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Y.J. Kang et al. / Dyes and Pigments 114 (2015) 278e282
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cupper iodide, Triethylborate and n-BuLi were purchased from
Aldrich. Chem. Co. Tetrakis(triphenylphosphine)palladium, were
purchased from P&H Co. These chemical were used without further
purification. THF was distilled over sodium and calcium hydride.
Chemical characterization of the synthesized material was carried
out according to the method reported in the literature [14].
(9H-carbazol-9-yl)dibenzofuran-4-yl)boronic acid (1.9 g, 5.0 mmol)
were dissolved in dry tetrahydrofuran under nitrogen. Tetrakis(-
triphenylphosphine)palladium(0) (37.0 mg, 0.2 mmol) and 2 M
aqueous potassium carbonate (8.3 g, 60.0 mmol) were added to the
reaction mixture successively and the solution was refluxed for
overnight. After cooling the solution to room temperature, a white
powder was filtered off and a filtrate was extracted using ethyl
acetate. Ethyl acetate was evaporated and a solid product was pu-
rified by column chromatography on silica gel using chloroform/n-
hexane (1: 2) as an eluent. A white product was obtained after
purification by vacuum train sublimation (2.2 g, yield: 66%).
2.2. Synthesis
2-Iododibenzofuran Dibenzofuran (10.0 g, 59.4 mmol) and
periodic acid (16.2 g, 71.3 mmol) were dissolved in acetic acid
(600 ml) and iodine (9.0 g, 71.3 mmol) was added to the solution.
The solution was stirred at 60 ꢁC for 30 min followed by addition of
distilled water (120 ml) and sulfuric acid (1.20 ml). The solution was
refluxed for 12 h, cooled to room temperature and poured into
distilled water. White powder was filtered off and then the filtrate
was extracted using ethyl acetate. The extracted solution was
washed with 5% NaOH solution and aqueous sodium sulfate. Ethyl
acetate was removed by evaporation and yellowish white powder
was obtained (12.0 g, yield: 69%) after drying in vacuum. 2-
Iododibenzofuran was included 85% of all powder and it was
used in amination without purification.
1H NMR (400 MHZ, CDCl3):
d
8.46 (d, 2H, J ¼ 1.0 Hz), 8.226 (m,
6H), 8.00 (d, 2H, J ¼ 3.8 Hz), 7.72 (d, 4H, J ¼ 4 Hz), 7.63 (d, 2H,
J ¼ 4 Hz), 7.54e7.50 (m, 6H), 7.42e7.34 (m, 6H) 13C NMR (100 MHZ,
CDCl3):
d 156.92, 152.31, 141.42, 133.01, 128.19, 127.54, 126.64,
126.14, 123.82, 123.56, 123.40, 121.22, 121.07, 120.49, 120.17, 119.17,
112.25, 110.03, MS (FAB) miz 664 [(M)þ]. Elemental Analysis
(calculated for C48H28N2O2): C, 86.73; H, 4.25; N, 4.21; O, 4.81.
Found: C, 86.31; H, 4.24; N, 4.12; O, 5.05.
2.3. Device fabrication and measurements
9-(Dibenzofuran-2-yl)-9H-carbazole
2-Iododibenzofuran
Green phosphorescent OLEDs were fabricated using vacuum
evaporation process by stacking 4,4'-cyclohexylidenebis[N,N-bis(4-
methylphenyl)aniline] (TAPC, 20 nm), N,N'-dicarbazolyl-3,5-
benzene (mCP, 10 nm), BDBFCz:Ir(ppy)3 (25 nm), diphenylphos-
phine oxide-4-(triphenylsilyl)phenyl (TSPO1, 30 nm), LiF (1 nm)
and Al (200 nm) on poly(3,4-ethylenedioxythiophene); poly(-
styrenesulfonate) (PEDOT:PSS, 60 nm) coated indium tin oxide
(ITO, 120 nm) substrate. The BDBFCz:Ir(ppy)3 emitting layer was
deposited by co-evaporation of BDBFCz and Ir(ppy)3 at a relative
weight ratio of 97:3 (3%), 95:5 (5%) and 90:10 (10%). A control de-
vice with 4,40-bis(N-carbazolyl)-1,10-biphenyl (CBP) as a host was
fabricated for comparison. Hole only device was fabricated by
depositing TAPC (30 nm), mCP (10 nm), BDBFCz (25 nm) and Al
(200 nm) on ITO (120 nm)/PEDOT:PSS (60 nm) substrate and
electron only device was prepared by evaporating Ca (5 nm),
BDBFCz (25 nm), TSPO1 (30 nm), LiF (1 nm) and Al (200 nm),
consecutively. Green phosphorescent OLEDs, hole only and electron
only devices were protected from moisture and oxygen by encap-
sulating the device with a glass cover with a desiccant inside.
Electrical characterization of the green phosphorescent OLEDs and
single carrier devices was carried out in ambient condition using
Keithley 2400 source measurement unit and CS 2000
spectroradiometer.
(11.0 g, 37.4 mmol) and carbazole (7.2 g, 43.0 mmol) were dis-
solved in 1,4-dioxane (250 ml) at room temperature under nitrogen.
After 30 min, trans-1,2-diaminocyclohexane (2.0 ml,18.7 mmol) was
added to the solution and the solution was refluxed overnight. After
cooling to room temperature, the solution was extracted using
methylene chloride. Methylene chloride was removed by evapora-
tion and obtained product was purified by column chromatography
on silica gel using toluene/n-hexane (1: 2) as an eluent. A white
powder was obtained as a product (7.9 g, yield: 63%).
1H NMR (400 MHZ, CDCl3):
d
8.17 (d, 2H, J ¼ 3.8 Hz), 8.11 (d, 1H,
J ¼ 1 Hz), 7.94 (d, 1H, J ¼ 4 Hz), 7.78 (d, 1H, J ¼ 4 Hz), 7.66e7.59 (m,
2H), 7.54e7.50 (m, 1H), 7.41e7.35 (m, 5H), 7.31e7.25 (m, 2H).
9-(4-Iododibenzofuran-2-yl)-9H-carbazole 9-(Dibenzofuran-
2-yl)-9H-carbazole (3.9 g, 12.0 mmol) was dissolved in dry tetra-
hydrofuran (50 ml) under a nitrogen atmosphere at room tem-
perature. The solution was cooled to ꢀ78 ꢁC and 2.5 M n-
butyllithium solution (5.4 ml, 14.0 mmol) was slowly added to the
solution. After 3 h, the mixture was warmed to room temperature
for 30 min and then cooled to ꢀ78 ꢁC. Diiodoethane (3.8 g,
14.0 mmol) in dry tetrahydrofuran (30 ml) was slowly added to the
solution and was stirred for overnight. The reaction was quenched
with distilled water and the solution was extracted using methy-
lene chloride and aqueous sodium sulfate solution. The methylene
chloride layer was separated and dried in vacuum oven after
removing methylene chloride by evaporation. A white powder was
obtained as a crude product and it was used without further
purification.
3. Results and discussion
Recently, there was a report that carbazole modified dibenzo-
furan compounds could improve the quantum efficiency of the
mixed host based phosphorescent OLEDs due to high triplet energy
and good hole transport properties [4]. Triplet excitons and carriers
were confined in the emitting layer and efficient light emission was
observed in the mixed host device of the carbazole modified
dibenzofuran host. That work motivated us to develop a bidi-
benzofuran derivative as the host material for phosphorescent
OLEDs because better thermal stability and high quantum effi-
ciency can be obtained by proper design of the bidibenzofuran
based host material. The design concept of the BDBFCz was to
develop 4,4’-bidibenzofuran core based carbazole compound for
high triplet energy, high thermal stability and good charge trans-
port properties. In particular, the bidibenzofuran core can improve
the thermal stability significantly compared with a common
dibenzofuran core structure because of a rigid zig-zag type design.
(2-(9H-carbazol-9-yl)dibenzofuran-4-yl)boronic
acid
9-
(Dibenzofuran-2-yl)-9H-carbazole (4.0 g, 12.0 mmol) was dissolved
in dry tetrahydrofuran (50 ml) under a nitrogen atmosphere at
room temperature. The solution was cooled to ꢀ78 ꢁC and 2.5 M n-
butyllithium solution (5.5 ml, 14.0 mmol) was slowly added. After
3 h, the mixture was warmed to room temperature and cooled
to ꢀ78 ꢁC. Triethylborate (2.4 ml, 14.0 mmol) was slowly added to
the solution and the solution was stirred at ꢀ78 ꢁC for 3 h. The
reaction was quenched with a 5% HCl solution and the solution was
extracted with methylene chloride. After removing methylene
chloride, crude product was obtained as a white powder. The crude
product was used for the coupling reaction without further
purification.
2,2′-Di(9H-carbazol-9-yl)-4,4'-bidibenzofuran
Iododibenzofuran-2-yl)-9H-carbazole (1.4 g, 5.0 mmol) and (2-
9-(4-