Efficient post-polymerization functionalization of conducting poly(3,4-ethylenedioxythiophene) (PEDOT) via 'click'-reaction

Article abstract of DOI:10.1016/j.tet.2010.12.022

The possibility to functionalize polymers after a successful polymerization process is often an important challenge in macromolecular science. Herein, modified electrodes based on azide-containing potentiodynamically electropolymerized PEDOT derivatives are reported. This reactive coatings are subsequently modified under mild heterogeneous conditions by copper-catalyzed Huisgen 1,3-dipolar cycloaddition with terminal alkynes, the so-called 'click'-reaction. A series of terminal alkynes have been successfully used for the facile immobilization of neutral, electron-accepting and electron-donating units to the conducting PEDOT with high conversion efficiencies showing the broad scope of the strategy. The route is devoid of the limitations generated by the various steric and electronic impacts of the substituents when attached to the monomer before polymerization.

Full text of DOI:10.1016/j.tet.2010.12.022

Tetrahedron 67 (2011) 1114e1125
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Efficient post-polymerization functionalization of conducting
poly(3,4-ethylenedioxythiophene) (PEDOT) via ‘click’-reaction
a
a
a
a
a
b,
*
€
€
ꢀ
Hang-Beom Bu , Gunther Gotz , Egon Reinold , Astrid Vogt , Sylvia Schmid , Jose L. Segura
,
b
b
a,
*
ꢀ
ꢀ
€
Raul Blanco , Rafael Gomez , Peter Bauerle
a Institute of Organic Chemistry II, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany
b
ꢀ
Departamento de Quimica Organica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The possibility to functionalize polymers after a successful polymerization process is often an important
challenge in macromolecular science. Herein, modified electrodes based on azide-containing potentio-
dynamically electropolymerized PEDOT derivatives are reported. This reactive coatings are subsequently
modified under mild heterogeneous conditions by copper-catalyzed Huisgen 1,3-dipolar cycloaddition
with terminal alkynes, the so-called ‘click’-reaction. A series of terminal alkynes have been successfully
used for the facile immobilization of neutral, electron-accepting and electron-donating units to the
conducting PEDOT with high conversion efficiencies showing the broad scope of the strategy. The route is
devoid of the limitations generated by the various steric and electronic impacts of the substituents when
attached to the monomer before polymerization.
Received 17 September 2010
Received in revised form 7 December 2010
Accepted 9 December 2010
Available online 15 December 2010
Keywords:
Conjugated polymer
Electrochemistry
Functionalization of polymers
Polythiophenes
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
to electronic and steric limitations of the attached functional
groups during electropolymerization with the result that elec-
With the class of polythiophenes a great variety of properties
can be realized related to a polyconjugated backbone, their sta-
bility, processability, and structural versatility, which are bene-
ficial for applications in organic electronics.1 In particular,
thiophene-based conjugated polymers are receiving widespread
attention as active materials in electronic devices, such as light
emitting diodes,2 organic solar cells,3 field effect transistors,4 and
chemical and biological sensors.5 Some of these applications are
based on the synthesis via electropolymerization of defined
thiophene-containing oligo- or monomers resulting in modified
tropolymerization is hindered. Thus, easily oxidized groups can
interfere with, or even inhibit, the polymerization process. In this
regard, co-electropolymerization8 or the incorporation of addi-
tional thiophene units in the monomer9 are sometimes required
for successful polymerization of monomers bearing strong
donating substituents.
An alternate approach to obtaining derivatized polymers is post-
functionalization of precursor polymers,10 which has been exten-
sively applied to conventional non-p-conjugated polymers. This
strategy has also been applied to poly(pyrrole),11 poly(aniline),12
electrodes coated with a
p
-conjugated electroactive polymer.6
and poly(thiophene)s.13
The main feature of electrochemical synthesis is the application
of defined potentials to induce a polymerization reaction that
allows a rapid growth of polymer films of a few hundred nano-
meters thickness. Additionally, electropolymerization represents
a straightforward method for the elaboration of modified elec-
trodes in which the inherent electrochemical and/or optical
properties of the conjugated polymer backbone are associated
with specific properties of covalently bound functional groups.7
Despite its apparent simplicity, the concept fails sometimes due
Among conducting polymers, PEDOT has evolved as one of the
most important materials because of the unique combination of
high stability, high conductivity, and optical transparency in the
visible spectral range. The significance and main applications of
PEDOT and its derivatives have been discussed at length in recent
reviews.14
One approach to functionalize PEDOT is to covalently link the
functional unit to monomeric EDOT.15,16 Consequently, the chem-
istry of the EDOT monomer itself and the modification of the basic
structure have been developed in parallel. Very recently, Roncali
et al. have reviewed the opportunities offered by the EDOT building
block for the design and synthesis of new classes of functional
* Corresponding authors. E-mail addresses: segura@quim.ucm.es (J.L. Segura),
peter.baeuerle@uni-ulm.de (P. Bauerle).
p
-conjugated systems.17
€
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.12.022

H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
1115
The post-polymerization functionalization of PEDOT derivatives
has been less explored yet. Besbes et al.18 reported on functionali-
zation of PEDOT derivatives bearing -iodoalkyl or -iodo-poly-
2. Results and discussion
u
u
2.1. Synthesis of functionalized EDOTs (4aed,f,g)
ether chains attached at the ethylenedioxy bridges. Lyskawa et al.
explored the potential of this strategy to prepare modified elec-
trodes for Pb2þ detection.19 In 2008, Balog et al. introduced a func-
tionalized EDOT derivative bearing a highly nucleophilic thiolate
group, which after electropolymerization afforded a functionaliz-
able PEDOT derivative.20 The electrogenerated polymer could be
efficiently functionalized with the strong electron donor tetrathia-
fulvalene (TTF). In 2009, Bhandari et al.21 reported the post-poly-
merization functionalization of a PEDOT film electropolymerized
from an aqueous micellar solution encompassing the EDOT mono-
mer and the dopant sodium bis(2-ethylhexyl)sulfosuccinate. The
post-polymerization reaction consisted of a photochemical nitrene
reaction by the reactive 1-fluoro-2-nitro-4-azidobenzene (FNAB)
typically used for biochemical applications. In general, this strategy
is devoid of the limitations generated by the various steric and
electronic impacts of the substituents when attached to the mono-
mer before polymerization.
Maintaining the integrity of the PEDOT polyconjugated back-
bone implies that substitution of an EDOT monomer can only be
realized at the ethylenedioxy bridge. Thus, we introduced chlor-
omethyl-EDOT (1), which turned out to be a universal building
block for a series of further substitution reactions to yield a number
of functionalized EDOTs.15 By nucleophilic substitution with
sodium azide, EDOT 1 was easily transformed in 97% yield to cor-
responding azidomethyl-EDOT (N3-EDOT) 2 (Scheme 1). In order to
obtain functionalized monomeric units, N3-EDOT 2 was converted
to the corresponding 1,2,3-triazolo-substituted EDOTs 4 via click-
reaction with a series of terminal alkynes 3. In order to demonstrate
the broad scope of the strategy alkynes bearing neutral moieties
(3a,b), redox active electron acceptors (3cef), and electron donors
(3g,h) were chosen and furnished the click-products 4aed,feh in
37e91% yield. In Scheme 1 an overview of our strategy toward post-
functionalization of PEDOT via click reactions is presented.
In polymer-analogous reactions the formation of side products
can be a deficit if their separation is cumbersome. Therefore, the
use of a clean addition reaction without the release of unwanted
byproducts would be even more advantageous. In this respect, the
Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of azides and
terminal alkynes, frequently referred to as ‘click’-reaction, would
represent an ideal post-functionalization reaction and is mean-
while increasingly applied in many fields of chemistry due to its
reliability, specificity, and biocompatibility.22
In principle, the [3þ2] cycloaddition reaction between an
organic azide and an acetylene derivative needs rather harsh con-
ditions as described by Huisgen23 in a review about cycloaddition
reactions. However, Sharpless24 and Meldal25 found that the acti-
vation threshold is dramatically reduced if the reaction is catalyzed
by Cu(I), which was generated in early times from Cu(II) in presence
of sodium ascorbate. Thus, this reaction has been developed to an
efficient coupling method for a large variety of substrates and re-
agents, which works not only at room temperature (or even lower)
but also under environmentally benign conditions, furnishing
regioselectively the 1,4-substituted 1H-[1,2,3]triazoles. Therefore,
this type of reaction fits nicely to the criteria of ‘click’ chemistry
defined by Sharpless et al.
Related to our approach, it has been successfully used, for both,
architectural modifications of mainly flexible (co)polymers,26,27
and immobilizations on surfaces.28 Very recently, some exam-
ples of side-chain modification of semiconducting polymers29 and
a variety of functional soft materials30 have been reported in
solution by means of the click reaction. In 2008, we reported the
first example of efficient post-functionalization of an electro-
chemically polymerized conductive polymer, poly(3,4-ethyl-
enedioxythiophene) (PEDOT), by Cu(I) catalyzed click-addition
under mild heterogeneous conditions with high conversion
efficiencies.31 Hvilsted et al. later reported functionalization of
a chemically polymerized PEDOT applying click-chemistry also
under heterogeneous conditions.32 The same group has shown, by
using alkyne-modified fluoresceine, that post-functionalization of
PEDOT via click-chemistry can be performed in micrometer-sized
areas.33
In this article, we want to report the general scope of our ori-
ginal strategy31 for the post-functionalization of PEDOT through Cu
(I)-catalyzed click-cycloaddition. For this purpose, we have syn-
thesized a family of terminal alkynes substituted with electron
donor and acceptor moieties and performed efficient post-func-
tionalization of poly(azidomethyl-EDOT) (P2, Scheme 1) under
mild heterogeneous conditions with high conversion efficiencies
and characterized the functionalized electrodes electrochemically.
In Scheme 2 the preparation of the newalkynes 3 is summarized,
in which the crucial step, starting from literature known or com-
mercially available compounds, is represented. We decided for
a rather simple design of 3 with few synthetic steps needed to
introduce the alkyne unit at the functional group. Thus, a series of
acetylene derivatives with rather short linkers up to two methylene
units between the terminal group and the triple bond have been
selected.
We subsequently investigated the Cu(I)-catalyzed Huisgen 1,3-
dipolar cycloaddition of the EDOT monomer 2 and alkynes
3aed,feh first under the conditions previously described in liter-
ature, i.e., with CuSO4/sodium ascorbate in a protic polar solvent
mixture (mainly tert-BuOHewater), at room temperature.24 In
analytical scale reactions the conversion was monitored by TLC and
after several hours the cycloaddition product was detected in most
cases. However, the conversions were not complete even after
a reaction time of more than one day. In order to evaluate the click-
reaction in solution more quantitatively, we used 1-hexine 3a and
azidomethyl-EDOT 2 in equimolar amounts in t-BuOHewater
mixture under Cu(II)/ascorbate catalysis and found a conversion of
11% after 24 h at room temperature. Solubility was also an issue for
some acetylenes 3 in the aqueous t-butanol medium with the result
that no reaction was observed for TTF-derivative 3g. Similar results
were observed by Fokin and Sharpless in the model reaction of
phenylacetylene and benzylazide in aqueous t-butanol and found
a yield of 21% for 1-benzyl-4-phenyl-[1,2,3]-triazole formation
catalyzed by CuSO4/Na-ascorbate and of 1% in the catalysis with Cu
(CH3CN)4PF6 each after 24 h.34 In this regard, the same authors
investigated polytriazoles as Cu(I)-stabilizing ligands and experi-
enced a remarkable acceleration in catalysis of the cycloaddition
reaction, later improved by polybenzimidazoles.35a,b On the other
hand, Leigh et al. showed better results by performing the cyclo-
addition reaction in non-aqueous organic solvents in presence of
catalytic amounts of Cu(CH3CN)4PF6 (5 mol %).36 Thus, we have also
tested these reaction conditions with our compounds. In order to
avoid oxidation of the Cu(I) catalyst in solution, elemental Cu
(powder) was added to the reaction mixture in equimolar amounts.
In presence of this Cu(I)-salt, soluble in acetonitrile, 1-hexine 3a
and azidomethyl-EDOT 2 formed EDOT-substituted alkyltriazole 4a
in a 66% conversion after 24 h. Apart from unreacted 2 no further
byproducts were detected by NMR. With the intention to develop
a universal procedure for the cycloaddition reaction other acety-
lenes 3 were reacted with azidomethyl-EDOT 2 under very similar
conditions just changing the solvent according to the solubility of
component 3. After a reaction time of three days at room temper-
ature, triazoles 4 were isolated in mainly good yields up to 90% after

1116
H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
R
Cl
N
N3
N
N
O
O
O
O
O
O
R
+
(i)
(ii)
S
1
S
S
2
3a-d,f-h
4a-d,f-h
(iii)
(iii)
R
N
N3
N
N
O
O
O
O
R
*
*
*
*
+
S
S
(ii)
n
n
P2
3a-h
P4a-h
AcO
OAc
O
O
O
N
O
O
AcO
AcO
R-
=
H9C4-
-
-
N
(CH2)2
N
O
(CH2)2
C8H17
-
OCH2
O
c
a
d
b
O
-
OCH2
-
S
S
S
S
NH-CH2
+
-
+
N
(CH2)2
CH3
N
Fe
-
2 PF6
N
e
g
f
h
Conditions: i) NaN3/DMF, 120°C; (ii) Cu/Cu(CH3CN)4PF6/CH3CN or THF or PhCN, r.t.; (iii) CH3CN or
PhCN/Bu4NPF6, -ne-/-nH+.
Scheme 1.
purification by column chromatography or recrystallization. The
only exception was TTF-derivative 4g, which was isolated in only
37% yield, due to solubility problems of the acetylene compound
3g. Thus, a series of functionalized EDOT derivatives 4 were
well available for further electrochemical characterization and
polymerization.
growth of a conducting polymer is depicted, characterized by the
appearance of a broad novel redox wave at lower potentials than
this of the monomer oxidation, which gradually increases in sub-
sequent potential cycles (solid lines). The thickness of the electro-
active polymer film is steadily increased and can be controlled by
the number of cycles.
The novel azidomethyl-PEDOT film P2 was electrochemically
characterized in an electrolyte free of monomer (acetonitrile/
TBAHPF (0.1 M) (Fig. 2, solid line)). In the CV, a broad redox wave
corresponding to the p-doping/dedoping of the PEDOT backbone
can be observed. The charging of the conjugated backbone, which is
concomitant with the transition from the semiconducting to the
conducting state, starts at around Elim¼ꢀ0.93 V, which is similar to
that recorded for an unsubstituted PEDOT polymerized from EDOT
under the same conditions (Fig. 2, dotted line). These results reveal,
that the electrochemical behavior of azido-substituted EDOT and
PEDOT is practically not much influenced by the substituent.
In order to investigate the stability of azidomethyl-substituted
polymer film P2 under recurrent redox cycling, the second and
100th cycles are compared in Fig. 3. Although a loss of charging
capacity of 18% is estimated from these measurements the onset
potential of the polymer film stays nearly constant or even shifts to
slightly more negative values.
2.2. Electrochemical studies
Starting with the new EDOT derivative N3-EDOT 2 its electro-
chemical behavior was investigated by cyclic voltammetry (CV)
in dichloromethane (DCM) and tetrabutyl ammonium hexa-
fluorophosphate (TBAHFP) as electrolyte. Reduction and oxidation
potentials were measured relative to the internal standard ferro-
ceneeferricenium (Fc/Fcþ). Thus, single potential scans of electro-
lytic solutions of N3-EDOT 2 showed an irreversible anodic peak at
ca. 1.07 V corresponding to the formation of the EDOT radical cation
(Fig. 1, dashed line). These values are comparable to methyl-
substituted EDOT (Me-EDOT), which exhibits an irreversible anodic
peak at 1.03 V under identical conditions.37
Potentiodynamic electropolymerization of N3-EDOT 2 yielded
the corresponding polymer P2 as a conducting film strongly
adhering to the working electrode. In Fig. 1 the formation and

Conditions: i) 16h, reflux (79%),; ii) o-DCB, reflux, 2h (83%); iii) o-DCB, reflux, 8h (34%); iv) MeCN, r.t. -
50°C, 22h (83%); v) 1.) MeCN, 80 °C, 84h (73%), 2.) H2O, r.t. (quant.); vi) DCM, Et3N, r.t., 18h
(57%). Yields given in paranthesis.
Scheme 2.
30
20
10
0
8,0x10-5
4,0x10-5
-10
-20
0,0
-1,0
-0,5
0,0
0,5
1,0
E [V vs. Fc/Fc+]
-1,0
-0,5
0,0
0,5
1,0
E [V vs. Fc/Fc+]
Fig. 2. Characterization of corresponding P(N3-EDOT) P2 in acetonitrile/TBAHPF
(0.1 M) (solid line). For comparison the CV of PEDOT polymerized from EDOT under the
same conditions is shown (dotted line).
Fig. 1. Electrochemical oxidation of N3-EDOT 2 in dichloromethane/TBAHFP (0.1 M).
First scan (dashed), successive scans second to 10th (solid).

1118
H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
On the other hand, in presence of redox active groups the po-
25
20
15
10
5
lymerization tendency of EDOT is also reported to be problematic
and the preparation of the respective polymers is achieved in
a post-functionalization reaction of the substituted EDOT after its
polymerization.18 Nevertheless, examples of acceptor-substituted
EDOTs are known, which readily polymerize with formation of
good electroactive polymer films.15a,b From these different obser-
vations it is difficult to make reliable predictions with respect to
polymerization of redox-functionalized EDOTs.
The electrochemical behavior of triazole-substituted EDOT de-
rivatives (4aeh) was investigated under conditions similar to that
used for N3-EDOT 2, just exchanging the solvent by acetonitrile
(Fig. 4). Acetonitrile was chosen as the solvent because it can be used
to investigate both EDOT and PEDOT derivatives thus allowing
0
-5
-10
-15
a
more systematic comparison between the electrochemical
behavior of the pendant groups in the monomer and the polymer. In
the positive potential regime, the CVs of 4bed, feh showed the
typical irreversible anodic peak at potentials higher than 1 V
corresponding to the formation of EDOT radical cations. Addition-
ally, the characteristic reversible oxidation waves corresponding to
TTF and ferrocene moieties were also observed for 4g and 4h, re-
spectively. For electron acceptor-substituted derivatives, a potential
scan toward negative potentials showed the characteristic reduction
waves corresponding to phthalimide (4c), naphtalenebisimide (4d),
and viologen (4f). Attempts to electropolymerize triazole deriva-
tives 4 typically did not result in polymer deposition. The only
triazole derivative that could be electropolymerized was hexylsub-
stituted triazole 4a.
-1,0
-0,5
0,0
0,5
E [V vs. Fc/Fc+]
Fig. 3. Electrochemical characterization of P2 in acetonitrile/TBAHFP (0.1 M),
100 mVsꢀ1, second (solid) and 100th sweep (dashed).
Although the polymerization behavior of functionalized EDOTs
can be versatile, almost nothing is known about the electro-
chemical behavior of 1,4-disubstituted 1H-[1,2,3]-triazoles. The
oxidation potential of redox active groups attached to this hetero-
cycle experienced a shift to more positive values due to its electron
Fig. 4. Electrochemical behavior of triazoles 4 (5 mmol/L) in acetonitrile/TBAHFP (0.1 M).
deficient nature. To give a more quantitative impression, this ob-
servation has been exploited to determine the Hammett sp value
for the 4,5-di(methoxycarbonyl)-1H-[1,2,3]-triazol-1-ylmethyl
moiety linked to ferrocene.38 Plotting the oxidation potentials of
ferrocene derivatives as function of the substituent parameter sp
results in a linear correlation for which a value of sp¼0.56 is de-
termined, lying in between the isocyano-(0.58) and CF3-group
(0.54) but is significant lower than the cyano-substituent (0.66).
Differences in electrochemical behavior and polymerization ten-
dency of triazole 4a can be observed depending on monomer con-
centration, which were disclosed by the IeE-curves in Fig. 5 for
concentrations of 5 and 50 mmol/L. In contrast to pristine or some
functionalized EDOTs, demonstrating their high reactivity in a trace
crossing39 at least in the first scan, the reactivity of the EDOT moiety
in 4a at an oxidationpotential of Ep¼1.26 V is remarkably diminished.
Compared to 2 (Ep¼1.12 V) the peak potential is slightly higher, which

H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
1119
Fig. 5. Electrochemical oxidation of 4a in acetonitrile/TBAHFP (0.1 M) at two different concentrations; first scan (dashed), successive scans second to 10th (solid). (a) c¼5 mmol/L;
(b) c¼50 mmol/L.
might be attributed to the acceptor ability of the triazole unit. At the
lower concentration the peak current drops in successive cycles
(Fig. 5 (a)). At higher concentrations and after a delay of about five
cycles the peak current of the oxidation step starts to increase with
formation of current loops in the last four cycles. Additionally broad
redox waves evolve at potentials slightly below 0 V versus Fc/Fcþ
indicating the growth of a redox active polymer film.
electropolymerization. The electroactivity of a polymer film, if it is
formed, is of minor stability.
2.3. Post-functionalization of polymer film P2 via
click-reaction with acetylenes 3 and their
electrochemical characterization
The electrochemical response of a freshly prepared film P4a
after 30 sweeps of potentiodynamic polymerization is depicted in
Fig. 6. The onset potential of this polymer is determined at ꢀ0.42 V.
During a series of successive measurements with different scan
speed (25, 50, 100, 150, and 200 mVsꢀ1) and increasing reverse
potentials (0.68, 098, and 1.18 V) the polymer significantly looses its
initial electroactivity during multiple charging and discharging.
Compared to PEDOT or P2 (Fig. 2) the polymer P4a approximates
a current plateau of highest redox activity at a remarkably higher
potential of around 0.3 V. We assume that the film consists mainly
of shorter oligomeric chains, which do not show a tendency of
chain elongation in the film during recurrent charging.
Taking these observations into account we investigated the
possibility to modify azido-substituted EDOT-polymer P2 in
a polymer-analogous heterogeneous click-reaction according to the
conversion of monomer 2 in solution. Therefore, electrodes coated
with polymer P2 were treated with terminal acetylenes 3 by dip-
ping the electrode in solutions of 3 in an appropriate organic sol-
vent in presence of catalytic amounts of Cu(I) salt and Cu(0)
powder. In the case of hexyne 3a post-modification of P2 was
alternatively catalyzed by Cu(II) salt plus sodium ascorbate in
aqueous t-butanol. After three days at room temperature with oc-
casional gentle swirling, the electrodes were electrochemically
characterized after copious rinsing to remove reagents and the
catalyst from the polymer film. The electrochemical characteriza-
tion was performed in acetonitrile/TBAHFP (0.1 M).
These results clearly show that triazole units exert an influence
on the electrochemical behavior of attached EDOT moieties
remarkably diminishing or even inhibiting their propensity to
Changes in the electrochemical behavior of the polymer films
are demonstrated in Fig. 7, comparing the initial (P2) with the
modified one (P4a), prepared in the system acetonitrile/Cu
(CH3CN)4PF6. As no further electroactive moiety is introduced via
6
4
the reaction with 1-hexyne, a shift in the onset potential of
DEon-
¼þ120 mV for the product P4a (ꢀ775 mV) already clearly in-
set
dicates, that click-reaction also works under heterogeneous
conditions at the solideliquid interface of the polymer film.
This first hint is further supported in the so-called polymer
electrochemical stability tests by multiple electrochemical scan-
ning. In Fig. 8 cyclic voltammograms of polymer films modified by
1-hexyne 3a are depicted, one reaction catalyzed by the system Cu
(II)/sodium ascorbate in aqueous alcohol (Fig. 8a) and the other by
Cu(CH3CN)4PF6 in acetonitrile (Fig. 8b) but under otherwise equal
conditions. In both figures the second and 100th cycle is plotted.
From these plots the polymer stability can be determined by
integration of the area encircled by the IeV-curve. For the Cu(II)-
catalyzed polymer P4a(Cu(II)) a retain of charging/discharging of
93% after 100 cycles is observed. In the case of the modified poly-
mer film catalyzed by Cu(I) P4a(Cu(I)) a similar value of 91% is
estimated. Thus, introduction of alkyltriazole units doesn’t result
in a remarkable loss of PEDOT electroactivity in both samples.
On the other hand, the shift in onset potentials during multiple
2
0
-2
-4
-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0
0.2
0.4
0.6
E [V vs. Fc/Fc+]
Fig. 6. Polymer characterization of P4a (30 cycles) in acetonitrile/TBAHFP (0.1 M),
100 mVsꢀ1
.

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H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
Further and somewhat more quantitative support is given by
12
10
8
FT-IR measurements. In Fig. 9 FT-IR spectroscopic characterizations
of rather thick and neutral P(N3-EDOT) P2 films prepared on ITO
glass before and after click-modification with 1-hexyne 3a and the
Cu/Cuþ system revealed a high conversion of ca. 95% azido to 1,2,3-
triazole groups indicated by the nearly complete disappearance of
the strong azido band at 2098 cmꢀ1 in P2 and the appearance of the
CeC double bond stretching vibration of the triazole ring at
1514 cmꢀ1 in P4a.
6
4
2
0
95
90
85
80
-2
-4
-6
-1,0
-0,5
0,0
0,5
E [V vs. Fc/Fc+]
(C=C)
ν
Fig. 7. Typical IeE curves, characterizing polymers P2 (solid) and P4a (dashed); in
acetonitrile/TBAHFP, 100 mVsꢀ1
triazole
.
(N )
ν
3
75
electrochemical cycling is determined to
D
E
onsetzþ250 mV for P4a
(Cu(II)), significant lower value than for P4a(Cu(I)) with
a
þ440 mV. In contrast, the starting polymer P2 doesn’t show such
a change in onset potential (see Fig. 3). This may be due to the fact
that via the post-modification reaction non-polar side chains are
introduced in the PEDOT film. In the subsequent multiple cycling
experiments a rearrangement of the polymer chains takes place
resulting, at least partially, in a phase separation in the polar
electrolyte and a change in film morphology. This gives rise to
a shift in the onset potential to higher values in agreement with the
same trend observed for PEDOT films, electrochemically prepared
from EDOT monomer substituted with longer alkyl groups (hexyl)
in the 2- and 3-position of the 2,3-dihydro-[1,4]dioxine ring com-
pared to PEDOTs with short chains (methyl) or the unsubstituted
one.32 Taking this explanation into account one can conclude from
the results shown in Fig. 8 that the post-modification reaction in
pure organic solvent is more effective after the same reaction
time than in the aqueous solvent system as was observed for the
click-reaction of monomer 2 with hexyne 3a.
70
4000
3000
2000
1000
wave number (cm-1)
Fig. 9. IR-spectrum of precursor polymer P(N3-EDOT) P2 in KBr (dashed line) and 4-
butyl-1,2,3-triazole-modified PEDOT P4a after derivatization (solid line). The black
arrow indicates the strong N3-absorption at 2098 cmꢀ1 in P2 and the red arrow the C]
C-absorption at 1514 cmꢀ1 in P4a.
A
general click-protocol was used to post-functionalize
P2-coated electrodes with various alkynes 3beh. In contrast to
other previously post-polymerization strategies used for PEDOT
functionalization in which cyanoethylene leaving groups are
formed and strong basic medium are required,18 the use of this
click protocol offers the possibility of performing clean addition
reactions under mild conditions without the release of unwanted
byproducts.
(b)
(a)
30
30
20
10
0
20
10
0
-10
-20
-10
-20
-1,0
-0,5
0,0
0,5
-1,0
-0,5
0,0
0,5
E [V vs. Fc/Fc+]
E [V vs. Fc/Fc+]
Fig. 8. Cyclic voltammograms of P2 film after surface modification with 3a catalyzed by (a) CuSO4/sodium ascorbate and (b) Cu(acn)4PF6; the second (solid) and 100th cycle
(dashed) is plotted.

H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
1121
The resulting PEDOT films P4beh were electrochemically
characterized and the potential values are summarized in Table 1. In
Fig.10 the CVs of P4beh are shown in comparison to corresponding
alkynes 3ceh labeled with an electroactive moiety. Except for
sugar-modified polymer P4b, which revealed an electrochemical
behavior quite similar to P4a, the CVs of post-functionalized
polymers P4ceh clearly showed the reversible waves and redox
transitions of the donor or acceptor groups, which are super-
imposed to the electrochemical response of the conjugated
backbone. Thus, redox systems, which are basically characterized
by, e.g., two or multiple successive electron transfer steps retained
their behavior after click-functionalization and their redox poten-
tials fairly well coincided (ꢁ10 mV) with those of alkynes 3ceh and
triazolo-EDOT monomers 4c,d,feh. High current stability of the
corresponding redox waves in multiple cycling experiments man-
ifested the covalent attachment of the alkynes by the cycloaddition
reaction. Compared to parent polymer P2, the onset potential of
PEDOTs P4bed decorated with neutral (sugar) or electron-accept-
ing redox units were shifted positively by 0.3e0.4 V likewise to
butyltriazole-PEDOT P4a after multiple cycling. On the other hand,
the electrochemical characterization of polymers P4g and P4h,
with electron donor groups, show that the contribution of the
conducting PEDOT backbone is masked by the oxidation waves of
the donor electroactive moieties. This behavior is consistent with
that previously reported for other PEDOT derivatives covalently
attached to such strong electron-donating moieties as tetrathia-
fulvalene20 and ferrocene.8,40 For polymers P4e,f Eonset could not be
determined because the electron transfer of the pendant redox
system takes place in the same potential range as the charging of
the polymer backbone.
Table 1
Electrochemical data of post-functionalized PEDOTs P4aeh in comparison to parent
P(N3-EDOT) P2. N denotes neutral, Acc acceptor, Do donor, FG functional group and
n.d. not determined. Values of corresponding electroactive alkynes 3ceh measured
in solution are given in brackets. Potentials versus Fc/Fcþ
PEDOT (type)
Eonset [V]
E1FG [V]
E2FG [V]
P2 (N)
P4a (N)
P4b (N)
P4c (Acc)
P4d (Acc)
P4e (Acc)
P4f (Acc)
P4g (Do)
P4h (Do)
ꢀ0.85
ꢀ0.78
ꢀ0.45
ꢀ0.56
ꢀ0.50
n.d.
d
d
d
d
d
d
ꢀ1.94 (ꢀ1.87)
ꢀ1.11 (ꢀ1.06)
ꢀ1.08 (ꢀ1.04)
ꢀ0.75 (ꢀ0.80)
0.08 (0.01)
0.12 (0.16)
d
ꢀ1.51 (ꢀ1.52)
ꢀ1.48 (ꢀ1.45)
ꢀ1.30 (ꢀ1.22)
0.50 (0.39)
d
n.d.
ꢀ0.96
3. Summary and conclusions
ꢀ0.71
In summary, we have carried out the straightforward synthesis of
a versatile azidomethyl-EDOT derivative 2, which provides easy
access to a poly(azidomethyl-EDOT) P2 by potentiodynamic elec-
tropolymerization. We have also carried out the synthesis of a series
of terminal alkynes bearing neutral moieties (3a, 3b), redox active
electron acceptors (3cef), and electron donors (3g,h) suitable to react
with the azide-substituted EDOTand PEDOT by Cuþ-catalyzed ‘click’-
cycloadditions. The family of alkynes was chosen in order to dem-
onstrate the broad scope of the strategy. Differences in conversion
efficiency was observed between catalysis with Cu(acn)4PF6/Cu0 in
acetonitrile under anhydrous conditions and the often applied
CuSO4/sodium ascorbate in aqueous t-butanol. In model reactions
between hexyne 3a and N3-EDOT 2 or P(N3-EDOT) P2 we observed
better results for the Cu(I)-salt under water free conditions.
N3-EDOT 2 was converted to the corresponding 1,2,3-triazolo-
substituted EDOTs 4 via ‘click’-reaction with terminal alkynes 3 in
moderate to good yields. However, in the presence of triazole units
the propensity to electropolymerization is dramatically diminished
or inhibited and the electroactivity of the film, if it is formed, is of
minor stability.
On the other hand, we have developed a versatile synthetic
protocol for the post-polymerization of poly(azidomethyl-EDOT)
P2 and terminal alkynes under mild heterogeneous conditions. The
route is devoid of the limitations generated by the various elec-
tronic impacts of the substituents when attached to the monomer
before polymerization. The experiments described gave clear proof
that efficient post-functionalization of PEDOT films was achieved
even with the bulky fullerene moiety. Thus, this strategy may
provide a good platform for the functionalization of polymer films
with more complex biomolecules, which may pave the way for the
development of novel amperometric biosensors.
4. Experimental section
4.1. Materials
2-Chloromethyl-2,3-dihydro thieno[3,4-b][1,4]dioxine 1,15a,b
2-propynyl 2,3,4,6-tetra-O-acetyl-a-D
-mannopyranoside 3b,41 ethy-
nyl-ferrocene 3h,42 7-octyl-2-oxa-7-aza pyrene-1,3,6,8-tetraone,43
3-butynylamine,44 4-prop-2-ynyloxybenzaldehyde,45 N-(2-ethyl-
hexyl)-glycine,46 3-butynyltosylate47 and tetrathiafulvalene-4-car-
bonylchloride48 were synthesized according literature. Hex-1-yne 3a
Fig. 10. Cyclic voltammograms of post-functionalized polymers P4beh (black) in
comparison to corresponding alkynes 3ceh (red) in acetonitrile or benzonitrile/
TBAHFP (0.1 M), calibrated versus Fc/Fcþ. The blue vertical dotted line gives the onset
potential of P(N3-EDOT) P2.

1122
H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
and 4,40-bipyridine were purchased from Merck. 2-But-3-ynyl-iso-
indole-1,3-dione 3c, 2-propynylamine, 1-octylamine, [60]fullerene
and Cu(CH3CN)4PF6 were purchased from Aldrich.
1.58 mmol), and C60 (567 mg, 0.79 mmol) in 100 ml of 1,2-di-
chlorobenzene was refluxed for 8 h. After cooling to room tem-
perature, the solvent was evaporated under reduced pressure and
the residue was purified by flash chromatography (silica gel,
hexane/toluene 8:2) to yield 271 mg (34%) of 3e as a black solid. 1H
4.2. Characterization
NMR (CDCl3):
d
¼7.73 (d, 3J¼8.7 Hz, 2H, Ph), 7.00 (d, 3J¼8.7 Hz, 2H,
NMR spectra were recorded on a Bruker AMX 400 spectrometer
at 25 ꢂC (1H NMR: 400 MHz, 13C NMR: 100 MHz) and Bruker AC-200
spectrometer at 25 ꢂC (1H NMR: 200 MHz, 13C NMR: 50 MHz).
Ph), 5.07 (d, 3J¼9.8 Hz, 1H, CH2eN), 4.99 (s, 1H, CHeN), 4.69 (d,
4J¼2.3 Hz, 2H, CH2eO), 4.03 (d, 2J¼9.8 Hz, 1H, CH2eN), 2.98 (m, 1H,
CH2e), 2.51 (m, 1H, CH2e), 2.43 (m, 1H, CH<), 1.99 (m, 1H, C2H),
Chemical shift values (
d
) are expressed in parts per million using the
1.25 (m, 8H, CH2e), 0.95 (m, 6H, CH3); 13C NMR (CDCl3):
d
¼158.04,
internal standard tetramethylsilane (1H NMR, dH¼0.00) or the sol-
vent as reference (13C NMR, dC¼77.00 for CDCl3, 39.52 for DMSO-d6
29.84 for acetone-d6). The following abbreviations reflect the mul-
tiplicity of the signals obtained: s¼singlet, d¼doublet, t¼triplet,
m¼multiplet, combination dd¼double of doublets, dt¼double of
tiplets. Infrared (FT-IR) spectra were recorded on a PerkineElmer
FT-IR Spectrum 2000, absorptions are reported in cmꢀ1. Mass
spectra were measured on a Varian Saturn 2000. Melting points
157.17, 154.77, 154.15, 154.14, 147.72, 147.71, 147.26, 146.94, 146.73,
146.72, 146.67, 146.63, 146.56, 146.54, 146.51, 146.35, 146.33,
146.18, 146.17, 146.02, 146.00, 145.97, 145.94, 145.88, 145.73,
145.68, 145.64, 145.60, 145.58, 145.54, 145.13, 145.07, 144.83,
144.81, 143.57, 143.56, 143.52, 143.40, 143.09, 142.99, 142.96,
142.80, 142.78, 142.70, 142.56, 142.54, 142.53, 142.43, 142.41,
142.39, 142.37, 142.22, 142.08, 141.93, 140.57, 140.53, 140.30,
139.91, 137.19, 137.17, 136.93, 136.91, 136.20, 136.18, 136.10, 131.18,
130.85, 115.27, 82.98, 82.95, 78.87, 77.25, 76.00, 69.36, 69.35,
67.69, 67.59, 58.04, 57.95, 56.31, 38.74, 38.32, 33.34, 31.67, 29.92,
€
were determined using a Buchi B-545 apparatus. Elemental analyses
were performed on an Elemental Vario EL (Ulm University). Pre-
parative flash column chromatography was performed using glass
25.84, 24.65, 14.59, 12.16; IR (KBr):
n
(cmꢀ1)¼3293, 2924, 2853,
columns packed with silica gel 60 (particle size 40e63
m
m, Merck).
2134, 1609, 1508, 1461, 1217, 1030, 829; MS (FAB) (m/z): 1006
(Mþþ1); elemental analysis: C79H27NO (Mw 1006.09), calcd(%) C
94.32, H 2.69, N 1.39, found C 93.98, H 2.40, N 1.28.
4.3. Synthesis of acetylenes, EDOT-monomers and -polymers
4.3.1. 2-Azidomethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine(2). Under
an inert atmosphere, 2.42 g (37.2 mmol) sodium azide were added to
a magnetically stirred solution of 3.55 g (18.6 mmol) 2-chloromethyl-
2,3-dihydro-thieno[3,4-b][1,4]dioxine 1 in 180 mL abs DMF. The
reaction mixture was heated up to 120 ꢂC for 3 h. After cooling, the
solvent was removed by rotary evaporation under vacuum. Then,
200 mL water was added to the residue and the product was
extracted three times with 150 mL diethyl ether each. The organic
phases were combined, washed with 100 mL water, and dried using
MgSO4. Subsequently, the diethyl ether was evaporated yielding
4.3.4. N-(3-Butynyl)-N0-methyl-4,40-bipyridinium bis(hexafluorophos-
phate) (3f). Methyl-tosylate (5.39 g, 29 mmol) dissolved in 35 ml
acetonitrile, was added to a intensively stirred solution of 4,40-bipyr-
idine (7.80 g, 50 mmol) in 15 ml acetonitrile at room temperature
within 1 h. After 15 h at room temperature and 6 h at 50 ꢂC the solvent
was evaporated under reduced pressure and the residue was treated
with benzene six times each with 10 ml in an ultra-sonic bath and at
slightly elevated temperatures. The solid residue was recrystallized
from aqueous acetone (<5% water) affording 1-methyl-4-(4-pyridyl)
pyridinium 4-methylbenzene-sulfonate in a total yield of 8.31 g (92%).
3.56 g (97%) of a nearly colorless oil. 1H NMR (CDCl3):
d¼6.36
Mp 185e186 ꢂC. 1H NMR (DMSO-d6):
d
¼9.12 (d, 3J¼6.8 Hz, 2H, bipy-
4
(AB-system, JAB¼3.7 Hz, 2H, Th), 4.30 (m, 1H, CHeO), 4.18 (dd,
J1¼11.7 Hz, J2¼2.3 Hz,1H, CH2eO), 4.04 (dd, J1¼11.7 Hz, J2¼6.9 Hz,1H,
CH2eO), 3.56 (dd, J1¼13.1 Hz, J2¼6.0 Hz, 1H, CH2eN3), 3.47 (dd,
H2/H6), 8.86 (dd, 3J¼4.6 Hz, J¼1.5 Hz, 2H, bipy-H20/H60), 8.60 (d,
3J¼6.8 Hz, 2H, bipy-H3/H5), 8.03 (dd, 3J¼4.6 Hz, 4J¼1.6 Hz, 2H, py-H30/
H50), 7.47 (d, 3J¼8.0 Hz, 2H, Tos-H2/H6), 7.09 (d, 3J¼8.0 Hz, 2H, Tos-H3/
H5), 4.38 (s, 3H, CH3eNþ), 2.26 (s, 3H, CH3ePh); elemental analysis:
C18H18N2O3S (Mw 342.41), calcd(%) C 63.14, H 5.03, N 8.18, S 9.36, found
C 62.90, H 5.33, N 7.89, S 9.66.
J1¼13.1 Hz, J2¼5.2 Hz, 1H, CH2eN3); 13C NMR (CDCl3):
¼141.0, 140.6,
d
100.21, 100.04, 72.4, 65.7, 50.5; IR (liq.):
n
(cmꢀ1)¼3114, 2926, 2876,
2104, 1674, 1485, 1185, 1023, 763; EI-MS: m/e¼197 (Mþ, 100%);
elemental analysis: C7H7N3O2S (Mw 197.2), calcd(%) C 42.63, H 3.58, N
21.31, found C 42.87, H 3.65, N 21.22.
1-Methyl-4-(4-pyridyl)pyridinium 4-methylbenzene-sulfonate
(1.70 g, 5 mmol) and 3-butynyl-tosylate (2.24 g, 10 mmol) dissolved
in 5 ml acetonitrile, were refluxed for 84 h. After cooling, the
solvent was evaporated under reduced pressure furnishing viscous
oil. The residue was first treated with diethyl ether and acetone
three times each with 20 ml, then dissolved in 10 ml acetonitrile
and precipitated in 150 ml acetone under vigorous stirring.
A colorless oil was formed, which, after removal of the solvent in
vacuum, solidifies as colorless foam in 2.08 g (73%) yield. 1H NMR
4.3.2. 2-But-3-ynyl-7-octyl-benzo[lmn][3,8]phenanthroline-1,3,6,8-
tetraone (3d). To a stirred solution of 7-Octyl-2-oxa-7-aza-pyrene-
1,3,6,8-tetraone(350mg, 0.92mmol)in30mlof1,2-dichlorobenzene,
3-butynylamine (253 mg, 3.68 mmol) was added. The solution was
refluxed for 2 h and after cooling to room temperature, the solvent
was evaporated. The residue was purified by flash chromatography
(silica gel, dichloromethane) to yield 328 mg (83%) of 3d as a pale
(DMSO-d6):
d
¼9.38 (d, 3J¼6.7 Hz, 2H, bipy-H2/H6), 9.25 (d,
yellow solid. 1H NMR (CDCl3):
d
¼8.77 (s, 4H, Naphth), 4.43 (t,
3J¼6.7 Hz, 2H, bipy-H20/H60), 8.81 (d, 3J¼6.8 Hz, 2H, bipy-H3/H5),
3J¼7.1 Hz, 2H, CH2eN), 4.19 (t, 3J¼7.4 Hz, 2H, CH2eN), 2.71 (dt,
3J¼7.1 Hz, 4J¼2.7 Hz, 2H, CH2eC2), 1.96 (t, 4J¼2.7 Hz, 1H, C2H), 1.77 to
8.74 (d, J¼6.5 Hz, 2H, bipy-H30/H50), 7.47 (d, 3J¼8.0 Hz, 2H,
3
Tos-H2/H6), 7.09 (d, 3J¼7.9 Hz, 2H, Tos-H3/H5), 4.86 (t, 3J¼6.6 Hz,
2H, CH2eNþ), 4.44 (s, 3H, CH3eNþ), 3.10 (t, 3J¼2.5 Hz,1H, C2H), 3.03
(dt, 3J¼6.5 Hz, 4J¼2.4 Hz, 2H, CH2eC2), 2.27 (s, 6H, CH3ePh); 13C NMR
1.68 (m, 2H, CH2e), 1.39 to 1.27 (m, 10H, CH2e), 0.87 (t, 3H, CH3); 13
C
NMR (CDCl3):
d
¼162.73 (C]O), 162.70 (C]O), 131.12, 130.91, 126.83,
126.75, 126.70, 126.30, 80.39, 70.18, 41.01, 38.97, 31.78, 29.26, 28.06,
(DMSO-d6):
d¼148.90, 147.81, 146.50, 145.93, 145.50, 137.57, 127.97,
27.06, 22.61, 17.69, 14.06; IR (KBr):
n
(cmꢀ1)¼2924, 2853, 2123, 1703,
126.21, 126.01, 125.36, 78.96, 75.19, 58.64, 47.90, 20.65, 20.25.
To a solution of the intermediate product (2.08 g, 3.7 mmol) in
5 ml water a concentrated aqueous solution of ammonium hexa-
fluorophosphate (1.80 g, 11 mmol) was added at room temperature.
A colorless precipitate formed immediately. Heating up the mixture
to 90e100 ꢂC dissolves the product, which crystallizes on cooling to
room temperature in colorless needles, delivering 3f in a yield of
1661, 1627, 1468, 1353, 1264, 768; EI-MS: m/e¼430 (Mþ, 100%); ele-
mental analysis: C26H26N2O4 (Mw 430.50), calcd(%) C 72.54, H 6.09, N
6.51, found C 72.21, H 6.15, N 6.57.
4.3.3. N-(2-Ethylhexyl)-2-(4-prop-2-ynyloxyphenyl)-3,4-fullero-
pyrrolidine (3e). A stirred solution of 4-prop-2-ynyloxybenzalde-
hyde (630 mg, 3.94 mmol), N-(2-ethylhexyl)glycine (295 mg,
1.85 g (98%). 1H NMR (acetone-d6):
d¼9.44 (d, J¼6.9 Hz, 2H, bipy-

H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
1123
H2/H6), 9.32 (d, J¼6.6 Hz, 2H, bipy-H20/H60), 8.86 (d, J¼6.6 Hz, 2H,
bipy-H3/H5), 8.74 (d, J¼6.3 Hz, 2H, bipy-H30/H50), 5.12 (t, J¼6.5 Hz,
2H, CH2eNþ), 4.72 (s, 3H, CH3eNþ), 3.18 (dt, J1¼6.4 Hz, J2¼2.5 Hz,
2H, CH2eC2), 2.68 (t, J¼2.5 Hz, 1H, C2H); 13C NMR (acetone-d6):
J1¼10 Hz, J2¼6 Hz, 1H, CH2eN), 4.54 (m, 1H, CHeO), 4.23 (dd,
J1¼11.9 Hz, J2¼2.3 Hz, 1H, CH2eOeTh), 4.22 (d, J¼12 Hz, 1H, man-
H6), 4.04 (br d, J¼12 Hz, 1H, man-H6), 4.00 (m, 1H, man-H5), 3.86/
3.84 (dd, J1¼11.9 Hz, J2¼6.2 Hz, 1H, CH2eOeTh), 2.08, 2.05, 1.97/
d¼151.49, 150.48, 147.78, 147.11, 127.96, 127.74, 78.97, 74.94, 61.00,
1.96, 1.91 (4s, 12H, CH3); 13C NMR (CDCl3):
d
¼170.70, 170.06, 169.91,
49.38, 21.54; elemental analysis: C15H16F12N2P2 (Mw 514.23), calcd
(%) C 35.04, H 3.14, N 5.45, found C 34.83, H 3.20, N 5.34.
169.73 (C]O), 151.65, 140.87, 140.09, 121.03, 100.84, 100.63, 97.00/
96.95, 71.82/71.81, 69.54, 69.05, 68.85, 66.19/66.17, 65.50, 62.46,
61.12/61.06, 50.08/50.06, 20.90, 20.72, 20.81, 20.70 (CH3); CI-MS:
m/e¼584 (HMþ, 100%); elemental analysis: C24H29N3O12S (Mw
583.57), calcd(%) C 49.40, H 5.01, N 7.20, S 5.49, found C 49.28, H
5.07, N 7.07, S 5.66.
4.3.5. Tetrathiafulvalene-4-carboxylic acid prop-2-ynylamide (3g). To
a stirred solution of tetrathiafulvalene-4-carbonylchloride (200 mg,
0.75 mmol) and propargylamine (184 mg, 3.35 mmol) in 15 ml of
anhydrous dichloromethane, was added triethylamine (1 ml, excess)
and stirring was continued at room temperature for 18 h. The solvent
was evaporated, and the residue was purified by flash
chromatography (silica gel, dichloromethane) to yield 122 mg (57%)
4.4.3. 2-{2-[1-(2,3-Dihydro-thieno[3,4-b][1,4]dioxin-2-ylmethyl)-1H-
[1,2,3]triazol-4-yl]-ethyl}-isoindole-1,3-dione (4c). According general
procedure, starting from 59.2 mg (0.3 mmol) 2, 59.7 mg (0.3 mmol)
of 3g as an orange solid.1H NMR (CDCl3):
d
¼7.15 (s,1H, Vinyl-H), 6.34
3c, 5.6 mg (15 mmol) Cu[CH3CN]4(PF6), and 19.1 mg (0.3 mmol)
(s, 2H, Vinyl-H), 5.72 (br s,1H, NH), 4.13 (dd, J1¼5.2 Hz, J2¼2.5 Hz, 2H,
Cu-powder in 1.2 ml acetonitrile. 4c was isolated as colorless solid in
87 mg (73%) yield by column chromatography (elution with
dichloromethane/ethyl acetate¼1:1 v/v). Mp 159 ꢂC.1H NMR (CDCl3):
CH2eN), 2.28 (t, J¼2.5 Hz, 1H, C2H); IR (KBr):
n
(cmꢀ1)¼3293, 3035,
2924, 2133, 1703, 1615, 1545, 1410, 1255, 948; EI-MS: m/e¼285 (Mþ,
100%); elemental analysis: C10H7NOS4 (Mw 285.41), calcd(%) C 42.08,
H 2.47, N 4.91, found C 41.91, H 2.39, N 4.80.
d
¼7.78 (m, 2H, Ph), 7.68 (m, 2H, Ph), 7.53 (s, 1H, triazole), 6.37 (d,
JAB¼3.7 Hz,1H, Th), 6.34 (d, JAB¼3.7 Hz,1H, Th), 4.62 (d, J¼5.4 Hz, 2H,
CH2etriazoleN), 4.51 (m, 1H, CHeO), 4.23 (dd, J1¼11.9 Hz, J2¼2.2 Hz,
1H, CH2eO), 4.02 (t, J¼7.0 Hz, 2H, CH2eimideN), 3.80 (dd, J1¼11.9 Hz,
J2¼6.5 Hz, 1H, CH2eO), 3.16 (t, J¼7.0 Hz, 2H, CH2etriazole); 13C NMR
4.4. General procedure for the synthesis of 1,2,3-triazolo-
functionalized EDOTs (4aed,feh)
(CDCl3):
d
¼168.1, 144.7, 140.9, 140.3, 133.95, 132.0, 123.2, 122.8,100.6,
Azidomethyl-EDOT 2, alkyne 3, and tetrakis(acetonitrile)copper
(I) hexafluorophosphate in a molar ratio of 1:1:0.05 (unless oth-
erwise stated) were dissolved in the given organic solvent. One
equivalent of copper powder was added and the mixture was
stirred for three days at room temperature. Subsequently, the
mixture was diluted with dichloromethane, chloroform or THF.
After separation of elemental copper by filtration, the solvent was
evaporated and the residue was purified by recrystallization or
column chromatography on silica gel.
100.4, 71.9, 65.4, 49.9, 37.5, 24.85; IR:
n
(cmꢀ1)¼3148, 3116, 2938,
2867,1770,1708,1484, 1188, 757, 723; CI-MS: m/e¼397 (HMþ, 100%);
elemental analysis: C19H16N4O4S (Mw 396.4), calcd(%) C 57.57, H 4.07,
N 14.13, found C 57.46, H 4.11, N 13.95.
4.4.4. 2-[2-(2,3-Dihydro-thieno[3,4-b][1,4]dioxin-2-ylmethyl)-1H-
[1,2,3]triazol-4-yl-ethyl]-7-octyl-benzo[lmn][3,8]phenanthroline-
1,3,6,8-tetraone (4d). According general procedure, starting from
72.4 mg (170 mmol) 3d, 63 mg (320 mmol) 2, 4 mg (11 mmol) Cu
[CH3CN]4(PF6), and 12.7 mg (0.2 mmol) Cu-powder in 0.5 ml THF. 4d
4.4.1. 4-Butyl-1-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-ylmethyl)-
1H-[1,2,3]triazole (4a). According general procedure, starting from
592 mg (3 mmol) 2, 247 mg (3 mmol) hex-1-yne 3a, 56 mg
(0.15 mmol) Cu[CH3CN]4(PF6), and 191 mg (3 mmol) Cu-powder in
12 ml acetonitrile. 4a was isolated as colorless solid in 704 mg (84%)
yield by column chromatography (elution with dichloromethane/
ethyl acetate, stepwise increasing ethyl acetate up to 25 volume
was isolated as colorless solid in 96 mg (90%) yield, recrystallized
from benzeneeethanol (1:1). 1H NMR (CD2Cl2):
d¼8.65 (AB-system,
JAB¼7.5 Hz, 4H, naphth), 7.71 (br s, 1H, triazole), 6.33 (AB-system,
JAB¼3.6 Hz, 2H, Th), 4.64 (d, J¼4.7 Hz, 2H, CH2etriazoleN), 4.49 (m,
3H, CH2eimideN, CHeO), 4.23 (dd, J1¼11.8 Hz, J2¼1.6 Hz, 1H,
CH2eO), 4.15 (t, J¼7.6 Hz, 2H, CH2eimide), 3.75 (dd, J1¼11.8 Hz,
J2¼6.9 Hz, 1H, CH2eO), 3.20 (br s, 2H, CH2etriazole), 1.72 (ddt,
J¼7.5 Hz, 2H, CH2e),1.47 to 1.22 (m,10H, CH2e), 0.87 (t, J¼6.9 Hz, 3H,
percent). Mp 83 ꢂC. 1H NMR (CDCl3):
d
¼7.40 (s, 1H, triazole), 6.39
(AB-system, JAB¼3.7 Hz, 2H, Th), 4.63 (m, 2H, CH2eN), 4.56 (m, 1H,
CHeO), 4.27 (dd, J1¼11.9 Hz, J2¼2.1 Hz, 1H, CH2eO), 3.85 (dd,
CH3); 13C NMR (CD2Cl2):
d
¼163.21, 163.13 (C]O), 149.46, 141.45,
140.91, 131.16, 131.05, 127.22, 127.06, 126.74, 100.75, 100.57, 72.40,
65.97, 50.39, 41.24, 40.41, 32.23, 29.71, 29.62, 28.42, 27.52, 24.52,
J1¼11.9 Hz, J2¼6.2 Hz, 1H, CH2eO), 2.73 (t, J¼7.7 Hz, 2H,
a-CH2), 1.67
(m, 2H,
NMR (CDCl3):
49.7, 31.5, 25.3, 22.3, 13.8; IR (KBr):
b
-CH2), 1.39 (m, 2H,
g
-CH2), 0.94 (t, J¼7.3 Hz, 2H, CH3); 13
C
23.06, 14.26; IR:
n
(cmꢀ1)¼3114, 2955, 2925, 2854, 1707, 1663, 1485,
d
¼148.8, 140.8, 140.2,122.0, 100.46, 100.45, 71.9, 65.4,
1339, 1243, 1187, 1018, 769; CI-MS: m/e¼628 (HMþ, 100%); HRMS
n
(cmꢀ1)¼3111, 3065, 2958,
(ESI) calcd for C33H34N5O6S: 628.2224 (HMþ), found 628.2221.
2927, 2874, 1492, 1202, 1055, 1024, 777; EI-MS: m/e¼279 (Mþ,
100%); elemental analysis: C13H17N3O2S (Mw 279.3), calcd(%) C
55.89, H 6.13, N 15.04, found C 55.70, H 5.99, N 14.91.
4.4.5. N-{2-[1-(2,3-Dihydro-thieno[3,4-b][1,4]dioxin-2-ylmethyl)-
1H-[1,2,3]triazol-4-yl]-ethyl}-N0-methyl-4,40-bipyridinium bis(hexa-
fluorophosphate) (4f). According general procedure, starting from
4.4.2. 4-(2,3,4,6-Tetra-O-acetyl-
a
-
D
-mannopyranosyloxymethyl)-1-
59.2 mg (0.3 mmol) 2, 154.3 mg (0.3 mmol) 3f, 5.6 mg (15 mmol) Cu
(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-ylmethyl)-1H-[1,2,3]triazole
(4b). According general procedure, starting from 115.9 mg
(0.3 mmol) 3b, 59.2 mg (0.3 mmol) 2, 19.1 mg (0.3 mmol) Cu, and
5.6 mg (15 mmol) Cu[CH3CN]4(PF6), in 1.2 ml acetonitrile. 4b was
isolated as colorless, viscous oil in 143 mg (81%) yield by column
[CH3CN]4(PF6), and 19.1 mg (0.3 mmol) Cu-powder in 1.2 ml aceto-
nitrile. The crude product was dissolved in acetone (100 mg/ml) and
precipitated by addition of n-hexane. During magnetic stirring the
viscous oil crystallized yielding 4f as nearly colorless solid in 179 mg
(83%). Mp 180e190 ꢂC (decomposition). 1H NMR (acetone-d6):
chromatography (elution with dichloromethane/ethyl acetate¼1:1
d
¼9.37 (d, J¼6.6 Hz, 2H, bipy-H2/H6), 9.35 (d, J¼6.6 Hz, 2H, bipy-
v/v). 1H NMR (CDCl3):
d
¼7.66 (s, 1H, triazole), 6.37 (d, JAB¼3.7 Hz,
H20/H60), 8.77 (d, J¼6.3 Hz, 4H, bipy-H3/H5/H30/H50), 7.99 (s, 1H, tri-
azole), 6.47 (d, JAB¼3.6 Hz, 1H, Th), 6.43 (d, JAB¼3.6 Hz, 1H, Th), 5.32
(t, J¼6.5 Hz, 2H, CH2eNþ), 4.82 (dd, J1¼14.9 Hz, J2¼4.2 Hz, 1H,
CH2etriazoleN), 4.74 (dd, J1¼14.9 Hz, J2¼7.0 Hz, 1H, CH2etriazoleN),
4.74 (s, 3H, CH3eNþ), 4.61 (m, 1H, CHeO), 4.34 (dd, J1¼11.9 Hz,
J2¼2.2 Hz, 1H, CH2eO), 3.91 (dd, J1¼11.9 Hz, J2¼7.0 Hz, 1H, CH2eO),
1H, Th), 6.31 (d, JAB¼3.6 Hz, 1H, Th), 5.26 (dd, J1¼10.1 Hz, J2¼3.0 Hz,
1H, man-H3), 5.23 (t, J¼10.3 Hz, 1H, man-H4), 5.175 (dd, J1¼2.8 Hz,
J2¼1.4 Hz, 1H, man-H2), 4.90 (d, J¼1.7 Hz, 1H, man-H1), 4.80/4.79
(d, J¼12.4 Hz, 1H, CH2-triazole), 4.66/4.64 (d, J¼12.5 Hz, 1H, CH2-
triazole), 4.64 (dd, J1¼10 Hz, J2¼4 Hz, 1H, CH2eN), 4.62/4.61 (dd,

1124
H.-B. Bu et al. / Tetrahedron 67 (2011) 1114e1125
3.70 (t, J¼6.5 Hz, 2H, CH2etriazoleC); 13C NMR (acetone-d6):
d
¼151.1,
tetrabutyl-ammonium hexafluorophosphate (TBAHFP, Fluka) was
used as electrolyte in dichlormethane, distilled over sulfuric acid in
an argon atmosphere or deaerated acetonitrile (Lichrosolv, Merck),
which were rinsed over highly active, basic alumina prior to use. In
electrochemical monomer characterization and polymerizations
concentrations of 5ꢃ10ꢀ3 mol Lꢀ1 of the electroactive species were
applied, whereas polymer films were characterized in neat elec-
trolyte solutions free of monomer. All potentials were internally
referenced to the ferroceneeferricenium couple.
150.4, 148.8, 147.76, 147.0, 142.1, 141.5, 127.8, 127.7, 127.6, 101.1,
100.9, 72.9, 66.3, 62.0, 50.8, 49.4, 27.9; HRMS (ESI) calcd for
C22H23F6N5O2PSþ: 566.12143 (MꢀPFꢀ6 ), found 566.11998, and for
C22H23N5O2S2þ: 421.15725 (Mꢀ2PFꢀ6 ), found 421.15642.
4.4.6. Tetrathiafulvalene-4-carboxylic acid 1-(2,3-dihydro-thieno
[3,4-b][1,4]dioxin-2-ylmethyl)-1H-[1,2,3]triazol-4-ylmethylamide
(4g). According general procedure, starting from 39.4 mg (0.2 mmol)
2, 28.5 mg (0.1 mmol) 3g, 1.9 mg (5 mmol) Cu[CH3CN]4(PF6), and
6.4 mg (0.1 mmol) Cu-powderin 2.5 mlTHF. 4gwasisolated asorange
colored crystals in 18 mg (37%) yield after column chromatography by
4.7. Preparation of poly(azidomethyl-EDOT) films (P2)
elution with ethyl acetate. Mp 198 ꢂC. 1H NMR (THF-d8):
d¼8.00 (br t,
Electropolymerization of monomer 2 was carried out by suc-
cessive potential scanning between ꢀ1.0 and þ1.5 V (vs reference
electrode) in several cycles with the polymer film left in a partially
oxidized state applying a final potential of ꢀ0.2 V. In the case ITO
glasses as electrodes an end potential of ꢀ1 V was applied for
several seconds, which provides a polymer film in the reduced
state. The electrodes were removed, washed with acetonitrile, and
dried in vacuum. Finally polymer films of azidomethyl-PEDOT P2
were characterized electrochemically in acetonitrile/0.1 M TBAHFP
or post-functionalized.
J¼5.4 Hz,1H, CONH), 7.80 (s,1H, triazole), 7.13 (s,1H, Vinyl-H), 6.49 (d,
J¼6.4 Hz, 1H, Vinyl-H), 6.46 (d, J¼6.4 Hz, 1H, Vinyl-H), 6.40 (d,
JAB¼3.6 Hz, 1H, Th), 6.38 (d, JAB¼3.6 Hz, 1H, Th), 4.64 (m, 2H,
CH2etriazoleN), 4.55 (m, 1H, CHeO), 4.45 (d, J¼5.7 Hz, 2H,
CH2eamideN), 4.26 (dd, J1¼11.8 Hz, J2¼2.2 Hz, 1H, CH2eO), 3.88 (dd,
J1¼11.8 Hz, J2¼6.8 Hz,1H, CH2eO); 13C NMR (THF-d8):
¼159.8, 145.8,
d
142.4, 141.8, 135.0, 124.7, 120.3, 119.8, 113.0, 108.2, 100.8, 100.5, 73.2,
66.6, 50.3, 36.0; HRMS (EI) calcd for C17H14N4O3S5: 481.96695 (Mþ),
found 481.96609.
4.4.7. 4-Ferrocenyl-1-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl-
methyl)-1H-[1,2,3]triazole (4h). According general procedure, start-
ing from 59.2mg (0.3mmol)2, 63mg(0.3mmol)3h, 5.6 mg(15mmol)
4.8. Attempted polymerization of 1,2,3-triazolo-
functionalized EDOTs 4a,c,h
Electrolyte solutions of monomers 4a, 4c, and 4h (c¼5x10ꢀ3 M in
acetonitrile/0.1 M TBAHFP) in the described electrochemical set-up
were subjected to potentiodynamic scanning between ꢀ1.0 V and
þ1.65 V (vs. Ag/AgCl). After 10 cycles ending at a potential of ꢀ0.2 V
the electrodes were removed without precipitation of a polymer
film. In a repeating experiment with 4a (c¼5x10ꢀ2 M) applying 30
cycles but otherwise same conditions furnished a polymer coated
electrode, which was rinsed copiously with acetonitrile, dried in
vacuum, and electrochemically characterized.
Cu[CH3CN]4(PF6), and 19.1 mg (0.3 mmol) Cu-powder in 2.5 ml ace-
tonitrile. 4h was isolated as a pale orange solid in 78 mg (64%) yield,
recrystallized from chloroform/n-hexane. Mp 172 ꢂC. 1H NMR
(CDCl3):
d
¼7.57 (s,1H, triazole), 6.40 (AB-system, JAB¼3.7 Hz, 2H, Th),
4.72(m, 2H, Fc), 4.65(m, 2H, CH2etriazoleN), 4.61(m,1H, CHeO), 4.30
(m, 2H, Fc), 4.29(dd, J1¼11.9Hz, J2¼2.1 Hz,1H, CH2eO), 4.07 (s, 5H, Fc),
3.89(dd,J1¼11.9Hz,J2¼6.1Hz,1H, CH2eO);13CNMR(CDCl3):
¼147.2,
d
140.9, 140.2, 120.3, 100.60, 100.53, 75.0, 71.9, 69.6, 68.7, 66.7, 65.5,
49.8; EI-MS: m/e¼407 (Mþ, 52%), 408 (HMþ, 100%); elemental anal-
ysis: C19H17FeN3O2S (Mw 407.3), calcd(%) C 56.03, H 4.21, N 10.32,
found C 55.90, H 4.22, N 10.29.
Acknowledgements
4.5. Post-functionalization of azidomethyl-PEDOT P2 films
with alkynes 3aeh
Wethank Fonds derChemischen Industrie, UCM-BSCH(GR58/08),
CAM (S2009/MAT-1467), the MCyT of Spain (CTQ2007-60459 and
CTQ2010-14982) and the Universidad Complutense/Flores Valles
Company for financial support.
Pt electrodes coated with azidomethyl-PEDOT P2, obtained by 5
repetitive electrochemical cycles, were dipped into a solution of the
alkyne 3 (0.6 mmol) and Cu(CH3CN)4 PF6 (5 mol %) in 1.2 mL aceto-
nitrile, THFor benzonitrile (appropriate to dissolve the acetylene 3) to
which copper powder (0.3 mmol) was added. After three days at
room temperature with occasional gentle swirling the coated elec-
trodes were steeped and rinsed with acetonitrile, THF or benzonitrile
several times, washed with methanol and diethyl ether and dried in
vacuum. Finally the polymer film was characterized electrochemi-
cally in acetonitrile/0.1 M TBAHFP. P2 coated ITO electrodes were
treated in a similar way. The resulting polymer film was scratched off
from the glass to prepare KBr pellets for IR measurement.
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