Communications
DOI: 10.1002/anie.201005664
Tellurophene Polymers
Polytellurophenes with Properties Controlled by Tellurium-
Coordination**
Ashlee A. Jahnke, Graeme W. Howe, and Dwight S. Seferos*
The field of conjugated polymers is multidisciplinary and
highly competitive given the potential for application in
optoelectronic devices including transistors, light emitting
oxidative polymerization of tellurophene were first described
[
10]
by Tsukagoshi and co-workers in 1985. Similar results were
reported in two papers by Ogura and co-workers in the mid
1990s using higher homologues of tellurophene as mono-
[
1]
diodes, and solar cells. From a chemistry perspective,
polythiophenes and thiophene-containing copolymers are
arguably the most successful classes of conjugated polymers
and have been the focus of the majority of research in this
[
11,12]
[13]
mers,
as well as by Otsubo in 2000. In 1995 the Wittig-
condensation polymerization of tellurophene dialdehyde with
a phenyl diphosphonium salt was reported by Kubo and co-
[2]
[14]
field. Thiophene polymers, however, do face certain limi-
tations and intense research is taking place to develop new
polymers with improved properties. In recent years, poly-
selenophenes have been developed that have narrow
workers. In 1999 the synthesis and oxidative polymerization
of 3-butylthiophene-tellurophene-3-butylthiophene was
[
15]
reported by Chan and co-workers. The syntheses of Kubo
and Chan are distinct because they are the only reports where
soluble products were isolated. Most recently, in 2009, the
synthesis and electrochemical polymerization of 3,4-dime-
thoxytellurophene was reported by Bendikov and co-work-
[
3]
HOMO–LUMO gaps, high ambipolar charge transport
[
4]
characteristics, and can be designed to undergo phase
[
5]
separation into nanostructures in the solid state. All of
these properties are desirable for optoelectronics, and
although these studies are early and limited in number, they
highlight the opportunities that arise when conjugated
polymers are synthesized from heavier group 16 heterocycles.
Tellurophene, the heaviest known group 16 heterocycle,
should prove even more useful for improving and tailoring
optoelectronic properties. Specifically, tellurophene has a
narrow HOMO–LUMO gap and thus polytellurophenes are
[
16]
ers. This promising polytellurophene had markedly differ-
ent properties than its selenium analog, however the authors
noted that its identity was difficult to determine.
The fact that there are only a few reports in the 25-year
history of polytellurophenes indicates that there are serious
challenges associated with the synthesis of these potentially
useful organic electronic materials. Palladium-catalyzed con-
densation polymerizations, which have proven to be one of
the best methods for synthesizing well-defined conjugated
polymers, have not been developed or described for tellur-
ophenes. One significant obstacle is a lack of suitable
monomers to carry out these syntheses. Herein we describe
the synthesis of a novel, bifunctional tellurophene monomer,
and a study that determines the conditions required to
prepare polytellurophenes by solution-based palladium-cata-
lyzed polymerization of this monomer. This synthesis pre-
pares well-defined polytellurophenes that are stable, process-
able materials with distinct optoelectronic properties that can
be controlled by coordination chemistry at their tellurium
centers.
[
6]
predicted to have desirable light-absorption properties.
Tellurium is a metalloid with relatively large spin–orbit
coupling, therefore polytellurophenes should have easily
[7]
populated triplet excited states. Indeed, there are some
excellent examples of transition metal containing polymers
[
8]
that have these favorable properties. Due to its metalloid
nature, tellurium forms hypervalent coordination com-
[9]
plexes, which should enable supramolecular interactions
that offer a means to further control structure and properties.
Despite this promise and decades of conjugated polymer
research, the solid state optoelectronic properties of well-
defined polytellurophenes have not been described or inves-
tigated.
We first designed and carried out a synthetic route to
prepare a dihalogenated bitellurophene monomer that is
suitable for condensation polymerization reactions. Telluro-
phene was prepared by the method of Stephens and co-
Polytellurophenes have only been reported in the liter-
ature a handful of times, and with very limited character-
ization data. Insoluble black powders formed from the
[
17]
workers,
with tBuLi and copper(II) chloride at À788C by following a
modified literature method (Figure 1). To prepare the
and converted to bitellurophene by treatment
[
11]
[*] A. A. Jahnke, G. W. Howe, Prof. D. S. Seferos
Department of Chemistry, University of Toronto
desired monomer for polymerization, bitellurophene must be
halogenated at the 5 and 5’ positions. However, dihalotellur-
ophenes are to our knowledge unknown compounds, likely
due to difficulties associated with halogenating tellurophene
heterocycles. Indeed, while several conditions for aromatic
halogenation exist, most of these are not suitable for
tellurophene. Specifically, tellurophene forms complexes
80 St. George, Toronto, ON M5S 3H6 (Canada)
E-mail: dseferos@chem.utoronto.ca
Homepage: http://www.chem.utoronto.ca/staff/seferos/
[
**] This work was supported by the University of Toronto and the
National Science and Engineering Council of Canada’s Discovery
Grants Program. The authors thank Timothy Bender and Brett
Kamino for assistance with GPC measurements.
with Br , and therefore conditions that require elemental
bromine must be avoided. Acids must also be avoided
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ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2010, 49, 10140 –10144