Preparation, structure, and redox behavior of bis(diarylmethylene)dihydrothiophene and Its π-extended analogues

Article abstract of DOI:10.1021/acs.joc.5b00021

The preparation, X-ray structure, and optoelectronic properties of bis(diarylmethylene)dihydrothiophene 1 and its π-extended analogues 2 are described. The development of a simple, short-step synthetic route allowed us to prepare derivatives with differen

Full text of DOI:10.1021/acs.joc.5b00021

Note
pubs.acs.org/joc
Preparation, Structure, and Redox Behavior of
Bis(diarylmethylene)dihydrothiophene and Its π‑Extended
Analogues
Takashi Takeda* and Tomoyuki Akutagawa
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Miyagi 980-8577, Japan
S
* Supporting Information
ABSTRACT: The preparation, X-ray structure, and optoelectronic proper-
ties of bis(diarylmethylene)dihydrothiophene 1 and its π-extended analogues
2 are described. The development of a simple, short-step synthetic route
allowed us to prepare derivatives with different aryl units. X-ray crystallo-
graphic analysis of 1b and 2b revealed their quinoidal structures, which exhibit
strong electronic absorption in the visible region. Cyclic voltammetry
measurements revealed their strong electron-donating properties. 1b showed
two-step electrochromic behavior between the corresponding radical cation
and dication.
uinoidal compounds have attracted considerable
examined, little is known about those with electron-donating
substituents. Although bis(diphenylmethylene)dihydrothio-
phene 1a and its π-extended analogue have been reported
sporadically,14 their molecular structures and their optical and
electronic properties have not been well examined.
Q attention with respect to their reactivity and diradical
character. For example, o-quinodimethane, the simplest
quinoidal molecule, shows high reactivity.1 Recently, π-
conjugated quinoidal molecules with diradical character have
been reported to show low-energy light absorption that reached
to the near-infrared (NIR) region.2
In this work, we prepared bis(diarylmethylene)dihydrothio-
phene 1 and its π-extended analogues 2 by a simple and
versatile synthetic route. Because quinoidal bithiophene with
diphenylmethylene groups has been reported to isomerize in
solution,15 we chose thienothiophene instead to expand the
thiophene core. X-ray structural analysis of 1 and 2 revealed
their quinoidal molecular structure. Extension of a π-electron
unit and the manipulation of electron-donating and -accepting
groups on an aryl group strongly affect their absorption spectra.
With regard to the electrochemistry of these derivatives,
different redox behaviors were observed depending on the
electron-donating and -accepting properties on the terminal
aryl group. Compound 1b with a simple molecular structure
showed tricolor electrochromic behavior.
We first sought to identify an efficient synthetic route for 1
and 2. It has been reported that fluorene-fused dihydrothieno-
thiophene with a quinoidal molecular structure could be
synthesized from the corresponding diol by dehydration in the
solid state or in a photochemical reaction and from the
corresponding dihydro derivative by deprotonation followed by
oxidation.14c However, some of these reactions require extreme
reaction conditions. Nakayama et al. reported the preparation
of 1a−c from the corresponding dication species.14b However,
during the course of our studies, we found that these cations
Polythiophene,3 thienothiophene, and their derivatives, such
as P3HT4 and BTBT,5 have been extensively studied from the
viewpoint of conducting organic materials in hole-transporting
materials for use in organic field-effect transistors6 and bulk
heterojunction solar cells.7 Polythiophene derivatives are
characterized by strong electron-donating properties and a
narrower HOMO−LUMO gap due to the long π-conjugation
of electron-donating thiophene units. The relationships
between the number of thiophene rings and photophysical
and/or electronic properties have been extensively studied with
oligothiophene derivatives.8
On the basis of the unique properties of quinoidal molecules
and oligothiophene and/or thienothiophene, quinoidal oligo-
thiophene should be an interesting structural motif with regard
to its electronic, photonic, and diradical characteristics. In fact,
quinoidal oligothiophene and thienothiophene with dicyano-
methylene groups have been extensively studied as organic
conductors,9 optical materials,10 and organic field-effect
transistors.11 For example, Otsubo et al. studied an
oligothiophene with a dicyanomethylene group up to a
hexamer and reported amphoteric redox behavior and the
emergence of a diradical character with extension of the
thienoquinoidal framework.12 Dihydrothienothiophenes with
dicyanomethylene units have also been prepared for examina-
tion of their photophysical and conductive properties.13 While
quinoidal oligothiophenes and thienothiophene with electron-
withdrawing dicyanomethylene units have been extensively
Received: January 7, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.5b00021
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The Journal of Organic Chemistry
Note
Single-crystal X-ray crystallographic analyses and DFT
calculations were performed for neutral donors 1 and 2 and
their respective dicationic states 12+ and 22+ to examine their
molecular structures. Figure 1 shows ORTEP drawings of 1b
and 2b and optimized structures for 1b2+ and 2b2+. Crystal data,
data collection, and reduction parameters for crystals 1a, 1b, 2a,
and 2b and selected bond lengths and torsion angles of 1a, 1b,
and 2b are summarized in Table 2 and Table S1 of the
Supporting Information. The bond length was successfully
determined with a high degree of accuracy in the crystal
structures of 1a, 1b, and 2b, which allowed us to examine the
bonding characteristics of these compounds. Because disorder
in the thienothiophene ring of 2a made it difficult to determine
the precise bond lengths, structural data for 2a were excluded
from the discussion. The CA−CB (1 and 2), CC−CC′ (1), and
CC−CD (2) bonds are shorter than the CB−CC bond, indicating
the formation of a quinoidal structure, which is consistent with
the optimized molecular structure obtained using DFT
calculations (see Tables S2 and S3 of the Supporting
Information). The terminal aryl moieties and central thiophene
ring are twisted because of steric repulsion between hydrogens
on the aryl group and hydrogen or sulfur on the thiophene ring.
Dicationic species 12+ and 22+ are relatively unstable toward
moisture, which made it difficult to grow a single crystal that
was suitable for X-ray analysis. Thus, we performed DFT
calculations at the B3LYP/6-31G(d) level of theory. In contrast
to those of neutral donors 1 and 2, the CA−CB bonds in
dications 12+ and 22+ are longer than the CB−CC bonds (Table
S4 of the Supporting Information), which reflects a benzenoid
molecular structure. This switching of the quinoid−benzenoid
structure based on electron transfer should be interesting with
regard to the change in photophysical properties.
Next, we examined photophysical properties. Figure 2 shows
UV−vis and fluorescence spectra of 1 and 2 in dichloro-
methane. Thienoquinoid 1a showed strong absorption in the
visible region at 422 nm, which can be assigned to the
HOMO−LUMO transition of the thienoquinoid substructure,
which was supported by DFT calculations [B3LYP/6-31G(d)
(see Figure 3)]. Extension of the central π-electron unit from a
thienoquinoid unit to a thienothienoquinoid unit caused a huge
red shift of 44 nm for 2a in contrast to that of 1a due to
narrowing of the HOMO−LUMO gap through the extension
of π-conjugation. The absorption spectra of 1 and 2 were also
strongly affected by the substituents on the terminal aryl
moieties. The introduction of both electron-donating methoxy
units and electron-accepting chloro atoms on phenyl moieties
caused a red shift. Table 1 summarizes the energy levels of
showed moderate instability toward moisture, which hampered
their purification.
Thus, we developed a simple, versatile synthetic route for 1,
as summarized in Scheme 1. The addition of diarylketone to
dilithiothiophene generated from dibromothiophene gave the
corresponding diol 3. Diols 3b and 3c were purified by silica gel
column chromatography, whereas phenyl derivative 3a′ was
isolated as an ethoxy derivative after recrystallization of the
crude product from ethanol. In the previous paper,14b the
dication was generated from the corresponding diol by the
reaction with Brønsted acidic medium consisting of aq HClO4
in acetic anhydride, which cannot be easily removed because of
the low volatility of the reagents. Thus, we chose a Lewis acid,
TMSClO4, with 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a
solvent to generate the corresponding dicationic species,
because all of the reagent and solvent could be removed by
evaporation,16 which allowed us to reduce the dicationic species
in situ. Treatment of the diol with TMSClO4 in HFIP followed
by reduction of the generated dicationic species with Zn in
MeCN successfully gave the corresponding thienoquinoid 1.
The dication could also be obtained from ethoxy derivative 3a′,
which was reduced to give 1a. The versatility of this route was
demonstrated by the preparation of 1b, 1c, and 2a−c, which
have different aryl moieties and/or thiophene units. Electron-
donating aryl moieties and an electron-deficient aryl group can
be introduced by this method. Notably, the yield of 1c was
drastically improved from 6% with HClO4 and Ac2O14b to 99%
with TMSClO4 and HFIP. While extension of the thiophene
unit to thienothiophene was also successfully demonstrated, the
introduction of a stronger electron-donating aryl unit such as
Me2NC6H4 and further extension of the thiophene spacer such
as dithieno[3,2-b:2′,3′-d]thiophene failed. Because of the strong
electron-donating properties of 1b and 2a (vide infra), these
quinoid compounds should be oxidized and decompose during
workup and purification.
Scheme 1. Preparation of 1 and 2 with Different Aryl Groups
B
DOI: 10.1021/acs.joc.5b00021
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The Journal of Organic Chemistry
Note
Figure 1. (a) ORTEP drawings of 1b (left) and 2b (right) and (b) optimized structures of 1b2+ (left) and 2b2+ (right).
Figure 2. UV−vis (left) and fluorescence (right) spectra of 1 and 2 in CH2Cl2.
Figure 3. (a) HOMO and (b) LUMO of molecules 1a (left) and 2a (right).
Table 1. HOMO and LUMO Energy Levels of 1 and 2
Calculated at the B3LYP/6-31G* Level of Theory
Electrochemical properties were examined by cyclic
voltammetry (CV). Figure S1 of the Supporting Information
shows a CV chart for 1b and 2b. Both compounds showed
reversible one-wave two-electron oxidation waves, which
correspond to the generation of the dication species. The
oxidation potentials of 1b and 2b were 0.64 and 0.56 V versus
Ag/AgCl, respectively, which correspond to HOMO energies
of −4.83 and −4.73 eV, respectively, which demonstrates
strong electron-donating properties. The oxidation potential
could be tuned by not only the length of the thienoquinoid π-
system but also the substituents on the aryl group. The less
electron-rich phenyl derivative and 4-chlorophenyl derivative
showed irreversible one-wave oxidation waves at 0.98 (1a), 0.83
(2a), 1.13 (1c), and 0.94 V (2c), indicating the facile
decomposition of cation radical species in an electron-poor
cation radical intermediate. In addition to electron-donating
properties, the conjugation effect of the methoxy group in 1b
1a
1b
1c
2a
2b
2c
HOMO (eV−1
LUMO (eV−1
)
−4.70
−1.84
−4.37
−1.60
−5.14
−2.34
−4.58
−2.09
−4.28
−1.87
−4.98
−2.55
)
HOMO and LUMO for 1 and 2. While the introduction of an
electron-donating methoxy group increased the HOMO energy
more than the LUMO energy, an electron-accepting chloro
atom decreased the LUMO energy more than the HOMO
energy. As a result, the HOMO−LUMO gap narrowed in both
cases to cause a significant red shift in 1 and 2. Compounds 1
and 2 exhibited weak fluorescence in solution. The tendency of
the wavelength of emission maxima was in accord with that of
absorption maxima. Thienoquinoid 1 showed fluorescence also
in the solid state (Figure S4 of the Supporting Information).
Figure 4. Change in the UV−vis spectrum of 1b in MeCN containing 0.1 M Bu4NBF4 electrolyte upon constant-current electrolysis (20 μA; every 4
min). The durations of oxidation for the spectra on the left and right were from 0 to 16 min and from 16 to 28 min, respectively.
C
DOI: 10.1021/acs.joc.5b00021
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The Journal of Organic Chemistry
Note
Table 2. Crystal Data, Data Collection, and Reduction Parameters for Crystals 1a, 2a·CH2Cl2, 1b, and 2b
1a
C30H22S
2a·CH2Cl2
1b
2b
chemical formula
formula weight
space group
a (Å)
C32H20Cl2S2
551.51
C34H30O4S
534.67
C36H30O4S2
590.75
414.56
P21/n (No. 14)
12.0374(5)
12.5139(4)
14.3361(5)
P21/n (No. 14)
9.01922(16)
15.0820(3)
9.93380(18)
P1 (No. 2)
P21/c (No. 14)
15.5917(2)
̅
10.0009(3)
11.5470(3)
13.2679(4)
89.9142(16)
70.0107(13)
72.5011(13)
1364.45(7)
2
b (Å)
6.83809(10)
14.0291(2)
c (Å)
α (deg)
β (deg)
γ (deg)
99.098(3)
103.3317(9)
97.0284
V (Å3)
2132.35(13)
4
1314.86(5)
2
1484.51(4)
2
Z
Dcalc (g cm−1
)
1.291
1.393
3.863
14443
2393
1.301
1.321
1.942
15175
2720
μ (cm−1
)
1.441
1.358
no. of reflections measured
no. of independent reflections
no. of reflections used
23612
3852
14785
4867
3852
2393
4867
2720
a
R
0.0433
0.1104
0.0683
0.1967
1.113
0.0638
0.0489
0.1415
1.064
b
Rw(F2)
0.1673
goodness of fit
1.077
0.920
a
b
2
R = ∑||Fo| − |Fc||/∑|Fo|. Rw = [∑ω(|Fo| − |Fc|)2/∑ωFo ]1/2
.
and 2b might contribute to the improvement of the electron-
donating properties of the molecules and the stabilization of the
dicationic state.
CONCLUSION
■
In summary, we have developed a versatile synthetic route for
bis(diarylmethylene)dihydrothiophene 1. The versatility of this
method was demonstrated by the derivatization of aryl moieties
and π-extension of a thiophene unit. X-ray crystallographic
analysis of 1 and 2 revealed their quinoidal molecular
structures. The electronic absorption spectra of compounds 1
and 2 were strongly affected by the π-conjugation length and
the presence of electron-donating and/or electron-accepting
substituents on the aryl groups. While electron-poor molecules
1a, 2a, 1c, and 2c were unstable toward electrochemical
oxidation, molecules 1b and 2b with an electron-donating 4-
methoxyphenyl group showed reversible redox behavior
between dication species via the corresponding cation radical.
This oxidation process can be monitored by UV−vis spectra to
show tricolor electrochromic behavior. Redox active quinoidal
molecules with switching ability20 should be an interesting
molecular system, which may be useful in optoelectronic
materials.
We examined the electrochromic17,18 behavior of 1b. Figure
4 shows changes in the UV−vis spectra of 1b upon constant-
current oxidation, where two-stage electrochromic behaviors
were observed. In the early stage of oxidation, the absorption
intensity corresponding to neutral species 1b decreased,
whereas the new long-wave absorption intensity at ∼645 nm
increased. The absorption intensity of a new low-energy
absorption band remained constant even as electrolysis
proceeded. In the later stage, this absorption was suppressed
with a continuous decrease in the absorption intensity of the
intermediate, whereas the intensity of a new strong absorption
peak at ∼500 nm increased. Because 1b2+ was expected to show
absorption at ∼500 nm based on TDDFT calculations at the
B3LYP/6-31G(d) level of theory, this change in the UV−vis
spectrum should correspond to stepwise oxidation to dication
1b2+ via cation radical intermediate 1b+•. It is interesting to
compare the electrochromic behavior to that of bis[di(4-
methoxyphenyl)ethenyl]thiophene, which has an additional
conjugated carbon and shows bicolor electrochromism between
the neutral state and dication state.19 The difference in
electrochromic behavior could probably be ascribed to the
difference in the degree of interaction between the terminal
redox active diarylmethylene unit, which was directly connected
to a thiophene π-spacer in 1b and resulted in weak electronic
coupling to show two-step electrochromism. On the other
hand, diarylmethylene units were separated by two additional
carbon units in bis[di(4-methoxyphenyl)ethenyl]thiophene,
and the electronic coupling between terminal units was
negligible for the achievement of bicolor electrochromism. A
tricolor change could be triggered by two different mechanisms,
i.e., a change in the electronic nature of the thienoquinoid π-
unit and a change in the chromophore from thienoquinoid to
triarylmethylium.
EXPERIMENTAL SECTION
■
General Methods. All chemical reactions were performed under a
nitrogen atmosphere. Commercially available reagents and solvents
were used without further purification. TMSClO4 in toluene was
prepared according to a literature method.16 Chemical shifts (δ) in
parts per million were referenced to an internal standard of
tetramethylsilane or residual nondeuterated solvent (1H at 5.32 ppm
for CD2Cl2 and 13C at 77.0 ppm for CDCl3). Mass spectra were
obtained in EI mode with a magnetic sector mass spectrometer.
Infrared (IR, 400−4000 cm−1) spectra were measured on a KBr pellet
with a resolution of 4 cm−1.
X-ray Structural Analysis. Temperature-dependent crystallo-
graphic data (Table 2) were collected using a diffractometer equipped
with a rotating anode fit with multilayer confocal optics using Cu Kα
(λ = 1.54187 Å) radiation. Structural refinements were conducted
using the full-matrix least-squares method on F2. Calculations were
performed using the Crystal Structure and SHELEX software
packages.21 Parameters were refined using anisotropic temperature
factors except for the hydrogen atom.
Computational Methods. DFT calculations were performed with
the Gaussian 09 program package.22 The geometries of the molecules
D
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Note
were optimized using the B3LYP/6-31G* basis set. Stationary points
were assessed by a vibration frequency analysis.
Preparation of 1b. To a mixture of 3b (1.00 g, 2.82 mmol) in
1,1,1,3,3,3-hexafluoro-2-propanol (10 mL) was added TMSClO4 in
toluene (0.74 M, 8.6 mL, 6.36 mmol). After the mixture was stirred for
13 h at room temperature, the volatile solvent and reagent were
removed by evaporation. The obtained dicationic species was dissolved
in dry MeCN (20 mL), and Zn powder (1.43 g, 20.5 mmol) was
added. The mixture was stirred for 9 h, diluted with CH2Cl2, and
filtered. The filtrate was washed with brine and dried over Na2SO4.
The crude product was subjected to silica gel column chromatography
(hexane/CH2Cl2 = 1/4) to give 1b (800 mg, 89%) as a yellow solid.
Mp: 204−205 °C. 1H NMR (400 MHz, CDCl3): δ 7.30 (d, J = 8.0 Hz,
4H), 7.14 (d, J = 8.0 Hz, 4H), 6.86 (d, J = 8.6 Hz, 4H), 6.82 (d, J = 8.6
Hz, 4H), 6.77 (s, 2H), 3.81 (s, 6H), 3.79 (s, 6H). 13C NMR (100
MHz, CDCl3): δ 158.7, 140.8 (br), 135.1 (br), 134.6 (br), 133.0,
131.6, 131.0, 113.6, 113.5, 55.22, 55.17. IR: 3024, 2995, 2950, 2931,
2904, 2833, 1604, 1570, 1544, 1504, 1462, 1441, 1412, 1317, 1304,
1290, 1273, 1248, 1176, 1137, 1108, 1032, 969, 960, 939, 912, 837,
817, 810, 798, 789, 772, 732, 689, 657, 623, 613, 605, 586, 572, 555,
539, 522, 438 cm−1. HRMS (EI): calcd for C34H30O4S m/z 534.1865
(M+), found m/z 534.1867.
Preparation of 3a′. To a solution of 2,5-dibromothiophene (1.0
mL, 8.85 mmol) in dry THF (100 mL) was added n-butyllithium (1.60
M in hexane, 12.0 mL, 19.2 mmol) at −78 °C. The mixture was stirred
at this temperature for 60 min. Benzophenone (3.55 g, 19.5 mmol)
was then added in one portion. The mixture was allowed to gradually
warm to room temperature and stirred for 19 h. The reaction was
quenched by the addition of a saturated aqueous solution of NH4Cl.
The mixture was extracted with CH2Cl2. The combined organic layer
was washed with brine and dried over MgSO4. The crude product was
recrystallized from ethanol to give 3a′ (2.05 g, 46%) as a white solid.
1
Mp: 100−102 °C. H NMR (400 MHz, CDCl3): δ 7.52−7.47 (m,
8H), 7.31−7.19 (m, 12H), 6.76 (s, 2H), 3.23 (q, J = 6.9 Hz, 4H), 1.21
(t, J = 6.9 Hz, 6H). 13C NMR (100 MHz, CDCl3): δ 148.9, 144.6,
127.9, 127.7, 127.1, 84.6, 59.8, 15.3. IR: 3085, 3056, 3023, 2970, 2921,
2884, 1597, 1490, 1444, 1389, 1315, 1226, 1212, 1176, 1155, 1138,
1114, 1067, 1031, 1003, 943, 920, 868, 803, 770, 754, 742, 701, 678,
646, 491 cm−1. HRMS (EI): calcd for C34H32O2S m/z 504.2123 (M+),
found m/z 504.2123.
Preparation of 3b. To a mixture of 2,5-dibromothiophene (1.0 mL,
8.85 mmol) in dry THF (100 mL) was added n-BuLi (1.60 M in
hexane, 12.0 mmol, 19.2 mmol) at −78 °C. After the mixture was
stirred for 50 min at this temperature, 4,4′-dimethoxybenzophene
(4.71 g, 19.4 mmol) was added. The mixture was allowed to gradually
warm to room temperature and stirred for 17 h. After the addition of a
saturated aqueous solution of NH4Cl, the mixture was extracted with
CH2Cl2. The combined organic layer was washed with brine and dried
over Na2SO4. The crude product was subjected to silica gel column
chromatography (CHCl3/AcOEt = 100/3) to give 3b (2.70 g, 54%) as
a pale red solid. Mp: 78−79 °C. 1H NMR (400 MHz, CDCl3): δ 7.26
(d, J = 8.9 Hz, 8H), 6.82 (d, J = 8.9 Hz, 8H), 6.52 (s, 2H), 3.79 (s,
12H), 2.76 (s, 2H). 13C NMR (125 MHz, CDCl3): δ 158.9, 152.6,
138.9, 128.5, 125.9, 113.2, 79.6, 55.3. IR: 3471, 3000, 2953, 2933,
2905, 2835, 1608, 1583, 1509, 1463, 1442, 1414, 1302, 1251, 1175,
1112, 1033, 909, 826, 792, 605, 575 cm−1. HRMS (EI): calcd for
C34H32O6S m/z 568.1920 (M+), found m/z 568.1920.
Preparation of 1c. To a mixture of 3c (503 mg, 858 μmol) in
1,1,1,3,3,3-hexafluoro-2-propanol (10 mL) was added TMSClO4 in
toluene (0.74 M, 4.0 mL, 2.96 mmol). After the mixture was stirred for
6 h at room temperature, the volatile solvent and reagent were
removed by evaporation. The obtained dicationic species was dissolved
in dry MeCN (20 mL), and Zn powder (3.35 g, 51.2 mmol) was
added. The mixture was stirred for 22 h, diluted with CH2Cl2, and
filtered on a Celite pad. The solvent of the filtrate was evaporated and
then suspended with a small amount of CH2Cl2. The insoluble solid
was collected by filtration followed by washing with CH2Cl2 to give 1c
(240 mg) as a yellow solid. The filtrate was subjected to silica gel
column chromatography to give additional 1c (228 mg). The total
yield was 99%. Mp: 173−174 °C dec. 1H NMR (400 MHz, CDCl3): δ
7.32 (d, J = 8.6 Hz, 4H), 7.28 (br d, 8H), 7.14 (d, J = 8.6 Hz, 4H),
6.81 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 142.9, 140.0, 139.5,
133.9, 133.58, 13.55, 131.64, 130.9, 129.9, 129.7, 128.6. IR: 1587,
1487, 1398, 1173, 1140, 1091, 1015, 912, 850, 832, 817, 797, 726, 711,
650, 612, 567, 525, 491, 438 cm−1. HRMS (EI): calcd for C30H18Cl4S
m/z 549.9883 (M+), found m/z 549.9880.
Preparation of 3c. To a solution of 2,5-dibromothiophene (1.0 mL,
8.85 mmol) in dry THF (100 mL) was added n-BuLi (1.63 M in
hexane, 11.8 mL, 19.2 mmol) at −78 °C. After the mixture was stirred
for 45 min at this temperature, 4,4′-dichlorobenzophenone (4.87 g,
19.4 mmol) was added. The mixture was allowed to gradually warm to
room temperature and stirred for 18.5 h. After the addition of a
saturated aqueous solution of NH4Cl, the mixture was extracted with
CH2Cl2. The combined organic layer was washed with brine and dried
over Na2SO4. The crude product was subjected to silica gel column
chromatography (hexane/CH2Cl2 = 3/1 → 0/1) to give 3c (3.14 g,
Preparation of 4a. To a solution of 2,5-dibromothieno[3,2-
b]thiophene (2.50 g, 8.39 mmol) in dry THF (80 mL) was added
n-BuLi (1.55 M, 11.4 mL, 17.6 mmol) at −78 °C. After the mixture
was stirred at this temperature for 40 min, benzophenone (3.38 g, 18.5
mmol) was added. The mixture was allowed to gradually warm to
room temperature and stirred overnight. After the addition of a
saturated aqueous solution of NH4Cl, the mixture was extracted with
CH2Cl2. The combined organic layer was washed with brine and dried
over Na2SO4. The crude product was suspended with a small amount
of CHCl3, and the insoluble solid was collected by filtration to give 4a
1
61%) as a pale orange solid. Mp: 79−80 °C. H NMR (400 MHz,
CDCl3): δ 7.29 (s, 16H), 6.56 (s, 2H), 2.83 (s, 2H). 13C NMR (100
MHz, CDCl3): δ 151.7, 144.2, 133.9, 128.5, 128.3, 126.5, 79.3. IR:
3561, 3452, 3069, 1592, 1575, 1489, 1400, 1316, 1227, 1180, 1137,
1093, 1013, 909, 811, 530, 507 cm−1. HRMS (EI): calcd for
C30H20Cl4O2S m/z 583.9938 (M+), found m/z 583.9937.
1
(2.34 g, 55%) as a white solid. Mp: 218−220 °C dec. H NMR (400
MHz, CDCl3): δ 7.42−7.37 (m, 8H), 7.36−7.29 (m, 12H), 3.00 (s,
2H). 13C NMR (100 MHz, CDCl3): δ 154.0, 146.0, 138.3, 128.1,
127.3, 119.6, 80.6. IR: 3583, 3561, 3082, 3057, 3024, 1598, 1582,
1490, 1446, 1394, 1331, 1317, 1283, 1205, 1188, 1174, 1158, 1123,
1081, 1032, 1009, 925, 896, 838, 816, 769, 750, 701, 681, 657, 645,
586, 552, 511, 470, 406 cm−1. HRMS (EI): calcd for C32H24O2S2 m/z
504.1218 (M+), found m/z 504.1221.
Preparation of 1a. To a mixture of 3a′ (496 mg, 983 μmol) in
1,1,1,3,3,3-hexafluoro-2-propanol (10 mL) was added TMSClO4 in
toluene (0.74 M, 7.0 mL, 5.18 mmol). After the mixture was stirred for
2.5 h at room temperature, the volatile solvent and reagent were
removed by evaporation. The obtained dicationic species was dissolved
in dry MeCN (15 mL), and Zn powder (2.38 g, 36.4 mmol) was
added. The mixture was stirred for 24 h, diluted with CH2Cl2, and
filtered on a Celite pad. The filtrate was washed with brine and dried
over Na2SO4. The crude product was subjected to silica gel column
chromatography (hexane/CH2Cl2 = 1/3) to give 1a (373 mg, 92%) as
Preparation of 4b. To a solution of 2,5-dibromothieno[3,2-
b]thiophene (1.99 g, 6.68 mmol) in dry THF (60 mL) was added
n-BuLi (1.60 M, 8.8 mL, 14.1 mmol) at −78 °C. After the mixture was
stirred at this temperature for 60 min, 4,4′-dimethoxybenzophenone
(3.56 g, 14.7 mmol) was added. The mixture was allowed to gradually
warm to room temperature and stirred for 17 h. After the addition of a
saturated aqueous solution of NH4Cl, the mixture was extracted with
CH2Cl2. The combined organic layer was washed with brine and dried
over Na2SO4. The crude product was suspended with a small amount
of CH2Cl2, and the insoluble solid was collected by filtration to give 4b
(1.90 g) as a pale red solid. The filtrate was subjected to silica gel
column chromatography (CH2Cl2/AcOEt = 95/5) to give additional
1
a yellow solid. Mp: 199−200 °C. H NMR (400 MHz, CDCl3): δ
7.40−7.20 (m, 20H), 6.83 (s, 2H). 13C NMR (100 MHz, CDCl3): δ
142.4, 142.2, 141.7, 133.7, 131.8, 130.5, 129.6, 128.3, 128.2, 127.4,
127.2. IR: 3049, 3027, 1594, 1572, 1537, 1489, 1440, 1170, 1155,
1139, 1072, 1029, 999, 967, 924, 903, 856, 836, 824, 800, 789, 768,
757, 694, 662, 645, 624, 612, 573, 518, 420 cm−1. HRMS (EI): calcd
for C30H22S m/z 414.1442 (M+), found m/z 414.1442.
1
4b (414 mg). The total yield was 55%. Mp: 225−227 °C dec. H
E
DOI: 10.1021/acs.joc.5b00021
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
NMR (400 MHz, CDCl3): δ 7.29 (d, J = 8.9 Hz, 8H), 6.85 (d, J = 8.9,
8H), 6.78 (s, 2H), 3.80 (s, 12H), 2.88 (s, 2H). 13C NMR (100 MHz,
CDCl3): δ 159.0, 154.7, 138.5, 138.2, 128.6, 119.3, 113.3, 80.0, 55.3.
IR: 3491, 3002, 2956, 2934, 2906, 2836, 1608, 1584, 1509, 1461, 1441,
1414, 1331, 1298, 1253, 1177, 1111, 1032, 909, 832, 811, 781, 608,
579 cm−1. HRMS (EI): calcd for C36H32O6S2 m/z 624.1640 (M+),
found m/z 624.1641.
then suspended with a small amount of CH2Cl2. The insoluble solid
was collected by filtration followed by washing with CH2Cl2 to give 2c
1
(436 mg, 100%) as a red solid. Mp: 176−178 °C dec. H NMR (400
MHz, CD2Cl2): δ 7.37−7.30 (m, 12H), 7.19 (d, J = 8.2 Hz, 4H), 6.53
(s, 2H). 13C NMR could not be measured because of the low solubility
of 2c. IR: 1518, 1486, 1396, 1182, 1139, 1109, 1092, 1011, 961, 942,
924, 903, 826, 790, 708, 691, 648, 636, 627, 621, 524, 519, 473, 457,
414, 401 cm−1. HRMS (EI): calcd for C32H18Cl4S2 m/z 605.9604
(M+), found m/z 605.9603.
Preparation of 4c. To a solution of 2,5-dibromothieno[3,2-
b]thiophene (2.50 g, 8.39 mmol) in dry THF (100 mL) was added
n-BuLi (1.63 M, 10.8 mL, 17.6 mmol) at −78 °C. After the mixture
was stirred at this temperature for 40 min, 4,4′-dichlorobenzophenone
(4.75 g, 18.7 mmol) was added. The mixture was allowed to gradually
warm to room temperature and stirred for 18.5 h. After the addition of
a saturated aqueous solution of NH4Cl, the mixture was extracted with
CH2Cl2. The combined organic layer was washed with brine and dried
over Na2SO4. The crude product was subjected to silica gel column
chromatography (CH2Cl2) to give 4c (2.42 g, 43%) as a pale gray
ASSOCIATED CONTENT
* Supporting Information
■
S
Selected bond lengths and torsion angles in the optimized
structures of 1, 12+, 2 and 22+ determined by X-ray analyses and
DFT calculations, ORTEP drawings of 1a, 1b, 2a, and 2b,
photo of the fluorescence of 1a−c in the solid state, 1H and 13
C
1
solid. Mp: 135−137 °C. H NMR (400 MHz, CDCl3): δ 7.32 (br d,
NMR spectra of compounds 1−4, Cartesian coordinates for
optimized structures, and CIF files of 1a, 1b, 2a, and 2b. This
material is available free of charge via the Internet at http://
pubs.acs.org.
16H), 6.81 (s, 2H), 3.00 (s, 2H). 13C NMR (100 MHz, CDCl3): δ
153.5, 144.0, 138.5, 134.1, 128.7, 128.4, 119.7, 79.8. IR: 3560, 3441,
3083, 1592, 1575, 1489, 1400, 1336, 1318, 1179, 1123, 1094, 1014,
908, 827, 796, 738, 563, 528, 503, 465 cm−1. HRMS (EI): calcd for
C32H20Cl4O2S2 m/z 639.9659 (M+), found m/z 639.9659.
AUTHOR INFORMATION
Corresponding Author
*E-mail: takeda@tagen.tohoku.ac.jp.
Preparation of 2a. To a mixture of 4a (547 mg, 1.08 mmol) in
1,1,1,3,3,3-hexafluoro-2-propanol (10 mL) was added TMSClO4 in
toluene (0.74 M, 7.0 mL, 5.18 mmol). After the mixture was stirred for
2.5 h at room temperature, the volatile solvent and reagent were
removed by evaporation. The obtained dicationic species was dissolved
in dry MeCN (15 mL), and Zn powder (2.56 g, 39.1 mmol) was
added. The mixture was stirred for 24.5 h. After dilution with CH2Cl2,
the suspension was filtered. The filtrate was washed with brine and
dried over Na2SO4. The solvent was evaporated and then suspended
with a small amount of CH2Cl2. The insoluble solid was collected by
filtration followed by washing with CH2Cl2 to give 2a (266 mg) as a
red solid. The filtrate was subjected to silica gel column
chromatography (hexane/CH2Cl2 = 1/3) to give additional 2a (98
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by JSPS KAKENHI Grant Number
26410034.
■
REFERENCES
■
1
(1) (a) Charlton, J. L.; Alauddin, M. M. Tetrahedron 1987, 43, 2873−
2889. (b) Segura, J. L.; Martin, N. Chem. Rev. 1999, 99, 3199−3246.
(c) Yoshida, H.; Ohshita, J.; Kunai, A. Bull. Chem. Soc. Jpn. 2010, 83,
199−219.
mg). The total yield was 71%. Mp: 257−259 °C dec. H NMR (400
MHz, CDCl3): δ 7.41−7.25 (m, 20H), 6.53 (s, 2H). 13C NMR could
not be measured because of the low solubility of 2a. IR: 3052, 3026,
1594, 1526, 1489, 1440, 1175, 1154, 1137, 1076, 1029, 1001, 931, 899,
811, 767, 748, 701, 666, 650, 634, 617, 586, 502, 447 cm−1. HRMS
(EI): calcd for C32H22S2 m/z 470.1163 (M+), found m/z 470.1165.
Preparation of 2b. To a mixture of 4b (592 mg, 947 μmol) in
1,1,1,3,3,3-hexafluoro-2-propanol (10 mL) was added TMSClO4 in
toluene (0.74 M, 4.0 mL, 2.96 mmol). After the mixture was stirred for
13.5 h at room temperature, the volatile solvent and reagent were
removed by evaporation. The obtained dicationic species was dissolved
in dry MeCN (20 mL), and Zn powder (1.39 g, 21.3 mmol) was
added. The mixture was stirred for 10.5 h. After dilution with CH2Cl2,
the suspension was filtered. The filtrate was washed with brine and
dried over Na2SO4. The crude product was subjected to silica gel
column chromatography (hexane/CH2Cl2 = 1/4) to give 2b (461 mg,
(2) (a) Shimizu, A.; Kishi, R.; Nakano, M.; Shiomi, D.; Sato, K.;
Takui, T.; Hisaki, I.; Miyata, M.; Tobe, Y. Angew. Chem., Int. Ed. 2013,
52, 6076−6079. See also: (b) Shimizu, A.; Tobe, Y. Angew. Chem., Int.
Ed. 2011, 50, 6906−6910. (c) Chase, D. T.; Rose, B. D.; McClintock,
S. P.; Zakharov, L. N.; Haley, M. M. Angew. Chem., Int. Ed. 2011, 50,
1127−1130.
(3) (a) McCullough, R. D. Adv. Mater. (Weinheim, Ger.) 1998, 10,
93−116. (b) Fichou, D., Ed. Handbook of Oligo- and Polythiophenes;
Wiley-VCH: Weinheim, Germany, 1998. (c) Osaka, I.; McCullough,
R. D. Acc. Chem. Res. 2008, 41, 1202−1214. (d) Perepichka, I. F.,
Perepichka, D. F., Eds. Handbook of Thiophene-Based Materials; John
Wiley & Sons: Chichester, U.K., 2009.
1
(4) Review: Marrocchi, A.; Lanari, D.; Facchetti, A.; Vaccaro, L.
Energy Environ. Sci. 2012, 5, 8457−8474.
85%) as a red solid. Mp: 282−283 °C dec. H NMR (500 MHz,
CD2Cl2): δ 7.30 (d, J = 8.8 Hz, 4H), 7.17 (d, J = 8.8 Hz, 4H), 6.88 (d,
J = 8.8 Hz, 4H), 6.87 (d, J = 8.8 Hz, 4H), 6.50 (s, 2H), 3.81 (s, 12H).
13C NMR (125 MHz, CD2Cl2): δ 159.8, 150.3, 145.0, 135.5, 135.0,
132.2, 131.8, 130.8, 117.0, 114.3, 55.9. IR: 1603, 1569, 1526, 1503,
1457, 1440, 1412, 1318, 1304, 1293, 1277, 1241, 1175, 1137, 1110,
1035, 1023, 964, 942, 923, 904, 834, 820, 809, 781, 765, 731, 715, 662,
630, 619, 595, 555, 533, 496, 471, 423 cm−1. HRMS (EI): calcd for
C36H30O4S2 m/z 590.1585 (M+), found m/z 590.1588.
(5) (a) Kosa
̌ ́ ́
ta, B.; Kozmik, V.; Svoboda, J.; Novotana, V.; Vanak, P.;
Glogarva,
́
M. Liq. Cryst. 2003, 30, 603−610. (b) Takimiya, K.; Osaka,
I.; Mori, T.; Nakano, M. Acc. Chem. Res. 2014, 47, 1493−1502.
(c) Takimiya, K.; Ebata, H.; Sakamoto, K.; Izawa, T.; Otsubo, T.;
Kunugi, Y. J. Am. Chem. Soc. 2006, 128, 12604−12605. (d) Ebata, H.;
Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T.
J. Am. Chem. Soc. 2007, 129, 15732−15733. (e) Izawa, T.; Miyazaki,
E.; Takimiya, K. Adv. Mater. (Weinheim, Ger.) 2008, 20, 3388−3392.
(6) (a) Bao, Z.; Dodabalapur, A.; Lovinger, A. J. Appl. Phys. Lett.
1996, 69, 4108−4110. Review: (b) Wang, C.; Dong, H.; Hu, W.; Liu,
Y.; Zhu, D. Chem. Rev. 2012, 112, 2208−2267. (c) Zaumseil, J.;
Sirringhaus, H. Chem. Rev. 2007, 107, 1296−1323.
Preparation of 2c. To a mixture of 4c (509 mg, 792 μmol) in
1,1,1,3,3,3-hexafluoro-2-propanol (10 mL) was added TMSClO4 in
toluene (0.74 M, 4.0 mL, 2.96 mmol). After the mixture was stirred for
6.5 h at room temperature, the volatile solvent and reagent were
removed by evaporation. The obtained dicationic species was dissolved
in dry MeCN (20 mL), and Zn powder (5.21 g, 79.7 mmol) was
added. The mixture was stirred for 10.5 h. After dilution with CH2Cl2,
the suspension was filtered. The filtrate was washed with brine and
then dried over Na2SO4. The solvent of the filtrate was evaporated and
(7) Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery, K.;
Yang, Y. Nat. Mater. 2005, 4, 864−868.
(8) Izumi, T.; Kobashi, S.; Takimiya, K.; Aso, Y.; Otsubo, T. J. Am.
Chem. Soc. 2003, 125, 5286−5287.
F
DOI: 10.1021/acs.joc.5b00021
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
(9) (a) Yui, K.; Aso, Y.; Otsubo, T.; Ogura, F. J. Chem. Soc., Chem.
Commun. 1987, 1816−1817. (b) Yui, K.; Aso, Y.; Otsubo, T.; Ogura,
F. Bull. Chem. Soc. Jpn. 1989, 62, 1539−1546.
(10) Higuchi, H.; Nakayama, T.; Koyama, H.; Ojima, J.; Wada, T.;
Sasabe, H. Bull. Chem. Soc. Jpn. 1995, 68, 2363−2377.
(11) (a) Pappenfus, T. M.; Chesterfield, R. J.; Frisbie, C. D.; Mann,
K. R.; Casado, J.; Raff, J. D.; Miller, L. L. J. Am. Chem. Soc. 2002, 124,
4184−4185. (b) Pappenfus, T. M.; Raff, J. D.; Hukkanen, E. J.;
Burney, J. R.; Casado, J.; Drew, S. M.; Miller, L. L.; Mann, K. R. J. Org.
Chem. 2002, 67, 6015−6024. (c) Chesterfield, R. J.; Newman, C. R.;
Pappenfus, T. M.; Ewbank, P. C.; Haukaas, M. H.; Mann, K. R.; Miller,
L. L.; Frisbie, C. D. Adv. Mater. (Weinheim, Ger.) 2003, 15, 1278−
1282.
(12) Takahashi, T.; Matsuoka, K.; Takimiya, K.; Otsubo, T.; Aso, Y. J.
Am. Chem. Soc. 2005, 127, 8928−8929.
(13) (a) Yui, K.; Ishida, H.; Aso, Y.; Otsubo, T.; Ogura, F.;
Kawamoto, A.; Tanaka, J. Bull. Chem. Soc. Jpn. 1989, 62, 1547−1555.
(b) Yui, K.; Ishida, H.; Aso, Y.; Otsubo, T.; Ogura, F. Chem. Lett. 1987,
16, 2339−2342.
(14) (a) Hieber, G.; Hanack, M.; Wurst, K.; Strahle, J. Chem. Ber.
̈
1991, 124, 1597−1605. (b) Ishii, A.; Horikawa, Y.; Takaki, I.; Shibata,
J.; Nakayama, J.; Hoshino, M. Tetrahedron Lett. 1991, 32, 4313−4316.
(c) Mazaki, Y.; Murata, S.; Kobayashi, K. Tetrahedron Lett. 1991, 32,
4367−4370.
(15) Kawase, T.; Ueno, N.; Oda, M. Tetrahedron Lett. 1992, 33,
5405−5408.
(16) (a) Saitoh, T.; Yoshida, S.; Ichikawa, J. Org. Lett. 2004, 6, 4563−
4565. (b) Saitoh, T.; Yoshida, S.; Ichikawa, J. J. Org. Chem. 2006, 71,
6414−6419.
(17) Review on electrochromism: (a) Monk, P. M. S.; Mortimer, R.
J.; Rosseinsky, D. R. Electrochromism: Fundamentals and Applications;
John Wiley & Sons: Weinheim, Germany, 2008. (b) Monk, P.;
Mortimer, R.; Rosseinsky, D. Electrochromism and Electrochromic
Devices; Cambridge University Press: Cambridge, U.K., 2007.
(c) Suzuki, T.; Ohta, E.; Kawai, H.; Fujiwara, K.; Fukushima, T.
Synlett 2007, 851−869.
(18) (a) Hunig, S.; Kemmer, M.; Wenner, H.; Perepichka, I. F.;
̈
Bauerle, P.; Emge, A.; Gescheid, G. Chem.Eur. J. 1999, 5, 1969−
̈
1973. (b) Hunig, S.; Kemmer, M.; Wenner, H.; Barbosa, F.; Gescheidt,
̈
G.; Perepichka, I. F.; Bauerle, P.; Emge, A.; Peters, K. Chem.Eur. J.
̈
2000, 6, 2618−2632. (c) Suzuki, T.; Nishida, J.; Tsuji, T. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1329−1331. (d) Higuchi, H.; Ohta, E.;
Kawai, H.; Fujiwara, K.; Suzuki, T. J. Org. Chem. 2003, 68, 6605−6610.
(e) Ohta, E.; Higuchi, H.; Kawai, H.; Fujiwara, K.; Suzuki, T. Org.
Biomol. Chem. 2005, 3, 3024−3031. (f) Suzuki, T.; Sakano, Y.; Iwai,
T.; Iwashita, S.; Miura, Y.; Katoono, R.; Kawai, H.; Fujiwara, K.; Tsuji,
Y.; Fukushima, T. Chem.Eur. J. 2013, 19, 117−123. (g) Ohta, A.;
Ueki, C.; Uchiyama, Y.; Fujimori, K. Heterocycles 2006, 69, 365−375.
(h) Ohtake, T.; Tanaka, H.; Matsumoto, T.; Kimura, M.; Ohta, A. J.
Org. Chem. 2014, 79, 6590−6602.
(19) (a) Ishigaki, Y.; Kawai, H.; Katoono, R.; Fujiwara, K.; Suzuki, T.
Heterocycles 2015, 90, 136−143. (b) Suzuki, T.; Hoshiyama, Y.; Wada,
K.; Ishigaki, Y.; Miura, Y.; Kawai, H.; Katoono, R.; Fujiwara, K.;
Fukushima, T. Chem. Lett. 2013, 42, 1004−1006.
(20) (a) Kamada, K.; Fuku-en, S.; Minamide, S.; Ohta, K.; Kishi, R.;
Nakano, M.; Matsuzaki, H.; Okamoto, H.; Higashikawa, H.; Inoue, K.;
et al. J. Am. Chem. Soc. 2013, 135, 232−241. (b) Takeda, T.; Sugihara,
H.; Suzuki, Y.; Kawamata, J.; Akutagawa, T. J. Org. Chem. 2014, 79,
9669−9677.
(21) Sheldrick, G. M. Acta Crystallogr. 2008, 64A, 112−122.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; et al. Gaussian 09, revision C 01; Gaussian, Inc.:
Wallingford, CT, 2009.
G
DOI: 10.1021/acs.joc.5b00021
J. Org. Chem. XXXX, XXX, XXX−XXX