Novel polymeric metal complexes as dye sensitizers for Dye-sensitized solar cells based on poly thiophene containing complexes of 8-hydroxyquinoline with Zn(II),Cu(II) and Eu(III) in the side chain

Article abstract of DOI:10.1016/j.tet.2010.02.039

Novel polymeric metal complexes as dye sensitizer for dye-sensitized solar cells (DSSCs) based on poly thiophene containing complexes of 8-hydroxyquinoline with Zn(II),Cu(II), and Eu(III) in the side chain have been synthesized according to the Stille coupling method and characterized by FTIR, GPC, and Elemental analysis. The UV-vis absorption spectroscopy, photoluminescence spectroscopy, cyclic voltammetry, and the applications in dye-sensitized solar cells (DSSCs) are also determined and studied. The DSSCs fabricated by PZn(Q)₂-co-3MT, PCu(Q)₂-co-3MT, and PEu(Q)₃-co-3MT exhibit good device performance with a power conversion efficiency of up to 0.56%, 0.78%, and 1.16%, respectively, under simulated AM 1.5 G solar irradiation (100 mW/cm²). They possess excellent stabilities and their thermal decomposition temperatures are 340 °C, 400 °C, and 540 °C, respectively, indicating polymeric metal complexes are suitable for the fabrication processes of optoelectronic devices.

Full text of DOI:10.1016/j.tet.2010.02.039

Tetrahedron 66 (2010) 2835–2842
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Novel polymeric metal complexes as dye sensitizers for Dye-sensitized solar cells
based on poly thiophene containing complexes of 8-hydroxyquinoline with
Zn(II),Cu(II) and Eu(III) in the side chain
*
Lifen Xiao, Yuan Liu, Qian Xiu, Lirong Zhang, Lihui Guo, Hailiang Zhang, Chaofan Zhong
Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University, College of Chemistry, Xiangtan, Hunan 411105, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel polymeric metal complexes as dye sensitizer for dye-sensitized solar cells (DSSCs) based on poly
thiophene containing complexes of 8-hydroxyquinoline with Zn(II),Cu(II), and Eu(III) in the side chain
have been synthesized according to the Stille coupling method and characterized by FTIR, GPC, and
Elemental analysis. The UV–vis absorption spectroscopy, photoluminescence spectroscopy, cyclic vol-
tammetry, and the applications in dye-sensitized solar cells (DSSCs) are also determined and studied. The
DSSCs fabricated by PZn(Q)2-co-3MT, PCu(Q)2-co-3MT, and PEu(Q)3-co-3MT exhibit good device per-
formance with a power conversion efficiency of up to 0.56%, 0.78%, and 1.16%, respectively, under sim-
ulated AM 1.5 G solar irradiation (100 mW/cm2). They possess excellent stabilities and their thermal
decomposition temperatures are 340 ꢀC, 400 ꢀC, and 540 ꢀC, respectively, indicating polymeric metal
complexes are suitable for the fabrication processes of optoelectronic devices.
Received 26 November 2009
Received in revised form 4 February 2010
Accepted 8 February 2010
Available online 12 February 2010
Keywords:
Dye-sensitized solar cells
Polymeric metal complexes
Thiophene
8-Hydroxyquinoline
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
solubility. Recently, many scientists are paying a good deal of at-
tention to thiophene-linked different functionalized group de-
Dye-sensitized solar cells (DSSCs) have attracted considerable
attentions due to the most promising low cost.1–3 Up to now, DSSCs
based on metal-free organic dyes,4–7 porphyrin dyes,8–10 metal-
phthalocyanine,11,12 and natural dyes13,14 have been reported and
developed. Although the efficiencies of DSSCs have not yet
approached the theoretical limit and are not competitive with the
silicon-based solar cells, organic dyes have their own advantages,15
such as low cost, high absorption coefficient and easy control of
redox potentials of the highest occupied molecular orbital (HOMO)
and the lowest unoccupied molecular orbital (LUMO) levels. Im-
portantly, the champion data of power conversion efficiency
obtained for metal complexes, which are based on ruthenium-
containing metallorganic dyes adsorbed on nanocrystalline TiO2
is 11.3–11.5%,16 showing the promising potential in the application.
However, the ruthenium dyes that are facing the problem of en-
vironmental issues will limit the large-scale application of this type
solar cells.17
rivatives for dye-sensitized solar cells.17,23–25 Among them, C217
has been demonstrated to show photo conversion efficiency (
h) up
to 9.8% under AM 1.5 irradiation and an excellent stability.26
For further development of highly efficient dyes in DSSCs, the
dye must fulfill the following criteria: a donor- -conjugation-
linkage-acceptor (D– -A) structure required for a wide range ab-
p
p
sorption extending to the near-infrared or infrared region, which is
due to produce a large photocurrent response. In addition, suitable
energy levels and location of the HOMO and LUMO orbitals of the
photosensitizer are required to match the iodine/iodide redox po-
tential and the conduction band edge level of the TiO2 semi-
conductor.27,28 Based on the previous reports of organic dyes used
in DSSCs so far, an oligothiophene moiety was successfully selected
as the conjugation unit of the dye molecule between the donor and
acceptor groups, resulting in maximum absorption bands shifting
to the longer wavelength.29
It is well known that metal chelates of 8-HQ derivatives are
most super materials as an electro transporter, especially, the
introduction of functional group substituting in the 5-position of
8-hydroxyquinoline have been used in many fields.30,31 Although
the report of their application as dye sensitizer for dye-sensitized
solar cells is rare, there is no doubt that chemical modifications
between PTs and 8-HQ may satisfy application requirements to
make an effective way to suppress charge recombination and
hence to improve open-circuit photovoltage (Voc).
Polythiophenes (PTs) are good candidates for donor or
p-con-
jugated unit in polymer solar cells (PSCs).18–20 Even since the first
synthesis in 1986,21,22 poly(3-alkylthiophenes) (PATs) have attrac-
ted increasing interest owing to the significant improvement in
* Corresponding author. Tel.: þ86 731 5829202; fax: þ86 731 58292447.
E-mail address: zhongcf798@yahoo.com.cn (C. Zhong).
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.02.039

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L. Xiao et al. / Tetrahedron 66 (2010) 2835–2842
According to the above-mentioned points, we have designed
and synthesized three D– -A dyes possessing a metal-8HQ as an
acceptor (A), methyl-functionalized oligothiophenes as a -conju-
p
p
gation linkage, and a thiophene as a donor group (D), which are
shown in Scheme 1. Moreover, the optical properties, thermal
properties, and photovoltaic properties of polymeric metal com-
plexes are also investigated in this paper.
2. Results and discussion
2.1. Synthesis and characterization
Scheme 2 outlines synthetic route of the ligand: D8QTH, which
was synthesized by the wittig reaction and Figure 1 gives the
corresponding 1H NMR spectra. The vinyl proton peaks appeared
at around 7.0–7.25 ppm and the hydrogen proton of thiophene
locating at the 3 position is observed at 7.30 ppm, 8.81 ppm, 8.50–
8.52 ppm, 7.77–7.79 ppm, 7.48–7.66 ppm are attributed to the
hydrogen protons of 8-hydroxyquinoline, but there is no detect-
able signal for the OH group in CDCl3.32
Figure 1. 1H NMR spectra of D8QTH in CDCl3.
S
S
S
N
O
O
Eu
S
S
N
S
S
O
N
N
N
S
S
S
M
O
O
PZn(Q)2-co-3MT
PCu(Q)2-co-3MT
(M= Zn)
(M=Cu)
x=y=0.5
PEu(Q)3-co-3MT
x=y=0.5
Scheme 1. Molecular Structures of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT and PEu(Q)3-co-3MT.
S
Br
Br
CHO
CH3CH2OH/CH3CH2ONa
K2CO3
S
Br
Br
CH2PPh3Br
+
N
OTs
N
OH
(1)
(2)
(D8QTH)
Br
Br
(CH3COO)2Zn.2H2O
(n=2)
(n=2)
(n=3)
Q
Q
Q
Zn(D8QTH)2
Cu(D8QTH)2
O
S
or (CH3COO)2Cu.H2O,EuCl3 6H2O
.
M
N
n
Eu(D8QTH)3
PZn(Q)2-co-3MT
PCu(Q)2-co-3MT
NiCl2(PPh3)2
PPh3
Zn/BPY
S
Br
Br
CH3
PEu(Q)3-co-3MT
Scheme 2. Synthesis of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT and PEu(Q)3-co-3MT.

L. Xiao et al. / Tetrahedron 66 (2010) 2835–2842
2837
PZn(Q)2-co-3MT, PCu(Q)2-co-3MT, PEu(Q)3-co-3MT were syn-
thesized by the stille coupling reaction between the metal com-
plexes and 2,5-dibromo-3-methyl-thiophene. The molecular
weight determined by GPC is summarized in Table 1. The Mn of
PZn(Q)2-co-3MT, PCu(Q)2-co-3MT, PEu(Q)3-co-3MT synthesized by
this method are only 3.9–9.5 K. We thought that steric hindrance of
the metal complexes should be the main reason for the low poly-
merization degree. The obtained polymers are readily soluble in
organic solvents, such as DMF, toluene, and DMSO, however, they
present poor solubility in some solvent, such as chloroform,
dichloromethane and THF.
Figure 3b–d show IR spectra of Zn(D8QTH)2, PZn(Q)2-co-3MT,
Cu(D8QTH)2, PCu(Q)2-co-3MT, Eu(D8QTH)3, PEu(Q)3-co-3MT. The
presence of broad absorption band in the region 3450–3360 cmꢁ1
is probably due to the existence of lattice and/or coordinated
water in the molecule, and make it difficult to see the bands due to
the O–H stretching vibrations, which would appear in this region.
Table 1
Molecular weight and thermal properties of PZn(Q)2-co-3MT. PCu(Q)2-co-3MT and
PEu(Q)3-co-3MT
Mn [ꢂ103]
Mw [ꢂ103]
PDI
a
Tg [ꢀC]
b
Td [ꢀC]
PZn(Q)2-co-3MT
PCu(Q)2-co-3MT
PEu(Q)3-co-3MT
3.9
4.1
9.5
4.2
4.3
10.6
1.07
1.06
1.12
156
168
202
340
400
540
a
Glass transition temperature, measured from DSC traces of the polymers.
The data were obtained from TGA of the polymers. In both case (DSC and TGA),
b
the data were measured under N2 atmosphere at a heating rate of 20 ꢀC/min.
Figure 2a shows IR spectra of the D8QTH, a sharp absorption
peak at 3356 cmꢁ1, which corresponds to O–H stretching of
8-hydroxyquinoline and aromatic and vinylic C–H at 3092 and
2939 cmꢁ1, respectively. The peaks at 1494 and 793 cmꢁ1 are the
characteristic absorption peaks of thiophene; the peak at
1599 cmꢁ1 is due to C]N stretching vibration; and the peak at
1526 cmꢁ1 is caused by C]C stretching vibration.
Figure 3. Normalized absorption spectra of the D8QTH, PZn(Q)2-co-3MT, PCu(Q)2-co-
3MT and PEu(Q)3-co-3MT in DMF solution.
Figure 2. FTIR spectra of D8QTH (a), Zn(D8QTH)2, PZn(Q)2-co-3MT(b), Cu(D8QTH)2, PCu(Q)2-co-3MT(c), Eu(D8QTH)3, PEu(Q)3-co-3MT (d).

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L. Xiao et al. / Tetrahedron 66 (2010) 2835–2842
The metal complexes and polymeric metal complexes have
Figure 4 gives the absorption spectra of PZn(Q)2-co-3MT,
PCu(Q)2-co-3MT and PEu(Q)3-co-3MT on TiO2 films. The absorption
spectra of dyes attached to TiO2 film are all broadened to the long
wavelength, which is attributed to the formation of dye aggregates
on the TiO2 surface and due to an interaction between the dyes and
TiO2,34 which would benefit the photoelectrical conversion effi-
ciency of the dye-sensitized solar cells.35
similar bands, but they have shown red shifts. There are sharp
absorption band at 1097, 1154, 1102 cmꢁ1 for the Zn(D8QTH)2,
Cu(D8QTH)2, and Eu(D8QTH)3, respectively, which should be
associated with C–O vibrations at the C–O–M site.33With increasing
the length of the polymers, the peaks of the corresponding poly-
meric metal complexes show red-shift comparing with the metal
complexes, and the C–Br stretching vibration observed at 573,
538, 590 cmꢁ1 for Zn(D8QTH)2, Cu(D8QTH)2, and Eu(D8QTH)3,
respectively, are disappeared in the corresponding polymeric
complexes, which is the evidence of the success of
polymerization.
2.2. Photophysical properties
The UV–vis absorption spectra could provide a good deal of
information on the electronic structures of the polymeric metal
complexes. The absorption spectra of the ligand and the polymeric
metal complexes in DMF solution are shown in Figure 3 and the
corresponding optical data of the polymeric metal complexes are
summarized in Table 2. The ligand D8QTH shows a UV–vis nor-
malized absorption peak in DMF located at 360 nm, corresponding
to the
p–
p electron transitions of the conjugated molecules, which
*
was observed in the intramolecular charge transfer (ICT) between
the rings of 8-hydroxyline and thiophene. In comparison with
D8QTH, The absorption peak of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT,
PEu(Q)3-co-3MT is 356, 337 and 323 nm, respectively, which show
blue shifts of the high energy
p–
*
p transitions with respect to the
Figure 4. Normalized absorption spectra of PZn(Q)2-co-3MT, PCu(Q)2-co-co-3MT and
PEu(Q)3-co-3MT adsorbed on TiO2 films.
corresponding complex, which can be attributed to the electron
donating 3-methyl group in the polymers. The other weak and
broad band is in the visible region (430–480 nm) that can be
The photoluminescent spectra of the three polymeric com-
plexes in DMF solution and the solid are shown in Fig. 5a and
Fig. 5b, respectively. The excitation wavelengths were set to the
absorption maxima from the UV–vis absorption spectra. It can be
seem that the PL peak of PZn(Q)2-co-3MT, PCu(8Q)2-co-3MT, and
PEu(Q)3-co-3MT is 539, 532, 520 nm, respectively. And in the
solid state, they red-shifted by ca.73, 75, 50 nm in comparison
with that of the solution, respectively, indicating that the con-
formation of the three polymeric metal complexes changed sig-
nificantly in the solid state.
assigned to MLCT or d–d transition and the overlap of the
p
–
p
*
transitions of the 3-methyl thiophene. An additional weak band at
362 nm was observed in PEu(Q)3-co-3MT, corresponding to direct
singlet–triplet absorption, leading to the Eu-centered 3MLCT states,
this behavior could be another clue about the formation of the two
charge-transfer bands in the europium complex.
Table 2
Optical properties of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT and PEu(Q)3-co-3MT
abs
max
abs
onset
a
l
(nm)
l
(nm) PL (nm)
Egopt (eV)
Solution
PZn(Q)2-co-3MT 356
PCu(Q)2-co-3MT 337
Solution
473 530
442 532
Solution Solid
2.3. Thermal stability
539
532
520
612
607
570
2.34
2.33
2.32
PEu(Q)3-co-3MT 323 362,441 534
The thermal properties of the copolymers were by thermogra-
vimetric (TGA) and differential scanning calorimetric (DSC) analy-
ses and are also reported in Table 1. The TGA (Fig. 6) results reveal
a
The optical band gap was obtained from the empirical formula Eg¼1240/ledge, in
which the ledge is the onset value of absorption spectrum in long wave direction.42
Figure 5. PL spectra of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT, and PEu(Q)3-co-3MT in DMF solution (a) and the solid state (b).

L. Xiao et al. / Tetrahedron 66 (2010) 2835–2842
2839
that PZn(Q)2-co-3MT, PCu(Q)2-co-3MT, and PEu(Q)3-co-3MT were
thermally stable with 5% weight loss at temperatures of 340 ꢀC,
400 ꢀC, and 540 ꢀC in nitrogen, respectively, which indicate that the
polymers are as steadily as ploy(3-alkylthiophene).36 Obviously, the
stability of the polymers is adequate for the fabrication processes of
optoelectronic devices.
of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT, and PEu(Q)3-co-3MT. The cyclic
voltammetry of complexes were measured in DMF containing
[Bu4N]BF6(Bu¼butyl) as supporting electrolyte and SCE reference
electrode at a scan rate of 100 mV/s. From the onset oxidation po-
tentials (Eox) and the onset reduction potentials (Ered) of the poly-
mers, HOMO, and LUMO energy levels as well as the energy gap of
the polymers were calculated according to the equations.39,40
HOMO ¼ ꢁeðEox þ 4:40ÞðeVÞ; LUMO ¼ ꢁeðEred þ 4:40ÞðeVÞ;
Egec ¼ eðEox ꢁ EredÞðeVÞ
The values obtained are listed in Table 3. The reduction
and oxidation potentials of PZn(Q)2-co-3MT were measured to be
Eox¼0.92 V and Ered¼ꢁ1.23 V, respectively, and the energy band
gap was 2.15 eV, the energy value of the HOMO was calculated to be
ꢁ5.32 eV and the energy value of the LUMO was calculated to be
ꢁ3.17 eV. In the same case of PCu(Q)2-co-3MT and PEu(Q)3-co-3MT,
their Eg is 2.05 eV and 1.93 eV, respectively. On the basis of the CV
data, the electron accepting ability of the complexes follows the
order of PZn(Q)2-co-3MT<PCu(Q)2-co-3MT<PEu(Q)3-co-3MT. And
the Eg of PEu(Q)3-co-3MT is more suitable for the fabrication of
optoelectronic devices than other two ones.
Table 3
Cyclic voltammetric results of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT and PEu(Q)3-
co-3MT
Figure 6. TGA plots of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT and PEu(Q)3-co-3MT with
a heating rate of 20 ꢀC/min under nitrogen atmosphere.
ox
red
E
(V)
E
(V) HOMO (eV) LUMO (eV) EgEC (eV)
onset
onset
PZn(Q)2-co-3MT 0.92
PCu(Q)2-co-3MT 0.84
PEu(Q)3-co-3MT 0.83
ꢁ1.23
ꢁ1.21
ꢁ1.10
ꢁ5.32
ꢁ5.24
ꢁ5.23
ꢁ3.17
ꢁ3.19
ꢁ3.30
2.15
2.05
1.93
The differential scanning calorimetry (DSC) analysis reveals the
glass transitions at 156 ꢀC for PZn(Q)2-co-3MT, 168 ꢀC for PCu(Q)2-
co-3MT, and 202 ꢀC for PEu(Q)3-co-3MT during heating, which is
noted that the materials may increase the stability of devices.37 But
there was no melting point, suggesting that the polymers are
amorphous. The lack of crystallinity in the polymers could serve as
a drawback for the use in organic solar cells.38 Further optimization
of the conditions for polymerization reaction and chemical struc-
ture of polymers may be necessary to obtain polymers with higher
molecular weight and crystallinity.
2.5. Photovoltaic performances of dye-sensitized solar cells
(DSSCs)
Figure 8 shows current density–voltage (J–V) characteristics of
devices based on the three polymeric metal complexes. And the
corresponding open-circuit voltage (Voc), short-circuit current
density (Jsc), fill factor (FF) and power conversion efficiency (PCE)
are listed in Table 4. It can be seen that Voc, Isc, FF, and PCE are all
increased from PZn(Q)2-co-3MT to PEu(Q)3-co-3MT. The Jsc based
on PEu(Q)3-co-3MT reached 2.53 mA/cm2, which is nearly 1.7 times
of that of the device based on PZn(Q)2-co-3MT (1.55 mA/cm2); the
power conversion efficiency (PCE) based on PEu(Q)3-co-3MT
2.4. Electrochemical properties
Electronic energy level is an important property for organic ma-
terials used in solar cells. Figure 7 shows the cyclic voltammograms
Figure 7. CV curves of PZn(Q)2-co-3MT, PCu(Q)2-co-3MT PZn(Q)2-co-3MT and
PEu(Q)3-co-3MT measured in DMF solution containing [Bu4N]BF6(Bu¼butyl) as sup-
porting electrolyte at a scan rate of 100 mV/s.
Figure 8. J–V curves of DSSCs based on PZn(Q)2-co-3MT, PCu(Q)2-co-3MT and
PEu(Q)3-co-3MT in DMSO solution.

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L. Xiao et al. / Tetrahedron 66 (2010) 2835–2842
reached 1.16%, which is more than two times of that of the device
based on PZn(Q)2-co-3MT (0.56%). The lower Jsc of PZn(Q)2-co-3MT
and PCu(Q)2-co-3MT might be ascribed to the poor charge sepa-
ration and transportation. It suggests that the europium complex
could make better electric contact than zinc and copper complexes.
Weak adsorption onto the surface of TiO2 and recombination losses
due to the short alkyl in the thiophene ring are two major factors
that limit the efficiencies of dye-sensitized solar cells (DSSCs). And
further work on optimizing the device performance is under
investigation.
reference. Infrared (FTIR) spectra were recorded on KBr pellets
250 mg of dried KBr and 2 mg of lyophilized samples with a Per-
kin–Elmer Spectrum One Fourier transform infrared spectrometer
over the 4000–450 cmꢁ1 range, at a rate of 16 nm/s. Thermogra-
vimetric analyses were run on a Shimadzu TGA-7 Instrument in
nitrogen atmosphere at a heating rate of 20 K/min from 25 ꢀC to
900 ꢀC. Differential Scanning Calorimetry was performed on ma-
terials using a Perkin–Elmer DSC-7 thermal analyzer in nitrogen
atmosphere at a heating rate of 20 ꢀC/min from 25 ꢀC to 250 ꢀC.
UV–vis spectra were taken on a Lambda 25 spectrophotometer.
Samples were dissolved in DMF and diluted to a concentration
(10ꢁ4–10ꢁ5 M). Photoluminescent spectra were taken on a Per-
kin–Elmer LS55 luminescence spectrometer with a xenon lamp as
the light source. Elemental analysis for C, H, and N was carried out
using a Perkin–Elmer 2400 II instrument, metal ion, and chlorine
ion were measured by chemical method. Gel Permeation Chro-
matography (GPC) analyses were done on WATER 2414system
equipped with a set of HT3, HT4, and HT5, l-styrayel columns with
DMF as an eluent (1.0 mL/min) at 80 ꢀC, calibrated by polystyrene
standard. Cyclic voltammetry was conducted on a CH Instruments
chi630c Electrochemical Workstation, in a 0.1 mol/L[Bu4N]BF4
(Bu¼butyl) DMF solution at a scan rate of 100 mV/s at room
temperature. The working electrode was a glassy carbon elec-
trode, the auxiliary electrode was a Pt wire electrode, and satu-
rated calomel electrode (SCE) was used as reference electrode.
Table 4
The data of Photovoltaic Performances of DSSCs
Solvent Illumination Jsc (mA/cm2) Voc (V) ff
h (%)
time (min)
PZn(Q)2-co-3MT DMSO
PCu(Q)2-co-3MT DMSO
PEu(Q)3-co-3MT DMSO
8
8
10
1.55
1.872
2.531
0.61
0.63
0.68
0.59 0.56
0.65 0.78
0.67 1.16
3. Conclusions
In this paper, we have successfully synthesized three novel
polymeric metal complexes comprising thiophene and 8-hydroxy-
quinoline with D–p-A structure based on poly thiophene containing
complexes of 8-hydroxyquinoline with Zn(II),Cu(II), and Eu(III) in
the side chain and applied them in dye-sensitized solar cells (DSSCs).
The three materials based on PZn(Q)2-co-3MT, PCu(Q)2-co-3MT, and
PEu(Q)3-co-3MT have good stabilities and their thermal de-
composition temperatures are 340 ꢀC, 400 ꢀC, and 540 ꢀC, re-
spectively. The power conversion efficiencies of them are 0.56%,
0.78%, and 1.16%, respectively, suggesting their potential in DSSCs
applications. The results may open up the possibility of controlling
not only the gap band but also the semiconducting properties of
novel materials. Overall, the present results highlight the potential of
the conjugated polymeric metal complexes as models for DSSCs, as
well as a new class of functional conjugated materials.
However, there are some shortcomings and improvements of
the polymeric metal complexes as dye sensitizer for dye-sensitized
solar cells: (1) Due to the solubility limits, the exact structure of the
polymeric metal complexes can not be determined and the UV–vis
spectra of the corresponding film can not be obtained because of
the poor film-forming at room temperature. (2)The absorption re-
gion of the polymeric metal complexes is not wide enough and
should be a red shift in comparison of the ligand. (3) One or two
anchoring groups, such as carboxylic acid or sulfonic acid groups
and long alkyls should be introduced in the structure for good
solubility and strong adsorption onto the surface of TiO2.41 To im-
prove the solubility and get better photovoltaic materials, we still
have much work to do and the next investigation will be reported in
future.
4.2. General procedures for fabrication of the DSSCs devices
Titania paste was prepared following a procedure: Fluorine-
doped SnO2 conducting glass (FTO) was cleaned and immersed in
aqueous 40 mM TiCl4 solution at 70 ꢀC for 30 min, then washed
with water and ethanol, sintered at 450 ꢀC for 30 min. The 20–
30 nm particles sized TiO2 colloid was coated onto the above FTO
glass by sliding glass rod method to obtain a TiO2 film of 10–15 mm
thickness. After drying, the TiO2-coated FTO glass were sintered at
450 ꢀC for 30 min, then treated with TiCl4 solution and calcined at
450 ꢀC for 30 min again. After cooling to 100 ꢀC, the TiO2 electrodes
were soaked in 0.5 mM the dye-sensitized samples dyes in di-
methyl sulfoxide (DMSO) solution, then kept at room temperature
under dark for 24 h. An 3-methoxypropionitrile solution containing
LiI (0.5 M), I2 (0.05 M), and 4-tert-butylpyridine (TBP) (0.5 M) was
used as the electrolyte. A Pt foil used as counter electrode was
clipped onto the top of the TiO2 using as working electrode. And
photoelectrochemical performance of the solar cell was measured
using a Keithley 2602 Source meter controlled by a computer. The
cell parameters were obtained under an incident light with in-
tensity 100 mW/cm2, which was generated by a 150 W Xe lamp
passing through an AM 1.5 G filter.
4.3. Synthesis
2,5-Dibromo-3-triphenylphosphoniomethylbromo-thiophene
(1): A solution of 2,5-dibromo-3-bromomethylthiophene(synthe-
sized according to the lit.42)(6.7 g, 20 mmol) and triphenylphos-
phine (6.3 g, 24 mmol) in 150 mL of dried p-xylene was stirred at
reflux for 12 h. The reaction system was then allowed to cool to
room temperature and the white precipitate was collected by fil-
tration, washed with dried ether and acetone repeatedly followed
by drying, the white solid was obtained (9.3 g, yield 83%) 1H NMR
4. Experimental section
4.1. Materials and instruments
NiCl2(PPh3)2, 3-methyl thiophene, and NBS were obtained from
Aldrich Chemical Co. and used as received. N,N-Dimethylforma-
mide was dried by distillation over CaH2, ethanol was dried over
molecular sieves and freshly distilled prior to use. The other ma-
terials were common commercial grade and used as received. All
chemicals used were of an analytical grade. Solvents were purified
with conventional methods.
(400 MHz, CDCl3,
5.63 (d, 2H).
d, ppm): 7.68–7.85 (m, 15H), 6.94(s, 1H), 5.57, and
5-Formyl-8-tosyloxyquinoline (2): 5-formyl-8-hydroxyquino-
line (synthesized according to the lit.43) (15 mmol, 2.6 g) was dis-
solved in methylene chloride (80 mL), TsCl (18 mmol, 3.2 g) was
added in the solution in one portion under the ice-water and then
stirred at ambient temperature. After 12 h, the solution was poured
All 1H NMR were performed in CDCl3 and recorded on a Bruker
NMR 400 spectrometer, and using TMS (0.00 ppm) as the internal

L. Xiao et al. / Tetrahedron 66 (2010) 2835–2842
2841
into the cool water. The organic layer was collected and dried over
anhydrous MgSO4, a yellow solid compound was obtained after the
H, 3.46; N, 3.69; S, 16.91; Found: C, 63.25; H, 3.38; N, 3.48; S, 17.26;
Mn¼4.1 K, Mw/Mn¼1.06.
removal of solvent. (5.1 g, yield 98%). 1H NMR (CDCl3,
d
, ppm):
PEu(Q)3-co-3MT: With the similar synthetic method as
Zn(D8QTH)2 to afford yellow solids(0.51 g, 61%). FTIR (KBr, cmꢁ1):
3075, 2935, 2846 (aromatic and vinylic C–H), 1558 (C]N),1499
(C]C), 1082 (C–O–M). Anal. Calcd for [C60H39S6O3N3Eu]: C, 60.34;
H, 3.29; N, 3.51; S, 16.11. Found: C, 61.03; H, 3.18; N, 3.38; S, 16.92;
Mn¼9.5 K, Mw/Mn¼1.12.
10.26(s, 1H), 9.75(d, 1H), 9.55–9.61 (d, 1H), 8.00–8.06 (d, 1H), 7.80–
7.82 (d, 1H), 7.58–7.59 (d, 2H), 7.40–7.42 (d, 2H), 7.35–7.40 (d, 1H),
0.85–0.88 (t, 3H).
4.3.1. 2,5-Dibromo-3-[2-(8-hydroxyquinoline)-vinyl]thiophene
(D8QTH). 2,5-Dibromo-3-triphenylphosphoniomethylbromo-thio-
phene (0.597 g, 10 mmol) and 5-formyl-8-tosyloxyquinoline were
dissolved in 200 mL of anhydrous ethanol. Under an ice-water bath,
NaOEt (0.4 g sodium in 20 mL of anhydrous ethanol) was added
into the solution. After 30 min, the solution was stirred for 12 h at
ambient temperature. Then the solution was added potassium
carbonate (0.21 g, 15 mmol) and refluxed for 8 h. The yellow solid
was collected at the end of the condensation reaction and washed
with distilled water and icy methanol. After dried in vacuum at
45 ꢀC, the compound was obtained as pale yellow solid (2.1 g, yield
Acknowledgements
This work was financially supported by the Open Project Pro-
gram of Key Laboratory of Environmentally Friendly Chemistry and
Applications of Ministry of Education, China (No. 09HJYH10).
References and notes
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7.79 (d, 1H), 7.48–7.66 (d, 2H), 7.30(s, 1H), 7.22–7.25 (d, 1H), 6.95–
6.99 (d, 1H). FTIR (KBr, cmꢁ1): 3356(O–H), 3092, 2939 (aromatic
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1494 (thiophene C–H), 793(thiophene C–S). Anal. Calcd for
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Zn(D8QTH)2: A ethanol solution (10 mL) of Zn(CH3COO)2$2H2O-
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D8QTH (0.41 g, 1 mmol). The reaction mixture was neutralized care-
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(aromatic and vinylic C–H), 1579 (C]N), 1496 (C]C), 1097 (C–O–M).
Anal. Calcd for [C30H18S2O2N2Br4Zn]: C, 40.59; H, 2.04; N, 3.16; S, 7.22.
Found: C, 40.21; H, 2.18; N, 3.28; S, 7.12.
Cu(D8QTH)2: In the same manner as described for Zn(D8QTH)2,
Yield(%): 86%, a red solid. FTIR (KBr, cmꢁ1): 3149, 2872(aromatic and
vinylic C–H), 1578 (C]N), 1514 (C]C), 1472,793 (thiophene),1154
(C–O–M). Anal. Calcd for [C30H18S2O2N2Br4Cu]: C, 40.68; H, 2.05; N,
3.16; S, 7.24. Found: C, 41.01; H, 2.36; N, 3.21; S, 7.14.
Eu(D8QTH)3: With the similar synthetic method as Eu(D8QTH)3.
Yield(%): 80%, a yellow solid. FTIR (KBr, cmꢁ1): 3055, 2966, 2926
(aromatic and vinylic C–H), 1579 (C]N), 1509 (C]C), 1102
(C–O–M). Anal. Calcd for [C45H27S3O3N3Br6Eu]: C, 39.02; H, 1.96; N,
3.03; S, 6.94; Found: C, 38.75; H, 2.01; N, 2.98; S, 6.85.
Poly[2,5-dibromo-3-[2-(8-hydroxyquinoline)-vinyl]thiophene-
Zn-co-3-methyl- thiophene] PZn(Q)2-co-3MT: The copolymer was
synthesized by Yamamoto coupling method according to the lit.44
Zn(D8QTH)2 (0.355 g,0.4 mmol), bis(triphenylphosphine) nick-
el(II) chloride (0.26 g,0.4 mmol), 3-methyl thiophene (synthesized
according to the lit.42) (0.205 g,0.8 mmol), zinc (0.13 g,2 mmol),
triphenylphosphine (0.209 g,0.8 mmol), and a little bipyridine
(0.006 g,0.038 mmol)were dissolved in DMF(15 mL) under nitro-
gen. Then the mixture was stirring at 90 ꢀC for 48 h. The yellow
solid were precipitated into a large excess of methanol solution. The
crude product was washed with methanol, distilled water, and THF
sequentially, then dried in vacuum at 60 ꢀC for one day to afford
pale yellow solids (0.25 g, 59%) FTIR (KBr, cmꢁ1): 3063, 2972, 2907
(aromatic and vinylic C–H), 1578 (C]N), 1488 (C]C), 1086
(C–O–M). Anal. Calcd for [C40H26S4O2N2Zn]: C, 63.12; H, 3.45; N,
3.68; S, 16.87. Found: C, 63.42; H, 3.26; N, 3.88; S, 17.13; Mn¼3.9 K,
Mw/Mn¼1.07.
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