Synthesis of alkyl-substituted tribenzopentaphenes as versatile polycondensed aromatic hydrocarbon π-π Stacking building blocks

Article abstract of DOI:10.1055/s-0031-1291010

We show the versatile synthesis of four tribenzopentaphene derivatives bearing alkyl side chains at three different positions. Substitutions on two of these positions led to subtle intensity changes at the lines of the blue emission, whereas alkylation in the bay region led to dimerization of the pentaphene derivative, resulting in a distortion of the chromophore geometry and an emission shift to green. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0031-1291010

1928▌
PAPER
paper
Synthesis of Alkyl-Substituted Tribenzopentaphenes as Versatile
Polycondensed Aromatic Hydrocarbon π–π Stacking Building Blocks
Synthesis of Alkyl-Substituted Tribenzopentaphenes
Bassam Alameddine,a Sofia Martin Caba,b Mauro Schindler,b Titus A. Jenny*b
a
Department of Mathematics and Natural Sciences, Gulf University for Science and Technology, Hawally 32093, Kuwait
b
Chemistry Department, University of Fribourg, chemin du Musée 9, 1700 Fribourg, Switzerland
Fax +41(26)3009739; E-mail: titus.jenny@unifr.ch
Received: 29.12.2011; Accepted after revision: 12.04.2012
TBP and variously substituted derivatives had been inves-
tigated previously as materials for optoelectronic devic-
es.6 A TBP derivative substituted in all six positions
investigated in this work has been reported but not further
Abstract: We show the versatile synthesis of four tribenzopenta-
phene derivatives bearing alkyl side chains at three different posi-
tions. Substitutions on two of these positions led to subtle intensity
changes at the lines of the blue emission, whereas alkylation in the
bay region led to dimerization of the pentaphene derivative, result- investigated.7 It should be noted that a too dense substitu-
ing in a distortion of the chromophore geometry and an emission
shift to green.
tion pattern severely impedes the stacking of the PAH
core and thereby reduces the desired π–π interactions. An
Key words: fused-ring systems, cross-coupling, Diels–Alder reac-
tion, cyclodehydrogenation, polycycles
easy access to specifically substituted TBP derivatives is
therefore desirable.
Scheme 1 summarizes the general strategy we adopted7 to
synthesize the TBP derivatives 1a–d bearing pairs of side
chains at specific positions. This strategy offers the great
advantage of being short and versatile (in view of chang-
ing the nature of the side chains), requiring at most four
steps starting from commercially available compounds.
The reaction steps involve a double Knoevenagel conden-
sation between benzil or 4,4′-dibromobenzil and diphen-
ylpropan-2-one or 1,3-bis(4-bromophenyl)propan-2-one,8
a Diels–Alder cycloaddition reaction with concomitant
CO extrusion, a Kumada cross-coupling,9 and, finally, a
Scholl cyclodehydrogenation reaction, using FeCl3/nitro-
methane reagent,10 of the resulting tetraphenylbenzene
derivatives 4a–d into the desired PAH target molecules
1a–d. The synthons 2a–c are described elsewhere,11 and
Self-assembled polycondensed aromatic hydrocarbons
(PAHs) have drawn much attention in the past two de-
cades because of their remarkable stability and unsur-
passed non-covalent π–π stacking1 bonding, which
bestows on them remarkable physicochemical2 and
optoelectronic3 properties. Considerable experimental ef-
fort has been invested in the synthesis of various PAH
structures of different shapes and sizes. Nevertheless,
most of the synthetic approaches reported to date concen-
trate on designing highly symmetrical PAH derivatives
ranging from linear to disc-shaped,4 which complicates
the decoration of their peripheries with dissimilar pending
groups5 and impedes the π–π stacking.
We present herein the versatile synthesis of a less sym- 3b was generated by carrying out a slightly modified route
metrical (as compared to hexabenzocoronene, for exam- to that previously reported.12 The brominated tetraphenyl-
ple)
half-lunar-shaped
polycondensed
aromatic benzene building blocks 3a–c were synthesized by apply-
hydrocarbon tribenzo[fg,ij,rst]pentaphene 1 (TBP; Figure ing an improved [4+2] Diels–Alder cycloaddition
1) carrying solubilizing sidechains in various positions. reaction in which acetylene is replaced by the more effi-
The convergent synthesis of these compounds requires cient ethyne source phenylvinylsulfoxide.13 Attachment
only a few steps starting from commercially available ma- of the aliphatic side chains to the aromatic cores were car-
terials (Scheme 1).
ried out under typical Kumada cross-coupling reaction
conditions in which an excess of the aliphatic Grignard re-
agent was reacted with 3a–c using [Pd(dppf)Cl2], which
afforded 4a–c in good yields. Compound 4d was finally
obtained by reacting tetraphenylcyclopentanone with
commercially available 8-hexadecyne in diphenyl ether at
reflux.
R2
R2
R1
R1
The delicate final cyclodehydrogenation step was
achieved by reacting the synthons 4a–d with anhydrous
iron(III) chloride and nitromethane in dichloromethane,
affording the desired derivatives 1a–c in acceptable
yields. These latter derivatives were purified through a se-
ries of precipitation and filtrations on Millipore filters
(1 μm pore size). The structures of compounds 1a–c were
confirmed by NMR and mass spectrometry analyses.
R3
R3
1
Figure 1 Structure of tribenzo[fg,ij,rst]pentaphene (TBP) 1 indicating
the three investigated substitution sites
SYNTHESIS 2012, 44, 1928–1934
Advanced online publication: 14.05.2012
DOI: 10.1055/s-0031-1291010; Art ID: SS-2011-Z1194-OP
© Georg Thieme Verlag Stuttgart · New York
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Synthesis of Alkyl-Substituted Tribenzopentaphenes
1929
O
R1
R1
R1
R1
i
R2
R2
R2
R2
2a R1 = H; R2 = Br; (64%)
2b R1 = Br; R2 = H; (87%)
2c R1 = Br; R2 = Br; (77%)
2d R1 = H; R2 = H
3a R1 = H; R2 = Br; (98%)
3b R1 = Br; R2 = H; (39%)
3c R1 = Br; R2 = Br; (97%)
ii
iii
R3
R3
R3
R3
iv
R1
R1
R1
R1
R2
R2
R2
R2
1a R1, R3 = H; R2 = C8H17; (42%)
4a R1, R3 = H; R2 = C8H17; (74%)
4b R1 = C8H17; R2, R3 = H; (77%)
4c R1, R2 = C8H17; R3 = H; (68%)
4d R1, R2 = H; R3 = C7H15; (81%)
1b R1 = C8H17; R2, R3 = H; (48%)
1c R1, R2 = C8H17; R3 = H; (47%)
1d R1, R2 = H; R3 = C7H15; (0%)
Scheme 1 Synthesis of pentaphene derivatives. Reagents and conditions: (i) phenylvinyl sulfoxide, toluene, reflux, (ii) for 2d: 8-hexadecyne,
diphenyl ether, reflux, (iii) C8H17MgBr, [Pd(dppf)Cl2·CH2Cl2], THF, reflux; (iv) FeCl3, MeNO2, CH2Cl2, 45 °C.
Despite numerous attempts, compound 1d could not be together with a minor amount of dimer 1f (m/z = 1150), as
detected in the complex reaction mixture obtained from a solid during work-up. In the filtrate, representing about
oxidation of 4d under standard conditions. Instead, a di- 10% of the total mass, we identified an equimolar mixture
mer (m/z = 1138) was obtained as the major product, of starting material 5d, the desired compound 1d, and a di-
which failed to yield resolved NMR spectra, either be- mer 1g (m/z =1142). NMR analysis revealed the latter
cause of excessive stacking and/or because of paramag- compound to possess the 5,5′-linked dimeric structure
netic impurities [e.g., traces of the abundant oxidant shown in Figure 3.
Fe(III)]. When the reaction time and reaction temperature
were reduced (i.e., at r.t. for 10 min with FeCl3/nitrometh-
ane), the dimeric side product 1e, CH2-bridged at the 6,6′-
position, was isolated in trace amounts; this compound
presumably stems from a double Friedel–Crafts coupling
(Figure 2).
R
R
O
i
5d
R
R
ii
R
CH2
R
R
R
1e R = C7H15
R = C7H15
Figure 2 Structure of the 6,6′-CH2-bridged pentaphene dimer deriv-
ative 1e
1d
Scheme 2 Synthesis of 1d: Reagents and conditions: (i) 8-hexadec-
yne, diphenyl ether, reflux, 60%; (ii) FeCl3, MeNO2, CH2Cl2, r.t., 10
min, trace (ca. 1%).
In an alternative attempt, we synthesized compound 5d
using an analogous Diels–Alder reaction, to that used to
generate 4d (Scheme 2), but employing the commercially
available phencyclone instead of tetracyclone (2d). When
the Scholl reaction was repeated with 5d, dimer 1h (m/z =
1138) was again isolated as a major product, but this time
We therefore conclude that oxidative dimerization always
predominates over intramolecular aryl–aryl coupling,
since we observe the completely oxidized dimer 1h as a
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1928–1934

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B. Alameddine et al.
PAPER
major product even before complete consumption of the
starting material. Moreover, the observation of a dimer
(m/z = 1150) that corresponds to a singly linked starting
molecule, as well as singly linked but fully oxidized dimer
1
(for which a 5,5′-link was deduced from H NMR spec-
trum), permits us to propose a reaction sequence: 5d → 1f
→ 1g → 1h, for the major pathway, and: 5d → 1d, for the
minor pathway. In addition, these findings permit the
structure of dimer 1h to be proposed (Figure 3).
R
R
R
R
R
R
R
R
1f
oxidation (– 4 x H2)
R
R
1g
oxidation (– 2 x H2)
R
R
1h
R = C7H15
Figure 3 Structures of dimers 1f–h
The TBP derivatives 1a–c show similar UV/Vis absorp-
tion spectra, with a strong band at approximately 306 nm
and two smaller absorption bands at approximately 355
and 376 nm. They fluoresce in the blue region with similar
emission bands (Figure 4).
It is worth noting that the intensities of these bands differ
considerably from one derivative to the other, which dem-
onstrates the important influence these lateral substituents
exert on the chromophore and on the aggregation behavior
of the aromatic core. Due to the reduced symmetry com-
pared to HBC, the 0→0 transition bands for 1a–c gains in
Figure 4 Normalized absorption (red) and emission (green) spectra of
the tribenzopentaphene derivatives in toluene: (a) emission (λex
307 nm) of 1a; (b) emission (λex = 306 nm) of 1b; (c) emission (λex
307 nm) of 1c; (d) emission (λex = 313 nm) of 1d; (e) emission (λex
314 nm) of 1e, and (f) emission (λex = 317 nm) of 1h.
=
=
=
Synthesis 2012, 44, 1928–1934
© Georg Thieme Verlag Stuttgart · New York

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Synthesis of Alkyl-Substituted Tribenzopentaphenes
1931
2′,3′-Bis(4-bromophenyl)-1,1′:4′,1′′-terphenyl (3a)
intensity and is clearly visible at a similar wavelength for
all compounds (ca. 395 nm). As expected, compound 1e
deviates from this scheme; in this case, all transitions are
shifted to somewhat longer wavelengths. We attribute this
phenomenon to the distorting effect of the substituents.
Their location in the bay regions of the molecule forces
the TBP core to deviate from planarity, leading to a to
contorted sp2 hybridized manifold, which is known to red-
shift the absorption14a,b and emission bands (from pale
blue to blue-green). Whereas compound 1d shows
UV/Vis and emission spectra that are nearly identical to
the CH2-bridged dimer 1e, the fully oxidized dimer 1h
shows a very different absorption spectrum and a green
emission due to the more extended dibenzo[fg,lm]diben-
zo[5,6:8,9]heptaceno[2,1,18,17,16,15,14-uvwxyza1b1c1d1a]hep-
tacene core structure.15
A mixture of 2a11c (27.45 g, 50.62 mmol) and phenylvinylsulfoxide
(11.55 g, 75.93 mmol) in toluene (210 mL) was heated at reflux for
24 h. After cooling to r.t., the mixture was filtered through a short
plug of silica gel and the remaining solvents were evaporated in
vacuo. The residue was purified by column chromatography (hex-
anes–EtOAc, 10:1) to give 3a.
Yield: 25.91 g (98%); white solid.
1H NMR (360 MHz, CDCl3): δ = 7.50 (s, 2 H), 7.15–7.23 (m, 6 H),
7.03–7.12 (m, 8 H), 6.65 (d, J = 8.6 Hz, 4 H).
13C NMR (90.55 MHz, CDCl3): δ = 141.47 (2 C, Ar), 141.17 (2 C,
Ar), 138.97 (2 C, Ar), 138.76 (2 C, Ar), 133.22 (4 C, Ar), 130.52 (4
C, Ar), 129.98 (2 C, Ar), 129.95 (4 C, Ar), 127.94 (4 C, Ar), 126.63
(2 C, Ar), 120.30 (2 C, Ar).
MS (EI): m/z (%) = 540 (100) [M]·+.
2′,3′-Bis(4-octylphenyl)-1,1′:4′,1′′-terphenyl (4a)
A solution of 1-bromooctane (773 mg, 4.0 mmol) in anhydrous
THF (3 mL) was added dropwise to magnesium turnings (100 mg,
4.0 mmol). After complete consumption of the magnesium turnings,
the Grignard reagent was added to a mixture of 3a (540 mg, 1.0
mmol) and [PdCl2(dppf)] (110 mg, 0.15 mmol) in anhydrous THF
(7 mL). The resulting mixture was heated at reflux for 24 h. After
cooling, the reaction mixture was quenched by addition of MeOH
(10 mL), diluted with CH2Cl2 (100 mL) and extracted with sat. aq
NH4Cl (30 mL) and H2O (30 mL). The combined organic layers
were dried and the solvent was removed in vacuo. The resulting
mixture was separated by column chromatography (pentane–
CH2Cl2, 1:1) to give the desired product 4a.
In conclusion, we show the versatile synthesis of three
tribenzopentaphene derivatives substituted at different
positions; all of which were obtained in good yields.
Emission spectroscopy reveals that alkyl substituents in
the examined derivatives 1a–c exert only a very minor in-
fluence on the aggregation behavior of the PAH core. In-
terestingly, intermolecular oxidation products were
detected instead of the expected tribenzopentaphene de-
rivative when the alkyl substituents were placed in posi-
tions 15 and 16. Thus, the seemingly minor modification
in the positions of the alkyl chains has a drastic effect on
the reactivity of the tribenzopentaphene derivative, lead-
ing to a facile intermolecular Scholl reaction that affords
the fully oxidized dimer 1h even under mild reaction con-
ditions. Further computational work will be carried out to
study the influence the alkyl chains have when placed in
the aforementioned positions, and which led to polymer-
ization. In contrast to the more symmetrical PAH struc-
tures, such as the disc-shaped hexabenzocoronene (HBC),
the less symmetrical trapezoidal tribenzopentaphene of-
fers the possibility for more complex functionalization at
the periphery without disturbing the π–π stacking of the
aromatic core, according to preliminary calculations.
Yield: 450 mg (74%); white powder.
1H NMR (360 MHz, CDCl3): δ = 7.46 (s, 2 H, ArH), 7.07–7.14 (m,
10 H, PhH), 6.67 (d, J = 7.9 Hz, 4 H, ArH), 6.63 (d, J = 7.9 Hz, 4 H,
ArH), 2.37 (t, J = 7.4 Hz, 4 H, Ar-CH2-C7H15), 1.35–1.46 (m, 4 H,
Ar-CH2-CH2-C6H13), 1.05–1.30 (m, 20 H, Ar-C2H4-C5H10-CH3),
0.85 (t, J = 6.7 Hz, 6 H, Ar-C7H14-CH3).
13C NMR (90.55 MHz, CDCl3): δ = 144.21 (2 C, Ar), 141.70 (2 C,
Ar), 140.98 (2 C, Ar), 139.21 (2 C, Ar), 139.13 (2 C, Ar), 130.88 (4
C, Ar), 130.44 (4 C, Ar), 129.91 (2 C, Ar), 129.12 (4 C, Ar), 128.08
(4 C, Ar), 126.79 (2 C, Ar), 35.70 (2 C, Ar-CH2-C7H15), 31.99 (2 C,
Ar-C5H10-CH2-C2H5), 31.41 (2 C, Ar-CH2-CH2-C6H13), 29.54,
29.41, 29.12 (6 C, Ar-C2H4-C3H6-C3H7), 22.57 (2 C, Ar-C6H12-
CH2-CH3), 14.02 (2 C, Ar-C7H14-CH3).
MS (EI): m/z (%) = 606.2 (100) [M]·+.
6,9-Dioctyltribenzo[fg,ij,rst]pentaphene (1a)
To a solution of 4a (200 mg, 0.33 mmol) in CH2Cl2 (20 mL), purged
with argon for 20 min, was added a degassed solution of FeCl3 (960
mg, 5.93 mmol, 3 equiv per H to be removed) in MeNO2 (3.5 mL)
over 20 min. The reaction medium was heated to 45 °C and bubbled
with argon throughout the entire 40 min reaction time (the color
turned from slight yellow to green, and finally to brown). The mix-
ture was cooled to r.t., quenched with MeOH (80 mL), and then
placed in the refrigerator overnight. The brown precipitate was then
filtered several times through a Millipore filter.
All chemicals were used without further purification as purchased
from Acros, Aldrich, Fluka, Merck, Riedel-de-Haën, Strem, or TCI
unless otherwise notified. All the reactions were performed under a
protective atmosphere using dry nitrogen or argon. The solvents,
CH2Cl2, Et2O, pentane, THF, and toluene, were dried and deoxy-
genated by passage over molecular sieves using a system similar to
the that proposed by Grubbs.16 Column chromatography was car-
ried out with silica gel 60, 0.04–0.06, from either Merck or
Brunschwig. Thin-layer chromatography was performed on alumi-
num sheets coated with silica gel 60 F254 and revealed either by UV
irradiation or by developing in a solution of KMnO4. Mass spectra
were recorded with the following spectrometers: EI spectra were re-
corded with a HP5988A Quadrupol spectrometer, MALDI-ICR
spectra were recorded with a FT/ICR Bruker 4.7 T BioApex II spec-
trometer. All MALDI spectra used DCTB or TNCQ as matrix with
a 337 nm nitrogen laser. NMR spectra were recorded with Bruker
Avance DPX 360 MHz (1H: 360 MHz, 13C: 90.55 MHz) and
Avance III 500 MHz (1H: 500 MHz, 13C: 126 MHz) spectrometers
using CDCl3 as solvent; chemical shifts (δ) are given in ppm, cou-
pling constants (J) in Hz, and are referenced to tetramethylsilane
(TMS).
The resulting very dark powder was extracted with CH2Cl2 and
H2O. The volume of the combined organic layers was reduced to 5
mL and poured over a short silica gel plug using CH2Cl2 as eluent
to give 1a.
Yield: 83 mg (42%); orange powder.
1H NMR (360 MHz, CDCl3): δ = 8.97 (br s, 2 H, ArH), 8.75–8.82
(m, 4 H, ArH), 8.72 (br s, 2 H, ArH), 8.66 (br s, 2 H, ArH), 7.66–
7.72 (m, 4 H, ArH), 3.09 (t, J = 7.7 Hz, 4 H, Ar-CH2-C7H15), 1.93
(quin, J = 7.7 Hz, 4 H, Ar-CH2-CH2-C6H13), 1.27–1.59 (m, 20 H,
Ar-C2H4-C5H10-CH3), 0.89 (t, J = 6.4 Hz, 6 H, Ar-C7H14-CH3).
© Georg Thieme Verlag Stuttgart · New York
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B. Alameddine et al.
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13C NMR (90.55 MHz, CDCl3): δ = 141.04 (Ar), 130.32 (Ar),
130.14 (Ar), 130.12 (Ar), 129.92 (Ar), 127.44 (Ar), 127.32 (Ar),
127.12 (Ar), 123.81 (Ar), 123.73 (Ar), 123.43 (Ar), 122.93 (Ar),
122.01 (Ar), 121.69 (Ar), 120.56 (Ar), 37.30 (Ar-CH2-C7H15),
32.44 (Ar-C5H10-CH2-C2H5), 32.10 (Ar-CH2-CH2-C6H13), 29.86,
29.81, 29.53 (Ar-C2H4-C3H6-C3H7), 22.86 (Ar-C6H12-CH2-CH3),
14.29 (Ar-C7H14-CH3).
MS (EI): m/z (%) = 599.9 (100) [M]·+.
UV/Vis (CH2Cl2, 10–5 M): λmax = 298, 306, 355, 374 nm.
Fluorescence (toluene, 10–5 M): λmax = 403, 417, 427, 442, 454
(sh) nm.
The resulting precipitate was extracted with CH2Cl2 and H2O. The
volume of the combined organic layers was reduced to 5 mL and fil-
tered through a short silica gel plug using CH2Cl2 as eluent. The vol-
ume of the organic layers was reduced and the product was
recrystallized several times (CH2Cl2–EtOH) and passed through a
Millipore filter to give 1b.
Yield: 80 mg (48%); dark-yellow solid.
1H NMR (360 MHz, CDCl3): δ = 9.11 (s, 2 H, ArH), 9.02 (d, J =
7.7 Hz, 2 H, ArH), 8.95 (d, J = 7.7 Hz, 2 H, ArH), 8.80 (d, J =
8.2 Hz, 2 H, ArH), 8.62 (s, 2 H, ArH), 8.06 (t, J = 7.7 Hz, 2 H), 7.60
(d, J = 8.2 Hz, 2 H, ArH), 2.94 (t, J = 7.7 Hz, 4 H, Ar-CH2-C7H15),
1.78–1.91 (m, 4 H, Ar-CH2-CH2-C6H13), 1.18–1.67 (m, 20 H, Ar-
C2H4-C5H10-CH3), 0.89 (t, J = 6.4 Hz, 6 H, Ar-C7H14-CH3).
13C NMR (90.55 MHz, CDCl3): δ = 142.29 (2 C, Ar), 130.39 (2 C,
Ar), 130.08 (2 C, Ar), 130.07 (2 C, Ar), 128.58 (2 C, Ar), 128.27 (2
C, Ar), 127.51 (2 C, Ar), 126.51 (2 C, Ar), 124.89 (2 C, Ar), 123.82
(2 C, Ar), 123.36 (2 C, Ar), 123.20 (2 C, Ar), 121.71 (2 C, Ar),
121.66 (2 C, Ar), 121.02 (2 C, Ar), 36.60 (2 C, Ar-CH2-C7H15),
32.08 (2 C, Ar-C5H10-CH2-C2H5), 31.90 (2 C, Ar-CH2-CH2-C6H13),
29.75, 29.66, 29.48 (6 C, Ar-C2H4-C3H6-C3H7), 22.85 (2 C, Ar-
C6H12-CH2-CH3), 14.28 (2 C, Ar-C7H14-CH3).
3′,6′-Bis(4-bromophenyl)-1,1′:2′,1′′-terphenyl (3b)
Compound 2b11d (1.3 g, 2.4 mmol) and phenylvinylsulfoxide (547
mg, 3.6 mmol) were dissolved in toluene (10 mL) and heated at re-
flux under argon for 48 h. After cooling to r.t., the mixture was pu-
rified by column chromatography (pentane–CH2Cl2, 1:1) to give
3b.
Yield: 500 mg (39%); white solid.
1H NMR (360 MHz, CDCl3): δ = 7.46 (s, 2 H, ArH), 7.24–7.32 (m,
6 H, ArH), 6.92–6.99 (m, 8 H, ArH), 6.79 (d, J = 8.6 Hz, 4 H, ArH).
HRMS (MALDI-ICR; DCTB): m/z (%) = 402.1390 (13) [M –
(C7H15)2], 501.2555 (76) [M – C7H15], 600.3750 (100) [M]·+ (m/z
calcd for C46H48+: 600.37505).
13C NMR (90.55 MHz, CDCl3): δ = 140.81 (2 C, Ar), 140.60 (2 C,
Ar), 140.12 (2 C, Ar), 139.49 (2 C, Ar), 131.60 (4 C, Ar), 131.53 (4
C, Ar), 130.91 (4 C, Ar), 129.43 (2 C, Ar), 127.31 (4 C, Ar), 126.08
(4 C, Ar), 120.76 (2 C, Ar).
MS (EI): m/z (%) = 600.2 (100) [M]·+, 488.0 (60) [M – C8H16]·+,
376.1 (5) [M – 2 × C8H16]·+.
MS (EI): m/z (%) = 540 (100) [M]·+.
UV/Vis (CH2Cl2, 10–5 M): λmax = 297, 306, 355, 376 nm.
Fluorescence (toluene, 10–5 M): λmax = 403, 415, 423, 427, 441
3′,6′-Bis(4-octylphenyl)-1,1′:2′,1′′-terphenyl (4b)
A solution of 1-bromooctane (428 mg, 2.2 mmol) in anhydrous
THF (2 mL) was added dropwise to magnesium turnings (55 mg,
2.2 mmol). After the complete consumption of the magnesium turn-
ings, the Grignard reagent was added to a mixture of 3b12 (300 mg,
0.55 mmol) and [PdCl2(dppf)] (61 mg, 8.33·10–5 mol) in anhydrous
THF (4 mL). The resulting mixture was heated at reflux for 24 h.
After cooling, the reaction mixture was quenched by addition of
MeOH (5 mL), diluted with CH2Cl2 (50 mL) and extracted with sat.
aq NH4Cl (20 mL) and H2O (10 mL). The combined organic layers
were dried and the volume was reduced to 5 mL in vacuo and pre-
cipitated by addition of EtOH. The product was recrystallized sev-
eral times (CH2Cl2–EtOH) to give 4b.
(sh) nm.
4,4′′-Dibromo-2′,3′-bis(4-bromophenyl)-1,1′:4′,1′′-terphenyl
(3c)
2,3,4,5-Tetrakis(4-bromophenyl)cyclopenta-2,4-dienone
2c11e
(1.44 g, 2.06 mmol) and phenylvinylsulfoxide (407 mL, 470 mg,
1.5 equiv) were dissolved in toluene (10 mL) and heated at reflux
under argon for 4 d. After cooling to r.t., the product was purified
by column chromatography (pentane–CH2Cl2, 1:1) to give 3c.
Yield: 1.39 g (97%); white powder.
1H NMR (360 MHz, CDCl3): δ = 7.45 (s, 2 H, ArH), 7.32 (d, J =
8.2 Hz, 4 H, ArH), 7.12 (d, J = 8.6 Hz, 4 H, ArH), 6.92 (d, J =
8.2 Hz, 4 H, ArH), 6.63 (d, J = 8.6 Hz, 4 H, ArH).
13C NMR (90.55 MHz, CDCl3): δ = 140.24 (2 C, Ar), 140.23 (2 C,
Ar), 130.09 (2 C, Ar), 138.19 (2 C, Ar), 133.04 (4 C, Ar), 131.48 (4
C, Ar), 131.18 (4 C, Ar), 130.80 (4 C, Ar), 129.91 (2 C, Ar), 121.12
(2 C, Ar), 120.67 (2 C, Ar).
Yield: 258 mg (77%); white solid.
1H NMR (360 MHz, CDCl3): δ = 7.49 (br s, 2 H, ArH), 7.00 (d, J =
7.7 Hz, 4 H, ArH), 6.95 (d, J = 7.7 Hz, 4 H, ArH), 6.87–6.93 (m,
6 H, ArH), 6.76–6.84 (m, 4 H, ArH), 2.51 (t, J = 7.7 Hz, 4 H, Ar-
CH2-C7H15), 1.49–1.61 (m, 4 H, Ar-CH2-CH2-C6H13), 1.18–1.35
(m, 20 H, Ar-C2H4-C5H10-CH3), 0.88 (t, J = 6.8 Hz, 6 H, Ar-C7H14-
CH3).
13C NMR (90.55 MHz, CDCl3): δ = 140.69 (2 C, Ar), 140.67 (2 C,
Ar), 140.24 (2 C, Ar), 140.13 (2 C, Ar), 139.11 (2 C, Ar), 131.59 (4
C, Ar), 129.72 (4 C, Ar), 129.37 (2 C, Ar), 127.52 (4 C, Ar), 126.80
(4 C, Ar), 125.42 (2 C, Ar), 35.49 (2 C, Ar-CH2-C7H15), 31.87 (2 C,
Ar-C5H10-CH2-C2H5), 31.26 (2 C, Ar-CH2-CH2-C6H13), 29.45,
29.27, 29.26 (6 C, Ar-C2H4-C3H6-C3H7), 22.68 (2 C, Ar-C6H12-
CH2-CH3), 14.11 (2 C, Ar-C7H14-CH3).
MS (EI): m/z (%) = 697.9 (100) [M]·+, 616.9 (5) [M – Br]+, 537.9
(20) [M – Br2]·+.
MS (MALDI-ICR; DCTB): m/z = 716.79 (100) [M + Na]·+.
4,4′′-Dioctyl-2′,3′-bis(4-octylphenyl)-1,1′:4′,1′′-terphenyl (4c)
A solution of 1-bromooctane (2.12 mL, 3.07 g, 15.9 mmol) in anhy-
drous THF (50 mL) was added dropwise to magnesium turnings
(387 mg, 15.9 mmol). After the complete consumption of the mag-
nesium turnings, the Grignard reagent was added to a mixture of
4,4′′-dibromo-3′,4′-bis(4-bromophenyl)-1,1′:2′,1′′-terphenyl (3c;
1.39 g, 20.0 mmol) and [PdCl2(dppf)] (407 mg, 0.53 mmol, 28
mol%) in anhydrous THF (50 mL). The resulting mixture was heat-
ed at reflux for 48 h. After cooling, the reaction mixture was
quenched by addition of MeOH (30 mL), diluted with CH2Cl2 (300
mL) and extracted with sat. NH4Cl (80 mL) and H2O (80 mL). The
combined organic layers were dried and reduced to 10 mL and the
product was precipitated by adding EtOH. The product was recrys-
tallized several times (CH2Cl2–EtOH) to give 4c.
MS (MALDI-ICR; DCTB): m/z (%) = 606.42 (100) [M]·+.
3,12-Dioctyltribenzo[fg,ij,rst]pentaphene (1b)
To a solution of 4b (170 mg, 0.28 mmol) in CH2Cl2 (20 mL), purged
with argon for 30 min, was added a degassed solution of FeCl3 (817
mg, 5.04 mmol, 18 equiv) in MeNO2 (2.5 mL) over 20 min. The re-
action medium was heated to 45 °C and bubbled with argon
throughout the entire 40 min reaction time (the color turned from
slight yellow to green, and finally to opaque brown). The mixture
was cooled to r.t., quenched with MeOH (65 mL), and then placed
in the refrigerator overnight. The orange-brown suspension was
then passed through a Millipore filter several times.
Yield: 1.12 g (68%); white powder.
Synthesis 2012, 44, 1928–1934
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of Alkyl-Substituted Tribenzopentaphenes
1933
1H NMR (360 MHz, CDCl3): δ = 7.47 (s, 2 H, ArH), 6.99 (d, J =
7.7 Hz, 4 H, ArH), 6.93 (d, J = 7.7 Hz, 4 H, ArH), 6.69 (d, J =
8.2 Hz, 4 H, ArH), 6.65 (d, J = 8.2 Hz, 4 H, ArH), 2.51 (t, J =
8.2 Hz, 4 H, Ar-CH2-C7H15), 2.40 (t, J = 8.2 Hz, 4 H, Ar-CH2-
C7H15), 1.55 (quin, 3JH–H = 7.3 Hz, 4 H, Ar-CH2-CH2-C6H13), 1.44
(quin, J = 7.3 Hz, 4 H, Ar-CH2-CH2-C6H13), 1.10–1.35 (m, 40 H,
Ar-C2H4-C5H10-CH3), 0.88 (t, J = 7.5 Hz, 12 H, Ar-C7H14-CH3).
was quenched by addition of MeOH (80 mL). The volume of the
mixture was reduced to 5 mL and injected with agitation into pen-
tane (100 mL). The precipitate was removed by filtration and cen-
trifugation. After extraction of the remaining solution with EDTA
solution (0.1 M, 3 × 50 mL), the organic phase was removed in vac-
uo and the residue was purified by repeated column chromatogra-
phy on Alox® (pentane–CH2Cl2 gradient).
13C NMR (90.55 MHz, CDCl3): δ = 140.79 (2 C, Ar), 140.66 (2 C,
Ar), 140.61 (2 C, Ar), 139.81 (2 C, Ar), 139.50 (2 C, Ar), 137.51 (2
C, Ar), 131.57 (4 C, Ar), 129.92 (4 C, Ar), 129.29 (2 C, Ar), 127.59
(4 C, Ar), 127.01 (4 C, Ar), 35.69 (2 C, alk), 35.54 (2 C, alk), 32.12
(2 C, alk), 32.07 (2 C, alk), 31.47 (2 C, alk), 31.42 (2 C, alk), 29.68
(2 C, alk), 29.65 (2 C, alk), 29.53 (2 C, alk), 29.46 (2 C, alk), 29.00
(4 C, alk), 22.85 (4 C, Ar-C6H12-CH2-CH3), 14.28 (4 C, Ar-C7H14-
CH3).
1H NMR (500 MHz, CD2Cl2): δ = 9.06 (s, 2 H), 8.98 (d, J = 8.0 Hz,
2 H), 8.92 (s, 2 H), 8.83 (d, J = 7.7 Hz, 2 H), 8.73 (d, J = 7.4 Hz, 2
H), 8.72 (d, J = 7.4 Hz, 2 H), 8.57 (d, J = 7.4 Hz, 2 H), 8.56 (d, J =
7.4 Hz, 2 H), 7.96 (t, J = 7.8 Hz, 2 H), 7.69 (t, J = 7.4 Hz, 2 H), 7.63
(t, J = 7.4 Hz, 2 H), 7.62 (t, J = 7.4 Hz, 4 H), 4.89 (s, COSY cross-
peak with 9.06, 8.92, 2 H), 3.59 (m, 8 H), 1.52 (m, 8 H), 1.2–1.4 (m,
32 H), 0.88 (t, J = 7.0 Hz, 12 H).
HRMS (MALDI; DCTB): m/z (%) = 401.1326 (95), 499.2414 (53),
+
MS (EI): m/z (%) = 830.4 (100) [M]·+.
585.3543 (89), 1156.6871 (100) [M]·+ (m/z calcd for C89H88
:
1156.68805).
3,6,9,12-Tetraoctyltribenzo[fg,ij,rst]pentaphene (1c)
UV/Vis (CH2Cl2, 10–5 M): λmax = 314, 361, 380, 420 (sh), 448 (sh),
486 nm.
Fluorescence (toluene, 10–5 M): λmax = 425, 449, 489 (sh) nm.
To a solution of 4c (2.00 g, 2.41 mmol) in CH2Cl2 (160 mL), purged
with argon for 40 min, was added a degassed solution of FeCl3 (7.02
g, 433 mmol, 18 equiv) in MeNO2 (160 mL) over 20 min. The reac-
tion medium was heated to 45 °C and bubbled with argon through-
out the entire 2 h reaction time (the color turned from slight-yellow
to green, and finally to brown). The mixture was cooled to r.t.,
quenched with MeOH (550 mL), and then placed in a refrigerator
overnight. The orange-brown suspension was then passed through a
Millipore filter several times to give 1c.
2,3-Diheptyl-1,4-diphenyltriphenylene (5d)
Phenylcyclone (260 mg, 0.68 mmol) and 8-hexadecyne (227 mg,
1.02 mmol) were dissolved in diphenyl ether (6 mL) and heated to
250 °C in the absence of light and under an inert atmosphere for 4
d. The diphenyl ether was distilled off and the resulting mixture was
separated by column chromatography (pentane–CH2Cl2 gradient) to
give 5d.
Yield: 933 mg (47%); yellow powder.
HRMS (MALDI; DCTB): m/z (%) = 824.62584 (100) [M]·+ (m/z
calcd for C62H80+: 824.62545), 726.52 (20), 627.40 (15), 515.28
(15).
UV/Vis (CH2Cl2, 10–6 M): λmax = 297, 306, 357, 377 nm.
Fluorescence (toluene, 10–5 M): λmax = 405, 418, 427, 441 (sh) nm.
Yield: 220 mg (60%); white powder.
1H NMR (500 MHz, CD2Cl2): δ = 8.37 [ddd, J = 8.1, 1.4, 0.6 Hz,
2 H, H-C(8,9)], 7.59 [ddd, J = 8.5, 1.3, 0.6 Hz, 2 H, H-C(8,9)], 7.42
[app t, 4 H, H-C(3′,3′′,5′,5′′)], 7.40 [m, 2 H, H-C(4′,4′′)], 7.35 [br. d,
4 H, H-C(2′,2′′,6′,6′′)], 7.33 [ddd, J = 8.1, 7.0, 1.2 Hz, 2 H, H-
C(7,10)], 6.98 [ddd, J = 8.5, 7.0, 1.4 Hz, 2 H, H-C(6,11)], 2.51 [app
t, J = 8.4 Hz, 4 H, Ar-CH2-C6H13], 1.41 (m, 4 H, Ar-CH2-CH2-
C5H11), 1.20 (sext, J = 7.2 Hz, 4 H, Ar-C5H10-CH2-CH3), 1.06–1.15
(m, 12 H, Ar-C2H4-C3H6-CH2CH3), 0.83 (t, 6 H, J = 7.2 Hz, Ar-
C6H12-CH3).
13C NMR (125.77 MHz, CD2Cl2): δ = 143.6, 139.2, 137.9, 131.8,
131.2, 130.9, 129.7, 128.5, 126.7, 125.7, 123.0, 32.0, 31.5, 31.1,
30.4, 28.9, 23.0, 14.2.
MS (MALDI; DCTB): m/z (%) = 576.38 (54) [M]·+, 392.16 (100)
[M – (C6H13, C7H15)].
2′,3′-Diheptyl-5′,6′-diphenyl-1,1′:4′,1′′-terphenyl (4d)
Commercial tetraphenylcyclopentadienone (1.02 g, 2.6 mmol) and
8-hexadecyne (880 mg, 3.9 mmol, 1.5 equiv) were dissolved in di-
phenyl ether (22 mL) and heated to 250 °C for 4 d. The reaction
mixture turned from dark red to pale yellow as an indication of the
evolving reaction.
The diphenyl ether was distilled off in high vacuum (turbomolecu-
lar pump) and the resulting mixture was separated by column chro-
matography (pentane–CH2Cl2, 8:2) to give 4d.
Yield: 2.56 g (81%); white powder.
1H NMR (500 MHz, CD2Cl2): δ = 7.14 [app t, J = 7.2 Hz, 4 H, Ter,
H-C(3,3′′, 5,5′′)], 7.05–7.10 [m, 6 H, Ter, H-C(2,2′′,4,4′′,6,6′′)],
6.77–6.82 [m, 8 H, Ph, H-C(2,3,5,6)], 6.73–6.77 [m, 2 H, Ter, H-
C(4,4′′)], 2.51 (app t, J = 8.4 Hz, 4 H, Ar-CH2-C6H13), 1.41 (m, 4 H,
Ar-CH2-CH2-C5H11), 1.20 (sext, J = 7.2 Hz, 4 H, Ar-C5H10-CH2-
CH3), 1.06–1.15 (m, 12 H, Ar-C2H4-C3H6-CH2CH3), 0.83 (t, J =
7.2 Hz, 6 H, Ar-C6H12-CH3).
13C NMR (125.77 MHz, CD2Cl2): δ = 141.67 [2 C, Ter, C(1,1′′)],
141.56 [2 C, Ph, C(1)], 141.38 [2 C, Ter C(1′,4′)], 139.06 [2 C, Ar,
C(5′,6′)], 138.93 [2 C, Ter, C(2′,3′)], 131.67 [4 C, Ph, C(2,6)],
131.05 [4 C, Ter, C(2,2′′,6,6′′)], 127.46 [4 C, Ter, C(3,3′′,5,5′′)],
126.65 [4 C, Ph, C(3,5)], 126.16 [2 C, Ter, C(4,4′′)], 125.21 [2 C,
Ph, C(4)], 32.00 [2 C, Alk, C(5)], 31.51 [2 C, Alk, C(2)], 31.07 [2
C, Alk, C(1)], 30.43 [2 C, Alk, C(3)], 28.95 [2 C, Alk, C(4)], 22.99
[2 C, Alk, C(6)], 14.23 [2 C, Alk, C(7)].
15,16-Diheptyltribenzo[fg,ij,rst]pentaphene (1d)
A solution of 5d (ca. 100 mg, 0.173 mmol) in anhydrous CH2Cl2 (45
mL) was degassed with argon during 30 min and FeCl3 (561 mg, 20
equiv, 5 equiv per H to be removed) dissolved in MeNO2 (3 mL)
was added dropwise during 30 min at r.t. After 10 min, the reaction
was quenched with MeOH (40 mL) and filtered through Millipore.
The liquid was evaporated and the brown solid was purified over a
silica gel plate (pentane–EtOAc, 9:1) to give 1d.
Yield: 1 mg (ca. 1%); dark-yellow solid.
1H NMR (500 MHz, CD2Cl2): δ = 9.04 [dd, J = 8.5, 0.9 Hz, 2 H, H-
C(7,8)], 8.89 [ddd, J = 7.9, 0.9, 0.6 Hz, 2 H, H-C(5,10)], 8.78 [ddd,
J = 8.2, 0.9, 0.5 Hz, 2 H, H-C(4,11)], 8.58 [ddd, J = 8.2, 0.9, 0.5 Hz,
2 H, H-C(1,14)], 8.06 (t, J = 7.9 Hz, 2 H), 7.72 [ddd, J = 8.1, 6.9,
1.3 Hz, 2 H, H-C(2,13)], 7.65 [ddd, J = 8.1, 6.9, 1.3 Hz, 2 H, H-
C(3,12)], 3.59 (m, 4 H), 1.52 (m, 4 H), 1.2–1.4 (m, 16 H), 0.88 (t,
J = 7.0 Hz, 6 H).
HRMS (MALDI; DCTB): m/z (%) = 578.39084 (100) [M]·+ (m/z
calcd for C44H50+: 578.39070).
HRMS (MALDI; DCTB): m/z (%) = 388.13120 (100) [M – (C6H13,
C7H15)], 400.13134 (53), 572.34841 (24) [M]·+ (m/z calcd for
C44H44+: 572.34375).
UV/Vis (CH2Cl2, 10–5 M): λmax = 314, 361, 380, 420 (sh), 448 (sh),
6,6′-Bis-15,16-diheptyltribenzo[fg,ij,rst]pentaphene (1e)
A solution of 4d (150 mg, 0.259 mmol) in anhydrous CH2Cl2 (45
mL) was degassed with argon for 30 min and FeCl3 (1.232 g, 7.6
mmol, 5 equiv per H to be removed) dissolved in MeNO2 (7 mL)
was added dropwise during 30 min at r.t. After 10 min, the reaction
486 nm.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1928–1934

1934
B. Alameddine et al.
PAPER
Chem. Soc. 2006, 128, 10700. (h) Pisula, W.; Menon, A.;
Fluorescence (toluene, 10–7 M): λmax = 425, 449, 489 (sh) nm.
Stepputat, M.; Lieberwirth, I.; Kolb, U.; Tracz, A.;
Sirringhaus, H.; Pakula, T.; Muellen, K. Adv. Mater.
(Weinheim, Ger.) 2005, 17, 684. (i) Dimitrakopoulos, C. D.;
Malenfant, P. R. L. Adv. Mater. (Weinheim, Ger.) 2002, 14,
99. (j) Schmidt-Mende, L.; Fechtenchötter, A.; Müllen, K.;
Moons, E.; Friend, R. H.; MacKenzie, J. D. Science 2001,
293, 1119. (k) Xiao, S.; Myers, M.; Miao, Q.; Sanaur, S.;
Pang, K.; Steigerwald, M.; Nuckolls, C. Angew. Chem. Int.
Ed. 2005, 44, 7390.
10,10′,11,11′-Tetraheptyl-9,9′,12,12′-tetraphenyl-2,2′-bitriphe-
nylene (1f)
Found as a minor impurity in compound 1h.
MS (MALDI; DCTB): m/z (%) = 1150.68 (6) [M]·+, 966.44 (10) [M
– (C6H13, C7H15)], 782.21 (25) [M – (C6H13, C7H15)2].
15,15′,16,16′-Tetraheptyl-5,5′-bitribenzo[fg,ij,rst]pentaphene
(1g)
1H NMR (500 MHz, CD2Cl2): δ = 9.40 (dd, J = 8.2, 1.2 Hz, 2 H),
8.98 (dd, J = 7.9, 0.6 Hz, 2 H), 8.89 (dd, J = 8.1, 0.6 Hz, 2 H), 8.87
(dd, J = 8.5, 0.4 Hz, 2 H), 8.79 (dd, J = 8.2, 1.4 Hz, 2 H), 8.61 (dd,
J = 8.2, 1.2 Hz, 2 H), 8.46 (dd, J = 8.0, 1.2 Hz, 2 H), 8.07 (t, J =
8.0 Hz, 2 H), 8.06 (d, J = 8.5 Hz, 2 H), 7.3 (ddd, J = 8.0, 7.0, 1.2 Hz,
2 H), 7.67 (ddd, J = 8.2, 7.0, 1.3 Hz, 2 H), 7.64 (ddd, J = 8.1, 7.0,
1.3 Hz, 2 H), 7.59 (ddd, J = 8.3, 7.0, 1.4 Hz, 2 H), 3.59 (m, 8 H),
1.52 (m, 8 H), 1.2–1.4 (m, 32 H), 0.88 (t, J = 7.0 Hz, 12 H).
(4) (a) Konishi, A.; Hirao, Y.; Nakano, M.; Shimizu, A.; Botek,
E.; Champagne, B.; Shiomi, D.; Sato, K.; Takui, T.;
Matsumoto, K.; Kurata, H.; Kubo, T. J. Am. Chem. Soc.
2010, 132, 11021. (b) Fogel, Y.; Zhi, L.; Rouhanipour, A.;
Andrienko, D.; Joachim-Raeder, H.; Muellen, K.
Macromolecules 2009, 42, 6878. (c) Feng, X.; Pisula, W.;
Ai, M.; Groeper, S.; Rabe, J. P.; Muellen, K. Chem. Mater.
2008, 20, 1191. (d) Feng, X.; Wu, J.; Ai, M.; Pisula, W.; Zhi,
L.; Rabe, J. P.; Muellen, K. Angew. Chem. Int. Ed. 2007, 46,
3033. (e) Okamoto, T.; Senatore, M. L.; Ling, M.-M.;
Mallik, A. B.; Tang, M. L.; Bao, Z. Adv. Mater. (Weinheim,
Ger.) 2007, 19, 3381. (f) Terasawa, N.; Monobe, H.;
Kiyohara, K.; Shimizu, Y. Chem. Lett. 2003, 32, 214.
(g) Lee, M.; Kim, J.-W.; Peleshanko, S.; Larson, K.; Yoo,
Y.-S.; Vaknin, D.; Markutsya, S.; Tsukruk, V. V. J. Am.
Chem. Soc. 2002, 124, 9121. (h) Yatabe, T.; Harbison, M.
A.; Brand, J. D.; Wagner, M.; Müllen, K.; Samori, P.; Rabe,
J. P. J. Mater. Chem. 2000, 10, 1519. (i) Henderson, P.;
Ringsdorf, H.; Shuhmacher, P. Liq. Cryst. 1995, 18, 191.
(5) (a) Feng, X.; Pisula, W.; Takase, M.; Dou, X.; Enkelmann,
V.; Wagner, M.; Ding, N.; Muellen, K. Chem. Mater. 2008,
20, 2872. (b) Chih-Wei, C.; Hong-Yi, C.; Shern-Long, L.; I-
Jui, H.; Jey-Jau, L.; Chun-hsien, C.; Tien-Yau, L.
HRMS (MALDI; DCTB): m/z (%) = 774.22969 (100) [M – (C6H13,
C7H15)2], 958.44657 (29) [M – (C6H13, C7H15)], 1142.67510 (55)
[M]·+ (m/z calcd for C88H86+: 1142.67240).
UV/Vis (CH2Cl2, 10–5 M): λmax = 314, 361, 380, 420 (sh), 448 (sh),
486 nm.
Fluorescence (toluene, 10–7 M): λmax = 425, 449, 489 (sh) nm.
3,3′,4,4′-Tetraheptyl-dibenzo[fg,lm]dibenzo[5,6:8,9]hepta-
cene[2,1,18,17,16,15,14-uvwxyza1b1c1d1a]heptacene (1h)
HRMS (MALDI; DCTB): m/z (%) = 770.2115 (100) [M – (C6H13,
C7H15)2], 856.3234 (28), 954.4157 (50) [M – (C6H13, C7H15)],
1138.6415 (92) [M]·+ (m/z calcd for C88H82+: 1138.64110).
UV/Vis (CH2Cl2, 10–5 M): λmax = 314, 361, 380, 420 (sh), 448 (sh),
486 nm.
Fluorescence (toluene, 10–7 M): λmax = 425, 449, 489 (sh) nm.
Macromolecules 2010, 43, 8741.
(6) (a) Fujiyama, T.; Toya, Y.; Nakatsuka, M. Jpn. Kokai
Tokkyo Koho JP 2008098357, 2008. (b) Nakatsuka, M.;
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