Asymmetric tribranched dyes: An intramolecular cosensitization approach for dye-sensitized solar cells

Article abstract of DOI:10.1002/ejoc.201300962

A new multidonor and multianchoring asymmetric tribranched organic photosensitizer (i.e., TB-PT) for dye-sensitized solar cells containing three different (D-π-D, D-π₁-A, and D-π₂-A; D = electron-rich moiety, A = electron-poor moiety

Full text of DOI:10.1002/ejoc.201300962

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FULL PAPER
DOI: 10.1002/ejoc.201300962
Asymmetric Tribranched Dyes: An Intramolecular Cosensitization Approach
for Dye-Sensitized Solar Cells
Valentina Leandri,[a] Riccardo Ruffo,[a] Vanira Trifiletti,[a] and Alessandro Abbotto*[a]
Keywords: Solar cells / Dyes/Pigments / Sensitizers / Conjugation / Multianchoring
A
new multidonor and multianchoring asymmetric tri-
and compared with the corresponding symmetric dyes. TB-
PT combines the advantages arising from its π-extended tri-
branched architecture and the intramolecular cosensitization
approach, which results in enhanced tailored optical and
energetic properties and, eventually, photovoltaic perform-
ances.
branched organic photosensitizer (i.e., TB-PT) for dye-sensi-
tized solar cells containing three different (D–π–D, D–π1–A,
and D–π2–A; D = electron-rich moiety, A = electron-poor moi-
ety, π = conjugated bridge) polar branches, two donor cores,
and two acceptor/anchoring groups to TiO2 was investigated
branches possess complementary absorption properties
(Figure 1, middle). Even if the dye is constituted by a single
π-conjugated framework, the net result is equivalent to an
intramolecular cosensitization effect. This architecture is
the evolution of our previous design based on an A–π1–D–
π–D–π1–A tribranched structural motif (Figure 1, left) in
which the presence of two donor and two acceptor/anchor-
ing[6] fragments allowed enhanced optical and stability
properties.[7] To further improve the optical properties
through an intramolecular cosensitization approach, we
have now modified the design by introducing two different
D–π–A side arms (D–π1–A and D–π2–A) with complemen-
tary absorption properties. The resulting dye can be re-
garded, in terms of intramolecular cosensitization, as a
multichromophore structure that is derived from the combi-
nation of two linear D–π–A dyes linked through donor end-
capping moieties by a conjugated bridge. We stress that our
approach differs from the other reports of intramolecular
cosensitization in that the two D–π–A arms are connected
through saturated nonconjugated links, which thus limits π-
structure extension.[8]
Introduction
In the last decades, dye-sensitized solar cells (DSSCs)[1]
have become very attractive because of their easy and cheap
manufacturing procedures combined with over 12% record
efficiencies.[2] Metal-free organic photosensitizers, providing
several advantages over conventional metal complexes, typi-
cally own a linear dipolar D–π–A structure, in which the
electron-rich (D) and the electron-poor (A) moieties are
connected through a conjugated (π) bridge.[3] Unfortu-
nately, these compounds present a single, often narrow, ab-
sorption band in the visible region, related to intramolecu-
lar charge transfer, which limits sunlight harvesting. Cosen-
sitization, that is, the use of two or more dyes having com-
plementary absorption spectra, is an attractive strategy to
reach a panchromatic absorption and to enhance light har-
vesting,[3,4] as in the case of the recent record efficiency.[2]
However, conventional intermolecular cosensitization suf-
fers from a number of drawbacks: (1) The concentration of
each cosensitizing dye on the TiO2 surface is about half of
that in the absence of cosensitization, which thus negates
the beneficial effects of improved optical properties.
(2) Well-separated complementary absorption bands of the
two dyes implies the presence of a region in the cosensitized
spectrum in which the absorption intensity is very low.[5]
(3) Intermolecular charge- and energy-transfer processes
decrease cell performances as a result of intimate mixing of
the two dyes.[4]
We here propose an original approach consisting of the
use of a multibranched dye in which three π-conjugated
Figure 1. General design strategy for the multibranched dyes: sym-
metric tribranched (left), new geometry (middle), monobranched
(right).
[a] Department of Materials Science and Milano-Bicocca Solar
Energy Research Center – MIB-Solar, University of Milano-
Bicocca, INSTM Unit,
The new asymmetric dye TB-PT (see Figure 2) was de-
signed on the basis of the most common building blocks
for DSSC sensitizers, that is, D = triarylamino, A = 2-cy-
anoacrylic acid, and π1 and π2 = benzene and thiophene.
Via Cozzi 53, 20125 Milano, Italy
E-mail: alessandro.abbotto@unimib.it
Homepage: http://www.mater.unimib.it/utenti/abbotto
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300962.
Eur. J. Org. Chem. 0000, 0–0
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V. Leandri, R. Ruffo, V. Trifiletti, A. Abbotto
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Figure 2. Symmetric (i.e., TB-T, TB-P) and asymmetric tribranched (i.e., TB-PT) dyes and monobranched reference dyes (i.e., L1 and
TC105).
The electron-donating strength of the D moiety was in- metric dyes TB-P and TB-T by validating the intramo-
creased by donor alkoxy substituents (RO-), and long linear lecular cosensitization model.
R chains were introduced to improve the solubility and to
minimize cell recombination losses.[9] TB-PT can thus be
Results and Discussion
seen as the intramolecular combination of the linear dyes
L1[10] and TC105[11] reported in the literature (Figure 2).
The new dye was investigated in terms of its optical, electro-
chemical, and photovoltaic properties and compared with
the corresponding symmetric tribranched dyes TB-P and
Synthesis, Spectroscopic, and Electrochemical
Characterization
TB-PT was conveniently prepared, with steps that pro-
TB-T (Figure 2). We will show how the optical response of vided products in yields from 70% to quantitative, by a con-
the asymmetric dye TB-PT can be effectively obtained from vergent route characterized by the Horner–Emmons con-
a linear combination of the absorption bands of the sym- densation of branched precursors 1 and 2 (Scheme 1, see
Scheme 1. Synthesis of TB-PT. Reagents and conditions: (i) Diphenylamine, 1,10-phenanthroline, CuCl, KOH, toluene, reflux; (ii) DMF,
POCl3, CH2Cl2, –5 °C to r.t.; (iii) N-bromosuccinimide (NBS), DMF, –18 °C; (iv) pinacol, p-toluenesulfonic acid (PTSA), toluene, reflux;
(v) 4, Pd(dppf)Cl2 [dppf = 1,1Ј-bis(diphenylphosphanyl)ferrocene], K2CO3, toluene/MeOH, microwave; (vi) NaBH4, THF, r.t.; (vii)
P(OEt)3, I2; (viii) 4, Pd(dppf)Cl2, K2CO3, toluene/MeOH, microwave; (ix) tBuONa, THF, r.t.; (x) 10% HCl/THF, 50 °C; (xi) cyanoacetic
acid, piperidine (cat.), CHCl3, reflux.
2
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Cosensitization Approach for Dye-Sensitized Solar Cells
the Supporting Information for the synthesis of symmetric Table 1. Optical and electrochemical parameters of the dyes.[a]
dyes TB-P and TB-T). Asymmetric bis-aldehyde 3 was sub-
[b]
Dye
λabs [nm]
(εϫ10–4
f
HOMO[c]
[eV]
LUMO[c]
[eV]
m
–1 cm–1)
mitted, in the last step, to double Knoevenagel condensa-
tion with a 25-fold excess amount of cyanoacetic acid to
afford pure TB-PT as a dark solid. Both side building
blocks were prepared by starting from common triarylam- TB-P
ine block 4 through a Suzuki–Miyaura cross-coupling reac-
tion with the p-formylboronic esters of thiophene and benz-
ene, in their protected forms 5 and 6, respectively. A diver-
gent approach, similar to that used for the previously de-
scribed tribranched dyes,[7b] was tested but discarded as a
result of lower reproducibility and yields.
TB-T
388 (4.6)
482 (6.1)
401 (4.8)
439 (5.3)
394 (5.2)
460 (5.5)
1.96
1.58
1.98
–5.7
–5.5
–5.6
–3.5
–3.1
–3.4
TB-PT
[a] In THF. [b] Oscillator strength measured in the 350–800 nm
range. [c] From cyclic voltammetry potential measurements vs. fer-
rocene/ferrocenium (Fc/Fc+); energy levels were calculated by using
a value of – 5.2 eV vs. vacuum for Fc/Fc+ (–4.5 eV vs. vacuum for
NHE).
TB dyes exhibit two UV/Vis absorption bands (Figure 3),
one more intense at lower energies (430–490 nm), which is
due to intramolecular D–π–A charge transfer of the side
arms, and one at higher energies (385–395 nm), which is
due to a local transition of the donor core.[6] The main
quantitative optical parameters are collected in Table 1. In
close agreement with the design strategy, the absorption
spectrum of TB-PT nicely combines the optical features of
the symmetric counterparts TB-P and TB-T. In particular,
the intramolecular charge-transfer peak of the asymmetric
chromophore is bathochromically and hypsochromically
shifted relative to the corresponding band of TB-P and TB-
T, respectively. Even more significant is the fact that the
integrated intensity of the asymmetric dye absorption was
higher than that of both symmetric compounds (see oscil-
lator strengths in Table 1), and this suggests a cooperative
enhancement effect of the two different side arms.
εTB-PT = 0.50εTB-P + 0.50εTB-T
(1)
shape, and the difference in intensity is within experimental
error. The optical response of the target dye TB-PT can
thus be effectively obtained from a linear combination of
the absorption bands of the symmetric dyes, in agreement
with the proposed intramolecular cosensitization model.
The perfect matching between the experimental and the
predicted spectrum of TB-PT is valuable in terms of the
design of new panchromatic dyes with predefined optical
properties once the absorption properties of the two consti-
tuting monobranched units are properly selected and inves-
tigated.
The electrochemical properties and HOMO/LUMO en-
ergies of dyes TB-P, TB-T, and TB-PT were measured by
cyclic voltammetry (CV) and spectroelectrochemical mea-
surements. The current potential profiles are shown in Fig-
ure 4 and the derived HOMO and LUMO energies are col-
lected in Table 1 and graphically depicted in Figure S1
(Supporting Information) and compared to DSSC reference
energies (conduction band of TiO2 and Nerst potential of
–
the redox pair I3 /I–). All the observed oxidative waves were
reversible. It is clearly seen from the electrochemical data
that, similarly to the optical properties, TB-PT combines
the energetic properties of TB-P and TB-T. In particular,
the HOMO/LUMO energies of TB-PT lie in between those
of the two symmetric dyes. Spectroelectrochemical analysis,
Figure 3. Absorption spectra of symmetric (i.e., TB-T, TB-P) and
asymmetric (i.e., TB-PT) tribranched dyes in THF (solid line); cal-
culated spectrum of TB-PT according to Equation (1) (dashed
line).
The premise of the strategy proposed here was to demon-
strate that the new molecule is actually equivalent to an
intramolecular mixture of two different molecules with
complementary absorption properties. Indeed, we found
that both the position and intensity of the experimental
spectrum of TB-PT could be nicely predicted (dashed line
in Figure 3) by simply applying a 1:1 linear combination of
the spectra of the symmetric dyes, as shown in Equation (1).
in which ε is the molar absorptivity at each wavelength. The
Figure 4. Cyclic voltammetry traces (vs. Fc) of dyes TB-P, TB-T,
calculated and the experimental spectra nicely match in and TB-PT.
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showing the change in the absorption properties of dye TB- However, it should be noted that our goal was to demon-
PT upon oxidation, is described in the Supporting Infor- strate, in addition to enhanced optical properties, improved
mation (Figure S2). The potential (0.45 V vs. Fc) was ap- photovoltaic efficiencies relative to the symmetric counter-
plied until no change in the optical properties was observed. parts, as achieved. The very simple structure of the conven-
tional donor, spacer, and acceptor groups and the nature of
the monobranched reference dyes L1 and TC105 were not
selected with the goal of reaching, at this time, higher effi-
ciencies close to those of present record dyes.
Photovoltaic Investigation in DSSCs
The dyes were used as photosensitizers in DSSCs by
using a double-layer TiO2 film (20 nm particles 10 μm layer
+ scattering 4 μm layer) in the presence of chenodeoxy-
cholic acid (CDCA)[12] as a deaggregating co-adsorbent
agent (Table 2). Two electrolyte solutions were tested by
varying the concentrations of LiI. The best average power
conversion efficiencies were measured by using the electro-
lyte Z960 (1.0 m 1,3-dimethylimidazolium iodide, 0.03 m I2,
0.05 m LiI, 0.10 m guanidinium thiocyanate, and 0.50 m 4-
tert-butylpyridine in acetonitrile/valeronitrile, 85:15).
Table 2 summarizes the photovoltaic parameters in com-
parison with the DSSC benchmark dye N719 [bis(2,2Ј-bi-
pyridyl-4,4Ј-dicarboxylate)ruthenium(II) bis(tetrabutylam-
monium) salt].[13] The overall conversion efficiencies PCE
were derived from the equation PCE = Jsc ϫVoc ϫFF, in
which Jsc is the short circuit current density, Voc is the open
circuit voltage, and FF is the fill factor. Figure 5 shows the
photocurrent–voltage curves of the devices.
The incident monochromatic photon-to-current conver-
sion efficiencies (IPCE, 0–100%) of the devices based on
the three dyes are shown in Figure 6. TB-PT summarizes
the conversion proprieties of the two symmetric molecules
over the whole range. To investigate this term in deeper de-
tail, we separately examined the two constituting factors of
IPCE according to the equation IPCE(λ) = LHE(λ)ϫ
APCE(λ) (Figure 7) in which LHE (0–100%) is the light-
harvesting efficiency associated to the ability of the cell to
harvest light and APCE (0–100%) is the absorbed mono-
chromatic photon-to-current conversion efficiency; this
term gives the true quantum efficiency of the cell of gener-
ating electric current (internal quantum efficiency), and it
is related to the electron injection efficiency from the dye to
the semiconductor oxide, the dye regeneration efficiency,
and the charge collection efficiency.[1] IPCE and LHE are
experimentally determined. APCE is thus derived by divid-
ing the IPCE number by LHE. Given that LHE can be
directly measured only for transparent dye-coated films, as
similarly performed for previous representative studies,[2]
the whole set of comparative IPCE, LHE, and APCE spec-
tra was recorded and derived for transparent 9 μm thick
nanocrystalline TiO2 monolayers. It is evident that APCE
is excellent (≈100%) for almost the entire range of visible
light, whereas the external quantum efficiency IPCE is
much more modest, limited by the low LHE.
Table 2. Photovoltaic parameters for TB-based DSSCs.
Dye
CDCA/dye
Jsc
Voc
FF
PCE
[%]
[mAcm–2] [mV]
TB-P
TB-T
TB-PT 100:1
N719 1:1
100:1
100:1
10.0
10.9
11.7
14.4
722
687
708
707
0.66
0.65
0.66
0.69
4.8
4.9
5.4
7.1
Figure 6. Incident photon-to-electric current conversion efficiencies
as a function of wavelength of DSSCs sensitized by TB-P, TB-T,
and TB-PT.
Figure 5. Current–voltage characteristics of DSSCs sensitized by
TB-P, TB-T, and TB-PT.
In agreement with the superior optical properties and os-
Electrochemical impedance spectroscopy (EIS) was used
cillator strength (Table 1), the asymmetric dye TB-PT ex- to further investigate the comparative behavior of the three
hibited the highest current and approximately 10% im- dyes in DSSC.[14] In this experiment, a small sinusoidal volt-
proved power conversion efficiency relative to the two sym- age stimulus of a fixed frequency was applied to an electro-
metric dyes. The absolute efficiency of TB-PT is not very chemical cell and its current response was measured. The
high if compared to recent values on organic sensitizers.[3] alternating current (ac) behavior of an electrochemical sys-
4
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Cosensitization Approach for Dye-Sensitized Solar Cells
Figure 8. Nyquist plots of DSSCs sensitized by TB-P, TB-T, and
TB-PT. Continuous lines represent the data fitting by using the
equivalent circuit shown in the onset.
figure in which, in addition to the TiO2/electrolyte interface
parameters, RS is the serial resistance [mainly due to the
fluorine-doped tin oxide (FTO) layers], ZD is the Warburg
diffusion of the ionic species (I–) in the electrolyte, and RCE
and CCE are the charge-transfer resistance and double-layer
capacity at the counter electrode, respectively. The results
of the EIS investigation are summarized in Table 3. Rrec val-
ues can be determined by the width of the central arc,
whereas the capacitance Cμ can be deduced by fitting the
data with the equivalent circuit in Figure 8. The apparent
electron lifetime in the oxide, τn, can thus be calculated
from τn = RrecCμ and corresponds to the angular frequency
at the top of the middle arc.[14]
Figure 7. LHE (top) and APCE (bottom) as a function of wave-
length of the DSSCs sensitized by TB-P, TB-T, and TB-PT.
tem can be investigated by sweeping the frequency over sev-
eral orders of magnitude (generally from a few mHz to sev-
eral MHz). The analysis of the impedance spectra is usually
performed in terms of Nyquist plots in which the imaginary
part of the impedance is plotted as a function of the real
Table 3. Parameters calculated from EIS data plots of DSSCs based
on TB-P, TB-T, and TB-PT sensitizers in comparison with the
benchmark dye N719.
Dye
Rrec [Ωcm2]
Cμ [Fcm–2]
τn [ms]
part over the range of frequencies. The impedance of the TB-P
25
14
17
15
5.8ϫ10–4
8.1ϫ10–4
5.7ϫ10–4
1.1ϫ10–3
15
11
10
16
TB-T
cell can be described by an equivalent circuit model (Fig-
TB-PT
ure 8, inset), in which the different cell components and
N719
their interfaces are treated as discrete electrical elements.[14]
Under illumination under open-circuit voltage conditions,
Yet again, asymmetric sensitizer TB-PT exhibited inter-
mediate properties between those of symmetrical TB-P and
TB-T. For the three dyes, the most relevant parameter, that
is, the recombination resistance, Rrec, was comparable, or
even slightly higher, than that of the benchmark dye N719.
Therefore, detrimental charge recombination from TiO2 to
the electrolyte is equally or less efficient in the DSSCs by
using the three organic dyes than for the N719 sensitizer.
This result is consistent with their APCE spectra. However,
the corresponding capacitances, which probe the charge
carrier accumulation in the oxide film and the density of
states in the band gap, are lower than the reference DSSC
by one order of magnitude. The net result is lower electron
lifetimes, which affects cell performance.
the DSSC Nyquist plot shows three arcs corresponding to
the I–/I3– redox process at the counter electrode in the high-
frequency region (104Ϭ102 Hz), the TiO2/dye/electrolyte
interface at intermediate frequencies (1Ϭ10 Hz), and the
Nernst diffusion within the electrolyte of the ionic species
(I–) in the low-frequency region (0.01Ϭ1 Hz).[14] Under
these conditions, the properties of the TiO2/electrolyte inter-
face can be derived from the central arc in terms of recom-
bination resistance (Rrec) and chemical capacitance for
charge accumulation (Cμ). Both parameters are associated
to charge-transfer (recombination) phenomena and repre-
sent detrimental back processes between the injected elec-
trons in the oxide and the oxidized form of the electro-
lyte.[15]
Figure 8 shows the Nyquist plots for the DSSC devices
obtained by EIS at the open circuit voltage under
250 Wm–2 (0.25 sun) illumination. The data can be fitted
Conclusions
In conclusion, a new multidonor–multiacceptor/anchor-
by using the equivalent circuit reported in the inset of the ing tribranched asymmetric dye, TB-PT, with two different
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V. Leandri, R. Ruffo, V. Trifiletti, A. Abbotto
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4-{[4-(Hexyloxy)phenyl](phenyl)amino}benzaldehyde (9): Phos-
phorus oxychloride (0.752 mL, 8.21 mmol) was added dropwise to
dry DMF (0.634 mL, 8.22 mmol) at –5 °C. The formation of a
white solid was observed, and the reaction was kept at –5 °C for
15 min. CH2Cl2 (30 mL) was added, and the solid was allowed to
reach room temperature. After complete dissolution, 8 (2.04 g,
5.91 mmol) was added, and the mixture was stirred for 24 h. The
reaction was quenched by the addition of water saturated with
K2CO3, and the organic phase was washed with water (3ϫ
120 mL), dried, and filtered. Purification by column chromatog-
side dipolar branches having complementary absorption
properties was designed and investigated as a DSSC sensi-
tizer. The optical, electrochemical, and photovoltaic prop-
erties were compared with those of the corresponding sym-
metric counterparts, TB-P and TB-T. The results suggested
a cooperative enhancement of the two different branches in
terms of light-harvesting properties. Indeed, the measured
current density of the DSSC based on TB-PT was higher
than those of cells based on the symmetric dyes, resulting
in an approximately 10% increase in the power conversion raphy over silica gel (CH2Cl2/cyclohexane, 1:1) resulted in a yellow
oil (2.10 g, 5.63 mmol, 95%). 1H NMR (CDCl3): δ = 9.78 (s, 1 H),
7.64 (d, J = 8.8 Hz, 2 H), 7.32 (dd, J = 7.5, 7.4 Hz, 2 H), 7.17 (d,
J = 7.5 Hz, 2 H), 7.14 (t, J = 7.4 Hz, 1 H), 7.1 (d, J = 8.9 Hz, 2
H), 6.94 (d, J = 8.8 Hz, 2 H), 6.89 (d, J = 8.9 Hz, 2 H), 1.46–1.44
efficiency.
A novel intramolecular cosensitization strategy to en-
hance the optical response and, ultimately, the photovoltaic
efficiency of DSSCs was demonstrated. In particular, we
believe that the experimental validation of Equation (1),
which shows that the panchromatic behavior of a new sensi-
tizer can be built by appropriately selected constituting mo-
(t, 2 H), 3.91 (t, J = 6.6 Hz, 2 H), 1.81–1.71 (m, 2 H), 1.52–1.42
(m, 2 H), 1.40–1.30 (m, 4 H), 0.90 (t, J = 7.0 Hz, 3 H) ppm. 13C
NMR (CDCl3): δ = 190.35 (CH), 157.08 (C), 153.66 (C), 146.11
(C), 138.52 (C), 131.33 (CH), 129.60 (CH), 128.43 (CH), 128.39
lecules with complementary optical and photovoltaic prop-
erties, will facilitate the search for new efficient sensitiz-
ers.[16]
(C), 125.79 (CH), 124.77 (CH), 118.05 (CH), 115.62 (CH), 68.25
(CH2), 31.57 (CH2), 29.24 (CH2), 25.73 (CH2), 22.60 (CH2), 14.04
(CH3) ppm. HRMS (ESI): calcd. for [M + Na]+ C25H27NNaO2
396.19340; found 394.19267.
4-{(4-Bromophenyl)[4-(hexyloxy)phenyl]amino}benzaldehyde (4): A
solution of freshly recrystallized NBS (863 mg, 4.85 mmol) in
DMF (10 mL) was added dropwise to a stirred solution of 9
(1.81 g, 4.85 mmol) in DMF (15 mL). The mixture was left at
–18 °C for 15 h and then poured into water (50 mL). Diethyl ether
was added, and the resulting organic phase was washed with water
(4ϫ 120 mL), dried, and filtered. Removal of the solvent under
reduced pressure yielded the pure product (2.06 g, 4.55 mmol, 94%)
Experimental Section
General: NMR spectra were recorded with an instrument operating
at 500.13 (1H) and 125.77 MHz (13C). 13C signals were assigned on
the basis of the results of J-MOD experiments. HRMS measure-
ments were performed by using a ESI source and an ion trap (Fou-
rier transform ion cyclotron resonance FT-ICR) as a mass ana-
lyzer. Flash chromatography was performed with silica gel 230–
400 mesh (60 Å). Reactions performed under a nitrogen atmo-
sphere were performed in oven-dried glassware and monitored by
thin-layer chromatography by using UV light (254 and 365 nm) as
a visualizing agent. All reagents were obtained from commercial
suppliers at the highest purity and used without further purifica-
tion. Anhydrous solvents were purchased from commercial suppli-
ers and used as received. Extracts were dried with anhydrous
Na2SO4 and filtered before removal of the solvent by evaporation.
1
as a yellow gummy oil. H NMR (CDCl3): δ = 9.80 (s, 1 H), 7.66
(d, J = 8.8 Hz, 2 H), 7.41 (d, J = 8.8 Hz, 2 H), 7.08 (d, J = 8.9 Hz,
2 H), 7.03 (d, J = 8.8 Hz, 2 H), 6.96 (d, J = 8.7 Hz, 2 H), 6.89 (d,
J = 8.9 Hz, 2 H), 3.91 (t, J = 6.6 Hz, 2 H), 1.81–1.71 (m, 2 H),
1.52–1.42 (m, 2 H), 1.40–1.31 (m, 4 H), 0.90 (t, J = 7.1 Hz, 3 H)
ppm. 13C NMR (CDCl3): δ = 190.38 (CH), 157.25 (C), 153.14 (C),
145.35 (C), 138.16 (C), 132.61 (CH), 131.35 (CH), 128.95 (C),
128.36 (CH), 126.86 (CH), 118.69 (CH), 117.24 (C), 115.73 (CH),
68.28 (CH2), 31.57 (CH2), 29.22 (CH2), 25.73 (CH2), 22.61 (CH2),
1-(Hexyloxy)-4-iodobenzene (7): A procedure reported in the litera-
ture was adapted with some modifications.[17] 1-Bromohexane
(3.81 mL, 27.30 mmol) and K2CO3 (12.56 g, 90.91 mmol) were
added at room temperature to a solution of 4-iodophenol (9.99 g,
45.43 mmol) in dry acetone (50 mL). After stirring at reflux for
30 h, the mixture was filtered to remove the solid, and the solvent
was evaporated under reduced pressure. The residual oil was ex-
tracted (CH2Cl2) and washed with 3 m NaOH, water, and brine.
The organic phase was dried, filtered, and concentrated in vacuo
to give the desired product as a colorless oil (6.64 g, 21.82 mmol,
85%).
14.05 (CH3) ppm. HRMS (ESI): calcd. for [M
C25H26NNaO2Br 474.10391; found 474.10369.
+
Na]+
4,4,5,5-Tetramethyl-2-[5-(4,4,5,5-tetramethyl-1,3-dioxolan-2-yl)-
thiophen-2-yl]-1,3,2-dioxaborolane (5): A solution of 5-formyl-2-thi-
enylboronic acid (802 mg, 5.14 mmol), 2,3-dimethyl-butane-2,3-
diol (3.02 g, 25.70 mmol), and a catalytic amount of p-toluene-
sulfonic acid in toluene (40 mL) was heated at reflux by using a
Dean–Stark receiver for 2 h. The reaction mixture was then washed
with water (3ϫ 100 mL), dried, and filtered, and the solvent was
evaporated under reduced pressure. The product was purified over
silica gel (petroleum ether/ethyl acetate, 4:1) to give the desired
product as light yellow needle-shaped crystals (1.22 g, 3.60 mmol,
71%); m.p. 128.5–129.5 °C. 1H NMR (CDCl3): δ = 7.49 (d, J =
3.5 Hz, 2 H), 7.194 (d, J = 3.5 Hz, 2 H), 6.20 (s, 1 H), 1.32 (s, 12
H), 1.29 (s, 6 H), 1.28 (s, 6 H) ppm. 13C NMR (CDCl3): δ = 151.00
(C), 136.82 (CH), 127.22 (CH), 96.48 (CH), 84.07 (C), 83.09 (C),
24.73 (CH3), 24.20 (CH3), 22.07 (CH3) ppm; the signal for the car-
bon atom directly attached to boron was not observed owing to
quadrupolar relaxation. C17H27BO4S (338.27): calcd. C 60.36, H
8.06; found C 60.38, H 7.83.
4-(Hexyloxy)-N,N-diphenylaniline (8): A procedure reported in the
literature was adapted with some modifications.[18] A two-necked,
round-bottomed flask equipped with a Dean–Stark apparatus was
charged with diphenylamine (4.59 g, 27.10 mmol) and toluene
(50 mL). Then,
7 (5.51 g, 18.12 mmol), 1,10-phenanthroline
(652 mg, 3.61 mmol), cuprous chloride (358 mg, 3.61 mmol), and
potassium hydroxide (4.06 g, 72.30 mol) were added. The reaction
mixture was heated at reflux for 20 h, and then, water (150 mL)
was added. The crude product was extracted with CH2Cl2, and
the organic layer was washed with water, dried, and filtered. After
removing the solvent under reduced pressure, the residue was puri-
fied by column chromatography (petroleum ether/CH2Cl2, 1:1) on
silica gel to obtain a colorless oil (4.39 g, 12.71 mmol, 70%).
4-([4-(Hexyloxy)phenyl]{4-[5-(4,4,5,5-tetramethyl-1,3-dioxolan-2-
yl)thiophen-2-yl]phenyl}amino)benzaldehyde (1b): Pd(dppf)-
6
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30962
/KAP1
Date: 20-08-13 11:41:22
Pages: 10
Cosensitization Approach for Dye-Sensitized Solar Cells
Cl2·CH2Cl2 (91 mg, 0.110 mmol), 5 (400 mg, 1.18 mmol), and
K2CO3 (628 mg, 4.55 mmol) were added to a solution of 4 (0.411 g,
32.47 (1J
13C,31
P
= 139.6 Hz, CH2), 31.59 (CH2), 29.29 (CH2), 25.74
(CH2), 24.27 (CH3), 22.60 (CH2), 22.06 (CH3), 16.42/16.37 (3J
13C,31
P
0.910 mmol) in toluene/MeOH (1:1, 6 mL) in a microwave vial. The = 6.3 Hz, CH3), 14.03 (CH3) ppm. HRMS (ESI): calcd. for [M +
resulting mixture was heated in a microwave reactor at 75 °C for
20 min. After cooling to room temperature, the reaction mixture
was poured into water and extracted with diethyl ether. The organic
phase was washed with water (3ϫ 100 mL), dried, filtered, and
concentrated under reduced pressure. Flash chromatography purifi-
cation (cyclohexane/ethyl acetate, 9:1) gave the product as an
Na]+ C50H42NNaO6SP 728.31452; found 728.31367.
4,4,5,5-Tetramethyl-2-[4-(4,4,5,5-tetramethyl-1,3-dioxolan-2-yl)-
phenyl]-1,3,2-dioxaborolane (6): A solution of 4-formylphenyl-
boronic acid (610 mg, 6.67 mmol), 2,3-dimethyl-butane-2,3-diol
(3.94 g, 33.34 mmol), and a catalytic amount of p-toluenesulfonic
acid in toluene (40 mL) was heated at reflux by using a Dean–Stark
receiver for 3 h. The reaction mixture was then washed with water
(3ϫ 100 mL), dried, and concentrated. The product was purified
over silica gel (petroleum ether/ethyl acetate, 9:1) to give the desired
product as colorless needle-shaped crystals (1.73 g, 5.20 mmol,
70%); m.p. 143.6–144.0 °C. 1H NMR (CDCl3): δ = 7.81 (d, J =
8.0 Hz, 2 H), 7.49 (d, J = 8.0 Hz, 2 H), 6.0 (s, 1 H), 1.32 (s, 12 H),
1.29 (s, 6 H), 1.23 (s, 6 H) ppm. 13C NMR (CDCl3): δ = 142.99
(C), 134.69 (CH), 125.33 (CH), 99.66 (CH), 83.71 (C), 82.62 (C),
24.87 (CH3), 24.17 (CH3), 22.17 (CH3) ppm; the signal for the car-
bon atom directly attached to boron was not observed owing to
quadrupolar relaxation. C19H29BO4 (332.25): calcd. C 68.69, H
8.80; found C 68.77, H 8.77.
1
orange sticky oil (414 mg, 0.710 mmol, 78%). H NMR (CDCl3):
δ = 9.78 (s, 1 H), 7.67 (d, J = 8.7 Hz, 2 H), 7.52 (d, J = 8.6 Hz, 2
H), 7.16–7.08 (m, 6 H), 7.00 (d, J = 8.7 Hz, 2 H), 6.90 (d, J =
8.9 Hz, 2 H), 6.18 (s, 1 H), 3.96 (t, J = 6.5 Hz, 2 H), 1.83–1.72 (m,
2 H), 1.52–1.42 (m, 2 H), 1.38–1.30 (m, 10 H), 1.29 (s, 6 H), 0.90
(t, J = 7.0 Hz, 3 H) ppm. 13C NMR (CDCl3): δ = 190.11 (CH3),
157.22 (C), 153.24 (C), 145.55 (C), 144.32 (C), 142.91 (C), 138.34
(C), 131.28 (CH), 130.63 (C), 128.90 (C), 128.39 (CH), 127.04
(CH), 126.90 (CH), 125.46 (CH), 122.33 (CH), 118.75 (CH), 115.76
(CH), 96.72 (CH), 83.02 (C), 68.27 (CH2), 31.57 (CH2), 29.25
(CH2), 25.74 (CH2), 24.27 (CH3), 22.59 (CH2), 22.08 (CH3), 14.05
(CH3) ppm. HRMS (ESI): calcd. for [M + Na]+ C36H41NNaO4S
606.26485; found 606.26500.
4-{[4-(Hexyloxy)phenyl][4Ј-(4,4,5,5-tetramethyl-1,3-dioxolan-2-yl)bi-
phenyl-4-yl]amino}benzaldehyde (2): Pd(dppf)Cl2·CH2Cl2 (111 mg,
0.137 mmol), 6 (682 mg, 2.05 mmol), and K2CO3 (946 mg,
6.85 mmol) were added to a solution of 4 (620 mg, 1.37 mmol) in
toluene/MeOH (1:1, 10 mL) in a microwave vial. The resulting mix-
ture was heated in a microwave reactor at 75 °C for 20 min. After
cooling to room temperature, the reaction mixture was poured into
water and extracted with ethyl acetate. The organic phase was
washed with water (3ϫ 150 mL), dried, filtered, and concentrated
under reduced pressure. Flash chromatography purification (cyclo-
hexane/ethyl acetate, 4:1) gave the product as a yellow sticky oil
(633 mg, 1.10 mmol, 82%). 1H NMR (CDCl3): δ = 9.80 (s, 1 H),
7.67 (d, J = 8.9 Hz, 2 H), 7.69–7.51 (m, 6 H), 7.21 (d, J = 8.6 Hz,
2 H), 7.14 (d, J = 8.9 Hz, 2 H), 7.01 (d, J = 8.2 Hz, 2 H), 6.91 (d,
J = 8.9 Hz, 2 H), 3.96 (t, J = 6.5 Hz, 2 H), 1.85–1.74 (m, 2 H),
1.52–1.42 (m, 2 H), 1.39–1.32 (m, 10 H), 1.29 (s, 6 H), 0.90 (t, J =
7.0 Hz, 3 H) ppm. 13C NMR (CDCl3): δ = 190.32 (CH), 157.18
(C), 153.49 (C), 145.46 (C), 140.57 (C), 138.70 (C), 138.47 (C),
137.05 (C), 131.32 (CH), 128.66 (C), 128.47 (CH), 128.16 (CH),
126.78 (CH), 126.70 (CH), 125.64 (CH), 118.49 (CH), 115.70 (CH),
99.72 (CH), 82.72 (C), 68.29 (CH2), 31.57 (CH2), 29.24 (CH2),
25.73 (CH2), 24.37 (CH3), 22.59 (CH2), 22.20 (CH3), 14.01 (CH3)
ppm. C38H43NO4 (577.76): calcd. C 79.00, H 7.50, N 2.42; found
C 79.20, H 7.57, N 2.43.
[4-([4-(Hexyloxy)phenyl]{4-[5-(4,4,5,5-tetramethyl-1,3-dioxolan-2-
yl)thiophen-2-yl]phenyl}amino)phenyl]·MeOH (1a): A solution of
NaBH4 (63.0 mg, 1.65 mmol) in THF (5 mL) was added dropwise
to a solution of 1b (740 mg, 1.27 mmol) at –10 °C in THF (25 mL).
The mixture was stirred for 5 h at room temperature and then
quenched by the addition of water. Ethyl acetate was added, and
the resulting organic phase was washed with water (3ϫ 110 mL),
dried, filtered, and concentrated under reduced pressure. The pure
product was isolated as a light yellow sticky oil (709 mg,
1
1.21 mmol, 95.2%). H NMR (CDCl3): δ = 7.41 (d, J = 8.7 Hz, 2
H), 7.23 (d, J = 8.5 Hz, 2 H), 7.10–7.03 (m, 6 H), 6.99 (d, J =
8.7 Hz, 2 H), 6.84 (d, J = 8.9 Hz, 2 H), 6.17 (s, 1 H), 3.95 (t, J =
6.5 Hz, 2 H), 1.82–1.73 (m, 2 H), 1.52–1.42 (m, 2 H), 1.40–1.33 (m,
10 H), 1.31 (s, 6 H), 0.93 (t, J = 7.0 Hz, 3 H) ppm. 13C NMR
(CDCl3): δ = 156.00 (C), 147.56 (C), 147.25 (C), 145.26 (C), 141.60
(C), 139.99 (C), 134.71 (C), 128.25 (CH), 127.72 (C), 127.43 (CH),
127.21 (CH), 126.57 (CH), 123.23 (CH), 122.32 (CH), 121.47 (CH),
115.38 (CH), 96.83 (CH), 83.04 (C), 68.23 (CH2), 64.94 (CH2),
31.63 (CH2), 29.32 (CH2), 25.79 (CH2), 24.30 (CH3), 22.65 (CH2),
22.08 (CH3), 14.12 (CH3) ppm. HRMS (ESI): calcd. for [M +
Na]+ C36H43NNaO4S 608.28050; found 608.28059.
Diethyl-4-([4-(Hexyloxy)phenyl]{4-[5-(4,4,5,5-tetramethyl-1,3-di-
oxolan-2-yl)thiophen-2-yl]phenyl}amino)benzylphosphonate (1):
Alcohol 1a (709 mg, 1.21 mmol) was dissolved in P(OEt)3 (15 mL)
at –5 °C, and a solution of I2 (1.27 g, 5.01 mmol) in P(OEt)3 (5 mL) (E)-N-[4-(Hexyloxy)phenyl]-N-{4-[4-([4-(hexyloxy)phenyl]{4-[5-
was added dropwise. The reaction mixture was stirred for 24 h at
room temperature. The excess amount of P(OEt)3 was distilled off
under reduced pressure, and the pure product was obtained after
flash chromatography on silica gel (CH2Cl2/ethyl acetate, 5:5) as a
dark yellow oil (615 mg, 0.871 mmol, 72%). H NMR (CDCl3): δ
= 7.38 (d, J = 8.7 Hz, 2 H), 7.15 (d, J = 8.6 Hz, 2 H), 7.07–7.01
(m, 4 H), 6.99 (d, J = 8.3 Hz, 2 H), 6.95 (d, J = 8.6 Hz, 2 H), 6.82
(4,4,5,5-tetramethyl-1,3-dioxolan-2-yl)thiophen-2-yl]phenyl}amino)-
styryl]phenyl}-4Ј-(4,4,5,5-tetramethyl-1,3-dioxolan-2-yl)biphenyl-4-
amine (3a): Under a nitrogen atmosphere, tBuOK (147 mg,
1.30 mmol) was added to a –10 °C, stirred solution of 1 (615 mg,
0.871 mmol) and 2 (503 mg, 0.871 mmol) in anhydrous THF
(30 mL). The reaction immediately became red and was stirred at
room temperature for 5 h. The mixture was poured into water satu-
1
(d, J = 8.9 Hz, 2 H), 6.14 (s, 1 H), 4.05 (m, 4 H), 3.92 (t, J = rated with NH4Cl, and ethyl acetate was added. The organic layer
6.5 Hz, 2 H), 3.07 (d, J = 21.3 Hz, 2 H), 1.82–1.73 (m, 2 H), 1.52–
1.42 (m, 2 H), 1.40–1.33 (m, 10 H), 1.31 (s, 6 H), 1.26 (t, J = 7.1 Hz,
was separated, washed with water (3ϫ 120 mL), dried, and filtered.
The solvent was removed under reduced pressure, and purification
6 H) 0.93 (t, J = 7.0 Hz, 3 H) ppm. 13C NMR (CDCl3): δ = 156.02 by column chromatography (petroleum ether/ethyl acetate, 4:1)
(C), 147.54 (C), 146.53 (C), 145.24 (C), 141.71 (C), 139.98 (C), gave the pure product as a yellow solid (757 mg, 0.670 mmol, 77%);
130.54/130.50 (3J
= 5.0 Hz, CH), 127.73 (C), 127.43 (CH), m.p. 85.3–86.0 °C. 1H NMR (CDCl3): δ = 7.59–7.51 (m, 4 H), 7.46
13C,31
P
127.08 (CH), 126.55 (CH), 125.08/125.02 (2J
= 6.3 Hz, C), (d, J = 8.7 Hz, 2 H), 7.43 (d, J = 8.7 Hz, 2 H), 7.37 (d, J = 8.7 Hz,
P
13C,31
123.25 (CH), 122.28 (CH), 121.45 (CH), 115.37 (CH), 96.82 (CH),
2 H), 7.13–7.01 (m, 14 H), 6.94 (s, 2 H), 6.90–6.84 (m, 4 H), 6.18
(s, 1 H), 6.02 (s, 1 H), 3.95 (m, 4 H), 1.82–1.76 (m, 4 H), 1.51–1.42
82.99 (C), 68.24 (CH2), 62.11,62.06 (2J
P = 6.3 Hz, CH2), 33.58/
13C,31
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

Job/Unit: O30962
/KAP1
Date: 20-08-13 11:41:22
Pages: 10
V. Leandri, R. Ruffo, V. Trifiletti, A. Abbotto
FULL PAPER
(m, 4 H), 1.38–1.33 (m, 20 H), 1.31–1.29 (m, 12 H), 0.92 (m, 6 H)
ppm. 13C NMR (CDCl3): δ = 156.12 (C), 156.07 (C), 147.37 (C),
147.27 (C), 147.12 (C), 146.88 (C), 145.23 (C), 141.77 (C), 141.02
(C), 140.04 (C), 139.87 (C), 138.11 (C), 134.21 (C), 131.61 (C),
131.39 (C), 127.97 (C), 127.71 (CH), 127.54 (CH), 127.51 (CH),
127.16 (CH), 127.09 (CH), 126.74 (CH), 126.60 (CH), 126.51 (CH),
126.48 (CH), 126.32 (CH), 122.99 (CH), 122.91 (CH), 122.82 (CH),
122.67 (CH), 121.53 (CH), 115.40 (CH), 99.86 (CH), 96.86 (CH),
83.02 (C), 82.69 (C), 68.24 (CH2), 31.64 (CH2), 29.34 (CH2), 26.94
(CH2), 25.80 (CH2), 24.42 (CH3), 24.31 (CH3), 22.66 (CH2), 22.25
(CH3), 22.10 (CH3), 14.11 (CH3) ppm. C74H84N2O6S (1129.55):
calcd. C 78.69, H 7.50, N 2.48; found C 78.66, H 7.62, N 2.41.
22.54 (CH2), 14.37 (CH3) ppm. C68H62N4O6S (1063.32): calcd. C
76.81, H 5.88, N 5.27; found C 76.51, H 6.13, N 5.29.
Electrochemical and Spectroelectrochemical Characterization: Dyes
TB-P, TB-T, and TB-PT were submitted to electrochemical charac-
terization. Each sample was dissolved (10–4 m) in a 0.1 m solution
of tetrabutylammonium perchlorate (Fluka, electrochemical grade,
99.0%) in anhydrous THF (Aldrich) as the supporting electrolyte.
Cyclic voltammetry (CV) was performed at a scan rate of 50 mVs–1
by using a PARSTA2273 potentiostat in a two-chamber three-elec-
trode electrochemical cell in a glove box filled with argon ([O2] Ͻ
1 ppm). The working, counter, and pseudoreference electrodes were
a glassy carbon (GC) pin, a Pt flag, and an Ag/AgCl wire, respec-
tively. The working electrode disc was well polished with a 0.1 μm
alumina suspension, sonicated for 15 min in deionized water and
washed with 2-propanol before use. The Ag/AgCl pseudoreference
electrode was calibrated by adding ferrocene (10–3 m) to the test
solution.
(E)-5-(4-{[4-(4-{(4Ј-Formylbiphenyl-4-yl)[4-(hexyloxy)phenyl]-
amino}styryl)phenyl][4-(hexyloxy)phenyl]amino}phenyl)thiophene-
2-carbaldehyde (3): Compound 3a (757 mg, 0.670 mmol) was dis-
solved in 10% HCl/THF (1:2, 30 mL). The mixture was heated at
50 °C for 3 h and then poured into water. Ethyl acetate was added,
and the organic layer was washed with water until neutral pH, dried
with anhydrous Na2SO4, and filtered. The solvent was removed
under reduced pressure, and purification by column chromatog-
raphy (cyclohexane/ethyl acetate, 4:1) followed by crystallization
from THF gave the pure product as an orange solid (517 mg,
0.553 mmol, 81%); m.p. 182.4–183.3 °C. 1H NMR (CDCl3): δ =
10.03 (s, 1 H), 9.85 (s, 1 H), 7.92 (d, J = 8.3 Hz, 2 H), 7.72 (d, J =
8.3 Hz, 2 H), 7.71 (d, J = 4.0 Hz, 1 H), 7.51 (m, 4 H), 7.49 (m, 4
H), 7.29 (d, J = 4.0 Hz, 1 H), 7.16–7.02 (m, 12 H), 6.97 (s, 2 H),
6.88 (m, 4 H), 3.95 (m, 4 H), 1.82–1.75 (m, 4 H), 1.51–1.43 (m, 4
H), 1.39–1.33 (m, 8 H), 0.91 (m, 6 H) ppm. 13C NMR (CDCl3): δ
= 191.78 (CH), 182.52 (CH), 156.59 (C), 156.40 (C), 154.69 (C),
149.17 (C), 148.42 (C), 146.81 (C), 146.62 (C), 146.29 (C), 141.19
(C), 139.64 (C), 139.28 (C), 137.69 (CH), 134.63 (C), 132.47 (C),
132.25 (C), 131.87 (C), 130.32 (CH), 127.95 (CH), 127.85 (CH),
127.75 (CH), 127.21 (CH), 126.90 (CH), 126.79 (CH), 126.50 (CH),
125.62 (C), 123.91 (CH), 123.42 (CH), 122.68 (CH), 122.22 (CH),
121.48 (CH), 115.57 (CH), 115.52 (CH), 68.30 (CH2), 31.59 (CH2),
29.30 (CH2), 29.28 (CH2), 25.75 (CH2), 22.60 (CH2), 14.02 (CH3)
ppm. C62H60N2O4S (929.23): calcd. C 80.14, H 6.51, N 3.01; found
C 80.26, H 6.52, N 3.07.
Spectroelectrochemical analysis of TB-PT was performed by using
a three-electrode cell arranged in a thin layer quartz glass cell. The
gold gauze working electrode was confined in the thin portion of
the cell (wall thickness 0.5 mm) to minimize the diffusion length of
the electroactive molecule. The change in the absorption properties
of TB-PT upon oxidation is depicted in Figure S2 (Supporting In-
formation). The potential (0.45 V vs. Fc) was applied until no
change in the optical properties was observed.
Fabrication of the DSSCs: The DSSCs were prepared by adapting
a procedure reported in the literature.[19] To exclude metal contami-
nation, all of the containers were glass or Teflon and were treated
with EtOH and 10% HCl prior to use. Plastic spatulas and tweezers
were used throughout the procedure. FTO glass plates (Solaronix
TCO 22–7, 2.2 mm thickness, 7 Ωsquare–1) were cleaned in a deter-
gent solution for 15 min by using an ultrasonic bath, and then
rinsed with pure water and EtOH. After treatment in a UV-O3
system (Novascan PSD Pro Series – Digital UV Ozone System) for
18 min, the FTO plates were treated with a freshly prepared 40 mm
aqueous solution of TiCl4 for 30 min at 70 °C and then rinsed with
water and EtOH. A first transparent nanocrystalline layer (20 nm
particles, Dyesol 18NR-T) was screen-printed and dried at 125 °C
for 6 min. The working electrodes were screen-printed and dried
again with the same procedure to obtain a 10 μm transparent
double layer. A scattering 4 μm layer containing optically dispers-
ing anatase particles (Dyesol WER2-O) was screen-printed on the
previous electrodes. The coated films were kept in a cabinet for
5 min and then thermally treated under an air flow at 125 °C for
6 min, 325 °C for 10 min, 450 °C for 15 min, and 500 °C for 15 min.
The heating ramp rate was 5–10 °Cmin–1. The thickness of the lay-
ers was measured by using a VEECO Dektak 8 Stylus Profiler. The
sintered layer was treated again with 40 mm aqueous TiCl4 (70 °C
for 30 min), rinsed with EtOH, and heated at 500 °C for 30 min.
After cooling down to 80 °C the TiO2 coated plate was immersed
3-[5-(4-{[4-((E)-4-{[4Ј-(2-Carboxy-2-cyanovinyl)biphenyl-4-yl][4-
(hexyloxy)phenyl]amino}styryl)phenyl][4-(hexyloxy)phenyl]-
amino}phenyl)thiophen-2-yl]-2-cyanoacrylic acid (TB-PT): Cya-
noacetic acid (192 mg, 2.26 mmol) and a catalytic amount of piper-
idine were added to a solution of 3 (210 mg, 0.226 mmol) in CHCl3
(15 mL). The reaction mixture was heated at refluxed for 18 h,
poured into 15% HCl (100 mL), and stirred overnight at room tem-
perature. After evaporation of the solvent, a dark precipitate was
formed. Isolation of the precipitate by vacuum filtration afforded
the pure product as a dark-red solid (233 mg, 0.220 mmol, 97.3%);
m.p. Ͼ 200 °C (decomp.). 1H NMR ([D6]DMSO): δ = 8.45 (s, 1
H), 8.32 (s, 1 H), 8.10 (d, J = 8.6 Hz, 2 H), 7.92 (d, J = 4.1 Hz, 1
H), 7.88 (d, J = 8.5 Hz, 2 H), 7.72 (d, J = 8.8 Hz, 2 H), 7.67 (d, J into a 2.0ϫ 10–4 m solution of organic dyes in THF/EtOH (1:1)
= 8.8 Hz, 2 H), 7.63 (d, J = 4.1 Hz, 1 H), 7.54–7.50 (m, 4 H), 7.13–
containing 2.0ϫ 10–2 m chenodeoxycholic acid (CDCA) for 20 h at
7.08 (m, 6 H), 7.16–6.99 (m, 6 H), 6.98–94 (m, 6 H), 3.96 (m, 4 H), room temperature in the dark. For the reference devices with N719,
1.75–1.67 (m, 4 H), 1.47–1.38 (m, 4 H), 1.36–1.27 (m, 8 H), 0.89
the plate was immersed into a 5.0ϫ 10–4 m solution of the dye in
EtOH containing equimolar CDCA under the same experimental
(m, 6 H) ppm. 13C NMR ([D6]DMSO): δ = 164.25 (C), 163.91 (C),
156.64 (C), 156.47 (C), 154.04 (CH), 153.87 (C), 149.15 (C), 148.37 conditions. Counter electrodes were prepared according to the fol-
(C), 146.95 (CH), 146.57 (C), 146.04 (C), 144.36 (C), 142.11 (CH), lowing procedure: A 1 mm hole was made in a FTO plate by using
139.34 (C), 138.99 (C), 133.79 (C), 132.81 (C), 132.16 (C), 131.94 diamond drill bits. The electrodes were then cleaned with a deter-
(CH), 131.42 (C), 130.17 (CH), 128.31 (CH), 128.29 (CH), 128.23 gent solution for 15 min by using an ultrasonic bath, 10% HCl,
(CH), 127.88 (CH), 127.81 (CH), 127.15 (CH), 126.82 (CH), 126.75 and finally acetone for 15 min by using an ultrasonic bath. After
(CH), 125.18 (C), 124.22 (CH), 123.58 (CH), 121.90 (CH), 121.21
treatment in the UV-O3 system for 18 min, a drop of a 5ϫ10–3
m
(CH), 117.12 (C), 116.90 (C), 116.14 (CH), 116.12 (CH), 102.96 solution of H2PtCl6 in EtOH was added and the thermal treatment
(C), 97.60 (C), 68.12 (CH2), 31.48 (CH2), 29.17 (CH2), 25.69 (CH2), at 400 °C for 15 min was repeated.
8
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30962
/KAP1
Date: 20-08-13 11:41:22
Pages: 10
Cosensitization Approach for Dye-Sensitized Solar Cells
[3]
[4]
For recent reviews, see: a) B. G. Kim, K. Chung, J. Kim, Chem.
Eur. J. 2013, 19, 5220; b) Y. S. Yen, H. H. Chou, Y. C. Chen,
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The dye-adsorbed TiO2 electrode and Pt counter electrode were
assembled into a sealed sandwich-type cell by heating with a hot-
melt ionomer-class resin (Surlyn 25-μm thickness) as a spacer be-
tween the electrodes. A drop of the electrolyte solution (Z960: 1.0 m
1,3-dimethylimidazolium iodide, 0.03 m I2, 0.05 m LiI, 0.10 m gua-
nidinium thiocyanate, and 0.50 m 4-tert-butylpyridine in acetoni-
trile/valeronitrile, 85:15; for N719-based cells the standard electro-
lyte A6141 was used: 0.6 m N-butyl-N-methylimidazolium iodide,
0.03 m I2, 0.10 m guanidinium thiocyanate, and 0.5 m 4-tert-butyl-
pyridine in acetonitrile/valeronitrile, 85:15) was added to the hole
and introduced inside the cell by vacuum backfilling. Finally, the
hole was sealed with a sheet of Bynel and a cover glass. A reflective
foil at the back side of the counter electrode was taped to reflect
unabsorbed light back to the photoanode.
Photovoltaic and Photoelectrical Characterization of DSSCs: Photo-
voltaic measurements of the DSSCs were performed with an antire-
flective layer on top of the cells under a 500 W xenon light source
(ABET Technologies Sun 2000 class ABA Solar Simulator). The
power of the simulated light was calibrated to AM 1.5
(100 mWcm–2) by using a reference Si cell photodiode equipped
with an IR cutoff filter (KG-5, Schott) to reduce the mismatch in
the region of 350–750 nm between the simulated light and the AM
1.5 spectrum. Values were recorded after 3 and 24 h and 3 and 7 d
of ageing in the dark. Curves I–V were obtained by applying an
external bias to the cell and measuring the generated photocurrent
with a Keithley model 2400 digital source meter. Incident photon-
to-current conversion efficiencies (IPCE) was recorded as a func-
tion of excitation wavelength by using a monochromator (Omni
300 LOT ORIEL) with single grating in Czerny–Turner optical de-
sign, in AC mode by using a chopping frequency of 1 Hz and a
bias of white light (0.3 sun). EIS spectra were obtained by using
an Eg&G PARSTAT 2263 galvanostat potentiostat. The measure-
ments were performed in the frequency range from 100 kHz to
100 mHz under ac stimulus with an amplitude of 10 mV and no
applied voltage bias. The obtained Nyquist plots were fitted by a
nonlinear least-square procedure by using the equivalent circuit
model in Figure 8.
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Acknowledgments
The authors thank Consorzio per le Richerche sui Materiali Avanzi
(CORIMAV) (Pirelli S.p.A. - University of Milano-Bicocca) and
the Ministero dell’Università e della Ricerca (MIUR-PRIN) (grant
number 2008CSNZFR) for financial support.
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Received: June 29, 2013
Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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9

Job/Unit: O30962
/KAP1
Date: 20-08-13 11:41:22
Pages: 10
V. Leandri, R. Ruffo, V. Trifiletti, A. Abbotto
FULL PAPER
Dye-Sensitized Solar Cells
A multibranched organic dye combining
the complementary structural, optical, and
electronic properties of the constituting
monobranched units is introduced as an in-
tramolecular cosensitization strategy for
dye-sensitized solar cells.
V. Leandri, R. Ruffo, V. Trifiletti,
A. Abbotto* .................................... 1–10
Asymmetric Tribranched Dyes: An Intra-
molecular Cosensitization Approach for
Dye-Sensitized Solar Cells
Keywords: Solar cells / Dyes/Pigments /
Sensitizers / Conjugation / Multianchoring
10
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0