M.-S. Gong et al. / Organic Electronics 42 (2017) 66e74
67
as host materials than carbazole because of their electron donor
moiety and thermal stability, which improves their quantum effi-
ciency [35,36].
3H), 7.35e7.31 (t, 3H). Mass (FAB) m/z 290 [(Mþ1)þ]. Anal. Calcd.
for C18H11NO3: C, 74.73%; H, 3.83%; N, 4.84%; O, 16.59%. Found: C,
74.9%; H, 3.40%; N, 4.43%; O, 16.12%.
In this study, instead of mCP with carbazole, 1,3-bis(5H-benzo-
furo[3,2-c]carbazol-5-yl)benzene (BFCz) and 1,3-bis(5H-benzo[4,5]
thieno[3,2-c]carbazol-5-yl)benzene (BTCz) were synthesized using
benzofurocarbazole and benzothienocarbazole, respectively. BFCz
and BTCz exhibit high triplet energies (2.94 eV and 2.93 eV,
respectively) and are very suitable for use as blue phosphorescent
host materials. In addition, they exhibit high thermal stability and
have glass transition temperatures of 147 ꢀC (BFCz) and 157 ꢀC
(BTCz), respectively. The PHOLED with BTCz exhibited high quan-
tum efficiency (16.1%) and good color stability, between 100 cd/m2
and 3000 cd/m2, with increasing voltage.
2.3. Preparation of 5H-benzofuro[3,2-c]carbazole
4-(2-Nitrophenyl)dibenzo[b,d]furan (10.00 g, 34.57 mmol) was
dissolved in triethylphosphite (100 mL) and refluxed for 10 h. The
reaction mixture was cooled to room temperature and extracted
with ethyl acetate and distilled water. The organic layer was treated
with anhydrous magnesium sulfate, and the solvent was removed
by rotary evaporation. Impurities were removed by column chro-
matography on silica gel using dichloromethane/n-hexane to
obtain a yellowish powder. The results are as follows:
Yield 95%. 1H NMR (300 MHz, CDCl3)
d 11.8 (s, 1H), 8.32e8.35 (d,
2. Materials and methods
1H), 7.82e7.84 (d, 1H), 7.64e7.61 (d, 1H), 7.58e7.51 (d, 1H),
7.49e7.41 (m, 3H), 7.35e7.31 (t, 3H). Mass (FAB) m/z 257 [(Mþ1)þ].
Anal. Calcd. for C18H10NO: C, 87.36%; H, 3.93%; N, 5.47%; O, 6.24%.
Found: C, 87.7%; H, 3.4%; N, 5.03%; O, 6.41%.
2.1. Materials and instruments
Dibenzo[b,d]furan-4-ylboronic acid, dibenzo[b,d]thiophen-4-
ylboronic
cyclohexanediamine, copper(I) iodide, 1,3-diiodobenzene, tripo-
tassium phosphate, triethylphosphite, tetrakis(-
acid,
1-bromo-2-nitrobenzene,
( )-trans-1,2-
2.4. Preparation of 1,3-bis(5H-benzofuro[3,2-c]carbazol-5-yl)
benzene (BFCz)
triphenylphosphine)palladium(0), and tripotassium phosphate
(Aldrich Chem. Co. St. Louis, MO, USA) were used without further
purification. Potassium carbonate, toluene, dichloromethane, ethyl
acetate, n-hexane, 1,4-dioxane, and ethanol (Duksan Chem. Co.
Seoul, Korea) were used as received. The solvents were dried and
degassed following standard procedures.
5H-benzofuro[3,2-c]carbazole (5.00 g, 19.43 mmol), 1,3-
diiodobenzene (3.05 g, 9.25 mmol), copper(I) iodide (0.18 g,
0.93 mmol), and tripotassium phosphate (4.32 g, 20.36 mmol) were
dissolved in 1,4-dioxane (80 mL) and then added to the flask. After
stirring for 1 h at room temperature under a nitrogen atmosphere, a
( )-trans-1,2-cyclohexanediamine (0.11 g, 0.93 mmol) was added.
The reaction mixture was stirred for 48 h at 100 ꢀC, and the reaction
was quenched with toluene (300 mL). The solvent was removed by
rotary evaporation, and the crude product was washed with water.
Impurities were removed by column chromatography on silica gel
using dichloromethane/n-hexane. Additionally, BFCz was purified
by sublimation under a vacuum. As a result, the title compound was
obtained as a white powder. The results are as follows:
1H and 13C nuclear magnetic resonance (NMR) spectra were
recorded on a Varian, Unity Inova (300 MHz) system. Fourier
transform infrared (FT-IR) spectra were obtained with a Varian 640
FT-IR device. Gas chromatography (GC) mass spectra were recorded
using a Jeol (JMS-AX505WA) and HP 5890 Series II (Brea, CA, USA)
in fast atom bombardment (FAB) mode. Elemental analyses were
performed using a CE Instruments EA1110 device (Hindley Green,
Wigan, UK). The ultravioletevisible (UVevis) spectra were recor-
ded on a UVevis spectrophotometer (Shimadzu, UV-1601PC;
Tokyo, Japan) and photoluminescence (PL) spectra were obtained
using a fluorescence spectrophotometer (Jasco FP-6500; Tokyo,
Japan). Differential scanning calorimetry (DSC) measurements
were performed on a Shimadzu DSC-60 under nitrogen at a heating
rate of 10 ꢀC/min. Thermogravimetric analysis (TGA) was per-
formed on a Shimadzu TGA-50 at a heating rate of 10 ꢀC/min. Cyclic
voltammetry measurements were carried out in an acetonitrile
solution with 0.1-M tetrabutylammonium perchlorate. Silver (Ag)
metal was used as the quasi-reference electrode, Pt wire was used
as a counter electrode, and polished glassy carbon was used as the
working electrode.
Yield 45%. Mp: 298 ꢀC. 1H NMR (300 MHz, CDCl3)
d 8.61 (d, 2H),
7.95e8.03 (m, 4H), 7.91e7.94 (m, 2H), 7.84e7.88 (m, 2H), 7.62e7.67
(d, 2H), 7.5e7.59 (d, 2H), 7.42e7.48 (m, 4H), 7.44e7.48 (m, 4H),
7.38e7.43 (t, 2H). 13C NMR (300 MHz, CDCl3)
d 156.2, 151, 141, 139.5,
138.5, 138, 132, 126.1, 125.8, 125.6, 125.4, 125.2, 125, 123.6, 122.4,
122.2, 121.6, 118.2, 118.1, 117, 111.5, 110, 109, 108, 107.5, 106. FT-IR
(KBr, cmꢁ1) 3050, 3020 (aromatic C-H). Mass (FAB) m/z 588
[(Mþ1)þ]. Anal. Calcd. for C42H24N2O2: C, 85.70%; H, 4.11%; N, 4.76%;
O, 5.44%. Found: C, 84.22%; H, 4.01%; N, 4.71%; O, 4.30%.
2.5. Preparation of 4-(2-nitrophenyl)dibenzo[b,d]thiophene
The method used to synthesize 4-(2-nitrophenyl)dibenzo[b,d]
thiophene was the same as that for 4-(2-nitrophenyl)dibenzo[b,d]
furan, except that dibenzothiophene-4-boronic acid (10.76 g,
47.16 mmol) was used instead of dibenzofuran-4-boronic acid. The
results are as follows:
2.2. Preparation of 4-(2-nitrophenyl)dibenzo[b,d]furan
Dibenzo[b,d]furan-4-ylboronic acid (10.00 g, 47.16 mmol), 1-
bromo-2-nitrobenzene (7.94 g, 39.31 mmol), and tetrakis(-
triphenylphosphine)palladium(0) (1.59 g, 1.38 mmol) were dis-
solved in a solution of 2-M potassium carbonate (70 mL) and
toluene (200 mL). The reaction mixture was refluxed under nitro-
gen for 24 h. The mixture was diluted with dichloromethane and
washed with distilled water. The organic layer was treated with
anhydrous magnesium sulfate and evaporated in vacuo to yield the
crude product, which was purified by column chromatography
using dichloromethane/n-hexane to obtain a yellow powder. The
results are as follows:
Yield 80%. 1H NMR (300 MHz, CDCl3)
d 8.39e8.38 (d, 2H),
8.14e8.11 (m, 2H), 7.72e7.69 (d, 1H), 7.67e7.64 (t, 1H), d7.57e7.46
(m, 3H),
d
7.39e7.35 (m, 2H). Mass (FAB) m/z 306 [(Mþ1)þ]. Anal.
Calcd. for C18H11NO2S: C, 70.80%; H, 3.63%; N, 4.59%; O, 10.48%; S,
10.50%. Found: C, 70.4%; H, 3.22%; N, 4.43%; O, 10.8%; S, 10.0%.
2.6. Preparation of 5H-benzo[4,5]thieno[3,2-c]carbazole
The method used to synthesize 5H-benzo[4,5]thieno[3,2-c]
carbazole was the same as that for 5H-benzofuro[3,2-c]carbazole,
except that 4-(2-nitrophenyl)dibenzo[b,d]thiophene (10.56 g,
34.57 mmol) was used instead of 4-(2-nitrophenyl)dibenzo[b,d]
Yield 85%. 1H NMR (300 MHz, CDCl3)
7.82e7.84 (d,1H), 7.64e7.61 (d,1H), 7.58e7.51 (d,1H), 7.49e7.41 (m,
d 8.12e8.15 (m, 2H),