A new tetracyclic lactam building block for thick, broad-bandgap photovoltaics

Article abstract of DOI:10.1021/ja5051692

A new tetracyclic lactam building block for polymer semiconductors is reported that was designed to combine the many favorable properties that larger fused and/or amide-containing building blocks can induce, including improved solid-state packing, high charge carrier mobility, and improved charge separation. Copolymerization with thiophene resulted in a semicrystalline conjugated polymer, PTNT, with a broad bandgap of 2.2 eV. Grazing incidence wide-angle X-ray scattering of PTNT thin films revealed a strong tendency for face-on π-stacking of the polymer backbone, which was retained in PTNT:fullerene blends. Corresponding solar cells featured a high open-circuit voltage of 0.9 V, a fill factor around 0.6, and a power conversion efficiency as high as 5% for >200 nm thick active layers, regardless of variations in blend stoichiometry and nanostructure. Moreover, efficiencies of >4% could be retained when thick active layers of ～400 nm were employed. Overall, these values are the highest reported for a conjugated polymer with such a broad bandgap and are unprecedented in materials for tandem and particularly ternary blend photovoltaics. Hence, the newly developed tetracyclic lactam unit has significant potential as a conjugated building block in future organic electronic materials.

Full text of DOI:10.1021/ja5051692

Communication
pubs.acs.org/JACS
A New Tetracyclic Lactam Building Block for Thick, Broad-Bandgap
Photovoltaics
Renee Kroon,*,†,‡ Amaia Diaz de Zerio Mendaza,‡ Scott Himmelberger,§ Jonas Bergqvist,∥ Olof Backe,⊥
̈
Gregorio Couto Faria,§,# Feng Gao,∥ Abdulmalik Obaid,∇ Wenliu Zhuang,‡ Desta Gedefaw,‡ Eva Olsson,⊥
́
Olle Inganas,∥ Alberto Salleo,§ Christian Muller,*,‡ and Mats R. Andersson†,‡
̈
̈
†Ian Wark Research Institute, University of South Australia, Adelaide, SA 5095, Australia
‡Department of Chemical and Biological Engineering and Department of Applied Physics, Chalmers University of Technology,
⊥
41296 Goteborg, Sweden
̈
§Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
∥Department of Physics, Chemistry and Biology, Linkoping University, 58183 Linkoping, Sweden
̈
̈
#Instituto de Física de Sao Carlos, Universidade de Sao Paulo, Sao Carlos, SP 13560-970, Brazil
̃
̃
̃
∇Department of Physics, Wake Forest University, Winston-Salem, North Carolina 27106, United States
S
* Supporting Information
devices. For instance, to ensure reproducibility in large-area OSC
ABSTRACT: A new tetracyclic lactam building block for
polymer semiconductors is reported that was designed to
combine the many favorable properties that larger fused
and/or amide-containing building blocks can induce,
including improved solid-state packing, high charge carrier
mobility, and improved charge separation. Copolymeriza-
tion with thiophene resulted in a semicrystalline
conjugated polymer, PTNT, with a broad bandgap of 2.2
eV. Grazing incidence wide-angle X-ray scattering of
PTNT thin films revealed a strong tendency for face-on π-
stacking of the polymer backbone, which was retained in
PTNT:fullerene blends. Corresponding solar cells featured
a high open-circuit voltage of 0.9 V, a fill factor around 0.6,
and a power conversion efficiency as high as 5% for >200
nm thick active layers, regardless of variations in blend
stoichiometry and nanostructure. Moreover, efficiencies of
>4% could be retained when thick active layers of ∼400
nm were employed. Overall, these values are the highest
reported for a conjugated polymer with such a broad
bandgap and are unprecedented in materials for tandem
and particularly ternary blend photovoltaics. Hence, the
newly developed tetracyclic lactam unit has significant
potential as a conjugated building block in future organic
electronic materials.
production, deposition of a thick active layer (>200 nm) is
preferred because it allows for the formation of more-uniform
films with a lower defect density (pinholes).4 Additionally,
increasing the active layer thickness enhances the number of
absorbed photons and thus, potentially, the extracted photo-
current. For very thick active layers (>400 nm), the optical
absorption becomes nearly impervious to destructive interfer-
ence, which further enhances the reproducibility of OSCs.5 Aside
from offering a high open-circuit voltage (Voc), broad bandgap
materials for tandem cells ideally enable the deposition of thick
active layers, as a high but invariant short-circuit current density
(Jsc) for one cell would allow for easier optimization of the
second subcell’s current density at the maximum power point
(MPP).6 Furthermore, materials that enable thick photoactive
layers are usually characterized by high charge carrier mobilities,
which would benefit charge transport (CT) and optical density in
OSCs incorporating sensitizer-based ternary blends.7
Unfortunately, most OSCs incorporate materials that offer
optimized power conversion efficiencies (PCEs) when ∼100 nm
thick active layers are employed. Increasing the active layer
thickness usually causes increased internal resistance and space
charge limited currents, aggravating bimolecular recombination.
This is expressed in a reduced fill factor (FF) that is consequently
detrimental to the photovoltaic performance.8
So far, only a limited number of donor polymers have been
reported that can be used in OSCs with thick polymer:fullerene
active layers but high FFs and PCEs. The most widely studied are
regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-
butyric acid methyl ester (PCBM), which continue to perform
well with an active layer >200 nm.5,9 Recently, other, more exotic
polymer structures have been reported that also enable thick
polymer:fullerene active layers in OSCs. For instance, high-
performance diketopyrrolopyrrole copolymer:fullerene-based
OSCs with a thickness up to 400 nm were reported by Li et
rganic solar cells (OSCs) continue to attract scientific
Ointerest because they offer the prospect of an economically
feasible high-throughput production process.1 Extensive research
efforts using laboratory-scale devicesprimarily incorporating
photoactive layers based on polymer:fullerene blendshave
already led to benchmark efficiencies of 9−10%.2 Meanwhile,
important advances have been made with regard to tuning high-
throughput techniques such as roll-to-roll processing, inkjet-
printing, or spray-coating for large-scale production of OSCs.3
Employing thick active layers in OSCs is of outmost
importance, as it would solve a number of issues in photovoltaic
Received: May 23, 2014
Published: July 24, 2014
© 2014 American Chemical Society
11578
dx.doi.org/10.1021/ja5051692 | J. Am. Chem. Soc. 2014, 136, 11578−11581

Journal of the American Chemical Society
Communication
a
purification was necessary, which makes NT suitable for up-
scaling. 6 can then be N-alkylated with an alkyl bromide, in this
work 2-hexyldecyl bromide, to ensure solubility (7). To
brominate the alkylated monomer, we found that slightly
elevated temperatures and a catalytic amount of acetic acid
were necessary to drive the reaction and form 8. After
purification, 8 was polymerized with 2,5-bis(trimethylstannyl)-
thiophene to yield PTNT.
Scheme 1. Synthetic Route toward NT and PTNT
PTNT is soluble in solvents such as toluene, chloroform,
chlorobenzene, and in particular ortho-dichlorobenzene (o-
DCB), which permits the dissolution of higher concentrations
of 10−20 g/L. The molecular weight was determined via size
exclusion chromatography in 1,2,4-trichlorobenzene (1,2,4-
TCB) at 150 °C. For both a relative calibration against
polystyrene and universal calibration, high number-average
molecular weights were found, Mn ≈ 45 kg/mol (PDI = 3.5)
and Mn ≈ 38 kg/mol (PDI = 2.9), respectively. Moreover,
linearization of the Mark−Houwink−Sakurada equation [η] =
KMα, where [η] is the intrinsic viscosity and K and α are
parameters, yielded K = 122 × 10−5 dL/g and α = 0.5 (SI),
indicating theta solvent conditions for PTNT in 1,2,4-TCB at
a
Reagents and conditions: (a) Ac2O, triethylamine, 150 °C; (b) step 1,
oxalyl chloride, acetone, 0 °C; step 2, NaN3(aq), 0 °C; (c) Bu3N,
diphenyl ether, 250 °C; (d) HNO3, AcOH, EtAc; (e) Pd/C, H2, THF,
30 °C; (f) ethyl chloroformate, Et3N, THF, 0 °C; (g) Bu3N, diphenyl
ether, 250 °C; (i) K2CO3, 2-HDBr, KI, DMF, 90 °C; (j) NBS, AcOH,
CHCl3, 50 °C; (h) 2,5-bis(trimethylstannyl)thiophene, Pd2(dba)3,
P(o-Tol)3, toluene, 90 °C.
150 °C.
onset
The oxidation and reduction potentials of PTNT, V
= 0.81
ox
al.10 However, the best donor polymers reported to date are
based on benzotriazole, thiazolothiazole, or naphtha-bisbenzo-
thiadiazole units, which not only sustain a maximum PCE ≈ 6−
9% for 200−280 nm layers but also can give 1 μm thick active
layers with PCE ≈ 6−8%.11
= −1.56 V (SI) vs Fc/Fc+, were measured by square-
onset
V and V
red
wave voltammetry, yielding an electrochemical bandgap Egec
=
2.37 eV. From these values the HOMO and LUMO were
estimated to be −5.94 and −3.57 eV, respectively. UV/vis
absorption spectra of o-DCB solutions as well as thin solid films
reveal an absorption onset of only 560 nm (Figure 1a), which
corresponds to a broad solid-state optical bandgap of 2.2 eV.
When PTNT is blended with PCBM, the broad bandgap and
deep HOMO can be expected to result in a high photovoltage,
which would make PTNT a suitable material for tandem solar
cells. Additionally, the broad bandgap of PTNT results in solid-
state emission in the visible range of the spectrum.
Initially, we probed the ability of PTNT to order by melting
1,3,5-trichlorobenzene (1,3,5-TCB) crystals on a thick PTNT
film, which dissolves the polymer. During cooling of the liquid
1,3,5-TCB, this typically results in partial alignment of
semicrystalline conjugated polymers by directional epitaxial
Here we describe the synthesis and characterization of a new
polymer, poly(2,5-thiophene-alt-4,9-bis(2-hexyldecyl)-4,9-
dihydrodithieno[3,2-c:3′,2′-h][1,5]naphthyridine-5,10-dione)
(PTNT), which yields high OSC efficiencies in devices with thick
active layers. PTNT is a broad bandgap polymer that
incorporates the novel unit 4,9-bis(2-hexyldecyl)-4,9-dihydro-
dithieno[3,2-c:3′,2′-h][1,5]naphthyridine-5,10-dione (NT), a
tetracyclic fused lactam ring that was designed to combine the
many favorable properties that larger fused and/or amide-
containing building blocks can induce, such as improved solid-
state packing, high charge carrier mobility, and improved charge
separation.12 Poduval et al. and Cao et al. recently adopted the
same strategy;13 particularly the work of Cao et al. shows the
feasibility of this strategy, reporting OSCs with 8% PCE. PTNT
enables the fabrication of OSCs with PCEs as high as 5% and thus
represents a valuable addition to the growing library of polymer
semiconductors.
A synthetic route previously reported by Bisagni et al.14 was
modified for the synthesis of NT and PTNT (Scheme 1; see SI
for synthetic details). First, 2-thiopheneacetic acid and 2-
thiophene carboxaldehyde were reacted via Perkin condensation
to yield 1.15 We found that a second crop of the E-isomer could
be obtained by heating the Z-isomer for 4 days under the same
reaction conditions.16 In this way, a batch process for the E-
isomer can be created which mitigates the low yield of this
reaction. After formation of the acyl azide, conversion via Curtius
rearrangement at high temperatures gave the intermediate
isocyanate, which, under these conditions, immediately con-
verted to 2. Nitration of 2 at low temperature seemed to be
selective for the proton on the 7-position and offered 3.
Reduction with hydrogen + Pd/C then resulted in 4. Subsequent
reaction with ethyl chloroformate offered the pending carbamate
group (5). Subjecting 5 to high temperatures caused nucleophilic
attack of the thiophene to the carbonyl, after which the NT unit 6
was obtained. We note that, up to this point, no extensive
Figure 1. Physicochemical properties of PTNT. (a) Optical absorption
of PTNT in o-DCB solution (red circles) + neat films (open diamonds)
and solid-state photoluminescence. (b) Polarized optical microscopy
images of 1,3,5-TCB nucleated PTNT samples on a glass substrate (5×
magnification). (c) 2D-GIWAXS pattern of neat PTNT. (d) In-plane
and out-of-plane GIWAXS scans (left) and pole figures (right) of the
polymer π-stacking peak at q = 1.76 Å−1 with Gaussian fit curve (gray
dotted line).
11579
dx.doi.org/10.1021/ja5051692 | J. Am. Chem. Soc. 2014, 136, 11578−11581

Journal of the American Chemical Society
Communication
crystallization on solidified 1,3,5-TCB crystallites, followed by
removal of 1,3,5-TCB through sublimation.17 Indeed, polarized
optical microscopy revealed distinct birefringent structures
(Figure 1b), confirming the presence of ordered polymer
domains that persisted at temperatures as high as 300 °C (SI).
To characterize the solid-state order of PTNT in detail, we
carried out grazing incidence wide-angle X-ray scattering
(GIWAXS) on neat polymer films that were spin-coated from
o-DCB (Figure 1c and SI). A distinct signal at q010 ≈ 1.76 Å−1 in
the out-of-plane direction is assigned to π-stacking, which
corresponds to a short π-stacking distance, d010 = 2π/q010 ≈ 3.57
Å, assuming that PTNT crystallizes with an orthorhombic unit
cell. The out-of-plane orientation of q010 indicates a predom-
inantly face-on orientation of PTNT with respect to the silicon
substrate. Pole figures of the π-stacking peak (Figure 1d) were
used to extract a Herman’s orientation factor with a high value of
S010 ≈ 0.89, where S010 = 1 corresponds to perfect out-of-plane
alignment and S010 = 0 to an isotropic distribution of crystallites,
indicating a strong tendency of PTNT crystals to order face-on
with respect to the silicon substrate. Moreover, three orders of
the lamellar diffraction peak at q100 ≈ 0.28 Å−1, q200 ≈ 0.55 Å−1,
and q300 ≈ 0.85 Å−1 are apparent in the in-plane direction, which
correspond to an interchain spacing of 22.1 Å. Coherence lengths
of D010 ≈ 2.4 nm and D100 ≈ 12.6 nm were calculated via the
Scherrer equation, corresponding to ordering of 5−6 and 6−7
PTNT segments in the π-stacking and lamellar-stacking
direction, respectively. Pure PTNT was used in field-effect
transistors (FETs), which showed hole-only transport with
moderate values of (2−3) × 10−3 cm2/(V·s) (SI), likely due to
the perpendicular stacking of PTNT with respect to the lateral
CT in FETs.
Figure 3. PTNT:fullerene photovoltaic characteristics: (a) J−V and (b)
EQE of 2:3 PTNT:PC71BM-based (blue diamonds) and 1:2
PTNT:PC61BM-based (green triangles) OSCs; (c) Jsc, including values
from transfer matrix modeling (black squares); and (d) MPP as a
function of active layer thickness for 1:2 (red circles) and 2:3
PTNT:PC71BM-based devices. Red line functions as guide to the eye.
Open/closed symbols correspond to devices with/without DIO.
(SI). Similar to neat PTNT, blend films are characterized by
lamellar- and π-stacking signals at 0.28 and 1.76 Å−1, respectively.
Moreover, we observe a high Herman’s orientation factor S ≈
0.82, indicating a strong preference for face-on stacking of the
polymer backbone with respect to the substrate, which according
to literature benefits vertical CT across the active layer.11b,18 To
obtain a measure for the majority charge-carrier mobility of the
blend, devices were probed with photo-charge extraction by
linearly increasing voltage, which yielded values of (1−2) × 10−4
cm2/(V·s) (SI). Despite the strong effect of DIO on the blend
nanostructure, for 2:3 PTNT:PC71BM layers with similar
thickness, the external quantum efficiency (EQE) increased
from only ∼50% to ∼60% in the 350−550 nm absorption region
and resulted in a small increase in Jsc by ∼1.5 mA cm −2. This
improvement was accompanied by a slight drop in Voc by 0.04 V
and a substantial decrease in FF (Figure 3a,b). The slight drop in
Voc can be explained by an enhanced solid-state order of the
polymer that such processing agents can induce, which then
would lower the CT energy and slightly reduce the Voc.19 Overall,
the MPP remained virtually unchanged (SI); we therefore
conclude that the PCE of PTNT:PC71BM is relatively robust
with regard to changes in nanostructure.
A conventional solar cell device architecture comprising ITO/
PEDOT:PSS/active layer/LiF/Al was employed to evaluate the
photovoltaic performance of 1:1, 2:3, and 1:2 PTNT:PC71BM
blends. Active layers were spin-coated from o-DCB due to the
superior solubility of PTNT in this solvent.
To investigate the influence of blend nanostructure on the
photovoltaic performance, we compared a set of neat blends,
spin-coated from o-DCB, and blends processed from o-DCB with
addition of 3% of the “processing additive” diiodooctance (DIO).
Spin-coating of PTNT:PC71BM photovoltaic active layer blends
from o-DCB readily resulted in the formation of smooth thin
films, as evidenced by a low root-mean-square roughness of 1.6
0.2 nm, obtained by atomic force microscopy (AFM) for 2:3
PTNT:PC71BM films. AFM and transmission electron micros-
copy (TEM) revealed the existence of 50−100 nm small domains
in neat blend films (Figure 2a,c), in contrast to significantly more
fine-grained DIO-processed active layers (Figure 2b,d).
GIWAXS of a 2:3 PTNT:PC71BM film revealed that the
tendency of PTNT to order persists upon blending with PC71BM
To investigate the influence of film thickness, in a further set of
experiments we prepared active layers ranging from 60 to 395 nm
thick by adjusting the blend solution concentration and spin-
coating speed (Figure 3c,d). Independent of the active layer
thickness, the devices were characterized by an invariant Voc
≈
0.9 V. The FF decreased only slightly with increasing film
thickness: thinner active layers (60−200 nm) had FF ≈ 0.68−
0.60, whereas thicker films (200−400 nm) had FF ≈ 0.60−0.54.
Jsc was more strongly affected by changes in active layer thickness.
For both 1:2 and 2:3 PTNT:PC71BM we note two regimes, one
at 60−170 nm with a low Jsc ≈ 5−6 mA/cm2 and a second one at
180−400 nm with an improved Jsc ≈ 7−10 mA/cm2. Transfer
matrix modeling on a 1:2 PTNT:PC71BM film revealed that
these two regimes coincide with the first and second interference
minima at thicknesses of 80 and 220 nm, respectively. Thus, the
typical internal quantum efficiency is between 60 and 70%.
Overall, MPP = 4−5 mW/cm2 is retained for a broad range of
thicknesses (200−400 nm).
Figure 2. Morphology of PTNT:PC71BM blends. AFM height images
(left) and TEM bright-field micrographs (right) of the active layer in
photovoltaic devices of (a,c) 2:3 PTNT:PC71BM and (b,d) 2:3
PTNT:PC71BM processed with 3% DIO. Root-mean-square values of
1.6 0.2 nm. The scale bar is representative for all images.
11580
dx.doi.org/10.1021/ja5051692 | J. Am. Chem. Soc. 2014, 136, 11578−11581

Journal of the American Chemical Society
Communication
The EQE spectra of PTNT:PC71BM devices feature a strong
signal between 560 and 700 nm due to the good absorption of
PC71BM in this region (Figure 3b). For parallel-connected
tandem solar cells, transparency in this region is required, which
can be readily achieved by instead using PC61BM as the acceptor
material. Indeed, EQE spectra of PTNT:PC61BM devices offer
improved transparency above the bandgap of PTNT. Never-
theless, a promising MPP > 3 mW/cm2 could be maintained for
active layers as thick as 425 nm (SI).
REFERENCES
■
(1) Espinosa, N.; Hosel, M.; Angmo, D.; Krebs, F. C. Energy Environ.
Sci. 2012, 5, 5117.
(2) (a) He, Z.; Zhong, C.; Su, S.; Xu, M.; Wu, H.; Cao, Y. Nat. Photonics
2012, 6, 591. (b) You, J.; Dou, L.; Yoshimura, K.; Kato, T.; Ohya, K.;
Moriarty, T.; Emery, K.; Chen, C.; Gao, J.; Li, G.; Yang, Y. Nat. Commun.
2013, 4, 1446.
(3) Søndergaard, R. R.; Hosel, M.; Krebs, F. C. J. Polym. Sci., Part B:
Polym. Phys. 2013, 51, 16.
(4) (a) Lee, J.-H.; Sagawa, T.; Yoshikawa, S. Thin Solid Films 2013, 529,
464. (b) Li, G.; Shrotriya, V.; Huang, J.; You, Y.; Moriarty, T.; Emery, K.;
Yang, Y. Nat. Mater. 2005, 4, 864.
(5) Dennler, G.; Scharber, M. C.; Brabec, C. J. Adv. Mater. 2009, 21,
1323.
(6) Ameri, T.; Li, N.; Brabec, C. J. Energy Environ. Sci. 2013, 6, 2390.
(7) Ameri, T.; Khoram, P.; Min, J.; Brabec, C. J. Adv. Mater. 2013, 25,
4245.
́
(8) (a) Moule, A. J.; Bonekamp, J. B.; Meerholz, K. J. Appl. Phys. 2006,
100, 094503. (b) Lenes, M.; Koster, L. J. A.; Mihailetchi, V. D.; Blom, P.
W. M. Appl. Phys. Lett. 2006, 88, 243502.
(9) Lee, S.; Nam, S.; Kim, H.; Kim, Y. Appl. Phys. Lett. 2010, 97,
103503.
(10) Li, W.; Hendriks, K. H.; Roelofs, W. S. C.; Kim, Y.; Wienk, M. M.;
̈
We have reported the synthesis of a new tetracyclic lactam
acceptor unit, NT, for conjugated polymers, which is
characterized by a high degree of planarity. Copolymerization
with thiophene resulted in the donor polymer PTNT, which has
a broad bandgap of only 2.2 eV. Optical microscopy and
GIWAXS revealed that PTNT is semicrystalline and predom-
inantly orders face-on in thin films, which persists upon blending
with fullerenes. As a result, OSCs based on PTNT:fullerene
blends offer a good photovoltaic performance, with Voc ≈ 0.9 V
and a PCE up to 5% that is relatively robust with regard to
variations in active layer thickness up to 400 nm as well as blend
stoichiometry and nanostructure. Varying processing parame-
ters, such as thermal or vapor annealing as well as energy level
engineering, are likely to result in further gains in photovoltaic
performance of PTNT-based OSCs. Furthermore, active layers
up to 425 nm thick still resulted in PCE ≈ 3% for
PTNT:PC61BM-based devices. We attribute these favorable
physicochemical and optoelectronic properties of PTNT to the
incorporation of the NT unit; thus, we conclude that the novel
NT unit is a promising building block for donor polymers. The
combined properties of PTNT are unprecedented, which makes
PTNT an outstanding material for use in tandem solar cells and,
in particular, ternary blend photovoltaics.
Janssen, R. A. J. Adv. Mater. 2013, 25, 3182.
(11) (a) Price, S. C.; Stuart, A. C.; Yang, L.; Zhou, H.; You, W. J. Am.
Chem. Soc. 2011, 133, 4625. (b) Osaka, I.; Saito, M.; Koganezawa, T.;
Takimiya, K. Adv. Mater. 2014, 26, 331. (c) Hu, X.; Yi, C.; Wang, M.;
Hsu, C.; Liu, S.; Zhang, K.; Zhong, C.; Huang, F.; Gong, X.; Cao, Y. Adv.
Energy Mater. 2014, 201400378.
(12) (a) Zhang, X.; Richter, L. J.; DeLongchamp, D. M.; Kline, R. J.;
Hammond, M. R.; McCulloch, I.; Heeney, M.; Ashraf, R. S.; Smith, J. N.;
Anthopoulos, T. D.; Schroeder, B.; Geerts, Y. H.; Fischer, D. A.; Toney,
M. F. J. Am. Chem. Soc. 2011, 133, 15073. (b) Bronstein, H.; Chen, Z.;
Ashraf, R. S.; Zhang, W.; Du, J.; Durrant, J. R.; Shakya Tuladhar, P.;
Song, K.; Watkins, S. E.; Geerts, Y.; Wienk, M. M.; Janssen, R. A. J.;
Anthopoulos, T. D.; Sirringhaus, H.; Heeney, M.; McCulloch, I. J. Am.
Chem. Soc. 2011, 133, 3272. (c) Chen, Z.; Zheng, Y.; Yan, H.; Facchetti,
A. J. Am. Chem. Soc. 2008, 131, 8. (d) Zheng, Q.; Jung, B. J.; Sun, J.; Katz,
H. E. J. Am. Chem. Soc. 2010, 132, 5394. (e) Biniek, L.; Schroeder, B. C.;
Donaghey, J. E.; Yaacobi-Gross, N.; Ashraf, R. S.; Soon, Y. W.; Nielsen,
C. B.; Durrant, J. R.; Anthopoulos, T. D.; McCulloch, I. Macromolecules
2013, 46, 727. (f) Xu, Y.-X.; Chueh, C.-C.; Yip, H.-L.; Ding, F.-Z.; Li, Y.-
X.; Li, C.-Z.; Li, X.; Chen, W.-C.; Jen, A. K. Y. Adv. Mater. 2012, 24,
6356. (g) Chang, C.-Y.; Cheng, Y.-J.; Hung, S.-H.; Wu, J.-S.; Kao, W.-S.;
Lee, C.-H.; Hsu, C.-S. Adv. Mater. 2012, 24, 549. (h) Schwarz, C.;
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental details and characterization data and images. This
material is available free of charge via the Internet at http://pubs.
acs.org.
AUTHOR INFORMATION
Bassler, H.; Bauer, I.; Koenen, J.-M.; Preis, E.; Scherf, U.; Kohler, A. Adv.
Mater. 2010, 24, 922.
(13) (a) Poduval, M. K.; Burrezo, P. M.; Casado, J.; Lop
T.; Ortiz, R. P.; Kim, T. Macromolecules 2013, 46, 9220. (b) Cao, J.; Liao,
̈
̈
■
Corresponding Authors
renee.kroon@unisa.edu.au
christian.muller@chalmers.se
́
ez Navarrete, J.
Q.; Du, X.; Chen, J.; Xiao, Z.; Zuo, Q.; Ding, L. Energy Environ. Sci. 2013,
6, 3224.
Notes
(14) Bisagni, E.; Landras, C.; Thirot, S.; Huel, C. Tetrahedron 1996, 52,
10427.
The authors declare no competing financial interest.
(15) Pavlicic, D.; Koruznjak, J.; Banic-Tomisi
̌
c, Z.; Karminski-Zamola,
yesi, T. In Electronic
̈
̌
G. Molecules 2002, 7, 871.
ACKNOWLEDGMENTS
■
(16) Pal
́
inko,
́
I.; Torok, B.; Tasi, G.; Kortvel
́
̈
̈
We thank the Chalmers Areas of Advance Materials Science,
Energy and Nanoscience and Nanotechnology as well as the
Swedish Research Council and Formas for funding. R.K.
acknowledges the Swedish Energy Agency for financial support.
A.D. was supported by the Linnaeus Centre for Bioinspired
Supramolecular Function and Design. S.H. thanks the National
Science Foundation for assistance in the form of a Graduate
Research Fellowship. Use of the Stanford Synchrotron Radiation
Lightsource, SLAC National Accelerator Laboratory, is sup-
ported by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences under Contract No. DE-AC02-
76SF00515.
Conferences on Trends in Organic Chemistry (ECTOC-1); Rzepa, H. S.,
Goodman, J. M., Leach, C., Eds.; Royal Society of Chemistry: London,
1995; http://www.ch.ic.ac.uk/ectoc/ectoc-1.html.
(17) Muller, C.; Aghamohammadi, M.; Himmelberger, S.; Sonar, P.;
Garriga, M.; Salleo, A.; Campoy-Quiles, M. Adv. Funct. Mater. 2013, 23,
̈
2368.
(18) Gomez, E. D.; Barteau, K. P.; Wang, H.; Toney, M. F.; Loo, Y.-L.
Chem. Commun. 2011, 47, 436.
(19) Vandewal, K.; Gadisa, A.; Oosterbaan, W. D.; Bertho, S.;
Banishoeib, F.; van Severen, I.; Lutsen, L.; Cleij, T. J.; Vanderzande, D.;
Manca, J. V. Adv. Funct. Mater. 2008, 18, 2064.
11581
dx.doi.org/10.1021/ja5051692 | J. Am. Chem. Soc. 2014, 136, 11578−11581