Developing conjugated polymers with high electron affinity by replacing a c-c unit with a b←n unit

Article abstract of DOI:10.1002/anie.201411973

The key parameters of conjugated polymers are lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Few approaches can simultaneously lower LUMO and HOMO energy levels of conjugated polymers to a large ext

Full text of DOI:10.1002/anie.201411973

Angewandte
Chemie
DOI: 10.1002/anie.201411973
Electron Transport
Hot Paper
Developing Conjugated Polymers with High Electron Affinity by
!
ꢀ
Replacing a C C Unit with a B N Unit**
Chuandong Dou, Zicheng Ding, Zijian Zhang, Zhiyuan Xie, Jun Liu,* and Lixiang Wang
Abstract: The key parameters of conjugated polymers are
lowest unoccupied molecular orbital (LUMO) and highest
occupied molecular orbital (HOMO) energy levels. Few
approaches can simultaneously lower LUMO and HOMO
energy levels of conjugated polymers to a large extent
(> 0.5 eV). Disclosed herein is a novel strategy to decrease
both LUMO and HOMO energy levels of conjugated poly-
levels of conjugated polymers. To decrease LUMO and
increase HOMO energy levels for narrow band gaps of
conjugated polymers, one may enforce coplanarity of the
polymer backbone, increase quinoidal character of the
polymer backbone, or use alternating electron-poor and
electron-rich units.[4] To slightly increase (or decrease) both
the LUMO and HOMO energies of conjugated polymers, one
may introduce electron-rich (or electron-poor) substituents to
the polymer backbone.[5] However, few approaches can
simultaneously lower both the LUMO and HOMO energy
levels of conjugated polymers to a large extent (> 0.5 eV).[6]
Thus, novel molecular design strategies to greatly decrease
both the LUMO and HOMO energies of conjugated poly-
mers for high electron affinity are important and challenging.
Thanks to the recent progress in organic boron chemis-
try,[7] conjugated polymers containing boron elements have
received great attention.[8] Jꢀkle, Chujo, and Wagner et al.
have reported several families of boron-containing conju-
gated polymers which exhibit either unusual properties or
excellent performance.[8] Bazan et al. have performed rever-
ꢀ
mers by about 0.6 eV through replacement of a C C unit by
a B N unit. The replacement makes the resulting polymer
!
transform from an electron donor into an electron acceptor,
and is proven by fluorescence quenching experiments and the
photovoltaic response. This work not only provides an effective
approach to tune the LUMO/HOMO energy levels of
conjugated polymers, but also uses organic boron chemistry
as a new toolbox to develop conjugated polymers with high
electron affinity for polymer optoelectronic devices.
C
onjugated polymers with p-electrons delocalized over the
backbones are an important class of semiconducting materials
and have been used in various devices, such as organic light-
emitting diodes (OLEDs), organic field-effect transistors
(OFETs), polymer solar cells (PSCs), etc.[1] The key param-
eters of conjugated polymers are lowest unoccupied molec-
ular orbital (LUMO)/highest occupied molecular orbital
(HOMO) energy levels. Accordingly, there are many p-type
conjugated polymers with high LUMO/HOMO energies and
many ambipolar conjugated polymers with low LUMO and
high HOMO energies.[2] In comparison, n-type conjugated
polymers with low-lying LUMO/HOMO levels and high
electron affinity are scare, irrespective of their applications as
electron transport materials in OLEDs, n-type materials in
OFETs, or electron acceptor materials in PSCs, etc.[3] Several
strategies have been reported to tune the LUMO/HOMO
ꢀ
sible intermolecular B N coordination reactions to tune the
!
emission color of conjugated polymers.[9] The B N unit and
[10]
ꢀ
ꢀ
C C unit are isoelectronic and isosteric. In a C C unit,
each carbon atom has four valence electrons. In a B N unit,
!
the boron atom has three valence electrons and the nitrogen
ꢀ
atom has five valence electrons. Therefore, in contrast to C C
being a covalent bond with a dipole of zero and bond
!
dissociation energy of 90.1 kcalmolꢀ1, B N is a coordination
bond with a dipole of 5.2 D and bond dissociation energy of
!
27.2 kcalmolꢀ1.[11] The B N unit has been used by Yama-
guchi et al., S. Wang et al., and Y. Wang et al. to develop
conjugated small molecules with high electron affinity.[12]
These molecules have been applied as electron transport
materials or emitters in OLEDs and n-type semiconductors in
ꢀ
OFETs. Herein, we report that replacing a C C unit by
a B N unit in conjugated polymers can lower both the
!
[*] Dr. C. Dou, Dr. Z. Ding, Z. Zhang, Prof. Z. Xie, Prof. J. Liu,
Prof. L. Wang
LUMO and HOMO energies by about 0.6 eV (Figure 1). As
a result, the replacement changes the resulting conjugated
polymer from an electron donor to an electron acceptor. Our
results indicate that organic boron chemistry provides a new
toolbox for developing conjugated polymers with high
electron affinity, which is required for OLEDs, OFETs, and
OPVs.
Figure 1 shows the chemical structures of the model
polymer with the C C unit, poly[(4,4-bis(2-ethylhexyl)cyclo-
penta-[2,1-b:3,4-b’]-dithiophene-2,6-diyl)-alt-(5-(2-octyldo-
decyl)thieno[3,4-c]pyrrole-4, 6-dione-1,3-diyl)] (P-CC), and
the corresponding polymer with a B N unit, poly[((3-
State Key Laboratory of Polymer Physics and Chemistry Changchun
Institute of Applied Chemistry
Chinese Academy of Sciences
Changchun 130022 (P. R. China)
E-mail: liujun@ciac.ac.cn
[**] We are grateful for financial support by the 973 Project (No.
2014CB643504), the Nature Science Foundation of China (No.
51373165, No. 21404099), the “Thousand Talents Program” of
China, and the Strategic Priority Research Program of the Chinese
Academy of Sciences (No. XDB12010200). We thank Prof. Shigehiro
Yamaguchi (Nagoya University) and Prof. Hongyu Zhang (Jilin
University) for the fruitful discussions on photophysical results and
theoretical calculation results.
ꢀ
!
diphenylboryl-2-thienyl)-2-thiazole-2,6-diyl)-alt-(5-(2-octyl-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201411973.
dodecyl)thieno[3,4-c]pyrrole-4,6-dione-1,3-diyl)]
(P-BN).
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
Supporting Information). Our attempts to synthesize the
diethylboryl analogue of P-BN failed because its correspond-
!
ing B N-containing monomer was sensitive to air and
moisture, and unsuitable for polymerization.
!
To elucidate the effects of the B N unit, we performed
density-functional theory (DFT) calculations at the B3LYP/6-
31G* level of theory on the model compounds of P-CC and P-
BN (M-CC-Me and M-BN-Ph; Figure 2).[14] Both M-CC-Me
and M-BN-Ph contain two repeat units with the long alkyl
Figure 1. a) Chemical structures of the model polymer P-CC containing
!
ꢀ
a C C unit and the designed polymer P-BN containing a B N unit.
Note that the chemical structure of P-BN should be regiorandom as
!
a result of the unsymmetric B N-containing unit. b) LUMO/HOMO
energy levels of the two polymers.
The thieno[3,4-c]pyrrole-4,6-dione-1,3-diyl (TPD) unit is used
for the two alternating copolymers because of its weak
electron-accepting feature. Thus, P-CC is a typical conjugated
polymer with alternating electron-rich cyclopenta-[2,1-b:3,4-
b’]-dithiophene units (CPDT) and electron-poor TPD
units.[13] P-BN can be used to investigate the effects of
!
ꢀ
replacing a C C with B N in a conjugated polymer.
Scheme 1 illustrates the synthetic routes to P-BN and P-
CC. The diphenylboryl-substituted thienylthiazole 1 was
prepared according to the previous report of the dimesityl-
boryl analogue from the group of Yamaguchi.[12d] Lithiation
with 2.2 equivalents of nBuLi on 1, and subsequent treatment
with Me3SnCl produced the key monomer 2. Stille polymer-
ization of 2 and 5 readily afforded P-BN in 77% yield. With
the unsymmetric BN-containing unit, P-BN should be regio-
random because both head-to-head and head-to-tail bonding
modes of the BN-containing unit and the TPD unit may exist.
The chemical structure of P-BN was verified by 1H NMR and
11B NMR spectroscopy, as well as elemental analysis. The
sharp signal at d = 0.6 ppm in the 11B NMR spectrum suggests
a tetracoordinated boron center (see the Supporting Infor-
mation). P-CC was synthesized by the Stille polymerization of
!
ꢀ
Figure 2. Electronic effects of replacing a C C unit by a B N unit on
the model compounds, which is calculated at the B31 LYP/6-31G*
level.
chains replaced by the methyl groups. Their optimized
structures show fully planar skeletons owing to the fusion
!
ꢀ
with the C C or B N unit (see the Supporting Information).
This effect is in stark contrast to the distorted backbone of
conjugated polymers with an intermolecular B–N Lewis acid–
base effect reported by Bazan et al., and is due to the steric
hindrance of the boron-containing moieties.[9] The calculation
indicates that the HOMO of M-CC-Me is mainly localized on
the electron-rich CPDT unit, and the LUMO is mainly
localized on the electron-poor TPD unit, thus suggesting an
electron-donor–acceptor feature with the intramolecular
charge transfer of P-CC. In contrast, the HOMO and
LUMO of M-BN-Ph were both well delocalized over the
ꢀ
the corresponding C C-containing monomer 4 and 5. Both P-
CC and P-BN are stable enough to be purified in air, and they
have good thermal stability and photostability (see the
!
ꢀ
entire framework. Thus, replacing the C C unit by a B
unit in conjugated polymers obviously affects the distribution
of electron densities and decreases the electron-donor–
N
!
acceptor character. To clarify the effects of the B N unit
on LUMO/HOMO energy levels, the DFT calculations on the
dimethylboryl analogue M-BN-Me was also conducted.
!
ꢀ
Replacing a C C unit in M-CC-Me by a B N unit in M-
BN-Me decreases the LUMO/HOMO energy levels by 0.39/
0.59 eV. The substituents on the boron atom can further lower
the LUMO/HOMO energy levels. The LUMO/HOMO
energy levels of M-BN-Ph are lowered by 0.50 eV/0.69 eV
compared to those of M-CC-Me. Thus, DFT calculations
!
suggest that the B N unit can endow conjugated polymers
with high electron affinity.
To verify the effects of the B N unit substitution on the
LUMO/HOMO energy levels of the polymers, we measured
Scheme 1. Synthesis of P-BN and P-CC. Reagents and conditions:
a) nBuLi, tetrahydrofuran, ꢀ788C, then Me3SnCl, from ꢀ788C to 258C;
b) 5, [Pd2(dba)3], P(o-Tolyl)3, toluene, 1208C, then phenylboronic acid
and bromobenzene. Ph=Phenyl, R1 =2-octyldodecyl, R2 =2-ethylhexyl.
!
cyclic voltammetry of the polymer films (Figure 3). P-CC
2
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Figure 3. Cyclic voltammogram of the films of P-BN and P-CC.
shows a reversible reduction wave and two quasireversible
oxidation waves with the onset reduction potential (Eonsetred vs.
Fc/Fc+) of ꢀ1.69 V and onset oxidation potential (Eonsetox) of
0.57 V. In comparison, P-BN shows multiple irreversible
reduction and oxidation processes with more-positive onset
reduction and oxidation potentials (Eonsetred = ꢀ1.04 V,
Eonsetox = 1.10 V). According to these onset reduction and
oxidation potentials, the LUMO/HOMO energy levels of the
two polymers are estimated and listed in Table 1. Compared
with those of P-CC, the LUMO and HOMO of P-BN are
lowered by 0.53 eV and 0.65 eV, respectively. This lowering is
consistent with the DFT calculation results and manifests the
Figure 4. UV/Vis absorption spectra and fluorescence spectra of a) P-
CC and b) P-BN in CHCl3 solution and in film. Insets: photographs of
P-CC and P-BN in CHCl3 solution.
quantum efficiencies of 0.21 and 0.16, respectively, the peak of
the fluorescence spectrum of P-BN is blue-shifted by 43 nm
compared to that of P-CC.
For a blend of two organic/polymeric materials, if the
DLUMO (or DHOMO) of the two materials is larger than
0.3–0.4 eV, electron transfer (or hole transfer) between them
can occur and leads to exciton dissociation and fluorescence
quenching, thus photovoltaic performance may be
expected.[15] The fluorescence quenching experiments of P-
CC and P-BN were performed on thin films. As shown in
Figure 5, the P-CC film shows no detectable fluorescence and
the P-BN film exhibits fluorescence with the peaks at l = 650/
710 nm. The fluorescence of the film of a P-CC/P-BN (1:1)
blend is undetectable, thus indicating that the fluorescence of
P-BN is fully quenched by P-CC. This fluorescence quenching
is assigned to the electron/hole transfer between the two
polymers and confirms the low-lying LUMO/HOMO energy
!
effects of B N unit. The low-lying LUMO/HOMO energies
of P-BN (ELUMO = ꢀ3.76 eV, EHOMO = ꢀ5.90 eV) imply that
P-BN has a high electron affinity. Indeed, its LUMO/HOMO
energy levels are fairly comparable to those of Phenyl-C61-
butyric acid methyl ester (PC61BM;
E
LUMO = ꢀ3.88 eV,
E
HOMO = ꢀ6.10 eV), a widely used electron-acceptor material
in PSCs (see the Supporting Information).
!
ꢀ
The replacement of a C C unit by a B N unit in the
conjugated polymers leads to a blueshift of the absorption
spectra and fluorescence spectra, as well as increase of the
optical band gap. As shown in Figure 4, the absorption
spectrum of P-CC in solution shows a broad band with peaks
at l = 646/598 nm, while the absorption spectrum of P-BN in
solution exhibits an absorption maxima at l = 574 nm with
a shoulder at l = 610 nm. This difference is evidenced by the
different color of the solutions of the two polymers as shown
in the insets of Figure 4. In the thin film, P-BN exhibits an
onset absorption at l = 660 nm, thus corresponding to the
optical band gap of 1.88 eV. In comparison, P-CC shows an
onset absorption at l = 730 nm, thus indicating the optical
band gap of 1.69 eV. Both P-BN and P-CC show an obvious
redshift in absorption spectra in going from solution to film
because the planar configurations of the polymer backbones
facilitate the interactions of polymer backbones in the solid
state. While both P-BN and P-CC show high fluorescence
Figure 5. Fluorescence spectra of the films of P-CC, P-BN, and P-CC/P-
BN (1:1), excited at l=570 nm.
Table 1: Photophysical properties, electrochemical properties, and energy levels of P-BN and P-CC.
[a]
[a]
[a]
[b]
ox[c]
red[c]
[d]
[d]
Polymer
labs
[nm]
emax
[mꢀ1 cmꢀ1
lem
[nm]
fF[a]
labs
[nm]
E [eV]
Eonset
[V]
Eonset
[V]
EHOMO
[eV]
ELUMO
[eV]
]
P-CC
P-BN
598, 646
574, 610
78900
89600
681
638
0.16
0.21
667, 612
614, 574
1.69
1.88
0.57
1.10
ꢀ1.69
ꢀ1.04
ꢀ5.37
ꢀ5.90
ꢀ3.11
ꢀ3.76
[a] Measured in CHCl3 solution. [b] Measured in thin film. [c] Onset potential vs. Fc/Fc+. [d] Calculated using the equation
(EHOMO =ꢀ(4.80+Eonsetox) eV, ELUMO =ꢀ(4.80+Eonsetred) eV).
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
levels of P-BN. Encouraged by this result, we fabricated PSC
devices with a P-CC/P-BN blend as the active layer. The
device exhibits a photovoltaic response with an open-circuit
In summary, we demonstrate a strategy to greatly lower
both the LUMO and HOMO energy levels of conjugated
ꢀ
polymers for high electron affinity by replacing a C C unit by
!
voltage of 1.08 V,
a
short-circuit current density of
a B N unit. With the replacement, the LUMO and HOMO
0.35 mAcmꢀ2, a fill factor of 0.23, and a power conversion
efficiency of 0.085% (see the Supporting Information). The
device performance is not so satisfactory, probably because of
the large phase separation size of the blend film (see the
Supporting Information). Both the fluorescence quenching
experiment and the photovoltaic response suggest that the
energy levels are lowered by 0.65 eVand 0.53 eV, respectively,
thus making the conjugated polymer transform from an
electron donor to an electron acceptor. This transformation is
confirmed by fluorescence quenching experiments and the
photovoltaic response. Following this strategy, further studies
on conjugated polymers containing a B N unit as an
electron acceptor material in PSCs are in progress in our
laboratory.
!
!
ꢀ
replacement of a C C unit in P-CC by a B N unit in P-BN
changes the polymer from an electron donor to an electron
acceptor.
Received: December 12, 2014
Revised: January 9, 2015
Published online: && &&, &&&&
To clearly verify the capability of P-BN as an electron-
acceptor/hole donor when blended with normal conjugated
polymers, we selected a typical electron donor, poly(3-
hexylthiophene) (P3HT), and conducted the fluorescence
quenching experiments in solution.[16] As shown in Figure 6a,
Keywords: boron · conjugation · electron transport ·
.
fluorescence · polymers
[1] For recent reviews and articles on conjugated polymers, see:
a) X. Guo, A. Facchetti, T. J. Marks, Chem. Rev. 2014, 114, 8943;
b) C. Wang, H. Dong, W. Hu, Y. Liu, D. Zhu, Chem. Rev. 2012,
112, 2208; c) X. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A.
Ratner, M. R. Wasielewski, S. R. Marder, Adv. Mater. 2011, 23,
268; d) C. Li, M. Liu, N. G. Pschirer, M. Baumgarten, K. Mꢁllen,
Chem. Rev. 2010, 110, 6817; e) C.-Y. Chiu, H. Wang, F. G.
Brunetti, F. Wudl, C. J. Hawker, Angew. Chem. Int. Ed. 2014, 53,
3996; Angew. Chem. 2014, 126, 4077; f) P. M. Beaujuge, H. N.
Tsao, M. R. Hansen, C. M. Amb, C. Risko, J. Subbiah, K. R.
Choudhury, A. Mavrinskiy, W. Pisula, J.-L. Brꢂdas, F. So, K.
Mꢁllen, J. R. Reynolds, J. Am. Chem. Soc. 2012, 134, 8944;
g) J. D. Yuen, J. Fan, J. Seifter, B. Lim, R. Hufschmid, A. J.
Heeger, F. Wudl, J. Am. Chem. Soc. 2011, 133, 20799.
[2] a) Y.-J. Cheng, S.-H. Yang, C.-S. Hsu, Chem. Rev. 2009, 109,
5868; b) S. Allard, M. Forster, B. Souharce, H. Thiem, U. Scherf,
Angew. Chem. Int. Ed. 2008, 47, 4070; Angew. Chem. 2008, 120,
4138.
Figure 6. Fluorescence quenching spectra of P3HT/P-BN in CHCl3
(mgmLꢀ1) with varying a) P-BN and b) P3HT concentrations
(lex =453 nm). Insets: schematic of the energy level alignments and
electron/hole transfer of P3HT and P-BN.
[3] a) A. J. Heeger, Adv. Mater. 2014, 26, 10; b) Y. Lin, H. Fan, Y. Li,
X. Zhan, Adv. Mater. 2012, 24, 3087; c) Y. Shirota, H. Kageyama,
Chem. Rev. 2007, 107, 953.
[4] a) L. Dou, W.-H. Chang, J. Gao, C.-C. Chen, J. You, Y. Yang,
Adv. Mater. 2013, 25, 825; b) X. Guo, M. Zhang, J. Tan, S. Zhang,
L. Huo, W. Hu, Y. Li, J. Hou, Adv. Mater. 2012, 24, 6536; c) F. He,
W. Wang, W. Chen, T. Xu, S. B. Darling, J. Strzalka, Y. Liu, L. Yu,
J. Am. Chem. Soc. 2011, 133, 3284.
[5] a) L. Ye, S. Zhang, L. Huo, M. Zhang, J. Hou, Acc. Chem. Res.
2014, 47, 1595; b) A. C. Stuart, J. R. Tumbleston, H. Zhou, W. Li,
S. Liu, H. Ade, W. You, J. Am. Chem. Soc. 2013, 135, 1806; c) H.
Zhou, L. Yang, S. C. Price, K. J. Knight, W. You, Angew. Chem.
Int. Ed. 2010, 49, 7992; Angew. Chem. 2010, 122, 8164.
[6] a) K. Takimiya, I. Osaka, M. Nakano, Chem. Mater. 2014, 26,
587; b) P. M. Beaujuge, J. R. Reynolds, Chem. Rev. 2010, 110,
268.
[7] For recent reviews on organic boron chemistry, see: a) D. Frath,
J. Massue, G. Ulrich, R. Ziessel, Angew. Chem. Int. Ed. 2014, 53,
2290; Angew. Chem. 2014, 126, 2322; b) Z. M. Hudson, S. Wang,
Dalton Trans. 2011, 40, 7805; c) C. R. Wade, A. E. J. Brooms-
grove, S. Aldridge, F. P. Gabbaꢃ, Chem. Rev. 2010, 110, 3958;
d) M. J. D. Bosdet, W. E. Piers, Can. J. Chem. 2008, 86, 8; e) S.
Yamaguchi, A. Wakamiya, Pure Appl. Chem. 2006, 78, 1413;
f) C. D. Entwistle, T. B. Marder, Chem. Mater. 2004, 16, 4574;
g) C. D. Entwistle, T. B. Marder, Angew. Chem. Int. Ed. 2002, 41,
2927; Angew. Chem. 2002, 114, 3051.
P3HT exhibits a strong orange fluorescence peak around l =
573 nm in CHCl3 solution (10 mgmLꢀ1). When P-BN was
added to the P3HT solution, the intensity of P3HT fluores-
cence gradually decreased. Considering the energy level
alignments of P3HTand P-BN (see the inset of Figure 6a), we
attribute the fluorescence quenching of P3HT by P-BN to the
electron transfer from P3HT to P-BN with the LUMO
difference of 0.56 eV (see the Supporting Information).
Similarly, as shown in Figure 6b, the red fluorescence of P-
BN can also be quenched by P3HT because of the hole
transfer from P-BN to P3HT with the HOMO difference of
0.70 eV.[17] The fluorescence quenching of P-BN and P3HT is
further confirmed by the smaller fluorescence intensities of
the blend of P-BN and P3HT in solution compared with the
individual solutions of the two polymers at the same concen-
tration (see the Supporting Information). The PSC device
with a P3HT/P-BN blend as the active layer also exhibits
photovoltaic performance with a power conversion efficiency
of 0.14% (see the Supporting Information). The fluorescence
quenching results and the photovoltaic response of P-BN and
P3HT confirm the effects of the low-lying LUMO/HOMO
energy levels of P-BN.
4
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
[8] a) K. Tanaka, Y. Chujo, Macromol. Rapid Commun. 2012, 33,
1235; b) A. Lorbach, A. Hꢁbner, M. Wagner, Dalton Trans. 2012,
41, 6048; c) F. Jꢀkle, Chem. Rev. 2010, 110, 3985; d) Y. Tokoro,
A. Nagai, Y. Chujo, Macromolecules 2010, 43, 6229; e) A.
Lorbach, M. Bolte, H. Li, H.-W. Lerner, M. C. Holthausen, F.
Jꢀkle, M. Wagner, Angew. Chem. Int. Ed. 2009, 48, 4584; Angew.
Chem. 2009, 121, 4654; f) F. Jꢀkle, Coord. Chem. Rev. 2006, 250,
1107.
[9] a) P. Zalar, Z. B. Henson, G. C. Welch, G. C. Bazan, T.-Q.
Nguyen, Angew. Chem. Int. Ed. 2012, 51, 7495; Angew. Chem.
2012, 124, 7613; b) G. C. Welch, G. C. Bazan, J. Am. Chem. Soc.
2011, 133, 4632; c) G. C. Welch, R. Coffin, J. Peet, G. C. Bazan, J.
Am. Chem. Soc. 2009, 131, 10802.
[10] a) P. G. Campbell, A. J. V. Marwitz, S.-Y. Liu, Angew. Chem. Int.
Ed. 2012, 51, 6074; Angew. Chem. 2012, 124, 6178; b) M. J. D.
Bosdet, W. E. Piers, T. S. Sorensen, M. Parvez, Angew. Chem.
Int. Ed. 2007, 46, 4940; Angew. Chem. 2007, 119, 5028.
[11] a) D. J. Grant, D. A. Dixon, J. Phys. Chem. A 2006, 110, 12955;
b) S. J. Blanksby, G. B. Ellison, Acc. Chem. Res. 2003, 36, 255;
c) L. R. Thorne, R. D. Suenram, F. J. Lovas, J. Chem. Phys. 1983,
78, 167.
[12] a) D. Li, H. Zhang, Y. Wang, Chem. Soc. Rev. 2013, 42, 8416;
b) Y.-L. Rao, S. Wang, Inorg. Chem. 2011, 50, 12263; c) A. Job,
A. Wakamiya, G. Kehr, G. Erker, S. Yamaguchi, Org. Lett. 2010,
12, 5470; d) A. Wakamiya, T. Taniguchi, S. Yamaguchi, Angew.
Chem. Int. Ed. 2006, 45, 3170; Angew. Chem. 2006, 118, 3242.
[13] X. Guo, H. Xin, F. S. Kim, A. D. T. Liyanage, S. A. Jenekhe,
M. D. Watson, Macromolecules 2011, 44, 269.
[14] DFT calculations were performed using Gaussian09: M. J.
Frisch, et al. Gaussian 09, revision A.02; Gaussian, Inc.: Wall-
ingford, CT, 2009. For details, see the Supporting Information.
[15] B. C. Thompson, J. M. J. Frꢂchet, Angew. Chem. Int. Ed. 2008,
47, 58; Angew. Chem. 2008, 120, 62.
[16] a) S. Wei, J. Xia, E. J. Dell, Y. Jiang, R. Song, H. Lee, P.
Rodenbough, A. L. Briseno, L. M. Campos, Angew. Chem. Int.
Ed. 2014, 53, 1832; Angew. Chem. 2014, 126, 1863; b) J. L.
Jellison, C.-H. Lee, X. Zhu, J. D. Wood, K. N. Plunkett, Angew.
Chem. Int. Ed. 2012, 51, 12321; Angew. Chem. 2012, 124, 12487.
[17] T. Zhou, T. Jia, B. Kang, F. Li, M. Fahlman, Y. Wang, Adv.
Energy Mater. 2011, 1, 431.
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Electron Transport
C. Dou, Z. Ding, Z. Zhang, Z. Xie, J. Liu,*
L. Wang
&&&& — &&&&
Developing Conjugated Polymers with
ꢀ
High Electron Affinity by Replacing a C C
Unit with a B N Unit
!
!
N
ꢀ
Transforming units: Disclosed herein is
a novel strategy to decrease both LUMO
and HOMO energy levels of conjugated
polymers, by about 0.6 eV, through
replacement of a C C unit by a B
unit. The replacement transforms the
resulting polymer from an electron donor
into an electron acceptor.
6
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
These are not the final page numbers!