Selective F or Br Functionalization of Dibenzofuran for Application as Host Materials of Phosphorescent Organic Light-Emitting Diodes

Article abstract of DOI:10.1002/chem.201703307

Four dibenzofuran-type host materials substituted with a carbazolylcarbazole moiety were synthesized to investigate the effect of substitution position on the material parameters and device performances of host materials. The carbazolylcarbazole moiety was substituted at the 1-, 2-, 3-, and 4-positions of dibenzofuran by F or Br for a comprehensive study of the positional effect of dibenzofuran-derived host materials. Systematic synthesis and comparison of the four host materials revealed that 1-, 2-, and 4-position modification was better than 3-position modification for high triplet energy and high external quantum efficiency.

Full text of DOI:10.1002/chem.201703307

A Journal of
Accepted Article
Title: Selective F or Br functionalization of dibenzofuran for application
as host materials of phosphorescent organic light-emitting diodes
Authors: Ji Gwang Yu, Sung Yong Byeon, Si Hyun Han, and Jun Yeob
Lee
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Selective F or Br functionalization of dibenzofuran for application as host
materials of phosphorescent organic light-emitting diodes
Ji Gwang Yu, Sung Yong Byeon, Si Hyun Han, Jun Yeob Lee*
School of Chemical Engineering, Sungkyunkwan University
2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi, 440-746, Korea
* Correspoinding author
E-mail : leej17@skku.edu
Abstract
Four dibenzofuran type host materials substituted with a carbazolylcarbazole moiety were
synthesized to investigate the effect of substitution position on the material parameters and
device performances of host materials. The carbazolylcarbazole moiety was substituted at 1-,
2-, 3-, and 4- positions of dibenzofuran by F or Br functionalization approach for
comprehensive study of positional effect of dibenzofuran derived host materials. Systematic
synthesis and comparison of the four host materials revealed that 1-, 2-, and 4- position
modification is better than 3- position modification for high triplet energy and high external
quantum efficiency.
Key words : dibenzofuran, carbazolylcarbazole, efficiency, substitution position
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Introduction
High triplet energy host materials are essential in the development of high efficiency blue
phosphorescent organic light-emitting diodes (PHOLEDs) because their major role is to harvest
triplet excitons of phosphorescent emitters and to manage the triplet exciton formation in the
emitting layer1-5. High triplet energy is needed for triplet exciton harvesting and carrier control
is necessary for the triplet exciton formation. One of candidates of the triplet exciton harvesting
and managing hosts is a carbazole modified dibenzofuran compound6-10. Although only a few
host materials sharing the dibenzofuran and carbazole platform are present, they already proved
potential as the high triplet energy host materials. Both dibenzofuran and carbazole are high
triplet energy moieties for triplet exciton harvesting and they can carry electrons and holes by
electron poor and electron rich character of the dibenzofuran and carbazole, respectively.
Therefore, the molecular design merging the dibenzofuran and carbazole moieties can be
considered as a candidate of host materials for blue PHOLEDs. The dibenzofuran moiety has
four different positions for functionalization and functionalization position may have great
impact on the photophysical characteristics and device properties of the dibenzofuran derived
host materials11. Although a few papers examined the effect of functionalization position of the
dibenzofuran derivatives11-13, comprehensive study covering the host materials functionalized
at all positions of dibenzofuran was not reported. In this work, four hosts derived from
dibenzofuran and carbazolylcarbazole, 9-(dibenzo[b,d]furan-1-yl)-9H-3,9’-bicarbazole
(1DBFCz), 9-(dibenzo[b,d]furan-2-yl)-9H-3,9’-bicarbazole (2DBFCz), 9-(dibenzo[b,d]furan-
3-yl)-9H-3,9’-bicarbazole (3DBFCz), and 9-(dibenzo[b,d]furan-4-yl)-9H-3,9’-bicarbazole
(4DBFCz), were synthesized by functionalizing all positions of dibenzofuran using either Br
or F functional groups for carbazolycarbazole substitution. It was demonstrated that 1-, 2-, and
4- position substitution is better than 3- position substitution for high triplet energy and high
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external quantum efficiency (EQE). A high EQE over 25% was demonstrated using the
dibenzofuran type hosts.
Results and discussion
1-, 2-, 3-, and 4- positions of dibenzofuran were functionalized with either F or Br to introduce
carbazolylcarbazole in the molecular structure. The 2- and 4- positions were modified with Br
according to well-known synthetic methods14-17 and the 1- and 3- positions were functionalized
with F by ring closing reaction of F containing intermediates18. In general, the 1, and 3-
positions of dibenzofuran cannot be functionalized with halogen units because those positions
are not activated for direct electrophilic halogen substitution. Therefore, we utilized one Br and
two F substituted benzenes as starting materials to prepare the 1- and 3- position functionalized
dibenzofuran units. 2-Bromo-1,3-difluorobenzene and (2-methoxyphenyl)boronic acid were
starting materials for the 1- position functionalized dibenzofuran and 2-bromo-1,4-
difluorobenzene and (2-methoxyphenyl)boronic acid were starting materials for the 3- position
functionalized dibenzofuran. Pd assisted Suzuki coupling reaction followed by BBr3 aided
deprotection and K2CO3 mediated ring closing reaction produced the 1-
fluorodibenzo[b,d]furan and 3-fluorodibenzo[b,d]furan intermediates. The Br functionalized
dibenzofuran intermediates were coupled with carbazolylcarbazole by Pd catalyzed reaction
and the F functionalized intermediates were jointed with carbazolylcarbazole by NaH initiated
reaction. Preparation scheme of 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz is shown in
Scheme 1.
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+
℃
℃
+
+
+
+
Scheme 1. Synthetic scheme of 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz.
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Overall material parameters of the four dibenzofuran derivatives were firstly estimated by
examining electronic molecular orbital calculated using Gaussian 09 program based on B3LYP
6-31G basis set. Figure 1 shows the molecular orbital distribution represented by the highest
occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). The
substitution position of dibenzofuran had little effect on the HOMO and LUMO dispersion of
the dibenzofuran derivatives. In all compounds, the HOMO was dominantly dispersed over the
carbazolylcarbazole unit and the LUMO was scattered over the dibenzofuran unit. Although
the substitution position of dibenzofuran was different, the molecular orbital distribution was
of little difference because both electron rich carbazolylcarbazole and electron poor
dibenzofuran were included in the molecular structure. Electron donating and accepting nature
of the building moieties synchronized the HOMO and LUMO distribution.
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HOMO
LUMO
1DBFCz
2DBFCz
3DBFCz
4DBFCz
Figure 1. HOMO and LUMO distribution of 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz by
Gaussian molecular simulation.
The calculated HOMO and LUMO values were verified by experimental measurement using
cyclic voltammetry (CV) which electrochemically analyzes the oxidation and reduction. The
CV scan data in Figure 2 provided the HOMO/LUMO of -5.99/-2.58, -5.96/-2.56, -5.99/-2.63,
and -5.99/-2.62 eV in 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz, respectively. The HOMO
was quite similar in the four compounds because it is governed by the same
carbazolylcarbazole unit. The HOMO of the four compounds was shifted by about 0.10 eV
from that of common carbazole host because of electron richness of carbazolylcarbazole.
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1DBFCz
2DBFCz
3DBFCz
4DBFCz
-4
-3
-2
-1
0
1
2
3
Voltage (V)
Figure 2. Oxidation and reduction scan data of 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz
using cyclic voltammetry.
In addition to the HOMO and LUMO levels governing the device performances, singlet energy
and triplet energy of the hosts were analyzed by photophysical characterization. Photophysical
data of the hosts are presented in Figure 3(a) and (b). Room temperature fluorescence and low
temperature phosphorescence of the hosts were characterized by photoluminescence (PL)
measurement using a dilute toluene solution (1.0  10-5 M). The low temperature
phosphorescence measurement delivered triplet energies of 2.97, 2.98, 2.86, and 3.00 eV in the
1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz, respectively. Except for the 3DBFCz host, all hosts
showed very high triplet energy over 2.90 eV. The direct connection of dibenzofuran with
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carbazolylcarbazole through 1-, 2-, and 4- position did not degrade the triplet energy of the
hosts, but the connection through 3- position decreased the triplet energy because of para-
orientation of aromatic units. The triplet energy of all compounds was higher than that of a
common mCBP. The fluorescence emission energy was also high in the 1DBFCz, 2DBFCz
and 4DBFCz as compared in the fluorescent emission spectra. Ultraviolet-visible (UV-vis)
absorption data are presented in Figure 4 and little change of the UV-vis absorption according
to the substitution position was observed. All material analysis data are summarized in Table
1.
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(a)
1DBFCz
2DBFCz
3DBFCz
4DBFCz
300
400
500
Wavelength (nm)
(b)
1DBFCz
2DBFCz
3DBFCz
4DBFCz
300
400
500
600
Wavelength (nm)
Figure 3. Room temperature PL (a) and low temperature PL (b) spectra of 1DBFCz,
2DBFCz, 3DBFCz and 4DBFCz.
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1DBFCz
2DBFCz
3DBFCz
4DBFCz
240
280
320
360
400
Wavelength (nm)
Figure 4. UV-vis absorption spectra of 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz.
Table 1. Summary of analysis data of 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz.
1DBFCz
-5.99
-2.58
3.38
2DBFCz
-5.99
-2.56
3.31
3DBFCz
-5.99
-2.63
3.37
4DBFCz
-5.99
-2.62
3.40
mCBP
-6.00
-2.40
3.42
HOMO (eV)
LUMO (eV)
Singlet energy (eV)
Triplet energy (eV)
2.97
2.98
2.86
3.00
2.80
The high triplet energy of the hosts allowed application of 1DBFCz, 2DBFCz, 3DBFCz and
4DBFCz as hosts of blue PhOLEDs with a tris[1-(2,4-diisoproplydibnezo[b,d]furan-3-yl)-2-
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phenyl-1H-imidazole]-iridium(III) complex [Ir(dbi)3] phosphorescent emitter. The Ir(dbi)3
emitter was doped at a doping concentration of 5% in the four hosts to assess the performance
of the hosts. A reference device with mCBP as the host was also studied. A device structure
fully confining carriers and excitons was built to evaluate the hosts as explained in the
experimental part. The device behavior of the four PhOLEDs was examined and the voltage
sweep measurement of the blue PhOLEDs generated the current density (J) - voltage (V) and
luminance (L) – voltage (V) plots (Figure 5). The J-V and L-V data of the blue PhOLEDs
established that 2DBFCz is a high J provider and 3DBFCz is a low J supplier. 1DBFCz and
4DBFCz were in between 2DBFCz and 3DBFCz in terms of J and L values of the blue
PhOLEDs. The J and L dependence of the blue PhOLEDs on the four hosts can be appreciated
by studying the hole and electron transport performance of the hosts evaluated by hole and
electron current densities of single carrier devices in Figure 6 and 7. The hole current density
of the hole only devices was relatively high in the 2DBFCz and 3DBFCz hosts compared to
1DBFCz and 4DBFCZ hosts. On the other hand, the electron current density of the electron
only devices was in the order of 2DBFCz > 1DBFCz ≈ 4DBFCz > 3DBFCz. In spite of high
hole current density, the electron current density was very low in the 3DBFCz, which reduced
the overall current density of the 3DBFCz blue PhOLEDs. In the case of the mCBP host, the
hole current density was high, but the electron current density was very low relative to that of
other hosts.
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40
35
30
25
20
15
10
5
100000
10000
1000
100
1DBFCz
2DBFCz
3DBFCz
4DBFCz
mCBP
10
1
0
0.1
0
2
4
6
8
10
Voltage (V)
Figure 5. Current density and luminance against voltage plots of the1DBFCz, 2DBFCz,
3DBFCz and 4DBFCz devices.
1000
10
0.1
1DBFCz
0.001
0.00001
2DBFCz
3DBFCz
4DBFCz
mCBP
0.0000001
0
2
4
6
8
10
Voltage (V)
Figure 6. Current density against voltage plots of hole only devices of the1DBFCz, 2DBFCz,
3DBFCz and 4DBFCz devices.
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1000
10
0.1
0.001
0.00001
1DBFCz
2DBFCz
3DBFCz
4DBFCz
mCBP
0.0000001
0
2
4
6
8
10
Voltage (V)
Figure 7. Current density against voltage plots of electron only devices of the1DBFCz,
2DBFCz, 3DBFCz and 4DBFCz devices.
External quantum efficiency (EQE) of blue PhOLEDs obtained from the electrical and
photometric measurements is plotted in Figure 8. The EQE of the 1DBFCz, 2DBFCz, and
4DBFCz devices was over 25%, but the EQE of the 3DBFCz device was 22.2%. There was
only marginal difference of EQE in the 1DBFCz, 2DBFCz, and 4DBFCz devices. The high
EQE of the three blue PhOLEDs demonstrates the superiority of the dibenzofuran type hosts
due to high triplet energy and efficient carrier recombination. The rather low EQE of the
3DBFCz device is caused by the low electron density disrupting the carrier balance which is
critical to the EQE. Analogously, the EQE of mCBP device was also lower than that of the
blue PhOLEDs with the dibenzofuran derived hosts. The electroluminescence (EL) spectra of
the blue PhOLEDs were pure Ir(dbi)3 emission spectra because of high triplet energy of the
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dibenzofuran type hosts inhibiting reverse triplet energy transfer (Figure 9). All devices
showed the same EL spectra irrespective of the hosts, demonstrating energy transfer from all
hosts to Ir(dbi)3. All device performances are summarized in Table 2.
Table 2. Summarized device performances of 1DBFCz, 2DBFCz, 3DBFCz and 4DBFCz.
Color
coordinate
(x, y)
Voltage
(V)
Q. E
(%)
C. E
P. E
Devices
1DBFCz
2DBFCz
3DBFCz
4DBFCz
mCBP
(cd/A)
(lm/W)
6.9
6.6
7.7
7.1
8.1
(0.18, 0.40)
(0.17, 0.40)
(0.18, 0.40)
(0.18, 0.40)
(0.19, 0.40)
26.4
25.7
22.2
26.2
14.8
61.0
59.0
51.6
61.4
34.4
38.3
40.7
35.7
38.6
17.1
30
25
20
15
10
5
1DBFCz
2DBFCz
4DBFCz
3DBFCz
mCBP
0
1
10
100
1000
10000
Luminance (cd/m2)
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Figure 8. External quantum efficiency against current density plots of the1DBFCz, 2DBFCz,
3DBFCz and 4DBFCz devices.
1DBFCz
2DBFCz
3DBFCz
4DBFCz
mCBP
380
480
580
680
780
Wavelength (nm)
Figure 9. Normalized electroluminescence spectra of the 1DBFCz, 2DBFCz, 3DBFCz and
4DBFCz devices at 1,000 cd/m2
Conclusions
Four dibenzofuran type hosts, 1DBFCz, 2DBFCz, 3DBFCz, and 4DBFCz, were synthesized
by selective F- or Br- functionalization of dibenzofuran and clarified the effect of substitution
position of carbazole type hole transport unit to the dibenzofuran unit. In material and device
aspects, 1- and 4- position substitution was equivalent, but the 3- position substitution was
inferior to other substitution by providing relatively low triplet energy and EQE. The 2-
position substitution was better than other position substitution in terms of carrier transport,
but triplet energy and EQE were similar to those of 1- and 4- position substitution. 1DBFCz,
2DBFCz and 4DBFCz exhibited high triplet energy over 2.90 eV and EQE over 25% in the
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blue PhOLEDs. Therefore, this work can guide the selection of substitution position in the
design of high triplet energy hosts.
Experimental
General information
(2-Methoxyphenyl)boronic acid and 1-bromo-2,4-difluorobenzene were purchased from Alfa
Aesar Co. copper(I) Iodide(CuI), 1,10-phenanthroline and boron tribromide(BBr3) were
purchased from Sigma-Aldrich. Co. 2-bromo-1,3-difluorobenzene was purchased from Combi-
Blocks Inc. 2-bromodibenzo[b,d]furan was purchased from INCO. 4-bromodibenzo[b,d]furan
and tetrakis(triphenylphosphine)palladium(0)(Pd(pph3)4). 9H-3,9’bicarbazole was purchased
from Sunfine global Co. Ltd. Dichloromethane(MC) for high performance liquid
chromatography and Potassium carbanate(K2CO3) were purchased from Duksan Sci. Co. Tetr
ahydrofuran (THF) was purchased from Samchun pure chemical Co. Ltd and distilled with
sodium and calcium hydride.
The ultraviolet- visible (UV-Vis) spectra were measured to analyze absorption of compounds
using a sample dissolved in refined THF. The photoluminescence (PL) were measured to
analyze PL spectra of compounds dissolved in refined tetrahydrofuran. Low temperature PL
measurement was carried out at 77k to measure triplet energy of compounds. The 1H and 13C
nuclear magnetic resonance (NMR) spectra were recorded to identify the compounds. Samples
1
13
were dissolved in deuterated dimethyl sulfoxide(DMSO) for H and C NMR measurement.
The mass were recorded by liquid chromatography-mass spectrometer (LC-MS) to measure
the molecular weight of compounds. Detailed method is described in the literature19.
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Synthesis
2,6-Difluoro-2’-methoxy-1,1’-biphenyl (1)
(2-Methoxyphenyl)boronic acid (5.0 g, 32.9 mmol), 2-bromo-1,3-difluorobenzene (7.6 g, 39.5
mmol), potassium carbonate (13.6 g, 98.7 mmol) and tetrakis(triphenylphosphine)palladium(0)
(1.9 g , 1.65 mmol) were stirred in a round-bottomed flask filled with tetrahydrofuran (100 ml)
and distilled water (50 ml) under a nitrogen atmosphere at 260 ℃overnight. After reaction, the
mixture was cooled to room temperature and extracted with dichloromethane and distilled
water. The dichloromethane layer was separated and the dichloromethane was evaporated.
Purification by column chromatography (dichloromethane : n-hexane (20:80)) and drying
1
afforded a white powder as a product (4.5 g, 62.7 % yield). H NMR (500 MHz,
dimethylsulfoxide-d6): δ 3.72 (s, 3H), 7.01-7.04 (t, 1H, J=7.5Hz), 7.11-7.15 (t, 3H, J=10.0Hz),
7.21-7.23 (d, 1H, J=10.0Hz), 7.41-7.47 (m, 2H), MS (API-) m/z: 221.2 [(M + H)-].
2’,6’-Difluoro-[1,1’-biphenyl]-2-ol (2)
Compound 1 (4.5 g, 20.4 mmol) was stirred in dichloromethane (30 ml) under a nitrogen
o
atmosphere at -78 C for 20 min followed by injection of boron tribromide (13.9 ml, 81.6
mmol). After 2 h, the mixture was heated to room temperature and was stirred for additional 1
h. The reaction mixture was quenched carefully with sodium hydroxide (2.4 g, 2 M) aqueous
solution (30 ml) followed by extraction with dichloromethane and distilled water. The
dichloromethane layer was separated, dried and evaporated to provide a light yellow product
(3.5 g, 83.2% yield). 1H NMR (500 MHz, dimethylsulfoxide-d6): δ 6.85-6.88 (t, 1H, J=7.5Hz),
6.94-6.96 (d, 1H, J=10.0Hz), 7.08-7.14 (m, 3H), 7.22-7.26 (t, 1H, J=10.0Hz), 7.38-7.44 (m,
1H), 9.63 (s, 1H), MS (API-) m/z: 207.2 [(M + H)-].
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1-Fluorodibenzo[b,d]furan (3)
Compound 2 (3.5 g, 17.0 mmol) and potassium carbonate (4.7g, 34 mmol) were stirred in a
two-neck round-bottomed flask filled with dimethylformamide (DMF, 40 ml) under a nitrogen
atmosphere at 160 oC overnight. After cooling to room temperature, the reaction mixture was
extracted with dichloromethane and distilled water. The dichloromethane layer was separated
and evaporated. Crude product was purified by column chromatography (dichloromethane:n-
haxane (10:90)). After column chromatography, vacuum sublimation afforded a white product
1
(2.8 g, 88.6% yield). H NMR (300 MHz, dimethylsulfoxide-d6): δ 8.07-7.31 (m, 7H), MS
(API-) m/z: 187.5 [(M + H)-].
2,4-Difluoro-2’-methoxy-1,1’-biphenyl (4)
2,4-Difluoro-2’-methoxy-1,1’-biphenyl was synthesized according to the synthetic method of
2,6-difluoro-2’-methoxy-1,1’-biphenyl using 1-bromo-2,4-difluorobenzene (6.05 g, 31.38
mmol) as a starting material instead of 2-bromo-1,3-difluorobenzene. A white powder was
obtained as a final product (5.2 g, 75.2% yield). 11H NMR (500 MHz, dimethylsulfoxide-d6):
δ 3.72 (s, 3H), 7.00-7.03 (t, 1H, J=7.5Hz), 7.08-7.13 (t, 2H, J=10.0Hz), 7.19-7.26 (m, 2H),
7.34-7.41 (m, 2H), MS (API-) m/z: 221.3 [(M + H)-].
2’,4’-Difluoro-[1,1’-biphenyl]-2-ol (5)
2’,4’-Difluoro-[1,1’-biphenyl]-2-ol was synthesized according to the synthetic method of 2’,6’-
difluoro-[1,1’-biphenyl]-2-ol using 2,4-difluoro-2’-methoxy-1,1’-biphenyl(5.72g ,26.0 mmol)
instead of 2,6-difluoro-2’-methoxy-1,1’-biphenyl. A light yellow powder was obtained as a
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1
product (4.5 g, 84% yield). H NMR (500 MHz, dimethylsulfoxide-d6): δ 6.84-6.87 (t, 1H,
J=7.5Hz), 6.90-6.92 (d, 1H, J=10.0Hz), 7.08-7.13 (m, 2H), 7.18-7.24 (m, 2H), 7.35-7.40 (m,
1H), 9.54 (s, 1H), MS (API-) m/z: 207.1 [(M + H)-].
3-Fluorodibenzo[b,d]furan (6)
3-Fluorodibenzo[b,d]furan was synthesized according to the synthetic method of 1-
fluorodibenzo[b,d]furan using 2’,4’-difluoro-[1,1’-biphenyl]-2-ol (3.83 g, 18.6 mmol) instead
of 2’,6’-difluoro-[1,1’-biphenyl]-2-ol. A white powder was obtained as a product (3.2 g, 92.3%
yield)
1H NMR (300 MHz, dimethylsulfoxide-d6): δ 8.20 (s, 1H), 7.73-7.l3 (m, 6H), MS (API-) m/z:
187.2 [(M + H)-].
9-(Dibenzo[b,d]furan-1-yl)-9H-3,9’-bicarbazole (1DBFCz)
9H-3,9’-bicarbazole (2.0 g, 6.0 mmol) and sodium hydride (0.14 g, 6.0 mmol) were stirred in
DMF (10 ml) under a nitrogen atmosphere. After 40 min, compound 3 (2 g, 4.0 mmol) in DMF
(10 ml) was injected slowly and the mixture was stirred at 60 oC for 3 h. The reaction mixture
was cooled to room temperature and quenched with distilled water. Extraction of the reaction
mixture using dichloromethane and distilled water, separation of the dichloromethane layer and
evaporation of dichloromethane produced a crude product. Purification of the crude product by
column chromatography (dichloromethane : n-hexane (10:90)) followed by vacuum train
sublimation afforded a pure white powder as a final product (1.35 g, 45% yield).
1H NMR (500 MHz, dimethylsulfoxide-d6): δ 8.65 (s, 1H), 8.45 (d, 1H, J=8.0Hz), 8.27 (d, 2H,
J=8.0Hz), 8.03 (d, 1H, J=7.5Hz), 7.89 (t, 1H, J=8.0Hz), 7.80-7.77 (m, 2H), 7.54 (d, 1H,
J=8.5Hz), 7.48-7.40 (m, 4H), 7.38-7.33 (m, 4H), 7.30 (t, 2H, J=8.0Hz), 7.15 (d, 1H, J=8.0Hz),
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Chemistry - A European Journal
13
7. 07 (t, 1H, J=8.0Hz), 6.33 (d, 1H, J=8.5Hz). C NMR (125 MHz, dimethylsulfoxide-d6):
δ156.7, 155.6, 141.0, 140.7, 140.0, 139.1, 130.3, 129.4, 128.7, 128.1, 127.0, 126.1, 125.4,
123.9, 123.2, 123.1, 122.5, 122.4, 122.4, 122.0, 121.9, 121.4, 121.3, 121.0, 120.5, 120.4, 119.8,
119.8, 119.7, 119.7, 119.6, 112.2, 111.8, 111.2, 110.2, 109.6, MS (API-) m/z: 499.5 [(M + H)-].
9-(Dibenzo[b,d]furan-2-yl)-9H-3,9’-bicarbazole (2DBFCz)
2-Bromodibenzofuran (2.0 g, 8.0 mmol), 9H-3,9’-bicarbazole (3.2 g, 9.6 mmol), copper(I)
iodide (0.76 g, 4.0 mmol), and potassium carbonate (3.3 g, 24.0 mmol) were put into a round-
bottomed flask filled with DMF (50ml) under a nitrogen atmosphere. And 1 10-phenanthroline
(0.72 g, 4.0 mmol) in DMF (10 ml) was added to the mixture. The reaction mixture was stirred
o
at 100 C for overnight and then the reaction was quenched with distilled water. After
quenching, the reaction mixture was extracted with dichloromethane and distilled water. Crude
product obtained from dichloromethane layer was purified by column chromatography
(dichloromethane : n-hexane (10:90)) followed by vacuum train sublimation afforded a pure
white powder as a final product (3.35g ,84% yield)
1H NMR (500 MHz, dimethylsulfoxide-d6): δ 8.55 (s, 1H), 8.47 (d, 1H, J=8.0Hz), 8.36 (d, 1H,
J=8.0Hz), 8.29 (t, 3H, J=8.0Hz), 8.15 (s, 1H), 7.79 (d, 1H, J=8.0Hz), 7.75 (d, 1H, J=10.0Hz)
7.71 (d, 1H, J=8.5Hz) 7.6 (t, 2H, J=9.0Hz), 7.54-7.47 (m, 3H), 7.44 (t, 2H, J=8.0Hz), 7.37-7.31
13
(m, 3H), 7.30 (t, 2H, J=7.5Hz). C NMR (125 MHz, dimethylsulfoxide-d6): δ156.2, 156.0,
141.1, 139.4, 135.7, 129.3, 127.9, 127.0, 126.1, 126.1, 125.5, 125.4, 123.9, 123.5, 123.4, 123.2,
123.0, 122.5, 122.4, 122.3, 122.0, 121.4, 121.1, 120.4, 120.3, 120.3, 119.7, 119.7, 119.6, 119.6,
119.5, 111.8, 111.1, 111.1, 110.6, 110.0, 109.6, MS (API-) m/z: 499.4 [(M + H)-].
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10.1002/chem.201703307
Chemistry - A European Journal
9-(Dibenzo[b,d]furan-3-yl)-9H-3,9’-bicarbazole (3DBFCz)
3DBFCz was synthesized according to the synthetic method of 1DBFCz using
3-
Fluorodibenzo[b,d]furan (0.7g, 3.5 mmol) instead of 1-Fluorodibenzo[b,d]furan.. A white
powder was obtained as a final product (0.9 g, 51% yield).
1H NMR (500 MHz, dimethylsulfoxide-d6): δ 8.60 (s, 1H), 8.42 (d, 1H, J=8.5Hz), 8.40 (d, 1H,
J=8.0Hz), 8.31 (d, 1H, J=9.0Hz), 8.27 (d, 1H, J=8.0Hz), 7.90 (d, 1H, J=7.5Hz), 7.73 (t, 1H,
J=7.8Hz) 7.64 (d, 1H, J=8.0Hz), 7.58 (d, 1H, J=9.5Hz), 7.55 (t, 1H, J=8.3Hz), 7.49-7.32 (m,
13
8H), 7.30-7.25 (m, 3H). C NMR (125 MHz, dimethylsulfoxide-d6): δ155.5, 150.6, 141.1,
141.0, 141.0, 139.4, 129.4, 128.2, 127.0, 126.6, 126.2, 126.1, 125.4, 124.4, 124.0, 123.7, 123.4,
122.6, 122.4, 121.5, 121.2, 120.7, 120.5, 120.4, 119.7, 119.6, 119.6, 119.6, 119.6, 119.5, 112.0,
112.0, 112.0, 111.3, 110.3, 109.6, MS (API-) m/z: 499.6 [(M + H)-].
9-(Dibenzo[b,d]furan-4-yl)-9H-3,9’-bicarbazole (4DBFCz)
4DBFCz was synthesized according to the synthetic method of 2DBFCz using 4-
bromodibenzo[b,d]furan (1.0 g, 4.0 mmol) instead of 2-bromodibenzo[b,d]furan. A white
product was obtained (1.2 g, 60% yield).
1H NMR (500 MHz, dimethylsulfoxide-d6): δ 8.57 (d, 2H, J=10.0Hz), 8.37 (d, 1H, J=7.5Hz),
8.27 (d, 3H, J=8.0Hz), 8.03 (d, 1H, J=8.5Hz), 7.84-7.79 (m, 2H), 7.63-7.58 (m, 3H), 7.52 (t,
1H, J=8.0Hz), 7.46-7.41 (m, 4H), 7.37-7.27 (m, 5H). 13C NMR (125 MHz, dimethylsulfoxide-
d6): δ156.2, 154.5, 141.6, 141.1, 140.0, 131.8, 129.1, 129.1, 128.3, 126.9, 126.7, 126.2, 126.1,
125.3, 125.3, 123.6, 123.4, 123.4, 123.3, 123.2, 122.4, 122.3, 121.8, 121.2, 120.5, 120.4, 120.4,
120.2, 119.7, 119.6, 119.5, 113.2, 111.8, 110.1, 109.9, 109.6, MS (API-) m/z: 499.5 [(M + H)-].
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10.1002/chem.201703307
Chemistry - A European Journal
Device fabrication and characterization
The device structure of blue PhOLEDs was PEDOT:PSS (60 nm)/TAPC (20 nm)/mCP (10
nm)/1DBFCz, 2DBFCz, 3DBFCz or 4DBFCz:Ir(dbi)3 (25 nm, 5 wt%)/TSPO1 (5 nm)/TPBi
(20 nm)/LiF (1.5 nm)/Al (200 nm), where PEDOT:PSS is poly(3,4-
ethylenedioxythiophene):poly(styrenesulfonate), TAPC is 4,4′-cyclohexylidenebis[N,N-bis(4-
methylphenyl)benzenamine], mCP is
1,3-bis(N-carbazolyl)benzene, TSPO1 is
diphenylphosphine oxide-4-(triphenylsilyl)phenyl, and TPBi is 2,2′,2"-(1,3,5-benzinetriyl)-
tris(1-phenyl-1-H-benzimidazole). Devices were fabricated by thermal evaporation in vacuum
5107
under a pressure of
torr. J-V-L characteristics of 1DBFCz, 2DBFCz, 3DBFCz or
4DBFCz devices were analyzed by a Keithley 2400 programmable source meter and a PR650
(Photo Research) spectrometer according to the method in the literature20.
Acknowledgements
This work was supported by Basic Science Research Program (2016R1A2B3008845) and
Nano Materials Research Program (2016M3A7B4909243) through the National Research
Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning.
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10.1002/chem.201703307
Chemistry - A European Journal
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Chemistry - A European Journal
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