Synthesis, characterization and photovoltaic properties of di-anchoring organic dyes

Article abstract of DOI:10.1590/S0103-50532011000400023

Three new organic dyes comprising carbazole, iminodibenzyl and phenothiazine moieties, as electron donors and di-anchoring rhodanine rings as the electron acceptors, were synthesized and evaluated for use in dye-sensitized solar cells. A solar cell employing dye-containing phenothiazine as a hole-transporting unit and di-anchoring rhodanine rings as the electron acceptors exhibits a short circuit photocurrent density of 10.6 mA cm ^-2, an open-circuit voltage of 0.658 V and a fill factor of 0.7, corresponding to an overall conversion efficiency of 4.91percent at standard AM 1.5 sunlight. ?2011 Sociedade Brasileira de Qui?mica.

Full text of DOI:10.1590/S0103-50532011000400023

J. Braz. Chem. Soc., Vol. 22, No. 4, 780-789, 2011.
Printed in Brazil - ©2011 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Article
A
Synthesis, Characterization and Photovoltaic Properties of
Di-Anchoring Organic Dyes
Tzi-Yi Wu,a,b Ming-Hsiu Tsao,a Shyh-Gang Su,a H. Paul Wang,c,d Yuan-Chung Lin,e
Fu-Lin Chen,a Cheng-Wen Changa and I-Wen Sun*,a,c
aDepartment of Chemistry, cSustainable Environment Research Center and dDepartment of
Environmental Engineering, National Cheng Kung University, Tainan 701, Taiwan
bDepartment of Polymer Materials, Kun Shan University, Tainan 71003, Taiwan
eInstitute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
Três novos pigmentos orgânicos contendo grupamentos carbazol, iminodibenzil e fenotiazina
como doadores de elétrons e anéis rodanina bi-ancoradores como receptores de elétrons, foram
sintetizados e avaliados como fotossensibilizadores em células solares. Células solares empregando
corantes com grupos fenotiazinas como unidades transportadora de buracos e anéis rodanina
biancoradores como receptores de elétrons exibiram uma densidade de fotocorrente de curto
circuito de 10,6 mA cm-2, voltagem de circuito aberto de 0,658 V e fator de preenchimento de
0,7, correspondendo a uma eficiência de conversão total de 4,91% sob luz solar padrão AM 1.5.
Three new organic dyes comprising carbazole, iminodibenzyl and phenothiazine moieties,
as electron donors and di-anchoring rhodanine rings as the electron acceptors, were synthesized
and evaluated for use in dye-sensitized solar cells. A solar cell employing dye-containing
phenothiazine as a hole-transporting unit and di-anchoring rhodanine rings as the electron
acceptors exhibits a short circuit photocurrent density of 10.6 mA cm-2, an open-circuit voltage
of 0.658 V and a fill factor of 0.7, corresponding to an overall conversion efficiency of 4.91%
at standard AM 1.5 sunlight.
Keywords: dye-sensitized solar cells, electrochemistry, organic dyes, electron donor, rhodanine
Introduction
cells. The physical and chemical properties of donor-
acceptor materials can be modified by selecting suitable
donor moieties or/and acceptor moieties.
Compounds with extending conjugated p-electron
systems are of importance in a wide variety of
applications, such as optical, electronic, optoelectronic
and magnetic materials.1-7 The development of
organic electroactive and photoactive materials has
progressed significantly in recent years due to their
potential applications in optoelectronic devices, such
as electroluminescence (EL) devices, photovoltaic
devices, thin film transistors and solid-state lasers.8,9
Donor-acceptor (D-A) organic molecules are one of the
most important conjugated organic materials; they have
attracted considerable attention as electroluminescent
(EL) materials for organic light-emitting diodes
(OLEDs) and as photovoltaic materials for organic solar
Studies of donor (D)-p (bridge)-acceptor (A)
chromophores have found that the intramolecular
charge transfer characteristics of these molecules in the
excited state are essential for dye sensitizers in dye-
sensitized solar cells (DSSCs),10 since the light-induced
intramolecular electron transfer can easily occur from
the electron donor to the electron acceptor through the
p-bridge, which favors photocurrent generation.11 D-A
p-conjugated organic dyes have several advantages,
such as their ease of synthesis, high molar extinction
coefficient, tunable absorption spectral response from the
visible to the near infrared (NIR) region, environmental
friendliness and inexpensive production techniques
compared to those for Ru complexes. In addition, both
modeling and experimental results have shown that
*e-mail: iwsun@mail.ncku.edu.tw

Vol. 22, No. 4, 2011
Wu et al.
781
anchoring units, such as carboxylic groups, are necessary
for efficient dye adsorption on the surface of TiO2 to
favor charge injection.12
Preparation of dye-sensitized TiO2 electrode (photoanode)
and counter electrode
Recently, impressive photovoltaic performance has
been reported for some organic coumarin,13 indoline,14
merocyanine,15 and hemicyanine dyes.16 Reasonable
photo-conversion efficiencies have been achieved
with some push-pull-type organic chromophores.17
However, due to the formation of dye aggregates
on the semiconductor surface and the presence of
unstable radical species during redox reaction cycles,
many organic dyes exhibit conversion efficiency
and operational stability lower than those of metal-
complex dyes in DSSCs. Thus, it is desired to develop
efficient stable organic dyes which do not aggregate.
Phenothiazine is a well-known heterocyclic compound
that has electron rich sulfur and nitrogen heteroatoms.
Iminodibenzyl is a diphenylamine, wherein two
ortho positions are joined by a dimethylene bridge.
Phenothiazine-based organic dyes have found numerous
applications in electronics and optoelectronics, including
light-emitting diodes,18 photovoltaic cells, thin film
transistors,19 and electrochromic cells.20,21 The highly
nonplanar structure of iminodibenzyl and phenothiazine
units impedes p-stacking aggregation and intermolecular
excimer formation, making them suitable for diverse
optoelectronic applications.22
In previous work, Wu et al.23 have reported some
organic dyes with a rhodanine ring as mono-anchoring
acceptors. In the present work, new metal-free carbazole,
iminodibenzyl and phenothiazine sensitizers with
two electron acceptors of rhodanine-3-acetic acid are
reported. These acceptor-donor-acceptor p-conjugated
dyes with an amine derivative act as the electron donors
and two rhodanine-3-acetic acid moieties acts as the
anchoring group for attachment on the metal oxide and
as the electron acceptors. A p-conjugated methane unit
connects the donor and acceptor units. We investigate
the electron-donating nature and structural variations of
the amine unit and study its optical, electrochemical and
photovoltaic properties.
The working TiO2 electrode (photoanode) and counter
electrode for dye-sensitized solar cells were prepared as
follows. F-doped tin oxide (FTO) glass plates (3 mm thick,
7 Ω cm-2) were first cleaned in a cleaning detergent aqueous
solution with an ultrasonic bath for 15 min and rinsed with
water and ethanol. Then, the FTO electrodes were immersed
o
into 40 mmol L-1 TiCl4 (aqueous) at 70 C for 30 min and
rinsed with water and ethanol. Two kinds of TiO2 paste,
containing nanocrystalline (ca. 25 nm) TiO2 (Degussa P25,
paste A) and 500 nm submicroparticle TiO2 (TOHO, Japan,
paste B), respectively, were prepared using a previously
reported procedure.25 To prepare paste A, commercial titania
powder (3 g, Degussa P25) was ground in a mortar with
a small amount of water (1 mL) containing acetylacetone
(0.1 mL), which was added to prevent reaggregation of the
particles.AftertheTiO2 particlesweredispersed,thepastewas
diluted by the slow addition of water (3 mL) under continued
grindingandasurfactant,TritonX-100(0.05mL), wasadded
to facilitate the spreading of the colloid on the substrate.
Paste A was kept in ultrasound bath for about 24 h, at 28 oC.
Paste B was prepared by a similar method. The spin coating
procedure for paste A was repeated to get the appropriate
thickness of TiO2 films (12 mm). After paste A was dried at
125oC, pasteBwascoatedtwomoretimes, insuchawaythat
the TiO2 films with 500 nm particles for the scattering layer
were ca. 4 mm thick. The electrodes coated with TiO2 pastes
weregraduallyheated(5 oCmin–1)underairflowupto450 oC,
which was kept for 30 min. The electrodes were treated with
40 mmol L-1 solution of TiCl4 in (solvent ethanol). The TiO2
films were then rinsed with water and ethanol and sintered
again at 450 oC for 30 min. An active area of 0.5 × 0.5 cm
was selected from a sintered electrode. The electrodes were
immersed in a 5 × 10–4 mol L-1 solution of dye containing
tetrahydrofuran (THF). Dye coatings were applied at room
temperature for 24-30 h. The dye-adsorbed TiO2 films were
takenoutandrinsedwithdryethanol.Therinsingprocesswas
repeated several times to remove unbound dyes completely.
Finally, thedye-adsorbedTiO2 filmsweredriedinair. Counter
electrodeswerepreparedbysputteringa50nmthickplatinum
layer on an FTO substrates using a Hitachi E 1045 instrument
andcontrollingtheamountofsputteredplatinumwithaquartz
crystal thickness monitor. The thicknesses of the TiO2 films
were determined by profilometry.
Experimental
Chemicals
All starting materials and tetrabutylammonium
perchlorate (TBAP) were commercial available and used
as received. 1,2-dimethyl-3-propylimidazolium iodide
(DMPImI) were synthesized and purified according to
a procedure in the literature.24
DSSC assembly
ThedyeadsorbedTiO2 electrodeandPt-counterelectrode
were assembled into a sandwich sealed type cell by heating

782
Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
them with hot-melt ionomer film (25 mm thick, Solaronix)
as a spacer. A drop of electrolyte solution [0.1 mol L-1 LiI,
0.05 mol L-1 I2, 0.6 mol L-1 DMPII, 0.5 mol L-1 tert-butyl
pyridine (TBP) in acetonitile (ACN)] was injected through a
hole in the counter electrode, which was then sealed with hot-
melt ionomer film and glass. The electrolyte was introduced
into the cell and sealed with AB epoxy 906 Adhesive for
30 min. The working area of the electrode was 0.25 cm2.
dyes S1-S3 were obtained using the Gaussian 03 program
package.27 The calculation was optimized using B3LYP
(Becke three parameter hybrid function with Lee-Yang-
Perdew correlation functions) with the Pople 6–31+g(d)
atomic basis set.
Results and Discussion
Synthesis and structure of sensitizers
Characterizationofthedyesandphotovoltaicmeasurements
of the solar cells
In Figure 1, S1-S3 are the carbazole, iminodibenzyl
and phenothiazine-containing dyes, respectively. The
rhodanine dialdehydes 4a-c were prepared using the well-
known Vilsmeier reaction in a way similar to that reported
by Chen et al.28
1
The H spectra were obtained on a Bruker 400 MHz
FT-NMR. Chemical shifts were reported in ppm relative
to tetramethylsilane d units. The absorption spectra of the
dyes in solution and adsorbed on TiO2 films were recorded
on a Cary 100 UV-Vis spectrophotometer. Fluorescence
measurements were carried out using a Hitachi F-4500
fluorescence spectrophotometer. Cyclic voltammetry was
performed using an electrochemical workstation (CH
instruments Inc., CHI, model 750A) and conducted using
0.1 mol L-1 tetrabutylammonium perchlorate (TBAP) as the
supporting electrolyte. The working electrode was a glassy
carbon electrode, the auxiliary electrode was a Pt wire and
the reference electrode was Ag/Ag+. The scan rate was
100 mV s-1 and the temperature was 25 oC. Ferrocene was
added to each sample solution at the end of the experiments.
The ferrocenium/ferrocene (Fc/Fc+) redox couple was used
as an internal potential reference. The potential vs. SCE in
DMF was calibrated according to a procedure published
by Matsui et al.26 The photovoltaic measurements of the
DSSCs were performed using a Newport M-66907 450 W
xenon light source through an infrared blocking filter and a
Keithley 2400 digital source meter linked to a computerized
control and data acquisition system. The light intensity was
1000W m-2 under anAM 1.5 light source. Cell temperatures
were kept at 25 oC during the illumination. Light intensity
was calibrated using a mono-Si reference solar cell
(PVM134). The incident photon-to-current conversion
efficiency (IPCE) as a function of excitation wavelength
was measured using an incident light 300 W xenon lamp.
A 300 W xenon arc lamp solar simulator (#91160A, Oriel)
with an AM 1.5 Globe filter (#59044, Oriel) was used to
measure the I-V characteristics of the quasi-solid-state
DSSC. The illumination was fixed at 100 mW cm-2 using
a reference solar cell and meter (#91150, Oriel).
C6H13
H
N
t-BuOK
N
2a
N
C6H13Br
+
+
+
DMF
1a
H
N
t-BuOK
DMF
C2H5
I
1b
2b
H
N
t-BuOK
DMF
N
C
2H5I
S
S
1c
2c
F3COC
N
N
CH3CN
CF3CO2
2(CF3CO)2O
CF3COOH
+
+
N
N
H
COCF3
R
N
COCF3
R
N
COCF3
N
HCl
2a, 2b or 2c
N
N
X
CH3CN
CH3CN
N
OHC
X
CHO
F3COC
COCF3
4a: X = none; R = C6H13
4b: X = CH2CH2; R = C2H5
4c: X = S; R = C2H5
3a: X = none; R = C6H13
3b: X = CH2CH2; R = C2H5
3c: X = S; R = C2H5
R
O
COOH
HOOC
O
N
N
N
S
S
S
S
S
S
X
N
COOH
O
NH4OAc
AcOH
S1: X = none; R = C6H13
S2: X = CH2CH2; R = C2H5
S3: X = S; R =C2H5
Figure 1. Synthesis of three organic dyes with double electron acceptors.
However, the Vilsmeier reaction gave low yields for
the dialdehyde compounds. Therefore, a two-step strategy
was used for their preparation.29 N-hexylcarbazole (2a),
N-ethyliminodibenzyl (2b) and N-ethylphenothiazine
(2c) were first treated with a reactive derived from the
reaction of imidazole and trifluoroacetic anhydride to give
the respective intermediates containing trifluoroacetyl
(CF3CO) groups (3a-c) that could be readily hydrolyzed to
dialdehydes (4a-c). The final products S1, S2 and S3 were
obtained by the condensation of the respective aldehyde
Computation methods
The geometric and electronic properties of the
carbazole, iminodibenzyl and phenothiazine-containing

Vol. 22, No. 4, 2011
Wu et al.
783
with rhodanine-3-acetic acid via the Knoevenagel reaction
in the presence of ammonium acetate. The structural
differences of those photosensitizers (Table 1 and Figure 2)
were evaluated from their optimized structures. When
viewed from the top, the angles (∠1) of the S1 carbazole,
the S2 iminodibenzyl and the S3 phenothiazine rings are
108.6o, 124.4o and 122.0o, respectively, implying that
the addition of a dimethylene bridge and sulfur units
significantly increases the angle (∠1) of nitrogen atoms.
The angle between two phenyl units in the carbazole unit
(∠4) is 106.4o; however, the angle between the phenyl unit
and dimethylene bridge inside the iminodibenzyl unit (∠4)
is 125.9o. This can be attributed to the incorporation of a
dimethylene bridge between two phenyl units increasing
the steric hindrance, which increases the angles ∠1 and
∠4. The angle of the S3 phenothiazine sulfur atom (∠8)
is 99.0o, which is smaller than that of the phenothiazine
nitrogen atom (∠1: 122.0o). This may be attributed to the
character between nitrogen and sulfur atoms.
Table 1. Optimized geometric parameters (angle, degree) of S1, S2
and S3
S1
S2
S3
∠1
∠2
∠3
∠4
∠5
∠6
∠7
∠8
∠9
∠10
∠11
108.6
125.6
125.7
106.4
134.0
106.4
134.0
124.3
124.3
124.4
119.1
116.5
125.9
115.9
119.6
121.3
115.6
110.0
125.6
125.0
122.0
118.5
118.5
120.5
118.3
120.5
118.3
99.0
125.4
125.4
When viewed from the front, the carbazole unit is
coplanar with two rhodanine rings; the dimethylene bridge
decreases the coplanarity of the iminodibenzyl unit and
induces the nonplanar geometry of S2. The phenothiazine
is bent along the N-S axis, as confirmed by X-ray structural
analysis.30 The nitrogen atom in the phenothiazine moiety
induces a nonplanar geometry similar to that of the
sp3-hybridized pyramidal nitrogen.
Figure 2. Optimized geometric structures of (a) S1 top view, (b) S1
front view, (c) S2 top view, (d) S2 front view, (e) S3 top view and (f)
S3 front view.
Optical properties
The UV-Vis absorption and emission spectra of S1,
S2 and S3 in DMF solution and the absorption spectra
of the corresponding dyes adsorbed on TiO2 film are
shown in Figure 3 and the lmax values are listed in Table 2.
The absorption spectrum of S2 in DMF exhibits two

784
Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
major prominent bands, appearing at 300-400 nm and
at 400-600 nm, respectively. The former is ascribed to a
localized aromatic p–p* transition and the latter is of charge-
transfer character between the iminodibenzyl-based donor
and the rhodanine-3-acetic acid,31 providing efficient charge
separation at the excited state. Under similar conditions, the
S1 sensitizer had an absorption peak at 450 nm that was
slightly red-shifted relative to the peaks of S2, implying
that the incorporation of the carbazole unit leads to better
coplanarity than that achieved by the iminodibenzyl unit.
of S3 relative to S1 and S2 is due to stronger intramolecular
charge transfer in S3 as a result of phenothiazine being
a stronger electron-donating ring than are carbazole and
iminodibenzyl. Red-shifting in the absorption spectra helps
utilize solar light. The absorption spectra of S1-S3 on a
TiO2 electrode are broader than those in DMF solution.
When the S1 and S3 sensitizers are adsorbed on the TiO2
electrode, there is a slight blue shift from 450 to 442 nm
and 489 to 488 nm (Table 2), respectively, implying that
dyes adsorbed on the TiO2 surface have partial H-type
aggregates. Under similar conditions, the S2 sensitizer has
a slight red shift from 445 to 447 nm after being adsorbed
on the TiO2 electrode. The molar extinction coefficients
(e) of S1, S2 and S3 are 26360 L mol-1 cm-1 (at 450 nm),
24040 L mol-1 cm-1 (at 445 nm) and 25480 L mol-1 cm-1
(at 489 nm), respectively; larger than that of Ru organic
complex (14200 L mol-1 cm-1),32 indicating that they are
beneficial to light harvesting.
Figure 3(a) shows the emission spectra of the dyes in
DMF solution. The excitation wavelength for emission
was the maximum absorption in the visible region. The
corresponding data are summarized in Table 2. It can be
seen that the maximum emission wavelengths in DMF
solution follow the order S3 > S2 > S1. The maximum
emission wavelength was red-shifted when iminodibenzyl
was substituted by phenothiazine (558 nm for S2
and 635 nm for S3), but the peak was blue-shifted by
introducing a 9-hexylcarbazole moiety as an electron donor
(521 nm for S1). S3 exhibited a relatively large Stokes
shift, which could be attributed to the geometrically relaxed
structure of the phenothiazine center upon excitation.33 A
large Stokes shift is advantageous because it minimizes
interference by the excitation light in the measurement of
the fluorescence emission.
Electrochemical properties
Figure 3. (a) Absorption and emission spectra of S1, S2 and S3 in DMF
(10–5 mol L-1), lexc = 420 nm and (b) absorption spectra of S1, S2 and S3
absorbed on TiO2 film.
To evaluate the thermodynamic allowed electron
transfer processes from the excited dye molecule to
the conduction band of TiO2, cyclic voltammetry (CV)
measurements were performed. The electrochemical
behavior of S1-S3 in the anodic direction was irreversible.
Wherein the phenothiazine unit substitutes the
carbazole or iminodibenzyl unit in S3, the absorption
maximum red-shifted to 489 nm. The significant red shift
Table 2. Absorption and emission properties of S1, S2 and S3 dyes
Absorption
Emission
Dye
Stokes shifta / nm
labsb / nm
295, 355, 403, 450
296, 346, 445
298, 357, 489
e / L mol-1 cm-1 (at labs
26360 (450 nm)
24040 (445 nm)
25480 (489 nm)
)
labsb / nm (on TiO2)
lemb / nm
521
S1b
S2
S3
442
447
488
71
558
113
146
635
aStokes shift = lem(solution) − labs(solution); babsorption and emission spectra were measured in DMF solution.

Vol. 22, No. 4, 2011
Wu et al.
785
The ground-state oxidation potentials (Eox) of the three dyes
were measured and the results summarized in Table 3. The
ferrocenium/ferrocene (Fc/Fc+) redox couple was used as
internal reference. The Eonset(ox) of S3 is less positive than
those of S1 and S2, indicating that the phenothiazine units
are much more effective in lowering the ionization potential
than are iminodibenzyl and carbazole units.
The ground-state oxidation potentials E(S+/S) of S1, S2
and S3, corresponding to the highest occupied molecular
orbital (HOMO) level of sensitizers, were estimated to be
0.64, 0.62 and 0.55V, respectively, vs. the normal hydrogen
electrode (NHE). The HOMO levels of S1 and S2 (0.64
and 0.62 V vs. NHE, respectively) are more positive than
that of S3 (0.55 V vs. NHE), indicating more efficient dye
regeneration for S1 and S2.
I− ions in the electrolyte. The LUMO levels of these dyes
were estimated from the difference between Eox and E0-0;
they are in the range of –1.63 to –1.92 V vs. NHE, which
are more negative than the conduction band edge of TiO2
(−0.5 V vs. NHE).35 Provided that an energy gap (between
dye LUMO and TiO2 conduction band (CB)) of 0.2 eV is
necessary for efficient electron injection,36 the driving force
is sufficient for efficient charge injection. Thus, the electron
injection process from the excited dye molecule to the TiO2
conduction band and the subsequent dye regeneration are
energetically permitted. Such electronic structures thus
ensure a favorable exothermic flow of charges throughout
the photo-electric conversion. However, in an actual device,
molecules have interfaces or other molecules as neighbors,
which a consequent modification of electronic structure
and molecular conformation implying in differences in
the energy levels.
Since energy levels in several cases, such as values
obtained using XPS (X-ray photoelectron spectroscopy)
or UPS (ultraviolet photoelectron spectroscopy), referring
these values to vacuum, we evaluate the ionization potential
(IP) and electroaffinity (EA) to realize and control the
electrical and optical properties.37-39 IP gives a good
indication of whether a given p-type dopant is capable
of ionizing a compound, whereas EA is important for
comprehending the n-type doping process. The positions
of the HOMO (IP) levels of S1, S2 and S3 relative to a
vacuum were estimated to be –5.15, –5.13 and –5.06 eV,
respectively. Similarly, the LUMO (EA) levels of S1, S2
and S3 relative to a vacuum were estimated to be –2.59,
–2.66 and –2.88 eV, respectively.
The excited-state oxidation potentials E(S+/S*), which
reflect the lowest occupied molecular orbital (LUMO) level
of the sensitizers, play an important role in the electron
injection process. The excited-state oxidation potential
E(S+/S*) was calculated using:34
E(S+/S*) = E(S+/S) – E0−0
(1)
where E0−0 is the zeroth-zeroth transition value obtained
from the intersection of the normalized lowest energy
absorption peak and highest energy fluorescence peak. The
LUMO levels of S1 and S2 (–1.92 and –1.85 V vs. NHE,
respectively) are more negative than that of S3 (–1.63 vs.
NHE), indicating that S1 and S2 dyes have more efficient
electron injection.
Figure 4 shows a schematic energy diagram of a
DSSC based on dyes attached to a nanocrystalline TiO2
film deposited on conducting fluorine-doped tin oxide
(FTO) glass. The oxidation potentials (approximately the
HOMO levels) of the dyes range from 0.55 to 0.64 V vs.
NHE. These values are more positive than the I3−/I− redox
potential (0.42 V vs. NHE),35 indicating that the oxidized
dye formed after electron injection into the conduction
band of TiO2 thermodynamically accepted electrons from
Molecular orbital calculations
To investigate the molecular structure and electron
distribution of the organic dyes, the geometries of the
organic dyes were optimized using density functional
theory (DFT) calculations at a B3LYP/6-31+g (d) level. The
isodensity surface plots of frontier orbitals involved in these
Table 3. Electrochemical properties and band gaps of S1, S2 and S3 dyes
HOMO (IP)f
/ eV
LUMO (EA)g
/ eV
c
Eonset(ox)
in DMF
E
onset(ox) vs.
E(S+/S)b,d vs.
NHE / V
E0-0
LUMO vs.
NHE / eV
e
Dye
Egap / V
EFOCa / V
(eV)
S1
S2
S3
0.31
0.29
0.22
0.35
0.33
0.26
0.64
0.62
0.55
2.56
2.47
2.18
–1.92
–1.85
–1.63
1.42
1.35
1.13
–5.15
–5.13
–5.06
–2.59
–2.66
–2.88
aEFOC = –0.04 V vs. Ag/Ag+; bthe ground-state oxidation potentials E(S+/S) were measured in DMF containing 0.1 mol L-1 tetrabutylammonium perchlorate
as supporting electrolyte using a glassy carbon working electrode, a Pt counter electrode and a Ag/Ag+ reference electrode; cthe E0-0 value was estimated
from the cross-section of absorption and emission spectra; dthe excited-state oxidation potential E(S+/S*) was calculated from E(S+/S) – E0−0; eEgap is the
f
energy gap between E(S+/S*) of the dye and the conduction band level of TiO2 (−0.5 V vs. NHE); ionization potential: IP = – 4.8 – (Eonset(ox) – EFOC);
gelectron affinity: EA − E0-0 = IP.

786
Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
HOMO and LUMO is ideal for dye sensitized solar cells,
as it facilitates rapid interfacial electron injection from the
excited dyes to the TiO2 conduction band and slows down
the recombination of injected electrons inTiO2 with oxidized
sensitizers due to their remoteness.
Photovoltaic performance
The sensitizers were used for fabricating DSSCs to
explore current–voltage characteristics. Figure 6 shows the
spectra of incident photon-to-current efficiency (IPCE) for
S1-S3-based solar cells. The IPCE values were measured
according to the following equation:40
Figure 4. Schematic energy level diagram for a DSSC based on dyes
attached to a nanocrystallineTiO2 film deposited on conducting FTO glass.
where l is the wavelength, short-circuit current (Jsc) and f is
the power of the incident radiation per unit area. The IPCE
values of dyes as a function of excitation wavelength plots
show that the IPCEs of S1, S2 and S3 are 48-58% in the
spectral range of 450 to 520 nm. The IPCE spectrum covers
thewholevisibleregionintherangeof400-750 nm, allowing
the DSSC to efficiently convert solar light into electricity.
A typical photocurrent–photovoltage (I–V) curve for
cells based on S1-S3 is shown in Figure 7. The detailed
photovoltaic parameters are summarized in Table 4. The
solar-energy-to-electricity conversion efficiency (η) of
the DSSCs is calculated from short-circuit current (Jsc),
the open-circuit photovoltage (Voc), the fill factor (FF) and
the intensity of the incident light (Pin) according to the
following equation:40
transitions are shown in Figure 5. The frontier molecular
orbitals of S1-S3 reveal that the HOMO levels of the dye
molecules are dominated by a p orbital contribution from
the carbazole, iminodibenzyl and phenothiazine units, with
a small contribution from the rhodanine-3-acetic acid moiety
and that the HOMO−1 levels are a p orbital mainly over
the dimethylene bridge and partial rhodanine ring, with a
small contribution from the carbazole, iminodibenzyl and
phenothiazine units. However, the LUMO levels are largely
p*, with major contributions from the phenyl groups of
donors, the dimethylene bridge and the rhodanine ring. The
LUMO+1 levels are also p* mainly across the dimethylene
bridge and rhodanine ring.At the excited state (LUMO) with
light illumination for S1-S3 dyes, intramolecular charge
transfer occurs, resulting in electron density movement
from the donor group to the acceptor groups (rhodanine-3-
acetic acid group). This orientationally spatial separation of
Figure 5. Computed isodensity surfaces of HOMO and LUMO orbitals of S1, S2 and S3.

Vol. 22, No. 4, 2011
Wu et al.
787
is probably due to the stronger electron-donating ability
of the phenothiazine unit when electrons transfer
from the phenothiazine unit to the rhodanine-3-acetic
acid group, and a possible vectorized photon-induced
charge transfer of the phenothiazine unit with respect
to electrodes. This character could not only depress the
interaction between molecules resulting in the energy
quenching of the excited states, but also suppress the
−
I3 ions in the electrolyte to the TiO2 surface that is in
favor of higher Voc.
Pathways of photon-to-current conversion in dye-
sensitized solar cells
Figure 6.Action spectra of IPCE for DSSCs based on S1, S2 and S3 dyes
under the same conditions.
Figure 8 shows a schematic representation of a DSSC
based on the S2 photosensitizer. A thin film of electrolyte
−
solution (I−/I3 dissolved in an organic solvent) is
sandwiched between the TiO2 electrode and a transparent
conducting electrode (counter electrode).
Figure 7. Current density-voltage characteristics for S1, S2 and S3 DSSCs
under illumination of simulated solar light (AM 1.5, 100 mW cm-2).
Table 4. Photovoltaic performances of DSSCs based on S1, S2 and S3 dyes
Figure 8. Schematic representation for a DSSC based on the S2
photosensitizer, I−/I3− redox electrolyte, TiO2 anode and counter cathode.
Dye
S1
Voc / V
0.589
0.597
0.658
Jsc / mA cm-2
7.61
Fill factor (FF)
η / %
2.81
3.59
4.91
0.63
0.61
0.7
S2
9.95
The general design principle for metal-free organic
dyes or sensitizers consists of a donor-acceptor-
substituted p-conjugated bridge and an anchoring group
to the TiO2 which is attached to the side of the acceptor
(Figure 9). Light-harvesting dyes absorb solar radiation
incident on them, which results in their excitation. The
excited molecules pass their energy by transferring
electrons onto a nanocrystalline TiO2 substrate onto
which they are adsorbed. The injected electrons in
S3
10.60
aMeasured under irradiation of AM 1.5 G simulated solar light
(100 mW cm-2) at room temperature, 0.25 cm2 working area; the
concentration of dye is 5 × 10–4 mol L-1 in tetrahydrofuran (THF),
and 0.6 mol L-1 tetrabutylammonium iodide (TBAI), 0.1 mol L-1 LiI,
0.05 mol L-1 I2, 0.6 mol L-1 DMPII, and 0.5 mol L-1 4-tert-butylpyridine
(TBP) in dry acetonitrile (ACN) as electrolyte.
b
As demonstrated in Table 4, S1 gives a light-to-
electricity conversion efficiency of 2.81% with a short-
circuit photocurrent density (Jsc) of 7.61 mA cm-2, a Voc
of 0.589 V and a FF of 0.63 under the standard global
AM 1.5 solar condition. Under similar conditions,
the photovoltaic parameters (Jsc, Voc and η) of cells
with the S2 sensitizer are 9.95 mA cm-2, 0.597 V and
3.59%, respectively, and those of the S3 sensitizer are
10.60 mA cm-2, 0.658 V and 4.91%, respectively. The
efficiency improvement exhibited by the S3 sensitizer
Figure 9. Design principle of organic dyes for TiO2 photoanodes in
DSSCs.

788
Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
the conduction band of TiO2 are transported toward
the counter electrode through the external load. At the
counter electrode, a redox couple is utilized (usually
iodide-triiodide) to regenerate the dye so the process
can be repeated.
7. Ferreira, J.; Girotto, E. M.; J. Braz. Chem. Soc. 2010, 21, 312.
8. Kulkarni,A. P.; Tonzola, C. J.; Babel,A.; Jenekhe, S.A.; Chem.
Mater. 2004, 16, 4556.
9. Wu, T.-Y.; Lee, N.-C.; Chen, Y.; Synth. Met. 2003, 139, 263.
10. Wu, T.-Y.; Tsao, M. H.; Chen, F. L.; Su, S. G.; Chang, C. W.;
Wang, H. P.; Lin,Y. C.; Ou-Yang, W.-C.; Sun, I. W.; Int. J. Mol.
Sci. 2010, 11, 329.
Conclusion
11. Chen, Z.; Li, F.; Huang, C.; Curr. Org. Chem. 2007, 11, 1241.
12. Yahagida, S.; Senadeera, G. K. R.; Nakamura, K.; Kitamura,
T.; Wada, Y.; J. Photoch. Photobio. A 2004, 166, 75.
13. Hara, K.; Tachibana,Y.; Ohga,Y.; Shinpo,A.; Suga, S.; Sayama,
K.; Sugihara, H.; Arakawa, H.; Sol. Energ. Mat. Sol. C. 2003,
77, 89.
We synthesized three di-anchoring organic dyes
containing carbazole, iminodibenzyl and phenothiazine
units, respectively, as donors to compare and study their
optical, electrochemical and photovoltaic properties. The
electron-donating groups of organic sensitizers show
different interactions on a TiO2 surface. The LUMO values
of S1 (–1.92 V), S2 (–1.85 V) and S3 (–1.63 V) are more
than 0.2 eV negative than the conduction band edge of
TiO2 (−0.5 V vs. NHE), implying that the driving force
is sufficient for efficient charge injection. The HOMO
values of S1 (0.64 V), S2 (0.62 V) and S3 (0.55 V) are
sufficiently more positive than the I3−/I− redox potential
(0.42 V vs. NHE). DSSCs based on the S3 dye showed the
best photovoltaic performance: a maximum IPCE of 58%,
a short-circuit photocurrent density (Jsc) of 10.60 mA cm-2,
a Voc of 0.658 V and a FF of 0.7, corresponding to an
overall conversion efficiency of 4.91% under 100 mW cm-2
irradiation. The proposed di-anchoring organic dyes are
promising candidates for DSSCs.
14. Horiuchi, T.; Miura, H.; Uchida, S.; Chem. Commun. 2003,
3036.
15. Sayama, K.; Tsukagoshi, S.; Hara, K.; Ohga, Y.; Shinpou, A.;
Abe, Y.; Suga, S.; Arakawa, H.; J. Phys. Chem. B 2002, 106,
1363.
16. Yao, Q.-H.; Shan, L.; Li, F.-Y.; Yin, D.-D.; Huang, C.-H.;
New J. Chem. 2003, 27, 1277.
17. Jung, I.; Lee, J. K.; Song, K. H.; Song, K.; Kang, S. O.; Ko, J.;
J. Org. Chem. 2007, 72, 3652.
18. Alam, M. M.; Jeneke, S. A.; Chem. Mater. 2002, 14, 4775.
19. Babel, A.; Jenekhe, S. A.; J. Phys. Chem. B 2003, 107, 1749.
20. Fungo, F.; Jenekhe, S. A.; Bard, A. J.; Chem. Mater. 2003, 15,
1264.
21. Sapp, S.A.; Sotzing, G.A.; Reynolds, J. R.; Chem. Mater. 1998,
10, 2101; Fungo, F.; Jenekhe, S. A.; Bard, A.; J. Chem. Mater.
2004, 15, 1264.
Supplementary Information
22. Wu, T.-Y.; Chen, Y.; J. Polym. Sci. Pol. Chem. 2002, 40, 4452.
23. Wu, T.-Y.; Tsao, M. H.; Chen, F. L.; Su, S. G.; Chang, C. W.;
Wang, H. P.; Lin, Y. C.; Sun, I. W.; J. Iran. Chem. Soc. 2010,
7, 707.
Supplementary data are available free of charge as PDF
file at http://jbcs.sbq.org.br.
Acknowledgement
24. Jang, S.Y.; Seshadri, V.; Khil, M. S.; Kumar, A.; Marquez, M.;
Mather, P. T.; Sotzing, G. A.; Adv. Mater. 2005, 17, 2177.
25. Wang, P.; Zakeeruddin, S. M.; Comte, P.; Charvet, R.; Humphry-
Baker, R.; Grätzel, M.; J. Phys. Chem. B 2003, 107, 14336.
26. Matsui, M.; Hashimoto, Y.; Funabiki, K.; Jin, J.; Yoshida, T.;
Minoura, H.; Synth. Met. 2005, 148, 147.
The authors would like to thank the National Science
Council of the Republic of China for financially supporting
this project.
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Submitted: June 6, 2010
Published online: February 17, 2011

J. Braz. Chem. Soc., Vol. 22, No. 4, S1-S10, 2011.
Printed in Brazil - ©2011 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Supplementary Information
SI
Synthesis, Characterization and Photovoltaic Properties of
Di-Anchoring Organic Dyes
Tzi-Yi Wu,a,b Ming-Hsiu Tsao,a Shyh-Gang Su,a H. Paul Wang,c,d Yuan-Chung Lin,e
Fu-Lin Chen,a Cheng-Wen Changa and I-Wen Sun*,a,c
aDepartment of Chemistry, cSustainable Environment Research Center and dDepartment of
Environmental Engineering, National Cheng Kung University, Tainan 701, Taiwan
bDepartment of Polymer Materials, Kun Shan University, Tainan 71003, Taiwan
eInstitute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan
Syntheticprocedureofcarbazole,iminodibenzyand
phenothiazine-containing dyes (S1-S3)
(3a: 3.55 g , 92%), which was used for the next step without
further purification. To a 250 mL glass reactor were added
with 3a (6.2 g, 8 mmol), 148 mL acetonitrile and 77 mL
1.9 mol L-1 HCl. The mixture was refluxed for 3 h and was
extracted with ethyl ether after cooling and neutralization.
The crude product obtained by removing ethyl ether were
purified by column chromatography (silica gel, 60-200 mm,
neutrality; n-hexane/ethyl acetate = 4/1) to give 4a (1.75 g,
71%, mp 143 oC). 1H NMR (CDCl3, ppm): d 10.04 (s, 2H),
8.83 (s, 2H), 8.01 (d, 2H), 7.80 (d, 2H), 4.46 (t, 2H), 1.69
(m, 2H), 1.16 (m, 6H), 0.73 (t, 3H). Elemental analysis
calculated (%) for C20H21NO2: C, 78.15; H, 6.89; N, 4.56.
Found: C, 77.98; H, 6.81; N, 4.65.
N-hexylcarbazole (2a)
To a 250 mL two necked flask was added with carbazole
(16.72 g, 100 mmol), 100 mL DMF and potassium
tert-butoxide (12.4 g, 110 mmol). After stirring for 30 min,
the mixture was added with N-bromohexane (17.34 g, 105
mmol) and allowed to reflux overnight. Pouring it into a
large amount of water precipitated 9-hexylcarbazole, which
were collected by filtration and then recrystallized twice in
methanol. The yield was 71% (mp 53 oC). 1H NMR (CDCl3),
d (ppm): 8.13-8.10 (d, 2H), 7.50-7.40 (m, 4H), 7.26-7.21
(m, 2H), 4.31 (t, J 7.0 Hz, 2H), 1.88 (quintet, J 5.4 Hz, 2H),
1.39 (m, 2H), 1.31 (m, 4H), 0.88 (t, J 3.3 Hz, 3H). Elemental
analysis calculated (%) for C18H21N: C, 86.01%; H, 8.42%;
N, 5.57%. Found: C, 85.96%; H, 8.40%; N, 5.55%.
5,5’-(9-Hexyl-carbazole-3,6-diyl)bis(methan-1-yl-1-ylidene)
bis(4-oxo-2-thioxothiazolidin-3-yl-5-ylidene)diacetic acid
(S1)
To a stirred 4a (0.615 g, 2 mmol) in CH3COOH (30 mL)
were added rhodanine-3-acetic acid (0.794 g, 4.15 mmol)
and ammonium acetate (0.125 g, 1.625 mmol). The mixture
was heated to 120 oC and the reaction was continued for 2 h
at the temperature. Then the reaction mixture was allowed
to cool to room temperature. The solid was collected
by filtration and washed with water thoroughly. After
drying in air, the crude product was purified by column
chromatography on silica gel with CH2Cl2/methanol
(10:1, v/v) as eluant to give S1 in 93% yield, mp > 200 oC.
1H NMR (DMSO-d6), d (ppm): 8.55 (s, 2H, -CH=), 8.03
(s, 2H, aromatichydrogen), 7.84(d, 2H, aromatichydrogen),
7.76 (d, 2H, aromatic hydrogen), 4.76 (s, 4H, O=C-CH2-N),
4.47 (t, 2H, N-CH2-), 1.79 (m, 2H, N-CH2-CH2-), 1.26
(m, 6H, N-CH2-CH2-CH2-CH2-CH2-CH3), 0.80 (t, 3H,
N-CH2-CH2-CH2-CH2-CH2-CH3). Elemental analysis
9-Hexylcarbazole-3,6-dicarbaldehyde (4a)
To a 50 mL glass reactor were added with imidazole
(0.718 g, 10.5 mmol) and 10 mL acetonitrile. The mixture
were added under stirring with trifluoroacetic anhydride
(5.775 g, 27.5 mmol) within 5 min, treated dropwise with
9-hexylcarbazole (2a: 1.257 g, 5 mmol) and then refluxed for
4 h.After adjusting pH > 7 with saturated aqueous solution of
Na2CO3, the appearing precipitates were isolated by filtration
and washed with water to give a precipitate. The precipitate
was dissolved in CH2Cl2, washed with saturated aqueous
NaHCO3, dried over anhydrous MgSO4 and the solvent
was removed under reduced pressure to afford 3,6-bis(1,3-
bistrifluoracetyl-4,5-dihydroimidazole-2-yl)-9-hexylcarbazole
*e-mail: iwsun@mail.ncku.edu.tw

S2
Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
calculated (%) for C30H27N3O6S4: C, 55.11%; H, 4.16%;
N, 6.43%. Found: C, 54.92%; H, 4.12%; N, 6.31%.
and ammonium acetate (0.125 g, 1.625 mmol). The mixture
was heated to 120 oC and the reaction was continued for 2 h
at the temperature. Then the reaction mixture was allowed
to cool to room temperature. The solid was collected
by filtration and washed with water thoroughly. After
drying in air, the crude product was purified by column
chromatography on silica gel with CH2Cl2/methanol
(10:1, v/v) as eluent to give S2 in 83% yield, mp > 200 oC.
1H NMR (DMSO-d6), d (ppm): 7.79 (s, 2H, -CH= and
aromatic hydrogen), 7.50 (m, 4H, aromatic hydrogen), 7.36
(d, 2H, aromatic hydrogen), 4.73 (s, 4H, O=C-CH2-N),
3.94 (q, 2H, N-CH2-), 3.18 (t, 4H, -CH2-CH2-), 1.19
(t, 3H, N-CH2-CH3). Elemental analysis calculated (%) for
C28H23N3O6S4: C, 53.74%; H, 3.70%; N, 6.72%. Found:
C, 53.51%; H, 3.62%; N, 6.58%.
11-Ethyl-iminodibenzyl (2b)
Iminodibenzyl (1b: 6.834 g, 35 mmol), iodoethane
(5.93 g, 38 mmol) and 80 mL of DMF were added to a 50
mL two-necked glass reactor. The solution was warmed
to 75 °C, treated portionwise with potassium tert-butoxide
(4.264 g, 38 mmol) and then refluxed for 24 h. After 150
mL of water was added, the mixture was extracted with
chloroform (75 mL). Crude oils obtained by removing the
solvent were purified by column chromatography (silica gels,
n-hexane/ethyl acetate: 20/1 as eluent) to give 2b as a white
solid (4.76 g, 61%, mp 54 oC). 1H NMR (CDCl3), d (ppm):
1.16 (t, 3H, CH3), 3.17 (m, 4H, CH2), 3.80 (m, 2H, CH2), 6.92
(m, 2H, ar), 7.12 (m, 6H, ar). Elemental analysis calculated
(%) for C16H17N: C, 86.05%; H, 7.67%; N, 6.27%. Found:
C, 85.96%; H, 7.73%; N, 6.20%.
10-Ethyl-phenothiazine (2c)
Phenothiazine (1c: 11.94 g, 60 mmol), iodoethane
(10.92 g, 70 mmol) and 80 mL of DMF were added to a
50 mL two-necked glass reactor. The solution was warmed
to 75 °C, treated portionwise with potassium tert-butoxide
(7.86 g, 70 mmol) and then refluxed for 24 h.After 150 mL
of water was added, the mixture was extracted with
chloroform (75 mL). Crude product obtained by removing
the solvent were purified by column chromatography (silica
gels, n-hexane/ethyl acetate: 20/1 as eluent) to give 2c as a
white solid (11.32 g, yield: 83%, mp 103-104 oC). 1H NMR
(CDCl3), d (ppm): 1.42 (t, 3H, CH3), 3.92 (m, 2H, CH2),
6.85-6.88 (m, 4H, ar), 7.11-7.16 (m, 4H, ar). Elemental
analysis calculated (%) for C14H13NS: C, 73.97%;
H,5.76%;N,6.16%;S,14.11%.Found:C,73.83%;H,5.73%;
N, 6.13%, S, 14.10%.
11-Ethyl-3,8-diformyliminodibenzyl (4b)
To a 50 mL glass reactor were added with imidazole
(0.718 g, 10.5 mmol) and 10 mL acetonitrile. The mixture
were added under stirring with trifluoroacetic anhydride
(5.775 g, 27.5 mmol) within 5 min, treated dropwise with
11-ethyl-iminodibenzyl (2b: 1.117 g, 5 mmol) and then
refluxedfor4h.AfteradjustingpH>7withsaturatedaqueous
solution of Na2CO3, the appearing precipitates were isolated
by filtration and washed with water to give a precipitate. The
precipitate was dissolved in CH2Cl2, washed with saturated
aqueous NaHCO3, dried over anhydrous MgSO4 and the
solvent was removed under reduced pressure to afford
3,8-bis(1,3-bis-trifluoracetyl-4,5-dihydroimidazole-2-yl)-
11-ethyliminodibenzyl (3b: 3.35 g, 90%), which was used
for the next step without further purification. To a 250 mL
glass reactor were added with 3b (5.95 g, 8 mmol), 148 mL
acetonitrile and 77 mL 1.9 mol L-1 HCl. The mixture was
refluxedfor3handwasextractedwithethyletheraftercooling
and neutralization. The crude products obtained by removing
ethyl ether were purified by column chromatography (silica
gel; n-hexane/ethyl acetate = 4/1) to give4b (1.77 g, 79%, mp
96 oC). 1H NMR (acetone-d6, ppm): d 9.72 (s, 2H, -CHO),
7.54 (d, J 7.4 Hz, 2H), 7.48 (s, 2H), 7.09 (d, J 7.3 Hz, 2H),
3.73 (t, 2H), 3.05 (s, 4H), 1.07 (t, J 3.3 Hz, 3H). Elemental
analysis calculated (%) for C18H17NO2: C, 77.40; H, 6.13;
N, 5.01. Found: C, 77.41; H, 6.16; N, 4.96.
10-Ethyl-3,7-diformylphenothiazine (4c)
To a 50 mL glass reactor were added with imidazole
(0.718 g, 10.5 mmol) and 10 mL acetonitrile. The mixture
were added under stirring with trifluoroacetic anhydride
(5.775 g, 27.5 mmol) within 5 min, treated dropwise with
10-ethyl-phenothiazine (2c: 1.137 g, 5 mmol) and then
refluxed for 4 h. After adjusting pH > 7 with saturated
aqueous solution of Na2CO3, the appearing precipitates
were isolated by filtration and washed with water to give
a precipitate. The precipitate was dissolved in CH2Cl2,
washed with saturated aqueous NaHCO3, dried over
anhydrous MgSO4 and the solvent was removed under
reduced pressure to afford 3,7-bis(1,3-bistrifluoracetyl-
4,5-dihydroimidazole-2-yl)-10-ethylphenothiazine (3c:
3.25 g , 87%), which was used for the next step without
further purification. To a 250 mL glass reactor were added
with 3c (5.98 g, 8 mmol), 148 mL acetonitrile and 77 mL
1.9 mol L-1 HCl. The mixture was refluxed for 3 h and was
5,5’-(11-Ethyl-iminodibenzyl-3,8-diyl)bis(methan-1-yl-1-
ylidene)bis(4-oxo-2-thioxothiazolidin-3-yl-5-ylidene)diacetic
acid (S2)
To a stirred 4b (0.558 g, 2 mmol) in CH3COOH (30 mL)
were added rhodanine-3-acetic acid (0.794 g, 4.15 mmol)

Vol. 22, No. 4, 2011
Wu et al.
S3
extracted with ethyl ether after cooling and neutralization.
The crude product obtained by removing ethyl ether
were purified by column chromatography (silica gel;
n-hexane/ethyl acetate = 4/1) to give 4c (1.74 g, 77%, mp
167 C). H NMR (CDCl3, ppm): d 9.84 (s, 2H, -CHO),
7.68 (dd, 2H, aromatic hydrogen), 7.59 (s, 2H, aromatic
hydrogen), 6.98 (d, 2H, aromatic hydrogen), 4.05 (q, 2H,
N-CH2-), 1.50 (t, 3H, N-CH2-CH3). Elemental analysis
calculated (%) for C16H13NO2S: C, 67.82; H, 4.62; N, 4.94.
Found: C, 67.84; H, 4.60; N, 4.91.
2.49 mmol) and ammonium acetate (0.075 g, 0.975 mmol).
The mixture was heated to 120 C and the reaction was
o
continued for 2 h at the temperature. Then the reaction
mixture was allowed to cool to room temperature. The
solid was collected by filtration and washed with water
thoroughly. After drying in air, the crude product was
purified by column chromatography on silica gel with
CH2Cl2/methanol (10:1, v/v) as eluant to give S3 in 86%
yield, mp > 200 oC. 1H NMR (DMSO-d6), d (ppm): 7.75
(s, 2H, -CH=), 7.47 (d, 2H, aromatic hydrogen), 7.40 (s,
2H, aromatic hydrogen), 7.19 (d, 2H, aromatic hydrogen),
4.71 (s, 4H, O=C-CH2-N), 4.00 (q, 2H, N-CH2-), 1.33 (t,
3H, N-CH2-CH3). Elemental analysis calculated (%) for
C26H19N3O6S5: C, 49.59%; H, 3.04%; N, 6.67%. Found:
C, 49.43%; H, 3.01%; N, 6.53%.
o
1
5,5’-(10-Ethyl-phenothiazine-3,7-diyl)bis(methan-1-yl-
1-ylidene)bis(4-oxo-2-thioxothiazolidin-3-yl-5-ylidene)
diacetic acid (S3)
To a stirred 4c (0.34 g, 1.2 mmol) in CH3COOH
(30 mL) were added rhodanine-3-acetic acid (0.476 g,
Figure S1. 1H NMR (300 MHz) spectrum of N-hexylcarbazole (2a).

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Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
Figure S2. 1H NMR (300 MHz) spectrum of 11-ethyl-iminodibenzyl (2b).
Figure S3. 1H NMR (300 MHz) spectrum of 10-ethyl-phenothiazine (2c).

Vol. 22, No. 4, 2011
Wu et al.
S5
Figure S4. 1H NMR (300 MHz) spectrum of 9-hexylcarbazole-3,6-dicarbaldehyde (4a).
Figure S5. 1H NMR (300 MHz) spectrum of 11-ethyl-3,8-diformyliminodibenzyl (4b).

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Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
Figure S6. 1H NMR (300 MHz) spectrum of 10-ethyl-3,7-diformylphenothiazine (4c).
Figure S7. 1H NMR (300 MHz) spectrum of S1.

Vol. 22, No. 4, 2011
Wu et al.
S7
Figure S8. 1H NMR (300 MHz) spectrum of S2.
Figure S9. 1H NMR (300 MHz) spectrum of S3.

S8
Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
Figure S10. 13C NMR (400 MHz) spectrum of N-hexylcarbazole (2a).
Figure S11. 13C NMR (400 MHz) spectrum of 11-ethyl-iminodibenzyl (2b).

Vol. 22, No. 4, 2011
Wu et al.
S9
Figure S12. 13C NMR (400 MHz) spectrum of 10-ethyl-phenothiazine (2c).
Figure S13. 13C NMR (400 MHz) spectrum of 9-hexylcarbazole-3,6-dicarbaldehyde (4a).

S10
Synthesis, Characterization and Photovoltaic Properties of Di-Anchoring Organic Dyes
J. Braz. Chem. Soc.
Figure S14. 13C NMR (400 MHz) spectrum of 11-ethyl-3,8-diformyliminodibenzyl (4b).
Figure S15. 13C NMR (400 MHz) spectrum of 10-ethyl-3,7-diformylphenothiazine (4c).