Synthesis of EDOT-containing organic dyes via one-pot, four-component Suzuki-Miyaura coupling and the evaluation of their photovoltaic properties

Article abstract of DOI:10.1016/j.tet.2014.09.039

We have developed a one-pot, four-component Suzuki-Miyaura coupling for the synthesis of thiophene-based donor-π-bridge-acceptor (D-π-A) dyes for dye-sensitized solar cells. Two D-π-A dyes, 19 and 20, retaining 3,4-ethylenedioxythiophene (EDOT) beside a c

Full text of DOI:10.1016/j.tet.2014.09.039

Tetrahedron xxx (2014) 1e6
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of EDOT-containing organic dyes via one-pot, four-
component SuzukieMiyaura coupling and the evaluation of their
photovoltaic properties
,
a
a
a
Shinichiro Fuse a , Yuya Asai , Sakae Sugiyama , Keisuke Matsumura ,
*
Masato M. Maitani a, Yuji Wada a, Yuhei Ogomi b, Shuzi Hayase b, Tatsuo Kaiho c,
Takashi Takahashi d
,
*
a Department of Applied Chemistry, Tokyo Institute of Technology, 2-12-1, Ookayama, Meguro, Tokyo 152-8552, Japan
b Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4, Hibikino, Wakamatsu, Kitakyusyu,
Fukuoka 808-0196, Japan
c Kanto Natural Gas Development Co., Ltd., Brine Resources Research & Development Division, 661, Mobara, Mobara-shi, Chiba 297-8550, Japan
d Yokohama College of Pharmacy, 601, Matano-cho, Totsuka-ku, Yokohama-shi, Kanagawa 245-0066, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2014
Received in revised form 12 September 2014
Accepted 12 September 2014
Available online xxx
We have developed a one-pot, four-component SuzukieMiyaura coupling for the synthesis of thiophene-
based donore
p
-bridgeeacceptor (De
p
eA) dyes for dye-sensitized solar cells. Two De
peA dyes, 19 and
20, retaining 3,4-ethylenedioxythiophene (EDOT) beside a cyanoacrylic acid moiety, and one De
peA dye
21 without EDOT (reference compound) were rapidly synthesized in accordance with the developed
procedure. The measurement of the absorption spectra and the electrochemical properties of synthe-
sized dyes, and the photovoltaic properties of solar cells that were prepared using the synthesized dyes
19e21, revealed that the dyes retaining only one EDOT beside a cyanoacrylic acid moiety would exert
Keywords:
Dyes
SuzukieMiyaura coupling
One-pot
a high Jsc
.
Ó 2014 Published by Elsevier Ltd.
Dye-sensitized solar cell
Thiophene
1. Introduction
coupled without extra steps such as protection, deprotection, and
introduction of activating groups; (2) the number of work-up and
purification steps should be minimized; (3) each of the coupling
steps should be compatible with a variety of functional groups; and,
(4) readily available, nontoxic, and environmentally benign sub-
strates and reagents should be employed with no generation of
toxic compounds. From this point of view, one-pot, Suzu-
kieMiyaura (SM) coupling32,33 is attractive.34e48
We have reported combinatorial library syntheses for drug and
material development based on a palladium-catalyzed cross-cou-
pling reaction.49e58 Recently, we also reported one-pot, three-
component SM coupling procedures for the synthesis of a thio-
phene-based organic dyes library for dye-sensitized solar cells,56
p-type organic semiconductors, and bioactive compounds for the
Oligo-thiophene compounds make up an important class of
compounds because they can be used in organic electronics such as
in dyes1e21 for dye-sensitized solar cells (DSSC)22e29 and in p-type
semiconductors for thin-film organic solar cells.30,31 In the past
three decades, many sophisticated synthetic procedures have been
developed and utilized for the construction of oligo-thiophene
compounds. Nevertheless, the development of divergent,
protection/deprotection-free, short synthetic routes remains
important.
One-pot, multi-component coupling approaches are very useful
methods for the rapid construction of large molecules from simple
and small materials. The approaches should meet the following
criteria: (1) the multiple components should be sequentially
inhibition of amyloid-
b
and phospholilated tau protein
aggregations.58
Herein, we wish to report a one-pot, four-component SM cou-
pling approach for the synthesis of three thiophene-based organic
dyes, and the evaluation of their photovoltaic properties.
* Corresponding authors. Tel.: þ81 3 5734 2111; fax: þ81 3 5734 2884 (S.F.); tel.:
þ81 45 859 1381; fax: þ81 45 859 1382 (T.T.); e-mail addresses: sfuse@apc.titech.
ac.jp (S. Fuse), ttak@hamayaku.ac.jp (T. Takahashi).
http://dx.doi.org/10.1016/j.tet.2014.09.039
0040-4020/Ó 2014 Published by Elsevier Ltd.
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2
S. Fuse et al. / Tetrahedron xxx (2014) 1e6
2. Results and discussion
For the development of a one-pot, four-component coupling
procedure, simple and typical donore -bridgeeacceptor
(De
eA) dye 1159e64 was selected as a target. We planned to ex-
a
p
p
amine two synthetic routes toward the synthesis of 11, i.e., routes A
and B (Scheme 1). Both routes included three sequential SM cou-
plings for oligo-thiophene chain elongation from the donor side to
the acceptor side in accordance with our recently developed, one-
pot, three-component SM coupling procedure.56,65 The combina-
tion of aryl bromides and aryl boronic acids or aryl boronic acid
pinacol (Pin) esters was switched between routes A and B.
Scheme 2. Examination of route A.
Scheme 1. One-pot, four-component coupling approach to the synthesis of thiophene-
based organic dye 11.
Scheme 3. Examination of route B.
The one-pot, four-component coupling of 1,66 3, 4, and 956 in
accordance with route A was investigated. Combinations of Pd
catalysts [Pd2(dba)3,67 and Pd(OAc)268], phosphine ligands {[(t-
Bu3P)H]BF4,69 Xphos,70 and Sphos70}, temperature, and quantities
of substrates were examined. As a result, the combination shown in
Scheme 2 afforded the desired coupling product in a 14% yield (one-
pot, three-step yield based on 4).
Next, route B was investigated based on the optimized combi-
nation of a Pd catalyst and a phosphine ligand (Scheme 3). To
a solution of 4-(diphenylamino)phenylboronic acid (2)56 (1.1 equiv)
and 2,5-dibromothiophene (6) (1.0 equiv) in toluene/H2O (1:1)
were added Na2CO3 (2.0 equiv), 4 mol % of Pd2(dba)3, and 8 mol % of
[(t-Bu3P)H]BF4 at room temperature. After being stirred at 90 ꢀC for
3 h, to the resultant solution were added 2,5-bis-thiopheneboronic
acid pinacol ester (8) (1.2 equiv), Na2CO3 (2.0 equiv), 4 mol % of
Pd2(dba)3, and 8 mol % of [(t-Bu3P)H]BF4. After being stirred at 60 ꢀC
for 3 h, to the resultant solution were added tert-butyl (E)-3-(5-
bromothiophen-2-yl)-2-cyanoacrylate (10) (1.5 equiv), Na2CO3
(2.0 equiv), 4 mol % of Pd2(dba)3, and 8 mol % of [(t-Bu3P)H]BF4.
After being stirred at 60 ꢀC for 5 h, the toluene layer was simply
removed from the reaction vessel using a pipette, and was purified
by silica gel column chromatography and gel permeation chroma-
tography (GPC) in order to afford the desired coupling product. The
desired coupling product, 11, was obtained in a slightly higher yield
(17%, one-pot, three-step yield based on 6) compared with route A.
Palomares, De Angelis and co-workers reported attractive
DepeA dyes retaining 3,4-ethylenedioxythiophene (EDOT) beside
a cyanoacrylic acid moiety.71 Inspired by this report, two EDOT-
containing organic dyes, 19 and 20, and the reference compound
2172e75 were selected as target dyes.
The necessary building blocks 13 and 15 were prepared as
shown in Scheme 4. The building block 13 was prepared from
a readily available aryl bromide 1210 via a lithiation/borylation se-
quence. The building block 15 was prepared from a commercially
available aldehyde 14 via Knoevenagel condensation.
Protected oligo-thiophene dyes 16e18 were obtained in accor-
dance with the developed procedure (route B) in one-pot as shown
in Scheme 5, although the yields of the desired products were low.
The following acidic removal of the tert-butyl group afforded the
desired dyes 19e21 in good yields.
The absorption spectra and electrochemical properties of the
three dyes were measured, as shown in Figs.1 and 2, and Table 1. The
absorption maxima of 20 and 21 in CH2Cl2 solutionwere 530 nm and
489 nm, respectively, as shown in Fig. 1 and Table 1. The 41 nm red-
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S. Fuse et al. / Tetrahedron xxx (2014) 1e6
3
Fig. 1. Absorption spectra of synthesized dyes 19e21 in CH2Cl2.
Scheme 4. Preparation of building blocks 13 and 15.
Fig. 2. Cyclic voltammograms of solutions (w0.3 mM) of synthesized dyes 19e21 with
LiClO4 (0.1 M) as a counter electrolyte in DMF equipped with Pt plate, Pt wire, and Ag/
Agþ (0.01 M of AgNO3 in DMF) as working, counter, and reference electrodes, re-
spectively. Before and after each measurement, the Ag/Agþ reference electrode was
calibrated independently by the redox potential of ferrocene (Fe(III)/Fe(II)) in DMF
referred to as þ0.853 [V] (vs NHE).76 Since 20 and 21 revealed peak separation of
approximately 60 mV between oxidation and reduction, the peak separation was also
assumed as 60 mV for 19, although the reduction peak was not clearly observed with
19.
shift for 20 compared with that of 21 can be ascribed to the lower
ELUMO of the EDOT-containing dye 21. The dyes 20 and 21, which
contained a hexyloxy chain on their donor moiety exerted higher
molar absorption coefficients than dye 19, which had no hexyloxy
chain. The highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) levels of the three dyes met
the minimum requirement for a dye-sensitizer in DSSCs: i.e., EHOMO
and ELUMO located more positive than the iodine/iodide redox po-
tential [þ0.4 V vs normal hydrogen electrode (NHE)], and more
negative than the conduction band edge of TiO2 (ꢁ0.5 V vs NHE77).
Scheme 5. Synthesis of three thiophene-based organic dyes 19e21.
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4
S. Fuse et al. / Tetrahedron xxx (2014) 1e6
Table 1
Photochemical and electrochemical properties of the dyes 19e21, and photovoltaic properties of solar cells prepared using the three dyes
[L molꢁ1 cmꢁ1
]
EHOMO [V]
ELUMOc [V]
(vs NHE)
hd [%]
FFd
Vocd [V]
Jscd [mA cmꢁ2
]
a
b
c
Dye
lmax [nm]
Optical absorption
edge [nm]
3
(vs NHE)
19
20
21
518
530
489
608
632
621
17,000
40,000
38,000
1.20
1.12
1.12
ꢁ0.83
ꢁ0.84
ꢁ0.88
3.6
5.4
2.6
0.57
0.63
0.61
0.58
0.63
0.57
11.0
13.4
7.6
a
Absorption maxima in CH2Cl2.
b
c
Molar absorption coefficients in CH2Cl2.
EHOMO was determined by the cyclic voltammetry (Fig. 2). EHOMOeELUMO gap was determined by the edge of absorption spectra defined by the wavelength where the
absorbance revealed 1/10 of the peak top; i.e., EHOMOeELUMO gap [eV] was calculated by 1240 [nm]/optical edge [nm]. ELUMO was thus calculated by the summation of the
HOMO potential and EHOMOeELUMO gap.
d
Average values from three or four independent experiments. FF, fill factor; Voc, open-circuit voltage; Jsc, short-circuit current.
Photovoltaic properties were evaluated for the solar cells that
were prepared using the three dyes 19e21 (Table 1 and Fig. 3). The
EDOT-containing dyes 19 and 20 exerted a higher Jsc than dye 21
without an EDOT moiety. Palomares, De Angelis and co-workers
reported that the DethiopheneeEDOTeA dye exerted a higher Jsc
than the DeEDOTeEDOTeA dye.71 Quite recently, we reported that
The hexyloxy group-containing dye 20 exerted a higher Jsc, Voc,
and FF than dye 19 without a hexyloxy group. The lower Jsc and Voc
of 19 can be ascribed to the low molar absorption coefficients and
larger dark current of the dye (Table 1 and Fig. 3b). The best-
performing dye 20 exerted high incident photon-to-current con-
version efficiency (IPCE) in a somewhat wide region that ranged
from 350 to 670 nm.
the D-EDOT-p
-A dye exerted an adverse effect on Jsc, Voc, and FF.56
From these previous reports and our obtained results, it was in-
dicated that the dyes that contained only one EDOT beside a cya-
noacrylic acid moiety would exert a high Jsc.
3. Conclusion
In summary, the framework of thiophene-based DepeA organic
dyes was rapidly assembled based on a one-pot, four-component
SM coupling procedure. The measurement of the absorption
spectra and electrochemical properties of synthesized dyes, and the
photovoltaic properties of solar cells that were prepared using the
synthesized dyes revealed that the dyes, which contain only one
EDOT beside a cyanoacrylic acid moiety would exert a high Jsc.
4. Experimental section
4.1. General
NMR spectra were recorded on a JEOL Model EX-270 (270 MHz for
1H, 67.8 MHz for 13C) or a JEOL Model ECP-400 (400 MHz for 1H,
100 MHz for 13C) instrument in the indicated solvent. Chemical shifts
are reported in units of parts per million (ppm) relative to the signal
for internal tetramethylsilane (0 ppm for 1H) for solutions in CDCl3.
NMR spectral data are reported as follows: chloroform (7.26 ppm for
1H), DMSO-d6 (2.50 ppm) or chloroform-d (77.1 ppm for 13C), DMSO-
d6 (49.8 ppm). Multiplicities are reported by using the following ab-
breviations: s, singlet; d, doublet; dd, doublet of doublets; t, triplet; tt,
triplet of triplets; m, multiplet; br, broad; and, J, coupling constants in
hertz (Hz). IR spectra were recorded on a Perkin Elmer Spectrum One
FT-IR spectrophotometer. Only the strongest and/or structurally im-
portant absorption is reported as the IR data in cmꢁ1. All reactions
were monitored by thin-layer chromatography carried out on 0.2 mm
E. Merck silica gel plates (60F-254) with UV light, visualized by p-
anisaldehyde solution, ceric sulfate or 10% ethanolic phosphomo-
lybdic acid. Merck silica gel 60N (0.063e0.200 mm) was used for
column chromatography. ESI-TOF mass spectra were measured with
Waters LCT PremierÔ XE. HRMS (ESI-TOF) were calibrated with leu-
cine enkephalin (SIGMA) as an internal standard.
4.2. General procedure for one-pot, four-component SM
coupling
To a solution of donor block 2 or 13 (1.1 equiv) and
p-bridge
block 6 (1.0 equiv) in toluene/H2O (1:1) were added Na2CO3 (2.0
equiv), 4 mol % Pd2(dba)3, and 8 mol % [(t-Bu3P)H]BF4 at room
temperature. After being stirred at 90 ꢀC for 3 h, to the resultant
Fig. 3. Photocurrentevoltage curves obtained with DSSCs based on 19 (green line), 20
(blue line), and 21 (red line) under standard AM1.5 solar conditions (a) and in the dark
(b). (c) Incident photon-to-current conversion efficiency (IPCE) spectra for DSSCs based
on 19 (green line), 20 (blue line), and 21 (red line).
solution were added
p-bridge block 3 (1.2 equiv), Na2CO3 (2.0
equiv), 4 mol % Pd2(dba)3, and 8 mol % [(t-Bu3P)H]BF4. After being
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S. Fuse et al. / Tetrahedron xxx (2014) 1e6
5
stirred at 60 ꢀC for 3 h, to the resultant solution were added ac-
ceptor block 1056 or 15 (1.5 equiv), Na2CO3 (2.0 equiv),s 4 mol % of
Pd2(dba)3, and 8 mol % of [(t-Bu3P)H]BF4. After being stirred at 60 ꢀC
for 5 h, the toluene layer was simply removed from the reaction
vessel using pipette, and was purified by silica gel column chro-
matography (elution solvent: toluene) in order to remove polar
undesired compounds and GPC to afford the desired coupling
products 16e18.
772 cmꢁ1; HRMS (ESI-TOF): [MþH]þ calcd for C36H25N2O4S3,
645.0976; found 645.0963.
4.3.2. Synthesis of 20. The dye 20 was prepared as a black solid
from 17. Yield 73%; mp 217e219 ꢀC; 1H NMR (400 MHz, DMSO-d6)
d
8.16 (s, 1H), 7.48e7.45 (m, 3H), 7.40 (d, J¼3.9 Hz, 1H), 7.35 (d,
J¼3.9 Hz, 1H), 7.32 (d, J¼3.9 Hz, 1H), 7.03 (d, J¼8.7 Hz, 4H), 6.90 (d,
J¼8.7 Hz, 4H), 6.74 (d, J¼8.7 Hz, 2H), 4.51 (s, 4H), 3.92 (t, J¼6.8 Hz,
4H), 1.72e1.65 (m, 4H), 1.44e1.36 (m, 4H), 1.32e1.28 (m, 8H), 0.87
4.2.1. Synthesis of 16. The dye 16 was prepared as a black solid from
(t, J¼6.8 Hz, 6H); 13C NMR (100 MHz, DMSO-d6)
d 164.0, 155.4,
2, 6, 8, and 15. Yield 8%; 1H NMR (400 MHz, CDCl3)
d
8.30 (s, 1H),
148.8, 148.2, 143.7, 139.6, 139.4, 138.7, 137.2, 133.2, 130.5, 127.4,
126.9, 126.1, 124.5, 124.2, 123.1, 121.0, 118.9, 117.1, 115.4, 108.2, 93.6,
79.1, 67.6, 65.8, 65.1, 31.0, 28.7, 25.2, 22.0, 13.9; FTIR (solid) 2930,
2214, 1681, 1535, 1506, 1421, 1220, 1071, 827, 772 cmꢁ1; HRMS (ESI-
TOF): [MþH]þ calcd for C48H49N2O6S3, 845.2753; found 845.2756.
7.45 (d, J¼8.7 Hz, 2H), 7.38 (d, J¼3.9 Hz, 1H), 7.27 (dd, J¼8.2, 7.7 Hz,
4H), 7.17 (d, J¼3.9 Hz,1H), 7.15e7.11 (m, 6H), 7.07e7.03 (m, 4H), 4.42
(s, 4H), 1.56 (s, 9H); 13C NMR (67.8 MHz, CDCl3)
d 162.4, 148.0, 147.5,
147.3,144.0, 140.3,139.6,136.7, 135.0,131.5, 129.3,127.6, 127.1, 126.4,
125.2, 124.6, 123.7, 123.3, 123.2, 123.0, 117.1, 109.8, 94.9, 82.6, 65.4,
64.8, 28.0; FTIR (solid) 2927, 2212, 1706, 1582, 1487, 1450, 1251,
1155, 1075, 756, 697 cmꢁ1; HRMS (ESI-TOF); [MþH]þ calcd for
4.3.3. Synthesis of 21. The dye 21 was prepared as a black solid
from 18. Yield 86%; mp 149e151 ꢀC; 1H NMR (400 MHz, DMSO-d6)
C
40H33N2O4S3, 701.1602; found 701.1608.
d
8.43 (s, 1H), 7.93 (d, J¼3.9 Hz, 1H), 7.55 (d, J¼3.9 Hz, 2H), 7.45 (d,
J¼8.7 Hz, 2H), 7.38 (d, J¼3.9 Hz, 1H), 7.33 (d, J¼3.9 Hz, 1H), 7.30 (d,
J¼3.9 Hz, 1H), 7.01 (d, J¼8.7 Hz, 4H), 6.89 (d, J¼8.7 Hz, 4H), 6.73 (d,
J¼8.7 Hz, 2H), 3.91 (t, J¼6.8 Hz, 4H), 1.70e1.64 (m, 4H), 1.42e1.37
(m, 4H), 1.39e1.27 (m, 8H), 0.86 (t, J¼6.8 Hz, 6H); FTIR (solid) 2930,
2216, 1683, 1599, 1220, 1050, 826, 772 cmꢁ1. The observed spectral
data were in good accordance with those of the previously
reported.72,74
4.2.2. Synthesis of 17. The dye 17 was prepared as a black solid
from 6, 8, 13, and 15. Yield 5%; 1H NMR (400 MHz, CDCl3)
8.30 (s,
1H), 7.39e7.36 (m, 3H), 7.15 (d, J¼3.9 Hz, 1H), 7.12 (d, J¼3.9 Hz, 1H),
7.09 (d, J¼3.9 Hz, 1H), 7.06 (d, J¼8.7 Hz, 4H), 6.90 (d, J¼8.7 Hz, 2H),
6.83 (d, J¼8.7 Hz, 4H), 4.41 (s, 4H), 3.93 (t, J¼6.8 Hz, 4H), 1.81e1.74
(m, 4H), 1.56 (s, 9H), 1.49e1.43 (m, 4H), 1.36e1.34 (m, 8H), 0.91 (t,
d
J¼6.8 Hz, 6H); 13C NMR (67.8 MHz, CDCl3)
d 162.5, 155.7, 148.6,
148.0, 144.6, 140.3, 140.2, 139.9, 136.6, 134.4, 131.3, 127.1, 126.8,
126.2, 125.5, 125.2, 123.5, 123.1, 122.4, 120.1, 117.1, 115.3, 109.7, 94.9,
82.7, 68.2, 65.4, 64.8, 31.6, 29.3, 28.1, 25.7, 22.6, 14.0; FTIR (solid)
4.4. Fabrication of DSSCs
A photoanode of dye-sensitized solar cell (DSSCs) was fabricated
using Ti-Nanoxide D/SP paste (Solaronix, SA) on Fluorene doped
Tin-oxide (FTO) transparent conducting oxide glass (Nippon Sheet
Glass Co. Ltd.) by employing the doctor blade technique. After
drying at room temperature, the substrate was then baked at
2930, 2211,1708,1580,1558,1507,1450,1239,1156,1075, 828 cmꢁ1
;
HRMS (ESI-TOF); [MþH]þ calcd for C52H57N2O6S3, 901.3379; found
901.3367.
4.2.3. Synthesis of 18. The dye 18 was prepared as a black solid
500 ꢀC for 30 min to fabricate a 12
mm thick, mesoporous TiO2 layer.
from 6, 8, 10, and 13. Yield 2%; 1H NMR (400 MHz, CDCl3)
d
8.17 (s,
An FTO-coated TiO2 substrate was then dipped into a 0.2 mM dye
solution containing 5 mM of chenodeoxycholic acid in CH2Cl2
(DCM) solution for 12 h at room temperature. After the dye ab-
sorption, this photoanode was then rinsed three times with CH2Cl2
at room temperature to remove un-adsorbed dyes on the substrate.
A Pt-sputtered (Shibaura Mechatronics, CFS-4EP-LL) FTO-coated
1H), 7.63 (d, J¼3.9 Hz, 1H), 7.39 (d, J¼8.7 Hz, 2H), 7.31 (d, J¼3.9 Hz,
1H), 7.21 (d, J¼3.9 Hz, 1H), 7.16 (d, J¼3.9 Hz, 1H), 7.12e7.10 (m, 2H),
7.06 (d, J¼8.7 Hz, 4H), 6.91 (d, J¼8.7 Hz, 2H), 6.83 (d, J¼8.7 Hz, 4H),
3.94 (t, J¼6.8 Hz, 4H), 1.80e1.74 (m, 4H), 1.57 (s, 9H), 1.48e1.45 (m,
4H), 1.36e1.34 (m, 8H), 0.91 (t, J¼6.8 Hz, 6H); 13C NMR (67.8 MHz,
CDCl3)
d
161.9, 155.9, 149.1, 147.5, 147.0, 145.3, 140.1, 138.7, 133.8,
glass was employed as the counter electrode. A 25 mm-thick
133.3, 127.5, 126.9, 126.4, 124.9, 123.7, 122.7, 119.8, 116.4, 115.4, 98.9,
83.3, 68.3, 31.6, 29.3, 28.0, 25.7, 22.6, 14.0; FTIR (solid) 2931, 2217,
Himilan film (Mitsui-DuPont Polychemical Co. Ltd.) was used as
spacer and sealant. Finally the fabrication of the DSSCs was com-
pleted by injecting an electrolyte solution consisting of LiI
(500 mM), iodine (50 mM), 4-tert-butylpyridine (580 mM), and
ethyl-methyl-imidazolium dicyanoimide (600 mM) in MeCN. The
cell area was 0.25 cm2 and was precisely defined by a black metal
mask.
1713, 1585, 1505, 1438, 1283, 1153, 758 cmꢁ1
.
4.3. General procedure for removal of tert-butyl group
A solution of tert-butyl ester 16, 17, or 18 was treated with
CH2Cl2/TFA (4:1) at room temperature under Ar. After being stirred
at the same temperature for 1e24 h (monitored by TLC), the mix-
ture was filtered and concentrated in vacuo. The residue was pu-
rified by column chromatography on silica gel, eluting with 0.01%
AcOH and 10% MeOH in CH2Cl2 to afford carboxylic acid 19, 20,
or 21.
4.5. DSSC characterization
Photovoltaic measurement of the fabricated DSSCs was con-
ducted using a solar simulator (Yamashita Densho YSS-50A)
equipped with a Xenon lamp for light exposure and a source-
measurement unit (Keithley, model 2400). The spectrum of the
solar simulator and its power were adjusted to 100 mW/cm2 at AM
1.5 using a spectro-radiometer (LS-100, Eiko Seiki). Currentevolt-
age characteristics were measured after the simulated solar irra-
diation to estimate the photovoltaic parameters such as short-
circuit current density (Jsc in mA/cm2), open-circuit voltage (Voc),
and the fill factor in order to estimate the photoconversion effi-
4.3.1. Synthesis of 19. The dye 19 was prepared as a black solid from
16. Yield 80%; mp 238e240 ꢀC;1H NMR (400 MHz, DMSO-d6)
d 8.16
(s, 1H), 7.56 (d, J¼8.7 Hz, 2H), 7.46 (d, J¼3.9 Hz, 1H), 7.42 (d,
J¼3.9 Hz, 1H), 7.39 (d, J¼3.9 Hz, 1H), 7.36 (d, J¼3.9 Hz, 1H), 7.32 (dd,
J¼7.7, 7.2 Hz, 4H), 7.10e7.04 (m, 6H), 6.95 (d, J¼8.7 Hz, 2H), 4.51 (s,
4H); 13C NMR (100 MHz, DMSO-d6)
d
163.9,149.0,147.1, 146.7, 143.2,
ciency (h) of the relationship.
139.7, 138.5, 137.4, 133.8, 130.7, 129.6, 127.6, 126.8, 126.4, 126.2,
124.6, 124.4, 124.0, 123.6, 122.7, 120.9, 117.0, 108.1, 93.6, 65.8, 65.2;
FTIR (solid) 2946, 2214, 1682, 1535, 1480, 1445, 1174, 1037, 851,
ꢀ
ꢂ
ꢁ
h
ð%Þ ¼ Jsc mA cm2 ꢂ VocðVÞ ꢂ FF
Please cite this article in press as: Fuse, S.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.09.039

6
S. Fuse et al. / Tetrahedron xxx (2014) 1e6
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€
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Xe lamp. Monochromatic light was exposed by DC mode and the
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interval). The monochromatic photon flux density was adjusted to
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