Synthesis of monodisperse oligocarbazoles-functionalized anthracenes with intense blue-emitting

Article abstract of DOI:10.1016/j.tetlet.2012.11.099

New well-defined monodisperse oligocarbazoles-functionalized anthracenes An-OCZn (n = 1, 2, 3) have been synthesized through Suzuki cross-coupling reaction of the brominated oligocarbazoles and 9,10-bis(4,4,5,5-tetramethyl-1,3, 2-dioxaborolan-2-yl)anthracene. They show good solubility in organic solvents, including dichloromethane, chloroform, toluene, ethyl acetate, and tetrahydrofuran. It should be noted that, in the case of An-OCZn, the formation of the excimer based on anthracene unit is suppressed completely due to the introduction of oligocarbazoles in 9,10-position of anthracene so that an intense blue-emitting has been afforded. In addition, the obtained An-OCZn exhibit good electrochemical and thermal stabilities. Thus, the oligocarbazoles-functionalized anthracenes can be a class of promising candidates for novel blue-emitting materials employed in OLEDs or related devices.

Full text of DOI:10.1016/j.tetlet.2012.11.099

Tetrahedron Letters 54 (2013) 594–599
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis of monodisperse oligocarbazoles-functionalized anthracenes
with intense blue-emitting
⇑
Yong Zhan, Kaiyu Cao, Pengchong Xue, Ran Lu
State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
New well-defined monodisperse oligocarbazoles-functionalized anthracenes An-OCZn (n = 1, 2, 3) have
been synthesized through Suzuki cross-coupling reaction of the brominated oligocarbazoles and 9,10-
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)anthracene. They show good solubility in organic sol-
vents, including dichloromethane, chloroform, toluene, ethyl acetate, and tetrahydrofuran. It should be
noted that, in the case of An-OCZn, the formation of the excimer based on anthracene unit is suppressed
completely due to the introduction of oligocarbazoles in 9,10-position of anthracene so that an intense
blue-emitting has been afforded. In addition, the obtained An-OCZn exhibit good electrochemical and
thermal stabilities. Thus, the oligocarbazoles-functionalized anthracenes can be a class of promising can-
didates for novel blue-emitting materials employed in OLEDs or related devices.
Received 5 September 2012
Revised 17 November 2012
Accepted 23 November 2012
Available online 1 December 2012
Keywords:
Oligocarbazole
Anthracene
Blue-emitting
Monodisperse conjugated oligomers
Electrochemical stability
Ó 2012 Elsevier Ltd. All rights reserved.
In recent years, well-defined monodisperse
p
-conjugated oligo-
port properties.17 However, the excimer with bathochromic-
shifted emission is often detected in some anthracene-based
emitting materials. The strategy of the restraint of the excimer
mers have attracted more scientific and technological interests due
1
2
18
to their potential applications in solar cells, electrical conductors,
filed-effect transistors (FETs),3 organic light-emitting diodes
formation will be helpful for preparation of novel blue-emitting
materials with high fluorescence efficiency. Miller and co-workers
have suggested that the formation of excimer can be completely
suppressed by the incorporation of 9,10-anthracene into the main
4
5
(
OLEDs), and light-harvesting molecular antenna systems. In
addition, the design of monodisperse conjugated oligomers is of
importance in understanding and predicting the properties of the
6
19
related polymers. Till now, a great number of functional oligomers
chain of polyfluorenes. Kwon and co-workers fabricated deep-blue
7
8
have been synthesized, including oligothiophenes, oligopyrroles,
OLEDs using anthracene derivatives bearing multi-phenyl-based
9
10
11
20
oligoanilines, oligofluorenes, and oligophenothiazine. In par-
ticular, the oligocarbazoles in different conformations have been
prepared as model compounds of polycarbazoles, which have
emerged as leading electroluminescent materials due to their
strong photoluminescence, high hole mobility, and high thermal
bulky substituents in 9,10-positions as emitters. We have found
that the formation of excimers can be suppressed with an increase
in the number of fluorece-vinylene units linked in 9,10-positions of
anthracene, but the emission from excimer was not quenched
2
1
completely. In order to obtain novel blue-emitting materials with
high fluorescence efficiency, we intended to introduce oligocarbaz-
ole units into 9,10-positions of anthracene. As shown in Chart 1 the
monodisperse oligocarbazole-functionalized anthracenes An-OCZn
(n = 1, 2, 3) have been synthesized. Notably, the formation of the
excimer based on anthracene unit is suppressed completely, and
intense blue-emitting has been afforded. Moreover, An-OCZn
exhibit high electrochemical and thermal stabilities. Therefore,
the oligocarbazole-functionalized anthracenes might be used as
good candidates for blue-emitting materials with high fluorescent
efficiencies employed in OLEDs or related devices with good
stability.
1
2
stability. For example, Strohriegl and co-workers reported the
stepwise synthesis of N-alkylcarbazol-3,6-diyl trimers and penta-
mers by Suzuki coupling reaction.13 Leclerc and co-workers pre-
pared 2,7-carbazolenevinylene-based oligomers used as active
semiconductor layer in OFETs.14 Song and co-workers synthesized
pyrene-centered starburst oligocarbazoles with strong blue emis-
1
5
sion. Our group has previously reported a series of molecular
antennae based on porphyrin or subporphyrin-centered 3,9-linked
1
6
oligocarbazoles. On the other hand, anthracene unit has been
widely used as a building block for conjugated small molecules,
oligomers, and polymers with excellent optoelectronic properties
on account of its promising light-emitting and charge carrier trans-
The synthetic routes for the monodisperse oligocarbazole-
functionalized anthracenes An-OCZn (n = 1, 2, 3) are sketched in
Schemes 1 and 2. The brominated oligocarbazoles 1, 8, and
compound 3 were firstly synthesized according to the reported
⇑
Corresponding author.
E-mail address: luran@mail.jlu.edu.cn (R. Lu).
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.11.099

Y. Zhan et al. / Tetrahedron Letters 54 (2013) 594–599
595
reactions between compound 7 and excess of the brominated
oligocarbazoles 1, 8, and 5 afforded the desired oligocarbazole-
functionalized anthracenes An-OCZn (n = 1, 2, 3) in yields of 66%,
6
2%, and 46%, respectively. All the intermediates and the final
products were purified by column chromatography, and the new
1
13
compounds were characterized with FT-IR, H NMR, C NMR, ele-
mental analysis, and MALDI/TOF mass spectroscopy.27 Due to the
introduction of octyl to 9-position of carbazole unit, the obtained
monodisperse oligomers were readily dissolved in common organ-
ic solvents, including dichloromethane, chloroform, toluene, ethyl
acetate, and tetrahydrofuran, which made it possible that An-OCZn
became solution-processible materials.
The UV–vis absorption and fluorescence emission spectra of An-
OCZn (n = 1, 2, 3) in CHCl are shown in Figure 1, and the corre-
3
sponding photophysical data are summarized in Table 1. The
⁄
absorption bands assigned to the
p–p
transitions of carbazole or
2
3
oligocarbazole units appeared at ca. 300 nm, and were similar
to those of dicarbazole 3 (see Fig. S1). These absorption bands
red-shifted slightly with the increase in the number of carbazole
units on account of the extending of
p-conjugation, for example,
the absorption maximum shifted from 298 nm for An-OCZ1 to
3
04 and 310 nm for An-OCZ2 and An-OCZ3, respectively (Table 1).
Chart 1. The molecular structures of An-OCZn.
⁄
Although the n–
p
transition bands of carbazole or oligocarbazole
overlapped with the absorption of anthracene core in the range of
30–370 nm, we could also detect the characteristic vibrational
patterns of the isolated anthracene group in An-OCZn (k = 356,
81 and 401 nm for An-OCZ1, k = 358, 381 and 401 nm for An-
3
3
1
8
OCZ2, k = 356, 381 and 401 nm for An-OCZ3). On the other hand,
we could find from Figure 1b that the compounds An-OCZn emit-
ted intense blue light maximized at ca. 450 nm when excited at
3
65 nm. With the increase in the number of carbazole units, the
fluorescent emission bands of An-OCZ2 and An-OCZ3 red-shifted
to 453 nm from 446 nm for An-OCZ1 on account of the extending
of p-conjugation. It indicated that the conjugation for oligocarbaz-
oles linked by 3,6-position would not be enlarged obviously with
the increase in the carbazole units. It should be noted that the exci-
mers with bathochromic-shifted emission were often detected for
anthracene derivatives, however, in the case of An-OCZn, the for-
mation of excimers was suppressed completely. Compared with
our previous result, we can deduce that the suppression effect of
carbazole on the formation of excimer of anthracene core is supe-
rior than that of fluorene since the formation of excimers is sup-
pressed by fluorene-vinylene units to a certain of extent, not
2
1
completely. As a result, the oligocarbazoles cored with anthra-
cene might become good candidates for blue-emitting materials.
In general, the fluorescence quantum yields (
cence derivatives not bearing other conjugated units were less
than 0.34 against quinine sulfate ( = 0.546, kex = 365 nm) as a
F
U ) of the anthra-
U
F
2
4
standard. However, when the anthracenes were linked by oligoc-
arbazoles in 9,10-positions, the quantum yields increased signifi-
cantly, they reached 0.76 for An-OCZ1, 0.66 for An-OCZ2, and
Scheme 1. The synthetic route for the brominated oligocarbazole 5.
0
.70 for An-OCZ3 in toluene. The reason for the high fluorescence
quantum yields of An-OCZn might be that the excitons could be
methods.15,22 The transformation of compound 1 into boronic acid
well confined in the low-band gap, highly chromophoric segment
2
5
2
was performed by lithium–bromide exchange at À78 °C, fol-
(
anthracene).
lowed by reaction with trimethyl borate at À78 °C and hydrolyzed
in hydrochloric acid at room temperature. The bromination reac-
tion of compound 3 afforded compound 4, which was transformed
into the brominated tricarbazole 5 via Suzuki cross-coupling reac-
tion with 1/3 equiv of boronic acid 2 catalyzed by palladium in a
yield of 48%. Meanwhile, 9,10-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)anthracene 7 was synthesized by the cross-coupling
reaction between bis(pinacolato)diboron and 9,10-dibromoanthra-
cene (6), which was obtained via the bromination reaction of
Figure 2 shows the absorption and emission spectra of An-OCZn
(
n = 1, 2, 3) in the films obtained via spinning the chloroform solu-
À1
tions (10 mg mL ) onto quartz slides. In comparison with the ones
in solutions, An-OCZn showed red-shift of 0–5 nm of the absorp-
tion and emission bands. For example, the absorption maximum
of An-OCZ3 in the films red-shifted to 315 nm from 310 nm in
the solution, meanwhile, its emission peak red-shifted to 456 nm
in the film from 453 nm in the solution, indicating the occurrence
of the intermolecular interaction in the solid state.
anthracene, in the presence of KOAc as a base and Pd(OAc)
2
as a
The electrochemical behaviors of An-OCZn (n = 1, 2, 3) have
been investigated by cyclic voltammetry (CV) using a standard
catalyst. Finally, the Pd(PPh -catalyzed Suzuki cross-coupling
3 4
)

5
96
Y. Zhan et al. / Tetrahedron Letters 54 (2013) 594–599
Scheme 2. Syntheses of oligocarbazoles-functionalized anthracenes An-OCZn.
Figure 1. UV–vis absorption (a) and fluorescence emission (b, kex = 365 nm) spectra of An-OCZn in chloroform (1.0 Â 10À6 M).
Table 1
Photophysical and thermal properties of An-OCZn (n = 1, 2, 3)
Photoluminescenceb
Solutiona
Film
U
F
c
T
m
d
(°C)
e
Compounds
Absorption
Film
d
T (°C)
Solutiona
An-OCZ1
An-OCZ2
An-OCZ3
298, 339, 356, 381, 401
304, 346, 358, 381, 401
310, 356, 381, 401
301, 337, 351, 384, 403
303, 345, 360, 401
315, 360 (shoulder), 404
446
453
453
447
453
456
0.76
0.66
0.70
274
184
107
410
462
457
a
b
c
Measured in chloroform.
Excited at 365 nm.
The fluorescence quantum yields were determined against quinine sulfate in 0.1 N H
Obtained from DSC measurement.
2 4 F
SO (U = 0.546) as a standard excited at 365 nm.
d
e
Obtained from TGA measurement (temperature at 5% weight loss under nitrogen, 10 °C/min ramp rate).

Y. Zhan et al. / Tetrahedron Letters 54 (2013) 594–599
597
Figure 2. Normalized UV–vis absorption (a) and PL (b, kex = 365 nm) spectra of An-OCZn in the films.
three-electrode cell and an electrochemical workstation (CHI 604)
under N atmosphere. Platinum button is used as the working elec-
trode, a platinum wire as the counter electrode, Ag/AgCl as the ref-
erence electrode, and ferrocene is used as a standard. The cyclic
2
2 2
voltammetry (CV) diagrams of An-OCZn in CH Cl in the presence
of Bu NPF as the supporting electrolyte are shown in Figure 3, and
4
6
the corresponding electrochemical data listed in Table S1. The re-
+
dox potential of Fc/Fc , which possesses an absolute energy level
of À4.8 eV relative to the vacuum level for calibration, is located
4 6 2 2
at 0.36 eV in 0.10 M Bu NPF /CH Cl solution at a scan rate of
À1 26
1
00 mV s
.
It was clear that An-OCZ1 and An-OCZ2 gave one
well-defined reversible redox peak with E1/2 (half-wave oxidation
potentials) being of 0.98 and 0.78 V. As to An-OCZ3, two reversible
redox peaks appeared at 0.70 and 0.83 V, and the E1/2 for An-OCZ3
was 0.70 V. Obviously, the oxidation potential decreases with the
increase in the number of carbazole units. On the basis of the
half-wave oxidation potentials, the highest occupied molecular
orbital (HOMO) energy levels can be estimated as À5.42, À5.22,
À5.14 eV for An-OCZ1, An-OCZ2, and An-OCZ3, respectively, based
on the equation of EHOMO = ÀE1/2À4.44 eV. It suggested that the
electron-donating ability would be enhanced with increasing the
length of the oligocarbazole arms. Although we did not observe re-
dox processes in the negative potential region, the lowest unoccu-
pied molecular orbital (LUMO) energy level of the An-OCZn could
be estimated from the HOMO energy level and energy band gap
2 2
Figure 3. The cyclic voltammograms of An-OCZn in CH Cl .
g
(E ) which was calculated from the absorption edge of An-OCZn
À1
Figure 4. (a) DSC and (b) TGA thermograms of An-OCZn under a nitrogen atmosphere at a heating rate of 10 °C min
.

5
98
LUMO = EHOMO + E
Y. Zhan et al. / Tetrahedron Letters 54 (2013) 594–599
(E
g
). The LUMO energy levels were À2.64, À2.35,
F.; Armaroli, N.; Ouali, L.; Krasnikov, V.; Hadziioannou, G. J. Am. Chem. Soc.
000, 122, 7467; (d) Wasielewski, M. R. Chem. Rev. 1992, 92, 435; (e) Imahori,
2
À2.23 eV for An-OCZ1, An-OCZ2, and An-OCZ3, respectively. Fig-
ures S2–S4 showed multiple cyclic voltammograms, which gave
very weak shifts (<1 mV) after 10 scan cycles for An-OCZn. It indi-
cated that the obtained oligocarbazoles-functionalized anthra-
cenes exhibited excellent electrochemical stability, and could
withstand the redox cycles for many times. We deduced that the
excellent electrochemical stability for An-OCZn might be due to
the introduction of substitutes in 3,6-positions of carbazole units,
which would restrain the electrochemical polymerizations. Thus,
these compounds might become potential candidates applied in
electrooptic devices.
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sis (TGA) in N
and Table 1, An-OCZn exhibited high melting points (T
range of 107–274 °C. Moreover, T of An-OCZn decreased with
the increase in the number of carbazole units. Based on TGA re-
sults, we could find that the decomposition temperatures (T , cor-
responding to a 5% weight loss) of An-OCZn were in the range of
2
at a heating rate of 10 °C/min. As shown in Figure 4
m
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m
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4
10–462 °C, indicating much higher thermal stability.
In summary, we have synthesized three new well-defined
monodisperse oligocarbazoles-functionalized anthracenes An-
OCZn (n = 1, 2, 3) via Suzuki cross-coupling reaction between the
brominated oligocarbazoles and 9,10-bis(4,4,5,5-tetramethyl
1
1
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0
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1
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Acknowledgments
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1. Zhou, H. P.; Lu, R.; Zhao, X.; Qiu, X. P.; Xue, P. C.; Liu, X. L.; Zhang, X. F.
This work is financially supported by the National Natural Sci-
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Supplementary data
2
2
2
6. Thelakkat, M.; Schmidt, H.-W. Adv. Mater. 1998, 10, 219.
7. An-OCZ1: 1H NMR (500 MHz, TMS, CDCl
): d (ppm) = 8.24 (s, 2H), 8.08 (t,
3
Supplementary data associated with this article can be found, in
J = 6.5 Hz, 2H), 7.83–7.81 (m, 4H), 7.64 (dd, J = 2.0 Hz, J = 8.5 Hz, 2H), 7.60 (d,
J = 8.5 Hz, 2H), 7.52–7.49 (m, 4H), 7.31–7.29 (m, 4H), 7.24–7.22 (m, 2H), 4.44 (t,
J = 7.0 Hz, 4H), 2.05–1.99 (m, 4H), 1.45–1.24 (m, 20H), 0.90 (t, J = 6.5 Hz, 6H)
the
online
version,
at
http://dx.doi.org/10.1016/j.tet-
let.2012.11.099. These data include MOL files and InChiKeys of
the most important compounds described in this article.
(
1
1
Fig. S14) 13C NMR (125 MHz, CDCl
3
) d (ppm) = 140.96, 139.89, 137.84, 130.73,
29.41, 129.06, 129.03, 125.87, 124.80, 123.25, 123.21, 122.96, 122.94, 122.77,
20.54, 120.52, 118.96, 108.88, 108.56, 108.53, 43.41, 31.86, 29.72, 29.47,
À1
References and notes
29.27, 29.18, 27.48, 22.67, 14.13 (Fig. S15). IR (KBr, cm ): 2930, 2850, 1650,
1
C
490, 1470, 1380, 1150, 1120, 804, 748. Elemental analysis calculated for
: C, 88.48; H, 7.70; N, 3.82. Found: C, 88.43; H, 7.69; N, 3.88. MS, m/z:
54 56 2
H N
1
2
3
4
.
.
.
.
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H.; Sumi, N.; Aso, Y.; Otsubo, T. J. Org. Chem. 1998, 63, 8632.
(a) Katz, H. E.; Bao, Z.; Gilat, S. L. Acc. Chem. Res. 2001, 34, 359; (b)
Dimitrakopoulos, C. D.; Malenfant, P. R. L. Adv. Mater. 2002, 14, 99; (c)
Horowitz, G. J. Mater. Chem. 1999, 9, 2021.
(a) Freeman, A. W.; Koene, S. C.; Malenfant, P. R. L.; Thompson, M. E.; Fréchet, J.
M. J. J. Am. Chem. Soc. 2000, 122, 12385; (b) Furuta, P.; Brooks, J.; Thompson, M.
E.; Fréchet, J. M. J. J. Am. Chem. Soc. 2003, 125, 13165; (c) Holder, E.; Langeveld,
B. M. W.; Schubert, U. S. Adv. Mater. 2005, 17, 1109; (d) Bolink, H. J.; Barea, E.;
Costa, R. D.; Sudhakar, S.; Zhen, C.; Sellinger, A. Org. Electron. 2008, 9, 155.
(a) Hutten, P. F. V.; Wideman, J.; Meetsma, A.; Hadziioannou, G. J. Am. Chem.
Soc. 1999, 121, 5910; (b) Garnier, F.; Yassar, A.; Hajlaoui, R.; Horowitz, G.;
Deloffre, F.; Servet, B.; Ries, S.; Alnot, P. J. Am. Chem. Soc. 1993, 115, 8716; (c)
Eckert, J. F.; Nicoud, J. F.; Nierengarten, J. F.; Liu, S.; Echegoyen, L.; Barigelletti,
1
calcd 733.0, found: 732.2 (Fig. S16). Mp >250.0 °C. An-OCZ2:
500 MHz, TMS, CDCl ): d (ppm) = 8.45–8.42 (m, 4H), 8.37 (s, 2H), 8.17 (d,
J = 8.0 Hz, 2H), 7.93–7.83 (m, 6H), 7.84 (d, J = 8.5 Hz, 2H), 7.70 (d, J = 8.5 Hz,
H NMR
(
3
2
4
4
H), 7.67–7.62 (m, 4H), 7.51–7.46 (m, 4H), 7.44–7.42 (m, 2H), 7.37–7.35 (m,
H), 7.27–7.23 (m, 2H), 4.52 (t, J = 7.5 Hz, 4H), 4.36–4.33 (m, 4H), 2.13–2.07 (m,
H), 1.94–1.91 (m, 4H), 1.49–1.27 (m, 40H), 0.94 (t, J = 6.0 Hz, 6H), 0.90–0.86
(
m, 6H) (Fig. S17) 13C NMR (125 MHz, CDCl
3
) d (ppm) = 140.91, 140.36, 140.06,
1
1
1
2
39.55, 133.58, 133.25, 130.77, 129.48, 129.16, 127.46, 125.78, 125.62, 125.43,
24.83, 123.42, 123.39, 123.22, 123.06, 120.45, 119.09, 119.06, 118.89, 118.72,
09.10, 108.90, 108.74, 108.67, 108.65, 43.56, 43.23, 31.89, 31.81, 29.72, 29.51,
9.41, 29.29, 29.26, 29.19, 29.05, 27.52, 27.36, 22.68, 22.61, 14.14, 14.08
À1
(
Fig. S18). IR (KBr, cm ): 2930, 2850, 1650, 1490, 1470, 1380, 1150, 1120, 804,
748. Elemental analysis calculated for C94
102 4
H N : C, 87.67; H, 7.98; N, 4.35.
Found: C, 87.62; H, 8.02; N, 4.41. MS, m/z: calcd 1287.8, found: 1286.2
5
.
1
(
(
(
3
Fig. S19). Mp: 184.0–186.0 °C. An-OCZ3: H NMR (500 MHz, TMS, CDCl ): d
ppm) = 8.49–8.36 (m, 10H), 8.18–8.13 (m, 2H), 7.94–7.92 (m, 2H), 7.89–7.77
m, 10H), 7.68–7.60 (m, 6H), 7.51–7.38 (m, 10H), 7.34–7.31 (m, 4H), 7.23–7.19

Y. Zhan et al. / Tetrahedron Letters 54 (2013) 594–599
599
(
2
0
m, 2H), 4.49 (t, J = 7.0 Hz, 4H), 4.38–4.29 (m, 6H), 4.18 (t, J = 7.0 Hz, 2H), 2.10–
118.70, 118.65, 109.12, 108.99, 108.88, 108.74, 108.66, 43.57, 43.23, 31.89,
31.83, 29.51, 29.43, 29.38, 29.30, 29.27, 29.17, 29.11, 29.07, 27.53, 27.38, 27.31,
22.69, 22.63, 14.14, 14.10 (Fig. S21). IR (KBr, cm ): 2930, 2850, 1650, 1490,
.14 (m, 4H), 1.96–1.88 (m, 6H), 1.82–1.77 (m, 2H), 1.47–1.20 (m, 60H), 0.92–
.89 (m, 6H), 0.88–0.85 (m, 9H), 0.82 (t, J = 7.0 Hz, 3H) (Fig. S20) 13C NMR
À1
(
3
125 MHz, CDCl ) d (ppm) = 140.91, 140.40, 140.37, 140.07, 140.02, 139.98,
1470, 1380, 1150, 1120, 804, 748. Elemental analysis calculated for
1
1
1
39.55, 137.86, 135.36, 133.58, 133.36, 133.27, 133.22, 130.78, 129.50, 127.47,
25.80, 125.72, 125.69, 125.57, 125.51, 125.48, 124.83, 123.76, 123.70, 123.48,
23.41, 123.27, 123.11, 121.37, 121.28, 120.51, 119.08, 118.99, 118.94, 118.83,
C
134
H
148
N
6
: C, 87.34; H, 8.10; N, 4.56. Found: C, 87.22; H, 8.04; N, 4.63. MS,
m/z: calcd 1842.6, found: 1841.1 (Fig. S22). Mp: 106.0–108.0 °C.