Core-substituted naphthalene bisimides: New fluorophors with tunable emission wavelength for FRET studies

Article abstract of DOI:10.1002/1521-3765(20021018)8:20<4742::AID-CHEM4742>3.0.CO;2-L

Highly colored and photoluminescent naphthalene bisimide dyes have been synthesized from 2,6-dichloronaphthalene bisanhydride 1 by means of a stepwise nucleophilic displacement of the two chlorine atoms by alkoxides and/or alkyl amines. The alkoxy-substit

Full text of DOI:10.1002/1521-3765(20021018)8:20<4742::AID-CHEM4742>3.0.CO;2-L

FULL PAPER
Core-Substituted Naphthalene Bisimides: New Fluorophors with Tunable
Emission Wavelength for FRET Studies**
[a]
FrankW¸rthner,* Shahadat Ahmed,[a] Christoph Thalacker,[a] and
Tony Debaerdemaeker[b]
Dedicated to Professor David N. Reinhoudt on the occasion of his 60th birthday
Abstract: Highly colored and photolu-
minescent naphthalene bisimide dyes
have been synthesized from 2,6-dichlor-
onaphthalene bisanhydride 1 by means
of a stepwise nucleophilic displacement
of the two chlorine atoms by alkoxides
and/or alkyl amines. The alkoxy-substi-
tuted derivatives are yellow dyes with
green emission and low photolumines-
cence quantum yields, whereas the
amine-substituted derivatives exhibit a
color range from red to blue with strong
photoluminescence up to 76%. Struc-
ture property relationships for this
class of two-dimensional chromophores
were evaluated based on a single-crystal
X-ray analysis for dye 5a, the observed
solvatochromism, and quantum-chemi-
cal calculations. Owing to the simple
tuning of the absorption properties over
the whole visible range by the respective
substituents, the pronounced brilliancy,
and the intense photoluminescence, this
class of dyes is considered to be highly
suited for numerous applications such as
fluorescent labeling of biomacromole-
cules and light-harvesting in supramo-
lecular assemblies. As an important step
towards such applications efficient
FRET(fluorescence resonance energy
transfer) has been demonstrated for a
covalently tethered bichromophoric
compound that contains a red and a
blue naphthalene bisimide dye.
Keywords: chromophores
pigments fluorescence
¥
dyes/
FRET
¥
¥
(fluorescence resonance energy
transfer) ¥ nucleophilic substitution
owing to their high fluorescence quantum yields and photo-
stability.[4, 5] Thus terrylene became one of the most applied
dyes in this field[4] and perylene, terrylene, and quaterrylene
bisimide dyes synthesized by the groups of M¸llen and
Langhals opened new possibilities.[5, 6] However, as a signifi-
cant drawback these dyes exhibit extended p systems that are
difficult to solubilize and exhibit a high tendency for the
undesired formation of dye aggregates.[7] On the other hand,
the smallest representative of the rylene bisimides, naphtha-
lene bisimide, exhibits a colorless nonfluorescent p system
that has been extensively applied in supramolecular chem-
istry,[8] DNA intercalation,[9] electrically conductive aggre-
gates,[10] and recently as the active layer of organic field effect
transistors.[11]
Introduction
Despite the multitude of available dyes there is ongoing
interest in new chromophoric systems that satisfy the special
demands of emerging technologies which are often at the
borders to biological[1] and physical sciences.[2] For example,
new interest in fluorophors with long-wavelength emission
has arisen in conjunction with single-molecule spectroscopy of
biomolecules[3] where most traditional dyes lack the required
fluorescence quantum yield and photostability or whose
performance is hampered by aggregation of their extended
p-conjugated cores. The second point holds especially true for
one of the most useful families of dyes, the rylenes, which
proved to be ideally suited for single-molecule spectroscopy
Herein we report on colored and fluorescent naphthalene
1,4,5,8-tetracarboxylic acid bisimides. We will show that
core substitution with electron-donor groups allows the
optical properties to be tuned over a wide spectral range
and high fluorescence quantum yields to be obtained that–
together with the easy access to these dyes–should open
exciting new opportunities for the above-mentioned fields of
research. Notably, these versatile fluorophors became avail-
able by means of a simple modification of dyes reported a long
time ago by Vollmann et al.,[12] that is replacement of
[a] Priv. Doz. Dr. F. W¸rthner, Dr. S. Ahmed, Dr. C. Thalacker
Abteilung Organische Chemie II
Universit‰t Ulm
Albert-Einstein-Allee 11, 89081 Ulm (Germany)
Fax : (‡49)731-5022840
E-mail: frank.wuerthner@chemie.uni-ulm.de
[b] Prof. Dr. T. Debaerdemaeker
Sektion Rˆntgen- und Elektronenbeugung
Universit‰t Ulm, Albert-Einstein-Allee 11
89081 Ulm (Germany)
[**] FRETˆ fluorescence resonance energy transfer.
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4742 4750
arylamines with alkyl amines in the 2- and/or 6-position of
naphthalene bisimides. These alkylamino-substituted deriv-
atives exhibit brilliant colors and intense fluorescence, where-
as Vollmann×s arylamino-substituted derivatives are dull
and nonfluorescent,[13] which might be the reason why this
class of chromophores did not receive much attention to
date.[14]
Optical properties: All these naphthalene bisimides are
isolated as colored solids with yellow (4), red (5), magenta
(6), and blue (7) hues. From the UV/Vis absorption spectra in
Figure 1 we see that each dye exhibits two intense absorption
Results and Discussion
Synthesis: Following Vollmann×s method 2,6-disubstituted
naphthalene-1,4,5,8-tetracarboxylic acid bisimides were pre-
pared as outlined in Scheme 1. Under acidic conditions 2,6-
dichloronaphthalene bisanhydride reacted selectively with
aryl (as well as alkyl)[13] amines at the anhydride carbonyl
groups to yield bisimide 2. Further reaction with nucleophilic
alkoxides or amines under mild conditions in protic or dipolar
aprotic solvents afforded the highly colored products 3 7.
Remarkably, the second chlorine atom of 2 is less readily
exchanged than the first one thus allowing a stepwise
nucleophilic displacement of the two chlorine atoms to give
the red dyes 5a and 5b or the blue dye 7 just by increasing the
concentration of the nucleophile and/or the reaction temper-
ature. Likewise dyes bearing one alkoxy substituent may be
prepared easily as demonstrated with 3 and 6 (Scheme 1).
Figure 1. UV/Vis absorption spectra of dyes 2 7 in dichloromethane.
bands, one at 350 nm that is not influenced by the 2,6
substituents and another one that is shifted through the whole
visible range, which is indicative of a strong electronic
interaction between the naphthalene core and the respective
substituents. The absorption maxima are located at about
470 nm for the yellow dye 4 bearing two alkoxy substituents,
at 530 nm for the red dye 5
bearing one amine and one chlor-
ine substituent, and at 620 nm for
the blue dye 7 bearing two amino
substituents (Table 1). This sug-
gests that the electron-donating
character (‡M effect) is of para-
mount importance for the posi-
tion of this absorption band sim-
ilar to the situation in merocya-
nines dyes.[15] However, the
bathochromic shift arising from
the substituent is much larger
than for merocyanine dyes (from
the alkoxy dye 4 to the alkyl-
amino derivative 7 we calculate
a bathochromic shift of Dl ˆ
151 nm or DnÄ ˆ 5200 cmÀ1) and
the band shape remains almost
unchanged (in contrast to mero-
cyanines[15b]). Another important
coloristic effect arises from the
unaltered position of the high-
energy transition in the UV spec-
trum at l < 380 nm; because this
transition does not move into the
visible range high brilliancy of all
dyes is realized owing to a single
absorption band in the visible
Scheme 1. Synthesis of naphthalene bisimide dyes 3 7.
range (Figure 1).
Chem. Eur. J. 2002, 8, No. 20
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F. W¸rthner et al.
FULL PAPER
Table 1. Optical properties of naphthalene bisimides 2 7 in dichloro-
methane.
contribute to prevent aggregation but even with simple n-
alkyl and other aryl substitutents well-soluble dyes are
obtained.[13] For dyes 5a and 7 the solvatochromic properties
were investigated in six solvents of different polarity and a
significant bathochromic shift of the absorption as well as
emission maxima was noted with increasing solvent polarity
(Table 2, Figure 3). For dye5a the bathochromic shift from n-
Color[a]
(solid)
labs
emax
[LmolÀ1cmÀ1
lem
Fem
[nm]
]
[nm]
[%]
2
3
4
5a
5b
6
yellowish white
pale yellow
yellow
red
red
violet
402
440
469
534
535
552
620
13900
14800
18200
15600
15500
17700
23300
< 0.1
< 0.1
22
64
63
484
564
565
582
650
Table 2. Solvent-dependent optical properties of dyes 5a and 7.
76
42
7
blue
Solvent
er
labs
lem
Fem
(5a)
[%]
labs
lem
Fem
(7)
[%]
(5a)
[nm]
(5a)
[nm]
(7)
[nm]
(7)
[nm]
[a] The colors are given for the crystalline materials because the coloristic
impression for solutions of some of these dyes is influenced by their strong
photoluminescence.
n-hexane
1.89
4.20
6.02
8.93
35.94
32.66
521
525
527
534
531
532
536
551
565
568
580
588
0.51
0.58
0.55
0.62
0.41
0.19
601
606
609
621
615
619
619
630
638
650
653
657
0.70
0.54
0.48
0.41
0.33
0.31
diethyl ether
ethyl acetate
dichloromethane
acetonitrile
methanol
Whilst the influence of the core substituent on the
absorption properties of these kind of dyes has been
reported,[12, 14] the appearance of intense photoluminescence
(Figure 2) was a surprise to us because Vollmann×s 2,6-aryl-
Figure 3. Fluorescence spectra of dye 7 for solvents of increasing polarity.
* * * *
From left to right: (––, thick) n-hexane, (- - - -) diethyl ether, (
acetate, (
methanol.
) ethyl
**
**
) dichloromethane, (short dashes) acetonitrile, (––, thin)
Figure 2. Absorption and fluorescence spectra of dyes 4 (solid line), 6
(dashed line) and 7 (dotted line) in dichloromethane.
hexane to methanol amounts to Dl ˆ 11 nm (DnÄ ˆ 400 cmÀ1)
in absorption and to Dl ˆ 52 nm (DnÄ ˆ 1650 cmÀ1) in emission
and for dye 7 the respective values are Dl ˆ 18 nm (DnÄ ˆ
480 cmÀ1) and Dl ˆ 38 nm (DnÄ ˆ 930 cmÀ1).
amino-substituted naphthalene bisimide dyes are nonfluores-
cent,[13] and hydrogen bonding to carbonyl groups is consid-
ered as a major pathway for radiationless deactivation of the
excited state that has been applied extensively in the design of
UV absorbers.[16] The existence of a strong intramolecular
hydrogen bond between the 2- and 6-amino substituents and
the proximate carbonyl oxygen atom of 5 7 was indeed
confirmed by the strongly downfield shifted proton resonance
signal of the NH hydrogen atom which appears as a well-
defined triplet (owing to the coupling to the neighboring
methylene protons) between d ˆ 9.33 and 10.05 ppm in
deuterated chloroform. Nevertheless, despite these argu-
ments dyes 4 7 exhibit photoluminescence with quantum
yields between 22 and 76% of green (4), orange (5), and red
(7) light (Table 1).
The solvatochromism of the absorption as well as the
emission maxima have been evaluated by means of linear free
energy relationships (LFER) to the common empirical
solvent polarity scales ET(30) and p* as well as the Lip-
pert Mataga equation.[19] All these scales have been shown to
be sensitive to the nonspecific (di)polarity of the solvent but
exhibit different sensitivities towards additional specific
interactions of the solute with the solvent. For example, the
ET(30) scale is strongly influenced by the presence of hydro-
gen bonding. Thus, it was not too surprising to us that the
correlation of the absorption maxima (in wavenumbers nÄ/
cmÀ1) was rather good for the apolar and dipolar aprotic
solvents hexane, diethyl ether, ethyl acetate, and acetonitrile
(whose polarity is mainly governed by the permittivity er) for
both dyes 5a and 7 with the p* as well as the ET(30) scale
(correlation coefficient >0.95), but dropped significantly if
dichloromethane (high contribution of polarizability) and/or
methanol (high contribution of hydrogen bonding) were
Owing to the rather small chromophoric system all dyes 3
7 exhibit a very good solubility and do not show any evidence
for aggregation even in solvents like methanol or n-hexane.[17]
Of course in the given case the sterically demanding 2,6-
diisopropylphenyl substitutents[18] at the imide-nitrogen atom
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Core-Substituted Naphthalene Bisimides
4742 4750
included in the linear regression analysis. In particular for
dichloromethane severe deviations from a LFER were
observed for the nÄmax values of both dyes and the ET(30)
value. In this context it seems especially remarkable that the
Stokes shifts, that is the difference between the absorption
and emission maxima, for both dyes in all solvents afforded an
excellent correlation to the Lippert Mataga polarity scale
f(er,n) ˆ (er À 1)/(2er ‡1) À (n2 À 1)/(2n2 ‡ 1) that describes
the solvent in a most simplistic dielectric continuum model
(correlation coefficient of 0.95 for 5a and of 0.97 for 7). In
contrast to the other scales this correlation (Figure 4) is not
anthraquinoid and indigoid dyes.[20, 21] For such two-dimen-
sional chromophores a significantly smaller number of double
bonds is required to achieve long-wavelength absorbance
than in traditional one-dimensional chromophores. For com-
parison, an extended chain of five conjugated double bonds
(leading to thermally and photochemically very unstable
dyes) is required to achieve blue color, that is absorption
bands above 600 nm, for cyanine and the best conjugated
merocyanine dyes.[15, 20] With regard to the fluorescence
intensity it seems noteworthy that the quantum yields remain
high as long as the solvent has no proton-donating capabilities
(Table 2). This points to a radiationless deactivation pathway
by means of intermolecular hydrogen bonds (in contrast to the
intramolecular hydrogen bonds discussed above) between the
solvent molecules and the carbonyl groups of the dyes. A
similar but not as pronounced solvent effect was observed
previously for structurally related perylene bisimide dyes.[7b, 22]
To shed more light onto the origin of the color properties of
these dyes we analyzed the HOMO and LUMO as well as the
transition densities involved in the lowest energy optical
transition of N,N'-dimethylnaphthalene-1,4,5,8-tetracarbox-
ylic acid bisimide and its 2- and 2,6-(bis)dimethylamino-
substituted derivatives. These molecular properties were
calculated with the CNDO/S method for AM1 optimized
geometries and the results are displayed in Figure 5.[23]
Figure 4. Correlation of the Stokes Shift between the absorption and
emission maxima DnÄ ˆ DnÄabs À DnÄem and the Lippert Mataga polarity
~
&
parameter of the solvent for dyes 5a ( ) and 7 ( ).
just an empirical LFER but has a physical meaning that
relates the positive slope to an increase of the dipole moment
Dm upon optical excitation (positive solvatochromism). How-
ever, owing to the molecular symmetry, for dye 7 only changes
in the quadrupole moment are feasible which is the most
likely reason why a much larger slope is observed for the
dipolar dye 5b.
The observed absorption properties of these dyes may be
explained tentatively based on Scheme 2, which suggests that
the electronic S0 S1 transition arises from an interaction of
the electron-donor substituents with the carbonyl functional
Figure 5. HOMO, LUMO, and transition density for a) N,N'-dimethyl
naphthaline 1,4,5,8-tetracarboxylic acid bisimide and its b) 2-chloro-6-
dimethylamino- and c) 2,6-dimethylamino-substituted derivatives accord-
ing to CNDO/S calculations of AM1 optimized molecules.
Scheme 2. Resonance model for dyes 3 7 which explains the strong
impact of electron donor substituents D on the absorption and emission
wavelengths as well as the significant positive solvatochromism.
The MO calculations reveal a unique change of the
transition density for the lowest energy optical transition
within the given series of dyes. Thus, whereas the HOMO
LUMO transition of the parent naphthalene bisimide is
polarized along the long molecular axis (i.e. between the two
imide groups), it is polarized perpendicular to this axis for the
2- and 2,6-substituted derivatives. This feature arises from a
'new' HOMO orbital that is created from the interaction of
the electron-donating 2,6-substituents with the naphthalene
groups. If the ground state is dominated by the left unpolar
formula and the excited state by the right zwitterionic one we
expect positive solvatochromism as observed for all these
compounds. To account for the spectral position of the S0 S1
transition at rather long wavelength, cross-conjugation be-
tween two donor acceptor systems is assumed to occur as in
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F. W¸rthner et al.
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Energy transfer in a bichromo-
phoric model compound: In the
last part of this study we dem-
onstrate one possible applica-
tion of these dyes that might be
of interest for FRET(fluores-
cence resonance energy trans-
fer)[24] studies of biomacromo-
lecules[1] and supramolecular
dye assemblies.[8, 9, 25] The use-
fulness of this class of dyes for
such studies became already
apparent from Figure 2 where
we see a strong overlap of the
emission spectrum of dye 4 with
the absorption spectrum of dye
6 and a similarly good overlap
of the emission spectrum of dye
6 with the absorption spectrum
of dye 7. According to Fˆrster×s
Figure 6. Structure of 5a (ORTEP plot) in the crystal showing the presence of four molecules of chloroform (one
of them disordered) that fill the space created by the orthogonal connection (q ˆ 838) of the naphthalene bisimide
and the diisopropylphenyl substituents.
[24]
theory of FRET, long-range
through-space resonance ener-
p-conjugated core. On the other hand the LUMO remains
unchanged and even the original naphthalene bisimide-
typical transition (Figure 5a, right) is also found as a higher
energy transition for the 2,6-substituted derivatives. Accord-
ingly the UV/Vis absorption spectra of dyes 3 7 (Figure 1)
can be explained based on two allowed optical transitions, one
at 350 nm that is characteristic for all naphthalene bisimides
(Figure 5a; right) and a new long-wavelength charge transfer
transition (Figure 5b,c; right) that is polarized perpendicular
to the former and whose spectral position is highly dependent
on the 2- and 6-electron donor substituents as well as the
solvent polarity.
gy transfer is expected if such an overlap of the absorption and
emission spectra (together with some other features like high
fluorescent quantum yields[24]) of the involved chromophores
occurs. Thus dyes 3 7 constitute a series of dyes that enables
the construction of energy transfer cascades[29] based on a
single p-conjugated scaffold. As a first example to support this
point we synthesized the bichromophoric compound 11
according to Scheme 3 from an amino-substituted derivative
of the −red× dye (8) and a carboxy-substituted derivative of
the −blue× dye (10) by DCC coupling in the presence of
1-hydroxybenzotriazole (BtOH). For this sequence it was
again very helpful that the first chlorine exchange takes place
with a much higher reactivity than the second. This enables
the isolation and further coupling of 8 as well as the stepwise
nucleophilic displacement of the two chlorine atoms of 2 with
two different amines to give 10.
For the bichromophoric compound 11, absorption, emis-
sion, and excitation spectroscopy was carried out in dilute
dichloromethane. Based on the structural properties (bulky
imide substituents) and the excellent additivity of the
absorption bands of the two chromophoric subunits
(Figure 7) we can exclude the possibility of intramolecular
aggregation due to folding of the flexible alkyl spacer. Such
aggregation would lead to strong coupling of the two dyes and
open alternative through-bond mechanisms of energy trans-
fer.[24b] In addition intermolecular FRETprocesses between
different molecules can be ruled out at the applied concen-
trations of our study because no energy transfer became
apparent for equimolar mixtures of dyes 5b and 7. In contrast,
upon selective illumination of the −red× dye in the bichromo-
phoric compound 11 at a wavelength of 500 nm we observe a
strong emission predominantly from the −blue× dye (Figure 8)
that is now attributed to an intramolecular FRETprocess.
From the ratio of the integrated emission bands <600 nm
(stemming from the −red× dye) and >600 nm (stemming from
the 'blue' dye) an energy transfer efficiency of about 96% is
calculated and a fluorescence quantum yield of 30% com-
Solid-state properties: Although the 2,6-diisopropylphenyl
substituents are not mandatory to prevent aggregation of
these dyes in solution[13] they are very supportive for isolating
the p systems also in the solid state. As a result the color of all
crystals obtained from dyes 3 7 essentially reflects the
spectral features in solution, and all crystals exhibit intense
solid-state photoluminescence. We have succeeded in growing
a single crystal of dye 5a suitable for an X-ray structural
analysis (Figure 6) and thus these properties can now be
studied in some detail.[18]
The most prominent feature of the structure of 5a is the
perpendicular orientation of the 2,6-diisopropylphenyl groups
with respect to the naphthalene bisimide chromophoric unit.
This leads to fully isolated chromophores which only expe-
rience the surrounding solid or liquid matrix but do not
aggregate even in low polarity environments or in the solid
state. In the given crystal four molecules of chloroform are
intercalated to −solvate× the dye or–in other words–fill the
empty space created by the conformationally restricted dye
molecules. All other structural features such as the bond
À
lengths and angles are not unusual. The C C bond lengths in
the planar naphthalene bisimide chromophore are all be-
tween 1.36 and 1.48 ä; the longest bonds are found for the
connection to the carbonyl groups.
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Core-Substituted Naphthalene Bisimides
4742 4750
Figure 8. Absorption (dotted line), excitation (solid line; fluorescence
detection at 660 nm), and fluorescence (dashed line; excitation at 500 nm)
spectra for dye 11 in dichloromethane.
one in the UV can be used to populate the lowest energy
excited state of the −blue× dye in 11. The slightly reduced
intensity of the excitation spectrum for the two bands at 350
and 500 nm (at lem ˆ 660 nm) compared to the absorption
spectrum is in accord with the additional weak fluorescence
from the 'red' dye (at < 600 nm) after excitation of these high
energy bands.
Conclusion
In summary, these studies showed that the introduction of
electron-donating alkoxy and alkylamino substituents at the
2,6-positions of naphthalene-1,4,5,8-tetracarboxylic acid bisi-
mides lead to interesting fluorophors. Depending on the
respective substituents yellow, red, or even blue dyes are
obtained that emit green, orange, or red light with fluores-
cence quantum yields of up to 76%. If these optical features
are combined with the possibility of covalent or supra-
molecular derivatization at the imide nitrogen atoms we
Scheme 3. Synthesis of bichromophoric compound 11.
expect a multitude of interesting applications for these
11, 25]
dyes.[8
One application was already demonstrated that
made use of the spectral overlap of the absorption and the
emission spectra between two different dyes of the given
series of compounds. This allowed us to measure an efficient
Fˆrster-type energy transfer (FRET) process within the
covalently tethered bichromophoric conjugate 11. Such pho-
tophysical processes are highly desirable for unraveling
binding and folding events for biomacromolecules. Therefore
it seems noteworthy that the two dyes 8 and 10 are already
equipped with useful functional groups for the covalent
labeling of oligopeptides and proteins.
Figure 7. Absorption spectra of a 1.5 Â 10À5 m solution of dye 11 (solid line)
and of a mixture of dyes 5a and 7 at the same concentration (dotted line) in
dichloromethane.
Experimental Section
Materials and methods: Solvents and reagents were purchased from Merck
(Darmstadt, Germany) unless otherwise stated and purified and dried
according to standard procedures.[26]
pared to that of 33% for direct excitation of the −blue× dye at
622 nm.
Further support for a highly efficient energy transfer
process is given by the excitation spectrum in Figure 8 which
shows that both absorption bands in the visible as well as the
2,6-Dichloronaphthalene anhydride
1 was obtained as described in
reference [12a]. Column chromatography was performed on silica gel
(Merck Silica Gel 60, mesh size 0.2 0.5 mm). The solvents for spectro-
scopic studies were of spectroscopic grade and used as received. UV/Vis
Chem. Eur. J. 2002, 8, No. 20
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F. W¸rthner et al.
FULL PAPER
spectra were recorded on a Perkin Elmer Lambda 40P spectrometer, and
fluorescence spectra were measured on a calibrated Perkin Elmer LS 50B
spectrometer in the conventional right-angle set-up in the presence of air
for dilute solutions (A < 0.04). Fluorescence quantum yields were deter-
mined relative to fluorescein (f ˆ 0.9, 0.1n NaOH)[27a] for dyes 2 4 and
relative to N,N'-di(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-
3,4:9,10-tetracarboxylic acid bisimide (f ˆ 0.96, CHCl3)[18a, 27b] for the other
dyes. NMR spectra were recorded on a Bruker DRX 400 spectrometer
using the proton signal of TMS or the carbon signal of the deuterated
solvent as internal standard. Mass spectra were recorded on Varian MAT
711 and Finnigan SSQ 7000 (both EI), Finnigan TSQ 7000 (FAB), and
Bruker Franzen Reflex III (MALDI-TOF) spectrometers. The calculated
and found m/z values correspond to the monoisotopic mass.
solution dichloronaphthalene bisimide 2 (300 mg, 0.45 mmol) was added
and the mixture was stirred at 258C for 4 h. This solution was poured into
1n HCl (100 mL) and the yellow precipitate was filtered, washed with
water, and dried. Purification by chromatography on a silica column with
1
CHCl3 afforded a yellow dye. Yield: 0.16 g (51%). M.p. 3478C; H NMR
(400 MHz, CDCl3, 258C): d ˆ 8.56 (s, 2H; H3,7), 7.47 (t, 2H; H4'), 7.33 (d,
4H; H3',5'), 4.49 (q, 4H; -OCH2), 2.71 (septet, 4H; iPr-H), 1.56 (t, 6H; -
OCH2CH3), 1.17 ppm (d, 24H; iPr-CH3); 13C NMR (100 MHz, CDCl3,
258C): d ˆ 162.45, 160.84, 160.47, 145.44, 130.51, 129.51, 127.43, 124.44,
123.99, 120.50, 111.41, 66.50, 29.12, 23.90, 14.69 ppm; UV/Vis (CH2Cl2): lmax
(emax) ˆ 469 (18200), 443 (13500), 361 (14500), 343(12400), 255 (48000) nm
(LmolÀ1 cmÀ1); fluorescence (CH2Cl2), lmax ˆ 484 nm, quantum yield ˆ
‡
0.22; MS (EI, 70 eV) m/z: 674 ([M] ); elemental analysis calcd (%) for
C42H46N2O6 (674.84): C 74.75, H 6.87, N 4.15; found: C 73.28, H 6.45, N 4.03.
X-ray crystal structure analysis of 5a: C40H42ClN3O4 ¥ 4CHCl3, Mr ˆ
1141.69, monoclinic, space group P21/n (no. 14), a ˆ 16.448(5), b ˆ
N,N'-Di-(2',6'-diisopropylphenyl)-2-n-butylamino-6-chloronaphthalene-
1,4,5,8-tetracarboxylic acid bisimide (5b): To a stirred solution of dichlor-
onaphthalene bisimide 2 (197 mg, 0.3 mmol) in CH2Cl2 (20 mL) at 258C
was added n-butylamine (0.5 mL, 5 mmol) and the reaction mixture was
stirred at 258C for 2 h. It was then poured into 1n HCl (20 mL) and the
organic layer was separated, washed with water (20 mL), and dried over
sodium sulfate. The solvent was removed and the product was purified by
chromatography on silica with CHCl3/n-hexane (3:2) to give a red dye.
Yield: 85 mg (41%). M.p. 2938C; 1H NMR (400 MHz, CDCl3, 258C): d ˆ
10.05 (t, 1H; NH), 8.78(s, 1H; H7), 8.41 (s, 1H; H3), 7.50 (q, 2H; H4'),
7.35(t, 4H; H3',5'), 3.60 (q, 2H; -NHCH2-), 2.68 (septet, 4H; iPr-H), 1.76
(mc, 2H; -NCH2CH2-), 1.48 (mc, 2H; CH2), 1.18 (d, 24H; iPr-CH3),
0.99 ppm (t, 3H; CH3); 13C NMR (100 MHz, CDCl3, 258C): d ˆ 166.33,
162.20, 162.01, 161.28, 152.31, 145.50, 135.57, 133.62, 130.28, 129.83, 129.32,
127.92, 124.20,124.08, 122.53, 122.12, 121.41, 99.90, 43.21, 31.22, 29.32, 29.24,
23.99, 23.89, 20.13, 13.69 ppm; UV/Vis (CH2Cl2): lmax (emax) ˆ 535 (15500),
503 (11200), 366 (13500), 348(12100), 270 (36600) nm (LmolÀ1 cmÀ1);
fluorescence (CH2Cl2): lmax ˆ 565 nm, quantum yield ˆ 0.63; MS (EI,
14.999(5), c ˆ 21.138(5) ä, b ˆ 91.765(5)8, Vˆ 5212(3) ä3 , Z ˆ 4 , 1calcd
ˆ
1.455 MgmÀ3 , m(MoKa) ˆ 0.732mmÀ1, crystal size 0.30  0.23  0.15 mm,
Tˆ 170 K, 10117 independent reflections collected, 794 parameters, R1 ˆ
0.0593 and wR2 ˆ 0.1463 for reflections with I > 2s(I), max./min. residual
electron density 0.746/ À 0.655 eäÀ3. Data were collected using a STOE-
IPDS diffractometer with monochromatic (graphite monochromator)
MoKa radiation (l ˆ 0.71073 ä, 2qmax ˆ 52.040, 2qmin ˆ 4.120); rotation scan
modus. The structure was solved by direct methods,[28a] refinement on F 2
using the full-matrix least-squares method.[28b] Hydrogen atoms localized in
final difference Fourier map. One molecule of 5a crystallizes with four
molecules of chloroform. One of these chloroform molecules is disordered
À
in the sense that it is rotating around its C H bond. Four main different
positions were located with an occupancy of 50, 30, 15, and 15%. In the
final Fourier map two other positions seem also likely but were not taken
into account. This explains the high final electron density of 0.746 eäÀ3 in
the map. CCDC-178616 contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge via www.ccdc.ca-
n.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic
Centre, 12 Union Road, Cambridge CB21EZ, UK; Fax: (‡44)1223-
336033; or deposit@ccdc.cam.ac.uk).
‡
70 eV): m/z: 691 ([M] ); elemental analysis calcd (%) for C42H46ClN3O4
(692.31): C 72.87, H 6.70, N 6.07; found: C 72.50, H 6.40, N 6.07.
N,N'-Di-(2',6'-diisopropylphenyl)-2-ethylamino-6-chloronaphthalene-
1,4,5,8-tetracarboxylic acid bisimide (5a): Dichloronaphthalene bisimide 2
(197 mg, 0.3 mmol) was dissolved in CH2Cl2 (30 mL), and ethylamine (70%
in water; 1 mL, 20 mmol) was added. The reaction mixture was stirred at
room temperature for 1 h, and then poured into 1n HCl (30 mL). The
organic layer was separated, washed with water (20 mL), and dried over
sodium sulfate. Removal of the solvent and chromatographic separation on
silica with CHCl3 afforded a red dye. Yield: 135 mg (68%). M.p. 3348C;
1H NMR (400 MHz, CDCl3, 258C): d ˆ 9.97 (t, 1H; NH), 8.77 (s, 1H; H7),
8.39 (s, 1H; H3), 7.50 (q, 2H; H4'), 7.35 (t, 4H; H3',5'), 3.62 (q, 2H; -
NHCH2-), 2.67 (septet, 4H; iPr-H), 1.42 (t, 3H; CH3), 1.17 ppm (d, 24H;
iPr-CH3); UV/Vis (CH2Cl2): lmax (emax) ˆ 534 (15600), 502 (11300),
366(13700), 348 (12300), 270 (39200) nm (LmolÀ1 cmÀ1); fluorescence
(CH2Cl2): lmax ˆ 564 nm, quantum yield ˆ 0.64; MS (EI, 70 eV): m/z: 663
N,N'-Di-(2',6'-diisopropylphenyl)-2,6-dichloronaphthalene-1,4,5,8-tetra-
carboxylic acid bisimide (2): 2,6-Dichloronaphthalene-1,4,5,8-tetracarbox-
ylic acid bisanhydride 1 (1 g, 2.96 mmol) was suspended in acetic acid
(40 mL) and heated at reflux. Into this mixture 2,6-diisopropylaniline
(3.75 mL, 20 mmol) was added and the mixture was kept at reflux at 1208C
for another 20 min. The solution was concentrated in vacuo and the
remaining residue was poured into methanol (40 mL). The precipitated
solid was filtered, dried, and recrystallized from acetic acid to afford a
yellowish white solid. Yield: 0.85 g (44%). M.p. 4098C; 1H NMR
(400 MHz, CDCl3, 258C): d ˆ 8.90 (s, 2H; H3, H7), 7.51 (t, 2H; H4'), 7.35
(d, 4H; H3',5'), 2.65 (septet, 4H; iPr-H), 1.17 ppm (d, 24H; iPr-CH3);
13C NMR (100 MHz, CDCl3, 258C): d ˆ 160.92, 160.42, 145.28, 140.71,
136.35, 130.00, 129.60, 127.89, 126.15, 124.21, 122.62, 29.29, 23.83 ppm; UV/
Vis (CH2Cl2): lmax (emax) ˆ 402 (13900), 381 (12000), 359 (18900), 251
‡
([M] ); elemental analysis calcd (%) for C40H42N3ClO4 (664.25): C 72.33, H
‡
(51500) nm (LmolÀ1 cmÀ1); MS (EI, 70 eV): m/z: 654 ([M] ); elemental
6.37, N 6.33; found: C 71.97, H 6.58, N 6.30.
analysis calcd (%) for C38H36Cl2O4N2 (655.63): C 69.62, H 5.53, N 4.27;
found: C 69.65, H 5.58, N 4.34.
N,N'-Di-(2',6'-diisopropylphenyl)-2-n-butylamino-6-ethoxynaphthalene-
1,4,5,8-tetracarboxylic acid bisimide (6): n- Butylamine (1 mL, 10 mmol)
and 2-chloro-6-ethoxynaphthalene bisimide 3 (100 mg, 0.15 mmol) were
stirred at 08C for 30 min during which time the color of the reaction
mixture changed to red. 1n HCl (25 mL) was added into the stirred mixture
to give a pink dye that was filtered, dried, and purified by chromatography
on silica with ethyl acetate/n-hexane (9:1). Yield: 50 mg (47%). M.p.
N,N'-Di-(2',6'-diisopropylphenyl)-2-chloro-6-ethoxynaphthalene-1,4,5,8-
tetracarboxylic acid bisimide (3): To a stirred solution of dichloronaph-
thalene bisimide
2 (0.325 g, 0.50 mmol) in CH2Cl2 (50 mL), sodium
ethoxide (136 mg, 2 mmol) was added and stirring was continued for
10 min. Then ethanol (0.5 mL) was added and the reaction mixture was
stirred at 258C for another 4 h before 1n HCl(10 mL) was added. The
organic layer was separated, washed with water (20 mL), and dried over
sodium sulfate. Filtration, removal of the solvent, and chromatographic
purification on silica with CHCl3 afforded a pale yellow solid. Yield: 0.15 g
(46%). M.p. 3128C; 1H NMR (400 MHz, CDCl3, 258C): d ˆ 8.84 (s, 1H;
H3), 8.61 (s, 1H; H7), 7.49 (q, 2H; H4'), 7.34 (t, 4H; H3',5'), 4.54 (q, 2H; -
OCH2), 2.68 (septet, 4H; iPr-H), 1.58 (t, 3H; OCH2CH3), 1.16 ppm (d,
24H; iPr-CH3); UV/Vis (CH2Cl2): lmax (emax) ˆ 440 (14800), 418 (10700),
362 (14600), 345 (11600), 212 (40500) nm (LmolÀ1 cmÀ1); MS (EI, 70 eV)
1
3178C; H NMR (400 MHz, CDCl3, 258C): d ˆ 9.79 (t, 1H; NH), 8.45 (s,
1H; H7), 8.37 (s, 1H; H3), 7.48 (mc, 2H; H4'), 7.34 (mc, 4H; H3',5'), 4.42 (q,
2H; -OCH2), 3.56 (q, 2H; -NHCH2), 2.71 (septet, 4H; iPr-H), 1.74 (mc, 2H;
-NHCH2CH2-), 1.53 (t, 3H; OCH2CH3), 1.47 (mc, 2H; CH2), 1.17(d, 24H;
iPr-CH3), 0.95 (t, 3H; CH3); UV/Vis (CH2Cl2): lmax (emax) ˆ 552 (17700),
511 (12200), 369 (12600), 351 (12900), 269 (41000) nm (LmolÀ1 cmÀ1);
fluorescence (CH2Cl2): lmax ˆ 582 nm, quantum yield ˆ 0.76; MS (EI,
‡
70 eV): m/z: 701 ([M] ); elemental analysis calcd (%) for C44H51N3O5
(701.91): C 75.29, H 7.32, N 5.99; found: C 75.26, H 7.62, N 5.67.
‡
m/z: 664 ([M] ); elemental analysis calcd (%) for C40H41N2ClO5 (655.24): C
N,N'-Di-(2',6'-diisopropylphenyl)-2,6-di-n-butylaminonaphthalene-1,4,5,8-
tetracarboxylic acid bisimide (7): n-Butylamine(1 mL, 10.1 mmol) and
dichloronaphthalene bisimide 2 (200 mg, 0.3 mmol) were stirred at 258C
for 15 min and then refluxed at 858C for another 45 min. After cooling to
room temperature the mixture was poured into 1n HCl (100 mL) and
72.22, H 6.21, N 4.21; found: C 70.48, H 6.30, N 3.96.
N,N'-Di-(2',6'-diisopropylphenyl)-2,6-diethoxynaphthalene-1,4,5,8-tetra-
carboxylic acid bisimide (4): An ethanolic sodium ethoxide solution was
prepared from sodium (46 mg, 2 mmol) and ethanol (1.2 mL). To this
4748
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2002, 8, No. 20

Core-Substituted Naphthalene Bisimides
4742 4750
stirred until a blue precipitate had separated. Filtration and purification by
(CH2Cl2): lmax ˆ 651.5 nm, quantum yield ˆ 0.40; MS (MALDI-TOF,
‡
column chromatography with CHCl3/n-hexane (1:1) afforded 7 as a blue
DHB) m/z: 786 ([M] ); HRMS (EI, 70eV) m/z: 786.4363 calcd for
1
dye (100 mg (45%)). M.p. 3048C; H NMR(400 MHz, CDCl3, 258C): d ˆ
C48H58N4O6: 786.4356; elemental analysis calcd (%) for C48H58N4O6 ¥
0.5H2O (796.02): C 72.42, H 7.47, N 7.03; found: C 72.23, H 7.42, N 6.84.
9.33 (t, 2H; NH), 8.26 (s, 2H; H3,7), 7.50 (t, 2H; H4'), 7.35 (d, 4H; H3',H5'),
3.51(mc, 4H; NHCH2), 2.70 (septet, 4H; iPr-H), 1.73 (mc, 4H; CH2), 1.47
(mc, 4H; CH2), 1.17 (d, 24H; iPr-CH3), 0.94 ppm (t, 3H; CH3);
13C NMR(100 MHz, CDCl3, 258C): d ˆ 160.53, 163.06, 149.71, 145.61,
130.80, 129.66, 126.30, 124.14, 122.09, 119.18, 101.81, 43.03, 31.28, 29.18,
24.02, 20.23, 13.75 ppm; UV/Vis (CH2Cl2): lmax (emax) ˆ 620 (23300), 579
(12300), 363(14100), 346 (12000), 281 (41400) nm (LmolÀ1 cmÀ1); fluo-
rescence (CH2Cl2): lmax ˆ 650 nm, quantum yield ˆ 0.42; MS (EI, 70 eV):
Bichromophoric dye 11: The red amino-substituted dye
8 (40 mg,
0.06 mmol) and the blue carboxy-substituted dye 10 (47 mg, 0.06 mmol)
were dissolved in CH2Cl2 (25 mL), and 1-hydroxybenzotriazole (8 mg,
0.06 mmol) and dicyclohexylcarbodiimide (25 mg, 0.12 mmol) were added
at a temperature of 08C under an argon atmosphere. The reaction mixture
was allowed to warm up to room temperature and was kept stirring under
argon for 24 h. Dicyclohexylurea was removed by filtration and washed
with CH2Cl2 (20 mL). The combined CH2Cl2 solution was evaporated to
give a blue solid that was purified by column chromatography on silica with
CH2Cl2/methanol (99:1). Yield: 50 mg (58%). M.p. 1658C; 1H NMR
(400 MHz, CDCl3, 258C): d ˆ 10.02 (t, 1H; NH), 9.33 (mc, 2H; NH), 8.77
(s, 1H; Naph-H), 8.33 (s, 1H; Naph-H), 8.26 (s, 1H; Naph-H), 8.22 (s, 1H;
Naph-H), 7.51 7.41 (mc, 4H; H4'), 7.35 7.31 (m, 8H; H3',5'), 6.28 (t, 1H;
NHCO), 3.53 3.28 (m, 8H; CH2), 2.70 - 2.61 (m, 8H; iPr-H), 2.13 (t, 2H;
CH2), 1.74 1.67 (m, 6H; CH2), 1.48 1.41 (m, 4H; CH2), 1.17 1.13 (m,
48H; iPr-CH3), 0.94 ppm (t, 3H; CH3); UV/Vis (CH2Cl2): lmax(emax) ˆ 622
(24600), 578 (12700), 531 (20200), 499 (13100), 365 (28500), 348 (21000),
331 (20000), 273 (76900), 228 (55900) nm (LmolÀ1 cmÀ1); fluorescence
‡
m/z: 728 ([M] ); elemental analysis calcd (%) for C46H56N4O4 (728.98): C
75.79, N 7.69, H 7.74; found: C 75.68, H 7.54, N 7.74.
N,N'-Di-(2',6'-diisopropylphenyl)-2-(2'-aminoethylamino)-6-chloronaph-
thalene-1,4,5,8-tetracarboxylic acid bisimide (8): Naphthalene bisimide 2
(200 mg, 0.30 mmol) was dissolved in CH2Cl2 (25 mL) and ethylenediamine
(400 mg, 6.66 mmol) was added. The reaction mixture was stirred at room
temperature for 24 h. The red colored solution was then poured into 1n
HCl (25 mL), the organic layer was separated, and the aqueous layer was
extracted twice with CH2Cl2 (25 mL). The combined organic extracts were
washed twice with water (20 mL) and dried over anhydrous sodium sulfate.
Solvent removal and column chromatography on silica with CH2Cl2/
methanol (98:2) afforded a red dye. Yield: 110 mg, (48%). M.p. 260 À
‡
(CH2Cl2): lmax ˆ 651 nm; HRMS (FAB, 3-nba): m/z: 1447.720 [M ‡ H] ;
1
calcd for C88H100ClN8O9: 1447.7302; elemental analysis calcd (%) for
C88H99ClN8O9 ¥ H2O (1462.28): C 72.28, H 6.96, N 7.66; found: C 71.91, H
6.66, N 7.44.
658C; H NMR (400 MHz, CDCl3, 258C): d ˆ 10.21 (t, 1H; NH), 8.79 (s,
1H; H7), 8.44 (s, 1H; H3), 7.51 (m, 2H; H4×), 7.36 (m, 4H; H3×,5×), 3.67 (mc,
2H; -NHCH2-), 3.10 (t, 2H; CH2), 2.68 (m, 4H; iPr-H), 1.39 (bs, 2H; -NH2),
1.18 ppm (mc, 24H; iPr-CH3); 13C NMR (100 MHz, CDCl3, 258C): d ˆ
166.33, 162.17, 162.01, 161.25, 152.49, 145.51, 135.63, 133.80, 130.23, 129.84,
129.27, 127.92, 124.18, 122.53, 122.20, 121.43, 100.27, 46.33, 41.15, 29.28,
23.97 ppm; UV/Vis (CH2Cl2): lmax (emax) ˆ 533 (14800), 366 (13500), 348
Acknowledgement
(12100), 271 (39000) nm (LmolÀ1cmÀ1); fluorescence (CH2Cl2): lmax
ˆ
We thank the Alexander von Humboldt Foundation (fellowship for S.A.),
the DFG (graduate fellowship for C.T.), and the Fonds der Chemischen
Industrie for financial support, and Professor R. Wortmann (Physical
Chemistry Institute, University of Kaiserslautern) and Professor G. U.
Nienhaus (Biophysics Institute, University of Ulm) for helpful discussions.
‡
570 nm, qunatm yield ˆ 0.53; MS (MALDI-TOF): m/z: 679 [M ‡ H] ;
‡
HRMS (EI, 70 eV): m/z: 678.2966 ([M] ); calcd for C40H43ClO4N4:
678.2972); elemental analysis calcd (%) for C40H43ClO4N4 ¥ 0.8CH2Cl2
(747.31): C 65.58, H 6.01, N 7.49; found: C 65.46, H 6.01, N 7.41.
N,N'-Di-(2',6'-diisopropylphenyl)-2-(6-carboxy-n-hexylamino)-6-chloro-
naphthalene-1,4,5,8-tetracarboxylic acid bisimide (9): Naphthalene bisi-
mide 2 (524 mg, 0.8 mmol) was dissolved in CH2Cl2 (50 mL), and 6-amino-
hexanoic acid (262 mg, 2 mmol) and 1,8-diazobicyclo[5,4,0]-undec-7-ene
(DBU) (0.3 mL, 2 mmol) were added. The reaction mixture was stirred at
room temperature for 16 h during which time the color of the reaction
mixture changed to red. It was then poured into 1n HCl (30 mL), and the
precipitate was filtered, dried, and purified by column chromatography on
silica with CH2Cl2/methanol (98:2) to give a red dye. Yield: 380 mg (63%).
M.p. 1828C; 1H NMR (400 MHz, CDCl3, 258C): d ˆ 10.05 (t, 1H; NH),
8.78 (s, 1H; H7), 8.39 (s, 1H; H3), 7.50 (m, 2H; H4×), 7.35 (m, 4H; H3',5'),
3.60 (mc, 2H; NH-CH2), 2.66 (mc, 4H; iPr-H), 2.33 (t, 2H; CH2), 1.80 (mc,
2H; CH2), 1.68 (mc, 2H; CH2), 1.50 (m, 2H; CH2), 1.17 ppm (d, 24H; iPr-
CH3); 13C NMR(100 MHz, CDCl3, 258C): d ˆ 175.99, 163.93, 159.76,
159.54, 158.79, 149.79, 143.03, 133.18, 131.30, 127.77, 127.43, 126.82,
121.73, 121.64, 120.09, 119.69, 118.81, 97.56, 40.74, 31.11, 26.87, 26.79,
26.44, 23.91, 21.69, 21.53, 21.48 ppm; UV/Vis (CH2Cl2): lmax (emax) ˆ 534
(15000), 500 (10600), 366 (13000), 348 (11700), 332 (8100), 270 (36800),
229 (21100) nm (LmolÀ1 cmÀ1); fluorescence (CH2Cl2): lmax ˆ 568 nm,
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1H NMR (400 MHz, CDCl3, 258C): d ˆ 9.34 (t, 2H; NH), 8.27 (s, 1H; H3 or
H7), 8.24 (s, 1H; H7 or H3), 7.50 (t, 2H; H4×), 7.35 (d, 4H; H3',5'), 3.50 (mc,
4H; NH-CH2), 2.70 (mc, 4H; iPr-H), 2.32 (t, 2H; CH2), 1.80 1.64 (m, 6H;
CH2), 1.49 (mc, 4H; CH2), 1.17 (d, 24H; iPr-CH3), 0.94 ppm (t, 3H; CH3);
UV/Vis (CH2Cl2): lmax(emax) ˆ 620 (22800), 576 (11800), 363 (13700), 346
(11700), 281 (38700), 227 (35200) nm (LmolÀ1 cmÀ1); fluorescence
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¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/02/0820-4749 $ 20.00+.50/0
4749

F. W¸rthner et al.
FULL PAPER
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solubility in ethanol and water/ethanol mixtures has been achieved
and a significant reduction of the fluorescence quantum yields has
been observed owing to the protic environment: P. Osswald, R.
Dobrawa, F. W¸rthner, unpublished results.
¬
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[18] To our knowledge 2,6-diisopropylphenyl substitutents were applied
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[29] Note added in proof (20. 8. 02): Recently a cascade of energy transfer
events was reported for dendrimers containing naphthalene, perylene,
and terylene dyes, see: T. Weil, E. Reuther, K. M¸llen, Angew. Chem.
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Received: January 29, 2002
Revised: May 22, 2002 [F4117]
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