An unusual thiazolo[5,4-d]thiazole sensitizer for dye-sensitized solar cells

Article abstract of DOI:10.1016/j.tetlet.2013.05.059

A novel unsymmetrical thiazolo[5,4-d]thiazole, TZ1, endowed with an unusual π-D-A structure featuring a highly conjugated light-harvesting backbone, has been synthesized and characterized from the photo- and electrochemical point of view. Although its structure did not resemble that of typical organic sensitizers, the new compound showed properties compatible with its employment in dye-sensitized solar cells. The experimental findings were supported by the results of DFT calculations. Indeed, when tested as a sensitizer in dye-sensitized solar cells, compound TZ1 gave rise to a high average open-circuit voltage (V_oc) of 0.712 V and an average short-circuit current (J_sc) of 7.0 mA cm^-2, resulting in a power conversion efficiency (η) of 2.55%.

Full text of DOI:10.1016/j.tetlet.2013.05.059

Tetrahedron Letters 54 (2013) 3944–3948
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
An unusual thiazolo[5,4-d]thiazole sensitizer for dye-sensitized solar
cells
b
b
b
b
Lorenzo Zani a, , Gianna Reginato , Alessandro Mordini , Massimo Calamante , Maurizio Peruzzini ,
Maurizio Taddei b,c, Adalgisa Sinicropi c, Maria Laura Parisi c, Fabrizia Fabrizi de Biani c, Riccardo Basosi c,
Alessandro Cavallaro d, Mara Bruzzi e
⇑
a CNR – Istituto per la Sintesi Organica e la Fotoreattività (CNR-ISOF), Via P. Gobetti 101, 40129 Bologna, Italy
b CNR – Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy
c Università degli Studi di Siena, Dipartimento di Biotecnologie, Chimica e Farmacia, Via A. Moro 2, 53100 Siena, Italy
d Università degli Studi di Firenze, Dipartimento di Ingegneria Industriale, Via S. Marta 3, 50139 Florence, Italy
e Università degli Studi di Firenze, Dipartimento di Fisica ed Astronomia, Via G. Sansone 1, 50019 Sesto Fiorentino, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel unsymmetrical thiazolo[5,4-d]thiazole, TZ1, endowed with an unusual p–D–A structure featuring
Received 16 April 2013
Revised 8 May 2013
Accepted 14 May 2013
Available online 21 May 2013
a highly conjugated light-harvesting backbone, has been synthesized and characterized from the photo-
and electrochemical point of view. Although its structure did not resemble that of typical organic sensi-
tizers, the new compound showed properties compatible with its employment in dye-sensitized solar
cells. The experimental findings were supported by the results of DFT calculations. Indeed, when tested
as a sensitizer in dye-sensitized solar cells, compound TZ1 gave rise to a high average open-circuit voltage
(Voc) of 0.712 V and an average short-circuit current (Jsc) of 7.0 mA cmꢀ2, resulting in a power conversion
Keywords:
Dye sensitized solar cells
Organic dye
efficiency (g) of 2.55%.
Ó 2013 Elsevier Ltd. All rights reserved.
Thiazole
DFT calculations
J–V measurements
The constant growth in global energy demand, coupled with
environmental and economic concerns, has led to an intense re-
search in the field of renewable energy sources,1 among which so-
lar energy is widely seen as particularly promising.2 In this context,
dye-sensitized solar cells (DSSC),3 first introduced in 1991,4 have
often been presented as a versatile and potentially inexpensive
alternative to traditional silicon-based devices. In DSSCs, light is
captured by a photosensitizer, which is adsorbed on a thin-layer
of a nanocrystalline semiconductor (usually TiO2) placed on the an-
ode. Upon excitation, the dye transfers an electron to the semicon-
ductor and from there to a back contact; the oxidized dye is
subsequently reduced by means of a suitable redox couple, which
is in turn reduced at the cathode; finally, the connection between
the two electrodes gives rise to an electric current. Thus, the pho-
tocurrent generated by the device is directly dependent on the
light-harvesting efficiency of the sensitizer, making it one of the
key components of a DSSC.
to 11% were reported.6 More recently, however, the attention in
the field of sensitizers has progressively moved toward organic
dyes,7,8 since they display some potentially favorable properties:
first, the absence of precious metals considerably lowers their cost;
secondly, they often show larger molar extinction coefficients
compared to Ru-complexes; finally, application of convergent syn-
thetic strategies allows the preparation of analogues with tunable
stereoelectronic properties. Most organic DSSC dyes have a conju-
gated backbone connecting donor and acceptor/anchoring groups
(D–p–A architecture): as a consequence, they usually show a broad
and intense absorption spectrum in the visible region and undergo
intramolecular charge-transfer upon photoexcitation, thus pro-
moting electron injection to the nanocrystalline semiconductor.
Very recently, we became interested in the possibility of prepar-
ing new DSSC sensitizers containing the thiazolo[5,4-d]thiazole
heterocyclic ring system.9,10 Our interest was motivated by the fact
that thiazolo[5,4-d]thiazoles (Fig. 1) had already been employed in
the fields of organic (opto)electronics and photovoltaics: for exam-
ple, they were used as spacer units in organic semiconductors for
polymer light-emitting diodes (PLEDs)11 and organic field-effect
transistors (OFETs).12 Moreover, they were incorporated in do-
nor/acceptor photoactive materials for bulk-heterojunction solar
cells,13 showing good light-harvesting properties coupled with
high charge-carrier mobility,13b and giving power conversion effi-
Traditionally, the most efficient sensitizers used in DSSCs have
been metallorganic complexes of ruthenium bearing bi- or terpyri-
dines as ligands,5 for which power conversion efficiencies superior
⇑
Corresponding author. Tel.: +39 051 6398301; fax: +39 051 6398349.
E-mail address: lorenzo.zani@isof.cnr.it (L. Zani).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.05.059

L. Zani et al. / Tetrahedron Letters 54 (2013) 3944–3948
3945
ethylcyanoacetate to obtain ethyl ester 6; finally, saponification
with KOH in ethanol furnished product TZ1 in moderate yields.15
It should be noted that TZ1 is an unsymmetrical disubstituted
thiazolo[5,4-d]thiazole: the synthesis of such structures has been
seldom reported in the past, and in general only for substances
having a much simpler composition than TZ1.9,14,16
As already pointed out, compound TZ1 is characterized by a p–
D–A architecture in which a conjugated unit, containing an elec-
tronwithdrawing thiazolo[5,4-d]thiazole heterocyclic ring flanked
by two electrondonating thiophenes, is directly attached to the do-
nor triphenylamine group. In addition, the dye contains the well-
characterized cyanoacrylate moiety as the acceptor/anchoring
group, and has alkyl chains on the thiophene rings to increase com-
pound solubility and prevent aggregation, both in solution and on
the semiconductor surface.17 It was therefore interesting to test the
capability of the new structure to broaden light absorption by
modulating the distance between frontier energy levels,13i with
Figure 1. The thiazolo[5,4-d]thiazole ring system and structure of compound TZ1.
ciencies of up to 5.8%.13e The sensitizers prepared in our laboratory
possessed a typical D–p–A structure with the thiazolothiazole moi-
the extended
vesting unit.
p-electron system acting as the molecule light-har-
ety acting as the central spacer unit, and yielded DSSCs with power
conversion efficiencies up to 3.5% under standard illumination
conditions.10,14
In the course of such work, we synthesized a new unsymmetri-
cal thiazolo[5,4-d]thiazole (TZ1) featuring a highly conjugated het-
erocyclic section directly attached to the donor triphenylamine
The UV–vis absorption and emission spectra of TZ1 are depicted
in Figure 2. The absorption spectrum in methanol solution
displays
a visible band with maximum (kabs) at 420 nm
(e
= 4.0 ꢁ 104 Mꢀ1 cmꢀ1), which was assigned to a delocalized
p
?
p⁄ transition; probably, the O–H bond of the carboxylic group
is greatly weakened by interaction with the polar solvent,18 since
addition of base caused only a small blue shift, with the absorption
moiety, thus giving rise to a much less common
p–D–A arrange-
ment (Fig. 1). In view of its peculiar structure, we deemed it inter-
esting to verify if compound TZ1 also possessed the appropriate
photo- and electrochemical properties to function as a sensitizer
in DSSCs.
The synthesis of compound TZ1 is presented in Scheme 1 (see
Supplementary data for experimental details). Thiazolo[5,4-d]thia-
zole 1 was prepared from 4-hexylthiophene carbaldehyde and
dithiooxamide by modification of a reported procedure,11 and
was then subjected to electrophilic bromination with NBS to give
monobromide 2; at this stage, it was observed that rigid control
of the stoichiometry of the reaction and of the purity of the starting
material was mandatory to obtain a good yield of the desired prod-
uct and avoid contamination by the dibrominated compound. Su-
zuki cross-coupling between compound 2 and boronic acid 3
afforded product 4 in moderate yields; the latter compound was
converted into aldehyde 5 by formylation under Vilsmeier–Haack
conditions, employing a mixture of POCl3 and DMF in 1,2-dichloro-
ethane; the reaction had to be carefully followed by TLC to avoid
the excessive formation of a diformylated derivative. Since direct
reaction of aldehyde 5 with cyanoacetic acid gave a product diffi-
cult to purify, we carried out a Knoevenagel condensation with
Figure 2. Normalized absorption spectra of TZ1 in MeOH (d) and CH2Cl2 (.), and
emission spectrum in MeOH (s).
Scheme 1. Synthetic pathway to compound TZ1.

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L. Zani et al. / Tetrahedron Letters 54 (2013) 3944–3948
The ground state oxidation potential (Eox) of TZ1 was evaluated
by means of cyclic voltammetry in dichloromethane solution
(Fig. 4). The dye exhibited a reversible oxidation wave at +0.45 V
versus Ag/AgCl 3 M (corresponding to +0.68 V vs NHE). This value
is more positive than the Iꢀ=Iꢀ3 redox potential (+0.4 V vs NHE),
thus assuring dye regeneration by the Iꢀ=I3ꢀ redox couple in a DSSC;
on the other hand, it has been observed that efficient dye regener-
ation by such redox mediator may need a larger driving force than
0.3 V:22 the influence of the small driving force for dye regenera-
tion on the photovoltaic performance of TZ1 will be discussed be-
low. It is worth noting that the Eox value of TZ1 is much less
positive than the reported first oxidation potential of triphenyl-
amine (+1.04 V versus SCE, corresponding to +1.28 V versus NHE
in CH2Cl2 solution);23 as a consequence, it can be inferred that
the oxidative process is not centered on the triphenylamine moi-
ety. This hypothesis was confirmed by DFT calculations (see below)
which showed that the dye HOMO level is mostly located on the
conjugated thiazolo[5,4-d]thiazole portion, suggesting that this is
where the oxidation likely takes place. The electrochemical behav-
ior of TZ1 was alike in MeCN and was not affected by the nature of
the working electrode material (Glassy Carbon, ITO), although with
the gold working electrode intense adsorption phenomena have
been observed. Considering the optical band gaꢂp (2.57 eV), we cal-
culated the excited state oxidation potential ðEOXÞ of the dye to be
ꢀ1.89 V (versus NHE): such value is sufficiently more negative
than that of the conduction band of TiO2 (ꢀ0.5 V) to guarantee
smooth electron injection from the dye to the semiconductor.
Figure 3. Normalized absorption spectra of TZ1 in CH2Cl2 solution (.) and on TiO2
film (}, obtained by difference from the spectrum of nonsensitized film).
maximum found at 418 nm. Accordingly, a pronounced negative
solvatochromism was observed in CH2Cl2, since the absorption
maximum was red-shifted to 438 nm. The UV–vis spectrum of
compound TZ1 on TiO2 film presents a broader
p ?
p⁄ absorption
band compared to that recorded in solution, with clearly red-
shifted absorption maximum and onset (Fig. 3), thus suggesting
the tendency of the dye to form J-aggregates on the semiconductor
surface.19 Interestingly, a sensitizer similar to TZ1 but lacking the
thiophene–thiazolothiazole unit was reported to have an absorp-
tion maximum below 400 nm, both in solution and adsorbed on
TiO2, as well as a larger optical band gap (see below):20 such result
supports our assumption that the highly conjugated heterocyclic
system of compound TZ1 is capable to enhance light absorption
in the visible region.
When irradiated at a wavelength corresponding to the absorp-
tion maximum in methanol solution, the dye gave a strong fluores-
cence band with a maximum at 563 nm (Fig. 2): the large Stokes
shift of 6048 cmꢀ1 (0.75 eV), together with the broad and structure-
less fluorescence spectrum, suggests a charge transfer character of
the electronic transition.21 Finally, from the intersection of the nor-
malized absorption and emission spectra we estimated the optical
band gap of the sensitizer (E0–0) to be approximately 2.57 eV.
Figure 5. Frontier molecular orbital plots and energy gap (in eV) between HOMO
and LUMO levels of TZ1. The same values for the known sensitizer D520,25 are
reported for comparison. The computed B3LYP and TD-CAM-B3LYP, both in vacuo
(in parentheses) and in MeOH {in brace}, energy differences (in eV) are shown
besides the vertical arrow. The conduction band edge (CBE) level of the TiO2
(ꢀ4.0 eV) and the redox potential of the couple Iꢀ=I3ꢀ (ꢃꢀ4.8 eV) are indicated as
dashed green and purple lines, respectively.
Figure 4. Cyclic voltammetry of TZ1 in CH2Cl2.

L. Zani et al. / Tetrahedron Letters 54 (2013) 3944–3948
3947
To learn more on the electronic structure of compound TZ1, we
computed the energy, geometry and electron density distribution
of its frontier orbitals by means of DFT calculations.24 The compu-
tational investigation confirmed that the HOMO and LUMO levels
are correctly aligned with the energy levels of TiO2 and the redox
couple to ensure electron transfer during operation of a solar cell
(Fig. 5); while the HOMO level of the dye is mainly localized on
the conjugate system centered on the thiazolothiazole bridge, its
LUMO is essentially located on the cyanoacrylic group with a smal-
ler contribution of the triphenylamine moiety, thus supporting the
charge transfer nature of the excitation process. TD-DFT studies
using the CAM-B3LYP functional gave a maximum absorption
son is prevented by the different fabrication and measurement
conditions applied in those cases; despite that, the possibility to
obtain a reasonable efficiency using a sensitizer with an alternative
structural arrangement was still noteworthy. The open-circuit po-
tential for TZ1 reached 0.712 V; such high value was comparable to
that obtained with N3, suggesting that the long alkyl chains pres-
ent on the dye backbone were effective in shielding the semicon-
ductor surface from the electrolyte, thus reducing the incidence
of dark current. On the other hand, the value of the short-circuit
current was much lower for the organic dye compared with the
ruthenium (II) complex: considering that the fill factor was the
same for both compounds, such difference is clearly the main rea-
son for the inferior performance of DSSCs built using the thiazolo-
thiazole sensitizer. The density of dye adsorbed on TiO2 measured
via UV–vis spectroscopy was 1.85 ꢁ 10ꢀ7 mol cmꢀ2. This value is of
the same order of magnitude of those found for other organic
dyes;26 furthermore, it is comparable to that reported in the liter-
ature for Ru-dye N3 (1.3 ꢁ 10ꢀ7 mol cmꢀ2).5a Therefore, we con-
clude that the observed short-circuit current densities should not
depend on the low adsorption of the sensitizer on TiO2 surface.
Possibly, the small driving force for dye regeneration deduced from
cyclic voltammetry experiments (see above) could be responsible
for the low Jsc. Indeed, regeneration of dye N3 has a much larger
driving force of approx. 0.75 V,27 which, coupled with its red-
shifted absorption compared to the new organic sensitizer, could
justify the difference in short-circuit current values reported in
Table 1.
wavelength in methanol of 408 nm with an excitation energy (Eexc
)
of 3.04 eV and an oscillator strength (f) of 2.419, in good agreement
with the experimental values; they also showed that photoexcita-
tion is mainly due to a HOMO ? LUMO transition, accounting for
approximately 53% of the total.
With the photoelectrochemical and computational data in
hand, we then proceeded to evaluate the performance of TZ1 as
a photosensitizer for DSSCs; the cells were fabricated using a pho-
toanode made with nanocrystalline TiO2-layered FTO glass, a Pt-
coated FTO glass as the cathode, and an electrolyte containing
the Iꢀ=Iꢀ3 redox couple (for experimental details, see Supplemen-
tary data). The results obtained under simulated AM 1.5 G
(131 mW cmꢀ2) illumination, including comparison with a refer-
ence cell built using the known ruthenium dye N3, are listed in Ta-
ble 1; a representative J–V curve is shown in Figure 6.
As can be seen from the table, the cells fabricated using com-
In summary, we reported the synthesis of a novel DSSC photo-
pound TZ1 had an average power conversion efficiency (
g
) of
sensitizer (TZ1) characterized by an unusual p–D–A architecture,
2.55%, corresponding to 44% of the value obtained with metal-sen-
sitizer N3 under the same conditions. The efficiency measured in
this study was therefore lower compared to those reported for
containing a highly conjugated light-harvesting system based on
alternate thiophene and thiazolo[5,4-d]thiazole heterocyclic units.
The compound was characterized from the photo- and electro-
chemical point of view, and its electronic structure and transitions
were investigated by means of DFT calculations. In spite of its pe-
culiar structure, compound TZ1 was found to have properties com-
patible with its employment in dye-sensitized solar cells. DSSCs
built with the new sensitizer had an average power conversion
efficiency of 2.55%, corresponding to 44% of the value obtained
with Ru-sensitizer N3 under the same conditions. The photovoltaic
devices showed high average open-circuit potential, comparable to
that obtained with the standard Ru-dye, but a relatively low short-
circuit current: the latter was attributed to an insufficient driving
force for dye regeneration when the Iꢀ=I3ꢀ redox couple was used.
We are currently addressing this problem through rational design
and synthesis of new unsymmetrical thiazolothiazole dyes with
optimized orbital energy levels: the results of these studies will
be reported in due course.
thiazolothiazole-containing D–p
–A dyes both by us (3.5%)10 and
by Zhou and co-workers (5.1%),14 even though a proper compari-
Table 1
Photovoltaic performance of DSSCs based on TZ1 and N3a
Dye
Jsc (mA cmꢀ2
)
Voc (mV)
Fill factor (ff)
g (%)
TZ1
N3
7.0
15.8
712
720
0.67
0.67
2.55
5.82
a
Measured under irradiation of AM 1.5 G simulated solar light (131 mW cmꢀ2) at
room temperature. Film thickness approx. 10
l
M, active area 0.25 cm2.
Acknowledgments
M.C. and M.L.P. are grateful to Regione Toscana within the POR-
FSE 2007–2013 program for a post-doctoral fellowship (FOTOSEN-
SORG project). A. C. and M. B. thank the ‘‘Polo di Innovazione Reg-
ionale, Progetto NANOXM – nanotecnologie per il mercato’’ for
financial support.
Supplementary data
Supplementary data (experimental procedures, synthesis and
characterization of all compounds, fabrication of dye-sensitized so-
lar cells and photoelectrochemical measurements.) associated with
this article can be found, in the online version, at http://dx.doi.org/
10.1016/j.tetlet.2013.05.059.
Figure 6. Representative J–V curves for
a DSSC built using dye TZ1 under
illumination (solid line) and in the dark (dashed line).

3948
L. Zani et al. / Tetrahedron Letters 54 (2013) 3944–3948
14. Recently, series of structurally related thiazolo[5,4-d]thiazole DSSC
a
References and notes
sensitizers has also been reported in combination with a quasi-solid state
electrolyte: Zhang, W.; Feng, Q.; Wang, Z.-S.; Zhou, G. Chem. Asian J. 2013, 8,
939–946.
1. See for example: (a) Balzani, V.; Armaroli, N. Energy for a Sustainable World;
Wiley-VCH: Weinheim, Germany, 2010; (b) Twidell, J.; Weir, T. Renewable
Energy Resources; Taylor & Francis: Oxon, United Kingdom, 2006.
2. Schiermeier, Q.; Tollefson, J.; Scully, T.; Witze, A.; Morton, O. Nature 2008, 454,
816–823.
3. Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Chem. Rev. 2010, 110,
6595–6663.
4. O’Reagan, B.; Grätzel, M. Nature 1991, 353, 737–740.
5. (a) Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.; Mueller, E.;
Liska, P.; Vlachopoulos, N.; Grätzel, M. J. Am. Chem. Soc. 1993, 115, 6382–6390;
(b) Nazeeruddin, M. K.; Pechy, P.; Renouard, T.; Zakeeruddin, S. M.; Humphry-
Baker, R.; Comte, P.; Liska, P.; Cevey, L.; Costa, E.; Shklover, V.; Spiccia, L.;
Deacon, G. B.; Bignozzi, C. A.; Grätzel, M. J. Am. Chem. Soc. 2001, 123, 1613–
1624.
6. Chen, C. Y.; Wang, M.; Li, J. Y.; Pootrakulchote, N.; Alibabaei, L.; Ngoc-le, C. H.;
Decoppet, J. D.; Tsai, J. H.; Grätzel, C.; Wu, C. G.; Zakeeruddin, S. M.; Grätzel, M.
ACS Nano 2009, 3, 3103–3109.
7. Mishra, A.; Fischer, M. K. R.; Bäuerle, P. Angew. Chem., Int. Ed. 2009, 48, 2474–
2499.
8. For recent developments, see: (a) Kanaparthi, R. K.; Kandhadi, J.; Giribabu, L.
Tetrahedron 2012, 68, 8383–8393; (b) Ooyama, Y.; Harima, Y. ChemPhysChem
2012, 13, 4032–4080.
9. First preparation: (a) Ephraim, J. Ber. Dtsch. Chem. Ges. 1891, 24, 1026–1031.
The correct structure of the thiazolothiazole ring was only recognized in 1960;
(b) Johnson, J. R.; Ketcham, R. J. Am. Chem. Soc. 1960, 82, 2719–2724.
10. Dessì, A.; Barozzino Consiglio, G.; Calamante, M.; Reginato, G.; Mordini, A.;
Peruzzini, M.; Taddei, M.; Sinicropi, A.; Parisi, M. L.; Fabrizi de Biani, F.; Basosi,
R.; Mori, R.; Spatola, M.; Bruzzi, M.; Zani, L. Eur. J. Org. Chem. 2013, 1916–1928.
11. Jung, I. H.; Jung, Y. K.; Lee, J.; Park, J.-H.; Woo, H. Y.; Lee, J.-I.; Chu, H. Y.; Shim,
H.-K. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 7148–7161.
12. (a) Ando, S.; Nishida, J.-I.; Tada, H.; Inoue, Y.; Tokito, S.; Yamashita, Y. J. Am.
Chem. Soc. 2005, 127, 5336–5337; (b) Mamada, M.; Nishida, J.-I.; Kumaki, D.;
Tokito, S.; Yamashita, Y. Chem. Mater. 2007, 19, 5404–5409; (c) Osaka, I.; Zhang,
R.; Sauvé, G.; Smilgies, D.-M.; Kowalewski, T.; McCullough, R. D. J. Am. Chem.
Soc. 2009, 131, 2521–2529; (d) Osaka, I.; Zhang, R.; Liu, J.; Smilgies, D.-M.;
Kowalewski, T.; McCullough, R. D. Chem. Mater. 2010, 22, 4191–4196.
13. Some recent examples: (a) Lee, S. K.; Cho, J. M.; Goo, Y.; Shin, W. S.; Lee, J.-C.;
Lee, W.-H.; Kang, I.-N.; Shim, H.-K.; Moon, S.-J. Chem. Commun. 2011, 1791–
1793; (b) Zhang, M.; Guo, X.; Li, Y. Adv. Energy Mater. 2011, 1, 557–560; (c)
Subramaniyan, S.; Xin, H.; Kim, F. S.; Shoaee, S.; Durrant, J. R.; Jenekhe, S. A. Adv.
Energy Mater. 2011, 1, 854–860; (d) Clarke, T. M.; Rodovsky, D.; Herzing, A. A.;
Peet, J.; Dennler, G.; DeLongchamp, D.; Lungenschmied, C.; Mozer, A. J. Adv.
Energy Mater. 2011, 1, 1062–1067; (e) Zhang, M.; Guo, X.; Wang, X.; Wang, H.;
Li, Y. Chem. Mater. 2011, 23, 4264–4270; (f) Huo, L.; Guo, X.; Zhang, S.; Li, Y.;
Hou, J. Macromolecules 2011, 44, 4035–4037; (g) Subramanyian, S.; Xin, H.;
Kim, F. S.; Jenekhe, S. Macromolecules 2011, 44, 6245–6248; (h) Clarke, T. M.;
Peet, J.; Denk, P.; Dennler, G.; Lungenschmied, C.; Mozer, A. J. Energy Environ.
Sci. 2012, 5, 5241–5245; (i) Dutta, P.; Yang, W.; Eom, S. H.; Lee, S.-H. Org.
Electron. 2012, 13, 273–282.
15. 2-Cyano-3-[4-(N-(4-(3-hexyl-5-(5-(4-hexylthiophen-2-yl)thiazolo[5,4-
d]thiazol-2-yl)thiophen-2-yl)phenyl)-N-phenyl)amino]phenylacrylic
acid
(TZ1). In a round-bottom Schlenk flask compound 6 (0.053 g, 0.063 mmol)
was dissolved in an ethanol/CH2Cl2 2:1 mixture (1.0 mL) at rt. A solution of
KOH in ethanol (5% w/w, 0.5 mL, approx. 0.47 mmol, 7.5 equiv) was then
added, and the reaction mixture was heated to reflux and stirred for 1.5 h. A
TLC check (EtOAc/petroleum ether 1:1) showed the disappearance of the
starting material. The reaction mixture was cooled down to rt, and it was
acidified with aq. HCl 1 M until pH 4. The aqueous layer was extracted with
CH2Cl2 (2 ꢁ 10 mL). The combined organic layers were washed with water
(15 mL) and Brine (15 mL) and dried over Na2SO4. Removal of the solvent
under reduced pressure afforded the crude as an orange paste. Purification by
flash column chromatography (methanol/CH2Cl2 1:6) gave acid TZ1 (0.025 g,
0.031 mmol, 50% yield) as an orange paste. 1H NMR (400 MHz, CDCl3): d (ppm)
8.08 (s, 1H), 7.67 (br s, 2H), 7.15–7.30 (m, 6H), 6.80–7.14 (m, 8H), 2.52–2.58
(m, 4H), 1.54–1.64 (m, 4H), 1.20–1.33 (m, 12H), 0.75–0.93 (m, 6H). 13C NMR
(100 MHz, CDCl3): d (ppm) 162.5, 162.4, 153.0, 152.9, 150.9, 149.9, 149.6,
145.9, 145.8, 144.5, 140.8, 139.8, 137.3, 134.9, 132.8, 130.1, 130.0, 129.8, 129.7,
129.3, 127.9, 126.7, 125.5, 125.0, 123.4, 120.5, 118.9, 102.4, 31.8, 31.7, 30.9,
30.5, 30.4, 29.3, 29.13, 29.07, 22.8, 22.7, 14.2 (ꢁ2). IR (neat)
m = 3050, 2965,
2929, 2856, 2214, 1726, 1629, 1587, 1506, 1480, 1327, 1182 cmꢀ1. ESI-HRMS:
m/z calcd for
C
46H43N4O2S4 [Mꢀ1]ꢀ (negative channel): 811.2274, found:
811.2216 (diff. 7.1 ppm).
16. (a) Johnson, J. R.; Rotenberg, D. H.; Ketcham, R. J. Am. Chem. Soc. 1970, 92,
4046–4050; (b) Knighton, R. C.; Hallett, A. J.; Kariuki, B. M.; Pope, S. J. A.
Tetrahedron Lett. 2010, 51, 5419–5422.
17. Koumura, N.; Wang, Z.-S.; Mori, S.; Miyashita, M.; Suzuki, E.; Hara, K. J. Am.
Chem. Soc. 2006, 128, 14256–14257.
18. Pastore, M.; Mosconi, E.; De Angelis, F.; Grätzel, M. J. Phys. Chem. C 2010, 114,
7205–7212.
19. (a) Li, S.-L.; Jiang, K.-J.; Shao, K.-F.; Yang, L.-M. Chem. Commun. 2006, 2792–
2794; (b) Liang, Y.; Peng, B.; Liang, J.; Tao, Z.; Chen, J. Org. Lett. 2010, 12, 1204–
1207.
20. Hagberg, D. P.; Marinado, T.; Karlsson, K. M.; Nonomura, K.; Qin, P.; Boschloo,
G.; Brinck, T.; Hagfeldt, A.; Sun, L. J. Org. Chem. 2007, 72, 9550–9556.
21. Peng, X.; Song, F.; Lu, E.; Wang, Y.; Zhou, W.; Fan, J.; Gao, Y. J. Am. Chem. Soc.
2005, 127, 4170–4171.
22. Kuciauskas, D.; Freund, M. S.; Gray, H. B.; Winkler, J. R.; Lewis, N. S. J. Phys.
Chem. B 2001, 105, 392–403.
23. Casalbore-Miceli, G.; Degli Esposti, A.; Fattori, V.; Marconi, G.; Sabatini, C. Phys.
Chem. Chem. Phys. 2004, 6, 3092–3096.
24. Yanai, T.; Tew, D.; Handy, N. Chem. Phys. Lett. 2004, 393, 51–57.
25. Hagberg, D. P.; Edvinsson, T.; Marinado, T.; Boschloo, G.; Hagfeldt, A.; Sun, L.
Chem. Commun. 2006, 2245–2247.
26. Wu, W.; Yiang, J.; Hua, J.; Tang, J.; Zhang, L.; Long, Y.; Tian, H. J. Mater. Chem.
2010, 20, 1772–1779.
27. Boschloo, G.; Hagfeldt, A. Acc. Chem. Res. 2009, 42, 1819–1826.