Synthesis of conjugated fluorene- alt -thiophene polymers with pendant perylenediimide units

Article abstract of DOI:10.1021/jo100816j

(Figure presented) In this article we present the synthesis, characterization, electrochemical, optical, and preliminary photophysical investigation of two novel poly(fluorene-alt-thiophene) conjugated polymers endowed with pendant perylenediimide electron acceptor units. We show a route to the synthesis of easily functionalizable monomers paving the way to the preparation of a variety of functionalized polymers with different properties and applications and reflecting the versatility of this synthetic methodology.

Full text of DOI:10.1021/jo100816j

pubs.acs.org/joc
Synthesis of Conjugated Fluorene-alt-thiophene Polymers with Pendant
Perylenediimide Units
ꢀ
Rafael Gomez,* Carlos Seoane, and Jose L. Segura*
ꢀ
´ ´
ꢀ
Departamento de Quımica Organica, Facultad de Quımica, Universidad Complutense de Madrid,
E-28040 Madrid, Spain
rafaelgomez@quim.ucm.es; segura@quim.ucm.es
Received April 28, 2010
In this article we present the synthesis, characterization, electrochemical, optical, and preliminary
photophysical investigation of two novel poly(fluorene-alt-thiophene) conjugated polymers endowed
with pendant perylenediimide electron acceptor units. We show a route to the synthesis of easily
functionalizable monomers paving the way to the preparation of a variety of functionalized polymers
with different properties and applications and reflecting the versatility of this synthetic methodology.
Introduction
that organic semiconductors offer, e.g. the tuning of absorp-
tion and emission properties, REDOX behavior, or HOMO-
LUMO band gaps by easy structural modifications, have
prompted the synthesis of a variety of molecular architectures
combining electron donor fragments covalently linked to ac-
ceptor units and exhibiting the transfer of one electron from the
donor to the acceptor unit after photoexcitation.5
The backbones of conjugated polymers can be covalently
linked to functional groups which provide specific physical and
chemical properties. In recent years this approach has been
widely explored and proved to be appealing in order to obtain
materials with novel properties and applications, such as
sensors6 or electrochromic or energy conversion materials.4 In
the latter regard, electron donor polymers substituted with
electron acceptor groups have been proposed as promising
candidates.7 Thus, in our pursuit of functional donor-acceptor
polymers, we have used different pendant electron acceptor
The exploration of organic semiconductors as active elements
in electronic devices, such as light emitting diodes,1 thin film
transistors,2 solid-state lasers,3 or organic solar cells,4 has
experienced much progress in recent years. This progress has
been possible due to the unique features that organic semicon-
ductors offer, such as the tuning of the electronic properties,
easy structural modifications, possibility of self-assembly, or
mechanical flexibility. All this enables the exploitation of
organic semiconductors as materials for large-area and low-
cost disposable electronic products.
Photoinduced electron transfer has a great importance in
both life and science. It is the fundamental process on which
photosynthesis is based and it also constitutes the basis of
molecular electronics.4 In this respect, the unique features
€
(1) (a) Organic Light-Emitting Devices; Mullen, K., Scherf, U., Eds.;
Wiley-VCH: Weinheim, Germany, 2006. (b) Organic Electroluminescence;
Kafafi, Z. H., Ed.; Taylor & Francis: Boca Raton, FL, 2005. (c) Organic
Light-Emitting Devices; Shinar, J., Ed.; Springer-Verlag: New York, 2003.
(5) For reviews, see: (a) Segura, J. L.; Martın, N.; Guldi, D. M. Chem.
Soc. Rev. 2005, 34, 31. (b) Imahori, H.; Mori, Y.; Matano, Y. J. Photochem.
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(2) Murphy, A. R.; Frechet, J. M. J. Chem. Rev. 2007, 107, 1066.
(3) (a) Samuel, I. D. W.; Turnbull, G. A. Chem. Rev. 2007, 107, 1272. (b)
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Photobiol., C 2003, 4, 51. (c) Gorgues, A.; Hudhomme, P.; Salle, M. Chem.
Rev. 2004, 104, 5151.
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Calzado, E. M.; Villalvilla, J. M.; Boj, P. G.; Quintana, A.; Gomez, R.;
Segura, J. L.; Dıaz-Garcıa, M. A. J. Phys. Chem. C 2007, 111, 13595.
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(4) Gomez, R.; Segura, J. L. In Handbook of Organic Electronics and
Photonics; American Scientific Publishers: Stevenson Ranch, CA, 2007; Vol. 3.
(6) (a) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000,
100, 2537. (b) Thomas, S. W., III; Joly, G. D.; Swager, T. M. Chem. Rev.
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DOI: 10.1021/jo100816j
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Published on Web 07/09/2010
J. Org. Chem. 2010, 75, 5099–5108 5099
2010 American Chemical Society

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Gomez et al.
JOCArticle
groups such as fullerenes,8 anthraquinones,9 or tetracyano-
anthraquinodimethane.10
easily functionalizable monomers paving the way to the pre-
paration of a variety of functionalized polymers with different
properties and applications and reflecting the versatility of this
synthetic methodology.
Perylenediimide (PDI) derivatives have evolved into one of
the most fascinating materials in both industry and academics
due to its good chemical stability, thermal stability, and photo-
stability.11 Specially remarkable for the construction of systems
showing photoinduced electron transfer are its good electron
accepting ability and high absorption of light in the visible. Thus
PDIs have been attached to [60]fullerene,12 oligophenylen-
evinylenes,13 pyrenes,14 oligothiophenes,15 phthalocyanines,16
porphirins,17 or tetrathiafulvalene (TTF).18 PDI has also been
introduced in the main chain of polymers19 and, interestingly,
covalently attached as pendant groups to conjugated polymers.
Our research group has been especially active within this
particular field.20 Thus, we have shown interesting photo-
physical processes in this type of materials,20a,c,d aggregation
phenomena via the π-π stacking of the pendant perylene-
diimide units,21 or the variation of the bandgap.20b
Results and Discussion
Synthesis. The preparation of the donor-acceptor poly-
(fluorene-alt-thiophene)s bearing PDI units PDI-PFT and
PDI-PFET (Scheme 3) and their respective reference poly-
mers, i.e. the same polymeric main chain without the pendant
perylenediimide units, namely poly[2,7-(9,9-dioctylfluorene)-
alt-2,5-thiophene] (PFT)22 and poly(9,9-dioctylfluoren-2,7-yle-
neethylene-alt-2,5-thiophene) (PFET) (Scheme 3), has been
carried out by using classical palladium-catalyzed coupling
reactions between a 2,5-dibromothiophene derivative bearing
a perylenediimide moiety and appropriately 2,7-difunctiona-
lized fluorene monomers. This approach has the advantage to
yield structurally well-defined alternating copolymers, thus
allowing control over the polymer structure to be gained and
making possible the tuning of the gradient of redox potentials
and their optical band gap, which are important factors that
determine the photophysical behavior of these materials, by
suppressing the spacer or introducing a triple bond.
In this article we go a step further in our investigation of this
type of materials and we present the synthesis, characterization,
electrochemical, optical, and preliminary photophysical inves-
tigation of two novel poly(fluorene-alt-thiophene) conjugated
polymers endowed with pendant perylenediimide electron ac-
ceptor units. Furthermore we show a route to the synthesis of
Synthesis of the 2,5-Dibromothiophene-perylenediimide
Monomer. The synthesis of the key monomer 2,5-dibro-
mothiophene-perylenediimide (10) (Scheme 2), used in the
synthesis of both perylenediimide functionalized polymers
PDI-PFT and PDI-PFET, has been accomplished following
two alternative approaches, involving either the 2,5-dibro-
mothiophene derivatives 5 or 7, whose synthesis is depicted
in Scheme 1. Besides, many of the prepared intermediates are
also interesting building blocks for the preparation of other
functional monomers and polymers following an analogous
synthetic route, as we have mentioned.
ꢀ
(8) (a) Martınez, G.; Gomez, M. A.; Gomez, R.; Segura, J. L. J. Polym.
Sci., Part A: Polym. Chem. 2007, 45, 5408. (b) Martınez, G.; Gomez, M. A.;
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Marco, C.; Ellis, G.; Gomez, R.; Segura, J. L. J. Polym. Sci., Part A: Polym.
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Chem. 2008, 46, 6722.
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(9) Gomez, R.; Blanco, R.; Veldman, D.; Segura, J. L.; Janssen, R. A. J.
J. Phys. Chem. B 2008, 112, 4953.
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(10) (a) Zerza, G.; Cravino, A.; Neugebauer, H.; Sariciftci, N. S.; Gomez,
R.; Segura, J. L.; Martın, N.; Svensson, M.; Andersson, M. R. J. Phys. Chem.
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A 2001, 105, 4172. (b) Segura, J. L.; Gomez, R.; Blanco, R.; Reinold, E.;
Bauerle, P. Chem. Mater. 2006, 18, 2834.
€
(11) (a) Zollinger, H. In Color Chemistry, 3rd ed.; VCH: Weinheim,
Germany, 2003. (b) Herbst, W.; Hunger, K. In Industrial Organic Pigments:
Production, Properties, Applications, 2nd ed.; Wiley-VCH: Weinheim, Germany,
As the direct bromination of thiophenes with molecular
bromine usually gives a mixture of mono- and dibromothio-
phenes, which cannot always be easily separated, better results
can be attained with N-bromosuccinimide (NBS) as the bromi-
nating agent. Indeed, bromination of arenes with NBS is known
to proceed with especially high selectivity in dipolar-aprotic
solvents, e.g. N,N-dimethylformamide (DMF).23 Thus, regiose-
lective dibromination of 40-thien-3-ylbenzonitrile (1)24 in the
thiophene R-positions with 2 mol equiv readily affords in a
smooth reaction the corresponding 2,5-dibromo-3-(40-cyano-
phenyl)thiophene (2) in excellent yield (Scheme 1). Subsequent
diisobutyl aluminum hydride (DIBAL-H) reduction of the
cyano group in 2 to aldehyde provides 3 in 93% yield. Com-
pound 3 is a common precursor to the two approaches followed
toward 2,5-dibromothiophene-perylenediimide monomer (10)
(Scheme 2). The first synthetic approach investigated involves
the preparation of the thiophene derivative 5.25 This synthon is
functionalized with three bromine atoms: one in a lateral chain,
which is suitable for nucleophilic substitution (e.g. with a
complementarily functionalized perylenediimide derivative),
€
1997. Recent reviews on PDI chemistry: (c) Wurthner, F. Chem. Commun.
2004, 1564. (d) Langhals, H. Helv. Chim. Acta 2005, 88, 1309.
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Baffreau, J.; Perrin, L.; Leroy-Lhez, S.; Hudhomme, P. Tetrahedron Lett.
2005, 46, 4599. (c) Hua, J.; Meng, F.; Ding, F.; Li, F.; Tian, H. J. Mater.
Chem. 2004, 14, 1849.
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Z.; Wurthner, F.; Janssen, R. A. J. J. Phys. Chem. A 2004, 108, 6933. (b)
Beckers, E. H. A.; Chen, Z.; Meskers, S. C. J.; Jonkheijm, P.; Schenning, A.
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P. H. J.; Li, X.-Q.; Osswald, P.; Wurthner, F.; Janssen, R. A. J. J. Phys.
Chem. B 2006, 110, 16967. (c) Beckers, E. H. A.; Meskers, S. C. J.; Schenning,
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A. P. H. J.; Chen, Z.; Wurthner, F.; Marsal, P.; Beljonne, D.; Cornil, J.;
Janssen, R. A. J. J. Am. Chem. Soc. 2006, 128, 649.
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De Cola, L.; Williams, R. J. Phys. Chem. A 2004, 108, 1900.
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Adv. Funct. Mater. 2007, 17, 3764.
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Fukuzumi, S.; Guldi, D. M.; Torres, T. Org. Lett. 2007, 9, 2481.
(17) (a) Prodi, A.; Chiorboli, C.; Scandola, F.; Iengo, E.; Alessio, E.;
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Dobrawa, R.; Wurthner, F. J. Am. Chem. Soc. 2005, 127, 1454. (b) Van der
Boom, T.; Hayes, R. T.; Zhao, Y.; Bushard, P. J.; Weiss, E. A.; Wasielewski,
M. R. J. Am. Chem. Soc. 2002, 124, 9582.
(18) (a) Leroy-Lehz, S.; Perrin, L.; Baffreau, J.; Perrin, L.; Levillain, E.;
Allain, M.; Blesa, M.-J.; Hudhomme, P. J. Org. Chem. 2005, 70, 6313. (b) Leroy-
Lhez, S.; Perrin, L.; Baffreau, J.; Hudhomme, P. C. R. Chem. 2006, 240.
(19) (a) Koyuncu, S.; Kus, M.; Demic, S.; Kaya, I.; Ozdemir, E. J. Polym.
Sci., Part A: Polym. Chem. 2008, 46, 1974. (b) Nielsen, C. B.; Veldman, D.;
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Martın-Rapun, R.; Janssen, R. A. J. Macromolecules 2008, 41, 1094.
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(20) (a) Gomez, R.; Veldman, D.; Blanco, R.; Seoane, C.; Segura, J. L.;
Janssen, R. A. J. Macromolecules 2007, 40, 2760. (b) Blanco, R.; Gomez, R.;
(22) Liu, B.; Yu, W.-L.; Lai, Y.-H.; Huang, W. Macromolecules 2000, 33,
8945.
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Segura, J. L.; Mena-Osteritz, E.; Bauerle, P. Org. Lett. 2007, 9, 2171. (c)
Segura, J. L.; Gomez, R.; Blanco, R.; Reinold, E.; Bauerle, P. Chem. Mater.
(23) Mitchell, R. H.; Lai, Y.-H.; Williams, R. V. J. Org. Chem. 1979, 44,
4733.
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2006, 18, 2834. (d) Segura, J. L.; Gomez, R.; Reinold, E.; Bauerle, P. Org.
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(24) Ferraris, J. P.; Eissa, M. M.; Brotherston, I. D.; Loveday, D. C.;
Moxey, A. A. J. Electroanal. Chem. 1998, 459, 57.
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Chem. Mater. 2006, 18, 4817.
Lett. 2005, 7, 2345.
(21) Montilla, F.; Esquembre, R.; Gomez, R.; Blanco, R.; Segura, J. L. J.
Phys. Chem. C 2008, 112, 16668.
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SCHEME 1
SCHEME 2
whereas the other two have been covalently attached to the
R-positions of the thiophene core, and thus are suitable for
palladium-catalized couplings, for instance with fluorene mono-
mers functionalized with either a boronic ester (11) (Suzuki
coupling) or terminal acetylene groups (12) (Sonogashira
reaction). Thus, sodium borohydride reduction of aldehyde 3
readily affords hydroxymethyl derivative 4, which can be easily
halogenated to yield the target bromomethyl derivative 5.
Following our methodology, this interesting precursor for the
preparation of chemically polymerizable functionalized mono-
mers has been obtained in 82% overall yield after four steps,
much higher than with the previously reported synthetic proto-
col (five steps, 25% yield).25
On the second synthetic approach, the treatment of aldehyde
3 with an excess of hydroxylamine hydrochloride in methanol,
in the presence of a catalytic amount of pyridine, affords in
nearly quantitative yield the corresponding oxyme 6, which can
be subsequently reduced with lithium aluminum hydride to the
J. Org. Chem. Vol. 75, No. 15, 2010 5101

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SCHEME 3
corresponding amino-functionalized thiophene derivative 2,5-
dibromo-3-[40-(aminomethyl)phenyl]thiophene (7). It is worth
noting that, in our hands, the direct hydride reduction of the
cyano derivative 2 to the corresponding amine 7 gives a complex
mixture of compounds, out of which no 7 could be isolated.
Finally, 7 can be directly used to condense it in good yield with
the corresponding N-(9-octylnonyl)perylene-3,4:9,10-tetracar-
boxylic acid monoimide monoanhydride (8)26 by the classical
protocol followed for the attachment of perylenediimides to a
variety of systems, i.e. direct heating in toluene for 24 h in the
presence of zinc acetate (Scheme 2).
10 is based on the alkylation of imides. This procedure,
although certainly much less exploited in perylenediimide che-
mistry than the former, is of high value as it constitutes a good
alternative for the preparation of unsymmetrically substituted
perylenediimides from difficult to prepare or unstable amines.
Thus, the presence in 9, readily affordable from the parent
monoimide monoanhydride 8 by heating with urea, of an acidic
imido hydrogen enables its further and convenient functiona-
lization by an N-alkylation reaction with the complementary
functionalized 2,5-dibromo-3-[40-(bromomethyl)phenyl]thio-
phene (5), using potassium carbonate as the base and sodium
iodide as catalyst. The presence in the perylenediimide moiety
of long and branched alkyl chains endowes monomer 10 with
good solubility in common organic solvents. Both synthetic
sequences leading to 2,5-dibromothiophene-perylenediimide
(10) monomer, shown in Scheme 2, provide analytically
The alternative synthetic approach also shown in Scheme 2
toward the 2,5-dibromothiophene-perylenediimide monomer
(26) Langhals, H.; Sprener, S.; Brandherm, M.-T. Liebigs Ann. 1995, 3,
481.
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identical batches of product in good yield. Thus, the 1H NMR
spectrum of monomer 10 displays at low fields a series of duplets
and multiplets arising from the unsymmetrical perylenediimide
aromatic core. Besides, the AA0BB0 system of the benzene
spacer is clearly shown around 7.5 ppm, and the singlet corres-
ponding to the 3-thiophene position appears at 6.9 ppm. The 1H
NMR spectrum is finally completed with a singlet (integrating
two protons) corresponding to the methylene group linked to
the benzene and the imide nitrogen, a multiplet (one proton)
arising from the methyne group directly linked to the imide
nitrogen, and the signals corresponding to the swallow-tail
solubilizing chains. In the 13C NMR spectrum the carbonyl
imide groups of the PDI moiety are clearly visible at around 163
ppm together with the signals of the aromatic carbons in the sp2
region, the methylene and methyne groups linked to the nitro-
gen (55 ppm), and the signals of the alkyl chain. As the PDI
moiety in 10 is not fully symmetrical, one could expect four
carbonyl signals in its 13C NMR spectrum, in spite of the free
rotation around the C-N bond. However, our spectrum shows
only two carbonyl signals: one sharp and another weak, which is
the characteristic pattern of the nonsymmetrical perylenedii-
mides reported in this article and also has been established in the
literature.27 Actually, the doubling of carbonyl signals from
swallowtailed imides suggests that the swallowtails assume an
asymmetrical conformation. The FTIR spectra of monomer 10
show the characteristic absorption pattern of the perylene
skeleton with bands at 1580 and 1595 cm-1. Besides, the
absorption bands at 1658 and 1698 cm-1 indicate the presence
of the imide group. Finally, further evidence concerning the
structure proposed for monomer 10 is given by mass spectro-
metry and evidence concerning its purity by elemental analyses,
which reveal mass percentages that are in accordance with the
expected values.
Synthesis of Electron Donor-Acceptor Polymers PDI-PFT
and PDI-PFET. Polymer PDI-PFT (Scheme 3) has been
synthesized by a Suzuki polycondensation of an equimolecular
mixture of the perylenediimide functionalized 2,5-dibromothio-
phene monomer 10 and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)-9,9-dioctylfluorene (11)28 in the presence of
5 mol % Pd(PPh3)4 in a mixture of dry degassed THF and
aqueous potassium carbonate for 72 h under reflux (Scheme 3).
Although boronic acids have been often directly used as
reagents in poly-Suzuki couplings, boronic esters like 11 have
proven to be more advantageous in this kind of reaction, since
the presence of the 1,1,2,2-tetramethylethylene glycol units has
a protective effect on the labile boronic acid precursor. Simul-
taneously to the polymerization, a hydroxylation deprotection
process takes place, in which the removal of such protecting
groups as ethylene glycol does not affect the couplings.29
On the other hand, the copolymer PDI-PFET (Scheme 3)
was synthesized by a Sonogashira polycondensation of an
equimolecular mixture of the perylenediimide functionalized
2,5-dibromothiophene monomer 10 and 2,7-diethynyl-9,9-
dioctylfluorene (12)30 in the presence of a palladium(II)
catalyst and triphenylphosphine (Scheme 1). The experimen-
tal conditions require the use of an amine as base (iPr2NH)
and a copper(I) salt (CoI) as a cocatalyst, whose role is
probably to activate the alkyne toward the transmetalation
step by forming copper σ- or π-acetylides. The formation of
butadiyne defects is one of the major drawbacks of the
polymerization coupling between bis(ethynyl) aromatic deri-
vatives and dihaloarenes to yield poly(arylene ethynylene)s
(PAEs). When Pd (II) is used, such defects are originated
partly by the reduction of Pd(II) to Pd(0) in the catalyst
activation step, but defects also derive from the oxidative
coupling of terminal bonds; the source of the oxidizing agent
remains unclear and cannot be avoided even under strict
exclusion of air.31 Even the use of Pd(0) complexes does not
eliminate the occurrence of butadyine units in the polymeric
chain. Although there is no direct measure to determine the
amount of butadiyne defects in PAEs, with an estimated
number ranging from 1% to 10% of all repeating units,32
13C NMR can be useful sometimes. In our case no signals
could be assigned to diyne defects showing that the number
of diyne defects is below the detection limit, that the noise of
the spectra hinders those signals to some extent, or, taking
into account the complexity of our spectra, those signals
could be overlapped. However, it is generally accepted that
butadiyne defects do not have a remarkable effect on either
the optical or the electronic properties of the PAEs.
The resulting copolymers PDI-PFT and PDI-PFET were
precipitated out of their respective thick reaction mixtures by
addition of methanol, purified by reprecipitation from
chloroform/methanol and further purified by washing with
acetone in a Soxhlet apparatus for 24 h to remove unreacted
materials, small molecules, oligomers, and catalyst residues.
The contamination by palladium nanoparticles formed dur-
ing the palladium-catalyzed chemical reaction is an impor-
tant drawback of these protocols. Metallic residues can act as
charge-trapping sites, thus impairing the charge carrier
mobility and/or producing device hysteresis.33 A few meth-
ods have been developed to remove such nanoparticles
although they tend to be relatively harsh or not generally
applicable.34 Happily, a substantial part of this palladium
contamination can be easily removed by a simple Soxhlet
extraction, as in our purification protocol.
To be used as reference materials we have also synthesized
poly[2,7-(9,9-dioctylfluorene)-alt-2,5-thiophene] (PFT)22 and
poly(9,9-dioctylfluoren-2,7-yleneethylene-alt-2,5-thiophene)
(PFET) by analogous Suzuki or Sonogashira couplings be-
tween 2,5-dibromothiophene and 2,7-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene (11) or 2,7-di-
ethynyl-9,9-dioctylfluorene (12) under the same conditions as
previously described for functionalized copolymers PDI-PFT
and PDI-PFET. Following the same experimental proce-
dure, reference polymers were precipitated out of the reac-
tion mixtures by addition of methanol, purified by repre-
cipitation from chloroform/methanol and further purified
by washing with acetone in a Soxhlet apparatus.
(27) Wescott, L. D.; Mattern, D. L. J. Org. Chem. 2003, 68, 10058.
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1996, 61, 6906.
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(31) Babudri, F.; Farinola, G. M.; Naso, F. J. Mater. Chem. 2004, 14, 11.
(32) Bunz, U. H. F. In Poly(arylene ethynylene)s: From Synthesis to
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2005; Vol. 177, p 1.
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TABLE 1. Electrochemical Dataa and SEC Characterization of
Donor-Acceptor Copolymers PDI-PFT and PDI-PFET and Their
Respective Reference Copolymers PFT and PFET and Dialkyl-PDI
compd
E1
1
/
E2
1
/
E1
E2
Mn
-1.31 0.33 1.29 30 300
-1.30 0.38 46 900 10 200 4.6
0.35 1.30 75 900 26 200 2.9
0.36 98 200 57 800 1.7
Mw
pd
2red
2red
ox
ox
PDI-PFET
PDI-PFT
PFET
-1.12
-1.12
5 800 5.2
PFT
Dialkyl-PDI -1.11
-1.31
aIn dichloromethane solutions, using platinum as working and counter
electrode and tetrabutylammonium hexafluorophosphate (10-3 M) as
supporting electrolyte. Room temperature; scan rate: 200 mV/s. Values
vs. Fc/Fcþ.
Size exclusion chromatography (SEC, Table 1) in chloro-
form vs polystryrene standards revealed that the polymers
have molecular weights (Mn) of 46 900 g/mol for PDI-PFT
and 30 300 g/mol for PDI-PFET. Polydispersities of 4.6 and
5.2 were obtained, respectively, for the above-mentioned
polymers. Differential scanning calorimetry (DSC) under
nitrogen atmosphere at a heating rate of 10 deg/min showed
a glass transition with an onset at 136 °C for PDI-PFT and
115 °C for PDI-PFET.
The alkyl side chains in the fluorene units and particularly
those at the perylenediimide pendant moieties provide mod-
erate solubility to these copolymers in common organic
solvents, enabling their complete characterization by
NMR, electrochemical, and optical techniques.
FIGURE 1. Cyclic voltammograms of the donor-acceptor poly-
mer PDI-PFET along with reference dialkyl-PDI (in dichloro-
methane solutions, using platinum as working and counter electrode
and tetrabutylammonium hexafluorophosphate (10-3 M) as sup-
porting electrolyte; room temperature; scan rate: 200 mV/s. Values
vs Fc/Fcþ).
copolymers PDI-PFT and PDI-PFET also evidence the
presence in the structure of perylenediimide moieties, as
the characteristic absorption pattern of the perylene skeleton
with bands at 1580 and 1595 cm-1 and the absorption bands
at 1658 and 1698 cm-1 indicating the presence of the imide
group is clearly visible. On the other hand, the good accor-
dance between the experimental and calculated elemental
analysis ensures the good purity of our materials.
The structural similarity of functionalized copolymers
PDI-PFT and PDI-PFET, i.e. they only differ in the spacer,
is responsible for the many common features depicted on
1
their NMR spectra. Thus, the H NMR spectra of copoly-
mers PDI-PFT and PDI-PFET show at low fields the
expected signals of the pendant PDI units (∼8.5 ppm) and
around 5.2 ppm those corresponding to the protons directly
linked to the imide nitrogen positions, similarly to monomer
10 (vide supra). Besides, the aromatic region also displays a
series of relatively broadened signals arising from the fluor-
ene, thiophene, and benzene fragments. The overlap of these
signals prevents an unequivocal assignation. The spectra are
completed with the signals, at high fields, arising from the
alkyl chains of the structure. As would be expected, the 1H
NMR spectra of reference copolymers PFT and PFET only
differ from those of their respective functionalized polymers
in the absence of the signals of the pendant PDI moieties
around 8.5 and 5.2 ppm and its alkyl chains. The 13C NMR
spectra of PDI-PFT and PDI-PFET show a good number of
signals, some of them characteristic of the PDI moiety, for
instance the imide carbonyl at around 164 ppm and the
methylene directly linked to the imide nitrogen around 55
ppm. The signals corresponding to the carbon bridge on the
fluorene moiety can also be seen at around 55 ppm, whereas
the methylene groups directly linked to the carbon bridge are
displayed at around 44 ppm. Additionally, the spectrum of
the ethynylene-containing copolymer PDI-PFET displays
weak signals around 83 ppm which can be assignad to the
triple bond spacer, as is also the case for its reference
copolymer PFET. The 13C NMR spectra are finally com-
pleted with signals corresponding to the rest of the aromatic
carbons and alkyl chains. The 13C NMR spectra of reference
copolymers PFT and PFET are very similar to that of the
parent PDI-containing analogues, but obviously lacking the
signals corresponding to the PDI rings. The FTIR spectra of
Electrochemistry. The electrochemical behavior of the
donor-acceptor copolymers PDI-PFT and PDI-PFET and
their respective reference copolymers PFT and PFET has
been investigated by cyclic voltammetry in dichloromethane
solutions and with platinum as the working and counter
electrode, tetrabutylammonium perchlorate as supporting
electrolyte, and a silver/silver chloride reference electrode.
The measurements were carried out at room temperature
and at a typical scan rate of 200 mV/s and the potentials were
referenced versus the ferrocene/ferrocenium couple. The
cyclic voltammograms of functionalized copolymers PDI-
PFT and PDI-PFET (Figure 1) are not very well resolved,
probably due to their moderate solubility, and show the
amphoteric behavior of these materials. On the negative
scan, the two one-electron reversible reduction waves char-
acteristic of the perylenediimide moiety are clearly visible at
around -1.12 and -1.30 V (Table 1). For comparison, the
reference compound N,N0-(1-hexylheptyl)perylene-3,4:9,10-
bis(dicarboximide), dialkyl-PDI,35 gives peaks at -1.11 and
-1.31 V under the same conditions. Many perylenediimide
derivatives substituted at the imide nitrogen have already
been electrochemically investigated and it has been observed
that the imide substituent has a negligible influence on the
electronic properties of perylenediimides because of the
presence of nodes of the HOMO and LUMO at the imide
nitrogen.36 Thus, perylenediimides can be regarded as closed
chromophoric systems whose electronic properties remain
(35) Demmig, S.; Langhals, H. Chem. Ber. 1988, 121, 225.
(36) Wu€rthner, F. Chem. Commun. 2004, 1564.
5104 J. Org. Chem. Vol. 75, No. 15, 2010

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Gomez et al.
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FIGURE 3. Fluorescence spectra of PDI-PFET along with refer-
ences PFET and dialkyl-PDI, in dichloromethane. Inset: Magnified
fluorescence spectrum of PDI-PFET.
FIGURE 2. Absorption spectra of PDI-substituted polymers PDI-
PFT and PDI-PFET along with references PFT, PFET, and dialkyl-
PDI in dichloromethane solutions.
350-450 nm region, arising from π-π* transitions in the
conjugated polymeric backbone as it can be inferred by
comparison to the reference polymers. Additionally, the
absorption spectra of PDI-substituted polymers show the
characteristic bands arising from the presence of the PDI side
groups, with maxima at 526, 490, and 460 nm in dichloro-
methane.
Fluorescence emission spectra of PDI-functionalized
polymers and their respective references were measured in
diluted dichloromethane solutions at fixed optical density
using the excitation wavelength corresponding to the ab-
sorption maxima of the conjugated backbone. The fluores-
cence properties of the polymer backbone in PDI-substituted
copolymers PDI-PFET and PDI-PFT are greatly affected by
the presence of the perylenediimide moiety. Thus, a strong
quenching (>90%) of both the conjugated backbone fluor-
escent emission and the perylenediimide pendant groups was
observed in these materials in comparison to the fluorescence
spectrum of references PFET and PFT (Figure 3).
To explain this strong fluorescence quenching, two plausible
explanations arise. On the one hand, one can expect a con-
tribution of energy transfer from the π-conjugated backbone
as it has a lower optical bandgap than the perylenediimide
moiety, i.e., there is spectral overlap between the absorption
spectrum of the p-conjugated backbone and the fluorescence
spectrum of the PDI fragment. On the other hand, the
electronic energy difference between the oxidation and reduc-
tion potential [e(Eox - Ered)] of the pendant donor-acceptor
polymers is about 1.5-1.7 eV. Hence, photoinduced electron
transfer from the conjugated backbone to the pendant electron
accepting PDI moieties seems to be an energetically favorable
relaxation process of the excited state for these polymers.
To find out if electron transfer is a likely process for PDI-
PFET and PDI-PFT we can use the Weller eq 1.40 We can use
the oxidation potentials (þ0.33 and þ0.63 V vs Fc/Fcþ, respec-
tively), the reduction potentials (-1.12 V vs Fc/Fcþ in both
cases), and the energy of the lowest excited singlet state, S1,
determined from the photoluminescence spectra of reference
polymers (2.60 and 2.48 eV for PDI-PFET and PDI-PFT,
unaltered by the imide substituent.37 In this regard, in
functionalized copolymers PDI-PFT and PDI-PFET no
electronic influence of the perylenediimide moiety on the
polymer main chain is expected as it is also observed in the
UV-vis spectra (vide infra).
Toward positive values, the electrochemical response of
functionalized polymers PDI-PFET and PDI-PFT is in
general not well-resolved. However, a broad quasireversible
oxidation wave can be identified in both cases, with an onset
at around þ0.33 V for PDI-PFET and þ0.38 V for PDI-
PFT. Reference copolymer PFET shows a broad and poorly
resolved oxidation wave with onset at around þ0.35 V.38 A
similar electrochemical behavior has been recorded for
copolymer PFT (0.36 V).39 For polymers PDI-PFET and
PFET, an additional quasireversible oxidation wave around
1.29 V has been observed, probably arising from the ethy-
nylene bonds.
The similar values observed for the oxidation and reduc-
tion processes of the two electroactive moieties in PDI-PFET
and PDI-PFT compared to the reference materials suggest
that there is no significant ground state interaction between
the electron-donating polymer backbone and the electron-
accepting PDI moieties.
Optical Properties. The UV-vis absorption spectra of the
donor-acceptor copolymers PDI-PFT and PDI-PFET to-
gether with their respective references PFT, PFET, and
dialkyl-PDI in diluted dichloromethane solutions are de-
picted in Figure 2. The absorption spectrum of the donor-
acceptor polymers consists of the approximate superposition
of the absorption features of its constitutive units (i.e., the
conjugated backbone and the pendant perylenediimide
units), confirming the minimal interaction between the chro-
mophores in the ground state, in agreement with the electro-
chemical data. The spectra display absorption bands in the
(37) Langhals, H.; Demmig, S.; Huber, H. Spectrochim. Acta 1998, 44A,
1189.
(38) A value of þ0.63 V vs Ag/Agþ has been reported for the oxidation
onset of a similar PFET in film: Zhan, X.; Liu, Y.; Yu, G.; Wu, X.; Zhu, D.;
Sun, R.; Wang, D.; Epstein, A. J. J. Mater. Chem. 2001, 11, 1606.
(39) A value of þ0.97 V vs Ag/Agþ has been reported for the oxidation
onset of PFT in film: Ranger, M.; Leclerc, M. Can. J. Chem. 1998, 76, 1571.
(40) Weller, A. Z. Phys. Chem. Neue Folge 1982, 133, 93.
J. Org. Chem. Vol. 75, No. 15, 2010 5105

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Gomez et al.
JOCArticle
respectively) to predict the Gibbs free energy for electron
transfer from the conjugated backbone to the PDI moieties
on the basis of the Weller equation:
unless otherwise specified. Solvents and reagents were dried by
the usual methods prior to use and typically used under inert gas
atmosphere.
2,5-Dibromo-3-(40-cyanophenyl)thiophene (2). Under argon
atmosphere, a solution of N-bromosuccinimide (2.48 g, 13.9
mmol) in 15 mL of anhydrous N,N-dimethylformamide is added
dropwise to a solution of 40-thien-3-ylbenzonitrile (1) (1.1 g, 5.9
mmol) in 25 mL of anhydrous N,N-dimethylformamide. The
reaction crude is allowed to react at room temperature for 24 h
and water is added slowly. The resulting mixture is stirred for 1 h
and extracted with diethyl ether. The combined organic extracts
are dried over anhydrous magnesium sulfate and vacuum
evaporated. The remaining residue is purified by column chro-
matography (silica gel, hexane/dichloromethane 1/1) to give 2,5-
dibromo-3-(40-cyanophenyl)thiophene (2) as a white solid in
96% yield.
ΔGCS ¼ - e½EoxðDÞ - EredðAÞꢀ þ EðS1Þ
ꢀ
ꢁꢀ
ꢁ
e2
e2
1
1
1
1
þ
þ
þ
-
ð1Þ
4πε0εsRcc 8πε0 rþ r-
εref εs
The radius of the PFET and PFT radical cations and the
-
PDI radical anion are set to rþ = 5.0 A and r = 4.7 A,
˚
˚
respectively,41,42 whereas the center-to-center chromophore
˚
distance (Rcc) was set at 10 A, which is the maximum distance
that can be reached.43 The resulting values for ΔGCS (-1.15 eV
for PDI-PFET and -0.73 eV for PDI-PFT) predict that
electron transfer from the conjugated polymer backbone to
the accepting PDI units competes with energy transfer.
Mp 98 °C; 1H NMR (CDCl3, 200 MHz) δ 7.66 (AA0BB0 system,
2H, J1 = 8.57 Hz, J2 = 1.94 Hz), 7.55 (AA0BB0 system, 2H, J1 =
8.57 Hz, J2 = 1.94 Hz), 6.96 (s, 1H); 13C NMR (CDCl3, 50 MHz) δ
138.3, 132.2, 130.9, 129.1, 112.2; FTIR (KBr, cm-1) ν 2926, 2855,
2227, 1661, 1499, 1020, 596; MS (EI, % I) 343 (Mþ, 100), 183 (65).
Anal. Calcd for C11H5NSBr2: C, 38.51; H, 1.47; N, 4.08; S, 9.35.
Found: C, 38.32; H, 1.36; N, 4.02; S, 9.18.
Conclusions
In this article we have presented a versatile route to the
synthesis of polymers functionalized with electroactive per-
ylenediimide units, which can be extended to other different
moieties. Electrochemical investigations show that both
electroactive units, the electron donor polymeric chain and
the electron acceptor perylenediimide unit, preserve their
nature in the ground state, which is confirmed by UV-vis
spectroscopy. Fluorescence spectroscopy evidence a strong
quenching of the intense fluorescence emission of the pen-
dant perylenediimide, which is in accordance with the energy
and/or electron transfer predicted by the Weller equation.
Work is in progress to further investigate the photophysical
processes taking place after the irradiation of these materials
and their potential applications, as well as the introduction
of other useful pendant structures.
2,5-Dibromo-3-(40-formylphenyl)thiophene (3). To a refluxing
solution of 2,5-dibromo-3-(40-cyanophenyl)thiophene (2) (1.96 g,
5.7 mmol) in 90 mL of dry dichloromethane is added a
diisobutylaluminium hydride dichloromethane solution (1M,
6.0 mL, 6.0 mmol) dropwise over a period of 2 h under argon
atmosphere. The solution is allowed to react at reflux tempera-
ture for 18 h and cooled to room temperature. Methanol is then
carefully added until the reaction crude becomes a thick suspen-
sion. After careful addition of water, the reaction crude is
treated with concentrated hydrochloric acid until complete
solution and extracted with chloroform. The combined organic
extracts are then washed with water and dried over anhydrous
magnesium sulfate. After vacuum evaporation of the solvent,
the remaining residue is purified by column chromatography
(silica gel, hexanes/dichloromethane 1/1) to afford 2,5-dibromo-
3-(40-formylphenyl)thiophene (3) as a white solid in 93% yield.
Experimental Section
1
Mp 76 °C; H NMR (CDCl3, 200 MHz) δ 9.99 (s, 1H), 7.88
(AA0BB0 system, 2H, J1 = 8.45 Hz, J2 = 1.82 Hz), 7.62 (AA0BB0
system, 2H, J1 = 8.45 Hz, J2 = 1.82 Hz), 6.99 (s, 1H); 13C NMR
(CDCl3, 50 MHz) δ 191.5, 131.2, 129.8, 129.0; FTIR (KBr, cm-1) ν
2923, 2834, 1682, 1604, 1423, 1214, 827, 811; MS (EI, % I) 346
(Mþ,100), 238 (32), 158 (26), 113 (22). Anal. Calcd for C11H6-
Br2SO: C, 38.18; H, 1.75; S, 9.26. Found: C, 38.36; H, 1.64; S, 9.32.
2,5-Dibromo-3-[40-(hydroxymethyl)phenyl]thiophene (4). Sodium
borohydride (92 mg, 2.43 mmol) is added portionwise to a solution
of 2,5-dibromo-3-(40-formylphenyl)thiophene (3) in 30 mL of
anhydrous tetrahydrofuran under argon atmosphere. The reaction
crude is stirred at room temperature for 24 h, and water is added.
The mixture is extracted with diethyl ether and the combined
organic extracts are dried over magnesium sulfate. After vacuum
evaporation of the solvent, the residue is purified by a short column
chromatography (silica gel, dichloromethane) to afford 2,5-dibro-
mo-3-[40-(hydroxymethyl)phenyl]thiophene (4) in 94% yield as a
white solid.
General. This section contains details for the synthesis of
the reported novel compounds. General synthetic methods
and the structural characterization of novel compounds des-
cribed in this article are contained in the Supporting Informa-
tion. 40-Thien-3-ylbenzonitrile (1),24 poly[2,7-(9,9-dioctylfluo-
rene)-alt-2,5-thiophene] (PFT),22 N-(9-octylnonyl)perylene-3,4:
9,10-tetracarboxylic acid monoimide monoanhydride (8),44 2,7-
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dihexyl-
fluorene (11),45 2,7-diethynyl-9,9-dihexylfluorene (13),46 and
N,N0-(1-hexylheptyl)perylene-3,4:9,10-bis(dicarboximide) (dialkyl-
PDI)47 were prepared following previously reported synthetic
procedures. All other chemicals were purchased from commer-
cial sources and used as received without further purification
(41) It is difficult to estimate a radius for the PFET and PFT cations. We
˚
have used a radius of 5 A, analogous to previous radii for conjugated systems
of similar length, see ref 20a and: Peeters, E.; van Hal, P. A.; Knol, J.; Brabec,
C. J.; Sariciftci, N. S.; Hummelen, J. C.; Janssen, R. A. J. J. Phys. Chem. B
2000, 104, 10174.
1
Mp 134 °C; H NMR (CDCl3, 200 MHz) δ 7.49 (AA0BB0
system, 2H, J1 = 8.45 Hz, J2 = 2.01 Hz), 7.62 (AA0BB0 system,
2H, J1 = 8.45 Hz, J2 = 2.01 Hz), 7.00 (s, 1H), 4.74 (s, 1H), 4.71
(s, 1H); 13C NMR (CDCl3, 50 MHz) δ 140.5, 133.2, 131.4, 128.5,
126.8, 111.1, 107.6, 64.8; FTIR (KBr, cm-1) ν 3384, 2922, 2853,
1635, 1506, 1423, 1409, 1043, 1017, 983, 811; MS (EI, % I):348
(Mþ, 100), 238 (47), 160 (55). Anal. Calcd. for C11H8Br2SO: C,
37.96; H, 2.32; S, 9.22. Found: C, 37.86; H, 2.27; S, 9.36.
2,5-Dibromo-3-[40-(bromomethyl)phenyl]thiophene (5).25 To
a solution of 2,5-dibromo-3-[40-(hydroxymethyl)phenyl]thiophene
(4) (770 mg, 2.2 mmol) and triphenylphosphine (864 mg, 3.3 mmol)
(42) The radius of the PDI anion was estimated from the density of N,N0-
dimethylperylene-3,4:9,10-tetracarboxylic diimide determined from the
ꢀ
X-ray crystallographic data: Hadicke, E.; Graser, F. Acta Crystallogr. C
1986, 42, 189.
(43) Estimated by semiempirical PM3 calculations, assuming a confor-
mation with both electroactive units as separated as possible.
(44) Langhals, H.; Karolin, J.; Johanssonet, B. A. J. Chem. Soc., Faraday
Trans. 1998, 94, 2919.
(45) Dudek, S. P.; Pouderoijen, M.; Abbel, R.; Schenning, A. H. P.;
Meijer, E. W. J. Am. Chem. Soc. 2005, 127, 11763.
(46) Lee, S. H.; Nakamura, T.; Tsutsui, T. Org. Lett. 2001, 13, 2005.
(47) Demmig, S.; Langhals, H. Chem. Ber. 1988, 121, 225.
5106 J. Org. Chem. Vol. 75, No. 15, 2010

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Gomez et al.
JOCArticle
in 25 mL of anhydrous tetrahydrofuran, a solution of N-bromo-
succinimide (587 mg, 3.3 mmol) in 10 mL of anhydrous tetra-
hydrofuran is slowly added over 20 min, under argon atmo-
sphere and at room temperature. After 1 h, the reaction crude is
filtered, the filtrate is evaporated under vacuum, and the residue
is purified by column chromatography (silica gel, hexanes/
dichloromethane 8/2) to afford 2,5-dibromo-3-[40-(bromomethyl)-
phenyl]thiophene (5) in 96% yield as a white solid.
853; MS (FAB) 628 (Mþ). Anal. Calcd for C41H44N2O4: C,
78.31; H, 7.05; N, 4.45. Found: C, 78.35; H, 7.00; N, 4.56.
2,5-Dibromothiophene Monomer 10. By Direct Imidation.
A mixture of N-(9-octylnonyl)perylene-3,4:9,10-tetracarboxy-
lic acid bisimide (8) (210 mg, 0.33 mmol), 2,5-dibromo-
3-[40-(aminomethyl)phenyl]thiophene (7) (476 mg, 1.32 mmol),
Zn(OAc)2 (48 mg, 0.26 mmol), and 2 g of imidazol is heated at
180 °C during 2 h under argon atmosphere. After cooling to
room temperature, the mixture is treated with 100 mL of an
aqueous 10% hydrochloric acid solution. The solid is collected
by filtration, washed with another portion of acid solution, then
thoroughly washed with water and finally with methanol. The
remaining solid is dried under vacuum and further purified by
flash chromatography (silica gel, dichloromethane) to yield 10
as a deep red solid in 84% yield.
Mp 65 °C; 1H NMR (CDCl3, 200 MHz) δ 7.65 (m, 4H), 7.15
(s, 1H), 4.53 (s, 2H); 13C NMR (CDCl3, 50 MHz) δ 141.3, 137.6,
134.2, 131.6, 129.2, 128.9, 111.5, 108.1, 33.0; FTIR (KBr, cm-1
)
ν 2924, 2852, 1610, 1502, 1420, 1407, 1226, 1202, 1019, 806, 604;
MS (EI, % I) 411 (Mþ, 75), 330 (100), 250 (43), 171 (96), 127
(63). Anal. Calcd for C11H7Br3S: C, 32.15; H, 1.72; S, 7.80.
Found: C, 32.26; H, 1.95; S, 7.62.
2,5-Dibromo-3-(40-hydroxyiminophenyl)thiophene (6). A solu-
tion of 2,5-dibromo-3-(40-formylphenyl)thiophene (3) (1.0 g, 2.9
mmol), hydroxylamine hydrochloride (800 mg, 11 mmol), and
pyridine (1 mL) in 35 mL of absolute methanol is heated at
reflux temperature for 24 h under argon atmosphere. After
vacuum evaporation of the solvent, the remaining residue is
treated with water and chloroform. The organic phase is dried
over anhydrous magnesium sulfate and evaporated under va-
cuum, to yield 2,5-dibromo-3-(40-hydroxyiminophenyl)thio-
phene (6) in 98% yield as a white solid that can be used without
additional purification.
By N-Alkylation. Under argon atmosphere, a mixture of
N-(9-octylnonyl)perylene-3,4:9,10-tetracarboxylic acid bisimide
(9) (150 mg, 0.23 mmol), 2,5-dibromo-3-[40-(bromomethyl)phe-
nyl]thiophene (5) (294 mg, 0.71 mmol), potassium carbonate (317
mg, 2.3 mmol), and a catalytic amount of sodium iodide in 30 mL of
anhydrous N,N-dimethylformamide are heated at 130 °C for 12 h
The reaction crude is allowed to cool to room temperature and then
water and a 1 M aqueous hydrochloric acid solution are added. The
resulting precipitate is filtered and thoroughly washed with water
and methanol. The collected solid is dried under vacuum and
purified by column chromatography (silica gel, dichloromethane)
to afford 2,5-dibromothiophene monomer 10 as a deep red solid in
86% yield.
Mp 176 °C; 1H NMR (DMSO, 200 MHz) δ 11.33 (s, 1H), 8.12
(s, 1H), 7.62 (AA0BB0 system, 2H, J = 8.46 Hz), 7.53 (AA0BB0
system, 2H, J = 8.46 Hz), 7.36 (s, 1H); 13C NMR (DMSO, 50
MHz) δ 147.7, 141.4, 134.0, 132.9, 132.3, 128.8, 126.6, 111.3,
107.7; FTIR (KBr, cm-1) ν 3424, 3286, 2920, 2852, 1631, 1608,
1017, 976, 840, 812; MS (EI, % I) 361 (Mþ, 100), 342 (25),
238 (26), 157 (20), 113 (16). Anal. Calcd for C11H7Br2SON: C,
36.59; H, 1.95; N, 3.88; S, 8.88. Found: C, 36.36; H, 1.87, N,
3.66; S, 8.72.
1
Mp >200 °C; H NMR (CDCl3, 200 MHz) δ 8.66-8.58 (m,
8H), 7.63-7.33 (m, 11H), 5.43 (s, 2H), 5.21 (s, 1H), 2.27 (br s, 4H),
1.90 (br s, 8H), 1.77-1.69 (br m, 8H), 1.36-1.04 (m, 36H), 0.85 (t,
12H); 13C NMR (CDCl3, 75 MHz) δ164.9 (w), 163.7, 142.0, 137.3,
135.2, 134.5, 133.8, 132.00, 131.9, 131.4, 129.8, 129.7, 129.0, 126.7,
126.6, 124.5, 123.5, 123.3, 111.6, 108.1, 55.3, 43.8, 32.8, 32.2, 30.00,
29.9, 29.7, 27.4, 23.0, 14.5; FTIR (KBr, cm-1) ν 2924, 2854, 1698,
1658, 1595, 1580, 1337, 851; MS (FAB): 958 (Mþ), 721. Anal.
Calcd for C52H50Br2N2O4S: C, 65.14; H, 5.25; N, 2.92; S, 3.34.
Found: C, 64.86; H, 5.61; N, 2.48; S, 3.07.
2,5-Dibromo-3-[40-(aminomethyl)phenyl]thiophene (7). Under
argon atmosphere, lithium aluminum hydride (421 mg, 11
mmol) is added portionwise during 2 h to a refluxing solution
of 2,5-dibromo-3-(40-hydroxyiminophenyl)thiophene (6) (1.0 g,
2.8 mmol) in 45 mL of anhydrous toluene. The reaction crude is
refluxed for 24 h, allowed to cool to room temperature, and first
methanol, then water, and finally a 1 M hydrochloric acid
aqueous solution are slowly added. The resulting mixture is
then extracted with chloroform. The combined organic extracts
are washed with water and dried over anhydrous magnesium
sulfate. Vacuum evaporation of the solvent yields 2,5-dibromo-
3-[40-(aminomethyl)phenyl]thiophene (7) in 86% yield, which
was used for the next step without further purification.
N-(9-Octylnonyl)perylene-3,4:9,10-tetracarboxylic Acid Bisi-
mide (9). Under argon atmosphere, a well-stirred suspension of
N-(9-octylnonyl)perylene-3,4:9,10-tetracarboxylic acid monoi-
mide monoanhydride (8) (315 mg, 0.5 mmol) and urea (4.5 g, 75
mmol) in 45 mL of anhydrous N,N-dimethylformamide is
heated at reflux temperature for 24 h. After cooling to room
temperature, water and an 1 M aqueous hydrochloric acid
solution are added to the reaction crude. The resulting precipi-
tate is filtered, and thoroughly washed with water and methanol.
The collected solid is then dried under vacuum and purified by
column chromatography (silica gel, dichloromethane/methanol
9.5/0.5) to afford N-(9-octylnonyl)perylene-3,4:9,10-tetracar-
boxylic acid bisimide (9) as a deep red solid in 64% yield.
Mp >200 °C; 1H NMR (CDCl3, 200 MHz) δ 8.55 (br s, 8H),
5.11 (br m, 1H), 2.18 (br m, 2H), 1.81 (br m, 2H), 1.55 (s, 6H),
1.22-1.14 (m, 18H), 0.75 (t, 6H, J = 6.62 Hz); 13C NMR
(CDCl3, 75 MHz) δ 164.9 (w), 163.7 (w), 163.4, 135.7, 134.4,
132.2, 131.6, 131.1, 129.8, 127.2, 126.6, 124.6, 123.7, 123.3,
123.2, 55.3, 32.8, 32.2, 29.9, 29.9, 29.7, 27.4, 23.0, 14.5; FTIR
(KBr, cm-1) ν 2924, 2854, 1697, 1658, 1594, 1578, 1343, 1272,
Polymer PDI-PFT. A mixture of 2,5-dibromothiophene
monomer 10 (95 mg, 0.1 mmol), 2,7-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene (11) (63 mg, 0.1
mmol), and tetrakis(triphenylphosphine)palladium (0) (2 mg,
2 ꢁ 10-3 mmol) in a deareated mixture of 22 mL of tetrahy-
drofuran and 18 mL of a 2 M potassium carbonate aqueous
solution was heated at reflux temperature under argon atmo-
sphere for 72 h. The thick reaction mixture was allowed to cool
to room temperature and methanol was added to give an
abundant precipitate. The solid was collected, dissolved in
chloroform, and precipitated out of methanol again. The poly-
mer was further purified by washing with acetone in a Soxhlet
apparatus for 24 h to remove small molecules, oligomers, and
catalyst residues. The final product was dried under vacuum to
afford polymer PDI-PFT as a deep red solid in 82% yield.
1H NMR (CDCl3, 200 MHz) δ 8.68-8.46 (br m, 8H),
7.68-7.50 (AA0BB0 system, 2H, J = 8.19 Hz), 7.39 (AA0BB0 sys-
tem, 2H, J = 8.19 Hz), 6.88 (m, 1H), 5.33 (s, 2H), 5.12 (br m, 1H),
2.17 (b, 8H), 1.82 (s, 12H), 1.13-0.96 (m, 36H), 0.75 (br s, 12H);
13C NMR (CDCl3, 125 MHz) δ 163.8, 142.4, 136.3, 135.7, 135.7,
135.2, 134.6, 132.0, 131.5, 131.5, 130.1, 129.9, 129.6, 129.5, 127.0,
126.7, 126.6, 123.6, 123.3, 120.7, 110.6, 55.5, 55.2, 53.8, 43.9, 40.7,
32.8, 32.2, 32.2, 30.4, 30.1, 30.0, 29.9, 29.6, 27.4, 24.1, 23.0, 22.9,
14.5; FTIR (KBr, cm-1) ν 2924, 2852, 1697, 1658, 1594, 1333, 811.
Anal. Calcd for C81H90N2O4S: C, 81.92; H, 7.64; N, 2.36; S, 2.70.
Found: C, 82.03; H, 7.42; N, 2.64; S, 2.56. SEC (vs PS) Mn =46900
g/mol; Mw = 10 200 g/mol; pd = 4.6.
Polymer PDI-PFET. A mixture of 2,5-dibromothiophene
monomer 10 (96 mg, 0.1 mmol), 2,7-diethynyl-9,9-dioctylfluorene
(12) (44 mg, 0.1 mmol), bis(triphenylphosphine)palladium(II)
J. Org. Chem. Vol. 75, No. 15, 2010 5107

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Gomez et al.
JOCArticle
dichloride (5 mg, 4.4 ꢁ 10-3 mmol), copper iodide (6 mg, 0.03
mmol), triphenylphosphine (30 mg, 0.11 mmol), and diisopropy-
lamine (2.0 mL) in 35 mL of deareated anhydrous toluene was
heated at reflux temperature for 72 h under argon atmosphere. The
reaction mixture was allowed to cool to room temperature and
slowly added into methanol to give a precipitate. The solid
was collected, dissolved in chloroform, and precipitated out of
methanol again. The polymer was further purified by washing
with acetone in a Soxhlet apparatus for 24 h to remove small
molecules, oligomers, and catalyst residues. The final product was
dried under vacuum to afford polymer PDI-PFET as a deep red
solid in 80% yield.
mixture was allowed to cool to room temperature and slowly
added into methanol to give a precipitate. The solid was
collected, dissolved in chloroform, and precipitated out of
methanol again. The polymer was further purified by washing
with acetone in a Soxhlet apparatus for 24 h to remove small
molecules, oligomers, and catalyst residues. The final product
was dried under vacuum to afford polymer PFET as a yellow
solid in 94% yield.
1H NMR (CDCl3, 500 MHz) δ 7.71 (s, 2H), 7.50 (br s, 4H),
7.29 (s, 2H), 2.01 (s, 1H, 4H), 1.67 (s, 4H), 1.24 (s, 12H), 0.85 (s,
8H), 0.64 (s, 6H); 13C NMR (CDCl3, 125 MHz) δ 151.6, 141.9,
141.4, 141.2, 132.5, 132.3, 132.1, 131.1, 130.6, 127.7, 127.6,
127.4, 126.2, 125.6, 125.2, 121.8, 121.7, 121.0, 120.7, 120.5,
113.5, 95.6, 95.5, 83.4, 83.2, 55.7, 40.7, 32.2, 30.4, 29.6, 24.1,
23.0, 14.5; FTIR (KBr, cm-1) ν 2925, 2852, 1636, 1462, 1417,
820, 799. Anal. Calcd for C52H50Br2N2O4S: C, 97.36; H, 1.08; S,
0.82. Found: C, 97.66; H, 0.96; S, 1.02. SEC (vs PS) Mn = 75 900
g/mol; Mw = 26 200 g/mol; pd = 2.9.
1H NMR (CDCl3, 200 MHz) δ 8.70-8.63 (br m, 8H),
7.88-7.47 (br m, 11H), 5.50 (br s, 2H), 5.12 (br s, 1H), 2.26
(br m, 2H), 1.97 (br m, 4H), 1.58 (s, 6H), 1.13-0.98 (m, 24H),
0.74 (s, 12H); 13C NMR (CDCl3, 125 MHz) δ 163.8, 151.7,
142.4, 141.0, 137.7, 135.4, 134.7, 134.6, 132.1, 132.1, 131.1,
131.0, 129.8, 128.5, 127.4, 126.9, 126.3, 126.0, 124.5, 123.9,
123.6, 123.4, 120.5, 82.1, 55.7, 55.2, 43.9, 40.6, 32.8, 32.2, 32.2,
30.4, 29.9, 29.6, 27.4, 24.1, 23.0, 14.5; FTIR (KBr, cm-1) ν 2926,
2855, 1699, 1661, 1596, 1466, 1439, 1406, 1337, 853. Anal. Calcd
for C85H90N2O4S: C, 82.62; H, 7.34; N, 2.27; S, 2.59. Found: C,
82.36; H, 7.55; N, 2.07; S, 2.23. SEC (vs PS) Mn = 30 300 g/mol;
Acknowledgment. We thank the MCyT (reference
CTQ2007-60459) and a Comunidad de Madrid-Universidad
Complutense de Madrid joint project (CCG08-UCM/PPQ-
3975) for financial support. Dr. M. Ramos (Universidad Rey
Juan Carlos) is acknowledged for her assistance with the
DSC and GPC characterization.
M
w = 5 800 g/mol; pd = 5.2.
Polymer PFET. A mixture of 2,5-dibromothiophene (48 mg,
0.2 mmol), 2,7-diethynyl-9,9-dioctylfluorene (12) (88 mg, 0.2
mmol), bis(triphenylphosphine)palladium(II) dichloride (8 mg,
6.5 ꢁ 10-3 mmol), copper iodide (9 mg, 0.03 mmol), triphenyl-
phosphine (60 mg, 0.2 mmol), and diisopropylamine (2.0 mL) in
35 mL of deareated anhydrous toluene was heated at reflux
temperature for 72 h under argon atmosphere. The reaction
Supporting Information Available: General experimental
procedures and compound characterization for all new com-
pounds along with copies of key spectra. This material is
available free of charge via the Internet at http://pubs.acs.org.
5108 J. Org. Chem. Vol. 75, No. 15, 2010