First synthesis of 2,3,6,7-tetrabromonaphthalene diimide

Article abstract of DOI:10.1021/ol701539z

N,N′-Bis(n-octyl)-2,3,6,7-tetrabromonaphthalene diimide (TBNDI) was synthesized by a new imidization reaction and characterized by HRMS, ¹H NMR, ¹³C NMR, elemental analyses, FT-IR, UV-vis, and single-crystal X-ray analysis. The TBNDIs are the key precursors for the synthesis of core-tetrasubstituted-naphthalene diimides.

Full text of DOI:10.1021/ol701539z

ORGANIC
LETTERS
2007
Vol. 9, No. 20
3917-3920
First Synthesis of
2,3,6,7-Tetrabromonaphthalene Diimide
Xike Gao, Wenfeng Qiu, Xiaodi Yang, Yunqi Liu,* Ying Wang, Hengjun Zhang,
Ting Qi, Ying Liu, Kun Lu, Chunyan Du, Zhigang Shuai, Gui Yu, and
Daoben Zhu*
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic
Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China
liuyq@mail.iccas.ac.cn
Received June 29, 2007
ABSTRACT
N,N′-Bis(n-octyl)-2,3,6,7-tetrabromonaphthalene diimide (TBNDI) was synthesized by a new imidization reaction and characterized by HRMS,
1H NMR, 13C NMR, elemental analyses, FT-IR, UV
of core-tetrasubstituted-naphthalene diimides.
−vis, and single-crystal X-ray analysis. The TBNDIs are the key precursors for the synthesis
Naphthalene diimides (NDIs) are an important class of
organic species. They have been extensively used in su-
pramolecular chemistry,1 electron-transfer systems,2 DNA
sensors,3 electrically conductive aggregates,4 and n-type
organic field effect transistors (OFETs).5 Two different
methods were used to achieve the chemical modification of
NDIs. One is to introduce substituents at N atoms of imide
groups, and the other is to functionalize the naphthalene core
of NDIs. The synthesis of the latter mostly uses 2,6-
dichloronaphthalene dianhydride (DCNDA) or 2,6-bro-
monaphthalene dianhydride (DBNDA) as precursors. Wu¨rth-
ner et al.6 reported core-substituted NDI dyes by introducing
one or two alkyl amines to the naphthalene core; these NDI
dyes exhibit intensive fluorescence with high quantum yields.
More excitingly, some of these chromophores have been
successfully used in artificial photosynthesis.7 Marks and
Wasielewski attached two cyano groups to the naphthalene
core of NDI and obtained air-stable, flexible, and optically
(1) (a) Lokey, R. S.; Iverson, B. L. Nature 1995, 375, 303. (b) Zych, A.
J.; Iverson, B. L. J. Am. Chem. Soc. 2000, 122, 8898. (c) Hansen, J. G.;
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10.1021/ol701539z CCC: $37.00
© 2007 American Chemical Society
Published on Web 09/07/2007

transparent n-type OFETs.8 However, up to now, core-
tetrasubstituted NDIs have not been available in the literature
owing to synthetic difficulty. In fact, 2,3,6,7-tetrabromonaph-
thalene diimides (TBNDIs) are the key precursors for the
synthesis of core-tetrasubstituted NDIs, using nucleophilic
aromatic substitution (SNAr),6,7,9 nucleophilic halogen ex-
change reaction,8,10 and the Suzuki or Stille cross-coupling
reaction.11,2e Herein, we report the first synthesis of TBNDIs,
N,N′-bis(n-octyl)-2,3,6,7-tetrabromonaphthalene diimide
(Scheme 1, 5).
hydride (TBPDA) could be obtained by brominating PDA
with Br2 in the mixture of sulfuric acid and oleum.11 By the
modification of the synthesis of TBPDA and as shown in
Scheme 1, 2 was synthesized by treatment of 1 and 5.3 equiv
of Br2 in the mixture of sulfuric acid and oleum (V:V )
4:1) at 140 °C for 4 weeks. High-purity 2 was obtained with
a high yield of 96%, which was characterized by elemental
analyses, HRMS, and FT-IR. To avoid the aforementioned
SNAr reactions, the synthesis of 5 was performed in acetic
acid, where most amino functions are protonated, and the
reactivity of the amines is sufficiently low.6b However, our
results showed that for an elongated reaction time (>30 min),
the reaction of 2 and 4 equiv of n-octylamines in refluxing
acetic acid could lead to more and more core-(n-octylamino)-
substituted compounds, with deep red color. The reaction
with a shortened reaction time (e30 min) also failed to afford
5. A yellow solid-state crude product was instead obtained,
which is difficult to purify further or to isolate. The MALDI-
TOF-MS indicated that 2,3,6,7-tetrabromo-4,8-bis(octylcar-
bamoyl)naphthalene-1,5-dicarboxylic acid (3) was contained
in the yellow solid.
Scheme 1. Synthesis of TBNDIs (5)
Obviously, the dehydration reaction of 3 could lead to the
formation of 5. Scheme 2 shows our attempts to prepare 5
Scheme 2. Attempts to Prepare 5 from 3
from 3. First, we tried the dehydration reaction of 3 in
refluxing organic solvents such as toluene, DMF, quinoline
with zinc acetate catalyst, and organic acids, but we failed.
Then, we carried out the dehydration reaction of 3 under
vacuum at 160 °C for several hours, which also gave no
hint of the formation of 5. This failure might be ascribed to
the strong electron-withdrawing ability of four Br atoms,
which makes 3 a strong organic acid and might form the
internal salt. Thus, the exploration of conceptually new
methodology is a compelling subject in aromatic bisimides
chemistry. It is well-known that the reactivity of acyl halide
is very high. As shown in Schemes 1 and 2, we tried new
ways to synthesize 5.13 Fortunately, the reaction of 3 with
excess PBr3 in refluxing toluene for 12 h afforded 5 in 31.4%
overall yield calculated from 1. The first TBNDIs, 5, was
2,3,6,7-Tetrabromonaphthalene dianhydride (TBNDA, 2)
is an ideal synthon for the synthesis of TBNDIs. 2 has been
reported as a small quantity of byproducts by brominating
NDA (1) with Br2 in sulfuric acid,12 but this protocol could
not be reproduced even for the synthesis of DBNDA.6b We
recently discovered that 1,6,7,12-tetrabromoperylene dian-
(7) Bhosale, S.; Sisson, A. L.; Talukdar, P.; Fu¨rstenberg, A.; Banerji,
N.; Vauthey, E.; Bollot, G.; Mareda, J.; Ro¨ger, C.; Wu¨rthner, F.; Sakai,
N.; Matile, S. Science 2006, 313, 84.
(8) Jones, B. A.; Facchetti, A.; Marks, T. J.; Wasielewski, M. R. Chem.
Mater. 2007, 19, 2703.
(9) Błaszczyk, A.; Fischer, M.; von Ha¨nisch, C.; Mayor, M. HelV. Chim.
Acta 2006, 89, 1986.
(10) (a) Ahrens, M. J.; Fuller, M. J.; Wasielewski, M. R. Chem. Mater.
2003, 15, 2684. (b) Jones, B. A.; Ahrens, M. J.; Yoon, M.-H.; Facchetti,
A.; Marks, T. J.; Wasielewski, M. R. Angew. Chem., Int. Ed. 2004, 43,
6363. (c) Wu¨rthner, F.; Osswald, P.; Schmidt, R.; Kaiser, T. E.; Mansikka-
ma¨ki, H.; Ko¨nemann, M. Org. Lett. 2006, 8, 3765.
1
characterized by HRMS, H NMR, 13C NMR, elemental
analyses, FT-IR, UV-vis, and single-crystal X-ray analysis.
As displayed in Scheme 1, the synthesis of 5 from 3 might
(11) Qiu, W.; Chen, S.; Sun, X.; Liu, Y.; Zhu, D. Org. Lett. 2006, 8,
867.
(12) Solomatin, G. G.; Filippov, M. P.; Shigalevskii, V. A. Zh. Org.
Khim. 1981, 17, 877; J. Org. Chem. USSR (Engl. Transl.) 1981, 17, 771.
(13) SOCl2 could also lead to the imidization reaction of 3 in refluxing
toluene and afforded the core-tetrasubstituted NDIs. But the unexpected
nucleophilic halogen exchange reactions occurred, affording various core-
tetrahalogenate NDIs with one or two Br atoms being replaced by Cl atoms.
3918
Org. Lett., Vol. 9, No. 20, 2007

involve two reaction steps: the first step is the formation of
2,3,6,7-tetrabromo-4,8-bis(octylcarbamoyl)naphthalene-1,5-
dicarbonyl dibromide (4), and the second one is the dehy-
drobromination reaction of 4, which leads to the formation
1
of 5. In H NMR spectrum of 5, there are no signals in the
aromatic region, indicating the core-tetrasubstituted behavior.
Only four carbon signals appear in the aromatic region of
the 13C NMR spectrum of 5, implying the symmetric core-
tetrasubstituted feature. The NMR data together with the data
of HRMS and elemental analyses demonstrate the accurate
chemical structure of 5.
Single crystals of 5 suitable for single-crystal X-ray
analysis were obtained by slowly diffusing methanol into
chloroform that contains 5. The molecular structure of 5 is
depicted in Figure 1. Unlike the core-unsubstituted NDIs,14
Figure 2. HOMO orbital (top) and LUMO orbital (bottom) of 5
obtained by DFT calculations.
DFT results show that 5 has a lower lying LUMO level and
narrower band gap comparable to those of NDI-C8.
Figure 1. ORTEP drawings of 5 (50% probability for thermal
ellipsoids): a face-on view (top) and a side view (bottom).
steric crowding of Br atoms and adjacent O atoms results in
a slightly unsymmeric molecular structure of 5 in crystal.
The naphthalene core together with four Br atoms are
coplanar with the mean atom deviation of 0.043 Å from the
plane. However, the two six-membered imide rings are
twisted because of the interatomic steric crowding. The mean
atom deviations from the N1 imide ring and the N2 imide
ring are 0.084 and 0.076 Å, respectively.
Figure 3. Normalized UV-vis absorption spectra of 5 (red line)
and NDI-C8 (black line) in CH2Cl2.
To estimate the position of frontier orbitals of 5 and its
counterpart compound (NDI-C8, a core-unsubstituted NDIs
with two terminal n-octyl chains), Density Functional Theory
(DFT) calculations were performed with Gaussian 03 at the
B3LYP/6-31G(d) level. As shown in Figure 2 (top), the
largest coefficients in the HOMO orbital of 5 are mainly
located on the ambient heteroatoms of the π-skeleton,
especially on four Br atoms, giving a polarized HOMO
orbital. Whereas the HOMO orbital of NDI-C8 is mainly
situated on the naphthalene core, for LUMO orbitals, both
5 and NDI-C8 have the strongest coefficients at aromatic
carbon atoms along the molecular long axis (Figure 2,
bottom). The energy values of HOMO and LUMO orbitals
of 5 and NDI-C8 were also calculated by DFT (HOMO:
-6.79 and -6.97 eV; LUMO: -3.61 and -3.35 eV; band
gap: 3.18 and 3.62 eV for 5 and NDI-C8, respectively). The
As shown in Figure 3, the absorption spectrum of NDI-
C8 exhibits the electronic S0-S1 absorption at 359 and 380
nm.6b However, the absorption of 5 showed much more red-
shift than that of NDI-C8, with the bands at 400 and 425
nm. The results demonstrate that the introduction of four Br
atoms to the naphthalene core greatly affects the electronic
structure of NDIs. The optical band gaps of 5 and NDI-C8,
estimated from the absorption edges, are 2.79 and 3.18 eV,
respectively, implying the decreased band gaps when four
Br atoms were introduced to the naphthalene skeleton.
Similar results were obtained by the above DFT calculations.
A thermogravimetric analysis (TGA) study reveals that 5
has excellent thermal stability with the onset decomposition
temperature of 336 °C. According to its differential scanning
calorimetry (DSC) measurement, a sharp melting endother-
mal peak was observed at 258 °C. The redox properties of
5 were investigated by cyclic voltammetry (CV) (see the
Supporting Information for details). The first reversible NDI0/
(14) Katz, H. E.; Siegrist, T.; Scho¨n, J. H.; Kloc, C.; Batlogg, B.;
Lovinger, A. J.; Johnson, J. ChemPhysChem 2001, 2, 167.
Org. Lett., Vol. 9, No. 20, 2007
3919

NDI- redox process was observed at -0.33 and -0.64 V
vs Ag/AgCl for 5 and NDI-C8, respectively, indicating a
310 mV positive-shift when four electron-withdrawing Br
atoms were attached to the naphthalene core of NDI. The
LUMO levels of 5 and NDI-C8, estimated from the onset
reduction potential relative to vacuum, are -4.12 and -3.84
eV, respectively. Although there is about 0.5 eV error, the
values obtained by CV are basically consistent with the
aforementioned DFT calculated LUMO energy levels (-3.61
and -3.35 eV, respectively), demonstrating the lower lying
LUMO level of 5 relative to that of NDI-C8, which benefits
the air-stable n-type OFETs.8,10
In summary, a hitherto unknown TBNDIs, 5, was syn-
thesized by a new imidization reaction. 5 has good thermal
property and low-lying LUMO level, which makes it a
promising n-type OFET material. More importantly, TBNDIs
(5 as one of its derivatives) can be widely used for the
synthesis of core-tetrasubstituted NDIs. The core-tetrasub-
stituted NDIs would open up new opportunities in many
applications, including organic dyes, organic field-effect
transistors, and other new fields. We are currently exploring
these avenues.
Acknowledgment. The present research was financially
supported by National Natural Science Foundation (20472089,
90206049, 20421101, 20573115, 20573115, 20472089,
60671047, 50673093), the Major State Basic Research
Development Program (2006CB806200, 2006CB932100),
and the Chinese Academy of Sciences.
Supporting Information Available: General experimen-
tal methods; synthesis and characterizations of compounds
2, 3, and 5; HRMS and FT-IR spectra of 2; MALDI-TOF-
MS spectrum of 3; HRMS, 1H NMR, 13C NMR, and FT-IR
spectra of 5; crystallographic data (CIF) of 5; TGA-DTA
and DSC images of 5; CV and DPV plots of 5 and NDI-C8;
and HOMO and LUMO orbitals of NDI-C8 obtained by DFT
calculations. This material is available free of charge via the
Internet at http://pubs.acs.org.
OL701539Z
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Org. Lett., Vol. 9, No. 20, 2007