Synthesis and properties of naphthobisbenzothiophene diimides

Article abstract of DOI:10.1021/ol400324w

Laterally extended naphthalene diimides composed of naphthobisbenzothiophene skeleton and two imide groups were synthesized, which exhibit interesting packing arrangements and optoelectrical properties.

Full text of DOI:10.1021/ol400324w

ORGANIC
LETTERS
2013
Vol. 15, No. 6
1366–1369
Synthesis and Properties of
Naphthobisbenzothiophene Diimides
Jing Gao,†,‡ Yan Li,*,† and Zhaohui Wang*,†
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China, and
University of Chinese Academy of Sciences, Beijing 100049, China
yanli@iccas.ac.cn; wangzhaohui@iccas.ac.cn
Received February 4, 2013
ABSTRACT
Laterally extended naphthalene diimides composed of naphthobisbenzothiophene skeleton and two imide groups were synthesized, which
exhibit interesting packing arrangements and optoelectrical properties.
Over the past decade, the design and synthesis of poly-
cyclic aromatic hydrocarbons (PAHs) with rigid, fused-
ring structures have received a great deal of attention due
to their potential application in various optoelectronic
devices, such as organic field-effect transistors (OFETs),
light-emitting diodes (LEDs), and organic photovol-
taics (OPVs).1 Among all the one-dimensional organic
π-conjugated materials, oligoacenes, particularly pentacene
and their derivatives, are of great interest owing to their
exceptional optical and electrochemical properties and
have been considered as the benchmark materials for
OFETs due to their appropriate molecular arrangement
in the solid state, which is decisive for efficient charge-
carrier transport.2 However, the linear expansion of the
acene system will lead to a high highest occupied molecular
orbital (HOMO). Pentacene and higher acenes usually
exhibit poor stability in ambient conditions.3 To improve
the stability of acenes, the introduction of sulfur atoms
into the aromatic system is considered one of the most
effective strategies.4
Linearly thiophene-fused heteroarenes, in particular,
acenebisbenzothiophenes (1, Figure 1) have been attract-
ing a great deal of interest because of their ability to not
(2) (a) Lin, Y.-Y.; Gundlach, D. J.; Nelson, S. F.; Jackson, T. N.
IEEE Electron Device Lett. 1997, 18, 606. (b) Klauk, H.; Halik, M.;
Zschieschang, U.; Schmid, G.; Radlik, W.; Weber, W. J. Appl. Phys.
2002, 92, 5259. (c) Holmes, D.; Kumaraswamy, S.; Matzger, A. J.;
Vollhardt, K. P. C. Chem.;Eur. J. 1999, 5, 3399.
(3) (a) Pannemann, C.; Diekmann, T.; Hilleringmann, U. J. Mater.
Res. 2004, 19, 1999. (b) Maliakal, A.; Raghavachari, K.; Katz, H.;
Chandross, E.; Siegrist, T. Chem. Mater. 2004, 16, 4980.
(4) (a) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. Rev. 2004,
104, 4891. (b) Minemawari, H.; Yamada, T.; Matsui, H.; Tsutsumi, J.;
Haas, S.; Chiba, R.; Kumai, R.; Hasegawa, T. Nature 2011, 475, 364. (c)
Takimiya, K.; Shinamura, S.; Osaka, I.; Miyazaki, E. Adv. Mater. 2011,
23, 4347. (d) Shinamura, S.; Osaka, I.; Miyazaki, E.; Nakao, A.;
Yamagishi, M.; Takeya, J.; Takimiya, K. J. Am. Chem. Soc. 2011,
133, 5024. (e) Mamada, M.; Minamiki, T.; Katagiri, H.; Tokito, S. Org.
Lett. 2012, 14, 4062.
† Institute of Chemistry, Chinese Academy of Sciences.
‡ University of Chinese Academy of Sciences.
(1) (a) Li, C.; Liu, M.; Pschirer, N. G.; Baumgarten, M.; Mullen, K.
€
€
Chem. Rev. 2010, 110, 6817. (b) Figueira-Duarte, T. M.; Mullen, K.
€
€
Chem. Rev. 2011, 111, 7260. (c) Gsanger, M.; Oh, J. H.; Konemann, M.;
€
€
Hoffken, H. W.; Krause, A.-M.; Bao, Z.; Wurthner, F. Angew. Chem.,
Int. Ed. 2010, 49, 740. (d) Schmidt, R.; Oh, J. H.; Sun, Y.-S.; Deppisch,
€
M.; Krause, A.-M.; Radacki, K.; Braunschweig, H.; Konemann, M.;
€
Erk, P.; Bao, Z.; Wurthner, F. J. Am. Chem. Soc. 2009, 131, 6215. (e)
Cao, X.-Y.; Zhang, W.-B.; Wang, J.-L.; Zhou, X.-H.; Lu, H.; Pei, J.
J. Am. Chem. Soc. 2003, 125, 12430. (f) Luo, J.; Zhou, Y.; Niu, Z.-Q.;
Zhou, Q.-F.; Ma, Y.; Pei, J. J. Am. Chem. Soc. 2007, 129, 11314. (g)
Mao, J.; He, N.; Ning, Z.; Zhang, Q.; Guo, F.; Chen, L.; Wu, W.; Hua,
J.; Tian, H. Angew. Chem., Int. Ed. 2012, 51, 9873. (h) Cho, D. M.;
Parkin, S. R.; Watson, M. D. Org. Lett. 2005, 7, 1067.
r
10.1021/ol400324w
Published on Web 02/28/2013
2013 American Chemical Society

only successfully lower the HOMO levels together with
higher air stability compared to pentacene but also preserve
the close crystal packing arrangements similar to that of
pentacene showing promising semiconducting properties.5
For example, benzo[1,2-b:4,5-b0]bis[b]benzothiophene,
which is an analogue of pentacene, has a herringbone
π-stacking motif in which the plane-to-plane distance is
facile one-pot synthesis of tetracene tetracarboxylic di-
imides based on the direct double ring extension of electron-
dificient NDIs involving metallacyclopentadienes, which
displays NIR absorption spectra and lower LUMO levels
than those of NDIs and is a promising candidate for
n-type semiconductors.11 Quite recently, we also reported the
effective synthesis of a series of six-membered heterocyclic
acene diimides conducted by the condensation of o-phenyl-
enediamine, 1,2-benzenedithiol, and 2-aminothiophenol
with 4Br-NDI, which turned NDIs from potential n-type
materials to promising p-type semiconductors.12 Herein,
we designed and synthesized novel laterally extended
naphthalene diimides (2, Figure 1), the structures of which
are composed of the naphthobisbenzothiophene skeleton
and two imide groups. We also elucidate the molecular
packing arrangement in single crystals and their unique
optical and electrochemical properties.
6
˚
ca. 3.52 A, whereas highly fluorinated benzobisbenzo-
thiophenes exhibit a brickstone arrangement with an
7
average face-to-face distance of 3.34 A. Naphthobisben-
˚
zothiophene and i-Pr3Si-substituted anthrabisbenzothio-
phene show highly ordered herringbone and brickstone
structures in single crystals, respectively. Field effect
transistors based on the anthrabisbenzothiophene deriv-
atives also exhibit high charge-carrier mobilities.8
Laterallyextendednaphthalene tetracarboxylicdiimides
(NDIs), especially heterocyclic naphthalene diimides, have
recently gained great attention due to their easily tunable
optical and electrical properties and potential application
as high performance organic semiconductors. For exam-
ple, core-expanded NDIs fused with 2-(1,3-dithiol-2-
ylidene)malonitrile groupsexhibitexcellent ambient stabil-
ity and high electron mobilities,9 whereas NDIs fused with
indole rings show ambipolar transport properties with a
large hole mobility.10
Scheme 1. Synthesis of Laterally Extended Naphthalene
Diimides
Figure 1. Acenebisbenzothiophenes (1) and laterally extended
naphthalene diimides (2).
We are particularly interested in the design and synthesis
of novel laterally extended naphthalene diimides with
unique optical and electrical poperties and supramolecular
self-assembly behavior. In previous work, we reported a
The synthesis of laterally extended naphthalene diimides
2 is shown in Scheme 1, and a monolaterally extended NDI
composed of naphthobenzothiophene skeleton and two
imides was also synthesized for comparison. The key
starting materials 2-stannyl and 2,6-distannyl NDIs (3
and 4) were prepared according to a known procedure.13
When 2-bromothioanisole was added to a toluene solution
containing compound 3 in the presence of Pd(PPh3)4 and
reacted at 110 °C for 12 h, compound 5 was obtained in
high yield. Analogously, compound 7 was prepared via
(5) (a) Zhou, Y.; Liu, W.-J.; Ma, Y.; Wang, H.; Qi, L.; Cao, Y.;
Wang, J.; Pei, J. J. Am. Chem. Soc. 2007, 129, 12386. (b) Gao, P.;
Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.; Pisula, W.;
€
Mullen, K. Chem. Commun. 2008, 44, 1548. (c) Gao, P.; Beckmann, D.;
Tsao, H. N.; Feng, X.; Enkelmann, V.; Baumgarten, M.; Pisula, W.;
€
Mullen, K. Adv. Mater. 2009, 21, 213.
(6) Ebata, H.; Miyazaki, E.; Yamamoto, T.; Takimiya, K. Org. Lett.
2007, 9, 4499.
(7) Wang, Y.; Parkin, S. R.; Gierschner, J.; Watson, M. D. Org. Lett.
2008, 10, 3307.
(8) (a) Yamamoto, K.; Katagiri, H.; Tairabune, H.; Yamaguchi, Y.;
Pu, Y.-J.; Nakayama, K.-I.; Ohba, Y. Tetrahedron Lett. 2012, 53, 1786.
(b) Lehnherr, D.; Hallani, R.; McDonald, R.; Anthony, J. E.; Tykwinski,
R. R. Org. Lett. 2012, 14, 62.
(9) (a) Gao, X.; Di, C.; Hu, Y.; Yang, X.; Fan, H.; Zhang, F.; Liu, Y.;
Li, H.; Zhu, D. J. Am. Chem. Soc. 2010, 132, 3697. (b) Zhao, Y.; Di, C.;
Gao, X.; Hu, Y.; Guo, Y.; Zhang, L.; Liu, Y.; Wang, J.; Hu, W.; Zhu, D.
Adv. Mater. 2011, 23, 2448.
€
(10) Suraru, S.-L.; Zschieschang, U.; Klauk, H.; Wurthner, F. Chem.
Commun. 2011, 47, 11504.
(11) Yue, W.; Gao, J.; Li, Y.; Jiang, W.; Di Motta, S.; Negri, F.;
Wang, Z. J. Am. Chem. Soc. 2011, 133, 18054.
(12) Li, C.; Xiao, C.; Li, Y.; Wang, Z. Org. Lett. 2013, 15, 682.
(13) Polander, L. E.; Romanov, A. S.; Barlow, S.; Hwang, D. K.;
Kippelen, B.; Timofeeva, T. V.; Marder, S. R. Org. Lett. 2012, 14, 918.
Org. Lett., Vol. 15, No. 6, 2013
1367

Stille coupling between 2-bromothioanisole and com-
pound 4. Oxidation of 5 and 7 with hydrogen peroxide in
a solution mixture of glacial acetic acid and chloroform
(1:1) gave intermediate compounds 6 and 8, respectively,
both of which had poor stability in ambient conditions.
Finally, the intramolecular ring closures of 6 and 8 were
performed with trifluoromethanesulfonic acid in the pres-
ence of phosphorus pentoxide and reacted at room tem-
perature for 72 h in the dark. The as-formed mixture was
poured into ice/water followed by filtration, drying, and
reflux in pyridine for 12 h. It should be noted that, in the
solvent trifluoromethanesulfonic acid, the migration of
alkyl groups around an aromatic ring usually occurs.14
After the intramolecular ring-closure reaction, it was found
that laterally extended NDIs had isomers. So we speculated
that also 2,6-diisopropylbenzene groups may undergo a
transalkylation reaction during the final ring-closure pro-
cess. To verify our speculation, the regioisomerically pure
compounds 9 and 10, which are the main products and
have good stability due to the introduction of two strong
electron-withdrawing groups, were gained after purification
by silica column chromatography and characterized by 1H,
13C NMR spectroscopy and HRMS. It was found that
1
two sets of signals with the same integration in the H
NMR of 9 were observed in the region 3.0ꢀ2.7 ppm which
was assigned to the protons of ꢀCH(CH3)2 in diisopro-
pylphenyl groups, whereas two sets of signals with the
integration of 1:3 in the same region together with unsym-
metrical signals in the aromatic region were observed in the
1H NMR of 10 (Supporting Information). So we speculated
the migration of isopropyl groups in compound 10.
Tofurtherconfirmthestructuresofcompounds9 and10
and study their arrangements in the solid state, attention
was focused toward single-crystal growth. Crystals suit-
ablefor single-crystalX-ray analysiswereobtainedbyslow
evaporation of the dichloromethane/methanol solution of
9 and 10, respectively, and the molecular structures and
crystal packing arrangements are depicted in Figure 2.
Four molecules of 9 and two molecules of 10 were found in
the unit cell, respectively. As can be seen from Figure 2a,
monolaterally extended NDI 9 has a slightly twisted
skeleton. The torsional angle between the benzothiophene
part and naphthalene plane is ∼10.7°. The crystal packing
arrangement of 9 is shown in Figure 2c, which reveals that
the introduction of two strong electron-withdrawing imide
groups to the thiophene-fused aromatics could cause the
naphthobenzothiophene diimides to retain a herringbone-
like arrangement along the b-axis, though the plane-to-
plane distance is relatively large due to the steric encum-
brance effect of diisopropylbenzene groups.
Figure 2. X-ray crystallographic structures of 9 (a) and 10 (b).
Crystal packing of 9 (c) and 10 (d, side view and top view).
coincident with our conjecture based on the phenomenon
1
in experiment and H NMR. The introduction of two
imide groups also makes the naphthobisbenzothiophene
skeleton twist slightly. The unsymmetrical torsional angles
between the benzothiophene part and naphthalene plane
are approximately 15.1° and 6.8°. The crystal packing
arrangement of 10 is shown in Figure 2d. Due to the strong
πꢀπ interaction between the naphthobisbenzothiophene
skeleton and the steric encumbrance effect of diisopropyl-
benzene groups, the molecules are arranged in stacks along
the b-axis, in which dimers are packed tightly with a plane-
˚
to-plane distance of ca. 3.4 A.
From Figure 2b we can see that laterally extended NDI
10 exhibits the migration of one isopropyl group which is
Figure 3 shows the comparison between the absorption
and emission spectra of laterally extended NDIs 9 and 10 in
CHCl3, both of which have good solubility in common or-
ganic solvents. Compared with NDI (N,N0-di(2,6-diisopropyl-
phenyl)-naphthalene-1,4,5,8-tetracarboxylic acid diimide),15
(14) (a) Roberts, R. M. G. J. Org. Chem. 1982, 47, 4050. (b) Bakoss,
H. J.; Roberts, R. M. G.; Sadri, A. R. J. Org. Chem. 1982, 47, 4053. (c)
Olah, G. A.; Farooq, O.; Farnia, S. M. F.; Olah, J. A. J. Am. Chem. Soc.
1988, 110, 2560. (d) Sherman, S. C.; Iretskii, A. V.; White, M. G.;
Gumienny, C.; Tolbert, L. M.; Schiraldi, D. A. J. Org. Chem. 2002, 67,
2034. (e) Ajaz, A.; McLaughlin, E. C.; Skraba, S. L.; Thamatam, R.;
Johnson, R. P. J. Org. Chem. 2012, 77, 9487. (f) Lee, P. H.; Kang, D.;
Choi, S.; Kim, S. Org. Lett. 2011, 13, 3470.
(15) Yue, W.; Zhen, Y.; Li, Y.; Jiang, W.; Lv, A.; Wang, Z. Org. Lett.
2010, 12, 3460.
1368
Org. Lett., Vol. 15, No. 6, 2013

Table 1. Summary of Electrochemical Properties of Laterally
Extended Naphthalene Diimides
LUMOb
(eV)
Eg
a
a
c
E1r
E2r
(V)
(V)
(eV)
NDId
9
ꢀ1.04
ꢀ0.94
ꢀ0.85
ꢀ1.60
ꢀ1.44
ꢀ1.27
ꢀ3.98
ꢀ4.04
ꢀ4.14
3.02
2.12
1.96
10
a Half-wave reduction potentials (vs Fc/Fcþ) measured in CH2Cl2 at
a scan rate of 0.1 V/s. The plot includes the signal of the ferrocene
standard with its oxidation potential at 0.47 V. b Estimated from the
onset potential of the first reduction wave with the onset potential of the
ferrocene standard at 0.38 V. c Obtained from the edge of the absorption
spectra. d NDI: N,N0-di(2,6-diisopropylphenyl)-naphthalene-1,4,5,8-
tetracarboxylic acid diimide.
Figure 3. UV/vis absorption and emission spectra of 9 (red) and
10 (black) in CHCl3 (10ꢀ5 M) at room temperature.
In summary, we report novel laterally extended naph-
thalene diimides composed of a fully conjugated naphtho-
bisbenzothiophene or naphthobenzothiophene skeleton
and two imide groups. Single-crystal X-ray analysis reveals
that the molecules have a herringbone-like or dimeric stack
arrangement despite the steric encumbrance effect of the
imide groups. In light of the interesting packing arrange-
ments and optoelectrical properties, these laterally ex-
tended NDIs are promising for use as n-type organic
semiconductors. Further studies of the laterally extended
NDIs bearing different substituents and applications in
electronic devices are currently underway.
9 and 10 exhibit broad and bathochromic-shifted absorp-
tion. Compound 9 shows three major absorption bands
in the 350ꢀ600 nm range with maxima at 378, 441, and
516 nm, whereas compound 10 has two absorption bands
in the 400ꢀ650 nm range with maxima at 494 and 586 nm.
Both of these compounds have weak fluorescence with
maxima at 600 nm for 9 and 622 nm for 10, correspond-
ing to Stokes shifts of 84 and 36 nm, respectively.
The electrochemical properties of NDI, 9, and 10 were
also investigated by cyclic voltammetry against the poten-
tial of the ferrocene/ferrocenium redox couple in CH2Cl2
(Figure S2), and the reduction potentials and energy levels
are shown in Table 1. Compounds 9 and 10 exhibit two
reversible reduction waves, whereas within the accessible
scanning range no oxidation waves could be detected. The
first half-wave reduction waves for 9 and 10 are observed
at ꢀ0.94 V, and ꢀ0.85 V vs Fc/Fcþ, respectively, both of
which have stronger electron-accepting ability than NDI.
Meanwhile, compounds 9 and 10 have lower LUMO levels
indicating their potential applications as n-type organic
semiconductors.
Acknowledgment. For financial support of this re-
search, wethank the NationalNatural ScienceFoundation
of China (21204091, 21225209, 91027043, and 21190032),
the 973 Program (2011CB932301 and 2012CB932903),
NSFC-DFG joint project TRR61, and the Chinese Acad-
emy of Sciences.
Supporting Information Available. Experimental details
and characterization of new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
The authors declare no competing financial interest.
Org. Lett., Vol. 15, No. 6, 2013
1369