Photovoltaic response to structural modifications on a series of conjugated polymers based on 2-aryl-2H-benzotriazoles

Article abstract of DOI:10.1002/pola.24959

The synthesis, characterization, and photovoltaic properties of a series of four conjugated polymers containing 2-aryl-2H-benzotriazoles and "bis(thiopheno)dialkylfluorenes" is described. The polymers were obtained via Suzuki-polycondensation and comprise

Full text of DOI:10.1002/pola.24959

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ARTICLE
Photovoltaic Response to Structural Modifications on a Series of
Conjugated Polymers Based on 2-Aryl-2H-benzotriazoles
Felix M. Pasker,1 Michael F. G. Klein,2 Monamie Sanyal,3 Esther Barrena,4 Uli Lemmer,2
Alexander Colsmann,2 Sigurd Ho¨ ger1
1Kekule´-Institut fur Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universitat Bonn, Gerhard-Domagk-Str. 1,
¨
¨
53121 Bonn, Germany
2Light Technology Institute, Karlsruhe Institute of Technology (KIT), Engesserstrasse 13, 76131 Karlsruhe, Germany
3Max-Planck-Institut fur Metallforschung, Heisenbergstr. 3, 70569 Stuttgart, Germany
¨
4ICMAB-CSIC, Campus UAM, 08193 Bellaterra, Barcelona, Spain
Correspondence to: S. Hoger (E-mail: hoeger@uni-bonn.de)
¨
Received 9 June 2011; accepted 16 August 2011; published online 9 September 2011
DOI: 10.1002/pola.24959
ABSTRACT: The synthesis, characterization, and photovoltaic
properties of a series of four conjugated polymers containing
2-aryl-2H-benzotriazoles and ‘‘bis(thiopheno)dialkylfluorenes’’ is
described. The polymers were obtained via Suzuki-polyconden-
sation and comprise alternating electron rich and electron poor
building blocks. The impact of systematic structural changes
on the electronic and morphological properties and device effi-
ciencies were studied. Application of these polymers as light-
harvesting and electron-donating materials in organic solar
cells using PCBM derivatives as electron accepting materials
resulted in power conversion efficiencies up to 1.8%. Both the
properties of the pristine polymers and the device performance
show that the impact of the substitution farther-off the back-
bone is negligible while substitution directly on the backbone
C
V
has a major impact. 2011 Wiley Periodicals, Inc. J Polym Sci
Part A: Polym Chem 49: 5001–5011, 2011
KEYWORDS: 2-phenyl-2H-benzotriazole; conducting polymers;
conjugated polymers; copolymerization; photovoltaic cells;
polyaromatics; structure-property relations; synthesis
INTRODUCTION In the last decade, organic photovoltaic (OPV)
devices have gained considerable attention due to the capability
for large area and low cost processing by methods such as
printing or coating.1–4 Dramatic progress has been achieved in
understanding the basic material requirements, fundamental
physical processes in the active layer of the solar cell1–5 and
processing conditions.6,7 Typically, the active layer comprises a
blend of an electron rich conjugated polymer for light harvest-
ing and hole transport (donor) and a fullerene derivative for
electron transport (acceptor). This so called bulk heterojunction
(BHJ), an interpenetrating binary mixture of fulleride crystalli-
tes in a polymer matrix, provides abundant donor/acceptor
interfaces for charge separation and pathways for charge trans-
port to the electrodes.1–3 Especially the growing number of
polymeric donor materials helps to improve solar cell perform-
ances and to gain insight into these fundamental processes.
achieved by using the donor/acceptor concept, where elec-
tron rich (donor) and electron poor (acceptor) moieties,
bearing solubilizing side groups, are incorporated alternat-
ingly into a polymer backbone. This concept helps to effi-
ciently tune the semiconducting polymer’s electronic proper-
ties.9–11 Systematic changes on the acceptor part in the
polymer backbone and a study on the related changes in the
electronic and morphological properties lead to a deeper
understanding of the relation between chemical modification
and device performance. By systematically incorporating a
series of different acceptor building blocks into a 2,7-carba-
zole based copolymer, Leclerc demonstrated the effect of
acceptor subunits on the LUMO levels and the effect of the
monomer symmetry on molecular order and crystallinity of
the copolymers.12 Another important work has been pub-
lished by Yu on thieno[3,4-b]thiophene and benzodithio-
phene based copolymers also showing the impact of small
structural modifications on energy levels and, as a result, on
solar cell efficiencies.13 Based on this donor/acceptor con-
cept very efficient solar cells have been reported with 6.1%
for the carbazole copolymer14 and 7.4% for the benzodithio-
phene copolymer.15,16
For the fabrication of efficient solar cells a favorable align-
ment of the energy levels of the donor with respect to the
acceptor energy levels is needed. Further, a certain degree of
crystallinity for charge transport and well absorbing com-
pounds exhibiting good spectral overlap with the solar spec-
trum have been proved beneficial.3,8 Such properties can be
Additional Supporting Information may be found in the online version of this article.
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A further well investigated class of donor copolymers com-
prises 2,7-dithien-2-yl-9,9-dialkylfluorene and various acceptor
units.17–21 A highlight is the very well investigated poly[2,7-
(9,9-dialkylfluorene)-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’)-benzo-
the possibility to fine-tune the absorption and energy levels
in arylbenzotriazole-fluorene copolymers to elucidate the
applicability of the arylbenzotriazole building block in OPV
devices and the impact of structural changes on solar cell
performance.
thiadiazole] (PFDTBT) incorporating
a benzothiadiazole
acceptor unit.22,23 Today it serves as a model compound for
the investigation of fundamental OPV processes.24–26 Effi-
ciencies up to 4.2% have been reported for PFDTBT with
decyl-chains attached to the fluorene monomer27 while
branched chains give increased efficiencies of 4.5%.28
Another important acceptor unit is the quinoxaline building
block. A series on systematic modifications in quinoxaline
fluorene copolymers has been reported by Andersson show-
ing increasing phase separation with increasing alkoxy chain
length,18 allowing for the fabrication of solar cells with
5.5% efficiency.29
RESULTS AND DISCUSSION
Three 4,7-dibromo-2-(phenyl)-2H-benzotriazoles (1 a-c)42
with different substitution patterns on the phenyl group
were subjected to Suzuki reaction conditions with 3-hexyl-
thiophene-2-boronic acid pinacol ester to give the 3-hexyl-
thiophene substituted benzotriazoles 3 a-c (Scheme 1).
Although the hexyl groups guaranteed a sufficient solubility
and the compounds 3 a-c were prepurified by column chro-
matography, they still contained minor amounts of unknown
byproducts having identical Rf values. An analytical sample
of 3 c could only be obtained by purification using prepara-
tive recycling gel permeation chromatography (recGPC).
Nevertheless, after bromination of the prepurified com-
pounds 3 a-c in THF with NBS the purification was easier to
perform and pure dibromo monomers 4 a-c could be
obtained in reasonable yields. Furthermore, the solubilising
decyloxy group of 1 c allowed also the Suzuki coupling with
2-thienylboronic acid pinacol ester (5) to yield 6 (83%). Af-
ter bromination with NBS in THF monomer 7 was obtained,
again in good yields (81%). However, the comparison
between the monomers 4 and 7 shows superior solubility
for the monomers 4 a-c while the monomer 7 is red shifted
in absorption (yellow vs. orange color of the compounds).
The influence of the alkyl substitution pattern on the electronic
properties and the photovoltaic behavior has been discussed
recently focusing on 4,7-dithienylbenzothiadiazoles with vary-
ing alkyl substituents on the thiophene units. Since the elec-
tronic properties are correlated to the delocalization of p-elec-
trons along the backbone, high dihedral angles between the
monomeric units disturb delocalization and therefore lead to a
rise in the band gap. In addition, intermolecular contacts and
therefore conductivities are smaller for nonplanar structures. In
the case of triphenylamine and thiophene-based donor mono-
mers, the impact of alkyl substitution in 3-position of the thio-
phene moiety is larger than substitution in 4-position since the
higher steric hindrance leads to larger torsion of the backbone
if the substituent in 5-position is smaller than the one in 2-posi-
tion. The device properties in field effect transistors30 as well as
in BHJ solar cells31,32 follow the expected trend, while in other
cases such factors as solubility and the molecular weight33 or
branching of these side chains34 dominate device properties.
Nevertheless, in any of these cases the electronic properties are
very sensitive to the parameters mentioned above giving the
lowest band gap for unsubstituted thiophene, followed by 4-
and 3-substitution.
Suzuki polycondensation of these monomers with the bispi-
nacol ester of dioctylfluorene bisboronic acid gave the poly-
mers P1, P2, P3, and P4 in very good yields (Scheme 1). All
polymers were end-capped with p-tolyl groups, precipitated
from methanol and, depending on the solubility and the mo-
lecular weight distribution (MWD), subjected to Soxhlet
extraction with various solvents or simply filtered through a
plug of celite. After dissolving the polymers again in a small
amount of an appropriate solvent the polymers were precipi-
tated from methanol. The polymers were collected by filtra-
tion through a hydrophobic PTFE membrane filter and dried
In this work we want to focus on copolymers comprising ben-
zotriazole acceptor units and their use for organic photovol-
taic devices. Benzotriazole is a promising building block as
demonstrated in some recent publications by Toppare, where
alkyl-substituted benzotriazole building blocks were copoly-
merized with thiophene derivatives and used as electrochro-
mic materials and electron donors in OPV devices.35,36
ꢀ
in vacuo (20 mbar, 70 C) to give them in yields between 66
and 92%, respectively.
The polymers were characterized by 1H NMR and 19F NMR
and/or 13C NMR where applicable. The molecular weights
were obtained by analytical GPC in THF (vs. PS), the thermal
stabilities were determined by thermogravimetric analyses
(TGA) and thermal transitions by differential scanning calo-
rimetry (DSC) and polarized optical microscopy (POM) (Ta-
ble 1). P1-P3 show molecular weights and a polydispersity
(PD) that are typical for Suzuki-polycondensation reactions
and correspond to degrees of polymerization (Pn) of 31, 44
and 21 for P1, P2 and P3 respectively (Table 1). Contrary,
P4 shows a multimodal MWD, has a remarkably high molec-
ular weight, with a corresponding Pn of 67 and a high PD
(Supporting Information Fig. S20). These results indicate
that the polymer is branched. Indeed, the dibromo com-
pound 7 was difficult to purify due to its restricted solubility
2-Alkyl-2H-benzotriazole with dialkylfluorene as monomeric
unit exhibited an optical band gap of 2.24 eV and gave 1.3%
efficient solar cells, while the respective carbazole deriva-
tives gave PCEs up to 2.75%.37,38 In addition, copolymers
comprising 2-alkyl-2H-benzotriazole with dialkoxy- and dia-
lkyl-benzodithiophene exhibited 1.7 and 7.1% efficiency in
solar cells, respectively.39,40
In our previous work we already demonstrated that the
absorption properties and orbital alignment of the benzotria-
zole unit can be fine-tuned through functionalization of an
aryl group attached in 2-position.41,42 Here, we investigate
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SCHEME 1 Monomer and polymer synthesis.
ꢀ
in the eluent mixture used for the column chromatography.
Although the 1H NMR spectrum displays no impurity (Sup-
porting Information Fig. S22), the 19F NMR spectrum shows
two signals with intensity ratios of about 100:1.65 at
ꢁ125.86 and ꢁ125.29 ppm (Supporting Information Fig.
S23). Additionally, mass spectrometric characterizations
show the presence of trace amounts of a threefold bromi-
nated byproduct (Supporting Information Fig. S24). Never-
theless, all polymers are well soluble in chlorinated solvents
and THF, with reduced solubility for P4. This can be attrib-
uted to fewer alkyl chains on the backbone of the polymer
together with a more planar structure and its much higher
molecular weight. The high molecular weight also leads to
very viscous solutions of P4 at room temperature.
DSC shows glass transitions for P1-P3 at 55–93 C and small
endothermic transitions at 248–270 ꢀC with transition
enthalpies (DH) of 0,033–0,045 J gꢁ1 (Fig. 1) indicating a
high amorphous fraction of these polymers in the solid state.
In contrast P4 shows two endothermic signals at 205 and
265 ꢀC with transition enthalpies of -0.98 J gꢁ1 and -0.041
J gꢁ1 indicating a higher degree of crystallinity below 205 C
ꢀ
than for P1-P3. Similar transitions have been reported for
poly(fluorene-alt-dithienyl-benzothiadiazole)s (175–180 ꢀC).23
The enthalpy of the higher temperature transition is similar
to the enthalpies for P1-P3. POM with crossed polarizers
shows a birefringent viscous liquid above 210 ꢀC for P4
ꢀ
which partially clears above 280 C [Fig. 1 (inset)]. The clear-
ing point is over 300 ꢀC and could not be observed.
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TABLE 1 Polymerization Results and Thermal Properties of the Polymers
Transition Temperature (ꢀC)
Mn (kg/mol)a
Mw (kg/mol)a
PDI
Tg
Tm
Tc
Td
b
c
d
e
Yield (%)
P1
P2
P3
P4
66
91
92
86
28.5
42.9
23.3
62.6
54.2
146
1.9
3.4
85
93
55
–
276 (ꢁ17)
256 (ꢁ42)
270 (ꢁ46)
205 (ꢁ980)
265 (ꢁ41)
236 (600)
241 (240)
241 (430)
200 (1060)
243 (420)
386
390
384
387
58.3
2.5
1050
16.7
a
Molecular weights were determined by GPC using THF as eluent and polystyrene standards.
Determined by onset of glass transition at a heating rate of 10 K/min.
b
c
Endothermal transitions observed in DSC heating cycles (10 K/min) (enthalpy of the transition in mJ/g).
Exothermal transitions observed in the cooling cycles (10 K/min) (enthalpy of the transition in mJ/g).
d
e
Determined by onset of weight loss measured by TGA at a heating rate of 20 K/min under nitrogen atmosphere (Supporting Information Fig. S21).
Thermogravimetric analyses (TGA) show a weight loss with
an onset at 384–390 ꢀC indicating high thermal stability
under nitrogen atmosphere.
chain. Polymer P1 with an unsubstituted phenyl benzotriazole
shows the highest energy absorption. A much stronger differ-
ence in absorption can be observed, when comparing P3 with
P4. While P4 has no substituents in 3 and 4 positions of the
thiophene unit, P3 has a hexyl substituent in 3 position that
prohibits a planar polymer backbone conformation. P4 can
adopt a much more planar conformation because of the lack
of steric hindrance between the thiophene and the benzotria-
zole units. The absorption maximum is therefore shifted by
92 nm and the optical band gap is reduced by 0.26 eV, which
is quite large if compared with the small differences between
P1, P2, and P3. Comparison with the respective 2-dodecyl-
2H-benzotriazole based copolymer PF-DTBTA shows that the
band gap of P4 is reduced by 0.16 eV.37 The emission spectra
[Fig. 2(b), -D-] show a similar trend. The differences in emis-
sion spectra are less pronounced than the differences dis-
cussed for the polymer absorption. P1 is red shifted com-
pared to P3 and the emission spectrum of P4 is rather similar
Electrochemical and Optical Properties
Due to the strong structural similarity, the comparison of the
optical and electronic properties of these polymers allows the
extraction of important structure–property relationships. Fig-
ure 2 shows a summary of the optical spectra of all polymers
in solution [Fig. 2(a)] and thin films [Fig. 2(c)]. UV/Vis
absorption and emission spectra in solution show a clear
trend for the polymer absorption (Table 2). Polymers P1-P3
show very similar absorption spectra with a bathochromic
shift upon substitution of the phenyl group at the benzotria-
zole monomer. P2 exhibits the lowest optical band gap as a
result of three electronegative fluorine atoms at the acceptor
unit. The absorption of P3 is blue shifted by 5 nm as one fluo-
rine atom is substituted by an electron donating decyloxy
FIGURE 2 (a) Normalized absorption spectra in CHCl3-solution
(P1, —, gray; P2, — —, gray; P3, — --, gray; and P4, — -, black).
(b) Emission spectra in CHCl3-solution. (c) Absorption spectra
of thin films spin cast from 1,2-dichlorobenzene, normalized on
higher wavelength absorption maximum.
FIGURE 1 DSC traces of polymers (P1 blue, —; P2 red, – –; P3
black, – ꢂꢂ; and P4 green, – ꢂ) heating (bottom) and cooling
(top) scans. Inset: POM image under crossed polarizers at
250 ꢀC 10 seconds after shearing the sample.
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TABLE 2 Summary of the Optical and Electrochemical Data of Copolymers P1-P4
opt
on
on
ec
Abs. Solution
kmax (nm)a
Abs. Film
kmax (nm)b
Emission
kmax (nm)a
Eg
Eox
Ered
HOMO
(eV)
LUMO
(eV)
Eg
(eV)c
(V)
(V)
(eV)
P1
P2
P3
P4
a
438
448
443
535
447
459
451
547
553
562
550
590
2.38
2.30
2.34
2.08
0.65
0.65
0.67
0.59
ꢁ1.77
ꢁ1.75
ꢁ1.80
ꢁ1.44
ꢁ5.45
ꢁ5.45
ꢁ5.47
ꢁ5.39
ꢁ3.03
ꢁ3.05
ꢁ3.00
ꢁ3.36
2.42
2.40
2.47
2.03
Chloroform solution.
b
c
Obtained by spin casting from dichlorobenzene solution.
Estimated from the onset wavelength of UV/Vis spectra in thin films.
to the other emission spectra. The emission spectrum of P4
has, with 1,740 cmꢁ1, a smaller Stokes shift than the other
polymers with 4,750, 4,530, and 4,390 cmꢁ1 for P1-P3,
respectively. This indicates a strong structural difference
between ground and excited states for polymers P1-P3 while
for P4 the geometry of the ground state and the excited state
should be more similar. The absorption spectra in thin films
[Fig. 2(c)] are comparable to the absorption spectra in
solution.
the LUMO energy of the resulting polymers while the HOMO
energy remains almost constant.
The fact that twisting of the molecular backbone only affects
the LUMO indicates that the HOMO is more or less localized
at the thiophene-fluorene-thiophene subunit of the polymer,
whereas the LUMO is more or less localized on the benzo-
triazole unit alone for P1-P3 while P4’s LUMO is more delo-
calized over the thiophene-arylbenzotriazole-thiophene subu-
nit (Supporting Information Fig. S25). The effect of
substituents at the phenyl ring of the benzotriazole subunit
is negligible and no clear trend could be observed by CV.
However, the electrochemical band gap fits well to optical
absorption measurements.
The HOMO and LUMO energy levels of the polymers were
determined by cyclic voltammetry (CV). Figure 3 shows
cyclic voltammograms of the four polymers measured as thin
films on a platinum disc electrode; the results are summar-
ized in Table 2. The HOMO and LUMO levels of P1-P3 are
equal within the experimental error. When comparing the
polymers P3 and P4 that are equally substituted at the tria-
zole unit, the HOMO of the latter is about 0.1 eV higher
while the LUMO is 0.36 eV lower than the LUMO of P3. Thus
while P3 can be considered as a moderate electron accepting
copolymer, P4 is much more electron deficient which leads
to a large shift in LUMO energy. Hence, the introduction of
alkyl chains at the thiophene subunit seems to affect only
To investigate the crystallinity of P4, X-ray scattering on a thin
polymer film on a glass substrate was performed. Before these
investigations, samples of P4 were annealed at 150 ꢀC or
230 ꢀC, respectively. The two-dimensional X-ray scattering
data ꢀobtained at grazing incidence of a P4 film annealed at
230 C comprises an isotropic diffraction ring. This indicates
the formation of randomly oriented crystallites without a pref-
erential orientation [Fig. 4(a)]. Further, measurements at graz-
ing incidence were performed with a point detector to mea-
sure the structure along the substrate with higher resolution,
henceforth known as the in–plane (IP) direction. Figure 4(b)
shows the IP diffraction peaks obtained for both samples. The
associated spacing is 18.93 Å and 18.38 Å for the films
ꢀ
annealed at 150 and 230 C, respectively. This spacing is con-
sistent with the distance between polymer layers in a confor-
mation of interdigitated alkyl chains (Supporting Information
Fig. S26). In addition the coherence length, which is a measure
of the average size of crystallites,43 is 218 and 600 Å for the
annealing temperatures of 150 and 230 ꢀC in P4, respectively.
This clearly shows that the overall crystallinity of the P4 films
increases with increasing annealing temperature, resulting in
a
slightly closer packed layered structure with larger
crystallites.
Photovoltaic Properties
To examine the photovoltaic properties of the polymers we
built solar cells comprising bulk-heterojunctions from P1,
P2, P3, or P4 with PC61BM between an ITO / PEDOT:PSS an-
ode and a calcium / aluminium cathode as depicted in Fig-
ure 5(a). Figure 5(b) shows the proposed energy levels of
the respective materials.
FIGURE 3 Cyclic voltammograms of the polymers (P1, —, gray;
P2, — —, gray; P3, — --, gray; and P4, — -, black) at a sweep
rate of 0.05 V/s. The current on the ordinate is normalized.
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FIGURE 4 (a) 2D X-ray diffraction pattern of a substrate coated with P4 and annealed at 230 ꢀC. The diffraction ring indicates ran-
domly oriented crystallites. (b) GIXD data with Gaussian fits of the P4 films annealed at 150 ꢀC (black squares-data, black line-fit)
and at 230 ꢀC (gray circles-data, gray line-fit).
The solar cell performance of each polymer was systemati-
cally optimized by varying the polymer/fullerene blend ratio,
by adjusting the layer thickness through changing the poly-
mer/fullerene concentration in solution and by varying the
spin coating speed, by exchanging the solvent dichloroben-
zene (DCB) with chlorobenzene (CB), and by substituting
PC61BM with PC71BM. Additionally, the effects of solvent
annealing and thermal annealing were studied.
exhibit a much lower JSC. We attribute this to a thinning of the
polymer backbone due to the alkyl chains and hence a reduced
absorption. For P4 the power conversion efficiency reaches g
¼ 1.83%. Its VOC is comparable to devices based on P3 (g ¼
0.67%), which comprises the same benzotriazole unit, while
the short current density of P4 is considerably improved. We
attribute this to a more planar backbone configuration of P4
that leads to a higher hole mobility and therefore to a more
balanced charge carrier transport.45–48 Consequently, the FF
of P4-devices is enhanced as compared to devices based on
P1-P3. Furthermore, the effect of substituting PC61BM with
PC71BM was investigated. The performance of P1-devices was
increased up to g ¼ 1.4% (Table 3) while P2 and P4 showed
inferior performances. The JV graphs of solar cells comprising
P1 blended with both fullerene derivatives are shown in the
Supporting Information (Fig. S27).
Solvent annealing did not lead to any improvement. Thermal
annealing increased the power conversion efficiency for P1,
P3, and P4 up to a factor of three. A summary of the opti-
mized experimental results is given in Table 3 and the re-
spective current density-voltage (JV) graphs of solar cells are
depicted in Figure 6.
The optimized blend ratio between polymer and fullerene is
1:4 in case of P1-P3 and 1:2 for P4. Devices based on P1 and
P2 show comparable short current densities. The open circuit
voltage (VOC) of P1 devices is about 0.11 V lower as compared
to devices comprising P2. In a 1:2 blend P1 enables a higher
EXPERIMENTAL
Materials and Characterization
V
OC of 937 mV being close to the VOC of P2 devices, according
THF was dried, distilled and stored under Argon if necessary.
Reagents were purchased at reagent grade from commercial
sources and used without further purification. 1 a-c were
prepared according to literature procedures.41 All air-sensi-
tive reactions were carried out using standard Schlenk
to the similar HOMO level energies of P1 and P2. However, for
a 1:2 blend the overall solar cell performance declines (JSC
¼
1.5 mA/cm2, g ¼ 0.47%). Due to similar HOMO levels of P2
and P3 the VOC is comparable, but devices incorporating P3
FIGURE 5 (a) Device architecture of the photovoltaic cells comprising the polymers P1-P4. The polymer:PC61BM bulk-heterojunc-
tion was spin cast from 1,2-dichlorobenzene (P1-P3) and from chlorobenzene (P4). (b) Proposed energy levels of the investigated
materials. Energy levels were taken from ref. 44.
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TABLE 3 Photovoltaic Properties of Organic Solar Cells Based on P1-P4 After Systematic Optimization
Ratio Polymer:
Fullerene
Polymer in
Polymer
Fullerene
Solvent
Solution (mg/mL)
JSC (mA/cm2)
VOC (mV)
FF (%)
g (%)
P1
PC61BM
PC71BM
PC61BM
PC61BM
PC61BM
1:4
1:4
1:4
1:4
1:2
DCB
DCB
DCB
DCB
CB
10
10
10
10
5
2.4
4.7
2.3
1.5
4.4
856
864
969
939
894
37
35
37
35
47
0.76
1.42
0.82
0.67
1.83
P2
P3
P4
Devices incorporating P1, P3, and P4 were annealed at 150 ꢀC for 10 minutes after deposition of the top electrode.
techniques under Argon. Macherey-Nagel precoated TLC
equipped with a LC-20 AD pump, a SPD-20 A UV-detector
and a set of three preparative columns from PSS (103 Å, 5 l,
20 ꢃ 300 mm) was used for the purification of 3 c. The sys-
tem operated at a flow rate of 5 mL/min. Cyclic voltammetry
was performed with a computer-controlled VA-Standard 663
and a lAutoLab Type III potentiostat of Metrohm AG, Suisse
on thin polymer films dropcast from chloroform solution on
a platinum disk (U ¼ 5 mm) as working electrode, in dried
and oxygen-free acetonitrile using 0.1 M tetrabutylammo-
nium hexafluorophosphate (electrochemical grade, FLUKA)
as supporting electrolyte, a glassy carbon counter electrode,
and an Ag/AgCl reference electrode. Redox potentials were
referenced against ferrocene/ferrocenium (Fc/Fcþ). The cor-
responding highest occupied molecular orbital (HOMO) and
lowest unoccupied molecular orbital (LUMO) were calculated
using the onset of Eox and Ered and using the absolute value
of -4.8 eV to vacuum for the Fc/Fcþ redox potential.49 POM
images were taken using a Leica DMLB microscope with
resistive heating socket controlled by a Leica LMW trans-
former and a Testo 925 digital thermometer. Thermogravi-
metric analysis (TGA) was carried out on a Mettler Toledo
TGA/SDTA 851e. Differential scanning calorimetry (DSC) was
performed on a Mettler Toledo DSC 823e.
R
plates (AlugramV SIL G/UV254, 0.2 mm) were used for thin-
layer chromatography (TLC) analysis. Silica gel 60
M
(Macherey-Nagel, 0.04–0.063 mm, 230–400 mesh) was used
as the stationary phase for column chromatography. 1H, 13C,
and 19F NMR spectra were recorded on Bruker DPX 300 (1H,
300 MHz; 13C, 75.5 MHz; 19F, 282 MHz), DPX 400 (1H, 400
MHz; 13C, 100.6 MHz) und DPX 500 (1H, 500 MHz; 13C,
125.8 MHz; 19F, 470 MHz) spectrometers, and chemical shifts
are reported as d values (ppm) and referenced to residual
1H or 13C signals in deuterated solvents. EI HRMS Mass spec-
tra were measured on a Finnigan ThermoQuest MAT 95 XL.
MS-50. UV/Vis absorption spectra were obtained from a Shi-
madzu UV-2100 or a Perkin-Elmer Lambda 18 and fluores-
cence spectra were received from a Horiba Jobin Yvon Fluo-
romax 4. Gel permeation chromatography (GPC) was
performed in THF (HPLC grade, stabilized with 2.5 ppm
BHT) at rt. GPC analyses were run on an Agilent Technolo-
gies system at a flow rate of 1 mL/min using an IsoPump
G1310 A, a diode array UV detector (G1315B) and PSS col-
umns (Polymer Standards Service, Mainz, Germany; 102, 103,
and 105 Å, 5 l, 8 x 300 mm). All molecular weights were
determined versus PS calibration (PS standards from PSS,
Mainz, Germany).
A Shimadzu Recycling GPC system,
Fabrication of OPV Devices
Solar cells were fabricated by spin casting according to the
layer sequence depicted in Figure 5. All processing steps
were carried out in a clean room. Structured ITO glass slides
(16 mm ꢃ 16 mm, 150 nm ITO, 12 X/h, VisionTek) were
R
cleaned with a cleaning agent (HellmanexV II), rinsed with
water and acetone and isopropyl alcohol afterward and then
dried in a nitrogen stream. The substrates were exposed to
oxygen plasma for 120 s, transferred to a glovebox with
nitrogen atmosphere and kept there for all following proc-
essing steps. After spin casting poly(3,4-ethylenedioxythio-
phene):polystyrenesulfonate (PEDOT:PSS) (CleviosTM P VP
AI4083, Heraeus) residual water was removed by drying the
substrates in a vacuum oven resulting in an average dry film
thickness of 45 nm (Dektak 8000 profiler). P1-P4 and the
fullerenes PC61BM and PC71BM (Solenne) were dissolved in
CB (anhydrous, 99.8%, Sigma Aldrich) or DCB (anhydrous,
99%, Sigma Aldrich) with various polymer/fullerene ratios
and overall solid contents between 5 and 10 mg/ml. The sol-
utions were kept at 85 ꢀC to reduce viscosity. The solutions
of P2, P3 and P4 were deposited on preheated substrates
(85 ꢀC). Due to the poor wetting properties of the P1
FIGURE 6 JV curves of Glass/ITO/PEDOT:PSS/polymer:PC61BM/
Ca/Al solar cells under illumination at 100 mW/cm2. The active
layers were spin cast from solution at T ¼ 85 ꢀC.
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solution, it was spin cast on non-heated substrates (room-
temperature). A calcium aluminium electrode (30–200 nm)
was vacuum deposited through a shadow mask in a Lesker
Spectros system at 3 ꢃ 10ꢁ6 mbar defining an active area of
4 mm2. The current voltage characteristics of the solar cells
were recorded with a source measure unit (Keithley 238). A
spectrally monitored Oriel 300 W solar simulator was used
to simulate the sunlight according to the ASTM-G173-03e1
standard for global solar irradiance.50
100.46 (m), 75.07 (t, J ¼ 2.98 Hz), 31.89, 31.66, 30.77,
29.95, 29.53, 29.29, 29.27, 25.61, 22.68, 22.58, 14.10, 14.01.
19F NMR (282 MHz, CDCl3, d, ppm): -125.53 (s, 2F). EI
HRMS m/z (Mþ) calcd for C42H55F2N3OS2þ: 719.3749; found
719.3750.
2-(4-Decyloxy-3,5-difluorophenyl)-4,7-di(thiophen-2-yl)-2H-
benzotriazole (6). A solution of 1 c (200 mg, 0.367 mmol)
and 5 (231 mg, 1.10 mmol) and a few drops of Aliquat 336
in a mixture of toluene (20 mL) and Na2CO3 in water (2 M,
4.5 mL) was purged with argon for about 1 h. Pd(PPh3)4
(9 mg, 7.78 lmol) was added in one portion and the mixture
was refluxed for 10 min and then stirred at 90 ꢀC for 48 h. The
reaction mixture was allowed to cool to rt and was diluted
with CH2Cl2 and washed two times with water and brine and
dried over anhydrous Na2SO4. The bright yellow substance
was purified by column chromatography on silica gel using
dichloromethane/petrol ether (1/9) as eluent and precipitated
from CH2Cl2/MeOH to yield 6 as yellow needles (169 mg,
83%).
X-Ray Analysis
GIXD study was done at MPI–MF beamline at Ångstrom-
quelle Karlsruhe (ANKA), Germany with an energy of 8 keV
and incidence angle 0.15ꢀ using a two dimensional MAR–
CCD camera and a point detector. The X-ray measurements
were performed at room temperature. The coherence length
was estimated from the full width at half maximum (FWHM)
of the in–plane scans measured with the point detector.
Synthesis
General Suzuki Reaction Conditions
1H NMR (300 MHz, CDCl3, d, ppm): 8.12 (d, J ¼ 3.66 Hz,
2H), 8.05 (d, J ¼ 8.71 Hz, 2H), 7.64 (s, 2H), 7.42 (d, J ¼
5.09 Hz, 2H), 7.22 (dd, J1 ¼ 5.01 Hz, J2 ¼ 3.74 Hz, 2H), 4.25
(t, J ¼ 6.52 Hz, 2H), 1.94-1.73 (m, 2H), 1.61-1.45 (m, 2H),
1.45-1.22 (m, 12H), 0.89 (t, J ¼ 6.59 Hz, 3H). 19F NMR (282
MHz, CDCl3, d, ppm): –125.33 (s, 2F). EI HRMS m/z (Mþ)
calcd for C30H31F2N3OS2þ: 551.1871; found 551.1876.
A solution of the dibromo compound 1 a-c (1.00 eq) and the
pinacol ester of 3-hexyl-2-thienylboronic acid (5, 3.00 eq) in
a mixture of toluene/ethanol/2 M aqueous solution K2CO3
(4:1:1; [dibromobenzotriazole] ¼ 0.02 M) was purged with
argon for about 1 h. Pd(PPh3)4 (ꢄ 8 mol%) was added in
one portion and the mixture was refluxed until the starting
material disappeared on TLC. The reaction mixture was
allowed to cool to rt, diluted with CH2Cl2 and washed two
times with water and brine and dried over anhydrous
Na2SO4. The bright yellow substance was purified by column
chromatography on silica gel using dichloromethane/petrol
ether (1/9) as eluent.
General Bromination Conditions
In a flame dried flask NBS (ꢄ 2 eq) was added in one portion
to a solution of dithienylbenzotriazoles 3 a-c, 6 (1.00 eq) in
THF ([dithienylbenzotriazole] ¼ 0.068 M) at –78 ꢀC under the
ꢀ
exclusion of light. The mixture was stirred at –78 C for 2 h
4,7-Bis(3-hexylthiophen-2-yl)-2-phenyl-2H-benzotriazole
(3 a). Following the general Suzuki reaction conditions, 1 a
(376 mg, 1.07 mmol) was stirred at 70 ꢀC for 14 h and at
90 ꢀC for 6 h. The crude product was used without further
purification.
and then allowed to warm to rt over night. If TLC indicates the
presence of residual starting material the reaction mixture
was cooled to –78 ꢀC and further NBS was added. After 1 h at
-78 ꢀC the reaction mixture was stirred at rt for 6 h. The reac-
tion mixture was dissolved in H2O/CH2Cl2 and the organic
layer was washed with brine and dried over anhydrous
Na2SO4 and the solvent was evaporated.
4,7-Bis(3-hexylthiophen-2-yl)-2-(3,4,5-trifluorophenyl)-2H-
benzotriazole (3 b). Following the general Suzuki reaction
conditions, 1 b (300 mg, 0.737 mmol) was stirred at 90 ꢀC
for three days. The crude product was used without further
purification.
4,7-Bis(5-bromo-3-hexylthiophen-2-yl)-2-phenyl-2H-ben-
zotriazole (4 a). Following the general bromination condi-
tions, 3 a (438 mg, 0.830 mmol) was stirred with NBS
(354 mg, 1.99 mmol) at –78 ꢀC for 3 h. After stirring
at rt foꢀr 4 h further NBS (105 mg, 0.590 mmol) was added
at –78 C. Purification was achieved by column chromatogra-
phy on silica gel using dichloromethane/petrol ether (1/9) as
eluent yielded in a viscous bright yellow oil (279 mg, 49%).
4,7-Bis(3-hexylthiophen-2-yl)-2-(4-decyloxy-3,5-difluoro-
phenyl)-2H-benzotriazole (3 c). Following the general
Suzuki reaction conditions 1 c (400 mg, 0.734 mmol) was
ꢀ
stirred at 90 C for 14 h. After work up as described above,
the product was purified by recycling GPC (6 cycles) to yield
3 c (395 mg, 75%).
1H NMR (500 MHz, CDCl3, d, ppm): 8.40-8.38 (m, J ¼
8.62 Hz, 2H), 7.56-7.52 (m, 2H), 7.48-7.44 (m, 1H), 7.42 (s,
2H), 7.07 (s, 2H), 2.78-2.68 (m, 4H), 1.67 (m, 4H), 1.33-1.25
(m, 4H), 1.25-1.18 (m, 8H), 0.81 (t, J ¼ 6.91 Hz, 6H). 13C
NMR (126 MHz, CDCl3, d, ppm): 144.01, 141.87, 140.08,
133.94, 132.21, 129.35, 129.23, 127.33, 123.89, 120.71,
120.68, 112.49, 112.48, 31.61, 30.57, 29.58, 29.15, 22.53,
14.03. EIMS (m/z (%)): 685.1 (100) [79, 81M]þ. EI HRMS m/
z (Mþ) calcd for C32H35Br2N3S2þ: 683.0634; found 683.0632.
1H NMR (400 MHz, CDCl3, d, ppm): 7.98 (d, J ¼ 8.63 Hz,
2H), 7.48 (s, 2H), 7.42 (d, J ¼ 5.18 Hz, 2H), 7.12 (d, J ¼
5.18 Hz, 2H), 4.21 (t, J ¼ 6.56 Hz, 2H), 2.88-2.66 (m, 4H),
1.85-1.75 (m, 2H), 1.70 (m, 4H), 1.53-1.43 (m, 2H), 1.41-1.15
(m, 24H), 0.89 (t, J ¼ 6.82 Hz, 3H), 0.82 (t, J ¼ 6.82 Hz, 6H).
13C NMR (101 MHz, CDCl3, d, ppm): 155.96 (dd, J1 ¼ 248.98
Hz, J2 ¼ 7.03 Hz), 144.53, 141.28, 136.44, 134.49 (t, J ¼
12.51 Hz), 132.22, 129.49, 128.05, 125.54, 124.72, 106.29-
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4,7-Bis(5-bromo-3-hexylthiophen-2-yl)-2-(3,4,5-trifluoro-
phenyl)-2H-benzotriazole (4 b). Following the general
bromination conditions, 3 b (200 mg, 0.344 mmol) was
stirred with NBS (125 mg, 0.701 mmol) at –78 ꢀC for 2 h
and at rt for 2 h. Purification was achieved by column chro-
matography on silica gel using dichloromethane/petrol ether
(1/19) as eluent yielded in a viscous bright yellow oil
(104 mg, 41%).
General Polymerization Conditions
A solution of dibromo compound (4 a-c, 7) (1.00 eq), bisbor-
onic ester 8 (1.00 eq) and few drops of Aliquat 336 in a mix-
ture of toluene and 2 M Na2CO3 in water (10/3; [8] ¼ 0.02 M)
was purged with argon for about 1 h. Then Pd(PPh3)4
(ꢄ 3 mol%) was added in one portion. After purging with ar-
ꢀ
gon for additional 20 min the mixture was heated to 110 C
ꢀ
for 4 h and stirred at 85 C for 40 h. For end capping p-tolyl-
boronic acid was added. After 6 h at 90 ꢀC p-bromotoluene
1H NMR (300 MHz, CDCl3, d, ppm): 8.08 (dd, J1 ¼ 8.24 Hz, J2 ¼
was added and the mixture was stirred for another 16 h.
6.14 Hz, 2H), 7.44 (s, 2H), 7.07 (s, 2H), 2.84-2.58 (m, 4H), 1.73-
1.58 (m, 4H), 1.35-1.14 (m, 12H), 0.81 (t, J ¼ 6.61 Hz, 6H). 13
C
P1. The general polymerization conditions were followed
starting from 3 a (150 mg, 0.219 mmol) and 8 (141 mg,
0.219 mmol). The polymer was end capped by the addition
NMR (75 MHz, CDCl3, d, ppm): 151.45 (ddd, J1 ¼ 251.29 Hz, J2
¼ 10.79 Hz, J3 ¼ 4.55 Hz), 144.45, 142.07, 135.38-135.02 (m),
128.13, 123.98, 112.82, 105.39-105.04 (m), 31.59, 30.57, 29.70,
29.53, 29.13, 22.53, 14.00. 19F NMR (282 MHz, CDCl3, d, ppm):
–131.20 (d, J ¼ 20.64 Hz, 2F), –158.70 (t, J ¼ 20.48 Hz, 1F).
EIMS (m/z (%)): 739.0 (100) [79, 81M]þ.
of
2-(3-hexylthiophen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (30 mg, 0.102 mmol), stirred at 90 ꢀC for 6 h and
then 2-bromo-3-hexylthiophene (110 mg, 0.445 mmol) was
added and the mixture was stirred for another 16 h. After
cooling to rt the aqueous phase was separated and the poly-
mer was precipitated by addition of the organic phase to
MeOH. The polymer was extracted (Soxhlet-apparatus) with
acetone for 14 h and then redissolved in CHCl3 and precipi-
tated with MeOH. The precipitate was collected by filtration
and dried in vacuum at 70 ꢀC to yield an orange solid
(87.5 mg, 66%).
4,7-Bis(5-bromo-3-hexylthiophen-2-yl)-2-(4-decyloxy-3,5-
trifluorophenyl)-2H-benzotriazole (4 c). Following the
general bromination conditions, 3 c (163 mg, 0.226 mmol)
was stirred with NBS (91 mg, 0.511 mmol) at –78 ꢀC for
3 h. After stirring at rt for 16 h further NBS (25 mg,
ꢀ
0.140 mmol) was added at –78 C. Purification was achieved
by column chromatography on silica gel using dichlorome-
thane/petrol ether (1/9) as eluent yielded in a viscous
bright yellow oil (125 mg, 63%).
1H NMR (300 MHz, CD2Cl2, d, ppm): 8.48-8.48 (m, 2H), 7.76-
7.71 (m, 4H), 7.67 (br s, 2H), 7.58-7.54 (m, J ¼ 3.98 Hz, 4H),
7.47-7.45 (m, 3H), 2.87 (br s, 4H), 2.10 (br s, 4H), 1.82 (br s,
4H), 1.38 (br s, 4H), 1.30-1.10 (m, 28H) 1.09-0.79 (m, 16H).
13C NMR (101 MHz, CDCl3, d, ppm): 151.74, 144.69, 144.33,
142.47, 140.36, 140.33, 133.29, 132.02, 129.30, 129.05,
127.53, 125.56, 124.76, 124.68, 120.82, 120.16, 120.10,
119.87, 109.96, 83.71, 55.37, 40.53, 31.81, 31.72, 30.87, 30.06,
29.94, 29.38, 29.26, 23.82, 22.62, 22.61, 14.07. GPC (THF, poly-
styrene): Mn ¼ 28500 g/mol, PDI ¼ 1.9.
1H NMR (500 MHz, CDCl3, d, ppm): 7.97 (d, J ¼ 8.48 Hz,
2H), 7.42 (s, 2H), 7.06 (s, 2H), 4.22 (t, J ¼ 6.58 Hz, 2H), 2.73-
2.66 (m, 4H), 1.87-1.73 (m, 2H), 1.66 (td, J1 ¼ 15.44 Hz, J2 ¼
7.61 Hz, 4H), 1.52-1.44 (m, 2H), 1.41-1.17 (m, 24H), 0.88 (t, J
¼ 6.95 Hz, 3H), 0.81 (t, J ¼ 6.91 Hz, 6H). 13C NMR (126 MHz,
CDCl3, d, ppm): 155.95 (dd, J1 ¼ 249.12 Hz, J2 ¼ 7.01 Hz),
144.66, 142.42, 136.67 (t, J ¼ 14.24 Hz), 134.21 (t, J ¼ 12.37
Hz), 134.03, 132.67, 128.24, 124.31, 113.13, 106.98-105.26
(m), 75.08 (t, J ¼ 2.95 Hz) 31.89, 31.59, 30.58, 29.94, 29.54,
29.53, 29.30, 29.29, 29.14, 25.60, 22.68, 22.54, 14.11,
14.01. 19F NMR (471 MHz, CDCl3, d, ppm): -124.25 (s, 2F).
EIMS (m/z (%)): 877.2 (100) [79, 81M]þ, 799.3 (20) [81M–Br þ
H]þ, 737.1 (5) [M–C10H20]þ.
P2. The general polymerization conditions were followed
starting from 3 b (104 mg, 0.141 mmol) and 8 (90.4 mg,
0.141 mmol). The polymer was end capped by the adꢀdition
of p-tolylboronic acid (11 mg, 80.9 lmol) stirred at 90 C for
6 h and then p-bromotoluene (59 mg, 0.345 mmol) was
added and the mixture was stirred for another 16 h. After
cooling to rt the aqueous phase was separated and the poly-
mer was precipitated by addition of the organic phase to ac-
etone. After filtration the residue was dissolved in THF, fil-
tered through a plug of celite, reduced in volume and
precipitated from MeOH, filtered and dried in vacuum at
4,7-Bis(5-bromothiophen-2-yl)-2-(4-decyloxy-3,5-difluor-
ophenyl)-2H-benzotriazole (7). Following the general bro-
mination conditions 6 (169 mg, 0.306ꢀ mmol) was stirred
with NBS (123 mg, 0.691 mmol) at –78 C for 3 h. After stir-
ring at rt for 14 h further NBS (50 mg, 0.281 mmol) was
added at –78 ꢀC. After slowly warming to rt it was stirred
for another 2 h. Purification was achieved by column chro-
matography on neutral Alox using dichloromethane/petrol
ether (1/4) as eluent and subsequent crystallization from
EtOAc to yield bright orange needles (81%).
ꢀ
70 C to yield a red solid (124 mg, 91%).
1H NMR (500 MHz, CDCl3, d, ppm): 8.16 (dd, J1 ¼ 7.93 Hz, J2
¼ 6.36 Hz, 2H), 7.77-7.71 (m, 4H), 7.67 (s, 2H), 7.59 (s, 2H),
7.45 (s, 2H) 2.87-2.79 (m, 4H), 2.2-2.0 (m, 4H), 1.86-1.74 (m,
4H), 1.41-1.31 (m, 4H), 1.31-1.22 (m, 8H), 1.21-1.06 (m, 20H),
0.86 (t, J ¼ 6.99 Hz, 6H), 0.80 (t, J ¼ 7.10 Hz, 6H), 0.80-0.68
(m, 4H). 13C NMR (126 MHz, CDCl3, d, ppm): 151.76, 151.44
(ddd, J1 ¼ 251.30 Hz, J2 ¼ 10.79 Hz, J3 ¼ 4.55 Hz), 144.97, 144.74,
142.65, 140.45, 140.27 (td, J1 ¼ 254.80 Hz, J2 ¼ 15.75 Hz), 135.40
(dt, J1 ¼ 4.14 Hz, J2 ¼ 10.80 Hz), 133.14, 131.39, 128.29, 125.54,
124.80, 124.71, 120.18, 119.83, 105.59 (d, J ¼ 25.12 Hz), 55.38,
1H NMR (300 MHz, CD2Cl2, d, ppm): 8.01 (d, J ¼ 9.13 Hz,
2H), 7.79 (d, J ¼ 3.98 Hz, 2H), 7.50 (s, 2H), 7.16 (d, J ¼
3.98 Hz, 2H), 4.26 (t, J ¼ 6.59 Hz, 2H), 1.88-1.76 (m, 2H),
1.57-1.45 (m, 2H), 1.44-1.22 (m, 12H), 0.89 (t, J ¼ 6.75 Hz,
3H). 19F NMR (282 MHz, CD2Cl2, d, ppm): –125.86 (s, 2F). EI
HRMS m/z (Mþ) calcd for C30H29Br2F3N3OS2þ: 707.0081;
found: 707.0085.
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40.53, 31.81, 31.70, 30.88, 30.04, 29.90, 29.38, 29.24, 23.81,
22.63, 22.60, 14.06. 19F NMR (471 MHz, CDCl3, d, ppm): –130.25-
–130.56 (m, 2F), –157.98- –158.25 (m, 1F). GPC (THF, polysty-
rene): Mn ¼ 42900 g/mol, PDI ¼ 3.4.
fluorene boronic acid derivative via Suzuki-Miyaura polycon-
densation. The resulting DA copolymers were characterized by
thermal and spectroscopic methods showing the influence of
backbone geometry on these properties. The corresponding
solar cells exhibited power conversion efficiencies up to 1.8%.
P3. The general polymerization conditions were followed start-
ing from 3 c (59.0 mg, 67.2 lmol) and 8 (43.2 mg, 67.2 lmol).
The polymer was end capped by the addition of p-tolylboronic
acid (8 mg, 58.8 lmol) stirred at 90 ꢀC for 6 h and then p-bro-
motoluene (45 mg, 0.263 mmol) was added and the mixture
was stirred for another 16 h. After cooling to rt the aqueous
phase was separated and the polymer was precipitated by addi-
tion of the organic phase to MeOH. After filtration the residue
was dissolved in THF, filtered through a plug of celite, reduced
in volume and precipitated from MeOH, filtered and dried
in vacuo at 70 ꢀC to yield an orange solid (144 mg, 92%).
Part of this work was funded by the German Research Founda-
tion (Deutsche Forschungsgemeinschaft – DFG) within the pri-
ority program 1355 ‘‘Elementary processes of organic
photovoltaics.’’ The authors thank Ralf Weigel for his support at
the MPI–MF beamline and thank Ångstromquelle Karlsruhe
(ANKA), Germany for providing synchrotron facility. They also
thank Benjamin Schmidt-Hansberg from the Institute of
Thermal Process Engineering, KIT Karlsruhe, for fruitful
discussions.
1H NMR (500 MHz, CDCl3, d, ppm): 8.08-8.00 (m, 2H), 7.76-
7.71 (m, 4H), 7.66 (s, 2H), 7.58 (s, 2H), 7.44 (s, 2H), 4.22 (t, J
¼ 6.20 Hz, 2H), 2.87-2.77 (m, 4H), 2.2-2.0 (m, 4H), 1.86-1.74
(m, 6H), 1.51-1.46 (m, 2H), 1.40-1.06 (m, 44H), 0.88 (t, J ¼
7.18 Hz, 3H), 0.85 (t, J ¼ 7.25 Hz, 6H), 0.80 (t, J ¼ 7.09 Hz,
6H), 0.80-0.68 (m, 4H). 13C NMR (126 MHz, CDCl3, d, ppm):
155.99 (dd, J1 ¼ 247.87 Hz, J2 ¼ 8.30 Hz), 151.75, 144.86,
144.51, 142.57, 141.32, 140.41, 135.51 (td, J1 ¼ 257.70 Hz, J2
¼ 13.09 Hz), 133.18, 131.61, 127.98, 125.54, 124.78, 124.63,
120.15, 119.83, 105.41-105.15 (m), 75.09, 55.38, 40.53, 31.89,
31.81, 31.71, 30.89, 30.04, 29.96, 29.91, 29.54, 29.39, 29.30,
29.24, 25.61, 23.80, 22.68, 22.63, 22.61, 14.11, 14.06. 19F
NMR (471 MHz, CDCl3, d, ppm) –124.45 (br s, 2F). GPC (THF,
polystyrene): Mn ¼ 23,300 g/mol, PDI ¼ 2.5.
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8.15 (d, J ¼ 3.64 Hz, 2H), 8.07 (d, J ¼ 8.47 Hz, 2H), 7.89 (s,
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¨
¨
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