Towards crystal engineering of solid-state polymerization in dibromothiophenes

Article abstract of DOI:10.1039/b822997j

Three new dibromothiophene monomers for solid-state polymerization have been synthesized and their solid-state structure was studied by X-ray crystallography. The substituents in the thiophene ring are introduced to induce an anti-orientation of the monom

Full text of DOI:10.1039/b822997j

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Towards crystal engineering of solid-state polymerization in
dibromothiophenes†
a
Marc Lepeltier, Jonathan Hiltz, Tobias Lockwood, Francine Belanger-Gariepy and
a
a
b
ꢀ
ꢀ
a
*
Dmitrii F. Perepichka
Received 23rd December 2008, Accepted 30th April 2009
First published as an Advance Article on the web 10th June 2009
DOI: 10.1039/b822997j
Three new dibromothiophene monomers for solid-state polymerization have been synthesized and their
solid-state structure was studied by X-ray crystallography. The substituents in the thiophene ring are
introduced to induce an anti-orientation of the monomer to resemble the s-trans structure of the
polythiophene. The details of the solid-state packing of the new monomers are compared to those of
the previously studied 2,5-dibromo(3,4-ethylenedioxythiophene) and related to their reactivity and to
the conductivity of the resulting polymers. The same polymers have also been prepared by
electrooxidative polymerization on the surface of an electrode.
the high intrinsic conductivity of PEDOT, and poses problems
Introduction
for long-term device operation.
Conjugated polymers have been a focus of attention in organic
materials chemistry for the last three decades, due to their
conductive properties that are unusual for organic compounds,
and numerous applications in electronic and optoelectronic
devices, including organic light-emitting diodes (OLEDs),
photovoltaic cells (OPVs), field-effect transistors (OFETs), and
chemical and bio-sensors.1 Among all intrinsically-conductive
polymers, polythiophenes and particularly poly(3,4-ethyl-
enedioxythiophene) (PEDOT) stand as the most industrially
important (and commercially successful) materials, owing to
their very high conductivity and unsurpassed stability.2 One of
the major problems for application of conducting polymers is
their very low solubility, which hampers processing. The solu-
bility of a neutral (non-doped) polymer can be enhanced by
introducing long alkyl-chain substituents, although these also act
as insulators, effectively ‘‘diluting’’ the conductive part (conju-
gated backbone) of the material. For PEDOTs, a clever way to
bring the polymer into solution, introduced by the Bayer com-
pany,2a was to prepare the polymer in the presence of a poly-
electrolyte (polystyrene sulfonic acid, PSS) which, acting as
a doping counter-anion, makes the positively charged doped
PEDOT soluble/dispersable in water. The resulting suspension,
sold as Baytron P, is widely used to produce uniform conductive
films which are currently used in OLEDs, OPVs, anti-static
coatings, sensors, etc. Despite the tremendous commercial
success of Baytron P, a possible phase separation between the
conductive PEDOT and insulating PSS chains3 has been limiting
An intriguing alternative for insoluble conjugated polymers is to
process a (soluble) precursor and to produce the conjugated polymer
directly in the solid state. Sotzing and co-workers have recently
demonstrated solid-state conversion of a soluble thiophene-silane
pre-polymer into a highly conducting PEDOT by electro-
desilanation reaction;4 however, the pre-polymer has to be deposited
on a surface of an electrode, which somewhat limits its applicability.
The pioneering work on topochemical solid-state synthesis of
conjugated polymers was done by Wegner on poly(diacetylenes),5
and MacDiarmid, Heeger and co-workers on poly(sulfur
nitride).6 In both cases, the spontaneous polymerization does not
require any reagent or electrode to occur and is favored by specific
arrangement/proximity of atoms in the monomer crystal struc-
ture (and dramatically suppressed in disordered (liquid) state). In
some cases a single crystal-to-single crystal polymerization has
been observed.7 The possibility of achieving crystalline order in
conjugated polymers is probably the most attractive feature of the
solid-state polymerization (SSP).
A few years ago, Wudl and co-workers showed that the concept
of spontaneous topochemical SSP can be realized in the poly-
thiophene series, and that highly conductive semi-crystalline
PEDOTs can be prepared by simple heating of 2,5-dibromo(3,4-
ethylenedioxy)thiophene (DBEDOT) and 2,5-diiodo(3,4-ethyl-
enedioxy)thiophene (DIEDOT).8 Similar behavior was earlier
observed (although not as a topochemical process) by Audebert and
Bidan for dibromopyrroles,9 and further evidence for SSP in halo-
genated electron-rich heteroaromatics was found by Skabara et al.
for 2,5-dibromo(3,4-alkylidenedithio)thiophenes (DBADTTs)10
and 2,5-dibromo(3,4-ethylenediseleno)thiophene,11 and Bendikov
et al. for 2,5-dibromo(3,4-ethylenedioxy)selenophene (DBE-
DOS).12
aDepartment of Chemistry, McGill University, 801 Sherbrooke str. West,
Montreal, H3A 2K6, Quebec, Canada. E-mail: dmitrii.perepichka@
mcgill.ca
bDeꢀpartment de Chimie, Universiteꢀ de Montreꢀal, Montreꢀal, H3C 3J7,
Queꢀbec, Canada
† Electronic supplementary information (ESI) available: Details of X-ray
crystallographic analysis; CP-MAS 13C NMR spectra for polymers B and
C; SEM micrographs of polymer A. Crystal structure data for 4a (CCDC
722202), 4b (CCDC 722203) and 4c (CCDC 722204) in CIF format see
DOI: 10.1039/b822997j
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However, the mechanism of the topochemical SSP in diha-
lothiophenes is not well understood. It was suggested that close
intermolecular halogen/halogen contacts13 are important for
the SSP which propagates along the p-stack of the monomer.,8b
Similar conclusions on the importance of halogen/halogen
contacts and p-stacking were drawn by Skabara and co-
workers for SSP of DBADTT derivatives.10 In DBEDOT, the
C2/C5 separation between the adjacent thiophene monomers
Results and discussion
Synthesis
The 3,4-ethylenedioxythiophene (EDOT) derivatives 1a–c were
prepared by Mitsunobu coupling of diethyl 3,4-dihydrox-
ythiophene-2,5-dicarboxylate with the corresponding diols
(meso-butan-2,3-diol (a), meso-tetrahydrofuran-3,4-diol (b) or
meso-tetrahydrothiophen-3,4-diol (c)) as previously reported for
other 1,2-diols (Scheme 1).16 The mechanism of the Mitsunobu
reaction involves a clean SN2 process that inverts the configu-
ration of chiral secondary alcohols.17 Accordingly, the structure
of the formed ethers (both substituents on the same side of the
dioxane ring) is dictated by the meso-configuration of the starting
alcohols, and no sign of racemization was observed in the NMR
spectra. The steric hindrance in the diol generally lowers the yield
of the Mitsunobu reaction,17,18 but acceptable yields of 33% to
70% were obtained for compounds 1a–c.
ꢁ
of the same stack (4.09 A) are the closest possible contacts
between the reacting centers. However, the all-syn (parallel)
orientation of the DBEDOT in the stack is in contrast to
the necessary all-anti conformation of the PEDOT, which
requires a significant rotational displacement of the monomer
during the SSP and could limit the structural order in the
resulting polymer.
With this in mind, we have synthesized and studied the SSP of
functionalized DBEDOT monomers. Bulky substituents in the
ethylenedioxy bridge were introduced to disfavor the parallel
molecular orientation in the stack, which could promote an
antiparallel (all-anti) stacking. In the present paper we describe
the synthesis of EDOT monomers 3a–c and their electro-
polymerization, and solid-state polymerizations of the bromi-
nated derivatives 4a–c to produce disubstituted PEDOT
polymers A–C. The possible effects of the solid-state packing of
4a–c on their SSP are analyzed by X-ray crystallography. We
also note that, despite a plethora of studies on mono-substituted
PEDOT derivatives,14 the only example of a disubstituted
PEDOT reported to date is electropolymerized 3,4-(cyclo-
hexyliden-1,2-dioxy)thiophene.15
Saponification of the diethyl esters 1a–c followed by copper
chromite-catalyzed decarboxylation of the obtained acids and
bromination with N-bromosuccinimide leads to the brominated
derivatives 4a–c with moderate total yields (over these three
steps) of 67%, 35% and 72%, respectively.8,16 Alternatively,
compounds 4a,b have been obtained with yields of 44% and 41%,
respectively, in a one-pot brominating decarboxylation reaction
by simultaneous action of sodium hydroxide and N-bromo-
succinimide.19
One of the initial objectives behind the synthesis of 1c was
a possible aromatization to yield the unknown bifunctional
thiophene
monomer
dithieno-[3,4-b;30,40-e]-1,4-dioxine.
However, attempts at dehydrogenation of 4c using molecular
bromine or NBS, or strong p-acceptors (2,3-dichloro-4,5-
dicyano-p-benzoquinone (DDQ)) have failed. The only isolated
products were sulfoxide 5c (in NBS and bromine reactions) or
sulfone derivative 6c (in DDQ reaction) (Scheme 2). The latter
can also be prepared by oxidation with m-chloroperbenzoic acid
(m-CPBA) in 36% yield. Such behavior of 4c is perhaps not
surprising; all reported oxidative aromatization reactions form-
ing thiophene derivatives started from partially unsaturated
Scheme 1 Synthesis of new EDOT monomers for solid-state polymerization.
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Scheme 2 Oxidation of the tetrahydrothiophene derivative 1c.
cycles (an sp2 carbon on C3 and/or C4 atoms). Attempts to
aromatize the sulfoxide 5c under various previously published
conditions20 have also proved unsuccessful; the aryloxy substit-
uent in the b-position to sulfoxide group acts as an excellent
leaving group, thus resulting in b-elimination of the intermediate
a-carbanion, which leads to a vinylsulfoxide and opens the
dioxane ring (followed by decomposition reactions).
All three polymers A–C are very stable and repeating doping/
dedoping electrochemical cycling in ambient atmosphere (i.e., no
protection from oxygen or moisture) results in less than 3% loss
of electrochemical activity after 15 cycles (Fig. 2).
X-ray crystallographic analysis of the monomers
Single crystals of the three dibromo derivatives 4a–c were grown
from ethanol solutions and studied by X-ray analysis in order to
understand structural features of SSP. The molecular structures
of 4a–c do not reveal any abnormalities which might be
Electropolymerization
The oxidative electropolymerization of 3a–c was performed
˚
responsible for SSP. The C–Br bond lengths (1.87 A) are typical
under potentiodynamic conditions. The oxidation of the mono-
ox
mers 3a,b was observed at E
for bromoaromatics. In the ethylenedioxy bridges, one of the
alkyl substituents (CH3 for 4a and CH2 for 4b, 4c) is axial and
another one is equatorial, which renders the molecule chiral. In
solution, however, a fast interconversion between the axial and
equatorial positions takes places, as the NMR pattern is
completely symmetric.
ꢀ1.0 V vs. Ag/AgCl and
onset
repeating cycling of the potential between ꢁ0.5 and 1.25 V leads
to a progressive growth of the polymer with concomitant
increase of the anodic peak and formation of a characteristic
black film on the electrode (Fig. 1). Cyclic voltammetry (CV) of
thus-modified electrodes in fresh electrolyte solution reveals
characteristic reversible p-doping/dedoping process with an
oxidation onset at about ꢁ0.7 V vs. Ag/AgCl, similar to the
doping characteristics of PEDOT obtained under identical
conditions, thus indicating a negligible electronic effect of the
substituents in the ethylenedioxy bridge (Fig. 2). Somewhat
surprisingly, no polymerization was observed for 3c in these
conditions, which is probably due to its low solubility in
propylene carbonate. However, normal polymer growth was
observed in dichloromethane, at somewhat higher potentials.
In the solid state a 1:1 (achiral) mixture of two enantiomers is
formed. All three compounds pack in a relatively complex
fashion (Pbca) with a large orthorhombic unit cell which
contains eight molecules. Earlier we have suggested that short
halogen/halogen intermolecular contacts might be responsible
for solid-state polymerization in DBEDOT and DCEDOT, as no
solid-state polymerization was observed for 2,5-dichloro-3,4-
ethylenedioxythiophene that lacked such contacts.8 Short Br/
Br contacts were also reported for the DBEDTT molecule, which
undergoes similar SSP.10 However, the current study indicates
Fig. 1 Electropolymerization of 3a–c in 0.2 M Bu4NPF6 solution, scan
rate 40 mV/s. Solvent is propylene carbonate for 3a,b and dichloro-
methane for 3c.
Fig. 2 CVs of polymers A–C (prepared as shown in Fig. 1). Electrolyte is
0.2 M Bu4NPF6 in propylene carbonate (A, B) or dichloromethane (C);
scan rate 40 mV/s.
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that such contacts are not critical for the SSP. While slightly
˚
C2/C2 distance between each third molecule in the chain (12.14
˚
A) is 55% longer than the corresponding distance in poly-
shortened Br/Br contacts (3.57–3.64 A) were observed for 4a,
22
˚
˚
the shortest Br/Br contacts for compounds 4b and 4c (3.91 A
thiophene chain (7.85 A ), which is too large for a SSP along this
direction. Thus, while the initial C–C bond formation most likely
occurs within the dimer, the following polymerization direction is
not clear. Considering the observed by-side reaction of the
bromine with tetrahydrofuran (see below), a disordered poly-
merization can be expected in this case.
˚
and 4.04 A, respectively) are much larger than the double van der
˚
Waals radius of bromine (3.7 A), and the SSP was indeed
observed for all three monomers.
Compound 4a forms antiparallel dimers, with an interplanar
ꢁ
distance of 5.26 A. Such a large distance is dictated by the
interaction of the axial CH3 substituent in one molecule with the
thiophene ring of another, and no p-stacking similar to that
observed in DBEDOT is formed. The closest Br/Br contacts are
The packing of compound 4c doesn’t show any obvious
pathway for SSP. The antiparallel molecules of 4c do not form
dimers, but are separated by tetrahydrothiophene units of other
molecules (Fig. 4b). The sulfur atoms of these tetrahy-
drothiophene units interact with the thiophene rings of adjacent
˚
˚
3.57 A and 3.64 A and are found between molecules of neigh-
boring dimers. The shortest intermolecular C2/C5 distance of
˚
˚
4.22 A is found between two thiophenes with a dihedral angle of
molecules with (thiophene)/S distance of 3.40 A. The shortest
46ꢂ. These C2/C5 intermolecular contacts form chains running
along crystallographic direction a and provide the most realistic
pathway for the polymerization (Fig. 3). The Br/Br contacts
occur between these chains, providing a sensible route for the
elimination of bromine, which then can occupy the interchain
spacing as a dopant. It should be, however, noted, that the C2/
C5 distance is larger than what is typically required in solid-state
observed C2/C5 distance is 5.15 A and such an arrangement
˚
can be expected to be the least favorable for the SSP.
Solid-state polymerization
Prolonged storage of the brominated derivatives 4a–c transforms
the initially white monomer into the black material which shows
all features of a doped PEDOT (characteristic absorbance,
conductivity), in line with the previous observations.8 This
spontaneous solid-state polymerization is most rapid for 4a, for
which the color change is already observed after less than a day at
room temperature (or after about one week when stored at 5 ꢂC).
SSP can be greatly accelerated by heating and the polymer
samples for analysis were obtained by incubating monomers 4a–
c at 60 ꢂC, 90 ꢂC and 100 ꢂC (that is, just below the melting
points), respectively, for 72 h. The polymerization is accompa-
nied by appearance of a brown bromine vapor and results in
black powders of polymers A, B and C, which were completely
insoluble in organic solvents.
21
˚
topological reactions for C–C bond formation (<4 A), and
8b
larger than the corresponding distance in DBEDOT (4.09 A ).
˚
Furthermore, the C2/C2 distance between each third molecule
˚
in the chain (8.73 A) is ꢀ11% longer than the corresponding
22
˚
distance in polythiophene (7.85 A ); this would lead to a signif-
icant crystal deformation during the SSP.
The packing of compound 4b also shows antiparallel dimers,
but, in contrast to 4a, the alkyl substituents (tetrahydrofuran
moiety) point outside the dimer, which allows for p/p interac-
˚
tions between the thiophene moieties (interplanar distance 3.50 A)
˚
(Fig. 4a). The shortest C2/C5 contacts (3.56 A) occur within the
dimer. Unfortunately, however, such interactions cannot trans-
late into a continuous p-stacking, which otherwise would have
provided an ideal pathway for SSP. The second shortest C2/C5
contacts, observed between the thiophene units with a dihedral
The polymer A was dedoped by treatment with hydrazine
hydrate and characterized by solid-state 13C NMR (Fig. 5). The
absence of a signal at d ¼ 85.2 ppm, characteristic for the C–Br
bond, and the new signal at d ¼ 109.0 ppm typical of C–C bonds
formed between thiophene rings indicate the formation of
ꢂ
˚
angle of 58 (4.58 A), is even larger than a corresponding distance
in 4a. These contacts form chains similar to those observed for 4a,
but running along the crystallographic direction b. In this case, the
a
conjugated polymer. The mass loss during dedoping
Fig. 3 The unit cell (left) and suggested polymerization direction (right) in 4a. The oval highlights the antiparallel dimers; pink dashed lines show short
˚
Br/Br contacts; green dashed lines show the shortest C2/C5 contacts; the numbers indicate corresponding distances in A.
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Fig. 4 Crystal packing of monomers 4b (a) and 4c (b). The dimer is highlighted with an oval; white and green dashed lines show the shortest C2/C5
˚
contacts; yellow dashed line shows thiophene/S intermolecular contacts for 4c; the numbers indicate corresponding distances in A.
Fig. 6 SSP of 4c followed by isothermal DSC.
set the highest temperature for SSP experiments) of monomers
Fig. 5 CP-MAS 13C NMR spectrum of SSP A.
4a–c does not allow one to study their SSP at the same temper-
ature. Fig. 6 shows temperature dependence of the polymeriza-
tion 4c. As previously observed for DBEDOT,8b the exothermic
ꢁ
corresponds to 0.6 of Br3 doping ions per thiophene unit (i.e.,
polymerization reaction occurs after a significant inductive
period which likely corresponds to accumulation of the molec-
ular bromine (acting as a catalyst). The maximum reaction rates
(corresponding to the DSC peaks maxima) are observed at 40
min, 120 min and at $400 at 110 ꢂC, 100 ꢂC and 90 ꢂC,
respectively (Fig. 6). Integration of the exothermic peak indicates
an SSP enthalpy of only ꢁ2.6 kcal/mol (at 110 ꢂC) which is
significantly lower than that observed for DBEDOT (ꢁ14 kcal/
mol8b). While the reason for this difference is not entirely clear, it
is likely associated with post-polymerization attack of bromine
(Br3ꢁ) on the EDOT side-group (see above) and also perhaps the
extensive structural rearrangements required to transform the
solid monomer into the very differently packed polymer (see
X-ray crystallography). Such low reaction enthalpy prevents
ca. one charge per two thiophene units). This is an extremely high
doping level, higher than that of the unsubstituted SSP-
PEDOT.8b The low residual Br in the dedoped polymer (<2%) is
associated with terminal C–Br bonds and suggests that the
molecular weight of A is at least 4 kDa. No GPC analysis could
be performed due to insolubility of the polymer.
For the polymers B and C, solid-state NMR (see ESI†) indi-
cates a partial reaction of the eliminating bromine with the
tetrahydrofuran and tetrahydrothiophene side groups, respec-
tively. However, this side-group reactivity does not seem to
interfere with the polymerization reaction per se.
Isothermal DSC measurements were performed in order to
semi-quantitatively estimate the kinetics of the SSP. Unfortu-
nately, the very different reactivity and the melting points (which
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accurate kinetic studies by DSC. Nevertheless, the general trend
of the reactivity 4a > 4b ꢀ 4c is clear from the DSC and visual
observation of the polymerization at room temperature.
chromatography on silica gel and recrystallized from ethanol to
give products 1a–c as white powders. 1a (0.8 g, 33%). mp 110–111
ꢂC (lit.: 105 ꢂC for a mixture of isomers16b). 1H NMR (300 MHz,
CDCl3, ppm): 4.47 (m, 2H), 4.35 (q, 4H, 3J ¼ 6.9 Hz), 1.39 (d, 3J
3
¼ 6.0 Hz, 6H), 1.37 (t, 6H, J ¼ 6.9 Hz). 13C NMR (125 MHz,
Conductivity
CDCl3), 160.8, 144.8, 111.1, 73.3, 61.1, 14.4, 14.0. MS (EI) m/z
¼314.2 (100%) [M+]. 1b (1.76 g, 70%). mp 121–122 ꢂC. 1H NMR
(300 MHz, CDCl3): 4.83 (m, 2H), 4.34 (q, 4H, 3J ¼ 6.9 Hz), 4.20
(m, 2H), 4.00 (m, 2H), 1.36 (t, 6H, 3J ¼ 6.9 Hz). 13C NMR (125
MHz, CDCl3, ppm): 160.8, 142.9, 112.3, 74.0, 69.7, 61.5, 14.4.
MS (ESI) m/z ¼ 351.0 (100%) [M + Na]. HRMS (EI) Calcd. for
C14H16O7S 328.06167; Found 328.06077. 1c (1.32 g, 50 %). mp
178 ꢂC. 1H NMR (300 MHz, CDCl3): 4.83 (m, 2H), 4.34 (q, 4H,
3J ¼ 7.0 Hz), 3.20 (m, 2H), 3.09 (m, 2H), 1.36 (t, 6H, 3J ¼ 7.0 Hz).
13C NMR (125 MHz, CDCl3): 160.8, 143.2, 112.4, 76.9, 70.2,
61.6, 14.5. MS (EI) m/z ¼ 344.2 (100 %) [M+]. HRMS (EI) Calcd.
for C14H16O6S2 344.03883; Found 344.03802.
The conductivity of polymers prepared by SSP has been
measured with a two-probe method23 in compressed pellets.
Facile oxidation of the stainless steel probes significantly
ꢁ
obstructs the measurements of halogen-doped polymer (Br3
dopant in this case); however, this problem can be eliminated by
adding a thin buffer layer of single-walled carbon nanotubes
(HipCO type) between the compressed pellet and the probe. The
highest conductivity was found for the polymer A (4.2 S/cm),
followed by lower values for polymer B (0.35 S/cm) and C (0.13
S/cm). This order corresponds to the reactivity of the corre-
sponding monomers (4a–c) and is line with X-ray crystallo-
graphic findings of unfavorable molecular arrangements of 4b
and 4c (see above). We note that parent SSP-PEDOT measured
under identical conditions shows even higher conductivity of 11.8
S/cm (although for materials with conductivity greater than ꢀ5
S/cm the two-probe method can be grossly inaccurate due to
relatively large contact resistance).
EDOT-R-COOH (2a–c). To
a solution of potassium
hydroxide (1.4 g, 25 mmol) in water (50 mL) was added EDOT-
diacid diethyl ester derivatives 1a–c (2.50 mmol). The reaction
mixture was stirred at reflux until complete dissolution (2 h).
After cooling down to room temperature, the solution was
acidified with HCl (1 M), the formed precipitated was filtered and
dried under vacuum to give the products as white powders. 2a
(0.60 g, 93 %). mp > 300 ꢂC (dec.). 1H NMR (300 MHz, DMSO-
d6, ppm): 4.47 (m, 2H), 1.21 (d, 3J ¼ 5.7 Hz, 6H). MS (EI) m/z ¼
257.9 (52 %) [M+]. 2b (0.67 g, 99 %). mp > 300ꢂ 1H NMR (300
MHz, DMSO-d6, ppm): 6.53 (s, 2H), 4.97 (m, 2H), 4.06 (m, 2H),
3.74 (m, 2H). MS (EI) m/z ¼ 271.2 (48 %) [M+]. 2c (0.68 g, 95 %).
mp > 300ꢂ 1H NMR (300 MHz, DMSO-d6, ppm): 4.94 (m, 2H),
3.18 (m, 2H), 2.86 (m, 2H). MS (EI) m/z ¼ 287.0 (57 %) [M+].
Conclusions
We have synthesized three new thiophene monomers which
undergo spontaneous solid-state polymerization upon heating.
The effect of substituents in the ethylenedioxythiophene ring on
the packing of the monomer and on the subsequent polymeri-
zation was studied with X-ray crystallography. While the orig-
inal goal of inducing an anti-orientation of the adjacent
molecules in the crystal was achieved, the increased intermolec-
ular spacing disfavors the topochemical polymerization reaction.
As a result, the conductivity of the prepared polymers, while still
high (0.13–4.2 S/cm), is lower than that of the parent PEDOT
prepared by solid-state polymerization (11.8 S/cm in the same
measurement). The intermolecular Hal/Hal contacts, which
were suggested earlier to be important, do not appear to be
critical for the solid-state polymerization.
EDOT-R-H (3a–c). To a solution of the diacid derivatives 2a–c
(2.00 mmol) in freshly distilled quinoline (5 mL) was added
Cr2Cu2O5 (62 mg, 0.20 mmol). The reaction mixture was heated
at 180 ꢂC for 2 h. After cooling down to room temperature, 100
mL of HCl (1 M) were added and the product was extracted with
3 ꢃ 50 mL of ethyl acetate. The organic phase was washed with
water and dried over MgSO4. After evaporation, the residue was
purified by column chromatography to give the product as oils
1
Experimental section
(3a–b) or a white powder (3c). 3a (0.27 g, 80 %). H NMR (300
MHz, CDCl3, ppm): 6.30 (s, 2H), 4.25 (m, 2H), 1.27 (d, 3J ¼ 6.6
meso-Tetrahydrothiophen-3,4-diol (c) was prepared according to
Benazza et al. from the meso-erithritol with 56% overall yield.24
Diethyl 3,4-dihydroxythiophene-2,5-dicarboxylate was prepared
according to Overberger and Lal from diethyl thiodiglycolate
and diethyl oxalate with 80% yield.25
Hz, 6H). 13C NMR (125.8 MHz, CDCl3): 141.4, 99.5, 72.9, 14.6.
1
MS (EI) m/z ¼ 170.1 (100 %) [M+]. 3b (m ¼ 0.28 g, 77 %). H
NMR (300 MHz, CDCl3, ppm): 6.39 (s, 2H), 4.66 (m, 2H), 4.13
(m, 2H), 3.95 (m, 2H). 13C NMR (125.8 MHz, CDCl3, ppm):
140.0, 100.3, 73.9, 69.8. MS (EI) m/z ¼ 183.9 (100 %) [M+].
HRMS (EI) Calcd. for C8H8O3S 184.01942; Found 184.01904.
Synthesis
ꢂ
1
3c (m ¼ 0.32 g, 80 %). mp 50 C. H NMR (300 MHz, CDCl3,
EDOT-R-COOEt (1a–c). To a solution of diethyl 3,4-dihy-
droxythiophene-2,5-dicarboxylate (2.00 g, 7.68 mmol), diols
(meso-butan-2,3-diol a, meso-tetrahydrofuran-3,4-diol b or meso-
tetrahydrothiophen-3,4-diol c) (7.68 mmol) and tribu-
tylphosphine (4.74 mL, 19.2 mmol) in THF (15 mL) was added
diisopropyl azodicarboxylate (3.78 mL, 19.2 mmol) over 20 min.
The reaction mixture was heated at reflux for 48 h. Then, it was
cooled down to room temperature and the solvent was evapo-
rated to afford an orange oil which was purified by column
ppm): 6.37 (s, 2H), 4.66 (m, 2H), 3.10 (m, 2H), 3.02 (m, 2H). 13
C
NMR (125.8 MHz, CDCl3, ppm): 139.8, 100.5, 76,7, 30.5. MS
(EI) m/z ¼ 200.0 (100 %) [M+]. HRMS (EI) Calcd. for C8H8O2S2
199.99657; Found 199.99628.
EDOT-R-Br (4a–c). (i) To a solution of the thiophene deriv-
atives 3a–c (1.00 mmol) in CHCl3 (4 mL) and AcOH (2 mL)
ꢂ
under argon at 0 C was added N-bromosuccinimide (360 mg,
2.02 mmol). The reaction mixture was stirred at 0 ꢂC overnight.
5172 | J. Mater. Chem., 2009, 19, 5167–5174
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Then, 50 mL of water were added and the product was extracted
with 3 ꢃ 50 mL of CHCl3. The organic phase was washed with
NaHCO3 (5%), water and dried over MgSO4. After evaporation,
the residue was purified by column chromatography and crys-
tallised from EtOH to give products 4a–c as white powders. 4a
(0.13 g, 41%). mp 65 ꢂC. 1H NMR (300 MHz, CDCl3): 4.31 (m,
The color of the material changed from white to black with the
appearance of bromine vapor in the vial. Then the polymer was
vacuum-dried overnight to afford the bromine-doped polymers
A–C. For dedoping, the polymers was stirred in ꢀ1% solution of
hydrazine in ethanol overnight at room temperature, filtered and
rinsed with ethanol under Ar.
2H), 1.32 (d, J ¼ 6.6 Hz, 6H). 13C NMR (125.8 MHz, CDCl3):
Polymer A: 100 mg of 4a produced 95 mg of the heavily
bromine-doped polymer. Prolonged (3 days) drying of the as-
prepared material in vacuum (0.1 mbar) resulted in partial loss of
the dopant. Anal. Calcd. for C8H8O2SBr: C, 38.7; H, 3.22; S,
12.9; Found: C, 37.44; H, 3.64; S, 13.21%. 31.7 mg of as-prepared
doped SSP-A were dedoped with hydrazine to give 16.8 mg
of neutral A. Anal. calcd. for C8H8O2S: C, 57.12; H, 4.79; O,
19.02; S, 19.06; Br, 0%; Found: C, 56.77, H, 4.60; O, 18.77; S,
18.39; Br < 2%
3
139.5, 85.2, 73.7, 14.5. MS (APCI) m/z ¼ 328.88 (100%) [M+].
HRMS (EI) Calcd. for C8H8O2SBr2 325.86117; found 325.86057.
ꢂ
1
4b (0.15 g, 44%). mp 97 C. H NMR (300 MHz, CDCl3): 4.72
(m, 2H), 4.16 (m, 2H), 3.96 (m, 2H). 13C NMR (125.8 MHz,
CDCl3): 138.0, 86.2, 74.4, 69.6. MS (APCI) m/z ¼ 342.92 [M+].
HRMS (EI) Calcd. for C8H6O3SBr2 339.84044; Found
ꢂ
1
339.83923. 4c (0.33 g, 91%). mp >100 C (dec.). H NMR (300
MHz, CDCl3, ppm): 4.72 (m, 2H), 3.15 (m, 2H), 3.04 (m, 2H).
13C [1H] NMR (125.8 MHz, CDCl3, ppm): 138.0, 86.3, 77.2, 30.3.
MS (EI) m/z ¼ 357.9 (71%) [M+]. HRMS (EI) Calcd. for
C8H6O2S2Br2 355.81760; Found 355.81684.
Electrochemistry
(ii) To a suspension of the diester derivatives 1a–b (1.0 mmol)
in ethanol (20 mL) was added sodium hydroxide (0.168 g, 7
mmol). The reaction mixture was refluxed for 2 h. After cooling
down to room temperature, water (20 mL) and N-bromosucci-
nimide (0.80 g, 4.5 mmol) were added. The reaction mixture was
then stirred overnight and the product was extracted with 3 ꢃ 50
mL of chloroform. The organic phase was then washed with 3 ꢃ
100 mL aqueous NaOH (1 M) and dried over MgSO4. The
product was purified by column chromatography and crystal-
lised from ethanol to give products 4a–b as white powders. 4a
(0.30 g, 91%). 4b (0.14 g, 41%).
Electrochemical experiments were carried out with CH Instru-
ments 760C electrochemical station in a three-electrode cell
equipped with a platinum disk (B 1.6 mm) as working electrode,
platinum wire as a counter electrode and Ag/AgCl reference
electrode. Electropolymerizations were performed at room
temperature in dry DCM or propylene carbonate solutions (5
mM of monomer), deoxygenated by argon bubbling, with 0.2 M
Bu4NPF6 as supporting electrolyte. Ferrocene (Fc) was used as
an internal standard and showed E0ox ¼ +0.49 V (vs. Ag/AgCl in
DCM), +0.46 V (vs. Ag/AgCl in propylene carbonate) under our
conditions.
EDOT-tthO-COOEt (5c). To a solution of 1c (32 mg, 0.093
ꢂ
mmol) in acetonitrile (2 mL) at ꢁ20 C under argon was added
References
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