Core-tetrasubstituted naphthalene diimides: Synthesis, optical properties, and redox characteristics

Article abstract of DOI:10.1021/jo7015357

(Chemical Equation Presented) 2,3,6,7-Tetrabromonaphthalene dianhydride has been synthesized by the bromination of naphthalene dianhydride with dibromoisocyanuric acid in excellent yield. The condensation of this dianhydride with 2,6-diisopropylaniline yi

Full text of DOI:10.1021/jo7015357

Core-Tetrasubstituted Naphthalene Diimides: Synthesis, Optical
Properties, and Redox Characteristics
Cornelia R o¨ ger and Frank W u¨ rthner*
UniVersit a¨ t W u¨ rzburg, Institut f u¨ r Organische Chemie, Am Hubland, 97074 W u¨ rzburg, Germany
wuerthner@chemie.uni-wuerzburg.de
ReceiVed July 13, 2007
2
,3,6,7-Tetrabromonaphthalene dianhydride has been synthesized by the bromination of naphthalene
dianhydride with dibromoisocyanuric acid in excellent yield. The condensation of this dianhydride with
,6-diisopropylaniline yielded the corresponding tetrabromo-substituted naphthalene diimide (NDI), which
2
is a versatile precursor for the synthesis of core-tetrafunctionalized NDIs. Nucleophilic substitution of
tetrabromo NDI with alkoxy, alkylthio, and alkylamino nucleophiles afforded a series of core-
tetrasubstituted NDI chromophores that complete the series of previously reported di- and trifunctionalized
NDI derivatives. The effects of electronic nature and number of core substituents on the optical and
electrochemical properties of NDIs have been investigated by UV-vis and fluorescence spectroscopy
and cyclic voltammetry. The absorption maxima (629-642 nm) of tetraamino NDIs are strongly
bathochromically shifted compared to those of other core-functionalized NDIs.
Introduction
,4,5,8-Naphthalenetetracarboxylic acid diimides (NDIs) are
CHART 1. Structures of Core-Unsubstituted NDI 1 and
Core-Di- and -Trisubstituted Derivatives 2 and 3
1
important compounds for materials and supramolecular chem-
istry. In past years, core-unsubstituted NDIs (structure 1, Chart
1
) were tailored for applications in numerous research fields.
Due to their n-type semiconducting properties, core-unsubsti-
tuted NDIs bearing alkyl or fluorinated alkyl groups in the imide
positions have been of interest as active layer in organic field-
1
effect transistors (OFETs). Since NDIs are easily reversibly
reduced to form stable radical anions, they serve as electron-
acceptor units in artificial photosynthetic systems for solar
2
energy conversion. In supramolecular chemistry, NDI-based
3
catenanes and rotaxanes have been designed and very recently
4
created. The propensity of NDIs to form excimers initiated the
a supramolecular switch, which can be turned on and off by
heating with a hydrogen-bonding guest molecule, has been
5
development of NDI-based fluorescent chemosensors, and they
have been used for DNA intercalating and sensing. NDIs can
6
form large supramolecular structures through hydrogen bonding,
leading to helical organic nanotubes of defined chirality. Also,
*
To whom correspondence should be addressed. Tel: + 49 (0)931-8885340.
Fax: + 49-(0)931-8884756.
1) (a) Katz, H. E.; Lovinger, A. J.; Johnson, J.; Kloc, C.; Siegrist, T.;
7
supramolecular arrangement by π-π interactions was achieved
resulting in rigid-rod π-helical architectures, whose structures
are untwisted into open cation channels by intercalation of
(
Li, W.; Lin, Y.-Y.; Dodabalapur, A. Nature 2000, 404, 478-481. (b) Katz,
H. E.; Johnson, J.; Lovinger, A. J.; Li, W. J. Am. Chem. Soc. 2000, 122,
7
787-7792. (c) W u¨ rthner, F. Angew. Chem. 2001, 113, 1069-1071; Angew.
8
dialkoxynaphthalene ligands. Furthermore, anions can be
Chem., Int. Ed. 2001, 40, 1037-1039. (d) Hizu, K.; Sekitani, T.; Someya,
T.; Otsuki, J. Appl. Phys. Lett. 2007, 90, 093504.
transported over lipid bilayers by anion-π interactions to
10.1021/jo7015357 CCC: $37.00 © 2007 American Chemical Society
8
070
J. Org. Chem. 2007, 72, 8070-8075
Published on Web 09/21/2007

Core-Tetrasubstituted Naphthalene Diimides
oligonaphthalene diimide rods, exhibiting halide selectivity.9
Naphthalene diimide organogels were built by noncovalent
interactions such as π-π stacking, hydrogen bonding, and van
der Waals forces which serve as supramolecular hosts and
sensors for different types of electron-rich naphthalene com-
pounds.1 Moreover, due to their charge-transfer interaction with
alkoxy-substituted naphthalenes, NDIs are applicable in flexible
foldable polymers forming a stacked charge transfer (CT)
transistors.16 Very recently, we have reported the first examples
of core-trisubstituted NDI derivatives, such as compound 3
(Chart 1), which show intense color and high fluorescence
1
7
quantum yield.
Core-di- and -trisubstituted NDIs are accessible from 2,6-
dichloronaphthalene dianhydride by imidization with primary
amines, followed by substitution of the chlorine atoms at the
0
12,17,18
naphthalene core.
In the past 2 years, several groups have
11
donor-acceptor structure.
also used 2,6-dibromonaphthalene dianhydride as precursor for
12c,16,19
core-disubstituted NDIs.
Two bromine substituents were
Functionalization of NDIs by core substitution triggered an
eminent progress in controlling the optical and redox properties
of this class of dyes and thus extended the scope of application.
NDIs bearing two electron-donating core substituents, such as
NDI 2 (Chart 1), have been previously synthesized by our group
introduced at the naphthalene core of 1,4,5,8-naphthalenetetra-
carboxylic acid dianhydride by electrophilic aromatic substitu-
tion under different reaction conditions. Application of a
stoichiometric amount of dibromoisocyanuric acid (DBI) in
oleum (20% SO3) at room temperature afforded a mixture
consisting of mainly 2,6-dibromonaphthalene dianhydride and
small amounts of 2-monobromo and 2,3,6-tribromo compounds,
1
2
that show highly brilliant colors and strong fluorescence.
Their interesting electronic properties arise from a new CT
transition in the visible wavelength range, which is strongly
influenced by the electron-donating strength of the core sub-
stituents. Such core-substituted NDIs have attracted interest as
light-harvesting chromophores in self-assembled artificial an-
tenna systems,13 and they have been used to drive a transmem-
brane proton gradient caused by a photoinitiated electron-transfer
12c
along with some unreacted naphthalene dianhydride. Alter-
natively, bromine has been used as a bromination agent in the
presence of catalytic amounts of iodine using oleum as a solvent
16
resulting mainly in desired dibrominated product. Recently,
it has been reported that quantitative and selective formation
of 2,6-dibromonaphthalene dianhydride can be achieved using
1
4
cascade. One potential future application of NDIs with
electron-donating core substituents might be the optically
triggered transport of currents on the molecular scale in metal-
NDI hybrid setups.15 Recently a core-dicyanated electron-
deficient NDI derivative has been reported, which provided high
mobility, air-stable, n-type transparent organic field-effect
19
DBI in concentrated sulfuric acid at 130 °C.
Although a broad variety of core-di- and -trisubstituted NDIs
can be synthesized starting from 2,6-dichloro- or 2,6-dibro-
monaphthalene dianhydride, to our knowledge, no route to NDIs
bearing four electron-donating substituents at the naphthalene
core has been reported in the literature. To complete the highly
interesting series of core-di- and -trisubstituted NDIs, we chose
2,3,6,7-tetrabromonaphthalene dianhydride 4 as a precursor. It
had been reported in the Russian literature that compound 4
was observed as a mixture with other brominated products in
bromination of naphthalene dianhydride with bromine, but no
procedure for the isolation and purification of 4 was given.20
Here we report a highly efficient method for the synthesis of
pure 2,3,6,7-tetrabromonaphthalene dianhydride 4. The latter
has been used as a starting material for the synthesis of
tetrabromo-substituted NDI 5 which was disclosed in a patent
shortly before our work was submitted for publication.21 NDI
5 was reacted in good yields with oxygen, nitrogen, and sulfur
nucleophiles to give NDIs bearing four electron-donating core-
(
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Chem. Eur. J. 2002, 8, 4742-4750. (b) Thalacker, C.; Miura, A.; De Feyter,
S.; De Schryver, F. C.; W u¨ rthner, F. Org. Biomol. Chem. 2005, 3, 414-
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(4) Lavin, J. M.; Shimizu, K. D. Chem. Commun. 2007, 228-230.
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S.-J.; Yoon, J. J. Am. Chem. Soc. 2007, 129, 3828-3829.
(
6) (a) Takenaga, S.; Uto, Y.; Saita, H.; Yokoyama, M.; Kondo, H.;
(13) R o¨ ger, C.; M u¨ ller, M. G.; Lysetska, M.; Miloslavina, Y.; Holzwarth,
A. R.; W u¨ rthner, F. J. Am. Chem. Soc. 2006, 128, 6542-6543.
(14) Bhosale, S.; Sisson, A. L.; Talukdar, P.; F u¨ rstenberg, A.; Banerji,
N.; Vauthey, E.; Bollot, G.; Mareda, J.; R o¨ ger, C.; W u¨ rthner, F.; Sakai,
N.; Matile, S. Science 2006, 313, 84-86.
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S.; Hoffman, D. W.; Iverson, B. L. J. Am. Chem. Soc. 2002, 124, 2864-
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Cao, Q.; Kang, S. J.; Rogers, J. A.; Tansil, N. C.; Gao, Z. Appl. Phys. Lett.
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J. Org. Chem, Vol. 72, No. 21, 2007 8071

R o¨ ger and W u¨ rthner
SCHEME 1. Synthesis of Core-Tetrasubstituted NDIs 5-9
substituents. We have studied the substituent effects on the
optical and redox properties for this new series of NDIs and
compared those with NDIs 1-3.
sodium ethanolate in ethanol at room temperature afforded the
tetraethoxy-substituted NDI 6 in good yield. Similarly, the
reaction of 5 with ethanethiol in the presence of potassium
carbonate in chloroform at 80 °C yielded the tetraethylthio-
substituted NDI 7 in reasonable yield. With n-hexylamine as
nucleophile, all four bromine atoms of 5 could be replaced,
resulting in the corresponding core-tetraamino-functionalized
NDI 8. Likewise, the reaction of NDI 5 with ethylene diamine
as a solvent under reflux leads to the formation of tetraamino-
substituted ring-closure product NDI 9.
Results and Discussion
Synthesis. The starting material for the synthesis of core-
tetrasubstituted NDI, 2,3,6,7-tetrabromonaphthalene dianhydride
4, was prepared by bromination of commercially available
naphthalene dianhydride with 2.5 equiv of DBI in oleum (20%
SO3) at room temperature in excellent yield (Scheme 1). This
bromination afforded selectively tetrabromonaphthalene dian-
Optical Properties. The tetrabromo-substituted NDI 5 is a
light yellow, nonfluorescent compound exhibiting an electronic
transition in the range of 350-440 nm (Figure 1). Compared
to the colorless core-unsubstituted NDI 1, the absorption
maximum of 5 is bathochromically shifted from 381 to 402 nm
and the absorption band of the latter is less structured which is
in accord with the previously reported dichlorinated NDIs.12
The absorption band of the light yellow tetraethoxy derivative
1
hydride 4 since the H NMR spectrum (DMSO-d6) of bromi-
nation product does not show any proton resonance, indicating
absence of lower brominated compounds. The purity of 4 was
confirmed by elemental analysis and a correct mass was obtained
by EI mass spectrometry.
For the imidization of tetrabromonaphthalene dianhydride 4
the rather bulky, less nucleophilic 2,6-diisopropylaniline was
chosen to suppress nucleophilic substitution of bromine atoms.
Indeed, the imidization of 4 with 2,6-diisopropylaniline in glacial
acetic acid afforded the desired tetrabromonaphthalene diimide
6
appears in the same wavelength region as NDI 5. In contrast
to 5, the tetraethoxy-substituteted NDI 6 is weakly fluorescent
with a quantum yield of about 2%. The fluorescence band of
NDI 6 is not in mirror-image relation to the absorption band,
indicating that the absorption band of 6 at 350-440 nm
comprises not only the S0-S1 absorption but presumably
overlaps with the next higher transition. Introduction of four
ethylthio substituents at the naphthalene core causes a new
electronic transition in the visible region with a maximum at
563 nm providing a violet color. As the tetrabromo derivative
5, tetrathio NDI 7 is not fluorescenct.
5
as a major product, along with some at core monoaminated
byproduct and unreacted naphthalene dianhydride that could be
removed by column chromatography.
Tetrabrominated NDI 5 was then used as precursor for the
synthesis of core-tetrafunctionalized NDIs by nucleophilic
substitution of bromine atoms with alkoxy, alkylthio, or
alkylamino nucleophiles (Scheme 1). Reaction of NDI 5 with
8072 J. Org. Chem., Vol. 72, No. 21, 2007

Core-Tetrasubstituted Naphthalene Diimides
FIGURE 1. Absorption spectra of tetrabromo NDI 5 (yellow line)
and tetraethylthio NDI 7 (violet line) and absorption and emission
spectra (excitation at 375 nm) of tetraethoxy derivative 6 (orange lines)
in dichloromethane. For comparison, the absorption spectrum of core-
unsubstituted NDI 1 (black line) is depicted.
12a
FIGURE 3. Absorption spectra of dialkylamino NDI 2 (blue line),
17
trialkylamino NDI 3 (pink line), and tetraalkylamino NDI 8 (bluish-
green line) in dichloromethane.
TABLE 1. Absorption Maxima (λabs), Absorption Coefficients (E),
Emission Maxima (λem), and Fluorescence Quantum Yields (Φfl) of
Core-Substituted NDIs 2,1 3, and 5-9 in Dichloromethane
2a
17
colora
λabs (nm)
ꢀ (M-1 cm-1
)
λem (nm)
Φfl
2
3
5
6
7
8
9
blue
violet
620
579
427
419
563
642
629
23 300
29 400
10 900
12 200
15 400
26 500
36 000
650
0.42
605
0.70
b
b
light yellow
light yellow
violet
turquoise
turquoise
477
0.02
b
b
687
646
0.13
0.19
a
The colors are given for the solid. b Not fluorescent.
TABLE 2. Redox Properties of at Core Diamino- and
Triaminosubstituted NDIs 2 and 3 and Tetrasubstituted NDIs 5-9
in Dichloromethanea
FIGURE 2. Absorption and emission spectra (excitation at 570 nm)
of NDIs 8 (dashed lines) and 9 (solid lines) in dichloromethane.
E1/2 (V vs Fc/Fc+)
-
2-
X/X-
X/X+
+
2+
X /X
X /X
2
3
5
7
6
8
9
-1.90
-1.41
-1.69
-0.75
-1.10
-1.27
-1.69
-1.85
0.65
0.41
1.52c
1.10
b
The absorption and emission spectra of tetraalkylamino NDIs
and 9 are depicted in Figure 2. The strongly electron-donating
0.92
b
-1.16
-1.50
-1.77
8
c
b
b
0.97
alkylamino substituents at the naphthalene core evoke a further
red-shift of the S0-S1 absorption band compared to the
tetraethylthio NDI 7 to 642 (for 8) and 629 nm (for 9),
respectively. The absorption band of NDI 9 shows a much more
pronounced vibronic fine structure than that of NDI 8, which
results from the higher rigidity of the former chromophore
bearing ethylene-bridged substitutents. NDIs 8 and 9 exhibit a
second absorption band located between 380 and 440 nm which
can be attributed to the electronic S0-S2 transition. In particular
for NDI 9, we note a close resemblance in the vibronic structure
and position of this band with that of the unsubstituted NDI 1
b
-2.12
0.01
-0.01
0.36
0.59
b
a
All measurements were conducted in dichloromethane; scan rate 100
mV s-1; concentration ca. 1.0 mM; supporting electrolyte: tetrabutylam-
monium hexafluorophosphate (NBu4PF6, 100 mM). b Not observed. Peak
c
potentials of irreversible oxidation.
emission, all alkylamino-substituted derivatives are fluorescent.
The dialkylamino derivative 2 exhibits a quantum yield of 42%,
and it is increased for the trialkylamino compound 3 to 70%.
12a,17
(
Figure 1). The presence of two absorption bands in the visible
Introduction of a forth amino substituent, however, decreases
the quantum yield to 13% for NDI 8. The optical properties of
diamino and triamino NDIs 2 and 3 and newly synthesized
tetrasubstituted NDIs 5-9 are summarized in Table 1.
Redox Properties. The examination of the optical properties
of tetrasubstituted NDIs 5-9 (Table 1) reveal that the electronic
nature of the core substitutents strongly influences the respective
absorption and emission properties of these chromophores. To
gain further insight into the electronic properties of core-
tetrasubstituted NDIs, cyclic voltammetry was performed in
dichloromethane. The observed reduction and oxidation poten-
tials are collected in Table 2. The cyclic voltammogram of NDI
5 bearing four bromo substituents at the core showed two
region provides the bluish-green color of NDIs 8 and 9. For
both of these tetraalkylamino-substituted derivatives, fluores-
cence bands are observed matching the mirror image of the
respective longest wavelength absorption band.
In Figure 3, the absorption spectrum of tetraalkylamino NDI
is shown together with the spectra of di- and trialkylamino
8
NDIs 2 and 3. The S0-S1 band of NDI 2 exhibits a maximum
at 620 nm,1 while this band is shifted to shorter wavelengths
for NDI 3 to 579 nm.17 Interestingly, the introduction of a forth
alkylamino substitutent provokes again a red-shift to 642 nm
for NDI 8. Thus, tetraalkylamino-substituted derivative 8 shows
the longest wavelength absorption maximum known for core-
substituted NDI chromophores so far. In contrast to core-
unsubstitued NDIs such as NDI 1, which do not exhibit any
2a
+
reversible reduction waves at -0.75 and -1.16 V vs Fc/Fc
(Fc: ferrocene) and irreversible oxidation was detected at 1.52
J. Org. Chem, Vol. 72, No. 21, 2007 8073

R o¨ ger and W u¨ rthner
Conclusion
Bromination of 1,4,5,8-naphthalenetetracarboxylic acid di-
anhydride by electrophilic aromatic substitution with DBI in
oleum provided a convenient and highly efficient method for
the preparation of 2,3,6,7-tetrabromonaphthalene dianhydride
4, which is a valuable starting material for the synthesis of core-
tetrasubstituted NDIs. Imidization of 4 with amines, in the
present case 2,6-diisopropylaniline, afforded the tetrabromo-
substituted NDI 5, the latter being a versatile precursor for the
synthesis of tetrafunctionalized NDI chromophores by nucleo-
philic aromatic substitution with a variety of nucleophiles. Thus,
at the naphthalene core tetraalkoxy-, tetraalkylthio-, and tet-
raalkylamino-substituted NDIs 6-9 could be made available.
The present tetrasubstituted NDI derivatives now complete the
series of di- and trifunctionalized NDI chromophores. Our
studies have further revealed that not only the nature but also
the number of core substituents has a strong effect on the
electronic properties of NDIs; thus, with increasing number of
alkylamino substituents, the redox potentials gradually shift to
more negative values. The tetralkylamino-substituted NDI 8
showed the most red-shifted absorption maximum known for
NDIs, while for NDI 9 the lowest oxidation potential could be
observed. Such electron-rich NDI dyes might enable entirely
new applications of NDI chromophores, i.e., as electron-donating
components in artificial photosynthesis and solar energy conver-
FIGURE 4. Cyclic voltammograms of core-tetrasubstituted NDIs 5-9.
2,14
sion devices or as p-type organic semiconductors. Along this
line, we are currently exploring the possibility to extend the
aromatic core by using tetrabromo NDI 5 to develop ambipolar
FIGURE 5. Cyclic voltammograms of dialkylamino and trialkylamino
derivatives 2 and 3 and tetraalkylamino-substituted NDI 9.
2
2
organic semiconductor materials.
V (Figure 4). Within the series of core-tetrasubstituted NDIs
5-8, a gradual shift of the two reduction potentials to more
Experimental Section
negative values was observed, indicating a strong influence of
the electron-donating character of the respective core substituents
on the redox properties. For the tetrathio-substituted derivative
2
,3,6,7-Tetrabromo-1,4,5,8-naphthalenetetracarboxylic Acid
Dianhydride (4). A solution of dibromoisocyanuric acid (3.59 g,
2.5 mmol) in oleum (20% SO , 25 mL) was poured into a solution
of 1,4,5,8-naphthalenetetracarboxylic acid dianhydride (1.34 g, 4.99
mmol) in oleum (20% SO , 40 mL), and the reaction mixture was
1
3
7
, reversible reduction (-1.10 and -1.50 V) and irreversible
oxidation (0.97 V) took place, while for tetraethoxy NDI 6
-1.27 and -1.77 V), no oxidation could be detected within
3
(
stirred vigorously for 3 h at room temperature. The resulting orange
suspension was poured into ice (400 g), and water was added (600
mL). The yellow precipitate was filtered, washed with water (100
mL), and dried over potassium hydroxide. Yield: 2.70 g (93%).
mp > 350 °C. MS (EI) m/z (%): 579.7 (17.3), 581.7 (67.7), 583.6
100) (calcd 583.63874), 585.7 (66.7), 587.7 (16.0). H NMR (400
the available potential range in dichloromethane. For the most
electron-rich NDI within this series, namely the tetraalkylamino-
substituted NDI 8, not only significantly lower reduction
potentials (-1.69 and -2.12 V) but also two reversible
oxidations (0.01 and 0.36 V) were observed, implying the
formation of stable radical cationic species. For NDI 9 bearing
the cyclic diaminoethyl core substituents, two reversible oxida-
tion waves at -0.01 and 0.59 V were detected, while only one
reversible reduction potential (-1.85 V) could be observed
within the available potential range.
We further examined the influence of the number of core
substituents on the electrochemical properties of NDIs by com-
paring the CV data of derivatives 2, 3, and 9 bearing two, three,
or four alkylamino substituents, respectively, at the naphthalene
core (Figure 5 and Table 2). Among this series of alkylamino-
substituted NDIs, derivative 2 shows the most positive oxidation
1
(
MHz, DMSO-d
6
): No proton signal was observed. Anal. Calcd
for C14Br : C, 28.81; Br, 54.75. Found: C, 29.06; Br, 54.61.
4
O
6
N,N′-Bis-(2′,6′-diisopropylphenyl)-2,3,6,7-tetrabromo-1,4,5,8-
naphthalenetetracarboxylic Acid Diimide (5). To a stirred
suspension of dianhydride 4 (200 mg, 0.343 mmol) in glacial acetic
acid (5 mL) 2,6-diisopropylaniline (425 mg, 2.40 mmol) was added.
After stirring for 6 h at 120 °C, the reaction mixture was cooled to
room temperature. Then, water (50 mL) was added and the reaction
mixture was neutralized with saturated NaHCO
extracted with chloroform (3 × 100 mL). The combined organic
phases were dried over anhydrous Na SO , and the solvent was
evaporated. Purification of the crude product by column chroma-
tography (n-pentane/CH Cl ) 2:1, silica gel) and subsequent HPLC
CH Cl /MeOH ) 16:84; flow rate) 10 mL min ) afforded
compound 5 (93 mg, 29%) as a light yellow solid. mp ) 346-349
3
solution and
2
4
2
2
(0.65 and 1.10 V) and reduction potentials (-1.41 and -1.90
-
1
(
2
2
V). With increasing number of alkylamino substituents a gradual
decrease of reduction (-1.69 V for 3, -1.85 V for 9) and
oxidation potentials (0.41 and 0.92 V for 3, -0.01 and 0.59 V
for 9) is observed. The fact that only one reversible reduction
wave was observed for NDI 9 within the available potential
range suggests that the second reduction potential of this NDI
should be lower than -2.2 V; thus, the tetrasubstituted NDI 9
is the most electron-rich NDI dye known so far.
1
°
(
C. H NMR (400 MHz, CDCl
d, J ) 7.7 Hz, 4H), 2.68 (sept, J ) 6.9 Hz, 4H), 1.20 (d, J ) 6.9
Hz, 24H). HRMS (ESI) m/z: calcd for C H Br N O 902.9295,
found 902.9245. UV/vis (CH
(10 900), 402 nm (12 100).
3
): δ 7.52 (t, J ) 7.7 Hz, 2H), 7.36
3
8
35
4
2
4
-
1
-1
2 2
Cl ): λmax/nm (ꢀ/M cm ) ) 427
(22) Zaumseil, J.; Sirringhaus, H. Chem. ReV. 2007, 107, 1296-1323.
8074 J. Org. Chem., Vol. 72, No. 21, 2007

Core-Tetrasubstituted Naphthalene Diimides
N,N′-Bis-(2′,6′-diisopropylphenyl)-2,3,6,7-tetra(ethoxy)-1,4,5,8-
naphthalenetetracarboxylic Acid Diimide (6). An ethanolic
solution of sodium ethoxide was prepared from sodium (28 mg,
(100 mL). Upon concentration under reduced pressure at room
temperature, a turquoise solid precipitated which was purified by
column chromatography (CH
give compound 8 (38 mg, 48%). mp ) 238-242 °C. H NMR
(400 MHz, CDCl ): δ 7.51 (t, J ) 7.8 Hz, 2H), 7.37 (d, J ) 7.8
2 2
Cl /n-pentane ) 1:2, silica gel) to
1
1.2 mmol) and ethanol (3 mL). To this solution NDI 5 (32 mg,
0.035 mmol) was added and the mixture was stirred at room
3
temperature for 5.5 h under an argon atmosphere. Then, 1 N HCl
20 mL) and dichloromethane (50 mL) were added and the phases
Hz, 4H), 3.42 (t, J ) 7.3 Hz, 8H), 2.69 (sept, J ) 6.8 Hz, 4H),
1.49 (m, 8H), 1.28-1.17 (m, 48H), 0.80 (t, J ) 6.9 Hz, 12H).
(
were separated. The aqueous phase was extracted with dichlo-
HRMS (ESI) m/z: calcd for C62
UV/vis (CH Cl
nm (11 200). Fluorescence (CH
91 6 4
H N O 983.7170, found 983.7072.
-
1
-1
romethane (2 × 50 mL), and the combined organic phases were
2
2
): λmax/nm (ꢀ/ M cm ) ) 642 (26 500), 459
dried over anhydrous Na
2
SO
4
. After removal of solvent, further
2
Cl ): λmax ) 687 nm (λex ) 570
2
purification by column chromatography (CH
2
Cl
2
/n-pentane ) 11:
nm); fluorescence quantum yield: Φfl ) 0.13.
8
, silica gel) afforded compound 6 (17 mg, 63%) as a yellow solid.
N,N′-Bis-(2′,6′-diisopropylphenyl)-5,6,11,12-(1,4,7,10-tetraaza-
1,2,3,4,7,8,9,10-octahydroanthracene)tetracarboxylic Acid Di-
imide (9). NDI 5 (42 mg, 0.047 mmol) was heated under argon in
ethylene diamine (5 mL) at 135 °C for 30 min. After the addition
of water (30 mL) and dichloromethane (30 mL), the aqueous phase
was separated and extracted with dichloromethane (2 × 30 mL).
The combined organic phases were washed with 1 N HCl (30 mL),
and the solvent was removed under vacuum. Further purification
1
mp > 350 °C. H NMR (400 MHz, CDCl
Hz, 2H), 7.35 (d, J ) 7.7 Hz, 4H), 4.28 (q, J ) 7.0 Hz, 8H), 2.73
sept, J ) 6.9 Hz, 4H), 1.49 (t, J ) 7.0 Hz, 12H), 1.18 (d, J ) 6.9
Hz, 24H). HRMS (ESI) m/z: calcd for C46 763.3958, found
63.3937. UV/vis (CH Cl ): max/nm (ꢀ/ M cm ) ) 419
12 200), 378 nm (18 200). Fluorescence (CH Cl ): λmax ) 477
3
): δ 7.49 (t, J ) 7.7
(
55 2 8
H N O
-
1
-1
7
(
2
2
λ
2
2
nm (λex ) 375 nm); fluorescence quantum yield: Φfl ) 0.02.
N,N′-Bis-(2′,6′-diisopropylphenyl)-2,3,6,7-tetra(ethylthio)-
2 2
of the residue by column chromatography (CH Cl , silica) yielded
1
,4,5,8-naphthalenetetracarboxylic Acid Diimide (7). A mixture
of compound 5 (20 mg, 0.022 mmol), potassium carbonate (30 mg,
.22 mmol), ethanethiol (2.5 mL), and chloroform (1 mL) was
refluxed for 3.5 h. The solvent was evaporated, and the remaining
solid was subjected to column chromatography (CHCl /n-hexane
1:1, silica gel) and subsequent HPLC (MeOH; flow rate ) 10
compound 9 (20 mg, 62%) as a bluish-green solid. mp > 350 °C.
1
H NMR (400 MHz, CDCl
Hz, 2H), 7.34 (d, J ) 7.7 Hz, 4H), 3.65 (br s, 8H), 2.71 (m, 4H),
1.17 (d, J ) 6.7 Hz, 24H). HRMS (ESI) m/z: calcd for C42
698.3580, found 698.3578. UV/vis (CH Cl ): λmax/nm (ꢀ/ M
cm ) ) 629 (36 000), 581 (15 500), 538 (5300), 432 (25 700),
408 (12 700), 387 nm (4200). Fluorescence (CH Cl ): λmax ) 698,
3
): δ 9.82 (br s, 4H), 7.48 (t, J ) 7.7
0
46 6 4
H N O
-
1
3
2
2
-
1
)
-
1
mL min ) to give the violet compound 7 (9 mg, 50%). mp )
2
2
1
3
2
23-325 °C. H NMR (400 MHz, CDCl
3
): δ 7.49 (t, J ) 7.8 Hz,
646 nm (λex ) 570 nm); fluorescence quantum yield: Φfl ) 0.19.
H), 7.34 (d, J ) 7.7 Hz, 4H), 3.00 (q, J ) 7.5 Hz, 8H), 2.70
Acknowledgment. We thank Ms. Ana-Maria Krause for the
cyclic voltammetry measurements. C.R. is grateful to the
Degussa Stiftung for a Ph.D. scholarship. Financial support of
our work by the Fonds der Chemischen Industrie is greatly
appreciated.
(
sept, J ) 6.8 Hz, 4H), 1.25-1.18 (m, 36H). HRMS (ESI) m/z:
calcd for C46 NaO 849.2864, found 849.2863. UV/vis (CH
Cl ): λmax/nm (ꢀ/M cm ) ) 563 (15 400), 329 nm (24 400).
N,N′-Bis-(2′,6′-diisopropylphenyl)-2,3,6,7-tetra(n-hexylamino)-
,4,5,8-naphthalenetetracarboxylic Acid Diimide (8). NDI 5 (74
H N
54 2
S
4 4
2
-
-
1
-1
2
1
mg, 0.082 mmol) was heated in n-hexylamine (10 mL) at 135 °C
for 5.5 h. Subsequently, n-hexylamine was removed under reduced
pressure at the rotary evaporator. The solid residue was dissolved
in dichloromethane (30 mL), and 1 N HCl (100 mL) was added.
The aqueous phase was extracted with dichloromethane (2 × 30
mL), and the combined organic phases were washed with water
Supporting Information Available: General experimental
methods, EI mass spectrum of compound 4, and H NMR spectra
of NDIs 5-9. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
JO7015357
J. Org. Chem, Vol. 72, No. 21, 2007 8075