Impact of pendant 1,2,3-triazole on the synthesis and properties of thiophene-based polymers

Article abstract of DOI:10.1021/ma101657e

π-Conjugated moieties are often attached to conjugated polymers to systematically alter their electronic properties. Herein, we report the synthesis and properties of a thiophene polymer bearing a triazole moiety in the third position. Through NMR-based quenching studies, we show that the placement of the triazole moiety alters reaction pathway of the Ni(0)-mediated Grignard metathesis polymerization possibly through chelation. When compared with a triazole on the main chain, the pendant triazole moiety acts as an electron donor and lowers the band gap of the polymer. The triazole moiety also does not hinder the packing of the conjugated backbone. We also show that the fluorescence of this polymer is quenched with PCBM, indicating its potential as a candidate for organic photovoltaic devices.

Full text of DOI:10.1021/ma101657e

Macromolecules 2010, 43, 8045–8050 8045
DOI: 10.1021/ma101657e
Impact of Pendant 1,2,3-Triazole on the Synthesis and Properties
of Thiophene-Based Polymers
G. Nagarjuna, Serkan Yurt, Kedar G. Jadhav, and D. Venkataraman*
Department of Chemistry, University of Massachusetts Amherst, 710. N. Pleasant Street, Amherst,
Massachusetts 01003
Received July 23, 2010; Revised Manuscript Received August 31, 2010
ABSTRACT: π-Conjugated moieties are often attached to conjugated polymers to systematically alter their
electronic properties. Herein, we report the synthesis and properties of a thiophene polymer bearing a triazole
moiety in the third position. Through NMR-based quenching studies, we show that the placement of the
triazole moiety alters reaction pathway of the Ni(0)-mediated Grignard metathesis polymerization possibly
through chelation. When compared with a triazole on the main chain, the pendant triazole moiety acts as an
electron donor and lowers the band gap of the polymer. The triazole moiety also does not hinder the packing
of the conjugated backbone. We also show that the fluorescence of this polymer is quenched with PCBM,
indicating its potential as a candidate for organic photovoltaic devices.
Introduction
ester (PCBM) (1:1 wt % with respect to polymer) was added and
spun-cast (600 rpm) onto a glass plate. These films were annealed
Functionalization of conjugated polymers with π-conjugated
side chains is receiving widespread attention to create next
generation active materials for organic-based devices such as
sensors, field effect transistors, and photovoltaic devices because
of their high mobility and the presence of broad absorption bands
in the UV-vis spectra.
used for the functionalization of polymers in general
jugated polymers in particular.
is a nonconjugated spacer between the polymer backbone and
triazole. We reasoned that the placement of the triazole moiety in
conjugation with a monomer such as thiophene through 1,3-
dipolar cycloaddition reaction may offer a convenient pathway to
append π-conjugated moieties to the conjugated polymer back-
bone and systematically alter the electronic properties of the
conjugated polymer. Herein, we show that the polymerization of
the monomer with the triazole moiety at the third position of
thiophene through Ni(0)-mediated Grignard metathesis poly-
merization reaction is not straightforward. The triazole moiety
reverses the typical selectivity of Grignard metathesis in 2,5-
dibromothiophene-based systems and stops the polymerization
reaction. We show that this problem can be overcome and report
in here a protocol for the synthesis of thiophene-based polymers
bearing a triazole moiety at the third position. We also present the
impact of the triazole moiety on the optical properties of the
polymer.
at 100 °C for 30 min. UV-vis and fluorescence spectra were
recorded before and after annealing. Fluorescence spectra were
measured on PTA fluorimeter for thin films and on a JASCO
FP-6500 spectrofluorometer for solution studies. Cyclic voltammetry
studies were done using a BAS CV-50 W instrument. Stock solutions
of polymer (1 wt % polymer in chloroform) were prepared, films
were drop-cast on to the platinum working electrode, and CV was
recorded with tetrabutylammonium hexafluorophosphate as a
supporting electrolyte (0.1 M) in acetonitrile. The redox potentials
1-14
15
1,3-Dipolar cycloaddition is widely
1
6,17
and con-
In all these cases, there
1
8-21
were determined against Ag/AgNO reference electrode. In these
3
þ
conditions, the redox potential of Fc/Fc (Fc = ferrocene) was
þ0.09 V versus Ag/Ag . It is assumed that the redox potential of
þ
þ
22-24
Fc/Fc has an absolute energy level of -4.80 eV to vacuum.
þ
HOMO and LUMO values were calculated using Fc/Fc as a
reference. The working and auxiliary electrodes were cleaned
after each run. Synthetic protocols for hitherto unknown
molecules 1, 4, M1, and M2 are discussed here. Synthetic
protocols for all other molecules are provided in the Supporting
Information.
3-Iodothiophene (1). A Schlenk tube was charged with CuI
0.70 g, 3.68 mmol) and NaI (22.0 g, 147.2 mmol) under a
(
nitrogen atmosphere. Xylene (57.6 mL) and diglyme (14.4 mL)
were added followed by the addition of the ligand N,N-dimethy-
lethylenediamine (0.79 g,7.36 mmol). Finally, 3-bromothiophene
(
12 g, 73.6 mmol) was added under a nitrogen atmosphere. The
Schlenk tube was sealed with a Teflon valve, and the reaction
mixture was stirred at 110 °C for 22-24 h. The resulting suspen-
sion was allowed to reach room temperature. The solvents xylene
and diglyme were removed under reduced pressure, and the
resulting mixture was extracted with hexanes (2ꢀ75 mL). The
combined organics were washed with water (1 ꢀ 75 mL) and
saturated NaCl solution (1 ꢀ 75 mL), dried over Na SO , and
Experimental Section
UV-vis absorption spectra were recorded with a Shimadzu UV
600PC spectrometer in Polymer-Based Materials Harvesting
3
Solar Energy (Energy Frontier Research Center at the University
of Massachusetts Amherst) EFRC laboratory. Stock solutions of
polymers (c = 1 mg/10 mL) were prepared in spectrophotometric
grade chloroform (Fisher, Optima). UV-vis experiments for thin
films were done by spin-casting (1400 rpm, 60 s) 1 wt % solution of
polymer in chloroform on a glass plate. Similarly to the 1 wt %
solution of polymer in chloroform, phenyl-C61-butyric acid methyl
2
4
concentrated, and the residue was purified by silica gel chroma-
tography (hexanes) to provide 1 as a yellow liquid (12.3 g, 80%).
1
H NMR (400 MHz, CDCl ): δ 7.41 (dd, J = 4.8, 3.0, 1H),
3
1
3
7.21-7.19 (m, 1H), 7.11-7.09 (dd, J = 4.8, 1H). C NMR (100
MHz, CDCl ): δ 134.74, 128.65, 127.34, 77.20.
3
4-(2,5-Dibromothiophen-3-yl)-1-hexyl-1H-1,2,3-triazole (M1).
To an oven-dried round-bottom flask was added CuI (0.472 g,
*Corresponding author. E-mail: dv@chem.umass.edu.
r 2010 American Chemical Society
Published on Web 09/20/2010
pubs.acs.org/Macromolecules

8
046 Macromolecules, Vol. 43, No. 19, 2010
Nagarjuna et al.
2.48 mmol) and THF (50 mL). To this stirred solution,
N,N-diisopropylethylamine (3.845 g, 29.81 mmol) and water
(
(
10 mL) were added followed by the addition of monomer
2,5-dibromothiopen-3-ylethnyl)trimethylsilane (3) (1.68 g,
4
.96 mmol) and 1-azidohexane (0.947 g, 7.45 mmol). The
reaction was stirred for 15 h under reflux conditions and
quenched with water. The layers were separated, and the
aqueous layer was extracted with ethyl acetate (2 ꢀ 50 mL).
The combined organics were washed with brine (2 ꢀ 50 mL),
dried over Na SO , filtered, and concentrated under reduced
2
4
pressure. Purification of the residue by silica gel chroma-
tography (20:80 EtOAc: hexanes) afforded M1 as a white solid
1
1.37 g, 70%). H NMR (400 MHz, CDCl
(
3
): δ 8.13 (s, 1H),
7
1
.64 (s, 1H), 4.42 (t, J = 7.0, 2H), 1.98-1.91 (m, 2H),
13
.37-1.29 (m, 6H), 0.90 (t, J = 7.0, 3H). C NMR (100
): δ 141.03, 132.61, 131.35, 120.65, 112.52,
07.02, 50.58, 31.14, 29.72, 26.15, 22.43, 13.96. MS (FABþ)
MHz, CDCl
1
3
Figure 1. NMR of products obtained after reacting (a) M2 and (b) M1
with Grignard and then quenching with water.
þ
m/z 393.9 [M þ H] .
-Bromo-3-iodothiophene (4). In the absence of light, NBS
7.8 g, 49.22 mmol) was added in one portion to a stirred solution
2
(
which was converted to 3-iodothiophene (1) using the Finkel-
3
2
of 1 (8.1 g, 44.74 mmol) in DMF (200 mL). After stirring at
room temperature for 12 h, the reaction was quenched with
water (200 mL) and extracted with hexanes (2 ꢀ 75 mL). The
combined organics were washed with brine (2 ꢀ 75 mL), dried
stein reaction. Dibromination of 3-iodothiophene followed
by the Sonogashira coupling with trimethylsilylacetylene
and 1,3-dipolar cycloaddition with 1-azidohexane gave M1
in good yields (Scheme 1). We then subjected M1 to
standard Ni(0)-mediated Grignard metathesis polymeriza-
over Na SO , filtered, and concentrated under reduced pres-
2
4
3
3,34
sure. Purification of the residue by silica gel chromatography
(
NMR (400 MHz, CDCl
tion (GRIM) condition.
When the reaction mixture was
1
hexanes) afforded 4 (8.35 g, 75%) as a pale yellow liquid. H
poured into methanol (see Supporting Information), no
precipitate was obtained, indicating the absence of poly-
meric products. We did not obtain a precipitate irrespective
of whether the polymerization was done at room tempera-
ture or at elevated temperatures for 24 h. We hypothesized
that the failure of the polymerization may be either due to
the inability of M1 to undergo Grignard metathesis or the
inability of the Grignard formed from M1 to undergo Ni(0)-
mediated polymerization or both.
3
): δ 7.22-7.24 (d, J = 5.6, 1H), 6.95-
1
3
6
1
.96 (d, J = 5.6, 1H) C NMR (75 MHz, CDCl ): δ 137.08,
3
16.31, 113.46, 85.21.
4-(2-Bromo-5-iodothiophen-3-yl)-1-hexyl-1H-1,2,3-triazole (M2).
Compound 6 (1.6 g, 5.091 mmol) was dissolved in dichloromethane.
To this solution, trifluoromethanesulfonic acid (3.82 g, 25.45 mmol)
was added and the solution cooled to 0 °C using an ice bath.
N-Iodosuccinimide (1.15 g, 5.091 mmol) was added in small por-
tions, and the reaction mixture was stirred for 12 h at room
temperature. The reaction mixture was quenched with ice water
and extracted with CH Cl
2
2
(3 ꢀ 25 mL). The combined organic
extracts were washed with aqueous 10% sodium bisulfate solution,
dried over sodium sulfate and the solvent was removed under
reduced pressure. The residue was purified by silica gel chromatog-
raphy (15% ethyl acetate/hexane) to provide M2 as a white powder.
1
3
H NMR (400 MHz, CDCl ): δ 8.15 (s, 1H), 7.85 (s, 1H), 4.42
(
7
t, J = 7.0, 2H), 1.98-1.91 (m, 2H), 1.37-1.29 (m, 6H),0.90(t, J =
1
3
.0,3H). C NMR (100 MHz, CDCl
3
): δ 140.84, 137.63, 133.85,
120.61, 110.84, 72.68, 50.70, 31.27, 30.42, 26.28, 22.56, 14.09.
Quenching Studies. M1 (134 mg, 0.340 mmol) was dissolved in
THF and transferred into a Schlenk flask under an argon
atmosphere. tert-Butylmagnesium chloride (0.22 mL, 0.374
mmol) was added via syringe, and the reaction mixture was
stirred at room temperature for 2 h. It was then quenched
with water and extracted with diethyl ether (3 ꢀ25 mL). The
combined organic extracts were washed with brine and dried
To probe whether M1 undergoes Grignard metathesis or
not, we reacted M1 with t-BuMgCl for 2 h and the reaction
mixture was quenched with H O (Scheme 2). The organic
2
components were extracted with diethyl ether, and the solvent
was removed under reduced pressure. The H NMR of residue
1
1
showed that ratio of the regioisomers was 17:83. For peaks
attributable to the product, each peak between δ 7.4 and 7.6
integrated to one proton consistent with a single component
with three aromatic protons. On the basis of precedence, the
peaks around δ 7.4-7.6 were assigned to protons on thio-
phene, and the peak at δ 7.6 was assigned to the triazole
proton. The coupling constant, J, of the peaks between δ 7.4
and 7.6 was found to be 1.6 Hz, consistent with a “meta”
over sodium sulfate and evaporated under reduced pressure. H
NMR was recorded without further purification (Figure 1). The
M2 was also subjected to same reaction conditions as M1, except
that the Schlenk was cooled to 0 °C throughout the reaction.
1
Workup for M2 was the same as M1, and H NMR was
recorded without further purification (Figure 1).
Results and Discussion
35
coupling. We therefore concluded that the Grignard metath-
Synthesis of Polymer and Halogen-Magnesium Exchange
Studies. We chose to synthesize (poly(3-(1-hexyl-1H-1,2,3-
triazole-4-yl)thiophene)), P3TzT, as this polymer would allow
us to understand the impact of triazole on the electronic proper-
ties of the polythiophene backbone by comparing it with poly-
esis occurred with -Br group at the second position, ortho to
the triazole moiety (Figure 1). The driving force for the
formation of Grignard at this position may be due to the
coordination of the triazole nitrogen and the monomer acting
2þ
as a chelating ligand for Mg
.
(3-hexylthiophene) (P3HT), which is commonly used in organic
electronic devices such as photovoltaic cells.
Although there are few reports indicating that the
Grignard metathesis at the second position does result in
25-31
We synthe-
sized the monomer from readily available 3-bromothiophene,
3
6,37
polymerization,
our result is consistent with earlier

Article
Macromolecules, Vol. 43, No. 19, 2010 8047
Scheme 1. Synthesis of P3TzT and the Trimer 7
Scheme 2. Quenching Studies for Monomers 1 and 2
3
8,39
studies
with 5-bromo-2-iodo-3-hexylthiophene, which
To direct the Grignard metathesis at the fifth position of
the thiophene, we designed M2 with iodine at the fifth
position and bromine at the second position. Since it is
known that Grignard metathesis occurs faster with a C-I
than a C-Br bond, we expected that the Grignard reagent
should preferentially react at the fifth position. The synthesis
of M2 is shown in Scheme 1. We screened a variety of
iodination conditions and found that N-iodosuccinimide
and trifluoromethanesulfonic acid (NIS/CF SO H) pro-
have shown that the metal-halogen exchange at second
position does not result in polymerization. It has been argued
that if the Grignard metathesis occurs at second position on
the thiophene ring, then the Ni(0) does not insert in the
carbon-bromine bond at the fifth position purportedly
due to lack of stabilization from the alkyl chain at the third
position. We believe that in our case, since the hexyl group
is away from the reaction side, the chelating ability
of the triazole moiety may stabilize the Grignard or the
nickel(II) complex that results from the Grignard and may
prevent further reaction.
3
3
vided the iodinated compound in excellent yields. M2 was
reacted with t-BuMgCl, and the reaction mixture was
quenched with water. The coupling constant in the peaks

8
048 Macromolecules, Vol. 43, No. 19, 2010
Nagarjuna et al.
Figure 2. UV-vis absorption and fluorescence spectra of (a) P3TzT in chloroform before and after addition of trifluoroacetic acid (TFA) and
b) P3TzT film before and after annealing.
(
a
Table 1. Optical and Electrochemical Data of Polymers
sol
max [nm]
film
opt
g
opt
LUMO [eV]
elec
LUMO [eV]
elec
g
polymer
λ
λ
max [nm]
E
[eV]
HOMO [eV]
E
[eV]
P3HT
P3TzT
449
415
395
353
460
564
506
1.83
1.90
-4.99
-4.97
-5.02
-5.37
-5.46
-3.16
-3.07
-2.94
-2.78
-2.80
2.03
2.24
2.57
P3TzT þ TFA
b
4RTaz/Th
375
492
2.61
1.98
-2.76
-3.48
b
2
D-PT
a
opt
elec
E
calculated from oxidation and reduction potentials obtained from cyclic voltammetry, E
g
calculated from the intersection of tangent on the low energetic edge of the absorption spectrum with baseline, HOMO and LUMO are
= LUMO - HOMO, LUMO calculated using the
elec elec opt
g
opt
b
equation HOMO þ E
g
. Data are taken from the refs 2, 46, and 47.
between δ 7.3 and δ 7.7 was found to be 5.7 Hz, consistent
with the coupling expected between the protons at the fourth
and fifth position; this observation is consistent with the
metathesis happening at the fifth position (Figure 1). We
were gratified to note that M2 polymerized under GRIM
(see Supporting Information). Powder X-ray diffraction
analysis of the polymer thin film shows peaks at 2.75, 1.52,
0.5, and 0.38 nm, indicating that the polymer is crystalline
(see Supporting Information). Even though the crystal struc-
tures indicate that the triazole moiety may not be coplanar
with thiophene backbone, the noncoplanarity seems to not
hinder the packing of the polymer in thin films.
3
5
conditions. The polymer (P3TzT, M = 24.7 kDa, PDI =
n
1
.48) is soluble in chloroform at room temperature and in
DMF at elevated temperature (see Supporting Information).
UV-vis Absorption and Fluorescence Spectra. In the lit-
erature, it has been shown that 1,2,3-triazole can act as an
4
0
41
electron donor or as an electron acceptor. If triazole acts
as electron donor, then we expect that the HOMO levels will
be affected whereas if triazole acts as an acceptor, LUMO
42-45
levels of the conjugated polymer backbone will be affected.
The resonance and inductive effects of triazole will also depend
on the orientation of the triazole ring with respect to the back-
bone. Therefore, the question is what is the impact of triazole on
the electronic structure of the conjugated polymer backbone and
on the frontier energy levels?
The UV-vis absorption and fluorescence spectra of the
polymer solution and thin film are shown in Figure 2.
Solution state UV-vis and fluorescence spectra were re-
corded using a solution of the polymer in chloroform. Thin
films for solid state measurements were cast from chloro-
form onto a glass slide, and the UV-vis and fluorescence
spectra were recorded before and after thermal annealing at
In order to understand the placement effect of triazole in
side chain compared to main chain, we compared P3TzT
with the polymer reported in the literature, 4RTaz/Th.
46,47
We find that in solution λmax of P3TzT absorption is red-
shifted by 62 nm compared to λmax of 4RTaz/Th (see Table 1).
The red shift in the solution absorption λmax of P3TzT
compared to 4RTaz/Th indicates that the conjugation length
has increased, and the band gap of P3TzT is lower compared
to 4RTaz/Th (Table 1). Therefore, we believe that 1,2,3-
triazole attached as a side chain in P3TzT increases the
conjugation and electron density on polymer better than
1,2,4-triazole introduced in the main chain. To understand
the effect of triazole versus thiophene as a side chain on the
1
00 °C for 30 min. There was no substantial change in
absorption and emission spectra before and after thermal
annealing, indicating that no substantial changes occurred in
the packing of molecules upon annealing. The absorption
λmax in solution is 415 nm and in thin film is 506 nm with a
red shift of 91 nm in thin films. In comparison, P3HT has a
red shift of 115 nm in thin films. Crystal structures of
M1 and terthiophene (7) bearing the triazole moiety show
that the triazole is twisted with respect to the thiophene
backbone with a dihedral angle of 32° and 45°, respectively
thiophene backbone, we compared P3TzT with the reported
of all the
2
polymer, 2D-PT. The thin film absorption λ
max

Article
Macromolecules, Vol. 43, No. 19, 2010 8049
polymers;4RTaz/Th, 2D-PT, and P3TzT;are blue-shifted
compared to P3HT. However, the λmax for P3TzT is much
closer to P3HT than 4RTaz/Th or 2D-PT. The red shift in
λmax of all the polymers from solution to thin film is in the
following order: P3HT > P3TzT > 2D-PT > 4RTaz/Th.
From the onset absorption values, the band gaps of P3TzT,
Electrochemical Properties and the Nature of Triazole
Interaction. P3TzT thin films were drop-cast from a chloroform
solution on to the Pt electrode and the oxidation/reduction
potentials obtained from the cyclic voltammogram were
compared with P3HT. The CV of P3TzT thin film was
recorded in two ways: (i) by oxidizing the polymer (positive
potential sweep); (ii) by first reducing the polymer (nega-
tive potential sweep) (Figure 3). Since the oxidation and
reduction of P3TzT are not completely reversible, the onset
oxidation and reduction potentials from Figure 3 were used
4
1
RTaz/Th, and 2D-PT were calculated to be 1.9, 2.61, and
.98 eV, respectively. It is noteworthy that the absorption
λmax of P3TzT in the solution is blue-shifted compared to
D-PT. Nonetheless, in thin films, the absorption maxima
2
elec
are close. There is a 91 nm red shift in P3TzT absorption
from solution to thin film absorption, whereas 2D-PT shows
only a 30 nm red shift. Since the red shifts in thin films are
related to polymer packing and interaction between the
polymer chains, we speculate that triazole facilitates better
packing in thin films in P3TzT than conjugated side chains in
to calculate the HOMO and LUMO energy levels (eq 1).
onset
ox
HOMO ¼ - eðE
þ 4:71Þ ðeVÞ
elec
onset
LUMO
¼ - eðEred þ 4:71Þ ðeVÞ
ð1Þ
2
D-PT. We had anticipated that the interaction between the
The onset oxidation and reduction potentials of P3HT and
polymer chains in this films will be poor in P3TzT because it
has 1,2,3-triazoles on every repeat unit and the triazole ring is
not coplanar with the polymer backbone. We therefore
conclude that 1,2,3-triazole as a side chain also provides
better π-π interactions between polymer chains in thin films
compared to that of thiophene side chains.
The solution and thin film emission λmax of P3TzT are
found to be 556 and 630 nm, respectively. The Stokes shift for
the solution and thin film are calculated to be 141 and 124
nm, respectively. The higher Stokes shift in P3TzT indicates
a higher degree of structural reorganization in P3TzT, which
might be facilitated by the conjugated triazole side chains.
P3TzT are 0.286, -2.18 V and 0.266, -1.766 V, respectively,
with respect to Ag/Ag . The HOMO, LUMO energy levels
and electrical band gaps of P3HT, P3TzT, 4RTaz/Th, and
þ
2D-PT are shown in Table 1 for comparison. The HOMO
levels of all the polymers, except P3TzT, are lower than
opt
P3HT. In 2D-PT, both the HOMO and LUMO levels are
lower in energy compared to P3TzT, but both the polymers
have very close band gap (Eg ).
opt
The electrochemical and UV-vis spectroscopic data are
consistent with the fact that triazole is behaving as an
electron donor instead of an electron acceptor. Electrostatic
charges calculated on a dimeric unit in P3TzT using the
RB3LYP method and 6-31G (D) basis set are also consistent
with the observation that 1,2,3-triazole behaves as an elec-
tron donor (see Supporting Information).
P3TzT was treated with trifluoroacetic acid (TFA) to
protonate the nitrogen on the triazole moiety and decrease
the electron-donating nature of triazole. After the addition
of TFA, the absorption and emission λmax of P3TzT, as
expected, are blue-shifted by 20 and 21 nm, respectively.
Cyclic voltammetry after addition of TFA indicates that the
elec
energy of the HOMO level is lowered and LUMO elecis
increased in energy, thus increasing the band gap (Eg ).
All the above observations indicate that 1,2,3-triazole when
attached as a pendant group to a thiophene backbone acts as
an electron-donating group, pushing both the HOMO and
LUMO levels up in energy and reducing the band gap. The
triazole moiety does not hinder the packing of the polymer
backbone in thin films.
Figure 3. Cyclic voltammograms of P3TzT with and without trifluoro-
acetic acid (TFA).
Fluorescence Quenching with PCBM. To demonstrate that
P3TzT polymer is a potential candidate for photovoltaic
Figure 4. (a) Increase in fluorescence quenching by the addition of more PCBM (in chloroform). (b) Complete fluorescence quenching in the thin film
of P3TzT and PCBM.

8
050 Macromolecules, Vol. 43, No. 19, 2010
Nagarjuna et al.
applications, fluorescence quenching studies with varying
weight ratios of PCBM were carried out and are shown in
Figure 4. The fluorescence intensity of P3TzT polymer was
observed to decrease gradually with the increase in the
weight ratio of PCBM, indicating the electron transfer from
P3TzT to PCBM and hence fluorescence quenching. Thin
films casted onto a glass plate from chloroform solution
containing 1:1 wt % P3TzT and PCBM did not exhibit any
fluorescence, indicating complete fluorescence quenching.
Thus, the above observations indicate that P3TzT is a
potential candidate for applications in photovoltaic devices.
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Conclusions
We have shown that the thiophene-based polymers with 1,2,3-
triazole moiety attached as a pendant group can be synthesized
using Ni(0)-mediated Grignard metathesis polymerization using
a modified monomer. When compared with a triazole on the
main chain, the pendant triazole moiety acts as an electron donor
and lowers the band gap of the polymer. The triazole moiety also
does not hinder the packing of the conjugated backbone. Wehave
also shown that the fluorescence of this polymer is quenched with
PCBM, indicating its potential as a candidate for organic PV
devices. Efforts are underway to evaluate the hole mobilities and
photovoltaic metrics of thiophene-based polymers with pendant
triazole moiety and will be reported in due course.
3
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Acknowledgment. We thank the Energy Frontier Research
Center supported by the US Department of Energy, Office of
Basic Energy Sciences, through Grant DE-SC0001087 and the
NSF Materials Research Science and Engineering Center at the
University of Massachusetts Amherst for financial support. We
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Supporting Information Available: Synthetic procedures
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