrometry and photoluminescence (PL) spectrometry. Fig.
3
displays their absorption and PL spectra. DBF-d-PO, DBT-d-
PO, DBF-d-Py, and DBT-d-Py showed major absorption bands
around 250 and 300 nm because of the π-π* transition. DBT-
d-PO and DBT-d-Py exhibited a long-wavelength absorption
tail because of the n-π* transition of the sulfur atom.1 The
9,42
g
E values of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py
were estimated as 3.53, 3.35, 3.54, and 3.32 eV, respectively
from their absorption spectra in film (Fig. S15). The maximum
fluorescent emission wavelengths of DBF-d-PO, DBT-d-PO,
DBF-d-Py, and DBT-d-Py were 367, 387, 366, and 379 nm,
respectively.
Fig. 3 (a) UV-vis absorption and fluorescence spectra in THF at room temperature
and (b) phosphorescence spectra in THF at 77 K.
E
T
values than DBF-d-Py and DBT-d-Py because the phosphine
oxide EWG completely broke the aromatic conjugation.
Interestingly, DBF-d-PO with the dibenzo[b,d]furan dimer and
phosphine oxide EWG showed the highest E compared with
T
T
The E values of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-
Py were determined by low temperature PL emission spectra
in tetrahydrofuran (THF) at 77 K. As shown in Fig. 3b, they
exhibited the highest energy sub-bands at 420 (DBF-d-PO), 459
those of DBT-d-PO, DBF-d-Py, and DBT-d-Py and was expected
to effectively suppress the triplet exciton leakage in the EML.
Cyclic voltammetry (CV) was performed using the ferrocene
(
DBT-d-PO), 452 (DBF-d-Py), and 462 nm (DBT-d-Py). The
corresponding E values were calculated as 2.95, 2.70, 2.74,
and 2.68 eV, respectively. This result clearly indicates that all
compounds possessed high E values suitable for blue
PhOLEDs. Moreover, DBF-d-PO and DBT-d-PO showed higher
+
couple (Fe/Fe ) as an internal standard to investigate the
T
HOMO and LUMO energy levels of DBF-d-PO, DBT-d-PO, DBF-
d-Py, and DBT-d-Py. Fig. S13 illustrates their reductive traces
on the CV measurements. The LUMO energy levels of HBMs
T
4
| J. Name., 2012, 00, 1-3
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Journal of Material Chemistry C
Paper
that the HOMO energy level of the host and the dopant
View Article Online
DOI: 10.1039/C9TC02689D
materials of the conventional blue PhOLEDs was below -6.0 eV,
the HOMO energy levels of DBF-d-PO, DBT-d-PO, DBF-d-Py,
and DBT-d-Py were deep. Thus, they were expected to
effectively confine the holes in the EML for highly efficient blue
PhOLEDs.
EODs were fabricated with the following device structure to
evaluate the electron transporting properties of DBF-d-PO,
DBT-d-PO, DBF-d-Py, and DBT-d-Py: ITO/Ca (5 nm)/HBMs (30
nm)/LiF (1 nm)/Al (150 nm). Fig. 4 displays traces of the current
density vs. voltage of the EODs. The electron transporting
properties of DBF-d-Py and DBT-d-Py were superior to those of
DBF-d-PO and DBT-d-PO because of the excellent
intermolecular interaction derived from the intermolecular
4
3-44
hydrogen bonds between the pyridine segments.
All
Fig. 4 Current density traces of EODs with DBF-d-PO, DBT-d-PO, DBF-d-Py, and
DBT-d-Py.
compounds exhibited high current densities up to a practical
voltage range; therefore, they are expected to easily transport
the electrons in OLED devices without electron accumulation.
Blue PhOLEDs were fabricated with the following device
structure to evaluate the performances of DBF-d-PO, DBT-d-
PO, DBF-d-Py, and DBT-d-Py as HBMs : ITO/ BPBPA:HATCN (40
nm, 30% co-evaporation of HATCN)/BPBPA (10 nm)/PCZAC (10
nm)/mCBPCN:oCBP:CNIr (30 nm, 50% and 10% doping of oCBP
and CNIr, respectively)/ DBF-d-PO (device 1, 5 nm), DBT-d-PO
were deduced though the reduction potential onset in the
cyclic voltammograms.
The HOMO energy levels of HBMs were calculated by their
LUMO energy levels and E
DBF-d-PO and DBT-d-PO exhibited the first reductive onset of
1.01 and -0.97 V, respectively, implying the LUMO energy
g
s. Table 1 lists the energy levels.
-
levels of DBF-d-PO and DBT-d-PO were -3.22 and -3.26 eV,
respectively. The first reductive onset of DBF-d-Py and DBT-d-
Py was shown at -0.82 and -0.84 V. The LUMO energy levels of
DBF-d-Py and DBT-d-Py were -3.41 and -3.39 eV, respectively.
The oxygen atom was more electronegative than the sulfur
atom; hence, DBF-d-PO and DBF-d-Py had deep HOMO energy
levels compared with DBT-d-PO and DBT-d-Py. Moreover, DBF-
d-Py and DBT-d-Py exhibited lower energy levels compared
with DBF-d-PO and DBT-d-PO because the pyridine EWG did
not block the π-conjugation, and the HOMO/LUMO
distributions were extended to the pyridine EWG. Considering
(device 2, 5 nm), DBF-d-Py (device 3, 5 nm), DBT-d-Py (device
4
, 5 nm), or BmPyPB (device 5, 5 nm)/ZADN (20 nm)/LiF (1
1
9
nm)/Al (200 nm). A mixed layer consisting of N,N,N ′ ,N ′ -
tetra[(1,1′-biphenyl)-4-yl]-(1,1′-biphenyl)-4,4′-diamine (BPBPA)
and 1, 4, 5, 8, 9, 11-hexaazatriphenylene hexacarbonitrile
(
HATCN) was used as a hole injecting layer. BPBPA was used as
an HTL.9,9-Dimethyl-10-(9-phenyl-9H-carbazol-3-yl)-9,10-
dihydroacridine (PCZAC) was introduced as an exciton blocking
4
5
layer. 9-(3′-(9H-Carbazole-9-yl)-5-cyano[1,1′-biphenyl]-3-yl)-
9
H-carbazole-3-carbonitrile (mCBPCN) and 9,9′-biphenyl-2,2′-
Fig. 5 Energy level diagrams, molecular structures, and device architecture of blue PhOLEDs.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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Page 6 of 11
Paper
Journal of Materials of Chemistry C
View Article Online
DOI: 10.1039/C9TC02689D
Fig. 6 (a) Current density and luminance traces vs. voltage, (b) external quantum efficiency traces vs. luminance, (c) current and power efficiency traces vs. luminance, and (d)
electroluminescence spectra of the blue PhOLEDs with DBF-d-PO, DBT-d-PO, DBF-d-Py, DBT-d-Py, and BmPyPB.
Table 2 EL performance of devices 1-5.
ona/V100b/V1000c
η
[%]
ext,100b/ηext,1000c/ηext,maxd
η
c,100 /ηc,1000c/ηc,max
b
d
η
p,100 /ηp,1000c/ηp,max
b
d
L
max
[cd m / V]
Device
HBM)
Device 1
DBF-d-PO)
Device 2
DBT-d-PO)
Device 3
DBF-d-Py)
Device 4
DBT-d-Py)
Device 5
BmPyPB)
V
[V]
-
1
-1
-2
(
[cd A ]
[lm W ]
3
3
3
3
3
.0/3.6/4.5
20.3/18.7/20.7
37.3/34.3/38.6
32.9/24.1/40.4
48,445 / 11.0
(
.0/3.7/4.8
.0/3.5/4.3
.0/3.5/4.5
.0/3.7/4.8
12.3/12.3/12.3
24.1/22.4/24.3
20.6/18.5/20.7
21.9/19.5/22.3
21.5/21.7/21.7
43.8/40.5/44.3
37.1/33.1/37.2
38.3/33.9/39.1
18.3/14.4/22.7
39.4/30.0/46.4
33.1/23.4/33.3
32.9/22.4/40.9
39,977 / 11.0
88,953 / 12.0
80,941 / 12.5
55,610 / 14.0
(
(
(
(
a
voltage at 1 cd m-2. b voltage, external quantum efficiency (ηext), current efficiency (η
) at 100 cd m-2. c voltage, ηext, η at 1000 cd m-2. d
p c p
), power efficiency (η , and η
c
maximum ηext, η , and η
c
p
.
diylbis-9H-carbazole (oCBP) were used as the EML host
materials. fac-Tris(1-(2,6-diisopropylphenyl)-2-(3-
structure and energy level diagrams of the materials used in
the OLED fabrication.
cyanophenyl)-1H-imidazolyl)iridium (III) (CNIr) was adopted as
a blue phosphorescent dopant. 2-[4-(9,10-Di-naphthalen-2-yl-
anthracene-2-yl)-phenyl]-1-phenyl-1H-benzimidazole (ZADN)
was used as an ETL. A blue PhOLED with a conventional
pyridine-based HBM (BmPyPB) was also fabricated as the
standard device (device 5). Fig. 5 depicts the chemical
Fig. 6 shows the current density and luminance vs. voltage,
η
ext, current efficiency (ηce), and power efficiency (ηpe) vs.
luminance, and electroluminescence (EL) spectra of the blue
PhOLEDs. Table 2 lists their device performances. Device 1 and
2 with DBF-d-PO and DBT-d-PO showed a similar current
density from 0 to 10 V. The turn-on voltage of devices 1 and 2
6
| J. Name., 2012, 00, 1-3
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Page 7 of 11
J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Journal of Material Chemistry C
Paper
PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py completely confined
View Article Online
DOI: 10.1039/C9TC02689D
the triplet excitons in the EML.
The device lifetime of the blue PhOLEDs was investigated by
-2
operating the devices at an initial luminance of 200 cd m . Fig.
shows the results. The lifetime characteristics such as T90
corresponding to the degradation time of 10% luminance loss)
7
(
and T50 (corresponding to the degradation time of 50%
luminance loss) of devices 1-4 were compared with those of
device 5 with BmPyPB. The T50 lifetime of devices 1 and 2 with
DBF-d-PO and DBT-d-PO was 72.2 h and 49.8 h, respectively.
This short lifetime may be due to the chemically unstable C-P
bond of the phosphine oxide segments in DBF-d-PO and DBT-
4
7
d-PO. However, The T90 lifetime of devices 3 and 4 with DBF-
d-Py and DBT-d-Py was 88.5 and 63.9 h, respectively. The half-
lifetime (T50) of devices 3 and 4 with DBF-d-Py and DBT-d-Py
was approximately 1070 h. On the contrary, device 5 with
BmPyPB initially exhibited steep luminance degradation. The
-2
Fig. 7 Lifetime test of devices 1-5 at an initial luminance of 200 cd m .
T
90 and T50 lifetimes of device 5 with BmPyPB were 27.8 and
with DBF-d-PO and DBT-d-PO was 3.0 V. The driving voltages
-2
429.5 h, respectively. This result clearly verified that the blue
PhOLEDs with DBF-d-Py and DBT-d-Py as HBMs showed a
highly enhanced lifetime compared with BmPyPB with an HBM.
The efficient hole blocking by the deep HOMO energy level
and the high thermal stability stabilizing HBL morphology can
be considered as major factors for the lifetime improvement
of devices 3 and 4 with DBF-d-Py and DBT-d-Py.
at 1000 cd m of devices 1 and 2 with DBF-d-PO and DBT-d-PO
were 4.5 and 4.8 V, respectively. These results clearly indicated
that DBF-d-PO and DBT-d-PO did not create any problems such
as electron trapping. However, the luminance of device 1 with
DBF-d-PO was higher than that of device 2 with DBT-d-PO.
Device 1 with DBF-d-PO showed a maximum external quantum
efficiency (ηext,max) of 20.7%, a maximum current efficiency
-1
(ηce,max) of 38.6 cd A , and a maximum power efficiency (ηpe,max)
-1
of 40.4 lm W , whereas device 2 with DBT-d-PO showed an
Conclusions
-
1
η
ext,max of 12.3%, an ηce,max of 21.7 cd A , and an ηpe,max of 22.7
-1
lm W . The efficiency of device 1 with DBF-d-PO was higher
than that of device 2 with DBT-d-PO. This result can be
In summary, we designed and synthesized herein four HBMs
based on dibenzo[b,d]furan and dibenzo[b,d]thiophene
molecular dimers, 2,2’-bidibenzo[b,d]furan and 2,2’-
bidibenzo[b,d]thiophene, (i.e. DBF-d-PO, DBT-d-PO, DBF-d-Py,
and DBT-d-Py) for high-efficiency and long-lived blue PhOLEDs.
We successfully synthesized dimeric intermediates using
dibenzo[b,d]furan and dibenzo[b,d]thiophene segments and
incorporated pyridine and phosphine oxide functional groups
as EWGs for HBMs. A computational simulation was used to
investigate the optimal structure, orbital distribution, and
physicochemical properties of the HBMs. Thermal, optical, and
electrochemical analyses showed that DBF-d-PO, DBT-d-PO,
DBF-d-Py, and DBT-d-Py possessed high thermal stability, deep
T
attributed to the high E and the deep HOMO energy level of
DBF-d-PO compared with DBT-d-PO.
Device 3 with DBF-d-Py showed the best efficiency with an
-
1
η
ext,max of 24.3%, an ηce,max of 44.3 cd A , and an ηpe,max of 46.4
-1
lm W , whereas device 4 with DBT-d-Py displayed an ηext,max of
0.7%, an ηce,max of 37.2 cd A , and an ηpe,max of 33.3 lm W-1.
-1
2
Note that the HBMs with pyridine EWGs exhibited higher
efficiency than the HBMs with phosphine oxide EWGs. This
result can be due to a significant increase in the electron
transporting property of the HBMs with pyridine EWGs
compared with the HBMs with phosphine oxide EWGs.
Furthermore, device 3 with DBF-d-Py exhibits an excellent ηext
T
HOMO energy levels (-6.61 – -6.95 eV), and high E (2.68 – 2.95
-2
of 22.4% at a practical luminance of 1000 cd m and a very
eV) values. Moreover, their EOD measurements indicated that
DBF-d-Py, and DBT-d-Py with pyridine EWGs had better
electron mobility than DBF-d-PO and DBT-d-PO with
phosphine oxide EWGs. The blue PhOLEDs with DBF-d-PO,
DBT-d-PO, DBF-d-Py, and DBT-d-Py as HBLs exhibited low turn-
on (3.0 V) and operating voltages (4.3 - 4.8 V), excellent
external quantum efficiency, and high current and power
efficiencies. A blue PhOLED with DBF-d-Py showed the best
efficiency with an ηext,max of 24.3%, an ηce,max of 44.3 cd A ,
and an ηpe,max of 46.4 lm W . It also exhibited an outstanding
ηext of 22.4% at a practical luminance of 1000 cd m and a very
high maximum luminance of 88,953 cd m at 12 V.
Furthermore, blue PhOLEDs with DBF-d-Py and DBT-d-Py
exhibited a highly improved lifetimes compared with the
conventional HBM, BmPyPB, with a pyridine electron
-2
high maximum luminance of 88,953 cd m at 12 V. In contrast,
the standard device 5 with BmPyPB showed an ηext of 19.5% at
-2
a practical luminance of 1000 cd m and a maximum
-2
luminance of 55,610 cd m at 14 V. This result confirmed that
device 3 with DBF-d-Py was far superior to device 5 with
BmPyPB in terms of driving voltage, luminance efficiency,
power efficiency, and maximum luminance. This result
confirmed that DBF-d-Py can successfully confine the holes in
the EML and suppress triplet quenching because of its deep
-1
-1
-2
HOMO energy level and high E
d, the EL spectra of devices 1-4 exhibited the same emission
peaks at 460 and 490 nm, which were consistent with the blue
T
. Furthermore, as shown in Fig.
-2
6
4
6
PhOLED with a CNIr dopant. This result indicates that DBF-d-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Page 8 of 11
Paper
Journal of Materials of Chemistry C
transport unit and a phenyl core structure. We anticipate that
novel HBMs based on dimeric dibenzo[b,d]furan and
dibenzo[b,d]thiophene molecules will be key materials for the
commercialization of high-performance blue PhOLEDs.
acetate
bis(diphenylphisphino)ferrocene]dichloropalladium
complex with dichloromethane (Pd(dppf)Cl ·CH Cl
(3.95
g,
40.22
mmol),
and
[1,1'-
(II)
, 0.55 g,
View Article Online
DOI: 10.1039/C9TC02689D
2
2
2
0.67 mmol) were stirred in dioxane (200 ml) and refluxed for
2 hours. Then, the distilled water and dichloromethane were
1
added to the reaction mixture and the organic phase was
extracted. The extracted organic phase was evaporated and
the crude mixture was purified by column chromatography
using hexane and dichloromethane as the eluents. The
Experimental
General information
Chemicals such as starting materials and solvent used in this
study were purchased commercially and used without further
purified compound (4.01 g, 10.75 mmol, 80%) was gained as
1
the beige solid. H NMR (400 MHz, chloroform-d
3
, δ): 8.43 (s,
1
13
purification. The NMR ( H, C) spectra were collected by using
an AVANCE III 400 NMR spectrometer. The molecular masses
of synthesized molecules were measured by using a 5977B gas
chromatography/mass selective detector. TGA and DSC were
performed by using a TA Instruments - Waters LLC and -
DISCOVERY units with the scanning rate of 10 C min . DTA
was carried out by using Rigaku - TG-DTA 8120 instrument with
the scanning rate of 5 C min . AFM images were obtained
from Park systems - XE7 unit. The absorption and
photoluminescence spectra were recorded on an Agilent - Cary
1
7
H), 7.98-7.95 (dd, 1H), 7.91-7.89 (dd, 1H), 7.66-7.64 (dd, 1H),
.62-7.60 (dd, 1H), 7.25-7.21 (t, 1H), 1.40 (s, 12H). GC/MS m/z:
+
[
M] calcd for C18
3
H18BBrO , 372.05; found, 372.2.
Synthesis of compound (2′)
Under N condition, compound 1 ′ (3.12 g, 13.41 mmol),
bis(pinacolato)diboron (2.65 g, 10.43 mmol), potassium
acetate (2.36 g, 24.06 mmol), and Pd(dppf)Cl ·CH Cl (0.33 g,
.40 mmol) were stirred in dioxane (200 ml) and refluxed for
2 hours. Then, the distilled water and dichloromethane were
o
-1
2
o
-1
2
2
2
0
1
5
00 and - Eclipse spectrophotometers. Low temperature
added to the reaction mixture and the organic phase was
extracted. The extracted organic phase was evaporated and
the crude mixture was used for the next reaction without
further purification.
phosphorescent spectra were measured from a PerkinElmer -
LS-55 spectrophotometer at 77 K. The electrochemical analysis
of the compounds was carried out in the dichloromethane
(DCM) solution by using a BioLogic - VMP3 unit. A platinum (Pt)
and silver/silver chloride (Ag/AgCl) were used as a counter and
reference electrodes, respectively. When investigating the
electrochemical properties, the ferrocene was used as an
internal standard.
Synthesis of compound (3)
Under N condition, compound 1 (4.00 g, 10.72 mmol),
2
compound
tetrakis(triphenylphosphine) (Pd(PPh
and sodium carbonate (Na CO , 2.27 g, 21.45 mmol) were
2
(4.00 g, 10.72 mmol), palladium
3 4
)
, 0.62 g, 0.54 mmol),
Synthesis
2
3
stirred in dioxane (150 ml) and distilled water (75 ml) and
refluxed for 12 hours. Then, the distilled water and
dichloromethane were added to the reaction mixture and the
organic phase was extracted. The extracted organic phase was
evaporated and the crude mixture was washed by methanol
and dichloromethane. The purified compound (2.67 g, 5.43
Synthetic routes of DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-
d-Py are described in Scheme 1. The synthesis of 6-bromo-2-
iododibenzo[b,d]furan (compound 1) was carried out through
1
9
previously reported literature.
Synthesis of compound (1′)
1
mmol, 51%) was gained as the white solid. H NMR (400 MHz,
2
Under N condition, 4-bromodibenzo[b,d]thiophene (5.00 g,
chloroform-d
3
, δ): 8.20-8.19 (dd, 2H), 7.98-7.96 (dd, 2H), 7.81-
1
9.00 mmol), iodobenzene diacetate (3.06 g, 9.50 mmol), and
7
.79 (dd, 2H), 7.77-7.75 (dd, 2H), 7.67-7.65 (dd, 2H), 7.30-7.28
iodine (2.41 g, 9.50 mmol) were stirred in acetic acid (25 ml)
and acetic anhydride (25 ml). Several drops of the sulfuric acid
were added to reaction mixture and the reaction mixture was
stirred for 24 hours at room temperature. Then, the methanol
1
3
(t, 2H, a peak of triplet is masked in the CHCl
3
). C NMR (100
MHz, chloroform-d
3
, δ): 155.53, 153.81, 136.84, 130.31,
1
1
4
27.62, 125.69, 124.82, 124.13, 119.84, 119.73, 112.33,
04.61. GC/MS m/z: [M] calcd for C24H12Br O , 492.2; found,
2 2
92.0.
+
(200 ml) was poured and the reaction mixture was filtered. The
purified compound (3.12 g, 8.02 mmol, 42%) was obtained as
1
the white solid. H NMR (400 MHz, chloroform-d
3
, δ): 7.44 (dd,
Synthesis of compound (3′)
Under N condition, compound 1′ (3.12 g, 8.02 mmol), crude
compound 2′ (3.12 g, 8.02 mmol, assumed that the theoretical
yield of the previous reaction is 100%), Pd(PPh (0.46 g, 0.40
mmol), and Na CO (1.70 g, 16.04 mmol) were stirred in
dioxane (150 ml) and distilled water (75 ml) and refluxed for
2 hours. Then, the distilled water and dichloromethane were
1
7
1
1
C
H), 8.07-8.05 (dd, 1H), 7.78-7.75 (dd, 1H), 7.65-7.62 (m, 2H),
1
3
2
.39-7.35 (t, 1H). C NMR (100 MHz, chloroform-d
3
, δ): 141.48,
38.45, 138.06, 135.69, 135.38, 131.20, 129.97, 126.02,
+
3 4
)
24.42, 120.38, 116.27, 89.20. GC/MS m/z: [M] calcd for
BrIS, 389.84; found, 389.8.
12 6
H
2
3
1
Synthesis of compound (2)
Under N condition, compound 1 (5.00 g, 13.41 mmol),
bis(pinacolato)diboron (4.43 g, 17.43 mmol), potassium
added to the reaction mixture and the organic phase was
extracted. The extracted organic phase was evaporated. The
crude mixture washed by methanol and dichloromethane and
2
8
| J. Name., 2012, 00, 1-3
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Page 9 of 11
J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Journal of Material Chemistry C
Paper
was used for the next reaction without further purification.
dichloromethane and methanol as the eluents. The purified
View Article Online
DOI: 10.1039/C9TC02689D
+
2 2
GC/MS m/z: [M] calcd for C24H12Br S , 523.87; found, 524.0.
compound (1.20 g, 2.46 mmol, 60%) was obtained as a white
1
solid. H NMR (400 MHz, chloroform-d
3
, δ): 9.20-9.19 (dd, 2H),
Synthesis of DBF-d-PO
8.70-8.69 (dd, 2H), 8.30-8.27 (m, 4H), 8.09-8.06 (dd, 2H), 7.82-
.80 (dd, 2H), 7.72-7.70 (d, 2H), 7.67-7.65 (dd, 2H), 7.53-7.48
7
2
Under N condition, compound 3 (3.00 g, 6.10 mmol) were
1
3
(m, 4H). C NMR (100 MHz, chloroform-d
3
, δ): 155.65, 153.88,
dissolved in tetrahydrofuran (THF, 100 ml) and the solution
o
149.66, 148.89, 136.71, 135.95, 132.14, 127.30, 126.74,
was cooled to -78 C. The 2.5 M n-butyllithium in hexane (5.85
1
25.18, 124.59, 123.56, 123.50, 122.51, 120.65, 119.55,
ml, 14.63 mmol) was added to the cooled solution and the
reaction mixture was stirred for 1.5 hours at -78 C. After 1.5
hours, the diphenylphosphine chloride (3.23 g, 14.63 mmol)
was added to the reaction mixture at -78 C and stirred for 12
hours at room temperature. Then, the reaction mixture was
quenched with the distilled water and dichloromethane. The
organic phase was extracted and stirred with the hydrogen
peroxide (10 ml) for 3 hours. Next, the distilled water (100 ml)
was added and the organic phase was extracted. The extracted
organic phase was evaporated and the crude mixture was
purified by column chromatography using ethyl acetate and
hexane as the eluents. The purified compounds (2.50 g, 8.13
+
o
112.07. GC/MS m/z: [M] calcd for C34
20 2 2
H N O , 488.15; found,
4
88.2.
o
Synthesis of DBT-d-Py
Under N condition, compound 3 ′ (2.00 g, 4.06 mmol),
pyridine-3-boronic acid (1.13 g, 9.16 mmol), Pd(dppf)Cl ·CH Cl
(0.31 g, 0.38 mmol), and K CO (2.64 g, 19.07 mmol) were
2
2
2
2
2
3
stirred in dioxane (100 ml) and distilled water (50 ml) and
refluxed for 12 hours. Then, the distilled water and
dichloromethane were added to the reaction mixture and the
organic phase was extracted. The extracted organic phase was
evaporated and the crude mixture was purified by column
chromatography using dichloromethane and methanol as the
1
mmol, 61%) was gained as the white solid. H NMR (400 MHz,
chloroform-d
3
, δ): 8.23-8.21 (dt, 2H), 8.18-8.17 (d, 2H), 7.86-
7
.80 (m, 10H), 7.69-7.67 (dd, 2H), 7.59-7.55 (m, 4H), 7.53-7.45
eluents. The purified compound (1.50 g, 2.88 mmol, 76%) was
+
1
(m, 12H). GC/MS m/z: [M] calcd for C48
32 4 2
H O P , 734.18; found,
obtained as a white solid. H NMR (400 MHz, chloroform-d
3
, δ):
7
34.4.
9.10-9.00 (dd, 1H), 8.73-8.72 (dd, 1H), 8.51 (d, 1H), 8.35-8.33
dd, 1H), 8.14-8.11 (m, 1H), 7.99-7.97 (dd, 1H), 7.87-7.84 (dd,
1H), 7.67-7.63 (t, 1H), 7.54-7.52 (dd, 1H), 7.51-7.47 (dd, 1H).
(
Synthesis of DBT-d-PO
Under N condition, compound 3′ (2.00 g, 3.81 mmol) were
1
3
C NMR (100 MHz, chloroform-d
3
, δ): 149.36, 149.30, 139.32,
2
1
38.50, 138.03, 136.47, 136.35, 136.21, 135.52, 133.59,
dissolved in THF (100 ml) and the solution was cooled to -78
o
127.30, 126.76, 125.42, 123.55, 123.13, 121.39, 120.51.
C. The 2.5 M n-butyllithium in hexane (3.66 ml, 9.16 mmol)
+
GC/MS m/z: [M] calcd for C34
20 2 2
H N S , 520.11; found, 520.2.
was added to the cooled solution and the reaction mixture was
stirred for 1.5 hours at -78 C. After 1.5 hours, the
diphenylphosphine chloride (2.02 g, 9.16 mmol) was added to
the reaction mixture at -78 C and stirred for 12 hours at room
temperature. Then, the reaction mixture was quenched with
the distilled water and dichloromethane. The organic phase
was extracted and stirred with the hydrogen peroxide (10 ml)
for 3 hours. Next, the distilled water (100 ml) was added and
the organic phase was extracted. The extracted organic phase
was evaporated and the crude mixture was purified by column
chromatography using ethyl acetate and hexane as the eluents.
o
Calculation of molecular energy level
o
The LUMO energy levels of HBMs were deduced though the
reduction potential onset (Eonset, red) with the redox potential
of ferrocene/ferrocenium (E1/2, Fe) couple in the cyclic
voltammograms. The HOMO energy levels of HBMs were
calculated by their LUMO energy levels and bandgaps in films
film
(E
g
). The calculated equations are shown below.
E
E
LUMO (eV) = -4.80 - (Eonset, red - E1/2, Fe
)
(1)
(2)
film
HOMO (eV) = ELUMO (eV) - E
g
(eV)
The purified compounds (2.20 g, 2.87 mmol, 75%) was gained
1
as the white solid. H NMR (400 MHz, chloroform-d
3
, δ): 8.45-
Device fabrication and analysis
8
.42 (m, 4H), 7.92-7.89 (d, 2H), 7.80-7.74 (m, 10H), 7.62-7.57
The electron-only devices and blue phosphorescent OLEDs
with four compounds were fabricated with the following
configuration: ITO/Ca (5 nm)/four compounds (30 nm)/LiF (1
nm)/Al (150 nm), ITO/ BPBPA:HATCN (40 nm, 30% co-
evaporation of HATCN)/BPBPA (10 nm)/PCZAC (10
nm)/mCBPCN:oCBP:CNIr (30 nm, 50% and 10% doping of oCBP
and CNIr, respectively)/HBMs (5 nm)/ZADN (20 nm)/LiF (1
nm)/Al (200 nm). When fabricating the device, the organic
layers were fabricated by the thermal vacuum deposition at
1.0 x 10 torr and devices were protected from the oxygen and
moisture by encapsulating the devices using the CaO getter.
The current density and luminance vs. voltage of the devices
were recorded by Keithley 2400 source meter unit and Konica
Minolta CS-2000 spectroradiometer unit.
+
(m, 4H), 7.55-7.44 (m, 12H). GC/MS m/z: [M] calcd for
48 32 2 2 2
C H O P S
, 766.13; found, 766.3.
Synthesis of DBF-d-Py
Under N condition, compound 3 (2.00 g, 4.06 mmol),
pyridine-3-boronic acid (1.20 g, 9.75 mmol),
Pd(dppf)Cl ·CH Cl (0.35 g, 0.41 mmol), and potassium
carbonate (K CO , 2.81 g, 20.32 mmol) were stirred in dioxane
100 ml) and distilled water (50 ml) and refluxed for 12 hours.
2
2
2
2
2
3
-7
(
Then, the distilled water and dichloromethane were added to
the reaction mixture and the organic phase was extracted. The
extracted organic phase was evaporated and the crude
mixture was purified by column chromatography using
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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Journal of Materials of Chemistry C
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2 V. I. Adamovich, S. R. Cordero, P. I. Djurovich, AV.ieTwaAmrtiaclyeoO,nMline.
Conflicts of interest
There are no conflicts to declare
E. Thompson, B. W. D’Andrade and S. R. Forrest, Org.
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Acknowledgements
This work was supported by the National Research Foundation
2
2
5 H. Sasabe, E. Gonmori, T. Chiba, Y.-J. Li, D. Tanaka, S.-J. Su, T.
Takeda, Y.-J. Pu, K.-I. Nakayama and J. Kido, Chem. Mater.,
(NRF-2018R1A5A1025594) of the Ministry of Science and ICT.
This research was also supported by Nano Material
Technology Development Program through the National
Research Foundation of Korea (NRF) funded by the Ministry of
Science and ICT (NRF-2016M3A7B4909293). This research was
also supported by the DGIST R&D program of the Ministry of
Science and ICT (19-BD-0404).
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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC02689D
A Table of Contents Entry
Novel hole blocking materials based on dibenzo[b,d]furan and dibenzo[b,d]thiophene
molecular dimers are synthesized for high-efficiency and long-lived blue phosphorescent
OLEDs.