Novel indolo[3,2,1-jk]carbazole-based bipolar host material for highly efficient thermally activated delayed-fluorescence organic light-emitting diodes

Article abstract of DOI:10.1016/j.tet.2021.132317

A novel bipolar material (ICzPyr) composed of electron-donating indolo[3,2,1-jk]carbazole and electron-withdrawing pyridmidine was developed and its use as a host material in thermally activated delayed-fluorescence (TADF) organic light-emitting diode (OL

Full text of DOI:10.1016/j.tet.2021.132317

Tetrahedron 94 (2021) 132317
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Novel indolo[3,2,1-jk]carbazole-based bipolar host material for highly
efficient thermally activated delayed-fluorescence organic light-
emitting diodes
, c, *
Yasuhide Hiraga a, Rempei Kuwahara a, Taizo Hatta b
a Hirata Corporation, 111, Hitotsugi, Ueki, Kita-ku, Kumamoto, 861-0198, Japan
b Department of Nanoscience, Faculty of Engineering, Sojo University, 4-22-1, Ikeda, Nishi-ku, Kumamoto, 860-0082, Japan
c Kumamoto Institute for Photo-Electro Organics (PHOENICS), 3-11-38 Higashi-machi, Higashi-ku, Kumamoto, 862-0901, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel bipolar material (ICzPyr) composed of electron-donating indolo[3,2,1-jk]carbazole and electron-
withdrawing pyridmidine was developed and its use as a host material in thermally activated delayed-
fluorescence (TADF) organic light-emitting diode (OLED) applications was investigated. This material
exhibited practical thermal and morphological stabilities, a high triplet energy, and suitable HOMO and
LUMO levels for TADF applications. A 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene-based (4CzIPN-
based) TADF OLED using ICzPyr as a host material exhibited a much lower driving voltage, higher lu-
minous efficiency, and a significantly longer lifetime than a conventional 3,30-di(9H-carbazol-9-yl)-1,10-
biphenyl/4CzIPN-based OLED.
Received 8 March 2021
Received in revised form
20 June 2021
Accepted 24 June 2021
Available online 9 July 2021
Keywords:
Indolo[3,2,1-jk]carbazole
Indolo[3,2,1-jk]carbazole-pyrimidine
Bipolar host material
Host for TADF OLED
© 2021 Elsevier Ltd. All rights reserved.
Long lifetime TADF OLED
1. Introduction
complicated task because of their dramatic influence on the per-
formance and lifetimes of OLEDs [4e22].
Recently, thermally activated delayed-fluorescence (TADF) ma-
terials are attracting significant amounts of attention as next-
generation emitting materials for organic light-emitting diodes
(OLEDs) because they not only exhibit higher quantum efficiencies
compared to those of conventional fluorescent materials but they
are also devoid of heavy metals. Since the pioneering work of
Adachi et al. [1], much effort has been paid to the development of
highly efficient TADF materials, and external quantum efficiencies
(EQEs) comparable to those of phosphorescent materials (close to
20%) have been achieved [2]. In particular, carbazolyl-
dicyanobenzene-based TADF materials (CDCBs) are promising due
to their high EQEs, color tunabilities, and low synthesis costs [3].
However, there has been a delay in optimizing peripheral materials
for CDCBs, with few reports focusing on this aspect. In this respect,
the development of host materials is the most important and
Ideal OLED host-guest emitting systems prefer host molecules
capable of mediating the injection and transportation of both holes
and electrons to guest molecules. Therefore, bipolar molecular
structures composed of both hole- and electron-injecting and
transporting moieties, with highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) level
that are moderately deeper and shallower than those of the guest
material, respectively, are desired as host materials [23]. In addi-
tion, higher singlet and triplet excitation energies than those of the
guest materials are also required to confine excitons in the guest
molecules. In this regard, designing host materials based on donor-
acceptor molecular architectures similar to TADF is an effective way
of optimizing the energy structures of host molecules for TADF
materials [4e9]. The alternative method involves finding suitable
combinations of hole and electron transporting moieties [10e22,
24], and better performance compared to those conventional uni-
polar 4,40-di(9H-carbazol-9-yl)-1,10-biphenyl-type (CBP-type) host
materials has been achieved by employing these molecular archi-
tectures. Among them, the almost bipolar host materials for TADF
applications reported so far have tended to use N-connected car-
bazoles as donor units due to their high singlet and triplet
* Corresponding author. Department of Nanoscience, Faculty of Engineering, Sojo
University, 4-22-1, Ikeda, Nishi-ku, Kumamoto, 860-0082, Japan.
E-mail addresses: y_hiraga@hirata.co.jp (Y. Hiraga), r_kuwahara@hirata.co.jp
(R. Kuwahara), hatta@nano.sojo-u.ac.jp (T. Hatta).
https://doi.org/10.1016/j.tet.2021.132317
0040-4020/© 2021 Elsevier Ltd. All rights reserved.

Y. Hiraga, R. Kuwahara and T. Hatta
Tetrahedron 94 (2021) 132317
excitation energies and HOMO levels that are suitable for host
materials. However, Nichols et al. previously reported that one of
most significant reasons that phosphorescent OLEDs degrade dur-
ing operation is due to the cleavage of weak CeN single bonds in
host molecules, such as the carbazole-biphenyl bond in CBP [25].
Therefore, we expected that removing the weak bond in the host
molecule would improve operational stability, assuming that the
mechanism responsible for the operational degradation of TADF
OLEDs is similar to that of phosphorescent OLEDs.
In this study, we focused on indolo[3,2,1-jk]carbazole as the
donor unit because it not only exhibits a high carrier-transport
ability, excellent thermal and morphological stabilities, and a
high triplet excitation energy [26,27], but it can also be introduced
to the host molecule without a weak CeN single bond. Hence, py-
rimidine, as an electron acceptor, linked to the indolo[3,2,1-jk]
carbazole moiety via a m-phenylene (i.e., ICzPyr), as a novel bipolar
host material, was developed and characterized as a host material
aminophenyl-9H-carbazole (4), which was converted into the cor-
responding diazonium salt by the addition of sodium nitrite in a
mixture of acetic acid and sulfuric acid; subsequent thermal
decomposition have indolo[3,2,1-jk]carbazole (5). Bromination of 5
with N-bromosuccinimide gave 2-bromoindolo[3,2,1-jk]carbazole
(6), which was subjected to MiyauraeIshiyama borylation to afford
boronic ester 7 as one SuzukieMiyaura cross-coupling precursor.
Enone 10, which was prepared by the aldol condensation of 3-
bromobenzaldehyde (8) and acetophenone (9), was reacted with
benzamidine hydrochloride (11) to give pyrimidine 12 as the other
precursor. Finally, the SuzukieMiyaura cross-coupling of 7 and 12
afforded ICzPyr.
We used density functional theory (DFT) within Gaussian 09w
to investigate the HOMO and LUMO distributions of ICzPyr. The
structure of ICzPyr was optimized at the B3LYP/6-31G* level and
then subjected to single-point calculations at the B3LYP/
6e311þþG** level. Fig. 1 shows the spatial distributions of the
HOMO and LUMO of ICzPyr, which clearly reveals that the HOMO is
localized on the electron-donating indolo[3,2,1-jk]carbazole moi-
ety while the LUMO is localized on the electron-withdrawing py-
rimidine and peripheral phenyl units, highlighting the bipolar
characteristics of ICzPyr.
for
a
1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene-based
(4CzIPN-based) TADF OLED.
2. Results and discussion
The thermal and morphological properties of ICzPyr were
investigated by differential scanning calorimetry (DSC) and ther-
mogravimetric analysis (TGA). DSC traces were acquired at a rate of
10 ꢀC/min and are shown in Fig. 2. The glass transition temperature
(Tg) of ICzPyr was determined to be 110 ꢀC during the second DSC
heating scan, which is significantly higher than that of the
commonly used CBP (62 ꢀC). In addition, TGA revealed that ICzPyr
has a high thermal-decomposition temperature of 398 ꢀC (Td, cor-
responding to 5% weight loss; Fig. 3). Fig. 4 shows the UV/Vis-
absorption, fluorescence, and phosphorescence spectra of ICzPyr.
The synthesis of ICzPyr is schematically shown in Scheme 1.
Accordingly, the reaction 9H-carbazole (1) with 1-fluoro-2-
nitrobenzene (2) in the presence of K2CO3 gave 2-
nitrophenylcarbazole (3) through an aromatic nuclear substitu-
tion process. Reduction of
3 using Fe and NH4Cl gave 2-
The singlet excitation energy (
to be 3.17 eV from the emission maximum wavelength (391 nm) in
the fluorescence spectrum, and the triplet excitation energy ( E(T1-
S0)) was determined to be 2.83 eV from the highest energy peak of
the phosphorescence spectrum acquired at 77 in 2-
methyltetrahydrofuran; the E(T1-S0) of ICzPyr is sufficient for it
to act as the host material of a green TADF material. The small
singlet-triplet energy gap ( E(S1-T1)) of 0.34 eV is ascribable to
DE(S1eS0)) of ICzPyr was determined
D
K
D
D
spatial separation of the HOMO/LUMO of ICzPyr similar to the
examples described in the literature [2]. The fluorescence spectrum
of ICzPyr shows a very narrow full width at half maximum of only
22 nm (0.33 eV), which suggests that the indolo[3,2,1-jk]carbazole
backbone has a very rigid architecture.
Cyclic voltammetry (CV) and differential pulse voltammetry
(DPV) were used to investigate the bipolar electrochemical char-
acter of ICzPyr. As shown Fig. 5, ICzPyr exhibits reversible oxida-
tion and reduction potentials at 0.96 and ꢁ2.33 V versus ferrocene/
ferrocenium (Fc/Fcþ), respectively.
ICzPyr was subjected to photoelectron spectroscopy to deter-
mine its HOMO and LUMO levels; the ionization potential of ICzPyr,
was determined to be 5.90 eV (Fig. 6). The above photophysical,
Fig. 1. B3LYP/6e311þþG**//B3LYP/6-31G*-calculated HOMO and LUMO spatial dis-
tributions of ICzPyr (Visualized by GaussView 5.0.9 with isovalue of 0.02).
Scheme 1. Synthesis of ICzPyr.
2

Y. Hiraga, R. Kuwahara and T. Hatta
Tetrahedron 94 (2021) 132317
Fig. 4. Room-temperature UV/Vis-absorption and fluorescence (FL) spectra of ICzPyr
in dichloromethane, and the phosphorescence spectrum (Phos) of ICzPyr in 2-
methyltetrahydrofuran at 77 K.
Fig. 2. DSC traces of ICzPyr: a) first and b) second heating.
Fig. 5. Cyclic and differential pulse voltammograms (CV and DPV traces) of ICzPyr.
Fig. 3. TGA trace of ICzPyr.
electrochemical, and thermal properties of ICzPyr are summarized
in Table 1.
Assuming that the ionization potential corresponds to the
HOMO level, and that the value obtained by adding the optical
bandgap (3.04 eV) calculated using the onset of the longest
Fig. 6. Measurement of ionization potential of ICzPyr.
3

Y. Hiraga, R. Kuwahara and T. Hatta
Tetrahedron 94 (2021) 132317
Table 1
Photophysical, electrochemical, and thermal properties of ICzPyr.
D
E(S1eS0)/eVa
3.17
D
E(T1-S0)/eVb
2.83
Eox vs. Fc/Fcþc
Ered vs. Fc/Fcþc
ꢁ2.33
Ip/eVd
5.90
Tm/oCe
Tg/oCe
Td/oCf
ICzPyr
0.96
255
110
398
a
Determined from the emission maximum wavelength (391 nm) in the fluorescence spectrum.
Determined from the emission maximum wavelength (438 nm) in the phosphorescence spectrum.
Determined from the first oxidation/reduction peaks in the DPV spectra.
Determined by photoelectron spectroscopy.
Determined by DSC.
5% weight loss by TG.
b
c
d
e
f
wavelength absorbance band to the HOMO level is the LUMO level,
then the HOMO and LUMO levels of ICzPyr are ꢁ5.90 eV
and ꢁ2.86 eV respectively. Given that the HOMO and LUMO levels
of 4CzIPN are ꢁ5.80 and ꢁ3.40 eV3, the HOMO and LUMO levels of
ICzPyr are clearly suitable for its use as a host material for 4CzIPN.
In order to predict carrier transporting behavior, calculation of
reorganization energy was performed. It is well known that carrier
mobility of organic semiconductor strongly correlated with reor-
ganization energy defined in Marcus theory [28e30]. Thus, the
balance of hole (
l
þ) and electron (
l-) reorganization energy can be
treated as an evidence of bipolar carrier transporting [31e33].
Calculated reorganization energies for ICzPyr and mCBP which is
known as a suitable host material for 4CzIPN were summarized in
Table 2.
respectively, and significantly smaller
rier transporting in mCBP is highly biased to hole. In contrast,
and -of ICzPyr were close (0.18 and 0.24 eV, respectively), and
well-balanced carrier transporting can be expected.
The molecular structures of the materials and the device
configuration of the green TADF OLEDs are shown in Fig. 7. The
current-densityevoltageeluminance (J-V-L) characteristics were
evaluated and the lifetime of the device was measured at a constant
current at room temperature.
The device characteristics of the TADF OLEDs are summarized in
Fig. 8 and Table 3. The device using ICzPyr as a host material
fabricated under identical conditions to those used for the refer-
ence device exhibited a much lower driving voltage and a signifi-
cantly higher current and power efficiency than the reference TADF
device [34] that uses 3,30-di(9H-carbazol-9-yl)-1,10-biphenyl
(mCBP) as the host material. In addition, lifetimes measured at an
initial luminance of 10000 cd/m2 revealed that the ICzPyr-based
device operated for five-times longer than the mCBP-based device
at 50% of the initial luminance (LT50). These results suggest that
bipolar ICzPyr realizes more balanced carrier injection and trans-
portation in the emission layer than unipolar mCBP, and that the
molecular architecture, in which all components are connected by
robust CeC bonds, is effective for improving operational stability.
l
þ and
l
-of mCBP were estimated to 0.04 eV and 0.48 eV
l
þ than -suggest that car-
l
lþ
l
Fig. 7. a) Molecular structures of materials and b) configuration of the TADF OLED
device.
and the same architecture. It was revealed that the device perfor-
mance of a TADF OLED strongly depends on the host material as
well as the TADF emitter. We are currently further optimizing the
molecular architecture of host materials to realize better perfor-
mance and operational stability of TADF OLEDs.
4. Experimental section
4.1. General information
All reagents (GR grade) were purchased from Tokyo Chemical
Industry Co., Ltd. All melting points were measured with a Yana-
gimoto MP-500 P Micro melting point apparatus and are uncor-
rected. Infrared (IR) spectra were recorded on a PerkinElmer
Spectrum 100 FT-IR spectrophotometer. Nuclear magnetic reso-
nance (NMR) spectra were recorded on a JEOL JNM-ECS400 spec-
trometer (1H: 400 MHz, 13C: 100.5 MHz) using tetramethylsilane
(TMS) as an internal standard and acquired in chloroform-d unless
otherwise indicated. Mass spectra were obtained on a BRUKER-
DALTONICS Autoflex II MAKDI-TOF mass spectrometer. EI-HR
mass spectrometry was conducted on a JEOL JMS-700 mass spec-
trometer at the Evaluation Center of Materials Properties and
Function in the Institute for Materials Chemistry and Engineering
attached to Kyushu University. UVeVis-absorption spectra were
recorded on a JASCO V-670 spectrophotometer. Fluorescence (FL)
and phosphorescence (PL) spectra were recorded on a PerkinElmer
LS55 Luminescence spectrophotometer. Differential scanning
calorimetry (DSC) and thermal gravimetry (TG) were performed on
Rigaku Thermo Plus 2 instruments. Cyclic and differential pulse
voltammograms were recorded on a BAS ALS model 612D elec-
trochemical analyzer. Oxidation and reduction potentials were
measured in dichloromethane solution (1 mM) containing 0.1 M of
3. Conclusion
We developed a novel hybrid indolo[3,2,1-jk]carbazole-pyrimi-
dine bipolar host material (ICzPyr) that is effective as a green TADF
emitter for 4CzIPN. The TADF OLED using ICzPyr as the host ma-
terial exhibited a lower driving voltage, higher efficiency, and a
much longer lifetime than the OLED with mCBP as the host material
Table 2
Calculated reorganization energies of mCBP and ICzPyr.
Reorganization energy/eV
hole (
lþ)
electron (l-)
mCBP
ICzPyr
0.043
0.182
0.480
0.237
4

Y. Hiraga, R. Kuwahara and T. Hatta
Tetrahedron 94 (2021) 132317
Fig. 8. Device characteristics of TADF OLEDs using mCBP and ICzPyr as host materials: a) IeV (hollow) and luminance (filled), b) current efficiency, c) power efficiency, and d)
lifetime.
Table 3
Summary of device performance of TADF OLEDs using mCBP and ICzPyr as host materials.
Host
Current efficiency/cd/A
Luminous efficacy/lm/W
EQE/%
LT50/h
@100 cd/m2
@1000 cd/m2
@100 cd/m2
@1000 cd/m2
@100 cd/m2
@1000 cd/m2
(L0 ¼ 10000 cd/m2)
mCBP
ICzPyr
35.1
47.8
28.9
45.3
13.4
30.1
8.7
22.2
10.9
10.0
9.0
13.9
1.0
5.5
tetrabutylammonium hexafluorophosphate as the supporting
electrolyte. A glassy carbon electrode and platinum wire were used
as the working and counter electrodes respectively, and voltam-
metry was performed at a scan rate of 100 mV/s. The ionization
potential was determined by photoelectron spectroscopy on a
RIKEN KEIKI AC-3 photoelectron spectrophotometer. Column
chromatography was carried out using silica gel (Fuji Silysia, BW-
300). Temperature gradient sublimation purification was per-
formed using an ULVAC TRS-1S sublimator. Reorganization energies
were calculated on DFT using Gaussian 09 W software. Optimized
structures in neutral and charged state were calculated on B3LY/6-
31G* level respectively, and energy calculations were performed on
B3LYP/6e311þþG** level.
131.57 mmol) under a nitrogen atmosphere. After the mixture was
stirred at 70 ꢀC for 12 h, it was poured into water (300 mL) and the
precipitates were collected by filtration. The obtained solid was
washed with water (200 mL) and methanol (200 mL) to give 9-(2-
nitrophenyl)-9H-carbazole (3) in 94% yield (32.41 g, 112.43 mmol)
as yellow needles.
m.p. 154e155 ꢀC.
IR (ATR, cmꢁ1):
n 3051, 1604, 1573, 1523, 1497, 1477, 1453, 1443,
1369, 1350, 1334, 1316, 1300, 1228, 1184, 1150, 1122, 1108, 1086,
1039, 1019, 1002, 994, 957, 942, 917, 872, 849, 782, 748, 725, 704,
667.
1H NMR (400 MHz, CDCl3):
d
7.09 (d, J ¼ 8.0 Hz, 2H, 1,8-H), 7.28
(t, J ¼ 7.2 Hz, 2H, 3,6-H), 7.36 (dd, J ¼ 7.2, 7.7 Hz, 2H, 2,7-H),
7.59e7.63 (m, 2H, 4,6-H in 2-ph), 7.77 (dd, J ¼ 7.6, 7.8 Hz, 1H, 5-H in
ph), 8.09e8.14 (m, 3H, 4,5-H and 3-H in ph).
4.2. Synthesis
13C NMR (100.5 MHz, CDCl3)
d 109.03, 120.53, 120.63, 123.81,
125.88, 126.28, 129.10, 131.21, 131.35, 134.19, 140.74, 147.35.
4.2.1. 9-(2-Nitrophenyl)-9H-carbazole (3)
MALDI-TOF-MS (positive, dithranol): m/z 288 ([Mþ]).
To a solution of 9H-carbazole 1 (20.00 g, 119.61 mmol) in N,N-
dimethylformamide (DMF, 150 mL) was added potassium carbon-
ate (33.06 g, 239.22 mmol) and 1-fluoro-2-nitrobenzene 2 (18.56 g,
5

Y. Hiraga, R. Kuwahara and T. Hatta
Tetrahedron 94 (2021) 132317
4.2.2. 9-(2-aminophenyl)-9H-carbazole (4)
7.57 (td, J ¼ 7.7, 1.1 Hz, 2H, 5,11-H), 7.88 (d, J ¼ 8.1 Hz, 2H, 7,9-H),
8.07 (d, J ¼ 7.7 Hz, 2H, 4,12-H), 8.15 (s, 2H, 1,3-H).
A
mixture of 9-(2-nitrophenyl)-9H-carbazole 3 (10.00 g,
34.69 mmol), iron powder (9.68 g, 173.43 mmol), and ammonium
chloride (9.28 g, 173.43 mmol) in ethanol/water (9:1 mixture v/v,
200 mL) was refluxed for 4 h under a nitrogen atmosphere. The
solid was removed by hot-filtration and the filtrate was allowed to
stand at room temperature for 1 h. The precipitates were collected
by filtration and washed with ethanol to give 9-(2-aminophenyl)-
9H-carbazole (4) in 86% yield (7.71 g, 29.83 mmol) as colorless
needles.
13C NMR (100.5 MHz, CDCl3):
d 112.25, 115.80, 119.63, 121.97,
122.24, 123.29, 127.36, 129.24, 138.99, 141.97.
MALDI-TOF-MS (positive, dithranol): m/z 319 (79Br), 321 (81Br)
[M þ].
4.2.5. 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)indolo-
[3,2,1-jk]carbazole (7)
2-bromoindolo[3,2,1-jk]carbazole 6 (1.00 g, 3.12 mmol), bispi-
nacolatodiboron (0.95 g, 3.74 mmol), and potassium acetate (1.22 g,
12.48 mmol) were added deaired dimethyl sulfoxide (15 mL) under
a nitrogen atmosphere and the mixture was warmed to 100 ꢀC.
m.p. 118e120 ꢀC.
IR (ATR, cmꢁ1):
n 3474, 3381, 3054, 1609, 1594, 1501, 1488, 1478,
1460, 1447, 1359, 1337, 1311, 1255, 1229, 1177, 1156, 1140, 1119, 1049,
1021, 998, 940, 911, 850, 824, 774, 744, 724.
[1,10-bis(diphenylphosphino)ferrocene]dichloropalladium
(II)
1H NMR (400 MHz, CDCl3):
d
3.00 (br-s, 2H, NH2), 6.91 (t,
dichloromethane adduct (127 mg, 0.16 mmol) was added to the
mixture, which was stirred for 4 h at 100 ꢀC under a nitrogen at-
mosphere. The reaction mixture was poured into water (100 mL)
and extracted with chloroform (50 mL). The organic phase was
washed with water (50 mL x 2) and dried over anhydrous mag-
nesium sulfate. The solvent was removed under reduced pressure
and the residue was purified by silica gel chromatography eluted
with dichloromethane/hexane (3:2 mixture (v/v)) and recrystalli-
zation from dichloromethane/hexane to give 2-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)indolo[3,2,1-jk]carbazole (7)
in 70% yield (802 mg, 2.18 mmol) as colorless cubes.
J ¼ 7.7 Hz, 1H, 5-H in 9-aminophenyl), 6.96 (d, J ¼ 8.0 Hz, 1H, 3-H in
9-aminophenyl), 7.18 (d, J ¼ 8.1 Hz, 2H, 1,8-H in carbazole),
7.27e7.34 (m, 4H, ArH), 7.41 (t, J ¼ 7.7 Hz, 2H, 2,7-H in carbazole),
8.15 (d, J ¼ 7.7 Hz, 2H, 4,5-H in carbazole).
13C NMR (100.5 MHz, CDCl3):
d 110.12, 116.52, 118.83, 119.86,
120.30, 122.27, 123.33, 126.00, 129.58, 129.61, 160.62, 144.00.
MALDI-TOF-MS (positive, dithranol): m/z 258 ([Mþ]).
4.2.3. Indolo[3,2,1-jk]carbazole (5)
To a solution of 9-(2-aminophenyl)-9H-carbazole 4 (5.00 g,
19.36 mmol) in acetic acid (50 mL) and sulfuric acid (5 mL) mixture
was added dropwise an aqueous solution of sodium nitrite (2.00 g,
29.04 mmol in 10 mL water) over a period of 15 min. The tem-
perature of the mixture was maintained below 15 ꢀC while addi-
tion. After that, the mixture was stirred at 15 ꢀC for 10 min and then
stirred at 130 ꢀC for 30 min. The reaction mixture was cooled to
room temperature and poured into water (200 mL). The solid was
collected by filtration and washed with water (100 mL) and
methanol (100 mL). The crude product was purified by flash silica
gel chromatography eluted with toluene and recrystallization from
dichloromethane/ethanol to give indolo[3,2,1-jk]carbazole (5) in
60% yield (2.80 g, 11.62 mmol) as colorless powder.
IR (ATR, cmꢁ1):
n 3054, 2976, 2924, 1648, 1603, 1585, 1504, 1469,
1449, 1420, 1402, 1368, 1377, 1329, 1308, 1297, 1264, 1246, 1220,
1209, 1164, 1135, 1086, 1071, 1037, 962, 926, 885, 868, 846, 835, 781,
753, 741, 736, 702, 683, 659.
1H NMR (400 MHz, CDCl3):
d
1.44 (s, 12H, CH3), 7.36 (td, J ¼ 7.7,
0.9 Hz, 2H, 6,10-H), 7.55 (td, J ¼ 7.7, 1.1 Hz, 2H, 5,11-H), 7.91 (d,
J ¼ 8.1 Hz, 2H, 7,9-H), 8.13 (dt, J ¼ 7.7, 0.9 Hz, 2H, 4,12-H), 8.56 (s, 2H,
1,3-H).
13C NMR (100.5 MHz, CDCl3):
d 24.99, 83.81, 112.12, 118.22,
121.89, 123.15, 126.30, 126.64, 129.96, 138.79, 145.86.
MALDI-TOF-MS (positive, dithranol): m/z 367 [M þ].
m.p. 155e156 ꢀC.
4.2.6. (E)-3-(3-bromophenyl)-1-phenylprop-2-en-1-one (10)
To a solution of 3-bromobenzaldehyde (10.00 g, 54.05 mmol)
and acetophenone (6.49 g, 54.05 mmol) in ethanol (100 mL) was
added sodium hydroxide (2.16 g, 54.05 mmol). After the mixture
was stirred at room temperature for 4 h, the precipitates were
collected by filtration and washed with methanol (100 mL) to give
(E)-3-(3-bromophenyl)-1-phenylprop-2-en-1-one (10) in 89% yield
(13.81 g, 48.10 mmol) as colorless powder.
IR (ATR, cmꢁ1):
n 3049, 1655, 1624, 1602, 1584, 1525, 1493, 1482,
1466, 1447, 1431, 1370, 1340, 1311, 1256, 1232, 1163, 1154, 1122, 1096,
1073, 1039, 1012, 994, 964, 953, 928, 893, 854, 841, 815, 794, 748,
727, 684.
1H NMR (400 MHz, CDCl3):
d
7.36 (td, J ¼ 7.6, 0.9 Hz, 2H, 6,10-H),
7.55 (td, J ¼ 7.6, 0.9 Hz, 2H, 5,11-H), 7.58 (t, J ¼ 7.5 Hz, 1H, 2-H), 7.91
(d, J ¼ 7.6 Hz, 2H, 7,9-H), 8.04 (d, J ¼ 7.4 Hz, 2H, 4,12-H), 8.14 (d,
J ¼ 7.7 Hz, 2H, 1,3-H).
m.p. 78e79 ꢀC.
13C NMR (100.5 MHz, CDCl3):
d
122.22, 118.55, 119.45, 121.74,
IR (ATR, cmꢁ1):
n 3062, 1656, 1604, 1593, 1578, 1553, 1478, 1448,
122.89, 123.20, 126.74, 130.13, 138.79, 143.84.
1415, 1345, 1334,1305, 1284, 1215, 1199, 1181, 1091, 1073, 1032, 1014,
989, 972, 931, 917, 897, 860, 820, 796, 771, 702, 681, 658.
MALDI-TOF-MS (positive, dithranol): m/z 241 ([M þ]).
1H NMR (400 MHz, CDCl3):
d
7.30 (t, J ¼ 7.8 Hz, 1H, 5-H in 3-
4.2.4. 2-bromoindolo[3,2,1-jk]carbazole (6)
bromophenyl), 7.51 (d, J ¼ 6.2 Hz, 1H, 6-H in 3-bromophenyl),
7.52e7.56 (m, 3H, 2-H and 3,5-H in 1-phenyl), 7.61 (tt, J ¼ 7.3,1.3 Hz,
1H, 4-H in 1-ph), 7.73 (d, J ¼ 15.8 Hz, 1H, 3-H), 7.80 (t, J ¼ 1.7 Hz, 1H,
2-H in 3-bromophenyl), 8.01 (d, J ¼ Hz, 2H, 2,6-H in 1-phenyl).
To a solution of indolo[3,2,1-jk]carbazole 5 (2.00 g, 8.29 mmol)
in chloroform (50 mL) was added dropwise N-bromosuccinimide
(1.48 g, 8.29 mmol) in DMF (20 mL) over a period of 10 min. After
the mixture was stirred for 8 h, it was washed with water (50 mL x
2) and dried over anhydrous magnesium sulfate. The solvent was
removed under reduced pressure and the residue was recrystal-
lized from dichloromethane/acetonitrile to give 2-bromoindolo
[3,2,1-jk]carbazole (6) in 41% yield (1.09 g, 3.40 mmol) as color-
less powder.
13C NMR (100.5 MHz, CDCl3):
d 123.09, 123.26, 127.23, 128.54,
128.70, 130.46, 130.83, 133.01, 133.23, 137.03, 137.90, 142.89, 189.98.
MALDI-TOF-MS (positive, dithranol): m/z 287 [MþH]þ.
4.2.7. 4-(3-bromophenyl)-2,6-diphenylpyrimidine (12)
To a solution of (E)-3-(3-bromophenyl)-1-phenylprop-2-en-1-
one 10 (10.00 g, 34.83 mmol) in acetonitrile (100 mL) was added
triethylamine (14.10 g, 19.34 mL, 139.32 mmol) and benzamidine
hydrochloride (5.45 g, 34.83 mmol). After the mixture was vigor-
ously stirred at 50 ꢀC for 24 h under air, it was poured into methanol
(150 mL) and allowed to stand at room temperature for 6 h. The
m.p. 204e206 ꢀC.
IR (ATR, cmꢁ1):
n 3053, 1652, 1603, 1569, 1496, 1468, 1445, 1415,
1368, 1339, 1301, 1268, 1229, 1163, 1151, 1135, 1084, 1049, 1030, 966,
927, 879, 859, 844, 801, 776, 756, 736, 726, 660.
1H NMR (400 MHz, CDCl3):
d
7.36 (td, J ¼ 7.7, 0.9 Hz, 2H, 6,10-H),
6

Y. Hiraga, R. Kuwahara and T. Hatta
Tetrahedron 94 (2021) 132317
precipitates were collected by filtration and washed with methanol
(50 mL) to give 4-(3-bromophenyl)-2,6-diphenyl-pyrimidine (12)
in 75% yield (10.12 g, 26.12 mmol) as colorless powder.
m.p. 125e126 ꢀC.
The current-densityevoltageeluminance (J-V-L) characteristics
of the device were evaluated using a Keithley 2400 source meter
and a Konica Minolta CS-2000 luminance meter, and the lifetime
was measured using a Konica Minolta CS-100 A luminance meter at
a constant current at room temperature.
IR (ATR, cmꢁ1):
n 3057, 1588, 1566, 1528, 1495, 1476, 1446, 1422,
1378, 1362, 1351, 1307, 1272,1234, 1174,1158, 1106,1070, 1050, 1023,
997, 924, 911, 863, 834, 807, 793, 774, 747, 698, 684, 660.
Declaration of competing interest
1H NMR (400 MHz, CDCl3):
d
7.44 (t, J ¼ 7.6 Hz, 1H, 4-H in 4-
bromophenyl), 7.53e7.59 (m, 6H, 3,4,5-H in 2,6-phenyl), 7.67
(ddd, J ¼ 8.2, 1.8, 0.9 Hz, 1H, 4-H in 4-bromophenyl), 7.98 (s, 1H, 5-
H), 8.21 (ddd, J ¼ 8.2, 1.8, 0.9 Hz, 1H, 6-H in 4-bromophenyl), 8.30
(m, 2H, 2,6-H in 6-phenyl), 8.44 (t, J ¼ 1.8 Hz, 1H, 2-H in 4-
bromophenyl), 8.72 (m, 2H, 2,6-H in 2-phenyl).
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.
Acknowledgements
13C NMR (100.5 MHz, CDCl3):
d 120.28, 123.21, 125.80, 127.30,
128.49, 128.94, 130.31, 130.39, 130.80, 130.94, 133.61, 137.23, 137.87,
139.59, 163.16, 164.59, 164.99.
This work was supported in part by Regional Innovation Strat-
egy Support Program from the Ministry of Education, Culture,
Sports, Science and Technology of Japan.
MALDI-TOF-MS (positive, dithranol): m/z 387 [M þH]þ.
4.2.8. 2-[3-(2,6-diphenylpyrimidin-4-yl)phenyl]indolo[3,2,1- jk]
carbazole (ICz-Pyr)
Appendix A. Supplementary data
4-(3-bromophenyl)-2,6-diphenylpyrimidine 12 (844 mg,
2.18 mmol) and 2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
indolo[3,2,1-jk]carbazole 7 (800 mg, 2.18 mmol) were added to the
mixture of toluene (10 mL), ethanol (5 mL) and 2 M sodium car-
bonate aq. (10 mL). After the mixture was refluxed for 5 min under
a nitrogen atmosphere, tetrakis(triphenylphosphine)- palladium(0)
(254 mg, 0.22 mmol) was added to the mixture, which was further
refluxed for 8 h. The reaction mixture was cooled to room tem-
perature and poured into water (100 mL). The mixture was
extracted with chloroform (50 mL x 2) and the organic phase was
dried over anhydrous magnesium sulfate. The solvent was removed
under reduced pressure and the residue was purified by flash silica
gel chromatography eluted with chloroform and recrystallization
from toluene to give 2-(3-(2,6-diphenyl-pyrimidin-4-yl)phenyl)
indolo[3,2,1-jk]carbazole (ICz-Pyr) in 65% yield (778 mg,
1.42 mmol) as colorless powder, which was further purified by
temperature gradient sublimation purification.
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132317.
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d 110.62, 112.40, 118.78, 119.52,
121.96, 123.41, 125.67, 127.08, 127.26, 127.38, 128.51, 128.56, 128.97,
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8