Structure-property relationship of different electron donors: Novel organic sensitizers based on fused dithienothiophene π-conjugated linker for high efficiency dye-sensitized solar cells

Article abstract of DOI:10.1016/j.tet.2013.02.058

Three novel organic dyes, coded Ba-01-03, based on D-π-A building blocks were synthesized and characterized for dye-sensitized solar cells (DSCs) to study the influence of different electron donors on photocurrent and photovoltage. The electron donor of Ba-01 was based on N-methoxyphenylcarbazole and the electron donors for Ba-02 and Ba-03 were based on different indoline analogs. The photovoltaic performance of these sensitizers was characterized using incident-photon-to-current conversion efficiency (IPCE), photovoltage measurements, and total solar-to-electric conversion efficiency (η). It was shown that photovoltage of indoline donor based dye Ba-03 showed the highest efficiency of 6.38% compared to carbazole donor based dye of Ba-01. DFT calculations were proven to be an effective tool in the prediction of the vertical electronic excitation, charge separation, and photovoltage as it effectively predicted the delocalization and coefficient size of the HOMO and LUMO for Ba-01-03.

Full text of DOI:10.1016/j.tet.2013.02.058

Tetrahedron 69 (2013) 3444e3450
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Structureeproperty relationship of different electron donors: novel
organic sensitizers based on fused dithienothiophene
p-conjugated
linker for high efficiency dye-sensitized solar cells
,
,
e,
*
Md. Akhtaruzzaman a b, Menggenbateer c, Ashraful Islam d , Ahmed El-Shafei
,
*
Naoki Asao c, Tienan Jin c, Liyuan Han c, Khalid A. Alamry f, Samia A. Kosa f,
Abdullah Mohamed Asiri f, Yoshinori Yamamoto c
,f,
*
a Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
b Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
c WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, 2-1-1 Katahira, Aobaku, Sendai 980-8577, Japan
d Photovoltaic Materials Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
e Polymer and Color Chemistry Program, North Carolina State University 1000 Main Campus Dr. Raleigh, NC 27695, USA
f Chemistry Department, Faculty of Science, and Center of Excellence for Advanced Materials Research, King Abdulaziz University, PO Box 80203, Jeddah,
Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 January 2013
Received in revised form 14 February 2013
Accepted 18 February 2013
Available online 26 February 2013
Three novel organic dyes, coded Ba-01e03, based on DepeA building blocks were synthesized and
characterized for dye-sensitized solar cells (DSCs) to study the influence of different electron donors on
photocurrent and photovoltage. The electron donor of Ba-01 was based on N-methoxyphenylcarbazole
and the electron donors for Ba-02 and Ba-03 were based on different indoline analogs. The photovoltaic
performance of these sensitizers was characterized using incident-photon-to-current conversion effi-
ciency (IPCE), photovoltage measurements, and total solar-to-electric conversion efficiency (h). It was
Keywords:
Dye-sensitized solar cells
Dithienothiophene
shown that photovoltage of indoline donor based dye Ba-03 showed the highest efficiency of 6.38%
compared to carbazole donor based dye of Ba-01. DFT calculations were proven to be an effective tool in
the prediction of the vertical electronic excitation, charge separation, and photovoltage as it effectively
predicted the delocalization and coefficient size of the HOMO and LUMO for Ba-01e03.
Ó 2013 Elsevier Ltd. All rights reserved.
Organic dye
Photovoltaic performance
IPCE (incident-photon-to-current
conversion efficiency)
1. Introduction
visible including the red region and extended up to the NIR region
while the ground and excited states oxidation potentials of the dyes
Compared to Ru(II)-based sensitizers, organic dyes have re-
cently received considerable academic and industrial attention
owing to the wide spectrum of possible chromophores that can be
used, high molar extinction coefficient, ease of structure modifi-
cations, tunable ground and excited states oxidation potentials, and
low cost of materials and fabrications.1e16 The most common
building block of organic dyes designed for DSCs comprises an
should be maintained thermodynamically favorable for the re-
duction of the oxidized dye with the electrolyte and electron in-
jection from the excited state of the dye into the conduction band
(CB) edge of TiO2, respectively. Recently, Ru-based black dye
showed remarkable efficiency of 11.4%, which has E0e0 energy gap
of 1.6 eV.16 However, most of the efficient organic dyes have an E0e0
energy gap of >2.0 eV. Therefore, there is still much room to tune
the HOMOeLUMO energy level to enhance light harvesting ability,
to achieve a high extinction coefficient, and to shift the energy
levels to improve the performance of the solar cell. To achieve this
electron donor, a
p-conjugated spacer, and an electron acceptor,
typically cyanoacrylic acid. For high efficiency DSCs, dyes should be
molecularly designed to harvest photons with high molar absorp-
tivity across a wide bandwidth of the solar spectrum covering the
we have selected here fused thiophene as
p-linker as it has been
exhibited strong electron injection properties into thin film.17,18
Furthermore, this fused ring system has been used to design new
organic sensitizers to get higher light harvesting and high total
conversion efficiency of DSCs.19e21 Recently, it was also reported
that employing a nonlinear structure and long aliphatic chain
prevents dye aggregation and minimize charge re-combinations,
* Corresponding authors. Tel.: þ81 22 217 6177; fax: þ81 22 217 5979 (Y.Y); tel.:
þ81 29 859 2129; fax: þ81 29 859 2304 (A.I.); tel./fax: þ1 919 515 6532 (A.E.-S.);
e-mail addresses: ISLAM.Ashraful@nims.go.jp (A. Islam), Ahmed_El-Shafei@
ncsu.edu (A. El-Shafei), yoshi@m.tohoku.ac.jp (Y. Yamamoto).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.02.058

Md. Akhtaruzzaman et al. / Tetrahedron 69 (2013) 3444e3450
3445
respectively.22 Molecular modeling investigation using DFT/TD-DFT
2.3. Fabrication of dye-sensitized solar cells
can also be a valuable screening tool, where it can be used effec-
tively prior to synthesis to screen several hundreds of dyes to
identify the most promising candidates that meet the above re-
quirements of efficient sensitizers for DSCs.
A double-layer TiO2 photoelectrode, (10þ5)
m
m in thickness
with a 10 mm thick nanoporous layer and a 5 mm thick scattering
layer (area: 0.25 cm2), was prepared by screen printing on con-
ducting glass substrate. A dye solution of 3ꢀ10ꢁ4 M concentration
in acetonitrile/tert-butyl alcohol (1/1, v/v) was used to up-take the
dye on to the TiO2 film. Deoxycholic acid (DCA) (20 mM) as a co-
adsorbent was added into the dye solution to prevent aggrega-
tion of the dye molecules. The TiO2 films were immersed into the
dye solution and then kept at 25 ꢂC for 30 h. Photovoltaic mea-
surements were performed in a sandwich type solar cell in con-
junction with an electrolyte consisting of a solution of 0.6 M
dimethylpropyl-imidazolium iodide (DMPII), 0.05 M I2, 0.1 M LiI,
and 0.5 M tert-butylpyridine (TBP) in acetonitrile (AN). The dye-
deposited TiO2 film and a platinum-coated conducting glass were
In this work, we present herewith a study that combines ex-
perimental and DFT/TD-DFT molecular modeling of a novel series
of low molecular weight organic sensitizers based on fused
dithienothiophene (Ba-01e03) for DSCs (Fig. 1) to study the dif-
ferent electron donors on the photovoltaic performance of these
sensitizers. While Ba-01 is based on carbazole electron donor, sp2-
carbons, Ba-02 and Ba-03 are based on different indoline electron
donor analogy, comprised of some sp3 carbons. Previously, we re-
ported that organic sensitizers containing the strong indoline do-
nor showed strong and intense absorption bands in the visible
region.23 In addition, this unit has a tendency to prevent
p-stacked
aggregation on the semiconductor surface. To enhance our un-
derstanding for developing high performances organic sensitizers,
we selected here another effective well known carbazole donor to
investigate the DSCs performances.24 It was expected that the
indoline-based electron donor would furnish sensitizers for
separated by a Surlyn spacer (40 mm thick) and sealed by heating
the polymer frame. Photocurrent densityevoltage (IeV) of sealed
solar cells was measured under AM 1.5G simulated solar light at
a light intensity of 100 mW cmꢁ2 with a metal mask of 0.25 cm2.
The photovoltaic parameters, i.e., short circuit current (Jsc), open
circuit voltage (Voc), fill factor (ff), and power conversion efficiency
DSCs that would exhibit much higher efficiency (h), compared to
carbazole-based donor sensitizers.
(h) were estimated from IeV characteristics under illumination.
2.4. Photophysical properties
Fig. 2a shows the experimental absorption spectra of dyes Ba-
01e03 in ethanol. Dyes Ba-02 and Ba-03 showed significant red
shifted absorption maxima (pep*) at 481 and 485 nm, respectively,
compared to 428 nm of dye Ba-01. The absorption band edge of Ba-
02 and Ba-03 was extended to 650 nm compared to 550 nm in the
case of Ba-01. On the other hand, the extinction coefficient of Ba-02
and Ba-03 was significantly higher than dye Ba-01. When dyes
absorbed on a transparent thin TiO2 film, all dyes exhibited broad
absorption spectra similar to those in solution, due to the in-
teraction between the carboxylate group and TiO2 (Fig. 2b). Upon
adsorption on the TiO2 film, the tail of the absorption spectrum of
Ba-02e03 dyes extended up to 700 nm, which is red-shifted by
50 nm compared to the carbazole donor based dye of Ba-01. This
broadening of absorption spectrum is highly desirable for har-
vesting more of the solar spectrum and translates into greater
photocurrent.
Fig. 1. Molecular structures of Ba-01e03.
2. Results and discussion
2.1. Synthesis
The ionization potential (IP) of Ba-01e03 bound to the nano-
crystalline TiO2 film was measured using the photoemission yield
spectrometer (Riken Keiki, AC-3E). Ground-state oxidation poten-
tial, Sþ/0, values of ꢁ5.39 eV, ꢁ5.31 eV, and ꢁ5.26 eV were obtained
for sensitizers Ba-01, Ba-02, and Ba-03, respectively. The IP values
of BA-01e03, which correspond to Sþ/0, were sufficiently lower
than the redox potential of I/I3 (ꢁ5.10 eV),30 which ensured favor-
able thermodynamic ground states for efficient regeneration of the
dye through the reaction of the oxidized dye with iodide. The IP
values of the indoline containing sensitizers (Ba-02e03) were
shifted to anodic direction, compared to the carbazole-based dye
(Ba-01) (Table 1). This anodic shift is due to the higher donating
ability of indoline donor, compared to carbazole donor, which fur-
nished more charge transfer from D to A in indoline-based dyes
(Ba-02e03) than that of the carbazole-based dye (Ba-01). More-
over, the anodic shift increased the negative free energy of electron
injection, which explained why Ba-02e03 furnished more photo-
current than Ba-01. The onset of the optical energy gap (E0e0) of Ba-
01e03 dyes was in the range of 1.86e1.94 eV (Table 1). The excited-
New dyes Ba-01e03 were synthesized in a straightforward
manner, and they were obtained in a range of 47e50% yields from
their precursors 4, 7, and 10 (Schemes 1e3, and see Experimental
section).
2.2. Molecular modeling
Ground state equilibrium molecular geometries of Ba-01e03
were calculated using the hybrid DFT energy functional B3LYP25,26
and the basis set DGDZVP (density Gauss double-z with polariza-
tion functions).27,28 Subsequently, a single point energy calculation
was performed on the optimized geometry using different long-
range corrected time-dependent DFT energy functional methods
including CAM-B3LYP29 with the basis set DGDZVP, and the elec-
tronic absorption spectra were extracted. The TD-DFT calculations
were performed in ethanol using the polarizable conductor calcu-
lation model (PCM). The DFT/TD-DFT calculations were performed
on the East Carolina University’s Super Computer Jasta using 8
processors and 4 GB of RAM. The solvent effect was accounted for
using the polarizable conductor calculation model (PCM), imple-
mented in Gaussian 09. All calculations were performed using
Gaussian 09.
state oxidation potential, Sþ/
, of sensitizers Ba-01e03 was in the
*
range of ꢁ3.45 to ꢁ3.40 eV (Table 1) and lay above the conduction
band edge (ꢁ4.2 eV)31 of the nanocrystalline TiO2 ensuring that the
excited states of these dyes are thermodynamically driven for ef-
ficient electron injection into the conduction band edge of TiO2.

3446
Md. Akhtaruzzaman et al. / Tetrahedron 69 (2013) 3444e3450
Scheme 1. Synthesis of new organic dye Ba-01.
Scheme 2. Synthesis of new organic dye Ba-02.
Scheme 3. Synthesis of new organic dye Ba-03.
Fig. 3 shows the calculated absorption spectrum in ethanol
2.5. Photovoltaic properties
using TD-DFT with the energy functional CAM-B3LYP and basis set
DGDZVP. While excellent agreement between the experimental
and calculated absorption maxima in ethanol for Ba-02 and Ba-03
(Table 2) were found, the calculated lmax for Ba-01 was over-
estimated by 0.27 eV.
Fig. 4 shows the delocalization of the HOMO and LUMO of Ba-
01e03. HOMOs are delocalized over the entire molecules except
COOH. The LUMOs were located on the electron acceptor segment
and extended up to the electron donor, confirming efficient charge
transfer and absence of charge traps.
Fig. 5 shows the IeV curves and Table 3 shows the photovoltaic
parameters for dyes Ba-01e03. The sensitizer Ba-02e03 showed
higher power conversion efficiency than Ba-01, as shown in Table 3.
The higher photocurrent of dye Ba-02e03 can be attributed to the
stronger donating ability of indoline analogs. The dye Ba-03
showed highest overall conversion efficiency (h) of 6.38% with Jsc of
16.17 mA cmꢁ2, Voc of 0.595 V, ff of 0.663, on the other hand, Ba-01
showed a Jsc of 13.45 mA cmꢁ2, Voc of 0.618 V and ff of 0.679, cor-
responding to an overall efficiency (h) of 5.64% under the same

Md. Akhtaruzzaman et al. / Tetrahedron 69 (2013) 3444e3450
3447
Fig. 2. Absorption spectra of Ba-01e03 in ethanol (left) and on TiO2 film (right).
conditions. The Voc values of Ba-02 and Ba-03 are lower than that of
Ba-01 may be due the higher level of ground state oxidation po-
tential of Ba-02e03 than Ba-01, which enhanced the back electron
transfer from conduction band to the oxidized dye.
Table 1
Photophysical properties of dyes Ba-01e03
c
*
(eV)e
Dye
lmax/nma
lonset/nmb
on TiO2 film
(IP)c
(eV)
E0e0
Sþ/
(εꢀ104 Mꢁ1 cmꢁ1
)
(eV)d
Fig. 6 shows the monochromatic incident-photon-to-current
conversion efficiency (IPCE) for DSCs based on Ba-01e03. Dye Ba-
03 showed excellent sensitization of nanocrystalline TiO2 from 400
to 600 nm with a quantum efficiency of >85% in the plateau region
and the sensitization covered a broader range of the solar spectrum
with onset at a longer wavelength of 810 nm compared to that Ba-
01 with onset at 720 nm. On the other hand, in the case of Ba-02,
the sensitization also covered a broader range of the solar spectrum
with onset similar to Ba-03, but quantum efficiency was about 80%
in the plateau region 400e600 nm.
Ba-01
Ba-02
Ba-03
428 (3.5)
353, 481 (4.0)
358, 485 (4.1)
610
660
665
ꢁ5.39
ꢁ5.31
ꢁ5.26
1.94
1.88
1.86
ꢁ3.45
ꢁ3.43
ꢁ3.40
a
Absorption maxima, measured in ethanol at room temperature.
Absorption measured on a transparent 4 mm TiO2 film. Adsorbed dye concen-
b
tration on TiO2 (mol cmꢁ2); Ba-01, 2.9ꢀ10ꢁ7; Ba-02, 3.3ꢀ10ꢁ7; Ba-03, 3.4ꢀ10ꢁ7
.
c
Ionization potential (IP) of absorbed dyes on the nanocrystalline TiO2 film was
determined by using the photoemission yield spectrometer (Riken Keiki, AC-3E).
d
E0e0 was estimated from the absorption onset of dye loaded on TiO2 film.
e
The excited-state oxidation potential, Sþ/
levels were calculated from the ex-
*
pression of Sþ/
*
¼IPꢁE0e0
.
3. Conclusions
A novel series (Ba-01e03) of low molecular weight sensitizers
based on DepeA building block of fused thiophene was synthe-
sized and characterized for DSCs with Ba-03 showing impressive
total solar-to-electric conversion efficiency of 6.38%. It has become
clear that the indoline-based electron donor is better than the
carbazole donor. DFT utilizing the energy functional CAM-B3LYP
and DGDZVP basis set was proven to be effective in the pre-
diction of vertical electronic excitation and delocalization of
HOMOs and LUMOs, which provided invaluable insights into the
charge separation efficiency and photovoltage performance of the
sensitizers.
4. Experimental section
4.1. General information for materials synthesis
1H NMR and 13C NMR spectra were recorded on JEOL JMTC-270/
54/SS (JASTEC, 400 MHz) spectrometers. 1H NMR spectra are re-
Fig. 3. The calculated absorption spectra in ethanol of Ba-01e03.
ported as follows: chemical shift in parts per million (d) relative to
the chemical shift of CDCl3 at 7.26 ppm, integration, multiplicities
(s¼singlet, d¼doublet, t¼triplet, q¼quartet and m¼multiple), and
Table 2
Comparison between the calculated and experimental lmax of dyes Ba-01e03
coupling constants (hertz). 13C NMR spectra reported in ppm (
d)
relative to the central line of triplet for CDCl3 at 77.00 ppm. High-
resolution mass spectra were obtained on a BRUKER APEXIII
spectrometer. Column chromatography was carried out employing
silica gel 60N (spherical, neutral, 40e100 mm, KANTO Chemical Co.).
Analytical thin-layer chromatography (TLC) was performed on
0.2 mm precoated plate Kieselgel 60 F254 (Merck). All other
Dyes
lmax (nm)
Expt.
Calcd
Ba-01
Ba-02
Ba-03
428
481
485
471
483
488

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Md. Akhtaruzzaman et al. / Tetrahedron 69 (2013) 3444e3450
Fig. 5. Photocurrent voltage characteristics of DSCs sensitized with dyes Ba-01e03.
Table 3
Photovoltaic performances of dyes Ba-01e03a
Dyes
Jsc [mA cmꢁ2
]
Voc [V]
ff
Eff, h [%]
Ba-01
Ba-02
Ba-03
13.45
15.85
16.17
0.618
0.589
0.595
0.679
0.671
0.663
5.64
6.11
6.38
a
Measurements were performed under AM 1.5 irradiation on the DSC devices
with 0.25 cm2 active surface area defined by a metal mask. Jsc: short circuit current;
Voc: open circuit voltage; ff: fill factor; h: conversion efficiency.
Fig. 6. Photocurrent action spectra (IPCE) obtained with dyes Ba-01e03 anchored on
nanocrystalline TiO2 film.
Fig. 4. Delocalization of HOMO and LUMO on Ba-01e03.
reagents and solvents commercially available were used without
further purification unless otherwise noted. The compound 1, 2, 5,
and 8 were synthesized according to the literature method.1,32
silica-gel column with toluene/hexane (1:5, v/v) as eluant to get
compound 3. Yield 56%; 1H NMR (DMSO-d6, 400 MHz):
d 3.88 (s,
3H), 7.22 (d, J¼8.5 Hz, 2H), 7.26e7.36 (m, 3H), 7.45 (dd, J¼7.8 Hz,
7.8 Hz, 1H), 7.53 (d, J¼6.3 Hz, 3H), 7.70 (d, J¼5.1 Hz, 1H), 7.77 (d,
J¼8.5 Hz, 1H), 7.96 (s, 1H), 8.33 (d, J¼7.8 Hz, 1H), 8.60 (s, 1H). 13C
4.2. Synthesis of compounds 3, 6, 9
NMR (DMSO-d6, 100 MHz):
d 55.4, 109.7, 110.2, 115.2, 116.4, 117.3,
4.2.1. Compound 3. Compound 1 (1 mmol), 2 (1.2 mmol), and tet-
rakis(triphenylphosphine)palladium (20 mol %, 0.2311 g) were
dissolved in the mixture of THF (30 mL) and 2 N potassium car-
bonate aqueous solution (6 mL). The reaction was performed at
70 ꢂC for 12 h under Ar. Then the mixture was poured into water
and extracted three times with CH2Cl2. The organic layer was
washed with a sodium carbonate aqueous solution and H2O, and
subsequently dried over anhydrous sodium sulfate. After removing
the solvent under reduced pressure, the residue was loaded onto
120.0, 120.7, 121.4, 122.1, 123.0, 123.9, 125.8, 126.6, 127.1, 128.0,
128.8, 130.2, 140.2, 140.55, 141.0, 142.0, 145.2, 158.5.
4.2.2. Compound 6. Following the same procedures of compound
3, the compound 6 was obtained as shown in Scheme 2. Yield 50%;
1H NMR (DMSO-d6, 400 MHz):
d 1.35e1.48 (m, 1H), 1.55e1.85 (m,
4H), 1.95e2.10 (m, 1H), 2.28 (s, 3H), 3.86 (dd, J¼7.8 Hz, 8.0 Hz, 1H),
4.88 (dd, J¼6.3 Hz, 6.3 Hz, 1H), 6.86 (d, J¼8.5 Hz, 1H), 7.15e7.25 (m,
4H), 7.33 (dd, 1.7 Hz, 8.1 Hz, 1H), 7.46 (s, 1H), 7.52 (d, J¼5.1 Hz, 1H),

Md. Akhtaruzzaman et al. / Tetrahedron 69 (2013) 3444e3450
3449
7.67 (d, J¼5.4 Hz, 1H), 7.73 (s, 1H). 13C NMR (DMSO-d6, 100 MHz):
(ESI): m/z: calcd for C31H18N2O3S3 (MꢁH), 561.04068; found,
d
20.4, 24.0, 33.1, 34.8, 44.5, 68.3, 107.0, 114.8, 119.6, 121.3, 121.7,
561.04051.
123.9, 124.9, 126.7, 126.9, 129.7, 130.2, 130.8, 135.6, 139.3, 140.1,
142.0, 145.4, 147.2.
4.4.2. Compound Ba-02. 1H NMR (DMSO-d6, 400 MHz):
d 1.35e1.48
(m, 1H), 1.55e1.85 (m, 4H), 1.95e2.10 (m, 1H), 2.28 (s, 3H),
3.82e3.90 (m, 1H), 4.86e4.95 (m, 1H), 6.86 (d, J¼8.3 Hz, 1H),
7.15e7.25 (m, 4H), 7.38 (d, J¼8.3 Hz, 1H), 7.51 (s, 1H), 7.83 (s, 1H),
8.35 (s, 1H), 8.55 (s, 1H). HRMS (ESI): m/z: calcd for C30H22N2O2S3
(MꢁH), 537.07706; found, 537.07698.
4.2.3. Compound 9. Following the same procedures of compound
3, the compound 9 was obtained as shown in Scheme 3. Yield 42%;
1H NMR (DMSO-d6, 400 MHz):
d 1.35e1.48 (m, 1H), 1.55e1.85 (m,
4H), 1.95e2.10 (m, 1H), 3.75 (s, 3H), 3.80e3.86 (m, 1H), 4.80e4.86
(m, 1H), 6.66 (d, J¼8.3 Hz, 1H), 6.97 (d, J¼9.0 Hz, 2H), 7.21e7.32 (m,
3H), 7.43 (s, 1H), 7.50 (d, J¼5.1 Hz, 1H), 7.65 (d, J¼5.1 Hz, 1H), 7.69 (s,
4.4.3. Compound Ba-03. 1H NMR (THF-d8, 400 MHz):
d 2.40e3.15
1H). 13C NMR (DMSO-d6, 100 MHz):
d
24.0, 32.9, 35.0, 44.5, 55.2,
(m, 6H), 4.80 (s, 3H), 4.85e4.92 (m, 1H), 5.86e5.95 (m, 1H), 7.70 (d,
J¼8.3 Hz, 1H), 8.0 (d, J¼8.8 Hz, 2H), 8.28 (d, J¼8.5 Hz, 2H), 8.36 (d,
J¼8.3 Hz, 1H), 8.50 (s, 1H), 8.79 (s, 1H), 9.13 (s, 1H), 9.23 (s, 1H).
HRMS (ESI): m/z: calcd for C30H22N2O3S3 (MꢁH), 553.07198; found,
553.07192.
68.9, 106.2, 114.5, 114.6, 121.3, 121.7, 122.4, 123.3, 124.9, 126.6, 126.8,
130.2, 134.9, 135.2, 140.1, 142.0, 145.5, 148.3, 154.8.
4.3. Synthesis of compounds 4, 7, 10
Acknowledgements
4.3.1. Compound 4. Compound 3 (1 mmol) was dissolved in THF
(20 mL). After cooling the solution to ꢁ78 ꢂC, n-BuLi (1.2 equiv) was
added drop-wise. The reaction mixture was kept at ꢁ78 ꢂC for 0.5 h
under Ar. Then 10 equiv DMF was added into the reaction mixture
and warming to room temperature slowly. The reaction mixture
was stirred at room temperature for 1 h, and reaction was
quenched by H2O, and purified by silica-gel column chromatogra-
phy to give compound 4 in 62% yields. 1H NMR (DMSO-d6,
This work was supported by World Premier International
Research Center Initiative (WPI), MEXT (Japan), and by King
Abdulaziz University (KAU) under grant No (HiCi/28-3-1432).
Supplementary data
400 MHz):
d
3.88 (s, 3H), 7.23 (d, J¼9.0 Hz, 2H), 7.29e7.40 (m, 3H),
Absorption spectra of Ba-01e03 in 1,4-dioxane,33 HRMS (ESI)
and H NMR spectra of Ba-01e03, 1H and 13C NMR spectra of 3, 6,
and 9 are available. Supplementary data related to this article can
be found at http://dx.doi.org/10.1016/j.tet.2013.02.058.
7.46 (dd, J¼7.3 Hz, 7.8 Hz, 1H), 7.55 (d, J¼8.8 Hz, 2H), 7.81 (d,
J¼8.5 Hz, 1H), 8.07 (s, 1H), 8.35 (d, J¼7.6 Hz, 1H), 8.48 (s, 1H), 8.66 (s,
1H), 9.98 (s, 1H). 13C NMR (THF-d8, 100 MHz):
d 55.0, 109.8, 110.2,
115.1, 115.8, 117.6, 120.0, 120.3, 122.9, 123.8, 124.0, 126.0, 126.3,
128.3, 128.6, 129.7, 130.4, 140.5, 141.5, 142.0, 144.0, 147.1, 150.2,
159.5, 182.1.
References and notes
€
1. (a) Mishra, A.; Fischer, M. K. R.; Bauerle, P. Angew. Chem., Int. Ed. 2009, 48, 2474;
4.3.2. Compound 7. Following the same procedures as for com-
pound 4, the compound 7 was obtained as shown in Scheme 2. 1H
NMR (DMSO-d6, 400 MHz): d 1.35e1.48 (m, 1H), 1.55e1.85 (m, 4H),
1.95e2.10 (m, 1H), 2.29 (s, 3H), 3.86 (dd, J¼8.1 Hz, 8.5 Hz, 1H), 4.90
(dd, J¼5.9 Hz, 7.1 Hz, 1H), 6.86 (d, J¼8.3 Hz, 1H), 7.15e7.25 (m, 4H),
7.38 (d, J¼8.5 Hz, 1H), 7.52 (s, 1H), 7.82 (s, 1H), 8.44 (s, 1H), 9.94
(s, 1H).
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condition. After evaporation of the solvent, the residue was purified
by silica-gel column chromatography to give compounds Ba-01e03
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33. A referee gave the following comment. Some researchers reported that the
blue-shift of absorption maximum in solution is attributed to dissociation of
proton from carboxyl group, leading to lowering of its electron-withdrawing
ability. Therefore, to gain insight into the optical properties of these three
dyes, authors should measure the absorption spectra in non-polar solvents,
such as 1,4-dioxane. Our response is following: the excited-state oxidation
potential, Sþ/
levels were calculated from the expression of Sþ/
¼IPꢁE0e0
,
*
*
where the E0e0 was estimated from the absorption onset of dye loaded on TiO2
film as shown in Fig. 2b. It was also observed from Table 1 that the excited-state
oxidation potential of all three dyes (Ba-01: ꢁ3.45 eV, Ba-02: ꢁ3.43 eV, Ba-03:
3.40 eV) lay above the conduction band edge (ꢁ4.2 eV) of the
nanocrystalline TiO2 ensuring that the excited states of the dyes are thermo-
dynamically driven for efficient electron injection into the conduction band
edge of TiO2.Therefore, authors think that the absorption spectra in ethanol is
enough for this manuscript. However, according to the comment of the referee,
the spectra in 1,4-dioxane were measured and shown in ESI.
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