Synthesis and properties of mono-, bis-, tris-, and tetrakis[1,1,4,4- tetracyano-2-(1-azulenyl)-1,3-butadien-3-yl] chromophores connected to a benzene ring by phenylethynyl- and 2-thienylethynyl spacers

Article abstract of DOI:10.1246/bcsj.20120037

Mono-bis-tris-, and tetrakis[(1-azulenylethynyl)phenylethynyl- and (1-azulenylethynyl)-2-thienylethynyl]benzenes have been prepared by Pd-catalyzed alkynylation of iodobenzene derivatives or 2-iodothiophene derivatives sub-stituted by 1-azulenylethynyl group with polyethynylbenzenes under Sonogashira-Hagihara cross-coupling conditions. These compounds reacted with tetracyanoethylene (TCNE) in a formal [2 + 2] cycloaddition-cycloreversion reaction to afford the corresponding 1,1,4,4-tetracyano-2-(5-isopropyl-3- methoxycarbonyl-1-azulenyl)-1,3-butadien-3-yl chromo-phores in excellent yields. The redox behavior of the novel azulene-substituted tetracyanobutadiene (TCBD) derivatives was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep electrochemical reduction properties. Moreover, a significant color change was observed by visible spectroscopy under the electrochemical reduction conditions.

Full text of DOI:10.1246/bcsj.20120037

© 2012 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 85, No. 7, 761-773 (2012)
761
Selected Papers
Synthesis and Properties of Mono-, Bis-, Tris-, and
Tetrakis[1,1,4,4-tetracyano-2-(1-azulenyl)-1,3-butadien-3-yl]
Chromophores Connected to a Benzene Ring by
Phenylethynyl- and 2-Thienylethynyl Spacers
Taku Shoji,*1 Mitsuhisa Maruyama,1 Shunji Ito,2 and Noboru Morita3
1Department of Chemistry, Faculty of Science, Shinshu University, Matsumoto, Nagano 390-8621
2Graduate School of Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561
3Department of Chemistry, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578
Received January 28, 2012; E-mail: tshoji@shinshu-u.ac.jp
Mono-, bis-, tris-, and tetrakis[(1-azulenylethynyl)phenylethynyl- and (1-azulenylethynyl)-2-thienylethynyl]ben-
zenes have been prepared by Pd-catalyzed alkynylation of iodobenzene derivatives or 2-iodothiophene derivatives sub-
stituted by 1-azulenylethynyl group with polyethynylbenzenes under Sonogashira-Hagihara cross-coupling conditions.
These compounds reacted with tetracyanoethylene (TCNE) in a formal [2 + 2] cycloaddition-cycloreversion reaction
to afford the corresponding 1,1,4,4-tetracyano-2-(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-1,3-butadien-3-yl chromo-
phores in excellent yields. The redox behavior of the novel azulene-substituted tetracyanobutadiene (TCBD) derivatives
was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), which revealed their multistep
electrochemical reduction properties. Moreover, a significant color change was observed by visible spectroscopy under
the electrochemical reduction conditions.
Conjugated organic compounds play an important role in
the development of a new generation of optical and electronic
materials. Therefore, a variety of conjugated compounds have
been synthesized to date.1
Particularly, ³-electron compounds expanded by poly-
ethynylbenzene derivatives are used as core structures for den-
dritic materials,2 and are utilized as functional dyes,3 supra-
molecular architectures,4 and potential nonlinear optical mate-
rials.5 Previously, we have also reported the synthesis of
poly(6-azulenylethynyl)benzene derivatives to exhibit multiple
functionalities, such as electrochromism and discotic liquid
crystalline behavior.6
reaction of the corresponding acetylene derivatives with TCNE.
Particularly, azulene-substituted TCBDs represent significant
color change with higher reversibility among them under the
redox conditions. The expanded ³-electron system by poly-
ethynylbenzenes exhibits various functionalities described in
the literature.1-6 However, there are few reports of the synthesis
and properties of TCBD derivatives connected with poly-
ethynylbenzenes, except for derivatives reported by Diederich
et al.7 Thus, the spectroscopic and electrochemical properties
of the TCBD system binding with polyethynylbenzenes give
important insight into the development of donor-acceptor based
organic electronic and optoelectronic materials.
Poly(phenylethynyl)benzenes with donor-acceptor units also
have a potential as organic electronics. Diederich et al. have
reported that N,N-dialkylaniline-substituted (DAA-substituted)
polyethynylbenzenes react with tetracyanoethylene (TCNE)
by a formal [2 + 2] cycloaddition-cycloreversion reaction to
give the DAA-substituted tetracyanobutadiene (TCBD) chro-
mophores in excellent yields.7 They have also reported that the
new class of chromophores is characterized by intense intra-
molecular charge-transfer (ICT) interactions with absorption
maxima in the visible region, as well as promising third-order
optical nonlinearities.8 Recently, we have also reported the
synthesis and electrochromic properties of TCBD derivatives
with 1-azulenyl,9 2-oxo-2H-cyclohepta[b]-3-furyl,10 and ferro-
cenyl substituents11 connected by various ³-electron com-
pounds, which have been prepared by the [2 + 2] cycloaddition
We describe herein the synthesis of polyethynylben-
zene derivatives connected with (1-azulenylethynyl)phenyl-
ethynyl and (1-azulenylethynyl)-2-thienylethynyl groups by
Sonogashira-Hagihara cross-coupling reaction, as well as the
reactivity of the products toward the [2 + 2] cycloaddition
reaction with TCNE to afford the corresponding TCBD
chromophores. The electronic properties of the novel ³-
expanded TCBD derivatives were observed by electrochemical
analysis and absorption spectroscopy.
Results and Discussion
Synthesis. Taking the first strategy, the preparation of (1-
azulenylethynyl)iodoarene units was required to construct the
novel azulene-substituted TCBD derivatives. Thus, the syn-
thesis of methyl 3-[(4-iodophenyl)ethynyl]-7-isopropylazulene-
Published on the web June 21, 2012; doi:10.1246/bcsj.20120037

762
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
Synthesis and Properties of Tetracyanobutadiene-Azulene Chromophores
MeO2C
I
Ar
Ar
I
I
CO2Me
i-Pr
i-Pr
2a, b
[Pd(PPh3)4], CuI
THF, Et3N
+
i-Pr
MeO2C
1
Ar
S
CO2Me
a:
, b:
Ar =
3a, b
i-Pr
Scheme 1.
2a, b
MeO2C
[Pd(PPh3)4], CuI
THF, Et3N
2a, b
[Pd(PPh3)4], CuI
THF, Et3N
Ar
4a, b
i-Pr
i-Pr
MeO2C
Scheme 2.
Ar
Ar
CO2Me
1-carboxylate (2a) and methyl 3-[(5-iodo-2-thienyl)ethynyl]-
7-isopropylazulene-1-carboxylate (2b) were examined via
the cross-coupling reaction of methyl 3-ethynyl-7-isopropyl-
azulene-1-carboxylate (1) with excess 1,4-diiodobenzene and
2,5-diiodothiophene under Sonogashira-Hagihara conditions.12
The Sonogashira-Hagihara cross-coupling reaction of 1-ethyn-
ylazulene 1, which was prepared by a procedure reported
by us,9a with 1,4-diiodobenzene and 2,5-diiodothiophene at
room temperature afforded methyl 3-[(4-iodophenyl)ethynyl]-
7-isopropylazulene-1-carboxylate (2a) and methyl 3-[(5-iodo-
2-thienyl)ethynyl]-7-isopropylazulene-1-carboxylate (2b) both
in 74% yield, along with 3a and 3b (3a: 12%, 3b: 10%)
(Scheme 1).9a
5a, b
i-Pr
Scheme 3.
2a, b
[Pd(PPh3)4], CuI
THF, Et3N
CO2Me
i-Pr
Preparation of polyethynylbenzene derivatives connected
with (1-azulenylethynyl)phenylethynyl and (1-azulenylethyn-
yl)-2-thienylethynyl groups 4a-7a and 4b-7b for the precur-
sors of the novel TCBD derivatives was accomplished by
a simple one-pot reaction involving repeated Pd-catalyzed
alkynylation of the corresponding ethynylbenzenes with 2a
and 2b under Sonogashira-Hagihara conditions. The cross-
coupling reaction of 2a with ethynylbenzene using [Pd(PPh3)4]
as a catalyst and subsequent chromatographic purification of
the reaction mixture on silica gel afforded the desired 4a in
97% yield. Likewise, the reaction of 2b with ethynylbenzene
afforded the desired 4b in 95% yield (Scheme 2). The cross-
coupling reaction of 1,4-diethynylbenzene with 2a and 2b in
the presence of the Pd catalyst afforded bis-adducts 5a (89%)
and 5b (85%), respectively (Scheme 3).
Ar
Ar
Ar
6a, b
i-Pr
MeO2C
CO2Me
i-Pr
Scheme 4.
Tris-adducts 6a and 6b were also obtained by similar Pd-
catalyzed reaction of 1,3,5-triethynylbenzene13 with 2a and 2b
in 85% and 80% yields, respectively (Scheme 4). Tetrakis-
adducts 7a and 7b were prepared by similar Pd-catalyzed reac-
tion of 2a and 2b with 1,2,4,5-tetraethynylbenzene14 in 77% and
74% yields, respectively (Scheme 5). These new compounds
4a-7a and 4b-7b possess fair solubility in chloroform, di-
chloromethane, and so on. Moreover, they are stable and show
no decomposition even after several weeks at room temperature.
The formal [2 + 2] cycloaddition-cycloreversion reaction of
the mono-, bis-, tris-, and tetrakis-adducts 4a-7a and 4b-7b
with TCNE was examined according to a procedure described
in the literature.7-10 The reaction of 4a with TCNE in refluxing
ethyl acetate yielded 8a in 97% yield. Likewise, the reaction
of 4b with TCNE afforded 8b in 96% yield (Scheme 6). The
[2 + 2] cycloaddition reaction of 8a and 8b in phenylethynyl

T. Shoji et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
763
2a, b
i-Pr
CN
CN
NC
NC
MeO2C
[Pd(PPh3)4], CuI
THF, Et3N
Ar
Ar
CO2Me
CN
CN
NC
NC
9a, b
i-Pr
CO2Me
MeO2C
i-Pr
CO2Me
i-Pr
i-Pr
Ar
Ar
Ar
Ar
CN
CN
NC
CN
Ar
i-Pr
i-Pr
CO2Me
MeO2C
7a, b
NC
CN
NC
CN
Ar
Scheme 5.
Ar
i-Pr
i-Pr
CN
NC
NC
CN
NC
CN
CO2Me
CO2Me
NC
MeO2C
MeO2C
10a, b
TCNE
AcOEt
MeO2C
4a, b
Ar =
Ar
NC
CN
CN
CN
i-Pr
i-Pr
i-Pr
Ar
NC
Ar
8a, b
i-Pr
NC
NC
CN
CN
NC
NC
CN
S
a:
, b:
CN
Ar
Ar
i-Pr
CN
NC
CN
NC
CN
NC
MeO2C
11a, b
CO2Me
MeO2C
Ar
Figure 1. Bis-, tris-, and tetrakis{4-[3,3-dicyano-1-(di-
cyanomethylene)-2-(5-isopropyl-3-methoxycarbonyl-1-
azulenyl)-1-propenyl]arylethynyl}benzenes 9a-11a and
9b-11b.
CN
NC
i-Pr
Scheme 6.
Table 1. Synthesis of Mono-, Bis-, Tris-, and Tetrakis{4-
[3,3-dicyano-1-(dicyanomethylene)-2-(5-isopropyl-3-
methoxycarbonyl-1-azulenyl)-1-propenyl]arylethynyl}ben-
zenes 8a-11a and 8b-11b
moiety did not proceed in DMF under the refluxing conditions,
even though excess TCNE was used. These results indicate the
low reactivity of the C¸C triple bond detached from 1-azulenyl
moiety, owing to the electron-withdrawing nature of TCBD at
the para-position.15
Substrate
Reaction time/h
Product
Yield/%
4a
4b
5a
5b
6a
6b
7a
7b
3
3
5
5
5
5
12
12
8a
8b
9a
9b
10a
10b
11a
11b
97
96
94
95
91
93
92
94
The TCBD chromophores with multiple TCBD units 9a-11a
and 9b-11b were also prepared in the same way starting from
the corresponding acetylenes 5a-7a and 5b-7b (Figure 1). The
yield of the products 9a-11a and 9b-11b are summarized in
Table 1. The double-addition of TCNE with 5a gave 9a in
94% yield by stirring with equimolar amounts of the starting
materials in refluxing ethyl acetate within 3 h. The TCBD
chromophore with 2-thienylethynyl linker 9b was also prepared
by the one-pot formal [2 + 2] cycloaddition-cycloreversion
reaction of 5b with TCNE in 95% yield. The TCBD chromo-
phores with three TCBD units 10a and 10b were obtained
in 91% and 93% yields, respectively, by the [2 + 2] cyclo-
addition-cycloreversion sequence between TCNE and the
acetylene precursors 6a and 6b, respectively. Although long
reaction periods were required, compounds 11a and 11b were
obtained in almost quantitative yields (11a: 92%, 11b: 94%) by
the cycloaddition reaction of TCNE with the corresponding
alkynes 7a and 7b, respectively, followed by the cyclorever-
sion reaction. These novel ³-expanded TCBD derivatives
8a-11a and 8b-11b are obtained as stable reddish crystals and
can be storable in crystalline state under ambient conditions.
Spectroscopic Properties. The new compounds were fully
characterized by spectral data, as shown in the Experimental
Section. Mass spectra of 2a-11a and 2b-11b ionized by ESI

764
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
Synthesis and Properties of Tetracyanobutadiene-Azulene Chromophores
Figure 3. UV-vis spectra of 8a (black line), 9a (gray line),
10a (black broken line), and 11a (gray broken line) in
dichloromethane.
Figure 2. UV-vis spectra of 4b (black line), 5b (gray line),
6b (black broken line), and 7b (gray broken line) in
dichloromethane.
showed the correct molecular ion peaks. The characteristic
stretching vibration band of the acetylene moiety of 2a-7a
¹1
and 2b-7b was observed at ¯ = 2182-2204 cm in their IR
spectra. The TCBD derivatives 8a-11a and 8b-11b exhibited a
¹1
characteristic C¸N stretching band at ¯ = 2191-2225 cm in
their IR spectra. These results are consistent with the structures
of these products.
Polyethynylbenzene derivatives have a tendency to form
self-aggregates attributable to ³-³ stacking interaction, which
causes significant line broadening and shielding effects in
1
their H NMR signals.16 We have also reported a solution of
hexakis(6-azulenylethynyl)benzene derivative exhibits high-
1
field shift of the chemical shifts in the H NMR spectrum with
increasing concentration, due to self-aggregation caused by
their ³-³ stacking interaction. Furthermore, Diederich et al.
have reported the intermolecular CN£C(CN)2 multipolar
interaction of TCBDs, recently.17 Thus, concentration depend-
Figure 4. UV-vis spectra of 8b (black line), 9b (gray line),
10b (black broken line), and 11b (gray broken line) in
dichloromethane.
1
ence of the H NMR chemical shifts for highly conjugated 7a
and 11a was investigated as a model case. The 1H NMR spectra
of 7a and 11a for each concentration are shown in the
Supporting Information. Despite being described in the liter-
ature, compound 7a did not show concentration dependence
maximum of 6b rather resembled that of 4b, although the
extinction coefficient of 6b was apparently larger than that of
4b. These results indicate the efficient expansion of the ³-
electron system through the phenylethynyl moiety in 1,4- and
1,2,4,5-arrangement of 5b and 7b, rather than that in 1,3,5-
arrangement of 6b.
The UV-visible spectra of TCBD derivatives 8a-11a and
8b-11b in dichloromethane are shown in Figures 3 and 4,
respectively. As expected from their resonance structures as
illustrated in Scheme 6, TCBD derivatives 8a-11a and 8b-11b
showed characteristic ICT absorption in the visible region.
Their absorption maxima and coefficients (log ¾) are summa-
rized in Table 2.
The absorption maxima of 9a-11a were nearly equal to that
of the simpler TCBD derivative 8a, although the extinction
coefficients show an increasing trend as the number of TCBD
units substituted (Figure 3). These effects suggest that the ³-
conjugation is less effective by the extension attributable to the
phenylethynyl spacer connected. The longest absorption maxi-
ma of 8b-11b were dependent on the arrangement of the TCBD
units on the central benzene ring with the difference from those
1
in its H NMR spectra, even though the concentration of 7a
was increased up to 1.0 © 10¹3 M. It means the ³-³ stacking
interaction of 7a is weak, and the high solubility of 7a might
be ascribed to less effective self-aggregation of the molecules.
Similar to 7a, concentration dependence of the 1H NMR
chemical shifts for 11a was not observed, when the concen-
tration was gradually changed from 1.0 © 10¹4 M up to 1.0 ©
10¹3 M. Thus, these results suggest less effective intermolecular
multipolar interaction between the cyano groups of 11a.
The UV-visible spectra of acetylene derivatives 4a-7a and
4b-7b showed characteristic weak absorptions arising from the
azulene system in the visible region. Although the extinction
coefficients increased with the number of azulene rings sub-
stituted, absorption maxima of these compounds were quite
different from each other. As shown in Figure 2, the absorp-
tion maxima of 5b (-max = 423 nm) and 7b (-max = 431 nm)
exhibited bathochromic shifts by 27 and 35 nm, respectively,
compared with that of 6b (-max = 396 nm). The absorption

T. Shoji et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
CN CN
765
Table 2. Absorption Maxima [nm] and Their Coefficients
(log ¾) of 8a-11a and 8b-11b in Dichloromethane and
in Hexane
NC
NC
S
MeO2C
MeO2C
Sample -max (log ¾) in CH2Cl2
-
(log ¾) in hexanea)
max
CN
CN
12b
NC
NC
8a
8b
9a
400 (4.42), 538 sh (3.87)
442 (4.62)
410 (4.61), 540 sh (4.02)
435 sh (4.85), 481 (4.90)
400 (4.76), 540 sh (4.19)
®
429 (4.62)
®
i-Pr
i-Pr
12a
Figure 6. 1,1,4,4-Tetracyano-2-aryl-3-(5-isopropyl-3-meth-
oxycarbonyl-1-azulenyl)-1,3-butadienes 12a and 12b.
9b
10a
432 sh (4.85), 462 (4.91)
®
Table 3. Reduction Potentials of Mono-, Bis-, Tris-, and
Tetrakis{4-[3,3-dicyano-1-(dicyanomethylene)-2-(5-iso-
propyl-3-methoxycarbonyl-1-azulenyl)-1-propenyl]aryl-
ethynyl}benzenes 8a-11a and 8b-11ba) and TCBD Deriva-
tives 12a and 12bb) for References
10b 442 (5.13)
435 (5.13)
11a
11b
466 sh (4.61), 546 sh (4.27) ®
451 (5.22), 508 sh (5.04)
445 (5.22), 506 sh (4.98)
a) Dichloromethane (8b: 10%, 9b: 20%, 10b: 30%, 11b: 30%)
was contained in hexane to maintain solubility of the
compounds.
Sample
Method
E1red/V
¹0.56
E2red/V
¹0.97
E3red/V
8a
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(DPV)
CV
(¹0.54)
¹0.58
(¹0.56)
¹0.56 (2e )
(¹0.54)
¹0.56 (2e )
(¹0.54)
¹0.56 (3e )
(¹0.54)
¹0.57 (3e )
(¹0.55)
¹0.56 (4e )
(¹0.54)
¹0.57 (4e )
(¹0.55)
¹0.61
¹0.64
(¹0.95)
¹0.90
(¹0.88)
¹0.97 (2e )
(¹0.95)
¹0.89 (2e )
(¹0.87)
¹0.97 (3e )
(¹0.95)
¹0.89 (3e )
(¹0.87)
¹0.97 (4e )
(¹0.95)
¹0.88 (4e )
(¹0.86)
¹1.03
¹1.03
(¹1.91)
(¹1.85)
(¹1.92)
(¹1.86)
(¹1.93)
(¹1.84)
(¹1.93)
(¹1.84)
8b
¹
¹
9a
¹
¹
9b
¹
¹
10a
10b
11a
11b
¹
¹
¹
¹
¹
¹
12a
12b
Figure 5. Cyclic voltammogram of the reduction of 9b
(1 mM) in benzonitrile containing Et4NClO4 (0.1 M) as the
CV
¹1
supporting electrolyte; scan rate = 100 mV s
.
a) Redox potentials were measured by CV and DPV [V vs.
Ag/AgNO3, 1 mM in benzonitrile containing Et4NClO4 (0.1
M), Pt electrode (internal diameter: 1.6 mm), scan rate = 100
mV s¹1, and Fc/Fc+ = +0.15 V]. The peak potentials mea-
sured by DPV are shown in parentheses. b) Redox potentials
were measured by CV [V vs. Ag/AgNO3, 1 mM in benzo-
nitrile containing Et4NClO4 (0.1 M), Pt electrode (internal
of 8a-11a (Figure 4). The absorption maximum of 10b (-max
=
442 nm) resembled that of 8b (-max = 442 nm), although the
extinction coefficient was almost three times larger than that
of 8b. This indicates that the conjugation in 10b did not
effectively expand by the 1,3,5-arrangement on the centered
benzene ring, whereas the longest absorption maximum of
9b (-max = 481 nm) and 11b (-max = 451 nm) exhibited bath-
ochromic shifts compared with that of 10b. This suggests that
the 1,4- and 1,2,4,5-arrangement of TCBDs on the benzene
ring efficiently extended the conjugation in 9b and 11b, rather
than that in the 1,3,5-arrangement of 10b. As a result, the 2-
thienylethynyl spacer between TCBD and the central benzene
ring effectively extended the ³-electron system, rather than
phenylethynyl spacer.
Most of the thiophene-substituted TCBD derivatives 8b-10b
showed solvatochromism, when the solvent was changed from
CH2Cl2 to CH2Cl2/hexane. A noticeable spectral feature of
9b is the presence of a distinct absorption band at 481 nm in
CH2Cl2, which exhibits blue-shifts by 19 nm (-max = 462 nm)
in less polar 20% CH2Cl2/hexane, suggesting the ICT nature of
this band (see the Supporting Information). It is assumed that
the first excited-state has a larger dipole moment than that in the
ground state due to the ICT character from the azulene ring to
the TCBD unit substituted.
diameter: 1.6 mm), scan rate = 100 mV s¹1, and Fc/Fc+
+0.15 V].
=
Electrochemistry. To clarify the electrochemical proper-
ties, the redox behavior of 8a-11a and 8b-11b was examined
by CV and DPV. Measurements were carried out with a
standard three-electrode configuration. Tetraethylammonium
perchlorate (0.1 M) in benzonitrile was used as a supporting
electrolyte with platinum wire and disk as auxiliary and work-
ing electrodes, respectively. All measurements were carried
out under an argon atmosphere, and potentials were related to
an Ag/AgNO3 reference electrode and Fc/Fc+ as an internal
reference, which discharges at +0.15 V. A cyclic voltammo-
gram for the reduction of 9b is shown in Figure 5. The redox
potentials (in volts vs. Ag/AgNO3) of TCNE-adducts 8a-11a
and 8b-11b and TCBD derivatives 12a and 12b (Figure 6) are
summarized in Table 3.
Electrochemical reduction of TCBD derivatives 8a-11a and
8b-11b displayed a reversible two-stage wave containing

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Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
Synthesis and Properties of Tetracyanobutadiene-Azulene Chromophores
multielectron transfer on CV. As shown in Table 3, the differ-
ence of the first reduction potentials between 8a-11a and
8b-11b was not observed, but the second reduction potentials
of 8a-11a series exhibited a slight negative shift compared
with those of 8b-11b. Recently, we have reported the redox
potentials of a series of azulene-substituted TCBD derivatives,
such as 12a and 12b (Figure 6). The study revealed the first
reduction potentials of azulene-substituted TCBD derivatives
substituted by benzene and thiophene cores are decreased by
increasing the number of substituted TCBD units. On the
whole, the reduction potentials of 8a-11a and 8b-11b resem-
bled to those of 12a and 12b, although the number of TCBD
units in the molecule was increased. Therefore, the redox
interaction among the azulene-substituted TCBD units are
almost negligible in electrochemical reduction of 9a-11a and
9b-11b. To investigate the durability of the compound toward
electrochemical reduction, repeated reduction of compound
9b by CV was also examined. The sequential electrochemical
reduction of 9b did not change the shape of the reduction wave
after one hundred redox cycles (see the Supporting Infor-
mation). These results indicate that the compound 9b possesses
high durability toward sequential electrochemical reduction.
We have reported the synthesis of various azulene-substi-
tuted redox-active chromophores with the aim of creating
stabilized electrochromic materials.6,18 In these studies, the
TCBD units connected with ³-electron systems exhibit sta-
bilized electrochromism with strong absorptions in visible and
near-infrared regions in their two-electron-reduced state. The
polyethynylbenzenes expanded by the TCBD units 8a-11a and
8b-11b might exemplify a new class of electrochromic system
by their reversible multielectron transfer as observed by CV.
Thus, to examine the color changes during the electrochemical
reactions, spectral changes of TCBD derivatives 8a-11a and
8b-11b were monitored by visible spectroscopy. Constant-
current reduction was applied to the solutions of 8a-11a and
8b-11b, with a platinum mesh as a working electrode and a
wire counter-electrode, and visible spectra were measured in
benzonitrile containing Et4NClO4 (0.1 M) as a supporting elec-
trolyte at room temperature under the electrochemical reduction
conditions (see the Supporting Information).
The longest absorptions of the TCBD derivatives with
ethynylbenzene spacer 8a-11a gradually decreased, and the
color of the solution changed from red to yellow during the
electrochemical reduction. However, the reversible oxidation
of the yellow solution did not regenerate the spectrum of the
corresponding starting compounds. The irreversibility of the
color changes might be attributed to the instability of the
reduced species of 8a-11a under the conditions for the spectral
measurements in contrast with the observation obtained by
CV analysis.
Although the TCBD derivatives linked by phenylethynyl
spacer 8a-11a did not show good reversibility of the color
changes, reversible color changes were observed in the TCBD
derivatives connected by 2-thienylethynyl spacer 8b-11b.
When the spectral changes of 8b were monitored during the
electrochemical reduction, the absorption in the visible region
gradually decreased with the development of new absorptions at
550 and 710 nm, which reached the near-infrared region. The
color change should be attributable to the formation of radical
anionic species formed by the single electron reduction of
8b. Reverse oxidation of the reduced species decreased the
new absorptions and regenerated the original color of 8b. A
reversible color change was also observed in the visible spectral
change of 9b under the electrochemical reduction conditions.
Presumed redox behavior is illustrated in Scheme 7. At the
beginning, new absorptions in the visible region, which reached
the near-infrared region, gradually developed and the red color
of the solution changed to blue during the electrochemical
reduction (Figure 7, top). As suggested by the results of cyclic
voltammetry, the color change of 9b should be ascribed by the
i-Pr
CN
CN
NC
S
NC
S
MeO2C
9b
CO2Me
CN
CN
NC
NC
-2e- +2e-
i-Pr
9b2
-2e- +2e-
i-Pr
CN
NC
CN
NC
S
S
MeO2C
·
·
·
·
CO2Me
CN
CN
NC
NC
i-Pr
Scheme 7. Presumed redox behavior of 9b under the reduction conditions.

T. Shoji et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
767
R1
R1
R2
R2
R2
R2
S
13: R1=Me, R2=t-Bu
14: R1=t-Bu, R2=t-Bu
15: R1=SMe, R2=H
16: R1=SMe, R2=t-Bu
R1
R1
Figure 8. Thienoquinoid compounds 13-16 with four
1-azulenyl substituents.
products generated by the electrochemical reduction. Mean-
while, the reversible color change and development of the new
absorption bands up to the near-infrared region, along with
the isosbestic point in visible region, of the TCBD derivatives
connected by 2-thienylethynyl spacer 8b-11b indicate the
formation of a stabilized closed-shell dianionic species with
a thienoquinoid structure in the two-electron reduction, as
suggested by the reversible CV waves under the electro-
chemical reduction conditions.20
A violene-cyanine hybrid was proposed by Hünig et al. for
the design of a stabilized organic electrochromic systems.21 We
have also reported a more general structural principle through
the combination of violene- and cyanine-type substructures
with a large variability.6,18 We have identified some novel
hybrid structures of violenes and cyanines during the study
on the synthesis and redox behaviors of azulene-substituted
TCBD9a and DCNQ derivatives9b and 2H-cyclohepta[b]furan-
2-one-substituted TCBD10a and DCNQ10b derivatives in addi-
tion to Hünig’s violene-cyanine hybrid structure. The TCBD
derivatives connected by 2-thienylethynyl spacer 8b-11b,
which exhibit reversible color changes during the electro-
chemical reaction, should be successful examples of an exten-
sion of our novel hybrid structures of violenes and cyanines
from the viewpoint of the generation of a closed-shell structure
by the two-electron transfer.
Figure 7. Continuous change in the UV-vis spectrum of
9b: constant-current electrochemical reduction (100 ¯A,
top) and reverse oxidation of the reduced species (100 ¯A,
bottom) in benzonitrile containing Et4NClO4 (0.1 M) at
20 s intervals.
two electron reduction of the two TCBD units to form dianionic
species, which could be described as closed-shell form as illus-
trated in Scheme 7. On reverse oxidation of the blue solu-
tion, the new absorption in the near-infrared region decreased
and the original absorption of 9b was regenerated in the visible
region (Figure 7, bottom).
The longest wavelength absorption band of 10b and 11b
in the visible region gradually increased, thus, the red solution
changed to purple and blue, respectively, during the electro-
chemical reduction. Reverse oxidation of the purple and blue
solutions regenerated the spectrum of 10b and 11b, respec-
tively, with good reversibility.
Previously, we reported the synthesis of thienoquinoid
compounds 13-16 with four 1-azulenyl substituents, which
showed broad absorption beyond to the infrared region in UV-
vis spectra, by the Zn-mediated reduction of the correspond-
ing dications (Figure 8).18g,19 Compounds 13-16 are relatively
stable and can be treated under aerobic conditions. However,
the reduction of 1,4-phenylenebis[di(1-azulenyl)methylium]
derivatives did not afford satisfactory results by similar reac-
tion, due to the fair instability of para-quinoid products. Thus,
the reason of the low reversibility for the color change of
8a-11a might be attributable to the instability of para-quinoid
Conclusion
Several polyethynylbenzene derivatives connected with
(1-azulenylethynyl)phenylethynyl and (1-azulenylethynyl)-2-
thienylethynyl groups 4a-7a and 4b-7b were prepared by
Sonogashira-Hagihara cross-coupling reaction. A series of
TCBD chromophores substituted by 1-azulenyl groups 8a-11a
and 8b-11b were synthesized in a one-step procedure consist-
ing of the formal [2 + 2] cycloaddition reaction of 4a-7a and
4b-7b with TCNE, followed by the ring-opening reaction
of the initially formed cyclobutene derivatives. Strong intra-
molecular CT absorption bands were observed in the UV-vis
spectra of these azulene-substituted TCBDs 8a-11a and 8b-
11b. An analysis by CV and DPV showed that compounds
8a-11a and 8b-11b exhibit a reversible two-stage reduction.
Moreover, a significant color change was observed during the
electrochemical reduction. In particular, thiophene derivatives
8b-11b exhibited a significant color change, arising from the
generation of thienoquinoid substructures during electrochem-
ical reduction. These results showed that the TCBD derivatives
with 2-thienylethynyl spacer 8b-11b behave as hybrids of

768
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
Synthesis and Properties of Tetracyanobutadiene-Azulene Chromophores
violene and cyanine in the view of the formation of the
stabilized cyanine substructures with thienoquinoid spacers
formed by the two-electron reduction.
To evaluate the scope of this class of molecules investigated
by this research, the preparation of novel TCBD chromophores
connected with various ³-electron cores is now in progress in
our laboratory.
Methyl 3-[(5-Iodo-2-thienyl)ethynyl]-7-isopropylazulene-
1-carboxylate (2b). The procedure used for the preparation
of 2a was adopted here. The reaction of 1 (2.52 g, 10.0 mmol)
with 2,5-diiodothiophene (6.72 g, 20.0 mmol) in triethylamine
(50 mL) and THF (50 mL) in the presence of CuI (190 mg,
1.00 mmol) and tetrakis(triphenylphosphine)palladium(0) (580
mg, 0.50 mmol) at room temperature for 1 h followed by col-
umn chromatography on silica gel with CH2Cl2 afforded 2b
(3.41 g, 74%) as purple crystals and 3b (584 mg, 10%) as green
Experimental
General.
Melting points were determined with a
crystals.9a
2b: Mp: 82.0-85.0 °C. HRMS (ESI): calcd for C21H17-
Yanagimoto MPS3 micro melting apparatus. Mass spectra
were obtained with a Bruker APEX II instrument. IR and
UV-vis spectra were measured with JASCO FT/IR-4100 and
Shimadzu UV-2550 spectrophotometers. 1H and 13C NMR
spectra were recorded with a JEOL GSX 400 (400 and 100
MHz, respectively) or a Bruker AVANCE400 (400 and 100
MHz, respectively). The voltammetry measurements were
carried out in benzonitrile containing Et4NClO4 (0.1 M) as a
supporting electrolyte by utilizing Pt working and auxiliary
electrodes and a reference electrode formed from Ag/AgNO3
(0.01 M) in acetonitrile containing n-Bu4NClO4 (0.1 M) at a
scan rate of 100 mV s¹1. The internal reference Fc/Fc+ dis-
charges at +0.15 V under these conditions. Elemental analyses
were performed at the Research and Analytical Center for Giant
Molecules, Graduate School of Science, Tohoku University.
Methyl 3-[(4-Iodophenyl)ethynyl]-7-isopropylazulene-1-
carboxylate (2a). To a degassed solution of 1 (2.52 g, 10.0
mmol), 1,4-diiodobenzene (6.60 g, 20.0 mmol), and CuI (190
mg, 1.00 mmol) in triethylamine (50 mL) and THF (50 mL) was
added tetrakis(triphenylphosphine)palladium(0) (580 mg, 0.50
mmol). The resulting mixture was stirred at room temperature
for 1 h under an Ar atmosphere. The reaction mixture was
poured into a 10% NH4Cl solution and extracted with hexane.
The organic layer was washed with brine, dried over MgSO4,
and concentrated under reduced pressure. The residue was
purified by column chromatography on silica gel with CH2Cl2
to give 2a (3.27 g, 74%) as purple crystals and 3a (694 mg,
12%) as green crystals.9a
IO2S + Na+ [M + Na]+ 482.9892; found 482.9886. IR (KBr
disk): ¯max 2950 (w), 2198 (w), 1687 (s, C=O), 1499 (w), 1449
(s), 1414 (s), 1373 (w), 1310 (w), 1224 (m), 1213 (s), 1191 (w),
1167 (m), 1126 (w), 1056 (w), 1026 (w), 958 (w), 943 (w), 935
(w), 915 (w), 869 (w), 805 (m), 796 (s), 776 (m), 760 (w), 733
(w), 660 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 243 (4.47),
283 (4.52), 315 (4.57), 362 sh (4.29), 402 (4.20), 426 sh (4.02),
1
572 (2.86), 627 sh (2.70) nm. H NMR (400 MHz, CDCl3): ¤
9.73 (d, J = 1.6 Hz, 1H, H8), 8.57 (d, J = 10.0 Hz, 1H, H4),
8.43 (s, 1H, H2), 7.82 (dd, J = 10.0, 1.6 Hz, 1H, H6), 7.52 (dd,
J = 10.0, 10.0 Hz, 1H, H5), 7.17 (d, J = 3.6 Hz, 1H, H3¤ of Th),
6.96 (d, J = 3.6 Hz, 1H, H4¤ of Th), 3.95 (s, 3H, CO2Me),
3.23 (sept, J = 6.8 Hz, 1H, i-Pr), 1.42 (d, J = 6.8 Hz, 6H,
i-Pr). 13C NMR (100 MHz, CDCl3): ¤ 165.34, 150.92, 144.78,
142.71, 141.38, 139.51, 138.45, 137.09, 136.23, 132.47,
130.16, 127.74, 115.22, 108.09, 90.56, 85.33, 73.87, 51.19,
39.23, 24.58. Elemental analysis calcd (%) for C21H17IO2S:
C, 54.79; H, 3.72%. Found: C, 54.77; H, 3.89%.
Methyl 7-Isopropyl-3-[4-(phenylethynyl)phenylethynyl]-
azulene-1-carboxylate (4a).
The procedure used for the
preparation of 2a was adopted here. The reaction of 2a (454
mg, 1.00 mmol) with ethynylbenzene (153 mg, 1.50 mmol) in
triethylamine (5 mL) and THF (5 mL) in the presence of CuI
(19 mg, 0.10 mmol) and tetrakis(triphenylphosphine)palla-
dium(0) (58 mg, 0.050 mmol) at room temperature for 6 h
followed by column chromatography on silica gel with CH2Cl2
afforded 4a (416 mg, 97%) as green crystals. Mp: 107.0-
111.0 °C. HRMS (ESI): calcd for C31H24O2 + Na+ [M + Na]+
451.1674; found 451.1669. IR (KBr disk): ¯max 2957 (w), 2193
(w), 1689 (s, C=O), 1593 (w), 1500 (m), 1444 (s), 1425 (m),
1406 (m), 1373 (m), 1307 (w), 1242 (m), 1211 (s), 1197 (m),
1167 (m), 1132 (m), 1118 (m), 1072 (m), 1047 (m), 960 (w),
920 (w), 871 (w), 802 (w), 775 (w), 754 (w), 721 (w), 688 (w),
648 (w), 542 (w), 524 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾)
238 (4.84), 316 (5.02), 340 (4.93), 356 sh (4.90), 400 (4.70),
422 sh (4.59), 568 (3.21), 616 sh (3.10) nm. 1H NMR (400
MHz, CDCl3): ¤ 9.74 (d, J = 1.6 Hz, 1H, H8), 8.67 (d,
J = 9.2 Hz, 1H, H4), 8.48 (s, 1H, H2), 7.82 (dd, J = 10.0,
1.6 Hz, 1H, H6), 7.59-7.51 (m, 7H, H5, Ph), 7.37-7.35 (m, 3H,
Ph), 3.96 (s, 3H, CO2Me), 3.24 (sept, J = 6.8 Hz, 1H, i-Pr),
1.43 (d, J = 6.8 Hz, 6H, i-Pr). 13C NMR (100 MHz, CDCl3):
¤ 165.44, 150.75, 144.86, 142.78, 141.35, 139.42, 138.39,
136.23, 131.60, 131.57, 131.20, 128.41, 128.38, 127.59,
123.75, 123.07, 122.51, 115.15, 108.80, 93.51, 91.11, 89.25,
86.86, 51.19, 39.24, 24.60. Elemental analysis calcd (%) for
C31H24O2: C, 86.89; H, 5.65%. Found: C, 86.64; H, 5.77%.
Methyl 7-Isopropyl-3-[5-(phenylethynyl)-2-thienylethy-
2a: Mp: 105.0-108.0 °C. HRMS (ESI): calcd for C23H19-
IO2 + Na+ [M + Na]+ 477.0327; found 477.0322. IR (KBr
disk): ¯max 3080 (w), 2966 (w), 2953 (m), 2204 (w), 1686 (s,
C=O), 1485 (m), 1448 (s), 1427 (m), 1410 (m), 1390 (m), 1367
(m), 1304 (m), 1244 (s), 1209 (s), 1169 (s), 1136 (m), 1118 (m),
1061 (m), 1047 (w), 1030 (w), 1005 (w), 972 (w), 941 (w),
920 (w), 885 (w), 875 (m), 819 (m), 779 (m), 756 (w), 729 (w),
700 (w), 673 (w), 646 (w), 634 (w), 586 (w), 526 (w), 474
(w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 249 (4.45), 275
(4.44), 315 (4.66), 330 sh (4.48), 346 (4.50), 398 (4.18), 415 sh
1
(4.11), 568 (2.84), 614 (2.74), 682 (2.18) nm. H NMR (400
MHz, CDCl3): ¤ 9.74 (d, J = 1.2 Hz, 1H, H8), 8.63 (d, J = 10.0
Hz, 1H, H4), 8.46 (s, 1H, H2), 7.81 (dd, J = 10.0, 1.2 Hz, 1H,
H6), 7.70 (d, J = 8.0 Hz, 2H, H3¤,5¤ of Ph), 7.51 (dd, J = 10.0,
10.0 Hz, 1H, H5), 7.31 (d, J = 8.0 Hz, 2H, H2¤,6¤ of Ph), 3.96
(s, 3H, CO2Me), 3.24 (sept, J = 6.8 Hz, 1H, i-Pr), 1.43 (d,
J = 6.8 Hz, 6H, i-Pr). 13C NMR (100 MHz, CDCl3): ¤ 165.39,
150.75, 144.82, 142.79, 141.32, 139.39, 138.42, 137.52,
136.17, 132.81, 127.56, 123.47, 115.20, 108.67, 93.37, 92.77,
86.39, 51.17, 39.24, 24.59. Elemental analysis calcd (%) for
C23H19IO2: C, 60.81; H, 4.22%. Found: C, 60.55; H, 4.32%.
nyl]azulene-1-carboxylate (4b).
The procedure used for

T. Shoji et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
769
the preparation of 2a was adopted here. The reaction of
2b (460 mg, 1.00 mmol) with ethynylbenzene (153 mg, 1.50
mmol) in triethylamine (5 mL) and THF (5 mL) in the presence
of CuI (19 mg, 0.10 mmol) and tetrakis(triphenylphosphine)-
palladium(0) (58 mg, 0.050 mmol) at room temperature for 6 h
followed by column chromatography on silica gel with CH2Cl2
afforded 4b (413 mg, 95%) as green crystals. Mp: 105.0-108.0
°C. HRMS (ESI): calcd for C29H22O2S + Na+ [M + Na]+
457.1238; found 457.1235. IR (KBr disk): ¯max 2962 (w),
2187 (w), 1692 (s, C=O), 1589 (w), 1507 (w), 1487 (w), 1460
(m), 1444 (m), 1418 (m), 1270 (w), 1221 (s), 1166 (m), 1132
(m), 1120 (w), 1072 (w), 1049 (m), 915 (w), 869 (w), 800 (s),
775 (m), 752 (s), 721 (w), 689 (m), 668 (w) cm¹1. UV-vis
(CH2Cl2): -max (log ¾) 242 (4.50), 282 (4.38), 310 (4.42), 342
sh (4.41), 354 (4.42), 382 sh (4.40), 413 sh (4.32), 440 sh
phosphine)palladium(0) (58 mg, 0.050 mmol) at room temper-
ature for 12 h followed by column chromatography on silica gel
with CH2Cl2 afforded 5b (672 mg, 85%) as green crystals. Mp:
185.0-188.0 °C. HRMS (ESI): calcd for C52H38O4S2 + Na+
[M + Na]+ 813.2109; found 813.2104. IR (KBr disk): ¯max
2955 (w), 2183 (m), 1691 (s, C=O), 1585 (w), 1521 (w), 1487
(w), 1447 (m), 1417 (s), 1270 (w), 1218 (s), 1166 (m), 1132
(w), 1072 (w), 1049 (w), 916 (w), 869 (w), 833 (m), 801 (m),
775 (m), 720 (w), 663 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾)
245 (4.83), 283 (4.77), 296 (4.77), 315 sh (4.73), 423 (4.90),
450 (4.83), 568 (3.26) nm. 1H NMR (400 MHz, CDCl3): ¤ 9.75
(d, J = 2.0 Hz, 2H, H8), 8.62 (d, J = 10.0 Hz, 2H, H4), 8.47
(s, 2H, H2), 7.84 (dd, J = 10.0, 1.6 Hz, 2H, H6), 7.54 (dd,
J = 10.0, 10.0 Hz, 2H, H5), 7.51 (s, 4H, Ph), 7.20 (br s, 4H,
H3¤,4¤ of Th), 3.96 (s, 6H, CO2Me), 3.24 (sept, J = 6.8 Hz,
2H, i-Pr), 1.43 (d, J = 6.8 Hz, 12H, i-Pr). 13C NMR (100 MHz,
CDCl3): ¤ 165.37, 151.02, 144.89, 142.84, 141.48, 139.57,
138.54, 136.32, 132.27, 131.39, 131.20, 127.79, 125.93,
123.64, 122.79, 115.37, 108.18, 93.70, 90.18, 86.29, 84.69,
51.21, 39.27, 24.59. Elemental analysis calcd (%) for
C52H38O4S2: C, 78.96; H, 4.84%. Found: C, 78.80; H, 4.95%.
1,3,5-Tris{4-[(5-isopropyl-3-methoxycarbonyl-1-azulen-
yl)ethynyl]phenylethynyl}benzene (6a). The procedure used
for the preparation of 2a was adopted here. The reaction of
2a (681 mg, 1.50 mmol) with 1,3,5-triethynylbenzene (50 mg,
0.50 mmol) in triethylamine (5 mL) and THF (5 mL) in the
presence of CuI (19 mg, 0.10 mmol) and tetrakis(triphenyl-
phosphine)palladium(0) (58 mg, 0.050 mmol) at room temper-
ature for 12 h followed by column chromatography on silica
gel with CH2Cl2 afforded 6a (480 mg, 85%) as green crystals.
Mp: 175.0-180.0 °C. HRMS (ESI): calcd for C81H60O6 + Na+
[M + Na]+ 1151.4288; found 1151.4282. IR (KBr disk): ¯max
2957 (m), 2189 (m), 1693 (s, C=O), 1578 (m), 1498 (m), 1444
(s), 1425 (m), 1406 (m), 1373 (m), 1333 (w), 1307 (w), 1244
(m), 1209 (s), 1196 (s), 1167 (m), 1132 (m), 1118 (m), 1070
(w), 1047 (w), 1016 (w), 958 (w), 920 (w), 871 (m), 833 (m),
800 (w), 773 (m), 721 (w), 700 (w), 677 (w), 650 (w), 590 (w),
542 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 240 (5.00), 316
(5.16), 358 (5.13), 370 sh (5.09), 402 (4.99), 424 sh (4.88), 568
1
(4.13), 572 (2.80) nm. H NMR (400 MHz, CDCl3): ¤ 9.74 (d,
J = 1.6 Hz, 1H, H8), 8.61 (d, J = 10.0 Hz, 1H, H4), 8.46 (s, 1H,
H2), 7.83 (dd, J = 10.0, 1.6 Hz, 1H, H6), 7.55-7.50 (m, 3H, H5,
Ph), 7.36-7.34 (m, 3H, Ph), 7.19 (br s, 2H, H3¤,4¤ of Th), 3.96
(s, 3H, CO2Me), 3.24 (sept, J = 6.8 Hz, 1H, i-Pr), 1.43 (d,
J = 6.8 Hz, 6H, i-Pr). 13C NMR (100 MHz, CDCl3): ¤ 165.37,
150.95, 144.86, 142.80, 141.43, 139.53, 138.49, 136.31,
131.93, 131.46, 131.14, 128.60, 128.40, 127.75, 125.45,
124.03, 122.68, 115.32, 108.24, 93.96, 89.84, 86.31, 82.45,
51.19, 39.25, 24.58. Elemental analysis calcd (%) for
C29H22O2S: C, 80.15; H, 5.10%. Found: C, 80.09; H, 5.16%.
1,4-Bis{4-[(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-
ethynyl]phenylethynyl}benzene (5a). The procedure used
for the preparation of 2a was adopted here. The reaction of
2a (908 mg, 2.00 mmol) with 1,4-diethynylbenzene (126 mg,
1.00 mmol) in triethylamine (5 mL) and THF (5 mL) in the
presence of CuI (19 mg, 0.10 mmol) and tetrakis(triphenyl-
phosphine)palladium(0) (58 mg, 0.050 mmol) at room temper-
ature for 6 h followed by column chromatography on silica gel
with CH2Cl2 afforded 5a (693 mg, 89%) as green crystals. Mp:
>300 °C. HRMS (ESI): calcd for C56H42O4 + Na+ [M + Na]+
801.2981; found 801.2975. IR (KBr disk): ¯max 2959 (w), 2191
(w), 1695 (s, C=O), 1508 (m), 1425 (m), 1408 (m), 1373 (w),
1338 (w), 1309 (w), 1244 (m), 1209 (s), 1197 (m), 1169 (m),
1132 (w), 1118 (w), 1074 (w), 1047 (w), 920 (w), 875 (w), 837
(m), 775 (w), 540 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 240
(4.81), 314 (4.85), 362 (4.97), 376 sh (4.97), 404 (4.90), 426
1
(3.41), 616 sh (3.29) nm. H NMR (400 MHz, CDCl3): ¤ 9.74
(d, J = 1.6 Hz, 3H, H8), 8.66 (d, J = 10.0 Hz, 3H, H4), 8.48 (s,
3H, H2), 7.82 (dd, J = 10.0, 1.6 Hz, 3H, H6), 7.68 (s, 3H, Ph),
7.61-7.51 (m, 15H, H5, Ph), 3.97 (s, 9H, CO2Me), 3.24 (sept,
J = 6.8 Hz, 3H, i-Pr), 1.43 (d, J = 6.8 Hz, 18H, i-Pr). 13C NMR
(100 MHz, CDCl3): ¤ 165.41, 150.79, 144.87, 142.79, 141.36,
139.43, 138.39, 136.21, 134.08, 131.67, 131.25, 127.63,
124.22, 123.96, 121.92, 115.17, 108.72, 93.48, 90.53, 89.46,
87.20, 51.20, 39.24, 24.59. Elemental analysis calcd (%) for
C81H60O6¢1/2H2O: C, 85.46; H, 5.40%. Found: C, 85.56; H,
5.67%.
1,3,5-Tris{5-[(5-isopropyl-3-methoxycarbonyl-1-azulen-
yl)ethynyl]-2-thienylethynyl}benzene (6b). The procedure
used for the preparation of 2b was adopted here. The reaction
of 2b (690 mg, 1.50 mmol) with 1,3,5-triethynylbenzene (50
mg, 0.50 mmol) in triethylamine (5 mL) and THF (5 mL) in
the presence of CuI (19 mg, 0.10 mmol) and tetrakis(triphenyl-
phosphine)palladium(0) (58 mg, 0.050 mmol) at room temper-
ature for 24 h followed by column chromatography on silica gel
with CH2Cl2 afforded 6b (459 mg, 80%) as green crystals. Mp:
1
sh (4.81), 568 (3.26), 616 sh (3.10) nm. H NMR (400 MHz,
CDCl3): ¤ 9.75 (d, J = 1.6 Hz, 2H, H8), 8.67 (d, J = 10.0 Hz,
2H, H4), 8.48 (s, 2H, H2), 7.83 (dd, J = 10.0, 1.6 Hz, 2H, H6),
7.60-7.52 (m, 14H, H5, Ph), 3.96 (s, 6H, CO2Me), 3.24 (sept,
J = 6.8 Hz, 2H, i-Pr), 1.43 (d, J = 6.8 Hz, 12H, i-Pr). 13C NMR
(100 MHz, CDCl3): ¤ 165.44, 150.80, 144.88, 142.81, 141.38,
139.44, 138.42, 135.56, 131.60, 131.57, 131.24, 127.62,
124.03, 123.06, 122.21, 115.19, 108.75, 93.50, 90.84, 87.10,
80.52, 51.21, 39.26, 24.61. Elemental analysis calcd (%) for
C56H42O4¢H2O: C, 84.40; H, 5.56%. Found: C, 84.64; H,
5.83%.
1,4-Bis{5-[(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-
ethynyl]-2-thienylethynyl}benzene (5b). The procedure used
for the preparation of 2a was adopted here. The reaction of
2b (920 mg, 2.00 mmol) with 1,4-diethynylbenzene (126 mg,
1.00 mmol) in triethylamine (5 mL) and THF (5 mL) in the
presence of CuI (19 mg, 0.10 mmol) and tetrakis(triphenyl-

770
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
Synthesis and Properties of Tetracyanobutadiene-Azulene Chromophores
146.0-150.0 °C. HRMS (ESI): calcd for C75H54O6S3 + Na+
[M + Na]+ 1169.2980; found 1169.2975. IR (KBr disk): ¯max
2957 (w), 2184 (w), 1695 (s, C=O), 1580 (m), 1504 (w), 1464
(m), 1441 (m), 1420 (m), 1372 (w), 1212 (s), 1165 (m), 1130
(w), 1072 (w), 1050 (w), 917 (w), 867 (w), 798 (m), 775 (w),
717 (w), 673 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 243
(5.01), 282 (4.93), 312 (4.94), 341 sh (4.91), 396 (5.02), 415 sh
(5.00), 440 sh (4.48), 569 (3.38) nm. 1H NMR (400 MHz,
CDCl3): ¤ 9.74 (d, J = 1.6 Hz, 3H, H8), 8.61 (d, J = 10.0 Hz,
3H, H4), 8.46 (s, 3H, H2), 7.82 (dd, J = 10.0, 1.6 Hz, 3H, H6),
7.63 (s, 3H, Ph), 7.53 (dd, J = 10.0, 10.0 Hz, 3H, H5), 7.21-
7.19 (m, 6H, H3¤,4¤ of Th), 3.96 (s, 9H, CO2Me), 3.24 (sept,
J = 6.8 Hz, 3H, i-Pr), 1.43 (d, J = 6.8 Hz, 18H, i-Pr). 13C NMR
(100 MHz, CDCl3): ¤ 165.34, 150.99, 144.88, 142.84, 141.46,
139.54, 138.51, 136.30, 133.65, 132.54, 131.16, 127.79,
126.20, 123.72, 123.24, 115.38, 108.16, 92.18, 90.29, 86.26,
83.98, 51.18, 39.25, 24.58. Elemental analysis calcd (%) for
C75H54O6S3: C, 78.51; H, 4.74%. Found: C, 78.33; H, 4.89%.
1,2,4,5-Tetrakis{4-[(5-isopropyl-3-methoxycarbonyl-1-
azulenyl)ethynyl]phenylethynyl}benzene (7a). The proce-
dure used for the preparation of 2a was adopted here. The
reaction of 2a (908 mg, 2.00 mmol) with 1,2,4,5-tetraethynyl-
benzene (87 mg, 0.50 mmol) in triethylamine (5 mL) and
THF (5 mL) in the presence of CuI (19 mg, 0.10 mmol) and
tetrakis(triphenylphosphine)palladium(0) (58 mg, 0.050 mmol)
at room temperature for 12 h followed by column chromatog-
raphy on silica gel with CH2Cl2 afforded 7a (570 mg, 77%)
as green crystals. Mp: 217.0-220.0 °C (CHCl3). HRMS (ESI):
calcd for C106H78O8 + Na+ [M + Na]+ 1501.5584; found
1501.5589. IR (KBr disk): ¯max 2959 (w), 2191 (w), 1695 (s,
C=O), 1500 (m), 1446 (s), 1425 (w), 1410 (m), 1373 (w), 1244
(m), 1209 (s), 1197 (m), 1169 (m), 1132 (w), 1120 (w), 1072
(w), 1049 (w), 920 (w), 893 (w), 871 (w), 833 (w), 800 (w),
775 (w), 650 (w), 592 (w), 542 (w) cm¹1. UV-vis (CH2Cl2):
IR (KBr disk): ¯max 2958 (w), 2182 (w), 1696 (m, C=O), 1580
(w), 1511 (w), 1464 (m), 1418 (m), 1372 (w), 1213 (s), 1165
(m), 1131 (w), 1073 (w), 1049 (w), 917 (w), 877 (w), 799 (m),
775 (m), 668 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 244
(5.09), 283 (5.05), 294 (5.05), 312 (5.02), 355 sh (4.92), 431
(5.10), 575 sh (3.59) nm. H NMR (400 MHz, CDCl3): ¤ 9.65
(br s, 4H, H8), 8.53 (br s, 4H, H4), 8.38 (br s, 4H, H2), 7.66 (br
s, 4H, H6), 7.41 (br s, 4H, H5), 7.29 (br s, 2H, Ph), 7.22 (m, 8H,
1
H
3¤,4¤), 3.91 (s, 12H, CO2Me), 3.15 (br s, 4H, i-Pr), 1.38 (br s,
24H, i-Pr). 13C NMR (100 MHz, CDCl3): ¤ 165.24, 150.88,
144.81, 142.65, 141.36, 139.44, 138.34, 136.24, 132.88,
132.82, 131.30, 127.82, 126.55, 124.58, 123.33, 115.27,
108.12, 92.19, 90.64, 89.18, 86.54, 51.14, 39.15, 24.51.
Elemental analysis calcd (%) for C98H70O8S4: C, 78.27; H,
4.69%. Found: C, 78.02; H, 4.88%.
Methyl 3-{3,3-Dicyano-1-(dicyanomethylene)-1-[4-(phen-
ylethynyl)phenyl]-2-propenyl}-7-isopropylazulene-1-car-
boxylate (8a). To a solution of 4a (214 mg, 0.50 mmol) in
ethyl acetate (5 mL) was added TCNE (128 mg, 1.00 mmol).
The resulting mixture was refluxed for 3 h under an Ar atmo-
sphere. The solvent was removed under reduced pressure. The
residue was purified by column chromatography on silica gel
with ethyl acetate and Bio-Beads with CH2Cl2 to give 8a
(270 mg, 97%) as reddish brown crystals. Mp: 158.0-160.0 °C.
HRMS (ESI): calcd for C37H24N4O2 + Na+ [M + Na]+
579.1797; found 579.1791. IR (KBr disk): ¯max 2962 (w),
2217 (m, C¸N), 1698 (m, C=O), 1601 (m), 1499 (s), 1442 (s),
1419 (s), 1366 (m), 1296 (w), 1231 (m), 1217 (s), 1179 (m),
1138 (m), 1053 (w), 900 (w), 846 (w), 815 (w), 779 (w), 758
(w), 728 (w), 690 (m), 672 (w) cm¹1. UV-vis (CH2Cl2): -max
(log ¾) 262 (4.53), 300 (4.53), 334 sh (4.42), 400 (4.42), 538 sh
(3.87) nm. 1H NMR (400 MHz, CDCl3): ¤ 10.03 (d, J = 1.6 Hz,
1H, H8), 8.47 (d, J = 10.0 Hz, 1H, H4), 8.28 (s, 1H, H2), 8.17
(dd, J = 10.0, 1.6 Hz, 1H, H6), 7.99 (dd, J = 10.0, 10.0 Hz, 1H,
H5), 7.84 (d, J = 8.8 Hz, 2H, Ph), 7.71 (d, J = 8.8 Hz, 2H,
Ph), 7.56 (dd, J = 8.0, 2.0 Hz, 2H, Ph), 7.40-7.38 (m, 3H, Ph),
3.96 (s, 3H, CO2Me), 3.36 (sept, J = 6.8 Hz, 1H, i-Pr), 1.48 (d,
J = 6.8 Hz, 6H, i-Pr). 13C NMR (100 MHz, CDCl3): ¤ 168.14,
164.37, 160.45, 157.14, 146.23, 142.60, 142.42, 142.01,
140.87, 137.60, 132.86, 132.32, 131.94, 131.21, 130.28,
129.80, 129.37, 128.55, 122.09, 119.57, 119.37, 113.64,
112.46, 112.09, 111.33, 95.60, 88.10, 87.26, 80.76, 51.74,
39.53, 24.49. Elemental analysis calcd (%) for C37H24N4O2:
C, 79.84; H, 4.35; N, 10.07%. Found: C, 79.66; H, 4.44; N,
10.22%.
-
max (log ¾) 242 (5.10), 312 (5.20), 364 (5.14), 408 (5.19), 430
1
sh (5.14), 564 (3.56), 616 sh (3.42) nm. H NMR (400 MHz,
CDCl3): ¤ 10.04 (d, J = 1.6 Hz, 4H, H8), 8.47 (d, J = 10.0 Hz,
4H, H4), 8.27 (s, 4H, H2), 8.18 (dd, J = 10.0, 1.6 Hz, 4H, H6),
8.00 (dd, J = 10.0, 10.0 Hz, 4H, H5), 7.85 (d, J = 8.0 Hz,
8H, Ph), 7.73 (d, J = 8.0 Hz, 8H, Ph), 7.57 (s, 2H, Ph), 3.97 (s,
12H, CO2Me), 3.37 (sept, J = 6.8 Hz, 4H, i-Pr), 1.49 (d, J =
6.8 Hz, 24H, i-Pr). 13C NMR (100 MHz, CDCl3): ¤ 168.15,
164.36, 160.38, 157.23, 146.25, 142.66, 142.42, 142.03,
140.92, 137.63, 132.92, 132.37, 132.01, 131.60, 129.86,
129.70, 122.99, 119.62, 119.43, 113.63, 112.46, 112.03,
111.23, 94.72, 90.39, 87.57, 80.70, 51.74, 39.53, 24.48.
Elemental analysis calcd (%) for C106H78O8¢1/4CHCl3: C,
84.54; H, 5.22%. Found: C, 84.44; H, 5.21%.
Methyl 3-{3,3-Dicyano-1-(dicyanomethylene)-1-[5-(phen-
ylethynyl)-2-thienyl]-2-propenyl}-7-isopropylazulene-1-car-
boxylate (8b). To a solution of 4b (217 mg, 0.50 mmol) in
ethyl acetate (5 mL) was added TCNE (128 mg, 1.00 mmol).
The resulting mixture was refluxed for 3 h under an Ar atmo-
sphere. The solvent was removed under reduced pressure. The
residue was purified by column chromatography on silica gel
with ethyl acetate and Bio-Beads with CH2Cl2 to give 8b
(270 mg, 96%) as reddish brown crystals. Mp: 105.0-108.0 °C
(CH2Cl2/hexane). HRMS (ESI): calcd for C35H22N4O2S +
Na+ [M + Na]+ 585.1361; found 585.1356. IR (KBr disk):
1,2,4,5-Tetrakis{5-[(5-isopropyl-3-methoxycarbonyl-1-
azulenyl)ethynyl]-2-thienylethynyl}benzene (7b). The pro-
cedure used for the preparation of 2a was adopted here. The
reaction of 2b (920 mg, 2.00 mmol) with 1,2,4,5-tetraethynyl-
benzene (87 mg, 0.50 mmol) in triethylamine (5 mL) and
THF (5 mL) in the presence of CuI (19 mg, 0.10 mmol) and
tetrakis(triphenylphosphine)palladium(0) (58 mg, 0.050 mmol)
at room temperature for 24 h followed by column chromatog-
raphy on silica gel with CH2Cl2 afforded 7b (556 mg, 74%) as
green crystals. Mp: 155.0-159.0 °C. HRMS (ESI): calcd for
C98H70O8S4 + Na+ [M + Na]+ 1525.3851; found 1525.3856.
¯
2962 (w), 2221 (w, C¸N), 2200 (w), 1702 (m, C=O),
max
1530 (m), 1500 (m), 1440 (m), 1421 (s), 1364 (m), 1309 (w),
1240 (w), 1213 (m), 1179 (m), 1135 (w), 1051 (w), 1021 (w),

T. Shoji et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
771
898 (w), 809 (w), 779 (w), 756 (m), 733 (w), 688 (w), 673 (w),
666 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 264 (4.54), 298
(4.44), 342 sh (4.28), 442 (4.62) nm. UV-vis (10% CH2Cl2/
hexane): -max (log ¾) 262 (4.49), 300 (4.41), 340 (4.28), 429
(4.62) nm. 1H NMR (400 MHz, CDCl3): ¤ 10.02 (d, J = 2.0 Hz,
1H, H8), 8.51 (d, J = 10.0 Hz, 1H, H4), 8.24 (s, 1H, H2), 8.18
(dd, J = 10.0, 2.0 Hz, 1H, H6), 8.02 (dd, J = 10.0, 10.0 Hz, 1H,
H5), 7.96 (d, J = 3.6 Hz, 1H, H4¤ of Th), 7.55 (dd, J = 7.6,
2.0 Hz, 2H, o-Ph), 7.44-7.40 (m, 4H, m-Ph, p-Ph, H3¤ of Th),
3.96 (s, 3H, CO2Me), 3.37 (sept, J = 6.8 Hz, 1H, i-Pr), 1.48 (d,
J = 6.8 Hz, 6H, i-Pr). 13C NMR (100 MHz, CDCl3): ¤ 164.38,
159.60, 158.13, 157.20, 146.38, 142.58, 142.33, 142.00,
140.77, 137.84, 137.32, 136.86, 135.36, 133.73, 132.42,
131.85, 130.06, 128.67, 121.22, 119.48, 118.59, 113.49,
112.93, 112.40, 111.90, 102.58, 81.40, 80.57, 79.79, 51.69,
39.51, 24.46. Elemental analysis calcd (%) for C35H22N4O2S:
C, 74.71; H, 3.94; N, 9.96%. Found: C, 74.55; H, 4.04; N,
9.90%.
(400 MHz, CDCl3): ¤ 10.01 (d, J = 2.0 Hz, 2H, H8), 8.50 (d,
J = 10.0 Hz, 2H, H4), 8.26 (s, 2H, H2), 8.17 (dd, J = 10.0,
1.6 Hz, 2H, H6), 7.96 (d, J = 4.4 Hz, 2H, H4¤ of Th), 7.60
(dd, J = 10.0, 10.0 Hz, 2H, H5), 7.56 (s, 4H, Ph), 7.43 (d,
J = 4.4 Hz, 2H, H3¤ of Th), 3.96 (s, 6H, CO2Me), 3.36 (sept,
J = 6.8 Hz, 2H, i-Pr), 1.48 (d, J = 6.8 Hz, 12H, i-Pr). 13C NMR
(100 MHz, CDCl3): ¤ 164.37, 159.49, 158.16, 157.31, 146.41,
143.38, 142.65, 142.31, 142.04, 140.83, 137.88, 137.26,
135.84, 134.15, 132.64, 132.49, 131.99, 122.74, 119.57,
118.60, 113.48, 112.85, 112.41, 111.78, 101.29, 84.05, 80.57,
51.74, 39.56, 24.50. Elemental analysis calcd (%) for C64H38-
N8O4S2: C, 73.41; H, 3.66; N, 10.70%. Found: C, 73.29; H,
3.78; N, 10.54%.
1,3,5-Tris{4-[3,3-dicyano-1-(dicyanomethylene)-2-(5-iso-
propyl-3-methoxycarbonyl-1-azulenyl)-1-propenyl]phenyl-
ethynyl}benzene (10a). The procedure used for the prepara-
tion of 8a was adopted here. The reaction of 6a (282 mg,
0.25 mmol) with TCNE (192 mg, 1.50 mmol) in ethyl acetate
(10 mL) for 5 h afforded 10a (344 mg, 91%) as red crystals.
Mp: >300 °C. HRMS (ESI): calcd for C99H60N12O6 + Na+
[M + Na]+ 1535.4656; found 1535.4651. IR (KBr disk): ¯max
2970 (w), 2219 (w, C¸N), 1737 (m, C=O), 1600 (w), 1499
(m), 1440 (m), 1419 (m), 1365 (s), 1215 (s), 1130 (w), 1097
(w), 1051 (w), 878 (w), 834 (w), 777 (w), 727 (w), 678 (w),
669 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 266 (4.89), 302
(4.99), 400 (4.76), 540 sh (4.19) nm. 1H NMR (400 MHz,
CDCl3): ¤ 10.04 (d, J = 1.6 Hz, 3H, H8), 8.48 (d, J = 10.0 Hz,
3H, H4), 8.27 (s, 3H, H2), 8.19 (dd, J = 10.0, 1.6 Hz, 3H, H6),
8.02 (dd, J = 10.0, 10.0 Hz, 3H, H5), 7.87 (d, J = 8.0 Hz,
6H, Ph), 7.77 (s, 3H, Ph), 7.74 (d, J = 8.0 Hz, 6H, Ph), 3.97 (s,
9H, CO2Me), 3.38 (sept, J = 6.8 Hz, 3H, i-Pr), 1.49 (d, J = 6.8
Hz, 18H, i-Pr). Low solubility hampered the measurement
of 13C NMR. Elemental analysis calcd (%) for C99H60N12O6:
C, 78.56; H, 4.00; N, 11.10%. Found: C, 78.78; H, 4.09; N,
11.13%.
1,3,5-Tris{5-[3,3-dicyano-1-(dicyanomethylene)-2-(5-
isopropyl-3-methoxycarbonyl-1-azulenyl)-1-propenyl]-2-
thienylethynyl}benzene (10b). The procedure used for the
preparation of 8a was adopted here. The reaction of 6b (287
mg, 0.25 mmol) with TCNE (192 mg, 1.50 mmol) in ethyl
acetate (10 mL) for 5 h afforded 10b (356 mg, 93%) as red
crystals. Mp: 230.0-235.0 °C. HRMS (ESI): calcd for C93H54-
N12O6S3 + Na+ [M + Na]+ 1553.3349; found 1553.3344. IR
(KBr disk): ¯max 2969 (w), 2221 (w, C¸N), 1738 (s, C=O),
1521 (m), 1496 (m), 1432 (s), 1419 (s), 1365 (s), 1215 (s), 1179
(m), 1134 (w), 1097 (w), 1061 (w), 1024 (w), 900 (w), 810 (w),
778 (w), 734 (w), 676 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾)
264 (4.98), 299 (4.90), 344 sh (4.77), 442 (5.13) nm. UV-vis
(30% CH2Cl2/hexane): -max (log ¾) 263 (4.97), 301 (4.88), 342
sh (4.77), 435 (5.13) nm. 1H NMR (400 MHz, CDCl3): ¤ 10.02
(s, 3H, H8), 8.51 (d, J = 10.0 Hz, 3H, H4), 8.22 (s, 3H, H2),
8.20 (dd, J = 10.0, 1.6 Hz, 3H, H6), 8.04 (dd, J = 10.0, 10.0
Hz, 3H, H5), 7.96 (d, J = 4.4 Hz, 3H, H4¤ of Th), 7.75 (s, 3H,
Ph), 7.46 (d, J = 4.4 Hz, 3H, H3¤ of Th), 3.96 (s, 9H, CO2Me),
3.37 (sept, J = 6.8 Hz, 3H, i-Pr), 1.49 (d, J = 6.8 Hz, 18H,
i-Pr). Low solubility hampered the measurement of 13C NMR.
Elemental analysis calcd (%) for C93H54N12O6S3: C, 72.93; H,
3.55; N, 10.97%. Found: C, 72.70; H, 3.69; N, 10.88%.
1,2,4,5-Tetrakis{4-[3,3-dicyano-1-(dicyanomethylene)-2-
1,4-Bis{4-[3,3-dicyano-1-(dicyanomethylene)-2-(5-iso-
propyl-3-methoxycarbonyl-1-azulenyl)-1-propenyl]phenyl-
ethynyl}benzene (9a). The procedure used for the preparation
of 8a was adopted here. The reaction of 5a (389 mg, 0.50
mmol) with TCNE (192 mg, 1.50 mmol) in ethyl acetate (10
mL) for 5 h afforded 9a (487 mg, 94%) as red crystals. Mp:
200.0-203.0 °C. HRMS (ESI): calcd for C68H42N8O4 + Na+
[M + Na]+ 1057.3227; found 1057.3232. IR (KBr disk): ¯max
2963 (w), 2222 (m, C¸N), 1702 (m, C=O), 1598 (m), 1499
(m), 1440 (m), 1419 (s), 1364 (m), 1295 (w), 1213 (s), 1179
(m), 1139 (w), 1052 (w), 901 (w), 841 (m), 777 (m), 731 (w),
669 (m) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 262 (4.60), 300
(4.69), 338 (4.62), 410 (4.61), 540 sh (4.02) nm. 1H NMR
(400 MHz, CDCl3): ¤ 10.04 (d, J = 1.6 Hz, 2H, H8), 8.47 (d,
J = 10.0 Hz, 2H, H4), 8.27 (s, 2H, H2), 8.18 (dd, J = 10.0,
1.6 Hz, 2H, H6), 8.00 (dd, J = 10.0, 10.0 Hz, 2H, H5), 7.85 (d,
J = 8.0 Hz, 4H, Ph), 7.73 (d, J = 8.0 Hz, 4H, Ph), 7.57 (s, 4H,
Ph), 3.97 (s, 6H, CO2Me), 3.37 (sept, J = 6.8 Hz, 2H, i-Pr),
1.49 (d, J = 6.8 Hz, 12H, i-Pr). 13C NMR (100 MHz, CDCl3):
¤ 168.15, 164.36, 160.38, 157.23, 146.25, 142.66, 142.42,
142.03, 140.92, 137.63, 132.92, 132.37, 132.01, 131.60,
129.86, 129.70, 122.99, 119.62, 119.43, 113.63, 112.46,
112.03, 111.23, 94.72, 90.39, 87.57, 80.70, 51.74, 39.53,
24.48. Elemental analysis calcd (%) for C68H42N8O4: C, 78.90;
H, 4.09; N, 10.83%. Found: C, 78.77; H, 4.26; N, 10.91%.
1,4-Bis{5-[3,3-dicyano-1-(dicyanomethylene)-2-(5-isopro-
pyl-3-methoxycarbonyl-1-azulenyl)-1-propenyl]-2-thienyl-
ethynyl}benzene (9b). The procedure used for the preparation
of 8a was adopted here. The reaction of 5b (396 mg, 0.50
mmol) with TCNE (192 mg, 1.50 mmol) in ethyl acetate (10
mL) for 5 h afforded 9b (497 mg, 95%) as red crystals. Mp:
170.0-175.0 °C (decomp.). HRMS (ESI): calcd for C64H38-
N8O4S2 + Na+ [M + Na]+ 1069.2355; found 1069.2350. IR
(KBr disk): ¯max 2962 (w), 2222 (w, C¸N), 2203 (w), 1711 (m,
C=O), 1535 (m), 1512 (m), 1498 (s), 1433 (m), 1416 (s), 1364
(m), 1304 (w), 1274 (w), 1247 (w), 1212 (s), 1179 (m), 1118
(w), 1091 (w), 1031 (w), 899 (w), 835 (w), 813 (w), 775 (w),
730 (w), 670 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 263
(4.78), 300 (4.74), 339 sh (4.60), 435 sh (4.85), 481 (4.90) nm.
UV-vis (20% CH2Cl2/hexane): -max (log ¾) 260 (4.76), 298
1
(4.72), 339 sh (4.53), 432 sh (4.85), 462 (4.91) nm. H NMR

772
Bull. Chem. Soc. Jpn. Vol. 85, No. 7 (2012)
Synthesis and Properties of Tetracyanobutadiene-Azulene Chromophores
References
(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-1-propenyl]-
phenylethynyl}benzene (11a). The procedure used for the
preparation of 8a was adopted here. The reaction of 7a (370
mg, 0.25 mmol) with TCNE (256 mg, 2.00 mmol) in ethyl
acetate (10 mL) for 12 h afforded 11a (458 mg, 92%) as red
crystals. Mp: >300 °C. HRMS (ESI): calcd for C130H78-
N16O8 + Na+ [M + Na]+ 2013.6086; found 2013.6081. IR
(KBr disk): ¯max 2969 (w), 2217 (w, C¸N), 1738 (s, C=O),
1600 (w), 1499 (m), 1440 (m), 1419 (m), 1365 (s), 1215 (s),
1180 (w), 1135 (w), 1052 (w), 905 (w), 814 (w), 777 (w), 731
(w), 669 (w) cm¹1. UV-vis (CH2Cl2): -max (log ¾) 300 (5.06),
346 sh (4.87), 390 (4.80), 466 sh (4.61), 546 sh (4.27) nm.
1H NMR (400 MHz, CDCl3): ¤ 10.03 (d, J = 1.6 Hz, 4H, H8),
8.47 (d, J = 10.0 Hz, 4H, H4), 8.30 (s, 4H, H2), 8.19 (dd,
J = 10.0, 1.6 Hz, 4H, H6), 8.01 (dd, J = 10.0, 10.0 Hz, 4H, H5),
7.86 (d, J = 8.0 Hz, 8H, Ph), 7.85 (s, 2H, Ph), 7.73 (d, J =
8.0 Hz, 8H, Ph), 3.97 (s, 12H, CO2Me), 3.37 (sept, J = 6.8 Hz,
4H, i-Pr), 1.49 (d, J = 6.8 Hz, 24H, i-Pr). Low solubility
hampered the measurement of 13C NMR. Elemental analysis
calcd (%) for C130H78N16O8¢3/4H2O: C, 77.85; H, 4.00; N,
11.17%. Found: C, 77.86; H, 4.03; N, 11.14%.
1,2,4,5-Tetrakis{5-[3,3-dicyano-1-(dicyanomethylene)-2-
(5-isopropyl-3-methoxycarbonyl-1-azulenyl)-1-propenyl]-2-
thienylethynyl}benzene (11b). The procedure used for the
preparation of 8a was adopted here. The reaction of 7b
(376 mg, 0.25 mmol) with TCNE (256 mg, 2.00 mmol) in ethyl
acetate (10 mL) for 12 h afforded 11b (474 mg, 94%) as red
crystals. Mp: 203.0-207.0 °C (decomp.). HRMS (ESI): calcd
for C122H70N16O8S4 + Na+ [M + Na]+ 2037.4343; found
2037.4338. IR (KBr disk): ¯max 2969 (w), 2221 (w, C¸N),
1738 (s, C=O), 1496 (m), 1439 (m), 1418 (s), 1365 (s), 1215
(s), 1180 (m), 1134 (w), 1090 (w), 1059 (w), 1021 (w), 899 (w),
810 (w), 778 (w), 731 (w), 659 (w) cm¹1. UV-vis (CH2Cl2):
1
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7
Gross, F. Diederich, Angew. Chem. 2007, 119, 6473; M. Kivala,
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-
(log ¾) 264 (5.07), 301 (5.04), 342 sh (4.90), 451 (5.22),
max
508 sh (5.04) nm. UV-vis (30% CH2Cl2/hexane): -max (log ¾)
263 (4.94), 303 (4.92), 344 sh (4.82), 457 (4.99), 541 sh
(4.82) nm. 1H NMR (400 MHz, CDCl3): ¤ 10.01 (d, J = 1.6 Hz,
4H, H8), 8.59 (d, J = 10.0 Hz, 4H, H4), 8.29 (s, 4H, H2), 8.18
(dd, J = 10.0, 1.6 Hz, 4H, H6), 8.02 (dd, J = 10.0, 10.0 Hz,
4H, H5), 7.86 (s, 2H, Ph), 7.80 (d, J = 4.4 Hz, 4H, H4¤ of Th),
7.53 (d, J = 4.4 Hz, 4H, H3¤ of Th), 3.95 (s, 12H, CO2Me), 3.36
(sept, J = 6.8 Hz, 4H, i-Pr), 1.47 (d, J = 6.8 Hz, 24H, i-Pr).
13C NMR (100 MHz, CDCl3): ¤ 164.38, 159.21, 158.28,
157.41, 146.49, 142.69, 142.51, 142.13, 140.83, 138.30,
137.84, 136.88, 134.06, 132.60, 125.21, 119.72, 118.68,
113.55, 112.80, 112.56, 111.63, 97.80, 97.72, 89.21, 89.13,
81.23, 80.23, 51.75, 39.53, 24.46. Elemental analysis calcd
(%) for C122H70N16O8S4¢H2O: C, 72.03; H, 3.57; N, 11.02%.
Found: C, 72.11; H, 3.60; N, 10.99%.
8
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This work was partially supported by a Grant-in-Aid for
Research Activity Start-up (Grant No. 22850007 to T.S.) from
the Ministry of Education, Culture, Sports, Science and
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Supporting Information
Figure of UV-vis spectra and cyclic voltammograms of
reported compounds. This material is available free of charge
via the Internet at http://www.csj.jp/journals/bcsj/.

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