One-pot synthesis of well-defined oligo-butadiynylene-naphthalene diimides

Article abstract of DOI:10.1021/ol101280e

(Equation Presented). A homogeneous series of well-defined oligo-butadiynylene-NDIs containing up to five naphthalene diimides (NDIs) moieties have been efficiently synthesized in one pot by oxidative homocoupling of 1,6-di((trimethylsilyl)ethynyl)naphthalene diimides in good yields.

Full text of DOI:10.1021/ol101280e

ORGANIC
LETTERS
2010
Vol. 12, No. 15
3460-3463
One-Pot Synthesis of Well-Defined
Oligo- Butadiynylene-Naphthalene
Diimides
Wan Yue,†,‡ Yonggang Zhen,†,‡ Yan Li,†,‡ Wei Jiang,†,‡ Aifeng Lv,†,‡ 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 Graduate School of the Chinese Academy of Sciences, Beijing 100190, China.
wangzhaohui@iccas.ac.cn
Received June 3, 2010
ABSTRACT
A homogeneous series of well-defined oligo-butadiynylene-NDIs containing up to five naphthalene diimides (NDIs) moieties have been efficiently
synthesized in one pot by oxidative homocoupling of 1,6-di((trimethylsilyl)ethynyl)naphthalene diimides in good yields.
Functional π-conjugated organic systems have attracted
considerable attention in recent years, as they have potential
applications in the emerging areas of molecular electronics
and nanotechnology.1 Of these conjugated systems, molecular
wires are especially important and pave the way for the
single-molecule devices.2
(aryl-Ct CsCt C-)n, have rarely been explored.4 They are not
only potential attractive substances for molecular wires but also
can undergo topchemical reactions upon UV-irradiation or
thermal-stimuli, leading unique butadiynylene supramolecules
to potential chemosenors and photonic materials.5
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Int. Ed. 2005, 44, 3806.
Molecular wires with ethynylenes have gained particular
interest from experimental and theoretical viewpoints.3 How-
ever, butadiynylene aromatic systems, with the generic structure
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† Institute of Chemistry, Chinese Academy of Sciences.
‡ Graduate School, Chinese Academy of Sciences.
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10.1021/ol101280e  2010 American Chemical Society
Published on Web 07/01/2010

Generally, the synthesis of the molecular wires by
traditional stepwise approaches or improved iterative divergent/
convergent methods requires a long and repetitious processes.
For example, the trimethylsilyl group is often employed as
a protective group for the preparation of a substrate for the
consequent Sonogashira or Glaser reaction, which is carried
out after deprotection of the silyl group.6 Thereby the
straightforward synthesis of these kinds of molecular wires
became very significant.
4.13 Subsequently, compound 2 was chosen as a model
substrate to undergo homocoupling with a stoichiometric
amount of CuCl in N,N-dimethylformamide (DMF) at room
temperature14 to directly give corresponding symmetrical
butadiynylene-NDIs in good yield (70%, 25% starting
material can be recovered; Scheme 1).
Scheme 1
Owing to their neutral, planar, chemically robust, redox-
active, and electron-deficient properties, naphthalene diimides
(NDIs) have been used extensively in supramolecular chem-
istry,7 electron-transfer systems,8 DNA sensors,9 and n-type
organic field effect transistors (OFETs).10 The chemical
modification of the NDIs can be achieved by two different
methods. One is to introduce substituents at the N atoms of
imide groups, and the other is functionalization of NDIs by
core substitution; however, only substitution on the core will
cause a significant effect on the optical and redox proper-
ties.11
Herein we report the one-pot synthesis of a homologous
series of soluble and linearly conjugated butadiynylene-NDI
oligomers containing up to five naphthalene moieties by
direct functionalization of 1,6-di((trimethylsilyl)ethynyl)-
NDIs under extremely mild conditions. Moreover, the
availability of a well-defined series of butadiynylene-NDIs
allows us to assess the extent of electron delocalization along
the backbone by comparing their optical spectra.
The UV-vis spectra of unsubstituted compound 1 (N,N′-
bis(2,6-diisopropylphenyl)-1,4,5,8-naphthalenetetracarboxy-
lic acid diimides), 2, and 3 in THF were shown in Figure 1;
Initially, 1-bromonaphthalene diimides and 1,6-dibro-
monaphthalene diimides were synthesized following a known
procedure.12 Stille cross-coupling of bromo-NDIs with
tributyl[(trimethylsilyl)ethynyl]stannane in the presence of
Pd(PPh3)4 as a catalyst in toluene afforded the trimethylsi-
lylethynyl-NDIs 2 and 1,6-di((trimethylsilyl)ethynyl)-NDIs
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Figure 1. UV-vis absorption spectra of compounds 1 (unsubsti-
tuted NDI), 2, and 3 in THF at room temperatue.
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in contrast with the white compound 1, the maximum
absorption of 2 is bathochromically shifted from 378 to 410
nm. Compared to compound 2, the butadiynylene-NDI 3
causes a larger shift of about 46 nm, as a reflection of the
extended conjugation length.15
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The redox properies of compounds 1, 2, and 3 were studied
by cyclic voltammogram in dichloromethane (in V vs Ag/
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Org. Lett., Vol. 12, No. 15, 2010
3461

Scheme 2
AgCl, see the Supporting Information). Compounds 1 and 2
showed two well-separated reversible reduction waves.
Compared with NDI 1 (-0.58 and -1.15 V), the reduction
potentials of NDI 2 (-0.52 and -1.06 V) are less negative,
which can be attributed to an extension of the LUMO orbitals
by the introduction of the ethynyl substituents. For NDI 3,
the second reduction waves were split into two waves
(-0.40, -0.90, and -1.02 V), indicating the substantial
electronic interaction between the two NDIs through the
butadiynylene spacer.16
We then anticipated that 1,6-dibromo-NDIs would be used
as a building block of larger butadiynylene-NDI arrays. Thus,
we examined the homocoupling of compound 4 under the
same conditions (Scheme 2). As expected, the 1,6-dibromo-
NDIs gave directly corresponding homogeneous symmetrical
butadiynylene-NDIs (Scheme 2) in good yields: 5 (32%), 6
(25%), 7 (16%), and 8 (7%). These novel oligomers could
be further endowed with terminal functionality suitable for
molecular wires, or attractive precursors of butadiynylene
monomers to form a unique poly-butadiynylene structure.
Figure 2. UV-vis absorption spectra of compounds 4, 5, 6, 7, and
8 in THF at room temperatue.
nm for 4, 5, 6, 7, and 8, respectively, as a reflection of
extended conjugation length of the NDI core. However, the
bathochromic shifts were not linearly proportional to the
enlargement of the molecular length; the interval value of
the bathochromic shifts (44, 16, 8, 4 nm) reveals that an
effective conjugation length approaches saturation.18 The
molar extinction coefficients of various oligo-butadiynylene-
The availability of the series of poly-butadiynylene-NDIs
oligomes gives us the opportunity to assess the extent of
electron delocalization along the backbone by comparing
their optical spectra. The solution UV-vis absorption spectra
of these homogeneous oligomers with different length units
in THF are shown in Figure 2; various butadiynylene-NDIs
showed broad and well-defined absorption bands that shifted
bathochromically17 with the increasing number of NDI units
with the longest maximum at 438, 482, 498, 506, and 510
(16) Maeda, C.; Shinokubo, H.; Osuka, A. Org. Lett. 2010, 12, 1820.
(17) Banerjee, M.; Shukla, R.; Rathore, R. J. Am. Chem. Soc. 2009,
131, 1780.
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Org. Lett., Vol. 12, No. 15, 2010

NDIs exhibited an approximate linear increase with the
increasing number of NDI units (about 40000-50000 M-1
cm-1 per unit), whereas the fluorescences were too weak to
be detected.
In summary, we have successfully synthesized well-
defined oligo-butadiynylene-NDIs containing up to five
naphthalene moieties in one pot by an efficient strategy of
oxidative homocoupling of 1,6-di((trimethylsilyl)ethynyl)-
NDIs. Further endowments with terminal functionality suit-
able for molecular wires and construction of related single
molecular devices are currently underway.
Acknowledgment. We thank the National Natural Science
Foundation of China, 973 Program (Grant 2006CB932101),
Chinese Academy of Sciences, and BASF SE for financial
support of this research.
Supporting Information Available: Experimental pro-
cedure and characterization of new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
(18) (a) Francke, V.; Mangel, T.; Mu¨llen, K. Macromolecules 1998, 31,
2447. (b) Lee, S. H.; Nakamura, T.; Tsutsui, T. Org. Lett. 2001, 3, 2005.
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