Highly efficient substituted triple rhodanine indoline dyes in zinc oxide dye-sensitized solar cell

Article abstract of DOI:10.1016/j.tet.2010.07.017

Substituited triple rhodanine indoline dyes showed higher performance than known triple rhodanine derivative (D150). A few triple rhodanine indoline derivatives showed comparable conversion efficiency to D149.

Full text of DOI:10.1016/j.tet.2010.07.017

Tetrahedron 66 (2010) 7405e7410
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Highly efficient substituted triple rhodanine indoline dyes in zinc oxide
dye-sensitized solar cell
,
a
a
a
b
Masaki Matsui a , Yoshinori Asamura , Yasuhiro Kubota , Kazumasa Funabiki , Jiye Jin ,
*
Tsukasa Yoshida c, Hidetoshi Miura d
a Department of Materials Science and Technology, Faculty of Engineering, Gifu University, 1-1 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, 1-1 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:
Substituited triple rhodanine indoline dyes showed higher performance than known triple rhodanine
derivative (D150). A few triple rhodanine indoline derivatives showed comparable conversion efficiency
to D149.
Received 23 March 2010
Received in revised form 8 July 2010
Accepted 9 July 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Available online 16 July 2010
Keywords:
Indoline dyes
Dye-sensitized solar cell
Rhodanine
Zinc oxide
1. Introduction
show high conversion efficiency. In a series of our study on survey
of sensitizers, we report herein the use of substituted triple rho-
Highly efficient organic sensitizers for dye-senisitized solar cell
have been focused on coumarin,1 carbazole,2 dimethylfluorene,3
arylamine,4 and indoline dyes.5 Among them, indoline dyes have
been reported to show excellent cell performance.5g,h Recently,
arylamine sensitizers having isophorone,6 cyclohexadienyl,7 furyl,8
and thiophene linkers3a,4b,9 have been reported to show good
performance. In the reported sensitizers, most anchor moiety is
cyanoacrylic group. Therefore, it is of interest to examine the other
anchor groups, which can cause bathochromic shift in the UVevis
absorption band. Because the bathochromic shift can increase
short-circuit photocurrent density (Jsc) to improve solar-light-to-
danine indoline dyes in a zinc oxide dye-sensitized solar cell.
2. Results and discussion
Triple rhodanine indoline dyes 30e35 were synthesized as
shown in Scheme 1. Single rhodanines 1e4 were allowed to react
with alkyl isothiocyanates 5e8 and ethyl bromoacetate (9) in the
presence of DBU to afford double rhodanines 10e15, which were
again allowed to react with ethyl isothiocyanatoacetate (16) and 9
in the presence of DBU to give triple rhodanine ethyl acetates
17e22. These compounds were hydrolyzed to produce the corre-
sponding triple rhodanine acetic acids 23e28. An indoline-7-car-
baldehyde 29 was allowed to react with 23e28 to give 30e35. Dye
30 is D150. D149 was also prepared as a reference compound.
The UVevis absorption and fluorescence spectra of 30e35 are
shown in Figure 1. The results are also listed in Table 1. The first and
secondabsorption maxima(lmax)of 30e35wereobservedat around
570 and 450 nm, respectively. As expected, the lmax were more
bathochromic than those of D149 (550 and 395 nm), respectively.
electricity conversion efficiency (h). Three series of indoline dyes
having cyanoacrylic acid (D131), single rhodanine (D102), and
double rhodanine acetic acid (D149) as an anchor moiety are
known. Among the series, the double rhodanine derivatives show
the highest efficiency. Triple rhodanine indoline dyes are more
bathochromic than the double rhodanine derivative due to in-
creased conjugation. Only one triple rhodanine indoline dye named
D150 has been reported to show
h
5.9% on titanium oxide.10 We
considered that substituted triple rhodanine indoline dyes could
The molar absorption coefficients (3) of 30e35 (60,700e101,200) at
first lmax were slightly larger than that of D149 (69,700). The fluo-
rescence maxima (Fmax) of 30e35 (649e662 nm) were more
* Corresponding author. E-mail address: matsuim@gifu-u.ac.jp (M. Matsui).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.07.017

7406
M. Matsui et al. / Tetrahedron 66 (2010) 7405e7410
R2
O
R2
N
O
S
i) R2-NCS (5-8)
S
iii) SCNCH2COOEt (16)
S
N
S
S
S
S
S
N
N
S
N
N
iv) BrCH2COOEt (9)
ii) BrCH2COOEt (9)
R1
O
R1
1-4
R1
O
O
O
10-15
S
COOEt
R1
17-22
Et
N
S
S
COOH
O
S
O
N
N
S
N
O
E
CHO
R2
7
S
COOH
O
E
O
N
N
N
S
vi)
H
8
Z
7
R2
N
N
O
S
29
S
v) HCl
S
D149
S
N
N
R1
23-28
O
O
30-35
COOH
10, 17, 23, 30 (D150): R1 = Et, R2 = Et
11, 18, 24, 31: R1 = Oct, R2 = Oct
1, 5: R1 = Et
2, 6: R1 = Oct
12, 19, 25, 32: R1 = CH2CH(Et)Bu, R2 = CH2CH(Et)Bu
13, 20, 26, 33: R1 = Bn, R2 = Bn
3, 7: R1 = CH2CH(Et)Bu
4, 8: R1 = Bn
14, 21, 27, 34: R1 = Oct, R2 = Bn
15, 22, 28, 35: R1 = Bn, R2 = Oct
Scheme 1. Reagents and conditions: (i) 1e4 (1.0 equiv), 5e8 (1.0 equiv), DBU (1.0 equiv), MeCN, 30 min, reflux, (ii) 9 (2.0 equiv), rt to reflux, 4 h, (iii) 10e15 (1.0 equiv), 16
(1.0 equiv), DBU (1.0 equiv), MeCN, rt to reflux, 4 h, (iv) 9 (2.0 equiv), rt to reflux, 4 h, (v) 17e22 (1.0 equiv), concd HCl (300 equiv), AcOH, reflux, 4 h, (vi) 23e28 (1.0 equiv), 29
(1.1 equiv), AcNH4 (4.9 equiv), reflux, 4 h.
30 (D150)
molecule, eight E/Z structural isomers are considerable. In addition,
31
4000
3000
2000
1000
syn- and anti-conformers between the carbonyl group in the inner
rhodanine moiety and aromatic-hydrogen at the 8-position are
considerable. Consequently, sixteen structural isomers are consid-
erable for 31. The structures were optimized by the AM1 method.
The results are shown in Figure S1 in supplementary data. Among
the isomers, the structure of dye 31 indicated in Scheme 1 was most
stable. Two olefinic bonds in the triple rhodanine moiety are
E-form. The olefinic bond on the 7-position is Z-form. The carbonyl-
oxygen and aromatic-hydrogen at the 8-position forms anti-con-
former. The most stable structure was calculated again by the
B3LYP/3-21 G level. Then, the HOMO and LUMO energy levels were
calculated by the B3LYP/6-31G(d,p) level as shown in Figure S2 in
supplementary data. The first absorption band of the optimized
31 was attributed to HOMO to LUMO transition. The HOMO and
LUMO energy levels of 31 were calculated to be ꢀ4.97 and
ꢀ2.34 eV, respectively. Thus, the HOMO level of 31 was less stable
1
32
33
34
35
D149
0.5
0
0
400
500
600
700
800
900
Wavelength / nm
Figure 1. UVevis absorption and fluorescence spectra of 30e35 and D149. Measured
on 1ꢁ10ꢀ5 mol dmꢀ3 of substrate in chloroform at 25 ꢂC. Solid and dotted lines rep-
resent UVevis absorption and fluorescence spectra, respectively.
Table 1
Properties of indoline dyes
Compd
lmax
(3
)a/nm
F
max=nma
RFIb
E
ox=Vc
Eox ꢀ Eoꢀo=Vd
HOMO=eVe
LUMO=eVe
ff
30 (D150)
31
32
33
34
35
D149
455 (38,700), 573 (82,200)
440 (28,400), 574 (101,200)
450 (26,600), 572 (88,300)
435 (29,300), 571 (68,400)
457 (30,800), 570 (60,700)
451 (25,700), 570 (73,000)
395 (33,300), 550 (69,700)
649
650
652
656
659
662
635
100
123
130
148
136
91
þ0.33
þ0.33
þ0.33
þ0.33
þ0.34
þ0.33
þ0.4
ꢀ1.70
ꢀ1.70
ꢀ1.70
ꢀ1.69
ꢀ1.67
ꢀ1.67
ꢀ1.70
d
d
d
ꢀ4.79
d
ꢀ2.34
d
ꢀ1.63
d
d
d
d
d
d
d
d
d
d
87
ꢀ5.07
ꢀ2.37
ꢀ1.61
a
Measured on 1.0ꢁ10ꢀ5 mol dmꢀ3 of substrate in chloroform at 25 ꢂC.
Relative fluorescence intensity.
b
c
d
e
f
Versus Fc/Fcþ in DMF.
Calculated on the basis of Eox and lint
Calculated by the B3LYP/6-31G(d,p)//B3LYP/3e21 G level.
Oscillator strength calculated by the INDO/S method.
.
bathochromic than that of D149 (635). The fluorescence of 30e35
(RFI¼91e148) was slightly more intense than that of D149 (87).
The most stable structure of triple rhodanine indoline dyes was
examined. In the case of 31, as there are three olefinic bonds in the
than that of D149 (ꢀ5.07 eV). The LUMO level of 31 (ꢀ2.34) was
slightly less stable than that of D149 (ꢀ2.37).
The oxidation potential of 30e35 was measured by cyclic vol-
tammetry. The voltammogram of 31 versus Ag quasi reference

M. Matsui et al. / Tetrahedron 66 (2010) 7405e7410
7407
electrode (QRE) in the presence of ferrocene as an internal standard
is shown in Figure 2. Three characteristic redox waves were ob-
served in the voltammogram. The first oxidative wave (I) at þ0.73 V
and the second wave (II) at þ1.09 V versus AgQRE were attributed
to the oxidation of ferrocene and 31, respectively. The third oxi-
dative wave (III) at around 1.2 V may arise from the further oxida-
tion of 31. Therefore, the oxidation peak potential (Epa) for 31 is
calculated to be þ0.36 V versus Fc/Fcþ in DMF. Although the stan-
dard oxidation potential (Eox) are not easily obtained experimen-
tally, it can be approximately estimated from the cyclic
voltammetric peak potential, which equals to (Epaꢀ29 mV), when
the electrochemical oxidation is a reversible step.11 Therefore, the
Eox of 31 was estimated to be þ0.33 V versus Fc/Fcþ. The Iꢀ/I3ꢀ redox
level was estimated at ꢀ0.05 V versus Fc/Fcþ. As the reduction
levels of 31 were not observed by the electrochemical measure-
ment, the potential level of EoxꢀE0e0, where E0e0 represents the
intersection of normalized absorption and the fluorescence spectra
in solution was calculated.12 The lint, which represents the in-
tersection wavelength in the normalized UVevis absorption and
fluorescence spectra of 31 was observed at 611 nm, corresponding
to E0e0 2.03 V. Therefore, the EoxꢀE0e0 level of 31 was calculated to
be ꢀ1.70 V versus Fc/Fcþ. The Eox and EoxꢀE0e0 of D149 were
obtained in the same way. The results are listed in Table 1.
relationship between the IPCE and Eox level of indoline dyes was
examined.5a It was found when the Eox level is more positive than
0.2 V versus Fc/Fcþ, highIPCEwasobtained. Therefore, itisreasonable
that triple indoline dyes 30e35 show the IPCE in the range of 71e77%,
which are slightly small compared to that of D149 (82%). However, as
triple rhodanine dyes 30e35 exhibit sensitization at around 670 nm
as shown in Figure 3b, no marked differences in Jsc were observed
between 30e35 (9.83e11.19 mA cmꢀ2
) and D149 (11.04). In-
terestingly, the open-circuit photovoltage (Voc) of substituted triple
rhodanine indoline dyes 31e35 (0.60e0.67 V) were significantly
higher than that of known 30 (D150, 0.56) as shown in Figure 3c.
Introduction of medium normal alkyl groups into the rhodanine rings
was effective to increase Voc. In the case of double rhodanine indoline
dyes, theoctyl derivative(D205)hasbeenreportedtoshowhigher Voc
than the ethyl derivative (D149), which can result from inhibition of
30 (D150)
(a)
31
3
32
33
34
35
2
D149
1
0
I
0
400
500
600
700
800
-1
-2
-3
II
Wavelength / nm
III
100
80
60
40
20
0
(b)
30 (D150)
31
31
32
33
1.2
Potential / V vs AgQRE in DMF
0.8
0.4
0
34
D149
Figure 2. Cyclic voltammogram of 31 in the presence of ferrocene. Measured in DMF
versus AgQRE at scan rate 100 mV sꢀ1
.
Theresults of photoelectrochemicalpropertiesof30e35 andD149
are shown in Figure 3 and Table 2. Figure 3a depicts that the first lmax
of triple rhodanine indoline dyes 30e35 on zinc oxide were observed
in the range of 540e560 nm, which were slightly hypsochromic
compared with those in chloroform (570e574 nm). This is a general
tendency for double rhodanine indoline dyes, such as D149 on zinc
oxide, which may come from decrease in electron-withdrawing
ability of the rhodanine moiety on zinc oxide. As expected, the first
lmax of 30e35 (540e560) on zinc oxide were more bathochromic
than that of D149 (516). The UVevis absorption spectra on zinc oxide
were broad compared with those in chloroform, indicating aggre-
gates formation. The IPCE values of 30e35 (71e77%) were signifi-
cantly lower than that of D149 (82) as shown in Figure 3b. The
EoxꢀE0e0 levels of 30e35 (ꢀ1.67 to ꢀ1.70 V) were sufficiently nega-
tive compared to the conduction band level of zinc oxide (ꢀ0.95 V),
there being the energy gap ca. 0.75 V. Meanwhile, the energy gap
between the Eox level of 30e35 (þ0.33 V) and Iꢀ/I3ꢀ redox level
(ꢀ0.05 V) is 0.38 V. In the case of titanium oxide, the energy gap of
0.2e0.3 V is required to proceed the electron transfer.12,13 Therefore,
the Eox level is more important factor than the EoxꢀE0e0 level to im-
prove the performance of indoline dyes. The Eox of triple rhodanine
dyes 30e35 (þ0.33 V vs Fc/Fcþ) were more negative than that of
double rhodanine dye D149 (þ0.40). In our previous paper, the
400
500
600
700
800
Wavelength / nm
(c)
30 (D150)
31
32
10
5
33
34
35
D149
0
0
0.2
0.4
0.6
0.8
1
Photovoltage / V
Figure 3. (a) UVevis absorption spectra on zinc oxide, (b) IPCE action spectra, and (c)
IeV curve of 30e35 and D149 on zinc oxide.

7408
M. Matsui et al. / Tetrahedron 66 (2010) 7405e7410
back electron transfer from semiconductor surface to triidodide
anions.5d,f,14 The fill factors (ff) of 31 (0.66), 33 (0.67), 34 (0.65), and 35
(0.66) were larger than those of 30 (0.62) and D149 (0.61). Conse-
quently, all of substituted triple rhodanine indoline dyes 31e35
showed higher conversion efficiency (4.09e4.36%) than known 30
(D150, 3.92). The conversion efficiencyof 31 (4.36) and 34 (4.35) were
comparable to that of D149 (4.48).
0.88 (t, J¼6.9 Hz, 3H), 1.20e1.43 (m, 20H), 1.65 (quin, J¼7.8 Hz, 2H),
1.72 (quin, J¼7.8 Hz, 2H), 3.81 (s, 2H), 3.85 (t, J¼7.8 Hz, 2H), 4.08 (t,
J¼7.8 Hz, 2H); 13C NMR (CDCl3)
¼14.2ꢁ2, 22.7ꢁ2, 26.5, 26.91,
d
26.93, 29.16ꢁ2, 29.21ꢁ2, 29.5, 31.6, 31.79, 31.85, 44.9, 45.1, 93.8,
151.5, 167.7, 173.0, 190.3; FABMS (NBA) m/z 457 (MHþ).
3.3.3. Double rhodanine 12. Yield 15%; mp 65e67 ꢂC; IR (KBr)
n
¼1731, 1657, 1513 cmꢀ1
;
1H NMR (CDCl3)
d
¼0.82e1.00 (m, 12H),
Table 2
1.16e1.46 (m, 16H), 1.85 (sep, J¼7.8 Hz, 1H), 2.08 (sep, J¼7.8 Hz, 1H),
Photoelectrochemical properties of indoline dyes
3.81 (d, J¼7.8 Hz, 2H), 3.82 (s, 2H), 4.00 (d, J¼7.8 Hz, 2H); 13C NMR
Compd
lmax/nm Abs
IPCE/% Jsc/mA cmꢀ2 Voc/V ff
h /%
(CDCl3)
d¼10.2, 10.7, 14.07, 14.12, 22.9, 23.09, 23.12, 24.0, 28.0, 28.5,
29.5, 30.6, 31.4, 37.0, 38.7, 48.8, 48.9, 94.1, 151.7, 168.3, 173.3, 190.6;
30 (D150) 540
1.75 75
0.92 77
2.55 77
1.31 71
2.69 71
2.60 71
11.19
10.61
11.16
10.28
10.36
9.83
0.56
0.62
0.62
0.59
0.65
0.64
0.66
0.62 3.92
0.66 4.36
0.60 4.12
0.67 4.09
0.65 4.35
0.66 4.15
0.61 4.48
FABMS (NBA) m/z 457 (MHþ).
31
550
550
560
550
550
516
32
33
3.3.4. Double rhodanine 13. Yield 48%; mp 195e197 ꢂC; IR (KBr)
34
35
n
¼1734, 1663, 1530 cmꢀ1
;
1H NMR (CDCl3)
d
¼3.93 (s, 2H), 5.16 (s,
D149
33.6
82
11.04
2H), 5.23 (s, 2H), 7.12e7.16 (m, 2H), 7.27e7.39 (m, 6H), 7.44e7.48
(m, 2H); 13C NMR (CDCl3)
d
¼31.4, 47.6, 47.7, 94.7, 125.9, 128.2, 128.4,
128.6, 129.2, 129.3, 133.7, 134.9, 151.1, 168.0, 173.1, 190.4; FABMS
(NBA) m/z 413 (MHþ).
In summary, the substituted triple rhodanine indoline dyes
significantly showed better performance than known triple rho-
danine indoline dye D150. A few triple rhodanine indoline dyes
showed comparable performance to D149.
3.3.5. Double rhodanine 14. Yield 31%; mp 104e106 ꢂC; IR (KBr)
n
¼1730, 1681, 1530 cmꢀ1; 1H NMR (CDCl3)
¼0.87 (t, J¼6.9 Hz, 3H),
d
1.20e1.39 (m, 10H), 1.64 (quin, J¼7.6 Hz, 2H), 3.94 (s, 2H), 4.02 (t,
J¼7.6 Hz, 2H), 5.17 (s, 2H), 7.12e7.17 (m, 2H), 7.28e7.42 (m, 3H); 13C
3. Experimental
3.1. General
NMR (CDCl3)
d¼14.2, 22.7, 26.9ꢁ2, 29.2ꢁ2, 31.4, 31.8, 44.9, 47.7,
94.9, 125.9, 128.3, 129.3, 133.7, 150.6, 167.8, 173.1, 190.4; FABMS
(NBA) m/z 435 (MHþ).
Melting points were measured with a Yanaco MP-13 micro-
melting-point apparatus. NMR spectra were obtained by a JEOL ECX
400P spectrometer. MS spectra were 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.
3.3.6. Double rhodanine 15. Yield 8%; mp 105e107 ꢂC; IR (KBr)
n
¼1731, 1664, 1508 cmꢀ1; 1H NMR (CDCl3)
¼0.88 (t, J¼6.9 Hz, 3H),
d
1.21e1.41 (m, 10H), 1.64 (quin, J¼7.6 Hz, 2H), 3.80 (s, 2H), 3.84 (t,
J¼7.6 Hz, 2H), 5.29 (s, 2H), 7.28e7.32 (m, 3H), 7.49e7.50 (m, 2H);
13C NMR (CDCl3)
d
¼14.2, 22.7, 26.5, 26.9, 29.1, 29.5, 31.6, 31.8, 45.1,
47.7, 93.6, 128.1, 128.6, 129.2, 135.0, 151.9, 167.7, 173.0, 190.2; FABMS
(NBA) m/z 435 (MHþ).
3.2. Materials
3.4. Synthesis of triple rhodanine ethyl esters 17e22
Single rhodanines 1 and 4, benzylisothiocyanate (8), and ethyl
bromoacetate (9) were purchased from Tokyo Kasei Co., Ltd. Ethyl
isothiocyanate (5) and octyl isothiocyanate (6) were purchased
from KANTO CHEMICAL CO., INC. and Wako Pure Chemical In-
dustries Ltd., respectively. Single rhodanines 2 and 3, 2-ethylhexyl
isothiocyanate (7), and ethyl isothiocyanatoacetate (16) were syn-
thesized as described in our previous paper.5c
To an acetonitrile solution (30 ml) of 10e15 (1 mmol) and ethyl
isocynatoacetate 16 (145 mg, 1 mmol) was added DBU (152 mg,
1 mmol) at room temperature. The mixture was stirred for 30 min.
Ethyl bromoacetate 9 (334 mg, 2 mmol) was added to the mixture
at room temperature and stirred for 30 min. Then, the mixture was
refluxed for 4 h. After the reaction was completed, the mixture
was concentrated in vacuo. Aqueous 2 N hydrochloric acid (200 ml)
was added and the pH value was adjusted below 3. The product was
extracted with chloroform (80 mlꢁ3) and purified by column
chromatography (SiO2, CH2Cl2/AcOEt¼20:1).
3.3. Synthesis of double rhodanines 10e15
To an acetonitrile solution (30 ml) of monorhodanine derivatives
1e4 (18 mmol) and isothiocyanates 5e8 (18 mmol) was added DBU
(2.74 g, 18 mmol) at room temperature. The mixture was stirred for
30 min. Then, to the mixture was added ethyl bromoacetate 9
(6.01 g, 36 mmol). The mixture was stirred for 30 min and then
refluxed for 4 h. After the reaction was completed, the mixture was
concentrated and dissolved in chloroform. Aqueous 2 N hydro-
chloric acid (100 ml) was added to the mixture. The pH value was
adjusted below 3.0. The product was extracted with chloroform
(80 mlꢁ3) and purified by column chromatography (SiO2, CHCl3).
3.4.1. Triple rhodanine ethyl ester 17. Yield 45%; mp 262e264 ꢂC; 1H
NMR (CDCl3)
d
¼1.28 (t, J¼7.2 Hz, 3H), 1.36 (t, J¼7.2 Hz, 3H), 1.39 (t,
J¼7.2 Hz, 3H), 3.90 (s, 2H), 4.05 (q, J¼7.2 Hz, 2H), 4.17 (q, J¼7.2 Hz,
2H), 4.34 (q, J¼7.2 Hz, 2H), 4.85 (s, 2H); FABMS (NBA) m/z 474 (MHþ).
3.4.2. Triple rhodanine ethyl ester 18. Yield 43%; mp 104e106 ꢂC; IR
(KBr)
n
¼1735, 1680, 1523, 1225 cmꢀ1
;
1H NMR (CDCl3)
d
¼0.88 (t,
J¼7.3 Hz, 3H), 0.89 (t, J¼6.9 Hz, 3H), 1.22e1.47 (m, 20H), 1.38 (t,
J¼7.3 Hz, 3H), 1.64e1.75 (m, 4H), 3.89 (s, 2H), 3.93 (t, J¼7.8 Hz, 2H),
4.07 (t, J¼7.8 Hz, 2H), 4.33 (q, J¼7.3 Hz, 2H), 4.85 (s, 2H); 13C NMR
3.3.1. Double rhodanine 10. Yield 43%; mp 183e185 ꢂC; 1H NMR
(CDCl3)
d¼14.10, 14.16ꢁ2, 22.7ꢁ2, 26.6, 26.9, 27.0, 29.19ꢁ2,
(CDCl3)
d
¼1.28 (t, J¼7.1 Hz, 3H),1.33 (t, J¼7.1 Hz, 3H), 3.81 (s, 2H), 3.96
29.22ꢁ2, 29.7, 31.3, 31.8, 31.9, 44.9, 45.1, 45.9, 63.0, 90.3, 92.9, 145.5,
(q, J¼7.1 Hz, 2H), 4.17 (q, J¼7.1 Hz, 2H); FABMS (NBA) m/z 289 (MHþ).
151.6, 166.4, 166.8, 167.0, 172.8, 189.8; FABMS (NBA) m/z 642 (MHþ).
3.3.2. Double rhodanine 11. Yield 18%; mp 60e61 ꢂC; IR (KBr)
3.4.3. Triple rhodanine ethyl ester 19. Yield 51%; oil; IR (KBr)
n
¼1735, 1666, 1528 cmꢀ1; 1H NMR (CDCl3)
d
¼0.87 (t, J¼6.9 Hz, 3H),
n
¼1735, 1669, 1522, 1181 cmꢀ1
;
1H NMR (CDCl3)
d¼0.83e0.97 (m,

M. Matsui et al. / Tetrahedron 66 (2010) 7405e7410
7409
12H), 1.17e1.45 (m, 16H), 1.39 (t, J¼7.3 Hz, 3H), 1.88 (sep, J¼7.8 Hz,
1H), 2.07 (sep, J¼7.3 Hz,1H), 3.89 (s, 2H), 3.90 (d, J¼7.8 Hz, 2H), 3.99
(d, J¼7.3 Hz, 2H), 4.33 (q, J¼7.3 Hz, 2H), 4.86 (s, 2H); 13C NMR
(s, 2H), 4.94 (s, 2H), 5.24 (s, 2H), 5.26 (s, 2H), 7.12e7.16 (m, 2H),
7.27e7.43 (m, 8H); 13C NMR (CDCl3)
d¼31.3, 45.6, 47.7, 47.8, 91.3,
92.2,126.0, 128.1,128.4,128.6,128.8, 129.3,133.8,134.9,145.6,152.5,
(CDCl3)
d
¼10.4, 10.8, 14.07, 14.12, 14.9, 23.1ꢁ2, 24.1ꢁ2, 28.0, 28.5,
166.8, 167.2, 167.8, 172.9, 189.9; FABMS (NBA) m/z 570 (MHþ).
29.6, 30.1, 31.7, 36.9, 39.0, 40.6, 48.9, 49.0, 61.7, 90.3, 91.4, 146.8,
152.8, 167.4ꢁ2, 167.6, 173.0, 190.0; FABMS (NBA) m/z 642 (MHþ).
3.5.5. Triple rhodanine acetic acid 27. Yield 78%; mp 121e123 ꢂC; IR
(KBr)
n
¼3448, 1735, 1654, 1534, 1137 cmꢀ1; 1H NMR (CDCl3)
¼0.87
d
3.4.4. Triple rhodanine ethyl ester 20. Yield 40%; mp 224e226 ꢂC;
(t, J¼6.9 Hz, 3H), 1.20e1.37 (m, 10H), 1.64 (quint, J¼7.8 Hz, 2H), 3.91
IR (KBr)
n
¼1730, 1664, 1522, 1202, 1153 cmꢀ1
;
1H NMR (CDCl3)
(s, 2H), 4.01 (t, J¼7.8 Hz, 2H), 4.97 (s, 2H), 5.26 (s, 2H), 7.10e7.42 (m,
d
¼1.38 (t, J¼7.3 Hz, 3H), 3.90 (s, 2H), 4.34 (q, J¼7.3 Hz, 2H), 4.88 (s,
5H); 13C NMR (CDCl3)
d¼14.2, 22.7, 26.88, 26.94, 29.2, 29.8, 31.4,
2H), 5.23 (s, 2H), 5.25 (s, 2H), 7.14e7.44 (m, 10H); 13C NMR (CDCl3)
31.8, 40.3, 44.9, 47.7, 91.5, 92.2, 126.0, 128.4, 129.3, 133.9, 145.3,
d
¼14.1, 31.4, 45.9, 47.7ꢁ2, 63.1, 91.1, 92.2, 126.0, 128.1, 128.3, 128.5,
152.4, 166.9, 167.2, 167.8, 173.2, 189.8; FABMS (NBA) m/z 592 (MHþ).
129.1, 129.3, 133.9, 135.1, 145.4, 152.4, 166.4, 166.9, 167.0, 172.8,
189.9; FABMS (NBA) m/z 598 (MHþ).
3.5.6. Triple rhodanine acetic acid 28. Yield 77%; mp 141e143 ꢂC; IR
(KBr)
n
¼3448, 1735, 1654, 1507, 1154 cmꢀ1; 1H NMR (CDCl3)
¼0.88
d
3.4.5. Triple rhodanine ethyl ester 21. Yield 22%; mp 130e132 ꢂC; IR
(t, J¼6.9 Hz, 3H), 1.21e1.45 (m, 10H), 1.68 (quint, J¼7.9 Hz, 2H), 3.89
(KBr)
n
¼1735, 1654, 1526, 1221, 1145 cmꢀ1; 1H NMR (CDCl3)
¼0.87
d
(s, 2H), 3.94 (t, J¼7.9 Hz, 2H), 4.91 (s, 2H), 5.29 (s, 2H), 7.28e7.44 (m,
(t, J¼6.9 Hz, 3H), 1.20e1.36 (m, 10H), 1.40 (t, J¼7.3 Hz, 3H), 1.64
(quint, J¼7.7 Hz, 2H), 3.90 (s, 2H), 4.01 (t, J¼7.7 Hz, 2H), 4.35 (q,
J¼7.3 Hz, 2H), 4.89 (s, 2H), 5.25 (s, 2H), 7.12e7.40 (m, 5H); 13C NMR
5H); 13C NMR (CDCl3)
d¼14.2, 22.7, 26.45, 26.54, 29.2, 29.2, 31.3,
31.8, 45.2, 45.7, 47.7, 90.2, 92.6,128.1,128.6,129.2, 135.0,146.3, 152.1,
166.7, 167.1, 168.4, 173.0, 189.6; FABMS (NBA) m/z 592 (MHþ).
(CDCl3)
d
¼14.2, 15.0, 22.7, 26.9, 27.0, 29.2, 31.7, 31.8, 33.7, 40.6, 45.0,
47.7, 61.6, 90.9, 91.1, 126.0, 128.3, 129.3, 134.1, 146.0, 153.5, 167.1,
3.6. Synthesis of triple rhodanine indoline dyes 30e35
167.2, 169.9, 173.0, 189.8; FABMS (NBA) m/z 620 (MHþ).
To an acetic acid solution (20 ml) containing 29 (75 mg,
0.17 mmol) and 23e28 (0.16 mmol) was added ammonium acetate
(60 mg, 0.78 mmol). The mixture was refluxed for 4 h. After the
reaction was completed, the mixture was concentrated in vacuo
and washed with methanol. The product was purified by column
chromatography (SiO2, CHCl3/MeOH¼20:1).
3.4.6. Triple rhodanine ethyl ester 22. Yield 27%; mp 165e167 ꢂC; IR
(KBr)
n
¼1735, 1672, 1513, 1192 cmꢀ1
;
1H NMR (CDCl3)
d
¼0.88 (t,
J¼6.9 Hz, 3H), 1.21e1.44 (m, 10H), 1.36 (t, J¼7.3 Hz, 3H), 1.68 (quint,
J¼8.0 Hz, 2H), 3.89 (s, 2H), 3.93 (t, J¼8.0 Hz, 2H), 4.31 (q, J¼7.3 Hz,
2H), 4.84 (s, 2H), 5.29 (s, 2H), 7.28e7.48 (m, 5H); 13C NMR (CDCl3)
d
¼14.1, 14.2, 22.7, 26.5ꢁ2, 29.2, 29.7, 31.3, 31.8, 45.2, 45.9, 47.7, 63.0,
90.1, 92.8, 128.1, 128.5, 129.1, 135.1, 145.9, 151.7, 166.4, 166.7, 169.9,
3.6.1. Triple rhodanine indoline dye 30 (D150). Yield 44%; mp
172.7, 189.7; FABMS (NBA) m/z 620 (MHþ).
>300 ꢂC; IR (KBr)
n
¼3375, 1643 cmꢀ1
;
1H NMR (DMSO-d6)
d
¼1.17
(t, J¼7.2 Hz, 3H), 1.28 (t, J¼7.2 Hz, 3H), 1.30e1.37 (m, 1H), 1.59e1.70
(m, 2H), 1.76e1.84 (m, 2H), 2.04e2.11 (m, 1H), 3.85e3.90 (m, 1H),
3.94e4.08 (m, 4H), 4.87 (s, 2H), 4.95e5.00 (m, 1H), 7.02e7.06 (m,
3H), 7.09 (s, 1H), 7.15e7.18 (m, 2H), 7.21 (d, J¼6.9 Hz, 2H), 7.27e7.37
(m, 5H), 7.40e7.49 (m, 5H), 7.67 (s, 1H); HRFABMS m/z 869.1974
(MHþ), calcd for C47H41N4O5S4: 869.1960.
3.5. Synthesis of triple rhodanine aceric acids 23e28
To an acetic acid solution (20 ml) of ethyl esters 17e22
(0.32 mmol), was added concd hydrochloric acid (8 ml). The mix-
ture was refluxed for 4 h. After the reaction was completed, the
product was extracted with chloroform (80 mlꢁ3). The crude
product was used without further purification.
3.6.2. Triple rhodanine indoline dye 31. Yield 35%; mp >300 ꢂC; IR
(KBr)
n
¼3402, 1647 cmꢀ1
;
1H NMR (DMSO-d6)
d
¼0.80e0.91 (m,
3.5.1. Triple rhodanine acetic acid 23. Yield 76%; mp 179e181 ꢂC; 1H
6H), 1.14e1.39 (m, 21H), 1.46e1.70 (m, 6H), 1.75e1.84 (m, 2H),
2.04e2.10 (m, 1H), 3.83e3.98 (m, 5H), 4.71 (s, 2H), 4.93e4.99 (m,
1H), 7.01e7.07 (m, 3H), 7.09 (s, 1H), 7.21 (d, J¼6.8 Hz, 2H), 7.18e7.23
(m, 2H), 7.23e7.37 (m, 5H), 7.37e7.49 (m, 5H), 7.63 (s, 1H);
HRFABMS m/z 1037.3827 (MHþ), calcd for C59H65N4O5S4:
1037.3838.
NMR (400 MHz, CDCl3)
d
¼1.29 (t, J¼7.2 Hz, 3H), 1.33 (t, J¼7.2 Hz,
3H), 3.90 (s, 2H), 3.96 (q, J¼7.2 Hz, 2H), 4.17 (q, J¼7.2 Hz, 2H), 4.90
(s, 2H); FABMS (NBA) m/z (rel intensity) 460 (MHþ).
3.5.2. Triple rhodanine acetic acid 24. Yield 71%; mp 180e182 ꢂC; IR
(KBr)
n
¼3495, 1735, 1654, 1518, 1143 cmꢀ1; 1H NMR (CDCl3)
¼0.88
d
(t, J¼6.9 Hz, 3H), 0.89 (t, J¼6.9 Hz, 3H), 1.21e1.45 (m, 20H),
3.6.3. Triple rhodanine indoline dye 32. Yield 52%; mp >300 ꢂC; IR
1.63e1.73 (m, 4H), 3.89 (s, 2H), 3.94 (t, J¼8.2 Hz, 2H), 4.07 (t,
(KBr)
n
¼3395, 1647 cmꢀ1
;
1H NMR (DMSO-d6)
d
¼0.72e0.92 (m,
J¼7.8 Hz, 2H), 4.91 (s, 2H); 13C NMR (CDCl3)
d
¼14.2ꢁ2, 22.7ꢁ2, 26.5,
12H), 1.06e1.40 (m, 17H), 1.56e1.70 (m, 2H), 1.70e1.88 (m, 3H),
1.88e2.00 (m, 1H), 2.00e2.12 (m, 1H), 3.72e3.90 (m, 5H), 4.73 (s,
2H), 4.90e4.98 (m, 1H), 7.00e7.06 (m, 3H), 7.08 (s, 1H), 7.20 (d,
J¼7.4 Hz, 2H), 7.17e7.23 (m, 2H), 7.26e7.50 (m, 10H), 7.62 (s, 1H);
HRFABMS m/z 1037.3770 (MHþ), calcd for C59H65N4O5S4:
1037.3838.
26.9, 27.0, 29.17ꢁ2, 29.23ꢁ2, 29.7, 31.3, 31.8, 31.9, 45.0, 45.2, 45.6,
90.6, 92.8, 145.7, 151.6, 166.7, 167.3, 168.8, 173.0, 189.6; FABMS (NBA)
m/z 614 (MHþ).
3.5.3. Triple rhodanine acetic acid 25. Yield 72%; mp 169e171 ꢂC; IR
(KBr)
n
¼3495, 1735, 1666, 1513, 1142 cmꢀ1
;
1H NMR (CDCl3)
d
¼0.81e9.99 (m, 12H), 1.17e1.45 (m, 16H), 1.88 (sep, J¼7.8 Hz, 1H),
3.6.4. Triple rhodanine indoline dye 33. Yield 43%; mp >300 ꢂC; IR
2.08 (sep, J¼7.4 Hz, 1H), 3.89 (s, 2H), 3.91 (d, J¼7.8 Hz, 2H), 4.00 (d,
(KBr)
n
¼3402, 1651 cmꢀ1; 1H NMR (DMSO-d6)
¼1.22e1.38 (m, 1H),
d
J¼7.4 Hz, 2H), 4.95 (s, 2H); 13C NMR (CDCl3)
d¼10.3, 10.7, 14.06,
1.54e1.68 (m, 2H), 1.70e1.84 (m, 2H), 1.96e2.10 (m, 1H), 3.78e3.86
(m, 1H), 4.61 (s, 2H), 4.88e4.96 (m, 1H), 5.11 (s, 2H), 5.28 (s, 2H),
6.96e7.94 (m, 28H), 7.61 (s, 1H); HRFABMS m/z 993.2192 (MHþ),
calcd for C57H45N4O5S4: 993.2273.
14.12, 23.1ꢁ2, 24.0ꢁ2, 28.0, 28.5, 29.6, 30.5, 31.3, 36.9, 39.0, 45.7,
49.0ꢁ2, 90.8, 92.7, 146.0, 151.6, 167.1, 167.8, 168.8, 173.1, 189.8;
FABMS (NBA) m/z 614 (MHþ).
3.5.4. Triple rhodanine acetic acid 26. Yield 70%; mp 170e172 ꢂC; IR
3.6.5. Triple rhodanine indoline dye 34. Yield 41%; mp >300 ꢂC; IR
(KBr)
n
¼3463, 1735, 1654, 1522, 1144 cmꢀ1; 1H NMR (CDCl3)
d¼3.90
(KBr)
n
¼3383, 1655 cmꢀ1
;
1H NMR (DMSO-d6)
d
¼0.84 (t,

7410
M. Matsui et al. / Tetrahedron 66 (2010) 7405e7410
J¼6.7 Hz, 3H), 1.17e1.35 (m, 11H), 1.47e1.68 (m, 4H), 1.70e1.83
(m, 2H), 1.97e2.06 (m, 1H), 3.78e3.89 (m, 3H), 4.57 (s, 2H),
4.88e4.95 (m, 1H), 5.26 (s, 2H), 6.93e7.48 (m, 23H), 7.58 (s, 1H);
HRFABMS m/z 1015.3074 (MHþ), calcd for C58H55N4O5S4:
1015.3055.
simulated sun light (100 mW cmꢀ2) through a shading mask
(5.0ꢁ4.0 mm) by using a Bunko-Keiki CEP-2000 system.
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).
3.6.6. Triple rhodanine indoline dye 35. Yield 40%; mp >300 ꢂC; IR
(KBr)
n
¼3402, 1647 cmꢀ1
;
1H NMR (DMSO-d6)
d
¼0.84 (t,
J¼7.8 Hz, 3H), 1.19e1.41 (m, 11H), 1.56e1.70 (m, 4H), 1.72e1.84
(m, 2H), 1.99e2.10 (m, 1H), 3.79e3.92 (m, 3H), 4.54 (s, 2H),
4.88e4.95 (m, 1H), 5.13 (s, 2H), 6.97e7.05 (m, 3H), 7.07 (s, 1H),
7.09e7.14 (m, 2H), 7.17e7.22 (m, 2H), 7.24e7.49 (m, 15H), 7.55 (s,
1H); HRFABMS m/z 1015.3030 (MHþ), calcd for C58H55N4O5S4:
1015.3055.
Supplementary data
Calculated total energy of structural isomers of 31 and the LUMO
and HOMO electron density of 31 calculated by the B3LYP/6-31G(d,
p)//B3LYP/3-21 G level. Supplementary data associated with this
article can be found online version at doi:10.1016/j.tet.2010.07.017.
3.7. Electrochemical measurements
References and notes
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 dmꢀ3) and ferrocene (ca. 1 mmol dmꢀ3) was prepared. The
electrochemical measurement was performed at the scan rate of
1. (a) Wang, Z.-S.; Cui, Y.; Dan-oh, Y.; Kasada, C.; Shinpo, A.; Hara, K. J. Phys. Chem.
C 2008, 112, 17011; (b) Wang, Z.-S.; Cui, Y.; Dan-oh, Y.; Kasada, C.; Shinpo, A.;
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Y.; Kasada, C.; Shinpo, A. Adv. Mater. 2007, 19, 1138.
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100 mV sꢀ1
.
3. (a) Choi, H.; Kang, S.-O.; Ko, J.; Gao, G.; Kang, H.-S.; Kang, M.-S.; Nazeeruddin, M.
€
K.; Gratzel, M. Angew. Chem., Int. Ed. 2009, 48, 5938; (b) Cho, N.; Choi, H.; Kim, D.;
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An aqueous potassium
€
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0.1 mol dmꢀ3) was electrolyzed at ꢀ1.0 V versus SCE with bub-
bling an oxygen gas at 70 ꢂC for 30 min. Platinum was used as
a counter electrode. To the pre-electrolyzed film was added an
aqueous solution of zinc chloride (5 mmol dmꢀ3). Then, the film
was electro-deposited again in the solution at ꢀ1.0 V versus SCE
at 70 ꢂC for 20 min with bubbling an oxygen gas. To the electro-
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Y
(50
m
mol dmꢀ3). The film was electro-deposited at ꢀ1.0 V versus
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for 1 h. The film was immersed in a chloroform solution of dye
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temperature for 1 h. In the case of D149, the film was immersed in
an acetonitrile-tert-butyl alcohol (1:1) mixed solution of dye
(0.5 mmol dmꢀ3) containing cholic acid (1.0 mmol dmꢀ3) at room
temperature. Then, the film was washed with the solution. Ace-
tonitrile/ethylenecarbonate (v/v¼1:4) containing tetrabuty-
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was used as an electrolyte.
)
€
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An action spectrum was measured under monochromatic light
with a constant photon number (0.5ꢁ1016 photon cmꢀ2 sꢀ1). IeV
characteristics were measured under illumination with AM 1.5
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Gratzel, M.; Durrant, J. R. J. Am. Chem. Soc. 2006, 128, 16376.