Application of novel N-(p-phenylene)-dicyanovinylidene double rhodanine indoline dye for zinc oxide dye-sensitized solar cell

Article abstract of DOI:10.1016/j.dyepig.2012.08.023

A new indoline dye in which a double rhodanine acceptor is attached to the indoline moiety by a p-phenylene spacer on the indoline-nitrogen, has been examined for its performance as a sensitizer for zinc oxide dye-sensitized solar cells. In the presence of cholic acid, chenodeoxycholic acid, or lithocholic acid; the performance was greatest for lithocholic acid as this showed the greatest reduction in dye H-Aggregate formation.

Full text of DOI:10.1016/j.dyepig.2012.08.023

Dyes and Pigments 96 (2013) 614e618
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Application of novel N-(p-phenylene)-dicyanovinylidene double rhodanine
indoline dye for zinc oxide dye-sensitized solar cell
,
a
a
a
a
b
Masaki Matsui a , Takuo Inoue , Masaomi Ono , Yasuhiro Kubota , Kazumasa Funabiki , Jiye Jin ,
*
Tsukasa Yoshida c, 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 Research Center of Organic Electronics, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan
d Chemicrea Co. Ltd., 1-133 Azaootsurugi, Shimokawa, Izumi, Iwaki, Fukushima 971-8183, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A new indoline dye in which a double rhodanine acceptor is attached to the indoline moiety by
a p-phenylene spacer on the indolineenitrogen, has been examined for its performance as a sensitizer for
zinc oxide dye-sensitized solar cells. In the presence of cholic acid, chenodeoxycholic acid, or lithocholic
acid; the performance was greatest for lithocholic acid as this showed the greatest reduction in dye
H-aggregate formation.
Received 3 August 2012
Received in revised form
22 August 2012
Accepted 22 August 2012
Available online 9 October 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Dye-sensitized solar cell
Indoline dyes
Sensitizers
DFT calculations
Zinc oxide
Cholic acids
1. Introduction
gap between the oxidation potential (Eox) of the indoline dye and
Iꢀ/Iꢀ3 redox level is small compared with that between the reduc-
Indoline dyes are known as one of the highly efficient organic
sensitizers in dye-sensitized solar cells. D149 in which a double
rhodanine ring is attached through a methine linkage at the 7-
position on the indoline ring has been reported to show excellent
conversion efficiency 9.0% on titanium oxide [1,2]. The double
rhodanine indoline dyes having two anchoring carboxyl groups [3],
an octyl group at the terminal rhodanine ring [4], a thiophene
spacer(s) [5], and dicyanovinylidene group [6,7] have been also
designed, synthesized, and evaluated as the sensitizers. Further-
more, indoline dyes of mono rhodanine [8], triple rhodanine [9],
cyanoacrylic acid acceptors [10e12], benzoindoline derivatives
[13], and naphthalimides attached with two indoline moieties [14]
have been reported. We suppose that the characteristic feature of
indoline dyes is a cyclopentane moiety which can depress aggre-
gates formation on semiconductors [15]. We have reported that
when a double rhodanine ring is used as the acceptor, the energy
tion potential of the indoline dye and the conduction level of zinc
oxide [16]. Therefore, the positive shift of Eox is desirable to obtain
a high incident-photon-to-current conversion efficiency (IPCE). On
the basis of these points, we have designed a new double rhodanine
indoline dye GU104, in which a double rhodanine acceptor is
attached to the indoline moiety by way of a p-phenylene spacer on
the indolineenitrogen and whose HOMO level was predicted to be
more stable (ꢀ5.35 eV) than D149 (ꢀ5.07) by the DFT calculations.
We report herein the application of novel indoline dye, GU104, to
zinc oxide dye-sensitized solar cell.
2. Results and discussion
2.1. Synthesis
A new indoline dye GU104 was synthesized as shown in
Scheme 1. An indoline
1 was allowed to react with 4-
bromobenzaldehyde (2) to give a formyl derivative 3 followed by
the reaction with a dicyanovinylidene double rhodanine acetic acid
4 to provide GU104.
* Corresponding author. Tel.: þ81 (0) 58 293 2601; fax: þ81 (0) 58 293 2794.
E-mail address: matsuim@gifu-u.ac.jp (M. Matsui).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.08.023

M. Matsui et al. / Dyes and Pigments 96 (2013) 614e618
615
S
S
COOH
O
C2H5
N
N
O
O
COOH
S
N
S
S
CN
O
N
N
O
N
N
Br
i)
CHO
CN
C8H17
COOH
2
4
S
ii)
N
NH
CHO
S
O
CN
CN
N
3
1
C8H17
GU104
D149
Scheme 1. Reagents and conditions: i) 1 (1.0 equiv), 2 (1.2 equiv), t-BuONa (1.4 equiv), Pd(OAc)2 (5 mol%), SPhos (10 mol%), toluene, reflux, overnight, ii) 3 (1.0 equiv), 4 (1.0 equiv),
piperidine (1.0 equiv), BuOH, 120 ꢁC, 4 h.
2.2. UVevis absorption and fluorescence spectra
indicate that GU104 consists of an intramolecular charge-transfer
chromophoric system from indoline to rhodanine moiety as
shown in Fig. 2c.
The UVevis absorption and fluorescence spectra of GU104 in
chloroform are indicated in Fig. 1. The results are also listed in
Table 1. The first absorption maximum (lmax) of GU104 was
observed at 541 nm with molar absorption coefficient
34,600 dm3 molꢀ1 cmꢀ1. Though no remarkable difference in the
lmax was observed between GU104 and D149 (542 nm), the value
2.4. Electrochemical measurements
(
3 )
Fig. 3 shows the cyclic voltammogram of GU104 vs Ag quasi
reference electrode (QRE) in DMF in the presence of ferrocene as an
internal standard. The oxidative wave at þ0.70 and 1.14 V corre-
spond to the oxidation of ferrocene and GU104, respectively.
Therefore, the oxidation potential (Eox) of GU104 is estimated to be
0.44 V vs Fc/Fcþ. That of D149 was estimated to be 0.40 V vs Fc/Fcþ.
Thus, the Eox level of GU104 was more positive than that of D149.
The result is consistent with the DFT calculations that the HOMO
level of GU104 (ꢀ5.35) is more stable than that of D149 (ꢀ5.07). The
Iꢀ/Iꢀ3 redox level was estimated to be ꢀ0.05 V vs Fc/Fcþ. As no
reduction potential peak was observed for GU104, the Eox ꢀ E0-
0 level was calculated as described in our previous paper [12]. The
Eox ꢀ E0-0 level of GU104 was calculated to be ꢀ1.67 V vs Fc/Fcþ. This
level is slightly more positive than that of D149 (ꢀ1.70 V vs Fc/Fcþ)
[12]. The conduction band level of zinc oxide is ꢀ0.95 V vs Fc/Fcþ.
Therefore, GU104 can thermodynamically sensitize zinc oxide and
the oxidized GU104 can accept electrons from Iꢀ.
3
of GU104 was significantly smaller than that of D149 (66,000). The
fluorescence maximum (Fmax) of GU104 was observed at 642 nm.
2.3. DFT calculations
The structure of GU104 was optimized by the B3LYP/3-21G level.
The results are shown in Fig. 2 and Table 1. Fig. 2a indicates that the
double bond at the 4-position on the p-phenylene ring adopts the
Z-conformation in order to minimize repulsion between the ortho-
phenyl hydrogen atom and the carbonyl oxygen of the inner rho-
danine carbonyl group. The double bond between the two rhoda-
nine moieties adopts the E-conformation as this avoids steric
repulsion between the N-carboxymethyl group of the inner rho-
danine ring and the carbonyl group of the terminal rhodanine ring.
The dihedral angles q1 and q2 are calculated to be 16.2 and 1.1ꢁ,
respectively. A large q
1 could be attributed to repulsion between the
hydrogen atom at the 3a-position in the indoline moiety and 6-
hydrogen atom on the p-phenylene ring. D149 ethyl ester has
been reported to be almost planar through indolineenitrogen to
2.5. Photoelectrochemical properties
double rhodanine acceptor [15]. Thus, a smaller value (34,600) of
3
The UVevis absorption spectra on zinc oxide, IPCE action
spectra, and IeV curve of GU104 in the presence of cholic acid (CA),
chenodeoxycholic acid (CDCA), and lithocholic acid (LCA) are
GU104 in the first absorption band, compared with that of D149
(66,000), could come from the less planarity of GU104. Fig. 2b
shows that the HOMO and LUMO levels of GU104 were calculated
to be ꢀ5.35 and ꢀ2.60 eV, respectively. Those of D149 were
calculated to be ꢀ5.07 and ꢀ2.37 eV, respectively [12]. Thus, the
HOMO level of GU104 was more stable than that of D149. The
isodensity surface plots of GU104 in the HOMO and LUMO levels
shown in Fig. 4 and Table 2. The conversion efficiency (h) of GU104
was higher in the order of the cholic acids: LCA (3.93) > CDCA
(3.67) > CA (3.35). No remarkable differences in open-circuit
photovoltage (Voc) and fill factor (ff) were observed among the
cholic acids. The
h value mainly depends on the short-circuit
photocurrent density (Jsc). Fig. 4a depicts that the absorbance
values were in the range of 1.95e2.11, indicating that similar
amount of dyes were adsorbed on zinc oxide. Actually, the
amounts of adsorbed GU104 were in the range of 2.81e
3.22 ꢂ 10ꢀ6 mol cmꢀ2. Therefore, the ratio of aggregated GU104
on zinc oxide could affect the Jsc value. The normalized UVevis
absorption spectra of GU104, depicted in Fig. 4b, significantly
show that the shoulder peak at around 470 nm comes from H-
aggregates and was broadened in the order of cholic acids:
CA > CDCA > LCA. The IPCE spectra clearly show that the sensiti-
zation of GU104 was larger in the order of cholic acids:
LCA > CDCA > CA as shown in Fig. 4c. Thus, LCA could most
effectively prevent H-aggregate formation of GU104 on zinc oxide
to show the best performance.
0.5
60
0.4
0.3
0.2
0.1
0
40
20
400
500
600
700
800
Wavelength / nm
Fig. 1. UVevis absorption and fluorescence spectra
(1.0 ꢂ 10ꢀ5 mol dmꢀ3) in chloroform at 25 ꢁC.
(lex
¼
540 nm) of GU104

616
M. Matsui et al. / Dyes and Pigments 96 (2013) 614e618
Table 1
Properties of GU104.
a
a
b
c
Compd
lmax
(
3 )
nm
Fmax
nm
Eox
V
Eox ꢀ E0-0
ꢀ1.67
V
HOMOd
eV
LUMOd
eV
fe
GU104
392 (15,100), 541 (34,600)
642
þ0.44
ꢀ5.35
ꢀ2.60
1.02
Measured on 1.0 ꢂ 10ꢀ5 mol dmꢀ3 of substrate in chloroform at 25 ꢁC.
a
b
c
vs Fc/Fcþ in DMF.
Calculated on the basis of Eox and lint
Calculated by the B3LYP/6-31G(d,p)//B3LYP/3-21G level.
Oscillator strength calculated by the INDO/S method.
.
d
e
3. Conclusion
2-dicyclohexylphosphyno-20,60-dimethoxybiphenyl (SPhos,1.000 g,
2.44 mmol). The mixture was refluxed overnight. After the reaction
was completed, the mixture was poured into water (300 mL). The
product was extracted with chloroform (100 mL ꢂ 3). The extract
was washed with water (100 mL ꢂ 3) and dried over anhydrous
sodium sulfate. The product was purified by column chromatog-
raphy (SiO2, CHCl3:C6H14 ¼1:1) to give pale yellow liquid. Yield 31%;
We have made a molecular design, synthesis, and evaluation of
a new indoline dye GU104 in which dicyanovinylidene rhodanine
moiety is attached to the indoline moiety through an p-phenylene
spacer on the indolineenitrogen atom. GU104 could have more
positive Eox level than D149. Cell performance in the presence of
CA, CDCA, or LDA was greatest for LCA as this showed the greatest
reduction in dye H-aggregate formation.
1H NMR (CDCl3)
d
¼ 0.85e0.99 (m,1H),1.24e1.32 (m,1H),1.38e1.52
(m, 1H), 1.63e1.75 (m, 1H), 1.89e2.12 (m, 2H), 3.87e3.94 (m, 1H),
4.58e4.74 (m, 1H), 6.89 (t, J ¼ 7.8 Hz, 1H), 7.14 (t, J ¼ 7.8 Hz, 1H), 7.18
(d, J ¼ 7.8 Hz,1H), 7.27 (d, J ¼ 7.8 Hz,1H), 7.34 (d, J ¼ 8.7 Hz, 2H), 7.81
4. Experimental
(d, J ¼ 8.7 Hz, 2H), 9.82 (s, 1H); 13C NMR (CDCl3)
¼ 24.7, 34.1 (2C),
d
45.5, 68.5,110.7,115.9 (2C),121.2,125.0,127.1,128.3,131.5 (2C),136.0,
144.7, 148.7, 190.3; IR (KBr) 2928, 2855, 1744, 1686, 1589, 1481,
1381 cmꢀ1; EIMS (70 eV) m/z (rel intensity) 263 (Mþ, 52), 234 (100),
104 (14); Anal. Found: 82.43; H, 6.90; N, 5.71%. Calcd for C18H17NO:
C, 82.10, H, 6.51; N, 5.32%.
4.1. Instruments
Melting points were measured with a Yanaco MP-S2 micro-
melting-point apparatus. NMR spectra were taken with a JEOL
JNM-ECX 400P spectrometer. Mass spectra were taken on a JEOL
MStation 700 spectrometer. Elemental analysis was performed
with a Yanaco MT-6 CHN corder. UVevis absorption and fluores-
cence spectra were taken on Hitachi U-3500 and F-4500 spec-
trophotometers, respectively. Electrochemical measurement was
carried out using an EG&G Princeton Applied Research Potentio-
stat/Galvanostat (Model 263A) driven by the M270 software
package.
4.4. Synthesis of GU104
To 1-butanol (10 mL) were added 3 (200 mg, 0.76 mmol),
a dicyanovinylidene double rhodanine acetic acid 4 (341 mg,
0.76 mmol). The mixture was heated to 120 ꢁC. Then, to the mixture
was added piperidine (65 mg, 0.76 mmol). The mixture was
refluxed for 4 h. After the reaction was completed, the solvent was
removed in vacuo. The product was purified by column chroma-
tography (SiO2, CHCl3:MeOH ¼ 20:1). The 13C NMR spectrum was
not measured due to low solubility. Yield 69%; mp 242e243 ꢁC; 1H
4.2. Materials
Compounds 1 and 4 were supplied from Chemicrea Co., Ltd.
NMR (DMSO-d6)
d
¼ 0.85 (t, J ¼ 6.6 Hz, 3H), 1.17e1.36 (m, 11H),
4.3. Synthesis of 10-(4-formylphenyl)-6b,7,8,9,9a,10-hexahydro[g]
cyclopenta[b]indole (3)
1.55e1.68 (m, 3H), 1.71e1.87 (m, 2H), 1.98e2.11 (m, 2H), 3.85e3.93
(m, 1H), 3.97 (s, 2H), 4.54 (s, 2H), 4.75e4.83 (m, 1H), 6.88 (t,
J ¼ 7.7 Hz, 1H), 7.13 (t, J ¼ 7.7 Hz, 1H), 7.23 (d, J ¼ 7.7 Hz, 1H), 7.32 (d,
J ¼ 7.7 Hz,1H), 7.46 (d, J ¼ 8.5 Hz, 2H), 7.67 (d, J ¼ 8.5 Hz, 2H), 7.76 (s,
1H); IR (KBr) 2928, 2195,1655,1578,1543,1508 cmꢀ1; FABMS (NBA)
m/z 680 (MHþ); Anal. Found: C, 65.07; H, 5.63; N, 10.39%. Calcd for
C37H37N5O4S2: C, 65.37; H, 5.49; N, 10.30%.
To toluene (300 mL) were added 1,2,3,3a,4,8b-hexahy-
drocyclopenta[b]indole (1, 3.986 g, 25.0 mmol), 4-bromobenzal-
dehyde (2, 6.547 g, 30.0 mmol), sodium t-butoxide (3.360 g,
35.0 mmol), palladium diacetate (0.281 g, 1.25 mmol), and
Fig. 2. DFT calculations (B3LYP/6-31G(d,p)//B3LYP/3-21G) of GU104. (a) optimized structure, (b) HOMO and LUMO levels, and (c) isodensity surface plots.

M. Matsui et al. / Dyes and Pigments 96 (2013) 614e618
617
Table 2
1
0
Photovoltaic properties of Gu104 on zinc oxide.
Run Additivesa Adsorbed GU104 mol dmꢀ3 Jscb mA cmꢀ2 Voc
V
ffb
hb
%
1
2
3
CA
CDCA
LCA
3.22 ꢂ 10ꢀ6
3.81 ꢂ 10ꢀ6
3.21 ꢂ 10ꢀ6
7.67
8.09
8.53
0.62 0.71 3.35
0.64 0.71 3.67
0.64 0.72 3.93
-1
-2
-3
-4
-5
a
Fc/Fc+
Two molar amounts of cholic acids for GU104.
AM 1.5 irradiation (100 mW cmꢀ2).
b
E
ox
prepared from nanoparticle ZnO-410 (Sumitomo Osaka Cement Co.,
Ltd). The thickness of zinc oxide layer was 12 m. An acetonitrile-
tert-butyl alcohol (v/v, 1:1) mixed solution of dye (0.5 mM) con-
taining a cholic acid (1.0 mM) was prepared. The zinc oxide elec-
trodes were immersed into the solution and kept at room
1.2
0.8
0.4
0
m
Potential / V vs. Ag (QRE)
Fig. 3. Cyclic voltammogram of GU104 in the presence of ferrocene. Measured in DMF
vs AgQRE at scan rate 100 mV sꢀ1
.
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
4.5. Electrochemical measurements
ionomer film (HIMILAN, 35 mm thick, DuPont), which is served as
The oxidation potential was measured by using small-size three
electrodes. Ag quasi reference electrode (AgQRE) 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 dye 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
a spacer between the electrodes. A drop of the electrolyte solution
was placed on a drilled hole in the counter electrode of the
assembled 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.
100 mV sꢀ1
.
4.7. Photoelectrochemical measurements
4.6. Film preparation
An action spectrum was obtained under monochromatic light
with a constant photon number (0.5 ꢂ 1016 photon cmꢀ2 sꢀ1). IeV
characteristics were measured under illumination with AM 1.5
simulated sun light (100 mW cmꢀ2) through a shading mast
(5.0 mm ꢂ 4.0 mm) by using a Bunko-Keiki CEP-2000 system.
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
a
3
b
CA
CA
1
CDCA
CDCA
LCA
LCA
2
0.5
1
0
0
500
600
700
400
400
500
600
700
Wavelength/nm
Wavelength / nm
d
c
80
CA
CA
⋅
10
5
CDCA
LCA
CDCA
LCA
60
40
20
0
0
300
400
500
600
700
800
0.2
0.4
0.6
0.8
Wavelength / nm
Voltage / V
Fig. 4. Photoelectrochemical properties of GU104 in the presence of cholic acids LCA, CDCA, and CA. (a) UVevis absorption spectra on zinc oxide, (b) normalized UVevis absorption
spectra, (c) IPCE spectra, and (d) IeV curve.

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M. Matsui et al. / Dyes and Pigments 96 (2013) 614e618
[7] Higashijima S, Inoue Y, Miura H, Kubota Y, Funabiki K, Yoshida T, et al. Organic
Acknowledgment
dyes containing fluorene-substituted indoline core for zinc oxide dye-
sensitized solar cell. RSC Adv 2012;2:2721e4.
This work was financially supported in part by Grants-in-Aid for
Science Research (No. 21550180) from Japan Society for the
Promotion of Science (JSPS) and Research for Promoting Techno-
logical Seeds. The authors also thank The Koshiyama Research
Grant for the financial support.
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for dye-sensitized solar cells.
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[10] Akhtaruzzaman M, Islam A, Yang F, Asao N, Kwon E, Singh Surya P, et al.
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novel metal-free panchromatic TiO2 sensitizer based on
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