2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione-based donor-acceptor alternating copolymer bearing 5,5′-Di(thiophen-2-yl)-2, 2′-biselenophene exhibiting 1.5 cm2·V -1·s-1 hole mobility in thin-film transistors

Article abstract of DOI:10.1021/ja203189h

A novel diketopyrrolopyrrole-based π-conjugated copolymer P(DPP-alt-DTBSe), 5, and a known copolymer P(DPP-alt-QT), 4, have been synthesized in 80-90% yield using the Stille coupling reaction. The molecular weights of 4 and 5 are 58 781 and 19 271 g/mol, respectively, with polydispersity values of 3.25-3.35. A relatively small band gap of 1.32-1.39 eV and excellent solubility in organic solvents were achieved in the two polymers. Thin-film transistors made of 5 exhibit outstanding performance (e.g., μ > 1.0-1.5 cm²·V^-1·s^-1, I _on/I_off > 10⁵-10⁶) with a conventional n-octyltrichlorosilane-SiO₂ gate dielectric.

Full text of DOI:10.1021/ja203189h

COMMUNICATION
pubs.acs.org/JACS
2,5-Bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione-Based
DonorꢀAcceptor Alternating Copolymer Bearing 5,50-Di
(thiophen-2-yl)-2,20-biselenophene Exhibiting
1.5 cm2 Vꢀ1 sꢀ1 Hole Mobility in Thin-Film
3
3
Transistors
Jae Seung Ha, Kyung Hwan Kim, and Dong Hoon Choi*
Department of Chemistry, Research Institute for Natural Sciences, Korea University, 5 Anam-dong, Sungbuk-gu, Seoul 136-701, Korea
S Supporting Information
b
field effect mobility of 5-based TFTs reached 1.5 cm2 Vꢀ1 sꢀ1
3
3
ABSTRACT: A novel diketopyrrolopyrrole-based π-con-
jugated copolymer P(DPP-alt-DTBSe), 5, and a known
copolymer P(DPP-alt-QT), 4, have been synthesized in
80ꢀ90% yield using the Stille coupling reaction. The
molecular weights of 4 and 5 are 58 781 and 19 271 g/
mol, respectively, with polydispersity values of 3.25ꢀ3.35. A
relatively small band gap of 1.32ꢀ1.39 eV and excellent
solubility in organic solvents were achieved in the two
polymers. Thin-film transistors made of 5 exhibit outstand-
after the film was annealed at 180 °C, although the molecular
weight (Mn) is relatively small. TFTs made from 4 after thermal
annealing at 150 °C also produce carrier mobilities of around
1.0 cm2 Vꢀ1 ꢀ1. The best mobility of 5 is slightly higher than
s
3
3
that of 4. To the best of the authors’ knowledge, selenophene-
containing P(DPP-alt-DTBSe) is another promising candidate
capable of showing very high mobility values, in addition to DPP-
thiophene-based polymers.9cꢀe
DPP-based chromophores are often employed as high-perfor-
mance organic pigments,16 and their solubility can be improved
by modifying their chemical structure.17ꢀ19 The DPP moiety
exhibits a planar conjugated bicyclic structure, which leads to
strong πꢀπ interactions. DPP-containing polymers are consid-
ered promising materials for optimizing the performance of
organic semiconductors.20ꢀ22
ing performance (e.g., μ > 1.0ꢀ1.5 cm2 Vꢀ1
s >
ꢀ1, Ion/Ioff
3
3
105ꢀ106) with a conventional n-octyltrichlorosilaneꢀSiO2
gate dielectric.
ecent developments of p-type organic semiconductors,
The polymer synthesized herein contains the DPP unit and
quaterthiophene (QT) or 5,50-di(thiophen-2-yl)-2,20-biseleno-
phene (DTBSe) in repeating groups. The influence of the
selenium atom on the electron distribution and, therefore, on
the charge transport property has been studied recently.23ꢀ25
Since selenium generally shows a stronger heteroaromatic inter-
action than sulfur, the replacement of sulfur by selenium offers
the opportunity to enhance the chain interaction between
neighboring chains and the carrier transport phenomenon. The
branched, long alkyl chains are tethered to the N,N-positions of
the lactam rings to control the πꢀπ stacking and physical
properties, including solubility, crystallization, energy levels,
band gaps, and self-assembly capacity.
The preparation of 3,6-bis(5-bromothiophen-2-yl)-2,5-bis
(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione, 1,
5,50-bis(trimethylstannyl)-2,20-bithiophene, 2, and 5,50-bis-
(trimethylstannyl)-2,20-biselenophene, 3, is outlined in Scheme S1.
2 and 3 were also synthesized in a pure form by literature meth-
ods.25ꢀ27 The synthetic procedures and characterization data are well
described in the Supporting Information. Polymerization via Stille
coupling was carried out using monomers 1and 2or 3in the presence
of tetrakis(triphenylphosphine)palladium(0) (see Scheme 1). The
polymerization reaction yielded the desired polymers as dark
purple solids. The resultant polymers 4 and 5 are alternating
R
namely, derivatives of polyacenes, rubrene, or fused thio-
phene, have led to very high hole mobilities on the order of
1 cm2 Vꢀ1 sꢀ1 in organic thin-film transistors (OTFTs).1ꢀ5
3
3
Deposition methods for thin films of these molecules under vacuum
or inert atmosphere, however, suffer from severe limitations in the
large-scale fabrication of the devices owing to the complexity of the
process. Unlike the small molecules mentioned above, highly
conjugated semicrystalline or liquid crystalline polymers with good
solution processability and film-forming abilities have been sug-
gested as the best candidates for large-scale device fabrication owing
to their potentially superior mechanical and semiconducting
properties.6ꢀ8 Thus far, homogeneous polymers composed of donor
and acceptor units in the repeating group have been reported to have
an excellent mobility of 0.94ꢀ3.3 cm2 Vꢀ1
s
ꢀ1,9 whereas specific
3
3
polymer blend systems have been reported to show mobilities higher
than 1.0ꢀ2.0 cm2 Vꢀ1
s .
ꢀ1 10,11 However, the high crystallinity and
3
3
mobility of conjugated polymers always require high molecular
weight, which sometimes hampers the solubility in solvents. More-
over, the reproduction of films with identical degrees of crystallinity
and molecular order remains extremely challenging, although some
progress has been made using various annealing processes.12ꢀ15 In
short, the technological thrust seems to lie in the development of a
new class of polymers that exhibit much better performance in
practical device applications.
In this Communication, the facile synthesis of diketopyrrolo-
pyrrole (DPP)-based conjugated polymers P(DPP-alt-QT), 4,
and P(DPP-alt-DTBSe), 5, is demonstrated. Interestingly, the
Received: April 20, 2011
Published: June 17, 2011
r
2011 American Chemical Society
10364
dx.doi.org/10.1021/ja203189h J. Am. Chem. Soc. 2011, 133, 10364–10367
|

Journal of the American Chemical Society
COMMUNICATION
Scheme 1. Polymerization of DPP-Containing Conjugated
Polymers P(DPP-alt-QT), 4, and P(DPP-alt-DTBSe), 5,
Exhibiting a Hole Mobility Higher than 1.0 cm2 Vꢀ1 sꢀ1
3
3
Figure 2. (a) X-ray diffraction (XRD) patterns of 4: powder (i), as-spun
film (ii), and annealed film at 100 °C (iii) and 150 °C (iv). (b) XRD
patterns of 5: powder (i), as-spun film (ii), and annealed film at 150 °C
(iii) and 180 °C (iv).
length and the electron-rich nature of the selenium atom. In general,
the small band gap results from the extended π-conjugation and the
intra- and intermolecular interaction between donor (QT or
DTBSe) and acceptor (DPP).
From the XRD patterns presented in Figure 2a, the crystalline
nature of 4 is evident, and the variation of the diffraction behavior
indicates the formation of well-grown polycrystallites in the spin-
coated film on n-octyltrichlorosilane (OTS)-modified SiO2/Si
substrate. The high crystallinity of the as-spun film of 4 is attributed
to the probable self-assembly into a highly ordered lamellar structure
in the film. As shown in the diffractogram of the as-spun film
(Figure 2a, (ii)), there are clear diffraction peaks arising from the
interlayer spacing up to the fourth order. Four highly resolved
diffraction peaks were observed at 2θ = 4.68° (d(100) =18.90 Å),
9.08°, 13.58°, and 18.08°, which indicates that the polymer chains
exhibit well-organized intermolecular ordering, resulting in the
enhanced crystallinity (see Figure 7S). Annealing the film at 100
and 150 °C increases the intensity of the diffraction peaks, thus
indicating an increase in the crystallinity of the sample. Based on
literature reports,9 4 forms a lamellar crystalline structure in the
thermally annealed film at 150 °C, with an interlayer distance of
d(100) = 19.10 Å and πꢀπ plane stacking distance of d(010) = 3.66 Å.
The short interlayer distance observed implies the existence of
interchain interactions induced by both πꢀπ stacking via planar
molecular units and the DꢀA polar interaction. As for 5, a more
significantly crystalline behavior could be observed in the film
sample. Before annealing the sample, we could observe relatively
higher intensity of (100) diffraction peak, well-resolved fourth-order
diffraction peaks, and an increase in the diffraction intensity with the
annealing temperature. The diffraction peaks were clearly observed
at 2θ = 4.77° (d(100) = 18.53 Å), 9.35°, 13.85°, and 18.34°, which
revealed that the polymer chains formed a lamellar crystalline
structure in the thin film. The very low intensity peak at 23.87°
originating from the πꢀπꢀstacking distance could be barely
observed. Selenophene-containing 5 also forms a lamellar crystalline
structure in the film, with an interlamellar distance of ∼18.53 Å (see
Figure 7S). This interaction is also quite promising in terms of
facilitating charge transport behavior in the TFT devices, resulting in
an enhancement of the carrier mobility. The above XRD results
unambiguously revealed the formation of highly ordered lamellar
stacking with a presumably edge-on orientation for the annealed and
even the nonannealed polymer thin films. The highly organized
polymer chains in the thin films are particularly favorable for charge
carrier transport via hopping through πꢀπ stacks in an OTFT
device.
Figure 1. (a) UVꢀvis absorption spectra of P(DPP-alt-QT), 4: (i)
solution and (ii) film. (b) UVꢀvis absorption spectra of P(DPP-alt-
DTBSe), 5: (iii) solution and (iv) film. Inset: images of polymer solution
and high-quality spin-coated film.
copolymers consisting of DPP and QT or DTBSe units, respec-
tively. All of the small molecules were purified by flash column
chromatography or recrystallization and were characterized by
1H NMR, mass spectroscopy, and CHN elemental analysis.
The final polymers were purified by reprecipitation and
Soxhlet extraction with methanol, acetone, hexane, and chloro-
form. They show good solubility in common solvents such as
chloroform, dichloromethane, toluene, THF, and chlorobenzene
(up to 12 mg/mL). New conjugated polymers having 2--
(octyldodecyl) aliphatic side-chain groups are known to have a
moderately high molecular weight (Mn). The Mn (19 271 g/mol)
of 5 was one-third that of 4 (58 781 g/mol), with polydispersity
values of 3.25ꢀ3.35. Because of the good solubility of both
polymers, all measurements were done in chloroform at 35 °C.
Figure 1 shows the UVꢀvis absorption spectra of the polymer
samples both in solution and in films. The solution spectra of
both polymers are structureless. 4 exhibited absorption maxima
at 784 (715 as a shoulder) nm and 796 (732) nm in the solution
and film, respectively (Figure 1a). The solution spectrum of 4
showed a broad, bathochromic absorbance, which extends from
500 to 900 nm; it is attributed to the πꢀπ transition as well as the
donorꢀacceptor (DꢀA) interaction between the thiophenes
and DPP moieties. Two absorption bands were observed in the
film samples of both polymers. In particular, the polymers in this
study contain plain QT and DTBSe without any side chain,
which are different from many DꢀA copolymers in the
literature.28ꢀ30 It can be inferred that the πꢀπ stacking of the
DPP units is suppressed and the DꢀA interactions become more
predominant. Obviously, spectrum (iv) shows a bathochromic shift
by 35 nm relative to (ii), and the baseline floats significantly due to
optical loss. This implies that selenophene-containing repeating
groups are highly interactive, forming self-assembled molecular
domains through strong electronic coupling. The optical band gaps
of 4 and 5 were determined from the UVꢀvis absorption onsets in
the solid state to be 1.39 and 1.32 eV, respectively. 5 has a much
lower band gap because of its long-range effective conjugation
Because 4 and 5 exhibit high solubility in organic solvents,
their thin films could easily be fabricated on an OTS-treated SiO2
10365
dx.doi.org/10.1021/ja203189h |J. Am. Chem. Soc. 2011, 133, 10364–10367

Journal of the American Chemical Society
COMMUNICATION
in both the pristine and annealed 5 films, which is different from
the images in the 4 films (Figures 9S and 10S). The selenophene-
containing polymer with relatively low Mn showed obvious
improvement in physical properties as well as the device proper-
ties. In brief, the significantly large mobilities are attributed to the
strong tendency toward strong DꢀA interaction between the
DPP acceptor unit and the alternating donor units in both
polymers, which leads to closer alignment of the polymer,
thereby facilitating charge transport in the film state.
In conclusion, we prepared novel conjugated alternating copoly-
mer with DPP and DTBSe monomers, including a DPP-QT-based
copolymer. This polymer, 5, exhibited a significantly high hole
Figure 3. IDS and IDS1/2 versus gate voltage (VG) for 4-based TFTs: (a)
with the pristine film and (b) with the annealed film (Tann.= 150 °C for
10 min). Inset: TFT device configuration and AFM images of each film
sample. The performances were measured at ambient conditions.
mobility (μ ≈ 1.5 cm2 Vꢀ1
s ,
ꢀ1), higher than 1.0 cm2 Vꢀ1 sꢀ1
3
3
3
3
which is one of the highest values obtained thus far from a
homogeneous polymer system. Besides the πꢀπ interactions
between identical conjugative moieties, donorꢀacceptor dyad
interactions were the most important driving force in the construc-
tion of a well-ordered morphological structure, which facilitates the
charge transport phenomenon. In particular, 5 showed promising
physical properties and device performances in terms of the carrier
mobility and good solubility accompanied with great film-forming
properties.
This study unambiguously demonstrates that the DPP and
DTBSe alternating copolymer with a relatively low Mn, high
degree of crystallinity, and great solubility can be effectively
utilized for fabricating significantly improved OTFT devices.
Figure 4. IDS and IDS1/2 versus gate voltage (VG) for 5-based TFTs: (a)
with the pristine film and (b) with the annealed film (Tann. = 180 °C for
10 min). Inset: TFT device configuration and AFM images of each film
sample. The performances were measured at ambient conditions.
’ ASSOCIATED CONTENT
S
Supporting Information. Complete experimental details
b
of syntheses, 1H NMR spectra, GPC chromatogams of polymers,
and device fabrication; magnified images of optical micrographs
and atomic force micrographs; output and transfer curves of TFT
devices; and complete ref 9e. This material is available free of
charge via the Internet at http://pubs.acs.org.
surface by a simple spin-coating method using a 1.0 wt %
chloroform or chlorobenzene solution. Top-contact bottom gate
TFT devices (W = 1500 μm, L = 100 μm) were fabricated using
the polymers, and the mobilities were obtained from the source-
drain currentꢀgate voltage curves (IDS vs VG) of more than 20
devices in well-resolved saturation regions. All devices made of 4
and 5 films exhibited typical p-channel transistor behavior.
Initially, the hole mobility of the pristine film of 4 (Figure 3a) was
’ AUTHOR INFORMATION
Corresponding Author
dhchoi8803@korea.ac.kr
measured to be 0.60 cm2 Vꢀ1
s
ꢀ1 (Ion/Ioff ≈ 106, Vth = ꢀ7 V).
3
3
However, subsequent to annealing at 150 °C, the mobility values
increased to 1.04 cm2 Vꢀ1
s
ꢀ1, maintaining an onꢀoff current
3
’ ACKNOWLEDGMENT
3
ratio of 105ꢀ106 (Figure 3b). The AFM images presented in the
inset of Figure 3 illustrate that, after annealing at 150 °C, the
polymer film surface was filled with uniform intertwined polymer
fibers that afford densely interconnected chain networks.
This research was supported by the National Research Foun-
dation (NRF) of Korea (No. 20100025252) and by Priority
Research Centers Program through the NRF funded by the
Ministry of Education, Science and Technology (NRF2011-
0018396).
The devices made of 5 exhibited IDSꢀVG characteristics quite
similar to those of 4. OTFT devices using as-spun 5 films without
thermal annealing showed a mobility of around 0.63 cm2 Vꢀ1 sꢀ1
3
3
’ REFERENCES
(1) Zhang, Y.; Petta, J. R.; Ambily, S.; Shen, Y.; Ralph, D. C.;
Malliaras, G. G. Adv. Mater. 2003, 15, 1632.
(2) Klauk, H.; Halik, M.; Zschieschang, U.; Schmid, G.; Radlik, W.
J. Appl. Phys. 2002, 92, 5259.
(3) Li, Z.; Du, J.; Tang, Q.; Wang, F.; Xu, J. B.; Yu, J. C.; Miao, Q.
Adv. Mater. 2010, 22, 3242.
(4) Zhang, L.; Tan, L.; Wang, Z.; Hu, W.; Zhu, D. Chem. Mater.
2009, 21, 1993.
(5) Gao, P.; Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.;
Baumgarten, M.; Pisula, W.; M€ullen, K. Adv. Mater. 2009, 21, 213.
(6) McCulloch, I.; Heeney, M.; Bailey, C.; Genevicius, K.; MacDonald,
I.; Shkunov, M.; Sparrowe, D.; Tierney, S.; Wagner, R.; Zhang, W.;
(Figure 4a), and after the sample was annealed at 180 °C, the
mobility abruptly increased to 1.5 cm2 Vꢀ1 sꢀ1 (Ion/Ioff ≈ 106,
3
3
Vth = ꢀ12 V) (Figure 4b). Surprisingly, the maximum mobilities
of the two polymers were determined to be higher than 1.0 cm2
3
Vꢀ1
s
ꢀ1 ; however, the TFTs with 5 films showed a little higher
3
mobility than the TFTs with 4 films. It was found that polymer 5
has a much smaller Mn than 4, which can aid the solubilization of
the selenophene-containing polymer. The strong interchain
interaction in P(DPP-alt-DTBSe), 5, induced slightly denser
chain packing than in P(DPP-alt-QT), 4, which is supported by
the XRD results (see Figure 8S). The topography in the AFM
images displayed highly developed crystalline fibrous structures
10366
dx.doi.org/10.1021/ja203189h |J. Am. Chem. Soc. 2011, 133, 10364–10367

Journal of the American Chemical Society
COMMUNICATION
Chabinyc, M. L.; Kline, R. J.; McGehee, M. D.; Toney, M. F. Nat. Mater.
2006, 5, 328.
(7) Umeda, T.; Kumaki, D.; Tokito, S. J. Appl. Phys. 2009,
105, 024516.
(8) Nelson, T. L.; Young, T. M.; Liu, J.; Mishra, S. P.; Belot, M. J.;
Balliet, C. L.; Javier, A. E.; Kowalewski, T.; McCullough, R. D. Adv.
Mater. 2010, 22, 4617.
(9) (a) Tsao, H. N.; Cho, D.; Andreasen, J. W.; Rouhanipour, A.;
Breiby, D. W.; Pisula, W.; M€ullen, K. Adv. Mater. 2009, 21, 209.
(b) Zhang, W.; Smith, J.; Watkins, S. E.; Gysel, R.; McGehee, M.; Salleo,
A.; Kirkpatrick, J.; Ashraf, S.; Anthopoulos, T.; Heeney, M.; McCulloch,
I. J. Am. Chem. Soc. 2010, 132, 11437. (c) Li, Y.; Singh, S. P.; Sonor, P.
Adv. Mater. 2010, 22, 4862. (d) Li, Y.; Sonar, P.; Singh, S. P.; Soh, M. S.;
van Meurs, M.; Tan, J. J. Am. Chem. Soc. 2011, 133, 2198. (e) Bronstein,
H.; et al. J. Am. Chem. Soc. 2011, 133, 2198. (f) Tsao, H. N.; Cho, D. M.;
Park, I.; Hansen, M. R.; Mavrinskiy, A.; Yoon, D. Y.; Graf, R.; Pisula, W.;
Spiess, H. W.; M€ullen, K. J. Am. Chem. Soc. 2011, 133, 2605.
(10) Hamilton, R.; Smith, J.; Ogier, S.; Heeney, M.; Anthony, J. E.;
McCulloch, I.; Veres, J.; Bradley, D. C.; Anthopoulos, T. D. Adv. Mater.
2009, 21, 1166.
(11) Smith, J.; Heeney, M.; McCulloch, I.; Malik, J. N.; Stingelin, N.;
Bradley, D. D. C.; Anthopoulos, T. D. Org. Electron. 2011, 12, 143.
(12) van Breemen, A. J. J. M.; Herwig, P. T.; Chlon, C. H. T.;
Sweelssen, J.; Schoo, H. F. M.; Benito, E. M.; de Leeuw, D. M.; Tanase,
C.; Wildeman, J.; Blom, P. W. M. Adv. Funct. Mater. 2005, 15, 872.
(13) Usta, H.; Lu, G.; Facchetti, A.; Marks, T. J. J. Am. Chem. Soc.
2006, 128, 9034.
(14) Ong, B. S.; Wu, Y.; Liu, P.; Gardner, S. Adv. Mater. 2005,
17, 1141.
(15) Heeney, M.; Bailey, C.; Genevicius, K.; Shkunov, M.; Sparrowe,
D.; Tierney, S.; McCulloch, I. J. Am. Chem. Soc. 2005, 127, 1078.
(16) Fukuda, M.; Kodoma, K.; Yamamoto, H.; Mito, K. Dyes Pigm.
2004, 63, 115.
(17) Choi, S. H.; Kwon, O. T.; Kim, N. R.; Yoon, C.; Kim, J. P.; Choi,
J. H. Bull. Kor. Chem. Soc. 2010, 4, 1073.
(18) Sonar, P.; Ng, G. M.; Lin, T. T.; Dodabalapur, A.; Chen, Z. K.
J. Mater. Chem. 2010, 20, 3626.
(19) Guo, F.; Qu, S.; Wu, W.; Li, J.; Ying, W.; Hua, J. Synth. Met.
2010, 160, 1767.
(20) Beyerein, T.; Tieke, B. Macromol. Rapid Commun. 2000,
21, 182.
(21) Sonar, P.; Singh, S. P.; Li, Y.; Soh, M. S.; Dodabalapur, A. Adv.
Mater. 2010, 22, 5409.
(22) Bijleveld, J. C.; Gevaerts, V. S.; Nuzzo, D. D.; Turbiez, M.;
Mathijssen, S. G. J.; de Leeuw, D. M.; Wienk, M. M.; Janssen, R. A. Adv.
Mater. 2010, 22, E242.
(23) Chen, Z.; Lekme, H.; Seifried, S. A.; Caironi, M.; Nielsen,
M. M.; Heeney, M.; Zhang, W.; McCulloch, I.; Sirringhaus, H.
Adv. Mater. 2010, 22, 2371.
(24) Kong, H.; Jung, Y. K.; Cho, N. S.; Kang, I. N.; Park, J. H.; Cho,
S.; Shim, H. K. Chem. Mater. 2009, 21, 2660.
(25) Kong, H.; Chung, D. S.; Kang, I. N.; Park, J. W.; Park, M. J.; Jing,
I. H.; Park, C. E.; Shim, H. K. J. Mater. Chem. 2009, 19, 3490.
(26) Fong, H. H.; Pozdin, V. A.; Amassian, A.; Malliaras, G. G.;
Smilgies, D. M.; He, M.; Gasper, S.; Zhang, F.; Sorensen, D. M. J. Am.
Chem. Soc. 2008, 130, 13202.
(27) Kim, Y. M.; Lim, E. H.; Kang, I. N.; Jung, J. B.; Lee, J. M.; Koo,
B. W.; Do, L. M.; Shim, H. K. Macromolecules 2006, 39, 4081.
(28) Cao, D.; Liu, Q.; Zeng, W.; Han, S.; Peng, J.; Liu, S. J. Polym. Sci.
Part A: Polym. Chem. 2006, 44, 2395.
(29) Kanimozhi, C.; Balraju, P.; Sharma, G. D.; Patil, S. J. Phys. Chem.
B 2010, 114, 3095.
(30) Qiao, Z.; Peng, J.; Jin, Y.; Liu, Q.; Weng, J.; He, Z.; Han, S.; Cao,
D. Polymer 2010, 51, 1016.
10367
dx.doi.org/10.1021/ja203189h |J. Am. Chem. Soc. 2011, 133, 10364–10367