Synthesis and characterization of poly(triarylamine)s containing isothianaphthene moieties

Article abstract of DOI:10.1021/ma0495947

We report the synthesis, characterization, and properties of a new class of hole-transport dyes, poly(dithienylisothianaphthene phenyldiamine)s (poly-DTITNPDs). These polymers are characterized by the presence of a low band gap isothianaphthene (ITN) and triarylamine units in the main chain. A modified Ullmann polycondensation reaction using a phase-transfer catalyst was utilized to prepare these polymers. The optical, thermal, and electrochemical properties were studied and compared to those of poly(triphenyldiamine ether) without having an ITN group and poly(dithienylisothianaphthene) without having triarylamine groups in the main chain. The new polymers, reported here, exhibit improved thermal stability and higher glass-transition temperatures. The incorporation of ITN group into the main chain of a polytriarylamine causes an appreciable lowering of the band gap energy up to 1.6 eV. This results in light-harvesting hole-transport dyes having less mismatch with the solar spectrum. Moreover, these polymers exhibit reversible redox behavior and possess HOMO values of about -4.7 eV and LUMO values of about -2.9 eV.

Full text of DOI:10.1021/ma0495947

Macromolecules 2004, 37, 8951-8958
8951
Synthesis and Characterization of Poly(triarylamine)s Containing
Isothianaphthene Moieties
Roman Kisselev and Mukundan Thelakkat*
Macromolecular Chemistry I, University of Bayreuth, D-95447 Bayreuth, Germany
Received March 1, 2004; Revised Manuscript Received September 14, 2004
ABSTRACT: We report the synthesis, characterization, and properties of a new class of hole-transport
dyes, poly(dithienylisothianaphthene phenyldiamine)s (poly-DTITNPDs). These polymers are characterized
by the presence of a low band gap isothianaphthene (ITN) and triarylamine units in the main chain. A
modified Ullmann polycondensation reaction using a phase-transfer catalyst was utilized to prepare these
polymers. The optical, thermal, and electrochemical properties were studied and compared to those of
poly(triphenyldiamine ether) without having an ITN group and poly(dithienylisothianaphthene) without
having triarylamine groups in the main chain. The new polymers, reported here, exhibit improved thermal
stability and higher glass-transition temperatures. The incorporation of ITN group into the main chain
of a polytriarylamine causes an appreciable lowering of the band gap energy up to 1.6 eV. This results
in light-harvesting hole-transport dyes having less mismatch with the solar spectrum. Moreover, these
polymers exhibit reversible redox behavior and possess HOMO values of about -4.7 eV and LUMO values
of about -2.9 eV.
Introduction
For obtaining efficient low molecular weight light-
harvesting dyes, we successfully incorporated an iso-
thianaphthene moiety and triarylamine units into oli-
gomers by Pd-catalyzed amination of 1,3-bis(5-bromo-
thiophen-2-yl)isothianaphthene.11 This allowed us to
combine the efficient hole-transport property of the
triarylamines and the low band gap nature of the
isothianaphthene unit into one molecule, generating a
new class of low molecular weight isothianaphthene
phenyldiamines (ITNPD) with Eg < 1.8 eV for the first
time, and they find application in vapor-deposited solar
cells. To extend this concept to film-forming polymers
soluble in usual solvents such as CHCl3, toluene, etc.,
a suitable synthetic strategy should be developed for
incorporating ITN and diarylamines in a polymer main
chain. We earlier demonstrated that poly(triarylamine
ether)s with and without solubilizing spacers are ef-
ficient photoconductive polymers which can be used in
electro-optical applications such as photorefractive ho-
lography,12 polymeric LEDs,13 and solar cells.14 The
motivation behind this work is to develop new polymeric
hole-conducting dyes combining the positive aspects of
ITN and triarylamine moieties.
In this paper we report the synthesis and character-
ization of a series of a new class of polymers, poly-
(dithienylisothianaphthene phenyldiamine)s (poly-DTIT-
NPDs), which carry ITN and triarylamine moieties in
the main chain. Our approach was to improve the hole
injection/transport properties of ITN-containing poly-
mers by introducing triarylamine units into the main
chain. Moreover, the poly(triarylamine)s which do not
absorb in the visible region (Eg ≈ 3 eV) become suitable
as light-harvesting hole-transport dyes via introduction
of an ITN group.11 Thus, this facilitates the preparation
of hole-transporting polymers with a band gap lower
than 2 eV, which is essential for application in solar
cells, as the solar spectrum has maximum flux below 2
eV. The optical, thermal, and electrochemical properties
of this new class of polymeric materials are also reported
here. For comparison of optical and electrochemical
properties, two polymers, (1) poly(triphenyldiamine
Organic semiconductor technology utilizing low mo-
lecular weight compounds as well as conjugated poly-
mers belonging to the classes of triarylamines and
thiophenes are widely studied for potential applications
in solar cells,1 organic light emitting diodes,2 field effect
transistors,3 etc.
In the case of triarylamines, the HOMO energy value
can be varied considerably in the range from -5 to -5.5
eV by chemical modification to suit the hole injection
from electrodes.4 In the case of thiophenes, the band gap
energy or wavelength of maximum absorption (λmax) can
be varied over a wide range in the visible region up to
600 nm, mainly by variation of the LUMO energy
value.2a,5 Moreover, modification of the thiophene ring
into benzo[c]thiophene results in a new class of com-
pounds generally called isothianaphthenes, which are
well known for their low band gap energy values of
about 1 eV.6 However, isothianaphthene monomers are
relatively unstable and poly(isothianaphthene) is in-
soluble.
At present the most widely used polymeric materials
for light absorption in polymer solar cells are substituted
poly(p-phenylene vinylene)s and polythiophenes. These
polymers exhibit an optical band gap (Eg) of about 2 eV
and there is a considerable mismatch between λmax and
irradiance of solar emission (below 2 eV). Hence, the
design and development of low band gap polymers with
Eg below 2 eV shall decrease this mismatch of the
absorption spectrum of the cell with the solar spectrum,
resulting in enhanced photon harvesting. In this respect,
low band gap polymers containing only a dithienyl-
isothianaphthene moiety with solubilizing substitu-
ents7,8 as well as copolymers of benzothiadiazole mono-
mers and hole conducting 9,9-dialkyl fluorine9 or
N-alkylpyrroles10 have been reported recently as novel
light-harvesting dyes for application in solar cells.
* To whom correspondence should be addressed. Phone: +49-
921-553108. Fax: +49-921-553206. E-mail: mukundan.thelakkat@
uni-bayreuth.de.
10.1021/ma0495947 CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/27/2004

8952 Kisselev and Thelakkat
Macromolecules, Vol. 37, No. 24, 2004
Scheme 1. Polycondensation of 1,3-Bis(5-iodo-2-thienyl)isothianaphthene (2) and Secondary Amines (1a-c) via
Modified Ullmann Procedure in Absolute o-Dichlorobenzene Using Excess Cu in Combination with 18-Crown-6
as a Phase-Transfer Catalyst and K2CO3 as Base at 180 °C
ether) (poly-TPDE)14 without an ITN group 6 and (2)
poly(dithienylisothianaphthene) (poly-DTITN) without
triarylamine groups in the main chain 7, were also
synthesized and studied. In this way the effect of ITN
and triarylamine groups in poly(DTITN)s on properties
can be better understood.
crown-6 as a phase-transfer catalyst and K2CO3 as a
base. Polymers 3a-c were obtained as dark-brown
solids. All the polymers possess solubility in common
organic solvents, such as CHCl3, THF, toluene, and
xylene. Compounds 3a and 3c formed thin and stable
amorphous films of high optical clarity by solution
casting on glass substrates. The trifluoromethyl groups
in polymer 3b were selected with an aim to obtain
hydrophobic material with a selective wetting property
on substrates. Accordingly, we found that this polymer
formed amorphous films only on hydrophobic substrates.
The starting diiodo compound, 1,3-bis(5-iodo-2-thien-
yl)isothianaphthene, 2, was prepared by the iodination
of 1,3-di(2-thienyl)isothianaphthene with N-iodosuccin-
imide in DMF at -55 °C by a similar procedure as that
for its dibromo analogue, 1,3-bis(5-bromo-2-thienyl)-
isothianaphthene, which was obtained by a three-step
synthesis as reported earlier.11
The bis(secondary)amines (1a-c) were synthesized
via Pd-catalyzed C-N coupling between anilines (4a-
c) and diiodides (5a,b) by refluxing them with Pd(dppf)-
Cl2 in combination with DPPF and t-BuONa as a base
in toluene for 16 h as shown in Scheme 2. The Pd-
catalyzed amination of aryl halides was intensively and
independently investigated by Buchwald18 and Hartwig,17
and an optimized procedure from the literature was
adopted here.19 For obtaining bis(secondary)amines in
good yields, an excess amount of aniline was used which
avoided formation of doubly substituted side products.
In this way, the target monomers 1a, 1b, and 1c were
obtained in relatively good yields of 46%, 60%, and 79%,
respectively. The final purification of 1a and 1c was
carried out by washing with concentrated HCl and
reprecipitation from concentrated THF solution into
methanol. Monomer 1b was purified by column chro-
matography with cyclohexane/ethyl acetate (5:1) as
eluent.
Results and Discussion
First attempts to synthesize main-chain polymeric
triarylamines by an Ullmann reaction from bis(second-
ary amine)s and diiodides resulted in oligomeric mix-
tures and insoluble products.15 A modified Ullmann
procedure16 with 18-crown-6 as the phase-transfer
catalyst was adopted by us for the synthesis of soluble
and film-forming triarylamine polymers with apprecia-
bly high molecular weights.12 On the other hand, Hart-
wig et al. reported oligomeric and polymeric triaryl-
amines by Pd-catalyzed polymerization of bis(secondary
amine)s and dibromides.17 Two basic problems in using
the Pd-catalyzed reaction for the synthesis of polymers
were (1) hydrodehalogenation of aryl halide, limiting the
formation of high molecular weight polymers, and (2)
the concurring cyclization reactions leading to cyclic
oligomers, which limits the molecular weight of the
polymers.17a These difficulties could be only partially
overcome by a suitable selection of phosphine ligands
and using “oligomeric monomers” with meta- and para-
linkages.17b
Therefore, we chose the modified Ullmann procedure
for preparation of the target polymers. The synthetic
route was selected in such a way as to obtain relatively
high molecular weight poly[bis(diarylaminothienyl)iso-
thianaphthene]s (3a-c) in good yields (see Scheme 1).
The polycondensation reactions of 1,3-bis(5-iodo-2-
thienyl)isothianaphthene (2) and different secondary
amines (1a-c) were carried out in absolute o-dichlo-
robenzene using excess Cu in combination with 18-

Macromolecules, Vol. 37, No. 24, 2004
Poly(triarylamine)s Containing Isothianaphthene Moieties 8953
Scheme 2. Synthesis of Bis(secondary amine)s 1a-c
by Pd-Catalyzed Coupling of Diiodides 4a,b and
Anilines 5a-c in the Presence of Pd(dppf)Cl2, DPPF,
and t-BuONa as Base in Toluene at 110 °C
Figure 1. Monitoring of the polycondensation of 1c and 2 via
modified Ullmann procedure using SEC. SEC eluogram (A) of
starting monomers 1a and 2, (B) precipitated product after 3
days reaction time, (C) precipitated polymer after 5 days
reaction time.
Table 1. SEC Data of Polymers 3a-c Determined Using
UV WAT 486 Detector (relative to polystyrene standards)
with THF Containing 0.25 wt % of tert-Butyl Ammonium
Bromide as Eluent
polymer
Mn (g/mol)
Mw (g/mol)
Mp (g/mol)
PDI
3a
3b
3c
6
10.480
5.980
7.240
4.240
9.160
127.520
47.540
28.990
12.010
26.390
146.580
45.280
18.820
8.040
12.1
7.9
4.0
2.8
2.9
7
11.240
The polymers were fully characterized by spectro-
scopic methods, such as FTIR, 1H NMR, etc. (see
Experimental Section). In polymers 3a-c the strong IR
absorptions at 3405-3419 cm-1 due to N-H stretching
in compounds 1a-c and 1189 cm-1 due to C-I stretch-
ing in compound 2 disappeared completely and the
characteristic C-N stretching of amine at 1250-1314
cm-1 and characteristic C-H stretching of thiophene
742-746 cm-1 were observed in the products. Addition-
ally, polymers 3a-c exhibited characteristic aromatic
absorptions at 3029-3064 cm-1 (C-H stretching) and
1492-1496, 1603-1617 cm-1 (C-C stretching) as well
as characteristic aliphatic absorptions at 2851-2858,
2924-2928 cm-1 (C-H stretching). All the proton
signals in the 1H NMR spectra for monomers and
polymers could be assigned accordingly. The end-group
(iodine) analysis of these polymers exhibits only a
negligible weight percent of iodine in the range of 0.02-
0.03 wt %, indicating a high degree of polymerization.
With each polycondensation the progress of reaction
was monitored by size exclusion chromatography (SEC).
The SEC elution curves for the reaction between 1c and
2 resulting in polymer 3c are shown in Figure 1. Curve
A represents the monomers, curve B represents the
product obtained after 3 days of reaction, and curve C
represents the polymer obtained after 5 days of reaction.
It can be clearly seen that the discrete oligomers up to
the pentamer stage formed in 2-3 days get converted
into high molecular weight polymers with prolonged
time of polymerization. Similar results were obtained
for the polycondensations of 1a and 1b with 2, resulting
in appreciably high molecular weights of 3a and 3b.
The SEC data for all the polymers with polystyrene
as standard and THF containing 0.25 wt % of tert-
butylammonium bromide as eluent is given in Table 1.
Polymers 3a, 3b, and 3c exhibit number-average mo-
lecular weights (Mn) of 10 480, 5980, and 7240 g/mol,
respectively. As expected for polycondensation, the
polydispersity varies over a wide range between 4 and
12 depending on the reactivity and concentration of
monomers. The weight-average molecular weights (Mw)
for 3a, 3b, and 3c are 127 520, 47 540, and 28 990 g/mol,
respectively. The highest molecular weight (Mw) was
obtained for polymer 3a carrying octyl groups, and the
lowest molecular weight was observed for polymer 3c
with hexyloxy groups, in agreement with the degree of
solubility due to the corresponding side groups. To study
the effect of the concentration of monomers on the
polycondensation reaction, polymer 3a was also pre-
pared under more dilute reaction conditions (0.09 M
instead 0.15 M). The resulting polymer has a lower
molecular weight of Mn ) 7730 g/mol, Mw ) 23 180
g/mol, and a narrow molecular weight distribution of
3. The low polydispersity can be explained as due to
efficient removal of the oligomers by repeated repre-
cipitation. In general, the SEC data obtained against
polystyrene standards have to be taken as relative
values. A comparison of end-group iodine analysis and
SEC values shows that the molecular weights obtained
by SEC are smaller than the values obtained from end-
group analysis. End-group iodine analysis of polymers
3a, 3b, and 3c shows iodine contents of 0.031, 0.028,
and 0.018 wt %, respectively; the corresponding average
molecular weights were 409 677, 453 570, and 705 555
g/mol.
For comparison purposes, two reference polymers, (1)
poly(triphenyldiamine ether) (poly-TPDE) without an
ITN group and (2) poly(dithienylisothianaphthene) (poly-
DTITN) without triarylamine groups in the main chain,
were also synthesized and studied (see Figure 2). This
allowed us to understand the effect of ITN and triaryl-
amine groups in 3a-c on electrochemical and optical
properties. The poly-TPDE (6) was also synthesized by
the Ullmann reaction as reported earlier.14 Poly-DTITN
was obtained by oxidative polymerization of 1,3-bis(3-
hexyl-2-thienyl)benzo[c]thiophene using anhydrous FeCl3
in CHCl3 by a general procedure known in the litera-
ture.20 Monomer 1,3-bis(3-hexyl-2-thienyl)benzo[c]thio-
phene was synthesized using 2-magnesiumbromo-3-

8954 Kisselev and Thelakkat
Macromolecules, Vol. 37, No. 24, 2004
Table 2. Optical and Thermal Properties of the Polymers
3a-c, 6, and 7a
UV-vis absorption,
Egopt (eV) (edge (nm))
thermal properties
polymer
in CHCl3
in film
Tg (°C)
T-5% (°C)
3a
3b
3c
6
1.77 (700)
1.81 (685)
1.90 (653)
3.17 (391)
2.18 (570)
1.67 (741)
1.56 (794)
1.64 (755)
3.12 (398)
2.03 (612)
132
108
130
105
90
381
393
385
405
315
7
a Eg ) optical band gap. Tg ) glass-transition temperature.
T-5% ) onset temperature at 5% weight loss.
opt
and in thin films prepared by spin coating from CHCl3
(3a-c, 6) and chlorobenzene (7) solutions, and the
various spectra in film are compared in Figure 3.
Figure 3A compares the UV-vis spectra of polymers
3a-c in thin films, and Figure 3B shows the spectra of
3a as an example compared to those of polymers 6 and
7. The absorption band edges obtained from solution and
film are also given in Table 2. All three polymers 3a-c
show similar absorption spectra with two vibronic
bands. However, polymer 3a has the highest absorption
coefficient compared to polymers 3b and 3c. Polymers
3a, 3b, and 3c absorb up to 750 nm, and they have Eg
values (as calculated from absorption edge) of 1.67, 1.56,
and 1.64 eV, respectively. On the other hand, polymers
6 and 7 exhibit Eg values of 3.12 and 2.03 eV, respec-
tively. Thus, incorporation of the ITN group results in
a red shift of 170 nm in 3a compared to that of polymer
6. Introduction of an ITN group in polymers 3a-c,
leading to a shifting of the absorption band edge to
longer wavelengths, is in agreement with our results
on low molecular weight DTITN diamines.11 Polymers
3a-c show a red shift of about 70 nm compared to
polymer 7, which carries an ITN group in the main
chain. This result can be explained as follows. The steric
hindrance due to the two hexyl substituents in polymer
7 causes a stronger torsion around the inter-ring bonds,
which leads to lower conjugation. In addition, incorpora-
tion of the triaryldiamine unit into polymers 3a-c leads
to longer conjugation, as already shown in our work11
for the case of low molecular weight DTITNPDs.
Figure 2. Chemical structures of the polymers used for
comparative studies, poly(triphenyldiamine ether) (poly-
TPDE 6) without having an ITN group and poly(dithienyl-
isothianaphthene) (poly-DTITN 7) without having triaryl-
amine groups in the main chain.
hexylthiophene as a Grignard reagent via a modified
procedure to that reported in the literature.21
The different methods of polymerization of thiophene
monomers were reviewed recently by R. D. McCullough.22
One of the simplest methods is polymerization of the
monomer with FeCl3, which is generally known to give
irregular poly(3-alkylthiophenes). However, poly-DTITN
(7), synthesized by the FeCl3 oxidative polymerization,
can have only regioregular structure due to the sym-
metrical nature of dithienylisothianaphthene used here.
One of the major problems in oxidative polymerization
with FeCl3 is the high Fe content in the resulting
polymer, which is detrimental to electronic materials,
because the Fe impurity level in a polymer affects the
performance of electrooptical devices. This problem was
overcome here by developing an improved purification
procedure to reduce Fe content in polymer 7. The Fe
content in polymer 7 was reduced to 0.013 wt % by
repeated washing with HCl, aqueous ammonia, and
finally KSCN solution (see Experimental Section). Poly-
mers 6 and 7 were also characterized by spectroscopic
methods such as FTIR, NMR, etc. (see Experimental
Section). The SEC data for both polymers 6 and 7 are
also given in Table 1.
The thermal properties of polymers 3a-c, 6, and 7
were examined by differential scanning calorimetry
(DSC) and thermogravimetric analysis (TGA) measure-
ments. TGA curves of polymers 3a-c and 7 obtained
at a heating rate of 10 K‚min-1 under nitrogen atmo-
sphere are shown in Figure 4. The onset temperatures
for the polymers for 5% weight loss (T-5%) are also given
in Table 2. It can be clearly seen that polymers 3a-c
The optical properties of 3a-c, 6, and 7 were studied
by measuring UV-vis spectra both in solution (CHCl3)
Figure 3. UV-vis spectra of polymers. (A) Poly-DTITNPDs 3a-c in film, and (B) comparison of UV-vis spectra of poly-DTITNPDs
3a, poly-TPDE 6 without any ITN group, and poly-DTITN 7 without triarylamine groups in film.

Macromolecules, Vol. 37, No. 24, 2004
Poly(triarylamine)s Containing Isothianaphthene Moieties 8955
Figure 4. Thermogravimetric analysis of poly-DTITNPDs
3a-c and poly-DTITN 7 at 10 K‚min-1 under N2 atmosphere.
Figure 6. Cyclic voltammograms of poly-DTITNPDs 3a and
poly-DTITN 7 (in THF containing 0.1 M tetrabutylammonium
hexafluorophosphate vs Ag/AgNO3 at a 50 mV/s scan rate).
Table 3. Electrochemical Properties of the Polymers
3a-c, 6, and 7 Obtained from Cyclic Voltammetry
Measured in THF vs Ag/AgNO3 as Reference Electrode
and Calibrated vs Ferrocene (Fc)a
EOX1 vs Fc HOMO ERED1 vs Fc LUMO band gap
polymer
(V)
(eV)
(V)
(eV)
(eV)
3a
3b
3c
6
-0.13
-0.10
0
0.22
0.15
-4.67
-4.70
-4.80
-5.02
-4.96
-1.88
-1.88
-1.85
b
-2.92
-2.92
-2.95
b
1.75
1.78
1.85
b
7
-2.12
-2.68
2.28
a HOMO/LUMO values are relative to vacuum level. b No
reduction observed up to -2.5 V vs Fc.
Figure 5. Determination of the glass-transition temperature
(Tg) from second heating curves of poly-DTITNPDs 3a-c and
poly-DTITN 7 using differential scanning calorimetry (DSC)
measurements (heating rate 10 K min-1).
brated as usual with the standard ferrocene/ferrocenium
(Fc) redox system.23 The HOMO and LUMO energy
values of the compounds were determined from the first
oxidation and first reduction potentials (Eox1 and Ered1),
respectively, taking a value of -4.8 eV as the HOMO
energy level for Fc with respect to zero vacuum level as
described by Daub et al. in the literature.24 The cyclic
voltammograms of polymers 3a, for example, and 7, for
comparison, measured at a scan rate of 50 mV‚s-1, are
given in Figure 6.
and 6 having triarylamine groups in the main chain are
more thermostable than polymer 7. The T-5% data for
3a, 3b, and 3c are 381, 393, and 385 °C, respectively.
Thus, introduction of triarylamine groups increases the
thermal stability of polymers 3a-c by about 70 °C
compared to poly-DTITN, 7, which shows onset by
315 °C.
The second heating curves obtained from DSC for
polymers 3a-c and 7 are shown in Figure 5. Polymers
3a-c exhibit a glass-transition temperature (Tg) in the
range of 108-130 °C depending on the substituents. In
comparison with polymers 6 and 7, this is an improve-
ment of about 30 °C, which gives an indication about
the rigidity of the DTITN unit in combination with
triarylamine units in polymers 3a-c. As is the case with
thermal stability, Tg is also improved in polymers 3a-c
due to incorporation of ITN and triarylamine groups into
the polymer main chain. The low Tg value in polymer 7
can be attributed to the higher weight percentage of the
side groups compared to the DTITN part as well as to
the high torsion arising from the steric effect. No
melting and no crystallization behavior on further
heating and cooling cycles between 40 and 230 °C at
10 K‚min-1 were observed for these polymers.
The polymers are electrochemically stable, and the
same redox potentials were observed for repeated cycles
of redox processes. They show completely reversible
oxidation and reduction steps after measuring three
cycles for the entire scan rate of 50-150 mV‚s-1
.
Polymers 3a, 3b, and 3c show a similar oxidation
behavior with Eox1 ) -0.13, -0.10, and 0 V and
reduction behavior with Ered1 ) -1.88,-1.88, and -1.85
V, respectively. Eox1 of 0.15 V and Ered1 of -2.12 V was
observed for polymer 7. The corresponding HOMO and
LUMO values for all of the polymers determined from
the first oxidation and reduction potentials with respect
to ferrocene/ferrocenium (Fc) as internal standard are
presented in Table 3. Polymers 3a-c have similar
HOMO values of about -4.7 eV, and polymers 6 and 7
have similar HOMO values of about -5.0 eV. Polymers
3a-c have similar LUMO values of about -2.9 eV, and
polymer 7 has a LUMO value of -2.7 eV. The electro-
chemical band gap (Egec) values, given in Table 3, were
calculated as the difference between the HOMO and
LUMO levels of the polymers. These values are in close
agreement with the optical band gap (Egopt) values
obtained from absorption band edges measured in
solution (see Table 2). Moreover, polymers 3a-c possess
lower band gap energy values than polymer 7, and this
lowering was achieved through an improvement of both
HOMO and LUMO values. These low band gap poly-
Electrochemical Properties. The electrochemical
stability and reversibility of the redox processes of
polymers 3a-c, 6, and 7 were studied using cyclic
voltammetry (CV). The measurements were carried out
using a glassy carbon electrode in a solution of carefully
dried THF containing 0.1 M tetrabutylammonium
hexafluorophosphate (TBAPF6) at room temperature.
The potentials were measured against Ag/AgNO3 as the
reference electrode, and each measurement was cali-

8956 Kisselev and Thelakkat
Macromolecules, Vol. 37, No. 24, 2004
analytisches Labor Pascher, An der Pulvermu¨hle 1, 53424
Remagen, Germany.
mers should be suitable as efficient light-harvesting
dyes with improved matching of absorption to the solar
spectrum.
1. Monomer Synthesis. (a) Bis(secondary)amines (1a-c).
Syntheses of 1a, 1b, and 1c were performed in dried toluene
with 6 mol % Pd(dppf)Cl2, 18 mol % DPPF, 4.5 equiv of
t-BuONa, and 3 equiv of aniline per 0.25 M of diiodide at
125 °C for 16 h under Ar. After completion of the reaction,
toluene was removed under reduced pressure. The reaction
mixture was dissolved in THF and filtered through Al2O3 on
a glass filter to remove polar impurities. The product was
precipitated in methanol from concentrated THF solution
(THF/methanol 20:200 mL). The precipitate was dissolved in
CH2Cl2, washed with aqueous 32% HCl to remove aniline,
followed by water, and dried over Na2SO4. After evaporation
of CH2Cl2, the product was dissolved in THF and precipitated
in methanol twice. White solid was collected.
Conclusion
It can be concluded that the strategy of incorporating
ITN and triarylamine groups into a polymer main chain
was successfully realized. The resulting polymers con-
stitute a new class of light-harvesting dyes with band
gap energy values below 1.8 eV. The thermal stability
and glass-transition temperatures were improved in
these polymers compared to poly(triphenyldiamine ether)
(poly-TPDE) without an ITN group and poly(dithienyl
isothianaphthene) (poly-DTITN) without triarylamine
groups. These polymers are promising candidates for
use in solar cells because they form stable films with
amorphous nature. Moreover, the absorption spectra of
these polymers are red shifted by more than 150 nm,
thus decreasing the mismatch with the solar spectrum.
Application of these polymers in thin-layer plastic solar
cells is under current research, and the results will be
published later.
(i) N,N′-Di(4-octylphenyl)-4,4′-diaminobiphenyl (1a). Molec-
ular formula (MF) ) C40H52N2; mol weight (Mw) ) 560.87
1
g/mol. Yield: 1.28 g (46%). H NMR (C6D6), δ [ppm]: 7.46 (d,
4H), 7.05 (d, 4H), 6.97 (d, 8H), 5.07 (s, 2H), 2.55 (t, 4H), 1.62
(m, 4H), 1.27 (m, 20H), 0.91 (t, 6H). FT-IR (KBr), v˜ [cm-1]:
3415, 3028, 2956, 2916, 2848, 1612, 1519, 1314, 816. MS [m/z]:
560 (M+), 461 ([C8H17-C6H4-NH-C6H4-C6H4-NH-C6H4d
CH]+), 181 ([C6H4-NH-C6H4dCH]2+).
(ii) 4,4′-Oxybis[N-(2,4-di(trifluoromethyl)phenyl)]benzenamine
(1b). MF ) C28H16F12N2O; Mw ) 624.43 g/mol. Precipitation
of product from THF into methanol, n-hexane, or petrolether
(bp 60-80 °C) did not work. Final purification by column
chromatography with cyclohexane/ethyl acetate (5:1) yielded
Experimental Section
Materials. Chloroform (CHCl3) was purified by distillation
over calcium hydride. Tetrahydrofuran (THF) and toluene
were dried over sodium and distilled under argon. o-Dichlo-
robenzene was refluxed and distilled with calcium hydride. 1,3-
Di-2-thienylbenyo[c]thiophene was prepared by a three-step
synthetic method as reported earlier.11 All other chemicals
were purchased from Aldrich Chemical Co. and used as
received.
1
1.40 g (60%). H NMR (CDCl3), δ [ppm]: 7.26 (s, 12H), 7.12
(d, 4H), 7.06 (d, 4H), 5.88 (s, 2H). FT-IR (KBr), v˜ [cm-1]: 3405,
1618, 1497, 1378, 1274, 1168, 1139, 870. MS [m/z]: 624 (M+),
320 ([(CF3)2-C6H4-NH-C6H4-O]+). mp: 116.4 °C.
(iii) Di(4-hexyloxyphenyl)-4,4′-diaminobiphenyl (1c). MF )
C36H44N2O2; Mw ) 536.76 g/mol. Yield: 1.36 g (79%). 1H NMR
(CDCl3), δ [ppm]: 7.37 (d, 4H), 7.04 (d, 4H), 6.95 (d, 4H), 6.86
(d, 4H), 5.50 (s, 2H), 3.92 (t, 4H), 1.76 (m, 4H), 1.45 (m, 4H),
1.32 (m, 4H), 0.89 (t, 6H). FT-IR (KBr), v˜ [cm-1]: 3419, 3029,
2954, 2934, 2871, 1611, 1517, 1250, 817. MS [m/z]: 536 (M+),
451 ([M - C6H13]+), 367, ([M - 2(C6H13)]2+), 184 ([C6H4-NH-
C6H4-O]2+). mp: 177.3 °C.
Instrumentation. Size exclusion chromatography (SEC)
measurements were performed on a Waters system with
Waters 410 RI and Waters 440 UV detectors at room temper-
ature by using THF containing 0.25 wt % of tert-butylammo-
nium bromide as an eluent. The molecular weights and
molecular weight distributions were calculated on the basis
of monodispersed polystyrene standards. 1H NMR (250 MHz)
spectra were obtained on a Bruker AC250 spectrometer.
Chemical shifts (δ) were reported in ppm downfield from
tetramethylsilane (TMS). The UV-vis measurements were
carried out on a Hitachi U-3000 spectrophotometer in CHCl3
solutions and in thin films prepared by spin coating from
CHCl3 or chlorobenzene solutions. Fourier-transformed infra-
red spectra (FT-IR) were measured on a BioRad Digilab FTS-
40 (FT-IR) using a potassium bromide (KBr) pellet for sub-
stances in the solid state and a sodium chloride (NaCl) pellet
for substances in the liquid state (16 scans; resolution, 4 cm-1).
Cyclic voltammetry measurements were carried out using
millimolar solutions of polymer in highly dried acetonitrile
(Acn) or THF at room temperature. A glassy carbon disk
electrode (0.2 cm2) was used as a working electrode. A
platinum wire was used as the counter electrode, and a silver
wire in a solution of AgNO3 was used as the reference
electrode. Each measurement was calibrated with an internal
standard, ferrocene/ferrocenium (Fc) redox system. The HOMO
and LUMO values were determined from the value of -4.8
eV for Fc with respect to vacuum level. Scan rates in the range
of 50-500 mV‚s-1 were used. Thermogravimetric analysis
(TGA) of polymers was conducted on a thermoanalysis ap-
paratus TGA/SDTA851e from Mettler Toledo Co. at a heating
rate of 10 K‚min-1 under a nitrogen flow rate of 75 cm3‚min-1
in the temperature range from 30 to 650 K. Differential
scanning calorimetry (DSC) measurements were carried out
using a Diamond DSC from Perkin-Elmer Co. The heating/
cooling rate was 10 K‚min-1 for all experiments. Melting point
measurements were performed on Leitz Laborlux 12-Pol
equipped with a Mettler FP 82 hot stage using a heating rate
of 5 K/min. The Fe content in polymer 7 and end-group iodine
amount for polymers 3a-c were analyzed at the Mikro-
(b) 1,2-Bis(5-iodo-2-thienyl)isothianaphthene (2). MF )
C16H8I2S3; Mw ) 550.24 g/mol. Under exclusion of light, a
solution of N-iodosuccinimide (6.80 g; 30.22 mmol) in abs. DMF
(200 mL) was added dropwise to a solution of 1,3-di-2-
thienylbenzo[c]thiophene (4.4 g; 14.74 mmol) in abs. DMF (130
mL) at -55 °C. The resulting mixture was kept for 4 h at
-55 °C, and then it was allowed to reach the room temperature
overnight. The black precipitate formed was collected on a
glass filter, washed with water, and dried in a vacuum. The
mother liquor was diluted with water, extracted with CH2Cl2,
washed with water, and dried over Na2SO4, and the solvent
was removed to obtain the rest of the product. The black
precipitate and this residue extract were combined, and final
purification by column chromatography on silica gel with
n-hexane/THF (20:1) yielded 4.28 g (52%) of red solid. The
product was finally recrystallized in a n-hexane/CHCl3 (10:1)
mixture. Bright-fluorescent, dark-red needles were obtained.
1H NMR (C6D6), δ [ppm]: 7.82 (m, 2H), 7.26 (d, 2H), 7.15
(m, 2H), 6.99 (d, 2H). FT-IR (KBr), v˜ [cm-1]: 1529, 1189,
875, 777, 582. MS [m/z]: 550 (M+, triplet), 423 ([M - I]+). mp:
133.9 °C.
(c) 1,3-Bis(3-hexyl-2-thienyl)benzo[c]thiophene. 1,3-Bis(3-
hexyl-2-thienyl)benzo[c]thiophene was synthesized by a three-
step synthetic procedure.
(i) Step 1: 2-Bromo-3-hexylthiophene. MF ) C10H15BrS;
Mw ) 247.20 g/mol. To a solution of 3-hexylthiophene in (3.1
g; 18.4 mmol) in CHCl3 (15 mL) and acetic acid (15 mL)
portions of N-bromosuccinimide (3.38 g; 19 mmol) were added
at 0 °C over 30 min. After being stirred for an additional
30 min at 0 °C, the mixture was diluted with water and
extracted with CHCl3. The extracts were washed first with
2 M KOH followed by water and then dried over Na2SO4. The
residue obtained after removal of solvent was purified by
column chromatography on silica gel with cyclohexane/ethyl

Macromolecules, Vol. 37, No. 24, 2004
Poly(triarylamine)s Containing Isothianaphthene Moieties 8957
acetate (20:1) as the eluent to give 2-bromo3-hexylthiophene
(3.06 g; 67%). 1H NMR (CDCl3), δ [ppm]: 7.15 (d, 1H), 6.78 (d,
1H), 2.54 (t, 2H), 1.55 (m, 2H), 1.28 (m, 6H), 0.87 (t, 3H). FT-
IR (KBr), v˜ [cm-1]: 3107, 2956, 2926, 2856, 1467, 1409, 992,
830, 713, 635. MS [m/z]: 246 (doublet), 97 ([C4H3SdCH]+).
1277, 1229, 1176, 1133, 875, 742, 682. UV-vis, λmax [nm]: 526
(CHCl3), 538 (film). End-group elemental analysis: 0.028 wt
% of iodine.
(iii) Polymer 3c. Further purification was done by repre-
cipitation of the polymer from CHCl3 in petrol ether (fraction
with a bp 60-80 °C). After drying in high vacuum, 0.77 g of
(ii) Step 2: 1,2-Bis(3’-hexylthienoyl)benzene. MF ) C28H34O2S2;
Mw ) 466.71 g/mol. 2-Bromo-3-hexylthiophene (5.0 g; 20.2
mmol) was slowly added to a refluxing mixture of iodine-
activated magnesium (0.49 g; 20.2 mmol) in abs. THF (30 mL).
After formation of the Grignard reagent (6 h reflux) it was
slowly added to a flask containing a solution of 1,2-di(S-
pyridinyl)benzenedithioate (3.40 g; 9.6 mmol) in abs. THF (150
mL) at 0 °C. The mixture was stirred for 30 min, and finally
10% HCl (15 mL) was added to hydrolyze the complex formed.
The product was extracted with ether repeatedly, and the
combined organic fractions were washed with 2 M NaOH
solution and water until neutral and dried over Na2SO4. After
evaporation of the solvent, a light-brown, honey-like product
was obtained. Final purification by column chromatography
with cyclohexane/ethyl acetate (3:1) yielded a yellowish viscous
liquid (3.54 g; 74%). 1H NMR (CDCl3), δ [ppm]: 7.62 (m, 2H),
7.55 (m, 2H), 7.40 (d, 2H), 6.96 (d, 2H), 2.78 (t, 4H), 1.52 (m,
4H), 1.22 (m, 12H), 0.83 (t, 6H). FT-IR (KBr), v˜ [cm-1]: 3101,
3067, 3018, 2956, 2928, 2856, 1638, 1519, 1465, 1408, 1294,
1278, 1250, 912. MS [m/z]: 466 (M+), 299 ([C6H13-C4H2S-
CO-C6H4-CO]+), 228 ([OtC-C6H4-CO-C4H3SdCH]2+), 215
([OtC-C6H4-CO-C4H2S]2+), 97 ([C4H4SdCH]+).
1
polymer was collected with a yield of 78%. H NMR (CDCl3),
δ [ppm]: 7.97, 7.34, 7.14, 6.82 (m, 24H), 3.88 (m, 4H), 1.71
(m, 4H), 1.31 (m, 12H), 0.87 (m, 6H). FT-IR (KBr), v˜ [cm-1]:
3033, 2928, 2858, 1606, 1492, 1240, 820, 746. UV-vis, λmax
[nm]: 430-520 (CHCl3), 440-540 (film). End-group elemental
analysis: 0.018 wt % of iodine.
(b) Poly[1,3-bis(3-hexyl-2-thienyl) benzo[c]thiophene] (7). To
a solution of 1,3-bis(3-hexyl-2-thienyl)benzo[c]thiophene (7.5
g; 16.2 mmol) in dried CHCl3 (300 mL), powdered anhydrous
FeCl3 (10.54 g; 65 mmol) was added slowly during 6 h under
Ar at room temperature. After stirring for an additional 18 h,
the reaction mixture was poured into n-hexane as a bluish-
black powder (17.3 g) was precipitated. Soxhlet extraction with
methanol to remove Fe salts and unreacted monomer gave a
brown solid (8.9 g of dedoped polymer). After further Soxhlet
extraction with THF to dissolve the polymer left, 1.95 g (26%)
of black residue insoluble in THF was obtained (0.25% of Fe
content), which is also insoluble in common organic solvents
such as CHCl3, NMP, DMF, and DMAc. The THF solution of
the polymer was added slowly to n-hexane under vigorous
stirring to precipitate 1.7 g (23%) of high molecular weight
polymer containing 0.43% of Fe. The THF/n-hexane mother
liquor after evaporation of solvents gave a residue, which on
GPC analysis was detected as oligomers (3.46 g; 46% yield).
1H NMR (CDCl3), δ [ppm]: 7.71, 7.55, 7.33, 7.11 (8H), 2.70
(4H), 1.65 (4H), 1.23 (12H), 0.81 (6H). FT-IR (KBr), v˜ [cm-1]:
3060, 2952, 2924, 2854, 1641, 1453, 746. The polymer fraction
was treated as follows using an improved purification proce-
dure to reduce Fe content. The polymer was diluted with
CHCl3 followed by washing with 15 wt % HCl to remove
possible Fe-containing compounds such as FeCl3, FeCl2, Fe2O3,
Fe(OH)2, and Fe(OH)3, then water until neutral and dedoping
of the organic material by refluxing the CHCl3 solution
repeatedly (3×) with aqueous 25% NH3 for 30 min when the
color of the material changed from deep blue to reddish-brown.
The product was washed with aqueous KSCN solution to
remove the rest of the Fe salts and after washing with water,
drying over Na2SO4, and evaporation of CHCl3, the pure
polymer with a Fe content of only 0.013 wt % was obtained by
precipitating it from THF solution into n-hexane.
(iii) Step 3: 1,3-Bis(3-hexyl-2-thienyl)benzo[c]thiophene.
MF ) C28H34S3; Mw ) 466.78 g/mol. A mixture of 2,4-bis-(4-
methoxyphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulfide,
known as Lawesson reagent (2.0 g; 5 mmol), 1,2-bis(3′-
hexylthienoyl)benzene (2.2 g; 4.7 mmol), and CH2Cl2 (150 mL)
was refluxed for 30 min. After evaporation of CH2Cl2, ethanol
(150 mL) was added and the mixture was refluxed for an
additional 30 min. Finally, 500 mL of water was added, and
the product was extracted with ether. The combined ether
fractions were washed with copious amounts 10% NaOH and
water and dried. Final purification was done by column
chromatography (CH2Cl2, n-hexane 9:1) to obtain 1.78 g (81%)
1
of a yellow oil. H NMR (CDCl3), δ [ppm]: 7.56 (m, 2H), 7.36
(d, 2H), 7.08 (m, 2H), 7.04 (d, 2H), 2.64 (t, 4H), 1.57 (m, 4H),
1.19-1.24 (m, 12H), 0.78 (t, 6H). FT-IR (KBr), v˜ [cm-1]: 3065,
2956, 2926, 2856, 1457, 747. MS [m/z]: 466 (M+), 395 ([C6H13-
C4H2S-C8H4S-C4H2SdCH]+), 309 ([C6H13-C4H2S-C8H4S]+),
227 ([C8H4S-C4H2SdCH]2+).
2. Polymer Synthesis. (a) Poly[bis(diarylaminothienyl)-
isothianaphthene]s (3a-c). Poly[bis(diarylaminothienyl)iso-
thianaphthene]s (3a-c) were prepared by the following gen-
eral polycondensation procedure: 1,3-bis(5-iodo-2-thienyl)benzo-
[c]thiophene 2 (0.15 M), bis(secondary)amine (1a, 1b, or 1c)
(0.15 M), copper[0] (0.6 M), 18-crown-6 as a phase-transfer
catalyst (0.03 M), and potassium carbonate (1.2 M) in anhy-
drous o-dichlorobenzene (7 mL) were mixed at room temper-
ature and refluxed under nitrogen atmosphere for 5 days. The
reaction mixture was diluted with THF, and inorganic salts
were filtered off. After removing the solvent, the polymer was
dissolved in CHCl3, followed by refluxing this polymer solution
with 25% aqueous ammonia for 30 min to dedope any in situ
doping of the material, washed with water and methanol, and
dried in a vacuum. Then the polymer was repeatedly precipi-
tated into n-hexane from CHCl3.
(i) Polymer 3a. Final purification was done by reprecipitation
of the polymer in cyclohexane from CHCl3 solution. After
drying in high vacuum, 0.51 g of polymer was collected with a
yield of 63%. 1H NMR (CDCl3), δ [ppm]: 7.89, 7.34, 7.14, 6.80
(m, 24H), 2.53 (m, 4H), 1.55 (m, 4H), 1.24 (m, 20H), 0.84 (m,
6H). FT-IR (KBr), v˜ [cm-1]: 3029, 2924, 2852, 1603, 1494,
1284, 1061, 815, 745. UV-Vis, λmax [nm]: 497 (CHCl3), 520
(film). End-group elemental analysis: 0.031 wt % of iodine.
Acknowledgment. We thank Mrs. Helga Wietasch
and Dr. Haridas R. Karickal for synthesis of polymer
6. We gratefully acknowledge Sonderforschungsbereich
481 (Project B4), German Research Council (DFG), for
providing financial support for this research work.
Supporting Information Available: 1H NMR data of the
monomers and SEC plots for polymers 3a-c. This material is
available free of charge via the Internet at http://pubs.acs.org.
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