Poly[(arylene ethynylene)-alt-(arylene vinylene)]s Based on Anthanthrone and Its Derivatives: Synthesis and Photophysical, Electrochemical, Electroluminescent, and Photovoltaic Properties

Article abstract of DOI:10.1021/acs.macromol.7b02136

Anthanthrone and its derivatives are large polycyclic aromatic compounds (PACs) that pose a number of challenges for incorporation into the structure of soluble conjugated polymers. For the first time, this group of PACs was employed as the building blocks for the synthesis of copolymers (P1-P5) based on poly[(arylene ethynylene)-alt-(arylene vinylene)]s backbone (-Ph-C=C-Anth-C=C-Ph-CH - CH-Ph-CH - CH-)_n. During the synthesis of P1-P5, different alkyloxy side chains were incorporated in order to tune the properties of the polymers. Of the copolymer series only P1 (containing anthanthrone and branched 2-ethylhexyloxy side chains on phenylenes), P2 and P3 (for which the anthanthrones containing carbonyl groups were converted to anthanthrene containing alkyloxy substituents) were soluble. The photophysical, electrochemical, electroluminescent and photovoltaic properties of P1-P3 are reported, compared and discussed with respect to the effects of side chains.

Full text of DOI:10.1021/acs.macromol.7b02136

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Cite This: Macromolecules XXXX, XXX, XXX-XXX
Poly[(arylene ethynylene)-alt-(arylene vinylene)]s Based on
Anthanthrone and Its Derivatives: Synthesis and Photophysical,
Electrochemical, Electroluminescent, and Photovoltaic Properties
Suru Vivian John,†,‡ Vera Cimrova,*,§ Christoph Ulbricht,‡,∥ Veronika Pokorna,§ Ales Ruzicka,§
̌
́
́
̌
̊
̌ ̌
Jean-Benoit Giguere,⊥ Antoine Lafleur-Lambert,⊥ Jean-Franco
̧
is Morin,⊥ Emmanuel Iwuoha,*,†
̀
and Daniel Ayuk Mbi Egbe*,‡,∥
†SensorLab, Department of Chemistry, University of Western Cape, Robert Sobukwe Road, Private Bag X17, Bellville, 7535, Cape
Town, South Africa
‡Linz Institute for Organic Solar Cells, Johannes Kepler University, Altenbergerstrasse 69, 4040 Linz, Austria
§Institute of Macromolecular Chemistry, The Czech Academy of Sciences, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic
́
∥Institute of Polymeric Materials and Testing, Johannes Kepler University, Altenbergerstrasse 69, 4040 Linz, Austria
⊥Department of Chemistry, Faculty of Science and Engineering, Universite
́ ́
Laval, Pavillon Alexandre-Vachon, local 1250B Quebec,
́
Quebec G1 V 0A6, Canada
S
* Supporting Information
ABSTRACT: Anthanthrone and its derivatives are large
polycyclic aromatic compounds (PACs) that pose a number
of challenges for incorporation into the structure of soluble
conjugated polymers. For the first time, this group of PACs
was employed as the building blocks for the synthesis of
copolymers (P1−P5) based on poly[(arylene ethynylene)-alt-
(arylene vinylene)]s backbone (−Ph−CC−Anth−CC−
Ph−CHCH−Ph−CHCH−)n. During the synthesis of
P1−P5, different alkyloxy side chains were incorporated in
order to tune the properties of the polymers. Of the copolymer series only P1 (containing anthanthrone and branched 2-
ethylhexyloxy side chains on phenylenes), P2 and P3 (for which the anthanthrones containing carbonyl groups were converted
to anthanthrene containing alkyloxy substituents) were soluble. The photophysical, electrochemical, electroluminescent and
photovoltaic properties of P1−P3 are reported, compared and discussed with respect to the effects of side chains.
applications. For example, large hexabenzocoronene PAC was
incorporated in the main chain of conjugated polymers.27
These materials, however, were insoluble in common organic
solvents and difficult to process. The synthesis of π-conjugated
small molecules based on anthanthrone28 is relatively simple,
but the preparation of their polymeric analogues is challenging.
Its rigidity coupled with its large and flat π surface hinders good
solubility in common organic solvents. Only very recently, the
synthesis and characterization of the first series of soluble
conjugated polymers based on anthanthrone derivative
(anthanthrene)29 and 4,10-bis(thiophen-2-yl)anthanthrone
(TANT) were reported.30
Herein we report for the first time the preparation of
poly[(arylene ethynylene)-alt-(arylene vinylene)]s (PAE-AVs)
from anthanthrone and anthanthrene building blocks, respec-
tively, using the Horner-Wadsworth-Emmons (HWE) poly-
condensation reaction (Scheme 1).
INTRODUCTION
■
Polycyclic aromatic compounds (PACs) have attracted
considerable attention as materials with potential applications
in supramolecular electronics1−3 and are becoming increasingly
popular for optoelectronic applications.4−9 The extensive
conjugated π-systems of PACs facilitate electron delocalization,
while the rigid flat geometry enables them to stack in well-
organized arrays for strong π-stacking interactions. The π-
conjugated systems influence the tuning of the optoelectronic
properties, while the flat geometry enables good light emitting
properties and intermolecular charge transport.10−15 These
combined features make PACs appealing building blocks for
the preparation of semiconducting polymers. In spite of this, a
comparatively low number of conjugated polymers incorporat-
ing large PACs building blocks have been reported so far.16−24
The low interest in PAC based polymers (especially for organic
photovoltaic cells) is as a result of their relatively high band gap.
Although the extension of the effective conjugation of the
polymers can be used to overcome this drawback,24−26 it is
often accompanied by a significant decrease in solubility, which
may hinder their processing into thin films for photovoltaic
Received: October 3, 2017
Revised: October 22, 2017
© XXXX American Chemical Society
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Scheme 1. Reaction Pathway for the Synthesis of the PAE-AVs Polymers
PAE-AVs are a class of polymeric materials that combine the
intrinsic properties of poly(arylene ethynylene) (PAE) and
poly(arylene vinylene) (PAV) into a single backbone with
additional structure-specific properties.31 The general constitu-
tional unit of the PAE-AV backbones in this study, (−Ph−C
C−Anth−CC−Ph−CHCH−Ph−CHCH−)n, contains
an anthanthrone or its analogue anthanthrene embedded
between two alkyne moieties (Figure 1b). To the best of our
knowledge, the use of anthanthrone and its derivative as
building blocks for polymer synthesis via the PAE-AV backbone
has never been reported. PAE-AV based on other structures
such as anthracene,32−41 thiophene and phenylene core31,42,43
have been reported. The aim of the current study was to
establish anthanthrone and its derivatives as suitable building
blocks for the design of novel PAE-AV backbones with good
solubility (through side chain incorporation and variation) and
to study their suitability as emitting or absorber materials in
organic light-emitting or photovoltaic (OPV) devices, respec-
tively.
RESULTS AND DISCUSSION
■
Synthesis. The synthesis of new polymers is schematically
displayed in Scheme 1. The synthesis of the dialdehydes Ma−
Mc and the bisphosphonates M1−M3 follows well-established
protocols.32,33,44,45 Starting both with the O-alkylation of
hydroquinone, their preparation involves overall 6 and 3
reaction steps, respectively. The reaction sequence for the
synthesis of the dialdehyde involves the dibromination of the
O-alkylated hydroquinone; the transformation of one bromo
substituent by formylation; the substitution of the remaining
bromo substituent by trimethylsilylethynyl via palladium-
catalyzed Sonogashira cross-coupling reaction; and the cleavage
of the trimethylsilane group to yield an alkyne functionalization,
which was reacted with the respective dibromo anthanthrone or
anthanthrene derivative in the final Sonogashira cross coupling
(Scheme 1a).
The chemical structure and purity of the synthesized
materials were confirmed by NMR spectroscopy. The 1H
NMR, 13C NMR and 31P NMR spectra of the bisphosphonate
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Figure 1. (a) Monomers (M1−M3 and Ma−Mc) and (b) polymers (P1−P5) and a small molecule (SM).
polycondensation comonomers, M1, M2, and M3, are depicted
in the Supporting Information (Figures S1−S9). The NMR
spectra of the dialdehyde polycondensation comonomers, Ma−
Mc, are displayed in Figures 2 and S10−S14. For the polymers
P1, P2, and P3, 1H NMR and FTIR spectroscopy were
conducted (Figures 3 and S15−S20), while for SM, only H
NMR was conducted (Figure S21).
The NMR spectra of the bisphosphonate polycondensation
the anthanthrone/anthanthrene unit and the phenylene group
appear in the range 8.94−7.09 ppm. The CH2 protons directly
linked to the oxygen in the alkoxy side chain, in the phenyl
group, as well as, in the anthanthrene unit, are visible in the
4.92−3.49 ppm region. The CH (ethylhexyloxy side chain) and
CH2 (decyloxy side chain) protons following the CH2 groups
directly linked to the oxygen of the alkoxy side chains are
assigned to the signals in the range 2.36−1.68 ppm. All other
CH2 protons present in the compounds show signals in the
range 1.68−1.03 ppm, while the signals of all CH3 protons are
clearly visible between 1.03 and 0.87 ppm. The 13C spectra of
1
comonomers (M1−M3, Figures S1−S9) are in good agreement
with literature.44−50 For Ma−Mc, the H signals (Figure 2 and
1
Figures S10−S12) in the range 10.49−10.44 ppm are attributed
to the CHO aldehyde protons while the aromatic protons of
C
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Mc was applied in HWE polycondensation reactions with the
bisphosphonate M1 and M3 to obtain the polymers P4 and P5,
respectively. However, the materials obtained from this reaction
showed no reasonable solubility in common solvents, which
prevented further characterization. Despite P1, P4, and P5
possessing identical backbones based on anthanthrone units,
the presence of only branched 2-ethylhexyloxy side chains
apparently granted partial solubility for P1 in common organic
solvents. The linear decyloxy side chains in P4 and P5 appear
much less efficient in promoting solubility. The significantly
better solubility of the polymers P2 and P3 can be apparently
attributed to the presence of anthanthrene instead of
anthanthrone building blocks in the polymer backbones. The
repeating units of P2 and P3 are isomeric. Their structures only
differ in the side chains, linear dodecyloxy and branched (3,7-
dimethyloctyl)oxy, introduced by the different bisphospho-
nates, which were used in the respective polycondensation
reaction. This was done in order to study the effect of various
side chains on the polymer properties.
1
Figure 2. H NMR spectra of Ma−Mc.
The characteristic FTIR signals associated with the molecular
vibrations of P1, P2, and P3 occur at 3073−3064, 2962−2850,
2198−2180, 1659, 1603−1575, 1500, 1464, 1380, and 1203
cm−1 (Figures S18−S20). The bands between 3073−3064
cm−1 are attributed to the stretching vibrations of aromatic 
C−H and unsaturated hydrocarbon (vinylene). Characteristic
aliphatic −C−H stretching vibrations of all three polymers
show high intensity signals at 2962−2850 cm−1, while the
vibrational stretching of the ethynylene linker bond (−CC−)
gives a weak signal at 2198−2180 cm−1 for all the three
polymers. These FTIR spectral signals confirm a disubstituted
ethynylene linker bond. The characteristic stretching vibration
associated with the ketone group (−CO) of P1 is observed
at 1659 cm−1, and as expected, this ketone signal is completely
absent in the spectra of P2 and P3. The signals around 1603−
1575 cm−1 are produced by the vinylene linker bond stretching,
while those observed at 1500 and 1203−1031 cm−1 are for the
stretching vibrations of aromatic −CC− and aromatic−
aliphatic −CC−O−C− bonds, respectively. The bands
observed at 969 and 861−869 cm−1 are attributed to the
vinylene double bonds.
1
Figure 3. H NMR spectra of P1−P3.
Ma and Mb have been schematically illustrated and explained
as shown in Figures S13 and S14, respectively.
While the 1H NMR spectra of the polycondensation
comonomers, bisphosphonates, and dialdehydes are well-
resolved and show defined signals, the spectra of the HWE
polycondensation products are characterized by a distinct signal
broadening and low resolution. The depletion or absence of the
characteristic signals for the reactive functionalities of the
comonomers, CHO (∼10.5 ppm) and CH2−P (3.5 ppm),
indicates the successful formation of polymeric species. The
signals between 9.25 and 8.41 ppm in P1 are assigned to the
protons of the anthanthrone core. Between 8.07 and 6.67 ppm
arylene vinylene proton signals can be identified. The signals in
the region 4.37−3.20 ppm and 2.49−0.37 ppm are the protons
of the alkyloxy side chains (Figure 3). The presence of a
residual aldehyde signal in the 1H NMR spectrum of P1 (∼10.5
ppm) suggests that the soluble fraction of P1 consists of low-
molecular weight species with aldehyde end groups. Figure 3
Molecular Mass and Thermal Studies. Results obtained
from SEC (THF as eluent, polystyrene standards) and
thermogravimetric analyses (TGA) are provided in Table 1.
a
Table 1. Synthesis and TGA Data of the Copolymers
b
material
T (°C)
yield (%)
Mw (g/mol)
Đ
Td (°C)
P1
P2
P3
P3
118
118
118
111
95
*95
*33
*73
3570
11730
7820
2
325
314
331
−
3.7
2.7
3.2
11800
a
T is the reaction temperature, Mw is the weight-average molecular
weight, Đ is the dispersity, and Td is the thermal decomposition
b
temperature @ 5% weight loss). Measured by SEC in tetrahydrofuran
as the mobile phase, and polystyrene standards were used for
calibration. * Determined for the soluble fraction.
1
shows the H NMR signals of P2 and P3. The broad NMR
peaks occurring at 9.05−8.22 ppm are the anthanthrenylene
protons and that at 7.65−6.92 ppm are due to the arylene
vinylene protons. The peaks in the regions 4.61−3.28 ppm and
2.41−0.42 ppm are those of the protons of the alkoxy side
chains. In contrast to P1 the 1H NMR spectra of P2 and P3 do
not show any sign of a residual aldehyde signal.
The molecular masses of the polymers P1, P2, and P3 are
relatively low. The difficulty in the preparation of polymers of
high molecular masses that contain anthanthrone or anthan-
threne building blocks, is apparent from the results obtained for
polymers P1−P3. The low Mn value obtained for P1 can be
attributed to the rapid precipitation from the reaction mixture
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during the polycondensation as a result of the poor solubility of
the polymer. The thermogravimetric analysis (TGA) data
indicates good thermal stability for all three polymers (P1, P2,
and P3). Only a 5% weight loss was observed between 314 and
331 °C (Table 1 and Figure S22).
Photophysical Properties. The photophysical properties
of the soluble polymers P1, P2, and P3 and the anthanthrene
small molecule (SM) (which is used as a model compound)
were investigated by UV−vis absorption spectroscopy and
photoluminescence spectroscopy, for both the solutions and
thin films of the materials. The absorption spectra obtained for
measurements taken with dilute solutions and thin films are
displayed in Figures 4 and 5, respectively, and their character-
istic data are summarized in Tables 2 and 3.
moiety, which is also influenced by conjugation. It is
noteworthy that only very thin films of good quality could be
prepared by spin-coating due to the limited solubility of P1.
The absorption spectra of the P2 and P3 copolymers with
anthanthrene unit significantly differ from the spectra of P1.
The corresponding SM model compound for P2 and P3
exhibits well resolved absorption spectrum in toluene and DCB
solutions that are typical of fused conjugated systems,51−54 with
maxima at 327, 400, 447, and 477 nm in toluene and slightly
red-shifted maxima at 332, 405, 450, and 480 nm in DCB. The
absorption spectrum of SM thin film is not so well resolved
reflecting the intermolecular interactions in solid state. The
absorption maxima of the thin film were red-shifted and an
absorption extension of up to 550 nm was observed when
compared with the spectra obtained for solution. The P2 and
P3 exhibit broad-band absorption in solution and thin films.
The absorption spectra in their toluene solutions are less
resolved but similar for both P2 and P3 copolymers, with the
main maximum occurring at 478 and 479 nm, respectively. P2
exhibited more extended shoulder at long wavelengths.
Qualitatively different absorption spectrum was observed for
P2 when measured in DCB solutions. The P2 absorption
spectrum in DCB solution (see Figure 4) shows broad
structureless absorption in the visible region from 400 to 600
nm, which is red-shifted compared to its toluene solution
spectrum and also the P3 and SM spectra. Broad red-shifted
band indicates more planar backbone configuration and also
aggregate formation in DCB, whereas the P3 DCB spectra are
of similar shape to its absorption spectra measured in toluene
with slightly red-shifted maxima. Similar absorption behavior as
in P2 toluene solution was observed in its tetrahydrafuran
solution, and on the other hand, the aggregation was also
observed in P2 chloroform solution. The P3 absorption
spectrum is also red-shifted compared to the SM spectrum or
its spectrum in toluene, but the red shift is not so pronounced.
Two long-wavelength maxima at 455 and 483 nm can be well
resolved in its DCB absorption spectra similarly to those of
toluene solution. The broad band in P2 absorption spectrum in
DCB reflects more planar structure than P3 and the molecular
aggregation in dilute solution. In the case of P2, the absorption
spectra of their thin films differ when the films are prepared
from toluene or DCB solutions, whereas such difference was
not observed for P3 thin films. The absorption spectra of P2
thin films prepared from DCB are significantly red-shifted and
differ in shape from the absorption spectra of P2 thin films
prepared from toluene solution, which are blue-shifted.
Figure 4. UV−vis absorption spectra of P1 (black), P2 (red), and P3
(blue) copolymers, and SM (green) model compound measured in
dilute toluene (solid curves) and DCB (dashed curves) solutions.
New polymers P2 and P3 also exhibit PL emission in both
solution and thin films, whereas the PL emission of new
polymer P1 was very weak, particularly in DCB solution and
thin films. The SM model compound is a highly luminescent
material in dilute solution. Therefore, PL properties of P1 were
studied in toluene solution and a more detailed PL study was
performed for SM, P2, and P3. The PL excitation and emission
spectra measured in toluene and DCB solutions are displayed
in Figures 6 and 7, respectively, and the characteristic data are
summarized in Table 2. In toluene solution (Figure 6), P1
exhibits a PL main maximum at 612 nm when excited at long
wavelength absorption maxima. If the excitation wavelength is
shorter an additional maximum appeared at about 500 nm
originating from anthranthrone-containing segments, which is
supported by the different excitation spectra for the emission
wavelengths for the 500 nm and the main maximum. In DCB
solution the PL emission of P1 is very weak. In toluene
Figure 5. UV−vis absorption spectra of P1 (black), P2 (red for thicker
and magenta for thinner films), P3 (blue for thicker and cyan for
thinner films), and SM (green) thin films prepared from toluene
(solid) and DCB (dashed) solutions.
The absorption of P1 covers the whole visible spectral region
and its spectra exhibited broad absorption bands in both
solutions and as thin films. The long wavelength maxima are
located at 429 and 569 nm for measurements done in toluene
and red-shifted to 433 and 607 nm in DCB solution spectra. In
thin film spectra, the maxima were slightly blue-shifted (427,
604 nm) relative to the DCB solution spectra. The long-
wavelength band can be assigned to the π−π* transition of the
conjugated polymer backbone and the band at higher energy to
the n−π* transition from the carbonyl of the anthanthrone
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Table 2. Photophysical Properties of the Copolymers Measured in Dilute Toluene and DCB Solutions (λabsmax, Absorption
Maximum; λPLmax, Emission Maximum; λPLexcmax, Maximum of the Excitation Spectrum; ηPL, Photoluminescence Quantum
Yield; Primary Maxima in Bold)
a
b
material
solvent
λabsmax (nm)
λPLmax (nm)
λPLexcmax (nm)
ηPL
P1
P1
P2
P2
P3
P3
SM
SM
toluene
DCB
363sh, 429, 487 sh, 569
433, 607
502, 612
−
519, 554
533, 589
520, 551
533
349, 550
−
−
0.47
−
c
d
c
c
c
c
toluene
DCB
333, 451, 478
332, 447, 478
337, 484, 530
332, 450, 480
334, 451, 484
334, 396, 447, 477
331, 405, 449, 480
332, 492 (523)
334, 450, 479
0.54
0.47
0.53
0.92
0.95
toluene
DCB
334, 455, 483
toluene
DCB
327, 400, 447, 477
332, 405, 450, 480
488, 518
499
a
b
c
d
Excitation wavelength at λabsmax; Emission wavelength at λPLmax, Fluorescein used as the standard. Rhodamine 6G used as the standard.
Table 3. Photophysical Properties of the Copolymers Measured as Thin Films Prepared from Toluene or DCB (λabsmax
,
Absorption Maximum; λPLmax, Emission Maximum; λPLexcmax, Maximum of the Excitation Spectrum; d, Film Thickness; Primary
Maxima in Bold)
a
b
thin film
prepared from
d (nm)
λabsmax (nm)
213, 304, 427, 604
λPLmax (nm)
λPLexcmax (nm)
P1
P2
P2
P2
P2
P3
P3
P3
P3
SM
DCB
10
46
−
625
625
621
623
609
604
605
611
567
−
DCB
212, 286, 557, 591
212, 286, 547, 581
213, 336, 488, 590
212, 336, 484, 584
213, 337, 483
488, 531, 571
DCB
87
487, 529, 570
toluene
toluene
DCB
52
333, 457, 486, 523, 577
336, 458, 484, 525, 589
335, 454, 485
157
47
DCB
70
213, 335, 479
331, 451, 482
toluene
toluene
DCB
30
214, 337, 484
335, 454, 485
111
43
213, 334, 462
334, 456, 485
206, 231, 258, 342, 423, 455 sh, 525 sh
339, 421
a
b
Excitation wavelength at λabsmax; Emission wavelength at λPLmax
solution, P2 and P3 emit yellowish light, which is red-shifted
when compared with SM model compound’s emission of
greenish light. In DCB solution the P2 emission is significantly
red-shifted and the emitted light is of orange-red color whereas
PL emission of P3 is similar to its toluene solution. Similarly, as
in the absorption study, the PL emission spectra of P2 and P3
measured in toluene solutions are similar, but significantly differ
in DCB solutions. In the toluene solution, the emission spectra
show vibration structure with main maxima at 519 and 520 nm
for P2 and P3, respectively, and the excitation ones are well
resolved and follow absorption ones. In the DCB solution PL
emission spectra of P2 and P3 (Figure 7, parts a and b)
significantly differ. The PL maximum of P2 DCB solution
spectrum, located at 589 nm, significantly red-shifted when
compared with the maximum of its emission spectrum in
toluene and with the 533 nm of the P3 DCB solution spectrum.
The maximum at about 530 nm is also observed in the P2
emission spectrum for the shorter excitation wavelength of 482
nm, but the maximum at 589 nm dominates.
The excitation spectra of P2 in DCB depended on the
emission wavelength. For the emission at 531 nm, the PL
excitation spectrum is similar to that measured in toluene,
whereas for the emission at 589 nm the PL excitation spectrum
is broader with a better resolved structure, but it follows the
shape of absorption spectrum in DCB. The excitation spectrum
of P3 exhibited better-resolved vibration structure when
compared with the corresponding absorption spectra and
follows well the shape of the absorption one. The PL behavior
of P2 supports the results from the absorption study
concerning the better planarity and aggregation of P2
molecules in the DCB. The PL quantum yields determined
for P2 and P3 in their toluene and DCB solutions were similar
for both polymers in the same solution, and both P2 and P3
have slightly higher values in their DCB solutions. PL emission
and excitation spectra of the SM model compound are shown
in Figures 6 and 7 for comparison. In toluene the PL emission
spectrum for SM is better resolved and exhibited a maximum at
488 nm, whereas the maximum of the SM spectrum in DCB is
slightly red-shifted at 499 nm. The excitation spectra are well
resolved for both solvents and similar to the absorption ones.
The PL spectra measured for the thin films are displayed in
Figure 8, and the characteristic data are summarized in Table 3.
For the thin films, the emission maxima are red-shifted
compared to their solutions. In the PL the emission maxima
are at 621−623 nm in the spectra of P2 films prepared from
toluene and are slightly red-shifted to 625 nm for P2 prepared
from DCB. The shape of emission spectra is similar for both P2
films, but the excitation spectra significantly differ. The
excitation spectrum of P2 film prepared from toluene follows
a similar pattern to its absorption spectrum, but the excitation
spectrum of the P2 film prepared from DCB differs in shape
from its absorption one. In the case of P3 films the PL emission
with maxima at 605−611 nm is slightly blue-shifted when
compared with P2 films and there is nearly no difference for the
P3 films prepared from toluene or DCB. The excitation spectra
follow a similar behavior to those of the absorption ones and
are better resolved. Compared with the toluene solution red
shift in the emission maxima of the PL thin film spectra is about
100 nm for P2 and 70 nm for P3 films, which indicates excimer
and/or aggregate formation in solid state for both polymers,
which is also evident from the large Stokes shifts.
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Figure 7. PL emission and excitation spectra of (a) P2, (b) P3, and
(c) SM measured in dilute DCB solutions. Normalized absorption
spectra are shown in dashed lines.
curves of P1, P2, and P3 polymer thin films and SM film coated
on a Pt wire are displayed in Figure 9. Quasi-reversibility in the
oxidation and reduction of all new polymers and also SM
model compound was observed. The ionization potential
(HOMO level), EIP, and electron affinity (LUMO level), EA,
were estimated from the onset potentials, Eonset, of the
oxidation and reduction peaks based on the reference energy
level of ferrocene (4.8 eV below the vacuum level) using the
equation EIP (EA) = |−(Eonset − Eferr) − 4.8| eV, where Eferr is
the half-wave potential for ferrocene vs the Ag/Ag+ electrode.
The CV curve of SM exhibited a small prepeak in the
reduction, which is in good correlation with the shoulder in the
thin film absorption spectra. The similar EIP (−EHOMO) values
of 5.05, 5.12, and 5.15 eV were evaluated for P2, P3 and SM,
respectively, which are lower than the value of 5.36 eV obtained
for P1. The EA (−ELUMO) value of 3.87 eV for P1 was higher
than 2.92, 2.85, and 2.62/2.84 eV evaluated for P2, P3 and SM,
respectively. The EA values reflect the higher electron affinity of
the anthanthrone block (which possesses two electron-
withdrawing keto groups at the 6- and 12-positions of the
anthanthrone unit) than the anthanthrene unit. Electrochemical
bandgap values of 1.49, 2.13, and 2.27 eV were determined for
Figure 6. PL emission and excitation spectra of (a) P1, (b) P2, (c) P3,
and (d) SM measured in dilute toluene solutions. Normalized
absorption spectra are shown in dashed lines.
The PL spectra of SM thin film are also shown in Figure 8c.
A red shift of the PL emission spectrum is also observed. The
shape of the excitation spectrum matches well with the
absorption spectrum shape. The relative PL efficiency of a
thin film,
Φ
PLrel, was used to compare the PL efficiencies of the
polymers. The ΦPLrel of the films prepared from toluene is
similar for both copolymers P2 and P3, whereas ΦPLrel of P2
films prepared from DCB is by more than three times higher
than the ΦPLrel of P3.
Electrochemical Properties. Cyclic voltammetry (CV)
measurements were performed to obtain information on the
electronic structures of the new polymers. Representative CV
G
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Figure 9. Representative cyclic voltammograms of (a) P1, (b) P2, (c)
P3, and (d) SM thin films coated on a Pt wire, recorded at a scan rate
of 50 mV s−1.
Figure 8. PL emission and excitation spectra of 52 nm (blue) and 46
nm (black) thick P2 films, 111 nm (blue) and 70 nm (black) thick P3
films prepared from toluene (blue) and DCB (black) solutions,
respectively, and 43 nm thick SM prepared from DCB. Normalized
absorption spectra are shown in dashed lines.
The P2 LED exhibited better performance than the P3 LED,
which is in good agreement with the relative PL efficiencies of
the thin films. An example of the typical dependences of the
luminance on the applied voltage measured on the ITO/
PEDOT:PSS/polymer/Ca/Al LED is shown in Figure 11. The
P2 LED produced higher luminance values (of up to 200 cd
m−2, where saturation occurred) and a lower EL onset voltage
(of 1.9−2 V) than P3. Lower EL onset voltages for P2 (in
comparison with P3) are in good correspondence with the
lower bandgap values of P2 compared with P3. The EL results
obtained with the nonoptimized simple LEDs gave an
interesting comparison of the two new copolymers. P2 seems
to be more promising for further polymer or device
optimization: for example, by the modification of the injection
electrodes, or by using various blends of EL polymers (in the
case of polymer-blend LEDs) with appropriate electro-
luminescent or charge-transporting polymers to make charge
injection and transport more balanced.55−62
P1, P2 and P3, respectively, which were slightly higher values
than the optical bandgap values determined from the
absorption edge (except for P1), but there was good correlation
between the values for the polymers and SM. (see Table 4).
Electroluminescent Properties. The new polymers P2
and P3 were used to create active layers in samples of light-
emitting diodes (LEDs). LEDs with a hole-injecting electrode
formed by indium-tin oxide (ITO) covered with a poly[3,4-
(ethylenedioxy)thiophene]/poly(styrenesulfonate) (PE-
DOT:PSS) layer and an electron-injecting electrode of calcium
covered with aluminum (Ca/Al) were prepared and studied.
The electroluminescent (EL) spectra of the LEDs are shown in
Figure 10. The EL spectrum of the P2 LEDs was similar to the
PL thin film spectrum. The EL emission maximum was at 624
nm. The EL spectra of P3 LEDs were slightly blue-shifted to
the PL thin film spectra. The EL maximum of the P3 LEDs
depended slightly on the applied voltage; a blue shift was
observed as voltage increased. Similarity in EL and PL thin-film
spectra indicated that similar centers occur in the EL and PL
emission processes.
Photovoltaic Properties. To investigate the performance
of the new polymers P1−P3 as absorbers in bulk hetero-
junction solar cell applications, organic photovoltaic devices
(OPVs) with nonoptimized configurations were fabricated and
investigated. The OPV devices {ITO/PEI/Polymer:[60]-
PCBM(1:2)/MoOx/Ag} consisted of active blend layers of
P1, P2, and P3 copolymers and the fullerene derivative [6,6]-
H
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Table 4. Electronic Properties of the Copolymers (EIP, Ionization Potential; EA, Electron Affinity; Egelc, Electrochemical
Bandgap; Egopt, Optical Bandgap)
material
EIP (eV) (−EHOMO
)
EA (eV) (−ELUMO
)
Egelc (eV)
Egopt (eV)
P1
P2
P3
SM
5.36
5.05
5.12
5.15
3.87
2.92
2.85
1.49
2.13
2.27
1.6
1.98
2.21
a
a
2.62/ 2.84
2.53/ 2.33
2.51/2.2
a
Evaluated from the reduction prepeak onset.
Figure 10. Normalized EL spectra (solid) of the ITO/PEDOT:PSS/
P2/Ca/Al LED (blue) and ITO/PEDOT:PSS/P3/Ca/Al LED (red)
measured at 3 V. PL emission spectra of the corresponding thin films
(dashed) are displayed for comparison.
phenyl-C61-butyric acid methyl ester ([60]PCBM), in an
inverted cell architecture where polyethylenimine (PEI) and
molybdenum oxide were used as interfacial layers. The
current−voltage characteristics of the OPV devices involving
P1−P3 are shown in Figure 12, parts a and b. The OPVs based
on P2 and P3 copolymers with anthranthrene unit exhibited
better performance with power conversion efficiency (PCE)
values of 1.17% and 0.61%, respectively, than the OPVs based
on P1 with anthranthrone unit having a PCE of 0.18% (Table
5).
The higher efficiency realized with P2-based OPV can be
attributed to higher Jsc and FF. The Voc ideally correlates with
the energetic difference between the EIP (HOMO) of the donor
polymer and the EA (LUMO) of the [60]PCBM acceptor. The
OPVs based on P2 and P3 showed resemblance in their Voc
values (0.76 and 0.78 V, respectively), which is in good
agreement with the similar ionization potentials EIP (HOMO
levels) of P2 (5.05 eV) and P3 (5.12 eV). The Voc value for P1
based OPV is higher (Voc = 0.93 V) as expected due to higher
EIP value of P1 (5.36 eV). The difference in the EA values of the
[60]PCBM and copolymer (LUMO energy offset) is for P1
only 0.03 eV, which is probably too low value for exciton
dissociation to be efficient enough, and this could implicate the
low JSC value for P1 based OPV. On the other hand, LUMO
energy offsets for P2 and P3 (of 1 eV) are large enough for the
exciton dissociation. The EA value of 3.9 eV used for
[60]PCBM was obtained from our CV measurement. The
low FF values of P1 and P3 based OPVs are likely to be
Figure 11. Dependence of current density (a) and luminance (b) on
the applied voltage measured on the ITO/PEDOT:PSS/P2/Ca/Al
(circles) and ITO/PEDOT:PSS/P3/Ca/Al (squares) LEDs.
attributed to nonsuitable film morphologies. The solubility of
conducting polymers plays a major role in the film morphology.
Low solubility leads to poor quality of films, which induce low
FFs values and invariably lower the efficiency of OPV devices.
Low solubility also seems to cause poor miscibility with the
electron acceptor [60]PCBM, which might partly explain the
limited performance of the devices. Besides other character-
istics, generally the solubility, molecular weight, intermolecular
interactions, and charge carrier mobilities of the conjugated
semiconducting polymers can largely affect their photovoltaic
properties.63−68
The external quantum efficiency (EQE), which is the
measure of the efficiency of a cell to convert incident photons
into free charge carriers, was also investigated. Figure 13 shows
EQE curves for the OPVs. As a result, high EQE values can be
achieved by the combined effect of efficient exciton generation
in the bulk of the active blend layer, the dissociation into free
charge carriers, and the charge transport to the respective
electrode. The linear correlation between Jsc and EQE can be
seen in P1−P3 (Figure 13, Table 5). P2 that has the highest Jsc
I
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Figure 13. External quantum efficiencies of ITO/PEI/Polymer:
[60]PCBM(1:2)/MoOx/Ag OPV devices using P1 (black), P2
(red), and P3 (blue).
demonstrate the preparation of the anthanthrone based PAE-
AV polymer with soluble fractions. This was not possible with
P4 and P5 with linear decyloxy side chains formed as insoluble
materials. Substitution of anthanthrone with anthanthrene units
appeared to be an efficient strategy to prepare polymers with
appreciable solubility (P2 and P3). P1, P2, and P3 were
studied in detail. All three polymers exhibited interesting
photophysical properties. The absorption spectrum of P1 in
solution and thin films covered the whole visible spectral
region. The PL of P1 was weak, particularly in DCB and thin
films. The “transformation” of the anthanthrone’s carbonyl
groups into anthanthrene’s alkyloxy substituents in the
synthesis of P2 and P3 affected the photophysical properties
of the resultant copolymers significantly. The properties of P2
and P3 indicated that they were not only dominated by the
polycyclic chromophore, but were also influenced by the nature
of the side chains on the phenylene−vinylene unit (decyloxy in
P2 and 3,7-dimethyloctyloxy in P3). The absorption and PL
properties of P2 and P3 were similar in their toluene solution
only, whereas in DCB solutions they differ. The absorption
spectra of P2 thin films differed whether the thin films were
prepared from toluene or from DCB solutions, contrary to P3
thin films for which such a difference was not observed. PL
studies also revealed differences in the P2 and P3 behavior in
solutions and thin films. The results of the photophysical
studies indicate the formation of aggregates in P2 DCB
solution, and more pronounced planarity and excimer or
aggregate formation in P2 films than in P3 ones. The ionization
potential (HOMO level) and electron affinity (LUMO level)
values determined for P1 were higher than the corresponding
values for P2 and P3, thereby reflecting the higher electron
affinity of anthanthrone block than that of anthanthrene unit.
The copolymers P2 and P3 were tested as active layers in
polymer LEDs. The performance of the LEDs with P2 as an
active layer was better than that of the P3 LEDs, which is in
Figure 12. Current−voltage characteristics of ITO/PEI/polymer:
[60]PCBM(1:2)/MoOx/Ag OPV devices using (a) P1, (b) P2
(circles), and P3 (squares), which were measured in the dark and
under illumination by solar simulator at 100 mW cm−2.
value exhibits the highest EQE value, while P1, with the lowest
Jsc, has the lowest EQE value.
P1−P3 were tested in OPV devices without any optimization
and, therefore, the photovoltaic performance is also limited.
Optimization of several parameters such as the morphology,
variation of the mutual component ratio in blends and
utilization of more appropriate device architecture could further
improve the OPV devices.63−68 We have recently shown that
fullerene aggregation occurs in the blend layers, which can
negatively influence the device performance.69 Using blends
with a nonfullerene acceptor for the active layer is another way
to improve the stability and performance of OPV.70−76
CONCLUSIONS
■
Polycyclic aromatic building blocks based on anthanthrone and
anthanthrene, were incorporated for the first time into the
backbone of poly[(arylene ethynylene)-alt-(arylene vinylene)]s
yielding new copolymers P1−P5. With copolymer P1, which
possesses 4,10-linked anthanthrone building blocks and an all-
branched 2-ethylhexyloxy side chains, it was possible to
Table 5. Photovoltaic Characteristic Data of ITO/PEI/Polymer:[60]PCBM(1:2)/MoOx/Ag Devices Based on P1, P2, and P3
(Jsc: short-circuit current density; Voc: open-circuit voltage; FF: fill factor; PCE: power conversion efficiency; d: active layer
thickness)
polymer
d (nm)
Jsc (mA cm−2
)
Voc (V)
FF
PCE (%)
J @ −2 V (mA cm−2
)
J @ + 2 V (mA cm−2
)
P1
P2
P3
92
104
134
0.58
2.90
2.02
0.93
0.76
0.78
0.33
0.53
0.39
0.18
1.17
0.61
−0.94
−3.19
−2.53
0.05
22.74
0.95
J
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atmosphere. Thin layer chromatography (TLC) was used to monitor
the progress of the reaction. Toluene (40 mL) was added and the
heating was removed. After cooling to room temperature, the mixture
was precipitated in cold methanol and refrigerated for 4 h. The
precipitate was filtered off, redissolved in toluene, and purified through
column chromatography (silica gel) toluene as eluent to yield 350 mg
good agreement with the relative PL efficiencies of the thin
films. P1, P2, and P3 containing [60]PCBM in blend layers
were also tested for photovoltaic applications. Similarly,
photovoltaic devices based on P2 exhibited better performance
than those based on P3. The replacement of decyloxy side
chains in P2 with 3,7-dimethyloctyloxy in P3 resulted in lower
yield and decrease in photovoltaic efficiency. Optimization of
the device composition and architecture might yield significant
enhancements of the LED efficiency and the photovoltaic
performance.
1
(37%) of a purplish black substance. H NMR (300 MHz, CDCl3): δ
10.47 (s, 2H), 8.87−8.66 (m, 4H), 8.60 (s, 2H), 7.95−7.73 (m, 2H),
7.32 (s, 2H), 7,17 (s, 2H), 4.17−3.82 (m, 8H), 2.03−1.73 (m, 4H),
1.73−1.16 (m, 32H), 1.1−0.8 (m, 24H). 13C NMR (100 MHz,
CDCl3): δ 188.98, 182.12, 155.49, 154.07, 134.07, 133.74, 131.28,
129.53, 129.30, 128.63, 127.60, 125.45, 124.11, 119.09, 117.49, 109.36,
94.20, 93.96, 71.72, 71.65, 39.57, 39.48, 30.65, 30.34, 29.71, 29.14,
29.01, 24.04, 23.77, 23.11, 23.08, 14.13, 14.07, 11.26, 11.06.
EXPERIMENTAL SECTION
■
Synthesis of Mb. A mixture of 4,10-dibromo-6,12-bis(2-
ethylhexyloxy)anthanthrene (200 mg, 0.29 mmol), diisopropylamine
(10 mL), and toluene (20 mL) was deaerated for 30 min. Pd(PPh3)4
(16.7 mg, 0.015 mmol), and CuI (2.8 mg, 0.02 mmol) were added.
After another hour a deaerated solution of 2,5-bis(decyloxy)-4-
ethynylbenzaldehyde (320 mg, 0.72 mmol) in toluene (15 mL) was
added dropwise into the mixture. The reaction mixture was heated to
70−80 °C for 24 h in a nitrogen atmosphere and monitored with
TLC. Toluene (40 mL) was added. After the reaction cooled to room
temperature, the precipitated diisopropylammonium bromide was
filtered off and the solvent was evaporated under vacuum. The residue
was subjected to column chromatography−silica gel with toluene:hex-
ane (4:1) as eluent. 380 mg (93% yield) of a greenish substance was
Synthesis. All starting materials and solvents were purchased from
commercial suppliers (Sigma-Aldrich, Merck and Alfa Aesar and
VWR). Most of the details describing the synthesis steps toward the
HWE polycondensation monomers, dialdehydes (Ma−Mc) and
bisphosphonates (M1−M3) (Scheme 1), are given in the Supporting
Information.
Monomer Synthesis. Synthesis of M1. A mixture of 1,4-
bis(bromomethyl)-2,5-bis(2-ethylhexyloxy)benzene (15.2 g, 18.97
mmol) and an excess of triethylphosphite (9.47 g, 57.0 mmol) was
stirred and heated slowly to 150−160 °C; simultaneously, the evolving
ethyl bromide was distilled off. After 4 h, vacuum was applied for 30
min at 180 °C to distill off the excess triethylphosphite. The residual
oily product was allowed to cool to room temperature (14.4 g, 83%
yield). 1H NMR (300 MHz, CDCl3): δ 6.92 (d, J = 1.6 Hz, 2H), 4.08−
3.89 (m, 8H), 3.79 (d, J = 5.6 Hz, 4H), 3.15 (d, J = 20.1 Hz, 4H),
1.76−1.59 (m, 2H), 1.55−1.34 (m, 10H), 1.34−1.11 (m, 18H), 0.99−
0.63 (m, 12H). 13C NMR (75 MHz, CDCl3): δ 150.43, 119.30,
114.50, 71.17, 61.8, 39.65, 30.58, 29.09, 27.06, 25.21, 23.89, 23.00,
16.30, 14.01, 11.12.
1
obtained. H NMR (300 MHz, CDCl3): δ 10.49 (s, 2H), 8.94 (d, J =
7.4 Hz, 2H), 8.80 (d, J = 8.1 Hz, 2H), 8.73 (s, 2H), 8.19 (m, 2H), 7.38
(s, 2H), 7.22 (s, 2H), 4.29 (d, J = 5.5 Hz, 4H), 4.21−4.07 (m, 8H),
2.23−1.68 (m, 10H), 1.68−1.08 (m, 78H), 1.03 (t, J = 7.0 Hz, 6H),
0.90 (t, J = 6.6 Hz, 6H), 0.77 (t, J = 6.7 Hz, 6H). 13C NMR (100 MHz,
CDCl3): δ 189.13, 155.51, 153.95, 150.13, 130.72, 127.58, 125.98,
125.61, 124.88, 124.52, 123.95, 121.27, 120.54, 120.22, 119.50, 117.12,
109.28, 96.16, 90.48, 69.26, 59.55, 41.30, 38.17, 31.94, 31.86, 31.26,
30.48, 29.70, 29.62, 29.46, 29.32, 26.12, 24.03, 23.31, 22.72, 22.58,
14.32, 14.15, 14.05, 11.56.
M2 and M3 were prepared under similar reaction conditions as
described for M1
Synthesis of M2. A mixture of 1,4-bis(bromomethyl)-2,5-bis-
(decyloxy)benzene (3.37 g, 5.85 mmol) and an excess of
triethylphosphite (3.0 g, 17.6 mmol) were stirred and heated slowly
to 150−160 °C, and the evolving ethyl bromide was distilled off
simultaneously. The reaction proceeded for 4 h, after which vacuum
was applied for 1 h at 180 °C to distill off any excess of
triethylphosphite left in the mixture. The resulting oil was allowed
to cool to room temperature to form a white solid, which was
recrystallized from diethyl ether (30 mL), yielding a white powder (3.9
g, 97%). 1H NMR (400 MHz, CDCl3): δ 6.89 (s, 2H), 4.00 (m, 8H),
3.90 (t, J = 6.5 Hz, 4H), 3.20 (d, J = 20.3 Hz, 4H), 1.82−1.65 (m, 4H),
1.41−1.15 (m, 40H), 0.86 (t, J = 6.6 Hz, 6H). 13C NMR (100 MHz,
CDCl3): δ 150.31, 119.28, 114.70, 68.89, 61.69, 31.89, 29.61, 29.56,
29.47, 29.44, 29.32, 26.92, 26.13, 25.54, 22.67, 16.38, 16.34, 16.31,
14.10.
Synthesis of Mc. A mixture of 4,10-dibromoanthanthrone (200 mg,
0.43 mmol), diisopropylamine (12 mL), and toluene (20 mL) was
deaerated. Pd(PPh3)4 (20.3 mg, 0.02 mmol) and CuI (3.3 mg, 0.02
mmol) were added. After 30 min, a deaerated solution of 2,5-
bis(decyloxy)-4-ethynylbenzaldehyde (390 mg, 0.88 mmol) in toluene
was added dropwise. The reaction mixture was heated to 70−80 °C for
24 h in a nitrogen atmosphere. Toluene was added and the mixture
was allowed to cool to room temperature. The precipitated
diisopropylammonium bromide was filtered off and the solvent was
distilled off using a rotary evaporator. The residue was subjected to
column chromatography using silica gel, with toluene as eluent to yield
130 mg (26% yield) of a purple substance. The same reaction was
conducted in THF at 60 °C for 72 h. After cooling, the mixture was
reprecipitated in cold methanol (100 mL). The precipitate was
recovered via filtration, and the crude residue was purified by column
chromatography (silica gel) with toluene as eluent to afford Mc as a
Synthesis of M3. A mixture of 1,4-bis(bromomethyl)-2,5-bis(3,7-
dimethyloctyloxy)benzene (5.10 g, 8.70 mmol) and an excess of
triethylphosphite (4.40 g, 26.1 mmol) was stirred and heated slowly to
150−160 °C, and the evolving ethyl bromide was concurrently
distilled off. After 4 h, vacuum was applied for 30 min at 180 °C to
distill off any excess of triethylphosphite. The residual yellow oil was
1
purplish black solid (74% yield). H NMR (300 MHz, CDCl3): δ
10.44 (s, 2H), 8.72 (d, d, J = 6.9 Hz, 4H), 8.49 (s, 2H), 7.82−7.68 (m,
2H), 7.24−7.13 (m, 2H), 7.09 (s, 2H), 4.06 (t, t, J = 6.6 Hz, 8H), 2.17
(m, 4H), 1.91 (m, 8H), 1.66−1.08 (m, 56H), 0.87 (t, t, J = 6.2 Hz, 6H,
6H). Acquisition of the 13C NMR spectrum of Mc proved unsuccessful
because of the poor solubility and precipitation of the product during
the course of the acquisition.
Polymer Synthesis. Synthesis of P1. For the synthesis of P1, a
solution of Ma (150 mg, 0.14 mmol) and M1 (89.0 mg, 0.14 mmol) in
dry toluene (12 mL) was mechanically stirred and heated under
nitrogen to reflux. The polymerization was initiated by the addition of
potassium tert-butoxide (63.0 mg, 0.56 mmol) and a spontaneous
color change from deep pink to black was observed. The reaction
mixture was stirred for 45 min, and toluene (100 mL) was added. The
reaction was quenched with aqueous HCl (10 wt %, 10 mL). The
organic phase was separated and washed with deionized water until a
pH of ∼7 was obtained. Residual water was removed from the mixture
1
allowed to cool to room temperature (5.73 g, 96% yield). H NMR
(400 MHz, CDCl3): δ 6.85 (s, 2H), 4.07−3.79 (m, 12H), 3.14 (d, J =
20.4 Hz, 4H), 1.86−1.37 (m, 8H), 1.32−1.01 (m, 24H), 0.86 (d, J =
Hz, 6H), 0.79 (d, J = 6.6 Hz, 12H). 13C NMR (100 MHz, CDCl3): δ
150.15, 119.18, 114.60, 67.01, 61.61, 38.99, 37.09, 36.23, 29.63, 27.72,
26.71, 25.32, 24.45, 22.45, 22.34, 19.44, 16.09.
Synthesis of Ma. 4,10-Dibromoanthanthrone (408 mg, 0.88 mmol)
was given to a mixture of diisopropylamine (15 mL) and
tetrahydrofuran (40 mL). After deaeration of the reaction for 30
min, Pd(PPh3)4 (45.1 mg, 0.04 mmol) and CuI (7.4 mg, 0.04 mmol)
were added. The mixture was allowed to stir and deaerate for another
30 min. Thereafter, 2,5-bis(2-ethylhexyloxy)-4-ethynylbenzaldehyde
(750 mg, 2.0 mmol, dissolved in deaerated THF) was added dropwise.
The reaction mixture was heated to 60 °C for 72 h in a nitrogen
K
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by heating to reflux in a Dean−Stark apparatus. The water-free mixture
was concentrated with a rotary evaporator, precipitated in cold
methanol, and then kept in the refrigerator for 24 h. Afterward the
precipitate was filtered off in a Soxhlet thimble, which was transferred
into a Soxhlet extractor. Extraction was performed with methanol in
order to remove oligomers and any impurity. The extraction continued
until the extract appeared colorless. The polymer was redissolved in
toluene, reprecipitated in cold methanol and stored in the refrigerator.
After 24 h, it was filtered and dried under air to obtain a black, partially
soluble polymeric material (190 mg, 95% yield). SEC of the soluble
fractions (THF as eluent; polystyrene standards): Mn = 1830 g/mol,
2.38−0.42 (m, alkyl H’s). FTIR, cm−1: 3073 (ν(C−H)), 2962,
2924, and 2850 (ν(C−H)), 2198 (ν(CC)), 1603 (ν(CC)
vinylene), 1500 (ν(CC) aromatic ring), 1464 (δ(CH2)), 1203
(ν(CC−O−C) aromatic−aliphatic).
P4 and P5 were synthesized under similar reaction conditions as
described for P1−P3. For P4, monomers Mc and M1 were employed
while for P5; monomers Mc and M3 were employed. Both
polycondensation reactions produced materials that appeared
completely insoluble and could not be further characterized.
Synthesis of SM. Mb (190 mg, 0.14 mmol) and diethyl
benzylphosphonate (79.0 mg, 0.34 mmol) were dissolved in dried
toluene (15 mL) to give a greenish brown color while stirring
vigorously under nitrogen and heating under reflux. Potassium-tert-
butoxide (62 mg, 0.50 mmol) was added (and the reaction mixture
was heated at reflux for 30 min. After 30 min, toluene was added, heat
was removed, and aqueous HCl (10 wt %) was added. The purification
1
Mw = 3570 g/mol, and Đ = 2. H NMR of the soluble fractions (300
MHz, CDCl3): δ 10.48 (s), 9.25−8.41 (m, anthanthronylene H’s),
8.07−6.67 (m, arylene vinylene H’s), 4.37−3.20 (m, −CH2O−),
2.49−0.37 (m, alkyl H’s). FTIR, cm−1: 3064 (ν(C−H)), 2962,
2934, and 2878 (ν(C−H)), 2198 (ν(CC)), 1659 (ν(CO)), 1575
(ν(CC) vinylene), 1500 (ν(CC) aromatic ring), 1464 (δ(CH2)),
1380 (δ(CH3)), 1203 (ν(CC−O−C) aromatic−aliphatic).
P2−P5 were prepared under similar reaction conditions as
described for P1
1
process yielded a greenish material (170 mg, 79%). H NMR (300
MHz, CDCl3): δ 9.08 (d, J = 7.3 Hz, 2H), 8.92−8.78 (m, 2H), 8.27 (t,
J = 7.7 Hz, 2H), 7.64 (d, J = 7.6 Hz, 4H), 7.56−7.18 (m, 16H), 4.37
(d, J = 5.2 Hz, 4H), 4.28 (t, J = 6.4 Hz, 4H), 4.15 (t, J = 6.2 Hz, 4H),
2.19 (m, 2H), 1.94−1.03 (m, 80H), 0.94 (d, J = 6.6 Hz, 12H), 0.83 (t,
J = 6.2 Hz, 12H).
Synthesis of P2. A solution of Mb (170 mg, 0.12 mmol) and M2
(83.0 mg, 0.12 mmol) in dry toluene (12 mL) was mechanically stirred
and heated under nitrogen to reflux. Potassium tert-butoxide (54 mg,
0.48 mmol) was added at a stable temperature to initiate the reaction.
A color change from bright green to dark green was observed. The
reaction mixture was stirred for 80 min. Thereafter, toluene (100 mL)
was added, and the reaction was quenched with aqueous HCl (10 wt
%, 10 mL). The mixture was cooled to room temperature; the organic
phase separated and washed with deionized water until a pH of ∼7 was
obtained. Residual water was removed from the mixture by heating to
reflux in a Dean−Stark apparatus. The obtained solution was
concentrated, precipitated in cold methanol, and kept in the
refrigerator for 24 h. Afterward the precipitate was filtered off,
transferred into a Soxhlet extractor, and extracted using methanol. The
polymer was redissolved in chloroform and reprecipitated in cold
methanol. It was filtered and dried for 24 h to obtain a brownish green
polymeric material (220 mg, 95% yield). SEC (THF as eluent;
polystyrene standards): Mn = 3200 g/mol, Mw = 11 730 g/mol, and Đ
Instrumentation. NMR spectra were recorded in CDCl3 with a
Gemini 300 MHz spectrometer and a Bruker Avance IIIHD 400 MHz
Nanobay NMR spectrometer equipped with a 5 mm BBO. Fourier
transform infrared (FTIR) spectroscopy was performed with a
PerkinElmer ATR TWO FTIR Spectrometer at room temperature.
Size exclusion chromatography (SEC) measurements were performed
using a Pump Deltachrom (Watrex Comp.) with a Midas autosampler
and two columns of MIXED-B LS PL gel, particle size 10 μm. An
evaporative light scattering detector (PL-ELS-1000 from Polymer
Laboratories) was used; THF was the mobile phase and polystyrene
standards were used for calibration. Thermogravimetric analysis
(TGA) were performed using PerkinElmer TGA 7 in the range
between 20 and 600 °C at a heating rate of 10 K/min in nitrogen
atmosphere.
Sample Preparation. Thin films were prepared by spin-coating
from toluene and 1,2-dichlorobenzene solutions. Thin films were spin-
coated onto fused silica substrates for optical studies or coated on a Pt
wire electrode by dipping for electrochemical measurements. For
polymer light-emitting devices (LED), polymer layers were prepared
on indium−tin oxide (ITO) substrates covered with a thin layer of
poly[3,4-(ethylenedioxy)thiophene]/poly(styrenesulfonate) (PE-
DOT:PSS). All polymer films were dried in a vacuum (10−3 Pa) at
353 K for 2 h. The ITO glass substrates were purchased from Merck
(Germany). PEDOT:PSS (CLEVIOS P VP AI 4083) from Heraeus
Clevios GmbH (Germany) was used for LED preparation. The 50 nm
thick PEDOT:PSS layers were prepared by spin-coating and dried in
air at 396 K for 15 min. The calcium (20 nm) and, subsequently, 60−
80 nm thick aluminum electrodes were vacuum-evaporated on top of
the polymer films to form LEDs. Typical active areas of the LEDs were
4 mm2. Layer thicknesses were measured using a KLA-Tencor P-10
profilometer. All thin film preparations and the device fabrication were
carried out in a glovebox under a nitrogen atmosphere. For the
fabrication of organic photovoltaic (OPV) devices ITO-coated glass
substrates (15 Ω/sq, Xin Yan Tech. LTD) were employed. Polymer
blend layers composed of polymer and [60]PCBM (Sigma-Aldrich)
were spin-coated on the ITO substrate covered with polyethylenimine
(PEI). PEI was treated at 378 K. The MoOx (10 nm) and,
subsequently, 100 nm thick silver (Ag) electrodes were vacuum-
evaporated on top of the polymer films to finalize OPVs. The
thickness of the films was characterized with a Bruker DektakXT
profilometer.
1
= 3.7. H NMR (300 MHz, CDCl3): δ 9.05−8.22 (anthanthrenylene
H’s), 7.58−6.92 (arylene vinylene H’s), 4.28−3.28 (m, −CH2O−),
2.41−0.42 (m, alkyl H’s). FTIR, cm−1: 3064 (ν(C−H)), 2962,
2924, and 2850 (ν(C−H)), 2180 (ν(CC)), 1594 (ν(CC)
vinylene), 1500 (ν(CC) aromatic ring), 1464 (δ(CH2)), 1203
(ν(CC−O−C) aromatic−aliphatic).
Synthesis of P3. P3 was obtained from a solution of Mb (190 mg,
0.14 mmol) and M3 (93 mg, 0.15 mmol) in dry toluene (13 mL). The
polymerization was initiated by the addition of potassium tert-butoxide
(60 mg, 0.56 mmol). A color change from bright green to dark green
was observed. The reaction mixture was stirred for 80 min.
Chloroform (100 mL) was thereafter added, and the reaction was
quenched with aqueous HCl (10 wt %, 10 mL). Mixture was cooled to
room temperature; the organic phase was separated and washed with
deionized water until a pH of ∼7 was obtained. Residual water was
removed from the mixture by heating to reflux in a Dean−Stark
apparatus. The obtained solution was concentrated, precipitated in
cold methanol, and kept in the fridge for 24 h. Afterward the
precipitate was filtered off using a thimble, transferred into a Soxhlet
extractor, and extracted with methanol. The polymer was redissolved
in chloroform and reprecipitated in methanol. It was filtered and dried
to obtain a brownish green polymeric material. This polymerization
was conducted twice using different oil bath temperatures, 111 °C
[SEC (THF as eluent; polystyrene standards): Mn = 3650 g/mol, Mw
= 11 800 g/mol, Đ = 3.2] and 118 °C [SEC (THF as eluent;
polystyrene standards): Mn 2880 g/mol, Mw 7820 g/mol, and Đ =
2.7]. The polycondensation reaction conducted at 111 °C yielded
material that is soluble in common organic solvents (180 mg, 73%
yield). The reaction performed at higher temperature(118 °C) yielded
material only partially soluble at elevated temperatures (33% yield). 1H
NMR (300 MHz, CDCl3): δ 8.73 (m, (anthanthreneylene H’s)),
7.65−6.90 (m, arylene vinylene H’s), 4.61−3.48 (m, −CH2O−),
Cyclic Voltammetric Measurements. Cyclic voltammetry (CV)
was performed with a PA4 polarographic analyzer (Laboratory
Instruments, Prague, CZ) with a three-electrode cell. Platinum (Pt)
wire electrodes were used as both working and counter electrodes. A
nonaqueous Ag/Ag+ electrode (Ag in 0.1 M AgNO3 solution) was
used as the reference electrode. CV measurements were made in an
electrolyte solution of 0.1 M tetrabutylammonium hexafluorophos-
L
DOI: 10.1021/acs.macromol.7b02136
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Article
phate ((TBA)PF6) in anhydrous acetonitrile under a nitrogen
atmosphere in a glovebox. Typical scan rates were 20, 50, and 100
mV s−1.
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* Supporting Information
Supplementary data related to this article are available free of
charge via the Internet at The Supporting Information is
available free of charge on the ACS Publications website at
DOI: 10.1021/acs.macromol.7b02136.
Synthesis of precursors, NMR and FTIR spectra, and
thermo-gravimetric analysis plots (PDF)
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Corresponding Authors
*E-mail (V.C.): cimrova@imc.cas.cz or cimrova@gmail.com.
*E-mail (E.I.): eiwuoha@uwc.ac.za.
*E-mail (D.A.M.E.): daniel_ayuk_mbi.egbe@jku.at.
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Turro, N. J.; Steigerwald, M. L.; Li, H.; Nuckolls, C.; et al. Controlled
Doping in Thin-Film Transistors of Large Contorted Aromatic
Compounds. Angew. Chem., Int. Ed. 2013, 52, 4558−4562.
ORCID
Vera Cimrova: 0000-0001-5952-6320
̌
́
Jean-Franco
̧
is Morin: 0000-0002-9259-9051
(16) He, B.; Tian, H.; Geng, Y.; Wang, F.; Mullen, K. Facile Synthesis
̈
Emmanuel Iwuoha: 0000-0001-6102-0433
Notes
The authors declare no competing financial interest.
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Optical Properties. Macromolecules 2008, 41, 7933−7937.
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(18) Saleh, M.; Park, Y.-S.; Baumgarten, M.; Kim, J.-J.; Mullen, K.
̈
We thank the Czech Science Foundation (Grant 13-26542S),
FWF (Project No. I 1703-N20) and the National Research
Foundation (NRF) South African Agency for Science and
Technology Advancement (Project No. UID-85102) for
financial support. S.V.J. is grateful to the International Centre
for Theoretical Physics (ICTP) and the African Network for
Solar Energy (ANSOLE), as well as the NRF of South Africa,
for financial support.
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DOI: 10.1021/acs.macromol.7b02136
Macromolecules XXXX, XXX, XXX−XXX