Preparation of (substituted) picenes via solar light-induced Mallory photocyclization

Article abstract of DOI:10.1039/c5ra02855h

Picenes 2a-c were readily obtained via photocyclization of dinaphthylethenes 1a-c by a straightforward solar light-induced Mallory reaction. The product was easily recovered by simple filtration after exposure of the reaction mixture to sunlight. The polyene obtained was then characterized by means of Raman spectroscopy and X-ray diffraction.

Full text of DOI:10.1039/c5ra02855h

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Preparation of (substituted) picenes via solar light-
induced Mallory photocyclization†
Cite this: RSC Adv., 2015, 5, 27470
a
b
c
d
c
Stefano Protti, Gianluca A. Artioli, Francesco Capitani, Carlo Marini, Paolo Dore,
c
b
a
Paolo Postorino, Lorenzo Malavasi and Maurizio Fagnoni*
Received 13th February 2015
Accepted 12th March 2015
Picenes 2a–c were readily obtained via photocyclization of dinaphthylethenes 1a–c by a straightforward
solar light-induced Mallory reaction. The product was easily recovered by simple filtration after exposure
of the reaction mixture to sunlight. The polyene obtained was then characterized by means of Raman
spectroscopy and X-ray diffraction.
DOI: 10.1039/c5ra02855h
www.rsc.org/advances
challenge. For this aim, different approaches (either metal-
Introduction
catalyzed or photochemical) have been devised for this
8–10
Organic molecular systems with extended p-conjugation have target;
Scheme 1 summarizes the most recent ones. The rst
attracted attention because of their potential use in organic route involved a Pd-mediated intramolecular cross-coupling of
1
electronic materials. In particular, semiconducting polycyclic 2,3-bis[(1Z)-2-phenylethenyl]benzene I at a high temperature
ꢁ
aromatic compounds, such as pentacene and anthracene, have (150 C) with the concomitant formation of two Ar–Ar bonds
8
been used in organic eld-effect-transistors (FETs) due to their (path a). Milder conditions were adopted in the gold catalyzed
9
mechanical exibility, light weight, low cost and environmental conversion of substituted terphenyl II (path b). In the latter
2
stability. In general, pentacenes are employed in the prepara- cases the reactions were carried out on a small scale in yields up
8,9
tion of the active layers of p-channel thin lm FETs with high to ca. 50%. There is, however, a great interest in the use of
2
ꢀ1 ꢀ1 3,4
mobility values (m ca. 1 cm V
s
).
photochemical reactions for the straightforward preparation of
For analogous reasons, organic molecules have been objects polyaromatic compounds such as helicene or helicene-like
of intense research in the eld of superconductivity. Early
5
evidences have been obtained with tetraselenafulvalene and
6
tetrathiafulvalene derivatives. However, the most striking
discovery related to C-based organic superconductors was that
of Mitsuhashi and co-workers in 2010, who reported a critical
c
temperature (T ) as high as 18 K by K-intercalation of the
hydrocarbon picene (C H ). This was the rst example of a
2
2
14
molecular superconductor in which the organic component
contains only C and H atoms and it led to a huge revitalization
of the eld of superconducting p-electron materials and of
7
superconductivity in general.
Following the discovery of superconductivity in metal-doped
picene, researchers faced the problem of having organic mole-
cules of this type available in high purity and large scale. As a
matter of fact, the development of a synthetic protocol for the
synthesis of (substituted) picene (V, Scheme 1) is currently a
a
Photogreen Lab, Department of Chemistry, V. Le Taramelli 12, 27100 Pavia, Italy.
E-mail: fagnoni@unipv.it; Fax: +39 0382 987323; Tel: +39 0382 987198
b
Dept. of Chemistry and INSTM, University of Pavia, Viale Taramelli 12, I-27100,
Pavia, Italy
c
Dipartimento di Fisica, Sapienza Universit a` di Roma, P.le Aldo Moro 2, 00185 Roma,
Italy
d
European Synchrotron Radiation Facility, BP 220, 38043 Grenoble Cedex, France
Scheme 1 Thermal and photochemical approaches to the synthesis
of (substituted) picenes V.
1
13
†
Electronic supplementary information (ESI) available: H NMR, C NMR,
spectra for compounds 1a–c, 2a–c. See DOI: 10.1039/c5ra02855h
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1
1,12
derivatives.
As an example, Kubozono and his coworkers Table 2 Effect of solvents and irradiation source in the synthesis of
picenes 2a–c
recently developed the photosensitized (by 9-uorenone)
conversion of 1,2-dinaphthylethane III to picene albeit in a poor
yield (19%, Scheme 1, path c). The most promising route,
however, is E/Z isomerization followed by oxidative photo-
13
14
cyclizations of stilbenes (the so-called Mallory reactions).
Accordingly, differently substituted picenes V were formed
upon irradiation of 1,2-naphthylethenes IV in the presence of
iodine and oxygen (path d), and the process can also be carried
out under ow conditions in a very short time (residence time ¼
Entry 1, M
Solvent
Light source tirr (h) Picene, % yield
a
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1a, 0.019
1a, 0.019 Toluene
1a, 0.019 C H CF
3
1a, 0.019 Acetone
1a, 0.019 CH Cl
1a, 0.019 CHCl
1a, 0.019
6
C H
6
310 nm
16
16
16
16
16
16
16
16
8
8
8
8
8
18
18
10
10
10
10
2a, 93
2a, 40
2a, 55
2a, 46
2a, 55
2a, 63
2a, 75
2a, 75c
2a, 77c
2a, 80
8c,15
6
min).
a
310 nm
a
The latter photochemical reactions, however, suffer from the
310 nm
6
5
a
310 nm
use of articial light, e.g. by requiring a high-pressure Hg arc
lamp. The use of solar light in photochemical processes is
obviously desirable to improve eco-sustainability and, at the
a
2
2
310 nm
a
3
310 nm
a
6
C H
12
310 nm
16
same time, minimize the energetic expenditure of the process.
a
1a, 0.019 Ethyl acetate 310 nm
b
b
Accordingly, the aim of this work was to develop the rst
straightforward sunlight induced synthesis of (substituted)
picenes by optimization of the Mallory cyclization.
1a, 0.019 C6H6
1a, 0.019 Ethyl acetate SolarBox
1a, 0.038
SolarBoxb
0
1
2
3
4
c
6
C H
6
SolarBoxb
2a, 72c
c,d
1a, 0.038 Ethyl acetate SolarBoxb
2a, 81 (70
)
c
1a, 0.057
1a, 0.038
C
C
6
H
H
6
SolarBox
Sunlighte
2a, 20c
e
6
6
2a, 69
2a, 72
c
Results and discussion
15
1a, 0.038 Ethyl acetate Sunlight
b
c
1
6
1b, 0.038
1b, 0.038 Ethyl acetate SolarBoxb
1c, 0.038 SolarBox
1c, 0.038 Ethyl acetate SolarBox
6
C H
6
SolarBoxb
2b, 60c
We preliminary focused on the preparation of picene 2a. Dia- 17
rylethene 1a was synthesized in a E/Z mixture by a Wittig 18
2b, 68c
2c, 71
6 6
C H
b
f
19
2c, 54
condensation between naphthylaldehyde and (naphthylmethyl)-
17
a
triphenylphosphonium salts. The photocyclization step was
optimized by varying the reaction conditions as illustrated in
Tables 1 and 2. Initially, we chose benzene as the reaction
Conditions: a 20 mL oxygen saturated solution of 1a in the chosen
solvent irradiated at 310 nm (10 ꢂ 15 W lamps) for 16 h in a test
b
tube. Irradiation carried out in a solar simulator (SolarBox) on a 10
c
mL volume placed in a Pyrex glass vessel. Picenes 2a–c isolated by
d
medium, since it is reportedly one of the preferred solvents for simple ltration of the end mixture. Reaction carried out on 1 gram
e
14
of 1a (100 mL solution). Irradiation by sunlight for 3 days (6 h per
the photocyclization reaction. We tested the effect of the
amount of iodine and oxygen on the reaction. As apparent from
Table 1, the photolysis of oxygen-saturated solutions gave
consistently better results than those that were air-equilibrated
and a nearly quantitative yield of 2a was achieved by increasing
f
day). Picene 2c puried by column chromatography.
out from the solution and the yields were determined only by
weighing the separated solid (Table 1). The purity of the picene
the [I ] up to 15% w/w. In each case, the product precipitated
2
2a did not differ substantially from that puried by sublima-
tion, as was apparent from NMR analyses (see ESI†).
Table 1 Optimization of the photochemical conversion of stilbene 1a
in picene 2a
a
Different media were then tested in order to nd safe alter-
natives to benzene for the reaction (Table 2). Again, the yields
reported are those measured by weighing the solid picene
formed. Other aromatic solvents (toluene and a,a,a-tri-

uorotoluene) however, gave picene in lower yields (40–55%,
entries 2–3). Similar results were obtained with medium
polarity solvents such as acetone, chloroform and methylene
chloride (46–63% yield, entries 4–6). Results comparable to
those observed with benzene were obtained with cyclohexane
and ethyl acetate (75% yield of 2a, entries 7–8). Benzene and the
more eco-sustainable ethyl acetate were then used for the
remaining investigations, in which either a solar simulator or
sunlight was used as the irradiation source and a Pyrex glass
2
a,
1
a, M
I
2
, %w/w
Picene, % yield
b
0.019
0.019
0.019
0.019
0.019
0.019
3.5
3.5
7
29
80
53
82
57
93
b
b
7
15
15
18,19
vessel as the photochemical reactor (Fig. 1).
As shown in Table 2, shiing to simulated sunlight did not
Conditions: a 20 mL oxygen-saturated solution of 1a in C H irradiated affect the overall yield of 2a, nor did an increase of [1a] up to
6 6
a
at 310 nm (10 ꢂ 15 W lamps) for 16 h in a test tube. The yields were
0.038 M (entries 11–12). In the latter case, a good yield was
determined from the solid picene precipitated out aer irradiation.
b
likewise observed (70%) when the reaction was repeated on a
Air equilibrated solution.
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gently pressed between two glass slides and back-illuminated is
shown in Fig. 2. Whitish areas consist of assemblies of grains
smaller than 1 mm, while darker regions are characterized by the
presence of larger grains. Using a set of optical lters, prelimi-
nary Raman measurements were carried out by varying the laser
power impinging on the sample surface to avoid sample
20
degradation and to check possible sample heating. Owing to
the transparency of picene grains, neither degradation nor
detectable sample heating was observed even with the highest
laser power. We collected data from different points of the
picene samples without observing any detectable difference in
Fig. 1 Pyrex glass vessel (20 mL capacity) used for the sunlight the Raman spectra, a result that indicates high sample homo-
synthesis of picenes 2a–c. As shown, the product precipitated out
upon prolonged exposure to solar radiation.
geneity, at least on the micrometer scale. A polarization analysis
of the Raman spectrum carried out on several points of the
sample did not show signicant variation of the Raman peak
intensities thus showing the absence of highly oriented crystals.
A representative Raman spectrum of solid picene at ambient
conditions is shown in Fig. 3. The spectrum is background-
bigger scale (1 gram of 1a) by irradiating a 100 mL ethyl acetate
solution in a larger Pyrex glass vessel. A detrimental effect was
found when the concentration of stilbene 1a was increased up
to 0.57 M (entry 13). The optimized conditions found in entries
subtracted and it is presented over two spectral ranges, 20–
ꢀ1
2
00 and 200–1700 cm . All the measured spectroscopic
11–12 were thenceforth adopted for irradiation under natural
features are in excellent agreement with previously published
solar light. Photochemical reactions were performed by placing
the glass vessel on a window ledge of the Department of
Chemistry of the University of Pavia in July 2014. Complete
consumption of stilbene was achieved aer three days (18 h
overall) irradiation and satisfactory yields were obtained in both
of the solvents tested (entries 14 and 15).
21–23
experimental and theoretical Raman data on picene.
These studies make it possible to easily assign the peaks in
Fig. 3a to intermolecular vibrational modes (or lattice
21
phonons), whereas the peaks in Fig. 3b, are assigned to
22,23
intramolecular vibrational modes.
The low frequency region
(Fig. 3a) is dominated by vibrations involving the relative
Diarylethenes 1b (E/Z 50 : 50) and 1c (E/Z 70 : 30) were then
prepared and irradiated in benzene and ethyl acetate in the
SolarBox apparatus for 10 h (entries 16–19). 5-Methylpicene 2b
and 5-methoxypicene 2c were formed in benzene in 60% and
motion of molecules, such as translations and librations, and
are thus more directly related to the overall lattice structure. The
ꢀ1
2
00–1000 cm spectral range (Fig. 3b) is characterized by both
out-of-plane and in-plane intramolecular modes, whereas only
71% yield, respectively and, as for 2a, the product was recovered
ꢀ1
in-plane modes can be found between 1000–1700 cm
by simple ltration. The reaction was effective likewise in ethyl
acetate although 2c did not precipitate out at the end of the
reaction and it was puried by column chromatography.
Raman spectroscopy and X-ray diffraction analyses were
then carried out on a portion of picene 1a puried by subli-
mation. A micro-photograph (50ꢂ objective) of a picene sample
(
Fig. 3b). An exhaustive assignment of the observed Raman
22
peaks was presented previously, along with a discussion of
infrared measurements. In summary, our spectroscopic anal-
ysis does show the high quality of picene samples and a
complete absence of any impurity detectable by Raman
investigation.
Fig. 3 Raman spectrum of solid picene in the low frequency region (a),
characterized by intermolecular vibrations, and in the high frequency
region (b), characterized by intramolecular vibrations. The intensity in
Fig. 2 Micro-photograph (50ꢂ objective) of a picene sample used for panel (a) has been multiplied by a factor of ꢃ0.5. The peak at ꢃ1300
ꢀ1
Raman spectroscopy (see below).
cm is truncated at about 1/3 of its maximum intensity value.
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substrate (up to ca. 0.04 M) in non-renewable (benzene) but
likewise in eco-friendly (ethyl acetate) solvents, using a
renewable energy source (the sun), thus signicantly
reducing the production of waste and CO2 emissions.
Furthermore, the process optimization and scale-up could be
improved and the reaction times shortened, by means of
1
6b
solar concentrators.
On the other hand, the use of a poorly atom-economical (%
26
AE ¼ 40–50%) Wittig condensation for the synthesis of stil-
benes 1 remains a limitation to the development of an efficient
photochemical route to picenes and phenacenes in general. The
experimental techniques employed demonstrate the high
quality of the picene crystals obtained through our novel
synthetic route, with a complete absence of any detectable
impurity.
Fig. 4 Le Bail profile fitting results of the X-ray diffraction pattern of
picene powder. The background was subtracted after the fitting
process. The wavelength is 0.4129 A.
ꢀ
Experimental
General information
1
13
H and C NMR spectra were recorded on a 300 MHz spec-
trometer (Bruker, UltraShield™ 300). Attributions were made
The X-ray powder diffraction pattern of picene at ambient
conditions is shown in Fig. 4. Experimental data were analyzed
by means of a Le Bail tting procedure based on the monoclinic
1
13
on the basis of H and C NMR, as well as distortionless
enhancement by polarization transfer (DEPT)-135 experiments;
chemical shis are reported in ppm downeld from tetrame-
thylsilane (TMS). Solvents of HPLC purity were employed in the
photochemical reactions.
24,25
P21 unit cell described elsewhere.
The nal unit cell
˚
˚
parameters obtained are: a ¼ 8.614(6) A, b ¼ 6.104(6) A, c ¼
˚
ꢁ
1
3.62(2) A, b ¼ 93.45(7) , which are in good agreement with
24,25
previously reported structural data.
In addition, the XRD
Raman measurements were carried out with a Horiba Lab-
RAM HR Evolution micro-spectrometer in backscattering
geometry. Picene samples, in appearance nely ground
powders, were excited by the 632.8 nm radiation of a He–Ne
laser with 30 mW output power. The laser power at the sample
surface was reduced by a factor of about 2 from internal
reection and absorption along the optical path. Elastically
scattered light was removed by a state-of-the-art optical ltering
peak proles indicate good crystallinity of the prepared picene.
Within the framework of the development of new carbon
based superconductors, a straightforward and eco-friendly
preparation of polycyclic aromatics is mandatory. The photo-
chemical approach having recourse to the Mallory or Mallory-
type reactions is a valid tool for the mild metal-free formation
11,12
of Ar–Ar bonds via a photocyclization process.
Although it is
widely accepted that the reaction is initiated by the cleavage of
the I–I bond in visible light absorbing iodine, the use of
sunlight (an inexhaustible energy source) for this purpose has
27
device based on three BragGrate notch lters. This experi-
mental setup allowed us to collect a good Raman signal down to
ꢀ1 27
very low wavenumbers (about 20 cm ). Raman spectra over
14a
rarely been adopted.
This work clearly demonstrates that
ꢀ1
the 10–1700 cm wavenumber range were collected by a Peltier
solar radiation is the ideal energy source for this type of pho-
tocyclization, and it can be accomplished in a very simple
manner by exposing the solution (placed in an inexpensive glass
vessel) to ambient light on a window ledge.
ꢀ1
cooled CCD detector with a resolution better than 1 cm
,
achieved thanks to an 1800 grooves per mm grating and an 800
mm focal length. The spectrometer was equipped with a
confocal microscope. Test measurements carried out using
different optical congurations allowed us to nd the optimum
experimental conditions using a confocal hole of 100 mm and a
In conclusion, the proposed approach allows for the
preparation of gram quantitites of picene (the product can be
easily recovered by ltration) with no articial energy
consumption. Importantly, the yields of picene obtained are
signicantly higher than those from other photochemical
approaches, such as the uorenone-photocatalyzed synthesis
5
0ꢂ objective. With these choices, the scattering volume was
2
approximately a cylinder with an ꢃ1 mm base and a few
microns in height. The high spatial resolution allowed us to
carefully verify the sample homogeneity. Polarization rotators
properly located along the internal optical path allowed for a
polarization analysis of the Raman spectrum.
1
3
of picene proposed by Kubozono et al. As hinted above, the
Mallory reaction has been recently applied to the multigram
synthesis of variously substituted phenacenes (including
substituted picenes) under continuous ow conditions.
However, the process requires highly dilute conditions (down
Powder X-ray diffraction measurements were performed on
the ID-09 beamline of the ESRF synchrotron (Grenoble, France)
˚
with a xed wavelength of 0.4129 A. The sample-to-detector
ꢀ3
8c
to 10 M of the starting stilbene) and a 450 W high pres-
sure Hg arc lamp as the light source. The approach reported
herein allows the use of a higher concentration of the
distance and the image plate orientation angles were cali-
brated using a CeO standard. The two-dimensional diffraction
2
images, acquired by a MAR445 detector, were converted into
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one dimensional diffraction patterns using the FIT2D 129.0, 129.5, 130.5, 131.3, 131.8. Anal. calcd for C23
H16O: C,
28
soware.
89.58; H, 5.23. Found: C, 89.7; H, 5.2.
Photochemical syntheses of 2a
An oxygen-saturated solution of stilbene 1a (E/Z 60/40) (53 mg,
.019 M) and iodine (8 mg, 15% w/w) in the chosen solvent (10
Acknowledgements
17
This work was supported by the Fondazione Cariplo (grant no.
013-0632). We thank Prof. P. E. Hoggard (Santa Clara Univer-
0
2
mL) was irradiated by means of different photochemical appa-
ratuses, including a multilamp reactor equipped with 10 ꢂ 15
W Hg phosphor-coated lamps (lem ¼ 310 nm) and a SolarBox
sity) for fruitful discussions.
ꢀ2
Notes and references
1
500e (CO.FO.ME.GRA s.r.l., Milan) Xe lamp set at 500 W m ,
equipped with an “outdoor” lter (cut off 280 nm). Photo-
chemical reactions were carried out in quartz tubes or in Pyrex
glass vessels when the multilamp reactor or the SolarBox were
used, respectively. The synthesized picene 2a was recovered by
1
2
3
G. A. Artioli and L. Malavasi, J. Mater. Chem. C, 2014, 2, 1577.
J. H. Sch ¨o n, C. Kloc and B. Batlogg, Org. Electron., 2000, 1, 57.
C. D. Dimitrakopoulos and P. R. L. Malenfant, Adv. Mater.,
2002, 14, 99, and references therein.

ltration from the photolyzed solutions. Spectroscopic data for
4
For recent examples see: (a) L.-K. Mao, J.-C. Hwang,
T.-H. Chang, C.-Y. Hsieh, L.-S. Tsai, Y.-L. Chueh,
S. S. H. Hsu, P.-C. Lyu and T.-J. Liu, Org. Electron., 2013,
7
14
2a are in accordance with the literature. Anal. calcd for C22H :
C, 94.93; H, 5.07. Found: C, 94.9; H, 5.1. The same process was
carried out on a gram scale, by pouring an oxygen saturated
solution of 1 g of 1a (0.038 M) and iodine (15% w/w) in ethyl
acetate into a Pyrex glass vessel and irradiating it in the SolarBox
apparatus for 6 h.
1
4, 1170; (b) H. Okamoto, N. Kawasaki, Y. Kaji,
Y. Kubozono, A. Fujiwara and M. Yamaji, J. Am. Chem. Soc.,
008, 130, 10470; (c) H. Okamoto, S. Hamao, H. Goto,
2
Y. Sakai, M. Izumi, S. Gohda, Y. Kubozono and R. Eguchi,
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H. Okamoto, S. Hamao, H. Goto, Y. Sakai, M. Izumi,
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(a) H. Mori, X.-C. Chen, N.-H. Chang, S. Hamao,
Y. Kubozono, K. Nakajima and Y. Nishihara, J. Org. Chem.,
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I. Masayuki, Jpn. Kokai Tokkyo Koho, 2014, JP 2014058501 A
20140403.
5
6
Solar light-induced synthesis of 2a
An oxygen-saturated solution of stilbene 1a (106 mg, 0.038 M)
and iodine (16 mg, 15% w/w) in the chosen solvent (10 mL) was
poured into a Pyrex glass vessel and exposed to sunlight on a
ꢁ
0
ꢁ
0
window ledge (Italy, latitude 45 11 N, 9 09 E, 77 m above sea
level). The picene obtained was removed from the photolysed
solution by ltration.
7
8
Photochemical syntheses of 5-methylpicene (2b)
From 1b (112 mg, 0.038 M, E/Z 50/50) and iodine (17 mg, 15% w/
w) in oxygen saturated C H or ethyl acetate, irradiated in the
6
6
SolarBox apparatus for 10 h. Picene 2b was collected by ltra-
1
tion of the photolysed solution. 2b: H NMR (d, CDCl
3
) 2.95 (s,
9
T. Nakae, R. Ohnishi, Y. Kitahata, T. Soukawa, H. Sato,
S. Mori, T. Okujima, H. Uno and H. Sakaguchi, Tetrahedron
Lett., 2012, 53, 1617.
3
8
1
H), 7.65–7.80 (m, 4H), 8.00–8.05 (m, 2H), 8.20–8.25 (m, 1H),
1
3
.65 (s, 1H), 8.80–9.00 (m, 5H). C NMR, (d, CDCl
3 3
) 20.7 (CH ),
20.7 (CH), 121.4 (CH), 121.5 (CH), 121.7 (CH), 123.0 (CH), 123.4
1
0 (a) R. G. Harvey, J. Pataki, C. Cortez, P. Di Raddo and
C. X. Yang, J. Org. Chem., 1991, 56, 1210; (b) L. Minuti,
A. Taticchi, E. Gacs-Baitz and A. Marrocchi, Tetrahedron,
(
1
CH), 124.6 (CH), 126.4 (3CH), 126.1 (CH), 127.1 (CH), 127.8,
28.0, 128.2, 128.3, 128.4 (CH), 128.6, 130.4, 131.7, 131.8, 133.2.
Anal. calcd for C H : C, 94.48; H, 5.52. Found: C, 94.5; H, 5.5.
2
3
16
1998, 54, 10891; (c) S. Some, B. Dutta and J. K. Ray,
Tetrahedron Lett., 2006, 47, 1221.
1 N. Hoffmann, J. Photochem. Photobiol., C, 2014, 19, 1.
Photochemical syntheses of 5-methoxypicene (2c)
1
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6
H
6
1
NMR, (d, CDCl
3
) 4.30 (s, 3H), 7.40 (s, 1H), 7.65–7.80 (m, 4H),
F. B. Mallory and C. W. Mallory, Org. React., 1984, 30, 1; (c)
For recent example see: F. B. Mallory, C. K. Regan,
J. M. Bohen, C. W. Mallory, A. A. Bohen and P. J. Carroll, J.
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8
.00–8.05 (m, 3H), 8.45–8.50 (dd, 1H J ¼ 1 and 8 Hz), 8.70–8.75
1
3
(d, 1H, J ¼ 8 Hz), 8.80–8.90 (m, 4H). C NMR, (d, CDCl ) 55.4
3
(
CH ), 97.7 (CH), 119.1 (CH), 121.4 (CH), 121.5 (CH), 122.4 (CH),
3
1
1
22.9 (CH), 123.1 (CH), 124.2, 125.9, 126.4 (CH), 126.5 (CH), 15 H. Okamoto, T. Takane, S. Gohda, Y. Kubozono, K. Sato,
26.6 (CH), 126.8 (CH), 127.3 (CH), 127.7, 128.2, 128.3 (CH),
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