Highly efficient new indoline dye having strong electron-withdrawing group for zinc oxide dye-sensitized solar cell

Article abstract of DOI:10.1016/j.tet.2011.06.016

New indoline dye (DN319) having strong electron-withdrawing dicyanovinylidene moiety and octyl group in the terminal rhodanine ring gave higher efficiency than D205, which was known as an excellent organic dye sensitizer. This result is attributed to the

Full text of DOI:10.1016/j.tet.2011.06.016

Tetrahedron 67 (2011) 6289e6293
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Highly efficient new indoline dye having strong electron-withdrawing
group for zinc oxide dye-sensitized solar cell
,
b
,
a
b
b
b
Shinji Higashijima a , Hidetoshi Miura , Tomoki Fujita , Yasuhiro Kubota , Kazumasa Funabiki ,
*
Tsukasa Yoshida c, Masaki Matsui b
a Tsukuba Research Center, Chemicrea Inc., 2-1-6, Sengen, Tsukuba, Ibaraki 305-0047, Japan
b Department of Material Science and Technology, Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
c Environmental and Renewable Energy System Division, Graduate School of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 May 2011
Received in revised form 5 June 2011
Accepted 7 June 2011
Available online 14 June 2011
New indoline dye (DN319) having strong electron-withdrawing dicyanovinylidene moiety and octyl
group in the terminal rhodanine ring gave higher efficiency than D205, which was known as an excellent
organic dye sensitizer. This result is attributed to the bathochromic shift in the UVevis absorption band
and positive shift in the Eox level of DN319.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Indoline dyes
Dye-sensitized solar cell
Electron-withdrawing group
Zinc oxide
1. Introduction
HOMO energy level and strong pushepull system of the sensitizer,
an electron-withdrawing group should be introduced into the ac-
Dye-sensitized solar cells (DSSCs) have been extensively in-
vestigated as potential candidates for renewable-energy systems.1
The highest conversion efficiency (h) of 11.2% was achieved by
ceptor moiety. Moreover, D205 in which the terminal amido moiety
is substituted with octyl group has been reported to show im-
proved open-circuit voltage (Voc).4 On the basis of these consider-
ations, new indoline dyes DN317 and DN319 were synthesized. We
report herein their photoelectrochemical properties.
N719 on nanocrystalline-titanium oxide.2 On the other hand, costly
and environmentally friend metal-free organic dyes, such as oli-
gothiophenes,3a coumarins,3b oligo(phenylenevinylene) deriva-
tives3c and indolines3d have been also developed for the DSSC
applications. In particular, indoline dye D205, indicated in Scheme
1, is known as the most efficient organic dye sensitizer on titanium
2. Results and discussion
Scheme 1 shows the synthesis of DN317 and DN319. Known
double rhodanine ethyl acetate 1 was oxidized by hydrogen per-
oxide in the presence of thionyl chloride to afford 2, whose ester
moiety was hydrolyzed to give 3.8 Malononitrile 5 was allowed to
react with octyl isothiocyanate and ethyl bromoacetate in the
presence of DBU to provide 6, which was again allowed to react
with ethyl isothiocyanatoacetate and ethyl bromoacetate in the
presence of DBU to give 7. Compound 7 was hydrolyzed to produce
the corresponding acetic acid 8. A carbaldehyde 4 was allowed to
react with 3 and 8 to give DN317 and DN319, respectively.
The procedure for the fabrication of DSSC is as follows: the
electrodes were formed by the screen printing of zinc oxide
(0.28 cm2) films on F-doped tin-oxide-coated (FTO) glass plates
(Nippon Sheet Glass, Solar, 4 mm thick) with zinc oxide pastes
prepared from nanoparticle ZnO-410 (Sumitomo Osaka Cement Co.,
oxide showing
h
of 9.5%.4 Zinc oxide is a versatile semiconductor
having similar band gap energy to titanium oxide and can be tai-
lored to various nanostructures.5 D205 also shows high perfor-
mance on zinc oxide.6
We have previously reported that the positive shift of oxidation
potential (Eox) in indoline dyes can improve the incident photon-to-
electron conversion efficiency (IPCE) to increase short-circuit
photocurrent density (Jsc).7 The Eox level should be more positive
than ca. 0.2 V versus Fc/Fcþ to show high IPCE, corresponding to
HOMO level more stable than 4.9 eV by the density functional
theory (DFT) calculations. To achieve both the stabilization of
* Corresponding author. Tel.: þ81 29 863 6040; fax: þ81 29 863 6041; e-mail
address: higashis@chemicrea.co.jp (S. Higashijima).
Ltd). The thickness of zinc oxide layer was 12 mm. An acetonitrile-
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.06.016

6290
S. Higashijima et al. / Tetrahedron 67 (2011) 6289e6293
O
C8H17
CHO
N
S
N
COOH
O
N
iii)
S
O
4
S
N
C8H17
O
C8H17
O
C8H17
S
N
N
N
C8H17
ii) HCl
N
i) H2O2, SOCl2
S
DN317
S
S
S
O
O
O
COOH
O
N
S
N
S
N
S
N
S
COOC2H5
COOC2H5
COOH
O
O
O
O
3
2
1
N
NC
CN
C8H17
N
O
S
NC
NC
COOH
O
C8H17
C8H17
CN
CN
N
NC
C8H17
CN
S
vi)
SCN
D205
N
N
S
iv) C8H17-NCS
v) BrCH2COOEt
ix)
4
COOC2H5
vii) BrCH2COOEt
viii) HCl
CN
CN
S
N
S
N
O
O
N
S
S
O
COOH
COOC2H5
N
O
O
DN319
5
7
6
8
Scheme 1. Reagents and conditions: (i) 1 (1.0 equiv), 35% H2O2 (10 equiv), SOCl2 (5.0 equiv), EtOH, 1 h, 50 ꢁC, (ii) 2 (1.0 equiv), concd HCl, AcOH, reflux, 3 h, (iii) 3 (1.0 equiv), 4
(1.0 equiv), AcONH4 (0.04 equiv), AcOH, reflux, 2 h, (iv) 5 (1.0 equiv), C8H17NCS (1.1 equiv), DBU (1.0 equiv), MeCN, rt, 30 min, (v) BrCH2COOEt (1.7 equiv), rt to reflux, 3 h, (vi) 6
(1.0 equiv), SCNCH2COOEt (1.05 equiv), DBU (1.0 equiv), MeCN, rt, 30 min, (vii) BrCH2COOEt (1.7 equiv), rt to reflux, 3 h, (viii) 7 (1.0 equiv), concd HCl, AcOH, reflux, 3 h, (ix) 8
(1.0 equiv), 4 (1.0 equiv), AcONH4 (0.04 equiv), AcOH, reflux, 2 h.
tert-butyl alcohol (v/v, 1:1) mixed solution of dye (0.5 mM) con-
taining cholic acid (1.0 mM) was prepared. The zinc oxide elec-
trodes were immersed into the solution and kept at room
temperature for 90 min. Platinum (6 mm thick) sputtered FTO glass
(a)
1.2
1
D205
plates were used as the counter electrode. The dye-adsorbed zinc
oxide electrode and platinum counter electrode were assembled
into a sealed sandwich-type cell by heating with a hot melt type
DN317
DN319
0.8
0.6
0.4
0.2
0
ionomer film (HIMILAN, 35 mm thick, DuPont), which is served as
a spacer between the electrodes. A drop of the electrolyte solution
was placed on a drilled hole in the counter electrode of the as-
sembled cell, and was driven into the cell by means of vacuum
backfilling method. The electrolyte composed of 1.0 M tetrapro-
pylammonium iodide and 0.1 M iodine in acetonitrileeethylene
carbonate (v/v, 1:4) mixture. Finally, the hole was sealed using
additional HIMILAN and a cover glass.
Fig. 1a shows the normalized UVevis absorption and fluores-
cence spectra of D205, DN317 and DN319 in chloroform, showing
the absorption maxima (lmax) at 554, 521 and 566 nm, respectively.
As expected, the lmax of DN319 was the most bathochromic due to
strong electron-withdrawing dicyanovinylidene group. The results
are also listed in Table 1. No marked difference in molar absorption
350
450
550
650
750
Wavelength / nm
(b) 2.5
D205
DN317
DN319
2
1.5
1
coefficient (3) was observed. Fig. 1b depicts the UVevis absorption
spectra of indoline dyes on zinc oxide. DN319 showed the most
bathochromic absorption band on zinc oxide followed by D205 and
DN317. The order of bathochromicity of these dyes on zinc oxide
was same as that in chloroform. The lmax of DN319 on zinc oxide
was slightly hypsochromic compared to that in chloroform. The
absorption band on zinc oxide was broad due to aggregates
formation.6
The oxidation potentials of these dyes were measured in DMF as
reported in our previous paper.7 The Eox of DN319 was estimated to
be þ0.37 V versus Fc/Fcþ. The I/I3 redox level was estimated at
0.05 V versus Fc/Fcþ. As the reduction peaks of these dyes were not
observed by the electrochemical measurement, the EoxꢀE0e0 levels,
0.5
0
400
500
600
700
800
Wavelength / nm
Fig. 1. (a) Normalized UVevis absorption (solid line) and fluorescence (dotted line)
spectra of indoline dyes in chloroform and (b) UVevis absorption spectra of indoline
dyes on zinc oxide.

S. Higashijima et al. / Tetrahedron 67 (2011) 6289e6293
6291
Table 1
Physical properties of indoline dyes
Dye
lmax
(
3
)a/nm
lmax
Fmaxa/nm
Eoxb/V
EoxE0e0c/V
HOMOd/eV
LUMOd/eV
on ZnO/nm
D205
395 (38,100),
554 (74,700)
373 (28,200),
521 (61,900)
400 (36,700),
566 (68,000)
540
505
542
641
608
662
þ0.35
þ0.35
þ0.37
1.73
1.85
1.66
5.06
4.99
5.18
2.36
2.15
2.53
DN317
DN319
a
Measured on 1.0ꢂ105 mol dm3 of substrate in chloroform at 25 ꢁC.
b
c
Versus Fc/Fcþ in DMF.
Calculated on the basis of Eox and lint
.
d
Calculated by the B3LYP/6-31G(d,p)//B3LYP/3-21G level.
where E0e0 represents the intersection of normalized absorption
and the fluorescence spectra in chloroform, were calculated.9 These
results are indicated in Table 1. As expected, the Eox of DN319 was
the most positive among D205, DN317 and DN319.
The DFT calculation was performed to confirm the molecular
design of these dyes. The structures of indoline dyes were opti-
mized by the B3LYP/3-21G level, and then the HOMO and LUMO
levels were calculated by the B3LYP/6-31G (d,p) level. The results
indicated that the HOMO level of DN319 was more stable than D205
followed by DN317 as shown in Table 1. The order is inconsistent
with that of Eox level. The HOMO level of DN319 was calculated to
be 5.18 eV, being sufficiently stable to show high IPCE.7
D205
DN317
DN319
10
5
0
The IPCE action spectra of D205, DN317 and DN319 are shown in
Fig. 2. The spectra indicate that no significant differences in the
maximum IPCE value between D205 and DN319 are observed.
However, in comparison with D205, DN319 showed additional
sensitization of zinc oxide at around 650 nm. DN317 could sensitize
zinc oxide in hypsochromic region with less IPCE value.
0
0.2
0.4
Photovoltage / V
0.6
0.8
Fig. 3. Current density versus voltage characteristics for DSSC with indoline dyes as
sensitizers under AM1.5 simulated sunlight (100 mW cm2) illumination.
Table 2
Photovoltaic characteristics of indoline dyes
100
Dye
Jsc/mA cm2
Voc/V
FF
h/%
D205
80
D205
DN317
DN319
11.03
7.95
11.82
0.66
0.66
0.66
0.63
0.64
0.65
4.59
3.38
5.01
DN317
DN319
60
3. Experimental
40
20
0
3.1. General procedure
Melting points weremeasured with a METTLER FP62 instrument.
NMR spectra were obtained by a JEOL JNM-AL400 spectrometer. MS
spectrawere recorded on a JEOL MStation 700 spectrometer. UVevis
absorption and fluorescence spectra were taken on Hitachi U-3500
and F-4500 spectrophotometers, respectively. Electrochemical
measurement was carried out using an EG&G Princeton Applied
Research Potentiostat/Galvanostat (Model 263A) driven by the
M270 software package. The solvents were distilled and dried, if
necessary, by standard methods. Double rhodanine 1, carbaldehyde
4 and indoline dye D205 were synthesized as described in the pre-
vious paper.4 Reagents and starting materials were purchased from
Aldrich, Wako, Kanto Chemical, TCI and Merck.
350
450
550
650
750
Wavelength / nm
Fig. 2. IPCE action spectra of indoline dyes.
Fig. 3 shows the photovoltaic characteristics of DSSCs of D205,
DN317 and DN319 under AM1.5 simulated sunlight (100 mW cm2)
illumination. Table 2 summarizes the results. The Voc values of three
indoline dyes were same. No significant differences in fill factor (FF)
were observed among these dyes. In contrast, the Jsc values of these
dyes are different. DN319 showed the highest Jsc value
11.82 mA cm2, which is 0.79 mA cm2 higher than that of D205. In
contrast, DN317 showed 3.08 mA cm2 lower Jsc value than D205.
These results come from the most bathochromic UVevis absorption
band and positive Eox level of DN319.
3.2. Synthesis
In summary, we have made a molecular design, synthesis and
evaluation of novel indoline dyes. DN319, whose terminal group is
attached with electron-withdrawing dicyanovinylidene group,
exhibited higher conversion efficiency than D205, which is known
as one of the best sensitizers in DSSC. This result is attributed to the
bathochromic shift in the UVevis absorption band and positive
shift in the Eox level.
3.2.1. Synthesis of 2. To an ethanol solution (24 ml) of double rho-
danine 1 (2.60 g, 6.10 mmol) and 35% hydrogen peroxide (6.00 g,
61.0 mmol) was added thionyl chloride (3.65 g, 30.5 mmol) at 50 ꢁC.
The mixture was stirred for 1 h. After cooling, water (200 ml) was
added to the mixture. The product was extracted with chloroform
(200 ml). The organic layer was dried over anhydrous sodium sulfate.
After evaporating the extract invacuo, the crude product was purified

6292
S. Higashijima et al. / Tetrahedron 67 (2011) 6289e6293
by column chlomatography (SiO2, CHCl3) to give 2 (0.15 g, 0.36 mmol,
6%) as a pale yellow solid: mp 93e95 ꢁC; IR (KBr)
¼1767, 1736, 1663,
1545, 1354 cm1; 1H NMR (400 MHz, CDCl3)
¼0.88 (t, J¼6.8 Hz, 3H),
mixture was refluxed for 3 h. After cooling, water (50 ml) was
added. The product was extracted with chloroform (50 mlꢂ2).
The combined organic layer was dried over anhydrous sodium
sulfate. The extract was concentrated in vacuo. The crude product
was washed with hexane (30 ml) to provide 8 (1.39 g, 3.20 mmol,
n
d
1.26e1.35 (m, 13H), 1.59e1.63 (m, 2H), 3.69 (t, J¼7.2 Hz, 2H), 3.88 (s,
2H), 4.29 (q, J¼7.2 Hz, 2H), 4.69 (s, 2H); 13C NMR (100 MHz, CDCl3)
d
¼14.0, 14.1, 22.6, 26.7, 27.7, 29.0, 29.1, 31.3, 31.7, 42.1, 45.2, 62.7, 91.9,
78%) as an orange solid: mp 164e167 ꢁC; IR (KBr)
n
¼2205, 1740,
149.9, 165.9, 166.2, 166.3, 172.7; EIMS (70 eV) m/z (rel intensity) 414
(Mþ, 41), 231 (100); Anal. Calcd for C18H26N2O5S2: C, 52.15; H, 6.32; N,
6.76. Found C, 52.55; H, 6.22; N, 6.81.
1684, 1541, 1279 cm1; 1H NMR (400 MHz, DMSO-d6)
d
¼0.86 (t,
J¼6.4 Hz, 3H), 1.25e1.28 (m, 10H), 1.62 (m, 2H), 4.01 (t, J¼7.6 Hz,
2H), 4.22 (s, 2H), 4.70 (s, 2H), 13.9 (br s, 1H); 13C NMR (100 MHz,
DMSO-d6)
d
¼13.9, 22.0, 25.3, 25.4, 27.8, 28.4, 31.1, 31.2, 44.5, 45.6,
3.2.2. Synthesis of 3. To an acetic acid solution (1 ml) of 2 (149 mg,
0.359 mmol) was added concd hydrochloric acid (0.5 ml). The
mixture was refluxed for 3 h. After cooling, water (50 ml) was added.
The product was extracted with chloroform (50 mlꢂ2). The com-
bined organic layer was dried over anhydrous sodium sulfate. After
evaporating the extract under reduced pressure, the crude product
was washed with hexane (30 ml) to afford 3 (46.7 mg, 0.121 mmol,
48.7, 87.1, 113.5, 114.5, 157.5, 165.5, 165.6, 167.9, 173.3; FABMS
(NBA) m/z 435 (MHþ).
3.2.6. Synthesis of indoline dye DN317. To an acetic acid solution
(1 ml) containing 3 (46.7 mg, 0.121 mmol) and carbaldehyde 4
(53.4 mg, 0.121 mmol) was added ammonium acetate (0.2 mg). The
mixture was refluxed for 2 h. After cooling, the resulting precipitate
was filtered, washed with methanol (2 ml) and purified by column
chlomatography (SiO2, CHCl3/MeOH¼20:1) to give DN317 (61.6 mg,
0.076 mmol, 63%) as a brown powder: mp 231e232 ꢁC; IR (KBr)
34%) as a pale yellow solid: mp 152e153 ꢁC; IR (KBr)
n
¼3254, 2922,
1719,1655,1134, 866 cm1; 1H NMR (400 MHz, DMSO-d6)
d
¼0.853 (t,
J¼6.8 Hz, 3H), 1.24 (m, 10H), 1.53 (m, 2H), 3.59 (t, J¼7.2 Hz, 2H), 4.12
(s, 2H), 4.59 (s, 2H), 13.7 (br s, 1H); 13C NMR (100 MHz, DMSO-d6)
n
¼2924, 2855, 1719, 1485, 1387, 1128 cm1; 1H NMR (400 MHz,
d
¼13.9, 22.0, 26.1, 27.0, 28.4, 28.5, 30.7, 31.1, 41.2, 45.3, 89.5, 152.0,
DMSO-d6)
d
¼0.85 (t, J¼4.8 Hz, 3H), 1.18e1.34 (m, 11H), 1.50e1.72
165.0, 166.1, 168.2, 173.3; FABMS (NBA) m/z 387 (MHþ).
(m, 4H), 1.73e1.84 (m, 2H), 2.00e2.12 (m, 1H), 3.61 (t, J¼6.8 Hz, 2H),
3.85e3.89 (m, 2H), 4.75 (s, 2H), 4.94e4.98 (m, 1H), 7.02e7.04 (m,
3H), 7.09 (s, 1H), 7.15 (d, J¼8.8 Hz, 2H), 7.20 (d, J¼6.8 Hz, 2H),
7.29e7.37 (m, 5H), 7.39e7.48 (m, 5H), 7.65 (s,1H),13.8 (br s,1H); 13C
3.2.3. Synthesis of 6. To an acetonitrile solution (166 ml) of malo-
nonitrile 5 (3.65 g, 55.3 mmol) and octyl isothiocyanate (9.95 g,
59.0 mmol) was added DBU (8.42 g, 55.3 mmol) at room temperature.
The mixture was stirred for 30 min. Then, to the mixture was added
ethyl bromoacetate (15.7 g, 94.0 mmol). The mixture was stirred for
1 h and then refluxed for 3 h. After the reaction was completed, the
mixture was concentrated, acidified with aqueous 2 N hydrochloric
acid (150 ml) and extracted with chloroform (150 mlꢂ2). The com-
bined organic layer was dried over anhydrous sodium sulfate. The
extract was concentrated in vacuo. The crude product was washed
with hexane (200 ml) to give 6 (14.0 g, 50.5 mmol, 91%) as a pale
NMR (100 MHz, DMSO-d6)
d
¼13.9, 22.0, 23.8, 26.1, 27.0, 28.4, 28.5,
31.1, 32.8, 34.8, 37.5, 41.4, 44.0, 68.4, 90.1, 108.1, 113.2, 119.2 (2C),
123.8, 126.8 (3C), 127.1, 127.3, 127.6, 128.3 (3C), 129.1 (2C), 129.7
(2C), 130.3 (2C), 131.2, 133.4, 136.5, 139.4, 140.1, 140.2, 142.6, 144.9,
148.6, 164.8, 166.0, 166.3, 168.2; FABMS (NBA) m/z 810 (MHþ); Anal.
Calcd for C48H47N3O5S2: C, 71.17; H, 5.85; N, 5.19. Found C, 71.46; H,
5.84; N, 5.19.
3.2.7. Synthesis of indoline dye DN319. To an acetic acid solution
(13 ml) containing 7 (1.00 g, 2.30 mmol) and aldehyde 4 (1.02 g,
2.30 mmol) was added ammonium acetate (7.0 mg). The mixture
was refluxed for 2 h. After cooling, the resulting precipitate was
filtered, washed with methanol (20 ml) and then purified by col-
umn chlomatography (SiO2, CHCl3/MeOH¼20:1) to obtain DN319
(0.66 g, 0.77 mmol, 33%) as a brown powder: mp >250 ꢁC; IR (KBr)
yellow solid: mp 73e74 ꢁC; IR (KBr)
n
¼2220, 2203, 1736, 1537,
1460 cm1; 1H NMR (400 MHz, CDCl3)
d
¼0.88 (t, J¼6.6 Hz, 3H),
1.27e1.37 (m, 10H), 1.65e1.72 (m, 2H), 4.00 (s, 2H), 4.08 (t, J¼8.0 Hz,
2H); 13C NMR (100 MHz, CDCl3)
32.3, 45.3, 56.7, 111.6, 112.8, 171.5, 171.6; EIMS (70 eV) m/z (rel in-
tensity) 277 (Mþ,13), 212 (100); Anal. Calcd for C14H19N3OS: C, 60.62;
H, 6.90; N, 15.15. Found C, 60.60; H, 6.77; N, 15.23.
d
¼14.0, 22.6, 25.9, 28.5, 29.0, 31.6,
n
¼2214, 1522, 1485, 1387, 1128 cm1; 1H NMR (400 MHz, DMSO-d6)
d
¼0.86 (t, J¼6.4 Hz, 3H), 1.19e1.37 (m, 12H), 1.57e1.69 (m, 3H),
3.2.4. Synthesis of 7. To an acetonitrile solution (200 ml) of 6 (11.1 g,
40.0 mmol) and ethyl isothiocyanatoacetate (6.08 g, 42.0 mmol) was
added DBU (6.08 g, 40.0 mmol) at room temperature. The mixture
was stirred for 30 min. Then, to the mixture was added ethyl bro-
moacetate (11.4 g, 68.0 mmol). The mixture was stirred for 1 h and
then refluxed for 3 h. After the reaction was completed, the mixture
was concentrated, acidified with aqueous 2 N hydrochloric acid
(150 ml). The product was extracted with chloroform (150 mlꢂ2).
The combined organic layer was dried over anhydrous sodium sul-
fate. The extract was concentrated in vacuo. The crude product was
purified by column chromatography (SiO2, CHCl3) to give 7 (3.80 g,
8.21 mmol, 21%) as a pale yellow solid: mp 133e135 ꢁC; IR (KBr)
1.74e1.82 (m, 2H), 2.02e2.12 (m, 1H), 3.84e3.88 (m, 1H), 4.96e4.04
(m, 2H), 4.70 (br s, 2H), 4.94e5.00 (m, 1H), 7.01e7.05 (m, 3H), 7.09,
(s, 1H), 7.15 (d, J¼8.8 Hz, 2H), 7.18e7.22 (m, 2H), 7.27e7.37 (m, 5H),
7.40e7.49 (m, 5H), 7.72 (s, 1H); 13C NMR (100 MHz, THF-d8)
d
¼14.5,
23.5, 24.6, 24.7, 25.9, 26.0, 26.9, 29.4, 30.1, 32.7, 34.2, 36.0, 45.7, 70.1,
79.7, 88.7, 109.2, 113.8, 114.0, 114.7, 120.3 (2C), 125.4, 128.0, 128.1
(2C), 128.2, 128.3, 128.4, 128.9 (2C), 129.7 (2C), 131.1 (2C), 131.4 (2C),
133.1, 133.7, 135.8, 137.7, 140.8, 141.8, 142.2, 144.4, 150.4, 151.3, 165.9,
166.0, 166.5, 167.3; HRFABMS m/z 858.3186 (MHþ), Calcd for
C51H48N5O4S2: 858.3148.
3.3. Electrochemical measurements
n
¼2214, 2205, 1744, 1684, 1522 cm1; 1H NMR (400 MHz, CDCl3)
d
¼0.88 (t, J¼6.8 Hz, 3H), 1.27e1.31 (m, 10H), 1.38 (t, J¼7.2 Hz, 3H),
Electrochemical measurement of indoline dyes was performed
in DMF. The oxidation potential (Eox) was measured by using small-
size three electrodes. Ag quasi reference electrode (QRE) was used
as a reference. Platinum wire was used as the working and counter
electrodes. All electrode potentials were calibrated with respect to
ferrocene (Fc)/ferrocenium (Fcþ) redox couple. A DMF solution
(2 ml) of dyes containing tetrabutylammonium perchlorate
(0.1 mol dm3) and ferrocene (ca. 1 mmol dm3) was prepared. The
electrochemical measurement was performed at the scan rate of
1.68e1.75 (m, 2H), 3.93 (s, 2H), 4.15 (t, J¼8.0 Hz, 2H), 4.33 (q,
J¼7.2 Hz, 2H), 4.73 (s, 2H); 13C NMR (100 MHz, CDCl3)
¼14.0, 14.1,
d
22.6, 25.9, 28.7, 29.0, 29.1, 31.2, 31.7, 45.2, 45.5, 52.0, 63.3, 88.8,112.5,
113.5,155.3,164.5,165.9,166.1,172.3; EIMS (70 eV) m/z (rel intensity)
462 (Mþ, 71), 397 (100); Anal. Calcd for C21H26N4O4S2: C, 54.52; H,
5.67; N, 12.11. Found C, 54.85; H, 5.61; N, 12.21.
3.2.5. Synthesis of 8. To an acetic acid solution (12 ml) of 7 (1.90 g,
4.11 mmol) was added concd hydrochloric acid (6 ml). The
100 mV sꢀ1
.

S. Higashijima et al. / Tetrahedron 67 (2011) 6289e6293
6293
3. (a) Koumura, N.; Wang, Z.-S.; Mori, S.; Miyashita, M.; Suzuki, E.; Hara, K. J. Am.
Chem. Soc. 2006, 128, 14256; (b) Wang, Z.-S.; Cui, Y.; Dan-oh, Y.; Kasada, C.;
Shinpo, A.; Hara, K. J. Phys. Chem. C 2007, 111, 7224; (c) Hwang, S.; Lee, J. H.; Park,
C.; Lee, H.; Kim, C.; Park, C.; Lee, M.-H.; Lee, W.; Park, J.; Kim, K.; Park, N.-G.; Kim,
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Commun. 2003, 3036; Horiuchi, T.; Miura, H.; Sumioka, K.; Uchida, S. J. Am. Chem.
Soc. 2004, 126, 12218.
3.4. Photoelectrochemical measurements
An action spectrum was measured under monochromatic light
with a constant photon number (0.5ꢂ1016 photon cm2
s
ꢀ1). IeV
characteristics were measured under illumination with AM1.5
simulated sunlight (100 mW cm2) through a shading mask
(5.0 mmꢂ4.0 mm) by using a Bunko-Keiki CEP-2000 system.
ꢀ
4. Ito, S.; Miura, H.; Uchida, S.; Takata, M.; Sumioka, K.; Liska, P.; Comte, P.; Pechy,
€
P.; Gratzel, M. Chem. Commun. 2008, 5194.
5. (a) Law, M.; Greene, L. E.; Johnson, J. C.; Saykally, R.; Yang, P. D. Nat. Mater. 2005,
4, 455; (b) Hosono, E.; Fujihara, S.; Honda, I.; Zhou, H. Adv. Mater. 2005, 17, 2091;
(c) Chou, T. P.; Zhang, Q.; Fryxell, G. E.; Cao, G. Adv. Mater. 2007, 19, 2588.
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7. Matsui, M.; Fujita, T.; Kubota, Y.; Funabiki, K.; Jin, J.; Yoshida, T.; Miura, H. Dyes
Pigm. 2010, 86, 143.
References and notes
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€
Wang, M.; Humphry-Baker, R.; Wang, P.; Zakeeruddin, S. M.; Gratzel, M. Chem.
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