Lateral Extension of a Benzodithiophene System: Construction of Heteroacenes Containing Various Chalcogens

Article abstract of DOI:10.1002/asia.201700552

A series of linear acenes with five fused rings, which contain thiophene, selenophene, and tellurophene as the outmost rings, have been synthesized from well-known benzodithiophene (BDT). It was found that the optical, electrochemical properties and crystal packing motifs could be modulated by changing heteroatoms in the outmost rings.

Full text of DOI:10.1002/asia.201700552

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Lateral Extension of Benzodithiophene System: Construction of
Heteroacenes Containing Various Chalcogens
Authors: Lei Zhang, Jichang Wei, Dong Meng, and Zhaohui Wang
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Asian J. 10.1002/asia.201700552
Link to VoR: http://dx.doi.org/10.1002/asia.201700552
A Journal of
A sister journal of Angewandte Chemie
and Chemistry – A European Journal

10.1002/asia.201700552
Chemistry - An Asian Journal
COMMUNICATION
Lateral Extension of Benzodithiophene System: Construction of
Heteroacenes Containing Various Chalcogens
Jichang Wei,[a,b,c] Dong Meng,[a,c] Lei Zhang*[b] and Zhaohui Wang[a]
Abstract: A series of novel linear acenes with five fused rings, which
contain thiophene, selenophene, and tellurophene as the outmost
R
R
S
polymerization
S
annulation
rings, have been successfully synthesized from well-known
benzodithiophene (BDT). It was found that the optical,
electrochemical properties and crystal packing motifs could be
modulated by changing heteroatoms in the outmost rings.
S
Ar
Ar
π
n
S
S
S
R
R
BDT
BDT polymers
Extended BDT
Scheme 1. Typical Design Strategy to the BDT-based Conjugated Materials
for Organic Devices.
The BDT building block has been incorporated into a number of
fascinating molecules, including extended linear acenes, as well
as two-dimensional conjugated polymers, which have shown
significant potentials for applications in electronic devices, such
as photovoltaic cells and organic field effect transistors (Scheme
1).1 This is attributable to the ease of synthesis, particularly with
respect to selectively modifying the BDT core on the benzene
ring (4-, 8- positions) that have great impact on the material
properties.1,2 Indeed, this functionalization strategy is known to
be valuable for tuning the photovoltaic properties of the BDT-
based donor-acceptor copolymers, as demonstrated by the
successful molecular engineering for improved device
performance.1a,1d,2c
Another attractive feature of the BDT derivatives is the ability to
use well established synthetic chemistry for the lateral fusion of
aromatic rings to the thiophene rings in BDT.3 In general, this
pattern of ring fusion, especially five-membered rings containing
group 16 elements, such as thiophene, and selenophene, has
been found to be a powerful approach for extending the
molecular conjugation length, which strongly influences the
optical and electronic properties of the materials.4 It is also
indicated by theoretical investigation that the increased
conjugation length could be beneficial for improving electronic
coupling and reducing reorganization energies in the solid state.5
The incorporation of the heterocycles into a rigid, tricyclic BDT
system should therefore lead to a significantly higher degree of
conjugation.3a,3b,3d In addition, the use of heteroatom substituent
to tune the properties of the materials is very promising as such
subtle changes can often result in significant changes in the
electronic, optical, and physical properties of the resultant
materials. For example, our recent work incorporating
lead to a promising class of non-fullerene electron acceptors for
organic solar cells with power conversion efficiencies over 9%.6
It should be noted that heavier elements (Se, Te) with larger
polarizable radius offer certain advantageous properties relative
to their lighter analogues (O, S), including a narrow optical band
gap, stronger intermolecular interactions, enhanced planarity,
and a distinct solid-state structure, which are generally beneficial
for improving charge transport.7
To fully realize the potential of heterocycles as candidates for
promising optoelectronic materials, it is critical to develop
efficient procedures for their synthesis as well as their
incorporation into more complex, extended π-conjugated
systems. Although the synthetic procedures are well established
for compounds containing light elements, synthetic access to
containing heavy ones, in particular for tellurophene-based
molecules, remains great challenges due to the generally high
reactivity of carbon−heteroatom bond and weaker orbital overlap
when the heteroatom is present.7,8 Herein, we describe the
synthesis of a series of heteroacenes by linear fusion of
chalcogenophenes to the BDT cores. The resulting linear acene
derivatives constitute five fused rings with thiophene,
selenophene, and tellurophene as the outmost rings,
respectively. In addition, these heteroatoms, along with the
substituents on the benzene, are expected to provide a mean of
fine-tuning of the characteristic of the acenes.
Scheme 2 shows the synthesis of linear heteroacene derivatives
from the BDT. Our synthetic strategy relies on the intramolecular
cyclization of a chalcogenol to an ethynyl group. Compound 6
was prepared using BDT 7 as the starting material according to
the literature.9 A palladium-catalyzed cross coupling reaction
between 6 and trimethylsilylacetylene allowed us to produce
compound 5 in a 45% yield, which was readily lithiated with
butyllithium (n-BuLi) and quenched with chalcogen powders (S,
Se,Te) and ethanol to generate the chalcogenol intermediates.
The resulting chalcogenols subsequently underwent the
intramolecular cyclization in situ with the ethynyl groups to form
4 and the deprotection of trimethylsilyl (TMS) groups in present
of tetrabutylammonium fluoride (TBAF) gave 3 with high yields.
Although 3a has been synthesized previously by a tandem
directed metalation, this approach provides flexibility for
embedding different heteroatoms into linear acenes. It should be
heteroatoms (S, Se) into rylene diimides arrays,
has
demonstrated that the advantageous features of the atomic
engineering to fine tune the electronic structures of the materials,
which
[a]
J. Wei, D. Meng, Z. Wang
Beijing National Laboratory for Molecular Sciences, Key Laboratory
of Organic Solids
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190, China
[b]
J. Wei, L. Zhang
College of Energy, Beijing Advanced Innovation Center for Soft
Matter Science and Engineering
Beijing University of Chemical Technology
Beijing 100029, China
noted that our initial attempt to prepare
4 via another
E-mail: zhl@mail.buct.edu.cn
intramolecular cyclization reaction between the acetylene group
and the chalcogenate with Na2X (X=S, Se) as nucleophile, a
general approach which has drawn much attention as a route to
[c]
J. Wei, D. Meng
University of Chinese Academy of Sciences
Beijing 100049, China
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201700552
Chemistry - An Asian Journal
COMMUNICATION
a variety of chalcogenophene fused acenes,10 led only to a
complex mixture and no significant product was isolated.
A)
B)
Figure 1. (A) UV-vis spectra of 1a, 1b and 1c in chloroform solution, (B)
Electrochemical properties of 1a, 1b and 1c in dichloromethane with
tetrabutylammonium hexafluorophosphate (TBAPF6) as the supporting
electrolyte.
The cyclic voltammetry (CV) of these compounds exhibits two or
three irreversible oxidation peaks and no reduction peak was
observed (Fig 1B). According to the onset potential, the highest
occupied molecular orbitals (HOMO) were estimated to be -5.16
eV for 1a, -5.14 eV for 1b, and -4.95 eV for 1c. The very similar
HOMO values of 1a and 1b indicate the replacement of sulfur
with selenium has a relatively minor influence of the oxidation
potential. While, compared to 1a, the HOMO level of 1c is
increased to a greater extent due to the lower aromaticity of
tellurophene. The lowest unoccupied molecular orbitals (LUMO)
were roughly estimated from the optical band gap to be -2.20 eV
for 1a, -2.24 eV for 1b, and -2.14 eV for 1c. The comparable
LUMO values indicate that the chalcogen atoms in the outmost
rings have a negligible influence on the reduction potential,
which is in agreement with the study of Takimiya, who
suggested that incorporation of heavy chalcogen atoms into
annulated acenes led to the HOMO level increased and the
LUMO level relatively constant.12
Scheme 2. Synthesis of Heteroacene Derivatives with Five Fused Rings
Containing Various Chalcogens.
When compounds 3 were oxided by ammoniumceric nitrate,
quinones 2 were obtained in 60-70% yields. These quinone
scaffolds could serve as coupling components for the
development of low band-gap, high-crystalline conjugated
materials by selectively modification on five-membered ring, and
six-membered ring positions. To expand further the versatility of
the quinone scaffolds 2, we considered the triisopropylsilyl
(TIPS) ethynyl moiety, which was well known for improvement
the
solubility
and
crystallinity.11
Lithiation
of
triisopropylsilylacetylene in THF with n-BuLi to form its anion and
subsequent treatment with quinones 2 gave the relative alcohol
derivatives, followed by a reductive aromatization with SnCl2,
providing the desired products 1a, 1b, and 1c in 30%, 25%, and
20% yields, respectively. These linear heteroacenes are soluble
in common solvents and exhibit excellent tolerant for oxygen,
and silica gel, allowing for purification by chromatography. The
molecular structures were unambiguously characterized by NMR,
mass spectrometry, and x-ray crystallography (see the
supporting information).
The UV-vis absorption spectra of 1a, 1b, and 1c were measured
in chloroform solution (Figure 1A). The spectra of 1a, and 1b are
generally similar in shape and exhibit two major absorption
bands: a set of absorption band at short wavelength, and a
broad longest-wavelength absorption band from 350 to 420 nm,
which are characteristic of the acene-like derivatives.12 However,
for 1c, the spectrum possesses three sets of absorption bands:
a prominent band centered at 306 nm, the other band at 340 nm,
and another broad absorption band from 370 to 450 nm. As
expected, the progressive red-shifts in absorption were found
when the heteroatoms within the chalcogenophenes were
changed from S to Se to Te with λmax values of 402 to 413 to 423
nm. As a result, the optical band-gaps estimated from absorption
edges are 2.96 eV, 2.90 eV, and 2.81 eV for 1a, 1b, and 1c,
respectively.
Figure 2. The HOMO, and LUMO levels of 1a, 1b, and 1c calculated by DFT
at the B3LYP/6-31(d.p) level (hydrogen atoms omitted for clarity).
To better understand the electronic structures of these three
compounds, density functional theory (DFT) calculations were
performed in gas phase with Gaussian03 at the B3LYP level.
The calculated data are summarized in Table 1, and
HOMO/LUMO orbitals of the compounds are shown in Figure 2.
It can be seen that these three compounds possess very similar
HOMO and LUMO distributions. Their HOMO orbitals are
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201700552
Chemistry - An Asian Journal
COMMUNICATION
distributed over the aromatic cores and C ≡ C bonds. The
calculated HOMO levels by DFT are -5.30 eV for 1a, -5.25 eV
for 1b, and -5.21 eV for 1c, which are in good consistent with the
trend of the experimental values. The calculated LUMO levels
are -1.97 eV, -1.96 eV, and -1.98 eV for 1a, 1b and 1c,
respectively and the DFT result confirmed the fact that the
introduction of heavy heteroatom into the linear acene is
beneficial to reducing the bang gap due to the increase of the
HOMO level that occurs.
addition, the 1c molecules are also linked by C-H···π
interactions (2.84 Å) between the TIPS groups and adjacent
acene cores with an interplanar dihedral angle of 50.11°. Due to
the large size of Te, the C-Te bond length is 2.067 Å and the C–
Te–C angle is 80.79° .
A)
Table 1. Absorption, and electrochemical properties of 1a, 1b and 1c.
[d]
Head 1
λmax (nm)
HOMO[a]
(theor) [b]
(eV)
LUMO[c]
(theor) [b]
(eV) [c]
Eg
(eV)
B)
1a
1b
1c
a
402
413
423
-5.16 (-5.30)
-5.14 (-5.25)
-4.95 (-5.21)
-2.20 (-1.97)
-2.24 (-1.96)
-2.14 (-1.96)
2.96
2.90
2.81
b
HOMO values calculated from the onset of the first oxidation peaks;
HOMO and LUMO values calculated by DFT; c LUMO values estimated from
HOMO and optical band gap; d Optical band gap calculated from the onset of
the absorption peak.
C)
Single crystals of 1a, 1b and 1c were readily grown from hexane
and dichloromethane, and their solid-state arrangements were
determined by single-crystal X-ray diffraction (Figure 3). These
three molecules all have nearly planar frameworks. 1a exhibits a
slipped one-dimensional π-stacking arrangement with an
interplanar distance of 3.46 Å. Short C-H···π and Si···H contacts
between TIPS groups and acene cores in adjacent stacks are
2.81 Å and 2.89 Å, respectively, and no S···S interactions is
observed. The replacement of S with Se yields compound 1b
and induces a significant change in packing motif. 1b packs in a
herringbone-like motif with the TIPS group pointing toward the
center of the five membered core of an adjacent molecule. The
C-H···π interactions (2.81 Å) between the TIPS groups and
acene cores connect adjacent molecules together with an
interplanar dihedral angle of 64.63°. However, there is no π-π
interaction between acene cores. The C–Se–C angle is 86.69°
and the C-Se bond length is 1.863 Å, which are comparable with
that of unfused selenophene derivatives.13 The structure of 1c
presents a striking contrast to that of 1b. At first glance, the
structure appears similar to that of 1b, but there are four
molecules and per dichloromethane (DCM), which are linked
together by Cl···Te (3.65 Å), C···Cl (3.34 Å) and C-H···π
interactions (2.89 Å). The driving force between 1c and DCM
molecule is likely due to the low electronegativity of tellurium,
which leads to the polarized acene core with tellurium positively
charged (Teδ+−Cδ-), thus favoring the intermolecular interactions.
Therefore, DCM molecule appears to act as an adhesive
between the adjacent molecules through multiple intermolecular
interactions to stabilize the two dimensional crystal network. It
appears that the heteroatoms in the outmost rings play a crucial
role on the crystal packing, as these chalcogens have different
atom size and electronegativity, which impact the electron
distribution and the dipole moment on the π-systems.7 In
.
Figure 3. X-ray structures and crystal packing of the heteroacenes: A) 1a, B)
1b, and C) 1c.
In conclusion, we have developed a versatile synthetic route
to a novel class of heteroacenes by fusion of thiophene,
selenophene, and tellurophene to lateral positions of the BDT.
These substituted linear acenes and five-membered quinone
scaffolds serve as promising building blocks to synthesize a
series of π-conjugated materials. Our investigation indicates that
the heavier chalcogen atoms play an important role on the
optical, electrochemical properties, and crystal packing motifs.
We are currently exploring use of these building blocks for the
preparation of new donor-acceptor copolymers, as well as for
even larger, expanded π-conjugated heteroacens for organic
devices.
Experimental Section
Experimental and characterization details can be found in the Sup-
porting Information.
Acknowledgements
We thank the financial support from the National Natural
Science Foundation of China (NSFC) (No., 21428304,
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201700552
Chemistry - An Asian Journal
COMMUNICATION
[5]
[6]
V. Coropceanu, J. Cornil, D. A. da Silva Filho, Y. Olivier, R. Silbey, J. L.
Brédas, Chem. Rev. 2007, 107, 926-952.
91427303). L.Z thanks the National Natural Science Foundation
of China (21672020).
a) D. Meng, H. Fu, C. Xiao, X. Meng, T. Winands, W. Ma, W. Wei, B.
Fan, L. Huo, N. L. Doltsinis, Y. Li, Y. Sun, Z. Wang, J. Am. Chem. Soc.
2016, 138, 10184-10190. b) D. Meng, D. Sun, C. Zhong, T. Liu, B. Fan,
Y. Li, W. Jiang, H. Choi, T. Kim, J. Kim, Y. Sun, Z. Wang, A. J. Heeger,
J. Am. Chem. Soc. 2016, 138, 375-380. C) D. Sun, D. Meng, Y. Cai, B.
Fan, Y. Li, W. Jiang, L. Huo, Y. Sun, Z. Wang, J. Am. Chem. Soc. 2015,
137, 11156–11162.
Keywords: heteroacene • chalcogenophene • linear acene •
Benzodithiophene • heterocycle
[1]
a) M. E. Cinar, T. Ozturk, Chem. Rev. 2015, 115, 3036-3140. b) L. Lu,
T. Zheng, Q. Wu, A. M. Schneider, D. Zhao, L. Yu, Chem. Rev. 2015,
115, 12666-12731. c) J. Subbiah, B. Purushothaman, M. Chen, T. Qin,
M. Gao, D. Vak, F. H. Scholes, X. Chen, S. E. Watkins, G. J. Wilson, A.
B. Holmes, W. W. Wong, D. J. Jones, Adv. Mater. 2015, 27, 702-705.
d) H. Yao, L. Ye, H. Zhang, S. Li, S. Zhang, J. Hou, Chem. Rev. 2016,
116, 7397-7457. e) L. Huo, T. Liu, X. Sun, Y. Cai, A. J. Heeger, Y. Sun,
Adv. Mater. 2015, 27, 2938–2944.
[7]
a) M. Jeffries-EL, B. M. Kobilka, B. J. Hale, Macromolecules 2014, 47,
7253-7251. b) E. I. Carrera, D. S. Seferos, Macromolecules 2015, 48,
297-308. c) E. Rivard, Chem. Lett. 2015, 44, 730–736. d) K. Takimiya.
Y. Kunugi, Y. Konda, H. Ebata, Y. Toyoshima, T. Otsubo, J. Am. Chem.
Soc. 2006, 128, 3044-3050.
[8]
[9]
a) J. Hollinger, D. Gao, D. S. Seferos, Isr. J. Chem. 2014, 54, 440-453.
b) M. Al-Hashimi, Y. Han, J. Smith, S. S. Hassan, S. Y. A. Alqaradawi,
S. E. Watkins, T. D. Anthopoulos, M. Heeney, Chem. Sci. 2016, 7,
1093-1099.
[2]
[3]
a) J. Hou, M.-H. Park, S. Zhang, Y. Yao, L.-M. Chen, J.-H. Li, Y. Yang,
Macromolecules 2008, 41, 6012-6018. b) T. Qin, W. Zajaczkowski, W.
Pisula, M. Baumgarten, M. Chen, M. Gao, G. Wilson, C. D. Easton, K.
Müllen, S. E. Watkins, J. Am. Chem. Soc. 2014, 136, 6049-6055. c) L.
Ye, S. Zhang, L. Huo, M. Zhang, J. Hou, Acc. Chem. Res. 2014, 47,
1595-1603. d) L. Huo, S. Zhang, X. Guo, F. Xu, Y. Li, J. Hou, Angew.
Chem. Int. Ed. 2011, 50, 9697 –9702.
H. Son, W. Wang, T. Xu, Y. Liang, Y. Wu, G. Li, L. Yu, J. Am. Chem.
Soc. 2011, 133, 1885-1894.
[10] a) S. Shinamura, I. Osaka, E. Miyazaki, A. Nakao, M. Yamagishi, J.
Takeya, K. Takimiya, J. Am. Chem. Soc. 2011, 133, 5024-5035. b) T.
Kashiki, S. Shinamura, M. Kohara, E. Miyazaki, K. Takimiya, M. Ikeda,
H. Kuwabara, Org. Lett. 2009, 11, 2473-2475.
a) S. Sun, P. Zhang, J. Li, Y. Li, J. Wang, S. Zhang, Y. Xia, X. Meng, D.
Fan, J. Chu, J. Mater. Chem. A, 2014, 2, 15316-15325. b) T. Zheng, Z.
Cai, R. Ho-Wu, S. Yau, V. Shaparov, T. Goodson III, L. Yu, J. Am.
Chem. Soc. 2016, 138, 868-875. c) T. Zheng, L. Lu, N. E. Jackson, S. J.
Lou, L. X. Chen, L. Yu, Macromolecules 2014, 47, 6252-6259. d) H.
Yun, Y. Lee, S. Yoo, D. Chung, Y. Kim, S. Kwon, Chem. Eur. J. 2013,
19, 13242-13248. e) Y. Wu, Z. Li, X. Guo, H. Fan, L. Huo, J. Hou, J.
Mater. Chem. 2012, 22, 21362–21365.
[11] a) J. E. Anthony, Angew. Chem., Int. Ed. 2008, 47, 452-483. b) J. E.
Anthony, Chem. Rev. 2006, 106, 5028-5048.
[12] a) K. Takimiya, Y. Konda, H. Ebata, N. Niihara, T. Otsubo, J. Org. chem.
2005, 70, 10569-10571. b) L. Zhang, A. Fonari, Y. Zhang, G. Zhao, V.
Coropceanu, W. Hu, S. Parkin, J. L. Brédas, A. L. Briseno, Chem. Eur.
J. 2013, 19,17907-17916.
[13] a) Y. H. Wijsboom, A. Patra, S. S. Zade, M. Li, Y. Sheynin, L. J. W.
Shimon, M. Bendikov, Angew. Chem. Int. Ed. 2009, 48, 5443-5447. b)
A. Patra, M. Bendikov, J. Mater. Chem. 2010, 20, 422-433.
[4]
a) K. Takimiya, I. Osaka, T. Mori, M. Nakano, Acc. Chem. Res. 2014,
47, 1493-1502. b) T. Okamoto, K. Kudoh, A. Wakamiya, S. Yamaguchi,
Org. Lett. 2005, 7, 5301-5304.
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.

10.1002/asia.201700552
Chemistry - An Asian Journal
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 1:
COMMUNICATION
Text for Table of Contents
Jichang Wei, Dong Meng, Zhaohui
Wang, Lei Zhang *
Page No.1 – Page No.4
Lateral Extension of
Benzodithiophene System:
Construction of Heteroacenes
Containing Various Chalcogens
For internal use, please do not delete. Submitted_Manuscript
This article is protected by copyright. All rights reserved.