Utilizing 9,10-dihydroacridine and pyrazine-containing donor-acceptor host materials for highly efficient red phosphorescent organic light-emitting diodes

Article abstract of DOI:10.1039/c6tc02180h

Two novel materials, 10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrFPhAc) and 10-(6-(dibenzo[b,d]thiophen-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (PrTPhAc), were designed and synthesized by introducing heter

Full text of DOI:10.1039/c6tc02180h

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DOI: 10.1039/C6TC02180H
Journal Name
RSCPublishing
ARTICLE
Utilizing 9,10-Dihydroacridine and Pyrazine-
Containing Donor-Acceptor Host Materials for High
Efficient Red Phosphorescent Organic Light-Emitting
Diodes
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
Xiang-Yang Liu, Feng Liang, Yi Yuan, Zuo-Quan Jiang,* Liang-Sheng Liao*
DOI: 10.1039/x0xx00000x
Two
dihydroacridine
novel materials
10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-
and 10-(6-(dibenzo[b,d]thiophen-1-yl)pyrazin-2-yl)-9,9-
www.rsc.org/
(PrFPhAc)
diphenyl-9,10-dihydroacridine (PrTPhAc) were designed and synthesized by introducing
heterocyclic pyrazine between 9,10-dihydroacridine and dibenzofuran/dibenzothiophene
moieties. The basic properties, such as thermal, photophysical and electrochemical
properties, were systematically investigated and compared. Both materials have suitable
triplet energies for red phosphorescent organic light-emitting diodes, and dibenzofuran
(DBF) derivative PrFPhAc was finally achieved superior external quantum efficiency of
22%.
Introduction
Generally speaking, red phosphors will suffer from much worse
triplet-involved quenching processes as compared to blue and
Organic light-emitting diodes (OLEDs), since invented in
1987,1 have attracted massive attention due to their superior
potential applications in lighting and display.2 In the early stage
of OLEDs, it is commonly known that the process of charge
recombination to form singlet and triplet excitons was
controlled by spin statistics and the ratio of singlet to triplet
excitons formed is 1:3, thus the internal quantum efficiency
(IQE) of OLEDs was limited within 25% in theory and nearly
75% triplet excitons was wasted.3 It is clear that if one pathway
can improve the utilization ratio of triplet excitons, the quantum
efficiency of OLEDs will be quadrupled ideally. Fortunately,
by using heavy metal complex (such as, iridium or platinum) as
emitters doped into the organic matrix can break the law of spin
statistics via strong spin-orbit coupling effect, OLEDs can
achieved nearly 100% IQE by harvesting both singlet and
triplet excitons through fast intersystem crossing (ISC)
process.3,4 Because this mechanism normally requires the
phosphorescent emitters to be doped into an appropriate host to
avoid several triplet excitons quenching processes, such as
aggregation-caused quenching (ACQ) and triplet-triplet
annihilation (TTA). Thus, host matrix is indispensable in highly
efficient phosphorescent OLEDs (PHOLEDs). For a good host
material for PHOLEDs, favorable electroactivity and suitable
excited energy are required for confining triplet excitons in
dopants and suppressing triplet-involved quenching effects has
been one of the significant challenges.5,6
green phosphors due to their high polarity, narrow energy gap
Eg), and longer exciton lifetime, which result in serious device
(
efficiency reduction.6 And even with a light-doping device
configuration, which will also lead to remarkable triplet
quenching effects between host-host and host-guest
molecules.4d,6,7 Although red PHOLEDs have been studied
widely, there are still some important issues to be resolved,
such as triplet quenching and carrier trapping processes and one
challenge of them is designing suitable host.6c Up to now, only
a few of red phosphorescent host materials have been reported
with good electroluminescent (EL) performance.6c,8 But the
triplet states are normally distributed on the charge transport
groups, which will simultaneously be involved in triplet
quenching process and further speed up the efficiency roll-off.6c
For a suitable host material for red PHOLEDs, good thermal
stability, high triplet energy (ET, at least higher than that of red
phosphors) and suitable energy level are necessary. Besides,
balanced charge transporting ability is also demanded.9
In this contribution, we designed and synthesized two novel red
host materials 10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-
diphenyl-9,10-dihydroacridine
(PrFPhAc)
and
10-(6-
(dibenzo[b,d]thiophen-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-di-
hydroacridine (PrTPhAc). We selected 9,10-dihydro-acridine as
the donor group to facilitate hole injection and two appended
phenyl rings to enhance molecular thermal stability. On the
other hand, electron-deficient pyrazine along with dibenzofuran
(DBF) or dibenzothiophene (DBT) are introduced in ortho
-
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DOI: 10.1039/C6TC02180H
linking direction. Experimental results showed that both PrFPhAc is red-shifted by 6 nm as compared to that of
materials presented good thermal stability and suitable triplet PrTPhAc (from 412 to 418 nm).
energy for red phosphorescent emitters, which qualified them
as host materials for red PHOLEDs. Therefore,
bis(2-
methyldibenzo-[f,h]-quinoxaline) Ir(III) (acetylacetonate)
(Ir(MDQ)2(acac)) doped devices were fabricated. As a result,
the champion external quantum efficiency (EQE) of 22% was
achieved by PrFPhAc based device.
Fig. 1 Room-temperature UV-vis absorption and PL spectra in toluene solution,
and Phos spectra in 2-MeTHF matrix at 77 K (inset).
Scheme 1 Molecular structure and synthetic routes of PrFPhAc, and PrTPhAc.
The PL spectra of PrFPhAc and PrTPhAc are peak at 498 and
496 nm, respectively. Furthermore, the PL emission is nearly
symmetric, featureless and spectrally broader, which is likely to
be correlated to the charge-transfer nature of these materials.10
Fig. 1 (inset) also shows the Phos spectra of both materials in 2-
MeTHF matrix. PrFPhAc and PrTPhAc exhibited the highest
vibronic bands at around 502 and 504 nm, corresponding to ET
of 2.47 and 2.46 eV, respectively. These results indicated both
materials could be developed for hosting red emitter in
PHOLEDs.
Results and discussions
Synthesis and characterization
Syntheses of 10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-
diphenyl-9,10-dihydroacridine
(dibenzo[b,d]thiophen-1-yl)pyrazin-2-yl)-9,9-diphenyl-9,10-di-
hydroacridine (PrTPhAc) are outlined in Scheme 1. The key
(PrFPhAc)
and
10-(6-
intermediate
of
9,9-diphenyl-9,10-dihydroacridine
was
synthesized according to our previous work.2i Then it was
readily converted to 10-(6-chloropyrazin-2-yl)-9,9-diphenyl-
9,10-dihydroacridine through the classic Buchwald−Hartwig
C−N coupling reaction between. At last, the final products
(PrFPhAc and PrTPhAc) can be obtained via Pd-catalyzed
Thermal property
Suzuki−Miyaura
coupling
reaction
between
10-(6-
chloropyrazin-2-yl)-9,9-diphenyl-9,10-di-hydroacridine and the
corresponding boronic acid of dibenzofuran (DBF) and
dibenzothiophene (DBT) in good yields.
Photophysical property
The UV-vis absorption and photoluminescence (PL) spectra of
these materials were measured at room temperature in toluene
solution and the phosphorescence (Phos) spectra were
measured in 2-methyltetrahydrofuran (2-MeTHF) matrix at low
temperature (77 K). The detailed data are shown in Fig. 1 and
summarized in Table 1. Their UV-vis absorption spectra are
quite similar with the maximum peaks and shoulders for
PrFPhAc and PrTPhAc, respectively. The absorption peaks at
301 and 296 nm could be attributed to the n→π* transitions of
the 9,10-dihydroacridine chromophore. The shoulder peaks at
Fig. 2 TGA and DSC (inset) curves of PrFPhAc and PrTPhAc.
A donor-acceptor configuration cannot only bring the ICT
effect but also increase the intermolecular force, reflected by
the thermal property. As shown in Fig. 2, we found both
PrFPhAc and PrTPhAc showed high glass transition
around 370 nm (369 and 379 nm) can be attributed to π
→π*
transitions of the pyrazine. Besides, the absorption onset of
o
o
temperature (Tg), 118 C for the former and 123 C for the
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C6TC02180H
latter. The appending phenyl rings to construct 3-D noting that both molecules showed similar thermal
configuration can be partly responsible for this result, but the decomposition temperatures (Td, corresponding to 5% weight
o
o
Tgs are still over 20 C higher than those of the host materials loss, Fig. 2) with 397 and 403 C for PrFPhAc and PrTPhAc,
with the similar structure with the benzene instead of pyrazine with tiny differences between the phenyl-core materials,2i
as the central core.2i Thus, the stronger intermolecular which indicated that the molecular size was the major
interaction following the increased molecular polarity also determinant for thermal stability.
contributed to better morphological stability.8f,11 It was worth
Table 1 Summary of the physical properties of PrFPhAc and PrTPhAc.
b
c
d
e
Absa
PLa
Tg
Td
Eg
ET
HOMOf/LUMOg
[eV]
Host
[nm]
[nm]
[oC]
118
123
[oC]
397
403
[eV]
2.97
3.00
[eV]
2.47
2.46
PrFPhAc
PrTPhAc
301, 377
296, 373
498
496
-6.04/-3.07
-6.02/-3.02
a) Measured in toluene solution at room temperature. b) Tg: Glass transition temperature. c) Td: Decomposition temperature. d)
Eg: Band gaps, calculated from the corresponding absorption onset. e) ET: Measured in 2-MeTHF glass matrix at 77 K. f)
HOMO levels, calculated from UPS data. g) LUMO levels calculated from the HOMOs and corresponding Egs.
Theoretical calculations
DFT calculations were utilized to simulate the frontier
molecular orbital (FMO) spatial distributions at a B3LYP/6-
31G(d) level for the structure of PrFPhAc and PrTPhAc. As
Fig. 3 shows, both molecule have similar HOMO distributions,
which are almost localized at the electron-rich 9,10-
dihydroacridine centers, while the LUMOs of PrFPhAc and
PrTPhAc are distributed on the pyrazine core and the phenyl in
each DBF and DBT. As to the specific values of HOMO and
LUMO levels, we can found that both materials had very close
HOMO because of the same dihydroacridine donor dominated
the HOMO distributions, and only 0.03 eV difference was
observed. On the other hand, the 0.15 eV difference in LUMO
can be attributed to the different acceptor groups, whereas the
O atom in DBF had stronger electronegativity than S atom in
Fig. 3 HOMO/LUMO spatial distributions and optimized geometry.
DBT and thus lead to relatively lower LUMO of PrFPhAc. In
general, the PrFPhAc possessed slightly narrower bandgap as
compared to PrTPhAc, which was consistent with the UV
spectra. Besides, the singlet and triplet energy difference (ꢀEST
)
were also calculated to be 0.34 and 0.41 eV for PrFPhAc and
PrTPhAc, respectively.
Electrochemical properties and HOMO/LUMO levels
The electrochemical properties of PrFPhAc and PrTPhAc were
firstly measured by cyclic voltammetry (CV) using typically tri-
electrode configuration method with ferrocene as the internal
standard in dichloromethane solution with 0.1 M n-Bu4NPF6 as
the supporting electrolyte (Fig. 4). We calculated the HOMO
levels of PrFPhAc and PrTPhAc as -5.50 and -5.48 eV,
respectively, from the onset of the first oxidation wave.
Fig. 4 Cyclic voltammograms of PrFPhAc and PrTPhAc.
The more reliable HOMOs of these materials were tested by
ultraviolet photoemission spectroscopy (UPS, Fig. 5) next. The
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HOMOs can be determined as follows: EHOMO = Ek – hν, where, hν To investigate the electroluminescence characteristics of these
is the light energy of the light source (normally hν = 21.22 eV); Ek is materials, red PHOLEDs were fabricated with typical device
the kinetic energy distribution of the photo-electrons. The LUMOs structure as following: ITO/HAT-CN (10 nm)/TAPC (45
can be calculated by ELUMO = Eg + EHOMO, Eg is the optical energy nm)/TCTA (10 nm)/Host:
4 wt% Ir(MDQ)2(acac) (20
gap and measured by UV-vis absorption spectra. As a result, the nm)/TmPyPB (45 nm)/Liq (2 nm)/Al (120 nm). PrFPhAc and
HOMO/LUMO levels were measured as -6.04/-3.07 and -6.02/-3.02 PrTPhAc were doped with 4% Ir(MDQ)2(acac) to form the
eV for PrFPhAc and PrTPhAc, respectively. Overall, the UPS emitting layer (EML). The current density–voltage–luminance
studies is consistent with DFT calculation and CV results in trend.
(
J–V–L
)
characteristics; current efficiency (CE), power
efficiency (PE) and external quantum efficiency (EQE) as a
function of luminance and electroluminescence (EL) spectra of
red devices are included in Fig. 6. The detailed performance is
summarized in Table 2.
As Fig. 6 (a) shows, the operating voltage PrFPhAc-based
OLED at 100 cd m-2 is 3.9 V, which is lower than the device
hosted by PrTPhAc (4.1 V). As shown in Fig. 5 (b), both
devices exhibited the identical emission with conventional CIE
coordinates of (0.61, 0.39) of Ir(MDQ)2(acac). And in Fig. 6
(c), the maximum CE, PE and EQE reached 32.0 cd A-1, 23.1
lm W-1, and 19.2%, respectively, for PrTPhAc-based device.
The device based on PrFPhAc showed better performance with
36.0 cd A-1, 29.1 lm W-1 and 22.0% for CE, PE and EQE,
respectively. Additionally, we carried hole-only and electron-
only measurements for two hosts, and PrFPhAc exhibited better
hole and electron transport ability as compared to PrTPhAc
(Fig. 7), which could be an important reason why the PrFPhAc
is superior to PrTPhAc in OLED devices.
Fig. 5 UPS spectra of PrFPhAc and PrTPhAc.
Electroluminescence properties
Table 2 Summary of electroluminescence performance for red PHOLEDs.
Vb
ηCE
ηPE
ηext
CIEd
c
c
c
Hosta
[V]
[cd A-1]
[lm W-1]
[%]
[x, y]
PrFPhAc
PrTPhAc
3.9
4.1
36.0, 30.9, 27.2
32.0, 29.8, 26.7
29.1, 17.7, 10.0
23.1, 16.7, 9.9
22.0, 19.1, 16.4
19.2, 18.2, 16.1
0.61, 0.39
0.61, 0.39
a) Device configuration: ITO/HAT-CN (10 nm)/TAPC (45 nm)/TCTA (10 nm)/HOST: 4 wt % Ir(MDQ)2(acac) (20
nm)/TmPyPB (45 nm)/Liq (2 nm)/Al (120 nm). b) Voltages at 100 cd m-2. c) Efficiencies in the order of the maxima, at 1000
cd m-2 and at 5000 cd m-2. d) Commission International de Ieelaiage coordinates measured at 5 mA cm-2.
4 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C6TC02180H
and vibration analyses. The ground states and triplet states of
molecules in vacuum were optimized without any assistance of
experimental data by the restricted and unrestricted formalism
of three-parameter hybrid exchange functional and correlation
functional (B3LYP)/6-31G(d), respectively.12 All computations
were performed using the Gaussian 03 package. Transient PL
decays were measured by
a
single photon counting
spectrometer from HORIBA JOBIN YVON with a Nano LED
pulse lamp as the excitation source. Cyclic voltammetry (CV)
was carried out on a CHI600 voltammetric analyzer at room
temperature with ferrocenium-ferrocene (Fc+/Fc) as the internal
standard.
Device fabrication and measurements
Fig. 6 (a) J–V–L characteristics; (b) EL spectra and (c) CE-, PE- and EQE–L curves of
red PHOLEDs.
The OLEDs were fabricated through vacuum deposition of the
materials at ca. 2×10-6 Torr onto commercially avaliable ITO-
coated glass substrates having a sheet resistance of ca. 30 ꢁ per
square. The ITO surface was cleaned sequentially with acetone,
ethanol, and deionized water, in an ultrasonically bath, dried in
an oven, and finally exposed to UV-ozone for about 15 min.
Organic layers were deposited at
a rate of 2-3 Å/s,
subsequently, HAT-CN and Liq were deposited at 0.2-0.3 Å/s,
finally the Al electrode was deposited (ca. 5 Å/s) through a
shadow mask without breaking the vacuum. For all the devices,
the emitting areas were determined by the overlap of two
electrodes as 0.09 cm2. The EL performance of the blue and
white devices were measured with a PHOTO RESEARCH
SpectraScan PR 655 PHOTOMETER and a KEITHLEY 2400
SourceMeter constant current source at room-temperature. The
EQE values were calculated according to the previously
reported methods.
Fig. 7 J-V characteristics of hole-only and electron-only devices. Hole-only devive:
ITO/MoO3 (10 nm)/Host (100 nm)/MoO3 (10 nm)/Al (100 nm); electron-only
device: ITO/TmPyPB (20 nm)/Host (100 nm)/ TmPyPB (20 nm)/Liq (2 nm)/Al(100
nm).
Synthesis of 10-(6-chloropyrazin-2-yl)-9,9-diphenyl-9,10-
dihydroacridine
Experimental Section
Materials and methods
9,9-diphenylacridane2i (10 g, 30 mmol), 2,6-dichloropyrazine
(4.47 g, 30 mmol), tris(dibenzylideneacetone)dipalladium(0)
(Pd2(dba)3, 0.27 g, 0.3 mmol), 2-dicyclohexylphosphino-2',6'-
All chemicals and reagents were used as received from
commercial sources without further purification. THF was
purified by PURE SOLV (Innovative Technology) purification
dimethoxy-1,1'-biphenyl (S-Phos, 0.37 g, 0.9 mmol), sodium
t-
butoxide ( -BuONa, 5.76 g, 60 mmol) were dissolved in toluene
t
o
under argon and heated to 110 C. After 20 h reaction under
stirring, the reaction was cooled to room temperature and 200
mL water was added. The product was extracted with
dichloromethane (DCM, 3×100 mL), the combined organic
layers were washed with brine and dried over anhydrous
sodium sulfate (NaSO4). Filtered and evaporated under reduced
pressure. The crude product was purified by column
chromatography using petroleum ether/dichloromethane (2/1,
v/v) to give 10-(6-chloropyrazin-2-yl)-9,9-diphenyl-9,10-
1
system. H NMR and 13C NMR spectra were recorded on a
Bruker 400 spectrometer at room temperature. Mass spectra
were recorded on a Thermo ISQ mass spectrometer using a
direct exposure probe. UV-vis absorption spectra were recorded
on a Perkin Elmer Lambda 750 spectrophotometer. PL spectra
and phosphorescent spectra were recorded on a Hitachi F-4600
fluorescence
spectrophotometer.
Differential
scanning
calorimetry (DSC) was performed on a TA DSC 2010 unit at a
o
heating rate of 10 C min-1 under nitrogen. The glass transition
1
dihydroacridine as a white crystalline powder (4.3 g, 32%). H
temperatures (Tg) were determined from the second heating
NMR (400 MHz, CDCl3):
Hz, 2H), 7.61 (s, 1H), 7.38 (m, 2H), 7.22-7.17 (m, 10H), 7.01
(m, 2H), 6.88 (d,
= 3.8 Hz, 2H) ppm. 13C NMR (100 MHz,
CDCl3): 151.48, 145.52, 144.02, 141.80, 140.01, 134.69,
131.64, 130.38, 129.10 (d, = 10.7 Hz), 128.24, 127.76,
δ 7.89 (s, 1H), 7.76 (dd, J = 8.0, 1.0
scan. Thermogravimetric analysis (TGA) was performed on a
o
TA SDT 2960 instrument at a heating rate of 10 C min-1 under
J
nitrogen. Temperature at 5% weight loss was used as the
decomposition temperature (Td). The DFT simulations were
carried out with different parameters for structure optimizations
δ
J
126.87, 125.31, 124.88, 124.02, 58.42 ppm. MS m/z: 445.82.
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Anal. Calcd for C29H20ClN3 (%): C 78.11, H 4.52, N 9.42; result, high efficiencies red devices were obtained using
found: C 78.03, H 4.74, N 9.28.
PrFPhAc and PrTPhAc as host materials. The champion device
was achieved PrFPhAc-based device with the maximum CE,
PE and EQE of 36.0 cd A-1, 29.1 lm W-1, and 22.0%,
respectively.
Synthesis of 10-(6-(dibenzo[b,d]furan-1-yl)pyrazin-2-yl)-9,9-
diphenyl-9,10-dihydroacridine (PrFPhAc)
10-(6-chloropyrazin-2-yl)-9,9-diphenyl-9,10-dihydroacridine (2
g, 4.5 mmol), dibenzofuran-4-boronic acid (1.4 g, 6.7 mmol)
and tetrakis(triphenylphosphine)- palladium(0) (Pd(PPh3)4, 0.35
g, 0.3 mmol) were dissolved in THF under argon, and then 2 M
K2CO3 (THF/Water = 5/1, v/v) was added. The resulting
Acknowledgements
We thank to the financial support from the Natural Science
Foundation of China (Nos. 61177016 and 21572152). This
project is also funded by Collaborative Innovation Center (CIC)
of Suzhou Nano Science and Technology, Soochow University,
and by the Priority Academic Program Development of the
Jiangsu Higher Education Institutions (PAPD).
o
solution was heated at 70 C overnight. After cooled to room
temperature, the mixture was evaporated to remove solvents.
The residue was washed with water and extracted with
dichloromethane for 3 times. The organic layer was collected
and evaporated. The crude product was purified by
chromatography on silica gel using petroleum ether as eluent to
afford a white powder (2.3 g, 90%). 1H NMR (400 MHz,
Notes and references
Jiangsu Key Laboratory for Carbon-Based Functional Materials &
Devices, Institute of Functional Nano & Soft Materials (FUNSOM),
Soochow University
CDCl3):
(m, 2H), 7.79 (dd,
= 8.2 Hz, 1H), 7.58-7.51 (m, 2H), 7.46-7.33 (m, 3H), 7.24-7.14
(m, 8H), 7.03 (dd, = 7.8, 1.4 Hz, 2H), 6.99-6.92 (m, 4H) ppm.
13C NMR (100 MHz, CDCl3):
156.07, 151.56, 146.06,
144.66, 140.84, 139.55, 138.05, 135.73, 130.44, 129.33,
127.74, 127.54, 127.08, 126.76 (d, = 5.8 Hz), 125.30, 123.77,
δ
9.30 (s, 1H), 8.34 (dd,
J = 7.7, 1.2 Hz, 1H), 8.09-8.00
J
= 8.0, 1.0 Hz, 2H), 7.75 (s, 1H), 7.69 (d, J
Email: zqjiang@suda.edu.cn; lsliao@suda.edu.cn*
J
δ
1
2
C. W. Tang and S. A. Van Slyke, Appl. Phys. Lett., 1987, 51, 913.
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123.36, 123.14, 122.14, 121.92, 121.22, 120.72, 111.87, 58.14
ppm. MS m/z: 577.62. Anal. Calcd for C41H27N3O (%): C
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1
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MHz, CDCl3):
8.20 (m, 1H), 7.96 (d,
7.66 (m, 3H), 7.60 (t,
δ
8.68 (s, 1H), 8.28 (d,
J
= 7.8 Hz, 1H), 8.24-
= 7.5 Hz, 1H), 7.85-7.81 (m, 1H), 7.72-
= 7.7 Hz, 1H), 7.48 (dd, = 5.8, 3.0 Hz,
J
J
J
C, 2015,
3, 9053; (i) X.-Y. Liu, F. Liang, L.-S. Cui, X.-D. Yuan, Z.-Q.
2H), 7.30 (t,
= 8.0 Hz, 2H), 7.03 (d,
ppm. 13C NMR (100 MHz, CDCl3):
141.43, 140.96, 139.90, 138.07, 137.22, 135.94, 135.30 (d,
10.5 Hz), 134.61, 131.05, 130.53, 129.27, 127.72, 126.99 (d,
= 25.9 Hz), 126.69, 125.62 (d, = 7.0 Hz), 124.53 (d,
Hz), 124.20, 123.80, 122.99, 122.58, 122.45 (d, = 7.4 Hz),
121.43 (d, = 4.4 Hz, 58.26 ppm. MS m/z: 593.70. Anal. Calcd
J
= 7.7 Hz, 3H), 7.26 (s, 2H), 7.19 (s, 1H), 7.16 (d,
= 7.7 Hz, 3H), 7.00-6.94 (m, 5H)
151.14, 149.30, 144.56,
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δ
J
=
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3
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J = 8.0
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4.33, N 7.46.
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