α,α′-N-boc-substituted Bi- and terthiophenes: Fluorescent precursors for functional materials

Article abstract of DOI:10.1021/jo300687d

Fluorescent α,α′-diamide substituted bi- and terthiophene derivatives were prepared by Stille and Suzuki couplings. Their one-pot deprotection and coupling with 2-thiophene carboxaldehyde led to stable conjugated azomethines. These exhibited electrochromic properties, and they were used to fabricate a working electrochromic device.

Full text of DOI:10.1021/jo300687d

Note
pubs.acs.org/joc
α,α′-N-Boc-Substituted Bi- and Terthiophenes: Fluorescent
Precursors for Functional Materials
Yanmei Dong, Daminda Navarathne, Andreanne Bolduc, Nicholas McGregor,† and W. G. Skene*
́
Laboratoire de Caracter
́
isation Photophysique des Mater
́ ́
iaux Conjugues, Department of Chemistry, Pavillon JA Bombardier,
Universite de Montreal, CP 6128, succ. Centre-ville, Montreal, Quebec H3C 3J6, Canada
́
́
S
* Supporting Information
ABSTRACT: Fluorescent α,α′-diamide substituted bi- and terthiophene derivatives were prepared by Stille and Suzuki
couplings. Their one-pot deprotection and coupling with 2-thiophene carboxaldehyde led to stable conjugated azomethines.
These exhibited electrochromic properties, and they were used to fabricate a working electrochromic device.
2-Aminothiophenes have successfully been used in a wide range
of fields, including medicinal chemistry as pharmaceutically
active compounds1−4 and as precursors for conjugated
azomethines for use in plastic electronics such as electro-
chromic devices and emitting applications.5−8 The preparation
of 4- and 5-substituted 2-aminothiophenes is typically done via
the Gewald reaction involving α-methylene carbonyl thio-
phenes.9,10 However, 2-aminobithiophenes and higher ordered
oligomeric derivatives such as 3−5 are not possible with this
strategy. This is a result of the instability of the required
corresponding α-methylene carbonyl thiophenes for synthesiz-
ing such derivatives. As a consequence, there are no reports for
the double Gewald reaction for the preparation of α,α′-
diaminooligothiophenes. In fact, such stable compounds
consisting of primary, secondary, or even Boc-protected
amino derivatives have not been reported.
Alternate approaches to the Gewald reaction for preparing
α,α′-diaminoterthiophenes are Suzuki and Stille couplings
involving a 2-amino-5-bromothiophene derivative.11,12 While
Suzuki coupling has been applied to prepare a limited number
of 2-amino-5-arylthiophene derivatives,13−23 there is only one
reported example of a 2-aminobithiophene derivative (1, Figure
Figure 1. α,α′-N-Boc-substituted bi- and terthiophenes prepared and
representative analogues.
1) prepared via this method.24 Interestingly, neither Suzuki nor
Stille couplings have been applied for obtaining α,α′-diamino
bi- or terthiophenes derivatives. Such oligothiophene deriva-
tives are interesting because they are expected to possess high
fluorescence quantum yields (Φfl). This is because comple-
mentary electronic substituents incorporated in the α,α′-
positions (2x) are known to suppress excited-state deactivation
by intersystem crossing (ISC) in bithiophenes.25,26 The
additional advantage of 2-aminothiophene derivatives is that
the primary amine can be further reacted. This provides the
means to both tailor the fluorescence wavelength and prepare
conjugated azomethines for use as functional materials by
condensing with aryl aldehydes.5,6,8,25
Given the high Φfl expected from α,α′-diamino bi- and
terthiophenes in addition to being desired precursors for
functional materials synthesis, we were incited to prepare 3−5.
Received: April 6, 2012
Published: May 18, 2012
© 2012 American Chemical Society
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Note
We were further motivated to prepare such derivatives to
demonstrate that both Stille and Suzuki coupling protocols can
be used for preparing amino end-capped bi- and terthiophenes.
Such derivatives are of importance not only as fluorescence
sensors, but also for pharmaceutical and plastic electronics
applications. Therefore, the successful preparation of α,α′-
diamino bi- and terthiophene derivatives provides an alternate
means of preparing new materials that are otherwise not
possible due to the limited stability of the precursors required
for the Gewald reaction. The preparation of the conjugated
thiophenes 3−5 are herein presented in addition to their
fluorescence quantum yields. Their use as precursors for
functional materials is further demonstrated by preparing
azomethine conjugated materials. To confirm the use of the
azomethines for use in plastic electronics, the optoelectronic
characterization and electrochromic device fabricated from 7
are also presented.
The 2-amino-5-bromo derivative 10 is the required precursor
for undertaking the targeted Stille and Suzuki couplings for
preparing 3−5. In turn, 10 was prepared from the 2-
aminothiophene 9. The starting synthon (8) was prepared in
64% yield by the base-catalyzed Gewald reaction with 1,4-
dithiane-2,5-diol and ethylcyano acetate.26 The resulting
primary amine was subsequently protected with tert-butyl
carbamate anhydride using standard conditions with catalytic
DMAP to afford 9 in 65% yield (Scheme 1). N-Protection was
palladium.27 Unlike with the Suzuki coupling, no homocoupled
product was observed with the Stille coupling.
While cleavage of the Boc group is normally quantitative
under acid conditions, 3−5 were found to resist weak acidic
conditions (1−12 M HCl in ethanol) at both room
temperature and elevated temperature. Meanwhile, strong
acids (TFA and HBr in dichloromethane) resulted in their
decomposition. Decomposition of 3−5 was also observed with
other known deprotecting reagents such as AlCl3, TsOH, and
Bu4NF. This was unexpected since removal of the of N-Boc
protecting group of 2-aminothiophenes that are substituted
with electron-withdrawing groups in the 3-position occurs with
standard deprotecting conditions without decomposition. In
fact, such 2-aminothiophene derivatives are extremely stable,
and they can be handled under ambient conditions without
special precautions.26,28,29 The reactive intermediate could,
however, immediately be trapped with 2-thiophenecarboxalde-
hyde leading to air-stable conjugated azomethine products.
Product formation (6 and 7) was possible in one-pot by
cleaving the Boc group with TFA at room temperature in the
presence of an excess of 2-thiophenecarboxaldehyde (Scheme
1). Despite using an excess of the aldehyde, a mixture of both
mono- (20%) and biscoupled (65%) products was obtained.
The fluorescence of 3−5 was investigated owing to their
expected high fluorescence quantum yield. The fluorescence
quantum yields of 3−7 were measured with an integrating
sphere, which allowed the calculation of absolute Φfl. As seen in
Table 1, 4−5 fluoresced with near-quantitative yields (Table 1,
Scheme 1. Synthetic Scheme for the Preparation of 3−7
Table 1. Photophysical and Electrochemical Data of 3−7
b
c
c
a
a
compd
λabs (nm)
λem (nm)
Φfl
Epa (V)
Epc (V)
3
4
5
6
7
297
424
451
458
485
610
0.31
0.93
1.05
−1.14
−1.25
−1.14
−1.15
−1.31
387
0.86
400
0.87
0.77, 1.03
0.44, 0.64
0.89
412, 485sh
500
0.02
<0.01
a
b
Measured in deaerated dichloromethane. Absolute quantum yield.
c
Relative to Ag/Ag+ with ferrocene as an internal standard (Epa = 453
mV).
inset Figure 2), compared to their unsubstituted terthiophene
counterpart, whose Φfl = 0.06.30 Meanwhile, the Φfl of 3 is less
than 4 and 5. However, it is exceptionally high compared to its
unsubstituted counterparts such as bithiophene (Φfl = 0.018)31
and 2a (Φfl = 0.06).26 The fluorescence data suggest that
fluorescent bi- and terthiophenes are possible by incorporating
electronic groups in the α,α′-positions, which suppress the
otherwise efficient fluorescence quenching by intersystem
crossing (ISC).
Cryofluorescence was further done to provide insight into
the different Φfl of 3 relative to 4 and 5. Variable-temperature
fluorescence was also used to probe the quenched fluorescence
of 6 and 7. Given that ISC is an intrinsic property, it is
temperature independent. Therefore, any temperature-depend-
ent fluorescence changes would confirm fluorescence deactiva-
tion by molecular dynamics. As seen in Figure 2, the
fluorescence of 3 increases with decreasing temperature.
Correcting for the solvent refractive index change at different
temperatures, the Φfl of 3 increased to 0.5 at 180 K. This
provides evidence that deactivation of the singlet excited state
occurs predominately by rotation around the aryl−aryl bond
and not by ISC. This is further supported by extrapolating the
required for obtaining a stable 5-brominated derivative.
Otherwise, the unprotected 2-bromo-5-aminothiophene deriv-
ative spontaneously polymerizes at room temperature. From
the N-Boc-protected 9, the bromo derivative 10 was obtained
in 87%, which was stable under ambient conditions for
extended periods of time. The heterocoupled product 4 was
obtained in 57% yield by reacting 10 with 2,5-thiophene
bisboronic acid via Suzuki coupling with tetrakis-
(triphenylphosphine)palladium. The homocoupled product 3
was also obtained as a side product from the heterocoupling
reaction, and it was isolated in 41% yield. Compound 5 was
prepared in 59% yield via Stille coupling between 10 and
bis(tributylstannyl)-EDOT with tetrakis(triphenylphosphine)-
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Figure 2. Cryofluorescence of 3 between 298 (red line) and 180 K
(black line) in dichloromethane. Inset: photographs showing the
fluorescence of 3−7 (from left to right) when excited with an UV
lamp.
Figure 3. CIE L*a*b* color coordinates of the electrochromic device
of 7 in the oxidized and neutral states. Photographs of the neutral (top
right) and oxidized (lower right) states of the device. Top left:
spectroelectrochemistry of 7 by applying a potential of 1 V for 0 (black
line), 1 (red line), 2 (deep red line), 4 (green line), and 8 (blue line)
and 10 min (orange line). Lower left: photographs showing the
reversible color change of 7 at the platinum mesh electrode when
oxidized (right) and neutralized (left).
cryofluorescence to reduced temperatures (Figure S24,
Supporting Information), where Φfl ≈ 1 was calculated. The
fluorescence measurements were done at low concentrations to
ensure no bimolecular quenching. In contrast, the fluorescence
of 6 and 7 is quenched at room temperature. This is a result of
the azomethine linkage, which is a known efficient excited-state
deactivator.26,32−36 While the fluorescence of 7 increased by ca.
80 times at 77 K, the fluorescence of 6 increased to only 9% at
reduced temperature. The fluorescence of 7 is therefore most
likely quenched by molecular dynamics, while 6 is deactivated
by other means.33,34,37
neutral 7 decreases upon applying a potential of 1 V. A new
absorbance occurs at 635 nm, corresponding to the radical
cation. This simultaneously occurs with the disappearance of
the absorbance at 500 nm. The resulting reversible color
transitions between the neutral (orange) and oxidized states
(blue) are shown in the lower left panel of Figure 3. Similarly, 6
could also be reversibly oxidized with the formation of a green
color corresponding to an absorbance at 625 nm (see the
Supporting Information).
The oxidation potentials (Epa) were measured by cyclic
voltammetry. The effect of the degree of conjugation and the
EDOT moiety on the Epa is apparent from the cyclic
voltammograms (Figure S25, Supporting Information). For
example, 4 is shifted by 200 mV to less positive potentials
relative to 3, courtesy of its higher degree of conjugation.
Similarly, 5 is shifted by 100 mV to less positive potential
relative to 4, owing to the strong electron donating EDOT
moiety. The Epa for 3−7 are all above 500 mV vs Ag/Ag+,
confirming their stability under ambient conditions. This is in
part due to the electron withdrawing ester groups that increase
the Epa. This is evident when comparing the Epa of α,α′-di(N,N-
diphenyl)bi- and terthiophene whose Epa is ca. 300 mV vs Ag/
Ag+.38 The lowest Epa of the series examined was of 6, as a
result of the electronic push−pull effect of the terminal donating
amine and the withdrawing azomethine. Meanwhile, the two
azomethine bonds of 7 increase the Epa such that it is 450 mV
more positive than 6. Interestingly, the one-electron oxidation
process for the diaminothiophenes was reversible only for 5 and
6. This is in contrast to 3, 4, and 7, whose oxidations are
irreversible. This most likely is a result of radical cation
coupling at the unsubstituted positions on the bithiophenes.
Conjugated azomethines such as 6 and 7 are interesting
materials because of their strong absorbance in the visible
region. In addition, their radical cations exhibit high color
contrasts from the neutral state. These spectroscopic properties
concomitant with their low oxidation potentials make them
suitable candidates for electrochromic applications. The
solution spectroelectrochemistry of the two azomethines were
therefore investigated in 0.1 M TBAPF6/CH2Cl2 electrolyte. As
seen in the upper left panel of Figure 3, the absorbance of the
To demonstrate the suitability and stability of the
azomethines as functional materials, an electrochromic device
was prepared using heteroconjugated materials as the electro-
chrome. Devices were prepared by spray-coating thin films of 7
onto ITO glass slides and sandwiching a UV curable gel
electrolyte between ITO coated working and counter electro-
des followed by UV curing.39 The device was assembled by
placing a counter ITO electrode on top of the spray-coated
layers followed by UV curing. The devices were tested by
continuous cycling between the oxidized and neutral states.
Figure 3 shows the plot of the CIE L*a*b* color coordinates of
the electrochromic device prepared from 7 and the digital
photographs of the device in its neutral and oxidized states. In
the neutral state, the device had a red-orange color (L* =
73.15011, a* = 45.45454, b* = 37.84355), while in the oxidized
state, a deep blue color (L* = 53.69979, a* = 3.787879, b* =
−31.92389) was observed. The device colors are consistent
with those observed by spectroelectrochemistry, implying the
same oxidized stated is produced in both cases. It should be
noted that no color bleaching or color degradation, which
would otherwise indicate the decomposition of 7, were
observed when cycling between the two states. This
demonstrates the robustness of the materials and their
resistance toward oxidative degradation, especially in the
harsh redox environment of the electrochromic device.
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Note
°C. The reaction mixture was then diluted with H2O, extracted with
ethyl acetate, washed with brine, dried over Na2SO4, and filtered. The
crude product was purified by silica gel chromatography to give 4 as a
pale yellow solid (90 mg, 57%): mp 212−214 °C; 1H NMR (acetone-
d6) δ 10.11 (bs, 2H), 7.30 (s, 2H), 7.21 (s, 2H), 4.37 (J4 = 7.12 Hz,
4H), 1.58 (s, 9H), 1.40 (J3 = 7.12 Hz, 6H); 13C NMR (CDCl3) δ
165.1, 152.0, 150.0, 135.3, 125.7, 123.6, 119.9, 111.7, 82.6, 60.7, 28.2,
14.4; HRMS (ESI, quadrupole, positive mode) calcd for
C28H34N2O8S3 [M + H]+ 622.14718, found 622.14679.
In summary, α,α′-diamino-protected bi- and terthiophenes
were prepared by Stille and Suzuki coupling with 2-amino-
thiophene derivatives. Not only are the N-Boc-protected
derivatives stable, but they fluoresce more than their
unsubstituted counterparts. The high Φfl confirms that
deactivation modes by intersystem crossing are negligible.
While terthiophenes were prepared as a proof of concept, the
Stille and Suzuki coupling with the 2-amino-5-bromothiophene
derivative is amenable to any bis(boronic acid) or bis-
(stannylated) homo- or heterocycle. This offers the possibility
of preparing diaminothiophene end-capped oligomers with
central cores of varying electron density. In turn, this opens the
possibility of tailoring both the oxidation potential and
emission wavelength, while maintaining high fluorescence
quantum yields. Meanwhile, the one-pot protecting group
cleavage and azomethine formation affords the means to
prepare colored conjugated materials with interesting opto-
electronic properties that can successfully be used in electro-
chromic devices.
Diethyl 5,5′-Bis((tert-butoxycarbonyl)amino)[2,2′-bithio-
phene]-4,4′-dicarboxylate (3). The dimer 3 was obtained during
the preparation of 4 and was isolated by silica gel column
chromatography (hexane/ethyl acetate/dichloromethane 250:25:0.1
mL). The title compound was isolated as a yellow solid (23 mg, 41%):
1
mp 216−218 °C; H NMR (CDCl3) δ 10.07 (bs, 2H), 7.17 (s, 2H),
4.32 (J4 = 7.13 Hz, 4H), 1.56 (s, 18H), 1.40 (J3 = 7.13 Hz, 6H); 13C
NMR (CDCl3) δ 165.1, 152.1, 149.5, 125.5, 119.2, 111.6, 82.5, 60.6,
28.151, 14.3; HRMS (ESI, quadrupole, positive mode) calcd for
C24H32N2O8S2 [M + H]+ 541.16728, found 541.16651.
Diethyl 5,5′-(2,3-Dihydrothieno[3,4-b][1,4]dioxine-5,7-diyl)-
bis(2-((tert-butoxycarbonyl)amino)thiophene-3-carboxylate)
(5). Bis(tributylstannyl) EDOT (266 mg, 0.4 mmol) and 10 (349 mg,
1 mmol) were dissolved in DMF (6 mL) in a microwave reactor
followed by Pd(PPh3)4 (116 mg, 0.1 mmol). The mixture was
degassed for 30 min with N2, and the reaction was run for 2 h at 120
°C in a microwave oven. The reaction mixture was quenched with
H2O, extracted with ethyl acetate, washed with satd NaCl, dried by
Na2SO4, and filtered, and the solvent was evaporated under vacuum.
The crude product was purified by silica gel chromatography to give 5
as a yellow solid (160 mg, 59%): mp 227−229 °C; 1H NMR (CDCl3)
δ 10.09 (bs, 2H), 7.18 (s, 2H), 4.35 (s and q, 8H), 1.56 (s, 18H), 1.41
(J3 = 7.06 Hz, 6H); 13C NMR (CDCl3) δ 165.2, 152.0, 150.1, 137.3,
123.6, 118.7, 111.1, 108.6, 82.2, 64.9, 60.6, 28.2, 14.3; HRMS (ESI,
quadrupole, positive mode) calcd for C30H36N2O10S3 [M + Na]+
703.14243, found 703.14124.
EXPERIMENTAL SECTION
■
Ethyl 2-Aminothiophene-3-carboxylate (8). The preparation
was performed similarly to previous reports.26,40 Triethylamine (3.6 g,
50 mmol) was added dropwise to a mixture of 1,4-dithiane-2,5-diol
(7.6 g, 50 mmoL), ethyl cyanoacetate (11.3 g, 100 mmol), and DMF
(20 mL) at 0 °C. The mixture was stirred at room temperature for 3 h,
diluted with water (200 mL), extracted with dichloromethane (4 × 40
mL), washed with water (2 × 40 mL), and then dried with Na2SO4.
After filtering and removal of the solvent, the residue was purified by
silica gel chromatography. The collected eluents were evaporated
under reduced pressure and diluted with hexane. The flask was cooled
overnight, whereupon 8 crystallized to give a pale yellow solid (11 g,
64%): mp 47−48 °C; 1H NMR (acetone-d6) δ 6.95 (bs, 2H), 6.90 (J2
= 5.6 Hz, 1H), 6.24 (J2 = 5.6 Hz, 1H), 4.23 (q, J = 7.2 Hz, 2H), 1.29
(J3 = 7.2 Hz, 3H); 13C NMR (acetone-d6) δ 165.3, 164.3, 125.8, 106.6,
105.9, 59.4, 14.4.
(E)-Ethyl 2-Amino-5-(7-(4-(ethoxycarbonyl)-5-((thiophene-2-
ylmethylene)amino)thiophene-2-yl)-2,3-dihydrothieno[3,4-b]-
[1,4]dioxin-5-yl)thiophene-3-carboxylate (6) and (E)-Diethyl
5,5′-(2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-diyl)bis(2-((E)-
(thiophene-2-ylmethylene)amino)thiophene-3-carboxylate)
(7). TFA (0.1 mL) was added dropwise to the mixture of 5 (0.34 g, 0.5
mmol) and thiophene-2-carbaldehyde (0.56 g, 5 mmol) at room
temperature. The reaction mixture was stirred neat for 1 h, and then it
was diluted with dichloromethane. Silica gel was then added, and the
resulting powder was applied to a silica gel column for purification.
(E)-Ethyl 2-Amino-5-(7-(4-(ethoxycarbonyl)-5-((thiophene-2-
ylmethylene)amino)thiophene-2-yl)-2,3-dihydrothieno[3,4-b]-
[1,4]dioxin-5-yl)thiophene-3-carboxylate (6). The title com-
Ethyl 2-((tert-Butoxycarbonyl)amino)thiophene-3-carboxy-
late (9). To a solution of 8 (3.42 g, 20 mmol) and Boc2O (5.45 g,
25 mmol) in dioxane (50 mL) was added 4-dimethylaminopyridine
(0.244 g, 2 mmol) at room temperature. The mixture was stirred
overnight at 80 °C. Water was then added at 0 °C. The reaction
mixture was extracted by ethyl acetate, dried over Na2SO4, and then
filtered. The crude product was purified by silica gel chromatography
1
to give 9 as a colorless oil (3.52 g, 65%): H NMR (CDCl3) δ 10.03
(bs, 1H), 7.05 (J2 = 5.80 Hz, 1H), 6.55 (J2 = 5.80 Hz, 1H), 4.22 (J4 =
7.13 Hz, 2H), 1.47 (s, 9H), 1.29 (J3 = 7.13 Hz, 3H); 13C NMR
(CDCl3) δ 164.9, 151.7, 150.7, 123.8, 114.1, 111.0, 81.6, 60.1, 27.8,
14.020; HRMS (ESI, quadrupole, positive mode) calcd for
C12H17NO4S [M + H]+ 272.09511, found 272.09517.
1
pound was obtained as a solid (69 mg, 20%): mp 118−120 °C; H
NMR (CDCl3, 500 MHz) δ 8.60 (s, 1H), 7.59 (dt, J1 = 5.0 Hz, J2 = 1.0
Hz, 1H), 7.53 (dd, J1 = 3.5 Hz, J2 = 1.0 Hz, 1H), 7.46 (s, 1H), 7.16
(dd, J1 = 5.0 Hz, J2 = 4.0 Hz, 1H), 7.13 (s, 1H), 6.03 (bs, 2H), 4.39
(m, 6H), 4.33 (q, J = 7.0 Hz, 2H), 1.45 (t, J = 7.0 Hz, 3H), 1.40 (t, J =
7.0 Hz, 3H); 13C NMR (CDCl3, 128.5 MHz) d 165.2, 163.0, 162.1,
155.5, 151.8, 142.6, 138.4, 136.6, 132.9, 131.9, 128.1, 127.8, 125.2,
123.7, 121.6, 115.6, 110.6, 107.8, 107.1, 65.1, 64.9, 60.8, 59.9, 14.5,
14.4; HRMS (ESI, quadrupole, positive mode) calcd for
C25H22N2O6S4 [M + H]+ 575.04335, found 575.04258.
Ethyl 5-bromo-2-((tert-butoxycarbonyl)amino)thiophene-3-
carboxylate (10). To solution of 9 (35 mg, 1.3 mmol) in anhydrous
dichloromethane (2 mL) and acetic acid (2 mL) was added NBS (278
mg, 1.56 mmol) at 0 °C. The mixture was stirred for 1.5 h at room
temperature, and then it was diluted with H2O, extracted with ethyl
acetate, washed with NaHCO3 and brine, dried over anhydrous
Na2SO4, and filtered. The crude product was purified by silica gel
(E)-Diethyl 5,5′-(2,3-Dihydrothieno[3,4-b][1,4]dioxine-5,7-
diyl)bis(2-((E)-(thiophene-2-ylmethylene)amino)thiophene-3-
carboxylate) (7). The title compound was obtained as a red solid
1
chromatography to give 10 as a colorless oil (39 mg, 87%): H NMR
(CDCl3) δ 10.02 (bs, 1H), 7.04 (s, 1H), 4.25 (J4 = 7.11 Hz, 2H), 1.49
(s, 9H), 1.31 (J3 = 7.11 Hz, 3H); 13C NMR (CDCl3) δ 164.0, 151.8,
151.0, 125.8, 110.8, 102.2, 82.355, 77.3, 77.0, 76.7, 60.5, 27.9, 14.1;
HRMS (ESI, quadrupole, positive mode) calcd for C12H16BrNO4S [M
+ Na]+ 371.98756, found 371.98822.
Diethyl 5,5″-Bis((tert-butoxycarbonyl)amino)[2,2′:5′,2″-ter-
thiophene]-4,4″-dicarboxylate (4). To the solution of 10 (175
mg, 0.5 mmol), 2,5-thiophene bisboronic acid (43 mg, 0.25 mmol),
and Pd(PPh3)4 (57.75 mg, 0.05 mmol) in DMF (5 mL) was added
K2CO3 (207 mg, 1.5 mmol) followed by H2O (1 mL). The mixture
was degassed for 30 min under N2 and then stirred for 16 h at 70−80
1
(186 mg, 65%): mp 118−120 °C; H NMR (CDCl3, 128.5 MHz) δ
8.60 (s, 1H), 7.59 (dt, J1 = 5.0 Hz, J2 = 1.0 Hz, 1H), 7.53 (dd, J1 = 3.5
Hz, J2 = 1.0 Hz, 1H), 7.46 (s, 1H), 7.16 (dd, J1 = 5.0 Hz, J2 = 4.0 Hz,
1H), 7.13 (s, 1H), 6.03 (bs, 2H), 4.39 (m, 6H), 4.33 (q, J = 7.0 Hz,
2H), 1.45 (t, J = 7.0 Hz, 3H), 1.40 (t, J = 7.0 Hz, 3H); 13C NMR
(CDCl3, 500 MHz) d 165.2, 163.0, 162.1, 155.5, 151.8, 142.6, 138.4,
136.6, 132.9, 131.9, 128.1, 127.8, 125.2, 123.7, 121.6, 115.6, 110.6,
107.8, 107.1, 65.1, 64.9, 60.8, 59.9, 14.5, 14.4; HRMS (ESI,
quadrupole, positive mode) calcd for C25H22N2O6S4 [M + H]+
575.04335, found 575.04258.
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Note
Thomson, S. A.; Dickerson, S. H.; Peat, A. J.; Sparks, S. M.; Banker, P.;
Cooper, J. P. WO2006052722A1, 2006.
(17) Fukatsu, K.; Kamata, M.; Yamashita, T. WO2008102749A1,
ASSOCIATED CONTENT
■
S
* Supporting Information
General experimental methods, characterization details, 1H
NMR and 13C NMR spectra, absorbance and fluorescence
spectra, cyclic voltammograms, spectroelectrochemistry spectra,
and absorbance spectra of electrochromic device from 7. This
material is available free of charge via the Internet at http://
pubs.acs.org/.
2008.
(18) Ashwell, S.; Gero, T.; Ioannidis, S.; Janetka, J.; Lyne, P.; Su, M.;
Toader, D.; Yu, D.; Yu, Y. WO2005066163A2, 2005.
(19) Malherbe, P.; Masciadri, R.; Norcross, R. D.; Ratni, H.; Thomas,
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: w.skene@umontreal.ca.
Present Address
†Department of Chemistry & Chemical Biology, McMaster
University, Hamilton, Ontario L8S 4M1, Canada.
Notes
The authors declare no competing financial interest.
(25) Bolduc, A.; Dong, Y.; Guer
Chem. Phys. 2012, 14, 6946−6956.
́
in, A.; Skene, W. G. Phys. Chem.
ACKNOWLEDGMENTS
(26) Dong, Y.; Bolduc, A.; McGregor, N.; Skene, W. G. Org. Lett.
2011, 13, 1844−1847.
■
The Natural Sciences and Engineering Research Council of
Canada is thanked for Discovery, Strategic Research, and
Research Tools and Instruments grants, and the Canada
Foundation for Innovation is thanked for equipment funding.
The Centre for Self-Assembled Chemical Structures is also
acknowledged. A.B. is grateful to NSERC for a graduate
scholarship. N.M. thanks CSACS for an undergraduate
scholarship.
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