Polymerization of tellurophene derivatives by microwave-assisted palladium-catalyzed ipso-arylative polymerization

Article abstract of DOI:10.1002/anie.201406068

We report the synthesis of a tellurophene-containing low-bandgap polymer, PDPPTe2T, by microwave-assisted palladium-catalyzed ipso-arylative polymerization of 2,5-bis[(α-hydroxy-α,α-diphenyl)methyl]tellurophene with a diketopyrrolopyrrole (DPP) monomer. Compared with the corresponding thiophene analog, PDPPTe2T absorbs light of longer wavelengths and has a smaller bandgap. Bulk heterojunction solar cells prepared from PDPPTe2T and PC₇₁BM show PCE values of up to 4.4 %. External quantum efficiency measurements show that PDPPTe2T produces photocurrent at wavelengths up to 1 μm. DFT calculations suggest that the atomic substitution from sulfur to tellurium increases electronic coupling to decrease the length of the carbon-carbon bonds between the tellurophene and thiophene rings, which results in the red-shift in absorption upon substitution of tellurium for sulfur. Telluric rings: The tellurophene-containing low-bandgap polymer PDPPTe2T, prepared by microwave-assisted ipso-arylative polymerization, exhibited red-shifted absorption spectra compared to the thiophene analogue. Bulk heterojunction solar-cell devices from PDPPTe2T and PC₇₁BM reach a power conversion efficiency of 4.4 % and produce photocurrent at wavelengths up to 1 μm.

Full text of DOI:10.1002/anie.201406068

Angewandte
Chemie
DOI: 10.1002/anie.201406068
Organic Photovoltaics
Polymerization of Tellurophene Derivatives by Microwave-Assisted
Palladium-Catalyzed ipso-Arylative Polymerization**
Young S. Park, Qin Wu, Chang-Yong Nam, and Robert B. Grubbs*
Abstract: We report the synthesis of a tellurophene-containing
low-bandgap polymer, PDPPTe2T, by microwave-assisted
palladium-catalyzed ipso-arylative polymerization of 2,5-
bis[(a-hydroxy-a,a-diphenyl)methyl]tellurophene with a dike-
topyrrolopyrrole (DPP) monomer. Compared with the corre-
sponding thiophene analog, PDPPTe2Tabsorbs light of longer
wavelengths and has a smaller bandgap. Bulk heterojunction
solar cells prepared from PDPPTe2T and PC BM show PCE
values of up to 4.4%. External quantum efficiency measure-
ments show that PDPPTe2T produces photocurrent at wave-
lengths up to 1 mm. DFT calculations suggest that the atomic
substitution from sulfur to tellurium increases electronic
coupling to decrease the length of the carbon–carbon bonds
between the tellurophene and thiophene rings, which results in
the red-shift in absorption upon substitution of tellurium for
sulfur.
mance such as molecular weight, polydispersity, and regior-
egularity are controlled by the efficiency and regioregularity
of the specific coupling reactions used for polymerization.
[6]
Typically, these reactions involve the coupling of aryl halide
with an organometallic aryl reagent. The formation of aryl–
aryl bonds through the cleavage of aryl–carbon bonds would
allow polymerization to proceed without the need for reactive
inorganic leaving groups, however, there are a limited number
of examples of such reactions because of the high bond
7
1
[
7]
dissociation energy for carbon–carbon bonds. We have
previously found that the use of ipso-arylative cross-coupling
reactions offers advantages in the coupling reactions of
tellurophene derivatives—specifically diphenylcarbinol-sub-
stituted benzotellurophenes—and these results have
prompted us to further investigate this methodology for the
challenge of preparing tellurophene-based conjugated poly-
[
8]
mers.
The recent synthesis of solution-processable poly(3-alkyl-
F
orming carbon–carbon bonds is fundamental to the con-
[
9]
struction of organic compounds. In the synthesis of p-
conjugated organic polymer containing polyaryl and/or poly-
heteroaryl structures, the most common synthetic strategies
use transition metal-mediated reactions to form carbon–
carbon bonds between the aryl rings. For example, poly(3-
alkylthiophene)s, the most-studied polymers in organic pho-
tovoltaic (OPV) devices, have been prepared by a range of
transition metal-mediated aryl coupling methodologies
tellurophene)s by GRIM polymerization has proven the
great potential of tellurophene-based materials for optoelec-
tronic applications. In comparison with poly(3-alkylthio-
phene)s, Seferos and co-workers have observed red-shifted
absorption spectra and smaller bandgaps from poly(3-alkyl-
[9]
tellurophene)s. In a related development, Choi and co-
workers have prepared a tellurophene-containing low-
bandgap polymer by Stille cross-coupling and reported that
replacing sulfur atoms with tellurium atoms in conjugated
polymers reduces the bandgap and improves the hole
[1]
[2]
including McCullough, Rieke, and Grignard metathesis
[3]
[4]
[5]
(
GRIM) methods as well as Stille and Suzuki cross-
[10]
coupling reactions. Properties critical to polymer perfor-
mobility, potentially enhancing the performance of OPV
materials.
Tellurophene, the Group 16 tellurium analog of thiophene
and selenophene, is an interesting building block for organic
optoelectronic materials because tellurium is a metalloid and
its large spin–orbit coupling may allow tellurophene-based
[
*] Dr. Y. S. Park, Dr. Q. Wu, Dr. C.-Y. Nam, Prof. R. B. Grubbs
Center for Functional Nanomaterials
Brookhaven National Laboratory
Upton, NY 11973 (USA)
E-mail: rgrubbs@bnl.gov
[11]
semiconductors to populate long-lived triplet excited states
Prof. R. B. Grubbs
Department of Chemistry, Stony Brook University
Stony Brook, NY 11794 (USA)
by intersystem crossing. The longer triplet exciton lifetimes
should increase exciton diffusion lengths allowing more
photocurrent collection and result in higher solar cell power
[
**] This research was carried out at the Center for Functional Nano-
materials, Brookhaven National Laboratory, which is supported by
the U.S. Department of Energy, Office of Basic Energy Sciences,
under Contract No. DE-AC-02-98CH10886. This research was also
supported by the BNL Laboratory Directed Research and Develop-
ment Award 09-003. Mass spectrometry was performed at the
Proteomic Center, Stony Brook University, shared instrumentation
grant: NIH/NCRR 1 S10 RR023680-1.
[
12]
conversion efficiencies (PCEs). However, the paucity of
synthetic methods available for tellurophene synthesis and
modification has hampered the more detailed investigation of
devices based on tellurophene derivatives. Herein, we de-
scribe the first example of palladium-catalyzed ipso-arylative
copolymerization of a tellurophene monomer (1) with
a diketopyrrolopyrrole (DPP) unit (2) (Scheme 1), in
Supporting information for this article (general experimental
details, synthesis and characterization for compounds, UV/Vis
absorption spectra, cyclic voltammetry, gel-permeation chroma-
tography, details of device fabrications, computation details, and
NMR spectra) is available on the WWW under http://dx.doi.org/10.
[10]
a method complementary to widely used Stille
and
Suzuki–Miyaura polymerizations, and demonstrate use of
the resulting polymer in photovoltaic devices. We compare
the optoelectronic properties of the tellurophene-based
polymer with those of its thiophene analogue and illustrate
1002/anie.201406068.
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
as has previously been observed in ipso-arylative couplings
[16,17]
with 2-thienyl- and 2-furyl(diphenyl)methanol,
in prefer-
ence to the undesired ortho-arylation pathway that can occur
with carbinol leaving groups.
The high yields and regioselectivities observed with the
model substrate led us to investigate the polymerization of
tellurophene monomer 1 with the DPP-based monomer 3,6-
bis(5-bromo-2-thienyl)-2,5-dihydro-2,5-di(2-hexyldecyl)-
pyrrolo[3,4-c]pyrrolo-1,4-dione (2, Scheme 1) at 1808C for 3 h
under microwave irradiation, to enable rapid polymeri-
Scheme 1. Palladium-catalyzed ipso-arylative polymerization.
[
18]
zation
and facilitate the formation of high molecular
[
19]
potential applications of tellurophene-containing materials in
OPVs.
weight polymer. In aliquots withdrawn from the polymer-
ization mixture for spectroscopic analysis (SI), both the
absorption peaks and absorbance onset were observed to shift
toward the red as the polymer chains grew, with the onset of
absorption reaching almost 1000 nm after 2 h.
We designed a new monomer, 2,5-bis[(a-hydroxy-a,a-
diphenyl)methyl]tellurophene (1), for copolymerization with
dihaloarenes based on our recent synthesis of a molecular
semiconductor through the palladium-catalyzed ipso-aryla-
tive coupling of a benzotellurophenyl-substituted diphenyl-
During purification by Soxhlet extraction, PDPPTe2T (3)
was separated into a lower-molecular weight chloroform-
[8]
carbinol with the DPP core 2. In this approach, the organic
benzophenone leaving group enables coupling reactions to be
run without generation of a stoichiometric amount of
trialkyltin halides, which are toxic and can remain as potential
soluble fraction (SEC vs polystyrene standards: M =
n
À1
8.0 kgmol ; ꢀ = 3.8) and a higher-molecular weight chloro-
form-insoluble fraction (SEC vs polystyrene standards: M =
n
À1
23.2 kgmol ; ꢀ = 3.7). The high molecular weight fraction
was observed to be soluble in chloroform ( ꢀ 7.5 mgmL ) at
[
13]
À1
impurities for OPV devices,
acid-functionalized monomers with their accompanying diffi-
culties in purification.
or the synthesis of boronic
808C.
[
14]
Tellurophene monomer 1 can be
Regardless of molecular weight, PDPPTe2T exhibited
[
20]
easily prepared on multi-gram scales by addition of dilithiated
tellurophene to benzophenone and purified by flash chroma-
tography (isolated yields of 65%, Supporting Information
a red-shifted absorption relative to PDPP3T, with two local
maxima near 900 nm and 810 nm in o-dichlorobenzene
(ODCB) (Figure 1a). As observed in PDPP3T absorption
[
20]
(
SI)). Monomer 1 has been stored for more than a year under
spectra,
the intensity of the longer wavelength peak
refrigeration without any observable degradation.
becomes more pronounced as polymer molecular weight
increases (Figure 1a). From the onset of absorption, we
Model coupling reactions with tellurophene monomer
1
(1 equiv) and 2-bromo-5-methylthiophene 4 (3 equiv) as
estimated the optical bandgap of PDPPTe2T (M =
23.2 kgmol , ꢀ = 3.7) to be 1.28 eV in ODCB solution
n
À1
substrates were carried out with Pd(OAc) as the catalyst
2
precursor, PCy as a ligand, and Cs CO as a base in o-xylene
(Figure 1a), which is smaller than the 1.36 eV reported for the
3
2
3
À1
[20]
under conventional heating at 1408C and under microwave
thiophene analogue PDPP3T (M = 54 kgmol , ꢀ = 3.15).
n
[
15]
irradiation at 1808C (Table 1). After careful inspection of
the reaction mixtures, only product 5 (isolated yields of 93%
for conventional heating and 78% for microwave irradiation,
respectively) and benzophenone 6 could be observed, sug-
gesting that monomer 1 exclusively undergoes ipso-arylation,
From cyclic voltammetry measurements, the onsets of
À1
oxidation and reduction of PDPPTe2T (M = 23.2 kgmol ,
n
ꢀ = 3.7) in a thin film were found at 0.30 and À1.17 V vs Fc/
+
Fc (SI), corresponding to HOMO and LUMO energy levels
at À5.40 and À3.93 eV vs vacuum, respectively. The electro-
chemical bandgap of PDPPTe2T was calculated as 1.47 eV
which is smaller than the 1.56 eV bandgap reported for
[
20]
PDPP3T, though this latter value was measured in solution
and not in a thin film.
Table 1: Model coupling reactions.
In order to compare the ipso-arylative polymerization
approach to the widely used Stille and Suzuki–Miyaura
methods, we attempted polymerization of appropriate tellur-
ophene derivatives (7 and 8) with monomer 2 by these two
methods under similar conditions (SI). It is difficult to make
a fair comparison between these polymerization methods
because of method-necessitated changes in polymerization
conditions: different palladium sources and ligands (Pd-
(
OAc) with PCy or Pd(PPh ) ) are used since Pd(OAc) with
2 3 3 4 2
Entry Reagents (equiv)
Conditions Yield
PPh often generates ortho-arylated products as well as ipso-
arylated products, different solvents are required depend-
ing on polymerization methods (o-xylene for ipso-arylative
polymerization, toluene for Stille polymerization and tolu-
ene/water for Suzuki polymerization), and only high molec-
ular-weight (chloroform-insoluble) fractions were analyzed.
3
[
c]
[%]
[17]
[
[
a]
b]
1
2
Pd(OAc) (0.05), PCy (0.10), Cs CO (4.0) 1408C
93
78
2
3
2
3
Pd(OAc) (0.05), PCy (0.30), Cs CO (6.0) 1808C
2
3
2
3
[
[
a] By conventional heating for 72 h. [b] By microwave irradiation for 1 h.
c] Yield of isolated product.
2
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Figure 1. Optical absorption spectra of PDPPTe2T synthesized by
a) ipso-arylative polymerization in ODCB and b) ipso-arylative, Stille,
and Suzuki polymerizations in chloroform.
Molecular weights of polymers were obtained as M =
n
Figure 2. a) J–V curves and b) IPCE measurements for solar cells
prepared from PDPPTe2T. Device structure: indium tin oxide (ITO)/
MoO /PDPPTe2T:PC71BM/LiF or TiO /Al.
À1
À1
2
5.1 kgmol (PDI = 3.5) for Stille and M = 25.9 kgmol
n
(
PDI = 2.7) for Suzuki polymerization, respectively. Optical
x
x
absorption spectra of PDPPTe2T obtained from three differ-
ent polymerization methods showed similar relative inten-
Table 2: Solar cell device parameters.
sities of two absorption maxima (I /I0 in Figure S2) and
1
absorption edges, indicating that all the polymerization
methods tested are synthetically efficient protocols (Fig-
ure 1b).
PDPPTe2T
Cathode
interlayer [V]
Voc
Jsc
[mAcm
FF
PCE [%]
max avgÆstd
À2
]
[a]
Low MW
LiF
TiOx
LiF
0.59
0.60
0.60 10.4
0.61 12.9
6.6
8.3
0.55 2.2
0.50 2.5
0.60 3.7
0.56 4.4
2.08Æ0.08
2.44Æ0.05
3.63Æ0.10
4.14Æ0.19
To understand how substitution of tellurium for sulfur in
the conjugated heterocyclic backbone of the polymer affects
materials properties, photovoltaic characteristics were inves-
tigated for bulk heterojunction (BHJ) solar cells containing
PDPPTe2T (low- and high-molecular weight portions) pre-
pared by ipso-arylative polymerization as the electron donor
and [6,6]-phenyl-C71-butyric acid methyl ester (PC BM) as
[
b]
High MW
TiOx
À1
À1
[
a] M =8.0 kgmol (PDI=3.81). [b] M =23.2 kgmol (PDI=3.67).
n
n
[c] All PCEs were averaged over 9 devices.
7
1
À2
the electron acceptor (device structure: indium tin oxide
ITO)/MoOx (9 nm)/PDPPTe2T:PC BM/LiF (1 nm)/Al).
tially by increasing photocurrent (J = 10.0 mAcm , SI),
sc
(
whereas thermal annealing (1508C, 10 min) deteriorated
performance. It is interesting to note similar improvements
could be achieved by casting active layers from mixtures of
chloroform and ODCB.
Blends of high- and low-molecular weight portions of
PDPPTe2T with PC BM at 1:3 weight ratio
71
PDPPTe2T/PC BM weight ratios from 1:1 to 1:4 were
7
1
examined. Current density–voltage (J–V) characteristics
[
18]
from the optimized devices under simulated air mass 1.5
À2
global (AM 1.5G) irradiation at 100 mWcm are shown in
Figure 2a and summarized in Table 2. Devices processed
a
7
1
solely from chloroform generated a low photocurrent (J =
(PDPPTe2T:PC BM) cast from a mixture of chloroform
and ODCB (4:1, v/v) resulted in the best performing devices
with measured PCEs of 3.7% (high molecular weight) and
sc
71
À2
0
.64 mAcm , SI). The use of 1-chloronaphthalene as a proc-
[
21]
essing additive improved the device performance substan-
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
2
.2% (low molecular weight), respectively. Incident photon
carbon bond lengths between tellurophene and thiophene
rings in PDPPTe2Tare calculated to be shorter (1.433 ꢀ) than
those between thiophene rings (1.438 ꢀ) in the same positions
in PDPP3T. This can be interpreted as resulting from an
increased contribution of the quinoid form to the frontier
orbitals of PDPPTe2T. As a consequence, the HOMO level
is higher in PDPPTe2T than in PDPP3T, while the LUMO
level is lower, even though electronic distributions of the
frontier orbitals do not appear to differ significantly between
PDPPTe2T and PDPP3T (SI).
TDDFT calculations of the optical bandgaps verify this
conclusion. For every chain length, the first excitation energy
for PDPPTe2T is consistently lower than that for PDPP3T.
We estimate the optical gap at infinite chain length to be
1.14 eV for PDPPTe2T and 1.24 eV for PDPP3T, in good
agreement with optical absorption spectra (SI). Together, the
calculations suggest that the replacement of one thiophene in
a terthiophene group with a tellurophene can make a signifi-
cant impact on the optoelectronic characteristics of a poly-
mer.
conversion efficiency (IPCE) measurements showed that the
onsets of photocurrents from PDPPTe2T devices reached
almost 1 mm (Figure 2b), reconfirming that the tellurium
substitution indeed contributes to enhancing light harvesting
at longer wavelengths than seen for PDPP3T which has
a photoresponse up to 900 nm. The superior performance
from the device prepared from the high-molecular weight
portion of PDPPTe2T can be attributed to the enhanced
IPCE in the 700 to 950 nm range. This illustrates the
importance polymer molecular weight can play in high
[
28]
[
20]
[
22–25]
efficiency solar cell materials.
In order to further improve solar cell efficiencies, we used
TiO , prepared by a solution-based sol–gel process, as an air-
stable optical spacer and hole-blocking cathode inter-
layer,
were measured for the high and low molecular weight
fractions in these devices, mainly as a result of an increase
in J (12.9 from 10.4 mAcm for the high molecular weight
sample and 8.3 from 6.6 mAcm for low molecular weight
x
[26,27]
instead of LiF. Higher PCEs of 4.4% and 2.5%
À2
sc
À2
samples) (Figure 2a and Table 2). These results are supported
In conclusion, we have synthesized a tellurophene-con-
taining donor–acceptor type low-bandgap polymer by palla-
dium-catalyzed ipso-arylative polymerization. PDPPTe2T/
PC BM bulk heterojunction photovoltaic devices—the first
by superior quantum efficiencies for the TiO devices in the
x
region of 450 to 650 nm (Figure 2b). Compared to PDPP3T-
based PV cells, PDPPTe2T devices showed a comparable
7
1
PCE (4.4 vs 4.7%) but a slightly enhanced J (12.9 vs
reported PV devices prepared from tellurophene-containing
polymers—reached PCEs of 4.4%. IPCE measurements on
these devices show that atomic substitution from sulfur to
tellurium causes a red-shift in absorption and enables donor
materials to collect photocurrent up to 1 mm. In this study, we
reconfirmed that the molecular weights of polymers play
important roles in obtaining high PCE solar cell devi-
sc
À2
1
1.8 mAcm ), though the PDPP3T device architecture
(
ITO/PEDOT:PSS/PDPP3T:PC BM/LiF/Al) differs enough
71
[20]
that direct comparisons should be made with caution.
To further elucidate the effect of substituting tellurium
PDPPTe2T) for sulfur (PDPP3T) on the observed optoelec-
(
tronic properties at the molecular level, we performed density
functional theory (DFT) and time-dependent DFT (TDDFT)
calculations on model oligomers of PDPPTe2T and PDPP3T
with finite chain lengths (n = 2, 4, and 6). In all molecules, 2-
hexyldecyl side chains were replaced with methyl groups for
simplicity and full geometry optimization was performed with
the repeating unit as shown in SI to examine the molecular
structure and the optical bandgap. All molecules maintain
backbone planarity and the electronic distributions of the
frontier orbitals for PDPPTe2T and PDPP3T are very similar
[
19,20,22]
ces.
Currently, we are in the process of side chain
modification to further improve polymer solubility, which
limits the molecular weights that can be obtained during
synthesis. We are working to generalize this palladium-
catalyzed polymerization method and to apply this method-
ology toward the synthesis of new polymer systems for high
efficiency solar cell materials.
Received: June 10, 2014
Revised: June 18, 2014
Published online: && &&, &&&&
(
Figure 3; full orbital descriptions are shown in the SI).
Nonetheless, there are some small differences. Tellurium has
no contribution to the highest occupied orbital (HOMO),
while sulfur contributes. On the other hand, tellurium
contributes slightly more to the lowest unoccupied orbital
Keywords: ipso-arylative polymerization ·
.
low-bandgap polymers · microwave-assisted reactions ·
organic solar cells · tellurophene
(
LUMO) than sulfur. The calculated bond lengths display
some subtle differences, too. Most importantly, the carbon–
[
[
[
1] R. D. McCullough, R. D. Lowe, M. Jayaraman, D. Anderson, J.
Org. Chem. 1993, 58, 904 – 912.
2] T.-A. Chen, R. D. Rieke, J. Am. Chem. Soc. 1992, 114, 10087 –
1
0088.
3] R. S. Loewe, M. Khersonsky, R. D. McCullough, Adv. Mater.
999, 11, 250 – 253.
1
[4] A. Iraqi, G. W. Barker, J. Mater. Chem. 1998, 8, 25 – 29.
[5] S. Guillerez, G. Bidan, Synth. Met. 1998, 93, 123 – 126.
[6] I. Osaka, R. D. McCullough, Acc. Chem. Res. 2008, 41, 1202 –
1214.
Figure 3. Calculated frontier orbitals of PDPPTe2T (top) and PDPP3T
[7] H. Wakui, S. Kawasaki, T. Satoh, M. Miura, M. Nomura, J. Am.
Chem. Soc. 2004, 126, 8658 – 8659.
(
bottom) oligomers.
4
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
[
8] Y. S. Park, T. S. Kale, C. Y. Nam, D. Choi, R. B. Grubbs, Chem.
Commun. 2014, DOI 10.1039/c4cc01862a.
[19] R. C. Coffin, J. Peet, J. Rogers, G. C. Bazan, Nat. Chem. 2009, 1,
657 – 661.
[
9] A. A. Jahnke, B. Djukic, T. M. McCormick, E. Buchaca Do-
mingo, C. Hellmann, Y. Lee, D. S. Seferos, J. Am. Chem. Soc.
[20] J. C. Bijleveld, A. P. Zoombelt, S. G. J. Mathijssen, M. M. Wienk,
M. Turbiez, D. M. de Leeuw, R. A. J. Janssen, J. Am. Chem. Soc.
2009, 131, 16616 – 16617.
2013, 135, 951 – 954.
[
10] M. Kaur, D. S. Yang, J. Shin, T. W. Lee, K. Choi, M. J. Cho, D. H.
Choi, Chem. Commun. 2013, 49, 5495 – 5497.
[21] C. H. Woo, P. M. Beaujuge, T. W. Holcombe, O. P. Lee, J. M. J.
Frꢂchet, J. Am. Chem. Soc. 2010, 132, 15547 – 15549.
[22] P. Schilinsky, U. Asawapirom, U. Scherf, M. Biele, C. J. Brabec,
Chem. Mater. 2005, 17, 2175 – 2180.
[23] A. Zen, J. Pflaum, S. Hirschmann, W. Zhuang, F. Jaiser, U.
Asawapirom, J. P. Rabe, U. Scherf, D. Neher, Adv. Funct. Mater.
2004, 14, 757 – 764.
[
11] M. A. Baldo, D. F. OꢁBrien, Y. You, A. Shoustikov, S. Sibley,
M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151 – 154.
12] Y. Shao, Y. Yang, Adv. Mater. 2005, 17, 2841 – 2844.
13] M. P. Nikiforov, B. Lai, W. Chen, S. Chen, R. D. Schaller, J.
Strzalka, J. Maser, S. B. Darling, Energy Environ. Sci. 2013, 6,
[
[
1
513 – 1520.
[24] R. J. Kline, M. D. McGehee, E. N. Kadnikova, J. Liu, J. M. J.
Frꢂchet, M. F. Toney, Macromolecules 2005, 38, 3312 – 3319.
[25] M. T. Dang, L. Hirsch, G. Wantz, J. D. Wuest, Chem. Rev. 2013,
113, 3734 – 3765.
[
[
14] G. A. Molander, M. R. Rivero, Org. Lett. 2002, 4, 107 – 109.
15] M. Iwasaki, S. Hayashi, K. Hirano, H. Yorimitsu, K. Oshima,
Tetrahedron 2007, 63, 5200 – 5203.
[
[
[
16] Y. Terao, H. Wakui, T. Satoh, M. Miura, M. Nomura, J. Am.
[26] J. Y. Kim, S. H. Kim, H. H. Lee, K. Lee, W. Ma, X. Gong, A. J.
Heeger, Adv. Mater. 2006, 18, 572 – 576.
[27] S. H. Park, A. Roy, S. Beauprꢂ, S. Cho, N. Coates, J. S. Moon, D.
Moses, M. Leclerc, K. Lee, A. J. Heeger, Nat. Photonics 2009, 3,
297 – 302.
Chem. Soc. 2001, 123, 10407 – 10408.
17] Y. Terao, H. Wakui, M. Nomoto, T. Satoh, M. Miura, M.
Nomura, J. Org. Chem. 2003, 68, 5236 – 5243.
18] H. Bronstein, Z. Chen, R. S. Ashraf, W. Zhang, J. Du, J. R.
Durrant, P. Shakya Tuladhar, K. Song, S. E. Watkins, Y. Geerts,
M. M. Wienk, R. A. J. Janssen, T. Anthopoulos, H. Sirringhaus,
M. Heeney, I. McCulloch, J. Am. Chem. Soc. 2011, 133, 3272 –
[28] Y.-J. Cheng, S.-H. Yang, C.-S. Hsu, Chem. Rev. 2009, 109, 5868 –
5923.
3275.
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Organic Photovoltaics
Telluric rings: The tellurophene-contain-
ing low-bandgap polymer PDPPTe2T,
prepared by microwave-assisted ipso-ary-
lative polymerization, exhibited red-
shifted absorption spectra compared to
the thiophene analogue. Bulk hetero-
junction solar-cell devices from
Y. S. Park, Q. Wu, C.-Y. Nam,
R. B. Grubbs*
&&&& — &&&&
Polymerization of Tellurophene
Derivatives by Microwave-Assisted
Palladium-Catalyzed ipso-Arylative
Polymerization
PDPPTe2T and PC BM reach a power
7
1
conversion efficiency of 4.4% and pro-
duce photocurrent at wavelengths up to
1
mm.
6
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 1 – 6
These are not the final page numbers!