Laterally extended naphthalene tetracarboxylic bisimides

Article abstract of DOI:10.1021/jo101520a

The colorless naphthalene tetracarboxylic bisimides were laterally extended with imidazole rings to give colored and highly fluorescent materials. Donor-substituted phenyl groups at the imidazole rings cause further bathochromic shifts in fluorescence where the strong solvent influence in the spectra is typical for a TICT process. Applications are discussed.

Full text of DOI:10.1021/jo101520a

pubs.acs.org/joc
Laterally Extended Naphthalene Tetracarboxylic Bisimides
Heinz Langhals* and Simon Kinzel
Department of Chemistry, LMU University of Munich, Butenandtstrasse 13, D-81377 Munich, Germany
Langhals@lrz.uni-muenchen.de
Received August 16, 2010
The colorless naphthalene tetracarboxylic bisimides were laterally extended with imidazole rings to
give colored and highly fluorescent materials. Donor-substituted phenyl groups at the imidazole
rings cause further bathochromic shifts in fluorescence where the strong solvent influence in the
spectra is typical for a TICT process. Applications are discussed.
Naphthalene tetracarboxylic bisimides1 (1) with aliphatic
N substituents are colorless materials and may be applied as
white pigments.2 Many attempts were made to shift their
absorption into the visible1a,3 such as the substitution of the
aromatic core with a single or with several donor groups, pref-
erently in the positions 2,7 and 2,6. A ring closure between
donor groups in the positions 2 and 3 was described where
bathochromic absorption of such materials was observed.
The lateral extension of 1 by means of a heterocyclic anne-
llation is still lacking.
amide form 2,4,6-triphenyl-s-triazine as a byproduct; however,
this can be removed without problems.
We attached the solubility increasing 1-hexylheptyl sub-
stituent4 (swallow-tail substituent) to the nitrogen atoms of
naphthalene tetracarboxylic bisimide to form 1a and allowed
the reaction with sodium amide in the dipolar aprotic benzo-
nitrile in the presence of atmospheric oxygen in analogy to
perylenetetracarboxylic imides.5 A substitution of the aromatic
core of 1a proceeded two times at vicinal positions with the
incorporation of benzonitrile to form the imidazole deriva-
tive 2a. The lateral extension proceeds even a second time to
form the bis-imidazole derivative 3a with two lateral exten-
sions. The formation of 3a becomes dominating for a high con-
centration of sodium amide, whereas appreciable amounts
of 2a are formed for higher dilution. Benzonitrile and sodium
The lateral extensions of 1 are not limited to the applica-
tion of benzonitrile, but can be extended to further substi-
tuted nitriles. A melt of 2-naphthonitrile forms predominantly
3b, whereas 2b can be obtained with the application of compa-
rably high diluted sodium amide; the structure of 2b is unam-
biguous because of its characteristic UV/vis spectrum; how-
ever, a full characterization was not successful due to the low
yield. The lateral extension proceeds even with the electron-
rich 1-dimethylamino benzonitrile to form 2c and 3c; however,
the purification proved to be more tedious.
(1) (a) Langhals, H.; Jaschke, H. Chem.;Eur. J. 2006, 12, 2815–2824.
(b) Hensel, W. Ph. D. Thesis, University ofFrankfurt/Main, 1958. (c) Ried, W.;
Schaeffer, A.; Hensel, W. Melliand Textilber. 1923-1969 1958, 39, 780–784.
Chem. Abstr. 1958. 52, 100615. (d) Kranzlein, G.; Vollmann, H. I. G.
Farbenindustrie AG, Ger. Patent DE 552760, August 15, 1930; Chem. Abstr,
1932, 26, 54154.
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2007012611, July 21, 2006.
DOI: 10.1021/jo101520a
r
Published on Web 10/22/2010
J. Org. Chem. 2010, 75, 7781–7784 7781
2010 American Chemical Society

Langhals and Kinzel
JOCArticle
FIGURE 2. UV/vis spectra in chloroform: 1a, dotted line; 2c, dashed
line; and 3c, solid line. Left: absorption; right: fluorescence.
FIGURE 1. UV/vis spectra in chloroform: 1a, dotted line; 2a, solid
line; and 3a, dashed line. Left: absorption; right: fluorescence.
The hypsochromic absorption of 1 is shifted bathochro-
mically into the visible by the lateral extension of 2a to form
yellow solutions (see Figure 1). Moreover, the very weak fluor-
escence of 1a becomes intensified in 2a so that green shining
solutions are obtained with a fluorescence quantum yield of
28% (Figure 2). The second lateral extension in 2a causes
a further bathochromic shift in 3a so that orange solutions
are formed with a yellow fluorescence of 53% quantum yield.
The extension of the side chain in 2b causes a further bath-
ochromic shift of some 10 nm. The shift in the fluorescence is
slightly larger.
The introduction of the electron donating dimethylamino
group into the side chain in 2c and 3c, respectively, causes
appreciable further bathochromic shifts both in absorption
and fluorescence so that blue solutions with a strong red
fluorescence are obtained for 3c. The UV/vis spectra of 3c are
noticeably solvent dependent being shown for mixtures of
1-butanol as the polar component and toluene with lower
polarity in Figure 3. The absorption of 3c exhibits a positive
solvatochromism where continuous bathochromic shifts with
increasing solvent polarity were obtained. The induced bath-
ochromic shift as a function of the molar concentration of
the polar component can be described6 by a relation between
the molar energy of excitation (ET) and a logarithmic func-
tion (ln (c/c* þ 1) of the molar concentration c of the more
polar component such as for other polarity probes; see the
insert in Figure 3.
FIGURE 3. Solvatochromism of 2c in toluene with increasing
amounts of 1-butanol as the more polar component. Left: absorp-
tion; right: fluorescence. Insert: Analysis of the solvatochromism in
absorption where the molar energy of excitation (ET) is plotted
versus ln (c/c* þ 1) with c as the molar concentration of 1-butanol
and c* a constant of 0.2 mol L-1; correlation number r = -0.98
3
with 22 points.
A completely different behavior is observed for the fluor-
escence because obviously two different species are involved
where the hypsochromically fluorescent species dominates in
solutions with lower polarity and the bathochromically ab-
sorbing one in the more polar 1-butanol. We interpret these
results with the formation of TICT states7 (twisted intramo-
lecular charge transfer) being typical for dimethylamino
groups. These states are stabilized in more polar media and
are becoming dominating there. As a consequence, the Stokes’
shift increased with the solvent polarity because the absorp-
tion is less influenced by these effects than fluorescence.
Large Stokes’ shifts are of special interest for many applica-
tions of fluorescence dyes such as for lasers and in analytics
because of the suppressed reabsorption of the fluorescence
light.
We may presume that naphthalene tetracarboxylic bisi-
mides 1 can be efficiently laterally extended with imidazole
rings by the treatment with sodium amide and benzonitrile to
form bathochromically absorbing and fluorescent chromo-
phores. The introduction of dimethylamino groups increases
not only a further bathochromic shift, but also forms TICT
states in polar media with increased Stokes’ shifts.
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P.; Marechal, E. Bull. Soc. Chim. Fr. 1976, 504–506. (d) Bondarenko, E. F.;
Shigalevskii, V. A.; Gerasimenko, Yu. E. Zh. Org. Khim. 1979, 15, 2520–2525.
Chem. Abstr. 1980, 92, 215109. (e) Mishima, M.; Yamazaki, H.; Akiyama, K.;
Sakuma, T. Jpn. Kokai Tokkyo Koho JP 05019510 A, Jan 29, 1993; Chem.
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Abstr. 1993, 119, 213970. (f) Wurthner, F.; Ahmed, S.; Thalacker, C. Chem.;
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Neuburger, M.; Fischer, M.; Schafer, G.; Mayor, M. Org. Biomol. Chem.
2009, 7, 3222–3229. (k) Doria, F.; di Antonio, M.; Benotti, M.; Verga, D.;
Freccero, M. J. Org. Chem. 2009, 74, 8616–8625.
(4) (a) Langhals, H.; Demmig, S.; Potrawa, T. J. Prakt. Chem. 1991, 333,
733–748. (b) Langhals, H.; Demmig, S. Chem. Ber. 1988, 121, 225–230.
(5) Langhals, H.; Esterbauer, A. J.; Kinzel, S. New J. Chem. 2009, 33,
1829–1832.
(6) Langhals, H. Angew. Chem. 1982, 94, 739–749. Langhals, H. Angew.
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7782 J. Org. Chem. Vol. 75, No. 22, 2010

Langhals and Kinzel
JOCArticle
Experimental Section
6 H, CHaryl), 8.43 ppm (d, 3J = 6.6 Hz, 4 H, CHaryl). 13C NMR
(100 MHz, CDCl3, 25 °C) δ 14.3, 22.6, 22.8, 27.4, 29.5, 32.0, 32.7,
55.2, 110.8, 111.5, 121.8, 128.1, 128.7, 129.5, 132.9, 143.4, 161.1,
164.0, 164.8 ppm. UV/vis (CHCl3) λmax (ε) 463.5 (sh, 43400), 492.5
(55010), 512.4 nm (40990). Fluorescence (CHCl3, λexc = 462 nm)
N,N0-Bis-1-hexylheptylnaphthalenetetracarboxylic-1,8:4,5-
biscarboximide (1a). Naphthalenetetracarboxylic-1,8:4,5-bisan-
hydride (3.00 g, 11.2 mmol) and 1-hexylheptylamine (5.58 g,
28.0 mmol) were suspended in DMF (100 mL), and the resulting
mixture was stirred at 110 °C for 4 h (complete dissolution of all
components), allowed to cool to room temperature, quenched by
the addition of hydrochloric acid (2 N, 200 mL), extracted with
chloroform (3 ꢀ 200 mL), dried with magnesium sulfate, evapo-
rated, purified by column separation (silica gel, chloroform), evapo-
rated, and allowed to crystallize (viscous, very slowly crystallizing,
orange oil). Yield 5.63 g (79.7%) of a nearly colorless solid,
mp 67-68 °C. Rf (silica gel, chloroform) 0.79. IR (ATR) ν~ 2922
(m), 2854 (m), 2361 (w), 2338 (w), 1702 (s), 1660 (vs), 1577 (m),
1452 (m), 1398 (w), 1326 (vs), 1245 (s), 1213 (w), 1186 (w), 1092 (w),
λmax (Irel) = 528.1 nm (1.00). Fluorescence quantum yield (λexc =
462 nm, E462 nm/1 cm = 0.0233, CHCl3, reference 2,9-bis-(1-
hexylheptyl)anthra[2,1,9-def;6,5,10-d0e0f0]diisoquinoline-1,3,8,10-
tetraone, RN 110590-84-6, with Φ = 1.00) Φ = 0.53. HRMS
(C54H66N6O4) m/z calcd 862.5146, found 862.5145, Δ = -0.0001.
C54H66N6O4 (863.1) Calcd: C 75.14, H 7.71, N 9.74. Found:
C 74.78, H 7.36, N 9.68.
N,N0-Bis-1-hexylheptyl-2-(2-naphthyl)imidazolo[4,5:b]naph-
thalenetetracarboxylic-1,8:4,5-biscarboximide (2b) and N,N0-Bis-
1-hexylheptyl-bis-2,20-(2-naphthyl)imidazolo[4,5:b;4,5:e]napht-
halenetetracarboxylic-1,8:4,5-biscarboximide (3b). N,N0-Bis-1-
hexylheptylnaphthalenetetracarboxylic-1,8:4,5-biscarboximide
(1a) (300 mg, 0.476 mmol) and sodium amide (95% powder, 300
mg, 7.69 mmol) were dispersed in 2-naphthonitrile (5 g), and the
resulting solution was heated at 165 °C (color change to reddish
orange), stirred at 165 °C for 3 h (solidification of the mixture
after 2 h), allowed to cool to room temperature, treated with
aqueous HCl (2 N, 50 mL), extracted with chloroform (3 ꢀ 50 mL),
dried with magnesium sulfate, evaporated, and purified by
column separation (silica gel, chloroform/isohexane 3:1, remov-
ing of the monoadduct and the excess of naphthonitrile, second
column separation with chloroform/isohexane 1:1).
887 (vw),773 (m) 733 (w) cm-1. H NMR (600 MHz, CDCl3,
1
25 °C) δ 0.80 (t, 3J = 7.1 Hz, 12 H, CH3), 1.11-1.35 (m, 32 H,
CH2), 1.78-1.86 (m, 4 H, β-CH2), 2.12-2.23 (m, 2 H, β-CH2),
5.09-5.18 (m, 2 H, CH-N), 8.64-8.76 ppm (br, 4 H, CHaryl). 13
C NMR (75 MHz, CDCl3, 25 °C) δ 14.2, 22.8, 27.1, 29.4, 31.9,
32.5, 55.4, 127.0, 130.8, 131.6, 163.2, 164.4 ppm. UV/vis
(CHCl3) λmax (Erel) 342.8 (0.52), 361.6 (0.82), 382.4 nm (1.00).
MS (DEIþ, 70 eV) m/z (%) 632.4 (4.6), 631.4 (19.9), 630.4 (47.8)
[Mþ], 452.2 (3.1), 451.2 (19.1), 450.2 (89.4), 449.2 (100.0) [Mþ
-
C13H24], 269.0 (6.4), 268.0 (31.27), 267.0 (29.6) [Mþ - C26H50].
HRMS (C40H58N2O4) m/z calcd 630.4397, found 630.4389,
Δ = -0.0018.
First Fraction: N,N0-Bis-1-hexylheptyl-2-(2-naphthyl)imidazolo
[4,5:b]naphthalenetetracarboxylic-1,8:4,5-biscarboximide (2b). UV/
vis (CHCl3) λmax 445.4 nm. Fluorescence (CHCl3, λexc = 421 nm)
λmax = 505.5 nm. Fluorescence quantum yield (λexc = 421 nm,
N,N0-Bis-1-hexylheptyl-2-phenylimidazolo[4,5:b]naphthalene-
tetracarboxylic-1,8:4,5-biscarboximide (2a) and N,N0-Bis-1-hex-
ylheptyl-bis-2,20-phenylimidazolo[4,5:b;4,5:e]naphthalenetetracar-
boxylic-1,8:4,5-biscarboximide (3a). N,N0-Bis-1-hexylheptylnaphtha-
lenetetracarboxylic-1,8:4,5-biscarboximide (1a, 300 mg, 0.476 mmol)
and sodium amide (99% powder, 300 mg, 7.69 mmol) were dispersed
in benzonitrile (20 mL), and the resulting solution was heated at
165 °C (color change to reddish orange), stirred at 165 °C for 2 h,
allowed to cool, evaporated in medium vacuum, treated with aqueous
HCl (2 N, 50 mL), extracted with chloroform (3 ꢀ 50mL),driedwith
magnesium sulfate, filtrated, and purified by column separation
(silica gel, chloroform/isohexane 3:1).
E421
= 0.0173, CHCl3, reference 2,9-bis(1-hexylheptyl)
nm/1 cm
anthra[2,1,9-def;6,5,10-d0e0f0]diisoquinoline-1,3,8,10-tetraone, RN
110590-84-6, with Φ = 1.00) Φ = 0.30.
Second Fraction: N,N0-Bis-1-hexylheptyl-bis-2,20-(2-naphthyl)
imidazolo[4,5:b;4,5:e]naphthalenetetracarboxylic-1,8:4,5-biscar-
boximide (3b). Yield 128 mg (28%), deeply red solid, mp g250
°C. Rf (silica gel, chloroform/isohexane 1:1) 0.15. IR (ATR) ν~
3413.5 m, 3054.2 w, 2955.0 m, 2921.2 s, 2852.2 s, 2361.8 w,
1698.3 s, 1668.3 w, 1638.6 vs, 1535.3 m, 1496.2 s, 1461.8 vs,
1416.4 m, 1362.5 w, 1326.2 w, 1281.6 vs, 1233.3 m, 1208.5 w,
1197.9 w, 1181.5 m, 1154.5 w, 963.7 w, 949.3 w, 911.1 w, 855.3 m,
First Fraction: N,N0-Bis-1-hexylheptyl-2-phenylimidazolo[4,5:
b]naphthalenetetracarboxylic-1,8:4,5-biscarboximide (2a). Yield
44 mg (12%), yellowish, viscous oil. Rf (silica gel, chloroform/
isohexane 3:1) 0.47. 1H NMR (600 MHz, CDCl3, 25 °C) δ 0.79
(t, 3J = 7.0 Hz, 12 H, CH3), 1.12-1.40 (m, 32 H, CH2), 1.84-1.94
(m, 4 H, β-CH2), 2.18-2.35 (m, 4 H, β-CH2), 5.19-5.28 (m, 2 H,
CH-N), 7.58-7.67 (m, 3 H, CHaryl), 8.41 (d, 3J = 7.0 Hz, 2 H,
CHaryl), 8.69-8.79 ppm (br, 2 H, CHnaphthalene). 13C NMR (150
MHz, CDCl3, 25 °C) δ 14.3, 22.8, 27.3, 29.5, 30.4, 31.7, 32.0,
32.7, 55.2, 55.5, 124.2, 127.8, 128,7, 129.5, 130.3, 133.2, 161.9,
163.7, 164.9 ppm. UV/vis (CHCl3) λmax (Erel) 251.8 (0.98), 304.0
819.7 w, 804.1 w, 793.0 w, 751.7 m, 725.5 w, 633.8 w cm-1
.
1H NMR (600 MHz, CDCl3, 25 °C) δ 0.80 (t, 3J = 6.9 Hz, 12 H,
CH3), 1.14-1.27 (m, 18 H, CH2), 1.28-1.39 (m, 12 H, CH2),
1.39-1.51 (m, 4 H, CH2), 1.97-2.05 (m, 4 H, β-CH2), 2.35-2.45
(m, 4 H, β-CH2), 5.36-5.44 (m, 2 H, CH-N), 7.57-7.66 (m, 4 H,
CHnaphthyl), 7.87-7.95 (m, 2 H, CHnaphthyl), 8.05 (d, 3J = 8.6 Hz,
4 H, CHnaphthyl), 8.49 (d, 3J = 7.9 Hz, 4 H, CHnaphthyl), 8.97 ppm
(s, 2 H, CHnaphthyl). 13C NMR (150 MHz, CDCl3, 25 °C) δ 14.3,
22.8, 27.5, 29.6, 32.0, 32.8, 55.3, 121.9, 124.6, 125.2, 127.5, 128.2,
128.7, 129.4, 129.6, 133.2, 135.5, 161.1, 164.1, 164.9 ppm. UV/vis
(CHCl3) λmax (Erel) = 499.4 (1.00), 528.0 nm (0.84). Fluores-
cence (CHCl3, λexc = 470 nm) λmax (Irel) = 550.7 nm (1.00).
Fluorescence quantum yield (λexc = 470 nm, E470 nm/1 cm = 0.0185,
CHCl3, reference 2,9-bis-(1-hexylheptyl)anthra[2,1,9-def;6,5,
10-d0e0f0]diisoquinoline-1,3,8,10-tetraone, RN 110590-84-6,
with Φ = 1.00): Φ = 0.79. HRMS (C62H70N6O4) m/z calcd
962.5459, found 962.5436, Δ = -0.0023. C62H70N6O4 (963.3)
Calcd: C 77.31, H 7.32, N 8.72. Found: C 76.65, H 7.36, N 8.43.
N,N0-Bis-1-hexylheptyl-2-(4-dimethylaminophenyl)imidazolo-
[4,5:b]naphthalenetetracarboxylic-1,8:4,5-biscarboximide (2c) and
N,N0-Bis-1-hexylheptyl-bis-2,20-(4-dimethylaminophenyl)imidaz-
olo[4,5:b;4,5:e]naphthalenetetracarboxylic-1,8:4,5-biscarboximide
(3c). N,N0-Bis-1-hexylheptylnaphthalenetetracarboxylic-1,8:4,5-
biscarboximide (1a, 300mg, 0.476 mmol), sodiumamide (300 mg,
7.69 mmol), and 4-dimethylaminobenzonitrile (5 g, 34.2 mmol)
were allowed to react and purified analogously to 2a and 3a.
(0.37), 316.6 (0.36), 442.4 nm (1.00). Fluorescence (CHCl3, λexc
=
417 nm) λmax (Irel) = 480.5 (1.00), 507.6 nm (0.88). Fluorescence
quantum yield (λexc = 417 nm, E417 nm/1 cm = 0.0281, CHCl3,
reference 2,9-bis-(1-hexylheptyl)anthra[2,1,9-def;6,5,10-d0e0f0]
diisoquinoline-1,3,8,10-tetraone, RN 110590-84-6, with Φ =
1.00) Φ = 0.28. HRMS (C32H38N2O3) m/z calcd 746.4771, found
746.4761, Δ = -0.0010.
Third Fraction: N,N0-Bis-1-hexylheptyl-bis-2,20-phenylimidazolo-
[4,5:b;4,5:e]naphthalenetetracarboxylic-1,8:4,5-biscarboximide (3a).
Yield 230 mg (56.0%), orange solid, mp g250 °C. Rf (silica gel,
chloroform/isohexane 3:1):0.28. IR (ATR) ν~ 3409 (s), 2952 (m),
2923 (s), 2854 (m), 1702 (s), 1671 (w), 1640 (vs), 1540 (m), 1460 (vs),
1416(m),1329(w),1307(w),1279(vs),1226(w),1208(w),1190(m),
1046 (w), 953 (w), 940 (w), 834 (w), 834 (w), 778 (m), 686 (m) cm-1
.
1H NMR (600 MHz, CDCl3, 25 °C) δ 0.70-0.90 (m, 12 H, CH3),
1.13-1.51 (m, 32 H, CH2), 1.92-2.01 (m, 4 H, β-CH2), 2.31-2.40
(m, 4 H, β-CH2), 5.32-5.39 (m, 2 H, CH-N), 7.62 (t, 3J = 6.8 Hz,
J. Org. Chem. Vol. 75, No. 22, 2010 7783

Langhals and Kinzel
JOCArticle
First Fraction: N,N0-Bis-1-hexylheptyl-2-(4-dimethylaminophenyl)
imidazolo[4,5:b]naphthalenetetracarboxylic-1,8:4,5-biscarboximide
(2c). Yield 34 mg (9.0%), black powder. Rf (silica gel, chloroform)
0.50. 1H NMR (600 MHz, CDCl3, 25 °C) δ 0.80 (t, 3J = 7.0 Hz,
12 H, CH3), 1.10-1.46 (m, 32 H, CH2), 1.82-1.95 (m, 4 H,
β-CH2), 2.16-2.36 (m, 4 H, β-CH2), 3.15 (s, 6 H, NCH3),
mp >250 °C. Rf (silica gel, chloroform) 0.12. 1H NMR (600 MHz,
CDCl3, 25 °C) δ 0.80 (t, 3J = 6.9 Hz, 12 H, CH3), 1.10-1.48 (m,
32 H, CH2), 1.92-2.01 (m, 4 H, β-CH2), 2.28-2.43 (m, 4 H,
β-CH2), 3.14 (s, 12 H, N-CH3), 5.30-5.40 (m, 2 H, CH-N), 6.84
(d, J = 8.2 Hz, 4 H, CHaryl), 8.31 ppm (d, J = 8.2 Hz, 4 H,
CHaryl). UV/vis (CHCl3) λmax (Erel) = 303.0 (0.78), 460.8 (0.28),
493.6 (0.55), 627.4 nm (1.00). Fluorescence (CHCl3, λexc = 493.
6 nm): λmax (Irel) = 702.0 nm (1.00). HRMS (C58H77N8O4) m/z
calcd 949.6068, found 949.6014, Δ = -0.0054.
3
3
3
5.19-5.30 (m, 2 H, R-CH), 6.87 (d, J = 8.3 Hz, 2 H, CHaryl),
3
8.31 (d, J = 7.9 Hz, 2 H, CHaryl), 8.63-8.75 ppm (m, 2 H,
CHnaphthyl). 13C NMR (150 MHz, CDCl3, 25 °C) δ 14.3, 22.8, 27.3,
29.5, 29.5, 32.0, 32.6, 32.7, 40.7, 55.0, 55.3, 112.4, 114.6, 124.1,
128.8, 129.6, 130.9, 153.4, 162.6, 163.9, 164.8, 165.1 ppm. UV/vis
(CHCl3) λmax (Erel) = 303.2 (0.74), 424.6 (0.54), 450.6 (0.91),
558.6 nm (1.00). Fluorescence (CHCl3, λexc = 451 nm) λmax (Irel)
= 684.8 nm (1.00). HRMS (C49H67N5O4) m/z calcd 790.5227,
found 790.5233, Δ = þ0.0006.
Acknowledgment. This work was supported by the Fond
der Chemischen Industrie and the CIPS cluster in Munich.
Supporting Information Available: 1H NMR and 13C NMR
of compounds 1a, 2a, 2c, 3a, 3b, and 1H NMR of 3c. This
material is available free of charge via the Internet at http://pubs.
acs.org.
Second Fraction: N,N0-Bis-1-hexylheptyl-bis-2,20-(4-dimethyl-
aminophenyl)imidazolo[4,5:b;4,5:e]naphthalenetetracarboxylic-1,
8:4,5-biscarboximide (3c). Yield 23 mg (5.1%), black powder,
7784 J. Org. Chem. Vol. 75, No. 22, 2010