N-(2-Alkoxyphenyl)-substituted double rhodanine indoline dyes for zinc oxide dye-sensitized solar cell

Article abstract of DOI:10.1016/j.tet.2012.03.060

The effect of N-(2-alkoxyphenyl) group in double rhodanine indoline dye on the performance of zinc oxide dye-sensitized solar cell was examined. Both J_sc and V_oc were improved by introducing long alkoxy group due to prevention of H-a

Full text of DOI:10.1016/j.tet.2012.03.060

Tetrahedron 68 (2012) 4286e4291
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
N-(2-Alkoxyphenyl)-substituted double rhodanine indoline dyes for zinc oxide
dye-sensitized solar cell
,
a
a
a
b
c
Masaki Matsui a , Takahiro Shiota , Yasuhiro Kubota , Kazumasa Funabiki , Jiye Jin , Tsukasa Yoshida ,
*
Shinji Higashijima d, Hidetoshi Miura d
a Department of Materials Science and Technology, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan
b Department of Chemistry, Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621, Japan
c Environmental and Renewable Energy System Division, Graduate School of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan
d Chemicrea Co. Ltd., 2-1-6 Sengen, Tsukuba, Ibaragi 305-0047, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The effect of N-(2-alkoxyphenyl) group in double rhodanine indoline dye on the performance of zinc
oxide dye-sensitized solar cell was examined. Both Jsc and Voc were improved by introducing long alkoxy
group due to prevention of H-aggregates formation and inhibition of electron recombination from zinc
oxide surface to electrolyte.
Received 19 January 2012
Received in revised form 12 March 2012
Accepted 17 March 2012
Available online 23 March 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Indoline dyes
Dye-sensitized solar cell
Zinc oxide
Sensitizers
Aggregation
1. Introduction
2. Results and discussion
Indoline dyes are known as highly efficient sensitizer in dye-
2.1. Synthesis
sensitized solar cell.1e5 Especially, D149 has been reported to
show excellent conversion efficiency (
h
) 9.0% on titanium oxide.6
Indoline dyes 18e22 were synthesized as shown in Scheme 1.
Compound 1 wasallowed to reactwith2-alkoxybromobenzenes2e6
to give N-(2-alkoxyphenyl) derivatives 7e11, followed by formylation
to afford 12e16. These formyl derivatives 12e16 were allowed to
react with double rhodanine acetic acid 17 to afford 18e22.
The relationship between the oxidation potential (Eox) of indoline
dyes and conversion efficiency has been also clarified.7 The X-ray
crystallography of D149 ethyl ester suggests that the saturated five-
membered ring can act as steric hindrance to prevent in-
termolecular
pep
stacking.8 D205, in which an octyl group is at-
tached on the nitrogen atom at the terminal rhodanine ring, has
been reported to show higher Voc than D149.9 On the basis of these
results, we considered that a long alkoxy group attached at the
indoline moiety could have suitable energy level and act as steric
hindrance to improve the cell performance. We report herein the
effect of 2-alkoxyphenyl group at the indoline-nitrogen in double
rhodanine indoline dye on the performance of zinc oxide dye-
sensitized solar cell.
2.2. UVevis absorption and fluorescence spectra
The UVevis absorption and fluorescence spectra of 18e22 are
shown in Fig. 1. The results are also listed in Table 1. The indoline
dyes 18e22 showed first and second absorption maxima (lmax) at
around 545 and 384 nm, respectively. The molar absorption co-
efficients ( ) of 18e22 at the first absorption band were observed in
3
the range of 69,700e78,800 dm3 molꢀ1 cmꢀ1, there being no sig-
nificant difference among them. The fluorescence maxima (Fmax) of
18e22 were observed at around 606 nm.
* Corresponding author. E-mail address: matsuim@gifu-u.ac.jp (M. Matsui).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.03.060

M. Matsui et al. / Tetrahedron 68 (2012) 4286e4291
4287
Table 1
Properties of indoline dyes
Br
RO
)a/nm Fmax
nm
/
RFIb Eox
/
Eoxꢀ
E0e0d/V
q e
/
ꢁ
HOMOf/ LUMOf/
eV eV
a
c
i)
Compd lmax
(
3
V
2-6
18
19
20
21
22
384 (24,100), 606
543 (70,100)
383 (23,900), 607
545 (74,600)
383 (22,700), 605
545 (69,700)
384 (27,600), 606
547 (78,800)
78 0.40 ꢀ1.73
96 0.39 ꢀ1.74
101 0.39 ꢀ1.75
100 0.38 ꢀ1.75
100 0.39 ꢀ1.73
54.8 ꢀ5.06
54.7 ꢀ5.04
55.0 ꢀ5.04
55.5 ꢀ5.04
55.0 ꢀ5.04
ꢀ2.24
ꢀ2.23
ꢀ2.22
ꢀ2.22
ꢀ2.22
N
N
H
RO
7-11
1
CHO
ii)
DMF, POCl3
384 (26,000), 608
547 (78,100)
N
a
Measured on 1.0ꢂ10ꢀ5 mol dmꢀ3 of substrate in chloroform at 25 ꢁC.
Relative fluorescence intensity.
RO
b
c
Versus Fc/Fcþ in acetonitrile.
12-16
d
Obtained on the basis of Eox, UVevis absorption band, and fluorescence
spectrum.
O
C8H17
e
iii)
Calculated dihedral angle.
N
S
f
Calculated by the B3LYP/6e31G(d,p)//B3LYP/3-21G level.
S
C8H17
S
S
N
S
N
COOH
2.4. DFT calculations
O
HOOC
17
O
N
S
O
The optimized structure of 22 calculated by the B3LYP/3-
21G(d,p) level is depicted in Fig. 2. The double bond on the 7-
position is Z-form, coming from less steric repulsion between the
hydrogen atom at the 8-position and the carbonyl-oxygen at the
inner rhodanine ring. The double bond in the double rhodanine
8
Compd
OR
2, 7, 12, 18
3, 8, 13, 19
4, 9, 14, 20
5, 10, 15, 21
6, 11, 16, 22
OMe
N
OBu
OOct
RO
moiety is E-form. The dihedral angle
(q) between the 2-
ODodec
OOctadec
2
alkoxyphenyl group on the nitrogen atom and planar chromo-
phoric moiety in 18e22 is calculated to be ca. 55ꢁ, there being
slightly larger than that of D149 ethyl ester (DFT calculation: 37.3ꢁ,
X-ray: 35ꢁ).8,10 This result comes from steric hindrance between the
alkoxy group and indoline moiety. A side view suggests that a long
18-22
Scheme 1. Reagents and reaction conditions: (i)
1
(1.0 equiv), 2e6 (1.2 equiv),
Pd(OAc)2 (0.05 equiv), SPhos (0.1 equiv), t-BuONa (1.4 equiv), toluene, reflux, over-
night; (ii) 7e11 (1.0 equiv), DMF, POCl3 (1.0 equiv), room temperature, overnight; (iii)
12e16 (1.1 equiv), 17 (1.0 equiv), piperidine (0.95 equiv), BuOH, reflux, 4 h.
alkoxy group can act as steric hindrance to prevent
between the planar chromophores.
pep interactions
[ 106]
18
19
1
20
21
1
22
0.5
0.5
0
400
500
600
700
800
Wavelength / nm
Fig. 1. UVevis absorption and fluorescence spectra of 18e22. Measured on
1.0ꢂ10ꢀ5 mol dmꢀ3 of substrate in chloroform at 25 ꢁC.
Fig. 2. Optimized structure of 22.
2.3. Electrochemical measurements
Then, the HOMO and LUMO energy levels of the optimized
structures were calculated by the B3LYP/6-31G(d,p) level. The re-
sults are shown in Table 1. The first absorption band was attributed
to the HOMOeLUMO transition. No remarkable differences of re-
spective HOMO and LUMO levels among 18e22 were calculated.
The HOMO level of 22 was calculated to be ꢀ5.04 eV, there being
similar to those of D149 (ꢀ5.07 eV).11
The oxidation potential (Eox) of 18e22 was measured as de-
scribed in our previous paper.7 The results are listed in Table 1. The
Eox of 18e22 was observed in the range of 0.38e0.40 V versus Fc/
Fcþ, there being similar to that of D149 (0.39 V). The Iꢀ/Iꢀ3 redox
level was estimated to be ꢀ0.05 V versus Fc/Fcþ. As the reduction
potential of 18e22 was not observed, the EoxꢀE0e0 level was cal-
culated as described in our previous paper.7 The conduction band
level of zinc oxide is estimated to be ꢀ0.95 V versus Fc/Fcþ. Thus,
the Eox level of 18e22 is ca. 0.45 V more positive than Iꢀ/I3ꢀ redox
level. The EoxꢀE0e0 level of 18e22 is ca. 0.78 V more negative than
the conduction band level. These results indicate that dyes 18e22
can thermodynamically act as sensitizers.
2.5. Photoelectrochemical properties
The UVevis absorption spectra of 18e22 on zinc oxide are shown
in Fig. 3a. The absorption maxima were observed at around 520 nm
with absorbance in the range of 1.76e2.02, indicating that similar
amounts of dyes were adsorbed on zinc oxide and more than 90% of

4288
M. Matsui et al. / Tetrahedron 68 (2012) 4286e4291
3. Conclusion
UV-vis absorption spectra
normalized UV-vi s absorption spectra
(a)
(b)
18
19
20
21
22
18
19
20
21
22
2
1
1
0.8
0.6
0.4
Long 2-alkoxyphenyl group on the indoline ring in double
rhodanine indoline dye could inhibit H-aggregates formation and
prevent back electron-transfer from zinc oxide surface to electro-
lyte resulting in improvement of both the Jsc and Voc values. Con-
sequently, the 2-(octadecyloxy)phenyl derivative showed the
highest conversion efficiency.
0
400
500
600
400
500
600
700
Wavelength / nm
Wavelength / nm
(c)
(d)
4. Experimental
4.1. Instruments
IPCE spectra
I-V curve
80
18
19
20
21
22
18
19
20
21
22
10
5
60
40
20
0
Melting points were measured with a Yanaco MT-6 micro-
melting-point apparatus. NMR spectra were obtained by JEOL ECX-
400P and ECA-600 spectrometers. Mass spectra were taken on JEOL
MStation 700 spectrometer. UVevis absorption, fluorescence, and
reflection spectra were taken on Hitachi U-3500, F-4500, and
U-4000 spectrophotometers, respectively.
400
500
600
700
800
0
0.2
0.4
Voltage / V
0.6
0.8
Wavelength / nm
Fig. 3. Photoelectrochemical properties of 18e22. (a) UVevis absorption spectra on
zinc oxide, (b) normalized UVevis absorption spectra on zinc oxide, (c) IPCE spectra,
and (d) IeV curve.
4.2. Materials
2-Bromophenol (1) was supplied from Chemicrea Co. Ltd. 2-
Bromophenol and 2-methoxybromobenzene (2) were purchased
from Wako Pure Chemical Co. Ltd. Compound 17 was prepared as
described in the literature.11
photonwas absorbed by the sensitizers. The normalized ones shown
in Fig. 3b indicate that the shoulder peak at around 480 nm is broad
as shorter is the alkoxy group. This result suggests that H-aggregates
are more easily formed on zinc oxide as shorter is the alkoxy group.
The IPCE action spectra in Fig. 3c depict that the sensitization is
significantly larger as longer is the alkoxy group. Consequently, the
Jsc value increasedas longer was the alkoxygroup as shown in Fig. 3d.
Thus, prevention of H-aggregates formation by long alkoxy group
could improve Jsc in the indoline dyes. The data are listed in Table 2.
4.3. Synthesis of 2-alkoxybromobenzenes 3e6
To a DMF solution (200 ml) of 1 (2.07 g, 12.0 mmol) were added
an alkyl iodide (10.8 mmol) and aqueous solution (20 ml) of
sodium hydroxide (0.48 g, 12.0 mmol). The mixture was stirred for
4 h at room temperature. After the reaction was completed, the
mixture was poured into water (100 ml). The product was
extracted with ether (100 mlꢂ3). The extract was dried over an-
hydrous sodium sulfate. The product was purified by column
chromatography (SiO2, C6H14). The physical and spectral data are
shown below.
Table 2
Photoelectrochemical properties of 18e22
Run
Compd
Absorbance
IPCE/%
Jsc/mA cmꢀ2
Voc/V
ff
h/%
1
2
3
4
5
18
19
20
21
22
2.02
1.93
1.76
1.82
1.87
66
66
67
69
69
7.92
7.82
8.23
8.85
8.94
0.59
0.61
0.61
0.61
0.62
0.70
0.67
0.65
0.68
0.67
3.26
3.21
3.33
3.65
3.69
4.3.1. 1-Bromo-2-butoxybenzene (3). Yield 66%; oil; 1H NMR
(CDCl3)
d
¼0.98 (t, J¼7.1 Hz, 3H), 1.53 (sex, J¼7.1 Hz, 2H), 1.81 (quin,
J¼7.1 Hz, 2H), 4.01 (t, J¼7.1 Hz, 2H), 6.80 (t, J¼7.9 Hz, 1H), 6.87 (d,
Table 2 also indicates that the Voc values gradually increased
from 0.59 to 0.62 as longer was the alkoxy group. As the Voc values
are affected by the electron lifetimes, those of 18e22 on zinc oxide
was measured. The results are shown in Fig. 4. The electron lifetime
of 22 was longest, and then the lifetime decreased as shorter was
the alkoxy group. Thus, the long alkyl moiety could also prevent
back electron-transfer from zinc oxide surface to electrolyte to
improve Voc. This is the first report that both Jsc and Voc values were
improved by introducing a long alkoxy group into indoline dyes.
J¼7.9 Hz, 1H), 7.22 (t, J¼7.9 Hz, 1H), 7.51 (d, J¼7.9 Hz, 1H); 13C NMR
(CDCl3)
155.6; IR (NaCl)
d
¼14.0, 19.4, 31.3, 68.9, 112.4, 113.3, 121.7, 128.5, 133.4,
n
1249, 1031 cmꢀ1; EIMS (70 eV) m/z (rel intensity)
230 (Mþþ2, 10), 228 (Mþ, 11), 174 (96), 172 (100); HRMS m/z
228.0149 (Mþ), calcd for C10H13BrO: 228.0150.
4.3.2. 1-Bromo-2-octyloxybenzene (4). Yield 78%; oil; 1H NMR
(CDCl3)
d
¼0.89 (t, J¼7.2 Hz, 3H), 1.25e1.39 (m, 8H), 1.49 (quin,
J¼7.2 Hz, 2H), 1.82 (quin, J¼7.2 Hz, 2H), 4.00 (t, J¼7.2 Hz, 2H), 6.79
(t, J¼7.8 Hz, 1H), 6.86 (d, J¼7.8 Hz, 1H), 7.22 (t, J¼7.8 Hz, 1H), 7.51 (d,
J¼7.8 Hz, 1H); 13C NMR (CDCl3)
¼14.1, 22.6, 26.0, 29.1, 29.2, 29.3,
d
0.2
18
19
20
21
22
31.8, 69.1, 112.2, 113.1, 121.5, 128.3, 133.2, 155.4; IR (NaCl)
n 1249,
1031 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 286 (Mþþ2, 7), 284
(Mþ, 7), 174 (98), 172 (100); HRMS m/z 284.0750 (Mþ), calcd for
C14H21BrO: 284.0776.
0.1
0
4.3.3. 1-Bromo-2-dodecyloxybenzene (5). Yield 32%; oil; 1H NMR
(CDCl3)
d
¼0.88 (t, J¼7.1 Hz, 3H), 1.23e1.38 (m, 16H), 1.49 (quin,
J¼7.1 Hz, 2H), 1.82 (quin, J¼7.1 Hz, 2H), 3.99 (t, J¼7.1 Hz, 2H), 6.79 (t,
J¼7.8 Hz, 1H), 6.86 (d, J¼7.8 Hz, 1H), 7.21 (t, J¼7.8 Hz, 1H), 7.51 (d,
400
450
500
Voc / mV
550
J¼7.8 Hz, 1H); 13C NMR (CDCl3)
¼14.1, 22.7, 26.0, 29.1, 29.32, 29.35,
d
29.55, 29.58, 29.6, 29.7, 31.9, 69.0, 112.2, 113.1, 121.5, 128.3, 133.2,
Fig. 4. Electron lifetime measurements of 18e22.
155.4; IR (NaCl) n
1249, 1031 cmꢀ1; EIMS (70 eV) m/z (rel intensity)

M. Matsui et al. / Tetrahedron 68 (2012) 4286e4291
4289
342 (Mþþ2, 5), 340 (Mþ, 5), 174 (97), 172 (100); HRMS m/z 340.1383
6.59 (t, J¼7.5 Hz, 1H), 6.88e6.96 (m, 3H), 7.05 (d, J¼7.5 Hz, 1H), 7.11
(Mþ), calcd for C18H29BrO: 340.1402.
(t, J¼7.8 Hz, 1H), 7.33 (d, J¼7.8 Hz, 1H); 13C NMR (CDCl3)
¼14.3,
d
22.9, 24.3, 26.2, 29.48 (2C), 29.52, 29.69, 29.73, 29.80, 29.83, 32.1,
33.3, 35.8, 46.1, 68.4, 69.0, 107.2, 113.5, 117.2, 120.8, 124.4, 125.8,
4.3.4. 1-Bromo-2-octadecyloxybenzene
37e39 ꢁC; 1H NMR (CDCl3)
(6). Yield
¼0.88 (t, J¼7.1 Hz, 3H), 1.24e1.33 (m,
38%;
mp
d
127.1 (2C), 131.8, 134.0, 150.6, 155.0; IR (NaCl) n ;
1262, 1023 cmꢀ1
28H), 1.49 (quin, J¼7.1 Hz, 2H), 1.83 (quin, J¼7.1 Hz, 2H), 4.01 (t,
EIMS (70 eV) m/z (rel intensity) 419 (Mþ, 100), 390 (11), 222 (41);
HRMS m/z 419.3203 (Mþ), calcd for C29H41NO: 419.3188.
J¼7.1 Hz, 2H), 6.80 (t, J¼7.8 Hz, 1H), 6.88 (d, J¼7.8 Hz, 1H), 7.23 (t,
J¼7.8 Hz, 1H), 7.52 (d, J¼7.8 Hz, 1H); 13C NMR (CDCl3)
¼14.1, 22.7,
d
26.0, 29.1, 29.3, 29.4, 29.56, 29.58, 29.66 (2C), 29.70 (6C), 31.9, 69.1,
4.4.5. 4-(2-Octadecaoxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta
112.2, 113.2, 121.5, 128.3, 133.3, 155.5; IR (NaCl)
n
1249, 1031 cmꢀ1
;
[b]indole (11). Yield 45%; oil; 1H NMR (CDCl3)
d¼0.88 (t, J¼6.6 Hz,
EIMS (70 eV) m/z (rel intensity) 426 (Mþþ2, 2), 424 (Mþ, 2),174 (96),
3H), 1.20e1.34 (m, 30H), 1.44e1.50 (m, 1H), 1.54e1.61 (m, 2H),
1.64e1.76 (m, 3H), 1.80e1.87 (m, 1H), 1.91e2.00 (m, 1H), 3.79 (t,
J¼7.7 Hz, 1H), 3.92 (t, J¼6.6 Hz, 2H), 4.91 (t, J¼7.7 Hz, 1H), 6.31 (d,
J¼7.2 Hz, 1H), 6.59 (t, J¼7.2 Hz, 1H), 6.88e6.96 (m, 3H), 7.05 (d,
J¼7.2 Hz, 1H), 7.11 (t, J¼7.8 Hz, 1H), 7.33 (d, J¼7.8 Hz, 1H); 13C NMR
172 (100); HRMS m/z 424.2341 (Mþ), calcd for C24H41BrO: 424.2341.
4.4. Synthesis of 7e11
To a toluene solution (60 ml) of 1 (4.0 mmol) were added 2-
alkoxybromobenzenes (2e6, 4.8 mmol), palladium diacetate
(CDCl3)
d
¼14.3, 22.8, 24.3, 26.1, 29.45, 29.47, 29.5, 29.68, 29.72, 29.8
(2C), 29.9 (6C), 32.1, 33.3, 35.8, 46.1, 68.4, 69.0,107.2,113.5,117.2,120.8,
(0.04 g,
0.2 mmol),
2-dicyclohexylphosphino-20,60-dimethox-
124.4, 125.8, 127.0 (2C), 131.8, 134.0, 150.6, 155.0; IR (NaCl) n 1262,
ybiphenyl (SPhos, 0.16 g, 0.4 mmol), and sodium tert-butoxide
(0.56 g, 5.6 mmol). The mixture was refluxed overnight. After the
reaction was completed, the mixture was poured into water
(100 ml). The product was extracted with dichloromethane
(100 mlꢂ3). The extract was dried over anhydrous sodium sulfate.
The product was purified by column chromatography (SiO2, CH2Cl2/
C6H14¼1:3). The physical and spectral data are shown below.
1023 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 503 (Mþ, 100), 250 (14),
222 (29); HRMS m/z 503.4117 (Mþ), calcd for C35H53NO: 503.4127.
4.5. Synthesis of 4-(2-alkoxyphenyl)-1,2,3,3a,4,8b-
hexahydrocyclopenta[b]indole-7-carbaldehydes 12e16
To DMF (3 ml) was added phosphoryl chloride (0.46 g,
3.0 mmol). Then, to this mixture was added a DMF solution (1 ml)
of 7e11 (1.5 mmol). The mixture was stirred overnight at room
temperature. After the reaction was completed, to the mixture was
poured into ice-water (ca. 10 ml) and neutralized with 1 N aqueous
sodium hydroxide. The product was extracted with dichloro-
methane (100 mlꢂ3). After the extract was dried over anhydrous
sodium sulfate, the solvent was removed in vacuo. The product was
purified by silica gel column chromatography (SiO2, CH2Cl2).
4.4.1. 4-(2-Methoxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]in-
dole (7). Yield 68%; oil; 1H NMR (CDCl3)
d
¼1.46e1.62 (m, 3H),
1.67e1.73 (m, 1H), 1.82e1.89 (m, 1H), 1.94e2.02 (m, 1H), 3.81 (s,
3H), 3.82e3.85 (m, 1H), 4.91 (t, J¼6.4 Hz, 1H), 6.32 (d, J¼7.6 Hz, 1H),
6.62 (t, J¼7.6 Hz, 1H), 6.91e6.99 (m, 3H), 7.07 (d, J¼7.6 Hz, 1H), 7.16
(t, J¼7.6 Hz, 1H), 7.34 (d, J¼7.6 Hz, 1H); 13C NMR (CDCl3)
¼24.2,
d
33.0, 35.5, 45.9, 55.6, 68.6, 107.0, 112.4, 117.2, 120.8, 124.3, 125.7,
126.7, 127.0, 131.4, 133.9, 150.1, 155.3; IR (NaCl)
n ;
1262, 1024 cmꢀ1
EIMS (70 eV) m/z (rel intensity) 265 (Mþ, 100), 236 (78), 222 (48);
HRMS m/z 265.1457 (Mþ), calcd for C18H19NO: 265.1467.
4.5.1. 4-(2-Methoxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]in-
dole-7-carbaldehyde (12). Yield 68%; oil; 1H NMR (CDCl3)
d
¼1.46e1.60 (m, 2H),1.64e1.76 (m, 2H),1.85e1.92 (m,1H),1.96e2.07
4.4.2. 4-(2-Butoxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]in-
(m, 1H), 3.81 (s, 3H), 3.86 (t, J¼7.9 Hz, 1H), 4.97 (t, J¼7.9 Hz, 1H), 6.16
(d, J¼8.2 Hz, 1H), 6.98e7.03 (m, 2H), 7.24e7.31 (m, 2H), 7.44 (d,
dole (8). Yield 57%; oil; 1H NMR (CDCl3)
d
¼0.88 (t, J¼7.1 Hz, 3H), 1.36
(sep, J¼7.1 Hz, 2H), 1.45e1.54 (m, 2H), 1.56e1.63 (m, 1H), 1.67 (quin,
J¼7.1 Hz, 2H), 1.70e1.77 (m, 1H), 1.81e1.88 (m, 1H), 1.93e2.01 (m, 1H),
3.80 (t, J¼8.1 Hz, 1H), 3.94 (t, J¼7.1 Hz, 2H), 4.91 (t, J¼8.1 Hz, 1H), 6.33
(d, J¼7.5 Hz, 1H), 6.60 (t, J¼7.5 Hz, 1H), 6.89e6.97 (m, 3H), 7.06 (d,
J¼7.5 Hz, 1H), 7.12 (t, J¼7.7 Hz, 1H), 7.34 (d, J¼7.7 Hz, 1H); 13C NMR
J¼8.2 Hz,1H), 7.61 (s,1H), 9.65 (s,1H); 13C NMR (CDCl3)
¼24.1, 32.8,
d
35.9, 44.9, 55.6, 70.0, 105.5, 112.5, 121.1, 125.0, 127.2, 127.9, 128.3,
128.6, 133.9, 134.7, 155.8, 156.3, 190.0; IR (KBr)
n 2740, 1262,
1024 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 293 (Mþ, 71), 264 (100),
248 (18); HRMS m/z 293.1423 (Mþ), calcd for C19H19NO2: 293.1416.
(CDCl3)
d
¼13.7, 19.2, 24.1, 31.3, 33.1, 35.6, 45.9, 67.9, 68.7, 107.1, 113.3,
117.0,120.6,124.2,125.6,126.8,126.9,131.6,133.9,150.4,154.8; IR (NaCl)
4.5.2. 4-(2-Butoxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]in-
n
1262, 1023 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 307 (Mþ,100), 278
dole-7-carbaldehyde (13). Yield 67%; oil; 1H NMR (CDCl3)
d
¼0.86 (t,
(75), 222 (45); HRMS m/z 307.1917 (Mþ), calcd for C21H25NO: 307.1936.
J¼7.0 Hz, 3H), 1.25e1.36 (m, 2H), 1.47e1.60 (m, 2H), 1.62e1.70 (m,
3H),1.74e1.80 (m, 1H), 1.86e1.93 (m, 1H), 1.98e2.03 (m, 1H), 3.86 (t,
J¼8.0 Hz, 1H), 3.96 (t, J¼7.0 Hz, 2H), 4.96 (t, J¼8.0 Hz, 1H), 6.15 (d,
J¼7.3 Hz, 1H), 6.95e7.02 (m, 2H), 7.23e7.28 (m, 2H), 7.43 (d,
4.4.3. 4-(2-Octyloxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]in-
dole (9). Yield 45%; oil; 1H NMR (CDCl3)
d
¼0.87 (t, J¼6.6 Hz, 3H),
1.20e1.36 (m,10H),1.44e1.51 (m, 2H), 1.56e1.61 (m, 2H), 1.65e1.72 (m,
2H),1.80e1.88 (m, 1H), 1.93e2.01 (m,1H), 3.80 (t, J¼7.3 Hz,1H), 3.93 (t,
J¼6.6 Hz, 2H), 4.91 (t, J¼7.3 Hz, 1H), 6.31 (d, J¼7.5 Hz, 1H), 6.60 (t,
J¼7.5 Hz,1H), 6.88e6.96(m, 3H), 7.06(d, J¼7.5 Hz, 1H), 7.12 (t, J¼7.7 Hz,
J¼7.3 Hz, 1H), 7.61 (s, 1H), 9.66 (s, 1H); 13C NMR (CDCl3)
¼13.8,
d
19.2, 24.1, 31.3, 32.9, 35.9, 44.9, 67.9, 70.4, 105.7, 113.2, 120.9, 124.9,
127.2, 127.9, 128.4, 128.9, 133.7, 134.6, 155.4, 156.5, 189.9; IR (KBr)
n
2740, 1262, 1023 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 335 (Mþ,
100), 306 (65), 250 (34); HRMS m/z 335.1876 (Mþ), calcd for
C22H25NO2: 335.1885.
1H), 7.33 (d, J¼7.7 Hz, 1H); 13C NMR (CDCl3)
¼14.2, 22.8, 24.3, 26.1,
d
29.3, 29.4, 29.5, 31.9, 33.3, 35.7, 46.0, 68.4, 68.9,107.2,113.5,117.2,120.8,
124.3, 125.8, 127.1, 129.5, 131.8, 134.0, 150.6, 155.0; IR (NaCl)
n 1262,
1023 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 363 (Mþ, 100), 334 (24),
222 (51); HRMS m/z 363.2539 (Mþ), calcd for C25H33NO: 363.2562.
4.5.3. 4-(2-Octyloxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]in-
dole-7-carbaldehyde (14). Yield 66%; oil; 1H NMR (CDCl3)
d
¼0.86 (t,
J¼6.7 Hz, 3H), 1.15e1.30 (m, 10H), 1.47e1.58 (m, 2H), 1.60e1.69 (m,
3H), 1.73e1.79 (m, 1H), 1.85e1.92 (m, 1H), 1.97e2.03 (m, 1H), 3.85 (t,
J¼7.7 Hz, 1H), 3.94 (t, J¼6.7 Hz, 2H), 4.94 (t, J¼7.7 Hz, 1H), 6.14 (d,
J¼8.2 Hz, 1H), 6.95e7.01 (m, 2H), 7.22e7.28 (m, 2H), 7.42 (d,
4.4.4. 4-(2-Dodecyloxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]
indole (10). Yield 44%; oil; 1H NMR (CDCl3)
d
¼0.88 (t, J¼6.7 Hz, 3H),
1.20e1.34 (m, 18H), 1.44e1.50 (m, 1H), 1.54e1.61 (m, 2H), 1.64e1.76
(m, 3H), 1.80e1.87 (m, 1H), 1.91e2.00 (m, 1H), 3.79 (t, J¼7.8 Hz, 1H),
3.92 (t, J¼6.7 Hz, 2H), 4.91 (t, J¼7.8 Hz, 1H), 6.31 (d, J¼7.5 Hz, 1H),
J¼8.2 Hz, 1H), 7.60 (s, 1H), 9.65 (s, 1H); 13C NMR (CDCl3)
¼14.2,
d
22.7, 24.1, 26.0, 29.3 (3C), 31.8, 32.9, 35.9, 44.9, 68.3, 70.4, 105.7,

4290
M. Matsui et al. / Tetrahedron 68 (2012) 4286e4291
113.2, 120.9, 124.9, 127.2, 127.9, 128.4, 128.9, 133.8, 134.6, 155.4,
719 (MHþ). Anal. Found: C, 63.11; H, 5.96; N, 6.11%. Calcd for
C38H45N3O5S3: C, 63.39; H, 6.30; N, 5.84%.
156.5, 189.9; IR (KBr) n
2740, 1262, 1023 cmꢀ1; EIMS (70 eV) m/z (rel
intensity) 391 (Mþ, 100), 362 (14), 250 (57); HRMS m/z 391.2502
(Mþ), calcd for C26H33NO2: 391.2511.
4.6.3. Dye 20. Yield 52%; mp 184e185 ꢁC; 1H NMR (DMSO-d6)
d
¼0.76 (t, J¼6.9 Hz, 3H), 0.85 (t, J¼6.6 Hz, 3H), 1.03e1.32 (m, 20H),
4.5.4. 4-(2-Dodecyloxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]
1.44e1.67 (m, 8H), 1.76e1.84 (m, 1H), 2.00e2.09 (m, 1H), 3.89e4.02
(m, 5H), 4.73 (s, 2H), 4.98 (t, J¼6.6 Hz, 1H), 6.13 (d, J¼8.7 Hz, 1H),
7.02 (t, J¼8.3 Hz, 1H), 7.15 (d, J¼8.3 Hz, 1H), 7.26e7.37 (m, 3H), 7.39
indole-7-carbaldehyde (15). Yield 63%; oil; 1H NMR (CDCl3)
d
¼0.88
(t, J¼6.7 Hz, 3H), 1.16e1.34 (m, 16H), 1.47e1.57 (m, 2H), 1.58e1.71
(m, 5H), 1.73e1.79 (m, 1H), 1.86e1.92 (m, 1H), 1.97e2.06 (m, 1H),
3.85 (t, J¼7.8 Hz, 1H), 3.94 (t, J¼6.7 Hz, 2H), 4.95 (t, J¼7.8 Hz, 1H),
6.14 (d, J¼8.2 Hz, 1H), 6.95e7.01 (m, 2H), 7.23e7.28 (m, 2H), 7.42 (d,
(s, 1H) 7.69 (s, 1H); 13C NMR (DMSO-d6)
d
¼14.39, 14.44, 22.57, 22.61,
24.1, 26.0, 26.7, 26.8, 28.99, 29.02, 29.16, 29.2, 29.3, 31.67, 31.69,
32.8, 36.2, 44.7, 45.0, 46.5, 68.2, 70.6, 92.6, 107.5, 110.9, 113.9, 121.4,
122.4, 127.4, 128.1, 128.42, 128.48, 134.0, 135.6, 136.3, 147.2, 153.6,
J¼8.2 Hz, 1H), 7.60 (s, 1H), 9.65 (s, 1H); 13C NMR (CDCl3)
¼14.2,
d
22.8, 24.1, 26.0, 29.27, 29.30, 29.4, 29.6 (2C), 29.7 (2C), 32.0, 32.9,
35.9, 44.9, 68.3, 70.4, 105.7, 113.2, 120.9, 124.9, 127.2, 127.9, 128.4,
155.2, 166.5, 166.7, 168.6, 189.4; IR (NaCl) n
1675, 1266 cmꢀ1; FABMS
(NBA) m/z 775 (MHþ). Anal. Found: C, 65.29; H, 6.82; N, 5.39%. Calcd
128.9, 133.8, 134.6, 155.4, 156.5, 189.9; IR (KBr)
n
2740, 1262,
for C42H53N3O5S3: C, 65.00; H, 6.88; N, 5.41%.
1023 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 447 (Mþ, 100), 250
(59), 222 (24); HRMS m/z 447.3134 (Mþ), calcd for C30H41NO2:
447.3137.
4.6.4. Dye 21. Yield 50%; mp 182e183 ꢁC; 1H NMR (CDCl3)
d
¼0.83e0.90 (m, 6H), 1.14e1.40 (m, 28H), 1.48e1.59 (m, 2H),
1.61e1.79 (m, 6H), 1.87e1.94 (m, 1H), 1.99e2.11 (m, 1H), 3.89 (t,
J¼7.7 Hz, 1H), 3.95 (t, J¼6.4 Hz, 2H), 4.09 (t, J¼7.8 Hz, 2H), 4.92 (s,
2H), 4.99 (t, J¼7.7 Hz, 1H), 6.22 (d, J¼8.2 Hz, 1H), 6.95e7.01 (m, 2H),
7.22e7.28 (m, 3H), 7.35 (s, 1H), 7.76 (s, 1H); 13C NMR (CDCl3)
4.5.5. 4-(2-Octadecyloxyphenyl)-1,2,3,3a,4,8b-hexahydrocyclopenta
[b]indole-7-carbaldehyde (16). Yield 60%; oil; 1H NMR (CDCl3)
d
¼0.88 (t, J¼6.9 Hz, 3H), 1.16e1.34 (m, 30H), 1.47e1.58 (m, 2H),
1.60e1.71 (m, 3H), 1.73e1.80 (m, 1H), 1.86e1.93 (m, 1H), 1.98e2.06
(m, 1H), 3.85 (t, J¼7.9 Hz, 1H), 3.94 (t, J¼6.5 Hz, 2H), 4.95 (t,
J¼7.9 Hz, 1H), 6.14 (d, J¼8.1 Hz, 1H), 6.95e7.01 (m, 2H), 7.23e7.28
(m, 2H), 7.42 (d, J¼8.1 Hz, 1H), 7.60 (s, 1H), 9.65 (s, 1H); 13C NMR
d
¼14.17, 14.21, 22.7, 22.8, 24.1, 26.1, 27.0 (2C), 29.2 (3C), 29.27, 29.34,
29.4, 29.6 (2C), 29.7 (2C), 31.9, 32.0, 32.8, 36.2, 45.1, 45.2, 68.3, 70.4,
93.2, 107.2, 110.2, 113.2, 120.9, 122.5, 127.4, 127.8, 128.0, 128.7, 134.5,
135.6, 137.5, 146.4, 154.0, 155.1, 167.0, 167.2, 169.3, 188.8; IR (KBr)
n
(CDCl3)
d¼14.2, 22.8, 24.1, 26.0, 29.27, 29.31, 29.5, 29.61, 29.63, 29.7
1674, 1266 cmꢀ1; FABMS (NBA) m/z 831 (MHþ). Anal. Found: C,
66.40; H, 7.61; N, 4.89%. Calcd for C46H61N3O5S3: C, 66.39; H, 7.39;
N, 5.05%.
(2C), 29.8 (6C), 32.0, 32.9, 35.9, 44.9, 68.3, 70.4, 105.7, 113.2, 120.9,
124.9, 127.2, 127.9, 128.4, 128.9, 133.8, 134.6, 155.4, 156.5, 189.9; IR
(KBr) n
2740, 1262, 1023 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 531
(Mþ, 19), 250 (100), 222 (19); HRMS m/z 531.4094 (Mþ), calcd for
4.6.5. Dye 22. Yield 47%; mp 177e178 ꢁC; 1H NMR (CDCl3)
d
¼0.88
C36H53NO2: 531.4076.
(t, J¼7.0 Hz, 6H), 1.15e1.39 (m, 40H), 1.49e1.59 (m, 2H), 1.63e1.78
(m, 6H), 1.87e1.94 (m, 1H), 2.00e2.10 (m, 1H), 3.89 (t, J¼7.7 Hz, 1H),
3.95 (t, J¼7.0 Hz, 2H), 4.09 (t, J¼7.0 Hz, 2H), 4.92 (s, 2H), 4.96 (t,
J¼7.7 Hz, 1H), 6.22 (d, J¼8.2 Hz, 1H), 6.95e7.01 (m, 2H), 7.22e7.28
4.6. Synthesis of dyes 18e22
To a butanol solution of (50 ml) of 12e16 (1.0 mmol) and double
rhodanine acetic acid 17 (0.38 g, 0.95 mmol) was added piperidine
(0.07 g, 0.9 mmol). The mixture was refluxed for 4 h. After the re-
action was completed, the solvent was removed in vacuo. The
resulting precipitate was purified by column chromatography
(SiO2, CHCl3/MeOH¼20:1). The physical and spectral data are
shown below.
(m, 3H), 7.36 (s, 1H), 7.75 (s, 1H); 13C NMR (CDCl3)
d
¼14.18, 14.22,
22.7, 22.8, 24.1, 26.1, 27.0 (2C), 29.2 (3C), 29.29, 29.34, 29.5, 29.7
(2C), 29.76 (2C), 29.81 (6C), 31.9, 32.0, 32.8, 36.2, 45.06, 45.14, 68.3,
70.4, 93.2, 107.3, 110.3, 113.2, 120.9, 122.5, 127.4, 127.8, 128.0, 128.7,
134.4, 135.6, 137.5, 146.5, 154.0, 155.1, 167.0, 167.2, 169.2, 188.9; IR
(KBr) n
1675, 1266 cmꢀ1; FABMS (NBA) m/z 916 (MHþ). Anal. Found:
C, 68.24; H, 8.33; N, 4.42%. Calcd for C52H73N3O5S3: C, 68.16; H, 8.03;
N, 4.59%.
4.6.1. Dye 18. Yield 52%; mp 147e149 ꢁC; 1H NMR (DMSO-d6)
d
¼0.85 (t, J¼6.4 Hz, 3H), 1.20e1.32 (m, 10H), 1.41e1.54 (m, 2H),
4.7. Film preparation
1.56e1.68 (m, 4H), 1.76e1.84 (m, 1H), 2.00e2.10 (m, 1H), 3.80 (s,
3H), 3.90e4.00 (m, 3H), 4.64 (s, 2H), 5.01 (t, J¼6.6 Hz, 1H), 6.17 (d,
J¼8.3 Hz, 1H), 7.04 (t, J¼7.9 Hz, 1H), 7.19 (d, J¼7.9 Hz, 1H), 7.29e7.38
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.,
(m, 3H), 7.40 (s, 1H) 7.68 (s, 1H); 13C NMR (DMSO-d6)
d¼14.5, 22.6,
24.2, 26.7, 26.8, 29.0, 29.1, 31.7, 32.6, 36.2, 44.7, 44.8, 46.8, 56.1, 70.0,
92.7, 107.2, 111.4, 113.5, 121.6, 122.6, 127.5, 127.9, 128.3, 128.4, 134.1,
Ltd). The thickness of zinc oxide layer was 12 mm. An acetonitrile/
135.8, 136.0, 147.4, 153.4, 155.7, 166.6, 166.8, 168.4, 189.6; IR (KBr)
n
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
1676, 1266 cmꢀ1; FABMS (NBA) m/z 677 (MHþ). Anal. Found: C,
61.88; H, 5.85; N, 5.98%. Calcd for C35H39N3O5S3: C, 62.01; H, 5.80;
N, 6.20%.
temperature for 90 min. Platinum (6 mm thick) sputtered FTO glass
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
4.6.2. Dye 19. Yield 48%; mp 153e154 ꢁC; 1H NMR (DMSO-d6)
d
¼0.80 (t, J¼7.3 Hz, 3H), 0.85 (t, J¼6.7 Hz, 3H), 1.19e1.32 (m, 10H),
1.42e1.68 (m, 10H), 1.77e1.84 (m, 1H), 2.00e2.10 (m, 1H),
3.89e4.03 (m, 5H), 4.52 (s, 2H), 4.99 (t, J¼6.6 Hz, 1H), 6.17 (d,
J¼8.2 Hz, 1H), 7.01 (t, J¼7.9 Hz, 1H), 7.16 (d, J¼7.9 Hz, 1H), 7.26e7.36
ionomer film (HIMILAN, 35 mm thick, DuPont), which 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 acetonitrile/ethylene
carbonate (v/v, 1:4) mixture. Finally, the hole was sealed using
additional HIMILAN and a cover glass.
(m, 3H), 7.39 (s, 1H), 7.66 (s, 1H); 13C NMR (DMSO-d6):
d¼14.1, 14.5,
19.1, 22.6, 22.8, 24.1, 26.7, 26.8, 29.05, 29.06, 31.3, 31.7, 32.7, 36.2,
44.1, 45.0, 47.8, 67.9, 70.3, 92.6, 107.4, 111.8, 114.0, 121.4, 122.6, 127.3,
128.0, 128.3, 128.5, 133.8, 135.7, 135.8, 147.9, 153.4, 155.1, 166.6,
166.8, 168.1, 189.7; IR (KBr)
n
1684, 1266 cmꢀ1; FABMS (NBA) m/z

M. Matsui et al. / Tetrahedron 68 (2012) 4286e4291
4291
4.8. Photoelectrochemical measurements
References and notes
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a constant photon number (0.05ꢂ1016 photon cmꢀ2 sꢀ1). IeV char-
acteristics were measured under illumination with AM 1.5 simu-
lated sun light (100 mW cmꢀ2) by using a Bunko-Keiki CEP-2000
system.
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€
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Acknowledgements
ꢀ
€
This work was financially supported in part by Grants-in-Aid for
Science Research (No. 21550180) from Japan Society for the Pro-
motion of Science (JSPS).
8. Matsui, M.; Fujita, T.; Kubota, Y.; Funabiki, K.; Miura, H.; Shiro, M. Bull. Chem.
Soc. Jpn. 2010, 83, 709e711.
ꢀ
9. Ito, S.; Miura, H.; Uchida, S.; Takata, M.; Sumioka, K.; Liska, P.; Comte, P.; Pechy,
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Supplementary data
10. Matsui, M.; Kotani, M.; Kubota, Y.; Funabiki, K.; Jin, J.; Yoshida, T.; Higashijima,
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M. Tetrahedron 2011, 67, 6289e6293.
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2012.03.060.