Synthesis and optical and redox properties of core-substituted naphthalene diimide dyes

Article abstract of DOI:10.1021/jo0612269

2,6-Dichloronaphthalene dianhydride has been synthesized by a modified procedure. The imidization of this dichlorinated anhydride with amines and subsequent stepwise nucleophilic exchange of the chlorine atoms by alkyl- or arylamines afforded a series of hitherto unknown monoamino- and diamino-substituted naphthalene diimides. An alternative route for the synthesis of diamino-substituted naphthalene diimides is also reported. Optical and electrochemical properties of the newly synthesized amino-functionalized naphthalene diimides were studied in detail. The absorption maxima (530-620 nm) of these dyes are appreciably bathochromically shifted compared to those of the corresponding core-unsubstituted compounds. At the naphthalene core alkylamino-substituted diimides exhibit fluorescence quantum yields up to 60%.

Full text of DOI:10.1021/jo0612269

Synthesis and Optical and Redox Properties of Core-Substituted
Naphthalene Diimide Dyes
Christoph Thalacker, Cornelia Ro¨ger, and Frank Wu¨rthner*
UniVersita¨t Wu¨rzburg, Institut fu¨r Organische Chemie, Am Hubland, 97074 Wu¨rzburg, Germany
wuerthner@chemie.uni-wuerzburg.de
ReceiVed June 14, 2006
2,6-Dichloronaphthalene dianhydride has been synthesized by a modified procedure. The imidization of
this dichlorinated anhydride with amines and subsequent stepwise nucleophilic exchange of the chlorine
atoms by alkyl- or arylamines afforded a series of hitherto unknown monoamino- and diamino-substituted
naphthalene diimides. An alternative route for the synthesis of diamino-substituted naphthalene diimides
is also reported. Optical and electrochemical properties of the newly synthesized amino-functionalized
naphthalene diimides were studied in detail. The absorption maxima (530-620 nm) of these dyes are
appreciably bathochromically shifted compared to those of the corresponding core-unsubstituted
compounds. At the naphthalene core alkylamino-substituted diimides exhibit fluorescence quantum yields
up to 60%.
Introduction
core-unsubstituted NDIs show absorption only in the UV
region,4 core-unsubstituted perylene diimides with larger π
system are red dyes with absorption maxima (λmax) at around
530 nm and fluorescence emission (λem) bands in the range of
500-560 nm.1c,5 With one more naphthalene unit extended
terrylene diimides are blue colorants (λmax ≈ 650 nm), and they
show fluorescence around 670 nm,2 while quaterrylene diimides
exhibit absorption (λmax ≈ 760 nm) and fluorescence maxima
The higher homologues of 1,4,5,8-naphthalenetetracarboxylic
acid diimide (NDI, this class of compounds is also called as
naphthalene bisimide), namely perylene,1 terrylene,2 and qua-
terrylene3 diimides, are well-established fluorescent colorants
with outstanding lightfastness, chemical inertness, and high
fluorescence quantum yields. Their outstanding optical proper-
ties can be ascribed to the extended aromatic π system. While
(3) (a) Quante, H.; Mu¨llen, K. Angew. Chem. 1995, 107, 1487-1489;
Angew. Chem., Int. Ed. Engl. 1995, 34, 1323-1325. (b) Geerts, Y.; Quante,
H.; Platz, H.; Mahrt, R.; Hopmeier, M.; Bo¨hm, A.; Mu¨llen, K. J. Mater.
Chem. 1998, 8, 2357-2369. (c) Ko¨nemann, M.; Bo¨hm, A.; Bidlingmaier,
H.; Rieger, R.; Blaschka, P.; Reichelt, H.; Krieger, M. (BASF AG), German
Pat. DE 102004041604A1, 2006. (d) Pschirer, N. G.; Kohl, C.; Nolde, F.;
Qu, J.; Mu¨llen, K. Angew. Chem. 2006, 118, 1429-1432.
* To whom correspondence should be addressed. Tel: + 49 (0)931-8885340.
Fax: + 49-(0)931-8884756.
(1) (a) Zollinger, H. Color Chemistry, 2nd ed.; VCH: Weinheim, 1991.
(b) Herbst, W.; Hunger, K. Industrial Organic Pigments, Production,
Properties, Applications; Wiley-VCH: Weinheim, 1997. (c) Langhals, H.
Heterocycles 1995, 40, 477-500. (d) Wu¨rthner, F. Chem. Commun. 2004,
1564-1579.
(4) (a) Alp, S.; Erten, U.; Karapire, C.; Ko¨z, B.; Doroshenko, A. O.;
Ic¸li, S. J. Photochem. Photobiol. A 2000, 135, 103-110. (b) Licchelli, M.;
Biroli, A. O.; Poggi, A. Org. Lett. 2006, 8, 915-918.
(2) (a) Holtrup, F. O.; Mu¨ller, G. R. J.; Quante, H.; De Feyter, S.; De
Schryver, F. C.; Mu¨llen, K. Chem. Eur. J. 1997, 3, 219-225. (b) Mais, S.;
Tittel, J.; Basche´, T.; Bra¨uchle, C.; Go¨hde, W.; Fuchs, H.; Mu¨ller, G.;
Mu¨llen, K. J. Phys. Chem. A 1997, 101, 8435-8440.
(5) Wu¨rthner, F.; Chen, Z.; Dehm, V.; Stepanenko, V. Chem. Commun.
2006, 1188-1190.
10.1021/jo0612269 CCC: $33.50 © 2006 American Chemical Society
Published on Web 09/19/2006
8098
J. Org. Chem. 2006, 71, 8098-8105

Core-Substituted Naphthalene Diimide Dyes
CHART 1. Structures of NDIs 1 and “Perinone” Pigments 2a
SCHEME 1. Synthesis of Regioisomerically Pure
Naphthalene Dianhydride 6a
a In the solid state, the trans isomer of 2 is orange and the cis isomer is
red.
(λem ≈ 780 nm) approaching the near-infrared region.3 Due to
the lack of absorption in the visible range for core-unsubstituted
NDIs, technical application of NDI-based colorants has been
restricted to derivatives with extended aromatic systems such
as “perinones” (Chart 1); the latter can be obtained by
condensation of naphthalene dianhydride with o-phenylenedi-
amine and have been used as vat dyes since the 1930s and as
pigments since the 1950s.1a,b
NDIs with bathochromically shifted absorption maxima can
be achieved by functionalization at the naphthalene core.6
Recently, we have shown that attachment of electron-donating
alkylamino and alkyloxy substituents at the 2,6-positions of NDI
1 (Chart 1) can even afford valuable fluorophores with
fluorescence quantum yields up to 80% and tunable emission
wavelengths from the green to red spectral region.7 In this work,
we present a broader range of new NDIs bearing different amino
substituents at the naphthalene core. The effect of alkylamino
and arylamino substituents on the optical and redox properties
of NDIs has been studied in detail to elicit a structure-property
relationship. Furthermore, a new route to core-substituted NDI
is introduced.
a Reagents and conditions: (a) Cl2 (g), I2 (in catalytic amounts), 1,2,4-
trichlorobenzene, 25-110 °C, 6 h, yield 36-38% of 3; (b) KOH, ethanol,
80 °C, 5 h, yield 96-97% of 4a,b as an isomeric mixture; (c) fuming HNO3,
0-5 °C, 15 min, yield 32-45% of 5a (isomer 5b was not purified); (d)
fuming HNO3, concd H2SO4, 100 °C, 5 min, yield 45-49% of 6.
reaction mixture. For this reaction, we used fuming nitric acid,
instead of concentrated nitric acid as used in the previously
reported procedure. The trans isomer 5a was separated by
filtration, and purification could be achieved by sublimation.
The 1H NMR spectrum of 5a in deuterated concentrated sulfuric
acid showed only two signals at 7.96 and 6.76 ppm, which can
be taken as an evidence for the isolated trans product.
Reaction of 6 with primary aliphatic or aromatic amines in
refluxing glacial acetic acid yielded the corresponding 2,6-
dichloro-substituted NDIs 7a,b (Scheme 2). In this highly protic
solvent, where most amino functions are protonated, the
reactivity of the amines is sufficiently low; thus, imide formation
is more favored over substitution of the chlorine atoms. Only
for an elongated reaction time did nucleophilic aromatic
substitution (SNAr) take place to a small extent.
Reaction of dichlorinated NDIs 7a,b with n-octylamine at
room temperature in aprotic organic solvents, such as dichlo-
romethane, leads to selective substitution of one chlorine atom
to afford the corresponding monochloroalkylaminonaphthalene
diimides 8a,c. This convincingly demonstrates the high pro-
pensity of these electron-deficient aromatic compounds toward
nucleophilic substitution, since amination of aryl halides usually
requires either very harsh reaction conditions or transition metal
catalysis.8 Selective monosubstitution by less nucleophilic
aromatic amines, e.g., 4-tert-butylaniline, was achieved in
N-ethyldiisopropylamine at 140 °C. The resulting 2-chloro-6-
arylaminonaphthalene diimide 8b could be subjected to a second
nucleophilic substitution with an alkylamine at 140 °C to yield
the unsymmetrically substituted 2,6-diaminonaphthalene diimide
9a.
Results and Discussion
Synthesis. Vollmann’s synthesis6a of core-substituted NDIs
starts with naphthalene dianhydride 6 (Scheme 1). The latter
can be obtained in four steps from pyrene by subsequent
chlorination, HCl elimination, and oxidation.6a However, the
procedure reported in this classical publication6a could not be
reproduced in a satisfying manner. Modification of this proce-
dure resulted in successful synthesis of 6, which we describe
in detail in the Experimental Section. In the course of chlorina-
tion of pyrene (Scheme 1, reaction a), it is essential to adjust
the reaction temperature in particular time intervals. The
separation of 2,6- and 2,7-dichloro isomers was achieved at the
quinone stage where the 2,6 isomer 5a precipitated from the
(6) (a) Vollmann, H.; Becker, H.; Corell, M.; Streeck, H. Liebigs Ann.
1937, 531, 1-159. (b) Bonnet, E.; Gangneux, P.; Mare´chal, E. Bull. Soc.
Chim. Fr. 1976, 504-506. (c) Bondarenko, E. F.; Shigalevskii, V. A.;
Gerasimenko, Y. E. Zh. Org. Khim. 1979, 15, 2520-2525; J. Org. Chem.
USSR (Engl. Transl.) 1979, 15, 2279-2284. (d) Bondarenko, E. F.;
Shigalevskii, V. A.; Yugai, G. A. Zh. Org. Khim. 1982, 18, 610-615; J.
Org. Chem. USSR (Engl. Transl.) 1982, 18, 530-535.
(7) Wu¨rthner, F.; Ahmed, S.; Thalacker, C.; Debaerdemaeker, T. Chem.
Eur. J. 2002, 8, 4742-4750. For a recent application of these chromophores
in artificial photosynthesis, see: 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, 84-86.
NDIs 9b and 9c with two identical amino substituents were
obtained directly by the reaction of 2,6-dichloro diimide 7a or
J. Org. Chem, Vol. 71, No. 21, 2006 8099

Thalacker et al.
SCHEME 2. Synthesis of Core-Substituted NDIs 7-9a
a Reagents and conditions: (a) Respective amine, glacial acetic acid, 120 °C, yield 70% of 7a and 60% of 7b; (b) 8a,c: n-octylamine, CH2Cl2, 25 °C,
4.5-24 h, yield 96% of 8a and 87% of 8c; 8b 4-tert-butylaniline, N-ethyldiisopropylamine, Ar, 140 °C, 1 h, yield 97% of 8b; (c) n-octylamine, Ar, 140 °C,
45 min, yield 59% of 9a; (d) respective amine, Ar, 140-180 °C, 40-60 min, yield 57% of 9b and 43% of 9c; (e) amine, Ar, 140 °C, 40-120 min, yield
70% of 9d and 45% of 9e.
7b, respectively, with an appropriate amine at 140 °C (alkyl-
amine for 9c) or at 180 °C (aromatic amine for 9b). During the
synthesis of 9c, a partial exchange of the aromatic imide
substituents for the alkylamine took place, owing to the large
excess of alkylamine. Apparently, arylamines are easily replaced
by alkylamines, while the inverse reaction was not observed
during the synthesis of 9b. The use of transition-metal-catalyzed
reactions8 for the introduction of the second amino function
might be helpful to overcome this problem by employing milder
reaction conditions under which an exchange of the imide
substituents should be disfavored. Finally, NDIs 9d and 9e
bearing the same substituents at both imide and core positions
could be obtained in a one-step reaction from dianhydride 6
and the respective amines under heating at 140 °C (Scheme 2).
The synthesis of the precursor 6 for amino-functionalized
NDIs 8,9 is rather cumbersome as depicted in Scheme 1.
Therefore, we have been looking for an alternative route to
aminonaphthalene diimides. In this regard, the functionalization
of the readily available unsubstituted naphthalene dianhydride
10 appears to be promising. It was previously reported that
naphthalene dianhydride 10 can be directly brominated with
bromine in concentrated sulfuric acid.9 However, this protocol
could not be reproduced. Fortunately, the bromination of 10
was achieved using dibromoisocyanuric acid (DBI) in oleum
(20% SO3), which is known as one of the most powerful
brominating agents (Scheme 3).10 Application of a stoichiometric
amount of DBI afforded a mixture consisting of mainly 2,6-
dibromonaphthalene dianhydride 11 and small amounts of
2-monobromo and 2,3,6-tribromo compounds, along with some
unreacted naphthalene dianhydride. The reaction of dibromo-
naphthalene dianhydride 11 with 2-ethylhexylamine at 140 °C
afforded in a single step the 2,6-diamino-substituted NDI 9e
bearing identical substituents at the imide and core positions.
Thus, a new route for the synthesis of symmetrically substituted
diaminonaphthalene diimides with different substituents at the
imide positions and naphthalene core may be synthesized from
compound 9e by hydrolysis of the latter to the corresponding
diaminonaphthalene dianhydride and its subsequent imidization
with different amines. Unfortunately, NDI 9e, in contrast to
structurally related perylene diimides,11 could not be saponified
to the corresponding dianhydride with KOH in alcohol. Instead,
under these conditions lactam imide 12 was formed in good
yield (Scheme 3, reaction c). Variation of reaction conditions
(KOH/t-BuOH/water or KOH/18-crown-6/toluene) and pro-
longed reaction time (up to 48 h) did not lead to the formation
of desired product. Rather, lactam imide 12 along with small
(9) (a) Solomatin, G. G.; Filippov, M. P.; Shigalevskii, V. A. Zh. Org.
Khim. 1981, 17, 877-879; J. Org. Chem. USSR (Engl. Transl.) 1981, 17,
771-773. (b) Jacquignon, P.; Buu-Ho¨ı, N. P.; Mangane, M. Bull. Soc. Chim.
Fr. 1964, 2517-2523.
(10) (a) Gottardi, W. Monatsh. Chem. 1968, 99, 815-822. (b) Gottardi,
W. Monatsh. Chem. 1969, 100, 42-50. (c) Gottardi, W. Monatsh. Chem.
1977, 108, 1067-1084. (d) Becker, H. G. O., et al. Organikum, 19th ed.;
Barth: Leipzig, 1993; pp 329-333.
(11) (a) Wu¨rthner, F.; Stepanenko, V.; Chen, Z.; Saha-Mo¨ller, C. R.;
Kocher, N.; Stalke, D. J. Org. Chem. 2004, 69, 7933-7939. (b) Zhao, Y.;
Wasielewski, M. R. Tetrahedron Lett. 1999, 40, 7047-7050. (c) Bo¨hm,
A.; Arms, H.; Henning, G. Blaschka, P. (BASF AG), German Pat. DE
19547209A1, 1997; Chem. Abstr. 1997, 127, 96569g.
(8) Reviews on amination of aryl halides can be found in: (a) Wolfe, J.
P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc. Chem. Res. 1998, 31,
805-818. (b) Hartwig, J. F. Angew. Chem. 1998, 110, 2154-2177; Angew.
Chem., Int. Ed. 1998, 37, 2046-2067. Transition-metal-catalyzed amination
of activated aryl halides at room temperature is described in: (c) Wolfe, J.
P.; Buchwald, S. L. Angew. Chem. 1999, 111, 2570-2573; Angew. Chem.,
Int. Ed. 1999, 38, 2413-2416. (d) Stauffer, S. R.; Lee, S.; Stambuli, J. P.;
Hauck, S. I.; Hartwig, J. F. Org. Lett. 2000, 2, 1423-1426. (e) Wolfe, J.
P.; Tomori, H.; Sadighi, J. P.; Yin, J.; Buchwald, S. L. J. Org. Chem. 2000,
65, 1158-1174.
8100 J. Org. Chem., Vol. 71, No. 21, 2006

Core-Substituted Naphthalene Diimide Dyes
SCHEME 3. Synthesis of 2,6-Diaminonaphthalene Diimide
9e by Functionalization of Naphthalene Dianhydride 10 in
Two Stepsa
FIGURE 2. Absorption and emission spectra of 8c (solid lines) and
absorption spectrum of 8b (dotted line) in dichloromethane. The
excitation wavelength was 530 nm. The absorption and fluorescence
spectra of 8a are very similar to those of 8c.
CHART 2. Structures of Previously Synthesized
Disubstituted NDIs 13a,b7 and 14a,b14
a Reagents and conditions: (a) dibromoisocyanuric acid (DBI), oleum
(20% SO3), 25 °C, 5 h, yield 80% of 11; (b) 2-ethylhexylamine, Ar, 140
°C, 2 h, yield 45% of 9e; (c) KOH, t-BuOH, water, 80 °C, 24 h, yield 64%
of 12.
structure is quite different (Figure 1). The dichlorosubstituted
NDIs 7a,b are also not fluorescent. Upon introduction of amino
substituents to the naphthalene core, significant changes in
optical properties of NDIs were observed.6,7,14,15 Thus, one
amino substituent (compounds 8a-c and 13a, 14a (Chart 2))
leads to red dyes with a new absorption band in the visible
region at around 530 nm (Figure 2 and Table 1). For compounds
bearing alkylamino groups (8a,c, 13a, 14a) at the naphthalene
core, the S0-S1 band exhibits a shoulder at lower wavelengths.
In aliphatic solvents this shoulder is more pronounced, and an
additional shoulder occurs at even lower wavelengths. As the
energy of the fine structure is again in the order of ca. 1300
cm-1 (0.16 eV), they can be attributed to a vibronic fine structure
arising from the skeletal vibrations of the aromatic core.
Interestingly, strong fluorescence bands were observed for the
alkylamino-functionalized NDIs 8a,c, which are mirror images
of the S0-S1 absorption bands of these chromophores as
exemplarily shown for 8c in Figure 2. In contrast to alkylamino-
substituted dyes 8a,c, for the monoarylamino derivative 8b
neither fine vibronic structure nor fluorescence could be
observed (Figure 2).
FIGURE 1. Absorption spectra of core-unsubstituted NDI 1a (solid
line) and 2,6-dichloronaphthalene diimide 7a (dotted line) in dichlo-
romethane.
amounts of unreacted NDI 9e was isolated. It is noteworthy
that such transformations have been reported earlier for other
NDI derivatives11e,12 and for some perylene diimides under
special conditions as well.13
Optical Properties. The absorption spectra of core-unsub-
stituted NDIs 1 exhibit as major feature the electronic S0-S1
absorption band at 250-400 nm. The pronounced vibronic fine
structure of the absorption band indicates the rigid nature of
these chromophores and its energy in the order of ca. 1300 cm-1
(0.16 eV) corresponds to the skeletal vibrations of the aromatic
system (Figure 1). While the higher homologue perylene
diimides exhibit very strong fluorescence,1,5 virtually no emis-
sion could be observed for unsubstituted NDIs 1.4 The S0-S1
band of the 2,6-dichloro-substituted NDIs 7a,b is located at
almost the same position as for NDIs 1, but the vibronic fine
Introduction of a second electron-donating amino substituent
at the naphthalene core evokes a further red shift of the new
absorption band observed for the monoamino-substituted com-
pounds to 610-620 nm providing the blue dyes 9a-e, 13b,
and 14b (Figure 3 and Table 1). As in the case of arylamino-
(12) (a) Bondarenko, E. F.; Shigalevskii, V. A. Zh. Org. Khim. 1986,
22, 1282-1286; J. Org. Chem. USSR (Engl. Transl.) 1986, 22, 1155-
1163. (b) Langhals, H.; v. Unold, P. C. (Ciba Specialty Chemicals Corp.),
US Pat. 5886183, 1999.
(13) Kaiser, H.; Lindner, J.; Langhals, H. Chem. Ber. 1991, 124, 529-
535.
(14) Thalacker, C.; Miura, A.; De Feyter, S.; De Schryver, F. C.;
Wu¨rthner, F. Org. Biomol. Chem. 2005, 3, 414-422.
(15) Thalacker, C. Ph.D. Thesis, Universita¨t Ulm, 2001.
J. Org. Chem, Vol. 71, No. 21, 2006 8101

Thalacker et al.
TABLE 1. Absorption Maxima (λabs), Absorption Coefficients (E),
Emission Maxima (λem), and Fluorescence Quantum Yields (Φfl) of
Red NDI Dyes 8a-c, 13a, and 14a and Blue Dyes 9a-e, 13b, and
14b in Dichloromethane
nm which can be attributed to the electronic S0-S2 transition.
With its strongly pronounced vibronic fine structure with an
energy order of ca. 1300 cm-1 (0.16 eV), this band strongly
resembles the S0-S1 band of core-unsubstituted NDIs 1.
substituent
λabs
ꢀ
λem
(nm)
As mentioned above and shown in Table 1, alkylamino- and
arylamino-functionalized NDI dyes possess quite different
optical properties. NMR studies and molecular modeling provide
a reasonable explanation for the observed differences. 1H NMR
spectra of alkylamino- and arylamino-substituted NDI show a
sharp signal for the amino proton at 9 to 11 ppm, even in highly
polar solvents such as DMSO, which clearly suggests that both
of these chromophore systems are rigidified by strong intramo-
lecular hydrogen bonding between the amino proton and the
adjacent carbonyl group. As a consequence of this intramolecular
hydrogen bonding, the amino groups at the naphthalene core
are arranged in such a way that the nitrogen lone pair can fully
conjugate to the electron-poor naphthalene diimide core in both
alkylamino- and arylamino-functionalized NDIs (Figure 4).16
This affords donor-acceptor chromophores with similar absorp-
tion maxima for both alkylamino and arylamino derivatives as
well as strong solvatochromic properties as discussed in detail
in our earlier work.7 A further consequence of the hydrogen
bonding is that in the case of the arylamino-substituted
compounds, the fixed conformation provokes sterical hindrance
between the naphthalene core and the aryl substituent. Indeed,
molecular modeling studies revealed a pronounced distortion
of the aryl substituent relative to the molecule plane. Such a
twisted conformation is prone to vibrational degrees of freedom
(“librations”) leading to a loss of the vibronic fine structure of
absorption spectra. Furthermore, new channels for radiationless
deactivation of excited states such as twisted internal charge
transfer (TICT) process17 and so-called loose-bolt mechanism18
may emanate from such twisted geometry which might be
responsible for the luminescence quenching of arylamino-
substituted NDIs 8b, 9a, and 9b (Table 1).
compd imide
core
(nm) (M-1 cm-1
)
Φfl
8a
8b
8c
13a
14a
9a
9b
9c
9d
9e
13b
14b
alkyl
alkyl
aryl
aryl
H
alkyl
alkyl
aryl
alkyl
alkyl
aryl
H
NHalkyl
NHaryl
NHalkyl
NHalkyl
NHalkyl
532
523
534
535
537b
15 300
12 900
16 000
15 500
16 200b
22 200
22 800
23 600
23 000
22 100
23 300
22 200b
567
a
0.58
a
0.58
0.63
566
565
565b 0.57b
NHalkyl/aryl 613
NHaryl
a
a
a
a
0.55
0.53
0.53
0.42
612
618
615
619
620
620b
NHalkyl
NHalkyl
NHalkyl
NHalkyl
NHalkyl
650
646
647
650
648b 0.53b
a
Not fluorescent. b Chloroform was used instead of dichloromethane
for better solubility.
FIGURE 3. Absorption and emission spectra of 9d (solid lines) and
absorption spectrum of 9a (dotted line) in dichloromethane. The
excitation wavelength for 9d was 610 nm.
Redox Properties. Our detailed investigations of the optical
properties of these NDIs (vide supra) have shown that substit-
uents at the naphthalene core have dramatic effect on the
electronic properties of these dyes. Further insight into the
influence of core substituents on the electronic properties of
NDIs was gained by cyclic voltammetry which was carried out
for a selection of NDIs bearing different substitution patterns
at the naphthalene core. The results are summarized in Table
2. The cyclic voltammograms of compounds 7a, 1a, and 8a
bearing n-octylamine substituents at the imide positions showed
two reversible reduction waves (Figure 5), implying the forma-
tion of radical anions and dianions, but no reversible oxidation
of these compounds could be observed up to 1.2 V vs Fc/Fc+
(Fc: ferrocene). Within this series, the dichloro-substituted
naphthalene diimide 8b, for the diaminosubstituted NDIs 9a
and 9b bearing one or two arylamino substituents at the
naphthalene core the S0-S1 band is not well structured and they
do not exhibit any fluorescence.
In contrast to the distinct effect of alkyl- versus arylamino
substituents at the naphthalene core on the optical properties of
NDIs, few changes in absorption and emission properties were
noted for NDIs containing different substituents at the imide
positions. Thus, compounds 8a,c and 14a show very similar
absorption and fluorescence spectra and quantum yields (Table
1), despite the fact that they bear different types of substituents
(alkyl, aryl, or hydrogen) at the imide positions.
Both series of dyes (red, 8a,c, 13a, 14a; blue, 9a-e, 13b,
14b) exhibit a second absorption band between 320 and 370
FIGURE 4. Energy-minimized structures of a 2,6-diarylamino-substituted (left) and a 2,6-dialkylamino-substituted (right) NDI obtained from
semiempirical calculations (AM1).16
8102 J. Org. Chem., Vol. 71, No. 21, 2006

Core-Substituted Naphthalene Diimide Dyes
TABLE 2. Redox Properties of Alkylamino- (7a, 1a, 8a, and 9d)
and Arylamino-Substituted (8b, 9a, and 9b) NDIs Bearing Different
Patterns of Donor and Acceptor Substituents at the Naphthalene
Corea
E
1/2 (V vs Fc/Fc+)
X-/X2-
X/X-
X/X+
X+/X2+
7a
1a
8a
9d
8b
9a
9b
-1.38
-1.51
-1.64
-1.80
-1.57
-1.74
-1.68
-0.95
-1.10
-1.24
-1.40
-1.21
-1.41
-1.38
b
b
b
0.60
1.03
0.62
0.64
b
b
b
b
b
1.06
1.03
FIGURE 6. Cyclic voltammograms of arylamino-substituted NDIs 8b,
9a, and 9b.
a All measurements were conducted in dichloromethane; scan rate 100
mV s-1, concentration 1.0 mM, supporting electrolyte: tetrabutylammonium
hexafluorophosphate (NBu4PF6, 100 mM). b Not observed.
monoarylamino-monoalkylamino derivative 9a and the diaryl-
amino derivative 9b showed similar reduction potentials as their
dialkylamino counterpart 9d. But, in contrast to the irreversible
oxidation of the latter, both 9a (0.62 and 1.06 V) and 9b (0.64
and 1.03 V) display two reversible oxidations, implying an
increase in stability of the radical cationic and the dicationic
species of arylamino-substituted NDIs compared to those of
alkylamino-substituted derivatives.
Conclusion
Selective and stepwise nucleophilic substitution of 2,6-
dichloronaphthalene dianhydride 6 with alkyl- and arylamines
provided a series of intensely colored red and blue NDI
chromophores. With this series of differently core-substituted
NDIs, a structure-property relationship could be explored for
this class of dyes. Our studies have shown that alkylamino
groups with strong electron-donating properties strongly enhance
the fluorescence, while arylamino groups diminish fluorescence.
The redox properties of NDIs are also influenced by core
substituents. As the dichloro-substituted NDI 7a possesses a
low reduction potential, it is a promising candidate for n-type
organic semiconducting materials which are still very rare.19 In
contrast, substituents at the imide positions do not have any
significant effect on the chromophore properties.
FIGURE 5. Cyclic voltammograms of alkylamino-substituted NDIs
7a, 1a, 8a, and 9d.
compound 7a exhibited the most positive reduction potentials
of -0.95 and -1.38 V. A gradual shift of the reduction
potentials to more negative values was observed for the core-
unsubstituted compound 1a (-1.51 and -1.10 V) and the
monochloromonoalkylamino derivative 8a (-1.64 and -1.24
V) revealing a direct relationship between the electron-donating
properties of the core substituents and the electrochemical
properties of NDIs. Indeed, for the most electron-rich dialkyl-
amino-substituted naphthalene diimide 9d significantly lower
reduction potentials (-1.80 and -1.40 V) were observed, and
the reductions are irreversible. An additional irreversible oxida-
tion wave was observed for 9d at around +0.6 V vs Fc/Fc+
(Figure 5). It is noteworthy that at higher scan speeds no
quasireversible behavior was observed for 9d, which suggests
that the charged species of this compound is of lower stability
compared with those of other naphthalene diimides studied here.
For comparison, the redox properties of arylamino-substituted
NDIs 8b, 9a, and 9b have been studied. The redox potentials
of these compounds are given in Table 2, and the cyclic
voltammograms are shown in Figure 6. The monochloromono-
arylamino NDI 8b showed reduction potentials at -1.57 and
-1.21 V that are in the same range as observed for its
alkylamino-substituted counterpart 8a (-1.64 and -1.24 V)
(Table 2). However, in contrast to 8a, for NDI 8b a reversible
oxidation potential was observed at 1.03 V. Analogously, the
Experimental Section
1,2,3,5,6,7,8,10-Octachloro-1,2,6,7-tetrahydropyrene (3). In a
2-L three-necked flask equipped with a mechanical stirrer, a gas
inlet tube, and an outlet tube pyrene (100 g, 0.494 mol) and iodine
(3.0 g) were dissolved in 1,2,4-trichlorobenzene (1 L) to result in
a violet solution. Chlorine gas was then bubbled through the solution
constantly. After 45 min, the flask was heated to 50 °C by an oil
bath and the formation of a light green solid was observed. After
an additional 45 min, the temperature was increased to 110 °C,
and after 2.5 h at this temperature, the solid dissolved again. After
an additional 2 h, addition of chlorine was stopped, the heating
was turned off, and the reaction mixture was cooled to room
temperature gradually. A white solid precipitated, which was
separated by filtration, washed with toluene (2 × 200 mL), and
dried in vacuo. Yield: 89.0 g (38%). Mp: 290 °C. MS (EI) m/z:
481.9 (13) [M+] (calcd 481.9). Anal. Calcd for C16H6Cl8: C, 39.88;
H, 1.26. Found: C, 40.03; H, 1.50. Due to its extremely low
(16) CAChe Work System Pro Version 6.1.12.33, Fujitsu.
(17) Grabowski, Z. R.; Rotkiewicz, K.; Rettig, W. Chem. ReV. 2003,
103, 3899-4031.
(18) Rademacher, A.; Ma¨rkle, S.; Langhals, H. Chem. Ber. 1982, 115,
2927-2934.
(19) (a) Jones, B. A.; Ahrens, M. J.; Yoon, M.-H.; Facchetti, A.; Marks,
T. J.; Wasielewski, M. R. Angew. Chem., Int. Ed. 2004, 43, 6363-6366.
(b) Chen, Z.; Debije, M. G.; Debaerdemaeker, T.; Osswald, P.; Wu¨rthner,
F. ChemPhysChem 2004, 5, 137-140. (c) Wu¨rthner, F.; Schmidt, R.
ChemPhysChem 2006, 7, 793-797.
J. Org. Chem, Vol. 71, No. 21, 2006 8103

Thalacker et al.
solubility in common organic solvents, no NMR spectrum could
be obtained for 3.
599.1504, found 599.1495. Anal. Calcd for C34H28Cl2N2O4: C,
68.12; H, 4.71; N, 4.67. Found: C, 67.73; H, 4.86; N, 4.39.
N,N′-Di-n-octyl-2-chloro-6-n-octylamino-1,4,5,8-naphthalene-
tetracarboxylic Acid Diimide (8a). A solution of diimide 7a (0.16
g, 0.28 mmol) and n-octylamine (1 mL, 6.0 mmol) in dichlo-
romethane (20 mL) was stirred under exclusion of light at room
temperature for 4.5 h. The resulting red solution (intense yellow
fluorescence) was poured into a mixture of concd HCl (2 mL) and
methanol (70 mL). This mixture was concentrated at room
temperature under reduced pressure, and a waxy red solid precipi-
tated, which was isolated by centrifugation and washed with
methanol. Yield: 0.18 g (96%). Mp: 197 °C. 1H NMR (400 MHz,
CDCl3, TMS): δ 10.05 (t, J ) 5.2 Hz, 1H), 8.60 (s, 1H), 8.26 (s,
1H), 4.15 (m, 4H), 3.57 (m, 2H), 1.83 (m, 2H), 1.72 (m, 4H), 1.5-
1.2 (m, 30H), 0.89 (m, 9H). HRMS (ESI, THF) m/z: calcd for
1,3,5,6,8,10-Hexachloropyrene (4a) and 1,3,5,7,8,10-Hexachlo-
ropyrene (4b) Regioisomers. Compound 3 (89.0 g, 0.186 mol)
and ethanol (700 mL) were placed in a 3-L three-necked flask
equipped with a mechanical stirrer and a condenser. Potassium
hydroxide (64.4 g, 1.12 mol) was then added slowly. The suspension
was refluxed for 5 h, and the resultant yellow solid was separated
by filtration and washed with boiling water (500 mL) to obtain
73.6 g (97%) of an isomeric mixture of 4a/4b. Mp: >350 °C.
MS (EI) m/z: 407.9 (100) [M+] (calcd 407.9). Anal. Calcd for
C16H4Cl6: C, 47.00; H, 0.99; Cl, 52.02. Found: C, 46.68; H, 1.25;
Cl, 52.22. Due to its extremely low solubility in common organic
solvents, no NMR spectrum could be obtained for 4a and 4b.
2,5,7,10-Tetrachloropyrene-3,8-quinone (5a). In a 100-mL
three-necked flask equipped with a thermometer fuming nitric acid
(24 mL) was cooled with an ice bath. A portion of the regioisomeric
mixture of 4a and 4b (8.18 g, 20.0 mmol) was added slowly to
maintain the temperature between -5 and +5 °C. The cooled
reaction mixture was stirred for a further 15 min. During the
reaction, regioisomer 5a precipitated as orange solid. The precipitate
was separated by filtration with a G3 frit and washed with acetic
acid (5 × 20 mL) and water (2 × 20 mL). The crude product was
purified by sublimation (1 mbar, 240-280 °C) to obtain 3.33 g
(45%) of 5a. Mp: 320-325 °C. MS (EI) m/z: 369.9 (100) [M+]
C38H55ClN3O4 652.3881, found 652.3875. UV/vis (CH2Cl2): λmax
/
nm (ꢀ/ M-1 cm-1) ) 532 (15 300), 504 (11 400, sh), 367 (13 100),
348 (10 700), 331 (8300, sh), 271 nm (43 100). Fluorescence
(CH2Cl2): λmax ) 567 nm. Fluorescence quantum yield: Φfl
)
0.58. Anal. Calcd for C38H54ClN3O4: C, 69.97; H, 8.34; N, 6.44.
Found: C, 69.70; H, 8.36; N, 6.44.
N,N′-Di-n-octyl-2-chloro-6-(4-tert-butylphenylamino)-1,4,5,8-
naphthalenetetracarboxylic Acid Diimide (8b). A suspension of
diimide 7a (0.12 g, 0.2 mmol) and 4-tert-butylaniline (0.1 mL, 0.6
mmol) in N-ethyldiisopropylamine (3 mL) was stirred under argon
for 1 h at 140 °C. The obtained red solution was poured into a
mixture of concd HCl (2 mL) and methanol (10 mL). A red solid
precipitated which was separated by centrifugation and washed with
methanol. Yield: 0.14 g (97%). Mp: 113 °C. 1H NMR (400 MHz,
CDCl3, TMS): δ 11.65 (s, 1H), 8.67 (s, 1H), 8.56 (s, 1H), 7.50 (d,
J ) 6.0 Hz, 2H), 7.28 (d, J ) 6.0 Hz, 2H), 4.12 (m, 4H), 1.75 (m,
4H), 1.5-1.2 (m, 20H), 1.38 (s, 9H), 0.87 (m, 6H). HRMS (ESI,
THF) m/z: calcd for C40H51ClN3O4 672.3568, found 672.3562. UV/
vis (CH2Cl2): λmax/nm (ꢀ/ M-1 cm-1) ) 523 (12 900), 369 (11 200),
351 (10 800), 333 (9000), 286 nm (35 000). Anal. Calcd for
C40H50ClN3O4: C, 71.46; H, 7.50; N, 6.25. Found: C, 71.39; H,
7.30; N, 6.13.
1
(calcd 369.9). H NMR (400 MHz, D2SO4): δ 7.96 (s, 2H), 6.75
(s, 2H). Anal. Calcd for C16H4Cl4O2: C, 51.94; H, 1.09. Found:
C, 51.38; H, 1.10.
2,6-Dichloro-1,4,5,8-naphthalenetetracarboxylic Acid Dian-
hydride (6). In a 100-mL three-necked flask equipped with a
thermometer and a condenser, 2.02 g (5.46 mmol) of 5a were
dissolved in concd sulfuric acid (28 mL). The solution was heated
with an oil bath at 100 °C under stirring for 10 min. Then fuming
nitric acid (3.1 mL) was added slowly by a syringe, whereupon
the reaction temperature increased to 130 °C and a yellow solid
precipitated. The oil bath was removed, and the reaction mixture
was cooled to 70 °C and poured into a portion of ice. The
precipitated solid was filtered with a frit (G3) and dried in vacuo.
Recrystallization with acetic acid provided 0.908 g (49%) of
compound 6. Mp: >350 °C. MS (EI) m/z: 336.1 (70) [M+] (calcd
336.1), 292.0 (100) [M - CO2+] (calcd 291.9). 1H NMR (400 MHz,
THF-d8): δ 8.79 (s, 2H). Anal. Calcd for C14H2Cl2O6: C, 49.89;
H, 0.60. Found: C, 49.90; H, 0.68.
General Procedure for the Preparation of 2,6-Dichloro-
1,4,5,8-naphthalenetetracarboxylic Acid Diimides 7a,b. To a
stirred suspension of 1 equiv of dianhydride 6 in glacial acetic acid
(10 mL per mmol dianhydride) was slowly added 4-14 equiv of
the respective amine at room temperature. After being heated to
reflux for 10 min, the reaction mixture was cooled to room
temperature. The resulting colorless to slightly brown precipitate
was collected on a Bu¨chner funnel and purified by recrystallization
with glacial acetic acid.
N,N′-Di(4-tert-butylphenyl)-2-chloro-6-n-octylamino-1,4,5,8-
naphthalenetetracarboxylic Acid Diimide (8c). A solution of
diimide 7b (30 mg, 0.05 mmol) and n-octylamine (0.12 mL, 0.72
mmol) in dichloromethane (4 mL) was stirred for 24 h under
exclusion of light at room temperature. The resulting red solution
(bright yellow fluorescence) was subjected to column chromatog-
raphy (dichloromethane/hexane ) 2:1, silica gel). Upon concentra-
tion under reduced pressure at room temperature, an orange solid
precipitated which was separated by centrifugation and washed with
1
hexane. Yield: 30 mg (87%). Mp: 212 °C. H NMR (400 MHz,
CDCl3, TMS): δ 9.99 (t, J ) 5.1 Hz, 1H), 8.70 (s, 1H), 8.36 (s,
1H), 7.59 (m, 4H), 7.25 (m, 4H), 3.54 (m, 2H), 1.75 (m, 2H), 1.5-
1.2 (m, 10H), 1.39 (s, 18H), 0.86 (t, J ) 7.0 Hz, 3H). HRMS (ESI,
THF) m/z: calcd for C42H47ClN3O4 692.3255, found 692.3244. UV/
vis (CH2Cl2): λmax/nm (ꢀ/M-1 cm-1) ) 534 (16 000), 505 (11 800,
sh), 365 (14 400), 348 (13 300), 332 (9200, sh), 270 nm (39 500).
Fluorescence (CH2Cl2): λmax ) 566 nm. Fluorescence quantum
yield: Φfl ) 0.58. Anal. Calcd for C42H46ClN3O4: C, 72.87; H,
6.70; N, 6.07. Found: C, 72.91; H, 6.52; N, 6.12.
N,N′-Di-n-octyl-2-(4-tert-butylphenylamino)-6-n-octylamino-
1,4,5,8-naphthalenetetracarboxylic Acid Diimide (9a). A solution
of diimide 8b (30 mg, 0.045 mmol) in n-octylamine (3 mL) was
stirred under argon at 140 °C for 45 min. After being cooled to
room temperature, the resulting blue solution was poured into a
mixture of concd HCl (2 mL) and methanol (10 mL). The blue
precipitate was separated by centrifugation and washed with
methanol. Yield: 20 mg (59%). Mp: 216 °C. 1H NMR (400 MHz,
CDCl3, TMS): δ 10.95 (s, 1H), 9.52 (t, J ) 5.2 Hz, 1H), 8.55 (s,
1H), 8.17 (s, 1H), 7.49 (d, J ) 6.0 Hz, 2H), 7.28 (d, J ) 6.0 Hz,
2H), 4.17 (m, 4H), 3.46 (m, 2H), 1.81 (m, 4H), 1.73 (m, 2H),
1.5-1.2 (m, 30H), 1.37 (s, 9H), 0.87 (m, 9H). HRMS (ESI, THF)
m/z: calcd for C48H68N4O4 764.5240, found 764.5226. UV/vis
N,N′-Di-n-octyl-2,6-dichloro-1,4,5,8-naphthalenetetracarboxy-
lic Acid Diimide (7a). Compound 7a was prepared from 6 (0.51
g, 1.5 mmol) and n-octylamine (5.0 mL, 20.5 mmol) according to
the general procedure. Yield: 0.59 g (70%). Mp: 240 °C. 1H NMR
(400 MHz, CDCl3, TMS): δ 8.78 (s, 2H), 4.18 (t, J ) 7.7 Hz,
4H), 1.74 (m, 4H), 1.5-1.2 (m, 20H), 0.88 (t, J ) 6.9 Hz, 6H).
UV/vis (CH2Cl2):
λ
max/nm (ꢀ/ M-1 cm-1) ) 400 (13 000),
380 (11 800), 359 (17 200), 252 (55 600). Anal. Calcd for
C30H36Cl2N2O4: C, 64.40; H, 6.49; N, 5.01. Found: C, 64.15; H,
6.53; N, 4.94.
N,N′-Di(4-tert-butylphenyl)-2,6-dichloro-1,4,5,8-naphthalene-
tetracarboxylic Acid Diimide (7b). Compound 7b was prepared
from 6 (0.17 g, 0.5 mmol) and 4-tert-butylaniline (0.32 mL, 2.0
mmol) according to the general procedure. Yield: 0.18 g (60%).
1
Mp: >350 °C. H NMR (400 MHz, CDCl3, TMS): δ 8.85 (s,
2H), 7.60 (d, J ) 8.6 Hz, 4H), 7.24 (d, J ) 8.6 Hz, 4H), 1.40 (s,
18H). HRMS (ESI, dichloromethane) m/z: calcd for C34H29Cl2N2O4
8104 J. Org. Chem., Vol. 71, No. 21, 2006

Core-Substituted Naphthalene Diimide Dyes
(CH2Cl2): λmax/nm (ꢀ/M-1 cm-1) ) 613 (22 200), 575 (13 400,
sh), 367 (16 000), 349 (13 600), 286 nm (37 900). Anal. Calcd for
C48H68N4O4: C, 75.35; H, 8.96; N, 7.32. Found: C, 75.24; H, 9.06;
N, 7.32.
mixture was stirred at room temperature for 1 h and then cautiously
poured onto ice (500 g) to give a bright yellow precipitate. Water
(1.5 L) was added, and the mixture was allowed to stand for 3 h.
The yellow solid was collected on a Bu¨chner funnel, washed with
dilute HCl, and dried. Yield: 3.41 g (80%) of crude product, which
was used without further purification. Mp: >350 °C. MS (EI)
m/z: 425.7 (100) [M+] (calcd 426.0). Anal. Calcd for C14H2-
Br2O6: C, 39.48; H, 0.47. Found: C, 38.90; H, 0.42. Due to its
extremely low solubility, no NMR spectrum could be obtained of
11.
N,N′-Di-n-octyl-2,6-di(4-tert-butylphenylamino)-1,4,5,8-naph-
thalenetetracarboxylic Acid Diimide (9b). A suspension of
diimide 7a (50 mg, 0.09 mmol) in 4-tert-butylaniline (1 mL) was
heated under argon to 180 °C for 1 h. After being cooled to room
temperature, the resulting blue solution was poured into a mixture
of concd HCl (2 mL) and ethanol (10 mL). The blue precipitate
was separated by centrifugation, washed with ethanol, and purified
by column chromatography (dichloromethane/hexane ) 2:1, silica
N,N′-Di(2-ethylhexyl)-2,6-di(2-ethylhexylamino)-1,4,5,8-naph-
thalenetetracarboxylic Acid Diimide (9e). Dianhydride 11 (2.12
g, 5.0 mmol) was heated in 2-ethylhexylamine (15 mL) under argon
at 140 °C for 2 h. The resulting dark blue solution was cooled to
room temperature and poured into a mixture of concd HCl (10 mL)
and methanol (100 mL). The blue precipitate was collected on a
Bu¨chner funnel and washed with methanol. Purification was
achieved by column chromatography (dichloromethane/hexane )
2:1, silica gel). Yield: 1.67 g (45%). Mp: 146 °C. 1H NMR (200
MHz, CDCl3, TMS): δ 9.40 (t, J ) 5.3 Hz, 2H), 8.10 (s, 2H),
4.11 (d, 4H), 3.40 (m, 4H), 1.93 (m, 2H), 1.72 (m, 2H), 1.5-1.2
(m, 32H), 0.89 (m, 24H). HRMS (ESI, THF) m/z: C46H72N4O4
1
gel). Yield: 40 mg (57%). Mp: 208 °C. H NMR (400 MHz,
CDCl3, TMS): δ 11.06 (s, 2H), 8.56 (s, 2H), 7.50 (d, J ) 6.0 Hz,
4H), 7.28 (d, J ) 6.0 Hz, 4H), 4.16 (m, 4H), 1.72 (m, 4H), 1.5-
1.2 (m, 20H), 1.37 (s, 18H), 0.86 (t, J ) 6.8 Hz, 6H). HRMS (ESI,
THF) m/z: calcd for C50H64N4O4 784.4927, found 784.4920. UV/
vis (CH2Cl2): λmax/nm (ꢀ/M-1 cm-1) ) 612 (22 800), 369 (15 300),
349 (14 800), 311 nm (39 700). Anal. Calcd for C50H64N4O4: C,
76.50; H, 8.22; N, 7.14. Found: C, 76.29; H, 8.07; N, 7.10.
N,N′-Di(4-tert-butylphenyl)-2,6-di-n-octylamino-1,4,5,8-naph-
thalenetetracarboxylic Acid Diimide (9c). Diimide 7b (30 mg,
0.05 mmol) was heated under argon in n-octylamine (2 mL) at 140
°C for 40 min. After being cooled to room temperature, the resulting
blue solution was poured into a mixture of concd HCl (2 mL) and
ethanol (10 mL). The blue precipitate was separated by centrifuga-
tion and washed with ethanol. Isolation of 9c from the byproducts
of an exchange of the imide substituents, i.e., N-(4-tert-butylphenyl)-
N′-(n-octyl)diimide and N,N′-di-n-octyldiimide, was achieved by
744.5553, found 744.5547. UV/vis (CH2Cl2): λmax/nm (ꢀ/M-1 cm-1
)
) 619 (22 100), 576 (11 600, sh), 365 (12 400), 347 (9700), 330
(4700, sh), 283 nm (44 800). Fluorescence (CH2Cl2): λmax ) 647
nm. Fluorescence quantum yield: Φfl ) 0.53. Anal. Calcd for
C46H72N4O4: C, 74.15; H, 9.74; N, 7.52. Found: C, 74.12; H, 9.72;
N, 7.49.
N,N′-Di(2-ethylhexyl)-3,7-di(2-ethylhexylamino)-1-amino-4,5,8-
naphthalenetricarboxylic Acid 1,8-Lactam 4,5-Imide (12). A
suspension of 9e (0.60 g, 0.8 mmol) and KOH (6.73 g, 120 mmol)
in a mixture of tert-butyl alcohol (60 mL) and water (3 mL) was
refluxed for 24 h. After being cooled to room temperature, the red
reaction mixture was poured slowly into a stirred aqueous 1 N HCl
solution (200 mL). The resulting suspension of an oily violet product
was extracted with dichloromethane (2 × 50 mL). The combined
extracts were dried with NaCl, concentrated, and subjected to
column chromatography (dichloromethane/hexane ) 1:1, silica gel).
From the concentrated fractions a tarry product was precipitated
by addition of methanol. Yield: 0.37 g (64%). Mp: not detected.
1H NMR (200 MHz, CDCl3, TMS): δ 9.57 (t, J ) 5.5 Hz, 1H),
7.71 (s, 1H), 6.38 (s, 1H), 5.83 (t, J ) 5.6 Hz, 1H), 4.10 (m, 2H),
3.73 (m, 2H), 3.32 (m, 4H), 1.92 (m, 2H), 1.71 (m, 2H), 1.5-1.2
(m, 32H), 0.93 (m, 24H). MS (CI) m/z: 717.5 (100) [M+] (calcd
717.1). Anal. Calcd for C45H72N4O3: C, 75.37; H, 10.12; N, 7.81.
Found: C, 74.99; H, 10.07; N, 7.71.
1
column chromatography. Yield: 17 mg (43%). Mp: 258 °C. H
NMR (400 MHz, CDCl3, TMS): δ 9.26 (t, J ) 5.2 Hz, 2H), 8.22
(s, 2H), 7.59 (d, J ) 8.7 Hz, 4H), 7.25 (d, J ) 8.7 Hz, 4H), 3.45
(m, 4H), 1.72 (m, 4H), 1.5-1.2 (m, 20H), 1.40 (s, 18H), 0.86 (t, J
) 7.0 Hz, 6H). HRMS (ESI, THF) m/z: calcd for C50H64N4O4
784.4927, found 784.4920. UV/vis (CH2Cl2): λmax/nm (ꢀ/M-1 cm-1
)
) 618 (23 600), 578 (12 500, sh), 363 (14 100), 346 (12 300), 331
(6300, sh), 283 nm (40 900). Fluorescence (CH2Cl2): λmax ) 650
nm. Fluorescence quantum yield: Φfl ) 0.55. Anal. Calcd for
C50H64N4O4: C, 76.50; H, 8.22; N, 7.14. Found: C, 76.27; H, 8.12;
N, 7.15.
N,N′-Di-n-octyl-2,6-di-n-octylamino-1,4,5,8-naphthalenetetra-
carboxylic Acid Diimide (9d). Dianhydride 6 (0.22 g, 0.67 mmol)
was heated in n-octylamine (3 mL) under argon at 140 °C for 40
min. After being cooled to room temperature, the dark blue solution
was poured into a mixture of concd HCl (3 mL) and methanol (50
mL). The blue precipitate was collected on a Bu¨chner funnel and
recrystallized from 2-propanol. Yield: 0.35 g (70%). Mp: 205 °C.
1H NMR (400 MHz, CDCl3, TMS): δ 9.33 (t, J ) 5.1 Hz, 2H),
8.13 (s, 2H), 4.16 (t, J ) 7.8 Hz, 4H), 3.48 (m, 4H), 1.80 (m, 4H),
1.72 (m, 4H), 1.5-1.2 (m, 40H), 0.88 (m, 12H). HRMS (ESI, THF)
m/z: calcd for C46H72N4O4 744.5553, found 744.5541. UV/vis (CH2-
Cl2): λmax/nm (ꢀ/M-1 cm-1) ) 575 (12 600, sh), 364 (13 600), 346
(10 800), 331 (6300, sh), 282 nm (46 800). Fluorescence (CH2-
Cl2): λmax ) 646 nm. Fluorescence quantum yield: Φfl ) 0.53.
Anal. Calcd for C46H72N4O4: C, 74.15; H, 9.74; N, 7.52. Found:
C, 73.92; H, 9.61; N, 7.50.
Acknowledgment. This work is dedicated to Prof. Manfred
Christl on the occasion of his 65th birthday. We thank Prof. P.
Ba¨uerle, Prof. U. Nienhaus, Dr. E. Mena-Osteritz, and Dr. Go¨tz
(all Universita¨t Ulm) for helpful discussions, in particular, with
regard to the photoluminescence and cyclic voltammetry
investigations. 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.
2,6-Dibromo-1,4,5,8-naphthalenetetracarboxylic Acid Dian-
hydride (11). A solution of dibromoisocyanuric acid (2.86 g, 10.0
mmol) in oleum (20% SO3, 50 mL) was added at room temperature
to a solution of naphthalene dianhydride 10 (2.68 g, 10.0 mmol) in
oleum (20% SO3, 100 mL) over a period of 4 h. The resulting
Supporting Information Available: General experimental
methods. This material is available free of charge via the Internet
at http://pubs.acs.org.
JO0612269
J. Org. Chem, Vol. 71, No. 21, 2006 8105